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One type of chiral auxiliary is based on the trans-2-phenylcyclohexanol motif as introduced by James K. Whitesell and coworkers in 1985. This chiral auxiliary was used in ene reactions of the derived ester of glyoxylic acid.
In the total synthesis of (−)-heptemerone B and (−)-guanacastepene E, attached with trans-2-phenylcyclohexanol, the glyoxylate reacted with 2,4-dimethyl-pent-2-ene, in the presence of tin(IV) chloride, yielding the desired anti adduct as the major product, together with a small amount of its syn isomer with 10:1 diastereomeric ratio.
For even greater conformational control, switching from a phenyl to a trityl group gives trans-2-tritylcyclohexanol (TTC). In 2015, the Brown group published an efficient chiral permanganate-mediated oxidative cyclization with TTC. | 4 | Stereochemistry |
4-Nitrophenol irritates the eyes, skin, and respiratory tract. It may also cause inflammation of those parts. It has a delayed interaction with blood and forms methaemoglobin which is responsible for methemoglobinemia, potentially causing cyanosis, confusion, and unconsciousness. When ingested, it causes abdominal pain and vomiting. Prolonged contact with skin may cause allergic response. Genotoxicity and carcinogenicity of 4-nitrophenol are not known. The in mice is 282 mg/kg and in rats is 202 mg/kg (p.o.). | 3 | Analytical Chemistry |
If a container with an ideal gas is expanded instantaneously, the temperature of the gas doesn't change at all, because none of the molecules slow down. The molecules keep their kinetic energy, but now the gas occupies a bigger volume. If the container expands slowly, however, so that the ideal gas pressure law holds at any time, gas molecules lose energy at the rate that they do work on the expanding wall. The amount of work they do is the pressure times the area of the wall times the outward displacement, which is the pressure times the change in the volume of the gas:
If no heat enters the gas, the energy in the gas molecules is decreasing by the same amount. By definition, a gas is ideal when its temperature is only a function of the internal energy per particle, not the volume. So
where is the specific heat at constant volume. When the change in energy is entirely due to work done on the wall, the change in temperature is given by
This gives a differential relationship between the changes in temperature and volume, which can be integrated to find the invariant. The constant is just a unit conversion factor, which can be set equal to one:
So
is an adiabatic invariant, which is related to the entropy
Thus entropy is an adiabatic invariant. The N log(N) term makes the entropy additive, so the entropy of two volumes of gas is the sum of the entropies of each one.
In a molecular interpretation, S is the logarithm of the phase-space volume of all gas states with energy E(T) and volume V.
For a monatomic ideal gas, this can easily be seen by writing down the energy:
The different internal motions of the gas with total energy E define a sphere, the surface of a 3N-dimensional ball with radius . The volume of the sphere is
where is the gamma function.
Since each gas molecule can be anywhere within the volume V, the volume in phase space occupied by the gas states with energy E is
Since the N gas molecules are indistinguishable, the phase-space volume is divided by , the number of permutations of N molecules.
Using Stirlings approximation for the gamma function, and ignoring factors that disappear in the logarithm after taking N' large,
Since the specific heat of a monatomic gas is 3/2, this is the same as the thermodynamic formula for the entropy. | 7 | Physical Chemistry |
There are typically two different ways of mathematically describing how an electromagnetic wave interacts with the elements within an ellipsometer (including the sample): the Jones matrix and the Mueller matrix formalisms. In the Jones matrix formalism, the electromagnetic wave is described by a Jones vector with two orthogonal complex-valued entries for the electric field (typically and ), and the effect that an optical element (or sample) has on it is described by the complex-valued 2×2 Jones matrix. In the Mueller matrix formalism, the electromagnetic wave is described by Stokes vectors with four real-valued entries, and their transformation is described by the real-valued 4x4 Mueller matrix. When no depolarization occurs both formalisms are fully consistent. Therefore, for non-depolarizing samples, the simpler Jones matrix formalism is sufficient. If the sample is depolarizing the Mueller matrix formalism should be used, because it also gives the amount of depolarization. Reasons for depolarization are, for instance, thickness non-uniformity or backside-reflections from a transparent substrate. | 7 | Physical Chemistry |
Thermodynamic potentials are functions that characterize the equilibrium state of a substance. An example is the Gibbs free energy , which is a function of pressure and temperature. Knowing any one thermodynamic potential is sufficient to compute all equilibrium properties of a substance, often simply by taking derivatives of . Thus, a single correlation for can replace separate correlations for individual properties. Conversely, a variety of experimental measurements (e.g., density, heat capacity, vapor pressure) can be incorporated into the same fit; in principle, this would allow one to predict hard-to-measure properties like heat capacity in terms of other, more readily available measurements (e.g., vapor pressure). | 7 | Physical Chemistry |
Steric hindrance is a consequence of steric effects. Steric hindrance is the slowing of chemical reactions due to steric bulk. It is usually manifested in intermolecular reactions, whereas discussion of steric effects often focus on intramolecular interactions. Steric hindrance is often exploited to control selectivity, such as slowing unwanted side-reactions.
Steric hindrance between adjacent groups can also affect torsional bond angles. Steric hindrance is responsible for the observed shape of rotaxanes and the low rates of racemization of 2,2'-disubstituted biphenyl and binaphthyl derivatives. | 4 | Stereochemistry |
HOT was founded to understand the processes controlling the fluxes of carbon and associated bioelements in the ocean and to document changes in the physical structure of the water column. To achieve this, the HOT program has several specific goals:
:1. Quantify temporal (seasonal to decadal) changes in reservoirs and fluxes of carbon and associated bioelements (nitrogen, oxygen, phosphorus, and silicon).
:2. Identify processes controlling air-sea carbon exchange, rates of carbon transformation through the planktonic food web, and fluxes of carbon into the ocean.
:3. Form a multi-decadal baseline based on the gathered data that will allow researchers to decipher natural and anthropogenic influences on the NPSG ecosystem.
:4. Provide scientific and logistical support to other scientific programs that benefit from the research and services performed by the HOT program. This includes projects implementing, testing, and validating new methodologies, models, and transformative ocean sampling technologies.
The dissolved inorganic carbon data set that has been accumulated over the course of the HOT program shows the increase of carbon dioxide in the surface waters of the Pacific and subsequent acidification of the ocean. The data collected by these cruises are available online.
The 200th cruise of the HOT program was in 2008. HOT recently celebrated its 25th year in operation, with the 250th research cruise occurring in March 2013. | 9 | Geochemistry |
Photofragment ion imaging or, more generally, Product Imaging is an experimental technique for making measurements of the velocity of product molecules or particles following a chemical reaction or the photodissociation of a parent molecule. The method uses a two-dimensional detector, usually a microchannel plate, to record the arrival positions of state-selected ions created by resonantly enhanced multi-photon ionization (REMPI). The first experiment using photofragment ion imaging was performed by David W Chandler and Paul L Houston in 1987 on the phototodissociation dynamics of methyl iodide (iodomethane, CHI). | 7 | Physical Chemistry |
He died on January 4, 1882, at his home in Hastings-on-Hudson, New York, at the age of 70. The funeral was held at St Mark's Church in-the-Bowery in New York City. He was buried in Green-Wood Cemetery, Brooklyn, New York. | 5 | Photochemistry |
Certain nitrogen-based ylides also exist such as azomethine ylides with the general structure:
These compounds can be envisioned as iminium cations placed next to a carbanion. The substituents R, R are electron withdrawing groups. These ylides can be generated by condensation of an α-amino acid and an aldehyde or by thermal ring opening reaction of certain N-substituted aziridines.
The further-unsaturated nitrile ylides are known almost exclusively as unstable intermediates.
A rather exotic family of dinitrogen-based ylides are the isodiazenes (RRN=N), which generally decompose by extrusion of dinitrogen.
Stable carbenes also have a ylidic resonance contributor, e.g.: | 0 | Organic Chemistry |
In chemistry, a pentagonal bipyramid is a molecular geometry with one atom at the centre with seven ligands at the corners of a pentagonal bipyramid. A perfect pentagonal bipyramid belongs to the molecular point group D.
The pentagonal bipyramid is a case where bond angles surrounding an atom are not identical (see also trigonal bipyramidal molecular geometry). This is one of the three common shapes for heptacoordinate transition metal complexes, along with the capped octahedron and the capped trigonal prism.
Pentagonal bipyramids are claimed to be promising coordination geometries for lanthanide-based single-molecule magnets, since (a) they present no extradiagonal crystal field terms, therefore minimising spin mixing, and (b) all of their diagonal terms are in first approximation protected from low-energy vibrations, minimising vibronic coupling. | 4 | Stereochemistry |
T independent antigen elicits antibody production by B lymphocytes without T lymphocyte involvement. There are 2 distinct subgroups of TI antigens, different in mechanism of activating B lymphocytes. TI-1 antigen, which has an activity that can directly activate B cells and TI-2 antigen, which has highly repetitive structure and causes simultaneous cross-linking of specific B cell receptors (BCR) on B lymphocyte. The most commonly released isotype of antibodies in this type of immune reaction is low affinity IgM. | 1 | Biochemistry |
As discussed above, an extensive form of entropy is recovered if we divide the volume of phase space, , by n!. An alternative approach is to argue that the dependence on particle number cannot be trusted on the grounds that changing also changes the dimensionality of phase space. Such changes in dimensionality lie outside the scope of Hamiltonian mechanics and Liouville's theorem. For that reason it is plausible to allow the arbitrary constant to be a function of . Defining the function to be, , we have:
which has extensive scaling: | 7 | Physical Chemistry |
The Warburg coefficient (or Warburg constant; denoted or ) is the diffusion coefficient of ions in solution, associated to the Warburg element, . The Warburg coefficient has units of
The value of can be obtained by the gradient of the Warburg plot, a linear plot of the real impedance () against the reciprocal of the square root of the frequency (). This relation should always yield a straight line, as it is unique for a Warburg.
Alternatively, the value of can be found by:
where
* is the ideal gas constant;
* is the thermodynamic temperature;
* is the Faraday constant;
* is the valency;
* is the diffusion coefficient of the species, where subscripts and stand for the oxidized and reduced species respectively;
* is the concentration of the and species in the bulk;
* is the concentration of the electrolyte;
* denotes the surface area;
* denotes the fraction of the and species present.
