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Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atoms electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons. Electronegativity serves as a simple way to quantitatively estimate the bond energy, and the sign and magnitude of a bonds chemical polarity, which characterizes a bond along the continuous scale from covalent to ionic bonding. The loosely defined term electropositivity is the opposite of electronegativity: it characterizes an element's tendency to donate valence electrons.
On the most basic level, electronegativity is determined by factors like the nuclear charge (the more protons an atom has, the more "pull" it will have on electrons) and the number and location of other electrons in the atomic shells (the more electrons an atom has, the farther from the nucleus the valence electrons will be, and as a result, the less positive charge they will experience—both because of their increased distance from the nucleus and because the other electrons in the lower energy core orbitals will act to shield the valence electrons from the positively charged nucleus).
The term "electronegativity" was introduced by Jöns Jacob Berzelius in 1811,
though the concept was known before that and was studied by many chemists including Avogadro.
In spite of its long history, an accurate scale of electronegativity was not developed until 1932, when Linus Pauling proposed an electronegativity scale which depends on bond energies, as a development of valence bond theory. It has been shown to correlate with a number of other chemical properties. Electronegativity cannot be directly measured and must be calculated from other atomic or molecular properties. Several methods of calculation have been proposed, and although there may be small differences in the numerical values of the electronegativity, all methods show the same periodic trends between elements.
The most commonly used method of calculation is that originally proposed by Linus Pauling. This gives a dimensionless quantity, commonly referred to as the Pauling scale (χ), on a relative scale running from 0.79 to 3.98 (hydrogen = 2.20). When other methods of calculation are used, it is conventional (although not obligatory) to quote the results on a scale that covers the same range of numerical values: this is known as an electronegativity in Pauling units.
As it is usually calculated, electronegativity is not a property of an atom alone, but rather a property of an atom in a molecule. Even so, the electronegativity of an atom is strongly correlated with the first ionization energy. The electronegativity is slightly negatively correlated (for smaller electronegativity values) and rather strongly positively correlated (for most and larger electronegativity values) with the electron affinity. It is to be expected that the electronegativity of an element will vary with its chemical environment, but it is usually considered to be a transferable property, that is to say that similar values will be valid in a variety of situations.
Caesium is the least electronegative element (0.79); fluorine is the most (3.98). | 3 | Analytical Chemistry |
The awards were started because of the challenge that editors faced of effectively covering the trade show, which in 2015 hosted 925 exhibitors. New exhibitors at the Morial Convention Center totalled 130 companies. Walking past every booth at an event such as this represents a trek of over .
Accredited media representatives, of whom there were more than 150 per year, were invited to list up to three new products on a nomination form provided on registration at the Media Center. Editors were invited to attend a judging session towards the end of the trade show. They reviewed entries and voted on the nominated products. The only criterion was that products must have appeared at the exhibition for the first time, but winning products usually featured innovations in technology or industrial design, or enabled new analytical applications.
Gold, Silver and Bronze winners were determined and plaques were awarded to the booth personnel of the winning companies on the final morning of the four-day exposition. Other nominated products received an Honourable Mention. | 3 | Analytical Chemistry |
In 2008, Ardisson and his co-workers reported a strategy that applies a crotyltitanation reaction repeatedly to yield homoallylic (Z)-O-ene-carbamate alcohols with excellent selectivity. This crotyltitanation reaction not only efficiently produces the syn-anti methyl-hydroxy-methyl triads of (+)-discodermolide, but also yields products that can be easily converted to terminal (Z)-diene. The C13-C14 (Z)-olefin is installed through a highly selective dyotropic rearrangement. The Ardission synthesis of (+)-discodermolide has an overall yield of 1.6% with a longest linear sequence of 21 steps. | 0 | Organic Chemistry |
The high molecular weight of biopolymers make their synthesis inherently laborious. Further challenges can arise from specific spatial arrangement adopted by the natural biopolymer, which may be vital for its properties/activity but not easily reproducible in the synthetic copy. Despite this, chemical approaches to obtain biopolymer are highly desirable to overcome issues arising from low abundance of the target biopolymer in Nature, the need for cumbersome isolation processes or high batch-to-batch variability or inhomogeneity of the naturally-sourced species. | 1 | Biochemistry |
Alternating D/L peptide macrocycles are known to self-aggregate into nanotubes, and the resulting nanotubes have been shown to act as ion channels in lipid membranes.
Other architectures use peptide helices as a scaffold to attach other functionalities, such as crown ethers of different sizes. The property of these peptide-crown channels depend strongly on the identity of the capping end-groups. | 6 | Supramolecular Chemistry |
A laser SBSP could also power a base or vehicles on the surface of the Moon or Mars, saving on mass costs to land the power source. A spacecraft or another satellite could also be powered by the same means. In a 2012 report presented to NASA on space solar power, the author mentions another potential use for the technology behind space solar power could be for solar electric propulsion systems that could be used for interplanetary human exploration missions. | 7 | Physical Chemistry |
Dispersive soils are more common in older landscapes where leaching and illuviation processes have had more time to work. A source of sodium is also required. Possible sources can include weathering from soil parent materials or wind-blown salt deposition. Sodium ions are highly mobile in the soil solution and so they accumulate in the lower parts of the landscape.
The dispersive portion of a soil profile is generally confined to the subsoil, where soil-forming processes concentrate clay minerals and sodium. This means that dispersive soils may not be identified until they are disturbed in a way that exposes the subsoil to running water.
When observed in situ, dispersive soil textures may feel soapy, and in many cases the physical structure of subsoil layers will be prismatic or columnar. A simplified version of the Emerson soil dispersion test can be completed in the field on a 20-minute to two-hour timescale.
Laboratory tests used to diagnose a soil as dispersive focus on the cation exchange capacity of a soil sample and its cation breakdown. Soil cations are dominated by Ca, Mg, K, and Na, as well as H in acidic soils. The exchangeable sodium percentage ( "ESP", (sodium / (total cations)) * 100 ) is a key indicator derived from these measurements. Where ESP exceeds 5%, dispersive behaviour becomes possible, and is highly likely where ESP exceeds 15%. | 9 | Geochemistry |
2D correlation analysis originated from 2D NMR spectroscopy. Isao Noda developed perturbation based 2D spectroscopy in the 1980s. This technique required sinusoidal perturbations to the chemical system under investigation. This specific type of the applied perturbation severely limited its possible applications. Following research done by several groups of scientists, perturbation based 2D spectroscopy could be developed to a more extended and generalized broader base. Since the development of generalized 2D correlation analysis in 1993 based on Fourier transformation of the data, 2D correlation analysis gained widespread use. Alternative techniques that were simpler to calculate, for example the disrelation spectrum, were also developed simultaneously. Because of its computational efficiency and simplicity, the Hilbert transform is nowadays used for the calculation of the 2D spectra. To date, 2D correlation analysis is used for the interpretation of many types of spectroscopic data (including XRF, UV/VIS spectroscopy, fluorescence, infrared, and Raman spectra), although its application is not limited to spectroscopy. | 7 | Physical Chemistry |
*X-ray crystallography
Just like other organic molecule study, X-ray crystallography is a very useful tool to know the detail information on the interaction between carbohydrate and protein.
*NMR Study
By using titration, NOESY(Nuclear Overhauser Effect SpectroscopY), CIDNP experiments, the specificity and affinity of binding, association constants and equilibrium thermodynamic parameters of carbohydrate–protein binding can be studied.
*Molecular Modeling
In many cases, the conformation information is required, however, sometimes it is not able to get directly from the experiments. So the knowledge-based model building approach is used.
*Fluorescence Spectrometry
Fluorescence spectrometry is a useful tool and has its advantages: no procedure for separation and plenty of ways to get fluorophore source: there are some of amino acids and ligands that have fluorophore after they are activated.
*Dual polarisation interferometry
Dual polarisation interferometry is a label free analytical technique for measuring interactions and associated conformational changes. | 0 | Organic Chemistry |
Many pesticides achieve their intended use of killing pests by disrupting the nervous system. Due to similarities in brain biochemistry among many different organisms, there is much speculation that these chemicals can have a negative impact on humans as well. Children are especially vulnerable to exposure to pesticides, especially at critical windows of development. Infants and children consume higher amounts of food relative to their body-weight, and have a more permeable blood–brain barrier, all of which can contribute to increased risks from exposure to pesticide residues. However in 2008 the OECD report that the existing guideline represents the best available science for assessing the potential for developmental neurotoxicity in human health risk assessment. | 2 | Environmental Chemistry |
The inorganic cycle begins with the production of carbonic acid (HCO) from rainwater and gaseous carbon dioxide. Due to this process, normal rain has a pH of around 5.6. Carbonic acid is a weak acid, but over long timescales, it can dissolve silicate rocks (as well as carbonate rocks). Most of the Earth's crust (and mantle) is composed of silicates. These substances break down into dissolved ions as a result. For example, calcium silicate (CaSiO), or wollastonite, reacts with carbon dioxide and water to yield a calcium ion, Ca, a bicarbonate ion, HCO, and dissolved silica. This reaction structure is representative of general silicate weathering of calcium silicate minerals. The chemical pathway is as follows:
River runoff carries these products to the ocean, where marine calcifying organisms use Ca and HCO to build their shells and skeletons, a process called carbonate precipitation:
Two molecules of CO are required for silicate rock weathering; marine calcification releases one molecule back to the atmosphere. The calcium carbonate (CaCO) contained in shells and skeletons sinks after the marine organism dies and is deposited on the ocean floor.
