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Spectral responsivity is a similar measurement, but it has different units: amperes per watt (A/W); (i.e. how much current comes out of the device per unit of incident light power). Responsivity is ordinarily specified for monochromatic light (i.e. light of a single wavelength). Both the quantum efficiency and the responsivity are functions of the photons' wavelength (indicated by the subscript λ).
To convert from responsivity (, in A/W) to QE (on a scale 0 to 1):
where is the wavelength in nm, h is the Planck constant, c is the speed of light in vacuum, and e is the elementary charge. Note that the unit W/A (watts per ampere) is equivalent to V (volts). | 0 | Theoretical and Fundamental Chemistry |
Some well-known brands of glass-ceramics are Pyroceram, Ceran, Eurokera, Zerodur, and Macor. Nippon Electric Glass is a predominant worldwide manufacturer of glass ceramics, whose related products in this area include FireLite [https://www.neg.co.jp/en/product/cg/firelite] and NeoCeram [https://www.neg.co.jp/en/product/cg/neoceram], ceramic glass materials for architectural and high temperature applications respectively. [https://www.vetrotech.com/en-us/keralite-family Keralite], manufactured by [https://www.vetrotech.com/en-us Vetrotech] Saint-Gobain, is a specialty glass-ceramic fire and impact safety rated material for use in fire-rated applications. Glass-ceramics manufactured in the Soviet Union/Russia are known under the name Sitall. Macor is a white, odorless, porcelain-like glass ceramic material and was developed originally to minimize heat transfer during crewed spaceflight by Corning Inc. StellaShine, launched in 2016 by Nippon Electric Glass Co., is a heat-resistant, glass-ceramic material with a thermal shock resistance of up to 800 degrees Celsius. This was developed as an addition to Nippon's line of heat-resistant cooking range plates along with materials like [https://www.neg.co.jp/en/product/cg/neoceram Neoceram]. [https://www.kangertech.com/ KangerTech] is an ecigarette manufacturer which began in Shenzhen, China which produces glass ceramic materials and other special hardened-glass applications like vaporizer modification tanks.
The same class of material is also used in Visions and CorningWare glass-ceramic cookware, allowing it to be taken from the freezer directly to the stovetop or oven with no risk of thermal shock while maintaining the transparent look of glassware. | 0 | Theoretical and Fundamental Chemistry |
Carboxylic acids are polar. Because they are both hydrogen-bond acceptors (the carbonyl ) and hydrogen-bond donors (the hydroxyl ), they also participate in hydrogen bonding. Together, the hydroxyl and carbonyl group form the functional group carboxyl. Carboxylic acids usually exist as dimers in nonpolar media due to their tendency to "self-associate". Smaller carboxylic acids (1 to 5 carbons) are soluble in water, whereas bigger carboxylic acids have limited solubility due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be soluble in less-polar solvents such as ethers and alcohols. Aqueous sodium hydroxide and carboxylic acids, even hydrophobic ones, react to yield water-soluble sodium salts. For example, enanthic acid has a low solubility in water (0.2 g/L), but its sodium salt is very soluble in water. | 0 | Theoretical and Fundamental Chemistry |
Peptide Receptor Radionuclide Therapy (PRRT)
A radioactively labeled analogue of minigastrin, PP-F11, conjugated with NOTA, DOTA, or NODAGA, was studied to view the effects they have on peptide receptor radionuclide therapy (PRRT) and cancer cell tracing. When mice with CCK2 tumors were injected with 64Cu-labeled DOTA-PP-F11, NOTA-PP-F11, and NODAGA-PP-F11, the mice labeled with NOTA displayed a tumor uptake of 7.20 ± 0.44% ID/g and a high tumor-to-blood ratio. Further studies are being investigated on how to reduce the background levels to obtain clearer images.
The inhibition of rapamycin complex 1 improves the tumor uptake of radioactively labeled minigastrin. Treatment of A431/CCKBR tumor cells were assessed with DOTA-PP-F11N. This treatment in combination with RAD001 in mice, resulted in an average size tumor reduction of about 0.3 cm³ in comparison to the control group which had an average tumor size of 0.97 cm³. The treatment group also had a higher survival rate where the control group median life span was 19.5 days and the group that received treatment had an average life span of 43 days. | 1 | Applied and Interdisciplinary Chemistry |
Tailings contain heavy metals and radioactive radium. Radium then decays over thousands of years and radioactive radon gas is produced. Tailings are kept in piles for long-term storage or disposal and need to be maintained and monitored for leaks over the long term.
If uranium tailings are stored aboveground and allowed to dry out, the radioactive sand can be carried great distances by the wind, entering the food chain and bodies of water. The danger posed by such sand dispersal is uncertain at best given the dilution effect of dispersal. The majority of tailing mass will be inert rock, just as it was in the raw ore before the extraction of the uranium, but physically altered, ground up, mixed with large amounts of water and exposed to atmospheric oxygen, which can substantially alter chemical behaviour.
An EPA estimate of risk based on uranium tailings deposits existing in the United States in 1983 gave the figure of 500 lung cancer deaths per century if no countermeasures are taken. | 0 | Theoretical and Fundamental Chemistry |
Firefly luciferase is the light-emitting enzyme responsible for the bioluminescence of fireflies and click beetles. The enzyme catalyses the oxidation of firefly luciferin, requiring oxygen and ATP. Because of the requirement of ATP, firefly luciferases have been used extensively in biotechnology. | 1 | Applied and Interdisciplinary Chemistry |
In addition to the qualities mentioned for Genetic engineering, a Genetic tool also:-
* Used for analysis of gene expression and protein functioning in signature-tagging mutagenesis.
** This analytical tool allows researchers the ability to determine phenotypic expression of gene sequences. Also, this analytic technique mutates the desired locus of interest so that the phenotypes of the original and the mutated gene can be compared. | 1 | Applied and Interdisciplinary Chemistry |
PCAF forms complexes with numerous proteins that guide its activity. For example PCAF is recruited by ATF to acetylate histones and promote transcription of ATF4 target genes. | 1 | Applied and Interdisciplinary Chemistry |
In and of themselves, pH indicators are usually weak acids or weak bases. The general reaction scheme of acidic pH indicators in aqueous solutions can be formulated as:
:HInd + +
where, "HInd" is the acidic form and "Ind" is the conjugate base of the indicator.
Vice versa for basic pH indicators in aqueous solutions:
:IndOH + + +
where "IndOH" stands for the basic form and "Ind" for the conjugate acid of the indicator.
The ratio of concentration of conjugate acid/base to concentration of the acidic/basic indicator determines the pH (or pOH) of the solution and connects the color to the pH (or pOH) value. For pH indicators that are weak electrolytes, the Henderson–Hasselbalch equation can be written as:
:pH = pK + log
:pOH = pK + log
The equations, derived from the acidity constant and basicity constant, states that when pH equals the pK or pK value of the indicator, both species are present in a 1:1 ratio. If pH is above the pK or pK value, the concentration of the conjugate base is greater than the concentration of the acid, and the color associated with the conjugate base dominates. If pH is below the pK or pK value, the converse is true.
Usually, the color change is not instantaneous at the pK or pK value, but a pH range exists where a mixture of colors is present. This pH range varies between indicators, but as a rule of thumb, it falls between the pK or pK value plus or minus one. This assumes that solutions retain their color as long as at least 10% of the other species persists. For example, if the concentration of the conjugate base is 10 times greater than the concentration of the acid, their ratio is 10:1, and consequently the pH is pK + 1 or pK + 1. Conversely, if a 10-fold excess of the acid occurs with respect to the base, the ratio is 1:10 and the pH is pK − 1 or pK − 1.
For optimal accuracy, the color difference between the two species should be as clear as possible, and the narrower the pH range of the color change the better. In some indicators, such as phenolphthalein, one of the species is colorless, whereas in other indicators, such as methyl red, both species confer a color. While pH indicators work efficiently at their designated pH range, they are usually destroyed at the extreme ends of the pH scale due to undesired side reactions. | 0 | Theoretical and Fundamental Chemistry |
Wu was born 1 January 1928 in Jinan, Shandong, Republic of China. He graduated from the Department of Chemistry of Fudan University in 1951, and was hired as a faculty member by the university. In September 1954, he began his graduate studies in the Department of Chemistry of the Moscow State University, and earned his associate doctor degree (Ph.D. equivalent) in June 1958.
After returning to China, Wu was assigned to the newly founded Zhengzhou University to help establish its chemistry department, where he worked for the rest of his career. He later served as chairman of the department and a doctoral advisor.
Wu published more than 160 research articles. He won a National Science Congress Award in 1978, and the Henan Science and Technology Progress Award (First Class) in 2001. He was elected an academician of the Chinese Academy of Sciences in 2003. | 0 | Theoretical and Fundamental Chemistry |
The study of dynamics in multiferroic systems is concerned with understanding the time evolution of the coupling between various ferroic orders, in particular under external applied fields. Current research in this field is motivated both by the promise of new types of application reliant on the coupled nature of the dynamics, and the search for new physics lying at the heart of the fundamental understanding of the elementary MF excitations. An increasing number of studies of MF dynamics are concerned with the coupling between electric and magnetic order parameters in the magnetoelectric multiferroics. In this class of materials, the leading research is exploring, both theoretically and experimentally, the fundamental limits (e.g. intrinsic coupling velocity, coupling strength, materials synthesis) of the dynamical magnetoelectric coupling and how these may be both reached and exploited for the development of new technologies.
At the heart of the proposed technologies based on magnetoelectric coupling are switching processes, which describe the manipulation of the material's macroscopic magnetic properties with electric field and vice versa. Much of the physics of these processes is described by the dynamics of domains and domain walls. An important goal of current research is the minimization of the switching time, from fractions of a second ("quasi"-static regime), towards the nanosecond range and faster, the latter being the typical time scale needed for modern electronics, such as next generation memory devices.
