text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
The systematic name of this enzyme class is ubiquinol:ferricytochrome-c oxidoreductase. Other names in common use include: | 1 | Biochemistry |
* Jean-Claude Duplessy was one of the lead authors of the "paleoclimatology" chapter of the report of the Intergovernmental Panel on Climate Change (IPCC), which was published in 2007.
* His mission was to coordinate the activities of some twenty scientists from the international community with the objective of showing how the study of ancient climates makes it possible to better understand the mechanisms that could come into play in a world whose climate is disrupted by greenhouse gas and dust emissions. He was co-recipient, with his IPCC colleagues, of the 2007 Nobel Peace Prize in this capacity.
* He has been a member of the French Academy of Sciences since 2011 in the "Sciences of the Universe" section.
* He is a member of the European Academy of Sciences, Academia europaea since 1989
* Winner of the Aimé Berthé Prize of the Academy of Sciences (1987)
* Milankovitch Medal of the EGS (1995).
* Winner of the Georges Lemaître Prize of the Catholic University of Louvain (1997)
* Dr Honoris Causa from the University of Kiel, Germany (2003).
* Grand Prix Louis D of the Institut de France 2004.
* Prestwich Prize of the French Geological Society 2004.
* Grand Prix Dolomieu of BRGM awarded by the Academy of Sciences in 2004. | 9 | Geochemistry |
The first description of what would come to be called paramutation was given by William Bateson and Caroline Pellew in 1915, when they described "rogue" peas that always passed their "rogue" phenotype onto their progeny. However, the first formal description of paramutation was given by R.A. Brink at the University of Wisconsin–Madison in the 1950s, who did his work in maize (Zea mays). Brink noticed that specific weakly expressed alleles of the red1 (r1) locus in maize, which encodes a transcription factor that confers red pigment to corn kernels, can heritably change specific strongly expressed alleles to a weaker expression state. The weaker expression state adopted by the changed allele is heritable and can, in turn, change the expression state of other active alleles in a process termed secondary paramutation. Brink showed that the influence of the paramutagenic allele could persist for many generations. | 1 | Biochemistry |
The synthesis of isocyanates from amines illustrates the electrophilic character of this reagent and its use in introducing the equivalent synthon "CO":
:, where R = alkyl, aryl
Such reactions are conducted on laboratory scale in the presence of a base such as pyridine that neutralizes the hydrogen chloride side-product.
Phosgene is used to produce chloroformates such as benzyl chloroformate:
In these syntheses, phosgene is used in excess to prevent formation of the corresponding carbonate ester.
With amino acids, phosgene (or its trimer) reacts to give amino acid N-carboxyanhydrides. More generally, phosgene acts to link two nucleophiles by a carbonyl group. For this purpose, alternatives to phosgene such as carbonyldiimidazole (CDI) are safer, albeit expensive. CDI itself is prepared by reacting phosgene with imidazole.
Phosgene is stored in metal cylinders. In the US, the cylinder valve outlet is a tapered thread known as "CGA 160" that is used only for phosgene. | 0 | Organic Chemistry |
Dexlansoprazole is the (R)-(+)-enantiomer of lansoprazole, which is a racemic mixture of its (R)-(+) and (S)-(−)-enantiomers. The Takeda drug has a dual release pharmaceutical formulation, with two types of granules of dexlansoprazole, each with a coating that dissolves at a different pH level. | 4 | Stereochemistry |
Directed overflow is a special case of damage pre-emption, where excess of a normal, but reactive metabolite could lead to toxic products. Preventing this excess is thus pre-emption of potential damage.
The first two intermediates in riboflavin biosynthesis are highly reactive and can spontaneously break down to 5-phosphoribosylamine and Maillard reaction products, which are highly reactive and harmful. The enzyme COG3236 hydrolyzes these two first intermediates into two less harmful products, thus preventing the harm they would otherwise cause. | 1 | Biochemistry |
The most complex macromolecular machines are found within cells, often in the form of multi-protein complexes. Important examples of biological machines include motor proteins such as myosin, which is responsible for muscle contraction, kinesin, which moves cargo inside cells away from the nucleus along microtubules, and dynein, which moves cargo inside cells towards the nucleus and produces the axonemal beating of motile cilia and flagella. "[I]n effect, the [motile cilium] is a nanomachine composed of perhaps over 600 proteins in molecular complexes, many of which also function independently as nanomachines ... Flexible linkers allow the mobile protein domains connected by them to recruit their binding partners and induce long-range allostery via protein domain dynamics." Other biological machines are responsible for energy production, for example ATP synthase which harnesses energy from proton gradients across membranes to drive a turbine-like motion used to synthesise ATP, the energy currency of a cell. Still other machines are responsible for gene expression, including DNA polymerases for replicating DNA, RNA polymerases for producing mRNA, the spliceosome for removing introns, and the ribosome for synthesising proteins. These machines and their nanoscale dynamics are far more complex than any molecular machines that have yet been artificially constructed.
Biological machines have potential applications in nanomedicine. For example, they could be used to identify and destroy cancer cells. Molecular nanotechnology is a speculative subfield of nanotechnology regarding the possibility of engineering molecular assemblers, biological machines which could re-order matter at a molecular or atomic scale. Nanomedicine would make use of these nanorobots, introduced into the body, to repair or detect damages and infections, but these are considered to be far beyond current capabilities. | 6 | Supramolecular Chemistry |
Alzheimer’s is a neurodegenerative disease involving progressive memory loss and other declines in brain function. One common cause of familial Alzheimer’s is mutation in the PSEN1 gene. This gene encodes a protein that cleaves certain intracellular peptides which, once free in the cytoplasm, promote CBP<nowiki/>degradation. Mutations in PSEN1 decrease its production or ability to cleave proteins. This derepresses the CBP proteins, and allows them to perform their function of upregulating transcription of their target genes. | 1 | Biochemistry |
Cast bronzes are known to have been produced in Africa by the 9th century AD in Igboland (Igbo-Ukwu) in Nigeria, the 12th century AD in Yorubaland (Ife) and the 15th century AD in the kingdom of Benin. Some portrait heads remain.
Benin mastered bronze during the 16th century, produced portraiture and reliefs in the metal using the lost wax process. | 8 | Metallurgy |
Research in the RajanBabu lab is focused on development of new methodology for stereoselective synthesis. Major research areas include:
</u>
RajanBabu developed methodology surrounding C-C bond formation via metal-catalyzed hydroformylation. They reported several asymmetric examples through the usage of chiral phosphine ligand with a hemilabile coordinating group. This method was applicable using vinylarenes, 1,3-dienes and strained olefins as substrates. Applications of this chemistry include a new synthesis of (S)-ibuprofen and a new approach to controlling the exocyclic side-chain stereochemistry in helioporin D and pseudopterocins. Related to this methodology, RajanBabu also developed a tandem [2+2] cycloaddition/asymmetric hydrovinylation reaction to allow conversion of simple precursors (ethylene, enynes) to structurally complex cyclobutanes.
</u>
The RajanBabu group developed methodology in the area of hydrocyanation, leveraging the reaction of vinylarenes with HCN in the presence of Ni(0) complexes. Based on the phosphorus ligands within the Ni complex, the reaction can be rendered asymmetric. The enantioselectivity could be further improved by tuning the electronics of the phosphine ligands to electronically differentiate the phosphorus chelates. Electronic tuning was accomplished, for example, using widely available sugars such as D-glucose and D-fructose.
</u>
For further information on the Nugent-RajanBabu reagent, please see Bis(cyclopentadienyl)titanium(III) chloride.
</u>
One area of interest to the RajanBabu group is catalytic multicomponent addition/cyclization reactions. This methodology allows for formation of carbocyclic and heterocyclic compounds from acyclic precursors including unactivated olefins and acetylenes. This method leverages the reactivity of bifunctional reagents (X-Y) where X-Y in above scheme can represent RSi−SiR‘, RSi−SnR‘, RSi−BR‘, RSn−BR‘, and trialkylsilicon- and trialkyltin- hydrides. The reactions are palladium-catalyzed, and incorporation of the X and Y species allows for vast diversification of the end products. Application of this methodology afforded syntheses of highly alkylated indolizidines such as IND-223A.
</u>
RajanBabu has evaluated asymmetric aziridine openings with high enantioselectivity using yttrium- and lanthanide- salen complexes. The RajanBabu group has also developed water-soluble Rhodium(I) complexes, allowing for reactions to be run in aqueous media. | 0 | Organic Chemistry |
In 2001, Gal Bitan, Aleksey Lomakin, and David B. Teplow applied PICUP to study amyloid β-protein (Aβ) oligomerization, which is observed in Alzheimer's disease. PICUP allowed for identifying and quantifying the Aβ oligomers that are metastable because of its ability to rapidly cross-link. Coupling PICUP with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the distribution of oligomers in rapid equilibrium was quantified. This application allowed for the study of amyloidogenic proteins associated with neurodegenerative diseases and opened doors for possible future therapeutic mechanisms. Neurodegenerative diseases are currently suggested to be the result of neurotoxic proteins, so the ability to study their oligomer distribution is effective in understanding how and under what conditions these oligomers are formed. | 1 | Biochemistry |
Axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate. This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in cooling towers. Axial flow fans are applied in air conditioning and industrial process applications. Standard axial flow fans have diameters of 300–400 mm or 1,800–2,000 mm and work under pressures up to 800 Pa. Special types of fans are used as low-pressure compressor stages in aircraft engines.
