text stringlengths 11 320k | source stringlengths 26 161 |
|---|---|
A subsumption lattice is a mathematical structure used in the theoretical background of automated theorem proving and other symbolic computation applications.
A term t 1 is said to subsume a term t 2 if a substitution σ exists such that σ applied to t 1 yields t 2 . In this case, t 1 is also called more general than t 2 , and t 2 is called more specific than t 1 , or an instance of t 1 .
The set of all (first-order) terms over a given signature can be made a lattice over the partial ordering relation " ... is more specific than ... " as follows:
This lattice is called the subsumption lattice. Two terms are said to be unifiable if their meet differs from Ω.
The join and the meet operation in this lattice are called anti-unification and unification , respectively. A variable x and the artificial element Ω are the top and the bottom element of the lattice, respectively. Each ground term , i.e. each term without variables, is an atom of the lattice. The lattice has infinite descending chains , e.g. x , g ( x ), g ( g ( x )), g ( g ( g ( x ))), ..., but no infinite ascending ones.
If f is a binary function symbol, g is a unary function symbol, and x and y denote variables, then the terms f ( x , y ), f ( g ( x ), y ), f ( g ( x ), g ( y )), f ( x , x ), and f ( g ( x ), g ( x )) form the minimal non-modular lattice N 5 (see Pic. 1); its appearance prevents the subsumption lattice from being modular and hence also from being distributive .
The set of terms unifiable with a given term need not be closed with respect to meet; Pic. 2 shows a counter-example.
Denoting by Gnd( t ) the set of all ground instances of a term t , the following properties hold: [ 2 ]
The set of linear terms, that is of terms without multiple occurrences of a variable, is a sub-poset of the subsumption lattice, and is itself a lattice. This lattice, too, includes N 5 and the minimal non-distributive lattice M 3 as sublattices (see Pic. 3 and Pic. 4) and is hence not modular, let alone distributive.
The meet operation yields always the same result in the lattice of all terms as in the lattice of linear terms.
The join operation in the all terms lattice yields always an instance of the join in the linear terms lattice; for example, the (ground) terms f ( a , a ) and f ( b , b ) have the join f ( x , x ) and f ( x , y ) in the all terms lattice and in the linear terms lattice, respectively. As the join operations do not in general agree, the linear terms lattice is not properly speaking a sublattice of the all terms lattice.
Join and meet of two proper [ 3 ] linear terms, i.e. their anti-unification and unification, corresponds to intersection and union of their path sets, respectively. Therefore, every sublattice of the lattice of linear terms that does not contain Ω is isomorphic to a set lattice, and hence distributive (see Pic. 5).
Apparently, the subsumption lattice was first investigated by Gordon D. Plotkin , in 1970. [ 4 ] | https://en.wikipedia.org/wiki/Subsumption_lattice |
A subsurface dyke is a structure that is built in an aquifer with the intention of obstructing the natural flow of ground water, thereby raising the ground water level and increasing the amount of water stored in the aquifer . Acting as an underground barrier impermeable to water, it controls the groundwater flow in an aquifer and raises the water table .
Although the total amount of water on Earth is generally assumed to have remained virtually constant, the rapid growth in population, together with the extension of irrigated agriculture and industrial development, are putting stress on the quality and quantity aspects of natural system. Several institutions have experimented with the use of subsurface dykes to conserve water in water-scarce areas. The ideal location for a dyke is a well defined, wide, greatly sloping valley with a narrow outlet having limited thickness of loose soil or porous rock on the top with massive or impervious rock below. A subsurface dyke has many advantages. It does not require additional surface reservoir, there is no loss of agricultural land, there is minimum evaporation loss since the storage is subsurface, there is no siltation and loss of reservoir capacity, the cost of maintenance is negligible, and it is relatively environment-friendly. [ citation needed ]
One such example was a recent sub-surface dyke constructed in India. For more information about this project, see Krishi Vigyan Kendra Kannur .
Other rainwater harvesting technologies include stone pitched contour bunds , dry rubble check dams, protection of seasonal spring by afforestation , moisture conservation pits, sprinkler and drip irrigation and roof water harvesting system. [ citation needed ] | https://en.wikipedia.org/wiki/Subsurface_dyke |
Subsurface engineers (also known as "completion engineers" [ 1 ] ) are a subset within Petroleum Engineering and typically work closely with Drilling engineers . The job of a Subsurface Engineer is to effectively select equipment that will best suit the subsurface environment in order to best produce the hydrocarbon reserves. Once the hardware has been selected, a Subsurface Engineer will monitor and adjust the equipment to ensure the well and reservoir produces under ideal circumstances.
Subsurface engineers must design a successful well completion system by selecting equipment that is adequate for both downhole environments and applications. Considerations must be given to the various functions under which the completion equipment must operate and the effects any changes in temperatures or differential pressure will have on the equipment. The completion system must also be efficient and cost effective to achieve maximum production and financial goals. Another factor in the selection of specific completion equipment is the production rates of the well. The typical job duties of a Subsurface engineer include managing the interface between the reservoir and the well, including perforations, sand control , artificial lift , downhole flow control , and downhole monitoring equipment . Additional responsibilities of a Subsurface engineer include: performing a cost and risk analysis on the design, contacting vendors for the rental, purchase, and shipment of equipment, and working closely with fellow employees ( geologists , reservoir engineers , drilling engineers , and production engineers ).
The Society of Petroleum Engineers (SPE) has technical disciplines which allow SPE members to focus their attention on the technical activities that most interest them. Drilling and Completions historically have been intertwined work within Petroleum Engineering . In 2016, SPE split the Drilling and Completions technical disciplines so SPE members would be able to focus more on Drilling or Completions. [ 2 ] SPE continues to publish the SPE Drilling & Completions journal, [ 3 ] it has been publishing the journal since 1993. SPE illustrates the technical activities of Drilling and Completions on its website and also hosts a page about SPE offerings related to Completions engineering. [ 4 ] [ 5 ] SPE also has many on demand webinars on Completions topics. [ 6 ]
The design components considered to perform a well completion may include:
Clegg, Joe Dunn. Production Operations Engineering . Richardson, TX: SPE, 2007. Print.
[ 7 ] | https://en.wikipedia.org/wiki/Subsurface_engineer |
Subsurface flow , in hydrology , is the flow of water beneath Earth's surface as part of the water cycle .
In the water cycle, when precipitation falls on the Earth's land, some of the water flows on the surface forming streams and rivers . The remaining water, through infiltration , penetrates the soil traveling underground, hydrating the vadose zone soil, recharging aquifers , with the excess flowing in subsurface runoff. In hydrogeology it is measured by the Groundwater flow equation .
Water flows from areas where the water table is higher to areas where it is lower. This flow can be either surface runoff in rivers and streams, or subsurface runoff infiltrating rocks and soil. The amount of runoff reaching surface and groundwater can vary significantly, depending on rainfall, soil moisture, permeability , groundwater storage, evaporation, upstream use, and whether or not the ground is frozen. The movement of subsurface water is determined largely by the water gradient, type of substrate, and any barriers to flow. The groundwater flow may be through either confined or phreatic aquifers, with smaller flow systems overlying or within. The residence time generally ranges from several decades to many centuries, implying the establishment of a complete chemical equilibrium with the aquifer. Mapping scales are between 1:250,000 and 1:2,000,000. (see, for example, Engelen et al. 1988). [ 1 ]
Subsurface water may return to the surface in groundwater flow , such as from a spring , seep , or a water well , or subsurface return to streams , rivers , and oceans . Water returns to the land surface at a lower elevation than where infiltration occurred, under the force of gravity or gravity induced pressures. Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years. Mainly, water flows through the ground which leads to the ocean where the cycle begins again.
Flow within the soil body may take place under unsaturated conditions, but faster subsurface flow is associated with localized soil saturation.
This hydrology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Subsurface_flow |
Subsurface lithoautotrophic microbial ecosystems , or "SLIMEs" (also abbreviated "SLMEs" or "SLiMEs"), are a type of endolithic ecosystems . They are defined by Edward O. Wilson as "unique assemblages of bacteria and fungi that occupy pores in the interlocking mineral grains of igneous rock beneath Earth's surface." [ 1 ]
Endolithic systems are still at an early stage of exploration. In some cases its biota can support simple invertebrates; in most, organisms are unicellular. Near-surface layers of rock may contain blue-green algae but most energy comes from chemical synthesis of minerals. The limited supply of energy limits the rates of growth and reproduction. In deeper rock layers microbes are exposed to high pressures and temperatures. [ 2 ]
This ecology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Subsurface_lithoautotrophic_microbial_ecosystem |
Subsurface Utilities are the utility networks generally laid under the ground surface. These utilities include pipeline networks for water supply, sewage disposal, petrochemical liquid transmission, petrochemical gas transmission or cable networks for power transmission, telecom data transmission, any other data or signal transmission. In North America alone, there are an estimated 35 million miles of subsurface infrastructure [ 1 ] that deliver critical services to homes and businesses.
The field of engineering dealing with the locating and mapping subsurface utilities is termed as Subsurface Utility Engineering (SUE).
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Subsurface_utilities |
Subsurface utility engineering ( SUE ) refers to a branch of engineering that involves managing certain risks associated with utility mapping at appropriate quality levels, utility coordination, utility relocation design and coordination, utility condition assessment, communication of utility data to concerned parties, utility relocation cost estimates, implementation of utility accommodation policies, and utility design. [ 1 ]
The SUE process begins with a work plan that outlines the scope of work, project schedule, levels of service vs. risk allocation and desired delivery method. Non-destructive surface geophysical methods are then leveraged to determine the presence of subsurface utilities and to mark their horizontal position on the ground surface. Vacuum excavation techniques are employed to expose and record the precise horizontal and vertical position of the assets. This information is then typically presented in CAD format or a GIS -compatible map. A conflict matrix is also created to evaluate and compare collected utility information with project plans, identify conflicts and propose solutions. The concept of SUE is gaining popularity worldwide as a framework to mitigate costs associated with project redesign and construction delays and to avoid risk and liability that can result from damaged underground utilities.
The practice of collecting, recording and managing subsurface data has historically been widely unregulated. In response to this challenge, in 2003, The American Society of Civil Engineers (ASCE) developed standard 38-02: Guideline for the Collection and Depiction of Existing Subsurface Utility Data, which defined the practice of SUE. Many countries followed the U.S. lead by creating similar standards including Malaysia, Canada, Australia, Great Britain and most recently, Ecuador. Developed and refined over the last 20 years, SUE classifies information according to quality levels with an objective to vastly improve data reliability. This provides project owners and engineers with a benchmark to determine the integrity of utility data at the outset of an infrastructure project.
A number of standards for care have been developed to maintain the use of SUE.
The update to ASCE Standard 38-02 has been published by ASCE and is available from the ASCE library. The updated Standard contains significant commentary and examples, new and revised definitions, and new provisions for guidance in performing utility investigations, learned since 38-02 was released.
In 2003, the American Society of Civil Engineers (ASCE) published Standard 38-02 titled Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data . [ 2 ] The standard defined SUE and set guidance for the collection and depiction of subsurface utility information. ASCE involvement with SUE is substantially through Utility Engineering & Surveying Institute (UESI). The ASCE standard presents a system to classify the quality of existing subsurface utility data, in accordance with four quality levels:
The Standard Guideline for Underground Utility Mapping in Malaysia was launched in 2006 to create, populate and maintain the national underground utility database.
This standard addresses issues such as roles of stakeholders and how utility information can be obtained, and was a call to action from the Malaysian government due to increasing demands for improvements on basic infrastructure facilities including utilities.
The Standard is similar to ASCE 38-02, using quality levels D-A as its basis. Although it does not classify utility definition, colours or symbols, the Malaysian standard does specify an accuracy ±10 cm for both horizontal and vertical readings. The Standard is supported by the Malaysian government but is not backed by an Association or governing body. [ 4 ]
In 2011, the Canadian Standards Association (CSA) released Standard S250 Mapping of Underground Utility Infrastructure . The Standard is described as a collective framework for best practices to map, depict and manage records across Canada. [ 4 ] CSA S250 complements and extends ASCE Standard 38-02 by setting out requirements for generating, storing, distributing, and using mapping records to ensure that underground utilities are readily identifiable and locatable. Accuracy levels expand upon ASCE 38-02 Quality Level A, prescribing a finer level of detail to define the positional location of the infrastructure.
In June, 2013, the Standards Australia Committee IT-036 on Subsurface Utility Engineering Information launched Standard 5488-2013 Classification of Subsurface Utility Information to provide utility owners, operators and locators with a framework for the consistent classification of information concerning subsurface utilities. The standard also provides guidance on how subsurface utility information can be obtained and conveyed to users. [ 5 ]
In 2019 the standard was split into:
The standards was since revised in 2022.
An industry consultation event in January 2012 kicked off the development of a British SUE standard. The first technical draft was reviewed by the committee in December 2012 and it was released for public/general industry review in March 2013. PAS 128 applies to the detection, verification and location of active, abandoned, redundant or unknown underground utilities and associated surface features that facilitate the location and identification of underground utility infrastructure. It sets out the accuracy to which the data is captured for specific purposes, the quality expected of that data and a means by which to assess and indicate the confidence that can be placed in the data. [ 6 ]
In March, 2015 the Ecuadorian Institute for Standardization ( INEN ) have published the Standard NTE INEN 2873 for the Detection and Mapping of Utilities and Underground Infrastructure . This Standard establishes procedures for the mapping of utilities for the purposes of reducing the uncertainties created by existing underground utilities. Its systematic use can provide both a means for continual improvement in the reliability, accuracy, and precision of future utility records; and immediate value during project development. It combines two basic concepts. The first concept is the means of classifying the reliability of the existence and location of utilities already installed and hidden in the ground. It is used during project development and is a major component of Subsurface Utility Engineering (SUE). The second concept is how to specify the recording of utilities exposed during their installation or during maintenance/repair operations so that future records are reliable. It is used primarily during utility installation. It is fundamentally a traditional survey and documentation function. Combining these concepts will lead to a continual reduction in the risks created by underground utilities during future projects involving excavation of any kind. [ 7 ]
SUE is mainly used at the design stage of a capital works project and when information is being collected for asset management purposes. In both situations, a similar process is followed but the scope of the work and presentation of the information may vary.
When a SUE investigation is carried out for a capital works project prior to construction, the objective is generally to collect accurate utility information within the project area to avoid conflict at later stages of the project.
For initiatives involving asset management, project owners may be missing information about their underground utilities or have inaccurate data. In this situation a SUE provider would collect the required information and add it to the asset management database, according to the four quality levels prescribed by ASCE Standard 38-02. | https://en.wikipedia.org/wiki/Subsurface_utility_engineering |
Subtelomeres are segments of DNA between telomeric caps and chromatin.
Telomeres are specialized protein – DNA constructs present at the ends of eukaryotic chromosomes, which prevent them from degradation and end-to-end chromosomal fusion. Most vertebrate telomeric DNA consists of long ( T T A G G G )n repeats of variable length, often around 3-20kb. Subtelomeres are segments of DNA between telomeric caps and chromatin . In vertebrates, each chromosome has two subtelomeres immediately adjacent to the long (TTAGGG)n repeats. Subtelomeres are considered to be the most distal (farthest from the centromere ) region of unique DNA on a chromosome, and they are unusually dynamic and variable mosaics of multichromosomal blocks of sequence. The subtelomeres of such diverse species as humans, Plasmodium falciparum , Drosophila melanogaster , and Saccharomyces cerevisiae are structurally similar in that they are composed of various repeated elements, but the extent of the subtelomeres and the sequence of the elements vary greatly among organisms. [ 1 ] In yeast ( S. cerevisiae ), subtelomeres are composed of two domains: the proximal and distal (telomeric) domains. The two domains differ in sequence content and extent of homology to other chromosome ends, and they are often separated by a stretch of degenerate telomere repeats (TTAGGG) and an element called 'core X', which is found at all chromosome ends and contains an autonomously replicating sequence (ARS) and an ABF1 binding site. [ 2 ] [ 3 ] The proximal domain is composed of variable interchromosomal duplications (<1-30 kb ); this region can contain genes such Pho , Mel , and Mal . [ 4 ] The distal domain is composed of 0-4 tandem copies of the highly conserved Y' element; the number and chromosomal distribution of Y′ elements varies among yeast strains. [ 5 ] Between the core X and the Y' element or the core X and TTAGGG sequence there is often a set of 4 subtelomeric repeats elements (STR): STR-A, STR-B, STR-C and STR-D which consists of multiple copies of the vertebrate telomeric motif TTAGGG. [ 6 ] This two-domain structure is remarkably similar to the subtelomere structure in human chromosomes 20p, 4q and 18p in which proximal and distal subtelomeric domains are separated by a stretch of degenerate TTAGGG repeats, but the picture that emerges from studies of the subtelomeres of other human chromosomes indicates that the two-domain model does not apply universally. [ 1 ]
This structure with repeated sequences is responsible for frequent duplication events, which create new genes, and recombination events, at the origin of combination diversity. These properties generate diversity at an individual scale and therefore contribute to adaptation of organisms to their environments. For example, in Plasmodium falciparum during interphase of the erythrocytic stage , the chromosomic extremities are gathered at the cell nucleus periphery, where they undergo frequent deletion and telomere position effect (TPE). This event, in addition to expansion and deletion of subtelomeric repeats, gives rise to chromosome size polymorphisms and thus, subtelomeres undergo epigenetic and genetic controls. Because of the properties of subtelomeres, Plasmodium falciparum evades host immunity by varying the antigenic and adhesive character of infected erythrocytes (see Subtelomeric transcripts). [ 7 ] [ 8 ]
Variation of subtelomeric regions are mostly variation on STRs, due to recombination of large-scale stretches delimited by (TTAGGG)n-like repeated sequences, which play an important role in recombination and transcription. Haplotype (DNA sequence variants) and length differences are therefore observed between individuals.
Subtelomeric transcripts largely consist of either pseudogenes (transcribed genes producing RNA sequences not translated into protein) or gene families . In humans, they code for olfactory receptors , immunoglobulin heavy chains , and zinc-finger proteins . In other species, several parasites such as Plasmodium and Trypanosoma brucei have developed sophisticated evasion mechanisms to adapt to the hostile environment posed by the host, such as exposing variable surface antigens to escape the immune system. Genes coding for surface antigens in these organisms are located at subtelomeric regions, and it has been speculated that this preferred location facilitates gene switching and expression, and the generation of new variants. [ 9 ] [ 10 ] For example, the genes belonging to the var family in Plasmodium falciparum (agent of malaria) are mostly localized in subtelomeric regions. Antigenic variation is orchestrated by epigenetic factors, including monoallelic var transcription at separate spatial domains at the nuclear periphery ( nuclear pore ), differential histone marks on otherwise identical var genes, and var silencing mediated by telomeric heterochromatin . Other factors such as non-coding RNA produced in subtelomeric regions adjacent or within var genes may contribute as well to antigenic variation . [ 11 ] [ 12 ] In Trypanosoma brucei (agent of sleeping sickness), variable surface glycoprotein (VSG) antigenic variation is a relevant mechanism used by the parasite to evade the host immune system. VSG expression is exclusively subtelomeric and occurs either by in situ activation of a silent VSG gene or by DNA rearrangement that inserts an internal silent copy of a VSG gene into an active telomeric expression site. To contrast with Plasmodium falciparum , in Trypanosoma brucei , antigenic variation is orchestrated by epigenetic and genetic factors. [ 13 ] [ 14 ]
In Pneumocystis jirovecii major surface glycoprotein (MSG) gene family cause antigenic variation. MSG genes are like boxes at chromosome ends, and only the MSG gene at the unique locus UCS (upstream conserved sequence) is transcribed . Different MSG genes can occupy the expression site (UCS), suggesting that recombination can take a gene from a pool of silent donors and install it at the expression site, possibly via crossovers , activating transcription of a new MSG gene, and changing the surface antigen of Pneumocystis jirovecii . Switching at the expression site is probably facilitated by the subtelomeric locations of expressed and silent MSG genes. A second subtelomeric gene family, MSR, is not strictly regulated at the transcriptional level, but may contribute to phenotypic diversity. Antigenic variation in P. jirovecii is dominated by genetic regulation. [ 15 ] [ 16 ]
Loss of telomeric DNA through repeated cycles of cell division is associated with senescence or somatic cell aging. In contrast, germ line and cancer cells possess an enzyme, telomerase , which prevents telomere degradation and maintains telomere integrity, causing these types of cells to be very long-lived.
In humans, the role of subtelomere disorders is demonstrated in facioscapulohumeral muscular dystrophy (FSHD), Alzheimer's disease , epilepsy [ 17 ] and peculiar syndromic diseases ( malformation and mental retardation). For example, FSHD is associated with a deletion in the subtelomeric region of chromosome 4q. A series of 10 to >100 kb repeats is located in the normal 4q subtelomere, but FSHD patients have only 1–10 repeat units. This deletion is thought to cause disease owing to a position effect that influences the transcription of nearby genes, rather than through the loss of the repeat array itself. [ 1 ]
Subtelomeres are homologous to other subtelomeres that are located at different chromosomes and are a type of transposable element , DNA segments that can move around the genome. Although subtelomeres are pseudogenes and do not code for protein, they provide an evolutionary advantage by diversifying genes. The duplication, recombination, and deletion of subtelomeres allow for the creation of new genes and new chromosomal properties. [ 1 ] The advantages of subtelomeres have been studied in different species such as Plasmodium falciparum , [ 1 ] Drosophila melanogaster , [ 1 ] and Saccharomyces cerevisiae , [ 1 ] since they have similar genetic elements to humans, not accounting for length and sequence. [ 1 ] Subtelomeres might have the same role in plants since the same advantage have been found in a common bean plant known as Phaseolus vulgaris . [ 18 ]
Different varieties of subtelomeres are frequently rearranging during meiotic and mitotic recombination, indicating that subtelomeres are frequently shuffling, which causes new and rapid genetic changes in chromosomes. [ 1 ] In Saccharomyces cerevisiae , 15kb region of chromosome 7L in subtelomeres maintained cell viability in the removal of telomerase, while the removal of the last 15kb increased chromosome senescence . [ 19 ] The knockout of subtelomeres in fission yeast, Schizosaccharomyces pombe , cells does not impede mitosis and meiosis from occurring, indicating that subtelomeres are not necessary for cell division. [ 20 ] They are not needed for the procession of mitosis and meiosis yet, subtelomeres take advantage of cellular DNA recombination. The knockout of subtelomeres in Schizosaccharomyces pombe cells does not affect the regulation of multiple stress responses, when treated with high doses of hydroxyurea , camptothecin , ultraviolet radiation , and thiabendazole . [ 20 ] Knockout of Subtelomeres in Schizosaccharomyces pombe cells did not affect the length of telomeres, indicating that they play no role it the regulation of length. [ 20 ] However, subtelomeres strongly influences the replication timing of telomeres. [ 21 ] Knockout of subtelomeres in Schizosaccharomyces pombe cells after the loss of telomerase does not affect cell survival, indicating that subtelomeres are not necessary for cell survival. [ 20 ] An explanation as to why subtelomeres are not necessary after the loss of telomerase is because the chromosomes can use intra or inter-chromosomal circularization [ 22 ] or HAATI [ 23 ] to maintain chromosomal stabilization. However, the use of inter-chromosomal circularization engenders chromosome instability by creating two centromeres in a single chromosome, causing chromosomal breakage during mitosis. In response to this, the chromosome could induce centromere inactivation to impede the formation of two centromeres, but this would induce heterochromatin formation in centromeres. Heterochromatin can be deleterious if it gets into a location that it is not supposed to be in. Subtelomeres are responsible to block heterochromatin from getting into the euchromatin region. Subtelomeres can mitigate the effects of heterochromatin invasion, by distributing heterochromatin around the ends of the subtelomeres. Without subtelomeres, heterochromatin would spread around the region of subtelomeres, getting too close to important genes. At this distance, heterochromatin can silence genes that are nearby, resulting in a higher sensitivity to osmotic stress . [ 20 ]
Subtelomeres carry out essential functions with Shugoshin protein . Shugoshin is a centromere protein for chromosome segregation during meiosis and mitosis. There are two types of Shugoshin protein: SGOL1 and SGOL2 . Sgo1 is only expressed in meiosis 1 for centromeric cohesion of the sister chromosomes, [ 24 ] while Sgo2, expressed in meiosis and mitosis, is responsible for the segregation of chromosomes at centromeres in the M phase. In fission yeast, Sgo2 is localized not only in centromeres, but also in subtelomeres. Sgo2 interacts with subtelomeres during interphase; middle of the G2 phase and plays a major role in forming "knob", which is a highly condensed chromatin body. Sgo2 remains in subtelomeres, whose cells lack telomere DNA. Sgo2 represses the expression of subtelomeric genes that is in a different pass-way from the H3K9me3 - Swi6-mediated heterochromatin. Sgo2 has also repressive effects for timing of subtelomeres replication by suppressing Sld3, [ 25 ] a replication factor, at the start of the replication. [ 26 ] Thus, Sgo2 regulate gene expressions and replication to ensure proper subtelomeric gene expression and replication timing.
Subtelomere analysis, especially sequencing and profiling of patient subtelomeres, is difficult because of the repeated sequences, length of stretches, and lack of databases on the topic.
[ original research? ] | https://en.wikipedia.org/wiki/Subtelomere |
In geometry , an angle subtended (from Latin for "stretched under") by a line segment at an arbitrary vertex is formed by the two rays between the vertex and each endpoint of the segment.
For example, a side of a triangle subtends the opposite angle.
More generally, an angle subtended by an arc of a curve is the angle subtended by the corresponding chord of the arc.
For example, a circular arc subtends the central angle formed by the two radii through the arc endpoints.
If an angle is subtended by a straight or curved segment, the segment is said to subtend the angle. Sometimes the term "subtend" is applied in the opposite sense, and the angle is said to subtend the segment. Alternately, the angle can be said to intercept or enclose the segment.
The above definition of a subtended plane angle remains valid in three-dimensional space (3D), as one vertex and two endpoints (assumed non-collinear) define an Euclidean plane in 3D .
For example, an arc of a great circle on a sphere subtends a central plane angle, formed by the two radii between the center of the sphere and each of the two arc endpoints.
More generally, a surface subtends a solid angle if its boundary defines the cone of the angle.
Many theorems in geometry relate to subtended angles. If two sides of a triangle are congruent , then the angles they subtend are also congruent, and conversely if two angles are congruent then they are subtended by congruent sides (propositions I.5–6 in Euclid's Elements ), forming an isosceles triangle . More generally, the law of sines states that the sine of each angle of a triangle is proportional to the side subtending it. The inscribed angle theorem states that when the vertex of an angle inscribed in a circle lies on the same side of the chord subtending it as the center of the circle, then the central angle subtended by the same chord is twice the inscribed angle.
By extension, an angle subtended by a more complex geometric figure may be defined in terms of the figure's convex hull and its diameter ; for example, the angle subtended by a tree as viewed in a camera ( see angular size ). [ 1 ] A subtended plane angle can also be defined for any two arbitrary isolated points and a vertex, as in two lines of sight from a particular viewer; for example, the angle subtended by two stars as seen from Earth ( see angular separation ). [ 2 ]
This elementary geometry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Subtended_angle |
Subterranean fauna refers to animal species that are adapted to live in an underground environment . Troglofauna and stygofauna are the two types of subterranean fauna. Both are associated with hypogeal habitats – troglofauna is associated with terrestrial subterranean environment ( caves and underground spaces above the water table ), and stygofauna with all kind of subterranean waters ( groundwater , aquifers , subterranean rivers , dripping bowls, gours , etc.).
Subterranean fauna is found worldwide and includes representatives of many animal groups , mostly arthropods and other invertebrates . However, there is a number of vertebrates (such as cavefishes and cave salamanders ), although they are less common. Because of the complexity in exploring underground environments, many subterranean species are yet to be discovered and described.
Peculiarities of underground habitat make it an extreme environment and, consequently, underground species are usually less than species living in epigean habitats . The main characteristic of underground environment is the lack of sunlight . Climatic values, like temperature and relative humidity , are generally almost stable – temperature corresponds to annual mean temperature in the place where the cavity opens, relative humidity rarely drops below 90%. Food sources are limited and localized. The lack of sunlight inhibits photosynthetic processes , so food comes only from epigean environment (through percolating water , gravity , or passive transport by animals). An exception are caves like the Movile Cave , where chemosynthesis forms the foundation of the food chain. Caves that are close to the surface, such as lava tubes , often have tree roots hanging from the cave roof, which provide nutrients for sap-feeding insects. [ 1 ] [ 2 ] Other important food sources in underground habitats are animals being decomposed and bat guano , [ 3 ] [ 4 ] [ 5 ] that creates large invertebrate communities in such caves. [ 6 ] [ 7 ]
Cave dwelling animals show different levels of adaptations to underground environment. According to a recent classification, animals living in terrestrial subterranean habitats can be classified into 3 categories, based on their ecology :
Regarding stygofauna , the corresponding words stygobionts (or stygobites ), stygophiles and stygoxenes are used.
Characteristics of underground environment caused cave dwelling animals to evolve a number of adaptations , both morphological and physiological . Examples of morphological adaptations include depigmentation (loss of external pigmentation), a reduction of cuticle thickness and the often extreme decrease of eyesight culminating in anophthalmia (complete loss of eyes). Exceptions, however, are harvestmen (Opiliones) in New Zealand caves, which possess large, functional eyes, presumably because these spider-like chelicerates feed on cave-dwelling, light-emitting glowworm larvae Arachnocampa which they detect visually. [ 9 ] Other adaptations include the development and elongation of antennal and locomotory appendages , in order to better move around and respond to environmental stimuli . These structures are well endowed with chemical , tactile and humidity receptors [ 3 ] [ 4 ] [ 5 ] [ 10 ] (such as Hamann's organ in the cave beetle Leptodirus hochenwartii [ 11 ] ).
Physiological adaptations include slow metabolism and reduced energy consumption, due to limited food supply and low energy efficiency. This is likely to be realized through reducing movements, erasing aggressive interactions , improving feeding capability and food usage efficiency, and through ectothermy . As a consequence, cave dwelling animals can resist without eating for long time, live more than comparable epigean species, reproduce late in their lifespan, and produce fewer and bigger eggs . [ 3 ] [ 4 ] [ 12 ]
Subterranean fauna have evolved in isolation. [ 13 ] Stratigraphic barriers, such as rock walls and layers, and fluvial barriers, such as rivers and streams, prevent or hinder the dispersal of these animals. [ 14 ] Consequently, subterranean fauna habitat and food availability can be very disjunct and precludes the great range of observed diversity across landscapes.
Floodwaters can be detrimental to subterranean species, by dramatically changing the availability of habitat, food and connectivity to other habitats and oxygen. Many subterranean fauna are likely to be sensitive to changes in their environment and floods, which can accompany a drop in temperature, may adversely affect some animals. [ 15 ]
Humans also pose a threat to troglofauna. Mismanagement of contaminants (e.g. pesticides and sewage) may poison subterranean fauna communities [ 13 ] and removal of habitat (e.g. rising/lowering of the watertable or various forms of mining) can also be a major threat. | https://en.wikipedia.org/wiki/Subterranean_fauna |
A subterranean river (also known as an underground river ) is a river or watercourse that runs wholly or partly beneath the ground , one where the riverbed does not represent the surface of the Earth. [ 1 ] It is distinct from an aquifer , which may flow like a river but is contained within a permeable layer of rock or other unconsolidated materials. A river flowing below ground level in an open gorge is not classed as subterranean. [ 2 ]
Some natural rivers may be entirely subterranean, collecting in and flowing through cave systems. In karst topography , rivers that originate above ground can disappear into sinkholes , continuing underground until they reappear on the surface downstream, possibly having merged with other subterranean rivers. The longest subterranean river in the world is the Sistema Sac Actun cave system in Mexico. [ 3 ]
Subterranean rivers can also be the result of covering over a river or diverting its flow into culverts , usually as part of urban development . [ 4 ] Reversing this process is known as "daylighting" a watercourse and is a major form of visible river restoration. Successful examples include the Cheonggyecheon in the centre of Seoul . [ 5 ] [ 6 ]
Some fish (colloquially known as cavefish ) and other troglobite organisms are adapted to life in subterranean rivers and lakes. [ 7 ]
Examples of subterranean rivers also occur in mythology and literature.
There are many natural examples of subterranean rivers. Among them:
In many cities there are natural streams which have been partially or entirely built over. Such man-made examples of subterranean urban streams are too numerous to list, but notable examples include:
Some fish (popularly known as cavefish ) and other troglobite organisms are adapted to life in subterranean rivers and lakes.
Greek mythology included the Styx , Phlegethon , Acheron , Cocytus , and Lethe as rivers within the Underworld . Dante Alighieri , in his Inferno , included the Acheron , Phlegethon , and Styx as rivers within his subterranean Hell . Similar references were made in John Milton 's Paradise Lost . The river Alph, running "Through caverns measureless to man / Down to a sunless sea" is central to the poem Kubla Khan , by Samuel Taylor Coleridge .
The characters in Jules Verne 's Journey to the Center of the Earth encounter a subterranean river:
"Hans was not mistaken," he said. "What you hear is the rushing of a torrent."
"A torrent?" I exclaimed.
"There can be no doubt; a subterranean river is flowing around us." [ 13 ]
Several other novels also feature subterranean rivers. [ 4 ] The subterranean rivers of London feature in the novel Drowning Man by Michael Robotham as well as in the novel Thrones, Dominations by Dorothy L. Sayers and Jill Paton Walsh in which a character remarks:
"You can bury them deep under, sir; you can bind them in tunnels, but in the end where a river has been, a river will always be." [ 14 ] | https://en.wikipedia.org/wiki/Subterranean_river |
A subterrene ( Latin : subterrina , Russian : Подземная лодка ) is a vehicle that travels underground (through solid rock or soil) much as a submarine travels underwater, either by mechanical drilling, or by melting its way forward. Subterrenes existed first in fiction as mechanical drillers, [ citation needed ] with real-world thermal designs and examples following in the second half of the 20th century.
Fictional subterrenes are often depicted as cylindrical in shape with conical drill heads at one or both ends, sometimes with some kind of tank-tread for propulsion, and described either as leaving an empty tunnel behind them, or as filling the space behind it with mining debris, as is the case with the Mole from the British stop-motion TV series Thunderbirds . The plausibility of such machines has declined with the advent of the real-world tunnel boring machines , which demonstrate the reality of the boring task. Tunnel boring machine themselves are not usually considered to be subterrenes, possibly because they lack the secondary attributes – mobility and independence – that are normally applied to vehicles.
A real-world, mobile subterrene must work thermally, using very high temperature and immense pressure to melt and push through rock. The front of the machine is equipped with a stationary drill tip which is kept at 700–930 °C (1,300–1,700 °F). The molten rock is pushed around the edges as the vehicle is forced forward, and cools to a glass-like lining of the tunnel. Massive amounts of energy are required to heat the drill head, supplied via nuclear power or electricity. Patents issued in the 1970s [ 1 ] indicate that U.S. scientists had planned to use nuclear power to liquefy lithium metal and circulate it to the front of the machine (drill). An onboard nuclear reactor can permit a truly independent subterrene, but cooling the reactor is a difficult problem. [ 2 ]
Online information [ clarification needed ] presents research that was funded by the United States Government for the Los Alamos Scientific Laboratories University of California, Los Alamos, New Mexico for a project Camelot under the heading Systems and Cost Analysis for a Nuclear Subterrene Tunneling Machine . [ 3 ] A patent was subsequently issued under number 3,693,731 on 26 September 1972. [ 4 ]
The design concepts fall into similar designs of current technology of the nuclear submarine fleet and existing tunnel boring technology as used in the Channel Tunnel between England and France, but with the added feature of melting rock for the tunnel wall lining. | https://en.wikipedia.org/wiki/Subterrene |
In electronics , a subtractor is a digital circuit that performs subtraction of numbers, and it can be designed using the same approach as that of an adder . The binary subtraction process is summarized below. As with an adder, in the general case of calculations on multi-bit numbers, three bits are involved in performing the subtraction for each bit of the difference : the minuend ( X i {\displaystyle X_{i}} ), subtrahend ( Y i {\displaystyle Y_{i}} ), and a borrow in from the previous (less significant) bit order position ( B i {\displaystyle B_{i}} ). The outputs are the difference bit ( D i {\displaystyle D_{i}} ) and borrow bit B i + 1 {\displaystyle B_{i+1}} . The subtractor is best understood by considering that the subtrahend and both borrow bits have negative weights, whereas the X and D bits are positive. The operation performed by the subtractor is to rewrite X i − Y i − B i {\displaystyle X_{i}-Y_{i}-B_{i}} (which can take the values -2, -1, 0, or 1) as the sum − 2 B i + 1 + D i {\displaystyle -2B_{i+1}+D_{i}} .
where ⊕ represents exclusive or .
Subtractors are usually implemented within a binary adder for only a small cost when using the standard two's complement notation, by providing an addition/subtraction selector to the carry-in and to invert the second operand.
The half subtractors can be designed through the combinational Boolean logic circuits [2] as shown in Figure 1 and 2. The half subtractor is a combinational circuit which is used to perform subtraction of two bits. It has two inputs, the minuend X {\displaystyle X} and subtrahend Y {\displaystyle Y} and two outputs the difference D {\displaystyle D} and borrow out B out {\displaystyle B_{\text{out}}} . The borrow out signal is set when the subtractor needs to borrow from the next digit in a multi-digit subtraction. That is, B out = 1 {\displaystyle B_{\text{out}}=1} when X < Y {\displaystyle X<Y} . Since X {\displaystyle X} and Y {\displaystyle Y} are bits, B out = 1 {\displaystyle B_{\text{out}}=1} if and only if X = 0 {\displaystyle X=0} and Y = 1 {\displaystyle Y=1} . An important point worth mentioning is that the half subtractor diagram aside implements X − Y {\displaystyle X-Y} and not Y − X {\displaystyle Y-X} since B out {\displaystyle B_{\text{out}}} on the diagram is given by
This is an important distinction to make since subtraction itself is not commutative , but the difference bit D {\displaystyle D} is calculated using an XOR gate which is commutative.
The truth table for the half subtractor is:
Using the table above and a Karnaugh map , we find the following logic equations for D {\displaystyle D} and B out {\displaystyle B_{\text{out}}} :
Consequently, a simplified half-subtract circuit, advantageously avoiding crossed traces in particular as well as a negate gate is:
where lines to the right are outputs and others (from the top, bottom or left) are inputs.
The full subtractor is a combinational circuit which is used to perform subtraction of three input bits : the minuend X {\displaystyle X} , subtrahend Y {\displaystyle Y} , and borrow in B in {\displaystyle B_{\text{in}}} . The full subtractor generates two output bits: the difference D {\displaystyle D} and borrow out B out {\displaystyle B_{\text{out}}} . B in {\displaystyle B_{\text{in}}} is set when the previous digit is borrowed from X {\displaystyle X} . Thus, B in {\displaystyle B_{\text{in}}} is also subtracted from X {\displaystyle X} as well as the subtrahend Y {\displaystyle Y} . Or in symbols: X − Y − B in {\displaystyle X-Y-B_{\text{in}}} . Like the half subtractor, the full subtractor generates a borrow out when it needs to borrow from the next digit. Since we are subtracting Y {\displaystyle Y} and B in {\displaystyle B_{\text{in}}} from X {\displaystyle X} , a borrow out needs to be generated when X < Y + B in {\displaystyle X<Y+B_{\text{in}}} . When a borrow out is generated, 2 is added in the current digit. (This is similar to the subtraction algorithm in decimal. Instead of adding 2, we add 10 when we borrow.) Therefore, D = X − Y − B in + 2 B out {\displaystyle D=X-Y-B_{\text{in}}+2B_{\text{out}}} .
The truth table for the full subtractor is:
Therefore the equation is:
D = X ⊕ Y ⊕ B i n {\displaystyle D=X\oplus Y\oplus B_{in}}
B o u t = X ¯ B i n + X ¯ Y + Y B i n {\displaystyle B_{out}={\bar {X}}B_{in}+{\bar {X}}Y+YB_{in}} | https://en.wikipedia.org/wiki/Subtractor |
A subtropical climate vegetated roof ( SCV roof ) is a type of green building practice that employs a planted soil media installed above a waterproof roof deck to obtain environmental benefits and address sustainability concerns, similar to traditional green roofs located in northern continental United States. Soil media, plant palettes, and green roof systems that can adapt to the adverse weather conditions and physical characteristics of the humid, subtropical regions of the United States are utilized in the construction and design of subtropical climate vegetated roofs.
Green roofs are used for various reasons including: urban oasis , storm water mitigation, carbon reduction , energy conservation , aesthetics, and therapeutic values depending on the geographic location and the intended specific goals of the project. [ 1 ] Most of the current green roof research pertains to northern parts of the continental United States, whereas, very limited research has been conducted in humid, subtropical regions. [ 2 ]
Although similar characteristics and principles exist, there are several differences between the two types of environmentally sound roofing systems. These differences are comparable to the differences found between regions of the United States in conventional landscaping and gardening or the variations found in forms of landscaping. Plant species and landscaping methods utilized in northern parts of the United States are not suitable for humid, subtropical regions of United States due to the extreme temperatures and rain events that occur. This accounts for the most significant difference between a green roof in northern United States and a subtropical climate vegetated roof (SCV roof).
A subtropical climate vegetated roof that is well designed according to the specific geographic locations climate can lower roof surface temperatures by as much 38° and depending on the amount of the event retain up to 88% of rainfall. [ 2 ] An improperly designed subtropical climate vegetated (SCV roof) using incorrect soil media and plant species can fail by not achieving the intended goals. [ 2 ] This roofing method also contributes towards growing the green economy , clean energy technology policies, and qualifies for Federal and local tax incentives, set in place by the United States government.
Compared with other parts of the United States, the number of vegetated roofs currently in the Southeast is significantly less. Vegetated roofs in humid subtropical regions rely on the same core green roof terminologies that are used throughout the world and other parts of the United States. Extensive, intensive, soil media, ballast, filter fabric, drainage layer, waterproof membrane are some of the core green roof component terms associated with SCV roofs. [ 3 ]
Regional terms, plant palettes, and technologies are forming to adapt to recent innovations and increased popularity of green roofs in the humid, subtropical regions of the United States. All forms of green roofs have the potential to retain stormwater on the roof surface and lower the thermal loading on buildings. Due to high temperatures, prolonged heat, and excessive amounts of precipitation, humid subtropical regions of the United States receive the greatest environmental benefits provided by SCV roofs, which are: reduced rainwater input into storm water retention systems during rainfall and increased energy performance ratings in buildings. [ 2 ] SCV and green roofs increase energy efficiencies of buildings by stabilizing roof surface temperatures. In other regions of the United States, the greatest environmental benefits of green roof design may be different based upon the type of climate the area possesses.
Recent advancements in soil engineering and plastic technologies allow vegetated roofs the ability to adapt to different locations within the humid, subtropical region of the United States. Soil media moisture content and capacity levels can be regulated by using soil elements that adapt to the climate of each specific geographic location and client needs. The amount of moisture retained depends on the maximum moisture retention capacity, the permeability and the depth of the soil media. [ 4 ] High density plastics permit SCV roof systems to withstand the weather elements and adjust to varying building types of the region.
As defined by green roof industry standards, extensive green roofs have a soil media of less than 6 inches in depth and intensive green roofs have a soil media of more than 6 inches in depth. [ 5 ] Most SCV roofs that are greater than 6 inches in depth are expensive and found on residential high rise structures, often containing pools and other amenities.
An SCV roofs requires a unique soil media mixture to adapt to the harsh weather conditions and physical characteristics of the southern United States. Expanded shall and clay are typically used to form a base and comprise up to 90% of some soil media mixtures used throughout the United States. Perlite , vermiculite , ash, tire crumbs, sand, peat moss , and recycled vegetation are some of the other elements utilized in soil media engineering. Albedo and heat transfer rates are key variables to consider when designing an SCV roof and do not have a significant effect on green roofs in the northern continental United States.
There are three basic SCV and green roof systems available in today's market: built-up, modular, and mat. These systems vary from manufacture to manufacture and are composed of different materials such as: foam , high density plastic, and fabrics. Many of the systems have geographic limitations and do not perform well in humid, subtropical regions based upon the intent of the system and the materials being used.
Multi-layered systems containing the following functional layers: root barrier , protection layer, drainage layer, filter layer, growing medium and plant level. [ 6 ]
Self-contained units, typically square in shape, that require only the soil medium and vegetative layer for a functioning green roof. These systems are easy to install and remove. Some modular systems are pre-grown at nurseries to client specifications, forming an instant vegetative layer. [ 6 ]
Singled-layered systems of this type are drained by a multi-layer fabric mat called a “drainage mat” that combines soil separation, drainage, and protection functions. Current research suggests that the depth of the soil media, material, and number of layers affect the success rate of an individual green or SCV roof. [ 6 ]
A suitable plant species for SCV roofs consist of the following features: drought tolerant, minimal root structure, minimal height, ability to form a vegetative mat, non-rangy, heat tolerant, frost tolerant, and the ability to adapt to a non-traditional soil media. Plant species that have extensive root system and tend to be rangy can puncture waterproofing elements or grow into unwanted areas causing mold and mildew . Water, high nutrient , and shade -dependent plants are not suitable for SCV roofs and should be avoided and can lead to expensive failures.
Some of the most successful SCV roof plant species are in the families Crassulaceae and Aizoaceae , which are CAM plants. A plant that uses the crassulacean acid metabolism (CAM) as an adaptation for arid conditions. [ 7 ] CO 2 entering the stomata during the night is converted into organic acids , which release [[CO 2 ]] for the Calvin Cycle during the day, when the stomata are closed. [ 8 ] CAM plants often show xerophytic features, such as thick, reduced leaves with a low surface-area-to-volume ratio, thick cuticle, and stomata sunken into pits. [ 8 ]
Green roofs in the northern continental United States rely on sedums which are in the family Crassulaceae. Most varieties of Sedums are not appropriate for humid, subtropical climates and experience root rot and disease problems due to high temperatures and humidity levels. However, two Sedum cultivars, ‘Lemon Coral’ and’ Florida Friendly Gold’ are currently [ when? ] being researched at the University of Florida and appear to be adapting to the humid, subtropical climate of Gainesville, Florida .
Example SCV roof plant palette
SCV roofs confront a magnitude of challenges due to the adverse weather conditions of the Southeastern United States. High humidity levels, excessive rain amounts, prolonged heat, mold, mildew, insects, disease, weeds, soil borne disease, maintenance concerns, and sloped roofs are the major challenges faced in designing a SCV roof. High humidity levels, excessive rain amounts, prolonged heat lead to decreased plant health on CAM plants that are standard in green roof design. The decreased plant health causes diseases, insects, root rot, and plant fatality.
Soil-borne diseases occur more frequently due to warm, rainy, humid environment rhythm of the humid, subtropical region. [ 9 ] SCV roof plants are researched and tested at several different universities throughout the southeast to avoid system failure and economic loses. Mold and mildew can form on areas of the roof and building when proper ventilation is not taken into consideration and are also repercussions of high humidity levels and prolonged heat.
One of the greatest challenges to SCV roofs can be hurricanes . The strong hurricane winds can cause uplifting of the roofs. High winds can scour the growth media where the plants are established. [ 10 ] Scouring is the blowing of the particles in the growth media from the surface of the vegetated roof, thereby reducing the volume and weight of growth media and its ability to ballast the green roof. [ 11 ]
Sloped roofs that are prevalent in the southeastern United States also pose a significant challenge for SCV roofs. Soil media erosion and poor plant establishment are the most common problems and can occur on any angle of sloped roof if not designed properly. Erosion blankets and green roof soil media stabilization products are used to mitigate the effects of sloped roofs. Flat roofs and low sloped roofs are conventional roof slopes by the building industry in the southeastern United States and allow for successful implementation of SCV roofs.
Flat roofs – 1% to 2% slope
Low slope-3:12 to 5:12
Medium Slope-6:12 to 9:12
High Slope-10:12 to 12:12
Here are some of the states where humid subtropical climates can be found:
The climate in many of these states can vary and be extreme.
Benefits (Performance ratings)
Initially, vegetated roofs can have a high short-term capital but the long-term energy and maintenance savings outweigh them. Even the U.S. Green Building Council and some new advances in green roofs suggest that green buildings don't necessarily have to cost more than a conventional one.
Project name: Shadow Wood Preserve Green Roof Demonstration
Project name: Charles R. Perry Construction Yard, University of Florida
Project name: Student Union Expansion at the University of Central Florida (UCF) | https://en.wikipedia.org/wiki/Subtropical_climate_vegetated_roof |
A subunit vaccine is a vaccine that contains purified parts of the pathogen that are antigenic , or necessary to elicit a protective immune response . [ 1 ] [ 2 ] Subunit vaccine can be made from dissembled viral particles in cell culture or recombinant DNA expression, [ 3 ] in which case it is a recombinant subunit vaccine .
A "subunit" vaccine doesn't contain the whole pathogen, unlike live attenuated or inactivated vaccine , but contains only the antigenic parts such as proteins , polysaccharides [ 1 ] [ 2 ] or peptides . [ 4 ] Because the vaccine doesn't contain "live" components of the pathogen, there is no risk of introducing the disease, and is safer and more stable than vaccines containing whole pathogens. [ 1 ] Other advantages include being well-established technology and being suitable for immunocompromised individuals. [ 2 ] Disadvantages include being relatively complex to manufacture compared to some vaccines, possibly requiring adjuvants and booster shots , and requiring time to examine which antigenic combinations may work best. [ 2 ]
The first recombinant subunit vaccine was produced in the mid-1980s to protect people from Hepatitis B . Other recombinant subunit vaccines licensed include Engerix-B ( hepatitis B ), Gardasil 9 [ 5 ] ( Human Papillomavirus ), Flublok [ 6 ] ( influenza ), Shingrix [ 7 ] ( Herpes zoster ) and Nuvaxovid [ 8 ] ( Coronavirus disease 2019 ).
After injection , antigens trigger the production of antigen-specific antibodies , which are responsible for recognising and neutralising foreign substances. Basic components of recombinant subunit vaccines include recombinant subunits, adjuvants and carriers. Additionally, recombinant subunit vaccines are popular candidates for the development of vaccines against infectious diseases (e.g. tuberculosis , [ 9 ] dengue [ 10 ] ).
Recombinant subunit vaccines are considered to be safe for injection. The chances of adverse effects vary depending on the specific type of vaccine being administered. Minor side effects include injection site pain, fever, and fatigue , and serious adverse effects consist of anaphylaxis and potentially fatal allergic reaction . The contraindications are also vaccine-specific; they are generally not recommended for people with the previous history of anaphylaxis to any component of the vaccines. Advice from medical professionals should be sought before receiving any vaccination.
The first certified subunit vaccine by clinical trials on humans is the hepatitis B vaccine, containing the surface antigens of the hepatitis B virus itself from infected patients and adjusted by newly developed technology aiming to enhance the vaccine safety and eliminate possible contamination through individuals plasma. [ 11 ]
Subunit vaccines contain fragments of the pathogen, such as protein or polysaccharide, whose combinations are carefully selected to induce a strong and effective immune response. Because the immune system interacts with the pathogen in a limited way, the risk of side effects is minimal. [ 2 ] An effective vaccine would elicit the immune response to the antigens and form immunological memory that allows quick recognition of the pathogens and quick response to future infections. [ 1 ]
A drawback is that the specific antigens used in a subunit vaccine may lack pathogen-associated molecular patterns which are common to a class of pathogen. These molecular structures may be used by immune cells for danger recognition, so without them, the immune response may be weaker. Another drawback is that the antigens do not infect cells , so the immune response to the subunit vaccines may only be antibody-mediated , not cell-mediated , and as a result, is weaker than those elicited by other types of vaccines.
To increase immune response, adjuvants may be used with the subunit vaccines, or booster doses may be required. [ 2 ]
A protein subunit is a polypeptide chain or protein molecule that assembles (or " coassembles ") with other protein molecules to form a protein complex . [ 12 ] [ 13 ] [ 14 ] Large assemblies of proteins such as viruses often use a small number of types of protein subunits as building blocks. [ 15 ] A key step in creating a recombinant protein vaccine is the identification and isolation of a protein subunit from the pathogen which is likely to trigger a strong and effective immune response, without including the parts of the virus or bacterium that enable the pathogen to reproduce. Parts of the protein shell or capsid of a virus are often suitable. The goal is for the protein subunit to prime the immune system response by mimicking the appearance but not the action of the pathogen. [ 16 ] Another protein-based approach involves self‐assembly of multiple protein subunits into a virus-like particle (VLP) or nanoparticle. The purpose of increasing the vaccine's surface similarity to a whole virus particle (but not its ability to spread) is to trigger a stronger immune response. [ 17 ] [ 16 ] [ 18 ]
Protein subunit vaccines are generally made through protein production , manipulating the gene expression of an organism so that it expresses large amounts of a recombinant gene . [ 16 ] [ 19 ] A variety of approaches can be used for development depending on the vaccine involved. [ 17 ] Yeast , baculovirus , or mammalian cell cultures can be used to produce large amounts of proteins in vitro. [ 16 ] [ 19 ] [ 20 ]
Protein-based vaccines are being used for hepatitis B and for human papillomavirus (HPV). [ 17 ] [ 16 ] The approach is being used to try to develop vaccines for difficult-to-vaccinate-against viruses such as ebolavirus and HIV . [ 21 ] Protein-based vaccines for COVID-19 tend to target either its spike protein or its receptor binding domain. [ 17 ] As of 2021, the most researched vaccine platform for COVID-19 worldwide was reported to be recombinant protein subunit vaccines. [ 16 ] [ 22 ]
Vi capsular polysaccharide vaccine (ViCPS) against typhoid caused by the Typhi serotype of Salmonella enterica . [ 23 ] Instead of being a protein, the Vi antigen is a bacterial capsule polysacchide, made up of a long sugar chain linked to a lipid. [ 24 ] Capsular vaccines like ViCPS tend to be weak at eliciting immune responses in children. Making a conjugate vaccine by linking the polysacchide with a toxoid increases the efficacy. [ 25 ]
A conjugate vaccine is a type of vaccine which combines a weak antigen with a strong antigen as a carrier so that the immune system has a stronger response to the weak antigen. [ 26 ]
A peptide-based subunit vaccine employs a peptide instead of a full protein . [ 27 ] Peptide-based subunit vaccine mostly used due to many reasons,such as, it is easy and affordable for massive production. Adding to that, its greatest stability, purity and exposed composition. [ 28 ] Three steps occur leading to creation of peptide subunit vaccine; [ 29 ]
When compared with conventional attenuated vaccines and inactivated vaccines , recombinant subunit vaccines have the following special characteristics:
However, there are also some drawbacks regarding recombinant subunit vaccines:
Vaccination is a potent way to protect individuals against infectious diseases . [ 34 ]
Active immunity can be acquired artificially by vaccination as a result of the body's own defense mechanism being triggered by the exposure of a small, controlled amount of pathogenic substances to produce its own antibodies and memory cells without being infected by the real pathogen. [ 35 ]
The processes involved in primary immune response are as follows:
Under specific circumstances, low doses of vaccines are given initially, followed by additional doses named booster doses . Boosters can effectively maintain the level of memory cells in the human body, hence extending a person's immunity . [ 32 ] [ 33 ] [ 42 ]
The manufacturing process of recombinant subunit vaccines are as follows: [ citation needed ]
Candidate subunits will be selected primarily by their immunogenicity . [ 43 ] To be immunogenic , they should be of foreign nature and of sufficient complexity for the reaction between different components of the immune system and the candidates to occur. [ 44 ] Candidates are also selected based on size, nature of function (e.g. signalling ) and cellular location (e.g. transmembrane ). [ 43 ]
Upon identifying the target subunit and its encoding gene , the gene will be isolated and transferred to a second, non-pathogenic organism, and cultured for mass production . [ 45 ] The process is also known as heterologous expression . [ citation needed ]
A suitable expression system is selected based on the requirement of post-translational modifications , costs, ease of product extraction and production efficiency. Commonly used systems for both licensed and developing recombinant subunit vaccines include bacteria , yeast , mammalian cells, insect cells. [ 46 ]
Bacterial cells are widely used for cloning processes , genetic modification and small-scale productions. [ 47 ] Escherichia coli (E. Coli) is widely utilised due to its highly explored genetics , widely available genetic tools for gene expression , accurate profiling and its ability to grow in inexpensive media at high cell densities. [ 48 ]
E. Coli is mostly appropriate for structurally simple proteins owing to its inability to carry out post-translational modifications , lack of protein secretary system and the potential for producing inclusion bodies that require additional solubilisation. [ 47 ] [ 48 ] [ 49 ] Regarding application, E.Coli is being utilised as the expression system of the dengue vaccine . [ 10 ]
Yeast matches bacterial cells' cost-effectiveness, efficiency and technical feasibility. [ 47 ] Moreover, yeast secretes soluble proteins and has the ability to perform post-translational modifications similar to mammalian cells. [ 49 ]
Notably, yeast incorporates more mannose molecules during N-glycosylation when compared with other eukaryotes , [ 50 ] which may trigger cellular conformational stress responses . Such responses may result in failure in reaching native protein conformation, implying potential reduction of serum half-life and immunogenicity . [ 47 ] Regarding application, both the hepatitis B virus surface antigen ( HBsAg ) and the virus-like particles ( VLPs ) of the major capsid protein L1 of human papillomavirus type 6, 11, 16, 18 are produced by Saccharomyces cerevisiae . [ citation needed ]
Mammalian cells are well known for their ability to perform therapeutically essential post-translational modifications and express properly folded, glycosylated and functionally active proteins. [ 48 ] [ 51 ] [ 52 ] However, efficacy of mammalian cells may be limited by epigenetic gene silencing and aggresome formation (recombinant protein aggregation). [ 48 ] For mammalian cells, synthesised proteins were reported to be secreted into chemically defined media, potentially simplifying protein extraction and purification. [ 47 ]
The most prominent example under this class is Chinese Hamster Ovary (CHO) cells utilised for the synthesis of recombinant varicella zoster virus surface glycoprotein (gE) antigen for SHINGRIX . [ 7 ] CHO cells are recognised for rapid growth and their ability to offer process versatility. They can also be cultured in suspension-adapted culture in protein-free medium, hence reducing risk of prion -induced contamination. [ 47 ] [ 48 ]
The baculovirus - insect cell expression system has the ability to express a variety of recombinant proteins at high levels and provide significant eukaryotic protein processing capabilities, including phosphorylation , glycosylation , myristoylation and palmitoylation . [ 53 ] Similar to mammalian cells, proteins expressed are mostly soluble , accurately folded, and biologically active. [ 54 ] However, it has slower growth rate and requires higher cost of growth medium than bacteria and yeast , and confers toxicological risks. [ 47 ] A notable feature is the existence of elements of control that allow for the expression of secreted and membrane -bound proteins in Baculovirus-insect cells. [ 47 ] [ 53 ]
Licensed recombinant subunit vaccines that utilises baculovirus - insect cells include Cervarix (papillomavirus C-terminal truncated major capsid protein L1 types 16 and 18) [ 47 ] [ 55 ] and Flublok Quadrivalent ( hemagglutinin ( HA ) proteins from four strains of influenza viruses ). [ 6 ]
Throughout history, extraction and purification methods have evolved from standard chromatographic methods to the utilisation of affinity tags . [ 56 ] However, the final extraction and purification process undertaken highly depends on the chosen expression system . Please refer to subunit expression and synthesis for more insights. [ citation needed ]
Adjuvants are materials added to improve immunogenicity of recombinant subunit vaccines . [ 57 ]
Adjuvants increase the magnitude of adaptive response to the vaccine and guide the activation of the most effective forms of immunity for each specific pathogen (e.g. increasing generation of T cell memory). [ 57 ] [ 58 ] [ 59 ] [ 60 ] Addition of adjuvants may confer benefits including dose sparing and stabilisation of final vaccine formulation. [ 57 ] [ 60 ]
Appropriate adjuvants are chosen based on safety, tolerance, compatibility of antigen and manufacturing considerations. [ 57 ] Commonly used adjuvants for recombinant subunit vaccines are Alum adjuvants (e.g. aluminium hydroxide ), Emulsions (e.g. MF59 ) and Liposomes combined with immunostimulatory molecules (e.g. AS01 B ). [ 57 ] [ 59 ]
Delivery systems are primarily divided into polymer-based delivery systems ( microspheres and liposomes ) and live delivery systems ( gram-positive bacteria , gram-negative bacteria and viruses ) [ citation needed ]
Vaccine antigens are often encapsulated within microspheres or liposomes . Common microspheres made using Poly-lactic acid (PLA) [ 61 ] and poly-lactic-co-glycolic acid (PLGA) [ 61 ] allow for controlled antigen release by degrading in vivo while liposomes including multilamellar or unilamellar vesicles allow for prolonged release. [ 59 ]
Polymer-based delivery systems confer advantages such as increased resistance to degradation in GI tract , controlled antigen release, raised particle uptake by immune cells and enhanced ability to induce cytotoxic T cell responses. [ 59 ] An example of licensed recombinant vaccine utilising liposomal delivery is Shringrix .
Live delivery systems , also known as vectors , are cells modified with ligands or antigens to improve the immunogenicity of recombinant subunits via altering antigen presentation , biodistribution and trafficking. [ 62 ] Subunits may either be inserted within the carrier or genetically engineered to be expressed on the surface of the vectors for efficient presentation to the mucosal immune system . [ 45 ]
Recombinant subunit vaccines are safe for administration. [ 65 ] [ 66 ] However, mild local reactions, including induration and swelling of the injection site, along with fever , fatigue and headache may be encountered after vaccination. [ 65 ] [ 67 ] [ 68 ] Occurrence of severe hypersensitivity reactions and anaphylaxis is rare, [ 69 ] but can possibly lead to deaths of individuals. Adverse effects can vary among populations depending on their physical health condition, age, gender and genetic predisposition. [ 70 ] [ 71 ]
Recombinant subunit vaccines are contraindicated to people who have experienced allergic reactions and anaphylaxis to antigens or other components of the vaccines previously. [ 72 ] [ 73 ] Furthermore, precautions should be taken when administering vaccines to people who are in diseased state and during pregnancy , [ 72 ] in which their injections should be delayed until their conditions become stable and after childbirth respectively.
ENGERIX-B (produced by GSK) and RECOMBIVAX HB (produced by merck) are two recombinant subunit vaccines licensed for the protection against hepatitis B . Both contain HBsAg harvested and purified from Saccharomyces cerevisiae and are formulated as a suspension of the antigen adjuvanted with alum . [ 74 ] [ 75 ]
Antibody concentration ≥10mIU/mL against HBsAg are recognized as conferring protection against hepatitis B infection. [ 74 ] [ 75 ]
It has been shown that primary 3-dose vaccination of healthy individuals is associated with ≥90% seroprotection rates for ENGERIX-B , despite decreasing with older age. Lower seroprotection rates are also associated with presence of underlying chronic diseases and immunodeficiency . Yet, GSK HepB still has a clinically acceptable safety profile in all studied populations. [ 76 ]
Cervarix , GARDASIL and GARDASIL9 are three recombinant subunit vaccines licensed for the protection against HPV infection. They differ in the strains which they protect the patients from as Cervarix confers protection against type 16 and 18, [ 55 ] Gardasil confers protection against type 6, 11, 16 and 18, [ 77 ] and Gardasil 9 confers protection against type 6, 11, 16, 18, 31, 33, 45, 52, 58 [ 5 ] respectively. The vaccines contain purified VLP of the major capsid L1 protein produced by recombinant Saccharomyces cerevisiae . [ citation needed ]
It has been shown in a 2014 systematic quantitative review that the bivalent HPV vaccine ( Cervarix ) is associated with pain (OR 3.29; 95% CI: 3.00–3.60), swelling (OR 3.14; 95% CI: 2.79–3.53) and redness (OR 2.41; 95% CI: 2.17–2.68) being the most frequently reported adverse effects. For Gardasil, the most frequently reported events were pain (OR 2.88; 95% CI: 2.42–3.43) and swelling (OR 2.65; 95% CI: 2.0–3.44). [ 78 ]
Gardasil was discontinued in the U.S. on May 8, 2017, after the introduction of Gardasil 9 [ 79 ] and Cervarix was also voluntarily withdrawn in the U.S. on August 8, 2016. [ 80 ]
Flublok Quadrivalent is a licensed recombinant subunit vaccine for active immunisation against influenza . It contains HA proteins of four strains of influenza virus purified and extracted using the Baculovirus - insect expression system . The four viral strains are standardised annually according to United States Public Health Services (USPHS) requirements. [ 6 ]
Flublok Quadrivalent has a comparable safety profile to traditional trivalent and quadrivalent vaccine equivalents. Flublok is also associated with less local reactions (RR = 0.94, 95% CI 0.90–0.98, three RCTs, FEM, I2 = 0%, low‐ certainty evidence) and higher risk of chills (RR = 1.33, 95% CI 1.03–1.72, three RCTs, FEM, I2 = 14%, low‐certainty evidence). [ 81 ]
SHINGRIX is a licensed recombinant subunit vaccine for protection against Herpes Zoster , whose risk of developing increases with decline of varicella zoster virus (VZV) specific immunity . The vaccine contains VZV gE antigen component extracted from CHO cells , which is to be reconstituted with adjuvant suspension AS01 B . [ 7 ]
Systematic reviews and meta-analyses have been conducted on the efficacy, effectiveness and safety of SHINGRIX in immunocompromised 18–49 year old patients and healthy adults aged 50 and over. These studies reported humoral and cell-mediated immunity rate ranged between 65.4 and 96.2% and 50.0–93.0% while efficacy in patients (18–49 yo) with haematological malignancies was estimated at 87.2% (95%CI, 44.3–98.6%) up to 13 months post-vaccination with an acceptable safety profile . [ 82 ] [ 83 ]
NUVAXOVID is a recombinant subunit vaccine licensed for the prevention of SARS-CoV-2 infection . Market authorization was issued on 20 December 2021. [ 84 ] The vaccine contains the SARS-CoV-2 spike protein produced using the baculovirus expression system , which is eventually adjuvanted with the Matrix M adjuvant. [ 8 ]
While the practice of immunisation can be traced back to the 12th century , in which ancient Chinese at that time employed the technique of variolation to confer immunity to smallpox infection, [ citation needed ] the modern era of vaccination has a short history of around 200 years. It began with the invention of a vaccine by Edward Jenner in 1798 to eradicate smallpox by injecting relatively weaker cowpox virus into the human body. [ citation needed ]
The middle of the 20th century marked the golden age of vaccine science. [ citation needed ] Rapid technological advancements during this period of time enabled scientists to cultivate cell culture under controlled environments in laboratories, [ 85 ] subsequently giving rise to the production of vaccines against poliomyelitis , measles and various communicable diseases . [ citation needed ] Conjugated vaccines were also developed using immunologic markers including capsular polysaccharide and proteins . [ 85 ] Creation of products targeting common illnesses successfully lowered infection-related mortality and reduced public healthcare burden.
