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Chiral molecules have two forms (at each point of asymmetry), which differ in their optical characteristics: The levorotatory form (the (−)-form) will rotate counter-clockwise on the plane of polarization of a beam of light, whereas the dextrorotatory form (the (+)-form) will rotate clockwise on the plane of polarization of a beam of light. The two forms, which are non-superposable when rotated in 3-dimensional space, are said to be enantiomers. The notation is not to be confused with and naming of molecules which refers to the similarity in structure to -glyceraldehyde and -glyceraldehyde. Also, (R)- and (S)- refer to the chemical structure of the molecule based on Cahn–Ingold–Prelog priority rules of naming rather than rotation of light. R/S notation is the primary notation used for +/- now because D and L notation are used primarily for sugars and amino acids.
Racemization occurs when one pure form of an enantiomer is converted into equal proportion of both enantiomers, forming a racemate. When there are both equal numbers of dextrorotating and levorotating molecules, the net optical rotation of a racemate is zero. Enantiomers should also be distinguished from diastereomers which are a type of stereoisomer that have different molecular structures around a stereocenter and are not mirror images.
Partial to complete racemization of stereochemistry in solutions are a result of SN1 mechanisms. However, when complete inversion of stereochemistry configuration occurs in a substitution reaction, an SN2 reaction is responsible. | 0 | Theoretical and Fundamental Chemistry |
In 1935, the first scientific work devoted to the thermodynamics of biological systems was published - the book of the Hungarian-Russian theoretical biologist Erwin S. Bauer (1890-1938) "Theoretical Biology". E. Bauer formulated the "Universal Law of Biology" in the following edition: "All and only living systems are never in equilibrium and perform constant work at the expense of their free energy against the equilibrium required by the laws of physics and chemistry under existing external conditions". This law can be considered the 1st law of thermodynamics of biological systems.
In 1957, German-British physician and biochemist Hans Krebs and British-American biochemist Hans Kornberg in the book "Energy Transformations in Living Matter" first described the thermodynamics of biochemical reactions. In their works, H. Krebs and Hans Kornberg showed how in living cells, as a result of biochemical reactions, adenosine triphosphate (ATP) is synthesized from food, which is the main source of energy of living organisms (the Krebs–Kornberg cycle).
In 2006, the Israeli-Russian scientist Boris Dobroborsky (1945) published the book "Thermodynamics of Biological Systems", in which the general principles of functioning of living organisms from the perspective of nonequilibrium thermodynamics were formulated for the first time and the nature and properties of their basic physiological functions were explained. | 0 | Theoretical and Fundamental Chemistry |
Aside from its immense environmental impacts, R114, like most chlorofluoroalkanes, forms phosgene gas when exposed to a naked flame. | 1 | Applied and Interdisciplinary Chemistry |
The recrystallization behavior of materials containing a wide distribution of particle sizes can be difficult to predict. This is compounded in alloys where the particles are thermally-unstable and may grow or dissolve with time. In various systems, abnormal grain growth may occur giving rise to unusually large crystallites growing at the expense of smaller ones. The situation is more simple in bimodal alloys which have two distinct particle populations. An example is Al-Si alloys where it has been shown that even in the presence of very large (<5 μm) particles the recrystallization behavior is dominated by the small particles (Chan & Humphreys 1984). In such cases the resulting microstructure tends to resemble one from an alloy with only small particles. | 1 | Applied and Interdisciplinary Chemistry |
Feng Yunhe hailed from Lijin, Shandong Province in China. She attended primary and secondary school at the Jinan Girls Junior Normal School and the Beijing Girls Higher Normal School. In 1920 she was admitted to the United States to study chemical engineering at Ohio State University, where she received her master's degree in 1928 and her doctorate in chemical engineering in 1931, making her the first woman to obtain a doctoral degree in chemical engineering in the United States. Whilst in America, she was known as Yun Hao Feng or Ruth Feng. In 1930 she and Mary Bucher were members of the American Institute of Chemical Engineers Student Chapter in Ohio, the first cohort group to allow female membership. | 1 | Applied and Interdisciplinary Chemistry |
The cell cycle is composed of a number of well-ordered, consecutive stages that result in cellular division. The fact that cells do not begin the next stage until the last one is finished, is a significant element of cell cycle regulation. Cell cycle checkpoints are characteristics that constitute an excellent monitoring strategy for accurate cell cycle and divisions. Cdks, associated cyclin counterparts, protein kinases, and phosphatases regulate cell growth and division from one stage to another. The cell cycle is controlled by the temporal activation of Cdks, which is governed by cyclin partner interaction, phosphorylation by particular protein kinases, and de-phosphorylation by Cdc25 family phosphatases. In response to DNA damage, a cell's DNA repair reaction is a cascade of signaling pathways that leads to checkpoint engagement, regulates, the repairing mechanism in DNA, cell cycle alterations, and apoptosis. Numerous biochemical structures, as well as processes that detect damage in DNA, are ATM and ATR, which induce the DNA repair checkpoints
The cell cycle is a sequence of activities in which cell organelles are duplicated and subsequently separated into daughter cells with precision. There are major events that happen during a cell cycle. The processes that happen in the cell cycle include cell development, replication and segregation of chromosomes. The cell cycle checkpoints are surveillance systems that keep track of the cell cycles integrity, accuracy, and chronology. Each checkpoint serves as an alternative cell cycle endpoint, wherein the cells parameters are examined and only when desirable characteristics are fulfilled does the cell cycle advance through the distinct steps. The cell cycles goal is to precisely copy each organisms DNA and afterwards equally split the cell and its components between the two new cells. Four main stages occur in the eukaryotes. In G1, the cell is usually active and continues to grow rapidly, while in G2, the cell growth continues while protein molecules become ready for separation. These are not dormant times; they are when cells gain mass, integrate growth factor receptors, establish a replicated genome, and prepare for chromosome segregation. DNA replication is restricted to a separate Synthesis in eukaryotes, which is also known as the S-phase. During mitosis, which is also known as the M-phase, the segregation of the chromosomes occur. DNA, like every other molecule, is capable of undergoing a wide range of chemical reactions. Modifications in DNAs sequence, on the other hand, have a considerably bigger impact than modifications in other cellular constituents like RNAs or proteins because DNA acts as a permanent copy of the cell genome. When erroneous nucleotides are incorporated during DNA replication, mutations can occur. The majority of DNA damage is fixed by removing the defective bases and then re-synthesizing the excised area. On the other hand, some DNA lesions can be mended by reversing the damage, which may be a more effective method of coping with common types of DNA damage. Only a few forms of DNA damage are mended in this fashion, including pyrimidine dimers caused by ultraviolet (UV) light changed by the insertion of methyl or ethyl groups at the purine rings O6 position. | 1 | Applied and Interdisciplinary Chemistry |
Locascio was born November 21, 1961, in Cumberland, Maryland. Her father was a physicist at the Allegany Ballistics Laboratory. He fostered her interest in science. She attended Bishop Walsh High School. In 1977, she was awarded an educational development certificate. Locascio had an early interest in biology and won her school's senior science award. She graduated in 1979. | 0 | Theoretical and Fundamental Chemistry |
Another potential complication results from the presence of large one bond J-coupling constants between carbon and hydrogen (typically from 100 to 250 Hz). While potentially informative, these couplings can complicate the spectra and reduce sensitivity. For these reasons, C-NMR spectra are usually recorded with proton NMR decoupling. Couplings between carbons can be ignored due to the low natural abundance of C. Hence in contrast to typical proton NMR spectra, which show multiplets for each proton position, carbon NMR spectra show a single peak for each chemically non-equivalent carbon atom.
In further contrast to H NMR, the intensities of the signals are often not proportional to the number of equivalent C atoms. Instead, signal intensity is strongly influenced by (and proportional to) the number of surrounding spins (typically H). Integrations are more quantitative if the delay times are long, i.e. if the delay times greatly exceed relaxation times.
The most common modes of recording C spectra are proton-noise decoupling (also known as noise-, proton-, or broadband- decoupling), off-resonance decoupling, and gated decoupling. These modes are meant to address the large J values for C - H (110–320 Hz), C - C - H (5–60 Hz), and C - C - C - H (5–25 Hz) which otherwise make completely proton coupled C spectra difficult to interpret.
With proton-noise decoupling, in which most spectra are run, a noise decoupler strongly irradiates the sample with a broad (approximately 1000 Hz) range of radio frequencies covering the range (such as 100 MHz for a 23,486 gauss field) at which protons change their nuclear spin. The rapid changes in proton spin create an effective heteronuclear decoupling, increasing carbon signal strength on account of the nuclear Overhauser effect (NOE) and simplifying the spectrum so that each non-equivalent carbon produces a singlet peak. The relative intensities are unreliable because some carbons have a larger spin-lattice relaxation time and others have weaker NOE enhancement.
In gated decoupling, the noise decoupler is gated on early in the free induction delay but gated off for the pulse delay. This largely prevents NOE enhancement, allowing the strength of individual C peaks to be meaningfully compared by integration, at a cost of half to two-thirds of the overall sensitivity.
With off-resonance decoupling, the noise decoupler irradiates the sample at 1000–2000 Hz upfield or 2000–3000 Hz downfield of the proton resonance frequency. This retains couplings between protons immediately adjacent to C atoms but most often removes the others, allowing narrow multiplets to be visualized with one extra peak per bound proton (unless bound methylene protons are non-equivalent, in which case a pair of doublets may be observed). | 0 | Theoretical and Fundamental Chemistry |
According to Mendelian inheritance, variations in an organism's phenotype (observable physical and behavioral characteristics) are due in part to variations in its genotype (particular set of genes). Each gene specifies a particular trait with a different sequence of a gene (alleles) giving rise to different phenotypes. Most eukaryotic organisms (such as the pea plants Mendel worked on) have two alleles for each trait, one inherited from each parent.
Alleles at a locus may be dominant or recessive; dominant alleles give rise to their corresponding phenotypes when paired with any other allele for the same trait, whereas recessive alleles give rise to their corresponding phenotype only when paired with another copy of the same allele. If you know the genotypes of the organisms, you can determine which alleles are dominant and which are recessive. For example, if the allele specifying tall stems in pea plants is dominant over the allele specifying short stems, then pea plants that inherit one tall allele from one parent and one short allele from the other parent will also have tall stems. Mendel's work demonstrated that alleles assort independently in the production of gametes, or germ cells, ensuring variation in the next generation. Although Mendelian inheritance remains a good model for many traits determined by single genes (including a number of well-known genetic disorders) it does not include the physical processes of DNA replication and cell division. | 1 | Applied and Interdisciplinary Chemistry |
CFC-13like all chlorofluorocarbon compoundscontains atoms of carbon (C), chlorine (Cl), and fluorine (F).
