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A memory foam mattress is usually denser than other foam mattresses, making it both more supportive and heavier. Memory foam mattresses are often sold for higher prices than traditional mattresses. Memory foam used in mattresses is commonly manufactured in densities ranging from less than 24kg/m (1.5 lb/ft) to 128kg/m (8 lb/ft) density. Most standard memory foam has a density of 16–80 kg/m (1 to 5 lb/ft). Most bedding, such as topper pads and comfort layers in mattresses, has a density of 48–72 kg/m (3 to 4.5 lb/ft). High densities such as 85 kg/m (5.3 lb/ft) are used infrequently.
The firmness property (hard to soft) of memory foam is used in determining comfort. It is measured by a foams indentation force deflection (IFD) rating. However, it is not a complete measurement of a "soft" or "firm" feel'. A foam of higher IFD but lower density can feel soft when compressed.
IFD measures the force in newtons (or pounds-force) required to make a dent 1 inch into a foam sample by a 323 cm (50 sq in, 8-inch-diameter) disc—known as IFD @ 25% compression. IFD ratings for memory foams range between super soft (IFD 10) and semi-rigid (IFD 12). Most memory foam mattresses are firm (IFD 12 to IFD 16).
Second and third generation memory foams have an open-cell structure that reacts to body heat and weight by molding to the sleepers body, helping relieve pressure points, preventing pressure sores, etc. Manufacturers claim that this may help relieve pressure points to relieve pain and promote more restful sleep, although there are no objective studies supporting the mattresses claimed benefits.
Memory foam mattresses retain body heat, so they can be excessively warm in hot weather. However, gel-type memory foams tend to be cooler due to their greater breathability. | 0 | Theoretical and Fundamental Chemistry |
Classical examples of polymorphism are the pair of minerals calcite and aragonite, both forms of calcium carbonate. Allotropy is the term used for elements, for example diamond versus graphite, and in metallurgy.
β-HgS precipitates as a black solid when Hg(II) salts are treated with HS. With gentle heating of the slurry, the black polymorph converts to the red form. | 0 | Theoretical and Fundamental Chemistry |
The Edmond–Ogston model is a thermodynamic model proposed by Elizabeth Edmond and Alexander George Ogston in 1968 to describe phase separation of two-component polymer mixtures in a common solvent. At the core of the model is an expression for the Helmholtz free energy
that takes into account terms in the concentration of the polymers up to second order, and needs three virial coefficients and as input. Here is the molar concentration of polymer , is the universal gas constant, is the absolute temperature, is the system volume. It is possible to obtain explicit solutions for the coordinates of the critical point
where represents the slope of the binodal and spinodal in the critical point. Its value can be obtained by solving a third order polynomial in ,
which can be done analytically using Cardano's method and choosing the solution for which both and are positive.
The spinodal can be expressed analytically too, and the Lambert W function has a central role to express the coordinates of binodal and tie-lines.
The model is closely related to the Flory–Huggins model. | 0 | Theoretical and Fundamental Chemistry |
cAMP is associated with kinases function in several biochemical processes, including the regulation of glycogen, sugar, and lipid metabolism.
In eukaryotes, cyclic AMP works by activating protein kinase A (PKA, or cAMP-dependent protein kinase). PKA is normally inactive as a tetrameric holoenzyme, consisting of two catalytic and two regulatory units (CR), with the regulatory units blocking the catalytic centers of the catalytic units.
Cyclic AMP binds to specific locations on the regulatory units of the protein kinase, and causes dissociation between the regulatory and catalytic subunits, thus enabling those catalytic units to phosphorylate substrate proteins.
The active subunits catalyze the transfer of phosphate from ATP to specific serine or threonine residues of protein substrates. The phosphorylated proteins may act directly on the cell's ion channels, or may become activated or inhibited enzymes. Protein kinase A can also phosphorylate specific proteins that bind to promoter regions of DNA, causing increases in transcription. Not all protein kinases respond to cAMP. Several classes of protein kinases, including protein kinase C, are not cAMP-dependent.
Further effects mainly depend on cAMP-dependent protein kinase, which vary based on the type of cell.
Still, there are some minor PKA-independent functions of cAMP, e.g., activation of calcium channels, providing a minor pathway by which growth hormone-releasing hormone causes a release of growth hormone.
However, the view that the majority of the effects of cAMP are controlled by PKA is an outdated one. In 1998 a family of cAMP-sensitive proteins with guanine nucleotide exchange factor (GEF) activity was discovered. These are termed Exchange proteins activated by cAMP (Epac) and the family comprises Epac1 and Epac2. The mechanism of activation is similar to that of PKA: the GEF domain is usually masked by the N-terminal region containing the cAMP binding domain. When cAMP binds, the domain dissociates and exposes the now-active GEF domain, allowing Epac to activate small Ras-like GTPase proteins, such as Rap1. | 1 | Applied and Interdisciplinary Chemistry |
The company sells a special soap – available to authorities but not the general public – that neutralises the smell of skunk water if officers are accidentally sprayed. It has been suggested that rubbing a surface contaminated with skunk with ketchup, similar to treating a real skunk spray with tomato juice, and then washing it off, may diminish perception of the odor (due to the effects of olfactory fatigue). In 1993, American chemist Paul Krebaum developed a compound that chemically neutralizes natural skunk spray by changing the odor-causing thiols into odorless acids. This compound can be prepared as a mixture of: 1 quart of 3% hydrogen peroxide, ¼ cup of baking soda, and 1-2 teaspoons of liquid dish soap. | 1 | Applied and Interdisciplinary Chemistry |
Once the mutation has been codified and the protein is functional, there is no chance to turn back and we will speak about a mutated individual. However, if the mutant dally is codified but it is not performing its function yet, a chaperone can identify it and try to correct the mutation, or directly send it to a proteasome using ubiquitins and degrade it.
Notwithstanding, there is another possible solution when malformations have occurred as a result of Wg activity loss. Ectopic dally can potentiate Wg signaling but this effect is dependent on some Wg activity remaining at the cell surface. Moreover, ectopic expression of dally+ from hs-dally+ transgene, stimulates Wg signaling. Thus, naked larval cuticle loss is recuperated and once the larva has become an adult, its tissues execute their normal function. Despite this fact, an intense expression of dally+ results in the death of most of the Drosophila melanogaster’s embryos. | 1 | Applied and Interdisciplinary Chemistry |
The linear (simple) types of inhibition can be classified in terms of the general equation for mixed inhibition at an inhibitor concentration :
in which is the competitive inhibition constant and is the uncompetitive inhibition constant. This equation includes the other types of inhibition as special cases:
* If the second parenthesis in the denominator approaches and the resulting behaviour is competitive inhibition.
* If the first parenthesis in the denominator approaches and the resulting behaviour is uncompetitive inhibition.
* If both and are finite the behaviour is mixed inhibition.
* If the resulting special case is pure non-competitive inhibition.
Pure non-competitive inhibition is very rare, being mainly confined to effects of protons and some metal ions. Cleland recognized this, and he redefined noncompetitive to mean mixed. Some authors have followed him in this respect, but not all, so when reading any publication one needs to check what definition the authors are using.
In all cases the kinetic equations have the form of the Michaelis–Menten equation with apparent constants, as can be seen by writing the equation above as follows:
with apparent values and defined as follows: | 0 | Theoretical and Fundamental Chemistry |
Downregulation of gene expression via siRNA has been an important research tool in in vitro studies. Susceptibility of siRNAs to nuclease degradation, though, makes use of them in vivo problematic. In 2005, researchers working with hepatitis B virus(HBV) in rodents, determined that certain modifications of the siRNA prevented degradation by nucleases within the plasma and lead to increased gene silencing compared to unmodified siRNA. Modifications to the sense and antisense strands were made differentially. With respect to both sense and antisense strands, 2-OH was substituted with 2-fluoro at all pyrimidine positions. In addition, sense strands were modified at all purine positions with deoxyribose, antisense strands modified with 2-O-methyl at the same positions. The 5 and 3 ends of the sense strand were capped with abasic inverted repeats, while a phosphorothioate linkage was incorporated at the 3 end of the antisense strand.
Although this research demonstrated a potential RNAi therapy using modified siRNA, the 90% reduction in HBV DNA in rodents resulted from a 30 mg/kg dosage with frequent administration. Because this is not a viable dosing regime, this same group looked at the effects of encapsulating the siRNA in a PEGylated lipid bilayer, or SNALP. Specifically, the lipid bilayer facilitates uptake into the cell and subsequent release from the endosome, the PEGylated outer layer providing stability during formulation due to the resulting hydrophilicity of the exterior. According to this 2005 study, researchers obtained 90% reduction in HBV DNA with a 3 mg/kg/day dose of siRNA for three days, a dose substantially lower than the earlier study. In addition, in contrast to unmodified or modified and non-encapsulated siRNA, administration of SNALP-delivered siRNA resulted in no detectable levels of interferons, such as IFN-a, or inflammatory cytokines associated with immunostimulation. Even so, researchers acknowledged that more work was necessary in order to reach a feasible dose and dosing regime.
In 2006, researchers working on silencing of apolipoprotein B(ApoB) in non-human primates achieved 90% silencing with a single dose of 2.5 mg/kg of SNALP-delivered APOB-specific siRNA. ApoB is a protein involved with the assembly and secretion of very-low-density lipoprotein(VLDL) and low-density lipoprotein(LDL), and it is expressed primarily in the liver and jejunum. Both VLDL and LDL are important in cholesterol transport and its metabolism. Not only was this degree of silencing observed very quickly, in about 24 hours post-administration, but the silencing effects maintained for over 22 days after only a single dose. Researchers tested a 1 mg/kg single dose, too, obtaining a 68% silencing of the target gene, indicating dose-dependent silencing. This dose-dependent silencing was evident not only on the degree of silencing but the duration of silencing, expression of the target gene recovering 72 hours post-administration.
