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As in other areas of chemistry, electron counting is useful for organizing organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of organometallic complexes, for example metal carbonyls and metal hydrides. The 18e rule has two representative electron counting models, ionic and neutral (also known as covalent) ligand models, respectively. The hapticity of a metal-ligand complex, can influence the electron count. Hapticity (η, lowercase Greek eta), describes the number of contiguous ligands coordinated to a metal. For example, ferrocene, [(η-CH)Fe], has two cyclopentadienyl ligands giving a hapticity of 5, where all five carbon atoms of the CH ligand bond equally and contribute one electron to the iron center. Ligands that bind non-contiguous atoms are denoted the Greek letter kappa, κ. Chelating κ2-acetate is an example. The covalent bond classification method identifies three classes of ligands, X,L, and Z; which are based on the electron donating interactions of the ligand. Many organometallic compounds do not follow the 18e rule. The metal atoms in organometallic compounds are frequently described by their d electron count and oxidation state. These concepts can be used to help predict their reactivity and preferred geometry. Chemical bonding and reactivity in organometallic compounds is often discussed from the perspective of the isolobal principle.
A wide variety of physical techniques are used to determine the structure, composition, and properties of organometallic compounds. X-ray diffraction is a particularly important technique that can locate the positions of atoms within a solid compound, providing a detailed description of its structure. Other techniques like infrared spectroscopy and nuclear magnetic resonance spectroscopy are also frequently used to obtain information on the structure and bonding of organometallic compounds. Ultraviolet-visible spectroscopy is a common technique used to obtain information on the electronic structure of organometallic compounds. It is also used monitor the progress of organometallic reactions, as well as determine their kinetics. The dynamics of organometallic compounds can be studied using dynamic NMR spectroscopy. Other notable techniques include X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and elemental analysis.
Due to their high reactivity towards oxygen and moisture, organometallic compounds often must be handled using air-free techniques. Air-free handling of organometallic compounds typically requires the use of laboratory apparatuses such as a glovebox or Schlenk line. | 0 | Theoretical and Fundamental Chemistry |
Ionic transfer is the transfer of ions from one liquid phase to another. This is related to the phase transfer catalysts which are a special type of liquid-liquid extraction which is used in synthetic chemistry.
For instance nitrate anions can be transferred between water and nitrobenzene. One way to observe this is to use a cyclic voltammetry experiment where the liquid-liquid interface is the working electrode. This can be done by placing secondary electrodes in each phase and close to interface each phase has a reference electrode. One phase is attached to a potentiostat which is set to zero volts, while the other potentiostat is driven with a triangular wave. This experiment is known as a polarised Interface between Two Immiscible Electrolyte Solutions (ITIES) experiment. | 0 | Theoretical and Fundamental Chemistry |
Recycle reactors are PFRs with a recycle loop. Consequently, they behave like a hybrid between PFRs and CSTRs.
In all of these equations : is the consumption rate of A, a reactant. This is equal to the rate expression A is involved in. The rate expression is often related to the fractional conversion both through the consumption of A and through any k changes through temperature changes that are dependent on conversion. | 0 | Theoretical and Fundamental Chemistry |
Salahuddin died on 29 November 1996 at the age of 59 after a difficult illness. His passing away saddened his family and his students. Eulogies by his former students were read at the Annual meeting of the Aligarh Alumni Association Washington DC;
by others at a session at AMU Aligarh on 3 Jan 2019. At his death he was survived by his wife and two daughters. | 1 | Applied and Interdisciplinary Chemistry |
Spiro compounds (compounds with a twisted structure of two or more rings) can have inherent chirality at the spiroatom, due to the twisting of the achiral ring system.
Inherently chiral alkenes have been synthesized through the use of a "buckle" where in an achiral, linear alkene is forced into a chiral conformation. Alkenes have no classical chirality, so generally, an external stereogenic center must be introduced. However, by locking the alkene into a conformation through the use of an achiral buckle allows for the creation of an inherently chiral alkene. Inherently chiral alkenes have been synthesized through the use of dialkoxysilanes, with a large enough racemization barrier that enantiomers have been isolated. | 0 | Theoretical and Fundamental Chemistry |
True vapor pressure (TVP) is a common measure of the volatility of petroleum distillate fuels. It is defined as the
equilibrium partial pressure exerted by a volatile organic liquid as a function of temperature as determined by the test method ASTM D 2879.
