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The spacer is an integral part of the FSL Kode construct and gives it several important characteristics including water dispersibility.
* Length – the spacer can be varied in length, for example 1.9 nm (Ad), 7.2 nm (CMG2), 11.5 nm (CMG4), allowing for enhanced presentation of Functional groups at the biosurface.
* Optimizes F presentation – The presentation of the bioactive (functional group) on a spacer reduces steric hindrance and increases the bioactive surfaces exposed and available for interactions
* Rigidity – the spacer can be modified to be either flexible or rigid depending upon desired characteristics
* Substitutions (represented by the leaves on the stalk) – the spacer can be modified both in charge, and polarity.
* Branches – usually the spacer is linear, but it can also be branched including specific spacing of the branches to optimize presentation and interaction of the F group.
* Inert – important to the design of FSL Kode constructs is the biologically inert nature of the spacer. Importantly this feature means the S-L components of the constructs are unreactive with undiluted serum. Consequently, the constructs are compatible in vivo use, and can improve diagnostic assay sensitivity by allowing for the use of undiluted serum. | 1 | Biochemistry |
*Crankshaft reconditioning or conditioning
*Corrosion protection
*Fouling protection
*Altering thermal conductivity or electrical conductivity
*Wear control: either hardfacing (wear-resistant) or abradable coating
*Repairing damaged surfaces
*Temperature/oxidation protection (thermal barrier coatings)
*Medical implants coatings (by using polymer derived ceramics)
*Production of functionally graded materials (for any of the above applications) | 8 | Metallurgy |
* Journal of Photochemistry and Photobiology [https://www.sciencedirect.com/journal/journal-of-photochemistry-and-photobiology]
* ChemPhotoChem [https://chemistry-europe.onlinelibrary.wiley.com/journal/23670932]
* Photochemistry and Photobiology [https://onlinelibrary.wiley.com/journal/17511097]
* Photochemical & Photobiological Sciences [https://www.springer.com/journal/43630]
* Photochemistry [https://www.mdpi.com/journal/molecules/sections/photochemistry] | 5 | Photochemistry |
Most equilibrium fractionations are thought to result from the reduction in vibrational energy (especially zero-point energy) when a more massive isotope is substituted for a less massive one. This leads to higher concentrations of the massive isotopes in substances where the vibrational energy is most sensitive to isotope substitution, i.e., those with the highest bond force constants.
In a reaction involving the exchange of two isotopes, X and X, of element "X" in molecules AX and BX,
each reactant molecule is identical to a product except for the distribution of isotopes (i.e., they are isotopologues). The amount of isotopic fractionation in an exchange reaction can be expressed as a fractionation factor:
indicates that the isotopes are distributed evenly between AX and BX, with no isotopic fractionation. indicates that X is concentrated in substance AX, and indicates X is concentrated in substance BX. is closely related to the equilibrium constant (K):
where is the product of the rotational symmetry numbers of the products (right side of the exchange reaction), is the product of the rotational symmetry numbers of the reactants (left side of the exchange reaction), and is the number of atoms exchanged.
An example of equilibrium isotope fractionation is the concentration of heavy isotopes of oxygen in liquid water, relative to water vapor,
At 20 °C, the equilibrium fractionation factor for this reaction is
Equilibrium fractionation is a type of mass-dependent isotope fractionation, while mass-independent fractionation is usually assumed to be a non-equilibrium process.
For non-equilibrium reactions, isotopic effects are better described by the GEBIK and GEBIF equations for transient kinetic isotope fractionation, which generalize non-steady isotopic effects in any chemical and biochemical reactions. | 9 | Geochemistry |
(+)-Discodermolide is a highly potent antiproliferative agent. (+)-Discodermolide treated murine Do11.10T hybridoma cells could not proceed normal cell cycling. In untreated controls, 68% of cells were found at G1 phase, and 31% were found at S phase, and less than 1% was found at the G2/M phase. However, after 3 hours (+)-discodermolide treatment, 52% were found at G1 phase, 40% at S phase, and 58% at G2 and M phase. This result indicated that (+)-discodermolide blocks the cell cycle at G2 and M phase. This inhibition effect was also found to be reversible. Cells resume normal cycling within 48 hours after removal of (+)-discodermolide from the cell culture medium.
(+)-Discodermolide arrests cell cycle via binding and stabilization of the microtubule network. Hyper-stabilization of the mitotic spindle causes cell cycle arresting at G2 and M phase and eventually leads to cell death by apoptosis. At 10µM concentration, (+)-discodermolide is able to promote microtubules assembly without microtubule-associated proteins and GTP. With microtubule-associated protein and GTP presented, 10µM (+)-discodermolide is able to initiate tubulin polymerization at 0 °C. | 0 | Organic Chemistry |
Any process that results in the production of methane and its release into the atmosphere can be considered a "source". The known sources of methane are predominantly located near the Earth's surface. Two main processes that are responsible for methane production include microorganisms anaerobically converting organic compounds into methane (methanogenesis), which are widespread in aquatic ecosystems, and ruminant animals. Other natural sources include melting permafrost, wetlands, plants, and methane clathrates. | 2 | Environmental Chemistry |
After leaching, the leach liquor must normally undergo concentration of the metal ions that are to be recovered. Additionally, undesirable metal ions sometimes require removal.
*Precipitation is the selective removal of a compound of the targeted metal or removal of a major impurity by precipitation of one of its compounds. Copper is precipitated as its sulfide as a means to purify nickel leachates.
*Cementation is the conversion of the metal ion to the metal by a redox reaction. A typical application involves addition of scrap iron to a solution of copper ions. Iron dissolves and copper metal is deposited.
*Solvent Extraction
*Ion exchange
*Gas reduction. Treating a solution of nickel and ammonia with hydrogen affords nickel metal as its powder.
*Electrowinning is a particularly selective if expensive electrolysis process applied to the isolation of precious metals. Gold can be electroplated from its solutions. | 8 | Metallurgy |
(p)ppGpp, guanosine pentaphosphate and tetraphosphate, also known as the "magic spot" nucleotides, are alarmones involved in the stringent response in bacteria that cause the inhibition of RNA synthesis when there is a shortage of amino acids. This inhibition by (p)ppGpp decreases translation in the cell, conserving amino acids present. Furthermore, ppGpp and pppGpp cause the up-regulation of many other genes involved in stress response such as the genes for amino acid uptake (from surrounding media) and biosynthesis. | 1 | Biochemistry |
Sialyl lewis x is important in ABO blood antigen determination.
SLex is also important to proper immune response. P-selectin release from Weibel-Palade bodies, on blood vessel endothelial cells, can be induced by a number of factors. One such factor is the response of the endothelial cell to certain bacterial molecules, such as peptidoglycan. P-selectin binds to the SLex structure that is present on neutrophils in the bloodstream and helps to mediate the extravasation of these cells into the surrounding tissue during infection.
O-linked glycans, in particular mucin, have been found to be important in developing normal intestinal microflora. Certain strains of intestinal bacteria bind specifically to mucin, allowing them to colonize the intestine.
Examples of O-linked glycoproteins are:
*Glycophorin, a protein in erythrocyte cell membranes
*Mucin, a protein in saliva involved in formation of dental plaque
*Notch, a transmembrane receptor involved in development and cell fate decisions
*Thrombospondin
*Factor VII
*Factor IX
*Urinary type plasminogen activator | 0 | Organic Chemistry |
Vincenzo Balzani (born 15 November 1936 in Forlimpopoli, Italy) is an Italian chemist, now emeritus professor at the University of Bologna. | 5 | Photochemistry |
Crack extension, as opposed to crack onset, is the rate determining step for solid induced-metal embrittlement. The main mechanism leading to solid metal induced embrittlement is multilayer surface self-diffusion of the embrittler at the crack tip. Propagation rate of a crack undergoing metal-induced embrittlement is a function of the supply of embrittler present at the crack tip. Crack velocities in SMIE are much slower than LMIE velocities. Catastrophic failure of a material via SMIE occurs as a result of the propagation of cracks to a critical point. To this end, the propagation of the crack is controlled by the transport rate and mechanisms of the embrittler at the tip of nucleated cracks. SMIE can be mitigated by increasing the tortuosity of crack paths such that resistance to intergranular cracking increases. | 8 | Metallurgy |
Spalling is a common mechanism of rock weathering, and occurs at the surface of a rock when there are large shear stresses under the surface. This form of mechanical weathering can be caused by freezing and thawing, unloading, thermal expansion and contraction, or salt deposition. | 8 | Metallurgy |
In UIT, ultrasonic waves are produced by an electro-mechanical ultrasonic transducer, and applied to a workpiece. An acoustically tuned resonator bar is caused to vibrate by energizing it with a magnetostrictive or Piezoelectric ultrasonic transducer. The energy generated from these high frequency impulses is imparted to the treated surface through the contact of specially designed steel pins. These transfer pins are free to move axially between the resonant body and the treated surface.
When the tool, made up of the ultrasonic transducer, pins and other components, comes into contact with the work piece it acoustically couples with the work piece, creating harmonic resonance. This harmonic resonance is performed at a carefully calibrated frequency, to which metals respond very favorably, resulting in compressive residual stress, stress relief and grain structure improvements.
Depending on the desired effects of treatment a combination of different frequencies and displacement amplitude is applied. Depending on the tool and the Original Equipment Manufacturer, these frequencies range between 15 and 55 kHz, with the displacement amplitude of the resonant body of between . | 8 | Metallurgy |
The Bailey peptide synthesis is a name reaction in organic chemistry developed 1949 by J. L. Bailey. It is a method for the synthesis of a peptide from α-amino acid-N-carboxylic acid anhydrides (NCAs) and amino acids or peptide esters. The reaction is characterized by short reaction times and a high yield of the target peptide.
