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A protein subject to regulation through raft-associated translocation can undergo activation upon substrate presentation. For instance, an enzyme that translocates within the membrane towards its substrate can be activated by localizing to the substrate, irrespective of any conformational changes in the enzyme itself. | 1 | Applied and Interdisciplinary Chemistry |
In commerce, the term "polysulfide" usually refers to a class of polymers with alternating chains of several sulfur atoms and hydrocarbons. They have the formula . In this formula n indicates the number of sulfur atoms (or "rank"). Polysulfide polymers can be synthesized by condensation polymerization reactions between organic dihalides and alkali metal salts of polysulfide anions:
Dihalides used in this condensation polymerization are dichloroalkanes (such as 1,2-dichloroethane, bis-(2-chloroethyl)formal (), and 1,3-dichloropropane). The polymers are called thiokols. In some cases, polysulfide polymers can be formed by ring-opening polymerization reactions.
Polysulfide polymers are also prepared by the addition of polysulfanes to alkenes. An idealized equation is:
In reality, homogeneous samples of are difficult to prepare.
Polysulfide polymers are insoluble in water, oils, and many other organic solvents. Because of their solvent resistance, these materials find use as sealants to fill the joints in pavement, automotive window glass, and aircraft structures.
Polymers containing one or two sulfur atoms separated by hydrocarbon sequences are usually not classified polysulfides, e.g. poly(p-phenylene) sulfide . | 1 | Applied and Interdisciplinary Chemistry |
20.^ A. R. Piriz, O. D. Cortazar, J. J. López Cela, and N. A. Tahir, "The Rayleigh-Taylor instability", Am. J. Phys.74, 1095(2006) | 1 | Applied and Interdisciplinary Chemistry |
The solid potassium chlorate is melted into a liquid.
KClO + energy → KClO
The liquid potassium chlorate decomposes into potassium perchlorate and potassium chloride.
4 KClO → KCl + 3 KClO
The potassium perchlorate decomposes into potassium chloride and oxygen.
KClO → KCl + 2 O
The sugar in the candy reacts with oxygen, forming water and carbon dioxide. The reaction is exothermic and produces heat, smoke, and fire.
CHO + 12 O → 12 CO + 11 HO + energy | 1 | Applied and Interdisciplinary Chemistry |
For the past 30 years, isothermal titration calorimetry has been used in a wide array of fields. In the old days, this technique was used to determine fundamental thermodynamic values for basic small molecular interactions. In recent years, ITC has been used in more industrially applicable areas, such as drug discovery and testing synthetic materials. Although it is still heavily used in fundamental chemistry, the trend has shifted over to the biological side, where label-free and buffer independent values are relatively harder to achieve. | 0 | Theoretical and Fundamental Chemistry |
(p)ppGpp is created via pppGpp synthase, also known as RelA, and is converted from pppGpp to ppGpp via pppGpp phosphohydrolase. RelA is associated with about every one in two hundred ribosomes and it becomes activated when an uncharged transfer RNA (tRNA) molecule enters the A site of the ribosome, due to the shortage of amino acid required by the tRNA. If a mutant bacterium is relA it is said to be relaxed and no regulation of RNA production due to amino acid absence is seen. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, a semicarbazone is a derivative of imines formed by a condensation reaction between a ketone or aldehyde and semicarbazide. They are classified as imine derivatives because they are formed from the reaction of an aldehyde or ketone with the terminal -NH group of semicarbazide, which behaves very similarly to primary amines. | 0 | Theoretical and Fundamental Chemistry |
The Tattvartha Sutra is regarded as one of the earliest, most authoritative book on Jainism, and the only text authoritative in both the Digambara and Śvētāmbara sects, and its importance in Jainism is comparable with that of the Brahma Sutras and Yoga Sutras of Patanjali in Hinduism. | 1 | Applied and Interdisciplinary Chemistry |
Optical reflectivity and the Brillouin zones are closely linked, since the band gap energy in the Brillouin zone determines if a photon is absorbed or reflected. If the band gap energy in the Brillouin zone is smaller than the photon energy, the photon will be absorbed, while the photon will be transmitted/reflected if the band gap energy is larger than the photon energy. For example, the photon energies of visible light lie in a range between 1.8 eV (red light) and 3.1 eV (violet light), So if the band gap energy is larger than 3.2 eV, photons of visible light will not be absorbed, but reflected/transmitted: the material appears transparent. This is the case for diamond, quartz etc. But if the band gap is roughly 2.6 eV (this is the case for cadmium sulfide) only blue and violet light is absorbed, while red and green light are transmitted, resulting in a reddish looking material.
When an electric field is added to a (semi)conductor, the material will try to cancel this field by inducing an electric field at its surface. Because of this electric field, the optical properties of the surface layer will change, due to the change in size of critical band gaps, and hence changing its energy. Since the change in band gap only occurs on the surface of the (semi)conductor, optical properties will not change in the core of bulk materials, but for very thin films, where almost all particles can be found at the surface, the optical properties can change: absorption or transmittance of certain wavelengths depending on the strength of the electric field. This can result in more accurate measurements in case there are multiple compounds in the semiconductor, practically canceling the background noise of data.
Commonly, the band gaps are smallest close to, or at the Brillouin zone boundary. Adding an electric field will alter the whole band structure of the material where the electric field penetrates, but the effect will be especially noticeable at the Brillouin zone boundary. When the smallest band gap changes in size, this alters the optical reflectivity of the material more than the change in an already larger band gap. This can be explained by noticing that the smallest band gap determines a lot of the reflectivity, as lower energy photons cannot be absorbed and re-emitted. | 0 | Theoretical and Fundamental Chemistry |
A lactam is a cyclic amide, formally derived from an amino alkanoic acid through cyclization reactions. The term is a portmanteau of the words lactone + amide. | 0 | Theoretical and Fundamental Chemistry |
Diana E. Northup is an American microbiologist, speleologist, ecologist, Visiting Professor of Biology, and Professor Emerita of Library Sciences with the University of New Mexico. Her research focuses on the microbial ecology of caves around the world. Dr. Northup is a Fellow of the National Speleological Society and the Cave Research Foundation. She wrote the Wiley textbook Microbial Ecology. She was awarded the National Speleological Society Science Prize in 2013. | 0 | Theoretical and Fundamental Chemistry |
The orthoreoviruses (reoviruses) are the prototypic members of the virus Reoviridae family and representative of the turreted members, which comprise about half the genera. Like other members of the family, the reoviruses are non-enveloped and characterized by concentric capsid shells that encapsidate a segmented dsRNA genome. In particular, reovirus has eight structural proteins and ten segments of dsRNA. A series of uncoating steps and conformational changes accompany cell entry and replication. High-resolution structures are known for almost all of the proteins of mammalian reovirus (MRV), which is the best-studied genotype. Electron cryo-microscopy (cryoEM) and X-ray crystallography have provided a wealth of structural information about two specific MRV strains, type 1 Lang (T1L) and type 3 Dearing (T3D). | 1 | Applied and Interdisciplinary Chemistry |
The European Union Waste Electrical and Electronic Equipment Directive and Restriction of Hazardous Substances Directive were adopted in early 2003 and came into effect on July 1, 2006, restricting the inclusion of lead in most consumer electronics sold in the EU, and having a broad effect on consumer electronics sold worldwide. In the US, manufacturers may receive tax benefits by reducing the use of lead-based solder. Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals. Most lead-free replacements for conventional 60/40 and 63/37 Sn-Pb solder have melting points from 50 to 200 °C higher, though there are also solders with much lower melting points. Lead-free solder typically requires around 2% flux by mass for adequate wetting ability.
When lead-free solder is used in wave soldering, a slightly modified solder pot may be desirable (e.g. titanium liners or impellers) to reduce maintenance cost due to increased tin-scavenging of high-tin solder.
Lead-free solder is prohibited in critical applications, such as aerospace, military and medical projects, because joints are likely to suffer from metal fatigue failure under stress (such as that from thermal expansion and contraction). Although this is a property that conventional leaded solder possesses as well (like any metal), the point at which stress fatigue will usually occur in leaded solder is substantially above the level of stresses normally encountered.
Tin-silver-copper (Sn-Ag-Cu, or SAC) solders are used by two-thirds of Japanese manufacturers for reflow and wave soldering, and by about 75% of companies for hand soldering. The widespread use of this popular lead-free solder alloy family is based on the reduced melting point of the Sn-Ag-Cu ternary eutectic behavior (), which is below the 22/78 Sn-Ag (wt.%) eutectic of and the 99.3/0.7 Sn-Cu eutectic of . The ternary eutectic behavior of Sn-Ag-Cu and its application for electronics assembly was discovered (and patented) by a team of researchers from Ames Laboratory, Iowa State University, and from Sandia National Laboratories-Albuquerque.
Much recent research has focused on the addition of a fourth element to Sn-Ag-Cu solder, in order to provide compatibility for the reduced cooling rate of solder sphere reflow for assembly of ball grid arrays. Examples of these four-element compositions are 18/64/14/4 tin-silver-copper-zinc (Sn-Ag-Cu-Zn) (melting range 217–220 °C) and 18/64/16/2 tin-silver-copper-manganese (Sn-Ag-Cu-Mn; melting range of 211–215 °C).
Tin-based solders readily dissolve gold, forming brittle intermetallic joins; for Sn-Pb alloys the critical concentration of gold to embrittle the joint is about 4%. Indium-rich solders (usually indium-lead) are more suitable for soldering thicker gold layers as the dissolution rate of gold in indium is much slower. Tin-rich solders also readily dissolve silver; for soldering silver metallization or surfaces, alloys with addition of silver are suitable; tin-free alloys are also a choice, though their wetting ability is poorer. If the soldering time is long enough to form the intermetallics, the tin surface of a joint soldered to gold is very dull. | 1 | Applied and Interdisciplinary Chemistry |
In 1900 just 13% of the global population lived in cities. By 2005, 49% of the global population lived in urban areas. In 2030 it is predicted that this statistic will rise to 60%. Attempts to expand water supply by governments are costly and often not sufficient. The building of new illegal settlements makes it hard to map, and make connections to, the water supply, and leads to inadequate water management. In 2002, there were 158 million people with inadequate water supply. An increasing number of people live in slums, in inadequate sanitary conditions, and are therefore at risk of disease. | 1 | Applied and Interdisciplinary Chemistry |
In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate-determining step (RDS or RD-step or r/d step) or rate-limiting step. For a given reaction mechanism, the prediction of the corresponding rate equation (for comparison with the experimental rate law) is often simplified by using this approximation of the rate-determining step.
In principle, the time evolution of the reactant and product concentrations can be determined from the set of simultaneous rate equations for the individual steps of the mechanism, one for each step. However, the analytical solution of these differential equations is not always easy, and in some cases numerical integration may even be required. The hypothesis of a single rate-determining step can greatly simplify the mathematics. In the simplest case the initial step is the slowest, and the overall rate is just the rate of the first step.
Also, the rate equations for mechanisms with a single rate-determining step are usually in a simple mathematical form, whose relation to the mechanism and choice of rate-determining step is clear. The correct rate-determining step can be identified by predicting the rate law for each possible choice and comparing the different predictions with the experimental law, as for the example of and CO below.
The concept of the rate-determining step is very important to the optimization and understanding of many chemical processes such as catalysis and combustion. | 0 | Theoretical and Fundamental Chemistry |
Grain boundaries are interfaces where crystals of different orientations meet. A grain boundary is a single-phase interface, with crystals on each side of the boundary being identical except in orientation. The term "crystallite boundary" is sometimes, though rarely, used. Grain boundary areas contain those atoms that have been perturbed from their original lattice sites, dislocations, and impurities that have migrated to the lower energy grain boundary.
Treating a grain boundary geometrically as an interface of a single crystal cut into two parts, one of which is rotated, we see that there are five variables required to define a grain boundary. The first two numbers come from the unit vector that specifies a rotation axis. The third number designates the angle of rotation of the grain. The final two numbers specify the plane of the grain boundary (or a unit vector that is normal to this plane).
