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Argillaceous rocks are those in which clay minerals are a significant component. For example, argillaceous limestones are limestones consisting predominantly of calcium carbonate, but including 10-40% of clay minerals: such limestones, when soft, are often called marls. Similarly, argillaceous sandstones such as greywacke, are sandstones consisting primarily of quartz grains, with the interstitial spaces filled with clay minerals. | 9 | Geochemistry |
Yulia Sister (, ; born September 12, 1936, in Chișinău, Bessarabia, Romania) is a Soviet Moldavian and Israeli analytical chemist engaged in chemical research with the use of polarography and chromatography, a science historian, and a researcher of Russian Jewry in Israel, France, and other countries. She holds the position of Director General of the Research Centre for Russian Jews abroad and in Israel. | 3 | Analytical Chemistry |
The presence of water in a solution of sodium chloride must be examined in respect to its reduction and oxidation in both electrodes. Usually, water is electrolysed as mentioned above in electrolysis of water yielding gaseous oxygen in the anode and gaseous hydrogen in the cathode. On the other hand, sodium chloride in water dissociates in Na and Cl ions. The cation, which is the positive ion, will be attracted to the cathode (−), thus reducing the sodium ion. The chloride anion will then be attracted to the anode (+), where it is oxidized to chlorine gas.
The following half reactions should be considered in the process mentioned:
# Cathode: Na + e → NaE° = –2.71 V
# Anode: 2 Cl → Cl + 2 eE° = +1.36 V
# Cathode: 2 HO + 2 e → H + 2 OHE° = –0.83 V
# Anode: 2 HO → O + 4 H + 4 eE° = +1.23 V
Reaction 1 is discarded as it has the most negative value on standard reduction potential thus making it less thermodynamically favorable in the process.
When comparing the reduction potentials in reactions 2 and 4, the oxidation of chloride ion is favored over oxidation of water, thus chlorine gas is produced at the anode and not oxygen gas.
Although the initial analysis is correct, there is another effect, known as the overvoltage effect. Additional voltage is sometimes required, beyond the voltage predicted by the E°. This may be due to kinetic rather than thermodynamic considerations. In fact, it has been proven that the activation energy for the chloride ion is very low, hence favorable in kinetic terms. In other words, although the voltage applied is thermodynamically sufficient to drive electrolysis, the rate is so slow that to make the process proceed in a reasonable time frame, the voltage of the external source has to be increased (hence, overvoltage).
The overall reaction for the process according to the analysis is the following:
:Anode (oxidation): 2 Cl → Cl + 2 e
:Cathode (reduction): 2 HO + 2 e → H + 2 OH
:Overall reaction: 2 HO + 2 Cl → H + Cl + 2 OH
As the overall reaction indicates, the concentration of chloride ions is reduced in comparison to OH ions (whose concentration increases). The reaction also shows the production of gaseous hydrogen, chlorine and aqueous sodium hydroxide. | 7 | Physical Chemistry |
The identification of the genetic basis for the causative agent of a disease can be an important component of understanding its effects and spread. Location and content of structural genes can elucidate the evolution of virulence, as well as provide necessary information for treatment. Likewise understanding the specific changes in structural gene sequences underlying a gain or loss of virulence aids in understanding the mechanism by which diseases affect their hosts.
For example, Yersinia pestis (the bubonic plague) was found to carry several virulence and inflammation-related structural genes on plasmids. Likewise, the structural gene responsible for tetanus was determined to be carried on a plasmid as well. Diphtheria is caused by a bacterium, but only after that bacterium has been infected by a bacteriophage carrying the structural genes for the toxin.
In Herpes simplex virus, the structural gene sequence responsible for virulence was found in two locations in the genome despite only one location actually producing the viral gene product. This was hypothesized to serve as a potential mechanism for strains to regain virulence if lost through mutation.
Understanding the specific changes in structural genes underlying a gain or loss of virulence is a necessary step in the formation of specific treatments, as well the study of possible medicinal uses of toxins. | 1 | Biochemistry |
As in simpler alkanes, carbon in the CFCs bond with tetrahedral symmetry. Because the fluorine and chlorine atoms differ greatly in size and effective charge from hydrogen and from each other, the methane-derived CFCs deviate from perfect tetrahedral symmetry.
The physical properties of CFCs and HCFCs are tunable by changes in the number and identity of the halogen atoms. In general, they are volatile but less so than their parent alkanes. The decreased volatility is attributed to the molecular polarity induced by the halides, which induces intermolecular interactions. Thus, methane boils at −161 °C whereas the fluoromethanes boil between −51.7 (CFH) and −128 °C (CF). The CFCs have still higher boiling points because the chloride is even more polarizable than fluoride. Because of their polarity, the CFCs are useful solvents, and their boiling points make them suitable as refrigerants. The CFCs are far less flammable than methane, in part because they contain fewer C-H bonds and in part because, in the case of the chlorides and bromides, the released halides quench the free radicals that sustain flames.
The densities of CFCs are higher than their corresponding alkanes. In general, the density of these compounds correlates with the number of chlorides.
CFCs and HCFCs are usually produced by halogen exchange starting from chlorinated methanes and ethanes. Illustrative is the synthesis of chlorodifluoromethane from chloroform:
:HCCl + 2 HF → HCFCl + 2 HCl
Brominated derivatives are generated by free-radical reactions of hydrochlorofluorocarbons, replacing C-H bonds with C-Br bonds. The production of the anesthetic 2-bromo-2-chloro-1,1,1-trifluoroethane ("halothane") is illustrative:
:CFCHCl + Br → CFCHBrCl + HBr | 2 | Environmental Chemistry |
The shape memory effect (SME) occurs because a temperature-induced phase transformation reverses deformation, as shown in the previous hysteresis curve. Typically the martensitic phase is monoclinic or orthorhombic (B19' or [https://www.atomic-scale-physics.de/lattice/struk/b19.html B19]). Since these crystal structures do not have enough slip systems for easy dislocation motion, they deform by twinning—or rather, detwinning.
Martensite is thermodynamically favored at lower temperatures, while austenite ([https://www.atomic-scale-physics.de/lattice/struk/b2.html B2] cubic) is thermodynamically favored at higher temperatures. Since these structures have different lattice sizes and symmetry, cooling austenite into martensite introduces internal strain energy in the martensitic phase. To reduce this energy, the martensitic phase forms many twins—this is called "self-accommodating twinning" and is the twinning version of geometrically necessary dislocations. Since the shape memory alloy will be manufactured from a higher temperature and is usually engineered so that the martensitic phase is dominant at operating temperature to take advantage of the shape memory effect, SMAs "start" highly twinned.
When the martensite is loaded, these self-accommodating twins provide an easy path for deformation. Applied stresses will detwin the martensite, but all of the atoms stay in the same position relative to the nearby atoms—no atomic bonds are broken or reformed (as they would be by dislocation motion). Thus, when the temperature is raised and austenite becomes thermodynamically favored, all of the atoms rearrange to the B2 structure which happens to be the same macroscopic shape as the B19' pre-deformation shape. This phase transformation happens extremely quickly and gives SMAs their distinctive "snap".
Repeated use of the shape-memory effect may lead to a shift of the characteristic transformation temperatures (this effect is known as functional fatigue, as it is closely related with a change of microstructural and functional properties of the material). The maximum temperature at which SMAs can no longer be stress induced is called M, where the SMAs are permanently deformed. | 8 | Metallurgy |
Acute beryllium poisoning is acute chemical pneumonitis resulting from the toxic effect of beryllium in its elemental form or in various chemical compounds, and is distinct from berylliosis (also called chronic beryllium disease). After occupational safety procedures were put into place following the realization that the metal caused berylliosis around 1950, acute beryllium poisoning became extremely rare. | 1 | Biochemistry |
After a cell passes the restriction point, Cyclin E - Cdk 2 hyper-phosphorylates all mono-phosphorylated isoforms. While the exact mechanism is unknown, one hypothesis is that binding to the C-terminus tail opens the pocket subunit, allowing access to all phosphorylation sites. This process is hysteretic and irreversible, and it is thought accumulation of mono-phosphorylated pRb induces the process. The bistable, switch like behavior of pRb can thus be modeled as a bifurcation point: | 1 | Biochemistry |
The binding of glycan-binding proteins (GBPs) to glycans could be modeled with simple equilibrium. Denoting glycans as and proteins as :
With an associated equilibrium constant of
Which is rearranged to give dissociation constant following biochemical conventions:
Given that many GBPs exhibit multivalency, this model may be expanded to account for multiple equilibria:
Denoting cumulative equilibrium of binding with ligands as
With corresponding equilibrium constant:
And writing material balance for protein ( denotes the total concentration of protein):
Expressing the terms through an equilibrium constant, a final result is found:
The concentration of free protein is, thus:
If , i.e. there is only one carbohydrate receptor domain, the equation reduces to
With increasing the concentration of free protein decreases; hence, the apparent decreases too. | 1 | Biochemistry |
The principle of minimum energy can be generalized to apply to constraints other than fixed entropy. For other constraints, other state functions with dimensions of energy will be minimized. These state functions are known as thermodynamic potentials. Thermodynamic potentials are at first glance just simple algebraic combinations of the energy terms in the expression for the internal energy. For a simple, multicomponent system, the internal energy may be written:
where the intensive parameters (T, P, μ) are functions of the internal energy's natural variables via the equations of state. As an example of another thermodynamic potential, the Helmholtz free energy is written:
where temperature has replaced entropy as a natural variable. In order to understand the value of the thermodynamic potentials, it is necessary to view them in a different light. They may in fact be seen as (negative) Legendre transforms of the internal energy, in which certain of the extensive parameters are replaced by the derivative of internal energy with respect to that variable (i.e. the conjugate to that variable). For example, the Helmholtz free energy may be written:
and the minimum will occur when the variable T becomes equal to the temperature since
The Helmholtz free energy is a useful quantity when studying thermodynamic transformations in which the temperature is held constant. Although the reduction in the number of variables is a useful simplification, the main advantage comes from the fact that the Helmholtz free energy is minimized at equilibrium with respect to any unconstrained internal variables for a closed system at constant temperature and volume. This follows directly from the principle of minimum energy which states that at constant entropy, the internal energy is minimized. This can be stated as:
where and are the value of the internal energy and the (fixed) entropy at equilibrium. The volume and particle number variables have been replaced by x which stands for any internal unconstrained variables.
