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Levofloxacin is rapidly and essentially completely absorbed after oral administration, with a plasma concentration profile over time that is essentially identical to that obtained from intravenous administration of the same amount over 60 minutes. As such, the intravenous and oral formulations of levofloxacin are considered interchangeable. Levofloxacin's ability to bind to proteins in the body ranges from 24 to 38%.
The drug undergoes widespread distribution into body tissues. Peak levels in skin are achieved 3 hours after administration and exceed those in plasma by a factor of 2. Similarly, lung tissue concentrations range from two-fold to five-fold higher than plasma concentrations in the 24 hours after a single dose.
The mean terminal plasma elimination half-life of levofloxacin ranges from approximately 6 to 8 hours following single or multiple doses of levofloxacin given orally or intravenously. Elimination occurs mainly via excretion of unmetabolized drug in the urine. Following oral administration, 87% of an administered dose was recovered in the urine as unchanged drug within 2 days. Less than 5% was recovered in the urine as the desmethyl and N-oxide metabolites, the only metabolites identified in humans. | 4 | Stereochemistry |
TILLING (Targeting Induced Local Lesions in Genomes) is a method in molecular biology that allows directed identification of mutations in a specific gene. TILLING was introduced in 2000, using the model plant Arabidopsis thaliana, and expanded on into other uses and methodologies by a small group of scientists including Luca Comai. TILLING has since been used as a reverse genetics method in other organisms such as zebrafish, maize, wheat, rice, soybean, tomato and lettuce. | 1 | Biochemistry |
Ethers () consist of an oxygen atom between the two attached carbon chains. The shorter of the two chains becomes the first part of the name with the -ane suffix changed to -oxy, and the longer alkane chain becomes the suffix of the name of the ether. Thus, is methoxymethane, and is methoxyethane (not ethoxymethane). If the oxygen is not attached to the end of the main alkane chain, then the whole shorter alkyl-plus-ether group is treated as a side-chain and prefixed with its bonding position on the main chain. Thus is 2-methoxypropane.
Alternatively, an ether chain can be named as an alkane in which one carbon is replaced by an oxygen, a replacement denoted by the prefix "oxa". For example, could also be called 2-oxabutane, and an epoxide could be called oxacyclopropane. This method is especially useful when both groups attached to the oxygen atom are complex. | 0 | Organic Chemistry |
Vitamin B is the preeminent bioorganometallic species. Vitamin B is actually a collection of related enzyme cofactors, several of which contain cobalt–alkyl bonds, and is involved in biological methylation and 1,2-carbon rearrangement reactions. For a long time since its structure was elucidated by Hodgkin in 1955, it was believed to be the only example of a naturally occurring bioorganometallic system.
Several bioorganometallic enzymes carry out reactions involving carbon monoxide. Carbon monoxide dehydrogenase (CODH) catalyzes the water–gas shift reaction, which provides CO (through a nickelacarboxylate intermediate) for the biosynthesis of acetylcoenzyme A. The latter step is effected by the Ni–Fe enzyme CO-methylating acetyl-CoA synthase (ACS). CODH and ACS often occur together in a tetrameric complex, the CO being transported via a tunnel and the methyl group being provided by methyl cobalamin.
Hydrogenases are bioorganometallic in the sense that their active sites feature Fe–CO functionalities, although the CO ligands are only spectators. The binuclear [FeFe]-hydrogenases have a Fe(μ-SR)(μ-CO)(CO)(CN) active site connected to a 4Fe4S cluster via a bridging thiolate. The active site of the [NiFe]-hydrogenases are described as (NC)(OC)Fe(μ-SR)Ni(SR) (where SR is cysteinyl). Mononuclear [Fe]-hydrogenases contain an Fe(CO)(SR)(LX) active site, where LX is a 6-acylmethyl-2-pyridinol ligand, bound to the Fe center through the pyridyl nitrogen (L) and the acyl carbon (X). This class of hydrogenases thus provides examples of naturally occurring iron acyl complexes.
Methanogenesis, the biosynthesis of methane, entails as its final step, the scission of a nickel–methyl bond in cofactor F430.
The iron–molybdenum cofactor (FeMoco) of nitrogenases contains an FeC unit and is an example of an interstitial carbide found in biology.
The first example of a naturally-occurring arylmetal species, a pincer complex containing a nickel–aryl bond, has been reported to form the active site of lactate racemase. | 0 | Organic Chemistry |
Zearalenone has two major phase I metabolites: α-zearalenol and β-zearalenol. When exposed orally ZEN is absorbed by the intestinal lining and metabolized there as well as in the liver. Research into the metabolism of ZEN has been difficult because of the significant difference in biotransformation between species making comparison challenging. | 1 | Biochemistry |
The unique features of NICE-OHMS, in particular its high sensitivity, imply that it has a large potential for a variety of applications. First developed for frequency standard applications, with an astonishing detectability of 10 cm, it has later been used for spectroscopic investigations as well as chemical sensing and trace species detection, with detectabilities in the 10 - 10 cm range. However, although the NICE-OHMS technique has shown to possess an extremely high detectability, it has so far only sparsely been developed towards trace gas analysis.
One of the biggest hurdles for implementation of the NICE-OHMS technique is indisputably the locking of the frequency of the laser to that of a cavity mode. Although the requirements for the performance of the lock are less stringent than for other direct cw-CEAS techniques (due to the noise-immune principle), the laser frequency still has to be kept locked within the cavity mode during signal acquisition, i.e. it should follow the mode while the cavity is scanned, including a possible wavelength modulation. It can be difficult to achieve these goals if the free-running linewidth of the laser is significantly larger than the cavity mode width and if the laser is prone to sudden frequency excursions due to technical noise from the surroundings. This is usually the case when working with medium- or high finesse cavities (with transmission mode widths in the low kHz range) and standard types of lasers, e.g. external cavity diode lasers (ECDLs), with free-running linewidths in the MHz range. Electronic feedback loops with high bandwidths (typically a few MHz) and high gain are then needed to couple a substantial amount of the laser power into a cavity mode and to ensure stable performance of the lock.
With the advent of narrow linewidth fiber lasers, the problems connected to laser locking can be significantly reduced. Fiber lasers with free-running linewidths as narrow as 1 kHz (measured over a fraction of a second), thus two to three orders of magnitude below those of ECDLs, are available today. Evidently, this feature simplifies the feedback electronics (bandwidths as low as 10 kHz are sufficient) and the locking procedure considerably. Moreover, the design and working principle of fiber lasers make them less affected by external disturbances, e.g. mechanical and acoustical noise, than other solid state lasers or ECDLs. In addition, the availability of integrated-optics components, such as fiber based electro-optic modulators (fiber EOMs), offers the possibility to further reduce the complexity of the setup. The first realizations of a NICE-OHMS system based upon a fiber laser and a fiber EOM have recently been demonstrated. It was shown that CH could be detected down to 4.5•10 atm (4.5 ppt) with an instrumentation that is very sturdy. It is clear that this has brought NICE-OHMS a step closer to become a practically useful technique for ultra-sensitive trace species detection! | 7 | Physical Chemistry |
* Cryobiology, the branch of biology that studies the effects of low temperatures on living things
* Cryonics, the low-temperature preservation of people who cannot be sustained by contemporary medicine
* Cryoprecipitate, a blood-derived protein product used to treat some bleeding disorders
* Cryotherapy, medical treatment using cold
** Cryoablation, tissue removal using cold
** Cryosurgery, surgery using cold
* Cryo-electron microscopy (cryoEM), a technique that fires beams of electrons at proteins that have been frozen in solution, to deduce the biomolecules’ structure | 1 | Biochemistry |
Bismuth compounds have been used because of their astringent, antiphlogistic, bacteriostatic, and disinfecting actions. In dermatology bismuth subgallate is still used in vulnerary salves and powders as well as in antimycotics. In the past, bismuth has also been used to treat syphilis and malaria. | 1 | Biochemistry |
In any solid at any temperature, the primary particles (e.g. atoms or molecules) are not stationary, but rather vibrate about mean positions. In insulators the capacity of the solid to store thermal energy is due almost entirely to these vibrations. Many physical properties of the solid (e.g. modulus of elasticity) can be predicted given knowledge of the frequencies with which the particles vibrate. The simplest assumption (by Einstein) is that all the particles oscillate about their mean positions with the same natural frequency ν. This is equivalent to the assumption that all atoms vibrate independently with a frequency ν. Einstein also assumed that the allowed energy states of these oscillations are harmonics, or integral multiples of hν. The spectrum of waveforms can be described mathematically using a Fourier series of sinusoidal density fluctuations (or thermal phonons).
Debye subsequently recognized that each oscillator is intimately coupled to its neighboring oscillators at all times. Thus, by replacing Einstein's identical uncoupled oscillators with the same number of coupled oscillators, Debye correlated the elastic vibrations of a one-dimensional solid with the number of mathematically special modes of vibration of a stretched string (see figure). The pure tone of lowest pitch or frequency is referred to as the fundamental and the multiples of that frequency are called its harmonic overtones. He assigned to one of the oscillators the frequency of the fundamental vibration of the whole block of solid. He assigned to the remaining oscillators the frequencies of the harmonics of that fundamental, with the highest of all these frequencies being limited by the motion of the smallest primary unit.
The normal modes of vibration of a crystal are in general superpositions of many overtones, each with an appropriate amplitude and phase. Longer wavelength (low frequency) phonons are exactly those acoustical vibrations which are considered in the theory of sound. Both longitudinal and transverse waves can be propagated through a solid, while, in general, only longitudinal waves are supported by fluids.
In the longitudinal mode, the displacement of particles from their positions of equilibrium coincides with the propagation direction of the wave. Mechanical longitudinal waves have been also referred to as compression waves. For transverse modes, individual particles move perpendicular to the propagation of the wave.
According to quantum theory, the mean energy of a normal vibrational mode of a crystalline solid with characteristic frequency ν is:
The term (1/2)hν represents the "zero-point energy", or the energy which an oscillator will have at absolute zero. E(ν) tends to the classic value kT at high temperatures
By knowing the thermodynamic formula,
the entropy per normal mode is:
The free energy is:
which, for kT >> hν, tends to:
In order to calculate the internal energy and the specific heat, we must know the number of normal vibrational modes a frequency between the values ν and ν + dν. Allow this number to be f(ν)dν. Since the total number of normal modes is 3N, the function f(ν) is given by:
The integration is performed over all frequencies of the crystal. Then the internal energy U will be given by: | 7 | Physical Chemistry |
Hexahydroxybenzene trisoxalate is a chemical compound, an oxide of carbon with formula . Its molecule consists of a benzene core with the six hydrogen atoms replaced by three oxalate groups. It can be seen as a sixfold ester of benzenehexol and oxalic acid.
The compound was first described by H. S. Verter and R. Dominic in 1967. | 0 | Organic Chemistry |
In the case of a scale-invariant type of system (where a system of volume has exactly the same set of microstates as systems of volume ), then when the system expands new particles and energy will flow in from the reservoir to fill the new volume with a homogeneous extension of the original system.