Emergence of genetic engineering techniques revolutionised the creation of vaccines. By the end of the 20th century, researchers had the ability to create recombinant vaccines apart from traditional whole-cell vaccine , for instance Hepatitis B vaccine , which uses the viral antigens to initiate immune responses . [ 85 ]
As the manufacturing methods continue to evolve, vaccines with more complex constitutions will inevitably be generated in the future to extend their therapeutic applications to both infectious and non-infectious diseases , [ citation needed ] in order to safeguard the health of more people.
Recombinant subunit vaccines are used in development for tuberculosis , [ 9 ] dengue fever , [ 10 ] soil-transmitted helminths , [ 86 ] feline leukaemia [ 87 ] and COVID-19 . [ 88 ]
Subunit vaccines are not only considered effective for SARS-COV-2, but also as candidates for evolving immunizations against malaria, tetanus, salmonella enterica, and other diseases. [ 11 ]
Research has been conducted to explore the possibility of developing a heterologous SARS-CoV receptor-binding domain (RBD) recombinant protein as a human vaccine against COVID-19 . The theory is supported by evidence that convalescent serum from SARS-CoV patients have the ability to neutralise SARS-CoV-2 (corresponding virus for COVID-19 ) and that amino acid similarity between SARS-CoV and SARS-CoV-2 spike and RBD protein is high (82%). [ 88 ] | https://en.wikipedia.org/wiki/Subunit_vaccine |
A subvariety (Latin: subvarietas ) in botanical nomenclature is a taxonomic rank . They are rarely used to classify organisms.
Subvariety is ranked:
Subvariety is an infraspecific taxon . [ 1 ]
Its name consists of three parts:
To indicate the subvariety rank, the abbreviation "subvar." is put before the infraspecific epithet.
This botany article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Subvariety_(botany) |
A subwoofer (or sub ) is a loudspeaker designed to reproduce low-pitched audio frequencies , known as bass and sub-bass , that are lower in frequency than those which can be (optimally) generated by a woofer . The typical frequency range that is covered by a subwoofer is about 20–200 Hz for consumer products, [ 1 ] below 100 Hz for professional live sound, [ 2 ] and below 80 Hz in THX -certified systems. [ 3 ] Thus, one or more subwoofers are important for high-quality sound reproduction as they are responsible for the lowest two to three octaves of the ten octaves that are audible. This very low-frequency (VLF) range reproduces the natural fundamental tones of the bass drum, electric bass, double bass, grand piano, contrabassoon , tuba, in addition to thunder, gunshots, explosions, etc.
Subwoofers are never used alone, as they are intended to substitute the VLF sounds of "main" loudspeakers that cover the higher frequency bands. VLF and higher-frequency signals are sent separately to the subwoofer(s) and the mains by a " crossover " network, typically using active electronics, including digital signal processing (DSP). Additionally, subwoofers are fed their own low-frequency effects (LFE) signals that are reproduced at 10 dB higher than standard peak level. [ 4 ]
Subwoofers can be positioned more favorably than the main speakers' woofers in the typical listening room acoustic, as the very low frequencies they reproduce are nearly omnidirectional and their direction largely indiscernible. However, much digitally recorded content contains lifelike binaural cues that human hearing may be able to detect in the VLF range, reproduced by a stereo crossover and two or more subwoofers. [ 5 ] Subwoofers are not acceptable to all audiophiles, likely due to distortion artifacts produced by the subwoofer driver after the crossover and at frequencies above the crossover. [ 6 ]
While the term "subwoofer" technically only refers to the speaker driver, in common parlance, the term often refers to a subwoofer driver mounted in a speaker enclosure (cabinet), often with a built-in amplifier .
Subwoofers are made up of one or more woofers mounted in a loudspeaker enclosure —often made of wood—capable of withstanding air pressure while resisting deformation. Subwoofer enclosures come in a variety of designs, including bass reflex (with a port or vent), using a subwoofer and one or more passive radiator speakers in the enclosure, acoustic suspension (sealed enclosure), infinite baffle , horn-loaded , tapped horn , transmission line , bandpass or isobaric designs. Each design has unique trade-offs with respect to efficiency, low-frequency range, loudness, cabinet size, and cost. Passive subwoofers have a subwoofer driver and enclosure, but they are powered by an external amplifier. Active subwoofers include a built-in amplifier. [ 7 ]
The first home audio subwoofers were developed in the 1960s to add bass response to home stereo systems. Subwoofers came into greater popular consciousness in the 1970s with the introduction of Sensurround in movies such as Earthquake , which produced loud low-frequency sounds through large subwoofers. With the advent of the compact cassette and the compact disc in the 1980s, the reproduction of deep and loud bass was no longer limited by the ability of a phonograph record stylus to track a groove, [ 8 ] and producers could add more low-frequency content to recordings. As well, during the 1990s, DVDs were increasingly recorded with " surround sound " processes that included a low-frequency effects (LFE) channel, which could be heard using the subwoofer in home-cinema (also called home theater ) systems. During the 1990s, subwoofers also became increasingly popular in home stereo systems , custom car audio installations, and in PA systems . By the 2000s, subwoofers became almost universal in sound reinforcement systems in nightclubs and concert venues.
Unlike a system's main loudspeakers, subwoofers can be positioned more optimally in a listening room's acoustic. However, subwoofers are not universally accepted by audiophiles amid complaints of the difficulty of "splicing" the sound with that of the main speakers around the crossover frequency. This is largely due to the subwoofer driver's non-linearity producing harmonic and intermodulation distortion products well above the crossover frequency, and into the range where human hearing can "localize" them, wrecking the stereo "image".
From about 1900 to the 1950s, the "lowest frequency in practical use" in recordings, broadcasting and music playback was 100 Hz. [ 9 ] When sound was developed for motion pictures, the basic RCA sound system was a single 8-inch (20 cm) speaker mounted in straight horn, an approach which was deemed unsatisfactory by Hollywood decisionmakers, who hired Western Electric engineers to develop a better speaker system. [ 10 ] The early Western Electric experiments added a set of 18-inch drivers for the low end in a large, open-backed baffle (extending the range down to 40 Hz) and a high-frequency unit, but MGM was not pleased with the sound of the three-way system, as they had concerns about the delay between the different drivers. [ 10 ]
In 1933, the head of MGM's sound department, Douglas Shearer , worked with John Hilliard and James B. Lansing (who would later found Altec Lansing in 1941 and JBL in 1946) to develop a new speaker system that used a two-way enclosure with a W-shaped bass horn that could go as low as 40 Hz. [ 10 ] The Shearing-Lansing 500-A ended up being used in "screening rooms, dubbing theaters, and early sound reinforcement". [ 10 ] In the late 1930s, Lansing created a smaller two-way speaker with a 15-inch (38 cm) woofer in a vented enclosure, which he called the Iconic system; it was used as a studio monitor and in high-end home hi-fi set-ups. [ 10 ]
During the 1940s swing era , to get deeper bass, "pipelike opening[s]" were cut into speaker enclosures, creating bass reflex enclosures, as it was found that even a fairly inexpensive speaker enclosure, once modified in this way, could "transmit the driving power of a heavy...drumbeat—and sometimes not much else—to a crowded dancefloor." [ 9 ] Prior to the development of the first subwoofers, woofers were used to reproduce bass frequencies, usually with a crossover point set at 200 Hz and a 4-inch (10 cm) loudspeaker in an infinite baffle or in professional sound applications, a "hybrid horn-loaded" bass reflex enclosure (such as the 15-inch Altec Lansing A-7 enclosure nicknamed the "Voice of the Theater", which was introduced in 1946). [ 11 ] In the mid-1950s, the Academy of Motion Picture Arts and Sciences selected the "big, boxy" Altec A-7 as the industry standard for movie sound reproduction in theaters. [ 12 ]
In September 1964, Raymon Dones, of El Cerrito, California, received the first patent for a subwoofer specifically designed to augment omnidirectionally the low frequency range of modern stereo systems (US patent 3150739). It was able to reproduce distortion-free low frequencies down to 15 cycles per second (15 Hz). A specific objective of Dones's invention was to provide portable sound enclosures capable of high fidelity reproduction of low frequency sound waves without giving an audible indication of the direction from which they emanated. Dones's loudspeaker was marketed in the US under the trade name "The Octavium" [ 13 ] from the early 1960s to the mid-1970s. The Octavium was utilized by several recording artists of that era, most notably the Grateful Dead , bassist Monk Montgomery , bassist Nathan East , and the Pointer Sisters . The Octavium speaker and Dones's subwoofer technology were also utilized, in a few select theaters, to reproduce low pitch frequencies for the 1974 blockbuster movie Earthquake . During the late 1960s, Dones's Octavium was favorably reviewed by audiophile publications including Hi-Fi News and Audio Magazine .
Another early subwoofer enclosure made for home and studio use was the separate bass speaker for the Servo Statik 1 by New Technology Enterprises. [ 14 ] Designed as a prototype in 1966 by physicist Arnold Nudell and airline pilot Cary Christie in Nudell's garage, it used a second winding around a custom Cerwin-Vega 18-inch (45 cm) driver to provide servo control information to the amplifier, and it was offered for sale at $1795, some 40% more expensive than any other complete loudspeaker listed at Stereo Review . [ 14 ] In 1968, the two found outside investors and reorganized as Infinity . [ 14 ] The subwoofer was reviewed positively in Stereophile magazine's winter 1968 issue as the SS-1 by Infinity. The SS-1 received very good reviews in 1970 from High Fidelity magazine. [ 14 ]
Another of the early subwoofers was developed during the late 1960s by Ken Kreisel, the former president of the Miller & Kreisel Sound Corporation in Los Angeles. When Kreisel's business partner, Jonas Miller, who owned a high-end audio store in Los Angeles, told Kreisel that some purchasers of the store's high-end electrostatic speakers had complained about a lack of bass response in the electrostatics, Kreisel designed a powered woofer that would reproduce only those frequencies that were too low for the electrostatic speakers to convey. [ 15 ] Infinity's full range electrostatic speaker system that was developed during the 1960s also used a woofer to cover the lower frequency range that its electrostatic arrays did not handle adequately.
The first use of a subwoofer in a recording session was in 1973 for mixing the Steely Dan album Pretzel Logic , when recording engineer Roger Nichols arranged for Kreisel to bring a prototype of his subwoofer to Village Recorders . [ 16 ] Further design modifications were made by Kreisel over the next ten years, and in the 1970s and 1980s by engineer John P. D'Arcy ; record producer Daniel Levitin served as a consultant and " golden ears " for the design of the crossover network (used to partition the frequency spectrum so that the subwoofer would not attempt to reproduce frequencies too high for its effective range, and so that the main speakers would not need to handle frequencies too low for their effective range). In 1976, Kreisel created the first satellite speakers and subwoofer system, named "David and Goliath". [ 17 ]
Subwoofers received a great deal of publicity in 1974 with the movie Earthquake , which was released in Sensurround . Initially installed in 17 U.S. theaters, the Cerwin-Vega "Sensurround" system used large subwoofers that were driven by racks of 500 watt amplifiers, triggered by control tones printed on one of the audio tracks on the film. Four of the subwoofers were positioned in front of the audience under (or behind) the film screen and two more were placed together at the rear of the audience on a platform. Powerful noise energy and loud rumbling in the range of 17 to 120 Hz were generated at the level of 110–120 decibels of sound pressure level , abbreviated dB(SPL). The new low frequency entertainment method helped the film become a box office success. More Sensurround systems were assembled and installed. By 1976, there were almost 300 Sensurround systems leapfrogging through select theaters. Other films to use the effect include the WW II naval battle epic Midway in 1976 and Rollercoaster in 1977. [ 18 ]
For owners of 33 rpm LPs and 45 rpm singles, loud and deep bass was limited by the ability of the phonograph record stylus to track the groove. [ 8 ] While some hi-fi aficionados had solved the problem by using other playback sources, such as reel-to-reel tape players which were capable of delivering accurate, naturally deep bass from acoustic sources, or synthetic bass not found in nature, with the popular introduction of the compact cassette in the late 1960s it became possible to add more low frequency content to recordings. [ 19 ] By the mid-1970s, 12-inch vinyl singles, which allowed for "more bass volume", were used to record disco, reggae, dub and hip-hop tracks; dance club DJs played these records in clubs with subwoofers to achieve "physical and emotional" reactions from dancers. [ 20 ]
In the early 1970s, David Mancuso hired sound engineer Alex Rosner [ 21 ] to design additional subwoofers for his disco dance events, along with "tweeter arrays" to "boost the treble and bass at opportune moments" at his private, underground parties at The Loft . [ 22 ] The demand for sub-bass sound reinforcement in the 1970s was driven by the important role of "powerful bass drum" in disco, as compared with rock and pop; to provide this deeper range, a third crossover point from 40 to 120 Hz (centering on 80 Hz) was added. [ 11 ] The Paradise Garage discotheque in New York City, which operated from 1977 to 1987, had "custom designed 'sub-bass' speakers" developed by Alex Rosner's disciple, sound engineer Richard ("Dick") Long [ 21 ] that were called "Levan Horns" (in honor of resident DJ Larry Levan ). [ 20 ]
By the end of the 1970s, subwoofers were used in dance venue sound systems to enable the playing of "[b]ass-heavy dance music" that we "do not 'hear' with our ears but with our entire body". [ 22 ] At the club, Long used four Levan bass horns, one in each corner of the dancefloor, to create a "haptic and tactile quality" in the sub-bass that you could feel in your body. [ 23 ] To overcome the lack of sub-bass frequencies on 1970s disco records (sub-bass frequencies below 60 Hz were removed during mastering), Long added a DBX 100 "Boom Box" subharmonic pitch generator into his system to synthesize 25 to 50 Hz sub-bass from the 50 to 100 Hz bass on the records. [ 23 ]
By the later 1970s, disco club sound engineers were using the same large Cerwin-Vega Sensurround-style folded horn subwoofers that were used in Earthquake and similar movies in dance club system installations. [ 11 ] In the early 1980s, Long designed a sound system for the Warehouse dance club, with "huge stacks of subwoofers" which created "deep and intense" bass frequencies that "pound[ed] through your system" and "entire body", enabling clubgoers to "viscerally experience" the DJs' house music mixes. [ 24 ]
In Jamaica in the 1970s and 1980s, sound engineers for reggae sound systems began creating "heavily customized" subwoofer enclosures by adding foam and tuning the cabinets to achieve "rich and articulate speaker output below 100 Hz". [ 9 ] The sound engineers who developed the "bass-heavy signature sound" of sound reinforcement systems have been called "deserving as much credit for the sound of Jamaican music as their better-known music producer cousins". [ 25 ] The sound engineers for Stone Love Movement (a sound system crew), for example, modified folded horn subwoofers they imported from the US to get more of a bass reflex sound that suited local tone preferences for dancehall audiences, as the unmodified folded horn was found to be "too aggressive" sounding and "not deep enough for Jamaican listeners". [ 9 ]
In sound system culture, there are both "low and high bass bins" in "towering piles" that are "delivered in large trucks" and set up by a crew of "box boys", and then positioned and adjusted by the sound engineer in a process known as "stringing up", all to create the "sound of reggae music you can literally feel as it comes off these big speakers". [ 26 ] Sound system crews hold ' sound clash ' competitions, where each sound system is set up and then the two crews try to outdo each other, [ 27 ] both in terms of loudness and the "bass it produced". [ 28 ]
In the 1980s, the Bose Acoustimass AM-5 became a popular subwoofer and small high-range satellite speaker system for home listening. [ 30 ] Steve Feinstein stated that with the AM-5, the system's "appearance mattered as much as, if not more than, great sound" to consumers of this era, as it was considered to be a "cool" look. [ 30 ] The success of the AM-5 led to other makers launching subwoofer-satellite speaker systems, including Boston Acoustics Sub Sat 6 and 7, and the Cambridge SoundWorks Ensemble systems (by Kloss). [ 30 ] Claims that these sub-satellite systems showed manufacturers and designers that home-cinema systems with a hidden subwoofer could be "feasible and workable in a normal living room" for mainstream consumers. Despite criticism of the AM-5 from audio experts, regarding a lack of bass range below 60 Hz, an "acoustic hole" in the 120 to 200 Hz range and a lack of upper range above 13 kHz for the satellites, the AM-5 system represented 30% of the US speaker market in the early 1990s. [ 30 ]
In the 1980s, Origin Acoustics developed the first residential in-wall subwoofer named Composer. It used an aluminum 10-inch (25.4 cm) driver and a foam-lined enclosure designed to be mounted directly into wall studs during the construction of a new home. [ 31 ] The frequency response for the Composer is 30 to 250 Hz. [ 32 ]
While in the 1960s and 1970s deep bass speakers were once an exotic commodity owned by audiophiles, by the mid-1990s they were much more popular and widely used, with different sizes and capabilities of sound output. [ 33 ] An example of 1990s subwoofer use in sound reinforcement is the Ministry of Sound dance club which opened in 1991 in London. The dancefloor's sound system was based on Richard Long's design at Paradise Garage. The club spent about £500,000 on a sound system that used Martin Audio components in custom-built cabinets, including twelve 21" 9,500 watt active subwoofers, twelve 18-inch subwoofers and twelve Martin Audio W8C mid-high speakers. [ 34 ]
The popularity of the CD made it possible to add more low frequency content to recordings and satisfy a larger number of consumers. [ 19 ] Home subwoofers grew in popularity, as they were easy to add to existing multimedia speaker setups and they were easy to position or hide. [ 35 ]
In 2015, Damon Krukowski wrote an article entitled "Drop the Bass: A Case Against Subwoofers" for Pitchfork magazine, based on his performing experience with Galaxie 500 ; he argues that "for certain styles of music", especially acoustic music genres, "these low-end behemoths are actually ruining our listening experience" by reducing the clarity of the low end. [ 36 ] In 2015, John Hunter from REL Acoustics stated that audiophiles tend to "have a love/hate relationship with subwoofers" because most subs have "awful", "entry-level" sound quality and they are used in an "inappropriate way", without integrating the bass seamlessly. [ 37 ]
In 2018, some electronic dance music (EDM) sound systems for venues that play hardcore bass have multiple subwoofer arrays to deal with upper-bass (80–100 Hz), mid-bass (40–80 Hz), and " sub-bass " (20–40 Hz). [ 9 ]
Loudspeaker and enclosure design
Subwoofers use speaker drivers ( woofers ) typically between 8-inch (20 cm) and 21-inch (53 cm) in diameter. Some uncommon subwoofers use larger drivers, and single prototype subwoofers as large as 60-inch (152 cm) have been fabricated. [ 38 ] On the smaller end of the spectrum, subwoofer drivers as small as 4-inch (10 cm) may be used. Small subwoofer drivers in the 4-inch range are typically used in small computer speaker systems and compact home-cinema subwoofer cabinets. The size of the driver and number of drivers in a cabinet depends on the design of the loudspeaker enclosure , the size of the cabinet, the desired sound pressure level, the lowest frequency targeted and the level of permitted distortion. The most common subwoofer driver sizes used for sound reinforcement in nightclubs, raves and pop/rock concerts are 10-, 12-, 15- and 18-inch models (25 cm, 30 cm, 38 cm, and 45 cm respectively). The largest available sound reinforcement subwoofers, 21-inch (53 cm) drivers, are less commonly seen. [ citation needed ]
The reference efficiency of a loudspeaker system in its passband is given by: [ 39 ] [ 40 ] [ 41 ] [ 42 ]
where c {\displaystyle c} is the speed of sound in air and the variables are Thiele/Small parameters: f s {\displaystyle f_{s}} is the resonance frequency of the driver, V a s {\displaystyle V_{as}} is the volume of air having the same acoustic compliance as the driver suspension, and Q e s {\displaystyle Q_{es}} is the driver Q {\displaystyle Q} at f s {\displaystyle f_{s}} considering the electrical DC resistance of the driver voice coil. Deep low-frequency extension is a common goal for a subwoofer and small box volumes are also considered desirable, to save space and reduce the size for ease of transportation (in the case of sound reinforcement and DJ subwoofers). Hofmann 's "Iron Law" therefore mandates low efficiency under those constraints, and indeed most subwoofers require considerable power, much more than other individual drivers. [ citation needed ]
So, for the example of a closed-box loudspeaker system, the box volume V a b {\displaystyle V_{ab}} to achieve a given total Q {\displaystyle Q} of the system Q t c {\displaystyle Q_{tc}} is proportional to V a s {\displaystyle V_{as}} : [ 40 ]
where α {\displaystyle \alpha } is the system compliance ratio given by the ratio of the driver compliance and the enclosure compliance, which can be written as: [ 43 ]
where f c {\displaystyle f_{c}} is the system resonance frequency.
Therefore, a decrease in box volume (i.e., a smaller speaker cabinet) and the same f 3 {\displaystyle f_{3}} will decrease the efficiency of the subwoofer. The normalized half-power frequency of a closed-box loudspeaker system is given by: [ 43 ]
Here we note that if Q t c = 1 / 2 ≈ 0.7071 {\displaystyle Q_{tc}=1/{\sqrt {2}}\approx 0.7071} , then f 3 = f c {\displaystyle f_{3}=f_{c}} .
As the efficiency is proportional to f s 3 {\displaystyle f_{s}^{3}} , small improvements in low-frequency extension with the same driver and box volume will result in very significant reductions in efficiency. For these reasons, subwoofers are typically very inefficient at converting electrical energy into sound energy. This combination of factors accounts for the higher amplifier power required to drive subwoofers, and the requirement for greater power handling for subwoofer drivers. Enclosure variations (e.g., bass reflex designs with a port in the cabinet) are often used for subwoofers to increase the efficiency of the driver/enclosure system, helping to reduce the amplifier power requirements. Vented-box loudspeaker systems have a maximum theoretical efficiency that is 2.9 dB greater than that of the closed-box system. [ 44 ]
Subwoofers are typically constructed by mounting one or more woofers in a cabinet of medium-density fibreboard (MDF), oriented strand board (OSB), plywood, fiberglass, aluminum or other stiff materials. Because of the high air pressure that they produce in the cabinet, subwoofer enclosures often require internal bracing to distribute the resulting forces. [ 45 ]
Subwoofers have been designed using a number of enclosure approaches: bass reflex (with a port or vent), using a subwoofer and one or more passive radiator speakers in the enclosure, acoustic suspension (sealed enclosure), infinite baffle , horn-loaded , tapped horn , transmission line and bandpass . Each enclosure type has advantages and disadvantages in terms of efficiency increase, bass extension, cabinet size, distortion, and cost. [ 45 ]
Multiple enclosure types may even be combined in a single design, such as in computer audio with the subwoofer design of the Labtec LCS-2424 (later acquired by Logitech and used for their Z340/Z540/Z640/Z3/Z4), which is a (primitive) passive radiator bandpass enclosure with a bass reflex dividing chamber. [ 45 ]
While not necessarily an enclosure type, isobaric (such as push-pull) coupled loading of two drivers has sometimes been used in subwoofer products of computer, [ 45 ] home cinema [ 46 ] and sound reinforcement [ 47 ] class, and also DIY versions in automotive applications, to provide relatively deep bass for their size. Self-contained "isobaric-like" driver assemblies have been manufactured since the 2010s. [ 48 ] [ 49 ] [ 50 ]
The smallest subwoofers are typically those designed for desktop multimedia systems. The largest common subwoofer enclosures are those used for concert sound reinforcement systems or dance club sound systems. An example of a large concert subwoofer enclosure is the 1980s-era Electro-Voice MT-4 "Bass Cube" system, which used four 18-inch (45 cm) drivers. An example of a subwoofer that uses a bass horn is the Bassmaxx B-Two, which loads an 18-inch (45 cm) driver onto an 11-foot (3.4 m) long folded horn. [ 51 ] Folded horn-type subwoofers can typically produce a deeper range with greater efficiency than the same driver in an enclosure that lacks a horn. [ 51 ] However, folded horn cabinets are typically larger and heavier than front-firing enclosures, so folded horns are less commonly used. Some experimental fixed-installation subwoofer horns have been constructed using brick and concrete to produce a very long horn that allows a very deep sub-bass extension. [ 52 ]
Subwoofer output level can be increased by increasing cone surface area or by increasing cone excursion. Since large drivers require undesirably large cabinets, most subwoofer drivers have large excursions. Unfortunately, high excursion, at high power levels, tends to produce more distortion from inherent mechanical and magnetic effects in electro-dynamic drivers (the most common sort). [ 53 ] The conflict between assorted goals can never be fully resolved; subwoofer designs necessarily involve tradeoffs and compromises. Hofmann's Iron Law (the efficiency of a woofer system is directly proportional to its cabinet volume (as in size) and to the cube of its cutoff frequency, that is how low in pitch it will go) applies to subwoofers just as it does to all loudspeakers. [ 53 ] Thus, a subwoofer enclosure designer aiming at the deepest-pitched bass will probably have to consider using a large enclosure size; a subwoofer enclosure designer instructed to create the smallest possible cabinet (to make transportation easier) will need to compromise how low in pitch their cabinet will go. [ 53 ]
The frequency response specification of a speaker describes the range of frequencies or musical tones a speaker can reproduce, measured in hertz (Hz). [ 54 ] The typical frequency range for a subwoofer is between 20–200 Hz. [ 1 ] Professional concert sound system subwoofers typically operate below 100 Hz, [ 2 ] and THX -certified systems operate below 80 Hz. [ 3 ] Subwoofers vary in terms of the range of pitches that they can reproduce, depending on a number of factors such as the size of the cabinet and the construction and design of the enclosure and driver(s). Specifications of frequency response depend wholly for relevance on an accompanying amplitude value—measurements taken with a wider amplitude tolerance will give any loudspeaker a wider frequency response. For example, the JBL 4688 TCB Subwoofer System, a now-discontinued system which was designed for movie theaters, had a frequency response of 23–350 Hz when measured within a 10-decibel boundary (0 dB to −10 dB) and a narrower frequency response of 28–120 Hz when measured within a 6-decibel boundary (±3 dB). [ 55 ]
Subwoofers also vary in regard to the sound pressure levels achievable and the distortion levels that they produce over their range. Some subwoofers, such as The Abyss by MartinLogan for example, can reproduce pitches down to around 18 Hz (which is about the pitch of the lowest rumbling notes on a huge pipe organ with 32-foot (9.8 m) 16 Hz bass pipes) to 100 Hz (±3 dB). Nevertheless, even though the Abyss subwoofer can go down to 18 Hz, its lowest frequency and maximum SPL with a limit of 10% distortion is 35.5 Hz and 79.8 dB at 2 meters. [ 56 ] This means that a person choosing a subwoofer needs to consider more than just the lowest pitch that the subwoofer can reproduce.
'Active subwoofers' include their own dedicated amplifiers within the cabinet. Some also include user-adjustable equalization that allows boosted or reduced output at particular frequencies; these vary from a simple "boost" switch, to fully parametric equalizers meant for detailed speaker and room correction. Some such systems are even supplied with a calibrated microphone to measure the subwoofer's in-room response, so the automatic equalizer can correct the combination of subwoofer, subwoofer location, and room response to minimize the effects of room modes and improve low-frequency performance.
'Passive subwoofers' have a subwoofer driver and enclosure, but they do not include an amplifier. They sometimes incorporate internal passive crossovers, with the filter frequency determined at the factory. These are generally used with third-party power amplifiers, taking their inputs from active crossovers earlier in the signal chain. Inexpensive home-theater-in-a-box (HTIB) packages often come with a passive subwoofer cabinet that is amplified by the multi-channel amplifier. While few high-end home-cinema systems use passive subwoofers, this format is still popular in the professional sound industry. [ 57 ]
Equalization can be used to adjust the in-room response of a subwoofer system. [ 58 ] Designers of active subwoofers sometimes include a degree of corrective equalization to compensate for known performance issues (e.g. a steeper than desired low end roll-off rate). In addition, many amplifiers include an adjustable low-pass filter, which prevents undesired higher frequencies from reaching the subwoofer driver. For example, if a listener's main speakers are usable down to 100 Hz, then the subwoofer filter can be set so the subwoofer only works below 100 Hz. [ 3 ] Typical filters involve some overlap in frequency ranges; a steep 4th-order 24 dB/octave low-pass filter is generally desired for subwoofers in order to minimize the overlap region. The filter section may also include a high-pass " infrasonic " or "subsonic" filter, which prevents the subwoofer driver from attempting to reproduce frequencies below its safe capabilities. Setting an infrasonic filter is important on bass reflex subwoofer cabinets, as the bass reflex design tends to create the risk of cone overexcursion at pitches below those of the port tuning, which can cause distortion and damage the subwoofer driver. For example, in a ported subwoofer enclosure tuned to 30 Hz, one may wish to filter out pitches below the tuning frequency; that is, frequencies below 30 Hz.
Some systems use parametric equalization in an attempt to correct for room frequency response irregularities. [ 59 ] Equalization is often unable to achieve flat frequency response at all listening locations, in part because of the resonance (i.e. standing wave ) patterns at low frequencies in nearly all rooms. Careful positioning of the subwoofer within the room can also help flatten the frequency response. [ 60 ] Multiple subwoofers can manage a flatter general response since they can often be arranged to excite room modes more evenly than a single subwoofer, allowing equalization to be more effective. [ 61 ]
Changing the relative phase of the subwoofer with respect to the woofers in other speakers may or may not help to minimize unwanted destructive acoustic interference in the frequency region covered by both the subwoofer and the main speakers. It may not help at all frequencies, and may create further problems with frequency response, but even so is generally provided as an adjustment for subwoofer amplifiers. [ 62 ] Phase control circuits may be a simple polarity reversal switch or a more complex continuously variable circuit.
Continuously variable phase control circuits are common in subwoofer amplifiers, and may be found in crossovers and as do-it-yourself electronics projects. [ 63 ] [ 64 ] [ 65 ] [ 66 ] [ 67 ] Phase controls allow the listener to change the arrival time of the subwoofer sound waves relative to the same frequencies from the main speakers (i.e. at and around the crossover point to the subwoofer). A similar effect can be achieved with the delay control on many home-cinema receivers. The subwoofer phase control found on many subwoofer amplifiers is actually a polarity inversion switch. [ 68 ] It allows users to reverse the polarity of the subwoofer relative to the audio signal it is being given. This type of control allows the subwoofer to either be in phase with the source signal, or 180 degrees out of phase.
The subwoofer phase can still be changed by moving the subwoofer closer to or further from the listening position, however this may not be always practical.
Some active subwoofers use a servo feedback mechanism based on cone movement that modifies the signal sent to the voice coil. The servo feedback signal is derived from a comparison of the input signal to the amplifier versus the actual motion of the cone. [ 69 ] The usual source of the feedback signal is a few turns of voice coil attached to the cone or a microchip-based accelerometer placed on the cone itself. [ 70 ] [ 71 ] An advantage of a well-implemented servo subwoofer design is reduced distortion making smaller enclosure sizes possible. [ 72 ] The primary disadvantages are cost and complexity. [ 73 ]
Servo-controlled subwoofers are not the same as Tom Danley 's ServoDrive subwoofers, whose primary mechanism of sound reproduction avoids the normal voice coil and magnet combination in favor of a high-speed belt-driven servomotor . [ 74 ] The ServoDrive design increases output power, reduces harmonic distortion and virtually eliminates power compression , the loss of loudspeaker output that results from an increase in voice coil impedance due to overheating of the voice coil. This feature allows high-power operation for extended periods of time. [ 75 ] [ 76 ] [ 77 ] Intersonics was nominated for a TEC Award for its ServoDrive Loudspeaker (SDL) design in 1986 and for the Bass Tech 7 model in 1990. [ 78 ] [ 79 ]
The use of a subwoofer augments the bass capability of the main speakers, and allows them to be smaller without sacrificing low-frequency capability. A subwoofer does not necessarily provide superior bass performance in comparison to large conventional loudspeakers on ordinary music recordings due to the typical lack of very low frequency content on such sources. However, there are recordings with substantial low-frequency content that most conventional loudspeakers are ill-equipped to handle without the help of a subwoofer, especially at high playback levels, such as music for pipe organs with 32' (9.75 meter) bass pipes (16 Hz), very large bass drums on symphony orchestra recordings and electronic music with extremely low synth bass parts, such as bass tests or bass songs.
Frequencies which are sufficiently low are not easily localized by humans, hence many stereo and multichannel audio systems feature only one subwoofer channel and a single subwoofer can be placed off-center without affecting the perceived sound stage, since the sound that it produces will be difficult to localize. The intention in a system with a subwoofer is often to use small main speakers (of which there are two for stereo and five or more for surround sound or movie tracks) and to hide the subwoofer elsewhere (e.g. behind furniture or under a table), or to augment an existing speaker to save it from having to handle woofer-destroying low frequencies at high levels. This effect is possible only if the subwoofer is restricted to quite low frequencies, usually taken to be, say, 100 Hz and below—still less localization is possible if restricted to even lower maximum frequencies. Higher upper limits for the subwoofer (e.g. 120 Hz) are much more easily localized, making a single subwoofer impractical. Home-cinema systems typically use one subwoofer cabinet (the "1" in 5.1 surround sound ). However, to "improve bass distribution in a room that has multiple seating locations, and prevent nulls with weakened bass response, some home-cinema enthusiasts use 5.2- or 7.2- or 9.2-channel surround sound systems with two subwoofer cabinets in the same room. [ 80 ]
Some users add a subwoofer because high levels of low-frequency bass are desired, even beyond what is in the original recording, as in the case of house music enthusiasts. Thus, subwoofers may be part of a package that includes satellite speakers, may be purchased separately, or may be built into the same cabinet as a conventional speaker system. For instance, some floor-standing tower speakers include a subwoofer driver in the lower portion of the same cabinet. Physical separation of subwoofer and satellite speakers not only allows placement in an inconspicuous location, but since sub-bass frequencies are particularly sensitive to room location (due to room resonances and reverberation 'modes'), the best position for the subwoofer is not likely to be where the satellite speakers are located.
Higher end home-cinema systems and enthusiasts may also opt to take low-frequency bass reproduction even further by incorporating two or more external subwoofers. [ 81 ] Having two subwoofers placed around the room ensures even distribution of bass, reducing subwoofer localization and pressurizing the room with low frequency notes that can be felt, just like the cinemas. [ 82 ]
For greatest efficiency and best coupling to the room's air volume, subwoofers can be placed in a corner of the room, far from large room openings, and closer to the listener. This is possible since low bass frequencies have a long wavelength ; hence there is little difference between the information reaching a listener's left and right ears, and so they cannot be readily localized. All low-frequency information is sent to the subwoofer. However, unless the sound tracks have been carefully mixed for a single subwoofer channel, it is possible to have some cancellation of low frequencies if bass information in one channel's speaker is out of phase with another.
The physically separate subwoofer/satellite arrangement, with small satellite speakers and a large subwoofer cabinet that can be hidden behind furniture, has been popularized by multimedia speaker systems such as Bose Acoustimass Home Entertainment Systems , Polk Audio RM2008 Series and Klipsch Audio Technologies ProMedia, among many others. [ 83 ] [ 84 ]
Low-cost HTIB systems advertise their integration and simplicity. Particularly among lower cost HTIB systems and with boomboxes , however, the inclusion of a subwoofer may be little more than a marketing technique. It is unlikely that a small woofer in an inexpensively-built compact plastic cabinet will have better bass performance than well-designed conventional (and typically larger) speakers in a plywood or MDF cabinet. Mere use of the term "subwoofer" is no guarantee of good or extended bass performance. Many multimedia subwoofers might better be termed "mid-bass cabinets" (80 to 200 Hz), as they are too small to produce deep bass in the typical 20 to 100 Hz range. [ 85 ]
Further, poorly-designed systems often leave everything below about 120 Hz (or even higher) to the subwoofer, meaning that the subwoofer handles frequencies which the ear can use for sound source localization, thus introducing an undesirable subwoofer "localization effect". This is usually due to poor crossover designs or choices (too high a crossover point or insufficient crossover slope) used in many computer and home-cinema systems; localization also comes from port noise [ 86 ] and from typically large amounts of harmonic distortion in the subwoofer design. [ 87 ] Home subwoofers sold individually usually include crossover circuitry to assist with the integration of the subwoofer into an existing system.
Automobiles are not well suited for the "hidden" subwoofer approach due to space limitations in the passenger compartments. It is not possible, in most circumstances, to fit such large drivers and enclosures into doors or dashboards, so subwoofers are installed in the trunk or back seat space. Some car audio enthusiasts compete to produce very high sound pressure levels in the confines of their vehicle's cabin; sometimes dangerously high sound pressure levels. The "SPL wars" have drawn much attention to subwoofers in general, but subjective competitions in sound quality ("SQ") have not gained equivalent popularity. Top SPL cars are not able to play normal music, or perhaps even to drive normally as they are designed solely for competition. Many non-competition subwoofers are also capable of generating high levels in cars due to the small volume of a typical car interior. High sound levels can cause hearing loss and tinnitus if one is exposed to them for an extended period of time. [ 88 ]
In the 2000s, several car audio manufacturers produced subwoofers using non-circular shapes, including Boston Acoustic, Kicker, Sony, Bazooka, and X-Tant. Other major car audio manufacturers like Rockford Fosgate did not follow suit since non-circular subwoofer shapes typically carry some sort of distortion penalties. [ 89 ] [ 90 ] In situations of limited mounting space they provide a greater cone area and assuming all other variables are constant, greater maximum output. An important factor in the "square sub vs round sub" argument is the effects of the enclosure used. In a sealed enclosure, the maximum displacement is determined by
V d = x m a x × S d {\displaystyle V_{\mathrm {d} }=x_{\mathrm {max} }\times S_{\mathrm {d} }}
where
These are some of the Thiele/Small parameters which can either be measured or found with the driver specifications.
After the introduction of Sensurround, movie theater owners began installing permanent subwoofer systems. Dolby Stereo 70 mm Six Track was a six-channel film sound format introduced in 1976 that used two subwoofer channels for stereo reproduction of low frequencies. In 1981, Altec introduced a dedicated cinema subwoofer model tuned to around 20 Hz: the 8182. Starting in 1983, THX certification of the cinema sound experience quantified the parameters of good audio for watching films, including requirements for subwoofer performance levels and enough isolation from outside sounds so that noise did not interfere with the listening experience. [ 91 ] This helped provide guidelines for multiplex cinema owners who wanted to isolate each individual cinema from its neighbors, even as louder subwoofers were making isolation more difficult. Specific cinema subwoofer models appeared from JBL , Electro-Voice , Eastern Acoustic Works , Kintek, Meyer Sound Laboratories and BGW Systems in the early 1990s. In 1992, Dolby Digital 's six-channel film sound format incorporated a single LFE channel, the "point one" in 5.1 surround sound systems.
Tom Horral, a Boston-based acoustician, blames complaints about modern movies being too loud on subwoofers. He says that before subwoofers made it possible to have loud, relatively undistorted bass, movie sound levels were limited by the distortion in less capable systems at low frequency and high levels. [ 92 ]
Professional audio subwoofers used in rock concerts in stadia, DJ performances at dance music venues (e.g. electronic dance music ) and similar events must be capable of very high bass output levels, at very low frequencies, with low distortion. This is reflected in the design attention given in the 2010s to the subwoofer applications for sound reinforcement, public address systems , dance club systems and concert systems. Cerwin-Vega states that when a subwoofer cabinet is added to an existing full-range speaker system, this is advantageous, as it moves the "...lowest frequencies from your main [full-range] PA speakers" thus "...eliminat[ing] a large amount of the excess work that your main top [full-range] box was trying to reproduce. As a result, your main [full-range] cabinets will run more efficiently and at higher volumes." [ 93 ] A different argument for adding subwoofer cabinets is that they may increase the "level of clarity" and "perceived loudness" of an overall PA system, even if the SPL is not actually increased. [ 94 ] Sound on Sound states that adding a subwoofer enclosure to a full-range system will reduce "cone excursion", thus lowering distortion, leading to an overall cleaner sound. [ 95 ]
Consumer applications (as in home use) are considerably less demanding due to much smaller listening space and lower playback levels. Subwoofers are now almost universal in professional sound applications such as live concert sound, churches, nightclubs, and theme parks. Movie theaters certified to the THX standard for playback always include high-capability subwoofers. Some professional applications require subwoofers designed for very high sound levels, using multiple 12-, 15-, 18- or 21-inch drivers (30 cm, 40 cm, 45 cm, 53 cm respectively). Drivers as small as 10-inch (25 cm) are occasionally used, generally in horn-loaded enclosures.
The number of subwoofer enclosures used in a concert depends on a number of factors, including the size of the venue, whether it is indoors or outdoors, the amount of low-frequency content in the band's sound, the desired volume of the concert, and the design and construction of the enclosures (e.g. direct-radiating versus horn-loaded). A tiny coffeehouse may only need a single 10-inch subwoofer cabinet to augment the bass provided by the full-range speakers. A small bar may use one or two direct-radiating 15-inch (40 cm) subwoofer cabinets. A large dance club may have a row of four or five twin 18-inch (45 cm) subwoofer cabinets, or more. In the largest stadium venues, there may be a very large number of subwoofer enclosures. For example, the 2009–2010 U2 360° Tour used 24 Clair Brothers BT-218 subwoofers (a double 18-inch (45 cm) box) around the perimeter of the central circular stage, and 72 proprietary Clair Brothers cardioid S4 subwoofers placed underneath the ring-shaped "B" stage which encircles the central main stage. [ 96 ] [ 97 ]
The main speakers may be 'flown' from the ceiling of a venue on chain hoists, and 'flying points' (i.e. attachment points) are built into many professional loudspeaker enclosures. Subwoofers can be flown or stacked on the ground near the stage. One of the reasons subwoofers may be installed on the ground is that on-the-ground installation can increase the bass performance, particularly if the subwoofer is placed in the corner of a room (conversely, if a subwoofer cabinet is perceived as too loud, alternatives to on-the-ground or in-corner installation may be considered). There can be more than 50 double-18-inch (45 cm) cabinets in a typical rock concert system. Just as consumer subwoofer enclosures can be made of medium-density fibreboard (MDF), oriented strand board (OSB), plywood , plastic or other dense material, professional subwoofer enclosures can be built from the same materials. [ 98 ] [ 99 ] MDF is commonly used to construct subwoofers for permanent installations as its density is relatively high and weatherproofing is not a concern. Other permanent installation subwoofers have used very thick plywood: the Altec 8182 (1981) used 7-ply 28 mm birch-faced oak plywood. [ 100 ] Touring subwoofers are typically built from 18–20 mm thick void-free Baltic birch ( Betula pendula or Betula pubescens ) plywood from Finland, Estonia or Russia; such plywood affords greater strength for frequently transported enclosures. [ 101 ] Not naturally weatherproof, Baltic birch is coated with carpet, thick paint or spray-on truck bedliner to give the subwoofer enclosures greater durability. [ 102 ] [ 103 ]
Touring subwoofer cabinets are typically designed with features that facilitate moving the enclosure (e.g. wheels, a "towel bar" handle and recessed handles), a protective grille for the speaker (in direct radiating-style cabinets), metal or plastic protection for the cabinets to protect the finish as the cabinets are being slid one on top of another, and hardware to facilitate stacking the cabinets (e.g. interlocking corners) and for "flying" the cabinets from stage rigging. In the 2000s, many small- to mid-size subwoofers designed for bands' live sound use and DJ applications are "powered subs"; that is, they have an integrated power amplifier . These models typically have a built-in crossover. Some models have a metal-reinforced hole in which a speaker pole can be mounted for elevating full-frequency range cabinets.
In professional concert sound system design, subwoofers can be incorporated seamlessly with the main speakers into a stereo or mono full-range system by using an active crossover . The audio engineer typically adjusts the frequency point at which lower frequency sounds are routed to the subwoofer speaker(s), and mid-frequency and higher frequency sounds are sent to the full-range speakers. Such a system receives its signal from the main mono or stereo mixing console mix bus and amplifies all frequencies together in the desired balance. If the main sound system is stereo, the subwoofers can also be in stereo. Otherwise, a mono subwoofer channel can be derived within the crossover from a stereo mix, depending on the crossover make and model. While 2010-era subwoofer cabinet manufacturers suggest placing subwoofers on either side of a stage (as implied by the inclusion of pole cups for the full-range PA cabinets), Dave Purton argues that for club gigs, having two subwoofer cabinets on either side of a stage will lead to gaps in bass coverage in the venue; he states that putting the two subwoofer cabinets together will create a more even, omnidirectional sub-bass tone. [ 95 ]
Instead of being incorporated into a full-range system, concert subwoofers can be supplied with their own signal from a separate mix bus on the mixing console; often one of the auxiliary sends ("aux" or "auxes") is used. This configuration is called "aux-fed subwoofers", and has been observed to significantly reduce low-frequency "muddiness" that can build up in a concert sound system which has on stage a number of microphones each picking up low frequencies and each having different phase relationships of those low frequencies. [ 2 ] The aux-fed subwoofers method greatly reduces the number of sources feeding the subwoofers to include only those instruments that have desired low-frequency information; sources such as kick drum , bass guitar , samplers and keyboard instruments . This simplifies the signal sent to the subwoofers and makes for greater clarity and low punch. [ 104 ] Aux-fed subwoofers can even be stereo, if desired, using two auxiliary mix buses.
To keep low-frequency sound focused on the audience area and not on the stage, and to keep low frequencies from bothering people outside of the event space, a variety of techniques have been developed in concert sound to turn the naturally omnidirectional radiation of subwoofers into a more directional pattern. Several examples of sound reinforcement system applications where sound engineers seek to provide more directional bass sound are: music festivals , which often have several bands performing at the same time on different stages; large raves or EDM events, where there are multiple DJs performing at the same time in different rooms or stages; and multiplex movie theaters , in which there are many films being shown simultaneously in auditoriums that share common walls. These techniques include: setting up subwoofers in a vertical array; using combinations of delay and polarity inversion; and setting up a delay-shaded system. With a cardioid dispersion pattern, two end-fire subwoofers can be placed one in front of the other. The enclosure nearest the listener is delayed by a few milliseconds. The second subwoofer is delayed a precise amount corresponding to the time it takes sound to traverse the distance between speaker grilles.
Stacking or rigging the subwoofers in a vertical array focuses the low frequencies forward to a greater or lesser extent depending on the physical length of the array. Longer arrays have a more directional effect at lower frequencies. The directionality is more pronounced in the vertical dimension, yielding a radiation pattern that is wide but not tall. This helps reduce the amount of low-frequency sound bouncing off the ceiling indoors and assists in mitigating external noise complaints outdoors.
Another cardioid subwoofer array pattern can be used horizontally, one which takes few channels of processing and no change in required physical space. This method is often called "cardioid subwoofer array" or "CSA" [ 105 ] even though the pattern of all directional subwoofer methods is cardioid. The CSA method reverses the enclosure orientation and inverts the polarity of one out of every three subwoofers across the front of the stage, and delays those enclosures for maximum cancellation of the target frequency on stage. Polarity inversion can be implemented electronically, by reversing the wiring polarity, or by physically positioning the enclosure to face rearward. This method reduces forward output relative to a tight-packed, flat-fronted array of subwoofers, but can solve problems of unwanted low-frequency energy coming into microphones on stage. Compared to the end-fire array, this method has less on-axis energy but more even pattern control throughout the audience, and more predictable cancellation rearward. The effect spans a range of slightly more than one octave. [ 105 ]
A second method of rear delay array combines end-fire topology with polarity reversal, using two subwoofers positioned front to back, the drivers spaced one-quarter wavelength apart, the rear enclosure inverted in polarity and delayed by a few milliseconds for maximum cancellation on stage of the target frequency. [ 106 ] This method has the least output power directed toward the audience, compared to other directional methods.
The end-fire subwoofer method, also called "forward steered arrays", [ 107 ] places subwoofer drivers co-axially in one or more rows, using destructive interference to reduce emissions to the sides and rear. This can be done with separate subwoofer enclosures positioned front to back with a spacing between them of one-quarter wavelength of the target frequency, the frequency that is least wanted on stage or most desired in the audience. Each row is delayed beyond the first row by an amount related to the speed of sound in air; the delay is typically a few milliseconds. The arrival time of sound energy from all the subwoofers is near-simultaneous from the audience's perspective, but is canceled out to a large degree behind the subwoofers because of offset sound wave arrival times. Directionality of the target frequency can achieve as much as 25 dB rear attenuation, and the forward sound is coherently summed in line with the subwoofers. [ 108 ] The positional technique of end-fire subwoofers came into widespread use in European live concert sound in 2006. [ 109 ]
The end-fire array trades a few decibels of output power for directionality, so it requires more enclosures for the same output power as a tight-packed, flat-fronted array of enclosures. Sixteen enclosures in four rows were used in 2007 at one of the stages of the Ultra Music Festival , to reduce low-frequency interference to neighboring stages. [ 110 ] Because of the physical size of the end-fire array, few concert venues are able to implement it. The output pattern suffers from comb-filtering off-axis, but can be further shaped by adjusting the frequency response of each row of subwoofers. [ 107 ]
A long line of subwoofers placed horizontally along the front edge of the stage can be delayed such that the center subwoofers fire several milliseconds prior to the ones flanking them, which fire several milliseconds prior to their neighbors, continuing in this fashion until the last subwoofers are reached at the outside ends of the subwoofer row ( beamforming ). This method helps to counteract the extreme narrowing of the horizontal dispersion pattern seen with a horizontal subwoofer array. Such delay shading can be used to virtually reshape a loudspeaker array. [ 111 ]
Some subwoofer enclosure designs rely on drivers facing to the sides or to the rear in order to achieve a degree of directionality. [ 112 ] [ 113 ] End-fire drivers can be positioned within a single enclosure that houses more than one driver. [ 114 ]
Some less commonly-used bass enclosures are variants of the subwoofer enclosure's normal range, such as the upper-bass cabinet (80–200 Hz) and the infrasonic (extra low) subwoofer (below 20 Hz).
Front-loaded subwoofers have one or more subwoofer speakers in a cabinet, typically with a grille to protect the speakers. In practice, many front-loaded subwoofer cabinets have a vent or port in the speaker cabinet, thus creating a bass reflex enclosure. Even though a bass reflex port or vent creates some additional phase delay, it adds SPL, which is often a key factor in PA and sound reinforcement system applications. As such, non-vented front-firing subwoofer cabinets are rare in pro audio applications.
Horn-loaded subwoofers have a subwoofer speaker that has a pathway following the loudspeaker. To save space, the pathway is often folded, so that the folded pathway will fit into a box-style cabinet. Cerwin-Vega states that its folded horn subwoofer cabinets, "...on average, produce 6 dB more output at 1 watt than a dual 18[-inch] vented box" giving "four times the output with half the number of drivers". [ 93 ] The Cerwin-Vega JE-36C has a five feet long folded horn chamber length in the wooden cabinet. [ 93 ]
Manifold subwoofers have two or more subwoofer speakers that feed the throat of a single horn. This increases SPL for the subwoofer, at the cost of increased distortion. EV has a manifold speaker cabinet in which four drivers are mounted as close together as practical. This is a different design than the "multiple drivers in one throat" approach. An unusual example of manifold subwoofer design is the Thomas Mundorf (TM) approach of having four subwoofers facing each other and sitting close together, which is used for theater in the round shows, where the audience surrounds the performers in a big circle (e.g. Metallica has used this in some concerts). The TM approach produces an omnidirectional bass sound. [ 115 ] Cerwin-Vega defines a manifold enclosure as one in which "...the driver faces into a tuned ported cavity. You hear sound directly from the back of the driver in addition to the sound that emanates out of the port. This type of enclosure design extends the frequency capability of the driver lower than it would reproduce by itself." [ 93 ]
Bandpass subwoofers have a sealed cabinet within another cabinet, with the "outer" cabinet typically having a vent or port.
In rare cases, sound reinforcement subwoofer enclosures are also used for bass instrument amplification by electric bass players and synth bass players. For most bands and most small- to mid-size venues (e.g. nightclubs and bars), standard bass guitar speaker enclosures or keyboard amplifiers will provide sufficient sound pressure levels for onstage monitoring. Since a regular electric bass has a low "E" (41 Hz) as its lowest note, most standard bass guitar cabinets are only designed with a range that goes down to about 40 Hz. However, in some cases, performers wish to have extended sub-bass response that is not available from standard instrument speaker enclosures, so they use subwoofer cabinets. Just as some electric guitarists add huge stacks of guitar cabinets mainly for show, some bassists will add immense subwoofer cabinets with 18-inch woofers mainly for show, and the extension subwoofer cabinets will be operated at a lower volume than the main bass cabinets.
Bass guitar players who may use subwoofer cabinets include performers who play with extended range basses that include a low "B" string (about 31 Hz), bassists who play in styles where a very powerful sub-bass response is an important part of the sound (e.g. funk, Latin, gospel, R & B, etc.), and/or bass players who perform in stadium-size venues or large outdoor venues. Keyboard players who use subwoofers for on-stage monitoring include electric organ players who use bass pedal keyboards (which go down to a low "C" which is about 33 Hz) and synth bass players who play rumbling sub-bass parts that go as low as 18 Hz. Of all of the keyboard instruments that are amplified onstage, synthesizers can produce some of the lowest pitches, because unlike a traditional electric piano or electric organ, which have as their lowest notes a low "A" and a low "C", respectively, a synth does not have a fixed lowest octave. A synth player can add lower octaves to a patch by pressing an "octave down" button, which can produce pitches that are at the limits of human hearing.
Several concert sound subwoofer manufacturers suggest that their subs can be used for bass instrument amplification. Meyer Sound suggests that its 650-R2 Concert Series Subwoofer, a 14-square-foot (1.3 m 2 ) enclosure with two 18-inch drivers (45 cm), can be used for bass instrument amplification. [ 116 ] While performers who use concert sound subwoofers for onstage monitoring may like the powerful sub-bass sound that they get onstage, sound engineers may find the use of large subwoofers (e.g. two 18-inch drivers (45 cm)) for onstage instrument monitoring to be problematic, because it may interfere with the "Front of House" sub-bass sound.
Since infrasonic bass is felt, sub-bass can be augmented using tactile transducers . Unlike a typical subwoofer driver, which produces audible vibrations, tactile transducers produce low-frequency vibrations that are designed to be felt by individuals who are touching the transducer or indirectly through a piece of furniture or a wooden floor. Tactile transducers have recently emerged as a device class, called variously "bass shakers", "butt shakers" and "throne shakers". They are attached to a seat, for instance a drummer's stool ("throne") or gamer's chair, car seat or home-cinema seating, and the vibrations of the driver are transmitted to the body then to the ear in a manner similar to bone conduction . [ 117 ] [ 118 ] They connect to an amplifier like a normal subwoofer. They can be attached to a large flat surface (for instance a floor or platform) to create a large low- frequency conduction area, although the transmission of low frequencies through the feet is not as efficient as through the seat. [ 119 ]
The advantage of tactile transducers used for low frequencies is that they allow a listening environment that is not filled with loud low-frequency sound waves in the air. This helps the drummer in a rock music band to monitor their kick drum performance without filling the stage with powerful, loud low-frequency sound from a 15-inch (40 cm) subwoofer monitor and an amplifier, which can "leak" into other drum mics and lower the quality of the sound mix. By not having a large, powerful subwoofer monitor, a bass shaker also enables a drummer to lower the sound pressure levels that they are exposed to during a performance, reducing the risk of hearing damage. For home cinema or video game use, bass shakers help the user avoid disturbing others in nearby apartments or rooms, because even powerful sound effects such as explosion sounds in a war video game or the simulated rumbling of an earthquake in an adventure film will not be heard by others. However, some critics argue that the felt vibrations are disconnected from the auditory experience, and they claim that that music is less satisfying with the "butt shaker" than sound effects. As well, critics have claimed that the bass shaker itself can rattle during loud sound effects, which can distract the listener. [ 120 ]
With varying measures upon which to base claims, several subwoofers have been said to be the world's largest, loudest or lowest.
The Matterhorn is a subwoofer model completed in March 2007 by Danley Sound Labs in Gainesville, Georgia after a U.S. military request for a loudspeaker that could project infrasonic waves over a distance. The Matterhorn was designed to reproduce a continuous sine wave from 15 to 20 Hz, and generate 94 dB at a distance of 250 meters (820 ft), and more than 140 dB for music playback measured at the horn mouth. [ 121 ] It can generate a constant 15 Hz sine wave tone at 140 dB for 24 hours a day, seven days a week with extremely low harmonic distortion. The subwoofer has a flat frequency response from 15 to 100 Hz, and is down 3 dB at 12 Hz. [ 122 ] It was built within an intermodal container 20 feet (6.1 m) long and 8 by 8 feet (2.4 m × 2.4 m) square. [ 123 ] The container doors swing open to reveal a tapped horn driven by 40 long-throw 15-inch (40 cm) MTX speaker drivers each powered by its own 1000-watt amplifier. [ 124 ] [ 125 ] The manufacturer claims that 53 13-ply 18 mm 4-by-8-foot (1.2 m × 2.4 m) sheets of plywood were used in its construction, [ 124 ] though one of the fabricators wrote that double-thickness 26-ply sheets were used for convenience. [ citation needed ]
A diesel generator is housed within the enclosure to supply electricity when external power is unavailable. [ 123 ] At the annual National Systems Contractors Association (NSCA) convention in March 2007, the Matterhorn was barred from making any loud demonstrations of its power because of concerns about damaging the building of the Orange County Convention Center . [ 121 ] Instead, using only a single 20 amp electrical circuit for safety, visitors were allowed to step inside the horn of the subwoofer for an "acoustic massage" as the fractionally powered Matterhorn reproduced low level 10–15 Hz waves. [ citation needed ]
Another subwoofer claimed to be the world's biggest is a custom installation in Italy made by Royal Device primarily of bricks, concrete and sound-deadening material [ 52 ] consisting of two subwoofers embedded in the foundation of a listening room. [ 126 ] The horn-loaded subwoofers each have a floor mouth that is 2.2 square meters (24 sq ft), and a horn length that is 9.5 meters (31 ft), in a cavity 1 meter (3 ft 3 in) under the floor of the listening room. Each subwoofer is driven by eight 18-inch subwoofer drivers with 100 millimeters (3.9 in) voice coils. The designers assert that the floor mouths of the horns are additionally loaded acoustically by a vertical wooden horn expansion and the room's ceiling to create a 10 Hz "full power" wave at the listening position.
A single 60-inch (1,500 mm) diameter subwoofer driver was designed by Richard Clark and David Navone with the help of Eugene Patronis of the Georgia Institute of Technology . The driver was intended to break sound pressure level records when mounted in a road vehicle, calculated to be able to achieve more than 180 dBSPL. It was built in 1997, driven by DC motors connected to a rotary crankshaft somewhat like in a piston engine . The cone diameter was 54 inches (1,400 mm) and was held in place with a 3-inch (76 mm) surround. With a 6-inch (150 mm) peak-to-peak stroke, it created a one-way air displacement of 6,871 cubic inches (112,600 cm 3 ). [ 127 ] It was capable of generating 5–20 Hz sine waves at various DC motor speeds—not as a response to audio signal—it could not play music. The driver was mounted in a stepvan owned by Tim Maynor but was too powerful for the amount of applied reinforcement and damaged the vehicle. [ 127 ] MTX's Loyd Ivey helped underwrite the project and the driver was then called the MTX "Thunder 1000000" (one million). [ citation needed ]
Still unfinished, the vehicle was entered in an SPL competition in 1997 at which a complaint was lodged against the computer control of the DC motor. Instead of using the controller, two leads were touched together in the hope that the motor speed was set correctly. The drive shaft broke after one positive stroke which created an interior pressure wave of 162 dB. The Concept Design 60-inch was not shown in public after 1998. [ 128 ]
The heaviest production subwoofer intended for use in automobiles is the MTX Jackhammer by MTX Audio , which features a 22-inch (560 mm) diameter cone. The Jackhammer has been known to take upwards of 6000 watts sent to a dual voice coil moving within a 900-ounce (26 kg) strontium ferrite magnet. The Jackhammer weighs in at 369 pounds (167 kg) and has an aluminum heat sink . [ 129 ] The Jackhammer has been featured on the reality TV show Pimp My Ride . [ citation needed ] | https://en.wikipedia.org/wiki/Subwoofer |
Successive Interference Cancellation (SIC) is a technique a receiver uses in a wireless data transmission that allows decoding of two or more packets that arrived simultaneously (in a regular system, more packets arriving simultaneously cause a collision).
SIC is achieved by the receiver decoding the stronger signal first, subtracting it from the combined signal and then decoding the difference as the weaker signal. [ 1 ]
This article about wireless technology is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Successive_interference_cancellation |
In mathematics , the successor function or successor operation sends a natural number to the next one. The successor function is denoted by S , so S ( n ) = n + 1. For example, S (1) = 2 and S (2) = 3. The successor function is one of the basic components used to build a primitive recursive function .
Successor operations are also known as zeration in the context of a zeroth hyperoperation : H 0 ( a , b ) = 1 + b . In this context, the extension of zeration is addition , which is defined as repeated succession.
The successor function is part of the formal language used to state the Peano axioms , which formalise the structure of the natural numbers. In this formalisation, the successor function is a primitive operation on the natural numbers, in terms of which the standard natural numbers and addition are defined. [ 1 ] For example, 1 is defined to be S (0), and addition on natural numbers is defined recursively by:
This can be used to compute the addition of any two natural numbers. For example, 5 + 2 = 5 + S (1) = S (5 + 1) = S (5 + S (0)) = S ( S (5 + 0)) = S ( S (5)) = S (6) = 7.
Several constructions of the natural numbers within set theory have been proposed. For example, John von Neumann constructs the number 0 as the empty set {}, and the successor of n , S ( n ), as the set n ∪ { n }. The axiom of infinity then guarantees the existence of a set that contains 0 and is closed with respect to S . The smallest such set is denoted by N , and its members are called natural numbers. [ 2 ]
The successor function is the level-0 foundation of the infinite Grzegorczyk hierarchy of hyperoperations , used to build addition , multiplication , exponentiation , tetration , etc. It was studied in 1986 in an investigation involving generalization of the pattern for hyperoperations. [ 3 ]
It is also one of the primitive functions used in the characterization of computability by recursive functions .
This mathematical logic -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Successor_function |
Microbial production of Succinic acid can be performed with wild bacteria like Actinobacillus succinogenes , [ 1 ] Mannheimia succiniciproducens and Anaerobiospirillum succiniciproducens or genetically modified Escherichia coli , Corynebacterium glutamicum and Saccharomyces cerevisiae . Understanding of the central carbon metabolism of these organisms is crucial in determining the maximum obtainable yield of succinic acid on the carbon source employed as substrate.
Neglecting the carbon utilised for biomass formation (known to be a small fraction of the total carbon utilised) basic biochemistry balances can be performed based on the established metabolic pathways [ 2 ] of these organisms. Using glucose as substrate the natural producing succinic acid producers are first considered. These organisms use the excretion of acetic acid (and sometimes formic acid ) to balance the NADH requirement of succinic acid production. Two possible paths exist as indicated in Figure 1 and Figure 2. The difference between the two pathways lies in the pyruvate oxidation step where pyruvate formate lyase is employed in Figure 1 and pyruvate dehydrogenase employed in Figure 2. The additional NADH generated in Figure 2 results in 66% of the molar glucose flux ending up as succinic acid compared to the 50% of Figure 1. The overall yields can be expressed on a mass basis where the pathway in Figure 1 results in a 0.66 gram succinic acid per gram of glucose consumed (g/g). The pathway in Figure 2 results in a yield of 0.87 g/g.
The metabolic pathway can be genetically engineered in order to have succinic acid as the only excretion product. [ 3 ] This can be achieved by using the oxidative section of the tricarboxylic acid cycle (TCA) under anaerobic conditions as illustrated in Figure 3. Alternatively the glyoxylate bypass can be utilised (Figure 4) to give the same result. For both these scenarios the mass based succinic acid yield is 1.12 g/g. This implies that the theoretical maximum yield is such that more succinic acid is formed than glucose consumed due to the fixation of carbon dioxide. | https://en.wikipedia.org/wiki/Succinic_acid_fermentation |
Succinimidyl 4-( N -maleimidomethyl)cyclohexane-1-carboxylate ( SMCC ) is a heterobifunctional amine-to-sulfhydryl crosslinker, which contains two reactive groups at opposite ends: N-hydroxysuccinimide -ester and maleimide , reactive with amines and thiols respectively. SMCC is often used in bioconjugation to link proteins with other functional entities (fluorescent dyes, tracers, nanoparticles, cytotoxic agents). [ 1 ] For example, a targeted anticancer agent – trastuzumab emtansine ( antibody-drug conjugate containing an antibody trastuzumab chemically linked to a highly potent drug DM-1 ) – is prepared using SMCC reagent. | https://en.wikipedia.org/wiki/Succinimidyl_4-(N-maleimidomethyl)cyclohexane-1-carboxylate |
Succinyl coenzyme A synthetase ( SCS , also known as succinyl-CoA synthetase or succinate thiokinase or succinate-CoA ligase ) is an enzyme that catalyzes the reversible reaction of succinyl-CoA to succinate . [ 3 ] The enzyme facilitates the coupling of this reaction to the formation of a nucleoside triphosphate molecule (either GTP or ATP ) from an inorganic phosphate molecule and a nucleoside diphosphate molecule (either GDP or ADP ). It plays a key role as one of the catalysts involved in the citric acid cycle , a central pathway in cellular metabolism , and it is located within the mitochondrial matrix of a cell. [ 4 ]
Succinyl CoA synthetase catalyzes the following reversible reaction :
where Pi denotes inorganic phosphate, NDP denotes nucleotide diphosphate (either GDP or ADP), and NTP denotes nucleotide triphosphate (either GTP or ATP). As mentioned, the enzyme facilitates coupling of the conversion of succinyl CoA to succinate with the formation of NTP from NDP and Pi. The reaction has a biochemical standard state free energy change of -3.4 kJ/mol. [ 4 ] The reaction takes place by a three-step mechanism [ 3 ] which is depicted in the image below. The first step involves displacement of CoA from succinyl CoA by a nucleophilic inorganic phosphate molecule to form succinyl phosphate. The enzyme then utilizes a histidine residue to remove the phosphate group from succinyl phosphate and generate succinate. Finally, the phosphorylated histidine transfers the phosphate group to a nucleoside diphosphate, which generates the high-energy carrying nucleoside triphosphate.
Bacterial and mammalian SCSs are made up of α and β subunits . [ 5 ] In E. coli two αβ heterodimers link together to form an α 2 β 2 heterotetrameric structure. However, mammalian mitochondrial SCSs are active as αβ dimers and do not form a heterotetramer. [ 6 ] The E. coli SCS heterotetramer has been crystallized and characterized in great detail. [ 6 ] [ 7 ] As can be seen in Image 2, the two α subunits (pink and green) reside on opposite sides of the structure and the two β subunits (yellow and blue) interact in the middle region of the protein. The two α subunits only interact with a single β unit, whereas the β units interact with a single α unit (to form the αβ dimer) and the β subunit of the other αβ dimer. [ 6 ] A short amino acid chain links the two β subunits which gives rise to the tetrameric structure.