The final stage of the process involves the movement of the seafloor. At subduction zones, the carbonate sediments are buried and forced back into the mantle. Some carbonate may be carried deep into the mantle where high pressure and temperature conditions allow it to combine metamorphically with SiO to form CaSiO and CO, which is released from the interior into the atmosphere via volcanism, thermal vents in the ocean, or soda springs, which are natural springs that contain carbon dioxide gas or soda water:
This final step returns the second CO molecule to the atmosphere and closes the inorganic carbon budget. 99.6% of all carbon on Earth (equating to roughly 10 billion tons of carbon) is sequestered in the longterm rock reservoir. And essentially all carbon has spent time in the form of carbonate. By contrast, only 0.002% of carbon exists in the biosphere. | 9 | Geochemistry |
Washing the polymer plates after they have been exposed to ultra-violet light may result in monomers entering the sewer system, eventually adding to the plastic content of the oceans. Current water purification installations are not able to remove monomer molecules from sewer water. Some monomers, such as styrene, are toxic or carcinogenic. | 5 | Photochemistry |
In a horizontal sedimentation tank, some particles may not follow the diagonal line in Fig. 1, while settling faster as they grow. So this says that particles can grow and develop a higher settling velocity if a greater depth with longer retention time. However, the collision chance would be even greater if the same retention time were spread over a longer, shallower tank. In fact, in order to avoid hydraulic short-circuiting, tanks usually are made 3–6 m deep with retention times of a few hours. | 3 | Analytical Chemistry |
Andreev reflection (AR), named after the Russian physicist Alexander F. Andreev, is a type of particle scattering which
occurs at interfaces between a superconductor (S) and a normal state material (N). It is a charge-transfer process by which normal current in N is converted to supercurrent in S. Each Andreev reflection transfers a charge 2e across the interface, avoiding the forbidden single-particle transmission within the superconducting energy gap. | 7 | Physical Chemistry |
* The term corrosion refers to the electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion: it forms as a result of the oxidation of iron metal. Common rust often refers to iron(III) oxide, formed in the following chemical reaction:
* The oxidation of iron(II) to iron(III) by hydrogen peroxide in the presence of an acid:
:Here the overall equation involves adding the reduction equation to twice the oxidation equation, so that the electrons cancel: | 9 | Geochemistry |
In thin layer chromatography (TLC) color reactions are frequently used to detect compound spots by dipping the plate into the reagent or by spraying the reagent onto the plates. | 7 | Physical Chemistry |
The Arrhenius equation gives the quantitative basis of the relationship between the activation energy and the rate at which a reaction proceeds. From the equation, the activation energy can be found through the relation
where A is the pre-exponential factor for the reaction, R is the universal gas constant, T is the absolute temperature (usually in kelvins), and k is the reaction rate coefficient. Even without knowing A, E can be evaluated from the variation in reaction rate coefficients as a function of temperature (within the validity of the Arrhenius equation).
At a more advanced level, the net Arrhenius activation energy term from the Arrhenius equation is best regarded as an experimentally determined parameter that indicates the sensitivity of the reaction rate to temperature. There are two objections to associating this activation energy with the threshold barrier for an elementary reaction. First, it is often unclear as to whether or not reaction does proceed in one step; threshold barriers that are averaged out over all elementary steps have little theoretical value. Second, even if the reaction being studied is elementary, a spectrum of individual collisions contributes to rate constants obtained from bulk (bulb) experiments involving billions of molecules, with many different reactant collision geometries and angles, different translational and (possibly) vibrational energies—all of which may lead to different microscopic reaction rates. | 7 | Physical Chemistry |
When the two intersecting planes are described in terms of Cartesian coordinates by the two equations
the dihedral angle, between them is given by:
and satisfies It can easily be observed that the angle is independent of and .
Alternatively, if and are normal vector to the planes, one has
where is the dot product of the vectors and is the product of their lengths.
and b and through b and b, respectively. -->
The absolute value is required in above formulas, as the planes are not changed when changing all coefficient signs in one equation, or replacing one normal vector by its opposite.
However the absolute values can be and should be avoided when considering the dihedral angle of two half planes whose boundaries are the same line. In this case, the half planes can be described by a point of their intersection, and three vectors , and such that , and belong respectively to the intersection line, the first half plane, and the second half plane. The dihedral angle of these two half planes is defined by
and satisfies In this case, switching the two half-planes gives the same result, and so does replacing with In chemistry (see below), we define a dihedral angle such that replacing with changes the sign of the angle, which can be between and . | 4 | Stereochemistry |
The second stage is the oxidation of the carbon in the remaining sample in the form of carbon dioxide (CO) and other gases. Modern TOC analyzers perform this oxidation step by several processes:
* High temperature combustion
* High temperature catalytic oxidation (HTCO)
* Photo-oxidation alone
* Thermo-chemical oxidation
* Photo-chemical oxidation
* Electrolytic oxidation | 3 | Analytical Chemistry |
* [http://www.jove.com/video/3532/synthesis-of-nine-atom-deltahedral-zintl-ions-of-germanium-and-their-functionalization-with-organic-groups Video of preparation of KGe (subscription required)] | 7 | Physical Chemistry |
Monoclonal antibodies for research applications can be found directly from antibody suppliers, or through use of a specialist search engine like CiteAb. Below are examples of clinically important monoclonal antibodies. | 1 | Biochemistry |
Heterofermentative bacteria produce less lactate and less ATP, but produce several other end products:
:Glucose + ADP + P → Lactate + Ethanol + CO + ATP
Examples include Leuconostoc mesenteroides, Lactobacillus bifermentous, and Leuconostoc lactis. | 1 | Biochemistry |
The RNA markers consist of RNA transcripts of various incrementing lengths. For example, the Lonza 0.5-9 kbp marker has bands marking 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, and 9 kilobase pairs. Markers are dissolved in a storage buffer, such as EDTA, and can have a shelf life of up to 2 years when stored at -80 °C. To use the marker, such as for northern blot analysis, it is first thawed, and then stained so that it is detectable on a gel electrophoresis. One of the most common dyes used for markers is ethidium bromide.
The range of a particular marker refers to variety of bands it can map. A "high" range refers to relatively large fragments (measured in kb) while a "low" range refers to markers that distinguish between small fragments (measured in bp). Some markers can even be described as "ultra-low range", but even more precise is the microRNA marker. A microRNA marker can be used to measure RNA fragments within a dozen nucleotides, such as the 17-25 nt microRNA marker. | 1 | Biochemistry |
Osmond iron (also spelt osmund and also called osborn) was wrought iron made by a particular process. This is associated with the first European production of cast iron in furnaces such as Lapphyttan in Sweden.
Osmonds appear in some of the earliest English Customs accounts, for example in 1325. The kappe is a Swedish iron weight used for osmond occurs in a commercial treaty in Novgorod in 1203, and this implies the production of osmond iron.
Osmond iron was made by melting pig iron in a hearth that is narrower and deeper than a typical finery in an English finery forge. The hearth had a charcoal fire blown with bellows through a tuyere. As the iron melted, the drops fell through the blast and congealed. They were then lifted with an iron bar into the blast. As they melted they were caught on the end of a large staff, held in the fire and turned rapidly so that the drops spread out, forming a ball.
Osmonds reached England during the later Middle Ages through the port of Gdańsk. However, there were hammer mills in its hinterland and that of Lübeck, which made the osmonds into bar iron. In the 1620s, Gustav II Adolf of Sweden prohibited his subjects from exporting unfinished iron, and all trade in osmonds ceased.
The osmond process was also used in the county of Mark in Westphalia, in southern Germany and Switzerland.
The process was introduced to Wales in connection with the establishment by William Humfrey and others of wireworks at Tintern in 1566, an enterprise that was shortly afterwards taken over by the Company of Mineral and Battery Works. Humfrey arranged to bring an expert maker of Osmond iron, Corslett Tinkhaus, from southwest Westphalia, where the production had reached a high level of technical proficiency. Tinkhaus arrived in Wales in 1567 and began working at Rhydygwern in the Glamorgan part of the lordship of Machen. This was where the first Machen Forge was, and he was evidently making osmond iron there. The iron was apparently forged with a tilt hammer, rather than the helve hammer, usual in finery forges. This was the raw material for the wireworks at Tintern. Osmond iron was made at Pontypool in the 18th century to supply wireworks there, and one of the forges there was still called the Osborn Forge in the 19th century. | 8 | Metallurgy |
The characteristics of supersaturation have practical applications in terms of pharmaceuticals. By creating a supersaturated solution of a certain drug, it can be ingested in liquid form. The drug can be made driven into a supersaturated state through any normal mechanism and then prevented from precipitating out by adding precipitation inhibitors. Drugs in this state are referred to as "supersaturating drug delivery services," or "SDDS." Oral consumption of a drug in this form is simple and allows for the measurement of very precise dosages. Primarily, it provides a means for drugs with very low solubility to be made into aqueous solutions. In addition, some drugs can undergo supersaturation inside the body despite being ingested in a crystalline form. This phenomenon is known as in vivo supersaturation.
The identification of supersaturated solutions can be used as a tool for marine ecologists to study the activity of organisms and populations. Photosynthetic organisms release O gas into the water. Thus, an area of the ocean supersaturated with O gas can likely determined to be rich with photosynthetic activity. Though some O will naturally be found in the ocean due to simple physical chemical properties, upwards of 70% of all oxygen gas found in supersaturated regions can be attributed to photosynthetic activity.
