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The mammalian PDEs share a common structural organization and contain three functional domains, which include the conserved catalytic core, a regulatory N-terminus, and the C-terminus. The conserved catalytic core is much more similar within PDE families, with about 80% amino acid identity, than between different families. It is believed that the core contains common structural elements that are important for the hydrolysis of cAMP and cGMP phosphodiester bonds. It is also believed that it contains family-specific determinants for differences in affinity for substrates and sensitivity for inhibitors.
The catalytic domain of PDE3 is characterized by a 44-amino acid insert, but this insert is unique to the PDE3 family, and is a factor when determining a structure for a potent and selective PDE3 inhibitor.
The crystal structure of the catalytic domains of several PDEs, including PDE3B, have shown that they contain three helical subdomains:
# N-terminal cyclin fold region
# Linker region
# C-terminal helical bundle
At the interface of these domains a deep hydrophobic pocket is formed by residues that are highly conserved among all PDEs. This pocket is the active site and is composed of four subsites :
# Metal binding site (M site)
# Core pocket (Q pocket)
# Hydrophobic pocket (H pocket)
# Lid region (L region)
The M site is at the bottom of the hydrophobic binding pocket and contains two divalent metal binding sites. The metal ions that can bind to these sites are either zinc or magnesium. The zinc binding site has two histidine and two aspartic acid residues that are absolutely conserved among those PDEs studied to date.
The N-terminal portions of PDEs are widely divergent and contain determinants that are associated with regulatory properties specific to different gene families. For PDE3, those determinants are the hydrophobic membrane association domains and cAMP-dependent protein kinase phosphorylation sites. | 1 | Applied and Interdisciplinary Chemistry |
BLOSUM matrices are obtained by using blocks of similar amino acid sequences as data, then applying statistical methods to the data to obtain the similarity scores.
Statistical Methods Steps : | 1 | Applied and Interdisciplinary Chemistry |
Tashiro's indicator is a pH indicator (pH value: 4.4–6.2), mixed indicator composed of a solution of methylene blue (0.1%) and methyl red (0.03%) in ethanol or in methanol.
It can be used e.g. for the titration of ammonia in Kjeldahl analysis. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, an imide is a functional group consisting of two acyl groups bound to nitrogen. The compounds are structurally related to acid anhydrides, although imides are more resistant to hydrolysis. In terms of commercial applications, imides are best known as components of high-strength polymers, called polyimides. Inorganic imides are also known as solid state or gaseous compounds, and the imido group (=NH) can also act as a ligand. | 0 | Theoretical and Fundamental Chemistry |
Metabolomics can be applied to oncometabolism, since the changes in cancer's genomic, transcriptomic, and proteomic profiles can result in changes in downstream metabolic pathways. With this information we can elucidate the responsible pathways and oncometabolites for various diseases. Actually, through the use of this technique, the dysregulation of the pyruvate kinase enzyme in glucose metabolism was discovered in cancer cells. Another common used technique is glucose or glutamine labeled with 13C to show that the TCA cycle is used to generate large amounts of fatty acids (phospholipids) and to replenish the TCA cycle intermediates. But oncometabolomics does not necessarily need to be used on cancer cells, but on cells immediately surrounding them in the TME.
Metabolomics applied to cancer has the potential to significantly improve current oncological treatments and has a great diagnostic value, since metabolic changes are the prequel of phenotypic changes in cells (thus tissues and organs) making it suitable for early detection of difficult-to-detect cancers. This also leads to a more personalized medicine and customize an individual's cancer treatment according to their specific oncometabolite profiles, which would allow for better cancer therapy customization or informed adjustments. | 1 | Applied and Interdisciplinary Chemistry |
* If it takes more than five minutes to form 1/8 in. cake thicknesses, continuous filtration should not be attempted.
* For negligible cake build up in clarification, cartridges, pre-coat drums, or sand filters are used for filtration
*When the filtering surface is expected to be more than a few square meters, it is advisable to do laboratory tests to determine whether cake washing is critical. If there is a problem with the cake drying, filter precoating might be needed.
* For finely ground ores and minerals, rotary drum filtration rates may be 1500 lb/(day)(sqft), at 20 rev/h and 18-25 inch Hg vacuum
* Coarse solids and crystals may be filtered at rates of 6000 lb/ (day) (sqft) at 20 rev/h, 2-6 inch Hg vacuum.
* Surface areas in porous ceramics: Porous ceramics processed by a sol-gel technique have extremely large surface areas, ranging from 200 to 500 square meters per gram | 0 | Theoretical and Fundamental Chemistry |
Plant nutrients consist of more than a dozen minerals absorbed through roots, plus carbon dioxide and oxygen absorbed or released through leaves. All organisms obtain all their nutrients from the surrounding environment.
Plants absorb carbon, hydrogen and oxygen from air and soil in the form of carbon dioxide and water. Other nutrients are absorbed from soil (exceptions include some parasitic or carnivorous plants). Counting these, there are 17 important nutrients for plants: these are macronutrients; nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), carbon (C), oxygen(O) and hydrogen (H), and the micronutrients; iron (Fe), boron (B), chlorine (Cl), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo) and nickel (Ni). In addition to carbon, hydrogen and oxygen; nitrogen, phosphorus, and sulfur are also needed in relatively large quantities. Together, the "Big Six" are the elemental macronutrients for all organisms.
They are sourced from inorganic matter (for example, carbon dioxide, water, nitrates, phosphates, sulfates, and diatomic molecules of nitrogen and, especially, oxygen) and organic matter (carbohydrates, lipids, proteins). | 0 | Theoretical and Fundamental Chemistry |
The tris(pyrazolyl)borate ligand is often known as Tp to many inorganic chemists - using different pyrazoles substituted in the 3,4, and 5 positions, a range of different ligands can be formed. In this article we will group all the trispyrazolylborates together.
These compounds are usually synthesized by reacting pyrazole with alkali-metal borohydrides, such as sodium borohydride NaBH, under reflux. H is evolved as the borohydride is sequentially converted first to pyrazolylborate [HB(CNH)], then to bis(pyrazolyl)borate [HB(CNH)], and finally to tris(pyrazolyl)borate [HB(CNH)]. Bulky pyrazolyl borates can be prepared from 3,5-disubstituted pyrazoles, such as the dimethyl derivative. These bulky pyrazolyl borates have proven especially valuable in the preparation of catalysts and models for enzyme active sites. Utilizing scorpionate ligands in the syntheses of metal catalysts may allow simpler and more accurate methods to be developed. Ligands allow for good shielding of the bound metal while strong sigma bonds between the nitrogens and the metal stabilize the metal; these attributes help scorpionate compounds with creating highly symmetrical supramolecular silver complexes and olefin polymerization (with the compound hydrotris(pyrazolyl) borate Mn). | 0 | Theoretical and Fundamental Chemistry |
Below 912 °C (1,674 °F), iron has a body-centered cubic (bcc) crystal structure and is known as α-iron or ferrite. It is thermodynamically stable and a fairly soft metal. α-Fe can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form termed ε-Fe discussed below.
Magnetically, α-iron is paramagnetic at high temperatures. However, below its Curie temperature (T or A) of 771 °C (1044K or 1420 °F), it becomes ferromagnetic. In the past, the paramagnetic form of α-iron was known as beta iron (β-Fe). Even though the slight tetragonal distortion in the ferromagnetic state does constitute a true phase transition, the continuous nature of this transition results in only minor importance in steel heat treating. The A line forms the boundary between the beta iron and alpha fields in the phase diagram in Figure 1.
Similarly, the A boundary is of only minor importance compared to the A (eutectoid), A and A critical temperatures. The A, where austenite is in equilibrium with cementite + γ-Fe, is beyond the right edge in Fig. 1. The α + γ phase field is, technically, the β + γ field above the A. The beta designation maintains continuity of the Greek-letter progression of phases in iron and steel: α-Fe, β-Fe, austenite (γ-Fe), high-temperature δ-Fe, and high-pressure hexaferrum (ε-Fe).
The primary phase of low-carbon or mild steel and most cast irons at room temperature is ferromagnetic α-Fe. It has a hardness of approximately 80 Brinell. The maximum solubility of carbon is about 0.02 wt% at and 0.001% at . When it dissolves in iron, carbon atoms occupy interstitial "holes". Being about twice the diameter of the tetrahedral hole, the carbon introduces a strong local strain field.
Mild steel (carbon steel with up to about 0.2 wt% C) consists mostly of α-Fe and increasing amounts of cementite (FeC, an iron carbide). The mixture adopts a lamellar structure called pearlite. Since bainite and pearlite each contain α-Fe as a component, any iron-carbon alloy will contain some amount of α-Fe if it is allowed to reach equilibrium at room temperature. The amount of α-Fe depends on the cooling process. | 1 | Applied and Interdisciplinary Chemistry |
A similar method of obtaining new deoxyribozymes is through in vitro evolution. Though this term is often used interchangeably with in vitro selection, in vitro evolution more appropriately refers to a slightly different procedure in which the initial oligonucleotide pool is genetically altered over subsequent rounds through genetic recombination or through point mutations. For point mutations, the pool can be amplified using error-prone PCR to produce many different strands of various random, single mutations. As with in vitro selection, the evolved strands with increased activity will tend to dominate the pool after multiple selection steps, and once a sufficient catalytic activity is reached, the pool can be sequenced to identify the most active strands.
The initial pool for in vitro evolution can be derived from a narrowed subset of sequence space, such as a certain round of an in vitro selection experiment, which is sometimes also called in vitro reselection. The initial pool can also be derived from amplification of a single oligonucleotide strand. As an example of the latter, a recent study showed that a functional deoxyribozyme can be selected through in vitro evolution of a non-catalytic oligonucleotide precursor strand. An arbitrarily chosen DNA fragment derived from the mRNA transcript of bovine serum albumin was evolved through random point mutations over 25 rounds of selection. Through deep sequencing analysis of various pool generations, the evolution of the most catalytic deoxyribozyme strand could be tracked through each subsequent single mutation.
This first successful evolution of catalytic DNA from a non-catalytic precursor could provide support for the RNA World hypothesis. In another recent study, an RNA ligase ribozyme was converted into a deoxyribozyme through in vitro evolution of the inactive deoxyribo-analog of the ribozyme. The new RNA ligase deoxyribozyme contained just twelve point mutations, two of which had no effect on activity, and had a catalytic efficiency of approximately 1/10 of the original ribozyme, though the researches hypothesized that the activity could be further increased through further selection.
