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The LHCGRs become desensitized when exposed to LH for some time. A key reaction of this downregulation is the phosphorylation of the intracellular (or cytoplasmic) receptor domain by protein kinases. This process uncouples Gs protein from the LHCGR. | 1 | Biochemistry |
A related term "clarke of concentration" or "concentration clarke", synonym: "concentration factor (mineralogy)", is a measure to see how rich a particular ore is.
That is, the ratio between the concentrations of a chemical element in the ore, and its concentration in the whole Earth's crust (i.e. "clarke") .
If the concentration of a commodity in an ore X is , and the "clarke" of that commodity is ,
then "the clarke of concentration" of that commodity X is (dimensionless).
The value represents the degree to which the commodity is concentrated from crustal abundances to the ore by natural geochemical processes; a clue for whether the commodity could be mined economically. | 9 | Geochemistry |
Expression of phosphocholine-modified and unsubstituted C. elegans paucimannosidic glycans is reportedly development stage-specific, implying important roles in nematodal development. In support, C. elegans hex-2 gene knock-out mutants displayed reduced paucimannosidic protein levels and altered sensitivity towards nematotoxic lectins relative to wild-type worms, a correlation suggesting involvement of paucimannosidic proteins in key C. elegans survival processes. Functionally, phosphocholine-containing paucimannosidic glycans were demonstrated to display immune-modulating roles in parasitic nematodes. Paucimannosidic glycans were suggested to play roles in the nematodal innate immune system by impacting the nematode's ability to fight and survive pathogenic bacteria | 1 | Biochemistry |
Poly(ADP-ribose)polymerases (PARPs) can function in DNA repair of single strand breaks as well as double strand breaks. In single-strand break repair (base excision repair) the PARP can either facilitate removal of an oxidized sugar or strand cleavage. PARP1 binds the single-strand breaks and pulls any nearby base excision repair intermediates close. These intermediates include XRCC1 and APLF and they can be recruited directly or through the PBZ domain of the APLF. This leads to the synthesis of poly(ADP-ribose). The PBZ domain is present in many proteins involved in DNA repair and allows for the binding of the PARP and thus ADP-ribosylation which recruits repair factors to interact at the break site. PARP2 is a secondary responder to DNA damage but serves to provide functional redundancy in DNA repair.
There are many mechanisms for the repair of damaged double stranded DNA. PARP1 may function as a synapsis factor in alternative non-homologous end joining. Additionally, it has been proposed that PARP1 is required to slow replication forks following DNA damage and promotes homologous recombination at replication forks that may be dysfunctional. It is possible that PARP1 and PARP3 work together in repair of double-stranded DNA and it has been shown that PARP3 is critical for double-stranded break resolution. There are two hypotheses by which PARP1 and PARP3 coincide. The first hypothesis states that the two (ADP-ribosyl)transferases serve to function for each other's inactivity. If PARP3 is lost, this results in single-strand breaks, and thus the recruitment of PARP1. A second hypothesis suggests that the two enzyme work together; PARP3 catalyzes mono(ADP-ribosyl)ation and short poly(ADP-ribosyl)ation and serves to activate PARP1.
The PARPs have many protein targets at the site of DNA damage. KU protein and DNA-PKcs are both double-stranded break repair components with unknown sites of ADP-ribosylation. Histones are another protein target of the PARPs. All core histones and linker histone H1 are ADP-ribosylated following DNA damage. The function of these modifications is still unknown, but it has been proposed that ADP-ribosylation modulates higher-order chromatin structure in efforts to facilitate more accessible sites for repair factors to migrate to the DNA damage. | 1 | Biochemistry |
Not only is PHY closely related to Substance P (SP), but it also has a higher affinity for the mammalian neurokinin receptors that Substance P can bind to. Researchers can make use of this behavior of PHY to study the behavior of smooth muscle - a tissue where NK1 can be found. Shiina et al. (2010) used PHY to show that tachykinins as a whole can cause the longitudinal contraction of smooth muscle tissue in esophageal tissue.
Singh et Maji made use of PHYs similarity to SP along with its sequence similarity to Amyloid B-peptide 25-35 [AB(25-35)]. Despite its sequence similarity to SP, Singh et Maji showed that PHY had distinct amyloid forming capabilities . Under artificially elevated concentrations of tetrafluoroethylene (TFE) and a short incubation time, PHY was able to form amyloid fibrils. These fibrils originating from tackynins like PHY were also shown to reduce the neurotoxicity of other Amyloid fibers associated with amyloid induced diseases such as Alzheimers disease. | 1 | Biochemistry |
Asymmetric hydrogenations operate by conventional mechanisms invoked for other hydrogenations. This includes inner sphere mechanisms, outer sphere mechanisms and the σ-bond metathesis mechanisms. The type of mechanism employed by a catalyst is largely dependent on the ligands used in a system, which in turn leads to certain catalyst-substrate affinities. | 0 | Organic Chemistry |
Many human-made chemicals are derived from fossil fuels (such as petroleum or coal) in which is greatly depleted because the age of fossils far exceeds the half-life of . The relative absence of is therefore used to determine the relative contribution (or mixing ratio) of fossil fuel oxidation to the total carbon dioxide in a given region of the Earth's atmosphere.
Dating a specific sample of fossilized carbonaceous material is more complicated. Such deposits often contain trace amounts of carbon-14. These amounts can vary significantly between samples, ranging up to 1% of the ratio found in living organisms, a concentration comparable to an apparent age of 40,000 years. This may indicate possible contamination by small amounts of bacteria, underground sources of radiation causing the (n,p) reaction, direct uranium decay (although reported measured ratios of /U in uranium-bearing ores would imply roughly 1 uranium atom for every two carbon atoms in order to cause the / ratio, measured to be on the order of 10), or other unknown secondary sources of carbon-14 production. The presence of carbon-14 in the isotopic signature of a sample of carbonaceous material possibly indicates its contamination by biogenic sources or the decay of radioactive material in surrounding geologic strata. In connection with building the Borexino solar neutrino observatory, petroleum feedstock (for synthesizing the primary scintillant) was obtained with low content. In the Borexino Counting Test Facility, a / ratio of 1.94×10 was determined; probable reactions responsible for varied levels of in different petroleum reservoirs, and the lower levels in methane, have been discussed by Bonvicini et al. | 9 | Geochemistry |
Primer-design software uses algorithms that check for the potential of DNA secondary structure formation and annealing of primers to itself or within primer pairs. Physical parameters that are taken into account by the software are potential self-complementarity and GC content of the primers; similar melting temperatures of the primers; and absence of secondary structures, such as stem-loops, in the DNA target sequence. | 1 | Biochemistry |
Atmospheric methane is the methane present in Earths atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases. Methanes radiative forcing (RF) of climate is direct, and it is the second largest contributor to human-caused climate forcing in the historical period. Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe, and 28 in terms of its impact over a 100-year timeframe.
Since the beginning of the Industrial Revolution (around 1750) the methane concentration in the atmosphere has increased by about 160%, and this increase is almost entirely caused by human activities. Since 1750 methane has contributed 3% of greenhouse gas (GHG) emissions in terms of mass but is responsible for approximately 23% of radiative or climate forcing. By 2019, global methane concentrations had risen from 722 parts per billion (ppb) in pre-industrial times to 1866 ppb. This is an increase by a factor of 2.6 and the highest value in at least 800,000 years.
Methane increases the amount of ozone (O) in the troposphere ( to from the Earths surface) and also in the stratosphere (from the troposphere to above the Earths surface). Both water vapour and ozone are GHGs, which in turn add to climate warming. | 2 | Environmental Chemistry |
All the reactions associated with synthesis of biomolecule converge into the following pathway, viz., glycolysis, the Krebs cycle and the electron transport chain, exist as an amphibolic pathway, meaning that they can function anabolically as well as catabolically.
Other important amphibolic pathways are the Embden-Meyerhof pathway, the pentose phosphate pathway and the Entner–Doudoroff pathway. | 1 | Biochemistry |
Since directing groups are ligands, their effectiveness correlates with their affinities for metals. Common functional groups such as ketones usually are only weak ligands and thus often are poor DGs. This problem is solved by the use of a transient directing group. Transient DGs reversibly convert weak DGs (e.g., ketones) into strong DG's (e.g., imines) via a Schiff base condensation. Subsequent to serving their role as DGs, the imine can hydrolyze, regenerating the ketone and amine. | 0 | Organic Chemistry |
Even remote substituents on the benzene ring can affect the electron density on the aromatic ring and in turn influence the selectivity. In the hydrogenation of ketones using CBS catalysts, the ketone coordinates to the boron atom with the lone pair on the oxygen atom. In the following example, the inductive influence of the substituents can lead to differentiation of the two sp lone pairs on the oxygen atom.
The relevant stereoelectronic interaction in the starting material is the n → σ*(C–C) interaction. The electron-withdrawing substituent on the benzene ring depletes the electron density on the aromatic ring and thus makes the σ*(C–C) orbital a better acceptor than σ*(C–C). These two stereoelectronic interactions use different lone pairs on the oxygen atom (the one antiperiplanar to the σ* in question for each), leading to lone pairs with different electron densities. In particular, the enhanced depletion of electron density from the lone pair antiperiplanar to the 4-nitrophenyl group leads to weakened ability for that lone pair to coordinate to boron. This in turn results in the lone pair antiperiplanar to the 4-methoxyphenyl binding preferentially to the catalyst, leading to well-defined facial selectivity. Under optimized conditions, the product is formed with excellent levels of enantioselectivity (95% ee). | 4 | Stereochemistry |
In normal cellular operations, there is a balance between the production of lipids, and their oxidation or transport. In lipotoxic cells, there is an imbalance between the amount of lipids produced and the amount used. Upon entrance of the cell, fatty acids can be converted to different types of lipids for storage. Triacylglycerol consists of three fatty acids bound to a glycerol molecule and is considered the most neutral and harmless type of intracellular lipid storage. Alternatively, fatty acids can be converted to lipid intermediates like diacylglycerol, ceramides and fatty acyl-CoAs. These lipid intermediates can impair cellular function, which is referred to as lipotoxicity.
Adipocytes, the cells that normally function as lipid store of the body, are well equipped to handle the excess lipids. Yet, too great of an excess will overburden these cells and cause a spillover into non-adipose cells, which do not have the necessary storage space. When the storage capacity of non-adipose cells is exceeded, cellular dysfunction and/or death result. The mechanism by which lipotoxicity causes death and dysfunction is not well understood. The cause of apoptosis and extent of cellular dysfunction is related to the type of cell affected, as well as the type and quantity of excess lipids. A theory has been put forward by Cambridge researchers relating the development of lipotoxicity to the perturbation of membrane glycerophospholipid/sphingolipid homeostasis and their associated signalling events.
Currently, there is no universally accepted theory for why certain individuals are afflicted with lipotoxicity. Research is ongoing into a genetic cause, but no individual gene has been named as the causative agent. The causative role of obesity in lipotoxicity is controversial. Some researchers claim that obesity has protective effects against lipotoxicity as it results in extra adipose tissue in which excess lipids can be stored. Others claim obesity is a risk factor for lipotoxicity. Both sides accept that high fat diets put patients at increased risk for lipotoxic cells. Individuals with high numbers of lipotoxic cells usually experience both leptin and insulin resistance. However, no causative mechanism has been found for this correlation. | 1 | Biochemistry |
If the measured particles are smaller than λ/20, the form factor P(θ) can be neglected (P(θ)→1). Therefore, the Zimm equation is simplified to the Debye equation, as follows:
Note that this is also the result of an extrapolation to zero scattering angle. By acquiring data on concentration and scattering intensity, the Debye plot is constructed by plotting Kc/ΔR(θ) vs. concentration. The intercept of the fitted line gives the molecular mass, while the slope corresponds to the 2 virial coefficient.