The equation for applies to both reversible and quasi-reversible reactions for which both halves of the couple are soluble. | 7 | Physical Chemistry |
Neurotrophin-4 (NT-4) is a neurotrophic factor that signals predominantly through the TrkB receptor tyrosine kinase. It is also known as NT4, NT5, NTF4, and NT-4/5. | 1 | Biochemistry |
Previous work from MUSE includes the detection of endogenous fluorescent molecules in intact clinical and human tissues for functional and structural characterization, which is limited by the relatively dim autofluorescence found in tissue. However, the use of bright exogenous dyes can provide substantially more remitted light than the autofluorescence approach.
Several dyes have been studied for MUSE's application, including eosin, rhodamine, DAPI, Hoechst, acridine orange, propidium iodide, and proflavine. Eosin and rhodamine stain the cytoplasm and the extracellular matrix, making the bulk of the tissue visible. Hoechst and DAPI fluoresce brightly when bound to DNA, allowing them to serve as excellent nuclear stains. | 5 | Photochemistry |
Many atropisomers occur in nature, and some have applications to drug design. The natural product mastigophorene A has been found to aid in nerve growth.
Other examples of naturally occurring atropisomers include vancomycin isolated from an Actinobacterium, and knipholone, which is found in the roots of Kniphofia foliosa of the family Asphodelaceae. The structure complexity in vancomycin is significant because it can bind with peptides due to the complexity of its stereochemistry, which includes multiple stereocenters, two chiral planes in its stereogenic biaryl axis. Knipholone, with its axial chirality, occurs in nature and has been shown to offer good antimalarial and antitumor activities particularly in the M form.
The use of atropisomeric drugs provides an additional way for drugs to have stereochemical variations and specificity in design. One example is , a drug that was discovered to aid in chemotherapy cancer treatment.
Telenzepine is atropisomeric in the conformation of its central thienobenzodiazepine ring. The two enantiomers have been resolved, and it was found that the (+)-isomer which is about 500-fold more active than the (–)-isomer at muscarinic receptors in rat cerebral cortex. However, drug design is not always aided by atropisomerism. In some cases, making drugs from atropisomers is challenging because isomers may interconvert faster than expected. Atropisomers also might interact differently in the body, and as with other types of stereoisomers, it is important to examine these properties before administering drugs to patients. | 4 | Stereochemistry |
Initiation of translation is regulated by the accessibility of ribosomes to the Shine-Dalgarno sequence. This stretch of four to nine purine residues are located upstream the initiation codon and hybridize to a pyrimidine-rich sequence near the 3 end of the 16S RNA within the 30S bacterial ribosomal subunit. Polymorphism in this particular sequence has both positive and negative effects on the efficiency of base-pairing and subsequent protein expression. Initiation is also regulated by proteins known as initiation factors which provide kinetic assistance to the binding between the initiation codon and tRNA, which supplies the 3-UAC-5' anticodon. IF1 binds the 30S subunit first, instigating a conformational change that allows for the additional binding of IF2 and IF3. IF2 ensures that tRNA remains in the correct position while IF3 proofreads initiation codon base-pairing to prevent non-canonical initiation at codons such as AUU and AUC. Generally, these initiation factors are expressed in equal proportion to ribosomes, however experiments using cold-shock conditions have shown to create stoichiometric imbalances between these translational machinery. In this case, two to three fold changes in expression of initiation factors coincide with increased favorability towards translation of specific cold-shock mRNAs. | 1 | Biochemistry |
GC–MS is becoming the tool of choice for tracking organic pollutants in the environment. The cost of GC–MS equipment has decreased significantly, and the reliability has increased at the same time, which has contributed to its increased adoption in environmental studies. | 3 | Analytical Chemistry |
The advent of inexpensive microarray experiments created several specific bioinformatics challenges: the multiple levels of replication in experimental design (Experimental design); the number of platforms and independent groups and data format (Standardization); the statistical treatment of the data (Data analysis); mapping each probe to the mRNA transcript that it measures (Annotation); the sheer volume of data and the ability to share it (Data warehousing). | 1 | Biochemistry |
Chemical materials developed to assist in the production of food, feed, and fiber include herbicides, insecticides, fungicides, and other pesticides. Pesticides are chemicals that play an important role in increasing crop yield and mitigating crop losses. These work to keep insects and other animals away from crops to allow them to grow undisturbed, effectively regulating pests and diseases.
Disadvantages of pesticides include contamination of the ground and water (see persistent organic pollutants). They may be toxic to non-target species, including birds, fish, pollinators, as well as the farmworkers themselves. | 1 | Biochemistry |
Mostafa A. El-Sayed (Arabic: مصطفى السيد) is an Egyptian-American physical chemist, nanoscience researcher, member of the National Academy of Sciences and US National Medal of Science laureate. He is known for the spectroscopy rule named after him, the El-Sayed rule. | 1 | Biochemistry |
By the early 1950s it was known from metabolic labeling studies using radioactive phosphate that phosphate groups attached to phosphoproteins inside cells can sometimes undergo rapid exchange of new phosphate for old. In order to perform experiments that would allow isolation and characterization of the enzymes involved in attaching and removing phosphate from proteins, there was a need for convenient substrates for protein kinases and protein phosphatases. Casein has been used as a substrate since the earliest days of research on protein phosphorylation. By the late 1960s, cyclic AMP-dependent protein kinase had been purified, and most attention was centered on kinases and phosphatases that could regulate the activity of important enzymes. Casein kinase activity associated with the endoplasmic reticulum of mammary glands was first characterized in 1974, and its activity was shown to not depend on cyclic AMP. | 1 | Biochemistry |
Gene silencing can be achieved by introducing into cells a short "antisense oligonucleotide" that is complementary to an RNA target. This experiment was first done by Zamecnik and Stephenson in 1978 and continues to be a useful approach, both for laboratory experiments and potentially for clinical applications (antisense therapy). Several viruses, such as influenza viruses Respiratory syncytial virus (RSV) and SARS coronavirus (SARS-CoV), have been targeted using antisense oligonucleotides to inhibit their replication in host cells.
If the antisense oligonucleotide contains a stretch of DNA or a DNA mimic (phosphorothioate DNA, 2′F-ANA, or others) it can recruit RNase H to degrade the target RNA. This makes the mechanism of gene silencing catalytic. Double-stranded RNA can also act as a catalytic, enzyme-dependent antisense agent through the RNAi/siRNA pathway, involving target mRNA recognition through sense-antisense strand pairing followed by target mRNA degradation by the RNA-induced silencing complex (RISC). The R1 plasmid hok/sok system provides yet another example of an enzyme-dependent antisense regulation process through enzymatic degradation of the resulting RNA duplex.
Other antisense mechanisms are not enzyme-dependent, but involve steric blocking of their target RNA (e.g. to prevent translation or to induce alternative splicing). Steric blocking antisense mechanisms often use oligonucleotides that are heavily modified. Since there is no need for RNase H recognition, this can include chemistries such as 2′-O-alkyl, peptide nucleic acid (PNA), locked nucleic acid (LNA), and Morpholino oligomers. | 1 | Biochemistry |
In thermodynamics, the chemical potential of a species is the energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. The chemical potential of a species in a mixture is defined as the rate of change of free energy of a thermodynamic system with respect to the change in the number of atoms or molecules of the species that are added to the system. Thus, it is the partial derivative of the free energy with respect to the amount of the species, all other species' concentrations in the mixture remaining constant. When both temperature and pressure are held constant, and the number of particles is expressed in moles, the chemical potential is the partial molar Gibbs free energy. At chemical equilibrium or in phase equilibrium, the total sum of the product of chemical potentials and stoichiometric coefficients is zero, as the free energy is at a minimum. In a system in diffusion equilibrium, the chemical potential of any chemical species is uniformly the same everywhere throughout the system.
In semiconductor physics, the chemical potential of a system of electrons at zero absolute temperature is known as the Fermi level. | 7 | Physical Chemistry |
Spoil tips sometimes increased to millions of tons, and, having been abandoned, remain as huge piles today. They trap solar heat, making it difficult (although not impossible) for vegetation to take root; this encourages erosion and creates dangerous, unstable slopes. Existing techniques for regreening spoil tips include the use of geotextiles to control erosion as the site is resoiled and simple vegetation such as grass is seeded on the slope.
The piles also create acid rock drainage, which pollutes streams and rivers. Environmental problems have included surface runoff of silt, and leaching of noxious chemical compounds from spoil banks exposed to weathering. These cause contamination of ground water, and other problems.
In the United States, current state and federal coal mining regulations require that the earth materials from excavations be removed in such a fashion that they can be replaced after the mining operations cease in a process called mine reclamation, with oversight of mining corporations. This requires adequate reserves of monetary bonds to guarantee a completion of the reclamation process when mining becomes unprofitable or stops. (See for example, the Surface Mining Control and Reclamation Act of 1977.) | 8 | Metallurgy |
The field has expanded significantly since the publication in 1973 with biochemists Stanley N. Cohen and Herbert W. Boyer by using E. coli bacteria to learn how to cut fragments, rejoin different fragments, and insert the new genes. The field has expanded tremendously in terms of precision and accuracy since then. Computers and technology have made it technologically easier to achieve narrowing of error and expand understanding in this field. Computers having a high capacity for data and calculations which made processing the large volume of information tangible, i.e., the use of ChIP and gene sequence. | 1 | Biochemistry |
Cobalt sensors have been made that capitalize on the breaking of C-O bonds by Co(II) in a fluorescent probe known as Cobalt Probe 1 (CP1). | 5 | Photochemistry |
The test method involves variables limiting reproducibility. Tests normally show observations varying plus or minus ten to twenty percent around the mean. | 3 | Analytical Chemistry |
The stomach contents can also be analyzed. This can help with the post-mortem interval identification by looking at the stage of digestion. The contents can also be analyzed for drugs or poisons to help determine a cause of death if it is unknown. | 1 | Biochemistry |
Generally, the background is calculated as a Chebyshev polynomial. In GSAS and GSAS-II they appear as follows. Again, background is treated as a Chebyshev polynomial of the first kind ("Handbook of Mathematical Functions", M. Abramowitz and IA. Stegun, Ch. 22), with intensity given by:
where are the coefficients of the Chebyshev polynomial taken from Table 22.3, pg. 795 of the Handbook. The coefficients have the form:
and the values for are found in the Handbook. The angular range () is converted to to make the Chebyshev polynomial orthogonal by
And, the orthogonal range for this function is –1 to +1. | 3 | Analytical Chemistry |
In geometry, Hermann–Mauguin notation is used to represent the symmetry elements in point groups, plane groups and space groups. It is named after the German crystallographer Carl Hermann (who introduced it in 1928) and the French mineralogist Charles-Victor Mauguin (who modified it in 1931). This notation is sometimes called international notation, because it was adopted as standard by the International Tables For Crystallography since their first edition in 1935.