Supersaturation in vapor phase is usually present in the expansion process through steam nozzles that operate with superheated steam at the inlet, which transitions to saturated state at the outlet. Supersaturation thus becomes an important factor to be taken into account in the design of steam turbines, as this results in an actual mass flow of steam through the nozzle being about 1 to 3% greater than the theoretically calculated value that would be expected if the expanding steam underwent a reversible adiabatic process through equilibrium states. In these cases supersaturation occurs due to the fact that the expansion process develops so rapidly and in such a short time, that the expanding vapor cannot reach its equilibrium state in the process, behaving as if it were superheated. Hence the determination of the expansion ratio, relevant to the calculation of the mass flow through the nozzle, must be done using an adiabatic index of approximately 1.3, like that of the superheated steam, instead of 1.135, which is the value that should have to be used for a quasi-static adiabatic expansion in the saturated region.
The study of supersaturation is also relevant to atmospheric studies. Since the 1940s, the presence of supersaturation in the atmosphere has been known. When water is supersaturated in the troposphere, the formation of ice lattices is frequently observed. In a state of saturation, the water particles will not form ice under tropospheric conditions. It is not enough for molecules of water to form an ice lattice at saturation pressures; they require a surface to condense on to or conglomerations of liquid water molecules of water to freeze. For these reasons, relative humidities over ice in the atmosphere can be found above 100%, meaning supersaturation has occurred. Supersaturation of water is actually very common in the upper troposphere, occurring between 20% and 40% of the time. This can be determined using satellite data from the Atmospheric Infrared Sounder. | 7 | Physical Chemistry |
Amyl nitrite is administered to treat cyanide poisoning. It works by converting hemoglobin to methemoglobin, which allows for the binding of cyanide (CN) anions by ferric (Fe) cations and the formation of cyanomethemoglobin. The immediate goal of forming this cyanide adduct is to prevent the binding of free cyanide to the cytochrome a group in cytochrome c oxidase. | 1 | Biochemistry |
While there are multitudes of molecules in existence which would appear to be antiaromatic on paper, the number of molecules that are antiaromatic in actuality is considerably less. This is compounded by the fact that one cannot typically make derivatives of antiaromatic molecules by adding more antiaromatic hydrocarbon rings, etc. because the molecule typically loses either its planar nature or its conjugated system of π-electrons and becomes nonaromatic. In this section, only examples of antiaromatic compounds which are non-disputable are included.
Pentalene is an antiaromatic compound which has been well-studied both experimentally and computationally for decades. It is dicyclic, planar and has eight π-electrons, fulfilling the IUPAC definition of antiaromaticity. Pentalene’s dianionic and dicationic states are aromatic, as they follow Hückel’s 4n +2 π-electron rule. | 7 | Physical Chemistry |
Any polar chromatographic surface can be used for HILIC separations. Even non-polar bonded silicas have been used with extremely high organic solvent composition, thanks to the exposed patches of silica in between the bonded ligands on the support, which can affect the interactions. With that exception, HILIC phases can be grouped into five categories of neutral polar or ionic surfaces:
*simple unbonded silica silanol or diol bonded phases
*amino or anionic bonded phases
*amide bonded phases
*cationic bonded phases
*zwitterionic bonded phases | 1 | Biochemistry |
Coherent Stokes Raman spectroscopy (CSRS pronounced as "scissors") is a form of spectroscopy used primarily in chemistry, physics and related fields. It is closely related to Raman spectroscopy and lasing processes. It is very similar to Raman spectroscopy, but involves a lasing process that dramatically improves the signal.
It is very similar to the more common CARS except it uses an anti-Stokes frequency stimulation beam and a Stokes frequency beam is observed (the opposite of CARS). This is disadvantageous because anti-stokes processes must start in a less populated excited state. | 3 | Analytical Chemistry |
Lisinopril leaves the body completely unchanged in the urine. The half-life of lisinopril is 12 hours, and is increased in people with kidney problems. While the plasma half-life of lisinopril has been estimated between 12 and 13 hours, the elimination half-life is much longer, at around 30 hours. The full duration of action is between 24 and 30 hours.
Lisinopril is the only water-soluble member of the ACE inhibitor class, and thus has no metabolism by the liver. | 4 | Stereochemistry |
*Photosynthesis: Plants use solar energy to convert carbon dioxide and water into glucose and oxygen.
*Human formation of vitamin D by exposure to sunlight.
*Bioluminescence: e.g. In fireflies, an enzyme in the abdomen catalyzes a reaction that produces light.
*Polymerizations started by photoinitiators, which decompose upon absorbing light to produce the free radicals for radical polymerization.
*Photodegradation of many substances, e.g. polyvinyl chloride and Fp. Medicine bottles are often made from darkened glass to protect the drugs from photodegradation.
*Photochemical rearrangements, e.g. photoisomerization, hydrogen atom transfer, and photochemical electrocyclic reactions.
*Photodynamic therapy: Light is used to destroy tumors by the action of singlet oxygen generated by photosensitized reactions of triplet oxygen. Typical photosensitizers include tetraphenylporphyrin and methylene blue. The resulting singlet oxygen is an aggressive oxidant, capable of converting C–H bonds into C–OH groups.
*Diazo printing process
*Photoresist technology, used in the production of microelectronic components.
*Vision is initiated by a photochemical reaction of rhodopsin.
*Toray photochemical production of ε-caprolactame.
*Photochemical production of artemisinin, an anti-malaria drug.
*Photoalkylation, used for the light-induced addition of alkyl groups to molecules.
*DNA: photodimerization leading to cyclobutane pyrimidine dimers. | 5 | Photochemistry |
Two-hybrid screening (originally known as yeast two-hybrid system or Y2H) is a molecular biology technique used to discover protein–protein interactions (PPIs) and protein–DNA interactions by testing for physical interactions (such as binding) between two proteins or a single protein and a DNA molecule, respectively.
The premise behind the test is the activation of downstream reporter gene(s) by the binding of a transcription factor onto an upstream activating sequence (UAS). For two-hybrid screening, the transcription factor is split into two separate fragments, called the DNA-binding domain (DBD or often also abbreviated as BD) and activating domain (AD). The BD is the domain responsible for binding to the UAS and the AD is the domain responsible for the activation of transcription. The Y2H is thus a protein-fragment complementation assay. | 1 | Biochemistry |
Transparent wood composites are novel wood materials which have up to 90% transparency. Some have better mechanical properties than wood itself. They were made for the first time in 1992. These materials are significantly more biodegradable than glass and plastics. Transparent wood is also shatterproof, making it suitable for applications like cell phone screens. | 7 | Physical Chemistry |
Absorbance of a material is also related to its decadic attenuation coefficient by
where
* is the thickness of that material through which the light travels, and
* is the decadic attenuation coefficient of that material at .
If a(z) is uniform along the path, the attenuation is said to be a linear attenuation, and the relation becomes
Sometimes the relation is given using the molar attenuation coefficient of the material, that is its attenuation coefficient divided by its molar concentration:
where
* is the molar attenuation coefficient of that material, and
* is the molar concentration of that material at .
If is uniform along the path, the relation becomes
The use of the term "molar absorptivity" for molar attenuation coefficient is discouraged. | 7 | Physical Chemistry |
Blood glucose levels are maintained at a steady state concentration by balancing the rate of entry of glucose into the blood stream (i.e. by ingestion or released from cells) and the rate of glucose uptake by body tissues. Changes in the rate of input will be met with a change in consumption, and vice versa, so that blood glucose concentration is held at about 5 mM in humans. A change in blood glucose levels triggers the release of insulin or glucagon, which stimulates the liver to release glucose into the bloodstream or take up glucose from the bloodstream in order to return glucose levels to steady state. Pancreatic beta cells, for example, increase oxidative metabolism as a result of a rise in blood glucose concentration, triggering secretion of insulin. Glucose levels in the brain are also maintained at steady state, and glucose delivery to the brain relies on the balance between the flux of the blood brain barrier and uptake by brain cells. In teleosts, a drop of blood glucose levels below that of steady state decreases the intracellular-extracellular gradient in the bloodstream, limiting glucose metabolism in red blood cells. | 7 | Physical Chemistry |
Succinic semialdehyde (SSA) is a GABA metabolite. It is formed from GABA by the action of GABA transaminase (4-aminobutyrate aminotransferase) and further oxidised to become succinic acid, which enters TCA cycle. SSA is oxidized into succinic acid by the enzyme succinic semialdehyde dehydrogenase, which uses NAD as a cofactor. When the oxidation of succinic semialdehyde to succinic acid is impaired, accumulation of succinic semialdehyde takes place which leads to succinic semialdehyde dehydrogenase deficiency. | 1 | Biochemistry |
The experimental objections to the Thomsen–Berthelot principle include incomplete dissociation, reversibility, and spontaneous endothermic processes. Such cases were dismissed by orthadox thermochemist as outliers not covered by the principle, or the experiments were manipulated to fit it through with somewhat contrived justifications was later disproved. In 1873, Thomsen acknowledged that his theory might not have universal or definitive credibility. Later, under newly created chemical thermodynamics framework, the principle was explained to only be valid as an idealization under extreme conditions (i.e., absolute zero). Thomsen openly admitted that his initial understanding was merely a close estimate of the reality, emphasizing that while chemical reactions typically release heat, this heat isn't always a trustworthy indicator of the strength of the bonds formed. On the other hand, Berthelot, was more resistant and continued to assert the validity of the principle until 1894. In 1882 the German scientist Hermann von Helmholtz proved that affinity was not given by the heat evolved in a chemical reaction but rather by the maximum work, or free energy, produced when the reaction was carried out reversibly. | 7 | Physical Chemistry |
Northwestern University researchers announced a solution to a primary problem of DSSCs, that of difficulties in using and containing the liquid electrolyte and the consequent relatively short useful life of the device. This is achieved through the use of nanotechnology and the conversion of the liquid electrolyte to a solid. The current efficiency is about half that of silicon cells, but the cells are lightweight and potentially of much lower cost to produce. | 5 | Photochemistry |
The BANA test (referring to the enzymatic breakdown of [N-benzoyl-dL-arginine-2-napthylamide]) is used to determine the proteolytic activity of certain oral anaerobes that contribute to oral malodor. Some bacteria, e.g. Prophyromona gingivalis, Treponema denticola, and Bacteroides forsythus (Red complex) produce waste products that are quite odiferous, and as a result contribute to bad breath.