As the Debye plot is a simplification of the Zimm equation, the same limitations of the latter apply, i.e., samples should present a monodisperse nature. For polydisperse samples, the resulting molecular mass from a static light-scattering measurement will represent an average value. An advantage of the Debye plot is the possibility to determine the second virial coefficient. This parameter describes the interaction between particles and the solvent. In macromolecule solutions, for instance, it can assume negative (particle-particle interactions are favored), zero, or positive values (particle-solvent interactions are favored). | 7 | Physical Chemistry |
The Schilling test has multiple stages. As noted below, it can be done at any time after vitamin B supplementation and body store replacement, and some clinicians recommend that in severe deficiency cases, at least several weeks of vitamin repletion be done before the test (more than one B shot, and also oral folic acid), in order to ensure that impaired absorption of B (with or without intrinsic factor) is not occurring due to damage to the intestinal mucosa from the B and folate deficiency themselves. | 1 | Biochemistry |
Ultraviolet lamps are used to sterilize workspaces and tools used in biology laboratories and medical facilities. Commercially available low-pressure mercury-vapor lamps emit about 86% of their radiation at 254 nanometers (nm), with 265 nm being the peak germicidal effectiveness curve. UV at these germicidal wavelengths damage a microorganism's DNA/RNA so that it cannot reproduce, making it harmless, (even though the organism may not be killed). Since microorganisms can be shielded from ultraviolet rays in small cracks and other shaded areas, these lamps are used only as a supplement to other sterilization techniques.
UV-C LEDs are relatively new to the commercial market and are gaining in popularity. Due to their monochromatic nature (±5 nm) these LEDs can target a specific wavelength needed for disinfection. This is especially important knowing that pathogens vary in their sensitivity to specific UV wavelengths. LEDs are mercury free, instant on/off, and have unlimited cycling throughout the day.
Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in municipal drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection has been researched for cheaply treating contaminated water using natural sunlight. The UV-A irradiation and increased water temperature kill organisms in the water.
Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. UV can be used to pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet source. The effectiveness of such a process depends on the UV absorbance of the juice.
Pulsed light (PL) is a technique of killing microorganisms on surfaces using pulses of an intense broad spectrum, rich in UV-C between 200 and 280 nm. Pulsed light works with xenon flash lamps that can produce flashes several times per second. Disinfection robots use pulsed UV.
The antimicrobial effectiveness of filtered far-UVC (222 nm) light on a range of pathogens, including bacteria and fungi showed inhibition of pathogen growth, and since it has lesser harmful effects, it provides essential insights for reliable disinfection in healthcare settings, such as hospitals and long-term care homes. UVC has also been shown to be effective at degrading SARS-CoV-2 virus. | 5 | Photochemistry |
Cancer research has been ongoing for centuries, trying to elucidate the origin of its cause. As cancer research evolves with time, the scientific community tends to pay more attention to cell metabolism and how to target these metabolic needs and changes that cells undergo during carcinogenesis. There is growing evidence that metabolic dependencies in cancer are influenced by tissue environment, being this important to consider the TME for different in vitro and in vivo models to study oncometabolism in different cancer scenarios.
There is extensive research on the modulation of BET proteins in cancer models of breast. These proteins appear to be involved in oncometabolism and targeting and uncoupling BRD4 actions in carcinogenic cells, as well as stopping pro-migratory signals and changing cytokine metabolism, particularly IL-6. The same group has reported on the importance of exosomes in the TME and how these vesicles, shed by adipocytes, can carry a specific molecular cargo that causes metabolic changes in the cell, leading to pro-metastatic changes in the recipient breast cancer cells. | 1 | Biochemistry |
Reductive elimination generally occurs more rapidly from a more sterically hindered metal center because the steric encumbrance is alleviated upon reductive elimination. Additionally, wide ligand bite angles generally accelerate reductive elimination because the sterics force the eliminating groups closer together, which allows for more orbital overlap. | 0 | Organic Chemistry |
Pewter, being a softer material, can be manipulated in various ways such as being cast, hammered, turned, spun and engraved.
Given that pewter is soft at room temperature, a pewter bell does not ring clearly. Cooling it in liquid nitrogen hardens it and enables it to ring, but also makes it more brittle. | 8 | Metallurgy |
Corrosion in space is the corrosion of materials occurring in outer space. Instead of moisture and oxygen acting as the primary corrosion causes, the materials exposed to outer space are subjected to vacuum, bombardment by ultraviolet and X-rays, and high-energy charged particles (mostly electrons and protons from solar wind). In the upper layers of the atmosphere (between 90–800 km), the atmospheric atoms, ions, and free radicals, most notably atomic oxygen, play a major role. The concentration of atomic oxygen depends on altitude and solar activity, as the bursts of ultraviolet radiation cause photodissociation of molecular oxygen. Between 160 and 560 km, the atmosphere consists of about 90% atomic oxygen. | 8 | Metallurgy |
In crystallography, a fractional coordinate system (crystal coordinate system) is a coordinate system in which basis vectors used to the describe the space are the lattice vectors of a crystal (periodic) pattern. The selection of an origin and a basis define a unit cell, a parallelotope (i.e., generalization of a parallelogram (2D) or parallelepiped (3D) in higher dimensions) defined by the lattice basis vectors where is the dimension of the space. These basis vectors are described by lattice parameters (lattice constants) consisting of the lengths of the lattice basis vectors and the angles between them .
Most cases in crystallography involve two- or three-dimensional space. In the three-dimensional case, the basis vectors are commonly displayed as with their lengths denoted by respectively, and the angles denoted by , where conventionally, is the angle between and , is the angle between and , and is the angle between and . | 3 | Analytical Chemistry |
Common applications of BLI include in vivo studies of infection (with bioluminescent pathogens), cancer progression (using a bioluminescent cancer cell line), and reconstitution kinetics (using bioluminescent stem cells).
Researchers at UT Southwestern Medical Center have shown that bioluminescence imaging can be used to determine the effectiveness of cancer drugs that choke off a tumor's blood supply. The technique requires luciferin to be added to the bloodstream, which carries it to cells throughout the body. When luciferin reaches cells that have been altered to carry the firefly gene, those cells emit light.
The BLT inverse problem of 3D reconstruction of the distribution of bioluminescent molecules from data measured on the animal surface is inherently ill-posed. The first small animal study using BLT was conducted by researchers at the University of Southern California, Los Angeles, USA in 2005. Following this development, many research groups in USA and China have built systems that enable BLT.
Mustard plants have had the gene that makes fireflies' tails glow added to them so that the plants glow when touched. The effect lasts for an hour, but an utra-sensitive camera is needed to see the glow. | 1 | Biochemistry |
Antibody is famous for its high affinity and selectivity, so it is the good way to detect AMPylated proteins. Recently, ɑ- AMP antibodies is used to directly detect and isolate AMPylated proteins (especially AMPylated tyrosine and AMPylated threonine) from cells and cell lysates. AMPylation is a post-translational modification, so it will modify protein properties by giving the polar character of AMP and hydrophobicity. Thus, instead of using antibodies that detect a whole peptide sequence, raising AMP antibodies directly targeted to specific amino acids are preferred. | 1 | Biochemistry |
In the first experiments with laser heating, temperature came from a calibration of laser power made with known melting points of various materials. When using the pulsed ruby laser this was unreliable due to the short pulse. YAG lasers quickly become the standard, heating for relatively long duration, and allowing observation of the sample throughout the heating process. It was with the first use of YAG lasers that Bassett used an optical pyrometer to measure temperatures in the range of 1000 °C to 1600 °C. The first temperature measurements had a standard deviation of 30 °C from the brightness temperature, but due to the small sample size was estimated to be 50 °C with the possibility that the true temperature of the sample being was 200 °C higher than that of the brightness measurement. Spectrometry of the incandescent light became the next method of temperature measurement used in Bassett's group. The energy of the emitted radiation could be compared to known black-body radiation spectra to derive a temperature. Calibration of these systems is done with published melting points or melting points as measured by resistive heating. | 7 | Physical Chemistry |
In December 2021, the FDA came up with a draft guidance for the use of ASO drug products. This draft guidance was directed towards sponsor-investigators who are developing individualized investigational antisense oligonucleotides (ASO) drug products for severely debilitating or life threatening diseases. Severely debilitating corresponds to a disease or condition that causes major irreversible morbidity. However, life-threatening is defined as the disease or condition has a likelihood of death unless the course of treatment leads to an endpoint of survival. Usually individuals that have a severely debilitating life threatening disease don't have any alternative treatment options, and their diseases will be rapidly progressing, leading to an early death and/or devastating or irreversible morbidity within a short time frame without treatment.
Drug development is usually targeted for a large number of individuals, in this case that is not possible because of the specificity of the mechanism of action of the ASO combined with the rarity of the treatment-amenable patient population. Under FDA regulations, a protocol under which an individual ASO product is administered to a human subject must be reviewed and approved by an institutional review board (IRB) before it can be administered to human subjects. When the individual is a child, additional safeguards need to be identified in order to prevent any developmental issues from occurring that may affect the life of the individual. The sponsor-investigator needs to get informed consent from the individual or from the person who is responsible for the individual. The consent needs to include a description of reasonably foreseeable risks or discomforts as part of the use of the ASO drug. The sponsor also needs to get individuals clinical and genetic diagnosis to confirm that the ASO will be beneficial. The analysis may be through gene sequencing, enzymatic analysis, biochemical testing, imaging evaluations. All results need to be included in the application. Also the sponsor needs to include evidence that establishes the role of the gene variant targeted by the ASO drug. The sponsor/investigator need to also provide evidence that the identified gene variant or variants are unique to the individual.
The guidance suggests that the starting dose should be based on available non-clinical data that has been collected from model organisms or in vitro studies and should be in correlation with other ASO drug product dosing information that is available. At the starting dose, pharmacological effects are expected. Furthermore, It is advised that a dosing escalation method be utilized. This includes the step of escalating the dodge from its initial dose based on pharmacodynamic effects and/or trial participants' response to the ASO.
In addition, protocols submitted to the FDA need to have a clear dosing plan and justification for selecting the starting dose, dosing interval, and plan for dose escalation or dose reduction based on clinical pharmacodynamic effects of the drug on the individual. Also all anticipated outcomes should be included in the drug plan when submitted to the FDA. It is extremely important for the investigators to monitor the patient closely during dose escalation. During the escalation period, adequate time should be provided in order to see therapeutic results. It is advised that the investigator not make concurrent changes to the dosing interval along with the dose without justification. The submitted plan should include a de-escalation/discontinuation plan if toxicity is observed. All drug administration needs to take place in an inpatient setting just to get a grasp of the adverse effects the drug may have. Once drug toxicity, beneficiancy and adverse effects are identified, the drug can be administered in an outpatient manner as long as the same concentration of drug is administered. | 1 | Biochemistry |
A thermodynamic cycle is constructed as a sequence of stages or steps. Each stage consists of a thermodynamic operation followed by a thermodynamic process. For example, an initial thermodynamic operation of a cycle of a Carnot heat engine could be taken as the setting of the working body, at a known high temperature, into contact with a thermal reservoir at the same temperature (the hot reservoir), through a wall permeable only to heat, while it remains in mechanical contact with the work reservoir. This thermodynamic operation is followed by a thermodynamic process, in which the expansion of the working body is so slow as to be effectively reversible, while internal energy is transferred as heat from the hot reservoir to the working body and as work from the working body to the work reservoir. Theoretically, the process terminates eventually, and this ends the stage. The engine is then subject to another thermodynamic operation, and the cycle proceeds into another stage. The cycle completes when the thermodynamic variables (the thermodynamic state) of the working body return to their initial values. | 7 | Physical Chemistry |
In chemical thermodynamics, an exergonic reaction is a chemical reaction where the change in the free energy is negative (there is a net release of free energy). This indicates a spontaneous reaction if the system is closed and initial and final temperatures are the same. For processes that take place in a closed system at constant pressure and temperature, the Gibbs free energy is used, whereas the Helmholtz energy is relevant for processes that take place at constant volume and temperature. Any reaction occurring at constant temperature without input of electrical or photon energy is exergonic, according to the second law of thermodynamics. An example is cellular respiration.