It can be prepared by reacting carbon tetrachloride with hydrogen fluoride in the presence of a catalytic amount of antimony pentachloride:
CCl + 3HF CClF + 3HCl
This reaction can also produce trichlorofluoromethane (CClF), dichlorodifluoromethane (CClF) and tetrafluoromethane (CF). | 1 | Applied and Interdisciplinary Chemistry |
Radioactive medical waste tends to contain beta particle and gamma ray emitters. It can be divided into two main classes. In diagnostic nuclear medicine a number of short-lived gamma emitters such as technetium-99m are used. Many of these can be disposed of by leaving it to decay for a short time before disposal as normal waste. Other isotopes used in medicine, with half-lives in parentheses, include:
* Y-90, used for treating lymphoma (2.7 days)
* I-131, used for thyroid function tests and for treating thyroid cancer (8.0 days)
* Sr-89, used for treating bone cancer, intravenous injection (52 days)
* Ir-192, used for brachytherapy (74 days)
* Co-60, used for brachytherapy and external radiotherapy (5.3 years)
* Cs-137, used for brachytherapy and external radiotherapy (30 years)
* Tc-99, product of the decay of Technetium-99m (221,000 years) | 0 | Theoretical and Fundamental Chemistry |
Electrocoagulation (EC) is a technique used for wastewater treatment, wash water treatment, industrially processed water, and medical treatment. Electrocoagulation has become a rapidly growing area of wastewater treatment due to its ability to remove contaminants that are generally more difficult to remove by filtration or chemical treatment systems, such as emulsified oil, total petroleum hydrocarbons, refractory organics, suspended solids, and heavy metals. There are many brands of electrocoagulation devices available, and they can range in complexity from a simple anode and cathode to much more complex devices with control over electrode potentials, passivation, anode consumption, cell REDOX potentials as well as the introduction of ultrasonic sound, ultraviolet light and a range of gases and reactants to achieve so-called Advanced Oxidation Processes for refractory or recalcitrant organic substances. | 1 | Applied and Interdisciplinary Chemistry |
Polyurethane is an option offered as an internal lining for ductile iron pipes in lieu of cement mortar. However, as PUR provides only passive protection it becomes vitally important that the coating is not damaged during handling and installation. Manufacturers will specify strict handling, transport and installation procedures to ensure PUR coatings are protected. If pipes are deformed Polyurethane's elasticity, does in some situations allow the coating to remain intact. [https://web.archive.org/web/20120702200903/http://www.russellcorrosion.com/PublicPages/Home.aspx Corrosion Experts]
Polyurethane coatings were first used in 1972. In comparison with other coatings, the internal polyurethane lining exhibits a high resistance to various different media such as drinking water, wastewater, de-mineralised water, industrial water and gas, as well as to aggressive solutions such as sulphuric acid.
Polyurethane is a thermosetting plastic with no solvents, with a three-dimensionally linked molecular structure giving it mechanical stability. The polyurethane lining used for internal coating has the following standard properties is standardised by EN 15655:2009 (Ductile iron pipes, fittings and accessories – Internal polyurethane lining for pipes and fittings – Requirements and test methods). | 1 | Applied and Interdisciplinary Chemistry |
Plane groups can be depicted using the Hermann–Mauguin system. The first letter is either lowercase p or c to represent primitive or centered unit cells. The next number is the rotational symmetry, as given above. The presence of mirror planes are denoted m, while glide reflections are only denoted g. Screw axes do not exist in two dimension, they required 3D space. | 0 | Theoretical and Fundamental Chemistry |
Semicarbazide is used in preparing pharmaceuticals including nitrofuran antibacterials (furazolidone, nitrofurazone, nitrofurantoin) and related compounds. It is also a product of degradations of the blowing agent azodicarbonamide (ADC). Semicarbazide forms in heat-treated flour containing ADC as well as breads made from ADC-treated flour.
Semicarbazide is used as a detection reagent in thin layer chromatography (TLC). Semicarbazide stains α-keto acids on the TLC plate, which can then be viewed under ultraviolet light. | 0 | Theoretical and Fundamental Chemistry |
Salicylate testing is a category of drug testing that is focused on detecting salicylates such as acetysalicylic acid for either biochemical or medical purposes. | 0 | Theoretical and Fundamental Chemistry |
Mass transfer finds extensive application in chemical engineering problems. It is used in reaction engineering, separations engineering, heat transfer engineering, and many other sub-disciplines of chemical engineering like electrochemical engineering.
The driving force for mass transfer is usually a difference in chemical potential, when it can be defined, though other thermodynamic gradients may couple to the flow of mass and drive it as well. A chemical species moves from areas of high chemical potential to areas of low chemical potential. Thus, the maximum theoretical extent of a given mass transfer is typically determined by the point at which the chemical potential is uniform. For single phase-systems, this usually translates to uniform concentration throughout the phase, while for multiphase systems chemical species will often prefer one phase over the others and reach a uniform chemical potential only when most of the chemical species has been absorbed into the preferred phase, as in liquid-liquid extraction.
While thermodynamic equilibrium determines the theoretical extent of a given mass transfer operation, the actual rate of mass transfer will depend on additional factors including the flow patterns within the system and the diffusivities of the species in each phase. This rate can be quantified through the calculation and application of mass transfer coefficients for an overall process. These mass transfer coefficients are typically published in terms of dimensionless numbers, often including Péclet numbers, Reynolds numbers, Sherwood numbers, and Schmidt numbers, among others. | 1 | Applied and Interdisciplinary Chemistry |
In mathematics, potential flow around a circular cylinder is a classical solution for the flow of an inviscid, incompressible fluid around a cylinder that is transverse to the flow. Far from the cylinder, the flow is unidirectional and uniform. The flow has no vorticity and thus the velocity field is irrotational and can be modeled as a potential flow. Unlike a real fluid, this solution indicates a net zero drag on the body, a result known as dAlemberts paradox. | 1 | Applied and Interdisciplinary Chemistry |
Primary aromatic amines are used as a starting material for the manufacture of azo dyes. It reacts with nitrous acid to form diazonium salt, which can undergo coupling reaction to form an azo compound. As azo-compounds are highly coloured, they are widely used in dyeing industries, such as:
* Methyl orange
* Direct brown 138
* Sunset yellow FCF
* Ponceau | 0 | Theoretical and Fundamental Chemistry |
Microfluidic flows need only be constrained by geometrical length scale – the modalities and methods used to achieve such a geometrical constraint are highly dependent on the targeted application. Traditionally, microfluidic flows have been generated inside closed channels with the channel cross section being in the order of 10 μm x 10 μm. Each of these methods has its own associated techniques to maintain robust fluid flow which have matured over several years. | 1 | Applied and Interdisciplinary Chemistry |
The importance of tin to the success of Bronze Age cultures and the scarcity of the resource offers a glimpse into that time periods trade and cultural interactions, and has therefore been the focus of intense archaeological studies. However, a number of problems have plagued the study of ancient tin such as the limited archaeological remains of placer mining, the destruction of ancient mines by modern mining operations, and the poor preservation of pure tin objects due to tin disease or tin pest'. These problems are compounded by the difficulty in provenancing tin objects and ores to their geological deposits using isotopic or trace element analyses. Current archaeological debate is concerned with the origins of tin in the earliest Bronze Age cultures of the Near East. | 1 | Applied and Interdisciplinary Chemistry |
Electrogravimetry is a method used to separate and quantify ions of a substance, usually a metal. In this process, the analyte solution is electrolyzed. Electrochemical reduction causes the analyte to be deposited on the cathode. The mass of the cathode is determined before and after the experiment, and the difference is used to calculate the mass of analyte in the original solution.
Controlling the potential of the electrode is important to ensure that only the metal being analyzed will be deposited on the electrode.
The process is similar to electroplating.
The phenomenon of polarization exerts a back EMF in electrolysis, which reduces the actual EMF of the cell. Thus electrolysis of an electrolyte is possible only when this back EMF is overcome.
If two separated platinum electrodes are placed in a dilute solution of copper sulfate and if a source of potential is applied, no appreciable current will flow through the system, until some minimum potential is applied after which the current will increase as the applied potential increases. The applied voltage which is just sufficient to overcome the back EMF due to polarization and also to bring about the electrolysis of an electrolyte without any hindrance is known as decomposition potential.
The decomposition potential Ed is composed of various potentials and is given by:
:Ea (min)= Ed= Eb+ Es+ Ev
where:
*Ea = applied potential
*Ed = decomposition potential
*Eb = theoretical counter or back potential
*Ev = overvoltage.
The origins of electrogravimetry date back to the 19th century, when Oliver Wilcott Gibbs, an American chemist, studied the electrolytic precipitation of copper and nickel. This procedure was the first of its kind until Carl Luckow did similar research on electric metal analysis. Today, these two are credited with the invention of the electrogravimetry, known at the time as “electrochemical analysis,” “electroanalysis,” or “electrolytic analysis”.
All methods of electrogravimetry involve a traditional quartz crystal microbalance (QCM) system in which a sensor is used from an AT cut quartz crystal. The groundwork of the QCM is built upon the notion that any mass delivered on the quartz electrode's interfacial region can be detected through the resonating frequency of the vibrating quartz crystal. While most vibrational modes occurring in the AT cut quartz are negligible, the vibration mode is known as thickness shear mode. These vibrations are extremely sensitive, which permits accurate detection of atomic interactions near the sensor, allowing these techniques to be used in analytical chemistry .
Through combining the techniques of QCM with classic electrochemical techniques, the electrochemical quartz crystal microbalance (EQCM) was created. EQCM is a new device used to perform the process of electrogravimetry. This device employs a high frequency acoustic wave generated by a piezoelectric resonator to store and dissipate energy infused into the device's interfacial region.
Electrogravimetry has been useful in polymer studies, copper electrodeposition, gold oxidation in an acidic medium, and passivity of iron in a sulfuric medium, as well as Ionic insertion in WO3. | 0 | Theoretical and Fundamental Chemistry |
Additional reported applications of genome-wide CRISPR screens include the study of: mitochondrial metabolism, bacterial toxin resistance, genetic drivers of metastasis, cancer drug resistance, West Nile virus-induced cell death, and immune cell gene networks. | 1 | Applied and Interdisciplinary Chemistry |
The method was invented by Joseph Louis Gay-Lussac. Justus von Liebig studied the method while working with
Gay-Lussac between 1822 and 1824 and improved the method in the following years to a level that it could be used as standard procedure for organic analysis. | 0 | Theoretical and Fundamental Chemistry |
*1984 P Metz
*1983 I K MacGregor
*1982 G W van Stein Callenfels
*1981 Sir I McLennan
*1980 M Tenenbaum
*1979 H O H Haavisto
*1978 Karl Brotzmann
*1977 H Morrogh
*1976 J D Joy
*1975 Richard Weck
*1974 Sir M Finniston | 1 | Applied and Interdisciplinary Chemistry |
Leprecan is a protein associated with osteogenesis imperfecta type VIII.
