text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Using the convexity of the log function appearing in the exact perturbation analysis result, together with Jensen's inequality, gives an inequality in the linear level; combined with the analogous result for the B ensemble one gets the following version of the Gibbs-Bogoliubov inequality:
Note that the inequality agrees with the negative sign of the coefficient of the (positive) variance term in the second order result. | 7 | Physical Chemistry |
α-Endopsychosin is a putative antagonist of the phencyclidine site of the NMDA receptor which was discovered in extracts of porcine brain and may also be endogenous in humans. The compound appears to be a peptide, but has yet to be purified and fully characterized. | 1 | Biochemistry |
Awards that Ramsey has received include the Ralph N. Adams Award in Bioanalytical Chemistry (2013), the CASSS Award for Outstanding Achievements in Separation Science (2012), the American Chemical Society Award in Chromatography (2007), the Pittsburgh Analytical Chemistry Award (2006), the ACS Division of Analytical Chemistry Award in Chemical Instrumentation (2003), the Battelle Distinguished Inventor Award (2003), and the Frederick Conference Capillary Electrophoresis Award (2000).
Ramsey holds professional memberships with National Academy of Engineering, the American Chemical Society, and the Analytical Division of the American Chemical Society.
He has 108 issues patents, 2 allowed patents, and 20 pending patents. | 3 | Analytical Chemistry |
Experimentally Pierre Louis Dulong and Alexis Thérèse Petit had found in 1819 that the heat capacity per weight (the mass-specific heat capacity) for 13 measured elements was close to a constant value, after it had been multiplied by a number representing the presumed relative atomic weight of the element. These atomic weights had shortly before been suggested by John Dalton and modified by Jacob Berzelius.
Dulong and Petit were unaware of the relationship with R, since this constant had not yet been defined from the later kinetic theory of gases. The value of 3R is about 25 joules per kelvin, and Dulong and Petit essentially found that this was the heat capacity of certain solid elements per mole of atoms they contained.
The Kopp's law developed in 1865 by Hermann Franz Moritz Kopp extended the Dulong–Petit law to chemical compounds from further experimental data.
Amedeo Avogadro remarked in 1833 that the law did not fit the experimental data of carbon samples. In 1876, Heinrich Friedrich Weber, noticed that the specific heat of diamond was sensible to temperature.
In 1877, Ludwig Boltzmann showed that the constant value of Dulong–Petit law could be explained in terms of independent classical harmonic oscillators. With the advent of quantum mechanics, this assumption was refined by Weber's student, Albert Einstein in 1907, employing quantum harmonic oscillators to explain the experimentally observed decrease of the heat capacity at low temperatures in diamond.
Peter Debye followed in 1912 with a new model based on Max Plancks photon gas, where the vibrations are not to individual oscillators but as vibrational modes of the ionic lattice. Debyes model allowed to predict the behavior of the ionic heat capacity at temperature close to 0 kelvin, and as the Einstein solid, both recover the Dulong–Petit law at high temperature.
The electronic heat capacity was overestimated by the 1900 Drude-Lorentz model to be half of the value predicted by Dulong–Petit. With the development of the quantum mechanical free electron model in 1927 by Arnold Sommerfeld the electronic contribution was found to be orders of magnitude smaller. This model explained why conductors and insulators have roughly the same heat capacity at large temperatures as it depends mostly on the lattice and not on the electronic properties. | 3 | Analytical Chemistry |
Cyanobacteria possess carboxysomes, which increase the concentration of around RuBisCO to increase the rate of photosynthesis. An enzyme, carbonic anhydrase, located within the carboxysome, releases CO from dissolved hydrocarbonate ions (HCO). Before the CO can diffuse out outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the cytosol they turn back into CO very slowly without the help of carbonic anhydrase. This causes the HCO ions to accumulate within the cell from where they diffuse into the carboxysomes. Pyrenoids in algae and hornworts also act to concentrate around RuBisCO. | 5 | Photochemistry |
In crystallography, an anti-structure is obtained from a salt structure by exchanging anion and cation positions.
For instance, calcium fluoride, CaF, crystallizes in a cubic motif called the fluorite structure. The same crystal structure is found in numerous ionic compounds with formula AB, such as ceria (CeO), zirconia (cubic ZrO), uranium dioxide (UO). In the corresponding anti-structure, called the antifluorite structure, anions and cations are swapped, such as beryllium carbide (BeC) or lithium oxide (LiO), potassium sulfate (KSO).
Other anti-structures include:
* anti-SnO: TiN
* anti-PbCl: CoP
* anti-CdCl: CoN
* anti-CdI: CsO
* anti-NbS: HfS
* anti-ReO: CuN
* anti-LaF: CuP, CuAs | 3 | Analytical Chemistry |
Whereas the methods above describe various sequencing methods, separate related terms are used when a large portion of a genome is sequenced. Several platforms were developed to perform exome sequencing (a subset of all DNA across all chromosomes that encode genes) or whole genome sequencing (sequencing of the all nuclear DNA of a human). | 1 | Biochemistry |
The electromigration degradation of the on-chip power grid network/interconnect depends on the IR drop noise of the power grid interconnect.
The electromigration-aware lifetime of the power grid interconnects as well as the chip decreases if the chip suffers from a high value of the IR drop noise. | 7 | Physical Chemistry |
Although 1,3-dipolar cycloaddition is a useful method for the generation of five-membered heterocyclic compounds, few methods exist to synthesize five-membered carbocyclic rings in a single step via annulation. Most of these, like TMM cycloaddition, rely on the generation of a suitable three-atom component for combination with a stable two-atom partner such as an alkene or alkyne. When heated, cyclopropene acetals rearrange to vinylcarbenes, which can serve as the three-atom component in cycloadditions with highly electron-deficient alkenes. Zinc homoenolates can also serve as indirect three-atom components, and undergo cyclization to cyclopentenones in the presence of an unsaturated ester. Tandem intermolecular-intramolecular cyclization of homopropargylic radicals leads to methylenecyclopropanes. | 0 | Organic Chemistry |
Uranium is well mixed in the ocean, and its decay produces Pa and Th at a constant activity ratio (0.093). The decay products are rapidly removed by adsorption on settling particles, but not at equal rates. Pa has a residence equivalent to the residence time of deep water in the Atlantic basin (around 1000 yrs) but Th is removed more rapidly (centuries). Thermohaline circulation effectively exports Pa from the Atlantic into the Southern Ocean, while most of the Th remains in Atlantic sediments. As a result, there is a relationship between Pa/Th in Atlantic sediments and the rate of overturning: faster overturning produces lower sediment Pa/Th ratio, while slower overturning increases this ratio. The combination of δC and Pa/Th can therefore provide a more complete insight into past circulation changes. | 9 | Geochemistry |
* The source material containing the compound to be extracted is placed inside the thimble.
* The thimble is loaded into the main chamber of the Soxhlet extractor.
* The extraction solvent to be used is placed in a distillation flask.
* The flask is placed on the heating element.
* The Soxhlet extractor is placed atop the flask.
* A reflux condenser is placed atop the extractor. | 3 | Analytical Chemistry |
Lateral adhesion is the adhesion associated with sliding one object on a substrate such as sliding a drop on a surface. When the two objects are solids, either with or without a liquid between them, the lateral adhesion is described as friction. However, the behavior of lateral adhesion between a drop and a surface is tribologically very different from friction between solids, and the naturally adhesive contact between a flat surface and a liquid drop makes the lateral adhesion in this case, an individual field. Lateral adhesion can be measured using the centrifugal adhesion balance (CAB), which uses a combination of centrifugal and gravitational forces to decouple the normal and lateral forces in the problem. | 6 | Supramolecular Chemistry |
Another example is hematite on magnetite . The magnetite structure is based on close-packed oxygen anions stacked in an ABC-ABC sequence. In this packing the close-packed layers are parallel to (111) (a plane that symmetrically "cuts off" a corner of a cube). The hematite structure is based on close-packed oxygen anions stacked in an AB-AB sequence, which results in a crystal with hexagonal symmetry.
If the cations were small enough to fit into a truly close-packed structure of oxygen anions then the spacing between the nearest neighbour oxygen sites would be the same for both species. The radius of the oxygen ion, however, is only 1.36 Å and the Fe cations are big enough to cause some variations. The Fe radii vary from 0.49 Å to 0.92 Å, depending on the charge (2+ or 3+) and the coordination number (4 or 8). Nevertheless, the O spacings are similar for the two minerals hence hematite can readily grow on the (111) faces of magnetite, with hematite (001) parallel to magnetite (111). | 3 | Analytical Chemistry |
If the data for different samples are going to be contrasted with each other, one can perform downsampling on the reads to achieve comparability. The reported sequencing coverage depth for reasonable analysis results was reported as bigger than 500 folds, thus any sample whose mean sequencing depth does not exceed the number can be dropped for more accurate outcomes. Also, EPIC-seq uses estimated expected cfDNA fragment length density of 140-185, based on chromatosomal length. The samples that have outlier fragment length density can be dropped for higher correlation results. As the last quality control step, mapping quality should be considered. A looser threshold can be dictated on EPIC-seq reads, compared to WGS, due to the TSS selection criteria imposed during design phases making the reads more unique for EPIC-seq. | 1 | Biochemistry |
In the Cassie–Baxter model, the drop sits on top of the textured surface with trapped air underneath. During the wetting transition from the Cassie state to the Wenzel state, the air pockets are no longer thermodynamically stable and liquid begins to nucleate from the middle of the drop, creating a "mushroom state" as seen in Figure 10. The penetration condition is given by:
where
:* θ is the critical contact angle
:* Φ is the fraction of solid/liquid interface where drop is in contact with surface
:* r is solid roughness (for flat surface, r = 1)
The penetration front propagates to minimize the surface energy until it reaches the edges of the drop, thus arriving at the Wenzel state. Since the solid can be considered an absorptive material due to its surface roughness, this phenomenon of spreading and imbibition is called hemiwicking. The contact angles at which spreading/imbibition occurs are between 0 and π/2.
The Wenzel model is valid between θ and π/2. If the contact angle is less than Θ, the penetration front spreads beyond the drop and a liquid film forms over the surface. Figure 11 depicts the transition from the Wenzel state to the surface film state. The film smoothes the surface roughness and the Wenzel model no longer applies. In this state, the equilibrium condition and Young's relation yields:
By fine-tuning the surface roughness, it is possible to achieve a transition between both superhydrophobic and superhydrophilic regions. Generally, the rougher the surface, the more hydrophobic it is. | 7 | Physical Chemistry |
A crystal system is a set of point groups in which the point groups themselves and their corresponding space groups are assigned to a lattice system. Of the 32 point groups that exist in three dimensions, most are assigned to only one lattice system, in which case the crystal system and lattice system both have the same name. However, five point groups are assigned to two lattice systems, rhombohedral and hexagonal, because both lattice systems exhibit threefold rotational symmetry. These point groups are assigned to the trigonal crystal system.