The true vapor pressure (TVP) at 100 °F differs slightly from the Reid vapor pressure (RVP) (per definition also at 100 °F), as it excludes dissolved fixed gases such as air. Conversions between the two can be found in [https://www.epa.gov/sites/default/files/2020-10/documents/ch07s01.pdf AP 42, Fifth Edition, Volume I Chapter 7: Liquid Storage Tanks] (p 7.1-54 and onwards) | 0 | Theoretical and Fundamental Chemistry |
Polymers can be classified in many ways. Polymers, strictly speaking, comprise most solid matter: minerals (i.e. most of the Earth's crust) are largely polymers, metals are 3-d polymers, organisms, living and dead, are composed largely of polymers and water. Often polymers are classified according to their origin:
* biopolymers
* synthetic polymers
* inorganic polymers
Biopolymers are the structural and functional materials that comprise most of the organic matter in organisms. One major class of biopolymers are proteins, which are derived from amino acids. Polysaccharides, such as cellulose, chitin, and starch, are biopolymers derived from sugars. The polynucleic acids DNA and RNA are derived from phosphorylated sugars with pendant nucleotides that carry genetic information.
Synthetic polymers are the structural materials manifested in plastics, synthetic fibers, paints, building materials, furniture, mechanical parts, and adhesives. Synthetic polymers may be divided into thermoplastic polymers and thermoset plastics. Thermoplastic polymers include polyethylene, teflon, polystyrene, polypropylene, polyester, polyurethane, Poly(methyl methacrylate), polyvinyl chloride, nylons, and rayon. Thermoset plastics include vulcanized rubber, bakelite, Kevlar, and polyepoxide. Almost all synthetic polymers are derived from petrochemicals. | 0 | Theoretical and Fundamental Chemistry |
Positive material identification (PMI) is the analysis of a material, this can be any material but is generally used for the analysis of metallic alloy to establish composition by reading the quantities by percentage of its constituent elements. Typical methods for PMI include X-ray fluorescence (XRF) and optical emission spectrometry (OES).
PMI is a portable method of analysis and can be used in the field on components.
X-ray fluorescence (XRF) PMI can not detect small elements such as carbon. This means that when undertaking analysis of stainless steels such as grades 304 and 316 the low carbon L variant can not be determined. This however can be analysed with optical emission spectrometry (OES) | 0 | Theoretical and Fundamental Chemistry |
Hydrogen pinch analysis (HPA) is a hydrogen management method that originates from the concept of heat pinch analysis. HPA is a systematic technique for reducing hydrogen consumption and hydrogen generation through integration of hydrogen-using activities or processes in the petrochemical industry, petroleum refineries hydrogen distribution networks and hydrogen purification. | 1 | Applied and Interdisciplinary Chemistry |
Human chorionic gonadotropin interacts with the LHCG receptor of the ovary and promotes the maintenance of the corpus luteum for the maternal recognition of pregnancy at the beginning of pregnancy. This allows the corpus luteum to secrete the hormone progesterone during the first trimester. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus.
It has been hypothesized that hCG may be a placental link for the development of local maternal immunotolerance. For example, hCG-treated endometrial cells induce an increase in T cell apoptosis (dissolution of T cells). These results suggest that hCG may be a link in the development of peritrophoblastic immune tolerance, and may facilitate the trophoblast invasion, which is known to expedite fetal development in the endometrium. It has also been suggested that hCG levels are linked to the severity of morning sickness or hyperemesis gravidarum in pregnant women.
Because of its similarity to LH, hCG can also be used clinically to induce ovulation in the ovaries as well as testosterone production in the testes. As the most abundant biological source is in women who are presently pregnant, some organizations collect urine from pregnant women to extract hCG for use in fertility treatment.
Human chorionic gonadotropin also plays a role in cellular differentiation/proliferation and may activate apoptosis. | 1 | Applied and Interdisciplinary Chemistry |
The Bernoulli equation is invertible, and pressure should rise when a fluid slows down. Nevertheless, if there is an expansion of the tube section, turbulence will appear, and the theorem will not hold. In all experimental Venturi tubes, the pressure in the entrance is compared to the pressure in the middle section; the output section is never compared with them. | 1 | Applied and Interdisciplinary Chemistry |
Lovelock has suggested that global biological feedback mechanisms could evolve by natural selection, stating that organisms that improve their environment for their survival do better than those that damage their environment. However, in the early 1980s, W. Ford Doolittle and Richard Dawkins separately argued against this aspect of Gaia. Doolittle argued that nothing in the genome of individual organisms could provide the feedback mechanisms proposed by Lovelock, and therefore the Gaia hypothesis proposed no plausible mechanism and was unscientific. Dawkins meanwhile stated that for organisms to act in concert would require foresight and planning, which is contrary to the current scientific understanding of evolution. Like Doolittle, he also rejected the possibility that feedback loops could stabilize the system.
