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Laser spectroscopy is a spectroscopic technique that uses lasers to be able determine the emitted frequencies of matter. The laser was invented because spectroscopists took the concept of its predecessor, the maser, and applied it to the visible and infrared ranges of light. The maser was invented by Charles Townes and other spectroscopists to stimulate matter to determine the radiative frequencies that specific atoms and molecules emitted. While working on the maser, Townes realized that more accurate detections were possible as the frequency of the microwave emitted increased. This led to an idea a few years later to use the visible and eventually the infrared ranges of light for spectroscopy that became a reality with the help of Arthur Schawlow. Since then, lasers have gone on to significantly advance experimental spectroscopy. The laser light allowed for much higher precision experiments specifically in the uses of studying collisional effects of light as well as being able to accurately detect specific wavelengths and frequencies of light, allowing for the invention of devices such as laser atomic clocks. Lasers also made spectroscopy that used time methods more accurate by using speeds or decay times of photons at specific wavelengths and frequencies to keep time. Laser spectroscopic techniques have been used for many different applications. One example is using laser spectroscopy to detect compounds in materials. One specific method is called Laser-induced Fluorescence Spectroscopy, and uses spectroscopic methods to be able to detect what materials are in a solid, liquid, or gas, in situ. This allows for direct testing of materials, instead of having to take the material to a lab to figure out what the solid, liquid, or gas is made of. | 7 | Physical Chemistry |
Lupeol has a complex pharmacology, displaying antiprotozoal, antimicrobial, antiinflammatory, antitumor and chemopreventive properties.
Animal models suggest lupeol may act as an anti-inflammatory agent. A 1998 study found lupeol to decrease paw swelling in rats by 39%, compared to 35% for the standardized control compound indomethacin.
One study has also found some activity as a Dipeptidyl peptidase-4 inhibitor and prolyl oligopeptidase inhibitor at high concentrations (in the millimolar range).
It is an effective inhibitor in laboratory models of prostate and skin cancers.
As an anti-inflammatory agent, lupeol functions primarily on the interleukin system. Lupeol to decreases IL-4 (interleukin 4) production by T-helper type 2 cells.
Lupeol has been found to have a contraceptive effect due to its inhibiting effect on the calcium channel of sperm (CatSper).
Lupeol has also been shown to exert anti-angiogenic and anti-cancer effects via the downregulation of TNF-alpha and VEGFR-2.
Famous anti-inflammatory ethno-medicinal plant Camellia japonica contains anti-inflammatory component lupeol in its leaf. | 0 | Organic Chemistry |
The term is used in contrast to a latent heat, which is the amount of heat exchanged that is hidden, meaning it occurs without change of temperature. For example, during a phase change such as the melting of ice, the temperature of the system containing the ice and the liquid is constant until all ice has melted. The terms latent and sensible are correlative.
The sensible heat of a thermodynamic process may be calculated as the product of the bodys mass (m) with its specific heat capacity (c') and the change in temperature ():
Sensible heat and latent heat are not special forms of energy. Rather, they describe exchanges of heat under conditions specified in terms of their effect on a material or a thermodynamic system.
In the writings of the early scientists who provided the foundations of thermodynamics, sensible heat had a clear meaning in calorimetry. James Prescott Joule characterized it in 1847 as an energy that was indicated by the thermometer.
Both sensible and latent heats are observed in many processes while transporting energy in nature. Latent heat is associated with changes of state, measured at constant temperature, especially the phase changes of atmospheric water vapor, mostly vaporization and condensation, whereas sensible heat directly affects the temperature of the atmosphere.
In meteorology, the term sensible heat flux means the conductive heat flux from the Earths surface to the atmosphere. It is an important component of Earths surface energy budget. Sensible heat flux is commonly measured with the eddy covariance method. | 7 | Physical Chemistry |
In polymer chemistry, reversible-deactivation radical polymerizations (RDRPs) are members of the class of reversible-deactivation polymerizations which exhibit much of the character of living polymerizations, but cannot be categorized as such as they are not without chain transfer or chain termination reactions.
Several different names have been used in literature, which are:
*Living radical polymerization
*Living free radical polymerization
*Controlled/"living" radical polymerization
*Controlled radical polymerization
*Reversible deactivation radical polymerization
Though the term "living" radical polymerization was used in early days, it has been discouraged by IUPAC, because radical polymerization cannot be a truly living process due to unavoidable termination reactions between two radicals. The commonly-used term controlled radical polymerization is permitted, but reversible-deactivation radical polymerization or controlled reversible-deactivation radical polymerization (RDRP) is recommended. | 7 | Physical Chemistry |
The equation is also usable as a PVT equation for compressible fluids (e.g. polymers). In this case specific volume changes are small and it can be written in a simplified form:
where p is the pressure, V is specific volume, T is the temperature and A, B, C are parameters. | 7 | Physical Chemistry |
The rhodophyte, or red algae chloroplast group is another large and diverse chloroplast lineage. Rhodophyte chloroplasts are also called rhodoplasts, literally "red chloroplasts".
Rhodoplasts have a double membrane with an intermembrane space and phycobilin pigments organized into phycobilisomes on the thylakoid membranes, preventing their thylakoids from stacking. Some contain pyrenoids. Rhodoplasts have chlorophyll a and phycobilins for photosynthetic pigments; the phycobilin phycoerythrin is responsible for giving many red algae their distinctive red color. However, since they also contain the blue-green chlorophyll a and other pigments, many are reddish to purple from the combination. The red phycoerytherin pigment is an adaptation to help red algae catch more sunlight in deep water—as such, some red algae that live in shallow water have less phycoerythrin in their rhodoplasts, and can appear more greenish. Rhodoplasts synthesize a form of starch called floridean starch, which collects into granules outside the rhodoplast, in the cytoplasm of the red alga. | 5 | Photochemistry |
Material properties such as strength, chemical reactivity, stress corrosion cracking resistance, weldability, deformation behavior, resistance to radiation damage, and magnetic susceptibility can be highly dependent on the material’s texture and related changes in microstructure. In many materials, properties are texture-specific, and development of unfavorable textures when the material is fabricated or in use can create weaknesses that can initiate or exacerbate failures. Parts can fail to perform due to unfavorable textures in their component materials. Failures can correlate with the crystalline textures formed during fabrication or use of that component. Consequently, consideration of textures that are present in and that could form in engineered components while in use can be a critical when making decisions about the selection of some materials and methods employed to manufacture parts with those materials. When parts fail during use or abuse, understanding the textures that occur within those parts can be crucial to meaningful interpretation of failure analysis data. | 8 | Metallurgy |
In 2016, a new approach was described for producing hybrid photovoltaic wafers combining the high efficiency of III-V multi-junction solar cells with the economies and wealth of experience associated with silicon. The technical complications involved in growing the III-V material on silicon at the required high temperatures, a subject of study for some 30 years, are avoided by epitaxial growth of silicon on GaAs at low temperature by plasma-enhanced chemical vapor deposition (PECVD).
Si single-junction solar cells have been widely studied for decades and are reaching their practical efficiency of ~26% under 1-sun conditions. Increasing this efficiency may require adding more cells with bandgap energy larger than 1.1 eV to the Si cell, allowing to convert short-wavelength photons for generation of additional voltage. A dual-junction solar cell with a band gap of 1.6–1.8 eV as a top cell can reduce thermalization loss, produce a high external radiative efficiency and achieve theoretical efficiencies over 45%. A tandem cell can be fabricated by growing the GaInP and Si cells. Growing them separately can overcome the 4% lattice constant mismatch between Si and the most common III–V layers that prevent direct integration into one cell. The two cells therefore are separated by a transparent glass slide so the lattice mismatch does not cause strain to the system. This creates a cell with four electrical contacts and two junctions that demonstrated an efficiency of 18.1%. With a fill factor (FF) of 76.2%, the Si bottom cell reaches an efficiency of 11.7% (± 0.4) in the tandem device, resulting in a cumulative tandem cell efficiency of 29.8%. This efficiency exceeds the theoretical limit of 29.4% and the record experimental efficiency value of a Si 1-sun solar cell, and is also higher than the record-efficiency 1-sun GaAs device. However, using a GaAs substrate is expensive and not practical. Hence researchers try to make a cell with two electrical contact points and one junction, which does not need a GaAs substrate. This means there will be direct integration of GaInP and Si. | 7 | Physical Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), and Valine (Val, V). | 1 | Biochemistry |
Linear material constitutive relations in physics can be expressed in the form
where are two vectors representing physical quantities and is a second-order material tensor. In matrix form,
Examples of physical problems that fit the above template are listed in the table below.
Using in the matrix implies that . Using leads to and . Energy restrictions usually require and hence we must have . Therefore, the material properties of a transversely isotropic material are described by the matrix | 3 | Analytical Chemistry |
Spinodal decomposition is a mechanism by which a single thermodynamic phase spontaneously separates into two phases (without nucleation). Decomposition occurs when there is no thermodynamic barrier to phase separation. As a result, phase separation via decomposition does not require the nucleation events resulting from thermodynamic fluctuations, which normally trigger phase separation.
Spinodal decomposition is observed when mixtures of metals or polymers separate into two co-existing phases, each rich in one species and poor in the other. When the two phases emerge in approximately equal proportion (each occupying about the same volume or area), characteristic intertwined structures are formed that gradually coarsen (see animation). The dynamics of spinodal decomposition is commonly modeled using the Cahn–Hilliard equation.
Spinodal decomposition is fundamentally different from nucleation and growth. When there is a nucleation barrier to the formation of a second phase, time is taken by the system to overcome that barrier. As there is no barrier (by definition) to spinodal decomposition, some fluctuations (in the order parameter that characterizes the phase) start growing instantly. Furthermore, in spinodal decomposition, the two distinct phases start growing in any location uniformly throughout the volume, whereas a nucleated phase change begins at a discrete number of points.
