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Examination of this reaction's mechanism suggests that the formation of the silonate is all that is needed to activate addition of the organosilane to the palladium center. The presence of a pentavalent silicon is not needed and kinetic analysis has shown that this reaction has first order dependence on silonate concentration. This is due to the key bond being formed, the Pd-O bond during the transmetalation step, that then allows for transfer of the carbon fragment onto the palladium center. Based on this observation, it seems that the rate limiting step in this catalytic cycle is the Pd-O bond formation, in which increased silonate concentrations increase the rate of this reaction (indicative of faster reactions). | 0 | Theoretical and Fundamental Chemistry |
Rutherford backscattering spectrometry is named after Lord Rutherford, a physicist sometimes referred to as the father of nuclear physics. Rutherford supervised a series of experiments carried out by Hans Geiger and Ernest Marsden between 1909 and 1914 studying the scattering of alpha particles through metal foils. While attempting to eliminate "stray particles" they believed to be caused by an imperfection in their alpha source, Rutherford suggested that Marsden attempt to measure backscattering from a gold foil sample. According to the then-dominant plum-pudding model of the atom, in which small negative electrons were spread through a diffuse positive region, backscattering of the high-energy positive alpha particles should have been nonexistent. At most small deflections should occur as the alpha particles passed almost unhindered through the foil. Instead, when Marsden positioned the detector on the same side of the foil as the alpha particle source, he immediately detected a noticeable backscattered signal. According to Rutherford, "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you."
Rutherford interpreted the result of the Geiger–Marsden experiment as an indication of a Coulomb collision with a single massive positive particle. This led him to the conclusion that the atoms positive charge could not be diffuse but instead must be concentrated in a single massive core: the atomic nucleus. Calculations indicated that the charge necessary to accomplish this deflection was approximately 100 times the charge of the electron, close to the atomic number of gold. This led to the development of the Rutherford model of the atom in which a positive nucleus made up of Ne positive particles, or protons, was surrounded by N' orbiting electrons of charge -e to balance the nuclear charge. This model was eventually superseded by the Bohr atom, incorporating some early results from quantum mechanics.
If the energy of the incident particle is increased sufficiently, the Coulomb barrier is exceeded and the wavefunctions of the incident and struck particles overlap. This may result in nuclear reactions in certain cases, but frequently the interaction remains elastic, although the scattering cross-sections may fluctuate wildly as a function of energy and no longer be calculable analytically. This case is known as "Elastic (non-Rutherford) Backscattering Spectrometry" (EBS). There has recently been great progress in determining EBS scattering cross-sections, by solving Schrödinger's equation for each interaction. However, for the EBS analysis of matrices containing light elements, the utilization of experimentally measured scattering cross-section data is also considered to be a very credible option. | 0 | Theoretical and Fundamental Chemistry |
In general, we can use the either Rb or Cs alkali metal atoms with inert nitrogen gas. However, we are using Cs atoms with nitrogen to make the spin exchange with Xe for number of advantages:
* Cs has natural perfect abundance while rubidium has two (Rb and Rb) isotopes. Abstraction of one isotope separately from these two (Rb and Rb) is difficult compare to collect the Cs isotope. Abstraction of Cs is convenient.
* Optical pumping cell normally is operated at lower temperature to avoid chemically breakdown issue. SEOP is using Cs at low temperature and hence it has fewer chemical corrosion with SEOP cell wall glass.
* Cs-Xe couple have spin exchange rate about 10% that is more compare to the Rb-Xe couple have.
Although Xe has a bunch of preferable characteristic applications in NMR technique, Kr can also be used since it has a lot of advantages in NMR techniques in different ways than Xe.
* Kr stable isotope has spin I=9/2 and has larger Van der Waals size 2.02A. It has quadrupolar effect can be diffuse to nearby environment shortly & distinctively (polar to nonpolar media in vivo system).
* Chemical composition of materials can influence the longitudinal relaxation of hyperpolarized Kr.
* The relaxation can distinguish among the hydrophobic and hydrophilic substrate. Although He and Xe have spin half but they are not quadrupolar active.
* However, the Ne (I=3/2), Kr(I=9/2) and Xe (I=3/2) have Quadrupolar moment. Quadrupolar interactions make these isotopes having spin relaxation.
* Due to this spin relaxation and evolution, these isotopes can be used as contrasting agents to say about the probe can determine the structural feature and chemical compositions of the surfaces for a permeable media.
* SEOP can calculate the relaxation of spin T by using the equation nonlinear least-squares fitting for Kr signal as a function of time as well as experimental number of media flip angle (≈12°) for NMR experimenting radio frequency pulses.
* Hyperpolarized Kr is being separated from Rb gases after spin exchanging in the optical pumping process and then used in variety of in vivo system to get MRI signal. This is the first isotope showed lots of applicability for MRI technique even though has the spin is 9½.
* During experiment of canine lung tissue, the using magnet was 9.4 T, media was porous and similar porosity to alveolar dimensions which is disseminated at atmospheric pressure. Spin lattice relaxation was reasonably long enough so it is applicable in vivo system although the oxygen level could be 20%.
* As Kr contrasting agent is promising to develop pristine in vivo MRI methodology to identify the lung diseases epically those effect have been caused in parenchyma surface due to the surfactant concentration.
* Boyed the boundary this particular contrasting agent can work to figure out the size of pour of porous media in materials science.
* In addition, this technique can take us about to prepare the surface coating, spatial fluctuations of surfaces. Eventually, never ending the good sign of this contrasting agent like natural abundance (11.5% of Kr) makes it easy to get with reasonable price $5/L. | 0 | Theoretical and Fundamental Chemistry |
Rosocyanine is a dark green solid with a glossy, metallic shine that forms red colored solutions. It is almost insoluble in water and some organic solvents, very slightly soluble (up to 0.01%) in ethanol, and somewhat soluble (approximately 1%) in pyridine, sulfuric acid, and acetic acid. An alcoholic solution of rosocyanine temporarily turns deeply blue on treatment with alkali.
In rubrocurcumin one molecule of curcumin is replaced with oxalic acid. Rubrocurcumin produces a similar red colored solution. Rosocyanine is an ionic compound, while rubrocurcumin is a neutral complex. | 0 | Theoretical and Fundamental Chemistry |
Dissolution of an organic solid can be described as an equilibrium between the substance in its solid and dissolved forms. For example, when sucrose (table sugar) forms a saturated solution
An equilibrium expression for this reaction can be written, as for any chemical reaction (products over reactants):
where K</sup> is called the thermodynamic solubility constant. The braces indicate activity. The activity of a pure solid is, by definition, unity. Therefore
The activity of a substance, A, in solution can be expressed as the product of the concentration, [A], and an activity coefficient, γ. When K,
is obtained. This is equivalent to defining the standard state as the saturated solution so that the activity coefficient is equal to one. The solubility constant is a true constant only if the activity coefficient is not affected by the presence of any other solutes that may be present. The unit of the solubility constant is the same as the unit of the concentration of the solute. For sucrose K = 1.971 mol dm at 25 °C. This shows that the solubility of sucrose at 25 °C is nearly 2 mol dm (540 g/L). Sucrose is unusual in that it does not easily form a supersaturated solution at higher concentrations, as do most other carbohydrates. | 0 | Theoretical and Fundamental Chemistry |
Electroviscous effects, in chemistry of colloids and surface chemistry, according to an IUPAC definition, are the effects of the particle surface charge on viscosity of a fluid.
Viscoelectric is an effect by which an electric field near a charged interface influences the structure of the surrounding fluid and affects the viscosity of the fluid.
Kinematic viscosity of a fluid, η, can be expressed as a function of electric potential gradient (electric field), , by an equation in the form:
where f is the viscoelectric coefficient of the fluid.
The value of f for water (ambient temperature) has been estimated to be (0.5–1.0) × 10 V m. | 0 | Theoretical and Fundamental Chemistry |
Many of the simplest Z-ligands are simple Lewis acids with electron-deficient center atoms such as BX, BH, BR, AlX, etc. While these molecules typically have trigonal planar geometry, when bonded to a metal center, they become tetrahedral.
This geometry change can be stabilized by the addition of an L-ligand on the metal center. The electrons donated from the L-ligand stabilize the Lewis acid into a tetrahedral form. Therefore, these Z-ligands can attack at (a) the metal (even in 18 electron compounds), (b) the metal-ligand bond, or (c) the ligands.
<br>In addition to the simple Lewis acids, there are several complex molecules that can act as both L- and Z-ligands. These are referred to donor buttresses, and are typically formed when large boron-alkyl molecules complex with a metal center.
In addition to the geometry changes involved in the dative bonding from the metal to the Z-ligand complex, the bond itself can differ greatly depending on the type of buttresses involved. Typical boron-boron bonds are around 1.59 Å. However, due to the dative bond character, the metal-boron bond distance can vary greatly depending on the bonding motif, as well as the various ligands attached to the metal. The boride and borylene motifs tend to have the shortest bonds, typically from 2.00 to 2.15 Å. Boryl complexes have metal-boron bond distances from 2.45 to 2.52 Å, and borane complexes have the largest range of metal-boron bond distances, 2.07-2.91 Å. In addition, for the metal base-stabilized borane complexes, the L-ligand that donates to the metal center plays an important role in the metal-boron bond length. Typically, the donor buttresses with sulfur and nitrogen donor ligands have metal-boron bond lengths of 2.05-2.25 Å, and donor buttresses with phosphorus donor ligands have metal-boron bond lengths of 2.17-2.91 Å. | 0 | Theoretical and Fundamental Chemistry |
Discodermolide competes with paclitaxel for microtubule binding, but with higher affinity and is also effective in paclitaxel- and in epothilone-resistant cancer cells. Discodermolide also seems to demonstrate a remarkably consistent 3D molecular conformation in the solid-state, in solution and when bound to tubulin; molecules with the conformational flexibility of discodermolide usually present very different conformations in different environments. | 0 | Theoretical and Fundamental Chemistry |
Weder’s early research activities in the 1990s focused on polymers with special optical properties. This involved the development of nonlinear optical polymers and investigations of the structure-property relationships of photoluminescent poly(p-phenylene ethynylene)s. He demonstrated the usefulness of these semiconducting polymers as the active layer in polymer-based light-emitting diodes. His group also exploited the possibility to orient such rod-like molecules to create fluorescent materials that display linearly polarized absorption and emission. Such materials formed the basis of security features that Weder’s group developed, which were used as an anti-counterfeiting element in security paper. His team also discovered a light-polarizing energy transfer effect that can be used to produce highly efficient fluorescent polarizers. Such elements are useful in display and other applications.
Weder’s research focus turned to stimuli-responsive polymers shortly after he moved to CWRU in 2001. In 2002, Weder’s research lab developed a novel method to create polymeric materials that change their fluorescence color upon deformation. Recognizing the potential for practical applications this effect had, Weder established a research program to develop polymers that translate mechanical forces into optical signals, which is still active today, and shortly thereafter, mechanochromic polymers began to attract widespread interest. Most of the mechanochrochromic materials reported by Weder’s group in the following two decades operate on the basis of the same general transduction principle, which involves changing the interactions among optically active motifs in response to mechanical deformation. Recent discoveries include the development of new mechanically responsive motifs or “mechanophores” based on rotaxanes and loop-forming dye pairs.