Examples of axial fans are:
* Table fan: Basic elements of a typical table fan include the fan blade, base, armature, and lead wires, motor, blade guard, motor housing, oscillator gearbox, and oscillator shaft. The oscillator is a mechanism that motions the fan from side to side. The armature axle shaft comes out on both ends of the motor, one end of the shaft is attached to the blade and the other is attached to the oscillator gearbox. The motor case joins to the gearbox to contain the rotor and stator. The oscillator shaft combines the weighted base and the gearbox. A motor housing covers the oscillator mechanism. The blade guard joins to the motor case for safety.
* Domestic extractor fan: Wall- or ceiling-mounted, the domestic extractor fan is employed to remove moisture and stale air from domestic dwellings. Bathroom extractor fans typically utilize a four-inch (100 mm) impeller, whilst kitchen extractor fans typically use a six-inch (150 mm) impeller as the room itself is often bigger. Axial fans with five-inch (125 mm) impellers are also used in larger bathrooms though are much less common. Domestic axial extractor fans are not suitable for duct runs over 3 m or 4 m, depending on the number of bends in the run, as the increased air pressure in longer pipework inhibits the performance of the fan. [https://extractorfans.shop/pages/bathroom-fans-a-comprehensive-guide]
* Continuous running extractor fans run continuously at a very slow rate, running fast when necessary, for example when a bathroom light is switched on. At working speed they are just normal extractor fans. At continuous speed they extract typically 5 to 10 l/sec and use little electricity, 1 or 2 watts, for low annual cost. Some have humidity sensors to control trickle operation. They have the advantage of ensuring ventilation and preventing build-up of humidity. Alternatively, a normal extractor fan may be fitted to operate intermittently at full power for the same purpose. In cold weather they may have noticeably cool the room they are in, or, if the door is open, the house.
* Electro-mechanical fans: Among collectors, are rated according to their condition, size, age, and number of blades. Four-blade designs are the most common. Five-blade or six-blade designs are rare. The materials from which the components are made, such as brass, are important factors in fan desirability.
* Ceiling fan is a fan suspended from the ceiling of a room. Most ceiling fans rotate at relatively low speeds and, being inaccessible to reach, do not have blade guards. Ceiling fans are used in both residential and industrial/commercial settings.
* In automobiles, a mechanical or electrically driven fan provides engine cooling and prevents the engine from overheating by blowing or drawing air through a coolant-filled radiator. The fan may be driven with a belt and pulley off the engine's crankshaft or an electric motor switched on or off by a thermostatic switch.
* Computer fan for cooling electrical components and in laptop coolers
* Fans inside audio power amplifiers help to draw heat away from the electrical components.
* Variable pitch fan: A variable-pitch fan is used where precise control of static pressure within supply ducts is required. The blades are arranged to rotate upon a control-pitch hub. The fan wheel will spin at a constant speed. The blades follow the control pitch hub. As the hub moves toward the rotor, the blades increase their angle of attack and an increase in flow results. | 7 | Physical Chemistry |
Phosphomimetics are amino acid substitutions that mimic a phosphorylated protein, thereby activating (or deactivating) the protein. Within cells, proteins are commonly modified at serine, tyrosine and threonine amino acids by adding a phosphate group. Phosphorylation is a common mode of activating or deactivating a protein as a form of regulation. However some non-phosphorylated amino acids appear chemically similar to phosphorylated amino acids. Therefore, by replacing an amino acid, the protein may maintain a higher level of activity. For example, aspartic acid can be considered chemically similar to phospho-serine, due to it also carrying a negative charge. Therefore, when an aspartic acid replaces a serine, it is a phosphomimetic of phospho-serine and can imitate the protein always in its phosphorylated form. However, differences in between the phosphomimetics compound and the phosphorylated residue, notably differences in ramachandran distributions, charge states and size, can alter the protein sufficiently to result in significant differences in behavior. Phosphonate-based compounds have been used as phosphotyrosine analogues, as they are less enzyme labile and are physiologically more stable. | 1 | Biochemistry |
Multiphoton excitation is a way of focusing the viewing plane of the microscope by taking advantage of the phenomenon where two simultaneous low energy photons are absorbed by a fluorescent moiety which normally absorbs one photon with double their individual energy: say two NIR photons (800 nm) to excite a UV dye (400 nm). | 1 | Biochemistry |
Catenation occurs most readily with carbon, which forms covalent bonds with other carbon atoms to form longer chains and structures. This is the reason for the presence of the vast number of organic compounds in nature. Carbon is most well known for its properties of catenation, with organic chemistry essentially being the study of catenated carbon structures (and known as catenae). Carbon chains in biochemistry combine any of various other elements, such as hydrogen, oxygen, and biometals, onto the backbone of carbon.
However, carbon is by no means the only element capable of forming such catenae, and several other main-group elements are capable of forming an expansive range of catenae, including hydrogen, boron, silicon, phosphorus, sulfur and halogens.
The ability of an element to catenate is primarily based on the bond energy of the element to itself, which decreases with more diffuse orbitals (those with higher azimuthal quantum number) overlapping to form the bond. Hence, carbon, with the least diffuse valence shell p orbital is capable of forming longer p-p sigma bonded chains of atoms than heavier elements which bond via higher valence shell orbitals. Catenation ability is also influenced by a range of steric and electronic factors, including the electronegativity of the element in question, the molecular orbital n and the ability to form different kinds of covalent bonds. For carbon, the sigma overlap between adjacent atoms is sufficiently strong that perfectly stable chains can be formed. With other elements this was once thought to be extremely difficult in spite of plenty of evidence to the contrary. | 0 | Organic Chemistry |
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the absorbate) is dissolved by or permeates a liquid or solid (the absorbent). While adsorption does often precede absorption, which involves the transfer of the absorbate into the volume of the absorbent material, alternatively, adsorption is distinctly a surface phenomenon, wherein the adsorbate does not penetrate through the material surface and into the bulk of the adsorbent. The term sorption encompasses both adsorption and absorption, and desorption is the reverse of sorption.
Like surface tension, adsorption is a consequence of surface energy. In a bulk material, all the bonding requirements (be they ionic, covalent or metallic) of the constituent atoms of the material are fulfilled by other atoms in the material. However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms and therefore can attract adsorbates. The exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption (characteristic of weak van der Waals forces) or chemisorption (characteristic of covalent bonding). It may also occur due to electrostatic attraction. The nature of the adsorption can affect the structure of the adsorbed species. For example, polymer physisorption from solution can result in squashed structures on a surface.
Adsorption is present in many natural, physical, biological and chemical systems and is widely used in industrial applications such as heterogeneous catalysts, activated charcoal, capturing and using waste heat to provide cold water for air conditioning and other process requirements (adsorption chillers), synthetic resins, increasing storage capacity of carbide-derived carbons and water purification. Adsorption, ion exchange and chromatography are sorption processes in which certain adsorbates are selectively transferred from the fluid phase to the surface of insoluble, rigid particles suspended in a vessel or packed in a column. Pharmaceutical industry applications, which use adsorption as a means to prolong neurological exposure to specific drugs or parts thereof, are lesser known.
The word "adsorption" was coined in 1881 by German physicist Heinrich Kayser (1853–1940). | 7 | Physical Chemistry |
Protein electrophoresis is a method for analysing the proteins in a fluid or an extract. The electrophoresis may be performed with a small volume of sample in a number of alternative ways with or without a supporting medium, namely agarose or polyacrylamide. Variants of gel electrophoresis include SDS-PAGE, free-flow electrophoresis, electrofocusing, isotachophoresis, affinity electrophoresis, immunoelectrophoresis, counterelectrophoresis, and capillary electrophoresis. Each variant has many subtypes with individual advantages and limitations. Gel electrophoresis is often performed in combination with electroblotting or immunoblotting to give additional information about a specific protein. | 1 | Biochemistry |
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy groups. Both the negatively charged anion , called hydroxide, and the neutral radical , known as the hydroxyl radical, consist of an unbonded hydroxy group.
According to IUPAC definitions, the term hydroxyl refers to the hydroxyl radical () only, while the functional group is called a hydroxy group. | 0 | Organic Chemistry |
Heat engines are not the most efficient ones, and with the use of bimetallic strips the efficiency of the heat engine is even lower as there is no chamber to contain the heat. Moreover, the bimetallic strips cannot produce strength in its moves, the reason why is that in order to achieve reasonables bendings (movements) both metallic strips have to be thin to make the difference between the expansion noticeable. So the uses for metallic strips in heat engines are mostly in simple toys that have been built to demonstrate how the principle can be used to drive a heat engine. | 8 | Metallurgy |
Natural phenols show optical properties characteristic of benzene, e.g. absorption near 270 nm. According to Woodward's rules, bathochromic shifts often also happen suggesting the presence of delocalised π electrons arising from a conjugation between the benzene and vinyls groups.
As molecules with higher conjugation levels undergo this bathochromic shift phenomenon, a part of the visible spectrum is absorbed. The wavelengths left in the process (generally in red section of the spectrum) recompose the color of the particular substance. Acylation with cinnamic acids of anthocyanidins shifted color tonality (CIE Lab hue angle) to purple.