The minimization is with respect to the unconstrained variables. In the case of chemical reactions this is usually the number of particles or mole fractions, subject to the conservation of elements. At equilibrium, these will take on their equilibrium values, and the internal energy will be a function only of the chosen value of entropy . By the definition of the Legendre transform, the Helmholtz free energy will be:
The Helmholtz free energy at equilibrium will be:
where is the (unknown) temperature at equilibrium. Substituting the expression for :
By exchanging the order of the extrema:
showing that the Helmholtz free energy is minimized at equilibrium.
The Enthalpy and Gibbs free energy, are similarly derived. | 7 | Physical Chemistry |
A multi-component reaction (or MCR), sometimes referred to as a "Multi-component Assembly Process" (or MCAP), is a chemical reaction where three or more compounds
react to form a single product. By definition, multicomponent reactions are those reactions whereby more than two reactants combine in a sequential manner to give highly selective products that retain majority of the atoms of the starting material. | 7 | Physical Chemistry |
The main difference with absorption cycle, is that in adsorption cycle, the refrigerant (adsorbate) could be ammonia, water, methanol, etc., while the adsorbent is a solid, such as silica gel, activated carbon, or zeolite, unlike in the absorption cycle where absorbent is liquid.
The reason adsorption refrigeration technology has been extensively researched in recent 30 years lies in that the operation of an adsorption refrigeration system is often noiseless, non-corrosive and environment friendly. | 7 | Physical Chemistry |
Fluorine may interact with biological systems in the form of fluorine-containing compounds. Though elemental fluorine (F) is very rare in everyday life, fluorine-containing compounds such as fluorite occur naturally as minerals. Naturally occurring organofluorine compounds are extremely rare. Man-made fluoride compounds are common and are used in medicines, pesticides, and materials. Twenty percent of all commercialized pharmaceuticals contain fluorine, including Lipitor and Prozac. In many contexts, fluorine-containing compounds are harmless or even beneficial to living organisms; in others, they are toxic.
Aside from their use in medicine, man-made fluorinated compounds have also played a role in several noteworthy environmental concerns. Chlorofluorocarbons (CFCs), once major components of numerous commercial aerosol products, have proven damaging to Earth's ozone layer and resulted in the wide-reaching Montreal Protocol; though in truth the chlorine in CFCs is the destructive actor, fluorine is an important part of these molecules because it makes them very stable and long-lived. Similarly, the stability of many organofluorine compounds has raised the issue of biopersistence. Long-lived molecules from waterproofing sprays, for example PFOA and PFOS, are found worldwide in the tissues of wildlife and humans, including newborn children.
Fluorine biology is also relevant to a number of cutting-edge technologies. PFCs (perfluorocarbons) are capable of holding enough oxygen to support human liquid breathing. Organofluorine in the form of its radioisotope F is also at the heart of a modern medical imaging technique known as positron emission tomography (PET). A PET scan produces three-dimensional colored images of parts of the body that use a lot of sugar, particularly the brain or tumors. | 1 | Biochemistry |
Detection limits may vary greatly with the cross section of the core state of interest and the background signal level. In general, photoelectron cross sections increase with atomic number. The background increases with the atomic number of the matrix constituents as well as the binding energy, because of secondary emitted electrons. For example, in the case of gold on silicon where the high cross section Au4f peak is at a higher kinetic energy than the major silicon peaks, it sits on a very low background and detection limits of 1ppm or better may be achieved with reasonable acquisition times. Conversely for silicon on gold, where the modest cross section Si2p line sits on the large background below the Au4f lines, detection limits would be much worse for the same acquisition time. Detection limits are often quoted as 0.1–1.0 % atomic percent (0.1% = 1 part per thousand = 1000 ppm) for practical analyses, but lower limits may be achieved in many circumstances. | 7 | Physical Chemistry |
ZMapp is an experimental biopharmaceutical drug comprising three chimeric monoclonal antibodies under development as a treatment for Ebola virus disease. Two of the three components were originally developed at the Public Health Agency of Canada's National Microbiology Laboratory (NML), and the third at the U.S. Army Medical Research Institute of Infectious Diseases; the cocktail was optimized by Gary Kobinger, a research scientist at the NML and underwent further development under license by Mapp Biopharmaceutical. ZMapp was first used on humans during the Western African Ebola virus epidemic, having only been previously tested on animals and not yet subjected to a randomized controlled trial. The National Institutes of Health (NIH) ran a clinical trial starting in January 2015 with subjects from Sierra Leone, Guinea, and Liberia aiming to enroll 200 people, but the epidemic waned and the trial closed early, leaving it too statistically underpowered to give a meaningful result about whether ZMapp worked.
In 2016, a clinical study comparing ZMapp to the current standard of care for Ebola was inconclusive. | 1 | Biochemistry |
To understand the electronic behavior of a solar cell, it is useful to create a model which is electrically equivalent, and is based on discrete ideal electrical components whose behavior is well defined. An ideal solar cell may be modelled by a current source in parallel with a diode; in practice no solar cell is ideal, so a shunt resistance and a series resistance component are added to the model. The resulting equivalent circuit of a solar cell is shown on the right. Also shown, on the left, is the schematic representation of a solar cell for use in circuit diagrams. There are several electrical models that translate the solar cell's behaviour. The most used one is presented below, but others novel models have been proposed, like the d1MxP | 7 | Physical Chemistry |
Tissue fixation is performed by chemical fixation using formalin. This prevents the postmortem degeneration of the tissue and hardens soft tissue. The tissue is dehydrated using ethanol and the alcohol is cleared using an organic solvent such as xylene. The tissue is embedded in paraffin which infiltrates the microscopic spaces present throughout the tissue. The embedded tissue is sliced using a microtome and subsequently stained to produce contrast needed to visualize the tissue. | 1 | Biochemistry |
Terepthalaldehyde can be synthesised from p-xylene in two steps. First, p-xylene can be reacted with bromine to create α,α,α,α-Tetrabromo-p-xylene. Next, sulphuric acid is introduced to create terephthaldehyde. Alternative procedures also describe the conversion of similar p-xylene derivatives into terephthalaldehyde. | 0 | Organic Chemistry |
Roldán Cuenya studied at the University of Oviedo in Spain and received her doctorate degree from the University of Duisburg-Essen in Germany under the supervision of
Werner Keune. As a postdoc she worked at the University of California, Santa Barbara in the group of Eric McFarland and subsequently became professor at the University of Central Florida in Orlando (USA). In 2013, she accepted a Chair Faculty position in Solid State Physics at the Ruhr University Bochum in Germany. She holds two roles at the Fritz Haber Institute - since 2017 as Director of the Department of Interface Science, and since April 2023 as interim Director of the Department of Inorganic Chemistry.
Her main research interests are the synthesis of nanostructured materials with tunable surface properties and the experimental investigation of structure-reactivity relationships in thermal and electro-catalysis using in situ and operando methods. Applications of her work are in the areas of environmental remediation and energy conversion. | 7 | Physical Chemistry |
Homozygosity/Autozygosity mapping is a powerful technique, but is only valid when searching for a mutation segregating within a small, closed population. Such a small population, possibly created by the founder effect, will have a limited gene pool, and thus any inherited disease will probably be a result of two copies of the same mutation segregating on the same haplotype. Since affected individuals will probably be homozygous in the regions, looking at SNPs in a region is an adequate marker of regions of homozygosity and heterozygosity. Modern day SNP arrays are used to survey the genome and identify large regions of homozygosity. Homozygous blocks in the genomes of affected individuals can then be laid on top of each other, and the overlapping region should contain the disease gene.
This analysis is often extended by analyzing autozygosity, an extension of homozygosity, in the genomes of affected individuals. This can be accomplished by plotting a cumulative LOD score alongside the overlaid blocks of homozygosity. By taking into consideration the population allele frequencies for all SNPs via autozygosity mapping, the results of homozygosity can be confirmed. Furthermore, if two suspicious regions appear as a result of homozygosity mapping, autozygosity mapping may be able to distinguish between the two (ex. If one block of homozygosity is a result of a very non-diverse region of the genome, the LOD score will be very low).
Tools for Homozygosity Mapping
# HomSI: a homozygous stretch identifier from next-generation sequencing data A tool that identifies homozygous regions using deep sequence data. | 1 | Biochemistry |
Dioxiranes are generated by combining the ketone precursor with a buffered aqueous solution of KHSO. The volatile dioxiranes DMD and TFD are isolated via distillation of the crude reaction mixture. Baeyer-Villiger oxidation may compete with dioxirane formation. Once isolated, dioxiranes are kept in solutions of the corresponding ketones and dried with molecular sieves. Air-free technique is unnecessary unless the substrate or product is air-sensitive or hydrolytically labile, and most oxidations are carried out in the open air in Erlenmeyer flasks.