Spinodal decomposition occurs when a homogenous phase becomes thermodynamically unstable. An unstable phase lies at a maximum in free energy. In contrast, nucleation and growth occur when a homogenous phase becomes metastable. That is, another biphasic system becomes lower in free energy, but the homogenous phase remains at a local minimum in free energy, and so is resistant to small fluctuations. J. Willard Gibbs described two criteria for a metastable phase: that it must remain stable against a small change over a large area. | 7 | Physical Chemistry |
O concentrations in the ocean have decreased since the 1980s. Part of this decrease is due to increased ocean heat content (OHC) from global warming decreasing O solubility. As solubility in surface oceans decreases, O out gasses to the atmosphere. Increased AOU is likely also contributing to declining ocean O concentrations. Changes in AOU in the ocean could be caused by multiple forcings, such as changes in subduction rates, changes in water mass boundaries, initial O from water mass formation, biochemical consumption of O, or changes in eddy mixing. Based on observations, global AOU increase seems to be linked to increasing OHC. | 9 | Geochemistry |
Homoaromaticity can better be explained using Perturbation Molecular Orbital Theory (PMO) as described in a 1975 study by Robert C. Haddon. The homotropenylium cation can be considered as a perturbed version of the tropenylium cation due to the addition of a homoconjugate linkage interfering with the resonance of the original cation. | 7 | Physical Chemistry |
Potential application as long-lasting dyes is based on the enhanced stability of the inner portion of the dumbbell-shaped molecule. Studies with cyclodextrin-protected rotaxane azo dyes established this characteristic. More reactive squaraine dyes have also been shown to have enhanced stability by preventing nucleophilic attack of the inner squaraine moiety. The enhanced stability of rotaxane dyes is attributed to the insulating effect of the macrocycle, which is able to block interactions with other molecules. | 6 | Supramolecular Chemistry |
Fluoroalkenes and fluorinated alkynes are reactive and many are toxic for example perfluoroisobutene. To produce polytetrafluoroethylene various fluorinated surfactants are used, in the process known as Emulsion polymerization, and the surfactant included in the polymer can bioaccumulate. | 2 | Environmental Chemistry |
Two mechanisms have been proposed for lithium–halogen exchange.
One proposed pathway involves a nucleophilic mechanism that generates a reversible "ate-complex" intermediate. Farnham and Calabrese crystallized an "ate-complex" lithium bis(pentafluorophenyl) iodinate complexed with TMEDA.
The "ate-complex" further reacts with electrophiles and provides pentafluorophenyl iodide and CHLi. A number of kinetic studies also support a nucleophilic pathway in which the carbanion on the lithium species attacks the halogen atom on the aryl halide. Another proposed mechanism involves single electron transfer with the generation of radicals. In reactions of secondary and tertiary alkyllithium and alkyl halides, radical species were detected by EPR spectroscopy. The mechanistic studies of lithium–halogen exchange are complicated by the formation of aggregates of organolithium species. | 0 | Organic Chemistry |
There are three well-characterized families of opioid peptides produced by the body: enkephalins, β-endorphin, and dynorphins. The met-enkephalin peptide sequence is coded for by the enkephalin gene; the leu-enkephalin peptide sequence is coded for by both the enkephalin gene and the dynorphin gene. The proopiomelanocortin gene (POMC) also contains the met-enkephalin sequence on the N-terminus of beta-endorphin, but the endorphin peptide is not processed into enkephalin. | 1 | Biochemistry |
In enzymology, enzymes that add a fructose group to a molecule are called fructosyl-transferases, beta-D-fructofuranosyl transferases or fructotranferases. Examples are:
* aldose beta-D-fructosyltransferase
* 2,1-fructan:2,1-fructan 1-fructosyltransferase
* 6G-fructosyltransferase
* Inulin fructotransferase (DFA-I-forming)
* Inulin fructotransferase (DFA-III-forming)
* Levan fructotransferase (DFA-IV-forming)
* Levansucrase | 1 | Biochemistry |
In the first step, a delocalized allyloxocarbenium ion (2) is formed, typically with the aid of a Lewis acid like indium(III) chloride or boron trifluoride. This ion reacts in situ with an alcohol, yielding a mixture of the α (3) and β (4) anomers of the 2-glycoside, with the double bond shifted to position 3,4. | 0 | Organic Chemistry |
PERK (encoded in humans by the gene EIF2AK3) responds mainly to endoplasmic reticulum stress and has two modes of activation. This kinase has a unique luminal domain that plays a role in activation. The classical model of activation states that the luminal domain is normally bound to 78-kDa glucose-regulated protein (GRP78). Once there is a buildup of unfolded proteins, GRP78 dissociates from the luminal domain. This causes PERK to dimerize, leading to autophosphorylation and activation. The activated PERK kinase will then phosphorylate eIF2α, causing a cascade of events. Thus, the activation of this kinase is dependent on the aggregation of unfolded proteins in the endoplasmic reticulum. PERK has also been observed to activate in response to activity of the proto-oncogene MYC. This activation causes ATF4 expression, resulting in tumorigenesis and cellular transformation. | 1 | Biochemistry |
Acid–base imbalance is an abnormality of the human body's normal balance of acids and bases that causes the plasma pH to deviate out of the normal range (7.35 to 7.45). In the fetus, the normal range differs based on which umbilical vessel is sampled (umbilical vein pH is normally 7.25 to 7.45; umbilical artery pH is normally 7.18 to 7.38). It can exist in varying levels of severity, some life-threatening. | 7 | Physical Chemistry |
acid is a monocarboxylic β-hydroxy acid and natural product with the molecular formula . At room temperature, pure acid occurs as a transparent, colorless to light yellow liquid which is soluble in water. acid is a weak acid with a pK of 4.4. Its refractive index () is 1.42. | 1 | Biochemistry |
A generalized compound is a mixture of chemical compounds of constant composition, despite possible changes in the total amount. The concept is used in the Dynamic Energy Budget theory, where biomass is partitioned into a limited set of generalised compounds, which contain a high percentage of organic compounds. The amount of generalized compound can be quantified in terms of weight, but more conveniently in terms of C-moles. The concept of strong homeostasis has an intimate relationship with that of generalised compound. | 1 | Biochemistry |
A lot of emphasis has been given to RNA-Seq data after the Encyclopedia of DNA Elements (ENCODE) and The Cancer Genome Atlas (TCGA) projects have used this approach to characterize dozens of cell lines and thousands of primary tumor samples, respectively. ENCODE aimed to identify genome-wide regulatory regions in different cohort of cell lines and transcriptomic data are paramount to understand the downstream effect of those epigenetic and genetic regulatory layers. TCGA, instead, aimed to collect and analyze thousands of patient's samples from 30 different tumor types to understand the underlying mechanisms of malignant transformation and progression. In this context RNA-Seq data provide a unique snapshot of the transcriptomic status of the disease and look at an unbiased population of transcripts that allows the identification of novel transcripts, fusion transcripts and non-coding RNAs that could be undetected with different technologies. | 1 | Biochemistry |
Several approaches to simulate NMR observables of carbohydrates has been reviewed. They include:
*Universal statistical database approaches (ACDLabs, Modgraph, etc.)
*Usage of neural networks to refine the predictions
*Regression based methods
*CHARGE
*Carbohydrate-optimized empirical schemes (CSDB/BIOPSEL, CASPER).
*Combined molecular mechanics/dynamics geometry calculation and quantum-mechanical simulation/iteration of NMR observables (PERCH NMR Software)
*ONIOM approaches (optimization of different parts of molecule with different accuracy)
*Ab initio calculations.
Growing computational power allows usage of thorough quantum-mechanical calculations at high theory levels and large basis sets for refining the molecular geometry of carbohydrates and subsequent prediction of NMR observables using GIAO and other methods with or without solvent effect account. Among combinations of theory level and a basis set reported as sufficient for NMR predictions were B3LYP/6-311G++(2d,2p) and PBE/PBE (see review). It was shown for saccharides that carbohydrate-optimized empirical schemes provide significantly better accuracy (0.0-0.5 ppm per C resonance) than quantum chemical methods (above 2.0 ppm per resonance) reported as best for NMR simulations, and work thousands times faster. However, these methods can predict only chemical shifts and perform poor for non-carbohydrate parts of molecules.
As a representative example, see figure on the right. | 0 | Organic Chemistry |
Metabolic ecology is a field of ecology aiming to understand constraints on metabolic organization as important for understanding almost all life processes. Main focus is on the metabolism of individuals, emerging intra- and inter-specific patterns, and the evolutionary perspective.
Two main metabolic theories that have been applied in ecology are Kooijman's Dynamic energy budget (DEB) theory and the West, Brown, and Enquist (WBE) theory of ecology. Both theories have an individual-based metabolic underpinning, but have fundamentally different assumptions.
Models of individual's metabolism follow the energy uptake and allocation, and can focus on mechanisms and constraints of energy transport (transport models), or on dynamic use of stored metabolites (energy budget models). | 1 | Biochemistry |
Recent discoveries implicating RNA in the pathogenesis of several forms of cancer and neuromuscular diseases have created a paradigm shift in drug discovery. This work combined with advances in structural characterization techniques such as NMR spectroscopy and X-ray crystallography together with computational modeling, has pushed forward the realization that RNA is a dynamic yet viable drug target. Traditionally, RNA was thought to be a mediator between DNA sequence-encoded instructions and functional protein. However, recent reports have shown that there are a large number of non-coding RNAs (ncRNAs) that are not translated into protein. Whereas 85% of the human genome is transcribed into RNA only 3% of the transcripts code for functional protein. Although, ncRNAs do affect gene expression levels by a variety of mechanisms. Further, RNA can adopt discrete secondary or tertiary structures which play a pivotal role in many biological processes and disease pathology. For these reasons, RNA is being recognized as an attractive drug target for small molecules.
The earliest attempts to target RNA led to the discovery that aminoglycosides could bind to human RNA. In an early report, Noller discovered that several classes of antibiotics (streptomycin, tetracycline, spectinomycin, edeine, hygromycin, and the neomycins) could "protect" nucleotides in 16S ribosomal RNA by binding to this RNA. Subsequent studies by Schroeder and Green began to plant the seed that RNA could be targeted. Schroeder uncovered that aminoglycosides could inhibit protein synthesis by interacting with the ribosome through interactions with the 3’ end of the 16S RNA of E. coli taking advantage of RNA conformational changes. Green and coworkers further confirmed this idea, discovering that aminoglycosides blocked the interaction of HIV-1 Rev protein and its viral RNA-binding site.