Ultrafast processes operating at picosecond, femtosecond, and even attosecond scale are both driven by, and studied using, optical methods that are at the front line of modern science. The physics underpinning the observations at these short time scales is governed by non-equilibrium dynamics, and usually makes use of resonant processes. One demonstration of ultrafast processes is the switching from collinear antiferromagnetic state to spiral antiferromagnetic state in CuO under excitation by 40 fs 800 nm laser pulse. A second example shows the possibility for the direct control of spin waves with THz radiation on antiferromagnetic NiO. These are promising demonstrations of how the switching of electric and magnetic properties in multiferroics, mediated by the mixed character of the magnetoelectric dynamics, may lead to ultrafast data processing, communication and quantum computing devices.
Current research into MF dynamics aims to address various open questions; the practical realisation and demonstration of ultra-high speed domain switching, the development of further new applications based on tunable dynamics, e.g. frequency dependence of dielectric properties, the fundamental understanding of the mixed character of the excitations (e.g. in the ME case, mixed phonon-magnon modes – electromagnons), and the potential discovery of new physics associated with the MF coupling. | 0 | Theoretical and Fundamental Chemistry |
In the International System of Units (SI), the coherent unit for molar concentration is mol/m. However, most chemical literature traditionally uses mol/dm, which is the same as mol/L. This traditional unit is often called a molar and denoted by the letter M, for example:
:1 mol/m = 10 mol/dm = 10 mol/L = 10 M = 1 mM = 1 mmol/L.
The SI prefix "mega" (symbol M) has the same symbol. However, the prefix is never used alone, so "M" unambiguously denotes molar.
Sub-multiples, such as "millimolar" (mM) and "nanomolar" (nM), consist of the unit preceded by an SI prefix: | 0 | Theoretical and Fundamental Chemistry |
The GUS reporter system (GUS: β-glucuronidase) is a reporter gene system, particularly useful in plant molecular biology and microbiology. Several kinds of GUS reporter gene assay are available, depending on the substrate used. The term GUS staining refers to the most common of these, a histochemical technique. | 1 | Applied and Interdisciplinary Chemistry |
In cell biology and protein biochemistry, heterologous expression means that a protein is experimentally put into a cell that does not normally make (i.e., express) that protein. Heterologous (meaning derived from a different organism) refers to the fact that often the transferred protein was initially cloned from or derived from a different cell type or a different species from the recipient.
Typically the protein itself is not transferred, but instead the correctly edited genetic material coding for the protein (the complementary DNA or cDNA) is added to the recipient cell. The genetic material that is transferred typically must be within a format that encourages the recipient cell to express the cDNA as a protein (i.e., it is put in an expression vector).
Methods for transferring foreign genetic material into a recipient cell include transfection and transduction. The choice of recipient cell type is often based on an experimental need to examine the proteins function in detail, and the most prevalent recipients, known as heterologous expression systems, are chosen usually because they are easy to transfer DNA into or because they allow for a simpler assessment of the proteins function. | 1 | Applied and Interdisciplinary Chemistry |
The very nature of hyrax middens implies that they comprise a mixture of materials, which include animal metabolic products, undigested food, and any allochtonous material blown into the middens or deposited via feet or fur. In terms of organic matter, the existence of such potentially distinct sources (i.e. extraneous organic matter and animal metabolites) implies that a range of information concerning inter alia: animal diet, animal behaviour, metabolic responses to environmental stress, changing behaviour, as well the wider palaeoecological setting of the site may all be preserved within hyraceum. | 0 | Theoretical and Fundamental Chemistry |
The second annual Empowering Women in Organic Chemistry Conference was held virtually on Thursday, August 13, 2020, and Friday, August 14, 2020.
2020 Career Panel featured Shanina Sanders Johnson (Spelman College), Davita Watkins (Univ of Mississippi), Niki Patel (Merck), Stacy Fosu (Abbvie), Beth Lorsbach (Corteva Agriscience), Sibrina Collins (Marburger STEM Center, Lawrence Technological University), Shana Cyr (Bristol Myers Squibb), Sherri Pietranico-Cole (Novartis), Gabby Nepomuceno (California Department of Toxic Substances Control). | 0 | Theoretical and Fundamental Chemistry |
The combined RT-PCR and qPCR technique has been described as quantitative RT-PCR or real-time RT-PCR (sometimes even called quantitative real-time RT-PCR), has been variously abbreviated as qRT-PCR, RT-qPCR, RRT-PCR, and rRT-PCR. In order to avoid confusion, the following abbreviations will be used consistently throughout this article:
Not all authors, especially earlier ones, use this convention and the reader should be cautious when following links. RT-PCR has been used to indicate both real-time PCR (qPCR) and reverse transcription PCR (RT-PCR). | 1 | Applied and Interdisciplinary Chemistry |
A melatonergic agent (or drug) is a chemical which functions to directly modulate the melatonin system in the body or brain. Examples include melatonin receptor agonists and melatonin receptor antagonists. | 1 | Applied and Interdisciplinary Chemistry |
__NOTOC__
Binary chemical weapons or munitions are chemical weapons which contain the toxic agent in its active state as chemical precursors that are significantly less toxic than the agent. This improves the safety of storing, transporting, and disposing of the weapon. Commonly, firing the munition removes a barrier between two precursors. These react to form the intended agent which is then aerosolized and distributed by a bursting charge.
Binary chemical weapons are chemical weapons within the scope of the Chemical Weapons Convention and therefore their production, use and stockpiling is forbidden in most countries, as at least one of the individual chemicals is likely to be a Schedule 1 chemical for which large scale production is forbidden. | 1 | Applied and Interdisciplinary Chemistry |
James Prescott Joule first published in December 1840, an abstract in the Proceedings of the Royal Society, suggesting that heat could be generated by an electrical current. Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current flowing through the wire for a 30 minute period. By varying the current and the length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the immersed wire.
In 1841 and 1842, subsequent experiments showed that the amount of heat generated was proportional to the chemical energy used in the voltaic pile that generated the template. This led Joule to reject the caloric theory (at that time the dominant theory) in favor of the mechanical theory of heat (according to which heat is another form of energy).
Resistive heating was independently studied by Heinrich Lenz in 1842.
The SI unit of energy was subsequently named the joule and given the symbol J. The commonly known unit of power, the watt, is equivalent to one joule per second. | 0 | Theoretical and Fundamental Chemistry |
β-agonists are used to treat asthma, an inflammatory disease in the airways. The inflammation makes the bronchia sensitive to some factors in the environment, which causes bronchoconstriction. When this constriction occurs, the airways get narrow and it causes symptoms like wheezing, chest tightness, shortness of breath, and coughing. The muscles in the airways tighten, and cells in the airway start to produce more mucus than usual, which narrows the airways even more. The symptoms often start in childhood, but it can start at any age | 1 | Applied and Interdisciplinary Chemistry |
A special class of closed-cell foams, known as syntactic foam, contains hollow particles embedded in a matrix material. The spheres can be made from several materials, including glass, ceramic, and polymers. The advantage of syntactic foams is that they have a very high strength-to-weight ratio, making them ideal materials for many applications, including deep-sea and space applications. One particular syntactic foam employs shape memory polymer as its matrix, enabling the foam to take on the characteristics of shape memory resins and composite materials; i.e., it has the ability to be reshaped repeatedly when heated above a certain temperature and cooled. Shape memory foams have many possible applications, such as dynamic structural support, flexible foam core, and expandable foam fill. | 0 | Theoretical and Fundamental Chemistry |
RASSLs and DREADDs are families of designer G-protein-coupled receptors (GPCRs) built specifically to allow for precise spatiotemporal control of GPCR signaling in vivo. These engineered GPCRs are unresponsive to endogenous ligands but can be activated by nanomolar concentrations of pharmacologically inert, drug-like small molecules. Currently, RASSLs exist for the interrogation of several GPCR signaling pathways, including those activated by Gs, Gi, Gq, Golf and β-arrestin. A major cause for success of RASSL resources has been open exchange of DNA constructs, and RASSL related resources.
The hM4Di-DREADDs inhibitory effects are a result of the CNOs stimulation and resulting activation of the G-protein inwardly rectifying potassium (GIRK) channels. This causes hyperpolarization of the targeted neuronal cell and thus attenuates subsequent activity. | 1 | Applied and Interdisciplinary Chemistry |
To produce titanium foams via expansion of pressurized gas, the titanium precursor mixture is placed within a gas-tight metal can, which is evacuated after filling. The metal can is pressurized with inert gas—most commonly argon – and is pressed isostatically. The gas-filled pores are contained within the compacted matrix, and upon exposure to elevated temperatures, these bubbles expand through creep of the surrounding metal matrix. Since processing titanium foams using hot isostatic pressing (HIP) eliminates the need for separate compaction and sintering processes, a wider variety of custom shapes and sizes are possible than via loose powder sintering techniques. Disadvantages of this process include reduced pore connectivity, limited achievable porosity, and a complicated experimental set-up. However, a unique aspect of the HIP process with respect to titanium (and other polymorphic materials) is that transformation superplasticity can be enhanced through the HIP process by way of thermal cycling, or by cycling around the alpha/beta allotropic temperature boundaries of the metal. | 0 | Theoretical and Fundamental Chemistry |
In selective ion monitoring (SIM) certain ion fragments are entered into the instrument method and only those mass fragments are detected by the mass spectrometer. The advantages of SIM are that the detection limit is lower since the instrument is only looking at a small number of fragments (e.g. three fragments) during each scan. More scans can take place each second. Since only a few mass fragments of interest are being monitored, matrix interferences are typically lower. To additionally confirm the likelihood of a potentially positive result, it is relatively important to be sure that the ion ratios of the various mass fragments are comparable to a known reference standard. | 0 | Theoretical and Fundamental Chemistry |
CDP works with corporations, cities, states, and regions to help develop carbon emissions reductions strategies. The collection of self-reported data from the companies is supported by over 800 institutional investors with about US$100 trillion in assets.