Leprecan is part of a superfamily of 2OG-Fe(II) dioxygenase, along with DNA repair protein AlkB, and disease resistant EGL-9. The enzyme was found to be a type of hydroxylases used in the substrate formation of protein glycosylation. | 1 | Applied and Interdisciplinary Chemistry |
* The enzyme is bound covalently to an insoluble support (such as silica gel or macroporous polymer beads with epoxide groups). This approach provides the strongest enzyme/support interaction, and so the lowest protein leakage during catalysis.
* The activity of the enzyme being covalently bound is dependent on several factors including: shape, and size of carrier material, coupling method type, the composition and coupling special conditions of carrier material.
Affinity-tag binding: is an immobilization method combining physical, and chemical methods where enzymes may be immobilized to a surface, e.g. in a porous material, using non-covalent or covalent Protein tags. This technology has been established for protein purification purposes. This technique is the generally applicable, and can be performed without prior enzyme purification with a pure preparation as the result. Porous glass and derivatives thereof are used, where the porous surface can be adapted in terms of hydrophobicity to suit the enzyme in question. | 0 | Theoretical and Fundamental Chemistry |
Lipids have been drawing considerable attention as a substrate for biodiesel production owing to its sustainability, non-toxicity and energy efficient properties. However, due to cost reasons, attention must be focused on the non-edible sources of lipids, in particular oleaginous microorganisms. Such microbes have the ability to assimilate the carbon sources from a medium and convert the carbon into lipid storage materials. The lipids accumulated by these oleaginous cells can then be transesterified to form biodiesel. | 0 | Theoretical and Fundamental Chemistry |
A scoring matrix or a table of values is required for evaluating the significance of a sequence alignment, such as describing the probability of a biologically meaningful amino-acid or nucleotide residue-pair occurring in an alignment. Typically, when two nucleotide sequences are being compared, all that is being scored is whether or not two bases are the same at one position. All matches and mismatches are respectively given the same score (typically +1 or +5 for matches, and -1 or -4 for mismatches). But it is different for proteins. Substitution matrices for amino acids are more complicated and implicitly take into account everything that might affect the frequency with which any amino acid is substituted for another. The objective is to provide a relatively heavy penalty for aligning two residues together if they have a low probability of being homologous (correctly aligned by evolutionary descent). Two major forces drive the amino-acid substitution rates away from uniformity: substitutions occur with the different frequencies, and lessen functionally tolerated than others. Thus, substitutions are selected against.
Commonly used substitution matrices include the blocks substitution (BLOSUM) and point accepted mutation (PAM) matrices. Both are based on taking sets of high-confidence alignments of many homologous proteins and assessing the frequencies of all substitutions, but they are computed using different methods.
Scores within a BLOSUM are log-odds scores that measure, in an alignment, the logarithm for the ratio of the likelihood of two amino acids appearing with a biological sense and the likelihood of the same amino acids appearing by chance. The matrices are based on the minimum percentage identity of the aligned protein sequence used in calculating them. Every possible identity or substitution is assigned a score based on its observed frequencies in the alignment of related proteins. A positive score is given to the more likely substitutions while a negative score is given to the less likely substitutions.
To calculate a BLOSUM matrix, the following equation is used:
Here, is the probability of two amino acids and replacing each other in a homologous sequence, and and are the background probabilities of finding the amino acids and in any protein sequence. The factor is a scaling factor, set such that the matrix contains easily computable integer values. | 1 | Applied and Interdisciplinary Chemistry |
Tetraethylammonium (TEA) is a molecule found to be a weak agonist of the muscle‐type nicotinic receptor. Since receptor activation occurs as isolated bursts, it has been proposed that the receptors have a very low channel‐opening rate constant when bound to TEA. | 1 | Applied and Interdisciplinary Chemistry |
The Tafel equation is an equation in electrochemical kinetics relating the rate of an electrochemical reaction to the overpotential. The Tafel equation was first deduced experimentally and was later shown to have a theoretical justification. The equation is named after Swiss chemist Julius Tafel.
Where an electrochemical reaction occurs in two half reactions on separate electrodes, the Tafel equation is applied to each electrode separately. On a single electrode the Tafel equation can be stated as:
where
* the plus sign under the exponent refers to an anodic reaction, and a minus sign to a cathodic reaction,
* : overpotential, V
* : "Tafel slope", V
* : current density, A/m
* : "exchange current density", A/m.
A verification plus further explanation for this equation can be found here. The Tafel equation is an approximation of the Butler-Volmer equation in the case of . Also, at a given electrode the Tafel equation assumes that the reverse half reaction rate is negligible compared to the forward reaction rate. | 0 | Theoretical and Fundamental Chemistry |
In March 1865 Macadam sailed to New Zealand to give evidence at the trial of Captain W. A. Jarvey, accused of fatally poisoning his wife, but the jury did not reach a verdict. During the return voyage, Macadam fractured his ribs during a storm. He was advised, on medical grounds, not to return for the adjourned trial but did so and died on the ship on 2 September 1865. His medical-student assistant John Drummond Kirkland gave evidence at the trial in Macadam's place, and Jarvey was convicted.
The Australian News commented, "At the time of his death, Dr Macadam was but 38 years of age; there can be little doubt that the various and onerous duties he discharged for the public must be attributed in great measure the shortening of his days." The Australian Medical Journal stated, "For some time it had been evident to his friends that his general health was giving way: that a frame naturally robust and vigorous was gradually becoming undermined by the incessant and harassing duties of the multifarious offices he filled." The inquest verdict (he died at sea) stated, "His death was caused by excessive debility and general exhaustion." | 0 | Theoretical and Fundamental Chemistry |
Volatile phenolic compounds are found in plant resin where they may attract benefactors such as parasitoids or predators of the herbivores that attack the plant.
In the kelp species Alaria marginata, phenolics act as chemical defence against herbivores. In tropical Sargassum and Turbinaria species that are often preferentially consumed by herbivorous fishes and echinoids, there is a relatively low level of phenolics and tannins. Marine allelochemicals generally are present in greater quantity and diversity in tropical than in temperate regions. Marine algal phenolics have been reported as an apparent exception to this biogeographic trend. High phenolic concentrations occur in brown algae species (orders Dictyotales and Fucales) from both temperate and tropical regions, indicating that latitude alone is not a reasonable predictor of plant phenolic concentrations. | 0 | Theoretical and Fundamental Chemistry |
The Bertozzi group further developed one of Huisgen's copper-free click reactions to overcome the cytotoxicity of the CuAAC reaction. Instead of using Cu(I) to activate the alkyne, the alkyne is instead introduced in a strained (DIFO), in which the electron-withdrawing, propargylic, gem-fluorines act together with the ring strain to greatly destabilize the alkyne. This destabilization increases the reaction driving force, and the desire of the cycloalkyne to relieve its ring strain.
This reaction proceeds as a concerted [3+2] cycloaddition to the triple bond in a cyclooctyne in the same mechanism as the Huisgen 1,3-dipolar cycloaddition. Substituents other than fluorines, such as benzene rings, are also allowed on the cyclooctyne.
This reaction has been used successfully to probe for azides in living systems, even though the reaction rate is somewhat slower than that of the CuAAC. Moreover, because the synthesis of cyclooctynes often gives low yield, probe development for this reaction has not been as rapid as for other reactions. But cyclooctyne derivatives such as DIFO, dibenzylcyclooctyne (DIBO) and biarylazacyclooctynone (BARAC) have all been used successfully in the SPAAC reaction to probe for azides in living systems. | 0 | Theoretical and Fundamental Chemistry |
In Gilbert’s syndrome, glucuronyl transferase activity is reduced by approximately 70%, leading to mild accumulation of unconjugated bilirubin in the plasma. | 1 | Applied and Interdisciplinary Chemistry |
Lanthanum(III) iodide is an inorganic compound containing lanthanum and iodine with the chemical formula . | 0 | Theoretical and Fundamental Chemistry |
Methylenedioxy is the term used in the field of chemistry, particularly in organic chemistry, for a functional group with the structural formula R-O-CH-O-R' which is connected to the rest of a molecule by two chemical bonds. The methylenedioxy group consists of two oxygen atoms connected to a methylene bridge (-CH- unit). The methylenedioxy group is generally found attached to an aromatic structure such as phenyl where it forms the methylenedioxyphenyl or benzodioxole functional group which is widely found in natural products, including safrole, and drugs and chemicals such as tadalafil, MDMA, paroxetine and piperonyl butoxide.
Enzymes within the cytochrome P450 superfamily are able to form methylenedioxy bridges by closure of an open, adjacent phenol and methoxy group. Examples of products formed by this process are canadine and berberine. Similarly, ortho-demethylenation can be carried out by other members of the superfamily to open a bridge; a process which is applied to, as examples, both MDMA and MDA during their metabolism. | 0 | Theoretical and Fundamental Chemistry |
Consider the force F(h) between two identical spheres of radius R as an illustration. The surfaces of the two respective spheres are thought to be sliced into infinitesimal disks of width dr and radius r as shown in the figure. The force is given by the sum of the corresponding swelling pressures between the two disks
where x is the distance between the disks and dA the area of one of these disks. This distance can be expressed as x=h+2y. By considering the Pythagorean theorem on the grey triangle shown in the figure one has
Expanding this expression and realizing that y ≪ R one finds that the area of the disk can be expressed as
The force can now be written as
where W(h) is the surface free energy per unit area introduced above. When introducing the equation above, the upper integration limit was replaced by infinity, which is approximately correct as long as h ≪ R. | 0 | Theoretical and Fundamental Chemistry |
*Bayley, J. (1990) "The Production of Brass in Antiquity with Particular Reference to Roman Britain" in Craddock, P.T. (ed.) 2000 Years of Zinc and Brass London: British Museum
*Craddock, P.T. and Eckstein, K (2003) "Production of Brass in Antiquity by Direct Reduction" in Craddock, P.T. and Lang, J. (eds) Mining and Metal Production Through the Ages London: British Museum
*Day, J. (1990) "Brass and Zinc in Europe from the Middle Ages until the 19th century" in Craddock, P.T. (ed.) 2000 Years of Zinc and Brass London: British Museum
*Day, J (1991) "Copper, Zinc and Brass Production" in Day, J and Tylecote, R.F (eds) The Industrial Revolution in Metals London: The Institute of Metals
*Rehren, T. and Martinon Torres, M. (2008) "Naturam ars imitate: European brassmaking between craft and science" in Martinon-Torres, M and Rehren, T. (eds) Archaeology, History and Science Integrating Approaches to Ancient Material: Left Coast Press | 1 | Applied and Interdisciplinary Chemistry |
Planck (1914, page 40) refers to a condition of thermodynamic equilibrium, in which "any two bodies or elements of bodies selected at random exchange by radiation equal amounts of heat with each other."