David Wilson and David Draper were the first to suggest that RNA structures could be targeted by small molecules. They hypothesized that RNA could be "druggable" by targeting the 3D structure in the same way as protein 3D structures are used as drug targets and furthered the idea that targeting RNA could be used to treat diseases. Czarnik and co-workers at Parke-Davis completed a screen on HIV Tat. They found multiple small molecule inhibitors of the HIV-1 Tat—TAR system that recognized the bulge, lower stem, or loop region of the TAR RNA. One of the compounds discovered, 2,4,5,6-tetraaminoquinozaline, binds to the loop region of TAR, downregulates cellular Tat transactivation, and ultimately inhibits HIV-1 replication.
The use of aminoglycosides, while an early start to RNA-targeting, came with some challenges. These molecules were only modestly selective and showed unfavorable toxicity levels at relevant therapeutic concentrations. As another strategy for targeting RNA, antisense oligonucleotides were developed which have been pushed forward through the clinic for several diseases. By this principle, if one can identify an RNA involved in disease then the sequence can be used to design a complementary antisense oligonucleotide, and that agent can be introduced into cells to treat the disease. But, this approach in its basic form has been met with several challenges. The most obvious are their large size and propensity to degradation by nucleases. In order for cellular RNA to be effective it must enter the cells intact. While backbone modifications to antisense oligonucleotides in order to prevent nuclease degradation have been shown to work, this approach is still somewhat limited. Small molecules may present a better way to target RNA and subsequently DNA because they can be designed to be more "drug-like" and have a better chance of reaching their target, most by oral administration. For this reason, there is an emerging interest in designing and discovering small molecules to target RNA secondary and tertiary structures to ultimately treat new diseases. | 1 | Biochemistry |
REST/NRSF in conjunction with RE1/NRSE also acts outside the nervous system as regulators and repressors. Current research has linked RE1/NRSE activity with the regulation of the expression of the atrial natriuretic peptide (ANP) gene. An NRSE regulatory region is present in the 3’ untranslated region of the ANP gene and acts as a mediator for its appropriate expression. The protein encoded by the ANP gene is important during embryonic development for the maturation and development of cardiac myocytes. However, during early childhood and throughout adulthood, ANP expression is suppressed or kept to a minimum in the ventricle. Thus, an abnormal induction of the ANP gene can lead to ventricular hypertrophy and severe cardiac consequences. In order to maintain the repression of the gene, NRSF (neuron-restrictive silencer factor) or REST binds to the NRSE region in the 3’untranslated region of the ANP gene. Furthermore, the NRSF-NRSE complex recruits a transcriptional corepressor known as mSin3. This leads to the activity of histone deacetylase in the region and the repression of the gene. Therefore, studies have revealed the correlation between REST/NRSF and RE1/NRSE in regulating the ANP gene expression in ventricular myocytes. A mutation in either the NRSF or NRSE can lead to an undesirable development of ventricular myocytes, due to lack of repression, which can then cause ventricular hypertrophy. Left ventricular hypertrophy, for example, increases an individuals chance of sudden death due to a ventricular arrhythmia resulting from the increased ventricular mass. In addition to the influence on the ANP' gene, the NRSE sequence regulates other cardiac embryonic genes, such as brain natriuretic peptide BNP, skeletal α-actin, and Na, K – ATPase α3 subunit. Hence, the regulatory activity of both NRSE and NRSF in mammals prevents not only neural dysfunctions but also physiological and phenotypical abnormalities in other non-neuronal regions of the body. | 1 | Biochemistry |
* Neighborhood: Similar genomic context in different species suggest a similar function of the proteins.
* Fusion-fission events: Proteins that are fused in some genomes are very likely to be functionally linked (as in other genomes where the genes are not fused).
* Occurrence: Proteins that have a similar function or an occurrence in the same metabolic pathway, must be expressed together and have similar phylogenetic profile.
* Coexpression: Predicted association between genes based on observed patterns of simultaneous expression of genes. | 1 | Biochemistry |
Lactic acid fermentation is used in many areas of the world to produce foods that cannot be produced through other methods. The most commercially important genus of lactic acid-fermenting bacteria is Lactobacillus, though other bacteria and even yeast are sometimes used. Two of the most common applications of lactic acid fermentation are in the production of yogurt and sauerkraut. | 1 | Biochemistry |
In a simple equilibrium between two species:
where the reaction starts with an initial concentration of reactant A, , and an initial concentration of 0 for product P at time t=0.
Then the equilibrium constant K is expressed as:
where and are the concentrations of A and P at equilibrium, respectively.
The concentration of A at time t, , is related to the concentration of P at time t, , by the equilibrium reaction equation:
The term is not present because, in this simple example, the initial concentration of P is 0.
This applies even when time t is at infinity; i.e., equilibrium has been reached:
then it follows, by the definition of K, that
and, therefore,
These equations allow us to uncouple the system of differential equations, and allow us to solve for the concentration of A alone.
The reaction equation was given previously as:
For this is simply
The derivative is negative because this is the rate of the reaction going from A to P, and therefore the concentration of A is decreasing. To simplify notation, let x be , the concentration of A at time t. Let be the concentration of A at equilibrium. Then:
Since:
the reaction rate becomes:
which results in:
A plot of the negative natural logarithm of the concentration of A in time minus the concentration at equilibrium versus time t gives a straight line with slope k + k. By measurement of [A] and [P] the values of K and the two reaction rate constants will be known. | 7 | Physical Chemistry |
In the early 1950s, Frohring received patents for Frohring Cement Mixers, a line of compact, portable mixers than can be moved out to a field and operated by hand, electric motor, gasoline motor or tractor motor. In 1953, Frohring patented a neurological research device known as a biothesiometer, used to determine a patient's sensitivity to vibration. Other patents include a formula for hypo-alergic milk, a process of making liquid malted milk, and a method for determining vitamin A deficiency, and a method for extracting carotene.
He was made an honorary doctor of science by McKinley-Roosevelt College in Chicago, Illinois. | 7 | Physical Chemistry |
The chloroplast gene rbcL, which codes for the large subunit of RuBisCO has been widely used as an appropriate locus for analysis of phylogenetics in plant taxonomy. | 5 | Photochemistry |
Research aimed at engineered resistance follows multiple strategies. One is to transfer useful PRRs into species that lack them. Identification of functional PRRs and their transfer to a recipient species that lacks an orthologous receptor could provide a general pathway to additional broadened PRR repertoires. For example, the Arabidopsis PRR EF-Tu receptor (EFR) recognizes the bacterial translation elongation factor EF-Tu. Research performed at Sainsbury Laboratory demonstrated that deployment of EFR into either Nicotiana benthamianaor Solanum lycopersicum (tomato), which cannot recognize EF-Tu, conferred resistance to a wide range of bacterial pathogens. EFR expression in tomato was especially effective against the widespread and devastating soil bacterium Ralstonia solanacearum. Conversely, the tomato PRR Verticillium 1 (Ve1) gene can be transferred from tomato to Arabidopsis, where it confers resistance to race 1 Verticillium isolates. | 1 | Biochemistry |
Dispersions do not display any structure; i.e., the particles (or in case of emulsions: droplets) dispersed in the liquid or solid matrix (the "dispersion medium") are assumed to be statistically distributed. Therefore, for dispersions, usually percolation theory is assumed to appropriately describe their properties.
However, percolation theory can be applied only if the system it should describe is in or close to thermodynamic equilibrium. There are only very few studies about the structure of dispersions (emulsions), although they are plentiful in type and in use all over the world in innumerable applications (see below).
In the following, only such dispersions with a dispersed phase diameter of less than 1 µm will be discussed. To understand the formation and properties of such dispersions (incl emulsions), it must be considered that the dispersed phase exhibits a "surface", which is covered ("wet") by a different "surface" that, hence, are forming an interface (chemistry). Both surfaces have to be created (which requires a huge amount of energy), and the interfacial tension (difference of surface tension) is not compensating the energy input, if at all.
Experimental evidence suggests dispersions have a structure very much different from any kind of statistical distribution (which would be characteristics for a system in thermodynamic equilibrium), but in contrast display structures similar to self-organisation, which can be described by non-equilibrium thermodynamics. This is the reason why some liquid dispersions turn to become gels or even solid at a concentration of a dispersed phase above a critical concentration (which is dependent on particle size and interfacial tension). Also, the sudden appearance of conductivity in a system of a dispersed conductive phase in an insulating matrix has been explained. | 7 | Physical Chemistry |
The starting E. coli culture volume is 15-25 mL of Lysogeny broth (LB) and the expected DNA yield is 100-350 µg. | 1 | Biochemistry |
Cyclohexane is considered a benchmark in determining ring strain in cycloalkanes and it is commonly accepted that there is little to no strain energy. In comparison, smaller cycloalkanes are much higher in energy due to increased strain. Cyclopropane is analogous to a triangle and thus has bond angles of 60°, much lower than the preferred 109.5° of an sp hybridized carbon. Furthermore, the hydrogens in cyclopropane are eclipsed. Cyclobutane experiences similar strain, with bond angles of approximately 88° (it isn't completely planar) and eclipsed hydrogens. The strain energy of cyclopropane and cyclobutane are 27.5 and 26.3 kcal mol, respectively. Cyclopentane experiences much less strain, mainly due to torsional strain from eclipsed hydrogens: its preferred conformations interconvert by a process called pseudorotation.
Ring strain can be considerably higher in bicyclic systems. For example, bicyclobutane, CH, is noted for being one of the most strained compounds that is isolatable on a large scale; its strain energy is estimated at 63.9 kcal mol (267 kJ mol). | 4 | Stereochemistry |
As highly reduced species in solution, Zintl ions offer many and often unexpected, reaction possibilities, and their discrete nature positions them as potentially important starting materials in inorganic synthesis.