Grain boundaries disrupt the motion of dislocations through a material. Dislocation propagation is impeded because of the stress field of the grain boundary defect region and the lack of slip planes and slip directions and overall alignment across the boundaries. Reducing grain size is therefore a common way to improve strength, often without any sacrifice in toughness because the smaller grains create more obstacles per unit area of slip plane. This crystallite size-strength relationship is given by the Hall–Petch relationship. The high interfacial energy and relatively weak bonding in grain boundaries makes them preferred sites for the onset of corrosion and for the precipitation of new phases from the solid.
Grain boundary migration plays an important role in many of the mechanisms of creep. Grain boundary migration occurs when a shear stress acts on the grain boundary plane and causes the grains to slide. This means that fine-grained materials actually have a poor resistance to creep relative to coarser grains, especially at high temperatures, because smaller grains contain more atoms in grain boundary sites. Grain boundaries also cause deformation in that they are sources and sinks of point defects. Voids in a material tend to gather in a grain boundary, and if this happens to a critical extent, the material could fracture.
During grain boundary migration, the rate determining step depends on the angle between two adjacent grains. In a small angle dislocation boundary, the migration rate depends on vacancy diffusion between dislocations. In a high angle dislocation boundary, this depends on the atom transport by single atom jumps from the shrinking to the growing grains.
Grain boundaries are generally only a few nanometers wide. In common materials, crystallites are large enough that grain boundaries account for a small fraction of the material. However, very small grain sizes are achievable. In nanocrystalline solids, grain boundaries become a significant volume fraction of the material, with profound effects on such properties as diffusion and plasticity. In the limit of small crystallites, as the volume fraction of grain boundaries approaches 100%, the material ceases to have any crystalline character, and thus becomes an amorphous solid.
Grain boundaries are also present in magnetic domains in magnetic materials. A computer hard disk, for example, is made of a hard ferromagnetic material that contains regions of atoms whose magnetic moments can be realigned by an inductive head. The magnetization varies from region to region, and the misalignment between these regions forms boundaries that are key to data storage. The inductive head measures the orientation of the magnetic moments of these domain regions and reads out either a “1” or “0”. These bits are the data being read. Grain size is important in this technology because it limits the number of bits that can fit on one hard disk. The smaller the grain sizes, the more data that can be stored.
Because of the dangers of grain boundaries in certain materials such as superalloy turbine blades, great technological leaps were made to minimize as much as possible the effect of grain boundaries in the blades. The result was directional solidification processing in which grain boundaries were eliminated by producing columnar grain structures aligned parallel to the axis of the blade, since this is usually the direction of maximum tensile stress felt by a blade during its rotation in an airplane. The resulting turbine blades consisted of a single grain, improving reliability. | 1 | Applied and Interdisciplinary Chemistry |
Examples of response elements include:
* Nuclear receptor response elements – two 6-meric repeats for dimeric binding
** Type 2 NR response elements: direct repeat RGKTCA motifs, canonically AGGTCA
*** Vitamin D response element (VDRE)
*** Retinoic acid response elements (RAREs)
*** ROR-response element
*** Thyroid hormone response element
*** Growth hormone response element (GHRE)
*** Peroxisome proliferator hormone response elements (PPREs)
** Type 1 NR response elements (typical of hormone response elements) – inverted repeat
*** estrogen response elements (EREs)
*** androgen response elements (AREs)
*** glucocorticoid response elements (GREs)
*cAMP response element (CRE)
*B recognition element
*AhR-, dioxin- or xenobiotic- responsive element
*Hypoxia-responsive elements
*Serum response element (SRE)
*Metal-responsive element (MRE)
*DNA damage response element (DRE)
*IFN-stimulated response elements (ISREs)
*[https://www.ebi.ac.uk/interpro/entry/IPR029309 Calcium-response element CaRE1]
*Antioxidant response element (ARE)
*[http://p53.iarc.fr/TargetGenes.aspx p53 response element]
*Sterol regulatory element
*Polycomb Response Elements (PREs)
*Rev response element (RRE)
*Wnt response element (WRE), core CTTTG | 1 | Applied and Interdisciplinary Chemistry |
Cell walls are made of a variety of polysaccharides. Protoplasts can be made by degrading cell walls with a mixture of the appropriate polysaccharide-degrading enzymes:
During and subsequent to digestion of the cell wall, the protoplast becomes very sensitive to osmotic stress. This means cell wall digestion and protoplast storage must be done in an isotonic solution to prevent rupture of the plasma membrane. | 1 | Applied and Interdisciplinary Chemistry |
Serine/arginine-rich splicing factor 1 (SRSF1) also known as alternative splicing factor 1 (ASF1), pre-mRNA-splicing factor SF2 (SF2) or ASF1/SF2 is a protein that in humans is encoded by the SRSF1 gene. ASF/SF2 is an essential sequence specific splicing factor involved in pre-mRNA splicing. SRSF1 is the gene that codes for ASF/SF2 and is found on chromosome 17. The resulting splicing factor is a protein of approximately 33 kDa. ASF/SF2 is necessary for all splicing reactions to occur, and influences splice site selection in a concentration-dependent manner, resulting in alternative splicing. In addition to being involved in the splicing process, ASF/SF2 also mediates post-splicing activities, such as mRNA nuclear export and translation. | 1 | Applied and Interdisciplinary Chemistry |
Several models exist to describe chiral induction at carbonyl carbons during nucleophilic additions. These models are based on a combination of steric and electronic considerations and are often in conflict with each other. Models have been devised by Cram (1952), Cornforth (1959), Felkin (1969) and others. | 0 | Theoretical and Fundamental Chemistry |
DLVO theory describes the interaction potential between charged surfaces. It is the sum of electrostatic double layer, which can be either attractive of repulsive, and attractive Van der Waals interactions of the charge surfaces. DLVO theory is applied widely in explaining the aggregation and deposition of colloidal and nano particles such as Fullerene C60 in aquatic system. Because bacteria and colloid particles both share the similarities in size and surface charge, the deposition of bacteria also can be describe by the DLVO theory. The prediction is based on sphere-plate interaction for one cell and the surface.<br />
The electrostatic double layer interactions could be describes by the expression for the constant surface potential
Where εis the vacuum permittivity, ε is the relative dielectric permittivity of water, a is the equivalent spherical radius of the bacteria, κ is the inverse of Debye length, h is the separation distance between the bacterium and the collector surface; ψ and ψ are the surface potentials of the bacterial cell and the collector surface. Zeta potential at the surface of the bacteria and the collector were used instead of the surface potential.
The retarded Van der Waals interaction potential was calculated using the expression from Gregory, 1981 .
With A is Hamaker constant for bacteria-water-surface collector (quartz) = 6.5 x 10 J and λ is the characteristic wavelength of the dielectric and could be assumed 100 nm, a is the equivalent radius of the bacteria, h is the separation distance from the surface collector to the bacteria.
Thus, the total interaction between bacteria and charged surface can be expressed as follow | 0 | Theoretical and Fundamental Chemistry |
Three extreme possibilities have been proposed for the mechanism of NPP-catalyzed phosphoryl transfer. They are distinguished by the sequence in which bonds to phosphorus are made and broken. Though this phenomenon is subtle, it is important for understanding the physiological roles of AP superfamily enzymes, and also to molecular dynamic modeling.
1) A two-step "dissociative" (elimination-addition or D + A) mechanism that proceeds via a trigonal metaphosphate intermediate. This mechanism is represented by the red dashed lines in the figure at right.
2) A two-step "associative" (addition-elimination or A + D) mechanism that proceeds via a pentavalent phosphorane intermediate. This is represented by the blue dashed lines in the figure at right.
3) A one-step fully synchronous mechanism analogous to S2 substitution. Bond formation and breakage occur simultaneously and at the same rate. This is represented by the black dashed line in the figure at right.
The above three cases represent archetypes for the reaction mechanism, and the actual mechanism probably falls somewhere in between them. The red and blue dotted lines in Fig. 2a represent more realistic "concerted" mechanisms in which addition and elimination overlap, but are not fully synchronous. The difference in initial rates of the two steps implies different charge distribution in the transition state (TS).
When the addition step occurs more quickly than elimination (an AD mechanism), more positive charge develops on the nucleophile, and the transition state is said to be "tight." Conversely, if elimination occurs more quickly than addition (DA), the transition state is considered "loose."
López-Canut et al. modeled substitution of a phosphodiester substrate using a hybrid quantum mechanics/molecular mechanics model. Notably, the model predicted an AD concerted mechanism in aqueous solution, but a DA mechanism in the active site of Xac NPP. | 1 | Applied and Interdisciplinary Chemistry |
Alloenzymes (or also called allozymes) are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus. These are opposed to isozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci.
Alloenzymes are common biological enzymes that exhibit high levels of functional evolutionary conservation throughout specific phyla and kingdoms. They are used by phylogeneticists as molecular markers to gauge evolutionary histories and relationships between different species. This can be done because allozymes do not have the same structure. They can be separated by capillary electrophoresis. However, some species are monomorphic for many of their allozymes which would make it difficult for phylogeneticists to assess the evolutionary histories of these species. In these instances, phylogeneticists would have to use another method to determine the evolutionary history of a species.
These enzymes generally perform very basic functions found commonly throughout all lifeforms, such as DNA polymerase, the enzyme that repairs and copies DNA. Significant changes in this enzyme reflect significant events in evolutionary history of organisms. As expected DNA polymerase shows relatively small differences in its amino acid sequence between phyla and even kingdoms.
The key to choosing which alloenzyme to use in a comparison between multiple species is to choose one that is as variable as possible while still being present in all the organisms. By comparing the amino acid sequence of the enzyme in the species, more amino acid similarities should be seen in species that are more closely related, and fewer between those that are more distantly related. The less well conserved the enzyme is, the more amino acid differences will be present in even closely related species. | 1 | Applied and Interdisciplinary Chemistry |
By far the most common and perhaps standard form of ionization is electron ionization (EI). The molecules enter into the MS (the source is a quadrupole or the ion trap itself in an ion trap MS) where they are bombarded with free electrons emitted from a filament, not unlike the filament one would find in a standard light bulb. The electrons bombard the molecules, causing the molecule to fragment in a characteristic and reproducible way. This "hard ionization" technique results in the creation of more fragments of low mass-to-charge ratio (m/z) and few, if any, molecules approaching the molecular mass unit. Hard ionization is considered by mass spectrometrists as the employ of molecular electron bombardment, whereas "soft ionization" is charge by molecular collision with an introduced gas. The molecular fragmentation pattern is dependent upon the electron energy applied to the system, typically 70 eV (electronvolts). The use of 70 eV facilitates comparison of generated spectra with library spectra using manufacturer-supplied software or software developed by the National Institute of Standards (NIST-USA). Spectral library searches employ matching algorithms such as Probability Based Matching and dot-product matching that are used with methods of analysis written by many method standardization agencies. Sources of libraries include NIST, Wiley, the AAFS, and instrument manufacturers. | 0 | Theoretical and Fundamental Chemistry |
Under AC conditions with varying frequency ω, heterogeneous systems and composite materials exhibit a universal dielectric response, in which overall admittance exhibits a region of power law scaling with frequency. . | 0 | Theoretical and Fundamental Chemistry |
Compounds that have a monocyclic, planar conjugated system containing (4n + 2) π-electrons for whole numbers n are aromatic and exhibit an unusual stability. The classic example benzene has a system of six π electrons, which, together with the planar ring of C–C σ bonds containing 12 electrons and radial C–H σ bonds containing six electrons, forms the thermodynamically and kinetically stable benzene ring, the common core of the benzenoid aromatic compounds. For benzene itself, there are two equivalent conjugated contributing Lewis structures (the so-called Kekulé structures) that predominate. The true electronic structure is therefore a quantum-mechanical combination (resonance hybrid) of these contributors, which results in the experimentally observed C–C bonds which are intermediate between single and double bonds and of equal strength and length. In the molecular orbital picture, the six p atomic orbitals of benzene combine to give six molecular orbitals. Three of these orbitals, which lie at lower energies than the isolated p orbital and are therefore net bonding in character (one molecular orbital is strongly bonding, while the other two are equal in energy but bonding to a lesser extent) are occupied by six electrons, while three destabilized orbitals of overall antibonding character remain unoccupied. The result is strong thermodynamic and kinetic aromatic stabilization. Both models describe rings of π electron density above and below the framework of C–C σ bonds. | 0 | Theoretical and Fundamental Chemistry |
Chemerin peptides are short peptides (on the order of 9 amino acids) that are produced from the carboxyl terminus of the chemokine chemerin. They display the same activities as chemerin, although at higher efficacy and potency.