Oxidations with in situ generated dioxiranes are more convenient than isolation methods, provided the substrate is stable towards hydrolysis. Reactions can either be carried out in truly biphasic media with mechanical stirring, or in a homogeneous medium derived from water and a miscible organic solvent, such as acetonitrile. Asymmetric epoxidations are commonly carried out under the latter conditions. Some ketone catalysts are more persistent under slightly basic homogeneous conditions. | 0 | Organic Chemistry |
Froth flotation is applied to a wide range of separations. An estimated 1B tons of materials are processed in this manner annually. | 8 | Metallurgy |
Electrochemistry, a branch of chemistry, went through several changes during its evolution from early principles related to magnets in the early 16th and 17th centuries, to complex theories involving conductivity, electric charge and mathematical methods. The term electrochemistry was used to describe electrical phenomena in the late 19th and 20th centuries. In recent decades, electrochemistry has become an area of current research, including research in batteries and fuel cells, preventing corrosion of metals, the use of electrochemical cells to remove refractory organics and similar contaminants in wastewater electrocoagulation and improving techniques in refining chemicals with electrolysis and electrophoresis. | 7 | Physical Chemistry |
For low nuclearity clusters, bonding is often described as if it is localized. For this purpose, the 18-electron rule is used. Thus, 34 electrons in an organometallic complex predicts a dimetallic complex with a metal-metal bond. For higher nuclearity clusters, more elaborate rules are invoked including Jemmis mno rules and polyhedral skeletal electron pair theory.
Although clusters are often written with discrete M-M bonds, the nature of this bonding is unclear, especially when there are bridging ligands. | 7 | Physical Chemistry |
Hypoxia (hypo: "below", oxia: "oxygenated") refers to low oxygen conditions. For air-breathing organisms, hypoxia is problematic but for many anaerobic organisms, hypoxia is essential. Hypoxia applies to many situations, but usually refers to the atmosphere and natural waters. | 9 | Geochemistry |
Electromagnetic radiation is emitted by a light source and linearly polarized by a polarizer. It can pass through an optional compensator (retarder, quarter wave plate) and falls onto the sample. After reflection the radiation passes a compensator (optional) and a second polarizer, which is called an analyzer, and falls into the detector. Instead of the compensators, some ellipsometers use a phase-modulator in the path of the incident light beam. Ellipsometry is a specular optical technique (the angle of incidence equals the angle of reflection). The incident and the reflected beam span the plane of incidence. Light which is polarized parallel to this plane is named p-polarized. A polarization direction perpendicular is called s-polarized (s-polarised), accordingly. The "s" is contributed from the German "" (perpendicular). | 7 | Physical Chemistry |
All atoms that are not carbon or hydrogen are signified by their chemical symbol, for instance Cl for chlorine, O for oxygen, Na for sodium, and so forth. In the context of organic chemistry, these atoms are commonly known as heteroatoms (the prefix hetero- comes from Greek ἕτερος héteros, meaning "other").
Any hydrogen atoms bonded to heteroatoms are drawn explicitly. In ethanol, CHOH, for instance, the hydrogen atom bonded to oxygen is denoted by the symbol H, whereas the hydrogen atoms which are bonded to carbon atoms are not shown directly.
Lines representing heteroatom-hydrogen bonds are usually omitted for clarity and compactness, so a functional group like the hydroxyl group is most often written −OH instead of −O−H. These bonds are sometimes drawn out in full in order to accentuate their presence when they participate in reaction mechanisms.
Shown below for comparison are a skeletal formula (top), its Lewis structure (middle) and its ball-and-stick model (bottom) of the actual 3D structure of the ethanol molecule in the gas phase, as determined by microwave spectroscopy. | 0 | Organic Chemistry |
Aliphatic azo compounds (R and/or R′ = aliphatic) are less commonly encountered than the aryl azo compounds. A commercially important alkyl azo compound is azobisisobutyronitrile (AIBN), which is widely used as an initiator in free-radical polymerizations and other radical-induced reactions. It achieves this initiation by decomposition, eliminating a molecule of nitrogen gas to form two 2-cyanoprop-2-yl radicals:
For instance a mixture of styrene and maleic anhydride in toluene will react if heated, forming the copolymer upon addition of AIBN.
A simple dialkyl diazo compound is diethyldiazene, , which can be synthesized through a variant of the Ramberg–Bäcklund reaction. Because of their instability, aliphatic azo compounds pose the risk of explosion.
AIBN is produced by converting acetone cyanohydrin to the hydrazine derivative followed by oxidation: | 0 | Organic Chemistry |
From the commercial perspective, the most important phosphite salt is basic lead phosphite. Many salts containing the phosphite ion have been investigated structurally, these include sodium phosphite pentahydrate (NaHPO·5HO). (NH)HPO·HO, CuHPO·HO, SnHPO and Al(HPO)·4HO. The structure of is approximately tetrahedral.
has a number of canonical resonance forms making it isoelectronic with bisulfite ion, , which has a similar structure. | 0 | Organic Chemistry |
DTDP-glucose is produced by the enzyme glucose-1-phosphate thymidylyltransferase and is synthesized from dTTP and glucose-1-phosphate. Pyrophosphate is a byproduct of the reaction. | 1 | Biochemistry |
Reactions of alkenyl- and alkynylaluminium compounds involve the transfer of a nucleophilic alkenyl or alkynyl group attached to aluminium to an electrophilic atom. Stereospecific hydroalumination, carboalumination, and terminal alkyne metalation are useful methods for generation of the necessary alkenyl- and alkynylalanes. | 0 | Organic Chemistry |
Inhaled vancomycin can also be used off-label, via nebulizer, for the treatment of various infections of the upper and lower respiratory tract. | 0 | Organic Chemistry |
Tributyltin azide is synthesized by the salt metathesis reaction of tributyltin chloride and sodium azide.
It is a reagent used in the synthesis of tetrazoles, which in turn are used to generate angiotensin II receptor antagonists. In some applications, tributyltin azide has been replaced by the less toxic trioctyltin azide and organoaluminium azides. | 0 | Organic Chemistry |
Most cases of bacterial gastroenteritis are caused by food-borne enteric microorganisms, such as Salmonella and Campylobacter; however, it is also important to understand the risk of exposure to pathogens via recreational waters. This is especially the case in watersheds where human or animal wastes are discharged to streams and downstream waters are used for swimming or other recreational activities. Other important pathogens other than bacteria include viruses such as rotavirus, hepatitis A and hepatitis E and protozoa like giardia, cryptosporidium and Naegleria fowleri. Due to the difficulties associated with monitoring pathogens in the environment, risk assessments often rely on the use of indicator bacteria. | 3 | Analytical Chemistry |
Many chemical compounds are aromatic rings with other functional groups attached. Examples include trinitrotoluene (TNT), acetylsalicylic acid (aspirin), paracetamol, and the nucleotides of DNA. | 7 | Physical Chemistry |
There exist multiple transcription and translation mechanisms to prevent lethality due to deleterious mutations in the coding region. Such measures include proofreading by some DNA Polymerases during replication, mismatch repair following replication, and the Wobble Hypothesis which describes the degeneracy of the third base within an mRNA codon. | 1 | Biochemistry |
The first generation of the Edwards equation was
where k and k are the rate constants for a nucleophile and a standard (HO). H is a measure of the basicity of the nucleophile relative to protons, as defined by the equation:
where the pK is that of the conjugate acid of the nucleophile and the constant 1.74 is the correction for the pK of HO.
E is the term Edwards introduced to account for the polarizability of the nucleophile. It is related to the oxidation potential (E) of the reaction (oxidative dimerization of the nucleophile) by the equation:
where 2.60 is the correction for the oxidative dimerization of water, obtained from a least-squares correlation of data in Edwards’ first paper on the subject. α and β are then parameters unique to specific nucleophiles that relate the sensitivity of the substrate to the basicity and polarizability factors.
However, because some β's appeared to be negative as defined by the first generation of the Edwards equation, which theoretically should not occur, Edwards adjusted his equation. The term E was determined to have some dependence on the basicity relative to protons (H) due to some factors that affect basicity also influencing the electrochemical properties of the nucleophile. To account for this, E was redefined in terms of basicity and polarizability (given as molar refractivity, R):
: where
The values of a and b, obtained by the method of least squares, are 3.60 and 0.0624 respectively. With this new definition of E, the Edwards equation can be rearranged:
where A= αa and B = β + αb. However, because the second generation of the equation was also the final one, the equation is sometimes written as , especially since it was republished in that form in a later paper of Edwards’, leading to confusion over which parameters are being defined. | 7 | Physical Chemistry |
In host–guest chemistry, a carcerand () is a host molecule that completely entraps its guest (which can be an ion, atom or other chemical species) so that it will not escape even at high temperatures. This type of molecule was first described in 1985 by Donald J. Cram and coworkers. The complexes formed by a carcerand with permanently imprisoned guests are called carceplexes.
In contrast, hemicarcerands allow guests to enter and exit the cavity at high temperatures but will form stable complexes at ambient temperatures. The complexes formed by a hemicarcerand and a guest are called hemicarceplexes. | 6 | Supramolecular Chemistry |
Acidogenesis is the second stage in the four stages of anaerobic digestion:
* Hydrolysis: A chemical reaction where particulates are solubilized and large polymers converted into simpler monomers;
* Acidogenesis: A biological reaction where simple monomers are converted into volatile fatty acids;
* Acetogenesis: A biological reaction where volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen
* Methanogenesis: A biological reaction where acetates are converted into methane and carbon dioxide, while hydrogen is consumed.
Anaerobic digestion is a complex biochemical process of biologically mediated reactions by a consortium of microorganisms to convert organic compounds into methane and carbon dioxide. It is a stabilization process, reducing odor, pathogens, and mass reduction.
Hydrolytic bacteria form a variety of reduced end-products from the fermentation of a given substrate. One fundamental question that arises concerns the metabolic features that control carbon and electron flow to a given reduced end-product during pure culture and mixed methanogenic cultures of hydrolytic bacteria. Thermoanaerobium brockii is a representative thermophilic, hydrolytic bacterium, which ferments glucose, via the Embden–Meyerhof Parnas Pathway. T. brockii is an atypical hetero-lactic acid bacterium because it forms molecular hydrogen (H), in addition to lactic acid and ethanol. The reduced end-products of glucose fermentation are enzymatically formed from pyruvate, via the following mechanisms: lactate by fructose 1-6 all-phosphate (F6P) activated lactate dehydrogenase; H2 by pyruvate ferredoxin oxidoreductase and hydrogenase; and ethanol via NADH- and NADPH-linked alcohol dehydrogenase.