In solution, individual Zintl ions can react with each other to form oligomers and polymers. In fact, anions with high nuclearity can be viewed as oxidative coupling products of monomers. After oxidation, the clusters may sometimes persist as radicals that can be used as precursors in other reactions. Zintl ions can oxidize without the presence of specific oxidizing agents through solvent molecules or impurities, for example in the presence of cryptand, which is often used to aid crystallization.
Zintl ion clusters can be functionalized with a variety of ligands in a similar reaction to their oligomerization. As such, functionalization competes with those reactions and both can be observed to occur. Organic groups, for example phenyl, TMS, and bromomethane, form exo bonds to the electronegative main group atoms. These ligands can also stabilize high nuclearity clusters, in particular heteroatomic examples.
Similarly in solids, Zintl phases can incorporate hydrogen. Such Zintl phase hydrides can be either formed by direct synthesis of the elements or element hydrides in a hydrogen atmosphere or by a hydrogenation reaction of a pristine Zintl phase. Since hydrogen has a comparable electronegativity as the post-transition metal it is incorporated as part of the polyanionic spatial structure. There are two structural motifs present. A monatomic hydride can be formed occupying an interstitial site that is coordinated by cations exclusively (interstitial hydride) or it can bind covalently to the polyanion (polyanionic hydride).
The Zintl ion itself can also act as a ligand in transition metal complexes. This reactivity is usually seen in clusters composed of greater than 9 atoms, and it is more common for group 15 clusters. A change in geometry often accompanies complexation; however zero electrons are contributed from the metal to the complex, so the electron count with respect to Wade's rules does not change. In some cases the transition metal will cap the face of the cluster. Another mode of reaction is the formation of endohedral complexes where the metal is encapsulated inside the cluster. These types of complexes lend themselves to comparison with the solid state structure of the corresponding Zintl phase. These reactions tend to be unpredictable and highly dependent on temperature, among other reaction conditions. | 7 | Physical Chemistry |
Chelation in the intestinal tract is a cause of numerous interactions between drugs and metal ions (also known as "minerals" in nutrition). As examples, antibiotic drugs of the tetracycline and quinolone families are chelators of Fe, Ca, and Mg ions.
EDTA, which binds to calcium, is used to alleviate the hypercalcemia that often results from band keratopathy. The calcium may then be removed from the cornea, allowing for some increase in clarity of vision for the patient.
Homogeneous catalysts are often chelated complexes. A representative example is the use of BINAP (a bidentate phosphine) in Noyori asymmetric hydrogenation and asymmetric isomerization. The latter has the practical use of manufacture of synthetic (–)-menthol. | 7 | Physical Chemistry |
Kineticists have historically relied on linearization of rate data to extrapolate rate constants, perhaps best demonstrated by the widespread use of the standard Lineweaver–Burk linearization of the Michaelis–Menten equation. Linearization techniques were of particular importance before the advent of computing techniques capable of fitting complex curves, and they remain a staple in kinetics due to their intuitively simple presentation. It is important to note that linearization techniques should NOT be used to extract numerical rate constants as they introduce a large degree of error relative to alternative numerical techniques. Graphical rate laws do, however, maintain that intuitive presentation of linearized data, such that visual inspection of the plot can provide mechanistic insight regarding the reaction at hand. The basis for a graphical rate law rests on the rate (v) vs. substrate concentration ([S]) plots discussed above. For example, in the simple cycle discussed with regard to different-excess experiments a plot of vs. [B] and its twin vs. [A] can provide intuitive insight about the order of each of the reagents. If plots of vs. [B] overlay for multiple experiments with different-excess, the data are consistent with a first-order dependence on [A]. The same could be said for a plot of vs. [A]; overlay is consistent with a first-order dependence on [B]. Non-overlaying results of these graphical rate laws are possible and are indicative of higher order dependence on the substrates probed. Blackmond has proposed presenting the results of different-excess experiments with a series of graphical rate equations (that she presents in a flow-chart adapted here), but it is important to note that her proposed method is only one of many possible methods to display the kinetic relationship. Furthermore, while the presentation of graphical rate laws may at times be considered a visually simplified way to present complex kinetic data, fitting the raw kinetic data for analysis by differential or other rigorous numerical methods is necessary to extract accurate and quantitative rate constants and reaction orders. | 7 | Physical Chemistry |
These effects have been supposed to exist since the time of Michael Faraday.
There have also been observations on the existence of Hall effect in electrolytes. Until these observations, magnetoelectrochemistry was an esoteric curiosity, though
this field has had a rapid development in the past years and is now an active area of research. Other scientific fields which contributed to the development of magnetoelectrochemistry are magnetohydrodynamics and convective diffusion theory. | 7 | Physical Chemistry |
Dissolved and particulate material in water can cause it to be appear more green, tan, brown, or red. For instance, dissolved organic compounds called tannins can result in dark brown colors, or algae floating in the water (particles) can impart a green color. Color variations can be measured with reference to a standard color scale. Two examples of standard color scales for natural water bodies are the Forel-Ule scale and the Platinum-Cobalt scale. For example, slight discoloration is measured against the Platinum-Cobalt scale in Hazen units (HU).
The color of a water sample can be reported as:
* Apparent color is the color of a body of water being reflected from the surface of the water, and consists of color from both dissolved and suspended components. Apparent color may also be changed by variations in sky color or the reflection of nearby vegetation.
* True color is measured after a sample of water has been collected and purified (either by centrifuging or filtration). Pure water tends to look cyan in color and a sample can be compared to pure water with a predetermined color standard or comparing the results of a spectrophotometer.
Testing for color can be a quick and easy test which often reflects the amount of organic material in the water, although certain inorganic components like iron or manganese can also impart color.
Water color can reveal physical, chemical and bacteriological conditions. In drinking water, green can indicate copper leaching from copper plumbing and can also represent algae growth. Blue can also indicate copper, or might be caused by syphoning of industrial cleaners in the tank of commodes, commonly known as backflowing. Reds can be signs of rust from iron pipes or airborne bacteria from lakes, etc. Black water can indicate growth of sulfur-reducing bacteria inside a hot water tank set to too low a temperature. This usually has a strong sulfur or rotten egg (HS) odor and is easily corrected by draining the water heater and increasing the temperature to or higher. The odor will always be in the hot water pipes if sulfate reducing bacteria are the cause and never in the cold water plumbing. Learning the water impurity indication color spectrum can make identifying and solving cosmetic, bacteriological and chemical problems easier. | 3 | Analytical Chemistry |
By the time of his retirement in 1906 he had published some 65 chemical papers, most of them in the Spanish language, on such diverse topics as the chemical compositions of Argentine rivers, the medicinal plants of Córdoba Province, Argentina, the incrustation of locomotive boilers, the presence of organic matter in drinking water, the caffeine content of yerba mate, the adulteration of saffron, the wines of the Argentine Republic, compositions of meteorites fallen in Buenos Aires Province, Patagonian guano, the petroleum of Jujuy Province, a new alkaloid he isolated from Ruprechtia salicifolia, Cape Virgins gold, Tierra del Fuego platinum, well water, the cement of a failed dam, the destruction of masonry by cloacal gases, and a silver-yielding manganese ore from Mendoza Province.
According to Rapela and Depetris, Kyle was the first Argentine geochemist. Of his papers,
On a vanadiferous lignite found in the Argentine Republic with analysis of the ash was read before the British Association Edinburgh meeting in 1892. His last work, published in Ambrosetti, El bronce en la region calchaquí established that the Calchaquí Amerindians were a Bronze Age people. He died in Buenos Aires on 23 February 1922. | 9 | Geochemistry |
In 1985, the first public symposium on the Gaia hypothesis, Is The Earth a Living Organism? was held at University of Massachusetts Amherst, August 1–6. The principal sponsor was the National Audubon Society. Speakers included James Lovelock, Lynn Margulis, George Wald, Mary Catherine Bateson, Lewis Thomas, Thomas Berry, David Abram, John Todd, Donald Michael, Christopher Bird, Michael Cohen, and William Fields. Some 500 people attended. | 9 | Geochemistry |
Several variations of thermal spraying are distinguished:
*Plasma spraying
*Detonation spraying
*Wire arc spraying
*Flame spraying
*High velocity oxy-fuel coating spraying (HVOF)
*High velocity air fuel (HVAF)
*Warm spraying
*Cold spraying
*Spray and Fuse
In classical (developed between 1910 and 1920) but still widely used processes such as flame spraying and wire arc spraying, the particle velocities are generally low (< 150 m/s), and raw materials must be molten to be deposited. Plasma spraying, developed in the 1970s, uses
a high-temperature plasma jet generated by arc discharge
with typical temperatures >15,000 K, which makes it
possible to spray refractory materials such as oxides, molybdenum, etc. | 8 | Metallurgy |
One of the primary challenges in the study of planetary accretion is the fact that many tracers of the processes occurring in the early Solar System have been eliminated as a result of subsequent geologic events. Because transition metals do not show large stable isotope fractionations as a result of these events and because iron is one of the most abundant elements in the terrestrial planets, its isotopic variability has been used as a tracer of early Solar System processes.
Variations in δFe between samples from Vesta, Mars, the Moon, and Earth have been observed, and these variations cannot be explained by any known petrological, geochemical, or planetary processes, thus, it has been inferred that the observed fractionations are a result of planetary accretion. It is interesting to note that the isotopic compositions of the Earth and the Moon are much heavier than that of Vesta and Mars. This provides strong support for the giant-impact hypothesis as an impact of this energy would generate large amounts of energy, which would melt and vaporize iron, leading to the preferential escape of the lighter iron isotopes to space. More of the heavier isotopes would remain, resulting in the heavier iron isotopic compositions observed for the Earth and the Moon. The samples from Vesta and Mars exhibit minimal fractionation, consistent with the theory of runaway growth for their formations, as this process would not yield significant fractionations. Further study of the stable isotope of iron in other planetary bodies and samples could provide further evidence and more precise constraints for planetary accretion and other processes that occurred in the early Solar System. | 9 | Geochemistry |
M2DS is one of the several types of X-linked intellectual disability. The cause of M2DS is a duplication of the MECP2 or Methyl CpG binding protein 2 gene located on the X chromosome (Xq28). The MeCP2 protein plays a pivotal role in regulating brain function. Increased levels of MECP2 protein results in abnormal neural function and impaired immune system. Mutations in the MECP2 gene are also commonly associated with Rett syndrome in females. Advances in genetic testing and more widespread use of Array Comparative Genomic Hybridization has led to increased diagnosis of MECP2 duplication syndrome. It is thought to represent ~1% of X-linked male mental disability cases. Females affected by this condition often do not show symptoms. | 1 | Biochemistry |
In chemical separation processes, a mass separating agent (MSA) is a chemical species that is added to ensure that the intended separation process takes place. It is analogous to an energy separating agent, which aids separations processes via addition of energy. An MSA may be partially immiscible with one or more mixture components and frequently is the constituent of highest concentration in the added phase. Alternatively, the MSA may be miscible with a liquid feed mixture, but may selectively alter partitioning of species between liquid and vapor phases.