In total there are seven crystal systems: triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic. | 3 | Analytical Chemistry |
Carbon dioxide is not a typical feedstock for FT catalysis. Hydrogen and carbon dioxide react over a cobalt-based catalyst, producing methane. With iron-based catalysts unsaturated short-chain hydrocarbons are also produced. Upon introduction to the catalyst's support, ceria functions as a reverse water-gas shift catalyst, further increasing the yield of the reaction. The short-chain hydrocarbons were upgraded to liquid fuels over solid acid catalysts, such as zeolites. | 0 | Organic Chemistry |
Recently the late-stage sulfoximidation of electron-rich arenes by photoredox catalysis was reported and several examples were discussed. | 5 | Photochemistry |
* Post doctorate visit on a senior scholar Fulbright fellowship University of Massachusetts (September – December 1985)
* Post doctorate visit on Association of Commonwealth Universities Fellowship University of Leeds, UK (October 1984 – July 1985)
* Visiting post-doctorate fellow at the University of Reading, UK (1980)
In 2010 he was selected and worked as an expert in Europe-Africa Quality Connect: A collaborative project in five African universities between European Universities Association (EUA) and the Association of African Universities (AAU), sponsored by European Commission. | 1 | Biochemistry |
is a common Lewis-acid catalyst for Friedel-Crafts reactions, both acylations and alkylations. Important products are detergents and ethylbenzene. These types of reactions are the major use for aluminium chloride, for example, in the preparation of anthraquinone (used in the dyestuffs industry) from benzene and phosgene. In the general Friedel-Crafts reaction, an acyl chloride or alkyl halide reacts with an aromatic system as shown:
The alkylation reaction is more widely used than the acylation reaction, although its practice is more technically demanding. For both reactions, the aluminium chloride, as well as other materials and the equipment, should be dry, although a trace of moisture is necessary for the reaction to proceed. Detailed procedures are available for alkylation and acylation of arenes.
A general problem with the Friedel-Crafts reaction is that the aluminium chloride catalyst sometimes is required in full stoichiometric quantities, because it complexes strongly with the products. This complication sometimes generates a large amount of corrosive waste. For these and similar reasons, the use of aluminium chloride has often been displaced by zeolites.
Aluminium chloride can also be used to introduce aldehyde groups onto aromatic rings, for example via the Gattermann-Koch reaction which uses carbon monoxide, hydrogen chloride and a copper(I) chloride co-catalyst. | 0 | Organic Chemistry |
Aces II (Advanced Concepts in Electronic Structure Theory) is an ab initio computational chemistry package for performing high-level quantum chemical ab initio calculations. Its major strength is the accurate calculation of atomic and molecular energies as well as properties using many-body techniques such as many-body perturbation theory (MBPT) and, in particular coupled cluster techniques to treat electron correlation. The development of ACES II began in early 1990 in the group of Professor Rodney J. Bartlett at the Quantum Theory Project (QTP) of the University of Florida in Gainesville. There, the need for more efficient codes had been realized and the idea of writing an entirely new program package emerged. During 1990 and 1991 John F. Stanton, Jürgen Gauß, and John D. Watts, all of them at that time postdoctoral researchers in the Bartlett group, supported by a few students, wrote the backbone of what is now known as the ACES II program package. The only parts which were not new coding efforts were the integral packages (the MOLECULE package of J. Almlöf, the VPROP package of P.R. Taylor, and the integral derivative package ABACUS of T. Helgaker, P. Jorgensen J. Olsen, and H.J. Aa. Jensen). The latter was modified extensively for adaptation with Aces II, while the others remained very much in their original forms.
Ultimately, two different versions of the program evolved. The first was maintained by the Bartlett group at the University of Florida, and the other (known as ACESII-MAB) was maintained by groups at the University of Texas, Universitaet Mainz in Germany, and ELTE in Budapest, Hungary. The latter is now called CFOUR.
Aces III is a parallel implementation that was released in the fall of 2008. The effort led to definition of a new architecture for scalable parallel software called the super instruction architecture. The design and creation of software is divided into two parts:
# The algorithms are coded in a domain specific language called super instruction assembly language or SIAL, pronounced "sail" for easy communication.
# The SIAL programs are executed by a MPMD parallel virtual machine called the super instruction processor or SIP.
The ACES III program consists of 580,000 lines of SIAL code of which 200,000 lines are comments, and 230,000 lines of C/C++ and Fortran of which 62,000 lines are comments. The latest version of the program was released on August 1, 2014. | 7 | Physical Chemistry |
A saturated compound is a chemical compound (or ion) that resists addition reactions, such as hydrogenation, oxidative addition, and binding of a Lewis base. The term is used in many contexts and for many classes of chemical compounds. Overall, saturated compounds are less reactive than unsaturated compounds. Saturation is derived from the Latin word saturare, meaning to fill. | 0 | Organic Chemistry |
Sørensen was born in Havrebjerg Denmark in 1868 as the son of a farmer. He began his studies at the University of Copenhagen at the age of 18. He wanted to make a career in medicine, but under the influence of chemist Sophus Mads Jørgensen decided to change to chemistry.
While studying for his doctorate he worked as assistant in chemistry at the laboratory of the Technical University of Denmark, assisted in a geological survey of Denmark, and also worked as a consultant for the Royal Navy Dockyard.
Sørensen was married twice. His second wife was Margrethe Høyrup Sørensen, who collaborated with him in his studies. | 3 | Analytical Chemistry |
To provide further evidence on the mechanism of the dienone in which there is bonding between the two double bonds,
the case of 4,4-diphenylcyclohexenone is presented here. It is seen that the rearrangement is quite different; thus two double bonds are required for a type A rearrangement. With one double bond one of the phenyl groups, originally at C-4, has migrated to C-3 (i.e. the beta carbon).
When one of the aryl groups has a para-cyano or para-methoxy group, that substituted aryl group migrates in preference. Inspection of the alternative phenonium-type species, in which an aryl group has begun to migrate to the beta-carbon, reveals the greater electron delocalization with a substituent para on the migrating aryl group and thus a more stabilized pathway. | 5 | Photochemistry |
The Great Oxygenation Event (GOE) that occurred 2.4 billion years ago altered the course of life on Earth forever by increasing the abundance of oxygen in the atmosphere. Bacteria that existed before the GEO did not rely on the presence of oxygen as a source for metabolism, such as the billion-year-old Cyanobacteria. Melainabacteria is a close relative to Cyanobacteria, though Melainabacteria diverged and do not photosynthesize. Cyanobacteria produced atmospheric oxygen and supported the development of early plant cells. | 2 | Environmental Chemistry |
Mid-infrared (MIR) spectroscopy probes fundamental molecular vibrations, which arise in the spectral range 2,500-25,000 nm. Commercial imaging implementations in the MIR region employ hyperspectral imagers or Fourier Transform Infrared (FT-IR) interferometers, depending on the application. The MIR absorption bands tend to be relatively narrow and well-resolved; direct spectral interpretation is often possible by an experienced spectroscopist. MIR spectroscopy can distinguish subtle changes in chemistry and structure, and is often used for the identification of unknown materials. The absorptions in this spectral range are relatively strong; for this reason, sample presentation is important to limit the amount of material interacting with the incoming radiation in the MIR region. Data can be collected in reflectance, transmission, or emission mode. Water is a very strong absorber of MIR radiation and wet samples often require advanced sampling procedures (such as attenuated total reflectance). Commercial instruments include point and line mapping, and imaging. Mid-infrared chemical imaging can also be performed with nanometer level spatial resolution using atomic force microscope based infrared spectroscopy (AFM-IR). Hyperspectral imaging of the entire bandwidth of the mid-infrared can be achieved within seconds using ultrashort mid-infrared pulses.
For types of MIR microscope, see Microscopy#Infrared microscopy.
Atmospheric windows in the infrared spectrum are also employed to perform chemical imaging remotely. In these spectral regions the atmospheric gases (mainly water and CO) present low absorption and allow infrared viewing over kilometer distances. Target molecules can then be viewed using the selective absorption/emission processes described above. An example of the chemical imaging of a simultaneous release of SF and NH is shown in the image. | 7 | Physical Chemistry |
Water molecules stay close to each other (cohesion), due to the collective action of hydrogen bonds between water molecules. These hydrogen bonds are constantly breaking, with new bonds being formed with different water molecules; but at any given time in a sample of liquid water, a large portion of the molecules are held together by such bonds.
Water also has high adhesion properties because of its polar nature. On clean, smooth glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. In biological cells and organelles, water is in contact with membrane and protein surfaces that are hydrophilic; that is, surfaces that have a strong attraction to water. Irving Langmuir observed a strong repulsive force between hydrophilic surfaces. To dehydrate hydrophilic surfaces—to remove the strongly held layers of water of hydration—requires doing substantial work against these forces, called hydration forces. These forces are very large but decrease rapidly over a nanometer or less. They are important in biology, particularly when cells are dehydrated by exposure to dry atmospheres or to extracellular freezing. | 2 | Environmental Chemistry |
Polishing is abrasion by free abrasives that are suspended in a lubricant and can roll or slide between the specimen and paper. Polishing erases grinding marks and smooths the specimen to a mirror-like finish. Polishing on a bare metallic platen is called lapping. A typical polishing sequence for ceramics is 5–10 minutes each on 15-, 6- and 1-µm diamond paste or slurry on napless paper rotating at 240 rpm. The specimen is again washed in an ultrasonic bath after each step. The three sets of specimens in Fig. 3 have been sawed, embedded, ground and polished. | 8 | Metallurgy |
A pre-supposed guiding principle of thermodynamics is the conservation of energy. The total energy of a system is the sum of its internal energy, of its potential energy as a whole system in an external force field, such as gravity, and of its kinetic energy as a whole system in motion. Thermodynamics has special concern with transfers of energy, from a body of matter, such as, for example a cylinder of steam, to the surroundings of the body, by mechanisms through which the body exerts macroscopic forces on its surroundings so as to lift a weight there; such mechanisms are the ones that are said to mediate thermodynamic work.
Besides transfer of energy as work, thermodynamics admits transfer of energy as heat. For a process in a closed (no transfer of matter) thermodynamic system, the first law of thermodynamics relates changes in the internal energy (or other cardinal energy function, depending on the conditions of the transfer) of the system to those two modes of energy transfer, as work, and as heat. Adiabatic work is done without matter transfer and without heat transfer. In principle, in thermodynamics, for a process in a closed system, the quantity of heat transferred is defined by the amount of adiabatic work that would be needed to effect the change in the system that is occasioned by the heat transfer. In experimental practice, heat transfer is often estimated calorimetrically, through change of temperature of a known quantity of calorimetric material substance.
Energy can also be transferred to or from a system through transfer of matter. The possibility of such transfer defines the system as an open system, as opposed to a closed system. By definition, such transfer is neither as work nor as heat.
Changes in the potential energy of a body as a whole with respect to forces in its surroundings, and in the kinetic energy of the body moving as a whole with respect to its surroundings, are by definition excluded from the body's cardinal energy (examples are internal energy and enthalpy). | 7 | Physical Chemistry |
After a surface has been abrasion blasted and/or machined a thin layer of molybdenum, nickel-chromium alloys or nickel aluminide can be spayed before the final detonation spray coating to improve the bond strength. This is known as a bond coating. Bond coatings are often used when spray coating materials of ceramic composites are being applied. The component may need to be machined and/or abrasion blasted slightly deeper for the purpose of allowing space for the bond coating and spray coating to fit flush on the component surface.