A particular synthetic chemerin-derived peptide, termed C15, was developed at Oxford University. It showed anti-inflammatory activities. Intraperitoneal administration of C15 (0.32 ng/kg) to mice before zymosan challenge conferred significant protection against zymosan-induced peritonitis, suppressing neutrophil (63%) and monocyte (62%) recruitment with a concomitant reduction in proinflammatory mediator expression.
C15 was found to promote phagocytosis and efferocytosis in peritoneal macrophages at picomolar concentrations. C15 enhanced macrophage clearance of microbial particles and apoptotic cells by factor of 360% in vitro | 1 | Applied and Interdisciplinary Chemistry |
From an operational point of view the Hill coefficient can be calculated as:
where and are the input values needed to produce the 10% and 90% of the maximal response, respectively. | 1 | Applied and Interdisciplinary Chemistry |
The Hepatitis B viral protein X is believed to cause hepatocellular carcinoma through transformation, typically of liver cells. The viral DNA is incorporated into the host cell's genome causing rapid cell replication and tumor growth. | 1 | Applied and Interdisciplinary Chemistry |
The Faraday paradox was a once inexplicable aspect of the reaction between nitric acid and steel. Around 1830, the English scientist Michael Faraday found that diluted nitric acid would attack steel, but concentrated nitric acid would not. The attempt to explain this discovery led to advances in electrochemistry. | 0 | Theoretical and Fundamental Chemistry |
James Clerk Maxwell in his 1871 Theory of Heat outlines four stipulations for the definition of heat:
* It is something which may be transferred from one body to another, according to the second law of thermodynamics.
* It is a measurable quantity, and so can be treated mathematically.
* It cannot be treated as a material substance, because it may be transformed into something that is not a material substance, e.g., mechanical work.
* Heat is one of the forms of energy. | 0 | Theoretical and Fundamental Chemistry |
In 2018, Alnylam Pharmaceuticals became the first company to have a siRNA therapy approved by the FDA. Onpattro (patisiran) was approved for the treatment of polyneuropathy of hereditary transthyretin-mediated (hATTR) amyloidosis in adults. hATTR is a rare, progressively debilitating condition. During hATTR amyloidosis, misfolded transthyretin (TTR) protein is deposited in the extracellular space. Under typical folding conditions, TTR tetramers are made up of four monomers. Hereditary ATTR amyloidosis is caused by a fault or mutation in the transthyretin (TTR) gene which is inherited. Changing just one amino-acid changes the tetrameric transthyretin proteins, resulting in unstable tetrameric transthyretin protein that aggregates in monomers and forms insoluble extracellular amyloid deposits. Amyloid buildup in various organ systems causes cardiomyopathy, polyneuropathy, gastrointestinal dysfunction. It affects 50,000 people worldwide. To deliver the drug directly to the liver, siRNA is encased in a lipid nanoparticle. The siRNA molecule halts the production of amyloid proteins by interfering with the RNA production of abnormal TTR proteins. This prevents the accumulation of these proteins in different organs of the body and helps the patients manage this disease.
Traditionally, liver transplantation has been the standard treatment for hereditary transthyretin amyloidosis, however its effectiveness may be limited by the persistent deposition of wild-type transthyretin amyloid after transplantation. There are also small molecule medications that provide temporary relief. Before Onpattro was released, the treatment options for hATTR were limited. After the approval of Onpattro, FDA awarded Alnylam with the Breakthrough Therapy Designation, which is given to drugs that are intended to treat a serious condition and are a substantial improvement over any available therapy. It was also awarded Orphan Drug Designations given to those treatments that are intended to safely treat conditions affecting less than 200,000 people.
Along with Onpattro, another RNA interference therapeutic drug has also been discovered (Partisiran) which has property of inhibiting hepatic synthesis of transthyretin. Target messenger RNA (mRNA) is cleaved as a result by tiny interfering RNAs coupled to the RNA-induced silencing complex. Patisiran, an investigational RNAi therapeutic drug, uses this process to decrease the production of mutant and wild-type transthyretin by cleaving on 3-untranslated region of transthyretin mRNA.
In 2019, FDA approved the second RNAi therapy, Givlaari (givosiran) used to treat acute hepatic porphyria (AHP). The disease is caused due to the accumulation of toxic porphobilinogen (PBG) molecules which are formed during the production of heme. These molecules accumulate in different organs and this can lead to the symptoms or attacks of AHP.
Givlaari is an siRNA drug that downregulates the expression of aminolevulinic acid synthase 1 (ALAS1), a liver enzyme involved in an early step in heme production. The downregulation of ALAS1 lowers the levels of neurotoxic intermediates that cause AHP symptoms.
Years of research has led to a greater understanding of siRNA therapies beyond those affecting the liver. As of 2019, Alnylam Pharmaceuticals was involved in therapies that may treat amyloidosis and CNS disorders like Huntingtons disease and Alzheimers disease. They have also partnered with Regeneron Pharmaceuticals to develop therapies for CNS, eye and liver diseases.
As of 2020, ONPATTRO and GIVLAARI, were available for commercial application, and two siRNAs, lumasiran (ALN-GO1) and inclisiran, have been submitted for new drug application to the FDA. Several siRNAs are undergoing phase 3 clinical studies, and more candidates are in the early developmental stage. In 2020, Alnylam and Vir pharmaceuticals announced a partnership and have started working on a RNAi therapy that would treat severe cases of COVID-19.
Other companies that have had success in developing a pipeline of siRNA therapies are Dicerna Pharmaceuticals, partnered Eli Lilly and Company and Arrowhead Pharmaceuticals partnered with Johnson and Johnson. Several other big pharmaceutical companies such as Amgen and AstraZeneca have also invested heavily in siRNA therapies as they see the potential success of this area of biological drugs. | 1 | Applied and Interdisciplinary Chemistry |
The Mediator complex is composed at least 31 subunits in all eukaryotes studied: MED1, MED4, MED6, MED7, MED8, MED9, MED10, MED11, MED12, MED13, MED13L, MED14, MED15, MED16, MED17, MED18, MED19, MED20, MED21, MED22, MED23, MED24, MED25, MED26, MED27, MED28, MED29, MED30, MED31, CCNC, and CDK8. There are three fungal-specific components, referred to as Med2, Med3 and Med5.
The subunits form at least three structurally distinct submodules. The head and the middle modules interact directly with RNA polymerase II, whereas the elongated tail module interacts with gene-specific regulatory proteins. Mediator containing the CDK8 module is less active than Mediator lacking this module in supporting transcriptional activation.
*The head module contains: MED6, MED8, MED11, SRB4/MED17, SRB5/MED18, ROX3/MED19, SRB2/MED20 and SRB6/MED22.
*The middle module contains: MED1, MED4, NUT1/MED5, MED7, CSE2/MED9, NUT2/MED10, SRB7/MED21 and SOH1/MED31. CSE2/MED9 interacts directly with MED4.
*The tail module contains: MED2, PGD1/MED3, RGR1/MED14, GAL11/MED15 and SIN4/MED16.
*The CDK8 module contains: MED12, MED13, CCNC and CDK8. Individual preparations of the Mediator complex lacking one or more distinct subunits have been variously termed ARC, CRSP, DRIP, PC2, SMCC and TRAP. | 1 | Applied and Interdisciplinary Chemistry |
The primary limitations of TMM cycloadditions employing diazenes are competitive MCP and dimer formation. To circumvent these problems, either very high concentrations of alkene must be used or the cycloaddition must be intramolecular. Stereoselectivity and site selectivity may also be higher in intramolecular variants of cycloadditions starting from diazenes.
Usually, unless a cyclic pi system is involved TMM cycloadditions exhibit 2π periselectivity and do not react with larger pi systems. Polar MCPs, for example, react only with the 2,3 double bond of polyunsaturated esters.
Transition-metal catalyzed reactions have the potential to quickly generate an interesting functionality. Propellanes have been generated from intramolecular cyclization under palladium catalysis.
Silylated allylic acetates may be employed for intra- or intermolecular applications. Carbonyl compounds may be used as the 2π component under the appropriate conditions. For instance, in the presence of an indium co-catalyst, the reactive 2π component of the cycloaddition below switches from the C-C to the C-O double bond.
Polarized trimethylenemethanes generated from polar MCPs are also useful substrates for (3+2) reactions with polar double bonds as the 2π component. Orthoester products are generally favored over ketene acetals. | 0 | Theoretical and Fundamental Chemistry |
The Acree-Rosenheim reaction is a chemical test used for detecting the presence of tryptophan in proteins. A protein mixture is mixed with formaldehyde. Concentrated sulfuric acid is added to form two layers. A purple ring appears between the two layers if the test is positive for tryptophan.
The test was named after two greats in biochemistry, namely, Solomon Farley Acree (1875–1957), a distinguished American Biochemist at Johns Hopkins University, and Sigmund Otto Rosenheim (1871–1955), an Anglo-German Medical Chemist at the University of Manchester. | 0 | Theoretical and Fundamental Chemistry |
*AMCA Publication 501 - Application Manual for Louvers provides general information and comments on factors to be considered when designing or specifying installations requiring louvers. It also serves as a guide to understanding the various types of louvers available and includes items to be considered to ensure their proper use.
*AMCA Publication 502 - Damper Application Manual for Heating, Ventilating, and Air Conditioning is a guide to understanding the various types of dampers available and items to be considered for their proper use. Dampers classified as fire dampers, heat dampers, and smoke dampers are not included. Includes much of the information not found in the companion guide, AMCA Publication 503.
*AMCA Publication 503 - Fire, Ceiling (Radiation), Smoke, and Fire/Smoke Damper Application Manual details information for individuals that design, purchase, or specify systems in which fire and/or smoke is a factor. Includes much of the information not found in the companion guide, AMCA Publication 502.
*AMCA Publication 600 - Application Manual for Airflow Measurement Stations is intended to assist designers and users with the proper application, performance considerations, selection and limitations of airflow measurement stations. | 1 | Applied and Interdisciplinary Chemistry |
The Michigan PFAS Action Response Team (MPART) was launched in 2017 and is the first multi-agency action team of its kind in the nation. Agencies representing health, environment, and other branches of state government have joined together to investigate sources and locations of PFAS contamination in the state, take action to protect people's drinking water, and keep the public informed.
Groundwater is tested at locations throughout the state by various parties to ensure safety, compliance with regulations, and proactively detect and remedy potential problems. In 2010, the Michigan Department of Environmental Quality (MDEQ) discovered levels of PFASs in groundwater monitoring wells at the former Wurtsmith Air Force Base. As additional information became available from other national testing, Michigan expanded its investigations into other locations where PFAS compounds were potentially used.
In 2018, the MDEQs Remediation and Redevelopment Division (RRD) established cleanup criteria for groundwater used as drinking water of 70 ppt of PFOA and PFOS, individually or combined. The RRD staff are responsible for implementing these criteria as part of their ongoing efforts to clean up sites of environmental contamination. The RRD staff are the lead investigators at most of the PFAS sites on the MPART website and also conduct interim response activities, such as coordinating bottled water or filter installations with local health departments at sites under investigation or with known PFAS concerns. Most of the groundwater sampling at PFAS sites under RRDs lead is conducted by contractors familiar with PFAS sampling techniques. The RRD also has a Geologic Services Unit, with staff who install monitoring wells and are also well versed with PFAS sampling techniques.