This first evidence for transfer of function between different nucleic acids could provide support for various pre-RNA World hypotheses. | 0 | Theoretical and Fundamental Chemistry |
The predecessor of modern countercurrent chromatography theory and practice was countercurrent distribution (CCD). The theory of CCD was described in the 1930s by Randall and Longtin. Archer Martin and Richard Laurence Millington Synge developed the methodology further during the 1940s. Finally, Lyman C. Craig introduced the Craig countercurrent distribution apparatus in 1944 which made CCD practical for laboratory work. CCD was used to separate a wide variety of useful compounds for several decades. | 0 | Theoretical and Fundamental Chemistry |
Podocin is a membrane protein of the band-7-stomatin family, consisting of 383 amino acids. It has a transmembrane domain forming a hairpin structure, with two cytoplasmic ends at the N- and C-terminus, the latter of which interacts with the cytosolic tail of nephrin, with CD2AP serving as an adaptor. | 1 | Applied and Interdisciplinary Chemistry |
A "transient complex" model was first proposed by Huetz et al. to explain this competitive exchange. This transient complex exchange occurs in three distinct steps. Initially a protein embeds itself into the monolayer of an already adsorbed homogenous protein monolayer. The aggregation of this new heterogenous protein mixture causes the "turning" of the double-protein complex which exposes the initially adsorbed protein to the solution. In the third step, the protein that was initially adsorbed can now diffuse out into the solution and the new protein takes over. This 3 part "transient complex mechanism" is further explained and verified through AFM imaging by Hirsh et al. | 0 | Theoretical and Fundamental Chemistry |
Thermotropic phases are those that occur in a certain temperature range. If the temperature rise is too high, thermal motion will destroy the delicate cooperative ordering of the LC phase, pushing the material into a conventional isotropic liquid phase. At too low temperature, most LC materials will form a conventional crystal. Many thermotropic LCs exhibit a variety of phases as temperature is changed. For instance, a particular type of LC molecule (called a mesogen) may exhibit various smectic phases followed by the nematic phase and finally the isotropic phase as temperature is increased. An example of a compound displaying thermotropic LC behavior is para-azoxyanisole. | 0 | Theoretical and Fundamental Chemistry |
Insulators have zero density of states at the Fermi level due to their band gaps. Thus, the density of states-based electronic entropy is essentially zero in these systems.
Metals have non-zero density of states at the Fermi level. Metals with free-electron-like band structures (e.g. alkali metals, alkaline earth metals, Cu, and Al) generally exhibit relatively low density of states at the Fermi level, and therefore exhibit fairly low electronic entropies. Transition metals, wherein the flat d-bands lie close to the Fermi level, generally exhibit much larger electronic entropies than the free-electron like metals.
Oxides have particularly flat band structures and thus can exhibit large , if the Fermi level intersects these bands. As most oxides are insulators, this is generally not the case. However, when oxides are metallic (i.e. the Fermi level lies within an unfilled, flat set of bands), oxides exhibit some of the largest electronic entropies of any material.
Thermoelectric materials are specifically engineered to have large electronic entropies. The thermoelectric effect relies on charge carriers exhibiting large entropies, as the driving force to establish a gradient in electrical potential is driven by the entropy associated with the charge carriers. In the thermoelectric literature, the term band structure engineering refers to the manipulation of material structure and chemistry to achieve a high density of states near the Fermi level. More specifically, thermoelectric materials are intentionally doped to exhibit only partially filled bands at the Fermi level, resulting in high electronic entropies. Instead of engineering band filling, one may also engineer the shape of the band structure itself via introduction of nanostructures or quantum wells to the materials. | 0 | Theoretical and Fundamental Chemistry |
Bone ash is used in foundries for various purposes. Examples include release agents and protective barriers for tools exposed to molten metal, and as a sealant for seams and cracks. Applied as a powder or water slurry, bone ash has many unique characteristics. First of all, the powder has high thermal stability, so it maintains its form in extremely high temperatures. The powder coating itself adheres to metal well and does not drip, run, cause much corrosion, or create noticeable streaks. Using the bone ash is easy as well, as it comes in a powder form, is easy to clean up, and does not separate into smaller parts (therefore requiring no extra mixing). | 0 | Theoretical and Fundamental Chemistry |
Intermolecular forces such as Van der Waals forces, hydrogen bonds, and dipole–dipole interactions are typically not sufficiently strong to hold two apparently conformal rigid bodies together, since the forces drop off rapidly with distance, and the actual area in contact between the two bodies is small due to surface roughness and minor imperfections.
However, if the bodies are conformal to an accuracy of better than 10 angstroms (1 nanometer), then a sufficient surface area is in close enough contact for the intermolecular interactions to have an observable macroscopic effect—that is, the two objects stick together. Such a condition requires a high degree of accuracy and surface smoothness, which is typically found in optical components, such as prisms. | 0 | Theoretical and Fundamental Chemistry |
Human engineered cardiac tissues (hECTs) are derived by experimental manipulation of pluripotent stem cells, such as human embryonic stem cells (hESCs) and, more recently, human induced pluripotent stem cells (hiPSCs) to differentiate into human cardiomyocytes. Interest in these bioengineered cardiac tissues has risen due to their potential use in cardiovascular research and clinical therapies. These tissues provide a unique in vitro model to study cardiac physiology with a species-specific advantage over cultured animal cells in experimental studies. hECTs also have therapeutic potential for in vivo regeneration of heart muscle. hECTs provide a valuable resource to reproduce the normal development of human heart tissue, understand the development of human cardiovascular disease (CVD), and may lead to engineered tissue-based therapies for CVD patients. | 1 | Applied and Interdisciplinary Chemistry |
Unsaponifiables are components of a fatty substance (oil, fat, wax) that fail to form soaps when treated with alkali and remain insoluble in water but soluble in organic solvents. For instance, typical soybean oil contains, by weight, 1.5 – 2.5% of unsaponifiable matter. Unsaponifiables include nonvolatile components : alkanes, sterols, triterpenes, fatty alcohols, tocopherols and carotenoids as well as those that mainly result from the saponification of fatty esters (sterols esters, wax esters, tocopherols esters, ...). This fraction may also contain environmental contaminants and residues of plasticizers, pesticides, mineral oil hydrocarbons and aromatics.
Unsaponifiable constituents are an important consideration when selecting oil mixtures for the manufacture of soaps. Unsaponifiables can be beneficial to a soap formula because they may have properties such as moisturization, conditioning, antioxidant, texturing etc. On the other hand, when proportion of unsaponifiables is too high (> 3%), or the specific unsaponifiables present do not provide significant benefits, a defective or inferior soap product can result. For example, shark oil is not suitable for soap making as it may contain more than 10% of unsaponifiable matter.
For edible oils, the tolerated limit of unsaponifiable matter is 1.5% (olive, refined soybean), while inferior quality crude or pomace oil could reach 3%.
Determination of unsaponifiables involves a saponification step of the sample followed by extraction of the unsaponifiable using an organic solvent (i.e. diethyl ether). Official methods for animal and vegetable fats and oils are described by ASTM D1065 - 18, ISO 3596: 2000 or 18609: 2000, AOCS method Ca 6a-40. | 0 | Theoretical and Fundamental Chemistry |
There are various methods of adequately identifying and monitoring hydrogen damage, including ultrasonic echo attenuation method, amplitude-based backscatter, velocity ratio, creeping waves/time-of-flight measurement, pitch-catch mode shear wave velocity, advanced ultrasonic backscatter techniques (AUBT), time of flight diffraction (TOFD), thickness mapping and in-situ metallography – replicas. For hydrogen damage, the backscatter technique is used to detect affected areas in the material. To cross-check and confirm the findings of the backscatter measurement, the velocity ratio measurement technique is used. For the detection of micro and macro cracks, time of flight diffraction is a suitable method to use. | 1 | Applied and Interdisciplinary Chemistry |
Another class of plant disease resistance genes opens a “trap door” that quickly kills invaded cells, stopping pathogen proliferation. Xanthomonas and Ralstonia transcription activator–like (TAL) effectors are DNA-binding proteins that activate host gene expression to enhance pathogen virulence. Both the rice and pepper lineages independently evolved TAL-effector binding sites that instead act as an executioner that induces hypersensitive host cell death when up-regulated. Xa27 from rice and Bs3 and Bs4c from pepper, are such “executor” (or "executioner") genes that encode non-homologous plant proteins of unknown function. Executor genes are expressed only in the presence of a specific TAL effector.
Engineered executor genes were demonstrated by successfully redesigning the pepper Bs3 promoter to contain two additional binding sites for TAL effectors from disparate pathogen strains. Subsequently, an engineered executor gene was deployed in rice by adding five TAL effector binding sites to the Xa27 promoter. The synthetic Xa27 construct conferred resistance against Xanthomonas bacterial blight and bacterial leaf streak species. | 1 | Applied and Interdisciplinary Chemistry |
A few gamma rays in astronomy are known to arise from gamma decay (see discussion of SN1987A), but most do not.
Photons from astrophysical sources that carry energy in the gamma radiation range are often explicitly called gamma-radiation. In addition to nuclear emissions, they are often produced by sub-atomic particle and particle-photon interactions. Those include electron-positron annihilation, neutral pion decay, bremsstrahlung, inverse Compton scattering, and synchrotron radiation. | 0 | Theoretical and Fundamental Chemistry |
The amino radical may also be produced by reaction of e(aq) with hydroxylamine (). Several studies also utilized the redox system of for the production of amino radicals using electron paramagnetic resonance (ESR) spectroscopy and polarography. | 0 | Theoretical and Fundamental Chemistry |
Commonly studied regulons in bacteria are those involved in response to stress such as heat shock. The heat shock response in E. coli is regulated by the sigma factor
σ32 (RpoH), whose regulon has been characterized as containing at least 89 open reading frames.
Regulons involving virulence factors in pathogenic bacteria are of particular research interest; an often-studied example is the phosphate regulon in E. coli, which couples phosphate homeostasis to pathogenicity through a two-component system. Regulons can sometimes be pathogenicity islands.
The Ada regulon in E. coli is a well-characterized example of a group of genes involved in the adaptive response form of DNA repair.
Quorum sensing behavior in bacteria is a commonly cited example of a modulon or stimulon, though some sources describe this type of intercellular auto-induction as a separate form of regulation. | 1 | Applied and Interdisciplinary Chemistry |
The RIC experiment is first performed with a n-dodecane–air–rock system to determine the constant ∁ of the Washburn Equation. N-dodecane imbibes into one of the core samples and the imbibition curve is recorded in Figure 2. Dodecane is an alkane that has low surface energy, very strongly wetting the rock sample in the presence of air, with contact angle θ equal to zero. Constant ∁ is determined by the contact angle value for dodecane/air/rock system, determining physical properties of n-dodecane (ρ,μ,γ) and rearranging equation 1; | 1 | Applied and Interdisciplinary Chemistry |
If an abnormality is found, i.e. the B12 in the urine is only present in low levels, the test is repeated, this time with additional oral intrinsic factor.
* If this second urine collection is normal, this shows a lack of intrinsic factor production. This is by definition pernicious anemia.
* A low result on the second test implies abnormal intestinal absorption (malabsorption), which could be caused by coeliac disease, biliary disease, Whipple's disease, small bowel bacterial overgrowth syndrome, fish tapeworm infestation (Diphyllobothrium latum), or liver disease. Malabsorption of B can be caused by intestinal dysfunction from a low vitamin level in-and-of-itself (see below), causing test result confusion if repletion has not been done for some days previously. | 1 | Applied and Interdisciplinary Chemistry |
Non-covalent interactions have a significant effect on the boiling point of a liquid. Boiling point is defined as the temperature at which the vapor pressure of a liquid is equal to the pressure surrounding the liquid. More simply, it is the temperature at which a liquid becomes a gas. As one might expect, the stronger the non-covalent interactions present for a substance, the higher its boiling point. For example, consider three compounds of similar chemical composition: sodium n-butoxide (CHONa), diethyl ether (CHO), and n-butanol (CHOH).