Much of the data elicited has never been collected before. This information is helpful to investors, corporations, and regulators in making informed decisions on taking action towards a sustainable economy by measuring and understanding their environmental impact and taking steps to address and limit their risk to climate change, deforestation and water security. | 1 | Applied and Interdisciplinary Chemistry |
Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermodynamic equilibrium, there are no net macroscopic flows of matter nor of energy within a system or between systems. In a system that is in its own state of internal thermodynamic equilibrium, no macroscopic change occurs.
Systems in mutual thermodynamic equilibrium are simultaneously in mutual thermal, mechanical, chemical, and radiative equilibria. Systems can be in one kind of mutual equilibrium, while not in others. In thermodynamic equilibrium, all kinds of equilibrium hold at once and indefinitely, until disturbed by a thermodynamic operation. In a macroscopic equilibrium, perfectly or almost perfectly balanced microscopic exchanges occur; this is the physical explanation of the notion of macroscopic equilibrium.
A thermodynamic system in a state of internal thermodynamic equilibrium has a spatially uniform temperature. Its intensive properties, other than temperature, may be driven to spatial inhomogeneity by an unchanging long-range force field imposed on it by its surroundings.
In systems that are at a state of non-equilibrium there are, by contrast, net flows of matter or energy. If such changes can be triggered to occur in a system in which they are not already occurring, the system is said to be in a meta-stable equilibrium.
Though not a widely named "law," it is an axiom of thermodynamics that there exist states of thermodynamic equilibrium. The second law of thermodynamics states that when an isolated body of material starts from an equilibrium state, in which portions of it are held at different states by more or less permeable or impermeable partitions, and a thermodynamic operation removes or makes the partitions more permeable, then it spontaneously reaches its own new state of internal thermodynamic equilibrium and this is accompanied by an increase in the sum of the entropies of the portions. | 0 | Theoretical and Fundamental Chemistry |
The total volume available for small spheres increases when the excluded volumes around large spheres overlap. The increased volume allotted for small spheres allows them greater translational freedom which increases their entropy. Because the canonical ensemble is an athermal system at a constant volume the Helmholtz free energy is written
where is the Helmholtz free energy, is the entropy and is the temperature. The system's net gain in entropy is positive from increased volume, thus the Helmholtz free energy is negative and depletion flocculation happens spontaneously.
The free energy of the system is obtained from a statistical definition of Helmholtz free energy
where is the partition function for the canonical ensemble. The partition function contains statistical information that describes the canonical ensemble including its total volume, the total number of small spheres, the volume available for small spheres to occupy, and the de Broglie wavelength. If hard-spheres are assumed, the partition function is
The volume available for small spheres, was calculated above. is the number of small spheres and is the de Broglie wavelength. Substituting into the statistical definition, the Helmholtz free energy now reads
The magnitude of the depletion force, is equal to the change in Helmholtz free energy with distance between two large spheres and is given by
The entropic nature of depletion forces was proven experimentally in some cases. For example, some polymeric crowders induce entropic depletion forces that stabilize proteins in their native state.
Other examples include many systems with hard-core only interactions. | 0 | Theoretical and Fundamental Chemistry |
For a targeted treatment, the visibility and accessibility of the transition in the welded areas are required.
Existing structures typically are prepared at the transition for surface finishing. The parts must be free of loose rust and old paint. If necessary, previous sandblasting is required.
The device operates with a compressed air supply of 6–8 bar. | 1 | Applied and Interdisciplinary Chemistry |
Pullulan bioconjugates are systems that use pullulan as a scaffold to attach biological materials to, such as drugs. These systems can be used to enhance the delivery of drugs to specific environments or the mechanism of delivery. These systems can be used in order to deliver drugs in response to stimuli, create a more controlled and sustained release, and provide a more targeted delivery of certain drugs. | 1 | Applied and Interdisciplinary Chemistry |
The first instance of a self-cleaning surface was created in 1995. Paz et al. created a transparent titanium dioxide (TiO) film that was used to coat glass and provide the ability for the glass to self-clean. The first commercial application of this self-cleaning surface, Pilkington Activ, was developed by Pilkington glass in 2001. This product implements a two-stage cleaning process. The first stage consists of photocatalysis of any fouling matter on the glass. This stage is followed by the glass becoming superhydrophilic and allowing water to wash away the catalyzed debris on the surface of the glass. Since the creation of self-cleaning glass, titanium dioxide has also been used to create self-cleaning nanoparticles that can be incorporated into other material surfaces to allow them to self-clean. | 0 | Theoretical and Fundamental Chemistry |
* Carbon
* Hydrogen
* Oxygen
* Nitrogen
* Phosphorus
* Potassium
* Sulfur
* Calcium
* Magnesium
* Iron
* Boron
* Manganese
* Copper
* Zinc
* Nickel
* Chlorine | 0 | Theoretical and Fundamental Chemistry |
* Foreign DNA inserted
* Insertional mutagenesis (but not lethal for the plant cell – as the organism is diploid)
* Transformation DNA fed to rodents ends up in their phagocytes and rarely in other cells. Specifically, this refers to bacterial and M13 DNA. (This preferential accumulation in phagocytes is thought to be real and not a detection artefact since these DNA sequences are thought to provoke phagocytosis.) However, no gene expression is known to have resulted, and this is not thought to be possible. | 1 | Applied and Interdisciplinary Chemistry |
Viral RdRps were discovered in the early 1960s from studies on mengovirus and polio virus when it was observed that these viruses were not sensitive to actinomycin D, a drug that inhibits cellular DNA-directed RNA synthesis. This lack of sensitivity suggested that there is a virus-specific enzyme that could copy RNA from an RNA template and not from a DNA template. | 1 | Applied and Interdisciplinary Chemistry |
The Prefil method is similar to PoDFA but, in addition to the metallographic analysis, Prefil provides also an immediate feedback on metal cleanliness from the metal flowrate through the filter. Because everything about the filtration is well controlled (pressure, metal temperature, ...), the only parameter affecting the filtration speed is the inclusion content. One can determine the cleanliness level from the filtration curve (weight of metal filtered as a function of time). | 1 | Applied and Interdisciplinary Chemistry |
Laser spectroscopy is a spectroscopic technique that uses lasers to be able determine the emitted frequencies of matter. The laser was invented because spectroscopists took the concept of its predecessor, the maser, and applied it to the visible and infrared ranges of light. The maser was invented by Charles Townes and other spectroscopists to stimulate matter to determine the radiative frequencies that specific atoms and molecules emitted. While working on the maser, Townes realized that more accurate detections were possible as the frequency of the microwave emitted increased. This led to an idea a few years later to use the visible and eventually the infrared ranges of light for spectroscopy that became a reality with the help of Arthur Schawlow. Since then, lasers have gone on to significantly advance experimental spectroscopy. The laser light allowed for much higher precision experiments specifically in the uses of studying collisional effects of light as well as being able to accurately detect specific wavelengths and frequencies of light, allowing for the invention of devices such as laser atomic clocks. Lasers also made spectroscopy that used time methods more accurate by using speeds or decay times of photons at specific wavelengths and frequencies to keep time. Laser spectroscopic techniques have been used for many different applications. One example is using laser spectroscopy to detect compounds in materials. One specific method is called Laser-induced Fluorescence Spectroscopy, and uses spectroscopic methods to be able to detect what materials are in a solid, liquid, or gas, in situ. This allows for direct testing of materials, instead of having to take the material to a lab to figure out what the solid, liquid, or gas is made of. | 0 | Theoretical and Fundamental Chemistry |
Cortisone acetate exists in at least five different polymorphs, four of which are unstable in water and change to a stable form. | 0 | Theoretical and Fundamental Chemistry |
As expected, the concentration of the unknown will have some error which can be calculated from the formula below. This formula assumes that a linear relationship is observed for all the standards. It is important to note that the error in the concentration will be minimal if the signal from the unknown lies in the middle of the signals of all the standards (the term goes to zero if )
*, is the standard deviation in the residuals
* is the slope of the line
* is the y-intercept of the line
* is the number of standards
* is the number of replicate unknowns
* is the measurement of the unknown
* is the average measurement of the standards
* are the concentrations of the standards
* is the average concentration of the standards | 1 | Applied and Interdisciplinary Chemistry |
The following example illustrates how a Boolean network can model a GRN together with its gene products (the outputs) and the substances from the environment that affect it (the inputs). Stuart Kauffman was amongst the first biologists to use the metaphor of Boolean networks to model genetic regulatory networks.
# Each gene, each input, and each output is represented by a node in a directed graph in which there is an arrow from one node to another if and only if there is a causal link between the two nodes.
# Each node in the graph can be in one of two states: on or off.
# For a gene, "on" corresponds to the gene being expressed; for inputs and outputs, "on" corresponds to the substance being present.
# Time is viewed as proceeding in discrete steps. At each step, the new state of a node is a Boolean function of the prior states of the nodes with arrows pointing towards it.
The validity of the model can be tested by comparing simulation results with time series observations. A partial validation of a Boolean network model can also come from testing the predicted existence of a yet unknown regulatory connection between two particular transcription factors that each are nodes of the model. | 1 | Applied and Interdisciplinary Chemistry |
Plasma spraying offers versatility of usable coatings, and high-temperature performance. Plasma spraying can accommodate a wide range of materials, versus other techniques. As long as the difference between melting and decomposition temperatures is greater than 300 K, plasma spraying is viable. | 1 | Applied and Interdisciplinary Chemistry |
The term archaerhodopsin is a portmanteau of archaea (the domain in which the proteins are found) and rhodopsin (a photoreceptor responsible for vision in the mammalian eye).
