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Maleic hydrazide, often known by the brand name Fazor is a plant growth regulator that reduces growth through preventing cell division but not cell enlargement. It is applied to the foliage of potato, onion, garlic and carrot crops to prevent sprouting during storage. It can also be used to control volunteer potatoes that are left in the field during harvesting. It was first identified in the 1940s but was not used commercially in the United Kingdom until 1984. The banning of chlorpropham as a sprout suppressant in 2019 has led renewed interest in how maleic hydrazide can be used in potatoes. | 0 | Organic Chemistry |
Given the definition of the elasticity coefficient in terms of a partial derivative, it is possible, for example, to determine the elasticity of an arbitrary rate law by differentiating the rate law by the independent variable and scaling. For example, the elasticity coefficient for a mass-action rate law such as:
where is the reaction rate, the reaction rate constant, is the ith chemical species involved in the reaction and the ith reaction order, then the elasticity, can be obtained by differentiating the rate law with respect to and scaling:
That is, the elasticity for a mass-action rate law is equal to the order of reaction of the species.
For example the elasticity of A in the reaction where the rate of reaction is given by: , the elasticity can be evaluated using:
Elasticities can also be derived for more complex rate laws such as the Michaelis–Menten rate law. If
then it can be easily shown than
This equation illustrates the idea that elasticities need not be constants (as with mass-action laws) but can be a function of the reactant concentration. In this case, the elasticity approaches unity at low reactant concentration (s) and zero at high reactant concentration.
For the reversible Michaelis–Menten rate law:
where is the forward , the forward , the equilibrium constant and the reverse , two elasticity coefficients can be calculated, one with respect to substrate, S, and another with respect to product, P. Thus:
where is the mass-action ratio, that is . Note that when p = 0, the equations reduce to the case for the irreversible Michaelis–Menten law.
As a final example, consider the Hill equation:
where n is the Hill coefficient and is the half-saturation coefficient (cf. Michaelis–Menten rate law), then the elasticity coefficient is given by:
Note that at low concentrations of S the elasticity approaches n. At high concentrations of S the elasticity approaches zero. This means the elasticity is bounded between zero and the Hill coefficient. | 7 | Physical Chemistry |
Many standard states are non-physical states, often referred to as "hypothetical states". Nevertheless, their thermodynamic properties are well-defined, usually by an extrapolation from some limiting condition, such as zero pressure or zero concentration, to a specified condition (usually unit concentration or pressure) using an ideal extrapolating function, such as ideal solution or ideal gas behavior, or by empirical measurements. Strictly speaking, temperature is not part of the definition of a standard state. However, most tables of thermodynamic quantities are compiled at specific temperatures, most commonly or, somewhat less commonly, . | 7 | Physical Chemistry |
RNA-induced transcriptional silencing (RITS) is a form of RNA interference by which short RNA molecules – such as small interfering RNA (siRNA) – trigger the downregulation of transcription of a particular gene or genomic region. This is usually accomplished by posttranslational modification of histone tails (e.g. methylation of lysine 9 of histone H3) which target the genomic region for heterochromatin formation. The protein complex that binds to siRNAs and interacts with the methylated lysine 9 residue of histones H3 (H3K9me2) is the RITS complex.
RITS was discovered in the fission yeast Schizosaccharomyces pombe, and has been shown to be involved in the initiation and spreading of heterochromatin in the mating-type region and in centromere formation. The RITS complex in S. pombe contains at least a piwi domain-containing RNase H-like argonaute, a chromodomain protein Chp1, and an argonaute interacting protein Tas3 which can also bind to Chp1, while heterochromatin formation has been shown to require at least argonaute and an RNA-dependent RNA polymerase. Loss of these genes in S. pombe results in abnormal heterochromatin organization and impairment of centromere function, resulting in lagging chromosomes on anaphase during cell division. | 1 | Biochemistry |
The reflection point groups, defined by 1 to 3 mirror planes, can also be given by their Coxeter group and related polyhedra. The [3,3] group can be doubled, written as , mapping the first and last mirrors onto each other, doubling the symmetry to 48, and isomorphic to the [4,3] group. | 4 | Stereochemistry |
Fish exhibit a wide range of tactics to counteract aquatic hypoxia, but when escape from the hypoxic stress is not possible, maintaining oxygen extraction and delivery becomes an essential component to survival. Except for the Antarctic ice fish that does not, most fish use hemoglobin (Hb) within their red blood cells to bind chemically and deliver 95% of the oxygen extracted from the environment to the working tissues. Maintaining oxygen extraction and delivery to the tissues allows continued activity under hypoxic stress and is in part determined by modifications in two different blood parameters: hematocrit and the binding properties of hemoglobin. | 9 | Geochemistry |
The basic property of fluorescence are extensively used, such as a marker of labelled components in cells (fluorescence microscopy) or as an indicator in solution (Fluorescence spectroscopy), but other additional properties, not found with radioactivity, make it even more extensively used. | 1 | Biochemistry |
EU legislation has been approved banning the use of highly toxic pesticides including those that are carcinogenic, mutagenic or toxic to reproduction, those that are endocrine-disrupting, and those that are persistent, bioaccumulative and toxic (PBT) or very persistent and very bioaccumulative (vPvB) and measures have been approved to improve the general safety of pesticides across all EU member states.
In 2023 The Environment Committee of European Parliament approved a decision aiming to reduce pesticide use by 50% (the most hazardous by 65%) by the year 2030 and ensure sustainable use of pesticides (for example use them only as a last resort). The decision also includes measures for providing farmers with alternatives. | 2 | Environmental Chemistry |
Due to the similarity with polyketide synthases (PKS), many secondary metabolites are, in fact, fusions of NRPs and polyketides. In essence, this occurs when PK modules follow NRP modules, and vice versa. Although there is high degree of similarity between the Carrier (PCP/ACP) domains of both types of synthetases, the mechanism of condensation is different from a chemical standpoint:
* PKS, carbon-carbon bond formation through Claisen condensation reaction
* NRPs, the C domain catalyzes the amide bond formation between the amino acid it adds to the chain (on the PCP of one module) and the nascent peptide(on the PCP of the next module). | 1 | Biochemistry |
Experimental work by White and Brantley (2003) highlighted some of the limitations of the Goldich dissolution series, most notably that some variations in weathering rates of different minerals are not as pronounced as Goldich argues. According to the Goldich dissolution series, anorthite, a plagioclase feldspar, should weather quickly, with a lifetime of 10 years quantified by Kowalski and Rimstidt. Conversely, the lifetime of K-feldspar should be much longer, at 10 years based again on Kowalski and Rimstidt’s work. However, White and Brantley’s experimental results demonstrate that the relative weathering rates of K-feldspar and plagioclase feldspar are quite similar, and mainly moderated by the extent to which the minerals had already been weathered (in an exponentially decreasing function). This demonstrates that the Goldich series may not apply across all kinds of weathering processes, and likewise does not take into account the effect of exponential decay in weathering rate of a surface. | 9 | Geochemistry |
In chemistry, volatility is a material quality which describes how readily a substance vaporizes. At a given temperature and pressure, a substance with high volatility is more likely to exist as a vapour, while a substance with low volatility is more likely to be a liquid or solid. Volatility can also describe the tendency of a vapor to condense into a liquid or solid; less volatile substances will more readily condense from a vapor than highly volatile ones. Differences in volatility can be observed by comparing how fast substances within a group evaporate (or sublimate in the case of solids) when exposed to the atmosphere. A highly volatile substance such as rubbing alcohol (isopropyl alcohol) will quickly evaporate, while a substance with low volatility such as vegetable oil will remain condensed. In general, solids are much less volatile than liquids, but there are some exceptions. Solids that sublimate (change directly from solid to vapor) such as dry ice (solid carbon dioxide) or iodine can vaporize at a similar rate as some liquids under standard conditions. | 7 | Physical Chemistry |
The term operando first appeared in catalytic literature in 2002. It was coined by Miguel A. Bañares, who sought to name the methodology in a way that captured the idea of observing a functional material — in this case a catalyst — under actual working, i.e. device operation, conditions. The first international congress on operando spectroscopy took place in Lunteren, Netherlands, in March 2003, followed by further conferences in 2006 (Toledo, Spain),2009 (Rostock, Germany), 2012 (Brookhaven, USA), and 2015 (Deauville, France). The name change from in situ to operando for the research field of spectroscopy of catalysts under working conditions was proposed at the Lunteren congress.
The analytical principle of measuring the structure, property and function of a material, a component disassembled or as part of a device simultaneously under operation conditions is not restricted to catalysis and catalysts. Batteries and fuel cells have been subject to operando studies with respect to their electrochemical function. | 7 | Physical Chemistry |
There are many types of defects which result from many different causes. Some of the solutions to certain defects can be the cause for another type of defect.
The following defects can occur in sand castings. Most of these also occur in other casting processes. | 8 | Metallurgy |
During the 1950s, theoretical condensed matter physicists arrived at an understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg–Landau theory (1950) and the microscopic BCS theory (1957).
In 1950, the phenomenological Ginzburg–Landau theory of superconductivity was devised by Landau and Ginzburg. This theory, which combined Landau's theory of second-order phase transitions with a Schrödinger-like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Abrikosov showed that Ginzburg–Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau had received the 1962 Nobel Prize for other work, and died in 1968). The four-dimensional extension of the Ginzburg–Landau theory, the Coleman-Weinberg model, is important in quantum field theory and cosmology.
Also in 1950, Maxwell and Reynolds et al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element. This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity.
The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper and Schrieffer. This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972.
The BCS theory was set on a firmer footing in 1958, when N. N. Bogolyubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian. In 1959, Lev Gor'kov showed that the BCS theory reduced to the Ginzburg–Landau theory close to the critical temperature.
Generalizations of BCS theory for conventional superconductors form the basis for the understanding of the phenomenon of superfluidity, because they fall into the lambda transition universality class. The extent to which such generalizations can be applied to unconventional superconductors is still controversial. | 7 | Physical Chemistry |
In one study a coupling reaction between an indole and a quinone takes place at room temperature without catalyst in water in 82% chemical yield even though reactants and products are insoluble in this medium. The reaction is much less efficient in homogeneous systems such as dichloromethane, toluene and acetonitrile or even the solvent free reaction or even the water reaction but now at 50°C.
The on water effect is also studied in cycloadditions of the type:
In this reaction the alkyne methyl 2-octynoate reacts with triphenylphosphine to an intermediate zwitterionic allenolate, a dipolarophile for the 1,3-dipole 2-phenylnitrone. The primary regioselective [3+2]dipolar cycloaddition product then rearranges to a dihydroisoxazole with regeneration of the phosphine. This reaction only takes place in water with lithium chloride added even though the reactants do not dissolve in this medium. In organic solvents such as toluene or dichloromethane no reaction takes place. | 0 | Organic Chemistry |
The anti-Markovnikov addition selectivity to aldehyde can be achieved through exploiting inherent stereoelectronics of the substrate. Placement of directing group at homo-allylic (i.e. Figure 3, A) and allylic position (i.e. Figure 3, B) to the terminal olefin favors the anti-Markovnikov aldehyde product, which suggests that in the catalytic cycle the directing group chelates to the palladium complex such that water attacks at the anti-Markovnikov carbon to generate the more thermodynamically stable palladacycle. Anti-Markovnikov selectivity is also observed in styrenyl substrates (i.e. Figure 3, C), presumably via η-palladium-styrene complex after water attacks anti-Markovnikov. More examples of substrate-controlled, anti-Markovnikov Tsuji-Wacker Oxidation of olefins are given in reviews by Namboothiri, Feringa, and Muzart.