The crystal structure of Succinyl-CoA synthetase alpha subunit (succinyl-CoA-binding isoform) was determined by Joyce et al. to a resolution of 2.10 A, with PDB code 1CQJ. [1] . [ 8 ]
Crystal structures for the E. coli SCS provide evidence that the coenzyme A binds within each α-subunit (within a Rossmann fold ) in close proximity to a histidine residue (His246α). [ 7 ] This histidine residue becomes phosphorylated during the succinate forming step in the reaction mechanism. The exact binding location of succinate is not well-defined. [ 9 ] The formation of the nucleotide triphosphate occurs in an ATP grasp domain, which is located near the N-terminus of the each β subunit. However, this grasp domain is located about 35 Å away from the phosphorylated histidine residue. [ 8 ] This leads researchers to believe that the enzyme must undergo a major change in conformation to bring the histidine to the grasp domain and facilitate the formation of the nucleoside triphosphate. Mutagenesis experiments have determined that two glutamate residues (one near the catalytic histidine, Glu208α and one near the ATP grasp domain, Glu197β) play a role in the phosphorylation and dephosphorylation of the histidine, but the exact mechanism by which the enzyme changes conformation is not fully understood. [ 9 ]
Johnson et al. describe two isoforms of succinyl-CoA synthetase in amniotes , one that specifies synthesis of ATP, and one that synthesises GTP. [ 10 ]
In amniotes, the enzyme is a heterodimer of an α- and a β-subunit. The specificity for either adenosine or guanosine phosphates is defined by the β-subunit, [ 10 ] which is encoded by 2 genes. SUCLG2 is GTP-specific and SUCLA2 is ATP-specific, while SUCLG1 encodes the common α-subunit. β variants are produced at different amounts in different tissues, [ 10 ] causing GTP or ATP substrate requirements.
Mostly consuming tissues such as heart and brain have more ATP-specific succinyl-CoA synthetase (ATPSCS), while synthetic tissues such as kidney and liver have the more GTP-specific form (GTPSCS). [ 11 ] Kinetics analysis of ATPSCS from the breast muscle of pigeons and GTPSCS from pigeon liver showed that their apparent Michaelis constants were similar for CoA, but different for the nucleotides, phosphate, and succinate. The largest difference was for succinate: K m app of ATPSCS = 5mM versus that of GTPSCS = 0.5mM. [ 10 ]
SCS is the only enzyme in the citric acid cycle that catalyzes a reaction in which a nucleotide triphosphate (GTP or ATP) is formed by substrate-level phosphorylation . [ 4 ] Research studies have shown that E. coli SCSs can catalyze either GTP or ATP formation. [ 7 ] However, mammals possess different types of SCSs that are specific for either GTP (G-SCS) or ATP (A-SCS) and are native to different types of tissue within the organism. An interesting study using pigeon cells showed that GTP specific SCSs were located in pigeon liver cells, and ATP specific SCSs were located in the pigeon breast muscle cells. [ 12 ] Further research revealed a similar phenomenon of GTP and ATP specific SCSs in rat, mouse, and human tissue. It appears that tissue typically involved in anabolic metabolism (like the liver and kidneys) express G-SCS, whereas tissue involved in catabolic metabolism (like the brain, the heart, and muscular tissue) express A-SCS. [ 11 ]
SCS facilitates the flux of molecules into other metabolic pathways by controlling the interconversion between succinyl CoA and succinate. [ 13 ] This is important because succinyl CoA is an intermediate necessary for porphyrin , heme , [ 14 ] and ketone body biosynthesis . [ 15 ]
In some bacteria, the enzyme is regulated at the transcriptional level. [ 16 ] It has been demonstrated that the gene for SCS (sucCD) is transcribed along with the gene for α-ketoglutarate dehydrogenase (sucAB) under the control of a promoter called sdhC, which is part of the succinate dehydrogenase operon . This operon is up-regulated by the presence of oxygen and responds to a variety of carbon sources. Antibacterial drugs that prevent phosphorylation of histidine, like the molecule LY26650, are potent inhibitors of bacterial SCSs. [ 17 ]
Measurements (performed using a soy bean SCS) indicate an optimal temperature of 37 °C and an optimal pH of 7.0-8.0. [ 18 ]
Fatal infantile lactic acidosis: Defective SCS has been implicated as a cause of fatal infantile lactic acidosis , which is a disease in infants that is characterized by the build-up of toxic levels of lactic acid. The condition (when it is most severe) results in death usually within 2–4 days after birth. [ 19 ] It has been determined that patients with the condition display a two base pair deletion within the gene known as SUCLG1 that encodes the α subunit of SCS. [ 19 ] As a result, functional SCS is absent in metabolism causing a major imbalance in flux between glycolysis and the citric acid cycle. Since the cells do not have a functional citric acid cycle, acidosis results because cells are forced to choose lactic acid production as the primary means of producing ATP. | https://en.wikipedia.org/wiki/Succinyl_coenzyme_A_synthetase |
Sucrose esters or sucrose fatty acid esters are a group of non-naturally occurring surfactants chemically synthesized from the esterification of sucrose and fatty acids (or glycerides ). This group of substances is remarkable for the wide range of hydrophilic-lipophilic balance (HLB) that it covers. The polar sucrose moiety serves as a hydrophilic end of the molecule, while the long fatty acid chain serves as a lipophilic end of the molecule. Due to this amphipathic property, sucrose esters act as emulsifiers ; i.e., they have the ability to bind both water and oil simultaneously. Depending on the HLB value, some can be used as water-in-oil emulsifiers, and some as oil-in-water emulsifiers. Sucrose esters are used in cosmetics, food preservatives, food additives, and other products. A class of sucrose esters with highly substituted hydroxyl groups, olestra , is also used as a fat replacer in food. [ 1 ]
Sucrose esters were first mentioned in 1880 by Herzfeld who described the preparation of sucrose octaacetate. The substance is still in use today as a food additive. [ 2 ] In 1921, Hess and Messner synthesized sucrose octapalmitate and sucrose octastearate. Both are sucrose fatty acid esters.
Rosenthal, in 1924, synthesized highly substituted sucrose fatty acid esters using the classical condensation reaction between sucrose and the acid chloride of the drying oil fatty acid; pyridine was used as a solvent. Rheineck, Rabin, and Long followed the same procedure using alternative polyhydroxyl molecules such as mannitol. These condensation gave low yields, and the products, which were dark in color, needed extensive purification. Moreover, pyridine is a toxic solvent, so the synthesis was not commercially successful.
In 1939, Cantor, who patented a production route of sucrose fatty acid esters from starch factory by-products, claimed that the products could be used as emulsifying agents or fats. The classical esterification was used with a mixture of pyridine and either chloroform or carbontetrachloride as a solvent.
Later, the concept of synthesizing sucrose ester from sucrose and fatty acids was patented in 1952. The new synthesis pathway, which involved transesterification of triglycerides and sucrose in the new solvent dimethylformamide or DMF, was invented and seemed promising.
In 1950s, Foster Snell and his team conducted research on the production of several mono- and di-substituted sucrose esters. Many processes are still used in commercial production today. [ 3 ]
Sucrose is a disaccharide formed from condensation of glucose and fructose to produce α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside. Sucrose has 8 hydroxyl groups which can be reacted with fatty acid esters to produce sucrose esters. Among the 8 hydroxyl groups on sucrose, three (C6, C1', and C6') are primary while the others (C2, C3, C4, C3', and C4') are secondary. (The numbers 1-6 indicate the position of the carbons on glucose while the numbers 1'-6' indicate the position of the carbons on fructose.) The three primary hydroxyl groups are more reactive due to lower steric hindrance , so they react with fatty acids first, resulting in a sucrose mono-, di-, or triester. Typical saturated fatty acids that are used to produce sucrose esters are lauric acid , myristic acid , palmitic acid , stearic acid and behenic acid , and typical unsaturated fatty acids are oleic acid and erucic acid . [ 1 ]
Due to the hydrophilic property of sucrose and the lipophilic property of fatty acids, the overall hydrophilicity of sucrose esters can be tuned by the number of hydroxyl groups that are reacted with fatty acids and the identity of the fatty acids. The fewer free hydroxyl groups and the more lipophilic fatty acids, the less hydrophilic the resulting sucrose ester becomes. Sucrose esters' HLB values can range from 1-16. Low HLB (3.5-6.0) sucrose esters act as a water-in-oil emulsifier while high HLB (8-18) sucrose esters act as an oil-in-water emulsifier. [ 1 ]
Sucrose esters are off-white powders. Though produced from sucrose, sucrose esters do not have a sweet taste, but are bland or bitter.
The melting point of sucrose esters is between 40 °C and 60 °C depending on the type of fatty acids and the degree of substitution. Sucrose esters can be heated to 185 °C without losing their functionality. However, the color of the product might change due to caramelization of sucrose. [ 1 ]
Sucrose esters are stable in the pH range of 4 to 8, so they can be used as an additive in most foods. At pH higher than 8, saponification (hydrolysis of the ester bond to release the original sucrose and the salt of fatty acids) might occur. Hydrolysis could also occur at pH lower than 4. [ 1 ]
This part of the article aims at disambiguating of the notion of HLB, " Hydrophile - Lipophile Balance ", attributed to Sucrose Fatty Acid Ester surfactants (also named sucrose esters or sugar esters).
The attribution of HLB values to sucrose esters emulsifiers at the origin is unclear, since no bibliographic source can be found on how the attribution has been made. There is no early scientific data, dating back to the 1990s or earlier, supporting experimentally the current HLB scale attributed to sucrose esters. However, a clear numerical correlation is found between the Griffin HLB scale defined for non-ionic poly(ethylene oxide) (PEO) surfactants [ 4 ] and the HLB scale attributed to marketed sucrose esters. [ 5 ]
For polyethylene oxide non ionic surfactants the HLB is defined by the Griffin's scale (Equation 1):
H L B = 20 × ( M a s s o f t h e h y d r o p h i l i c p a r t o f t h e s u r f a c t a n t ( P E O p a r t ) T o t a l m a s s o f t h e s u r f a c t a n t ) {\displaystyle HLB=20\times \left({\frac {Mass\ of\ the\ hydrophilic\ part\ of\ the\ surfactant\ (PEO\ part)}{Total\ mass\ of\ the\ surfactant}}\right)}
For sucrose esters, it became (Equation 2):
H L B = 20 × ( M a s s o f s u c r o s e m o n o e s t e r s i n t h e s u c r o s e e s t e r s b l e n d T o t a l m a s s o f t h e s u c r o s e e s t e r b l e n d ) {\displaystyle HLB=20\times \left({\frac {Mass\ of\ sucrose\ monoesters\ in\ the\ sucrose\ esters\ blend}{Total\ mass\ of\ the\ sucrose\ ester\ blend}}\right)}
For example, for a sucrose ester mixture containing 80% of sucrose monoester, HLB = 16. This equation has been applied regardless the length of the fatty chain. A correspondence table can be written for different grades of sucrose esters according to this equation. The values calculated correspond quite closely with the data given by the suppliers (the data have been harvested from the respective suppliers' websites in March 2020).
Sisterna sucrose ester
L-1695
PS750
S-1570
OWA-1570
L70
SP70
SP50
SP30
B-370
SP10
(Equation 2)
Ryoto
Sisterna
11
6
Notes: % monoesters and HLB reported in this table are the approximative values indicated by the suppliers for each blend. B= Behenate (22 carbon chain) - S = stearate (18 carbon chain) - O = Oleate (18 carbon chain, 1 unsaturation) - P = Palmitate (16 carbon chain) - M = myristate (14 carbon chain) - L = Laurate (12 carbon chain)
It means that a transposition of the HLB scale of the PEO surfactants has been made for defining the HLB of sucrose esters, because both families of surfactants are non-ionic surfactants. There are two issues with this transposition. The first one is that in this numerical transposition of the Griffin's scale to sucrose esters, the monoesters content is supposed to correspond the hydrophilic part of the surfactant what is a strong approximation because the monoesters fraction is not purely hydrophilic, since it also contains a high proportion of hydrophobic fatty chains in mass percent. It means also that, for example, a sucrose laurate blend (a sucrose grafted with a 12 carbon fatty acid) and a sucrose stearate blend (a sucrose grafted with a 18 carbon fatty acid) have the same HLB (see Table), despite the fact that sucrose laurates are really more hydrophilic and water-soluble than sucrose stearates.
The second issue is that this HLB scale, established for non-ionic PEO surfactants on the basis of experimental data, is valid only for the latter. [ 6 ] This scale has a genuine predictive value for choosing the right PEO surfactant for a given application, typically oil-in-water or water-in-oil emulsification. Because of that, the same predictive effect is expected for the HLB index of sucrose ester, although this index has not be built on the basis of an experimental scale, but on the basis of a calculation. By using the same notion of HLB for different categories of surfactants, it is also expected that this tool would be predictive for comparing surfactants belonging to different families, e.g. PEO surfactants and sucrose esters emulsifiers. It is not the case as long as experiments have not brought evidence that correspondences are possible between the scales applied to different surfactants families. Otherwise, it brings confusion.
Non-ionic carbohydrate surfactants have a very different chemical structure and different physicochemical properties compared to polyethylene oxide surfactants family. It is the case notably for their emulsifying properties, for their sensitivity to temperature and their interaction with water through hydrogen bonding. Hence, by using the same calculated HLB scale for sucrose fatty acid esters and for polyethylene surfactants, instead of an experimental HLB scale, it is very likely that this scale will not predict properly the properties of sucrose esters. For the same reason, comparison of sucrose esters with non-ionic carbohydrate based surfactants such as Tween series is also uncertain, because the latter are grafted with polyethylene oxide chains that make them behave as PEO surfactants rather than carbohydrate surfactants.
Therefore, the HLB scale of sucrose esters as defined by suppliers up to now (March 2020) should be merely considered as an index ranking them from the most hydrophilic (high HLB) to the most lipophilic (low HLB). It is useful for comparing their properties within the sucrose ester family, but it should not be used as an experimental predictive tool for comparing their emulsifying properties to other kinds of surfactants, especially for high HLB index.
The HLB scales, defined in the 1950s, have been built from experimental methods. [ 6 ] It is notably the case of the Griffin's scale set above, that has been established experimentally by comparing the stability of emulsions involving different oils and stabilized by a large range of POE surfactants. From this large quantity of experimental data, an experimental HLB scale has been built up. Since a relationship between the surfactant structure and the results was observed, then a numerical equation has been worked out. [ 4 ] The equation facilitated the determination of the HLB of new PEO surfactants without the need of new experiments. This calculation thus is strictly valid within the limit of the PEO surfactants family.
Efforts to clarify the HLB of sucrose esters and related carbohydrate surfactants by experimental methods has been made in few works. [ 5 ] [ 7 ] [ 8 ] [ 9 ] Methods are based on the comparison of the stability of emulsions, on the "water number method" or on the "Phase Inversion Temperature" (PIT) method. The results tend to show that the experimental HLB of sucrose monoesters, composed of 100% of monoesters for purified products and around 70-80% for industrial blends, would be rather around 11-12 for short fatty chains (6 to 12 carbons) and around 10-11 for long fatty chains (14 to 18 carbons). These values would better describe their emulsifying behavior and would better make the correspondence with other families of surfactants. Notably, the experimental range of HLB of sucrose esters would not be so wide as the calculated HLB indicated on suppliers technical sheets, especially not as high as HLB 16. It is also important to point out the fact that in experiments, the residual amount of fatty acid (even less than 2% in weight) and the state of protonation of the latter has a significant effect on the phase properties and the emulsifying properties of sucrose esters, because the deprotonated fatty acid is highly surface active while the protonated fatty acid is not. This state of protonation has also an impact on the experimental determination of the HLB.
The "wide range of HLB" currently defined for sucrose esters marketed blends, which is supposed to spread up to 16, should be considered with a critical point of view at the light of these observations. While the use of the different grades of sucrose esters is well documented in some applications, notably for food formulations, clarifying their HLB scale on an experimental basis will help their implementation in new applications not yet documented.
Sucrose esters are mainly manufactured by using interesterification, the transfer of fatty acid from one ester to another. In this case, it means that the fatty acids used for the synthesis of sucrose esters are themselves in the esterified form. There are three processes that have been developed. [ 1 ]
The process involves transesterification of sucrose and triglycerides under a basic condition at 90 °C. DMF was used as a solvent at first, but was later substituted with dimethyl sulfoxide or DMSO, which is less hazardous and cheaper. This process produces a mixture of sucrose monoesters and more substituted esters at about a 5:1 ratio. [ 10 ]
The other method involves transesterification of sucrose and fatty acid methyl ester using sodium methoxide as a basic catalyst. The by-product methanol can be removed via distillation to drive the equilibrium to favor sucrose esters.
The process does not work for food industry because DMF is poisonous and may not be used in food production.
The concept of microemulsion is applied in this process. The transesterification involves sucrose and fatty acid methyl ester in a solvent, propylene glycol . A basic catalyst, such as anhydrous potassium carbonate , and soap, or a fatty acid salt, are added. The reaction is carried out at 130-135 °C. Propylene glycol is removed through distillation under vacuum at above 120 °C. The purified product is achieved by filtration. The yield of the reaction is 96%. 85% of sucrose esters is monosubstituted and 15% is disubstituted. [ 11 ]
Molten sucrose is used instead of solvent. The reaction involves molten sucrose and fatty acid ester (methyl ester or triglyceride) with a basic catalyst, potassium carbonate or potassium soap. The high temperature (170-190 °C) is required for this process. [ 12 ] Since the process is carried out at a high temperature, sucrose can be degraded.
Later, a new synthesis pathway was introduced. First, sucrose and fatty acid soap are dissolved in water. Then, fatty acid ester and a basic catalyst are added to the solution. The solution must be heated and the pressure should be reduced to remove water and form a molten mixture. The transesterification is carried in the temperature range of 110-175 °C. [ 13 ]
Some sucrose esters, such as sucrose distearate, sucrose dilaurate, sucrose palmitate, etc. are added in cosmetics products as an emulsifier. Some have a function in skin conditioning and emollient. [ 14 ] Cosmetics products that might have sucrose esters as an ingredient includes eyelash products, hair treatments, oil gels, skin products and deodorants. [ 10 ]
Sucrose esters of fatty acid ( E 473 ) are used for surface treatment of some climacteric fruits such as peaches, pears, cherries, apples, bananas, etc. E473 is allowed for application on fruit surfaces in the EU at whatever level is needed to achieve a technical effect (‘quantum satis’) and has limited allowance in the US as a component of protective coatings for fruits (CFR §172.859, limited categories inc. avocados, apples, limes [but not other citrus], peaches, pars, plums, pineapples).The coating preserves the fruits by blocking respiratory gases. [ 15 ]
Due to their surfactant properties, sucrose esters are used in pharmaceutical research as a stabilizer or a surfactant on vesicles for drug delivery systems. [ 16 ]
Sucrose esters are used as food additives in a variety of food. European Parliament and Council Directive No 95/2/EC limited the use of sucrose esters under E 473 in each kind of food. [ 17 ] No longer in force, Date of end of validity: 20/01/2010; Repealed by 32008R1333 .
Dietetic formulae for weight control intended to replace
total daily food intake or an individual meal
Japan was the first country that allowed the use of sucrose esters as food additives. The Japanese Ministry of Health and Welfare approved sucrose esters in 1959. Then, in 1969, FAO / WHO approved the use of sucrose esters. [ 18 ]
Sucrose esters were approved and registered by European Food Safety Authority or EFSA under the E number of E 473. [ 19 ]
In the US, sucrose esters were approved by the FDA (Food and Drug Administration). [ 20 ] [ 21 ] | https://en.wikipedia.org/wiki/Sucrose_esters |
Suction is the day-to-day term for the movement of gases or liquids along a pressure gradient with the implication that the movement occurs because the lower pressure pulls the gas or liquid. However, the forces acting in this case do not originate from just the lower pressure side, but also from the side of the higher pressure, as a reaction to the pressure difference.
When the pressure in one part of a physical system is reduced relative to another, the fluid or gas in the higher pressure region will exert a force relative to the region of lowered pressure, referred to as pressure-gradient force . If all gas or fluid is removed the result is a perfect vacuum in which the pressure is zero. Hence, no negative pressure forces can be generated. Accordingly, from a physics point of view, the objects are not pulled but pushed.
Pressure reduction may be static , as in a piston and cylinder arrangement, or dynamic , as in the case of a vacuum cleaner when air flow results in a reduced pressure region.
When animals breathe, the diaphragm and muscles around the rib cage cause a change of volume in the lungs. The increased volume of the chest cavity decreases the pressure inside, creating an imbalance with the ambient air pressure, resulting in suction. Similarly, when a straw is used to suck a liquid from a glass into the mouth, the atmospheric pressure on the fluid in the glass pushes the liquid up through the straw along the pressure gradient.
A common semantic mistake in aviation accident reporting is describing people or objects as being 'sucked out' during rapid decompression events, when physically they are 'blown out' by the higher internal cabin pressure rushing toward the lower ambient pressure outside the plane — the opposite phenomenon to what happens when an object is placed too close to a running jet engine creating the risk of being sucked in. [ 2 ] [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Suction |
Suction caissons (also referred to as suction anchors , suction piles or suction buckets ) are a form of fixed platform anchor in the form of an open bottomed tube embedded in the sediment and sealed at the top while in use so that lifting forces generate a pressure differential that holds the caisson down. They have a number of advantages over conventional offshore foundations, mainly being quicker to install than deep foundation piles and being easier to remove during decommissioning. Suction caissons are now used extensively worldwide for anchoring large offshore installations, like oil platforms , offshore drillings and accommodation platforms to the seafloor at great depths. In recent years, suction caissons have also seen usage for offshore wind turbines in shallower waters.
Oil and gas recovery at great depth could have been a very difficult task without the suction anchor technology, which was developed and used for the first time in the North Sea 30 years ago. [ 1 ] The use of suction caissons/anchors has now become common practice worldwide. Statistics from 2002 revealed that 485 suction caissons had been installed in more than 50 different localities around the world, in depths to about 2000 m. Suction caissons have been installed in most of the deep water oil producing areas around the world: The North Sea , Gulf of Mexico , offshore West Africa, offshore Brazil, West of Shetland, South China Sea , Adriatic Sea and Timor Sea . No reliable statistics have been produced after 2002, but the use of suction caissons is still rising. [ 2 ]
A suction caisson can effectively be described as an inverted bucket that is embedded in the marine sediment . Attachment to the sea bed is achieved either through pushing or by creating a negative pressure inside the caisson skirt by pumping water out of the caisson; both of these techniques have the effect of securing the caisson into the sea bed. The foundation can also be rapidly removed by reversing the installation process, pumping water into the caisson to create an overpressure. [ 3 ]
The concept of suction technology was developed for projects where gravity loading is not sufficient for pressing foundation skirts into the ground. The technology was also developed for anchors subject to large tension forces due to waves and stormy weather. The suction caisson technology functions very well in a seabed with soft clays or other low strength sediments . The suction caissons are in many cases easier to install than piles, which must be driven (hammered) into the ground with a pile driver . [ 4 ]
Mooring lines are usually attached to the side of the suction caisson at the optimal load attachment point, which must be calculated for each caisson. Once installed, the caisson acts much like a short rigid pile and is capable of resisting both lateral and axial loads. Limit equilibrium methods or 3D finite element analysis are used to calculate the holding capacity. [ 5 ]
Suction caissons were first used as anchors for floating structures in the offshore oil and gas industry, including offshore platforms such as the Draupner E oil rig .
There are great differences between the first small suction caissons that were installed for Shell at the Gorm field in the North Sea in 1981 and the large suction caissons that were installed for the Diana platform in the Gulf of Mexico in 1999. The twelve suction caissons on the Gorm field were intended to secure a simple loading buoy device at a depth of 40 metres, while the installation of suction anchors for the Diana platform was a world record in itself at that time, concerning water depth and size of anchors. The height of the Diana suction caissons is 30 metres, their diameter 6.5 metres, and they were installed at a depth of about 1500 m on soft clay deposits. Since then, suction caissons have been installed at even larger depths, but the Diana installation was a technology breakthrough for the 20th century. [ 6 ] An important development step for the suction caisson technology emerged from cooperation between the former operator in the North Sea, Saga Petroleum AS , and Norwegian Geotechnical Institute (NGI). Saga Petroleum's oil-producing Snorre A platform was a tension-leg platform of a type that in other parts of the world would have been founded with up to 90 metres long piles. Unfortunately on the Snorre oil field , it was difficult to use long piles due to the presence of huge pebbles at 60 m depth under the seabed. Saga Petroleum decided therefore to use suction caissons, which were analysed by NGI. These analyses were verified from extensive model tests. The calculations showed that the platform could be safely secured by suction caissons of only 12 m in length. Snorre A started to produce oil in 1992 and is now operated by the Norwegian oil company Statoil .
Suction buckets were tested with offshore wind turbines at Frederikshavn in 2002, at Horns Rev in 2008 [ 7 ] [ 8 ] and Borkum Riffgrund in 2014, and are to be used in a third of the foundations at the initial development at Hornsea Wind Farm . [ 9 ] Statoil have gone on to use the technology for windfarms. [ 10 ] They are also planned to be used for some of the wind turbines in the Hornsea Project One wind farm scheduled to be completed in 2020. [ 11 ] [ 12 ] Similarly, a suction bucket contract has been awarded for the Aberdeen Bay Wind Farm .
Suction caissons have a lot of similarities with foundation design principles and solutions for the big gravity oil platforms that were installed in the North Sea when the offshore oil production started there in the beginning of 1970's. The first gravity oil platform on the Ekofisk oil field had a foundation area that was as big as a football field, and it was placed on a seabed with very dense sand. The platform was designed to tolerate waves up to 24 m in height.
As the installation of oil platforms continued in the North Sea, in areas with poor ground conditions such as soft clays, they were designed to survive even higher storm waves. These platforms were founded on a system of cylindrical skirts that were penetrated into the ground under combined gravity load and underpressure. The oil platform at the Gullfaks C field was equipped with 22 m long skirts. The Troll A platform is founded in 330 m depth with 30 m long skirts and is the world's biggest gravity platform.
The Norwegian Geotechnical Institute (NGI) has been heavily involved with the concept development, design and installation of suction anchors from the start. The project "Application of offshore bucket foundations and anchors in lieu of conventional designs" (1994-1998) was sponsored by 15 international petroleum and industry companies and was one of the most important studies. The project “Skirted foundations and anchors in clay” (1997-1999) was sponsored by 19 international companies organized through the Offshore Technology Research Center (OTRC) in the US, and the project “Skirted offshore foundations and anchors in sand” (1997-2000) was sponsored by 8 international companies. The main conclusions from the projects were presented in the 1999 OTC paper no 10824.
An industry sponsored study on the design and analysis of deepwater anchors in soft clay was completed in 2003, where NGI participated together with OTRC and Centre for Offshore Foundation Systems (COFS) in Australia. The overall objective was to provide the API Geotechnical Workgroup (RG7) and the Deepstar Joint Industry Project VI with background, data and other information needed to develop a widely applicable recommended practice for the design and installation of deepwater anchors.
The Norwegian classification society DNV ( Det Norske Veritas ), active worldwide in risk analysis and safety evaluation of special constructions, has produced a recommended practice report on the design procedures for suction anchors which is based on close cooperation with NGI. The main information from the project was presented in the 2006 OTC paper no 18038.
In 2002 NGI established the subsidiary NGI Inc in Houston. The subsidiary has since been awarded the detailed geotechnical design for more than 15 suction anchor projects in the Gulf of Mexico, and among these the challenging Mad Dog Spar project involving design of anchors located in old slide deposits below the Sigsbee Escarpment . For further information reference can be made to the 2006 OTC papers no 17949 and 17950. [ 13 ] | https://en.wikipedia.org/wiki/Suction_caisson |
A suction excavator , or vacuum excavator , is a construction vehicle that removes heavy debris or other materials from a hole on land using vacuuming. Suction excavators are meant to be less destructive than regular excavators . [ 1 ] The suction excavator uses suction fans for the airflow to suck up the material that is then transported into the holding tank .
Hydro excavation , a type of suction excavator using high-pressure water jets , is sometimes referred to as daylighting , as the underground utilities are exposed to daylight during the process. [ 2 ] Some suction excavators also use an air filter .
Since 1993, RSP UK Suction Excavators Ltd. has produced suction structures mounted onto two, three, and four-axle vehicles, stationary suction units, and custom-made machines. [ 3 ] Pacific Tek, [ 4 ] also founded in 1993, has created the Angled Vacuum Excavator Tank (1997) and the 180° Swivel Mount Valve Operator (1999).
In 1998, the Mobile Tiefbau Saugsysteme produced another type of suction excavator. [ 5 ]
The global market size for suction excavators was estimated to be valued at US$ 924.7 million in 2020. [ 6 ]
Suction excavators are sometimes used for removing earth around buried utilities and tree roots . It can suck up liquids, e.g., water from a hollow. Typically, vacuum excavation loosens the soil with a blunt-nosed high-pressure air lance or water source and vacuums away loosened material.
Depending on the machine used and soil conditions, a 12-inch-square, 5-foot-deep pothole can be completed in 20 minutes or less. [ 7 ] Vacuum excavation is sometimes used in conjunction with conventional underground (one-call) locating services. Because of overlapping buried utility lines, locating devices often miss some of the buried utilities on a site and cannot completely or accurately mark a site.
According to New Mexico 811's (NM811) Aligning Change, Locating with Potholing , "One-call paint marks and flags are the first steps in making the process of locating underground utilities safer, the use of vacuum excavation technology adds an additional margin of safety ." [ 8 ]
Media related to Suction excavators at Wikimedia Commons | https://en.wikipedia.org/wiki/Suction_excavator |
Vacuum filtration is a fast filtration technique used to separate solids from liquids .
By flowing through the aspirator , water will suck out the air contained in the vacuum flask and the Büchner flask . There is therefore a difference in pressure between the exterior and the interior of the flasks : the contents of the Büchner funnel are sucked towards the vacuum flask. The filter , which is placed at the bottom of the Büchner funnel, separates the solids from the liquids.
The solid residue , which remains at the top of the Büchner funnel, is therefore recovered more efficiently: it is much drier than it would be with a simple filtration.
The rubber conical seal ensures the apparatus is hermetically closed, preventing the passage of air between the Büchner funnel and the vacuum flask. It maintains the vacuum in the apparatus and also avoids physical points of stress (glass against glass.)
Filtration is a unit operation that is commonly used both in laboratory and production conditions. This apparatus, adapted for laboratory work, is often used to isolate the product of synthesis of a reaction when the product is a solid in suspension. The product of synthesis is then recovered faster, and the solid is drier than in the case of a simple filtration. Other than isolating a solid, filtration is also a stage of purification: the soluble impurities in the solvent are eliminated in the filtrate (liquid).
This apparatus is often used to purify a liquid. When a synthesised product is filtered, the insolubles (catalysers, impurities, sub-products of the reaction, salts, ...) remain in the filter. In this case, vacuum filtration is also more efficient that a simple filtration: there is more liquid recovered, and the yield is therefore better.
It is often necessary to maintain the Büchner flask and, incidentally, the vacuum flask. The rigidity of the vacuum pipes and the difference in height between the different parts of the apparatus (as visible in the diagram) make such an apparatus relatively unstable.
Therefore, a three-pronged clamp should be used to maintain the Büchner flask. This clamp should be placed such that the two prongs surround the part of the flask connected to the vacuum tube, the lasting prong resting on the other side.
If it is also necessary to maintain the vacuum flask we use either a mandible clamp, or a three-pronged clamp, depending on the apparatus and its stability. The clamp to use is left to the judgement of the operator.
Before closing the tap, it is necessary to "break the vacuum" (letting in the air in through any area in the apparatus, by removing the funnel for example), otherwise water goes up the apparatus from the aspirator. The vacuum flask prevents the water from going up the Büchner flask.
Vacuum Filtration
Vacuum Filtration , retrieved 2017-01-14 | https://en.wikipedia.org/wiki/Suction_filtration |
Suctorial pertains to the adaptation for sucking or suction, [ 1 ] as possessed by marine parasites such as the Cookiecutter shark , [ 2 ] specifically in a specialised lip organ enabling attachment to the host.
Suctorial organs of a different form are possessed by the Solifugae arachnids , enabling the climbing of smooth, vertical surfaces. [ 3 ]
Another variation on the suctorial organ can be found as part of the glossa proboscis of Masarinae (pollen wasps), enabling nectar feeding from the deep and narrow corolla of flowers. [ 4 ]
This biology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Suctorial |
In the theory of computation , the Sudan function is an example of a function that is recursive , but not primitive recursive . This is also true of the better-known Ackermann function .
In 1926, David Hilbert conjectured that every computable function was primitive recursive. This was refuted by Gabriel Sudan and Wilhelm Ackermann — both his students — using different functions that were published in quick succession: Sudan in 1927, [ 1 ] Ackermann in 1928. [ 2 ]
The Sudan function is the earliest published example of a recursive function that is not primitive recursive. [ 3 ]
The last equation can be equivalently written as
These equations can be used as rules of a term rewriting system (TRS) .
The generalized function F ( x , y , n ) = d e f F n ( x , y ) {\displaystyle F(x,y,n){\stackrel {\mathrm {def} }{=}}F_{n}(x,y)} leads to the rewrite rules
At each reduction step the rightmost innermost occurrence of F is rewritten, by application of one of the rules (r1) - (r3).
Calude (1988) gives an example : compute F ( 2 , 2 , 1 ) → ∗ 12 {\displaystyle F(2,2,1)\rightarrow _{*}12} . [ 5 ]
The reduction sequence is [ 6 ]
F 0 ( x , y ) = x + y
F 1 ( x , y ) = 2 y · (x + 2) − y − 2 | https://en.wikipedia.org/wiki/Sudan_function |
Sudarsky's classification of gas giants for the purpose of predicting their appearance based on their temperature was outlined by David Sudarsky and colleagues in the paper Albedo and Reflection Spectra of Extrasolar Giant Planets [ 1 ] and expanded on in Theoretical Spectra and Atmospheres of Extrasolar Giant Planets , [ 2 ] published before any successful direct or indirect observation of an extrasolar planet atmosphere was made. It is a broad classification system with the goal of bringing some order to the likely rich variety of extrasolar gas-giant atmospheres.
Gas giants are split into five classes (numbered using Roman numerals ) according to their modeled physical atmospheric properties. In the Solar System, only Jupiter and Saturn are within the Sudarsky classification, and both are Class I.
The appearance of planets that are not gas giants cannot be predicted by the Sudarsky system, for example terrestrial planets such as Earth and Venus , or ice giants such as Uranus (14 Earth masses) and Neptune (17 Earth masses). [ citation needed ]
The appearance of extrasolar planets is largely unknown because of the difficulty in making direct observations. In addition, analogies with planets in the Solar System can apply to few of the extrasolar planets known because most are wholly unlike any of our planets, for example, the hot Jupiters .
Bodies that transit their star can be spectrographically mapped, for instance HD 189733 b . [ 3 ] That planet has further been shown to be blue with an albedo greater (brighter) than 0.14. [ 4 ] Most planets so mapped have been large and close-orbiting "hot Jupiters".
Speculation on the appearances of unseen extrasolar planets currently relies upon computational models of the likely atmosphere of such a planet, for instance how the atmospheric temperature–pressure profile and composition would respond to varying degrees of insolation .
Gaseous giants in this class have appearances dominated by ammonia clouds. These planets are found in the outer regions of a planetary system . They exist at temperatures less than about 150 K (−120 °C; −190 °F). The predicted Bond albedo of a class I planet around a star like the Sun is 0.57, compared with a value of 0.343 for Jupiter [ 5 ] and 0.342 for Saturn . [ 6 ] The discrepancy can be partially accounted for by taking into account non-equilibrium condensates such as tholins or phosphorus , which are responsible for the coloured clouds in the Jovian atmosphere, and are not modelled in the calculations.
The temperatures for a class I planet requires either a cool star or a distant orbit. The former may mean the star(s) are too dim to be visible, where the latter may mean the orbits are so large that their effect is too subtle to be detected until several observations of those orbits' complete "years" (cf. Kepler's third law ). The increased mass of superjovians would make them easier to observe, however a superjovian of comparable age to Jupiter would have more internal heating , which could push it to a higher class.
Gaseous giants in class II are too warm to form ammonia clouds; instead their clouds are made up of water vapor . These characteristics are expected for planets with temperatures below around 250 K (−23 °C; −10 °F). [ 2 ] Water clouds are more reflective than ammonia clouds, and the predicted Bond albedo of a class II planet around a Sun-like star is 0.81. Even though the clouds on such a planet would be similar to those of Earth , the atmosphere would still consist mainly of hydrogen and hydrogen-rich molecules such as methane .
Sudarsky et al. listed Epsilon Eridani b , Upsilon Andromedae d , and 55 Cancri d as possible Class II planets. [ 2 ]
Gaseous giants with equilibrium temperatures between about 350 K (170 °F, 80 °C) and 800 K (980 °F, 530 °C) do not form global cloud cover, because they lack suitable chemicals in the atmosphere to form clouds. [ 2 ] (They would not form sulfuric acid clouds like Venus due to excess hydrogen.) These planets would appear as featureless azure-blue globes because of Rayleigh scattering and absorption by methane in their atmospheres, appearing like Jovian-mass versions of Uranus and Neptune . Because of the lack of a reflective cloud layer, the Bond albedo is low, around 0.12 for a class-III planet around a Sun-like star. They exist in the inner regions of a planetary system, roughly corresponding to the location of Mercury .
Sudarsky et al. listed Upsilon Andromedae c , Gliese 876 b , and Gliese 876 c as possible Class III planets. [ 2 ] Above 700 K (800 °F, 430 °C), sulfides and chlorides might provide cirrus -like clouds. [ 2 ]
Above 900 K (630 °C/1160 °F), carbon monoxide becomes the dominant carbon-carrying molecule in a gas giant's atmosphere (rather than methane ). Furthermore, the abundance of alkali metals , such as sodium substantially increase, and spectral lines of sodium and potassium are predicted to be prominent in a gas giant's spectrum . These planets form cloud decks of silicates and iron deep in their atmospheres, but this is not predicted to affect their spectrum. The Bond albedo of a class IV planet around a Sun-like star is predicted to be very low, at 0.03 because of the strong absorption by alkali metals. Gas giants of classes IV and V are referred to as hot Jupiters .
Sudarsky et al. listed 55 Cancri b as a possible Class IV planet. [ 2 ]
HD 209458 b at 1300 K (1000 °C) would be another such planet, with a geometric albedo of, within error limits, zero; and in 2001, NASA witnessed atmospheric sodium in its transit, though less than predicted. This planet hosts an upper cloud deck absorbing so much heat that below it is a relatively cool stratosphere . The composition of this dark cloud, in the models, is assumed to be titanium/vanadium oxide (sometimes abbreviated "TiVO"), by analogy with red dwarfs, but its true composition is yet unknown; it could well be as per Sudarsky. [ 7 ] [ 8 ]
For the very hottest gas giants, with temperatures above 1400 K (2100 °F, 1100 °C) or cooler planets with lower gravity than Jupiter, the silicate and iron cloud decks are predicted to lie high up in the atmosphere. The predicted Bond albedo of a class V planet around a Sun-like star is 0.55, due to reflection by the cloud decks. At such temperatures, a gas giant may glow red from thermal radiation but the reflected light generally overwhelms thermal radiation. For stars of visual apparent magnitude under 4.50, such planets are theoretically visible to our instruments. [ 9 ] Sudarsky et al. listed 51 Pegasi b , Upsilon Andromedae b , HD 209458 b , and Tau Boötis b as possible Class V planets. [ 2 ] | https://en.wikipedia.org/wiki/Sudarsky's_gas_giant_classification |
Sudden arrhythmic death syndrome ( SADS ) is a sudden unexpected death of adolescents and adults caused by a cardiac arrest . However, the exact cause of the cardiac arrest, and thus the exact cause of death, is unknown. These deaths occur mainly during sleep or at rest. [ 7 ] One type of conduction defect known as Brugada syndrome can be responsible. [ 8 ] [ 9 ]
The syndrome is rare in most areas around the world but occurs in populations that are culturally and genetically distinct. It was first noted in 1977 among southeast Asian Hmong refugees in the United States and Canada. [ 10 ] [ 11 ] The syndrome was again noted in Singapore when a retrospective review of records showed that 230 otherwise healthy Thai foreign workers living in Singapore died suddenly of unexplained causes between 1982 and 1990. [ 12 ]
Sudden death of a young person can be caused by heart disease (including cardiomyopathy , congenital heart disease , myocarditis, genetic connective tissue disorders ) or conduction disease ( WPW syndrome , etc.), medication-related causes or other causes. [ 13 ] Rare diseases called ion channelopathies may play a role such as long QT syndrome (LQTS), Brugada syndrome (BrS), CPVT ( catecholaminergic polymorphic ventricular tachycardia ), progressive cardiac conduction defect (PCCD), early repolarization syndrome , mixed sodium channel disease, and short QT syndrome . [ 13 ] In 20% of cases, no cause of death can be found, even after extensive examination. [ 13 ]
Sudden arrhythmic death syndrome in alcohol abuse is a significant cause of death among heavy drinkers, characterized by older age and severe liver damage, highlighting the need for family screening for heritable channelopathies. [ 4 ]
In young people with type 1 diabetes , unexplained deaths could be due to nighttime hypoglycemia triggering abnormal heart rhythms or cardiac autonomic neuropathy, damage to nerves that control the function of the heart. [ 5 ]
Medical examiners have taken into account various factors, such as nutrition, toxicology, heart disease, metabolism, and genetics. Although there is no real known definite cause, extensive research showed victims aged 18 or older were found to have had a hypertrophic cardiomyopathy , a condition in which the heart muscle becomes oddly thickened without any obvious cause. [ 3 ] This was the most commonly identified abnormality in sudden death of young adults. Where people have died suddenly, it is most commonly found that they had had CAD ( coronary artery disease ) or ASCAD (atherosclerotic coronary artery disease), or any level of stress. [ 3 ] However, studies reveal that people were known to have had symptoms within the week before the terminal event such as chest pain at ~52% of patients, dyspnea at ~22%, and syncope at ~7%. About 19% are not known to have experienced symptoms. [ 3 ] Scientists have also associated this syndrome with a mutation of gene SCN5A that affects the function of the heart. A 2011 autopsy-based study found that sudden death was attributed to a cardiac condition in 79.3% of cases, and was unexplained in 20.7%. [ 3 ]
In the Philippines, sudden adult death syndrome (or in their term, bangungot ) is mainly caused by the Brugada syndrome. [ 14 ]
By definition, the diagnosis can only occur post-mortem after other causes are ruled out.
A 2011 retrospective cohort study using demographic and autopsy data for a 10-year period comprising 15.2 million person-years of active surveillance suggested that prevention of sudden death in young adults should focus on evaluation for causes known to be associated with SCD (e.g., primary arrhythmia) among those under 35 years old, and emphasise atherosclerotic coronary disease in those older. [ 3 ]
A 2003 study found that the only proven way to prevent SADS is with an implantable cardioverter-defibrillator . Oral beta-blockers such as propranolol were found to be ineffective. [ 15 ]
In 1980, a reported pattern of sudden deaths was brought to the attention of the Centers for Disease Control . The first reported sudden death occurred in 1948 when there were 81 similar deaths of Filipino men in Oahu County, Hawaii . However, it did not become relevant because there was no associated pattern. This syndrome continued to become more significant as years went on. By 1981–1982, the annual rate in the United States was high with 92/100,000 among Laotians-Hmong, 82/100,000 among other Laotian ethnic groups, and 59/100,000 among Cambodians . [ 2 ]
In a 2008 study it was found that over half of SADS deaths could be attributed to inherited heart disease: unexplained premature sudden deaths in family, long QT syndrome, Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy and others. [ 1 ]
A national SADS study in England, funded by the British Heart Foundation, reported results in a 2007 journal article published in Health . [ 16 ] The study surveyed 117 coroners' jurisdictions in England. Researchers found that deaths from SADS reported by these coroners occurred "predominantly in young males". There were 500 cases a year in England, eight times more than had previously been estimated. Families are more at risk of SADS if they have a genetic cardiac disease. The study recommended that affected families should undergo "specialised cardiological evaluation". [ 16 ]
Southeast Asian immigrants, who were mostly fleeing the Vietnam War , most often had this syndrome, marking Southeast Asia as the area containing the most people with this fatal syndrome. There are other Asian populations that were affected, such as Filipinos and Chinese Filipinos , Japanese in Japan, and natives of Guam in the United States and Guam. [ 2 ] The immigrants with this syndrome were about 33 years old and seemingly healthy, and all but one of the Laotian Hmong refugees were men. [ 17 ] The condition appears to primarily affect young Hmong men from Laos (median age 33) [ 2 ] and Northeastern Thailand (where the population is mainly of Laotian descent). [ 18 ] [ 19 ]
Laotian Hmong were chosen for the study because they had one of the highest sudden death rates in the United States while sleeping. They were originally from Southern China and the highlands of North Vietnam, Laos, and Thailand. The location that was picked for this study was in Ban Vinai in the Loei Province , which is approximately 15 kilometers from the Lao border. This study took place between October 1982 and June 1983 as this syndrome became more of a pressing issue. Ban Vinai was the location chosen because it had 33,000 refugees in 1982, and the largest number of recorded SADS deaths. Because this syndrome was occurring most commonly in those particular men, researchers found it most beneficial and effective to study the populations they migrated from instead of studying victims and populations in the U.S. Because of local religious practices, the Hmong men in Ban Vinai did not receive autopsies. Therefore, the only results and research obtained were relating to deaths outside of the local religion or geographical area. [ 2 ]
An interview was arranged with the next of kin who lived with them, witnessed the death, or found the body. The interviews were open ended and allowed the person who was next of kin to describe what they witnessed and what preceding events they thought were relevant to the victim's death. The interviewers also collected information such as illness history, the circumstances of the death, demographic background, and history of any sleep disturbances. A genealogy was then created which included all the relatives and their vital status and/or circumstances of death. [ 2 ]
During the 1970s and 1980s, when an outbreak of this syndrome began, many Southeast Asians were not able to worship properly due to the Laotian Civil War . Hmong people believe that when they do not worship properly, do not perform religious rituals properly or forget to sacrifice, the ancestor spirits or the village spirits do not protect them, thus allowing evil spirits to reach them. These attacks induce a nightmare that leads to sleep paralysis, in which the victim is conscious and experiencing pressure on the chest. [ 17 ] It is also common to have a REM state that is out of sequence, where there is a mix of brain states that are normally held separate. [ 17 ] After the war, the United States government scattered the Hmong refugees across the U.S. in 53 different cities. [ 17 ] Once these nightmare visitations began, a shaman was recommended for psychic protection from the spirits of their sleep. [ 17 ] However, scattered across 53 different cities, these victims had no access to a shaman who could protect them.
Hmong people believed that rejecting the role of becoming a shaman , they are taken into the spirit world. [ clarification needed ]
The study author suggested that the Hmong who died were killed by their own beliefs in the spiritual world, otherwise known as nocturnal pressing spirit attacks . In Indonesia it is called digeuton , which translates to "pressed on" in English. [ 17 ] In China it is called bèi guǐ yā ( traditional Chinese : 被鬼壓 ; simplified Chinese : 被鬼压 ) which translates to "crushed by a ghost" in English. [ 17 ] The Dutch call the presence a nachtmerrie , the night-mare. [ 17 ] The "merrie" comes from the Middle Dutch mare , an incubus who "lies on people's chests, suffocating them". This phenomenon is known among the Hmong people of Laos, [ 20 ] who ascribe these deaths to a malign spirit, dab tsuam (pronounced "dah chua"), said to take the form of a jealous woman.
Bangungot is depicted in the Philippines as a mythological creature called batibat or bangungot . [ 21 ] This hag -like creature sits on the victim's face or chest so as to immobilize and suffocate him. When this occurs, the victim is usually experiencing sleep paralysis.
This phenomenon inspired the Nightmare On Elm Street film series. [ 22 ] | https://en.wikipedia.org/wiki/Sudden_arrhythmic_death_syndrome |
The Suess effect is a change in the ratio of the atmospheric concentrations of heavy isotopes of carbon ( 13 C and 14 C) by the admixture of large amounts of fossil-fuel derived CO 2 , which contains no 14 CO 2 and is depleted in 13 CO 2 relative to CO 2 in the atmosphere and carbon in the upper ocean and the terrestrial biosphere . [ 1 ] It was discovered by and is named for the Austrian chemist Hans Suess , [ 2 ] who noted the influence of this effect on the accuracy of radiocarbon dating . More recently, the Suess effect has been used in studies of climate change . The term originally referred only to dilution of atmospheric 14 CO 2 relative to 12 CO 2 . The concept was later extended to dilution of 13 CO 2 and to other reservoirs of carbon such as the oceans and soils, again relative to 12 C. [ 3 ]
Although the ratio of atmospheric 14 CO 2 to 12 CO 2 decreased over the industrial era (prior to atmospheric testing of nuclear weapons, commencing about 1950), because of the increase, due to fossil fuel emissions, in the amount of atmospheric CO 2 over this period, roughly 1850 to 1950, the amount of atmospheric 14 CO 2 actually increased over this period. [ 4 ]
Carbon has three naturally occurring isotopes . About 99% of carbon on Earth is carbon -12 ( 12 C ), about 1% is carbon-13 ( 13 C ), and a trace amount is carbon-14 ( 14 C ). The 12 C and 13 C isotopes are stable, while 14 C decays radioactively to nitrogen -14 ( 14 N ) with a half-life of 5730 years. 14 C on Earth is produced nearly exclusively by the interaction of cosmic radiation with the upper atmosphere. A 14 C atom is created when a thermal neutron displaces a proton in 14 N. Minuscule amounts of 14 C are produced by other radioactive processes; a large amount was produced in the atmosphere during nuclear testing before the Limited Test Ban Treaty . Natural 14 C production and hence atmospheric concentration varies only slightly over time.
Plants take up 14 C by fixing atmospheric carbon through photosynthesis . Animals then take 14 C into their bodies when they consume plants (or consume other animals that consume plants). Thus, living plants and animals have nearly the same ratio of 14 C to 12 C as the atmospheric CO 2 . Once organisms die they stop exchanging carbon with the atmosphere and thus no longer take up new 14 C. This effect is the basis of radiocarbon dating , with the proviso that mass-dependent fractionation and the decrease in 14 C due to radioactive decay and are accounted for.
Photosynthetically fixed carbon in terrestrial plants is depleted in 13 C compared to atmospheric CO 2 . [ 5 ] This fractionation of carbon isotopes is caused by kinetic isotope effects and mass dependence of CO 2 diffusivity. The overall effect is slight in C4 plants but much greater in C3 plants which form the bulk of terrestrial biomass worldwide. Depletion in CAM plants vary between the values observed for C3 and C4 plants. In addition, most fossil fuels originate from C3 biological material produced tens to hundreds of millions of years ago. C4 plants did not become common until about 6 to 8 million years ago, and although CAM photosynthesis is present in modern relatives of the Lepidodendrales of the Carboniferous lowland forests, even if these plants also had CAM photosynthesis they were not a major component of the total biomass.
Fossil fuels such as coal and oil are made primarily of plant material that was deposited millions of years ago. This period of time equates to thousands of half-lives of 14 C, so essentially all of the 14 C in fossil fuels has decayed. [ 6 ] Fossil fuels also are depleted in 13 C relative to the atmosphere, because they were originally formed from living organisms. Therefore, the carbon from fossil fuels that is returned to the atmosphere through combustion is depleted in both 13 C and 14 C compared to atmospheric carbon dioxide. | https://en.wikipedia.org/wiki/Suess_effect |
Sufficient similarity is a 20th-century para- legal concept used in the chemical industry for toxicological studies. [ 1 ] [ 2 ] The term was first employed in a restricted sense to assess surrogacy of chemical mixtures by the EPA , and has descended from there into the scientific argot. [ 2 ] [ 3 ]
The concept is somewhat nebulous, and statistics are involved. [ 4 ] A group of America researchers in 2018 posed themselves the question how similar must a product be in order to be well-represented by the tested reference sample ? [ 5 ] Because the concept was derived from the EPA, chemical similarity and biological similarity are equally important. [ 5 ] The concept is employed "so that safety data from the tested reference can be applied to untested materials," [ 5 ] because "when toxicity data are not available for a chemical mixture of concern, US EPA guidelines allow risk assessment to be based on data for a surrogate mixture considered “sufficiently similar” in terms of chemical composition and component proportions." [ 1 ]
This article relating to law in the United States or its constituent jurisdictions is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sufficient_similarity |
In statistics , sufficiency is a property of a statistic computed on a sample dataset in relation to a parametric model of the dataset. A sufficient statistic contains all of the information that the dataset provides about the model parameters. It is closely related to the concepts of an ancillary statistic which contains no information about the model parameters, and of a complete statistic which only contains information about the parameters and no ancillary information.
A related concept is that of linear sufficiency , which is weaker than sufficiency but can be applied in some cases where there is no sufficient statistic, although it is restricted to linear estimators. [ 1 ] The Kolmogorov structure function deals with individual finite data; the related notion there is the algorithmic sufficient statistic.
The concept is due to Sir Ronald Fisher in 1920. [ 2 ] Stephen Stigler noted in 1973 that the concept of sufficiency had fallen out of favor in descriptive statistics because of the strong dependence on an assumption of the distributional form (see Pitman–Koopman–Darmois theorem below), but remained very important in theoretical work. [ 3 ]
Roughly, given a set X {\displaystyle \mathbf {X} } of independent identically distributed data conditioned on an unknown parameter θ {\displaystyle \theta } , a sufficient statistic is a function T ( X ) {\displaystyle T(\mathbf {X} )} whose value contains all the information needed to compute any estimate of the parameter (e.g. a maximum likelihood estimate). Due to the factorization theorem ( see below ), for a sufficient statistic T ( X ) {\displaystyle T(\mathbf {X} )} , the probability density can be written as f X ( x ; θ ) = h ( x ) g ( θ , T ( x ) ) {\displaystyle f_{\mathbf {X} }(x;\theta )=h(x)\,g(\theta ,T(x))} . From this factorization, it can easily be seen that the maximum likelihood estimate of θ {\displaystyle \theta } will interact with X {\displaystyle \mathbf {X} } only through T ( X ) {\displaystyle T(\mathbf {X} )} . Typically, the sufficient statistic is a simple function of the data, e.g. the sum of all the data points.
More generally, the "unknown parameter" may represent a vector of unknown quantities or may represent everything about the model that is unknown or not fully specified. In such a case, the sufficient statistic may be a set of functions, called a jointly sufficient statistic . Typically, there are as many functions as there are parameters. For example, for a Gaussian distribution with unknown mean and variance , the jointly sufficient statistic, from which maximum likelihood estimates of both parameters can be estimated, consists of two functions, the sum of all data points and the sum of all squared data points (or equivalently, the sample mean and sample variance ).
In other words, the joint probability distribution of the data is conditionally independent of the parameter given the value of the sufficient statistic for the parameter . Both the statistic and the underlying parameter can be vectors.
A statistic t = T ( X ) is sufficient for underlying parameter θ precisely if the conditional probability distribution of the data X , given the statistic t = T ( X ), does not depend on the parameter θ . [ 4 ]
Alternatively, one can say the statistic T ( X ) is sufficient for θ if, for all prior distributions on θ , the mutual information between θ and T(X) equals the mutual information between θ and X . [ 5 ] In other words, the data processing inequality becomes an equality:
As an example, the sample mean is sufficient for the (unknown) mean μ of a normal distribution with known variance. Once the sample mean is known, no further information about μ can be obtained from the sample itself. On the other hand, for an arbitrary distribution the median is not sufficient for the mean: even if the median of the sample is known, knowing the sample itself would provide further information about the population mean. For example, if the observations that are less than the median are only slightly less, but observations exceeding the median exceed it by a large amount, then this would have a bearing on one's inference about the population mean.
Fisher's factorization theorem or factorization criterion provides a convenient characterization of a sufficient statistic. If the probability density function is ƒ θ ( x ), then T is sufficient for θ if and only if nonnegative functions g and h can be found such that
i.e., the density ƒ can be factored into a product such that one factor, h , does not depend on θ and the other factor, which does depend on θ , depends on x only through T ( x ). A general proof of this was given by Halmos and Savage [ 6 ] and the theorem is sometimes referred to as the Halmos–Savage factorization theorem. [ 7 ] The proofs below handle special cases, but an alternative general proof along the same lines can be given. [ 8 ] In many simple cases the probability density function is fully specified by θ {\displaystyle \theta } and T ( x ) {\displaystyle T(x)} , and h ( x ) = 1 {\displaystyle h(x)=1} (see Examples ).
It is easy to see that if F ( t ) is a one-to-one function and T is a sufficient
statistic, then F ( T ) is a sufficient statistic. In particular we can multiply a
sufficient statistic by a nonzero constant and get another sufficient statistic.
An implication of the theorem is that when using likelihood-based inference, two sets of data yielding the same value for the sufficient statistic T ( X ) will always yield the same inferences about θ . By the factorization criterion, the likelihood's dependence on θ is only in conjunction with T ( X ). As this is the same in both cases, the dependence on θ will be the same as well, leading to identical inferences.
Due to Hogg and Craig. [ 9 ] Let X 1 , X 2 , … , X n {\displaystyle X_{1},X_{2},\ldots ,X_{n}} , denote a random sample from a distribution having the pdf f ( x , θ ) for ι < θ < δ . Let Y 1 = u 1 ( X 1 , X 2 , ..., X n ) be a statistic whose pdf is g 1 ( y 1 ; θ ). What we want to prove is that Y 1 = u 1 ( X 1 , X 2 , ..., X n ) is a sufficient statistic for θ if and only if, for some function H ,
First, suppose that
We shall make the transformation y i = u i ( x 1 , x 2 , ..., x n ), for i = 1, ..., n , having inverse functions x i = w i ( y 1 , y 2 , ..., y n ), for i = 1, ..., n , and Jacobian J = [ w i / y j ] {\displaystyle J=\left[w_{i}/y_{j}\right]} . Thus,
The left-hand member is the joint pdf g ( y 1 , y 2 , ..., y n ; θ) of Y 1 = u 1 ( X 1 , ..., X n ), ..., Y n = u n ( X 1 , ..., X n ). In the right-hand member, g 1 ( y 1 ; θ ) {\displaystyle g_{1}(y_{1};\theta )} is the pdf of Y 1 {\displaystyle Y_{1}} , so that H [ w 1 , … , w n ] | J | {\displaystyle H[w_{1},\dots ,w_{n}]|J|} is the quotient of g ( y 1 , … , y n ; θ ) {\displaystyle g(y_{1},\dots ,y_{n};\theta )} and g 1 ( y 1 ; θ ) {\displaystyle g_{1}(y_{1};\theta )} ; that is, it is the conditional pdf h ( y 2 , … , y n ∣ y 1 ; θ ) {\displaystyle h(y_{2},\dots ,y_{n}\mid y_{1};\theta )} of Y 2 , … , Y n {\displaystyle Y_{2},\dots ,Y_{n}} given Y 1 = y 1 {\displaystyle Y_{1}=y_{1}} .
But H ( x 1 , x 2 , … , x n ) {\displaystyle H(x_{1},x_{2},\dots ,x_{n})} , and thus H [ w 1 ( y 1 , … , y n ) , … , w n ( y 1 , … , y n ) ) ] {\displaystyle H\left[w_{1}(y_{1},\dots ,y_{n}),\dots ,w_{n}(y_{1},\dots ,y_{n}))\right]} , was given not to depend upon θ {\displaystyle \theta } . Since θ {\displaystyle \theta } was not introduced in the transformation and accordingly not in the Jacobian J {\displaystyle J} , it follows that h ( y 2 , … , y n ∣ y 1 ; θ ) {\displaystyle h(y_{2},\dots ,y_{n}\mid y_{1};\theta )} does not depend upon θ {\displaystyle \theta } and that Y 1 {\displaystyle Y_{1}} is a sufficient statistics for θ {\displaystyle \theta } .
The converse is proven by taking:
where h ( y 2 , … , y n ∣ y 1 ) {\displaystyle h(y_{2},\dots ,y_{n}\mid y_{1})} does not depend upon θ {\displaystyle \theta } because Y 2 . . . Y n {\displaystyle Y_{2}...Y_{n}} depend only upon X 1 . . . X n {\displaystyle X_{1}...X_{n}} , which are independent on Θ {\displaystyle \Theta } when conditioned by Y 1 {\displaystyle Y_{1}} , a sufficient statistics by hypothesis. Now divide both members by the absolute value of the non-vanishing Jacobian J {\displaystyle J} , and replace y 1 , … , y n {\displaystyle y_{1},\dots ,y_{n}} by the functions u 1 ( x 1 , … , x n ) , … , u n ( x 1 , … , x n ) {\displaystyle u_{1}(x_{1},\dots ,x_{n}),\dots ,u_{n}(x_{1},\dots ,x_{n})} in x 1 , … , x n {\displaystyle x_{1},\dots ,x_{n}} . This yields
where J ∗ {\displaystyle J^{*}} is the Jacobian with y 1 , … , y n {\displaystyle y_{1},\dots ,y_{n}} replaced by their value in terms x 1 , … , x n {\displaystyle x_{1},\dots ,x_{n}} . The left-hand member is necessarily the joint pdf f ( x 1 ; θ ) ⋯ f ( x n ; θ ) {\displaystyle f(x_{1};\theta )\cdots f(x_{n};\theta )} of X 1 , … , X n {\displaystyle X_{1},\dots ,X_{n}} . Since h ( y 2 , … , y n ∣ y 1 ) {\displaystyle h(y_{2},\dots ,y_{n}\mid y_{1})} , and thus h ( u 2 , … , u n ∣ u 1 ) {\displaystyle h(u_{2},\dots ,u_{n}\mid u_{1})} , does not depend upon θ {\displaystyle \theta } , then
is a function that does not depend upon θ {\displaystyle \theta } .
A simpler more illustrative proof is as follows, although it applies only in the discrete case.
We use the shorthand notation to denote the joint probability density of ( X , T ( X ) ) {\displaystyle (X,T(X))} by f θ ( x , t ) {\displaystyle f_{\theta }(x,t)} . Since T {\displaystyle T} is a deterministic function of X {\displaystyle X} , we have f θ ( x , t ) = f θ ( x ) {\displaystyle f_{\theta }(x,t)=f_{\theta }(x)} , as long as t = T ( x ) {\displaystyle t=T(x)} and zero otherwise. Therefore:
with the last equality being true by the definition of sufficient statistics. Thus f θ ( x ) = a ( x ) b θ ( t ) {\displaystyle f_{\theta }(x)=a(x)b_{\theta }(t)} with a ( x ) = f X ∣ t ( x ) {\displaystyle a(x)=f_{X\mid t}(x)} and b θ ( t ) = f θ ( t ) {\displaystyle b_{\theta }(t)=f_{\theta }(t)} .
Conversely, if f θ ( x ) = a ( x ) b θ ( t ) {\displaystyle f_{\theta }(x)=a(x)b_{\theta }(t)} , we have
With the first equality by the definition of pdf for multiple variables , the second by the remark above, the third by hypothesis, and the fourth because the summation is not over t {\displaystyle t} .
Let f X ∣ t ( x ) {\displaystyle f_{X\mid t}(x)} denote the conditional probability density of X {\displaystyle X} given T ( X ) {\displaystyle T(X)} . Then we can derive an explicit expression for this:
With the first equality by definition of conditional probability density, the second by the remark above, the third by the equality proven above, and the fourth by simplification. This expression does not depend on θ {\displaystyle \theta } and thus T {\displaystyle T} is a sufficient statistic. [ 10 ]
A sufficient statistic is minimal sufficient if it can be represented as a function of any other sufficient statistic. In other words, S ( X ) is minimal sufficient if and only if [ 11 ]
Intuitively, a minimal sufficient statistic most efficiently captures all possible information about the parameter θ .
A useful characterization of minimal sufficiency is that when the density f θ exists, S ( X ) is minimal sufficient if and only if [ citation needed ]
This follows as a consequence from Fisher's factorization theorem stated above.
A case in which there is no minimal sufficient statistic was shown by Bahadur, 1954. [ 12 ] However, under mild conditions, a minimal sufficient statistic does always exist. In particular, in Euclidean space, these conditions always hold if the random variables (associated with P θ {\displaystyle P_{\theta }} ) are all discrete or are all continuous.
If there exists a minimal sufficient statistic, and this is usually the case, then every complete sufficient statistic is necessarily minimal sufficient [ 13 ] (note that this statement does not exclude a pathological case in which a complete sufficient exists while there is no minimal sufficient statistic). While it is hard to find cases in which a minimal sufficient statistic does not exist, it is not so hard to find cases in which there is no complete statistic.
The collection of likelihood ratios { L ( X ∣ θ i ) L ( X ∣ θ 0 ) } {\displaystyle \left\{{\frac {L(X\mid \theta _{i})}{L(X\mid \theta _{0})}}\right\}} for i = 1 , . . . , k {\displaystyle i=1,...,k} , is a minimal sufficient statistic if the parameter space is discrete { θ 0 , . . . , θ k } {\displaystyle \left\{\theta _{0},...,\theta _{k}\right\}} .
If X 1 , ...., X n are independent Bernoulli-distributed random variables with expected value p , then the sum T ( X ) = X 1 + ... + X n is a sufficient statistic for p (here 'success' corresponds to X i = 1 and 'failure' to X i = 0; so T is the total number of successes)
This is seen by considering the joint probability distribution:
Because the observations are independent, this can be written as
and, collecting powers of p and 1 − p , gives
which satisfies the factorization criterion, with h ( x ) = 1 being just a constant.
Note the crucial feature: the unknown parameter p interacts with the data x only via the statistic T ( x ) = Σ x i .
As a concrete application, this gives a procedure for distinguishing a fair coin from a biased coin .
If X 1 , ...., X n are independent and uniformly distributed on the interval [0, θ ], then T ( X ) = max( X 1 , ..., X n ) is sufficient for θ — the sample maximum is a sufficient statistic for the population maximum.
To see this, consider the joint probability density function of X ( X 1 ,..., X n ). Because the observations are independent, the pdf can be written as a product of individual densities
where 1 { ... } is the indicator function . Thus the density takes form required by the Fisher–Neyman factorization theorem, where h ( x ) = 1 {min{ x i }≥0} , and the rest of the expression is a function of only θ and T ( x ) = max{ x i }.
In fact, the minimum-variance unbiased estimator (MVUE) for θ is
This is the sample maximum, scaled to correct for the bias , and is MVUE by the Lehmann–Scheffé theorem . Unscaled sample maximum T ( X ) is the maximum likelihood estimator for θ .