Symbolically, the release of free energy, , in an exergonic reaction (at constant pressure and temperature) is denoted as
Although exergonic reactions are said to occur spontaneously, this does not imply that the reaction will take place at an observable rate. For instance, the disproportionation of hydrogen peroxide releases free energy but is very slow in the absence of a suitable catalyst. It has been suggested that eager would be a more intuitive term in this context.
More generally, the terms exergonic and endergonic relate to the free energy change in any process, not just chemical reactions. By contrast, the terms exothermic and endothermic relate to an enthalpy change in a closed system during a process, usually associated with the exchange of heat. | 7 | Physical Chemistry |
Baking powder is used to cause the dough for breads and cakes to "rise" by creating millions of tiny carbon dioxide bubbles. Baking powder is not to be confused with baking soda, which is sodium bicarbonate (). Baking powder is a mixture of baking soda (sodium bicarbonate) and acidic salts. The bubbles are created because, when the baking powder is combined with water, the sodium bicarbonate and acid salts react to produce gaseous carbon dioxide.
Whether commercially or domestically prepared, the principles behind baking powder formulations remain the same. The acid–base reaction can be generically represented as shown:
The real reactions are more complicated because the acids are complicated. For example, starting with sodium bicarbonate and monocalcium phosphate (), the reaction produces carbon dioxide by the following stoichiometry:
A typical formulation (by weight) could call for 30% sodium bicarbonate, 5–12% monocalcium phosphate, and 21–26% sodium aluminium sulfate. Alternately, a commercial baking powder might use sodium acid pyrophosphate as one of the two acidic components instead of sodium aluminium sulfate. Another typical acid in such formulations is cream of tartar (), a derivative of tartaric acid. | 7 | Physical Chemistry |
The substance loosely called selenium sulfide (with the approximate formula SeS) is the active ingredient in some anti-dandruff shampoos. The selenium compound kills the scalp fungus Malassezia, which causes shedding of dry skin fragments. The ingredient is also used in body lotions to treat Tinea versicolor due to infection by a different species of Malassezia fungus.
Several clinical trials have assessed the use of selenium supplements in critically ill adults; however, the effectiveness and potential benefits of selenium supplementation in this context is not well understood. | 1 | Biochemistry |
The motivation for the Fourier transformation comes from the study of a Fourier series. In the study of a Fourier series, complicated periodic functions are written as the sum of simple waves mathematically represented by sines and cosines. Due to the properties of sine and cosine, it is possible to recover the amount of each wave in the sum by an integral. In many cases it is desirable to use Eulers formula, which states that e = cos 2πθ + i sin 2πθ, to write Fourier series in terms of the basic waves e, with the distinct advantage of simplifying many unwieldy formulas.
The passage from sines and cosines to complex exponentials makes it necessary for the Fourier coefficients to be complex-valued. The usual interpretation of this complex number is that it gives both the amplitude (or size) of the wave present in the function and the phase (or the initial angle) of the wave. This passage also introduces the need for negative "frequencies". (E.G. If θ were measured in seconds then the waves e and e would both complete one cycle per second—but they represent different frequencies in the Fourier transform. Hence, frequency no longer measures the number of cycles per unit time, but is closely related.)
If A(β) is the amplitude of a Fourier component of wavelength λ and wavenumber β = 2π/λ the spatial variation in composition can be expressed by the Fourier integral:
in which the coefficients are defined by the inverse relationship:
Substituting, we obtain on equating coefficients:
This is an ordinary differential equation that has the solution:
in which A(β) is the initial amplitude of the Fourier component of wave wavenumber β and R(β) defined by:
or, expressed in terms of the diffusion coefficient D:
In a similar manner, the new diffusion equation:
has a simple sine wave solution given by:
where is obtained by substituting this solution back into the diffusion equation as follows:
For solids, the elastic strains resulting from coherency add terms to the amplification factor as follows:
where, for isotropic solids:
where E is Youngs modulus of elasticity, ν is Poissons ratio, and η is the linear strain per unit composition difference. For anisotropic solids, the elastic term depends on the direction in a manner that can be predicted by elastic constants and how the lattice parameters vary with composition. For the cubic case, Y is a minimum for either (100) or (111) directions, depending only on the sign of the elastic anisotropy.
Thus, by describing any composition fluctuation in terms of its Fourier components, Cahn showed that a solution would be unstable concerning to the sinusoidal fluctuations of a critical wavelength. By relating the elastic strain energy to the amplitudes of such fluctuations, he formalized the wavelength or frequency dependence of the growth of such fluctuations, and thus introduced the principle of selective amplification of Fourier components of certain wavelengths. The treatment yields the expected mean particle size or wavelength of the most rapidly growing fluctuation.
Thus, the amplitude of composition fluctuations should grow continuously until a metastable equilibrium is reached with preferential amplification of components of particular wavelengths. The kinetic amplification factor R is negative when the solution is stable to the fluctuation, zero at the critical wavelength, and positive for longer wavelengths—exhibiting a maximum at exactly times the critical wavelength.
Consider a homogeneous solution within the spinodal. It will initially have a certain amount of fluctuation from the average composition which may be written as a Fourier integral. Each Fourier component of that fluctuation will grow or diminish according to its wavelength.
Because of the maximum in R as a function of wavelength, those components of the fluctuation with times the critical wavelength will grow fastest and will dominate. This "principle of selective amplification" depends on the initial presence of these wavelengths but does not critically depend on their exact amplitude relative to other wavelengths (if the time is large compared with (1/R). It does not depend on any additional assumptions, since different wavelengths can coexist and do not interfere with one another.
Limitations of this theory would appear to arise from this assumption and the absence of an expression formulated to account for irreversible processes during phase separation which may be associated with internal friction and entropy production. In practice, frictional damping is generally present and some of the energy is transformed into thermal energy. Thus, the amplitude and intensity of a one-dimensional wave decrease with distance from the source, and for a three-dimensional wave, the decrease will be greater. | 7 | Physical Chemistry |
In creating the Flory–Stockmayer Theory, Flory made three assumptions that affect the accuracy of this model. These assumptions were:
# All functional groups on a branch unit are equally reactive
# All reactions occur between A and B
# There are no intramolecular reactions
As a result of these assumptions, a conversion slightly higher than that predicted by the Flory–Stockmayer Theory is commonly needed to actually create a polymer gel. Since steric hindrance effects prevent each functional group from being equally reactive and intramolecular reactions do occur, the gel forms at slightly higher conversion.
Flory postulated that his treatment can also be applied to chain-growth polymerization mechanisms, as the three criteria stated above are satisfied under the assumptions that (1) the probability of chain termination is independent of chain length, and (2) multifunctional co-monomers react randomly with growing polymer chains. | 7 | Physical Chemistry |
Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is the most common fatty acid β-oxidation disorder and a prevalent metabolic congenital error It is often identified through newborn screening. Although children are normal at birth, symptoms usually emerge between three months and two years of age, with some cases appearing in adulthood.
Medium-chain acyl-CoA dehydrogenase (MCAD) plays a crucial role in mitochondrial fatty acid β-oxidation, a process vital for generating energy during extended fasting or high-energy demand periods. This process, especially important when liver glycogen is depleted, supports hepatic ketogenesis. The specific step catalyzed by MCAD involves the dehydrogenation of acyl-CoA. This step converts medium-chain acyl-CoA to trans-2-enoyl-CoA, which is then further metabolized to produce energy in the form of ATP.
* Affected children, who seem healthy initially, may experience symptoms like low blood sugar without ketones (hypoketotic hypoglycemia) and vomiting
* Can escalate to lethargy, seizures and coma, typically triggered by illness
* Acute episodes may also involve enlarged liver (hepatomegaly) and liver issues
* Sudden death
* Administering simple carbohydrates
* Avoiding fasting
* Frequent feedings for infants
* For toddlers, a diet with less than 30% of total energy from fat
* Administering 2 g/kg of uncooked cornstarch at bedtime for sufficient overnight glucose
* Preventing hypoglycemia, especially due to excessive fasting.
* Avoiding infant formulas with medium-chain triglycerides as the main fat source | 1 | Biochemistry |
Chromatin remodeling plays a central role in the regulation of gene expression by providing the transcription machinery with dynamic access to an otherwise tightly packaged genome. Further, nucleosome movement by chromatin remodelers is essential to several important biological processes, including chromosome assembly and segregation, DNA replication and repair, embryonic development and pluripotency, and cell-cycle progression. Deregulation of chromatin remodeling causes loss of transcriptional regulation at these critical check-points required for proper cellular functions, and thus causes various disease syndromes, including cancer. | 1 | Biochemistry |
An unusual triad is found in sedolisin proteases. The low pK of the glutamate carboxylate group means that it only acts as a base in the triad at very low pH. The triad is hypothesised to be an adaptation to specific environments like acidic hot springs (e.g. kumamolysin) or cell lysosome (e.g. tripeptidyl peptidase). | 1 | Biochemistry |
It may be used in generic labels and store brands, Benylin DM, Mucinex DM, Camydex-20 tablets, Robitussin, NyQuil, Dimetapp, Vicks, Coricidin, Delsym, TheraFlu, Charcoal D, Cinfatós and others. It has been used in counterfeit medications. | 4 | Stereochemistry |
Enantiopure compounds consist of only one of the two enantiomers. Enantiopurity is of practical importance since such compositions have improved therapeutic efficacy. The switch from a racemic drug to an enantiopure drug is called a chiral switch. In many cases, the enantiomers have distinct effects. One case is that of Propoxyphene. The enantiomeric pair of propoxyphene is separately sold by Eli Lilly and company. One of the partner is dextropropoxyphene, an analgesic agent (Darvon) and the other is called levopropoxyphene, an effective antitussive (Novrad). It is interesting to note that the trade names of the drugs, DARVON and NOVRAD, also reflect the chemical mirror-image relationship. In other cases, there may be no clinical benefit to the patient. In some jurisdictions, single-enantiomer drugs are separately patentable from the racemic mixture. It is possible that only one of the enantiomers is active. Or, it may be that both are active, in which case separating the mixture has no objective benefits, but extends the drug's patentability. | 4 | Stereochemistry |
Deoxycytidine monophosphate (dCMP), also known as deoxycytidylic acid or deoxycytidylate in its conjugate acid and conjugate base forms, respectively, is a deoxynucleotide, and one of the four monomers that make up DNA. In a DNA double helix, it will base pair with deoxyguanosine monophosphate. | 1 | Biochemistry |
HeSE has been used to study the diffusion rates and mechanisms of atoms and molecules (adsorbates) at surfaces. A non-exhaustive list of the research themes associated with HeSE diffusion measurements include:
nuclear quantum effects in the surface diffusion of atomic hydrogen;
benchmarking the adsorbate/surface free energy landscape;
energy exchange (friction) between adsorbates and the surface; pairwise and many-body inter-adsorbate interactions. | 7 | Physical Chemistry |
Thiols are easily deprotonated. Relative to the alcohols, thiols are more acidic. The conjugate base of a thiol is called a thiolate. Butanethiol has a pK of 10.5 vs 15 for butanol. Thiophenol has a pK of 6, versus 10 for phenol. A highly acidic thiol is pentafluorothiophenol (CFSH) with a pK of 2.68. Thus, thiolates can be obtained from thiols by treatment with alkali metal hydroxides. | 0 | Organic Chemistry |
Aerobic exercise provokes a systemic cytokine response, including, for example, IL-6, IL-1 receptor antagonist (IL-1ra), and IL-10 (Interleukin 10) and the concentrations of chemokines, IL-8, macrophage inflammatory protein α (MIP-1α), MIP-1β, and MCP-1 rise after vigorous exercise. IL-6 was identified as a myokine based on the observation that it increased in an exponential fashion proportional to the length of exercise and the amount of muscle mass engaged in the exercise. This increase is followed by the appearance of IL-1ra and the anti-inflammatory cytokine IL-10. In general, the cytokine response to exercise and sepsis differs with regard to TNF-α. Thus, the cytokine response to exercise is not preceded by an increase in plasma-TNF-α. Following exercise, the basal plasma IL-6 concentration may increase up to 100-fold, but less dramatic increases are more frequent. The exercise-induced increase of plasma IL-6 occurs in an exponential manner and the peak IL-6 level is reached at the end of the exercise or shortly thereafter. It is the combination of mode, intensity, and duration of the exercise that determines the magnitude of the exercise-induced increase of plasma IL-6.