The reaction can be carried out at low temperatures in organic solvents. The residues R and R can be organic groups or hydrogen atoms, R is the used amino acid or peptide ester: | 1 | Biochemistry |
Permanent mold casting is a metal casting process that employs reusable molds ("permanent molds"), usually made from metal. The most common process uses gravity to fill the mold. However, gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds. Permanent molds, while lasting more than one casting still have a limited life before wearing out. | 8 | Metallurgy |
Of commercial interest, acyl chlorides react with HF to give acyl fluorides. Aromatic (as well as aliphatic) acyl fluorides are conveniently prepared directly from carboxylic acids, using stable, inexpensive commodity chemicals: , NBS and in a bench-top protocol. Cyanuric fluoride converts carboxylic acids to acyl fluorides.
Carboxylic acids react with sulfur tetrafluoride to give the acyl fluoride: | 0 | Organic Chemistry |
The transition temperature of an ELP depends to a certain extent on the identity of the "X" residue found at the fourth position of the pentapeptide monomeric unit. Residues that are highly hydrophobic, such as leucine and phenylalanine, tend to decrease the transition temperature. On the other hand, residues that are highly hydrophilic, such as serine and glutamine, tend to increase the transition temperature. The presence of a potentially charged residue at the "X" position will determine how the ELP responds to varying pHs, with glutamic acid and aspartic acid raising the T at pH values in which the residues are deprotonated and lysine and arginine raising the T at pH values in which the residues are protonated. The pH needs to be compatible with the charged states of these amino acids in order to raise the T. Also higher molecular mass ELPs and higher concentrations of ELPs in solution make it much easier for the polymer to form aggregates, in effect lowering the experimental T | 7 | Physical Chemistry |
Chlorophyll-a concentration is sometimes used to measure water clarity, especially when suspended sediments and colored dissolved organic matter concentrations are low. Chlorophyll-a concentration is a proxy for phytoplankton biomass, which is one way to quantify how turbid the water is due to biological primary production. Chlorophyll-a concentration is most useful for research on primary production, the contribution of phytoplankton to light attenuation, and harmful algal blooms. Chlorophyll-a concentration is also useful for long-term monitoring because these sensors are often low cost and sturdy enough for long deployments underwater. | 3 | Analytical Chemistry |
John Scott Newman (born November 17, 1938) is an American retired academic. A professor and renowned battery and electrochemical engineer researcher, he worked at the University of California in the Department of Chemical Engineering. The Newman Research Group was established with the goal of identifying "efficient and economical methods for electrochemical energy conversion and storage, development of mathematical models to predict the behavior of electrochemical systems and to identify important process parameters, and experimental verification of the completeness and accuracy of the models". Newman also worked for the Electrochemical Technologies Group at Lawrence Berkeley National Laboratory where he was a Faculty Senior Scientist. While at LBNL he served as director of several Department of Energy’s energy storage programs, including the Batteries for Advanced Transportation Technologies Program. He was elected a member of the National Academy of Engineering in 1999 for contributions to applied electrochemistry and for their reduction to practice through advances in electrochemical engineering. He was an Onsager Professor at the Norwegian University of Science and Technology in 2002. Newman is regarded by many as "the father of electrochemical engineering." The Newman Method is a "numerical technique...developed for solving coupled electrochemical reaction–diffusion equations".
Professor Newman has authored more than 339 scientific publications, with more the 47000 citations, and an h-index of 95. He is the author of Electrochemical Systems with Karen E. Thomas-Alyea which is "used throughout the world as a monograph and graduate text in electrochemical engineering."
In 2010 he received the Edward Goodrich Acheson Award of the Electrochemical Society, his tenth award from the society.
Newman has graduated thirty masters and forty-three Ph.D. students and seventeen have gone on to become faculty members as of 2008. The faculty include Thomas W. Chapman (Ph.D., 1967), Kemal Nisancioglu (Ph.D. 1973), Nader Vahdat (MS, 1972), Peter Willem Appel (Ph.D. 1976), Ralph Edward White (PhD, 1977), Peter S. Fedkiw (Ph.D., 1978), James Arthur Trainham, III (Ph.D., 1979), Richard Pollard (Ph.D., 1979), Mark Edward Orazem (Ph.D., 1983), Michael John Matlosz (Ph.D., 1985), Alan C. West (Ph.D., 1989), Thomas F. Fuller (Ph.D., 1992), Bavanethan Pillay (Ph.D., 1996), Jeremy Patrick Meyers (Ph.D., 1998), Heather Darya Yaros (Ph.D., 2002), Dean Richard Wheeler (Ph.D., 2002), Charles Monroe (Ph.D., 2004), Paul Albertus (Ph.D., 2009), and Maureen H. Tang (Ph.D., 2012). | 7 | Physical Chemistry |
Aside from the slowing and/or reversal of calcification, organisms may suffer other adverse effects, either indirectly through negative impacts on food resources, or directly as reproductive or physiological effects. For example, the elevated oceanic levels of may produce -induced acidification of body fluids, known as hypercapnia.
Increasing acidity has been observed to reduce metabolic rates in jumbo squid and depress the immune responses of blue mussels.
Atlantic longfin squid eggs took longer to hatch in acidified water, and the squid's statolith was smaller and malformed in animals placed in sea water with a lower pH. However, these studies are ongoing and there is not yet a full understanding of these processes in marine organisms or ecosystems. | 9 | Geochemistry |
Initially, in a glutamatergic synapse, the neurotransmitter glutamate is released from the neurons and is taken up into the synaptic cleft. Glutamate residing in the synapse must be rapidly removed in one of three ways:
# Uptake into the postsynaptic compartment,
# Re-uptake into the presynaptic compartment, or
# Uptake into a third, nonneuronal compartment.
Postsynaptic neurons remove little glutamate from the synapse. There is active reuptake into presynaptic neurons, but this mechanism appears to be less important than astrocytic transport. Astrocytes could dispose of transported glutamate in two ways. They could export it to blood capillaries, which abut the astrocyte foot processes. However, this strategy would result in a net loss of carbon and nitrogen from the system. An alternate approach would be to convert glutamate into another compound, preferably a non-neuroactive species. The advantage of this approach is that neuronal glutamate could be restored without the risk of trafficking the transmitter through extracellular fluid, where glutamate would cause neuronal depolarization. Astrocytes readily convert glutamate to glutamine via the glutamine synthetase pathway and released into the extracellular space. The glutamine is taken into the presynaptic terminals and metabolized into glutamate by the phosphate-activated glutaminase (a mitochondrial enzyme). The glutamate that is synthesized in the presynaptic terminal is packaged into synaptic vesicles by the glutamate transporter, VGLUT. Once the vesicle is released, glutamate is removed from the synaptic cleft by excitatory amino-acid transporters (EAATs). This allows synaptic terminals and glial cells to work together to maintain a proper supply of glutamate, which can also be produced by transamination of 2-oxoglutarate, an intermediate in the citric acid cycle. Recent electrophysiological evidence suggests that active synapses require presynaptically localized glutamine glutamate cycle to maintain excitatory neurotransmission in specific circumstances. In other systems, it has been suggested that neurons have alternate mechanisms to cope with compromised glutamate–glutamine cycling. | 1 | Biochemistry |
A star supplies its own energy from nuclear sources, and hence the temperature equilibrium cannot be defined in terms of incident energy only.
Cox and Giuli (1968/1984) define radiative equilibrium for a star, taken as a whole and not confining attention only to its atmosphere, when the rate of transfer as heat of energy from nuclear reactions plus viscosity to the microscopic motions of the material particles of the star is just balanced by the transfer of energy by electromagnetic radiation from the star to space. Note that this radiative equilibrium is slightly different from the previous usage. They note that a star that is radiating energy to space cannot be in a steady state of temperature distribution unless there is a supply of energy, in this case, energy from nuclear reactions within the star, to support the radiation to space. Likewise the condition that is used for the above definition of pointwise radiative equilibrium cannot hold throughout a star that is radiating: internally, the star is in a steady state of temperature distribution, not internal thermodynamic equilibrium. Cox and Giulis definition allows them to say at the same time that a star is in a steady state of temperature distribution and is in radiative equilibrium'; they are assuming that all the radiative energy to space comes from within the star. | 7 | Physical Chemistry |
The drug consists of exametazime as a chelating agent for the radioisotope technetium-99m. Both enantiomeric forms of exametazime are used—the drug is racemic. The third stereoisomer of this structure, the meso form, is not included. | 4 | Stereochemistry |
The catalysis of this mechanism is initiated by the deprotonation of TPP at the thiazolium ring. This carbanion then binds to the carbonyl of the donor substrate thus cleaving the bond between C-2 and C-3. This keto fragment remains covalently bound to the C-2 carbon of TPP. The donor substrate is then released, and the acceptor substrate enters the active site where the fragment, which is bound to the intermediate α-β-dihydroxyethyl thiamin diphosphate, is then transferred to the acceptor.
Experiments have also been conducted that test the effect replacing alanine for the amino acids at the entrance to the active site, Arg359, Arg528, and His469, which interact with the phosphate group of the substrate. This replacement creates a mutant enzyme with impaired catalytic activity. | 5 | Photochemistry |
While EPIC-seq offers significant potential in various biomedical applications, it also has limitations that warrant consideration in its implementation and interpretation. | 1 | Biochemistry |
A class of aliphatic acids (volatile fatty acids as a kind of carboxylic acid) was found in female rhesus monkeys that produced six types in the vaginal fluids. The combination of these acids is referred to as "copulins". One of the acids, acetic acid, was found in all of the sampled female's vaginal fluid. Even in humans, one-third of women have all six types of copulins, which increase in quantity before ovulation. Copulins are used to signal ovulation; however, as human ovulation is concealed it is thought that they may be used for reasons other than sexual communication. | 1 | Biochemistry |
While tubulin and related structural proteins also bind and hydrolyze GTP as part of their function to form intracellular tubules, these proteins utilize a distinct tubulin domain that is unrelated to the G domain used by signaling GTPases.