Controlling the interactions between molecular or nanoscale building blocks through an external stimulus has become one of Weder’s main design tools for the creation of stimuli-responsive polymers. In 2008, in collaboration with his colleague Stuart Rowan, Weder introduced stimuli-responsive mechanically adaptive polymer nanocomposites whose architecture and function was inspired by sea cucumbers. The mechanical properties of these materials, which were made by incorporating nanocellulose crystals as a reinforcing filler into polymer matrices, depend on the interactions among the cellulose nanocrystals (CNCs), and can be regulated by an external stimulus. The approach was initially used to create mechanically morphing implant materials, which soften upon exposure to physiological conditions. This work led to sustained research efforts in Weder’s group on bio-inspired mechanically morphing polymers, the development of protocols for the processing of CNC/polymer nanocomposites, and the development of new cellulose-based nanocomposites. Adaptive polymers that show such mechanical morphing upon exposure to physiological conditions were reported to increase the functionality of cortical implants.
The possibility to heal defects in polymeric materials can increase the reliability and durability of polymer products. In 2011, also in collaboration with Rowan, Weder demonstrated that the UV-light induced temporary disassembly of metallosupramolecular polymers can be used to heal defects in these materials. Expanding on this concept, Weder’s team introduced light healable nanocomposites, and modified the structure to include different binding motifs and architectures, for example glassy hydrogen-bonded supramolecular polymer networks. His group also used this approach to develop adhesives with the capability to bond or debond on demand. Weder’s group sought to push the mechanical properties of supramolecular polymers towards those of conventional thermoplastics. In 2019, his team demonstrated that it is possible to toughen stiff but brittle glassy supramolecular polymer networks by forming blends with a rubbery component. More recent versions of such materials were shown to be healable and to display property combinations that are comparable to some conventional plastics. | 0 | Theoretical and Fundamental Chemistry |
The history of the mole is intertwined with that of units of molecular mass, and the Avogadro constant.
The first table of standard atomic weight was published by John Dalton (1766–1844) in 1805, based on a system in which the relative atomic mass of hydrogen was defined as 1. These relative atomic masses were based on the stoichiometric proportions of chemical reaction and compounds, a fact that greatly aided their acceptance: It was not necessary for a chemist to subscribe to atomic theory (an unproven hypothesis at the time) to make practical use of the tables. This would lead to some confusion between atomic masses (promoted by proponents of atomic theory) and equivalent weights (promoted by its opponents and which sometimes differed from relative atomic masses by an integer factor), which would last throughout much of the nineteenth century.
Jöns Jacob Berzelius (1779–1848) was instrumental in the determination of relative atomic masses to ever-increasing accuracy. He was also the first chemist to use oxygen as the standard to which other masses were referred. Oxygen is a useful standard, as, unlike hydrogen, it forms compounds with most other elements, especially metals. However, he chose to fix the atomic mass of oxygen as 100, which did not catch on.
Charles Frédéric Gerhardt (1816–56), Henri Victor Regnault (1810–78) and Stanislao Cannizzaro (1826–1910) expanded on Berzelius' works, resolving many of the problems of unknown stoichiometry of compounds, and the use of atomic masses attracted a large consensus by the time of the Karlsruhe Congress (1860). The convention had reverted to defining the atomic mass of hydrogen as 1, although at the level of precision of measurements at that time – relative uncertainties of around 1% – this was numerically equivalent to the later standard of oxygen = 16. However the chemical convenience of having oxygen as the primary atomic mass standard became ever more evident with advances in analytical chemistry and the need for ever more accurate atomic mass determinations.
The name mole is an 1897 translation of the German unit Mol, coined by the chemist Wilhelm Ostwald in 1894 from the German word Molekül (molecule). The related concept of equivalent mass had been in use at least a century earlier. | 0 | Theoretical and Fundamental Chemistry |
Chlorprothixene has a strong sedative activity with a high incidence of anticholinergic side effects. The types of side effects encountered (dry mouth, massive hypotension and tachycardia, hyperhidrosis, substantial weight gain etc.) normally do not allow a full effective dose for the remission of psychotic disorders to be given. So cotreatment with another, more potent, antipsychotic agent is needed.
Chlorprothixene is structurally related to chlorpromazine, with which it shares, in principle, all side effects. Allergic side effects and liver damage seem to appear with an appreciable lower frequency. The elderly are particularly sensitive to anticholinergic side effects of chlorprothixene (precipitation of narrow angle glaucoma, severe obstipation, difficulties in urinating, confusional and delirant states). In patients >60 years the doses should be particularly low.
Early and late extrapyramidal side effects may occur but have been noted with a low frequency (one study with a great number of participants has delivered a total number of only 1%). | 0 | Theoretical and Fundamental Chemistry |
Thiolates are relatively basic ligands, being derived from conjugate acids with pK's of 6.5 (thiophenol) to 10.5 (butanethiol). Consequently, thiolate ligand often bridge pairs of metals. One example is Fe(SCH)(CO). Thiolate ligands, especially when nonbridging, are susceptible to attack by electrophiles including acids, alkylating agents, and oxidants. | 0 | Theoretical and Fundamental Chemistry |
The Chandrasekhar number is a dimensionless quantity used in magnetic convection to represent ratio of the Lorentz force to the viscosity. It is named after the Indian astrophysicist Subrahmanyan Chandrasekhar.
The number's main function is as a measure of the magnetic field, being proportional to the square of a characteristic magnetic field in a system. | 1 | Applied and Interdisciplinary Chemistry |
Hydrophilic interaction chromatography (or hydrophilic interaction liquid chromatography, HILIC) is a variant of normal phase liquid chromatography that partly overlaps with other chromatographic applications such as ion chromatography and reversed phase liquid chromatography. HILIC uses hydrophilic stationary phases with reversed-phase type eluents. The name was suggested by Andrew Alpert in his 1990 paper on the subject. He described the chromatographic mechanism for it as liquid-liquid partition chromatography where analytes elute in order of increasing polarity, a conclusion supported by a review and re-evaluation of published data. | 1 | Applied and Interdisciplinary Chemistry |
Chitin is a good inducer of plant defense mechanisms for controlling diseases. It has potential for use as a soil fertilizer or conditioner to improve fertility and plant resilience that may enhance crop yields. | 1 | Applied and Interdisciplinary Chemistry |
The society's headquarters is in Belgrave Square, London. There are semi-independent branches in the United States, Canada and Australia. | 1 | Applied and Interdisciplinary Chemistry |
The solubility product for the hydroxide of a metal ion, M, is usually defined, as follows:
However, general-purpose computer programs are designed to use hydrogen ion concentrations with the alternative definitions.
For hydroxides, solubility products are often given in a modified form, K*, using hydrogen ion concentration in place of hydroxide ion concentration. The two values are related by the self-ionization constant for water, K.
For example, at ambient temperature, for calcium hydroxide, Ca(OH), lg K is ca. −5 and lg K* ≈ −5 + 2 × 14 ≈ 23. | 0 | Theoretical and Fundamental Chemistry |
In piping and plumbing, a coupling (or coupler) is a very short length of pipe or tube, with a socket at one or both ends that allows two pipes or tubes to be joined, welded (steel), brazed or soldered (copper, brass etc.) together.
Alternatively, it is a short length of pipe with two female National pipe threads (NPT) (in North American terms, a coupler is a double female while a nipple is a double male) or two male or female British standard pipe threads.
If the two ends of a coupling are of different standards or joining methods, the coupling is called an adapter. Examples of adapters include one end BSP threaded with the other NPT threaded, and one end threaded with the other a plain socket for brazing.
A coupling whose ends use the same connection method but are of different sizes is called a reducing coupling or reducer. An example is a 3/4" NPT to 1/2" NPT coupling. | 1 | Applied and Interdisciplinary Chemistry |
Not all scholars of animal communication accept the interpretation of alarm signals in monkeys as having semantic properties or transmitting "information". Prominent spokespersons for this opposing view are Michael Owren and Drew Rendall, whose work on this topic has been widely cited and debated. The alternative to the semantic interpretation of monkey alarm signals as suggested in the cited works is that animal communication is primarily a matter of influence rather than information, and that vocal alarm signals are essentially emotional expressions influencing the animals that hear them. In this view monkeys do not designate predators by naming them, but may react with different degrees of vocal alarm depending on the nature of the predator and its nearness on detection, as well as by producing different types of vocalization under the influence of the monkey's state and movement during the different types of escape required by different predators. Other monkeys may learn to use these emotional cues along with the escape behaviour of the alarm signaller to help make a good decision about the best escape route for themselves, without there having been any naming of predators. | 1 | Applied and Interdisciplinary Chemistry |
Inhaled anesthetics inhibit nicotinic acetylcholine receptors (nAChRs) and potentiate neuromuscular blockage with nondepolarising NMBAs. It depends on the type of volatile anesthetic (desflurane > sevoflurane > isoflurane > nitrous oxide), the concentration and the duration of exposure. | 1 | Applied and Interdisciplinary Chemistry |
Equilibria are defined for specific crystal phases. Therefore, the solubility product is expected to be different depending on the phase of the solid. For example, aragonite and calcite will have different solubility products even though they have both the same chemical identity (calcium carbonate). Under any given conditions one phase will be thermodynamically more stable than the other; therefore, this phase will form when thermodynamic equilibrium is established. However, kinetic factors may favor the formation the unfavorable precipitate (e.g. aragonite), which is then said to be in a metastable state.
In pharmacology, the metastable state is sometimes referred to as amorphous state. Amorphous drugs have higher solubility than their crystalline counterparts due to the absence of long-distance interactions inherent in crystal lattice. Thus, it takes less energy to solvate the molecules in amorphous phase. The effect of amorphous phase on solubility is widely used to make drugs more soluble. | 0 | Theoretical and Fundamental Chemistry |
Racemization can be achieved by simply mixing equal quantities of two pure enantiomers. Racemization can also occur in a chemical interconversion. For example, when (R)-3-phenyl-2-butanone is dissolved in aqueous ethanol that contains NaOH or HCl, a racemate is formed. The racemization occurs by way of an intermediate enol form in which the former stereocenter becomes planar and hence achiral. An incoming group can approach from either side of the plane, so there is an equal probability that protonation back to the chiral ketone will produce either an R or an S form, resulting in a racemate.
Racemization can occur through some of the following processes:
* Substitution reactions that proceed through a free carbocation intermediate, such as unimolecular substitution reactions, lead to non-stereospecific addition of substituents which results in racemization.
* Although unimolecular elimination reactions also proceed through a carbocation, they do not result in a chiral center. They result instead in a set of geometric isomers in which trans/cis (E/Z) forms are produced, rather than racemates.
* In a unimolecular aliphatic electrophilic substitution reaction, if the carbanion is planar or if it cannot maintain a pyramidal structure, then racemization should occur, though not always.
* In a free radical substitution reaction, if the formation of the free radical takes place at a chiral carbon, then racemization is almost always observed.
The rate of racemization (from -forms to a mixture of -forms and -forms) has been used as a way of dating biological samples in tissues with slow rates of turnover, forensic samples, and fossils in geological deposits. This technique is known as amino acid dating. | 0 | Theoretical and Fundamental Chemistry |
The protein folding problem is concerned with three questions, as stated by Ken A. Dill and Justin L. MacCallum: (i) How can an amino acid sequence determine the 3D native structure of a protein? (ii) How can a protein fold so quickly despite a vast number of possible conformations (the Levinthals Paradox)? How does the protein know what conformations not to search? And (iii) is it possible to create a computer algorithm to predict a proteins native structure based on its amino acid sequence alone? Auxiliary factors inside the living cell such as folding catalysts and chaperones assist in the folding process but do not determine the native structure of a protein. Studies during the 1980s focused on models that could explain the shape of the energy landscape, a mathematical function that describes the free energy of a protein as a function of the microscopic degrees of freedom.