As studies have demonstrated IL-6 has pro-inflammatory functions when evaluated in regard to sepsis and obesity, it was initially hypothesized that the exercise-induced IL-6 response was related to muscle damage. However, a recent study suggests that eccentric exercise is not associated with a larger increase in plasma IL-6 than exercise involving concentric “nondamaging” muscle contractions. This finding supports the hypothesis that muscle damage is not required to provoke an increase in plasma IL-6 during exercise.
IL-6, among an increasing number of other recently identified myokines, remains an important topic of myokine research. It appears in muscle tissue and in the circulation during exercise at levels up to one hundred times basal rates, as noted, and may have a beneficial impact on health and bodily functioning with transient increases as P. Munoz-Canoves et al. write: "It appears consistently in the literature that IL-6, produced locally by different cell types, has a positive impact on the proliferative capacity of muscle stem cells. This physiological mechanism functions to provide enough muscle progenitors in situations that require a high number of these cells, such as during the processes of muscle regeneration and hypertrophic growth after an acute stimulus. IL-6 is also the founding member of the myokine family of muscle-produced cytokines. Indeed, muscle-produced IL-6 after repeated contractions also has important autocrine and paracrine benefits, acting as a myokine, in regulating energy metabolism, controlling, for example, metabolic functions and stimulating glucose production. It is important to note that these positive effects of IL-6 and other myokines are normally associated with its transient production and short-term action." | 1 | Biochemistry |
Another measure of human faecal contamination is the proportion of the two 3β-ol isomers of the saturated sterol form. 5α-cholestanol is formed naturally in the environment by bacteria and generally does not have a faecal origin. Samples with ratios greater than 0.7 may be contaminated with human faecal matter; samples with values less than 0.3 may be considered uncontaminated. Samples with ratios between these two cut-offs can not readily be categorised on the basis of this ratio alone.<br />
Sediments falling in the red region are classed as “contaminated” by both of the two ratios and those in the green region are classified as “uncontaminated” by the same measures. Those in the blue region are “uncontaminated” according to the 5β-coprostanol / cholesterol ratio and “uncertain” in the 5β-coprostanol / (5β-coprostanol + 5α-cholestanol) ratio. The majority of the samples between the 0.3 and 0.7 cut-offs are considered as “uncontaminated” according to the 5β-coprostanol / cholesterol ratio and so the 0.3 value must be considered as somewhat conservative. | 2 | Environmental Chemistry |
Sucrose of fatty acid esters (E 473) is used for surface treatment of some climacteric fruits such as peaches, pears, cherries, apples, bananas, etc. E473 is allowed for application on fruit surfaces in the EU at whatever level is needed to achieve a technical effect (‘quantum satis’) and has limited allowance in the US as a component of protective coatings for fruits (CFR §172.859, limited categories inc. avocados, apples, limes [but not other citrus], peaches, pars, plums, pineapples).The coating preserves the fruits by blocking respiratory gases. | 0 | Organic Chemistry |
Fluoride salts, like all salts, cause corrosion in most metals and alloys. FliNak is different from FLiBe in the sense that is a basic melt—or it has an excess of fluorine ions. As FLiNak melts, all three components are alkali fluorides and therefore disassociate into positive and negative ions. The concentration of molten fluorine ions are able to corrode any metallic structures if it is energetically favorable. This is in contrast to FLiBe, which in a 66-34 mol% mixture will be a chemically neutral mix, as fluorine ions from LiF are donated to BeF to create the tetrafluoroberyllate ion BeF. | 7 | Physical Chemistry |
Many modifications have been reported that influence the reactivity of this reagent. The compound adopts a complex cluster structure (the adjacent picture is a simplified cartoon), and additives that modify the cluster affect the reactivity of the reagent. For example, DMF, DMSO, hexamethylphosphoramide (HMPA), and 18-crown-6 interact with the potassium center, yielding solvent separated ion pairs such as K(DMSO) and tert-BuO. Whereas in benzene, on the other hand, the compound remains as a cluster structure, which is less basic. Even in polar solvents, it is not as strong as amide bases, e.g., lithium diisopropylamide, but stronger than potassium hydroxide. Its steric bulk inhibits the group from participating in nucleophilic addition, such as in a Williamson ether synthesis or related S2 reactions.
Substrates that are deprotonated by potassium t-butoxide include terminal acetylenes and active methylene compounds. It is useful in dehydrohalogenation reactions. Illustrating the latter behavior, potassium tert-butoxide reacts with chloroform yielding dichlorocarbene, which is useful for dichlorocyclopropanations. Potassium tert-butoxide can abstract a beta-proton from alkylammonium cations, leading to the Hofmann product via an elimination reaction. | 0 | Organic Chemistry |
Bioluminescence in bacteria can be regulated through a phenomenon known as autoinduction or quorum sensing. Quorum sensing is a form of cell-to-cell communication that alters gene expression in response to cell density. Autoinducer is a diffusible pheromone produced constitutively by bioluminescent bacteria and serves as an extracellular signalling molecule. When the concentration of autoinducer secreted by bioluminescent cells in the environment reaches a threshold (above 10 cells per mL), it induces the expression of luciferase and other enzymes involved in bioluminescence. Bacteria are able to estimate their density by sensing the level of autoinducer in the environment and regulate their bioluminescence such that it is expressed only when there is a sufficiently high cell population. A sufficiently high cell population ensures that the bioluminescence produced by the cells will be visible in the environment.
A well known example of quorum sensing is that which occurs between Aliivibrio fischeri and its host. This process is regulated by LuxI and LuxR, encoded by luxI and luxR respectively. LuxI is autoinducer synthase that produces autoinducer (AI) while LuxR functions as both a receptor and transcription factor for the lux operon. When LuxR binds AI, LuxR-AI complex activates transcription of the lux operon and induces the expression of luciferase. Using this system, A. fischeri has shown that bioluminescence is expressed only when the bacteria are host-associated and have reached sufficient cell densities.
Another example of quorum sensing by bioluminescent bacteria is by Vibrio harveyi, which are known to be free-living. Unlike Aliivibrio fischeri, V. harveyi do not possess the luxI/luxR regulatory genes and therefore have a different mechanism of quorum sensing regulation. Instead, they use the system known as three-channel quorum sensing system. Vibrio use small non-coding RNAs called Qrr RNAs to regulate quorum sensing, using them to control translation of energy-costly molecules. | 1 | Biochemistry |
* Cooper M. B., “Naturally Occurring Radioactive Material (NORM) in Australian Industries”, EnviroRad report ERS-006 prepared for the Australian Radiation Health and Safety Advisory Council (2005).
* Agrawal, K. K. Sahu, B. D. Pandey, "Solid waste management in non-ferrous industries in India", Resources, Conservation and Recycling 42 (2004), 99–120.
* Jongyeong Hyuna, Shigehisa Endoha, Kaoru Masudaa, Heeyoung Shinb, Hitoshi Ohyaa, "Reduction of chlorine in bauxite residue by fine particle separation", Int. J. Miner. Process., 76, 1–2, (2005), 13–20.
* Claudia Brunori, Carlo Cremisini, Paolo Massanisso, Valentina Pinto, Leonardo Torricelli, "Reuse of a treated red mud bauxite waste: studies on environmental compatibility", Journal of Hazardous Materials, 117(1), (2005), 55–63.
* Genc¸-Fuhrman H., TjellJ. C., McConchie D., "Increasing the arsenate adsorption capacity of neutralized red mud (Bauxsol™)", J. Colloid Interface Sci. 271 (2004) 313–320.
* Genc¸-Fuhrman H., Tjell J. C., McConchie D., Schuiling O., "Adsorption of arsenate from water using neutralized red mud", J. Colloid Interface Sci. 264 (2003) 327–334. | 2 | Environmental Chemistry |
The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for magnesium in 1997. If there is not sufficient information to establish EARs and RDAs, an estimate designated Adequate Intake (AI) is used instead. The current EARs for magnesium for women and men ages 31 and up are 265 mg/day and 350 mg/day, respectively. The RDAs are 320 and 420 mg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 350 to 400 mg/day depending on age of the woman. RDA for lactation ranges 310 to 360 mg/day for same reason. For children ages 1–13 years the RDA increases with age from 65 to 200 mg/day. As for safety, the IOM also sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of magnesium the UL is set at 350 mg/day. The UL is specific to magnesium consumed as a dietary supplement, the reason being that too much magnesium consumed at one time can cause diarrhea. The UL does not apply to food-sourced magnesium. Collectively the EARs, RDAs and ULs are referred to as Dietary Reference Intakes.
= Adequate intake
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women and men ages 18 and older the AIs are set at 300 and 350 mg/day, respectively. AIs for pregnancy and lactation are also 300 mg/day. For children ages 1–17 years the AIs increase with age from 170 to 250 mg/day. These AIs are lower than the U.S. RDAs. The European Food Safety Authority reviewed the same safety question and set its UL at 250 mg/day - lower than the U.S. value. The magnesium UL is unique in that it is lower than some of the RDAs. It applies to intake from a pharmacological agent or dietary supplement only, and does not include intake from food and water. | 1 | Biochemistry |
In spectroscopy and radiometry, vector radiative transfer (VRT) is a method of modelling the propagation of polarized electromagnetic radiation in low density media. In contrast to scalar radiative transfer (RT), which models only the first Stokes component, the intensity, VRT models all four components through vector methods.
For a single frequency, , the VRT equation for a scattering media can be written as follows:
where s is the path, is the propagation vector, K is the extinction matrix, is the absorption vector, B is the Planck function and Z is the scattering phase matrix.
All the coefficient matrices, K, and Z, will vary depending on the density of absorbers/scatterers present and must be calculated from their density-independent quantities, that is the attenuation coefficient vector, , is calculated from the mass absorption coefficient vector times the density of the absorber.
Moreover, it is typical for media to have multiple species causing extinction, absorption and scattering, thus these coefficient matrices must be summed up over all the different species.
Extinction is caused both by simple absorption as well as from scattering out of the line-of-sight, , therefore we calculate the extinction matrix from the combination of the absorption vector and the scattering phase matrix:
where I is the identity matrix.
The four-component radiation vector, where I, Q, U and V are the first through fourth elements of the Stokes parameters, respectively, fully describes the polarization state of the electromagnetic radiation.
It is this vector-nature that considerably complicates the equation.