There are also GTP-hydrolyzing proteins that use a P-loop from a superclass other than the G-domain-containg one. Examples include the NACHT proteins of its own superclass and McrB protein of the AAA+ superclass. | 1 | Biochemistry |
Nucleic acids have an important range of interactions with Mg. The binding of Mg to DNA and RNA stabilises structure; this can be observed in the increased melting temperature (T) of double-stranded DNA in the presence of Mg. In addition, ribosomes contain large amounts of Mg and the stabilisation provided is essential to the complexation of this ribo-protein. A large number of enzymes involved in the biochemistry of nucleic acids bind Mg for activity, using the ion for both activation and catalysis. Finally, the autocatalysis of many ribozymes (enzymes containing only RNA) is Mg dependent (e.g. the yeast mitochondrial group II self splicing introns).
Magnesium ions can be critical in maintaining the positional integrity of closely clustered phosphate groups. These clusters appear in numerous and distinct parts of the cell nucleus and cytoplasm. For instance, hexahydrated Mg ions bind in the deep major groove and at the outer mouth of A-form nucleic acid duplexes. | 1 | Biochemistry |
Reporter genes are used in some cloning vectors to facilitate the screening of successful clones by using features of these genes that allow successful clone to be easily identified. Such features present in cloning vectors may be the lacZα fragment for α complementation in blue-white selection, and/or marker gene or reporter genes in frame with and flanking the MCS to facilitate the production of fusion proteins. Examples of fusion partners that may be used for screening are the green fluorescent protein (GFP) and luciferase. | 1 | Biochemistry |
Pro-inflammatory cytokine IL-12 is produced in heterodimer form by B cells and antigen-presenting cells. Binding of IL-12 to IL-12R, which is composed of two different subunits (IL12Rβ1 and IL12Rβ2), leads to the interaction of IL12Rβ1 and IL12Rβ2 with JAK2 and TYK2, which is followed by phosphorylation of STAT4 tyrosine 693. The pathway then induces IFNγ production and Th1 differentiation. STAT4 is critical in promotion of antiviral response of natural killer (NK) cell by targeting of promotor regions of Runx1 and Runx3. | 1 | Biochemistry |
The Institute brings together over 200 technical and scientific staff with a panel of expertise ranging from theoretical chemistry to physics, through modeling, biochemistry, and analytical chemistry. The ISA also has a tip and global instrumentation equipment: NMR spectrometer (1Ghz), hosted by the «Very High Fields NMR European Center» (CRMN Lyon, France ).
The Institute organized its research activities in five areas:
* mass spectrometry
* modeling and applied analysis
* NMR spectroscopy
* separative sciences and surfaces
* (bio)Interfaces, micro / nanosystems.
The research focuses on developing new methods through technological innovation in the analysis of complex systems in all fields, with applications in biomedicine, calculation methods, environment, materials science and structural biology. | 3 | Analytical Chemistry |
Zero Carbon World were one of the Sponsors of the 2012 Bath Film Festival which included a showing of Revenge of the Electric Car. | 2 | Environmental Chemistry |
Anoxygenic photosynthesis is a special form of photosynthesis used by some bacteria and archaea, which differs from the better known oxygenic photosynthesis in plants in the reductant used (e.g. hydrogen sulfide instead of water) and the byproduct generated (e.g. elemental sulfur instead of molecular oxygen). | 5 | Photochemistry |
Although available commercially, diethyl azodicarboxylate can be prepared fresh in the laboratory, especially if required in pure, non-diluted form. A two-step synthesis starts from hydrazine, first by alkylation with ethyl chloroformate, followed by treating the resulting diethyl hydrazodicarboxylate with chlorine (bubbling through the solution), hypochlorous acid, concentrated nitric acid or red fuming nitric acid. The reaction is carried out in an ice bath, and the reagents are added dropwise so that the temperature does not rise above 20 °C. Diethyl hydrazodicarboxylate is a solid with melting temperature of 131–133 °C which is collected as a residue; it is significantly more stable to heating than DEAD and is conventionally dried at a temperature of about 80 °C. | 0 | Organic Chemistry |
The C-terminal telopeptide (CTX), also known as carboxy-terminal collagen crosslinks, is the C-terminal telopeptide of fibrillar collagens such as collagen type I and type II. It is used as a biomarker in the serum to measure the rate of bone turnover. It can be useful in assisting clinicians to determine a patients nonsurgical treatment response as well as evaluate a patients risk of developing complications during healing following surgical intervention. The test used to detect the CTX marker is called the Serum CrossLaps, and it is more specific to bone resorption than any other test currently available. | 1 | Biochemistry |
On the other hand, softer, more polarisable centres prefer to coordinate in a more covalent manner through the phosphorus atom. Examples of this include complexes accommodating a neutral or sparsely charged transition metal centre. The first example of this nature of PCO binding was published by Grutzmacher and co-workers in 2012. The groups studies used a Re(I) complex and the analysis of its bonding parameters and electronic structure showed that the phosphaethynolate anion coordinated in a bent fashion. This suggested the Re(I) – P bond possessed a highly covalent character thus the complex would be best described as a metallaphosphaketene. It wasnt until four years later that a second example of this coordination nature of PCO was identified. This time it came in the form of a W(0) pentacarbonyl complex produced by the Goicoechea group. | 7 | Physical Chemistry |
The number of entities (symbol N) in a one-mole sample equals the Avogadro number (symbol N), a dimensionless quantity.
Historically, N approximates the number of nucleons (protons or neutrons) in one gram of ordinary matter.
The Avogadro constant (symbol ) has numerical multiplier given by the Avogadro number with the unit reciprocal mole (mol).
The ratio is a measure of the amount of substance (with the unit mole). | 3 | Analytical Chemistry |
A three- dimensional translation slides every point in space by a fixed distance in the x-direction, a fixed distance in the y-direction, and a fixed distance in the z-direction. | 7 | Physical Chemistry |
An oceanographic water mass is an identifiable body of water with a common formation history which has physical properties distinct from surrounding water. Properties include temperature, salinity, chemical - isotopic ratios, and other physical quantities which are conservative flow tracers. Water mass is also identified by its non-conservative flow tracers such as silicate, nitrate, oxygen, and phosphate.
Water masses are generally distinguished not only by their respective tracers but also by their location in the Worlds' oceans. Water masses are also distinguished by their vertical position so that there are surface water masses, intermediate water masses and deep water masses. | 9 | Geochemistry |
In Chapter 12 of The Conservation of Orbital Symmetry, entitled "Violations," Woodward and Hoffmann famously stated:This pronouncement notwithstanding, it is important to recognize that the Woodward–Hoffmann rules are used to predict relative barrier heights, and thus likely reaction mechanisms, and that they only take into account barriers due to conservation of orbital symmetry. Thus it is not guaranteed that a WH symmetry-allowed reaction actually takes place in a facile manner. Conversely, it is possible, upon enough energetic input, to achieve an anti-Woodward-Hoffmann product. This is especially prevalent in sterically constrained systems, where the WH-product has an added steric barrier to overcome. For example, in the electrocyclic ring-opening of the dimethylbicyclo[0.2.3]heptene derivative (1), a conrotatory mechanism is not possible due to resulting angle strain and the reaction proceeds slowly through a disrotatory mechanism at 400 C to give a cycloheptadiene product. Violations may also be observed in cases with very strong thermodynamic driving forces. The decomposition of dioxetane-1,2-dione to two molecules of carbon dioxide, famous for its role in the luminescence of glowsticks, has been scrutinized computationally. In the absence of fluorescers, the reaction is now believed to proceed in a concerted (though asynchronous) fashion, via a retro-[2+2]-cycloaddition that formally violates the Woodward–Hoffmann rules.
Similarly, a recent paper describes how mechanical stress can be used to reshape chemical reaction pathways to lead to products that apparently violate Woodward–Hoffman rules. In this paper, they use ultrasound irradiation to induce a mechanical stress on link-functionalized polymers attached syn or anti on the cyclobutene ring. Computational studies predict that the mechanical force, resulting from friction of the polymers, induces bond lengthening along the reaction coordinate of the conrotatory mechanism in the anti-bisubstituted-cyclobutene, and along the reaction coordinate of the disrotatory mechanism in the syn-bisubstituted-cyclobutene. Thus in the syn-bisubstituted-cyclobutene, the anti-WH product is predicted to be formed.
This computational prediction was backed up by experiment on the system below. Link-functionalized polymers were conjugated to cis benzocyclobutene in both syn- and anti- conformations. As predicted, both products gave the same (Z,Z) product as determined by quenching by a stereospecific Diels-Alder reaction with the substituted maleimide. In particular, the syn-substituted product gave the anti-WH product, presumably as the mechanical stretching along the coordinate of the disrotatory pathway lowered the barrier of the reaction under the disrotatory pathway enough to bias that mechanism. | 7 | Physical Chemistry |
The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a magnetic tunnel junction.
This article deals with the term as a measurement of a devices electrical sensitivity to light. In a charge-coupled device (CCD) or other photodetector, it is the ratio between the number of charge carriers collected at either terminal and the number of photons hitting the devices photoreactive surface. As a ratio, QE is dimensionless, but it is closely related to the responsivity, which is expressed in amps per watt. Since the energy of a photon is inversely proportional to its wavelength, QE is often measured over a range of different wavelengths to characterize a device's efficiency at each photon energy level. For typical semiconductor photodetectors, QE drops to zero for photons whose energy is below the band gap. A photographic film typically has a QE of much less than 10%, while CCDs can have a QE of well over 90% at some wavelengths. | 7 | Physical Chemistry |
The fugacity is most useful in mixtures. It does not add any new information compared to the chemical potential, but it has computational advantages. As the molar fraction of a component goes to zero, the chemical potential diverges but the fugacity goes to zero. In addition, there are natural reference states for fugacity (for example, an ideal gas makes a natural reference state for gas mixtures since the fugacity and pressure converge at low pressure). | 7 | Physical Chemistry |
Circular DNA are more strongly affected by ethidium bromide concentration than linear DNA if ethidium bromide is present in the gel during electrophoresis. All naturally occurring DNA circles are underwound, but ethidium bromide which intercalates into circular DNA can change the charge, length, as well as the superhelicity of the DNA molecule, therefore its presence during electrophoresis can affect its movement in gel. Increasing ethidium bromide intercalated into the DNA can change it from a negatively supercoiled molecule into a fully relaxed form, then to positively coiled superhelix at maximum intercalation. Agarose gel electrophoresis can be used to resolve circular DNA with different supercoiling topology. | 1 | Biochemistry |
Spirapril, sold under the brand name Renormax among others, is an ACE inhibitor antihypertensive drug used to treat hypertension. It belongs to dicarboxy group of ACE inhibitors.