By its side, the acidogenic activity was found in the early 20th century, but it was not until the mid-1960s that the engineering of phases separation was assumed in order to improve the stability and waste digesters treatment. In this phase, complex molecules (carbohydrates, lipids, and proteins) are depolymerized into soluble compounds by hydrolytic enzymes (cellulases, hemicellulases, amylases, lipases and proteases). The hydrolyzed compounds are fermented into volatile fatty acids (acetate, propionate, butyrate, and lactate), neutral compounds (ethanol, methanol), ammonia, hydrogen and carbon dioxide.
Acetogenesis is one of the main reactions of this stage, in this, the intermediary metabolites produced are metabolized to acetate, hydrogen and carbonic gas by the three main groups of bacteria:
* homoacetogens;
* syntrophes; and
* sulphoreductors.
For the acetic acid production are considered three kind of bacteria:
* Clostridium aceticum;
* Acetobacter woodii; and
* Clostridium termoautotrophicum.
Winter y Wolfe, in 1979, demonstrated that A. woodii in syntrophic association with Methanosarcina produce methane and carbon dioxide from fructose, instead of three molecules of acetate. Moorella thermoacetica and Clostridium formiaceticum are able to reduce the carbonic gas to acetate, but they do not have hydrogenases which inhabilite the hydrogen use, so they can produce three molecules of acetate from fructose. Acetic acid is equally a co-metabolite of the organic substrates fermentation (sugars, glycerol, lactic acid, etc.) by diverse groups of microorganisms which produce different acids:
*Propionic bacteria (propionate + acetate);
* Clostridium (butyrate + acetate);
* Enterobacteria (acetate + lactate); and
* Hetero-fermentative bacteria (acetate, propionate, butyrate, valerate, etc.). | 1 | Biochemistry |
Because channels underlie the nerve impulse and because "transmitter-activated" channels mediate conduction across the synapses, channels are especially prominent components of the nervous system. Indeed, numerous toxins that organisms have evolved for shutting down the nervous systems of predators and prey (e.g., the venoms produced by spiders, scorpions, snakes, fish, bees, sea snails, and others) work by modulating ion channel conductance and/or kinetics. In addition, ion channels are key components in a wide variety of biological processes that involve rapid changes in cells, such as cardiac, skeletal, and smooth muscle contraction, epithelial transport of nutrients and ions, T-cell activation, and pancreatic beta-cell insulin release. In the search for new drugs, ion channels are a frequent target. | 1 | Biochemistry |
Although freeze fracture studies have revealed that the nodal axolemma in both the CNS and PNS is enriched in intra-membranous particles (IMPs) compared to the internode, there are some structural differences reflecting their cellular constituents. In the PNS, specialized microvilli project from the outer collar of Schwann cells and come very close to nodal axolemma of large fibers. The projections of the Schwann cells are perpendicular to the node and are radiating from the central axons. However, in the CNS, one or more of the astrocytic processes come in close vicinity of the nodes. Researchers declare that these processes stem from multi-functional astrocytes, as opposed to from a population of astrocytes dedicated to contacting the node. On the other hand, in the PNS, the basal lamina that surrounds the Schwann cells is continuous across the node. | 1 | Biochemistry |
The gene silencing effects of transfected designed siRNA are generally transient, but this difficulty can be overcome through an RNAi approach. Delivering this siRNA from DNA templates can be done through several recombinant viral vectors based on retrovirus, adeno-associated virus, adenovirus, and lentivirus. The latter is the most efficient virus that stably delivers siRNA to target cells as it can transduce nondividing cells as well as directly target the nucleus. These specific viral vectors have been synthesized to effectively facilitate siRNA that is not viable for transfection into cells. Another aspect is that in some cases synthetic viral vectors can integrate siRNA into the cell genome which allows for stable expression of siRNA and long-term gene knockdown. This technique is advantageous because it is in vivo and effective for difficult to transfect cell. However problems arise because it can trigger antiviral responses in some cell types leading to mutagenic and immunogenic effects.
This method has potential use in gene silencing of the central nervous system for the treatment of Huntington's disease. | 1 | Biochemistry |
In some molecules, torsional strain can contribute to ring strain in addition to angle strain. One example of such a molecule is cyclopropane. Cyclopropanes carbon-carbon bonds form angles of 60°, far from the preferred angle of 109.5° angle in alkanes, so angle strain contributes most to cyclopropanes ring strain. However, as shown in the Newman projection of the molecule, the hydrogen atoms are eclipsed, causing some torsional strain as well. | 7 | Physical Chemistry |
Hays test, also known as Hays sulphur powder test, is a chemical test used for detecting the presence of bile salts in urine. | 3 | Analytical Chemistry |
The ability of an engineered biomaterial to induce a physiological response that is supportive of the biomaterials function and performance is known as bioactivity. Most commonly, in bioactive glasses and bioactive ceramics this term refers to the ability of implanted materials to bond well with surrounding tissue in either osteo conductive or osseo productive roles. Bone implant materials are often designed to promote bone growth while dissolving into surrounding body fluid. Thus for many biomaterials good biocompatibility along with good strength and dissolution rates are desirable. Commonly, bioactivity of biomaterials is gauged by the surface biomineralization in which a native layer of hydroxyapatite is formed at the surface. These days, the development of clinically useful biomaterials is greatly enhanced by the advent of computational routines that can predict the molecular effects of biomaterials in a therapeutic setting based on limited in vitro' experimentation. | 1 | Biochemistry |
The UPS measures experimental molecular orbital energies for comparison with theoretical values from quantum chemistry, which was also extensively developed in the 1960s. The photoelectron spectrum of a molecule contains a series of peaks each corresponding to one valence-region molecular orbital energy level. Also, the high resolution allowed the observation of fine structure due to vibrational levels of the molecular ion, which facilitates the assignment of peaks to bonding, nonbonding or antibonding molecular orbitals.
The method was later extended to the study of solid surfaces where it is usually described as photoemission spectroscopy (PES). It is particularly sensitive to the surface region (to 10 nm depth), due to the short range of the emitted photoelectrons (compared to X-rays). It is therefore used to study adsorbed species and their binding to the surface, as well as their orientation on the surface.
A useful result from characterization of solids by UPS is the determination of the work function of the material. An example of this determination is given by Park et al. Briefly, the full width of the photoelectron spectrum (from the highest kinetic energy/lowest binding energy point to the low kinetic energy cutoff) is measured and subtracted from the photon energy of the exciting radiation, and the difference is the work function. Often, the sample is electrically biased negative to separate the low energy cutoff from the spectrometer response. | 7 | Physical Chemistry |
Butterfly wings are a new site of porphyrin synthesis and cleavage where bilin is portrayed; the expression of the lipocalin bilin-binding protein in Pieris brassicae. The function of the biliprotein during wing development is still unknown, as is the existence of an active pathway for porphyrin synthesis and cleavage in insect wings, which has been demonstrated here for the first time. The bilin-binding protein from Pieris brassicae, which was discovered to have a crystal structure, was one of the initial members of the lipocalins protein superfamily, which has since grown significantly. It is a blue pigment protein that can be clearly identified by its amino acid sequence and crystal structure. The bilin-binding protein is predominantly present in hemolymph, fat body, and epidermis in the last instar larval and in the wings of the adult insect of Pieris brassicae. Although it has recently been discovered that three swallowtail butterfly larval color patterns are correlated with the combination of bilin-binding protein and the yellow-related gene, additional physiological activities are still unknown. Normally, insect bilins are joined to proteins to create a variety of biliproteins that have been identified in Lepidoptera and other insects. The presence of the blue and yellow pigments contributes to the blue-green hue of some lepidopteran larvae. Blue pigments and yellow carotenoids are thought to work together as camouflage.
Bilin-binding protein is a member of the lipocalin family, which includes extracellular proteins with a number of molecular ligand features in common, including the ability to bind tiny, primarily lipophilic compounds like retinol. Members of the lipocalin family have mostly been classified as transport proteins, but it is clear that they also perform a range of other tasks, including retinol transport, invertebrate cryptic coloring, olfaction, and pheromone transmission. There is a lot of structural and functional variation in the lipocalin family, both within and between species. | 1 | Biochemistry |
For molecular biology in mammals, DNA demethylation causes replacement of 5-methylcytosine (5mC) in a DNA sequence by cytosine (C) (see figure of 5mC and C). DNA demethylation can occur by an active process at the site of a 5mC in a DNA sequence or, in replicating cells, by preventing addition of methyl groups to DNA so that the replicated DNA will largely have cytosine in the DNA sequence (5mC will be diluted out).
Methylated cytosine is frequently present in the linear DNA sequence where a cytosine is followed by a guanine in a 5 → 3 direction (a CpG site). In mammals, DNA methyltransferases (which add methyl groups to DNA bases) exhibit a strong sequence preference for cytosines at CpG sites. There appear to be more than 20 million CpG dinucleotides in the human genome (see genomic distribution). In mammals, on average, 70% to 80% of CpG cytosines are methylated, though the level of methylation varies with different tissues. Methylated cytosines often occur in groups or CpG islands within the promoter regions of genes, where such methylation may reduce or silence gene expression (see gene expression). Methylated cytosines in the gene body, however, are positively correlated with expression.
