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Several factors influence the energy penalty associated with the allylic strain. In order to relieve strain caused by interaction between the two methyl groups, the cyclohexanes will often exhibit a boat or twist-boat conformation. The boat conformation tends to be the major conformation to the strain. The effect of allylic strain on cis alkenes creates a preference for more linear structures. | 0 | Theoretical and Fundamental Chemistry |
By applying an additional electrode on a nanochannel as the gate electrode, it is possible to adjust the electrical potential inside the channel. A nanofluidic field-effect transistor can be made of silica nanotubes with an oxide as the dielectric material between the metal gate electrode and the channel. The tuning of the ionic current, therefore, can be achieved by changing the voltage applied on the gate. The gate bias and the source-drain bias are applied to adjust the cation and anion concentration within the nanochannel, therefore tuning the ionic current flowing through it.
This concept is an analogy to the structure of a metal-oxide semiconductor field-effect transistor (MOSFET) in electronic circuits. Similar to a MOSFET, a nanofluidic transistor is the fundamental element for building a nanofluidic circuitry. There is possibility to achieve a nanofluidic circuitry, which is capable of logic operation and manipulation for ionic particles.
Since the conductance of ionic current flow is controlled by the gate voltage, using a material with high dielectric constant as the wall of the channel is desired. In this case, there is a stronger field seen within the channel due to a higher gate capacitance. A channel surface with a low surface charge is also desired in order to strengthen the effect of potential tuning by gate electrode. This increases the ability to spatially and temporally tune the ionic and electrostatic environment in the channel. | 0 | Theoretical and Fundamental Chemistry |
Bacteria such as green sulfur bacteria and purple sulfur bacteria, which exist where the photic zone overlaps with euxinic water masses, leave pigments behind in sediments. These pigments can be used to identify past euxinic conditions. The pigments used to identify past presence of green sulfur bacteria are chlorobactane and isorenieratene. The pigments used to identify past presence of purple sulfur bacteria is okenane. | 0 | Theoretical and Fundamental Chemistry |
A risk of ovarian stimulation is the development of ovarian hyperstimulation syndrome, particularly if hCG is used for inducing final oocyte maturation. This results in swollen, painful ovaries. It occurs in 30% of patients. Mild cases can be treated with over the counter medications and cases can be resolved in the absence of pregnancy. In moderate cases, ovaries swell and fluid accumulated in the abdominal cavities and may have symptoms of heartburn, gas, nausea or loss of appetite. In severe cases, patients have sudden excess abdominal pain, nausea, vomiting and will result in hospitalisation.
During egg retrieval, there exists a small chance of bleeding, infection, and damage to surrounding structures such as bowel and bladder (transvaginal ultrasound aspiration) as well as difficulty in breathing, chest infection, allergic reactions to medication, or nerve damage (laparoscopy).
Ectopic pregnancy may also occur if a fertilised egg develops outside the uterus, usually in the fallopian tubes and requires immediate destruction of the foetus.
IVF does not seem to be associated with an elevated risk of cervical cancer, nor with ovarian cancer or endometrial cancer when neutralising the confounder of infertility itself. Nor does it seem to impart any increased risk for breast cancer.
Regardless of pregnancy result, IVF treatment is usually stressful for patients. Neuroticism and the use of escapist coping strategies are associated with a higher degree of distress, while the presence of social support has a relieving effect. A negative pregnancy test after IVF is associated with an increased risk for depression, but not with any increased risk of developing anxiety disorders. Pregnancy test results do not seem to be a risk factor for depression or anxiety among men when the relationships is between two cisgender, heterosexual people. Hormonal agents such as gonadotropin-releasing hormone agonist (GnRH agonist) are associated with depression.
Studies show that there is an increased risk of venous thrombosis or pulmonary embolism during the first trimester of IVF. When looking at long-term studies comparing patients who received or did not receive IVF, there seems to be no correlation with increased risk of cardiac events. There are more ongoing studies to solidify this.
Spontaneous pregnancy has occurred after successful and unsuccessful IVF treatments. Within 2 years of delivering an infant conceived through IVF, subfertile patients had a conception rate of 18%. | 1 | Applied and Interdisciplinary Chemistry |
Ionic additives, such as ammonium acetate and ammonium formate, are usually used to control the mobile phase pH and ion strength. In HILIC they can also contribute to the polarity of the analyte, resulting in differential changes in retention. For extremely polar analytes (e.g. aminoglycoside antibiotics (gentamicin) or adenosine triphosphate), higher concentrations of buffer (c. 100 mM) are required to ensure that the analyte will be in a single ionic form. Otherwise, asymmetric peak shape, chromatographic tailing, and/or poor recovery from the stationary phase will be observed. For the separation of neutral polar analytes (e.g. carbohydrates), no buffer is necessary.
Other salts, such as 100–300 mM sodium perchlorate, that are soluble in high-organic solvent mixtures (c. 70–90% acetonitrile), can be used to increase the mobile phase polarity to affect elution These salts are not volatile, so this technique is less useful with a mass spectrometer as the detector. Usually a gradient (to increasing amounts of water) is enough to promote elution.
All ions partition into the stationary phase to some degree, so an occasional "wash" with water is required to ensure a reproducible stationary phase. | 1 | Applied and Interdisciplinary Chemistry |
Industrial & Engineering Chemistry Research is a peer-reviewed scientific journal published by the American Chemical Society covering all aspects of chemical engineering. The editor-in-chief is Phillip E. Savage (Pennsylvania State University). | 1 | Applied and Interdisciplinary Chemistry |
Ribosome-mediated attenuation is a gene expression mechanism in which a transcriptional termination signal is regulated by translation. Attenuation occurs at the start of some prokaryotic operons at sequences called "attenuators", which have been identified in operons encoding amino acid biosynthesis enzymes, pyrimidine biosynthesis enzymes and antibiotic resistance factors. The attenuator functions via a set of mRNA sequence elements that coordinate the status of translation to a transcription termination signal:
* A short open reading frame encoding a "leader peptide"
* A transcription pause sequence
* A "control region"
* A transcription termination signal
Once the start of the leader open reading frame has been transcribed, RNA polymerase pauses due to folding of the nascent mRNA. This programmed arrest of transcription gives time for translation of the leader peptide to commence, and transcription to resume once coupled to translation. The downstream "control region" then modulates the elongation rate of either the ribosome or RNA polymerase. The factor determining this depends on the function of the downstream genes (e.g. the operon encoding enzymes involved in the synthesis of histidine contains a series of histidine codons is the control region). The role of the control region is to modulate whether transcription remains coupled to translation depending on the cellular state (e.g. a low availability of histidine slows translation leading to uncoupling, while high availability of histidine permits efficient translation and maintains coupling). Finally, the transcription terminator sequence is transcribed. Whether transcription is coupled to translation determines whether this stops transcription. The terminator requires folding of the mRNA, and by unwinding mRNA structures the ribosome elects the formation of either of two alternative structures: the terminator, or a competing fold termed the "antiterminator".
For amino acid biosynthesis operons, these allow the gene expression machinery to sense the abundance of the amino acid produced by the encoded enzymes, and adjust the level of downstream gene expression accordingly: transcription occurring only if the amino acid abundance is low and the demand for the enzymes is therefore high. Examples include the histidine (his) and tryptophan (trp) biosynthetic operons.
The term "attenuation" was introduced to describe the his operon. While it is typically used to describe biosynthesis operons of amino acids and other metabolites, programmed transcription termination that does not occur at the end of a gene was first identified in λ phage. The discovery of attenuation was significant as it represented a regulatory mechanism distinct from repression. The trp operon is regulated by both attenuation and repression, and was the first evidence that gene expression regulation mechanisms can be overlapping or redundant. | 1 | Applied and Interdisciplinary Chemistry |
Alarm signals need not be communicated only by auditory means. For example, many animals may use chemosensory alarm signals, communicated by chemicals known as pheromones. Minnows and catfish release alarm pheromones (Schreckstoff) when injured, which cause nearby fish to hide in dense schools near the bottom. At least two species of freshwater fish produce chemicals known as disturbance cues, which initiates a coordinated antipredator defence by increasing group cohesion in response to fish predators. Chemical communication about threats is also known among plants, though it is debated to what extent this function has been reinforced by actual selection. Lima beans release volatile chemical signals that are received by nearby plants of the same species when infested with spider mites. This message allows the recipients to prepare themselves by activating defense genes, making them less vulnerable to attack, and also attracting another mite species that is a predator of spider mites (indirect defence). Although it is conceivable that other plants are only intercepting a message primarily functioning to attract "bodyguards", some plants spread this signal on to others themselves, suggesting an indirect benefit from increased inclusive fitness.
Deceptive chemical alarm signals are also employed. For example, the wild potato, Solanum berthaultii, emits the aphid alarm-pheromone, (E)-β-farnesene, from its leaves, which functions as a repellent against the green peach aphid, Myzus persicae. | 1 | Applied and Interdisciplinary Chemistry |
Aminoallyl nucleotide is a nucleotide with a modified base containing an allylamine. They are used in post-labeling of nucleic acids by fluorescence detection in microarray. They are reactive with N-Hydroxysuccinimide ester group which helps attach a fluorescent dye to the primary amino group on the nucleotide. These nucleotides are known as 5-(3-aminoallyl)-nucleotides since the aminoallyl group is usually attached to carbon 5 of the pyrimidine ring of uracil or cytosine. The primary amine group in the aminoallyl moiety is aliphatic and thus more reactive compared to the amine groups that are directly attached to the rings (aromatic) of the bases. Common names of aminoallyl nucleosides are initially abbreviated with aa- or AA- to indicate aminoallyl. The 5-carbon sugar is indicated with or without the lowercase "d" indicating deoxyribose if included or ribose if not. Finally the nitrogenous base and number of phosphates are indicated (i.e. aa-UTP = aminoallyl uridine triphosphate). | 1 | Applied and Interdisciplinary Chemistry |
Cyclooxygenase and cytochrome P450 oxidase act upon docosatetraenoic acid to produce dihomoprostaglandins, dihomo-epoxyeicosatrienoic acids, and dihomo-EETs. | 1 | Applied and Interdisciplinary Chemistry |
Soil-borne nematodes have been shown to transmit viruses. They acquire and transmit them by feeding on infected roots. Viruses can be transmitted both non-persistently and persistently, but there is no evidence of viruses being able to replicate in nematodes. The virions attach to the stylet (feeding organ) or to the gut when they feed on an infected plant and can then detach during later feeding to infect other plants. Nematodes transmit viruses such as tobacco ringspot virus and tobacco rattle virus. | 1 | Applied and Interdisciplinary Chemistry |
Thermal mixing is an energy exchange phenomenon between the electron spin ensemble and the nuclear spin, which can be thought of as using multiple electron spins to provide hyper-nuclear polarization. Note that the electron spin ensemble acts as a whole because of stronger inter-electron interactions. The strong interactions lead to a homogeneously broadened EPR lineshape of the involved paramagnetic species. The linewidth is optimized for polarization transfer from electrons to nuclei, when it is close to the nuclear Larmor frequency. The optimization is related to an embedded three-spin (electron-electron-nucleus) process that mutually flips the coupled three spins under the energy conservation (mainly) of the Zeeman interactions. Due to the inhomogeneous component of the associated EPR lineshape, the DNP enhancement by this mechanism also scales as B. | 0 | Theoretical and Fundamental Chemistry |
A dispersed medium consists of two media that do not mix. More specifically, it contains discrete elements of one medium which are dispersed in a continuous second medium. The two media can be of very different nature. In particular, they can be a gas, a liquid or a solid.