Margulis argued in 1999 that "Darwins grand vision was not wrong, only incomplete. In accentuating the direct competition between individuals for resources as the primary selection mechanism, Darwin (and especially his followers) created the impression that the environment was simply a static arena". She wrote that the composition of the Earths atmosphere, hydrosphere, and lithosphere are regulated around "set points" as in homeostasis, but those set points change with time.
Evolutionary biologist W. D. Hamilton called the concept of Gaia Copernican, adding that it would take another Newton to explain how Gaian self-regulation takes place through Darwinian natural selection. More recently Ford Doolittle building on his and Inkpens ITSNTS (Its The Song Not The Singer) proposal proposed that differential persistence can play a similar role to differential reproduction in evolution by natural selections, thereby providing a possible reconciliation between the theory of natural selection and the Gaia hypothesis. | 0 | Theoretical and Fundamental Chemistry |
Countercurrent chromatography and centrifugal partition chromatography are two different instrumental realization of the same liquid–liquid chromatographic theory. Countercurrent chromatography usually uses a planetary gear motion without rotary seals, while centrifugal partition chromatography uses circular rotation with rotary seals for liquid connection. CCC has interchanging mixing and settling zones in the coil tube, so atomization, extraction and settling are time and zone separated. Inside centrifugal partition chromatography, all three steps happen continuously in one time, inside the cells.
Advantages of centrifugal partition chromatography:
* Higher flow rate for same volume size Laboratory scale example: 250 mL centrifugal partition chromatography has optimal flow rate of 5–15 mL/min, 250 mL countercurrent chromatography has optimal flow rate of 1–3 mL/min. Process scale example: 25 L countercurrent chromatography has optimal flow rate of 100–300 ml/min, 25 L centrifugal partition chromatography has optimal flow rate of 1000–3000 ml/min.
* Higher productivity (due to higher flow rate and faster separation time)
* Scalable up to tonnes per month
* Better stationary phase retention for most phases
Disadvantages of centrifugal partition chromatography:
* Higher pressure than CCC (typical operation pressures of 40–160 bar vs 5–25 bar)
* Rotary seal wear over time | 0 | Theoretical and Fundamental Chemistry |
Common side effects include rash, loss of appetite, nausea, diarrhea, and low blood white blood cell levels. Other serious side effects include liver problems, obliterative bronchiolitis, and myasthenia gravis. It is not recommended in people with lupus erythematosus. Use during pregnancy may result in harm to the baby. Penicillamine works by binding heavy metals; the resulting penicillamine–metal complexes are then removed from the body in the urine.
Bone marrow suppression, dysgeusia, anorexia, vomiting, and diarrhea are the most common side effects, occurring in ~20–30% of the patients treated with penicillamine.
Other possible adverse effects include:
* Nephropathy
* Hepatotoxicity
* Membranous glomerulonephritis
* Aplastic anemia (idiosyncratic)
* Antibody-mediated myasthenia gravis and Lambert–Eaton myasthenic syndrome, which may persist even after its withdrawal
* Drug-induced systemic lupus erythematosus
* Elastosis perforans serpiginosa
* Toxic myopathies
* Unwanted breast growth
* Oligospermia | 0 | Theoretical and Fundamental Chemistry |
With the discovery of the dual-membrane nature of mitochondria, the pioneers of mitochondrial ultrastructural research proposed different models for the organization of the mitochondrial inner membrane. Three models proposed were:
*Baffle model – According to Palade (1953), the mitochondrial inner membrane is convoluted in a baffle-like manner with broad openings towards the intra-cristal space. This model entered most textbooks and was widely believed for a long time.
*Septa model – Sjöstrand (1953) suggested that sheets of inner membrane are spanned like septa (plural of septum) through the matrix, separating it into several distinct compartments.
*Crista junction model – Daems and Wisse (1966) proposed that cristae are connected to the inner boundary membrane via tubular structures characterized by rather small diameters, termed crista junctions (CJs). In the middle of 1990s these structures were rediscovered by EM tomography, leading to the establishment of this currently widely accepted model.