The Hermann–Mauguin notation, compared with the Schoenflies notation, is preferred in crystallography because it can easily be used to include translational symmetry elements, and it specifies the directions of the symmetry axes. | 3 | Analytical Chemistry |
In glycolysis, hexokinase is directly inhibited by its product, glucose-6-phosphate, and pyruvate kinase is inhibited by ATP itself. The main control point for the glycolytic pathway is phosphofructokinase (PFK), which is allosterically inhibited by high concentrations of ATP and activated by high concentrations of AMP. The inhibition of PFK by ATP is unusual since ATP is also a substrate in the reaction catalyzed by PFK; the active form of the enzyme is a tetramer that exists in two conformations, only one of which binds the second substrate fructose-6-phosphate (F6P). The protein has two binding sites for ATP – the active site is accessible in either protein conformation, but ATP binding to the inhibitor site stabilizes the conformation that binds F6P poorly. A number of other small molecules can compensate for the ATP-induced shift in equilibrium conformation and reactivate PFK, including cyclic AMP, ammonium ions, inorganic phosphate, and fructose-1,6- and -2,6-biphosphate. | 1 | Biochemistry |
* A 32-inch diameter gas transmission pipeline, north of Natchitoches, Louisiana, belonging to the Tennessee Gas Pipeline exploded and burned from SCC on March 4, 1965, killing 17 people. At least 9 others were injured, and 7 homes 450 feet from the rupture were destroyed.
* SCC caused the catastrophic collapse of the Silver Bridge in December 1967, when an eyebar suspension bridge across the Ohio river at Point Pleasant, West Virginia, suddenly failed. The main chain joint failed and the entire structure fell into the river, killing 46 people who were traveling in vehicles across the bridge. Rust in the eyebar joint had caused a stress corrosion crack, which went critical as a result of high bridge loading and low temperature. The failure was exacerbated by a high level of residual stress in the eyebar. The disaster led to a nationwide reappraisal of bridges.
* USS Hartford submarine periscope: In 2009, the periscope of the submarine USS Hartford failed due to SCC. The periscope is used to provide a view of the surface while the submarine is submerged. The failure occurred when the periscope was extended through the hull of the submarine, causing seawater to enter the periscopes seal. The seawater caused SCC to occur in the periscopes steel support structure, which led to the periscope falling back into the submarine. Fortunately, there were no injuries, but the submarine had to be taken out of service for repairs.
* Trans-Alaska Pipeline: In 2001, a section of the Trans-Alaska Pipeline failed due to SCC. The pipeline is used to transport crude oil from the North Slope of Alaska to the Valdez Marine Terminal. The failure occurred when a 34-foot section of the pipeline ruptured, causing a spill of over 285,000 gallons of crude oil. The investigation into the failure found that SCC had occurred in the pipeline due to the presence of water and bacteria, which had created a corrosive environment.
* Aloha Airlines Flight 243: In 1988, Aloha Airlines Flight 243 experienced a partial fuselage failure due to SCC. The Boeing 737-200 was flying from Hilo to Honolulu, Hawaii when a section of the fuselage ruptured, causing a decompression event. The investigation into the failure found that SCC had occurred in the aluminum skin of the fuselage due to the repeated pressurization and depressurization cycles of the aircraft. The incident led to changes in maintenance procedures and inspections for aircraft to prevent similar failures in the future. | 8 | Metallurgy |
High-performance thin-layer chromatography (HPTLC) serves as an extension of thin-layer chromatography (TLC), offering robustness, simplicity, speed, and efficiency in the quantitative analysis of compounds. This TLC-based analytical technique enhances compound resolution for quantitative analysis. Some of these improvements involve employing higher-quality TLC plates with finer particle sizes in the stationary phase, leading to improved resolution. Additionally, the separation can be further refined through repeated plate development using a multiple development device. As a result, HPTLC provides superior resolution and lower Limit of Detection (LODs). | 3 | Analytical Chemistry |
The concept of magic numbers in the field of chemistry refers to a specific property (such as stability) for only certain representatives among a distribution of structures. It was first recognized by inspecting the intensity of mass-spectrometric signals of rare gas cluster ions. Then, the same effect was observed with sodium clusters.
In case a gas condenses into clusters of atoms, the number of atoms in these clusters that are most likely to form varies between a few and hundreds. However, there are peaks at specific cluster sizes, deviating from a pure statistical distribution. Therefore, it was concluded that clusters of these specific numbers of atoms dominate due to their exceptional stability. The concept was also successfully applied to explain the monodispersed occurrence of thiolate-protected gold clusters; here the outstanding stability of specific cluster sizes is connected with their respective electronic configuration.
The term magic numbers is also used in the field of nuclear physics. In this context, magic numbers refer to a specific number of protons or neutrons that forms complete nucleon shells. | 7 | Physical Chemistry |
Many proteins and hormones are synthesized in the form of their precursors - zymogens, proenzymes, and prehormones. These proteins are cleaved to form their final active structures. Insulin, for example, is synthesized as preproinsulin, which yields proinsulin after the signal peptide has been cleaved. The proinsulin is then cleaved at two positions to yield two polypeptide chains linked by two disulfide bonds. Removal of two C-terminal residues from the B-chain then yields the mature insulin. Protein folding occurs in the single-chain proinsulin form which facilitates formation of the ultimate inter-peptide disulfide bonds, and the ultimate intra-peptide disulfide bond, found in the native structure of insulin.
Proteases in particular are synthesized in the inactive form so that they may be safely stored in cells, and ready for release in sufficient quantity when required. This is to ensure that the protease is activated only in the correct location or context, as inappropriate activation of these proteases can be very destructive for an organism. Proteolysis of the zymogen yields an active protein; for example, when trypsinogen is cleaved to form trypsin, a slight rearrangement of the protein structure that completes the active site of the protease occurs, thereby activating the protein.
Proteolysis can, therefore, be a method of regulating biological processes by turning inactive proteins into active ones. A good example is the blood clotting cascade whereby an initial event triggers a cascade of sequential proteolytic activation of many specific proteases, resulting in blood coagulation. The complement system of the immune response also involves a complex sequential proteolytic activation and interaction that result in an attack on invading pathogens. | 1 | Biochemistry |
An optical delay-line is implemented using a movable stage to vary the path length of one of the two beam paths. A delay stage uses a moving retroreflector to redirect the beam along a well-defined output path but following a delay. Movement of the stage holding the retroreflector corresponds to an adjustment of path length and consequently the time at which the terahertz detector is gated relative to the source terahertz pulse. | 7 | Physical Chemistry |
In coordination chemistry transition metal imido complexes feature the NR ligand. They are similar to oxo ligands in some respects. In some the M-N-C angle is 180º but often the angle is decidedly bent. The parent imide (NH) is an intermediate in nitrogen fixation by synthetic catalysts. | 0 | Organic Chemistry |
A similar process (environmental stress cracking) occurs in polymers, when products are exposed to specific solvents or aggressive chemicals such as acids and alkalis. As with metals, attack is confined to specific polymers and particular chemicals. Thus polycarbonate is sensitive to attack by alkalis, but not by acids. On the other hand, polyesters are readily degraded by acids, and SCC is a likely failure mechanism. Polymers are susceptible to environmental stress cracking where attacking agents do not necessarily degrade the materials chemically.
Nylon is sensitive to degradation by acids, a process known as hydrolysis, and nylon mouldings will crack when attacked by strong acids.
For example, the fracture surface of a fuel connector showed the progressive growth of the crack from acid attack (Ch) to the final cusp (C) of polymer. In this case the failure was caused by hydrolysis of the polymer by contact with sulfuric acid leaking from a car battery. The degradation reaction is the reverse of the synthesis reaction of the polymer:
Cracks can be formed in many different elastomers by ozone attack, another form of SCC in polymers. Tiny traces of the gas in the air will attack double bonds in rubber chains, with natural rubber, styrene-butadiene rubber, and nitrile butadiene rubber being most sensitive to degradation. Ozone cracks form in products under tension, but the critical strain is very small. The cracks are always oriented at right angles to the strain axis, so will form around the circumference in a rubber tube bent over. Such cracks are dangerous when they occur in fuel pipes because the cracks will grow from the outside exposed surfaces into the bore of the pipe, so fuel leakage and fire may follow. Ozone cracking can be prevented by adding anti-ozonants to the rubber before vulcanization. Ozone cracks were commonly seen in automobile tire sidewalls, but are now seen rarely thanks to the use of these additives. On the other hand, the problem does recur in unprotected products such as rubber tubing and seals. | 8 | Metallurgy |
In a zinc finger protein, certain sequences of amino acid residues are able to recognise and bind to an extended target-site of four or even five nucleotides When this occurs in a ZFP in which the three-nucleotide subsites are contiguous, one zinc finger interferes with the target-site of the zinc finger adjacent to it, a situation known as target-site overlap. For example, a zinc finger containing arginine at position -1 and aspartic acid at position 2 along its alpha-helix will recognise an extended sequence of four nucleotides of the sequence 5-NNG(G/T)-3. The hydrogen bond between Asp and the N4 of either a cytosine or adenine base paired to the guanine or thymine, respectively defines these two nucleotides at the 3' position, defining a sequence that overlaps into the subsite of any zinc finger that may be attached N-terminally.
Target-site overlap limits the modularity of those zinc fingers which exhibit it, by restricting the number of situations to which they can be applied. If some of the zinc fingers are restricted in this way, then a larger repertoire is required to address the situations in which those zinc fingers cannot be used. Target-site overlap may also affect the selection of zinc fingers during by display, in cases where amino acids on a non-randomised finger, and the bases of its associated subsite, influence the binding of residues on the adjacent finger which contains the randomised residues. Indeed, attempts to derive zinc finger proteins targeting the 5-(A/T)NN-3 family of sequences by site-directed mutagenesis of finger two of the C7 protein were unsuccessful due to the Asp of the third finger of said protein.