Many materials which we encounter during the day are dispersed media. For example, milk consists of oil drops dispersed in water, fog contains tiny water drops dispersed in air, shaving cream contains bubbles dispersed in a liquid, sand consists of solid grains in air and a kitchen sponge of bubbles dispersed in a solid.
Dispersed media are commonly classified according to the nature of the two media and the volume fraction of the dispersed medium. At very low volume fraction the dispersed objects are not in contact with each other. At intermediate volume fraction they start to be in contact (they jam). And at even higher volume fraction, the dispersed objects deform in a tight packing.
Another classification takes into account the typical size of the dispersed objects. When the objects are very small (typically < 1 micrometer), for example, one speaks of colloids.
The following table provides an overview of the main types of dispersed media.
| style="text-align:center" | GASEOUS SUSPENSION<br />
| Liquid
| style="text-align:center" | AERATED LIQUID<br />
| style="text-align:center" | EMULSION<br />
| style="text-align:center" | LIQUID SUSPENSION<br />
| Solid
| style="text-align:center" | AERATED SOLIDS<br />
| style="text-align:center" | GEL<br />
| style="text-align:center" | IMPURE SUBSTANCE<br />
See also: Dispersion | 0 | Theoretical and Fundamental Chemistry |
Colloidal suspensions of nanoparticles of boric acid dissolved in petroleum or vegetable oil can form a remarkable lubricant on ceramic or metal surfaces with a coefficient of sliding friction that decreases with increasing pressure to a value ranging from 0.10 to 0.02. Self-lubricating films result from a spontaneous chemical reaction between water molecules and coatings in a humid environment. In bulk-scale, an inverse relationship exists between friction coefficient and Hertzian contact pressure induced by applied load.
Boric acid is used to lubricate carrom and novuss boards, allowing for faster play. | 0 | Theoretical and Fundamental Chemistry |
Early micro-fossils may have come from a hot world of gases such as methane, ammonia, carbon dioxide, and hydrogen sulfide, toxic to much current life. Analysis of the tree of life places thermophilic and hyperthermophilic bacteria and archaea closest to the root, suggesting that life may have evolved in a hot environment. The deep sea or alkaline hydrothermal vent theory posits that life began at submarine hydrothermal vents. William Martin and Michael Russell have suggested "that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments".
These form where hydrogen-rich fluids emerge from below the sea floor, as a result of serpentinization of ultra-mafic olivine with seawater and a pH interface with carbon dioxide-rich ocean water. The vents form a sustained chemical energy source derived from redox reactions, in which electron donors (molecular hydrogen) react with electron acceptors (carbon dioxide); see iron–sulfur world theory. These are exothermic reactions. | 0 | Theoretical and Fundamental Chemistry |
In 1956, Lev Landau developed the Fermi liquid theory, where he treated the case of a Fermi liquid, i.e., a system with repulsive, not necessarily small, interactions between fermions. The theory shows that the thermodynamic properties of an ideal Fermi gas and a Fermi liquid do not differ that much. It can be shown that the Fermi liquid is equivalent to a Fermi gas composed of collective excitations or quasiparticles, each with a different effective mass and magnetic moment. | 0 | Theoretical and Fundamental Chemistry |
Irreversible inhibitors first form a reversible non-covalent complex with the enzyme (EI or ESI). Subsequently, a chemical reaction occurs between the enzyme and inhibitor to produce the covalently modified "dead-end complex" EI* (an irreversible covalent complex). The rate at which EI* is formed is called the inactivation rate or k. Since formation of EI may compete with ES, binding of irreversible inhibitors can be prevented by competition either with substrate or with a second, reversible inhibitor. This protection effect is good evidence of a specific reaction of the irreversible inhibitor with the active site.
The binding and inactivation steps of this reaction are investigated by incubating the enzyme with inhibitor and assaying the amount of activity remaining over time. The activity will be decreased in a time-dependent manner, usually following exponential decay. Fitting these data to a rate equation gives the rate of inactivation at this concentration of inhibitor. This is done at several different concentrations of inhibitor. If a reversible EI complex is involved the inactivation rate will be saturable and fitting this curve will give k and K.
Another method that is widely used in these analyses is mass spectrometry. Here, accurate measurement of the mass of the unmodified native enzyme and the inactivated enzyme gives the increase in mass caused by reaction with the inhibitor and shows the stoichiometry of the reaction. This is usually done using a MALDI-TOF mass spectrometer. In a complementary technique, peptide mass fingerprinting involves digestion of the native and modified protein with a protease such as trypsin. This will produce a set of peptides that can be analysed using a mass spectrometer. The peptide that changes in mass after reaction with the inhibitor will be the one that contains the site of modification. | 1 | Applied and Interdisciplinary Chemistry |
Computational methods have been increasing in popularity as a method to test possible root because they do not need to sacrifice a component to prove a root cause. Common cases where computational methods are used are for failures due to erosion, failures of components under complex stress states, and for predictive analyses. Computational fluid dynamics is used to determine the flow pattern and shear stresses on a component that had failed due to erosive wear. Finite element analysis is used to model components under complex stress states. Finite element analysis as well as phase field models can be used for predicting crack propagation and failure, which are then used to prevent failure by influencing component design. | 1 | Applied and Interdisciplinary Chemistry |
Writing
where is the conductance, in W/(m K).
Fourier's law can also be stated as:
The reciprocal of conductance is resistance, is given by:
Resistance is additive when several conducting layers lie between the hot and cool regions, because and are the same for all layers. In a multilayer partition, the total conductance is related to the conductance of its layers by:
or equivalently
So, when dealing with a multilayer partition, the following formula is usually used:
For heat conduction from one fluid to another through a barrier, it is sometimes important to consider the conductance of the thin film of fluid that remains stationary next to the barrier. This thin film of fluid is difficult to quantify because its characteristics depend upon complex conditions of turbulence and viscosity—but when dealing with thin high-conductance barriers it can sometimes be quite significant. | 1 | Applied and Interdisciplinary Chemistry |
In NMR and MRI, shimming is used prior to the operation of the magnet to eliminate inhomogeneities in its field.
Initially, the magnetic field inside an NMR spectrometer or MRI scanner will be far from homogeneous compared with an "ideal" field of the device. This is a result of production tolerances and of the magnetic field of the environment. Iron constructions in walls and floor of the examination room become magnetized and disturb the field of the scanner. The probe and the sample or the patient become slightly magnetized when brought into the strong magnetic field and create additional inhomogeneous fields. The process of correcting for these inhomogeneities is called shimming the magnet, shimming the probe or shimming the sample, depending on the assumed source of the remaining inhomogeneity.
Field homogeneity of the order of 1 ppm over a volume of several liters is needed in an MRI scanner. High-resolution NMR spectroscopy demands field homogeneity better than 1 ppb within a volume of a few milliliters.
There are two types of shimming: active and passive.
Active shimming uses coils with adjustable current.
Passive shimming involves pieces of steel with good magnetic qualities. The steel pieces are placed near the permanent or superconducting magnet. They become magnetized and produce their own magnetic field.
In both cases, the additional magnetic fields (produced by coils or steel) add to the overall magnetic field of the superconducting magnet in such a way as to increase the homogeneity of the total field.
There are different ways to define inhomogeneity of a magnetic field in the center of the MR spectrometer. Currently, for medical MR scanners, the industry standard is to measure volume root mean square (VRMS) values of the field for the different (mostly concentric) volumes in the middle of the scanner. | 0 | Theoretical and Fundamental Chemistry |
Breaking C–F bonds is of interest as a way to decompose and destroy organofluorine "forever chemicals" such as PFOA and perfluorinated compounds (PFCs). Candidate methods include catalysts, such as platinum atoms; photocatalysts; UV, iodide, and sulfite, radicals; etc. | 0 | Theoretical and Fundamental Chemistry |
The Flory–Fox equation relates the number-average molecular weight, M, to the glass transition temperature, T, as shown below:
where T is the maximum glass transition temperature that can be achieved at a theoretical infinite molecular weight and K is an empirical parameter that is related to the free volume present in the polymer sample. It is this concept of “free volume” that is observed by the Flory–Fox equation.
Free volume can be most easily understood as a polymer chain's “elbow room” in relation to the other polymer chains surrounding it. The more elbow room a chain has, the easier it is for the chain to move and achieve different physical conformations. Free volume decreases upon cooling from the rubbery state until the glass transition temperature at which point it reaches some critical minimum value and molecular rearrangement is effectively “frozen” out, so the polymer chains lack sufficient free volume to achieve different physical conformations. This ability to achieve different physical conformations is called segmental mobility.
Free volume not only depends on temperature, but also on the number of polymer chain ends present in the system. End chain units exhibit greater free volume than units within the chain because the covalent bonds that make up the polymer are shorter than the intermolecular nearest neighbor distances found at the end of the chain. In other words, chain end units are less dense than the covalently bonded interchain units. This means that a polymer sample with low polydispersity and long chain lengths (high molecular weights) will have fewer chain ends per total units and less free volume than an equivalent polymer sample consisting of short chains. In short, chain ends can be viewed as an “impurity” when considering the packing of chains, and more impurity results in a lower T. Recent computer simulation study showed that the classical picture of mobility around polymer chain can differ in the presence of plasticizer, especially if molecules of plasticizer can create hydrogen bonds with specific sites of the polymer chain, such as hydrophilic or hydrophobic groups. In such a case, polymer chain ends exhibit only a mere increase of the associated free volume as compared to the average associated free volume around main chain monomers. In special cases, the free volume around hydrophilic main chain sites can exceed the free volume associated to the hydrophilic polymer ends.