Although SNALPs having a 100 nm diameter have been used effectively to target specific genes for silencing, there are a variety of systemic barriers that relate specifically to size. For example, diffusion into solid tumors is impeded by large SNALPs and, similarly, inflamed cells having enhanced permeation and retention make it difficult for large SNALPs to enter. In addition, reticuloendothelial elimination, blood–brain barrier size-selectivity and limitations of capillary fenestrae all necessitate a smaller SNALP in order to effectively deliver target-specific siRNA. In 2012, scientists in Germany developed what they termed "mono-NALPs" using a fairly simple solvent exchange method involving progressive dilution of a 50% isopropanol solution. What results is a very stable delivery system similar to traditional SNALPs, but one having only a diameter of 30 nm. The mono-NALPs developed here, however, are inactive, but can become active carriers by implementing specific targeting and release mechanisms used by similar delivery systems. | 1 | Applied and Interdisciplinary Chemistry |
Various polymers such as poloxamers exhibit in situ gelling properties. Because of these properties they can be administered as liquid formulations forming stable gels once having reached their site of application. An unintended rapid elimination or outflow of the formulation from mucosal membranes such as the ocular, nasal or vaginal mucosa can therefore be avoided. Thiolated polymers are capable of providing a comparatively more pronounced increase in viscosity after application, as an extensive crosslinking process by the formation of disulfide bonds between the polymer chains due to oxidation takes place. This effect was first described in 1999 by Bernkop-Schnürch et al. for polymeric excipients. In case of thiolated chitosan, for instance, a more than 10,000-fold increase in viscosity within a few minutes was shown. These high in situ gelling properties can also be used for numerous further reasons such as for parenteral formulations, as coating material or for food additives | 0 | Theoretical and Fundamental Chemistry |
In thermodynamics, an activity coefficient is a factor used to account for deviation of a mixture of chemical substances from ideal behaviour. In an ideal mixture, the microscopic interactions between each pair of chemical species are the same (or macroscopically equivalent, the enthalpy change of solution and volume variation in mixing is zero) and, as a result, properties of the mixtures can be expressed directly in terms of simple concentrations or partial pressures of the substances present e.g. Raoults law. Deviations from ideality are accommodated by modifying the concentration by an activity coefficient'. Analogously, expressions involving gases can be adjusted for non-ideality by scaling partial pressures by a fugacity coefficient.
The concept of activity coefficient is closely linked to that of activity in chemistry. | 0 | Theoretical and Fundamental Chemistry |
Spectral signature is the variation of reflectance or emittance of a material with respect to wavelengths (i.e., reflectance/emittance as a function of wavelength). The spectral signature of stars indicates the composition of the stellar atmosphere. The spectral signature of an object is a function of the incidental EM wavelength and material interaction with that section of the electromagnetic spectrum.
The measurements can be made with various instruments, including a task specific spectrometer, although the most common method is separation of the red, green, blue and near infrared portion of the EM spectrum as acquired by digital cameras. Calibrating spectral signatures under specific illumination are collected in order to apply a correction to airborne or satellite imagery digital images.
The user of one kind of spectroscope looks through it at a tube of ionized gas. The user sees specific lines of colour falling on a graduated scale. Each substance will have its own unique pattern of spectral lines.
Most remote sensing applications process digital images to extract spectral signatures at each pixel and use them to divide the image in groups of similar pixels (segmentation) using different approaches. As a last step, they assign a class to each group (classification) by comparing with known spectral signatures. Depending on pixel resolution, a pixel can represent many spectral signature "mixed" together - that is why much remote sensing analysis is done to "unmix mixtures". Ultimately correct matching of spectral signature recorded by image pixel with spectral signature of existing elements leads to accurate classification in remote sensing. | 0 | Theoretical and Fundamental Chemistry |
There are also three structural isomers of the hydrocarbon :
In two of the isomers, the three carbon atoms are connected in an open chain, but in one of them (propadiene or allene; I) the carbons are connected by two double bonds, while in the other (propyne or methylacetylene; II) they are connected by a single bond and a triple bond. In the third isomer (cyclopropene; III) the three carbons are connected into a ring by two single bonds and a double bond. In all three, the remaining valences of the carbon atoms are satisfied by the four hydrogens.
Again, note that there is only one structural isomer with a triple bond, because the other possible placement of that bond is just drawing the three carbons in a different order. For the same reason, there is only one cyclopropene, not three. | 0 | Theoretical and Fundamental Chemistry |
In humans and many other animals, acid–base homeostasis is maintained by multiple mechanisms involved in three lines of defense:
# Chemical: The first lines of defense are immediate, consisting of the various chemical buffers which minimize pH changes that would otherwise occur in their absence. These buffers include the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system.
# Respiratory component: The second line of defense is rapid consisting of the control the carbonic acid (HCO) concentration in the ECF by changing the rate and depth of breathing by hyperventilation or hypoventilation. This blows off or retains carbon dioxide (and thus carbonic acid) in the blood plasma as required.
# Metabolic component: The third line of defense is slow, best measured by the base excess, and mostly depends on the renal system which can add or remove bicarbonate ions () to or from the ECF. Bicarbonate ions are derived from metabolic carbon dioxide which is enzymatically converted to carbonic acid in the renal tubular cells. There, carbonic acid spontaneously dissociates into hydrogen ions and bicarbonate ions. When the pH in the ECF falls, hydrogen ions are excreted into urine, while bicarbonate ions are secreted into blood plasma, causing the plasma pH to rise. The converse happens if the pH in the ECF tends to rise: bicarbonate ions are then excreted into the urine and hydrogen ions into the blood plasma.
The second and third lines of defense operate by making changes to the buffers, each of which consists of two components: a weak acid and its conjugate base. It is the ratio concentration of the weak acid to its conjugate base that determines the pH of the solution. Thus, by manipulating firstly the concentration of the weak acid, and secondly that of its conjugate base, the pH of the extracellular fluid (ECF) can be adjusted very accurately to the correct value. The bicarbonate buffer, consisting of a mixture of carbonic acid (HCO) and a bicarbonate () salt in solution, is the most abundant buffer in the extracellular fluid, and it is also the buffer whose acid-to-base ratio can be changed very easily and rapidly. | 0 | Theoretical and Fundamental Chemistry |
Following its introduction to Europe from the New World in the late 15th century, natural rubber (polyisoprene) was regarded mostly as a fascinating curiosity. Its most useful application was its ability to erase pencil marks on paper by rubbing, hence its name. One of its most peculiar properties is a slight (but detectable) increase in temperature that occurs when a sample of rubber is stretched. If it is allowed to quickly retract, an equal amount of cooling is observed. This phenomenon caught the attention of the English physicist John Gough. In 1805 he published some qualitative observations on this characteristic as well as how the required stretching force increased with temperature.<br>
By the mid nineteenth century, the theory of thermodynamics was being developed and within this framework, the English mathematician and physicist Lord Kelvin showed that the change in mechanical energy required to stretch a rubber sample should be proportional to the increase in temperature. Later, this would be associated with a change in entropy. The connection to thermodynamics was firmly established in 1859 when the English physicist James Joule published the first careful measurements of the temperature increase that occurred as a rubber sample was stretched. This work confirmed the theoretical predictions of Lord Kelvin.<br>
In 1838 the American inventor Charles Goodyear found that natural rubbers elastic properties could be immensely improved by adding a few percent sulphur. The short sulfur chains produced chemical cross-links between adjacent polyisoprene molecules. Before it is cross-linked, the liquid natural rubber consists of very long polymer molecules, containing thousands of isoprene backbone units, connected head-to-tail (commonly referred to as chains). Every chain follows a random, three dimensional path through the polymer liquid and is in contact with thousands of other nearby chains. When heated to about 150C, reactive cross-linker molecules, such as sulfur or dicumyl peroxide, can decompose and the subsequent chemical reactions produce a chemical bond between adjacent chains. A crosslink can be visualized as the letter X' but with some of its arms pointing out of the plane. The result is a three dimensional molecular network. All of the polyisoprene molecules are connected together at multiple points by these chemical bonds (network nodes) resulting in a single giant molecule and all information about the original long polymers is lost. A rubber band is a single molecule, as is a latex glove! The sections of polyisoprene between two adjacent cross-links are called network chains and can contain up to several hundred isoprene units. In natural rubber, each cross-link produces a network node with four chains emanating from it. It is the network that gives rise to the elastic properties.
Because of the enormous economic and technological importance of rubber, predicting how a molecular network responds to mechanical strains has been of enduring interest to scientists and engineers. To understand the elastic properties of rubber, theoretically, it is necessary to know both the physical mechanisms that occur at the molecular level and how the random-walk nature of the polymer chain defines the network. The physical mechanisms that occur within short sections of the polymer chains produce the elastic forces and the network morphology determines how these forces combine to produce the macroscopic stress that we observe when a rubber sample is deformed, e.g. subjected to tensile strain. | 0 | Theoretical and Fundamental Chemistry |
Quantum crystallography is a branch of crystallography that investigates crystalline materials within the framework of quantum mechanics, with analysis and representation, in position or in momentum space, of quantities like wave function, electron charge and spin density, density matrices and all properties related to them (like electric potential, electric or magnetic moments, energy densities, electron localization function, one electron potential, etc.).
Like the quantum chemistry, Quantum crystallography involves both experimental and computational work. The theoretical part of quantum crystallography is based on quantum mechanical calculations of atomic/molecular/crystal wave functions, density matrices or density models, used to simulate the electronic structure of a crystalline material. While in quantum chemistry, the experimental works mainly rely on spectroscopy, in quantum crystallography the scattering techniques (X-rays, neutrons, γ-Rays, electrons) play the central role, although spectroscopy as well as atomic microscopy are also sources of information.
The connection between crystallography and quantum chemistry has always been very tight, after X-ray diffraction techniques became available in crystallography. In fact, the scattering of radiation enables mapping the one-electron distribution or the elements of a density matrix.
The kind of radiation and scattering determines the quantity which is represented (electron charge or spin) and the space in which it is represented (position or momentum space).
Although the wave function is typically assumed not to be directly measurable, recent advances enable also to compute wave functions that are restrained to some experimentally measurable observable (like the scattering of a radiation).
The term Quantum Crystallography was first introduced in revisitation articles by L. Huang, L. Massa and Nobel Prize winner Jerome Karle, who associated it with two mainstreams: a) crystallographic information that enhances quantum mechanical calculations and b) quantum mechanical approaches to improve crystallography information. This definition mainly refers to studies started in the 1960s and 1970s, when first attempts to obtain wave functions from scattering experiments appeared, together with other methods to constrain a wavefunction to experimental observations like the dipole moment. This field has been recently reviewed, within the context of this definition.
Parallel to studies on wave function determination, R. F. Stewart and P. Coppens investigated the possibilities to compute models for one-electron charge density from X-ray scattering (for example by means of pseudoatoms multipolar expansion), and later of spin density from polarized neutron diffraction, that originated the scientific community of charge, spin and momentum density.
In a recent review article, V. Tsirelson gave a more general definition: "Quantum crystallography is a research area exploiting the fact that parameters of quantum-mechanically valid electronic model of a crystal can be derived from the accurately measured set of X-ray coherent diffraction structure factors".
The book Modern Charge Density Analysis offers a survey of the research involving Quantum Crystallography and of the most adopted experimental or theoretical methodologies.
The International Union of Crystallography has recently established a commission on Quantum Crystallography, as extension of the previous commission on Charge, Spin and Momentum density, with the purpose of coordinating research activities in this field. | 0 | Theoretical and Fundamental Chemistry |
Sulfonate esters are often leaving groups in nucleophilic substitution reactions. See the articles on sulfonyl and sulfonate groups for further information.