Grubbs and co-workers paved way for anti-Markovnikov oxidation of stereoelectronically unbiased terminal olefins, through the use of palladium-nitrite system (Figure 2, D). In his system, the terminal olefin was oxidized to the aldehyde with high selectivity through a catalyst-control pathway. The mechanism is under investigation, however evidence suggests it goes through a nitrite radical adds into the terminal carbon to generate the more thermodynamically stable, secondary radical. Grubbs expanded this methodology to more complex, unbiased olefins. | 0 | Organic Chemistry |
Small, electronegative molecules such as nitrogen and oxygen, which are the primary gases in air, significantly impact the ability of surrounding molecules to participate in hydrogen bonding. These molecules compete with surrounding hydrogen bond acceptors for hydrogen bond donors, therefore acting as "hydrogen bond breakers" and weakening interactions between surrounding molecules in the environment. Antiparellel strands in DNA double helices are non-covalently bound by hydrogen bonding between base pairs; nitrogen and oxygen therefore maintain the potential to weaken the integrity of DNA when exposed to air. As a result, DNA strands exposed to air require less force to separate and exemplify lower melting temperatures. | 1 | Biochemistry |
The Illinois Soil Nitrogen Test ("ISNT") is a method for measuring the amount of Nitrogen in soil that is available for use by plants as a nutrient. The test predicts whether the addition of nitrogen fertilizer to agricultural land will result in increased crop yields.
Nitrogen is essential for plant development. Indeed, for crops that are destined to be food for farm animal or human consumption, incorporation of nitrogen into the crop is an important goal, since this forms the basis for protein in the human diet.
Nitrogen is commonly present in soils in many forms, and there are many ways to measure this nitrogen. None of these are completely satisfactory as a measure of the nitrogen that is available for use by crops. The ISNT is a new (2007) method for measuring nitrogen available for plant uptake.
ISNT estimates the amount of nitrogen present in the soil as amino sugar nitrogen. With respect to corn and soybeans, the optimal range for plant growth appears to be around 225 to 240 mg/Kg. Some form of nitrogen fertilizer is needed if levels are below this range. On the other hand, if levels are above this range, addition of nitrogen fertilizer will not increase crop yield.
In the corn belt, since about 1975, the predominant method of estimating the amount of nitrogen needed for corn has been the "yield-based" method. A farmer first estimates the yield of corn he intends to produce. He then applies 1.1 to 1.4 lbs of nitrogen per bushel of expected yield. ISNT represents an alternative approach to managing nitrogen application. However, ISNT does not offer a simple answer as to the amount of nitrogen fertilizer that is needed, or as to the optimal form of that fertilizer.
In field trials in Illinois, some fields have been found to be under-fertilized when managed according to the "yield-based" method, as judged by the ISNT. In the majority of trials, however, the yield-based method calls for the addition of nitrogen far in excess of the levels needed for optimal crop production. This nitrogen, which is applied by farmers at great cost, does not find its way into the crop, but is lost to the atmosphere or leaches into waterways.
Within the corn belt, stalks and other crop residues are left in the field with the intention of enhancing the amount of organic material in the soil. Excessive nitrogen application, however, appears to promote the rapid decomposition of organic matter in the soil, resulting in release of carbon dioxide. As a result, the amount of organic material in soils managed according to the yield-based method in the corn belt appears to be decreasing in spite of the large amounts of crop residues left in the fields. | 9 | Geochemistry |
This study examined the clinical history of the CSF and urine of two Greek siblings who were both diagnosed with SR deficiency. Both siblings displayed delayed psychomotor development and a movement disorder. The diagnosis was confirmed by measuring the SR enzyme activity and mutation analysis. The mutation analysis of the gene was performed using genomic DNA isolated from blood samples. The results concluded that both patients have low concentrations of HVA and HIAA and high concentrations of sepiapterin in the CSF, but neopterin and biopterin were abnormal in only one sibling. The results of this research indicates that when diagnosing the SR deficiency, the quantification of sepiapterin in the CSF is more important and indicative of SR deficiency than using neopterin and biopterin alone. The results also show that the urine concentrations of neurotransmitter metabolites are abnormal in patients with this disorder. This finding may provide an initial and easier indication of the deficiency before CSF analysis is performed. | 1 | Biochemistry |
Two-dimensional separations can be carried out in gas chromatography or liquid chromatography. Various different coupling strategies have been developed to "resample" from the first column into the second. Some important hardware for two-dimensional separations are Deans' switch and Modulator, which selectively transfer the first dimension eluent to second dimension column.
The chief advantage of two-dimensional techniques is that they offer a large increase in peak capacity, without requiring extremely efficient separations in either column. (For instance, if the first column offers a peak capacity (k)of 100 for a 10-minute separation, and the second column offers a peak capacity of 5 (k) in a 5-second separation, then the combined peak capacity may approach k × k=500, with the total separation time still ~ 10 minutes). 2D separations have been applied to the analysis of gasoline and other petroleum mixtures, and more recently to protein mixtures. | 3 | Analytical Chemistry |
Adaptive cells change their absorption/reflection characteristics depending on environmental conditions. An adaptive material responds to the intensity and angle of incident light. At the part of the cell where the light is most intense, the cell surface changes from reflective to adaptive, allowing the light to penetrate the cell. The other parts of the cell remain reflective increasing the retention of the absorbed light within the cell.
In 2014, a system was developed that combined an adaptive surface with a glass substrate that redirect the absorbed to a light absorber on the edges of the sheet. The system also includes an array of fixed lenses/mirrors to concentrate light onto the adaptive surface. As the day continues, the concentrated light moves along the surface of the cell. That surface switches from reflective to adaptive when the light is most concentrated and back to reflective after the light moves along. | 7 | Physical Chemistry |
The first known racemic mixture was racemic acid, which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid. He manually separated the crystals of a mixture, starting from an aqueous solution of the sodium ammonium salt of racemate tartaric acid. Pasteur benefited from the fact that ammonium tartrate salt gives enantiomeric crystals with distinct crystal forms (at 77 °F). Reasoning from the macroscopic scale down to the molecular, he reckoned that the molecules had to have non-superimposable mirror images.
A sample with only a single enantiomer is an enantiomerically pure or enantiopure compound. | 4 | Stereochemistry |
Coacervate ( or ) is an aqueous phase rich in macromolecules such as synthetic polymers, proteins or nucleic acids. It forms through liquid-liquid phase separation (LLPS), leading to a dense phase in thermodynamic equilibrium with a dilute phase. The dispersed droplets of dense phase are also called coacervates, micro-coacervates or coacervate droplets. These structures draw a lot of interest because they form spontaneously from aqueous mixtures and provide stable compartmentalization without the need of a membrane.
The term coacervate was coined in 1929 by Dutch chemist Hendrik G. Bungenberg de Jong and Hugo R. Kruyt while studying lyophilic colloidal dispersions. The name is a reference to the clustering of colloidal particles, like bees in a swarm. The concept was later borrowed by Russian biologist Alexander I. Oparin to describe the proteinoid microspheres proposed to be primitive cells (protocells) on early Earth. Coacervate-like protocells are at the core of the Oparin-Haldane hypothesis.
A reawakening of coacervate research was seen in the 2000s, starting with the recognition in 2004 by scientists at the University of California, Santa Barbara (UCSB) that some marine invertebrates (such as the sandcastle worm) exploit complex coacervation to produce water-resistant biological adhesives. A few years later in 2009 the role of liquid-liquid phase separation was further recognized to be involved in the formation of certain membraneless organelles by the biophysicists Clifford Brangwynne and Tony Hyman. Liquid organelles share features with coacervate droplets and fueled the study of coacervates for biomimicry. | 7 | Physical Chemistry |
The structure of histatin is unique depending on whether the protein of interest is histatin 1, 3 or 5. Nonetheless, histatins mainly possess a cationic (positive) charge due to the primary structure consisting mostly of basic amino acids. An amino acid that is crucial to histatin's function is histidine. Studies show that the removal of histidine (especially in histatin 5) resulted in reduction of antifungal activity. | 1 | Biochemistry |
The Society of Environmental Toxicology and Chemistry (SETAC) is an international environmental toxicology and environmental chemistry organization. | 2 | Environmental Chemistry |
More O’Ferrall–Jencks plots are two-dimensional representations of multiple reaction coordinate potential energy surfaces for chemical reactions that involve simultaneous changes in two bonds. As such, they are a useful tool to explain or predict how changes in the reactants or reaction conditions can affect the position and geometry of the transition state of a reaction for which there are possible competing pathways. | 7 | Physical Chemistry |
The hazards which accompany harmful algal blooms have hindered visitors' enjoyment of beaches and lakes in places in the U.S. such as Florida, California, Vermont, and Utah. Persons hoping to enjoy their vacations or days off have been kept away to the detriment of local economies. Lakes and rivers in North Dakota, Minnesota, Utah, California and Ohio have had signs posted warning about the potential of health risk.
Similar blooms have become more common in Europe, with France among the countries reporting them. In the summer of 2009, beaches in northern Brittany became covered by tonnes of potentially lethal rotting green algae. A horse being ridden along the beach collapsed and died from fumes given off by the rotting algae.
The economic damage resulting from lost business has become a serious concern. According to one report in 2016, the four main economic impacts from harmful algal blooms come from damage to human health, fisheries, tourism and recreation, and the cost of monitoring and management of area where blooms appear. EPA estimates that algal blooms impact 65 percent of the country's major estuaries, with an annual cost of $2.2 billion. In the U.S. there are an estimated 166 coastal dead zones. Because data collection has been more difficult and limited from sources outside the U.S., most of the estimates as of 2016 have been primarily for the U.S.
In port cities in the Shandong Province of eastern China, residents are no longer surprised when massive algal blooms arrive each year and inundate beaches. Prior to the Beijing Olympics in 2008, over 10,000 people worked to clear 20,000 tons of dead algae from beaches. In 2013 another bloom in China, thought to be its largest ever, covered an area of 7,500 square miles, and was followed by another in 2015 which blanketed an even greater 13,500 square miles. The blooms in China are thought to be caused by pollution from untreated agricultural and industrial discharges into rivers leading to the ocean. | 3 | Analytical Chemistry |
The properties of HFMs can be characterized using the same techniques commonly used for other types of membranes. The primary properties of interest for HFMs are average pore diameter and pore distribution, measurable via a technique known as porosimetry, a feature of several laboratory instruments used for measuring pore size. Pore diameter can also be measured via a technique known as evapoporometry, in which evaporation of 2-propanol through the pores of a membrane is related to pore-size via the Kelvin equation. Depending on the diameters of pores in an HFM, scanning electron microscopy or transmission electron microscopy can be used to yield a qualitative perspective of pore size. | 7 | Physical Chemistry |
Water is the medium of the oceans, the medium which carries all the substances and elements involved in the marine biogeochemical cycles.