The pressure, then, must be constant with respect to changes in volume:
and all extensive quantities (particle number, energy, entropy, potentials, ...) must grow linearly with volume, e.g.
In this case we simply have , as well as the familiar relationship for the Gibbs free energy.
The value of can be understood as the work that can be extracted from the system by shrinking it down to nothing (putting all the particles and energy back into the reservoir). The fact that is negative implies that the extraction of particles from the system to the reservoir requires energy input.
Such homogeneous scaling does not exist in many systems. For example, when analyzing the ensemble of electrons in a single molecule or even a piece of metal floating in space, doubling the volume of the space does double the number of electrons in the material.
The problem here is that, although electrons and energy are exchanged with a reservoir, the material host is not allowed to change.
Generally in small systems, or systems with long range interactions (those outside the thermodynamic limit), . | 7 | Physical Chemistry |
Eigen et al. and Woese proposed that the genomes of early protocells were composed of single-stranded RNA, and that individual genes corresponded to separate RNA segments, rather than being linked end-to-end as in present-day DNA genomes. A protocell that was haploid (one copy of each RNA gene) would be vulnerable to damage, since a single lesion in any RNA segment would be potentially lethal to the protocell (e.g. by blocking replication or inhibiting the function of an essential gene).
Vulnerability to damage could be reduced by maintaining two or more copies of each RNA segment in each protocell, i.e. by maintaining diploidy or polyploidy. Genome redundancy would allow a damaged RNA segment to be replaced by an additional replication of its homolog. For such a simple organism, the proportion of available resources tied up in the genetic material would be a large fraction of the total resource budget. Under limited resource conditions, the protocell reproductive rate would likely be inversely related to ploidy number, and the protocell's fitness would be reduced by the costs of redundancy. Consequently, coping with damaged RNA genes while minimizing the costs of redundancy would likely have been a fundamental problem for early protocells.
A cost-benefit analysis was carried out in which the costs of maintaining redundancy were balanced against the costs of genome damage. This analysis led to the conclusion that, under a wide range of circumstances, the selected strategy would be for each protocell to be haploid, but to periodically fuse with another haploid protocell to form a transient diploid. The retention of the haploid state maximizes the growth rate. The periodic fusions permit mutual reactivation of otherwise lethally damaged protocells. If at least one damage-free copy of each RNA gene is present in the transient diploid, viable progeny can be formed. For two, rather than one, viable daughter cells to be produced would require an extra replication of the intact RNA gene homologous to any RNA gene that had been damaged prior to the division of the fused protocell. The cycle of haploid reproduction, with occasional fusion to a transient diploid state, followed by splitting to the haploid state, can be considered to be the sexual cycle in its most primitive form. In the absence of this sexual cycle, haploid protocells with damage in an essential RNA gene would simply die.
This model for the early sexual cycle is hypothetical, but it is very similar to the known sexual behavior of the segmented RNA viruses, which are among the simplest organisms known. Influenza virus, whose genome consists of 8 physically separated single-stranded RNA segments, is an example of this type of virus. In segmented RNA viruses, "mating" can occur when a host cell is infected by at least two virus particles. If these viruses each contain an RNA segment with a lethal damage, multiple infection can lead to reactivation providing that at least one undamaged copy of each virus gene is present in the infected cell. This phenomenon is known as "multiplicity reactivation". Multiplicity reactivation has been reported to occur in influenza virus infections after induction of RNA damage by UV-irradiation, and ionizing radiation. | 9 | Geochemistry |
Schwinger variational principle is a variational principle which expresses the scattering T-matrix as a functional depending on two unknown wave functions. The functional attains stationary value equal to actual scattering T-matrix. The functional is stationary if and only if the two functions satisfy the Lippmann-Schwinger equation. The development of the variational formulation of the scattering theory can be traced to works of L. Hultén and J. Schwinger in 1940s. | 7 | Physical Chemistry |
A multidimensional population translation experiment was utilized to determine the detection limits of an ARS device, Populations with small multidimensional separation, in this case aspirin and ibuprofen, were used to determine that tablets with a 0.08 mm difference in thickness, 0.0046 g mass difference, and a difference in density of 0.01658 g/mL were not separable by ARS. Using vitamin C and acetaminophen for the largest multidimensional separation, tablets with a thickness difference of 0.27 mm, 0.0756 g mass difference, and 0.01157 g/mL density difference in density were inseparable. Experimentally the dynamic range of ARS is a factor of ten. | 7 | Physical Chemistry |
The traditional approach to supramolecular catalysts focuses on the design of macromolecular receptor with appropriately placed catalytic functional groups. These catalysts are often inspired by the structure of enzymes with the catalytic group mimicking reactive amino acid residues, but unlike real enzymes, the binding sites of these catalysts are rigid structure made from chemical building blocks. All of the examples in this article are developed via the design approach.
Jeremy Sanders pointed out that the design approach has not been successful and has produced very few efficient catalysts because of rigidity of the supramolecules. He argued that rigid molecules with a slight mismatch to the transition state cannot be an efficient catalyst. Rather than investing so much synthesis effort on one rigid molecule that we cannot determine its precise geometry to the sub-angstrom level which is required for good stabilization, Sanders suggested the use of many small flexible building blocks with competing weak interactions so that it is possible for the catalyst to adjust its structure to accommodate the substrate better. There is a direct trade-off between the enthalpic benefit from flexible structure and the entropic benefit from rigid structure. Flexible structure could perhaps bind the transition state better but it allows more room for the substrates to move and vibrate. Most supramolecular chemists in the past prefer to build rigid structures out of fear of entropic cost.
This problem could perhaps be mended by Baker and Houk's "inside-out approach" which allows a systematic de novo enzyme development. This computational method starts simply with a predicted transition state structure and slowly builds outward by optimizing the arrangement of functional groups to stabilize the transition state. Then it fills out the remainder of the active site and, finally, it generates an entire protein scaffold that could contain the designed active site. This method could potentially be applied to supramolecular catalysis, although a plethora of chemical building blocks could easily overwhelm the computational model intended to work with 20 amino acids. | 6 | Supramolecular Chemistry |
Myristoylation is an integral part of apoptosis, or programmed cell death. Apoptosis is necessary for cell homeostasis and occurs when cells are under stress such as hypoxia or DNA damage. Apoptosis can proceed by either mitochondrial or receptor mediated activation. In receptor mediated apoptosis, apoptotic pathways are triggered when the cell binds a death receptor. In one such case, death receptor binding initiates the formation of the death-inducing signaling complex, a complex composed of numerous proteins including several caspases, including caspase 3. Caspase 3 cleaves a number of proteins that are subsequently myristoylated by NMT. The pro-apoptotic BH3-interacting domain death agonist (Bid) is one such protein that once myristoylated, translocates to the mitochondria where it prompts the release of cytochrome c leading to cell death. Actin, gelsolin and p21-activated kinase 2 PAK2 are three other proteins that are myristoylated following cleavage by caspase 3, which leads to either the up-regulation or down-regulation of apoptosis. | 1 | Biochemistry |
Catalyzes the first step in the synthesis of DIMBOA, forming indole from indole-3-glycerol phosphate. The enzyme is called indole-3-glycerol phosphate lyase, chloroplast, EC 4.1.2.8 and is located in the chloroplast. The X-ray structure of BX1 protein has been resolved and compared with bacterial TSA (tryptophan synthase alpha subunit, Kulik et al. 2005). Three homologs of the BX1 protein occur in maize. One is encoded by the gene tsa1, tryptophan synthase alpha1(Frey et al. 1997, Melanson et al. 1997 ), on chromosome 7, another by igl1, indole-3-glycerol phosphate lyase1(Frey et al. 1997, on chromosome 1, and another by tsah1, TSA like" and located near the bx1' gene (Frey et al. 1997. ). | 1 | Biochemistry |
The einstein (symbol E) is an obsolete unit with two conflicting definitions. It was originally defined as the energy in one mole of photons ( photons). Because energy is inversely proportional to wavelength, the unit is frequency dependent. This unit is not part of the International System of Units (SI) and is redundant with the joule. If it were still in use, as of the 2019 redefinition of the SI base units, its value would be related to the frequency of the electromagnetic radiation by
: 1 einstein = 1 mol × = 1 mol × × × = × ,
where is the Avogadro constant, is the Planck constant, and is the frequency.
Sometime later, the unit was used differently in studies of photosynthesis to mean one mole of photons, rather than the energy in one mole of photons. As such, photosynthetically active radiation (PAR) was formerly often reported in microeinsteins per second per square meter (μE m s). This usage is also not part of the SI and when used this way it is redundant with the mole.
Since the unit does not have a standard definition and is not part of the SI system, it has long been considered obsolete. The same information about photosynthetically active radiation can be conveyed using the SI convention by stating something such as "The photon flux was 1500 μmol m s".
This unit was named after physicist Albert Einstein. | 5 | Photochemistry |
Flowers of sulfur (FOS) testing was developed to determine the porosity of metallic coatings susceptible to sulfur induced corrosion [see below ASTM B809-95(2018)]. Applicable substrates are silver, copper, copper alloys and any other metal or metal alloy with which sulfur will react. For porosity testing, coatings can be single or multiple layers of any metal that is not corroded and sealed by a self-limiting reaction in the reducing sulfur environment of the FOS test. The simplest recommended technique is to identify any porosity of the coating as revealed by the presence of surface spots. These surface spots form where the environmental sulfur has penetrated and reacted with the base metal, producing a metal sulfide. Chalcocite, copper (I) sulfide is dark-grey to black. Silver (I) sulfide is also grey-black.
The adoption of lead-free solders and lead-free soldering motivated the further development and application of immersion silver plating. Immersion silver improves wettability and solderability. Mixed flowing gas testing failed to alert the electronics manufacturing industry to weaknesses in immersion silver plating (for example, see Reference 7). This furthered the application of FOS. In particular, it was determined that moist, high-sulfur environments facilitated creep corrosion. The development of FOS testing for creep corrosion was furthered by efforts under the auspices of the International Electronics Manufacturing Initiative (INEMI) and the Surface Mount Technology Association (SMTA) by Haley Fu, et al. and Prabjit Singh et al. MFG testing also proved unreliable for high-sulfur environmental testing of chip resistors and their certification as sulfur resistant. There has been recent development in utilizing FOS testing for porosity of conformal coatings.
The material under test is suspended inside a container over a source of powdered sulfur. The powdered sulfur is placed in a dish. The temperature and internal humidity of the container are regulated. Temperature is typically controlled by placing the container in a constant temperature oven. Humidity inside the container is typically controlled with a saturated salt solution whose vapor pressure is well characterized at the temperature of the test. Saturated potassium nitrate solution is standard practice for humidity control in humid sulfur vapor testing. The saturated salt solution is placed physically outside of the sulfur containing dish. The sulfur containing dish may “float” in the saturated salt solution. The dish should provide an ample, available powdered sulfur surface.
Recommended materials for the test chamber are glass and acrylic. The materials under test must be suspended or supported above the saturated salt solution. Suspension materials are also recommended fabricated from glass or plastic. Frames made out of 316 stainless steel have seen use for hanging specimens. Monofilament line has been used for hanging objects under test. Recommended specimen placement is at least 75 mm from the surfaces of the sulfur and the saturated salt solutions, at least 25 mm from all internal vessel surfaces and at least 10 mm spacing from specimen to specimen.