Absorption will be different for each of the four components, moreover, whenever the radiation is scattered, there can be a complex transfer between the different Stokes components—see polarization mixing—thus the scattering phase function has 4*4=16 components. It is, in fact, a rank-two tensor. | 7 | Physical Chemistry |
The slow block to polyspermy in the sea urchin is mediated by the PIP secondary messenger system. Activation of the binding receptors activates PLC, which cleaves PIP in the egg plasma membrane, releasing IP into the egg cell cytoplasm. IP diffuses to the ER, where it opens Ca channels. | 1 | Biochemistry |
Each endocytic pathway focuses on a particular component, and FEME is primarily involved in transporting receptors. These include receptors for acetylcholine and IL-2. | 1 | Biochemistry |
In 1955, Ron Giovanelli published explicit expressions for several cases of interest which are touted as exact solutions to the radiative transfer equation for a semi-infinite ideal diffuser. His solutions have become the standard against which results from approximate theoretical treatments are measured. Many of the solutions appear deceptively simple due to the work of Subrahmanyan (Chandra) Chandrasekhar. For example, the total reflectance for light incident in the direction μ is
Here is known as the albedo of single scatter , representing the fraction of the radiation lost by scattering in a medium where both absorption () and scattering () take place. The function is called the H-integral, the values of which were tabulated by Chandrasekhar. | 7 | Physical Chemistry |
The detoxification of endogenous reactive metabolites such as peroxides and reactive aldehydes often cannot be achieved by the system described above. This is the result of these species' being derived from normal cellular constituents and usually sharing their polar characteristics. However, since these compounds are few in number, it is possible for enzymatic systems to utilize specific molecular recognition to recognize and remove them. The similarity of these molecules to useful metabolites therefore means that different detoxification enzymes are usually required for the metabolism of each group of endogenous toxins. Examples of these specific detoxification systems are the glyoxalase system, which acts to dispose of the reactive aldehyde methylglyoxal, and the various antioxidant systems that remove reactive oxygen species. | 1 | Biochemistry |
The Association of Applied Geochemists (AAG) is an international society that seeks to advance the study and application of geochemistry and represents scientists working in that field. | 9 | Geochemistry |
* Orbifold signature:
* Coxeter notation: [(∞,2),∞] or [∞,(2,∞)]
* Lattice: rectangular
* Point group: D
* The group pmg has two rotation centres of order two (180°), and reflections in only one direction. It has glide reflections whose axes are perpendicular to the reflection axes. The centres of rotation all lie on glide reflection axes.
;Examples of group pmg | 3 | Analytical Chemistry |
There are currently three methods in use that involve precisely targeting a DNA sequence in order to introduce a double-stranded break. Once this occurs, the cell's repair mechanisms will attempt to repair this double stranded break, often through non-homologous end joining (NHEJ), which involves directly ligating the two cut ends together. This may be done imperfectly, therefore sometimes causing insertions or deletions of base pairs, which cause frameshift mutations. These mutations can render the gene in which they occur nonfunctional, thus creating a knockout of that gene. This process is more efficient than homologous recombination, and therefore can be more easily used to create biallelic knockouts. | 1 | Biochemistry |
Progesterone is commercially produced by semisynthesis. Two main routes are used: one from yam diosgenin first pioneered by Marker in 1940, and one based on soy phytosterols scaled up in the 1970s. Additional (not necessarily economical) semisyntheses of progesterone have also been reported starting from a variety of steroids. For the example, cortisone can be simultaneously deoxygenated at the C-17 and C-21 position by treatment with iodotrimethylsilane in chloroform to produce 11-keto-progesterone (ketogestin), which in turn can be reduced at position-11 to yield progesterone. | 0 | Organic Chemistry |
Nevado joined the University of Zurich as an Assistant Professor in 2007. Her research has concentrated on catalysis and the development of selective, sustainable approaches to develop new materials. In particular, Nevado is interested in new approaches to construct C–C and C–X bonds based on transition metal catalysts. In 2011 Nevado was awarded a Starting Grant from the European Research Council to develop catalysts based on nature. These gold(I) and gold(III)-catalytic tools look to promote the synthesis of biologically relevant small molecules with high levels of stereocontrol. She was promoted to Professor in 2013. Nevado develops computational tools to study biological processes in an effort to understand cancer metastasis and progression.
She serves on the editorial board of the ACS Central Science and the advisory board of the Reaxys Doctoral Prize. | 0 | Organic Chemistry |
In organic synthesis, reagent control is an approach to selectively forming one stereoisomer out of many, the stereoselectivity is determined by the structure and chirality of the reagent used. When chiral allylmetals are used for nucleophilic addition reaction to achiral aldehydes, the chirality of the newly generated alcohol carbon is determined by the chirality of the allymetal reagents (Figure 1). The chirality of the allymetals usually comes from the asymmetric ligands used. The metals in the allylmetal reagents include boron, tin, titanium, silicon, etc.
Various chiral ligands have been developed to prepare chiral allylmetals for the reaction with aldehydes. H. C. Brown was the first to report the chiral allylboron reagents for asymmetric allylation reactions with aldehydes. The chiral allylboron reagents were synthesized from the natural product (+)-a-pinene in two steps. The TADDOL ligands developed by Dieter Seebach has been used to prepare chiral allyltitanium compounds for asymmetric allylation with aldehydes. Jim Leighton has developed chiral allysilicon compounds in which the release of ring strain facilitated the stereoselective allylation reaction, 95% to 98% enantiomeric excess could be achieved for a range of achiral aldehydes. | 4 | Stereochemistry |
Several other scales have been proposed for the ranking of the donor properties of ligands. The HEP scale ranks ligands on the basis of the C NMR shift of a reference ligand. Lever's electronic parameter ranking is related to the Ru(II/III) couple. Another scale evaluated ligands on the basis of the redox couples of [Cr(CO)L].
In a treatment akin to the TEP analysis, the donor properties of N-heterocyclic carbene (NHC) ligands have been ranked according to IR data recorded on cis-[RhCl(NHC)(CO)] complexes. | 0 | Organic Chemistry |
In organic chemistry, an ester is formed as the condensation product of a carboxylic acid and an alcohol, with water formed as the condensate by-product. An ester can also be produced with an acyl halide and an alcohol, in which case the condensate by-product is a hydrogen halide.
Polyesters are a category of polymers in which ester functionality repeats within the main chain. Polyesters are a classic example of step-growth polymer, in which a difunctional (or higher order) acid or acyl halide is reacted with a difunctional (or higher order) alcohol. Polyesters are produced commercially both as saturated and unsaturated resins. The most common and highest volume produced polyester is Polyethylene terephthalate (PET), which is an example of a saturated polyester and finds utilization in such applications as fibers for clothing and carpet, food and liquid containers (such as a water/soda bottles), as well as films.
In unsaturated polyester (UPR) chemistry, unsaturation sites are present along the chain, usually by incorporation of maleic anhydride, but maleic acid and fumaric acid are also used. Maleic acid and fumaric acid are isomers where maleic is the cis-isomer and fumaric is the trans-isomer. The ester forms of these two molecules are maleate and fumarate, respectively. When curing a UPR, the fumarate form is known to react more rapidly with the styrene radical, so isomerization catalysts, such as N,N-dimethylacetoacetamide (DMAA), are often employed in the synthesis process which converts the maleates into fumarates; the isomerization can also be encouraged with increased reaction time and temperature.
Within the UPR industry, the classification of the resins is generally based on the primary saturated acid. For example, a resin containing primarily terephthalic acid is known as a Tere resin, a resin containing primarily phthalic anhydride is known as an Ortho resin, and a resin containing primarily isophthalic acid is known as an Iso resin. Dicyclopentadiene (DCPD) is also a common UPR raw material, and can be incorporated two different ways. In one process, the DCPD is cracked in situ to form cyclopentadiene which can then be reacted with maleate/fumarate groups along the polymer chain via a Diels-alder reaction. This type of resin is known as a Nadic resin and is referred to as a poor man's Ortho, due to sharing many similar properties of an Ortho resin along with the extremely low cost of DCPD raw material. In another process, maleic anhydride is first opened with water or another alcohol to form maleic acid and is then reacted with DCPD where an alcohol from the maleic acid reacts across one of the double bonds of the DCPD. This product is then used to end-cap the UPR resin which yields a product with unsaturation on the end-groups. This type of resin is referred to as a DCPD resin.
Ortho resins comprise the most common type of UPR, and many are known as general purpose resins. FRP composites utilizing ortho resins are found in such application as boat hulls, bath ware, and bowling ball cores.
Iso resins are generally on the higher end of UPR products, both because of the relatively higher cost of the isophthalic acid as well as the superior properties they possess. Iso resins are the primary type of resin used in gel coat applications, which is similar to a paint, but is sprayed into a mold before the FRP is molded leaving a coating on the part. Gel coat resins must have lower color (almost clear) so as to not impart additional color to the part or so that they can be dyed properly. Gel coats must also have strong resistance to UV-weathering and water blistering.
Tere resins are often used when high modulus and strength are desired, but the low color properties of an Iso resin is not necessary. Terephthalic acid is generally lower cost than isophthalic acid, but both give similar strength characteristics to a UPR product. There exists a special sub-set of Tere resins, known as PET UPR resins, which are produced by catalytically cracking PET resin in the reactor to yield a mixture of terephthalic acid and ethylene glycol. Additional acids and glycols are then added along with maleic anhydride and a new polymer is produced. The end product is functionally the same as a Tere resin, but can often be lower cost to manufacture as scrap PET can be sourced cheaply. If a glycol-modified PET (PET-G) is used, exceptional properties can be imparted to the resin due to some of the exotic materials used in PET-G production. Tere and PET-UPR resins are used in many applications including cured-in-place pipe. | 7 | Physical Chemistry |
RNA splicing errors can have drastic effects on how proteins function, including the hormones secreted by the endocrine system. These effects on hormones have been identified as the cause of many endocrine disorders including thyroid-related pathological conditions, rickets, hyperinsulinemic hypoglycemia and congenital adrenal hyperplasia. One specific example of a splicing error causing an endocrine disease that has been studied using minigenes is a type of growth hormone deficiency called isolated growth hormone deficiency (IGHD), a disease that results in growth failure. IGHD type II is an autosomal dominant form caused by a mutation in the intervening sequence (IVS) adjacent to exon 3 of the gene encoding growth hormone 1, the GH-1 gene. This mutated form of IVS3 causes exon 3 to be skipped in the mRNA product. The mRNA (-E3) encodes a truncated form of hGH that then inhibits normal hGH secretion. Minigenes were used to determine that a point mutation within an intron splice enhancer (ISE) embedded in IVS3 was to blame for the skipping of E3. Moreover, it was determined that the function of the ISE is influenced by a nearby transposable AC element, revealing that this particular splicing error is caused by a trans-acting factor. | 1 | Biochemistry |
NCS is produced from succinimide by treatment with Cl+ sources, such as bleach (sodium hypochlorite), and t-butylhypochlorite, and even chlorine.
Electron-rich arenes are readily monochlorinated by NCS. Aniline and mesitylene are converted to the respective chlorinated derivatives. | 0 | Organic Chemistry |
Many researchers have shown that plants have the ability to use electrical signaling to communicate from leaves to stem to roots. Starting in the late 1800s scientists, such as Charles Darwin, examined ferns and Venus fly traps because they showed excitation patterns similar to animal nerves. However, the mechanisms behind this electrical signaling are not well known and are a current topic of ongoing research. A plant may produce electrical signaling in response to wounding, temperature extremes, high salt conditions, drought conditions, and other various stimuli.
There are two types of electrical signals that a plant uses. The first is the action potential and the second is the variation potential.