The predominant non-covalent interactions associated with each species in solution are listed in the above figure. As previously discussed, ionic interactions require considerably more energy to break than hydrogen bonds, which in turn are require more energy than dipole–dipole interactions. The trends observed in their boiling points (figure 8) shows exactly the correlation expected, where sodium n-butoxide requires significantly more heat energy (higher temperature) to boil than n-butanol, which boils at a much higher temperature than diethyl ether. The heat energy required for a compound to change from liquid to gas is associated with the energy required to break the intermolecular forces each molecule experiences in its liquid state. | 0 | Theoretical and Fundamental Chemistry |
In old pharmacy, a cucupha or cucufa was a cap, or cover for the head, with cephalic spices quilted in it, worn for certain nervous distempers, particularly those affecting the head. | 1 | Applied and Interdisciplinary Chemistry |
In April 2005, following the confirmation of asbestos fibres found on tree roots, the council asked developers to provide more detailed information relating to their contaminated land surveys, and placed the application on hold. They also announced that they were considering appointing their own environmental consultants to examine the site. Jason Addy said: "This is what we have been asking for since day one. The information handed in with the planning application was inaccurate, misleading and avoided many issues. As this site begins to reveal more of its murky secrets people are realising just how contaminated it is. We are very concerned about the asbestos contamination on the site. We are very worried about the way this is going, if it wasn't so serious it would be a farce." Rochdale councillor William Hobhouse said: "With no government regulations specifying safe levels of asbestos in soil, it is clear the council, working with outside consultants, will have to formulate what percentage of asbestos in the soil is safe." | 1 | Applied and Interdisciplinary Chemistry |
DNPH is a reagent in instructional laboratories on qualitative organic analysis. Bradys reagent or Borches reagent, is prepared by dissolving DNPH in a solution containing methanol and some concentrated sulfuric acid. This solution is used to detect ketones and aldehydes. A positive test is signalled by the formation of a yellow, orange or red precipitate of the dinitrophenylhydrazone. Aromatic carbonyls give red precipitates whereas aliphatic carbonyls give more yellow color. The reaction between DNPH and a generic ketone to form a hydrazone is shown below:
:RRC=O + CH(NO)NHNH → CH(NO)NHN=CRR + HO
This reaction is, overall, a condensation reaction as two molecules joining together with loss of water. Mechanistically, it is an example of addition-elimination reaction: nucleophilic addition of the -NH group to the C=O carbonyl group, followed by the elimination of a HO molecule:
DNP-derived hydrazones have characteristic melting points, facilitating identification of the carbonyl. In particular, the use of DNPH was developed by Brady and Elsmie. Modern spectroscopic and spectrometric techniques have superseded these techniques.
DNPH does not react with other carbonyl-containing functional groups such as carboxylic acids, amides, and esters, for which there is resonance-associated stability as a lone-pair of electrons interacts with the p orbital of the carbonyl carbon resulting in increased delocalization in the molecule. This stability would be lost by addition of a reagent to the carbonyl group. Hence, these compounds are more resistant to addition reactions. Also, with carboxylic acids, there is the effect of the compound acting as a base, leaving the resulting carboxylate negatively charged and hence no longer vulnerable to nucleophilic attack. | 0 | Theoretical and Fundamental Chemistry |
Mineral processing begins with beneficiation, consisting of initially breaking down the ore to required sizes depending on the concentration process to be followed, by crushing, grinding, sieving etc. Thereafter, the ore is physically separated from any unwanted impurity, depending on the form of occurrence and or further process involved. Separation processes take advantage of physical properties of the materials. These physical properties can include density, particle size and shape, electrical and magnetic properties, and surface properties. Major physical and chemical methods include magnetic separation, froth flotation, leaching etc., whereby the impurities and unwanted materials are removed from the ore and the base ore of the metal is concentrated, meaning the percentage of metal in the ore is increased. This concentrate is then either processed to remove moisture or else used as is for extraction of the metal or made into shapes and forms that can undergo further processing, with ease of handling.
Ore bodies often contain more than one valuable metal. Tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. Additionally, a concentrate may contain more than one valuable metal. That concentrate would then be processed to separate the valuable metals into individual constituents. | 1 | Applied and Interdisciplinary Chemistry |
Rowley was born in Mason Hall, Tobago, raised by his grandparents, who were prominent Tobago farmers. He was a pupil of Bishop's High School in Tobago, and graduated from the University of the West Indies (Mona) from where he graduated with a BSc. Geology (First Class Honors). He then went on to earn an MSc (1974) and a PhD (1978) from the University of the West Indies at St. Augustine in geology, specializing in geochemistry. At the university, as researcher, he held the positions of research fellow and later as head of the Seismic Research Unit. Rowley was general manager of state-owned National Quarries Company Limited as well. | 0 | Theoretical and Fundamental Chemistry |
Grain boundaries are interfaces where crystals of different orientations meet. A grain boundary is a single-phase interface, with crystals on each side of the boundary being identical except in orientation. The term "crystallite boundary" is sometimes, though rarely, used. Grain boundary areas contain those atoms that have been perturbed from their original lattice sites, dislocations, and impurities that have migrated to the lower energy grain boundary.
Treating a grain boundary geometrically as an interface of a single crystal cut into two parts, one of which is rotated, we see that there are five variables required to define a grain boundary. The first two numbers come from the unit vector that specifies a rotation axis. The third number designates the angle of rotation of the grain. The final two numbers specify the plane of the grain boundary (or a unit vector that is normal to this plane).
Grain boundaries disrupt the motion of dislocations through a material, so reducing crystallite size is a common way to improve strength, as described by the Hall–Petch relationship. Since grain boundaries are defects in the crystal structure they tend to decrease the electrical and thermal conductivity of the material. The high interfacial energy and relatively weak bonding in most grain boundaries often makes them preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. They are also important to many of the mechanisms of creep.
Grain boundaries are in general only a few nanometers wide. In common materials, crystallites are large enough that grain boundaries account for a small fraction of the material. However, very small grain sizes are achievable. In nanocrystalline solids, grain boundaries become a significant volume fraction of the material, with profound effects on such properties as diffusion and plasticity. In the limit of small crystallites, as the volume fraction of grain boundaries approaches 100%, the material ceases to have any crystalline character, and thus becomes an amorphous solid. | 0 | Theoretical and Fundamental Chemistry |
One main function of plasma and cell membranes is to maintain asymmetric concentrations of inorganic ions in order to maintain an ionic steady state different from electrochemical equilibrium. In other words, there is a differential distribution of ions on either side of the cell membrane - that is, the amount of ions on either side is not equal and therefore a charge separation exists. However, ions move across the cell membrane such that a constant resting membrane potential is achieved; this is ionic steady state. In the pump-leak model of cellular ion homeostasis, energy is utilized to actively transport ions against their electrochemical gradient. The maintenance of this steady state gradient, in turn, is used to do electrical and chemical work, when it is dissipated though the passive movement of ions across the membrane.
In cardiac muscle, ATP is used to actively transport sodium ions out of the cell through a membrane ATPase. Electrical excitation of the cell results in an influx of sodium ions into the cell, temporarily depolarizing the cell. To restore the steady state electrochemical gradient, ATPase removes sodium ions and restores potassium ions in the cell. When an elevated heart rate is sustained, causing more depolarizations, sodium levels in the cell increase until becoming constant, indicating that a new steady state has been reached. | 0 | Theoretical and Fundamental Chemistry |
The non-stoichiometric cycles with CeO can be describes with the following reactions:
::Reduction reaction: CeO → CeO + δ/2 O
::Oxidation reaction: CeO + δ HO → CeO + δ H
The reduction occurs when CeO, or ceria, is exposed to a inert atmosphere at around 1500 °C to 1600 °C, and hydrogen release occurs at 800 °C during hydrolysis when it is subjected to an atmosphere containing water vapor. One advantage of ceria over iron oxide lies in its higher melting point, which allows it to sustain higher temperature during reduction cycle. In addition, cerias ionic conductivity allows oxygen atoms to diffuse through its structure several orders of magnitude faster than Fe ions can diffuse through iron oxide. Consequently, the redox reactions of ceria can occur at occur at a larger length scale, making it an ideal candidate for thermochemical reactor testing. Ceria-based thermochemical reactor has been created and tested as early as 2010, and viability of cycling was corroborated under realistic solar concentrating conditions. One disadvantage that limits cerias application is its relatively lower oxygen storage capability. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, structural theory explains the large variety in chemical compounds in terms of atoms making up molecules, the arrangement of atoms within molecules and the electrons that hold them together. According to structural theory, from the structural formula of a molecule it is possible to derive physical and spectroscopic data and to predict chemical reactivity.
Beginning from about 1858, many scientists from several countries took part in the early development of structural theory, including August Kekule, Archibald Scott Couper, and Aleksandr Mikhailovich Butlerov. It was Butlerov who coined the phrase "chemical structure" in the following quotation from an article published in 1861: | 1 | Applied and Interdisciplinary Chemistry |
Transglycosylation, which involves the reversible transfer of a sugar moiety from one heterocyclic base to another, is effective for the conversion of pyrimidine nucleosides to purine nucleosides. Most other transglycosylation reactions are low yielding due to a small thermodynamic difference between equilibrating nucleosides.
Deoxyribose-derived electrophiles are unable to form the cyclic cation 1; as a result, the stereoselective synthesis of deoxyribonucleosides is more difficult than the synthesis of ribonucleosides. One solution to this problem involves the synthesis of a ribonucleoside, followed by protection of the 3- and 5-hydroxyl groups, removal of the 2'-hydroxyl group through a Barton deoxygenation, and deprotection. | 0 | Theoretical and Fundamental Chemistry |
The primary cause of change in the composition of a magma is cooling, which is an inevitable consequence of the magma being formed and migrating from the site of partial melting into an area of lower stress - generally a cooler volume of the crust.
Cooling causes the magma to begin to crystallize minerals from the melt or liquid portion of the magma. Most magmas are a mixture of liquid rock (melt) and crystalline minerals (phenocrysts).
Contamination is another cause of magma differentiation. Contamination can be caused by assimilation of wall rocks, mixing of two or more magmas or even by replenishment of the magma chamber with fresh, hot magma.
The whole gamut of mechanisms for differentiation has been referred to as the FARM process, which stands for fractional crystallization, assimilation, replenishment and magma mixing. | 0 | Theoretical and Fundamental Chemistry |
In the field of engineering, the hydrophobicity (or dewetting ability) of a flat surface (e.g., a counter top in kitchen or a cooking pan) can be measured by the contact angle of water droplet. A University of Nebraska-Lincoln team recently devised a computational approach that can relate the molecular hydrophobicity scale of amino-acid chains to the contact angle of water nanodroplet. The team constructed planar networks composed of unified amino-acid side chains with native structure of the beta-sheet protein. Using molecular dynamics simulation, the team is able to measure the contact angle of water nanodroplet on the planar networks (caHydrophobicity).
On the other hand, previous studies show that the minimum of excess chemical potential of a hard-sphere solute with respect to that in the bulk exhibits a linear dependence on cosine value of contact angle. Based on the computed excess chemical potentials of the purely repulsive methane-sized Weeks–Chandler–Andersen solute with respect to that in the bulk, the extrapolated values of cosine value of contact angle are calculated(ccHydrophobicity), which can be used to quantify the hydrophobicity of amino acid side chains with complete wetting behaviors. | 0 | Theoretical and Fundamental Chemistry |
Usually hydrolysis is a chemical process in which a molecule of water is added to a substance. Sometimes this addition causes both the substance and water molecule to split into two parts. In such reactions, one fragment of the target molecule (or parent molecule) gains a hydrogen ion. It breaks a chemical bond in the compound. | 0 | Theoretical and Fundamental Chemistry |
* constant strength - simple, large number of panels required
* linear varying strength - reasonable answer, little difficulty in creating well-posed problems
* quadratic varying strength - accurate, more difficult to create a well-posed problem
Some techniques are commonly used to model surfaces.