Water as found in nature almost always includes dissolved substances, so water has been described as the "universal solvent" for its ability to dissolve so many substances. This ability allows it to be the "solvent of life" Water is also the only common substance that exists as solid, liquid, and gas in normal terrestrial conditions. Since liquid water flows, ocean waters cycle and flow in currents around the world. Since water easily changes phase, it can be carried into the atmosphere as water vapour or frozen as an iceberg. It can then precipitate or melt to become liquid water again. All marine life is immersed in water, the matrix and womb of life itself. Water can be broken down into its constituent hydrogen and oxygen by metabolic or abiotic processes, and later recombined to become water again.
While the water cycle is itself a biogeochemical cycle, flow of water over and beneath the Earth is a key component of the cycling of other biogeochemicals. Runoff is responsible for almost all of the transport of eroded sediment and phosphorus from land to waterbodies. Cultural eutrophication of lakes is primarily due to phosphorus, applied in excess to agricultural fields in fertilizers, and then transported overland and down rivers. Both runoff and groundwater flow play significant roles in transporting nitrogen from the land to waterbodies. The dead zone at the outlet of the Mississippi River is a consequence of nitrates from fertilizer being carried off agricultural fields and funnelled down the river system to the Gulf of Mexico. Runoff also plays a part in the carbon cycle, again through the transport of eroded rock and soil. | 9 | Geochemistry |
The alternative oxidase (AOX) is an enzyme that forms part of the electron transport chain in mitochondria of different organisms. Proteins homologous to the mitochondrial oxidase and the related plastid terminal oxidase have also been identified in bacterial genomes.
The oxidase provides an alternative route for electrons passing through the electron transport chain to reduce oxygen. However, as several proton-pumping steps are bypassed in this alternative pathway, activation of the oxidase reduces ATP generation. This enzyme was first identified as a distinct oxidase pathway from cytochrome c oxidase as the alternative oxidase is resistant to inhibition by the poison cyanide. | 1 | Biochemistry |
The potential energy and unique bonding structure contained in the bonds of molecules with ring strain can be used to drive reactions in organic synthesis. Examples of such reactions are ring opening metathesis polymerisation, photo-induced ring opening of cyclobutenes, and nucleophilic ring-opening of epoxides and aziridines.
Increased potential energy from ring strain also can be used to increase the energy released by explosives or increase their shock sensitivity. For example, the shock sensitivity of the explosive 1,3,3-Trinitroazetidine could partially or primarily explained by its ring strain. | 7 | Physical Chemistry |
The pits that penetrate the bore are usually covered in a hard pale green nodule of copper sulfate and copper hydroxide salts. If the nodule is removed a hemispherical pit is revealed filled with coarse crystals of red cuprous oxide and green cuprous chloride. The pits are often referred to as Type 1 pits and the form of attack as Type 1 pitting. | 8 | Metallurgy |
δS records have been used to infer changes in seawater sulfate concentrations. Because the δS values of carbonate-associated sulfate are thought to be sensitive to seawater sulfate levels, these measurements have been used to reconstruct the history of seawater sulfate. δS values of pyrite have also been applied to reconstruct the concentration of seawater sulfate, based on expected biological fractionations at low sulfate concentrations. Both of these methods rely on assumptions about the depositional environment or the biological community, creating some uncertainty in the resulting reconstructions. | 9 | Geochemistry |
When dealing with rSOCs, the most important parameter to consider is the roundtrip efficiency, which is a measure of the efficiency of the system considering both the charge (SOEC) and discharge (SOFC) preocesses. The roundtrip efficiency for the single cell can be defined as:
where is the charge supplied or consumed during the reactions, and is the operating voltage. If the assumption of no current or reactants leakage is made, the exchanged charges during the reactions can be assumed to be equal. Then, the roundtrip efficiency can be written as:
To maximize the roundtrip efficiency, the two operating voltages must be as close as possible. This condition can be achieved by operating the rSOC with low current densities in both modalities. In SOFC mode this is easily pursuable, while in SOEC mode a too low voltage may lead to an endothermic operation. If the operating voltage in SOEC mode is lower than the thermoneutral voltage, additional heat sources at high temperature are needed to sustain the reaction. These could come from waste industrial heat or from nuclear reactors. If not easily accessible, though, electrical heating is necessary. This can be supplied by external additions or by operating the cell with an operating voltage higher than the thermoneutral one. Both solutions, though, would inevitably lower the roundtrip efficiency of the rSOC. For this reason, in reversible operation, the thermoneutral voltage poses significant limitations in achieving high roundtrip efficiencies.
On the other hand, the thermoneutral voltage is greatly affected by the reaction chemistry. It has been demonstrated that increasing the yield of methane in the electrolysis operation can substantially decreases the thermoneutral voltage and heat demand of the reaction. For conventional electrolyzers (operating at atmospheric pressure and 750°C), the methane content in the products is very low. It can be increased effectively by lowering the operating temperature to 600°C and increasing the operating pressure up to 10 bar. For example, the thermoneutral voltage is equal to 1.27 V at 750°C and 1 bar, while it becomes equal to 1.07 V at 600°C and 10 bar. In these conditions, the rSOC can even be operated in exothermic mode at reduced voltages, permitting to produce additional heat at high temperature. This result becomes very helpful in the design of high efficiency rSOC systems for energy storage purposes. | 7 | Physical Chemistry |
Neurotransmitter systems are systems of neurons in the brain expressing certain types of neurotransmitters, and thus form distinct systems. Activation of the system causes effects in large volumes of the brain, called volume transmission. Volume transmission is the diffusion of neurotransmitters through the brain extracellular fluid released at points that may be remote from the target cells with the resulting activation of extrasynaptic receptors, and with a longer time course than for transmission at a single synapse. Such prolonged transmitter action is called tonic transmission, in contrast to the phasic transmission that occurs rapidly at single synapses. | 1 | Biochemistry |
Acid rain has a much less harmful effect on oceans on a global scale, but it creates an amplified impact in the shallower waters of coastal waters. Acid rain can cause the oceans pH to fall, known as ocean acidification, making it more difficult for different coastal species to create their exoskeletons that they need to survive. These coastal species link together as part of the oceans food chain, and without them being a source for other marine life to feed off of, more marine life will die. Coral's limestone skeleton is particularly sensitive to pH decreases, because the calcium carbonate, a core component of the limestone skeleton, dissolves in acidic (low pH) solutions.
In addition to acidification, excess nitrogen inputs from the atmosphere promote increased growth of phytoplankton and other marine plants, which, in turn, may cause more frequent harmful algal blooms and eutrophication (the creation of oxygen-depleted "dead zones") in some parts of the ocean. | 2 | Environmental Chemistry |
Minerals are naturally occurring solids formed through various geological processes under high pressures. To be classified as a true mineral, a substance must have a crystal structure with uniform physical properties throughout. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. In contrast, a rock sample is a random aggregate of minerals and/or mineraloids, and has no specific chemical composition. The vast majority of the rocks of the Earth's crust consist of quartz (crystalline SiO), feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a few other minerals. Some minerals, like quartz, mica or feldspar are common, while others have been found in only a few locations worldwide. The largest group of minerals by far is the silicates (most rocks are ≥95% silicates), which are composed largely of silicon and oxygen, with the addition of ions of aluminium, magnesium, iron, calcium and other metals. | 7 | Physical Chemistry |
The OCO-2 satellite was built by Orbital Sciences Corporation, based around the LEOStar-2 bus. The spacecraft is being used to study carbon dioxide concentrations and distributions in the atmosphere.
OCO-2 was ordered after the original OCO spacecraft failed to achieve orbit. During the first satellite's launch atop a Taurus-XL in February 2009, the payload fairing failed to separate from around the spacecraft and the rocket did not have sufficient power to enter orbit with its additional mass. Although a Taurus launch was initially contracted for the reflight, the launch contract was cancelled after the same malfunction occurred on the launch of the Glory satellite two years later.
United Launch Alliance launched OCO-2 using a Delta II rocket at the beginning of a 30-second launch window at 09:56 UTC (2:56 PDT) on 2 July 2014. Flying in the 7320-10C configuration, the rocket launched from Space Launch Complex 2W at Vandenberg Air Force Base. The initial launch attempt on 1 July at 09:56:44 UTC was scrubbed at 46 seconds on the countdown clock due to a faulty valve on the water suppression system, used to flow water on the launch pad to dampen the acoustic energy during launch.
OCO-2 joined the A-train satellite constellation, becoming the sixth satellite in the group. Members of the A-train fly very close together in Sun-synchronous orbit, to make nearly simultaneous measurements of Earth. A particularly short launch window of 30 seconds was necessary to achieve a proper position in the train. As of it was in an orbit with a perigee of , an apogee of and a 98.2° inclination.
The mission is expected to cost , including design, development, launch and operations. | 2 | Environmental Chemistry |
Silicon wafers can be etched in hydrofluoric acid (HF) to remove the native oxide and form a hydrogen-terminated silicon surface. The hydrogen-terminated surfaces undergo hydrosilation with unsaturated compounds (such as terminal alkenes and alkynes), to form a stable monolayer on the surface. For example:
:Si-H + HC=CH(CH)CH → Si-CHCHH-(CH)CH
The hydrosilylation reaction can be initiated with UV light at room temperature or with heat (typical reaction temperature 120-200 °C), under moisture- and oxygen-free conditions. The resulting monolayer, which is stable and inert, inhibits oxidation of the base silicon layer, relevant to various device applications. | 7 | Physical Chemistry |
The CO fertilization effect or carbon fertilization effect causes an increased rate of photosynthesis while limiting leaf transpiration in plants. Both processes result from increased levels of atmospheric carbon dioxide (CO). The carbon fertilization effect varies depending on plant species, air and soil temperature, and availability of water and nutrients. Net primary productivity (NPP) might positively respond to the carbon fertilization effect. Although, evidence shows that enhanced rates of photosynthesis in plants due to CO fertilization do not directly enhance all plant growth, and thus carbon storage. The carbon fertilization effect has been reported to be the cause of 44% of gross primary productivity (GPP) increase since the 2000s. Earth System Models, Land System Models and Dynamic Global Vegetation Models are used to investigate and interpret vegetation trends related to increasing levels of atmospheric CO. However, the ecosystem processes associated with the CO fertilization effect remain uncertain and therefore are challenging to model.
Terrestrial ecosystems have reduced atmospheric CO concentrations and have partially mitigated climate change effects. The response by plants to the carbon fertilization effect is unlikely to significantly reduce atmospheric CO concentration over the next century due to the increasing anthropogenic influences on atmospheric CO. Earth's vegetated lands have shown significant greening since the early 1980s largely due to rising levels of atmospheric CO.
Theory predicts the tropics to have the largest uptake due to the carbon fertilization effect, but this has not been observed. The amount of uptake from fertilization also depends on how forests respond to climate change, and if they are protected from deforestation.