The term radiative exchange equilibrium can also be used to refer to two specified regions of space that exchange equal amounts of radiation by emission and absorption (even when the steady state is not one of thermodynamic equilibrium, but is one in which some sub-processes include net transport of matter or energy including radiation). Radiative exchange equilibrium is very nearly the same as Prevost's relative radiative equilibrium. | 0 | Theoretical and Fundamental Chemistry |
A key issue for the fusion–fission concept is the number and lifetime of the neutrons in the various processes, the so-called neutron economy.
In a pure fusion design, the neutrons are used for breeding tritium in a lithium blanket. Natural lithium consists of about 92% Li and the rest is mostly Li. Li breeding requires neutron energies even higher than those released by fission, around 5 MeV, well within the range of energies provided by fusion. This reaction produces tritium and helium-4, and another slow neutron. Li can react with high or low energy neutrons, including those released by the Li reaction. This means that a single fusion reaction can produce several tritiums, which is a requirement if the reactor is going to make up for natural decay and losses in the fusion processes.
When the lithium blanket is replaced, or supplanted, by fission fuel in the hybrid design, neutrons that do react with the fissile material are no longer available for tritium breeding. The new neutrons released from the fission reactions can be used for this purpose, but only in Li. One could process the lithium to increase the amount of Li in the blanket, making up for these losses, but the downside to this process is that the Li reaction only produces one tritium atom. Only the high-energy reaction between the fusion neutron and Li can create more than one tritium, and this is essential for keeping the reactor running.
To address this issue, at least some of the fission neutrons must also be used for tritium breeding in Li. Every one that does is no longer available for fission, reducing the reactor output. This requires a very careful balance if one wants the reactor to be able to produce enough tritium to keep itself running, while also producing enough fission events to keep the fission side energy positive. If these cannot be accomplished simultaneously, there is no reason to build a hybrid. Even if this balance can be maintained, it might only occur at a level that is economically infeasible. | 0 | Theoretical and Fundamental Chemistry |
The main way free oxygen is lost from the atmosphere is via respiration and decay, mechanisms in which animal life and bacteria consume oxygen and release carbon dioxide. | 0 | Theoretical and Fundamental Chemistry |
The vorticity equation of fluid dynamics describes the evolution of the vorticity of a particle of a fluid as it moves with its flow; that is, the local rotation of the fluid (in terms of vector calculus this is the curl of the flow velocity). The governing equation is:where is the material derivative operator, is the flow velocity, is the local fluid density, is the local pressure, is the viscous stress tensor and represents the sum of the external body forces. The first source term on the right hand side represents vortex stretching.
The equation is valid in the absence of any concentrated torques and line forces for a compressible, Newtonian fluid. In the case of incompressible flow (i.e., low Mach number) and isotropic fluids, with conservative body forces, the equation simplifies to the vorticity transport equation:
where is the kinematic viscosity and is the Laplace operator. Under the further assumption of two-dimensional flow, the equation simplifies to: | 1 | Applied and Interdisciplinary Chemistry |
An environment's plasmidome refers to the plasmids present in it.
The term is a portmanteau of the two English words Plasmid and Kingdom.
In biological research, plasmidome may refer to the actual plasmids that were found and isolated from a certain microorganism by means of culturing isolated microorganism and investigating the plasmids it possesses or by taking an environmental sample and performing a metagenomic survey using next generation sequencing methods in order to reveal and characterize plasmid genomes that belong to that environment. | 1 | Applied and Interdisciplinary Chemistry |
While tartaric acid is well-tolerated by humans and lab animals, an April 2021 letter to the editor of JAVMA hypothesized that the tartaric acid in grapes could be the cause of grape and raisin toxicity in dogs.
In dogs, the tartaric acid of tamarind causes acute kidney injury, which can often be fatal. | 0 | Theoretical and Fundamental Chemistry |
Iberia (modern Spain and Portugal) was possibly the Roman province richest in mineral ore, containing deposits of gold, silver, copper, tin, lead, iron, and mercury). From its acquisition after the Second Punic War to the Fall of Rome, Iberia continued to produce a significant amount of Roman metals.
Britannia was also very rich in metals. Gold was mined at Dolaucothi in Wales, copper and tin in Cornwall, and lead in the Pennines, Mendip Hills and Wales. Significant studies have been made on the iron production of Roman Britain; iron use in Europe was intensified by the Romans, and was part of the exchange of ideas between the cultures through Roman occupation. It was the importance placed on iron by the Romans throughout the Empire which completed the shift from the few cultures still using primarily bronze into the Iron Age.
Noricum (modern Austria) was exceedingly rich in gold and iron, Pliny, Strabo, and Ovid all lauded its bountiful deposits. Iron was its main commodity, but alluvial gold was also prospected. By 15 BC, Noricum was officially made a province of the Empire, and the metal trade saw prosperity well into the fifth century AD. Some scholars believe that the art of iron forging was not necessarily created, but well developed in this area and it was the population of Noricum which reminded Romans of the usefulness of iron. For example, of the three forms of iron (wrought iron, steel, and soft), the forms which were exported were of the wrought iron (containing a small percentage of uniformly distributed slag material) and steel (carbonised iron) categories, as pure iron is too soft to function like wrought or steel iron.
Dacia, located in the area of Transylvania, was conquered in 107 AD in order to capture the resources of the region for Rome. The amount of gold that came into Roman possession actually brought down the value of gold. Iron was also of importance to the region. The difference between the mines of Noricum and Dacia was the presence of a slave population as a workforce. | 1 | Applied and Interdisciplinary Chemistry |
A large variety of inorganic radicals are stable and in fact isolable. Examples include most first-row transition metal complexes.
With regard to main group radicals, the most abundant radical in the universe is also the most abundant chemical in the universe, H. Most main group radicals are not however isolable, despite their intrinsic stability. Hydrogen radicals for example combine eagerly to form H. Nitric oxide (NO) is well known example of an isolable inorganic radical. Fremy's salt (Potassium nitrosodisulfonate, (KSO)NO) is a related example. Many thiazyl radicals are known, despite limited extent of π resonance stabilization.
Many radicals can be envisioned as the products of breaking of covalent bonds by homolysis. The homolytic bond dissociation energies, usually abbreviated as "ΔH°" are a measure of bond strength. Splitting H into 2 H, for example, requires a ΔH° of +435 kJ/mol, while splitting Cl into two Cl requires a ΔH° of +243 kJ/mol. For weak bonds, homolysis can be induced thermally. Strong bonds require high energy photons or even flames to induce homolysis. | 1 | Applied and Interdisciplinary Chemistry |
Scattering experiments are a common method for learning about crystals. Such experiments typically involve a probe (e.g. X-rays or neutrons) and a crystalline solid. A well-characterized probe propagating towards the crystal may interact and scatter away in a particular manner. Mathematical expressions relating the scattering pattern, properties of the probe, properties of the experimental apparatus, and properties of the crystal then allow one to derive desired features of the crystalline sample.
The following derivation is based on chapter 14 of Simons The Oxford Solid State Basics and on the report Atomic Displacement Parameter Nomenclature by Trueblood et al. (available under #External links). It is recommended to consult these sources for a more explicit discussion. Background on the quantum mechanics involved may be found in Sakurai and Napolitanos Modern Quantum Mechanics.
Scattering experiments often consist of a particle with initial crystal momentum incident on a solid. The particle passes through a potential distributed in space, , and exits with crystal momentum . This situation is described by Fermis golden rule, which gives the probability of transition per unit time, , to the energy eigenstate from the energy eigenstate due to the weak perturbation caused by our potential .
By inserting a complete set of position states, then utilizing the plane-wave expression relating position and momentum, we find that the matrix element is simply a Fourier transform of the potential.
Above, the length of the sample is denoted by . We now assume that our solid is a periodic crystal with each unit cell labeled by a lattice position vector . Position within a unit cell is given by a vector such that the overall position in the crystal may be expressed as . Because of the translational invariance of our unit cells, the potential distribution of every cell is identical and . | 0 | Theoretical and Fundamental Chemistry |
Zhang's doctoral research was in the area of bioinorganic chemistry, and she worked on the development of a platinum-based library of chemotherapeutic candidates featuring anthraquinone ligands and redox activity. This involved using a variety of imaging techniques (including those based on synchrotron radiation) to study the biological distributions and metabolism of the chemotherapeutics in 3D solid tumour models, and synthetic strategies to generate new examples of such complexes.
Zhang sought a change in research field following her PhD, and in 2013 she joined the group of Professor Erwin Reisner at the University of Cambridge as a postdoctoral fellow after receiving a Marie Skłodowska-Curie International Fellowship, also becoming a Research Associate of St John's College. This brought her into sustainability research, in particular artificial photosynthesis. Her postdoctoral research involved developing ways to wire oxidoreductases to electrodes and use photosynthesis to generate a sustainable biofuel, especially photosystem II.
In 2018, Zhang was awarded a BBSRC David Phillips Fellowship to start her own, independent research group in the Department of Chemistry at Cambridge. In her independent career, she has continued to work on the re-wiring of photosynthesis but now focuses on doing so in live cells. She also became a Fellow of Corpus Christi College, where she is now Director of Studies in Natural Sciences Chemistry. Zhang was recognised for her contributions to semi-artificial photosynthesis with the award of the Felix Franks Biotechnology Medal from the RSC in 2020. | 0 | Theoretical and Fundamental Chemistry |
Gamma helix (or γ-helix) is a type of secondary structure in proteins that has been predicted by Pauling, Corey, and Branson, but has never been observed in natural proteins. The hydrogen bond in this type of helix was predicted to be between N-H group of one amino acid and the C=O group of the amino acid six residues earlier (or, as described by Pauling, Corey, Branson, "to the fifth amide group beyond it"). This can also be described as i + 6 → i bond and would be a continuation of the series (3 helix, alpha helix, pi helix and gamma helix). This theoretical helix contains 5.1 residues per turn.However, a fully developed gamma helix has characteristics of a structure that has 2.2 amino acid residues per turn, a rise of 2.75Å per residue, and a pseudo-cyclic (C7) structure closed by intramolecular H-bond. Depending on the amino acid's side chain (R) involved in this main-chain reversal motif, two stereoisomers can occur with their Cα-substituent located either in the axial or in the equatorial position relative to the H-bonded pseudo-cycle. | 1 | Applied and Interdisciplinary Chemistry |
Observations have shown that fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. A large fraction of particulate organic matter occurs in the form of marine snow aggregates (>0.5 mm) composed of phytoplankton, detritus, inorganic mineral grains, and fecal pellets in the ocean. Formation and sinking of these aggregates drive the biological carbon pump via export and sedimentation of organic matter from the surface mixed layer to the deep ocean and sediments. The fraction of organic matter that leaves the upper mixed layer of the ocean is, among other factors, determined by the sinking velocity and microbial remineralisation rate of these aggregates. Recent observations have shown that the fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and the organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. This has led to the hypothesis that organic carbon export is determined by the presence of ballast minerals within settling aggregates.