The extent to which target-site overlap occurs is largely unknown, with a variety of amino acids having shown involvement in such interactions. When interpreting the zinc finger repertoires presented by investigations using ZFP phage display, it is important to appreciate the effects that the rest of the zinc finger framework may have had in these selections. Since the problem only appears to occur in a limited number of cases, the issue is nullified in most situations in which there are a variety of suitable targets to choose from and only becomes a real issue if binding to a specific DNA sequence is required (e.g. blocking binding by endogenous DNA-binding proteins). | 1 | Biochemistry |
In thermodynamics, the binodal, also known as the coexistence curve or binodal curve, denotes the condition at which two distinct phases may coexist. Equivalently, it is the boundary between the set of conditions in which it is thermodynamically favorable for the system to be fully mixed and the set of conditions in which it is thermodynamically favorable for it to phase separate. In general, the binodal is defined by the condition at which the chemical potential of all solution components is equal in each phase. The extremum of a binodal curve in temperature coincides with the one of the spinodal curve and is known as a critical point. | 7 | Physical Chemistry |
Research has examined integrating RO with electrodialysis to improve recovery of valuable deionized products, or to reduce concentrate volumes. | 3 | Analytical Chemistry |
The range of applications for SMAs has grown over the years, a major area of development being dentistry. One example is the prevalence of dental braces using SMA technology to exert constant tooth-moving forces on the teeth; the nitinol archwire was developed in 1972 by orthodontist George Andreasen. This revolutionized clinical orthodontics. Andreasen's alloy has a patterned shape memory, expanding and contracting within given temperature ranges because of its geometric programming.
Harmeet D. Walia later utilized the alloy in the manufacture of root canal files for endodontics. | 8 | Metallurgy |
For molecular systems in thermal equilibrium, the addition of energy. e. g. by mechanical work, can cause a change in entropy. This is known from the theories of thermodynamics and statistical mechanics. Specifically, both theories assert that the change in energy must be proportional to the entropy change times the absolute temperature. This rule is only valid so long as the energy is restricted to thermal states of molecules. If a rubber sample is stretched far enough, energy may reside in non-thermal states such as the distortion of chemical bonds and the rule doesn't apply. At low to moderate strains, theory predicts that the required stretching force is due to a change in entropy in the network chains. If this is correct, then we expect that the force necessary to stretch a sample to some value of strain should be proportional to the temperature of the sample. Measurements showing how the tensile stress in a stretched rubber sample varies with temperature are shown in Fig. 4. In these experiments, the strain of a stretched rubber sample was held fixed as the temperature was varied between 10 and 70 degrees Celsius. For each value of fixed strain, it is seen that the tensile stress varied linearly (to within experimental error). These experiments provide the most compelling evidence that entropy changes are the fundamental mechanism for rubber elasticity.
The positive linear behavior of the stress with temperature sometimes leads to the mistaken notion that rubber has a negative coefficient of thermal expansion, i.e. the length of a sample shrinks when heated. Experiments have shown conclusively that, like almost all other materials, the coefficient of thermal expansion natural rubber is positive. | 7 | Physical Chemistry |
The FSP is used when metals properties want to be improved using other metals for support and improvement of the first. This is promising process for the automotive and aerospace industries where new material will need to be developed to improve resistance to wear, creep, and fatigue. (Misha) Examples of materials successfully processed using the friction stir technique include AA 2519, AA 5083 and AA 7075 aluminum alloys, AZ61 magnesium alloy, nickel-aluminium bronze and 304L stainless steel. | 8 | Metallurgy |
The reaction mechanism was first investigated by Scott Searles and coworkers at the University of Missouri. Overall, the reaction can be thought of as a reductive coupling of the carbonyl compound and the terminal alkyne. In the Crabbé reaction, the secondary amine serves as the hydride donor, which results in the formation of the corresponding imine as the byproduct. Thus, remarkably, the secondary amine serves as Brønsted base, ligand for the metal ion, iminium-forming carbonyl activator, and the aforementioned two-electron reductant in the same reaction.
In broad strokes, the mechanism of the reaction is believed to first involve a Mannich-like addition of the species into the iminium ion formed by condensation of the aldehyde and the secondary amine. This first part of the process is a so-called A coupling reaction (A stands for aldehyde-alkyne-amine). In the second part, the α-amino alkyne then undergoes a formal retro-imino-ene reaction, an internal redox process, to deliver the desired allene and an imine as the oxidized byproduct of the secondary amine. These overall steps are supported by deuterium labeling and kinetic isotope effect studies. Density functional theory computations were performed to better understand the second part of the reaction. These computations indicate that the uncatalyzed process (either a concerted but highly asynchronous process or a stepwise process with a fleeting intermediate) involves a prohibitively high-energy barrier. The metal-catalyzed reaction, on the other hand, is energetically reasonable and probably occurs via a stepwise hydride transfer to the alkyne followed by C–N bond scission in a process similar to those proposed for formal [3,3]-sigmatropic rearrangements and hydride transfer reactions catalyzed by gold(I) complexes. A generic mechanism showing the main features of the reaction (under Crabbé's original conditions) is given below:(The copper catalyst is shown simply as "CuBr" or "Cu", omitting any additional amine or halide ligands or the possibility of dinuclear interactions with other copper atoms. Condensation of formaldehyde and diisopropylamine to form the iminium ion and steps involving complexation and decomplexation of Cu are also omitted here for brevity.)
Since 2012, Ma has reported several catalytic enantioselective versions of the Crabbé reaction in which chiral PINAP (aza-BINAP) based ligands for copper are employed. The stepwise application of copper and zinc catalysis was required: the copper promotes the Mannich-type condensation, while subsequent one-step addition of zinc iodide catalyzes the imino-retro-ene reaction. | 0 | Organic Chemistry |
Simple:
* Strontium titanate
* Calcium titanate
* Lead titanate
* Bismuth ferrite
* Lanthanum ytterbium oxide
* Silicate perovskite
* Lanthanum manganite
* Yttrium aluminum perovskite (YAP)
* Lutetium aluminum perovskite (LuAP)
Solid solutions:
* Lanthanum strontium manganite
* LSAT (lanthanum aluminate – strontium aluminum tantalate)
* Lead scandium tantalate
* Lead zirconate titanate
* Methylammonium lead halide
* Methylammonium tin halide
* Formamidinium tin halide | 3 | Analytical Chemistry |
In most of the cases, agrochemicals refer to pesticides.
*Pesticides
**Insecticides
**Herbicides
**Fungicides
**Algaecides
**Rodenticides
**Molluscicides
**Nematicides
*Fertilisers
*Soil conditioners
*Liming and acidifying agents
*Plant growth regulators | 2 | Environmental Chemistry |
Plasma was first identified in laboratory by Sir William Crookes. Crookes presented a lecture on what he called "radiant matter" to the British Association for the Advancement of Science, in Sheffield, on Friday, 22 August 1879.
Systematic studies of plasma began with the research of Irving Langmuir and his colleagues in the 1920s. Langmuir also introduced the term "plasma" as a description of ionized gas in 1928:
Lewi Tonks and Harold Mott-Smith, both of whom worked with Langmuir in the 1920s, recall that Langmuir first used the term by analogy with the blood plasma. Mott-Smith recalls, in particular, that the transport of electrons from thermionic filaments reminded Langmuir of "the way blood plasma carries red and white corpuscles and germs." | 7 | Physical Chemistry |
In glycolysis, glucose and glycerol are metabolized to pyruvate. Glycolysis generates two equivalents of ATP through substrate phosphorylation catalyzed by two enzymes, phosphoglycerate kinase (PGK) and pyruvate kinase. Two equivalents of nicotinamide adenine dinucleotide (NADH) are also produced, which can be oxidized via the electron transport chain and result in the generation of additional ATP by ATP synthase. The pyruvate generated as an end-product of glycolysis is a substrate for the Krebs Cycle.
Glycolysis is viewed as consisting of two phases with five steps each. In phase 1, "the preparatory phase", glucose is converted to 2 d-glyceraldehyde-3-phosphate (g3p). One ATP is invested in Step 1, and another ATP is invested in Step 3. Steps 1 and 3 of glycolysis are referred to as "Priming Steps". In Phase 2, two equivalents of g3p are converted to two pyruvates. In Step 7, two ATP are produced. Also, in Step 10, two further equivalents of ATP are produced. In Steps 7 and 10, ATP is generated from ADP. A net of two ATPs is formed in the glycolysis cycle. The glycolysis pathway is later associated with the Citric Acid Cycle which produces additional equivalents of ATP. | 1 | Biochemistry |
All 3 types of photooxygenation have been applied in the context of organic synthesis. In particular, type II photooxygenations have proven to be the most widely used (due to the low amount of energy required to generate singlet oxygen) and have been described as "one of the most powerful methods for the photochemical oxyfunctionalization of organic compounds." These reactions can proceed in all common solvents and with a broad range of sensitizers.
Many of the applications of type II photooxygenations in organic synthesis come from
Waldemar Adam's investigations into the ene-reaction of singlet oxygen with acyclic alkenes. Through the cis effect and the presence of appropriate steering groups the reaction can even provide high regioselectively and diastereoselectivity - two valuable stereochemical controls. | 5 | Photochemistry |
Sulfuric acid is the most widely used solution to produce an anodized coating. Coatings of moderate thickness 1.8 μm to 25 μm (0.00007" to 0.001") are known as Type II in North America, as named by MIL-A-8625, while coatings thicker than 25 μm (0.001") are known as Type III, hard-coat, hard anodizing, or engineered anodizing. Very thin coatings similar to those produced by chromic anodizing are known as Type IIB. Thick coatings require more process control, and are produced in a refrigerated tank near the freezing point of water with higher voltages than the thinner coatings. Hard anodizing can be made between 13 and 150 μm (0.0005" to 0.006") thick. Anodizing thickness increases wear resistance, corrosion resistance, ability to retain lubricants and PTFE coatings, and electrical and thermal insulation. Sealing Type III will improve corrosion resistance at the cost of reducing abrasion resistance. Sealing will reduce this greatly. Standards for thin (Soft/Standard) sulfuric anodizing are given by MIL-A-8625 Types II and IIB, AMS 2471 (undyed), and AMS 2472 (dyed), BS EN ISO 12373/1 (decorative), BS 3987 (Architectural). Standards for thick sulphuric anodizing are given by MIL-A-8625 Type III, AMS 2469, BS ISO 10074, BS EN 2536 and the obsolete AMS 2468 and DEF STAN 03-26/1. | 8 | Metallurgy |
AFM-IR has been used to study miscibility and phase separation in drug polymer blends, the chemical analysis of nanocrystalline drug particles as small 90 nm across, the interaction of chromosomes with chemotherapeutics drugs, and of amyloids with pharmacological approaches to contrast neurodegeneration. | 3 | Analytical Chemistry |
Degrees of german carbonate hardness (°dKH or ; the dKH is from the German deutsche Karbonathärte) is a unit of water hardness, specifically for temporary or carbonate hardness. Carbonate hardness is a measure of the concentration of carbonates such as calcium carbonate (CaCO) and magnesium carbonate (MgCO) per volume of water. As a unit 1 dKH is the same as 1 °dH which is equal to approximately 0.1786 mmol/L or 17.86 milligrams (mg) of calcium carbonate per litre of water, i.e. 17.86 ppm.