Thus, glass transition temperature is dependent on free volume, which in turn is dependent on the average molecular weight of the polymer sample. This relationship is described by the Flory–Fox equation. Low molecular weight values result in lower glass transition temperatures whereas increasing values of molecular weight result in an asymptotic approach of the glass transition temperature to T . | 0 | Theoretical and Fundamental Chemistry |
For ISFET-based sensors, low-frequency noise is most detrimental to the overall SNR as it can interfere with biomedical signals which span in the same frequency domain. The noise has mainly three sources. The noise sources outside the ISFET itself are referred to as the external noise, such as environmental interference and instrument noise from terminal read-out circuits. The intrinsic noise refers to that appearing in the solid part of an ISFET, which is mainly caused by the trapping and de-trapping of carriers at the Oxide/Si interface. And the extrinsic noise is generally rooted in the liquid/oxide interface causing by the ion exchange at the liquid/oxide interface. Many methods are invented to suppress the noise of ISFET. For example, to suppress the external noise, we can integrate a bipolar junction transistor with ISFET to realize immediate the internal amplification of drain current. And to suppress the intrinsic noise we can replace the noisy oxide/Si interface by a Schottky junction gate. | 0 | Theoretical and Fundamental Chemistry |
Plastic grids allow for a 100% porous system using structural grid systems for containing and stabilizing either gravel or turf. These grids come in a variety of shapes and sizes depending on use; from pathways to commercial parking lots. These systems have been used readily in Europe for over a decade, but are gaining popularity in North America due to requirements by government for many projects to meet LEED environmental building standards. Plastic grid systems are also popular with homeowners due to their lower cost to install, ease of installation, and versatility. The ideal design for this type of grid system is a closed cell system, which prevents gravel/sand/turf from migrating laterally. | 1 | Applied and Interdisciplinary Chemistry |
The physics and chemistry of mantle largely depend on pressure. As mantle minerals are compressed, they are transformed into other minerals at certain depths. Seismic observations of velocity discontinuities and experimental simulations on phase boundaries both verified the structure transformations within the mantle. As such, the mantle can be further divided into three layers with distinct mineral compositions.
Since mantle mineral composition changes, the mineral hosting environment for polyvalent elements also alters. For each layer, the mineral combination governing the redox reactions is unique and will be discussed in detailed below. | 0 | Theoretical and Fundamental Chemistry |
In most cases, unidirectional transcription of enhancer regions generates long (>4kb) and polyadenylated eRNAs. Enhancers that generate polyA+ eRNAs have a lower H3K4me1/me3 ratio in their chromatin signature than 2D-eRNAs. PolyA+ eRNAs are distinct from long multiexonic poly transcripts (meRNAs) that are generated by transcription initiation at intragenic enhancers. These long non-coding RNAs, which accurately reflect the host gene's structure except for the alternative first exon, display poor coding potential. As a result, polyA+ 1D-eRNAs may represent a mixed group of true enhancer-templated RNAs and multiexonic RNAs. | 1 | Applied and Interdisciplinary Chemistry |
Structures containing covalent bonds can be treated using the ionic model providing they satisfy the topological conditions given above, but a special situation applies to hydrocarbons which allows the bond valence model to be reduced to the traditional bond model of organic chemistry. If an atom has a valence, V, that is equal to its coordination number, N, its bonding strength according to Eq. 3 is exactly 1.0 vu (valence units), a condition that greatly simplifies the model. This condition is obeyed by carbon, hydrogen and silicon. Since these atoms all have bonding strengths of 1.0 vu the bonds between them are all predicted to have integral valences with carbon forming four single bonds and hydrogen one. Under these conditions, the bonds are all single bonds (or multiples of single bonds). Compounds can be constructed by linking carbon and hydrogen atoms with bonds that are all exactly equivalent. Under certain conditions, nitrogen can form three bonds and oxygen two, but since nitrogen and oxygen typically also form hydrogen bonds, the resulting N-H and O-H bonds have valences less than 1.0 vu, leading through the application of Eq. 1, to the C-C and C-H bonds having valences that differ from 1.0 vu. Nevertheless, the simple bonding rules of organic chemistry are still good approximations, though the rules of the bond valence model are better. | 0 | Theoretical and Fundamental Chemistry |
In mammals, propionyl-CoA is converted to (S)-methylmalonyl-CoA by propionyl-CoA carboxylase, a biotin-dependent enzyme also requiring bicarbonate and ATP.
This product is converted to (R)-methylmalonyl-CoA by methylmalonyl-CoA racemase.
(R)-Methylmalonyl-CoA is converted to succinyl-CoA, an intermediate in the tricarboxylic acid cycle, by methylmalonyl-CoA mutase, an enzyme requiring
cobalamin to catalyze the carbon-carbon bond migration.
The methylmalonyl-CoA mutase mechanism begins with the cleavage of the bond between the 5 - of 5-deoxyadenosyl and the cobalt, which is in its 3+ oxidation state (III), which produces a 5'-deoxyadenosyl radical and cobalamin in the reduced Co(II) oxidation state.
Next, this radical abstracts a hydrogen atom from the methyl group of methylmalonyl-CoA, which generates a methylmalonyl-CoA radical. It is believed that this radical forms a carbon-cobalt bond to the coenzyme, which is then followed by the rearrangement of the substrates carbon skeleton, thus producing a succinyl-CoA radical. This radical then goes on to abstract a hydrogen from the previously produced 5-deoxyadenosine, again creating a deoxyadenosyl radical, which attacks the coenzyme to reform the initial complex.
A defect in methylmalonyl-CoA mutase enzyme results in methylmalonic aciduria, a dangerous disorder that causes a lowering of blood pH. | 1 | Applied and Interdisciplinary Chemistry |
Jet engines power jet aircraft, cruise missiles and unmanned aerial vehicles. In the form of rocket engines they power model rocketry, spaceflight, and military missiles.
Jet engines have propelled high speed cars, particularly drag racers, with the all-time record held by a rocket car. A turbofan powered car, ThrustSSC, currently holds the land speed record.
Jet engine designs are frequently modified for non-aircraft applications, as industrial gas turbines or marine powerplants. These are used in electrical power generation, for powering water, natural gas, or oil pumps, and providing propulsion for ships and locomotives. Industrial gas turbines can create up to 50,000 shaft horsepower. Many of these engines are derived from older military turbojets such as the Pratt & Whitney J57 and J75 models. There is also a derivative of the P&W JT8D low-bypass turbofan that creates up to 35,000 horsepower (HP)
Jet engines are also sometimes developed into, or share certain components such as engine cores, with turboshaft and turboprop engines, which are forms of gas turbine engines that are typically used to power helicopters and some propeller-driven aircraft. | 1 | Applied and Interdisciplinary Chemistry |
SQT measurements are scaled proportionately by relative impact and visually represented on triaxial graphs. Evaluation of sediment integrity and interrelationships between components can be determined by the size and morphology of the triangle. The magnitude of the triangle is indicative of the relative impact of contamination. Equilateral triangles imply agreement among components. (USEPA, 1994) | 1 | Applied and Interdisciplinary Chemistry |
As a long-acting injection, zuclopenthixol decanoate comes in a 200 mg and 500 mg ampoule. Doses can vary from 50 mg weekly to the maximum licensed dose of 600 mg weekly. In general, the lowest effective dose to prevent relapse is preferred. The interval may be shorter as a patient starts on the medication before extending to 3 weekly intervals subsequently. The dose should be reviewed and reduced if side effects occur, though in the short-term an anticholinergic medication benztropine may be helpful for tremor and stiffness, while diazepam may be helpful for akathisia. 100 mg of zuclopenthixol decanoate is roughly equivalent to 20 mg of flupentixol decanoate or 12.5 mg of fluphenazine decanoate.
In acutely psychotic and agitated inpatients, 50 – 200 mg of zuclopenthixol acetate may be given for a calming effect over the subsequent three days, with a maximum dose of 400 mg in total to be given. As it is a long-acting medication, care must be taken not to give an excessive dose.
In oral form zuclopenthixol is available in 2, 10, 25 and 40 mg tablets, with a dose range of 20–60 mg daily. | 0 | Theoretical and Fundamental Chemistry |
The convention for a nucleic acid sequence is to list the nucleotides as they occur from the 5 end to the 3 end of the polymer chain, where 5 and 3 refer to the numbering of carbons around the ribose ring which participate in forming the phosphate diester linkages of the chain. Such a sequence is called the primary structure of the biopolymer. | 1 | Applied and Interdisciplinary Chemistry |
Diffusiophoresis, by definition, moves colloidal particles, and so the applications of diffusiophoresis are to situations where we want to move colloidal particles. Colloidal particles are typically between 10 nanometres and a few micrometres in size. Simple diffusion of colloids is fast on length scales of a few micrometres, and so diffusiophoresis would not be useful, whereas on length scales larger than millimetres, diffusiophoresis may be slow as its speed decreases with decreasing size of the solute concentration gradient. Thus, typically diffusiophoresis is employed on length scales approximately in the range a micrometre to a millimetre. Applications include moving particles into or out of pores of that size, and helping or inhibiting mixing of colloidal particles.
In addition, solid surfaces that are slowly dissolving will create concentration gradients near them, and these gradients may drive movement of colloidal particles towards or away from the surface. This was studied by Prieve in the context of latex particles being pulled towards, and coating, a dissolving steel surface. | 0 | Theoretical and Fundamental Chemistry |
The theoretical plate height is given by
where L is the column length and N the number of theoretical plates. The relation between plate number and peak width at the base is given by | 0 | Theoretical and Fundamental Chemistry |
The first reported kinetic resolution was achieved by Louis Pasteur. After reacting aqueous racemic ammonium tartrate with a mold from Penicillium glaucum, he reisolated the remaining tartrate and found it was levorotatory. The chiral microorganisms present in the mold catalyzed the metabolization of (R,R)-tartrate selectively, leaving an excess of (S,S)-tartrate.