*Bs for the brosyl (p-bromobenzenesulfonyl) group; OBs is the brosylate group
*Ms for the mesyl (methanesulfonyl) group; OMs is the mesylate group
*Ns for the nosyl (p-nitrobenzenesulfonyl) group (Ns was the chemical symbol for nielsbohrium, but that was renamed bohrium, Bh); ONs is the nosylate group
*Tf for the triflyl (trifluoromethanesulfonyl) group; OTf is the triflate group
*Nf for the nonaflyl (nonafluorobutanesulfonyl) group, ; ONf is the nonaflate group
*Ts for tosyl (p-toluenesulfonyl) group (Ts is also the symbol for the element tennessine. However, tennessine is too unstable to ever be encountered in organic chemistry, so the use of Ts to represent tosyl never causes confusion); OTs is the tosylate group | 0 | Theoretical and Fundamental Chemistry |
Quinone molecules have been used as anolytes in alkaline AROFBs. Another anolyte candidate is fluorenone, reengineered to increase its water solubility. A reversible ketone (de)hydrogenation demonstration cell operated continuously for 120 days over 1,111 charging cycles at room temperature without a catalyst, retaining 97% percent capacity. The cell offers more than double the energy density of vanadium-based systems. The major challenge for alkaline AORFBs is the lack of a stable catholyte, holding their energy densities below 5 Wh/L. All reported alkaline AORFBs use excess potassium ferrocyanide catholyte because of the stability issue of ferrocyanide in alkaline solutions.
Metal-organic flow batteries use organic ligands to improve the properties of redox-active metals. The ligands can be chelates like EDTA, and can enable the electrolyte to be in neutral or alkaline conditions under which metal aquo complexes would otherwise precipitate. By blocking the coordination of water to the metal, organic ligands can inhibit metal-catalyzed water-splitting reactions, resulting in higher voltage all-aqueous systems. For example, the use of chromium coordinated to 1,3-propanediaminetetraacetate (PDTA), gave cell potentials of 1.62 V vs. ferrocyanide and a record 2.13 V vs. bromine. Metal-organic flow batteries may be known as coordination chemistry flow batteries, which represents the technology behind Lockheed Martin's Gridstar Flow technology. | 0 | Theoretical and Fundamental Chemistry |
There is now more than one two-phase region. The tie line drawn is from the solid alpha to the liquid and by dropping a vertical line down at these points the mass fraction of each phase is directly read off the graph, that is the mass fraction in the x axis element. The same equations can be used to find the mass fraction of alloy in each of the phases, i.e. w is the mass fraction of the whole sample in the liquid phase. | 1 | Applied and Interdisciplinary Chemistry |
The mechanism of action of aspirin involves irreversible inhibition of the enzyme cyclooxygenase; therefore suppressing the production of prostaglandins and thromboxanes, thus reducing pain and inflammation. This mechanism of action is specific to aspirin and is not constant for all nonsteroidal anti-inflammatory drugs (NSAIDs). Rather, aspirin is the only NSAID that irreversibly inhibits COX-1. | 1 | Applied and Interdisciplinary Chemistry |
Pacific West Coast Inorganic Lectureship, USA and Canada, 1985; Gold Medal "S. Cannizzaro", Italian Chemical Society, 1988; Doctorate "Honoris Causa", University of Fribourg (CH), 1989; Accademia dei Lincei Award in Chemistry, Italy, 1992; Ziegler-Natta Lecturer, Gesellschaft Deutscher Chemiker, Germany, 1994; Italgas European Prize for Research and Innovation, 1994; Centenary Lecturer, The Royal Chemical Society (U.K.), 1995; Porter Medal for Photochemistry, 2000; Prix Franco-Italien de la Société Française de Chimie, 2002; Grande Ufficiale dell’Ordine al Merito della Repubblica Italiana, 2006; Quilico Gold Metal, Organic Division, Italian Chemical Society, 2008; Honor Professor, East China University of Science and Technology of Shanghai, 2009; Blaise Pascal Medal, European Academy of Sciences, 2009; Rotary Club Galileo International Prize for scientific research, 2011; Nature Award for Mentoring in Science, 2013; Archiginnasio d’oro, Città di Bologna, 2016; Grand Prix de la Maison de la Chimie (France) 2016; Leonardo da Vinci Award, European Academy of Sciences, 2017; Nicholas J. Turro Award, Inter-American Photochemical Society, 2018; Cavaliere di Gran Croce della Repubblica Italiana per meriti scientifici, 2019; Primo Levi Award, Gesellschaft Deutscher Chemiker and Società Chimica Italiana, 2019; UNESCO-Russia Mendeleev Prize, 2021. | 0 | Theoretical and Fundamental Chemistry |
In early 1900, Max Trautz and William Lewis studied the rate of the reaction using collision theory, based on the kinetic theory of gases. Collision theory treats reacting molecules as hard spheres colliding with one another; this theory neglects entropy changes, since it assumes that the collision between molecules are completely elastic.
Lewis applied his treatment to the following reaction and obtained good agreement with experimental result.
2HI → H + I
However, later when the same treatment was applied to other reactions, there were large discrepancies between theoretical and experimental results. | 0 | Theoretical and Fundamental Chemistry |
In E. coli amino acid starvation inhibited DNA replication at the initiation stage at oriC, most probably owing to the lack of the DnaA replication initiation protein. In B. subtilis, the replication arrest due to (p)ppGpp accumulation is caused by the binding of an Rtp protein to specific sites about 100-200kb away from oriC in both directions. DNA primase (DnaG) was directly inhibited by (p)ppGpp. Unlike E. coli, B. subtilis accumulates more pppGpp than ppGpp; the more abundant nucleotide is a more-potent DnaG inhibitor. ppGpp can bind with Obg protein which belongs to the conserved, small GTPase protein family. Obg protein interacts with several regulators (RsbT, RsbW, RsbX) necessary for the stress activation of sigma B. | 1 | Applied and Interdisciplinary Chemistry |
Point groups in three dimensions, sometimes called molecular point groups after their wide use in studying symmetries of molecules.
They come in 7 infinite families of axial groups (also called prismatic), and 7 additional polyhedral groups (also called Platonic). In Schönflies notation,
* Axial groups: C, S, C, C, D, D, D
* Polyhedral groups: T, T, T, O, O, I, I
Applying the crystallographic restriction theorem to these groups yields the 32 crystallographic point groups.
|colspan=2|(*) When the Intl entries are duplicated, the first is for even n, the second for odd n. | 0 | Theoretical and Fundamental Chemistry |
The analytical and approximated solutions should now be compared in order to decide when it is valid to use the steady state approximation. The analytical solution transforms into the approximate one when because then and Therefore, it is valid to apply the steady state approximation only if the second reaction is much faster than the first ( is a common criterion), because that means that the intermediate forms slowly and reacts readily so its concentration stays low.
The graphs show concentrations of A (red), B (green) and C (blue) in two cases, calculated from the analytical solution.
When the first reaction is faster it is not valid to assume that the variation of [B] is very small, because [B] is neither low or close to constant: first A transforms into B rapidly and B accumulates because it disappears slowly. As the concentration of A decreases its rate of transformation decreases, at the same time the rate of reaction of B into C increases as more B is formed, so a maximum is reached when <br />From then on the concentration of B decreases.
When the second reaction is faster, after a short induction period during which the steady state approximation does not apply, the concentration of B remains low (and more or less constant in an absolute sense) because its rates of formation and disappearance are almost equal and the steady state approximation can be used.
The equilibrium approximation can sometimes be used in chemical kinetics to yield similar results to the steady state approximation. It consists in assuming that the intermediate arrives rapidly at chemical equilibrium with the reactants. For example, Michaelis-Menten kinetics can be derived assuming equilibrium instead of steady state. Normally the requirements for applying the steady state approximation are laxer: the concentration of the intermediate is only needed to be low and more or less constant (as seen, this has to do only with the rates at which it appears and disappears) but it is not required to be at equilibrium. | 0 | Theoretical and Fundamental Chemistry |
Infrared spectroscopy is based on the fact that molecules absorb electromagnetic radiation at characteristic frequencies related to their vibrational structure. Infrared (IR) spectroelectrochemistry is a technique that allows the characterization of molecules based on the resistance, stiffness and number of bonds present. It also detects the presence of compounds, determines the concentration of species during a reaction, the structure of compounds, the properties of the chemical bonds, etc. | 0 | Theoretical and Fundamental Chemistry |
Many liquids are used as solvents, to dissolve other liquids or solids. Solutions are found in a wide variety of applications, including paints, sealants, and adhesives. Naphtha and acetone are used frequently in industry to clean oil, grease, and tar from parts and machinery. Body fluids are water-based solutions.
Surfactants are commonly found in soaps and detergents. Solvents like alcohol are often used as antimicrobials. They are found in cosmetics, inks, and liquid dye lasers. They are used in the food industry, in processes such as the extraction of vegetable oil. | 0 | Theoretical and Fundamental Chemistry |
Dunne completed a Bachelor of Science and Master of Engineering degree from the Department of Mechanical Engineering, University of Bristol by 1989, and moved to the Department of Mechanical and Process Engineering, University of Sheffield, for a Doctor of Philosophy in Computer Aided Modelling of Creep-cyclic Plasticity Interaction in Engineering Materials and Structures. | 1 | Applied and Interdisciplinary Chemistry |
The metalation of carboranes is illustrated by the reactions of closo- with iron carbonyl sources. Two closo Fe- and -containing products are obtained, according to these idealized equations:
Base-induced degradation of carboranes give anionic nido derivatives, which can also be employed as ligands for transition metals, generating metallacarboranes, which are carboranes containing one or more transition metal or main group metal atoms in the cage framework. Most famous are the dicarbollide, complexes with the formula , where M stands for metal. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, the Schöniger oxidation (also known as the Schöniger flask test or the oxygen flask method) is a method of elemental analysis developed by Wolfgang Schöniger.
The test is conducted in an Erlenmeyer flask, or in a separatory funnel. It involves the combustion of a sample in pure oxygen, followed by the absorption of the combustion products by a solution of sodium hydroxide.
It allows quantitative determination of elemental chlorine, nitrogen and sulfur in a sample. | 0 | Theoretical and Fundamental Chemistry |
There are five stages in the treatment process:
#Fill
#React
#Settle
#Decant
#Idle
First, the inlet valve is opened and the tank is filled, while mixing is provided by mechanical means, but no air is added yet. This stage is also called the anoxic stage. During the second stage, aeration of the mixed liquor is performed by the use of fixed or floating mechanical pumps or by transferring air into fine bubble diffusers fixed to the floor of the tank. No aeration or mixing is provided in the third stage and the settling of suspended solids starts. During the fourth stage the outlet valve opens and the "clean" supernatant liquor exits the tank. | 1 | Applied and Interdisciplinary Chemistry |
* ATRX-syndrome (α-thalassemia X-linked mental retardation) and α-thalassemia myelodysplasia syndrome are caused by mutations in ATRX, a SNF2-related ATPase with a PHD finger domain.