Changes in atmospheric carbon dioxide may reduce the nutritional quality of some crops, with for instance wheat having less protein and less of some minerals. Food crops could see a reduction of protein, iron and zinc content in common food crops of 3 to 17%. | 2 | Environmental Chemistry |
The ab initio binding energy between the two water molecules is estimated to be 5-6 kcal/mol, although values between 3 and 8 have been obtained depending on the method. The experimentally measured dissociation energy (including nuclear quantum effects) of (HO) and (DO) are 3.16 ± 0.03 kcal/mol (13.22 ± 0.12 kJ/mol) and 3.56 ± 0.03 kcal/mol (14.88 ± 0.12 kJ/mol), respectively. The values are in excellent agreement with calculations. The O-O distance of the vibrational ground-state is experimentally measured at ca. 2.98 Å; the hydrogen bond is almost linear, but the angle with the plane of the acceptor molecule is about 57°. The vibrational ground-state is known as the linear water dimer (shown in the figure to the right), which is a near prolate top (viz., in terms of rotational constants, A > B ≈ C). Other configurations of interest include the cyclic dimer and the bifurcated dimer. | 7 | Physical Chemistry |
When translating a polycistronic mRNA, a 70S ribosome ends translation at a stop codon. It is now shown that instead of immediately splitting into its two halves, the ribosome can "scan" forward until it hits another Shine–Dalgarno sequence and the downstream initiation codon, initiating another translation with the help of IF2 and IF3. This mode is thought to be important for the translation of genes that are clustered in poly-cistronic operons, where the canonical binding mode can be disruptive due to small distances between neighboring genes on the same mRNA molecule. | 1 | Biochemistry |
Toxic metals can be present in the aqueous environment at trace or ultra-trace concentrations, yet still be toxicologically significant and thus cause harm to humans or the environment. Because these concentrations are so low, they would fall beyond the detection limits of most analytical instruments if the media had been sampled using traditional grab samples. Using SLMDs to passively collect metals over an extended period of time allows for trace metals to accumulate to detectable levels, which can give more accurate estimate of aquatic chemistry and contamination. SLMDs also have the advantage of being able to capture pulses of metal contamination that might otherwise go undetected when using grab samples.
SLMDs are limited to the assessment of labile metals, and cannot be used to monitor for organic contaminants. Further, while the ability of SLMDs to sample copper, zinc, nickel, lead, and cadmium has been repeatedly demonstrated, there has been little laboratory research on their ability to reliably uptake other toxic metals. Still, while laboratory studies on the effectiveness of SLMDs have only investigated copper, zinc, nickel, lead, and cadmium, SLMDs have been used with success in field studies to assess a wider range of metals. | 3 | Analytical Chemistry |
The first potash application was in England in 1993, where Jameson Cells were used to treat potash slimes (see Potash flotation). It has subsequently been applied at Israel Chemicals Limited's Dead Sea Works and by an unnamed producer in the Saskatchewan province of Canada. | 8 | Metallurgy |
The four phosphorus atoms are at the corners of a tetrahedron surrounding the palladium(0) center. This structure is typical for four-coordinate 18 e complexes. The corresponding complexes Ni(PPh) and Pt(PPh) are also well known. Such complexes reversibly dissociate PPh ligands in solution, so reactions attributed to Pd(PPh) often in fact arise from Pd(PPh) or even Pd(PPh). | 0 | Organic Chemistry |
Although little is known about the mechanism of the adaptive response, it is believed that changes in gene transcription and the activation of cellular defenses are involved. It has recently been suggested that specific mechanistic pathways of the adaptive response can active the important tumor suppressor protein p53. A key experiment that reveals the underlying mechanisms is that which involves the treatment with protein synthesis inhibitors to Oedogonium Chlamydomonas and Closterium cells. This experiment resulted in DNA-binding proteins being synthesized in the cells conditioned with the stressor. Furthermore, reverse adaptive response suggests that a high conditioning dose followed by a second low dose produces roughly the same magnitude of response. This could suggest that the mechanisms work by cellular response modulation, not prevention, to the impending damage. The adaptive response is not instantaneous and takes several hours to develop, however after development it can last for months given that the stressor exposure is limited and will not overwhelm the cell. This is known as being dose and time-dependent with a maximum response occurring at 4 hours after an initial conditioning dose of 100 cGy (centigray) radiation stressor. | 1 | Biochemistry |
The super-Tonks–Girardeau gas was experimentally observed in Ref. using an ultracold gas of cesium atoms. Reducing the magnitude of the attractive interactions caused the gas to became unstable to collapse into cluster-like bound states. Repulsive dipolar interactions stabilize the gas when instead using highly magnetic dysprosium atoms. This enabled the creation of prethermal quantum many-body scar states via the topological pumping of these super-Tonks-Girardeau gases. | 7 | Physical Chemistry |
Many sulfate reducers are organotrophic, using carbon compounds such as lactate and pyruvate (among many others) as electron donors, while others are lithotrophic, using hydrogen gas () as an electron donor. Some unusual autotrophic sulfate-reducing bacteria (e.g. Desulfotignum phosphitoxidans) can use phosphite () as an electron donor whereas others (e.g. Desulfovibrio sulfodismutans, Desulfocapsa thiozymogenes, Desulfocapsa sulfoexigens) are capable of sulfur disproportionation (splitting one compound into two different compounds, in this case an electron donor and an electron acceptor) using elemental sulfur (S), sulfite (), and thiosulfate () to produce both hydrogen sulfide () and sulfate (). | 1 | Biochemistry |
If an ion contains unpaired electrons, it is called a radical ion. Just like uncharged radicals, radical ions are very reactive. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions. Molecular ions that contain at least one carbon to hydrogen bond are called organic ions. If the charge in an organic ion is formally centred on a carbon, it is termed a carbocation (if positively charged) or carbanion (if negatively charged). | 7 | Physical Chemistry |
Feringa found that the early introduction of chiroptical molecular switches, based on the design of the first chiral overcrowded alkenes and the demonstration of optically controlled molecular switching and amplification of chirality in mesoscopic systems, lead to molecular rotary motors in which chirality plays a critical role in achieving the same function achieved by nature, for example, the unidirectional rotation of retinal in rhodopsin. This work led to the discovery of the worlds first unidirectional molecular rotary motor and this work has been laying the ground-work for a key component of future molecular nanotechnology i.e. nanomachines and nanorobots powered by molecular motors. Feringas design and synthesis of nanomolecular machines, specifically molecular switches and molecular motors, have initiated major novel approaches towards complex and dynamic chemical systems and the dynamic control of function.
Applications of molecular switches developed in his group include responsive materials and surfaces, liquid crystals, electrochromic devices for optoelectronics, photo-switchable DNA as a molecular memory stick, responsive gels, polymers, and light-switchable protein channels for nanoscale drug delivery systems, anion sensing, responsive catalysts and photopharmacology as well as entirely novel approaches using responsive drugs toward anticancer agents, antibiotic treatment and antibiotic resistance, and biofilm formation. Interfacing molecular motors with the macroscopic world by surface assembly on gold nanoparticles and a macroscopic gold film, has shown that the motor functions while chemically bound to a surface, a key result for future nanomachines such as a molecular conveyor belt. Experiments that involve doping liquid crystals with molecular motors demonstrate that the motion of the motor can be harnessed to make macroscopic objects rotate on a liquid crystal film and drive molecular systems out-of-equilibrium. Several of these discoveries were selected for the list of most important chemical discoveries of the year by Chemical & Engineering News.
In 2011, molecular ‘nanocar’, a molecule that contains molecular motor-based wheels and was shown to move on a solid surface upon subjection to electric current from an STM tip, was highlighted in international daily newspapers & magazines worldwide and selected by the Chinese Academy of Sciences as one of the 10 major discoveries in sciences worldwide. Towards the future discipline of Systems chemistry, the development of a multistage chiral catalysts which comprises an integrated supramolecular system that brings together molecular recognition, chirality transfer, catalysis, stereoelectronic control and enantio-selectivity while all these processes can be enabled or disabled via an internal motor function, moves the design and application of molecular motors to a whole new level of sophistication.
Aside from molecular motors and switches, Feringa's work has crossed many disciplines and includes the use of phosphoramidites as ligands in asymmetric catalysis, an excellent stereocontrol was archived in copper-catalysed C–C bond formation, which led to a breakthrough in catalytic asymmetric conjugate addition. As phosphoramidites found use in industry, recently they utilised them as starting reagents for asymmetric C-P bond formation. Traditionally, an external chiral ligand is used for chiral induction in a C–P coupling reaction, but the competitive coordination of initial and final phosphorus compounds with the metal catalysts, together with an external chiral ligand, reduces the enantioselectivity. As BINOL-containing phosphoramidites have the properties of an intrinsic chiral ligand and simultaneously can serve as a substrate, they hypothesized that they would increase stereoselectivity in C–P coupling processes with aryl compounds, and were delighted when that data confirmed that they did.
Moreover, many other highlighted works are chiral electromagnetic radiation to generate enantioselectivity, low molecular weight gelators, imaging porphyrins with STM, drying induced self-assembly, organic synthesis, CD spectroscopy, asymmetric catalysis, exploring the origins of chirality including the possibility of an extraterrestrial source and various aspects of surface science including surface modification, surface energy control, and porphyrin allayers. | 4 | Stereochemistry |
NOTE: this section currently gives formulas that apply in the Rayleigh–Jeans limit , and does not use a quantized (Planck) treatment of radiation. Thus a usual factor like does not appear. The appearance of in below is due to the quantum-mechanical treatment of collisions.
In a plasma, the free electrons continually collide with the ions, producing bremsstrahlung. A complete analysis requires accounting for both binary Coulomb collisions as well as collective (dielectric) behavior. A detailed treatment is given by Bekefi, while a simplified one is given by Ichimaru. In this section we follow Bekefi's dielectric treatment, with collisions included approximately via the cutoff wavenumber,
Consider a uniform plasma, with thermal electrons distributed according to the Maxwell–Boltzmann distribution with the temperature . Following Bekefi, the power spectral density (power per angular frequency interval per volume, integrated over the whole sr of solid angle, and in both polarizations) of the bremsstrahlung radiated, is calculated to be
where is the electron plasma frequency, is the photon frequency, is the number density of electrons and ions, and other symbols are physical constants. The second bracketed factor is the index of refraction of a light wave in a plasma, and shows that emission is greatly suppressed for (this is the cutoff condition for a light wave in a plasma; in this case the light wave is evanescent). This formula thus only applies for . This formula should be summed over ion species in a multi-species plasma.
The special function is defined in the exponential integral article, and the unitless quantity is
is a maximum or cutoff wavenumber, arising due to binary collisions, and can vary with ion species. Roughly, when (typical in plasmas that are not too cold), where eV is the Hartree energy, and is the electron thermal de Broglie wavelength. Otherwise, where is the classical Coulomb distance of closest approach.
For the usual case , we find
The formula for is approximate, in that it neglects enhanced emission occurring for slightly above
In the limit , we can approximate as where is the Euler–Mascheroni constant. The leading, logarithmic term is frequently used, and resembles the Coulomb logarithm that occurs in other collisional plasma calculations. For the log term is negative, and the approximation is clearly inadequate. Bekefi gives corrected expressions for the logarithmic term that match detailed binary-collision calculations.