If X 1 , . . . , X n {\displaystyle X_{1},...,X_{n}} are independent and uniformly distributed on the interval [ α , β ] {\displaystyle [\alpha ,\beta ]} (where α {\displaystyle \alpha } and β {\displaystyle \beta } are unknown parameters), then T ( X 1 n ) = ( min 1 ≤ i ≤ n X i , max 1 ≤ i ≤ n X i ) {\displaystyle T(X_{1}^{n})=\left(\min _{1\leq i\leq n}X_{i},\max _{1\leq i\leq n}X_{i}\right)} is a two-dimensional sufficient statistic for ( α , β ) {\displaystyle (\alpha \,,\,\beta )} .
To see this, consider the joint probability density function of X 1 n = ( X 1 , … , X n ) {\displaystyle X_{1}^{n}=(X_{1},\ldots ,X_{n})} . Because the observations are independent, the pdf can be written as a product of individual densities, i.e.
The joint density of the sample takes the form required by the Fisher–Neyman factorization theorem, by letting
Since h ( x 1 n ) {\displaystyle h(x_{1}^{n})} does not depend on the parameter ( α , β ) {\displaystyle (\alpha ,\beta )} and g ( α , β ) ( x 1 n ) {\displaystyle g_{(\alpha \,,\,\beta )}(x_{1}^{n})} depends only on x 1 n {\displaystyle x_{1}^{n}} through the function T ( X 1 n ) = ( min 1 ≤ i ≤ n X i , max 1 ≤ i ≤ n X i ) , {\displaystyle T(X_{1}^{n})=\left(\min _{1\leq i\leq n}X_{i},\max _{1\leq i\leq n}X_{i}\right),}
the Fisher–Neyman factorization theorem implies T ( X 1 n ) = ( min 1 ≤ i ≤ n X i , max 1 ≤ i ≤ n X i ) {\displaystyle T(X_{1}^{n})=\left(\min _{1\leq i\leq n}X_{i},\max _{1\leq i\leq n}X_{i}\right)} is a sufficient statistic for ( α , β ) {\displaystyle (\alpha \,,\,\beta )} .
If X 1 , ...., X n are independent and have a Poisson distribution with parameter λ , then the sum T ( X ) = X 1 + ... + X n is a sufficient statistic for λ .
To see this, consider the joint probability distribution:
Because the observations are independent, this can be written as
which may be written as
which shows that the factorization criterion is satisfied, where h ( x ) is the reciprocal of the product of the factorials. Note the parameter λ interacts with the data only through its sum T ( X ).
If X 1 , … , X n {\displaystyle X_{1},\ldots ,X_{n}} are independent and normally distributed with expected value θ {\displaystyle \theta } (a parameter) and known finite variance σ 2 , {\displaystyle \sigma ^{2},} then
is a sufficient statistic for θ . {\displaystyle \theta .}
To see this, consider the joint probability density function of X 1 n = ( X 1 , … , X n ) {\displaystyle X_{1}^{n}=(X_{1},\dots ,X_{n})} . Because the observations are independent, the pdf can be written as a product of individual densities, i.e.
The joint density of the sample takes the form required by the Fisher–Neyman factorization theorem, by letting
Since h ( x 1 n ) {\displaystyle h(x_{1}^{n})} does not depend on the parameter θ {\displaystyle \theta } and g θ ( x 1 n ) {\displaystyle g_{\theta }(x_{1}^{n})} depends only on x 1 n {\displaystyle x_{1}^{n}} through the function
the Fisher–Neyman factorization theorem implies T ( X 1 n ) {\displaystyle T(X_{1}^{n})} is a sufficient statistic for θ {\displaystyle \theta } .
If σ 2 {\displaystyle \sigma ^{2}} is unknown and since s 2 = 1 n − 1 ∑ i = 1 n ( x i − x ¯ ) 2 {\displaystyle s^{2}={\frac {1}{n-1}}\sum _{i=1}^{n}\left(x_{i}-{\overline {x}}\right)^{2}} , the above likelihood can be rewritten as
The Fisher–Neyman factorization theorem still holds and implies that ( x ¯ , s 2 ) {\displaystyle ({\overline {x}},s^{2})} is a joint sufficient statistic for ( θ , σ 2 ) {\displaystyle (\theta ,\sigma ^{2})} .
If X 1 , … , X n {\displaystyle X_{1},\dots ,X_{n}} are independent and exponentially distributed with expected value θ (an unknown real-valued positive parameter), then T ( X 1 n ) = ∑ i = 1 n X i {\displaystyle T(X_{1}^{n})=\sum _{i=1}^{n}X_{i}} is a sufficient statistic for θ.
To see this, consider the joint probability density function of X 1 n = ( X 1 , … , X n ) {\displaystyle X_{1}^{n}=(X_{1},\dots ,X_{n})} . Because the observations are independent, the pdf can be written as a product of individual densities, i.e.
The joint density of the sample takes the form required by the Fisher–Neyman factorization theorem, by letting
Since h ( x 1 n ) {\displaystyle h(x_{1}^{n})} does not depend on the parameter θ {\displaystyle \theta } and g θ ( x 1 n ) {\displaystyle g_{\theta }(x_{1}^{n})} depends only on x 1 n {\displaystyle x_{1}^{n}} through the function T ( X 1 n ) = ∑ i = 1 n X i {\displaystyle T(X_{1}^{n})=\sum _{i=1}^{n}X_{i}}
the Fisher–Neyman factorization theorem implies T ( X 1 n ) = ∑ i = 1 n X i {\displaystyle T(X_{1}^{n})=\sum _{i=1}^{n}X_{i}} is a sufficient statistic for θ {\displaystyle \theta } .
If X 1 , … , X n {\displaystyle X_{1},\dots ,X_{n}} are independent and distributed as a Γ ( α , β ) {\displaystyle \Gamma (\alpha \,,\,\beta )} , where α {\displaystyle \alpha } and β {\displaystyle \beta } are unknown parameters of a Gamma distribution , then T ( X 1 n ) = ( ∏ i = 1 n X i , ∑ i = 1 n X i ) {\displaystyle T(X_{1}^{n})=\left(\prod _{i=1}^{n}{X_{i}},\sum _{i=1}^{n}X_{i}\right)} is a two-dimensional sufficient statistic for ( α , β ) {\displaystyle (\alpha ,\beta )} .
To see this, consider the joint probability density function of X 1 n = ( X 1 , … , X n ) {\displaystyle X_{1}^{n}=(X_{1},\dots ,X_{n})} . Because the observations are independent, the pdf can be written as a product of individual densities, i.e.
The joint density of the sample takes the form required by the Fisher–Neyman factorization theorem, by letting
Since h ( x 1 n ) {\displaystyle h(x_{1}^{n})} does not depend on the parameter ( α , β ) {\displaystyle (\alpha \,,\,\beta )} and g ( α , β ) ( x 1 n ) {\displaystyle g_{(\alpha \,,\,\beta )}(x_{1}^{n})} depends only on x 1 n {\displaystyle x_{1}^{n}} through the function T ( x 1 n ) = ( ∏ i = 1 n x i , ∑ i = 1 n x i ) , {\displaystyle T(x_{1}^{n})=\left(\prod _{i=1}^{n}x_{i},\sum _{i=1}^{n}x_{i}\right),}
the Fisher–Neyman factorization theorem implies T ( X 1 n ) = ( ∏ i = 1 n X i , ∑ i = 1 n X i ) {\displaystyle T(X_{1}^{n})=\left(\prod _{i=1}^{n}X_{i},\sum _{i=1}^{n}X_{i}\right)} is a sufficient statistic for ( α , β ) . {\displaystyle (\alpha \,,\,\beta ).}
Sufficiency finds a useful application in the Rao–Blackwell theorem , which states that if g ( X ) is any kind of estimator of θ , then typically the conditional expectation of g ( X ) given sufficient statistic T ( X ) is a better (in the sense of having lower variance ) estimator of θ , and is never worse. Sometimes one can very easily construct a very crude estimator g ( X ), and then evaluate that conditional expected value to get an estimator that is in various senses optimal.
According to the Pitman–Koopman–Darmois theorem, among families of probability distributions whose domain does not vary with the parameter being estimated, only in exponential families is there a sufficient statistic whose dimension remains bounded as sample size increases. Intuitively, this states that nonexponential families of distributions on the real line require nonparametric statistics to fully capture the information in the data.
Less tersely, suppose X n , n = 1 , 2 , 3 , … {\displaystyle X_{n},n=1,2,3,\dots } are independent identically distributed real random variables whose distribution is known to be in some family of probability distributions, parametrized by θ {\displaystyle \theta } , satisfying certain technical regularity conditions, then that family is an exponential family if and only if there is a R m {\displaystyle \mathbb {R} ^{m}} -valued sufficient statistic T ( X 1 , … , X n ) {\displaystyle T(X_{1},\dots ,X_{n})} whose number of scalar components m {\displaystyle m} does not increase as the sample size n increases. [ 14 ]
This theorem shows that the existence of a finite-dimensional, real-vector-valued sufficient statistics sharply restricts the possible forms of a family of distributions on the real line .
When the parameters or the random variables are no longer real-valued, the situation is more complex. [ 15 ]
An alternative formulation of the condition that a statistic be sufficient, set in a Bayesian context, involves the posterior distributions obtained by using the full data-set and by using only a statistic. Thus the requirement is that, for almost every x ,
More generally, without assuming a parametric model, we can say that the statistics T is predictive sufficient if
It turns out that this "Bayesian sufficiency" is a consequence of the formulation above, [ 16 ] however they are not directly equivalent in the infinite-dimensional case. [ 17 ] A range of theoretical results for sufficiency in a Bayesian context is available. [ 18 ]
A concept called "linear sufficiency" can be formulated in a Bayesian context, [ 19 ] and more generally. [ 20 ] First define the best linear predictor of a vector Y based on X as E ^ [ Y ∣ X ] {\displaystyle {\hat {E}}[Y\mid X]} . Then a linear statistic T ( x ) is linear sufficient [ 21 ] if | https://en.wikipedia.org/wiki/Sufficient_statistic |
Suffix Tree Clustering , often abbreviated as STC is an approach for clustering that uses suffix trees . [ 1 ] A suffix tree cluster keeps track of all n-grams of any given length to be inserted into a set word string , while simultaneously allowing differing strings to be inserted incrementally in a linear order. This has the advantage of ensuring that a large number of clusters can be handled sequentially. However, a potential disadvantage may be that it also increases the number of possible documents that need to be looked through when handling large sets of data . Suffix tree clusters can either be decompositional or agglomerative in nature, depending on the type of data being handled. [ 2 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Suffix_tree_clustering |
Sugar signal transduction is an evolutionarily conserved mechanism used by organisms to survive. Sugars have an overwhelming effect on gene expression . In yeast , glucose levels are managed by controlling the mRNA levels of hexose transporters, while in mammals , the response to glucose is more tightly controlled with glucose metabolism and is therefore much more complex. Several glucose-responsive DNA motifs and DNA binding protein complexes have been identified in liver and b-cells . Although not proven, glucose repression appears to be conserved in plants because in many cases, both sugar induction and sugar repression are initiated by turning off transcription factors . | https://en.wikipedia.org/wiki/Sugar_signal_transduction |
Sugars in wine are at the heart of what makes winemaking possible. During the process of fermentation , sugars from wine grapes are broken down and converted by yeast into alcohol ( ethanol ) and carbon dioxide . Grapes accumulate sugars as they grow on the grapevine through the translocation of sucrose molecules that are produced by photosynthesis from the leaves. During ripening the sucrose molecules are hydrolyzed (separated) by the enzyme invertase into glucose and fructose . By the time of harvest , between 15 and 25% of the grape will be composed of simple sugars . Both glucose and fructose are six- carbon sugars but three-, four-, five- and seven-carbon sugars are also present in the grape. Not all sugars are fermentable, with sugars like the five-carbon arabinose , rhamnose and xylose still being present in the wine after fermentation. Very high sugar content will effectively kill the yeast once a certain (high) alcohol content is reached. For these reasons, no wine is ever fermented completely " dry " (meaning without any residual sugar ). Sugar's role in dictating the final alcohol content of the wine (and such its resulting body and "mouth-feel") sometimes encourages winemakers to add sugar (usually sucrose ) during winemaking in a process known as chaptalization solely in order to boost the alcohol content – chaptalization does not increase the sweetness of a wine. [ 1 ]
Sucrose is a disaccharide , a molecule composed of the two monosaccharides glucose, and fructose. Invertase is the enzyme cleaves the glycosidic linkage between the glucose and fructose molecules.
In most wines, there will be very little sucrose, since it is not a natural constituent of grapes and sucrose added for the purpose of chaptalisation will be consumed in the fermentation. The exception to this rule is Champagne and other sparkling wines , to which an amount of liqueur d'expédition (typically sucrose dissolved in a still wine) is added after the second fermentation in bottle, a practice known as dosage .
Glucose, along with fructose, is one of the primary sugars found in wine grapes. In wine, glucose tastes less sweet than fructose. It is a six-carbon sugar molecule derived from the breakdown of sucrose. At the beginning of the ripening stage there is usually more glucose than fructose present in the grape (as much as five times more) but the rapid development of fructose shifts the ratio to where at harvest there are generally equal amounts. Grapes that are overripe, such as some late harvest wines , may have more fructose than glucose. During fermentation, yeast cells break down and convert glucose first. The linking of glucose molecules with aglycone , in a process that creates glycosides , also plays a role in the resulting flavor of the wine due to their relation and interactions with phenolic compounds like anthocyanins and terpenoids . [ 2 ]
Fructose, along with glucose, is one of the principal sugars involved in the creation of wine. At time of harvest, there is usually an equal amount of glucose and fructose molecules in the grape; however, as the grape overripens the level of fructose will become higher. In wine, fructose can taste nearly twice as sweet as glucose and is a key component in the creation of sweet dessert wines . During fermentation, glucose is consumed first by the yeast and converted into alcohol. A winemaker that chooses to halt fermentation (either by temperature control or the addition of brandy spirits in the process of fortification ) will be left with a wine that is high in fructose and notable residual sugars. The technique of süssreserve , where unfermented grape must is added after the wine's fermentation is complete, will result in a wine that tastes less sweet than a wine whose fermentation was halted. This is because the unfermented grape must will still have roughly equal parts of fructose and the less sweet tasting glucose. Similarly, the process of chaptalization where sucrose (which is one part glucose and one part fructose) is added will usually not increase the sweetness level of the wine. [ 3 ]
In wine tasting , humans are least sensitive to the taste of sweetness (in contrast to sensitivity to bitterness or sourness ) with the majority of the population being able to detect sugar or "sweetness" in wines between 1% and 2.5% residual sugar. Additionally, other components of wine such as acidity and tannins can mask the perception of sugar in the wine. [ 1 ]
Flash release is a technique used in wine pressing . [ 4 ] The technique allows for a better extraction of wine polysaccharides . [ 5 ] | https://en.wikipedia.org/wiki/Sugars_in_wine |
The Suhua Highway Improvement Project ( Chinese : 蘇花公路改善計畫 ; pinyin : Sū-Huā Gōnglù Gǎishàn Jìhuà ; colloquially 蘇花改, pinyin : Sūhuāgǎi ) was a major highway project in northeast Taiwan to improve and bypass dangerous sections of the Suhua Highway , part of Provincial Highway 9 . [ 1 ]
The Suhua Highway is the main road connecting Su'ao Township and Hualien City . A portion of the original alignment was built alongside very steep cliffs high above the Pacific Ocean . Because of the rugged terrain, it was often closed due to heavy rain, typhoons , or landslides , leading to injuries and deaths. [ 2 ]
In the 1990s, the Ministry of Transportation and Communications (MOTC) started planning a new freeway to connect Su'ao and Hualien, as part of National Freeway 5 . However, it was controversial because of its environmental impact. [ 3 ] Instead, the MOTC developed a scaled-down project, which constructed bridges and tunnels in three dangerous sections: Su'ao – Dong'ao (9.8 km, 6.1 mi), Nan'ao – Heping (20 km, 12 mi), and Heping– Qingshui (8.6 km, 5.3 mi). The improved highway has a speed limit of 60 kilometres per hour (37 mph), lower than a freeway, and still has only one lane in each direction. It cut travel time along the coastline from 2.5 hours to 80 minutes. Some parts of the old alignment was kept open for bicycles and small vehicles, with a speed limit of 30 kilometres per hour (19 mph). [ 3 ]
The project was named the Suhua Highway Alternative Project ( Chinese : 蘇花公路替代計畫 ; pinyin : Sū-Huā Gōnglù Tìdài Jìhuà ; colloquially 蘇花替 pinyin : Sūhuātì ) in 2008. Its name was changed to its current name in 2010.
Construction started in 2011 and was expected to take five years and cost 46.5 billion New Taiwan dollars . Due to difficulties in construction, [ 4 ] the project was finally completed in 2020 at a cost of 55.17 billion New Taiwan dollars. [ 5 ] | https://en.wikipedia.org/wiki/Suhua_Highway_Improvement_Project |
Suksin Lee ( Korean : 이석신 ; Hanja : 李錫申 ; 6 October 1896/7 – 12 December 1944) was a Korean biochemist and physician . He is considered a pioneer of biochemistry in Korea, [ 3 ] having been the first Korean to obtain a Ph.D. and to hold a full-time professorship in that field. [ 4 ] His studies of glucose metabolism and the chemical composition of common foods contributed to the scientific analysis of nutrition in the Korean diet. [ 5 ]
Suksin Lee was born in P'yŏngannam-do , Korea, the son of I Myŏngse and a woman of the Koksan Kang family. [ 6 ] He earned his medical degree from Kyŏngsŏng Medical College (now Seoul National University ) in 1921, and obtained his medical license in August of that year. [ 7 ] After graduation, he studied pathology for several months at Tokyo Imperial University in Japan. He then traveled to Germany in 1922 to pursue additional studies. [ 8 ]
After completing preliminary language instruction and various coursework in chemistry and physiological chemistry at the Friedrich Wilhelm University of Berlin, he earned a doctorate of medicine in 1926. [ 9 ] Lee's inaugural dissertation, Ueber Glykolyse , was a study of inorganic phosphates during blood glycolysis. His thesis advisors at the time included Otto Lubarsch of the Chemistry Department at the Pathological Institute, University of Berlin. [ 10 ]
While in his final year of studies, Lee obtained a position as a research assistant at a national hospital in Berlin, where he worked until 1927. During this time he published and co-published several papers on the effects of photosensitive substances on glucose metabolism and cellular respiration. [ 11 ]
Returning to his native Korea, he began studies of the staple Korean diet and its effects on metabolism as a research assistant at Kyŏngsŏng Medical College in February 1928. [ 12 ] He was appointed an instructor of physiology in the department of biochemistry of Severance Union Medical College (now Yonsei University College of Medicine) and an adjunct instructor of dietetics at Ewha Womans University College of Medicine. [ 13 ]
In 1932, Suksin Lee was the first Korean to earn a Ph.D. in biochemistry for his thesis, A Study on the Eating Habits of Koreans , presented to Kyoto Imperial University on the nutrition and metabolism of prisoners in Korea. [ 14 ] [ 15 ] Among his advisers at the time was Professor Sato of Keijo Imperial University. [ 16 ]
He was then appointed full-time professor of biochemistry in 1933 at Severance Union Medical College, the first Korean to hold such a position. [ 17 ] He continued to lead the department, later serving as Severance's Dean of Student Affairs, [ 18 ] until his death aged approximately 47 of a cerebral hemorrhage on 12 December 1944. [ 19 ]
As the first Ph.D. and full-time professor of biochemistry in Korea, Lee contributed to the establishment of biochemistry as a newly organized field of study in Korea. [ 20 ]
He began with a study of glycolysis. In the late 1920s, the role of phosphorylated compounds in glycolysis had not yet been fully explained. [ 21 ] Lee's work touched on early aspects of intermediary carbohydrate metabolism, which was also the subject of Nobel Prize-winning research by Otto Fritz Meyerhof, Otto Heinrich Warburg, and Hans Adolf Krebs. [ 22 ]
Lee maintained an interest in factors affecting glucose metabolism upon his return to Korea, where he continued his research with published studies of the Korean diet. [ 23 ] [ 24 ] Building upon work begun in 1928, he investigated the problem of identifying and quantifying the nutritional elements of the staple Korean diet and its effects on metabolism. [ 25 ] He identified nutritional sources in these foods for the healthy development of Korean children and adults [ 26 ] [ 27 ] during the Japanese occupation of Korea.
In addition to teaching and editing, [ 28 ] Lee authored and co-authored at least 10 scientific papers and articles in several languages throughout his brief career. [ 29 ] He did all of this despite working under conditions of widespread rationing at the end of World War II . [ 30 ] [ 31 ]
In 2014 and 2016 the Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, hosted academic symposiums to commemorate his life's work. [ 32 ]
A Special Memorial Exhibition was also held in 2015 at the Dong-Eun Museum of Medical Science in Seoul, Korea. The exhibit included a collection of papers left by the late Suksin Lee. [ 33 ] | https://en.wikipedia.org/wiki/Suksin_Lee |
In biological morphology and anatomy , a sulcus ( pl. : sulci ) is a furrow or fissure ( Latin fissura , pl. : fissurae ). It may be a groove, natural division, deep furrow, elongated cleft, or tear in the surface of a limb or an organ, most notably on the surface of the brain , but also in the lungs , certain muscles (including the heart ), as well as in bones , and elsewhere. Many sulci are the product of a surface fold or junction, such as in the gums , where they fold around the neck of the tooth.
In invertebrate zoology , a sulcus is a fold, groove, or boundary, especially at the edges of sclerites or between segments .
In pollen , a grain that is grooved by a sulcus is termed sulcate .
In the brain , a sulcus is a groove formed in the stage of gyrification by the folding of the cortex . There are many sulci and gyri formed. A larger than usual sulcus may instead be called a fissure such as the longitudinal fissure that separates the two hemispheres . | https://en.wikipedia.org/wiki/Sulcus_(morphology) |
In organic chemistry , sulfamoyl fluoride is an organic compound having the chemical formula F−SO 2 −N(−R 1 )−R 2 . Its derivatives are called sulfamoyl fluorides .
Examples of sulfamoyl fluorides include:
(S=O)
Sulfamoyl fluorides are contrasted with the sulfonimidoyl fluorides with structure R 1 -S(O)(F)=N-R 2 .
Sulfamoyl fluorides can be made by treating secondary amines with sulfuryl fluoride (SO 2 F 2 ) or sulfuryl chloride fluoride (SO 2 ClF). Cyclic secondary amines work as well, provided they are not aromatic . [ 1 ]
Sulfamoyl fluorides can also be made from sulfamoyl chlorides, by reacting with a substance that can supply the fluoride ion, such as NaF , KF , HF , or SbF 3 . [ 1 ]
Sulfonamides can undergo a Hofmann rearrangement when treated with a difluoro-λ 3 -bromane to yield a singly substituted N-sulfamoyl fluoride. [ 2 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfamoyl_fluoride |
Sulfarsazene is a chemical compound with the formula C 18 H 12 AsN 6 Na 3 O 8 S , a metal indicator. [ 1 ]
Sulfarsazene is used as a metal indicator for the spectrophotometric and titrimetric determination of Pb 2+ ions at pH 9.8–10.0 and Zn 2+ at pH 9.3–9.6 (color transition from orange-pink to lemon yellow). [ 2 ] [ 3 ] [ 4 ]
Sulfarsazene is soluble in water, easily soluble in an aqueous solution of sodium tetraborate , slightly soluble in 95% alcohol, practically insoluble in acetone , chloroform , benzene . | https://en.wikipedia.org/wiki/Sulfarsazene |
Sulfate-reducing microorganisms ( SRM ) or sulfate-reducing prokaryotes ( SRP ) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate ( SO 2− 4 ) as terminal electron acceptor , reducing it to hydrogen sulfide (H 2 S). [ 1 ] [ 2 ] Therefore, these sulfidogenic microorganisms "breathe" sulfate rather than molecular oxygen (O 2 ), which is the terminal electron acceptor reduced to water (H 2 O) in aerobic respiration .
Most sulfate-reducing microorganisms can also reduce some other oxidized inorganic sulfur compounds , such as sulfite ( SO 2− 3 ), dithionite ( S 2 O 2− 4 ), thiosulfate ( S 2 O 2− 3 ), trithionate ( S 3 O 2− 6 ), tetrathionate ( S 4 O 2− 6 ), elemental sulfur (S 8 ), and polysulfides ( S 2− n ). Other than sulfate reduction, some sulfate-reducing microorganisms are also capable of other reactions like disproportionation of sulfur compounds. Depending on the context, "sulfate-reducing microorganisms" can be used in a broader sense (including all species that can reduce any of these sulfur compounds) or in a narrower sense (including only species that reduce sulfate, and excluding strict thiosulfate and sulfur reducers , for example).
Sulfate-reducing microorganisms can be traced back to 3.5 billion years ago and are considered to be among the oldest forms of microbes, having contributed to the sulfur cycle soon after life emerged on Earth. [ 3 ]
Many organisms reduce small amounts of sulfates in order to synthesize sulfur -containing cell components; this is known as assimilatory sulfate reduction . By contrast, the sulfate-reducing microorganisms considered here reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste; this is known as dissimilatory sulfate reduction . [ 4 ] They use sulfate as the terminal electron acceptor of their electron transport chain . [ 5 ] Most of them are anaerobes ; however, there are examples of sulfate-reducing microorganisms that are tolerant of oxygen, and some of them can even perform aerobic respiration. [ 6 ] No growth is observed when oxygen is used as the electron acceptor. [ 7 ] In addition, there are sulfate-reducing microorganisms that can also reduce other electron acceptors, such as fumarate , nitrate ( NO − 3 ), nitrite ( NO − 2 ), ferric iron (Fe 3+ ), and dimethyl sulfoxide (DMSO). [ 1 ] [ 8 ]
In terms of electron donor , this group contains both organotrophs and lithotrophs . The organotrophs oxidize organic compounds , such as carbohydrates , organic acids (such as formate , lactate , acetate , propionate , and butyrate ), alcohols ( methanol and ethanol ), aliphatic hydrocarbons (including methane ), and aromatic hydrocarbons ( benzene , toluene , ethylbenzene , and xylene ). [ 9 ] The lithotrophs oxidize molecular hydrogen (H 2 ), for which they compete with methanogens and acetogens in anaerobic conditions. [ 9 ] Some sulfate-reducing microorganisms can directly use metallic iron (Fe 0 , also known as zerovalent iron , or ZVI) as an electron donor, oxidizing it to ferrous iron (Fe 2+ ). [ 10 ]
Sulfate occurs widely in seawater, sediment, and water rich in decaying organic material. [ 5 ] Sulfate is also found in more extreme environments such as hydrothermal vents, acid mine drainage sites, oil fields, and the deep subsurface, [ 11 ] including the world's oldest isolated ground water. [ 12 ] [ 13 ] Sulfate-reducing microorganisms are common in anaerobic environments where they aid in the degradation of organic materials. [ 14 ] In these anaerobic environments, fermenting bacteria extract energy from large organic molecules; the resulting smaller compounds such as organic acids and alcohols are further oxidized by acetogens and methanogens and the competing sulfate-reducing microorganisms. [ 5 ]
The toxic hydrogen sulfide is a waste product of sulfate-reducing microorganisms; its rotten egg odor is often a marker for the presence of sulfate-reducing microorganisms in nature. [ 14 ] Sulfate-reducing microorganisms are responsible for the sulfurous odors of salt marshes and mud flats. Much of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides . These metal sulfides, such as ferrous sulfide (FeS), are insoluble and often black or brown, leading to the dark color of sludge. [ 2 ]
During the Permian–Triassic extinction event (250 million years ago) a severe anoxic event seems to have occurred where these forms of bacteria became the dominant force in oceanic ecosystems, producing copious amounts of hydrogen sulfide. [ 15 ]
Sulfate-reducing bacteria also generate neurotoxic methylmercury as a byproduct of their metabolism, through methylation of inorganic mercury present in their surroundings. They are known to be the dominant source of this bioaccumulative form of mercury in aquatic systems. [ 16 ]
Some sulfate-reducing microorganisms can reduce hydrocarbons , and they have been used to clean up contaminated soils. Their use has also been proposed for other kinds of contaminations. [ 3 ]
Sulfate-reducing microorganisms are considered a possible way to deal with acid mine waters that are produced by other microorganisms. [ 17 ]
In engineering, sulfate-reducing microorganisms can create problems when metal structures are exposed to sulfate-containing water: Interaction of water and metal creates a layer of molecular hydrogen on the metal surface; sulfate-reducing microorganisms then oxidize the hydrogen while creating hydrogen sulfide, which contributes to corrosion .
Hydrogen sulfide from sulfate-reducing microorganisms also plays a role in the biogenic sulfide corrosion of concrete . It also occurs in sour crude oil . [ 3 ]
Some sulfate-reducing microorganisms play a role in the anaerobic oxidation of methane : [ 3 ]
An important fraction of the methane formed by methanogens below the seabed is oxidized by sulfate-reducing microorganisms in the transition zone separating the methanogenesis from the sulfate reduction activity in the sediments. This process is also considered a major sink for sulfate in marine sediments.
In hydraulic fracturing , fluids are used to frack shale formations to recover methane ( shale gas ) and hydrocarbons . Biocide compounds are often added to water to inhibit the microbial activity of sulfate-reducing microorganisms, in order to but not limited to, avoid anaerobic methane oxidation and the generation of hydrogen sulfide , ultimately resulting in minimizing potential production loss.
Before sulfate can be used as an electron acceptor, it must be activated. This is done by the enzyme ATP-sulfurylase , which uses ATP and sulfate to create adenosine 5′-phosphosulfate (APS). APS is subsequently reduced to sulfite and AMP . Sulfite is then further reduced to sulfide, while AMP is turned into ADP using another molecule of ATP. The overall process, thus, involves an investment of two molecules of the energy carrier ATP, which must to be regained from the reduction. [ 1 ]
The enzyme dissimilatory (bi)sulfite reductase, dsrAB (EC 1.8.99.5), that catalyzes the last step of dissimilatory sulfate reduction, is the functional gene most used as a molecular marker to detect the presence of sulfate-reducing microorganisms. [ 18 ]
The sulfate-reducing microorganisms have been treated as a phenotypic group , together with the other sulfur-reducing bacteria , for identification purposes. They are found in several different phylogenetic lines. [ 19 ] As of 2009, 60 genera containing 220 species of sulfate-reducing bacteria are known. [ 3 ]
Among the Thermodesulfobacteriota the orders of sulfate-reducing bacteria include Desulfobacterales , Desulfovibrionales , and Syntrophobacterales . This accounts for the largest group of sulfate-reducing bacteria, about 23 genera. [ 1 ]
The second largest group of sulfate-reducing bacteria is found among the Bacillota , including the genera Desulfotomaculum , Desulfosporomusa , and Desulfosporosinus .
In the Nitrospirota phylum we find sulfate-reducing Thermodesulfovibrio species.
Two more groups that include thermophilic sulfate-reducing bacteria are given their own phyla, the Thermodesulfobacteriota and Thermodesulfobium .
There are also three known genera of sulfate-reducing archaea: Archaeoglobus , Thermocladium and Caldivirga . They are found in hydrothermal vents, oil deposits, and hot springs.
In July 2019, a scientific study of Kidd Mine in Canada discovered sulfate-reducing microorganisms living 7,900 feet (2,400 m) below the surface. The sulfate reducers discovered in Kidd Mine are lithotrophs, obtaining their energy by oxidizing minerals such as pyrite rather than organic compounds. [ 20 ] [ 21 ] [ 22 ] Kidd Mine is also the site of the oldest known water on Earth. [ 23 ] | https://en.wikipedia.org/wiki/Sulfate-reducing_microorganism |
Sulfate conjugates are a heterogeneous class of polar , anionic organosulfate compounds containing an ester of sulfuric acid . Sulfate conjugates commonly result from the metabolic conjugation of endogenous and exogenous compounds with sulfate (-OSO 3 − ). [ 1 ]
Biosynthesis of sulfate esters requires an activated sulfate donor, usually adenosine 5'-phosphosulfate (APS) or 3'-phosphoadenosine-5'-phosphosulfate (PAPS). [ 2 ] Sulfate esters may be hydrolyzed by sulfatase enzyme to release the parent alcohol and a sulfate ion . [ 3 ]
Steroid sulfation is one of the most common of all forms of steroid conjugation. Except for cholesterol, dehydroepiandrosterone sulfate is the most abundant of all plasma steroids. Estrone sulfate is the most abundant of all the estrogens in the human body. [ 3 ] Estrone sulfate is synthesized by the enzyme estrone sulfotransferase .
Quercetin 3-O-sulfate
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfate_conjugate |
Sulfate crust is a zone observed in the axial (central) parts of burning coal dumps and related sites. It is a zone built mainly by anhydrous sulfate minerals, such as godovikovite and millosevichite . The outer zone can easily be hydrated giving rise to minerals like tschermigite and alunogen . The zone forms due to interaction with hot (even around 600 °C) coal-derived gases (mainly NH 3 and SO 3 ) with the "sterile" material (i.e. shales and other rocks serving as the source of Al 3+ , Fe 3+ , Ca 2+ and other cations) in case of the lack of vents for the gases to escape into the atmosphere. [ 1 ] [ 2 ] [ 3 ]
This combustion article is a stub . You can help Wikipedia by expanding it .
This article about mining is a stub . You can help Wikipedia by expanding it .
This article about a specific sulfate mineral is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfate_crust |
In organosulfur chemistry , sulfenamides (also spelled sulphenamides ) are a class of organosulfur compounds characterized by the general formula R−S−N(−R) 2 , where the R groups are hydrogen , alkyl , or aryl . [ 1 ] Sulfenamides have been used extensively in the vulcanization of rubber using sulfur . They are related to the oxidized compounds known as sulfinamides ( RS(O)NR 2 ) and sulfonamides ( RS(O) 2 NR 2 ).
Sulfenamides are usually prepared by the reaction of sulfenyl chlorides and amines : [ 2 ]
The S-N bond formation generally obeys standard bimolecular nucleophilic substitution rules, with the basic nitrogen centre being the nucleophile . Primary sulfenamide formation as shown above occurs with the reaction of the sulfenyl halide with ammonia . Additionally primary as well as secondary and tertiary amines form sulfenamides through reaction with, thiols , disulfides , and sulfenyl thiocyanates . [ 3 ] In one illustrative synthesis, triphenylmethanesulphenyl chloride and butylamine react in benzene at 25 C:
Many other routes to sulfenamides are known, starting from thiols and disulfides . [ 4 ]
Sulfenamides have been characterized by X-ray crystallography . The S-N bond in sulfenamides is a chiral axis that leads to formation of diastereomeric compounds. The existence of these distinct stereoisomers is due to the formation of a partial double bond between either sulfur or nitrogen 's lone pair and the other atom's antibonding orbitals . [ 1 ] Additionally bulky substituent groups and lone pair repulsion can contribute resistance to interconversion. The resulting torsional barriers can be quite large and vary from 12-20 kcal/mol. [ 2 ] The interactions are thought to be dependent on the torsional preferences (also known as the gauche effect ). [ 1 ] The nitrogen atom is usually pyramidal, but cyclic and strongly steric hindered acyclic sulfenamides can display a planar arrangement of bonds around the nitrogen atom.
The S-N bond in sulfenamides are labile in a variety of ways. [ 2 ] The sulfur atom tends to be the more electrophilic center of the S-N bond. Nucleophilic attack on sulfur can occur by amines, by thiols , and by alkyl-magnesium halides which leads to either new sulfenamide compounds or back to starting compounds such as sulfides and disulfides respectively. [ 1 ] Both the nitrogen and sulfur atoms comprising the S-N bond in sulfenamides have lone pairs of electrons in their outer shells, one and two for nitrogen and sulfur respectively. These lone pairs allow for the possibility of forming either higher order bonds(double, triple) or adding new substituent groups to the compound. For instance, the nitrogen in the S-N bond of 2-hydroxysulfenanilides can oxidize to an imine species with sodium dichromate . [ 2 ]
Lead dioxide oxidizes primary sulfenamides to metastable thiamino radicals (R–N • –S–R ′ ), which decompose over a period of months. [ 5 ]
Sulfenamides react with amino-azaheterocycles to form heterocyclic systems (often used as amino protecting groups in various other synthesis reactions). Chlorocarbonylsulfenyl chloride (ClCOSCl) also readily forms S-N bonds with 2-amino-azaheterocycles, but always of a cyclical nature.
A novel variant of the Appel reaction has been noted for sulfenamides. Reaction of o-nitrobenzenesulfenamide with PPh 3 and CCl 4 leads the formation of o-nitro-N-(triphenylphosphorany1idene)-benzenesulfenamide. In this variant reaction, the triphenyl phosphine forms a double bonded linkage with nitrogen in the sulfenamide instead of oxygen as is customary in the Appel reaction. Additionally in the traditional Apple reaction, the R-OH bond is cleaved leaving oxygen attached to triphenylphosphine. In this variant, the S-N bond is not cleaved.
Sulfenamides, e.g. cyclohexylthiophthalimide , are used extensively in the vulcanization of rubber . The sulfenamides are used to accelerate the process via the transient formation of labile S-N bonds. The substituents on the sulfenamides determine the point at which they will become active. Temperature dependent activation of sulfenamide accelerants is useful in the vulcanization process because the temperature at which the rubber polymerizes determines the length of the sulfur chains, and properties such as the elasticity of the final product. | https://en.wikipedia.org/wiki/Sulfenamide |
In organosulfur chemistry , a sulfenyl chloride is a functional group with the connectivity R−S−Cl , where R is alkyl [ 1 ] or aryl . Sulfenyl chlorides are reactive compounds that behave as sources of RS + . They are used in the formation of RS−N and RS−O bonds. According to IUPAC nomenclature they are named as alkyl thiohypochlorites, i.e. esters of thiohypochlorous acid.
Typically, sulfenyl halides are stabilized by electronegative substituents. This trend is illustrated by the stability of CCl 3 SCl obtained by chlorination of carbon disulfide .
Sulfenyl chlorides are typically prepared by chlorination of disulfides : [ 2 ] [ 3 ]
This reaction is sometimes called the Zincke disulfide reaction, in recognition of Theodor Zincke . [ 4 ] [ 5 ]
Some thioethers ( R−S−R’ ) with electron-withdrawing substituents undergo chlorinolysis of a C−S bond to afford the sulfenyl chloride. [ 6 ] [ 7 ]
In a variation on the Reed reaction , sulfur dichloride displaces hydrogen under UV light. [ 8 ]
Perchloromethyl mercaptan ( CCl 3 SCl ) reacts with N−H bonds in the presence of base to give the sulfenamides :
This method is used in the production of the fungicides Captan and Folpet .
Sulfenyl chlorides add across alkenes , for example cyclohexene [ 9 ] and ethylene [ 10 ]
They undergo chlorination to the trichlorides : [ 3 ]
Sulfenyl chlorides react with water and alcohols to give sulfenyl esters ( R−S−O−R′ ): [ 11 ]
Sulfenyl chlorides can be converted to sulfinyl chlorides (RS(O)Cl). In one approach, the sulfinyl chloride is generated in two steps starting with reaction of a thiol ( −SH ) with sulfuryl chloride ( SO 2 Cl 2 ). In some cases the sulfenyl chloride results instead, as happens with 2,2,2-trifluoro-1,1-diphenyl ethanethiol . A trifluoroperacetic acid oxidation then provides a general approach to formation of sulfinyl chlorides from sulfenyl chlorides: [ 12 ]
Sulfenyl fluorides and bromides are also known. [ 13 ] Simple sulfenyl iodides are unstable with respect to the disulfide and iodine , gradually decomposing over the course of several hours at low temperature:
They can be formed metastably from metal mercaptides and iodine , and even form fleetingly when iodine oxidizes neutral thiols to the disulfide. Indeed, sulfenyl iodides are believed to be the active iodinating agents in iodotyrosine biosynthesis. [ 14 ] Sulfenyl iodides that are heavily sterically hindered from dimerization are stable. [ 15 ]
A related class of compounds are the alkylsulfur trichlorides, as exemplified by methylsulfur trichloride, CH 3 SCl 3 . [ 16 ]
The corresponding selenenyl halides, R−SeCl , are more commonly encountered in the laboratory. Sulfenyl chlorides are used in the production of agents used in the vulcanization of rubber. | https://en.wikipedia.org/wiki/Sulfenyl_chloride |
Sulfidation (British spelling also sulphidation ) is a process of installing sulfide ions in a material or molecule. The process is widely used to convert oxides to sulfides but is also related to corrosion and surface modification.
Sulfidation is relevant to the formation of sulfide minerals . [ 1 ]
A large scale application of sulfidation is the conversion of molybdenum oxides to the corresponding sulfides. This conversion is a step in the preparation of catalysts for hydrodesulfurization wherein alumina impregnated with molybdate salts are converted to molybdenum disulfide by the action of hydrogen sulfide .
In organosulfur chemistry , sulfiding is often called thiation. The preparation of thioamides from amides involves thiation. A typical reagent is phosphorus pentasulfide (P 4 S 10 ). The idealized equation for this conversion is:
This conversion where an oxygen atom in the amide function is replaced by a sulfur atom involves no redox reaction.
It is known that aluminum improves the sulfidation resistance of iron alloys. [ 2 ] The sulfidation of tungsten is a multiple step process. The first step is an oxidation reaction, converting the tungsten to a tungsten bronze on the surface of the object. The tungsten bronze coating is then converted to a sulfide . [ 3 ]
One commonly encountered occurrence of sulfidation in manufacturing environments involves the sulfidic corrosion of metal piping. [ 4 ] The increased resistance to corrosion found in stainless steel is attributed to a layer of chromium oxide that forms due to oxidation of the chromium found in the alloy. [ 4 ]
The process of liquid sulfidation has also been used in the manufacturing of diamond-like carbon films. These films are generally used to coat surfaces to reduce the wear due to friction. The inclusion of sulfidation in the process has been shown to reduce the friction coefficient of the diamond-like carbon film. [ 5 ] | https://en.wikipedia.org/wiki/Sulfidation |
Sulfide (also sulphide in British English ) [ 2 ] is an inorganic anion of sulfur with the chemical formula S 2− or a compound containing one or more S 2− ions. Solutions of sulfide salts are corrosive. Sulfide also refers to large families of inorganic and organic compounds , e.g. lead sulfide and dimethyl sulfide . Hydrogen sulfide (H 2 S) and bisulfide (HS − ) are the conjugate acids of sulfide.
The sulfide ion does not exist in aqueous alkaline solutions of Na 2 S. [ 3 ] [ 4 ] Instead sulfide converts to hydrosulfide:
Upon treatment with an acid, sulfide salts convert to hydrogen sulfide :
Oxidation of sulfide is a complicated process. Depending on the conditions, the oxidation can produce elemental sulfur, polysulfides , polythionates , sulfite , or sulfate . Metal sulfides react with halogens , forming sulfur and metal salts.
Aqueous solutions of transition metals cations react with sulfide sources (H 2 S, NaHS, Na 2 S) to precipitate solid sulfides. Such inorganic sulfides typically have very low solubility in water, and many are related to minerals with the same composition (see below). One famous example is the bright yellow species CdS or " cadmium yellow ". The black tarnish formed on sterling silver is Ag 2 S. Such species are sometimes referred to as salts. In fact, the bonding in transition metal sulfides is highly covalent, which gives rise to their semiconductor properties, which in turn is related to the deep colors. Several have practical applications as pigments, in solar cells, and as catalysts. The fungus Aspergillus niger plays a role in the solubilization of heavy metal sulfides. [ 5 ]
Many important metal ores are sulfides. [ 6 ] Significant examples include: argentite ( silver sulfide), cinnabar ( mercury sulfide), galena ( lead sulfide), molybdenite ( molybdenum sulfide), pentlandite ( nickel sulfide), realgar ( arsenic sulfide), and stibnite ( antimony sulfide), sphalerite ( zinc sulfide), and pyrite ( iron disulfide), and chalcopyrite ( iron - copper sulfide). This sulfide minerals recorded information (like isotopes ) of their surrounding environment during their formation. Scientists use these minerals to study environments in the deep sea or in the Earth's past. [ 7 ]
Dissolved free sulfides (H 2 S, HS − and S 2− ) are very aggressive species for the corrosion of many metals such as steel, stainless steel, and copper. Sulfides present in aqueous solution are responsible for stress corrosion cracking (SCC) of steel, and is also known as sulfide stress cracking . Corrosion is a major concern in many industrial installations processing sulfides: sulfide ore mills, deep oil wells , pipelines transporting soured oil and Kraft paper factories.
Microbially-induced corrosion (MIC) or biogenic sulfide corrosion are also caused by sulfate reducing bacteria producing sulfide that is emitted in the air and oxidized in sulfuric acid by sulfur oxidizing bacteria. Biogenic sulfuric acid reacts with sewerage materials and most generally causes mass loss, cracking of the sewer pipes and ultimately, structural collapse. This kind of deterioration is a major process affecting sewer systems worldwide and leading to very high rehabilitation costs.
Oxidation of sulfide can also form thiosulfate ( S 2 O 2− 3 ), an intermediate species responsible for severe problems of pitting corrosion of steel and stainless steel while the medium is also acidified by the production of sulfuric acid when oxidation is more advanced.
In organic chemistry , "sulfide" usually refers to the linkage C–S–C, although the term thioether is less ambiguous. For example, the thioether dimethyl sulfide is CH 3 –S–CH 3 . Polyphenylene sulfide (see below) has the empirical formula C 6 H 4 S. Occasionally, the term sulfide refers to molecules containing the –SH functional group . For example, methyl sulfide can mean CH 3 –SH. The preferred descriptor for such SH-containing compounds is thiol or mercaptan, i.e. methanethiol, or methyl mercaptan.
Confusion arises from the different meanings of the term " disulfide ". Molybdenum disulfide (MoS 2 ) consists of separated sulfide centers, in association with molybdenum in the formal +4 oxidation state (that is, Mo 4+ and two S 2− ). Iron disulfide ( pyrite , FeS 2 ) on the other hand consists of S 2− 2 , or − S–S − dianion, in association with divalent iron in the formal +2 oxidation state (ferrous ion: Fe 2+ ). Dimethyldisulfide has the chemical binding CH 3 –S–S–CH 3 , whereas carbon disulfide has no S–S bond, being S=C=S (linear molecule analog to CO 2 ). Most often in sulfur chemistry and in biochemistry, the disulfide term is commonly ascribed to the sulfur analogue of the peroxide –O–O– bond. The disulfide bond (–S–S–) plays a major role in the conformation of proteins and in the catalytic activity of enzymes .
Sulfide compounds can be prepared in several different ways: [ 8 ]
Many metal sulfides are so insoluble in water that they are probably not very toxic. Some metal sulfides, when exposed to a strong mineral acid , including gastric acids , will release toxic hydrogen sulfide .
Organic sulfides are highly flammable. When a sulfide burns it produces sulfur dioxide (SO 2 ) gas.
Hydrogen sulfide, some of its salts, and almost all organic sulfides have a strong and putrid stench; rotting biomass releases these.
The systematic names sulfanediide and sulfide(2−) , valid IUPAC names, are determined according to the substitutive and additive nomenclatures, respectively. The name sulfide is also used in compositional IUPAC nomenclature which does not take the nature of bonding involved. Examples of such naming include selenium disulfide and titanium sulfide , which contain no sulfide ions. | https://en.wikipedia.org/wiki/Sulfide |
In ecology, sulfide intrusion refers to an excess of sulfide molecules (S 2- ) in the soil that interfere with plant growth, often seagrass . [ 1 ] [ 2 ] [ 3 ]
Seagrass bed sediment (soil) is typically anoxic, containing a reduced form of sulfur: hydrogen sulfide (H 2 S). H 2 S is a phytotoxin that results from anaerobic digestion , the decomposition of organic matter in the absence of oxygen. However, seagrass can persist in this environment because of physiological adaptations, as well as functional adaptations of other organisms in the ecosystem. For example, bivalves (clams) in the family Lucinidae host symbiotic bacteria that oxidize sulfides. Lucinid bivalves' gills house the bacteria, and the siphon supplies the bacteria and surrounding pore water with oxygenated water from above the sediment. Bacterial oxidation of the sulfides results in sulfates, reducing toxicity. [ 4 ] [ 5 ] | https://en.wikipedia.org/wiki/Sulfide_intrusion |
Sulfide stress cracking ( SSC ) is a form of hydrogen embrittlement which is a cathodic cracking mechanism. It should not be confused with the term stress corrosion cracking which is an anodic cracking mechanism. Susceptible alloys , especially steels , react with hydrogen sulfide ( H 2 S ), forming metal sulfides (MeS) and atomic hydrogen (H • ) as corrosion byproducts. Atomic hydrogen either combines to form H 2 at the metal surface or diffuses into the metal matrix. Since sulfur is a hydrogen recombination poison, the amount of atomic hydrogen which recombines to form H 2 on the surface is greatly reduced, thereby increasing the amount of diffusion of atomic hydrogen into the metal matrix. This aspect is what makes wet H 2 S environments so severe. [ 1 ]
Since SSC is a form of hydrogen embrittlement , it is most susceptibile to cracking at or slightly below ambient temperature.
Sulfide stress cracking has special importance in the gas and oil industry , as the materials being processed there ( natural gas and crude oil ) often contain considerable amounts of hydrogen sulfide. Equipment that comes in contact with H 2 S environments can be rated for sour service with adherence to NACE MR0175/ISO 15156 for oil and gas production environments or NACE MR0103/ISO17945 for oil and gas refining environments.
" High Temperature Hydrogen Attack " (HTHA) does not rely on atomic hydrogen. At high temperature and high hydrogen partial pressure, hydrogen can diffuse into carbon steel alloys. In susceptible alloys , hydrogen combines with carbon within the alloy and forms methane . The methane molecules create a pressure buildup in the metal lattice voids, which leads to embrittlement and even cracking of the metal.
This corrosion -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfide_stress_cracking |
In chemistry , a sulfilimine (or sulfimide ) is a type of chemical compound containing a sulfur -to- nitrogen bond which is often represented as a double bond ( S=N ). In fact, a double bond violates the octet rule , and the bond may be considered a single bond with a formal charge of +1 on the sulfur and a formal charge of −1 on the nitrogen. The parent compound is sulfilimine H 2 S=NH , which is mainly of theoretical interest.
Examples include S , S -diphenylsulfilimine [ 2 ] and sulfoximines [ Category ] such as methylphenylsulfoximine: [ 3 ]
In the case of a sulfoximine, the bonds can be considered single bonds, with formal charges of −1 on both the oxygen and the nitrogen, and a formal charge of +2 on the sulfur.
Most sulfilimines are N -substituted with electron-withdrawing groups. These compounds are typically prepared by oxidation of thioethers with electrophilic amine reagents, such as chloramine-T in the presence of a base: [ 4 ]
An alternative route involves reactions of electrophilic sulfur compounds with amines. The imidosulfonium reagents provide a source of " Me 2 S 2+ ", which are attacked by amines.
In general, aliphatic sulfilimines are not stable above −30 °C (−22 °F). [ 5 ]
KMnO 4 can oxidize sulfilimines to sulfoximines, but the latter are more generally produced from addition of azides to sulfoxides . [ 5 ]
Sulfilimine bonds stabilize collagen IV strands found in the extracellular matrix [ 6 ] and arose at least 500 mya. [ 7 ] These bonds covalently connect hydroxylysine and methionine residues of adjacent polypeptide strands to form a larger collagen trimer. | https://en.wikipedia.org/wiki/Sulfilimine |
In organosulfur chemistry , sulfinamide is a functional group with the structure R−S(O)−NR 2 (where R = alkyl or aryl ). [ 1 ] This functionality is composed of a sulfur - carbon ( S−C ) single bond , a sulfur- nitrogen ( S−N ) single bond , and a sulfur-oxygen (S-O) bond (see Sulfoxide for the nature of this bond). [ 2 ] As a non-bonding electron pair is present on the sulfur, the sulfur atom is a stable stereogenic centre, and so these compounds are chiral . They are sometimes referred to as S -chiral sulfinamides. Sulfinamides are amides of sulfinic acid ( R−S(O)OH ).
Sulfinamides do not undergo inversion. They can therefore be synthesised and/or isolated in enantiopure forms. This has led to their use as chiral ammonia equivalents and more broadly as chiral auxiliaries .
Sulfinamides are traditionally produced by the reaction of sulfinyl chlorides with primary or secondary amines. [ 1 ] They also arise by the addition of Grignard reagents to sulfinylamines , followed by protonation:
Yet another route entails peracid-oxidation of sulfenylphthalimides, which gives sulfinylphthalimides.
A common sulfinamide is tert -butanesulfinamide (Ellman's sulfinamide), p -toluenesulfinamide (Davis' sulfinamide), and mesityl sulfinamide. [ 4 ] [ 5 ] [ 6 ]
Sulfinamides arise in nature by the addition of nitroxyl (HNO) to thiols : [ 7 ] | https://en.wikipedia.org/wiki/Sulfinamide |
Sulfinic acids are oxoacids of sulfur with the structure RSO(OH). In these organosulfur compounds , sulfur is pyramidal . [ 1 ]
Sulfinic acids RSO 2 H are typically more acidic than the corresponding carboxylic acid RCO 2 H. [ 2 ] [ 3 ] Sulfur is pyramidal, consequently sulfinic acids are chiral. The free acids are typically unstable, disproportionating to the sulfonic acid RSO 3 H and thiosulfonate RSSO 2 R. [ 4 ] : 679 The formal anhydride of a sulfinic acid has no oxygen atom bridge, but is instead a sulfinyl sulfone (R–S + (–O − )–S 2+ (–O − ) 2 –R ′ ), [ 5 ] and disproportionation is believed to occur through the free-radical fission of this intermediate. [ 6 ]
Alkylation of sulfinic acids can give either sulfones or sulfinate esters, depending on the solvent and reagent. Strongly polarized reactants (e.g. trimethyloxonium tetrafluoroborate ) give esters, whereas relatively unpolarized reactants (e.g. an alkyl halide or enone ) give sulfones. [ 4 ] : 682 Sulfinates react with Grignard reagents to give sulfoxides , and undergo a variant of the Claisen condensation towards the same end. [ 4 ] : 686
Cobalt (III) salts can oxidize sulfinic acids to disulfones , although yields are only 30–50%. [ 7 ]
Sulfinic acids are often prepared in situ by acidification of the corresponding sulfinate salts, which are typically more robust than the acid. These salts are generated by reduction of sulfonyl chlorides with metals, [ 8 ] although thiolates also reduce sulfonate thioesters to a sulfinate and a disulfide . [ 4 ] : 681
An alternative route is the reaction of Grignard reagents with sulfur dioxide . Transition metal sulfinates are also generated by insertion of sulfur dioxide into metal alkyls, a reaction that may proceed via a metal sulfur dioxide complex .
Sulfones may eliminate in base, particularly if a strong nucleophile is present; thus for example sodium cyanide causes bis(2‑butanone-4‑yl) sulfone to split into levulinonitrile and 3‑oxobutane 1‑sulfinic acid: [ 4 ] : 681
The nitrile presumably forms through conjugate addition of cyanide to the corresponding enone .
Friedel-Crafts addition of thionyl chloride to an alkene gives an α‑chloro sulfinyl chloride, typically complexed to a Lewis acid. Likewise a carbanion can attack thionyl chloride to give a sulfinyl chloride. Careful hydrolysis then gives a sulfinic acid. [ 4 ] : 682, 684 Sulfinyl chlorides attack sulfinates to give sulfinyl sulfones (sulfinic anhydrides). [ 5 ]
Unsubstituted sulfinic acid, when R is the hydrogen atom, is a higher energy isomer of sulfoxylic acid , both of which are unstable.
An example of a simple, well-studied sulfinic acid is phenylsulfinic acid . A commercially important sulfinic acid is thiourea dioxide , which is prepared by the oxidation of thiourea with hydrogen peroxide . [ 4 ]
Another commercially important sulfinic acid is hydroxymethyl sulfinic acid, which is usually employed as its sodium salt (HOCH 2 SO 2 Na). Called Rongalite , this anion is also commercially useful as a reducing agent.
The conjugate base of a sulfinic acid is a sulfinate anion. The enzyme cysteine dioxygenase converts cysteine into the corresponding sulfinate. One product of this catabolic reaction is the sulfinic acid hypotaurine . Sulfinite also describes esters of sulfinic acid. Cyclic sulfinite esters are called sultines . | https://en.wikipedia.org/wiki/Sulfinic_acid |
A sulfite ester (also known as an organosulfite ) is a functional group with the structure (RO)(R'O)SO. They are in principle the esters of sulfurous acid , however as the acid cannot be produced they are in practice made via other routes.
They adopt a trigonal pyramidal molecular geometry due to the presence of lone pairs on the sulphur atom.
When substituents R and R' differ, the compound is chiral owing to the stereogenic sulphur centre; when the R groups are the same the compound will have idealised C s molecular symmetry .
They are commonly prepared by the reaction of thionyl chloride with alcohols. [ 1 ] The reaction is typically performed at room temperature to prevent the alcohol being converted into a chloroalkane . Bases such as pyridine can also be used to promote the reaction:
The pesticides endosulfan and propargite are sulfite esters. Other simple members include ethylene sulfite, dimethyl sulfite , and diphenylsulfite. Many examples have been prepared from diols, such as sugars. Sulfite esters can be powerful alkylation and hydroxyalkylation reagents. [ 2 ]
Mono-esters, with the general structure (RO)(HO)S=O are a rare subclass. Bufothionine is an example | https://en.wikipedia.org/wiki/Sulfite_ester |
The sulfite process produces wood pulp that is almost pure cellulose fibers by treating wood chips with solutions of sulfite and bisulfite ions. These chemicals cleave the bonds between the cellulose and lignin components of the lignocellulose. A variety of sulfite/bisulfite salts are used, including sodium (Na + ), calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ), and ammonium (NH 4 + ). The lignin is converted to lignosulfonates , which are soluble and can be separated from the cellulose fibers. For the production of cellulose, the sulfite process competes with the Kraft process which produces stronger fibers and is less environmentally costly.
The use of wood to make pulp for paper began with the development of mechanical pulping in the 1840s by Charles Fenerty in Nova Scotia [ 1 ] and by F. G. Keller [ 2 ] in Germany . Chemical processes quickly followed, first with Julius Roth 's use of sulfurous acid to treat wood in 1857, followed by Benjamin Chew Tilghman 's US patent on the use of calcium bisulfite , Ca(HSO 3 ) 2 , to pulp wood in 1867. [ 3 ] Almost a decade later in 1874 the first commercial sulfite pulp mill was built in Sweden . It used magnesium as the counter ion and was based on work by Carl Daniel Ekman .
By 1900 sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods. The competing chemical pulping process, the sulfate or kraft process was developed by Carl F. Dahl in 1879 and the first kraft mill started (in Sweden) in 1890. [ 3 ] The first sulphite mill in the United States was the Richmond Paper Company in Rumford, Rhode Island in the mid-1880s. The invention of the recovery boiler by G. H. Tomlinson in the early 1930s [ 2 ] allowed kraft mills to recycle almost all of their pulping chemicals. This, along with the ability of the kraft process to accept a wider variety of types of wood and produce stronger fibers [ 4 ] made the kraft process the dominant pulping process starting in the 1940s. [ 3 ] Sulfite pulps now account for less than 10% of the total chemical pulp production [ 3 ] and the number of sulfite mills continues to decrease. [ 5 ] [ 6 ] [ 7 ]
Magnesium was the standard counter ion until calcium replaced it in the 1950s.
The pulping liquor for most sulfite mills is generated by treating various bases (alkali metal or alkaline earth hydroxides) with sulfur dioxide:
Similar reactions are effected with divalent cations (Mg2+, Ca2+) and using carbonates in place of hydroxide.
The ratio of sulfite to bisulfite depends on pH; above pH=7, sulfite predominates.
The earliest process used calcium, obtained as inexpensive calcium carbonate , and there was little incentive to recover the inorganic materials. At least in Sweden the brown liquor from this process was previously frequently used for producing ethanol, while with other brown liquors the fermentable hexose sugars are left to contribute to the energy needed in the recovery process. Calcium sulfite, which is poorly soluble, converts to calcium bisulfite only at low pH. Therefore calcium-based sulfite processes require acidic conditions.
Ammonia-based processes do not allow recovery of the pulping chemicals since ammonia or ammonium salts are oxidized to nitrogen and nitrogen oxides when burned.
The recovery process used in magnesium-based sulfite pulping the "Magnefite" process is well developed. [ 8 ] The concentrated brown liquor is burned in a recovery boiler, producing magnesium oxide and sulfur dioxide , both of which are recovered from the flue gases. Magnesium oxide is recovered in a wet scrubber to give a slurry of magnesium hydroxide .
This magnesium hydroxide slurry is then used in another scrubber to absorb sulfur dioxide from the flue gases producing a magnesium bisulfite solution that is clarified, filtered and used as the pulping liquor.
Sodium-based processes use a recovery system similar to that used in the kraft recovery process , except that there is no "lime cycle".
The process is conducted in large pressure vessels called digesters. Sulfite pulping is carried out between pH 1.5 and 5. The pulp is in contact with the pulping chemicals for 4 to 14 hours and at temperatures ranging from 130 to 160 °C (266 to 320 °F ), again depending on the chemicals used.
Most of the intermediates involved in delignification in sulfite pulping are resonance-stabilized carbocations formed either by protonation of carbon-carbon double bonds or acidic cleavage of ether bonds which connect many of the constituents of lignin. It is the latter reaction which is responsible for most lignin degradation in the sulfite process. [ 2 ] The electrophilic carbocations react with bisulfite ions (HSO 3 − )to give sulfonates.
The sulfite process does not degrade lignin to the same extent that the kraft process does and the lignosulfonates from the sulfite process are useful byproducts .
The spent cooking liquor from sulfite pulping is usually called brown liquor, but the terms red liquor, thick liquor and sulfite liquor are also used (compared to black liquor in the kraft process ). Pulp washers, using countercurrent flow, remove the spent cooking chemicals and degraded lignin and hemicellulose. The extracted brown liquor is concentrated, in multiple effect evaporators . The concentrated brown liquor can be burned in the recovery boiler to generate steam and recover the inorganic chemicals for reuse in the pulping process or it can be neutralized to recover the useful byproducts of pulping. Recent developments in Chemrec's black liquor gasification process, adapting the technology to use in the sulfite pulping process, could make second generation biofuels production an alternative to the conventional recovery boiler technology. [ 9 ] Around 1906 Gösta Ekström a Swedish engineer patented a process of ethanol generation from the residual 2-2.5% fermentable hexose sugars in the spent liquor. [ 10 ]
The sulfite process can use calcium , ammonium , magnesium or sodium as a base.
The sulfite process is acidic and one of the drawbacks is that the acidic conditions hydrolyze some of the cellulose, which means that sulfite pulp fibers are not as strong as kraft pulp fibers. The yield of pulp (based on wood used) is higher than for kraft pulping and sulfite pulp is easier to bleach .
Sulfite pulp remains an important commodity , especially for specialty papers and as a source of cellulose for non-paper applications. It is used to make fine paper , tissue , glassine , [ 11 ] and to add strength to newsprint .
A special grade of bleached sulfite pulp is known as dissolving pulp [ 12 ] which is the raw material for a wide variety of cellulose derivatives, for example rayon , cellophane , cellulose acetate and methylcellulose .
Rayon is a reconstituted cellulose fiber used to make many fabrics.
Cellophane is a clear reconstituted cellulose film used in wrapping and windows in envelopes.
Cellulose acetate was used to make flexible films for photographic use, computer tapes and so on and also to make fibers.
Methylcellulose and other cellulose ether derivatives are used in a wide range of everyday products from adhesives to baked goods to pharmaceuticals . [ 13 ]
Sulfite pulping is generally less destructive than kraft pulping, so there are more usable byproducts.
Chief among sulfite process byproducts are lignosulfonates , which find a wide variety of uses where a relatively inexpensive agent is needed to make a water dispersion of a water-insoluble material. Lignosulfonates are used in tanning leather, making concrete , drilling mud , drywall and so on. [ 14 ]
Oxidation of lignosulfonates was used to produce vanillin (artificial vanilla), and this process is still used by one supplier ( Borregaard , Norway) while all North American production by this route ceased in the 1990s. [ 15 ]
Acid hydrolysis of hemicelluloses during sulfite pulping produces monosaccharides , predominantly mannose for softwoods and xylose for hardwoods, [ 2 ] which can be fermented to produce ethanol . | https://en.wikipedia.org/wiki/Sulfite_process |
Sulfoglycolysis is a catabolic process in primary metabolism in which sulfoquinovose (6-deoxy-6-sulfonato-glucose) is metabolized to produce energy and carbon-building blocks. [ 1 ] [ 2 ] Sulfoglycolysis pathways occur in a wide variety of organisms, and enable key steps in the degradation of sulfoquinovosyl diacylglycerol (SQDG), a sulfolipid found in plants and cyanobacteria into sulfite and sulfate. Sulfoglycolysis converts sulfoquinovose (C 6 H 12 O 8 S − ) into various smaller metabolizable carbon fragments such as pyruvate and dihydroxyacetone phosphate that enter central metabolism. The free energy is used to form the high-energy molecules ATP ( adenosine triphosphate ) and NADH (reduced nicotinamide adenine dinucleotide ). Unlike glycolysis , which allows metabolism of all carbons in glucose, sulfoglycolysis pathways convert only a fraction of the carbon content of sulfoquinovose into smaller metabolizable fragments; the remainder is excreted as C 3 -sulfonates 2,3-dihydroxypropanesulfonate (DHPS) or sulfolactate (SL); or C 2 -sulfonates isethionate or sulfoacetate .
Several sulfoglycolytic pathways are known:
Additionally, there are sulfoquinovose 'sulfolytic' pathways that allow degradation of sulfoquinovose through cleavage of the C-S bond. These include:
In all pathways, energy is formed by breakdown of the carbon-rich fragments in later stages through the ' pay-off ' phase of glycolysis through substrate-level phosphorylation to produce ATP and NADH.