Areas that are not to be sprayed must be covered in stop-off chemicals (chemicals that stop the spay from bonding) or tape. The chemicals and tape are then removed after the coating has cooled. | 8 | Metallurgy |
Cerimetry or cerimetric titration, also known as cerate oximetry, is a method of volumetric chemical analysis developed by Ion Atanasiu. It is a redox titration in which an iron(II)–1,10-phenanthroline complex (ferroin) color change indicates the end point. Ferroin can be reversibly discolored in its oxidized form upon titration with a Ce solution. The use of cerium(IV) salts as reagents for volumetric analysis was first proposed in the middle of 19th century, but systematic studies did not start until about 70 years later. Standard solutions can be prepared from different Ce salts, but often cerium sulfate is chosen.
Since cerimetry is linked to the Fe/Fe redox pair, it can be used for analyses of nonstoichiometric levels that either oxidize Fe or reduce Fe. For the case of oxidation, a precise excess of high-purity crystalline Mohr's salt is added upon the oxide digestion in aqueous hydrogen chloride (HCl), while for the case of reduction, an excess of 1 M iron trichloride (FeCl) is added. In both cases, Fe ions will be titrated subsequently. Because the Ce solution is prone to hydrolysis, the titration is done in a strongly HCl-acidic solution into which some phosphoric acid (HPO) is added to obtain a less colored phosphato complex of Fe.
According to tabulated values of standard potentials at pH 0 for the first-row transition metals, any nonstoichiometry below the following oxidation states will reduce 1 M FeCl solution whereas any nonstoichiometry above them will oxidize the Mohrs salt: Ti, V, Cr, Mn, Co, and Ni. In addition, any nonstoichiometry in the Fe(III)–Fe(II) range is titrated directly with no additives, any nonstoichiometry below Fe will reduce 1 M FeCl whereas any nonstoichiometry above Fe will oxidize Mohrs salt. In the second- and third-row transition metals, only the early elements would be suitable for the titration, and the limiting oxidation states are Zr, Nb, Mo, Hf, Ta, and W. Standard potentials involving rhenium ions are too close to E for Fe/Fe as well as to each other. Nonstoichiometry of oxides containing several elements in oxidation states suitable for cerimetry is determined in one titration. | 3 | Analytical Chemistry |
DMDO is not commercially available because of its instability. DMDO can be prepared as dilute solutions (~0.1 M) by treatment of acetone with potassium peroxymonosulfate , usually in the form of Oxone (2KHSO·KHSO·KSO).
The preparation of DMDO is rather inefficient (typical yields < 3%) and typically only yields a relatively dilute solution in acetone (only up to approximately 0.1 M). This is tolerable as preparation uses inexpensive substances: acetone, sodium bicarbonate, and potassium peroxymonosulfate (commercially known as "oxone"). The solution can be stored at low temperatures and its concentration may be assayed immediately prior to its use.
The more active compound methyl(trifluoromethyl)dioxirane can be similarly prepared from methyl trifluoromethyl ketone. | 0 | Organic Chemistry |
In 1970, Wanzlick's group generated imidazol-2-ylidene carbenes by the deprotonation of an imidazolium salt. Wanzlick as well as Roald Hoffmann, proposed that these imidazole-based carbenes should be more stable than their 4,5-dihydro analogues, due to Hückel-type aromaticity. Wanzlick did not however isolate imidazol-2-ylidenes, but instead their coordination compounds with mercury and isothiocyanate:
In 1988, Guy Bertrand and others isolated a phosphinocarbene. These species can be represented as either a λ-phosphinocarbene or λ-phosphaacetylene:
These compounds were called "push-pull carbenes" in reference to the contrasting electron affinities of the phosphorus and silicon atoms. They exhibit both carbenic and alkynic reactivity. An X-ray structure of this molecule has not been obtained and at the time of publication some doubt remained as to their exact carbenic nature.
In 1991, Arduengo and coworkers crystallized a diaminocarbene by deprotonation of an imidazolium cation:
This carbene, the forerunner of a large family of carbenes with the imidazol-2-ylidene core, is indefinitely stable at room temperature in the absence of oxygen and moisture. It melts at 240–241 °C without decomposition. The C NMR spectrum shows a signal at 211 ppm for the carbenic atom. The X-ray structure revealed longer N–C bond lengths in the ring of the carbene than in the parent imidazolium compound, indicating that there was very little double bond character to these bonds.
The first air-stable ylidic carbene, a chlorinated member of the imidazol-2-ylidene family, was obtained in 1997.
In 2000, Bertrand obtained additional carbenes of the phosphanyl type, including (phosphanyl)(trifluoromethyl)carbene, stable in solution at -30 °C and a moderately stable (amino)(aryl)carbene with only one heteroatom adjacent to the carbenic atom. | 0 | Organic Chemistry |
: Minimal fluorescence (arbitrary units). Fluorescence level of dark-adapted sample when all reaction centers of the photosystem II are open.
: Maximal fluorescence (arbitrary units). Fluorescence level of dark-adapted sample when a high intensity pulse has been applied. All reaction centers of the photosystem II are closed.
: Minimal fluorescence (arbitrary units). Fluorescence level of light-adapted sample when all reaction centers of the photosystem II are open; it is lowered with respect to by non-photochemical quenching.
: Maximal fluorescence (arbitrary units). Fluorescence level of light-adapted sample when a high intensity pulse has been applied. All reaction centers of the photosystem II are closed.
: Steady-state terminal fluorescence (arbitrary units). A steady-state fluorescence level decreased (= quenched) by photochemical and non-photochemical processes.
: Half rise time from to . | 5 | Photochemistry |
UNEP banned the use of Halon gases in the Montreal Protocol treaty in 1987 due to ozone depletion and the ozone-depleting effect of Halon gases. Developing countries were granted an extension to still use Halon until 2010. After 2010 UNEP recommended that those countries replace Halon with ozone friendly alternatives. | 2 | Environmental Chemistry |
A study published in September 2009 discussed a proof of concept experiment to determine if it was possible to identify causal genetic variants using exome sequencing. They sequenced four individuals with Freeman–Sheldon syndrome (FSS) (OMIM 193700), a rare autosomal dominant disorder known to be caused by a mutation in the gene MYH3. Eight HapMap individuals were also sequenced to remove common variants in order to identify the causal gene for FSS. After exclusion of common variants, the authors were able to identify MYH3, which confirms that exome sequencing can be used to identify causal variants of rare disorders. This was the first reported study that used exome sequencing as an approach to identify an unknown causal gene for a rare mendelian disorder.
Subsequently, another group reported successful clinical diagnosis of a suspected Bartter syndrome patient of Turkish origin. Bartter syndrome is a renal salt-wasting disease. Exome sequencing revealed an unexpected well-conserved recessive mutation in a gene called SLC26A3 which is associated with congenital chloride diarrhea (CLD). This molecular diagnosis of CLD was confirmed by the referring clinician. This example provided proof of concept of the use of whole-exome sequencing as a clinical tool in evaluation of patients with undiagnosed genetic illnesses. This report is regarded as the first application of next generation sequencing technology for molecular diagnosis of a patient.
A second report was conducted on exome sequencing of individuals with a mendelian disorder known as Miller syndrome (MIM#263750), a rare disorder of autosomal recessive inheritance. Two siblings and two unrelated individuals with Miller syndrome were studied. They looked at variants that have the potential to be pathogenic such as non-synonymous mutations, splice acceptor and donor sites and short coding insertions or deletions. Since Miller syndrome is a rare disorder, it is expected that the causal variant has not been previously identified. Previous exome sequencing studies of common single nucleotide polymorphisms (SNPs) in public SNP databases were used to further exclude candidate genes. After exclusion of these genes, the authors found mutations in DHODH that were shared among individuals with Miller syndrome. Each individual with Miller syndrome was a compound heterozygote for the DHODH mutations which were inherited as each parent of an affected individual was found to be a carrier.
This was the first time exome sequencing was shown to identify a novel gene responsible for a rare mendelian disease. This exciting finding demonstrates that exome sequencing has the potential to locate causative genes in complex diseases, which previously has not been possible due to limitations in traditional methods. Targeted capture and massively parallel sequencing represents a cost-effective, reproducible and robust strategy with high sensitivity and specificity to detect variants causing protein-coding changes in individual human genomes. | 1 | Biochemistry |
Above 973K, the Deacon reaction is reversed, yielding hydrogen chloride and oxygen from water and chlorine:
::HO + Cl → 2 HCl + 1/2 O | 7 | Physical Chemistry |
In September 2020, the European Medicines Agency recommended that the use of trabectedin in treating ovarian cancer remain unchanged. | 0 | Organic Chemistry |
Methyl vinyl ketone and ethyl acetoacetate undergo aldol cyclization in the presence of catalytic pyrrolidinum acetate or Triton B or sodium ethoxide to produce Hagemann's ester. This variant is a type of Robinson annulation. | 0 | Organic Chemistry |
It reacts with tertiary amines to trisubstituted hydrazinium salts and with pyridine to the 1-amino pyridinium salt.
From 1-aminopyridinium salts the photochemically active 1-N-iminopyridinium ylides are accessible by acylation. The photochemical rearrangement of the obtained 1-N-iminipyridinium ylides leads in high yields to 1H-1,2-diazepines
N-amination of 1H-benzotriazole with hydroxylamine-O-sulfonic acid yields a mixture of 1-aminobenzotriazole (major product) and 2-aminobenzotriazole (minor product). From 1-aminotriazole, benzyne is formed in an almost quantitative yield by oxidation with lead(IV) acetate, which rapidly dimerizes to biphenylene in good yields.
Electron deficient heterocycles, such as tetrazole, can be N-aminated with hydroxylamine-O-sulfonic acid, while even more electron-deficient compounds, such as 5-nitrotetrazole, react only with stronger aminating agents such as O-tosylhydroxylamine or O- mesitylene sulfonylhydroxylamine to amino compounds, which were investigated as explosives.
In the N-amination of the unsubstituted tetrazole, a mixture of 1-amino- and 2-aminotetrazole is obtained.
Also sulfur compounds (such as thioethers) can be aminated with hydroxylamine-O-sulfonic acid to sulfinimines (isosteric with sulfoxides but far more unstable) or phosphorus compounds (such as triphenylphosphine) can be aminated to phosphine imides via the intermediate aminotriphenylphosphonium hydrogen sulfate.
The reaction of hydroxylamine-O-sulfonic acid with metal salts of sulfinic acids in sodium acetate solution produces primary sulfonamides in very good yields.