Disadvantages of using an MSA are a need for an additional separator to recover the MSA for recycle, a need for MSA makeup, possible MSA product contamination, and more difficult design procedures.
Processes like absorption and stripping generally utilize various MSAs. | 3 | Analytical Chemistry |
Studies have reported that: 1) the levels of CMTM5-v1 in the malignant tissues of patients with prostate cancer are lower than the levels in their nearby normal prostate gland tissues as well as in the tissues of patients with benign prostate hyperplasia; 2) patients with lower prostate cancer tissue levels of CMTM5-v1 have higher prostate cancer Gleason scores and therefore poorer prognoses than patients with higher prostate cancer tissue levels of CMTM5-v1; and 3) the forced overexpression of CMTM5-v1 in cultured DU145 cells (a human prostate cancer cell line) reduces, while the forced higher expression of the CMTM5-v1 levels increases, their proliferation and migration. Similar findings for an unspecified CMTM5 isoform are reported in ovarian cancer, hepatocellular carcinoma, pancreatic cancer, non-small-cell lung carcinoma, renal cell carcinoma, and breast cancer. The forced over expression of CMTM5-v1 in Huh7 human hepatic cells also inhibited the ability of these cells to grow in a mouse model of cancer. Finally, various cancer human cell lines including those of the liver, breast, prostate, colon, stomach, nasopharynx, laryngopharynx, esophagus, lung, and cervix express low levels of, or no, CMTM5-v1 and concurrently have highly methylated CpG sites near to the CMTM5 gene. These findings suggest that the CMTM5 gene may act as a tumor suppressor gene, i.e. a normal gene whose product(s) inhibit the development and/or progression of various cancers. The findings also support further studies to confirm and expand these relationships and determine if the expression of CMTM5 isoforms can be used as tumor markers for these cancers severities/prognoses and/or targets as for treating them. | 1 | Biochemistry |
Suppose is very large compared to the diffusion process, so A and B react immediately. This is the classic diffusion limited reaction, and the corresponding diffusion limited rate constant, can be obtained from 8 as . 8 can then be re-written as the "diffusion influenced rate constant" as | 7 | Physical Chemistry |
In 2018, Bio-Rad Laboratories filed a lawsuit against 10x Genomics stating that their linked-read technology infringed on three patents which had been licensed from Bio-Rad at the University of Chicago. Bio-Rad was awarded a sum of $23,930,716 by a jury. The 10x Genomics filed a motion for judgement as a matter of law (JMOL) but were denied in 2019, and the court proceedings concluded in 2020. Following this lawsuit, 10x Genomics discontinued their linked-read assay. An exception was made for linked-read products which had already been sold by the company prior to the lawsuit, allowing 10x Genomics to continue to provide those researchers with services such as support and warranty maintenance for this technology. | 1 | Biochemistry |
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (−OH) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule.
Phenols are both synthesized industrially and produced by plants and microorganisms. | 0 | Organic Chemistry |
A non-competitive antagonist is a type of insurmountable antagonist that may act in one of two ways: by binding to an allosteric site of the receptor, or by irreversibly binding to the active site of the receptor. The former meaning has been standardised by the IUPHAR, and is equivalent to the antagonist being called an allosteric antagonist. While the mechanism of antagonism is different in both of these phenomena, they are both called "non-competitive" because the end-results of each are functionally very similar. Unlike competitive antagonists, which affect the amount of agonist necessary to achieve a maximal response but do not affect the magnitude of that maximal response, non-competitive antagonists reduce the magnitude of the maximum response that can be attained by any amount of agonist. This property earns them the name "non-competitive" because their effects cannot be negated, no matter how much agonist is present. In functional assays of non-competitive antagonists, depression of the maximal response of agonist dose-response curves, and in some cases, rightward shifts, is produced. The rightward shift will occur as a result of a receptor reserve (also known as spare receptors) and inhibition of the agonist response will only occur when this reserve is depleted.
An antagonist that binds to the active site of a receptor is said to be "non-competitive" if the bond between the active site and the antagonist is irreversible or nearly so. This usage of the term "non-competitive" may not be ideal, however, since the term "irreversible competitive antagonism" may also be used to describe the same phenomenon without the potential for confusion with the second meaning of "non-competitive antagonism" discussed below.
The second form of "non-competitive antagonists" act at an allosteric site. These antagonists bind to a distinctly separate binding site from the agonist, exerting their action to that receptor via the other binding site. They do not compete with agonists for binding at the active site. The bound antagonists may prevent conformational changes in the receptor required for receptor activation after the agonist binds. Cyclothiazide has been shown to act as a reversible non-competitive antagonist of mGluR1 receptor. Another example of a non-competitive is phenoxybenzamine which binds irreversibly (with covalent bonds) to alpha-adrenergic receptors, which in turn reduces the fraction of available receptors and reduces the maximal effect that can be produced by the agonist. | 1 | Biochemistry |
The nutritional value of sea salt and table salt are about the same as they are both primarily sodium chloride. Table salt is more processed than sea salt to eliminate minerals and usually contains an additive such as silicon dioxide to prevent clumping.
Iodine, an element essential for human health, is present only in small amounts in sea salt. Iodised salt is table salt mixed with a minute amount of various salts of the element iodine.
Studies have found some microplastic contamination in sea salt from the US, Europe and China. Sea salt has also been shown to be contaminated by fungi that can cause food spoilage as well as some that may be mycotoxigenic.
In traditional Korean cuisine, jugyeom (, 竹鹽), which means "bamboo salt", is prepared by roasting salt at temperatures between 800 and 2000 °C in a bamboo container plugged with mud at both ends. This product absorbs minerals from the bamboo and the mud, and is claimed to increase the anticlastogenic and antimutagenic properties of the fermented soybean paste known in Korea as doenjang. However, these claims are not substantiated by high-quality studies. | 9 | Geochemistry |
Dry DNPH is friction and shock sensitive. For this reason, it’s supplied damp or ‘wetted’ when a school purchases it from a chemical supplier. If DNPH is stored improperly and left to dry out, it can become explosive.
It is an artificial uncoupler of the electron transport chain (ETC). | 0 | Organic Chemistry |
The rAAV genome is built of single-stranded deoxyribonucleic acid (ssDNA), either positive- or negative-sensed, which is about 4.7 kilobases long. These single-stranded DNA viral vectors have high transduction rates and have a unique property of stimulating endogenous HR without causing double strand DNA breaks in the genome, which is typical of other homing endonuclease mediated genome editing methods. | 1 | Biochemistry |
Photocathodes operate in a vacuum, so their design parallels vacuum tube technology. Since
most cathodes are sensitive to air the construction of photocathodes typically occurs after the enclosure has been evacuated. In operation the photocathode requires an electric field with a nearby positive anode to assure electron emission. Molecular beam epitaxy is broadly applied in todays manufacturing of photocathode. By using a substrate with matched lattice parameters, crystalline photocathodes can be made and electron beams can come out from the same position in lattices Brillouin zone to get high brightness electron beams.
Photocathodes divide into two broad groups; transmission and reflective. A transmission type is typically a coating upon a glass window in which the light strikes one surface and electrons exit from the opposite surface. A reflective type is typically formed on an opaque metal electrode base, where the light enters and the electrons exit from the same side. A variation is the double reflection type, where the metal base is mirror-like, causing light that passed through the photocathode without causing emission to be bounced back for a second try. This mimics the retina on many mammals.
The effectiveness of a photocathode is commonly expressed as quantum efficiency, that being the ratio of emitted electrons vs. impinging quanta (of light). The efficiency varies with construction as well, as it can be improved with a stronger electric field. | 7 | Physical Chemistry |
Polymorphic and polyamorphic substances have multiple crystal or amorphous phases, which can be graphed in a similar fashion to solid, liquid, and gas phases. | 7 | Physical Chemistry |
There are several COF single crystals synthesized to date. There are a variety of techniques employed to improve crystallinity of COFs. The use of modulators, monofunctional version of precursors, serve to slow the COF formation to allow for more favorable balance between kinetic and thermodynamic control, hereby enabling crystalline growth. This was employed by Yaghi and coworkers for 3D imine-based COFs (COF-300, COF 303, LZU-79, and LZU-111). However, the vast majority of COFs are not able to crystallize into single crystals but instead are insoluble powders. The improvement of crystallinity of these polycrystalline materials can be improved through tuning the reversibility of the linkage formation to allow for corrective particle growth and self-healing of defects that arise during COF formation. | 6 | Supramolecular Chemistry |
7-Chlorokynurenic acid (7-CKA) is a tool compound that acts as a potent and selective competitive antagonist of the glycine site of the NMDA receptor. It produces ketamine-like rapid antidepressant effects in animal models of depression. However, 7-CKA is unable to cross the blood-brain-barrier, and for this reason, is unsuitable for clinical use. As a result, a centrally-penetrant prodrug of 7-CKA, 4-chlorokynurenine (AV-101), has been developed for use in humans, and is being studied in clinical trials as a potential treatment for major depressive disorder, and anti-nociception. In addition to antagonizing the NMDA receptor, 7-CKA also acts as a potent inhibitor of the reuptake of glutamate into synaptic vesicles (or as a vesicular glutamate reuptake inhibitor), an action that it mediates via competitive blockade of vesicular glutamate transporters (K = 0.59 mM). | 1 | Biochemistry |
Since gases fill the entirety of the container which they occupy, the volumetric thermal expansion coefficient at constant pressure, , is the only one of interest.