Similar to action potentials in animals, action potentials in plants are characterized as “all or nothing.” This is the understood mechanism for how plant action potentials are initiated:
* A stimulus transitorily and reversibly activates calcium ion channels
* A short burst of calcium ions into the cell through the open calcium channels
* Calcium ions reversibly inactivate H+-ATPase activity
* Depolarization (due to calcium ion influx) activates voltage gated chloride channels causing chloride ions to leave the cell and cause further depolarization
* Calcium-ATPases decreases intracellular calcium concentration by pumping calcium ions to the outside of the cell (this allows for the H+-ATPase to be reactivated and repolarization to be initiated)
* Repolarization occurs when the activated H+-ATPase pumps H+ out of the cell and the open K+ channels allow for the flow of K+ to the outside of the cell
Plant resting membrane potentials range from -80 to -200 mV. High H+-ATPase activity corresponds with hyperpolarization (up to -200mV), making it harder to depolarize and fire an action potential. This is why it is essential for calcium ions to inactivate H+-ATPase activity so that depolarization can be reached. When the voltage gated chloride channels are activated and full depolarization occurs, calcium ions are pumped out of the cell (via a calcium-ATPase) after so that H+-ATPase activity resumes so that the cell can repolarize.
Calciums interaction with the H+-ATPase is through a kinase. Therefore, calciums influx causes the activation of a kinase that phosphorylates and deactivates the H+-ATPase so that the cell can depolarize. It is unclear whether all of the heightened calcium ion intracellular concentration is solely due to calcium channel activation. It is possible that the transitory activation of calcium channels causes an influx of calcium ions into the cell which activates intracellular stores of calcium ions to be released and subsequently causes depolarization (through the inactivation of H+-ATPase and activation of voltage gated chloride channels).
Variation potentials have proven hard to study and their mechanism is less well known than action potentials. Variation potentials are slower than action potentials, are not considered “all or nothing,” and they themselves can trigger several action potentials. The current understanding is that upon wounding or other stressful events, a plant's turgor pressure changes which releases a hydraulic wave throughout the plant that is transmitted through the xylem. This hydraulic wave may activate pressure gated channels due to the sudden change in pressure. Their ionic mechanism is very different from action potentials and is thought to involve the inactivation of the P-type H+-ATPase.
Long distance electrical signaling in plants is characterized by electrical signaling that occurs over distances greater than the span of a single cell. In 1873, Sir John Burdon-Sanderson described action potentials and their long-distance propagation throughout plants. Action potentials in plants are carried out through a plants vascular network (particularly the phloem), a network of tissues that connects all of the various plant organs, transporting signaling molecules throughout the plant. Increasing the frequency of action potentials causes the phloem to become increasingly cross linked. In the phloem, the propagation of action potentials is dictated by the fluxes of chloride, potassium, and calcium ions, but the exact mechanism for propagation is not well understood. Alternatively, the transport of action potentials over short, local distances is distributed throughout the plant via plasmodesmatal connections between cells.
When a plant responds to stimuli, sometimes the response time is nearly instantaneous which is much faster than chemical signals are able to travel. Current research suggests that electrical signaling may be responsible. In particular, the response of a plant to a wound is triphasic. Phase 1 is an immediate great increase in expression of target genes. Phase 2 is a period of dormancy. Phase 3 is a weakened and delayed upregulation of the same target genes as phase 1. In phase 1, the speed of upregulation is nearly instantaneous which has led researchers to theorize that the initial response from a plant is through action potentials and variation potentials as opposed to chemical or hormonal signaling which is most likely responsible for the phase 3 response.
Upon stressful events, there is variation in a plants response. That is to say, it is not always the case that a plant responds with an action potential or variation potential. However, when a plant does generate either an action potential or variation potential, one of the direct effects can be an upregulation of a certain genes expression. In particular, protease inhibitors and calmodulin exhibit rapid upregulated gene expression. Additionally, ethylene has shown quick upregulation in the fruit of a plant as well as jasmonate in neighboring leaves to a wound. Aside from gene expression, action potentials and variation potentials also can result in stomatal and leaf movement.
In summary, electric signaling in plants is a powerful tool of communication and controls a plant's response to dangerous stimuli (like herbivory), helping to maintain homeostasis. | 1 | Biochemistry |
The M muscarinic receptors are located at many places in the body. They are located in the smooth muscles of the blood vessels, as well as in the lungs. Because the M receptor is G-coupled and mediates an increase in intracellular calcium, it typically causes contraction of smooth muscle, such as that observed during bronchoconstriction and bladder voiding. However, with respect to vasculature, activation of M on vascular endothelial cells causes increased synthesis of nitric oxide, which diffuses to adjacent vascular smooth muscle cells and causes their relaxation, thereby explaining the paradoxical effect of parasympathomimetics on vascular tone and bronchiolar tone. Indeed, direct stimulation of vascular smooth muscle, M mediates vasoconstriction in diseases wherein the vascular endothelium is disrupted.
The M receptors are also located in many glands, which help to stimulate secretion in, for example, the salivary glands, as well as other glands of the body.
Like the M muscarinic receptor, M receptors are G proteins of class G that upregulate phospholipase C and, therefore, inositol trisphosphate and intracellular calcium as a signaling pathway. | 1 | Biochemistry |
Some provitamins are:
* "Provitamin A" is a name for β-carotene, which has only about 1/6 the biological activity of retinol (vitamin A); the body uses an enzyme to convert β-carotene to retinol. In other contexts, both β-carotene and retinol are simply considered to be different forms (vitamers) of vitamin A.
* "Provitamin B5" is a name for panthenol, which may be converted in the body to vitamin B (pantothenic acid).
* Menadione is a synthetic provitamin of vitamin K.
* Provitamin D is ergosterol, and provitamin D is 7-dehydrocholesterol. They are converted by UV light into vitamin D. The human body produces provitamin D naturally; deficiency is usually caused by a lack of sun exposure, not a lack of the provitamin. | 1 | Biochemistry |
La confusion sexuelle or mating disruption, was first discussed by the Institut national de la recherche agronomique in 1974 in Bordeaux, France.
Winemakers in France, Switzerland, Spain, Germany, and Italy were the first to use the method to treat vines against the larvae of the moth genus Cochylis. | 1 | Biochemistry |
Source:
n-Butyllithium (14.0 mL of a 2.5 M solution in hexane, 35 mmol) was added dropwise to a solution of 2,6-dimethylanisole (4.95 mL, 35 mmol) in 60 mL of tetrahydrofuran at 0°, and the resulting solution was stirred at 0° for 1 hour and then at ambient temperature for 4 hours. The reaction mixture was cooled to 0°, treated with cyclohexanecarboxaldehyde (4.2 mL, 35 mmol), allowed to warm to ambient temperature again, and poured into saturated aqueous ammonium chloride solution. The mixture was extracted with ether and the ether extract was washed with water and brine and concentrated in vacuo. The residue was purified by silica gel chromatography (hexane-ether, 5:1 v/v) to give 4.2 g (48%) of the product as a colorless oil; H NMR (CDCl) δ 1.05–1.50 (m, 6H), 1.64–1.82 (m, 4H), 1.92 (m, 1H), 2.28 (d, 1H, J = 3 Hz), 2.31 (s, 3H), 2.68 (dd, 1H, J = 10, 13 Hz), 2.85 (dd, 1H, J = 3, 13 Hz), 3.57 (m, 1H), 3.75 (s, 3H), 6.95–7.10 (m, 3H). | 0 | Organic Chemistry |
CpG DNA methylation has showed a role to regulate the alternative splicing in social insects. In honey bees (Apis mellifera), CpG DNA methylation seems to regulate the exon skipping based on the first few genomic studies after honey bee genome was available. CpG DNA methylation regulated alternative splicing more extensively, not only affect exon skipping, but also intron retention, and other splicing events. | 1 | Biochemistry |
* They are considered to be among the strongest of all types of chemical bonds. This often causes ionic compounds to be very stable.
* Ionic bonds have high bond energy. Bond energy is the mean amount of energy required to break the bond in the gaseous state.
* Most ionic compounds exist in the form of a crystal structure, in which the ions occupy the corners of the crystal. Such a structure is called a crystal lattice.
* Ionic compounds lose their crystal lattice structure and break up into ions when dissolved in water or any other polar solvent. This process is called solvation. The presence of these free ions makes aqueous ionic compound solutions good conductors of electricity. The same occurs when the compounds are heated above their melting point in a process known as melting. | 6 | Supramolecular Chemistry |
Yttrium in the Solar System was created through stellar nucleosynthesis, mostly by the s-process (≈72%), but also by the r-process (≈28%). The r-process consists of rapid neutron capture by lighter elements during supernova explosions. The s-process is a slow neutron capture of lighter elements inside pulsating red giant stars.
Yttrium isotopes are among the most common products of the nuclear fission of uranium in nuclear explosions and nuclear reactors. In the context of nuclear waste management, the most important isotopes of yttrium are Y and Y, with half-lives of 58.51 days and 64 hours, respectively. Though Y has a short half-life, it exists in secular equilibrium with its long-lived parent isotope, strontium-90 (Sr) with a half-life of 29 years.
All group 3 elements have an odd atomic number, and therefore few stable isotopes. Scandium has one stable isotope, and yttrium itself has only one stable isotope, Y, which is also the only isotope that occurs naturally. However, the lanthanide rare earths contain elements of even atomic number and many stable isotopes. Yttrium-89 is thought to be more abundant than it otherwise would be, due in part to the s-process, which allows enough time for isotopes created by other processes to decay by electron emission (neutron → proton). Such a slow process tends to favor isotopes with atomic mass numbers (A = protons + neutrons) around 90, 138 and 208, which have unusually stable atomic nuclei with 50, 82, and 126 neutrons, respectively. This stability is thought to result from their very low neutron-capture cross-section. Electron emission of isotopes with those mass numbers is simply less prevalent due to this stability, resulting in them having a higher abundance. Y has a mass number close to 90 and has 50 neutrons in its nucleus.
At least 32 synthetic isotopes of yttrium have been observed, and these range in atomic mass number from 76 to 108. The least stable of these is Y with a half-life of >150 ns (Y has a half-life of >200 ns) and the most stable is Y with a half-life of 106.626 days. Apart from the isotopes Y, Y, and Y, with half-lives of 58.51 days, 79.8 hours, and 64 hours, respectively, all the other isotopes have half-lives of less than a day and most of less than an hour.
Yttrium isotopes with mass numbers at or below 88 decay primarily by positron emission (proton → neutron) to form strontium (Z = 38) isotopes. Yttrium isotopes with mass numbers at or above 90 decay primarily by electron emission (neutron → proton) to form zirconium (Z = 40) isotopes. Isotopes with mass numbers at or above 97 are also known to have minor decay paths of β delayed neutron emission.
Yttrium has at least 20 metastable ("excited") isomers ranging in mass number from 78 to 102. Multiple excitation states have been observed for Y and Y. While most of yttrium's isomers are expected to be less stable than their ground state, Y, Y, Y, Y, Y, Y, and Y have longer half-lives than their ground states, as these isomers decay by beta decay rather than isomeric transition. | 8 | Metallurgy |
In chemistry, a halogen bond (XB) occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. Like a hydrogen bond, the result is not a formal chemical bond, but rather a strong electrostatic attraction. Mathematically, the interaction can be decomposed in two terms: one describing an electrostatic, orbital-mixing charge-transfer and another describing electron-cloud dispersion. Halogen bonds find application in supramolecular chemistry; drug design and biochemistry; crystal engineering and liquid crystals; and organic catalysis. | 6 | Supramolecular Chemistry |
Trimethylsilyl iodide (iodotrimethylsilane or TMSI) is an organosilicon compound with the chemical formula (CH)SiI. It is a colorless, volatile liquid at room temperature. | 0 | Organic Chemistry |
Essential in synergetics is the order-parameter concept which was originally introduced in the Ginzburg–Landau theory in order to describe phase transitions in thermodynamics. The order parameter concept is generalized by Haken to the "enslaving-principle" saying that the dynamics of fast-relaxing (stable) modes is completely determined by the slow dynamics of, as a rule, only a few order-parameters (unstable modes). The order parameters can be interpreted as the amplitudes of the unstable modes determining the macroscopic pattern.