A range of bacteria can grow on sulfoquinovose or its glycosides as sole carbon source. E. coli can grow on sulfoquinovose, [ 3 ] methyl α-sulfoquinovoside and α-sulfoquinovosyl glycerol. [ 10 ] Growth on sulfoquinovosyl glycerol is both faster and leads to higher cell density than for growth on sulfoquinovose. [ 10 ] Pseudomonas aeruginosa strain SQ1, [ 11 ] Klebsiella sp. strain ABR11, [ 12 ] Klebsiella oxytoca TauN1, [ 11 ] Agrobacterium sp. strain ABR2, [ 12 ] and Bacillus aryabhattai [ 5 ] can grow on sulfoquinovose as sole carbon source. A strain of Flavobacterium was identified that could grow on methyl α-sulfoquinovoside. [ 13 ]
Sulfoquinovose is rarely found in its free form in nature; rather it occurs predominantly as a glycoside, SQDG. SQDG can be deacylated to form lyso -SQDG and sulfoquinovosylglycerol (SQGro). [ 14 ] [ 15 ] [ 16 ] Sulfoquinovose is obtained from SQ glycosides by the action of sulfoquinovosidases, which are glycoside hydrolases that can hydrolyse the glycosidic linkage in SQDG, or its deacylated form, sulfoquinovosyl glycerol (SQGro). [ 17 ]
There are two main classes of sulfoquinovosidases. The first are classical glycoside hydrolases (which belong to CAZy family GH31), and is exemplified by the sulfoquinovosidase YihQ from Escherichia coli . Family GH31 sulfoquinovosidases cleave SQ glycosides with retention of configuration, initially forming α-sulfoquinovose. YihQ sulfoquinovosidase exhibits a preference for the naturally occurring 2’ R -SQGro. [ 10 ] The second class of sulfoquinovosidases are NAD + -dependent enzymes (which belong to CAZy family GH188) that use an oxidoreductive mechanism to cleave both α- and β-glycosides of sulfoquinovose. [ 18 ]
Sulfoglycolysis encoding operons often contain gene sequences encoding aldose-1-epimerases that act as sulfoquinovose mutarotases, catalyzing the interconversion of the α and β anomers of sulfoquinovose. [ 19 ]
The major steps in the sulfo-EMP pathway [ 3 ] are:
Expression of proteins within the sulfo-EMP operon of E. coli is regulated by a transcription factor termed CsqR (formerly YihW). [ 22 ] CsqR binds to DNA sites within the operon encoding the sulfo-EMP pathway, functioning as a repressor. SQ, SQGro and the transiently formed intermediate sulforhamnose (but not lactose, glucose or galactose) function as derepressors of CsqR. [ 20 ]
The major steps in the sulfo-ED pathway [ 4 ] are:
The major steps in the sulfo-SFT pathway [ 5 ] are:
The transaldolase can also catalyze transfer of the C3-(glycerone)-moiety to erythrose-4-phosphate, giving sedoheptulose-7-phosphate.
The major steps in the Sulfo-TK pathway [ 23 ] are:
The sulfoacetaldehyde may be oxidized to sulfoacetate.
The C 3 sulfonates DHPS and SL are metabolized for their carbon content, as well as to mineralize their sulfur content. [ 2 ] Metabolism of DHPS typically involves conversion to SL. Metabolism of SL can occur in several ways including: | https://en.wikipedia.org/wiki/Sulfoglycolysis |
Sulfolene , or butadiene sulfone is a cyclic organic chemical with a sulfone functional group . It is a white, odorless, crystalline, indefinitely storable solid, which dissolves in water and many organic solvents. [ 3 ] The compound is used as a source of butadiene . [ 4 ]
Sulfolene is formed by the cheletropic reaction between butadiene and sulfur dioxide. The reaction is typically conducted in an autoclave. Small amounts of hydroquinone or pyrogallol are added to inhibit polymerization of the diene. The reaction proceeds at room temperature over the course of days. At 130 °C, only 30 minutes are required. [ 5 ] An analogous procedure gives the isoprene -derived sulfone. [ 6 ]
The compound is unaffected by acids. It can even be recrystallized from conc. HNO 3 . [ 7 ] [ 8 ]
The protons in the 2- and 5-positions rapidly exchange with deuterium oxide under alkaline conditions. [ 9 ] Sodium cyanide catalyzes this reaction. [ 10 ]
In the presence of base or cyanide, 3-sulfolene isomerizes to a mixture of 2-sulfolene and 3-sulfolene. [ 10 ]
At 50 °C an equilibrium mixture is obtained containing 42% 3-sulfolene and 58% 2-sulfolene. [ 11 ] The thermodynamically more stable 2-sulfolene can be isolated from the mixture of isomers as pure substance in the form of white plates (m.p. 48-49 °C) by heating for several days at 100 °C, because of the thermal decomposition of the 3-sulfolene at temperatures above 80 °C. [ 12 ]
Catalytic hydrogenation yields sulfolane , a solvent used in the petrochemical industry for the extraction of aromatics from hydrocarbon streams. The hydrogenation of 3-sulfolene over Raney nickel at approx. 20 bar and 60 °C gives sulfolane in yields of up to 65% only because of the poisoning of the catalyst by sulfur compounds. [ 13 ]
3-Sulfolene reacts in aqueous solution with bromine to give 3,4-dibromotetrohydrothiophene-1,1-dioxide , which can be dehydrobrominated to thiophene-1,1-dioxide with silver carbonate . [ 7 ]
Thiophene-1,1-dioxide, a highly reactive species, is also accessible via the formation of 3,4-bis(dimethylamino)tetrahydrothiophene-1,1-dioxide and successive double quaternization with methyl iodide and Hofmann elimination with silver hydroxide . [ 12 ] A less cumbersome two-step synthesis is the two-fold dehydrobromination of 3,4-dibromotetrohydrothiophene-1,1-dioxide with either powdered sodium hydroxide in tetrahydrofuran (THF) [ 14 ] or with ultrasonically dispersed metallic potassium . [ 15 ]
3-sulfolene is mainly valued as a stand-in for butadiene. [ 3 ] [ 4 ] The in situ production and immediate consumption of 1,3-butadiene largely avoids contact with the diene, which is a gas at room temperature. One potential drawback, aside from expense, is that the evolved sulfur dioxide can cause side reactions with acid-sensitive substrates.
Diels-Alder reaction between 1,3-butadiene and dienophiles of low reactivity usually requires prolonged heating above 100 °C. Such procedures are rather dangerous. If neat butadiene is used, special equipment for work under elevated pressure is required. With sulfolene no buildup of butadiene pressure could be expected as the liberated diene is consumed in the cycloaddition, and therefore the equilibrium of the reversible extrusion reaction acts as an internal "safety valve". [ 16 ]
3-Sulfolene reacts with maleic anhydride in boiling xylene to cis-4-cyclohexene-1,2-dicarboxylic anhydride, obtaining yields of up to 90%. [ 4 ]
3-Sulfolene reacts also with dienophiles in trans configuration (such as diethyl fumarate) at 110 °C with SO 2 elimination in 66–73% yield to the trans-4-cyclohexene-1,2-dicarboxylic diethyl ester. [ 17 ]
6,7-Dibromo-1,4-epoxy-1,4-dihydronaphthalene (6,7-Dibromonaphthalene-1,4-endoxide, accessible after debromination from 1,2,4,5-tetrabromobenzene using an equivalent of n-butyllithium and Diels-Alder reaction in furan in 70% yield [ 18 ] ) reacts with 3-sulfolene in boiling xylene to give a tricyclic adduct. This precursor yields, after treatment with perchloric acid, a dibromo dihydroanthracene which is dehydrogenated in the last step with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to 2,3-dibromoanthracene. [ 19 ]
1,3-Butadiene (formed in the retro-cheletrophic reaction of 3-sulfolene) reacts with dehydrobenzene ( benzyne , obtained by thermal decomposition of benzenediazonium-2-carboxylate) in a Diels-Alder reaction in 9% yield to give 1,4-dihydronaphthalene. [ 20 ]
In the presence of very reactive dienes (for example 1,3-diphenylisobenzofuran) butadienesulfone behaves as a dienophile and forms the corresponding Diels-Alder adduct. [ 21 ]
As early as 1938, Kurt Alder and co-workers reported Diels-Alder adducts from the isomeric 2-sulfolene with 1,3-butadiene and 2-sulfolene with cyclopentadiene . [ 22 ]
The base-catalyzed reaction of 3-sulfolene with carbon dioxide at 3 bar pressure produces 3-sulfolene-3-carboxylic acid in 45% yield. [ 23 ]
With diazomethane , 3-sulfolene forms in a 1,3-dipolar cycloadduct: [ 24 ]
In 1935, H. Staudinger and co-workers found that the reaction of butadiene and SO 2 at room temperature gives a second product in addition to 3-sulfolene. This second product is an amorphous solid polymer. By free-radical polymerization of 3-sulfolene in peroxide-containing diethyl ether, up to 50% insoluble high-molecular-weight poly-sulfolene was obtained. The polymer resists degradation by sulfuric and nitric acids. [ 8 ]
In subsequent investigations, polymerization of 3-sulfolene was initiated above 100 °C with the radical initiator azobis(isobutyronitrile) (AIBN). [ 25 ] 3-sulfolene does not copolymerize with vinyl compounds , however. On the other hand, 2-sulfolene does not homopolymerize , but forms copolymers with vinyl compounds, e.g. acrylonitrile and vinyl acetate .
The reversibility of the interconversion of 3-sulfolene with buta-1,3-diene and sulfur dioxide suggests the use of sulfolene as a recyclable aprotic dipolar solvent, in replacement for dimethyl sulfoxide (DMSO), which is often used but difficult to separate and poorly reusable. [ 26 ] As a model reaction, the reaction of benzyl azide with 4-toluenesulfonic acid cyanide forming 1-benzyl-5-(4-toluenesulfonyl)tetrazole was investigated. The formation of the tetrazole can also be carried out as a one-pot reaction without the isolation of the benzyl azide with 72% overall yield.
After the reaction, the solvent 3-sulfolene is decomposed at 135 °C and the volatile butadiene (b.p. −4.4 °C) and sulfur dioxide (b.p. −10.1 °C) are deposited in a cooling trap at −76 °C charged with excess sulfur dioxide. After the addition of hydroquinone as polymerization inhibition, 3-sulfoles is formed again quantitatively upon heating to room temperature. It appears questionable though, if 3-sulfolene with a useful liquid phase range of only 64 to a maximum of about 100 °C can be used as DMSO substitutes (easy handling, low cost, environmental compatibility) in industrial practice.
Aside from its synthetic versatility (see above), sulfolene is used as an additive in electrochemical fluorination . It can increase the yield of perfluorooctanesulfonyl fluoride by about 70%. [ 27 ] It is "highly soluble in anhydrous HF and increases the conductivity of the electrolyte solution". [ 27 ] In this application, it undergoes a ring opening and is fluorinated to form perfluorobutane sulfonyl fluoride . | https://en.wikipedia.org/wiki/Sulfolene |
Sulfolipids are a class of lipids which possess a sulfur -containing functional group . An abundant sulfolipid is sulfoquinovosyl diacylglycerol , which is composed of a glycoside of sulfoquinovose and diacylglycerol . In plants, sulfoquinovosyl diacylglycerides (SQDG) are important members of the sulfur cycle . [ 1 ] Other important sulfolipids include sulfatide and seminolipid , each of which are sulfated glycolipids. Sulfolipids have been implicated in the functions of two of the core components of the photosynthetic electron transport chain and while not necessarily essential, might have a protective function when the photosynthetic apparatus is under stress.
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfolipid |
In organic chemistry , the sulfonamide functional group (also spelled sulphonamide ) is an organosulfur group with the structure R−S(=O) 2 −NR 2 . It consists of a sulfonyl group ( O=S=O ) connected to an amine group ( −NH 2 ). Relatively speaking this group is unreactive . Because of the rigidity of the functional group, sulfonamides are typically crystalline ; for this reason, the formation of a sulfonamide is a classic method to convert an amine into a crystalline derivative which can be identified by its melting point . Many important drugs contain the sulfonamide group. [ 1 ]
A sulfonamide (compound) is a chemical compound that contains this group. The general formula is R−SO 2 NR'R" or R−S(=O) 2 −NR'R" , where each R is some organic group; for example, "methanesulfonamide" (where R = methane , R' = R" = hydrogen ) is CH 3 SO 2 NH 2 . Any sulfonamide can be considered as derived from a sulfonic acid by replacing a hydroxyl group ( −OH ) with an amine group.
In medicine , the term "sulfonamide" is sometimes used as a synonym for sulfa drug , a derivative or variation of sulfanilamide. The first sulfonamide was discovered in Germany in 1932. [ 2 ]
Sulfonamides can be prepared in the laboratory in many ways. The classic approach entails the reaction of sulfonyl chlorides with an amine . [ citation needed ]
A base such as pyridine is typically added to absorb the HCl that is generated. Illustrative is the synthesis of sulfonylmethylamide. [ 3 ] The reaction of primary and secondary amines with benzenesulfonyl chloride is the basis of the Hinsberg reaction , a method for detecting primary and secondary amines.
Sulfonamides undergo a variety of acid-base reactions. The N-H bond can be deprotonated. The alkylsulfonamides can be deprotonated at carbon. Arylsulfonamides undergo ortho-lithiation . [ 4 ]
Sultams are cyclic sulfonamides. Bioactive sultams include the antiinflammatory ampiroxicam and the anticonvulsant sulthiame . Sultams are prepared analogously to other sulfonamides, allowing for the fact that sulfonic acids are deprotonated by amines. They are often prepared by one-pot oxidation of disulfides or thiols linked to amines. [ 5 ] An alternative synthesis of sultams involves initial preparation of a linear sulfonamide, followed by intramolecular C-C bond formation (i.e. cyclization), a strategy that was used in the synthesis of a sultam-based deep-blue emitter for organic electronics . [ 6 ]
The related sulfinamides (R(S=O)NHR) are amides of sulfinic acids (R(S=O)OH) (see sulfinyl ). Chiral sulfinamides such as tert -butanesulfinamide , p -toluenesulfinamide [ 7 ] [ 8 ] and 2,4,6-trimethylbenzenesulfinamide [ 9 ] are relevant to asymmetric synthesis .
Bis(trifluoromethanesulfonyl)aniline is a source of the triflyl ( CF 3 SO + 2 ) group.
The disulfonimides are of the type R−S(=O) 2 −N(H)−S(=O) 2 −R' with two sulfonyl groups flanking an amine. [ 10 ] As with sulfinamides, this class of compounds is used as catalysts in enantioselective synthesis. [ 10 ] [ 11 ] [ 12 ] | https://en.wikipedia.org/wiki/Sulfonamide |
In organic chemistry , a sulfonanilide group is a functional group found in certain organosulfur compounds . It possesses the chemical structure R−S(=O) 2 −N(−C 6 H 5 )−R' , and consists of a sulfonamide group ( R−S(=O) 2 −NR'R" ) where one of the two nitrogen substituents (R' or R") is a phenyl group ( C 6 H 5 ). It can be viewed as a derivative of aniline ( C 6 H 5 NH 2 ). [ 1 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfonanilide |
In organosulfur chemistry , a sulfonate is a salt , anion or ester of a sulfonic acid . Its formula is R−S(=O) 2 −O − , containing the functional group − S (= O ) 2 −O − , where R is typically an organyl group , amino group or a halogen atom. Sulfonates are the conjugate bases of sulfonic acids. Sulfonates are generally stable in water, non- oxidizing , and colorless. Many useful compounds and even some biochemicals feature sulfonates.
Anions with the general formula R−SO − 3 are called sulfonates. They are the conjugate bases of sulfonic acids with formula R−S(=O) 2 −OH . As sulfonic acids tend to be strong acids , the corresponding sulfonates are weak bases . Due to the stability of sulfonate anions, the cations of sulfonate salts such as scandium triflate have application as Lewis acids .
A classic preparation of sulfonates is the Strecker sulfite alkylation , in which an alkali sulfite salt displaces a halide , typically in the presence of an iodine catalyst: [ 1 ]
An alternative is the condensation of a sulfonyl halide with an alcohol in pyridine: [ 2 ]
Esters with the general formula R 1 SO 2 OR 2 are called sulfonic esters . Individual members of the category are named analogously to how ordinary carboxyl esters are named . For example, if the R 2 group is a methyl group and the R 1 group is a trifluoromethyl group, the resulting compound is methyl trifluoromethanesulfonate .
Sulfonic esters are used as reagents in organic synthesis, chiefly because the RSO 3 − group is a good leaving group , especially when R is electron-withdrawing. Methyl triflate , for example, is a strong methylating reagent.
Sulfonates are commonly used to confer water solubility to protein crosslinkers such as N -hydroxysulfosuccinimide (Sulfo-NHS), BS3 , Sulfo-SMCC, etc.
Cyclic sulfonic esters are called sultones . [ 3 ] Two examples are propane-1,3-sultone and 1,4-butane sultone . Some sultones are short-lived intermediates, used as strong alkylating agents to introduce a negatively charged sulfonate group. In the presence of water, they slowly hydrolyze to the hydroxy sulfonic acids. Sultone oximes are key intermediates in the synthesis of the anti-convulsant drug zonisamide . [ 4 ]
Tisocromide is an example of a sultone. | https://en.wikipedia.org/wiki/Sulfonate |
In organic chemistry , a sulfone is a organosulfur compound containing a sulfonyl ( R−S(=O) 2 −R’ ) functional group attached to two carbon atoms. The central hexavalent sulfur atom is double-bonded to each of two oxygen atoms and has a single bond to each of two carbon atoms, usually in two separate hydrocarbon substituents . [ 1 ]
Sulfones are typically prepared by organic oxidation of thioethers , often referred to as sulfides . Sulfoxides are intermediates in this route. [ 2 ] For example, dimethyl sulfide oxidizes to dimethyl sulfoxide and then to dimethyl sulfone . [ 1 ]
Sulfur dioxide is a convenient and widely used source of the sulfonyl functional group. Specifically, Sulfur dioxide participates in cycloaddition reactions with dienes. [ 3 ] The industrially useful solvent sulfolane is prepared by addition of sulfur dioxide to buta-1,3-diene followed by hydrogenation of the resulting sulfolene. [ 4 ]
Sulfones are prepared under conditions used for Friedel–Crafts reactions using sources of RSO + 2 derived from sulfonyl halides and sulfonic acid anhydrides . Lewis acid catalysts such as AlCl 3 and FeCl 3 are required. [ 5 ] [ 6 ] [ 7 ]
Sulfones have been prepared by nucleophilic displacement of halides by sulfinates : [ 8 ] ArSO 2 Na + Ar ′ Cl ⟶ Ar ( Ar ′ ) SO 2 + NaCl {\displaystyle {\ce {ArSO2Na + Ar'Cl -> Ar(Ar')SO2 + NaCl}}} In general, relatively nonpolar (" soft ") alkylating agents react with sulfinic acids to give sulfones, whereas polarized ("hard") alkylating agents form esters. [ 9 ] Allyl , propargyl , [ 10 ] and benzyl [ 11 ] sulfinates can thermally rearrange to the sulfone, but esters without an activated bond generally do not rearrange so. [ 12 ]
Sulfone is a relatively inert functional group, typically less oxidizing and 4 bel more acidic than sulfoxides. In the Ramberg–Bäcklund reaction and the Julia olefination , sulfones are converted to alkenes by the elimination of sulfur dioxide . [ 13 ] However, sulfones are unstable to bases, eliminating to give an alkene. [ 14 ]
Sulfones can also undergo desulfonylation .
Vinyl sulfones are electrophilic and behave as Michael acceptors .
Sulfolane is used to extract valuable aromatic compounds from petroleum. [ 4 ]
Some polymers containing sulfone groups are useful engineering plastics. They exhibit high strength and resistance to oxidation, corrosion, high temperatures, and creep under stress. For example, some are valuable as replacements for copper in domestic hot water plumbing. [ 15 ] Precursors to such polymers are the sulfones bisphenol S and 4,4′-dichlorodiphenyl sulfone .
Examples of sulfones in pharmacology include dapsone , a drug formerly used as an antibiotic to treat leprosy , dermatitis herpetiformis , tuberculosis , or pneumocystis pneumonia (PCP). Several of its derivatives, such as promin , have similarly been studied or actually been applied in medicine, but in general sulfones are of far less prominence in pharmacology than for example the sulfonamides . [ 17 ] [ 18 ] | https://en.wikipedia.org/wiki/Sulfone |
In organic chemistry , sulfonic acid (or sulphonic acid ) refers to a member of the class of organosulfur compounds with the general formula R−S(=O) 2 −OH , where R is an organic alkyl or aryl group and the S(=O) 2 (OH) group a sulfonyl hydroxide. [ 1 ] As a substituent, it is known as a sulfo group . A sulfonic acid can be thought of as sulfuric acid with one hydroxyl group replaced by an organic substituent . The parent compound (with the organic substituent replaced by hydrogen) is the parent sulfonic acid, HS(=O) 2 (OH) , a tautomer of sulfurous acid , S(=O)(OH) 2 . [ a ] Salts or esters of sulfonic acids are called sulfonates .
Aryl sulfonic acids are produced by the process of sulfonation . Usually the sulfonating agent is sulfur trioxide . A large scale application of this method is the production of alkylbenzenesulfonic acids :
In this reaction, sulfur trioxide is an electrophile and the arene is the nucleophile. The reaction is an example of electrophilic aromatic substitution . [ 1 ] In a related process, carboxylic acids react with sulfur trioxide to give the sulfonic acids. [ 2 ] Direct reaction of alkanes with sulfur trioxide is used for the conversion methane to methanedisulfonic acid .
Alkylsulfonic acids can be prepared by sulfoxidation whereby alkanes are irradiated with a mixture of sulfur dioxide and oxygen . This reaction is employed industrially to produce alkyl sulfonic acids, which are used as surfactants . [ 3 ]
From terminal alkenes, alkane sulfonic acids can be obtained by the addition of bisulfite .
Bisulfite can also be alkylated by alkyl halides : [ 3 ]
Sulfonic acids can be prepared by oxidation of thiols :
This pathway is the basis of the biosynthesis of taurine .
Many sulfonic acids are prepared by hydrolysis of sulfonyl halides and related precursors. Thus, perfluorooctanesulfonic acid is prepared by hydrolysis of the sulfonyl fluoride, which in turn is generated by the electrofluorination of octanesulfonic acid. Similarly the sulfonyl chloride derived from polyethylene is hydrolyzed to the sulfonic acid. These sulfonyl chlorides are produced by free-radical reactions of chlorine, sulfur dioxide, and the hydrocarbons using the Reed reaction .
Vinylsulfonic acid is derived by hydrolysis of carbyl sulfate , ( C 2 H 4 (SO 3 ) 2 ), which in turn is obtained by the addition of sulfur trioxide to ethylene .
Sulfonic acids are strong acids. They are around a million times stronger than the corresponding carboxylic acid. For example, p -Toluenesulfonic acid and methanesulfonic acid have p K a values of −2.8 and −1.9, respectively, while those of benzoic acid and acetic acid are 4.20 and 4.76, respectively. The p K a of methanesulfonic acid has been reported to be as high as −0.6 [ 4 ] or as low as −6.5. [ 5 ] Sulfonic acids are known to react with solid sodium chloride ( salt ) to form the sodium sulfonate and hydrogen chloride. [ 6 ] This observation implies an acidity greater than that of HCl.
Because of their polarity, sulfonic acids tend to be crystalline solids or viscous, high-boiling liquids. [ citation needed ] They are also usually colourless and nonoxidizing, [ 7 ] which makes them suitable for use as acid catalysts in organic reactions. Their polarity, in conjunction with their high acidity, renders short-chain sulfonic acids water-soluble, while longer-chain ones exhibit detergent-like properties. [ 3 ]
The structure of sulfonic acids is illustrated by the prototype, methanesulfonic acid . The sulfonic acid group, RSO 2 OH features a tetrahedral sulfur centre, meaning that sulfur is at the center of four atoms: three oxygens and one carbon. The overall geometry of the sulfur centre is reminiscent of the shape of sulfuric acid . [ 8 ]
Both alkyl and aryl sulfonic acids are known, most large-scale applications are associated with the aromatic derivatives.
Detergents and surfactants are molecules that combine highly nonpolar and highly polar groups. Traditionally, soaps are the popular surfactants, being derived from fatty acids . Since the mid-20th century, the usage of sulfonic acids has surpassed soap in advanced societies. For example, an estimated 2 billion kilograms of alkylbenzenesulfonates are produced annually for diverse purposes. Lignin sulfonates, produced by sulfonation of lignin are components of drilling fluids and additives in certain kinds of concrete . [ 9 ]
Many if not most of the anthraquinone dyes are produced or processed via sulfonation. [ 10 ] Sulfonic acids tend to bind tightly to proteins and carbohydrates . Most "washable" dyes are sulfonic acids (or have the functional sulfonyl group in them) for this reason. p-Cresidinesulfonic acid is used to make food dyes.
Being strong acids, sulfonic acids are also used as catalysts . The simplest examples are methanesulfonic acid , CH 3 SO 2 OH and p -toluenesulfonic acid , which are regularly used in organic chemistry as acids that are lipophilic (soluble in organic solvents). Polymeric sulfonic acids are also useful. Dowex resin are sulfonic acid derivatives of polystyrene and is used as catalysts and for ion exchange ( water softening ). Nafion , a fluorinated polymeric sulfonic acid is a component of proton exchange membranes in fuel cells . [ 11 ]
Sulfa drugs , a class of antibacterials, are produced from sulfonic acids.
In the sulfite process for paper-making, lignin is removed from the lignocellulose by treating wood chips with solutions of sulfite and bisulfite ions. These reagents cleave the bonds between the cellulose and lignin components and especially within the lignin itself. The lignin is converted to lignosulfonates , useful ionomers , which are soluble and can be separated from the cellulose fibers.
The reactivity of the sulfonic acid group is so extensive that it is difficult to summarize. [ 12 ]
When treated with strong base, benzenesulfonic acid derivatives convert to phenols. [ 13 ]
In this case the sulfonate behaves as a pseudohalide leaving group.
Arylsulfonic acids are susceptible to hydrolysis, the reverse of the sulfonation reaction:
Whereas benzenesulfonic acid hydrolyzes above 200 °C, many derivatives are easier to hydrolyze. Thus, heating aryl sulfonic acids in aqueous acid produces the parent arene. This reaction is employed in several scenarios. In some cases the sulfonic acid serves as a water-solubilizing protecting group, as illustrated by the purification of para-xylene via its sulfonic acid derivative. In the synthesis of 2,6-dichlorophenol , phenol is converted to its 4-sulfonic acid derivative, which then selectively chlorinates at the positions flanking the phenol. Hydrolysis releases the sulfonic acid group. [ 14 ]
Sulfonic acids can be converted to esters . This class of organic compounds has the general formula R−SO 2 −OR. Sulfonic esters such as methyl triflate are considered good alkylating agents in organic synthesis . Such sulfonate esters are often prepared by alcoholysis of the sulfonyl chlorides:
Sulfonyl halide groups (R−SO 2 −X) are produced by chlorination of sulfonic acids using thionyl chloride . Sulfonyl fluorides can be produced by treating sulfonic acids with sulfur tetrafluoride : [ 15 ]
Although strong, the (aryl)C−SO 3 − bond can be broken by nucleophilic reagents. Of historic and continuing significance is the α-sulfonation of anthroquinone followed by displacement of the sulfonate group by other nucleophiles, which cannot be installed directly. [ 10 ] An early method for producing phenol involved the base hydrolysis of sodium benzenesulfonate , which can be generated readily from benzene. [ 16 ]
The conditions for this reaction are harsh, however, requiring 'fused alkali' or molten sodium hydroxide at 350 °C for benzenesulfonic acid itself. [ 17 ] Unlike the mechanism for the fused alkali hydrolysis of chlorobenzene, which proceeds through elimination-addition ( benzyne mechanism), benzenesulfonic acid undergoes the analogous conversion by an S N Ar mechanism, as revealed by a 14 C labeling, despite the lack of stabilizing substituents. [ 18 ] Sulfonic acids with electron-withdrawing groups (e.g., with NO 2 or CN substituents) undergo this transformation much more readily.
Arylsulfonic acids react with two equiv of butyl lithium to give the ortho-lithio derivatives, i.e., ortho-lithiation . These dilithio compounds are poised for reactions with many electrophiles. [ 12 ] | https://en.wikipedia.org/wiki/Sulfonic_acid |
In organosulfur chemistry , a sulfonyl group is either a functional group found primarily in sulfones , or a substituent obtained from a sulfonic acid by the removal of the hydroxyl group, similarly to acyl groups . [ 1 ] : 1470–1476
Sulfonyl groups can be written as having the general formula R−S(=O) 2 −R′ , where there are two double bonds between the sulfur and oxygen . [ 1 ] : 53 [ 2 ]
Sulfonyl groups can be reduced to the sulfide with diisobutylaluminium hydride (DIBALH). Lithium aluminium hydride ( LiAlH 4 ) reduces some but not all sulfones to sulfides. [ 1 ] : 1851
In inorganic chemistry , when the group −S(=O) 2 − is not connected to any carbon atoms, it is referred to as sulfuryl . [ 3 ]
The names of sulfonyl groups typically end in -syl, such as: [ 1 ] : 497 | https://en.wikipedia.org/wiki/Sulfonyl_group |
In chemistry , a sulfonyl halide consists of a sulfonyl ( >S(=O) 2 ) group singly bonded to a halogen atom. They have the general formula RSO 2 X , where X is a halogen. The stability of sulfonyl halides decreases in the order fluorides > chlorides > bromides > iodides , all four types being well known. The sulfonyl chlorides and fluorides are of dominant importance in this series. [ 1 ] [ 2 ]
Sulfonyl halides have tetrahedral sulfur centres attached to two oxygen atoms, an organic radical, and a halide. In a representative example, methanesulfonyl chloride , the S=O, S−C, and S−Cl bond distances are respectively 142.4, 176.3, and 204.6 pm. [ 3 ]
Sulfonic acid chlorides, or sulfonyl chlorides, are a sulfonyl halide with the general formula RSO 2 Cl .
Arylsulfonyl chlorides are made industrially in a two-step, one-pot reaction from an arene (in this case, benzene ) and chlorosulfuric acid : [ 4 ]
The intermediate benzenesulfonic acid can be chlorinated with thionyl chloride as well. Benzenesulfonyl chloride, the most important sulfonyl halide, can also be produced by treating sodium benzenesulfonate with phosphorus pentachlorides . [ 5 ]
Benzenediazonium chloride reacts with sulfur dioxide and copper(I) chloride to give the sulfonyl chloride:
For alkylsulfonyl chlorides, one synthetic procedure is the Reed reaction :
Sulfonyl chlorides react with water to give the corresponding sulfonic acid :
These compounds react readily with many other nucleophiles as well, most notably alcohols and amines (see Hinsberg reaction ). If the nucleophile is an alcohol, the product is a sulfonate ester; if it is an amine, the product is a sulfonamide : [ citation needed ]
However, sulfonyl chlorides also react frequently as a source of RSO − 2 and Cl + . [ 6 ] For example benzenesulfonyl chloride chlorinates ketene acetals [ 7 ] and mesyl chloride chlorinates para -xylene under Friedel-Crafts conditions. [ 8 ] Using sodium sulfite as the nucleophilic reagent, p-toluenesulfonyl chloride is converted to its sulfinate salt, CH 3 C 6 H 4 SO 2 Na . [ 9 ] Chlorosulfonated alkanes are susceptible to crosslinking via reactions with various nucleophiles. [ 10 ]
Sulfonyl chlorides readily undergo Friedel–Crafts reactions with arenes giving sulfones , for example: [ citation needed ] [ dubious – discuss ]
A readily available arylsulfonyl chloride source is tosyl chloride . [ 11 ] The desulfonation of arylsulfonyl chlorides provides a route to aryl chlorides:
1,2,4-Trichlorobenzene is made industrially in this way.
Treatment of alkanesulfonyl chlorides having α-hydrogens with amine bases can give sulfenes , highly unstable species that can be trapped:
Reduction with tetrathiotungstate ions ( WS 2− 4 ) induces dimerization to the disulfide . [ 12 ]
Chlorosulfonated polyethylene (CSPE) is produced industrially by chlorosulfonation of polyethylene. CSPE is noted for its toughness, hence its use for roofing shingles. [ 10 ]
An industrially important derivative is benzenesulfonyl chloride . In the laboratory, useful reagents include tosyl chloride , brosyl chloride, nosyl chloride and mesyl chloride.
Sulfonyl fluorides have the general formula RSO 2 F. They can be produced by treating sulfonic acids with sulfur tetrafluoride : [ 13 ]
Perfluorooctanesulfonyl derivatives, such as PFOS , are produced from their sulfonyl fluoride, which are produced by electrofluorination [ 14 ]
In the molecular biology, sulfonyl fluorides are used to label proteins. They specifically react with serine , threonine , tyrosine , lysine , cysteine , and histidine residues. The fluorides are more resistant than the corresponding chlorides and are therefore better suited to this task. [ 15 ]
Some sulfonyl fluorides can also be used as deoxyfluorinating reagents, such as 2-pyridinesulfonyl fluoride (PyFluor) and N -tosyl-4-chlorobenzenesulfonimidoyl fluoride (SulfoxFluor). [ 16 ] [ 17 ]
Sulfonyl bromides have the general formula RSO 2 Br. In contrast to sulfonyl chlorides, sulfonyl bromides readily undergo light-induced homolysis affording sulfonyl radicals, which can add to alkenes , as illustrated by the use of bromomethanesulfonyl bromide, BrCH 2 SO 2 Br in Ramberg–Bäcklund reaction syntheses. [ 18 ] [ 19 ]
Sulfonyl iodides, having the general formula RSO 2 I, are quite light-sensitive. Methanesulfonyl iodide evolves iodine in vacuum and branched-alkyl sulfonyl iodides are worse. [ 20 ] Perfluoroalkanesulfonyl iodides, prepared by reaction between silver perfluoroalkanesulfinates and iodine in dichloromethane at −30 °C, react with alkenes to form the normal adducts, RFSO 2 CH 2 CHIR and the adducts resulting from loss of SO 2 , RFCH 2 CHIR. [ 21 ]
Arenesulfonyl iodides, prepared from reaction of arenesulfinates or arenehydrazides with iodine, are much more stable [ 20 ] and can initiate the synthesis of poly(methyl methacrylate) containing C–I, C–Br and C–Cl chain ends. [ 22 ] Their reduction with silver gives the disulfone: [ 20 ]
In the episode "Encyclopedia Galactica" of his TV series Cosmos: A Personal Voyage , Carl Sagan speculates that some intelligent extraterrestrial beings might have a genetic code based on polyaromatic sulfonyl halides instead of DNA . | https://en.wikipedia.org/wiki/Sulfonyl_halide |
In biochemistry , sulfotransferases ( SULTs ) are transferase enzymes that catalyze the transfer of a sulfo group ( R−SO − 3 ) from a donor molecule to an acceptor alcohol ( R−OH ) or amine ( R−NH 2 ). [ 1 ] The most common sulfo group donor is 3'-phosphoadenosine-5'-phosphosulfate (PAPS). In the case of alcohol as acceptor, the product is a sulfate ( R−OSO − 3 ):
whereas an amine leads to a sulfamate ( R−NH−SO − 3 ):
Both reactive groups for a sulfonation via sulfotransferases may be part of a protein , lipid , carbohydrate or steroid . [ 2 ]
The following are examples of sulfotransferases:
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfotransferase |
in chemistry , sulfoxidation refers to two distinct reactions.
In one meaning, sulfoxidation refers to the reaction of alkanes with a mixture of sulfur dioxide and oxygen . This reaction is employed industrially to produce alkyl sulfonic acids , which are used as surfactants . The reaction requires UV-radiation . [ 1 ]
The reaction favors secondary positions in accord with its free-radical mechanism. Mixtures are produced. Semiconductor-sensitized variants have been reported. [ 2 ]
Sulfoxidation can also refer to the oxidation of a thioether to a sulfoxide .
A typical source of oxygen is hydrogen peroxide . [ 3 ] | https://en.wikipedia.org/wiki/Sulfoxidation |
In organic chemistry , a sulfoxide , also called a sulphoxide , is an organosulfur compound containing a sulfinyl ( >SO ) functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides . Examples of important sulfoxides are alliin , a precursor to the compound that gives freshly crushed garlic its aroma, and dimethyl sulfoxide (DMSO), a common solvent . [ 1 ]
Sulfoxides feature relatively short S–O distances. In DMSO, the S–O distance is 1.531 Å. The sulfur center is pyramidal; the sum of the angles at sulfur is about 306°. [ 3 ] Sulfoxides are generally represented with the structural formula R−S(=O)−R', where R and R' are organic groups. The bond between the sulfur and oxygen atoms is intermediate of a dative bond and a polarized double bond . [ 4 ] The double-bond resonance form implies 10 electrons around sulfur (10-S-3 in N-X-L notation ). The double-bond character of the S−O bond may be accounted for by donation of electron density into C−S antibonding orbitals ("no-bond" resonance forms in valence-bond language). Nevertheless, due to its simplicity and lack of ambiguity, the IUPAC recommends use of the expanded octet double-bond structure to depict sulfoxides, rather than the dipolar structure or structures that invoke "no-bond" resonance contributors. [ 5 ] The S–O interaction has an electrostatic aspect, resulting in significant dipolar character, with negative charge centered on oxygen.
A lone pair of electrons resides on the sulfur atom, giving it tetrahedral electron-pair geometry and trigonal pyramidal shape (steric number 4 with one lone pair; see VSEPR theory ). When the two organic residues are dissimilar, the sulfur atom is a chiral center , for example, in methyl phenyl sulfoxide . The energy barrier required to invert this stereocenter is sufficiently high that sulfoxides are optically stable near room temperature. That is, the rate of racemization is slow at room temperature. The enthalpy of activation for racemization is in the range 35 - 42 kcal/mol and the corresponding entropy of activation is -8 - +4 cal/mol-K. The barriers are lower for allylic and benzylic substituents. [ 6 ]
Sulfoxides are typically prepared by oxidation of sulfides , sometimes referred to as sulfoxidation . [ 7 ] hydrogen peroxide is a typical oxidant, but periodate has also been used. [ 8 ] In these oxidations, care is required to avoid over oxidation to form the sulfone . For example, dimethyl sulfide is oxidized to dimethyl sulfoxide and then further to dimethyl sulfone . Unsymmetrical sulfides are prochiral , thus their oxidation gives chiral sulfoxides. This process can be performed enantioselectively. [ 9 ] [ 10 ]
Symmetrical sulfoxides can be formed from a diorganylzinc compound and liquid sulfur dioxide . [ 11 ]
In addition to the oxidation routes, di aryl sulfoxides can be prepared by two Friedel–Crafts arylations of sulfur dioxide using an acid catalyst:
Both aryl sulfinyl chlorides and diaryl sulfoxides can be also prepared from arenes through reaction with thionyl chloride in the presence of Lewis acid catalysts such as BiCl 3 , Bi(OTf) 3 , LiClO 4 , or NaClO 4 . [ 12 ] [ 13 ]
Sulfoxides undergo deoxygenation to give sulfides. Typically metal complexes are used to catalyze the reaction, using hydrosilanes as the stoichiometric reductant. [ 14 ] The deoxygenation of dimethylsulfoxide is catalyzed by DMSO reductase , a molybdoenzyme: [ 15 ]
The α-CH groups of alkyl sulfoxides are susceptible to deprotonation by strong bases, such as sodium hydride : [ 16 ]
In the Pummerer rearrangement , alkyl sulfoxides react with acetic anhydride to give migration of the oxygen from sulfur to the adjacent carbon as an acetate ester. The first step of the reaction sequence involves the sulfoxide oxygen acting as a nucleophile :
Sulfoxide undergo thermal elimination via an E i mechanism to yield vinyl alkenes and sulfenic acids . [ 17 ] [ 18 ]
The acids are powerful antioxidants , but lack long-term stability. [ 19 ] Some parent sulfoxides are therefore marketed as antioxidant polymer stabilisers . [ 20 ] Structures based on thiodipropionate esters are popular. [ 21 ] The reverse reaction is possible.
Sulfoxides, especially DMSO, form coordination complexes with transition metals. Depending on the hard-soft properties of the metal, the sulfoxide binds through either the sulfur or the oxygen atom. The latter is particularly common. [ 22 ]
DMSO is a widely used solvent.
The sulfoxide functional group occurs in several drugs. Notable is esomeprazole , the optically pure form of the proton-pump inhibitor omeprazole . Another commercially important sulfoxides include armodafinil .
Methionine sulfoxide forms from the amino acid methionine and its accumulation is associated with aging. The enzyme DMSO reductase catalyzes the interconversion of DMSO and dimethylsulfide.
Naturally-occurring chiral sulfoxides include alliin and ajoene . | https://en.wikipedia.org/wiki/Sulfoxide |
Sulfur assimilation is the process by which living organisms incorporate sulfur into their biological molecules. [ 1 ] In plants, sulfate is absorbed by the roots and then transported to the chloroplasts by the transipration stream where the sulfur are reduced to sulfide with the help of a series of enzymatic reactions . Furthermore, the reduced sulfur is incorporated into cysteine , [ 2 ] an amino acid that is a precursor to many other sulfur-containing compounds. In animals, sulfur assimilation occurs primarily through the diet, as animals cannot produce sulfur-containing compounds directly. Sulfur is incorporated into amino acids such as cysteine and methionine , which are used to build proteins and other important molecules. [ 2 ]
Sulfate uptake occurs in roots. [ 3 ] The maximal sulfate uptake rate is generally already reached at sulfate levels of 0.1 mM and lower. The uptake of sulfate by the roots and its transport to the shoot appears to be one of the primary regulatory sites of sulfur assimilation. [ 3 ]
Sulfate is actively taken up across the plasma membrane of the root cells, subsequently loaded into the xylem vessels and transported to the shoot by the transpiration stream. [ 4 ] The uptake and transport of sulfate is ATP-dependent. [ 5 ] Sulfate is reduced in the chloroplasts. Sulfate in plant tissue is predominantly present in the vacuole , since the concentration of sulfate in the cytoplasm is kept rather constant.
Distinct sulfate transporter proteins mediate the uptake, transport and subcellular distribution of sulfate. [ 6 ] The sulfate transporters gene family has been classified in up to 5 different groups according to their cellular and sub-cellular gene expression , and possible functioning. [ 7 ] Each group of transporter proteins may be expressed exclusively in the roots or shoots of the plant, or both.
Regulation and expression of the majority of sulfate transporters are controlled by the sulfur nutritional status of the plants. [ 8 ] Upon sulfate deprivation, the rapid decrease in root sulfate is regularly accompanied by a strongly enhanced expression of most sulfate transporter genes (up to 100-fold) accompanied by enhanced sulfate uptake capacity. It is not yet fully understood whether sulfate and other metabolic products of sulfur assimilation ( O-acetylserine , cysteine , glutathione ) act as signals in the regulation of sulfate uptake and transport, or in the expression of the sulfate transporters involved.
Sulfate reduction predominantly takes place in the leaf chloroplasts . Here, the reduction of sulfate to sulfide occurs in three steps beginning with its conversion to adenosine 5'-phosphosulfate (APS). This first step is catalyzed by ATP sulfurylase. The affinity of this enzyme for sulfate is low (Km approximately 1 mM), and the in situ sulfate concentration in the chloroplast is most likely one of the limiting/regulatory steps in sulfur reduction. Subsequently, APS is reduced to sulfite, catalyzed by APS reductase. Glutathione is the propsed reductant .
The latter reaction is assumed to be one of the primary regulation points in the sulfate reduction, since the activity of APS reductase is the lowest of the enzymes of the sulfate reduction pathway and it has a fast turnover rate. Sulfite is with high affinity reduced by sulfite reductase to sulfide with ferredoxin as a reductant. The remaining sulfate in plant tissue is transferred into the vacuole . The remobilization and redistribution of the vacuolar sulfate reserves appear to be rather slow and sulfur-deficient plants may still contain detectable levels of sulfate. [ 9 ]
Sulfide is incorporated into cysteine , catalyzed by O-acetylserine (thiol)lyase, with O-acetylserine as substrate. The synthesis of O-acetylserine is catalyzed by serine acetyltransferase and together with O-acetylserine (thiol)lyase it is associated as enzyme complex named cysteine synthase .
The formation of cysteine is the direct coupling step between sulfur ( sulfur metabolism ) and nitrogen assimilation in plants. This differs from the process in yeast, where sulfide must be incorporated first in homocysteine then converted in two steps to cysteine.
Cysteine is sulfur donor for the synthesis of methionine , the major other sulfur-containing amino acid present in plants. This happens through the transsulfuration pathway and the methylation of homocysteine .
Both cysteine and methionine are sulfur-containing amino acids and are of great significance in the structure, conformation and function of proteins and enzymes , but high levels of these amino acids may also be present in seed storage proteins. The thiol groups of the cysteine residues in proteins can be oxidized resulting in disulfide bridges with other cysteine side chains (and form cystine ) and/or linkage of polypeptides .
Disulfide bridges ( disulfide bonds ) make an important contribution to the structure of proteins. The thiol groups are also of great importance in substrate binding of enzymes, in metal-sulfur clusters in proteins (e.g. ferredoxins ) and in regulatory proteins (e.g. thioredoxins ).
Glutathione or its homologues, e.g. homoglutathione in Fabaceae ; hydroxymethylglutathione in Poaceae are the major water-soluble non- protein thiol compounds present in plant tissue and account for 1-2% of the total sulfur. [ 10 ] The content of glutathione in plant tissue ranges from 0.1 – 3 mM. Cysteine is the direct precursor for the synthesis of glutathione (and its homologues). First, γ-glutamylcysteine is synthesized from cysteine and glutamate catalyzed by gamma-glutamylcysteine synthetase . Second, glutathione is synthesized from γ-glutamylcysteine and glycine (in glutathione homologues, β-alanine or serine ) catalyzed by glutathione synthetase. Both steps of the synthesis of glutathione are ATP dependent reactions. [ 11 ] Glutathione is maintained in the reduced form by an NADPH -dependent glutathione reductase and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) generally exceeds a value of 7. [ 12 ] Glutathione fulfils various roles in plant functioning. In sulfur metabolism it functions as reductant in the reduction of APS to sulfite. It is also the major transport form of reduced sulfur in plants. Roots likely largely depend for their reduced sulfur supply on shoot/root transfer of glutathione via the phloem , since the reduction of sulfur occurs predominantly in the chloroplast. Glutathione is directly involved in the reduction and assimilation of selenite into selenocysteine . Furthermore, glutathione is of great significance in the protection of plants against oxidative and environmental stress and it depresses/scavenges the formation of toxic reactive oxygen species , e.g. superoxide , hydrogen peroxide and lipid hydroperoxides . Glutathione functions as reductant in the enzymatic detoxification of reactive oxygen species in the glutathione- ascorbate cycle and as thiol buffer in the protection of proteins via direct reaction with reactive oxygen species or by the formation of mixed disulfides. The potential of glutathione as protectant is related to the pool size of glutathione, its redox state (GSH/GSSG ratio) and the activity of glutathione reductase . Glutathione is the precursor for the synthesis of phytochelatins, which are synthesized enzymatically by a constitutive phytochelatin synthase. The number of γ-glutamyl-cysteine residues in the phytochelatins may range from 2 – 5, sometimes up to 11. Despite the fact that the phytochelatins form complexes which a few heavy metals, viz. cadmium , it is assumed that these compounds play a role in heavy metal homeostasis and detoxification by buffering of the cytoplasmatic concentration of essential heavy metals. Glutathione is also involved in the detoxification of xenobiotics , compounds without direct nutritional value or significance in metabolism, which at too high levels may negatively affect plant functioning. Xenobiotics may be detoxified in conjugation reactions with glutathione catalyzed by glutathione S-transferase , which activity is constitutive; different xenobiotics may induce distinct isoforms of the enzyme. Glutathione S-transferases have great significance in herbicide detoxification and tolerance in agriculture and their induction by herbicide antidotes (' safeners ') is the decisive step for the induction of herbicide tolerance in many crop plants. Under natural conditions glutathione S-transferases are assumed to have significance in the detoxification of lipid hydroperoxides , in the conjugation of endogenous metabolites, hormones and DNA degradation products, and in the transport of flavonoids .
Sulfolipids are sulfur containing lipids. Sulfoquinovosyl diacylglycerols are the predominant sulfolipids present in plants. In leaves its content comprises up to 3 - 6% of the total sulfur present. [ 13 ] This sulfolipid is present in plastid membranes and likely is involved in chloroplast functioning. The route of biosynthesis and physiological function of sulfoquinovosyl diacylglycerol is still under investigation. From recent studies it is evident that sulfite it the likely sulfur precursor for the formation of the sulfoquinovose group of this lipid.
Brassica species contain glucosinolates , which are sulfur-containing secondary compounds . Glucosinolates are composed of a β-thioglucose moiety, a sulfonated oxime and a side chain. The synthesis of glucosinolates starts with the oxidation of the parent amino acid to an aldoxime , followed by the addition of a thiol group (through conjugation with glutathione) to produce thiohydroximate . The transfer of a glucose and a sulfate moiety completes the formation of the glucosinolates.
The physiological significance of glucosinolates is still ambiguous, though they are considered to function as sink compounds in situations of sulfur excess. Upon tissue disruption glucosinolates are enzymatically degraded by myrosinase and may yield a variety of biologically active products such as isothiocyanates , thiocyanates , nitriles and oxazolidine-2-thiones. The glucosinolate-myrosinase system is assumed to play a role in plant- herbivore and plant- pathogen interactions.
Furthermore, glucosinolates are responsible for the flavor properties of Brassicaceae and recently
have received attention in view of their potential anti- carcinogenic properties. Allium species contain γ- glutamylpeptides and alliins (S-alk(en)yl cysteine sulfoxides). The content of these sulfur-containing secondary compounds strongly depends on stage of development of the plant, temperature, water availability and the level of nitrogen and sulfur nutrition. In onion bulbs their content may account for up to 80% of the organic sulfur fraction. [ 14 ] Less is known about the content of secondary sulfur compounds in the seedling stage of the plant.
It is assumed that alliins are predominantly synthesized in the leaves, from where they are subsequently transferred to the attached bulb scale. The biosynthetic pathways of synthesis of γ-glutamylpeptides and alliins are still ambiguous. γ-Glutamylpeptides can be formed from cysteine (via γ-glutamylcysteine or glutathione) and can be metabolized into the corresponding alliins via oxidation and subsequent hydrolyzation by γ-glutamyl transpeptidases .
However, other possible routes of the synthesis of γ-glutamylpeptides and alliins may not be excluded. Alliins and γ-glutamylpeptides are known to have therapeutic utility and might have potential value as phytopharmaceutics. The alliins and their breakdown products (e.g. allicin ) are the flavor precursors for the odor and taste of species. Flavor is only released when plant cells are disrupted and the enzyme alliinase from the vacuole is able to degrade the alliins, yielding a wide variety of volatile and non- volatile sulfur-containing compounds. The physiological function of γ-glutamylpeptides and alliins is rather unclear.
Unlike in plants, animals do not have a pathway for the direct assimilation of inorganic sulfate into organic compounds. In animals, the primary source of sulfur is dietary methionine , an essential amino acid that contains a sulfur atom. Methionine is first converted to S-adenosylmethionine (SAM), a compound that is involved in many important biological processes, including DNA methylation and neurotransmitter synthesis.
SAM can then be used to synthesize other important sulfur-containing compounds such as cysteine , taurine , and glutathione . Cysteine is a precursor for the synthesis of several important proteins and peptides, as well as glutathione, a powerful antioxidant that protects cells from oxidative stress. Taurine is involved in a variety of physiological processes, including osmoregulation , modulation of calcium signaling , and regulation of mitochondrial function.
In bacteria and fungi , the sulfur assimilation pathway is similar to that in plants, where inorganic sulfate is reduced to sulfide, and then incorporated into cysteine and other sulfur-containing compounds.
Bacteria and fungi can absorb inorganic sulfate from the environment through a sulfate transporter, which is regulated by the presence of sulfate in the medium. Once inside the cell, sulfate is activated by ATP sulfurylase to form adenosine 5'-phosphosulfate (APS), which is then reduced to sulfite by APS reductase. Sulfite is further reduced to sulfide by sulfite reductase, which is then incorporated into cysteine by enzyme.
Cysteine, once synthesized, can be used for the biosynthesis of methionine and other important biomolecules. In addition, microorganisms also use sulfur-containing compounds for various other purposes, such as the synthesis of antibiotics .
Sulfur assimilation in microorganisms is regulated by a variety of environmental factors, including the availability of sulfur in the medium and the presence of other nutrients. The activity of key enzymes in the sulfur assimilation pathway is also regulated by feedback inhibition from downstream products, similar to the regulation seen in plants.
Sulfur assimilation is highly regulated and influenced by both external environmental factors and internal metabolic feedback pathways, in order to maintain sulfur homeostasis. Under sulfur-deficient conditions, plants modify their internal pathways to enhance sulfur uptake. In plants, a key regulator is the transcription factor SLIM1 (Sulfur Limitation 1), which functions in activating genes involved in sulfur transport like SULTR1;2 (a high-affinity transporter) and those involved in sulfur assimilation like ATP sulfurylase and APS reductase. [ 15 ] The post-transcriptional regulation of these genes are done via a microRNA called miR395. When sulfur uptake is sufficient and is no longer limited, this microRNA targets the SULTR2;1(a low-affinity transporter) and degrades/inhibits its translation. [ 16 ] Besides the transcriptional regulation of sulfur assimilation, there also lies post-translational mechanisms that control this process. This includes feedback inhibition by the accumulation of end products such as glutathione and cysteine , as well as regulation of the enzyme APS reductase which is activated or inhibited by the redox state of the cell. [ 17 ]
In fungi, specifically the Aspergillus fumigatus , sulfur assimilation is managed by the transcription factor MetR. [ 18 ] This transcription factor functions similarly to SLIM1, in which under sulfur-limiting conditions it activates genes responsible for sulfur uptake. [ 19 ] MetR also plays a key role in protecting the fungus’s virulence against the host-immune system. [ 18 ] Additionally, the regulation of sulfur plays an interconnected role with other nutrient cycles like carbon, nitrogen, and iron. For example, if MetR is impaired, the management of iron homeostasis is at risk. In plants, under sulfur-limiting conditions they optimize nitrogen assimilation to maintain metabolic homeostasis. [ 20 ]
In animals, since sulfur uptake is primarily obtained through the diet in the form of cysteine or methionine, the regulation of sulfur metabolism is done via the transsulfuration pathway . [ 21 ] In this pathway, methionine is converted to homocysteine and then later converted to cysteine via the enzymes Cystathionine Beta-synthase (CBS) and Cystathionine gamma-lyase (CGL). [ 21 ] Cysteine is utilized for glutathione production, and high levels of glutathione feedback negatively to downregulate the enzymes CBS and CGL. [ 22 ]
Regulation of sulfur assimilation is tightly controlled to ensure balanced production of sulfur-compounds like cysteine, methionine, and glutathione. [ 17 ] These are key molecules that play a role in redox balance, and protein synthesis. Sulfur levels are also interconnected with other nutrient cycles to maintain an overall metabolic balance in plants, animals, and fungi. [ 23 ]
The rapid economic growth, industrialization and urbanization are associated with a strong increase in energy demand and emissions of air pollutants including sulfur dioxide (see also acid rain ) and hydrogen sulfide , which may affect plant metabolism . Sulfur gases are potentially phytotoxic , however, they may also be metabolized and used as sulfur source and even be beneficial if the sulfur fertilization of the roots is not sufficient.
Plant shoots form a sink for atmospheric sulfur gases, which can directly be taken up by the foliage (dry deposition). The foliar uptake of sulfur dioxide is generally directly dependent on the degree of opening of the stomates , since the internal resistance to this gas is low. Sulfite is highly soluble in the apoplastic water of the mesophyll , where it dissociates under formation of bisulfite and sulfite .
Sulfite may directly enter the sulfur reduction pathway and be reduced to sulfide , incorporated into cysteine, and subsequently into other sulfur compounds. Sulfite may also be oxidized to sulfate , extra- and intracellularly by peroxidases or non-enzymatically catalyzed by metal ions or superoxide radicals and subsequently reduced and assimilated again. Excessive sulfate is transferred into the vacuole; enhanced foliar sulfate levels are characteristic for exposed plants.
The foliar uptake of hydrogen sulfide appears to be directly dependent on the rate of its metabolism into cysteine and subsequently into other sulfur compounds. There is strong evidence that O-acetyl-serine (thiol)lyase is directly responsible for the active fixation of atmospheric hydrogen sulfide by plants.
Plants are able to transfer from sulfate to foliar absorbed atmospheric sulfur as sulfur source and levels of 60 ppb or higher appear to be sufficient to cover the sulfur requirement of plants. There is an interaction between atmospheric and pedospheric sulfur utilization. For instance, hydrogen sulfide exposure may result in a decreased activity of APS reductase and a depressed sulfate uptake. | https://en.wikipedia.org/wiki/Sulfur_assimilation |
Sulfur concrete , sometimes named thioconcrete or sulfurcrete , is a composite construction material, composed mainly of sulfur and aggregate (generally a coarse aggregate made of gravel or crushed rocks and a fine aggregate such as sand ). Cement and water, important compounds in normal concrete , are not part of sulfur concrete. The concrete is heated above the melting point of elemental sulfur (115.21 °C (239.38 °F)) at ca. 140 °C (284 °F) in a ratio of between 12% and 25% sulfur, the rest being aggregate . [ 1 ]
Low-volatility (i.e., with a high boiling point ) organic admixtures (sulfur modifiers), such as dicyclopentadiene (DCPD), styrene , turpentine , or furfural , are also added to the molten sulfur to inhibit its crystallization and to stabilize its polymeric structure after solidification. [ 2 ]
In the absence of modifying agents, elemental sulfur crystallizes in its most stable allotropic ( polymorphic ) crystal phase at room temperature. With the addition of some modifying agents, elemental sulfur forms a copolymer (linear chains with styrene, cross-linking structure with DCPD [ 3 ] ) and remains plastic. [ 2 ] [ a ]
Sulfur concrete then achieves high mechanical strength within ~ 24 hours of cooling. It does not require a prolonged curing period like conventional cement concrete , which after setting (a few hours) must still harden to reach its expected nominal strength at 28 days. The rate of hardening of sulfur concrete depends on its cooling rate and also on the nature and concentration of modifying agents (cross-linking process). [ 2 ] Its hardening is governed by the fairly rapid liquid/solid state change and associated phase transition processes (the added modifiers maintaining the plastic state while avoiding its recrystallization). It is a thermoplastic material whose physical state depends on temperature. It can be recycled and reshaped in a reversible way, simply by remelting it at high temperature.
A sulfur concrete patent was already registered in 1900 by McKay. [ 4 ] [ 5 ] Sulfur concrete was studied in the 1920s and 1930s and received renewed interest in the 1970s because of the accumulation of large quantities of sulfur as a by-product of the hydrodesulfurization process of oil and gas production and its low cost. [ 5 ] [ 6 ] [ 7 ]
Sulfur concrete has a low porosity and is a poorly permeable material. Its low hydraulic conductivity slows down water ingress in its low porosity matrix and so decreases the transport of harmful chemical species, such as chloride ( pitting corrosion ), towards the steel reinforcements (physical protection of steel as long as no microcracks develop in the sulfur concrete matrix). It is resistant to some compounds like acids which attack normal concrete.
Beside its impermeability , Loov et al. (1974) also consider amongst the beneficial characteristics of sulfur concrete its low thermal and electrical conductivities . Sulfur concrete does not cause adverse reaction with glass (no alkali–silica reaction ), does not produce efflorescences , and also presents a smooth surface finish. They also mention amongst its main limitations, its high coefficient of thermal expansion , the possible formation of acid under the action of water and sunlight . It also reacts with copper and produces a smell when melted.
Sulfur concrete was developed and promoted as a building material to get rid of large amounts of stored sulfur produced by hydrodesulfurization of gas and oil ( Claus process ). As of 2011, sulfur concrete has only been used in small quantities when fast curing or acid resistance is necessary. [ 8 ] [ 5 ] The material has been suggested by researchers as a potential building material on Mars , where water and limestone are not easily available, but sulfur is. [ 9 ] [ 10 ] [ 11 ]
More recently, [ when? ] it has been proposed as a near- carbon-neutral construction material. Its waterless and less energy-intensive production (in comparison with ordinary cement and regular concrete) makes it a potential alternative for high- CO 2 -emission portland-cement -based materials. Due to improvements in fabrication techniques, it can be produced in high quality and large quantities. [ citation needed ] Recyclable sulfur concrete sleepers are used in Belgium for the railways infrastructure , and are mass-produced locally. [ 12 ] THIO TUBE is the brand name for certified acid-resistant DWF (dry weather flow) discharge pipes used in Belgium.
Sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) produce hydrogen sulfide ( H 2 S ) and sulfuric acid ( H 2 SO 4 ) respectively. When the sulfur cycle is active in sewers and H 2 S emanations from the effluent waters are oxidized in H 2 SO 4 by atmospheric oxygen at the moist surface of tunnel walls, sulfuric acid can attack the hydrated Portland cement paste of cementitious materials, especially in the non-totally immersed sections of sewers (non-completely water-filled vadose zone ). [ 13 ] It causes extensive damages to masonry mortar and concrete in older sewage infrastructures. [ 14 ] [ 15 ] Sulfur concrete, if proven resistant to long-term chemical and bacterial attacks, could provide an effective and long-lasting solution to this problem. However, since elemental sulfur itself participates in redox reactions used by some autotrophic bacteria to produce the energy they need from the sulfur cycle , elemental sulfur could contribute directly fueling the bacterial activity. [ 16 ] Biofilms adhering to the surface of sewer walls could harbor autotrophic microbial colonies that can degrade sulfur concrete if they are able to use elemental sulfur directly as an electron donor to reduce nitrate (autotrophic denitrification process), [ 17 ] [ 18 ] [ 19 ] [ 20 ] or sulfate , present in wastewater . Studies and real life tests have shown that only bio sulfur is accessible to these bacteria.
The very long-term durability of sulfur concrete also depends on physicochemical factors such as those controlling, among other things, the diffusion of modifying agents (if not completely chemically fixed) out of the elemental sulfur matrix and their leaching by water. The resulting changes in the physical properties of the material will determine its long-term mechanical strength and chemical behavior. The biodegradability of the organic admixtures (sulfur modifiers), or their resistance to microbial activity , and their possible biocidal properties (which may protect the sulfur concrete from microbial attack) are important aspects in assessing the durability of the material. This could also depend on the progressive recrystallization of elemental sulfur over time, or on the rate of plastic deformation of its structure modified by the different types of organic admixtures.
Swamy and Jurjees (1986) have pointed out the limitations of sulfur concrete. [ 21 ] They questioned the stability and the long-term durability of sulfur concrete beams with steel reinforcement, especially for sulfur concrete modified with dicyclopentadiene and dipentene. Even when dry, modified concrete beams show strength loss with ageing. Ageing in a wet environment leads to softening of sulfur concrete and loss of strength. It causes structural damages in sulfur concrete beams leading to shear failures and cracking. Swamy and Jurjees (1986) also observed severe corrosion of steel reinforcements. [ 21 ] They concluded that the stability of reinforced sulfur concrete beams can only be guaranteed when they are unmodified and kept dry. [ 21 ]
Being based on the use of elemental sulfur (S 0 , or S 8 ) as a binder, sulfur concrete applications are expected to suffer the same limitations as those of elemental sulfur which is not a really inert material, can burn, and is also known to be a potent corrosive agent . [ 22 ] [ 23 ] [ 24 ]
In case of fire, this concrete is flammable and will generate toxic and corrosive fumes of sulfur dioxide ( SO 2 ), and sulfur trioxide ( SO 3 ), ultimately leading to the formation of sulfuric acid ( H 2 SO 4 ).
According to Maldonado-Zagal and Boden (1982), [ 23 ] the hydrolysis of elemental sulfur (octa-atomic sulphur, S 8 ) in water is driven by its disproportionation into oxidised and reduced forms in the ratio H 2 S / H 2 SO 4 = 3/1. Hydrogen sulfide ( H 2 S ) causes sulfide stress cracking (SSC) and in contact with air is also easily oxidized into thiosulfate ( S 2 O 2− 3 ), responsible for pitting corrosion .
Like pyrite ( FeS 2 , iron(II) disulfide ), in the presence of moisture, sulfur is also sensitive to oxidation by atmospheric oxygen and could ultimately produce sulfuric acid ( H 2 SO 4 ), sulfate ( SO 2− 4 ), and intermediate chemical species such as thiosulfates ( S 2 O 2− 3 ), or tetrathionates ( S 4 O 2− 6 ), which are also strongly corrosive substances ( pitting corrosion ), as all the reduced species of sulfur. [ 22 ] [ 25 ] [ 26 ] Therefore, long-term corrosion problems of steels and other metals ( aluminium , copper ...) need to be anticipated, and correctly addressed, before selecting sulfur concrete for specific applications.
The formation of sulfuric acid could also attack and dissolve limestone ( CaCO 3 ) and concrete structures while also producing expansive gypsum ( CaSO 4 ·2H 2 O ), aggravating the formation of cracks and fissures in these materials.
If the local physico-chemical conditions are conducive (sufficient space and water available for their growth), sulfur-oxidizing bacteria ( microbial oxidation of sulfur ) could also thrive at the expense of concrete sulfur and contribute to aggravate potential corrosion problems. [ 27 ]
The degradation rate of elemental sulfur depends on its specific surface area . The degradation reactions are the fastest with sulfur dust , or crushed powder of sulfur, while intact compact blocks of sulfur concrete are expected to react more slowly. The service life of components made of sulfur concrete depends thus on the degradation kinetics of elemental sulfur exposed to atmospheric oxygen, moisture and microorganisms , on the density/concentration of microcracks in the material, and on the accessibility of the carbon-steel surface to the corrosive degradation products present in aqueous solution in case of macrocracks or technical voids exposed to water ingress. All these factors need to be taken into account when designing structures, systems and components (SSC) based on sulfur concrete, certainly if they are reinforced, or pre-stressed, with steel elements ( rebar or tensioning cables respectively).
While the process of elemental sulfur oxidation will also lower the pH value, aggravating carbon steel corrosion, in contrast to ordinary Portland cement and classical concrete , fresh sulfur concrete does not contain alkali hydroxides (KOH, NaOH), nor calcium hydroxide ( Ca(OH) 2 ), and therefore does not provide any buffering capacity to maintain a high pH passivating the steel surface. In other words, intact sulfur concrete does not chemically protect steel reinforcement bars (rebar) against corrosion. The corrosion of steel elements embedded into sulfur concrete will thus depends on water ingress through cracks and to their exposure to aggressive chemical species of sulfur dissolved in the seeping water. The presence of microorganisms fuelled by elemental sulfur could also play a role and accelerate the corrosion rate. | https://en.wikipedia.org/wiki/Sulfur_concrete |
The sulfur cycle is a biogeochemical cycle in which the sulfur moves between rocks, waterways and living systems. It is important in geology as it affects many minerals and in life because sulfur is an essential element ( CHNOPS ), being a constituent of many proteins and cofactors , and sulfur compounds can be used as oxidants or reductants in microbial respiration. [ 1 ] The global sulfur cycle involves the transformations of sulfur species through different oxidation states, which play an important role in both geological and biological processes.