After introducing the term in 1987, Ken A. Dill surveyed the polymer theory in protein folding, in which it addresses two puzzles, the first one being the Blind Watchmakers Paradox in which biological proteins could not originate from random sequences, and the second one being Levinthals Paradox that protein folding cannot happen randomly. Dill pulled the idea from the Blind Watchmaker into his metaphor for protein folding kinetics. The native state of protein can be achieved through a folding process involving some small bias and random choices to speed up the search time. That would mean even residues at very different positions in the amino acid sequence will be able to come into contact with each other. Yet, a bias during the folding process can change the folding time by tens to hundreds of orders of magnitude.
As protein folding process goes through a stochastic search of conformations before reaching its final destination, the vast number of possible conformations is considered irrelevant, while the kinetic traps begin to play a role. The stochastic idea of protein intermediate conformations reveals the concept of an “energy landscape” or "folding funnel" in which folding properties are related to free energy and that the accessible conformations of a protein are reduced as it approaches native-like structure. The y-axis of the funnel represents the "internal free energy" of a protein: the sum of hydrogen bonds, ion-pairs, torsion angle energies, hydrophobic and solvation free energies. The many x-axes represent the conformational structures, and those that are geometrically similar to each other are close to one another in the energy landscape. The folding funnel theory is also supported by Peter G Wolynes, Zaida Luthey-Schulten and Jose Onuchic, that folding kinetics should be considered as progressive organization of partially folded structures into an ensemble (a funnel), rather than a serial linear pathway of intermediates.
Native states of proteins are shown to be thermodynamically stable structures that exist in physiological conditions, and are proven in experiments with ribonuclease by Christian B. Anfinsen (see Anfinsens dogma). It is suggested that because the landscape is encoded by the amino-acid sequence, natural selection has enabled proteins to evolve so that they are able to fold rapidly and efficiently. In a native low-energy structure, theres no competition among conflicting energy contributions, leading to a minimal frustration. This notion of frustration is further measured quantitatively in spin glasses, in which the folding transition temperature T is compared to the glass transition temperature T. T represents the native interactions in the folded structure and T represents the strength of non-native interactions in other configurations. A high T/T ratio indicates a faster folding rate in a protein and fewer intermediates compared to others. In a system with high frustration, mild difference in thermodynamic condition can lead to different kinetic traps and landscape ruggedness. | 1 | Applied and Interdisciplinary Chemistry |
A Rivlin–Ericksen temporal evolution of the strain rate tensor such that the derivative translates and rotates with the flow field. The first-order Rivlin–Ericksen is given by
where
: is the fluid's velocity and
: is -th order Rivlin–Ericksen tensor.
Higher-order tensor may be found iteratively by the expression
The derivative chosen for this expression depends on convention. The upper-convected time derivative, lower-convected time derivative, and Jaumann derivative are often used. | 1 | Applied and Interdisciplinary Chemistry |
Cations which are left after carefully separating previous groups are considered to be in the sixth analytical group. The most important ones are Mg, Li, Na and K. All the ions are distinguished by flame color: lithium gives a red flame, sodium gives bright yellow (even in trace amounts), potassium gives violet, and magnesium, colorless (although magnesium metal burns with a bright white flame). Magnesium can also be distinguished from other cations in this group by adding sodium hydroxide to drive the pH to 11 or higher, which selectively precipitates Mg(OH). | 0 | Theoretical and Fundamental Chemistry |
While arsenic was most likely originally mixed with copper as a result of the ores already containing it, its use probably continued for a number of reasons. First, it acts as a deoxidizer, reacting with oxygen in the hot metal to form arsenous oxides which vaporize from the liquid metal. If a great deal of oxygen is dissolved in liquid copper, when the metal cools the copper oxide separates out at grain boundaries, and greatly reduces the ductility of the resulting object. However, its use can lead to a greater risk of porous castings, owing to the solution of hydrogen in the molten metal and its subsequent loss as a bubble (although any bubbles could be forge-welded and still leave the mass of the metal ready to be work-hardened).
Second, the alloy is capable of greater work-hardening than is the case with pure copper, so that it performs better when used for cutting or chopping. An increase in work-hardening capability arises with an increasing percentage of arsenic, and the bronze can be work-hardened over a wide range of temperatures without fear of embrittlement. Its improved properties over pure copper can be seen with as little as 0.5 to 2 wt% As, giving a 10-to-30% improvement in hardness and tensile strength.
Third, in the correct percentages, it can contribute a silvery sheen to the article being manufactured. There is evidence of arsenical bronze daggers from the Caucasus and other artifacts from different locations having an arsenic-rich surface layer which may well have been produced deliberately by ancient craftsmen, and Mexican bells were made of copper with sufficient arsenic to color them silver. | 1 | Applied and Interdisciplinary Chemistry |
Sialic acids are highly abundant in vertebrate tissues where they are involved in many different biological processes. Originally discovered within the Deuterostome lineage of animals, sialic acids can be actually considered as a subset of a more ancient family of 9-carbon backbone monosaccharides called nonulosonic acids (NulOs), which more recently have been also found in Eubacteria and Archaea.
Many pathogenic bacteria incorporate sialic acid into cell surface features like their lipopolysaccharide or capsule polysaccharides, which helps them to evade the innate immune response of the host.
A recent genome level study examined a large set of sequenced microbial genomes, which indicated that biosynthetic pathways to produce nonulosonic acids (NulOs) are far more widely distributed across the phylogenetic tree of life, than previously realized. This finding is moreover supported by recent lectin staining studies and a molecular level survey on prokaryotic nonulosonic acids, showing that also many non-pathogenic and purely environmental strains produce bacterial sialic acids (NulOs). Some (anammox) bacteria produce NulOs that in addition to the very acidic alpha-keto acid group also display (neutralizing) basic groups (free amines). Comparable cell surface sialic acids have been produced by chemical remodelling to manipulate the cell surface charge by producing a free amine at C5, which neutralizes the negatively charged carboxyl group at C1. | 0 | Theoretical and Fundamental Chemistry |
At the start, electrodes were made mainly from wires or metal sheets.
Nowadays, the electric field in DEP is created by means of electrodes which minimize the magnitude of the voltage needed. This has been possible using fabrication techniques such as photolithography, laser ablation and electron beam patterning.
These small electrodes allow the handling of small bioparticles.
The most used electrode geometries are isometric, polynomial, interdigitated, and crossbar. Isometric geometry is effective for particle manipulation with DEP but repelled particles do not collect in well defined areas and so separation into two homogeneous groups is difficult. Polynomial is a new geometry producing well defined differences in regions of high and low forces and so particles could be collected by positive and negative DEP. This electrode geometry showed that the electrical field was highest at the middle of the inter-electrode gaps. Interdigitated geometry comprises alternating electrode fingers of opposing polarities and is mainly used for dielectrophoretic trapping and analysis. Crossbar geometry is potentially useful for networks of interconnects. | 0 | Theoretical and Fundamental Chemistry |
Bacterial resistance to the cephalosporin compounds can take place by three mechanisms.
* Modifications in target PBP
* Drug inactivation by bacterial β-lactamases
* Drug not being able to reach target PBP in the bacterial cell
Cephalosporins must get through the bacterial cell wall in order to reach the target PBP. In comparison, it is easier to penetrate the cell wall of gram-positive bacteria than the cell wall of gram-negative bacteria. The cell wall structure of gram-positive bacteria is made routinely up by peptidoglycan which allows the passage of cephalosporin-sized molecules. The cell wall structure of gram-negative bacteria is more complex, composed of polysaccharides, lipids and proteins, and is harder to penetrate. Particles get through the outer membrane through water-filled channels, or porins, which are trans membrane proteins.
During exposure to cephalosporins the bacteria can form resistance by itself or as selection of the next generation of bacteria after reproducing itself, by mutation.
Bacteria species such as pneumococci and meningococci can acquire exogenous genetic material, and incorporate it into their own chromosomes which leads to antimicrobial resistance.
In that manner the target PBP can be altered to have their attraction for cephalosporins and other β-lactam antibiotics lowered. The bacteria can also replace the PBP that is vulnerable to Beta-lactam antibiotics with PBP that is less vulnerable.
β-lactam antibiotics can be inactivated by many types of β-lactamases, which are produced by bacteria. The enzymes hydrolyze the bond between the carbon and nitrogen atom of the β-lactam ring. There are many beta lactamases which vary in substrate specificity and host range. The enzymes active site is easily regenerated hydrolytically so it is re-usable many times, in that way can a comparatively small amount of beta-lactamases destroy a large amount of drug. Gram-positive bacteria, such as a staphylococci, have a high release of beta-lactamases into their extracellular space, where they meet the drug outside the cell wall. Gram-negative bacteria on the other hand follow a more conservative course. They secrete their beta-lactamases into the periplasmic space between the inner and outer membrane so they cant easily escape into the extracellular space, and dont have to be biosynthesized in high quantities. | 1 | Applied and Interdisciplinary Chemistry |
An example of a spontaneous (without addition of an external energy source) decomposition is that of hydrogen peroxide which slowly decomposes into water and oxygen ):
: 2 HO → 2 HO + O
This reaction is one of the exceptions to the endothermic nature of decomposition reactions.
Other reactions involving decomposition do require the input of external energy. This energy can be in the form of heat, radiation, electricity, or light. The latter being the reason some chemical compounds, such as many prescription medicines, are kept and stored in dark bottles which reduce or eliminate the possibility of light reaching them and initiating decomposition.
When heated, carbonates will decompose. A notable exception is carbonic acid, (HCO). Commonly seen as the "fizz" in carbonated beverages, carbonic acid will spontaneously decompose over time into carbon dioxide and water. The reaction is written as:
: HCO → HO + CO
Other carbonates will decompose when heated to produce their corresponding metal oxide and carbon dioxide. The following equation is an example, where M represents the given metal:
: MCO → MO + CO
A specific example is that involving calcium carbonate:
: CaCO → CaO + CO
Metal chlorates also decompose when heated. In this type of decomposition reaction, a metal chloride and oxygen gas are the products. Here, again, M represents the metal:
: 2 MClO → 2 MCl+ 3 O
A common decomposition of a chlorate is in the reaction of potassium chlorate where oxygen is the product. This can be written as:
: 2 KClO → 2 KCl + 3 O | 0 | Theoretical and Fundamental Chemistry |
The nuclear chemistry associated with the nuclear fuel cycle can be divided into two main areas, one area is concerned with operation under the intended conditions while the other area is concerned with maloperation conditions where some alteration from the normal operating conditions has occurred or (more rarely) an accident is occurring. Without this process, none of this would be true. | 0 | Theoretical and Fundamental Chemistry |
While introductory levels of chemistry teaching use postulated oxidation states, the IUPAC recommendation and the Gold Book entry list two entirely general algorithms for the calculation of the oxidation states of elements in chemical compounds. | 0 | Theoretical and Fundamental Chemistry |
Mitochondrial ferritin has many roles pertaining to molecular function. It participates in ferroxidase activity, binding, iron ion binding, oxidoreductase activity, ferric iron binding, metal ion binding as well as transition metal binding. Within the realm of biological processes it participates in oxidation-reduction, iron ion transport across membranes and cellular iron ion homeostasis. | 1 | Applied and Interdisciplinary Chemistry |
* Gamma (γ): This phase composes the matrix of Ni-based superalloy. It is a solid solution fcc austenitic phase of the alloying elements. The alloying elements most found in commercial Ni-based alloys are, C, Cr, Mo, W, Nb, Fe, Ti, Al, V, and Ta. During the formation of these materials, as they cool from the melt, carbides precipitate, and at even lower temperatures γ' phase precipitates.