The MDEQ has been conducting environmental clean-up of regulated contaminants for decades. Due to the evolving nature of PFAS regulations as new science becomes available, the RRD is evaluating the need for regular PFAS sampling at Superfund sites and is including an evaluation of PFAS sampling needs as part of a Baseline Environmental Assessment review.
Earlier in 2018, the RRD purchased lab equipment that will allow the MDEQ Environmental Lab to conduct analyses of certain PFAS samples. (Currently, most samples are shipped to one of the few labs in the country that conduct PFAS analysis, in California, although private labs in other parts of the country, including Michigan, are starting to offer these services.) As of August 2018, RRD has hired additional staff to work on developing the methodology and conducting PFAS analyses.
In 2020 Michigan Attorney General Dana Nessel filed a lawsuit against 17 companies, including 3M, Chemours, and DuPont, for hiding known health and environmental risks from the state and its residents. Nessels complaint identifies 37 sites with known contamination. The Michigan Department of Environment, Great Lakes, and Energy introduced some of the strictest drinking water standards in the country for PFAS, setting maximum contaminant levels (MCLs) for PFOA and PFOS to 8 and 16 ppt respectively (down from previous existing groundwater cleanup standards of 70 ppt for both), and introducing MCLs for 5 other previously unregulated PFAS compounds, limiting PFNA to 6 ppt, PFHxA to 400,000 ppt, PFHxS to 51 ppt, PFBS to 420 ppt and HFPO-DA to 370 ppt. The change adds 38 additional sites to the states list of known PFAS contaminated areas, bringing the total number of known sites to 137. About half of these sites are landfills and 13 are former plating facilities.
In 2022 PFOS was found in beef produced at a Michigan farm: the cattle had been fed crops fertilized with contaminated biosolids. State agencies issued a consumption advisory, but did not order a recall, because there currently is no PFOS contamination in beef government standards. | 0 | Theoretical and Fundamental Chemistry |
Assimilation can be broadly defined as a process where a mass of magma wholly or partially homogenizes with materials derived from the wall rock of the magma body. Assimilation is a popular mechanism to partly explain the felsification of ultramafic and mafic magmas as they rise through the crust: a hot primitive melt intruding into a cooler, felsic crust will melt the crust and mix with the resulting melt. This then alters the composition of the primitive magma. Also, pre-existing mafic host rocks can be assimilated by very hot primitive magmas.
Effects of assimilation on the chemistry and evolution of magma bodies are to be expected, and have been clearly proven in many places. In the early 20th century there was a lively discussion on the relative importance of the process in igneous differentiation. More recent research has shown, however, that assimilation has a fundamental role in altering the trace element and isotopic composition of magmas, in formation of some economically important ore deposits, and in causing volcanic eruptions. | 0 | Theoretical and Fundamental Chemistry |
Margaret Melhase Fuchs (August 13, 1919August 8, 2006) was an American chemist and a co-discoverer, with Glenn T. Seaborg, of the isotope caesium-137. | 0 | Theoretical and Fundamental Chemistry |
The geomagnetic field strength and hence precession frequency varies with location and time.
: Larmor precession frequency = magnetogyric ratio x magnetic field
: Proton magnetogyric ratio = 42.576 Hz/μT (also written 42.576 MHz/T or 0.042576 Hz/nT)
: Earth's magnetic field: 30 μT near Equator to 60 μT near Poles, around 50 μT at mid-latitudes.
Thus proton (hydrogen nucleus) EFNMR frequencies are audio frequencies of about 1.3 kHz near the Equator to 2.5 kHz near the Poles, around 2 kHz being typical of mid-latitudes. In terms of the electromagnetic spectrum EFNMR frequencies are in the VLF and ULF radio frequency bands, and the audio-magnetotelluric (AMT) frequencies of geophysics.
Examples of molecules containing hydrogen nuclei useful in proton EFNMR are water, hydrocarbons such as natural gas and petroleum, and carbohydrates such as occur in plants and animals. | 0 | Theoretical and Fundamental Chemistry |
Ff phages have been engineered for applications in biological and medical sciences. Many applications build on experiments showing that the DNA sequence determining resistance to the antibiotic kanamycin can be inserted in a functional form into the non-coding intergenic sequence of fd phage DNA. Such modified phage are correspondingly longer that wild-type filamentous fd, because the longer DNA is coated with correspondingly more gene 8 coat proteins, but the phage life-cycle is not otherwise disrupted. The traditional “tadpole” or isometric shaped-phage, on the other hand, which have a limited-sized capsid, cannot be so easily used to encapsidate a larger DNA molecule. The modified phage can be selected by infecting kanamycin-sensitive bacteria with modified phage to introduce resistance to kanamycin, and growing the infected bacteria in media containing an otherwise lethal concentration of kanamycin.
This result was extended by inserting foreign DNA expressing a foreign peptide into fd phage gene 3, rather than into the intergenic sequence, so that the foreign peptide appears on the surface of the phage as a part of the gene 3 adsorption protein. Phage carrying the foreign peptide can then be detected using appropriate antibodies. The reverse of this approach is to insert DNA coding for antibodies into gene 3 and detect their presence by appropriate antigens.
These techniques have been extended over the years in many ways, for instance by inserting foreign DNA into the genes coding for phage coat proteins other than gene 3, and/or duplicating the gene of interest to modify only some of the corresponding gene products. Phage display technology has been widely used for many purposes. | 1 | Applied and Interdisciplinary Chemistry |
In aqueous solution, bromocresol green will ionize to give the monoanionic form (yellow), that further deprotonates at higher pH to give the dianionic form (blue), which is stabilized by resonance:
The acid dissociation constant (pK) of this reaction is 4.8. Tap water is sufficiently basic to give a solution of bromocresol green its characteristic blue-green color.
The acid and basic forms of this dye have an isosbestic point in their UV-Visible spectrum, around 515 nm, indicate that the two forms interconvert directly without forming any other substance.
An ethanol solution (0.04 wt%) of bromocresol green has been proposed for TLC staining and is suitable for visualisation of the compounds with functional groups whose pK is below 5.0 (carboxylic acids, sulfonic acids, etc.). These appear as yellow spots on a light or dark blue background; no heating is necessary. Bromophenol blue solution can be used for the same purpose.
The compound is synthesized by bromination of cresol purple (m-cresolsulfonphthalein). | 0 | Theoretical and Fundamental Chemistry |
Several radioisotopes and compounds are used for medical treatment, usually by bringing the radioactive isotope to a high concentration in the body near a particular organ. For example, iodine-131 is used for treating some disorders and tumors of the thyroid gland. | 0 | Theoretical and Fundamental Chemistry |
7-nt primer ligates in the open state of the hairpin, which will block rezipping of the last seven nucleotides and increase the distance between the surface and the magnetic bead by ~5 nm. If the ligation is not successful, no change in the hairpin length is observed. | 1 | Applied and Interdisciplinary Chemistry |
The Dukhin number () is a dimensionless quantity that characterizes the contribution of the surface conductivity to various electrokinetic and electroacoustic effects, as well as to electrical conductivity and permittivity of fluid heterogeneous systems. The number was named after Stanislav and Andrei Dukhin. | 0 | Theoretical and Fundamental Chemistry |
The liquid used in wet methods can be added directly to the product or via a humid environment. Using a fluidized bed dryer and multiple step spray drying are two examples of wet methods while roller compacting and extrusion are two examples of dry methods.
Advantages of agglomeration for food include:
# Dust reduction: Dust reduction is achieved when the smallest particles (or "fines") in the product are combined into larger particles.
# Improved flow: Flow improvement occurs as the larger, and sometimes more spherical, particles more easily pass over each other than the smaller or more irregularly-shaped particles in the original material.
# Improved dispersion and/or solubility: Improved dispersion and solubility is sometimes achieved with instantization, in which the solubility of a product allows it to instantly dissolve upon its addition to water. For a powder to be considered instant it should go through wettability, sinkability, dispersibility, and solubility within a few seconds. Non-fat dry milk and high quality protein powders are good examples of instant powders.
# Optimized bulk density: Consistent bulk density is important in accurate and consistent filling of packaging.
# Improved product characteristics
# Increased homogeneity of the finished product, reducing segregation of fine particles (such as powdered vitamins or spray-dried flavors) from larger particles (such as granulated sugars or acids). As a powder is agitated, smaller particles will fall to the bottom, and larger raise to the top. Agglomeration can reduce the range of particle sizes present in the product, reducing segregation.
Disadvantages of food agglomeration:
# Extra cost. The benefits of handling an agglomerate often outweigh the extra cost involved in processing.
# Additional processing time. Agglomeration of a finished blend is an additional step after blending.
Particle size distribution is an important parameter to monitor in agglomerated food products. In both wet and dry agglomeration, particles of undesired sizes must be removed to ensure the best possible finished product performance. High-powered cyclones are the most common way to separate undesired fine particles (or "fines") from larger agglomerates (or "overs"). Cyclones utilize the combination of wind power and the different densities of the two products to pull the fines out of the mix. The fines can then be reworked through the agglomeration process to reduce yield loss. In contrast, shaker screens are often used to separate out the overs from the rest of the product. The overs can be reworked into the process by first being broken into smaller particles. | 1 | Applied and Interdisciplinary Chemistry |
T cells play an important role in the adaptive immune system. They are capable of orchestrating, regulating and coordinating complex immune responses. A wide array of clinically relevant aspects are associated with the function or malfunction of T-cells: Autoimmune diseases, control of viral or bacterial pathogens, development of cancer or graft versus host responses.
Over the past years, various methods (ELISpot Assay, intracellular cytokine staining, secretion assay) have been developed for the identification of T cells, but only major histocompatibility complex (MHC) procedures allow identification and purification of antigen-specific T cells independent of their functional status.
In principle, MHC procedures are using the T cell receptor (TCR) ligand, which is the MHC-peptide complex, as a staining probe. The MHC interacts with the TCR, which in turn is expressed on the T cells. Because TCR-MHC interactions have only a very weak affinity towards each other, monomeric MHC-epitope complexes cannot provide stable binding. This problem can be solved by using multimerized MHC-epitopes, which increases the binding avidity and therefore allows stable binding. Fluorochromes conjugated to the MHC-multimers then can be used for identification of T cells by flow cytometry.
Nowadays, MHC molecules can be produced recombinantly together with the antigenic peptides which are known for a fast-growing number of diseases. | 1 | Applied and Interdisciplinary Chemistry |
Metal carbene complexes have applications in hetereogeneous and homogeneous catalysis, and as reagents for organic reactions. | 0 | Theoretical and Fundamental Chemistry |
Sociophysics uses tools and concepts from physics and physical chemistry to describe some aspects of social and political behavior. It attempts to explain why and how humans behave much like atoms, at least in some aspects of their collective lives. The law of mass action (generalized if it is necessary) is the main tool to produce the equation of interactions of humans in sociophysics. | 0 | Theoretical and Fundamental Chemistry |
In isotope hydrology, stable isotopes of water (H and O) are used to estimate the source, age, and flow paths of water flowing through ecosystems. The main effects that change the stable isotope composition of water are evaporation and condensation. Variability in water isotopes is used to study sources of water to streams and rivers, evaporation rates, groundwater recharge, and other hydrological processes. | 0 | Theoretical and Fundamental Chemistry |
Witold Rybczynski and Jacques Hadamard developed an equation to calculate the velocity of bubbles that rise in foam with the assumption that the bubbles are spherical with a radius .
with velocity in units of centimeters per second. ρ and ρ is the density for a gas and liquid respectively in units of g/cm and ῃ and ῃ is the dynamic
viscosity of the gas and liquid respectively in units of g/cm·s and g is the acceleration of gravity in units of cm/s.