Here is a series of UV visible spectra of molecules classified from left to right according to their conjugation level:
The absorbance pattern responsible for the red color of anthocyanins may be complementary to that of green chlorophyll in photosynthetically active tissues such as young Quercus coccifera leaves. | 0 | Organic Chemistry |
The synthetically most useful reaction of the nitrile ylides is the 1,3-dipolar cycloaddition to dipolarophiles: with electron-deficient alkenes, good yields of pyrrolines are obtained. Alkynes, carbonyl compounds, imines and azirines can also act as dipolarophile.
Nitrile ylides react with weak acids like methanol by protonation finally leading to a methoxyimine. | 0 | Organic Chemistry |
Inside the body oxygen is delivered to cells and in the cells to mitochondria, where it is consumed in the process generating most of the energy required by the organism.
Mitochondrial respirometry measures the consumption of oxygen by the mitochondria without involving an entire living animal and is the main tool to study mitochondrial function. Three different types of samples may be subjected to such respirometric studies:
isolated mitochondria (from cell cultures, animals or plants); permeabilized cells (from cell cultures); and permeabilized fibers or tissues (from animals). In the latter two cases the cellular membrane is made permeable by the addition of chemicals leaving selectively the mitochondrial membrane intact. Therefore, chemicals that usually would not be able to cross the cell membrane can directly influence the mitochondria. By the permeabilization of the cellular membrane, the cell stops to exist as a living, defined organism, leaving only the mitochondria as still functional structures.
Unlike whole-animal respirometry, mitochondrial respirometry takes place in solution, i.e. the sample is suspended in a medium. Today mitochondrial respirometry is mainly performed with a closed-chamber approach. | 1 | Biochemistry |
Surface conductivity is an additional conductivity of an electrolyte in the vicinity of the charged interfaces. Surface and volume conductivity of liquids correspond to the electrically driven motion of ions in an electric field. A layer of counter ions of the opposite polarity to the surface charge exists close to the interface. It is formed due to attraction of counter-ions by the surface charges. This layer of higher ionic concentration is a part of the interfacial double layer. The concentration of the ions in this layer is higher as compared to the ionic strength of the liquid bulk. This leads to the higher electric conductivity of this layer.
Smoluchowski was the first to recognize the importance of surface conductivity at the beginning of the 20th century.
There is a detailed description of surface conductivity by Lyklema in "Fundamentals of Interface and Colloid Science"
The Double Layer (DL) has two regions, according to the well established Gouy-Chapman-Stern model. The upper level, which is in contact with the bulk liquid is the diffuse layer. The inner layer that is in contact with interface is the Stern layer.
It is possible that the lateral motion of ions in both parts of the DL contributes to the surface conductivity.
The contribution of the Stern layer is less well described. It is often called "additional surface conductivity".
The theory of the surface conductivity of the diffuse part of the DL was developed by Bikerman. He derived a simple equation that links surface conductivity κ with the behaviour of ions at the interface. For symmetrical electrolyte and assuming identical ions diffusion coefficients D=D=D it is given in the reference:
where
:F is the Faraday constant
:T is the absolute temperature
:R is the gas constant
:C is the ionic concentration in the bulk fluid
:z is the ion valency
:ζ is the electrokinetic potential
The parameter m characterizes the contribution of electro-osmosis to the motion of ions within the DL:
The Dukhin number is a dimensionless parameter that characterizes the contribution of the surface conductivity to a variety of electrokinetic phenomena, such as, electrophoresis and electroacoustic phenomena. This parameter and, consequently, surface conductivity can be calculated from the electrophoretic mobility using appropriate theory. Electrophoretic instrument by Malvern and electroacoustic instruments by Dispersion Technology contain software for conducting such calculations. | 7 | Physical Chemistry |
The Inco Superstack in Sudbury, Ontario, with a height of , is the tallest chimney in Canada and the Western Hemisphere, and the second-tallest freestanding chimney in the world after the Ekibastuz GRES-2 Power Station in Kazakhstan. It is also the second-tallest freestanding structure of any type in Canada, behind the CN Tower but ahead of First Canadian Place. As of 2023, it is the 51st-tallest freestanding structure in the world. The Superstack is located on top of the largest nickel smelting operation in the world at Vale's Copper Cliff processing facility in the city of Greater Sudbury.
In 2018, Vale announced that the stack would be decommissioned and dismantled, beginning in 2020. Two new, smaller stacks were constructed under the company's Clean Atmospheric Emissions Reduction Project. In July 2020, Vale announced that the Superstack had been officially taken out of service, but would remain operational in standby mode for two more months as a backup in the event of a malfunction in the new system, following which the dismantling of the Superstack would begin. As of 2024, however, Vale has not yet announced the awarding of a demolition contract on the Superstack, and it remains unknown when demolition will actually begin; some have called for the stack to be left in place as a tourist attraction.
In addition to further reducing sulphur dioxide emissions by 85 per cent, the decommissioning of the stack is expected to cut the complex's natural gas consumption in half. | 8 | Metallurgy |
Although MRM has been used extensively in metabolomics and proteomics, its high sensitivity and linear response over a wide dynamic range make it especially suited for glycan biomarker research and discovery. MRM is performed on a triple quadrupole (QqQ) instrument, which is set to detect a predetermined precursor ion in the first quadrupole, a fragmented in the collision quadrupole, and a predetermined fragment ion in the third quadrupole. It is a non-scanning technique, wherein each transition is detected individually and the detection of multiple transitions occurs concurrently in duty cycles. This technique is being used to characterize the immune glycome.
Table 1:Advantages and disadvantages of mass spectrometry in glycan analysis | 0 | Organic Chemistry |
In a polyrotaxane, unlike a conventional polymer, the molecules are linked by mechanical bonding, such as hydrogen boding or charge transfer, not covalent bonds. Also, the rings are capable of rotating on or shuttling around the axles, resulting in the large amount of freedom of polyrotaxanes. This unconventional combination of molecules leads to the distinctive properties of polyrotaxanes. | 6 | Supramolecular Chemistry |
The gauche effect is very sensitive to solvent effects, due to the large difference in polarity between the two conformers. For example, 2,3-dinitro-2,3-dimethylbutane, which in the solid state exists only in the gauche conformation, prefers the gauche conformer in benzene solution by a ratio of 79:21, but in carbon tetrachloride, it prefers the anti conformer by a ratio of 58:42. Another case is trans-1,2 difluorocyclohexane, which has a larger preference for the di-equatorial conformer, rather than the anti-diaxial conformer, in more polar solvents. | 4 | Stereochemistry |
ATM is uniquely suited to measure resonant molecular vibrations in proteins. Molecular motions in proteins occur with frequencies in the terahertz range of the spectrum (0.3 THz to 3 THz). These structural changes include hinge motions in which two regions of molecules are connected together in a flexible way that bends like a mechanical hinge or joint and other conformational changes that occur within systems of protein molecules.
Protein molecules are typically surrounded by water molecules and are arranged in random orientations. For this reason, it is common to arrange protein molecules in crystal form such that their orientations all the same. In particular, in a protein crystal the dipole of all protein molecules are naturally aligned. This allows us to perform microspectroscopy with polarized THz light and ascertain the spatial orientation of vibrations within molecules. | 7 | Physical Chemistry |
A free-radical reaction is any chemical reaction involving free radicals. This reaction type is abundant in organic reactions. Two pioneering studies into free radical reactions have been the discovery of the triphenylmethyl radical by Moses Gomberg (1900) and the lead-mirror experiment described by Friedrich Paneth in 1927. In this last experiment tetramethyllead is decomposed at elevated temperatures to methyl radicals and elemental lead in a quartz tube. The gaseous methyl radicals are moved to another part of the chamber in a carrier gas where they react with lead in a mirror film which slowly disappears.
When radical reactions are part of organic synthesis the radicals are often generated from radical initiators such as peroxides or azobis compounds. Many radical reactions are chain reactions with a chain initiation step, a chain propagation step and a chain termination step. Reaction inhibitors slow down a radical reaction and radical disproportionation is a competing reaction. Radical reactions occur frequently in the gas phase, are often initiated by light, are rarely acid or base catalyzed and are not dependent on polarity of the reaction medium. Reactions are also similar whether in the gas phase or solution phase. | 0 | Organic Chemistry |
Ferritin genes are highly conserved between species. All vertebrate ferritin genes have three introns and four exons. In human ferritin, introns are present between amino acid residues 14 and 15, 34 and 35, and 82 and 83; in addition, there are one to two hundred untranslated bases at either end of the combined exons. The tyrosine residue at amino acid position 27 is thought to be associated with biomineralization. | 1 | Biochemistry |
Correct selection of the material by the design engineer affects the design life of a structure. Sometimes stainless steel is not the correct choice and carbon steel would be better. There is a misconception that stainless steel has excellent corrosion resistance and will not corrode. This is not always the case and should not be used to handle deoxygenated solutions for example, as the stainless steel relies on oxygen to maintain passivation and is also susceptible to crevice corrosion.