Mineral ballasting is associated with about 60% of the flux of particulate organic carbon (POC) in the high-latitude North Atlantic, and with about 40% of the flux in the Southern Ocean. Strong correlations exist also in the deep ocean between the presence of ballast minerals and the flux of POC. This suggests ballast minerals enhance POC flux by increasing the sink rate of ballasted aggregates. Ballast minerals could additionally provide aggregated organic matter some protection from degradation.
It has been proposed that organic carbon is better preserved in sinking particles due to increased aggregate density and sinking velocity when ballast minerals are present and/or via protection of the organic matter due to quantitative association to ballast minerals. In 2002, Klaas and Archer observed that about 83% of the global particulate organic carbon (POC) fluxes were associated with carbonate, and suggested carbonate was a more efficient ballast mineral as compared to opal and terrigenous material. They hypothesized that the higher density of calcium carbonate compared to that of opal and the higher abundance of calcium carbonate relative to terrigenous material might be the reason for the efficient ballasting by calcium carbonate. However, the direct effects of ballast minerals on sinking velocity and degradation rates in sinking aggregates are still unclear.
A 2008 study demonstrated copepod fecal pellets produced on a diet of diatoms or coccolithophorids show higher sinking velocities as compared to pellets produced on a nanoflagellate diet. Carbon-specific respiration rates in pellets, however, were similar and independent of mineral content. These results suggest differences in mineral composition do not lead to differential protection of POC against microbial degradation, but the enhanced sinking velocities may result in up to 10-fold higher carbon preservation in pellets containing biogenic minerals as compared to that of pellets without biogenic minerals
Minerals seem to enhance the flocculation of phytoplankton aggregates and may even act as a catalyst in aggregate formation. However, it has also been shown that incorporation of minerals can cause aggregates to fragment into smaller and denser aggregates. This can potentially lower the sinking velocity of the aggregated organic material due to the reduced aggregate sizes, and, thus, lower the total export of organic matter. Conversely, if the incorporation of minerals increases the aggregate density, its size-specific sinking velocity may also increase, which could potentially increase the carbon export. Therefore, there is still a need for better quantitative investigations of how the interactions between minerals and organic aggregates affect the degradation and sinking velocity of the aggregates and, hence, carbon sequestration in the ocean. | 0 | Theoretical and Fundamental Chemistry |
The word effusion derives from the Latin word, effundo, which means "shed, pour forth, pour out, utter, lavish, waste." | 0 | Theoretical and Fundamental Chemistry |
Several reuptake inhibitors of VMATs are known to exist, including reserpine (RES), tetrabenazine (TBZ), dihydrotetrabenazine (DTBZOH), and ketanserin (KET). It is thought that RES exhibits competitive inhibition, binding to the same site as the monoamine substrate, as studies have shown that it can be displaced via introduction of norepinephrine. TBZ, DTBZOH, and KET are thought to exhibit non-competitive inhibition, instead binding to allosteric sites and decreasing the activity of the VMAT rather than simply blocking its substrate binding site. It has been found that these inhibitors are less effective at inhibiting VMAT1 than VMAT2, and the inhibitory effects of the tetrabenazines on VMAT1 is negligible. | 1 | Applied and Interdisciplinary Chemistry |
As the tartrate salt, levorphanol is marketed by Hikma Pharmaceuticals USA Inc. and Virtus Pharmaceuticals in the U.S., and Canada under the brand name Levo-Dromoran. | 0 | Theoretical and Fundamental Chemistry |
N6,2'-O-dimethyladenosine, abundant in polyA+ mRNAs, occurs at the first nucleotide after the 5’ cap, when an additional methyl group is added to a 2ʹ-O-methyladenosine residue at the ‘capped’ 5ʹ end of mRNA.
Since m6Am can be recognized by anti-m6A antibodies at transcription start sites, the methods used for m6A profiling can be and were adapted for m6Am profiling, namely m6A-seq, and miCLIP (see m6A-seq and miCLIP descriptions above). | 1 | Applied and Interdisciplinary Chemistry |
In mathematics, a symmetry operation is a geometric transformation of an object that leaves the object looking the same after it has been carried out. For example, a turn rotation of a regular triangle about its center, a reflection of a square across its diagonal, a translation of the Euclidean plane, or a point reflection of a sphere through its center are all symmetry operations. Each symmetry operation is performed with respect to some symmetry element (a point, line or plane). Symmetry operations can be classified either as point symmetry operations or as travel symmetry operations.
In the context of molecular symmetry, a symmetry operation is a permutation of atoms such that the molecule or crystal is transformed into a state indistinguishable from the starting state.
Two basic facts follow from this definition, which emphasizes its usefulness.
# Physical properties must be invariant with respect to symmetry operations.
# Symmetry operations can be collected together in groups which are isomorphic to permutation groups.
In the context of molecular symmetry, quantum wavefunctions need not be invariant, because the operation can multiply them by a phase or mix states within a degenerate representation, without affecting any physical property. | 0 | Theoretical and Fundamental Chemistry |
Chemokine (C-C motif) ligand 7 (CCL7) is a small cytokine that was previously called monocyte-chemotactic protein 3 (MCP3). CCL7 is a small protein that belongs to the CC chemokine family and is most closely related to CCL2 (previously called MCP1). | 1 | Applied and Interdisciplinary Chemistry |
The Bantu people in Cuvette Central use peatlands for fishing, hunting and gathering, as well as small-scale agriculture near terra firme forests. | 1 | Applied and Interdisciplinary Chemistry |
Anaplerotic reactions, a term coined by Hans Kornberg and originating from the Greek [http://en.wiktionary.org/wiki/%E1%BC%80%CE%BD%CE%AC#Ancient_Greek ἀνά]= up and [http://en.wiktionary.org/wiki/%CF%80%CE%BB%CE%B7%CF%81%CF%8C%CF%89 πληρόω]= to fill, are chemical reactions that form intermediates of a metabolic pathway. Examples of such are found in the citric acid cycle (TCA cycle). In normal function of this cycle for respiration, concentrations of TCA intermediates remain constant; however, many biosynthetic reactions also use these molecules as a substrate. Anaplerosis is the act of replenishing TCA cycle intermediates that have been extracted for biosynthesis (in what are called anaplerotic reactions).
The TCA cycle is a hub of metabolism, with central importance in both energy production and biosynthesis. Therefore, it is crucial for the cell to regulate concentrations of TCA cycle metabolites in the mitochondria. Anaplerotic flux must balance cataplerotic flux in order to retain homeostasis of cellular metabolism. | 1 | Applied and Interdisciplinary Chemistry |
The human gastrointestinal tract is around long. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal, and the process of digestion normally takes between 24 and 72 hours.
Digestion begins in the mouth with the secretion of saliva and its digestive enzymes. Food is formed into a bolus by the mechanical mastication and swallowed into the esophagus from where it enters the stomach through the action of peristalsis. Gastric juice contains hydrochloric acid and pepsin which would damage the walls of the stomach and mucus and bicarbonates are secreted for protection. In the stomach further release of enzymes break down the food further and this is combined with the churning action of the stomach. Mainly proteins are digested in stomach. The partially digested food enters the duodenum as a thick semi-liquid chyme. In the small intestine, the larger part of digestion takes place and this is helped by the secretions of bile, pancreatic juice and intestinal juice. The intestinal walls are lined with villi, and their epithelial cells are covered with numerous microvilli to improve the absorption of nutrients by increasing the surface area of the intestine. Bile helps in emulsification of fats and also activates lipases.
In the large intestine, the passage of food is slower to enable fermentation by the gut flora to take place. Here, water is absorbed and waste material stored as feces to be removed by defecation via the anal canal and anus. | 1 | Applied and Interdisciplinary Chemistry |
Direct photons and dileptons are arguably most penetrating tools to study relativistic heavy ion collisions. They are produced, by various mechanisms spanning the space-time evolution of the strongly interacting fireball. They provide in principle a snapshot on the initial stage as well. They are hard to decipher and interpret as most of the signal is originating from hadron decays long after the QGP fireball has disintegrated. | 0 | Theoretical and Fundamental Chemistry |
Early studies of the phenomenon were conducted with sodium sulfate, also known as Glauber's Salt because, unusually, the solubility of this salt in water may decrease with increasing temperature. Early studies have been summarised by Tomlinson. It was shown that the crystallization of a supersaturated solution does not simply come from its agitation, (the previous belief) but from solid matter entering and acting as a "starting" site for crystals to form, now called "seeds". Expanding upon this, Gay-Lussac brought attention to the kinematics of salt ions and the characteristics of the container having an impact on the supersaturation state. He was also able to expand upon the number of salts with which a supersaturated solution can be obtained. Later Henri Löwel came to the conclusion that both nuclei of the solution and the walls of the container have a catalyzing effect on the solution that cause crystallization. Explaining and providing a model for this phenomenon has been a task taken on by more recent research. Désiré Gernez contributed to this research by discovering that nuclei must be of the same salt that is being crystallized in order to promote crystallization. | 0 | Theoretical and Fundamental Chemistry |
Oligocrystalline material owns a microstructure consisting of a few coarse grains, often columnar and parallel to the longitudinal ingot axis. This microstructure can be found in the ingots produced by electron beam melting (EBM). | 0 | Theoretical and Fundamental Chemistry |
E3 ubiquitin-protein ligase TRIM33, also known as (ectodermin homolog and tripartite motif-containing 33) is a protein encoded in the human by the gene TRIM33, a member of the tripartite motif family.
TRIM33 is thought to be a transcriptional corepressor. However unlike the related TRIM24 and TRIM28 proteins, few transcription factors such as SMAD4 that interact with TRIM33 have been identified. | 1 | Applied and Interdisciplinary Chemistry |
The method uses scattering parameters of a material sample embedded in a waveguide, namely and , to calculate permittivity and permeability data. and correspond to the cumulative reflection and transmission coefficient of the sample that are referenced to the each sample end, respectively: these parameters account for the multiple internal reflections inside the sample, which is considered to have a thickness of . The reflection coefficient of the bulk sample is:
where
The sign of the root for the reflection coefficient is chosen appropriately to ensure its passivity (). Similarly, the transmission coefficient of the bulk sample can be written as:
Thus, the effective permeability () and permittivity () of the material can be written as:
where
and
* is the free-space wavelength.
* is the guided mode wavelength of the unfilled transmission line.
