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The lipid tail is essential for enabling lipid membrane insertion and retention but also for giving the construct amphiphilic characteristics that enable hydrophilic surface coating (due to formation of bilipid layers). Different membrane lipids that can be used to create FSLs have different membrane physiochemical characteristics and thus can affect biological function of the FSL. Lipids in FSL Kode constructs include:
* Diacyl/diakyl e.g. DOPE
* Sterols e.g. cholesterol
* Ceramides | 1 | Biochemistry |
In nature, variations in isotopic ratios of trace metals on the order of a few tenths to several ‰ are observed within and across diverse environments spanning the geosphere, hydrosphere and biosphere. A complete understanding of all processes that fractionate trace metal isotopes is presently lacking, but in general, isotopes of trace metals are fractionated during various chemical and biological processes due to kinetic and equilibrium isotope effects. | 9 | Geochemistry |
In 2017, the FDA granted RT001 orphan drug designation in the treatment of phospholipase 2G6-associated neurodegeneration (PLAN). | 1 | Biochemistry |
Chemical substances can modulate the activity of ion channels, for example by blocking or activating them. | 1 | Biochemistry |
Nonsense mutations are changes in DNA sequence that introduce a premature stop codon, causing any resulting protein to be abnormally shortened. This often causes a loss of function in the protein, as critical parts of the amino acid chain are no longer assembled. Because of this terminology, stop codons have also been referred to as nonsense codons. | 1 | Biochemistry |
When a molecule rotates, the centrifugal force pulls the atoms apart. As a result, the moment of inertia of the molecule increases, thus decreasing the value of , when it is calculated using the expression for the rigid rotor. To account for this a centrifugal distortion correction term is added to the rotational energy levels of the diatomic molecule.
where is the centrifugal distortion constant.
Therefore, the line positions for the rotational mode change to
In consequence, the spacing between lines is not constant, as in the rigid rotor approximation, but decreases with increasing rotational quantum number.
An assumption underlying these expressions is that the molecular vibration follows simple harmonic motion. In the harmonic approximation the centrifugal constant can be derived as
where k is the vibrational force constant. The relationship between and
where is the harmonic vibration frequency, follows. If anharmonicity is to be taken into account, terms in higher powers of J should be added to the expressions for the energy levels and line positions. A striking example concerns the rotational spectrum of hydrogen fluoride which was fitted to terms up to [J(J+1)]. | 7 | Physical Chemistry |
Most analytical methods for hydrogen embrittlement involve evaluating the effects of (1) internal hydrogen from production and/or (2) external sources of hydrogen such as cathodic protection. For steels, it is important to test specimens in the lab that are at least as hard (or harder) than the final parts will be. Ideally, specimens should be made of the final material or the nearest possible representative, as fabrication can have a profound impact on resistance to hydrogen-assisted cracking.
There are numerous ASTM standards for testing for hydrogen embrittlement:
* ASTM B577 is the Standard Test Methods for Detection of Cuprous Oxide (Hydrogen Embrittlement Susceptibility) in Copper. The test focuses on hydrogen embrittlement of copper alloys, including a metallographic evaluation (method A), testing in a hydrogen charged chamber followed by metallography (method B), and method C is the same as B but includes a bend test.
* ASTM B839 is the Standard Test Method for Residual Embrittlement in Metallic Coated, Externally Threaded Articles, Fasteners, and Rod-Inclined Wedge Method.
* ASTM F519 is the Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments. There are 7 different samples designs and the two most commons tests are (1) the rapid test, the Rising step load testing (RSL) method per ASTM F1624 and (2) the sustained load test, which takes 200 hours. The sustained load test is still included in many legacy standards, but the RSL method is increasingly being adopted due to speed, repeatability, and the quantitative nature of the test. The RSL method provides an accurate ranking of the effect of hydrogen from both internal and external sources.
* ASTM F1459 is the Standard Test Method for Determination of the Susceptibility of Metallic Materials to Hydrogen Gas Embrittlement (HGE) Test. The test uses a diaphragm loaded with a differential pressure.
* ASTM G142 is the Standard Test Method for Determination of Susceptibility of Metals to Embrittlement in Hydrogen Containing Environments at High Pressure, High Temperature, or Both. The test uses a cylindrical tensile specimen tested into an enclosure pressurized with hydrogen or helium.
* ASTM F1624 is the Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique. The test uses the incremental step loading (ISL) or Rising step load testing (RSL) method for quantitatively testing for the Hydrogen Embrittlement threshold stress for the onset of Hydrogen-Induced Cracking due to platings and coatings from Internal Hydrogen Embrittlement (IHE) and Environmental Hydrogen Embrittlement (EHE). F1624 provides a rapid, quantitative measure of the effects of hydrogen both from internal sources and external sources (which is accomplished by applying a selected voltage in an electrochemical cell). The F1624 test is performed by comparing a standard fast-fracture tensile strength to the fracture strength from a Rising step load testing practice where the load is held for hour(s) at each step. In many cases it can be performed in 30 hours or less.
* ASTM F1940 is the Standard Test Method for Process Control Verification to Prevent Hydrogen Embrittlement in Plated or Coated Fasteners. While the title now explicitly includes the word fasteners, F1940 was not originally intended for these purposes. F1940 is based on the F1624 method and is similar to F519 but with different root radius and stress concentration factors. When specimens exhibit a threshold cracking of 75% of the net fracture strength, the plating bath is considered to be non-embrittling.
There are many other related standards for hydrogen embrittlement:
* NACE TM0284-2003 (NACE International) Resistance to Hydrogen-Induced Cracking
* ISO 11114-4:2005 (ISO)Test methods for selecting metallic materials resistant to hydrogen embrittlement.
* Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments | 7 | Physical Chemistry |
Cyclohexane is the most stable of the cycloalkanes, due to the stability of adapting to its chair conformer. This conformer stability allows cyclohexane to be used as a standard in lab analyses. More specifically, cyclohexane is used as a standard for pharmaceutical reference in solvent analysis of pharmaceutical compounds and raw materials. This specific standard signifies that cyclohexane is used in quality analysis of food and beverages, pharmaceutical release testing, and pharmaceutical method development; these various methods test for purity, biosafety, and bioavailability of products. The stability of the chair conformer of cyclohexane gives the cycloalkane a versatile and important application when regarding the safety and properties of pharmaceuticals. | 4 | Stereochemistry |
Different blocking agents for isocyanates have different unblocking temperatures.
* Sodium bisulfite
* Diethyl malonate =
* 3,5-Dimethylpyrazole =
* MEKO =
* Phenol =
* Caprolactam = | 0 | Organic Chemistry |
While yeasts have only a single CaM gene, plants and vertebrates contain an evolutionarily conserved form of CaM genes. The difference between plants and animals in Ca signaling is that the plants contain an extended family of the CaM in addition to the evolutionarily conserved form. Calmodulins play an essential role in plant development and adaptation to environmental stimuli.
Calcium plays a key role in the structural integrity of the cell wall and the membrane system of the cell. However, high calcium levels can be toxic to a plant's cellular energy metabolism and, hence, the Ca concentration in the cytosol is maintained at a submicromolar level by removing the cytosolic Ca to either the apoplast or the lumen of the intracellular organelles. Ca pulses created due to increased influx and efflux act as cellular signals in response to external stimuli such as hormones, light, gravity, abiotic stress factors and also interactions with pathogens. | 1 | Biochemistry |
Electron microprobe analysis is ubiquitous in the analysis of major and minor elements in melt inclusions and provide oxide concentrations used in determining parental magma types of the melt inclusions and phenocryst hosts. | 9 | Geochemistry |
Vector selection requires one to ensure the library made is representative of the entire genome. Any insert of the genome derived from a restriction enzyme should have an equal chance of being in the library compared to any other insert. Furthermore, recombinant molecules should contain large enough inserts ensuring the library size is able to be handled conveniently. This is particularly determined by the number of clones needed to have in a library. The number of clones to get a sampling of all the genes is determined by the size of the organism's genome as well as the average insert size. This is represented by the formula (also known as the Carbon and Clarke formula):
where,
is the necessary number of recombinants
is the desired probability that any fragment in the genome will occur at least once in the library created
is the fractional proportion of the genome in a single recombinant
can be further shown to be:
where,
is the insert size
is the genome size
Thus, increasing the insert size (by choice of vector) would allow for fewer clones needed to represent a genome. The proportion of the insert size versus the genome size represents the proportion of the respective genome in a single clone. Here is the equation with all parts considered: | 1 | Biochemistry |
Traditionally, SSF has been used in Asian countries to produce Koji using rice to manufacture alcoholic beverages such as Sake or Koji using soybean seeds. The latter produces sauces such as soy sauce or other foods. In Western countries, the traditional manufacturing process of many foods uses SSF. Examples include fermented bakery products such as bread or for the maturing of cheese. SSF is also widely used to prepare raw materials such as chocolate and coffee; typically cacao bean fermentation and coffee bean skin removal are SSF processes carried out under natural tropical conditions. | 1 | Biochemistry |
The first Ramachandran plot was calculated just after the first protein structure at atomic resolution was determined (myoglobin, in 1960), although the conclusions were based on small-molecule crystallography of short peptides. Now, many decades later, there are tens of thousands of high-resolution protein structures determined by X-ray crystallography and deposited in the Protein Data Bank (PDB). Many studies have taken advantage of this data to produce more detailed and accurate φ,ψ plots (e.g., Morris et al. 1992; Kleywegt & Jones 1996; Hooft et al. 1997; Hovmöller et al. 2002; Lovell et al. 2003; Anderson et al. 2005. Ting et al. 2010).
The four figures below show the datapoints from a large set of high-resolution structures and contours for favored and for allowed conformational regions for the general case (all amino acids except Gly, Pro, and pre-Pro), for Gly, and for Pro. The most common regions are labeled: α for α helix, Lα for left-handed helix, β for β-sheet, and ppII for polyproline II. Such a clustering is alternatively described in the ABEGO system, where each letter stands for α (and 3) helix, right-handed β sheets (and extended structures), left-handed helixes, left-handed sheets, and finally unplottable cis peptide bonds sometimes seen with proline; it has been used in the classification of motifs and more recently for designing proteins.
While the Ramachandran plot has been a textbook resource for explaining the structural behavior of peptide bond, an exhaustive exploration of how a peptide behaves in every region of the Ramachandran plot was only recently published (Mannige 2017).