* Gamma prime (γ): This phase constitutes the precipitate used to strengthen the alloy. It is an intermetallic phase based on Ni(Ti,Al) which have an ordered FCC L1 structure. The γ phase is coherent with the matrix of the superalloy having a lattice parameter that varies by around 0.5%. Ni(Ti,Al) are ordered systems with Ni atoms at the cube faces and either Al or Ti atoms at the cube edges. As particles of γ precipitates aggregate, they decrease their energy states by aligning along the <100> directions forming cuboidal structures. This phase has a window of instability between 600 °C and 850 °C, inside of which γ will transform into the HCP η phase. For applications at temperatures below 650 °C, the γ" phase can be utilized for strengthening.
* Gamma double prime (γ"): This phase typically is NiNb or NiV and is used to strengthen Ni-based superalloys at lower temperatures (<650 °C) relative to γ'. The crystal structure of γ" is body-centered tetragonal (BCT), and the phase precipitates as 60 nm by 10 nm discs with the (001) planes in γ" parallel to the {001} family in γ. These anisotropic discs form as a result of lattice mismatch between the BCT precipitate and the FCC matrix. This lattice mismatch leads to high coherency strains which, together with order hardening, are the primary strengthening mechanisms. The γ" phase is unstable above approximately 650 °C.
* Carbide phases: Carbide formation is usually deleterious although in Ni-based superalloys they are used to stabilize the structure of the material against deformation at high temperatures. Carbides form at the grain boundaries, inhibiting grain boundary motion.
*Topologically close-packed (TCP) phases: The term "TCP phase" refers to any member of a family of phases (including the σ phase, the χ phase, the μ phase, and the Laves phase), which are not atomically close-packed but possess some close-packed planes with HCP stacking. TCP phases tend to be highly brittle and deplete the γ matrix of strengthening, solid solution refractory elements (including Cr, Co, W, and Mo). These phases form as a result of kinetics after long periods of time (thousands of hours) at high temperatures (>750 °C). | 1 | Applied and Interdisciplinary Chemistry |
MTV techniques have proven to allow measurements of velocities in inhospitable environments, like jet engines, flames, high-pressure vessels, where it is difficult for techniques like Pitot, hot-wire velocimetry and PIV to work. The field of MTV is fairly young; the first demonstration of implementation emerged within the 1980s and the number of schemes developed and investigated for use in air is still fairly small. These schemes differ in the molecule that is created, whether seeding the flow with foreign molecules is necessary and what wavelength of light is being used. | 1 | Applied and Interdisciplinary Chemistry |
Angiogenesis or the growth of new blood vessels has been reported to correspond with MM progression where vascular endothelial growth factor (VEGF) and its receptor, bFGF and IL-6 appear to be required for endothelial cell migration during angiogenesis. Thalidomide and its analogs are believed to suppress angiogenesis through modulation of the above-mentioned factors where potency in anti-angiogenic activity for lenalidomide and pomalidomide was 2-3 times higher than for thalidomide in various in vivo assays, Thalidomide has also been shown to block NF-κB activity through the blocking of IL-6, and NF-κB has been shown to be involved in angiogenesis. Inhibition of TNF-α is not the mechanism of thalidomide's inhibition of angiogenesis since numerous other TNF-α inhibitors do not inhibit angiogenesis. | 1 | Applied and Interdisciplinary Chemistry |
Carbenes behave like very aggressive Lewis acids. They can attack lone pairs, but their primary synthetic utility arises from attacks on π bonds, which give cyclopropanes; and on σ bonds, which cause carbene insertion. Other reactions include rearrangements and dimerizations. A particular carbene's reactivity depends on the substituents, including any metals present. | 0 | Theoretical and Fundamental Chemistry |
Molten sucrose is used instead of solvent. The reaction involves molten sucrose and fatty acid ester (methyl ester or triglyceride) with a basic catalyst, potassium carbonate or potassium soap. The high temperature (170-190 °C) is required for this process. Since the process is carried out at a high temperature, sucrose can be degraded.
Later, a new synthesis pathway was introduced. First, sucrose and fatty acid soap are dissolved in water. Then, fatty acid ester and a basic catalyst are added to the solution. The solution must be heated and the pressure should be reduced to remove water and form a molten mixture. The transesterification is carried in the temperature range of 110-175 °C. | 0 | Theoretical and Fundamental Chemistry |
L.G. Loitsianskii derived an integral invariant for the decay of the turbulence by taking the fourth moment of the Kármán–Howarth equation in 1939, i.e.,
If decays faster than as and also in this limit, if we assume that vanishes, we have the quantity,
which is invariant. Lev Landau and Evgeny Lifshitz showed that this invariant is equivalent to conservation of angular momentum. However, Ian Proudman and W.H. Reid showed that this invariant does not hold always since is not in general zero, at least, in the initial period of the decay. In 1967, Philip Saffman showed that this integral depends on the initial conditions and the integral can diverge under certain conditions. | 1 | Applied and Interdisciplinary Chemistry |
When α chains of laminin-111 bind to cell surface receptors integrins α1β1, α3β1, α4β1, α6β1 and Cdc42 GTPase are activated. The activated GTPase then activates Cdc42 which further activates c-Jun kinases and phosphorylation of Jun. Activation of c-Jun kinases leads to high levels of c-Jun expression which results in neurite outgrowth. The synthesis of Nitric Oxides resides somewhere in the pathway and is yet to be determined. Weston et al. (2000) proposed that the synthesis of Nitric Oxide may be upstream to the activation of Cdc42. Nonetheless, Nitric Oxide synthesis is shown to be an important element in laminin-mediated neurite outgrowth. | 0 | Theoretical and Fundamental Chemistry |
Organic geochemists also have an interest in studying the diagenesis of biogenic substances in petroleum and how they are transformed in sediment and fossils. While 90% of this organic material is insoluble in common organic solvents – called kerogen – 10% is in a form that is soluble and can be extracted, from where biogenic compounds can then be isolated. Saturated linear fatty acids and pigments have the most stable chemical structures and are therefore suited to withstanding degradation from the diagenesis process and being detected in their original forms. However, macromolecules have also been found in protected geological regions. Typical sedimentation conditions involve enzymatic, microbial and physicochemical processes as well as increased temperature and pressure, which lead to transformations of biogenic substances. For example, pigments that arise from dehydrogenation of chlorophyll or hemin can be found in many sediments as nickel or vanadyl complexes. A large proportion of the isoprenoids in sediments are also derived from chlorophyll. Similarly, linear saturated fatty acids discovered in the Messel oil shale of the Messel Pit in Germany arise from organic material of vascular plants.
Additionally, alkanes and isoprenoids are found in soluble extracts of Precambrian rock, indicating the probable existence of biological material more than three billion years ago. However, there is the potential that these organic compounds are abiogenic in nature, especially in Precambrian sediments. While Studier et al.’s (1968) simulations of the synthesis of isoprenoids in abiogenic conditions did not produce the long-chain isoprenoids used as biomarkers in fossils and sediments, traces of C-C isoprenoids were detected. It is also possible for polyisoprenoid chains to be stereoselectively synthesised using catalysts such as Al(CH) – VCl. However, the probability of these compounds being available in the natural environment is unlikely. | 0 | Theoretical and Fundamental Chemistry |
Some drug molecules are chiral, and the enantiomers have different effects on biological entities. They can be sold as one enantiomer or as a racemic mixture. Examples include thalidomide, ibuprofen, cetirizine and salbutamol. A well known drug that has different effects depending on its ratio of enantiomers is amphetamine. Adderall is an unequal mixture of both amphetamine enantiomers. A single Adderall dose combines the neutral sulfate salts of dextroamphetamine and amphetamine, with the dextro isomer of amphetamine saccharate and D/L-amphetamine aspartate monohydrate. The original Benzedrine was a racemic mixture, and isolated dextroamphetamine was later introduced to the market as Dexedrine. The prescription analgesic tramadol is also a racemate.
In some cases (e.g., ibuprofen and thalidomide), the enantiomers interconvert or racemize in vivo. This means that preparing a pure enantiomer for medication is largely pointless. However, sometimes samples containing pure enantiomers may be made and sold at a higher cost in cases where the use requires specifically one isomer (e.g., for a stereospecific reagent); compare omeprazole and esomeprazole. Moving from a racemic drug to a chiral specific drug may be done for a better safety profile or an improved therapeutic index. This process is called chiral switching and the resulting enantiopure drug is called a chiral switch. As examples, esomeprazole is a chiral switch of (±)-omeprazole and levocetirizine is a chiral switch of (±)-cetirizine.
While often only one enantiomer of the drug may be active, there are cases in which the other enantiomer is harmful, like salbutamol and thalidomide. The (R) enantiomer of thalidomide is effective against morning sickness, while the (S) enantiomer is teratogenic, causing birth defects. Since the drug racemizes, the drug cannot be considered safe for use by women of child-bearing age, and its use is tightly controlled when used for treating other illness.
Methamphetamine is available by prescription under the brand name Desoxyn. The active component of Desoxyn is dextromethamphetamine hydrochloride. This is the right-handed isomer of methamphetamine. The left-handed isomer of methamphetamine, levomethamphetamine, is an OTC drug that is less centrally-acting and more peripherally-acting. Methedrine during the 20th century was a 50:50 racemic mixture of both methamphetamine isomers (levo and dextro). | 0 | Theoretical and Fundamental Chemistry |
Conventional cryoprotectants are glycols (alcohols containing at least two hydroxyl groups), such as ethylene glycol , propylene glycol and glycerol. Ethylene glycol is commonly used as automobile antifreeze; while propylene glycol has been used to reduce ice formation in ice cream. Dimethyl sulfoxide (DMSO) is also regarded as a conventional cryoprotectant. Glycerol and DMSO have been used for decades by cryobiologists to reduce ice formation in sperm, oocytes, and embryos that are cold-preserved in liquid nitrogen. Cryoconservation of animal genetic resources is a practice that involves conventional cryoprotectants to store genetic material with the intention of future revival. Trehalose is non-reducing sugar produced by yeasts and insects in copious amounts. Its use as a cryoprotectant in commercial systems has been patented widely. | 1 | Applied and Interdisciplinary Chemistry |
The streaming potential is an electric potential that develops during the flow of liquid through a capillary. In nature, a streaming potential may occur at a significant magnitude in areas with volcanic activities. The streaming potential is also the primary electrokinetic phenomenon for the assessment of the zeta potential at the solid material-water interface. A corresponding solid sample is arranged in such a way to form a capillary flow channel. Materials with a flat surface are mounted as duplicate samples that are aligned as parallel plates. The sample surfaces are separated by a small distance to form a capillary flow channel. Materials with an irregular shape, such as fibers or granular media, are mounted as a porous plug to provide a pore network, which serves as capillaries for the streaming potential measurement. Upon the application of pressure on a test solution, liquid starts to flow and to generate an electric potential. This streaming potential is related to the pressure gradient between the ends of either a single flow channel (for samples with a flat surface) or the porous plug (for fibers and granular media) to calculate the surface zeta potential.
Alternatively to the streaming potential, the measurement of streaming current offers another approach to the surface zeta potential. Most commonly, the classical equations derived by Maryan Smoluchowski are used to convert streaming potential or streaming current results into the surface zeta potential.
Applications of the streaming potential and streaming current method for the surface zeta potential determination consist of the characterization of surface charge of polymer membranes, biomaterials and medical devices, and minerals. | 0 | Theoretical and Fundamental Chemistry |
The analytical near infrared (NIR) region spans the range from 780 nm to 2,500 nm. The absorption bands seen in this spectral range arise from overtones and combination bands of O-H, N-H, C-H and S-H stretching and bending vibrations. Absorption is one to two orders of magnitude smaller in the NIR compared to the MIR; this phenomenon eliminates the need for extensive sample preparation. Thick and thin samples can be analyzed without any sample preparation, it is possible to acquire NIR chemical images through some packaging materials, and the technique can be used to examine hydrated samples, within limits. Intact samples can be imaged in transmittance or diffuse reflectance.