Standard test procedures call for performing the specimen exposure at 50 °C for at least 24 hours. Activity of the sulfur and its products with humid air increase with temperature. Exposure periods can be extended into the week range. Decisions on length of exposure is commonly motivated by observations from shorter-term tests. Standard procedure calls for equilibrating the test chamber at temperature and relative humidity before inserting the test specimens.
Porosity results are determined by the distribution, number and sizes of dark spots on the materials under test. Again, the dark spots are due to reaction of the moist sulfur vapors with the underlying silver or copper material. One may choose to include silver or both silver and copper reference coupons into the humid sulfur test. The accumulation of copper(I) sulfate and silver (I) sulfate deposits on the coupons, determined by weight change, allows comparisons to ISA 71.04 severity levels for mixed flowing gas testing. | 8 | Metallurgy |
When carbon dioxide is held above its critical pressure (73.773 bar) and temperature (30.9780 °C), it can behave both as a gas and as a liquid, that is it expands to fill entirely its container like a gas but has a density similar to that of a liquid.
Supercritical CO is chemically stable, very cheap, and non-flammable, making it suitable as a working fluid for transcritical cycles. For example, it is employed in domestic water heat pumps, which can reach high efficiencies.
Moreover, when used in power generation plants that employ Brayton and Rankine cycles, it can improve efficiency and power output. Its high density enables a strong reduction in turbomachines dimensions, still ensuring the high efficiency of these components. Simpler designs can therefore be adopted, while steam turbines require multiple turbine stages, which necessarily yield larger dimensions and costs.
By contrast, mechanical components within sCO Brayton cycles, especially turbomachinery and heat exchangers, suffer from corrosion. | 7 | Physical Chemistry |
With the control of all growth conditions such as temperature, bond strength, diffusion, and saturation level, desired morphology could be formed by choosing the right parameters. Following is the demonstration how to obtain some interesting surface features: | 7 | Physical Chemistry |
Mixtures with air of the gas 1,1,1,2-tetrafluoroethane are not flammable at atmospheric pressure and temperatures up to 100 °C (212 °F). However, mixtures with high concentrations of air at elevated pressure and/or temperature can be ignited. Contact of 1,1,1,2-tetrafluoroethane with flames or hot surfaces in excess of 250 °C (482 °F) may cause vapor decomposition and the emission of toxic gases including hydrogen fluoride and carbonyl fluoride, however the decomposition temperature has been reported as above 370 °C. 1,1,1,2-Tetrafluoroethane itself has an of 1,500 g/m in rats, making it relatively non-toxic, apart from the dangers inherent to inhalant abuse. Its gaseous form is denser than air and will displace air in the lungs. This can result in asphyxiation if excessively inhaled. This contributes to most deaths by inhalant abuse.
Aerosol cans containing 1,1,1,2-tetrafluoroethane, when inverted, become effective freeze sprays. Under pressure, 1,1,1,2-tetrafluoroethane is compressed into a liquid, which upon vaporization absorbs a significant amount of thermal energy. As a result, it will greatly lower the temperature of any object it contacts as it evaporates. | 2 | Environmental Chemistry |
Singlet oxygen luminesces concomitant with its decay to the triplet ground state. This phenomenon was first observed in the thermal degradation of the endo peroxide of rubrene. | 7 | Physical Chemistry |
MK-886, or L-663536, is a leukotriene antagonist. It may perform this by blocking the 5-lipoxygenase activating protein (FLAP), thus inhibiting 5-lipoxygenase (5-LOX), and may help in treating atherosclerosis. | 1 | Biochemistry |
Flucloxacillin can reduce the excretion of methotrexate, potentially resulting in a risk of methotrexate toxicity. The level of flucloxacillin in the blood may rise in kidney failure and with the use of probenecid. | 4 | Stereochemistry |
The US Food and Drug Administration issued a Premarket Submission and Labeling Recommendations for Drugs of Abuse Screening Tests. Its availability was announced in the Federal Register, Vol. 68, No. 231 on December 2, 2003 and is listed under "Notices." Presumptive testing has found widespread use by employers and public entities. Most people who take a drug test take a presumptive test, cheaper and faster than other methods of testing. However, it is less accurate and can render false results. The FDA recommends for confirmatory testing to be conducted and the placing of a warning label on the presumptive drug test: "This assay provides only a preliminary result. Clinical consideration and professional judgment should be applied to any drug of abuse test result, in evaluating a preliminary positive result. To obtain a confirmed analytical result, a more specific alternate chemical method is needed. Gas chromatography/mass spectrometry (GC/MS) is the recommended confirmatory method." | 3 | Analytical Chemistry |
PPA is a metastable polymer known for its ease of synthesis and rapid depolymerization. In addition, its properties can be easily influenced and manipulated upon either functionalizing the phthalaldehyde monomer with different groups, most efficiently, electron withdrawing groups, or employing different functional groups as end caps. | 7 | Physical Chemistry |
DNA profiling (also called DNA fingerprinting and genetic fingerprinting) is the process of determining an individual's deoxyribonucleic acid (DNA) characteristics. DNA analysis intended to identify a species, rather than an individual, is called DNA barcoding.
DNA profiling is a forensic technique in criminal investigations, comparing criminal suspects' profiles to DNA evidence so as to assess the likelihood of their involvement in the crime. It is also used in paternity testing, to establish immigration eligibility, and in genealogical and medical research. DNA profiling has also been used in the study of animal and plant populations in the fields of zoology, botany, and agriculture. | 1 | Biochemistry |
In genetics, attenuation is a regulatory mechanism for some bacterial operons that results in premature termination of transcription. The canonical example of attenuation used in many introductory genetics textbooks, is ribosome-mediated attenuation of the trp operon. Ribosome-mediated attenuation of the trp operon relies on the fact that, in bacteria, transcription and translation proceed simultaneously. Attenuation involves a provisional stop signal (attenuator), located in the DNA segment that corresponds to the leader sequence of mRNA. During attenuation, the ribosome becomes stalled (delayed) in the attenuator region in the mRNA leader. Depending on the metabolic conditions, the attenuator either stops transcription at that point or allows read-through to the structural gene part of the mRNA and synthesis of the appropriate protein.
Attenuation is a regulatory feature found throughout Archaea and Bacteria causing premature termination of transcription. Attenuators are 5-cis' acting regulatory regions which fold into one of two alternative RNA structures which determine the success of transcription. The folding is modulated by a sensing mechanism producing either a Rho-independent terminator, resulting in interrupted transcription and a non-functional RNA product; or an anti-terminator structure, resulting in a functional RNA transcript. There are now many equivalent examples where the translation, not transcription, is terminated by sequestering the Shine-Dalgarno sequence (ribosomal binding site) in a hairpin-loop structure. While not meeting the previous definition of (transcriptional) attenuation, these are now considered to be variants of the same phenomena and are included in this article. Attenuation is an ancient regulatory system, prevalent in many bacterial species providing fast and sensitive regulation of gene operons and is commonly used to repress genes in the presence of their own product (or a downstream metabolite). | 1 | Biochemistry |
AOAC International holds an Annual Meeting & Conference, typically held in August or September of each year, which is moved around the United States and held in major cities. In addition, a mid-year meeting is held every March near the headquarters in Rockville, Maryland. | 3 | Analytical Chemistry |
Another category of multipass cells is generally referred to as circular multipass reflection cells. They were first introduced by Thoma and co-workers in 1994. Such cells rely on a circular arrangement of mirrors. The beam enters the cell under an angle and propagates on a star-shaped pattern (see picture on the right). The path length in circular multipass cells can be varied by adjusting the incidence angle of the beam. An advantage lies in their robustness towards mechanical stress such as vibrations or temperature changes. Furthermore, circular multipass cells stand out because of the small detection volumes they provide. A stable beam propagation is achieved by shaping individual reflection points to form a non-concentric mirror-arrangement.
In a special case, a circular mirror is used, allowing continuous adjustment of the angle of incidence. A drawback of this circular cell configuration is the inherent concentric mirror arrangement which leads to imperfect imaging after a large number of reflections. | 7 | Physical Chemistry |
*Microarray-Based Study by Metal Nanoparticle Probes
Recently, studies by using metal nanoparticle probes to detect the carbohydrate–protein interactions were reported. Use of gold and silver nanoparticle probes in resonant light scattering (RLS) gives particular high sensitivity. Zhenxin Wang and coworker the same principle applied this method to detect the interaction between carbohydrate and protein.
*Carbohydrate biosensor
As Lectin can strongly bind to specific carbohydrate, scientists develop several lectin-based carbohydrate biosensors. Designed lectin contains specific groups can be detected by analytical method.
*Isothermal Titration Calorimetry | 0 | Organic Chemistry |
In transcriptional silencing, SIR2,3,4 are required in stoichiometric amounts to silence specific chromosomal regions. In yeast, SIR proteins bind sites on nucleosome tails and form a multimeric compound of SIR2,3,4 that condenses chromatin and is thought to physically occlude promoters in the silenced interval, preventing their interaction with transcription machinery. The establishment of SIR-repressed heterochromatin domains is a complicated process that involves different subsets of proteins and regulatory proteins depending on the locus in the genome. At the silent mating type loci and at yeast telomeres, the transcription factors Abf1 (ARS binding factor) and Rap1 (repressor-activator protein) associate with specific nucleotide sequences in the silencers that flank heterochromatic regions. Rap1 contains a Sir3-binding domain that recruits SIR3 to the silencers. Once at the silencers, Sir3 recruits Sir4-Sir2 dimers to the chromatin nucleation site. Sir2 then deacetylates histone H3 and H4 tails, and free Sir3 binds the now-deacetylated lysine residues H4K16,79, and recruits additional Sir4-Sir2 dimers to promote the further spreading of the heterochromatin domain.
Once it has spread to cover a genomic locus, the SIR2,3,4 effectively prevents transcription from the region it occupies, in a process that is thought to depend on the physical occlusion of DNA by SIR proteins. Recently, it has been shown that certain promoters are capable of directing transcription inside regions that are otherwise silenced by SIR proteins. Specifically, if an inducible promoter is induced inside a silent chromatin domain, it can achieve ~200x increase in expression levels with little detectable change in covalent histone modifications. | 1 | Biochemistry |
A monolayer is a single, closely packed layer of entities, commonly atoms or molecules.
Monolayers can also be made out of cells.
Self-assembled monolayers form spontaneously on surfaces.