For an ideal gas, a formula can be readily obtained by differentiation of the ideal gas law, . This yields
where is the pressure, is the molar volume (, with the total number of moles of gas), is the absolute temperature and is equal to the gas constant.
For an isobaric thermal expansion, , so that and the isobaric thermal expansion coefficient is:
which is a strong function of temperature; doubling the temperature will halve the thermal expansion coefficient. | 7 | Physical Chemistry |
Post-translational modification of histones either by acetylation or crotonylation is important for the active transcription of genes. Histone crotonylation is regulated by the concentration of crotonyl-coA which can change based on environmental cell conditions or genetic factors. | 1 | Biochemistry |
Ketone bodies can be used as fuels, yielding 22 ATP and 2 GTP molecules per acetoacetate molecule when oxidized in the mitochondria. Ketone bodies are transported from the liver to other tissues, where acetoacetate and beta-hydroxybutyrate can be reconverted to acetyl-CoA to produce reducing equivalents (NADH and FADH), via the citric acid cycle. Ketone bodies cannot be used as fuel by the liver, because the liver lacks the enzyme β-ketoacyl-CoA transferase, also called thiolase. Acetoacetate in low concentrations is taken up by the liver and undergoes detoxification through the methylglyoxal pathway which ends with lactate. Acetoacetate in high concentrations is absorbed by cells other than those in the liver and enters a different pathway via 1,2-propanediol. Though the pathway follows a different series of steps requiring ATP, 1,2-propanediol can be turned into pyruvate. | 1 | Biochemistry |
Many enzymes including serine protease, cysteine protease, protein kinase and phosphatase evolved to form transient covalent bonds between them and their substrates to lower the activation energy and allow the reaction to occur. This process can be divided into 2 steps: formation and breakdown. The former step is rate-limit step while the later step is needed to regenerate intact enzyme.
Nucleophilic catalysis: This process involves the donation of electrons from the enzymes nucleophile to a substrate to form a covalent bond between them during the transition state. The strength of this interaction depends on two aspects.: the ability of the nucleophilic group to donate electrons and the electrophile to accept them. The former one is mainly affected by the basicity(the ability to donate electron pairs) of the species while the later one is in regard to its pK'. Both groups are also affected by their chemical properties such as polarizability, electronegativity and ionization potential. Amino acids that can form nucleophile including serine, cysteine, aspartate and glutamine.
Electrophilic catalysis: The mechanism behind this process is exactly same as nucleophilic catalysis except that now amino acids in active site act as electrophile while substrates are nucleophiles. This reaction usually requires cofactors as the amino acid side chains are not strong enough in attracting electrons. | 1 | Biochemistry |
The value of fish caught from US commercial fisheries in 2007 was valued at $3.8 billion and of that 73% was derived from calcifiers and their direct predators. Other organisms are directly harmed as a result of acidification. For example, decrease in the growth of marine calcifiers such as the American lobster, ocean quahog, and scallops means there is less shellfish meat available for sale and consumption. Red king crab fisheries are also at a serious threat because crabs are also calcifiers. Baby red king crab when exposed to increased acidification levels experienced 100% mortality after 95 days. In 2006, red king crab accounted for 23% of the total guideline harvest levels and a serious decline in red crab population would threaten the crab harvesting industry. | 9 | Geochemistry |
The compound has been prepared in a multistep process starting with the base hydrolysis of phosphorus pentasulfide:
:PS + 6 NaOH → 2 NaPOS + HS + 2 HO
The salt is isolated as the hydrate NaPOS(HO). It is prone to hydrolysis, especially when it is heated as an aqueous solutions:
:NaPOS + 2 HO → NaPOS + HS
Its structure has been examined by X-ray crystallography. | 8 | Metallurgy |
LISICONs can be used as the solid electrolyte in lithium-based solid-state batteries, such as solid state nickel–lithium battery. For this application, solid lithium electrolytes require ionic conductivities greater than 10 S/cm, negligible electronic conductivity, and a wide range of electrochemcial stability. | 7 | Physical Chemistry |
Ceruloplasmin (or caeruloplasmin) is a ferroxidase enzyme that in humans is encoded by the CP gene.
Ceruloplasmin is the major copper-carrying protein in the blood, and in addition plays a role in iron metabolism. It was first described in 1948. Another protein, hephaestin, is noted for its homology to ceruloplasmin, and also participates in iron and probably copper metabolism. | 1 | Biochemistry |
The molar ionic conductivity of each ionic species is proportional to its electrical mobility (μ), or drift velocity per unit electric field, according to the equation
where z is the ionic charge, and F is the Faraday constant.
The limiting molar conductivity of a weak electrolyte cannot be determined reliably by extrapolation. Instead it can be expressed as a sum of ionic contributions, which can be evaluated from the limiting molar conductivities of strong electrolytes containing the same ions. For aqueous acetic acid as an example,
Values for each ion may be determined using measured ion transport numbers. For the cation:
and for the anion:
Most monovalent ions in water have limiting molar ionic conductivities in the range of . For example:
The order of the values for alkali metals is surprising, since it shows that the smallest cation Li moves more slowly in a given electric field than Na, which in turn moves more slowly than K. This occurs because of the effect of solvation of water molecules: the smaller Li binds most strongly to about four water molecules so that the moving cation species is effectively . The solvation is weaker for Na and still weaker for K. The increase in halogen ion mobility from F to Cl to Br is also due to decreasing solvation.
Exceptionally high values are found for H () and OH (), which are explained by the Grotthuss proton-hopping mechanism for the movement of these ions. The H also has a larger conductivity than other ions in alcohols, which have a hydroxyl group, but behaves more normally in other solvents, including liquid ammonia and nitrobenzene.
For multivalent ions, it is usual to consider the conductivity divided by the equivalent ion concentration in terms of equivalents per litre, where 1 equivalent is the quantity of ions that have the same amount of electric charge as 1 mol of a monovalent ion: mol Ca, mol , mol Al, mol , etc. This quotient can be called the equivalent conductivity, although IUPAC has recommended that use of this term be discontinued and the term molar conductivity be used for the values of conductivity divided by equivalent concentration. If this convention is used, then the values are in the same range as monovalent ions, e.g. for Ca and for .
From the ionic molar conductivities of cations and anions, effective ionic radii can be calculated using the concept of Stokes radius. The values obtained for an ionic radius in solution calculated this way can be quite different from the ionic radius for the same ion in crystals, due to the effect of hydration in solution. | 7 | Physical Chemistry |
Sir John Warcup Cornforth Jr., (7 September 1917 – 8 December 2013) was an AustralianBritish chemist who won the Nobel Prize in Chemistry in 1975 for his work on the stereochemistry of enzyme-catalysed reactions, becoming the only Nobel laureate born in New South Wales.
Cornforth investigated enzymes that catalyse changes in organic compounds, the substrates, by taking the place of hydrogen atoms in a substrate's chains and rings. In his syntheses and descriptions of the structure of various terpenes, olefins, and steroids, Cornforth determined specifically which cluster of hydrogen atoms in a substrate were replaced by an enzyme to effect a given change in the substrate, allowing him to detail the biosynthesis of cholesterol. For this work, he won a share of the Nobel Prize in Chemistry in 1975, alongside co-recipient Vladimir Prelog, and was knighted in 1977. | 0 | Organic Chemistry |
Silverquant is a labeling and detection method for DNA microarrays or protein microarrays. A synonym is <colorimetric> detection.
In contrast to the classical signal detection on microarrays by using fluorescence, the colorimetric detection is more sensitive and ozone-stable. | 1 | Biochemistry |
In the area of metal cluster chemistry, a butterfly cluster compound usually describes tetrametallic clusters containing five M-M bonds. A prototype of this motif is [Re(CO)]. Most butterfly clusters have additional bridging ligands. One example is the pentaphosphide Rh(CO)(PPh) where all Rh---Rh edges are bridged by PPh. A carbide-containing butterfly cluster is [FeC(CO)] where the carbide is bonded to all four Fe centers.
Bonding in such clusters is often discussed in the context of polyhedral skeletal electron pair theory. This theory predicts that tetrametallic clusters with 60 valence electrons will adopt tetrahedral geometry with six M-M bonds. Tetrahedral clusters is classified as nido clusters. By addition of 2e, the 60e cluster opens one edge, as manifested in the butterfly motif. | 7 | Physical Chemistry |
Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the major progestogen in the body. Progesterone has a variety of important functions in the body. It is also a crucial metabolic intermediate in the production of other endogenous steroids, including the sex hormones and the corticosteroids, and plays an important role in brain function as a neurosteroid.
In addition to its role as a natural hormone, progesterone is also used as a medication, such as in combination with estrogen for contraception, to reduce the risk of uterine or cervical cancer, in hormone replacement therapy, and in feminizing hormone therapy. It was first prescribed in 1934. | 0 | Organic Chemistry |
Chemokines are functionally divided into two groups:
*Homeostatic: are constitutively produced in certain tissues and are responsible for basal leukocyte migration. These include: CCL14, CCL19, CCL20, CCL21, CCL25, CCL27, CXCL12 and CXCL13. This classification is not strict; for example, CCL20 can act also as pro-inflammatory chemokine.