Diimine can formed in situ from hydroxylamine-O-sulfonic acid respectively hydroxylamine-O-sulfonic acid hydroxylamine sulfate mixtures, which hydrogenates selectively conjugated multiple bonds.[20] | 0 | Organic Chemistry |
Nondepolarizing NMBAs can be used to induce muscle relaxation that improves surgical conditions, including laparoscopic, robotic, abdominal and thoracic procedures. It can reduce patient movement, muscle tone, breathing or coughing against ventilator and allow lower insufflation pressure during laparoscopy. Administration of NMBAs should be individualized according to patient’s parameters. However, many operations can be performed without the need to apply any NMBAs as adequate anesthesia during surgery can achieve many of the theoretical benefits of neuromuscular blockage. | 1 | Biochemistry |
The principle of detailed balance was explicitly introduced for collisions by Ludwig Boltzmann. In 1872, he proved his H-theorem using this principle. The arguments in favor of this property are founded upon microscopic reversibility.
Five years before Boltzmann, James Clerk Maxwell used the principle of detailed balance for gas kinetics with the reference to the principle of sufficient reason. He compared the idea of detailed balance with other types of balancing (like cyclic balance) and found that "Now it is impossible to assign a reason" why detailed balance should be rejected (pg. 64).
Albert Einstein in 1916 used the principle of detailed balance in a background for his quantum theory of emission and absorption of radiation.
In 1901, Rudolf Wegscheider introduced the principle of detailed balance for chemical kinetics. In particular, he demonstrated that the irreversible cycles are impossible and found explicitly the relations between kinetic constants that follow from the principle of detailed balance. In 1931, Lars Onsager used these relations in his works, for which he was awarded the 1968 Nobel Prize in Chemistry.
The principle of detailed balance has been used in Markov chain Monte Carlo methods since their invention in 1953. In particular, in the Metropolis–Hastings algorithm and in its important particular case, Gibbs sampling, it is used as a simple and reliable condition to provide the desirable equilibrium state.
Now, the principle of detailed balance is a standard part of the university courses in statistical mechanics, physical chemistry, chemical and physical kinetics. | 7 | Physical Chemistry |
The oxhydroelectric effect consists in the generation of voltage and electric current in pure liquid water, without any electrolyte, upon exposure to electromagnetic radiation in the infrared range, after creating a physical (not chemical) asymmetry in liquid water e.g. thanks to a strongly hydrophile polymer, such as Nafion.
Since the publication of the first seminal research, other independent research has been published, which refer to this effect, in scientific peer reviewed, reputable journals (with impact factors higher than the median in the respective fields).
The system can be described as a photovoltaic cell operating in the infrared electromagnetic range, based on liquid water instead of a semiconductor. | 7 | Physical Chemistry |
* 1.D.1 The Gramicidin A Channel Family
* 1.D.2 The Channel-forming Syringomycin Family
* 1.D.3 The Channel-Forming Syringopeptin Family
* 1.D.4 The Tolaasin Channel-forming Family
* 1.D.5 The Alamethicin or Peptaibol Antibiotic Channel-forming Family
* 1.D.6 The Complexed Poly 3-Hydroxybutyrate Ca Channel (cPHB-CC) Family
* 1.D.7 The Beticolin Family
* 1.D.8 The Saponin Family
* 1.D.9 The Polyglutamine Ion Channel (PG-IC) Family
* 1.D.10 The Ceramide-forming Channel Family
* 1.D.11 The Surfactin Family
* 1.D.12 The Beauvericin (Beauvericin) Family
* 1.D.13 DNA-delivery Amphipathic Peptide Antibiotics (DAPA)
* 1.D.14 The Synthetic Leu/Ser Amphipathic Channel-forming Peptide (l/S-SCP) Family
* 1.D.15 The Daptomycin (Daptomycin) Family
* 1.D.16 The Synthetic Amphipathic Pore-forming Heptapeptide (SAPH) Family
* 1.D.17 Combinatorially-designed, Pore-forming, β-sheet Peptide Family
* 1.D.18 The Pore-forming Guanosine-Bile Acid Conjugate Family
* 1.D.19 Ca Channel-forming Drug, Digitoxin Family
* 1.D.20 The Pore-forming Polyene Macrolide Antibiotic/fungal Agent (PMAA) Family
* 1.D.21 The Lipid Nanopore (LipNP) Family
* 1.D.22 The Proton-Translocating Carotenoid Pigment, Zeaxanthin Family
* 1.D.23 Phenylene Ethynylene Pore-forming Antimicrobial (PEPA) Family
* 1.D.24 The Marine Sponge Polytheonamide B (pTB) Family
* 1.D.25 The Arylamine Foldamer (AAF) Family
* 1.D.26 The Dihydrodehydrodiconiferyl alcohol 9'-O-β-D-glucoside (DDDC9G) Family
* 1.D.27 The Thiourea isosteres Family
* 1.D.28 The Lipopeptaibol Family
* 1.D.29 The Macrocyclic Oligocholate Family
* 1.D.30 The Artificial Hydrazide-appended pillar[5]arene Channels (HAPA-C) Family
* 1.D.31 The Amphotericin B Family
* 1.D.32 The Pore-forming Novicidin Family
* 1.D.33 The Channel-forming Polytheonamide B Family
* 1.D.34 The Channel-forming Oligoester Bolaamphiphiles
* 1.D.35 The Pore-forming cyclic Lipodepsipeptide Family
* 1.D.36 The Oligobornene Ion Channel Family
* 1.D.37 The Hibicuslide C Family
* 1.D.38 The Cyclic Peptide Nanotube (cPepNT) Family
* 1.D.39 The Light-controlled Azobenzene-based Amphiphilic Molecular Ion Channel (AAM-IC) Family
* 1.D.40 The Protein-induced Lipid Toroidal Pore Family
* 1.D.41 The Sprotetonate-type Ionophore (Spirohexanolide) Family
* 1.D.42 The Phe-Arg Tripeptide-Pillar[5]Arene Channel (TPPA-C) Family
* 1.D.43 The Triazole-tailored Guanosine Dinucleoside Channel (TT-GDN-C) Family
* 1.D.44 The Synthetic Ion Channel with Redox-active Ferrocene (ICRF) Family
* 1.D.45 The Sonoporation and Electroporation Membrane Pore (SEMP) Family
* 1.D.46 The DNA Nanopore (DnaNP) Family
* 1.D.47 The Pore-forming Synthetic Cyclic Peptide (PSCP) Family
* 1.D.48 The Pore-forming Syringomycin E Family
* 1.D.49 The Transmembrane Carotenoid Radical Channel (CRC) Family
* 1.D.50 The Amphiphilic bis-Catechol Anion Transporter (AC-AT) Family
* 1.D.51 The Protein Nanopore (ProNP) Family
* 1.D.52 The Aromatic Oligoamide Macrocycle Nanopore (OmnNP) Family
* 1.D.53 The alpha, gamma-Peptide Nanotube (a,gPepNT) Family
* 1.D.54 The potassium-selective Hexyl-Benzoureido-15-Crown-5-Ether Ion Channel (HBEC) Family
* 1.D.55 The Porphyrin-based Nanopore (PorNP) Family
* 1.D.56 The Alpha-Aminoisobutyrate (Aib) Oligomeric Nanopore (AibNP) Family
* 1.D.57 The Lipid Electro-Pore (LEP) Family
* 1.D.58 The Anion Transporting Prodigiosene (Prodigiosene) Family
* 1.D.59 The Anion Transporting Perenosin (Perenosin) Family
* 1.D.60 The Alpha,Gamma-Cyclic Peptide (AGCP) Family
* 1.D.61 The Anionophoric (ABBP) Family
* 1.D.62 The Bis-Triazolyl DiGuanosine Derivative Channel-forming (TDG) Family
* 1.D.63 The Peptide-based Nanopore (PepNP) Family
* 1.D.64 The Carbon Nanotube (CarNT) Family
* 1.D.65 The Pore-forming Amphidinol (Amphidinol) Family
* 1.D.66 The Helical Macromolecule Nanopore (HmmNP) Family
* 1.D.67 The Crown Ether-modified Helical Peptide Ion Channel (CEHP) Family
* 1.D.68 The Pore-forming Pleuronic Block Polymer (PPBP) Family
* 1.D.69 The Conical Nanopore (ConNP) Family
* 1.D.70 The Metallic (Au/Ag/Pt/graphene) Nanopore (MetNP) Family
* 1.D.71 The Synthetic TP359 Peptide (TP359) Family
* 1.D.72 The Chloride Carrier Triazine-based Tripodal Receptor (CCTTR) Family
* 1.D.73 The Mesoporous Silica Nanopore (SilNP) Family
* 1.D.74 The Stimulus-responsive Synthetic Rigid p-Octiphenyl Stave Pore (SSROP) Family | 1 | Biochemistry |
No study has led to the isolation of true human sex pheromones. While humans are highly dependent upon visual cues, when in close proximity, smells also play a role in sociosexual behaviors. An inherent difficulty in studying human pheromones is the need for cleanliness and odorlessness in human participants. | 1 | Biochemistry |
Photochlorination is a chlorination reaction that is initiated by light. Usually a C-H bond is converted to a C-Cl bond. Photochlorination is carried out on an industrial scale. The process is exothermic and proceeds as a chain reaction initiated by the homolytic cleavage of molecular chlorine into chlorine radicals by ultraviolet radiation. Many chlorinated solvents are produced in this way. | 5 | Photochemistry |
The word "transcriptome" was first used in the 1990s. In 1995, one of the earliest sequencing-based transcriptomic methods was developed, serial analysis of gene expression (SAGE), which worked by Sanger sequencing of concatenated random transcript fragments. Transcripts were quantified by matching the fragments to known genes. A variant of SAGE using high-throughput sequencing techniques, called digital gene expression analysis, was also briefly used. However, these methods were largely overtaken by high throughput sequencing of entire transcripts, which provided additional information on transcript structure such as splice variants. | 1 | Biochemistry |
S. cerevisiae (yeast) can stably exist as either a diploid or a haploid. Both haploid and diploid yeast cells reproduce by mitosis, with daughter cells budding from mother cells. Haploid cells are capable of mating with other haploid cells of the opposite mating type (an a cell can only mate with an α cell, and vice versa) to produce a stable diploid cell. Diploid cells, usually upon facing stressful conditions such as nutrient depletion, can undergo meiosis to produce four haploid spores: two a spores and two α spores. | 1 | Biochemistry |
A typical intracellular concentration of ATP may be 1–10 μmol per gram of tissue in a variety of eukaryotes. The dephosphorylation of ATP and rephosphorylation of ADP and AMP occur repeatedly in the course of aerobic metabolism.
ATP can be produced by a number of distinct cellular processes; the three main pathways in eukaryotes are (1) glycolysis, (2) the citric acid cycle/oxidative phosphorylation, and (3) beta-oxidation. The overall process of oxidizing glucose to carbon dioxide, the combination of pathways 1 and 2, known as cellular respiration, produces about 30 equivalents of ATP from each molecule of glucose.