More recent research (2019) finds rows of ATP synthase dimers (formerly known as "elementary particles" or "oxysomes") forming at the cristae. These membrane-curving dimers have a bent shape, and may be the first step to cristae formation. They are situated at the base of the crista. A mitochondrial contact site cristae organizing system (MICOS) protein complex occupies the crista junction. Proteins like OPA1 are involved in cristae remodeling.
Crista are traditionally sorted by shapes into lamellar, tubular, and vesicular cristae. They appear in different cell types. It is debated whether these shapes arise by different pathways. | 1 | Applied and Interdisciplinary Chemistry |
Imipenem is rapidly degraded by the renal enzyme dehydropeptidase 1 when administered alone, and is almost always coadministered with cilastatin to prevent this inactivation. | 0 | Theoretical and Fundamental Chemistry |
µSR requires a particle accelerator for the production of a muon beam. This is presently achieved at few large scale facilities in the world: the CMMS continuous source at TRIUMF in Vancouver, Canada; the SµS continuous source at the Paul Scherrer Institut (PSI) in Villigen, Switzerland; the ISIS Neutron and Muon Source and RIKEN-RAL pulsed sources at the Rutherford Appleton Laboratory in Chilton, United Kingdom; and the J-PARC facility in Tokai, Japan, where a new pulsed source is being built to replace that at KEK in Tsukuba, Japan.
Muon beams are also available at the Laboratory of Nuclear Problems, Joint Institute for Nuclear Research (JINR) in Dubna, Russia.
The International Society for µSR Spectroscopy (ISMS) exists to promote the worldwide advancement of µSR. Membership in the society is open free of charge to all individuals in academia, government laboratories and industry who have an interest in the society's goals. | 0 | Theoretical and Fundamental Chemistry |
As the siphon is a single system, the constant in all four equations is the same. Setting equations 1 and 4 equal to each other gives:
Solving for v:
:Velocity of siphon:
The velocity of the siphon is thus driven solely by the height difference between the surface of the upper reservoir and the drain point. The height of the intermediate high point, h, does not affect the velocity of the siphon. However, as the siphon is a single system, v = v and the intermediate high point does limit the maximum velocity. The drain point cannot be lowered indefinitely to increase the velocity. Equation 3 will limit the velocity to retain a positive pressure at the intermediate high point to prevent cavitation. The maximum velocity may be calculated by combining equations 1 and 3:
Setting P = 0 and solving for v:
:Maximum velocity of siphon:
The depth, −d, of the initial entry point of the siphon in the upper reservoir, does not affect the velocity of the siphon. No limit to the depth of the siphon start point is implied by Equation 2 as pressure P increases with depth d. Both these facts imply the operator of the siphon may bottom skim or top skim the upper reservoir without impacting the siphon's performance.
This equation for the velocity is the same as that of any object falling height h. This equation assumes P is atmospheric pressure. If the end of the siphon is below the surface, the height to the end of the siphon cannot be used; rather the height difference between the reservoirs should be used. | 1 | Applied and Interdisciplinary Chemistry |
The early gunpowder formula contained too little saltpeter (about 50%) to be explosive, but the mixture was highly flammable, and contemporary weapons reflected this in their deployment as mainly shock and incendiary weapons. One of the first, if not the first of these weapons was the fire arrow. The first possible reference to the use of fire arrows was by the Southern Wu in 904 during the siege of Yuzhang. An officer under Yang Xingmi by the name of Zheng Fan (鄭璠) ordered his troops to "shoot off a machine to let fire and burn the Longsha Gate", after which he and his troops dashed over the fire into the city and captured it, and he was promoted to Prime Minister Inspectorate for his efforts and the burns his body endured. A later account of this event corroborated with the report and explained that "by let fire (飛火) is meant things like firebombs and fire arrows." Arrows carrying gunpowder were possibly the most applicable form of gunpowder weaponry at the time. Early gunpowder may have only produced an effective flame when exposed to oxygen, thus the rush of air around the arrow in flight would have provided a suitably ample supply of reactants for the reaction. | 1 | Applied and Interdisciplinary Chemistry |
In higher eukaryotes, TTF-I binds and bends the termination site at the 3' end of the transcribed region. This will force Pol I to pause. TTF-I, with the help of transcript-release factor PTRF and a T-rich region, will induce Pol I into terminating transcription and dissociating from the DNA and the new transcript. Evidence suggests that termination might be rate-limiting in cases of high rRNA production. TTF-I and PTRF will then indirectly stimulate the reinitiation of transcription by Pol I at the same rDNA gene.