* is the cutoff wavelength of the unfilled transmission line
The constitutive relation for admits an infinite number of solutions due to the branches of the complex logarithm. The ambiguity regarding its result can be resolved by taking the group delay into account. | 0 | Theoretical and Fundamental Chemistry |
A few Gram-positive bacteria are intrinsically resistant to vancomycin: Leuconostoc and Pediococcus species, but these organisms rarely cause diseases in humans. Most Lactobacillus species are also intrinsically resistant to vancomycin, with the exception of L. acidophilus and L. delbrueckii, which are sensitive. Other Gram-positive bacteria with intrinsic resistance to vancomycin include Erysipelothrix rhusiopathiae, Weissella confusa, and Clostridium innocuum.
Most Gram-negative bacteria are intrinsically resistant to vancomycin because their outer membranes are impermeable to large glycopeptide molecules (with the exception of some non-gonococcal Neisseria species). | 0 | Theoretical and Fundamental Chemistry |
In many examples of 3D optical data storage systems, several wavelengths (colors) of light are used (e.g. reading laser, writing laser, signal; sometimes even two lasers are required just for writing). Therefore, as well as coping with the high laser power and variable spherical aberration, the optical system must combine and separate these different colors of light as required. | 0 | Theoretical and Fundamental Chemistry |
The locus of enterocyte effacement-encoded regulator (Ler) is a regulatory protein that controls bacterial pathogenicity of enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic Escherichia coli (EHEC). More specifically, Ler regulates the locus of enterocyte effacement (LEE) pathogenicity island genes, which are responsible for creating intestinal attachment and effacing lesions and subsequent diarrhea: LEE1, LEE2, and LEE3. LEE1, 2, and 3 carry the information necessary for a type III secretion system. The transcript encoding the Ler protein is the open reading frame 1 on the LEE1 operon.
The mechanism of Ler regulation involves competition with histone-like nucleoid structuring protein (H-NS), a negative regulator of the LEE pathogenicity island. Ler is regulated by many factors such as plasmid encoded regulator (Per), integration host factor, Fis, BipA, a positive regulatory loop involving GrlA, and quorum sensing mediated by luxS.
__TOC__ | 1 | Applied and Interdisciplinary Chemistry |
When a hot steel work-piece is quenched, the area in contact with the water immediately cools and its temperature equilibrates with the quenching medium. The inner depths of the material however, do not cool so rapidly, and in work-pieces that are large, the cooling rate may be slow enough to allow the austenite to transform fully into a structure other than martensite or bainite. This results in a work-piece that does not have the same crystal structure throughout its entire depth; with a softer core and harder "shell". The softer core is some combination of ferrite and cementite, such as pearlite.
The hardenability of ferrous alloys, i.e. steels, is a function of the carbon content and other alloying elements and the grain size of the austenite. The relative importance of the various alloying elements is calculated by finding the equivalent carbon content of the material.
The fluid used for quenching the material influences the cooling rate due to varying thermal conductivities and specific heats. Substances like brine and water cool the steel much more quickly than oil or air. If the fluid is agitated cooling occurs even more quickly. The geometry of the part also affects the cooling rate: of two samples of equal volume, the one with higher surface area will cool faster. | 1 | Applied and Interdisciplinary Chemistry |
In the 1980s the NCEC developed the Chemdata hazardous material database, which was provided to British fire services for use in case of chemical accidents.
Chemdata lists over 61,600 safety data sheets (SDS) for dangerous substances. It is published in six languages. | 1 | Applied and Interdisciplinary Chemistry |
The unit sphere in three-dimensional space is the set of points such that . Let be the "north pole", and let be the rest of the sphere. The plane runs through the center of the sphere; the "equator" is the intersection of the sphere with this plane.
For any point on , there is a unique line through and , and this line intersects the plane in exactly one point , known as the stereographic projection of onto the plane.
In Cartesian coordinates on the sphere and on the plane, the projection and its inverse are given by the formulas
In spherical coordinates on the sphere (with the zenith angle, , and the azimuth, ) and polar coordinates on the plane, the projection and its inverse are
Here, is understood to have value when = 0. Also, there are many ways to rewrite these formulas using trigonometric identities. In cylindrical coordinates on the sphere and polar coordinates on the plane, the projection and its inverse are | 0 | Theoretical and Fundamental Chemistry |
Tautomers are structural isomers which readily interconvert, so that two or more species co-exist in equilibrium such as
Important examples are keto-enol tautomerism and the equilibrium between neutral and zwitterionic forms of an amino acid. | 0 | Theoretical and Fundamental Chemistry |
Since PXA has antibiotic activity against organisms as diverse as bacteria, protozoans, fungi, plants and animal cells including human cancer cells, it has to affect a cellular feature that is evolutionarily highly conserved. A recent study has shown that PXA directly affects the mitochondria by disrupting both their biochemical functions and their membrane architecture. The mitochondria are cellular organelles that are present in almost all eukaryotes. According to the theory of symbiogenesis, they are derived from bacteria and share many characteristics with them, including several properties of their membrane composition.
One of the main functions of the mitochondria is to produce the cellular energy currency ATP through the process of oxidative phosphorylation (OxPhos). OxPhos depends on the mitochondrial membrane potential, which is generated by the electron transport chain (ETC) via the consumption of oxygen. PXA was shown to interfere with all of these functions of the mitochondria: not only does it decrease ATP synthesis and depolarise the mitochondria, but it also inhibits the ETC and cellular oxygen consumption. This sets it apart from uncoupling agents such as protonophores. While these also decrease ATP synthesis and depolarise the mitochondria, they increase respiration at the same time due to increased ETC activity in an attempt to restore the membrane potential.
In addition to this inhibition of the function of mitochondria, PXA also disrupts their membrane architecture. In many cell types, the mitochondria normally form an intricate tubular network that undergoes a constant process of balanced mitochondrial fission and mitochondrial fusion. Treatment with PXA or many other mitochondrial stressors, such as protonophores, causes excessive fission that results in mitochondrial fragmentation. In the case of PXA, however, this fragmentation process was shown to be different from canonical fragmentation, caused by other agents such as protonophores, in several ways: first, it is considerably faster, resulting in complete fragmentation within a minute as opposed to about 30–60 minutes for canonical fragmentation; second, it is independent from the mitochondrial fission and fusion regulators DRP1 and OPA1; and third, while PXA causes fragmentation of both the outer mitochondrial membrane (OMM) and the mitochondrial matrix in wild type cells, it causes exclusive fragmentation of the matrix in cells that lack DRP1. This last feature is especially unusual since no active mechanism for exclusive matrix fission is known in higher eukaryotes. Examination of the mitochondrial ultrastructure revealed that PXA causes cristae disruption and complete distortion of the mitochondrial matrix. It is probably through this effect that PXA induces programmed cell death in the form of apoptosis. | 1 | Applied and Interdisciplinary Chemistry |
The association of the Vps35-Vps29-Vps26 complex with the cytosolic domains of cargo molecules on endosomal membranes initiates the activation of retrograde trafficking and cargo capture. The nucleation complex is formed through the interaction of VPS complex with GTP-activated Rab7 with clathrin, clathrin-adaptors and various binding proteins.
The SNX-BAR dimer enters the nucleation complex via direct binding or lateral movement on endosomal surface. The increased level of Retromer SNX-BARs causes a conformational switch to a curvature-inducing mode which initiates membrane tubule formation. Once the cargo carriers are matured, the carrier scission is then catalyzed by dynamin-II or EHD1, together with the mechanical forces generated by actin polymerization and motor activity.
The cargo carrier is transported to the TGN by motor proteins such as dynein. Tethering of the cargo carrier to the recipient compartment is thought to lead to the uncoating of the carrier, which is driven by ATP-hydrolysis and Rab7-GTP hydrolysis. Once released from the carrier, the Vps35-Vps29-Vps26 complex and the SNX-BAR dimers get recycled back onto the endosomal membranes. | 1 | Applied and Interdisciplinary Chemistry |
There are also fluids whose strain rate is a function of time. Fluids that require a gradually increasing shear stress to maintain a constant strain rate are referred to as rheopectic. An opposite case of this is a fluid that thins out with time and requires a decreasing stress to maintain a constant strain rate (thixotropic). | 1 | Applied and Interdisciplinary Chemistry |
By 1964, the ETH group had accomplished the first corrin model synthesis, and also the preparation of a ring-B precursor as part of a construction of the B molecule itself. Since independent progress of the two groups towards their long-term objective was so clearly complementary, Woodward and Eschenmoser decided in 1965 to join forces and to pursue from then on the project of a B synthesis collaboratively, planning to utilize the ligand construction (ring coupling of components) strategy of the ETH model system.
By 1966, the ETH group had succeeded in synthesizing the B-C-component ("eastern half") by coupling their ring-B precursor to the ring-C precursor. The latter had also been prepared at Harvard from (−)-camphor by a strategy conceived and used earlier by A. Pelter and J. W. Cornforth in 1961. At ETH, the synthesis of the B-C-component involved the implementation of the C,C-condensation reaction via sulfide contraction. This newly developed method turned out to provide a general solution to the problem of constructing the characteristic structural elements of the corrin chromophore, the vinylogous amidine systems bridging the four peripheral rings.
Early in 1967, the Harvard group accomplished the synthesis of the model A-D-component, with the f-side chain undifferentiated, bearing a methyl ester function like all other side chains. From then on, the two groups systematically exchanged samples of their respective halves of the corrinoid target structure. By 1970, they had collaboratively connected Harvards undifferentiated A-D-component with ETHs B-C-component, producing dicyano-cobalt(III)-5,15-bisnor-heptamethyl-cobyrinate 1 (fig. 4). The ETH group identified this totally synthetic corrinoid intermediate by direct comparison with a sample produced from natural vitamin B.
In this advanced model study, reaction conditions for the demanding processes of the C/D-coupling and the A/B-cyclization via sulfide contraction method were established. Those for the C/D-coupling were successfully explored in both laboratories, the superior conditions were those found at Harvard, while the method for the A/B-ring closure via an intramolecular version of the sulfide contraction was developed at ETH. Later it was shown at Harvard that the A/B-ring closure could also be achieved by -iminoester/enamine condensation.