*Inflammatory: these are formed under pathological conditions (on pro-inflammatory stimuli, such as IL-1, TNF-alpha, LPS, or viruses) and actively participate in the inflammatory response attracting immune cells to the site of inflammation. Examples are: CXCL-8, CCL2, CCL3, CCL4, CCL5, CCL11, CXCL10. | 1 | Biochemistry |
A radiocarbon dating study in 2018 found that after the 30-meter isobath, only around 10% of the methane in surface waters can be attributed to ancient permafrost or methane hydrates. The authors suggested that even a significantly accelerated methane release would still largely fail to reach the atmosphere. | 6 | Supramolecular Chemistry |
Many lichens reproduce asexually, either by a piece breaking off and growing on its own (vegetative reproduction) or through the dispersal of diaspores containing a few algal cells surrounded by fungal cells. Because of the relative lack of differentiation in the thallus, the line between diaspore formation and vegetative reproduction is often blurred. Fruticose lichens can fragment, and new lichens can grow from the fragment (vegetative reproduction). Many lichens break up into fragments when they dry, dispersing themselves by wind action, to resume growth when moisture returns. Soredia (singular: "soredium") are small groups of algal cells surrounded by fungal filaments that form in structures called soralia, from which the soredia can be dispersed by wind. Isidia (singular: "isidium") are branched, spiny, elongated, outgrowths from the thallus that break off for mechanical dispersal. Lichen propagules (diaspores) typically contain cells from both partners, although the fungal components of so-called "fringe species" rely instead on algal cells dispersed by the "core species". | 2 | Environmental Chemistry |
Sulfur is present in the environment in solids, gases, and aqueous species. Sulfur-containing solids on Earth include the common minerals pyrite (FeS), galena (PbS), and gypsum (CaSO•2HO). Sulfur is also an important component of biological material, including in the essential amino acids cysteine and methionine, the B vitamins thiamine and biotin, and the ubiquitous substrate coenzyme A. In the ocean and other natural waters, sulfur is abundant as dissolved sulfate. Hydrogen sulfide is also present in some parts of the deep ocean where it is released from hydrothermal vents. Both sulfate and sulfide can be used by specialized microbes to obtain energy or to grow. Gases including sulfur dioxide and carbonyl sulfide make up the atmospheric component of the sulfur cycle. Any process that transports or chemically transforms sulfur between these many natural materials also has the potential to fractionate sulfur isotopes. | 9 | Geochemistry |
Dialysis is useful for many of the same desalting and buffer exchange applications performed with gel filtration chromatography, as both methods are based on similar molecular weight cut-off limits. Gel filtration has the advantage of speed (a few minutes vs. hours for dialysis) along with the ability to remove contaminants from relatively small-volume samples compared to dialysis which is an important feature when working with toxic or radioactive substances. Dialysis, on the other hand, is much less dependent on sample size as related to device format. For dialysis applications, achieving a high percentage sample recovery and molecule removal is generally straight forward with little optimization. For gel filtration applications it is important to select a column size and format that is suitable for your sample. | 3 | Analytical Chemistry |
The topographic image of a uniform crystal with a perfectly regular lattice, illuminated by a homogeneous beam, is uniform (no contrast). Contrast arises when distortions of the lattice (defects, tilted crystallites, strain) occur; when the crystal is composed of several different materials or phases; or when the thickness of the crystal changes across the image domain. | 3 | Analytical Chemistry |
Charles B. Harris was born in New York City and spent most of his youth in Grosse Pointe. He attended the University of Michigan and received his bachelor's degree in 1963. In 1966 he received his Ph.D. in chemistry at the Massachusetts Institute of Technology under F. Albert Cotton. The following year, Harris went to the University of California, Berkeley, where he became a professor in the chemistry department. He headed this department from 2003 and was dean of the faculty from 2004 to 2007. In 2015 he retired. His research focus was in the field of ultrafast dynamics and electron dynamics as well as the dynamics of chemical reactions in liquids.
He educated multiple generations of scientists in chemical dynamics and ultrafast science who have since become leaders in the field including, as Ph.D. students, Paul Alivisatos, Michael D. Fayer, Roseanne Sension, Nien-hui Ge, Kelly Gaffney and as postdocs, Ahmed Zewail and Alan Campion. | 7 | Physical Chemistry |
Work is progressing on bypassing the conventional route of atomising wrought feedstock or sponge and the inherent cost associated with the traditional Kroll process. Several of these processes, such as the FFC, MER Corporation, OS, Ginatta and BHP Billiton processes rely on the electrolytic reduction of TiO (a cheap and abundant material) to form Ti metal. So far, no material from these processes has been sold commercially on the open market, and cost models have yet to be published, but they offer the possibility of inexpensive titanium powder in the near future. The countries that have such facilities to generate Titanium Sponge are Saudi Arabia, China, Japan, Russia, Kazakhstan, the USA, Ukraine and India. The Titanium Sponge Plant in India is the only one in the world that can undertake all the different activities of manufacturing aerospace grade titanium sponge under one roof. | 8 | Metallurgy |
Organophosphines are organophosphorus compounds with the formula PRH, where R is an organic substituent. These compounds can be classified according to the value of n: primary phosphines (n = 1), secondary phosphines (n = 2), tertiary phosphines (n = 3). All adopt pyramidal structures. Organophosphines are generally colorless, lipophilic liquids or solids. The parent of the organophosphines is phosphine (PH). | 0 | Organic Chemistry |
In gases, the scintillation process is due to the de-excitation of single atoms excited by the passage of an incoming particle (a very rapid process: ≈1 ns). | 5 | Photochemistry |
In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate () and tetrasodium pyrophosphate (), among others. Often pyrophosphates are called diphosphates. The parent pyrophosphates are derived from partial or complete neutralization of pyrophosphoric acid. The pyrophosphate bond is also sometimes referred to as a phosphoanhydride bond, a naming convention which emphasizes the loss of water that occurs when two phosphates form a new bond, and which mirrors the nomenclature for anhydrides of carboxylic acids. Pyrophosphates are found in ATP and other nucleotide triphosphates, which are important in biochemistry. The term pyrophosphate is also the name of esters formed by the condensation of a phosphorylated biological compound with inorganic phosphate, as for dimethylallyl pyrophosphate. This bond is also referred to as a high-energy phosphate bond. | 1 | Biochemistry |
Vitamin D is produced when the skin is exposed to UVB, whether from sunlight or an artificial source. It is needed for mineralization of bone and bone growth. Areas in which vitamin D's role is being investigated include reducing the risk of cancer, heart disease, multiple sclerosis and glucose dysregulation. Exposing arms and legs to a minimal 0.5 erythemal (mild sunburn) UVB dose is equal to consuming about 3000 IU of vitamin D3. In a study in Boston, MA, researchers found that adults who used tanning beds had "robust" levels of 25(OH)D (46 ng/mL on average), along with higher hip bone density, compared to adults who did not use them.
Obtaining vitamin D from indoor tanning has to be weighed against the risk of developing skin cancer. The indoor-tanning industry has stressed the relationship between tanning and the production of vitamin D. According to the US National Institutes of Health, some researchers have suggested that "5–30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient vitamin D synthesis and that the moderate use of commercial tanning beds that emit 2%–6% UVB radiation is also effective". Most researchers say the health risks outweigh the benefits, that the UVB doses produced by tanning beds exceed what is needed for adequate vitamin D production, and that adequate vitamin D levels can be achieved by taking supplements and eating fortified foods. | 5 | Photochemistry |
Located in the East San Francisco Bay, the neighborhood of West Oakland is home to mainly low-income African American and Latino residents who are exposed to a disproportionate amount of airborne toxins as compared to the rest of the surrounding Alameda County. West Oakland's close proximity to highways and the Port of Oakland leave residents highly exposed to pollutants caused by moving and stationary sources of diesel pollution, thus leaving them at higher risk for health complications such as asthma and even shorter life expectancy than surrounding neighborhoods averages.
High emissions of toxic chemicals and airborne particulate matter in West Oakland that cause health issues are due to diesel fuels used for transportation in the Port of Oakland and surrounding highways. Traffic and transportation-related air pollutants include carbon monoxide, nitrogen dioxide, black carbon, and diesel particulate matter. Residents are more exposed to harmful pollutants compared to other areas of the Bay Area and Oakland and therefore more at risk for harmful health effects. Compared to the State of California, West Oakland produces 90 times more diesel emission particulates per square mile per day. These pollutants have detrimental health effects such as asthma and reduced life expectancy while putting children at higher susceptibility for health complications.
Inequitable economic, residential, and environmental conditions in this low-income community of color leave residents of West Oakland with poor and inequitable health outcomes. African-American and Latino children of 10–18 years in West Oakland are more susceptible to onset lung defects such as asthma. According to Alameda County Vital Statistics, an African American child born in West Oakland is expected to live 14 fewer years than a white child born in the more wealthy Oakland Hills. Children 5 and under in west Oakland visit the emergency room for asthma three times more often than children in the county as a whole.
There are multiple efforts and strategies to spur legislation for equitable environmental conditions in low-income communities. There are many environmental justice groups and organizations in the Bay Area that encourage community participation in pursuing environmental justice. For example, data is collected by a Community-based participatory research (CBPR) and collaborated with West Oakland Environmental Indicators Project (WOEIP) in order to find effective and accurate findings to prove injustice and eventually spur reform in environmental policy. These research efforts can be used to document and communicate trends in air quality in West Oakland to policymakers. Effectiveness of efforts by these groups are multiplied by and increasing availability of environmental poverty lawyers who empower legislation in the legal system. | 2 | Environmental Chemistry |
Blum studied chemistry as an undergraduate at the University of Michigan. She participated in multiple teaching and research projects, winning outstanding American Chemical Society student chapter, the UM Alumni Leadership award, and a National Science Foundation fellowship to attend graduate school at the University of California, Berkeley, where she earned a PhD working with Robert G. Bergman. Blum published multiple first-author papers and received teaching awards throughout her tenure at the University of California, Berkeley. She completed a postdoctoral fellowship at Harvard Medical School in 2006. | 0 | Organic Chemistry |
Polychorinated biphenyls, or PCBs, are a type of chemical that was widely used in the 1960s and 1970s, and which are a contamination source of soil and water. They are fairly stable and therefore persistent in the environment. Bioremediation of PCBs is the use of microorganisms to degrade PCBs from contaminated sites, relying on multiple microorganisms' co-metabolism. Anaerobic microorganisms dechlorinate PCBs first, and other microorganisms that are capable of doing BH pathway can break down the dechlorinated PCBs to usable intermediates like acyl-CoA or carbon dioxide. If no BH pathway-capable microorganisms are present, dechlorinated PCBs can be mineralized with help of fungi and plants. However, there are multiple limiting factors for this co-metabolism. | 1 | Biochemistry |
Thiolated polymers designated thiomers are functional polymers used in biotechnology product development with the intention to prolong mucosal drug residence time and to enhance absorption of drugs. The name thiomer was coined by Andreas Bernkop-Schnürch in 2000. Thiomers have thiol bearing side chains. Sulfhydryl ligands of low molecular mass are covalently bound to a polymeric backbone consisting of mainly biodegradable polymers, such as chitosan, hyaluronic acid, cellulose derivatives, pullulan, starch, gelatin, polyacrylates, cyclodextrins, or silicones.