In organisms such as budding yeast the process seems to be much more complicated and is still not completely elucidated. | 1 | Applied and Interdisciplinary Chemistry |
An aldehyde differs from a ketone in that it has a hydrogen atom attached to its carbonyl group, making aldehydes easier to oxidize. Ketones do not have a hydrogen atom bonded to the carbonyl group, and are therefore more resistant to oxidation. They are oxidized only by powerful oxidizing agents which have the ability to cleave carbon–carbon bonds. | 0 | Theoretical and Fundamental Chemistry |
The enantioselective version of the Tsuji–Trost reaction is called the Trost asymmetric allylic alkylation (Trost AAA) or simply, asymmetric allylic alkylation (AAA). These reactions are often used in asymmetric synthesis. The reaction was originally developed with a palladium catalyst supported by the Trost ligand, although suitable conditions have greatly expanded since then.
Enantioselectivity can be imparted to the reaction during any of the steps aside from the decomplexation of the palladium from the alkene since the stereocenter is already set at that point. Five main ways have been conceptualized to take advantage of these steps and yield enantioselective reaction conditions.
These methods of enantiodiscrimination were previously reviewed by Trost:
# Preferential ionization via enantioselective olefin complexation
# Enantiotopic ionization of leaving groups
# Attack at enantiotopic ends of the allyl complex
# Enantioface exchange in the -allyl complex
# Differentiation of prochiral nucleophile faces
The favored method for enantiodiscrimination is largely dependent on the substrate of interest, and in some cases, the enantioselectivity may be influenced by several of these factors. | 0 | Theoretical and Fundamental Chemistry |
2-Amino-4-hydroxy-6-pyrophosphoryl-methylpteridine (7,8-Dihydropterin pyrophosphate, dihydropterin-CH2OH-diphosphate) is a pteridine; a precursor to dihydrofolic acid. | 1 | Applied and Interdisciplinary Chemistry |
The U.S. Standard Atmosphere, 1976 (USSA1976) defines the gas constant R as:
:R = = .
Note the use of kilomoles, with the resulting factor of in the constant. The USSA1976 acknowledges that this value is not consistent with the cited values for the Avogadro constant and the Boltzmann constant. This disparity is not a significant departure from accuracy, and USSA1976 uses this value of R for all the calculations of the standard atmosphere. When using the ISO value of R, the calculated pressure increases by only 0.62 pascal at 11 kilometers (the equivalent of a difference of only 17.4 centimeters or 6.8 inches) and 0.292 Pa at 20 km (the equivalent of a difference of only 33.8 cm or 13.2 in).
Also note that this was well before the 2019 SI redefinition, through which the constant was given an exact value. | 0 | Theoretical and Fundamental Chemistry |
Like almost all riffle beetles, spider water beetles are aquatic, feeding on algae and decaying wood tissue. However, they can not actively swim. They can be found crawling along or clinging with their claws on boulders or submerged wood in lotic riffles of streams and rivers.
The larvae are exclusively aquatic. They breathe by means of tracheal gills. Spider water beetle adults, like all members of the subfamily Elminae, can also remain indefinitely underwater by means of a plastron, a thin film of gas trapped by hydrophobic bristles (setae) on their body. As the insect breathes, the oxygen concentration in the gas film drops in comparison to the surrounding water, causing new oxygen to diffuse again into the plastron.
Because of their reliance on the plastron for breathing, spider water beetles are restricted to the highly oxygenated environments in moderate to fast-moving permanent running water. They are therefore extremely sensitive to water pollution and are potentially valuable bioindicators for measuring the health of river ecosystems.
Members of the Ancyronyx variegatus species group are mostly found in slightly to moderately polluted (mesosaprobic) rivers, almost always found on submerged wood (with the exception of Ancyronyx yunju which were collected from sand and grass roots). Members of the Ancyronyx patrolus species group, meanwhile, are only found in clean permanent streams, usually among rocks.