* Body Thickness by line sources
* Body Lift by line doublets
* Wing Thickness by constant source panels
* Wing Lift by constant pressure panels
* Wing-Body Interface by constant pressure panels | 1 | Applied and Interdisciplinary Chemistry |
Coordinate covalent bonding is ubiquitous. In all metal aquo-complexes [M(HO)], the bonding between water and the metal cation is described as a coordinate covalent bond. Metal-ligand interactions in most organometallic compounds and most coordination compounds are described similarly.
The term dipolar bond is used in organic chemistry for compounds such as amine oxides for which the electronic structure can be described in terms of the basic amine donating two electrons to an oxygen atom.
: → O
The arrow → indicates that both electrons in the bond originate from the amine moiety. In a standard covalent bond each atom contributes one electron. Therefore, an alternative description is that the amine gives away one electron to the oxygen atom, which is then used, with the remaining unpaired electron on the nitrogen atom, to form a standard covalent bond. The process of transferring the electron from nitrogen to oxygen creates formal charges, so the electronic structure may also be depicted as
This electronic structure has an electric dipole, hence the name polar bond. In reality, the atoms carry partial charges; the more electronegative atom of the two involved in the bond will usually carry a partial negative charge. One exception to this is carbon monoxide. In this case, the carbon atom carries the partial negative charge although it is less electronegative than oxygen.
An example of a dative covalent bond is provided by the interaction between a molecule of ammonia, a Lewis base with a lone pair of electrons on the nitrogen atom, and boron trifluoride, a Lewis acid by virtue of the boron atom having an incomplete octet of electrons. In forming the adduct, the boron atom attains an octet configuration.
The electronic structure of a coordination complex can be described in terms of the set of ligands each donating a pair of electrons to a metal centre. For example, in hexamminecobalt(III) chloride, each ammonia ligand donates its lone pair of electrons to the cobalt(III) ion. In this case, the bonds formed are described as coordinate bonds. In the Covalent Bond Classification (CBC) method, ligands that form coordinate covalent bonds with a central atom are classed as L-type, while those that form normal covalent bonds are classed as X-type. | 0 | Theoretical and Fundamental Chemistry |
The composition of coordination complexes have been known since the early 1800s, such as Prussian blue and copper vitriol. The key breakthrough occurred when Alfred Werner reconciled formulas and isomers. He showed, among other things, that the formulas of many cobalt(III) and chromium(III) compounds can be understood if the metal has six ligands in an octahedral geometry. The first to use the term "ligand" were Alfred Werner and Carl Somiesky, in relation to silicon chemistry. The theory allows one to understand the difference between coordinated and ionic chloride in the cobalt ammine chlorides and to explain many of the previously inexplicable isomers. He resolved the first coordination complex called hexol into optical isomers, overthrowing the theory that chirality was necessarily associated with carbon compounds. | 0 | Theoretical and Fundamental Chemistry |
Free quarks probably existed in the extreme conditions of the very early universe until about 30 microseconds after the Big Bang, in a very hot gas of free quarks, antiquarks and gluons. This gas is called quark–gluon plasma (QGP), since the quark-interaction charge (color charge) is mobile and quarks and gluons move around. This is possible because at a high temperature the early universe is in a different vacuum state, in which normal matter cannot exist but quarks and gluons can; they are deconfined (able to exist independently as separate unbound particles). In order to recreate this deconfined phase of matter in the laboratory it is necessary to exceed a minimum temperature, or its equivalent, a minimum energy density. Scientists achieve this using particle collisions at extremely high speeds, where the energy released in the collision can raise the subatomic particles' energies to an exceedingly high level, sufficient for them to briefly form a tiny amount of quark–gluon plasma that can be studied in laboratory experiments for little more than the time light needs to cross the QGP fireball, thus about 10 s. After this brief time the hot drop of quark plasma evaporates in a process called hadronization. This is so since practically all QGP components flow out at relativistic speed. In this way, it is possible to study conditions akin to those in the early Universe at the age of 10–40 microseconds.
Discovery of this new QGP state of matter has been announced both at CERN and at Brookhaven National Laboratory (BNL). Preparatory work, allowing for these discoveries, was carried out at the Joint Institute for Nuclear Research (JINR) and Lawrence Berkeley National Laboratory (LBNL) at the Bevalac. New experimental facilities, FAIR at the GSI Helmholtz Centre for Heavy Ion Research (GSI) and NICA at JINR, are under construction. Strangeness as a signature of QGP was first explored in 1983. Comprehensive experimental evidence about its properties is being assembled. Recent work by the ALICE collaboration at CERN has opened a new path to study of QGP and strangeness production in very high energy pp collisions. | 0 | Theoretical and Fundamental Chemistry |
Induction of proliferation by the EpoR is likely cell type-dependent. It is known that EpoR can activate mitogenic signaling pathways and can lead to cell proliferation in erythroleukemic cell lines in vitro, various non-erythroid cells, and cancer cells. So far, there is no sufficient evidence that in vivo, EpoR signaling can induce erythroid progenitors to undergo cell division, or whether Epo levels can modulate the cell cycle. EpoR signaling may still have a proliferation effect upon BFU-e progenitors, but these progenitors cannot be directly identified, isolated and studied. CFU-e progenitors enter the cell cycle at the time of GATA-1 induction and PU.1 suppression in a developmental manner rather than due to EpoR signaling. Subsequent differentiation stages (proerythroblast to orthochromatic erythroblast) involve a decrease in cell size and eventual expulsion of the nucleus, and are likely dependent upon EpoR signaling only for their survival. In addition, some evidence on macrocytosis in hypoxic stress (when Epo can increase 1000-fold) suggests that mitosis is actually skipped in later erythroid stages, when EpoR expression is low/absent, in order to provide emergency reserve of red blood cells as soon as possible. Such data, though sometimes circumstantial, argue that there is limited capacity to proliferate specifically in response to Epo (and not other factors). Together, these data suggest that EpoR in erythroid differentiation may function primarily as a survival factor, while its effect on the cell cycle (for example, rate of division and corresponding changes in the levels of cyclins and Cdk inhibitors) in vivo awaits further work. In other cell systems, however, EpoR may provide a specific proliferative signal. | 1 | Applied and Interdisciplinary Chemistry |
The apparent cleavage is triggered by ribosomal skipping of the peptide bond between the proline (P) and glycine (G) in C-terminal of 2A peptide, resulting in the peptide located upstream of the 2A peptide to have extra amino acids on its C-terminal end while the peptide located downstream the 2A peptide will have an extra proline on its N-terminal end. The exact molecular mechanism of 2A-peptide-mediated cleavage is still unknown. However, it is believed to involve ribosomal "skipping" of glycyl-prolyl peptide bond formation rather than true proteolytic cleavage. | 1 | Applied and Interdisciplinary Chemistry |
Persistent stimulation at the neuronal synapse can lead to markedly different outcomes for the post-synaptic neuron. Extended weak signaling can result in long-term depression (LTD), in which activation of the post-synaptic neuron requires a stronger signal than before LTD was initiated. In contrast, long-term potentiation (LTP) occurs when the post-synaptic neuron is subjected to a strong stimulus, and this results in strengthening of the neural synapse (i.e., less neurotransmitter signal is required for activation).
In the CA1 region of the hippocampus, the decision between LTD and LTP is mediated solely by the level of intracellular at the post-synaptic dendritic spine. Low levels of (resulting from low-level stimulation) activates the protein phosphatase calcineurin, which induces LTD. Higher levels of results in activation of /calmodulin-dependent protein kinase II (CaMKII), which leads to LTP. The difference in Ca concentration required for a cell to undergo LTP is only marginally higher than for LTD, and because neurons show bistability (either LTP or LTD) following persistent stimulation, this suggests that one or more components of the system respond in a switch-like, or ultrasensitive manner. Bradshaw et al. demonstrated that CaMKII (the LTP inducer) responds to intracellular calcium levels in an ultrasensitive manner, with <10% activity at 1.0 uM and ~90% activity at 1.5 uM, resulting in a Hill coefficient of ~8. Further experiments showed that this ultrasenstivity was mediated by cooperative binding of CaMKII by two molecules of calmodulin (CaM), and autophosphorylation of activated CaMKII leading to a positive feedback loop.
In this way, intracellular calcium can induce a graded, non-ultrasensitive activation of calcineurin at low levels, leading to LTD, whereas the ultrasensitive activation of CaMKII results in a threshold intracellular calcium level that generates a positive feedback loop that amplifies the signal and leads to the opposite cellular outcome: LTP. Thus, binding of a single substrate to multiple enzymes with different sensitivities facilitates a bistable decision for the cell to undergo LTD or LTP. | 1 | Applied and Interdisciplinary Chemistry |
The Nevada Test Site (NTS), is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about 65 miles (105 km) northwest of the city of Las Vegas. Formerly known as the Nevada Proving Grounds, the site was established on 11 January 1951 for the testing of nuclear devices, covering approximately of desert and mountainous terrain. Nuclear testing at the Nevada Test Site began with a bomb dropped on Frenchman Flat on 27 January 1951. Many of the iconic images of the nuclear era come from the NTS.
During the 1950s, the mushroom clouds from atmospheric tests could be seen for almost . The city of Las Vegas experienced noticeable seismic effects, and the distant mushroom clouds, which could be seen from the downtown hotels, became tourist attractions. St. George, Utah, received the brunt of the fallout of above-ground nuclear testing in the Yucca Flats/Nevada Test Site. Winds routinely carried the fallout of these tests directly through St. George and southern Utah. Marked increases in cancers, such as leukemia, lymphoma, thyroid cancer, breast cancer, melanoma, bone cancer, brain tumors, and gastrointestinal tract cancers, were reported from the mid-1950s through 1980.
From 1986 through 1994, two years after the United States put a hold on full-scale nuclear weapons testing, 536 anti-nuclear protests were held at the Nevada Test Site involving 37,488 participants and 15,740 arrests, according to government records. Those arrested included the astronomer Carl Sagan and the actors Kris Kristofferson, Martin Sheen, and Robert Blake.
The Nevada Test Site contains 28 areas, 1,100 buildings, 400 miles (640 km) of paved roads, 300 miles of unpaved roads, ten heliports, and two airstrips. The most recent test was a sub-critical test of the properties of plutonium, conducted underground on December 7, 2012. | 1 | Applied and Interdisciplinary Chemistry |
Electroacoustic phenomena arise when ultrasound propagates through a fluid containing ions. The associated particle motion generates electric signals because ions have electric charge. This coupling between ultrasound and electric field is called electroacoustic phenomena. The fluid might be a simple Newtonian liquid, or complex heterogeneous dispersion, emulsion or even a porous body. There are several different electroacoustic effects depending on the nature of the fluid.
*Ion vibration current (IVI) and potential, an electric signal that arises when an acoustic wave propagates through a homogeneous fluid.
*Streaming vibration current (SVI) and potential, an electric signal that arises when an acoustic wave propagates through a porous body in which the pores are filled with fluid.
*Colloid vibration current (CVI) and potential, an electric signal that arises when ultrasound propagates through a heterogeneous fluid, such as a dispersion or emulsion.