ATP production by a non-photosynthetic aerobic eukaryote occurs mainly in the mitochondria, which comprise nearly 25% of the volume of a typical cell. | 1 | Biochemistry |
Due to the central role of the glyoxylate cycle in the metabolism of pathogenic species including fungi and bacteria, enzymes of the glyoxylate cycle are current inhibition targets for the treatment of diseases. Most reported inhibitors of the glyoxylate cycle target the first enzyme of the cycle (ICL). Inhibitors were reported for Candida albicans for potential use as antifungal agents. The mycobacterial glyoxylate cycle is also being targeted for potential treatments of tuberculosis. | 1 | Biochemistry |
A system of vibrations in a crystalline solid lattice can be modeled as an Einstein solid, i.e. by considering N quantum harmonic oscillator potentials along each degree of freedom. Then, the free energy of the system can be written as
where the index α sums over all the degrees of freedom. In the 1907 Einstein model (as opposed to the later Debye model) we consider only the high-energy limit:
Then
and we have
Define geometric mean frequency by
where g measures the total number of spatial degrees of freedom of the system.
Thus we have
Using energy
we have
This gives heat capacity at constant volume
which is independent of the temperature.
For another more precise derivation, see Debye model. | 3 | Analytical Chemistry |
Unlike the above assumption of a fundamental split between prokaryotes and eukaryotes, the most important difference between biota may be the division between bacteria and the rest (archaea and eukaryota). For instance, DNA replication differs fundamentally between bacteria and archaea (including that in eukaryotic nuclei), and it may not be homologous between these two groups. Moreover, ATP synthase, though common (homologous) in all organisms, differs greatly between bacteria (including eukaryotic organelles such as mitochondria and chloroplasts) and the archaea/eukaryote nucleus group. The last common antecessor of all life (called LUCA, last universal common ancestor) should have possessed an early version of this protein complex. As ATP synthase is obligate membrane bound, this supports the assumption that LUCA was a cellular organism. The RNA world hypothesis might clarify this scenario, as LUCA might have been a ribocyte (also called ribocell) lacking DNA, but with an RNA genome built by ribosomes as primordial self-replicating entities. A Peptide-RNA world (also called RNP world) hypothesis has been proposed based on the idea that oligopeptides may have been built together with primordial nucleic acids at the same time, which also supports the concept of a ribocyte as LUCA. The feature of DNA as the material base of the genome might have then been adopted separately in bacteria and in archaea (and later eukaryote nuclei), presumably by help of some viruses (possibly retroviruses as they could reverse transcribe RNA to DNA). As a result, prokaryota comprising bacteria and archaea may also be polyphyletic. | 1 | Biochemistry |
Low levels of vitamin D are associated with two major forms of human inflammatory bowel disease: Crohn's disease and ulcerative colitis. Deficiencies in vitamin D have been linked to the severity of the case of inflammatory bowel disease, however, whether vitamin D deficiency causes inflammatory bowel disease or is a symptom of the disease is not clear.
There is some evidence that vitamin D supplementation therapy for people with inflammatory bowel disease may be associated with improvements in scores for clinical inflammatory bowel disease activity and biochemical markers. Vitamin D treatment may be associated with less frequent relapse of symptoms in IBD. It is not clear if this treatment improves the person's quality of life or what the clinical response to vitamin D treatment. The ideal treatment regime and dose of vitamin D therapy has not been well enough studied. | 1 | Biochemistry |
Direct-current plasma (DCP) is a type of plasma source used for atomic emission spectroscopy that utilizes three electrodes to produce a plasma stream. The most common three-electrode DCP apparatus consists of two graphite anode blocks and a tungsten cathode block arranged in an inverted-Y arrangement. An argon gas source is situated between the anode blocks and argon gas flows through the anode blocks. The plasma stream is produced by briefly contacting the cathode with the anodes. Temperatures at the arc core exceed 8000 K. This three-electrode arrangement is illustrated in Figure 1. | 3 | Analytical Chemistry |
NASA Launch Services Program (LSP) investigators have determined the technical root cause for the Taurus XL launch failures of NASAs Orbiting Carbon Observatory (OCO) and Glory missions in 2009 and 2011, respectively: faulty materials provided by aluminium manufacturer, Sapa Profiles, Inc. (SPI). LSPs technical investigation led to the involvement of NASA's Office of the Inspector General and the U.S. Department of Justice (DOJ). The efforts of the DOJ, recently made public, resulted in the resolution of criminal charges and alleged civil claims against SPI, and its agreement to pay $46 million to the U.S. government and other commercial customers. This relates to a 19-year scheme that included falsifying thousands of certifications for aluminium extrusions to hundreds of customers.
On 24 February 2009, a Taurus XL rocket (Taurus T8) carrying NASAs Orbiting Carbon Observatory (OCO) satellite failed to reach orbit. The Taurus T8 mission failed because the payload fairing did not separate during ascent, causing the rocket to not shed weight. As a result of the extra weight, the Taurus rocket failed to reach orbital velocity, resulting in a total loss of the mission. On 4 March 2011, another Taurus rocket (Taurus T9) carrying NASAs Glory scientific satellite failed to reach orbit. The Taurus T9 mission also concluded in a failure of the payload fairing to separate. The Taurus T8 and T9 missions both reentered earths atmosphere resulting in break-up and/or burnup of the rocket and satellite, and any surviving pieces would have been dispersed in the Pacific Ocean near Antarctica. The combined cost of both mission failures was in excess of $700 million. This documents purpose is to provide a top-level outline of NASA's updated findings pertaining to the cause of both mishaps.
The Taurus T8 and T9 rockets both used 63-inch diameter payload fairings to cover and protect the spacecraft during ground operations and launch. The payload fairing halves are structurally joined and attached to the rocket using frangible joints. A frangible joint is a structural separation system that is initiated using ordnance. Initiation of the ordnance causes the ligament of the frangible joint extrusion to fracture, allowing the two payload fairing halves to be separated and subsequently jettisoned from the Taurus rocket. The frangible joints for T8 and T9 were made and assembled together, at the same time. The T8 and T9 frangible joint extrusions were manufactured by Sapa Profiles, Inc. (SPI) in its Technical Dynamics Aluminum (TDA) plant, in Portland, Oregon. | 2 | Environmental Chemistry |
In the field of molecular biology, the ETS (E26 transformation-specific or E-twenty-six. (Erythroblast Transformation Specific)) family is one of the largest families of transcription factors and is unique to animals. There are 29 genes in humans, 28 in the mouse, 10 in Caenorhabditis elegans and 9 in Drosophila. The founding member of this family was identified as a gene transduced by the leukemia virus, E26. The members of the family have been implicated in the development of different tissues as well as cancer progression. | 1 | Biochemistry |
The Society of PEth Research published a harmonization document (2022 Consensus of Basel) for the interpretation of phosphatidylethanol concentrations in the clinical and forensic setting. This consensus represents the first internationally established harmonization document on PEth and was created by an assembly of the world's leading experts in phosphatidylethanol research. The consensus defines the target measurand (PEth 16:0/18:1 in whole blood), cutoff concentrations (20 ng/mL and 200 ng/mL), and minimal requirements for the applied analytical method (accuracy and precision within 15%). | 1 | Biochemistry |
*Leland Hartwell et al.. 2004. Genetics – From Genes to Genomes 2nd Ed. McGraw-Hill
*Engels, W. R. [https://web.archive.org/web/20060111010249/http://engels.genetics.wisc.edu/Pelements/Pt.html P Elements in Drosophila] | 1 | Biochemistry |
This clock reaction uses sodium, potassium or ammonium persulfate to oxidize iodide ions to iodine. Sodium thiosulfate is used to reduce iodine back to iodide before the iodine can complex with the starch to form the characteristic blue-black color.
Iodine is generated:
And is then removed:
Once all the thiosulfate is consumed the iodine may form a complex with the starch. Potassium persulfate is less soluble (cfr. Salters website) while ammonium persulfate has a higher solubility and is used instead in the reaction described in examples from Oxford University. | 7 | Physical Chemistry |
Companion planting was practiced in various forms by the indigenous peoples of the Americas prior to the arrival of Europeans. These peoples domesticated squash 8,000 to 10,000 years ago, then maize, then common beans, forming the Three Sisters agricultural technique. The cornstalk served as a trellis for the beans to climb, the beans fixed nitrogen, benefitting the maize, and the wide leaves of the squash plant provide ample shade for the soil keeping it moist and fertile.
Authors in classical Greece and Rome, around 2000 years ago, were aware that some plants were toxic (allelopathic) to other plants nearby. Theophrastus reported that the bay tree and the cabbage plant enfeebled grapevines. Pliny the Elder wrote that the "shade" of the walnut tree (Juglans regia) poisoned other plants.
In China, mosquito ferns (Azolla spp.) have been used for at least a thousand years as companion plants for rice crops. They host a cyanobacterium (Anabaena azollae) that fixes nitrogen from the atmosphere, and they block light from plants that would compete with the rice. | 1 | Biochemistry |
Esters derived from carboxylic acids and alcohols contain a carbonyl group C=O, which is a divalent group at C atom, which gives rise to C–C–O and O–C–O angles. Unlike amides, carboxylic acid esters are structurally flexible functional groups because rotation about the C–O–C bonds has a low barrier. Their flexibility and low polarity is manifested in their physical properties; they tend to be less rigid (lower melting point) and more volatile (lower boiling point) than the corresponding amides. The pK of the alpha-hydrogens on esters of carboxylic acids is around 25 (alpha-hydrogen is a hydrogen bound to the carbon adjacent to the carbonyl group (C=O) of carboxylate esters).
Many carboxylic acid esters have the potential for conformational isomerism, but they tend to adopt an S-cis (or Z) conformation rather than the S-trans (or E) alternative, due to a combination of hyperconjugation and dipole minimization effects. The preference for the Z conformation is influenced by the nature of the substituents and solvent, if present. Lactones with small rings are restricted to the s-trans (i.e. E) conformation due to their cyclic structure. | 0 | Organic Chemistry |
The term “equivalent weight” had a distinct meaning in gravimetric analysis: it meant the mass of precipitate produced from one gram of analyte (the species of interest). The different definitions came from the practice of quoting gravimetric results as mass fractions of the analyte, often expressed as a percentage. A related term was the equivalence factor, one gram divided by equivalent weight, which was the numerical factor by which the mass of precipitate had to be multiplied to obtain the mass of analyte.
For example, in the gravimetric determination of nickel, the molar mass of the precipitate bis(dimethylglyoximate)nickel [Ni(dmgH)] is 288.915(7) , while the molar mass of nickel is 58.6934(2) : hence 288.915(7)/58.6934(2) = 4.9224(1) grams of [Ni(dmgH)] precipitate is equivalent to one gram of nickel and the equivalence factor is 0.203151(5). For example, 215.3±0.1 mg of [Ni(dmgH)] precipitate is equivalent to (215.3±0.1 mg) × 0.203151(5) = 43.74±0.2 mg of nickel: if the original sample size was 5.346±0.001 g, the nickel content in the original sample would be 0.8182±0.0004%.
Gravimetric analysis is one of the most precise of the common methods of chemical analysis, but it is time-consuming and labour-intensive. It has been largely superseded by other techniques such as atomic absorption spectroscopy, in which the mass of analyte is read off from a calibration curve. | 7 | Physical Chemistry |
The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple light scattering coupled with vertical scanning. This method, known as turbidimetry, is based on measuring the fraction of light that, after being sent through the sample, it backscattered by the colloidal particles. The backscattering intensity is directly proportional to the average particle size and volume fraction of the dispersed phase. Therefore, local changes in concentration caused by sedimentation or creaming, and clumping together of particles caused by aggregation, are detected and monitored. These phenomena are associated with unstable colloids.