Steps of the sulfur cycle are:
These are often termed as follows:
Sulfur can be found under several oxidation states in nature, mainly −2, −1, 0, +2 (apparent), +2.5 (apparent), +4, and +6. When two sulfur atoms are present in the same polyatomic oxyanion in an asymmetrical situation, i.e, each bound to different groups as in thiosulfate , the oxidation state calculated from the known oxidation state of accompanying atoms (H = +1, and O = −2) can be an apparent average (+2 as in thiosulfate), and even differ from an entire number (+2.5 as in tetrathionate ). This is the direct consequence of the different valence of each sulfur atoms present in the oxyanion. The most common sulfur species participating to the sulfur cycle are listed hereafter from the most reduced to the most oxidized :
Sulfur is found in oxidation states ranging from +6 in SO 2− 4 to −2 in sulfides . Thus, elemental sulfur can either give or receive electrons depending on its environment. On the anoxic early Earth, most sulfur was present in minerals such as pyrite (FeS 2 ). Over Earth history, the amount of mobile sulfur increased through volcanic activity as well as weathering of the crust in an oxygenated atmosphere. [ 1 ] Earth's main sulfur sink is the oceans SO 2− 4 available as electron acceptor for microorganisms in anoxic waters . [ 3 ]
When SO 2− 4 is assimilated by organisms, it is reduced and converted to organic sulfur, which is an essential component of proteins . However, the biosphere does not act as a major sink for sulfur, instead the majority of sulfur is found in seawater or sedimentary rocks including: pyrite rich shales , evaporite rocks ( anhydrite and baryte ), and calcium and magnesium carbonates (i.e. carbonate-associated sulfate ). The amount of sulfate in the oceans is controlled by three major processes: [ 5 ]
The primary natural source of sulfur to the atmosphere is sea spray or windblown sulfur-rich dust, [ 6 ] neither of which is long lived in the atmosphere. In recent times, the large annual input of sulfur from the burning of coal and other fossil fuels has added a substantial amount of SO 2 which acts as an air pollutant . In the geologic past, igneous intrusions into coal measures have caused large scale burning of these measures, and consequential release of sulfur to the atmosphere. This has led to substantial disruption to the climate system, and is one of the proposed causes of the Permian–Triassic extinction event . [ citation needed ]
Dimethylsulfide [(CH 3 ) 2 S or DMS] is produced by the decomposition of dimethylsulfoniopropionate (DMSP) from dying phytoplankton cells in the ocean's photic zone , and is the major biogenic gas emitted from the sea, where it is responsible for the distinctive “smell of the sea” along coastlines. [ 1 ] DMS is the largest natural source of sulfur gas, but still only has a residence time of about one day in the atmosphere and a majority of it is redeposited in the oceans rather than making it to land. However, it is a significant factor in the climate system, as it is involved in the formation of clouds.
Through the dissimilatory sulfate reduction pathway, sulfate can be reduced either bacterially (bacterial sulfate reduction) or inorganically (thermochemical sulfate reduction). This pathway involves the reduction of sulfate by organic compounds to produce hydrogen sulfide, which occurs in both processes.
The main products and reactants of bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR) are very similar. For both, various organic compounds and dissolved sulfate are the reactants, and the products or by-products are as follows: H 2 S , CO 2 , carbonates , elemental sulfur and metal sulfides. [ 7 ] However, the reactive organic compounds differ for BSR and TSR because of the mutually exclusive temperature regimes. Organic acids are the main organic reactants for BSR and branched/ n - alkanes are the main organic reactants for TSR. The inorganic reaction products in BSR and TSR are H 2 S (HS − ) and HCO − 3 (CO 2 ). [ 8 ]
These processes occur because there are two very different thermal regimes in which sulfate is reduced, particularly in low-temperature and high-temperature environments. [ 7 ] BSR usually occurs at lower temperatures from 0−80 °C, while TSR happens at much higher temperatures around 100–140 °C. [ 8 ] Temperatures for TSR are not as well defined; the lowest confirmed temperature is 127 °C and the highest temperatures occur in settings around 160−180 °C. [ 8 ] These two different regimes appear because at higher temperatures most sulfate-reducing microbes can no longer metabolize due to the denaturation of proteins or deactivation of enzymes, [ 9 ] so TSR takes over. However, in hot sediments around hydrothermal vents BSR can happen at temperatures up to 110 °C. [ 10 ]
BSR and TSR occur at different depths. BSR takes place in low-temperature environments, which are shallower settings such as oil and gas fields. BSR can also take place in modern marine sedimentary environments such as stratified inland seas, continental shelves, organic-rich deltas, and hydrothermal sediments which have intense microbial sulfate reduction because of the high concentration of dissolved sulfate in the seawater. [ 11 ] Additionally, the high amounts of hydrogen sulfide found in oil and gas fields is thought to arise from the oxidation of petroleum hydrocarbons by sulfate. [ 12 ] Such reactions are known to occur by microbial processes but it is generally accepted that TSR is responsible for the bulk of these reactions, especially in deep or hot reservoirs. [ 13 ] Thus, TSR occurs in deep reservoirs where the temperatures are much higher. BSR is geologically instantaneous in most geologic settings, while TSR occurs at rates in the order of hundreds of thousands of years. [ 14 ] [ 7 ] Although much slower than BSR, even TSR appears to be a geologically fairly fast process.
BSR in shallow environments and TSR in deep reservoirs are key processes in the oceanic sulfur cycle. [ 15 ] [ 7 ] Approximately, 10% (of the total gas) of H 2 S is produced in BSR settings, whereas 90% of the H 2 S is produced in TSR settings. [ 8 ] If there is more than a few percent of H 2 S in any deep reservoir, then it is assumed that TSR has taken over. This is due to the fact that thermal cracking of hydrocarbons doesn't provide more than 3% of H 2 S. [ 7 ] The amount of H 2 S is affected by several factors such as, the availability of organic reactants and sulfate and the presence/availability of base and transition metals. [ 16 ]
Sulfide oxidation is performed by both bacteria and archaea in a variety of environmental conditions. Aerobic sulfide oxidation is usually performed by autotrophs that use sulfide or elemental sulfur to fix carbon dioxide. The oxidation pathway includes the formation of various intermediate sulfur species, including elemental sulfur and thiosulfate. Under low oxygen concentrations, microbes will oxidize to elemental sulfur. [ 17 ] This elemental sulfur accumulates as sulfur globules, intracellularly or extracellularly, to be consumed under low sulfur concentrations. [ 18 ] To ameliorate low oxidant concentrations (that is, to find an electron sink), sulfur oxidizers like cable bacteria form long chains that span the length between oxic and sulfidic zones of the coastal sediments. The bacteria present in the sulfide rich zones oxidize the sulfide and transport the electrons to the bacteria present in the oxygen rich zone through multiple periplasmic strings where the oxygen is reduced. [ 19 ]
Anaerobic sulfide oxidation is performed by both phototrophs and chemotrophs . Green sulfur bacteria (GSB) and purple sulfur bacteria (PSB) perform anoxygenic photosynthesis fueled by sulfide oxidation. Some PSB can also perform aerobic sulfide oxidation in the presence of oxygen and can even grow chemoautotrophically under low light conditions. [ 20 ] GSB lack this metabolic potential and have compensated by developing efficient light harvesting systems. PSB can be found in various environments ranging from hot sulfur springs and alkaline lakes to wastewater treatment plants. GSB populate stratified lakes with high reduced sulfur concentrations and can even grow in hydrothermal vents by using infra-red light to perform photosynthesis. [ 21 ]
Hydrothermal vents emit hydrogen sulfide that support the carbon fixation of chemolithotrophic bacteria that oxidize hydrogen sulfide with oxygen to produce elemental sulfur or sulfate. [ 22 ] The chemical reactions are as follows:
In modern oceans, Thiomicrospira , Halothiobacillus , and Beggiatoa are primary sulfur oxidizing bacteria, [ 22 ] and form chemosynthetic symbioses with animal hosts. [ 23 ] The host provides metabolic substrates (e.g., CO 2 , O 2 , H 2 O) to the symbiont while the symbiont generates organic carbon for sustaining the metabolic activities of the host. The produced sulfate usually combines with the leached calcium ions to form gypsum , which can form widespread deposits on near mid-ocean spreading centers. [ 24 ]
Sulfur metabolizing microbes are often engaged in close symbiotic relationships with other microbes, and even animals. PSB and sulfate reducers form microbial aggregates called “pink berries” in the salt marshes of Massachusetts within which sulfur cycling occurs through the direct exchange of sulfur species. [ 25 ] The Vestimentiferan tube worms that grow around hydrothermal vents lack a digestive tract but contain specialized organelles called trophosomes within which autotrophic, sulfide oxidizing bacteria are housed. The tube worms provide the bacteria with sulfide and the bacteria shares the fixed carbon with the worms. [ 26 ]
Although there are 25 known isotopes of sulfur , only four are stable and of geochemical importance. Of those four, two ( 32 S, light and 34 S, heavy) comprise (99.22%) of sulfur on Earth. The vast majority (95.02%) of sulfur occurs as 32 S with only 4.21% in 34 S. The ratio of these two isotopes is fixed in the Solar System and has been since its formation. The bulk Earth sulfur isotopic ratio is thought to be the same as the ratio of 22.22 measured from the Canyon Diablo troilite (CDT), a meteorite . [ 27 ] That ratio is accepted as the international standard and is therefore set at δ = 0.00. Deviation from 0.00 is expressed as the δ 34 S which is a ratio in per mill (‰) . Positive values correlate to increased levels of 34 S, whereas negative values correlate with greater 32 S in a sample.
Formation of sulfur minerals through non-biogenic processes does not substantially differentiate between the light and heavy isotopes, therefore sulfur isotope ratios in gypsum or barite should be the same as the overall isotope ratio in the water column at their time of precipitation. Sulfate reduction through biologic activity strongly differentiates between the two isotopes because of the more rapid enzymic reaction with 32 S. [ 27 ] Average present day seawater values of δ 34 S are on the order of +21‰.
Prior to 2010s, it was thought that sulfate reduction could fractionate sulfur isotopes up to 46 permil and fractionation larger than 46 permil recorded in sediments must be due to disproportionation of sulfur intermediates in the sediment. This view has changed since the 2010s that sulfate reduction can fractionate to 66 permil. [ 28 ] As substrates for disproportionation are limited by the product of sulfate reduction, the isotopic effect of disproportionation should be less than 16 permil in most sedimentary settings. [ 29 ]
Throughout geologic history the sulfur cycle and the isotopic ratios have coevolved with the biosphere becoming overall more negative with the increases in biologically driven sulfate reduction, but also show substantial positive excursion. In general positive excursions in the sulfur isotopes mean that there is an excess of pyrite deposition rather than oxidation of sulfide minerals exposed on land. [ 27 ]
The marine sulfur cycle is driven by sulfate reduction because hydrogen sulfide is oxidized by microbes for energy or is oxidized abiotically. Dissimilatory sulfate reduction is driven by the degradation of buried organic matter and anaerobic oxidation of methane (AOM) both of which produce carbon dioxide. At depths where sulfate is depleted, methanogenesis is prevalent. At the sulfate-methane transition zone (SMTZ), the upwelling of methane produced by the methanogens is met by the anaerobic methanotrophic archaea in the SMTZ which oxidize it using sulfate as an electron acceptor. More sulfate is present at the SMTZ than methane. A 4:1 ratio of sulfate: methane is observed and the excess sulfate is directed towards organic matter degradation. [ 30 ] Syntrophic aggregates of sulfate reducers and methanotrophs have been discovered and the underlying mechanisms observed include direct interspecies electron transfer using large multi heme complexes. [ 31 ]
Sulfide produced by sulfate reduction can be oxidized by iron minerals to make iron sulfides and pyrite or used as electron donor or to sulfurize organic matter by microbes. [ 17 ] Pyrite is formed through two pathways: the polysulfide and the hydrogen sulfide pathway. The polysulfide pathway is dominant until the depletion of elemental sulfur since elemental sulfur is necessary in the formation of polysulfides, then the hydrogen sulfide pathway takes over. [ 32 ] Microbial sulfur oxidation utilizes multiple oxidants because the concentrations of the electron acceptors are depth dependent. In the upper sediment layers oxygen and nitrate are the preferred oxidants because of the high energy yield from the reaction, and in the suboxic zones iron and manganese take on the role. [ 17 ] Sulfide oxidation yields various sulfur intermediates such as elemental sulfur, thiosulfate, sulfite, and sulfate.The sulfur intermediates formed during sulfide oxidation are unique to this process and thus are indicative of sulfide oxidation when found in environmental samples. Sulfur isotope fractionation of these intermediates and other sulfur species has been a useful tool in the study of sulfide oxidation. [ 33 ]
The sulfur cycle in marine environments has been well-studied via the tool of sulfur isotope systematics expressed as δ 34 S. The modern global oceans have sulfur storage of 1.3 × 10 18 kg , [ 34 ] mainly occurring as sulfate with the δ 34 S value of +21‰. [ 35 ] The overall input flux is 1.0 × 10 11 kg/a with the sulfur isotope composition of ~3‰. [ 35 ] Riverine sulfate derived from the terrestrial weathering of sulfide minerals ( δ 34 S = +6‰) is the primary input of sulfur to the oceans. Other sources are metamorphic and volcanic degassing and hydrothermal activity ( δ 34 S = 0‰), which release reduced sulfur species (such as H 2 S and S 0 ). There are two major outputs of sulfur from the oceans. The first sink is the burial of sulfate either as marine evaporites (such as gypsum) or carbonate-associated sulfate (CAS), which accounts for 6 × 10 10 kg/a ( δ 34 S = +21‰). The second sulfur sink is pyrite burial in shelf sediments or deep seafloor sediments ( 4 × 10 10 kg/a ; δ 34 S = −20‰). [ 36 ] The total marine sulfur output flux is 1.0 × 10 11 kg/a which matches the input fluxes, implying the modern marine sulfur budget is at steady state. [ 35 ] The residence time of sulfur in modern global oceans is 13,000,000 years. [ 37 ]
Sulfurization of organic matter is a significant sulfur pool, containing 35-80% of the reduced sulfur in marine sediments. [ 38 ] These organo-sulfur molecules are also desulfurized to release oxidized sulfur species like sulfite and sulfate. This desulfurization may allow degradation of the organic matter and thus this process determines if the organic matter is assimilated or buried. [ 38 ] Sulfurization increases molecular weight and introduces a new moiety to the organic molecule which may inhibit its recognition by catabolic enzymes that degrade organic matter. Microbial ability for desulfurization is reflected by the presence of sulfatase genes. [ 39 ]
The isotopic composition of sedimentary sulfides provides primary information on the evolution of the sulfur cycle.
The total inventory of sulfur compounds on the surface of the Earth (nearly 10 19 kg of sulfur) represents the total outgassing of sulfur through geologic time. [ 40 ] [ 27 ] Rocks analyzed for sulfur content are generally organic-rich shales meaning they are likely controlled by biogenic sulfur reduction. Average seawater curves are generated from evaporites deposited throughout geologic time because again, since they do not discriminate between the heavy and light sulfur isotopes, they should mimic the ocean composition at the time of deposition.
4.6 billion years ago (Ga) the Earth formed and had a theoretical δ 34 S value of 0. Since there was no biologic activity on early Earth there would be no isotopic fractionation . [ 35 ] All sulfur in the atmosphere would be released during volcanic eruptions. When the oceans condensed on Earth, the atmosphere was essentially swept clean of sulfur gases, owing to their high solubility in water. Throughout the majority of the Archean (4.6–2.5 Ga) most systems appeared to be sulfate-limited. Some small Archean evaporite deposits require that at least locally elevated concentrations (possibly due to local volcanic activity) of sulfate existed in order for them to be supersaturated and precipitate out of solution. [ 41 ]
3.8–3.6 Ga marks the beginning of the exposed geologic record because this is the age of the oldest rocks on Earth. Metasedimentary rocks from this time still have an isotopic value of 0 because the biosphere was not developed enough (possibly at all) to fractionate sulfur. [ 42 ]
3.5 Ga anoxyogenic photosynthesis is established and provides a weak source of sulfate to the global ocean with sulfate concentrations incredibly low the δ 34 S is still basically 0. [ 41 ] Shortly after, at 3.4 Ga the first evidence for minimal fractionation in evaporitic sulfate in association with magmatically derived sulfides can be seen in the rock record. This fractionation shows possible evidence for anoxygenic phototrophic bacteria.
2.8 Ga marks the first evidence for oxygen production through photosynthesis. This is important because there cannot be sulfur oxidation without oxygen in the atmosphere. This exemplifies the coevolution of the oxygen and sulfur cycles as well as the biosphere.
2.7–2.5 Ga is the age of the oldest sedimentary rocks to have a depleted δ 34 S which provide the first compelling evidence for sulfate reduction. [ 41 ]
2.3 Ga sulfate increases to more than 1 mM; this increase in sulfate is coincident with the " Great Oxygenation Event ", when redox conditions on Earth's surface are thought by most workers to have shifted fundamentally from reducing to oxidizing. [ 43 ] This shift would have led to an incredible increase in sulfate weathering which would have led to an increase in sulfate in the oceans. The large isotopic fractionations that would likely be associated with bacteria reduction are produced for the first time. Although there was a distinct rise in seawater sulfate at this time it was likely still only less than 5–15% of present-day levels. [ 43 ]
At 1.8 Ga, Banded iron formations (BIF) are common sedimentary rocks throughout the Archean and Paleoproterozoic ; their disappearance marks a distinct shift in the chemistry of ocean water. BIFs have alternating layers of iron oxides and chert . BIFs only form if the water is allowed to supersaturate in dissolved iron (Fe 2+ ) meaning there cannot be free oxygen or sulfur in the water column because it would form Fe 3+ (rust) or pyrite and precipitate out of solution. Following this supersaturation, the water must become oxygenated in order for the ferric rich bands to precipitate it must still be sulfur poor otherwise pyrite would form instead of Fe 3+ . It has been hypothesized that BIFs formed during the initial evolution of photosynthetic organisms that had phases of population growth, causing over production of oxygen. Due to this over production they would poison themselves causing a mass die off, which would cut off the source of oxygen and produce a large amount of CO 2 through the decomposition of their bodies, allowing for another bacterial bloom. After 1.8 Ga sulfate concentrations were sufficient to increase rates of sulfate reduction to greater than the delivery flux of iron to the oceans. [ 41 ]
Along with the disappearance of BIF, the end of the Paleoproterozoic also marks the first large scale sedimentary exhalative deposits showing a link between mineralization and a likely increase in the amount of sulfate in sea water. In the Paleoproterozoic the sulfate in seawater had increased to an amount greater than in the Archean, but was still lower than present day values. [ 43 ] The sulfate levels in the Proterozoic also act as proxies for atmospheric oxygen because sulfate is produced mostly through weathering of the continents in the presence of oxygen. The low levels in the Proterozoic simply imply that levels of atmospheric oxygen fell between the abundances of the Phanerozoic and the deficiencies of the Archean.
750 million years ago (Ma) there is a renewed deposition of BIF which marks a significant change in ocean chemistry . This was likely due to snowball Earth episodes where the entire globe including the oceans was covered in a layer of ice cutting off oxygenation. [ 44 ] In the late Neoproterozoic high carbon burial rates increased the atmospheric oxygen level to >10% of its present-day value. In the Latest Neoproterozoic another major oxidizing event occurred on Earth's surface that resulted in an oxic [ check spelling ] deep ocean and possibly allowed for the appearance of multicellular life. [ 43 ]
During the last 600 million years, seawater SO 4 has generally varied between +10‰ and +30‰ in δ 34 S, with an average value close to that of today. Notably changes in seawater δ 34 S occurred during extinction and climatic events during this time. [ 45 ] [ 46 ] [ 47 ] [ 48 ] [ 49 ] [ 50 ] [ 51 ]
Over a shorter time scale (ten million years) changes in the sulfur cycle are easier to observe and can be even better constrained with oxygen isotopes. Oxygen is continually incorporated into the sulfur cycle through sulfate oxidation and then released when that sulfate is reduced once again. [ 5 ] Since different sulfate sources within the ocean have distinct oxygen isotopic values it may be possible to use oxygen to trace the sulfur cycle. Biological sulfate reduction preferentially selects lighter oxygen isotopes for the same reason that lighter sulfur isotopes are preferred. By studying oxygen isotopes in ocean sediments over the last 10 million years [ 52 ] were able to better constrain the sulfur concentrations in sea water through that same time. They found that the sea level changes due to Pliocene and Pleistocene glacial cycles changed the area of continental shelves which then disrupted the sulfur processing, lowering the concentration of sulfate in the sea water. This was a drastic change as compared to preglacial times before 2 million years ago.
The Great Oxygenation Event (GOE) is characterized by the disappearance of sulfur isotope mass-independent fractionation (MIF) in the sedimentary records at around 2.45 billion years ago (Ga). [ 53 ] The MIF of sulfur isotope (Δ 33 S) is defined by the deviation of measured δ 33 S value from the δ 33 S value inferred from the measured δ 34 S value according to the mass dependent fractionation law. The Great Oxidation Event represented a massive transition of global sulfur cycles. Before the Great Oxidation Event, the sulfur cycle was heavily influenced by the ultraviolet (UV) radiation and the associated photochemical reactions , which induced the sulfur isotope mass-independent fractionation (Δ 33 S ≠ 0). The preservation of sulfur isotope mass-independent fractionation signals requires the atmospheric O 2 lower than 10 −5 of present atmospheric level (PAL). [ 40 ] The disappearance of sulfur isotope mass-independent fractionation at ~2.45 Ga indicates that atmospheric p O 2 exceeded 10 −5 present atmospheric level after the Great Oxygenation Event. [ 53 ] Oxygen played an essential role in the global sulfur cycles after the Great Oxygenation Event, such as oxidative weathering of sulfides. [ 54 ] The burial of pyrite in sediments in turn contributes to the accumulation of free O 2 in Earth's surface environment. [ 55 ]
Sulfur is intimately involved in the production of fossil fuels and most metal deposits because it acts as an oxidizing or reducing agent. The vast majority of the major mineral deposits on Earth contain a substantial amount of sulfur including, but not limited to sedimentary exhalative deposits (SEDEX), Carbonate-hosted lead-zinc ore deposits (Mississippi Valley-Type MVT), and porphyry copper deposits. Iron sulfides, galena , and sphalerite will form as by-products of hydrogen sulfide generation as long as the respective transition or base metals are present or transported to a sulfate reduction site. [ 8 ] If the system runs out of reactive hydrocarbons, economically viable elemental sulfur deposits may form. Sulfur also acts as a reducing agent in many natural gas reservoirs, and generally, ore-forming fluids have a close relationship with ancient hydrocarbon seeps or vents. [ 43 ]
Important sources of sulfur in ore deposits are generally deep-seated, but they can also come from local country rocks, seawater, or marine evaporites . The presence or absence of sulfur is one of the limiting factors in the concentration of precious metals and their precipitation from solution. pH , temperature and especially redox states determine whether sulfides will precipitate. Most sulfide brines will remain in concentration until they reach reducing conditions, a higher pH, or lower temperatures.
Ore fluids are generally linked to metal-rich waters that have been heated within a sedimentary basin under elevated thermal conditions, typically in extensional tectonic settings. The redox conditions of the basin lithologies exert an important control on the redox state of the metal-transporting fluids, and deposits can form from both oxidizing and reducing fluids. [ 43 ] Metal-rich ore fluids tend to be, by necessity, comparatively sulfide deficient, so a substantial portion of the sulfide must be supplied from another source at the site of mineralization. Bacterial reduction of seawater sulfate or a euxinic (anoxic and H 2 S-containing) water column is a necessary source of that sulfide. When present, the δ 34 S values of barite are generally consistent with a seawater sulfate source, suggesting baryte formation by reaction between hydrothermal barium and sulfate in ambient seawater. [ 43 ]
Once fossil fuels or precious metals are discovered and either burned or milled, sulfur becomes a waste product that must be dealt with properly, or it can become a pollutant. The burning of fossil fuels has greatly increased the amount of sulfur in our present-day atmosphere. Sulfur acts as a pollutant and an economic resource at the same time.
Human activities have a major effect on the global sulfur cycle. The burning of coal , natural gas , and other fossil fuels has greatly increased the amount of sulfur in the atmosphere and ocean and depleted the sedimentary rock sink. Without human impact sulfur would stay tied up in rocks for millions of years until it was uplifted through tectonic events and then released through erosion and weathering processes. Instead it is being drilled, pumped and burned at a steadily increasing rate. Over the most polluted areas there has been a 30-fold increase in sulfate deposition. [ 56 ]
Although the sulfur curve shows shifts between net sulfur oxidation and net sulfur reduction in the geologic past, the magnitude of the current human impact is probably unprecedented in the geologic record. Human activities greatly increase the flux of sulfur to the atmosphere , some of which is transported globally. Humans are mining coal and extracting petroleum from the Earth's crust at a rate that mobilizes 150 x 10 12 gS/yr, which is more than double the rate of 100 years ago. [ 57 ] The result of human impact on these processes is to increase the pool of oxidized sulfur (SO 4 ) in the global cycle, at the expense of the storage of reduced sulfur in the Earth's crust. Therefore, human activities do not cause a major change in the global pools of sulfur, but they do produce massive changes in the annual flux of sulfur through the atmosphere. [ 27 ]
When SO 2 is emitted as an air pollutant, it forms sulfuric acid through reactions with water in the atmosphere. Once the acid is completely dissociated in water the pH can drop to 4.3 or lower causing damage to both man-made and natural systems. According to the EPA, acid rain is a broad term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere containing higher than normal amounts of nitric and sulfuric acids. Distilled water (water without any dissolved constituents), which contains no carbon dioxide , has a neutral pH of 7. Rain naturally has a slightly acidic pH of 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a very weak acid. Around Washington, D.C. , however, the average rain pH is between 4.2 and 4.4. Since pH is on a log scale dropping by 1 (the difference between normal rain water and acid rain) has a dramatic effect on the strength of the acid. In the United States, roughly two thirds of all SO 2 and one fourth of all NO 3 come from electric power generation that relies on burning fossil fuels, like coal.
As it is an important nutrient for plants , sulfur is increasingly used as a component of fertilizers. Recently sulfur deficiency has become widespread in many countries in Europe. [ 58 ] [ 59 ] [ 60 ] Because of actions taken to limit acid rains atmospheric inputs of sulfur continue to decrease, As a result, the deficit in the sulfur input is likely to increase unless sulfur fertilizers are used. [ 61 ] [ 62 ] | https://en.wikipedia.org/wiki/Sulfur_cycle |
Sulfur diimides are chemical compounds of the formula S(NR) 2 . Structurally, they are the di imine of sulfur dioxide . The parent member, S(NH) 2 , is of only theoretical interest. Other derivatives where R is an organic group are stable and useful reagents.
A particularly stable derivative is di- t -butyl sulfurdiimide. [ 1 ] It is prepared by reaction of tert -butylamine with sulfur dichloride to give the intermediate "S(N- t -Bu)", which decomposes at 60 °C to give the diimide.
However, most sulfur diimides are not produced from such elimination reactions . Typically, sulfur diimides arise from treatment of sulfur tetrafluoride with amines, or from transamidation reactions. The latter typically requires amide reactants that are less basic than the products, [ 2 ] as with disulfonylsulfodiimide...
...or with N , N' -Bis(methoxycarbonyl)sulfur diimide (MeO 2 C-N=S=N-CO 2 Me) from methyl carbamate . [ 3 ] Alternatively, the presence of a strong base to absorb the released SO 2 can drive transamidation from sulfinylamines. [ 2 ]
These compounds are related to SO 2 . They have planar C–N=S=N–C cores with bent C–N=S and N=S=N geometries, and various combinations of E and Z isomers are observed for the two N=S bonds. [ 4 ]
Sulfur diimides are electrophilic . [ 1 ] Organolithium reagents attack at the sulfur to give the corresponding nitrogen anion:
The triimido analogues of sulfite can be generated by treating the sulfur diimides with a metal amide : [ 5 ]
Sulfur diimides undergo Diels–Alder reactions with dienes . [ 1 ] Fluorine gas oxidizes them to difluorosulfur diimides: [ 2 ] | https://en.wikipedia.org/wiki/Sulfur_diimide |
Selenium dioxide Polonium dioxide
Sulfur dioxide ( IUPAC -recommended spelling) or sulphur dioxide (traditional Commonwealth English ) is the chemical compound with the formula S O 2 . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is released naturally by volcanic activity and is produced as a by-product of metals refining and the burning of sulfur - bearing fossil fuels. [ 9 ]
Sulfur dioxide is somewhat toxic to humans, although only when inhaled in relatively large quantities for a period of several minutes or more. It was known to medieval alchemists as "volatile spirit of sulfur". [ 10 ]
SO 2 is a bent molecule with C 2v symmetry point group .
A valence bond theory approach considering just s and p orbitals would describe the bonding in terms of resonance between two resonance structures.
The sulfur–oxygen bond has a bond order of 1.5. There is support for this simple approach that does not invoke d orbital participation. [ 11 ] In terms of electron-counting formalism, the sulfur atom has an oxidation state of +4 and a formal charge of +1.
Sulfur dioxide is found on Earth and exists in very small concentrations in the atmosphere at about 15 ppb . [ 12 ]
On other planets, sulfur dioxide can be found in various concentrations, the most significant being the atmosphere of Venus , where it is the third-most abundant atmospheric gas at 150 ppm. There, it reacts with water to form clouds of sulfurous acid ( SO 2 + H 2 O ⇌ HSO − 3 + H + ), and is a key component of the planet's global atmospheric sulfur cycle . It has been implicated as a key agent in the warming of early Mars , with estimates of concentrations in the lower atmosphere as high as 100 ppm, [ 13 ] though it only exists in trace amounts. On both Venus and Mars, as on Earth, its primary source is thought to be volcanic. The atmosphere of Io , a natural satellite of Jupiter , is 90% sulfur dioxide [ 14 ] and trace amounts are thought to also exist in the atmosphere of Jupiter . The James Webb Space Telescope has observed the presence of sulfur dioxide on the exoplanet WASP-39b , where it is formed through photochemistry in the planet's atmosphere. [ 15 ]
As an ice, it is thought to exist in abundance on the Galilean moons —as subliming ice or frost on the trailing hemisphere of Io , [ 16 ] and in the crust and mantle of Europa , Ganymede , and Callisto , possibly also in liquid form and readily reacting with water. [ 17 ]
Sulfur dioxide is primarily produced for sulfuric acid manufacture (see contact process , but other processes predated that at least since 16th century [ 10 ] ). In the United States in 1979, 23.6 million metric tons (26 million U.S. short tons) of sulfur dioxide were used in this way, compared with 150,000 metric tons (165,347 U.S. short tons) used for other purposes. Most sulfur dioxide is produced by the combustion of elemental sulfur . Some sulfur dioxide is also produced by roasting pyrite and other sulfide ores in air. [ 18 ]
Sulfur dioxide is the product of the burning of sulfur or of burning materials that contain sulfur:
To aid combustion, liquified sulfur (140–150 °C (284–302 °F) is sprayed through an atomizing nozzle to generate fine drops of sulfur with a large surface area. The reaction is exothermic , and the combustion produces temperatures of 1,000–1,600 °C (1,830–2,910 °F). The significant amount of heat produced is recovered by steam generation that can subsequently be converted to electricity. [ 18 ]
The combustion of hydrogen sulfide and organosulfur compounds proceeds similarly. For example:
The roasting of sulfide ores such as pyrite , sphalerite , and cinnabar (mercury sulfide) also releases SO 2 : [ 19 ]
A combination of these reactions is responsible for the largest source of sulfur dioxide, volcanic eruptions. These events can release millions of tons of SO 2 .
Sulfur dioxide can also be a byproduct in the manufacture of calcium silicate cement; CaSO 4 is heated with coke and sand in this process:
Until the 1970s commercial quantities of sulfuric acid and cement were produced by this process in Whitehaven , England. Upon being mixed with shale or marl , and roasted, the sulfate liberated sulfur dioxide gas, used in sulfuric acid production, the reaction also produced calcium silicate, a precursor in cement production. [ 20 ]
On a laboratory scale, the action of hot concentrated sulfuric acid on copper turnings produces sulfur dioxide.
Tin also reacts with concentrated sulfuric acid but it produces tin(II) sulfate which can later be pyrolyzed at 360 °C into tin dioxide and dry sulfur dioxide.
The reverse reaction occurs upon acidification:
Sulfites result by the action of aqueous base on sulfur dioxide:
Sulfur dioxide is a mild but useful reducing agent . It is oxidized by halogens to give the sulfuryl halides, such as sulfuryl chloride :
Sulfur dioxide is the oxidising agent in the Claus process , which is conducted on a large scale in oil refineries . Here, sulfur dioxide is reduced by hydrogen sulfide to give elemental sulfur:
The sequential oxidation of sulfur dioxide followed by its hydration is used in the production of sulfuric acid.
Sulfur dioxide dissolves in water to give " sulfurous acid ", which cannot be isolated and is instead an acidic solution of bisulfite , and possibly sulfite , ions.
Sulfur dioxide is one of the few common acidic yet reducing gases. It turns moist litmus pink (being acidic), then white (due to its bleaching effect). It may be identified by bubbling it through a dichromate solution, turning the solution from orange to green (Cr 3+ (aq)). It can also reduce ferric ions to ferrous. [ 21 ]
Sulfur dioxide can react with certain 1,3- dienes in a cheletropic reaction to form cyclic sulfones . This reaction is exploited on an industrial scale for the synthesis of sulfolane , which is an important solvent in the petrochemical industry .
Sulfur dioxide can bind to metal ions as a ligand to form metal sulfur dioxide complexes , typically where the transition metal is in oxidation state 0 or +1. Many different bonding modes (geometries) are recognized, but in most cases, the ligand is monodentate, attached to the metal through sulfur, which can be either planar and pyramidal η 1 . [ 9 ] As a η 1 -SO 2 (S-bonded planar) ligand sulfur dioxide functions as a Lewis base using the lone pair on S. SO 2 functions as a Lewis acids in its η 1 -SO 2 (S-bonded pyramidal) bonding mode with metals and in its 1:1 adducts with Lewis bases such as dimethylacetamide and trimethyl amine . When bonding to Lewis bases the acid parameters of SO 2 are E A = 0.51 and E A = 1.56.
The overarching, dominant use of sulfur dioxide is in the production of sulfuric acid . [ 18 ]
Sulfur dioxide is an intermediate in the production of sulfuric acid, being converted to sulfur trioxide , and then to oleum , which is made into sulfuric acid. Sulfur dioxide for this purpose is made when sulfur combines with oxygen. The method of converting sulfur dioxide to sulfuric acid is called the contact process . Several million tons are produced annually for this purpose.
Sulfur dioxide is sometimes used as a preservative for dried apricots, dried figs, and other dried fruits, owing to its antimicrobial properties and ability to prevent oxidation , [ 22 ] and is called E 220 [ 23 ] when used in this way in Europe. As a preservative, it maintains the colorful appearance of the fruit and prevents rotting . Historically, molasses was "sulfured" as a preservative and also to lighten its color. Treatment of dried fruit was usually done outdoors, by igniting sublimed sulfur and burning in an enclosed space with the fruits. [ 24 ] Fruits may be sulfured by dipping them into sodium bisulfite , sodium sulfite or sodium metabisulfite . [ 24 ]
Sulfur dioxide was first used in winemaking by the Romans, when they discovered that burning sulfur candles inside empty wine vessels keeps them fresh and free from vinegar smell. [ 25 ]
It is still an important compound in winemaking, and is measured in parts per million ( ppm ) in wine. It is present even in so-called unsulfurated wine at concentrations of up to 10 mg/L. [ 26 ] It serves as an antibiotic and antioxidant , protecting wine from spoilage by bacteria and oxidation – a phenomenon that leads to the browning of the wine and a loss of cultivar specific flavors. [ 27 ] [ 28 ] Its antimicrobial action also helps minimize volatile acidity. Wines containing sulfur dioxide are typically labeled with "containing sulfites ".
Sulfur dioxide exists in wine in free and bound forms, and the combinations are referred to as total SO 2 . Binding, for instance to the carbonyl group of acetaldehyde , varies with the wine in question. The free form exists in equilibrium between molecular SO 2 (as a dissolved gas) and bisulfite ion, which is in turn in equilibrium with sulfite ion. These equilibria depend on the pH of the wine. Lower pH shifts the equilibrium towards molecular (gaseous) SO 2 , which is the active form, while at higher pH more SO 2 is found in the inactive sulfite and bisulfite forms. The molecular SO 2 is active as an antimicrobial and antioxidant, and this is also the form which may be perceived as a pungent odor at high levels. Wines with total SO 2 concentrations below 10 ppm do not require "contains sulfites" on the label by US and EU laws. The upper limit of total SO 2 allowed in wine in the US is 350 ppm; in the EU it is 160 ppm for red wines and 210 ppm for white and rosé wines. In low concentrations, SO 2 is mostly undetectable in wine, but at free SO 2 concentrations over 50 ppm, SO 2 becomes evident in the smell and taste of wine. [ citation needed ]
SO 2 is also a very important compound in winery sanitation. Wineries and equipment must be kept clean, and because bleach cannot be used in a winery due to the risk of cork taint , [ 29 ] a mixture of SO 2 , water, and citric acid is commonly used to clean and sanitize equipment. Ozone (O 3 ) is now used extensively for sanitizing in wineries due to its efficacy, and because it does not affect the wine or most equipment. [ 30 ]
Sulfur dioxide is also a good reductant . In the presence of water, sulfur dioxide is able to decolorize substances. Specifically, it is a useful reducing bleach for papers and delicate materials such as clothes. This bleaching effect normally does not last very long. Oxygen in the atmosphere reoxidizes the reduced dyes, restoring the color. In municipal wastewater treatment, sulfur dioxide is used to treat chlorinated wastewater prior to release. Sulfur dioxide reduces free and combined chlorine to chloride . [ 31 ]
Sulfur dioxide is fairly soluble in water, and by both IR and Raman spectroscopy; the hypothetical sulfurous acid , H 2 SO 3 , is not present to any extent. However, such solutions do show spectra of the hydrogen sulfite ion, HSO 3 − , by reaction with water, and it is in fact the actual reducing agent present:
In the beginning of the 20th century sulfur dioxide was used in Buenos Aires as a fumigant to kill rats that carried the Yersinia pestis bacterium, which causes bubonic plague. The application was successful, and the application of this method was extended to other areas in South America. In Buenos Aires, where these apparatuses were known as Sulfurozador , but later also in Rio de Janeiro, New Orleans and San Francisco, the sulfur dioxide treatment machines were brought into the streets to enable extensive disinfection campaigns, with effective results. [ 32 ]
Sulfur dioxide or its conjugate base bisulfite is produced biologically as an intermediate in both sulfate-reducing organisms and in sulfur-oxidizing bacteria, as well. The role of sulfur dioxide in mammalian biology is not yet well understood. [ 33 ] Sulfur dioxide blocks nerve signals from the pulmonary stretch receptors and abolishes the Hering–Breuer inflation reflex .
It is considered that endogenous sulfur dioxide plays a significant physiological role in regulating cardiac and blood vessel function, and aberrant or deficient sulfur dioxide metabolism can contribute to several different cardiovascular diseases, such as arterial hypertension , atherosclerosis , pulmonary arterial hypertension , and stenocardia . [ 34 ]
It was shown that in children with pulmonary arterial hypertension due to congenital heart diseases the level of homocysteine is higher and the level of endogenous sulfur dioxide is lower than in normal control children. Moreover, these biochemical parameters strongly correlated to the severity of pulmonary arterial hypertension. Authors considered homocysteine to be one of useful biochemical markers of disease severity and sulfur dioxide metabolism to be one of potential therapeutic targets in those patients. [ 35 ]
Endogenous sulfur dioxide also has been shown to lower the proliferation rate of endothelial smooth muscle cells in blood vessels, via lowering the MAPK activity and activating adenylyl cyclase and protein kinase A . [ 36 ] Smooth muscle cell proliferation is one of important mechanisms of hypertensive remodeling of blood vessels and their stenosis , so it is an important pathogenetic mechanism in arterial hypertension and atherosclerosis.
Endogenous sulfur dioxide in low concentrations causes endothelium-dependent vasodilation . In higher concentrations it causes endothelium-independent vasodilation and has a negative inotropic effect on cardiac output function, thus effectively lowering blood pressure and myocardial oxygen consumption. The vasodilating and bronchodilating effects of sulfur dioxide are mediated via ATP-dependent calcium channels and L-type ("dihydropyridine") calcium channels. Endogenous sulfur dioxide is also a potent antiinflammatory, antioxidant and cytoprotective agent. It lowers blood pressure and slows hypertensive remodeling of blood vessels, especially thickening of their intima. It also regulates lipid metabolism. [ 37 ]
Endogenous sulfur dioxide also diminishes myocardial damage, caused by isoproterenol adrenergic hyperstimulation, and strengthens the myocardial antioxidant defense reserve. [ 38 ]
Sulfur dioxide is a versatile inert solvent widely used for dissolving highly oxidizing salts. It is also used occasionally as a source of the sulfonyl group in organic synthesis . Treatment of aryl diazonium salts with sulfur dioxide and cuprous chloride yields the corresponding aryl sulfonyl chloride, for example: [ 39 ]
As a result of its very low Lewis basicity , it is often used as a low-temperature solvent/diluent for superacids like magic acid (FSO 3 H/SbF 5 ), allowing for highly reactive species like tert -butyl cation to be observed spectroscopically at low temperature (though tertiary carbocations do react with SO 2 above about −30 °C, and even less reactive solvents like SO 2 ClF must be used at these higher temperatures). [ 40 ]
Being easily condensed and possessing a high heat of evaporation , sulfur dioxide is a candidate material for refrigerants. Before the development of chlorofluorocarbons , sulfur dioxide was used as a refrigerant in home refrigerators .
Sulfur dioxide content in naturally-released geothermal gasses is measured by the Icelandic Meteorological Office as an indicator of possible volcanic activity. [ 41 ]
In the United States, the Center for Science in the Public Interest lists the two food preservatives, sulfur dioxide and sodium bisulfite , as being safe for human consumption except for certain asthmatic individuals who may be sensitive to them, especially in large amounts. [ 42 ] Symptoms of sensitivity to sulfiting agents, including sulfur dioxide, manifest as potentially life-threatening trouble breathing within minutes of ingestion. [ 43 ] Sulphites may also cause symptoms in non-asthmatic individuals, namely dermatitis , urticaria , flushing , hypotension , abdominal pain and diarrhea, and even life-threatening anaphylaxis . [ 44 ]
Incidental exposure to sulfur dioxide is routine, e.g. the smoke from matches, coal, and sulfur-containing fuels like bunker fuel . Relative to other chemicals, it is only mildly toxic and requires high concentrations to be actively hazardous. [ 45 ] However, its ubiquity makes it a major air pollutant with significant impacts on human health. [ 46 ]
In 2008, the American Conference of Governmental Industrial Hygienists reduced the short-term exposure limit to 0.25 parts per million (ppm). In the US, the OSHA set the PEL at 5 ppm (13 mg/m 3 ) time-weighted average. Also in the US, NIOSH set the IDLH at 100 ppm. [ 47 ] In 2010, the EPA "revised the primary SO 2 NAAQS by establishing a new one-hour standard at a level of 75 parts per billion (ppb) . EPA revoked the two existing primary standards because they would not provide additional public health protection given a one-hour standard at 75 ppb." [ 46 ]
Major volcanic eruptions have an overwhelming effect on sulfate aerosol concentrations in the years when they occur: eruptions ranking 4 or greater on the Volcanic Explosivity Index inject SO 2 and water vapor directly into the stratosphere , where they react to create sulfate aerosol plumes. [ 48 ] Volcanic emissions vary significantly in composition, and have complex chemistry due to the presence of ash particulates and a wide variety of other elements in the plume. Only stratovolcanoes containing primarily felsic magmas are responsible for these fluxes, as mafic magma erupted in shield volcanoes doesn't result in plumes which reach the stratosphere. [ 49 ] However, before the Industrial Revolution , dimethyl sulfide pathway was the largest contributor to sulfate aerosol concentrations in a more average year with no major volcanic activity. According to the IPCC First Assessment Report , published in 1990, volcanic emissions usually amounted to around 10 million tons in 1980s, while dimethyl sulfide amounted to 40 million tons. Yet, by that point, the global human-caused emissions of sulfur into the atmosphere became "at least as large" as all natural emissions of sulfur-containing compounds combined : they were at less than 3 million tons per year in 1860, and then they increased to 15 million tons in 1900, 40 million tons in 1940 and about 80 millions in 1980. The same report noted that "in the industrialized regions of Europe and North America, anthropogenic emissions dominate over natural emissions by about a factor of ten or even more". [ 50 ] In the eastern United States in the early 2000s, sulfate particles were estimated to account for 25% or more of all air pollution . [ 51 ] Exposure to sulfur dioxide emissions by coal power plants (coal PM 2.5 ) in the US was associated with 2.1 times greater mortality risk than exposure to PM 2.5 from all sources. [ 52 ] Meanwhile, the Southern Hemisphere had much lower concentrations due to being much less densely populated, with an estimated 90% of the human population in the north. In the early 1990s, anthropogenic sulfur dominated in the Northern Hemisphere , where only 16% of annual sulfur emissions were natural, yet amounted for less than half of the emissions in the Southern Hemisphere. [ 53 ]
Such an increase in sulfate aerosol emissions had a variety of effects. At the time, the most visible one was acid rain , caused by precipitation from clouds carrying high concentrations of sulfate aerosols in the troposphere . [ 54 ] At its peak, acid rain has eliminated brook trout and some other fish species and insect life from lakes and streams in geographically sensitive areas, such as Adirondack Mountains in the United States. [ 55 ] Acid rain worsens soil function as some of its microbiota is lost and heavy metals like aluminium are mobilized (spread more easily) while essential nutrients and minerals such as magnesium can leach away because of the same. Ultimately, plants unable to tolerate lowered pH are killed, with montane forests being some of the worst-affected ecosystems due to their regular exposure to sulfate-carrying fog at high altitudes. [ 56 ] [ 57 ] [ 58 ] [ 59 ] [ 60 ] While acid rain was too dilute to affect human health directly, breathing smog or even any air with elevated sulfate concentrations is known to contribute to heart and lung conditions, including asthma and bronchitis . [ 51 ] Further, this form of pollution is linked to preterm birth and low birth weight , with a study of 74,671 pregnant women in Beijing finding that every additional 100 μg/m 3 of SO 2 in the air reduced infants' weight by 7.3 g, making it and other forms of air pollution the largest attributable risk factor for low birth weight ever observed. [ 61 ]
Due largely to the US EPA's Acid Rain Program , the U.S. has had a 33% decrease in emissions between 1983 and 2002 (see table). This improvement resulted in part from flue-gas desulfurization , a technology that enables SO 2 to be chemically bound in power plants burning sulfur-containing coal or petroleum.
In particular, calcium oxide (lime) reacts with sulfur dioxide to form calcium sulfite :
Aerobic oxidation of the CaSO 3 gives CaSO 4 , anhydrite . Most gypsum sold in Europe comes from flue-gas desulfurization.
To control sulfur emissions, dozens of methods with relatively high efficiencies have been developed for fitting of coal-fired power plants. [ 63 ] Sulfur can be removed from coal during burning by using limestone as a bed material in fluidized bed combustion . [ 64 ]
Sulfur can also be removed from fuels before burning, preventing formation of SO 2 when the fuel is burnt. The Claus process is used in refineries to produce sulfur as a byproduct. The Stretford process has also been used to remove sulfur from fuel. Redox processes using iron oxides can also be used, for example, Lo-Cat [ 65 ] or Sulferox. [ 66 ]
Fuel additives such as calcium additives and magnesium carboxylate may be used in marine engines to lower the emission of sulfur dioxide gases into the atmosphere. [ 67 ]
Sulfur dioxide aerosols in the stratosphere can contribute to ozone depletion in the presence of chlorofluorocarbons and other halogenated ozone-depleting substances. [ 68 ] The effects of volcanic eruptions containing sulfur dioxide aerosols on the ozone layer are complex, however. In the absence of anthropogenic or biogenic halogenated compounds in the lower stratosphere, depletion of dinitrogen pentoxide in the middle stratosphere associated with its reactivity to the aerosols can promote ozone formation. [ 68 ] Injection of sulfur dioxide and large amounts of water vapor into the stratosphere following the 2022 eruption of Hunga Tonga-Hunga Haʻapai resulted in altered atmospheric circulation that promoted a decrease in ozone in the southern latitudes but an increase in the tropics. [ 69 ] [ 70 ] The additional presence of hydrochloric acid in eruptions can result in net ozone depletion. [ 68 ]
Since changes in aerosol concentrations already have an impact on the global climate, they would necessarily influence future projections as well. In fact, it is impossible to fully estimate the warming impact of all greenhouse gases without accounting for the counteracting cooling from aerosols. [ 80 ] [ 81 ]
Regardless of the current strength of aerosol cooling, all future climate change scenarios project decreases in particulates and this includes the scenarios where 1.5 °C (2.7 °F) and 2 °C (3.6 °F) targets are met: their specific emission reduction targets assume the need to make up for lower dimming. [ 82 ] Since models estimate that the cooling caused by sulfates is largely equivalent to the warming caused by atmospheric methane (and since methane is a relatively short-lived greenhouse gas), it is believed that simultaneous reductions in both would effectively cancel each other out. [ 83 ]
As the real world had shown the importance of sulfate aerosol concentrations to the global climate, research into the subject accelerated. Formation of the aerosols and their effects on the atmosphere can be studied in the lab, with methods like ion-chromatography and mass spectrometry [ 90 ] Samples of actual particles can be recovered from the stratosphere using balloons or aircraft, [ 91 ] and remote satellites were also used for observation. [ 92 ] This data is fed into the climate models , [ 93 ] as the necessity of accounting for aerosol cooling to truly understand the rate and evolution of warming had long been apparent, with the IPCC Second Assessment Report being the first to include an estimate of their impact on climate, and every major model able to simulate them by the time IPCC Fourth Assessment Report was published in 2007. [ 94 ] Many scientists also see the other side of this research, which is learning how to cause the same effect artificially. [ 95 ] While discussed around the 1990s, if not earlier, [ 96 ] stratospheric aerosol injection as a solar geoengineering method is best associated with Paul Crutzen 's detailed 2006 proposal. [ 97 ] Deploying in the stratosphere ensures that the aerosols are at their most effective, and that the progress of clean air measures would not be reversed: more recent research estimated that even under the highest-emission scenario RCP 8.5 , the addition of stratospheric sulfur required to avoid 4 °C (7.2 °F) relative to now (and 5 °C (9.0 °F) relative to the preindustrial) would be effectively offset by the future controls on tropospheric sulfate pollution, and the amount required would be even less for less drastic warming scenarios. [ 98 ] This spurred a detailed look at its costs and benefits, [ 99 ] but even with hundreds of studies into the subject completed by the early 2020s, some notable uncertainties remain. [ 100 ]
Table of thermal and physical properties of saturated liquid sulfur dioxide: [ 101 ] [ 102 ] | https://en.wikipedia.org/wiki/Sulfur_dioxide |
A sulfur globule is an intracellular, and sometimes extracellular, aggregate used by various sulfur oxidizing bacteria as storage for elemental sulfur . Sulfur globules were first explained in 1887 by Sergei Winogradsky , [ 1 ] and their complete structure and chemical composition has been a debate since then. [ 1 ] More recently, tools of fluorescence microscopy and genomics have begun to shed light on the structure, formation, and function of sulfur globules.
Further, sulfur globules have been primarily described in chemoautotrophs and phototrophs belonging to the phylum proteobacteria . Sulfur globules can be formed and deposited intracellularly or extracellularly. The formation of extracellular sulfur globules is generally characteristic of green sulfur bacteria and sulfur oxidizers from the family Ectothiorhodospiraceae , whereas intracellular sulfur globules are more typical of magnetotactic sulfur oxidizers, purple sulfur bacteria from the Chromatiaceae family, as well as sulfur-oxidizing bacterial endosymbionts . [ 2 ]
Currently, the model organism for studying the structure and function of these sulfur globules is Allochromatium vinosum. [ 3 ]
Allochromatium vinosum is a purple sulfur bacteria, belonging to the Chromatiaceae family, that oxidizes both thiosulfate and sulfide from its surrounding environments. [ 4 ] While A. vinosum is usually found in lakes or ponds, it can also be found in sewage lagoons or salt marshes, where it plays an important role in re-oxidizing sulfide produced from the sulfate-reducing bacteria in its immediate environment. [ 4 ]
Modern technologies including fluorescence microscopy, proteomics, genomics, and other molecular methods have shed light onto the location and structure of sulfur globules in A. vinosum. Such methods have demonstrated that these sulfur globules are about 1 micrometer in diameter and can make up approximately 34% of the cellular dry weight. Structure wise, A. vinosum sulfur globules generally consist of three hydrophobic proteins: SgpA, SgpB, and SgpC. [ 2 ] These 3 proteins are essential to the formation, expansion, and degradation of sulfur globules, though their complete function is still being explored. Sulfur globules in A. vinosum are intracellular- meaning within the cell wall- but are located in the periplasm along with essential periplasmic sulfur oxidizing enzymes and thiosulfate. Research on the A. vinosum species has also helped to explain the mechanisms by which sulfur globule-containing bacteria decompose said sulfur globules. Perhaps the most studied of these mechanisms involves the dissimilatory sulfite reductase genes, otherwise denoted as the dsr genes. [ 1 ]
Intracellular sulfur globules are generally round in shape, and have a diameter that ranges from 1 μm-3 μm, however, some have been found to be larger than 15 μm. [ 5 ] [ 2 ] The chemical composition of sulfur globules can vary between bacterial species. Purple sulfur bacteria contain globules that consist of long sulfur chains. Chemotrophic sulfur oxidizers such as Beggiatoa alba and Thiomargarita namibiensis contain cyclo- octasulfur as their primary form. Other species, namely Acidithiobacillus ferrooxidans, store sulfur as long chains of polythionates . [ 2 ]
Likewise, techniques in X-ray absorption structure analysis have indicated that the sulfur chains found within these globules usually contain organic end groups and resemble the sulfur found in purple sulfur bacteria- implying that the process of sulfur globule formation in bacteria may be a phylogenetically ancient trait. [ 6 ]
The location of intracellular sulfur globules varies throughout bacterial species. Oftentimes, they are found in the periplasm, along with the presence of active sulfur oxidizing enzymes. Sulfur globules in the model organism A. vinosum, for instance, have been shown to be located in the periplasm based on evidence from peptide coding sequences present in the globule envelope. [ 2 ] They have also been found to be scattered asymmetrically, for example in Thiovulum, where they congregate to one pole of the cell.
Many sulfur globules are enclosed by electron dense layers (2-14 nm thick) that resemble cytoskeletal keratins or proteins of a plant cell wall. Thioalkalivibrio , Beggiatoa , and Thiothrix are species of bacteria that this layer is present in. Analyses of the genome dealing with proteins that encode common sulfur globule proteins show that they are found among many sulfur oxidizing bacteria.
Intracellular and extracellular sulfur globules serve as a temporary reservoir for sulfur in bacteria that oxidize reduced sulfur compounds such as hydrogen sulfide, thiosulfate, or sulfite. These globules allow bacteria to store sulfur, when abundant, to be utilized when conditions become less favorable. This enables the bacteria to better survive while providing a metabolic advantage in fluctuating environments. [ 3 ]
In addition to serving as temporary energy reserves, research has also demonstrated that the pool of sulfur in intracellular globules may also act as a buffer in reduction-oxidation reactions that take place in phototrophic sulfur bacteria. [ 1 ]
[ 1 ] | https://en.wikipedia.org/wiki/Sulfur_globule |
Esaflon Sulfur(VI) fluoride
Sulfur tetrafluoride
Sulfuryl fluoride Tellurium hexafluoride Polonium hexafluoride
Sulfur hexafluoride or sulphur hexafluoride ( British spelling ) is an inorganic compound with the formula SF 6 . It is a colorless, odorless, non- flammable , and non-toxic gas. SF 6 has an octahedral geometry , consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule . [ citation needed ]
Typical for a nonpolar gas, SF 6 is poorly soluble in water but quite soluble in nonpolar organic solvents. It has a density of 6.12 g/L at sea level conditions, considerably higher than the density of air (1.225 g/L). It is generally stored and transported as a liquefied compressed gas . [ 8 ]
SF 6 has 23,500 times greater global warming potential (GWP) than CO 2 as a greenhouse gas (over a 100-year time-frame) but exists in relatively minor concentrations in the atmosphere. Its concentration in Earth's troposphere reached 11.50 parts per trillion (ppt) in October 2023, rising at 0.37 ppt/year. [ 9 ] The increase since 1980 is driven in large part by the expanding electric power sector, including fugitive emissions from banks of SF 6 gas contained in its medium- and high-voltage switchgear . Uses in magnesium, aluminium, and electronics manufacturing also hastened atmospheric growth. [ 10 ] The 1997 Kyoto Protocol , which came into force in 2005, is supposed to limit emissions of this gas. In a somewhat nebulous way it has been included as part of the carbon emission trading scheme. In some countries this has led to the defunction of entire industries. [ 11 ]
Sulfur hexafluoride on Earth exists primarily as a synthetic industrial gas, but has also been found to occur naturally. [ 12 ]
SF 6 can be prepared from the elements through exposure of S 8 to F 2 . This was the method used by the discoverers Henri Moissan and Paul Lebeau in 1901. Some other sulfur fluorides are cogenerated, but these are removed by heating the mixture to disproportionate any S 2 F 10 (which is highly toxic) and then scrubbing the product with NaOH to destroy remaining SF 4 . [ clarification needed ]
Alternatively, using bromine , sulfur hexafluoride can be synthesized from SF 4 and CoF 3 at lower temperatures (e.g. 100 °C), as follows: [ 13 ]
There is virtually no reaction chemistry for SF 6 . A main contribution to the inertness of SF 6 is the steric hindrance of the sulfur atom, whereas its heavier group 16 counterparts, such as SeF 6 are more reactive than SF 6 as a result of less steric hindrance. [ 14 ] It does not react with molten sodium below its boiling point, [ 15 ] but reacts exothermically with lithium . As a result of its inertness, SF 6 has an atmospheric lifetime of around 3200 years, and no significant environmental sinks other than the ocean. [ 16 ]
By 2000, the electrical power industry is estimated to use about 80% of the sulfur hexafluoride produced, mostly as a gaseous dielectric medium . [ 17 ] Other main uses as of 2015 included a silicon etchant for semiconductor manufacturing , and an inert gas for the casting of magnesium . [ 18 ]
SF 6 is used in the electrical industry as a gaseous dielectric medium for high-voltage sulfur hexafluoride circuit breakers , switchgear , and other electrical equipment, often replacing oil-filled circuit breakers (OCBs) that can contain harmful polychlorinated biphenyls (PCBs). SF 6 gas under pressure is used as an insulator in gas insulated switchgear (GIS) because it has a much higher dielectric strength than air or dry nitrogen . The high dielectric strength is a result of the gas's high electronegativity and density . This property makes it possible to significantly reduce the size of electrical gear. This makes GIS more suitable for certain purposes such as indoor placement, as opposed to air-insulated electrical gear, which takes up considerably more room.
Gas-insulated electrical gear is also more resistant to the effects of pollution and climate, as well as being more reliable in long-term operation because of its controlled operating environment. Exposure to an arc chemically breaks down SF 6 though most of the decomposition products tend to quickly re-form SF 6 , a process termed "self-healing". [ 19 ] Arcing or corona can produce disulfur decafluoride ( S 2 F 10 ), a highly toxic gas, with toxicity similar to phosgene . S 2 F 10 was considered a potential chemical warfare agent in World War II because it does not produce lacrimation or skin irritation, thus providing little warning of exposure.
SF 6 is also commonly encountered as a high voltage dielectric in the high voltage supplies of particle accelerators , such as Van de Graaff generators and Pelletrons and high voltage transmission electron microscopes .
Alternatives to SF 6 as a dielectric gas include several fluoroketones. [ 20 ] [ 21 ] Compact GIS technology that combines vacuum switching with clean air insulation has been introduced for a subset of applications up to 420 kV . [ 22 ]
SF 6 is used to provide a tamponade or plug of a retinal hole in retinal detachment repair operations [ 23 ] in the form of a gas bubble. It is inert in the vitreous chamber . [ 24 ] The bubble initially doubles its volume in 36 hours due to oxygen and nitrogen entering it, before being absorbed in the blood in 10–14 days. [ 25 ]
SF 6 is used as a contrast agent for ultrasound imaging. Sulfur hexafluoride microbubbles are administered in solution through injection into a peripheral vein. These microbubbles enhance the visibility of blood vessels to ultrasound. This application has been used to examine the vascularity of tumours. [ 26 ] It remains visible in the blood for 3 to 8 minutes, and is exhaled by the lungs. [ 27 ]
Sulfur hexafluoride was the tracer gas used in the first roadway air dispersion model calibration; this research program was sponsored by the U.S. Environmental Protection Agency and conducted in Sunnyvale, California on U.S. Highway 101 . [ 28 ] Gaseous SF 6 is used as a tracer gas in short-term experiments of ventilation efficiency in buildings and indoor enclosures, and for determining infiltration rates. Two major factors recommend its use: its concentration can be measured with satisfactory accuracy at very low concentrations, and the Earth's atmosphere has a negligible concentration of SF 6 .
Sulfur hexafluoride was used as a non-toxic test gas in an experiment at St John's Wood tube station in London , United Kingdom on 25 March 2007. [ 29 ] The gas was released throughout the station, and monitored as it drifted around. The purpose of the experiment, which had been announced earlier in March by the Secretary of State for Transport Douglas Alexander , was to investigate how toxic gas might spread throughout London Underground stations and buildings during a terrorist attack.
Sulfur hexafluoride is also routinely used as a tracer gas in laboratory fume hood containment testing. The gas is used in the final stage of ASHRAE 110 fume hood qualification. A plume of gas is generated inside of the fume hood and a battery of tests are performed while a gas analyzer arranged outside of the hood samples for SF 6 to verify the containment properties of the fume hood.
It has been used successfully as a transient tracer in oceanography to study diapycnal mixing and air-sea gas exchange. [ 30 ] The concentration of sulfur hexafluoride in seawater (typically on the order of femtomoles per kilogram [ 31 ] ) has been classified by the international oceanography community as a "level one" measurement, denoting the highest priority data for observing ocean changes. [ 32 ]
According to the Intergovernmental Panel on Climate Change , SF 6 is the most potent greenhouse gas . Its global warming potential of 23,900 times that of CO 2 when compared over a 100-year period. [ 45 ] Sulfur hexafluoride is inert in the troposphere and stratosphere and is extremely long-lived, with an estimated atmospheric lifetime of 800–3,200 years. [ 46 ]
Measurements of SF 6 show that its global average mixing ratio has increased from a steady base of about 54 parts per quadrillion [ 12 ] prior to industrialization, to over 11.5 parts per trillion (ppt) as of October 2023, and is increasing by about 0.4 ppt (3.5%) per year. [ 9 ] [ 47 ] Average global SF 6 concentrations increased by about 7% per year during the 1980s and 1990s, mostly as the result of its use in magnesium production, and by electrical utilities and electronics manufacturers. Given the small amounts of SF 6 released compared to carbon dioxide , its overall individual contribution to global warming is estimated to be less than 0.2%, [ 48 ] however the collective contribution of it and similar man-made halogenated gases has reached about 10% as of 2020. [ 49 ] Alternatives are being tested. [ 50 ] [ 51 ]
In Europe, SF 6 falls under the F-Gas directive which ban or control its use for several applications. [ 52 ] Since 1 January 2006, SF 6 is banned as a tracer gas and in all applications except high-voltage switchgear . [ 53 ] It was reported in 2013 that a three-year effort by the United States Department of Energy to identify and fix leaks at its laboratories in the United States such as the Princeton Plasma Physics Laboratory , where the gas is used as a high voltage insulator, had been productive, cutting annual leaks by 1,030 kilograms (2,280 pounds). This was done by comparing purchases with inventory, assuming the difference was leaked, then locating and fixing the leaks. [ 54 ]
Sulfur hexafluoride is a nontoxic gas, but by displacing oxygen in the lungs, it also carries the risk of asphyxia if too much is inhaled. [ 55 ] Since it is more dense than air, a substantial quantity of gas, when released, will settle in low-lying areas and present a significant risk of asphyxiation if the area is entered. That is particularly relevant to its use as an insulator in electrical equipment since workers may be in trenches or pits below equipment containing SF 6 . [ 56 ]
As with all gases, the density of SF 6 affects the resonance frequencies of the vocal tract, thus changing drastically the vocal sound qualities, or timbre , of those who inhale it. It does not affect the vibrations of the vocal folds. The density of sulfur hexafluoride is relatively high at room temperature and pressure due to the gas's large molar mass . Unlike helium , which has a molar mass of about 4 g/mol and pitches the voice up, SF 6 has a molar mass of about 146 g/mol, and the speed of sound through the gas is about 134 m/s at room temperature, pitching the voice down. For comparison, the molar mass of air, which is about 80% nitrogen and 20% oxygen, is approximately 30 g/mol which leads to a speed of sound of 343 m/s. [ 57 ]
Sulfur hexafluoride has an anesthetic potency slightly lower than nitrous oxide ; [ 58 ] it is classified as a mild anesthetic. [ 59 ] | https://en.wikipedia.org/wiki/Sulfur_hexafluoride |
Sulfur isotope biogeochemistry is the study of the distribution of sulfur isotopes in biological and geological materials. In addition to its common isotope, 32 S, sulfur has three rare stable isotopes: 34 S, 36 S, and 33 S. The distribution of these isotopes in the environment is controlled by many biochemical and physical processes, including biological metabolisms, mineral formation processes, and atmospheric chemistry. Measuring the abundance of sulfur stable isotopes in natural materials, like bacterial cultures, minerals, or seawater, can reveal information about these processes both in the modern environment and over Earth history. [ 1 ]
Sulfur has 24 known isotopes , [ 2 ] 4 of which are stable (meaning that they do not undergo radioactive decay ). [ 3 ] 32 S, the common isotope of sulfur, makes up 95.0% of the natural sulfur on Earth. [ 2 ] In the atomic symbol of 32 S, the number 32 refers to the mass of each sulfur atom in daltons , the result of the 16 protons and 16 neutrons of 1 dalton each that make up the sulfur nucleus. The three rare stable isotopes of sulfur are 34 S (4.2% of natural sulfur), 33 S (0.75%), and 36 S (0.015%). [ 4 ] These isotopes differ from 32 S in the number of neutrons in each atom, but not the number of protons or electrons ; as a result, each isotope has a slightly different mass, but has nearly identical chemical properties. [ 3 ]
Small differences in mass between stable isotopes of the same element can lead to a phenomenon called an "isotope effect," where heavier or lighter isotopes are preferentially incorporated into different natural materials depending on the materials' chemical composition or physical state. [ 5 ] Isotope effects are divided into two main groups: kinetic isotope effects and equilibrium isotope effects . [ 5 ] A kinetic isotope effect occurs when a reaction is irreversible, meaning that the reaction only proceeds in the direction from reactants to products. [ 3 ] [ 5 ] Kinetic isotope effects cause isotopic fractionation —meaning that they affect the isotopic composition of reactant and product compounds—because the mass differences between stable isotopes can affect the rate of chemical reactions. [ 5 ] It takes more energy to reach the transition state of a reaction if the compound has bonds with a heavier isotope, which causes the compound with heavier isotopes to react more slowly. [ 5 ] Normal kinetic isotope effects cause the lighter isotope (or isotopes) to be preferentially included in a reaction's product. [ 5 ] The products are then said to be "depleted" in the heavy isotope relative to the reactant. [ 3 ] Rarely, inverse kinetic isotope effects may occur, where the heavier isotope is preferentially included in a reaction's product. [ 5 ] [ 6 ]
Equilibrium isotope effects cause fractionation because it is more chemically favorable for heavy isotopes to take part in stronger bonds. [ 5 ] An equilibrium isotope effect occurs when a reaction is at equilibrium, meaning that the reaction is able to occur in both directions simultaneously. [ 3 ] When a reaction is at equilibrium, heavy isotopes will preferentially accumulate where they can form the strongest bonds. [ 3 ] For example, when the water in a sealed, half-full bottle is in equilibrium with the vapor above it, the heavier isotopes 2 H and 18 O will accumulate in the liquid, where they form stronger bonds, while the lighter isotopes 1 H and 16 O will accumulate in the vapor. [ 7 ] The liquid is then said to be "enriched" in the heavy isotope relative to the vapor. [ 3 ]
Differences in the abundance of stable isotopes among natural materials are usually very small (natural differences in the ratio of rare to common isotope are almost always below 0.1%, and sometimes much smaller). [ 5 ] Nevertheless, these very small differences can record meaningful biological and geological processes. To facilitate comparison of these small but meaningful differences, isotope abundances in natural materials are often reported relative to isotope abundances in designated standards. [ 3 ] [ 5 ] The convention for reporting the measured difference between a sample and a standard is called "delta notation." For example, imagine an element X for which we wish to compare the rare, heavy stable isotope with atomic mass A ( A X) to the light, common isotope with atomic mass B ( B X). The abundance of A X and B X in any given material is reported with the notation δ A X. δ A X for the sample material is calculated as follows: [ 5 ]
δ values are most commonly reported in parts per thousand, commonly referred to in isotope chemistry as per mille and represented by the symbol ‰. To report δ values in per mille, the δ value as calculated above should be multiplied by 1000:
While an isotope effect is the physical tendency for stable isotopes to distribute in a particular way, the isotopic fractionation is the measurable result of this tendency. [ 5 ] The isotopic fractionation of a natural process can be calculated from measured isotope abundances. The calculated value is called a "fractionation factor," and allows the effect of different processes on isotope distributions to be mathematically compared. [ 5 ] For example, imagine a chemical reaction Reactant → Product. Reactant and Product are materials that both contain the element X, and X has two stable isotopes, A X (the heavy isotope, with a mass of A) and B X (the light isotope, with a mass of B). The fractionation factor for the element X in the reaction Reactant → Product is represented by the notation
Fractionation factors can also be reported using the notation A ε Product/Reactant , which is sometimes called the "enrichment factor" and is calculated as follows: [ 5 ]
Like δ values, ε values can be reported in per mille by multiplying by 1000.