Galvanizing or hot-dip galvanizing is used to coat steel with a layer of metallic zinc. Lead or antimony are often added to the molten zinc bath, and also other metals have been studied. | 8 | Metallurgy |
Chiral molecules can be described as ones with a set of stereoisomers or left and right-handed enantiomers. As defined by Lord Kelvin, a molecule has chirality “if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself.” In other words, a chiral molecule is asymmetrical in the sense that its mirror image will not be an exact copy of itself. Chirality is key to understand in many fields such as drug development as one enantiomer of a drug may cause severe adverse effects while the other provides relief from an ailment. This is significant in terms of Fischer Projections as chirality is an important factor to consider when both drawing and reading them. A great benefit of the model is the ability to interpret chirality with ease based on the orientation of the substituents. Slight changes in the formatting of these models can cause the stereochemistry to be interpreted differently thereby meaning that the molecule has been depicted incorrectly. Fischer Projections provide aid in visualizing chirality as well as where substituents are oriented within space which is why their application can be useful to many. | 4 | Stereochemistry |
Multiple companies have offered exome sequencing to consumers. Knome was the first company to offer exome sequencing services to consumers, at a cost of several thousand dollars. Later, 23andMe ran a pilot WES program that was announced in September 2011 and was discontinued in 2012. Consumers could obtain exome data at a cost of $999. The company provided raw data, and did not offer analysis.
In November 2012, DNADTC, a division of Gene by Gene started offering exomes at 80X coverage and introductory price of $695. This price per DNADTC web site is currently $895. In October 2013, BGI announced a promotion for personal whole exome sequencing at 50X coverage for $499.
In June 2016 Genos was able to achieve an even lower price of $399 with a CLIA-certified 75X consumer exome sequenced from saliva.
A 2018 review of 36 studies found the cost for exome sequencing to range from $555USD to $5,169USD, with a diagnostic yield ranging from 3% to 79% depending on patient groups. | 1 | Biochemistry |
Binding affinity data alone does not determine the overall potency of a drug or a naturally produced (biosynthesized) hormone.
Potency is a result of the complex interplay of both the binding affinity and the ligand efficacy. | 1 | Biochemistry |
In Schoenflies notation, point groups are denoted by a letter symbol with a subscript. The symbols used in crystallography mean the following:
*C (for cyclic) indicates that the group has an n-fold rotation axis. C is C with the addition of a mirror (reflection) plane perpendicular to the axis of rotation. C is C with the addition of n mirror planes parallel to the axis of rotation.
*S (for Spiegel, German for mirror) denotes a group with only a 2n-fold rotation-reflection axis.
*D (for dihedral, or two-sided) indicates that the group has an n-fold rotation axis plus n twofold axes perpendicular to that axis. D has, in addition, a mirror plane perpendicular to the n-fold axis. D has, in addition to the elements of D, mirror planes parallel to the n-fold axis.
*The letter T (for tetrahedron) indicates that the group has the symmetry of a tetrahedron. T includes improper rotation operations, T excludes improper rotation operations, and T is T with the addition of an inversion.
*The letter O (for octahedron) indicates that the group has the symmetry of an octahedron (or cube), with (O) or without (O) improper operations (those that change handedness).
Due to the crystallographic restriction theorem, n = 1, 2, 3, 4, or 6 in 2- or 3-dimensional space.
D and D are actually forbidden because they contain improper rotations with n=8 and 12 respectively. The 27 point groups in the table plus T, T, T, O and O constitute 32 crystallographic point groups. | 3 | Analytical Chemistry |
A bevel protractor is a graduated circular protractor with one pivoted arm; used for measuring or marking off angles. Sometimes Vernier scales are attached to give more precise readings. It has wide application in architectural and mechanical drawing, although its use is decreasing with the availability of modern drawing software or CAD.
Universal bevel protractors are also used by toolmakers; as they measure angles by mechanical contact they are classed as mechanical protractors.
The bevel protractor is used to establish and test angles to very close tolerances. It reads to 5 arcminutes (5′ or °) and can measure angles from 0° to 360°.
The bevel protractor consists of a beam, a graduated dial, and a blade which is connected to a swivel plate (with Vernier scale) by a thumb nut and clamp. When the edges of the beam and blade are parallel, a small mark on the swivel plate coincides with the zero line on the graduated dial. To measure an angle between the beam and the blade of 90° or less, the reading may be obtained directly from the graduation number on the dial indicated by the mark on the swivel plate. To measure an angle of over 90°, subtract the number of degrees as indicated on the dial from 180°, as the dial is graduated from opposite zero marks to 90° each way.
Since the spaces, both on the main scale and the Vernier scale, are numbered both to the right and the left from zero, any angle can be measured. The readings can be taken either to the right or to the left, according to the direction in which the zero on the main scale is moved. | 7 | Physical Chemistry |
Magnetoelectrochemistry is a branch of electrochemistry dealing with magnetic effects in electrochemistry. | 7 | Physical Chemistry |
Yeast fungi, being facultative anaerobes, can either produce energy through ethanol fermentation or aerobic respiration. When the O concentration is low, the two pyruvate molecules formed through glycolysis are each fermented into ethanol and carbon dioxide. While only 2 ATP are produced per glucose, this method is utilized under anaerobic conditions because it oxidizes the electron shuttle NADH into NAD for another round of glycolysis and ethanol fermentation.
If the concentration of oxygen increases, pyruvate is instead converted to acetyl CoA, used in the citric acid cycle, and undergoes oxidative phosphorylation. Per glucose, 10 NADH and 2 FADH are produced in cellular respiration for a significant amount of proton pumping to produce a proton gradient utilized by ATP Synthase. While the exact ATP output ranges based on considerations like the overall electrochemical gradient, aerobic respiration produces far more ATP than the anaerobic process of ethanol fermentation. The increased ATP and citrate from aerobic respiration allosterically inhibit the glycolysis enzyme phosphofructokinase 1 because less pyruvate is needed to produce the same amount of ATP.
Despite this energetic incentive, Rosario Lagunas has shown that yeast continue to partially ferment available glucose into ethanol for many reasons. First, glucose metabolism is faster through ethanol fermentation because it involves fewer enzymes and limits all reactions to the cytoplasm. Second, ethanol has bactericidal activity by causing damage to the cell membrane and protein denaturing, allowing yeast fungus to outcompete environmental bacteria for resources. Third, partial fermentation may be a defense mechanism against environmental competitors depleting all oxygen faster than the yeast's regulatory systems could fully switch from aerobic respiration to ethanol fermentation. | 1 | Biochemistry |
The API gravity of a crude oil is a measurement of purity - i.e., amount of impurities, such as sulphur, nitrogen, or oxygen. Impurities increase the density of the crude. | 9 | Geochemistry |
Using the above definition for z , the cumulative distribution function (CDF) can be found as follows:
Substituting the definition of the Faddeeva function (scaled complex error function) yields for the indefinite integral:
which may be solved to yield
where is a hypergeometric function. In order for the function to approach zero as x approaches negative infinity (as the CDF must do), an integration constant of 1/2 must be added. This gives for the CDF of Voigt: | 7 | Physical Chemistry |
Chan is a founding member of the Democratic Party. He was elected as chairman of the New Territories East Branch in 1999, and later became the party's minister of organization affairs and central committee member. He ran for the chairmanship election in 2004 but lost to Lee Wing-tat. He was then elected vice-chairman of the party. He also served as a part-time member of Central Policy Unit of the Hong Kong Government between 2004 and 2006.
He ran again for the chairmanship in December 2006, but lost to Albert Ho. He did not seek to run for the vice-chairmanship in the 2006 election. In 2010, the Democratic Party decided to support the government's proposal of the political reform package to expand the numbers of legislative council members from 30 to 35 in Geographical Constituency and 30 to 35 of Functional Constituency by adopting the idea of the "Super-district Councillors" which will be voted across the territory after nominations by District Councillors. Younger members of the Democratic Party including Chan believed that such proposal could not provide any significant progress towards democratic development in local political agenda.
In December 2010, Chan quit the party due to the electoral reform to found the Neo Democrats and is the incumbent convenor of the party. The Neo Democrats campaigned in the 2011 District Council election and won a total of 8 seats. | 1 | Biochemistry |
Such is the case in building applications where artificial light can be replaced by sunlight through a light transmittance design. Based on research and simulation performed by Joseph Arehart at the University of Colorado Boulder, transparent wood as a glass glazing system replacement could reduce the space conditioning energy consumption by 24.6% to 33.3% in medium (climate zone 3C, San Francisco, CA) and large office spaces (climate zone 4C, Seattle, Washington) respectably. These are relevant insights in transparent wood's potential functionality because it shows lower thermal conductivity and better impact strength compared to popular glass glazing systems. | 7 | Physical Chemistry |
The yield strength anomaly is exploited in the design of gas turbines and jet engines that operate at high temperatures, where the materials used are selected based on their paramount yield and creep resistance. Superalloys can withstand high temperature loads far beyond the capabilities of steels and other alloys, and allow operation at higher temperatures, which improves efficiency. | 8 | Metallurgy |
The main uses of fluoride, in terms of volume, are in the production of cryolite, NaAlF. It is used in aluminium smelting. Formerly, it was mined, but now it is derived from hydrogen fluoride. Fluorite is used on a large scale to separate slag in steel-making. Mined fluorite (CaF) is a commodity chemical used in steel-making. Uranium hexafluoride is employed in the purification of uranium isotopes. | 1 | Biochemistry |
Carboximidates (or more general imidates) are organic compounds, which can be thought of as esters formed between a imidic acid (R-C(=NR)OH) and an alcohol, with the general formula R-C(=NR)OR".