However, since the density and viscosity of a liquid is much greater than the gas, the density and viscosity of the gas can be neglected, which yields the new equation for velocity of bubbles rising as:
However, through experiments it has been shown that a more accurate model for bubbles rising is:
Deviations are due to the Marangoni effect and capillary pressure, which affect the assumption that the bubbles are spherical.
For laplace pressure of a curved gas liquid interface, the two principal radii of curvature at a point are R and R. With a curved interface, the pressure in one phase is greater than the pressure in another phase. The capillary pressure P is given by the equation of:
where is the surface tension. The bubble shown below is a gas (phase 1) in a liquid (phase 2) and point A designates the top of the bubble while point B designates the bottom of the bubble.
At the top of the bubble at point A, the pressure in the liquid is assumed to be p as well as in the gas. At the bottom of the bubble at point B, the hydrostatic pressure is:
where ρ and ρ is the density for a gas and liquid respectively. The difference in hydrostatic pressure at the top of the bubble is 0, while the difference in hydrostatic pressure at the bottom of the bubble across the interface is gz(ρ − ρ). Assuming that the radii of curvature at point A are equal and denoted by R and that the radii of curvature at point B are equal and denoted by R, then the difference in capillary pressure between point A and point B is:
At equilibrium, the difference in capillary pressure must be balanced by the difference in hydrostatic pressure. Hence,
Since, the density of the gas is less than the density of the liquid the left hand side of the equation is always positive. Therefore, the inverse of R must be larger than the R. Meaning that from the top of the bubble to the bottom of the bubble the radius of curvature increases. Therefore, without neglecting gravity the bubbles cannot be spherical. In addition, as z increases, this causes the difference in R and R too, which means the bubble deviates more from its shape the larger it grows.
Foam destabilization occurs for several reasons. First, gravitation causes drainage of liquid to the foam base, which Rybczynski and Hadamar include in their theory; however, foam also destabilizes due to osmotic pressure causes drainage from the lamellas to the Plateau borders due to internal concentration differences in the foam, and Laplace pressure causes diffusion of gas from small to large bubbles due to pressure difference. In addition, films can break under disjoining pressure, These effects can lead to rearrangement of the foam structure at scales larger than the bubbles, which may be individual (T1 process) or collective (even of the "avalanche" type). | 0 | Theoretical and Fundamental Chemistry |
Human activities have also dramatically altered the global nitrogen cycle via production of nitrogenous gases, associated with the global atmospheric nitrogen pollution. There are multiple sources of atmospheric reactive nitrogen (Nr) fluxes. Agricultural sources of reactive nitrogen can produce atmospheric emission of ammonia (), nitrogen oxides () and nitrous oxide (). Combustion processes in energy production, transportation and industry can also result in the formation of new reactive nitrogen via the emission of , an unintentional waste product. When those reactive nitrogens are released to the lower atmosphere, they can induce the formation of smog, particulate matter and aerosols, all of which are major contributors to adverse health effects on human health from air pollution. In the atmosphere, can be oxidized to nitric acid (), and it can further react with to form ammonium nitrate (), which facilitates the formation of particulate nitrate. Moreover, can react with other acid gases (sulfuric and hydrochloric acids) to form ammonium-containing particles, which are the precursors for the secondary organic aerosol particles in photochemical smog. | 1 | Applied and Interdisciplinary Chemistry |
* American Institute of Hydrology (AIH)
*Geological Society of America (GSA) – Hydrogeology Division
* American Geophysical Union (AGU) – Hydrology Section
* National Ground Water Association (NGWA)
* American Water Resources Association
* Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI)
* International Association of Hydrological Sciences (IAHS)
* Statistics in Hydrology Working Group (subgroup of IAHS)
* German Hydrological Society (DHG: Deutsche Hydrologische Gesellschaft)
* Italian Hydrological Society (SII-IHS) – [http://www.sii-ihs.it Società Idrologica Italiana]
* Nordic Association for Hydrology
* British Hydrological Society
* Russian Geographical Society (Moscow Center) – Hydrology Commission
* International Association for Environmental Hydrology
* International Association of Hydrogeologists
* [http://soham.org.np/ Society of Hydrologists and Meteorologists – Nepal] | 1 | Applied and Interdisciplinary Chemistry |
Electrons form notional shells around the nucleus. These are naturally in a ground state but can be excited by the absorption of energy from light (photons), magnetic fields, or interaction with a colliding particle (typically other electrons).
Electrons that populate a shell are said to be in a bound state. The energy necessary to remove an electron from its shell (taking it to infinity) is called the binding energy. Any quantity of energy absorbed by the electron in excess of this amount is converted to kinetic energy according to the conservation of energy. The atom is said to have undergone the process of ionization.
In the event that the electron absorbs a quantity of energy less than the binding energy, it may transition to an excited state or to a virtual state. After a statistically sufficient quantity of time, an electron in an excited state will undergo a transition to a lower state via spontaneous emission. The change in energy between the two energy levels must be accounted for (conservation of energy). In a neutral atom, the system will emit a photon of the difference in energy. However, if the lower state is in an inner shell, a phenomenon known as the Auger effect may take place where the energy is transferred to another bound electrons causing it to go into the continuum. This allows one to multiply ionize an atom with a single photon.
There are strict selection rules as to the electronic configurations that can be reached by excitation by light—however there are no such rules for excitation by collision processes. | 0 | Theoretical and Fundamental Chemistry |
An improvement on optical mapping, called "Nanocoding", has potential to boost throughput by trapping elongated DNA molecules in nanoconfinements. | 1 | Applied and Interdisciplinary Chemistry |
Photoelectrochemistry has been intensively studied in the field of hydrogen production from water and solar energy. The photoelectrochemical splitting of water was historically discovered by Fujishima and Honda in 1972 onto TiO electrodes. Recently many materials have shown promising properties to split efficiently water but TiO remains cheap, abundant, stable against photo-corrosion. The main problem of TiO is its bandgap which is 3 or 3.2 eV according to its crystallinity (anatase or rutile). These values are too high and only the wavelength in the UV region can be absorbed. To increase the performances of this material to split water with solar wavelength, it is necessary to sensitize the TiO. Currently Quantum Dots sensitization is very promising but more research is needed to find new materials able to absorb the light efficiently. | 0 | Theoretical and Fundamental Chemistry |
In materials science, the yield strength anomaly refers to materials wherein the yield strength (i.e., the stress necessary to initiate plastic yielding) increases with temperature.
For the majority of materials, the yield strength decreases with increasing temperature. In metals, this decrease in yield strength is due to the thermal activation of dislocation motion, resulting in easier plastic deformation at higher temperatures.
In some cases, a yield strength anomaly refers to a decrease in the ductility of a material with increasing temperature, which is also opposite the trend in the majority of materials. Anomalies in ductility can be more clear, as an anomalous effect on yield strength can be obscured by its typical decrease with temperature. In concert with yield strength or ductility anomalies, some materials demonstrate extrema in other temperature dependent properties, such as a minimum in ultrasonic damping, or a maximum in electrical conductivity.
The yield strength anomaly in β-brass was one of the earliest discoveries such a phenomenon, and several other ordered intermetallic alloys demonstrate this effect. Precipitation-hardened superalloys exhibit a yield strength anomaly over a considerable temperature range. For these materials, the yield strength shows little variation between room temperature and several hundred degrees Celsius. Eventually, a maximum yield strength is reached. For even higher temperatures, the yield strength decreases and, eventually, drops to zero when reaching the melting temperature, where the solid material transforms into a liquid. For ordered intermetallics, the temperature of the yield strength peak is roughly 50% of the absolute melting temperature. | 1 | Applied and Interdisciplinary Chemistry |
Cobalt oleate can be synthesized by heating a solution of sodium oleate and cobalt(II) chloride to 70 °C. | 0 | Theoretical and Fundamental Chemistry |
In recursive directional ligation, the gene encoding the monomer is inserted into a plasmid with restriction sites that are recognized by at least two endonucleases. The endonucleases will cut the plasmid, releasing the gene of interest. Then, this single gene is inserted into a recipient plasmid vector already containing one copy of the ELP monomer gene via digestion of the recipient plasmid with the same restriction endonucleases used on the donor plasmid and a subsequent ligation step. From this process, a sequence of two ELP monomer genes is retrieved. RDL allows for the controlled synthesis of ELP gene oligomers, in which single gene segments are sequentially added. However, the restriction endonucleases used are limited to those that do not cut within the ELP monomer gene itself, as this would lead to loss of crucial nucleotides and a potential frameshift mutation in the protein. | 0 | Theoretical and Fundamental Chemistry |
For most reactions the activation enthalpy and activation entropy are unknown, but, if these parameters have been measured and a linear relationship is found to exist (meaning an LFER was found to hold), the following equation describes the relationship between and :
Inserting the Gibbs free-energy equation and combining like terms produces the following equation:
where is constant regardless of substituents and is different for each substituent.
In this form, has the dimension of temperature and is referred to as the isokinetic (or isoequilibrium) temperature.
Alternately, the isokinetic (or isoequilibrium) temperature may be reached by observing that, if a linear relationship is found, then the difference between the s for any closely related reactants will be related to the difference between s for the same reactants:
Using the Gibbs free-energy equation,
In both forms, it is apparent that the difference in Gibbs free-energies of activations () will be zero when the temperature is at the isokinetic (or isoequilibrium) temperature and hence identical for all members of the reaction set at that temperature.
Beginning with the Arrhenius equation and assuming kinetic compensation (obeying ), the isokinetic temperature may also be given by
The reactions will have approximately the same value of their rate constant at an isokinetic temperature. | 0 | Theoretical and Fundamental Chemistry |
Automated treatment planning has become an integrated part of radiotherapy treatment planning. There are in general two approaches of automated planning. 1) Knowledge based planning where the treatment planning system has a library of high quality plans, from which it can predict the target and dose-volume histogram of the organ at risk. 2) The other approach is commonly called protocol based planning, where the treatment planning system tried to mimic an experienced treatment planner and through an iterative process evaluates the plan quality from on the basis of the protocol. | 0 | Theoretical and Fundamental Chemistry |
For a first-order reaction (including a unimolecular one-step process), there is a direct relationship between the unimolecular rate constant and the half-life of the reaction: . Transition state theory gives a relationship between the rate constant and the Gibbs free energy of activation a quantity that can be regarded as the free energy change needed to reach the transition state. In particular, this energy barrier incorporates both enthalpic and entropic changes that need to be achieved for the reaction to take place: The result found from transition state theory is where h is the Planck constant and R the molar gas constant. As useful rules of thumb, a first-order reaction with a rate constant of 10 s will have a half-life (t) of approximately 2 hours. For a one-step process taking place at room temperature, the corresponding Gibbs free energy of activation (ΔG) is approximately 23 kcal/mol. | 0 | Theoretical and Fundamental Chemistry |
Before the 20th century in Europe, sewers usually discharged into a body of water such as a river, lake, or ocean. There was no treatment, so the breakdown of the human waste was left to the ecosystem. This could lead to satisfactory results if the assimilative capacity of the ecosystem is sufficient which is nowadays not often the case due to increasing population density.
Today, the situation in urban areas of industrialized countries is usually that sewers route their contents to a sewage treatment plant rather than directly to a body of water. In many developing countries, however, the bulk of municipal and industrial wastewater is discharged to rivers and the ocean without any treatment or after preliminary treatment or primary treatment only. Doing so can lead to water pollution. Few reliable figures exist on the share of the wastewater collected in sewers that is being treated in the world. A global estimate by UNDP and UN-Habitat in 2010 was that 90% of all wastewater generated is released into the environment untreated. A more recent study in 2021 estimated that globally, about 52% of sewage is treated. However, sewage treatment rates are highly unequal for different countries around the world. For example, while high-income countries treat approximately 74% of their sewage, developing countries treat an average of just 4.2%. As of 2022, without sufficient treatment, more than 80% of all wastewater generated globally is released into the environment. High-income nations treat, on average, 70% of the wastewater they produce, according to UN Water. Only 8% of wastewater produced in low-income nations receives any sort of treatment.