*Electric sonic amplitude (ESA), the inverse of the CVI effect, in which an acoustic field arises when an electric field propagates through a heterogeneous fluid. | 0 | Theoretical and Fundamental Chemistry |
*Hermann Staudinger's research on macromolecular chemistry at the University of Freiburg between 1926 and 1956
*Synthesis of physostigmine by Percy Lavon Julian at DePauw University in 1935, which made physostigmine readily available for the treatment of glaucoma
*Work of Antoine Lavoisier to elucidate the principles of modern chemistry in the late 1700s
*Synthesis of progesterone by Russell Marker at Pennsylvania State University in 1938 (a process now known as Marker degradation), and the development of the Mexican steroid hormone industry by Syntex S.A. in the 1940s
*Separation of rare earth elements by Charles James at the University of New Hampshire in the early 1900s
*Discovery of polypropylene and development of a new high-density polyethylene by J. Paul Hogan and Robert Banks at Phillips Petroleum Company in 1951
*Discovery of penicillin by Alexander Fleming at St Mary's Hospital, London in 1928, and its large-scale development between 1939 and 1945 at the USDA Northern Regional Research Laboratory, Abbott Laboratories, Lederle Laboratories, Merck & Co., Inc., Chas. Pfizer & Co., Inc., and E.R. Squibb & Sons | 1 | Applied and Interdisciplinary Chemistry |
In materials science, recrystallization is a process by which deformed grains are replaced by a new set of defect-free grains that nucleate and grow until the original grains have been entirely consumed. Recrystallization is usually accompanied by a reduction in the strength and hardness of a material and a simultaneous increase in the ductility. Thus, the process may be introduced as a deliberate step in metals processing or may be an undesirable byproduct of another processing step. The most important industrial uses are softening of metals previously hardened or rendered brittle by cold work, and control of the grain structure in the final product. Recrystallization temperature is typically 0.3–0.4 times the melting point for pure metals and 0.5 times for alloys. | 1 | Applied and Interdisciplinary Chemistry |
In December, 2023, as part of a four-year legal battle, the EPA banned Inhance -- a Houston, Texas-based manufacturer that produces an estimated 200m containers annually with a process that creates, among other chemicals, PFOA -- from using the manufacturing process. In March, 2024, the Fifth Circuit federal appeals court overturned the ban. While the court did not deny the containers’ health risks, it said that the EPA could not regulate the manufactured containers under the statute it used. | 0 | Theoretical and Fundamental Chemistry |
Transition metal benzyne complexes represent a special case of alkyne complexes since the free benzynes are not stable in the absence of the metal. | 0 | Theoretical and Fundamental Chemistry |
Hydrogenases are subclassified into three different types based on the active site metal content: iron–iron hydrogenase, nickel–iron hydrogenase, and iron hydrogenase.
All hydrogenases catalyze reversible H uptake, but while the [FeFe] and [NiFe] hydrogenases are true redox catalysts, driving H oxidation and H reduction
:H 2 H + 2 e
the [Fe] hydrogenases catalyze the reversible heterolytic cleavage of H.
:H H + H | 1 | Applied and Interdisciplinary Chemistry |
Flocculation and sedimentation are widely employed in the purification of drinking water as well as in sewage treatment, storm-water treatment and treatment of industrial wastewater streams. Typical treatment processes consist of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection. As the demand for eco-friendly solutions in the flocculation process continues to grow, biopolymers are emerging as a highly promising solution. Among these, chitosan stands out for its exceptional properties, making it a top contender in this environmentally-conscious endeavor. Chitosan is not only biodegradable but also exhibits a unique ability to bind with a wide range of contaminants, including heavy metals and organic pollutants, effectively removing them from water sources. | 1 | Applied and Interdisciplinary Chemistry |
The typical framework building blocks are polyhedral units, with 6-coordinate metal centres. Usually, these units share edges and/or vertices. The coordination number of the oxide ligands varies according to their location in the cage. Surface oxides tend to be terminal or doubly bridging oxo ligands. Interior oxides are typically triply bridging or even octahedral. POMs are sometimes viewed as soluble fragments of metal oxides.
Recurring structural motifs allow POMs to be classified. Iso-polyoxometalates (isopolyanions) feature octahedral metal centers. The heteropolymetalates form distinct structures because the main group center is usually tetrahedral. The Lindqvist and Keggin structures are common motifs for iso- and heteropolyanions, respectively.
Polyoxometalates typically exhibit coordinate metal-oxo bonds of different multiplicity and strength. In a typical POM such as the Keggin structure , each addenda center connects to single terminal oxo ligand, four bridging µ-O ligands and one bridging µ-O deriving from the central heterogroup. Metal–metal bonds in polyoxometalates are normally absent and owing to this property, F. Albert Cotton opposed to consider polyoxometalates as form of cluster materials. However, metal-metal bonds are not completely absent in polyoxometalates and they are often present among the highly reduced species. | 0 | Theoretical and Fundamental Chemistry |
Aristotles brief comments on minima naturalia in the Physics and Meteorology' prompted further speculations by later philosophers. The idea was taken up by John Philoponus and Simplicius of Cilicia in late Antiquity and by the Islamic Aristotelian Averroes (Ibn Rushd).
Minima naturalia were discussed by Scholastic and Renaissance thinkers including Roger Bacon, Albertus Magnus, Thomas Aquinas, Giles of Rome, Siger of Brabant, Boethius of Dacia, Richard of Middleton, Duns Scotus, John of Jandun, William of Ockham, William Alnwick, Walter Bury, Adam de Wodeham, Jean Buridan, Gregory of Rimini, John Dumbleton, Nicole Oresme, John Marsilius Inguen, John Wycliffe, Albert of Saxony, Facinus de Ast, Peter Alboinis of Mantua, Paul of Venice, Gaetano of Thiene, Alessandro Achillini, Luis Coronel, Juan de Celaya, Domingo de Soto, Didacus de Astudillo, Ludovicus Buccaferrea, Francisco de Toledo, and Benedict Pereira. Of this list, the most influential Scholastic thinkers on minima naturalia were Duns Scotus and Gregory of Rimini.
A chief theme in later commentary is reconciling minima naturalia with the general Aristotelian principle of infinite divisibility. Commentators like Philoponus and Aquinas reconciled these aspects of Aristotles thought by distinguishing between mathematical and "natural" divisibility. For example, in his commentary on Aristotles Physics, Aquinas writes of natural minima that, "although a body, considered mathematically, is divisible to infinity, the natural body is not divisible to infinity. For in a mathematical body nothing but quantity is considered. And in this there is nothing repugnant to division to infinity. But in a natural body the form also is considered, which form requires a determinate quantity and also other accidents. Whence it is not possible for quantity to be found in the species of flesh except as determined within some termini." | 1 | Applied and Interdisciplinary Chemistry |
LacI finds its target operator DNA surprisingly fast. In vitro the search is 10-100 times faster than the theoretical upper limit for two particles searching for each other via diffusion in three dimensions (3D). To explain the fast search, it was hypothesized that LacI and other transcription factors (TFs) find their binding sites by facilitated diffusion, a combination of free diffusion in 3D and 1D-sliding on the DNA. During sliding the repressor is in contact with the DNA helix, sliding around and tracking its major groove, which speeds up the search process by extending the target length when the TF slides in onto the operator from the side. In vivo single-molecule experiments with E.coli cells have now tested and verified the facilitated diffusion model, and shown that the TF scans on average 45 bp during each sliding event, before the TF detaches spontaneously and resumes exploring the genome in 3D. These experiments also suggest that LacI slides over the O operator several times before binding, meaning that different DNA sequences can have different probabilities to be recognized at each encounter with the TF. This implies a trade-off between fast search on nonspecific sequences and binding to specific sequences. In vivo and in vitro experiments have shown that it is this probability to recognize the operator that changes with DNA sequence, while the time the TF remains in the bound conformation on the operator changes less with sequence. The TF often leaves the sequence it is intended to regulate, but at a strong target site, it almost always make a very short journey before finding the way back again. On the macroscopic scale, this looks like a stable interaction. This binding mechanism explains how DNA binding proteins manage to quickly search through the genome of the cell without getting stuck too long at sequences that resemble the true target.
An all-atom molecular dynamics simulation suggests that the transcription factor encounters a barrier of 1 kT during sliding and 12 kT for dissociation, implying that the repressor will slide over 8 bp on average before dissociating. The in vivo search model for the lac repressor includes intersegment transfer and hopping as well as crowding by other proteins which make the genome in E.coli cells less accessible for the repressor. The existence of hopping, where the protein slips out of the major groove of DNA to land in another nearby groove along the DNA chain, has been proven more directly in vitro, where the lac repressor has been observed to bypass operators, flip orientation, and rotate with a longer pitch than the 10.5 bp period of DNA while moving along it. | 1 | Applied and Interdisciplinary Chemistry |
Silicon has three major advantages over GaAs for integrated circuit manufacture. First, silicon is abundant and cheap to process in the form of silicate minerals. The economies of scale available to the silicon industry has also hindered the adoption of GaAs.
In addition, a Si crystal has a very stable structure and can be grown to very large diameter boules and processed with very good yields. It is also a fairly good thermal conductor, thus enabling very dense packing of transistors that need to get rid of their heat of operation, all very desirable for design and manufacturing of very large ICs. Such good mechanical characteristics also make it a suitable material for the rapidly developing field of nanoelectronics. Naturally, a GaAs surface cannot withstand the high temperatures needed for diffusion; however a viable and actively pursued alternative as of the 1980s was ion implantation.
The second major advantage of Si is the existence of a native oxide (silicon dioxide, SiO), which is used as an insulator. Silicon dioxide can be incorporated onto silicon circuits easily, and such layers are adherent to the underlying silicon. SiO is not only a good insulator (with a band gap of 8.9 eV), but the Si-SiO interface can be easily engineered to have excellent electrical properties, most importantly low density of interface states. GaAs does not have a native oxide, does not easily support a stable adherent insulating layer, and does not possess the dielectric strength or surface passivating qualities of the Si-SiO.
Aluminum oxide (AlO) has been extensively studied as a possible gate oxide for GaAs (as well as InGaAs).
The third advantage of silicon is that it possesses a higher hole mobility compared to GaAs (500 versus 400 cmVs). This high mobility allows the fabrication of higher-speed P-channel field-effect transistors, which are required for CMOS logic. Because they lack a fast CMOS structure, GaAs circuits must use logic styles which have much higher power consumption; this has made GaAs logic circuits unable to compete with silicon logic circuits.
For manufacturing solar cells, silicon has relatively low absorptivity for sunlight, meaning about 100 micrometers of Si is needed to absorb most sunlight. Such a layer is relatively robust and easy to handle. In contrast, the absorptivity of GaAs is so high that only a few micrometers of thickness are needed to absorb all of the light. Consequently, GaAs thin films must be supported on a substrate material.
Silicon is a pure element, avoiding the problems of stoichiometric imbalance and thermal unmixing of GaAs.
Silicon has a nearly perfect lattice; impurity density is very low and allows very small structures to be built (down to 5 nm in commercial production as of 2020). In contrast, GaAs has a very high impurity density, which makes it difficult to build integrated circuits with small structures, so the 500 nm process is a common process for GaAs.
Silicon has about three times the thermal conductivity of GaAs, with less risk of local overheating in high power devices. | 0 | Theoretical and Fundamental Chemistry |
In the U.S. in 1975, under the authority of the Safe Drinking Water Act, the U.S. Environmental Protection Agency determined the National Interim Primary Drinking Water Regulation levels of arsenic (inorganic contaminant – IOCs) to be 0.05 mg/L (50 parts per billion – ppb).