Kinetic resolution by synthetic means was first reported by Marckwald and McKenzie in 1899 in the esterification of racemic mandelic acid with optically active (−)-menthol. With an excess of the racemic acid present, they observed the formation of the ester derived from (+)-mandelic acid to be quicker than the formation of the ester from (−)-mandelic acid. The unreacted acid was observed to have a slight excess of (−)-mandelic acid, and the ester was later shown to yield (+)-mandelic acid upon saponification. The importance of this observation was that, in theory, if a half equivalent of (−)-menthol had been used, a highly enantioenriched sample of (−)-mandelic acid could have been prepared. This observation led to the successful kinetic resolution of other chiral acids, the beginning of the use of kinetic resolution in organic chemistry. | 0 | Theoretical and Fundamental Chemistry |
Vargulin is found in certain ostracods and deep-sea fish, to be specific, Poricthys. Like the compound coelenterazine, it is an imidazopyrazinone and emits primarily blue light in the animals. | 1 | Applied and Interdisciplinary Chemistry |
Morphological control on the nanoscale is still limited as COFs lack synthetic control in higher dimensions due to the lack of dynamic chemistry during synthesis. To date, researchers have attempted to establish better control through different synthetic methods such as solvothermal synthesis, interface-assisted synthesis, solid templation as well as seeded growth. First one of the precursors is deposited onto the solid support followed by the introduction of the second precursor in vapor form. This results in the deposition of the COF as a thin film on the solid support. | 0 | Theoretical and Fundamental Chemistry |
Maharram Mammadyarov was born in Yayji, Julfa, Nakhichivan ASSR. In 1941, he graduated from Nakhchivan Pedagogical Technical School. He participated in WWII, serving in the Army. Mammadyarov graduated from Azerbaijan State University in 1949, and in 1953 from Leningrad Technical University by obtaining PhD. During 1953–1955, he worked as scientific secretary at Institute of Chemistry of Azerbaijan of National Academy of Sciences of Azerbaijan Soviet Socialist Republic. In 1955–1959 he was Senior Research Fellow at the Institute of Organic Chemistry named after N. Zelinski of the USSR Academy of Sciences. In 1959–1969 Mammadyarov worked at the Institute of Petrochemical Processes named after Y.H. Mammadaliyev. In 1973–1979 he was the head of Nakhchivan regional scientific center of ANAS. For his work on the use of carbon dioxide in the industry, he was awarded the State Prize of the Republic of Azerbaijan. In 1975–1978 Mammadyarov worked as teacher at the Nakhchivan State Pedagogical Institute (present Nakhchivan State University). From 1981 to 1994 he worked as the head of the department, and from 1994 to 2002 he worked as director of the Microbiology Institute of ANAS. Since 1969 he had been working at the Institute of Petrochemical Processes named after Y.H. Mammadaliyev as the Head of Synthesis and Technology of Synthetic Fats laboratory until his death in 2022.
Mammadyarov died on 2 January 2022, at the age of 97. He was the father of Minister of Foreign Affairs of Azerbaijan, Elmar Mammadyarov. | 0 | Theoretical and Fundamental Chemistry |
Wotiz began studying of chemical engineering at the Czech Technical University in Prague, but went to the US with his brother in 1939 because of the German occupation of Czechoslovakia. In 1941 he received a bachelors degree in chemistry from Furman University and in 1943 a masters degree from the University of Richmond. At the end of World War II he served in the United States Army as Lieutenant of chemical weaponry. In 1944 he became a US citizen. In 1948 he earned a PhD in chemistry under Melvin S. Newman at Ohio State University.
Wotiz was an instructor and from 1954 an associate professor at the University of Pittsburgh. He went to work in industry at the Diamond Alkali Company in Painesville in 1957. There he was involved in authoring 44 patents. In 1962 he became a professor at Marshall University in Huntington, West Virginia, and in 1967 at Southern Illinois University in Carbondale.
In 1980 Wotiz was Chairman of the History Division of the American Chemical Society. Starting in 1971 he organized trips to Europe regarding the history of chemistry. As a chemical historian, he was particularly concerned with August Kekulé. He was involved in establishing a center for the history of chemistry, the Chemical Heritage Foundation (now the Science History Institute).
Wotiz retired in 1989. He was particularly committed to international exchange with Eastern Europe and was involved in comparative studies of chemical education in the Soviet Union, Eastern Europe and Asia. He and his wife Kathryn died as a result of a car accident on August 21, 2001. | 1 | Applied and Interdisciplinary Chemistry |
Flow measurement is the quantification of bulk fluid movement. Flow can be measured using devices called flowmeters in various ways. The common types of flowmeters with industrial applications are listed below:
* Obstruction type (differential pressure or variable area)
* Inferential (turbine type)
* Electromagnetic
* Positive-displacement flowmeters, which accumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow.
* Fluid dynamic (vortex shedding)
* Anemometer
* Ultrasonic flow meter
* Mass flow meter (Coriolis force).
Flow measurement methods other than positive-displacement flowmeters rely on forces produced by the flowing stream as it overcomes a known constriction, to indirectly calculate flow. Flow may be measured by measuring the velocity of fluid over a known area. For very large flows, tracer methods may be used to deduce the flow rate from the change in concentration of a dye or radioisotope. | 1 | Applied and Interdisciplinary Chemistry |
His wide-ranging studies of protein structure have contributed insights to viral architecture, DNA–protein recognition, and cellular signaling.
Harrison has made important contributions to structural biology, most notably by determining and analyzing the structures of viruses and viral proteins, by crystallographic analysis of protein–DNA complexes, and by structural studies of protein-kinase switching mechanisms. The initiator of high-resolution virus crystallography, he has moved from his early work on tomato bushy stunt virus (1978) to the study of more complex human pathogens, including the capsid of human papillomavirus, the envelope of dengue virus, and several components of HIV. He has also turned some of his research attention to even more complex assemblies, such as clathrin-coated vesicles. He led the Structural Biology team at the Center for HIV/AIDS Vaccine Immunology (CHAVI) when it received National Institute of Allergy and Infectious Diseases (NIAID) funding of around $300 million to address key immunological roadblocks to HIV vaccine development and to design, develop and test novel HIV vaccine candidates. | 1 | Applied and Interdisciplinary Chemistry |
Fluorine may interact with biological systems in the form of fluorine-containing compounds. Though elemental fluorine (F) is very rare in everyday life, fluorine-containing compounds such as fluorite occur naturally as minerals. Naturally occurring organofluorine compounds are extremely rare. Man-made fluoride compounds are common and are used in medicines, pesticides, and materials. Twenty percent of all commercialized pharmaceuticals contain fluorine, including Lipitor and Prozac. In many contexts, fluorine-containing compounds are harmless or even beneficial to living organisms; in others, they are toxic.
Aside from their use in medicine, man-made fluorinated compounds have also played a role in several noteworthy environmental concerns. Chlorofluorocarbons (CFCs), once major components of numerous commercial aerosol products, have proven damaging to Earth's ozone layer and resulted in the wide-reaching Montreal Protocol; though in truth the chlorine in CFCs is the destructive actor, fluorine is an important part of these molecules because it makes them very stable and long-lived. Similarly, the stability of many organofluorine compounds has raised the issue of biopersistence. Long-lived molecules from waterproofing sprays, for example PFOA and PFOS, are found worldwide in the tissues of wildlife and humans, including newborn children.
Fluorine biology is also relevant to a number of cutting-edge technologies. PFCs (perfluorocarbons) are capable of holding enough oxygen to support human liquid breathing. Organofluorine in the form of its radioisotope F is also at the heart of a modern medical imaging technique known as positron emission tomography (PET). A PET scan produces three-dimensional colored images of parts of the body that use a lot of sugar, particularly the brain or tumors. | 1 | Applied and Interdisciplinary Chemistry |
Chemical reaction engineering aims at studying and optimizing chemical reactions in order to define the best reactor design. Hence, the interactions of flow phenomena, mass transfer, heat transfer, and reaction kinetics are of prime importance in order to relate reactor performance to feed composition and operating conditions. Although originally applied to the petroleum and petrochemical industries, its general methodology combining reaction chemistry and chemical engineering concepts allows optimization of a variety of systems where modeling or engineering of reactions is needed. Chemical reaction engineering approaches are indeed tailored for the development of new processes and the improvement of existing technologies. | 1 | Applied and Interdisciplinary Chemistry |
The dominant technology used for the production of transgenic plants for transient expression is Agrobacterium-mediated genetic transformation, or "agroinfiltration," and virus expression machinery. Agrobacterium tumefaciens and related Agrobacterium species are well-known plant pathogens that have been engineered to efficiently transfer specific pieces of DNA (called transfer DNA, or T-DNA) into the plant nucleus using binary vector systems, which consists of a T-DNA binary vector and a vir helper plasmid. This binary vector separates T-DNA from trans-acting virulence proteins that help mediate the transfer. Advantages of this method include modularity of broad host-range plasmids of small size through standard molecular biology techniques. Furthermore, since the parent tumor-inducing plasmid in Agrobacterium strains have been disarmed and only non-reproductive cells have been modified (as opposed to germ-line modifications), the process is considered environmentally harmless.
Applications of this process has resulted in advancements made in the use of plants to synthetic biology. Plant-derived bioproducts show promise of high competitiveness towards traditional mammalian cell expression systems. | 1 | Applied and Interdisciplinary Chemistry |
In 1952 he became the first president of the German Society for Electron Microscopy. In 1955 he received the Alfred Stock Memorial Prize, in 1964 the Seger Plaque, and in 1965 the Wolfgang Ostwald Prize. He was a member of the Heidelberg Academy of Sciences (1961) and the Leopoldina (1962). In 1968 he received an honorary doctorate from the University of Munich. | 0 | Theoretical and Fundamental Chemistry |
Esters are generally identified by gas chromatography, taking advantage of their volatility. IR spectra for esters feature an intense sharp band in the range 1730–1750 cm assigned to ν. This peak changes depending on the functional groups attached to the carbonyl. For example, a benzene ring or double bond in conjugation with the carbonyl will bring the wavenumber down about 30 cm. | 0 | Theoretical and Fundamental Chemistry |
Methane was typically measured using gas chromatography. Gas chromatography is a type of chromatography used for separating or analyzing chemical compounds. It is less expensive in general, compared to more advanced methods, but it is more time and labor-intensive.
Spectroscopic methods were the preferred method for atmospheric gas measurements due to its sensitivity and precision. Also, spectroscopic methods are the only way of remotely sensing the atmospheric gases. Infrared spectroscopy covers a large spectrum of techniques, one of which detects gases based on absorption spectroscopy. There are various methods for spectroscopic methods, including Differential optical absorption spectroscopy, Laser-induced fluorescence, and Fourier Transform Infrared.