They are also known as imino ethers, since they resemble imines (>C=N-) with an oxygen atom connected to the carbon atom of the C=N double bond. | 0 | Organic Chemistry |
Experimental reconstruction of tools used in prehistoric mining is often written about in conjunction with the tools use after the process of firesetting. The experimental mining tool assemblage are primarily made up of hammerstones and antler picks that are reconstructed using willow and hazel sticks, rawhide, and hemp string to implement various hafting techniques and methods of utilization. | 8 | Metallurgy |
A dyotropic reaction (from the Greek dyo, meaning two) in organic chemistry is a type of organic reaction and more specifically a pericyclic valence isomerization in which two sigma bonds simultaneously migrate intramolecularly. The reaction type is of some relevance to organic chemistry because it can explain how certain reactions occur and because it is a synthetic tool in the synthesis of organic molecules for example in total synthesis. It was first described by Manfred T. Reetz in 1971
In a type I reaction two migrating groups interchange their relative positions and a type II reaction involves migration to new bonding sites without positional interchange. | 0 | Organic Chemistry |
Piperacillin irreversibly binds to the enzyme penicillin-binding proteins, inhibiting the biosynthesis of bacterial cell walls. | 4 | Stereochemistry |
Mefloquine is metabolized primarily through the liver. Its elimination in persons with impaired liver function may be prolonged, resulting in higher plasma levels and an increased risk of adverse reactions. The mean elimination plasma half-life of mefloquine is between two and four weeks. Total clearance is through the liver, and the primary means of excretion is through the bile and feces, as opposed to only 4% to 9% excreted through the urine. During long-term use, the plasma half-life remains unchanged.
Liver function tests should be performed during long-term administration of mefloquine. Alcohol use should be avoided during treatment with mefloquine. | 4 | Stereochemistry |
White light is directed vertically onto a multiple-layer system of a SiO, a high-refractive TaO and an additional SiO layer (this additional layer can be chemically modified). The partial beams of the white light are reflected at each phase boundary and then refracted (transmitted). These reflected partial beams superimpose which results in an interference spectrum that is detected using a diode array spectrometer.<br>
Through chemical modification the upper SiO layer is changed in a way to allow interaction with target molecules. This interaction causes a change in the thickness of the physical layer d and the refractive index n within this layer. The product of both defines the optical thickness of the layer: n • d.<br>
A change in the optical thickness results in a modulation of the interference spectrum. Monitoring this change over time allows to observe the binding behaviour of the target molecules. | 7 | Physical Chemistry |
The main use of -ascorbic acid and its salts is as food additives, mostly to combat oxidation. It is approved for this purpose in the EU with E number E300, the US, Australia, and New Zealand. | 1 | Biochemistry |
Although generally considered less-than-lethal when properly used (targets should exclude the face, eyes, throat or spine), one death has occurred when they have been fired at inappropriate areas. In one well-publicized incident in 2004, the Boston Police Department's use of an FN 303 during a crowd control situation resulted in the fatal shooting of Victoria Snelgrove, when the projectile struck her in the eye.
Also in 2004, University of California, Davis (UC Davis) police who wanted to break up a block party shot a pepperball at an unarmed student and damaged his eye—the student subsequently lost his athletic scholarship and dropped out of college. In 2012, a federal appeals court ruled that the police could be sued over the incident. In 2013, the student was awarded $774,000. | 1 | Biochemistry |
Ravi Bhushan (born 12 April 1953, in Muzaffarnagar, India) was a Professor of Chemistry at Indian Institute of Technology Roorkee who worked in the areas of natural products chemistry, protein chemistry, and chiral analysis by liquid chromatography. | 3 | Analytical Chemistry |
In biology, the SECIS element (SECIS: selenocysteine insertion sequence) is an RNA element around 60 nucleotides in length that adopts a stem-loop structure. This structural motif (pattern of nucleotides) directs the cell to translate UGA codons as selenocysteines (UGA is normally a stop codon). SECIS elements are thus a fundamental aspect of messenger RNAs encoding selenoproteins, proteins that include one or more selenocysteine residues.
In bacteria the SECIS element appears soon after the UGA codon it affects. In archaea and eukaryotes, it occurs in the 3 UTR of an mRNA, and can cause multiple UGA codons within the mRNA to code for selenocysteine. One archaeal SECIS element, in Methanococcus, is located in the 5 UTR.
The SECIS element appears defined by sequence characteristics, i.e. particular nucleotides tend to be at particular positions in it, and a characteristic secondary structure. The secondary structure is the result of base-pairing of complementary RNA nucleotides, and causes a hairpin-like structure. The eukaryotic SECIS element includes non-canonical A-G base pairs, which are uncommon in nature, but are critically important for correct SECIS element function. Although the eukaryotic, archaeal and bacterial SECIS elements each share a general hairpin structure, they are not alignable, e.g. an alignment-based scheme to recognize eukaryotic SECIS elements will not be able to recognize archaeal SECIS elements. However, in Lokiarcheota, SECIS elements are more similar to eukaryotic elements.
In bioinformatics, several computer programs have been created that search for SECIS elements within a genome sequence, based on the sequence and secondary structure characteristics of SECIS elements. These programs have been used in searches for novel selenoproteins. | 1 | Biochemistry |
Host guest systems have been utilized to remove hazardous materials from the environment. They can be made in different sizes and different shapes to trap a variety of chemical guests. One application is the ability of p-tert-butycalix[4]arene to trap a cesium ion. Cesium-137 is radioactive and there is a need to remove it from nuclear waste in an efficient manner. Host–guest chemistry has also been used to remove carcinogenic aromatic amines, and their N-nitroso derivatives from water. These waste materials are used in many industrial processes and found in a variety of products such as: pesticides, drugs, and cosmetics. | 6 | Supramolecular Chemistry |
Iminium salts hydrolyse to give the corresponding ketone or aldehyde:
Iminium cations are reduced to the amines, e.g. by sodium cyanoborohydride. Iminium cations are intermediates in the reductive amination of ketones and aldehydes.
Unsymmetrical iminium cations undergo cis-trans isomerization. The isomerization is catalyzed by nucleophiles, which add to the unsaturated carbon, breaking the C=N double bond. | 0 | Organic Chemistry |
The use of two or more herbicides which have differing modes of action can reduce the selection for resistant genotypes. Ideally, each component in a mixture should:
* Be active at different target sites
* Have a high level of efficacy
* Be detoxified by different biochemical pathways
* Have similar persistence in the soil (if it is a residual herbicide)
* Exert negative cross-resistance
* Synergise the activity of the other component
No mixture is likely to have all these attributes, but the first two listed are the most important. There is a risk that mixtures will select for resistance to both components in the longer term. One practical advantage of sequences of two herbicides compared with mixtures is that a better appraisal of the efficacy of each herbicide component is possible, provided that sufficient time elapses between each application. A disadvantage with sequences is that two separate applications have to be made and it is possible that the later application will be less effective on weeds surviving the first application. If these are resistant, then the second herbicide in the sequence may increase selection for resistant individuals by killing the susceptible plants which were damaged but not killed by the first application, but allowing the larger, less affected, resistant plants to survive. This has been cited as one reason why ALS-resistant Stellaria media has evolved in Scotland recently (2000), despite the regular use of a sequence incorporating mecoprop, a herbicide with a different mode of action. | 2 | Environmental Chemistry |
The 3-hydroxypropionate bicycle, also known as the 3-hydroxypropionate pathway, is a process that allows some bacteria to generate 3-hydroxypropionate using carbon dioxide. It is divided into two parts or reactions. The overall reaction of the 3-hydroxypropionate pathway is 3 HCO3− + 5 ATP + 6 NADPH + 1 quinone → 1 pyruvate + 6 NADP + 1 quinoneH2 + 3 ADP + 3 phosphate + 2 AMP + 2 pyrophosphate. | 1 | Biochemistry |
Controlling pests and plant disease vectors
*Improved crop yields
*Improved crop/livestock quality
*Invasive species controlled
Controlling human/livestock disease vectors and nuisance organisms
*Human lives saved and disease reduced. Diseases controlled include malaria, with millions of lives having been saved or enhanced with the use of DDT alone.