Dynamic light scattering can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards a colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond the typical size range for colloidal particles. | 7 | Physical Chemistry |
Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L (pronounced "osmolar"), in the same way that the molarity of a solution is expressed as "M" (pronounced "molar"). Whereas molarity measures the number of moles of solute per unit volume of solution, osmolarity measures the number of osmoles of solute particles per unit volume of solution. This value allows the measurement of the osmotic pressure of a solution and the determination of how the solvent will diffuse across a semipermeable membrane (osmosis) separating two solutions of different osmotic concentration. | 3 | Analytical Chemistry |
Hyperconjugation was suggested as the reason for the increased stability of carbon-carbon double bonds as the degree of substitution increases. Early studies in hyperconjugation were performed by in the research group of George Kistiakowsky. Their work, first published in 1937, was intended as a preliminary progress report of thermochemical studies of energy changes during addition reactions of various unsaturated and cyclic compounds. The importance of hyperconjugation in accounting for this effect has received support from quantum chemical calculations. The key interaction is believed to be the donation of electron density from the neighboring C–H σ bond into the π* antibonding orbital of the alkene (σ→π*). The effect is almost an order of magnitude weaker than the case of alkyl substitution on carbocations (σ→p), since an unfilled p orbital is lower in energy, and, therefore, better energetically matched to a σ bond. When this effect manifests in the formation of the more substituted product in thermodynamically controlled E1 reactions, it is known as Zaitsevs rule, although in many cases the kinetic product also follows this rule. (See Hofmanns rule for cases where the kinetic product is the less substituted one.)
One set of experiments by Kistiakowsky involved collected heats of hydrogenation data during gas-phase reactions of a range of compounds that contained one alkene unit. When comparing a range of monoalkyl-substituted alkenes, they found any alkyl group noticeably increased the stability, but that the choice of different specific alkyl groups had little to no effect.
A portion of Kistiakowsky's work involved a comparison of other unsaturated compounds in the form of CH=CH(CH)n-CH=CH (n=0,1,2). These experiments revealed an important result; when n=0, there is an effect of conjugation to the molecule where the ΔH value is lowered by 3.5 kcal. This is likened to the addition of two alkyl groups into ethylene. Kistiakowsky also investigated open chain systems, where the largest value of heat liberated was found to be during the addition to a molecule in the 1,4-position. Cyclic molecules proved to be the most problematic, as it was found that the strain of the molecule would have to be considered. The strain of five-membered rings increased with a decrease degree of unsaturation. This was a surprising result that was further investigated in later work with cyclic acid anhydrides and lactones. Cyclic molecules like benzene and its derivatives were also studied, as their behaviors were different from other unsaturated compounds.
Despite the thoroughness of Kistiakowsky's work, it was not complete and needed further evidence to back up his findings. His work was a crucial first step to the beginnings of the ideas of hyperconjugation and conjugation effects. | 7 | Physical Chemistry |
Bacteriorhodopsin belongs to the microbial rhodopsin family. Its homologs include the archaerhodopsins, the light-driven chloride pump halorhodopsin (for which the crystal structure is also known), and some directly light-activated channels such as channelrhodopsin.
Bacteriorhodopsin is similar to vertebrate rhodopsins, the pigments that sense light in the retina. Rhodopsins also contain retinal; however, the functions of rhodopsin and bacteriorhodopsin are different, and there is limited similarity in their amino acid sequences. Both rhodopsin and bacteriorhodopsin belong to the 7TM receptor family of proteins, but rhodopsin is a G protein-coupled receptor and bacteriorhodopsin is not. In the first use of electron crystallography to obtain an atomic-level protein structure, the structure of bacteriorhodopsin was resolved in 1990. It was then used as a template to build models of G protein-coupled receptors before crystallographic structures were also available for these proteins. It has been excessively studied on both mica and glass substrates using Atomic force microscopy and Femtosecond crystallography.
All other phototrophic systems in bacteria, algae, and plants use chlorophylls or bacteriochlorophylls rather than bacteriorhodopsin. These also produce a proton gradient, but in a quite different and more indirect way involving an electron transfer chain consisting of several other proteins. Furthermore, chlorophylls are aided in capturing light energy by other pigments known as "antennas"; these are not present in bacteriorhodopsin-based systems. It is possible that phototrophy independently evolved at least twice, once in bacteria and once in archaea. | 5 | Photochemistry |
In biological research, the Van t Hoff plot is also called Van t Hoff analysis. It is most effective in determining the favored product in a reaction. It may obtain results different from direct calorimetry such as differential scanning calorimetry or isothermal titration calorimetry due to various effects other than experimental error.
Assume two products B and C form in a reaction:
:a A + d D → b B,
:a A + d D → c C.
In this case, can be defined as ratio of B to C rather than the equilibrium constant.
When > 1, B is the favored product, and the data on the Van 't Hoff plot will be in the positive region.
When < 1, C is the favored product, and the data on the Van 't Hoff plot will be in the negative region.
Using this information, a Van 't Hoff analysis can help determine the most suitable temperature for a favored product.
In 2010, a Van t Hoff analysis was used to determine whether water preferentially forms a hydrogen bond with the C-terminus or the N-terminus of the amino acid proline. The equilibrium constant for each reaction was found at a variety of temperatures, and a Van t Hoff plot was created. This analysis showed that enthalpically, the water preferred to hydrogen bond to the C-terminus, but entropically it was more favorable to hydrogen bond with the N-terminus. Specifically, they found that C-terminus hydrogen bonding was favored by 4.2–6.4 kJ/mol. The N-terminus hydrogen bonding was favored by 31–43 J/(K mol).
This data alone could not conclude which site water will preferentially hydrogen-bond to, so additional experiments were used. It was determined that at lower temperatures, the enthalpically favored species, the water hydrogen-bonded to the C-terminus, was preferred. At higher temperatures, the entropically favored species, the water hydrogen-bonded to the N-terminus, was preferred. | 7 | Physical Chemistry |
Dissimilatory metal reducers are a diverse group of microorganisms, which is reflected in the factors that affect the different forms of metal reduction. The process of dissimilatory metal reduction occurs in the absence of oxygen (O), but dissimilatory metal reducers include both obligate (strict) anaerobes, such as the family Geobacteraceae, and facultative anaerobes, such as Shewanella spp. As well, across the dissimilatory metal reducers species, various electron donors are used in the oxidative reaction that is coupled to metal reduction. For instance, some species are limited to small organic acids and hydrogen (H), whereas others may oxidize aromatic compounds. In certain instances, such as Cr(VI) reduction, the use of small organic compounds can optimize the rate of metal reduction. Another factor that influences metal respiration is environmental acidity. Although acidophilic and alkaliphilic dissimilatory metal reducers exist, the neutrophilic metal reducers group contains the most well-characterized genera. In soil and sediment environments, where the pH is often neutral, metals like iron are found in their solid oxidized forms, and exhibit variable reduction potential, which can affect their use by microorganisms.
Due to the impermeability of the cell wall to minerals and the insolubility of metal oxides, dissimilatory metal reducers have developed ways to reduce metals extracellularly via electron transfer. Cytochromes c, which are transmembrane proteins, play an important role in transporting electrons from the cytosol to enzymes attached to the outside of the cell. The electrons are then further transported to the terminal electron acceptor via direct interaction between the enzymes and the metal oxide. In addition to establishing direct contact, dissimilatory metal reducers also display the ability to perform ranged metal reduction. For instance, some species of dissimilatory metal reducers produce compounds that can dissolve insoluble minerals or act as electron shuttles, enabling them to perform metal reduction from a distance. Other organic compounds frequently found in soils and sediments, such as humic acids, may also act as electron shuttles. In biofilms, nanowires and multistep electron hopping (in which electrons jump from cell to cell towards the mineral) have also been suggested as methods for reducing metals without requiring direct cell contact. It has been proposed that cytochromes c are involved in both of these mechanisms. In nanowires, for instance, cytochromes c function as the final component that transfers electrons to the metal oxide. | 1 | Biochemistry |
PCLake is a dynamic, mathematical model used to study eutrophication effects in shallow lakes and ponds. PCLake models explicitly the most important biotic groups and their interrelations, within the general framework of nutrient cycles. PCLake is used both by scientist and water managers. PCLake is in 2019 extended to PCLake+, which can be applied to stratifying lakes. | 2 | Environmental Chemistry |
The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the glass state, is called vitrification.
The glass-transition temperature T of a material characterizes the range of temperatures over which this glass transition occurs (as an experimental definition, typically marked as 100 s of relaxation time). It is always lower than the melting temperature, T, of the crystalline state of the material, if one exists.
Hard plastics like polystyrene and poly(methyl methacrylate) are used well below their glass transition temperatures, i.e., when they are in their glassy state. Their T values are both at around . Rubber elastomers like polyisoprene and polyisobutylene are used above their T, that is, in the rubbery state, where they are soft and flexible; crosslinking prevents free flow of their molecules, thus endowing rubber with a set shape at room temperature (as opposed to a viscous liquid).
Despite the change in the physical properties of a material through its glass transition, the transition is not considered a phase transition; rather it is a phenomenon extending over a range of temperature and defined by one of several conventions. Such conventions include a constant cooling rate () and a viscosity threshold of 10 Pa·s, among others. Upon cooling or heating through this glass-transition range, the material also exhibits a smooth step in the thermal-expansion coefficient and in the specific heat, with the location of these effects again being dependent on the history of the material. The question of whether some phase transition underlies the glass transition is a matter of ongoing research. | 7 | Physical Chemistry |
Micro-sized ZnO tetrapodal particles added to pilot paper production. The most common are one-dimensional nanostructures, such as nanorods, nanotubes, nanofibers, nanowires, but also nanoplates, nanosheets, nanospheres, tetrapods. ZnO is strongly oxidative, chemically stable, with enhanced photocatalytic activity, and has a large free-exciton binding energy. It is non-toxic, abundant, biocompatible, biodegradable, environmentally friendly, low cost, and compatible with simple chemical synthesis. ZnO faces limits to its widespread use in photocatalysis under solar radiation. Several approaches have been suggested to overcome this limitation, including doping for reducing the band gap and improving charge carrier separation. | 5 | Photochemistry |
The Journal of Separation Science is a biweekly peer-reviewed scientific journal covering analytical chemistry. It was established in 1978 as the Journal of High Resolution Chromatography & Chromatography Communications: HRC & CC. In 1989, it was renamed the Journal of High Resolution Chromatography. It obtained its current name in 2001, when it also absorbed the preexisting Journal of Microcolumn Separations, which had been established in 1989. It is an organ of the European Society for Separation Science and the California Separation Science Society. The editor-in-chief is František Švec (Charles University). According to the Journal Citation Reports, the journal has a 2020 impact factor of 3.645, ranking it 25th out of 83 journals in the category "Chemistry, Analytical". | 3 | Analytical Chemistry |
mTOR Complex 1 (mTORC1) is composed of mTOR, regulatory-associated protein of mTOR (Raptor), mammalian lethal with SEC13 protein 8 (mLST8) and the non-core components PRAS40 and DEPTOR. This complex functions as a nutrient/energy/redox sensor and controls protein synthesis. The activity of mTORC1 is regulated by rapamycin, insulin, growth factors, phosphatidic acid, certain amino acids and their derivatives (e.g., -leucine and β-hydroxy β-methylbutyric acid), mechanical stimuli, and oxidative stress. | 1 | Biochemistry |
Suppose that we have two multivariate normal distributions, with means and with (non-singular) covariance matrices If the two distributions have the same dimension, , then the relative entropy between the distributions is as follows:
The logarithm in the last term must be taken to base e (mathematical constant)| since all terms apart from the last are base- logarithms of expressions that are either factors of the density function or otherwise arise naturally. The equation therefore gives a result measured in nats. Dividing the entire expression above by yields the divergence in bits.