When a sample of a patient's saliva that contains these bacteria is placed within the BANA testing compound, it causes the breakdown of the N-benzoyl enzyme. As a result of this biodegradation occurs, the test compound changes color, indicating a positive reaction.
Uses: Used to identify volatile Sulphur compounds in halitosis patients. | 1 | Biochemistry |
The interest in reducing as much as possible the costs of the catalyst for electrochemical processes led to the use of fine catalyst powders since the specific surface area increases as the average particle size decreases. For instance, most common PEM fuel cells and electrolyzers design is based on a polymeric membrane charged in platinum nanoparticles as an electrocatalyst (the so-called platinum black).
Although the surface area to volume ratio is commonly considered to be the main parameter relating electrocatalyst size with its activity, to understand the particle-size effect, several more phenomena need to be taken into account:
* Equilibrium shape: for any given size of a nanoparticle there is an equilibrium shape which exactly determines its crystal planes
* Reaction sites relative number: a given size for a nanoparticle corresponds to a certain number of surface atoms and only some of them host a reaction site
* Electronic structure: below a certain size, the work function of a nanoparticle changes and its band structure fades away
* Defects: the crystal lattice of a small nanoparticle is perfect; thus, reactions enhanced by defects as reaction sites get slowed down as the particle size decreases
* Stability: small nanoparticles have the tendency to lose mass due to the diffusion of their atoms towards bigger particles, according to the Ostwald ripening phenomenon
* Capping agents: in order to stabilize nanoparticles it is necessary a capping layer, therefore part of their surface is unavailable for reactants
* Support: nanoparticles are often fixed onto a support in order to stay in place, therefore part of their surface is unavailable for reactants | 7 | Physical Chemistry |
The second type of photocyte granule contains a large crystal surrounded by several small crystals within a matrix with no definite shape or form. T microtubules in the type two granules are associated with the face of the crystal. In addition ferritin has been found to be associated with the crystals. Type II granules are hypothesized to exist in Amphiurus filiformis photocytes. | 1 | Biochemistry |
The restriction modification system (RM system) is found in bacteria and other prokaryotic organisms, and provides a defense against foreign DNA, such as that borne by bacteriophages.
Bacteria have restriction enzymes, also called restriction endonucleases, which cleave double-stranded DNA at specific points into fragments, which are then degraded further by other endonucleases. This prevents infection by effectively destroying the foreign DNA introduced by an infectious agent (such as a bacteriophage). Approximately one-quarter of known bacteria possess RM systems and of those about one-half have more than one type of system.
As the sequences recognized by the restriction enzymes are very short, the bacterium itself will almost certainly contain some within its genome. In order to prevent destruction of its own DNA by the restriction enzymes, methyl groups are added. These modifications must not interfere with the DNA base-pairing, and therefore, usually only a few specific bases are modified on each strand.
Endonucleases cleave internal/non-terminal phosphodiester bonds. They do so only after recognising specific sequences in DNA which are usually 4–6 base pairs long, and often palindromic. | 1 | Biochemistry |
Under certain conditions the Beer–Lambert law fails to maintain a linear relationship between attenuation and concentration of analyte. These deviations are classified into three categories:
# Real—fundamental deviations due to the limitations of the law itself.
# Chemical—deviations observed due to specific chemical species of the sample which is being analyzed.
# Instrument—deviations which occur due to how the attenuation measurements are made.
There are at least six conditions that need to be fulfilled in order for the Beer–Lambert law to be valid. These are:
# The attenuators must act independently of each other.
# The attenuating medium must be homogeneous in the interaction volume.
# The attenuating medium must not scatter the radiation—no turbidity—unless this is accounted for as in DOAS.
# The incident radiation must consist of parallel rays, each traversing the same length in the absorbing medium.
# The incident radiation should preferably be monochromatic, or have at least a width that is narrower than that of the attenuating transition. Otherwise a spectrometer as detector for the power is needed instead of a photodiode which cannot discriminate between wavelengths.
# The incident flux must not influence the atoms or molecules; it should only act as a non-invasive probe of the species under study. In particular, this implies that the light should not cause optical saturation or optical pumping, since such effects will deplete the lower level and possibly give rise to stimulated emission.
If any of these conditions are not fulfilled, there will be deviations from the Beer–Lambert law. | 7 | Physical Chemistry |
There are no widely accepted functions for the resulting truncated RNA transcripts. However, a study in 1981 found evidence that there was a relationship between the number of abortive transcripts produced and the time until long RNA strands are successfully produced. When RNA polymerase undergoes abortive transcription in the presence of ATP, UTP, and GTP, a complex is formed that has a much lower capacity for abortive recycling and a much higher rate of synthesis of the full-length RNA transcript. A study in 2010 found evidence that these truncated transcripts inhibit termination of RNA synthesis by a RNA hairpin-dependent intrinsic terminator. | 1 | Biochemistry |
In 1746 in Birmingham, John Roebuck adapted this method to produce sulfuric acid in lead-lined chambers, which were stronger, less expensive, and could be made larger than the previously used glass containers. This process allowed the effective industrialization of sulfuric acid production. After several refinements, this method, called the lead chamber process or "chamber process", remained the standard for sulfuric acid production for almost two centuries. | 7 | Physical Chemistry |
* “Vibrational Spectroscopy of Biomolecules and Polymers” V.G. Gregoriou and M. Braiman, Editors, Taylor & Francis Co, New York, NY, (2006).
* “Polymer Spectroscopy” V.G. Gregoriou Editor, Wiley-VCH, Weinheim, Germany (2004).
* “Modern Infrared Spectroscopy: Principles and Applications” A.A. Christy, Y. Ozaki, and V.G. Gregoriou, Elsevier Science, Amsterdam, the Netherlands (2001). | 7 | Physical Chemistry |
Signal transduction is a mechanism in which the cell responds to a signal from the environment by activating several proteins and enzymes that will give a response to the signal.
Feedback mechanism might involve negative and positive feedbacks. In the negative feedback, the pathway is inhibited and the result of the transduction pathway is reduced or limited. In positive feedback, the transduction pathway is promoted and stimulated to produce more products. | 1 | Biochemistry |
β-TG is a chemoattractant, strongly for fibroblasts and weakly for neutrophils. It is a stimulator of mitogenesis, extracellular matrix synthesis, glucose metabolism, and plasminogen activator synthesis in human fibroblasts.
β-TG also affects megakaryocyte maturation, and thus helps in regulating platelet production. | 1 | Biochemistry |
A photopolymer or light-activated resin is a polymer that changes its properties when exposed to light, often in the ultraviolet or visible region of the electromagnetic spectrum. These changes are often manifested structurally, for example hardening of the material occurs as a result of cross-linking when exposed to light. An example is shown below depicting a mixture of monomers, oligomers, and photoinitiators that conform into a hardened polymeric material through a process called curing.
A wide variety of technologically useful applications rely on photopolymers; for example, some enamels and varnishes depend on photopolymer formulation for proper hardening upon exposure to light. In some instances, an enamel can cure in a fraction of a second when exposed to light, as opposed to thermally cured enamels which can require half an hour or longer. Curable materials are widely used for medical, printing, and photoresist technologies.
Changes in structural and chemical properties can be induced internally by chromophores that the polymer subunit already possesses, or externally by addition of photosensitive molecules. Typically a photopolymer consists of a mixture of multifunctional monomers and oligomers in order to achieve the desired physical properties, and therefore a wide variety of monomers and oligomers have been developed that can polymerize in the presence of light either through internal or external initiation. Photopolymers undergo a process called curing, where oligomers are cross-linked upon exposure to light, forming what is known as a network polymer. The result of photo-curing is the formation of a thermoset network of polymers. One of the advantages of photo-curing is that it can be done selectively using high energy light sources, for example lasers, however, most systems are not readily activated by light, and in this case a photoinitiator is required. Photoinitiators are compounds that upon radiation of light decompose into reactive species that activate polymerization of specific functional groups on the oligomers. An example of a mixture that undergoes cross-linking when exposed to light is shown below. The mixture consists of monomeric styrene and oligomeric acrylates.