* CHARGE syndrome, an autosomal dominant disorder, has been linked recently to haploinsufficiency of CHD7, which encodes the CHD family ATPase CHD7. | 1 | Applied and Interdisciplinary Chemistry |
More organic matter is preserved in sediments if there is high primary production, or the sediment is fine-grained. The lack of oxygen helps preservation greatly, and that also is caused by a large supply of organic matter. Soil does not usually preserve organic matter, it would need to be acidified or water logged, as in the bog. Rapid burial ensures the material gets to an oxygen free depth, but also dilutes the organic matter. A low energy environment ensures the sediment is not stirred up and oxygenated. Salt marshes and mangroves meet some of these requirements, but unless the sea level is rising will not have a chance to accumulate much. Coral reefs are very productive, but are well oxygenated, and recycle everything before it is buried. | 0 | Theoretical and Fundamental Chemistry |
As of 2016, challenges including optimizing sample treatment, optimizing disk surfaces, developing readers that can deploy multiple colors of light delivery and sensing for multiplexing, and for clinical use, obtaining regulatory approvals. The field is similar to lab-on-a-chip platforms.
As of 2010 companies including Gyros AB, Tecan, and Burstein Technologies were working on bringing CD/DVD based immunoassays and equipment to market. | 1 | Applied and Interdisciplinary Chemistry |
The reverse Krebs cycle, also known as reverse TCA cycle (rTCA) or reductive citric acid cycle, is an alternative to the standard Calvin-Benson cycle for carbon fixation. It has been found in strict anaerobic or microaerobic bacteria (as Aquificales) and anaerobic archea. It was discovered by Evans, Buchanan and Arnon in 1966 working with the photosynthetic green sulfur bacterium Chlorobium limicola. In particular, it is one of the most used pathways in hydrothermal vents by the Campylobacterota. This feature is very important in oceans. Without it, there would be no primary production in aphotic environments, which would lead to habitats without life. So this kind of primary production is called "dark primary production".
The cycle involves the biosynthesis of acetyl-CoA from two molecules of CO. The key steps of the reverse Krebs cycle are:
* Oxaloacetate to malate, using NADH + H
* Fumarate to succinate, catalyzed by an oxidoreductase, Fumarate reductase
* Succinate to succinyl-CoA, an ATP dependent step
* Succinyl-CoA to alpha-ketoglutarate, using one molecule of CO
* Alpha-ketoglutarate to isocitrate, using NADPH + H and another molecule of CO
* Citrate converted into oxaloacetate and acetyl-CoA, this is an ATP dependent step and the key enzyme is the ATP citrate lyase
This pathway is cyclic due to the regeneration of the oxaloacetate.
The bacteria Gammaproteobacteria and Riftia pachyptila switch from the Calvin-Benson cycle to the rTCA cycle in response to concentrations of HS. | 0 | Theoretical and Fundamental Chemistry |
T-1123 can be produced from m-diethylaminophenol, methyl isocyanate and methyl iodide. First, m-diethylaminophenol is reacted with methyl isocyanate to produce a methylcarbamate. The resulting methylcarbamate is then reacted with methyl iodide to produce T-1123. | 1 | Applied and Interdisciplinary Chemistry |
The active sites in PepA and in bovine lens LAP have been found to be similar. Shown in the picture below is the proposed model for the active site of LAP-A in tomato based on the work of Strater et al. It is also known that the biochemistry of the LAPs from these three kingdoms is very similar. PepA, bovine lens LAP, and LAP-A preferentially cleave N-terminal leucine, arginine, and methionine residues. These enzymes are all metallopeptidases requiring divalent metal cations for their enzymatic activity Enzymes are active in the presence of Mn, Mg and Zn. These enzymes are also known to have high pH (pH 8) and temperature optima. At pH 8, the highest enzymatic activity is seen at 60 °C. PepA, bovine lens LAP and LAP-A are also known to form hexamers in vivo. The Gu et al. from 1999 demonstrated that six 55kDA enzymatically inactive LAP-A protomers come together to form the 353kDa bioactive LAP-A hexamer. Structures of the bovine lens LAP protomer and the biologically active hexamer have been constructed can be found through Protein Data Bank (2J9A). | 1 | Applied and Interdisciplinary Chemistry |
Prebiotic synthesis of amino acids, nucleobases, lipids, and other building blocks of protocells and metabolisms is still poorly understood. Proposed reactions that produce individual components such as the Strecker synthesis of amino acids, the formose reaction for the production of sugars, and prebiotic syntheses for the production of nucleobases. These syntheses often rely on different starting reagents, different conditions (temperature, pH, catalysts, etc.), and often will interfere with each other. These challenges have made determining the conditions for the origin of life difficult. Researchers have turned to systems chemistry type approaches to help overcome some of these challenges. Systems chemistry approaches form multiple products form a single synthesis under the same conditions and tend to be more similar to biological processes in that they have emergent properties, self-organization, and autocatalysis. Cyanosulfidic prebiotic synthesis is a systems chemistry approach. | 0 | Theoretical and Fundamental Chemistry |
Microbial Prospecting for oil and gas (MPOG) can be used to identify prospective areas for oil and gas occurrences. In many cases, oil and gas is known to seep toward the surface as a hydrocarbon reservoir will usually leak or have leaked towards the surface through buoyancy forces overcoming sealing pressures. These hydrocarbons can alter the chemical and microbial occurrences found in the near-surface soils or can be picked up directly. Techniques used for MPOG include DNA analysis, simple bug counts after culturing a soil sample in a hydrocarbon-based medium or by looking at the consumption of hydrocarbon gases in a culture cell. | 1 | Applied and Interdisciplinary Chemistry |
The synthesis consists of three steps. In the first step, 2-iodobenzoic acid is oxidized by sodium periodate and cyclized to 1-hydroxy-1,2-benziodoxol-3(1H)-one. The target compound can then be obtained by acylation with acetic anhydride and subsequent substitution reaction with trifluoromethyltrimethylsilane.
Alternatively, trichloroisocyanuric acid can be used as oxidant in the place of sodium periodate for a newer one-pot synthesis method. | 0 | Theoretical and Fundamental Chemistry |
For experimental setups of chemisorption, the amount of adsorption of a particular system is quantified by a sticking probability value.
However, chemisorption is very difficult to theorize. A multidimensional potential energy surface (PES) derived from effective medium theory is used to describe the effect of the surface on absorption, but only certain parts of it are used depending on what is to be studied. A simple example of a PES, which takes the total of the energy as a function of location:
where is the energy eigenvalue of the Schrödinger equation for the electronic degrees of freedom and is the ion interactions. This expression is without translational energy, rotational energy, vibrational excitations, and other such considerations.
There exist several models to describe surface reactions: the Langmuir–Hinshelwood mechanism in which both reacting species are adsorbed, and the Eley–Rideal mechanism in which one is adsorbed and the other reacts with it.
Real systems have many irregularities, making theoretical calculations more difficult:
* Solid surfaces are not necessarily at equilibrium.
* They may be perturbed and irregular, defects and such.
* Distribution of adsorption energies and odd adsorption sites.
* Bonds formed between the adsorbates.
Compared to physisorption where adsorbates are simply sitting on the surface, the adsorbates can change the surface, along with its structure. The structure can go through relaxation, where the first few layers change interplanar distances without changing the surface structure, or reconstruction where the surface structure is changed. A direct transition from physisorption to chemisorption has been observed by attaching a CO molecule to the tip of an atomic force microscope and measuring its interaction with a single iron atom.
For example, oxygen can form very strong bonds (~4 eV) with metals, such as Cu(110). This comes with the breaking apart of surface bonds in forming surface-adsorbate bonds. A large restructuring occurs by missing row. | 0 | Theoretical and Fundamental Chemistry |
While the colloidal gold assay is the most sensitive in-solution colorimetric protein assay, it may be equally sensitive or surpassed in sensitivity by fluorescent protein assays such as the CBQCA, FQ, NanoOrange, Quant-iT, and EZQ assays. | 1 | Applied and Interdisciplinary Chemistry |
Different polymer surfaces have different side chains on their monomers that can become charged due to the adsorption or dissociation of adsorbates. For example, polystyrene sulfonate has monomers containing negatively charged side chains which can adsorb positively charged adsorbates. Polystyrene sulfonate will adsorb more positively charged adsorbate than negatively charged. Conversely, for a polymer that contains positively charged side chains, such as poly(diallyldimethylammonium chloride), negatively charged adsorbates will be strongly attracted. | 0 | Theoretical and Fundamental Chemistry |
In mathematics, Ladyzhenskayas inequality is any of a number of related functional inequalities named after the Soviet Russian mathematician Olga Aleksandrovna Ladyzhenskaya. The original such inequality, for functions of two real variables, was introduced by Ladyzhenskaya in 1958 to prove the existence and uniqueness of long-time solutions to the Navier–Stokes equations in two spatial dimensions (for smooth enough initial data). There is an analogous inequality for functions of three real variables, but the exponents are slightly different; much of the difficulty in establishing existence and uniqueness of solutions to the three-dimensional Navier–Stokes equations stems from these different exponents. Ladyzhenskayas inequality is one member of a broad class of inequalities known as interpolation inequalities.
Let be a Lipschitz domain in for and let be a weakly differentiable function that vanishes on the boundary of in the sense of trace (that is, is a limit in the Sobolev space of a sequence of smooth functions that are compactly supported in ). Then there exists a constant depending only on such that, in the case :
and in the case : | 1 | Applied and Interdisciplinary Chemistry |
The regulatory subunit dimer of PKA is important for localizing the kinase inside the cell. The dimerization and docking (D/D) domain of the dimer binds to the A-kinase binding (AKB) domain of A-kinase anchor protein (AKAP). The AKAPs localize PKA to various locations (e.g., plasma membrane, mitochondria, etc.) within the cell.
AKAPs bind many other signaling proteins, creating a very efficient signaling hub at a certain location within the cell. For example, an AKAP located near the nucleus of a heart muscle cell would bind both PKA and phosphodiesterase (hydrolyzes cAMP), which allows the cell to limit the productivity of PKA, since the catalytic subunit is activated once cAMP binds to the regulatory subunits. | 1 | Applied and Interdisciplinary Chemistry |
Place has worked since the 1970s as a sculptor, jeweler and illustrator. His sculpture has been exhibited on the White House Christmas tree, in the New York State Museum, the Delaware Art Museum, and the Irish American Heritage Museum. Place’s jewelry has been exhibited in the American Craft Museum, the Philadelphia Museum of Art, the Montclair Art Museum, the Summit Art Center, the International Wilhelm Muller Competition (which toured museums in Germany), the Birmingham Institute of Art and Design, and in numerous galleries in the United States, Ireland, Britain, and Japan. He was awarded a 1984-85 New Jersey State Council on the Arts Fellowship and the Niche Magazine award for outstanding achievement in metal sculpture in 1990 and 1991. | 1 | Applied and Interdisciplinary Chemistry |
Despite the promising outcomes of the two techniques, pronuclear transfer and spindle transfer, mitochondrial gene replacement raises ethical and social concerns.
Mitochondrial donation involves modification of the germline, and hence such modifications would be passed on to subsequent generations. Using human embryos for in vitro research is also controversial, as embryos are created specifically for research and egg donors are induced to undergo the procedure by financial compensation.