Almost 100% DNA demethylation occurs by a combination of passive dilution and active enzymatic removal during the reprogramming that occurs in early embryogenesis and in gametogenesis. Another large demethylation, of about 3% of all genes, can occur by active demethylation in neurons during formation of a strong memory. After surgery, demethylations are found in peripheral blood mononuclear cells at sites annotated to immune system genes. Demethylations also occur during the formation of cancers. During global DNA hypomethylation of tumor genomes, there is a minor to moderate reduction of the number of methylated cytosines (5mC) amounting to a loss of about 5% to 20% on average of the 5mC bases. | 1 | Biochemistry |
The major steps in the sulfo-ED pathway are:
* oxidation of sulfoquinovose to sulfogluconolactone (catalyzed by sulfoquinovose dehydrogenase with NAD co-factor);
* hydrolysis of sulfogluconolactone to sulfogluconate acid (catalyzed by sulfogluconolactonase with water);
* dehydration of sulfogluconic acid to 2-keto-3,6-dideoxy-6-sulfogluconate (catalyzed by sulfogluconate dehydratase);
* retro-aldol cleavage of 2-keto-3,6-dideoxy-6-sulfogluconate to give pyruvate and (S)-sulfolactaldehyde (catalyzed by sulfoketogluconate dehydrogenase with NAD co-factor);
* oxidation of sulfolactaldehyde to (S)-sulfolactate (catalyzed by sulfolactaldehyde dehydrogenase with NAD co-factor). | 1 | Biochemistry |
A reaction rate can have a negative partial order with respect to a substance. For example, the conversion of ozone (O) to oxygen follows the rate equation in an excess of oxygen. This corresponds to second order in ozone and order (−1) with respect to oxygen.
When a partial order is negative, the overall order is usually considered as undefined. In the above example, for instance, the reaction is not described as first order even though the sum of the partial orders is , because the rate equation is more complex than that of a simple first-order reaction. | 7 | Physical Chemistry |
Stationary phases can react with CDAs to form chiral stationary phases which can resolve chiral molecules. By reacting with alcohols on a silicate stationary phase, CDAs add a chiral center to the stationary phase, which allows for the separation of chiral molecules. | 4 | Stereochemistry |
At first, the study of biometals was referred to as bioinorganic chemistry. Each branch of bioinorganic chemistry studied separate, particular sub-fields of the subject. However, this led to an isolated view of each particular aspect in a biological system. This view was revised into a holistic approach of biometals in metallomics.
Metal ions in biology were studied in various specializations. In nutrition, it was to define the essentials for life; in toxicology, to define how the adverse effects of certain metal ions in biological systems and in pharmacology for their therapeutic effects. In each field, at first, they were studied and separated on a basis of concentration. In low amounts, metal ions in a biological system could perform at their optimal functionality whereas in higher concentrations, metal ions can prove fatal to biological systems. However, the concentration gradients were proved to be arbitrary as low concentrations of non-essential metals (like lithium or helium) in essential metals (like sodium or potassium) can cause an adverse effect in biological systems and vice versa.
Investigations into biometals and their effects date back to the 19th century and even further back to the 18th century with the identification of iron in blood. Zinc was identified to be essential in fungal growth of yeast as shown by Jules Raulin in 1869 yet no proof for the need of zinc in human cells was shown until the late 1930s where its presence was demonstrated in carbonic anhydrase and the 1960s where it was identified as a necessary element for humans. Since then, understanding of zinc in human biology has advanced to the point that it is considered as important as iron. Modern advancements in analytical technology have made it clear the importance of biometals in signalling pathways and the initial thoughts on the chemical basis of life. | 1 | Biochemistry |
In humans, there exist three paraologous ANT isoforms:
* SLC25A4 – found primarily in heart and skeletal muscle
* SLC25A5 – primarily expressed in fibroblasts
* SLC25A6 – primarily express in liver | 1 | Biochemistry |
Cells use glucose for energy. This normally occurs by phosphorylation from the enzyme hexokinase. However, if large amounts of glucose are present (as in diabetes mellitus), hexokinase becomes saturated and the excess glucose enters the polyol pathway when aldose reductase reduces it to sorbitol. This reaction oxidizes NADPH to NADP+. Sorbitol dehydrogenase can then oxidize sorbitol to fructose, which produces NADH from NAD+. Hexokinase can return the molecule to the glycolysis pathway by phosphorylating fructose to form fructose-6-phosphate. However, in uncontrolled diabetics that have high blood glucose - more than the glycolysis pathway can handle - the reactions mass balance ultimately favors the production of sorbitol.
Activation of the polyol pathway results in a decrease of reduced NADPH and oxidized NAD+; these are necessary co-factors in redox reactions throughout the body, and under normal conditions they are not interchangeable. The decreased concentration of these NADPH leads to decreased synthesis of reduced glutathione, nitric oxide, myo-inositol, and taurine. Myo-inositol is particularly required for the normal function of nerves. Sorbitol may also glycate nitrogens on proteins, such as collagen, and the products of these glycations are referred-to as AGEs - advanced glycation end-products. AGEs are thought to cause disease in the human body, one effect of which is mediated by RAGE (receptor for advanced glycation end-products) and the ensuing inflammatory responses induced. They are seen in the hemoglobin A1C tests performed on known diabetics to assess their levels of glucose control. | 1 | Biochemistry |
Thus it was noted that along the reaction coordinate of pericyclic processes one could have either a Möbius or a Hückel array of basis orbitals. With 4n or 4n + 2 electrons, one is then led to a prediction of allowedness or forbiddenness. Additionally, the M–H mnemonics give the MOs at part reaction. At each degeneracy there is a crossing of MOs. Thus one can determine if the highest occupied MO becomes antibonding with a forbidden reaction resulting. Finally, the M–H parity of sign inversions was utilized in the 1970 W–H treatment of allowedness and forbiddenness. The parity of sign inversions between bonds and atoms was used in place of the M–H use of atoms; the two approaches are equivalent. | 7 | Physical Chemistry |
The nephelauxetic effect is a term used in the inorganic chemistry of transition metals. It refers to a decrease in the Racah interelectronic repulsion parameter, given the symbol B, that occurs when a transition-metal free ion forms a complex with ligands. The name "nephelauxetic" comes from the Greek for cloud-expanding and was proposed by the Danish inorganic chemist C. K. Jorgensen. The presence of this effect highlights the disadvantages of crystal field theory, which treats metal-ligand interactions as purely electrostatic, since the nephelauxetic effect reveals the covalent character in the metal-ligand interaction. | 7 | Physical Chemistry |
Chargaff's rules (given by Erwin Chargaff) state that in the DNA of any species and any organism, the amount of guanine should be equal to the amount of cytosine and the amount of adenine should be equal to the amount of thymine. Further, a 1:1 stoichiometric ratio of purine and pyrimidine bases (i.e., ) should exist. This pattern is found in both strands of the DNA. They were discovered by Austrian-born chemist Erwin Chargaff in the late 1940s. | 1 | Biochemistry |
The ATP synthase isolated from bovine (Bos taurus) heart mitochondria is, in terms of biochemistry and structure, the best-characterized ATP synthase. Beef heart is used as a source for the enzyme because of the high concentration of mitochondria in cardiac muscle. Their genes have close homology to human ATP synthases.
Human genes that encode components of ATP synthases:
* ATP5A1
* ATP5B
* ATP5C1, ATP5D, ATP5E, ATP5F1, ATP5G1, ATP5G2, ATP5G3, ATP5H, ATP5I, ATP5J, ATP5J2, ATP5L, ATP5O
* MT-ATP6, MT-ATP8 | 5 | Photochemistry |
The toxicity of phosphonates to organisms living in water is low. Reported values for 48-hour LC values for fish are between 0.1 and 1.1 mM. Also the bioconcentration factor for fish is very low. | 0 | Organic Chemistry |
The preparation of certified reference materials is described in general in ISO Guide 17034 and in more detail in ISO Guide 35. Preparation of biological reference standards is described in WHO Guidance. General steps required in production of a certified reference material typically include:
* Collection or synthesis of material
* Sample preparation (including homogenization, stabilization, bottling etc.)
* Homogeneity testing
* Stability assessment
* Value assignment ("characterization" in ISO REMCO terms).
In addition it may be important to assess the commutability of a reference material; this is especially important for biological materials. | 3 | Analytical Chemistry |
The mitochondrial intermembrane space is the space between the outer membrane and the inner membrane. It is also known as perimitochondrial space. Because the outer membrane is freely permeable to small molecules, the concentrations of small molecules, such as ions and sugars, in the intermembrane space is the same as in the cytosol. However, large proteins must have a specific signaling sequence to be transported across the outer membrane, so the protein composition of this space is different from the protein composition of the cytosol. One protein that is localized to the intermembrane space in this way is cytochrome c. | 1 | Biochemistry |
Isocyanide dichlorides are organic compounds containing the RN=CCl functional group. Classically they are obtained by chlorination of isocyanides. Phenylcarbylamine chloride is a well-characterized example. | 0 | Organic Chemistry |
The Kröhnke methodology has also been utilized to generate a number of interesting metal-binding ligands since polypyridyl complexes such as bipyridine (bipy) have been used extensively as ligands. The Kröhnke synthesis was used to prepare a family of tetrahydroquinoline-based N, S-type ligands. 2-thiophenylacetophenone (36) was reacted with iodine gas and pyridine in quantitative yield to generate acylmethylpyridinium iodide 37. Reaction with a chiral cyclic α, β-unsaturated ketone derived from 2-(+)-carene yielded the desired N, S-type ligand 38.
Novel, chiral P, N-ligands have been prepared using the Kröhnke method. α-pyridinium acyl ketone salt 39 was cyclized with pinocarvone derivative 40 to generate pyridine 41. The benzylic position of 41 was methylated and subsequent SnAr reaction with potassium diphenylphosphide to generate ligand 42.
The Kröhnke reaction has also enjoyed applicability to the synthesis of a number of biologically active compounds in addition to ones cataloged in combinatorial studies. Kelly and co-workers developed a route to cyclo-2,2′:4′,4′′:2′′,2′′′:4′′′,4′′′′:2′′′′,2′′′′′:4′′′′′,4-sexipyridine utilizing the Kröhnke reactions as the key macrocyclization step. Polypyridine complex 43 was treated with N-Bromosuccinimide in wet tetrahydrofuran followed by pyridine to generate the acylmethylpyridinium salt 44 which can then undergo the macrocyclization under standard conditions to yield the desired product 45. The Kröhnke method in this synthesis was crucial due to the failure of other cyclization techniques such as the Glaser coupling or Ullmann coupling.