It was patented in 1980 and approved for medical use in 1995. | 4 | Stereochemistry |
The term "physical chemistry" was coined by Mikhail Lomonosov in 1752, when he presented a lecture course entitled "A Course in True Physical Chemistry" () before the students of Petersburg University. In the preamble to these lectures he gives the definition: "Physical chemistry is the science that must explain under provisions of physical experiments the reason for what is happening in complex bodies through chemical operations".
Modern physical chemistry originated in the 1860s to 1880s with work on chemical thermodynamics, electrolytes in solutions, chemical kinetics and other subjects. One milestone was the publication in 1876 by Josiah Willard Gibbs of his paper, On the Equilibrium of Heterogeneous Substances. This paper introduced several of the cornerstones of physical chemistry, such as Gibbs energy, chemical potentials, and Gibbs' phase rule.
The first scientific journal specifically in the field of physical chemistry was the German journal, Zeitschrift für Physikalische Chemie, founded in 1887 by Wilhelm Ostwald and Jacobus Henricus van 't Hoff. Together with Svante August Arrhenius, these were the leading figures in physical chemistry in the late 19th century and early 20th century. All three were awarded the Nobel Prize in Chemistry between 1901 and 1909.
Developments in the following decades include the application of statistical mechanics to chemical systems and work on colloids and surface chemistry, where Irving Langmuir made many contributions. Another important step was the development of quantum mechanics into quantum chemistry from the 1930s, where Linus Pauling was one of the leading names. Theoretical developments have gone hand in hand with developments in experimental methods, where the use of different forms of spectroscopy, such as infrared spectroscopy, microwave spectroscopy, electron paramagnetic resonance and nuclear magnetic resonance spectroscopy, is probably the most important 20th century development.
Further development in physical chemistry may be attributed to discoveries in nuclear chemistry, especially in isotope separation (before and during World War II), more recent discoveries in astrochemistry, as well as the development of calculation algorithms in the field of "additive physicochemical properties" (practically all physicochemical properties, such as boiling point, critical point, surface tension, vapor pressure, etc.—more than 20 in all—can be precisely calculated from chemical structure alone, even if the chemical molecule remains unsynthesized), and herein lies the practical importance of contemporary physical chemistry.
See Group contribution method, Lydersen method, Joback method, Benson group increment theory, quantitative structure–activity relationship | 7 | Physical Chemistry |
Phosgene oxime is classified as a vesicant even though it does not produce blisters. It is toxic by inhalation, ingestion, or skin contact. The effects of the poisoning occur almost immediately. No antidote for phosgene oxime poisoning is known. Generally, any treatment is supportive. Typical physical symptoms of CX exposure are as follows:
*Skin: Blanching surrounded by an erythematous ring can be observed within 30 seconds of exposure. A wheal develops on exposed skin within 30 minutes. The original blanched area acquires a brown pigmentation by 24 hours. An eschar forms in the pigmented area by 1 week and sloughs after approximately 3 weeks. Initially, the effects of CX can easily be misidentified as mustard gas exposure. However, the onset of skin irritation resulting from CX exposure is a great deal faster than mustard gas, which typically takes several hours or more to cause skin irritation.
*Eyes: Eye examination typically demonstrates conjunctivitis, lacrimation, lid edema, and blepharospasm after even minute exposures. More severe exposures can result in keratitis, iritis, corneal perforation, and blindness.
*Respiratory: Irritation of the mucous membranes may be observed on examination of the oropharynx and nose. Evidence of pulmonary edema, including rales and wheezes, may be noted on auscultation. Pulmonary thromboses are prominent features of severe CX exposure.
*Gastrointestinal: Some animal data suggest that CX may cause hemorrhagic inflammatory changes in the GI tract. | 1 | Biochemistry |
It is synthesized as a by-product in the autoxidation of cumene, which mainly affords cumene hydroperoxide. Alternatively, it can be produced by the addition of hydrogen peroxide to α-methylstyrene.
Of the ca. 60,000 ton/y production of dialkyl peroxides, dicumyl peroxide is dominant. | 0 | Organic Chemistry |
In 2006, the wells of a neighborhood in Jacksonville, Maryland, were contaminated by a spill of 26,000 gallons of gasoline from an Exxon-Mobil station in the area, resulting in an ongoing court battle. The suit has been filed by the state of Marylands Department of the Environment on behalf of the areas residents, seeking millions of dollars in damages from Exxon-Mobil. Many residents also filed their own separate lawsuits.
The case began in 2006, when a gasoline tank sprang a leak that was not detected for 34 days. Testing of 120 wells resulted in dangerously high levels of MTBE being found. Residents were put in danger by the spill, and in order to prevent further health problems, they required bottled water for cooking, drinking, and brushing teeth. Residents of Jacksonville continue to use bottled water for all activities despite having MTBE filters and alarms installed in their homes. Home values also dropped as a result of the spill.
In September 2008, Exxon-Mobil settled the case with the state by agreeing to pay a $4 million fine, and face an additional $1 million in penalties annually if they did not work to clean up the spill.
In March 2009, a jury awarded $150 million in damages to some of the area's residents. The jury did not assess any punitive damages in the case, finding that Exxon Mobil did not act fraudulently. A separate case including over 150 property owners as plaintiffs began in early 2011. Punitive damages were awarded to the second group of plaintiffs, on the basis that Exxon acted fraudulently, however this decision was later reversed. | 2 | Environmental Chemistry |
Eukaryotic messages are subject to surveillance by nonsense-mediated decay (NMD), which checks for the presence of premature stop codons (nonsense codons) in the message. These can arise via incomplete splicing, V(D)J recombination in the adaptive immune system, mutations in DNA, transcription errors, leaky scanning by the ribosome causing a frame shift, and other causes. Detection of a premature stop codon triggers mRNA degradation by 5 decapping, 3 poly(A) tail removal, or endonucleolytic cleavage. | 1 | Biochemistry |
A reversible solid oxide cell (rSOC) is a solid-state electrochemical device that is operated alternatively as a solid oxide fuel cell (SOFC) and a solid oxide electrolysis cell (SOEC). Similarly to SOFCs, rSOCs are made of a dense electrolyte sandwiched between two porous electrodes. Their operating temperature ranges from 600°C to 900°C, hence they benefit from enhanced kinetics of the reactions and increased efficiency with respect to low-temperature electrochemical technologies.
When utilized as a fuel cell, the reversible solid oxide cell is capable of oxidizing one or more gaseous fuels to produce electricity and heat. When used as an electrolysis cell, the same device can consume electricity and heat to convert back the products of the oxidation reaction into valuable fuels. These gaseous fuels can be pressurized and stored for a later use. For this reason, rSOCs are recently receiving increased attention due to their potential as an energy storage solution on the seasonal scale. | 7 | Physical Chemistry |
In theoretical chemistry, the Empirical Valence Bond (EVB) approach is an approximation for calculating free-energies of a chemical reaction in condensed-phase. It was first developed by Israeli chemist Arieh Warshel, and was inspired by the way Marcus theory uses potential surfaces to calculate the probability of electron transfer.
Where most methods for reaction free-energy calculations require at least some part of the modeled system to be treated using quantum mechanics, EVB uses a calibrated Hamiltonian to approximate the potential energy surface of a reaction. For a simple 1-step reaction, that typically means that a reaction is modeled using 2 states. These states are valence bond descriptions of the reactants and products of the reaction. The function that gives the ground energy then becomes:
where and are the valence bond descriptions of the reactant and product state respectively, and is the coupling parameter. The and potentials are usually modeled using force field descriptions and . is a bit trickier as it needs to be parameterized using a reference reaction. This reference reaction can be experimental, typically from a reaction in water or other solvents. Alternatively quantum chemical calculations can be used for calibration. | 7 | Physical Chemistry |
Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure the intensity of a light beam at different wavelengths. Although spectrophotometry is most commonly applied to ultraviolet, visible, and infrared radiation, modern spectrophotometers can interrogate wide swaths of the electromagnetic spectrum, including x-ray, ultraviolet, visible, infrared, and/or microwave wavelengths. | 7 | Physical Chemistry |
Hydroxylamine or its salts (salts containing hydroxylammonium cations ) can be produced via several routes but only two are commercially viable. It is also produced naturally as discussed in a section on biochemistry. | 0 | Organic Chemistry |
There are several kinds of Dimetcote, designed for different working environments.
* Dimetcote 21-5
* Dimetcote 3a
* Dimetcote 9H
* Dimetcote 9
* Dimetcote 11
* Dimetcote 302H
* Dimetcote 4 | 8 | Metallurgy |
Because of differences in their electron shells, singlet and triplet oxygen differ in their chemical properties; singlet oxygen is highly reactive. The lifetime of singlet oxygen depends on the medium and pressure. In normal organic solvents, the lifetime is only a few microseconds whereas in solvents lacking C-H bonds, the lifetime can be as long as seconds. | 7 | Physical Chemistry |
Oxaloacetate forms in several ways in nature. A principal route is upon oxidation of -malate, catalyzed by malate dehydrogenase, in the citric acid cycle. Malate is also oxidized by succinate dehydrogenase in a slow reaction with the initial product being enol-oxaloacetate. <br>
It also arises from the condensation of pyruvate with carbonic acid, driven by the hydrolysis of ATP:
:CHC(O)CO + HCO + ATP → OCCHC(O)CO + ADP + Pi
Occurring in the mesophyll of plants, this process proceeds via phosphoenolpyruvate, catalysed by phosphoenolpyruvate carboxylase. <br>Oxaloacetate can also arise from trans- or de- amination of aspartic acid. | 1 | Biochemistry |
Sequence-based classification methods have proven to be a powerful way of generating hypotheses for protein function based on sequence alignment to related proteins. The carbohydrate-active enzyme database presents a sequence-based classification of glycosyltransferases into over 90 families. The same three-dimensional fold is expected to occur within each of the families. | 0 | Organic Chemistry |
The Jameson Cell grew out of a long-term research program aimed at improving the recovery of fine particles by flotation. The work started at Imperial College London, and continued when Jameson moved in 1978 to the University of Newcastle, NSW, Australia, where he is Laureate Professor (2015). | 8 | Metallurgy |
The reactor operates by converting organic analytes after GC separation into methane before detection by FID. The oxidation and reduction reactions occur sequentially, wherein the organic compound is first combusted into molecules of carbon dioxide, which are subsequently reduced to methane molecules. The following reactions demonstrate the combustion/reduction process for formic acid.