Mitochondrial donation also has the potential for psychological and emotional impacts on an offspring through an effect on the person's sense of identity. Ethicists question whether the genetic make-up of children born as a result of mitochondrial replacement might affect their emotional well-being when they become aware that they are different from other healthy children conceived from two parents.
Opponents argue that scientists are "playing God" and that children with three genetic parents may suffer both psychological and physical damage.
On the other hand, New York University researcher James Grifo, a critic of the American ban, has argued that society "would never have made the advances in treating infertility that we have if these bans had been imposed 10 years" earlier.
On February 3, 2016, the Institute of Medicine of the National Academies of Sciences, Engineering, and Medicine issued a report, commissioned by the U.S. Food and Drug Administration, addressing whether it is ethically permissible for clinical research into mitochondrial replacement techniques (MRT) to continue. The report, titled Mitochondrial Replacement Techniques: Ethical, Social, and Policy Considerations, analyzes multiple facets of the arguments surrounding MRT and concludes that it is ethically permissible to continue clinical investigations of MRT, so long as certain conditions are met. It recommended that initially the technique should only be used for male embryos to ensure that DNA with potential mitochondrial disease would not be passed on.
In 2018 Carl Zimmer compared the reaction to He Jiankui's human gene editing experiment to the debate over MRT. | 1 | Applied and Interdisciplinary Chemistry |
The evolutionary zoologist Thomas N. Sherratt suggests that different types of mimicry occur in brand and product marketing. He notes that distinctive forms like the Coca-Cola bottles shape are defended by businesses, whereas rival companies have often imitated such famous motifs to benefit from the investment and reputation of their well-known competitors, constituting Batesian mimicry. Sherratt observes that the packaging of British supermarket own brands of potato crisps are consistently colour-coded red for the ready-salted variety, green for salt and vinegar, and blue for cheese and onion, across the major chains Sainsburys, Tesco, Asda, and Waitrose. He argues that this sharing of pattern is very unlikely to have arisen by chance, in which case the resemblance is intentionally to inform customers reliably (honest signalling) of what each package contains, to mutual benefit in the manner of Müllerian mimicry. | 1 | Applied and Interdisciplinary Chemistry |
By sperm washing, the risk that a chronic disease in the individual providing the sperm would infect the birthing parent or offspring can be brought to negligible levels.
If the sperm donor has hepatitis B, The Practice Committee of the American Society for Reproductive Medicine advises that sperm washing is not necessary in IVF to prevent transmission, unless the birthing partner has not been effectively vaccinated. In birthing people with hepatitis B, the risk of vertical transmission during IVF is no different from the risk in spontaneous conception. However, there is not enough evidence to say that ICSI procedures are safe in birthing people with hepatitis B in regard to vertical transmission to the offspring.
Regarding potential spread of HIV/AIDS, Japan's government prohibited the use of IVF procedures in which both partners are infected with HIV. Despite the fact that the ethics committees previously allowed the Ogikubo, Tokyo Hospital, located in Tokyo, to use IVF for couples with HIV, the Ministry of Health, Labour and Welfare of Japan decided to block the practice. Hideji Hanabusa, the vice president of the Ogikubo Hospital, states that together with his colleagues, he managed to develop a method through which scientists are able to remove HIV from sperm.
In the United States, people seeking to be an embryo recipient undergo infectious disease screening required by the Food and Drug Administration (FDA), and reproductive tests to determine the best placement location and cycle timing before the actual embryo transfer occurs. The amount of screening the embryo has already undergone is largely dependent on the genetic parents' own IVF clinic and process. The embryo recipient may elect to have their own embryologist conduct further testing. | 1 | Applied and Interdisciplinary Chemistry |
In 1910, Goldberg married Ullman. In 1923, they moved back to Geneva when Ullman accepted a faculty position at Geneva University.
Her exact death date is not known, but her name does appear at the top of a list of people signing a memorial notice in a Geneva newspaper for her deceased husband, Fritz Ullmann in 1939. | 0 | Theoretical and Fundamental Chemistry |
Detailed predictions were made in the late 1970s for the production of jets at the CERN Super Proton–Antiproton Synchrotron. UA2 observed the first evidence for jet production in hadron collisions in 1981, which shortly after was confirmed by UA1.
The subject was later revived at RHIC. One of the most striking physical effects obtained at RHIC energies is the effect of quenching jets. At the first stage of interaction of colliding relativistic nuclei, partons of the colliding nuclei give rise to the secondary partons with a large transverse impulse ≥ 3–6 GeV/s. Passing through a highly heated compressed plasma, partons lose energy. The magnitude of the energy loss by the parton depends on the properties of the quark–gluon plasma (temperature, density). In addition, it is also necessary to take into account the fact that colored quarks and gluons are the elementary objects of the plasma, which differs from the energy loss by a parton in a medium consisting of colorless hadrons. Under the conditions of a quark–gluon plasma, the energy losses resulting from the RHIC energies by partons are estimated as . This conclusion is confirmed by comparing the relative yield of hadrons with a large transverse impulse in nucleon-nucleon and nucleus-nucleus collisions at the same collision energy. The energy loss by partons with a large transverse impulse in nucleon-nucleon collisions is much smaller than in nucleus-nucleus collisions, which leads to a decrease in the yield of high-energy hadrons in nucleus-nucleus collisions. This result suggests that nuclear collisions cannot be regarded as a simple superposition of nucleon-nucleon collisions. For a short time, ~1 μs, and in the final volume, quarks and gluons form some ideal liquid. The collective properties of this fluid are manifested during its movement as a whole. Therefore, when moving partons in this medium, it is necessary to take into account some collective properties of this quark–gluon liquid. Energy losses depend on the properties of the quark–gluon medium, on the parton density in the resulting fireball, and on the dynamics of its expansion. Losses of energy by light and heavy quarks during the passage of a fireball turn out to be approximately the same.
In November 2010 CERN announced the first direct observation of jet quenching, based on experiments with heavy-ion collisions. | 0 | Theoretical and Fundamental Chemistry |
For calculating the flow of liquid with a free surface, the hydraulic radius must be determined. This is the cross-sectional area of the channel divided by the wetted perimeter. For a semi-circular channel, it is a quarter of the diameter (in case of full pipe flow). For a rectangular channel, the hydraulic radius is the cross-sectional area divided by the wetted perimeter. Some texts then use a characteristic dimension that is four times the hydraulic radius, chosen because it gives the same value of for the onset of turbulence as in pipe flow, while others use the hydraulic radius as the characteristic length-scale with consequently different values of for transition and turbulent flow. | 1 | Applied and Interdisciplinary Chemistry |
Polyurethane foam is a specialist material used for thermal insulation and other applications. It is a solid polymeric foam based on polyurethane chemistry. | 0 | Theoretical and Fundamental Chemistry |
Transcriptional adaptation is a recently described type of genetic compensation by which a mutation in one gene leads to the transcriptional modulation of related genes, termed adapting genes or modifiers. | 1 | Applied and Interdisciplinary Chemistry |
Within statistical mechanics, the LCST may be modeled theoretically via the lattice fluid model, an extension of Flory–Huggins solution theory, that incorporates vacancies, and thus accounts for variable density and compressibility effects. | 0 | Theoretical and Fundamental Chemistry |
The cephalosporin class is very extensive so a good classification system is necessary to distinguish different cephalosporins from each other. There are few chemical and activity features that could be used for classification, for example chemical structure, side chain properties, pharmacokinetic, spectrum of activity or clinical properties. Despite these variable features the most common classification system for cephalosporins is to divide them into generations. The generation system is based on different antimicrobial activity shown by different cephalosporins. | 1 | Applied and Interdisciplinary Chemistry |
Bioluminescence is the process of light emission in living organisms. Bioluminescence imaging utilizes native light emission from one of several organisms which bioluminesce, also known as luciferase enzymes. The three main sources are the North American firefly, the sea pansy (and related marine organisms), and bacteria like Photorhabdus luminescens and Vibrio fischeri. The DNA encoding the luminescent protein is incorporated into the laboratory animal either via a viral vector or by creating a transgenic animal. Rodent models of cancer spread can be studied through bioluminescence imaging.for e.g.Mouse models of breast cancer metastasis.
Systems derived from the three groups above differ in key ways:
* Firefly luciferase requires D-luciferin to be injected into the subject prior to imaging. The peak emission wavelength is about 560 nm. Due to the attenuation of blue-green light in tissues, the red-shift (compared to the other systems) of this emission makes detection of firefly luciferase much more sensitive in vivo.
* Renilla luciferase (from the Sea pansy) requires its substrate, coelenterazine, to be injected as well. As opposed to luciferin, coelenterazine has a lower bioavailability (likely due to MDR1 transporting it out of mammalian cells). Additionally, the peak emission wavelength is about 480 nm.
* Bacterial luciferase has an advantage in that the lux operon used to express it also encodes the enzymes required for substrate biosynthesis. Although originally believed to be functional only in prokaryotic organisms, where it is widely used for developing bioluminescent pathogens, it has been genetically engineered to work in mammalian expression systems as well. This luciferase reaction has a peak wavelength of about 490 nm.
While the total amount of light emitted from bioluminescence is typically small and not detected by the human eye, an ultra-sensitive CCD camera can image bioluminescence from an external vantage point. | 1 | Applied and Interdisciplinary Chemistry |
Copper-catalyzed allylic substitutions are chemical reactions with unique regioselectivity compared to other transition-metal-catalyzed allylic substitutions such as the Tsuji-Trost reaction. They involve copper catalysts and "hard" carbon nucleophiles. The mechanism of copper-catalyzed allylic substitutions involves the coordination of copper to the olefin, oxidative addition and reductive elimination. Enantioselective versions of these reactions have been used in the synthesis of complex molecules, such as (R)-(-)-sporochnol and (S)-(-)-zearalenone. | 0 | Theoretical and Fundamental Chemistry |
It may be used in combination with other antibiotics to treat pneumonia and can be used to prevent infection before surgery, particularly heart, lung, or bone surgery. When used to treat endocarditis, in combination with other antibiotics or alone, the dose of flucloxacillin may need to exceed the usual dose. | 0 | Theoretical and Fundamental Chemistry |
In humans, anandamide is biosynthesized from N-arachidonoyl phosphatidylethanolamine (NAPE). In turn, NAPE arises by transfer of arachidonic acid from lecithin to the free amine of cephalin through an N-acyltransferase enzyme. Anandamide synthesis from NAPE occurs via multiple pathways and includes enzymes such as phospholipase A2, phospholipase C and N-acetylphosphatidylethanolamine-hydrolysing phospholipase D (NAPE-PLD).
The crystal structure of NAPE-PLD in complex with phosphatidylethanolamine and deoxycholate shows how the cannabinoid anandamide is generated from membrane N-acylphosphatidylethanolamines (NAPEs), and reveals that bile acids – which are mainly involved in the absorption of lipids in the small intestine – modulate its biogenesis.