:archaea from Ancient Greek [https://en.wiktionary.org/wiki/%E1%BC%80%CF%81%CF%87%CE%B1%E1%BF%96%CE%BF%CF%82#Ancient_Greek ἀρχαῖα] (arkhaîa, "ancient"), the plural and neuter form of [https://en.wiktionary.org/wiki/%E1%BC%80%CF%81%CF%87%CE%B1%E1%BF%96%CE%BF%CF%82#Ancient_Greek ἀρχαῖος] (arkhaîos, "ancient").
:rhodopsin from Ancient Greek [https://en.wiktionary.org/wiki/%E1%BF%A5%CF%8C%CE%B4%CE%BF%CE%BD#Ancient_Greek ῥόδον] (rhódon, "rose"), because of its pinkish color, and [https://en.wiktionary.org/wiki/%E1%BD%84%CF%88%CE%B9%CF%82#Ancient_Greek ὄψις] (ópsis, "sight"). | 0 | Theoretical and Fundamental Chemistry |
Glycoinformatics is a field of bioinformatics that pertains to the study of carbohydrates involved in protein post-translational modification. It broadly includes (but is not restricted to) database, software, and algorithm development for the study of carbohydrate structures, glycoconjugates, enzymatic carbohydrate synthesis and degradation, as well as carbohydrate interactions. Conventional usage of the term does not currently include the treatment of carbohydrates from the better-known nutritive aspect. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, a NONOate is a compound having the chemical formula RRN−(NO)−N=O, where R and R are alkyl groups. One example for this is 1,1-diethyl-2-hydroxy-2-nitrosohydrazine, or diethylamine dinitric oxide. These compounds are unusual in having three sequential nitrogen atoms: an amine functional group, a bridging NO group, and a terminal nitrosyl group. In contact with water, these compounds release NO (nitric oxide). | 0 | Theoretical and Fundamental Chemistry |
A future nanocar with a synthetic molecular motor has been developed by Jean-Francois Morin et al. It is fitted with carborane wheels and a light-powered helicene synthetic molecular motor. Although the motor moiety displayed unidirectional rotation in solution, light-driven motion on a surface has yet to be observed. Mobility in water and other liquids can be also realized by a molecular propeller in the future. | 0 | Theoretical and Fundamental Chemistry |
The air transports viruses and other pathogens. Since viruses are smaller than other bioaerosols, they have the potential to travel further distances. In one simulation, a virus and a fungal spore were simultaneously released from the top of a building; the spore traveled only 150 meters while the virus traveled almost 200,000 horizontal kilometers.
In one study, aerosols (<5 μm) containing SARS-CoV-1 and SARS-CoV-2 were generated by an atomizer and fed into a Goldberg drum to create an aerosolized environment. The inoculum yielded cycle thresholds between 20 and 22, similar to those observed in human upper and lower respiratory tract samples. SARS-CoV-2 remained viable in aerosols for 3 hours, with a decrease in infection titre similar to SARS-CoV-1. The half-life of both viruses in aerosols was 1.1 to 1.2 hours on average. The results suggest that the transmission of both viruses by aerosols is plausible, as they can remain viable and infectious in suspended aerosols for hours and on surfaces for up to days. | 0 | Theoretical and Fundamental Chemistry |
Indications of thermal rearrangements of aromatic hydrocarbons were first noted in the early 20th century by natural products chemists who were working with sesquiterpenes. At the time, they noticed the automerization of a substituted azulene shown below, but no further structural or mechanistic investigations were made.
The oldest characterized thermal rearrangement of an aromatic compound was that of the isomerization of azulene to naphthalene by Heilbronner et al. in 1947. Since then, many other isomerizations have been recorded, however the rearrangement of azulene to naphthalene has received the most attention. Likewise, since the characterization of the automerization of naphthalene by Scott in 1977, similar atom scramblings of other aromatic hydrocarbons such as pyrene, azulene, [[Benz(a)anthracene|benz[a]anthracene]] and even benzene have been described. While the existence of these reactions has been confirmed, the isomerization and automerization mechanisms remain unknown. | 0 | Theoretical and Fundamental Chemistry |
Sandwich panel cores are used throughout the aerospace industry; they are integrated within aircraft bodies, floors and internal panels. Sandwich constructions consist of two faces separated by a thick, light-weight core and are most commonly composed of balsa-wood, foamed polymers, glue-bonded aluminum or Nomex (paper) honeycombs. Typically, the cores are combined with reinforcing fibers to increase their shear modulus. Indeed, carbon fiber-reinforced polymers exhibit the highest specific stiffness and strength of these materials. However, polymers decompose at low temperatures; thus employment of the aforementioned materials pose inherent challenges due to the limited range of temperature they may be utilized within as well as their moisture-dependent properties.
The largest and most inadequately predicted failure within the core results from strain localization. Strain localization refers to the development of bands exhibiting intensive straining as a result of the localization of deformations in the solid.
For the best performance, the structure should exhibit low peak response force and high total energy absorption. Titanium foams are lightweight, stiff, and possess the capability to resist blast. Furthermore, the use of titanium-based foams exhibiting homogeneous porosity distribution would significantly decrease the risks associated with strain localization. The high strength-to-weight ratio of titanium foams offers an opportunity to provide increased bending and shearing stiffness as well as energy absorption capabilities during periods of bending. Titanium foams may be utilized in environments with elevated temperatures (up to 400 °C). Composite structures may also be produced; the incorporation of silicon carbide monofilaments into Ti-6-Al-4V foams was shown to exhibit an elastic modulus of 195 GPa and tensile strength of 800 MPa. | 0 | Theoretical and Fundamental Chemistry |
The turbine flowmeter (better described as an axial turbine) translates the mechanical action of the turbine rotating in the liquid flow around an axis into a user-readable rate of flow (gpm, lpm, etc.). The turbine tends to have all the flow traveling around it.
The turbine wheel is set in the path of a fluid stream. The flowing fluid impinges on the turbine blades, imparting a force to the blade surface and setting the rotor in motion. When a steady rotation speed has been reached, the speed is proportional to fluid velocity.
Turbine flowmeters are used for the measurement of natural gas and liquid flow. Turbine meters are less accurate than displacement and jet meters at low flow rates, but the measuring element does not occupy or severely restrict the entire path of flow. The flow direction is generally straight through the meter, allowing for higher flow rates and less pressure loss than displacement-type meters. They are the meter of choice for large commercial users, fire protection, and as master meters for the water distribution system. Strainers are generally required to be installed in front of the meter to protect the measuring element from gravel or other debris that could enter the water distribution system. Turbine meters are generally available for 4 to 30 cm (–12 in) or higher pipe sizes. Turbine meter bodies are commonly made of bronze, cast Iron, or ductile iron. Internal turbine elements can be plastic or non-corrosive metal alloys. They are accurate in normal working conditions but are greatly affected by the flow profile and fluid conditions.
Fire meters are a specialized type of turbine meter with approvals for the high flow rates required in fire protection systems. They are often approved by Underwriters Laboratories (UL) or Factory Mutual (FM) or similar authorities for use in fire protection. Portable turbine meters may be temporarily installed to measure water used from a fire hydrant. The meters are normally made of aluminum to be lightweight, and are usually 7.5 cm (3 in) capacity. Water utilities often require them for measurement of water used in construction, pool filling, or where a permanent meter is not yet installed. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups.
In inorganic chemistry, the anion appears in a few rare minerals, but the functional group has tremendous importance in biochemistry. Disulfide bridges formed between thiol groups in two cysteine residues are an important component of the secondary and tertiary structure of proteins.
Compounds of the form are usually called persulfides instead. | 0 | Theoretical and Fundamental Chemistry |
The North Atlantic Subpolar Gyre is an important part of the ocean's carbon dioxide drawdown mechanism. The photosynthesis of phytoplankton communities in this area seasonally depletes surface waters of carbon dioxide, removing it through primary production. This primary production occurs seasonally, with the highest amounts happening in summer. Generally, spring is an important time for photosynthesis as the light limitation imposed during winter is lifted and there are high levels of nutrients available. However, in the North Atlantic Subpolar Gyre, spring productivity is low in comparison to expected levels. It is hypothesized that this low productivity is because phytoplankton are less efficiently using light than they do in the summer months. | 1 | Applied and Interdisciplinary Chemistry |
The length of the carbon-hydrogen bond varies slightly with the hybridisation of the carbon atom. A bond between a hydrogen atom and an sp hybridised carbon atom is about 0.6% shorter than between hydrogen and sp hybridised carbon. A bond between hydrogen and sp hybridised carbon is shorter still, about 3% shorter than sp C-H. This trend is illustrated by the molecular geometry of ethane, ethylene and acetylene. | 0 | Theoretical and Fundamental Chemistry |
Relative density or specific gravity of the coal depends on the rank of the coal and degree of mineral impurity. Knowledge of the density of each coal play is necessary to determine the properties of composites and blends. The density of the coal seam is necessary for conversion of resources into reserves.
Relative density is normally determined by the loss of a sample's weight in water. This is best achieved using finely ground coal, as bulk samples are quite porous. To determine in-place coal tonnages however, it is important to preserve the void space when measuring the specific gravity. | 0 | Theoretical and Fundamental Chemistry |
Hollow fiber membranes (HFMs) are a class of artificial membranes containing a semi-permeable barrier in the form of a hollow fiber. Originally developed in the 1960s for reverse osmosis applications, hollow fiber membranes have since become prevalent in water treatment, desalination, cell culture, medicine, and tissue engineering. Most commercial hollow fiber membranes are packed into cartridges which can be used for a variety of liquid and gaseous separations. | 0 | Theoretical and Fundamental Chemistry |
Anhydrous reacts vigorously with bases, so suitable precautions are required.