In 2011, cavity ring-down spectroscopy was the most widely used IR absorption technique of detecting methane. It is a form of laser absorption spectroscopy which determines the mole fraction to the order of parts per trillion. | 1 | Applied and Interdisciplinary Chemistry |
In chemical analysis, capillary electrochromatography (CEC) is a chromatographic technique in which the mobile phase is driven through the chromatographic bed by electro-osmosis. Capillary electrochromatography is a combination of two analytical techniques, high-performance liquid chromatography and capillary electrophoresis. Capillary electrophoresis aims to separate analytes on the basis of their mass-to-charge ratio by passing a high voltage across ends of a capillary tube, which is filled with the analyte. High-performance liquid chromatography separates analytes by passing them, under high pressure, through a column filled with stationary phase. The interactions between the analytes and the stationary phase and mobile phase lead to the separation of the analytes. In capillary electrochromatography capillaries, packed with HPLC stationary phase, are subjected to a high voltage. Separation is achieved by electrophoretic migration of solutes and differential partitioning. | 1 | Applied and Interdisciplinary Chemistry |
Esketamine was introduced for medical use as an anesthetic in Germany in 1997, and was subsequently marketed in other countries. In addition to its anesthetic effects, the medication showed properties of being a rapid-acting antidepressant, and was subsequently investigated for use as such. Esketamine received a breakthrough designation from the for treatment-resistant depression (TRD) in 2013 and major depressive disorder (MDD) with accompanying suicidal ideation in 2016. In November 2017, it completed phase III clinical trials for treatment-resistant depression in the United States. Johnson & Johnson filed a Food and Drug Administration (FDA) New Drug Application (NDA) for approval on 4 September 2018; the application was endorsed by an FDA advisory panel on 12 February 2019, and on 5 March 2019, the FDA approved esketamine, in conjunction with an oral antidepressant, for the treatment of depression in adults. In August 2020, it was approved by the U.S. Food and Drug Administration (FDA) with the added indication for the short-term treatment of suicidal thoughts.
Since the 1980s, closely associated ketamine has been used as a club drug also known as "Special K" for its trip-inducing side effects. | 0 | Theoretical and Fundamental Chemistry |
Many of methylenes electronic states lie relatively close to each other, giving rise to varying degrees of radical chemistry. The ground state is a triplet radical with two unpaired electrons (X̃B), and the first excited state is a singlet non-radical (ãA'). With the singlet non-radical only 38 kJ above the ground state, a sample of methylene exists as a mixture of electronic states even at room temperature, giving rise to complex reactions. For example, reactions of the triplet radical with non-radical species generally involves abstraction, whereas reactions of the singlet non-radical not only involves abstraction, but also insertion or addition.
:(X̃B) + → + [HO]
:(ãA) + → + or
The singlet state is also more stereospecific than the triplet.
Unsolvated methylene will spontaneously autopolymerise to form various excited oligomers, the simplest of which, is the excited form of the alkene ethylene. The excited oligomers, decompose rather than decay to a ground state. For example, the excited form of ethylene decomposes to acetylene and atomic hydrogen.
:2 → → HCCH + 2 H
Unsolvated, excited methylene will form stable ground state oligomers. | 0 | Theoretical and Fundamental Chemistry |
The Association organizes a series of biennial International Applied Geochemistry Symposia (titled the International Geochemical Exploration Symposium until 2005), held recently in Oviedo, Spain, and Perth, Australia. | 0 | Theoretical and Fundamental Chemistry |
Aside from chlorofluorocarbons, tritium can act as a transient tracer and has the ability to "outline" the biological, chemical, and physical paths throughout the world oceans because of its evolving distribution. Tritium has thus been used as a tool to examine ocean circulation and ventilation and, for such purposes, is usually measured in Tritium Units, where 1 TU is defined as the ratio of 1 tritium atom to 10 hydrogen atoms, approximately equal to 0.118 Bq/liter. As noted earlier, nuclear weapons testing, primarily in the high-latitude regions of the Northern Hemisphere, throughout the late 1950s and early 1960s introduced large amounts of tritium into the atmosphere, especially the stratosphere. Before these nuclear tests, there were only about 3 to 4 kilograms of tritium on the Earth's surface; but these amounts rose by 2 or 3 orders of magnitude during the post-test period. Some sources reported natural background levels were exceeded by approximately 1,000 TU in 1963 and 1964 and the isotope is used in the northern hemisphere to estimate the age of groundwater and construct hydrogeologic simulation models. Estimated atmospheric levels at the height of weapons testing to approach 1,000 TU and pre-fallout levels of rainwater to be between 5 and 10 TU. In 1963 Valentia Island Ireland recorded 2,000 TU in precipitation. | 0 | Theoretical and Fundamental Chemistry |
Peculiarly, above 1,394 °C (2,541 °F) iron changes back into the bcc structure, known as δ-Fe. δ-iron can dissolve as much as 0.08% of carbon by mass at 1,475 °C. It is stable up to its melting point of 1,538 °C (2,800 °F). δ-Fe cannot exist above 5.2 GPa, with austenite instead transitioning directly to a molten phase at these high pressures. | 1 | Applied and Interdisciplinary Chemistry |
William Frohring was born in Cleveland, Ohio, the son of William Erhardt Frohring, a railroad engineer, and Martha Louise Bliss. He graduated from East Technical High School in Cleveland. After graduation, he worked as a motorcycle mechanic at the Luna Park, Cleveland Motordrome. In 1911, he received a two-year scholarship to Ohio State Agricultural College, where he majored in bacteriology and dairy technology. He graduated in 1915. | 0 | Theoretical and Fundamental Chemistry |
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 | Theoretical and Fundamental Chemistry |
# Using ATP as energy, citrate is broken down into the acetyl group and oxaloacetate.
# The acetyl group joins the coenzyme in the cytosol, forming acetyl-CoA. | 1 | Applied and Interdisciplinary Chemistry |
The Ellingham curve for the reaction 2C(s) + (g) → 2CO(g) slopes down and falls below the curves for all the metals. Hence, carbon can normally act as a reducing agent for all metal oxides at very high temperatures. But chromium formed at these temperatures reacts with carbon to form its carbide, which gives undesirable properties to the chromium metal obtained. Hence, for high temperature reduction of chromic oxide, carbon cannot be used. | 1 | Applied and Interdisciplinary Chemistry |
Drosatos received his B.Sc. from the department of biology at the Aristotle University of Thessaloniki, Greece in 2000. In 2000, he continued with graduate studies at the Molecular Biology-Biomedicine graduate program of the department of biology and the medical school of the University of Crete. He received his M.Sc. in 2002 and his Ph.D. in molecular biology-biomedicine in 2007. During his graduate studies (2002–2007) he was a visiting research scholar in the laboratory of Vassilis I. Zannis at Boston University Medical School. Following his graduation with a PhD in molecular biology-biomedicine in 2007, he joined the laboratory of Ira J. Goldberg at Columbia University, where he pursued post-doctoral training until 2012, when he was promoted to associate research scientist in the department of medicine at Columbia University. In 2014 he joined the faculty of the Lewis Katz School of Medicine at Temple University as an assistant professor in pharmacology and in 2020, he was promoted to associate professor with tenure in cardiovascular sciences (primary affiliation). In 2022, he was recruited at the University of Cincinnati College of Medicine, which he joined as the Ohio Eminent Scholar and Professor of Pharmacology and Systems Physiology | 1 | Applied and Interdisciplinary Chemistry |
For any given atom, there are quantum numbers that can specify the wavefunction of that atom. Using the hydrogen atom as an example, four quantum numbers are required to fully describe the state of the system. Quantum numbers that are eigenvalues of the operators that commute with the wavefunction to describe physical aspects of the system, and are called “good” numbers because of this. Once good quantum numbers have been found for a given atomic transition, the selection rules determine what changes in quantum numbers are allowed.
The electric dipole (E1) transition of a hydrogen atom can be described with the quantum numbers l (orbital angular momentum quantum number), m (magnetic quantum number), m (electron spin quantum number), and n (principal quantum number). When evaluating the effect of the electric dipole moment operator μ on the wavefunction of the system, we see that all values of the eigenvalue are 0, except for when the changes in the quantum numbers follow a specific pattern.
For example in the E1 transition, unless Δ l = ± 1, Δ m = 0 or ± 1, Δ m = 0, and Δ n = any integer, the equation above will yield a value equal to zero and the transition would be known as a “forbidden transition”. For example, this would occur for certain cases like when Δ l = 2. In this case, the transition would not be allowed and therefore would be much weaker than an allowed transition. These specific values for the changes in quantum numbers are known as the selection rules for the allowed transitions and are shown for common transitions in the table below: | 0 | Theoretical and Fundamental Chemistry |
Many of these encounters are reported only in the media, and are not examples of open-ocean rogue waves. Often, in popular culture, an endangering huge wave is loosely denoted as a "rogue wave", while the case has not been established that the reported event is a rogue wave in the scientific sense – i.e. of a very different nature in characteristics as the surrounding waves in that sea state] and with a very low probability of occurrence.
This section lists a limited selection of notable incidents. | 1 | Applied and Interdisciplinary Chemistry |
Venous collapse is important during exercise, when muscular compression of leg veins is used to pump blood against gravity up to the heart, and in therapeutic compression of leg veins for the treatment of deep-vein thrombosis
partial vessel collapse occurs in vessels which undergo conditions of higher external pressure relative to the fluid within and can be difficult to predict mathematically. As such, devices such as a Starling Resistor are often used to predict fluid flow under these conditions.
Fluid is forced through an elastically deforming tube which passes through a region of high external pressure causing a flattening of the tube depending on the relative pressures of the inside and outside of the tube.
In the absence of any flow (puD pd), an increase in pe generates a compressive stress in the tube wall causing it to buckle from a circular to an elliptic cross-section (except, of course, near its ends, where it is attached to the rigid tubes). Buckling to a shape with more than two lobes may arise in short, tethered, or inhomogeneous tubes. Once buckled, the tube becomes highly compliant so that small additional increases in pe lead to a substantial reduction in cross-sectional area ®. Further compression leads to contact of the opposite tube walls, first at a point, and then along a line (Figure 2, left); once in opposite-wall contact, the tube's compliance falls because strong bending forces in the tube wall at the bulbous end of each lobe provide an increasing resistance to area reductions. The “tube law,” the relation between transmural pressure P – Pexternal (where p is the internal pressure) and , for a long thin-walled tube can be approximated by thin-shell theory for an axially uniform elastic ring | 1 | Applied and Interdisciplinary Chemistry |
Böttger was born in Aschersleben, Germany in 1806. After attending the primary school there he joined the school of the Franksche Stiftung in Halle an der Saale at the age of eleven. In 1824, Böttger started to study theology, but in parallel also attended the science lectures at the University Halle. The lectures of Johann Salomo Christoph Schweigger had a strong influence on him. Böttger left the university in 1828 and worked as cleric and teacher at different locations. The contact with Schweigger never faded and in 1831 Böttger decided to leave the theology career. He was offered a job at the voluntary association for chemistry in Frankfurt in 1835. His first major work in Frankfurt was the improvement of the electrotyping method for the production of printing plates, he created the first practical nickel electroplating solution (1840). Böttger received his PhD from the University of Jena in 1837 and was appointed as full professor in Frankfurt in 1842. Böttger married Christiane Harpke in 1841, and they had eight children. He and Christian Friedrich Schönbein, a German-Swiss chemist, discovered nitrocellulose independently in 1846. Both scientists collaborated to earn money with the invention, but they were not successful. The development of the safety match in 1848 and the synthesis of the first organocopper compound, the explosive copper(I) acetylide CuC in 1859 were examples for his chemistry research. Böttger stayed at the University of Frankfurt am Main for the rest of his life, although he was offered positions at other universities. He died of a liver illness in 1881. | 0 | Theoretical and Fundamental Chemistry |
*It can be prepared by Jones oxidation of cyclooctanol.