Endogenous anandamide is present at very low levels and has a very short half-life due to the action of the enzyme fatty acid amide hydrolase (FAAH), which breaks it down into free arachidonic acid and ethanolamine. Studies of piglets show that dietary levels of arachidonic acid and other essential fatty acids affect the levels of anandamide and other endocannabinoids in the brain. High fat diet feeding in mice increases levels of anandamide in the liver and increases lipogenesis. Anandamide may be relevant to the development of obesity, at least in rodents.
Paracetamol (called acetaminophen in the US and Canada) is metabolically combined with arachidonic acid by FAAH to form AM404. This metabolite of paracetamol is a potent agonist at the TRPV1 vanilloid receptor, a weak agonist at both CB and CB receptors, and an inhibitor of anandamide reuptake. As a result, anandamide levels in the body and brain are elevated. In this fashion, paracetamol acts as a pro-drug for a cannabimimetic metabolite. This action may be partially or fully responsible for the analgesic effects of paracetamol.
Endocannabinoid transporters for anandamide and 2-arachidonoylglycerol include the heat shock proteins (Hsp70s) and fatty acid binding proteins (FABPs).
It is found that anandamide prefers cholesterol and ceramide more than other membrane lipids, and cholesterol can behave as a binding partner for it, and following an initial interaction mediated by the establishment of a hydrogen bond, the endocannabinoid is attracted towards the membrane interior, where it forms a molecular complex with cholesterol after a functional conformation adaptation to the apolar membrane milieu, and from there, the complex is further directed to the cannabinoid receptor (CB1) and out. | 1 | Applied and Interdisciplinary Chemistry |
Each article at WikiPathways is dedicated to a particular pathway. Many types of molecular pathways are covered, including metabolic, signaling, regulatory, etc. and the supported species include human, mouse, zebrafish, fruit fly, C. elegans, yeast, rice and arabidopsis, as well as bacteria and plant species. Using a search feature, one can locate a particular pathway by name, by the genes and proteins it contains, or by the text displayed in its description. The pathway collection can also be browsed with combinations of species names and ontology-based categories.
In addition to the pathway diagram, each pathway page also includes a description, bibliography, pathway version history and list of component genes and proteins with linkouts to public resources. For individual pathway nodes, users can access a list of other pathways with that node. Pathway changes can be monitored by displaying previous revisions or by viewing differences between specific revisions. Using the pathway history one can also revert to a previous revision of a pathway.
Pathways can also be tagged with ontology terms from three major BioPortal ontologies (Pathway, Disease and Cell Type).
The pathway content at WikiPathways is freely available for download in several data and image formats. WikiPathways is completely open access and open source. All content is available under [http://www.wikipathways.org/index.php/WikiPathways:License_Terms Creative Commons 0]. All source code for WikiPathways and the PathVisio editor is available under the [http://www.apache.org/licenses/ Apache License, Version 2.0]. | 1 | Applied and Interdisciplinary Chemistry |
In a normal thermal reactor, tin-121m has a very low fission product yield; thus, this isotope is not a significant contributor to nuclear waste. Fast fission or fission of some heavier actinides will produce Sn at higher yields. For example, its yield from U-235 is 0.0007% per thermal fission and 0.002% per fast fission. | 0 | Theoretical and Fundamental Chemistry |
Brinelling is a material surface failure caused by Hertz contact stress that exceeds the material limit. It usually occurs in situations where a significant load force is distributed over a relatively small surface area. Brinelling typically results from a heavy or repeated impact load, either while stopped or during rotation, though it can also be caused by just one application of a force greater than the material limit.
Brinelling can be caused by a heavy load resting on a stationary bearing for an extended length of time. The result is a permanent dent or "brinell mark". The brinell marks will often appear in evenly spaced patterns along the bearing races, resembling the primary elements of the bearing, such as rows of indented lines for needle or roller bearings or rounded indentations in ball bearings. It is a common cause of roller bearing failures, and loss of preload in bolted joints when a hardened washer is not used. For example, brinelling occurs in casters when the ball bearings within the swivel head produce grooves in the hard cap, thus degrading performance by increasing the required swivel force. | 1 | Applied and Interdisciplinary Chemistry |
SLMDs are known to accumulate cadmium, cobalt, copper, nickel, lead, and zinc, and have been deployed in freshwater monitoring studies by The Washington State Department of Ecology (Ecology) and the USGS.
Ecology deployed SLMDs in upper and lower Indian Creek for 28 and 27 days respectively. Metal concentrations on the SLMDs were used to estimate the true concentration of metals in the creek. The estimated concentration was expressed as a range based on sampling rate of SLMDs as well as the length of exposure. The purpose of the sampling was to investigate potential causes of sublethal effects of young trout and loss of benthic biodiversity in the creek. | 0 | Theoretical and Fundamental Chemistry |
Paraffinic hydrocarbons are part of the alkane series, and are the most common hydrocarbon found in crude oil. Paraffins are often a part of gasoline, making them comparatively more valuable.
Paraffinic hydrocarbons are also known as alkanes, and are represented by the formula CH, where n is a positive integer. | 0 | Theoretical and Fundamental Chemistry |
* Diplôme dÉtat de chimiste, École denseignement technique féminine, 1929
* Doctorat des Sciences, Sorbonne, 1946 | 1 | Applied and Interdisciplinary Chemistry |
Pyrazinamide has at least 4 polymorphs. All of them transforms to stable α form at room temperature upon storage or mechanical treatment. Recent studies prove that α form is thermodynamically stable at room temperature. | 0 | Theoretical and Fundamental Chemistry |
The extent of adsorption at a liquid interface can be evaluated using the surface tension concentration data and the Gibbs adsorption equation. The microtome blade method is used to determine the weight and molal concentration of an interface. The method involves attaining a one square meter portion of air-liquid interface of binary solutions using a microtome blade.
Another method that is used to determine the extent of adsorption at an air-water interface is the emulsion technique, which can be used to estimate the relative surface excess with respect to water.
Additionally, the Gibbs surface excess of a surface active component for an aqueous solution can be found using the radioactive tracer method. The surface active component is usually labeled with carbon-14 or sulfur-35. | 0 | Theoretical and Fundamental Chemistry |
Fragment-based lead discovery (FBLD) also known as fragment-based drug discovery (FBDD) is a method used for finding lead compounds as part of the drug discovery process. Fragments are small organic molecules which are small in size and low in molecular weight. It is based on identifying small chemical fragments, which may bind only weakly to the biological target, and then growing them or combining them to produce a lead with a higher affinity. FBLD can be compared with high-throughput screening (HTS). In HTS, libraries with up to millions of compounds, with molecular weights of around 500 Da, are screened, and nanomolar binding affinities are sought. In contrast, in the early phase of FBLD, libraries with a few thousand compounds with molecular weights of around 200 Da may be screened, and millimolar affinities can be considered useful. FBLD is a technique being used in research for discovering novel potent inhibitors. This methodology could help to design multitarget drugs for multiple diseases. The multitarget inhibitor approach is based on designing an inhibitor for the multiple targets. This type of drug design opens up new polypharmacological avenues for discovering innovative and effective therapies. Neurodegenerative diseases like Alzheimer’s (AD) and Parkinson’s, among others, also show rather complex etiopathologies. Multitarget inhibitors are more appropriate for addressing the complexity of AD and may provide new drugs for controlling the multifactorial nature of AD, stopping its progression. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, thioesters are organosulfur compounds with the molecular structure . They are analogous to carboxylate esters () with the sulfur in the thioester replacing oxygen in the carboxylate ester, as implied by the thio- prefix. They are the product of esterification of a carboxylic acid () with a thiol (). In biochemistry, the best-known thioesters are derivatives of coenzyme A, e.g., acetyl-CoA. The R and R' represent organyl groups, or H in the case of R. | 0 | Theoretical and Fundamental Chemistry |
Batesian mimicry is a case of protective or defensive mimicry, where the mimic does best by avoiding confrontations with the signal receiver. It is a disjunct system, which means that all three parties are from different species. An example would be the robber fly Mallophora bomboides, which is a Batesian mimic of its bumblebee model and prey, B. americanorum (now more commonly known as Bombus pensylvanicus), which is noxious to predators due to its sting.
Batesian mimicry stands in contrast to other forms such as aggressive mimicry, where the mimic profits from interactions with the signal receiver. One such case of this is in fireflies, where females of one species mimic the mating signals of another species, deceiving males to come close enough for them to eat. Mimicry sometimes does not involve a predator at all though. Such is the case in dispersal mimicry, where the mimic once again benefits from the encounter. For instance, some fungi have their spores dispersed by insects by smelling like carrion. In protective mimicry, the meeting between mimic and dupe is not such a fortuitous occasion for the mimic, and the signals it mimics tend to lower the probability of such an encounter.
A case somewhat similar to Batesian mimicry is that of mimetic weeds, which imitate agricultural crops. In weed or Vavilovian mimicry, the weed survives by having seeds which winnowing machinery identifies as belonging to the crop. Vavilovian mimicry is not Batesian, because man and crop are not enemies. By contrast, a leaf-mimicking plant, the chameleon vine, employs Batesian mimicry by adapting its leaf shape and colour to match that of its host to deter herbivores from eating its edible leaves.
Another analogous case within a single species has been termed Browerian mimicry (after Lincoln P. Brower and Jane Van Zandt Brower). This is a case of automimicry; the model is the same species as its mimic. Equivalent to Batesian mimicry within a single species, it occurs when there is a palatability spectrum within a population of harmful prey. For example, monarch (Danaus plexippus) caterpillars feed on milkweed species of varying toxicity. Some feed on more toxic plants and store these toxins within themselves. The more palatable caterpillars thus profit from the more toxic members of the same species.
Another important form of protective mimicry is Müllerian mimicry, discovered by and named after the naturalist Fritz Müller. In Müllerian mimicry, both model and mimic are aposematic, so mimicry may be mutual, does not necessarily constitute a bluff or deception and as in the wasps and bees may involve many species in a mimicry ring. | 1 | Applied and Interdisciplinary Chemistry |
Sodium trimethylsilyl propionate (TSP) is a related compound used as an NMR standard. It uses a carboxylic acid instead of the sulfonic acid found in DSS to confer water solubility. As a weak acid, TSP is more sensitive to changes in pH.
4,4-Dimethyl-4-silapentane-1-ammonium trifluoroacetate (DSA) has also been proposed as an alternative, to overcome certain drawbacks of DSS. | 0 | Theoretical and Fundamental Chemistry |
The cyclization of the enediyne functional group creates a transient reactive 1,4-benzenoid diradical that acts as a nucleophile and attacks electrophiles in order to achieve a more stable form. In biological systems, once the diradical is positioned in the minor groove of double-stranded DNA, it abstracts two hydrogen atoms from the sugars opposite strands at either the C1, C4, or C5 positions. The DNA radicals that form can then cause interstrand crosslinks or react with O, leading to double- or single-stranded DNA cleavage. | 0 | Theoretical and Fundamental Chemistry |
Albert devoted the last tractatus of De Bono to a theory of justice and natural law. Albert places God as the pinnacle of justice and natural law. God legislates and divine authority is supreme. Up until his time, it was the only work specifically devoted to natural law written by a theologian or philosopher. | 1 | Applied and Interdisciplinary Chemistry |
Chiral inversion is the process of conversion of one enantiomer of a chiral molecule to its mirror-image version with no other change in the molecule.