Ancyronyx malickyi have been caught using light traps, which might indicate phototaxis. | 1 | Applied and Interdisciplinary Chemistry |
The A ring synthesis (Scheme 3) started with a Diels-Alder reaction of diene 3.1 with the commercially available dienophile 2-chloroacrylonitrile 3.2 to give cyclohexene 3.3 with complete regioselectivity. Hydrolysis of the cyanochloro group and simultaneous cleavage of the acetate group led to hydroxyketone 3.4. The hydroxyl group was protected as a tert-butyldimethylsilyl ether (3.5). In preparation for a Shapiro reaction, this ketone was converted to hydrazone 3.6. | 0 | Theoretical and Fundamental Chemistry |
The vast majority of genetically modified animals are at the research stage with the number close to entering the market remaining small. As of 2018 only three genetically modified animals have been approved, all in the USA. A goat and a chicken have been engineered to produce medicines and a salmon has increased its own growth. Despite the differences and difficulties in modifying them, the end aims are much the same as for plants. GM animals are created for research purposes, production of industrial or therapeutic products, agricultural uses, or improving their health. There is also a market for creating genetically modified pets. | 1 | Applied and Interdisciplinary Chemistry |
The equations for the perturbation read:
but when the velocity field is:
In the far field ≫ 1, the viscous stress is dominated by the last term. That is:
The inertia term is dominated by the term:
The error is then given by the ratio:
This becomes unbounded for ≫ 1, therefore the inertia cannot be ignored in the far field. By taking the curl, Stokes equation gives Since the body is a source of vorticity, would become unbounded logarithmically for large This is certainly unphysical and is known as Stokes' paradox. | 1 | Applied and Interdisciplinary Chemistry |
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer. Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (AlO), the rest being a mixture of silica, various iron oxides, and titanium dioxide. The aluminium oxide must be further purified before it can be refined into aluminium.
The Bayer process is also the main source of gallium as a byproduct despite low extraction yields. | 1 | Applied and Interdisciplinary Chemistry |
The situation for a Lambertian surface (emitting or scattering) is illustrated in Figures 1 and 2. For conceptual clarity we will think in terms of photons rather than energy or luminous energy. The wedges in the circle each represent an equal angle dΩ, of an arbitrarily chosen size, and for a Lambertian surface, the number of photons per second emitted into each wedge is proportional to the area of the wedge.
The length of each wedge is the product of the diameter of the circle and cos(θ). The maximum rate of photon emission per unit solid angle is along the normal, and diminishes to zero for θ = 90°. In mathematical terms, the radiance along the normal is I photons/(s·m·sr) and the number of photons per second emitted into the vertical wedge is . The number of photons per second emitted into the wedge at angle θ is .
Figure 2 represents what an observer sees. The observer directly above the area element will be seeing the scene through an aperture of area dA and the area element dA will subtend a (solid) angle of dΩ, which is a portion of the observers total angular field-of-view of the scene. Since the wedge size d'Ω was chosen arbitrarily, for convenience we may assume without loss of generality that it coincides with the solid angle subtended by the aperture when "viewed" from the locus of the emitting area element dA. Thus the normal observer will then be recording the same photons per second emission derived above and will measure a radiance of
:<math>
I_0=\frac{I\, d\Omega\, dA}{d\Omega_0\, dA_0}
·sr).
The observer at angle θ to the normal will be seeing the scene through the same aperture of area dA (still corresponding to a dΩ wedge) and from this oblique vantage the area element dA is foreshortened and will subtend a (solid) angle of dΩ cos(θ). This observer will be recording photons per second, and so will be measuring a radiance of
:<math>
I_0=\frac{I \cos(\theta)\, d\Omega\, dA}{d\Omega_0\, \cos(\theta)\, dA_0}
=\frac{I\, d\Omega\, dA}{d\Omega_0\, dA_0}
·sr),
which is the same as the normal observer. | 0 | Theoretical and Fundamental Chemistry |
Cytotoxic drugs, therapeutic antibodies, sex hormones, aromatase inhibitors, somatostatin inhibitors, recombinant interleukins, G-CSF, erythropoietin. | 1 | Applied and Interdisciplinary Chemistry |
In this technique it is necessary to select a suitable interlayer by considering its wettability, flow characteristics, high stability to prevent reactions with the base materials, and the ability to form a composition having a remelt temperature higher than the bonding temperature. The joining technique dates back to ancient times.