All kinetic and equilibrium isotope effects result from differences in atomic mass. [ 3 ] [ 5 ] As a result, a reaction that fractionates 34 S will also fractionate 33 S and 36 S, and the fractionation factor for each isotope will be mathematically proportional to its mass. [ 3 ] Because of the mathematical relationships of their masses, the observed relationships between δ 34 S, δ 33 S, and δ 36 S in most natural materials are approximately δ 33 S = 0.515 × δ 34 S and δ 36 S = 1.90 × δ 34 S. [ 8 ] Rarely, natural processes can create deviations from this relationship, and these deviations are reported as Δ 33 S and Δ 36 S values, usually pronounced as "cap delta." These values are typically calculated as follows: [ 3 ] [ 9 ]
However, the method for calculating Δ 33 S and Δ 36 S values is not standardized, and can differ among publications. [ 10 ]
Agreed-upon reference materials are required so that reported δ values are comparable among studies. For the sulfur isotope system, δ 34 S values are reported on the Vienna-Cañon Diablo Troilite (VCDT) scale. [ 11 ] The original CDT scale was based on a sample of the mineral troilite recovered from the Canyon Diablo meteorite at Meteor Crater , Arizona, US. [ 3 ] The Cañon Diablo Troilite was assigned a δ 34 S value of 0‰. [ 3 ] However, troilite from the Canyon Diablo meteorite was later discovered to have variable sulfur isotope composition. [ 12 ] As a result, VCDT was established as a hypothetical sulfur isotope reference with a 34 R value of 0.044151 [ 11 ] and δ 34 S of 0‰, but no physical sample of VCDT exists. Samples are now measured in comparison to International Atomic Energy Agency (IAEA) reference materials, which are well-characterized, lab-prepared compounds with known δ 34 S values. [ 13 ] A commonly-used IAEA reference material is IAEA-S-1, a silver sulfide reference material with a δ 34 S value of −0.30‰ VCDT. [ 4 ] [ 14 ] 33 S and 36 S abundance can also be measured relative to IAEA reference materials and reported on the VCDT scale. [ 13 ] For these isotopes, too, VCDT is established as having δ 33 S and δ 36 S values of 0‰. [ 13 ] The 33 R value of VCDT is 0.007877 and the 36 R value is 0.0002. [ 13 ] IAEA-S-1 has a 33 R value of 0.0007878 and a δ 33 S value of −0.05‰ VCDT; it has a δ 36 S value of −0.6‰ VCDT. [ 13 ]
The sulfur isotopic composition of natural samples can be determined by Elemental Analysis-Isotope Ratio Mass Spectrometry (EA-IRMS), [ 15 ] [ 16 ] by Dual Inlet-Isotope Ratio Mass Spectrometry (DI-IRMS), [ 17 ] by Multi-Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS), [ 18 ] by Secondary Ion Mass Spectrometry (SIMS), [ 1 ] [ 19 ] or by Nanoscale secondary ion mass spectrometry (NanoSIMS). [ 20 ] MC-ICPMS can be paired with gas chromatography (GC-MC-ICPMS) to separate certain volatile compounds in a sample and measure the sulfur isotopic composition of individual compounds. [ 21 ] [ 22 ]
The sulfur isotopic compositions of minerals and porewater in sediment are subject to accumulation and diffusion after burial. Reactive transport models are often used to account for the effect of such physical processes and find out the isotopic effect of the process studied. [ 23 ] [ 24 ] [ 25 ]
Sulfur is present in the environment in solids, gases, and aqueous species. Sulfur-containing solids on Earth include the common minerals pyrite (FeS 2 ), galena (PbS), and gypsum (CaSO 4 •2H 2 O). Sulfur is also an important component of biological material, including in the essential amino acids cysteine and methionine , the B vitamins thiamine and biotin , and the ubiquitous substrate coenzyme A . In the ocean and other natural waters, sulfur is abundant as dissolved sulfate . Hydrogen sulfide is also present in some parts of the deep ocean where it is released from hydrothermal vents. Both sulfate and sulfide can be used by specialized microbes to obtain energy or to grow. [ 26 ] Gases including sulfur dioxide and carbonyl sulfide make up the atmospheric component of the sulfur cycle. Any process that transports or chemically transforms sulfur between these many natural materials also has the potential to fractionate sulfur isotopes.
Sulfur in natural materials can vary widely in isotopic composition: compilations of the δ 34 S values of natural sulfur-containing materials include values ranging from −55‰ to 135‰ VCDT. [ 27 ] The ranges of δ 34 S values vary across sulfur-containing materials: for example, the sulfur in animal tissue ranges from ~ −10 to +20‰ VCDT, while the sulfate in natural waters ranges from ~ −20 to +135‰ VCDT. [ 27 ] The range of sulfur isotope abundances in different natural materials results from the isotope fractionation associated with natural processes like the formation and modification of those materials, discussed in the next section.
Numerous natural processes are capable of fractionating sulfur isotopes. Microbes are capable of a wide variety of sulfur metabolisms, including the oxidation, reduction, and disproportionation (or simultaneous oxidation and reduction) of sulfur compounds. [ 1 ] The effect of these metabolisms on sulfur isotopic composition of the reactants and products is also highly variable, depending on the rate of relevant reactions, availability of nutrients, diagenesis , and other biological, physical and environmental parameters. [ 25 ] [ 28 ] [ 29 ] As an example, the microbial reduction of sulfate to sulfide generally results in a 34 S-depleted product, but the strength of this fractionation has been shown to range from 0 to 65.6‰ VCDT. [ 28 ] [ 30 ]
Many abiotic processes also fractionate sulfur isotopes. Small fractionations with ε values from 0–5‰ have been observed in the formation of the mineral gypsum, an evaporite mineral produced through the evaporation of seawater. [ 31 ] Some sulfide minerals , including pyrite and galena, can form through thermochemical sulfate reduction , a process in which seawater sulfate trapped in seafloor rock is reduced to sulfide by geological heat as the rock is buried; this process generally fractionates sulfur more strongly than gypsum formation. [ 32 ]
Prior to the rise of oxygen in Earth's atmosphere (referred to as the Great Oxidation Event ), additional sulfur-fractionating processes referred to as mass-anomalous or mass-independent fractionation uniquely affected the abundance of 33 S and 36 S in the rock record. [ 9 ] Mass-anomalous fractionations are rare, but they can occur through certain photochemical reactions of gases in the atmosphere. [ 33 ] [ 34 ] Studies have shown that photochemical reactions of atmospheric sulfur dioxide can cause substantial mass-anomalous fractionation of sulfur isotopes. [ 33 ] [ 34 ]
Sulfide: −8.6 to −5.5
All organisms metabolize sulfur, and it is incorporated into the structure of proteins , polysaccharides , steroids , and many coenzymes . [ 62 ] The biological pathway by which an organism takes up and/or removes sulfur can have significant impacts on the sulfur isotope composition of the organism and its environment.
Microorganisms that consume and reduce sulfate in relatively large quantities perform a different pathway of sulfur uptake called dissimilatory sulfate reduction . These organisms use sulfate reduction as an energy source as opposed to a way to synthesize new cell components, and remove the resulting sulfide as a waste product. Microbial sulfate reduction has been demonstrated to fractionate sulfur isotopes in bacteria, with some studies showing a dependence upon sulfate concentration [ 28 ] and/or temperature. [ 64 ] Studies examining dozens of species of dissimilatory sulfate reducing microbes have observed sulfur isotope fractionations ranging from −65.6‰ to 0‰. [ 28 ] [ 30 ] [ 39 ] [ 40 ] [ 41 ] [ 42 ] [ 43 ] [ 44 ] [ 45 ] [ 46 ] [ 47 ] [ 48 ]
Some organisms take in relatively small amounts of sulfate in a process called assimilatory sulfate reduction , for the purpose of synthesizing compounds that contain sulfur, such as the amino acids methionine and cysteine that can then be used to make proteins . [ 65 ] In phytoplankton, most of the sulfur taken up through assimilatory sulfate reduction is incorporated into biomass as proteins (~35%), sulfate esters (~20%), and low-weight sulfur-containing compounds (~40%). [ 66 ] [ 67 ] Literature on the isotopic fractionation effects of the assimilatory sulfate reduction pathway is much more limited than that discussing dissimilatory sulfate reduction, but some sources report slight isotopic variations ( δ 34 S = −4.4‰ to +0.5‰) in the resulting organic sulfur relative to the surrounding sulfate. [ 68 ]
While dissimilatory sulfate reduction and assimilatory sulfate reduction are two of the most common pathways by which organisms take up and utilize sulfate, there are many other pathways by which living things take up sulfur. For example, sulfur oxidation of compounds like hydrogen sulfide and elemental sulfur is performed by lithotrophic bacteria and chemosynthetic archaea . [ 69 ] [ 70 ] Most animals obtain sulfur directly from the methionine and cysteine in the protein they consume. [ 71 ]
Previous efforts to understand how sulfur metabolism and biosynthetic pathways relied on expensive labeling experiments using radioactive 35 S. By leveraging natural assimilatory processes, stable isotope ratios can be used to track the sources of sulfur for plants, plant organs used in sulfur acquisition, the movement of sulfur through plants.
Sulfur (S) stable isotope composition measurements are often performed using an Elemental Analysis-Isotope Ratio Mass Spectrometer, ( EA-IRMS ) [ 72 ] in which organic sulfur from biological samples is oxidized to sulfur dioxide (SO 2 ) and analyzed on a mass spectrometer. The mass spectrometer is used to quantify the ratio of the lighter ( 32 S 16 O 2 ) to the heavier ( 34 S 16 O 2 ) isotopologue of SO 2 , and this ratio is then compared to sulfur isotope standards in order to standardize data to the VSMOW scale. In biological materials, sulfur is scarce relative to other organic elements like carbon and oxygen, introducing some additional difficulty in measuring its stable isotope composition. The elemental S composition of plant matter is ≈0.2%, accounting for approximately 2 mmol/m 2 in most leaf tissue. [ 73 ] In order to reach detectable levels of 30 ng to 3 μg of elemental S to calculate reliable δ 34 S values, leaf tissue samples need to be between 2–5 mg.
Improvements in detection have been made in recent years in the utilization of gas chromatography coupled with multicollector ICP-MS (GC/MC-ICP-MS) [ 74 ] to be able to measure pmol quantities of organic S. Additionally, ICP-MS has been used to measure nanomolar quantities of dissolved sulfate. [ 75 ] Most studies have focused on measuring the bulk δ 34 S value of plant tissues and few studies have been performed on measuring the δ 34 S values of individual S-containing compounds. The coupling of high-performance liquid chromatography ( HPLC ) with ICP-MS has been proposed as a way to test individual S-containing compounds. [ 73 ]
Each year, approximately 0.3 gigatons of elemental sulfur is converted into organic matter by photosynthetic organisms. [ 76 ] This organic sulfur is allocated into a diversity of compounds such as amino acids – namely cysteine (Cys) and methionine (Met) – proteins, cofactors, antioxidants, sulfate groups, Fe-S centers and secondary metabolites. The three main sources of sulfur are atmospheric, soil, and aquatic.
Most vegetation can acquire sulfur from gaseous atmospheric compounds or various ions either in soil solutions or water bodies. [ 77 ] Uptake of gaseous and dissolved sulfur compounds apparently occurs with little accompanying isotopic selectivity. [ 78 ] Dissolved sulfate (SO 4 2- ) is considered to be the central pool which is metabolized by microorganisms and plants as most forms of atmospheric sulfur is oxidized into sulfate. Atmospheric sulfur is eventually returned to the soil when it is scrubbed from the atmosphere during precipitation or through dryfall. [ 77 ]
Many plants acquire sulfur through gaseous atmospheric compounds. Leaves of trees have δ 34 S values lying between those of air and soil, suggesting that there is uptake occurring from atmospheric and soil sources. The δ 34 S values of trees has also been demonstrated to be height dependent, with the foliage at the tops of conifers , bull rushes and deciduous trees having δ 34 S values more reflective of the atmosphere and lower foliage having δ 34 S values closer to that of soil. [ 77 ] It has been proposed that this is due to upper foliage exerting a canopy action on the lower branches, taking up atmospheric sulfur before it can reach lower levels. This is further supported with the epiphytic lichens and mosses having δ 34 S values close to atmospheric S compounds. This occurs due to lichens and mosses having no access to soil and relying on the direct uptake of gaseous sulfur, dissolved sulfur through rainfall and dry fall accumulation, providing a cumulative record of atmospheric sulfur isotope composition. [ 77 ] [ 79 ]
Main forms of atmospheric sulfur come from the natural sulfur emissions formed biologically and emitted as H 2 S or organic sulfur gases such as DMS (dimethyl sulfide), COS (carbonyl sulfide), and CS 2 (carbon disulfide). These gases are predominantly formed over oceans, wetlands, salt marshes, and estuaries by algae and bacteria. [ 80 ] Anthropogenic emissions have increased the concentration of sulfur in the atmosphere mainly through emissions of SO 2 , from coal, oil, industrial processes, and biomass burning. In 2000, global anthropogenic emission of sulfur was estimated of 55.2–68 Tg S per year, which is much higher than the natural sulfur emissions estimated to be 34 Tg S per year. [ 80 ] In the event of excess sulfur in plant tissue, it has been demonstrated that when exposed to high doses of sulfur dioxide, plants emit hydrogen sulfide (H 2 S) and possibly other reduced sulfur compounds in response to high sulfur loading [ 78 ]
If soil sulfur is derived consistently from one source, the water-soluble and insoluble organic S fractions acquire similar isotopic compositions. In the case that there are two or more sources and/or if the isotopic composition of atmospheric or groundwater sulfate fluctuates, there may not be sufficient time for isotopic homogenization among the various forms of sulfur. The primary form of sulfur in soil is sulfate, which is transported upwards through the root system with minimal δ 34 S fractionation by 1–2‰. [ 81 ] In contrast to higher canopy plants reflecting atmospheric δ 34 S, protected understory plants tend to reflect soil sulfur. [ 77 ]
The forms of sulfur available in aquatic environments depends on whether it is a marine or freshwater environment. Freshwater environments are more varied and subject to a multitude of sulfur inputs and outputs, including atmospheric deposition, runoff, diagenesis of bedrock and the presence of microbial sulfate reducers (MSR). Overall, the main species of sulfur in freshwater environments are hydrogen sulfide and sulfate. In estuaries, plant roots extend into sulfide-rich, 34 S-depleted sediments created by MSR, and incorporate that sulfide into their biomass. However, levels of sulfide produced by MSR can be toxic, and it has been proposed that these plants pump oxygen into their roots to oxidize sulfide into the less toxic sulfate. [ 78 ] In these environments algae will preferentially acquire sulfur from HS − if present, rather than the more abundant sulfate, as sulfide can be readily incorporated into the direct formation of cysteine. This is consistent with cyanobacteria being able to carry out anoxygenic photosynthesis using sulfide. [ 77 ]
In marine environments, the main forms of sulfur available is in sulfate at ~29 mM and a δ 34 S of 21‰ in seawater. At the surface of the sea, this excess in sulfur is subsequently converted into dimethylsulfoniopropionate (DMSP) by algae as an osmolyte and a repellent against grazing. DMSP also accounts for 50–100% of bacterial sulfur demand, making it the most important source of reduced sulfur for marine bacteria. DMSP's cleavage product dimethyl sulfide (DMS) is highly volatile, escaping the ocean into the atmosphere with emissions ranging between 15 and 33 Tg S year −1 [ 80 ] and accounting for 50–60% of the total natural reduced sulfur flux to the atmosphere. In seafloor sediments, microbial sulfate reduction is a major biogeochemical process that consumes organic carbon. [ 82 ] Microbial sulfate reduction can completely use up sulfate from the seawater and accumulate hydrogen sulfide in the sediment. Sulfide reoxidation and disproportionation are also thought to be major processes affecting the sulfur isotopic compositions of marine minerals and sediment porewater. [ 1 ] [ 25 ]
~90% of the organic sulfur in plants is concentrated in the amino acids cysteine and methionine. [ 81 ] Cysteine acts as the direct or indirect precursor to any other organic sulfur compounds in plants such as coenzyme-A, methionine, biotin, lipoic acid and glutathione. [ 78 ] The carbon skeleton necessary for sulfur assimilation are provided by glycolysis (acetyl-CoA), respiration (aspartic acid, Asp, which derives from oxaloacetate) and photorespiration (serine, Ser). [ 73 ] Because cysteine is a direct precursor to methionine, methionine is naturally 34 S-depleted in comparison to cysteine. [ 73 ] The majority of sulfur is generally in the organic form but, when excess sulfur is available in the environment, inorganic sulfate becomes the major sulfur form. In most plants, 34 S discrimination is minimal, and in a study of rice plants it was observed that discrimination takes place in the uptake stage, depleting imported sulfate by 1–2‰ from the source. [ 83 ] This effect is through the expression of SO 4 2− transporter genes (SULTR), 14 of which have been identified – which are expressed dependent on the availability of sulfate in the environment. When sulfate is plentiful low affinity transporters are expressed and when sulfate is scarce high affinity genes with greater 34 S discrimination are expressed. [ 73 ] [ 83 ]
Sulfate transported through the roots and SO 2 diffusing into leaves becomes the pool for plants to assimilate sulfur throughout their tissues. Though there is minimal fractionation from the source sulfur of the total plant organic matter, in wheat, roots and stems are depleted from soil by 2‰ and leaves and grain are 2‰ enriched. The 34 S enrichment in leaf whole matter is not caused by 34 S-enriched sulfate present in the leaf, but is the result of the 34 S-enrichment arriving at sink organs causing proteins in the leaves to be 34 S-enriched. [ 73 ] In rice, translocation from root to shoot does not discriminate S isotopes, however, the sulfate pools of the shoot are significantly 34 S-enriched with respect to the sulfate pools of both root and sap. As sulfate moves through the plant system and is incorporated into biomass, the pool becomes enriched, giving organs such as leaves and grains higher δ 34 S values than earlier tissues. [ 83 ]
Signatures of mass-anomalous sulfur isotope fractionation preserved in the rock record have been an important piece of evidence for understanding the Great Oxidation Event , the sudden rise of oxygen on the ancient Earth. [ 9 ] [ 84 ] Nonzero values of Δ 33 S and Δ 36 S are present in the sulfur-bearing minerals of Precambrian rock formed greater than 2.45 billion years ago, but completely absent from rock less than 2.09 billion years old. [ 9 ] Multiple mechanisms have been proposed for how oxygen prevents the fingerprints of mass-anomalous fractionation from being created and preserved; nevertheless, all studies of Δ 33 S and Δ 36 S records conclude that oxygen was essentially absent from Earth's atmosphere prior to 2.45 billion years ago. [ 9 ] [ 10 ] [ 33 ] [ 85 ] [ 86 ]
A number of microbial metabolisms fractionate sulfur isotopes in distinctive ways, and the sulfur isotopic fingerprints of these metabolisms can be preserved in minerals and ancient organic matter. [ 1 ] By measuring the sulfur isotopic composition of these preserved materials, scientists can reconstruct ancient biological processes and the environments where they occurred. [ 1 ] δ 34 S values in the geologic record have been inferred to reveal the history of microbial sulfate reduction [ 87 ] [ 88 ] and sulfide oxidation. [ 25 ] [ 89 ] Paired δ 34 S and Δ 33 S records have also been used to show ancient microbial sulfur disproportionation. [ 90 ] [ 29 ]
Microbial dissimilatory sulfate reduction (MSR), an energy-yielding metabolism performed by bacteria in anoxic environments, is associated with an especially large fractionation factor. [ 1 ] The observed 34 ε MSR values range from 0 to −65.6‰. [ 28 ] [ 30 ] [ 39 ] [ 40 ] [ 41 ] [ 42 ] [ 43 ] [ 44 ] Many factors influence the size of this fractionation, including sulfate reduction rate, [ 35 ] [ 40 ] sulfate concentration and transport, [ 28 ] [ 44 ] availability of electron donors and other nutrients, [ 30 ] [ 42 ] [ 43 ] and physiological differences like protein expression. [ 45 ] Sulfide produced through MSR may then go on to form the mineral pyrite, preserving the 34 S-depleted fingerprint of MSR in sedimentary rocks. [ 1 ] [ 60 ] Many studies have investigated the δ 34 S values of ancient pyrite in order to understand past biological and environmental conditions. [ 1 ] For example, pyrite δ 34 S records have been used to reconstruct shifts in primary productivity levels, [ 91 ] changing ocean oxygen content, [ 92 ] [ 93 ] and glacial-interglacial changes in sea level and weathering. [ 94 ] Some studies compare sulfur isotopes in pyrite to a second sulfur-containing material, like dissolved sulfate or preserved organic matter. [ 25 ] [ 91 ] [ 92 ] Comparing pyrite to another material gives a fuller picture of how sulfur moved through ancient environments: it provides clues about the size of ancient 34 ε MSR values and the environmental conditions controlling MSR fractionation of sulfur isotopes. [ 91 ] [ 92 ]
δ 34 S records have been used to infer changes in seawater sulfate concentrations. [ 95 ] Because the δ 34 S values of carbonate-associated sulfate are thought to be sensitive to seawater sulfate levels, these measurements have been used to reconstruct the history of seawater sulfate. [ 96 ] δ 34 S values of pyrite have also been applied to reconstruct the concentration of seawater sulfate, based on expected biological fractionations at low sulfate concentrations. [ 97 ] [ 98 ] Both of these methods rely on assumptions about the depositional environment or the biological community, creating some uncertainty in the resulting reconstructions. [ 28 ] [ 96 ] | https://en.wikipedia.org/wiki/Sulfur_isotope_biogeochemistry |
Sulfur mononitride is an inorganic compound with the molecular formula SN. It is the sulfur analogue of and isoelectronic to the radical nitric oxide , NO. It was initially detected in 1975, in outer space in giant molecular clouds and later the coma of comets. [ 1 ] This spurred further laboratory studies of the compound. Synthetically, it is produced by electric discharge in mixtures of nitrogen and sulfur compounds, or combustion in the gas phase and by photolysis in solution. [ 2 ]
The NS radical is a highly transient species, with a lifetime on the order of milliseconds, but it can be observed spectroscopically over short periods of time through several methods of generation. NS is too reactive to isolate as a solid or liquid, and has only been prepared as a vapor in low pressure or low-temperature matrices due to its tendency to rapidly oligomerize to more stable, diamagnetic species. [ 3 ]
Transmission of electric discharge through a glass tube with quartz windows containing a mixture of nitrogen and sulfur vapor (rigorously free of oxygen) results in the spectrum of emitted light gaining bands consistent with the formation of NS. [ 4 ]
Passing a mixture of gaseous N 2 and S 2 Cl 2 through the side arm of an absorption cell undergoing microwave discharge produces NS. Infrared diode laser spectroscopy taken using this method allowed for derivation of the equilibrium rotational constant, and therefore calculation of the equilibrium bond length as 1.4940 Å. [ 5 ]
With low pressure microwave discharge of elemental nitrogen and sulfur, followed by low temperature trapping in argon matrices, one obtains a mixture of products including NS, NNS, SNS, and NSS. By adding excess sulfur, SSNS is also produced. [ 6 ]
Methane was premixed with fuel in the form of either O 2 , N 2 O, or air and burned at ambient pressure. The source of nitrogen was introduced by addition of 1–5 mol% NH 3 gas and sulfur by 0.01–0.5 mol% H 2 S or SF 6 gas. A steady state concentration of NS within the flame front is observed by laser-induced fluorescence (LIF) spectrum. [ 7 ]
The NS radical was detected by LIF spectrum as the product of photolysis of tetranitrogen tetrasulfide (N 4 S 4 ) gas by a 248 nm laser. [ 8 ]
Aerated solutions of Cr(CH 3 CN) 5 (NS) 2+ are highly photoactive and prone to rapid decomposition. Deaerated solutions of Cr(CH 3 CN) 5 (NS) 2+ in acetonitrile are stable as long as they are kept in the dark. Continuous photolysis using 366 nm light is slow, while using a 355 nm pulsed laser results in faster labilization of NS. [ 9 ]
Evidence suggests that NS can react with itself to reach N 2 S 2 , N 4 S 4 , and polymers of the form (NS) x . (NS) x forms from polymerization of cyclo-N 2 S 2 . [ 3 ]
Trans -NSSN results from direct dimerization of NS. [ 3 ]
N 3 S 3 has been observed through photoelectron spectroscopy of vapors of the (SN) x , polymer, but has not yet been characterized further. Attempts to produce N 3 S 3 by oxidation of [PPN] [S 3 N 3 ] were unsuccessful. [ 10 ] Its theorized that rapid dimerization to (N 3 S 3 ) 2 will disproportionate irreversibly to N 4 S 4 and N 2 S 2 . [ 3 ]
The radical decay time of NS alone is on the order of 1-3 ms. As evident by no change to this decay time upon addition of NO or O 2 at ambient temperatures, the NS radical is unreactive with NO and O 2 . However, rapid, first-order decay is observed with the addition of NO 2 . This reaction is proposed to proceed through various intermediates, ultimately reaching final products of N 2 and SO 2 . [ 8 ] This rapid reaction occurs with a rate constant of k = (2.54 ± 0.12) × 10 −11 cm 3 molecules −1 s −1 at 295 K. By use of Density Functional Theory based computational calculations, the minima and transition states of the potential energy surface of this reaction have been predicted. [ 8 ]
Within the inner coma of comets, many reactions are theorized to be relevant to the formation and reactivity of the NS radical. [ 11 ]
As a ligand, NS acts as a σ-donor and π-acceptor, forming metal-thionitrosyl complexes. Transition-metal thionitrosyl complexes have been prepared by the following procedures: [ 12 ]
From X-ray crystallography of many of such metal-thionitrosyl complexes, one can observe that the M-N-S bond angle is nearly linear, suggesting sp hybridization about N. Short M-N distances and long N-S distances reflect the resonance structure of M=N=S having greater contribution than M-N≡S. [ 12 ]
Typical v (NS) IR stretching frequencies are approximately 1065 cm −1 for low-valent transition metal complexes and around 1390 cm −1 in the high valent cases, whereas the free gas-phase radical exhibits a 1204 cm −1 signal. [ 3 ]
The electronic structures of Fe(S 2 CNMe 2 ) 2 (NE), where E=O, S, or Se were calculated using Density Functional Theory methods. It was found that the large Mulliken spin density remained concentrated on the Fe(NE) core and Fe-N distances experienced little change from the chalcogen atom used. The HOMO of both nitrosyl and thionitrosyl complexes retained 1a 1 (d z 2 ) character. The small changes in the energies of the spin orbitals of the complexes, particularly the decreased energetic gap between 2b 2 and 1b 1 and 2b 1 and 1b 1 orbitals is attributed to NS being a weaker π-acceptor than NO. [ 9 ]
When a spin-trapping agent, such as Fe(S 2 CNEt 2 ) 2 is present during the photolysis of Cr(CH 3 CN) 5 (NS) 2+ , new S=1/2 EPR bands are observed, attributed to the formation of Fe(S 2 CNEt 2 ) 2 (NS), and the signal from Cr(CH 3 CN) 5 (NS) 2+ disappears. This suggests that the NS radical has transferred from the chromium complex to the iron complex. [ 9 ]
An example of an NS in situ transfer is the following reaction, which needs light to occur:
This was particularly significant as it was the first controlled and well-characterized reactivity of NS in solution. Further, it showed the potential for similar reactivity in known reactions with NO, such as use of this iron dithiocarbamate complex. [ 3 ]
The valence electrons of this compound match those of nitric oxide . Sulfur mononitride can be described as some average of a set of resonance structures . The singly bonded structure (first resonance structure shown) has little contribution. The formal bond order is considered to be 2.5.
The decreasing electronegativity with increasingly heavy chalcogenides leads to a reversal of the dipole. In NO, oxygen is the more electronegative element. In NS, nitrogen is more electronegative. The NS radical is significantly more unstable and prone to catenation than NO. [ 3 ]
Molecules in distant astronomical regions can be identified based on their unique rotational transitions, of which the corresponding microwave frequencies are detectable by antennae on Earth. The presence of interstellar sulfur mononitride was first reported in 1975 by back to back letters published in the Astrophysical Journal.
Interstellar NS was first identified in the giant molecular cloud Sagittarius B2 (Sgr B2). Its presence was reported in two concurrent articles. Measurements conducted with the National Radio Astronomy Observatory telescope at Kitt Peak, Arizona, picked up millimeter-wavelength radiation in Sgr B2 attributed to c- state transitions of NS in the 2 Π 1/2 state from J=5/2 to J=3/2 at 115.16 GHz. [ 15 ] This assignment was confirmed by measurements conducted at University of Texas Millimeter Wave Observatory on Mount Locke as well, demonstrating J=5/2 to J=3/2 c -state and d -state transitions at 115.16 GHz and 115.6 GHz, respectively. Hyperfine interactions arise from 14 N magnetic and electric-quadrupole moments. [ 16 ]
NS has been detected in regions responsible for forming massive stars, such as giant molecular clouds like Sg B2 and cold, dark clouds such as L134N and TMC-1. One survey found NS in 12 out of 14 GMC studied, additionally observing the J=7/2 to J=5/2 and J=3/2 to J=1/2 transitions at 161 and 69 GHz, respectively. The abundance of NS in these regions was approximated based on the ratio of observed to intrinsic hyperfine line strengths as well as modeling using a statistical equilibrium program, finding low abundance in all except the Orion molecular cloud. [ 17 ]
NS was also observed in the coma of the comets Hyakutake and Hale-Bopp . It is believed that the observed abundance is higher than gas-phase, ion-molecule models due to an unidentified species X-NS photo-dissociating to release NS. [ 11 ]
Detection of NS at steady state concentration in the reaction zone of the combustion of methane doped with ammonia and a fuel sulfur such as H 2 S suggests that NS may be an important reactive intermediate in burning of hydrocarbon flames in a reducing atmosphere, which is relevant to coal pyrolysis and combustion. [ 7 ]
Fossil fuels contain bound nitrogen, which releases elevated levels of nitric oxide emissions during combustion. NO x emissions can be controlled by denitrification of the fuel source, combustion chamber modification, or both. One developing technique is the reburning of NO x , which is reduced to N 2 . These fuels also contain variable amounts of sulfur, which is oxidized to SO 2 . Therefore, understanding the reactivity of NO and SO 2 is crucial to the process of reburning. The experimental apparatus to test this involved a primary flame for producing combustion products, which were mixed with NO and SO 2 to mimic coal burning byproducts. This mixture was fed into the burner at atmospheric pressure. 1–2% decrease in NO x concentration is observed at various percentages of total fuel inlet (reburn ratio) in the presence of 0.1% SO 2 , which is attributed to the formation of H 2 S, HS, and the resulting reaction with NO, giving rise to NS. The reaction is: [ 18 ] | https://en.wikipedia.org/wiki/Sulfur_mononitride |
Sulfur monoxide is an inorganic compound with formula S O . It is only found as a dilute gas phase. When concentrated or condensed, it converts to S 2 O 2 ( disulfur dioxide ). It has been detected in space but is rarely encountered intact otherwise.
The SO molecule has a triplet ground state similar to O 2 and S 2 , that is, each molecule has two unpaired electrons. [ 2 ] The S−O bond length of 148.1 pm is similar to that found in lower sulfur oxides (e.g. S 8 O, S−O = 148 pm) but is longer than the S−O bond in gaseous S 2 O (146 pm), SO 2 (143.1 pm) and SO 3 (142 pm). [ 2 ]
The molecule is excited with near infrared radiation to the singlet state (with no unpaired electrons). The singlet state is believed to be more reactive than the ground triplet state, in the same way that singlet oxygen is more reactive than triplet oxygen . [ 3 ]
The SO molecule is thermodynamically unstable, converting initially to S 2 O 2 . [ 2 ] Consequently controlled syntheses typically do not detect the presence of SO proper, but instead the reaction of a chemical trap or the terminal decomposition products of S 2 O 2 ( sulfur and sulfur dioxide ).
Production of SO as a reagent in organic syntheses has centred on using compounds that "extrude" SO. Examples include the decomposition of the relatively simple molecule ethylene episulfoxide : [ 4 ]
Yields directly from an episulfoxide are poor, and improve only moderately when the carbons are sterically shielded. [ 5 ] A much better approach decomposes a diaryl cyclic trisulfide oxide, C 10 H 6 S 3 O, produced from thionyl chloride and the di thiol . [ 6 ]
SO inserts into alkenes , alkynes and dienes producing thiiranes , molecules with three-membered rings containing sulfur. [ 7 ]
Sulfur monoxide may form transiently during the metallic reduction of thionyl bromide . [ 8 ]
In the laboratory, sulfur monoxide can be produced by treating sulfur dioxide with sulfur vapor in a glow discharge . [ 2 ] It has been detected in single-bubble sonoluminescence of concentrated sulfuric acid containing some dissolved noble gas . [ 9 ]
Benner and Stedman developed a chemiluminescence detector for sulfur via the reaction between sulfur monoxide and ozone : [ 10 ]
(* indicates an excited state )
As a ligand SO can bond in a number different ways: [ 11 ] [ 12 ]
Sulfur monoxide has been detected around Io , one of Jupiter 's moons, both in the atmosphere [ 15 ] and in the plasma torus . [ 16 ] It has also been found in the atmosphere of Venus , [ 17 ] in Comet Hale–Bopp , [ 18 ] in 67P/Churyumov–Gerasimenko , [ 19 ] and in the interstellar medium . [ 20 ]
On Io , SO is thought to be produced both by volcanic and photochemical routes. The principal photochemical reactions are proposed as follows: [ 21 ]
Sulfur monoxide has been found in NML Cygni . [ 22 ]
Sulfur monoxide may have some biological activity. The formation of transient SO in the coronary artery of pigs has been inferred from the reaction products, carbonyl sulfide and sulfur dioxide . [ 23 ]
Because of sulfur monoxide's rare occurrence in our atmosphere and poor stability, it is difficult to fully determine its hazards. But when condensed and compacted, it forms disulfur dioxide , which is relatively toxic and corrosive. This compound is also highly flammable (similar flammability to methane ) and when burned produces sulfur dioxide , a poisonous gas.
Sulfur dioxide SO 2 in presence of hexamethylbenzene C 6 (CH 3 ) 6 can be protonated under superacidic conditions ( HF·AsF 5 ) to give the non-rigid π-complex C 6 (CH 3 ) 6 SO 2+ . The SO 2+ moiety can essentially move barrierless over the benzene ring . The S−O bond length is 142.4(2) pm. [ 24 ]
SO converts to disulfur dioxide (S 2 O 2 ). [ 25 ] Disulfur dioxide is a planar molecule with C 2v symmetry . The S−O bond length is 145.8 pm, shorter than in the monomer, and the S−S bond length is 202.45 pm. The O−S−S angle is 112.7°. S 2 O 2 has a dipole moment of 3.17 D . [ 25 ] | https://en.wikipedia.org/wiki/Sulfur_monoxide |
Sulfur tetrachloride is an inorganic compound with chemical formula SCl 4 . It has only been obtained as an unstable pale yellow solid. The corresponding SF 4 is a stable, useful reagent.
It is obtained by treating sulfur dichloride with chlorine at 193 K:
It melts with simultaneous decomposition above −20 °C. [ 1 ]
Its solid structure is uncertain. It is probably the salt SCl 3 + Cl − , since related salts are known with noncoordinating anions . [ 2 ] [ 3 ] In contrast to this tetrachloride, SF 4 is a neutral molecule. [ 4 ]
It decomposes above −30 °C (242 K) to sulfur dichloride and chlorine.
It hydrolyzes readily:
Sulfur tetrachloride reacts with water, producing hydrogen chloride and sulfur dioxide through the hydrolysis process. Thionyl chloride is an implied intermediate. [ 5 ]
It can be oxidized by nitric acid : | https://en.wikipedia.org/wiki/Sulfur_tetrachloride |
Sulfur tetrafluoride is a chemical compound with the formula S F 4 . It is a colorless corrosive gas that releases dangerous hydrogen fluoride gas upon exposure to water or moisture. Sulfur tetrafluoride is a useful reagent for the preparation of organofluorine compounds , [ 3 ] some of which are important in the pharmaceutical and specialty chemical industries.
Sulfur in SF 4 is in the +4 oxidation state , with one lone pair of electrons. The atoms in SF 4 are arranged in a see-saw shape , with the sulfur atom at the center. One of the three equatorial positions is occupied by a nonbonding lone pair of electrons. Consequently, the molecule has two distinct types of F ligands, two axial and two equatorial. The relevant bond distances are S–F ax = 164.3 pm and S–F eq = 154.2 pm. It is typical for the axial ligands in hypervalent molecules to be bonded less strongly.
The 19 F NMR spectrum of SF 4 reveals only one signal, which indicates that the axial and equatorial F atom positions rapidly interconvert via pseudorotation . [ 4 ]
At the laboratory scale, sulfur tetrafluoride is prepared from elemental sulfur and cobaltic fluoride [ 5 ]
SF 4 is industrially produced by the reaction of SCl 2 and NaF with acetonitrile as a catalyst [ 6 ]
At higher temperatures (e.g. 225–450 °C), the solvent is superfluous. Moreover, sulfur dichloride may be replaced by elemental sulfur (S) and chlorine (Cl 2 ) . [ 7 ] [ 8 ]
A low-temperature (e.g. 20–86 °C) alternative to the chlorinative process above uses liquid bromine (Br 2 ) as oxidant and solvent: [ 9 ]
In organic synthesis , SF 4 is used to convert COH and C=O groups into CF and CF 2 groups, respectively. [ 10 ] The efficiency of these conversions are highly variable.
In the laboratory, the use of SF 4 has been superseded by the safer and more easily handled diethylaminosulfur trifluoride , (C 2 H 5 ) 2 NSF 3 , "DAST": [ 11 ] This reagent is prepared from SF 4 : [ 12 ]
Sulfur chloride pentafluoride ( SF 5 Cl ), a useful source of the SF 5 group, is prepared from SF 4 . [ 13 ]
Hydrolysis of SF 4 gives sulfur dioxide : [ 14 ]
This reaction proceeds via the intermediacy of thionyl fluoride , which usually does not interfere with the use of SF 4 as a reagent. [ 6 ]
When amines are treated with SF 4 and a base, aminosulfur difluorides result. [ 15 ]
SF 4 reacts inside the lungs with moisture, forming sulfur dioxide and hydrogen fluoride which forms highly toxic and corrosive hydrofluoric acid [ 16 ] | https://en.wikipedia.org/wiki/Sulfur_tetrafluoride |
Sulfur trifluoride is the inorganic chemical compound with the formula SF 3 . It is a radical . [ 1 ] [ 2 ]
Sulfur trifluoride is predicted to be pyramidal. [ 3 ] [ 4 ]
SF 3 is generated by irradiation of crystals of trifluorosulfonium tetrafluoroborate [SF 3 ] + [BF 4 ] − with gamma rays . [ 1 ]
A derivative formally derived from SF − 3 is the coordination complex Ir(Cl)(CO)(F)(SF 3 )(Et 3 P) 2 obtained by oxidative addition of sulfur tetrafluoride to Ir(Cl)(CO)(PEt 3 ) 2 (Et = C 2 H 5 ). [ 5 ] [ 6 ] | https://en.wikipedia.org/wiki/Sulfur_trifluoride |
Sulfur trioxide (alternative spelling sulphur trioxide ) is the chemical compound with the formula SO 3 . It has been described as "unquestionably the most [economically] important sulfur oxide ". [ 1 ] It is prepared on an industrial scale as a precursor to sulfuric acid .
Sulfur trioxide exists in several forms: gaseous monomer, crystalline trimer, and solid polymer. Sulfur trioxide is a solid at just below room temperature with a relatively narrow liquid range. Gaseous SO 3 is the primary precursor to acid rain . [ 6 ]
The molecule SO 3 is trigonal planar . As predicted by VSEPR theory , its structure belongs to the D 3h point group . The sulfur atom has an oxidation state of +6 and may be assigned a formal charge value as low as 0 (if all three sulfur-oxygen bonds are assumed to be double bonds) or as high as +2 (if the Octet Rule is assumed). [ 7 ] When the formal charge is non-zero, the S-O bonding is assumed to be delocalized. In any case the three S-O bond lengths are equal to one another, at 1.42 Å. [ 1 ] The electrical dipole moment of gaseous sulfur trioxide is zero.
Both liquid and gaseous [ 8 ] SO 3 exists in an equilibrium between the monomer and the cyclic trimer. The nature of solid SO 3 is complex and at least 3 polymorphs are known, with conversion between them being dependent on traces of water. [ 9 ]
Absolutely pure SO 3 freezes at 16.8 °C to give the γ -SO 3 form, which adopts the cyclic trimer configuration [S(=O) 2 ( μ -O)] 3 . [ 10 ] [ 1 ]
If SO 3 is condensed above 27 °C, then α -SO 3 forms, which has a melting point of 62.3 °C. α -SO 3 is fibrous in appearance. Structurally, it is the polymer [S(=O) 2 ( μ -O)] n . Each end of the polymer is terminated with OH groups. [ 1 ] β -SO 3 , like the alpha form, is fibrous but of different molecular weight, consisting of an hydroxyl-capped polymer, but melts at 32.5 °C. Both the gamma and the beta forms are metastable, eventually converting to the stable alpha form if left standing for sufficient time. This conversion is caused by traces of water. [ 11 ]
Relative vapor pressures of solid SO 3 are alpha < beta < gamma at identical temperatures, indicative of their relative molecular weights . Liquid sulfur trioxide has a vapor pressure consistent with the gamma form. Thus heating a crystal of α -SO 3 to its melting point results in a sudden increase in vapor pressure, which can be forceful enough to shatter a glass vessel in which it is heated. This effect is known as the "alpha explosion". [ 11 ]
Sulfur trioxide undergoes many reactions. [ 1 ]
SO 3 is the anhydride of H 2 SO 4 . Thus, it is susceptible to hydration:
Gaseous sulfur trioxide fumes profusely even in a relatively dry atmosphere owing to formation of a sulfuric acid mist.
SO 3 is aggressively hygroscopic . The heat of hydration is sufficient that mixtures of SO 3 and wood or cotton can ignite. In such cases, SO 3 dehydrates these carbohydrates . [ 11 ]
Akin to the behavior of H 2 O, hydrogen fluoride adds to give fluorosulfuric acid :
SO 3 reacts with dinitrogen pentoxide to give the nitronium salt of pyrosulfate:
Sulfur trioxide is an oxidant . It oxidizes sulfur dichloride to thionyl chloride .
SO 3 is a strong Lewis acid readily forming adducts with Lewis bases. [ 13 ] With pyridine , it gives the sulfur trioxide pyridine complex . Related adducts form from dioxane and trimethylamine .
Sulfur trioxide is a potent sulfonating agent , i.e. it adds SO 3 groups to substrates. Often the substrates are organic, as in aromatic sulfonation . [ 14 ] For activated substrates, Lewis base adducts of sulfur trioxide are effective sulfonating agents. [ 15 ]
The direct oxidation of sulfur dioxide to sulfur trioxide in air proceeds very slowly:
Industrially SO 3 is made by the contact process . Sulfur dioxide is produced by the burning of sulfur or iron pyrite (a sulfide ore of iron). After being purified by electrostatic precipitation, the SO 2 is then oxidised by atmospheric oxygen at between 400 and 600 °C over a catalyst. A typical catalyst consists of vanadium pentoxide (V 2 O 5 ) activated with potassium oxide K 2 O on kieselguhr or silica support. Platinum also works very well but is too expensive and is poisoned (rendered ineffective) much more easily by impurities. [ 16 ] The majority of sulfur trioxide made in this way is converted into sulfuric acid .
Sulfur trioxide can be prepared in the laboratory by the two-stage pyrolysis of sodium bisulfate . Sodium pyrosulfate is an intermediate product: [ 17 ]
The latter occurs at much lower temperatures (45–60 °C) in the presence of catalytic H 2 SO 4 . [ 18 ] In contrast, KHSO 4 undergoes the same reactions at a higher temperature. [ 17 ]
Another two step method involving a salt pyrolysis starts with concentrated sulfuric acid and anhydrous tin tetrachloride:
To further reduce water contamination, Oleum and a slight excess of Tin(IV) Chloride should be used. The slight excess of SnCl 4 can then be separated by carefully heating the solid Tin(IV) Sulfate under a vacuum to no more than 120 °C. The excess SO 3 from the Oleum and the remaining SnCl 4 will react during HCl formation and form Tin(IV) Oxide and Sulfuryl Chloride. If an excess of SO 3 in the Oleum is present relative to SnCl 4 , the Tin(IV) Oxide will absorb it and form more Tin(IV) Sulfate.
The advantage of this method over the sodium bisulfate one is that it can produce the pure trimer of SO 3 (since no water is present) while still using safe temperatures for normal borosilicate laboratory glassware. Other dry sulfate salt pyrolysis reactions require higher temperatures which increases the risk of shattering. A disadvantage is that it generates significant quantities of hydrogen chloride gas which needs to be captured as well.
SO 3 may also be prepared by dehydrating sulfuric acid with phosphorus pentoxide . [ 19 ]
Sulfur trioxide is a reagent in sulfonation reactions. Dimethyl sulfate is produced commercially by the reaction of dimethyl ether with sulfur trioxide : [ 20 ]
Sulfate esters are used as detergents , dyes , and pharmaceuticals . Sulfur trioxide is generated in situ from sulfuric acid or is used as a solution in the acid.
B 2 O 3 stabilized sulfur trioxide was traded by Baker & Adamson under the tradename " Sulfan " in the 20th century. [ 21 ]
Along with being an oxidizing agent, sulfur trioxide is highly corrosive. It reacts violently with water to produce highly corrosive sulfuric acid. | https://en.wikipedia.org/wiki/Sulfur_trioxide |
Sulfur trioxide pyridine complex is the compound with the formula C 5 H 5 NSO 3 . It is a colourless solid that dissolves in polar organic solvents. It is the adduct formed from the Lewis base pyridine and the Lewis acid sulfur trioxide . The compound is mainly used as a source of sulfur trioxide, for example in the synthesis of sulfate esters from alcohols : [ 1 ]
It also is useful for sulfamations :
The compound is used for sulfonylation reactions, especially in the sulfonylation of furans . [ 2 ] It is also an activating electrophile in a Parikh-Doering oxidation . [ 3 ]
This article about chemical compounds is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfur_trioxide_pyridine_complex |
Sulfur vulcanization is a chemical process for converting natural rubber or related polymers into materials of varying hardness, elasticity, and mechanical durability by heating them with sulfur or sulfur-containing compounds. [ 1 ] Sulfur forms cross-linking bridges between sections of polymer chains which affects the mechanical properties. [ 2 ] Many products are made with vulcanized rubber, including tires , shoe soles, hoses, and conveyor belts . The term vulcanization is derived from Vulcan , the Roman god of fire.
The main polymers subjected to sulfur vulcanization are polyisoprene (natural rubber, NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR), and ethylene propylene diene monomer rubber ( EPDM rubber ). All of these materials contain alkene groups adjacent to methylene groups . [ 3 ] Other specialty rubbers may also be vulcanized, such as nitrile rubber (NBR) and butyl rubber (IIR). Vulcanization, in common with the curing of other thermosetting polymers , is generally irreversible. Efforts have focussed on developing de-vulcanization (see tire recycling ) processes for recycling of rubber waste but with little success.
The details of vulcanization remain murky because the process converts mixtures of polymers to mixtures of insoluble derivatives. By design the reaction does not proceed to completion because fully crosslinked polymer would be too rigid for applications. [ 4 ] [ 5 ] There has long been uncertainly as to whether vulcanization proceeds in a radical or ionic manner. [ 1 ]
It is agreed that the reactive sites, often referred to as 'cure sites', are the allyl groups (-CH=CH-CH 2 -). [ 6 ] Sulfur forms bridge between these sites, crosslinking the polymer chains. These bridges may consist of one or several sulfur atoms and are separated by hundreds or thousands of carbons in the polymer chain. [ 5 ] Both the extent of crosslinking and the number of sulfur atoms in the crosslinks strongly influences the physical properties of the rubber produced: [ 7 ]
Sulfur, by itself, is a slow vulcanizing agent and does not vulcanize synthetic polyolefins. Even with natural rubber, large amounts of sulfur as well as high temperatures and prolonged heating periods are necessary, with the end products often being of an unsatisfactory quality.
Since the early 1900s, various chemical additives have been developed to improve the speed and efficiency of vulcanization, as well as to control the nature of the cross-linking. [ 8 ] When used together, this collection – the "cure package" – gives a rubber with particular properties.
The cure package consists of various reagents that modify the kinetics and chemistry of crosslinking. These include accelerants, activators, retarders and inhibitors. [ 8 ] [ 9 ] Note that these are merely the additives used for vulcanization and that other compounds may also be added to the rubber, such as fillers , tackifiers , polymer stabilizers and antiozonants .
Ordinary sulfur (octasulfur, or S 8 ) is rarely used, despite its low cost, because it is soluble in the polymer. [ 10 ] [ 11 ] High-temperature vulcanisation with ordinary sulfur leads to rubber supersaturated with S 8 , upon cooling this migrates to the surface and crystallises as sulfur bloom . This can cause problems if multiple layers of rubber are being added to form a composite item, such as a tire. Instead, various forms of polymeric sulfur are used, which are insoluble in the uncured rubber. It is also possible to replace sulfur with other sulfur-donating compounds, for example accelerants bearing disulfide groups, in what is often termed "efficient vulcanization" (EV). [ 1 ] Disulfur dichloride may also be used for "cold vulcanization".
Accelerants (accelerators) act much like catalysts allowing vulcanization to be performed cooler yet faster and with a more efficient use of sulfur. [ 1 ] [ 12 ] They achieve this by reacting with the sulfur to form a reactive intermediate, referred to as a sulfurating agent. This, in turn, reacts with cure sites in the rubber to bring about vulcanization.
There are two major classes of vulcanization accelerants: primary accelerants and secondary accelerants (also known as ultra accelerants). Primary activators date from the use of ammonia in 1881, [ 13 ] while secondary accelerants have been developed since around 1920. [ 14 ]
Primary accelerants perform the bulk of the accelerating and mostly consist of thiazoles , often derivatised with sulfenamide groups. [ 15 ] The principal compound is 2- mercaptobenzothiazole (MBT), which has been in use since the 1920s. [ 16 ] It remains a moderately fast curing agent giving sulfur chains of a medium length, but its relatively short induction period can be a disadvantage. Other primary accelerants are essentially "masked" forms of MBT, which take time to decompose into MBT during vulcanization and thus have longer inductions periods.
Oxidative dimerization of MBT gives mercaptobenzothiazole disulfide (MBTS), and sulfenamide derivatives are produced by reacting this with primary amines like cyclohexylamine or tert-butylamine . Secondary amines like dicyclohexylamine can be used and result in even slower accelerants. Such a slow accelerant is required in applications in which the rubber is being cured onto a metal component to which it is required to adhere, such as the steel cords in vehicle tires.
Secondary or ultra-accelerants are used in small amounts to augment the behaviour of primary accelerants. They act to boost the cure speed and increase cross-link density, but also shorten the induction time, which can lead to premature vulcanization. [ 8 ] Chemically, they consist mainly of thio-carbonyl species such as thiurams , dithiocarbamates , xanthates and organic thioureas ; aromatic guanidines are also used. These compounds need to be combined with activators, typically zinc ions, in order to be fully active.
Secondary accelerants have very fast vulcanization speeds with minimal induction time, making them unsuitable as primary accelerants in highly unsaturated rubbers such as NR or SBR. However, they can be used as primary accelerants in compounds with fewer curing site such as EPDM . Xanthates (principally, zinc isopropyl xanthate) are important in the vulcanization of latex, which is cured at relatively low temperatures (100-120 °C), and therefore needs an inherently rapid accelerant. The major thiurams used are TMTD ( tetramethylthiuram disulfide ) and TETD ( tetraethylthiuram disulfide ). The major dithiocarbamates are the zinc salts ZDMC ( zinc dimethyldithiocarbamate ), ZDEC (zinc diethyldithiocarbamate) and ZDBC (zinc dibutyldithiocarbamate).
Activators consist of various metal salts, fatty acids, as well as nitrogen-containing bases, the most important these being zinc oxide . Zinc actives many accelerants by coordination, for example causing thiuram to convert into ziram . [ 17 ] Zinc also coordinates to the sulfur-chains of sulfurating agents, changing the most likely bond to break during cross-link formation. Ultimately, activators promote the efficient use of sulfur to give a high density of cross-links. [ 18 ] Due to the low solubility of ZnO it is often combined with fatty acids such as stearic acid to form more soluble metallic soap, i.e. , zinc stearate .
To ensure high-quality vulcanization, the rubber, sulfur, accelerants, activators and other compounds are blended to give a homogeneous mixture. In practice, mixing can result in melting the sulfur (melting point 115 °C for S 8 ). At these temperatures vulcanization can begin prematurely, which is often undesirable, as the mixture may still need to be pumped and moulded into its final form before it sets solid. Premature vulcanization is often called " scorch ". Scorch can be prevented by the use of retarders or inhibitors, which increase the induction period before vulcanization commences and thus provide scorch resistance. A retarder slows both the onset and rate of vulcanization, whereas inhibitors only delay the start of vulcanization and do not affect the rate to any great extent. [ 19 ] In general inhibitors are preferred, with cyclohexylthiophthalimide (often termed PVI — pre-vulcanization inhibitor) being the most common example.
The market for new raw rubber or equivalent is large. The auto industry consumes a substantial fraction of natural and synthetic rubber. Reclaimed rubber has altered properties and is unsuitable for use in many products, including tires. Tires and other vulcanized products are potentially amenable to devulcanization, [ 20 ] [ 21 ] but this technology has not produced material that can supplant unvulcanized materials. The main problem is that the carbon-sulfur linkages are not readily broken, without the input of costly reagents and heat. Thus, more than half of scrap rubber is simply burned for fuel. [ 22 ]
Although polymeric sulfur reverts to its monomer at room temperature, polymers consisting mostly of sulfur can be stabilized with organic linkers such as 1,3‐diisopropenylbenzene. [ 23 ] This process is called inverse vulcanization and produces polymers where sulfur is the main component. [ 24 ]
The curing of rubber has been carried out since prehistoric times. [ 25 ] The name of the first major civilization in Guatemala and Mexico, the Olmec , means 'rubber people' in the Aztec language. Ancient Mesoamericans , spanning from ancient Olmecs to Aztecs, extracted latex from Castilla elastica , a type of rubber tree in the area. The juice of a local vine, Ipomoea alba , was then mixed with this latex to create processed rubber as early as 1600 BCE. [ 26 ] In the Western world, rubber remained a curiosity, although it was eventually used to produce waterproofed products, such as Mackintosh rainwear, beginning in the early 1800s. [ 27 ]
In 1832–1834 Nathaniel Hayward and Friedrich Ludersdorf discovered that rubber treated with sulfur lost its stickiness. It is likely Hayward shared his discovery with Charles Goodyear , possibly inspiring him to make the discovery of vulcanization. [ 28 ]
Charles Goodyear (1800–1860), a scientist and engineer, was the first to patent vulcanization of rubber. He was awarded a patent on June 15, 1844. A year later, after viewing Goodyear's work, Thomas Hancock was awarded the British Patent for the process. This was court granted after British scientist claimed that examining Goodyear's rubber could not produce the formula for vulcanizing rubber. [ 29 ] It was Hancock's friend William Brockedon who coined term 'vulcanization'. [ 30 ]
Goodyear claimed that he had discovered vulcanization earlier, in 1839. He wrote the story of the discovery in 1853 in his autobiographical book Gum-Elastica . Here is Goodyear's account of the invention , taken from Gum-Elastica . Although the book is an autobiography , Goodyear chose to write it in the third person so that the inventor and he referred to in the text are the author. He describes the scene in a rubber factory where his brother worked:
The inventor made experiments to ascertain the effect of heat on the same compound that had decomposed in the mail-bags and other articles. He was surprised to find that the specimen, being carelessly brought into contact with a hot stove, charred like leather.
Goodyear goes on to describe how his discovery was not readily accepted.
He directly inferred that if the process of charring could be stopped at the right point, it might divest the gum of its native adhesiveness throughout, which would make it better than the native gum. Upon further trial with heat, he was further convinced of the correctness of this inference, by finding that the India rubber could not be melted in boiling sulfur at any heat, but always charred.
He made another trial of heating a similar fabric before an open fire. The same effect, that of charring the gum, followed. There were further indications of success in producing the desired result, as upon the edge of the charred portion appeared a line or border, that was not charred, but perfectly cured.
Goodyear then goes on to describe how he moved to Woburn, Massachusetts and carried out a series of systematic experiments to optimize the curing of rubber, collaborating with Nathaniel Hayward .
On ascertaining to a certainty that he had found the object of his search and much more, and that the new substance was proof against cold and the solvent of the native gum, he felt himself amply repaid for the past, and quite indifferent to the trials of the future.
The discovery of the rubber-sulfur reaction revolutionized the use and applications of rubber, changing the face of the industrial world. Formerly, the only way to seal a small gap between moving machine parts was to use leather soaked in oil. This practice was acceptable only at moderate pressures, but above a certain point, machine designers were forced to compromise between the extra friction generated by tighter packing and greater leakage of steam. Vulcanized rubber solved this problem. It could be formed to precise shapes and dimensions, it accepted moderate to large deformations under load and recovered quickly to its original dimensions once the load is removed. These exceptional qualities, combined with good durability and lack of stickiness, were critical for an effective sealing material. Further experiments in the processing and compounding of rubber by Hancock and his colleagues led to a more reliable process. [ citation needed ]
Around 1900, disulfiram was introduced as a vulcanizing agent, and became widely used. [ 31 ]
In 1905 George Oenslager discovered that a derivative of aniline called thiocarbanilide accelerated the reaction of sulfur with rubber, leading to shorter cure times and reducing energy consumption . This breakthrough was almost as fundamental to the rubber industry as Goodyear's sulfur cure. Accelerators made the cure process faster, improved the reliability of the process and enabled vulcanization to be applied to synthetic polymers. One year after his discovery, Oenslager had found hundreds of applications for his additive. Thus, the science of accelerators and retarders was born. An accelerator speeds up the cure reaction, while a retarder delays it. A typical retarder is cyclohexylthiophthalimide . In the subsequent century chemists developed other accelerators and ultra-accelerators, which are used in the manufacture of most modern rubber goods. | https://en.wikipedia.org/wiki/Sulfur_vulcanization |
Sulfur water (or sulphur water ) is a condition where water is exposed to hydrogen sulfide gas, giving it a distinct "rotten egg" smell. This condition has different purposes in culture varying from health to implications for plumbing.
Sulfur water is made out of dissolved minerals that contain sulfate. These include baryte (BaSO 4 ), epsomite (MgSO 4 7H 2 O) and gypsum (CaSO 4 2H 2 0). [ 1 ] It is reported that a notable change in taste to the water is found dependent upon the type of sulfate affecting the water. For sodium sulfate, 250 to 500 mg/litre, with calcium sulfate at 250 to 1000 mg/litre and magnesium sulfate at 400 to 600 mg/litre. A study by Zoeteman found that having 270 mg of calcium sulfate and 90 mg of magnesium sulfate actually had improved the taste of the water.
Bathing in water high in sulfur or other minerals for its presumed health benefits is known as balneotherapy . These are said to give a person bathing in the waters "ageless beauty" and relief from aches and pains. [ 2 ]
While humans have been able to adapt to higher levels of concentrations with time, some effects of ingestion of sulfur water has found to have cathartic effects on people consuming water with sulfate concentrations of 600 mg/litre according to a study from the US Department of health in 1962. Some adverse effects that have been found include dehydration , with excess amounts of sodium or magnesium sulfate in a person's diet according to a study in 1980, with some populations, such as children and elderly people, being seen as higher risk.
A survey was done in North Dakota US to better derive whether there was direct causation of a laxative effect from having sulfur in drinking water. [ 3 ]
From this data, it was concluded that water containing more than 750 mg of sulfate per litre was due to a laxative effect, and below 600 was not. [ 4 ]
According to the Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention (CDC), drinking water with high levels of sulfate can cause diarrhea, especially in infants. [ 5 ]
At the University of Wyoming in America, sulfur water was studied to see the effects it can have upon the performance of steers that are on a forage-based diet. Due to sulfur being a requirement to living things, as it contains essential amino acids that are used to create proteins , sulfur water, which is commonly found in Western States of America, is a major contributor to sulfur in the herds diet. However, with a herd drinking high concentrate of sulfur water, ruminants may contract sulfur induced polioencephalomalacia (sPEM), which is a neurological disorder. Because of this finding, the study tries to reach the goal of finding a dietary supplement which can be used to counteract the negative health effects on the steers.
To reduce the extra sulfur in the ruminant's diet, ruminal bacteria break the excess down, resulting in Hydrogen Sulfide , which is soluble in water, but as temperature increases, the solubility decreases, which leads to the hydrogen sulfide gas being reinhaled by the animal, causing sulfur induced polioencephalomalacia. The study attempted to resolve this issue by introducing clinoptilolite to the diet of the herd, but has found inconclusive evidence which requires more study of clinoptilolite effects on methanogenesis and biohydrogenation.
There is also believed to be great health benefits within sulfur water, with sulfur water springs being a common thing within many cultures. Such springs can be found in many countries such as New Zealand, Japan and Greece. These sulfur springs are often created due to the local volcanic activity which contributes to heating up nearby water systems. This is due to volcanoes exhaling water vapour heavily encased in metals, with sulfur dioxide being one of them.
In New Zealand , the North Island was brought to fame in the 1800s, with its baths heated naturally from a volcano near the town of Rotorua . There are 28 spa hot pools which visitors can soak themselves, along with sulfur mud baths.
Another famous spring is the spring in Greece , Thermopylae , which means "hot springs" derives its name from its springs, as it was believed to be the entrance to Hades . [ 6 ]
The condition indicates a high level of sulfate-reducing bacteria in the water supply. This may be due to the use of well water, poorly treated city water, or water heater contamination.
Various methods exist to treat sulfur in water. These methods include
The Global Environment Monitoring System for Freshwater (GEMS/Water) has said that typical fresh water holds about 20 mg/litre of sulfur, and can range from 0 to 630 mg/litre in rivers, 2 to 250 mg/litre in lakes and 0 to 230 mg/litre in groundwater . [ citation needed ]
Canada's rain has been found to have sulfate concentrations of 1.0 and 3.8 mg/L in 1980, found in a study by Franklin published in 1985. [ 7 ] Western Canada in rivers ranged from 1 to 3040 mg/litre, with most concentrations below 580 mg/litre according to results from Environment Canada in 1984. Central Canada had levels that were also high in Saskatchewan , there were median levels of 368 mg/litre in drinking water from ground water supplies, and 97 mg/litre in surface water supplies, with a range of 32170 mg/litre.
A study conducted in Canada [ 8 ] found that a treatment to reduce sulfur in drinking water had actually increased it. This was conducted in Ontario , which had a mean sulfur level of 12.5 mg/litre when untreated, and 22.5 mg/litre after the treatment.
The Netherlands has had below 150 mg/litre concentrations of sulfur water in their underground water supplies. 65% of water treatment plants reported that the sulfur level of drinking water was below 25 mg/litre, as found in a study by Dijk-Looijaard & Fonds in 1985. [ 9 ]
The US had the Public Health Service in 1970 to measure levels of sulfate in drinking water sources in nine different geographic areas. The results concluded that all of the 106 surface water supplies that were sampled had sulfate present, as well as 645 of 658 ground water deposits that were tested. The levels of sulfur that was found ranged from less than 1 mg/litre to 770.