HCOH + 0.5O ↔ CO + HO
CO + 4H ↔ CH + 2HO
The reactions are faster compared to the time scales of typical chromatography, resulting in manageable peak broadening and tailing. Elements other than carbon are not ionized in the hydrogen and oxygen flames of the FID and thus do not contribute to the FID signal. | 3 | Analytical Chemistry |
Simple rows or clusters of sharpened sticks (nowadays also known as punji sticks), and small caltrops have been used in anti-infantry warfare since antiquity. However, due to the difficulty of mass-producing them in the pre-modern age, they were rarely used except in the defense of limited areas or chokepoints, especially during sieges, where they were used to help seal breaches. Increasing ease of production still did not prevent these methods from slowly falling out of favor from the late Middle Ages onward.
Caltrops are still sometimes used in modern conflicts, such as during the Korean War, where Chinese troops, often wearing only light shoes, were particularly vulnerable. In modern times, special caltrops are also sometimes used against wheeled vehicles with pneumatic tires. Some South American urban guerrillas such as the Tupamaros and Montoneros, who called them "miguelitos," have used caltrops to avoid pursuit after ambushes. | 1 | Biochemistry |
SedDB was developed, operated and maintained by a joint team of disciplinary scientists, data scientists, data managers and information technology developers at the Lamont–Doherty Earth Observatory as part of the Integrated Earth Data Applications ([http://www.iedadata.org/ IEDA]) Research Group funded by the US National Science Foundation. SedDB was built collaboratively by researchers and information technologists at the Lamont–Doherty Earth Observatory, Oregon State University, Boston University, and Boise State University. | 9 | Geochemistry |
One product of fatty acid metabolism are the prostaglandins, compounds having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are enzymatically derived from arachidonic acid, a 20-carbon polyunsaturated fatty acid. Every prostaglandin therefore contains 20 carbon atoms, including a 5-carbon ring. They are a subclass of eicosanoids and form the prostanoid class of fatty acid derivatives.
The prostaglandins are synthesized in the cell membrane by the cleavage of arachidonate from the phospholipids that make up the membrane. This is catalyzed either by phospholipase A acting directly on a membrane phospholipid, or by a lipase acting on DAG (diacyl-glycerol). The arachidonate is then acted upon by the cyclooxygenase component of prostaglandin synthase. This forms a cyclopentane ring roughly in the middle of the fatty acid chain. The reaction also adds 4 oxygen atoms derived from two molecules of O. The resulting molecule is prostaglandin G, which is converted by the hydroperoxidase component of the enzyme complex into prostaglandin H. This highly unstable compound is rapidly transformed into other prostaglandins, prostacyclin and thromboxanes. These are then released into the interstitial fluids surrounding the cells that have manufactured the eicosanoid hormone.
If arachidonate is acted upon by a lipoxygenase instead of cyclooxygenase, Hydroxyeicosatetraenoic acids and leukotrienes are formed. They also act as local hormones.
Prostaglandins have two derivatives: prostacyclins and thromboxanes. Prostacyclins are powerful locally acting vasodilators and inhibit the aggregation of blood platelets. Through their role in vasodilation, prostacyclins are also involved in inflammation. They are synthesized in the walls of blood vessels and serve the physiological function of preventing needless clot formation, as well as regulating the contraction of smooth muscle tissue. Conversely, thromboxanes (produced by platelet cells) are vasoconstrictors and facilitate platelet aggregation. Their name comes from their role in clot formation (thrombosis). | 1 | Biochemistry |
Peters died from hospital-acquired COVID-19 on April 13, 2020, four days before his 83rd birthday. He contracted the virus while in a Bloomington hospital recovering from a fall.
Peters name was included in the May 2020 New York Times tribute U.S. Deaths Near 100,000, An Incalculable Loss to the 100,000 Americans who lost their lives as a direct result of the pandemic. A reporter for the Indiana Daily Student' wrote that "Peters had a roaring voice that filled lecture halls". | 3 | Analytical Chemistry |
The C-B bonds generated by hydroboration are reactive with various reagents, the most common one being hydrogen peroxide. Because the addition of H-B to olefins is stereospecific, this oxidation reaction will be diastereoselective when the alkene is trisubstituted. Hydroboration-oxidation is thus an excellent way of producing alcohols in a stereospecific and anti-Markovnikov fashion.
Hydroboration can also lead to amines by treating the intermediate organoboranes with monochloramine or O-hydroxylaminesulfonic acid (HSA).
Terminal olefins are converted to the corresponding alkyl bromides and alkyl iodides by treating the organoborane intermediates with bromine or iodine. Such reactions have not however proven very popular, because succinimide based reagents such as NIS and NBS are more versatile and do not require rigorous conditions as do organoboranes.
etc. | 0 | Organic Chemistry |
The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for iodine in 2000. For people age 14 and up, the iodine RDA is 150 μg/day; the RDA for pregnant women is 220 μg/day and the RDA during lactation is 290 μg/day. For children aged 1–8 years, the RDA is 90 μg/day; for children aged 8–13 years, it is 130 μg/day. As a safety consideration, the IOM sets tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. The UL for iodine for adults is 1,100 μg/day. This UL was assessed by analyzing the effect of supplementation on thyroid-stimulating hormone. Collectively, the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes (DRIs).
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR; AI and UL are defined the same as in the United States. For women and men ages 18 and older, the PRI for iodine is set at 150 μg/day; the PRI during pregnancy or lactation is 200 μg/day. For children aged 1–17 years, the PRI increases with age from 90 to 130 μg/day. These PRIs are comparable to the U.S. RDAs with the exception of that for lactation. The EFSA reviewed the same safety question and set its adult UL at 600 μg/day, which is a bit more than half the U.S. value. Notably, Japan reduced its adult iodine UL from 3,000 to 2,200 µg/day in 2010, but then increased it back to 3,000 µg/day in 2015.
As of 2000, the median observed intake of iodine from food in the United States was 240 to 300 μg/day for men and 190 to 210 μg/day for women. In Japan, consumption is much higher due to the frequent consumption of seaweed or kombu kelp. The average daily intake in Japan ranges from 1,000 to 3,000 μg/day; previous estimates suggested an average intake as high as 13,000 μg/day. | 1 | Biochemistry |
The fucoxanthin dinophyte lineages (including Karlodinium and Karenia) lost their original red algal derived chloroplast, and replaced it with a new chloroplast derived from a haptophyte endosymbiont. Karlodinium and Karenia probably took up different heterokontophytes. Because the haptophyte chloroplast has four membranes, tertiary endosymbiosis would be expected to create a six membraned chloroplast, adding the haptophytes cell membrane and the dinophytes phagosomal vacuole. However, the haptophyte was heavily reduced, stripped of a few membranes and its nucleus, leaving only its chloroplast (with its original double membrane), and possibly one or two additional membranes around it.
Fucoxanthin-containing chloroplasts are characterized by having the pigment fucoxanthin (actually 19′-hexanoyloxy-fucoxanthin and/or 19′-butanoyloxy-fucoxanthin) and no peridinin. Fucoxanthin is also found in haptophyte chloroplasts, providing evidence of ancestry. | 5 | Photochemistry |
The determination of phosphorus, arsenic, silicon and germanium are examples of the use of heteropoly-molybdenum blue in analytical chemistry. The following example describes the determination of phosphorus. A sample containing the phosphate is mixed with an acid solution of Mo, for example ammonium molybdate, to produce , which has an α-Keggin structure. This anion is then reduced by, for example, ascorbic acid or SnCl, to form the blue coloured β-keggin ion, . The amount of the blue coloured ion produced is proportional to the amount of phosphate present and the absorption can be measured using a colorimeter to determine the amount of phosphorus. Examples of procedures are:
*the analysis of phosphate in sea water.
*standard methods for determining phosphorus and silicon content of metals and metal ores. (e.g. BSI and ISO standards)
*the determination of germanium and arsenic
The comparison of the measured absorption against readings taken for analyses of standard solutions means that a detailed understanding of the structure of the blue complex was unnecessary.
This colorimetric method is ineffective when comparable amounts of arsenate are present in solution with phosphate. This is due to the strong chemical likeness of arsenate and phosphate. The resultant molybdenum blue for arsenate, using the same procedure, does produce a slightly different spectral signature, however.
Recently, paper-based devices have become very attractive to use colorimetric determination for making inexpensive, disposable and convenient analytical devices for the determination of reactive phosphate in the field. By using an inexpensive and portable infrared Lightbox system, one can create uniform and repeatable lighting environments to take advantage of the peak absorbance of the molybdenum blue reaction in order to improve limit of detection of paper-based devices. This system may act as a substitute for expensive, lab-equipment spectrometers. | 7 | Physical Chemistry |
Cis and trans isomers have distinct physical properties. Their differing shapes influences the dipole moments, boiling, and especially melting points.