It can cause irritation to the eyes, skin, and the respiratory system if inhaled or on contact. | 0 | Theoretical and Fundamental Chemistry |
The herbicide glyphosate is an inhibitor of 3-phosphoshikimate 1-carboxyvinyltransferase, other herbicides, such as the sulfonylureas inhibit the enzyme acetolactate synthase. Both enzymes are needed for plants to make branched-chain amino acids. Many other enzymes are inhibited by herbicides, including enzymes needed for the biosynthesis of lipids and carotenoids and the processes of photosynthesis and oxidative phosphorylation. | 1 | Applied and Interdisciplinary Chemistry |
In astronomy, the curve of growth describes the equivalent width of a spectral line as a function of the column density of the material from which the spectral line is observed. | 0 | Theoretical and Fundamental Chemistry |
Following the successful clinical trials in LCA, researchers have been developing similar treatments using adeno-associated virus for age-related macular degeneration (AMD). To date, efforts have focused on long-term delivery of VEGF inhibitors to treat the wet form of macular degeneration. Whereas wet AMD is currently treated using frequent injections of recombinant protein into the eyeball, the goal of these treatments is long-term disease management following a single administration. One such study is being conducted at the Lions Eye Institute in Australia in collaboration with Avalanche Biotechnologies, a US-based biotechnology start-up. Another early-stage study is sponsored by Genzyme Corporation. | 1 | Applied and Interdisciplinary Chemistry |
The N-Acetylglucosamine (GlcNAc) receptor has been recently found to interact and bind with vimentins at the cell surface. Research indicates that the GlcNAc receptor can therefore be used to target vimentin-expressing cells for gene delivery via receptor-mediated endocytosis. | 1 | Applied and Interdisciplinary Chemistry |
The multiplicity function for a two state paramagnet, W(n,N), is the number of spin states such that n of the N spins point in the z-direction. This function is given by the combinatoric function C(N,n). That is:
It is primarily used in introductory statistical mechanics and thermodynamics textbooks to explain the microscopic definition of entropy to students. If the spins are non-interacting, then the multiplicity function counts the number of states which have the same energy in an external magnetic field. By definition, the entropy S is then given by the natural logarithm of this number: | 0 | Theoretical and Fundamental Chemistry |
Solvophobic theory attempts to explain interactions between polar solvents and non-polar solutes. In the pure solvent, there are relatively strong cohesive forces between the solvent molecules due to hydrogen bonding or other polar interactions. Hence, non-polar solutes tend not to be soluble in polar solvents because these solvent-solvent binding interactions must be overcome first. When applied to liquid chromatography (LC), solvophobic theory attributes the retention of solutes on the stationary phase partly to the rejection of solute molecules by the solvent, and partly to the attraction of the solute molecules by the stationary phase. | 0 | Theoretical and Fundamental Chemistry |
* In reductive decyanation the nitrile group is replaced by a proton. Decyanations can be accomplished by dissolving metal reduction (e.g. HMPA and potassium metal in tert-butanol) or by fusion of a nitrile in KOH. Similarly, α-aminonitriles can be decyanated with other reducing agents such as lithium aluminium hydride.
* In the so-called Franchimont Reaction (developed by the Belgian doctoral student Antoine Paul Nicolas Franchimont (1844-1919) in 1872), an α-cyanocarboxylic acid heated in acid hydrolyzes and decarboxylates to a dimer.
* Nitriles self-react in presence of base in the Thorpe reaction in a nucleophilic addition
* In organometallic chemistry nitriles are known to add to alkynes in carbocyanation: | 0 | Theoretical and Fundamental Chemistry |
Cesium chloride is a simple cubic crystal lattice with a basis of Cs at (0,0,0) and Cl at (1/2, 1/2, 1/2) (or the other way around, it makes no difference). Equation () becomes
We then arrive at the following result for the structure factor for scattering from a plane :
and for scattered intensity, | 0 | Theoretical and Fundamental Chemistry |
Genes encoding the MuvB complex were originally identified from loss-of-function mutation studies in C. elegans. When mutated, these genes produced worms with multiple vulva-like organs, hence the name ‘Muv’. Three classes of Muv genes were classified, with class B genes encoding homologues of mammalian RB, E2F, and DP1, and others such as LIN-54, LIN-37, LIN-7 and LIN-52, whose functions were not yet understood.
Studies in Drosophila melanogaster ovarian follicle cells identified a protein complex that bound to repeatedly amplifying chorion genes. The complex included genes that had close homology with the MuvB genes such as Mip130, Mip120 and Mip40. These Mip genes were identified as homologues of the MuvB genes LIN9, LIN54, and LIN37 respectively. Further studies in the fly embryo nuclear extracts confirmed the coexistence of these proteins with others such as the RB homologues Rbf1 and Rbf2, and others like E2f and Dp. The protein complex was thus termed as the Drosophila RBF, E2f2 and Mip (dREAM) complex. Disruption of the dREAM complex through RNAi knockdown of the components of dREAM complex led to higher expression of E2f regulated genes that are typically silenced, implicating dREAM’s role in gene down-regulation. Later in Drosophila melanogaster, there was also found a testis-specific paralog of the Myb-MuvB/DREAM complex known as tMAC (testis-specific meiotic arrest complex), which is involved in meiotic arrest.
A protein complex similar to dREAM was subsequently identified in C. elegans extract containing DP, RB, and MuvB, and was named as DRM. This complex included mammalian homologues of RB and DP, and other members of the MuvB complex.
The mammalian DREAM complex was identified following immunoprecipitation of p130 with mass-spectrometry analysis. The results showed that p130 was associated with E2F4, E2F5, the dimerization partner DP, and LIN9, LIN54, LIN37, LIN52, and RBBP4 that make up the MuvB complex. Immunoprecipitation of MuvB factors also revealed association of BMYB. Subsequent immunoprecipitation with BMYB yielded all the MuvB core proteins, but not other members of the DREAM complex – p130, p107, E2F4/5 and DP. This indicated that MuvB associated with BMYB to form the BMYB-MuvB complex or with p130/p107, E2F4/5 and DP to form the DREAM complex. The DREAM complex was found prevalent in quiescent or starved cells, and the BMYB-MuvB complex was found in actively dividing cells, hinting at separate functionalities of these two complexes.
MuvB-like complexes were also recently discovered in Arabidoposis that include E2F and MYB orthologs combined with LIN9 and LIN54 orthologs. | 1 | Applied and Interdisciplinary Chemistry |
For his work in applied chemical science on rutile sand, phosphate rock, graphite and beryl "which has contributed to the advancement of the welfare of the community", McTaggart was awarded the University of Melbourne's Grosvenor Laboratories Prize for 1946 by the Royal Australian Chemical Institute; and the Grimwade prize in industrial research for 1946 for his "Mineral Chlorination Studies.” He was among the first CSIRO officers to be awarded an honorary doctorate. | 0 | Theoretical and Fundamental Chemistry |
These groups have a strong electron-withdrawing inductive effect (-I) either by virtue of their positive charge or because of the powerfully electronegativity of the halogens. There is no resonance effect because there are no orbitals or electron pairs which can overlap with those of the ring. The inductive effect acts like that for the carboxylate anion but in the opposite direction (i.e. it produces small positive charges on the ortho and para positions but not on the meta position and it destabilises the Wheland intermediate.) Hence these groups are deactivating and meta directing: | 0 | Theoretical and Fundamental Chemistry |
Alclad sheeting has become a widely used material within the aviation industry for the construction of aircraft due to its favourable qualities, such as a high fatigue resistance and its strength. During the first half of the twentieth century, substantial studies were conducted into the corrosion qualities of various lightweight aluminium alloys for aviation purposes. The first aircraft to be constructed from Alclad was the all-metal US Navy airship ZMC-2, which was constructed in 1927 at Naval Air Station Grosse Ile. Prior to this, aluminium had been used on the pioneering zeppelins constructed by Ferdinand Zeppelin.
Alclad has been most commonly present in certain elements of an aircraft, including the fuselage, structural members, skin, and cowls. The aluminium alloy that Alclad is derived from has become one of the most commonly used of all aluminium-based alloys. While unclad aluminium has also continued to be extensively used on modern aircraft, which has a lower weight than Alclad, it is more prone to corrosion; the alternating use of the two materials is often defined by the specific components or elements that are composed of them. In aviation-grade Alclad, the thickness of the outer cladding layer typically varies between 1% and 15% of the total thickness. | 1 | Applied and Interdisciplinary Chemistry |
The exchange current is the current at equilibrium, i.e. the rate at which oxidized and reduced species transfer electrons with the electrode. In other words, the exchange current density is the rate of reaction at the reversible potential (when the overpotential is zero by definition). At the reversible potential, the reaction is in equilibrium meaning that the forward and reverse reactions progress at the same rates. This rate is the exchange current density.
The Tafel slope is measured experimentally. It can, however, be shown theoretically that when the dominant reaction mechanism involves the transfer of a single electron that
where A is defined as
where
* is Boltzmann's constant,
* is the absolute temperature,
* is the electric elementary charge of an electron,
* is the thermal voltage, and
* is the "charge transfer coefficient", the value of which must be between 0 and 1. | 0 | Theoretical and Fundamental Chemistry |
A diffuse series of triplet lines is designated by series letter d and formula 1p-md. The diffuse series of singlet lines has series letter S and formula 1P-mS. | 0 | Theoretical and Fundamental Chemistry |
Phelps struggled academically in college. Unable to find employment after graduating, she joined the United States Navy. Phelps enrolled in the Navy's Nuclear Power School, which she credits with teaching her "how to study". Phelps studied nuclear power, reactor theory, and thermodynamics, and graduated in the top 10% of her class of 300–400 students. In 2019, Phelps told an interviewer that she pursued nuclear chemistry in part because of the lack of black women in the field, commenting: "They needed to see somebody like me sitting in the same spaces that they were at, and excelling in that same space."