The total emission power density, integrated over all frequencies, is
: and decreases with ; it is always positive. For , we find
Note the appearance of due to the quantum nature of . In practical units, a commonly used version of this formula for is
This formula is 1.59 times the one given above, with the difference due to details of binary collisions. Such ambiguity is often expressed by introducing Gaunt factor , e.g. in one finds
where everything is expressed in the CGS units. | 7 | Physical Chemistry |
In this context exposure is defined as the contact between an agent and a target. Contact takes place at an exposure surface over an exposure period.
Mathematically, exposure is defined as <br>
where is exposure, is a concentration that varies with time between the beginning and end of exposure. It has dimensions of mass times time divided by volume. This quantity is related to the potential dose of contaminant by multiplying it by the relevant contact rate, such as breathing rate, food intake rate etc. The contact rate itself may be a function of time. | 2 | Environmental Chemistry |
The total synthesis of callystatin A has been reported by various groups since its discovery in 1997. These total syntheses vary in their approaches and strategies. | 0 | Organic Chemistry |
* Measurement of the emissivities of gases at temperatures up to 1000 °C. Emissivity values were required for gaseous aluminium chlorides as part of the development of the sub-halide distillation process mentioned above. A flowing column of the gas to be measured, heated in a refractory tube, was maintained at a fixed length by gas barriers at each end, formed by balanced opposing streams of argon. The radiation emitted by the gas was measured by a thermopile. A diaphragm was set up to shield this sensor from radiation emitted by the furnace and other hot parts of the equipment. The whole apparatus was mounted on a water-cooled optical bench.
* X-ray diffraction determination of the structures of liquid metals. There was a need for structural studies of liquid sodium and sodium-potassium alloys because these were used as coolants in fast-breeder reactors. Fulmer developed a high temperature x-ray diffractometer for investigating the structures of liquid metals and alloys. In addition to its studies of liquid alkali metals, Fulmer discovered that certain eutectics, such as those in the gold-silicon and gold-germanium systems, have a structure in the liquid phase that has to be disrupted on crystallization. This gives rise to considerable supercooling which results in multiple nucleation, and hence a very fine grain size in the resulting polycrystalline alloy.
* Production of high purity austenitic stainless steel. High purity austenitic stainless steel was of interest as a potential cladding material for nuclear fuel elements. Fulmer produced high purity chromium by electro-deposition from a fluoride bath. Zone refining using induction heating was used to produce high-purity iron and nickel and to remove oxygen from chromium. Impurity levels of 1-40 parts per million were achieved.
* Chromium with improved ductility. Uses of chromium as a high temperature material are limited by its brittleness. Starting with electro-deposited flakes of high purity chromium, investigators at Fulmer used argon-arc melting to form electrodes for ingot production in a consumable electrode furnace. Ingots were then heated in an inert or hydrogen atmosphere and extruded to give a fine grained structure. Critical warm working, below the recrystallization temperature, then gave improved room-temperature ductility.
* Statistical studies of the strength of ceramics. The strength of brittle materials such as ceramics is inherently variable. Fulmer undertook numerous strength tests on sets of nominally identical specimens of engineering ceramics such as silicon nitride and silicon carbide. They devised graphical techniques for finding the probability distribution of test results and contributed to criteria for engineering design with these materials. | 8 | Metallurgy |
Analysis of water hardness in major Australian cities by the Australian Water Association shows a range from very soft (Melbourne) to hard (Adelaide).
Total hardness levels of calcium carbonate in ppm are:
*Canberra: 40
* Melbourne: 10–26
* Sydney: 39.4–60.1
* Perth: 29–226
* Brisbane: 100
* Adelaide: 134–148
* Hobart: 5.8–34.4
* Darwin: 31 | 3 | Analytical Chemistry |
More than 5000 chloroplast genomes have been sequenced and are accessible via the NCBI organelle genome database. The first chloroplast genomes were sequenced in 1986, from tobacco (Nicotiana tabacum) and liverwort (Marchantia polymorpha). Comparison of the gene sequences of the cyanobacteria Synechocystis to those of the chloroplast genome of Arabidopsis provided confirmation of the endosymbiotic origin of the chloroplast. It also demonstrated the significant extent of gene transfer from the cyanobacterial ancestor to the nuclear genome.
In most plant species, the chloroplast genome encodes approximately 120 genes. The genes primarily encode core components of the photosynthetic machinery and factors involved in their expression and assembly. Across species of land plants, the set of genes encoded by the chloroplast genome is fairly conserved. This includes four ribosomal RNAs, approximately 30 tRNAs, 21 ribosomal proteins, and 4 subunits of the plastid-encoded RNA polymerase complex that are involved in plastid gene expression. The large Rubisco subunit and 28 photosynthetic thylakoid proteins are encoded within the chloroplast genome. | 5 | Photochemistry |
The G-less cassette transcription assay is a method used in molecular biology to determine promoter strength in vitro. The technique involves quantification of an mRNA product with the use of a plasmid. The G-less cassette is part of a pre-constructed vector, usually containing a multiple cloning site (MCS) upstream of the cassette. For this reason, promoters of interest can be inserted directly into the MCS to ultimately measure the accuracy and efficiency of a promoter in recruiting transcription machinery. | 1 | Biochemistry |
Prior to these studies, HPLC analyses were tuned by modifying the mobile and stationary phases only. Gradient elution for HPLC merely meant changing the ratio of solvents to improve column efficiency, and this requires the use of sophisticated solvent pumping mechanisms along with extra steps and precautions in the chromatographic analysis. Enlightened by the prospect of using temperature gradient elutions for HPLC analyses, Hosoya et al. sought to make surface modification of HPLC stationary phases more accessible. Their study utilizes graft-type copolymerization of PNIPAAm onto macroporous polymeric materials. The in-situ preparation compared the use of cyclohexanol and toluene as porogens in the preparation of the modified polystyrene seeds. Reverse-phased size-exclusion chromatography (SEC) revealed pore size and pore size distribution of the particles and its dependence on temperature. Cyclohexanol acted as a successful porogen showing a dependent relationship of pore size to temperature. The use of toluene as a porogen gave results that were similar to unmodified macroporous particles. This indicates that PNIPAAm can be successfully grafted onto the surface and within the pores of macroporous materials. The application of this preparatory technique gives rise to tunable pore sizes. Temperature gradient elutions can be used to improve column efficiency through the changing of pore size in SEC. The mechanism of the change in pore size is simple, the pores are smaller under LCST due to the elongated chains of PNIPAAm within the pores, as temperature increases to and above LCST, the chains retract into a globular formation increasing the pore size. | 3 | Analytical Chemistry |
Drospirenone is the generic name of the drug and its , , , and , while drospirénone is its . Its name is a shortened form of the name 1,2-dihydrospirorenone or dihydrospirenone. Drospirenone is also known by its developmental code names SH-470 and ZK-30595 (alone), BAY 86-5300, BAY 98-7071, and SH-T-00186D (in combination with ethinylestradiol), BAY 86-4891 (in combination with estradiol), and FSN-013 (in combination with estetrol). | 4 | Stereochemistry |
The Young equation assumes a perfectly flat and rigid surface. In many cases, surfaces are far from this ideal situation, and two are considered here: the case of rough surfaces , to the so-called receding contact angle, . The equilibrium contact angle () can be calculated from and as was shown by Tadmor as,
where | 7 | Physical Chemistry |
* Aluminium gallium arsenide
* Boron nitride
* Indium gallium arsenide
* Indium arsenide
* Gallium arsenide
* Gallium nitride
* Germanium
* Metallic hydrogen | 7 | Physical Chemistry |
Flame treatment is a controlled, rapid, cost-effective method of increasing surface energy and wettability of polyolefins and metallic components. This high-temperature plasma treatment uses ionized gaseous oxygen via jet flames across a surface to add polar functional groups while melting the surface molecules, locking them into place upon cooling.
Thermoplastic polyethylene and polypropylene treated with brief oxygen plasma exposure have seen contact angles as low as 22°, and the resulting surface modification can last years with proper packaging. Flame plasma treatment has become increasingly popular with intravascular devices such as balloon catheters due to the precision and cost-effectiveness demanded in the medical industry. | 7 | Physical Chemistry |
A FOCE system for studies of deep-sea benthic communities (designated dp-FOCE) was developed by Monterey Bay Aquarium Research Institute. The dpFOCE project, deployed at a depth of 900 m, was attached to the MARS cabled seafloor observatory in Monterey Bay, central California. The system used a flume concept for maintaining greater control over the experimental volume while still maintaining access to natural seafloor sediments and suspended particulate material. Time-delay wings attached to either end of the dpFOCE chamber allow for tidally driven changes in near-bottom currents, and provide sufficient time for full hydration of the injected CO enriched seawater before entering into the experiment chamber. Fans are integrated into the dpFOCE design to control flow rates through the experimental chamber and to simulate typical local-scale flow conditions. Multiple sensors (pH, CTD, ADV, and ADCP) used in conjunction with the fans and the enriched seawater injection system allow the control loop software to achieve the desired pH offset. dpFOCE connects to shore via the MARS cabled observatory, which provides power and data bandwidth. Enriched CO seawater is produced from liquid CO held in a small container near the dpFOCE chamber; seawater flowing slowly over the top of the liquid CO dissolves some of the liquid CO producing a CO-rich dissolution plume used for injection into the dpFOCE chamber. The dpFOCE system operated over 17 months and verified the effectiveness of the design hardware and software. | 9 | Geochemistry |
Evaporative cooling is an atomic physics technique to achieve high phase space densities which optical cooling techniques alone typically can not reach.
Atoms trapped in optical or magnetic traps can be evaporatively cooled via two primary mechanisms, usually specific to the type of trap in question: in magnetic traps, radiofrequency (RF) fields are used to selectively drive warm atoms from the trap by inducing transitions between trapping and non-trapping spin states; or, in optical traps, the depth of the trap itself is gradually decreased, allowing the most energetic atoms in the trap to escape over the edges of the optical barrier. In the case of a Maxwell-Boltzmann distribution for the velocities of the atoms in the trap, these atoms which escape/are driven out of the trap lie in the highest velocity tail of the distribution, meaning that their kinetic energy (and therefore temperature) is much higher than the average for the trap. The net result is that while the total trap population decreases, so does the mean energy of the remaining population. This decrease in the mean kinetic energy of the atom cloud translates into a progressive decrease in the trap temperature, cooling the trap.
The process is analogous to blowing on a cup of coffee to cool it: those molecules at the highest end of the energy distribution for the coffee form a vapor above the surface and are then removed from the system by blowing them away, decreasing the average energy, and therefore temperature, of the remaining coffee molecules. | 7 | Physical Chemistry |
Some volcanic eruptions are explosive because of the mixing between water and magma reaching the surface, which releases energy suddenly. However, in some cases, the eruption is caused by volatiles dissolved in the magma itself. Approaching the surface, pressure decreases and the volatiles come out of solution, creating bubbles that circulate in the liquid. The bubbles become connected together, forming a network. This promotes the fragmentation into small drops or spray or coagulate clots in gas.