*It can also be produced by ketonization reaction starting with azelaic acid. | 0 | Theoretical and Fundamental Chemistry |
Bilbao Crystallographic Server is an open access website offering online crystallographic database and programs aimed at analyzing, calculating and visualizing problems of structural and mathematical crystallography, solid state physics and structural chemistry. Initiated in 1997 by the Materials Laboratory of the Department of Condensed Matter Physics at the University of the Basque Country, Bilbao, Spain, the Bilbao Crystallographic Server is developed and maintained by academics. | 0 | Theoretical and Fundamental Chemistry |
There are four ways to crystallize a racemate; three of which H. W. B. Roozeboom had distinguished by 1899:
;Conglomerate (sometimes racemic conglomerate):If the molecules of the substance have a much greater affinity for the same enantiomer than for the opposite one, a mechanical mixture of enantiomerically pure crystals will result. The mixture of enantiomerically pure R and S crystals forms a eutectic mixture. Consequently, the melting point of the conglomerate is always lower than that of the pure enantiomer. Addition of a small amount of one enantiomer to the conglomerate increases the melting point. Roughly 10% of racemic chiral compounds crystallize as conglomerates.
;Racemic compound (sometimes true racemate):If molecules have a greater affinity for the opposite enantiomer than for the same enantiomer, the substance forms a single crystalline phase in which the two enantiomers are present in an ordered 1:1 ratio in the elementary cell. Adding a small amount of one enantiomer to the racemic compound decreases the melting point. But the pure enantiomer can have a higher or lower melting point than the compound. A special case of racemic compounds are kryptoracemic compounds (or kryptoracemates), in which the crystal itself has handedness (is enantiomorphic), despite containing both enantiomorphs in a 1:1 ratio.
;Pseudoracemate (sometimes racemic solid solution): When there is no big difference in affinity between the same and opposite enantiomers, then in contrast to the racemic compound and the conglomerate, the two enantiomers will coexist in an unordered manner in the crystal lattice. Addition of a small amount of one enantiomer changes the melting point slightly or not at all.
;Quasiracemate: A quasiracemate is a co-crystal of two similar but distinct compounds, one of which is left-handed and the other right-handed. Although chemically different, they are sterically similar (isosteric) and are still able to form a racemic crystalline phase. One of the first such racemates studied, by Pasteur in 1853, forms from a 1:2 mixture of the bis ammonium salt of (+)-tartaric acid and the bis ammonium salt of (−)-malic acid in water. Re-investigated in 2008, the crystals formed are dumbbell-shape with the central part consisting of ammonium (+)-bitartrate, whereas the outer parts are a quasiracemic mixture of ammonium (+)-bitartrate and ammonium (−)-bimalate. | 0 | Theoretical and Fundamental Chemistry |
In 1941, science fiction writer Isaac Asimov published the science fiction short story "Reason", in which a space station transmits energy collected from the Sun to various planets using microwave beams. The SBSP concept, originally known as satellite solar-power system (SSPS), was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g. from an SPS to Earth's surface) using microwaves from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna, on the ground.
Glaser then was a vice president at Arthur D. Little, Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems – chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space – it showed enough promise to merit further investigation and research. | 0 | Theoretical and Fundamental Chemistry |
An ecologically significant aspect of bacterial organohalide respiration is the reduction of tetrachloroethene (PCE) and Trichloroethene (TCE); anthropogenic pollutants with high neuro and hepatotoxicity. Their presence as environmental pollutants arose from their common industrial use as metal-degreasing agents from the 1920s - 1970. These xenobiotic compounds tend to form partially insoluble layers called dense non-aqueous phase liquids (DNAPLs) at the bottom of groundwater aquifers, which solubilize in a slow, reservoir-like manner, making TCE and PCE among the most common groundwater pollutants.
A commonly used strategy for the removal of TCE and PCE from groundwater is the use of bioremediation via enhanced reductive dechlorination (ERD). ERD involves in-situ injections of dehalorespiring bacteria, among fermentable organic substrates serving as electron donors, while the two pollutants, TCE and PCE, act as the electron acceptors. This facilitates the sequential dechlorination of PCE and TCE into noxious cis-dichloroethene (DCE) and Vinyl chloride (VC), which then suit as electron acceptors for the full dechlorination into innocuous ethene.
A wide array of bacteria across different genera have the capacity to partially dechlorinate PCE and TCE into cis-DCE and VC. One such example of this is the Magnetospirillum bacterium, strain MS-1, which can reduce PCE into cis-DCE under aerobic conditions. However, these daughter substrates have higher toxicity profiles than their parent compounds. As such, effective dechlorination of cis-DCE and VC into innocuous ethene is crucial for bioremediation of PCE and TCE-contaminated aquifers. Currently, bacteria of the Dehalococcoides genera are the only known organisms that can fully dechlorinate PCE into ethene. This is due to their specific transmembrane reductive dehalogenases (RDases) that metabolize the chlorine atoms on the xenobiotic pollutants for cellular energy. In particular, Dehalococcoides isolates VS and BAV1 encode Vinyl Chloride RDases, which metabolize VC into innocuous ethene, making them required species in ERD systems used in bioremediation of PCE and TCE. | 0 | Theoretical and Fundamental Chemistry |
SERS from pyridine adsorbed on electrochemically roughened silver was first observed by Martin Fleischmann, Patrick J. Hendra and A. James McQuillan at the Department of Chemistry at the University of Southampton, UK in 1973. This initial publication has been cited over 6000 times. The 40th Anniversary of the first observation of the SERS effect has been marked by the Royal Society of Chemistry by the award of a National Chemical Landmark plaque to the University of Southampton. In 1977, two groups independently noted that the concentration of scattering species could not account for the enhanced signal and each proposed a mechanism for the observed enhancement. Their theories are still accepted as explaining the SERS effect. Jeanmaire and Richard Van Duyne
proposed an electromagnetic effect, while Albrecht and Creighton
proposed a charge-transfer effect. Rufus Ritchie, of Oak Ridge National Laboratory's Health Sciences Research Division, predicted the existence of the surface plasmon. | 0 | Theoretical and Fundamental Chemistry |
Nascent state or in statu nascendi (Lat. newly formed moiety: in the state of being born or just emerging), is an obsolete theory in chemistry. It refers to the form of a chemical element (or sometimes compound) in the instance of their liberation or formation. Often encountered are atomic oxygen (O), nascent hydrogen (H), and similar forms of chlorine (Cl) or bromine (Br).
The concept of a "nascent state" was developed to explain the observation that gases generated in situ are frequently more reactive than identical chemicals that have been stored for an extended period of time. First usage of the term was in work by Joseph Priestley around 1790. Auguste Laurent expanded on the theory in the mid 19th century.
Constantine Zenghelis hypothesized in 1920 that the increased reactivity of the "nascent" state was due to the fine dispersion of the molecules, not their status as free atoms. Still popular in the early 20th century, the nascent state theory was recognized as declining by 1942.
A 1990 review noted that the term was still found as a passing mention in contemporary textbooks. The review summarized that the increased activity observed is actually caused by multiple kinetic effects, and that grouping all these effects into a single term could cause chemists to view the effect too simplistically. | 1 | Applied and Interdisciplinary Chemistry |
Monodisperse, nanometer-size clusters (also known as nanoclusters) are synthetically grown crystals whose size and structure influence their properties through the effects of quantum confinement. One method of growing these crystals is through inverse micellar cages in non-aqueous solvents. Research conducted on the optical properties of MoS nanoclusters compared them to their bulk crystal counterparts and analyzed their absorbance spectra. The analysis reveals that size dependence of the absorbance spectrum by bulk crystals is continuous, whereas the absorbance spectrum of nanoclusters takes on discrete energy levels. This indicates a shift from solid-like to molecular-like behavior which occurs at a reported cluster the size of 4.5 – 3.0 nm.
Interest in the magnetic properties of nanoclusters exists due to their potential use in magnetic recording, magnetic fluids, permanent magnets, and catalysis. Analysis of Fe clusters shows behavior consistent with ferromagnetic or superparamagnetic behavior due to strong magnetic interactions within clusters.
Dielectric properties of nanoclusters are also a subject of interest due to their possible applications in catalysis, photocatalysis, micro capacitors, microelectronics, and nonlinear optics. | 0 | Theoretical and Fundamental Chemistry |
In crystal growth, a Knudsen cell is an effusion evaporator source for relatively low partial pressure elementary sources (e.g. Ga, Al, Hg, As). Because it is easy to control the temperature of the evaporating material in Knudsen cells, they are commonly used in molecular-beam epitaxy. | 0 | Theoretical and Fundamental Chemistry |
Some forms of mutations are hereditary (germline mutations), or passed on from a parent to its offspring. Such mutated coding regions are present in all cells within the organism. Other forms of mutations are acquired (somatic mutations) during an organisms lifetime, and may not be constant cell-to-cell. These changes can be caused by mutagens, carcinogens, or other environmental agents (ex. UV). Acquired mutations can also be a result of copy-errors during DNA replication and are not passed down to offspring. Changes in the coding region can also be de novo (new); such changes are thought to occur shortly after fertilization, resulting in a mutation present in the offsprings DNA while being absent in both the sperm and egg cells. | 1 | Applied and Interdisciplinary Chemistry |
A huge variety of ionization techniques can be used to analyze single cells. The choice of ionization method is crucial for analyte detection. It can be decisive which type of compounds are ionizable and in which state they appear, e.g., charge and possible fragmentation of the ions. A few examples of ionization are mentioned in the paragraphs below. | 1 | Applied and Interdisciplinary Chemistry |
Unlike unanchored axial and universal expansion joints, lateral expansion joints do not load adjacent pipe supports with the axial compressive force from internal pressure since this force is absorbed by the tie rods.