Monolayers of layered crystals like graphene and molybdenum disulfide are generally called 2D materials. | 7 | Physical Chemistry |
Two classes of transcription terminators, Rho-dependent and Rho-independent, have been identified throughout prokaryotic genomes. These widely distributed sequences are responsible for triggering the end of transcription upon normal completion of gene or operon transcription, mediating early termination of transcripts as a means of regulation such as that observed in transcriptional attenuation, and to ensure the termination of runaway transcriptional complexes that manage to escape earlier terminators by chance, which prevents unnecessary energy expenditure for the cell. | 1 | Biochemistry |
21-Crown-7 is an organic compound with the formula [CHO] and the IUPAC name of 1,4,7,10,13,16,19-heptaoxacycloheneicosane. Like other crown ethers, 21-crown-7 functions as a ligand for some metal cations with a particular affinity for caesium cations. The dipole moment of 21-crown-7 varies in different solvents and under different temperatures. | 6 | Supramolecular Chemistry |
Diazomethane is prepared by hydrolysis of an ethereal solution of an N-methyl nitrosamide with aqueous base. The traditional precursor is N-nitroso-N-methylurea, but this compound is itself somewhat unstable, and nowadays compounds such as N-methyl-N-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitroso-p'-toluenesulfonamide (Diazald) are preferred.
CHN reacts with basic solutions of DO to give the deuterated derivative CDN.
The concentration of CHN can be determined in either of two convenient ways. It can be treated with an excess of benzoic acid in cold EtO. Unreacted benzoic acid is then back-titrated with standard NaOH. Alternatively, the concentration of CHN in EtO can be determined spectrophotometrically at 410 nm where its extinction coefficient, ε, is 7.2.
The gas-phase concentration of diazomethane can be determined using photoacoustic spectroscopy. | 0 | Organic Chemistry |
In humans, the major route of excretion of most arsenic compounds is via the urine. The biological half-life of inorganic arsenic is about 4 days, but is slightly shorter following exposure to arsenate than to arsenite. The main metabolites excreted in the urine of humans exposed to inorganic arsenic are mono- and dimethylated arsenic acids, together with some unmetabolized inorganic arsenic.
The biotransformation of arsenic for excretion is primarily done through the nuclear factor erythroid 2 related factor 2 (Nrf2) pathway. Under normal conditions the Nrf2 is bound to Kelch-like ECH associated protein 1 (Keap1) in its inactive form. With the uptake of arsenic within cells and the subsequent reactions that result in the production of reactive oxygen species (ROS), the Nrf2 unbinds and becomes active. Keap1 has reactive thiol moieties that bind ROS or electrophilic arsenic species such as monomethylted arsenic (III) and induces the release of Nrf2 which then travels through the cytoplasm to the nucleus. The Nrf2 then activates antioxidant responsive element (ARE) as well as electrophilic responsive element (EpRE) both of which contribute in the increase of antioxidant proteins. Of particular note in these antioxidant proteins is heme oxygenase 1 ([HO-1]), NAD(P)H-quinone oxidoreductase 1 (NQO1), and γ-glutamylcysteine synthase (γGCS) which work in conjunction to reduce the oxidative species such as hydrogen peroxide to decrease the oxidative stress upon the cell. The increase in γGCS causes an increased production of arsenite triglutathionine (As(SG)) an important adduct that is taken up by either multidrug associated protein 1 or 2 (MRP1 or MRP2) which removes the arsenic out of the cell and into bile for excretion. This adduct can also decompose back into inorganic arsenic.
Of particular note in the excretion of arsenic is the multiple methylation steps that take place which may increase the toxicity of arsenic due to MMeAsIII being a potent inhibitor of glutathione peroxidase, glutathione reductase, pyruvate dehydrogenase, and thioredoxin reductase. | 1 | Biochemistry |
K252a is an alkaloid isolated from Nocardiopsis bacteria. This staurosporine analog is a highly potent cell permeable inhibitor of CaM kinase and phosphorylase kinase (IC = 1.8 and 1.7 nmol/L, respectively). At higher concentrations it is also an efficient inhibitor of serine/threonine protein kinases (IC of 10 to 30 nmol/L).
K252a is reported to promote myogenic differentiation in C2 mouse myoblasts and has been shown to block the neuronal differentiation of rat pheochromocytoma PC12 cells by inhibition of trk tyrosine kinase activity.
K252a has been reported in preclinical research as a potential treatment for psoriasis
K252a inhibits tyrosine phosphorylation of Trk A induced by NGF. PC12 cells were incubated in the presence or absence of 10 ng/ml NGF with or without various concentrations of K252a. | 1 | Biochemistry |
Chlorotrifluoromethane, R-13, CFC-13, or Freon 13, is a non-flammable, non-corrosive, nontoxic chlorofluorocarbon (CFC) and also a mixed halomethane. It is a man-made substance used primarily as a refrigerant. When released into the environment, CFC-13 has a high ozone depletion potential, and long atmospheric lifetime. Only a few other greenhouse gases surpass CFC-13 in global warming potential (GWP). The IPCC AR5 reported that CFC-13's atmospheric lifetime was 640 years. | 2 | Environmental Chemistry |
When multiple copies of a polypeptide encoded by a gene self-assemble to form a complex, this protein structure is referred to as a "multimer". Genes that encode multimer-forming polypeptides appear to be common. When a multimer is formed from polypeptides produced by two different mutant alleles of a particular gene, the mixed multimer may exhibit greater functional activity than the unmixed multimers formed by each of the mutants alone. In such a case, the phenomenon is referred to as intragenic complementation. Jehle pointed out that, when immersed in a liquid and intermingled with other molecules, charge fluctuation forces favor the association of identical molecules as nearest neighbors. | 6 | Supramolecular Chemistry |
Liquid marbles are non-stick droplets (normally aqueous) wrapped by micro- or nano-metrically scaled hydrophobic, colloidal particles (Teflon, polyethylene, lycopodium powder, carbon black, etc.); representing a platform for a diversity of chemical and biological applications. Liquid marbles are also found naturally; aphids convert honeydew droplets into marbles. A variety of non-organic and organic liquids may be converted into liquid marbles. Liquid marbles demonstrate elastic properties and do not coalesce when bounced or pressed lightly. Liquid marbles demonstrate a potential as micro-reactors, micro-containers for growing micro-organisms and cells, micro-fluidics devices, and have even been used in unconventional computing. Liquid marbles remain stable on solid and liquid surfaces. Statics and dynamics of rolling and bouncing of liquid marbles were reported. Liquid marbles coated with poly-disperse and mono-disperse particles have been reported. Liquid marbles are not hermetically coated by solid particles but connected to the gaseous phase. Kinetics of the evaporation of liquid marbles has been investigated. | 7 | Physical Chemistry |
In the liver and peripheral tissues of humans, retinol is reversibly converted to retinal by the action of alcohol dehydrogenases, which are also responsible for the conversion of ethanol to acetaldehyde. Retinal is irreversibly oxidized to retinoic acid (RA) by the action of aldehyde dehydrogenases. RA regulates the activation or deactivation of genes. The oxidative degradation of RA is induced by RA - its presence triggers its removal, making for a short-acting gene transcription signal. This deactivation is mediated by a cytochrome P450 (CYP) enzyme system, specifically enzymes CYP26A1, CYP26B1 and CYP26C1. CYP26A1 is the predominant form in the human liver; all other human adult tissues contained higher levels of CYP26B1. CYP26C1 is expressed mainly during embryonic development. All three convert retinoic acid into 4-oxo-RA, 4-OH-RA and 18-OH-RA. Glucuronic acid forms water-soluble glucuronide conjugates with the oxidized metabolites, which are then excreted in urine and feces. | 1 | Biochemistry |
The chemical consists of rings of 8 sulfur atoms. It adopts a crown conformation with D point group symmetry. The S–S bond lengths are equal, at about 2.05 Å. Octasulfur crystallizes in three distinct polymorphs: rhombohedral, and two monoclinic forms, of which only two are stable at standard conditions. The rhombohedral crystal form is the accepted standard state. The remaining polymorph is only stable between 96 and 115 °C at 100 kPa. Octasulfur forms several allotropes: α-sulfur, β-sulfur, γ-sulfur, and λ-sulfur.
λ-Sulfur is the liquid form of octasulfur, from which γ-sulfur can be crystallised by quenching. If λ-sulfur is crystallised slowly, it will revert to β-sulfur. Since it must have been heated over 115 °C, neither crystallised β-sulfur or γ-sulfur will be pure. The only known method of obtaining pure γ-sulfur is by crystallising from solution.
Octasulfur easily forms large crystals, which are typically yellow and are somewhat translucent. | 1 | Biochemistry |
The electrons are partially transferred from a d-orbital of the metal to anti-bonding molecular orbitals of CO (and its analogs). This electron-transfer strengthens the metal–C bond and weakens the C–O bond. The strengthening of the M–CO bond is reflected in increases of the vibrational frequencies for the M–C bond (often outside of the range for the usual IR spectrophotometers). Furthermore, the M–CO bond length is shortened. The weakening of the C–O bond is indicated by a decrease in the wavenumber of the ν band(s) from that for free CO (2143 cm), for example to 2060 cm in Ni(CO) and 1981 cm in Cr(CO), and 1790 cm in the anion [Fe(CO)]. For this reason, IR spectroscopy is an important diagnostic technique in metal–carbonyl chemistry. The article infrared spectroscopy of metal carbonyls discusses this in detail.
Many ligands other than CO are strong "backbonders". Nitric oxide is an even stronger π-acceptor than CO and ν is a diagnostic tool in metal–nitrosyl chemistry. Isocyanides, RNC, are another class of ligands that are capable of π-backbonding. In contrast with CO, the σ-donor lone pair on the C atom of isocyanides is antibonding in nature and upon complexation the CN bond is strengthened and the ν increased. At the same time, π-backbonding lowers the ν. Depending on the balance of σ-bonding versus π-backbonding, the ν can either be raised (for example, upon complexation with weak π-donor metals, such as Pt(II)) or lowered (for example, upon complexation with strong π-donor metals, such as Ni(0)). For the isocyanides, an additional parameter is the MC=N–C angle, which deviates from 180° in highly electron-rich systems. Other ligands have weak π-backbonding abilities, which creates a labilization effect of CO, which is described by the cis effect. | 0 | Organic Chemistry |
Trichloroethylene (TCE) is a halocarbon with the formula CHCl, commonly used as an industrial degreasing solvent. It is a clear, colourless, non-flammable, volatile liquid with a chloroform-like pleasant mild smell and sweet taste. Its IUPAC name is trichloroethene. Trichloroethylene has been sold under a variety of trade names. Industrial abbreviations include TCE, trichlor, Trike, Tricky and tri. Under the trade names Trimar and Trilene, it was used as a volatile anesthetic and as an inhaled obstetrical analgesic. It should not be confused with the similar 1,1,1-trichloroethane, which is commonly known as chlorothene.
TCE is classified as a volatile organic compound. | 2 | Environmental Chemistry |
HMG proteins are thought to play a significant role in various human disorders. Disruptions and rearrangements in the genes coding for some of the HMG proteins are associated with some common benign tumors. Antibodies to HMG proteins are found in patients with autoimmune diseases. The SRY gene on the Y Chromosome, responsible for male sexual differentiation, contains an HMG-Box domain. A member of the HMG family of proteins, HMGB1, has also been shown to have an extracellular activity as a chemokine, attracting neutrophils and mononuclear inflammatory cells to the infected liver. The high-mobility group protein such as HMO1 alters DNA architecture by binding, bending and looping. Furthermore, these HMG-box DNA-binding proteins increase the flexibility of the DNA upon binding.