The Molecular Biophysics Unit at Indian Institute of Science celebrated 50 years of Ramachandran Map by organizing International Conference on Biomolecular Forms and Functions from 8–11 January 2013. | 1 | Biochemistry |
The use of micelles in high performance liquid chromatography was first introduced by Armstrong and Henry in 1980. The technique is used mainly to enhance retention and selectivity of various solutes that would otherwise be inseparable or poorly resolved. Micellar liquid chromatography (MLC) has been used in a variety of applications including separation of mixtures of charged and neutral solutes, direct injection of serum and other physiological fluids, analysis of pharmaceutical compounds, separation of enantiomers, analysis of inorganic organometallics, and a host of others.
One of the main drawbacks of the technique is the reduced efficiency that is caused by the micelles. Despite the sometimes poor efficiency, MLC is a better choice than ion-exchange LC or ion-pairing LC for separation of charged molecules and mixtures of charged and neutral species. Some of the aspects which will be discussed are the theoretical aspects of MLC, the use of models in predicting retentive characteristics of MLC, the effect of micelles on efficiency and selectivity, and general applications of MLC.
Reverse phase high-performance liquid chromatography (RP-HPLC) involves a non-polar stationary phase, often a hydrocarbon chain, and a polar mobile or liquid phase. The mobile phase generally consists of an aqueous portion with an organic addition, such as methanol or acetonitrile. When a solution of analytes is injected into the system, the components begin to partition out of the mobile phase and interact with the stationary phase. Each component interacts with the stationary phase in a different manner depending upon its polarity and hydrophobicity. In reverse phase HPLC, the solute with the greatest polarity will interact less with the stationary phase and spend more time in the mobile phase. As the polarity of the components decreases, the time spent in the column increases. Thus, a separation of components is achieved based on polarity. The addition of micelles to the mobile phase introduces a third phase into which the solutes may partition. | 3 | Analytical Chemistry |
As posited in a "Thioester World", thioesters are possible precursors to life. As Christian de Duve explains:
However, due to the high free energy change of thioester's hydrolysis and correspondingly their low equilibrium constants, it is unlikely that these compounds could have accumulated abiotically to any significant extent especially in hydrothermal vent conditions. | 0 | Organic Chemistry |
In some reactions, protons and hydroxide may directly act as acid and base in term of specific acid and specific base catalysis. But more often groups in substrate and active site act as Brønsted–Lowry acid and base. This is called general acid and general base theory. The easiest way to distinguish between them is to check whether the reaction rate is determined by the concentrations of the general acid and base. If the answer is yes then the reaction is the general type. Since most enzymes have an optimum pH of 6 to 7, the amino acids in the side chain usually have a pK of 4~10. Candidate include aspartate, glutamate, histidine, cysteine. These acids and bases can stabilise the nucleophile or electrophile formed during the catalysis by providing positive and negative charges. | 1 | Biochemistry |
Tartrate-resistant acid phosphatase may be used as a biochemical marker of osteoclast function during the process of bone resorption. | 1 | Biochemistry |
Some PSM products - such as cutlery - contain a mix of PSM and plastics. These plastics prevent the PSM from degrading, making the entire product non-biodegradable. | 7 | Physical Chemistry |
Design errors arise when the desired use case was not properly accounted for, leading to a ineffective design, such as the stress state in service or potential corrosive agents in the service environment. Design errors often include dimensioning and materials selection, but it can also be the complete design. | 8 | Metallurgy |
While this emerging field of drug delivery shows excellent promise in targeting specific cells and locations within the body, understanding current challenges and drawbacks can allow researchers to optimize design, development, and delivery to improve the overall outcome of their medical treatment. | 1 | Biochemistry |
Phenethylamine (PEA) is an organic compound, natural monoamine alkaloid, and trace amine, which acts as a central nervous system stimulant in humans. In the brain, phenethylamine regulates monoamine neurotransmission by binding to trace amine-associated receptor 1 (TAAR1) and inhibiting vesicular monoamine transporter 2 (VMAT2) in monoamine neurons. To a lesser extent, it also acts as a neurotransmitter in the human central nervous system. In mammals, phenethylamine is produced from the amino acid L-phenylalanine by the enzyme aromatic L-amino acid decarboxylase via enzymatic decarboxylation. In addition to its presence in mammals, phenethylamine is found in many other organisms and foods, such as chocolate, especially after microbial fermentation.
Phenethylamine is sold as a dietary supplement for purported mood and weight loss-related therapeutic benefits; however, in orally ingested phenethylamine, a significant amount is metabolized in the small intestine by monoamine oxidase B (MAO-B) and then aldehyde dehydrogenase (ALDH), which converts it to phenylacetic acid. This means that for significant concentrations to reach the brain, the dosage must be higher than for other methods of administration. Some authors postulated its role in people's falling-in-love without substantiating it with any direct evidence.
Phenethylamines, or more properly, substituted phenethylamines, are the group of phenethylamine derivatives that contain phenethylamine as a "backbone"; in other words, this chemical class includes derivative compounds that are formed by replacing one or more hydrogen atoms in the phenethylamine core structure with substituents. The class of substituted phenethylamines includes all substituted amphetamines, and substituted methylenedioxyphenethylamines (MDxx), and contains many drugs which act as empathogens, stimulants, psychedelics, anorectics, bronchodilators, decongestants, and/or antidepressants, among others. | 1 | Biochemistry |
The mechanism(s) of photoinhibition are under debate, several mechanisms have been suggested. Reactive oxygen species, especially singlet oxygen, have a role in the acceptor-side, singlet oxygen and low-light mechanisms. In the manganese mechanism and the donor side mechanism, reactive oxygen species do not play a direct role. Photoinhibited PSII produces singlet oxygen, and reactive oxygen species inhibit the repair cycle of PSII by inhibiting protein synthesis in the chloroplast. | 5 | Photochemistry |
The standard established for carbon-13 work was the Pee Dee Belemnite (PDB) and was based on a Cretaceous marine fossil, Belemnitella americana, which was from the Peedee Formation in South Carolina. This material had an anomalously high C:C ratio (0.0112372), and was established as δC value of zero. Since the original PDB specimen is no longer available, its C:C ratio can be back-calculated from a widely measured carbonate standard NBS-19, which has a δC value of +1.95‰. The C:C ratio of NBS-19 was reported as . Therefore, one could calculate the C:C ratio of PDB derived from NBS-19 as . Note that this value differs from the widely used PDB C:C ratio of 0.0112372 used in isotope forensics and environmental scientists; this discrepancy was previously attributed by a wikipedia author to a sign error in the interconversion between standards, but no citation was provided. Use of the PDB standard gives most natural material a negative δC. A material with a ratio of 0.010743 for example would have a δC value of −44‰ from . The standards are used for verifying the accuracy of mass spectroscopy; as isotope studies became more common, the demand for the standard exhausted the supply. Other standards calibrated to the same ratio, including one known as VPDB (for "Vienna PDB"), have replaced the original.
The C:C ratio for VPDB, which the International Atomic Energy Agency (IAEA) defines as δC value of zero is 0.01123720. | 9 | Geochemistry |
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry of the Siberian Branch of Russian Academy of Sciences () is a research institute in Akademgorodok of Novosibirsk, Russia. It was founded in 1958. | 0 | Organic Chemistry |
Rapid advance in cancer genomics and high-throughput ChIP-chip, ChIP-Seq and Bisulfite sequencing methods are providing more insight into role of chromatin remodeling in transcriptional regulation and role in cancer. | 1 | Biochemistry |
Although NPP primarily catalyzes phosphodiester hydrolysis, the enzyme will also catalyze the hydrolysis of phosphate monoesters, though to a much smaller extent. NPP preferentially hydrolyzes phosphate diesters over monoesters by factors of 10-10, depending on the identity of the diester substrate. This ability to catalyze a reaction with a secondary substrate is known as enzyme promiscuity, and may have played a role in NPP's evolutionary history.
NPP's promiscuity enables the enzyme to share substrates with alkaline phosphatase (AP), another member of the alkaline phosphate superfamily. Alkaline phosphatase primarily hydrolyzes phosphate monoester bonds, but it shows some promiscuity towards hydrolyzing phosphate diester bonds, making it a sort of opposite to NPP. The active sites of these two enzymes show marked similarities, namely in the presence of nearly superimposable Zn bimetallo catalytic centers. In addition to the bimetallo core, AP also has an Mg ion in its active site. | 1 | Biochemistry |
In a column published in Images Magazine, Ted Ellis calls on the younger generations of black artists to recognize the hardship faced by and the effort put in by the previous generation of black artists in order to pave the way for the newer generation to be able to succeed, and to do so with far less difficulty.
He says African-American are still not within the mainstream, and despite being the most financially minded black artists yet, that the current generation still earns less than it should. Ellis further assigns partial responsibility on an academic world that he sees as not paying sufficient attention to the genre.
He believes strongly that African-Americans should value their art on their terms, looking past aesthetics, and that only thus will the genre grow and be better appreciated. | 3 | Analytical Chemistry |
PUFAs are highly prone to oxidative damage through a purely chemical, non-enzymatic chain reaction. With tight packaging of PUFAs in membranes, the oxidation of a single PUFA molecule rapidly leads to a chain reaction resulting in oxidation of hundreds to thousands of adjacent PUFA molecules. Cell and organelle membranes contain small quantities of antioxidants such as vitamin E, and enact complex mechanisms to delete and replace oxidized PUFAs to maintain normal membrane function. However, in certain disease states, the natural PUFA maintenance system is not able to cope with disease-related increased levels of oxidation or decreased levels of repair. Once a PUFA molecule has been oxidized it is irreversibly damaged and must be
removed from the membrane and excreted.