Throughout the years, many studies reported dose-dependent effects of arsenic in drinking water and skin cancer. In order to prevent new cases and death from cancerous and non-cancerous diseases, the Safe Drinking Water Act directed the Environmental Protection Agency to revise arsenic's levels and specified the maximum contaminant level (MCL). MCLs are set as close to the health goals as possible, considering cost, benefits and the ability of public water systems to detect and remove contaminants using suitable treatment technologies.
In 2001, Environmental Protection Agency adopted a lower standard of MCL 0.01 mg/L (10 ppb) for arsenic in drinking water that applies to both community water systems and non-transient non-community water systems.
In some other countries, when developing national drinking water standards based on the guideline values, it is necessary to take account of a variety of geographical, socio-economic, dietary and other conditions affecting potential exposure. These factors lead to national standards that differ appreciably from the guideline values. That is the case in countries such as India and Bangladesh, where the permissible limit of arsenic in absence of an alternative source of water is 0.05 mg/L. | 1 | Applied and Interdisciplinary Chemistry |
There are two principal ways to prepare colloids:
* Dispersion of large particles or droplets to the colloidal dimensions by milling, spraying, or application of shear (e.g., shaking, mixing, or high shear mixing).
* Condensation of small dissolved molecules into larger colloidal particles by precipitation, condensation, or redox reactions. Such processes are used in the preparation of colloidal silica or gold. | 0 | Theoretical and Fundamental Chemistry |
Exon trapping is a molecular biology technique to identify potential exons in a fragment of eukaryote DNA of unknown intron-exon structure. This is done to determine if the fragment is part of an expressed gene.
The genomic fragment is inserted into the intron of a splicing vector consisting of a known exon - intron - exon sequence of DNA, and the vector is then inserted into an eukaryotic cell. If the fragment does not contain exons (i.e., consists solely of intron DNA), it will be spliced out together with the vectors original intron. On the other hand, if exons are contained, they will be part of the mature mRNA after transcription (with all intron material removed). The presence of trapped exons' can be detected by an increase in size of the mRNA, or through RT-PCR to amplify the DNA of interest.
The technique has largely been supplanted by the approach of sequencing cDNA generated from mRNA and then using bioinformatics tools such as NCBI's BLAST server to determine the source of the sequence, thereby identifying the appropriate exon-intron splice sites. | 1 | Applied and Interdisciplinary Chemistry |
Earthenware storage jars for drugs have been found on archaeological sites in Turkey, Iran, Iraq, Greece and Rome. The technology appears to have originated in Mesopotamia in 600–400 B.C. A number of innovations occurred in Western Asia regarding pottery decoration, particularly the development of tin glazes to enable jars to contain fluids. The tin glaze was believed to have originated in Mesopotamia in 600–400 B.C. By the 12th to 13th centuries jars were lustreware which gave a sheen to the surface of the jars.
Jars from Syria and Persia were taken to Spain from the 13th to 14th centuries after which Spanish and Italian potters began to manufacture jars. The tin glaze technique which allowed decoration of the jars was known in Europe as maiolica, faience or delftware. These different terms referred not to technical differences in the jars' manufacture but stylistic differences.
The style of jar known as albarello also came from the Middle Eastern Islamic potters. The albarello is cylindrical in shape usually with a narrow waist; it has a flange at the open end. A parchment cover could be tied over the flange to seal the contents. Other jars were ovoid or globular in shape. Syrup jars had spouts and handles. Other items used by apothecaries were dispensing and ointment pots, pill tiles and mortars.
Potteries producing jars were located in Spain, France, Italy, Sicily, Switzerland, Germany, Austria, Belgium, Holland, Sweden, and Britain.
Jars were widely used in Europe and Latin America at the beginning of the 19th century but during the 18th and 19th centuries production of glass storage bottles was increased.
Animal, mineral and vegetable ingredients were stored in the jars.
Vegetable ingredients included culinary herbs, fruits, roots, leaves, seeds, flowers, wood, oils, gums and resins. Spices used for medicinal purposes included cassia bark, tamarind, nux vomica, senna, sandalwood, cloves and nutmeg. These came from the Near East and later ingredients from the New World included copaiva balsam, sarsaparilla, tobacco, cinchona bark (quinine) and ipecacuanha.
Some common animal products were contained, such as honey, butter, beeswax and chicken fat as well as more unusual ingredients including foxes' lungs, earthworms, scorpions, musk, ambergris and ivory. Minerals used included precious stones and sulphur, mercury, antimony and other minerals. | 1 | Applied and Interdisciplinary Chemistry |
Chowdhury made pioneering contributions to the development of physical chemistry in the country, publishing more than 20 articles. He focused on cellulose fibers (of jute in particular), polyelectrolytes, and proteins. He also guided a number of PhD theses. | 0 | Theoretical and Fundamental Chemistry |
There is an independent invention theory supporting an Islamic origin of the gun, citing the Mamluk deployment of hand cannons in 1260 and a passage by Ibn Khaldun on the Marinid Siege of Sijilmassa in 1274: "[ The Sultan] installed siege engines … and gunpowder engines …, which project small balls of iron. These balls are ejected from a chamber … placed in front of a kindling fire of gunpowder; this happens by a strange property which attributes all actions to the power of the Creator." The passage, dated to 1382, and its interpretation has been rejected as anachronistic by most historians, who urge caution regarding claims of Islamic firearms use in the 1204–1324 period as late medieval Arabic texts used the same word for gunpowder, naft, as they did for an earlier incendiary, naphtha. Needham believes Ibn Khaldun was speaking of fire lances or proto-guns rather than hand cannon.
Historian Ahmad Y. al-Hassan, based on his analysis of 14th-century Arabic manuscripts which he argues to be copies of earlier texts, claims that hand cannons were used at the Battle of Ain Jalut in 1260. However Hassans claims have been refuted by other historians such as David Ayalon, Iqtidar Alam Khan, Joseph Needham, Tonio Andrade, and Gabor Ágoston. Khan argues that it was the Mongols who introduced gunpowder to the Islamic world, and believes cannons only reached Mamluk Egypt in the 1370s. According to Needham, fire lances or proto-guns were known to Muslims by the late 13th century and early 14th century. However the term midfa, dated to textual sources from 1342 to 1352, cannot be proven to be true hand-guns or bombards, and contemporary accounts of a metal-barrel cannon in the Islamic world do not occur until 1365. Needham also concludes that in its original form the term midfa' refers to the tube or cylinder of a naphtha projector (flamethrower), then after the invention of gunpowder it meant the tube of fire lances, and eventually it applied to the cylinder of hand-gun and cannon. Similarly, Andrade dates the textual appearance of cannon in middle eastern sources to the 1360s. Gabor Ágoston and David Ayalon believe the Mamluks had certainly used siege cannon by the 1360s, but earlier uses of cannon in the Islamic World are vague with a possible appearance in the Emirate of Granada by the 1320s, however evidence is inconclusive. | 1 | Applied and Interdisciplinary Chemistry |
Tetraterpenes are terpenes consisting of eight isoprene units and have the molecular formula CH. Tetraterpenoids (including many carotenoids) are tetraterpenes that have been chemically modified, as indicated by the presence of oxygen-containing functional groups.
Phytoene is biosynthesized via the head-to-head condensation of two GGPP molecules. One group of tetraterpenes, and possibly the most studied one, is the carotenoids pigments. Carotenoids have important biological functions, with roles in light capture, antioxidative activity and protection against free radicals, synthesis of plant hormones and as structural components of the membranes. Aside their biological relevance, carotenoids are also high-value compounds for the food and pharmaceutical industries. Carotenoids are biosynthesized by photosynthetic and non-photosynthetic organisms; however, in photosynthetic organisms, they are essential components as accessory pigments for the light-harvesting reaction centers. Xanthophylls are another group of tetraterpene pigments distributed widely in nature. | 1 | Applied and Interdisciplinary Chemistry |
Particle-laden flows refers to a class of two-phase fluid flow, in which one of the phases is continuously connected (referred to as the continuous or carrier phase) and the other phase is made up of small, immiscible, and typically dilute particles (referred to as the dispersed or particle phase). Fine aerosol particles in air is an example of a particle-laden flow; the aerosols are the dispersed phase, and the air is the carrier phase.
The modeling of two-phase flows has a tremendous variety of engineering and scientific applications: pollution dispersion in the atmosphere, fluidization in combustion processes, aerosol deposition in spray medication, along with many others. | 1 | Applied and Interdisciplinary Chemistry |
The development of NeSSI has been a collaborative effort between industrial end-users, manufacturers who supply the industries, and academic researchers working in the area of process analytics. CPAC continues as the focal point for NeSSI development, and sponsor of the NeSSI steering team. CPAC provides a neutral umbrella under which interested companies have been able to meet, discuss needs and issues, and make progress towards defining the future of industrial sampling and analyzer systems. The NeSSI name is trademarked by the University of Washington to ensure that it remains freely associated with the open nature of the initiative anyone can use the name NeSSI to refer to products or services that are consistent with the specifications and guidelines of NeSSI as long as they refrain from exclusively tying the name to a proprietary product or service. | 1 | Applied and Interdisciplinary Chemistry |
The eponymous title Baopuzi derives from Ge Hongs hao (), the hao being a type of sobriquet or pseudonym. Baopuzi literally means "The Master Who Embraces Simplicity;" compounded from the words bao () meaning "embrace; hug; carry; hold in both arms; cherish"; pu () meaning "uncarved wood", also being a Taoist metaphor for a "persons original nature; simple; plain"; and, zi (子) meaning "child; offspring; master (title of respect)". Baopu (Pao-pu; literally:"Simplex"), is a classical allusion to the Tao Te Ching' (19):
Ge Hong's autobiography explains his rationale for choosing his pen name Baopuzi.
<blockquote>
Compare these autobiography translations: "people all call me a pao-pu scholar (i.e., one who keeps his basic nature, one who is unperturbed by the desires of the world)"; "among the people of his district there were those who called him "The Scholar Who Embraces Simplicity"." Wu and Davis noted, "This name has been translated Old Sober-Sides, but Dr. Wu considers that it has no satirical intent and would better be translated Solemn-Seeming Philosopher'." Fabrizio Pregadio translates "Master Who Embraces Spontaneous Nature". | 1 | Applied and Interdisciplinary Chemistry |
Cast iron has been found in China dating to the 5th century BC, but the earliest extant blast furnaces in China date to the 1st century AD and in the West from the High Middle Ages. They spread from the region around Namur in Wallonia (Belgium) in the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal. The successful substitution of coke for charcoal is widely attributed to English inventor Abraham Darby in 1709. The efficiency of the process was further enhanced by the practice of preheating the combustion air (hot blast), patented by Scottish inventor James Beaumont Neilson in 1828. | 1 | Applied and Interdisciplinary Chemistry |
This is to give an overview of the evolving chirality nomenclature system commonly employed to distinguish enantiomers of a chiral drug. In the beginning, enantiomers were distinguished based on their ability to rotate the plane of plane-polarized light. The enantiomer that rotates the plane-polarized light to the right is named "dextro-rotatory", abbreviated as "dextro" or "d" and the counterpart as "levo" or "l". A racemic mixture is denoted as "(±)", "rac", or "dl". Now the d/l system of naming based on optical rotation is falling into disuse.