In mammalian cells, the HMG non-histone proteins can modulate the activity of major DNA repair pathways including base excision repair, mismatch repair, nucleotide excision repair and double-strand break repair. | 1 | Biochemistry |
Somatic-cell nuclear transfer, popularly known as SCNT, can also be used to create embryos for research or therapeutic purposes. The most likely purpose for this is to produce embryos for use in stem cell research. This process is also called "research cloning" or "therapeutic cloning". The goal is not to create cloned human beings (called "reproductive cloning"), but rather to harvest stem cells that can be used to study human development and to potentially treat disease. While a clonal human blastocyst has been created, stem cell lines are yet to be isolated from a clonal source.
Therapeutic cloning is achieved by creating embryonic stem cells in the hopes of treating diseases such as diabetes and Alzheimers. The process begins by removing the nucleus (containing the DNA) from an egg cell and inserting a nucleus from the adult cell to be cloned. In the case of someone with Alzheimers disease, the nucleus from a skin cell of that patient is placed into an empty egg. The reprogrammed cell begins to develop into an embryo because the egg reacts with the transferred nucleus. The embryo will become genetically identical to the patient. The embryo will then form a blastocyst which has the potential to form/become any cell in the body.
The reason why SCNT is used for cloning is because somatic cells can be easily acquired and cultured in the lab. This process can either add or delete specific genomes of farm animals. A key point to remember is that cloning is achieved when the oocyte maintains its normal functions and instead of using sperm and egg genomes to replicate, the donors somatic cell nucleus is inserted into the oocyte. The oocyte will react to the somatic cell nucleus, the same way it would to a sperm cells nucleus.
The process of cloning a particular farm animal using SCNT is relatively the same for all animals. The first step is to collect the somatic cells from the animal that will be cloned. The somatic cells could be used immediately or stored in the laboratory for later use. The hardest part of SCNT is removing maternal DNA from an oocyte at metaphase II. Once this has been done, the somatic nucleus can be inserted into an egg cytoplasm. This creates a one-cell embryo. The grouped somatic cell and egg cytoplasm are then introduced to an electrical current. This energy will hopefully allow the cloned embryo to begin development. The successfully developed embryos are then placed in surrogate recipients, such as a cow or sheep in the case of farm animals.
SCNT is seen as a good method for producing agriculture animals for food consumption. It successfully cloned sheep, cattle, goats, and pigs. Another benefit is SCNT is seen as a solution to clone endangered species that are on the verge of going extinct. However, stresses placed on both the egg cell and the introduced nucleus can be enormous, which led to a high loss in resulting cells in early research. For example, the cloned sheep Dolly was born after 277 eggs were used for SCNT, which created 29 viable embryos. Only three of these embryos survived until birth, and only one survived to adulthood. As the procedure could not be automated, and had to be performed manually under a microscope, SCNT was very resource intensive. The biochemistry involved in reprogramming the differentiated somatic cell nucleus and activating the recipient egg was also far from being well understood. However, by 2014 researchers were reporting cloning success rates of seven to eight out of ten and in 2016, a Korean Company Sooam Biotech was reported to be producing 500 cloned embryos per day.
In SCNT, not all of the donor cells genetic information is transferred, as the donor cells mitochondria that contain their own mitochondrial DNA are left behind. The resulting hybrid cells retain those mitochondrial structures which originally belonged to the egg. As a consequence, clones such as Dolly that are born from SCNT are not perfect copies of the donor of the nucleus. | 1 | Biochemistry |
Materials with high surface area to volume ratio (e.g. very small diameter, very porous, or otherwise not compact) react at much faster rates than monolithic materials, because more surface is available to react. An example is grain dust: while grain is not typically flammable, grain dust is explosive. Finely ground salt dissolves much more quickly than coarse salt.
A high surface area to volume ratio provides a strong "driving force" to speed up thermodynamic processes that minimize free energy. | 7 | Physical Chemistry |
In a photochemical process, the sunlight is directly used to split water into hydrogen and oxygen. Because the absorption spectrum of water does not overlap with the emission spectrum of the sun, direct dissociation of water cannot take place; a photosensitizer needs to be used. Several such catalysts have been developed as proof of concept, but not yet scaled up for commercial use; nevertheless, their relative simplicity gives the advantage of potential lower cost and increased energy conversion efficiency. One such proof of concept is the "artificial leaf" developed by Nocera and coworkers: a combination of metal oxide-based catalysts and a semiconductor solar cell produces hydrogen upon illumination, with oxygen as the only byproduct. | 5 | Photochemistry |
RiPPs are characterized by a common biosynthetic strategy wherein genetically-encoded peptides undergo translation and subsequent chemical modification by biosynthetic enzymes. | 1 | Biochemistry |
Macroscopically, the ideal gas law states that, for an ideal gas, the product of pressure and volume is proportional to the product of amount of substance and absolute temperature :
where is the molar gas constant (). Introducing the Boltzmann constant as the gas constant per molecule (being N the Avogadro constant) transforms the ideal gas law into an alternative form:
where is the number of molecules of gas. | 7 | Physical Chemistry |
At constant temperature, the reversibility of polymerization can be determined using the Gibbs free energy equation:
where is the change of entropy during polymerization. The change of enthalpy during polymerization, , is also known as the heat of polymerization, which is defined by
where and denote the activation energies for polymerization and depolymerization, respectively, on the assumption that depolymerization occurs by the reverse mechanism of polymerization.
Entropy is the measure of randomness or chaos. A system has a lower entropy when there are few objects in the system and has a higher entropy when there are many objects in the system. Because the process of depolymerization involves a polymer being broken down into its monomers, depolymerization increases entropy. In the Gibbs free energy equation, the entropy term is negative. Enthalpy drives polymerizations. At low temperatures, the enthalpy term is greater than the term, which allows polymerization to occur. At the ceiling temperature, the enthalpy term and the entropy term are equal, so that the rates of polymerization and depolymerization become equal and the net polymerization rate becomes zero. Above the ceiling temperature, the rate of depolymerization is greater than the rate of polymerization, which inhibits the formation of the given polymer. The ceiling temperature can be defined by | 7 | Physical Chemistry |
Thermal equilibrium of a body in itself refers to the body when it is isolated. The background is that no heat enters or leaves it, and that it is allowed unlimited time to settle under its own intrinsic characteristics. When it is completely settled, so that macroscopic change is no longer detectable, it is in its own thermal equilibrium. It is not implied that it is necessarily in other kinds of internal equilibrium. For example, it is possible that a body might reach internal thermal equilibrium but not be in internal chemical equilibrium; glass is an example.
One may imagine an isolated system, initially not in its own state of internal thermal equilibrium. It could be subjected to a fictive thermodynamic operation of partition into two subsystems separated by nothing, no wall. One could then consider the possibility of transfers of energy as heat between the two subsystems. A long time after the fictive partition operation, the two subsystems will reach a practically stationary state, and so be in the relation of thermal equilibrium with each other. Such an adventure could be conducted in indefinitely many ways, with different fictive partitions. All of them will result in subsystems that could be shown to be in thermal equilibrium with each other, testing subsystems from different partitions. For this reason, an isolated system, initially not its own state of internal thermal equilibrium, but left for a long time, practically always will reach a final state which may be regarded as one of internal thermal equilibrium. Such a final state is one of spatial uniformity or homogeneity of temperature. The existence of such states is a basic postulate of classical thermodynamics. This postulate is sometimes, but not often, called the minus first law of thermodynamics. A notable exception exists for isolated quantum systems which are many-body localized and which never reach internal thermal equilibrium. | 7 | Physical Chemistry |
Direct carbon-proton coupling constants are used to study the anomeric configuration of a sugar.
Vicinal proton-proton coupling constants are used to study stereo orientation of protons relatively to the other protons within a sugar ring, thus identifying a monosaccharide.
Vicinal heteronuclear H-C-O-C coupling constants are used to study torsional angles along glycosidic bond between sugars or along exocyclic fragments, thus revealing a molecular conformation.
Sugar rings are relatively rigid molecular fragments, thus vicinal proton-proton couplings are characteristic:
*Equatorial to axial: 1–4 Hz
*Equatorial to equatorial: 0–2 Hz
*Axial to axial non-anomeric: 9–11 Hz
*Axial to axial anomeric: 7–9 Hz
*Axial to exocyclic hydroxymethyl: 5 Hz, 2 Hz
*Geminal between hydroxymethyl protons: 12 Hz | 0 | Organic Chemistry |
Lipoidal estradiol (LE2) is the variety of endogenous C17β long-chain fatty acid esters of estradiol which are formed as metabolites of estradiol. Important examples of these esters include estradiol arachidonate, estradiol lineolate, estradiol oleate, estradiol palmitate, and estradiol stearate. LE2 are estrogens but do not bind to the estrogen receptor, instead acting as prohormones of estradiol. Relative to estradiol, they have far longer-lasting durations of effect due to their much slower rates of metabolism and clearance. It has been hypothesized that LE2 may serve as a store of estrogen for when estradiol levels become low. LE2 are highly lipophilic and hydrophobic and are found in highest concentrations in adipose tissue and other estrogen-sensitive tissues and in low but detectable concentrations in circulation, with none excreted in urine. They have been referred to as the "endogenous counterparts of the synthetic esters of estrogens" like estradiol valerate and estradiol cypionate.
Two of the estradiol esters that compose LE2, estradiol palmitate and estradiol stearate, have been developed and marketed for medical use as long-acting estrogens for use via depot intramuscular injection.
Estradiol is esterified into LE2 by lecithin–cholesterol acyltransferase (LCAT). | 1 | Biochemistry |
In organic chemistry, amine value is a measure of the nitrogen content of an organic molecule. Specifically, it is usually used to measure the amine content of amine functional compounds. It may be defined as the number of milligrams of potassium hydroxide (KOH) equivalent to one gram of epoxy hardener resin. The units are thus mg KOH/g. | 3 | Analytical Chemistry |
While SERS can be performed in colloidal solutions, today the most common method for performing SERS measurements is by depositing a liquid sample onto a silicon or glass surface with a nanostructured noble metal surface. While the first experiments were performed on electrochemically roughened silver, now surfaces are often prepared using a distribution of metal nanoparticles on the surface as well as using lithography or porous silicon as a support. Two dimensional silicon nanopillars decorated with silver have also been used to create SERS active substrates. The most common metals used for plasmonic surfaces in visible light SERS are silver and gold; however, aluminium has recently been explored as an alternative plasmonic material, because its plasmon band is in the UV region, contrary to silver and gold. Hence, there is great interest in using aluminium for UV SERS. It has, however, surprisingly also been shown to have a large enhancement in the infrared, which is not fully understood. In the current decade, it has been recognized that the cost of SERS substrates must be reduced in order to become a commonly used analytical chemistry measurement technique. To meet this need, plasmonic paper has experienced widespread attention in the field, with highly sensitive SERS substrates being formed through approaches such as soaking, in-situ synthesis, screen printing and inkjet printing.