These differences can be very small, as in the case of the boiling point of straight-chain alkenes, such as pent-2-ene, which is 37 °C in the cis isomer and 36 °C in the trans isomer. The differences between cis and trans isomers can be larger if polar bonds are present, as in the 1,2-dichloroethenes. The cis isomer in this case has a boiling point of 60.3 °C, while the trans isomer has a boiling point of 47.5 °C. In the cis isomer the two polar C–Cl bond dipole moments combine to give an overall molecular dipole, so that there are intermolecular dipole–dipole forces (or Keesom forces), which add to the London dispersion forces and raise the boiling point. In the trans isomer on the other hand, this does not occur because the two C−Cl bond moments cancel and the molecule has a net zero dipole moment (it does however have a non-zero quadrupole moment).
The differing properties of the two isomers of butenedioic acid are often very different.
Polarity is key in determining relative boiling point as strong intermolecular forces raise the boiling point. In the same manner, symmetry is key in determining relative melting point as it allows for better packing in the solid state, even if it does not alter the polarity of the molecule. Another example of this is the relationship between oleic acid and elaidic acid; oleic acid, the cis isomer, has a melting point of 13.4 °C, making it a liquid at room temperature, while the trans isomer, elaidic acid, has the much higher melting point of 43 °C, due to the straighter trans isomer being able to pack more tightly, and is solid at room temperature.
Thus, trans alkenes, which are less polar and more symmetrical, have lower boiling points and higher melting points, and cis alkenes, which are generally more polar and less symmetrical, have higher boiling points and lower melting points.
In the case of geometric isomers that are a consequence of double bonds, and, in particular, when both substituents are the same, some general trends usually hold. These trends can be attributed to the fact that the dipoles of the substituents in a cis isomer will add up to give an overall molecular dipole. In a trans isomer, the dipoles of the substituents will cancel out due to being on opposite sides of the molecule. Trans isomers also tend to have lower densities than their cis counterparts.
As a general trend, trans alkenes tend to have higher melting points and lower solubility in inert solvents, as trans alkenes, in general, are more symmetrical than cis alkenes.
Vicinal coupling constants (J), measured by NMR spectroscopy, are larger for trans (range: 12–18 Hz; typical: 15 Hz) than for cis (range: 0–12 Hz; typical: 8 Hz) isomers. | 4 | Stereochemistry |
In organic chemistry, a propynyl group is a propyl bearing a triple bond.
* The 1-propynyl group has the structure CH-C≡C–R.
* The 2-propynyl group is also known as a propargyl group, and has the structure HC≡C−CH–R. | 0 | Organic Chemistry |
Aminolevulinic acid utilization is promising in the field of cancer delineation, particularly in the context of fluorescence-guided surgery. This compound is utilized to enhance the visualization of malignant tissues during surgical procedures. When administered to patients, 5-ALA is metabolized to protoporphyrin IX (PpIX) preferentially in cancer cells, leading to their fluorescence under specific light wavelengths. This fluorescence aids surgeons in real-time identification and precise removal of cancerous tissue, reducing the likelihood of leaving residual tumor cells behind. This innovative approach has shown success in various cancer types, including brain and spine gliomas, bladder cancer, and oral squamous cell carcinoma. | 1 | Biochemistry |
Many reactions produce carboxylic acids but are used only in specific cases or are mainly of academic interest.
* Disproportionation of an aldehyde in the Cannizzaro reaction
* Rearrangement of diketones in the benzilic acid rearrangement
* Involving the generation of benzoic acids are the von Richter reaction from nitrobenzenes and the Kolbe–Schmitt reaction from phenols. | 0 | Organic Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V). | 1 | Biochemistry |
Figure 3 shows the line of contact where three phases meet. In equilibrium, the net force per unit length acting along the boundary line between the three phases must be zero. The components of net force in the direction along each of the interfaces are given by:
where α, β, and θ are the angles shown and γ is the surface energy between the two indicated phases. These relations can also be expressed by an analog to a triangle known as Neumanns triangle, shown in Figure 4. Neumanns triangle is consistent with the geometrical restriction that , and applying the law of sines and law of cosines to it produce relations that describe how the interfacial angles depend on the ratios of surface energies.
Because these three surface energies form the sides of a triangle, they are constrained by the triangle inequalities, γ + γ meaning that not one of the surface tensions can exceed the sum of the other two. If three fluids with surface energies that do not follow these inequalities are brought into contact, no equilibrium configuration consistent with Figure 3 will exist. | 7 | Physical Chemistry |
The CKLF-like MARVEL transmembrane domain-containing family (CMTM), previously termed the chemokine-like factor superfamily (CKLFSF), consists of 9 proteins, some of which have various isoforms due to alternative splicing of their respective genes. These proteins along with their isoforms are:
*Chemokine-like factor (CKLF), the founding member of this family, has 4 known isoforms, CKLF1 to CKLF4.
*CKLF like MARVEL transmembrane domain-containing 1 (CMTM1) has 23 known isoforms, CMTM1-v1 to CMTM1-v23.
*CKLF like MARVEL transmembrane domain-containing 2 (CMTM2) has no known isoforms.
*CKLF like MARVEL transmembrane domain-containing 3 (CMTM3) has no known isoforms.
*CKLF like MARVEL transmembrane domain-containing 4 (CMTM4) has 3 known isoforms, CMTM4-v1 to CMTM4-v3.
* CKLF-like MARVEL transmembrane domain-containing 5 (CMTM5) has 6 known isoforms, CMTM5-v1 to CMTM5-v6.
* CKLF like MARVEL transmembrane domain containing 6 (CMTM6) has no known isoforms.
* CKLF like MARVEL transmembrane domain containing 7 (CMTM7) has 2 isoforms, CMTM7-v1 and CMTM7-v2.
* CKLF like MARVEL transmembrane domain-containing 8 (CMTM8) has two isoforms, CMTM8 and CMTM8-v2 (Little is known about the CMTM8-v2 isoform and the CMTM8 isoform is referred to as CMTM8 rather than CMTM8-v1.).
All of these proteins have domains (i.e. regions) similar to analogous domains in the chemokine proteins; tetraspanin proteins (also termed transmembrane-4 superfamily proteins); myelin and lymphocyte protein (also termed MAR protein); proteins that direct membrane vesicle trafficking; and other proteins that are embedded in cell membranes. The genes encoding (i.e. directing the production of) these proteins, CKLF, CMTM1, CMTM2, CMTM3, CMTM4, CMTM5, CMTM6, CMTM7, and CMTM8, respectively, also share similar regions that encode the domains just cited for their proteins. (The 8 CMTM genes were formerly termed CKLFSF1, CKLFSF2, CKLFSF3, CKLFSF4, CKLFSF5, CKLFSF6, CKLFSF7, and CKLFSF8.) The CKLF, CMTM1, CMTM2, CTMT3, and CMTM4 genes cluster together in band 22 on the long (i.e. "q") arm of chromosome 16; the CMTM6, CMTM7, and CMTM8 genes form a second cluster in band 22 on the short (i.e. "p") of chromosome 3; and the CMTM5 gene, located in band 11.2 on the q arm of chromosome 14, is not clustered with the other CMTM genes. These structural similarities and clusterings reflect the close relationships of these proteins and genes. Studies suggest that the members of this family may be involved in the development of various cancers autoimmune diseases, cardiovascular diseases, the male reproductive system, and angiogenesis (i.e. development of new blood vessels from pre-existing blood vessels). In most of these cases, however, further studies are needed to determine if these CMTM proteins and/or their corresponding genes and mRNAs will be promising targets to help in the diagnosis, prognosis, and/or treatment of these disorders. | 1 | Biochemistry |
Gene targeting holds enormous promise to make targeted, user-defined sequence changes or sequence insertions in the genome. However its primary applications - human disease modelling and plant genome engineering - are hindered by the low efficiency of homologous recombination in comparison to the competing non-homologous end joining in mammalian and higher plant cells. As described above, there are strategies that can be employed to increase the frequencies of gene targeting in plants and mammalian cells. In addition, robust selection methods that allow the selection or specific enrichment of cells where gene targeting has occurred can increase the rates of recovery of gene-targeted cells. | 1 | Biochemistry |
More typically for laboratory operations, the Prilezhaev reaction is employed. This approach involves the oxidation of the alkene with a peroxyacid such as mCPBA. Illustrative is the epoxidation of styrene with perbenzoic acid to styrene oxide:
The reaction proceeds via what is commonly known as the "Butterfly Mechanism". The peroxide is viewed as an electrophile, and the alkene a nucleophile. The reaction is considered to be concerted. The butterfly mechanism allows ideal positioning of the sigma star orbital for π electrons to attack. Because two bonds are broken and formed to the epoxide oxygen, this is formally an example of a coarctate transition state.
Hydroperoxides are also employed in catalytic enantioselective epoxidations, such as the Sharpless epoxidation and the Jacobsen epoxidation. Together with the Shi epoxidation, these reactions are useful for the enantioselective synthesis of chiral epoxides. Oxaziridine reagents may also be used to generate epoxides from alkenes. | 0 | Organic Chemistry |
Only a small minority of enzyme-catalysed reactions have just one substrate, and even the number is increased by treating two-substrate reactions in which one substrate is water as one-substrate reactions the number is still small. One might accordingly suppose that the Michaelis–Menten equation, normally written with just one substrate, is of limited usefulness. This supposition is misleading, however. One of the common equations for a two-substrate reaction can be written as follows to express in terms of two substrate concentrations and :
the other symbols represent kinetic constants. Suppose now that is varied with held constant. Then it is convenient to reorganize the equation as follows:
This has exactly the form of the Michaelis–Menten equation
with apparent values and defined as follows: | 7 | Physical Chemistry |
There are two main non-correlation alternatives to FCS that are widely used to study the dynamics of fluorescent species. | 7 | Physical Chemistry |
After finishing his Ph.D., Willard returned to Michigan to rejoin the faculty; he became a full professor in 1922 and retired from the university, assuming professor emeritus status, in 1951. He was designated the Henry Russel Lecturer in 1948, noted as the university's highest distinction. He was known for his strong teaching skills and continued teaching at a variety of institutions after his retirement.