Generally, 95-99% of magma is liquid rock. However, the small percentage of gas present represents a very large volume when it expands on reaching atmospheric pressure. Gas is thus important in a volcano system because it generates explosive eruptions. Magma in the mantle and lower crust has a high volatile content. Water and carbon dioxide are not the only volatiles that volcanoes release; other volatiles include hydrogen sulfide and sulfur dioxide. Sulfur dioxide is common in basaltic and rhyolite rocks. Volcanoes also release a large amount of hydrogen chloride and hydrogen fluoride as volatiles. | 9 | Geochemistry |
An internal control region is a sequence of DNA located with the coding region of eukaryotic genes that binds regulatory elements such as activators or repressors. This region can recruit RNA Polymerase or contribute to splicing. | 1 | Biochemistry |
The mercury beating heart is an electrochemical redox reaction between the elements mercury, iron and chromium. The reaction causes a blob of mercury in water to oscillate.
The observeable reaction demonstrates an effect of a non-homogeneous electrical double layer. It is often used as a classroom demonstration. | 7 | Physical Chemistry |
When one substance is dissolved into another, a solution is formed. This is opposed to the situation when the compounds are insoluble like sand in water. In a solution, all of the ingredients are uniformly distributed at a molecular level and no residue remains. A solvent-solute mixture consists of a single phase with all solute molecules occurring as solvates (solvent-solute complexes), as opposed to separate continuous phases as in suspensions, emulsions and other types of non-solution mixtures. The ability of one compound to be dissolved in another is known as solubility; if this occurs in all proportions, it is called miscible.
In addition to mixing, the substances in a solution interact with each other at the molecular level. When something is dissolved, molecules of the solvent arrange around molecules of the solute. Heat transfer is involved and entropy is increased making the solution more thermodynamically stable than the solute and solvent separately. This arrangement is mediated by the respective chemical properties of the solvent and solute, such as hydrogen bonding, dipole moment and polarizability. Solvation does not cause a chemical reaction or chemical configuration changes in the solute. However, solvation resembles a coordination complex formation reaction, often with considerable energetics (heat of solvation and entropy of solvation) and is thus far from a neutral process.
When one substance dissolves into another, a solution is formed. A solution is a homogeneous mixture consisting of a solute dissolved into a solvent. The solute is the substance that is being dissolved, while the solvent is the dissolving medium. Solutions can be formed with many different types and forms of solutes and solvents. | 2 | Environmental Chemistry |
Mammalian expression vectors offer considerable advantages for the expression of mammalian proteins over bacterial expression systems - proper folding, post-translational modifications, and relevant enzymatic activity. It may also be more desirable than other eukaryotic non-mammalian systems whereby the proteins expressed may not contain the correct glycosylations. It is of particular use in producing membrane-associating proteins that require chaperones for proper folding and stability as well as containing numerous post-translational modifications. The downside, however, is the low yield of product in comparison to prokaryotic vectors as well as the costly nature of the techniques involved. Its complicated technology, and potential contamination with animal viruses of mammalian cell expression have also placed a constraint on its use in large-scale industrial production.
Cultured mammalian cell lines such as the Chinese hamster ovary (CHO), COS, including human cell lines such as HEK and HeLa may be used to produce protein. Vectors are transfected into the cells and the DNA may be integrated into the genome by homologous recombination in the case of stable transfection, or the cells may be transiently transfected. Examples of mammalian expression vectors include the adenoviral vectors, the pSV and the pCMV series of plasmid vectors, vaccinia and retroviral vectors, as well as baculovirus. The promoters for cytomegalovirus (CMV) and SV40 are commonly used in mammalian expression vectors to drive gene expression. Non-viral promoter, such as the elongation factor (EF)-1 promoter, is also known. | 1 | Biochemistry |
Amino acids from ingested food (or produced from catabolism of muscle protein) that are used for the synthesis of proteins and other biological substances can be oxidized by the body as an alternative source of energy, yielding urea and carbon dioxide. The oxidation pathway starts with the removal of the amino group by a transaminase; the amino group is then fed into the urea cycle. The first step in the conversion of amino acids into metabolic waste in the liver is removal of the alpha-amino nitrogen, which produces ammonia. Because ammonia is toxic, it is excreted immediately by fish, converted into uric acid by birds, and converted into urea by mammals.
Ammonia () is a common byproduct of the metabolism of nitrogenous compounds. Ammonia is smaller, more volatile, and more mobile than urea. If allowed to accumulate, ammonia would raise the pH in cells to toxic levels. Therefore, many organisms convert ammonia to urea, even though this synthesis has a net energy cost. Being practically neutral and highly soluble in water, urea is a safe vehicle for the body to transport and excrete excess nitrogen.
Urea is synthesized in the body of many organisms as part of the urea cycle, either from the oxidation of amino acids or from ammonia. In this cycle, amino groups donated by ammonia and -aspartate are converted to urea, while -ornithine, citrulline, -argininosuccinate, and -arginine act as intermediates. Urea production occurs in the liver and is regulated by N-acetylglutamate. Urea is then dissolved into the blood (in the reference range of 2.5 to 6.7 mmol/L) and further transported and excreted by the kidney as a component of urine. In addition, a small amount of urea is excreted (along with sodium chloride and water) in sweat.
In water, the amine groups undergo slow displacement by water molecules, producing ammonia, ammonium ions, and bicarbonate ions. For this reason, old, stale urine has a stronger odor than fresh urine. | 0 | Organic Chemistry |
The chemistry of the subsurface ocean of Europa may be Earthlike. The subsurface ocean of Enceladus vents hydrogen and carbon dioxide to space. | 9 | Geochemistry |
STAT4 is involved in several autoimmune and cancer diseases in animal models humans, significantly in the disease progression and pathology. STAT4 were significantly increased in patients with colitis ulcerative and skin T cells of psoriatic patients. Moreover, STAT4 -/- mice developed less severe experimental autoimmune encephalo-myelitis (EAE) than the wild type mice.
Intronic single nucleotide polymorphism (SNP) mostly in third intron of the STAT4 has shown to be associated with immune dysregulation and autoimmunity including systemic lupus erythematosus (SLE) and rheumatoid arthritis as well as Sjögren's disease (SD), systemic sclerosis, psoriasis and also type-1 diabetes. High incident of STAT4 genetic polymorphisms and susceptibility to autoimmune diseases is a reason to consider the STAT4 as general autoimmune disease susceptibility locus. | 1 | Biochemistry |
In 1972, C.W. Horsting of the RCA Corporation published a paper which reported test results on the reliability of semiconductor devices in which the connections were made using aluminium wires bonded ultrasonically to gold plated posts. His paper demonstrated the importance of the Kirkendall effect in wire bonding technology, but also showed the significant contribution of any impurities present to the rate at which precipitation occurred at the wire bonds. Two of the important contaminants that have this effect, known as Horsting effect (Horsting voids) are fluorine and chlorine. Both Kirkendall voids and Horsting voids are known causes of wire bond fractures, though historically this cause is often confused with the purple colored appearance of one of the five different gold-aluminium intermetallics, commonly referred to as "purple plague" and less often "white plague". | 8 | Metallurgy |
In electrochemistry, CO stripping is a special process of voltammetry where a monolayer of carbon monoxide already adsorbed on the surface of an electrocatalyst is electrochemically oxidized and thus removed from the surface. A well-known process of this type is CO stripping on Pt/C electrocatalysts in which the electrooxidation peak occurs somewhere between 0.5 to 0.9 V depending on the characteristics and structural properties of the specimen. | 7 | Physical Chemistry |
CW occurs after the polymer chain has grown somewhat on the metal catalyst. The precursor is a 16 e complex with the general formula [ML(CH)(chain)]. The ethylene ligand (the monomer) dissociates to produce a highly unsaturated 14 e cation. This cation is stabilized by an agostic interaction. β-Hydride elimination then occurs to give a hydride-alkene complex. Subsequent reinsertion of the M-H into the C=C bond, but in the opposite sense gives a metal-alkyl complex.
This process, a step in the chain walk, moves the metal from the end of a chain to a secondary carbon center. At this stage, two options are available: (1) chain walking can continue or (2) a molecule of ethylene can bind to reform the 16e complex. At this second resting state, the ethylene molecule can insert to grow the polymer or dissociate inducing further chain walking. If many branches can form, a hyperbranched topology results. Therefore, ethene only homopolymerization can provide branched polymer whereas the same mechanism leads to chain straightening in α-olefin polymerization. The variation of CW by changing T, monomer concentration, or catalyst switch can be used to produce block copolymer with amorphous and semi-crystalline blocks or with blocks of different topology. | 7 | Physical Chemistry |
The first boundary condition is
which constrains the sum of a and b. The second equation is
with the notable limit as (and ) of
The mixing rules become
The cross term still must be specified by a combining rule, either
or | 7 | Physical Chemistry |
At high pressures, water has a complex phase diagram with 15 known phases of ice and several triple points, including 10 whose coordinates are shown in the diagram. For example, the triple point at 251 K (−22 °C) and 210 MPa (2070 atm) corresponds to the conditions for the coexistence of ice Ih (ordinary ice), ice III and liquid water, all at equilibrium. There are also triple points for the coexistence of three solid phases, for example ice II, ice V and ice VI at 218 K (−55 °C) and 620 MPa (6120 atm).
For those high-pressure forms of ice which can exist in equilibrium with liquid, the diagram shows that melting points increase with pressure. At temperatures above 273 K (0 °C), increasing the pressure on water vapor results first in liquid water and then a high-pressure form of ice. In the range , ice I is formed first, followed by liquid water and then ice III or ice V, followed by other still denser high-pressure forms. | 7 | Physical Chemistry |
Growth EPDs measure the amount of weight a given offspring will gain due to the parent's genetics.
Calving ease predicts the level of difficulty first time heifers will have during birth. These are determined by the percentage of unassisted births for that particular animal.
Birth weight measures how much above or below the breed's average an offspring will gain due to the parent. It does not necessarily predict the exact weight of all offspring, but instead gives a general prediction of how much extra or less weight an offspring will weigh compared to if it had been sired by another bull. High birth weight is the biggest cause of difficulty in calving, so having a bull with a low birth weight EPD is high beneficial.
Weaning and yearling weight measure the amount of weight an offspring has gained by the time it is weaned and at the one year mark. Typically the weaning weight is measured at the 205-day mark and the yearling weight is taken at the 365-day mark. Typically a larger number is favored for both of these traits.
Milk EPDs give an estimate for the maternal portion of the weaning weight that determined by milk production of the dam. It is measured in pounds of weaning weight of a bulls grandprogeny due to the milk production of the bulls daughters. | 1 | Biochemistry |
Managing populations based on minimizing mean kinship values is often an effective way to increase genetic diversity and to avoid inbreeding within captive populations. Kinship is the probability that two alleles will be identical by descent when one allele is taken randomly from each mating individual. The mean kinship value is the average kinship value between a given individual and every other member of the population. Mean kinship values can help determine which individuals should be mated. In choosing individuals for breeding, it is important to choose individuals with the lowest mean kinship values because these individuals are least related to the rest of the population and have the least common alleles. This ensures that rarer alleles are passed on, which helps to increase genetic diversity. It is also important to avoid mating two individuals with very different mean kinship values because such pairings propagate both the rare alleles that are present in the individual with the low mean kinship value as well as the common alleles that are present in the individual with the high mean kinship value. This genetic management technique requires that ancestry is known, so in circumstances where ancestry is unknown, it might be necessary to use molecular genetics such as microsatellite data to help resolve unknowns. | 1 | Biochemistry |
A target peptide is a short (3-70 amino acids long) peptide chain that directs the transport of a protein to a specific region in the cell, including the nucleus, mitochondria, endoplasmic reticulum (ER), chloroplast, apoplast, peroxisome and plasma membrane. Some target peptides are cleaved from the protein by signal peptidases after the proteins are transported. | 1 | Biochemistry |
Click Chemistry is a powerful tool to probe for the cellular localization of small molecules. Knowing where a small molecules goes in the cell gives powerful insights into their mechanisms of action. This approach has been used in numerous studies, and discoveries include that salinomycin localizes to lysosomes to initiate ferroptosis in cancer stem cells and that metformin derivatives accumulate in mitochondria to chelate copper(II), affecting metabolism and epigenetic changes downstream in inflammatory macrophages.