For example, copper oxide painted as an interlayer and covered with tallow or glue to hold gold balls on to a gold article were heated in a reducing flame to form a eutectic alloy alloy at the bond area. | 1 | Applied and Interdisciplinary Chemistry |
Because of differences in their electron shells, singlet and triplet oxygen differ in their chemical properties; singlet oxygen is highly reactive. The lifetime of singlet oxygen depends on the medium and pressure. In normal organic solvents, the lifetime is only a few microseconds whereas in solvents lacking C-H bonds, the lifetime can be as long as seconds. | 0 | Theoretical and Fundamental Chemistry |
The electron-phonon coupling is responsible for electron generation in the pV cell. In this phenomenon, the phonon leads to ion motion which perturbs the highest occupied valence state (HOS). This state begins to overlap with the lowest unoccupied conduction state (LUS), and the electron can switch states if energy and momentum are conserved. If it does, an electron-hole pair is generated.
Using a taylor expansion of the change in electron potential, , due to the ionic displacement of a phonon provides a matrix element for use in Fermi's golden rule, and the derivation of a generation rate. This Taylor expansion gives the following matrix element
where is the average atomic mass, and are the frequency and atomic displacement due to a phonon with polarization and momentum , and is the electron wavefunction for an electron with momentum in band i. From Fermi's golden rule
where is the energy of an electron in band i and momentum , is the corresponding electron occupation, and is the phonon occupancy. | 0 | Theoretical and Fundamental Chemistry |
Coordination numbers become ambiguous when dealing with polyhapto ligands.
For π-electron ligands such as the cyclopentadienide ion [CH], alkenes and the cyclooctatetraenide ion [CH], the number of adjacent atoms in the π-electron system that bind to the central atom is termed the hapticity. In ferrocene the hapticity, η, of each cyclopentadienide anion is five, Fe(η-CH). Various ways exist for assigning the contribution made to the coordination number of the central iron atom by each cyclopentadienide ligand. The contribution could be assigned as one since there is one ligand, or as five since there are five neighbouring atoms, or as three since there are three electron pairs involved. Normally the count of electron pairs is taken. | 0 | Theoretical and Fundamental Chemistry |
Environmental bioassays are generally a broad-range survey of toxicity. A toxicity identification evaluation is conducted to determine what the relevant toxicants are. Although bioassays are beneficial in determining the biological activity within an organism, they can often be time-consuming and laborious. Organism-specific factors may result in data that are not applicable to others in that species. For these reasons, other biological techniques are often employed, including radioimmunoassays. See bioindicator.
Water pollution control requirements in the United States require some industrial dischargers and municipal sewage treatment plants to conduct bioassays. These procedures, called whole effluent toxicity tests, include acute toxicity tests as well as chronic test methods. The methods involve exposing living aquatic organisms to samples of wastewater for a specific length of time. Another example is the bioassay ECOTOX, which uses the microalgae Euglena gracilis to test the toxicity of water samples. (See Bioindicator#Microalgae in water quality) | 1 | Applied and Interdisciplinary Chemistry |
Isobornyl acetate is an organic compound consisting of the acetate ester or the terpenoid isoborneol. It is a colorless liquid with a pleasant pine-like scent, and it is produced on a multi-ton scale for this purpose. The compound is prepared by reaction of camphene with acetic acid in the presence of a strongly acidic catalyst such as sulfuric acid. Hydrolysis of isobornyl acetate gives isoborneol, a precursor to camphor.
Like many plant exudates, isobornyl acetate appears to have antifeedant properties. | 0 | Theoretical and Fundamental Chemistry |
The HITRAN compilation also provides collision-induced absorption (CIA) that was first introduced into HITRAN in the 2012 edition. CIA refers to absorption by transient electric dipoles induced by the interaction between colliding molecules. Instructions for accessing the CIA data files can be found on [https://hitran.org/cia/ HITRAN/CIA]. | 0 | Theoretical and Fundamental Chemistry |
While travelling down river, kayaking and canoeing paddlers will often stop and playboat in standing waves and hydraulic jumps. The standing waves and shock fronts of hydraulic jumps make for popular locations for such recreation.
Similarly, kayakers and surfers have been known to ride tidal bores up rivers.
Hydraulic jumps have been used by glider pilots in the Andes and Alps and to ride Morning Glory effects in Australia. | 1 | Applied and Interdisciplinary Chemistry |
Before it can be tested, the essential oils are first diluted to produce solutions of varying concentrations. In this way, the minimum inhibitory concentration can be calculated to obtain the most cost-effective antimicrobial agent. | 1 | Applied and Interdisciplinary Chemistry |
Shvab–Zeldovich–Liñán formulation was introduced by Amable Liñán in 1991 for diffusion-flame problems where the chemical time scale is infinitely small (Burke–Schumann limit) so that the flame appears as a thin reaction sheet. The reactants can have Lewis number that is not necessarily equal to one.