During his tenure at Michigan, Willard wrote several widely used and positively reviewed chemistry textbooks and laboratory course manuals, often with former students as coauthors. He also performed consulting work for local industry throughout his career, serving as the Director of the Chemistry and Metallurgy Laboratories for Detroit's Bureau of Aircraft Production in 1917-18 and as a long-term consultant for the Parker Rust-Proof Company.
Willard served as a director of the American Chemical Society from 1934 to 1940 and received the ACS' Fisher Award in Analytical Chemistry in 1951. He was the inaugural recipient of the Anachem Award given by the Association of Analytical Chemists in 1953. | 3 | Analytical Chemistry |
The mass–action ratio, often denoted by , is the ratio of the product concentrations, p, to reactant concentrations, s. The concentrations may or may not be at equilibrium.
This assumes that the stoichiometric amounts are all unity. If not, then each concentration must be raised to the power of its corresponding stoichiometric amount. If the product and reactant concentrations are at equilibrium then the mass–action ratio will equal the equilibrium constant. At equilibrium:
The ratio of the mass–action ratio to the equilibrium constant is often called the disequilibrium ratio, denoted by the symbol .
and is a useful measure for indicating how from equilibrium a given reaction is. At equilibrium . The ratio is always greater than zero, When the reaction is out of equilibrium, . If the reaction has a negative free energy, then .
For a uni-molecular reaction such as , where the net reaction rate is given by the reversible mass-action ratio:
At thermodynamic equilibrium the rate equals zero, that is . Rearranging gives:
but , therefore and therefore
In other words the disequilibrium ratio is the ratio of the reverse to the forward rate. When the reverse rate, is less than the forward rate, the ratio is less than one, , indicating that the net reaction is from left to right. | 7 | Physical Chemistry |
Primary hydrogen kinetic isotope effects refer to cases in which a bond to the isotopically labeled hydrogen is formed or broken at a rate- and/or product-determining step of a reaction. These are the most commonly measured kinetic isotope effects, and much of the previously covered theory refers to primary kinetic isotope effects.
When there is adequate evidence that transfer of the labeled hydrogen occurs in the rate-determining step of a reaction, if a fairly large kinetic isotope effect is observed, e.g. kH/kD of at least 5-6 or kH/kT about 10–13 at room temperature, it is quite likely that the hydrogen transfer is linear and that the hydrogen is fairly symmetrically located in the transition state. It is usually not possible to make comments about tunneling contributions to the observed isotope effect unless the effect is very large. If the primary kinetic isotope effect is not as large, it is generally considered to be indicative of a significant contribution from heavy-atom motion to the reaction coordinate, although it may also mean that hydrogen transfer follows a nonlinear pathway. | 7 | Physical Chemistry |
One of the major products of the methylcitrate cycle is pyruvate. This pyruvate can be used by metabolic enzymes for energy and biomass formation. The other major product, succinate, is used in the citric acid cycle and helps to carry the reaction forward and restarts the cycle. Succinate is used by the citric acid and glyoxylate cycles to generate oxaloacetate, one of the key substrates necessary to begin the methylcitrate cycle. | 1 | Biochemistry |
When two solid bodies come in contact, such as A and B in Figure 1, heat flows from the hotter body to the colder body. From experience, the temperature profile along the two bodies varies, approximately, as shown in the figure. A temperature drop is observed at the interface between the two surfaces in contact. This phenomenon is said to be a result of a thermal contact resistance existing between the contacting surfaces. Thermal contact resistance is defined as the ratio between this temperature drop and the average heat flow across the interface.
According to Fourier's law, the heat flow between the bodies is found by the relation:
where is the heat flow, is the thermal conductivity, is the cross sectional area and is the temperature gradient in the direction of flow.
From considerations of energy conservation, the heat flow between the two bodies in contact, bodies A and B, is found as:
One may observe that the heat flow is directly related to the thermal conductivities of the bodies in contact, and , the contact area , and the thermal contact resistance, , which, as previously noted, is the inverse of the thermal conductance coefficient, . | 7 | Physical Chemistry |
At higher temperatures RuBisCO is less able to discriminate between and . This is because the enediol intermediate is less stable. Increasing temperatures also lower the solubility of , thus lowering the concentration of relative to in the chloroplast. | 5 | Photochemistry |
The protein is 273 amino acids in length with the first 23 residues acting as a signal peptide which is subsequently cleaved. It has a Uniprot accession of [https://www.uniprot.org/uniprot/P02872 P02872]. There are over 20 structures of this protein in the PDB which reveal and all beta-sheet protein with a tetrameric quaternary structure. It is a member of the Lectin_legB PFAM family.
[http://www.ebi.ac.uk/pdbe/searchResults.html?display=both&term=P02872 Available Structures of peanut agglutinin] | 1 | Biochemistry |
An AFM probe has a sharp tip on the free-swinging end of a cantilever that protrudes from a holder. The dimensions of the cantilever are in the scale of micrometers. The radius of the tip is usually on the scale of a few nanometers to a few tens of nanometers. (Specialized probes exist with much larger end radii, for example probes for indentation of soft materials.) The cantilever holder, also called the holder chip—often 1.6 mm by 3.4 mm in size—allows the operator to hold the AFM cantilever/probe assembly with tweezers and fit it into the corresponding holder clips on the scanning head of the atomic force microscope.
This device is most commonly called an "AFM probe", but other names include "AFM tip" and "cantilever" (employing the name of a single part as the name of the whole device). An AFM probe is a particular type of SPM (scanning probe microscopy) probe.
AFM probes are manufactured with MEMS technology. Most AFM probes used are made from silicon (Si), but borosilicate glass and silicon nitride are also in use. AFM probes are considered consumables as they are often replaced when the tip apex becomes dull or contaminated or when the cantilever is broken. They can cost from a couple of tens of dollars up to hundreds of dollars per cantilever for the most specialized cantilever/probe combinations.
Just the tip is brought very close to the surface of the object under investigation, the cantilever is deflected by the interaction between the tip and the surface, which is what the AFM is designed to measure. A spatial map of the interaction can be made by measuring the deflection at many points on a 2D surface.
Several types of interaction can be detected. Depending on the interaction under investigation, the surface of the tip of the AFM probe needs to be modified with a coating. Among the coatings used are gold – for covalent bonding of biological molecules and the detection of their interaction with a surface, diamond for increased wear resistance and magnetic coatings for detecting the magnetic properties of the investigated surface. Another solution exists to achieve high resolution magnetic imaging : having the probe equip with a microSQUID. The AFM tips is fabricated using silicon micro machining and the precise positioning of the microSQUID loop is done by electron beam lithography. The additional attachment of a quantum dot to the tip apex of a conductive probe enables surface potential imaging with high lateral resolution, scanning quantum dot microscopy.
The surface of the cantilevers can also be modified. These coatings are mostly applied in order to increase the reflectance of the cantilever and to improve the deflection signal. | 6 | Supramolecular Chemistry |
The osmotic stress technique is a method for measuring the effect of water on biological molecules, particularly enzymes. Just as the properties of molecules can depend on the presence of salts, pH, and temperature, they can depend significantly on the amount of water present. In the osmotic stress technique, flexible neutral polymers such as polyethylene glycol and dextran are added to the solution containing the molecule of interest, replacing a significant part of the water. The amount of water replaced is characterized by the chemical activity of water. | 1 | Biochemistry |
Joseph Achille Le Bel (21 January 1847 in Pechelbronn – 6 August 1930, in Paris, France) was a French chemist. He is best known for his work in stereochemistry. Le Bel was educated at the École Polytechnique in Paris. In 1874 he announced his theory outlining the relationship between molecular structure and optical activity. This discovery laid the foundation of the science of stereochemistry, which deals with the spatial arrangement of atoms in molecules. This hypothesis was put forward in the same year by the Dutch physical chemist Jacobus Henricus van t Hoff and is currently known as Le Bel–vant Hoff rule. Le Bel wrote Cosmologie Rationelle (Rational Cosmology) in 1929. | 4 | Stereochemistry |
Escitalopram increases intrasynaptic levels of the neurotransmitter serotonin by blocking the reuptake of the neurotransmitter into the presynaptic neuron. Over time, this leads to a downregulation of pre-synaptic 5-HT receptors, which is associated with an improvement in passive stress tolerance, and delayed downstream increase in expression of brain-derived neurotrophic factor, which may contribute to a reduction in negative affective biases.
Of the SSRIs currently available, escitalopram has the highest selectivity for the serotonin transporter (SERT) compared to the norepinephrine transporter (NET), making the side-effect profile relatively mild in comparison to less-selective SSRIs.
Escitalopram is a substrate of P-glycoprotein and hence P-glycoprotein inhibitors such as verapamil and quinidine may improve its blood brain barrier penetrability. In a preclinical study in rats combining escitalopram with a P-glycoprotein inhibitor, its antidepressant-like effects were enhanced. | 4 | Stereochemistry |
Zintl phases can be prepared in regular solid state reactions, usually performed under an inert atmosphere or in a molten salt solution. Typical solid state methods include direct reduction of corresponding oxides in solution phase reactions in liquid ammonia or mercury. The product can be purified in some cases via zone refining, though often careful annealing will result in large single crystals of a desired phase. | 7 | Physical Chemistry |
Wetland restoration involves restoring a wetlands natural biological, geological, and chemical functions through re-establishment or rehabilitation. It has also been proposed as a potential climate change mitigation strategy. Wetland soil, particularly in coastal wetlands such as mangroves, sea grasses, and salt marshes, is an important carbon reservoir; 20–30% of the worlds soil carbon is found in wetlands, while only 5–8% of the world's land is composed of wetlands. Studies have shown that restored wetlands can become productive sinks and many restoration projects have been enacted in the US and around the world. Aside from climate benefits, wetland restoration and conservation can help preserve biodiversity, improve water quality, and aid with flood control.
The plants that make up wetlands absorb carbon dioxide (CO) from the atmosphere and convert it into organic matter. The waterlogged nature of the soil slows down the decomposition of organic material, leading to the accumulation of carbon-rich peat, acting as a long-term carbon sink. Additionally, anaerobic conditions in waterlogged soils hinder the complete breakdown of organic matter, promoting the conversion of carbon into more stable forms.