Most commonly, photopolymerized systems are typically cured through UV radiation, since ultraviolet light is more energetic. However, the development of dye-based photoinitiator systems have allowed for the use of visible light, having the potential advantages of being simpler and safer to handle. UV curing in industrial processes has greatly expanded over the past several decades. Many traditional thermally cured and solvent-based technologies can be replaced by photopolymerization technologies. The advantages of photopolymerization over thermally cured polymerization include higher rates of polymerization and environmental benefits from elimination of volatile organic solvents.
There are two general routes for photoinitiation: free radical and ionic. The general process involves doping a batch of neat polymer with small amounts of photoinitiator, followed by selective radiation of light, resulting in a highly cross-linked product. Many of these reactions do not require solvent which eliminates termination path via reaction of initiators with solvent and impurities, in addition to decreasing the overall cost. | 5 | Photochemistry |
The Takahashi Taxol total synthesis published by Takashi Takahashi in 2006 is one of several methods in taxol total synthesis. The method starts from geraniol and differs from the other 6 published methods that it is a formal synthesis (the final product is baccatin III which lacks the amide tail found in taxol itself) and that it is racemic (the product baccatin III is optically inactive). A key feature of the published procedure is that several synthetic steps (construction of rings A, B and C) were performed in an automated synthesizer on a scale up to 300 gram and that purification steps were also automated. | 0 | Organic Chemistry |
The Curtin–Hammett principle is used to explain the selectivity ratios for some stereoselective reactions. | 7 | Physical Chemistry |
Stress corrosion cracking mainly affects metals and metallic alloys. A comparable effect also known as environmental stress cracking also affects other materials such as polymers, ceramics and glass. | 8 | Metallurgy |
In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater. However, they eventually settle (rate determined by Stokes' law) and accumulate as sediment. Some can enter the atmosphere through wave action where they can act as cloud condensation nuclei (CCN). Many organisms filter particles out of the water with unique filtration mechanisms (filter feeders). Particles are often associated with high loads of toxins which attach to the surface. As these toxins are passed up the food chain they accumulate in fatty tissue and become increasingly concentrated in predators (see bioaccumulation). Very little is known about the dynamics of particles, especially when they are re-suspended by dredging. They can remain floating in the water and drift over long distances. The decomposition of some particles by bacteria consumes much oxygen and can cause the water to become hypoxic. | 2 | Environmental Chemistry |
In 1964 Sekeris accompanied Karlson when he moved to the position of Director of the Institut für Physiologische Chemie of the Philipps University of Marburg. In 1966 he became a Privatdozent at the Medical School where, in 1970, he was promoted to “Wissenschaftlicher Rat und Professor”, and then to a C3 Professor. In 1974 he moved to the German Cancer Research Centre (Deutsches Krebsforschungszentrum) in Heidelberg as the Head of the Section “Molecular Biology of the Cell” and a professor at the Science Faculty of Heidelberg University. In 1977, he finally moved home to Greece as a Professor of Biochemistry at the University of Athens, first at the Department of Biology and then (1993) at the Medical School. During his tenure at the University of Athens he held a joint appointment at the Institute of Biological Research at the National Hellenic Research Foundation, serving as its Director. In 2000, he reached the mandatory retirement age for the Greek Public Service, but kept performing research, unofficially, up until his death in 2009.
Sekeris’ main research interest was the mode of action of steroid hormones. He started his research working on tyrosine metabolism in insects and then rapidly moved to molecular endocrinology, where he stayed. Building on the work of Adolf_Butenandt (Karlsons father-in-law and director of the Munich Institute), Karlson and Sekeris early on proposed a model on how steroids function, which was very loosely based on Jacob and Monods model for the regulation of the lactose operon of Escherichia coli. He concentrated his later work on steroid receptor(s) including the binding of glucocorticoid receptor to mitochondrial DNA, which he and his group first described. His overall focus could be described as the elucidation of the role of glucocorticoids in the regulation of gene expression and cellular metabolism. This research led to research on post-transcriptional events such as mRNA processing. He was the first to describe the presence of small RNA species involved in the processing of hnRNA. He published more than 250 papers and book chapters, making him one of Greece's most prolific scientists in non-clinical life sciences.
In addition to his long-term directorship of the Institute of Biological Research at the National Hellenic Research Foundation, Sekeris was involved in science administration both in Greece and abroad. He was a member of the Greek Research Council and acted as the Chief Executive Officer of the National Hellenic Research Foundation. Among different honours that he received during his career one should mention his election to the European Molecular Biology Organization (EMBO) and the European Academy of Sciences. After leaving Germany he was made an Honorary Professor of Cell Biology at the Science Faculty of Heidelberg University. | 1 | Biochemistry |
Iodometry in its many variations is extremely useful in volumetric analysis. Examples include the determination of copper(II), chlorate, hydrogen peroxide, and dissolved oxygen:
Available chlorine refers to chlorine liberated by the action of dilute acids on hypochlorite. Iodometry is commonly employed to determine the active amount of hypochlorite in bleach responsible for the bleaching action. In this method, excess but known amount of iodide is added to known volume of sample, in which only the active (electrophilic) can oxidize iodide to iodine. The iodine content and thus the active chlorine content can be determined with iodometry.
The determination of arsenic(V) compounds is the reverse of the standardization of iodine solution with sodium arsenite, where a known and excess amount of iodide is added to the sample:
For analysis of antimony(V) compounds, some tartaric acid is added to solubilize the antimony(III) product. | 3 | Analytical Chemistry |
Galvanic phenomena were described in the literature before it was understood that they were of an electrical nature. In 1752, when the Swiss mathematician and physicist Johann Georg Sulzer placed his tongue between a piece of lead and a piece of silver, joined at their edges, he perceived a taste similar to that of iron(II) sulfate. Neither of the metals alone produced this taste. He realized that the contact between the metals probably did not produce a solution of either on the tongue. He did, however, not realize that this was an electrical phenomenon. He concluded that the contact between the metals caused their particles to vibrate, producing this taste by stimulating the nerves of the tongue. | 7 | Physical Chemistry |
In 2013, Diebold was the sole recipient of Austrias highest research award across all disciplines, the Wittgenstein Award. The award, which comes with substantial unrestricted research funds, is bestowed in support of the notion that scientists should be guaranteed the greatest possible freedom and flexibility in the performance of their research. It enabled Diebolds research activities to flourish without restriction. Other honors include:
* 2004 Fellow, American Physical Society, "For groundbreaking research on the role of defects in the interplay between bulk and surface properties of transition-metal oxides and on STM imaging of their surface structure.",
* 2005 Fellow of the American Vacuum Society
* 2007 Fellow, American Association for the Advancement of Science
* 2011, 2019 Advanced Grants by the European Research Council, for work on "Microscopic Processes and Phenomena at Oxide Surfaces and Interfaces" (2011), and "Water at Oxide Surfaces: a Fundamental Approach" (2019).
* 2013 Arthur W. Anderson Award of the American Chemical Society, for Distinguished Service in the Advancement of Surface Chemistry.
* 2013 Wittgenstein Award
*2014 European Academy of Sciences
*2014 Elected as a Full Member of the Austrian Academy of Sciences.
* 2015 Blaise Pascal medal in Materials Sciences by the European Academy of Sciences, for "Surfaces of Metal Oxides, Studied at the Atomic Scale".
* 2015 Debye Lecturer at Utrecht University, The Netherlands, entitled "Surface Science Studies of an Iron Oxide Model Catalyst" .
* 2015 21st Annual Schrödinger Lecturer at Trinity College Dublin, Ireland, with the title "An Atomic-Scale View at Oxide Surfaces".
* 2015 R. Brdička memorial lecturer at the J. Heyrovský Institute of Physical Chemistry, Prague, entitled "Surface Science of Metal Oxides".
*2015 Elected to the Leopoldina, the national academy of sciences in Germany,
*2019 Science award of the city of Vienna.
*2020 Gerhard Ertl Lecture Award
*2021 International Honorary Member of the American Academy of Arts and Sciences
*2022 Fellow of the Royal Society of Chemistry | 7 | Physical Chemistry |
An increase in permeability usually indicates a more open structure in the rammed sand, and if the increase continues, it will lead to penetration-type defects and rough castings. A decrease in permeability indicates tighter packing and could lead to blows and pinholes. | 8 | Metallurgy |
Magma mixing is the process by which two magmas meet, comingle, and form a magma of a composition somewhere between the two end-member magmas.
Magma mixing is a common process in volcanic magma chambers, which are open-system chambers where magmas enter the chamber, undergo some form of assimilation, fractional crystallisation and partial melt extraction (via eruption of lava), and are replenished.
Magma mixing also tends to occur at deeper levels in the crust and is considered one of the primary mechanisms for forming intermediate rocks such as monzonite and andesite. Here, due to heat transfer and increased volatile flux from subduction, the silicic crust melts to form a felsic magma (essentially granitic in composition). These granitic melts are known as an underplate. Basaltic primary melts formed in the mantle beneath the crust rise and mingle with the underplate magmas, the result being part-way between basalt and rhyolite; literally an intermediate composition. | 9 | Geochemistry |
Insulin is a peptide hormone that is critical for managing the body's metabolism. Insulin is released by the pancreas when blood sugar levels rise, and it has many effects that broadly promote the absorption and storage of sugars, including lipogenesis.