One method to reduce the rate of PUFA oxidation is to replace a portion of the dietary PUFAs with reinforced PUFAs of identical chemical structure to natural PUFA, but more resistant to oxidation. Those hydrogen atoms that are most prone to oxidation are replaced with deuterium atoms. This change has no discernible impact on the normal biochemical properties of D-PUFAs – their distribution within the human body remains unchanged, they undergo all the normal enzyme catalysed PUFA reactions, they function normally in all cell and organelle membranes, but once the levels of these D-PUFAs in various membranes reach a concentration of about 15-20%, all non-enzymatic chain oxidation stops including that of the normal, nondeuterated PUFAs. The result is the stabilization of cell membranes, even in the face of excess oxidative stress or diminished membrane repair, such as those elicited by disease states. | 7 | Physical Chemistry |
Exorphins can cause various symptoms of schizophrenia if mutation occurs at a few selected loci. Genetic mutation at one of these loci can lead to increased absorption of exorphins via receptor mediated endocytosis. Another possibility from these particular loci is that catabolization of exorphins can be disrupted thus allowing the exorphin to persist in the body. This would lead to exorphins entering the brain capillary, bypassing the blood brain barrier, and inflicting negative repercussion on the brain. This does not mean that exorphin will necessarily cause schizophrenia, as susceptibility to the disease is dependent on an individual's genetic makeup. However, by increasing the probability that exorphins enter the brain, it will also increase the chance of an individual displaying schizophrenic symptoms. | 1 | Biochemistry |
Charge-transfer interactions are also important in protein stabilization and surface interaction. In general donor-acceptor processes, one can think of excess electron density being present which can be donated to an electrophilic species. In aqueous media, these solute interactions are primarily due to pi orbital electron effects. | 1 | Biochemistry |
Hydrogel fiber is a hydrogel made into a fibrous state, where its width is significantly smaller than its length. The hydrogel's specific surface area at fibrous form is larger than that of the bulk hydrogel, and its mechanical properties also changed accordingly. As a result of these changes, hydrogel fiber has a faster matter exchange rate and can be woven into different structures.
As a water swollen network with usually low toxicity, hydrogel fiber can be used in a variety of biomedical applications such as drug carrier, optical sensor, and actuator.
But the production of hydrogel fiber can be challenging as the hydrogel is crosslinked and can not be shaped into a fibrous state after polymerization. To make hydrogel into a fibrous state, the pregel solution must be made into fibrous form and then crosslinked while maintaining this shape. | 7 | Physical Chemistry |
mTOR Complex 2 (mTORC2) is composed of MTOR, rapamycin-insensitive companion of MTOR (RICTOR), MLST8, and mammalian stress-activated protein kinase interacting protein 1 (mSIN1). mTORC2 has been shown to function as an important regulator of the actin cytoskeleton through its stimulation of F-actin stress fibers, paxillin, RhoA, Rac1, Cdc42, and protein kinase C α (PKCα). mTORC2 also phosphorylates the serine/threonine protein kinase Akt/PKB on serine residue Ser473, thus affecting metabolism and survival. Phosphorylation of Akt's serine residue Ser473 by mTORC2 stimulates Akt phosphorylation on threonine residue Thr308 by PDK1 and leads to full Akt activation. In addition, mTORC2 exhibits tyrosine protein kinase activity and phosphorylates the insulin-like growth factor 1 receptor (IGF-1R) and insulin receptor (InsR) on the tyrosine residues Tyr1131/1136 and Tyr1146/1151, respectively, leading to full activation of IGF-IR and InsR. | 1 | Biochemistry |
The definition of tetrads and pentads introduce further sophistication and precision to defining tacticity, especially when information on long-range ordering is desirable. Tacticity measurements obtained by carbon-13 NMR are typically expressed in terms of the relative abundance of various pentads within the polymer molecule, e.g. mmmm, mrrm. | 4 | Stereochemistry |
In situ thermal desorption (ISTD) is an intensive thermally enhanced environmental remediation technology that uses thermal conductive heating (TCH) elements to directly transfer heat to environmental media. The ISTD/TCH process can be applied at low (<100 °C), moderate (~100 °C) and higher (>100 °C) temperature levels to accomplish the remediation of a wide variety of contaminants, both above and below the water table. ISTD/TCH is the only major in situ thermal remediation (ISTR) technology capable of achieving subsurface target treatment temperatures above the boiling point of water and is effective at virtually any depth in almost any media. TCH works in tight soils, clay layers, and soils with wide heterogeneity in permeability or moisture content that are impacted by a broad range of volatile and semi-volatile organic contaminants. | 2 | Environmental Chemistry |
Earth absorbs some of the radiant energy received from the sun, reflects some of it as light and reflects or radiates the rest back to space as heat. A planets surface temperature depends on this balance between incoming and outgoing energy. When Earths energy balance is shifted, its surface becomes warmer or cooler, leading to a variety of changes in global climate. Radiative forcing is a metric calculated in watts per square meter, which characterizes the impact of an external change in a factor that influences climate. It is calculated as the difference in top-of-atmosphere (TOA) energy balance immediately caused by such an external change A positive forcing, such as from increased concentrations of greenhouse gases, means more energy arriving than leaving at the top-of-atmosphere, which causes additional warming, while negative forcing, like from sulfates forming in the atmosphere from sulfur dioxide, leads to cooling.
Within the lower atmosphere, greenhouse gases exchange thermal radiation with the surface and limit radiative heat flow away from it, which reduces the overall rate of upward radiative heat transfer. The increased concentration of greenhouse gases is also cooling the upper atmosphere, as it is much thinner than the lower layers, and any heat re-emitted from greenhouse gases is more likely to travel further to space than to interact with the fewer gas molecules in the upper layers. The upper atmosphere is also shrinking as the result. | 2 | Environmental Chemistry |
Transamination catalyzed by aminotransferase occurs in two stages. In the first step, the α amino group of an amino acid is transferred to the enzyme, producing the corresponding α-keto acid and the aminated enzyme. During the second stage, the amino group is transferred to the keto acid acceptor, forming the amino acid product while regenerating the enzyme. The chirality of an amino acid is determined during transamination. For the reaction to complete, aminotransferases require participation of aldehyde containing coenzyme, pyridoxal-5-phosphate (PLP), a derivative of Pyridoxine (Vitamin B). The amino group is accommodated by conversion of this coenzyme to pyridoxamine-5-phosphate (PMP). PLP is covalently attached to the enzyme via a Schiff Base linkage formed by the condensation of its aldehyde group with the ε-amino group of an enzymatic Lys residue. The Schiff base, which is conjugated to the enzyme's pyridinium ring, is the focus of the coenzyme activity.
:The product of transamination reactions depend on the availability of α-keto acids. The products usually are either alanine, aspartate or glutamate, since their corresponding alpha-keto acids are produced through metabolism of fuels. Being a major degradative aminoacid pathway, lysine, proline and threonine are the only three amino acids that do not always undergo transamination and rather use respective dehydrogenase.
:Alternative Mechanism
:A second type of transamination reaction can be described as a nucleophilic substitution of one amine or amide anion on an amine or ammonium salt. For example, the attack of a primary amine by a primary amide anion can be used to prepare secondary amines:
:RNH + RNH → RRNH + NH
:Symmetric secondary amines can be prepared using Raney nickel (2RNH → RNH + NH). And finally, quaternary ammonium salts can be dealkylated using ethanolamine:
:RN + NHCHCHOH → RN + RNHCHCHOH
:Aminonaphthalenes also undergo transaminations. | 0 | Organic Chemistry |
In terms of thermodynamics, more electron-deficient metal centers increase the likelihood of β-alkyl elimination. For example, β-alkyl elimination is more favorable than β-hydride elimination when it is bonded to electron-deficient early transition metals (Hf, Ti, Zr, Nb, etc.) with d configuration. Computational studies show a thermodynamic preference for β-Me elimination over β-H elimination in these complexes due to additional stability for the metal–alkyl species. The origin of the additional bonding interaction comes from an orbital centered on the CH weakly π-donating to the LUMO of the d of the metal center which is analogous to the hyperconjugation effect (see figure on the right), thus increasing the stability of M−CH over M−H species. Their calculations predict that a more electrophilic metal ion enhances the −CH π-donation, which consequently increases the stability of M−CH over M−H species. Conversely, a more electron-rich metal ion will favor M−H formation (for example, using the more electron-donating Cp* ligand in Cp*MX).
In terms of kinetics, steric effects of ligands could play a role in increasing the energy barrier of β-H elimination relative to β-alkyl elimination, specifically when the ligand is Cp*. A model was proposed to illustrate this effect: In both β-methyl elimination (A) and β-hydride elimination (B), the transferring group aligns perpendicular to the Cp*(centroid)−Zr−Cp*(centroid), allowing the σ or σ bond to overlap with the metal d-orbital. However, to achieve the prerequisite geometry for β-H elimination (B), the adjacent methyl group experiences a significant steric repulsion from the Cp* ligand, thereby elevating the barrier to hydride transfer. By contrast, transition state A for β-Me elimination experiences less steric interaction with the Cp* ligand. | 0 | Organic Chemistry |
As polymers get longer and their molecular weight increases, their viscosity tend to increase. Thus, the measured viscosity of polymers can provide valuable information about the average length of the polymer, the progress of reactions, and in what ways the polymer branches. | 7 | Physical Chemistry |
A number of virus genera are transmitted, both persistently and non-persistently, by soil borne zoosporic protozoa. These protozoa are not phytopathogenic themselves, but parasitic. Transmission of the virus takes place when they become associated with the plant roots. Examples include Polymyxa graminis, which has been shown to transmit plant viral diseases in cereal crops and Polymyxa betae which transmits Beet necrotic yellow vein virus. Plasmodiophorids also create wounds in the plant's root through which other viruses can enter. | 1 | Biochemistry |
The technique is closely related to using gas adsorption to measure pore sizes, but uses the Gibbs–Thomson equation rather than the Kelvin equation. They are both particular cases of the Gibbs Equations of Josiah Willard Gibbs: the Kelvin equation is the constant temperature case, and the Gibbs–Thomson equation is the constant pressure case.
This behaviour is closely related to the capillary effect and both are due to the change in bulk free energy caused by the curvature of an interfacial surface under tension.
The original equation only applies to isolated particles, but with the addition of surface interaction terms (usually expressed in terms of the contact wetting angle) can be modified to apply to liquids and their crystals in porous media. As such it has given rise to various related techniques for measuring pore size distributions. (See Thermoporometry and cryoporometry.)
The Gibbs–Thomson effect lowers both melting and freezing point, and also raises boiling point. However, simple cooling of an all-liquid sample usually leads to a state of non-equilibrium super cooling and only eventual non-equilibrium freezing. To obtain a measurement of the equilibrium freezing event, it is necessary to first cool enough to freeze a sample with excess liquid outside the pores, then warm the sample until the liquid in the pores is all melted, but the bulk material is still frozen. Then, on re-cooling the equilibrium freezing event can be measured, as the external ice will then grow into the pores.
This is in effect an "ice intrusion" measurement (cf. mercury intrusion), and as such in part may provide information on pore throat properties. The melting event can be expected to provide more accurate information on the pore body. | 7 | Physical Chemistry |
The hardenability of a ferrous alloy is measured by a Jominy test: a round metal bar of standard size (indicated in the top image) is transformed to 100% austenite through heat treatment, and is then quenched on one end with room-temperature water. The cooling rate will be highest at the end being quenched, and will decrease as distance from the end increases. Subsequent to cooling a flat surface is ground on the test piece and the hardenability is then found by measuring the hardness along the bar. The farther away from the quenched end that the hardness extends, the higher the hardenability. This information is plotted on a hardenability graph.