The lineshapes for overtone and combination bands tend to be much broader and more overlapped than for the fundamental bands seen in the MIR. Often, multivariate methods are used to separate spectral signatures of sample components. NIR chemical imaging is particularly useful for performing rapid, reproducible and non-destructive analyses of known materials. NIR imaging instruments are typically based on a hyperspectral camera, a tunable filter or an FT-IR interferometer. External light source is always needed, such as sun (outdoor scans, remote sensing) or a halogen lamp (laboratory, industrial measurements). | 0 | Theoretical and Fundamental Chemistry |
Semisynthesis, or partial chemical synthesis, is a type of chemical synthesis that uses chemical compounds isolated from natural sources (such as microbial cell cultures or plant material) as the starting materials to produce novel compounds with distinct chemical and medicinal properties. The novel compounds generally have a high molecular weight or a complex molecular structure, more so than those produced by total synthesis from simple starting materials. Semisynthesis is a means of preparing many medicines more cheaply than by total synthesis since fewer chemical steps are necessary. | 1 | Applied and Interdisciplinary Chemistry |
Brass vessels release a small amount of copper ions into stored water, thus killing fecal bacterial counts as high as 1 million bacteria per milliliter.
Copper sulfate mixed with lime (Bordeaux mixture) is used as a fungicide and antihelminthic. Copper sulfate is used chiefly to destroy green algae (algicide) that grow in reservoirs, stock ponds, swimming pools, and fish tanks. Copper 8-hydroxyquinoline is sometimes included in paint to prevent mildew.
Paint containing copper is used on boat bottoms to prevent barnacle growth (biofouling).
Copper also has the ability to destroy viruses, such as influenza viruses, noroviruses or human immunodeficiency virus (HIV). | 1 | Applied and Interdisciplinary Chemistry |
With increasing bainite content in steel, the hardness, yield and tensile strength remain almost constant for bainite content up to 50%, and then increase by ca. 30%. Hence meter-size shafts and plates of high-bainite steels have been commercially mass-produced by Rolls-Royce Holdings and Tata Steel.
In the railway industry, bainite steel is commonly alloyed with vanadium to produce rails of very high strength, with good wear and rolling contact fatigue resistance. Bainite rails fabricated by Corus were installed in the Channel Tunnel in 2006, and after 3 years showed no evidence of the cracks found in standard rails of the same age. | 1 | Applied and Interdisciplinary Chemistry |
An ISFET electrode sensitive to H concentration can be used as a conventional glass electrode to measure the pH of a solution. However, it also requires a reference electrode to operate. If the reference electrode used in contact with the solution is of the AgCl or HgCl classical type, it will suffer the same limitations as conventional pH electrodes (junction potential, KCl leak, and glycerol leak in case of gel electrode). A conventional reference electrode can also be bulky and fragile. A too large volume constrained by a classical reference electrode also precludes the miniaturization of the ISFET electrode, a mandatory feature for some biological or in vivo clinical analyses (disposable mini-catheter pH probe). The breakdown of a conventional reference electrode could also make problem in on-line measurements in the pharmaceutical or food industry if highly valuable products are contaminated by electrode debris or toxic chemical compounds at a late production stage and must be discarded for the sake of safety.
For this reason, since more than 20 years many research efforts have been dedicated to on-chip embedded tiny reference field effect transistors (REFET). Their functioning principle, or operating mode, can vary, depending on the electrode producers and are often proprietary and protected by patents. Semi-conductor modified surfaces required for REFET are also not always in thermodynamical equilibrium with the test solution and can be sensitive to aggressive or interfering dissolved species or not well characterized aging phenomena. This is not a real problem if the electrode can be frequently re-calibrated at regular time interval and is easily maintained during its service life. However, this may be an issue if the electrode has to remain immersed on-line for prolonged period of time, or is inaccessible for particular constrains related to the nature of the measurements itself (geochemical measurements under elevated water pressure in harsh environments or under anoxic or reducing conditions easily disturbed by atmospheric oxygen ingress or pressure changes).
A crucial factor for ISFET electrodes, as for conventional glass electrodes, remains thus the reference electrode. When troubleshooting electrode malfunctions, often, most of the problems have to be searched for from the side of the reference electrode. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, Vapochromism strongly overlaps with solvatochromism since vapochromic systems are ones in which dyes change colour in response to the vapour of an organic compound or gas. Vapochromic devices are the optical branch of electronic noses. The main applications are in sensors for detecting volatile organic compounds (VOCs) in a variety of environments, including industrial, domestic and medical areas.
An example of such a device is an array consisting of a metalloporphyrin (Lewis acid), a pH indicator dye and a solvatochromic dye. The array is scanned with a flat-bed recorder, and the result are compared with a library of known VOCs. Vaporchromic materials are sometimes Pt or Au complexes, which undergo distinct color changes when exposed to VOCs. | 0 | Theoretical and Fundamental Chemistry |
β-TG levels may increase with age. It is elevated in diabetes mellitus.
β-TG levels have been found to be increased by treatment with the synthetic estrogen ethinylestradiol, though were not significantly increased by the natural estrogen estradiol valerate. Levels of β-TG have also been found to be increased or unchanged during normal pregnancy. | 1 | Applied and Interdisciplinary Chemistry |
A heat number is an identification coupon number that is stamped on a material plate after it is removed from the ladle and rolled at a steel mill.
Industry quality standards require materials to be tested at the manufacturer and the results of these tests be submitted through a report, also called a mill sheet, mill certificate or mill test certificate (MTC). The only way to trace a steel plate back to its mill sheet is the heat number. A heat number is similar to a lot number, which is used to identify production runs of any other product for quality control purposes. | 1 | Applied and Interdisciplinary Chemistry |
Radiation chemistry is a subdivision of nuclear chemistry which studies the chemical effects of ionizing radiation on matter. This is quite different from radiochemistry, as no radioactivity needs to be present in the material which is being chemically changed by the radiation. An example is the conversion of water into hydrogen gas and hydrogen peroxide. | 0 | Theoretical and Fundamental Chemistry |
One potential scenario that has been envisioned is out-of-control self-replicating molecular assemblers in the form of gray goo which consumes carbon to continue its replication. If unchecked, such mechanical replication could potentially consume whole ecoregions or the whole Earth (ecophagy), or it could simply outcompete natural lifeforms for necessary resources such as carbon, ATP, or UV light (which some nanomotor examples run on). However, the ecophagy and grey goo scenarios, like synthetic molecular assemblers, are based upon still-hypothetical technologies that have not yet been demonstrated experimentally. | 0 | Theoretical and Fundamental Chemistry |
Monolayers have a multitude of applications both at the air-water and at air-solid interphases.
Nanoparticle monolayers can be used to create functional surfaces that have for instance anti-reflective or superhydrophobic properties.
Monolayers are frequently encountered in biology. A micelle is a monolayer, and the phospholipid lipid bilayer structure of biological membranes is technically two monolayers. Langmuir monolayers are commonly used to mimic cell membrane to study the effects of pharmaceuticals or toxins. | 0 | Theoretical and Fundamental Chemistry |
Pharmacogenomics, often abbreviated "PGx," is the study of the role of the genome in drug response. Its name (pharmaco- + genomics) reflects its combining of pharmacology and genomics. Pharmacogenomics analyzes how the genetic makeup of a patient affects their response to drugs. It deals with the influence of acquired and inherited genetic variation on drug response, by correlating DNA mutations (including point mutations, copy number variations, and structural variations) with pharmacokinetic (drug absorption, distribution, metabolism, and elimination), pharmacodynamic (effects mediated through a drug's biological targets), and/or immunogenic endpoints.
Pharmacogenomics aims to develop rational means to optimize drug therapy, with regard to the patients genotype, to achieve maximum efficiency with minimal adverse effects. It is hoped that by using pharmacogenomics, pharmaceutical drug treatments can deviate from what is dubbed as the "one-dose-fits-all" approach. Pharmacogenomics also attempts to eliminate trial-and-error in prescribing, allowing physicians to take into consideration their patients genes, the functionality of these genes, and how this may affect the effectiveness of the patients current or future treatments (and where applicable, provide an explanation for the failure of past treatments). Such approaches promise the advent of precision medicine and even personalized medicine, in which drugs and drug combinations are optimized for narrow subsets of patients or even for each individuals unique genetic makeup.
Whether used to explain a patient's response (or lack of it) to a treatment, or to act as a predictive tool, it hopes to achieve better treatment outcomes and greater efficacy, and reduce drug toxicities and adverse drug reactions (ADRs). For patients who do not respond to a treatment, alternative therapies can be prescribed that would best suit their requirements. In order to provide pharmacogenomic recommendations for a given drug, two possible types of input can be used: genotyping, or exome or whole genome sequencing. Sequencing provides many more data points, including detection of mutations that prematurely terminate the synthesized protein (early stop codon). | 1 | Applied and Interdisciplinary Chemistry |
Bernard Leslie Shaw, FRS (28 March 1930 – 8 November 2020) was an English chemist who made notable contributions to organometallic chemistry. He was Professor of Inorganic and Structural Chemistry at the University of Leeds. | 0 | Theoretical and Fundamental Chemistry |
pComb3H, a derivative of pComb3 optimized for expression of human fragments, is a phagemid used to express proteins such as zinc finger proteins and antibody fragments on phage pili for the purpose of phage display selection.
For the purpose of phage production, it contains the bacterial ampicillin resistance gene (for B-lactamase), allowing the growth of only transformed bacteria. | 1 | Applied and Interdisciplinary Chemistry |
Ceruloplasmin is the major copper-carrying protein in the blood. Ceruloplasmin exhibits oxidase activity, which is associated with possible oxidation of Fe(II) into Fe(III), therefore assisting in its transport in the blood plasma in association with transferrin, which can carry iron only in the Fe(III) state. | 1 | Applied and Interdisciplinary Chemistry |
Sorrento Therapeutics has been developing RTX as a means to provide pain relief for forms of advanced cancer.
The nerve desensitizing properties of RTX were once thought to be useful to treat overactive bladder (OAB) by preventing the bladder from transmitting "sensations of urgency" to the brain, similar to how they can prevent nerves from transmitting signals of pain; RTX has never received FDA approval for this use. RTX has also previously been investigated as a treatment for interstitial cystitis, rhinitis, and lifelong premature ejaculation (PE). | 0 | Theoretical and Fundamental Chemistry |
The iron catalyst is obtained from finely ground iron powder, which is usually obtained by reduction of high-purity magnetite (FeO). The pulverized iron is oxidized to give magnetite or wüstite (FeO, ferrous oxide) particles of a specific size. The magnetite (or wüstite) particles are then partially reduced, removing some of the oxygen. The resulting catalyst particles consist of a core of magnetite, encased in a shell of wüstite, which in turn is surrounded by an outer shell of metallic iron. The catalyst maintains most of its bulk volume during the reduction, resulting in a highly porous high-surface-area material, which enhances its catalytic effectiveness. Minor components include calcium and aluminium oxides, which support the iron catalyst and help it maintain its surface area. These oxides of Ca, Al, K, and Si are unreactive to reduction by hydrogen.
The production of the catalyst requires a particular melting process in which used raw materials must be free of catalyst poisons and the promoter aggregates must be evenly distributed in the magnetite melt. Rapid cooling of the magnetite, which has an initial temperature of about 3500 °C, produces the desired precursor. Unfortunately, the rapid cooling ultimately forms a catalyst of reduced abrasion resistance. Despite this disadvantage, the method of rapid cooling is often employed.