In a numerical implementation, it is helpful to express the result in terms of the Cholesky decompositions such that and . Then with and solutions to the triangular linear systems , and ,
A special case, and a common quantity in variational inference, is the relative entropy between a diagonal multivariate normal, and a standard normal distribution (with zero mean and unit variance):
For two univariate normal distributions and the above simplifies to
In the case of co-centered normal distributions with , this simplifies to: | 7 | Physical Chemistry |
In radical disproportionation reactions one molecule acts as an acceptor while the other molecule acts as a donor. In the most common disproportionation reactions, a hydrogen atom is taken, or abstracted by the acceptor as the donor molecule undergoes an elimination reaction to form a double bond. Other atoms such as halogens may also be abstracted during a disproportionation reaction. Abstraction occurs as a head to tail reaction with the atom that is being abstracted facing the radical atom on the other molecule. | 0 | Organic Chemistry |
De-AMPylation is the reverse reaction in which the AMP molecule is detached from the amino acid side of a chain protein.
There are three known mechanisms for this reaction.
The bacterial GS-ATase (GlnE) encodes a bipartite protein with separate N-terminal AMPylation and C-terminal de-AMPylation domains whose activity is regulated by P and associated posttranslational modifications. De-AMPylation of its substrate AMPylated glutamine synthetase proceeds by a phosphorolytic reaction between the adenyl-tyrosine of GS and orthophosphate, leading to the formation of ADP and unmodified glutamine synthetase.
SidD, a protein introduced in the host cell by the pathogenic bacteria Legionella pneumophila, de-AMPylates Rab1 a host protein AMPylated by a different Legionella pneumophila enzyme, the AMPylase SidM. Whilst the benefit to the pathogen of introducing these two antagonistic effectors in the host remains unclear, the biochemical reaction carried out by SidD involves the use of a phosphatase-like domain to catalyse the hydrolytic removal of the AMP from tyrosine 77 of the host's Rab1.
In animal cells the removal of AMP from threonine 518 of BiP/Grp78 is catalysed by the same enzyme, FICD, that AMPylates BiP. Unlike the bacterial GS-ATase, FICD carries out both reactions with same catalytic domain. | 1 | Biochemistry |
Agmatine was found to exert modulatory actions directly and indirectly at multiple key molecular targets underlying cellular control mechanisms of cardinal importance in health and disease. It is considered capable of exerting its modulatory actions simultaneously at multiple targets. The following outline indicates the categories of control mechanisms and identifies their molecular targets:
* Neurotransmitter receptors and receptor ionophores. Nicotinic, imidazoline I1 and I2, α2-adrenergic, glutamate NMDAr, and serotonin 5-HT2A and 5HT-3 receptors.
* Ion channels. Including: ATP-sensitive K+ channels, voltage-gated Ca channels, and acid-sensing ion channels (ASICs).
* Membrane transporters. Agmatine specific-selective uptake sites, organic cation transporters (mostly OCT2 subtype), extraneuronal monoamine transporters (ENT), polyamine transporters, and mitochondrial agmatine specific-selective transport system.
* Nitric oxide (NO) synthesis modulation. Both differential inhibition and activation of NO synthase (NOS) isoforms is reported.
* Polyamine metabolism. Agmatine is a precursor for polyamine synthesis, competitive inhibitor of polyamine transport, inducer of spermidine/spermine acetyltransferase (SSAT), and inducer of antizyme.
* Protein ADP-ribosylation. Inhibition of protein arginine ADP-ribosylation.
* Matrix metalloproteases (MMPs). Indirect down-regulation of the enzymes MMP 2 and 9.
* Advanced glycation end product (AGE) formation. Direct blockade of AGEs formation.
* NADPH oxidase. Activation of the enzyme leading to HO production. | 1 | Biochemistry |
pH indicators are frequently employed in titrations in analytical chemistry and biology to determine the extent of a chemical reaction. Because of the subjective choice (determination) of color, pH indicators are susceptible to imprecise readings. For applications requiring precise measurement of pH, a pH meter is frequently used. Sometimes, a blend of different indicators is used to achieve several smooth color changes over a wide range of pH values. These commercial indicators (e.g., universal indicator and Hydrion papers) are used when only rough knowledge of pH is necessary. For a titration, the difference between the true endpoint and the indicated endpoint is called the indicator error.
Tabulated below are several common laboratory pH indicators. Indicators usually exhibit intermediate colors at pH values inside the listed transition range. For example, phenol red exhibits an orange color between pH 6.8 and pH 8.4. The transition range may shift slightly depending on the concentration of the indicator in the solution and on the temperature at which it is used. The figure on the right shows indicators with their operation range and color changes. | 7 | Physical Chemistry |
The excitation P680 → P680 of the reaction center pigment P680 occurs here. These special chlorophyll molecules embedded in PSII absorb the energy of photons, with maximal absorption at 680 nm. Electrons within these molecules are promoted to a higher-energy state. This is one of two core processes in photosynthesis, and it occurs with astonishing efficiency (greater than 90%) because, in addition to direct excitation by light at 680 nm, the energy of light first harvested by antenna proteins at other wavelengths in the light-harvesting system is also transferred to these special chlorophyll molecules.
This is followed by the electron transfer P680 → pheophytin, and then on to plastoquinol, which occurs within the reaction center of PSII. The electrons are transferred to plastoquinone and two protons, generating plastoquinol, which released into the membrane as a mobile electron carrier. This is the second core process in photosynthesis. The initial stages occur within picoseconds, with an efficiency of 100%. The seemingly impossible efficiency is due to the precise positioning of molecules within the reaction center. This is a solid-state process, not a typical chemical reaction. It occurs within an essentially crystalline environment created by the macromolecular structure of PSII. The usual rules of chemistry (which involve random collisions and random energy distributions) do not apply in solid-state environments. | 5 | Photochemistry |
In 1946, some maple syrup producers started using RO to remove water from sap before boiling the sap to syrup. RO allows about 75–90% of the water to be removed, reducing energy consumption and exposure of the syrup to high temperatures. | 3 | Analytical Chemistry |
Synchronous coefficient of drag alteration (SCODA) is a biotechnology method for purifying, separating and/or concentrating bio-molecules. SCODA has the ability to separate molecules whose mobility (or drag) can be altered in sync with a driving field. This technique has been primarily used for concentrating and purifying DNA, where DNA mobility changes with an applied electrophoretic field. Electrophoretic SCODA has also been demonstrated with RNA and proteins. | 1 | Biochemistry |
Construction on bay mud sites is difficult because of the soil's low strength and high compressibility. Very lightweight buildings can be constructed on bay mud sites if there is a thick enough layer of non-bay-mud soil above the bay mud, but buildings which impose significant loads must be supported on deep foundations bearing on stiffer layers below the bay mud, or obtaining support from friction in the bay mud. Even with deep foundations, difficulties arise because the surrounding ground will likely settle over time, potentially damaging utility connections to the building and causing the entryway to sink below street level.
A number of notable buildings have been constructed over bay muds, typically employing special mitigation designs to withstand seismic risks and settlement issues. Complicating design issues, fill (beginning about 1850 CE) is sometimes found deposited on the surface level. For example, the Dakin Building in Brisbane, California, was designed in 1985 to sit on piles 150 feet deep, anchoring to the Franciscan formation, below the bay muds and through an upper fill layer. Furthermore, the structures entrance ramp has been set on a giant hinge to allow the surrounding land to settle, while the building absolute height remains constant. The Crowne Plaza high-rise hotel in Burlingame, California was also designed to sit over bay muds, as was the Westin Hotel in Millbrae, California, and Trinity Church in Bostons Copley Square. Indeed, Boston's entire Back Bay district is named for the tidal bay that it now covers. Logan International Airport and the San Francisco International Airport are also constructed over bay mud. | 2 | Environmental Chemistry |
Testicular tissue-derived seipin is essential for male fertility by modulating testicular phospholipid homeostasis. The lack of seipin in germ cells results in complete male infertility and teratozoospermia. Spermatids devoid of seipin in germ cells are morphologically abnormal with large ectopic lipid droplets and aggregate in dysfunctional clusters. Elevated levels of phosphatidic acid accompanied with an altered ratio of polyunsaturated to monounsaturated and saturated fatty acids show impaired phospholipid homeostasis during spermiogenesis. | 1 | Biochemistry |
The discovery of isofagomine and related glycosidase inhibitors, the discovery of stereoelectronic substituent effects and superarmed glycosyl donors, the creation of artificial enzymes that cause large rate increases., and writing the book "Carbohydrate Building Blocks" about using carbohydrates as a chirality source in synthesis. | 0 | Organic Chemistry |
Anti-PM-Scl antibodies are found in up to 50% of polymyositis/systemic sclerosis (PM/SSc) overlap syndrome. Around 80% of individuals with antibodies present in their blood serum will have the disorder. The presence of the antibodies is linked to limited cutaneous involvement of PM/SSc overlap syndrome. The antigenic targets of the antibodies are components of the RNA-processing exosome complex in the nucleolus. There are ten proteins in this complex and antibodies to eight of them are found at varying frequencies; PM/Scl-100 (70–80%), PM/Scl-75 (46–80%), hRrp4 (50%), hRrp42 (21%), hRrp46 (18%), hCs14 (14%), hRrp41 (10%) and hRrp40 (7%). | 1 | Biochemistry |
A solvated electron is a free electron in a solution, in which it behaves like an anion. An electron's being solvated in a solution means it is bound by the solution. The notation for a solvated electron in formulas of chemical reactions is "e". Often, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but solvated electrons also occur in water and many other solvents in fact, in any solvent that mediates outer-sphere electron transfer. The solvated electron is responsible for a great deal of radiation chemistry. | 0 | Organic Chemistry |
Alkaliphiles are a class of extremophilic microbes capable of survival in alkaline (pH roughly 8.5–11) environments, growing optimally around a pH of 10. These bacteria can be further categorized as obligate alkaliphiles (those that require high pH to survive), facultative alkaliphiles (those able to survive in high pH, but also grow under normal conditions) and haloalkaliphiles (those that require high salt content to survive). | 1 | Biochemistry |
Sulfides, formerly known as thioethers, are characterized by C−S−C bonds Relative to C−C bonds, C−S bonds are both longer, because sulfur atoms are larger than carbon atoms, and about 10% weaker. Representative bond lengths in sulfur compounds are 183 pm for the S−C single bond in methanethiol and 173 pm in thiophene. The C−S bond dissociation energy for thiomethane is 89 kcal/mol (370 kJ/mol) compared to methane's 100 kcal/mol (420 kJ/mol) and when hydrogen is replaced by a methyl group the energy decreases to 73 kcal/mol (305 kJ/mol). The single carbon to oxygen bond is shorter than that of the C−C bond. The bond dissociation energies for dimethyl sulfide and dimethyl ether are respectively 73 and 77 kcal/mol (305 and 322 kJ/mol).