Thiomers exhibit properties potentially useful for non-invasive drug delivery via oral, ocular, nasal, vesical, buccal and vaginal routes. Thiomers show also potential in the field of tissue engineering and regenerative medicine. Various thiomers such as thiolated chitosan and thiolated hyaluronic acid are commercialy available as scaffold materials. Thiomers can be directly compressed to tablets or given as solutions. In 2012, a second generation of thiomers – called "preactivated" or "S-protected" thiomers – were introduced.
In contrast to thiomers of the first generation, preactivated thiomers are stable towards oxidation and display comparatively higher mucoadhesive and permeation enhancing properties. Approved thiomer products for human use are for example eyedrops for treatment of dry eye syndrome or adhesive gels for treatment of nickel allergy. | 7 | Physical Chemistry |
Once the DNA is positioned optimally in the concentration gel the SCODA rotating fields are applied. The frequency of the fields can be tuned such that only specific DNA lengths are concentrated. To prevent boiling during the concentration stage due to Joule heating the separation medium may be actively cooled. It is also possible to reverse the phase of SCODA fields, so that molecules are de-focused. | 1 | Biochemistry |
The term nucleic acid is the overall name for DNA and RNA, members of a family of biopolymers, and is synonymous with polynucleotide. Nucleic acids were named for their initial discovery within the nucleus, and for the presence of phosphate groups (related to phosphoric acid). Although first discovered within the nucleus of eukaryotic cells, nucleic acids are now known to be found in all life forms including within bacteria, archaea, mitochondria, chloroplasts, and viruses (There is debate as to whether viruses are living or non-living). All living cells contain both DNA and RNA (except some cells such as mature red blood cells), while viruses contain either DNA or RNA, but usually not both.
The basic component of biological nucleic acids is the nucleotide, each of which contains a pentose sugar (ribose or deoxyribose), a phosphate group, and a nucleobase.
Nucleic acids are also generated within the laboratory, through the use of enzymes (DNA and RNA polymerases) and by solid-phase chemical synthesis. | 1 | Biochemistry |
Arabinosyl nucleosides are derivatives of the nucleosides. They contain β--arabinofuranose, in contrast to most nucleosides which contain β--ribofuranose. They are used as cytostatics or virostatics. | 0 | Organic Chemistry |
Crystal structures of the resting or ground states of AR1 (3.4 Å resolution), AR2 (1.8 Å resolution) and AR3 (1.07 and 1.3 Å) have been deposited in the Protein Data Bank. Proteins possess seven transmembrane α-helices and a two-stranded extracellular-facing β-sheet. Retinal is covalently bonded via Schiff base to a lysine residue on helix G. The conserved DLLxDGR sequence, close to the extracellular-facing N-terminus of both proteins, forms a tightly curved omega loop that has been implicated in bacterioruberin binding. The cleavage of the first 6 amino acids and the conversion of Gln7 to a pyroglutamate (PCA) residue was also observed in AR3, as previously reported for bacteriorhodopsin. | 5 | Photochemistry |
To date, the use of rAAV mediated genome engineering has been published in over 2100 peer reviewed scientific journals.
Another emerging application of rAAV based genome editing is for gene therapy in patients, due to the accuracy and lack of off-target recombination events afforded by the approach. | 1 | Biochemistry |
Polymer surfaces differ from non-polymer surfaces in that the subunits that make up the surface are covalently bonded to one another. Non-polymer surfaces can be bound by ionic bonds, metallic bonds or intermolecular forces (IMFs). In a two component system, non-polymer surfaces form when a positive net amount of energy is required to break self-interactions and form non-self-interactions. Therefore, the energy of mixing (ΔG) is positive. This amount of energy, as described by interfacial tension, varies for different combinations of materials. However, with polymer surfaces, the subunits are covalently bonded together and the bulk phase of the solid surface does not allow for surface tension to be measured directly. The intermolecular forces between the large polymer molecules are difficult to calculate and cannot be determined as easily as non-polymer surface molecular interactions. The covalently bonded subunits form a surface with differing properties as compared to non-polymer surfaces. Some examples of polymer surfaces include: polyvinyl chloride (PVC), nylon, polyethylene (PE), and polypropylene (PP). Polymer surfaces have been analyzed using a variety of techniques, including: scanning electron microscopy, scanning tunneling microscopy, and infrared spectroscopy. | 7 | Physical Chemistry |
His research has involved study of molecular and interfacial forces. His work is applicable to a wide range of industrial and fundamental science problems. In particular, he has contributed significantly to the understanding of colloidal dispersions, biological systems, and polymer engineering applications. He has studied interfacial phenomena, the physics of thin films, and fundamental questions in rheology and tribology of surfaces.
Israelachvili has developed numerous techniques for the static and dynamic measurement of material and molecular properties of vapors, liquids, and surfaces. In particular, he pioneered a sensitive interfacial force-sensing technique known as the surface forces apparatus (SFA). This instrument involves carefully approaching two surfaces (usually immersed in a solvent, such as water), and measuring the force of attraction and repulsion between them. Using piezoelectric positional movement and optical interferometry for position sensing, this instrument can resolve distances to within 0.1 nanometer, and forces at the 10 N level. This technique is similar to measuring the force of interaction between an atomic force microscope (AFM) and a sample surface, except that the specialized SFA can measure much longer-range forces and is intended for surface-surface interaction measurements (as opposed to tip-surface or molecule-surface measurements). The results of SFA experiments can be used to characterize the nature of intermolecular potentials and other molecular properties.
Israelachvili is also well known as the author of the textbook "Intermolecular and Surface Forces," published by Academic Press. This authoritative book describes the fundamental concepts and equations applicable to all intermolecular and interfacial science disciplines.
Israelachvili was also founder of SurForce, LLC. The company specializes in researching surface force interactions and producing SFA systems.[https://www.surforcellc.com/about-us/] | 6 | Supramolecular Chemistry |
AFM-IR enables nanoscale infrared spectroscopy, i.e. the ability to obtain infrared absorption spectra from nanoscale regions of a sample.
Chemical compositional mapping AFM-IR can also be used to perform chemical imaging or compositional mapping with spatial resolution down to ~10-20 nm, limited only by the radius of the AFM tip. In this case, the tuneable infrared source emits a single wavelength, corresponding to a specific molecular resonance, i.e. a specific infrared absorption band. By mapping the AFM cantilever oscillation amplitude as a function of position, it is possible to map out the distribution of specific chemical components. Compositional maps can be made at different absorption bands to reveal the distribution of difference chemical species. | 3 | Analytical Chemistry |
Tris((1-benzyl-4-triazolyl)methyl)amine (TBTA) is a tertiary amine containing the 1,2,3-triazole moiety. When used as a ligand, complexed to copper(I), it allows for quantitative, regioselective formal Huisgen 1,3-dipolar cycloadditions between alkynes and azides, in a variety of aqueous and organic solvents.
It is believed that the ligand promotes catalysis through the stabilization of the copper(I)-oxidation state, while still allowing for the catalytic cycle of the CuAAC reaction to proceed.
Single crystal X-ray diffraction of the Cu(I) complex of tris((1-benzyl-4-triazolyl)methyl)amine revealed an unusual dinuclear dication with one triazole unit bridging two metal centers, and is an effective catalyst for the click cycloaddition reaction. The structure of the complex of TBTA with Cu(II) in the crystalline state is trigonal bipyramidal and can be reduced to the active click catalyst form by sodium ascorbate, copper metal, or other reducing agents.
In the literature, it has been gaining widespread use as a biochemical tool for the tagging of proteins and enzymes. The compound is now commercially available through Sigma-Aldrich and Invitrogen. It may be prepared by the click reaction between tripropargylamine and benzyl azide: | 0 | Organic Chemistry |
Hydrazones are the basis for various analyses of ketones and aldehydes. For example, dinitrophenylhydrazine coated onto a silica sorbent is the basis of an adsorption cartridge. The hydrazones are then eluted and analyzed by high-performance liquid chromatography (HPLC) using a UV detector.
The compound carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (abbreviated as FCCP) is used to uncouple ATP synthesis and reduction of oxygen in oxidative phosphorylation in molecular biology.
Hydrazones are the basis of bioconjugation strategies. Hydrazone-based coupling methods are used in medical biotechnology to couple drugs to targeted antibodies (see ADC), e.g. antibodies against a certain type of cancer cell. The hydrazone-based bond is stable at neutral pH (in the blood), but is rapidly destroyed in the acidic environment of lysosomes of the cell. The drug is thereby released in the cell, where it exerts its function. | 0 | Organic Chemistry |
Biogeochemical cycling of elements is an essential component of lithotrophs within microbial environments. For example, in the carbon cycle, there are certain bacteria classified as photolithoautotrophs that generate organic carbon from atmospheric carbon dioxide. Certain chemolithoautotrophic bacteria can also produce organic carbon, some even in the absence of light. Similar to plants, these microbes provide a usable form of energy for organisms to consume. On the contrary, there are lithotrophs that have the ability to ferment, implying their ability to convert organic carbon into another usable form. Lithotrophs play an important role in the biological aspect of the iron cycle. These organisms can use iron as either an electron donor, Fe(II) --> Fe(III), or as an electron acceptor, Fe (III) --> Fe(II). Another example is the cycling of nitrogen. Many lithotrophic bacteria play a role in reducing inorganic nitrogen (nitrogen gas) to organic nitrogen (ammonium) in a process called nitrogen fixation. Likewise, there are many lithotrophic bacteria that also convert ammonium into nitrogen gas in a process called denitrification. Carbon and nitrogen are important nutrients, essential for metabolic processes, and can sometimes be the limiting factor that affects organismal growth and development. Thus, lithotrophs are key players in both providing and removing these important resource. | 1 | Biochemistry |
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