As with forests, for the sequestration process to succeed, the wetland must remain undisturbed. If it is disturbed somehow, the carbon stored in the plants and sediments will be released back into the atmosphere and the ecosystem will no longer function as a carbon sink. Additionally, some wetlands can release non- greenhouse gases, such as methane and nitrous oxide which could offset potential climate benefits. The amounts of carbon sequestered via blue carbon by wetlands can also be difficult to measure.
Wetlands are created when water overflows into heavily vegetated soil causing plants to adapt to a flooded ecosystem. Wetlands can occur in three different regions. Marine wetlands are found in shallow coastal areas, tidal wetlands are also coastal but are found farther inland, and non-tidal wetlands are found inland and have no effects from tides. Wetland soil is an important carbon sink; 14.5% of the worlds soil carbon is found in wetlands, while only 5.5% of the worlds land is composed of wetlands. Not only are wetlands a great carbon sink, they have many other benefits like collecting floodwater, filtering air and water pollutants, and creating a home for numerous birds, fish, insects, and plants.
Climate change could alter soil carbon storage changing it from a sink to a source. With rising temperatures comes an increase in greenhouse gasses from wetlands especially locations with permafrost. When this permafrost melts it increases the available oxygen and water in the soil. Because of this, bacteria in the soil would create large amounts of carbon dioxide and methane to be released into the atmosphere.
The link between climate change and wetlands is still not fully known. It is also not clear how restored wetlands manage carbon while still being a contributing source of methane. However, preserving these areas would help prevent further release of carbon into the atmosphere. | 5 | Photochemistry |
As a system is formed from a solid surface and a drop of liquid, energy minima and maxima are produced by the free energy of the system. When the solid surface is rough or homogeneous, the system, which is made up of a solid, a liquid, and a fluid, could have multiple minima produced from the free energy at different minima points. One of these minima is called the global minimum. The global minimum has the lowest free energy within the system and is defined to be the stable equilibrium state. Furthermore, the other minima illustrate the metastable equilibrium states of the system. In between these minima are the energy barriers which hinder the motion of energy between the various metastable states in the system. The transition of energy between metastable states is also affected by the availability of external energy to the system, which is associated with the volume of the liquid drop on top of the solid surface. As such, the volume of the liquid may have an impact on the locations of the minima points, which could influence the contact angles created by the solid and the liquid. The contact angles are directly related to whether the solid surface is ideal, in other words, whether it is a smooth, heterogeneous surface.
In the captive bubble method, the bubble indicating the liquid drop forms an angle with the solid surface called the contact angle. The stability of the liquid phase on the solid is measured with an intrinsic contact angle. Theoretically, the contact angle equals the value of the local intrinsic contact angle, assuming line tension has a negligible effect. | 7 | Physical Chemistry |
Since diffusion and transport of free ammonia across the cell membrane will affect the pH level of the cell, the more attractive and regulated way of transporting ammonia between the neuronal and the astrocytic compartment is via an amino-acid shuttle, of which there are two: leucine and alanine. The amino acid moves in the opposite direction of glutamine. In the opposite direction of the amino acid, a corresponding molecule is transported; for alanine this molecule is lactate; for leucine, α-ketoisocaproate. | 1 | Biochemistry |
*Allègre C.J., 2008. Isotope Geology (Cambridge University Press).
*Dickin A.P., 2005. Radiogenic Isotope Geology (Cambridge University Press).
*Faure G., Mensing T. M. (2004), Isotopes: Principles and Applications (John Wiley & Sons).
*Hoefs J., 2004. Stable Isotope Geochemistry (Springer Verlag).
*Sharp Z., 2006. Principles of Stable Isotope Geochemistry (Prentice Hall). | 9 | Geochemistry |
The prototypical super leaving group is triflate, and the term has come to mean any leaving group of comparable ability. Compounds where loss of a super leaving group can generate a stable carbocation are usually highly reactive and unstable. Thus, the most commonly encountered organic triflates are methyl triflate and alkenyl or aryl triflates, all of which cannot form stable carbocations on ionization, rendering them relatively stable. It has been noted that steroidal alkyl nonaflates (another super leaving group) generated from alcohols and perfluorobutanesulfonyl fluoride were not isolable as such but immediately formed the products of either elimination or substitution by fluoride generated by the reagent. Mixed acyl-trifluoromethanesulfonyl anhydrides smoothly undergo Friedel-Crafts acylation without a catalyst, unlike the corresponding acyl halides, which require a strong Lewis acid. Methyl triflate, however, does not participate in Friedel-Crafts alkylation reactions with electron-neutral aromatic rings.
Beyond super leaving groups in reactivity lie the "hyper" leaving groups. Prominent among these are λ-iodanes, which include diaryl iodonium salts, and other halonium ions. In one study, a quantitative comparison of these and other leaving groups was conducted. Relative to chloride (k = 1), reactivities increased in the order bromide (k = 14), iodide (k = 91), tosylate (k = 3.7), triflate (k = 1.4), phenyliodonium tetrafluoroborate (, k = 1.2). Along with the criterion that a hyper leaving group be a stronger leaving group than triflate is the necessity that the leaving group undergo reductive elimination. In the case of halonium ions this involves reduction from a trivalent halonium to a monovalent halide coupled with the release of an anionic fragment. Part of the exceptional reactivity of compounds of hyper leaving groups has been ascribed to the entropic favorability of having one molecule split into three.
Dialkyl halonium ions have also been isolated and characterized for simple alkyl groups. These compounds, despite their extreme reactivity towards nucleophiles, can be obtained pure in the solid state with very weakly nucleophilic counterions such as and . The strongly electrophilic nature of these compounds engendered by their attachment to extremely labile (R = alkyl, X = Cl, Br, I) leaving groups is illustrated by their propensity to alkylate very weak nucleophiles. Heating neat samples of under reduced pressure resulted in methylation of the very poorly nucleophilic carborane anion with concomitant expulsion of the leaving group. Dialkyl halonium hexafluoroantimonate salts alkylate excess alkyl halides to give exchanged products. Their strongly electrophilic nature, along with the instability of primary carbocations generated from ionization of their alkyl groups, points to their possible involvement in Friedel-Crafts alkylation chemistry. The order of increasing lability of these leaving groups is . | 0 | Organic Chemistry |
* m-Phenylene ethynylene oligomers are driven to fold into a helical conformation by solvophobic forces and aromatic stacking interactions.
* β-peptides are composed of amino acids containing an additional unit between the amine and carboxylic acid. They are more stable to enzymatic degradation and have been demonstrated to have antimicrobial activity.
* Peptoids are N-substituted polyglycines that utilize steric interactions to fold into polyproline type-I-like helical structures.
* Aedamers that fold in aqueous solutions driven by hydrophobic and aromatic stacking interactions.
* Aromatic oligoamide foldamers. These examples are some of the largest and best structurally characterized foldamers.
* Arylamide foldamers, such as brilacidin. | 6 | Supramolecular Chemistry |
A parasympatholytic agent is a substance or activity that reduces the activity of the parasympathetic nervous system.
The term parasympatholytic typically refers to the effect of a drug, although some poisons act to block the parasympathetic nervous system as well. Most drugs with parasympatholytic properties are anticholinergics.
Parasympatholytic agents and sympathomimetic agents have similar effects to each other, although some differences between the two groups can be observed. For example, both cause mydriasis, but parasympatholytics reduce accommodation (cycloplegia), whereas sympathomimetics do not.
__NOTOC__ | 1 | Biochemistry |
Uranus has an active methane cycle. Methane is converted to hydrocarbons through photolysis which condenses and as they are heated, release methane which rises to the upper atmosphere.
Studies by Grundy et al. (2006) indicate active carbon cycles operates on Titania, Umbriel and Ariel and Oberon through the ongoing sublimation and deposition of carbon dioxide, though some is lost to space over long periods of time. | 9 | Geochemistry |
The growth, development, and reproduction of organisms relies on cell division; the process by which a single cell divides into two usually identical daughter cells. This requires first making a duplicate copy of every gene in the genome in a process called DNA replication. The copies are made by specialized enzymes known as DNA polymerases, which "reads" one strand of the double-helical DNA, known as the template strand, and synthesize a new complementary strand. Because the DNA double helix is held together by base pairing, the sequence of one strand completely specifies the sequence of its complement; hence only one strand needs to be read by the enzyme to produce a faithful copy. The process of DNA replication is semiconservative; that is, the copy of the genome inherited by each daughter cell contains one original and one newly synthesized strand of DNA.
The rate of DNA replication in living cells was first measured as the rate of phage T4 DNA elongation in phage-infected E. coli and found to be impressively rapid. During the period of exponential DNA increase at 37 °C, the rate of elongation was 749 nucleotides per second.
After DNA replication is complete, the cell must physically separate the two copies of the genome and divide into two distinct membrane-bound cells. In prokaryotes (bacteria and archaea) this usually occurs via a relatively simple process called binary fission, in which each circular genome attaches to the cell membrane and is separated into the daughter cells as the membrane invaginates to split the cytoplasm into two membrane-bound portions. Binary fission is extremely fast compared to the rates of cell division in eukaryotes. Eukaryotic cell division is a more complex process known as the cell cycle; DNA replication occurs during a phase of this cycle known as S phase, whereas the process of segregating chromosomes and splitting the cytoplasm occurs during M phase. | 1 | Biochemistry |
Alkyl cycloalkanes are chemical compounds with an alkyl group with a single ring of carbons to which hydrogens are attached according to the formula
:CH.
They are named analogously to their normal alkane counterpart of the same carbon count: methylcyclopropane, methylcyclobutane, methylcyclopentane, methylcyclohexane, etc.
Methylcycloalkanes are classed into compounds with small, normal and bigger cycloalkanes, where cyclopropane and cyclobutane are the small ones, cyclopentane, cyclohexane, cycloheptane are the normal ones and the rest are the bigger ones.
__TOC__ | 0 | Organic Chemistry |
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