Later, the Fischer convention was introduced to specify the configuration of a stereogenic center and uses the symbols D and L. The use of capital letters is to differentiate from the "d" / "l" notation (optical descriptor) described earlier. In this system, the enantiomers are named with reference to D- and L-glyceraldehyde which is taken as the standard for comparison. The structure of the chiral molecule should be represented in the Fischer projection formula. If the hydroxyl group attached to the highest chiral carbon is on the right-hand side it is referred to as D-series and if on the left-hand side it is called L-series. This nomenclature system has also become obsolete. But D-/L-system of naming is still employed to designate the configuration of amino acids and sugars. In general the D/L system of nomenclature is superseded by the Cahn-Ingold-Prelog (CIP) rule to describe the configuration of a stereogenic/chiral center.
In the CIP or R/S convention, or sequence rule, the configuration, spatial arrangements of ligands/substituents around a chiral center, is labeled as either "R" or "S". This convention is now almost worldwide in use and become a part of the IUPAC (International Union of Pure and Applied Chemistry) rules of nomenclature. In this approach: identify the chiral center, label the four atoms directly attached to the stereogenic center in question, assign priorities according to the sequence rule ( from 1 to 4), rotate the molecule until the lowest priority (number 4) substituent is away from the observer/viewer, draw a curve from number 1 to number 2 to number 3 substituent. If the curve is clockwise, the chiral center is of R-absolute configuration, "R" (Latin, rectus = right). If the curve is counterclockwise, the chiral center is of S-absolute configuration, "S" (Latin, sinister = left). Refer to figure, the Cahn-Ingold-Prelog rule.
An overview of the nomenclature system is presented in the table below. | 0 | Theoretical and Fundamental Chemistry |
DXZ4 is a variable number tandemly repeated DNA sequence. In humans it is composed of 3kb monomers containing a highly conserved CTCF binding site. CTCF is a transcription factor protein and the main insulator responsible for partitioning of chromatin domains in the vertebrate genome.
In addition to being enriched in CpG-islands, DXZ4 transcribes long non-coding RNAs (lncRNAs) and small RNAs of unknown function. Repeat copy number of DXZ4 is highly polymorphic in human populations (varying between 50 and 100 copies). DXZ4 is one of many large tandem repeat loci defined as macrosatellites. Several macrosatellites have been described in humans and share similar features, such as high GC content, large repeat monomers, and high variability for repeat copy number within populations. DXZ4 plays an important role in the unique structural conformation of the inactive X chromosome (Xi) in female somatic cells by acting as a hinge point between two large “super domains”.
In addition to acting as the primary division between domains, DXZ4 forms long-range interactions with a number of other repeat rich regions along the inactive X chromosome. Knockout of the DXZ4 locus revealed loss of this structural conformation on the Xi with chromosome wide silencing being maintained. | 1 | Applied and Interdisciplinary Chemistry |
There is considerable interest in applying gene-editing methods to the treatment of diseases with a genetic component. However, there are multiple challenges associated with this approach. An effective treatment would require editing of a large number of target cells, which in turn would require an effective method of delivery and a great level of tissue specificity.
As of 2019, prime editing looks promising for relatively small genetic alterations, but more research needs to be conducted to evaluate whether the technology is efficient in making larger alterations, such as targeted insertions and deletions. Larger genetic alterations would require a longer RT template, which could hinder the efficient delivery of pegRNA to target cells. Furthermore, a pegRNA containing a long RT template could become vulnerable to damage caused by cellular enzymes. Prime editing in plants suffers from low efficiency ranging from zero to a few percent and needs significant improvement.
Some of these limitations have been mitigated by recent improvements to the prime editors, including motifs that protect pegRNAs from degradation. Further research is needed before prime editing could be used to correct pathogenic alleles in humans. Research has also shown that inhibition of certain MMR proteins, including MLH1 can improve prime editing efficiency. | 1 | Applied and Interdisciplinary Chemistry |
The multicopper active site of CP contains a type I (T1) mononuclear copper site and a trinuclear copper center ~ 12-13 Å away (see figure 2). The tricopper center consists of two type III (T3) coppers and one type II (T2) copper ion. The two T3 copper ions are bridged by a hydroxide ligand while another hydroxide ligand links the T2 copper ion to the protein. The T1 center is bridged to the tricopper center by two histidine (His1020, His1022) residues and one Cys(1021) residue. The substrate binds near the T1 center and is oxidized by the T1 Cu ion forming the reduced Cu oxidation state. The reduced T1 Cu then transfers the electron through the one Cys and two His bridging residues to the tricopper center. After four electrons have been transferred from the substrates to the copper centers, an O binds at the tricopper center and undergoes a four-electron reduction to form two molecules of water. | 1 | Applied and Interdisciplinary Chemistry |
Primer-design software uses algorithms that check for the potential of DNA secondary structure formation and annealing of primers to itself or within primer pairs. Physical parameters that are taken into account by the software are potential self-complementarity and GC content of the primers; similar melting temperatures of the primers; and absence of secondary structures, such as stem-loops, in the DNA target sequence. | 1 | Applied and Interdisciplinary Chemistry |
In physics, colloids are an interesting model system for atoms. Micrometre-scale colloidal particles are large enough to be observed by optical techniques such as confocal microscopy. Many of the forces that govern the structure and behavior of matter, such as excluded volume interactions or electrostatic forces, govern the structure and behavior of colloidal suspensions. For example, the same techniques used to model ideal gases can be applied to model the behavior of a hard sphere colloidal suspension. Phase transitions in colloidal suspensions can be studied in real time using optical techniques, and are analogous to phase transitions in liquids. In many interesting cases optical fluidity is used to control colloid suspensions. | 0 | Theoretical and Fundamental Chemistry |
Janus kinase (JAK) is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. They were initially named "just another kinase" 1 and 2 (since they were just two of many discoveries in a PCR-based screen of kinases), but were ultimately published as "Janus kinase". The name is taken from the two-faced Roman god of beginnings, endings and duality, Janus, because the JAKs possess two near-identical phosphate-transferring domains. One domain exhibits the kinase activity, while the other negatively regulates the kinase activity of the first. | 1 | Applied and Interdisciplinary Chemistry |
* 1970: Peter Goldacre Award from the Australian Society of Plant Scientists (previously called the Australian Society of Plant Physiologists).
* 1980: Charles F Kettering Award from the American Society of Plant Physiologists, shared with Hugo Kortschak and Marshall (Hal) Davidson Hatch.
* 1981: Rank Prize for Nutrition, shared with Hugo Kortschak and Marshall (Hal) Davidson Hatch.
* 1983: Elected as a Fellow of the Royal Society of New Zealand.
* 1989: Elected as a Fellow of the Royal Society. | 1 | Applied and Interdisciplinary Chemistry |
Carboxypeptidase A6 (CPA6) is a metallocarboxypeptidase enzyme that in humans is encoded by the CPA6 gene. It is highly expressed in the adult mouse olfactory bulb and is broadly expressed in the embryonic brain and other tissues.
The protein encoded by this gene belongs to the family of carboxypeptidases, which catalyze the release of C-terminal amino acid, and have functions ranging from digestion of food to selective biosynthesis of neuroendocrine peptides. Polymorphic variants and a reciprocal translocation t(6;8)(q26;q13) involving this gene, have been associated with Duane retraction syndrome.
CPA6 processes several neuropeptides, including [[Met-enkephalin|[Met]-]] and [[Leu-enkephalin|[Leu]-enkephalin]], angiotensin I, and neurotensin in vitro. Whereas CPA6 is capable of converting the enkephalins and neurotensin into inactive forms, it can convert the inactive angiotensin I into the active angiotensin II. CPA6 may have additional roles in processing peptides and proteins in vivo, but the nature of these substrates and the effects of these cleavages are currently unknown. | 1 | Applied and Interdisciplinary Chemistry |
Some species are named after siphons because they resemble siphons in whole or in part. Geosiphons are fungi. There are species of alga belonging to the family Siphonocladaceae in the phylum Chlorophyta which have tube-like structures. Ruellia villosa is a tropical plant in the family Acanthaceae that is also known by the botanical synonym, Siphonacanthus villosus Nees. | 1 | Applied and Interdisciplinary Chemistry |
The effect of frequency dispersion is that the waves travel as a function of wavelength, so that spatial and temporal phase properties of the propagating wave are constantly changing. For example, under the action of gravity, water waves with a longer wavelength travel faster than those with a shorter wavelength.
While two superimposed sinusoidal waves, called a bichromatic wave, have an envelope which travels unchanged, three or more sinusoidal wave components result in a changing pattern of the waves and their envelope. A sea state – that is: real waves on the sea or ocean – can be described as a superposition of many sinusoidal waves with different wavelengths, amplitudes, initial phases and propagation directions. Each of these components travels with its own phase velocity, in accordance with the dispersion relation. The statistics of such a surface can be described by its power spectrum. | 1 | Applied and Interdisciplinary Chemistry |
A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady state, although the liquid phase may still diffuse through this system.
Gels are mostly liquid by mass, yet they behave like solids because of a three-dimensional cross-linked network within the liquid. It is the cross-linking within the fluid that gives a gel its structure (hardness) and contributes to the adhesive stick (tack). In this way, gels are a dispersion of molecules of a liquid within a solid medium. The word gel was coined by 19th-century Scottish chemist Thomas Graham by clipping from gelatine.
The process of forming a gel is called gelation. | 0 | Theoretical and Fundamental Chemistry |
In vitro transcription (IVT) is performed on a linearized DNA plasmid template containing the targeted coding sequence. Then, naked mRNA or mRNA complexed in a nanoparticle will be delivered systemically or locally. Subsequently, a part of the exogenous naked mRNA or complexed mRNA will go through cell-specific mechanisms. Once in the cytoplasm, the IVT mRNA is translated by the protein synthesis machinery.
There are two identified RNA sensors, toll-like receptors (TLRs) and the RIG-I-like receptor family. TLRs are localized in the endosomal compartment of cells, such as DCs and macrophages. RIG-I-like family is as a pattern recognition receptor (PRR). However, the immune response mechanisms and process of mRNA vaccine recognition by cellular sensors and the mechanism of sensor activation are still unclear. | 1 | Applied and Interdisciplinary Chemistry |
pRb is able to be localize to sites of DNA breaks during the repair process and assist in non-homologous end joining and homologous recombination through complexing with E2F1. Once at the breaks, pRb is able to recruit regulators of chromatin structure such as the DNA helicase transcription activator BRG1. pRb has been shown to also be able to recruit protein complexes such as condensin and cohesin to assist in the structural maintenance of chromatin.
Such findings suggest that in addition to its tumor suppressive role with E2F, pRb is also distributed throughout the genome to aid in important processes of genome maintenance such as DNA break-repair, DNA replication, chromosome condensation, and heterochromatin formation. | 1 | Applied and Interdisciplinary Chemistry |
The Royal Commission on River Pollution, established in 1865, and the formation of the Royal Commission on Sewage Disposal in 1898 led to the selection in 1908 of BOD as the definitive test for organic pollution of rivers. Five days was chosen as an appropriate test period because this is supposedly the longest time that river water takes to travel from source to estuary in the U.K. In its sixth report the Royal Commission recommended that the standard set should be 15 parts by weight per million of water. However, in the Ninth report the commission had revised the recommended standard: This was the cornerstone 20:30 (BOD:Suspended Solids) + full nitrification standard which was used as a yardstick in the U.K. up to the 1970s for sewage works effluent quality.