The Jominy end-quench test was invented by Walter E. Jominy (1893-1976) and A.L. Boegehold, metallurgists in the Research Laboratories Division of General Motors Corp., in 1937. For his pioneering work in heat treating, Jominy was recognized by the American Society for Metals (ASM) with its Albert Sauveur Achievement Award in 1944. Jominy served as president of ASM in 1951. | 8 | Metallurgy |
Plastid terminal oxidase catalyzes the oxidation of the plastoquinone pool, which exerts a variety of effects on the development and functioning of plant chloroplasts. | 5 | Photochemistry |
CKLF like MARVEL transmembrane domain-containing 1 (i.e. CMTM1), formerly termed chemokine-like factor superfamily 1 (i.e. CKLFSF1), has 23 known isoforms, the CMTM1-v1 to CMTM1-v23 proteins. Protein isoforms are variant products that are made by alternative splicing of a single gene. The gene for these isoforms, CMTM1 (formerly termed CKLFSF1), is located in band 22 on the long (i.e. "q") arm of chromosome 16. The CMTM1 gene and its 23 isoforms belong to the CKLF-like MARVEL transmembrane domain-containing family of structurally and functionally related genes and proteins. CMTM1 (isoforms not specified) proteins are weakly express in a wide range of normal tissues but are far more highly expressed in normal testes as well as the malignant cells of certain types of cancer.
Studies have reported that the levels of CMTM1 (typically the CMTM1–v17 isoform) are more highly expressed in breast, kidney, lung, ovary, liver (i.e. hepatocellular carcinoma), and salivary gland adenoid cystic carcinoma malignant tissues than the nearby normal tissues of these respective organs. According to the Human Protein Atlas, higher levels of CMTM1 expression in hepatocellular carcinoma tissues are associated with shorter survival times. Another study found that the levels of CMTM1 mRNA (which directs the production of CMTM1 protein) were higher in stomach cancer compared to nearby normal stomach tissues. And, studies of glioblastoma found no significant difference between the levels of CMTM1 in this brain tumor's tissues versus nearby normal brain tissues but higher levels of tumor tissue CMTM1 were associated with poorer prognoses. In addition, the forced overexpression of CMTM1 in cultured glioblastoma cell lines increased their proliferation and invasiveness. These findings suggest that CMTM1 proteins may act to promote the cited cancers and support further studies to determine if these proteins contribute to the development and/or progression of the cited cancers, can be used as markers of disease severity and/or prognosis, or are targets for treating these cancers.
In contrast to the findings in the cancers just cited, cell culture studies indicated that the forced overexpression of the CMTM1-v5 isoform induced apoptosis (i.e. cell death due to the activation of cell death-inducing signaling pathways) in two types of lymphoma cell lines, Jurkat cells (a human T cell leukemia cell line) and Raji cells (a human non-Hodgkins lymphoma cell line). Simple addition of CMTM1-v5 protein to cultures of Daudi or Ramos cells (both are Burkitts lymphoma cell lines) or Jurkat cells likewise caused these cells to become apoptotic. Various other cultured hematological tumor cell lines had no such response to the CMTM1-v5 protein. Finally, the injection of CMTM1-v5 into mice containing Raji cell tumors in a xenotransplantation model of cancer inhibited the spread of these tumors and prolonged the survival of the mice. These findings suggest that CMTM1-v5 protein may act to suppress certain types of lymphoma in humans and support initial studies to define the CMTM1-v5 levels in the malignant cells of humans with these lymphomas. Further studies are also needed to determine the basis for the CMTM1 proteins promoting actions in the cited cancers versus' suppressing actions in the cited lymphomas. | 1 | Biochemistry |
The essential parts of a colorimeter are:
* a light source (often an ordinary low-voltage filament lamp);
* an adjustable aperture;
* a set of colored filters;
* a cuvette to hold the working solution;
* a detector (usually a photoresistor) to measure the transmitted light;
* a meter to display the output from the detector.
In addition, there may be:
* a voltage regulator, to protect the instrument from fluctuations in mains voltage;
* a second light path, cuvette and detector. This enables comparison between the working solution and a "blank", consisting of pure solvent, to improve accuracy.
There are many commercialized colorimeters as well as open source versions with construction documentation for education and for research. | 7 | Physical Chemistry |
The great interest in the study of the two-dimensional electron gas (2DEG) has also resulted in many investigations on the properties of polarons in two dimensions. A simple model for the 2D polaron system consists of an electron confined to a plane, interacting via the Fröhlich interaction with the LO phonons of a 3D surrounding medium. The self-energy and the mass of such a 2D polaron are no longer described by the expressions valid in 3D; for weak coupling they can be approximated as:
It has been shown that simple scaling relations exist, connecting the physical properties of polarons in 2D with those in 3D. An example of such a scaling relation is:
where () and () are, respectively, the polaron and the electron-band masses in 2D (3D).
The effect of the confinement of a Fröhlich polaron is to enhance the effective polaron coupling. However, many-particle effects tend to counterbalance this effect because of screening.
Also in 2D systems cyclotron resonance is a convenient tool to study polaron effects. Although several other effects have to be taken into account (nonparabolicity of the electron bands, many-body effects, the nature of the confining potential, etc.), the polaron effect is clearly revealed in the cyclotron mass. An interesting 2D system consists of electrons on films of liquid He. In this system the electrons couple to the ripplons of the liquid He, forming "ripplopolarons". The effective coupling can be relatively large and, for some values of the parameters, self-trapping can result. The acoustic nature of the ripplon dispersion at long wavelengths is a key aspect of the trapping.
For GaAs/AlGaAs quantum wells and superlattices, the polaron effect is found to decrease the energy of the shallow donor states at low magnetic fields and leads to a resonant splitting of the energies at high magnetic fields. The energy spectra of such polaronic systems as shallow donors ("bound polarons"), e. g., the D and D centres, constitute the most complete and detailed polaron spectroscopy realised in the literature.
In GaAs/AlAs quantum wells with sufficiently high electron density, anticrossing of the cyclotron-resonance spectra has been observed near the GaAs transverse optical (TO) phonon frequency rather than near the GaAs LO-phonon frequency. This anticrossing near the TO-phonon frequency was explained in the framework of the polaron theory.
Besides optical properties, many other physical properties of polarons have been studied, including the possibility of self-trapping, polaron transport, magnetophonon resonance, etc. | 7 | Physical Chemistry |
Newer versions of crystal structure databases integrate the visualization of crystal and molecular structures. Specialized or integrative crystallographic databases may provide morphology or tensor visualization output. | 7 | Physical Chemistry |
An electron-withdrawing group (EWG) is a group or atom that has the ability to draw electron density toward itself and away from other adjacent atoms. This electron density transfer is often achieved by resonance or inductive effects. Electron-withdrawing groups have significant impacts on fundamental chemical processes such as acid-base reactions, redox potentials, and substitution reactions. | 7 | Physical Chemistry |
π-effects have an important contribution to biological systems since they provide a significant amount of binding enthalpy. Neurotransmitters produce most of their biological effect by binding to the active site of a protein receptor. Pioneering work of Dennis A. Dougherty is a proof that such kind of binding stabilization is the effect of cation-π interactions of the acetylcholine (Ach) neurotransmitter. The structure of acetylcholine esterase includes 14 highly conserved aromatic residues. The trimethyl ammonium group of Ach binds to the aromatic residue of tryptophan (Trp). The indole site provides a much more intense region of negative electrostatic potential than benzene and phenol residue of Phe and Tyr. S-Adenosyl methionine (SAM) can act as a catalyst for the transfer of methyl group from the sulfonium compound to nucleophile. The nucleophile can be any of a broad range structures including nucleic acids, proteins, sugars or C=C bond of lipids or steroids. The van der Waals contact between S-CH unit of SAM and the aromatic face of a Trp residue, in favorable alignment for catalysis assisted by cation-π interaction.
A great deal of circumstantial evidence places aromatic residues in the active site of a number of proteins that interact with cations but the presence of cation-π interaction in biological system does not rule out the conventional ion-pair interaction. In fact there is a good evidence for the existence of both type of interaction in model system. | 6 | Supramolecular Chemistry |
The earliest reported drug checking activity began in Amsterdam in November 1970 with a group from the University Hospital of Amsterdam and samples obtained through psychiatrists working with people who used drugs.
The earliest reported drug checking service is the Drug Information and Monitoring System (DIMS) in the Netherlands supported by the Ministry of Health, Welfare and Sport. Since 1992 the service has tested over 100,000 drug samples at a national network of twenty-three testing facilities. Service users receive results within a week via phone or email and the service publishes aggregated results describing what substances are in use.
European countries have led the introduction of drug checking services, with Asociación Hegoak Elkartea founded in Spain in 1994, TechnoPlus in France founded in 1995, and Modus Fiesta in Belgium in 1996. DanceSafe have operated in the USA since 1998 providing reagent testing and harm reduction advice.
More recent services include Neutravel founded in Italy in 2007, The Loop founded in the UK in 2013 and KnowYourStuffNZ in New Zealand in 2015 with Pill Testing Australia launching after a successful trial in 2018.
In 2008, the Trans-European Drug Information network (TEDI) was created, a database compiling information from different non-profit drug checking services located in different European countries.
On March 31, 2017, a coalition of drug safety organisations hosted the first-ever International Drug Checking Day to raise awareness of safer drug use. The initiative was aimed at recreational users, with a particular emphasis on the nightlife community, and aims to promote harm reduction—accepting that people will choose to take drugs, and providing them with tools to minimise the risks.