By early 1971, the Harvard group had accomplished the synthesis of the final A-D-component, containing the f-side chain carboxyl function at ring D differentiated from all the carboxyl functions as a nitrile group (as shown in 2 in fig. 4; see also fig. 3). The A/D-part of the B structure incorporates the constitutionally and configurationally most intricate part of the vitamin molecule; its synthesis is regarded as the apotheosis of the Woodwardian art in natural product total synthesis. | 0 | Theoretical and Fundamental Chemistry |
The issue of limit of detection, or limit of quantification, is encountered in all scientific disciplines. This explains the variety of definitions and the diversity of juridiction specific solutions developed to address preferences. In the simplest cases as in nuclear and chemical measurements, definitions and approaches have probably received the clearer and the simplest solutions. In biochemical tests and in biological experiments depending on many more intricate factors, the situation involving false positive and false negative responses is more delicate to handle. In many other disciplines such as geochemistry, seismology, astronomy, dendrochronology, climatology, life sciences in general, and in many other fields impossible to enumerate extensively, the problem is wider and deals with signal extraction out of a background of noise. It involves complex statistical analysis procedures and therefore it also depends on the models used, the hypotheses and the simplifications or approximations to be made to handle and manage uncertainties. When the data resolution is poor and different signals overlap, different deconvolution procedures are applied to extract parameters. The use of different phenomenological, mathematical and statistical models may also complicate the exact mathematical definition of limit of detection and how it is calculated. This explains why it is not easy to come to a general consensus, if any, about the precise mathematical definition of the expression of limit of detection. However, one thing is clear: it always requires a sufficient number of data (or accumulated data) and a rigorous statistical analysis to render better signification statistically. | 0 | Theoretical and Fundamental Chemistry |
In 1877, Köhler and Michaelis claimed that they synthesized the first isolated diphosphene (PhP=PPh). However, the molecular weight determination and X-ray crystallographic analysis later proved that this "diphosphene" only had a P-P single bond. Then the research to diphosphenes kept silent over almost 120 years until Masaaki Yoshifuji and his coworkers isolated an unprecedented diphosphene, bis(2,4,6-tri-tert-butylphenyl)diphosphene, in 1981. They first synthesized the (2,4,6-tri-tert-butylphenyl)phosphorus dichloride by adding phosphorus trichloride to (2,4,6-tri-butylphenyl)lithium that was the product of the lithium and halogen exchange. The phosphorus dichloride dimerized to a diphosphene after magnesium extracted two chlorine atoms from (2,4,6-tri-tert-butylphenyl)phosphorus dichloride. The P-P bond distance is 2.034 Å, which is much shorter than the average bond length in (CHP) (2.217 Å) and (CHP) (2.237 Å), indicating its double bond character. This research was a milestone in diphosphene studies because the product here was the first reported compound that had the isolated localized P=P bond. Moreover, this bulky structure provided a instructive pathway for the future synthesis of diphosphenes. | 0 | Theoretical and Fundamental Chemistry |
The occurrence of symmetry-related pairs of H-C-C-H fragments is not limited to aromatic systems. For instance, magnetic inequivalence is found in 1,4-homodisubstituted butadienes. It might be expected in a molecule such as a symmetrical 2,3,4,5-tetrasubstituted pyrrolidine, but less rigid and less flat sp frameworks tend to show very weak long-range couplings (through 4 or more bonds) so as to not manifest much sign of magnetic inequivalence. Reich gives several additional examples of magnetic inequivalence in non-aromatic H-C-C-H pairs. | 0 | Theoretical and Fundamental Chemistry |
For polymeric nanoparticles, the induction of stimuli-responsiveness has usually relied heavily upon well-known polymers that possess an inherent stimuli-responsiveness. Certain polymers that can undergo reversible phase transitions due to changes in temperature or pH have aroused interest.
Arguably the most utilized polymer for activation-modulated delivery is the thermo-responsive polymer poly(N-isopropylacrylamide). It is readily soluble in water at room temperature but precipitates reversibly from when the temperature is raised above its lower critical solution temperature (LCST), changing from an extended chain conformation to a collapsed chain. This feature presents a way to change the hydrophilicity of a polymer via temperature.
Efforts also focus on dual stimuli-responsive drug delivery systems, which can be harnessed to control the release of the encapsulated drug. For example, the triblock copolymer of poly(ethylene glycol)-b-poly(3-aminopropyl-methacrylamide)-b-poly(N-isopropylacrylamide) (PEG-b-PAPMA-b-PNIPAm) can self-assemble to form micelles, possessing a core–shell–corona architecture above the lower critical solution temperature. It is also pH responsive. Therefore, drug release can be tuned by changing either temperature or pH conditions. | 0 | Theoretical and Fundamental Chemistry |
Opportunity Rover found that the soil at Meridiani Planum was very similar to the soil at Gusev crater and Ares Vallis; however in many places at Meridiani the soil was covered with round, hard, gray spherules that were named "blueberries." These blueberries were found to be composed almost entirely of the mineral hematite. It was decided that the spectra signal spotted from orbit by Mars Odyssey was produced by these spherules. After further study it was decided that the blueberries were concretions formed in the ground by water. Over time, these concretions weathered from what was overlying rock, and then became concentrated on the surface as a lag deposit. The concentration of spherules in bedrock could have produced the observed blueberry covering from the weathering of as little as one meter of rock. Most of the soil consisted of olivine basalt sands that did not come from the local rocks. The sand may have been transported from somewhere else. | 0 | Theoretical and Fundamental Chemistry |
Engine manufacturers typically rate their engines fuel consumption by the lower heating values since the exhaust is never condensed in the engine, and doing this allows them to publish more attractive numbers than are used in conventional power plant terms. The conventional power industry had used HHV (high heat value) exclusively for decades, even though virtually all of these plants did not condense exhaust either. American consumers should be aware that the corresponding fuel-consumption figure based on the higher heating value will be somewhat higher.
The difference between HHV and LHV definitions causes endless confusion when quoters do not bother to state the convention being used. since there is typically a 10% difference between the two methods for a power plant burning natural gas. For simply benchmarking part of a reaction the LHV may be appropriate, but HHV should be used for overall energy efficiency calculations if only to avoid confusion, and in any case, the value or convention should be clearly stated. | 0 | Theoretical and Fundamental Chemistry |
Important structure-activity relationship:
1. Strict steric constraint exists around the pyrrolidine ring of cyanopyrrolidine-based inhibitors, with only hydrogen, fluoro, acetylene, nitrile, or methano substitution permitted.
2. Presence of a nitrile moiety on the pyrrolidine ring is critical to achieving potent activity
Also, systematic SAR investigation has shown that the ring size and stereochemistry for the P2 position is quite conditioned. A 5-membered ring and L-configuration has shown better results than a 4-membered or 6-membered ring with D-configuration. Only minor changes on the pyrrolidine ring can be tolerated, since the good fit of the ring with the hydrophobic S1 pocket is very important for high affinity. Some trials have been made, e.g. by replacing the pyrrolidine with a thiazoline. That led to improved potency but also loss of chemical stability. Efforts to improve chemical stability often led to loss of specificity because of interactions with DPP-8 and DPP-9. These interactions have been connected with increased toxicity and mortality in animals. There are strict limitations in the P1 position and hardly any changes are tolerated. On the other hand, a variety of changes can be made in the P2 position. In fact, substitution with quite big branched side chains, e.g. tert-butylglycin, normally increased activity and chemical stability, which could lead to longer-lasting inhibition of the DPP-4 enzyme. It has also been noted that biaryl-based side chains can also give highly active inhibitors. It was originally believed that only lipophilic substitution would be tolerated. Now it is stated that also the substitution of polar negatively charged side-chains as well as hydrophilic substitution can lead to excellent inhibitory activity. | 1 | Applied and Interdisciplinary Chemistry |
Fat suppression is an MRI technique in which fat signal from adipose tissue is suppressed to better visualize uptake of contrast material by bodily tissues, reduce chemical shift artifact, and to characterize certain types of lesions such as adrenal gland tumors, bone marrow infiltration, fatty tumors, and steatosis by determining the fat content of the tissues. Due to short relaxation times, fat exhibits a strong signal in magnetic resonance imaging (MRI), easily discernible on scans.
Fat suppression can be achieved through various techniques as outlined below:
# Frequency Selective Pulses (CHESS): This method leverages the difference in resonance frequency with water, employing frequency selective pulses. Known as fat saturation (fat-sat) techniques, this approach facilitates effective fat suppression.
# Phase Contrast Techniques: Operating on the same principle as black boundary or india ink artifacts, phase contrast techniques contribute to suppressing fat signals in MRI.
# Inversion Recovery Sequences (STIR Technique): Utilizing short T1 relaxation time, the STIR technique involves inversion recovery sequences to achieve fat suppression.
# Dixon Method: A distinct approach to fat suppression that is primarily used to achieve uniform fat suppression.
# Hybrid Techniques (e.g., SPIR): Innovative approaches involve the combination of multiple fat suppression techniques, exemplified by SPIR, which integrates spectral presaturation with inversion recovery.
The choice of a specific fat suppression technique should be guided by several factors, including the intended purpose—whether it is for contrast enhancement or tissue characterization. Considerations such as the quantity of fat in the tissue under examination, the magnetic field strength, and the homogeneity of the main magnetic field play crucial roles in the selection process. | 0 | Theoretical and Fundamental Chemistry |
When the incoming field is very intense , the interaction of the electron with the electromagnetic field is completely equivalent to the interaction of the electron with multiple photons, with no need of explicitly quantize the electromagnetic field of the incoming low-energy radiation. While the interaction with the radiation field, i.e. the emitted photon, is treated with perturbation theory: the probability of photon emission is evaluated considering the transition between the states of the electron in presence of the electromagnetic field. This problem has been solved primarily in the case in which electric and magnetic fields are orthogonal and equal in magnitude (crossed field); in particular, the case of a plane electromagnetic wave has been considered. Crossed fields represent in good approximation many existing fields so the found solution can be considered quite general. The spectrum of non-linear inverse Compton scattering, obtained with this approach and valid for and , is:
where the parameter , is now defined as:A related quantity is the rate of photon emission:<math display="block">
\dfrac{dN}{dt}=\dfrac{\sqrt{3}}{2\pi}\dfrac{q^2 m c}{\hbar^2 }\dfrac{\chi}{\gamma} \int_0^{\chi}\dfrac{F(\chi,\eta)}{\eta}d\eta
no photons can be produced. This rate of photon emission depends explicitly on electron quantum parameter and on the Lorentz factor for the electron. | 0 | Theoretical and Fundamental Chemistry |
The more general form of the Butler–Volmer equation, applicable to the mass transfer-influenced conditions, can be written as:
where:
* j is the current density, A/m,
* c and c refer to the concentration of the species to be oxidized and to be reduced, respectively,
* c(0,t) is the time-dependent concentration at the distance zero from the surface of the electrode.
The above form simplifies to the conventional one (shown at the top of the article) when the concentration of the electroactive species at the surface is equal to that in the bulk.
There are two rates which determine the current-voltage relationship for an electrode. First is the rate of the chemical reaction at the electrode, which consumes reactants and produces products. This is known as the charge transfer rate. The second is the rate at which reactants are provided, and products removed, from the electrode region by various processes including diffusion, migration, and convection. The latter is known as the mass-transfer rate
. These two rates determine the concentrations of the reactants and products at the electrode, which are in turn determined by them. The slowest of these rates will determine the overall rate of the process.
The simple Butler–Volmer equation assumes that the concentrations at the electrode are practically equal to the concentrations in the bulk electrolyte, allowing the current to be expressed as a function of potential only. In other words, it assumes that the mass transfer rate is much greater than the reaction rate, and that the reaction is dominated by the slower chemical reaction rate. Despite this limitation, the utility of the Butler–Volmer equation in electrochemistry is wide, and it is often considered to be "central in the phenomenological electrode kinetics".