*Animal lives saved and disease reduced
Controlling organisms that harm other human activities and structures
*Drivers view unobstructed
*Tree/brush/leaf hazards prevented
*Wooden structures protected | 2 | Environmental Chemistry |
Although the pathogenic role of ANCA is still controversial, in vitro and animal models support the idea that the antibodies have a direct pathological role in the formation of small vessel vasculitides. MPO and PR3 specific ANCA can activate neutrophils and monocytes through their Fc and Fab'2 receptors, which can be enhanced by cytokines which cause neutrophils to display MPO and PR3 on their surface. Aberrant glycosylation of the MPO and PR3 specific ANCA enhances their ability to interact with activating Fc receptors on neutrophils. The activated neutrophils can then adhere to endothelial cells where degranulation occurs. This releases free oxygen radicals and lytic enzymes, resulting in damage to the endothelium via the induction of necrosis and apoptosis. Furthermore, neutrophils release chemoattractive signalling molecules that recruit more neutrophils to the endothelium, acting as a positive feedback loop. Animal models have shown that MPO antibodies can induce necrotizing crescentic glomerulonephritis and systemic small vessel vasculitis. In these animal models the formation of glomerulonephritis and vasculitis can occur in the absence of T-cells, however neutrophils must be present. Although ANCA titres have been noted to have limited correlation with disease activity, except for kidney disease, and with risk of relapse, this is explained by differences in the epitopes and affinity of ANCAs. ANCAs induce excess activation of neutrophils, resulting in the production of neutrophil extracellular traps (NETs), which cause damage to small blood vessels. In addition, in patients with active disease, treated with Rituximab, an anti-CD20 antibody which remove circulating B-cells, clinical remission correlates more to the decreasing number of circulating B-cells than decrease in ANCA titre, which in some patient does not change during treatment. The same study found that clinical relapse in some patients were in association with the return of circulating B-cells. Based on the above observations and that ANCA reactive B-cells can be found in circulation in patients with AAV, an alternative hypothesis have been proposed assigning a direct pathogenic role of these cells, whereby activated neutrophils and ANCA-reactive B-cells engage in intercellular cross-talk, which leads not only to neutrophil degranulation and inflammation but also to the proliferation and differentiation of ANCA-reactive B-cells. However, this hypothesis remains to be tested. | 1 | Biochemistry |
Steroid 21-hydroxylase is a protein that in humans is encoded by the CYP21A2 gene. The protein is an enzyme that hydroxylates steroids at the C21 position on the molecule. Naming conventions for enzymes are based on the substrate acted upon and the chemical process performed. Biochemically, this enzyme is involved in the biosynthesis of the adrenal gland hormones aldosterone and cortisol, which are important in blood pressure regulation, sodium homeostasis and blood sugar control. The enzyme converts progesterone and 17α-hydroxyprogesterone into 11-deoxycorticosterone and 11-deoxycortisol, respectively, within metabolic pathways which in humans ultimately lead to aldosterone and cortisol creation—deficiency in the enzyme may cause congenital adrenal hyperplasia.
Steroid 21-hydroxylase is a member of the cytochrome P450 family of monooxygenase enzymes that use an iron-containing heme cofactor to oxidize substrates.
In humans, the enzyme is localized in endoplasmic reticulum membranes of cells in adrenal cortex, and is encoded by the gene which is located near the CYP21A1P pseudogene that has high degree of sequence similarity. This similarity makes it difficult to analyze the gene at the molecular level, and sometimes leads to loss-of-function mutations of the gene due to intergenic exchange of DNA. | 1 | Biochemistry |
A physician may order many laboratory tests on one specimen, referred to as a test panel, when a single test cannot provide sufficient information to make a swift and accurate diagnosis and treatment plan. A test panel is a group of many tests a clinical chemists do on one sample to look for changes in many analytes that may be indicative of specific medical concerns or the health status of an organ system. Thus, panel tests provide a more extensive evaluation of a patient's health, have higher predictive values for confirming or disproving a disease, and are quick and cost-effective. | 1 | Biochemistry |
Proline organocatalysis is the use of proline as an organocatalyst in organic chemistry. This theme is often considered the starting point for the area of organocatalysis, even though early discoveries went unappreciated. Modifications, such as MacMillan’s catalyst and Jorgensen's catalysts, proceed with excellent stereocontrol.
Proline catalysis was initially reported by groups at Schering AG and Hoffmann-La Roche. Proline's chiral structure enables enantioselective synthesis, favoring a particular enantiomer or diastereomer. | 0 | Organic Chemistry |
The core histone proteins contains a characteristic structural motif termed the "histone fold", which consists of three alpha-helices (α1-3) separated by two loops (L1-2). In solution, the histones form H2A-H2B heterodimers and H3-H4 heterotetramers. Histones dimerise about their long α2 helices in an anti-parallel orientation, and, in the case of H3 and H4, two such dimers form a 4-helix bundle stabilised by extensive H3-H3' interaction. The H2A/H2B dimer binds onto the H3/H4 tetramer due to interactions between H4 and H2B, which include the formation of a hydrophobic cluster.
The histone octamer is formed by a central H3/H4 tetramer sandwiched between two H2A/H2B dimers. Due to the highly basic charge of all four core histones, the histone octamer is stable only in the presence of DNA or very high salt concentrations. | 1 | Biochemistry |
Degenerate matter exhibits quantum mechanical properties when a fermion system temperature approaches absolute zero. These properties result from a combination of the Pauli exclusion principle and quantum confinement. The Pauli principle allows only one fermion in each quantum state and the confinement ensures that energy of these states increases as they are filled. The lowest states fill up and fermions are forced to occupy high energy states even at low temperature.
While the Pauli principle and Fermi-Dirac distribution applies to all matter, the interesting cases for degenerate matter involve systems of many fermions. These cases can be understood with the help of the Fermi gas model. Examples include electrons in metals and in white dwarf stars and neutrons in neutron stars. The electrons are confined by Coulomb attraction to positive ion cores; the neutrons are confined by gravitation attraction. The fermions, forced in to higher levels by the Pauli principle, exert pressure preventing further compression.
The allocation or distribution of fermions into quantum states ranked by energy is called the Fermi-Dirac distribution. Degenerate matter exhibits the results of Fermi-Dirac distribution. | 7 | Physical Chemistry |
Low molecular weight simple amines, such as ethylamine, are only weakly toxic with between 100 and 1000 mg/kg. They are skin irritants, especially as some are easily absorbed through the skin. Amines are a broad class of compounds, and more complex members of the class can be extremely bioactive, for example strychnine. | 0 | Organic Chemistry |
The dynamically, or inelastically, scattered electrons provide several types of information about the sample as well. The brightness or intensity at a point on the detector depends on dynamic scattering, so all analysis involving the intensity must account for dynamic scattering. Some inelastically scattered electrons penetrate the bulk crystal and fulfill Bragg diffraction conditions. These inelastically scattered electrons can reach the detector to yield Kikuchi diffraction patterns, which are useful for calculating diffraction conditions. Kikuchi patterns are characterized by lines connecting the intense diffraction points on a RHEED pattern. Figure 6 shows a RHEED pattern with visible Kikuchi lines. | 3 | Analytical Chemistry |
A cyclopropyl group is a chemical structure derived from cyclopropane; it is typically produced in a cyclopropanation reaction. The group has an empirical formula of CH and chemical bonds from each of the three carbons to both of the other two. | 0 | Organic Chemistry |
The part to be coated is immersed in a bath of electrolyte which usually consists of a dilute alkaline solution such as KOH. It is electrically connected, so as to become one of the electrodes in the electrochemical cell, with the other "counter-electrode" typically being made from an inert material such as stainless steel, and often consisting of the wall of the bath itself.
Potentials of over 200 V are applied between these two electrodes. These may be continuous or pulsed direct current (DC) (in which case the part is simply an anode in DC operation), or alternating pulses (alternating current or "pulsed bi-polar" operation) where the stainless steel counter electrode might just be earthed. | 8 | Metallurgy |
The Standard addition method, often used in analytical chemistry, quantifies the analyte present in an unknown. This method is useful for analyzing complex samples where a matrix effect interferes with the analyte signal. In comparison to the calibration curve method, the standard addition method has the advantage of the matrices of the unknown and standards being nearly identical. This minimizes the potential bias arising from the matrix effect when determining the concentration. | 3 | Analytical Chemistry |
TALOS+. Predicts protein backbone torsion angles from chemical shift data. Frequently used to generate further restraints applied to a structure model during refinement. | 1 | Biochemistry |
A typical solid phase extraction involves five basic steps. First, the cartridge is equilibrated with a non-polar or slightly polar solvent, which wets the surface and penetrates the bonded phase. Then water, or buffer of the same composition as the sample, is typically washed through the column to wet the silica surface. The sample is then added to the cartridge. As the sample passes through the stationary phase, the polar analytes in the sample will interact and retain on the polar sorbent while the solvent, and other non-polar impurities pass through the cartridge. After the sample is loaded, the cartridge is washed with a non-polar solvent to remove further impurities. Then, the analyte is eluted with a polar solvent or a buffer of the appropriate pH.
A stationary phase of polar functionally bonded silicas with short carbons chains frequently makes up the solid phase. This stationary phase will adsorb polar molecules which can be collected with a more polar solvent. | 3 | Analytical Chemistry |
A substance that modifies the transition state to lower the activation energy is termed a catalyst; a catalyst composed only of protein and (if applicable) small molecule cofactors is termed an enzyme. A catalyst increases the rate of reaction without being consumed in the reaction. In addition, the catalyst lowers the activation energy, but it does not change the energies of the original reactants or products, and so does not change equilibrium. Rather, the reactant energy and the product energy remain the same and only the activation energy is altered (lowered).