In November 2021 New Zealand became the first country to make drug checking fully legal after previously allowing this under temporary legislation. Other countries like the Netherlands allow drug checking but do not have legislation to protect the clients or testers, and the practice exists in a legal grey area in countries like the US and UK. | 3 | Analytical Chemistry |
Low-template DNA can happen when there is less than 0.1 ng() of DNA in a sample. This can lead to more stochastic effects (random events) such as allelic dropout or allelic drop-in which can alter the interpretation of a DNA profile. These stochastic effects can lead to the unequal amplification of the 2 alleles that come from a heterozygous individual. It is especially important to take low-template DNA into account when dealing with a mixture DNA sample. This is because for one (or more) of the contributors in the mixture, they are more likely to have less than the optimal amount of DNA for the PCR reaction to work properly. Therefore, stochastic thresholds are developed for DNA profile interpretation. The stochastic threshold is the minimum peak height (RFU value), seen in an electropherogram where dropout occurs. If the peak height value is above this threshold, then it is reasonable to assume that allelic dropout has not occurred. For example, if only 1 peak is seen for a particular locus in the electropherogram but its peak height is above the stochastic threshold, then we can reasonably assume that this individual is homozygous and is not missing its heterozygous partner allele that otherwise would have dropped out due to having low-template DNA. Allelic dropout can occur when there is low-template DNA because there is such little DNA to start with that at this locus the contributor to the DNA sample (or mixture) is a true heterozygote but the other allele is not amplified and so it would be lost. Allelic drop-in can also occur when there is low-template DNA because sometimes the stutter peak can be amplified. The stutter is an artifact of PCR. During the PCR reaction, DNA Polymerase will come in and add nucleotides off of the primer, but this whole process is very dynamic, meaning that the DNA Polymerase is constantly binding, popping off and then rebinding. Therefore, sometimes DNA Polymerase will rejoin at the short tandem repeat ahead of it, leading to a short tandem repeat that is 1 repeat less than the template. During PCR, if DNA Polymerase happens to bind to a locus in stutter and starts to amplify it to make lots of copies, then this stutter product will appear randomly in the electropherogram, leading to allelic drop-in. | 1 | Biochemistry |
Chiral Lewis acids (CLAs) are a type of Lewis acid catalyst. These acids affect the chirality of the substrate as they react with it. In such reactions, synthesis favors the formation of a specific enantiomer or diastereomer. The method is an enantioselective asymmetric synthesis reaction. Since they affect chirality, they produce optically active products from optically inactive or mixed starting materials. This type of preferential formation of one enantiomer or diastereomer over the other is formally known as asymmetric induction. In this kind of Lewis acid, the electron-accepting atom is typically a metal, such as indium, zinc, lithium, aluminium, titanium, or boron. The chiral-altering ligands employed for synthesizing these acids often have multiple Lewis basic sites (often a diol or a dinitrogen structure) that allow the formation of a ring structure involving the metal atom.
Achiral Lewis acids have been used for decades to promote the synthesis of racemic mixtures in myriad different reactions. Since the 1960s, chemists have used Chiral Lewis acids to induce enantioselective reactions. This is useful when the desired product is a specific enantiomer, as is common in drug synthesis. Common reaction types include Diels–Alder reactions, the ene reaction, [2+2] cycloaddition reactions, hydrocyanation of aldehydes, and most notably, Sharpless epoxidations. | 4 | Stereochemistry |
Selective Scattering : In selective Scattering scattering depends upon the wavelength of light.
Mie scattering : Mie theory can describe how electromagnetic waves interact with homogeneously spherical particles. However, a theory for homogeneous spheres will completely fail to predict polarization effects. When the size of the molecules is greater than the wavelength of light, the result is a non-uniform scattering of light.
Lambertian Scattering: This type of scattering occurs when a surface has microscopic irregularities that scatter light perfectly uniformly in all directions, causing it to appear equally bright from all viewing angles.
Subsurface Scattering: This type of scattering occurs when light scatters within a material before exiting the surface at a different point.
Isotropic crystal scattering (aka powder diffraction): This type of scattering occurs when every crystalline orientation is represented equally in a powdered sample. Powder X-ray diffraction (PXRD) operates under the assumption that the sample is randomly arranged such that each plane will be represented in the signal. | 7 | Physical Chemistry |
These adenylyl cyclases are the most familiar based on extensive study due to their important roles in human health. They are also found in some bacteria, notably Mycobacterium tuberculosis where they appear to have a key role in pathogenesis. Most AC-III's are integral membrane proteins involved in transducing extracellular signals into intracellular responses. A Nobel Prize was awarded to Earl Sutherland in 1971 for discovering the key role of AC-III in human liver, where adrenaline indirectly stimulates AC to mobilize stored energy in the "fight or flight" response. The effect of adrenaline is via a G protein signaling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell (cytoplasm). The outside signal (in this case, adrenaline) binds to a receptor, which transmits a signal to the G protein, which transmits a signal to adenylyl cyclase, which transmits a signal by converting adenosine triphosphate to cyclic adenosine monophosphate (cAMP). cAMP is known as a second messenger.
Cyclic AMP is an important molecule in eukaryotic signal transduction, a so-called second messenger. Adenylyl cyclases are often activated or inhibited by G proteins, which are coupled to membrane receptors and thus can respond to hormonal or other stimuli. Following activation of adenylyl cyclase, the resulting cAMP acts as a second messenger by interacting with and regulating other proteins such as protein kinase A and cyclic nucleotide-gated ion channels.
Photoactivated adenylyl cyclase (PAC) was discovered in Euglena gracilis and can be expressed in other organisms through genetic manipulation. Shining blue light on a cell containing PAC activates it and abruptly increases the rate of conversion of ATP to cAMP. This is a useful technique for researchers in neuroscience because it allows them to quickly increase the intracellular cAMP levels in particular neurons, and to study the effect of that increase in neural activity on the behavior of the organism. A green-light activated rhodopsin adenylyl cyclase (CaRhAC) has recently been engineered by modifying the nucleotide binding pocket of rhodopsin guanylyl cyclase. | 1 | Biochemistry |
Green leaf volatiles (GLV) are organic compounds released by plants.
Some of these chemicals function as signaling compounds between either plants of the same species, of other species, or even different lifeforms like insects.
Green leaf volatiles are involved in patterns of attack and protection between species. They have been found to increase the attractive effect of pheromones of cohabiting insect species that protect plants from attacking insect species. For example, corn plants that are being fed on by caterpillars will release GLVs that attract wasps, who then attack the caterpillars. GLVs also have antimicrobial properties that can prevent infection at the site of injury.
GLVs include C6-aldehydes [(Z)-3-hexenal, n-hexanal] and their derivatives such as (Z)-3-hexenol, (Z)-3-hexen-1-yl acetate, and the corresponding E-isomers. | 1 | Biochemistry |
Also known as reductive Friedel–Crafts reaction, the Fischer–Hafner synthesis entails treatment of metal chlorides with arenes in the presence of aluminium trichloride and aluminium metal. The method was demonstrated in the 1950s with the synthesis of bis(benzene)chromium by Walter Hafner and his advisor E. O. Fischer. The method has been extended to other metals, e.g. [Ru(CMe)]. In this reaction, the AlCl serves to remove chloride from the metal precursor, and the Al metal functions as the reductant. The Fischer-Hafner synthesis is limited to arenes lacking sensitive functional groups. | 0 | Organic Chemistry |
Physical properties of elements and compounds that provide conclusive evidence of chemical composition include odor, color, volume, density (mass per unit volume), melting point, boiling point, heat capacity, physical form and shape at room temperature (solid, liquid or gas; cubic, trigonal crystals, etc.), hardness, porosity, index of refraction and many others. This section discusses some physical properties of materials in the solid state. | 7 | Physical Chemistry |
Fas receptor has been shown to interact with:
* Caspase 8,
* Caspase 10,
* CFLAR,
* FADD,
* Fas ligand,
* PDCD6, and
* Small ubiquitin-related modifier 1. | 1 | Biochemistry |
The latest efforts in integrating nanotechnology and biological research have been successful and show much promise for the future, including in fields such as nanobiomechanics. Since nanoparticles are a potential vehicle of drug delivery, the biological responses of cells to these nanoparticles are continuously being explored to optimize their efficacy and how their design could be improved. Pyrgiotakis et al. were able to study the interaction between CeO and FeO engineered nanoparticles and cells by attaching the engineered nanoparticles to the AFM tip. Studies have taken advantage of AFM to obtain further information on the behavior of live cells in biological media. Real-time atomic force spectroscopy (or nanoscopy) and dynamic atomic force spectroscopy have been used to study live cells and membrane proteins and their dynamic behavior at high resolution, on the nanoscale. Imaging and obtaining information on the topography and the properties of the cells has also given insight into chemical processes and mechanisms that occur through cell-cell interaction and interactions with other signaling molecules (ex. ligands). Evans and Calderwood used single cell force microscopy to study cell adhesion forces, bond kinetics/dynamic bond strength and its role in chemical processes such as cell signaling.
Scheuring, Lévy, and Rigaud reviewed studies in which AFM to explore the crystal structure of membrane proteins of photosynthetic bacteria.
Alsteen et al. have used AFM-based nanoscopy to perform a real-time analysis of the interaction between live mycobacteria and antimycobacterial drugs (specifically isoniazid, ethionamide, ethambutol, and streptomycine), which serves as an example of the more in-depth analysis of pathogen-drug interactions that can be done through AFM. | 6 | Supramolecular Chemistry |
Stable cell-cell interactions are required for cell adhesion within a tissue and controlling the shape and function of cells. These stable interactions involve cell junctions which are multiprotein complexes that provide contact between neighboring cells. Cell junctions allow for the preservation and proper functioning of epithelial cell sheets. These junctions are also important in the organization of tissues where cells of one type can only adhere to cells of the same tissue rather than to a different tissue. | 1 | Biochemistry |
Many scenarios in the real world are affected by thermal degradation. One of the things affected is fingerprints. When anyone touches something, there is residue left from the fingers. If fingers are sweaty, or contain more oils, the residue contains many chemicals. De Paoli and her collogues conducted a study testing thermal degradation on certain components found in fingerprints. For heat exposure, the amino acid and urea samples started degradation at and for lactic acid, the decomposition process started around . These components are necessary for further testing, so in the forensics discipline, decomposition of fingerprints is significant. | 7 | Physical Chemistry |
The fundamental idea behind spontaneous protein adsorption is that adsorption occurs when more energy is released than gained according to Gibbs law of free energy.