The Joint Monitoring Programme (JMP) for Water Supply and Sanitation by WHO and UNICEF report in 2021 that 82% of people with sewer connections are connected to sewage treatment plants providing at least secondary treatment.However, this value varies widely between regions. For example, in Europe, North America, Northern Africa and Western Asia, a total of 31 countries had universal (>99%) wastewater treatment. However, in Albania, Bermuda, North Macedonia and Serbia "less than 50% of sewered wastewater received secondary or better treatment" and in Algeria, Lebanon and Libya the value was less than 20% of sewered wastewater that was being treated. The report also found that "globally, 594 million people have sewer connections that don't receive sufficient treatment. Many more are connected to wastewater treatment plants that do not provide effective treatment or comply with effluent requirements.". | 1 | Applied and Interdisciplinary Chemistry |
GC content is found to be variable with different organisms, the process of which is envisaged to be contributed to by variation in selection, mutational bias, and biased recombination-associated DNA repair.
The average GC-content in human genomes ranges from 35% to 60% across 100-Kb fragments, with a mean of 41%. The GC-content of Yeast (Saccharomyces cerevisiae) is 38%, and that of another common model organism, thale cress (Arabidopsis thaliana), is 36%. Because of the nature of the genetic code, it is virtually impossible for an organism to have a genome with a GC-content approaching either 0% or 100%. However, a species with an extremely low GC-content is Plasmodium falciparum (GC% = ~20%), and it is usually common to refer to such examples as being AT-rich instead of GC-poor.
Several mammalian species (e.g., shrew, microbat, tenrec, rabbit) have independently undergone a marked increase in the GC-content of their genes. These GC-content changes are correlated with species life-history traits (e.g., body mass or longevity) and genome size, and might be linked to a molecular phenomenon called the GC-biased gene conversion. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, methenium (also called methylium, carbenium, methyl cation, or protonated methylene) is a cation with the formula . It can be viewed as a methylene radical (:) with an added proton (), or as a methyl radical (•) with one electron removed. It is a carbocation and an enium ion, making it the simplest of the carbenium ions. | 0 | Theoretical and Fundamental Chemistry |
In addition, it is involved in developing the Neo-GI Augment, a gastrointestinal development program; and Neo-Vessel Replacement, which targets various blood vessel applications consisting of vascular access grafts, arteriovenous, and shunts for patients with ESRD (end stage renal disease) undergoing hemodialysis treatment, as well as for vessel replacement for patients undergoing coronary or peripheral artery bypass procedures. | 1 | Applied and Interdisciplinary Chemistry |
A harpoon reaction is a type of chemical reaction, first proposed by Michael Polanyi in 1920, whose mechanism (also called the harpooning mechanism) involves two neutral reactants undergoing an electron transfer over a relatively long distance to form ions that then attract each other closer together. For example, a metal atom and a halogen might react to form a cation and anion, respectively, leading to a combined metal halide.
The main feature of these redox reactions is that, unlike most reactions, they have steric factors greater than unity; that is, they take place faster than predicted by collision theory. This is explained by the fact that the colliding particles have greater cross sections than the pure geometrical ones calculated from their radii, because when the particles are close enough, an electron "jumps" (therefore the name) from one of the particles to the other one, forming an anion and a cation which subsequently attract each other. Harpoon reactions usually take place in the gas phase, but they are also possible in condensed media.
The predicted rate constant can be improved by using a better estimation of the steric factor. A rough approximation is that the largest separation R at which charge transfer can take place on energetic grounds, can be estimated from the solution of the following equation that determines the largest distance at which the Coulombic attraction between the two oppositely charged ions is sufficient to provide the energy ΔE
With , where Ei is the ionization potential of the metal and Eea is the electron affinity of the halogen. | 0 | Theoretical and Fundamental Chemistry |
A 5-step process to synthesise levobupivacaine from N-CBZ (S)-lysine, published in 1996, is depicted in Scheme 1. The key steps in this process include oxidative de-animation and stereospecific ring closure to form the pipecolamide core structure. This method is claimed to be efficient, but showed to be dangerous for mass production due to the high risk of explosion of the diazonium salt intermediates.
A more recent patent from 2008, consists of a 3-step process (see Scheme 2) to synthesise levobupivacaine hydrochloride of an optical purity of at least 99%. (S)-2,6-pipecocholxylide (I) is reacted with 1-bromobutane and a base (a), such as potassium carbonate, to obtain a solution of (S)-bupivacaine (II) and its enantiomers. Recrystallisation of this solution with a solvent (b), preferably cyclohexane, can lead to an optical purity of at least 98% levobupivacaine. Lastly, the addition of hydrochloride (c) is possible. | 0 | Theoretical and Fundamental Chemistry |
The entire list of functions of UCP2 and UCP3 is not known. However, studies indicate that these proteins are involved in a negative-feedback loop limiting the concentration of reactive oxygen species (ROS). Current scientific consensus states that UCP2 and UCP3 perform proton transportation only when activation species are present. Among these activators are fatty acids, ROS, and certain ROS byproducts that are also reactive. Therefore, higher levels of ROS directly and indirectly cause increased activity of UCP2 and UCP3. This, in turn, increases proton leak from the mitochondria, lowering the proton-motive force across mitochondrial membranes, activating the electron transport chain. Limiting the proton motive force through this process results in a negative feedback loop that limits ROS production. Especially, UCP2 decreases the transmembrane potential of mitochondria, thus decreasing the production of ROS. Thus, cancer cells may increase the production of UCP2 in mitochondria. This theory is supported by independent studies which show increased ROS production in both UCP2 and UCP3 knockout mice.
This process is important to human health, as high-concentrations of ROS are believed to be involved in the development of degenerative diseases. | 1 | Applied and Interdisciplinary Chemistry |
Drago (Ohio St, 1954) < Sisler (Illinois, 1939) < Audrieth (Cornell, 1926) < Browne (Cornell, 1903) < Dennis (Michigan, 1886) < Hempel (Heidelberg, 1873) < Robert Bunsen (Göttingen, 1830) < Friedrich Stromeyer (Göttingen, 1800) < Louis Nicolas Vauquelin (Paris, 1790) < Antoine François, comte de Fourcroy (Paris, 1780) < Jean Baptiste Michel Bucquet (Paris 1770) and Antoine Lavoisier (Paris, 1764) | 0 | Theoretical and Fundamental Chemistry |
Some early literary works allude to lost-wax casting. Columella, a Roman writer of the 1st century AD, mentions the processing of wax from beehives in De Re Rustica, perhaps for casting, as does Pliny the Elder, who details a sophisticated procedure for making Punic wax. One Greek inscription refers to the payment of craftsmen for their work on the Erechtheum in Athens (408/7–407/6 BC). Clay-modellers may use clay moulds to make terracotta negatives for casting or to produce wax positives. Pliny portrays as a well-reputed ancient artist producing bronze statues, and describes Lysistratos of Sikyon, who takes plaster casts from living faces to create wax casts using the indirect process.
Many bronze statues or parts of statues in antiquity were cast using the lost wax process. Theodorus of Samos is commonly associated with bronze casting. Pliny also mentions the use of lead, which is known to help molten bronze flow into all areas and parts of complex moulds. Quintilian documents the casting of statues in parts, whose moulds may have been produced by the lost wax process. Scenes on the early-5th century BC Berlin Foundry Cup depict the creation of bronze statuary working, probably by the indirect method of lost-wax casting. | 1 | Applied and Interdisciplinary Chemistry |
The weak beta emission is stopped by the walls of laboratory glassware. Soft X-rays are emitted when the beta particles are stopped, but as long as the body is kept more than 30 cm away these should pose no problem. The primary hazard when working with technetium is inhalation of dust; such radioactive contamination in the lungs can pose a significant cancer risk. | 0 | Theoretical and Fundamental Chemistry |
In deriving the first equation, Darken referenced Simgelskas and Kirkendall's experiment, which tested the mechanisms and rates of diffusion and gave rise to the concept now known as the Kirkendall effect. For the experiment, inert molybdenum wires were placed at the interface between copper and brass components, and the motion of the markers was monitored. The experiment supported the concept that a concentration gradient in a binary alloy would result in the different components having different velocities in the solid solution. The experiment showed that in brass zinc had a faster relative velocity than copper, since the molybdenum wires moved farther into the brass. In establishing the coordinate axes to evaluate the derivation, Darken refers back to Smigelskas and Kirkendall’s experiment which the inert wires were designated as the origin.
In respect to the derivation of the second equation, Darken referenced W. A. Johnson’s experiment on a gold–silver system, which was performed to determine the chemical diffusivity. In this experiment radioactive gold and silver isotopes were used to measure the diffusivity of gold and silver, because it was assumed that the radioactive isotopes have relatively the same mobility as the non-radioactive elements. If the gold–silver solution is assumed to behave ideally, it would be expected the diffusivities would also be equivalent. Therefore, the overall diffusion coefficient of the system would be the average of each components diffusivity; however, this was found not to be true. This finding led Darken to analyze Johnson's experiment and derive the equation for chemical diffusivity of binary solutions. | 0 | Theoretical and Fundamental Chemistry |
The basic technique for the detection of RFLPs involves fragmenting a sample of DNA with the application of a restriction enzyme, which can selectively cleave a DNA molecule wherever a short, specific sequence is recognized in a process known as a restriction digest. The DNA fragments produced by the digest are then separated by length through a process known as agarose gel electrophoresis and transferred to a membrane via the Southern blot procedure. Hybridization of the membrane to a labeled DNA probe then determines the length of the fragments which are complementary to the probe. A restriction fragment length polymorphism is said to occur when the length of a detected fragment varies between individuals, indicating non-identical sequence homologies. Each fragment length is considered an allele, whether it actually contains a coding region or not, and can be used in subsequent genetic analysis. | 1 | Applied and Interdisciplinary Chemistry |
Surface roughness has a strong effect on the contact angle and wettability of a surface. The effect of roughness depends on if the droplet will wet the surface grooves or if air pockets will be left between the droplet and the surface.
If the surface is wetted homogeneously, the droplet is in Wenzel state. In Wenzel state, adding surface roughness will enhance the wettability caused by the chemistry of the surface. The Wenzel correlation can be written as
where is the measured contact angle, is the Young contact angle and is the roughness ratio. The roughness ratio is defined as the ratio between the actual and projected solid surface area.
If the surface is wetted heterogeneously, the droplet is in Cassie-Baxter state. The most stable contact angle can be connected to the Young contact angle. The contact angles calculated from the Wenzel and Cassie-Baxter equations have been found to be good approximations of the most stable contact angles with real surfaces. | 0 | Theoretical and Fundamental Chemistry |
Copper indium gallium selenide (CIGS) is a direct band gap material. It has the highest efficiency (~20%) among all commercially significant thin film materials (see CIGS solar cell). Traditional methods of fabrication involve vacuum processes including co-evaporation and sputtering. Recent developments at IBM and Nanosolar attempt to lower the cost by using non-vacuum solution processes. | 0 | Theoretical and Fundamental Chemistry |
Al-Kindi was a master of many different areas of thought and was held to be one of the greatest philosophers. His influence in the fields of physics, mathematics, medicine, philosophy, and music were far-reaching and lasted for several centuries. Ibn al-Nadim in his praised al-Kindi and his work stating:
Al-Kindi's major contribution was his establishment of philosophy in the Islamic world and his efforts in trying to harmonize the philosophical investigation along with the Islamic theology and creed. The philosophical texts which were translated under his supervision would become the standard texts in the Islamic world for centuries to come, even after his influence has been eclipsed by later Philosophers.
Al-Kindi was also an important figure in medieval Europe. Several of his books got translated into Latin influencing western authors like Robert Grosseteste and Roger Bacon. The Italian Renaissance scholar Geralomo Cardano (1501–1575) considered him one of the twelve greatest minds.