The commercial potential of click chemistry is great. The fluorophore rhodamine has been coupled onto norbornene, and reacted with tetrazine in living systems. In other cases, SPAAC between a cyclooctyne-modified fluorophore and azide-tagged proteins allowed the selection of these proteins in cell lysates.
Methods for the incorporation of click reaction partners into systems in and ex vivo contribute to the scope of possible reactions. The development of unnatural amino acid incorporation by ribosomes has allowed for the incorporation of click reaction partners as unnatural side groups on these unnatural amino acids. For example, an UAA with an azide side group provides convenient access for cycloalkynes to proteins tagged with this "AHA" unnatural amino acid. In another example, "CpK" has a side group including a cyclopropane alpha to an amide bond that serves as a reaction partner to tetrazine in an inverse diels-alder reaction.
The synthesis of luciferin exemplifies another strategy of isolating reaction partners, which is to take advantage of rarely-occurring, natural groups such as the 1,2-aminothiol, which appears only when a cysteine is the final N amino acid in a protein. Their natural selectivity and relative bioorthogonality is thus valuable in developing probes specific for these tags. The above reaction occurs between a 1,2-aminothiol and a 2-cyanobenzothiazole to make luciferin, which is fluorescent. This luciferin fluorescence can be then quantified by spectrometry following a wash, and used to determine the relative presence of the molecule bearing the 1,2-aminothiol. If the quantification of non-1,2-aminothiol-bearing protein is desired, the protein of interest can be cleaved to yield a fragment with a N Cys that is vulnerable to the 2-CBT.
Additional applications include:
*two-dimensional gel electrophoresis separation
*preparative organic synthesis of 1,4-substituted triazoles
*modification of peptide function with triazoles
*modification of natural products and pharmaceuticals
*natural product discovery
*drug discovery
*macrocyclizations using Cu(I) catalyzed triazole couplings
*modification of DNA and nucleotides by triazole ligation
*supramolecular chemistry: calixarenes, rotaxanes, and catenanes
*dendrimer design
*carbohydrate clusters and carbohydrate conjugation by Cu(1) catalyzed triazole ligation reactions
*polymers and biopolymers
*surfaces
*material science
*nanotechnology,
* bioconjugation, for example, azidocoumarin, and
*biomaterials
In combination with combinatorial chemistry, high-throughput screening, and building chemical libraries, click chemistry has hastened new drug discoveries by making each reaction in a multistep synthesis fast, efficient, and predictable. | 0 | Organic Chemistry |
Emerin is a protein that in humans is encoded by the EMD gene, also known as the STA gene. Emerin, together with LEMD3, is a LEM domain-containing integral protein of the inner nuclear membrane in vertebrates. Emerin is highly expressed in cardiac and skeletal muscle. In cardiac muscle, emerin localizes to adherens junctions within intercalated discs where it appears to function in mechanotransduction of cellular strain and in beta-catenin signaling. Mutations in emerin cause X-linked recessive Emery–Dreifuss muscular dystrophy, cardiac conduction abnormalities and dilated cardiomyopathy.
It is named after Alan Emery. | 1 | Biochemistry |
While the Toll and Imd signalling pathways of Drosophila are commonly depicted as independent for explanatory purposes, the underlying complexity of Imd signalling involves a number of likely mechanisms wherein Imd signalling interacts with other signalling pathways including Toll and JNK. While the paradigm of Toll and Imd as largely independent provides a useful context for the study of immune signalling, the universality of this paradigm as it applies to other insects has been questioned. In Plautia stali stinkbugs, suppression of either Toll or Imd genes simultaneously leads to reduced activity of classic Toll and Imd effectors from both pathways. | 1 | Biochemistry |
The ability to form carbon-carbon, carbon-nitrogen, and carbon-oxygen bonds enantioselectively under mild conditions makes the Trost asymmetric allylic alkylation extremely appealing for the synthesis of complex molecules.
An example of this reaction is the synthesis of an intermediate in the combined total synthesis of galantamine and morphine with 1 mol% [pi-allylpalladium chloride dimer], 3 mol% (S,S) Trost ligand, and triethylamine in dichloromethane at room temperature. These conditions result in the formation of the (−)-enantiomer of the aryl ether in 72% chemical yield and 88% enantiomeric excess.
Another Tsuji–Trost reaction was used during the initial stages of the synthesis of (−)-neothiobinupharidine. This recent work demonstrates the ability of this reaction to give highly diastereoselective (10:1) and enantioselective (97.5:2.5) products from achiral starting material with only a small amount of catalyst (1%). | 0 | Organic Chemistry |
Pewter () is a malleable metal alloy consisting of tin (85–99%), antimony (approximately 5–10%), copper (2%), bismuth, and sometimes silver. In the past it was an alloy of tin and lead, but most modern pewter, in order to prevent lead poisoning, is not made with lead. Pewter has a low melting point, around , depending on the exact mixture of metals. The word pewter is probably a variation of "spelter", a term for zinc alloys (originally a colloquial name for zinc). | 8 | Metallurgy |
When insulin binds to the cell's receptor, it results in negative feedback by limiting or stopping some other actions in the cell. It inhibits the release and production of glucose from the cells which is an important part in reducing the glucose blood level. Insulin will also inhibit the breakdown of glycogen into glucose by inhibiting the expression of the enzymes that catalyzes the degradation of Glycogen.
An example of negative feedback is slowing or stopping the intake of glucose after the pathway was activated. Negative feedback is shown in the insulin signal transduction pathway by constricting the phosphorylation of the insulin-stimulated tyrosine. The enzyme that deactivates or phosphorylates the insulin-stimulated tyrosine is called tyrosine phosphatases (PTPases). When activated, this enzyme provides a negative feedback by catalyzing the dephosphorylation of the insulin receptors. The dephosphorylation of the insulin receptor slows down glucose intake by inhibiting the activation (phosphorylation) of proteins responsible for further steps of the insulin transduction pathway. | 1 | Biochemistry |
Ellingham diagrams are a particular graphical form of the principle that the thermodynamic feasibility of a reaction depends on the sign of ΔG, the Gibbs free energy change, which is equal to ΔH − TΔS, where ΔH is the enthalpy change and ΔS is the entropy change.
The Ellingham diagram plots the Gibbs free energy change (ΔG) for each oxidation reaction as a function of temperature. For comparison of different reactions, all values of ΔG refer to the reaction of the same quantity of oxygen, chosen as one mole O ( mol ) by some authors and one mole by others. The diagram shown refers to 1 mole , so that e.g. the line for the oxidation of chromium shows ΔG for the reaction Cr(s) + (g) → (s), which is of the molar Gibbs energy of formation ΔG°(, s).
In the temperature ranges commonly used, the metal and the oxide are in a condensed state (solid or liquid), and oxygen is a gas with a much larger molar entropy. For the oxidation of each metal, the dominant contribution to the entropy change (ΔS) is the removal of mol , so that ΔS is negative and roughly equal for all metals. The slope of the plots is therefore positive for all metals, with ΔG always becoming more negative with lower temperature, and the lines for all the metal oxides are approximately parallel. Since these reactions are exothermic, they always become feasible at lower temperatures. At a sufficiently high temperature, the sign of ΔG may invert (becoming positive) and the oxide can spontaneously reduce to the metal, as shown for Ag and Cu.
For oxidation of carbon, the red line is for the formation of CO: C(s) + (g) → CO(g) with an increase in the number of moles of gas, leading to a positive ΔS and a negative slope. The blue line for the formation of is approximately horizontal, since the reaction C(s) + (g) → (g) leaves the number of moles of gas unchanged so that ΔS is small.
As with any chemical reaction prediction based on purely thermodynamic grounds, a spontaneous reaction may be very slow if one or more stages in the reaction pathway have very high activation energies E.
If two metals are present, two equilibria have to be considered. The oxide with the more negative ΔG will be formed and the other oxide will be reduced. | 8 | Metallurgy |
The first SPR immunoassay was proposed in 1983 by Liedberg, Nylander, and Lundström, then of the Linköping Institute of Technology (Sweden). They adsorbed
human IgG onto a 600-Ångström silver film, and used the assay to detect anti-human IgG in water solution. Unlike many other immunoassays, such as ELISA, an SPR immunoassay is label free in that a label molecule is not required for detection of the analyte. Additionally, the measurements on SPR can be followed real-time allowing the monitoring of individual steps in sequential binding events particularly useful in the assessment of for instance sandwich complexes. | 7 | Physical Chemistry |
The priming effect is characterized by intense changes in the natural process of soil organic matter (SOM) turnover, resulting from relatively moderate intervention with the soil. The phenomenon is generally caused by either pulsed or continuous changes to inputs of fresh organic matter (FOM). Priming effects usually result in an acceleration of mineralization due to a trigger such as the FOM inputs. The cause of this increase in decomposition has often been attributed to an increase in microbial activity resulting from higher energy and nutrient availability released from the FOM. After the input of FOM, specialized microorganisms are believed to grow quickly and only decompose this newly added organic matter. The turnover rate of SOM in these areas is at least one order of magnitude higher than the bulk soil.
Other soil treatments, besides organic matter inputs, which lead to this short-term change in turnover rates, include "input of mineral fertilizer, exudation of organic substances by roots, mere mechanical treatment of soil or its drying and rewetting."
Priming effects can be either positive or negative depending on the reaction of the soil with the added substance. A positive priming effect results in the acceleration of mineralization while a negative priming effect results in immobilization, leading to N unavailability. Although most changes have been documented in C and N pools, the priming effect can also be found in phosphorus and sulfur, as well as other nutrients.
Löhnis was the first to discover the priming effect phenomenon in 1926 through his studies of green manure decomposition and its effects on legume plants in soil. He noticed that when adding fresh organic residues to the soil, it resulted in intensified mineralization by the humus N. It was not until 1953, though, that the term priming effect was given by Bingeman in his paper titled, The effect of the addition of organic material on the decomposition of an organic soil. Several other terms had been used before priming effect was coined, including priming action, added nitrogen interaction (ANI), extra N and additional N. Despite these early contributions, the concept of the priming effect was widely disregarded until about the 1980s-1990s.
The priming effect has been found in many different studies and is regarded as a common occurrence, appearing in most plant soil systems. However, the mechanisms which lead to the priming effect are more complex then originally thought, and still remain generally misunderstood.