Angular expansion joint
The angular expansion joint absorbs bending and angular movement. Like a simple axial expansion joint, it consists of a metal bellows and connectors on both sides. It also features
* A hinged anchoring of these connectors for angular movements in a single plane, or
* A gimbal-mounted anchoring for angular movements in all planes
Thus, the anchoring determines the type of movement absorption. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, the Bates–Guggenheim Convention refers to a conventional method based on the Debye–Hückel theory to determine pH standard values. | 0 | Theoretical and Fundamental Chemistry |
Since buildings are not totally sealed (at the very minimum, there is always a ground level entrance), the stack effect will cause air infiltration. During the heating season, the warmer indoor air rises up through the building and escapes at the top either through open windows, ventilation openings, or unintentional holes in ceilings, like ceiling fans and recessed lights. The rising warm air reduces the pressure in the base of the building, drawing cold air in through either open doors, windows, or other openings and leakage. During the cooling season, the stack effect is reversed, but is typically weaker due to lower temperature differences.
In a modern high-rise building with a well-sealed envelope, the stack effect can create significant pressure differences that must be given design consideration and may need to be addressed with mechanical ventilation. Stairwells, shafts, elevators, and the like, tend to contribute to the stack effect, while interior partitions, floors, and fire separations can mitigate it. Especially in case of fire, the stack effect needs to be controlled to prevent the spread of smoke and fire, and to maintain tenable conditions for occupants and firefighters. While natural ventilation methods may be effective, such as air outlets being installed closer to the ground, mechanical ventilation is often preferred for taller structures or in buildings with limited space. Smoke extraction is a key consideration in new constructions and must be evaluated in design stages.
The Grenfell Tower fire, as a result of which 72 people died, was in part exacerbated by the stack effect. A cavity between the outer aluminium cladding and the inner insulation formed a chimney and drew the fire upwards. | 0 | Theoretical and Fundamental Chemistry |
Lack of assay sensitivity has different implications for trials intended to show a difference greater than zero between interventions (superiority trials) and trials intended to show non-inferiority. Non-inferiority trials attempt to rule out some margin of inferiority between a test and control intervention i.e. rule out that the test intervention is no worse than the control intervention by a chosen amount.
If a trial intended to demonstrate efficacy by showing superiority of a test intervention to control lacks assay sensitivity, it will fail to show that the test intervention is superior and will fail to lead to a conclusion of efficacy.
In contrast, if a trial intended to demonstrate efficacy by showing a test intervention is non-inferior to an active control lacks assay sensitivity, the trial may find an ineffective intervention to be non-inferior and could lead to an erroneous conclusion of efficacy.
When two interventions within a trial are shown to have different efficacy (i.e., when one intervention is superior), that finding itself directly demonstrates that the trial had assay sensitivity (assuming the finding is not related to random or systematic error). In contrast, a trial that demonstrates non-inferiority between two interventions, or an unsuccessful superiority trial, generally does not contain such direct evidence of assay sensitivity. However, the idea that non-inferiority trials lack assay sensitivity has been disputed. | 1 | Applied and Interdisciplinary Chemistry |
The "A260 unit" is used as a quantity measure for nucleic acids. One A260 unit is the amount of nucleic acid contained in 1 mL and producing an OD of 1. The same conversion factors apply, and therefore, in such contexts:
:1 A260 unit dsDNA = 50 µg
:1 A260 unit ssDNA = 33 µg
:1 A260 unit ssRNA = 40 µg | 0 | Theoretical and Fundamental Chemistry |
Atmospheric methane removal is a category of potential approaches being researched to accelerate the breakdown of methane that is in the atmosphere, for the purpose of mitigating some of the impacts of climate change.
Atmospheric methane has increased since pre-industrial times from 0.7 ppm to 1.9 ppm. From 2010 to 2019, methane emissions caused 0.5 °C (about 30%) of observed global warming. Global methane emissions approached a record 600 Tg CH per year in 2017. | 1 | Applied and Interdisciplinary Chemistry |
Translational glycobiology or applied glycobiology is the branch of glycobiology and glycochemistry that focuses on developing new pharmaceuticals through glycomics and glycoengineering. Although research in this field presents many difficulties, translational glycobiology presents applications with therapeutic glycoconjugates, with treating various bone diseases, and developing therapeutic cancer vaccines and other targeted therapies. Some mechanisms of action include using the glycan for drug targeting, engineering protein glycosylation for better efficacy, and glycans as drugs themselves. | 1 | Applied and Interdisciplinary Chemistry |
In 2012, Yu and co-workers reported a pioneering meta-selective C-H olefination using nitrile-containing templates to deliver the palladium to the meta-position via a macrocyclic cyclophane-like pre-transition state. The nitrile group is tethered to the aromatic ring by a removable linker. It coordinates weakly to palladium in an "end-on" fashion, which refers to the linear structure of C–CN–Pd bonds. The linear coordination is proposed to help overcome the high strain in the cyclophane-like pre-transition state that brings palladium to the vicinity of the meta-hydrogen. The template is designed as such that the flat arene linker keeps the substrate aromatic ring and the nitrile group coplanar. Bulky substituents on the arene linker "lock" the nitrile tether in the desired position. The delicate design results in high regioselectivity towards the meta-C-H bond. The templates can be removed easily to give toluene derivatives or hydrocinnamic acid derivatives in high yield.
In their subsequent works, Yu and co-workers report the application of the same strategy in meta-selective C-H cross-coupling, meta-C-H acetoxylation and meta-C–H olefination in a broad substrate scope. It is demonstrated that the "end-on" template not only work with the Pd(0)/Pd(II) catalytic cycle but is also compatible with the Pd(II)/Pd(IV) cycle. In all three works, addition of mono-N-protected amino acid (MPAA) such as N-acetyl glycine improves the reaction yields and enhances the regioselectivity. | 0 | Theoretical and Fundamental Chemistry |
Researchers at the École Polytechnique Fédérale de Lausanne and at the Université du Québec à Montréal claim to have overcome two of the DSC's major issues:
* "New molecules" have been created for the electrolyte, resulting in a liquid or gel that is transparent and non-corrosive, which can increase the photovoltage and improve the cell's output and stability.
* At the cathode, platinum was replaced by cobalt sulfide, which is far less expensive, more efficient, more stable and easier to produce in the laboratory. | 0 | Theoretical and Fundamental Chemistry |
The main uses of fluoride, in terms of volume, are in the production of cryolite, NaAlF. It is used in aluminium smelting. Formerly, it was mined, but now it is derived from hydrogen fluoride. Fluorite is used on a large scale to separate slag in steel-making. Mined fluorite (CaF) is a commodity chemical used in steel-making. Uranium hexafluoride is employed in the purification of uranium isotopes. | 1 | Applied and Interdisciplinary Chemistry |
Dextromethorphan is the dextrorotatory enantiomer of levomethorphan, which is the methyl ether of levorphanol, both opioid analgesics. It is named according to IUPAC rules as (+)-3-methoxy-17-methyl-9α,13α,14α-morphinan. As its pure form, dextromethorphan occurs as an odorless, opalescent white powder. It is freely soluble in chloroform and insoluble in water; the hydrobromide salt is water-soluble up to 1.5 g/100 mL at 25 °C. Dextromethorphan is commonly available as the monohydrated hydrobromide salt, and is also available in extended-release formulations (sold as dextromethorphan polistirex) contain dextromethorphan bound to an ion-exchange resin based on polystyrene sulfonic acid. Dextromethorphan's specific rotation in water is +27.6° (20 °C, Sodium D-line). | 0 | Theoretical and Fundamental Chemistry |
Charles Hatchett's work on chemistry occurred mostly between 1796 and 1806, a ten-year period. In 1796, he published "An analysis of the Corinthian molybdate of lead", resolving a dispute over the nature of the mineral. In 1797 he was elected a Fellow of The Royal Society, largely as a result of this work. In more than 20 additional papers, he addressed the chemistry of minerals, resins and natural products.
In 1800 Hatchett may have opened a small chemical works at Chiswick in London.
In 1798, Hatchett was asked by members of the Privy Council to work with Henry Cavendish and assess "the state of the coins of the realm" to ensure that they were not being adulterated.
He produced a 152-page-long report in 1803. He concluded that there was no important defect in the composition or quantity of the standard gold.
Hatchett developed a collection of over 7000 minerals, which he sold to the British Museum in London in 1799. He agreed to organize the museum's mineral collection, but retained the right to remove and analyze portions of some of the specimens.
In 1801, Hatchett analyzed a piece of columbite from the collection at the British Museum. Columbite turned out to be a very complex mineral, and Hachett discovered that it contained a "new earth" which implied the existence of a new element. Lavoisier had defined the term "element" a mere 13 years previously. Hatchett called this new element "columbium" (Cb) in honour of Christopher Columbus, the discoverer of America.
On 26 November of that year he announced his discovery before the Royal Society.
In 1802 Anders Gustaf Ekeberg (1767–1813) announced the discovery of another new element, "tantalum". For many years, there was confusion over whether columbium and tantalum were the same.
In 1846, German chemist Heinrich Rose argued that there were two additional elements in tantalite, which he named niobium and pelopium for the children of the Cyclops. Eventually, Roses niobium (atomic number 41) was found to be identical to Hatchetts columbium. In 1949, the name niobium was chosen for element 41 at the 15th Conference of the Union of Chemistry in Amsterdam. | 1 | Applied and Interdisciplinary Chemistry |
This reaction usually applies to the interconversion of di- and trivalent metal ions, which involves the exchange of only one electron. The process is called self-exchange, meaning that the ion appears to exchange electrons with itself. The standard electrode potential for the following equilibrium:
shows the increasing stability of the lower oxidation state as atomic number increases. The very large value for the manganese couple is a consequence of the fact that octahedral manganese(II) has zero crystal field stabilization energy (CFSE) but manganese(III) has 3 units of CFSE.