The measurements of total hardness (German Gesamthärte (GH)) and carbonate hardness (German Karbonathärte (KH)) are sometimes stated with units dKH and dGH to differentiate them from one another, although in both cases the unit they are measured in is German degrees (°dH). | 3 | Analytical Chemistry |
A subclass of acylureas known as benzoylureas are insecticides. They act as insect growth regulators by inhibiting the synthesis of chitin resulting in weakened cuticles and preventing molting. Members of this class include diflubenzuron, flufenoxuron, hexaflumuron, lufenuron, and teflubenzuron. | 0 | Organic Chemistry |
Classical molecular dynamics (MD) simulates liquids using Newtons law of motion; from Newtons second law (), the trajectories of molecules can be traced out explicitly and used to compute macroscopic liquid properties like density or viscosity. However, classical MD requires expressions for the intermolecular forces ("F" in Newton's second law). Usually, these must be approximated using experimental data or some other input. | 7 | Physical Chemistry |
Transcription-translation coupling is a mechanism of gene expression regulation in which synthesis of an mRNA (transcription) is affected by its concurrent decoding (translation). In prokaryotes, mRNAs are translated while they are transcribed. This allows communication between RNA polymerase, the multisubunit enzyme that catalyzes transcription, and the ribosome, which catalyzes translation. Coupling involves both direct physical interactions between RNA polymerase and the ribosome ("expressome" complexes), as well as ribosome-induced changes to the structure and accessibility of the intervening mRNA that affect transcription ("attenuation" and "polarity"). | 1 | Biochemistry |
The method outlined by Jordis in 1999 forms the basis for industrial galanthamine production.
This method is based on electrophilic halogenation of 3,4-dimethoxybenzaldehyde 1 (accessible from isovanillin) with bromine / acetic acid to organobromide 2 followed by regioselective demethylation with sulfuric acid to phenol 3. This compound reacts in a reductive amination (sodium borohydride) with tyramine 4 to amine 5 which is formylated with ethyl formate and formic acid in dioxane in the next step to compound 6. An oxidative phenol coupling takes place next with Potassium ferricyanide and potassium carbonate in toluene to 7. The C8a-C14 bond is formed in the first step followed by a Michael addition of the other phenolic group to the newly formed enone group. The reaction step creates two stereocenters leading to two diastereomeric pairs of enantiomers. By the nature of the ABD skeleton the desired S,S/R,R pair is the major product formed and the other pair S,R/R,S is removed in workup. The ketone group is protected as the ketal 8 with 1,2-propylene glycol enabling the organic reduction by lithiumaluminiumhydride of both the bromine group and the formyl group. In the second phase the ketal group is removed (hydrochloric acid) forming racemic (S,S/R,R) narwedine 9.
Enantiopure (−)-narwedine is obtained via the dynamic chiral resolution method pioneered by Shieh/Carlson and in the final step the ketone is reduced to the alcohol with L-selectride.
This final step is enantioselective producing the desired S,S,R compound because the approach of H is restricted to the Si face as the Re face is shielded by the DB ring system. Formation of the S,S,S epimer is also avoided by keeping the reaction temperature below −15 °C. | 0 | Organic Chemistry |
Firefly luciferin (also known as beetle luciferin) is the luciferin, or light-emitting compound, used for the firefly (Lampyridae), railroad worm (Phengodidae), starworm (Rhagophthalmidae), and click-beetle (Pyrophorini) bioluminescent systems. It is the substrate of luciferase (EC 1.13.12.7), which is responsible for the characteristic yellow light emission from many firefly species.
As with all other luciferins, oxygen is required to elicit light; however, it has also been found adenosine triphosphate (ATP) and magnesium are required for light emission. | 1 | Biochemistry |
The International Union of Biochemistry and Molecular Biology (IUBMB) is an international non-governmental organisation concerned with biochemistry and molecular biology. Formed in 1955 as the International Union of Biochemistry (IUB), the union has presently 79 member countries and regions (as of 2020). The Union is devoted to promoting research and education in biochemistry and molecular biology throughout the world, and gives particular attention to localities where the subject is still in its early development. | 1 | Biochemistry |
Exposure limits can be expressed as ceiling limits, a maximal value, short-term exposure limits (STEL), a 15-minute exposure limit or an 8-hour time-weighted average limit (TWA). Below is a sampling, not exhaustive, as less common isocyanates also have specific limits within the United States, and in some regions there are limits on total isocyanate, which recognizes some of the uncertainty regarding the safety of mixtures of chemicals as compared to pure chemical exposures. For example, while there is no OEL for HDI, NIOSH has a REL of 5 ppb for an 8-hour TWA and a ceiling limit of 20 ppb, consistent with the recommendations for MDI. | 0 | Organic Chemistry |
There are two main types of vibrations: free and forced. Free vibrations are the natural or normal modes of vibration for a substance. Forced vibrations are caused by some sort of excitation to make the analyte resonate beyond its normal modes. ARS employs forced vibrations upon the analyte unlike most commonly used techniques which use free vibrations to measure the analyte. ARS excites multiple normal modes by sweeping the excitation frequency of an analyte with no internal vibrations to obtain a resonance spectrum. These resonance frequencies greatly depend on the type of analyte being measured and also depend greatly on the physical properties of the analyte itself (mass, shape, size, etc.). The physical properties will greatly influence the range of frequencies produced by the resonating analyte. In general small analytes have megahertz frequencies while larger analytes can be only a few hundred hertz. The more complex the analyte the more complex the resonance spectrum. | 7 | Physical Chemistry |
Anti-Ro and anti-La antibodies, also known as SS-A and SS-B, respectively, are commonly found in primary Sjögrens syndrome, an autoimmune disorder that affects the exocrine glands. The presence of both antibodies is found in 30–60% of Sjögrens syndrome, anti-Ro antibodies alone are found in 50–70% of Sjögrens syndrome and 30% of SLE with cutaneous involvement, and anti-La antibodies are rarely found in isolation. Anti-La antibodies are also found in SLE; however, Sjögrens syndrome is normally also present. Anti-Ro antibodies are also found less frequently in other disorders including autoimmune liver diseases, coeliac disease, autoimmune rheumatic diseases, cardiac neonatal lupus erythematosus and polymyositis. During pregnancy, anti-Ro antibodies can cross the placenta and cause heart block and neonatal lupus in babies. In Sjögren's syndrome, anti-Ro and anti-La antibodies correlate with early onset, increased disease duration, parotid gland enlargement, disease outside the glands and infiltration of glands by lymphocytes. Anti-Ro antibodies are specific to components of the Ro-RNP complex, comprising 45kDa, 52kDa, 54kDa and 60kDa proteins and RNA. The 60kDa DNA/RNA binding protein and 52kDa T-cell regulatory protein are the best characterised antigens of anti-Ro antibodies. Collectively, these proteins are part of a ribonucleoprotein (RNP) complex that associate with the human Y RNAs, hY1-hY5. The La antigen is a 48kDa transcription termination factor of RNA polymerase III, which associates with the Ro-RNP complex.
The mechanism of antibody production in Sjögrens syndrome is not fully understood, but apoptosis (programmed cell death) and molecular mimicry may play a role. The Ro and La antigens are expressed on the surface of cells undergoing apoptosis and may cause the inflammation within the salivary gland by interaction with cells of the immune system. The antibodies may also be produced through molecular mimicry, where cross reactive antibodies bind to both virus and human proteins. This may occur with one of the antigens, Ro or La, and may subsequently produce antibodies to other proteins through a process known as epitope spreading. The retroviral gag protein shows similarity to the La protein and is proposed as a possible example for molecular mimicry in Sjögrens syndrome. | 1 | Biochemistry |
Ocean turbidity is a measure of the amount of cloudiness or haziness in sea water caused by individual particles that are too small to be seen without magnification. Highly turbid ocean waters are those with many scattering particulates in them. In both highly absorbing and highly scattering waters, visibility into the water is reduced. Highly scattering (turbid) water still reflects much light, while highly absorbing water, such as a blackwater river or lake, is very dark. The scattering particles that cause the water to be turbid can be composed of many things, including sediments and phytoplankton. | 3 | Analytical Chemistry |
Jeewanu protocells are synthetic chemical particles that possess cell-like structure and seem to have some functional living properties. First synthesized in 1963 from simple minerals and basic organics while exposed to sunlight, it is still reported to have some metabolic capabilities, the presence of semipermeable membrane, amino acids, phospholipids, carbohydrates and RNA-like molecules. The nature and properties of the Jeewanu remains to be clarified.
In a similar synthesis experiment a frozen mixture of water, methanol, ammonia and carbon monoxide was exposed to ultraviolet (UV) radiation. This combination yielded large amounts of organic material that self-organised to form globules or vesicles when immersed in water. The investigating scientist considered these globules to resemble cell membranes that enclose and concentrate the chemistry of life, separating their interior from the outside world. The globules were between , or about the size of red blood cells. Remarkably, the globules fluoresced, or glowed, when exposed to UV light. Absorbing UV and converting it into visible light in this way was considered one possible way of providing energy to a primitive cell. If such globules played a role in the origin of life, the fluorescence could have been a precursor to primitive photosynthesis. Such fluorescence also provides the benefit of acting as a sunscreen, diffusing any damage that otherwise would be inflicted by UV radiation. Such a protective function would have been vital for life on the early Earth, since the ozone layer, which blocks out the sun's most destructive UV rays, did not form until after photosynthetic life began to produce oxygen. | 9 | Geochemistry |
An equation similar to that of Kelvin can be derived for the solubility of small particles or droplets in a liquid, by means of the connection between vapour pressure and solubility, thus the Kelvin equation also applies to solids, to slightly soluble liquids, and their solutions if the partial pressure is replaced by the solubility of the solid () (or a second liquid) at the given radius, , and by the solubility at a plane surface (). Hence small particles (like small droplets) are more soluble than larger ones. The equation would then be given by:
These results led to the problem of how new phases can ever arise from old ones. For example, if a container filled with water vapour at slightly below the saturation pressure is suddenly cooled, perhaps by adiabatic expansion, as in a cloud chamber, the vapour may become supersaturated with respect to liquid water. It is then in a metastable state, and we may expect condensation to take place. A reasonable molecular model of condensation would seem to be that two or three molecules of water vapour come together to form a tiny droplet, and that this nucleus of condensation then grows by accretion, as additional vapour molecules happen to hit it. The Kelvin equation, however, indicates that a tiny droplet like this nucleus, being only a few ångströms in diameter, would have a vapour pressure many times that of the bulk liquid. As far as tiny nuclei are concerned, the vapour would not be supersaturated at all. Such nuclei should immediately re-evaporate, and the emergence of a new phase at the equilibrium pressure, or even moderately above it should be impossible. Hence, the over-saturation must be several times higher than the normal saturation value for spontaneous nucleation to occur.