Phelps served as a non-commissioned officer in the United States Navy Nuclear Power Program. She spent four and a half years aboard the aircraft carrier , operating the nuclear reactor and steam generator chemistry controls, and maintaining the water in the reactor. She was deployed twice, and was the only black woman in her division on the ship. | 0 | Theoretical and Fundamental Chemistry |
The Mond gas process was designed to convert cheap coal into flammable gas, which was made up of mainly hydrogen, while recovering ammonium sulfate. The gas produced was rich in hydrogen and poor in carbon monoxide. Although it could be used for some industrial purposes and power generation, the gas was limited for heating or lighting.
In 1897, the first Mond gas plant began at the Brunner Mond & Company in Northwich, Cheshire. Mond plants which recovered ammonia needed to be large in order to be profitable, using at least 182 tons of coal per week. | 0 | Theoretical and Fundamental Chemistry |
Alfred Matthew Hubbard is reputed to have introduced more than 6,000 people to LSD, including scientists, politicians, intelligence officials, diplomats, and church figures. He became known as the original "Captain Trips", travelling about with a leather case containing pharmaceutically pure LSD, mescaline, and psilocybin. He became a "freelance" apostle for LSD in the early 1950s after supposedly receiving an angelic vision telling him that something important to the future of mankind would soon be coming. When he read about LSD the next year, he immediately sought and acquired LSD, which he tried for himself in 1951.
Although he had no medical training, Hubbard collaborated on running psychedelic sessions with LSD with Ross McLean at Vancouvers Hollywood Hospital, with psychiatrists Abram Hoffer and Humphry Osmond; with Myron Stolaroff at the International Federation for Advanced Study in Menlo Park, California; and with Willis Harman at the Stanford Research Institute (SRI). At various times over the next 20 years, Hubbard also reportedly worked for the Canadian Special Services, the U.S. Justice Department and the U.S. Bureau of Alcohol, Tobacco & Firearms. It is also rumored that he was involved with the CIAs MK-ULTRA project. How his government positions actually interacted with his work with LSD is unknown. | 1 | Applied and Interdisciplinary Chemistry |
Ground substance is an amorphous gel-like substance in the extracellular space of animals that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin. Ground substance is active in the development, movement, and proliferation of tissues, as well as their metabolism. Additionally, cells use it for support, water storage, binding, and a medium for intercellular exchange (especially between blood cells and other types of cells). Ground substance provides lubrication for collagen fibers.
The components of the ground substance vary depending on the tissue. Ground substance is primarily composed of water and large organic molecules, such as glycosaminoglycans (GAGs), proteoglycans, and glycoproteins. GAGs are polysaccharides that trap water, giving the ground substance a gel-like texture. Important GAGs found in ground substance include hyaluronic acid, heparan sulfate, dermatan sulfate, and chondroitin sulfate. With the exception of hyaluronic acid, GAGs are bound to proteins called proteoglycans. Glycoproteins are proteins that attach components of the ground substance to one another and to the surfaces of cells. Components of the ground substance are secreted by fibroblasts. Usually it is not visible on slides, because it is lost during staining in the preparation process.
Link proteins such as vinculin, spectrin and actomyosin stabilize the proteoglycans and organize elastic fibers in the ECM. Changes in the density of ground substance can allow collagen fibers to form aberrant cross-links. Loose connective tissue is characterized by few fibers and cells, and a relatively large amount of ground substance. Dense connective tissue has a smaller amount of ground substance compared to the fibrous material.
The meaning of the term has evolved over time. | 1 | Applied and Interdisciplinary Chemistry |
Epothilone A and B are reported to be highly effective anticancer drugs. Several of their structural derivatives show very promising inhibition against breast cancer with only mild side effect and some of them are now under trials. In 1997, K. C. Nicolaou and coworkers reported the first total synthesis of both Epothilone A and B. Ender's alkylation reaction was utilized at the very beginning of the synthesis to install the stereogenic center at C8. The reaction proceeded with both high yield and high diastereoselectivity. | 0 | Theoretical and Fundamental Chemistry |
The Payne rearrangement is the isomerization, under basic conditions, of 2,3-epoxy alcohols to isomeric 1,2-epoxy alcohols with inversion of configuration. Aza- and thia-Payne rearrangements of aziridines and thiiraniums, respectively, are also known. | 0 | Theoretical and Fundamental Chemistry |
GaAs may have applications in spintronics as it can be used instead of platinum in spin-charge converters and may be more tunable. | 0 | Theoretical and Fundamental Chemistry |
For an ideal gas in equilibrium, the rate of collisions with the container wall and velocity distribution of particles hitting the container wall can be calculated based on naive kinetic theory, and the results can be used for analyzing effusive flow rates, which is useful in applications such as the gaseous diffusion method for isotope separation.
Assume that in the container, the number density (number per unit volume) is and that the particles obey Maxwell's velocity distribution:
Then for a small area on the container wall, a particle with speed at angle from the normal of the area , will collide with the area within time interval , if it is within the distance from the area . Therefore, all the particles with speed at angle from the normal that can reach area within time interval are contained in the tilted pipe with a height of and a volume of .
The total number of particles that reach area within time interval also depends on the velocity distribution; All in all, it calculates to be:
Integrating this over all appropriate velocities within the constraint yields the number of atomic or molecular collisions with a wall of a container per unit area per unit time:
This quantity is also known as the "impingement rate" in vacuum physics. Note that to calculate the average speed of the Maxwell's velocity distribution, one has to integrate over.
The momentum transfer to the container wall from particles hitting the area with speed at angle from the normal, in time interval is:Integrating this over all appropriate velocities within the constraint yields the pressure (consistent with Ideal gas law):If this small area is punched to become a small hole, the effusive flow rate will be:
Combined with the ideal gas law, this yields
The above expression is consistent with Graham's law.
To calculate the velocity distribution of particles hitting this small area, we must take into account that all the particles with that hit the area within the time interval are contained in the tilted pipe with a height of and a volume of ; Therefore, compared to the Maxwell distribution, the velocity distribution will have an extra factor of :
with the constraint . The constant can be determined by the normalization condition to be , and overall: | 0 | Theoretical and Fundamental Chemistry |
The radius ratio rule was first proposed by Gustav F. Hüttig in 1920. In 1926, Victor Goldschmidt extended the use to ionic lattices. In 1929, the rule was incorporated as the first of Pauling's rules for crystal structures. | 0 | Theoretical and Fundamental Chemistry |
The Henderson limit is the X-ray dose (energy per unit mass) a cryo-cooled crystal can absorb before the diffraction pattern decays to half of its original intensity. Its value is defined as 2 × 10 Gy (J/kg). | 1 | Applied and Interdisciplinary Chemistry |
*Erosion corrosion
*Pitting corrosion Oxygen pitting
*Hydrogen embrittlement
*Hydrogen-induced cracking (ASM term)
*Corrosion embrittlement (ASM term)
*Hydrogen disintegration (NACE term)
*Hydrogen-assisted cracking (ASM term)
*Hydrogen blistering
*Corrosion | 1 | Applied and Interdisciplinary Chemistry |
Lanthanide organometallic complexes have been synthesized by RT and RTLE. Lanthanides are very electropositive elements.
Organomercurials, such as HgPh, are common kinetically inert RT and RTLE reagents that allow functionalized
derivatives to be synthesized, unlike organolithiums and Grignard reagents. Diarylmercurials are often used to synthesize lanthanide organometallic complexes. Hg(CF) is a better RT reagent to use with lanthanides than HgPh because it does not require a step to activate the metal. However, phenyl-substituted lanthanide complexes are more thermally stable than the pentafluorophenyl complexes. The use of HgPh led to the synthesis of a ytterbium complex with different oxidation states on the two Yb atoms:
:Yb(CH)(THF) + HgPh → YbYbPh(THF)
In the Ln(CF) complexes, where Ln = Yb, Eu, or Sm, the Ln–C bonds are very reactive, making them useful in RTLE reactions. Protic substrates have been used as a reactant with the Ln(CF) complex as shown: Ln(CF) + 2LH → Ln(L) + 2CFH. It is possible to avoid the challenges of working with the unstable Ln(CF) complex by forming it in situ by the following reaction:
:Ln + HgR + 2 LH → Ln(L) + Hg + 2 RH
Organotins are also kinetically inert RT and RTLE reagents that have been used in a variety of organometallic reactions. They have applications to the synthesis of lanthanide complexes, such as in the following reaction:
:Yb + Sn(N(SiMe)) → Yb(N(SiMe)) + Sn | 0 | Theoretical and Fundamental Chemistry |
Nowadays, synthetic polymers are used in almost all walks of life. Modern society would look very different without them. The spreading of polymer use is connected to their unique properties: low density, low cost, good thermal/electrical insulation properties, high resistance to corrosion, low-energy demanding polymer manufacture and facile processing into final products. For a given application, the properties of a polymer can be tuned or enhanced by combination with other materials, as in composites. Their application allows to save energy (lighter cars and planes, thermally insulated buildings), protect food and drinking water (packaging), save land and lower use of fertilizers (synthetic fibres), preserve other materials (coatings), protect and save lives (hygiene, medical applications). A representative, non-exhaustive list of applications is given below.
* Clothing, sportswear and accessories: polyester and PVC clothing, spandex, sport shoes, wetsuits, footballs and billiard balls, skis and snowboards, rackets, parachutes, sails, tents and shelters.