The shape and size of the metal nanoparticles strongly affect the strength of the enhancement because these factors influence the ratio of absorption and scattering events. There is an ideal size for these particles, and an ideal surface thickness for each experiment. If concentration and particle size can be tuned better for each experiment this will go a long way in the cost reduction of substrates. Particles that are too large allow the excitation of multipoles, which are nonradiative. As only the dipole transition leads to Raman scattering, the higher-order transitions will cause a decrease in the overall efficiency of the enhancement. Particles that are too small lose their electrical conductance and cannot enhance the field. When the particle size approaches a few atoms, the definition of a plasmon does not hold, as there must be a large collection of electrons to oscillate together.
An ideal SERS substrate must possess high uniformity and high field enhancement. Such substrates can be fabricated on a wafer scale and label-free superresolution microscopy has also been demonstrated using the fluctuations of surface enhanced Raman scattering signal on such highly uniform, high-performance plasmonic metasurfaces.
Due to their unique physical and chemical properties, two-dimensional (2D) materials have gained significant attention as alternative substrates for surface-enhanced Raman spectroscopy (SERS). The use of 2D materials as SERS substrates offers several advantages over traditional metal substrates, including high sensitivity, reproducibility, and chemical stability.
Graphene is one of the most widely studied 2D materials for SERS applications. Graphene has a high surface area, high electron mobility, and excellent chemical stability, making it an attractive substrate for SERS. Graphene-based SERS sensors have also been shown to be highly reproducible and stable, making them attractive for real-world applications. In addition to graphene, other 2D materials, especially MXenes, have also been investigated for SERS applications. MXenes have a high surface area, good electrical conductivity, and chemical stability, making them attractive for SERS applications. As a result, MXene-based SERS sensors have been used to detect various analytes, including organic molecules, drugs and their metabolites.
As research and development continue, 2D materials-based SERS sensors will likely be more widely used in various industries, including environmental monitoring, healthcare, and food safety. | 7 | Physical Chemistry |
A transposase is any of a class of enzymes capable of binding to the end of a transposon and catalysing its movement to another part of a genome, typically by a cut-and-paste mechanism or a replicative mechanism, in a process known as transposition. The word "transposase" was first coined by the individuals who cloned the enzyme required for transposition of the Tn3 transposon. The existence of transposons was postulated in the late 1940s by Barbara McClintock, who was studying the inheritance of maize, but the actual molecular basis for transposition was described by later groups. McClintock discovered that some segments of chromosomes changed their position, jumping between different loci or from one chromosome to another. The repositioning of these transposons (which coded for color) allowed other genes for pigment to be expressed. Transposition in maize causes changes in color; however, in other organisms, such as bacteria, it can cause antibiotic resistance. Transposition is also important in creating genetic diversity within species and generating adaptability to changing living conditions.
Transposases are classified under EC number EC 2.7.7. Genes encoding transposases are widespread in the genomes of most organisms and are the most abundant genes known. During the course of human evolution, as much as 40% of the human genome has moved around via methods such as transposition of transposons. | 1 | Biochemistry |
The Barton decarboxylation is a radical reaction in which a carboxylic acid is converted to a thiohydroxamate ester (commonly referred to as a Barton ester). The product is then heated in the presence of a radical initiator and a suitable hydrogen donor to afford the decarboxylated product. This is an example of a reductive decarboxylation. Using this reaction it is possible to remove carboxylic acid moieties from alkyl groups and replace them with other functional groups. (See Scheme 1) This reaction is named after its developer, the British chemist and Nobel laureate Sir Derek Barton (1918–1998). | 0 | Organic Chemistry |
Highly-fermentable fiber residues, such as those from resistant starch, oat bran, pectin, and guar are transformed by colonic bacteria into short-chain fatty acids (SCFA) including butyrate, producing more SCFA than less fermentable fibers such as celluloses. One study found that resistant starch consistently produces more butyrate than other types of dietary fiber. The production of SCFA from fibers in ruminant animals such as cattle is responsible for the butyrate content of milk and butter.
Fructans are another source of prebiotic soluble dietary fibers which can be digested to produce butyrate. They are often found in the soluble fibers of foods which are high in sulfur, such as the allium and cruciferous vegetables. Sources of fructans include wheat (although some wheat strains such as spelt contain lower amounts), rye, barley, onion, garlic, Jerusalem and globe artichoke, asparagus, beetroot, chicory, dandelion leaves, leek, radicchio, the white part of spring onion, broccoli, brussels sprouts, cabbage, fennel, and prebiotics, such as fructooligosaccharides (FOS), oligofructose, and inulin. | 1 | Biochemistry |
Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
) At I = 0.1 M () At I = 2.5 M</small> | 7 | Physical Chemistry |
Huang Weiyuan (; December 15, 1921 – November 17, 2015) was a Chinese organic chemist and an academician of the Chinese Academy of Sciences. He served as President of the Shanghai Institute of Organic Chemistry and President of the Chinese Chemical Society. | 0 | Organic Chemistry |
Vertebrates can also biosynthesize defensive chemicals or sequester them from plants or prey. Sequestered compounds have been observed in frogs, natricine snakes, and two genera of birds, Pitohui and Ifrita. It is suspected that some well-known compounds such as tetrodotoxin produced by newts and pufferfish are derived from invertebrate prey. Bufadienolides, defensive chemicals produced by toads, have been found in glands of natricine snakes used for defense. | 1 | Biochemistry |
There remain a few ambiguities about the effect. The current theory of triboluminescence—based upon crystallographic, spectroscopic, and other experimental evidence—is that upon fracture of asymmetrical materials, charge is separated. When the charges recombine, the electrical discharge ionizes the surrounding air, causing a flash of light. Research further suggests that crystals that display triboluminescence often lack symmetry and are poor conductors. However, there are substances which break this rule, and which do not possess asymmetry, yet display triboluminescence, such as hexakis(antipyrine)terbium iodide. It is thought that these materials contain impurities, which make the substance locally asymmetric. Further information on some of the possible processes involved can be found in the page on the triboelectric effect.
The biological phenomenon of triboluminescence is thought to be controlled by recombination of free radicals during mechanical activation. | 5 | Photochemistry |
In base and precious metals flotation, the Jameson Cell has established itself as being particularly useful in several applications in flotation circuits that also use other types of flotation cells, such as mechanical cells. These applications include:
* preflotation roughers for removing naturally hydrophobic gangue materials (such as carbon, talc and elemental sulfur), where the Jameson Cell minimises the entrainment of the valuable minerals while eliminating naturally floating gangue minerals that would otherwise contaminate the concentrate
* rougher-scalper and roughing duties where selectivity and froth washing produce high-grade concentrate. In this application, the recovery in one Jameson Cell is normally equivalent to several mechanical cells, and where the feed contains fast-floating liberated particles, the Cell can produce final-grade product, thus reducing the number of mechanical cells required in a flotation circuit
* cleaner-scalper duties, in which the Jameson Cell recovers fast floating minerals to produce a final-grade concentrate, thus reducing the load on the rest of the cleaning circuit and reducing its size. In this application, it can also be used as a low-cost way of expanding the capacity of an existing cleaner circuit
* final cleaning duties where mechanical cleaning circuits are unable to consistently produce final grade concentrate because of entrained gangue, the Jameson Cell with its enhanced selectivity and froth washing, is able to remove the gangue | 8 | Metallurgy |
In addition to naturally occurring types of catalytic triads, protein engineering has been used to create enzyme variants with non-native amino acids, or entirely synthetic amino acids. Catalytic triads have also been inserted into otherwise non-catalytic proteins, or protein mimics.
Subtilisin (a serine protease) has had its oxygen nucleophile replaced with each of sulfur, selenium, or tellurium. Cysteine and selenocysteine were inserted by mutagenesis, whereas the non-natural amino acid, tellurocysteine, was inserted using auxotrophic cells fed with synthetic tellurocysteine. These elements are all in the 16th periodic table column (chalcogens), so have similar properties. In each case, changing the nucleophile reduced the enzyme's protease activity, but increased a different activity. A sulfur nucleophile improved the enzymes transferase activity (sometimes called subtiligase). Selenium and tellurium nucleophiles converted the enzyme into an oxidoreductase. When the nucleophile of TEV protease was converted from cysteine to serine, it protease activity was strongly reduced, but was able to be restored by directed evolution.
Non-catalytic proteins have been used as scaffolds, having catalytic triads inserted into them which were then improved by directed evolution. The Ser-His-Asp triad has been inserted into an antibody, as well as a range of other proteins. Similarly, catalytic triad mimics have been created in small organic molecules like diaryl diselenide, and displayed on larger polymers like Merrifield resins, and self-assembling short peptide nanostructures. | 1 | Biochemistry |
Norvaline (abbreviated as Nva) is an amino acid with the formula CH(CH)CH(NH)COH. The compound is a structural analog of valeric acid and also an isomer of the more common amino acid valine. Like most other α-amino acids, norvaline is chiral. It is a white, water-soluble solid. | 1 | Biochemistry |
Anthocyanins generally are degraded at higher pH. However, some anthocyanins, such as petanin (petunidin 3-[6-O-(4-O-(E)-p-coumaroyl-O-α--rhamnopyranosyl)-β--glucopyranoside]-5-O-β--glucopyranoside), are resistant to degradation at pH 8 and may be used effectively as a food colorant. | 3 | Analytical Chemistry |
Other factors such as iron-rich dust influx from large desert areas such as the Sahara are thought to play a role in causing HABs. Some algal blooms on the Pacific coast have also been linked to natural occurrences of large-scale climatic oscillations such as El Niño events. HABs are also linked to heavy rainfall. Although HABs in the Gulf of Mexico were witnessed in the early 1500s by explorer Cabeza de Vaca, it is unclear what initiates these blooms and how large a role nanthropogenic and natural factors play in their development. | 3 | Analytical Chemistry |
Maltase-glucoamylase, intestinal is an enzyme that in humans is encoded by the MGAM gene.
Maltase-glucoamylase is an alpha-glucosidase digestive enzyme. It consists of two subunits with differing substrate specificity. Recombinant enzyme studies have shown that its N-terminal catalytic domain has highest activity against maltose, while the C-terminal domain has a broader substrate specificity and activity against glucose oligomers. In the small intestine, this enzyme works in synergy with sucrase-isomaltase and alpha-amylase to digest the full range of dietary starches. | 1 | Biochemistry |
The Colworth Medal is awarded annually by the Biochemical Society to an outstanding research biochemist under the age of 35 and working mainly in the United Kingdom. The award is one of the most prestigious recognitions for young scientists in the UK, and was established by Tony James FRS at Unilever Research and Henry Arnstein of the Biochemical Society and takes its name from a Unilever research laboratory near Bedford in the UK, Colworth House.