Due to sulfates being used in industrial products, they are often discharged into water supplies in the environment. This includes mines, textile mills and other industrial processes that involve using sulfates. Sulfates, such as magnesium , potassium and sodium are all highly soluble in water, which is what creates sulfur water, while other sulfates which are metal based, such as calcium and barium are less soluble. Atmospheric sulfur dioxide, also can infect surface water, and sulfur trioxide can combine with water vapour in the air, and create sulfur water rain, or what is colloquially known as acid rain . [ 10 ] | https://en.wikipedia.org/wiki/Sulfur_water |
Sulfuric acid ( American spelling and the preferred IUPAC name ) or sulphuric acid ( Commonwealth spelling ), known in antiquity as oil of vitriol , is a mineral acid composed of the elements sulfur , oxygen , and hydrogen , with the molecular formula H 2 SO 4 . It is a colorless, odorless, and viscous liquid that is miscible with water. [ 7 ]
Pure sulfuric acid does not occur naturally due to its strong affinity to water vapor ; it is hygroscopic and readily absorbs water vapor from the air . [ 7 ] Concentrated sulfuric acid is a strong oxidant with powerful dehydrating properties, making it highly corrosive towards other materials, from rocks to metals. Phosphorus pentoxide is a notable exception in that it is not dehydrated by sulfuric acid but, to the contrary, dehydrates sulfuric acid to sulfur trioxide . Upon addition of sulfuric acid to water, a considerable amount of heat is released; thus, the reverse procedure of adding water to the acid is generally avoided since the heat released may boil the solution, spraying droplets of hot acid during the process. Upon contact with body tissue, sulfuric acid can cause severe acidic chemical burns and secondary thermal burns due to dehydration. [ 8 ] [ 9 ] Dilute sulfuric acid is substantially less hazardous without the oxidative and dehydrating properties; though, it is handled with care for its acidity.
Many methods for its production are known, including the contact process , the wet sulfuric acid process , and the lead chamber process . [ 10 ] Sulfuric acid is also a key substance in the chemical industry . It is most commonly used in fertilizer manufacture [ 11 ] but is also important in mineral processing , oil refining , wastewater treating , and chemical synthesis . It has a wide range of end applications, including in domestic acidic drain cleaners , [ 12 ] as an electrolyte in lead-acid batteries , as a dehydrating compound, and in various cleaning agents .
Sulfuric acid can be obtained by dissolving sulfur trioxide in water.
Although nearly 100% sulfuric acid solutions can be made, the subsequent loss of SO 3 at the boiling point brings the concentration to 98.3% acid. The 98.3% grade, which is more stable in storage, is the usual form of what is described as "concentrated sulfuric acid". Other concentrations are used for different purposes. Some common concentrations are: [ 13 ] [ 14 ]
"Chamber acid" and "tower acid" were the two concentrations of sulfuric acid produced by the lead chamber process , chamber acid being the acid produced in the lead chamber itself (<70% to avoid contamination with nitrosylsulfuric acid ) and tower acid being the acid recovered from the bottom of the Glover tower. [ 13 ] [ 14 ] They are now obsolete as commercial concentrations of sulfuric acid, although they may be prepared in the laboratory from concentrated sulfuric acid if needed. In particular, "10 M" sulfuric acid (the modern equivalent of chamber acid, used in many titrations ), is prepared by slowly adding 98% sulfuric acid to an equal volume of water, with good stirring: the temperature of the mixture can rise to 80 °C (176 °F) or higher. [ 14 ]
Sulfuric acid contains not only H 2 SO 4 molecules, but is actually an equilibrium of many other chemical species, as it is shown in the table below.
Sulfuric acid is a colorless oily liquid, and has a vapor pressure of <0.001 mmHg at 25 °C and 1 mmHg at 145.8 °C, [ 16 ] and 98% sulfuric acid has a vapor pressure of <1 mmHg at 40 °C. [ 17 ]
In the solid state, sulfuric acid is a molecular solid that forms monoclinic crystals with nearly trigonal lattice parameters. The structure consists of layers parallel to the (010) plane, in which each molecule is connected by hydrogen bonds to two others. [ 3 ] Hydrates H 2 SO 4 · n H 2 O are known for n = 1, 2, 3, 4, 6.5, and 8, although most intermediate hydrates are stable against disproportionation . [ 18 ]
Anhydrous H 2 SO 4 is a very polar liquid, having a dielectric constant of around 100. It has a high electrical conductivity , a consequence of autoprotolysis , i.e. self- protonation : [ 15 ]
The equilibrium constant for autoprotolysis (25 °C) is: [ 15 ]
The corresponding equilibrium constant for water , K w is 10 −14 , a factor of 10 10 (10 billion) smaller.
In spite of the viscosity of the acid, the effective conductivities of the H 3 SO + 4 and HSO − 4 ions are high due to an intramolecular proton-switch mechanism (analogous to the Grotthuss mechanism in water), making sulfuric acid a good conductor of electricity. It is also an excellent solvent for many reactions.
The hydration reaction of sulfuric acid is highly exothermic . [ 19 ]
As indicated by its acid dissociation constant , sulfuric acid is a strong acid:
The product of this ionization is HSO − 4 , the bisulfate anion. Bisulfate is a far weaker acid:
The product of this second dissociation is SO 2− 4 , the sulfate anion.
Concentrated sulfuric acid has a powerful dehydrating property, removing water ( H 2 O ) from other chemical compounds such as table sugar ( sucrose ) and other carbohydrates , to produce carbon , steam , and heat. Dehydration of table sugar (sucrose) is a common laboratory demonstration. [ 21 ] The sugar darkens as carbon is formed, and a rigid column of black, porous carbon called a carbon snake may emerge. [ 22 ]
Similarly, mixing starch into concentrated sulfuric acid gives elemental carbon and water. The effect of this can also be seen when concentrated sulfuric acid is spilled on paper. Paper is composed of cellulose , a polysaccharide related to starch. The cellulose reacts to give a burnt appearance in which the carbon appears much like soot that results from fire.
Although less dramatic, the action of the acid on cotton , even in diluted form, destroys the fabric.
The reaction with copper(II) sulfate can also demonstrate the dehydration property of sulfuric acid. The blue crystals change into white powder as water is removed.
Sulfuric acid reacts with most bases to give the corresponding sulfate or bisulfate.
Aluminium sulfate , also known as paper maker's alum, is made by treating bauxite with sulfuric acid:
Sulfuric acid can also be used to displace weaker acids from their salts. Reaction with sodium acetate , for example, displaces acetic acid , CH 3 COOH , and forms sodium bisulfate :
Similarly, treating potassium nitrate with sulfuric acid produces nitric acid . Sulfuric acid reacts with sodium chloride , and gives hydrogen chloride gas and sodium bisulfate :
When combined with nitric acid , sulfuric acid acts both as an acid and a dehydrating agent, forming the nitronium ion NO + 2 , which is important in nitration reactions involving electrophilic aromatic substitution . This type of reaction, where protonation occurs on an oxygen atom, is important in many organic chemistry reactions, such as Fischer esterification and dehydration of alcohols.
When allowed to react with superacids , sulfuric acid can act as a base and can be protonated, forming the [H 3 SO 4 ] + ion. Salts of [H 3 SO 4 ] + have been prepared (e.g. trihydroxyoxosulfonium hexafluoroantimonate(V) [H 3 SO 4 ] + [SbF 6 ] − ) using the following reaction in liquid HF :
The above reaction is thermodynamically favored due to the high bond enthalpy of the Si–F bond in the side product. Protonation using simply fluoroantimonic acid , however, has met with failure, as pure sulfuric acid undergoes self-ionization to give [H 3 O] + ions:
which prevents the conversion of H 2 SO 4 to [H 3 SO 4 ] + by the HF/ SbF 5 system. [ 23 ]
Even diluted sulfuric acid reacts with many metals via a single displacement reaction, like other typical acids , producing hydrogen gas and salts (the metal sulfate). It attacks reactive metals (metals at positions above copper in the reactivity series ) such as iron , aluminium , zinc , manganese , magnesium , and nickel .
Concentrated sulfuric acid can serve as an oxidizing agent , releasing sulfur dioxide: [ 8 ]
Lead and tungsten , however, are resistant to sulfuric acid.
Hot concentrated sulfuric acid oxidizes carbon [ 24 ] (as bituminous coal ) and sulfur :
Benzene and many derivatives undergo electrophilic aromatic substitution with sulfuric acid to give the corresponding sulfonic acids : [ 25 ]
Sulfuric acid can be used to produce hydrogen from water :
The compounds of sulfur and iodine are recovered and reused, hence the process is called the sulfur–iodine cycle . This process is endothermic and must occur at high temperatures, so energy in the form of heat has to be supplied. The sulfur–iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-based economy . It is an alternative to electrolysis , and does not require hydrocarbons like current methods of steam reforming . But note that all of the available energy in the hydrogen so produced is supplied by the heat used to make it. [ 26 ] [ 27 ]
Sulfuric acid is rarely encountered naturally on Earth in anhydrous form, due to its great affinity for water . Dilute sulfuric acid is a constituent of acid rain , which is formed by atmospheric oxidation of sulfur dioxide in the presence of water —i.e. oxidation of sulfurous acid . When sulfur-containing fuels such as coal or oil are burned, sulfur dioxide is the main byproduct (besides the chief products carbon oxides and water).
Sulfuric acid is formed naturally by the oxidation of sulfide minerals, such as pyrite :
The resulting highly acidic water is called acid mine drainage (AMD) or acid rock drainage (ARD).
The Fe 2+ can be further oxidized to Fe 3+ :
The Fe 3+ produced can be precipitated as the hydroxide or hydrous iron oxide :
The iron(III) ion (" ferric iron ") can also oxidize pyrite:
FeS 2 (s) + 14 Fe 3+ + 8 H 2 O → 15 Fe 2+ + 2 SO 2− 4 + 16 H +
When iron(III) oxidation of pyrite occurs, the process can become rapid. pH values below zero have been measured in ARD produced by this process.
ARD can also produce sulfuric acid at a slower rate, so that the acid neutralizing capacity (ANC) of the aquifer can neutralize the produced acid. In such cases, the total dissolved solids (TDS) concentration of the water can be increased from the dissolution of minerals from the acid-neutralization reaction with the minerals.
Sulfuric acid is used as a defense by certain marine species, for example, the phaeophyte alga Desmarestia munda (order Desmarestiales ) concentrates sulfuric acid in cell vacuoles. [ 28 ]
In the stratosphere , the atmosphere's second layer that is generally between 10–50 km above Earth's surface, sulfuric acid is formed by the oxidation of volcanic sulfur dioxide by the hydroxyl radical : [ 29 ]
Because sulfuric acid reaches supersaturation in the stratosphere, it can nucleate aerosol particles and provide a surface for aerosol growth via condensation and coagulation with other water-sulfuric acid aerosols. This results in the stratospheric aerosol layer. [ 29 ]
The permanent Venusian clouds produce a concentrated acid rain, as the clouds in the atmosphere of Earth produce water rain. [ 30 ] Sulfuric acid ice has been detected on Jupiter 's moon Europa , where it forms when sulfur ions from Jupiter's magnetosphere implant into the icy surface. [ 31 ]
Sulfuric acid is produced from sulfur , oxygen and water via the conventional contact process (DCDA) or the wet sulfuric acid process (WSA).
In the first step, sulfur is burned to produce sulfur dioxide.
The sulfur dioxide is oxidized to sulfur trioxide by oxygen in the presence of a vanadium(V) oxide catalyst . This reaction is reversible and the formation of the sulfur trioxide is exothermic.
The sulfur trioxide is absorbed into 97–98% H 2 SO 4 to form oleum ( H 2 S 2 O 7 ), also known as fuming sulfuric acid or pyrosulphuric acid. The oleum is then diluted with water to form concentrated sulfuric acid.
Directly dissolving SO 3 in water, called the " wet sulfuric acid process ", is rarely practiced because the reaction is extremely exothermic, resulting in a hot aerosol of sulfuric acid that requires condensation and separation.
In the first step, sulfur is burned to produce sulfur dioxide:
or, alternatively, hydrogen sulfide ( H 2 S ) gas is incinerated to SO 2 gas:
The sulfur dioxide then oxidized to sulfur trioxide using oxygen with vanadium(V) oxide as catalyst .
The sulfur trioxide is hydrated into sulfuric acid H 2 SO 4 :
The last step is the condensation of the sulfuric acid to liquid 97–98% H 2 SO 4 :
Burning sulfur together with saltpeter ( potassium nitrate , KNO 3 ), in the presence of steam, has been used historically. As saltpeter decomposes, it oxidizes the sulfur to SO 3 , which combines with water to produce sulfuric acid.
Prior to 1900, most sulfuric acid was manufactured by the lead chamber process . [ 32 ] As late as 1940, up to 50% of sulfuric acid manufactured in the United States was produced by chamber process plants.
A wide variety of laboratory syntheses are known, and typically begin from sulfur dioxide or an equivalent salt . In the metabisulfite method, hydrochloric acid reacts with metabisulfite to produce sulfur dioxide vapors. The gas is bubbled through nitric acid , which will release brown/red vapors of nitrogen dioxide as the reaction proceeds. The completion of the reaction is indicated by the ceasing of the fumes. This method conveniently does not produce an inseparable mist. [ citation needed ]
Alternatively, dissolving sulfur dioxide in an aqueous solution of an oxidizing metal salt such as copper(II) or iron(III) chloride: [ citation needed ]
Two less well-known laboratory methods of producing sulfuric acid, albeit in dilute form and requiring some extra effort in purification, rely on electrolysis . A solution of copper(II) sulfate can be electrolyzed with a copper cathode and platinum/graphite anode to give spongy copper at cathode and oxygen gas at the anode. The solution of dilute sulfuric acid indicates completion of the reaction when it turns from blue to clear (production of hydrogen at cathode is another sign): [ citation needed ]
More costly, dangerous, and troublesome is the electrobromine method, which employs a mixture of sulfur , water, and hydrobromic acid as the electrolyte. The sulfur is pushed to bottom of container under the acid solution. Then the copper cathode and platinum/graphite anode are used with the cathode near the surface and the anode is positioned at the bottom of the electrolyte to apply the current. This may take longer and emits toxic bromine /sulfur-bromide vapors, but the reactant acid is recyclable. Overall, only the sulfur and water are converted to sulfuric acid and hydrogen (omitting losses of acid as vapors): [ citation needed ]
Sulfuric acid is a very important commodity chemical, and a nation's sulfuric acid production was as recently as 2002 believed to be a good indicator of its industrial strength. [ 33 ] World production in the year 2004 was about 180 million tonnes , with the following geographic distribution: Asia 35%, North America (including Mexico) 24%, Africa 11%, Western Europe 10%, Eastern Europe and Russia 10%, Australia and Oceania 7%, South America 7%. [ 34 ] World production in 2022 was estimated at about 260 million tonnes. [ 35 ]
As of the late 20th century, most of the produced amount (≈60%) was consumed for fertilizers, particularly superphosphates, ammonium phosphate and ammonium sulfates. About 20% is used in chemical industry for production of detergents, synthetic resins, dyestuffs, pharmaceuticals, petroleum catalysts, insecticides and antifreeze , as well as in various processes such as oil well acidicizing, aluminium reduction, paper sizing, and water treatment. About 6% of uses are related to pigments and include paints, enamels , printing inks, coated fabrics and paper, while the rest is dispersed into a multitude of applications such as production of explosives, cellophane , acetate and viscose textiles, lubricants, non-ferrous metals , and batteries. [ 36 ]
The dominant use for sulfuric acid is in the "wet method" for the production of phosphoric acid , used for manufacture of phosphate fertilizers . In this method, phosphate rock is used, and more than 100 million tonnes are processed annually. This raw material is shown below as fluorapatite , though the exact composition may vary. This is treated with 93% sulfuric acid to produce calcium sulfate , hydrogen fluoride (HF) and phosphoric acid . The HF is removed as hydrofluoric acid . The overall process can be represented as:
Ammonium sulfate , an important nitrogen fertilizer, is most commonly produced as a byproduct from coking plants supplying the iron and steel making plants. Reacting the ammonia produced in the thermal decomposition of coal with waste sulfuric acid allows the ammonia to be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-chemicals industry.
Sulfuric acid is also important in the manufacture of dyestuffs solutions.
Sulfuric acid is used in steelmaking and other metallurgical industries as a pickling agent for removal of rust and fouling . [ 37 ] Used acid is often recycled using a spent acid regeneration (SAR) plant. These plants combust spent acid [ clarification needed ] with natural gas, refinery gas, fuel oil or other fuel sources. This combustion process produces gaseous sulfur dioxide ( SO 2 ) and sulfur trioxide ( SO 3 ) which are then used to manufacture "new" sulfuric acid.
Hydrogen peroxide ( H 2 O 2 ) can be added to sulfuric acid to produce piranha solution , a powerful but potentially hazardous cleaning solution with which substrate surfaces can be cleaned. Piranha solution is typically used in the microelectronics industry, and also in laboratory settings to clean glassware.
Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is the usual acid catalyst for the conversion of cyclohexanone oxime to caprolactam , used for making nylon . It is used for making hydrochloric acid from salt via the Mannheim process . Much H 2 SO 4 is used in petroleum refining , for example as a catalyst for the reaction of isobutane with isobutylene to give isooctane , a compound that raises the octane rating of gasoline (petrol). Sulfuric acid is also often used as a dehydrating or oxidizing agent in industrial reactions, such as the dehydration of various sugars to form solid carbon.
Sulfuric acid acts as the electrolyte in lead–acid batteries (lead-acid accumulator):
At anode :
At cathode :
Overall:
Sulfuric acid at high concentrations is frequently the major ingredient in domestic acidic drain cleaners [ 12 ] which are used to remove lipids , hair , tissue paper , etc. Similar to their alkaline versions , such drain openers can dissolve fats and proteins via hydrolysis . Moreover, as concentrated sulfuric acid has a strong dehydrating property, it can remove tissue paper via dehydrating process as well. Since the acid may react with water vigorously, such acidic drain openers should be added slowly into the pipe to be cleaned.
The study of vitriols (hydrated sulfates of various metals forming glassy minerals from which sulfuric acid can be derived) began in ancient times . Sumerians had a list of types of vitriol that they classified according to the substances' color. Some of the earliest discussions on the origin and properties of vitriol is in the works of the Greek physician Dioscorides (first century AD) and the Roman naturalist Pliny the Elder (23–79 AD). Galen also discussed its medical use. Metallurgical uses for vitriolic substances were recorded in the Hellenistic alchemical works of Zosimos of Panopolis , in the treatise Phisica et Mystica , and the Leyden papyrus X . [ 38 ] Medieval Islamic alchemists like the authors writing under the name of Jabir ibn Hayyan (died c. 806 – c. 816 AD, known in Latin as Geber), Abu Bakr al-Razi (865 – 925 AD, known in Latin as Rhazes), Ibn Sina (980 – 1037 AD, known in Latin as Avicenna), and Muhammad ibn Ibrahim al-Watwat (1234 – 1318 AD) included vitriol in their mineral classification lists. [ 39 ]
The Jabirian authors and al-Razi experimented extensively with the distillation of various substances, including vitriols. [ 40 ] In one recipe recorded in his Kitāb al-Asrār ( 'Book of Secrets' ), al-Razi may have created sulfuric acid without being aware of it: [ 41 ]
Take white (Yemeni) alum , dissolve it and purify it by filtration. Then distil (green?) vitriol with copper-green (the acetate), and mix (the distillate) with the filtered solution of the purified alum, afterwards let it solidify (or crystallise) in the glass beaker. You will get the best qalqadis (white alum) that may be had. [ 42 ]
In an anonymous Latin work variously attributed to Aristotle (under the title Liber Aristotilis , 'Book of Aristotle'), [ 43 ] to al-Razi (under the title Lumen luminum magnum , 'Great Light of Lights'), or to Ibn Sina, [ 44 ] the author speaks of an 'oil' ( oleum ) obtained through the distillation of iron(II) sulfate (green vitriol), which was likely 'oil of vitriol' or sulfuric acid. [ 45 ] The work refers multiple times to Jabir ibn Hayyan's Seventy Books ( Liber de septuaginta ), one of the few Arabic Jabir works that were translated into Latin. [ 46 ] The author of the version attributed to al-Razi also refers to the Liber de septuaginta as his own work, showing that he erroneously believed the Liber de septuaginta to be a work by al-Razi. [ 47 ] There are several indications that the anonymous work was an original composition in Latin, [ 48 ] although according to one manuscript it was translated by a certain Raymond of Marseilles, meaning that it may also have been a translation from the Arabic. [ 49 ]
According to Ahmad Y. al-Hassan , three recipes for sulfuric acid occur in an anonymous Garshuni manuscript containing a compilation taken from several authors and dating from before c. 1100 AD . [ 50 ] One of them runs as follows:
The water of vitriol and sulphur which is used to irrigate the drugs: yellow vitriol three parts, yellow sulphur one part, grind them and distil them in the manner of rose-water. [ 51 ]
A recipe for the preparation of sulfuric acid is mentioned in Risālat Jaʿfar al-Sādiq fī ʿilm al-ṣanʿa , an Arabic treatise falsely attributed to the Shi'i Imam Ja'far al-Sadiq (died 765). Julius Ruska dated this treatise to the 13th century, but according to Ahmad Y. al-Hassan it likely dates from an earlier period: [ 52 ]
Then distil green vitriol in a cucurbit and alembic, using medium fire; take what you obtain from the distillate, and you will find it clear with a greenish tint. [ 51 ]
Sulfuric acid was called 'oil of vitriol' by medieval European alchemists because it was prepared by roasting iron(II) sulfate or green vitriol in an iron retort . The first allusions to it in works that are European in origin appear in the thirteenth century AD, as for example in the works of Vincent of Beauvais , in the Compositum de Compositis ascribed to Albertus Magnus , and in pseudo-Geber 's Summa perfectionis . [ 53 ]
A method of producing oleum sulphuris per campanam, or "oil of sulfur by the bell", was known by the 16th century: it involved burning sulfur under a glass bell in moist weather (or, later, under a moistened bell). However, it was very inefficient (according to Gesner , 5 pounds (2.3 kg) of sulfur converted into less than 1 ounce (0.03 kg) of acid), and the resulting product was contaminated by sulfurous acid (or rather, solution of sulfur dioxide ) so most alchemists (including, for example, Isaac Newton) didn't consider it equivalent with the "oil of vitriol".
In the 17th century, Johann Rudolf Glauber discovered that adding saltpeter ( potassium nitrate , KNO 3 ) significantly improves the output, also replacing moisture with steam. As saltpeter decomposes, it oxidizes the sulfur to SO 3 , which combines with water to produce sulfuric acid. In 1736, Joshua Ward , a London pharmacist, used this method to begin the first large-scale production of sulfuric acid.
In 1746 in Birmingham, John Roebuck adapted this method to produce sulfuric acid in lead -lined chambers, which were stronger, less expensive, and could be made larger than the previously used glass containers. This process allowed the effective industrialization of sulfuric acid production. After several refinements, this method, called the lead chamber process or "chamber process", remained the standard for sulfuric acid production for almost two centuries with a purity of 62% and a conversion of 75%. [ 4 ]
Sulfuric acid created by John Roebuck's process approached a 65% concentration. Later refinements to the lead chamber process by French chemist Joseph Louis Gay-Lussac and British chemist John Glover improved concentration to 78%. However, the manufacture of some dyes and other chemical processes require a more concentrated product. Throughout the 18th century, this could only be made by dry distilling minerals in a technique similar to the original alchemical processes. Pyrite (iron disulfide, FeS 2 ) was heated in air to yield iron(II) sulfate, FeSO 4 , which was oxidized by further heating in air to form iron(III) sulfate , Fe 2 (SO 4 ) 3 , which, when heated to 480 °C, decomposed to iron(III) oxide and sulfur trioxide, which could be passed through water to yield sulfuric acid in any concentration. However, the expense of this process prevented the large-scale use of concentrated sulfuric acid. [ 4 ]
In 1831, British vinegar merchant Peregrine Phillips patented the contact process , which was a far more economical process for producing sulfur trioxide and concentrated sulfuric acid. Today, nearly all of the world's sulfuric acid is produced using this method. [ 33 ]
In the early to mid 19th century "vitriol" plants existed, among other places, in Prestonpans in Scotland, Shropshire and the Lagan Valley in County Antrim , Northern Ireland , where it was used as a bleach for linen. Early bleaching of linen was done using lactic acid from sour milk but this was a slow process and the use of vitriol sped up the bleaching process. [ 54 ]
Sulfuric acid is capable of causing very severe burns, especially when it is at high concentrations . In common with other corrosive acids and alkali , it readily decomposes proteins and lipids through amide and ester hydrolysis upon contact with living tissues , such as skin and flesh . In addition, it exhibits a strong dehydrating property on carbohydrates , liberating extra heat and causing secondary thermal burns . [ 8 ] [ 9 ] Accordingly, it rapidly attacks the cornea and can induce permanent blindness if splashed onto eyes . If ingested, it damages internal organs irreversibly and may even be fatal. [ 7 ] Personal protective equipment should hence always be used when handling it. Moreover, its strong oxidizing property makes it highly corrosive to many metals and may extend its destruction on other materials. [ 8 ] Because of such reasons, damage posed by sulfuric acid is potentially more severe than that by other comparable strong acids , such as hydrochloric acid and nitric acid .
Sulfuric acid must be stored carefully in containers made of nonreactive material (such as glass). Solutions equal to or stronger than 1.5 M are labeled "CORROSIVE", while solutions greater than 0.5 M but less than 1.5 M are labeled "IRRITANT". However, even the normal laboratory "dilute" grade (approximately 1 M, 10%) will char paper if left in contact for a sufficient time.
The standard first aid treatment for acid spills on the skin is, as for other corrosive agents , irrigation with large quantities of water. Washing is continued for at least ten to fifteen minutes to cool the tissue surrounding the acid burn and to prevent secondary damage. Contaminated clothing is removed immediately and the underlying skin washed thoroughly.
Preparation of diluted acid can be dangerous due to the heat released in the dilution process. To avoid splattering, the concentrated acid is usually added to water and not the other way around. A saying used to remember this is "Do like you oughta, add the acid to the water". [ 55 ] [ better source needed ] [ 56 ] Water has a higher heat capacity than the acid, and so a vessel of cold water will absorb heat as acid is added.
Also, because the acid is denser than water, it sinks to the bottom. Heat is generated at the interface between acid and water, which is at the bottom of the vessel. Acid will not boil, because of its higher boiling point. Warm water near the interface rises due to convection , which cools the interface, and prevents boiling of either acid or water.
In contrast, addition of water to concentrated sulfuric acid results in a thin layer of water on top of the acid. Heat generated in this thin layer of water can boil, leading to the dispersal of a sulfuric acid aerosol , or worse, an explosion .
Preparation of solutions greater than 6 M (35%) in concentration is dangerous, unless the acid is added slowly enough to allow the mixture sufficient time to cool. Otherwise, the heat produced may be sufficient to boil the mixture. Efficient mechanical stirring and external cooling (such as an ice bath) are essential.
Reaction rates double for about every 10-degree Celsius increase in temperature . [ 57 ] Therefore, the reaction will become more violent as dilution proceeds, unless the mixture is given time to cool. Adding acid to warm water will cause a violent reaction.
On a laboratory scale, sulfuric acid can be diluted by pouring concentrated acid onto crushed ice made from de-ionized water. The ice melts in an endothermic process while dissolving the acid. The amount of heat needed to melt the ice in this process is greater than the amount of heat evolved by dissolving the acid so the solution remains cold. After all the ice has melted, further dilution can take place using water.
Sulfuric acid is non-flammable.
The main occupational risks posed by this acid are skin contact leading to burns (see above) and the inhalation of aerosols. Exposure to aerosols at high concentrations leads to immediate and severe irritation of the eyes, respiratory tract and mucous membranes: this ceases rapidly after exposure, although there is a risk of subsequent pulmonary edema if tissue damage has been more severe. At lower concentrations, the most commonly reported symptom of chronic exposure to sulfuric acid aerosols is erosion of the teeth, found in virtually all studies: indications of possible chronic damage to the respiratory tract are inconclusive as of 1997. Repeated occupational exposure to sulfuric acid mists may increase the chance of lung cancer by up to 64 percent. [ 58 ] In the United States, the permissible exposure limit (PEL) for sulfuric acid is fixed at 1 mg/m 3 : limits in other countries are similar. There have been reports of sulfuric acid ingestion leading to vitamin B12 deficiency with subacute combined degeneration. The spinal cord is most often affected in such cases, but the optic nerves may show demyelination , loss of axons and gliosis .
International commerce of sulfuric acid is controlled under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances, 1988 , which lists sulfuric acid under Table II of the convention as a chemical frequently used in the illicit manufacture of narcotic drugs or psychotropic substances. [ 59 ] | https://en.wikipedia.org/wiki/Sulfuric_acid |
Sulfuric acid poisoning refers to ingestion of sulfuric acid , found in lead-acid batteries and some metal cleaners, pool cleaners, drain cleaners and anti-rust products.
For superficial injuries, washing ( therapeutic irrigation ) is important. Emergency treatments include protecting the airway, which might involve a tracheostomy . Further treatment will vary depending on the severity, but might include investigations to determine the extent of damage ( bronchoscopy for the airways and endoscopy for the gastrointestinal tract), followed by treatments including surgery (to debride and repair) and intravenous fluids. [ 1 ]
Gastric lavage is contraindicated in corrosive acid poisoning like sulfuric acid poisoning. Bicarbonate is also contraindicated as it liberates carbon dioxide which can cause gastric dilatation leading to rupture of stomach, leading to severe abominal damage or death.
Vitriolage is the act of throwing sulfuric acid or other corrosive acids on somebody's face. [ citation needed ] | https://en.wikipedia.org/wiki/Sulfuric_acid_poisoning |
See text
Sulfurospirillum ( /ˌsʌlfɜːroʊspɪˈrɪlʌm/ SULF-ur-oh-spə-RIHL-um ) is a genus of the gram-negative , aerotolerant , rod-shaped bacteria in the family Campylobactaeraceae . [ 2 ]
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) [ 3 ] and National Center for Biotechnology Information (NCBI) [ 4 ]
" S. alkalitolerans " Sorokin et al. 2013 [ 11 ]
" S. tamanensis " Frolova et al. 2023 [ 12 ]
S. arcachonense Finster et al. 1997 [ 13 ]
S. cavolei Kodama, Ha & Watanabe 2007 [ 14 ]
S. barnesii Stolz et al. 1999 [ 15 ]
S. deleyianum Schumacher, Kroneck & Pfennig 1993 [ 16 ]
S. diekertiae Jin et al. 2023
S. multivorans (Scholz-Muramatsu et al. 2002) Luijten et al. 2003 [ 17 ]
S. arsenophilum Stolz et al. 1999 [ 18 ]
S. halorespirans Luitjen et al. 2003 [ 17 ]
S. arcachonense
S. cavolei
S. barnesii
S. deleyianum
S. arsenophilum
S. oryzae Xie et al. 2024
S. diekertiae
S. halorespirans
S. multivorans
Unassigned Sulfurospirillum species:
Many species are microaerophillic , and are thus found in soil, groundwater, the deep sea, marine surface sediments, tube worm guts , and polluted environments. [ 21 ] Many species can grow on toxic compounds such as arsenate and selenate , and in fact flourish in contaminated sites. [ 21 ] The Sulfurospirillum genus contains the only species on the planet that can respire organohalides . [ 21 ] No species in the Sulfurospirillum genus have been found to be pathogenic thus far.
This microbiology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfurospirillum |
Sulfuric(IV) acid ( United Kingdom spelling: sulphuric(IV) acid ), also known as sulfurous (UK: sulphurous ) acid and thionic acid , [ citation needed ] is the chemical compound with the formula H 2 SO 3 .
Raman spectra of solutions of sulfur dioxide in water show only signals due to the SO 2 molecule and the bisulfite ion, HSO − 3 . [ 2 ] The intensities of the signals are consistent with the following equilibrium :
17 O NMR spectroscopy provided evidence that solutions of sulfurous acid and protonated sulfites contain a mixture of isomers, which is in equilibrium: [ 3 ]
Attempts to concentrate the solutions of sulfurous acid simply reverse the equilibrium, producing sulfur dioxide and water vapor. A clathrate with the formula 4SO 2 ·23H 2 O has been crystallised. It decomposes above 7 °C.
Sulfurous acid is commonly known not to exist in its free state, and owing to this, it is stated in textbooks that it cannot be isolated in the water-free form. [ 4 ] However, the molecule has been detected in the gas phase in 1988 by the dissociative ionization of diethyl sulfite . [ 5 ] The conjugate bases of this elusive acid are, however, common anions, bisulfite (or hydrogen sulfite) and sulfite . Sulfurous acid is an intermediate species in the formation of acid rain from sulfur dioxide. [ 6 ]
Aqueous solutions of sulfur dioxide, which sometimes are referred to as sulfurous acid, are used as reducing agents and as disinfectants, as are solutions of bisulfite and sulfite salts. They are oxidised to sulfuric acid or sulfate by accepting another oxygen atom. [ 7 ] | https://en.wikipedia.org/wiki/Sulfurous_acid |
In inorganic chemistry , the sulfuryl group is a functional group consisting of a sulfur atom covalently bound to two oxygen atoms ( S(=O) 2 X 2 ).
It occurs in compounds such as sulfuryl chloride , SO 2 Cl 2 and sulfuryl fluoride , SO 2 F 2 .
In organic chemistry , this group is found in sulfones ( RSO 2 R′ ) and sulfonyl halides ( RSO 2 X ), where it is called the sulfonyl group.
Greenwood, Norman N. ; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann . ISBN 978-0-08-037941-8 .
This article about an organic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulfuryl |
Sulfuryl fluoride (also spelled sulphuryl fluoride ) is an inorganic compound with the formula SO 2 F 2 . It is an easily condensed gas and has properties more similar to sulfur hexafluoride than sulfuryl chloride , being resistant to hydrolysis even up to 150 °C. [ 3 ] It is neurotoxic and a potent greenhouse gas , but is widely used as a fumigant insecticide to control termites .
The molecule is tetrahedral with C 2v symmetry . The S-O distance is 140.5 pm, S-F is 153.0 pm. As predicted by VSEPR , the O-S-O angle is more open than the F-S-F angle, 124° and 97°, respectively. [ 3 ]
One synthesis begins with the preparation of potassium fluorosulfite: [ 4 ]
This salt is then chlorinated to give sulfuryl chloride fluoride :
Heating the sulfuryl chloride fluoride with potassium fluorosulfite at 180 °C gives the desired product: [ 5 ]
Heating metal fluorosulfonate salts also gives this molecule: [ 3 ]
It can be prepared by direct reaction of fluorine with sulfur dioxide :
On a laboratory scale, sulfuryl fluoride has been conveniently prepared from 1,1'-sulfonyldiimidazole, in the presence of potassium fluoride and acid. [ 6 ] [ 7 ]
Sulfuryl fluoride is unreactive toward molten sodium metal. [ 3 ] Similarly it is slow to hydrolyze, but eventually converts to sulfur trioxide . [ 8 ] [ 9 ]
Sulfuryl fluoride gas is a precursor to fluorosulfates and sulfamoyl fluorides : [ 10 ]
Originally developed by the Dow Chemical Company , sulfuryl fluoride is in widespread use as a structural fumigant insecticide to control drywood termites , particularly in warm-weather portions of the southwestern and southeastern United States and in Hawaii. It has a non-specific mode of action ( IRAC group 8C). Less commonly, it can also be used to control rodents , powderpost beetles , deathwatch beetles , bark beetles , and bedbugs . Its use has increased as a replacement for methyl bromide , which was phased out because of harm to the ozone layer. It is an alternative to the use of phosphine , which is acutely toxic. [ 11 ]
During application, the building is enclosed and filled with the gas for a period of time, usually at least 16–18 hours, sometimes as long as 72 hours. The building must then be ventilated, generally for at least 6 hours, before occupants can return. California regulations are such that the tent will be on for three to five days, which includes ventilation. In the US, sulfuryl fluoride must be transported in a vehicle marked with "Inhalation Hazard 2" placards. [ 12 ] [ 13 ] Most states require a license or certification for the individual applying the fumigant.
The concentration is continuously monitored and maintained at the specified level using electronic equipment. Possible leakages are also checked by low range electronic detectors. Reentry to the home is allowed when the concentration level is at or below 5 ppm. [ 14 ] Sulfuryl fluoride is colorless and odorless, however, during the fumigation process, a warning agent called chloropicrin is first released into the building to ensure that no occupants remain. Tent fumigation is the most effective treatment for the extermination of known and unknown infestations of wood-destroying insects. Heat is the only other approved method for whole structure treatment for termites in California. [ 15 ] Sulfuryl fluoride provides no protection from future infestations, although heavy re-infestation can take several years since drywood termites have slower growing colonies than ground termites.
Sulfuryl fluoride is marketed in the U.S. by three manufacturers, under four different brand names. Vikane (Dow) (EPA Reg. No. 62719- 4-ZA) has been commercially available since the early 1960s, with Zythor (marketed by competitor Ensystex of North Carolina) (EPA Reg. No. 81824- 1-AA) being more recently introduced gradually as its use is approved by individual states (in Florida circa 2004, but not in California until October 2006, for example). Sulfuryl fluoride has been marketed as a post-harvest fumigant for dry fruits, nuts, and grains under the trade name ProFume (U.S. EPA Reg. No. 62719- 376-AA). [ 16 ] Most recently Drexel Chemical Company has registered Master Fume (EPA Reg. No. 19713-596-AA) for the structural market, competing against Vikane and Zythor . [ 17 ]
Inhalation of sulfuryl fluoride is hazardous and may result in respiratory irritation, pulmonary edema , nausea, abdominal pain, central nervous system depression, numbness in the extremities, muscle twitching, seizures, and death. [ 18 ] [ 19 ] [ 20 ] These high exposures occurred when people entered into structures illegally during fumigation or after insufficient aeration. Epidemiological studies showed that fumigation workers who used sulfuryl fluoride showed neurological effects, which included reduced performance on cognitive tests and pattern memory tests, and reduced olfactory function. [ 21 ]
In 1987, an elderly couple was exposed to sulfuryl fluoride in their house already cleared for reentry. [ 21 ] While the fumigation company opened windows and doors, and aerated the house with fans, sulfuryl fluoride level was not measured. It was not detected when the air was sampled 12 days after aeration. The couple experienced weakness, nausea and shortness of breath that evening. The man suffered a seizure and died the following day. His wife's condition got worse with pulmonary edema, and she died after a cardiovascular arrest 6 days later.
In 2015, a 10-year-old boy suffered severe brain damage and lost function of his left arm and leg after his home was treated with sulfuryl fluoride and insufficiently aerated, prompting a criminal investigation by the Department of Justice and the Florida Department of Agricultural and Consumer Services. [ 22 ] Two pest control workers later pled guilty to charges of misuse of the pesticide resulting in the boy's poisoning, and were each sentenced to one year in prison. [ 23 ]
In 2016, a 24-year-old man who allegedly entered an apartment that was being fumigated in Fremont, California to commit a burglary was exposed to sulfuryl fluoride and chloropicrin and died shortly thereafter. According to a police officer, he experienced labored breathing and was sweating before he collapsed just a few steps from the first floor window of the apartment he allegedly burglarized. [ 24 ]
In April 2024, In Pompano Beach Florida, two company pesticide workers died. The owner was also hospitalized but survived. [ 25 ]
Based on the first high frequency, high precision, in situ atmospheric and archived air measurements, sulfuryl fluoride has an atmospheric lifetime of 30–40 years, [ 8 ] much longer than the 5 years earlier estimated. [ 26 ]
Sulfuryl fluoride has been reported to be a greenhouse gas which is about 4000–5000 times more efficient in trapping infrared radiation (per kg) than carbon dioxide (per kg). [ 8 ] [ 27 ] [ 28 ] The amount of sulfuryl fluoride released into the atmosphere is about 2000 metric tons per year. [ 8 ] The most important loss process of sulfuryl fluoride is dissolution of atmospheric sulfuryl fluoride in the ocean followed by hydrolysis. | https://en.wikipedia.org/wiki/Sulfuryl_fluoride |
The sulfur–iodine cycle (S–I cycle) is a three-step thermochemical cycle used to produce hydrogen .
The S–I cycle consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen . All other chemicals are recycled. The S–I process requires an efficient source of heat.
The three reactions combined to produce hydrogen are the following:
The sulfur and iodine compounds are recovered and reused, hence the consideration of the process as a cycle. This S–I process is a chemical heat engine . Heat enters the cycle in high-temperature endothermic chemical reactions 2 and 3, and heat exits the cycle in the low-temperature exothermic reaction 1. The difference between the heat entering and leaving the cycle exits the cycle in the form of the heat of combustion of the hydrogen produced.
The S–I cycle was invented at General Atomics in the 1970s. [ 1 ] The Japan Atomic Energy Agency (JAEA) has conducted successful experiments with the S–I cycle in the Helium cooled High Temperature Test Reactor , [ 2 ] [ 3 ] [ 4 ] [ 5 ] a reactor which reached first criticality in 1998, JAEA have the aspiration of using further nuclear very high-temperature generation IV reactors ( VHTR ) to produce industrial scale quantities of hydrogen. (The Japanese refer to the cycle as the IS cycle.) Plans have been made to test larger-scale automated systems for hydrogen production. Under an International Nuclear Energy Research Initiative (INERI) agreement, the French CEA , General Atomics and Sandia National Laboratories are jointly developing the sulfur-iodine process. Additional research is taking place at the Idaho National Laboratory , and in Canada, Korea and Italy.
The S–I cycle involves operations with corrosive chemicals at temperatures up to about 1,000 °C (1,830 °F). The selection of materials with sufficient corrosion resistance under the process conditions is of key importance to the economic viability of this process. The materials suggested include the following classes: refractory metals, reactive metals, superalloys , ceramics, polymers, and coatings. [ 6 ] [ 7 ] Some materials suggested include tantalum alloys, niobium alloys, noble metals, high-silicon steels, [ 8 ] several nickel-based superalloys , mullite , silicon carbide (SiC), glass, silicon nitride (Si 3 N 4 ), and others. Recent research on scaled prototyping suggests that new tantalum surface technologies may be a technically and economically feasible way to make larger scale installations. [ 9 ]
The sulfur-iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-based economy . It does not require hydrocarbons like current methods of steam reforming but requires heat from combustion, nuclear reactions, or solar heat concentrators. | https://en.wikipedia.org/wiki/Sulfur–iodine_cycle |
In mathematics , Sullivan conjecture or Sullivan's conjecture on maps from classifying spaces can refer to any of several results and conjectures prompted by homotopy theory work of Dennis Sullivan . A basic theme and motivation concerns the fixed point set in group actions of a finite group G {\displaystyle G} . The most elementary formulation, however, is in terms of the classifying space B G {\displaystyle BG} of such a group. Roughly speaking, it is difficult to map such a space B G {\displaystyle BG} continuously into a finite CW complex X {\displaystyle X} in a non-trivial manner. Such a version of the Sullivan conjecture was first proved by Haynes Miller . [ 1 ] Specifically, in 1984, Miller proved that the function space , carrying the compact-open topology , of base point -preserving mappings from B G {\displaystyle BG} to X {\displaystyle X} is weakly contractible .
This is equivalent to the statement that the map X {\displaystyle X} → F ( B G , X ) {\displaystyle F(BG,X)} from X to the function space of maps B G {\displaystyle BG} → X {\displaystyle X} , not necessarily preserving the base point, given by sending a point x {\displaystyle x} of X {\displaystyle X} to the constant map whose image is x {\displaystyle x} is a weak equivalence . The mapping space F ( B G , X ) {\displaystyle F(BG,X)} is an example of a homotopy fixed point set. Specifically, F ( B G , X ) {\displaystyle F(BG,X)} is the homotopy fixed point set of the group G {\displaystyle G} acting by the trivial action on X {\displaystyle X} . In general, for a group G {\displaystyle G} acting on a space X {\displaystyle X} , the homotopy fixed points are the fixed points F ( E G , X ) G {\displaystyle F(EG,X)^{G}} of the mapping space F ( E G , X ) {\displaystyle F(EG,X)} of maps from the universal cover E G {\displaystyle EG} of B G {\displaystyle BG} to X {\displaystyle X} under the G {\displaystyle G} -action on F ( E G , X ) {\displaystyle F(EG,X)} given by g {\displaystyle g} in G {\displaystyle G} acts on a map f {\displaystyle f} in F ( E G , X ) {\displaystyle F(EG,X)} by sending it to g f g − 1 {\displaystyle gfg^{-1}} . The G {\displaystyle G} -equivariant map from E G {\displaystyle EG} to a single point ∗ {\displaystyle *} induces a natural map η: X G = F ( ∗ , X ) G {\displaystyle X^{G}=F(*,X)^{G}} → F ( E G , X ) G {\displaystyle F(EG,X)^{G}} from the fixed points to the homotopy fixed points of G {\displaystyle G} acting on X {\displaystyle X} . Miller's theorem is that η is a weak equivalence for trivial G {\displaystyle G} -actions on finite-dimensional CW complexes. An important ingredient and motivation for his proof is a result of Gunnar Carlsson on the homology of B Z / 2 {\displaystyle BZ/2} as an unstable module over the Steenrod algebra . [ 2 ]
Miller's theorem generalizes to a version of Sullivan's conjecture in which the action on X {\displaystyle X} is allowed to be non-trivial. In, [ 3 ] Sullivan conjectured that η is a weak equivalence after a certain p-completion procedure due to A. Bousfield and D. Kan for the group G = Z / 2 {\displaystyle G=Z/2} . This conjecture was incorrect as stated, but a correct version was given by Miller, and proven independently by Dwyer-Miller-Neisendorfer, [ 4 ] Carlsson, [ 5 ] and Jean Lannes , [ 6 ] showing that the natural map ( X G ) p {\displaystyle (X^{G})_{p}} → F ( E G , ( X ) p ) G {\displaystyle F(EG,(X)_{p})^{G}} is a weak equivalence when the order of G {\displaystyle G} is a power of a prime p, and where ( X ) p {\displaystyle (X)_{p}} denotes the Bousfield-Kan p-completion of X {\displaystyle X} . Miller's proof involves an unstable Adams spectral sequence , Carlsson's proof uses his affirmative solution of the Segal conjecture and also provides information about the homotopy fixed points F ( E G , X ) G {\displaystyle F(EG,X)^{G}} before completion, and Lannes's proof involves his T-functor. [ 7 ] | https://en.wikipedia.org/wiki/Sullivan_conjecture |
The Sullivan reaction is a chemical test used for detecting the presence of cysteine or cystine in proteins. A red colour appears when a protein with cysteine or cystine is heated with sodium 1,2-naphthoquinone-4-sulfonate ( Folin's reagent ) and sodium dithionite under alkaline conditions. [ 1 ] [ 2 ] [ 3 ] This was pioneered by the American organic and industrial chemist Eugene Cornelius Sullivan (1872–1962).
This article about analytical chemistry is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sullivan_reaction |
A sulphobe is a film composed of formaldehyde and thiocyanates alleged to have lifelike properties. The name is a portmanteau of sulphur microbe . Sulphobes were a subject in the researches of Alfonso L. Herrera , a biologist who studied the origin of life . [ 1 ] [ 2 ]
This chemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sulphobes |
The Sulston score is an equation used in DNA mapping to numerically assess the likelihood that a given "fingerprint" similarity between two DNA clones is merely a result of chance. Used as such, it is a test of statistical significance . That is, low values imply that similarity is significant , suggesting that two DNA clones overlap one another and that the given similarity is not just a chance event. The name is an eponym that refers to John Sulston by virtue of his being the lead author of the paper that first proposed the equation's use. [ 1 ]
Each clone in a DNA mapping project has a "fingerprint", i.e. a set of DNA fragment lengths inferred from (1) enzymatically digesting the clone, (2) separating these fragments on a gel, and (3) estimating their lengths based on gel location. For each pairwise clone comparison, one can establish how many lengths from each set match-up. Cases having at least 1 match indicate that the clones might overlap because matches may represent the same DNA. However, the underlying sequences for each match are not known. Consequently, two fragments whose lengths match may still represent different sequences. In other words, matches do not conclusively indicate overlaps. The problem is instead one of using matches to probabilistically classify overlap status.
Biologists have used a variety of means (often in combination) to discern clone overlaps in DNA mapping projects. While many are biological, i.e. looking for shared markers, others are basically mathematical, usually adopting probabilistic and/or statistical approaches.
The Sulston score is rooted in the concepts of Bernoulli and binomial processes , as follows. Consider two clones, α {\displaystyle \alpha } and β {\displaystyle \beta } , having m {\displaystyle m} and n {\displaystyle n} measured fragment lengths, respectively, where m ≥ n {\displaystyle m\geq n} . That is, clone α {\displaystyle \alpha } has at least as many fragments as clone β {\displaystyle \beta } , but usually more. The Sulston score is the probability that at least h {\displaystyle h} fragment lengths on clone β {\displaystyle \beta } will be matched by any combination of lengths on α {\displaystyle \alpha } . Intuitively, we see that, at most, there can be n {\displaystyle n} matches. Thus, for a given comparison between two clones, one can measure the statistical significance of a match of h {\displaystyle h} fragments, i.e. how likely it is that this match occurred simply as a result of random chance. Very low values would indicate a significant match that is highly unlikely to have arisen by pure chance, while higher values would suggest that the given match could be just a coincidence.
In what follows, let us refer to individual fragment lengths simply as lengths . Consider a specific length j {\displaystyle j} on clone β {\displaystyle \beta } and a specific length i {\displaystyle i} on clone α {\displaystyle \alpha } . These two lengths are arbitrarily selected from their respective sets i ∈ { 1 , 2 , … , m } {\displaystyle i\in \{1,2,\dots ,m\}} and j ∈ { 1 , 2 , … , n } {\displaystyle j\in \{1,2,\dots ,n\}} . We assume that the gel location of fragment j {\displaystyle j} has been determined and we want
the probability of the event E i j {\displaystyle E_{ij}} that the location of fragment i {\displaystyle i} will match that of j {\displaystyle j} . Geometrically, i {\displaystyle i} will be declared to match j {\displaystyle j} if it falls inside the window of size 2 t {\displaystyle 2t} around j {\displaystyle j} . Since fragment i {\displaystyle i} could occur anywhere in the gel of length G {\displaystyle G} , we have P ⟨ E i j ⟩ = 2 t / G {\displaystyle P\langle E_{ij}\rangle =2t/G} . The probability that i {\displaystyle i} does not match j {\displaystyle j} is simply the complement, i.e. P ⟨ E i , j C ⟩ = 1 − 2 t / G {\displaystyle P\langle E_{i,j}^{C}\rangle =1-2t/G} , since it must either match or not match.
Now, let us expand this to compute the probability that no length on clone α {\displaystyle \alpha } matches the single particular length j {\displaystyle j} on clone β {\displaystyle \beta } . This is simply the intersection of all individual trials i ∈ { 1 , 2 , … , m } {\displaystyle i\in \{1,2,\dots ,m\}} where the event E i , j C {\displaystyle E_{i,j}^{C}} occurs, i.e. P ⟨ E 1 , j C ∩ E 2 , j C ∩ ⋯ ∩ E m , j C ⟩ {\displaystyle P\langle E_{1,j}^{C}\cap E_{2,j}^{C}\cap \cdots \cap E_{m,j}^{C}\rangle } . This can be restated verbally as: length 1 on clone α {\displaystyle \alpha } does not match length j {\displaystyle j} on clone β {\displaystyle \beta } and length 2 does not match length j {\displaystyle j} and length 3 does not match, etc. Since each of these trials is assumed to be independent, the probability is simply
Of course, the actual event of interest is the complement: i.e. there is not "no matches". In other words, the probability of one or more matches is p = 1 − ( 1 − 2 t / G ) m {\displaystyle p=1-\left(1-2t/G\right)^{m}} . Formally, p {\displaystyle p} is the probability that at least one band on clone α {\displaystyle \alpha } matches band j {\displaystyle j} on clone β {\displaystyle \beta } .
This event is taken as a Bernoulli trial having a "success" (matching) probability of p {\displaystyle p} for band j {\displaystyle j} . However, we want to describe the process over all the bands on clone β {\displaystyle \beta } . Since p {\displaystyle p} is constant, the number of matches is distributed binomially . Given h {\displaystyle h} observed matches, the Sulston score S {\displaystyle S} is simply the probability of obtaining at least h {\displaystyle h} matches by chance according to
where C n , j {\displaystyle C_{n,j}} are binomial coefficients .
In a 2005 paper, [ 2 ] Michael Wendl gave an example showing that the assumption of independent trials is not valid. So, although the traditional Sulston score does indeed represent a probability distribution , it is not actually the distribution characteristic of the fingerprint problem. Wendl went on to give the general solution for this problem in terms of the Bell polynomials , showing the traditional score overpredicts P-values by orders of magnitude. (P-values are very small in this problem, so we are talking, for example, about probabilities on the order of 10×10 −14 versus 10×10 −12 , the latter Sulston value being 2 orders of magnitude too high.) This solution provides a basis for determining when a problem has sufficient information content to be treated by the probabilistic approach and is also a general solution to the birthday problem of 2 types .
A disadvantage of the exact solution is that its evaluation is computationally intensive and, in fact, is not feasible for comparing large clones. [ 2 ] Some fast approximations for this problem have been proposed. [ 3 ] | https://en.wikipedia.org/wiki/Sulston_score |
In chemistry , a sultine is a cyclic ester of a sulfinic acid . This class of organosulfur compounds has few applications. These compounds are typically prepared by the dehydration of hydroxy-sulfinic acids or their equivalent. Illustrative of an alternative route, xylylene dibromide reacts with sodium sulfoxylate (source of SO 2 2- ) to give the sultine C 6 H 4 (CH 2 S(O)OCH 2 ), which is a precursor to o- quinodimethane . [ 1 ] | https://en.wikipedia.org/wiki/Sultine |
Sum-frequency generation ( SFG ) is a second order nonlinear optical process based on the mixing of two input photons at frequencies ω 1 {\displaystyle \omega _{1}} and ω 2 {\displaystyle \omega _{2}} to generate a third photon at frequency ω 3 {\displaystyle \omega _{3}} . [ 1 ] As with any χ ( 2 ) {\displaystyle \chi ^{(2)}} optical phenomenon in nonlinear optics , this can only occur under conditions where:
the light is interacting with matter, that lacks centrosymmetry (for example, surfaces and interfaces);
the light has a very high intensity (typically from a pulsed laser ).
Sum-frequency generation is a "parametric process", [ 2 ] meaning that the photons satisfy energy conservation, leaving the matter unchanged:
A special case of sum-frequency generation is second-harmonic generation , in which ω 1 = ω 2 {\displaystyle \omega _{1}=\omega _{2}} . In fact, in experimental physics, this is the most common type of sum-frequency generation. This is because in second-harmonic generation, only one input light beam is required, but if ω 1 ≠ ω 2 {\displaystyle \omega _{1}\neq \omega _{2}} , two simultaneous beams are required, which can be more difficult to arrange. In practice, the term "sum-frequency generation" usually refers to the less common case in which ω 1 ≠ ω 2 {\displaystyle \omega _{1}\neq \omega _{2}} .
For sum-frequency generation to occur efficiently, phase-matching conditions must be satisfied: [ 3 ]
where k 1 , k 2 , k 3 {\displaystyle k_{1},k_{2},k_{3}} are the angular wavenumbers of the three waves as they travel through the medium. (Note that the equation resembles the equation for conservation of momentum .) As this condition is satisfied more and more accurately, the sum-frequency generation becomes more and more efficient.
Sum frequency generation spectroscopy uses two laser beams mixed at an interface to generate an output beam with a frequency equal to the sum of the two input frequencies. Sum frequency generation spectroscopy is used to analyze surfaces and interfaces, carrying complementary information to infrared and Raman spectroscopy . [ 4 ]
This optics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sum-frequency_generation |
The sum activity of peripheral deiodinases ( G D , also referred to as deiodination capacity , total deiodinase activity or, if calculated from levels of thyroid hormones, as SPINA-GD [ a ] ) is the maximum amount of triiodothyronine produced per time-unit under conditions of substrate saturation. [ 1 ] It is assumed to reflect the activity of deiodinases outside the central nervous system and other isolated compartments. GD is therefore expected to reflect predominantly the activity of type I deiodinase .
G D can be determined experimentally by exposing a cell culture system to saturating concentrations of T4 and measuring the T3 production. Whole body deiodination activity can be assessed by measuring production of radioactive iodine after loading the organism with marked thyroxine. [ 2 ]
However, both approaches are faced with draw-backs. Measuring deiodination in cell culture delivers little, if any, information on total deiodination activity. Using marked thyroxine exposes the body to thyrotoxicosis and radioactivity. Additionally, it is not possible to differentiate step-up reactions resulting in T3 production from the step-down reaction catalyzed by type 3 deiodination, which mediates production of reverse T3 . Distinguishing the contribution of distinct deiodinases is possible, however, by sequential approaches using deiodinase-specific blocking agents, but this approach is cumbersome and time-consuming. [ 2 ]
In vivo , it may therefore be beneficial to estimate G D from equilibrium levels of T4 and T3. It is obtained with
G ^ D = β 31 ( K M 1 + [ F T 4 ] ) ( 1 + K 30 [ T B G ] ) [ F T 3 ] α 31 [ F T 4 ] {\displaystyle {\hat {G}}_{D}={{\beta _{31}(K_{M1}+[FT_{4}])(1+K_{30}[TBG])[FT_{3}]} \over {\alpha _{31}[FT_{4}]}}}
or
G ^ D = β 31 ( K M 1 + [ F T 4 ] ) [ T T 3 ] α 31 [ F T 4 ] {\displaystyle {\hat {G}}_{D}={{\beta _{31}(K_{M1}+[FT_{4}])[TT_{3}]} \over {\alpha _{31}[FT_{4}]}}}
[ FT4 ]: Serum free T4 concentration (in pmol/L) [ FT3 ]: Serum free T3 concentration (in pmol/L) [ TT3 ]: Serum total T3 concentration (in nmol/L) α 31 {\displaystyle \alpha _{31}} : Dilution factor for T3 (reciprocal of apparent volume of distribution, 0.026 L −1 ) β 31 {\displaystyle \beta _{31}} : Clearance exponent for T3 (8e-6 sec −1 ) (i. e., reaction rate constant for degradation) K M 1 : Binding constant of type-1-deiodinase (5e-7 mol/L) K 30 : Binding constant T3-TBG (2e9 L/mol) [ 3 ]
The method is based on mathematical models of thyroid homeostasis. [ 1 ] [ 3 ] Calculating deiodinase activity with one of these equations is an inverse problem . Therefore, certain conditions (e.g. stationarity) have to be fulfilled to deliver a reliable result.
The product of SPINA-GD times the urinary iodine excretion can be used to assess iodine-independent factors affecting deiodinase activity, e.g. selenium deficiency. [ 4 ]
The equations and their parameters are calibrated for adult humans with a body mass of 70 kg and a plasma volume of ca. 2.5 L. [ 3 ]
SPINA-GD correlates to the T4-T3 conversion rate in slow tissue pools, as determined with isotope-based measurements in healthy volunteers. [ 1 ] It was also shown that GD correlates with resting energy expenditure , [ 5 ] body mass index [ 3 ] [ 6 ] [ 7 ] and thyrotropin levels in humans, [ 8 ] [ 9 ] and that it is reduced in nonthyroidal illness with hypodeiodination. [ 6 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] Multiple studies demonstrated SPINA-GD to rise after initiation of substitution therapy with selenium , a trace element that is essential for the synthesis of deiodinases. [ 14 ] [ 15 ] [ 16 ] [ 17 ] [ 18 ] Conversely, it was observed that SPINA-GD is reduced in persons positive for autoantibodies to selenoprotein P , which is assumed to be involved in transport and storage of selenium. [ 4 ]
Compared to both healthy volunteers and subjects with hypothyroidism and hyperthyroidism , SPINA-GD is reduced in subacute thyroiditis . In this condition, it has a higher specificity , positive and negative likelihood ratio than serum concentrations of thyrotropin , free T4 or free T3. [ 3 ] These measures of diagnostic utility are also high in nodular goitre , where SPINA-GD is elevated. [ 3 ] Among subjects with subclinical thyrotoxicosis, calculated deiodinase activity is significantly lower in exogenous thyrotoxicosis (resulting from therapy with levothyroxine) than in true hyperthyroidism (ensuing from toxic adenoma , toxic multinodular goitre or Graves' disease ). [ 19 ] SPINA-GD may therefore be an effective biomarker for the differential diagnosis of thyrotoxicosis. [ 20 ] [ 21 ]
Compared to healthy subjects, SPINA-GD is significantly reduced in euthyroid sick syndrome . [ 22 ]
Recent research revealed total deiodinase activity to be higher in untreated hypothyroid patients as long as thyroid tissue is still present. [ 9 ] This effect may ensue from the existence of an effective TSH-deiodinase axis or TSH-T3 shunt . After total thyroidectomy or high-dose radioiodine therapy (e.g. in treated thyroid cancer ) as well as after initiation of substitution therapy with levothyroxine the activity of step-up deiodinases decreases [ 23 ] [ 24 ] and the correlation of SPINA-GD to thyrotropin concentration is lost. [ 25 ] In patients suffering from toxic adenoma, toxic multinodular goitre and Graves’ disease low-dose radioiodine therapy leads to a significant reduction of SPINA-GD as well. [ 26 ]
SPINA-GD is elevated in obesity. This applies to both the metabolically healthy obese (MHO) or metabolically unhealthy obese (MUO) phenotypes. [ 27 ] In two large population-based cohorts within the Study of Health in Pomerania SPINA-GD was positively correlated to some markers of body composition including body mass index (BMI), waist circumference , fat-free mass and body cell mass, [ 28 ] confirming observations in the NHANES dataset [ 29 ] and in a Chinese study. [ 30 ] This positive association was age-dependent and with respect to BMI significant in young subjects only, but with respect to body cell mass stronger in elderly persons. [ 28 ] Generally, SPINA-GD seems to be upregulated in metabolic syndrome , as demonstrated by a significant correlation to the triglyceride-glucose index, a marker of insulin resistance . [ 31 ]
SPINA-GD is reduced in low-T3 syndrome [ 32 ] and certain chronic diseases, e.g. chronic fatigue syndrome , [ 33 ] [ 4 ] chronic kidney disease , [ 34 ] [ 35 ] short bowel syndrome [ 36 ] or geriatric asthma . [ 37 ] Six months after the primary infection, it correlates negatively to the FS-14 score for fatigue in patients affected by Long COVID (PASC). [ 38 ] In Graves' disease , SPINA-GD is initially elevated but decreases with antithyroid treatment in parallel to declining TSH receptor autoantibody titres. [ 5 ] Although takotsubo syndrome (TTS) results in most cases from psychosocial stressors , thereby reflecting type 2 allostatic load , SPINA-GD has been described to be reduced in TTS. [ 39 ] This may result from concomitant non-thyroidal illness syndrome , so that the clinical phenotype represents overlapping type 1 and type 2 allostatic response. In a large register-based study, reduced SPINA-GD predicted a poor outcome of Takotsubo syndrome. [ 40 ]
In certain psychiatric diseases, including major depression, bipolar disorder and schizophrenia SPINA-GD is reduced compared to healthy controls. [ 41 ] This observation is supported by negative correlation of SPINA-GD with the depression percentiles in the Hospital Anxiety and Depression Scale (HADS). [ 42 ]
In hyperthyroid [ 43 ] men both SPINA-GT and SPINA-GD negatively correlate to erectile function , intercourse satisfaction, orgasmic function and sexual desire . Substitution with selenomethionine results in increased SPINA-GD in subjects with autoimmune thyroiditis. [ 14 ] [ 15 ] [ 16 ] [ 17 ]
In subjects with diabetes mellitus SPINA-GD is positively correlated to several bone resorption markers including the N-mid fragment of osteocalcin and procollagen type I N-terminal propeptide (P1NP), as well as, however in men only, the β-C-terminal cross-linked telopeptides of type I collagen (β-CTX). [ 44 ] In the general population it is, however, positively associated with the bone mineral density of the femoral neck and with reduced risk of osteoporosis. [ 45 ] In both diabetic and non-diabetic subsjects it correlates (negatively) with age and concentrations of c-reactive protein , troponin T and B-type natriuretic peptide , and (positively) with the concentrations of total cholesterol , low-density lipoprotein and triglycerides . [ 46 ]
Deiodination capacity proved to be an independent predictor of substitution dose in several trials that included persons on replacement therapy with levothyroxine . [ 47 ] [ 48 ]
Probably as a consequence of non-thyroidal illness syndrome , SPINA-GD predicts mortality in trauma [ 22 ] and postoperative atrial fibrillation in patients undergoing cardiac surgery. [ 12 ] The association to mortality is retained even after adjustment for other established risk factors, including age, APACHE II score and plasma protein binding of thyroid hormones. [ 22 ] Correlations were also shown to age, total atrial conduction time, and concentrations of 3,5-diiodothyronine and B-type natriuretic peptide . [ 12 ] SPINA-GD also correlates with several components of the kynurenine pathway , which might mirror an assosication to a pro-inflammatory milieu. [ 49 ] Accordingly, in a population suffering from pyogenic liver abscess SPINA-GD correlated to markers of malnutrition , inflammation and liver failure . [ 32 ] A study on subjects with Parkinson's disease found SPINA-GD to be significantly decreased in tremor -dominant and mixed subtypes compared to the akinetic-rigid type. [ 50 ] Euthyroid sick syndrome may be the reason for variations of SPINA-GD in subjects treated with immune checkpoint inhibitors for cancer as well. [ 51 ]
Endocrine disruptors may have pronounced effects on step-up deiodinases, as suggested by positive correlation of SPINA-GD to combined exposure to polycyclic aromatic hydrocarbons (PAHs) [ 52 ] and urine concentrations of cadmium and phthalate metabolites, [ 53 ] [ 54 ] [ 55 ] [ 56 ] negative correlation to paraben , mercury and bisphenol A concentration [ 57 ] [ 53 ] [ 54 ] [ 58 ] and a nonlinear association to the concentrations of per- and polyfluoroalkyl substances . [ 59 ] In a cohort of manganese-exposed workers, SPINA-GD responded to a tenfold increase in concentrations of titanium, nickel, selenium and strontium. [ 60 ]
SPINA-GD is significantly elevated in residents of circumpolar regions [ 61 ] and carriers of the TT genotype of the rs3811787 polymorphism of the UCP1 gene. [ 62 ] Since this genotype is more prevalent in geographical regions near the North Pole, it is assumed that the variations of SPINA-GD are part of a natural selection mechanism for adaptation to a cold climate. [ 62 ]
In a longitudinal evaluation of a large sample of the general US population over 10 years, reduced SPINA-GD significantly predicted worse overall survival. [ 63 ] | https://en.wikipedia.org/wiki/Sum_activity_of_peripheral_deiodinases |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.