In 1986, the Royal Commission for Riyadh City inaugurated the Al Kindi Plaza in the Diplomatic Quarter district of Riyadh, Saudi Arabia. | 1 | Applied and Interdisciplinary Chemistry |
The α and β anomers are diastereomers of each other and usually have different specific rotations. A solution or liquid sample of a pure α anomer will rotate plane polarised light by a different amount and/or in the opposite direction than the pure β anomer of that compound. The optical rotation of the solution depends on the optical rotation of each anomer and their ratio in the solution.
For example, if a solution of β--glucopyranose is dissolved in water, its specific optical rotation will be +18.7°. Over time, some of the β--glucopyranose will undergo mutarotation to become α--glucopyranose, which has an optical rotation of +112.2°. The rotation of the solution will increase from +18.7° to an equilibrium value of +52.7° as some of the β form is converted to the α form. The equilibrium mixture is about 64% of β--glucopyranose and about 36% of α--glucopyranose, though there are also traces of the other forms including furanoses and open chained form.
The observed rotation of the sample is the weighted sum of the optical rotation of each anomer weighted by the amount of that anomer present. Therefore, one can use a polarimeter to measure the rotation of a sample and then calculate the ratio of the two anomers present from the enantiomeric excess, as long as one knows the rotation of each pure anomer. One can monitor the mutarotation process over time or determine the equilibrium mixture by observing the optical rotation and how it changes. | 0 | Theoretical and Fundamental Chemistry |
If any method is ever successful, a suggestion has been made to introduce the hybrids to a wildlife reserve in Siberia called the Pleistocene Park, but some biologists question the ethics of such recreation attempts. In addition to the technical problems, not much habitat is left that would be suitable for mammoth–elephant hybrids. Because both species are [were] social and gregarious, creating a few specimens would not be ideal. The time and resources required would be enormous, and the scientific benefits would be unclear, suggesting these resources should instead be used to preserve extant elephant species which are endangered. The ethics of using elephants as surrogate mothers in hybridisation attempts has also been questioned, as most embryos would not survive, and knowing the exact needs of a hybrid mammoth–elephant calf would be impossible. | 1 | Applied and Interdisciplinary Chemistry |
Good flow properties of granules and powders are important in the manufacturing of tablets and capsules. The distribution of particles should be uniform in terms of number and weight. Very small particle size causes attraction, which in turn destabilises the suspension by coagulating. | 0 | Theoretical and Fundamental Chemistry |
Tacticity (from , "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical properties of the polymer. The regularity of the macromolecular structure influences the degree to which it has rigid, crystalline long range order or flexible, amorphous long range disorder. Precise knowledge of tacticity of a polymer also helps understanding at what temperature a polymer melts, how soluble it is in a solvent and its mechanical properties.
A tactic macromolecule in the IUPAC definition is a macromolecule in which essentially all the configurational (repeating) units are identical. Tacticity is particularly significant in vinyl polymers of the type - where each repeating unit with a substituent R on one side of the polymer backbone is followed by the next repeating unit with the substituent on the same side as the previous one, the other side as the previous one or positioned randomly with respect to the previous one. In a hydrocarbon macromolecule with all carbon atoms making up the backbone in a tetrahedral molecular geometry, the zigzag backbone is in the paper plane with the substituents either sticking out of the paper or retreating into the paper. This projection is called the Natta projection after Giulio Natta. Monotactic macromolecules have one stereoisomeric atom per repeat unit, ditactic to n-tactic macromolecules have more than one stereoisomeric atom per unit. | 0 | Theoretical and Fundamental Chemistry |
Sustainable engineering is the process of designing or operating systems such that they use energy and resources sustainably, in other words, at a rate that does not compromise the natural environment, or the ability of future generations to meet their own needs. | 1 | Applied and Interdisciplinary Chemistry |
The model represents individuals as networks of interacting transcriptional regulators. Each individual expresses genes encoding transcription factors. The product of each gene can regulate the expression level of itself and/or the other genes through cis-regulatory elements. The interactions among genes constitute a gene network that is represented by a × regulatory matrix in the model. The elements in matrix R represent the interaction strength. Positive values within the matrix represent the activation of the target gene, while negative ones represent repression. Matrix elements with value 0 indicate the absence of interactions between two genes. | 1 | Applied and Interdisciplinary Chemistry |
Perhaps one of the most studied materials to exhibit negative thermal expansion is zirconium tungstate (). This compound contracts continuously over a temperature range of 0.3 to 1050 K (at higher temperatures the material decomposes). Other materials that exhibit NTE behaviour include other members of the family of materials (where A = or , M = or ) and and , though and only in their high temperature phase starting at 350 to 400 K. also is an example of controllable negative thermal expansion. Cubic materials like and also and are especially precious for applications in engineering because they exhibit isotropic NTE i.e. the NTE is the same in all three dimensions making it easier to apply them as thermal expansion compensators.
Ordinary ice shows NTE in its hexagonal and cubic phases at very low temperatures (below –200 °C). In its liquid form, pure water also displays negative thermal expansivity below 3.984 °C.
ALLVAR Alloy 30, a titanium-based alloy, shows NTE over a wide temperature range, with a -30 ppm/°C instantaneous coefficient of thermal expansion at 20 °C. ALLVAR Alloy 30's negative thermal expansion is anisotropic. This commercially available material is used in the optics, aerospace, and cryogenics industries in the form of optical spacers that prevent thermal defocus, ultra-stable struts, and washers for thermally-stable bolted joints.
Carbon fibers shows NTE between 20°C and 500°C. This property is utilized in tight-tolerance aerospace applications to tailor the CTE of carbon fiber reinforced plastic components for specific applications/conditions, by adjusting the ratio of carbon fiber to plastic and by adjusting the orientation of the carbon fibers within the part.
Quartz () and a number of zeolites also show NTE over certain temperature ranges. Fairly pure silicon (Si) has a negative coefficient of thermal expansion for temperatures between about 18 K and 120 K.
Cubic Scandium trifluoride has this property which is explained by the quartic oscillation of the fluoride ions. The energy stored in the bending strain of the fluoride ion is proportional to the fourth power of the displacement angle, unlike most other materials where it is proportional to the square of the displacement. A fluorine atom is bound to two scandium atoms, and as temperature increases the fluorine oscillates more perpendicularly to its bonds. This draws the scandium atoms together throughout the material and it contracts. exhibits this property from 10 to 1100 K above which it shows the normal positive thermal expansion. Shape memory alloys such as NiTi are a nascent class of materials that exhibit zero and negative thermal expansion. | 0 | Theoretical and Fundamental Chemistry |
This section contains a discussion of the three most important properties of time reversal in quantum mechanics; chiefly,
# that it must be represented as an anti-unitary operator,
# that it protects non-degenerate quantum states from having an electric dipole moment,
# that it has two-dimensional representations with the property (for fermions).
The strangeness of this result is clear if one compares it with parity. If parity transforms a pair of quantum states into each other, then the sum and difference of these two basis states are states of good parity. Time reversal does not behave like this. It seems to violate the theorem that all abelian groups be represented by one-dimensional irreducible representations. The reason it does this is that it is represented by an anti-unitary operator. It thus opens the way to spinors in quantum mechanics.
On the other hand, the notion of quantum-mechanical time reversal turns out to be a useful tool for the development of physically motivated quantum computing and simulation settings, providing, at the same time, relatively simple tools to assess their complexity. For instance, quantum-mechanical time reversal was used to develop novel boson sampling schemes and to prove the duality between two fundamental optical operations, beam splitter and squeezing transformations. | 0 | Theoretical and Fundamental Chemistry |
Virtual screening (VS) is a computational technique used in drug discovery to search libraries of small molecules in order to identify those structures which are most likely to bind to a drug target, typically a protein receptor or enzyme.
Virtual screening has been defined as "automatically evaluating very large libraries of compounds" using computer programs. As this definition suggests, VS has largely been a numbers game focusing on how the enormous chemical space of over 10 conceivable compounds can be filtered to a manageable number that can be synthesized, purchased, and tested. Although searching the entire chemical universe may be a theoretically interesting problem, more practical VS scenarios focus on designing and optimizing targeted combinatorial libraries and enriching libraries of available compounds from in-house compound repositories or vendor offerings. As the accuracy of the method has increased, virtual screening has become an integral part of the drug discovery process. Virtual Screening can be used to select in house database compounds for screening, choose compounds that can be purchased externally, and to choose which compound should be synthesized next. | 1 | Applied and Interdisciplinary Chemistry |
An equation similar to that of Kelvin can be derived for the solubility of small particles or droplets in a liquid, by means of the connection between vapour pressure and solubility, thus the Kelvin equation also applies to solids, to slightly soluble liquids, and their solutions if the partial pressure is replaced by the solubility of the solid () (or a second liquid) at the given radius, , and by the solubility at a plane surface (). Hence small particles (like small droplets) are more soluble than larger ones. The equation would then be given by:
These results led to the problem of how new phases can ever arise from old ones. For example, if a container filled with water vapour at slightly below the saturation pressure is suddenly cooled, perhaps by adiabatic expansion, as in a cloud chamber, the vapour may become supersaturated with respect to liquid water. It is then in a metastable state, and we may expect condensation to take place. A reasonable molecular model of condensation would seem to be that two or three molecules of water vapour come together to form a tiny droplet, and that this nucleus of condensation then grows by accretion, as additional vapour molecules happen to hit it. The Kelvin equation, however, indicates that a tiny droplet like this nucleus, being only a few ångströms in diameter, would have a vapour pressure many times that of the bulk liquid. As far as tiny nuclei are concerned, the vapour would not be supersaturated at all. Such nuclei should immediately re-evaporate, and the emergence of a new phase at the equilibrium pressure, or even moderately above it should be impossible. Hence, the over-saturation must be several times higher than the normal saturation value for spontaneous nucleation to occur.
There are two ways of resolving this paradox. In the first place, we know the statistical basis of the second law of thermodynamics. In any system at equilibrium, there are always fluctuations around the equilibrium condition, and if the system contains few molecules, these fluctuations may be relatively large. There is always a chance that an appropriate fluctuation may lead to the formation of a nucleus of a new phase, even though the tiny nucleus could be called thermodynamically unstable. The chance of a fluctuation is e, where ΔS is the deviation of the entropy from the equilibrium value.
It is unlikely, however, that new phases often arise by this fluctuation mechanism and the resultant spontaneous nucleation. Calculations show that the chance, e, is usually too small. It is more likely that tiny dust particles act as nuclei in supersaturated vapours or solutions. In the cloud chamber, it is the clusters of ions caused by a passing high-energy particle that acts as nucleation centers. Actually, vapours seem to be much less finicky than solutions about the sort of nuclei required. This is because a liquid will condense on almost any surface, but crystallization requires the presence of crystal faces of the proper kind.
For a sessile drop residing on a solid surface, the Kelvin equation is modified near the contact line, due to intermolecular interactions between the liquid drop and the solid surface. This extended Kelvin equation is given by
where is the disjoining pressure that accounts for the intermolecular interactions between the sessile drop and the solid and is the Laplace pressure, accounting for the curvature-induced pressure inside the liquid drop. When the interactions are attractive in nature, the disjoining pressure, is negative. Near the contact line, the disjoining pressure dominates over the Laplace pressure, implying that the solubility, is less than . This implies that a new phase can spontaneously grow on a solid surface, even under saturation conditions. | 0 | Theoretical and Fundamental Chemistry |
Although the type II reaction centers are structurally and sequentially analogous to photosystem II (PSII) in plant chloroplasts and cyanobacteria, known organisms that exhibit anoxygenic photosynthesis do not have a region analogous to the oxygen-evolving complex of PSII.