Insulin stimulates lipogenesis primarily by activating two enzymatic pathways. Pyruvate dehydrogenase (PDH), converts pyruvate into acetyl-CoA. Acetyl-CoA carboxylase (ACC), converts acetyl-CoA produced by PDH into malonyl-CoA. Malonyl-CoA provides the two-carbon building blocks that are used to create larger fatty acids.
Insulin stimulation of lipogenesis also occurs through the promotion of glucose uptake by adipose tissue. The increase in the uptake of glucose can occur through the use of glucose transporters directed to the plasma membrane or through the activation of lipogenic and glycolytic enzymes via covalent modification. The hormone has also been found to have long term effects on lipogenic gene expression. It is hypothesized that this effect occurs through the transcription factor SREBP-1, where the association of insulin and SREBP-1 lead to the gene expression of glucokinase. The interaction of glucose and lipogenic gene expression is assumed to be managed by the increasing concentration of an unknown glucose metabolite through the activity of glucokinase.
Another hormone that may affect lipogenesis through the SREBP-1 pathway is leptin. It is involved in the process by limiting fat storage through inhibition of glucose intake and interfering with other adipose metabolic pathways. The inhibition of lipogenesis occurs through the down regulation of fatty acid and triglyceride gene expression. Through the promotion of fatty acid oxidation and lipogenesis inhibition, leptin was found to control the release of stored glucose from adipose tissues.
Other hormones that prevent the stimulation of lipogenesis in adipose cells are growth hormones (GH). Growth hormones result in loss of fat but stimulates muscle gain. One proposed mechanism for how the hormone works is that growth hormones affects insulin signaling thereby decreasing insulin sensitivity and in turn down regulating fatty acid synthase expression. Another proposed mechanism suggests that growth hormones may phosphorylate with STAT5A and STAT5B, transcription factors that are a part of the Signal Transducer And Activator Of Transcription (STAT) family.
There is also evidence suggesting that acylation stimulating protein (ASP) promotes the aggregation of triglycerides in adipose cells. This aggregation of triglycerides occurs through the increase in the synthesis of triglyceride production. | 1 | Biochemistry |
Attempts to establish rates of vancomycin-induced ototoxicity are even more difficult due to the scarcity of quality evidence. The current consensus is that clearly related cases of vancomycin ototoxicity are rare. The association between vancomycin serum levels and ototoxicity is also uncertain. While cases of ototoxicity have been reported in patients whose vancomycin serum level exceeded 80 µg/mL, cases have been reported in patients with therapeutic levels, as well. Thus, whether therapeutic drug monitoring of vancomycin for the purpose of maintaining "therapeutic" levels will prevent ototoxicity also remains unproven. Still, therapeutic drug monitoring can be used during vancomycin therapy to minimize the risk of ototoxicity associated with excessive drug exposure. | 0 | Organic Chemistry |
Many if not most of the anthraquinone dyes are produced or processed via sulfonation. Sulfonic acids tend to bind tightly to proteins and carbohydrates. Most "washable" dyes are sulfonic acids (or have the functional sulfonyl group in them) for this reason. p-Cresidinesulfonic acid is used to make food dyes. | 0 | Organic Chemistry |
RNA-Seq has the potential to identify new disease biology, profile biomarkers for clinical indications, infer druggable pathways, and make genetic diagnoses. These results could be further personalized for subgroups or even individual patients, potentially highlighting more effective prevention, diagnostics, and therapy. The feasibility of this approach is in part dictated by costs in money and time; a related limitation is the required team of specialists (bioinformaticians, physicians/clinicians, basic researchers, technicians) to fully interpret the huge amount of data generated by this analysis. | 1 | Biochemistry |
The three related TET genes, TET1, TET2 and TET3 code respectively for three related mammalian proteins TET1, TET2, and TET3. All three proteins possess 5mC oxidase activity, but they differ in terms of domain architecture. TET proteins are large (~180- to 230-kDa) multidomain enzymes. All TET proteins contain a conserved double-stranded β-helix (DSBH) domain, a cysteine-rich domain, and binding sites for the cofactors Fe(II) and 2-oxoglutarate (2-OG) that together form the core catalytic region in the C terminus. In addition to their catalytic domain, full-length TET1 and TET3 proteins have an N-terminal CXXC zinc finger domain that can bind DNA. The TET2 protein lacks a CXXC domain, but the IDAX gene, that's a neighbor of the TET2 gene, encodes a CXXC4 protein. IDAX is thought to play a role in regulating TET2 activity by facilitating its recruitment to unmethylated CpGs. | 1 | Biochemistry |
In materials science and materials engineering, uranium metallurgy is the study of the physical and chemical behavior of uranium and its alloys.
Commercial-grade uranium can be produced through the reduction of uranium halides with alkali or alkaline earth metals. Uranium metal can also be made through electrolysis of KUF or UF, dissolved in a molten CaCl and NaCl. Very pure uranium can be produced through the thermal decomposition of uranium halides on a hot filament.
The uranium isotope U is used as the fuel for nuclear reactors and nuclear weapons. It is the only isotope existing in nature to any appreciable extent that is fissile, that is, fissionable by thermal neutrons. The isotope U is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope 239Pu (plutonium), which also is fissile. Uranium in its natural state comprises just 0.71% U and 99.3% U, and the main focus of uranium metallurgy is the enrichment of uranium through isotope separation. | 8 | Metallurgy |
When tin is combined with an alkali or alkaline earth metal some of the compounds formed have ionic structures containing monatomic or polyatomic tin anions (Zintl ions), such as Sn in MgSn or in KSn.
Even with these metals not all of the compounds formed can be considered to be ionic with localised bonding, for example SrSn, a metallic compound, contains {Sn} square pyramidal units. | 7 | Physical Chemistry |
Due to defining molecule-framework interactions, COFs can be used as chemical sensors in a wide range of environments and applications. Properties of the COF change when their functionalities interact with various analytes enabling the materials to serve as devices in various conditions: as chemiresistive sensors, as well as electrochemical sensors for small molecules. | 6 | Supramolecular Chemistry |
Devices that integrate multiple laboratory functions on a single chip of only a few square millimeters or centimeters in size and that are capable of handling extremely small fluid volumes down to less than picoliters. | 3 | Analytical Chemistry |
Unlike Q-FISH, Flow-FISH utilizes the quantitative properties of telomere specific PNA probe retention to quantify median fluorescence in a population of cells, via the use of a flow cytometer, instead of a fluorescence microscope. The primary advantage of this technique is that it eliminates the time required in Q-FISH to prepare metaphase spreads of cells of interest, and that flow cytometric analysis is also considerably faster than the methods required to acquire and analyze Q-FISH prepared slides. Flow-FISH thus allows for a higher throughput analysis of telomere length in blood leukocytes, which are a readily available form of human tissue sample. The most recent versions of the flow-FISH technique include an internal control population of cow thymocytes with a known telomere length detected by TRF or telomere restriction fragment analysis to which the fluorescence of a given unknown sample may be compared. Because cow thymocytes take up LDS751 dye to a lesser extent than their human counterparts, they may be reliably differentiated via plotting and gating the desired populations. Other cell types that have not in the past proven to be good candidates for flow-FISH can be analyzed via extraction of nuclei and performance of the technique on them directly. | 1 | Biochemistry |
Proteolysis is also involved in the regulation of many cellular processes by activating or deactivating enzymes, transcription factors, and receptors, for example in the biosynthesis of cholesterol, or the mediation of thrombin signalling through protease-activated receptors.
Some enzymes at important metabolic control points such as ornithine decarboxylase is regulated entirely by its rate of synthesis and its rate of degradation. Other rapidly degraded proteins include the protein products of proto-oncogenes, which play central roles in the regulation of cell growth. | 1 | Biochemistry |
Analysis of amplicons has been made possible by the development of amplification methods such as PCR, and increasingly by cheaper and more high-throughput technologies for DNA sequencing or next-generation sequencing, such as ion semiconductor sequencing, popularly referred to as the brand of the developer, Ion Torrent.
DNA sequencing technologies such as next-generation sequencing have made it possible to study amplicons in genome biology and genetics, including cancer genetics research, phylogenetic research, and human genetics. For example, using the 16S rRNA gene, which is part of every bacterial and archaeal genome and is highly conserved, bacteria can be taxonomically classified by comparison of the amplicon sequence to known sequences. This works similarly in the fungal domain with the 18S rRNA gene as well as the ITS1 non-coding region.
Irrespective of the approach used to amplify the amplicons, some technique must be used to quantitate the amplified product. Generally, these techniques incorporate a capture step and a detection step, although how these steps are incorporated depends on the individual assay.
Examples include the Amplicor HIV-1 Monitor Assay (RT-PCR), which has the capacity to recognize HIV in plasma; the HIV-1 QT (NASBA), which is used to measure plasma viral load by amplifying a segment of the HIV RNA; and transcription mediated amplification, which employs a hybridization protection assay to distinguish Chlamydia trachomatis infections. Various detection and capture steps are involved in each approach to assess the amplification product, or amplicon. With amplicon sequencing the high number of different amplicons resulting from amplification of a usual sample are concatenated and sequenced. After quality control classification is done by different methods, the counts of identical taxa representing their relative abundance in the sample. | 1 | Biochemistry |
The pure algebraic proof is more complex and requires consideration of the system equation:
where is the stoichiometry matrix and the rate vector. In this derivation, we assume there are no conserved moieties in the network, but this doesn't invalidate the proof. Using the chain rule and differentiating with respect to yields, after rearrangement:
The inverted term is the unscaled control coefficient so that after scaling, it is possible to write:
To derive the flux response coefficient theorem, we must use the additional equation: | 1 | Biochemistry |
An anti-graffiti coating is a coating that prevents graffiti paint from bonding to surfaces.