This is seen in the equation:
::</big>
where:
* ∆ is net change of the parameters
* G is Gibbs free energy
* T is the temperature (SI unit: kelvin)
* S is the entropy (SI unit: joule per kelvin)
* H is the enthalpy (SI unit: joule)
In order for the protein adsorption to occur spontaneously, ∆G must be a negative number. | 1 | Biochemistry |
Förster resonance energy transfer efficiency () is the quantum yield of the energy-transfer transition, i.e. the probability of the energy-transfer event occurring per donor excitation event:
where
* is the rate of energy transfer,
* the radiative decay rate (fluorescence) of the donor,
* are non-radiative relaxation rates (e.g., internal conversion, intersystem crossing, external conversion etc.). | 7 | Physical Chemistry |
The exploration of the antiangiogenic and immunomodulatory activities of thalidomide has led to the study and creation of thalidomide analogs. Celgene has sponsored numerous clinical trials with analogues to thalidomide, such as lenalidomide, that are substantially more powerful and have fewer side effects — except for greater myelosuppression. In 2005, Celgene received FDA approval for lenalidomide (Revlimid) as the first commercially useful derivative. Revlimid is available only in a restricted distribution setting to avoid its use during pregnancy. Further studies are being conducted to find safer compounds with useful qualities. Another more potent analog, pomalidomide, is now FDA approved. Additionally, apremilast was approved by the FDA in March 2014. These thalidomide analogs can be used to treat different diseases, or used in a regimen to fight two conditions.
Interest turned to pomalidomide, a derivative of thalidomide marketed by Celgene. It is a very active anti-angiogenic agent and also acts as an immunomodulator. Pomalidomide was approved in February 2013 by the FDA as a treatment for relapsed and refractory multiple myeloma. It received a similar approval from the European Commission in August 2013, and is expected to be marketed in Europe under the brand name Imnovid. | 4 | Stereochemistry |
Much like beta-oxidation, straight-chain fatty acid synthesis occurs via the six recurring reactions shown below, until the 16-carbon palmitic acid is produced.
The diagrams presented show how fatty acids are synthesized in microorganisms and list the enzymes found in Escherichia coli. These reactions are performed by fatty acid synthase II (FASII), which in general contains multiple enzymes that act as one complex. FASII is present in prokaryotes, plants, fungi, and parasites, as well as in mitochondria.
In animals as well as some fungi such as yeast, these same reactions occur on fatty acid synthase I (FASI), a large dimeric protein that has all of the enzymatic activities required to create a fatty acid. FASI is less efficient than FASII; however, it allows for the formation of more molecules, including "medium-chain" fatty acids via early chain termination. Enzymes, acyltransferases and transacylases, incorporate fatty acids in phospholipids, triacylglycerols, etc. by transferring fatty acids between an acyl acceptor and donor. They also have the task of synthesizing bioactive lipids as well as their precursor molecules.
Once a 16:0 carbon fatty acid has been formed, it can undergo a number of modifications, resulting in desaturation and/or elongation. Elongation, starting with stearate (18:0), is performed mainly in the endoplasmic reticulum by several membrane-bound enzymes. The enzymatic steps involved in the elongation process are principally the same as those carried out by fatty acid synthesis, but the four principal successive steps of the elongation are performed by individual proteins, which may be physically associated.
Abbreviations: ACP – Acyl carrier protein, CoA – Coenzyme A, NADP – Nicotinamide adenine dinucleotide phosphate.
Note that during fatty synthesis the reducing agent is NADPH, whereas NAD is the oxidizing agent in beta-oxidation (the breakdown of fatty acids to acetyl-CoA). This difference exemplifies a general principle that NADPH is consumed during biosynthetic reactions, whereas NADH is generated in energy-yielding reactions. (Thus NADPH is also required for the synthesis of cholesterol from acetyl-CoA; while NADH is generated during glycolysis.) The source of the NADPH is two-fold. When malate is oxidatively decarboxylated by “NADP-linked malic enzyme" pyruvate, CO and NADPH are formed. NADPH is also formed by the pentose phosphate pathway which converts glucose into ribose, which can be used in synthesis of nucleotides and nucleic acids, or it can be catabolized to pyruvate. | 1 | Biochemistry |
Glucose is mainly metabolized by a very important ten-step pathway called glycolysis, the net result of which is to break down one molecule of glucose into two molecules of pyruvate. This also produces a net two molecules of ATP, the energy currency of cells, along with two reducing equivalents of converting NAD (nicotinamide adenine dinucleotide: oxidized form) to NADH (nicotinamide adenine dinucleotide: reduced form). This does not require oxygen; if no oxygen is available (or the cell cannot use oxygen), the NAD is restored by converting the pyruvate to lactate (lactic acid) (e.g. in humans) or to ethanol plus carbon dioxide (e.g. in yeast). Other monosaccharides like galactose and fructose can be converted into intermediates of the glycolytic pathway. | 1 | Biochemistry |
Using the Weed Science Society of America (WSSA) and herbicide Resistance and World Grains (HRAC) systems, herbicides are classified by mode of action. Eventually the Herbicide Resistance Action Committee (HRAC) and the Weed Science Society of America (WSSA) developed a classification system. Groups in the WSSA and the HRAC systems are designated by numbers and letters, inform users awareness of herbicide mode of action and provide more accurate recommendations for resistance management. | 2 | Environmental Chemistry |
Silicate, or silicic acid (HSiO), is an important nutrient in the ocean. Unlike the other major nutrients such as phosphate, nitrate, or ammonium, which are needed by almost all marine plankton, silicate is an essential chemical requirement for very specific biota, including diatoms, radiolaria, silicoflagellates, and siliceous sponges. These organisms extract dissolved silicate from open ocean surface waters for the buildup of their particulate silica (SiO), or opaline, skeletal structures (i.e. the biota's hard parts). Some of the most common siliceous structures observed at the cell surface of silica-secreting organisms include: spicules, scales, solid plates, granules, frustules, and other elaborate geometric forms, depending on the species considered. | 1 | Biochemistry |
1,1-Difluoroethane is a synthetic substance that is produced by the mercury-catalyzed addition of hydrogen fluoride to acetylene:
:HCCH + 2 HF → CHCHF
The intermediate in this process is vinyl fluoride (CHF), the monomeric precursor to polyvinyl fluoride. | 2 | Environmental Chemistry |
Putative genes can be identified by clustering large groups of sequences by patterns and arranging by mutual similarity or can be inferred by potential TATA boxes.
Putative genes can also be identified by recognizing differences between well-known gene clusters and gene clusters with a unique profiling.
Software tools have been developed in order to automatically identify putative genes. This is done by searching for gene families and testing the validity of uncharacterized genes by comparison to already identified genes.
Protein products can be identified and used to characterize the putative gene that codes for it. | 1 | Biochemistry |
Jostel's TSH index (JTI or TSHI) helps to determine thyrotropic function of anterior pituitary on a quantitative level. It is reduced in thyrotropic insufficiency and in certain cases of non-thyroidal illness syndrome.
It is calculated with
Additionally, a standardized form of TSH index may be calculated with | 1 | Biochemistry |
The "MAXIM" (MAterials X-ray IMaging) method is another method combining diffraction analysis with spatial resolution. It can be viewed as serial topography with additional angular resolution in the exit beam. In contrast to the Rocking Curve Imaging method, it is more appropriate for more highly disturbed (polycrystalline) materials with lower crystalline perfection. The difference on the instrumental side is that MAXIM uses an array of slits / small channels (a so-called "multi-channel plate" (MCP), the two-dimensional equivalent of a Soller slit system) as an additional X-ray optical element between sample and CCD detector. These channels transmit intensity only in specific, parallel directions, and thus guarantee a one-to-one-relation between detector pixels and points on the sample surface, which would otherwise not be given in the case of materials with high strain and/or a strong mosaicity. The spatial resolution of the method is limited by a combination of detector pixel size and channel plate periodicity, which in the ideal case are identical. The angular resolution is mostly given by the aspect ratio (length over width) of the MCP channels.
Literature: | 3 | Analytical Chemistry |
The driving force behind radical clock reactions is their ability to rearrange. Some common radical clocks are radical cyclizations, ring openings, and 1,2-migrations. Two popular rearrangements are the cyclization of 5-hexenyl and the ring-opening of cyclopropylmethyl:
5-hexenyl radical undergoes cyclization to produce a five-membered ring because this is entropically and enthalpically more favored than the six-membered ring possibility. The rate-constant for this reaction is 2.3×10 s at 298 K.
Cyclopropylmethyl radical undergoes a very rapid ring opening rearrangement that relieves the ring strain and is enthalpically favorable. The rate-constant for this reaction is 8.6×10 s at 298 K.
In order to determine absolute rate constants for radical reactions, unimolecular clock reactions need to be calibrated for each group of radicals such as primary alkyls over a range of time. Through the usage of EPR spectroscopy, the absolute rate constants for unimolecular reactions can be measured with a variety of temperatures. The Arrhenius equation can then be applied to calculate the rate constant for a specific temperature at which the radical clock reactions are conducted.
When using a radical clock to study a reaction, there is an implicit assumption that the rearrangement rate of the radical clock is the same as when the rate of that rearrangement reaction rate is determined. A theoretical study of the rearrangement reactions of cyclobutylmethyl and of 5-hexenyl in a variety of solvents found that their reaction rates were only very slightly affected by the nature of the solvent.
The rates of radical clocks can be adjusted to increase or decrease by what types of substituents are attached to the radical clock. In the figure below, the rates of the radical clocks are shown with a variety of substituents attached to the clock.
By selecting among the general classes of radical clocks and the specific substituents on them, one can be chosen with a rate-constant suitable for studying reactions having a wide range of rates. Reactions having rates ranging from 10 to 10 M s have been studied using radical clocks. | 7 | Physical Chemistry |
In chemistry, cyclopentadienyl is a radical with the formula CH.
The cyclopentadienyl anion (formally related to the cyclopentadienyl radical by one-electron reduction) is aromatic, and forms salts and coordination compounds. | 0 | Organic Chemistry |
Fenton's reagent is used as a sewage treatment agent.
Fenton's reagent can be used in different chemical procesess that supply hydroxyl ion or oxidize certain compounds:
* The first stage of Fenton’s reaction (oxidation of Fe with hydrogen peroxide) is used in Haber–Weiss reaction
* Fenton's reagent can be used in organic synthesis reactions: e.g. hydroxylation of arenes via a free radical substitution
* Conversion of benzene into phenol by using Fenton's reagent
* Oxidation of barbituric acid into alloxan.
* Coupling reactions of alkanes | 2 | Environmental Chemistry |
Sputter deposition is a method of depositing thin films by sputtering that involves eroding material from a "target" source onto a "substrate", e.g. a silicon wafer, solar cell, optical component, or many other possibilities. Resputtering, in contrast, involves re-emission of the deposited material, e.g. SiO during the deposition also by ion bombardment.