The reduction of the precursor magnetite to α-iron is carried out directly in the production plant with synthesis gas. The reduction of the magnetite proceeds via the formation of wüstite (FeO) so that particles with a core of magnetite become surrounded by a shell of wüstite. The further reduction of magnetite and wüstite leads to the formation of α-iron, which forms together with the promoters the outer shell. The involved processes are complex and depend on the reduction temperature: At lower temperatures, wüstite disproportionates into an iron phase and a magnetite phase; at higher temperatures, the reduction of the wüstite and magnetite to iron dominates.
The α-iron forms primary crystallites with a diameter of about 30 nanometers. These crystallites form a bimodal pore system with pore diameters of about 10 nanometers (produced by the reduction of the magnetite phase) and of 25 to 50 nanometers (produced by the reduction of the wüstite phase). With the exception of cobalt oxide, the promoters are not reduced.
During the reduction of the iron oxide with synthesis gas, water vapor is formed. This water vapor must be considered for high catalyst quality as contact with the finely divided iron would lead to premature aging of the catalyst through recrystallization, especially in conjunction with high temperatures. The vapor pressure of the water in the gas mixture produced during catalyst formation is thus kept as low as possible, target values are below 3 gm. For this reason, the reduction is carried out at high gas exchange, low pressure, and low temperatures. The exothermic nature of the ammonia formation ensures a gradual increase in temperature.
The reduction of fresh, fully oxidized catalyst or precursor to full production capacity takes four to ten days. The wüstite phase is reduced faster and at lower temperatures than the magnetite phase (FeO). After detailed kinetic, microscopic, and X-ray spectroscopic investigations it was shown that wüstite reacts first to metallic iron. This leads to a gradient of iron(II) ions, whereby these diffuse from the magnetite through the wüstite to the particle surface and precipitate there as iron nuclei.
Pre-reduced, stabilized catalysts occupy a significant market share. They are delivered showing the fully developed pore structure, but have been oxidized again on the surface after manufacture and are therefore no longer pyrophoric. The reactivation of such pre-reduced catalysts requires only 30 to 40 hours instead of several days. In addition to the short start-up time, they have other advantages such as higher water resistance and lower weight. | 0 | Theoretical and Fundamental Chemistry |
In molecular biology, a response regulator is a protein that mediates a cell's response to changes in its environment as part of a two-component regulatory system. Response regulators are coupled to specific histidine kinases which serve as sensors of environmental changes. Response regulators and histidine kinases are two of the most common gene families in bacteria, where two-component signaling systems are very common; they also appear much more rarely in the genomes of some archaea, yeasts, filamentous fungi, and plants. Two-component systems are not found in metazoans. | 1 | Applied and Interdisciplinary Chemistry |
Gunnar Hägg (December 14, 1903 in Stockholm – May 28, 1986 in Uppsala) was a Swedish chemist and crystallographer. | 0 | Theoretical and Fundamental Chemistry |
Supramolecular electronics is the experimental field of supramolecular chemistry that bridges the gap between molecular electronics and bulk plastics in the construction of electronic circuitry at the nanoscale. In supramolecular electronics, assemblies of pi-conjugated systems on the 5 to 100 nanometer scale are prepared by molecular self-assembly with the aim to fit these structures between electrodes. With single molecules as researched in molecular electronics at the 5 nanometer scale this would be impractical. Nanofibers can be prepared from polymers such as polyaniline and polyacetylene. Chiral oligo(p-phenylenevinylene)s self-assemble in a controlled fashion into (helical) wires. An example of actively researched compounds in this field are certain coronenes. | 0 | Theoretical and Fundamental Chemistry |
In some cases, energy loss features due to plasmon excitations are also observed. This can either be a final state effect caused by core hole decay, which generates quantized electron wave excitations in the solid (intrinsic plasmons), or it can be due to excitations induced by photoelectrons travelling from the emitter to the surface (extrinsic plasmons).
Due to the reduced coordination number of first-layer atoms, the plasma frequency of bulk and surface atoms are related by the following equation:
so that surface and bulk plasmons can be easily distinguished from each other.
Plasmon states in a solid are typically localized at the surface, and can strongly affect IMFP. | 0 | Theoretical and Fundamental Chemistry |
The database can be searched by entering one or more of the following parameters: chemical name (is possible to request partial or full matching), molecular formula, number of different types of atoms present in the molecule (as a single value or as a range of values), molecular weight (as a single value or as a range of values), CAS Registry Number or SDBS number. In all cases “%” or “*” can be used as wildcards. The result of the search includes all the available spectra for the search parameters entered. Results can be sorted by molecular weight, number of carbons or SDBS number in ascending or descending order. | 0 | Theoretical and Fundamental Chemistry |
* Tribology Gold Medal, Institution of Mechanical Engineers (2013)
*ACS National Award in Colloid and Surface Chemistry (2009)
* Named by the AICHE as one of the “One Hundred Chemical Engineers of the Modern Era (2008)
* Honorary Degree of Doctor of Engineering – University of South Florida (2007)
* Honorary Degree of Doctor sc. h.c. - ETH Zurich (2006)
* Schlumberger Visiting Professor – University of Oxford, UK (2005)
* MRS Medal, awarded for recent work on adhesion and friction (2004)
* Elected to the US National Academy of Sciences in the area of Engineering Science (2004)
* Elected Fellow of the American Physical Society in the area of Biological Physics (2004)
* Adhesion Society Award for “excellence in adhesion science (2003)
* Fellow of the Royal Society (1988)
* Matthew Flinders Medal and Lecture (1986)
* David Syme Research Prize (1983)
* (FAA) (Elected a fellow of the Australian Academy of Science (1982)
* Pawsey Medal (1977) | 0 | Theoretical and Fundamental Chemistry |
The difference between the current that is actually obtained, at any particular value of the potential of the indicator or working electrode, for the reduction or oxidation of an ionic electroactive substance and the current that would be obtained, at the same potential, if there were no transport of that substance due to the electric field between the electrodes. The sign convention regarding current is such that the migration current is negative for the reduction of a cation or for the oxidation of an anion, and positive for the oxidation of a cation or the reduction of an anion. Hence the migration current may tend to either increase or decrease the total current observed. In any event the migration current approaches zero as the transport number of the electroactive substance is decreased by increasing the concentration of the supporting electrolyte, and hence the conductivity. | 0 | Theoretical and Fundamental Chemistry |
The δ values and absolute isotope ratios of common reference materials are summarized in Table 1 and described in more detail below. Alternative values for the absolute isotopic ratios of reference materials, differing only modestly from those in Table 1, are presented in Table 2.5 of Sharp (2007) (a [http://digitalrepository.unm.edu/unm_oer/1/ text freely available online]), as well as Table 1 of the 1993 IAEA report on isotopic reference materials. For an exhaustive list of reference material, refer to Appendix I of Sharp (2007), Table 40.1 of Gröning (2004), or the website of the International Atomic Energy Agency. Note that the C/C ratio of Vienna Pee Dee Belemnite (VPDB) and S/S ratio of Vienna Canyon Diablo Troilite (VCDT) are purely mathematical constructs; neither material existed as a physical sample that could be measured.
In Table 1, "Name" refers to the common name of the reference, "Material" gives its chemical formula and phase, "Type of ratio" is the isotopic ratio reported in "Isotopic ratio", "δ" is the δ value of the material with indicated reference frame, "Type" is the category of the material using the notation of Gröening (2004) (discussed below), "Citation" gives the article(s) reporting the isotopic abundances on which the isotope ratio is based, and "Notes" are notes. The reported isotopic ratios reflect the results from individual analyses of absolute mass fraction, aggregated in Meija et al. (2016) and manipulated to reach the given ratios. Error was calculated as the square root of the sum of the squares of fractional reported errors, consistent with standard error propagation, but is not propagated for ratios reached through secondary calculation. | 0 | Theoretical and Fundamental Chemistry |
In 1996, Qureshi retired from PAEC as Chief Scientific Officer and was made scientist emeritus, which allowed him to continue research at PINSTECH before moving to Karachi. He took up the professorship of chemistry at the Karachi University and headed the nuclear chemistry section at the H.E.J. Research Institute of Chemistry. During this time, he authored several articles and published books on nuclear chemistry. He retained his position till 2001 when he joined the Pakistan Nuclear Regulatory Authority (PNRA).
At PNRA, Qureshi served as the chief scientific officer and adviser to the government on nuclear policy issues. His contribution and policy efforts led to the physical security of the commercial nuclear power infrastructure in the country and helped launched the nuclear awareness campaign following the Fukushima nuclear disaster in 2011. He served until 2009 when he decided to accept the professorship of chemistry at the Institute of Engineering and Applied Sciences. In December 2012 Qureshi had a sudden breathing problem and died. He is buried in Karachi, Sindh. | 0 | Theoretical and Fundamental Chemistry |
In the book, Lane discusses what he considers to be a major gap in biology: why life operates the way that it does, and how it began. In his view as a biochemist, the core question is about energy, as all cells handle energy in the same way, relying on a steep electrochemical gradient across the very small thickness of a membrane in a cell – to power all the chemical reactions of life. The electrical energy is transformed into forms that the cell can use by a chain of energy-handling structures including ancient proteins such as cytochromes, ion channels, and the enzyme ATP synthase, all built into the membrane. Once evolved, this chain has been conserved by all living things, showing that it is vital to life. He argues that such an electrochemical gradient could not have arisen in ordinary conditions, such as the open ocean or Darwin's "warm little pond". He argues instead (following Günter Wächtershäuser) that life began in deep-sea hydrothermal vents, as these contain chemicals that effectively store energy that cells could use, as long as the cells provided a membrane to generate the needed gradient by maintaining different concentrations of chemicals on either side.
Once cells similar to bacteria (the first prokaryotes, cells without a nucleus) had emerged, he writes, they stayed like that for two and a half billion years. Then, just once, cells jumped in complexity and size, acquiring a nucleus and other organelles, and complex behavioural features including sex, which he notes have become universal in complex (eukaryotic) life forms including plants, animals, and fungi.
The book is illustrated with 37 figures taken by permission from a wide variety of research sources. They include a timeline, photographs, cladograms, electron flow diagrams and diagrams of the life cycle of cells and their chromosomes. | 1 | Applied and Interdisciplinary Chemistry |
The primary biological importance of phosphates is as a component of nucleotides, which
serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA. The double helix of our DNA is only possible because of the phosphate ester bridge that binds the helix. Besides making biomolecules, phosphorus is also found in bone and the enamel of mammalian teeth, whose strength is derived from calcium phosphate in the form of hydroxyapatite. It is also found in the exoskeleton of insects, and phospholipids (found in all biological membranes). It also functions as a buffering agent in maintaining acid base homeostasis in the human body. | 0 | Theoretical and Fundamental Chemistry |
As the total number of degrees of freedom approaches infinity, the system will be found in the macrostate that corresponds to the highest multiplicity. In order to illustrate this principle, observe the skin temperature of a frozen metal bar. Using a thermal image of the skin temperature, note the temperature distribution on the surface. This initial observation of temperature represents a "microstate". At some future time, a second observation of the skin temperature produces a second microstate. By continuing this observation process, it is possible to produce a series of microstates that illustrate the thermal history of the bar's surface. Characterization of this historical series of microstates is possible by choosing the macrostate that successfully classifies them all into a single grouping. | 0 | Theoretical and Fundamental Chemistry |
The dissociation constant is commonly used to describe the affinity between a ligand (such as a drug) and a protein ; i.e., how tightly a ligand binds to a particular protein. Ligand–protein affinities are influenced by non-covalent intermolecular interactions between the two molecules such as hydrogen bonding, electrostatic interactions, hydrophobic and van der Waals forces. Affinities can also be affected by high concentrations of other macromolecules, which causes macromolecular crowding.