Cleaning graffiti off buildings costs billions of dollars annually . Many cities have started anti-graffiti programs but vandalism is still a problem. Companies across the globe are attempting to develop coatings to prevent vandals from defacing public and private property. The coatings being developed can be the paint itself, or a clear coat added on top of existing paint or building facades. Depending on the substrate and the severity of graffiti, different coatings give different benefits and disadvantages. | 7 | Physical Chemistry |
In many cases, an initial set of phases are determined, and the electron density map for the diffraction pattern is calculated. Then the map is used to determine portions of the structure, which portions are used to simulate a new set of phases. This new set of phases is known as a refinement. These phases are reapplied to the original amplitudes, and an improved electron density map is derived, from which the structure is corrected. This process is repeated until an error term (usually ) has stabilized to a satisfactory value. Because of the phenomenon of phase bias, it is possible for an incorrect initial assignment to propagate through successive refinements, so satisfactory conditions for a structure assignment are still a matter of debate. Indeed, some spectacular incorrect assignments have been reported, including a protein where the entire sequence was threaded backwards. | 3 | Analytical Chemistry |
The bulk isotope ratio value of stable isotopes for petroleum depict the average isotopic compositions of the oil's components. Carbon stable isotopes are often used in this method. Whether a sample of petroleum originated in a marine environment or a non-marine environment can be seen using this ratio value, as can method distance and age of the oil. | 9 | Geochemistry |
TLC helps show the purity of a sample. A pure sample should only contain one spot by TLC. TLC is also useful for small-scale purification. Because the separated compounds will be on different areas of the plate, a scientist can scrape off the stationary phase particles containing the desired compound and dissolve them into an appropriate solvent. Once all the compound dissolves in the solvent, they filter out the silica particles, then evaporate the solvent to isolate the product. Big preparative TLC plates with thick silica gel coatings can separate more than 100 mg of material.
For larger-scale purification and isolation, TLC is useful to quickly test solvent mixtures before running flash column chromatography on a large batch of impure material. A compound elutes from a column when the amount of solvent collected is equal to 1/R. The eluent from flash column chromatography gets collected across several containers (for example, test tubes) called fractions. TLC helps show which fractions contain impurities and which contain pure compound.
Furthermore, two-dimensional TLC can help check if a compound is stable on a particular stationary phase. This test requires two runs on a square-shaped TLC plate. The plate is rotated by 90º before the second run. If the target compound appears on the diagonal of the square, it is stable on the chosen stationary phase. Otherwise, it is decomposing on the plate. If this is the case, an alternative stationary phase may prevent this decomposition.
TLC is also an analytical method for the direct separation of enantiomers and the control of enantiomeric purity, e.g. active pharmaceutical ingredients (APIs) that are chiral. | 3 | Analytical Chemistry |
ScBCSi (x = 0.52, y = 1.42, z = 1.17 and w = 0.02) has a hexagonal crystal structure with space group Pm2 (No. 187) and lattice constants a = b = 1.43055(8) and c = 2.37477(13) nm. Single crystals of this compound were obtained as an intergrowth phase in a float-zoned single crystal of ScBCSi. This phase is not described in the phase diagram of figure 17 because it is a quaternary compound. Its hexagonal structure is rare and has 79 atomic positions in the unit cell: eight partially occupied Sc sites, 62 B sites, two C sites, two Si sites and six B/C sites. Six B sites and one of the two Si sites have partial occupancies. The associated atomic coordinates, site occupancies and isotropic displacement factors are listed in table X.
There are seven structurally independent icosahedra I1–I7 which are formed by B1–B8, B9–B12, B13–B20, B/C21–B24, B/C25–B29, B30–B37 and B/C38–B42 sites, respectively; B43–B46 sites form the B polyhedron and B47–B53 sites construct the B polyhedron. B54–B59 sites form the irregularly shaped B polyhedron in which only 10.7 boron atoms are available because most of sites are too close to each other to be occupied simultaneously. Ten bridging sites C60–B69 interconnect polyhedron units or other bridging sites to form a 3D boron framework structure. One description of the crystal structure uses three pillar-like units that extend along the c-axis that however results in undesired overlaps between those three pillar-like units. An alternative is to define two pillar-like structure units. Figure 29 shows the boron framework structure of ScBCSi viewed along the c-axis, where the pillar-like units P1 and P2 are colored in dark green and light green respectively and are bridged by yellow icosahedra I4 and I7.
These pillar-like units P1 and P2 are shown in figures 30a and b, respectively. P1 consists of icosahedra I1 and I3, an irregularly shaped B polyhedron and other bridge site atoms where two supericosahedra can be seen above and below the B polyhedron. Each supericosahedron is formed by three icosahedra I1 and three icosahedra I3 and is the same as the supericosahedron O(1) shown in figure 24a.The P2 unit consists of icosahedra I2, I5 and I6, B polyhedron and other bridge site atoms. Eight Sc sites with occupancies between 0.49 (Sc8) and 0.98 (Sc1) spread over the boron framework.
As described above, this hexagonal phase originates from a cubic phase, and thus one may expect a similar structural element in these phases. There is an obvious relation between the hexagonal ab-plane and the cubic (111) plane. Figures 31a and b show the hexagonal (001) and the cubic (111) planes, respectively. Both network structures are almost the same that allows intergrowth of the hexagonal phase in the cubic phase. | 3 | Analytical Chemistry |
William B. Jensen notes that the earliest example of a continuous extractor is archaeological evidence for a Mesopotamian hot-water extractor for organic matter dating from approximately 3500 BC. The same mechanism is present in the Pythagorean cup. Before Soxhlet, the French chemist Anselme Payen also pioneered with continuous extraction in the 1830s.
A Soxhlet apparatus has been proposed as an effective technique for washing mass standards. | 3 | Analytical Chemistry |
Diagnostic biomarkers give intervention-independent information on identifying or aid in identifying if there is a presence or absence of the disease or a disease subcategory/subphenotype status. An example is the traumatic brain injury (TBI) blood-based biomarker test consisted of measuring the levels of neuronal Ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) and Glial fibrillary acidic protein (GFAP) to aid in the diagnosis of the presence of cranial lesion(s) among moderate to mild TBI patients that is(are) otherwise only diagnosable with the use of a CT scan of the head. | 1 | Biochemistry |
Carboamination is an efficient method to access nitrogen-containing molecules, especially N-heterocycles. (+)-Preussin, a pyrrolidine alkaloid, can be easily prepared via this methodology.
(–)-Tylophorine is another example, which can be synthesized using carboamination reaction. | 0 | Organic Chemistry |
The biggest advantage of GFP is that it can be heritable, depending on how it was introduced, allowing for continued study of cells and tissues it is expressed in. Visualizing GFP is noninvasive, requiring only illumination with blue light. GFP alone does not interfere with biological processes, but when fused to proteins of interest, careful design of linkers is required to maintain the function of the protein of interest. Moreover, if used with a monomer it is able to diffuse readily throughout cells. | 1 | Biochemistry |
Of the 32 crystallographic point groups, 10 are polar:
The space groups associated with a polar point group do not have a discrete set of possible origin points that are unambiguously determined by symmetry elements.
When materials having a polar point group crystal structure are heated or cooled, they may temporarily generate a voltage called pyroelectricity.
Molecular crystals which have symmetry described by one of the polar space groups, such as sucrose, may exhibit triboluminescence. | 3 | Analytical Chemistry |
In the presence of an oxidizing agent, the cyclized intermediate can be oxidized to aromatize the rings. For example, dihydrophenanthrene becomes phenanthrene. Oxygen and iodine are the most commonly employed oxidants. | 5 | Photochemistry |
* Water is essential for organisms within the soil profile, and it partially fills up the macropores in an ideal soil.
* Leaching of the soil occurs as water carries along with it ions deeper into the lower soil horizons, causing the soil to become more oxidized in other soil horizons.
* Water also will go from a higher water potential to a lower water potential, this can result in capillarity activity and gravitational force occurring with the water due to adhesion of the water to the soil surface and cohesion amongst the water molecules. | 9 | Geochemistry |
The purpose of a mineralizer is to facilitate the transport of insoluble “nutrient” to a seed crystal by means of a reversible chemical reaction. Over time, the seed crystal accumulates the material that was once in the nutrient and grows. Mineralizers are additives that aid the solubilization of the nutrient solid. When used in small quantities, mineralizers function as catalysts. Typically, a more stable solid is crystallized from a solution that consists of a less stable solid and a solvent. The process is done by dissolution-precipitation or crystallization process.