There are two ways of resolving this paradox. In the first place, we know the statistical basis of the second law of thermodynamics. In any system at equilibrium, there are always fluctuations around the equilibrium condition, and if the system contains few molecules, these fluctuations may be relatively large. There is always a chance that an appropriate fluctuation may lead to the formation of a nucleus of a new phase, even though the tiny nucleus could be called thermodynamically unstable. The chance of a fluctuation is e, where ΔS is the deviation of the entropy from the equilibrium value.
It is unlikely, however, that new phases often arise by this fluctuation mechanism and the resultant spontaneous nucleation. Calculations show that the chance, e, is usually too small. It is more likely that tiny dust particles act as nuclei in supersaturated vapours or solutions. In the cloud chamber, it is the clusters of ions caused by a passing high-energy particle that acts as nucleation centers. Actually, vapours seem to be much less finicky than solutions about the sort of nuclei required. This is because a liquid will condense on almost any surface, but crystallization requires the presence of crystal faces of the proper kind.
For a sessile drop residing on a solid surface, the Kelvin equation is modified near the contact line, due to intermolecular interactions between the liquid drop and the solid surface. This extended Kelvin equation is given by
where is the disjoining pressure that accounts for the intermolecular interactions between the sessile drop and the solid and is the Laplace pressure, accounting for the curvature-induced pressure inside the liquid drop. When the interactions are attractive in nature, the disjoining pressure, is negative. Near the contact line, the disjoining pressure dominates over the Laplace pressure, implying that the solubility, is less than . This implies that a new phase can spontaneously grow on a solid surface, even under saturation conditions. | 7 | Physical Chemistry |
Ram Charan Mehrotra was born in a middle-class family on 16 February 1922 in Kanpur in the Indian state of Uttar Pradesh to Ram Bharose Mehrotra, a small-time cloth merchant and his homemaker wife, Chameli Devi. He lost both his parents before he turned 10 and had to continue his studies depending on merit scholarships and part-time jobs like private tuition. His primary schooling was at Municipal School, Kanpur and later he joined Christ Church School (present-day Christ Church College, Kanpur) from where he passed the intermediate course, standing first in the state. Joining the University of Allahabad in 1939 for his graduate studies, he completed the course on the strength of three scholarships and passed BSc with Mathematics, Physics and Chemistry as optional subjects. He continued at the university for MSc in chemistry which he passed with first rank in 1943. During this period, he was also involved in student politics in connection with the Quit India Movement of 1942 and had to stay away from studies for four months.
Before starting his formal academic career by joining Allahabad University in 1944 as a member of faculty of inorganic chemistry, Mehrotra worked at Vigyan Kala Bhawan, Daurala, a local learning centre involved in teaching science to prospective young entrepreneurs, for ten months during 1943–44 and was also associated with Vigyan Pragati, a science magazine published by National Institute of Science Communication and Information Resources (NISCAIR) of the Council of Scientific and Industrial Research. He served the university till 1954; in between, he had a short stint of two years at Birkbeck College from 1950 to 1952 as a British Council Fellow and part-time faculty, working with Donald Charlton Bradley; he utilised this period to secure a PhD from the University of London in 1952. He returned to India the same year and resumed his service at Allahabad University when he was offered the position of a reader at Lucknow University in 1954. After serving four years there, he moved to Gorakhpur University in 1958 as a professor where, a year later, he was promoted as the dean of the faculty of science. It was during this time, he served as a member of the Review Committee in Chemistry of the University Grants Commission of India under the chairmanship of T. R. Seshadri, where his colleagues included Asima Chatterjee, a noted chemist.
In 1962, on invitation of Mohan Sinha Mehta, the then vice chancellor of the University of Rajasthan, he took up the post of a professor and head of the newly formed chemistry department and served the institution for two decades. In between, he had a five-year stint as the vice chancellor of Delhi University (from 1974 to 1979) and a short assignment as a UGC National Fellow in December 1979 but on completion of those assignments, he returned to Rajasthan University, where he stayed till 1982; on his move from the university, he was made an emeritus professor. That year, he became associated with the activities of the University Grants Commission, first as the chairman of the Commission on Revision of Pay Scales to Teachers which submitted its report to UGC in 1986. Simultaneously, when the National Commission on Teachers was constituted by the Government of India in 1983 under the chairmanship of D. P. Chattopadhyaya, he was appointed as a member of the Research Advisory Committee. After his assignment with the committee, he took up the chair of the Book Writing Project of the National Council of Educational Research and Training (NCERT) and in 1991, he was appointed as the vice chancellor of the University of Allahabad, a position he held in 1993.
Mehrotra was married to Suman, a Hindi scholar, whom he married in 1944 around the same time when he joined Allahabad University. The couple had two daughters, Rashmi and Shalini and one son, Piyush Mehrotra, in between. He died on 11 July 2004, reportedly due to chronic obstructive pulmonary disease, at the age of 82. | 0 | Organic Chemistry |
Butterfly wings possess not only ultra-hydrophobic trait but also directional adhesive characteristics. If the water bead is along the radial outward (RO) direction from the body’s central axis, it rolls off and cleans the dirt away, leading to self-cleaning. On the other hand, if droplets stand against the opposite direction, they are pinned at the surface, leading adhesion and securing the flight stability of the butterfly by preventing deposit of dirt on the wings near the center of the body. SEM micrographs of wings exhibit hierarchy along the RO direction, arising from aligned microgrooves, covered by fine lamella-stacking nanostripes. | 7 | Physical Chemistry |
In static methods a mixture is brought to equilibrium and the concentration of a species in the solution phase is determined by chemical analysis. This usually requires separation of the solid and solution phases. In order to do this the equilibration and separation should be performed in a thermostatted room. Very low concentrations can be measured if a radioactive tracer is incorporated in the solid phase.
A variation of the static method is to add a solution of the substance in a non-aqueous solvent, such as dimethyl sulfoxide, to an aqueous buffer mixture. Immediate precipitation may occur giving a cloudy mixture. The solubility measured for such a mixture is known as "kinetic solubility". The cloudiness is due to the fact that the precipitate particles are very small resulting in Tyndall scattering. In fact the particles are so small that the particle size effect comes into play and kinetic solubility is often greater than equilibrium solubility. Over time the cloudiness will disappear as the size of the crystallites increases, and eventually equilibrium will be reached in a process known as precipitate ageing. | 7 | Physical Chemistry |
For purposes of law enforcement, blood alcohol content is used to define intoxication and provides a rough measure of impairment. Although the degree of impairment may vary among individuals with the same blood alcohol content, it can be measured objectively and is therefore legally useful and difficult to contest in court. Most countries forbid operation of motor vehicles and heavy machinery above prescribed levels of blood alcohol content. Operation of boats and aircraft is also regulated. Some jurisdictions also regulate bicycling under the influence. The alcohol level at which a person is considered legally impaired to drive varies by country. | 1 | Biochemistry |
The affinity constants, k and k, of the 1879 paper can now be recognised as rate constants. The equilibrium constant, K, was derived by setting the rates of forward and backward reactions to be equal. This also meant that the chemical affinities for the forward and backward reactions are equal. The resultant expression
is correct even from the modern perspective, apart from the use of concentrations instead of activities (the concept of chemical activity was developed by Josiah Willard Gibbs, in the 1870s, but was not widely known in Europe until the 1890s). The derivation from the reaction rate expressions is no longer considered to be valid. Nevertheless, Guldberg and Waage were on the right track when they suggested that the driving force for both forward and backward reactions is equal when the mixture is at equilibrium. The term they used for this force was chemical affinity. Today the expression for the equilibrium constant is derived by setting the chemical potential of forward and backward reactions to be equal. The generalisation of the law of mass action, in terms of affinity, to equilibria of arbitrary stoichiometry was a bold and correct conjecture.
The hypothesis that reaction rate is proportional to reactant concentrations is, strictly speaking, only true for elementary reactions (reactions with a single mechanistic step), but the empirical rate expression
is also applicable to second order reactions that may not be concerted reactions. Guldberg and Waage were fortunate in that reactions such as ester formation and hydrolysis, on which they originally based their theory, do indeed follow this rate expression.
In general many reactions occur with the formation of reactive intermediates, and/or through parallel reaction pathways. However, all reactions can be represented as a series of elementary reactions and, if the mechanism is known in detail, the rate equation for each individual step is given by the expression so that the overall rate equation can be derived from the individual steps. When this is done the equilibrium constant is obtained correctly from the rate equations for forward and backward reaction rates.
In biochemistry, there has been significant interest in the appropriate mathematical model for chemical reactions occurring in the intracellular medium. This is in contrast to the initial work done on chemical kinetics, which was in simplified systems where reactants were in a relatively dilute, pH-buffered, aqueous solution. In more complex environments, where bound particles may be prevented from disassociation by their surroundings, or diffusion is slow or anomalous, the model of mass action does not always describe the behavior of the reaction kinetics accurately. Several attempts have been made to modify the mass action model, but consensus has yet to be reached. Popular modifications replace the rate constants with functions of time and concentration. As an alternative to these mathematical constructs, one school of thought is that the mass action model can be valid in intracellular environments under certain conditions, but with different rates than would be found in a dilute, simple environment .