Another use of the Kröhnke pyridine synthesis was the generation of a number of 2,4,6-trisubstituted pyridines that were investigated as potential topoisomerase 1 inhibitors. 2-acetylthiophene (46) was treated with iodine and pyridine to generate α-pyridinium acyl ketone 47. Reaction with Michael acceptor 48 under standard conditions yielded functionalized pyridine 49 in 60% overall yield.
Ultimately, the Kröhnke pyridine synthesis offers a facile and straightforward approach to the synthesis of a wide breadth of functionalized pyridines and poly aryl systems. The Kröhnke methodology has been applied to a number of strategies towards interesting ligands and biologically relevant molecules. Additionally, the Kröhnke reaction and its variations offer a number of advantages than alternative methods to pyridine synthesis ranging from one-pot, organic solvent-free variations to high atom economy. | 0 | Organic Chemistry |
In genetics, a regulator gene, regulator, or regulatory gene is a gene involved in controlling the expression of one or more other genes. Regulatory sequences, which encode regulatory genes, are often at the five prime end (5) to the start site of transcription of the gene they regulate. In addition, these sequences can also be found at the three prime end (3) to the transcription start site. In both cases, whether the regulatory sequence occurs before (5) or after (3) the gene it regulates, the sequence is often many kilobases away from the transcription start site. A regulator gene may encode a protein, or it may work at the level of RNA, as in the case of genes encoding microRNAs. An example of a regulator gene is a gene that codes for a repressor protein that inhibits the activity of an operator (a gene which binds repressor proteins thus inhibiting the translation of RNA to protein via RNA polymerase).
In prokaryotes, regulator genes often code for repressor proteins. Repressor proteins bind to operators or promoters, preventing RNA polymerase from transcribing RNA. They are usually constantly expressed so the cell always has a supply of repressor molecules on hand. Inducers cause repressor proteins to change shape or otherwise become unable to bind DNA, allowing RNA polymerase to continue transcription.
Regulator genes can be located within an operon, adjacent to it, or far away from it.
Other regulatory genes code for activator proteins. An activator binds to a site on the DNA molecule and causes an increase in transcription of a nearby gene. In prokaryotes, a well-known activator protein is the catabolite activator protein (CAP), involved in positive control of the lac operon.
In the regulation of gene expression, studied in evolutionary developmental biology (evo-devo), both activators and repressors play important roles.
Regulatory genes can also be described as positive or negative regulators, based on the environmental conditions that surround the cell. Positive regulators are regulatory elements that permit RNA polymerase binding to the promoter region, thus allowing transcription to occur. In terms of the lac operon, the positive regulator would be the CRP-cAMP complex that must be bound close to the site of the start of transcription of the lac genes. The binding of this positive regulator allows RNA polymerase to bind successfully to the promoter of the lac gene sequence which advances the transcription of lac genes; lac Z, lac Y, and lac A. Negative regulators are regulatory elements which obstruct the binding of RNA polymerase to the promoter region, thus repressing transcription. In terms of the lac operon, the negative regulator would be the lac repressor which binds to the promoter in the same site that RNA polymerase normally binds. The binding of the lac repressor to RNA polymerase's binding site inhibits the transcription of the lac genes. Only when a corepressor is bound to the lac repressor will the binding site be free for RNA polymerase to carry out transcription of the lac genes. | 1 | Biochemistry |
The advantages of supercritical fluid extraction (compared with liquid extraction) are that it is relatively rapid because of the low viscosities and high diffusivities associated with supercritical fluids. Alternative solvents to supercritical fluids may be poisonous, flammable or an environmental hazard to a much larger extent than water or carbon dioxide are. The extraction can be selective to some extent by controlling the density of the medium, and the extracted material is easily recovered by simply depressurizing, allowing the supercritical fluid to return to gas phase and evaporate leaving little or no solvent residues. Carbon dioxide is the most common supercritical solvent. It is used on a large scale for the decaffeination of green coffee beans, the extraction of hops for beer production, and the production of essential oils and pharmaceutical products from plants. A few laboratory test methods include the use of supercritical fluid extraction as an extraction method instead of using traditional solvents. | 7 | Physical Chemistry |
If chloride ions have penetrated beyond the surface more rigorous treatment is required.
This typically involves soaking in acetone to displace any water in the specimen. Then soaking in a benzotriazole (BTA)–ethanol solution to chelate the copper and make it unreactive. Pits and holes may be filled with zinc powder, which is then painted over with shellac coloured to look like the specimen. | 8 | Metallurgy |
The BBOC furnace is a cylindrical steel vessel with a protective internal lining of refractory bricks. It is mounted on a tilting frame that allows it to be held at different angles at different stages of its operating cycle (see Figure 2). A hood is fixed over the top of the furnace, providing a seal that prevents lead and other fumes from escaping during the furnace’s operation (see Figure 1).
The key feature of the BBOC is the shrouded lance that passes through the refractory bricks at the bottom of the furnace. This lance allows oxygen to be injected directly into the molten metal contained in the furnace, away from the refractory lining. Doing so allows the region of high reaction rates to be removed from the vicinity of the lining, thus reducing its wear.
By injecting the oxygen directly into the bath, rather than blowing it on top (as in the case of the reverberatory cupellation furnace or top-blown rotary converters), the oxygen transfer efficiency is not impeded by the presence of the slag layer. It results in an oxygen utilization efficiency approaching 100%.
The lack of interference in the oxygen transfer by the slag layer has a couple of key benefits. The first is that the increased certainty in the estimation of oxygen utilization efficiency means that it is easier to calculate the endpoint of the process, making process control much easier. The second is that a thicker slag layer can be tolerated (because the oxygen does not have to pass through it), and this means that the losses of silver to the slag are reduced (because it is the silver at the interface between the metal and slag that becomes entrained during the removal of the slag and the thicker the slag layer, the smaller the silver content of the removed slag). BRM reported a decrease in the silver content of the BBOC slag compared to the reverberatory furnace slag of 50%.
BRM found that the reaction rate of the BBOC was 10–20 times that of its reverberatory cupellation furnace.
Refractory wear in the BBOC is largely confined to the slag line, at the top of the metal, where attack by litharge (lead oxide) is greatest. This is combated by using fused-grain, direct-bonded magnesite-chrome bricks to line the inside of the furnace shell. | 8 | Metallurgy |
Transition state theory requires a value of the transmission coefficient, called in that theory. This value is often taken to be unity (i.e., the species passing through the transition state always proceed directly to products and never revert to reactants and ). To avoid specifying a value of , the rate constant can be compared to the value of the rate constant at some fixed reference temperature (i.e., ) which eliminates the factor in the resulting expression if one assumes that the transmission coefficient is independent of temperature. | 7 | Physical Chemistry |
The specific molecular mechanism of action of the ywIE protein is currently unknown. However, YwIE is believed to dephosphorylate phosphoarginine residues using a concerted, 2-step process via SN2 reactions. Step 1 involves a nucleophilic attack of Cys7 on the phosphorus atom of the phosphoric group. Then a thiophosphate intermediate is formed. In the second step, a phosphorylation-enzyme intermediate is hydrolyzed following the deprotonation of a water molecule by Asp118. Fuhrmann et al. (2016) believe that Asp118 likely promotes the reaction through the stabilization of the positive charge of the amino group via electrostatic interaction.
Sample general dephosphorylation reaction equation: | 1 | Biochemistry |
In kinetic theory of gases, the mean free path is the average distance traveled by a molecule, or a number of molecules per volume, before they make their first collision. Let be the collision cross section of one molecule colliding with another. As in the previous section, the number density is defined as the number of molecules per (extensive) volume, or . The collision cross section per volume or collision cross section density is , and it is related to the mean free path by
Notice that the unit of the collision cross section per volume is reciprocal of length. | 7 | Physical Chemistry |
When ethanol is present, PLD substitutes ethanol for water and covalently attaching the alcohol as the head group of the phospholipid; hence the name phosphatidylethanol. Normally PLD incorporates water to generate phosphatidic acid (PA); the process is termed transphosphatidylation. PLD continues to generate PA in the presence of ethanol and while PEth is generated and the effects of ethanol transphosphatidlyation are through the generation of the unnatural lipid not depletion of PA. | 1 | Biochemistry |
Plants contain CaM-related proteins (CMLs) apart from the typical CaM proteins. The CMLs have about 15% amino acid similarity with the typical CaMs. Arabidopsis thaliana contains about 50 different CML genes which leads to the question of what purpose these diverse ranges of proteins serve in the cellular function. All plant species exhibit this diversity in the CML genes. The different CaMs and CMLs differ in their affinity to bind and activate the CaM-regulated enzymes in vivo. The CaM or CMLs are also found to be located in different organelle compartments. | 1 | Biochemistry |
Isocyanides form coordination complexes with most transition metals. They behave as electron-rich analogues of carbon monoxide. For example tert-butyl isocyanide forms , which is analogous to . Although structurally similar, the analogous carbonyls differ in several ways, mainly because t-BuNC is a better donor ligand than CO. Thus, is easily protonated, whereas its counterpart is not. | 0 | Organic Chemistry |
Staircase voltammetry is a derivative of linear sweep voltammetry. In linear sweep voltammetry the current at a working electrode is measured while the potential between the working electrode and a reference electrode is swept linearly in time. Oxidation or reduction of species is registered as a peak or trough in the current signal at the potential at which the species begins to be oxidized or reduced.
In staircase voltammetry, the potential sweep is a series of stair steps. The current is measured at the end of each potential change, right before the next, so that the contribution to the current signal from the capacitive charging current is reduced. | 3 | Analytical Chemistry |
In organic chemistry, an oxime is an organic compound belonging to the imines, with the general formula , where R is an organic side-chain and R' may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted oximes form a closely related family of compounds. Amidoximes are oximes of amides () with general structure .