A catalyst is able to reduce the activation energy by forming a transition state in a more favorable manner. Catalysts, by nature, create a more "comfortable" fit for the substrate of a reaction to progress to a transition state. This is possible due to a release of energy that occurs when the substrate binds to the active site of a catalyst. This energy is known as Binding Energy. Upon binding to a catalyst, substrates partake in numerous stabilizing forces while within the active site (e.g. hydrogen bonding or van der Waals forces). Specific and favorable bonding occurs within the active site until the substrate forms to become the high-energy transition state. Forming the transition state is more favorable with the catalyst because the favorable stabilizing interactions within the active site release energy. A chemical reaction is able to manufacture a high-energy transition state molecule more readily when there is a stabilizing fit within the active site of a catalyst. The binding energy of a reaction is this energy released when favorable interactions between substrate and catalyst occur. The binding energy released assists in achieving the unstable transition state. Reactions without catalysts need a higher input of energy to achieve the transition state. Non-catalyzed reactions do not have free energy available from active site stabilizing interactions, such as catalytic enzyme reactions. | 7 | Physical Chemistry |
In analytical chemistry, a reagent is a compound or mixture used to detect the presence or absence of another substance, e.g. by a color change, or to measure the concentration of a substance, e.g. by colorimetry. Examples include Fehlings reagent, Millons reagent, and Tollens' reagent. | 0 | Organic Chemistry |
The Grove cell voltage is about 1.9 volts and arises from the following reaction:
: Zn + HSO + 2 HNO ZnSO + 2 HO + 2 NO↑ | 3 | Analytical Chemistry |
*The World's 500 Most influential Arabs in 2013 in the “scientist inventor” category for his outstanding contributions in the areas of innovation, research and community service.
*The World's 500 Most influential Arabs in 2012.
*Arabian Business Achievement Awards 2011 – Science and Innovation Award 2011
*First prize in Tomohat Shabab TV program(Young Innovation Award), Sharjah TV 2011
*First place in the “Voting for the Best Project” category, 4th UAE Software Development Trade Show, Wollongong University, Dubai 2010
*Third place in the “Business Judging” category, 4th UAE Software Development Trade Show, Wollongong University, Dubai 2010
*Best Research Paper in Faculty of Engineering, The Fifth Approach Student Scientific Conference 2009
*Best Project on Biomedical Day 2008. | 7 | Physical Chemistry |
Brian G. Wowk is a Canadian medical physicist and cryobiologist known for the discovery and development of synthetic molecules that mimic the activity of natural antifreeze proteins in cryopreservation applications, sometimes called "ice blockers". As a senior scientist at 21st Century Medicine, Inc., he was a co-developer with Greg Fahy of key technologies enabling cryopreservation of large and complex tissues, including the first successful vitrification and transplantation of a mammalian organ (kidney). Wowk is also known for early theoretical work on future applications of molecular nanotechnology, especially cryonics, nanomedicine, and optics. In the early 1990s he wrote that nanotechnology would revolutionize optics, making possible virtual reality display systems optically indistinguishable from real scenery as in the fictitious Holodeck of Star Trek. These systems were described by Wowk in the chapter "Phased Array Optics" in the 1996 anthology Nanotechnology: Molecular Speculations on Global Abundance , and highlighted in the September 1998 Technology Watch section of Popular Mechanics magazine. | 1 | Biochemistry |
Fans may be installed in various ways, according to the application. They are often used in a free installation, without any housing of any kind. There are also some specialised installations. | 7 | Physical Chemistry |
Abu Bakarr Kanu is a Sierra Leonean analytical chemist who is a professor at Winston-Salem State University. His research considers separation-type instrumentation for the rapid analysis of chemical and biological compounds. Kanu is also involved with education and outreach programmes, and works to bring hands-on chemistry lessons to young people in Sierra Leone. | 3 | Analytical Chemistry |
For an amino acid with only one amine and one carboxyl group, the pI can be calculated from the mean of the pKas of this molecule.
The pH of an electrophoretic gel is determined by the buffer used for that gel. If the pH of the buffer is above the pI of the protein being run, the protein will migrate to the positive pole (negative charge is attracted to a positive pole). If the pH of the buffer is below the pI of the protein being run, the protein will migrate to the negative pole of the gel (positive charge is attracted to the negative pole). If the protein is run with a buffer pH that is equal to the pI, it will not migrate at all. This is also true for individual amino acids. | 7 | Physical Chemistry |
Both p90 and p70 Rsk phosphorylate ribosomal protein s6, part of the translational machinery, but several other substrates have been identified, including other ribosomal proteins. Cytosolic substrates of p90 include protein phosphatase 1; glycogen synthase kinase 3 (GSK3); L1 CAM, a neural cell adhesion molecule; Son of Sevenless, the Ras exchange factor; and Myt1, an inhibitor of cdc2.
RSK phosphorylation of SOS1 (Son of Sevenless) at Serines 1134 and 1161 creates 14-3-3 docking site. This interaction of phospho SOS1 and 14-3-3 negatively regulates Ras-MAPK pathway.
p90 also regulates transcription factors including cAMP response element-binding protein (CREB); estrogen receptor-α (ERα); IκBα/NF-κB; and c-Fos. | 1 | Biochemistry |
As the total number of degrees of freedom approaches infinity, the system will be found in the macrostate that corresponds to the highest multiplicity. In order to illustrate this principle, observe the skin temperature of a frozen metal bar. Using a thermal image of the skin temperature, note the temperature distribution on the surface. This initial observation of temperature represents a "microstate". At some future time, a second observation of the skin temperature produces a second microstate. By continuing this observation process, it is possible to produce a series of microstates that illustrate the thermal history of the bar's surface. Characterization of this historical series of microstates is possible by choosing the macrostate that successfully classifies them all into a single grouping. | 7 | Physical Chemistry |
Early hot rolling strip mills did not produce strip suitable for tinning, but in 1929 cold rolling began to be used to reduce the gauge further, which made tinning achievable. The plate was then tinned using the process outlined above. | 8 | Metallurgy |
In oxidative phosphorylation, the key control point is the reaction catalyzed by cytochrome c oxidase, which is regulated by the availability of its substrate – the reduced form of cytochrome c. The amount of reduced cytochrome c available is directly related to the amounts of other substrates:
which directly implies this equation:
Thus, a high ratio of [NADH] to [NAD] or a high ratio of [ADP] [P] to [ATP] imply a high amount of reduced cytochrome c and a high level of cytochrome c oxidase activity. An additional level of regulation is introduced by the transport rates of ATP and NADH between the mitochondrial matrix and the cytoplasm. | 1 | Biochemistry |
Splicing is regulated by trans-acting proteins (repressors and activators) and corresponding cis-acting regulatory sites (silencers and enhancers) on the pre-mRNA. However, as part of the complexity of alternative splicing, it is noted that the effects of a splicing factor are frequently position-dependent. That is, a splicing factor that serves as a splicing activator when bound to an intronic enhancer element may serve as a repressor when bound to its splicing element in the context of an exon, and vice versa. The secondary structure of the pre-mRNA transcript also plays a role in regulating splicing, such as by bringing together splicing elements or by masking a sequence that would otherwise serve as a binding element for a splicing factor. Together, these elements form a "splicing code" that governs how splicing will occur under different cellular conditions.
There are two major types of cis-acting RNA sequence elements present in pre-mRNAs and they have corresponding trans-acting RNA-binding proteins. Splicing silencers are sites to which splicing repressor proteins bind, reducing the probability that a nearby site will be used as a splice junction. These can be located in the intron itself (intronic splicing silencers, ISS) or in a neighboring exon (exonic splicing silencers, ESS). They vary in sequence, as well as in the types of proteins that bind to them. The majority of splicing repressors are heterogeneous nuclear ribonucleoproteins (hnRNPs) such as hnRNPA1 and polypyrimidine tract binding protein (PTB). Splicing enhancers are sites to which splicing activator proteins bind, increasing the probability that a nearby site will be used as a splice junction. These also may occur in the intron (intronic splicing enhancers, ISE) or exon (exonic splicing enhancers, ESE). Most of the activator proteins that bind to ISEs and ESEs are members of the SR protein family. Such proteins contain RNA recognition motifs and arginine and serine-rich (RS) domains.
In general, the determinants of splicing work in an inter-dependent manner that depends on context, so that the rules governing how splicing is regulated form a splicing code. The presence of a particular cis-acting RNA sequence element may increase the probability that a nearby site will be spliced in some cases, but decrease the probability in other cases, depending on context. The context within which regulatory elements act includes cis-acting context that is established by the presence of other RNA sequence features, and trans-acting context that is established by cellular conditions. For example, some cis-acting RNA sequence elements influence splicing only if multiple elements are present in the same region so as to establish context. As another example, a cis-acting element can have opposite effects on splicing, depending on which proteins are expressed in the cell (e.g., neuronal versus non-neuronal PTB). The adaptive significance of splicing silencers and enhancers is attested by studies showing that there is strong selection in human genes against mutations that produce new silencers or disrupt existing enhancers. | 1 | Biochemistry |
The BioWatch program is funded and supervised by the Department of Homeland Security (DHS). The BioWatch program has three main components: sampling, analysis, and response. Each of these components is handled by three different agencies. The Environmental Protection Agency (EPA) handles the sampling component: the sensors that collect airborne particles. The Centers for Disease Control and Prevention (CDC) coordinates the analysis and laboratory testing of the samples. Local authorities are responsible for the public health response to positive findings. The Federal Bureau of Investigation (FBI) is designated as the lead agency for the law enforcement response if a bioterrorism event is detected. (Shea and Lister, 2003) | 3 | Analytical Chemistry |
The skeletal structure of an organic compound is the series of atoms bonded together that form the essential structure of the compound. The skeleton can consist of chains, branches and/or rings of bonded atoms. Skeletal atoms other than carbon or hydrogen are called heteroatoms.