The fact that Guldberg and Waage developed their concepts in steps from 1864 to 1867 and 1879 has resulted in much confusion in the literature as to which equation the law of mass action refers. It has been a source of some textbook errors. Thus, today the "law of mass action" sometimes refers to the (correct) equilibrium constant formula,
and at other times to the (usually incorrect) rate formula. | 7 | Physical Chemistry |
Fourier-transform spectroscopy is a measurement technique whereby spectra are collected based on measurements of the coherence of a radiative source, using time-domain or space-domain measurements of the radiation, electromagnetic or not. It can be applied to a variety of types of spectroscopy including optical spectroscopy, infrared spectroscopy (FTIR, FT-NIRS), nuclear magnetic resonance (NMR) and magnetic resonance spectroscopic imaging (MRSI), mass spectrometry and electron spin resonance spectroscopy.
There are several methods for measuring the temporal coherence of the light (see: field-autocorrelation), including the continuous-wave and the pulsed Fourier-transform spectrometer or Fourier-transform spectrograph.
The term "Fourier-transform spectroscopy" reflects the fact that in all these techniques, a Fourier transform is required to turn the raw data into the actual spectrum, and in many of the cases in optics involving interferometers, is based on the Wiener–Khinchin theorem. | 7 | Physical Chemistry |
In the adult brain, the endocannabinoid system facilitates the neurogenesis of hippocampal granule cells. In the subgranular zone of the dentate gyrus, multipotent neural progenitors (NP) give rise to daughter cells that, over the course of several weeks, mature into granule cells whose axons project to and synapse onto dendrites on the CA3 region. NPs in the hippocampus have been shown to possess fatty acid amide hydrolase (FAAH) and express CB and utilize 2-AG. Intriguingly, CB activation by endogenous or exogenous cannabinoids promote NP proliferation and differentiation; this activation is absent in CB knockouts and abolished in the presence of antagonist. | 1 | Biochemistry |
Malachite green is traditionally used as a dye. Kilotonnes of MG and related triarylmethane dyes are produced annually for this purpose.
MG is active against the oomycete Saprolegnia, which infects fish eggs in commercial aquaculture, MG has been used to treat Saprolegnia and is used as an antibacterial. It is a very popular treatment against Ichthyophthirius multifiliis in freshwater aquaria. The principal metabolite, leuco-malachite green (LMG), is found in fish treated with malachite green, and this finding is the basis of controversy and government regulation. See also Antimicrobials in aquaculture.
MG has frequently been used to catch thieves and pilferers. The bait, usually money, is sprinkled with the anhydrous powder. Anyone handling the contaminated money will find that on upon washing the hands, a green stain on the skin that lasts for several days will result. | 3 | Analytical Chemistry |
The mechanism of thiol–disulfide exchange between oxidoreductases is understood to begin with the nucleophilic attack on the sulfur atoms of a disulfide bond in the oxidised partner, by a thiolate anion derived from a reactive cysteine in a reduced partner. This generates mixed disulfide intermediates, and is followed by a second, this time intramolecular, nucleophilic attack by the remaining thiolate anion in the formerly reduced partner, to liberate both oxidoreductases. The balance of evidence discussed thus far supports a model in which oxidising equivalents are sequentially transferred from Ero1 via a thiol–disulfide exchange reaction to PDI, with PDI then undergoing a thiol–disulfide exchange with the nascent polypeptide, thereby enabling the formation of disulfide bonds within the nascent polypeptide. | 1 | Biochemistry |
Some synthetic macromolecules, such as catenanes and rotaxanes, dendrimers and hyperbranched polymers, and other assemblies, have molecular weights extending into the thousands or tens of thousands, where most ionization techniques have difficulty producing molecular ions. MALDI is a simple and fast analytical method that can allow chemists to rapidly analyze the results of such syntheses and verify their results. | 1 | Biochemistry |
Oxidation with dioxiranes refers to the introduction of oxygen into organic molecules through the action of a dioxirane. Dioxiranes are well known for their oxidation of alkenes to epoxides; however, they are also able to oxidize other unsaturated functionality, heteroatoms, and alkane C-H bonds. | 0 | Organic Chemistry |
The stability of emulsions can be characterized using techniques such as light scattering, focused beam reflectance measurement, centrifugation, and rheology. Each method has advantages and disadvantages. | 7 | Physical Chemistry |
The M30 Apoptosense® ELISA is a PEVIVA product owned by VLVbio (Nacka, Sweden) and was developed in collaboration with the Karolinska Institute in 2000.
Distributors:
* In the United States and Canada, the Peviva products are distributed by DiaPharma Group, Inc
* In the United Kingdom, the products are distributed by bioaxxess
* China - Boppard CO., Ltd.
* Distributors in Japan - Funakoshi Co., Ltd
* In Germany, Switzerland and Benelux, the products are distributed by TECOmedical | 1 | Biochemistry |
In organic chemistry, HPO can be used for the reduction of arenediazonium salts, converting to Ar–H. When diazotized in a concentrated solution of hypophosphorous acid, an amine substituent can be removed from arenes.
Owing to its ability to function as a mild reducing agent and oxygen scavenger it is sometimes used as an additive in Fischer esterification reactions, where it prevents the formation of colored impurities.
It is used to prepare phosphinic acid derivatives. | 0 | Organic Chemistry |
* Aircraft observations. Many aircraft campaigns have been conducted as part of the [https://web.archive.org/web/20070214031222/http://suborbital.nasa.gov/ Suborbital Science Program] and by the [https://web.archive.org/web/20060930215700/http://www.espo.nasa.gov/project/mission2.html Earth Science Project Office] an overview of these campaigns is available. The data can be accessed from the Earth Science Project Office [http://espoarchive.nasa.gov/archive/arcs/ archives].
* MOZAIC observations. The [https://web.archive.org/web/20070224072918/http://mozaic.aero.obs-mip.fr/web/ MOZAIC] program (Measurement of OZone and water vapour by AIrbus in-service airCraft) was initiated in 1993 by European scientists, aircraft manufacturers and airlines to collect experimental data. Its goal is to help understand the atmosphere and how it is changing under the influence of human activity, with particular interest in the effects of aircraft. MOZAIC consists of automatic and regular measurements of ozone and water vapour by five long range passenger airliners flying all over the world. The aim is to build a large database of measurements to allow studies of chemical and physical processes in the atmosphere, and hence to validate global chemistry transport models. MOZAIC data provide, in particular, detailed ozone and water vapour climatologies at 9–12 km where subsonic aircraft emit most of their exhaust and which is a very critical domain (e.g. radiatively and S/T exchanges) still imperfectly described in existing models. This will be valuable to improve knowledge about the processes occurring in the upper troposphere/ lower stratosphere (UT/LS), and the model treatment of near tropopause chemistry and transport. The MOZAIC data is restricted access, to obtain access the [https://web.archive.org/web/20070108203102/http://mozaic.aero.obs-mip.fr/web/features/database/access.html forms] need to be filled out.
* CARIBIC observations. The [http://www.caribic-atmospheric.com CARIBIC] (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) project is an innovative scientific project to study and monitor important chemical and physical processes in the Earth's atmosphere. Detailed and extensive measurements are made during long distance flights on board the Airbus A340-600 "Leverkusen" (http://www.flightradar24.com/data/airplanes/D-AIHE/). We deploy an airfreight container with automated scientific apparatuses, which are connected to an air and particle (aerosol) inlet underneath the aircraft. In contrast to MOZAIC, CARIBIC is only installed on one aircraft, but it measures a much wider spectrum of atmospheric constituents ([http://www.caribic-atmospheric.com/ CARIBIC -> instrumentation]). Both, CARIBIC and MOZAIC are integrated in [http://www.iagos.org IAGOS]. Data exist from 1998-2002 and from 2004-today. It can be requested via [http://www.caribic-atmospheric.com/ CARIBIC -> data access]. | 2 | Environmental Chemistry |
Functional genomics includes function-related aspects of the genome itself such as mutation and polymorphism (such as single nucleotide polymorphism (SNP) analysis), as well as the measurement of molecular activities. The latter comprise a number of "-omics" such as transcriptomics (gene expression), proteomics (protein production), and metabolomics. Functional genomics uses mostly multiplex techniques to measure the abundance of many or all gene products such as mRNAs or proteins within a biological sample. A more focused functional genomics approach might test the function of all variants of one gene and quantify the effects of mutants by using sequencing as a readout of activity. Together these measurement modalities endeavor to quantitate the various biological processes and improve our understanding of gene and protein functions and interactions. | 1 | Biochemistry |
A reservoir is a thermodynamic system which controls the state of a system, usually by "imposing" itself upon the system being controlled. This means that the nature of its contact with the system can be controlled. A reservoir is so large that its thermodynamic state is not appreciably affected by the state of the system being controlled. The term "atmospheric pressure" in the below description of a theoretical thermometer is essentially a "pressure reservoir" which imposes atmospheric pressure upon the thermometer.
Some common reservoirs are:
* Pressure reservoir - by far the most common pressure reservoir is the Earth's atmosphere.
* Temperature reservoir - A large quantity of water at its triple point forms an effective temperature reservoir. | 7 | Physical Chemistry |
One is known as "stockpile management," whereby an analyzer located upstream of the pile is able to track the cumulative chemistry of the pile. This allows the operator to direct haul trucks to different sections of the quarry in a way that will result in the final elemental composition of the pile close to target. | 3 | Analytical Chemistry |
Froth flotation is one of the processes used to recover recycled paper. In the paper industry this step is called deinking or just flotation. The target is to release and remove the hydrophobic contaminants from the recycled paper. The contaminants are mostly printing ink and stickies. Normally the setup is a two-stage system with 3,4 or 5 flotation cells in series.
* pH control: sodium silicate and sodium hydroxide
* Calcium ion source: hard water, lime or calcium chloride
* Collector: fatty acid, fatty acid emulsion, fatty acid soap and/or organo-modified siloxane | 8 | Metallurgy |
Glycogen is a multi-branched polysaccharide. It is primary means of glucose storage in animal cells. In the human body, the two main tissues which store glycogen are liver and skeletal muscle. Glycogen is typically more concentrated in the liver, but because humans have much more muscle mass, our muscles store about three quarters of the total glycogen in our body. | 1 | Biochemistry |
Solvent extraction and electrowinning (SX/EW) is a two-stage hydrometallurgical process that first extracts and upgrades copper ions from low-grade leach solutions into a solvent containing a chemical that selectively reacts with and binds the copper in the solvent. The copper is extracted from the solvent with strong aqueous acid which then deposits pure copper onto cathodes using an electrolytic procedure (electrowinning).