Using labels to keep track of the metals, the self-exchange process is written as:
The rates of electron exchange vary widely, the variations being attributable to differing reorganization energies: when the 2+ and 3+ ions differ widely in structure, the rates tend to be slow. The electron transfer reaction proceeds via an outer sphere electron transfer. Most often large reorganizational energies are associated with changes in the population of the e level, at least for octahedral complexes. | 0 | Theoretical and Fundamental Chemistry |
Sinter roasting involves heating the fine ores at high temperatures, where simultaneous oxidation and agglomeration of the ores take place. For example, lead sulfide ores are subjected to sinter roasting in a continuous process after froth flotation to convert the fine ores to workable agglomerates for further smelting operations. | 1 | Applied and Interdisciplinary Chemistry |
Close ties exists to the TU Dresden, one of eleven universities distinguished as a "University of Excellence" by the German Universities Excellence Initiative.
Due to joint appointments, the heads of the institutes and the research area simultaneously hold professorships at the Technische Universität Dresden (Faculties of Chemistry and Food Chemistry, Physics as well as Mechanical Science and Engineering). About 100 PhD students are permanently integrated in the research at the IPF and numerous diploma, master and bachelor theses are worked out and supervised here.
Common projects include the Max Bergmann Center of Biomaterials, the Center for Regenerative Therapies Dresden (CRTD) and the Center for Advancing Electronics Dresden (CfAED)., the B CUBE - Center for Molecular and Cellular Bioengineering, the so-called Cluster of Excellence "Physics of Life", and the Else Kröner-Fresenius Center for Digital Health. The IPF is together with TU Dresden and other research institutes in Dresden member of the research alliance DRESDEN-concept that was founded due to the German Universities Excellence Initiative mentioned above. | 1 | Applied and Interdisciplinary Chemistry |
Preparative methods for small scale reactions for research or for production of fine chemicals often employ expensive consumable reagents.
* Oxidation of primary alcohols or aldehydes with strong oxidants such as potassium dichromate, Jones reagent, potassium permanganate, or sodium chlorite. The method is more suitable for laboratory conditions than the industrial use of air, which is "greener" because it yields less inorganic side products such as chromium or manganese oxides.
* Oxidative cleavage of olefins by ozonolysis, potassium permanganate, or potassium dichromate.
* Hydrolysis of nitriles, esters, or amides, usually with acid- or base-catalysis.
* Carbonation of a Grignard reagent and organolithium reagents:
* Halogenation followed by hydrolysis of methyl ketones in the haloform reaction
* Base-catalyzed cleavage of non-enolizable ketones, especially aryl ketones: | 0 | Theoretical and Fundamental Chemistry |
Hydrolysis constants (log values) in critical compilations at infinite dilution, T = 298.15 K and I = 3 M NaClO () or 0.1 M Na medium, Data at I = 0 are not available (): | 0 | Theoretical and Fundamental Chemistry |
An isotopic tracer, (also "isotopic marker" or "isotopic label"), is used in chemistry and biochemistry to help understand chemical reactions and interactions. In this technique, one or more of the atoms of the molecule of interest is substituted for an atom of the same chemical element, but of a different isotope (like a radioactive isotope used in radioactive tracing). Because the labeled atom has the same number of protons, it will behave in almost exactly the same way as its unlabeled counterpart and, with few exceptions, will not interfere with the reaction under investigation. The difference in the number of neutrons, however, means that it can be detected separately from the other atoms of the same element.
Nuclear magnetic resonance (NMR) and mass spectrometry (MS) are used to investigate the mechanisms of chemical reactions. NMR and MS detects isotopic differences, which allows information about the position of the labeled atoms in the products' structure to be determined. With information on the positioning of the isotopic atoms in the products, the reaction pathway the initial metabolites utilize to convert into the products can be determined. Radioactive isotopes can be tested using the autoradiographs of gels in gel electrophoresis. The radiation emitted by compounds containing the radioactive isotopes darkens a piece of photographic film, recording the position of the labeled compounds relative to one another in the gel.
Isotope tracers are commonly used in the form of isotope ratios. By studying the ratio between two isotopes of the same element, we avoid effects involving the overall abundance of the element, which usually swamp the much smaller variations in isotopic abundances. Isotopic tracers are some of the most important tools in geology because they can be used to understand complex mixing processes in earth systems. Further discussion of the application of isotopic tracers in geology is covered under the heading of isotope geochemistry.
Isotopic tracers are usually subdivided into two categories: stable isotope tracers and radiogenic isotope tracers. Stable isotope tracers involve only non-radiogenic isotopes and usually are mass-dependent. In theory, any element with two stable isotopes can be used as an isotopic tracer. However, the most commonly used stable isotope tracers involve relatively light isotopes, which readily undergo fractionation in natural systems. See also isotopic signature. A radiogenic isotope tracer involves an isotope produced by radioactive decay, which is usually in a ratio with a non-radiogenic isotope (whose abundance in the earth does not vary due to radioactive decay). | 0 | Theoretical and Fundamental Chemistry |
Ionic bonding is a kind of chemical bonding that arises from the mutual attraction of oppositely charged ions. Ions of like charge repel each other, and ions of opposite charge attract each other. Therefore, ions do not usually exist on their own, but will bind with ions of opposite charge to form a crystal lattice. The resulting compound is called an ionic compound, and is said to be held together by ionic bonding. In ionic compounds there arise characteristic distances between ion neighbours from which the spatial extension and the ionic radius of individual ions may be derived.
The most common type of ionic bonding is seen in compounds of metals and nonmetals (except noble gases, which rarely form chemical compounds). Metals are characterized by having a small number of electrons in excess of a stable, closed-shell electronic configuration. As such, they have the tendency to lose these extra electrons in order to attain a stable configuration. This property is known as electropositivity. Non-metals, on the other hand, are characterized by having an electron configuration just a few electrons short of a stable configuration. As such, they have the tendency to gain more electrons in order to achieve a stable configuration. This tendency is known as electronegativity. When a highly electropositive metal is combined with a highly electronegative nonmetal, the extra electrons from the metal atoms are transferred to the electron-deficient nonmetal atoms. This reaction produces metal cations and nonmetal anions, which are attracted to each other to form a salt. | 0 | Theoretical and Fundamental Chemistry |
Metal thiolate functionality is pervasive in metalloenzymes. Iron-sulfur proteins, blue copper proteins, and the zinc-containing enzyme liver alcohol dehydrogenase feature thiolate ligands. Commonly thiolate is ligand is provided from the cysteine residue. All molybdoproteins feature thiolates in the form of cysteinyl and/or molybdopterin. | 0 | Theoretical and Fundamental Chemistry |
Matrix-M is a vaccine adjuvant, a substance that is added to various vaccines to stimulate the immune response. It was patented in 2020 by Novavax and is composed of nanoparticles from saponins extracted from Quillaja saponaria (soapbark) trees, cholesterol, and phospholipids. It is an immune stimulating complex (ISCOM), which are nanospheres formed when saponin is mixed with two types of fats.
Adjuvants increase the bodys immune response to a vaccine by creating higher levels of antibodies. They can either enhance, modulate, and/or prolong the bodys immune response, reducing the number of vaccinations needed for immunization.
The Matrix-M adjuvant is used in a number of vaccine candidates, including the malaria vaccine R21/Matrix-M, influenza vaccines, and in the approved Novavax COVID-19 vaccine. In 2021, the R21/Matrix-M malaria vaccine candidate showed a 77% efficacy over a 12-month period. In influenza vaccine candidates, Matrix-M was shown to offer cross-protection against multiple strains of influenza.
Novavax is also testing a combined flu and COVID-19 vaccine candidate with Matrix-M. | 1 | Applied and Interdisciplinary Chemistry |
Biochemical differences between different organisms and humans are useful for drug development. For instance, penicillin kills bacteria by inhibiting the bacterial enzyme DD-transpeptidase, destroying the development of the bacterial cell wall and inducing cell death. Thus, the study of binding sites is relevant to many fields of research, including cancer mechanisms, drug formulation, and physiological regulation. The formulation of an inhibitor to mute a protein's function is a common form of pharmaceutical therapy.
In the scope of cancer, ligands that are edited to have a similar appearance to the natural ligand are used to inhibit tumor growth. For example, Methotrexate, a chemotherapeutic, acts as a competitive inhibitor at the dihydrofolate reductase active site. This interaction inhibits the synthesis of tetrahydrofolate, shutting off production of DNA, RNA and proteins. Inhibition of this function represses neoplastic growth and improves severe psoriasis and adult rheumatoid arthritis.
In cardiovascular illnesses, drugs such as beta blockers are used to treat patients with hypertension. Beta blockers (β-Blockers) are antihypertensive agents that block the binding of the hormones adrenaline and noradrenaline to β1 and β2 receptors in the heart and blood vessels. These receptors normally mediate the sympathetic "fight or flight" response, causing constriction of the blood vessels.
Competitive inhibitors are also largely found commercially. Botulinum toxin, known commercially as Botox, is a neurotoxin that causes flaccid paralysis in the muscle due to binding to acetylcholine dependent nerves. This interaction inhibits muscle contractions, giving the appearance of smooth muscle. | 1 | Applied and Interdisciplinary Chemistry |
Advancing Chemistry by Enhancing Learning in the Laboratory (ACELL) is a project for improving the teaching of Chemistry in the Laboratory. | 1 | Applied and Interdisciplinary Chemistry |
A frigorific mixture may be used to obtain a liquid medium that has a reproducible temperature below ambient temperature. Such mixtures were used to calibrate thermometers. In chemistry a cooling bath may be used to control the temperature of a strongly exothermic reaction.
A frigorific mixture may be used as an alternative to mechanical refrigeration. For example to fit two machined metal parts together, one part is placed in a frigorific mixture, causing it to contract so that may be easily inserted into the uncooled second part; on warming the two parts are held together tightly. | 0 | Theoretical and Fundamental Chemistry |
During the study of a new pharmacological compound, the clinical trial is one of the phases before the market release.
At this level, following the directions of the clinical trial protocol, the new drug is administrated to the patient as a therapy, and the patient's clinical status is monitored aiming to evaluate possible side effects. | 1 | Applied and Interdisciplinary Chemistry |
Templating utilizes a mold to add nanostructure to a polymer. Molds can come from a variety of sources including natural sources, such as the lotus leaf, due to their self-cleaning properties. | 0 | Theoretical and Fundamental Chemistry |
Desalting spin columns are widely available with various volumes and MWCO limits:
* [http://www.piercenet.com/cat/desalting-columns Thermo Scientific Pierce Products]
* [http://www.bio-rad.com/en-us/category/bio-spin-micro-bio-spin-size-exclusion-columns Bio-Rad Laboratories, Inc.]
* [https://www.cytivalifesciences.com/en/us/shop/chromatography/prepacked-columns/desalting-and-buffer-exchange/ Cytiva ] | 0 | Theoretical and Fundamental Chemistry |
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