The formation of a ligand–protein complex can be described by a two-state process
the corresponding dissociation constant is defined
where , and represent molar concentrations of the protein, ligand, and protein–ligand complex, respectively.
The dissociation constant has molar units (M) and corresponds to the ligand concentration at which half of the proteins are occupied at equilibrium, i.e., the concentration of ligand at which the concentration of protein with ligand bound equals the concentration of protein with no ligand bound . The smaller the dissociation constant, the more tightly bound the ligand is, or the higher the affinity between ligand and protein. For example, a ligand with a nanomolar (nM) dissociation constant binds more tightly to a particular protein than a ligand with a micromolar (μM) dissociation constant.
Sub-picomolar dissociation constants as a result of non-covalent binding interactions between two molecules are rare. Nevertheless, there are some important exceptions. Biotin and avidin bind with a dissociation constant of roughly 10 M = 1 fM = 0.000001 nM.
Ribonuclease inhibitor proteins may also bind to ribonuclease with a similar 10 M affinity.
The dissociation constant for a particular ligand–protein interaction can change with solution conditions (e.g., temperature, pH and salt concentration). The effect of different solution conditions is to effectively modify the strength of any intermolecular interactions holding a particular ligand–protein complex together.
Drugs can produce harmful side effects through interactions with proteins for which they were not meant to or designed to interact. Therefore, much pharmaceutical research is aimed at designing drugs that bind to only their target proteins (negative design) with high affinity (typically 0.1–10 nM) or at improving the affinity between a particular drug and its in vivo protein target (positive design). | 0 | Theoretical and Fundamental Chemistry |
Magnesium is an essential element in biological systems. Magnesium occurs typically as the Mg ion. It is an essential mineral nutrient (i.e., element) for life and is present in every cell type in every organism. For example, adenosine triphosphate (ATP), the main source of energy in cells, must bind to a magnesium ion in order to be biologically active. What is called ATP is often actually Mg-ATP. As such, magnesium plays a role in the stability of all polyphosphate compounds in the cells, including those associated with the synthesis of DNA and RNA.
Over 300 enzymes require the presence of magnesium ions for their catalytic action, including all enzymes utilizing or synthesizing ATP, or those that use other nucleotides to synthesize DNA and RNA.
In plants, magnesium is necessary for synthesis of chlorophyll and photosynthesis. | 1 | Applied and Interdisciplinary Chemistry |
The Stokes number provides a means of estimating the quality of PIV data sets, as previously discussed. However, a definition of a characteristic velocity or length scale may not be evident in all applications. Thus, a deeper insight of how a tracking delay arises could be drawn by simply defining the differential equations of a particle in the Stokes regime. A particle moving with the fluid at some velocity will encounter a variable fluid velocity field as it advects. Let's assume the velocity of the fluid, in the Lagrangian frame of reference of the particle, is . It is the difference between these velocities that will generate the drag force necessary to correct the particle path:
The stokes drag force is then:
The particle mass is:
Thus, the particle acceleration can be found through Newton's second law:
Note the relaxation time can be replaced to yield:
The first-order differential equation above can be solved through the Laplace transform method:
The solution above, in the frequency domain, characterizes a first-order system with a characteristic time of . Thus, the −3 dB gain (cut-off) frequency will be:
The cut-off frequency and the particle transfer function, plotted on the side panel, allows for the assessment of PIV error in unsteady flow applications and its effect on turbulence spectral quantities and kinetic energy. | 1 | Applied and Interdisciplinary Chemistry |
Cohen et al. found that of a pair of co-expressed genes only one promoter has an Upstream Activating Sequence (UAS) associated with that expression pattern. They suggested that UASs can activate genes that are not in immediate adjacency to them. This explanation could explain the co-expression of small clusters, but many clusters contain to many genes to be regulated by a single UAS.
Chromatin changes are a plausible explanation for the co-regulation seen in clusters. Chromatin consists of the DNA strand and histones that are attached to the DNA. Regions were chromatin is very tightly packed are called heterochromatin. Heterochromatin consists very often of remains of viral genomes, transposons and other junk DNA. Because of tight packing the DNA is almost unreachable for the transcript machinery, covering deleterious DNA with proteins is the way in which the cell can protect itself. Chromatin which consists of functional genes is often an open structure were the DNA is accessible. However, most of the genes are not needed to be expressed all the time.
DNA with genes that aren't needed can be covered with histones. When a gene must be expressed special proteins can alter the chemical that are attached to the histones (histone modifications) that cause the histones to open the structure. When the chromatin of one gene is opened, the chromatin of the adjacent genes is also until this modification meets a boundary element. In that way genes is close proximity are expressed on the same time. So, genes are clustered in “expression hubs”. In comparison with this model Gilbert et al. (2004) showed that RIDGEs are mostly present in open chromatin structures.
However Johnidis et al. (2005) have shown that genes in the same cluster can be very differently expressed. How eukaryotic gene regulation, and associated chromatin changes, precisely works is still very unclear and there is no consensus about it. In order to get a clear picture about the mechanism of gene clusters first the workings chromatin and gene regulation needs to be illuminated.
Furthermore, most papers that identified clusters of co-regulated genes focused on transcription levels whereas few focused on clusters regulated by the same transcription-factors. Johnides et al. discovered strange phenomena when they did. | 1 | Applied and Interdisciplinary Chemistry |
Protecting a substrate with a PPG is commonly referred to as "photocaging." This term is especially popular in biological systems. For example, Ly et al. developed a p-iodobenzoate-based photocaged reagent, which would experience a homolytic photoclevage of the C-I bond. They found that the reaction could occur with excellent yields, and with a half-life of 2.5 minutes when a 15 W 254 nm light source was used. The resulting biomolecular radicals are necessary in many enzymatic processes. As a second example, researchers synthesized a cycloprene-modified glutamate photocaged with a 2-nitroveratrol-based PPG. As it is an excitatory amino acid neurotransmitter, the aim was to develop a bioorthagonal probe for glutamate in vivo. In a final example, Venkatesh et al. demonstrated the use of a PPG-based photocaged therapeutic. Their prodrug, which released one equivalent of caffeic acid and chlorambucil upon phototriggering, showed reasonable biocompatibility, cellular uptake and photoregulared drug release in vitro. | 0 | Theoretical and Fundamental Chemistry |
Translation initiation is the process by which the ribosome and its associated factors bind to an mRNA and are assembled at the start codon. This process is defined as either cap-dependent, in which the ribosome binds initially at the 5 cap and then travels to the stop codon, or as cap-independent, where the ribosome does not initially bind the 5 cap. | 1 | Applied and Interdisciplinary Chemistry |
As awareness about ocean acidification grows, policies geared towards increasing monitoring efforts of ocean acidification have been drafted. Previously in 2015, ocean scientist Jean-Pierre Gattuso had remarked that "The ocean has been minimally considered at previous climate negotiations. Our study provides compelling arguments for a radical change at the UN conference (in Paris) on climate change".
International efforts, such as the UN Cartagena Convention (entered into force in 1986), are critical to enhance the support provided by regional governments to highly vulnerable areas to ocean acidification. Many countries, for example in the Pacific Islands and Territories, have constructed regional policies, or National Ocean Policies, National Action Plans, National Adaptation Plans of Action and Joint National Action Plans on Climate Change and Disaster Risk Reduction, to help work towards SDG 14. Ocean acidification is now starting to be considered within those frameworks. | 0 | Theoretical and Fundamental Chemistry |
Creating separation between a sound source and any form of adjoining mass, hindering the direct pathway for sound transfer. | 1 | Applied and Interdisciplinary Chemistry |
Cyclization reactions, or intramolecular addition reactions, can be used to form cycloalkenes. These reactions primarily form cyclopentenones, a cycloalkene that contains two functional groups: the cyclopentene and a ketone group. However, other cycloalkenes, such as Cyclooctatetraene, can be formed as a result of this reaction. | 0 | Theoretical and Fundamental Chemistry |
The investigation of the TRPM genes and proteins in human cells is an area of intense recent study and, at times, debate. Montell et al. (2002) have reviewed the research into the TRP genes, and a second review by Montell (2003) has reviewed the research into the TRPM genes.
The TRPM family of ion channels has members throughout the metazoa. The TRPM6 and TRPM7 proteins are highly unusual, containing both an ion channel domain and a kinase domain (Figure 1.7), the role of which brings about the most heated debate.
The activity of these two proteins has been very difficult to quantify. TRPM7 by itself appears to be a Ca channel but in the presence of TRPM6 the affinity series of transported cations places Mg above Ca. The differences in reported conductance were caused by the expression patterns of these genes. TRPM7 is expressed in all cell types tested so far, while TRPM6 shows a more restricted pattern of expression. An unfortunate choice of experimental system by Voets et al., (2004) led to the conclusion that TRPM6 is a functional Mg transporter. However, later work by Chubanov et al. (2004) clearly showed that TRPM7 is required for TRPM6 activity and that the results of Voets et al. are explained by the expression of TRPM7 in the experimental cell line used by Voets et al. in their experiments. Whether TRPM6 is functional by itself is yet to be determined.
The predicted TM topology of the TPRM6 and TRPM7 proteins has been adapted from Nadler et al. (2001), Runnels et al. (2001) and Montell et al. (2002), this figure shows the computer predicted membrane topology of the TRPM6 and TRPM7 proteins in Homo sapiens. At this time, the topology shown should be considered a tentative hypothesis. The TM domains are shown in light blue, the pore loop in purple, the TRP motif in red and the kinase domain in green. The orientation in the membrane and the positions of the N- and C-termini are indicated and the figure is not drawn to scale.
The conclusions of the Voets et al. (2004) paper are probably incorrect in attributing the Mg dependent currents to TRPM7 alone, and their kinetic data are likely to reflect the combined TRPM7/ TRPM6 channel. The report presents a robust collection of data consistent with a channel-like activity passing Mg, based on both electrophysiological techniques and also mag-fura 2 to determine changes in cytoplasmic free Mg. | 1 | Applied and Interdisciplinary Chemistry |
*Spark plug
*Water cooled barrel
*Nitrogen inlet valve
*Fuel inlet valve
*Oxygen inlet valve
*Powder feedstock inlet valve | 1 | Applied and Interdisciplinary Chemistry |
A glycocalyx can also be found on the apical portion of microvilli within the digestive tract, especially within the small intestine. It creates a meshwork 0.3 μm thick and consists of acidic mucopolysaccharides and glycoproteins that project from the apical plasma membrane of epithelial absorptive cells. It provides additional surface for adsorption and includes enzymes secreted by the absorptive cells that are essential for the final steps of digestion of proteins and sugars. | 1 | Applied and Interdisciplinary Chemistry |
ScBC (x = 0.27, y = 1.1, z = 0.2) has an orthorhombic crystal structure with space group Pbam (No. 55) and lattice constants of a = 1.73040(6), b = 1.60738(6) and c = 1.44829(6) nm. This phase is indicated as ScBC (phase IV) in the phase diagram of figure 17. This rare orthorhombic structure has 78 atomic positions in the unit cell: seven partially occupied Sc sites, four C sites, 66 B sites including three partially occupied sites and one B/C mixed-occupancy site. Atomic coordinates, site occupancies and isotropic displacement factors are listed in table IX.
More than 500 atoms are available in the unit cell. In the crystal structure, there are six structurally independent icosahedra I1–I6, which are constructed from B1–B12, B13–B24, B25–B32, B33–B40, B41–B44 and B45–B56 sites, respectively; B57–B62 sites form a B polyhedron. The ScBC crystal structure is layered, as shown in figure 26. This structure has been described in terms of two kinds of boron icosahedron layers, L1 and L2. L1 consists of the icosahedra I3, I4 and I5 and the C65 "dimer", and L2 consists of the icosahedra I2 and I6. I1 is sandwiched by L1 and L2 and the B polyhedron is sandwiched by L2.