* Electronic and photonic technologies: organic field effect transistors (OFET), light emitting diodes (OLED) and solar cells, television components, compact discs (CD), photoresists, holography.
* Packaging and containers: films, bottles, food packaging, barrels.
* Insulation: electrical and thermal insulation, spray foams.
* Construction and structural applications: garden furniture, PVC windows, flooring, sealing, pipes.
* Paints, glues and lubricants: varnish, adhesives, dispersants, anti-graffiti coatings, antifouling coatings, non-stick surfaces, lubricants.
* Car parts: tires, bumpers, windshields, windscreen wipers, fuel tanks, car seats.
* Household items: buckets, kitchenware, toys (e.g., construction sets and Rubik's cube).
* Medical applications: blood bag, syringes, rubber gloves, surgical suture, contact lenses, prosthesis, controlled drug delivery and release, matrices for cell growth.
* Personal hygiene and healthcare: diapers using superabsorbent polymers, toothbrushes, cosmetics, shampoo, condoms.
* Security: personal protective equipment, bulletproof vests, space suits, ropes.
* Separation technologies: synthetic membranes, fuel cell membranes, filtration, ion-exchange resins.
* Money: polymer banknotes and payment cards.
* 3D printing. | 0 | Theoretical and Fundamental Chemistry |
The Jameson Cell has been found to be particularly effective in cleaning and recovering fine coal particles. For example, at BHP Coal's Goonyella mine (now part of the BHP Mitsubishi Alliance) eight Cells were installed to replace the entire 32 mechanical cell flotation circuit in 1995 in its 1800 t/h coal flotation plant. The result was an overall increase in yield for the plant of 3.5% (better than the predicted yield of 2.1% that was used to justify the project) and the production of a low-ash product.
Since then, Jameson Cells have been installed in many coal preparation plants around the world, with the largest installation at the Curragh coal mine in Australia, where 12 Cells treat over 5 million t/y of coal fines.
The Cell can also be applied to coal preparation plant tailings to recover fine coal previously discarded. | 1 | Applied and Interdisciplinary Chemistry |
The established method for the production of synthetic peptides in the lab is known as solid phase peptide synthesis (SPPS). Pioneered by Robert Bruce Merrifield, SPPS allows the rapid assembly of a peptide chain through successive reactions of amino acid derivatives on a macroscopically insoluble solvent-swollen beaded resin support.
The solid support consists of small, polymeric resin beads functionalized with reactive groups (such as amine or hydroxyl groups) that link to the nascent peptide chain. Since the peptide remains covalently attached to the support throughout the synthesis, excess reagents and side products can be removed by washing and filtration. This approach circumvents the comparatively time-consuming isolation of the product peptide from solution after each reaction step, which would be required when using conventional solution-phase synthesis.
Each amino acid to be coupled to the peptide chain N-terminus must be protected on its N-terminus and side chain using appropriate protecting groups such as Boc (acid-labile) or Fmoc (base-labile), depending on the side chain and the protection strategy used (see below).
The general SPPS procedure is one of repeated cycles of alternate N-terminal deprotection and coupling reactions. The resin can be washed between each steps. First an amino acid is coupled to the resin. Subsequently, the amine is deprotected, and then coupled with the activated carboxyl group of the next amino acid to be added. This cycle is repeated until the desired sequence has been synthesized. SPPS cycles may also include capping steps which block the ends of unreacted amino acids from reacting. At the end of the synthesis, the crude peptide is cleaved from the solid support while simultaneously removing all protecting groups using a reagent such as trifluoroacetic acid. The crude peptide can be precipitated from a non-polar solvent like diethyl ether in order to remove organic soluble byproducts. The crude peptide can be purified using reversed-phase HPLC. The purification process, especially of longer peptides can be challenging, because cumulative amounts of numerous minor byproducts, which have properties similar to the desired peptide product, have to be removed. For this reason so-called continuous chromatography processes such as MCSGP are increasingly being used in commercial settings to maximize the yield without sacrificing purity.
SPPS is limited by reaction yields due to the exponential accumulation of by-products, and typically peptides and proteins in the range of 70 amino acids are pushing the limits of synthetic accessibility. Synthetic difficulty also is sequence dependent; typically aggregation-prone sequences such as amyloids are difficult to make. Longer lengths can be accessed by using ligation approaches such as native chemical ligation, where two shorter fully deprotected synthetic peptides can be joined in solution. | 1 | Applied and Interdisciplinary Chemistry |
The Strong Field Limit is the exact opposite limit to the weak field where the square modulus of the Rabi frequency of the electromagnetic field is much larger than the rate of spontaneous emission of the two-level atom. When a strong field is applied to the atom, a single peak is no longer observed in fluorescent light's radiation spectrum. Instead, other peaks begin appearing on either side of the original peak. These are known as side bands. The sidebands are a result of the Rabi oscillations of the field causing a modulation in the dipole moment of the atom. This causes a splitting in the degeneracy of certain eigenstates of the hamiltonian, specifically and are split into doublets. This is known as dynamic Stark splitting and is the cause for the Mollow triplet, which is a characteristic energy spectrum found in Resonance fluorescence.
An interesting phenomena arises in the Mollow triplet where both of the sideband peaks have a width different than that of the central peak. If the Rabi frequency is allowed to become much larger than the rate of spontaneous decay of the atom, we can see that in the strong field limit will become .
From this equation it is clear where the differences in width of the peaks in the Mollow triplet arise from as the central peak has a width of and the sideband peaks have a width of where is the rate of spontaneous emission for the atom. Unfortunately this cannot be used to calculate a steady state solution as and in a steady state solution. Thus the spectrum would vanish in a steady state solution, which is not the actual case.
The solution that does allow for a steady state solution must take the form of a two-time correlation function as opposed to the above one-time correlation function. This solution appears as
Since this correlation function includes the steady state limits of the density matrix, where and , and the spectrum is nonzero, it is clear to see that the Mollow triplet remains the spectrum for the fluoresced light even in a steady state solution. | 0 | Theoretical and Fundamental Chemistry |
Duplex sequencing and the significant increase of sequencing accuracy has had an important impact on applications such as detection of rare human genetic variants, detection of subclonal mutations involved in mechanisms of resistance to therapy in genetically heterogeneous cancers, screening variants in circulating tumor DNA as a non-invasive biomarker, and prenatal screening for genetic abnormalities in a fetus. | 1 | Applied and Interdisciplinary Chemistry |
Certain phosphoramidites are also used as monodentate chiral ligands in asymmetric synthesis. A large group of such ligands is derived from the chiral diol BINOL and can be synthesised by reaction of BINOL with phosphorus trichloride to the chlorophosphite and then reaction with simple secondary amines. This type of ligand was first used in 1996 in an asymmetric copper-catalysed addition of dialkylzincs to enones. | 0 | Theoretical and Fundamental Chemistry |
Hurst was born in Nelson, New Zealand in 1915, the son of Percy Cecil Hurst, a commercial traveller, and his wife Margery Whitmore. He attended Nelson College from 1927 to 1932, and then was a student at Canterbury University College in Christchurch, from where he graduated with a Master of Science degree in physical chemistry in 1939. While at Canterbury, Hurst was a member of a student group assisting European Jews to escape the Nazis.
Following his graduation, Hurst was en route to the United Kingdom by ship to undertake doctoral studies at Emmanuel College, Cambridge, working his passage as a radio operator, when World War II broke out. | 0 | Theoretical and Fundamental Chemistry |
Wrinch developed this suggestion into a full-fledged model of protein structure. The basic cyclol model was laid out in her first paper (1936). She noted the possibility that polypeptides might cyclize to form closed rings (true) and that these rings might form internal crosslinks through the cyclol reaction (also true, although rare). Assuming that the cyclol form of the peptide bond could be more stable than the amide form, Wrinch concluded that certain cyclic peptides would naturally make the maximal number of cyclol bonds (such as cyclol 6, Figure 2). Such cyclol molecules would have hexagonal symmetry, if the chemical bonds were taken as having the same length, roughly 1.5 Å; for comparison, the N-C and C-C bonds have the lengths 1.42 Å and 1.54 Å, respectively.
These rings can be extended indefinitely to form a cyclol fabric (Figure 3). Such fabrics exhibit a long-range, quasi-crystalline order that Wrinch felt was likely in proteins, since they must pack hundreds of residues densely. Another interesting feature of such molecules and fabrics is that their amino-acid side chains point axially upwards from only one face; the opposite face has no side chains. Thus, one face is completely independent of the primary sequence of the peptide, which Wrinch conjectured might account for sequence-independent properties of proteins.
In her initial article, Wrinch stated clearly that the cyclol model was merely a working hypothesis, a potentially valid model of proteins that would have to be checked. Her goals in this article and its successors were to propose a well-defined testable model, to work out the consequences of its assumptions and to make predictions that could be tested experimentally. In these goals, she succeeded; however, within a few years, experiments and further modeling showed that the cyclol hypothesis was untenable as a model for globular proteins. | 1 | Applied and Interdisciplinary Chemistry |
The impairment of glucose metabolism by fatty acid oxidation is mediated by the short-term inhibition of several glycolytic processes. The extent of inhibition increases along the glycolytic pathway, being most severe at the level of pyruvate dehydrogenase and less severe at the level of glucose uptake and 6-phosphofructo-1-kinase (PFK-1). This sequence occurs because of the initial event, triggered by fatty acid oxidation, is an increase in the mitochondrial ratios of [acetyl-CoA]/[CoA] and [NADH]/[NAD+]. These both serve to inhibit pyruvate dehydrogenase activity. It has been proposed that these changes lead to an accumulation of cytosolic citrate, which in turn inhibits PFK-1, followed by an increase in glucose 6-phosphate, which eventually inhibits hexokinase. | 1 | Applied and Interdisciplinary Chemistry |
The applications of these various modes are numerous. Flow mode can be used in dampers and shock absorbers, by using the movement to be controlled to force the fluid through channels, across which a magnetic field is applied. Shear mode is particularly useful in clutches and brakes - in places where rotational motion must be controlled. Squeeze-flow mode, on the other hand, is most suitable for applications controlling small, millimeter-order movements but involving large forces. This particular flow mode has seen the least investigation so far.