Sulfides are typically prepared by alkylation of thiols. Alkylating agents include not only alkyl halides, but also epoxides, aziridines, and Michael acceptors.
They can also be prepared via the Pummerer rearrangement.
In the Ferrario reaction, phenyl ether is converted to phenoxathiin by action of elemental sulfur and aluminium chloride.
Thioacetals and thioketals feature C−S−C−S−C bond sequence. They represent a subclass of sulfides. The thioacetals are useful in "umpolung" of carbonyl groups. Thioacetals and thioketals can also be used to protect a carbonyl group in organic syntheses.
The above classes of sulfur compounds also exist in saturated and unsaturated heterocyclic structures, often in combination with other heteroatoms, as illustrated by thiiranes, thiirenes, thietanes, thietes, dithietanes, thiolanes, thianes, dithianes, thiepanes, thiepines, thiazoles, isothiazoles, and thiophenes, among others. The latter three compounds represent a special class of sulfur-containing heterocycles that are aromatic. The resonance stabilization of thiophene is 29 kcal/mol (121 kJ/mol) compared to 20 kcal/mol (84 kJ/mol) for the oxygen analogue furan. The reason for this difference is the higher electronegativity for oxygen drawing away electrons to itself at the expense of the aromatic ring current. Yet as an aromatic substituent the thio group is less electron-releasing than the alkoxy group. Dibenzothiophenes (see drawing), tricyclic heterocycles consisting of two benzene rings fused to a central thiophene ring, occurs widely in heavier fractions of petroleum. | 9 | Geochemistry |
AGA and AGG were thought to have become mitochondrial stop codons early in vertebrate evolution. However, at least in humans it has now been shown that AGA and AGG sequences are not recognized as termination codons. A -1 mitoribosome frameshift occurs at the AGA and AGG codons predicted to terminate the CO1 and ND6 open reading frames (ORFs), and consequently both ORFs terminate in the standard UAG codon. | 1 | Biochemistry |
The polymerase chain reaction (PCR) uses a pair of custom primers to direct DNA elongation toward each other at opposite ends of the sequence being amplified. These primers are typically between 18 and 24 bases in length and must code for only the specific upstream and downstream sites of the sequence being amplified. A primer that can bind to multiple regions along the DNA will amplify them all, eliminating the purpose of PCR.
A few criteria must be brought into consideration when designing a pair of PCR primers. Pairs of primers should have similar melting temperatures since annealing during PCR occurs for both strands simultaneously, and this shared melting temperature must not be either too much higher or lower than the reactions annealing temperature. A primer with a T (melting temperature) too much higher than the reactions annealing temperature may mishybridize and extend at an incorrect location along the DNA sequence. A T significantly lower than the annealing temperature may fail to anneal and extend at all.
Additionally, primer sequences need to be chosen to uniquely select for a region of DNA, avoiding the possibility of hybridization to a similar sequence nearby. A commonly used method for selecting a primer site is BLAST search, whereby all the possible regions to which a primer may bind can be seen. Both the nucleotide sequence as well as the primer itself can be BLAST searched. The free NCBI tool Primer-BLAST integrates primer design and BLAST search into one application, as do commercial software products such as ePrime and Beacon Designer. Computer simulations of theoretical PCR results (Electronic PCR) may be performed to assist in primer design by giving melting and annealing temperatures, etc.
As of 2014, many online tools are freely available for primer design, some of which focus on specific applications of PCR. Primers with high specificity for a subset of DNA templates in the presence of many similar variants can be designed using by some software (e.g. DECIPHER) or be developed independently for a specific group of animals.
Selecting a specific region of DNA for primer binding requires some additional considerations. Regions high in mononucleotide and dinucleotide repeats should be avoided, as loop formation can occur and contribute to mishybridization. Primers should not easily anneal with other primers in the mixture; this phenomenon can lead to the production of primer dimer products contaminating the end solution. Primers should also not anneal strongly to themselves, as internal hairpins and loops could hinder the annealing with the template DNA.
When designing primers, additional nucleotide bases can be added to the back ends of each primer, resulting in a customized cap sequence on each end of the amplified region. One application for this practice is for use in TA cloning, a special subcloning technique similar to PCR, where efficiency can be increased by adding AG tails to the 5′ and the 3′ ends. | 1 | Biochemistry |
Soft laser desorption is a soft ionization technique which desorbs and ionizes molecules from surfaces with minimal fragmentation. This is useful for a broad range of small and large molecules and molecules that fragment easily. The first soft laser desorption techniques included matrix-assisted laser desorption/ionization (MALDI) nanoparticles in glycerol. In MALDI, the analyte is first mixed with a matrix solution. The matrix absorbs energy from the laser pulse and transfers it to the analyte, causing desorption and ionization of the sample. MALDI generates [M+H] ions.
DIOS was first reported by Gary Siuzdak, Jing Wei and Jillian M. Buriak in 1999. It was developed as a matrix-free alternative to MALDI for smaller molecules. Because MALDI uses a matrix, background ions are introduced due to ionization of the matrix. These ions reduce the usefulness of MALDI for small molecules. In contrast, DIOS uses a porous silicon surface to trap the analyte. This surface is not ionized by the laser, therefore creating minimal background ionization and thus allowing for the analysis of small molecules. | 3 | Analytical Chemistry |
Calcareous coatings, or calcareous deposits, are mixtures of calcium carbonate and magnesium hydroxide that are deposited on cathodically protected surfaces because of the increased pH adjacent to the surface. | 9 | Geochemistry |
The most common tool to characterize the performances of a reversible solid oxide cell is the polarization curve. In this chart, the current density is related to operating voltage of the cell. The usual convention is the one of positive current density for the fuel cell operation, and negative current density for the electrolysis operation. When the rSOC electrical circuit is not closed and no current is extracted or supplied to the cell, the operating voltage is the so-called open circuit voltage (OCV). If the composition of the gas in the fuel electrode and the oxygen electrode are the same for both modalities, the polarization curve for the SOEC mode and the SOFC have the same OCV. When some current density is extracted or supplied to the cell, the operating voltage starts to diverge from the OCV. This phenomenon is due to the polarization losses, which depend on three main phenomena:
* the activation losses, predominant at very low current densities;
* the ohmic losses, increasing linearly with the current density;
* the concentration losses, occurring at very high current density, when the reactants inside the electrode get depleted.
The sum of the polarization losses takes the name of overpotential.
Other than the open circuit voltage, another fundamental theoretical voltage can be defined. The thermoneutral voltage depends on the enthalpy of the overall reaction taking place in the rSOC and the number of charges that are transferred within the electrochemical reactions. Its relationship with the operating voltage gives information about the heat demand or generation inside the cell.
During the electrolysis operation:
* if , the reaction is endothermic;
* if , the reaction is exothermic.
The fuel cell operation, instead, is always exothermic. | 7 | Physical Chemistry |
Silyl groups can be deprotected with fluoride ions resulting in a strong Si-F bond that is hard and challenging to break. For this reason, different polymer chemists started to employ PPA in fluoride sensing by using t-butyldimethylsily<nowiki/>l (TBS) containing initiators and terminators. The fluoride sensing ability of PPA has been previously used in applications such as drug release, as previously reported by DiLauro et al. Another application studied by Phillips and co-workers includes the use of fluoride-triggered PPA depolymerization in changing the structure of plastics in a predetermined way. | 7 | Physical Chemistry |
Genetic diversity is often lost within captive populations due to the founder effect and subsequent small population sizes. Minimizing the loss of genetic diversity within the captive population is an important component of ex situ conservation and is critical for successful reintroductions and the long term success of the species, since more diverse populations have higher adaptive potential. The loss of genetic diversity due to the founder effect can be minimized by ensuring that the founder population is large enough and genetically representative of the wild population. This is often difficult because removing large numbers of individuals from the wild populations may further reduce the genetic diversity of a species that is already of conservation concern. An alternative to this is collecting sperm from wild individuals and using this via artificial insemination to bring in fresh genetic material. Maximizing the captive population size and the effective population size can decrease the loss of genetic diversity by minimizing the random loss of alleles due to genetic drift. Minimizing the number of generations in captivity is another effective method for reducing the loss of genetic diversity in captive populations. | 1 | Biochemistry |
Some researchers study the occurrence of euxinia in ancient oceans because it was more prevalent then than it is today. Since ancient oceans cannot be directly observed, scientists use geology and chemistry to find evidence in sedimentary rock created under euxinic conditions. Some of these techniques come from studying modern examples of euxinia, while others are derived from geochemistry. Though modern euxinic environments have geochemical properties in common with ancient euxinic oceans, the physical processes causing euxinia most likely vary between the two. | 9 | Geochemistry |
Editing is differentially expressed in the cerebellum and cortex. This regulation is also present in mice suggesting conservation of editing regulation. No editing has been detected in human lung, heart, kidney or spleen tissue. | 1 | Biochemistry |
The internodes are the myelin segments and the gaps between are referred to as nodes. The size and the spacing of the internodes vary with the fiber diameter in a curvilinear relationship that is optimized for maximal conduction velocity. The size of the nodes span from 1–2 μm whereas the internodes can be up to (and occasionally even greater than)1.5 millimetres long, depending on the axon diameter and fiber type.
The structure of the node and the flanking paranodal regions are distinct from the internodes under the compact myelin sheath, but are very similar in CNS and PNS. The axon is exposed to the extra-cellular environment at the node and is constricted in its diameter. The decreased axon size reflects a higher packing density of neurofilaments in this region, which are less heavily phosphorylated and are transported more slowly. Vesicles and other organelles are also increased at the nodes, which suggest that there is a bottleneck of axonal transport in both directions as well as local axonal-glial signaling.
When a longitudinal section is made through a myelinating Schwann cell at the node, three distinctive segments are represented: the stereotypic internode, the paranodal region, and the node itself. In the internodal region, the Schwann cell has an outer collar of cytoplasm, a compact myelin sheath, and inner collar of cytoplasm, and the axolemma. At the paranodal regions, the paranodal cytoplasm loops contact thickenings of the axolemma to form septate –like junctions. In the node alone, the axolemma is contacted by several Schwann microvilli and contains a dense cytoskeletal undercoating. | 1 | Biochemistry |
Isopentenyl pyrophosphate converts to geranyl pyrophosphate, the precursor to tens of thousands of terpeness and terpenoids. | 1 | Biochemistry |
Since the generic term polyol is only derived from chemical nomenclature and just indicates the presence of several hydroxyl groups, no common properties can be assigned to all polyols. However, polyols are usually viscous at room temperature due to hydrogen bonding. | 7 | Physical Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.