Chiral inversion happens depending on various factors (viz. biological-, solvent-, light-, temperature- induced, etc.) and the energy barrier associated with the stereogenic element present in the chiral molecule. 2-Arylpropionic acid nonsteroidal anti-inflammatory drugs (NSAIDs) provide one of the best pharmaceutical examples of chiral inversion. Chirality is attributed to a molecule due to the presence of a stereogenic element (viz. center, planar, helical, or axis). Many pharmaceutical drugs are chiral and have a labile (configurationally unstable) stereogenic element. Chiral compounds with stereogenic center are found to have high energy barriers for inversion and generally undergo biologically mediated chiral inversion. While compounds with helical or planar chirality have low energy barriers and chiral inversions are often caused by solvent, light, temperature. When this happens, the configuration of the chiral molecule may rapidly change reversibly or irreversibly depending on the conditions. The chiral inversion has been intensively studied in the context of the pharmacological and toxicological consequences. Other than NSAIDs, chiral drugs with different chemical structures can also show this effect.
Chiral drugs have different effects on the body depending on whether one enantiomer or both enantiomers act on different biological targets. As a result, chiral inversion can change how a pharmaceutical drug works in the body. From a pharmacological and toxicological point of view, it is very important to learn more about chiral inversion, the things that make it happen, and the tools used to figure out chiral inversion. | 0 | Theoretical and Fundamental Chemistry |
NacNac ligands are diimine analogues of acetylacetonate ligands. An intermediate class of ligands are derived from monoimino-ketones. The first Dipp-NacNac ligand was synthesized by Dr. Francis S. Mair in 1998. | 0 | Theoretical and Fundamental Chemistry |
*Alkylation
*Methoxy
*Titanium–zinc methylenation
*Petasis reagent
*Nysted reagent
*Wittig reaction
*Tebbe's reagent | 0 | Theoretical and Fundamental Chemistry |
Only two elements are liquid at standard conditions for temperature and pressure: mercury and bromine. Four more elements have melting points slightly above room temperature: francium, caesium, gallium and rubidium. In addition, certain mixtures of elements are liquid at room temperature, even if the individual elements are solid under the same conditions (see eutectic mixture). An example is the sodium-potassium metal alloy NaK. Other metal alloys that are liquid at room temperature include galinstan, which is a gallium-indium-tin alloy that melts at , as well as some amalgams (alloys involving mercury).
Pure substances that are liquid under normal conditions include water, ethanol and many other organic solvents. Liquid water is of vital importance in chemistry and biology, and it is necessary for all known forms of life.
Inorganic liquids include water, magma, inorganic nonaqueous solvents and many acids.
Important everyday liquids include aqueous solutions like household bleach, other mixtures of different substances such as mineral oil and gasoline, emulsions like vinaigrette or mayonnaise, suspensions like blood, and colloids like paint and milk.
Many gases can be liquefied by cooling, producing liquids such as liquid oxygen, liquid nitrogen, liquid hydrogen and liquid helium. Not all gases can be liquified at atmospheric pressure, however. Carbon dioxide, for example, can only be liquified at pressures above 5.1 atm.
Some materials cannot be classified within the classical three states of matter. For example, liquid crystals (used in liquid-crystal displays) possess both solid-like and liquid-like properties, and belong to their own state of matter distinct from either liquid or solid. | 0 | Theoretical and Fundamental Chemistry |
The chemical plant Chemko in Strážske (east Slovakia) was an important producer of polychlorinated biphenyls for the former communist bloc (Comecon) until 1984. Chemko contaminated a large part of east Slovakia, especially the sediments of the Laborec river and reservoir Zemplínska šírava. | 1 | Applied and Interdisciplinary Chemistry |
In the 1970s and 1980s improved application technologies such as controlled droplet application (CDA) received extensive research interest, but commercial uptake has been disappointing. By controlling droplet size, ultra-low volume (ULV) or very low volume (VLV) application rates of pesticidal mixtures can achieve similar (or sometimes better) biological results by improved timing and dose-transfer to the biological target (i.e. pest). No atomizer has been developed able to produce uniform (monodisperse) droplets, but rotary (spinning disc and cage) atomizers usually produce a more uniform droplet size spectrum than conventional hydraulic nozzles (see: [http://www.dropdata.org/DD/sprayers.htm#CDA CDA & ULV application equipment]). Other efficient application techniques include: banding, baiting, specific granule placement, seed treatments and weed wiping.
CDA is a good example of a rational pesticide use (RPU) technology (Bateman, 2003), but unfortunately has been unfashionable with public funding bodies since the early 1990s, with many believing that all pesticide development should be the responsibility of pesticide manufacturers. On the other hand, pesticide companies are unlikely widely to promote better targeting and thus reduced pesticide sales, unless they can benefit by adding value to products in some other way. RPU contrasts dramatically with the promotion of pesticides, and many agrochemical concerns, have equally become aware that product stewardship provides better long-term profitability than high pressure salesmanship of a dwindling number of new “silver bullet” molecules. RPU may therefore provide an appropriate framework for collaboration between many of the stake-holders in crop protection.
Understanding the biology and life cycle of the pest is also an important factor in determining droplet size. The Agricultural Research Service, for example, has conducted tests to determine the ideal droplet size of a pesticide used to combat corn earworms. They found that in order to be effective, the pesticide needs to penetrate through the corns silk, where the earworms larvae hatch. The research concluded that larger pesticide droplets best penetrated the targeted corn silk. Knowing where the pest's destruction originates is crucial in targeting the amount of pesticide needed. | 1 | Applied and Interdisciplinary Chemistry |
As a result of the surface tension inherent to liquids, curved surfaces are formed in order to minimize the area. This phenomenon arises from the energetic cost of forming a surface. As such the Gibbs free energy of the system is minimized when the surface is curved.
The Kelvin equation is based on thermodynamic principles and is used to describe changes in vapor pressure caused by liquids with curved surfaces. The cause for this change in vapor pressure is the Laplace pressure. The vapor pressure of a drop is higher than that of a planar surface because the increased Laplace pressure causes the molecules to evaporate more easily. Conversely, in liquids surrounding a bubble, the pressure with respect to the inner part of the bubble is reduced, thus making it more difficult for molecules to evaporate. The Kelvin equation can be stated as:
where is the vapor pressure of the curved surface, is the vapor pressure of the flat surface, is the surface tension, is the molar volume of the liquid, is the universal gas constant, is temperature (in kelvin), and and are the principal radii of curvature of the surface. | 0 | Theoretical and Fundamental Chemistry |
Intraoperative radiation therapy (IORT) is applying therapeutic levels of radiation to a target area, such as a cancer tumor, while the area is exposed during surgery. | 0 | Theoretical and Fundamental Chemistry |
* Instead of relying on standard diffusion to transfer the proteins from the gel to the filter, electroblotting is commonly used because it removes the denaturing agent SDS thereby allowing the proteins to renature as they move to the filter.
* Skim milk is added to the filter before hybridizing with probes as it contains Bovine Serum Albumin (BSA) which prevents any unwanted or weak interactions of DNA to the nitrocellulose membrane.
* A rapid dimethylsulphate (DMS) protection assay can be used to identify non-specific binding vs. specific binding on blots.
* During the DNA probe hybridization step, defined amounts of salt are used to enhance specific interactions that occur between the DNA and proteins. | 1 | Applied and Interdisciplinary Chemistry |
A spectrohelioscope is a type of solar telescope designed by George Ellery Hale in 1924 to allow the Sun to be viewed in a selected wavelength of light. The name comes from Latin- and Greek-based words: "Spectro," referring to the optical spectrum, "helio," referring to the Sun, and "scope," as in telescope.
The basic spectrohelioscope is a complex machine that uses a spectroscope to scan the surface of the Sun. The image from the objective lens is focused on a narrow slit revealing only a thin portion of the Suns surface. The light is then passed through a prism or diffraction grating to spread the light into a spectrum. The spectrum is then focused on another slit that allows only a narrow part of the spectrum (the desired wavelength of light for viewing) to pass. The light is finally focused on an eyepiece so the surface of the Sun can be seen. The view, however, would be only a narrow strip of the Suns surface. The slits are moved in unison to scan across the whole surface of the Sun giving a full image. Independently nodding mirrors can be used instead of moving slits to produce the same scan: the first mirror selects a slice of the Sun, the second selects the desired wavelength.
The spectroheliograph is a similar device, but images the Sun at a particular wavelength photographically and is still in use in professional observatories. | 0 | Theoretical and Fundamental Chemistry |
In November 1949, with the seminal paper, "Sickle Cell Anemia, a Molecular Disease", in Science magazine, Linus Pauling, Harvey Itano and their collaborators laid the groundwork for establishing the field of molecular medicine. In 1956, Roger J. Williams wrote Biochemical Individuality, a prescient book about genetics, prevention and treatment of disease on a molecular basis, and nutrition which is now variously referred to as individualized medicine and orthomolecular medicine. Another paper in Science by Pauling in 1968, introduced and defined this view of molecular medicine that focuses on natural and nutritional substances used for treatment and prevention.
Published research and progress was slow until the 1970s' "biological revolution" that introduced many new techniques and commercial applications. | 1 | Applied and Interdisciplinary Chemistry |
Molecular recognition and self-assembly may be used with reactive species in order to pre-organize a system for a chemical reaction (to form one or more covalent bonds). It may be considered a special case of supramolecular catalysis. Non-covalent bonds between the reactants and a "template" hold the reactive sites of the reactants close together, facilitating the desired chemistry. This technique is particularly useful for situations where the desired reaction conformation is thermodynamically or kinetically unlikely, such as in the preparation of large macrocycles. This pre-organization also serves purposes such as minimizing side reactions, lowering the activation energy of the reaction, and producing desired stereochemistry. After the reaction has taken place, the template may remain in place, be forcibly removed, or may be "automatically" decomplexed on account of the different recognition properties of the reaction product. The template may be as simple as a single metal ion or may be extremely complex. | 0 | Theoretical and Fundamental Chemistry |
For compounds with the formula MX, the chief alternative to octahedral geometry is a trigonal prismatic geometry, which has symmetry D. In this geometry, the six ligands are also equivalent. There are also distorted trigonal prisms, with C symmetry; a prominent example is . The interconversion of Δ- and Λ-complexes, which is usually slow, is proposed to proceed via a trigonal prismatic intermediate, a process called the "Bailar twist". An alternative pathway for the racemization of these same complexes is the Ray–Dutt twist. | 0 | Theoretical and Fundamental Chemistry |
In polynuclear compounds with metal-metal bonds these are shown after the element name as follows:
(3 Os—Os) in Decacarbonyldihydridotriosmium.