The medal was first presented in 1963 and many of those receiving the award are recognised as outstanding scientists achieving international reputations. The lecture is published in Biochemical Society Transactions, previously Colworth Medal lectures were published in The Biochemical Journal. | 1 | Biochemistry |
Consecutively, the probe is incubated in a SAM to make the surface of the probe that is unoccupied unreactive to target or further aptamer binding. The optimized SAM thickness is thick enough for the surface to be passivated against target binding and thin enough to transfer electrons from the redox reporter to the electrode. SAM thickness can be measured as length. It has been reported that cocaine E-AB sensors generate more signal when the SAM is thinner and therefore more conductive. However, reducing the SAM from 6 carbons to 2 carbons decreases signal, and peak current is generated using a 6-carbon SAM. | 7 | Physical Chemistry |
Other variations of the Grignard reagent have been discovered to improve the chemoselectivity of the Grignard reaction, which include but are not limited to: Turbo-Grignards, organocerium reagents, and organocuprate (Gilman) reagents. | 0 | Organic Chemistry |
These include genotoxicity testing, human biomonitoring and molecular epidemiology, ecogenotoxicology, as well as fundamental research in DNA damage and repair. For example, Swain and Rao, using the comet assay reported marked increases in several types of DNA damages in rat brain neurons and astrocytes during aging, including single-strand breaks, double-strand breaks and modified bases (8-OHdG and uracil). | 1 | Biochemistry |
Deterministic theories can be divided into two subgroups: if the initial chiral influence took place in a specific space or time location (averaging zero over large enough areas of observation or periods of time), the theory is classified as local deterministic; if the chiral influence is permanent at the time the chiral selection occurred, then it is classified as universal deterministic. The classification groups for local determinist theories and theories based on chance mechanisms can overlap. Even if an external chiral influence produced the initial chiral imbalance in a deterministic way, the outcome sign could be random since the external chiral influence has its enantiomeric counterpart elsewhere.
In deterministic theories, the enantiomeric imbalance is created due to an external chiral field or influence, and the ultimate sign imprinted in biomolecules will be due to it. Deterministic mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the electroweak interaction (via cosmic rays) or asymmetric environments, such as those caused by circularly polarized light, quartz crystals, or the Earth's rotation, β-Radiolysis or the magnetochiral effect. The most accepted universal deterministic theory is the electroweak interaction. Once established, chirality would be selected for.
One supposition is that the discovery of an enantiomeric imbalance in molecules in the Murchison meteorite supports an extraterrestrial origin of homochirality: there is evidence for the existence of circularly polarized light originating from Mie scattering on aligned interstellar dust particles which may trigger the formation of an enantiomeric excess within chiral material in space. Interstellar and near-stellar magnetic fields can align dust particles in this fashion. Another speculation (the Vester-Ulbricht hypothesis) suggests that fundamental chirality of physical processes such as that of the beta decay (see Parity violation) leads to slightly different half-lives of biologically relevant molecules. | 4 | Stereochemistry |
Fermentation is a specific type of heterotrophic metabolism that uses organic carbon instead of oxygen as a terminal electron acceptor. This means that these organisms do not use an electron transport chain to oxidize NADH to and therefore must have an alternative method of using this reducing power and maintaining a supply of for the proper functioning of normal metabolic pathways (e.g. glycolysis). As oxygen is not required, fermentative organisms are anaerobic. Many organisms can use fermentation under anaerobic conditions and aerobic respiration when oxygen is present. These organisms are facultative anaerobes. To avoid the overproduction of NADH, obligately fermentative organisms usually do not have a complete citric acid cycle. Instead of using an ATP synthase as in respiration, ATP in fermentative organisms is produced by substrate-level phosphorylation where a phosphate group is transferred from a high-energy organic compound to ADP to form ATP. As a result of the need to produce high energy phosphate-containing organic compounds (generally in the form of Coenzyme A-esters) fermentative organisms use NADH and other cofactors to produce many different reduced metabolic by-products, often including hydrogen gas (). These reduced organic compounds are generally small organic acids and alcohols derived from pyruvate, the end product of glycolysis. Examples include ethanol, acetate, lactate, and butyrate. Fermentative organisms are very important industrially and are used to make many different types of food products. The different metabolic end products produced by each specific bacterial species are responsible for the different tastes and properties of each food.
Not all fermentative organisms use substrate-level phosphorylation. Instead, some organisms are able to couple the oxidation of low-energy organic compounds directly to the formation of a proton motive force or sodium-motive force and therefore ATP synthesis. Examples of these unusual forms of fermentation include succinate fermentation by Propionigenium modestum and oxalate fermentation by Oxalobacter formigenes. These reactions are extremely low-energy yielding. Humans and other higher animals also use fermentation to produce lactate from excess NADH, although this is not the major form of metabolism as it is in fermentative microorganisms. | 1 | Biochemistry |
2,2,2-Trichloroethoxycarbonyl (Troc) group is largely used as a protecting group for amines in organic synthesis. | 0 | Organic Chemistry |
A number of possible routes can be used to prepare crystal violet. The original procedure developed by the German chemists Kern and Caro involved the reaction of dimethylaniline with phosgene to give 4,4′-bis(dimethylamino)benzophenone (Michler's ketone) as an intermediate. This was then reacted with additional dimethylaniline in the presence of phosphorus oxychloride and hydrochloric acid.
The dye can also be prepared by the condensation of formaldehyde and dimethylaniline to give a leuco dye:
:CHO + 3 CHN(CH) → CH(CHN(CH)) + HO
Second, this colourless compound is oxidized to the coloured cationic form (hereafter with oxygen, but a typical oxidizing agent is manganese dioxide, MnO):
:CH(CHN(CH)) + HCl + O → [C(CHN(CH))]Cl + HO | 3 | Analytical Chemistry |
The mnemonics BrINClHOF, pronounced "Brinklehof", HONClBrIF, pronounced "Honkelbrif", “HOBrFINCl”, pronounced “Hoberfinkel”, and HOFBrINCl, pronounced "Hofbrinkle", have been coined to aid recall of the list of diatomic elements. Another method, for English-speakers, is the sentence: "Never Have Fear of Ice Cold Beer" as a representation of Nitrogen, Hydrogen, Fluorine, Oxygen, Iodine, Chlorine, Bromine. | 4 | Stereochemistry |
Ceruloplasmin (CP) is an enzyme () synthesized in the liver containing 6 atoms of copper in its structure. Ceruloplasmin carries more than 95% of the total copper in healthy human plasma. The rest is accounted for by macroglobulins. Ceruloplasmin exhibits a copper-dependent oxidase activity, which is associated with possible oxidation of Fe (ferrous iron) into Fe (ferric iron), therefore assisting in its transport in the plasma in association with transferrin, which can carry iron only in the ferric state. The molecular weight of human ceruloplasmin is reported to be 151kDa.
Despite extensive research, much is still unknown about the exact functions of CP, most of the functions are attributed to CP focus on the presence of the Cu centers. These include copper transport to deliver the Cu to extrahepatic tissues, amine oxidase activity that controls the level of biogenic amines in intestinal fluids and plasma, removal of oxygen and other free radicals from plasma, and the export of iron from cells for transport through transferrin.
Mutations have been known to disrupt the binding of copper to CP and will disrupt iron metabolism and cause an iron overload.
Ceruloplasmin is a relatively large enzyme (~10nm); the larger size prevents the bound copper from being lost in a person's urine during transport. | 1 | Biochemistry |
Water clarity is more specific than water quality. The term “water clarity” more strictly describes the amount of light that passes through water or an object’s visibility in water. The term “water quality” more broadly refers to many characteristics of water, including temperature, dissolved oxygen, the amount of nutrients, or the presence of algal blooms. How clear the water appears is only one component of water quality.
An underwater ecosystem can have high water clarity yet low water quality, and vice versa. Scientists have observed that many lakes are becoming less clear while also recovering from acid rain. This phenomenon has been seen in the northeastern United States and northern Europe. In the past, some lakes were ecologically bare, yet clear, while acidity was high. In recent years, as acidity is reduced and watersheds become more forested, many lakes are less clear but also ecologically healthier with higher concentrations of dissolved organic carbon and more natural water chemistry. | 3 | Analytical Chemistry |
There are no known contraindication to the use of dexmedetomidine. It has a biphasic effect on blood pressure with lower readings at lower drug concentrations and higher readings at higher concentrations. Common side effects include: hypotension, hypertension, with slight decreases in heart rate, arrhythmias, and hypoxia. Toxic doses may cause first-degree or second-degree atrioventricular block. These adverse events usually occur briefly after administering a loading dose of the drug. Thus, adverse effects may be reduced by omitting a loading dose. | 4 | Stereochemistry |
Weighting of the contributing structures in terms of their contribution to the overall structure can be calculated in multiple ways, using "Ab initio" methods derived from Valence Bond theory, or else from the Natural Bond Orbitals (NBO) approaches of Weinhold [http://www.chem.wisc.edu/~nbo5 NBO5] , or finally from empirical calculations based on the Hückel method. A Hückel method-based software for teaching resonance is available on the [http://www.hulis.free.fr HuLiS] Web site. | 7 | Physical Chemistry |
The hemocompatability of a medical device is dependent upon surface charge, energy and topography. Devices that fail to be hemocompatabile run the risk of forming a thrombus, proliferation and compromising the immune system. Polymer coatings are applied to devices to increase their hemocompatability. Chemical cascades lead to the formation of fibrous clots. By choosing to use hydrophilic polymer coatings, protein adsorption decreases and the chance of negative interactions with the blood diminishes as well. One such polymer coating that increases hemocompatability is heparin. Heparin is a polymer coating that interacts with thrombin to prevent coagulation. Heparin has been shown to suppress platelet adhesion, complement activation and protein adsorption. | 7 | Physical Chemistry |
Magnesium is required as a co-factor for thermostable DNA polymerase. Taq polymerase is a magnesium-dependent enzyme and determining the optimum concentration to use is critical to the success of the PCR reaction. Some of the components of the reaction mixture such as template concentration, dNTPs and the presence of chelating agents (EDTA) or proteins can reduce the amount of free magnesium present thus reducing the activity of the enzyme. Primers which bind to incorrect template sites are stabilized in the presence of excessive magnesium concentrations and so results in decreased specificity of the reaction. Excessive magnesium concentrations also stabilize double stranded DNA and prevent complete denaturation of the DNA during PCR reducing the product yield. Inadequate thawing of MgCl may result in the formation of concentration gradients within the magnesium chloride solution supplied with the DNA polymerase and also contributes to many failed experiments . | 1 | Biochemistry |
When the distance between the probe and the sample is brought to the range where atomic force may be detected, while a cantilever is excited in its natural eigenfrequency (f), the resonance frequency f of the cantilever may shift from its original resonance frequency. In other words, in the range where atomic force may be detected, a frequency shift (df =f–f) will also be observed. When the distance between the probe and the sample is in the non-contact region, the frequency shift increases in negative direction as the distance between the probe and the sample gets smaller.
When the sample has concavity and convexity, the distance between the tip-apex and the sample varies in accordance with the concavity and convexity accompanied with a scan of the sample along x–y direction (without height regulation in z-direction). As a result, the frequency shift arises. The image in which the values of the frequency obtained by a raster scan along the x–y direction of the sample surface are plotted against the x–y coordination of each measurement point is called a constant-height image.
On the other hand, the df may be kept constant by moving the probe upward and downward (See (3) of FIG.5) in z-direction using a negative feedback (by using z-feedback loop) while the raster scan of the sample surface along the x–y direction. The image in which the amounts of the negative feedback (the moving distance of the probe upward and downward in z-direction) are plotted against the x–y coordination of each measurement point is a topographic image. In other words, the topographic image is a trace of the tip of the probe regulated so that the df is constant and it may also be considered to be a plot of a constant-height surface of the df.