Hydrothermal growth involves the crystallization of a dissolved solid at elevated temperatures. Often high pressures are involved. Historically, the goal of hydrothermal growth was to grow large crystals. Due to the recent developments in nanotechnology, small nanocrystals are now desired and made by hydrothermal growth with crystal size controlled by mineralizers. Different mineralizers result in crystals of different sizes and shapes. Typical mineralizers are hydroxides (NaOH, KOH, LiOH), carbonates (NaCO) and halides (NaF, KF, LiF, NaCl, KCl, LiCl). | 7 | Physical Chemistry |
Thermosynthesis is a theoretical mechanism proposed by Anthonie Muller for biological use of the free energy in a temperature gradient to drive energetically uphill anabolic reactions. It makes use of this thermal gradient, or the dissipative structure of convection in this gradient, to drive a microscopic heat engine that performs condensation reactions. Thus negative entropy is generated. The components of the biological thermosynthesis machinery concern progenitors of today's ATP synthase, which functions according to the binding change mechanism, driven by chemiosmosis. Resembling primitive free energy generating physico-chemical processes based on temperature-dependent adsorption to inorganic materials such as clay, this simple type of energy conversion is proposed to have sustained the origin of life, including the emergence of the RNA World. For this RNA World it gives a model that describes the stepwise acquisition of the set of transfer RNAs that sustains the Genetic code. The phylogenetic tree of extant transfer RNAs is consistent with the idea.
Thermosynthesis may still occur in some terrestrial
and extraterrestrial environments. However, no organisms are known at present that use thermosynthesis as a source of energy, although it is possible that it might occur in extraterrestrial environments where no light is available, such as on the subsurface ocean that may exist on the moon Europa. Thermosynthesis also permits a simple model for the origin of photosynthesis. It has moreover been used to explain the origin of animals by symbiogenesis of benthic sessile thermosynthesizers at hydrothermal vents during the Snowball Earths of the Precambrian. Preliminary experiments have started to attempt to isolate thermosynthetic organisms. | 1 | Biochemistry |
The atmosphere contains three main gases, namely oxygen, carbon dioxide (CO) and nitrogen. In the atmosphere, oxygen is 20%, nitrogen is 79% and CO is 0.15% to 0.65% by volume. CO increases with the increase in the depth of soil because of decomposition of accumulated organic matter and abundance of plant roots. The presence of oxygen in the soil is important because it helps in breaking down insoluble rocky mass into soluble minerals and organic humification. Air in the soil is composed of gases that are present in the atmosphere, but not in the same proportions. These gases facilitate chemical reactions in microorganisms. Accumulation of soluble nutrients in the soil makes it more productive. If the soil is deficient in oxygen, microbial activity is slowed down or eliminated. Important factors controlling the soil atmosphere are temperature, atmospheric pressure, wind/aeration and rainfall. | 9 | Geochemistry |
As with conventional manufactured drugs, the main challenge in developing successful offshoots of the RNAi-based drugs is the precise delivery of the RNAi triggers to where they are needed in the body. The reason that the ocular macular degeneration antidote was successful sooner than the antidote with other diseases is that the eyeball is almost a closed system, and the serum can be injected with a needle exactly where it needs to be. The future successful drugs will be the ones who are able to land where needed, probably with the help of nanobots. Below is a rendition of a table that shows the existing means of delivery of the RNAi triggers. | 1 | Biochemistry |
Derived from “the addition of a hydrophilic heterocyclic group to the α-amino group of ampicillin”, the structure consists of a thiazolidine ring conjoined to a β-lactam ring contained within several ring compounds. The addition of this substituent increases the compounds affinity to penicillin-binding protein PBP-3, improving activity against Gram-negative bacteria, and thus broadening its spectrum of activity. Susceptible β-lactamase producing bacteria such as Staphylococcus spp. or Haemophilus influenzae', the combination of tazobactam (which shares a similar structure to sulbactam, another β-lactamase inhibitor), and piperacillin significantly improves the stability of the drug against β-lactamases. | 4 | Stereochemistry |
A device that can produce monochromatic light has many uses in science and in optics because many optical characteristics of a material are dependent on wavelength. Although there are a number of useful ways to select a narrow band of wavelengths (which, in the visible range, is perceived as a pure color), there are not as many other ways to easily select any wavelength band from a wide range. See below for a discussion of some of the uses of monochromators.
In hard X-ray and neutron optics, crystal monochromators are used to define wave conditions on the instruments. | 7 | Physical Chemistry |
Given the widespread use of pesticides, herbicides and insecticides in modern farming, dendrimers are also being used by companies to help improve the delivery of agrochemicals to enable healthier plant growth and to help fight plant diseases.
Dendrimers are also being investigated for use as blood substitutes. Their steric bulk surrounding a heme-mimetic centre significantly slows degradation compared to free heme, and prevents the cytotoxicity exhibited by free heme.
Dendritic functional polymer polyamidoamine (PAMAM) is used to prepare core shell structure i.e. microcapsules and utilized in formulation of self-healing coatings of conventional and renewable origins.
Different generations of polyamidoamine dendrimers have recently been implemented as selective contacts in photovoltaic devices. | 6 | Supramolecular Chemistry |
The ore is comminuted and the cobalt rich oxides are separated by froth flotation. The cobalt-bearing concentrate is then mixed with lime and coal, and then melted in a reducing atmosphere. Iron and lighter impurities float to the surface as solid dross or are expelled from the melt as gas. The remaining liquid is composed of a heavier copper smelt containing approximately 5% cobalt that is processed for its copper and a lighter slag that is approximately 40% cobalt that is further refined by hydrometallurgical and electrolytic processing. Concentrations of cobalt oxide (CoO) may also be reduced by the aluminothermic reaction or with carbon in a blast furnace. | 8 | Metallurgy |
Enedithiols, with the exception of aromatic examples, are rare. The parent aromatic example is benzenedithiol. The dithiol of 1,3-dithiole-2-thione-4,5-dithiolate is also known. | 0 | Organic Chemistry |
The application of transformations to retrosynthetic analysis can lead to powerful reductions in molecular complexity. Unfortunately, powerful transform-based retrons are rarely present in complex molecules, and additional synthetic steps are often needed to establish their presence. | 0 | Organic Chemistry |
Modafinil was studied for the treatment of stimulant dependence, but the results are mixed and inconclusive. Modafinil is not a controlled substance in some countries, unlike other medications, such as bupropion, which is also used to treat depression and nicotine dependence. The clinical trials that have tested modafinil as a treatment for stimulant abuse have failed to demonstrate its efficacy and the optimal dose and duration of modafinil treatment remain unclear, and modafinil is not a recommended treatment for stimulant abuse. | 4 | Stereochemistry |
Commonly reported adverse effects associated with the use of oxacillin include skin rash, diarrhea, nausea, vomiting, hematuria, agranulocytosis, eosinophilia, leukopenia, neutropenia, thrombocytopenia, hepatotoxicity, acute interstitial nephritis, and fever. High doses of oxacillin have been reported to cause renal, hepatic, and nervous system toxicity. Common to all members of the penicillin class of drugs, oxacillin may cause acute or delayed hypersensitivity reactions. As an injection, oxacillin may cause injection site reactions, which may be characterized by redness, swelling, and itching. | 4 | Stereochemistry |
Dicloxacillin is contraindicated in those with a previous history of allergy (hypersensitivity/anaphylactic reaction) to any penicillins. | 4 | Stereochemistry |
There are two types of bonds involved in a glycoprotein: bonds between the saccharides residues in the glycan and the linkage between the glycan chain and the protein molecule.
The sugar moieties are linked to one another in the glycan chain via glycosidic bonds. These bonds are typically formed between carbons 1 and 4 of the sugar molecules. The formation of glycosidic bond is energetically unfavourable, therefore the reaction is coupled to the hydrolysis of two ATP molecules.
On the other hand, the attachment of a glycan residue to a protein requires the recognition of a consensus sequence. N-linked glycans are almost always attached to the nitrogen atom of an asparagine (Asn) side chain that is present as a part of Asn–X–Ser/Thr consensus sequence, where X is any amino acid except proline (Pro).
In animal cells, the glycan attached to the asparagine is almost inevitably N-acetylglucosamine (GlcNAc) in the β-configuration. This β-linkage is similar to glycosidic bond between the sugar moieties in the glycan structure as described above. Instead of being attached to a sugar hydroxyl group, the anomeric carbon atom is attached to an amide nitrogen. The energy required for this linkage comes from the hydrolysis of a pyrophosphate molecule. | 0 | Organic Chemistry |
Thiolactones are a class of heterocyclic compounds in organic chemistry. They are analogs of the more common lactones in which an oxygen atom is replaced with a sulfur atom. The sulfur atom is within the ring system and adjacent to a carbonyl group. | 0 | Organic Chemistry |
Nitro compounds participate in several organic reactions, the most important being their reduction to the corresponding amines:
:RNO + 3 H → RNH + 2 HO
Virtually all aromatic amines (e.g. aniline) are derived from nitroaromatics through such catalytic hydrogenation. A variation is formation of a dimethylaminoarene with palladium on carbon and formaldehyde:
The α-carbon of nitroalkanes is somewhat acidic. The pK values of nitromethane and 2-nitropropane are respectively 17.2 and 16.9 in dimethyl sulfoxide (DMSO) solution, suggesting an aqueous pK of around 11. In other words, these carbon acids can be deprotonated in aqueous solution. The conjugate base is called a nitronate, and behaves similar to an enolate. In the nitroaldol reaction, it adds directly to aldehydes, and, with enones, can serve as a Michael donor. Conversely, a nitroalkene reacts with enols as a Michael acceptor.
Nitronates are also key intermediates in the Nef reaction: when exposed to acids or oxidants, a nitronate hydrolyzes to a carbonyl and azanone.
Grignard reagents combine with nitro compounds to give a nitrone; but a Grignard reagent with an α hydrogen will then add again to the nitrone to give a hydroxylamine salt. | 0 | Organic Chemistry |
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