The extended Butler–Volmer equation does not make this assumption, but rather takes the concentrations at the electrode as given, yielding a relationship in which the current is expressed as a function not only of potential, but of the given concentrations as well. The mass-transfer rate may be relatively small, but its only effect on the chemical reaction is through the altered (given) concentrations. In effect, the concentrations are a function of the potential as well. A full treatment, which yields the current as a function of potential only, will be expressed by the extended Butler–Volmer equation, but will require explicit inclusion of mass transfer effects in order to express the concentrations as functions of the potential. | 0 | Theoretical and Fundamental Chemistry |
Note: An e plane is a double glide plane, one having glides in two different directions. They are found in seven orthorhombic, five tetragonal and five cubic space groups, all with centered lattice. The use of the symbol e became official with .
The lattice system can be found as follows. If the crystal system is not trigonal then the lattice system is of the same type. If the crystal system is trigonal, then the lattice system is hexagonal unless the space group is one of the seven in the rhombohedral lattice system consisting of the 7 trigonal space groups in the table above whose name begins with R. (The term rhombohedral system is also sometimes used as an alternative name for the whole trigonal system.) The hexagonal lattice system is larger than the hexagonal crystal system, and consists of the hexagonal crystal system together with the 18 groups of the trigonal crystal system other than the seven whose names begin with R.
The Bravais lattice of the space group is determined by the lattice system together with the initial letter of its name, which for the non-rhombohedral groups is P, I, F, A or C, standing for the principal, body centered, face centered, A-face centered or C-face centered lattices. There are seven rhombohedral space groups, with initial letter R. | 0 | Theoretical and Fundamental Chemistry |
The determination of phosphorus, arsenic, silicon and germanium are examples of the use of heteropoly-molybdenum blue in analytical chemistry. The following example describes the determination of phosphorus. A sample containing the phosphate is mixed with an acid solution of Mo, for example ammonium molybdate, to produce , which has an α-Keggin structure. This anion is then reduced by, for example, ascorbic acid or SnCl, to form the blue coloured β-keggin ion, . The amount of the blue coloured ion produced is proportional to the amount of phosphate present and the absorption can be measured using a colorimeter to determine the amount of phosphorus. Examples of procedures are:
*the analysis of phosphate in sea water.
*standard methods for determining phosphorus and silicon content of metals and metal ores. (e.g. BSI and ISO standards)
*the determination of germanium and arsenic
The comparison of the measured absorption against readings taken for analyses of standard solutions means that a detailed understanding of the structure of the blue complex was unnecessary.
This colorimetric method is ineffective when comparable amounts of arsenate are present in solution with phosphate. This is due to the strong chemical likeness of arsenate and phosphate. The resultant molybdenum blue for arsenate, using the same procedure, does produce a slightly different spectral signature, however.
Recently, paper-based devices have become very attractive to use colorimetric determination for making inexpensive, disposable and convenient analytical devices for the determination of reactive phosphate in the field. By using an inexpensive and portable infrared Lightbox system, one can create uniform and repeatable lighting environments to take advantage of the peak absorbance of the molybdenum blue reaction in order to improve limit of detection of paper-based devices. This system may act as a substitute for expensive, lab-equipment spectrometers. | 0 | Theoretical and Fundamental Chemistry |
The effluent from the tailings from the mining of sulfidic minerals has been described as "the largest environmental liability of the mining industry". These tailings contain large amounts of pyrite (FeS) and Iron(II) sulfide (FeS), which are rejected from the sought-after ores of copper and nickel, as well as coal. Although harmless underground, these minerals are reactive toward air in the presence of microorganisms, which if not properly managed lead to acid mine drainage. | 1 | Applied and Interdisciplinary Chemistry |
Another method of flow measurement involves placing a bluff body (called a shedder bar) in the path of the fluid. As the fluid passes this bar, disturbances in the flow called vortices are created. The vortices trail behind the cylinder, alternatively from each side of the bluff body. This vortex trail is called the Von Kármán vortex street after von Kármán's 1912 mathematical description of the phenomenon. The frequency at which these vortices alternate sides is essentially proportional to the flow rate of the fluid. Inside, atop, or downstream of the shedder bar is a sensor for measuring the frequency of the vortex shedding. This sensor is often a piezoelectric crystal, which produces a small, but measurable, voltage pulse every time a vortex is created. Since the frequency of such a voltage pulse is also proportional to the fluid velocity, a volumetric flow rate is calculated using the cross-sectional area of the flowmeter. The frequency is measured and the flow rate is calculated by the flowmeter electronics using the equation
where is the frequency of the vortices, the characteristic length of the bluff body, is the velocity of the flow over the bluff body, and is the Strouhal number, which is essentially a constant for a given body shape within its operating limits. | 1 | Applied and Interdisciplinary Chemistry |
Given the extremely low interaction cross-sections, the number of particles required in the reaction area is enormous, well beyond any existing technology. But this assumes that the particles in question only get one pass through the system. If the particles that missed collisions can be recycled in a way that their energy can be retained and the particles have multiple chances to collide, the energy imbalance can be reduced.
One such solution would be to place the reaction area of a two-beam system between the poles of a powerful magnet. The field will cause the electrically charged particles to bend around into circular paths and come back into the reaction area again. However, such systems naturally defocus the particles, so this will not lead them back to their original trajectories accurately enough to produce the densities desired.
A better solution is to use a dedicated storage ring which includes focusing systems to maintain the beam accuracy. However, these only accept particles in a relatively narrow selection of original trajectories. If two particles approach closely and scatter off at an angle, they will no longer recycle into the storage area. It is easy to show that the loss rate from such scatterings is far greater than the fusion rate.
Many attempts have been made to address this scattering problem. | 0 | Theoretical and Fundamental Chemistry |
Søren Peter Lauritz Sørensen (9 January 1868 – 12 February 1939) was a Danish chemist, known for the introduction of the concept of pH, a scale for measuring acidity and alkalinity. | 0 | Theoretical and Fundamental Chemistry |
PABPII, or polyadenine binding protein II, is a protein involved in the assembly of the polyadenine tail added to newly synthesized pre-messenger RNA (mRNA) molecules during the process of gene transcription. It is a regulatory protein that controls the rate at which polyadenine polymerase (PAP) adds adenine nucleotides to the 3' end of the growing tail within the nucleus of the cell. In the absence of PABPII, PAP adds adenines slowly, typically about 12. PABPII then binds to the short polyadenine tail and induces an acceleration in the rate of addition by PAP until the tail has grown to about 200 adenines long. The mechanism by which PABPII signals the termination of the polymerization reaction once the tail has reached its required length is not clearly understood.
PABPII is distinct from the related protein PABPI in being localized to the cell nucleus rather than the cytoplasm. | 1 | Applied and Interdisciplinary Chemistry |
Ekimov was born in the Soviet Union. In 1967, he graduated from the Faculty of Physics, Leningrad State University. He went on to receive his PhD in physics at the Ioffe Institute of the Russian Academy of Sciences in 1974. | 0 | Theoretical and Fundamental Chemistry |
The most common types of bioconjugation include coupling of a small molecule (such as biotin or a fluorescent dye) to a protein. Antibody-drug conjugates such as Brentuximab vedotin and Gemtuzumab ozogamicin are examples falling into this category.
Protein-protein conjugations, such as the coupling of an antibody to an enzyme, or the linkage of protein complexes, is also facilitated via bioconjugations.
Other less common molecules used in bioconjugation are oligosaccharides, nucleic acids, synthetic polymers such as polyethylene glycol, and carbon nanotubes. | 1 | Applied and Interdisciplinary Chemistry |
DWSIM is also available on Android and iOS mobile operating systems, where it is free to download. On these platforms, DWSIM includes a basic set of features while more advanced modules can be unlocked through in-app purchases. | 1 | Applied and Interdisciplinary Chemistry |
It is also used to illuminate pictures painted with fluorescent colors, particularly on black velvet, which intensifies the illusion of self-illumination. The use of such materials, often in the form of tiles viewed in a sensory room under UV light, is common in the United Kingdom for the education of students with profound and multiple learning difficulties. Such fluorescence from certain textile fibers, especially those bearing optical brightener residues, can also be used for recreational effect, as seen, for example, in the opening credits of the James Bond film A View to a Kill. Black light puppetry is also performed in a black light theater. | 0 | Theoretical and Fundamental Chemistry |
Cosmogenic isotopes are formed by the interaction of cosmic rays with the nucleus of an atom. These can be used for dating purposes and for use as natural tracers. In addition, by careful measurement of some ratios of stable isotopes it is possible to obtain new insights into the origin of bullets, ages of ice samples, ages of rocks, and the diet of a person can be identified from a hair or other tissue sample. (See Isotope geochemistry and Isotopic signature for further details). | 0 | Theoretical and Fundamental Chemistry |
The electrophilic addition reaction of hydrogen bromide to 1,3-butadiene above room temperature leads predominantly to the thermodynamically more stable 1,4 adduct, 1-bromo-2-butene, but decreasing the reaction temperature to below room temperature favours the kinetic 1,2 adduct, 3-bromo-1-butene.
:The rationale for the differing selectivities is as follows: Both products result from Markovnikov protonation at position 1, resulting in a resonance-stabilized allylic cation. The 1,4 adduct places the larger Br atom at a less congested site and includes a more highly substituted alkene moiety, while the 1,2 adduct is the result of the attack by the nucleophile (Br) at the carbon of the allylic cation bearing the greatest positive charge (the more highly substituted carbon is the most likely place for the positive charge). | 0 | Theoretical and Fundamental Chemistry |
The Romans were already familiar with the ability of a prism to generate a rainbow of colors. Newton is traditionally regarded as the founder of spectroscopy, but he was not the first scientist who studied and reported on the solar spectrum. The works of Athanasius Kircher (1646), Jan Marek Marci (1648), Robert Boyle (1664), and Francesco Maria Grimaldi (1665), predate Newtons optics experiments (1666–1672). Newton published his experiments and theoretical explanations of dispersion of light in his Opticks. His experiments demonstrated that white light could be split up into component colors by means of a prism and that these components could be recombined to generate white light. He demonstrated that the prism is not imparting or creating the colors but rather separating constituent parts of the white light. Newtons corpuscular theory of light was gradually succeeded by the wave theory. It was not until the 19th century that the quantitative measurement of dispersed light was recognized and standardized. As with many subsequent spectroscopy experiments, Newton's sources of white light included flames and stars, including the Sun. Subsequent studies of the nature of light include those of Hooke, Huygens, Young. Subsequent experiments with prisms provided the first indications that spectra were associated uniquely with chemical constituents. Scientists observed the emission of distinct patterns of colour when salts were added to alcohol flames. | 0 | Theoretical and Fundamental Chemistry |
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