SX/EW processing is best known for its use by the copper industry, where it accounts for 20% of worldwide production, but the technology is also successfully applied to a wide range of other metals including cobalt, nickel, zinc and uranium. | 8 | Metallurgy |
Because these alloys are intended for high temperature applications their creep and oxidation resistance are of primary importance. Nickel (Ni)-based superalloys are the material of choice for these applications because of their unique γ' precipitates. The properties of these superalloys can be tailored to a certain extent through the addition of various other elements, common or exotic, including not only metals, but also metalloids and nonmetals; chromium, iron, cobalt, molybdenum, tungsten, tantalum, aluminium, titanium, zirconium, niobium, rhenium, yttrium, vanadium, carbon, boron or hafnium are some examples of the alloying additions used. Each addition serves a particular purpose in optimizing properties.
Creep resistance is dependent, in part, on slowing the speed of dislocation motion within a crystal structure. In modern Ni-based superalloys, the γ-Ni(Al,Ti) phase acts as a barrier to dislocation. For this reason, this γ; intermetallic phase, when present in high volume fractions, increases the strength of these alloys due to its ordered nature and high coherency with the γ matrix. The chemical additions of aluminum and titanium promote the creation of the γ phase. The γ phase size can be precisely controlled by careful precipitation strengthening heat treatments. Many superalloys are produced using a two-phase heat treatment that creates a dispersion of cuboidal γ particles known as the primary phase, with a fine dispersion between these known as secondary γ. In order to improve the oxidation resistance of these alloys, Al, Cr, B, and Y are added. The Al and Cr form oxide layers that passivate the surface and protect the superalloy from further oxidation while B and Y are used to improve the adhesion of this oxide scale to the substrate. Cr, Fe, Co, Mo and Re all preferentially partition to the γ matrix while Al, Ti, Nb, Ta, and V preferentially partition to the γ' precipitates and solid solution strengthen the matrix and precipitates respectively. In addition to solid solution strengthening, if grain boundaries are present, certain elements are chosen for grain boundary strengthening. B and Zr tend to segregate to the grain boundaries which reduces the grain boundary energy and results in better grain boundary cohesion and ductility. Another form of grain boundary strengthening is achieved through the addition of C and a carbide former, such as Cr, Mo, W, Nb, Ta, Ti, or Hf, which drives precipitation of carbides at grain boundaries and thereby reduces grain boundary sliding. | 8 | Metallurgy |
Test samples are filtered through standard filter paper and then transferred to M-endo or LES Endo Agar mediums. Colonies appear pinkish-red with green metallic sheen after 22–24 hours of incubation. These colonies can be confirmed as coliforms if they are inoculated in lauryl tryptose (LST), produce gas, and then inoculated in BGLB. If there is gas production in the BGLB tubes, the test is positive for the presence of coliform bacteria. | 3 | Analytical Chemistry |
Terminal inverted repeats have been observed in the DNA of various eukaryotic transposons, even though their source remains unknown. Inverted repeats are principally found at the origins of replication of cell organism and organelles that range from phage plasmids, mitochondria, and eukaryotic viruses to mammalian cells. The replication origins of the phage G4 and other related phages comprise a segment of nearly 139 nucleotide bases that include three inverted repeats that are essential for replication priming. | 1 | Biochemistry |
Currently there are many methods used to determine the zygosity status of a gene at a particular locus. These methods include the use of PCR with specifically designed probes to detect the variants of the genes (SNP typing is the simplest case). In cases where longer stretches of variation is implicated, post PCR analysis of the amplicons may be required. Changes in enzyme restriction, electrophoretic and chromatographic profiles can be measured. These methods are usually more time-consuming and increase the risk of amplicon contamination in the laboratory, due to the need to work with high concentrations of amplicons in the lab post-PCR. The use of HRM reduces the time required for analysis and the risk of contamination. HRM is a more cost-effective solution and the high resolution element not only allows the determination of homo and heterozygosity, it also resolves information about the type of homo and heterozygosity, with different gene variants giving rise to differing melt curve shapes. A study by Gundry et al. 2003, showed that fluorescent labelling of one primer (in the pair) has been shown to be favourable over using an intercalating dye such as SYBR green I. However, progress has been made in the development and use of improved intercalating dyes which reduce the issue of PCR inhibition and concerns over non-saturating intercalation of the dye. | 1 | Biochemistry |
Zero-point energy has many observed physical consequences. It is important to note that zero-point energy is not merely an artifact of mathematical formalism that can, for instance, be dropped from a Hamiltonian by redefining the zero of energy, or by arguing that it is a constant and therefore has no effect on Heisenberg equations of motion without latter consequence. Indeed, such treatment could create a problem at a deeper, as of yet undiscovered, theory. For instance, in general relativity the zero of energy (i.e. the energy density of the vacuum) contributes to a cosmological constant of the type introduced by Einstein in order to obtain static solutions to his field equations. The zero-point energy density of the vacuum, due to all quantum fields, is extremely large, even when we cut off the largest allowable frequencies based on plausible physical arguments. It implies a cosmological constant larger than the limits imposed by observation by about 120 orders of magnitude. This "cosmological constant problem" remains one of the greatest unsolved mysteries of physics. | 7 | Physical Chemistry |
The use of bracken fern as human food is mainly a historical question. The rhizomes of these plants served as human food in Scotland during the First World War. In America (USA, Canada), Russia, China and Japan, fern is grown commercially for human use. The usual procedure that is performed before eating the plant is to pre-treat the fern with boiling water in the presence of different chemicals, such as sodium bicarbonate and wood ash, to degrade or inactivate ptaquiloside and other toxic agents. Nevertheless, some carcinogenic activity persists even after the treatment. As shown by Kamon and Hirayama, the risk of oesophageal cancer was increased approximately by 2.1 in men and 3.7 in women who regularly consume bracken in Japan. Recent researches have suggested that sulfur-containing amino acids can potentially be used under appropriate conditions as detoxifying agents for ptaquiloside and selenium supplementation can prevent as well as reverse the immunotoxic effects induced by ptaquiloside.
Ptaquiloside in the aqueous extract of bracken can be detected using different instrumental methods: thin-layer chromatography–densitometry (TLC-densitometry), high-performance liquid chromatography (HPLC), gas chromatography–mass spectrometry (GCMS), and liquid chromatography–mass spectrometry (LC-MS). The diagnostic tests of ptaquiloside inside cells include gene mutation detection, immunohistochemical detection of tumor biomarkers, chromosomal aberrations, oxidative stress for EBH, PCR, real-time PCR and DNase-SISPA (sequence-independent single primer amplification). | 0 | Organic Chemistry |
The surface of a metal oxide consists of ordered arrays of acid–base centres. The cationic metal centres act as Lewis acid sites while the anionic oxygen centres act as Lewis bases. Surface hydroxyl groups can serve as Brønsted acid or base sites as they can give up or accept a proton. The surface of most metal oxides will be, to some extent, hydroxylated under normal conditions when water vapor is present. The strength and the amount of Lewis And Brønsted acid–base sites will determine the catalytic activity of many metal oxides. Due to this there is a great need to develop standard methods for the characterization of the strength, concentration, and distribution of surface acid–base sites.
The concepts of Lewis acid–base theory and Brønsted–Lowry acid–base theory may be applied to surfaces, however there is no general theory that serves to determine surface acidity or basicity. The qualitative treatment of Brønsted acid base theory is based on the thermodynamic equilibrium constant (K) of acid–base reactions between individual molecules in homogeneous systems. This treatment requires measurement of equilibrium concentrations of reactants and products. The presence of two phases also provides a problem for the quantitative acid–base determination of solids. When an acid or base is adsorbed on to an oxide surface it will perturb neighbouring acid–base sites. This perturbation will inevitably influence the relaxation of the surface and make it impossible to have acid–base reactions at the surface which only involve a single surface site. | 7 | Physical Chemistry |
Richard Llewellyns novel How Green Was My Valley (1939) describes the social and environmental effects of coal mining in Wales at the turn of the 20th century. The local mines spoil tip, which he calls a slag heap, is the central figure of devastation. Eventually the pile overtakes the entire valley and crushes Huw Morgan's house: | 8 | Metallurgy |
The Federation of Analytical Chemistry and Spectroscopy Societies or FACSS is a scientific society incorporated on June 28, 1972, with the goal of promoting research and education in analytical chemistry. The organization combined the many smaller meetings of the individual societies into an annual meeting that includes all of analytical chemistry. The meetings are intended to provide a forum for scientists to address the development of analytical chemistry, chromatography, and spectroscopy.
The society's main activity is its annual conference held every fall. These conference offer plenary sessions, workshops, job fairs, oral presentations, poster presentations, and conference networking events. The conference was held internationally for the first time in 1999 when it was hosted in Vancouver, BC. The annual conference is often discussed in the journal Applied Spectroscopy, Spectroscopy Magazine, and American Pharmaceutical Reviews.
At the 2011 FACSS Conference in Reno, NV, the FACSS organization changed the name of the annual conference to SciX. The first [http://scixconference.org/ SciX Conference] presented by FACSS was held in Kansas City, MO in 2012. The name change was discussed in Spectroscopy in fall 2011:
[https://archive.today/20130123212653/http://spectroscopyonline.findanalytichem.com/spectroscopy/article/articleDetail.jsp?id=744507]
[http://blogs.rsc.org/ja/2011/10/27/facss-names-their-annual-scientific-conference-scix/]. More information about the new name can be found at scixconference.org | 7 | Physical Chemistry |
One measure of air pollution used in air quality standards is the atmospheric concentration of particulate matter. This measure is usually expressed in μg/m (micrograms per cubic metre). In the current EU emission norms for cars, vans, and trucks and in the upcoming EU emission norm for non-road mobile machinery, particle number measurements and limits are defined, commonly referred to as PN, with units [#/km] or [#/kWh]. In this case, PN expresses a quantity of particles per unit distance (or work). | 7 | Physical Chemistry |
There are three major approaches to single-cell proteomics: antibody based methods, fluorescent protein based methods, and mass-spectroscopy based methods. | 1 | Biochemistry |
An ylide () or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms have full octets of electrons. The result can be viewed as a structure in which two adjacent atoms are connected by both a covalent and an ionic bond; normally written X–Y. Ylides are thus 1,2-dipolar compounds, and a subclass of zwitterions. They appear in organic chemistry as reagents or reactive intermediates.
The class name "ylide" for the compound should not be confused with the suffix "-ylide". | 0 | Organic Chemistry |
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