Overall, between these three modes of operation, MR fluids can be applied successfully to a wide range of applications. However, some limitations exist which are necessary to mention here. | 1 | Applied and Interdisciplinary Chemistry |
Only small amount of SNPs in the human genome may have impact on human diseases. Large scale GWAS has been done for the most important human diseases, including heart diseases, metabolic diseases, autoimmune diseases, and neurodegenerative and psychiatric disorders. Most of the SNPs with relatively large effects on these diseases have been identified. These findings have significantly improved understanding of disease pathogenesis and molecular pathways, and facilitated development of better treatment. Further GWAS with larger samples size will reveal the SNPs with relatively small effect on diseases. For common and complex diseases, such as type-2 diabetes, rheumatoid arthritis, and Alzheimer's disease, multiple genetic factors are involved in disease etiology. In addition, gene-gene interaction and gene-environment interaction also play an important role in disease initiation and progression. | 1 | Applied and Interdisciplinary Chemistry |
Since all natural waterways contain bacteria and nutrient, almost any waste compounds introduced into such waterways will initiate biochemical reactions (such as shown above). Those biochemical reactions create what is measured in the laboratory as the BOD.
Oxidizable chemicals (such as reducing chemicals) introduced into a natural water will similarly initiate chemical reactions (such as shown above). Those chemical reactions create what is measured in the laboratory as COD.
Both the BOD and COD tests are a measure of the relative oxygen-depletion effect of a waste contaminant. Both have been widely adopted as a measure of pollution effect. The BOD test measures the oxygen demand of biodegradable pollutants whereas the COD test measures the oxygen demand of oxidizable pollutants.
The so-called 5-day BOD measures the amount of oxygen consumed by biochemical oxidation of waste contaminants in a 5-day period. The total amount of oxygen consumed when the biochemical reaction is allowed to proceed to completion is called the "Ultimate BOD". Because the Ultimate BOD is so time consuming, the 5-day BOD has been almost universally adopted as a measure of relative pollution effect.
There are also many different COD tests of which the 4-hour COD is probably the most common.
There is no generalized correlation between the 5-day BOD and the ultimate BOD. Similarly there is no generalized correlation between BOD and COD. It is possible to develop such correlations for specific waste contaminants in a specific wastewater stream but such correlations cannot be generalized for use with any other waste contaminants or wastewater streams. This is because the composition of any wastewater stream is different. As an example an effluent consisting of a solution of simple sugars that might discharge from a confectionery factory is likely to have organic components that degrade very quickly. In such a case, the 5 day BOD and the ultimate BOD would be very similar since there would be very little organic material left after 5 days. However a final effluent of a sewage treatment works serving a large industrialised area might have a discharge where the ultimate BOD was much greater than the 5 day BOD because much of the easily degraded material would have been removed in the sewage treatment process and many industrial processes discharge difficult to degrade organic molecules.
The laboratory test procedures for the determining the above oxygen demands are detailed in many standard texts. American versions include Standard Methods for the Examination of Water and Wastewater.
Any oxidizable material present in an aerobic natural waterway or in an industrial wastewater will be oxidized both by biochemical (bacterial) or chemical processes. The result is that the oxygen content of the water will be decreased. | 0 | Theoretical and Fundamental Chemistry |
William B. Jensen notes that the earliest example of a continuous extractor is archaeological evidence for a Mesopotamian hot-water extractor for organic matter dating from approximately 3500 BC. The same mechanism is present in the Pythagorean cup. Before Soxhlet, the French chemist Anselme Payen also pioneered with continuous extraction in the 1830s.
A Soxhlet apparatus has been proposed as an effective technique for washing mass standards. | 0 | Theoretical and Fundamental Chemistry |
Since all pumps require well-developed inlet flow to meet their potential, a pump may not perform or be as reliable as expected due to a faulty suction piping layout such as a close-coupled elbow on the inlet flange. When poorly developed flow enters the pump impeller, it strikes the vanes and is unable to follow the impeller passage. The liquid then separates from the vanes causing mechanical problems due to cavitation, vibration and performance problems due to turbulence and poor filling of the impeller. This results in premature seal, bearing and impeller failure, high maintenance costs, high power consumption, and less-than-specified head and/or flow.
To have a well-developed flow pattern, pump manufacturer's manuals recommend about (10 diameters?) of straight pipe run upstream of the pump inlet flange. Unfortunately, piping designers and plant personnel must contend with space and equipment layout constraints and usually cannot comply with this recommendation. Instead, it is common to use an elbow close-coupled to the pump suction which creates a poorly developed flow pattern at the pump suction.
With a double-suction pump tied to a close-coupled elbow, flow distribution to the impeller is poor and causes reliability and performance shortfalls. The elbow divides the flow unevenly with more channeled to the outside of the elbow. Consequently, one side of the double-suction impeller receives more flow at a higher flow velocity and pressure while the starved side receives a highly turbulent and potentially damaging flow. This degrades overall pump performance (delivered head, flow and power consumption) and causes axial imbalance which shortens seal, bearing and impeller life.
To overcome cavitation:
Increase suction pressure if possible.
Decrease liquid temperature if possible.
Throttle back on the discharge valve to decrease flow-rate.
Vent gases off the pump casing. | 1 | Applied and Interdisciplinary Chemistry |
The key feature of the fourth-generation approach was the utilization of bidirectional fragment, vinyl iodide/phosphonium salt. phosphonium salt could be readily obtained as the trisubstituted vinyl iodide is less reactive than alkyl iodide. A Wittig reaction with followed by Suzuki coupling with alkyl iodide efficiently furnished the backbone of (+)-discodermolide. The Smith fourth-generation synthesis of (+)-discodermolide has an overall yield of 9.0% with a longest linear sequence of 17 steps and 36 total steps. | 0 | Theoretical and Fundamental Chemistry |
The main objective of the AVIRIS project is to identify, measure, and monitor constituents of the Earth's surface/ atmosphere based on molecular absorption and particle scattering signatures. Research with AVIRIS data is predominantly focused on understanding processes related to the global environment and climate change. AVIRIS research areas include ecology, oceanography, geology, snow hydrology, cloud and atmospheric studies. | 0 | Theoretical and Fundamental Chemistry |
Restriction sites can be used for multiple applications in molecular biology such as identifying restriction fragment length polymorphisms (RFLPs). | 1 | Applied and Interdisciplinary Chemistry |
The types of hydrogen-bond donors used in catalysis vary widely from reaction to reaction, even among similar catalytic strategies. While specific systems are often studied and optimized extensively, a general understanding of the optimal donor for a reaction or the relationship between catalyst structure and reactivity is greatly lacking. It is not yet practical to rationally design structures to promote a desired reaction with the desired selectivity. However, contemporary hydrogen-bond catalysis is primarily focused on a few types of systems that experimentally seem to be effective in a variety of situations. These are termed "privileged structures". However, it is worth noting that other structural scaffolds and motifs have also shown promising results, such as metal-coordinated hydrogen-bond donors.
*Ureas and thioureas are by far the most common structures and can stabilize a variety of negatively charged intermediates, as well as engage in anion-binding catalysis. Bifunctional urea and thiourea catalysis are abundant in the literature. Thioureas are often found to be stronger hydrogen-bond donors (i.e., more acidic) than ureas because their amino groups are more positively charged. Quantum chemical analyses revealed that this counterintuitive phenomenon, which is not explainable by the relative electronegativities of O and S, results from the effective steric size of the chalcogen atoms.
*Guanidinium and amidinium ions are structural relatives of ureas and thioureas and can catalyze similar reactions but, by virtue of their positive charge, are stronger donors and much more acidic. The mechanism of guanidinium and amidinium catalysis is thought to often involve partial protonation of substrate.
*Diol catalysts are thought to engage substrate with a single hydrogen bond, with the other hydroxyl participating in an internal hydrogen bond. These are some of the earliest hydrogen-bond catalysts investigated. They are most commonly used in stabilizing partial anionic charge in transition states, for example coordinating to aldehyde dienophiles in hetero-Diels-Alder reactions.
*Phosphoric acid catalysts are the most common strong acid catalysts and work by formation of chiral ion pairs with basic substrates such as imines. | 0 | Theoretical and Fundamental Chemistry |
A notable subclass of amidinium ions are the formamidinium cations; which can be represented by the chemical formula . Deprotonation of these gives stable carbenes which can be represented by the chemical formula . | 0 | Theoretical and Fundamental Chemistry |
Molecular data show that PSI likely evolved from the photosystems of green sulfur bacteria. The photosystems of green sulfur bacteria and those of cyanobacteria, algae, and higher plants are not the same, but there are many analogous functions and similar structures. Three main features are similar between the different photosystems. First, redox potential is negative enough to reduce ferredoxin. Next, the electron-accepting reaction centers include iron–sulfur proteins. Last, redox centres in complexes of both photosystems are constructed upon a protein subunit dimer. The photosystem of green sulfur bacteria even contains all of the same cofactors of the electron transport chain in PSI. The number and degree of similarities between the two photosystems strongly indicates that PSI and the analogous photosystem of green sulfur bacteria evolved from a common ancestral photosystem. | 0 | Theoretical and Fundamental Chemistry |
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