Sputtered atoms are ejected into the gas phase but are not in their thermodynamic equilibrium state, and tend to deposit on all surfaces in the vacuum chamber. A substrate (such as a wafer) placed in the chamber will be coated with a thin film. Sputtering deposition usually uses an argon plasma because argon, a noble gas, will not react with the target material. | 7 | Physical Chemistry |
Intrinsic termination is cued by signals directly encoded in the DNA and RNA. Signal appears in as a hairpin and is followed by 8 Uridines at the 3' end. This leads to a rapid dissociation of the elongation complex . Hairpin inactivates and destabilizes the TEC by weakening interactions in the RNA-DNA binding site and other sites that hold this complex together. The pausing induced by the stretch of uracils is important and provides time for hairpin formation. In absence of U-tract, hair pin formation does not result in efficient termination, indicating its importance in this process.
The elongation destabilization process occurs in four steps
# as RNA Polymerase transcribes the final nucleotides of the terminator U-tract, it pauses at end of U-tract, favoring the termination pathway in the kinetic competition between elongation and termination
# Terminator hairpin (Thp) Nucleation
# hairpin completion and elongation complex inactivation
# elongation complex dissociation A complete mechanism is likely to involve specific interactions of the polymerase, the RNA terminator hairpin, and dT-rich template sequences. | 1 | Biochemistry |
Stable and transient transfection differ in their long term effects on a cell; a stably transfected cell will continuously express transfected DNA and pass it on to daughter cells, while a transiently transfected cell will express transfected DNA for a short amount of time and not pass it on to daughter cells.
For some applications of transfection, it is sufficient if the transfected genetic material is only transiently expressed. Since the DNA introduced in the transfection process is usually not integrated into the nuclear genome, the foreign DNA will be diluted through mitosis or degraded. Cell lines expressing the Epstein–Barr virus (EBV) nuclear antigen 1 (EBNA1) or the SV40 large-T antigen allow episomal amplification of plasmids containing the viral EBV (293E) or SV40 (293T) origins of replication, greatly reducing the rate of dilution.
If it is desired that the transfected gene actually remain in the genome of the cell and its daughter cells, a stable transfection must occur. To accomplish this, a marker gene is co-transfected, which gives the cell some selectable advantage, such as resistance towards a certain toxin. Some (very few) of the transfected cells will, by chance, have integrated the foreign genetic material into their genome. If the toxin is then added to the cell culture, only those few cells with the marker gene integrated into their genomes will be able to proliferate, while other cells will die. After applying this selective stress (selection pressure) for some time, only the cells with a stable transfection remain and can be cultivated further.
Common agents for selecting stable transfection are:
* Geneticin, or G418, neutralized by the product of the neomycin resistance gene
* Puromycin
* Zeocin
* Hygromycin B
* Blasticidin S | 1 | Biochemistry |
The first case is a thick ring in an external magnetic field (Fig. 3a). The currents in a superconductor only flow in a thin layer at the surface. The thickness of this layer is determined by the so-called London penetration depth. It is of μm size or less. We consider a loop far away from the surface so that v = 0 everywhere so κ = 0. In that case the fluxoid is equal to the magnetic flux (Φ = Φ). If v = 0 Eq. () reduces to
Taking the rotation gives
Using the well-known relations and shows that the magnetic field in the bulk of the superconductor is zero as well. So, for thick rings, the total magnetic flux in the loop is quantized according to | 7 | Physical Chemistry |
Shrinkage defects
can occur when standard feed metal is not available to compensate for shrinkage as the thick metal solidifies. Shrinkage defects will have jagged or linear appearance. Shrinkage defects usually occur in either the cope or drag portion of the casting. Shrinkage defects can be split into two different types: open shrinkage defects and closed shrinkage defects. Open shrinkage defects are open to the atmosphere, therefore as the shrinkage cavity forms, air compensates. There are two types of open air defects: pipes and caved surfaces. Pipes form at the surface of the casting and burrow into the casting, while caved surfaces are shallow cavities that form across the surface of the casting.
Closed shrinkage defects, also known as shrinkage porosity, are defects that form within the casting. Isolated pools of liquid form inside solidified metal, which are called hot spots. The shrinkage defect usually forms at the top of the hot spots. They require a nucleation point, so impurities and dissolved gas can induce closed shrinkage defects. The defects are broken up into macroporosity and microporosity (or micro shrinkage), where macroporosity can be seen by the naked eye and microporosity cannot. | 8 | Metallurgy |
Supercritical carbon dioxide (SCD) can be used instead of PERC (perchloroethylene) or other undesirable solvents for dry-cleaning. Supercritical carbon dioxide sometimes intercalates into buttons, and, when the SCD is depressurized, the buttons pop, or break apart. Detergents that are soluble in carbon dioxide improve the solvating power of the solvent. CO-based dry cleaning equipment uses liquid CO, not supercritical CO, to avoid damage to the buttons. | 7 | Physical Chemistry |
Despite their potential for use as contrast agents for medical imaging techniques, their use in vivo is hindered by the cytotoxicity of cadmium. To address this issue, methods have been developed to “wrap” or “encapsulate” potentially-toxic QDs in bio-inert polymers to facilitate use in living tissue. While Cd-free QDs are commercially available, they are unsuitable for use as a substitute for organic contrasts. Another issue with CdSe(ZnS) nanoparticles is significant hydrophobicity, which hinders their ability to enter solution with aqueous media, such as blood or spinal fluid. Certain hydrophilic polymers could be used to render the dots water-soluble. | 7 | Physical Chemistry |
When H and OH ions are not involved in the reaction, the boundary line is horizontal and independent of pH. <br />The reaction equation is thus written:
As, the standard Gibbs free energy :
Using the definition of the electrode potential ∆G = -zFE, where F is the Faraday constant, this may be rewritten as a Nernst equation:
or, using base-10 logarithms:
For the equilibrium /, taken as example here, considering the boundary line between Fe and Fe, the half-reaction equation is:
Since H ions are not involved in this redox reaction, it is independent of pH.
E = 0.771 V with only one electron involved in the redox reaction.
The potential E is a function of temperature via the thermal voltage and directly depends on the ratio of the concentrations of the and ions:
For both ionic species at the same concentration (e.g., ) at STP, log 1 = 0, so, , and the boundary will be a horizontal line at E = 0.771 volts. The potential will vary with temperature. | 7 | Physical Chemistry |
During photosynthesis, natural electron acceptor NADP is reduced to NADPH in chloroplasts. The following equilibrium reaction takes place.
A reduction reaction that stores energy as NADPH:
: (Reduction)
An oxidation reaction as NADPH's energy is used elsewhere:
: (Oxidation)
Ferredoxin, also known as an NADP+ reductase, is an enzyme that catalyzes the reduction reaction. It is easy to oxidize NADPH but difficult to reduce NADP, hence a catalyst is beneficial. Cytochromes are conjugate proteins that contain a haem group. The iron atom from this group undergoes redox reactions:
: (Reduction)
: (Oxidation)
The light-dependent redox reaction takes place before the light-independent reaction in photosynthesis. | 5 | Photochemistry |
Lithium's therapeutic effects are thought to be partially attributable to its interactions with several signal transduction mechanisms. The cyclic AMP secondary messenger system is shown to be modulated by lithium. Lithium was found to increase the basal levels of cyclic AMP but impair receptor coupled stimulation of cyclic AMP production. It is hypothesized that the dual effects of lithium are due to the inhibition of G-proteins that mediate cyclic AMP production. Over a long period of lithium treatment, cyclic AMP and adenylate cyclase levels are further changed by gene transcription factors. | 1 | Biochemistry |
Common water masses in the world ocean are:
* Antarctic Bottom Water (AABW): Antarctic Bottom Water is a very important water mass. Antarctic Bottom Water is the left over part when sea ice is being made. It is very cold but, not quite freezing so the water moves down and along the ocean floor.
* North Atlantic Deep Water (NADW)
* Circumpolar Deep Water (CDW)
* Antarctic Intermediate Water (AAIW)
* Subantarctic Mode Water (SAMW)
* Arctic Intermediate Water (AIW)
* North Pacific Intermediate Water (NPIW)
* The central waters of various oceanic basins
* Various ocean surface waters. | 9 | Geochemistry |
In terms of complex numbers, the isometries of the plane are either of the form
or of the form
for some complex numbers and with |ω| = 1. This is easy to prove: if and and if one defines
then is an isometry, , and . It is then easy to see that g is either the identity or the conjugation, and the statement being proved follows from this and from the fact that .
This is obviously related to the previous classification of plane isometries, since:
* functions of the type are translations;
* functions of the type are rotations (when |ω| = 1);
* the conjugation is a reflection.
Note that a rotation about complex point p is obtained by complex arithmetic with
where the last expression shows the mapping equivalent to rotation at 0 and a translation.
Therefore, given direct isometry one can solve to obtain as the center for an equivalent rotation, provided that , that is, provided the direct isometry is not a pure translation. As stated by Cederberg, "A direct isometry is either a rotation or a translation." | 3 | Analytical Chemistry |
In its natural state, wood is not a transparent material because of its scattering and absorption of light. The tannish color in wood is due to its chemical polymer composition of cellulose, hemicellulose, and lignin. The woods lignin is mostly responsible for the woods distinctive color. Consequently, the amount of lignin determines the levels of visibility in the wood, around 80–95%. To make wood a visible and transparent material, both absorption and scattering need to be reduced in its production. The manufacturing process of transparent wood is based on removing all of the lignin called the delignification process. | 7 | Physical Chemistry |
Gene knockouts (also known as gene deletion or gene inactivation) are a widely used genetic engineering technique that involves the targeted removal or inactivation of a specific gene within an organism's genome. This can be done through a variety of methods, including homologous recombination, CRISPR-Cas9, and TALENs.
One of the main advantages of gene knockouts is that they allow researchers to study the function of a specific gene in vivo, and to understand the role of the gene in normal development and physiology as well as in the pathology of diseases. By studying the phenotype of the organism with the knocked out gene, researchers can gain insights into the biological processes that the gene is involved in.
There are two main types of gene knockouts: complete and conditional. A complete gene knockout permanently inactivates the gene, while a conditional gene knockout allows for the gene to be turned off and on at specific times or in specific tissues. Conditional knockouts are particularly useful for studying developmental processes and for understanding the role of a gene in specific cell types or tissues.
Gene knockouts have been widely used in many different organisms, including bacteria, yeast, fruit flies, zebrafish, and mice. In mice, gene knockouts are commonly used to study the function of specific genes in development, physiology, and cancer research.
The use of gene knockouts in mouse models has been particularly valuable in the study of human diseases. For example, gene knockouts in mice have been used to study the role of specific genes in cancer, neurological disorders, immune disorders, and metabolic disorders.