As a consequence, self-organization means an enormous reduction of degrees of freedom (entropy) of the system which macroscopically reveals an increase of order (pattern-formation). This far-reaching macroscopic order is independent of the details of the microscopic interactions of the subsystems. This supposedly explains the self-organization of patterns in so many different systems in physics, chemistry and biology. | 7 | Physical Chemistry |
Berthelots reagent is an alkaline solution of phenol and hypochlorite, used in analytical chemistry. It is named after its inventor, Marcellin Berthelot. Ammonia reacts with Berthelots reagent to form a blue product which is used in a colorimetric method for determining ammonia. The reagent can also be used for determining urea. In this case the enzyme urease is used to catalyze the hydrolysis of urea into carbon dioxide and ammonia. The ammonia is then determined with Berthelot's reagent. | 3 | Analytical Chemistry |
The mappae clavicula is a medieval Latin text containing manufacturing recipes for crafts materials, including for metals, glass, mosaics, and dyes and tints for materials. The information and style in the recipes is very terse. Each recipe consists of the names of the ingredients and typically about two sentences on combining the ingredients together. A small minority of the recipes go to about six sentences. The text comes with a short preamble, and other than that it is just recipes. The number of recipes was expanded over the course of the medieval centuries, and some medieval copies have deletions as well as additions, so it is better thought of as a family of texts with a largely common core, not a single text. Most of the Mappae Clavicula recipes are also in medieval Latin in a text known as the Compositiones ad Tingenda (English: "Recipes for Coloring (or Tingeing)"). | 8 | Metallurgy |
Formate dehydrogenases are a set of enzymes that catalyse the oxidation of formate to carbon dioxide, donating the electrons to a second substrate, such as NAD in formate:NAD+ oxidoreductase () or to a cytochrome in formate:ferricytochrome-b1 oxidoreductase (). This family of enzymes has attracted attention as inspiration or guidance on methods for the carbon dioxide fixation, relevant to global warming. | 1 | Biochemistry |
Signal transducer and activator of transcription 4 (STAT4) is a transcription factor belonging to the STAT protein family, composed of STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B, STAT6. STAT proteins are key activators of gene transcription which bind to DNA in response to cytokine gradient. STAT proteins are a common part of Janus kinase (JAK)- signalling pathways, activated by cytokines.STAT4 is required for the development of Th1 cells from naive CD4+ T cells and IFN-γ production in response to IL-12. There are two known STAT4 transcripts, STAT4α and STAT4β, differing in the levels of interferon-gamma (IFN-γ )production downstream. | 1 | Biochemistry |
Cucurbiturils are efficient host molecules in molecular recognition and have a particularly high affinity for positively charged or cationic compounds. High association constants with positively charged molecules are attributed to the carbonyl groups that line each end of the cavity and can interact with cations in a similar fashion to crown ethers. The affinity of cucurbiturils can be very high. For example, the affinity equilibrium constant of cucurbit[7]uril with the positively charged 1-aminoadamantane hydrochloride is experimentally determined at 4.23*10.
Host guest interactions also significantly influence solubility behavior of cucurbiturils. Cucurbit[6]uril dissolves poorly in just about any solvent but solubility is greatly improved in a solution of potassium hydroxide or in an acidic solution. The cavitand forms a positively charged inclusion compound with a potassium ion or a hydronium ion respectively which have much greater solubility than the uncomplexed neutral molecule.
CB[10] is large enough to hold other molecular hosts such as a calixarene molecule. With a calixarene guest different chemical conformations (cone, 1,2-alternate, 1,3-alternate) are in rapid equilibrium. Allosteric control is provided when an adamantane molecule forces a cone conformation with a calixarene - adamantane inclusion complex within a CB[10] molecule. | 6 | Supramolecular Chemistry |
Thiosulfoxides are orthogonally isomeric with disulfides, having the second sulfur branching from the first and not partaking in a continuous chain, i.e. >S=S rather than −S−S−.
Disulfide bonds are analogous but more common than related peroxide, thioselenide, and diselenide bonds. Intermediate compounds of these also exist, for example thioperoxides (also known as oxasulfides) such as hydrogen thioperoxide, have the formula ROSR (equivalently RSOR). These are isomeric to sulfoxides in a similar manner to the above; i.e. >S=O rather than −S−O−.
Thiuram disulfides, with the formula (RNCSS), are disulfides but they behave distinctly because of the thiocarbonyl group.
Compounds with three sulfur atoms, such as CHS−S−SCH, are called trisulfides, or trisulfide bonds. | 0 | Organic Chemistry |
Ziegler–Natta catalysts of the third class, non-metallocene catalysts, use a variety of complexes of various metals, ranging from scandium to lanthanoid and actinoid metals, and a large variety of ligands containing oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S). The complexes are activated using MAO, as is done for metallocene catalysts.
Most Ziegler–Natta catalysts and all the alkylaluminium cocatalysts are unstable in air, and the alkylaluminium compounds are pyrophoric. The catalysts, therefore, are always prepared and handled under an inert atmosphere. | 7 | Physical Chemistry |
In the 1960s and 1970s, GFP, along with the separate luminescent protein aequorin (an enzyme that catalyzes the breakdown of luciferin, releasing light), was first purified from the jellyfish Aequorea victoria and its properties studied by Osamu Shimomura. In A. victoria, GFP fluorescence occurs when aequorin interacts with Ca ions, inducing a blue glow. Some of this luminescent energy is transferred to the GFP, shifting the overall color towards green. However, its utility as a tool for molecular biologists did not begin to be realized until 1992 when Douglas Prasher reported the cloning and nucleotide sequence of wtGFP in Gene. The funding for this project had run out, so Prasher sent cDNA samples to several labs. The lab of Martin Chalfie expressed the coding sequence of wtGFP, with the first few amino acids deleted, in heterologous cells of E. coli and C. elegans, publishing the results in Science in 1994. Frederick Tsuji's lab independently reported the expression of the recombinant protein one month later. Remarkably, the GFP molecule folded and was fluorescent at room temperature, without the need for exogenous cofactors specific to the jellyfish. Although this near-wtGFP was fluorescent, it had several drawbacks, including dual peaked excitation spectra, pH sensitivity, chloride sensitivity, poor fluorescence quantum yield, poor photostability and poor folding at .
The first reported crystal structure of a GFP was that of the S65T mutant by the Remington group in Science in 1996. One month later, the Phillips group independently reported the wild-type GFP structure in Nature Biotechnology. These crystal structures provided vital background on chromophore formation and neighboring residue interactions. Researchers have modified these residues by directed and random mutagenesis to produce the wide variety of GFP derivatives in use today. Further research into GFP has shown that it is resistant to detergents, proteases, guanidinium chloride (GdmCl) treatments, and drastic temperature changes. | 1 | Biochemistry |
The survival of these bacteria is dependent on the physiochemical conditions of their environment. Although they are sensitive to certain factors such as quality of inorganic substrate, they are able to thrive under some of the most inhospitable conditions in the world, such as temperatures above 110 degrees Celsius and below 2 pH. The most important requirement for chemolithotropic life is an abundant source of inorganic compounds, which provide a suitable electron donor in order to fix CO and produce the energy the microorganism needs to survive. Since chemosynthesis can take place in the absence of sunlight, these organisms are found mostly around hydrothermal vents and other locations rich in inorganic substrate.
The energy obtained from inorganic oxidation varies depending on the substrate and the reaction. For example, the oxidation of hydrogen sulfide to elemental sulfur by ½O produces far less energy (50 kcal/mol or 210 kJ/mol) than the oxidation of elemental sulfur to sulfate (150 kcal/mol or 627 kJ/mol) by 3/2 O,. The majority of lithotrophs fix carbon dioxide through the Calvin cycle, an energetically expensive process. For some low-energy substrates, such as ferrous iron, the cells must cull through large amounts of inorganic substrate to secure just a small amount of energy. This makes their metabolic process inefficient in many places and hinders them from thriving. | 1 | Biochemistry |
Aggregates may also form from colloids trapped on the surface of rising bubbles. For example, Kepkay et al. found that bubble coagulation leads to an increase in bacterial respiration since more food is available to them. | 9 | Geochemistry |
A mass spectrum of an organic compound will usually contain a small peak of one mass unit greater than the apparent molecular ion peak (M) of the whole molecule. This is known as the M+1 peak and comes from the few molecules that contain a C atom in place of a C. A molecule containing one carbon atom will be expected to have an M+1 peak of approximately 1.1% of the size of the M peak, as 1.1% of the molecules will have a C rather than a C. Similarly, a molecule containing two carbon atoms will be expected to have an M+1 peak of approximately 2.2% of the size of the M peak, as there is double the previous likelihood that any molecule will contain a C atom.
In the above, the mathematics and chemistry have been simplified, however it can be used effectively to give the number of carbon atoms for small- to medium-sized organic molecules. In the following formula the result should be rounded to the nearest integer:
where C = number of C atoms, X = amplitude of the M ion peak, and Y = amplitude of the M +1 ion peak.
C-enriched compounds are used in the research of metabolic processes by means of mass spectrometry. Such compounds are safe because they are non-radioactive. In addition, C is used to quantify proteins (quantitative proteomics). One important application is in stable isotope labeling by amino acids in cell culture (SILAC). C-enriched compounds are used in medical diagnostic tests such as the urea breath test. Analysis in these tests is usually of the ratio of C to C by isotope ratio mass spectrometry.
The ratio of C to C is slightly higher in plants employing C4 carbon fixation than in plants employing C3 carbon fixation. Because the different isotope ratios for the two kinds of plants propagate through the food chain, it is possible to determine if the principal diet of a human or other animal consists primarily of C3 plants or C4 plants by measuring the isotopic signature of their collagen and other tissues. | 9 | Geochemistry |
Efforts of federal, state and local governments, working in partnership through the Chesapeake Bay Program along with the Chesapeake Bay Foundation and other nonprofit environmental groups, to restore or at least maintain the current water quality, have had mixed results. One particular obstacle to cleaning up the bay is that much of the polluting substances are discharged far upstream in states far removed from the bay: New York and Pennsylvania. Despite the State of Maryland spending over $100 million to restore the bay, conditions have continued to grow worse. In the mid-20th century, the Bay supported over 6,000 oystermen. As of 2008, there were fewer than 500.
In June 2000, the Chesapeake Bay Program adopted Chesapeake 2000, an agreement adopted by the member jurisdictions, intended to guide restoration activities throughout the Chesapeake Bay watershed through 2010. One component of this agreement was a series of upgrades to sewage treatment plants throughout the watershed. In 2016 EPA stated that the upgrades "have resulted in steep reductions in nitrogen and phosphorus pollution... despite increases in human population and wastewater volume."
EPA published a series of scientific documents on water quality criteria for the bay between 2004 and 2010. The criteria documents, which describe specific pollutants and their effects on aquatic species, are used by the states to develop water quality standards (WQS) for individual water bodies. Delaware, Maryland, Virginia, and the District of Columbia adopted WQS for various Chesapeake Bay tributaries in the mid-2000s, referencing the EPA criteria documents, as well as their own extensive data gathering and modeling efforts.