The United States includes BOD effluent limitations in its secondary treatment regulations. Secondary sewage treatment is generally expected to remove 85 percent of the BOD measured in sewage and produce effluent BOD concentrations with a 30-day average of less than 30 mg/L and a 7-day average of less than 45 mg/L. The regulations also describe "treatment equivalent to secondary treatment" as removing 65 percent of the BOD and producing effluent BOD concentrations with a 30-day average less than 45 mg/L and a 7-day average less than 65 mg/L. | 0 | Theoretical and Fundamental Chemistry |
Heme biosynthesis is used as biomarker in environmental toxicology studies. While excess production of porphyrins indicate organochlorine exposure, lead inhibits ALA dehydratase enzyme. | 1 | Applied and Interdisciplinary Chemistry |
Several heterocycles related to porphyrins are found in nature, almost always bound to metal ions. These include | 1 | Applied and Interdisciplinary Chemistry |
Electromagnetic transitions in atoms, molecules and condensed matter mainly take place at energies corresponding to the UV and visible part of the spectrum. Core electrons in atoms, and many other phenomena, are observed with different brands of XAS in the X-ray energy range. Electromagnetic transitions in atomic nuclei, as observed in Mössbauer spectroscopy, take place in the gamma ray part of the spectrum. The main factors that cause broadening of the spectral line into an absorption band of a molecular solid are the distributions of vibrational and rotational energies of the molecules in the sample (and also those of their excited states). In solid crystals the shape of absorption bands are determined by the density of states of initial and final states of electronic states or lattice vibrations, called phonons, in the crystal structure. In gas phase spectroscopy, the fine structure afforded by these factors can be discerned, but in solution-state spectroscopy, the differences in molecular micro environments further broaden the structure to give smooth bands. Electronic transition bands of molecules may be from tens to several hundred nanometers in breadth. | 0 | Theoretical and Fundamental Chemistry |
Organic carbon burial is an input of energy for underground biological environments and can regulate oxygen in the atmosphere at long time-scales (> 10,000 years). Burial can only take place if organic carbon arrives to the sea floor, making continental shelves and coastal margins the main storage of organic carbon from terrestrial and oceanic primary production. Fjords, or cliffs created by glacial erosion, have also been identified as areas of significant carbon burial, with rates one hundred times greater than the ocean average. Particulate organic carbon is buried in oceanic sediments, creating a pathway between a rapidly available carbon pool in the ocean to its storage for geological timescales. Once carbon is sequestered in the seafloor, it is considered blue carbon. Burial rates can be calculated as the difference between the rate at which organic matter sinks and the rate at which it decomposes. | 0 | Theoretical and Fundamental Chemistry |
According to al-Kindi, the goal of metaphysics is knowledge of God. For this reason, he does not make a clear distinction between philosophy and theology, because he believes they are both concerned with the same subject. Later philosophers, particularly al-Farabi and Avicenna, would strongly disagree with him on this issue, by saying that metaphysics is actually concerned with being qua being, and as such, the nature of God is purely incidental.
Central to al-Kindis understanding of metaphysics is Gods absolute oneness, which he considers an attribute uniquely associated with God (and therefore not shared with anything else). By this he means that while we may think of any existent thing as being "one", it is in fact both "one" and many". For example, he says that while a body is one, it is also composed of many different parts. A person might say "I see an elephant", by which he means "I see one elephant", but the term elephant refers to a species of animal that contains many. Therefore, only God is absolutely one, both in being and in concept, lacking any multiplicity whatsoever. Some feel this understanding entails a very rigorous negative theology because it implies that any description which can be predicated to anything else, cannot be said about God.
In addition to absolute oneness, al-Kindi also described God as the Creator. This means that He acts as both a final and efficient cause. Unlike later Muslim Neo-Platonic philosophers (who asserted that the universe existed as a result of Gods existence "overflowing", which is a passive act), al-Kindi conceived of God as an active agent. In fact, of God as the agent, because all other intermediary agencies are contingent upon Him. The key idea here is that God "acts" through created intermediaries, which in turn "act" on one another – through a chain of cause and effect – to produce the desired result. In reality, these intermediary agents do not "act" at all, they are merely a conduit for Gods own action. This is especially significant in the development of Islamic philosophy, as it portrayed the "first cause" and "unmoved mover" of Aristotelian philosophy as compatible with the concept of God according to Islamic revelation. | 1 | Applied and Interdisciplinary Chemistry |
For a general unimolecular reaction involving interconversion of different species, whose concentrations at time are denoted by through , an analytic form for the time-evolution of the species can be found. Let the rate constant of conversion from species to species be denoted as , and construct a rate-constant matrix whose entries are the .
Also, let be the vector of concentrations as a function of time.
Let be the vector of ones.
Let be the identity matrix.
Let be the function that takes a vector and constructs a diagonal matrix whose on-diagonal entries are those of the vector.
Let be the inverse Laplace transform from to .
Then the time-evolved state is given by
thus providing the relation between the initial conditions of the system and its state at time . | 0 | Theoretical and Fundamental Chemistry |
The Bailar twist is a mechanism proposed for the racemization of octahedral complexes containing three bidentate chelate rings. Such complexes typically adopt an octahedral molecular geometry, in which case they possess helical chirality. One pathway by which these compounds can racemize is via the formation of a trigonal prismatic intermediate with D3h point group symmetry. This pathway is named in honor of John C. Bailar, Jr., an inorganic chemist who investigated this process. An alternative pathway is called the Ray–Dutt twist. | 0 | Theoretical and Fundamental Chemistry |
Classified as an orphan disease, there is currently no therapy for OPMD, caused by a mutation in the poly(A) binding protein nuclear 1 (PABPN1) gene. Silencing the mutant gene using DDRNAI offers a potential therapeutic approach. | 1 | Applied and Interdisciplinary Chemistry |
Micro process engineering is the science of conducting chemical or physical processes (unit operations) inside small volumina,
typically inside channels with diameters of less than 1 mm
(microchannels) or other structures with sub-millimeter dimensions.
These processes are usually carried out in continuous flow mode, as opposed to batch production, allowing a throughput high enough to make micro process engineering a tool for chemical production. Micro process engineering is therefore not to be confused with microchemistry, which deals with very small overall quantities of matter.
The subfield of micro process engineering that deals with chemical
reactions, carried out in microstructured reactors or
"microreactors", is also known as microreaction technology.
The unique advantages of microstructured reactors or microreactors are enhanced heat transfer due to the large surface area-to-volume ratio, and enhanced mass transfer. For example, the length scale of diffusion processes is comparable to that of microchannels or even shorter, and efficient mixing of reactants can be achieved during very short times (typically milliseconds). The good heat transfer properties allow a precise temperature control of reactions. For example, highly
exothermic reactions can be conducted almost isothermally when the microstructured reactor contains a second set of microchannels ("cooling passage"), fluidically separated from the reaction channels ("reaction
passage"), through which a flow of cold fluid with sufficiently high
heat capacity is maintained. It is also possible to change the temperature of microstructured reactors very rapidly to intentionally achieve a non-isothermal behaviour. | 1 | Applied and Interdisciplinary Chemistry |
In materials science, grain-boundary strengthening (or Hall–Petch strengthening) is a method of strengthening materials by changing their average crystallite (grain) size. It is based on the observation that grain boundaries are insurmountable borders for dislocations and that the number of dislocations within a grain has an effect on how stress builds up in the adjacent grain, which will eventually activate dislocation sources and thus enabling deformation in the neighbouring grain as well. By changing grain size, one can influence the number of dislocations piled up at the grain boundary and yield strength. For example, heat treatment after plastic deformation and changing the rate of solidification are ways to alter grain size. | 1 | Applied and Interdisciplinary Chemistry |
The U.S. Food and Drug Administration (FDA) approved tramadol in March 1995, and an extended-release (ER) formulation in September 2005. ER Tramadol was protected by US patents nos. 6,254,887 and 7,074,430. The FDA listed the patents' expiration as 10 May 2014. However, in August 2009, US District Court for the District of Delaware ruled the patents invalid, a decision upheld the following year by the Court of Appeals for the Federal Circuit. Manufacture and distribution of generic equivalents of Ultram ER in the United States was therefore permitted prior to the expiration of the patents. | 0 | Theoretical and Fundamental Chemistry |
Enone–alkene cycloadditions often suffer from side reactions, e.g. those associated with the diradical intermediate. These side reactions can often be minimized by a judicious choice of reaction conditions.
Dissolved oxygen is avoided since it is photo reactive.
A variety of solvents can be used. Acetone is a useful solvent, because it can serve as a triplet sensitizer. Alkane-based solvents are selected to be free of alkenes. Excitation wavelength is important. For intermolecular reactions, excess of the alkene can be employed to avoid competitive dimerization of the enone. | 0 | Theoretical and Fundamental Chemistry |
Most neutron emission outside prompt neutron production associated with fission (either induced or spontaneous), is from neutron-heavy isotopes produced as fission products. These neutrons are sometimes emitted with a delay, giving them the term delayed neutrons, but the actual delay in their production is a delay waiting for the beta decay of fission products to produce the excited-state nuclear precursors that immediately undergo prompt neutron emission. Thus, the delay in neutron emission is not from the neutron-production process, but rather its precursor beta decay, which is controlled by the weak force, and thus requires a far longer time. The beta decay half lives for the precursors to delayed neutron-emitter radioisotopes, are typically fractions of a second to tens of seconds.
Nevertheless, the delayed neutrons emitted by neutron-rich fission products aid control of nuclear reactors by making reactivity change far more slowly than it would if it were controlled by prompt neutrons alone. About 0.65% of neutrons are released in a nuclear chain reaction in a delayed way due to the mechanism of neutron emission, and it is this fraction of neutrons that allows a nuclear reactor to be controlled on human reaction time-scales, without proceeding to a prompt critical state, and runaway melt down. | 0 | Theoretical and Fundamental Chemistry |
Depending on the nature of the adsorbent-to-surface bond, there are a multitude of mechanisms for desorption. The surface bond of a sorbant can be cleaved thermally, through chemical reactions or by radiation, all which may result in desorption of the species. | 0 | Theoretical and Fundamental Chemistry |
Spectral lines are the result of interaction between a quantum system (usually atoms, but sometimes molecules or atomic nuclei) and a single photon. When a photon has about the right amount of energy (which is connected to its frequency) to allow a change in the energy state of the system (in the case of an atom this is usually an electron changing orbitals), the photon is absorbed. Then the energy will be spontaneously re-emitted, either as one photon at the same frequency as the original one or in a cascade, where the sum of the energies of the photons emitted will be equal to the energy of the one absorbed (assuming the system returns to its original state).
A spectral line may be observed either as an emission line or an absorption line. Which type of line is observed depends on the type of material and its temperature relative to another emission source. An absorption line is produced when photons from a hot, broad spectrum source pass through a cooler material. The intensity of light, over a narrow frequency range, is reduced due to absorption by the material and re-emission in random directions. By contrast, a bright emission line is produced when photons from a hot material are detected, perhaps in the presence of a broad spectrum from a cooler source. The intensity of light, over a narrow frequency range, is increased due to emission by the hot material.
Spectral lines are highly atom-specific, and can be used to identify the chemical composition of any medium. Several elements, including helium, thallium, and caesium, were discovered by spectroscopic means. Spectral lines also depend on the temperature and density of the material, so they are widely used to determine the physical conditions of stars and other celestial bodies that cannot be analyzed by other means.
Depending on the material and its physical conditions, the energy of the involved photons can vary widely, with the spectral lines observed across the electromagnetic spectrum, from radio waves to gamma rays. | 0 | Theoretical and Fundamental Chemistry |
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