However, gene knockouts also have some limitations. For example, the loss of a single gene may not fully mimic the effects of a genetic disorder, and the knockouts may have unintended effects on other genes or pathways. Additionally, gene knockouts are not always a good model for human disease as the mouse genome is not identical to the human genome, and mouse physiology is different from human physiology.
The KO technique is essentially the opposite of a gene knock-in. Knocking out two genes simultaneously in an organism is known as a double knockout (DKO). Similarly the terms triple knockout (TKO) and quadruple knockouts (QKO) are used to describe three or four knocked out genes, respectively. However, one needs to distinguish between heterozygous and homozygous KOs. In the former, only one of two gene copies (alleles) is knocked out, in the latter both are knocked out. | 1 | Biochemistry |
Transposon mutagenesis, or transposition mutagenesis, is a biological process that allows genes to be transferred to a host organism's chromosome, interrupting or modifying the function of an extant gene on the chromosome and causing mutation. Transposon mutagenesis is much more effective than chemical mutagenesis, with a higher mutation frequency and a lower chance of killing the organism. Other advantages include being able to induce single hit mutations, being able to incorporate selectable markers in strain construction, and being able to recover genes after mutagenesis. Disadvantages include the low frequency of transposition in living systems, and the inaccuracy of most transposition systems. | 1 | Biochemistry |
Cryptophanes were discovered by André Collet and Jacqueline Gabard in 1981 when these researchers created, using template-directed synthesis, the first cryptophane, now known as cryptophane-A. | 6 | Supramolecular Chemistry |
A common goal in Bayesian experimental design is to maximise the expected relative entropy between the prior and the posterior. When posteriors are approximated to be Gaussian distributions, a design maximising the expected relative entropy is called Bayes d-optimal. | 7 | Physical Chemistry |
Initially traffic was slow and very sparse, but, as early as 1856, a newspaper said, "The cart was near to the right hand kerb. According to the rules of the road, it should have been on the left side. In turning sharp round a right-hand corner, a driver should keep away to the opposite side." That rule was codified when the first Highway Code was written in 1936. | 4 | Stereochemistry |
The peripheral attack model is based on predicting lowest energy conformations of an inherently complicated system, where nuanced perturbations can cause huge stereodifferentiating consequences. By modeling peripheral attack using the Curtin-Hammett scenario depicted above, the transition state is excluded from this conformation analysis by assuming that the barrier to each transition state from a given conformation is the same and thus that ground state conformations are the sole product determining factor. A significant criticism is the mapping of medium-sized ring conformations and influences onto larger ring systems. Macrocycles can possess varying degrees of rigidity in their structure, making a single peripheral attack model difficult to apply to all systems. Different classes of reactions might not fit the peripheral attack model, as reactions such as epoxidations, hydroxylations, alkylations, and reductions all proceed through different transition states. | 0 | Organic Chemistry |
Nucleic acid amplification is a technique used to produce several copies of a specific segment of RNA/DNA. Amplified RNA and DNA can be used for a variety of applications, such as genotyping, sequencing, and detection of bacteria or viruses. There are two different types of amplification, non-isothermal and isothermal. Non-isothermal amplification produces multiple copies of RNA/DNA through reiterative cycling between different temperatures. Isothermal amplification produces multiple copies of RNA/DNA at a constant reaction temperature. NASBA takes single stranded RNA, anneals primers to it at 65°C, and then amplifies it at 41°C to produce multiple copies of single stranded RNA. In order for successful amplification to occur, an enzyme cocktail containing, Avian Myeloblastosis Reverse Transcriptase (AMV-RT), RNase H, and RNA polymerase is used. AMV-RT synthesizes a complementary DNA strand (cDNA) from the RNA template once the primer is annealed. RNase H then degrades the RNA template and the other primer binds to the cDNA to form double stranded DNA, which RNA polymerase uses to synthesize copies of RNA. One key aspect of NASBA is that the starting material and end product is always single stranded RNA. That being said, it can be used to amplify DNA, but the DNA must be translated into RNA in order for successful amplification to occur.
Loop-mediated isothermal amplification (LAMP) is another isothermal amplification technique. | 1 | Biochemistry |
Simple N-heterocyclic carbene (NHC)-based ligands have proven impractical for asymmetrical hydrogenation.
Some C,N ligands combine an NHC with a chiral oxazoline to give a chelating ligand. NHC-based ligands of the first type have been generated as large libraries from the reaction of smaller libraries of individual NHCs and oxazolines. NHC-based catalysts featuring a bulky seven-membered metallocycle on iridium have been applied to the catalytic hydrogenation of unfunctionalized olefins and vinyl ether alcohols with conversions and ee's in the high 80s or 90s. The same system has been applied to the synthesis of a number of aldol, vicinal dimethyl and deoxypolyketide motifs, and to the deoxypolyketides themselves.
C-symmetric NHCs have shown themselves to be highly useful ligands for the asymmetric hydrogenation. | 0 | Organic Chemistry |
Secondary structures formed by the RBS can affect the translational efficiency of mRNA, generally inhibiting translation. These secondary structures are formed by H-bonding of the mRNA base pairs and are sensitive to temperature. At a higher-than-usual temperature (~42 °C), the RBS secondary structure of heat shock proteins becomes undone thus allowing ribosomes to bind and initiate translation. This mechanism allows a cell to quickly respond to an increase in temperature. | 1 | Biochemistry |
Dynamic recrystallization is the process of removing the internal strain that remains in grains during deformation. This happens by the reorganization of a material with a change in grain size, shape, and orientation within the same mineral. When recrystallization occurs after deformation has come to an end and particularly at high temperatures, the process is called static recrystallization or annealing. Dynamic recrystallization results in grain size-reduction and static recrystallization results in the formation of larger equant grains.
Dynamic recrystallization can occur under a wide range of metamorphic conditions, and can strongly influence the mechanical properties of the deforming material. Dynamic recrystallization is the result of two end-member processes: (1) The formation and rotation of subgrains (rotation recrystallization) and (2) grain-boundary migration (migration recrystallization).
# Rotation recrystallization (subgrain rotation) is the progressive misorientation of a subgrain as more dislocations move into the dislocation wall (a zone of dislocations resulting from climb, cross-slip, and glide), which increases the crystallographic mismatch across the boundary. Eventually, the misorientation across the boundary is sufficiently large enough to recognize individual grains (usually 10–15° misorientation). Grains tend to be elongate or ribbon-shape, with many subgrains, with a characteristic gradual transition from low-angle subgrains to high-angle boundaries.
# Migration recrystallization (grain-boundary migration) is the processes by which a grain grows at the expense of the neighboring grains. At low temperatures, the mobility of the grain boundary may be local, and the grain boundary may bulge into a neighboring grain with a high dislocation density and form new, smaller, independent crystals by a process called low-temperature grain boundary migration, or bulging recrystallization. The bulges produced can separate from the original grain to form new grains by the formation of subgrain (low-angle) boundaries, which can evolve into grain boundaries, or by migration of the grain boundary. Bulging recrystallization often occurs along boundaries of old grains at triple junctions. At high temperatures, the growing grain has a lower dislocation density than the grain(s) consumed, and the grain boundary sweeps through the neighboring grains to remove dislocations by high-temperature grain-boundary migration crystallization. Grain boundaries are lobate with a variable grain size, with new grains generally larger than existing subgrains. At very high temperatures, grains are highly lobate or ameboid, but can be nearly strain-free. | 8 | Metallurgy |
* Endogenous Expression of Oncogenic PI3K Mutation Leads to Activated PI3K Signaling and an Invasive Phenotype Poster Presented at AACR/EORTC Molecular Targets and Cancer Therapeutics, Boston, USA, Nov. 2009
* Endogenous Expression of Oncogenic PI3K Mutation Leads to accumulation of anti-apoptotic proteins in mitochondria Poster Presented at AACR 2010, Washington, D.C., USA, April. 2010
* The use of ‘X-MAN’ isogenic cell lines to define PI3-kinase inhibitor activity profiles Poster Presented at AACR 2010, Washington, D.C., USA, April. 2010
* The use of ‘X-MAN’ mutant PI3CA increases the expression of individual tubulin isoforms and promoted resistance to anti-mitotic chemotherapy drugs Poster Presented at AACR 2010, Washington, D.C., USA, April. 2010 | 1 | Biochemistry |
The sessile drop method is another popular way to measure contact angles, and is done by placing a two-dimensional drop on a solid surface and controlling the volume of liquid in the drop. The sessile drop method and the captive bubble method are usually interchangeable in performing experiments as they are both based on the properties of symmetry. Specifically, the axis of symmetry of the drop or bubble makes the contact line of the drop or bubble with the solid surface circular. This creates an observable contact angle corresponding to the contact radius of the drop or bubble.
However, interacting with a rough homogeneous surface in measurements of contact angles, the drop and bubble each present different behaviours in the measuring process, which are related to the volume of liquid and contact angles.
# On a rough homogeneous surface, the observed contact angle may not represent the actual contact angle with a local slope since it may not be observable on a rough surface. The observed contact angle on a rough surface is also called an apparent angle which is equivalent to the sum of the intrinsic contact angle and the local surface slope at the tangent of the contact slope for a drop or bubble. With the sessile drop method, the observed contact angle usually underestimated the intrinsic contact angle, while the observed contact angle in the captive bubble method overestimates the intrinsic contact angle of the rough surface.
# If a graph is plotted respectively for the measurements of contact angles using the sessile drop method and the captive bubble method concerning the volume of liquid within the drop or bubble and the measured contact angle, the geometrical relationships illustrate different characteristics for each method. In consideration of the relationship between contact angles and the position of the contact for a certain volume in the drop or bubble, the highest and lowest possible contact angles on volume are dependent on each other differently in the two methods.
# For the amplitude of oscillations shown in the graph, both of the drop and the captive bubble display a similar order of magnitude at a relatively low contact angle. On the other hand, on a rough surface with a relatively high contact angle, the amplitude shown for the drop is larger than that of a captive bubble. The amplitude of oscillation of the lowest highest possible contact angle demonstrates the difference for the drop method and the captive bubble method, in which the amplitude of the graph of the captive bubble method is comparatively larger than that of the graph of the sessile drop method.
# In terms of the wavelength of the graph, the wavelength for both methods spans over a large range of volume of liquid on the solid surface. Differences in behaviours of the drop and the bubble vary from the lowest possible contact angles to the highest possible contact angle. | 7 | Physical Chemistry |
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