The skeleton has hydrogen and/or various substituents bonded to its atoms. Hydrogen is the most common non-carbon atom that is bonded to carbon and, for simplicity, is not explicitly drawn. In addition, carbon atoms are not generally labelled as such directly (i.e. with "C"), whereas heteroatoms are always explicitly noted as such ("N" for nitrogen, "O" for oxygen, etc.)
Heteroatoms and other groups of atoms that give rise to relatively high rates of chemical reactivity, or introduce specific and interesting characteristics in the spectra of compounds are called functional groups, as they give the molecule a function. Heteroatoms and functional groups are collectively called "substituents", as they are considered to be a substitute for the hydrogen atom that would be present in the parent hydrocarbon of the organic compound. | 0 | Organic Chemistry |
Fellgetts advantage or the multiplex advantage is an improvement in signal-to-noise ratio (SNR) that is gained when taking multiplexed measurements rather than direct measurements. The name is derived from P. B. Fellgett, who first made the observation as part of his PhD. When measuring a signal whose noise is dominated by detector noise, a multiplexed measurement such as the signal generated by a Fourier transform spectrometer can produce a relative improvement in SNR, compared to an equivalent scanning monochromator, of the order of the square root of m, where m' is the number of sample points comprising the spectrum. | 7 | Physical Chemistry |
Hydrogen rich substances as ammonia and hydrazine are great for storing hydrogen. This is due to their energy density, for ammonia at least 1.3 times that of liquid hydrogen. Hydrazine is almost twice as dense in energy compared to liquid hydrogen, however a downside is that dilution is required in the use of direct hydrazine fuel cells, which lowers the overall power one can get from this fuel cell. Besides the high volumetric density, ammonia and hydrous hydrazine have a low flammability, which makes it superior to hydrogen by lowering the storage and transportation costs. | 5 | Photochemistry |
Diazo compounds can be obtained in an elimination reaction of N-alkyl-N-nitroso compounds, such as in the synthesis of diazomethane from Diazald or MNNG:
(The mechanism shown here is one possibility. For an alternative mechanism for the analogous formation of diazomethane from an N-nitrososulfonamide, see the page on Diazald.) | 0 | Organic Chemistry |
* Aggregates can form under varying conditions and differ from each other in soil horizon and structure
* Natural aggregates results in what are called peds, whereas artificial aggregates are called clods.
* Clods are formed due to disturbance of the field by ploughing or digging.
* Microbial activity also influences the formation of aggregates. | 9 | Geochemistry |
In organic chemistry, the triflyl group (systematic name: trifluoromethanesulfonyl group) is a functional group with the formula and structure . The triflyl group is often represented by –Tf.
The related triflate group (trifluoromethanesulfonate) has the formula , and is represented by –OTf. | 0 | Organic Chemistry |
Aquametry in analytical chemistry refer to analytical processes to measure the water present in materials.
The methods widely used in aquametry encompasses Karl Fischer titration, distillation, chromatography etc. | 3 | Analytical Chemistry |
Promoter activity is a term that encompasses several meanings around the process of gene expression from regulatory sequences —promoters and enhancers. Gene expression has been commonly characterized as a measure of how much, how fast, when and where this process happens. Promoters and enhancers are required for controlling where and when a specific gene is transcribed.
Traditionally the measure of gene products (i.e. mRNA, proteins, etc.) has been the major approach of measure promoter activity. However, this method confront with two issues: the stochastic nature of the gene expression and the lack of mechanistic interpretation of the thermodynamical process involved in the promoter activation.
The actual developments in metabolomics product of developments of next-generation sequencing technologies and molecular structural analysis have enabled the development of more accurate models of the process of promoter activation (e.g. the sigma structure of the polymerase holoenzyme domains) and a better understanding of the complexities of the regulatory factors involved. | 1 | Biochemistry |
The theorem is also useful on a more microscopic scale, in biology. Living systems, such as cells, can be analyzed thermodynamically. They are rather complex systems, where many energy transformations occur, and they often waste heat. Hence, the Gouy-Stodola theorem may be useful, in certain situations, to perform exergy analysis on such systems. In particular, it may help to highlight differences between healthy and diseased cells.
Generally, the theorem may find applications in fields of biomedicine, or where biology and physics cross over, such as biochemical engineering thermodynamics. | 7 | Physical Chemistry |
A few other elements have been proposed as candidates for supporting biological systems and processes as fundamentally as carbon does, for example, processes such as metabolism. The most frequently suggested alternative is silicon. Silicon, atomic number of 14, more than twice the size of carbon, shares a group in the periodic table with carbon, can also form four valence bonds, and also bonds to itself readily, though generally in the form of crystal lattices rather than long chains. Despite these similarities, silicon is considerably more electropositive than carbon, and silicon compounds do not readily recombine into different permutations in a manner that would plausibly support lifelike processes. Silicon is abundant on Earth, but as it is more electropositive, it mainly forms Si–O bonds rather than Si–Si bonds. Boron does not react with acids and does not form chains naturally. Thus boron is not a candidate for life. Arsenic is toxic to life, and its possible candidacy has been rejected. In the past (1960s-1970s) other candidates for life were plausible, but with time and more research, only carbon as the complexity and stability for life, to make very large molecules, like polymers. Thus life must be carbon based. | 1 | Biochemistry |
Homoepitaxial growth of semiconductor thin films are generally done by chemical or physical vapor deposition methods that deliver the precursors to the substrate in gaseous state. For example, silicon is most commonly deposited from silicon tetrachloride (or germanium tetrachloride) and hydrogen at approximately 1200 to 1250 °C:
:SiCl + 2H ↔ Si + 4HCl
where (g) and (s) represent gas and solid phases, respectively. This reaction is reversible, and the growth rate depends strongly upon the proportion of the two source gases. Growth rates above 2 micrometres per minute produce polycrystalline silicon, and negative growth rates (etching) may occur if too much hydrogen chloride byproduct is present. (Hydrogen chloride may be intentionally added to etch the wafer.) An additional etching reaction competes with the deposition reaction:
:SiCl + Si ↔ 2SiCl
Silicon VPE may also use silane, dichlorosilane, and trichlorosilane source gases. For instance, the silane reaction occurs at 650 °C in this way:
:SiH → Si + 2H
VPE is sometimes classified by the chemistry of the source gases, such as hydride VPE (HVPE) and metalorganic VPE (MOVPE or MOCVD).
The reaction chamber where this process takes place may be heated by lamps located outside the chamber. A common technique used in compound semiconductor growth is molecular beam epitaxy (MBE). In this method, a source material is heated to produce an evaporated beam of particles, which travel through a very high vacuum (10 Pa; practically free space) to the substrate and start epitaxial growth. Chemical beam epitaxy, on the other hand, is an ultra-high vacuum process that uses gas phase precursors to generate the molecular beam.
Another widely used technique in microelectronics and nanotechnology is atomic layer epitaxy, in which precursor gases are alternatively pulsed into a chamber, leading to atomic monolayer growth by surface saturation and chemisorption. | 3 | Analytical Chemistry |
Synaptic degeneration and death of nerve cells are defining features of Alzheimer's disease (AD), the most prevalent age-related neurodegenerative disorders. In AD, neurons in the hippocampus and basal forebrain (brain regions that subserve learning and memory functions) are selectively vulnerable. Studies of postmortem brain tissue from AD people have provided evidence for increased levels of oxidative stress, mitochondrial dysfunction and impaired glucose uptake in vulnerable neuronal populations. Studies of animal and cell culture models of AD suggest that increased levels of oxidative stress (membrane lipid peroxidation, in particular) may disrupt neuronal energy metabolism and ion homeostasis, by impairing the function of membrane ion-motive ATPases, glucose and glutamate transporters. Such oxidative and metabolic compromise may thereby render neurons vulnerable to excitotoxicity and apoptosis. Recent studies suggest that AD can manifest systemic alterations in energy metabolism (e.g., increased insulin resistance and dysregulation of glucose metabolism). Emerging evidence that dietary restriction can forestall the development of AD is consistent with a major "metabolic" component to these disorders, and provides optimism that these devastating brain disorders of aging may be largely preventable. | 7 | Physical Chemistry |
The primary essential parts for this phase include detailing the reaction conditions in full, giving both the amount of RNA used and the total volume of the reaction, give information on the oligonucleotide used as a primer and its concentration, the concentration and type of reverse transcriptase used, and lastly the temperature and amount of time done for the reaction. It is also desirable to have the catalog numbers of reagents used and their manufacturers, the standard deviation for the Cq with and without the transcriptase being involved, and how the cDNA was stored. | 1 | Biochemistry |
Methyl isocyanate is a colorless, poisonous, lachrymatory (tearing agent), flammable liquid. It is soluble in water to 6–10 parts per 100 parts, but it also reacts with water (see Reactions below).
It has a refractive index of 1.363 with a wavelength of 589 nm at a temperature of 20 °C | 9 | Geochemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.