Although there is a lot of uncertainty surrounding the reason for the priming effect, a few undisputed facts have emerged from the collection of recent research:
# The priming effect can arise either instantaneously or very shortly (potentially days or weeks) after the addition of a substance is made to the soil.
# The priming effect is larger in soils that are rich in C and N as compared to those poor in these nutrients.
# Real priming effects have not been observed in sterile environments.
# The size of the priming effect increases as the amount of added treatment to the soil increases.
Recent findings suggest that the same priming effect mechanisms acting in soil systems may also be present in aquatic environments, which suggests a need for broader considerations of this phenomenon in the future. | 0 | Organic Chemistry |
Transketolase activity is decreased in deficiency of thiamine, which in general is due to malnutrition. Several diseases are associated with thiamine deficiency, including beriberi, biotin-thiamine-responsive basal ganglia disease (BTBGD), Wernicke–Korsakoff syndrome, and others (see thiamine for a comprehensive listing).
In Wernicke–Korsakoff syndrome, while no mutations could be demonstrated, there is an indication that thiamine deficiency leads to Wernicke–Korsakoff syndrome only in those whose transketolase has a reduced affinity for thiamine. In this way, the activity of transketolase is greatly hindered, and, as a consequence, the entire pentose phosphate pathway is inhibited.
In Transketolase Deficiency, also known as SDDHD (Short Stature, Developmental Delay, and congenital Heart Defects), the disease is caused by an inherited autosomal recessive mutation in the TKT gene. A rare disorder of pentose phosphate metabolism with symptoms apparent in infancy including developmental delay and intellectual disability, delayed or absent speech, short stature, and congenital heart defects. Additional reported features include hypotonia, hyperactivity, stereotypic behavior, ophthalmologic abnormalities, hearing impairment, and variable facial dysmorphism, among others. Laboratory analysis shows elevated plasma and urinary polyols (erythritol, arabitol, and ribitol) and urinary sugar-phosphates (ribose-5-phosphate and xylulose/ribulose-5-phosphate). "Cell extracts from all 5 patients showed absent or low residual TKT activity. Boyle et al. (2016) suggested that the low TKT activity in some tissues, possibly from another protein with the same function, might explain why TKT deficiency is compatible with life even though TKT is an essential enzyme." | 5 | Photochemistry |
The half-life of delta bilirubin is equivalent to that of albumin since the former is bound to the latter, yields 2–3 weeks.
A free-of-bound bilirubin has a half-life of 2 to 4 hours. | 1 | Biochemistry |
Most (but not all; see minimalist channels) synthetic channels have chemical structures substantially larger than typical small molecules (molecular weights ~1-5kDa). This originates from the need to be amphiphilic, that is, have both sufficient hydrophobic portions to allow partitioning into lipid bilayer, as well as polar or charged "headgroups" to assert a defined orientation and geometry with respect to the membrane. | 6 | Supramolecular Chemistry |
In contrast to intake of CoQ as a constituent of food, such as nuts or meat, from which CoQ is normally absorbed, there is a concern about CoQ bioavailability when it is taken as a dietary supplement. Bioavailability of CoQ supplements may be reduced due to the lipophilic nature of its molecule and large molecular weight. | 1 | Biochemistry |
A biomolecule or biological molecule is loosely defined as a molecule produced by a living organism and essential to one or more typically biological processes. Biomolecules include large macromolecules such as proteins, carbohydrates, lipids, and nucleic acids, as well as small molecules such as vitamins and hormones. A more general name for this class of material is biological materials. Biomolecules are an important element of living organisms, those biomolecules are often endogenous, produced within the organism but organisms usually need exogenous biomolecules, for example certain nutrients, to survive.
Biology and its subfields of biochemistry and molecular biology study biomolecules and their reactions. Most biomolecules are organic compounds, and just four elements—oxygen, carbon, hydrogen, and nitrogen—make up 96% of the human body's mass. But many other elements, such as the various biometals, are also present in small amounts.
The uniformity of both specific types of molecules (the biomolecules) and of certain metabolic pathways are invariant features among the wide diversity of life forms; thus these biomolecules and metabolic pathways are referred to as "biochemical universals" or "theory of material unity of the living beings", a unifying concept in biology, along with cell theory and evolution theory. | 0 | Organic Chemistry |
During enzyme catalytic reaction, the substrate and active site are brought together in a close proximity. This approach has various purposes. Firstly, when substrates bind within the active site the effective concentration of it significantly increases than in solution. This means the number of substrate molecules involved in the reaction is also increased. This process also reduces the desolvation energy required for the reaction to occur. In solution substrate molecules are surrounded by solvent molecules and energy is required for enzyme molecules to replace them and contact with the substrate. Since bulk molecules can be excluded from the active site this energy output can be minimised. Next, the active site is designed to reorient the substrate to reduce the activation energy for the reaction to occur. The alignment of the substrate, after binding, is locked in a high energy state and can proceed to the next step. In addition, this binding is favoured by entropy as the energy cost associated with solution reaction is largely eliminated since solvent cannot enter active site. In the end, the active site may manipulate the Molecular orbital of the substrate into a suitable orientation to reduce activation energy.
The electrostatic states of substrate and active site must be complementary to each other. A polarized negatively charged amino acid side chain will repel uncharged substrate. But if the transition state involves the formation of an ion centre then the side chain will now produce a favourable interaction. | 1 | Biochemistry |
Phycobilins are a third group of pigments found in cyanobacteria, and glaucophyte, red algal, and cryptophyte chloroplasts. Phycobilins come in all colors, though phycoerytherin is one of the pigments that makes many red algae red. Phycobilins often organize into relatively large protein complexes about 40 nanometers across called phycobilisomes. Like photosystem I and ATP synthase, phycobilisomes jut into the stroma, preventing thylakoid stacking in red algal chloroplasts. Cryptophyte chloroplasts and some cyanobacteria don't have their phycobilin pigments organized into phycobilisomes, and keep them in their thylakoid space instead. | 5 | Photochemistry |
In chemical thermodynamics, isothermal titration calorimetry (ITC) is a physical technique used to determine the thermodynamic parameters of interactions in solution. It is most often used to study the binding of small molecules (such as medicinal compounds) to larger macromolecules (proteins, DNA etc.) in a label-free environment. It consists of two cells which are enclosed in an adiabatic jacket. The compounds to be studied are placed in the sample cell, while the other cell, the reference cell, is used as a control and contains the buffer in which the sample is dissolved.
The technique was developed by H. D. Johnston in 1968 as a part of his Ph.D. dissertation at Brigham Young University, and was considered niche until introduced commercially by MicroCal Inc. in 1988. Compared to other calorimeters, ITC has an advantage in not requiring any correctors since there was no heat exchange between the system and the environment. | 7 | Physical Chemistry |
Nuclear receptors bind to coactivators in a ligand-dependent manner. A common feature of nuclear receptor coactivators is that they contain one or more LXXLL binding motifs (a contiguous sequence of 5 amino acids where L = leucine and X = any amino acid) referred to as NR (nuclear receptor) boxes. The LXXLL binding motifs have been shown by X-ray crystallography to bind to a groove on the surface of ligand binding domain of nuclear receptors. Examples include:
* ARA (androgen receptor associated protein)
** ARA54 ()
** ARA55 ()
** ARA70 ()
* AIRE
* BCAS3 (breast carcinoma amplified sequence 3)
* CREB-binding protein
* CRTC (CREB regulated transcription coactivator)
** CRTC1 ()
** CRTC2 ()
** CRTC3 ()
* CARM1 (coactivator-associated arginine methyltransferase 1)
* Nuclear receptor coactivator (NCOA)
** NCOA1/SRC-1 (steroid receptor coactivator-1)/
** NCOA2/GRIP1 (glucocorticoid receptor interacting protein 1)/ TIF2 (transcriptional intermediary factor 2)
** NCOA3/AIB1 (amplified in breast)
** NCOA4/ARA70 (androgen receptor associated protein 70)
** NCOA5 ()
** NCOA6 ()
** NCOA7 ()
* p300
* PCAF (p300/CBP associating factor)
* PGC1 (proliferator activated receptor gamma coactivator 1)
** PPARGC1A ()
** PPARGC1B ()
* PNRC (proline-rich nuclear receptor coactivator 1)
** PNRC1 ()
** PNRC2 () | 1 | Biochemistry |
In electrochemistry, the electrode-electrolyte interface is generally charged. If the electrode is polarizable, then its surface charge depends on the electrode potential.
IUPAC defines the potential at the point of zero charge as the potential of an electrode (against a defined reference electrode) at which one of the charges defined is zero.
The potential of zero charge is used for determination of the absolute electrode potential in a given electrolyte.
IUPAC also defines the potential difference with respect to the potential of zero charge as:
where:
* E is the electrode potential difference with respect to the point of zero charge, E
* E is the potential of the same electrode against a defined reference electrode in volts
* E is the potential of the same electrode when the surface charge is zero, in the absence of specific adsorption other than that of the solvent, against the reference electrode as used above, in volts
The structure of electrolyte at the electrode surface can also depend on the surface charge, with a change around the pzc potential. For example, on a platinum electrode, water molecules have been reported to be weakly hydrogen-bonded with "oxygen-up" orientation on negatively charged surfaces, and strongly hydrogen-bonded with nearly flat orientation at positively charged surfaces.
At pzc, the colloidal system exhibits zero zeta potential (that is, the particles remain stationary in an electric field), minimum stability (exhibits maximum coagulation or flocculation rate), maximum solubility of the solid phase, maximum viscosity of the dispersion, and other peculiarities. | 7 | Physical Chemistry |
In the absence of active stabilization, the repetition rate and carrier–envelope offset frequency would be free to drift. They vary with changes in the cavity length, refractive index of laser optics, and nonlinear effects such as the Kerr effect. The repetition rate can be stabilized using a piezoelectric transducer, which moves a mirror to change the cavity length.
In Ti:sapphire lasers using prisms for dispersion control, the carrier–envelope offset frequency can be controlled by tilting the high reflector mirror at the end of the prism pair. This can be done using piezoelectric transducers.
In high repetition rate Ti:sapphire ring lasers, which often use double-chirped mirrors to control dispersion, modulation of the pump power using an acousto-optic modulator is often used to control the offset frequency. The phase slip depends strongly on the Kerr effect, and by changing the pump power one changes the peak intensity of the laser pulse and thus the size of the Kerr phase shift. This shift is far smaller than 6 rad, so an additional device for coarse adjustment is needed. A pair of wedges, one moving in or out of the intra-cavity laser beam can be used for this purpose.
The breakthrough which led to a practical frequency comb was the development of technology for stabilizing the carrier–envelope offset frequency.
An alternative to stabilizing the carrier–envelope offset frequency is to cancel it completely by use of difference frequency generation (DFG). If the difference frequency of light of opposite ends of a broadened spectrum is generated in a nonlinear crystal, the resulting frequency comb is carrier–envelope offset-free since the two spectral parts contributing to the DFG share the same carrier–envelope offset frequency (CEO frequency). This was first proposed in 1999 and demonstrated in 2011 using an erbium fiber frequency comb at the telecom wavelength. This simple approach has the advantage that no electronic feedback loop is needed as in conventional stabilization techniques. It promises to be more robust and stable against environmental perturbations. | 7 | Physical Chemistry |
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