A pair of brackets contain a count of the bonds formed (if greater than 1), followed by the italicised element atomic symbols separated by an "em-dash". | 0 | Theoretical and Fundamental Chemistry |
Perturb-seq couples CRISPR mediated gene knockdowns with single-cell gene expression. Linear models are used to calculate the effect of the knockdown of a single gene on the expression of multiple genes. | 1 | Applied and Interdisciplinary Chemistry |
In 2007, G. Wrigge, I. Gerhardt, J. Hwang, G. Zumofen, and V. Sandoghdar developed an efficient method to observe resonance fluorescence for an entire molecule as opposed to its typical observation in a single atom.
Instead of coupling the electric field to a single atom, they were able to replicate two-level systems in dye molecules embedded in solids.
They used a tunable dye laser to excite the dye molecules in their sample. Due to the fact that they could only have one source at a time, the proportion of shot noise to actual data was much higher than normal. The sample which they excited was a Shpol'skii matrix which they had doped with the dyes they wished to use, dibenzanthanthrene. To improve the accuracy of the results, single-molecule fluorescence-excitation spectroscopy was used. The actual process for measuring the resonance was measuring the interference between the laser beam and the photons that were scattered from the molecule. Thus the laser was passed over the sample, resulting in several photons were scattered back, allowing for the measurement of the interference in the electromagnetic field that resulted. The improvement to this technique was they used solid-immersion lens technology. This is a lens that has a much higher numerical aperture than normal lenses as it is filled with a material that has a large refractive index. The technique used to measure the resonance fluorescence in this system was originally designed to locate individual molecules within substances. | 0 | Theoretical and Fundamental Chemistry |
The Moon stands out as being very depleted in volatiles.
The Moon not only lacks water and atmospheric gases, but also lacks moderately volatile elements such as K, Na, and Cl. The Earth's K/U ratio is 12,000, while the Moon has a K/U ratio of only 2,000. This difference suggests that the material that formed the Moon was subjected to temperatures considerably higher than the Earth.
The prevailing theory is that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago, about 20 to 100 million years after the Solar System coalesced. This is called the Giant-impact hypothesis.
It is hypothesized that most of the outer silicates of the colliding body would be vaporized, whereas a metallic core would not. Hence, most of the collisional material sent into orbit would consist of silicates, leaving the coalescing Moon deficient in iron. The more volatile materials that were emitted during the collision probably would escape the Solar System, whereas silicates would tend to coalesce.
The ratios of the Moon's volatile elements are not explained by the giant-impact hypothesis. If the giant-impact hypothesis is correct, they must be due to some other cause. | 0 | Theoretical and Fundamental Chemistry |
Small nuclei that are larger than hydrogen can combine into bigger ones and release energy, but in combining such nuclei, the amount of energy released is much smaller compared to hydrogen fusion. The reason is that while the overall process releases energy from letting the nuclear attraction do its work, energy must first be injected to force together positively charged protons, which also repel each other with their electric charge.
For elements that weigh more than iron (a nucleus with 26 protons), the fusion process no longer releases energy. In even heavier nuclei energy is consumed, not released, by combining similarly sized nuclei. With such large nuclei, overcoming the electric repulsion (which affects all protons in the nucleus) requires more energy than is released by the nuclear attraction (which is effective mainly between close neighbors). Conversely, energy could actually be released by breaking apart nuclei heavier than iron.
With the nuclei of elements heavier than lead, the electric repulsion is so strong that some of them spontaneously eject positive fragments, usually nuclei of helium that form stable alpha particles. This spontaneous break-up is one of the forms of radioactivity exhibited by some nuclei.
Nuclei heavier than lead (except for bismuth, thorium, and uranium) spontaneously break up too quickly to appear in nature as primordial elements, though they can be produced artificially or as intermediates in the decay chains of heavier elements. Generally, the heavier the nuclei are, the faster they spontaneously decay.
Iron nuclei are the most stable nuclei (in particular iron-56), and the best sources of energy are therefore nuclei whose weights are as far removed from iron as possible. One can combine the lightest ones—nuclei of hydrogen (protons)—to form nuclei of helium, and that is how the Sun generates its energy. Alternatively, one can break up the heaviest ones—nuclei of uranium or plutonium—into smaller fragments, and that is what nuclear reactors do. | 0 | Theoretical and Fundamental Chemistry |
The crystallographic directions are geometric lines linking nodes (atoms, ions or molecules) of a crystal. Likewise, the crystallographic planes are geometric planes linking nodes. Some directions and planes have a higher density of nodes. These high density planes have an influence on the behavior of the crystal as follows:
*Optical properties: Refractive index is directly related to density (or periodic density fluctuations).
*Adsorption and reactivity: Physical adsorption and chemical reactions occur at or near surface atoms or molecules. These phenomena are thus sensitive to the density of nodes.
*Surface tension: The condensation of a material means that the atoms, ions or molecules are more stable if they are surrounded by other similar species. The surface tension of an interface thus varies according to the density on the surface.
*Microstructural defects: Pores and crystallites tend to have straight grain boundaries following higher density planes.
*Cleavage: This typically occurs preferentially parallel to higher density planes.
*Plastic deformation: Dislocation glide occurs preferentially parallel to higher density planes. The perturbation carried by the dislocation (Burgers vector) is along a dense direction. The shift of one node in a more dense direction requires a lesser distortion of the crystal lattice.
Some directions and planes are defined by symmetry of the crystal system. In monoclinic, trigonal, tetragonal, and hexagonal systems there is one unique axis (sometimes called the principal axis) which has higher rotational symmetry than the other two axes. The basal plane is the plane perpendicular to the principal axis in these crystal systems. For triclinic, orthorhombic, and cubic crystal systems the axis designation is arbitrary and there is no principal axis. | 0 | Theoretical and Fundamental Chemistry |
Transcription factor 7-like 2 (T-cell specific, HMG-box), also known as TCF7L2 or TCF4, is a protein acting as a transcription factor that, in humans, is encoded by the TCF7L2 gene. The TCF7L2 gene is located on chromosome 10q25.2–q25.3, contains 19 exons. As a member of the TCF family, TCF7L2 can form a bipartite transcription factor and influence several biological pathways, including the Wnt signalling pathway.
Single-nucleotide polymorphisms (SNPs) in this gene are especially known to be linked to higher risk to develop type 2 diabetes, gestational diabetes, multiple neurodevelopmental disorders including schizophrenia and autism spectrum disorder, as well as other diseases. The SNP rs7903146, within the TCF7L2 gene, is, to date, the most significant genetic marker associated with type 2 diabetes risk. | 1 | Applied and Interdisciplinary Chemistry |
Stereographic projection is also applied to the visualization of polytopes. In a Schlegel diagram, an -dimensional polytope in is projected onto an -dimensional sphere, which is then stereographically projected onto . The reduction from to can make the polytope easier to visualize and understand. | 0 | Theoretical and Fundamental Chemistry |
The lac repressor was first isolated by Walter Gilbert and Benno Müller-Hill in 1966. They showed that in vitro the protein bound to DNA containing the lac operon, and it released the DNA when IPTG (an analog of allolactose) was added. | 1 | Applied and Interdisciplinary Chemistry |
An acid test is a qualitative chemical or metallurgical assay utilizing acid. Historically, it often involved the use of a robust acid to distinguish gold from base metals. Figuratively, the term represents any definitive test for attributes, such as gauging a persons character or evaluating a products performance. | 0 | Theoretical and Fundamental Chemistry |
B. D. Kulkarni, born on 5 May 1949 into a Deshastha Brahmin family in Nagpur in the western Indian state of Maharashtra, did his schooling at New English High School and after passing the matriculation with distinction in 1964, he did his pre-university course at Hislop College before joining Laxminarayan Institute of Technology of Nagpur University from where he graduated in chemical engineering in 1970. He continued there to complete his master's degree in chemical engineering in 1972 and enrolled at National Chemical Laboratory, Pune (NCL) in 1973 for his doctoral degree under the guidance of L. K. Doraiswamy, a noted chemical engineer and Padma Bhushan recipient. He worked under Doraiswamy, who is credited with developing Organic Synthesis Engineering as a definitive scientific stream, and secured a PhD in 1978 during which time he was invited by Man Mohan Sharma, a Padma Vibhushan laureate, to join the Institute of Chemical Technology, Mumbai but, on advice from Doraiswamy, he remained at NCL where he would spend the rest of his career. He served the institution in various capacities as Scientist C (1979–84), Scientist EI (1984–88), Scientist EII (1988), Scientist F (1988–93) and superannuated as Scientist G in 2010. On the administration front, he served as the Deputy Director and Head of the Chemical Engineering Division. Post-retirement, he served NCL as a Distinguished Scientist and continues his researches. | 1 | Applied and Interdisciplinary Chemistry |
DSSCs degrade when exposed to light. In 2014 air infiltration of the commonly-used amorphous Spiro-MeOTAD hole-transport layer was identified as the primary cause of the degradation, rather than oxidation. The damage could be avoided by the addition of an appropriate barrier.
The barrier layer may include UV stabilizers and/or UV absorbing luminescent chromophores (which emit at longer wavelengths which may be reabsorbed by the dye) and antioxidants to protect and improve the efficiency of the cell. | 0 | Theoretical and Fundamental Chemistry |
The naturality of different aroma can also be checked using SNIF-NMR: for example for anethole, abundance of only six monodeuterated isotopomers can be measured by H-SNIF-NMR that allows differentiating the botanical origins fennel, star anise or pine.
Other applications:
The SNIF-NMR applied to benzaldehyde can detect adulterated bitter almond and cinnamon oils. It is demonstrated that the site specific deuterium contents of benzaldehyde allow the determination of the origin of the molecule: synthetic (ex-toluene and ex-benzal chloride), natural (ex-kernels from apricots, peaches, cherries and ex-bitter almond) and semisynthetic (ex-cinnamaldehyde extracted from cinnamon).
Other applications have also been published: raspberry ketone), heliotropine, ... | 0 | Theoretical and Fundamental Chemistry |
The wake is the region of disturbed flow (often turbulent) downstream of a solid body moving through a fluid, caused by the flow of the fluid around the body.
For a blunt body in subsonic external flow, for example the Apollo or Orion capsules during descent and landing, the wake is massively separated and behind the body is a reverse flow region where the flow is moving toward the body. This phenomenon is often observed in wind tunnel testing of aircraft, and is especially important when parachute systems are involved, because unless the parachute lines extend the canopy beyond the reverse flow region, the chute can fail to inflate and thus collapse. Parachutes deployed into wakes suffer dynamic pressure deficits which reduce their expected drag forces. High-fidelity computational fluid dynamics simulations are often undertaken to model wake flows, although such modeling has uncertainties associated with turbulence modeling (for example RANS versus LES implementations), in addition to unsteady flow effects. Example applications include rocket stage separation and aircraft store separation. | 1 | Applied and Interdisciplinary Chemistry |
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