Oximes are usually generated by the reaction of hydroxylamine with aldehydes () or ketones (). The term oxime dates back to the 19th century, a combination of the words oxygen and imine. | 0 | Organic Chemistry |
EpoRs role in lineage commitment is currently unclear. EpoR expression can extend as far back as the hematopoietic stem cell compartment. It is unknown whether EpoR signaling plays a permissive (i.e. induces only survival) or an instructive (i.e. upregulates erythroid markers to lock progenitors to a predetermined differentiation path) role in early, multipotent progenitors in order to produce sufficient erythroblast numbers. Current publications in the field suggest that it is primarily permissive. The generation of BFU-e and CFU-e progenitors was shown to be normal in rodent embryos knocked out for either Epo or EpoR. An argument against such lack of requirement is that in response to Epo or hypoxic stress, the number of early erythroid stages, the BFU-e and CFU-e, increases dramatically. However, it is unclear if it is an instructive signal or, again, a permissive signal. One additional point is that signaling pathways activated by the EpoR are common to many other receptors; replacing EpoR with prolactin receptor supports erythroid survival and differentiation in vitro. Together, these data suggest that commitment to erythroid lineage likely does not happen due to EpoRs as-yet-unknown instructive function, but possibly due to its role in survival at the multipotent progenitor stages. | 1 | Biochemistry |
(R)-2-Methyl-CBS-oxazaborolidine is an organoboron catalyst that is used in organic synthesis. This catalyst, developed by Itsuno and Elias James Corey, is generated by heating (R)-(+)-2-(diphenylhydroxymethyl) pyrrolidine along with trimethylboroxine or methylboronic acid. It is an excellent tool for the synthesis of alcohols in high enantiomeric ratio. Generally, 2-10 mol% of this catalyst is used along with borane-tetrahydrofuran (THF), borane-dimethylsulfide, borane-N,N-diethylaniline, or diborane as the borane source. Enantioselective reduction using chiral oxazaborolidine catalysts has been used in the synthesis of commercial drugs such as ezetimibe and aprepitant. | 0 | Organic Chemistry |
The anhydroglucose unit (AGU) refers to a single sugar molecule in a polymer. Each AGU is reduced to its functional groups, 3 hydroxyl groups per AGU.
Carbohydrate AGU:
Cellulose AGU: | 0 | Organic Chemistry |
The chelate effect is the greater affinity of chelating ligands for a metal ion than that of similar nonchelating (monodentate) ligands for the same metal.
The thermodynamic principles underpinning the chelate effect are illustrated by the contrasting affinities of copper(II) for ethylenediamine (en) vs. methylamine.
In () the ethylenediamine forms a chelate complex with the copper ion. Chelation results in the formation of a five-membered CuCN ring. In () the bidentate ligand is replaced by two monodentate methylamine ligands of approximately the same donor power, indicating that the Cu–N bonds are approximately the same in the two reactions.
The thermodynamic approach to describing the chelate effect considers the equilibrium constant for the reaction: the larger the equilibrium constant, the higher the concentration of the complex.
Electrical charges have been omitted for simplicity of notation. The square brackets indicate concentration, and the subscripts to the stability constants, β, indicate the stoichiometry of the complex. When the analytical concentration of methylamine is twice that of ethylenediamine and the concentration of copper is the same in both reactions, the concentration [Cu(en)] is much higher than the concentration [Cu(MeNH)] because β ≫ β.
An equilibrium constant, K, is related to the standard Gibbs free energy, by
where R is the gas constant and T is the temperature in kelvins. is the standard enthalpy change of the reaction and is the standard entropy change.
Since the enthalpy should be approximately the same for the two reactions, the difference between the two stability constants is due to the effects of entropy. In equation () there are two particles on the left and one on the right, whereas in equation () there are three particles on the left and one on the right. This difference means that less entropy of disorder is lost when the chelate complex is formed with bidentate ligand than when the complex with monodentate ligands is formed. This is one of the factors contributing to the entropy difference. Other factors include solvation changes and ring formation. Some experimental data to illustrate the effect are shown in the following table.
These data confirm that the enthalpy changes are approximately equal for the two reactions and that the main reason for the greater stability of the chelate complex is the entropy term, which is much less unfavorable. In general it is difficult to account precisely for thermodynamic values in terms of changes in solution at the molecular level, but it is clear that the chelate effect is predominantly an effect of entropy.
Other explanations, including that of Schwarzenbach, are discussed in Greenwood and Earnshaw (loc.cit). | 7 | Physical Chemistry |
The positive feedback of the rising phase slows and comes to a halt as the sodium ion channels become maximally open. At the peak of the action potential, the sodium permeability is maximized and the membrane voltage V is nearly equal to the sodium equilibrium voltage E. However, the same raised voltage that opened the sodium channels initially also slowly shuts them off, by closing their pores; the sodium channels become inactivated. This lowers the membranes permeability to sodium relative to potassium, driving the membrane voltage back towards the resting value. At the same time, the raised voltage opens voltage-sensitive potassium channels; the increase in the membranes potassium permeability drives V towards E. Combined, these changes in sodium and potassium permeability cause V to drop quickly, repolarizing the membrane and producing the "falling phase" of the action potential. | 7 | Physical Chemistry |
Formiminoglutamic acid (FIGLU; conjugate base, formiminoglutamate) is an intermediate in the catabolism of L-histidine to L-glutamic acid. It thus is also a biomarker for intracellular levels of folate. The FIGLU test is used to identify vitamin B₁₂ deficiency, folate deficiency, and liver failure or liver disease. It is elevated with folate trapping, where it is accompanied by decreased methylmalonic acid, increased folate and a decrease in homocysteine. | 1 | Biochemistry |
Completed genome sequences allow every open reading frame (ORF), the part of a gene that is likely to contain the sequence for the messenger RNA and protein, to be cloned and expressed as protein. These proteins are then purified and crystallized, and then subjected to one of two types of structure determination: X-ray crystallography and nuclear magnetic resonance (NMR). The whole genome sequence allows for the design of every primer required in order to amplify all of the ORFs, clone them into bacteria, and then express them. By using a whole-genome approach to this traditional method of protein structure determination, all of the proteins encoded by the genome can be expressed at once. This approach allows for the structural determination of every protein that is encoded by the genome. | 1 | Biochemistry |
Batesian mimicry of ants appears to have evolved in certain plants, as a visual anti-herbivory strategy, analogous to a herbivorous insects mimicking a well-defended insect to deter predators. Passiflora flowers of at least 22 species, such as P. incarnata', have dark dots and stripes on their flowers thought to serve this purpose. | 1 | Biochemistry |
Captopril's main uses are based on its vasodilation and inhibition of some renal function activities. These benefits are most clearly seen in:
* Hypertension
* Cardiac conditions such as congestive heart failure and after myocardial infarction
* Preservation of kidney function in diabetic nephropathy.
Additionally, it has shown mood-elevating properties in some patients. This is consistent with the observation that animal screening models indicate putative antidepressant activity for this compound, although one study has been negative. Formal clinical trials in depressed patients have not been reported.
It has also been investigated for use in the treatment of cancer. Captopril stereoisomers were also reported to inhibit some metallo-β-lactamases. | 4 | Stereochemistry |
Brigitte Zanda was a student at the École normale supérieure de jeunes filles from 1978 to 1982. She continued her education at the École nationale supérieure des mines de Paris where she was a research fellow from 1982 to 1984. From 1984 to 1989, she worked as a research engineer at the Institut d'astrophysique de Paris, affiliated with the CNRS.
She defended her doctoral thesis in fundamental geochemistry, entitled Les réactions nucléaires induites par le rayonnement cosmique dans les météorites de fer, at the University of Paris VII in 1988, under the supervision of Jean Audouze. A year later, Brigitte Zanda became an associate professor at the National Museum of Natural History, where she was responsible for the conservation of the national meteorite collection.