The electron transport chain of purple non-sulfur bacteria begins when the reaction center bacteriochlorophyll pair, P870, becomes excited from the absorption of light. Excited P870 will then donate an electron to bacteriopheophytin, which then passes it on to a series of electron carriers down the electron chain. In the process, it will generate an electrochemical gradient which can then be used to synthesize ATP by chemiosmosis. P870 has to be regenerated (reduced) to be available again for a photon reaching the reaction-center to start the process anew. Molecular hydrogen in the bacterial environment is the usual electron donor. | 0 | Theoretical and Fundamental Chemistry |
Masri is the visionary and founder of Rawabi City, and oversees the construction and development of the city. Rawabi City is a high-tech planned city, the first of its kind in Palestine, and it was funded fully by the private sector, Rawabi is considered the largest private sector investment is Palestine's history, the construction of the city so far has cost 1.4 billion dollars. Rawabi is being constructed by Bayti Real Estate Investment Company that is jointly owned by Qatari Diar Real Estate Investment Company and Massar International. With its more than 6,000 housing units built to serve families from multiple demographics, state-of-the-art infrastructure, and an emerging commercial hub, the city has already made a positive economic and social impact on Palestinians and it is constructed to provide housing for 25,000 person in its first stage and 40,000 people when it is done. Not only does the city provide affordable housing options it is also the second biggest generator of jobs, after the Palestinian Government, providing between 8,000 and 10,000 job opportunity a year for construction workers, in addition to thousands of job opportunities, whether in Massar International companies that moved there, or in the different shops and entertainment facilities the city provides.
Masri aims for the City of Rawabi to be the Silicon Valley and the Tech Hub for the State of Palestine, in attempts to provide spaces for promising technology and technology related startups at the city, and businesses from inside and outside of Palestine to the city.
In July 2022, Apple Inc.Apple announced that the company would be expanding their research and development centre in Rawabi. The expansion will take place via hiring contractor ASAL Technologies and Masri in order to achieve the expansion. | 1 | Applied and Interdisciplinary Chemistry |
A wide range of organosulfur compounds are known which contain one or more halogen atom ("X" in the chemical formulas that follow) bonded to a single sulfur atom, e.g.: sulfenyl halides, RSX; sulfinyl halides, RS(O)X; sulfonyl halides, RSOX; alkyl and arylsulfur trichlorides, RSCl and trifluorides, RSF; and alkyl and arylsulfur pentafluorides, RSF. Less well known are dialkylsulfur tetrahalides, mainly represented by the tetrafluorides, e.g., RSF. | 0 | Theoretical and Fundamental Chemistry |
The lower critical solution temperature (LCST) or lower consolute temperature is the critical temperature below which the components of a mixture are miscible in all proportions. The word lower indicates that the LCST is a lower bound to a temperature interval of partial miscibility, or miscibility for certain compositions only.
The phase behavior of polymer solutions is an important property involved in the development and design of most polymer-related processes. Partially miscible polymer solutions often exhibit two solubility boundaries, the upper critical solution temperature (UCST) and the LCST, both of which depend on the molar mass and the pressure. At temperatures below LCST, the system is completely miscible in all proportions, whereas above LCST partial liquid miscibility occurs.
In the phase diagram of the mixture components, the LCST is the shared minimum of the concave up spinodal and binodal (or coexistence) curves. It is in general pressure dependent, increasing as a function of increased pressure.
For small molecules, the existence of an LCST is much less common than the existence of an upper critical solution temperature (UCST), but some cases do exist. For example, the system triethylamine-water has an LCST of 19 °C, so that these two substances are miscible in all proportions below 19 °C but not at higher temperatures. The nicotine-water system has an LCST of 61 °C, and also a UCST of 210 °C at pressures high enough for liquid water to exist at that temperature. The components are therefore miscible in all proportions below 61 °C and above 210 °C (at high pressure), and partially miscible in the interval from 61 to 210 °C. | 0 | Theoretical and Fundamental Chemistry |
In addition to common uses previously mentioned, FRET and BRET are also effective in the study of biochemical reaction kinetics. FRET is increasingly used for monitoring pH dependent assembly and disassembly and is valuable in the analysis of nucleic acids encapsulation. This technique can be used to determine factors affecting various types of nanoparticle formation as well as the mechanisms and effects of nanomedicines. | 1 | Applied and Interdisciplinary Chemistry |
A solar cells quantum efficiency value indicates the amount of current that the cell will produce when irradiated by photons of a particular wavelength. If the cells quantum efficiency is integrated over the whole solar electromagnetic spectrum, one can evaluate the amount of current that the cell will produce when exposed to sunlight. The ratio between this energy-production value and the highest possible energy-production value for the cell (i.e., if the QE were 100% over the whole spectrum) gives the cell's overall energy conversion efficiency value. Note that in the event of multiple exciton generation (MEG), quantum efficiencies of greater than 100% may be achieved since the incident photons have more than twice the band gap energy and can create two or more electron-hole pairs per incident photon. | 0 | Theoretical and Fundamental Chemistry |
This gene encodes an E26 transformation-specific related transcription factor. The encoded protein is primarily expressed in lymphoid cells and can act as both an enhancer and a repressor to regulate transcription of various genes. Alternative splicing results in multiple transcript variants. | 1 | Applied and Interdisciplinary Chemistry |
According to a more specific definition presented by Trasatti, the absolute electrode potential is the difference in electronic energy between a point inside the metal (Fermi level) of an electrode and a point outside the electrolyte in which the electrode is submerged (an electron at rest in vacuum).
This potential is difficult to determine accurately. For this reason, a standard hydrogen electrode is typically used for reference potential. The absolute potential of the SHE is 4.44 ± 0.02 V at 25 °C. Therefore, for any electrode at 25 °C:
where:
: is electrode potential
:V is the unit volt
:M denotes the electrode made of metal M
:(abs) denotes the absolute potential
:(SHE) denotes the electrode potential relative to the standard hydrogen electrode.
A different definition for the absolute electrode potential (also known as absolute half-cell potential and single electrode potential) has also been discussed in the literature. In this approach, one first defines an isothermal absolute single-electrode process (or absolute half-cell process.) For example, in the case of a generic metal being oxidized to form a solution-phase ion, the process would be
:M → M +
For the hydrogen electrode, the absolute half-cell process would be
:H → H +
Other types of absolute electrode reactions would be defined analogously.
In this approach, all three species taking part in the reaction, including the electron, must be placed in thermodynamically well-defined states. All species, including the electron, are at the same temperature, and appropriate standard states for all species, including the electron, must be fully defined. The absolute electrode potential is then defined as the Gibbs free energy for the absolute electrode process. To express this in volts one divides the Gibbs free energy by the negative of Faraday's constant.
Rockwood's approach to absolute-electrode thermodynamics is easily expendable to other thermodynamic functions. For example, the absolute half-cell entropy has been defined as the entropy of the absolute half-cell process defined above. An alternative definition of the absolute half-cell entropy has recently been published by Fang et al. who define it as the entropy of the following reaction (using the hydrogen electrode as an example):
:H → H +
This approach differs from the approach described by Rockwood in the treatment of the electron, i.e. whether it is placed in the gas phase or the metal. The electron can also be in another state, that of a solvated electron in solution, as studied by Alexander Frumkin and B. Damaskin and others. | 0 | Theoretical and Fundamental Chemistry |
Some nonerythroid cells (i.e., cells other than the red blood cell line) contain hemoglobin. In the brain, these include the A9 dopaminergic neurons in the substantia nigra, astrocytes in the cerebral cortex and hippocampus, and in all mature oligodendrocytes. It has been suggested that brain hemoglobin in these cells may enable the "storage of oxygen to provide a homeostatic mechanism in anoxic conditions, which is especially important for A9 DA neurons that have an elevated metabolism with a high requirement for energy production". It has been noted further that "A9 dopaminergic neurons may be at particular risk of anoxic degeneration since in addition to their high mitochondrial activity they are under intense oxidative stress caused by the production of hydrogen peroxide via autoxidation and/or monoamine oxidase (MAO)-mediated deamination of dopamine and the subsequent reaction of accessible ferrous iron to generate highly toxic hydroxyl radicals". This may explain the risk of degeneration of these cells in Parkinsons disease. The hemoglobin-derived iron in these cells is not the cause of the post-mortem darkness of these cells (origin of the Latin name, substantia nigra'), but rather is due to neuromelanin.
Outside the brain, hemoglobin has non-oxygen-carrying functions as an antioxidant and a regulator of iron metabolism in macrophages, alveolar cells, and mesangial cells in the kidney. | 0 | Theoretical and Fundamental Chemistry |
The petite is characterized by a deficiency in cytochromes (a, a3 + b) and a lack of respiratory enzymes which engage in respiration in mitochondria. Due to the error in the respiratory chain pathway, petite yeast is incapable of growing on media containing only non-fermentable carbon sources (such as glycerol or ethanol) and forming small colonies when grown in the presence of fermentable carbon sources (such as glucose). The absence of mitochondria can cause the petite phenotype, or by deletion mutations in mitochondrial DNA (termed "cytoplasmic Petites") which is a deletion mutation, or by mutations in nuclear-encoded genes involved in oxidative phosphorylation. | 1 | Applied and Interdisciplinary Chemistry |
Many kinds of pollutants have been proposed, but few have been demonstrated in solving environmental challenges.
*Cadmium (Cd) is converted to immobile Cd metal.
*Chloramines are effectively reduced by ZVI.
*nitrate reduction by iron powder is observed only at pH≤4. Ammonia is the end product. Using nanoscale iron N gas is the product.
*Nitrated aromatics are reduced by bulk iron.
*Chlorinated pesticides such as DDT, DDD, and DDE. The rates of dechlorination are enhanced by the surfactant (Triton X-114). | 1 | Applied and Interdisciplinary Chemistry |
The five atoms bonded to the central atom are not all equivalent, and two different types of position are defined. For phosphorus pentachloride as an example, the phosphorus atom shares a plane with three chlorine atoms at 120° angles to each other in equatorial positions, and two more chlorine atoms above and below the plane (axial or apical positions).
According to the VSEPR theory of molecular geometry, an axial position is more crowded because an axial atom has three neighboring equatorial atoms (on the same central atom) at a 90° bond angle, whereas an equatorial atom has only two neighboring axial atoms at a 90° bond angle. For molecules with five identical ligands, the axial bond lengths tend to be longer because the ligand atom cannot approach the central atom as closely. As examples, in PF the axial P−F bond length is 158 pm and the equatorial is 152 pm, and in PCl the axial and equatorial are 214 and 202 pm respectively.
In the mixed halide PFCl the chlorines occupy two of the equatorial positions, indicating that fluorine has a greater apicophilicity or tendency to occupy an axial position. In general ligand apicophilicity increases with electronegativity and also with pi-electron withdrawing ability, as in the sequence Cl < F < CN. Both factors decrease electron density in the bonding region near the central atom so that crowding in the axial position is less important. | 0 | Theoretical and Fundamental Chemistry |
The term amphibolism () is used to describe a biochemical pathway that involves both catabolism and anabolism. Catabolism is a degradative phase of metabolism in which large molecules are converted into smaller and simpler molecules, which involves two types of reactions. First, hydrolysis reactions, in which catabolism is the breaking apart of molecules into smaller molecules to release energy. Examples of catabolic reactions are digestion and cellular respiration, where sugars and fats are broken down for energy. Breaking down a protein into amino acids, or a triglyceride into fatty acids, or a disaccharide into monosaccharides are all hydrolysis or catabolic reactions. Second, oxidation reactions involve the removal of hydrogens and electrons from an organic molecule. Anabolism is the biosynthesis phase of metabolism in which smaller simple precursors are converted to large and complex molecules of the cell. Anabolism has two classes of reactions. The first are dehydration synthesis reactions; these involve the joining of smaller molecules together to form larger, more complex molecules. These include the formation of carbohydrates, proteins, lipids and nucleic acids. The second are reduction reactions, in which hydrogens and electrons are added to a molecule. Whenever that is done, molecules gain energy.
The term amphibolism was proposed by B. Davis in 1961 to emphasise the dual metabolic role of such pathways. These pathways are considered to be central metabolic pathways which provide, from catabolic sequences, the intermediates which form the substrate of the metabolic processes. | 1 | Applied and Interdisciplinary Chemistry |
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