An alternative description is based on the same B(B)supericosahedron as in the YB structure. In the YB crystal structure, the supericosahedra form 3-dimensional boron framework as shown in figure 5. In this framework, the neighboring supericosahedra are rotated 90° with respect to each other. On the contrary, in ScBC the supericosahedra form a 2-dimensional network where the 90° rotation relation is broken because of the orthorhombic symmetry. The planar projections of the supericosahedron connection in ScBC and YB are shown in figures 27a and b, respectively. In the YB crystal structure, the neighboring 2-dimensional supericosahedron connections are out-of-phase for the rotational relation of the supericosahedron. This allows 3-dimensional
stacking of the 2-dimensional supericosahedron connection while maintaining the cubic symmetry.
The B boron cluster occupies the large space between four supericosahedra as described in the REB section. On the other hand, the 2-dimensional supericosahedron networks in the ScBC crystal structure stack in-phase along the z-axis. Instead of the B cluster, a pair of the I2 icosahedra fills the open space staying within the supericosahedron network, as shown in figure 28 where the icosahedron I2 is colored in yellow.
All Sc atoms except for Sc3 reside in large spaces between the supericosahedron networks, and the Sc3 atom occupies a void in the network as shown in figure 26. Because of the small size of Sc atom, the occupancies of the Sc1–Sc5 sites exceed 95%, and those of Sc6 and Sc7 sites are approximately 90% and 61%, respectively (see table IX). | 0 | Theoretical and Fundamental Chemistry |
Gold-crafting technology developed in Northwest China during the early Iron Age, following the arrival of new technological skills from the Central Asian steppes, even before the establishment of the Xiongnu (209 BCE-150 CE). These technological and artistic exchanges attest to the magnitude of communication networks between China and the Mediterranean, even before the establishment of the Silk Road. The sites of Dongtalede (Ch: 东塔勒德, 9th–7th century BCE) in Xinjiang, or Xigoupan (Ch:西沟畔, 4th–3rd century BCE) in the Ordos region of Inner Mongolia, are known for numerous artifacts reminiscent of the Scytho-Siberian art of Central Asia.
During the Qing dynasty the gold and silver smiths of Ningbo were noted for the delicacy and tastefulness of their work. | 1 | Applied and Interdisciplinary Chemistry |
As indicated in the Figure above, captioned "Demethylation of 5-methylcytosine," the first step in active demethylation is a TET oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). The demethylation process, in some tissues and at some genome locations, may stop at that point. As reviewed by Uribe-Lewis et al., in addition to being an intermediate in active DNA demethylation, 5hmC is often a stable DNA modification. Within the genome, 5hmC is located at transcriptionally active genes, regulatory elements and chromatin associated complexes. In particular, 5hmC is dynamically changed and positively correlated with active gene transcription during cell lineage specification, and high levels of 5hmC are found in embryonic stem cells and in the central nervous system. In humans, defective 5-hydroxymethylating activity is associated with a phenotype of lymphoproliferation, immunodeficiency and autoimmunity. | 1 | Applied and Interdisciplinary Chemistry |
P-substituted heavier group 14 analogues (Si, Ge, Sn, Pb) of diaminocarbenes are less established. It has been suggested this is due to a high energetic barrier associated with achieving a planar configuration at phosphorus, which would enable p(π)-p(π) overlap between the P lone pair and the empty p orbital of the group 14 center. Differences in donation ability of phosphorus versus nitrogen likely do not play a role in achieving p(π)-p(π) overlap because calculations indicate that the π donor capacity of phosphorus is similar to that of nitrogen. Consequently, all P atoms in reports on diphosphatetrylenes previous to ((Dipp)P)Ge contain pyramidal P with Ge-P bonds of exclusively σ character. By utilizing sterically encumbered (Dipp)P ligands, p(π)-p(π) in diphosphagermylene was achieved. This compound crystallizes as discrete monomers and is the first crystallographically characterized diphosphagermylene with a two-coordinate Ge center.
By crystal structure analysis, the bond lengths of the two germanium-phosphorus bonds are 2.2337 Å (P1-Ge) and 2.3823 Å (P2-Ge). While the phosphorus center of P1-Ge is pyramidal, the P2-Ge phosphorus is trigonal planar. Moreover, the planes of P1-Ge-P2 and C-P1-Ge are nearly in coincident. These results are consistent with multiple bond character between a trigonal planar phosphorus (P1) and Ge. It has been suggested that only one P of the diphosphagermylene is planar because there is competition between the two phosphorus lone pairs and the empty P orbitals at the Ge center if both phosphorus atoms are planar. This would result in a weaker P-Ge interaction that would not be sufficient to overcome the energy of planarizing both P atoms.
In addition, ((Dipp)P)Ge was modified such that an iPr groups was added to the para position of (Dipp)P, to make (Tripp)P. The donating effect of an additional iPr group has little effect on the bonding and structure of the diphosphagermylene. | 0 | Theoretical and Fundamental Chemistry |
Pestiviruses have a single stranded, positive-sense RNA genomes. They cause Classical swine fever (CSF) and Bovine viral diarrhea(BVD). Mucosal disease is a distinct, chronic persistent infection, whereas BVD is an acute infection. | 1 | Applied and Interdisciplinary Chemistry |
π-effects have an important contribution to biological systems since they provide a significant amount of binding enthalpy. Neurotransmitters produce most of their biological effect by binding to the active site of a protein receptor. Pioneering work of Dennis A. Dougherty is a proof that such kind of binding stabilization is the effect of cation-π interactions of the acetylcholine (Ach) neurotransmitter. The structure of acetylcholine esterase includes 14 highly conserved aromatic residues. The trimethyl ammonium group of Ach binds to the aromatic residue of tryptophan (Trp). The indole site provides a much more intense region of negative electrostatic potential than benzene and phenol residue of Phe and Tyr. S-Adenosyl methionine (SAM) can act as a catalyst for the transfer of methyl group from the sulfonium compound to nucleophile. The nucleophile can be any of a broad range structures including nucleic acids, proteins, sugars or C=C bond of lipids or steroids. The van der Waals contact between S-CH unit of SAM and the aromatic face of a Trp residue, in favorable alignment for catalysis assisted by cation-π interaction.
A great deal of circumstantial evidence places aromatic residues in the active site of a number of proteins that interact with cations but the presence of cation-π interaction in biological system does not rule out the conventional ion-pair interaction. In fact there is a good evidence for the existence of both type of interaction in model system. | 0 | Theoretical and Fundamental Chemistry |
The ratio of N to N is of relevance because in most biological contexts, N is preferentially uptaken as the lighter isotope. As a result, samples enriched in N can often be introduced through a non-biological context.
One use of N is as a tracer to determine the path taken by fertilizers applied to anything from pots to landscapes. Fertilizer enriched in N to an extent significantly different from that prevailing in the soil (which may be different from the atmospheric standard a) is applied at a point and other points are then monitored for variations in .
Another application is the assessment of human waste water discharge into bodies of water. The abundance of N is greater in human waste water than in natural water sources. Hence in benthic sediment gives an indication of the contribution of human waste to the total nitrogen in the sediment. Sediment cores analyzed for yield an historical record of such waste, with older samples at greater depths.
is also used to measure food chain length and the trophic level of a given organism; high values are positively correlated with higher trophic levels; likewise, organisms low on the food chain generally exhibit lower values. Higher values in apex predators generally indicate longer food chains. | 0 | Theoretical and Fundamental Chemistry |
Unlike direct DNA damage, which occurs in areas directly exposed to UV-B light, reactive chemical species can travel through the body and affect other areas—possibly even inner organs. The traveling nature of the indirect DNA damage can be seen in the fact that the malignant melanoma can occur in places that are not directly illuminated by the sun—in contrast to basal-cell carcinoma and squamous cell carcinoma, which appear only on directly illuminated locations on the body. | 0 | Theoretical and Fundamental Chemistry |
Corium, also called fuel-containing material (FCM) or lava-like fuel-containing material (LFCM), is a material that is created in a nuclear reactor core during a nuclear meltdown accident. Resembling lava in consistency, it consists of a mixture of nuclear fuel, fission products, control rods, structural materials from the affected parts of the reactor, products of their chemical reaction with air, water, steam, and in the event that the reactor vessel is breached, molten concrete from the floor of the reactor room. | 0 | Theoretical and Fundamental Chemistry |
Ted Ellis is involved with various causes and charitable organizations including United Way, ICLS, African American Visual Arts Association, Jack and Jill of America Inc., the United Negro College Fund, Heritage Christian Academy, and various public school districts. He was the featured artist of Big Brothers Big Sisters 2012 "Houston's Big Black Tie Ball" fundraiser gala and is a partner of the Houston Child Protective Services Black History Program. | 0 | Theoretical and Fundamental Chemistry |
Vesicle fusion is the merging of a vesicle with other vesicles or a part of a cell membrane. In the latter case, it is the end stage of secretion from secretory vesicles, where their contents are expelled from the cell through exocytosis. Vesicles can also fuse with other target cell compartments, such as a lysosome. Exocytosis occurs when secretory vesicles transiently dock and fuse at the base of cup-shaped structures at the cell plasma membrane called porosome, the universal secretory machinery in cells. Vesicle fusion may depend on SNARE proteins in the presence of increased intracellular calcium (Ca) concentration. | 1 | Applied and Interdisciplinary Chemistry |
Hillhouse was born on March 1, 1955, in Greenville, South Carolina. He attended the University of South Carolina in 1976 and received his Ph.D. from Indiana University Bloomington in 1980. He then became a postdoctoral research associate at California Institute of Technology, before taking a position in the department of chemistry at the University of Chicago in 1983.
He died from cancer at his home in Chicago on March 6, 2014, aged 59. | 0 | Theoretical and Fundamental Chemistry |
The word catabolism is from Neo-Latin, which got the roots from Greek: κάτω kato, "downward" and βάλλειν ballein, "to throw". | 1 | Applied and Interdisciplinary Chemistry |
Often molecules do form multilayers, that is, some are adsorbed on already adsorbed molecules, and the Langmuir isotherm is not valid. In 1938 Stephen Brunauer, Paul Emmett, and Edward Teller developed a model isotherm that takes that possibility into account. Their theory is called BET theory, after the initials in their last names. They modified Langmuir's mechanism as follows:
:A + S ⇌ AS,
:A + AS ⇌ AS,
:A + AS ⇌ AS and so on.
The derivation of the formula is more complicated than Langmuir's (see links for complete derivation). We obtain:
where x is the pressure divided by the vapor pressure for the adsorbate at that temperature (usually denoted ), v is the STP volume of adsorbed adsorbate, v is the STP volume of the amount of adsorbate required to form a monolayer, and c is the equilibrium constant K we used in Langmuir isotherm multiplied by the vapor pressure of the adsorbate. The key assumption used in deriving the BET equation that the successive heats of adsorption for all layers except the first are equal to the heat of condensation of the adsorbate.
The Langmuir isotherm is usually better for chemisorption, and the BET isotherm works better for physisorption for non-microporous surfaces. | 0 | Theoretical and Fundamental Chemistry |
Using the above definition for z , the cumulative distribution function (CDF) can be found as follows:
Substituting the definition of the Faddeeva function (scaled complex error function) yields for the indefinite integral:
which may be solved to yield
where is a hypergeometric function. In order for the function to approach zero as x approaches negative infinity (as the CDF must do), an integration constant of 1/2 must be added. This gives for the CDF of Voigt: | 0 | Theoretical and Fundamental Chemistry |
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