As part of her professional activities at the Museum, Brigitte Zanda is involved in the dissemination of scientific culture. She also works in the scientific direction of the Astronomy Festival of Fleurance and is responsible for the scientific organization of the AstroNomades festival. She also co-pilots the ANR FRIPON project and directs the / project "Vigie-Ciel". | 9 | Geochemistry |
Pirkle's alcohol is an off-white, crystalline solid that is stable at room temperature when protected from light and oxygen. This chiral molecule is typically used, in nonracemic form, as a chiral shift reagent in nuclear magnetic resonance spectroscopy, in order to simultaneously determine absolute configuration and enantiomeric purity of other chiral molecules. The molecule is named after William H. Pirkle, Professor of Chemistry at the University of Illinois whose group reported its synthesis and its application as a chiral shift reagent. | 4 | Stereochemistry |
The phenolic biosynthetic and metabolic pathways and enzymes can be studied by means of transgenesis of genes. The Arabidopsis regulatory gene for production of Anthocyanin Pigment 1 (AtPAP1) can be expressed in other plant species. | 0 | Organic Chemistry |
The diffraction from a crystalline material, and thus the intensity of the diffracted beam, changes with the type and number of atoms inside the crystal unit cell. This fact is quantitatively expressed by the structure factor. Different materials have different structure factors, and similarly for different phases of the same material (e.g. for materials crystallizing in several different space groups). In samples composed of a mixture of materials/phases in spatially adjacent domains, the geometry of these domains can be resolved by topography. This is true, for example, also for twinned crystals, ferroelectric domains, and many others. | 3 | Analytical Chemistry |
Several sets of data can be collected during the experimental process of smelting including fuel consumption rates, the effects of variation in furnace airflow,
temperatures, production time, and chemical composition. | 8 | Metallurgy |
Thomson scattering is the elastic scattering of electromagnetic radiation by a free charged particle, as described by classical electromagnetism. It is the low-energy limit of Compton scattering: the particle's kinetic energy and photon frequency do not change as a result of the scattering. This limit is valid as long as the photon energy is much smaller than the mass energy of the particle: , or equivalently, if the wavelength of the light is much greater than the Compton wavelength of the particle (e.g., for electrons, longer wavelengths than hard x-rays). | 7 | Physical Chemistry |
Of all aldehydes, formaldehyde is produced on the largest scale, about . It is mainly used in the production of resins when combined with urea, melamine, and phenol (e.g., Bakelite). It is a precursor to methylene diphenyl diisocyanate ("MDI"), a precursor to polyurethanes. The second main aldehyde is butyraldehyde, of which about are prepared by hydroformylation. It is the principal precursor to 2-ethylhexanol, which is used as a plasticizer. Acetaldehyde once was a dominating product, but production levels have declined to less than because it mainly served as a precursor to acetic acid, which is now prepared by carbonylation of methanol. Many other aldehydes find commercial applications, often as precursors to alcohols, the so-called oxo alcohols, which are used in detergents. Some aldehydes are produced only on a small scale (less than 1000 tons per year) and are used as ingredients in flavours and perfumes such as Chanel No. 5. These include cinnamaldehyde and its derivatives, citral, and lilial. | 0 | Organic Chemistry |
The Prefil method is similar to PoDFA but, in addition to the metallographic analysis, Prefil provides also an immediate feedback on metal cleanliness from the metal flowrate through the filter. Because everything about the filtration is well controlled (pressure, metal temperature, ...), the only parameter affecting the filtration speed is the inclusion content. One can determine the cleanliness level from the filtration curve (weight of metal filtered as a function of time). | 8 | Metallurgy |
Thermal ellipsoids, more formally termed atomic displacement parameters or anisotropic displacement parameters, are ellipsoids used in crystallography to indicate the magnitudes and directions of the thermal vibration of atoms in crystal structures. Since the vibrations are usually anisotropic (different magnitudes in different directions in space), an ellipsoid is a convenient way of visualising the vibration and therefore the symmetry and time averaged position of an atom in a crystal. Their theoretical framework was introduced by D. W. J. Cruickshank in 1956 and the concept was popularized through the program ORTEP (Oak Ridge Thermal-Ellipsoid Plot Program), first released in 1965.
Thermal ellipsoids can be defined by a tensor, a mathematical object which allows the definition of magnitude and orientation of vibration with respect to three mutually perpendicular axes. The three principal axes of the thermal vibration of an atom are denoted , , and , and the corresponding thermal ellipsoid is based on these axes. The size of the ellipsoid is scaled so that it occupies the space in which there is a particular probability of finding the electron density of the atom. The particular probability is usually 50%. | 3 | Analytical Chemistry |
Materials can transmit (e.g. glass) or reflect (e.g. metals) visible light.
Many materials will transmit some wavelengths while blocking others. For example, window glass is transparent to visible light, but much less so to most of the frequencies of ultraviolet light that cause sunburn. This property is used for frequency-selective optical filters, which can alter the color of incident light.
For some purposes, both the optical and mechanical properties of a material can be of interest. For example, the sensors on an infrared homing ("heat-seeking") missile must be protected by a cover that is transparent to infrared radiation. The current material of choice for high-speed infrared-guided missile domes is single-crystal sapphire. The optical transmission of sapphire does not actually extend to cover the entire mid-infrared range (3–5 µm), but starts to drop off at wavelengths greater than approximately 4.5 µm at room temperature. While the strength of sapphire is better than that of other available mid-range infrared dome materials at room temperature, it weakens above 600 °C. A long-standing trade-off exists between optical bandpass and mechanical durability; new materials such as transparent ceramics or optical nanocomposites may provide improved performance.
Guided lightwave transmission involves the field of fiber optics and the ability of certain glasses to transmit, simultaneously and with low loss of intensity, a range of frequencies (multi-mode optical waveguides) with little interference between them. Optical waveguides are used as components in integrated optical circuits or as the transmission medium in optical communication systems. | 7 | Physical Chemistry |
The IGSN was developed as part of SESAR with the support of the National Science Foundation at the Lamont–Doherty Earth Observatory. The project was initiated and managed by the Geoinformatics for Geochemistry Program under the direction of Kerstin Lehnert to address data curation obstacles such as different samples that share the same name, and samples that are renamed as they move between laboratories and thus generating analyses that are published under different aliases. As a result, metadata that ensure unique identification are often missing and this causes irritation for future reuse of data from a sample or the sample itself. Sample databases, such as the SESAR database, are designed to address these issues.
At a workshop hosted at the San Diego Supercomputer Center in 2011, a group of experts met to discuss how to transition the IGSN project into a sustainable infrastructure. The group recommended opening the system to other IGSN registration agents, making it international and transferring the operation and governance of the IGSN to an independent body. This recommendation led to the foundation of the International Geo Sample Implementation Organization e.V. (IGSN e.V.) and the founding event was held at the American Geophysical Union Fall Meeting 2011 in San Francisco, California. The IGSN e.V. is an incorporated organisation under German law and is registered at the Magistrates Court in Potsdam, Germany.
Membership in the organisation is open only to institutions, not to individuals. At present, IGSN e.V. has 16 full members.
In 2018, the Alfred P. Sloan Foundation awarded Columbia University's Lamont–Doherty Earth Observatory a grant for a project to modernise the IGSN business model and system architecture. The funding from the Sloan Foundation will support a series of workshops, at which international experts will come together to redesign the IGSN system and its management to allow researchers world-wide use the IGSN with confidence.
In September 2021, IGSN e.V. and DataCite entered a partnership under which DataCite will provide the IGSN ID registration services and supporting technology to enable the ongoing sustainability of the IGSN PID infrastructure. The IGSN e.V. will facilitate a Community of Communities to promote and support new research and innovation for standard methods of identifying, citing, and locating physical samples. The partnership allows IGSN to leverage DataCite DOI registration services and to focus community efforts on advocacy and expanding the global samples ecosystem.
IGSN and DataCite have a common purpose, and a close relationship in the future will provide mutual benefit to our shared vision of connecting research and identifying knowledge. The partnership brings years of experience across our organizations and communities to scale sample community engagement, develop sample identifier practice standards, and increase adoption globally. In a study published 2023 by [https://www.knowledge-exchange.info/ Knowledge Exchange] it is highlighted that IGSN IDs point to physical objects instead of intellectual property or outcomes (as DOIs mostly do) or their creators. Besides, the report emphasized that the service itself and its organisational framework were developed bottom-up in a sheer community-based effort. | 9 | Geochemistry |
Although not a strictly living form of polymerization catalytic chain transfer polymerization must be mentioned as it figures significantly in the development of later forms of living free radical polymerization.
Discovered in the late 1970s in the USSR it was found that cobalt porphyrins were able to reduce the molecular weight during polymerization of methacrylates.
Later investigations showed that the cobalt glyoxime complexes were as effective as the porphyrin catalysts and also less oxygen sensitive. Due to their lower oxygen sensitivity these catalysts have been investigated much more thoroughly than the porphyrin catalysts.
The major products of catalytic chain transfer polymerization are vinyl-terminated polymer chains. One of the major drawbacks of the process is that catalytic chain transfer polymerization does not produce macromonomers but instead produces addition fragmentation agents. When a growing polymer chain reacts with the addition fragmentation agent the radical end-group attacks the vinyl bond and forms a bond. However, the resulting product is so hindered that the species undergoes fragmentation, leading eventually to telechelic species.
These addition fragmentation chain transfer agents do form graft copolymers with styrenic and acrylate species however they do so by first forming block copolymers and then incorporating these block copolymers into the main polymer backbone.
While high yields of macromonomers are possible with methacrylate monomers, low yields are obtained when using catalytic chain transfer agents during the polymerization of acrylate and stryenic monomers. This has been seen to be due to the interaction of the radical centre with the catalyst during these polymerization reactions.
The reversible reaction of the cobalt macrocycle with the growing radical is known as cobalt carbon bonding and in some cases leads to living polymerization reactions. | 7 | Physical Chemistry |
Hydrocyanation is an industrial method for producing nitriles from hydrogen cyanide and alkenes. The process requires homogeneous catalysts. An example of hydrocyanation is the production of adiponitrile, a precursor to nylon-6,6 from 1,3-butadiene: | 0 | Organic Chemistry |
* Biology 12: a student resource, R. Prior.
* Lehmann, M. (2018). Endocrine and physiological regulation of neutral fat storage in Drosophila. Molecular and Cellular Endocrinology, 461, 165–177.
* Christoph Heier, Ronald P Kühnlein, Triacylglycerol Metabolism in Drosophila melanogaster, Genetics, Volume 210, Issue 4, 1 December 2018, Pages 1163–1184, | 1 | Biochemistry |
The process of detonation spraying was first developed in 1955 by H.B. Sargent, R.M. Poorman and H. Lamprey and was subsequently patented. It was first made commercially available as the D-Gun Process by Union Carbide in the same year. It was further developed in the 1960s by the Paton Institute in Kiev (Ukraine), into a technology that is still currently commercially available in the US by Demeton Technologies (West Babylon). | 8 | Metallurgy |
Jinhae Bay is the first of Koreas two major dead zones, hypoxia was first reported in Jinhae Bay in September of 1974. In 2011, a joint study was done to observe and record causes, effects, and what can be done about Koreas hypoxic zones. It was discovered that Jinhae Bay exhibits a seasonal dead zone from early June to late September. This dead zone is caused by "domestic and land use waste and thermal stratification". Jinhae Bay experiences hypoxia largely at the bottom of its bay. The ratios of Phosphorous to Nitrogen is imbalanced at the bottom, where its otherwise balanced at the top, with the exception of early June to late September where the Bay is experiencing eutrophication as a whole. The effects of Jinhae Bay's hypoxia is seen in the marine system surrounding Korea, with a loss of biological diversity, particularly of the calcareous shelled organisms. | 9 | Geochemistry |
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