Therefore, the topographic image of the AFM is not the exact surface morphology itself, but actually the image influenced by the bond-order between the probe and the sample, however, the topographic image of the AFM is considered to reflect the geographical shape of the surface more than the topographic image of a scanning tunnel microscope. | 6 | Supramolecular Chemistry |
Note: Where a given letter is used in both capital and lower case form (, and , ) the capital letter refers to the macroscopic observable and the lower case letter to the corresponding variable for an individual particle or layer of the material. Greek symbols are used for properties of a single particle.
: – absorption fraction of a single layer
: – remission fraction of a single layer
: – transmission fraction of a single layer
: , , – the absorption, remission, and transmission fractions for a sample composed of layers
: – absorption fraction of a particle
: – back-scattering from a particle
: – isotropic scattering from a particle
: – absorption coefficient defined as the fraction of incident light absorbed by a very thin layer divided by the thickness of that layer
: – scattering coefficient defined as the fraction of incident light scattered by a very thin layer divided by the thickness of that layer | 7 | Physical Chemistry |
Levocetirizine is used for allergic rhinitis. This includes allergy symptoms such as watery eyes, runny nose, sneezing, hives, and itching. | 4 | Stereochemistry |
Organobarium compounds of the type (allyl)BaCl can be prepared by reaction of activated barium (Rieke method reduction of barium iodide with lithium biphenylide) with allyl halides. These allylbarium compounds react with carbonyl compounds. Such reagents are more alpha-selective and more stereoselective than the related Grignards or organocalcium compounds. The metallocene (Cp*)Ba has also been reported. | 0 | Organic Chemistry |
To formally describe time-translation symmetry we say the equations, or laws, that describe a system at times and are the same for any value of and .
For example, considering Newton's equation:
One finds for its solutions the combination:
does not depend on the variable . Of course, this quantity describes the total energy whose conservation is due to the time-translation invariance of the equation of motion. By studying the composition of symmetry transformations, e.g. of geometric objects, one reaches the conclusion that they form a group and, more specifically, a Lie transformation group if one considers continuous, finite symmetry transformations. Different symmetries form different groups with different geometries. Time independent Hamiltonian systems form a group of time translations that is described by the non-compact, abelian, Lie group . TTS is therefore a dynamical or Hamiltonian dependent symmetry rather than a kinematical symmetry which would be the same for the entire set of Hamiltonians at issue. Other examples can be seen in the study of time evolution equations of classical and quantum physics.
Many differential equations describing time evolution equations are expressions of invariants associated to some Lie group and the theory of these groups provides a unifying viewpoint for the study of all special functions and all their properties. In fact, Sophus Lie invented the theory of Lie groups when studying the symmetries of differential equations. The integration of a (partial) differential equation by the method of separation of variables or by Lie algebraic methods is intimately connected with the existence of symmetries. For example, the exact solubility of the Schrödinger equation in quantum mechanics can be traced back to the underlying invariances. In the latter case, the investigation of symmetries allows for an interpretation of the degeneracies, where different configurations to have the same energy, which generally occur in the energy spectrum of quantum systems. Continuous symmetries in physics are often formulated in terms of infinitesimal rather than finite transformations, i.e. one considers the Lie algebra rather than the Lie group of transformations | 7 | Physical Chemistry |
Radical disproportionation encompasses a group of reactions in organic chemistry in which two radicals react to form two different non-radical products. Radicals in chemistry are defined as reactive atoms or molecules that contain an unpaired electron or electrons in an open shell. The unpaired electrons can cause radicals to be unstable and reactive. Reactions in radical chemistry can generate both radical and non-radical products. Radical disproportionation reactions can occur with many radicals in solution and in the gas phase. Due to the reactive nature of radical molecules, disproportionation proceeds rapidly and requires little to no activation energy. The most thoroughly studied radical disproportionation reactions have been conducted with alkyl radicals, but there are many organic molecules that can exhibit more complex, multi-step disproportionation reactions. | 0 | Organic Chemistry |
The manifold topographic techniques can be categorized according to several criteria.
One of them is the distinction between restricted-beam techniques on the one hand (such as section topography or pinhole topography) and extended-beam techniques on the other hand, which use the full width and intensity of the incoming beam. Another, independent distinction is between integrated-wave topography, making use of the full spectrum of incoming X-ray wavelengths and divergences, and plane-wave (monochromatic) topopgraphy, more selective in both wavelengths and divergence. Integrated-wave topography can be realized as either single-crystal or double-crystal topography. Further distinctions include the one between topography in reflection geometry (Bragg-case) and in transmission geometry (Laue case).
For a full discussion and a graphical hierarchy of topographic techniques, see
[https://web.archive.org/web/20041107130433/http://www.esrf.fr/exp_facilities/ID19/homepage/DiffTopo/X-raytopography.htm]. | 3 | Analytical Chemistry |
The generally accepted model of the formation of the Universe states that it happened as the result of the Big Bang. In this model, in the time interval of 10–10 s after the Big Bang, matter existed in the form of a quark–gluon plasma. It is possible to reproduce the density and temperature of matter existing of that time in laboratory conditions to study the characteristics of the very early Universe. So far, the only possibility is the collision of two heavy atomic nuclei accelerated to energies of more than a hundred GeV. Using the result of a head-on collision in the volume approximately equal to the volume of the atomic nucleus, it is possible to model the density and temperature that existed in the first instants of the life of the Universe. | 7 | Physical Chemistry |
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted by cells to create non-cellular structures, such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically converted to smaller molecules in the process of releasing energy, such as for carbohydrates, lipids, proteins, and fermentation products (ethanol or vinegar), leading to end-products of water and carbon dioxide. All organisms require water. Essential nutrients for animals are the energy sources, some of the amino acids that are combined to create proteins, a subset of fatty acids, vitamins and certain minerals. Plants require more diverse minerals absorbed through roots, plus carbon dioxide and oxygen absorbed through leaves. Fungi live on dead or living organic matter and meet nutrient needs from their host.
Different types of organisms have different essential nutrients. Ascorbic acid (vitamin C) is essential to humans and some animal species, but most other animals and many plants are able to synthesize it. Nutrients may be organic or inorganic: organic compounds include most compounds containing carbon, while all other chemicals are inorganic. Inorganic nutrients include nutrients such as iron, selenium, and zinc, while organic nutrients include, protein, fats, sugars, and vitamins.
A classification used primarily to describe nutrient needs of animals divides nutrients into macronutrients and micronutrients. Consumed in relatively large amounts (grams or ounces), macronutrients (carbohydrates, fats, proteins, water) are primarily used to generate energy or to incorporate into tissues for growth and repair. Micronutrients are needed in smaller amounts (milligrams or micrograms); they have subtle biochemical and physiological roles in cellular processes, like vascular functions or nerve conduction. Inadequate amounts of essential nutrients, or diseases that interfere with absorption, result in a deficiency state that compromises growth, survival and reproduction. Consumer advisories for dietary nutrient intakes, such as the United States Dietary Reference Intake, are based on the amount required to prevent deficiency, and provide macronutrient and micronutrient guides for both lower and upper limits of intake. In many countries, regulations require that food product labels display information about the amount of any macronutrients and micronutrients present in the food in significant quantities. Nutrients in larger quantities than the body needs may have harmful effects. Edible plants also contain thousands of compounds generally called phytochemicals which have unknown effects on disease or health, including a diverse class with non-nutrient status called polyphenols, which remain poorly understood as of 2017. | 9 | Geochemistry |
Since organochlorine compounds are the most abundant organohalides, most dehalogenations entail manipulation of C-Cl bonds. | 0 | Organic Chemistry |
A chromatography detector is a device that detects and quantifies separated compounds as they elute from the chromatographic column. These detectors are integral to various chromatographic techniques, such as gas chromatography, liquid chromatography, and high-performance liquid chromatography, and supercritical fluid chromatography among others. The main function of a chromatography detector is to translate the physical or chemical properties of the analyte molecules into measurable signal, typically electrical signal, that can be displayed as a function of time in a graphical presentation, called a chromatograms. Chromatograms can provide valuable information about the composition and concentration of the components in the sample.
Detectors operate based on specific principles, including optical, electrochemical, thermal conductivity, fluorescence, mass spectrometry, and more. Each type of detector has its unique capabilities and is suitable for specific applications, depending on the nature of the analytes and the sensitivity and selectivity required for the analysis.
There are two general types of detectors: destructive and non-destructive. The destructive detectors perform continuous transformation of the column effluent (burning, evaporation or mixing with reagents) with subsequent measurement of some physical property of the resulting material (plasma, aerosol or reaction mixture). The non-destructive detectors are directly measuring some property of the column eluent (for example, ultraviolet absorption) and thus affords greater analyte recovery. | 3 | Analytical Chemistry |
BCF is commercially synthesized in a two-step process from chloroform. Chloroform is fluorinated with hydrogen fluoride. The resulting chlorodifluoromethane is then reacted with elemental bromine at 400-600 °C, with reaction time limited to about 3 seconds. The overall yield is over 90%. | 2 | Environmental Chemistry |
Inverted repeats are often described as "hotspots" of eukaryotic and prokaryotic genomic instability. Long inverted repeats are deemed to greatly influence the stability of the genome of various organisms. This is exemplified in E. coli, where genomic sequences with long inverted repeats are seldom replicated, but rather deleted with rapidity. Again, the long inverted repeats observed in yeast greatly favor recombination within the same and adjacent chromosomes, resulting in an equally very high rate of deletion. Finally, a very high rate of deletion and recombination were also observed in mammalian chromosomes regions with inverted repeats. Reported differences in the stability of genomes of interrelated organisms are always an indication of a disparity in inverted repeats. The instability results from the tendency of inverted repeats to fold into hairpin- or cruciform-like DNA structures. These special structures can hinder or confuse DNA replication and other genomic activities. Thus, inverted repeats lead to special configurations in both RNA and DNA that can ultimately cause mutations and disease.
The illustration shows an inverted repeat undergoing cruciform extrusion. DNA in the region of the inverted repeat unwinds and then recombines, forming a four-way junction with two stem-loop structures. The cruciform structure occurs because the inverted repeat sequences self-pair to each other on their own strand.
Extruded cruciforms can lead to frameshift mutations when a DNA sequence has inverted repeats in the form of a palindrome combined with regions of direct repeats on either side. During transcription, slippage and partial dissociation of the polymerase from the template strand can lead to both deletion and insertion mutations. Deletion occurs when a portion of the unwound template strand forms a stem-loop that gets "skipped" by the transcription machinery. Insertion occurs when a stem-loop forms in a dissociated portion of the nascent (newly synthesized) strand causing a portion of the template strand to be transcribed twice. | 1 | Biochemistry |
The gas analyzers directly measure concentrations of multiple gas species using mid-infrared laser absorption spectroscopy with QCLs as light sources. This allows for highly specific and accurate gas detection along with maximum measurement sensitivity. | 7 | Physical Chemistry |
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