Restoration efforts that began in the 1990s have continued into the 21st century and show potential for growth of the native oyster population. Efforts to repopulate the bay using oyster hatcheries have been carried out by a group called the Oyster Recovery Partnership, with some success. In 2011 the group placed 6 million oysters on of the Trent Hall sanctuary. Scientists from the Virginia Institute of Marine Science at the College of William & Mary claim that experimental reefs created in 2004 now house 180 million native oysters, Crassostrea virginica, which is far fewer than the billions that once existed. | 2 | Environmental Chemistry |
Polyamorphism is the ability of a substance to exist in several different amorphous modifications. It is analogous to the polymorphism of crystalline materials. Many amorphous substances can exist with different amorphous characteristics (e.g. polymers). However, polyamorphism requires two distinct amorphous states with a clear, discontinuous (first-order) phase transition between them. When such a transition occurs between two stable liquid states, a polyamorphic transition may also be referred to as a liquid–liquid phase transition. | 7 | Physical Chemistry |
Isotopic ratio relative to the mass of the tracer element in each component;
where, and are the molecular weight of each isotopic expression of the substrate and product. | 7 | Physical Chemistry |
For the bacteria to use quorum sensing constitutively, they must possess three abilities: secretion of a signaling molecule, secretion of an autoinducer (to detect the change in concentration of signaling molecules), and regulation of gene transcription as a response. This process is highly dependent on the diffusion mechanism of the signaling molecules. QS signaling molecules are usually secreted at a low level by individual bacteria. At low cell density, the molecules may just diffuse away. At high cell density, the local concentration of signaling molecules may exceed its threshold level, and trigger changes in gene expression. | 1 | Biochemistry |
Initial desensitization due to rapid phosphorylation of activated receptors by kinases, which increases affinity for arrestin. Arrestin prevents protein-receptor interaction and the receptor becomes dephosphorylated and inhibited from signaling. This is a sufficient and rapid form of termination of PAR signaling. Irreversibly activated PAR1 is internalized and terminated from further signaling by clathrin-mediated endocytosis and lysosome degradation, preventing replenishment at the cell surface. | 1 | Biochemistry |
Without oxygen, pyruvate (pyruvic acid) is not metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. This serves the purpose of oxidizing the electron carriers so that they can perform glycolysis again and removing the excess pyruvate. Fermentation oxidizes NADH to NAD so it can be re-used in glycolysis. In the absence of oxygen, fermentation prevents the buildup of NADH in the cytoplasm and provides NAD for glycolysis. This waste product varies depending on the organism. In skeletal muscles, the waste product is lactic acid. This type of fermentation is called lactic acid fermentation. In strenuous exercise, when energy demands exceed energy supply, the respiratory chain cannot process all of the hydrogen atoms joined by NADH. During anaerobic glycolysis, NAD regenerates when pairs of hydrogen combine with pyruvate to form lactate. Lactate formation is catalyzed by lactate dehydrogenase in a reversible reaction. Lactate can also be used as an indirect precursor for liver glycogen. During recovery, when oxygen becomes available, NAD attaches to hydrogen from lactate to form ATP. In yeast, the waste products are ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation. The ATP generated in this process is made by substrate-level phosphorylation, which does not require oxygen.
Fermentation is less efficient at using the energy from glucose: only 2 ATP are produced per glucose, compared to the 38 ATP per glucose nominally produced by aerobic respiration. Glycolytic ATP, however, is produced more quickly. For prokaryotes to continue a rapid growth rate when they are shifted from an aerobic environment to an anaerobic environment, they must increase the rate of the glycolytic reactions. For multicellular organisms, during short bursts of strenuous activity, muscle cells use fermentation to supplement the ATP production from the slower aerobic respiration, so fermentation may be used by a cell even before the oxygen levels are depleted, as is the case in sports that do not require athletes to pace themselves, such as sprinting. | 1 | Biochemistry |
The purpose of both the (primary) bioluminescence (from aequorins action on luciferin) and the (secondary) fluorescence of GFP in jellyfish is unknown. GFP is co-expressed with aequorin in small granules around the rim of the jellyfish bell. The secondary excitation peak (480 nm) of GFP does absorb some of the blue emission of aequorin, giving the bioluminescence a more green hue. The serine 65 residue of the GFP chromophore is responsible for the dual-peaked excitation spectra of wild-type GFP. It is conserved in all three GFP isoforms originally cloned by Prasher. Nearly all mutations of this residue consolidate the excitation spectra to a single peak at either 395 nm or 480 nm. The precise mechanism of this sensitivity is complex, but, it seems, involves donation of a hydrogen from serine 65 to glutamate 222, which influences chromophore ionization. Since a single mutation can dramatically enhance the 480 nm excitation peak, making GFP a much more efficient partner of aequorin, A. victoria appears to evolutionarily prefer the less-efficient, dual-peaked excitation spectrum. Roger Tsien has speculated that varying hydrostatic pressure with depth may affect serine 65s ability to donate a hydrogen to the chromophore and shift the ratio of the two excitation peaks. Thus, the jellyfish may change the color of its bioluminescence with depth. However, a collapse in the population of jellyfish in Friday Harbor, where GFP was originally discovered, has hampered further study of the role of GFP in the jellyfish's natural environment.
Most species of lancelet are known to produce GFP in various regions of their body. Unlike A. victoria, lancelets do not produce their own blue light, and the origin of their endogenous GFP is still unknown. Some speculate that it attracts plankton towards the mouth of the lancelet, serving as a passive hunting mechanism. It may also serve as a photoprotective agent in the larvae, preventing damage caused by high-intensity blue light by converting it into lower-intensity green light. However, these theories have not been tested.
GFP-like proteins have been found in multiple species of marine copepods, particularly from the Pontellidae and Aetideidae families. GFP isolated from Pontella mimocerami has shown high levels of brightness with a quantum yield of 0.92, making them nearly two-fold brighter than the commonly used EGFP isolated from A. victoria. | 1 | Biochemistry |
Sintering is generally considered successful when the process reduces porosity and enhances properties such as strength, electrical conductivity, translucency and thermal conductivity. In some special cases, sintering is carefully applied to enhance the strength of a material while preserving porosity (e.g. in filters or catalysts, where gas absorbency is a priority). During the firing process, atomic diffusion drives powder surface elimination in different stages, starting at the formation of necks between powders to final elimination of small pores at the end of the process.
The driving force for densification is the change in free energy from the decrease in surface area and lowering of the surface free energy by the replacement of solid-vapor interfaces. It forms new but lower-energy solid-solid interfaces with a net decrease in total free energy. On a microscopic scale, material transfer is affected by the change in pressure and differences in free energy across the curved surface. If the size of the particle is small (and its curvature is high), these effects become very large in magnitude. The change in energy is much higher when the radius of curvature is less than a few micrometers, which is one of the main reasons why much ceramic technology is based on the use of fine-particle materials.
The ratio of bond area to particle size is a determining factor for properties such as strength and electrical conductivity. To yield the desired bond area, temperature and initial grain size are precisely controlled over the sintering process. At steady state, the particle radius and the vapor pressure are proportional to (p) and to (p), respectively.
The source of power for solid-state processes is the change in free or chemical potential energy between the neck and the surface of the particle. This energy creates a transfer of material through the fastest means possible; if transfer were to take place from the particle volume or the grain boundary between particles, particle count would decrease and pores would be destroyed. Pore elimination is fastest in samples with many pores of uniform size because the boundary diffusion distance is smallest. during the latter portions of the process, boundary and lattice diffusion from the boundary become important.
Control of temperature is very important to the sintering process, since grain-boundary diffusion and volume diffusion rely heavily upon temperature, particle size, particle distribution, material composition, and often other properties of the sintering environment itself. | 8 | Metallurgy |
Consider a typical chemical reaction in which two reactants A and B combine to form a product C:
This can also be written
The prefactors −1, −2 and 3 (with negative signs for reactants because they are consumed) are known as stoichiometric coefficients. One molecule of A combines with two of B to form 3 of C, so if we use the symbol [X] for the molar concentration of chemical X,
If the reaction takes place in a closed system at constant temperature and volume, without a build-up of reaction intermediates, the reaction rate is defined as
where is the stoichiometric coefficient for chemical X, with a negative sign for a reactant.
The initial reaction rate has some functional dependence on the concentrations of the reactants,
and this dependence is known as the rate equation or rate law. This law generally cannot be deduced from the chemical equation and must be determined by experiment. | 7 | Physical Chemistry |
4-PPBP is a neuroprotective cyclic amine which binds to sigma receptors.
4-PPBP decreases neuronal nitric oxide synthase (nNOS) activity and ischemia-evoked nitric oxide (NO) production. 4-PPBP provides neuroprotection; this involves the prevention of ischemia-induced intracellular Ca dysregulation. 4-PPBP protects neurons using a mechanism that activates the transcription factor cyclic adenosine monophosphate response element-binding protein (CREB). Neuroprotection that is associated with 4-PPBP increases Bcl-2 expression; Bcl-2 expression is regulated by CREB. | 1 | Biochemistry |
The adsorption and absorption rate of a diluted solute in gas or liquid solution to a surface or interface can be calculated using Fick's laws of diffusion. | 7 | Physical Chemistry |
NRC produces certified reference materials of biological tissues, isotopic standards, natural waters, sediments, supplements, and natural health products. With the exception of the ORMS, the river water CRM with elevated mercury, all materials contain natural levels of analytes in their native matrix.
* Biological tissues
** DOLT, dogfish liver for trace metals
** DORM, fish protein for trace metals
** LUTS, non-defatted lobster hepatopancreas for trace metals
** TORT, lobster hepatopancreas for trace metals
* Isotopic materials
** NIMS, natural inorganic mercury standard
** EMMS, isotopic methylmercury standard
* Natural waters
** CASS, near-shore seawater for trace metals
** MOOS, seawater for nutrients
** NASS, seawater for trace metals
** ORMS, river water for mercury
** SLEW, estuarine water for trace metals
** SLRS, river water for trace metals
* Sediments
** HISS and MESS, marine sediment for trace metals and major constituents
** PACS and SOPH, marine sediment for trace metals and major constituents
* Supplements and natural health products
** CACB, calcium carbonate for lead and cadmium
** FEBS, otolith for trace metals
** SELM, selenium-enriched yeast for selenium | 1 | Biochemistry |
In an aperiodic crystal the structure can no longer be simply described by three different vectors in real or reciprocal space. In general there is a substructure describable by three (e.g. ), similar to supercells above, but in addition there is some additional periodicity (one to three) which cannot be described as a multiple of the three; it is a genuine additional periodicity which is an irrational number relative to the subcell lattice. The diffraction pattern can then only be described by more than three indices.
An extreme example of this is for quasicrystals, which can be described similarly by a higher number of Miller indices in reciprocal space—but not by any translational symmetry in real space. An example of this is shown in Figure 15 for an Al-Cu-Fe-Cr decagonal quasicrystal grown by magnetron sputtering on a sodium chloride substrate and then lifted off by dissolving the substrate with water. In the pattern there are pentagons which are a characteristic of the aperiodic nature of these materials. | 7 | Physical Chemistry |
UbiD protein domain - ubiquitin—calmodulin ligase - UDP-3-O-N-acetylglucosamine deacetylase - UDP-4-amino-4,6-dideoxy-N-acetyl-alpha-D-glucosamine transaminase - undecaprenyl-phosphate 4-deoxy-4-formamido-L-arabinose transferase - untranslated RNA - upstream - upstream activator sequence - upstream DNA - upstream (transduction) - uracil - uracil/thymine dehydrogenase - ureidoglycolate hydrolase - | 1 | Biochemistry |
He joined the Baltimore Copper Smelting & Rolling Company in 1890, becoming vice president in 1895, and later, president of the company. Under his management, the company became one of the major copper producer of the United States. In 1928, the company merged with five other copper companies, to create the Revere Copper Company. Described as "one of the foremost metallurgists of his time", Peirce became the vice president, director and a member of the Executive Committee of Revere from its incorporation in 1928 until his resignation in 1933. | 8 | Metallurgy |
Sericitic alteration or sericitization is a process of mineral alteration caused by hydrothermal fluids invading permeable country rock. Plagioclase feldspar within the rock is converted to sericite (sericite is not a mineral; it is a term that is used to describe any fine-grained white phyllosilicate when a distinction cannot be determined), which typically consists of fine-grained white mica and related minerals. Sericitic alteration occurs within the phyllic alteration zone. | 9 | Geochemistry |