Suppose the non-dimensional scalar equations for fuel mass fraction (defined such that it takes a unit value in the fuel stream), oxidizer mass fraction (defined such that it takes a unit value in the oxidizer stream) and non-dimensional temperature (measured in units of oxidizer-stream temperature) are given by
where is the reaction rate, is the appropriate Damköhler number, is the mass of oxidizer stream required to burn unit mass of fuel stream, is the non-dimensional amount of heat released per unit mass of fuel stream burnt and is the Arrhenius exponent. Here, and are the Lewis number of the fuel and oxygen, respectively and is the thermal diffusivity. In the Burke–Schumann limit, leading to the equilibrium condition
In this case, the reaction terms on the right-hand side become Dirac delta functions. To solve this problem, Liñán introduced the following functions
where , is the fuel-stream temperature and is the adiabatic flame temperature, both measured in units of oxidizer-stream temperature. Introducing these functions reduces the governing equations to
where is the mean (or, effective) Lewis number. The relationship between and and between and can be derived from the equilibrium condition.
At the stoichiometric surface (the flame surface), both and are equal to zero, leading to , , and , where is the flame temperature (measured in units of oxidizer-stream temperature) that is, in general, not equal to unless . On the fuel stream, since , we have . Similarly, on the oxidizer stream, since , we have .
The equilibrium condition defines
The above relations define the piecewise function
where is a mean Lewis number. This leads to a nonlinear equation for . Since is only a function of and , the above expressions can be used to define the function
With appropriate boundary conditions for , the problem can be solved.
It can be shown that and are conserved scalars, that is, their derivatives are continuous when crossing the reaction sheet, whereas and have gradient jumps across the flame sheet. | 1 | Applied and Interdisciplinary Chemistry |
McDermott has won several awards and fellowships throughout her career including the DuPont Young Investigator Award (1992), the Cottrell Scholars Award (1994), the Alfred P. Sloan Research Fellowship (1995), the American Chemical Societys Award in Pure Chemistry (1996), the Eastern Analytic Symposium Award for Achievement in Magnetic Resonance (2005), and the Royal Society of Chemistrys Bourke Award (2014). In 2000, she was inducted into the American Academy of Arts and Sciences. In 2006, she was elected as a member of the National Academy of Sciences. | 0 | Theoretical and Fundamental Chemistry |
Since uranium and plutonium are nuclear weapons materials, there have been proliferation concerns. Ordinarily (in spent nuclear fuel), plutonium is reactor-grade plutonium. In addition to plutonium-239, which is highly suitable for building nuclear weapons, it contains large amounts of undesirable contaminants: plutonium-240, plutonium-241, and plutonium-238. These isotopes are extremely difficult to separate, and more cost-effective ways of obtaining fissile material exist (e.g., uranium enrichment or dedicated plutonium production reactors).
High-level waste is full of highly radioactive fission products, most of which are relatively short-lived. This is a concern since if the waste is stored, perhaps in deep geological storage, over many years the fission products decay, decreasing the radioactivity of the waste and making the plutonium easier to access. The undesirable contaminant Pu-240 decays faster than the Pu-239, and thus the quality of the bomb material increases with time (although its quantity decreases during that time as well). Thus, some have argued, as time passes, these deep storage areas have the potential to become "plutonium mines", from which material for nuclear weapons can be acquired with relatively little difficulty. Critics of the latter idea have pointed out the difficulty of recovering useful material from sealed deep storage areas makes other methods preferable. Specifically, high radioactivity and heat (80 °C in surrounding rock) greatly increase the difficulty of mining a storage area, and the enrichment methods required have high capital costs.
Pu-239 decays to U-235 which is suitable for weapons and which has a very long half-life (roughly 10 years). Thus plutonium may decay and leave uranium-235. However, modern reactors are only moderately enriched with U-235 relative to U-238, so the U-238 continues to serve as a denaturation agent for any U-235 produced by plutonium decay.
One solution to this problem is to recycle the plutonium and use it as a fuel e.g. in fast reactors. In pyrometallurgical fast reactors, the separated plutonium and uranium are contaminated by actinides and cannot be used for nuclear weapons. | 0 | Theoretical and Fundamental Chemistry |
It might appear from the above that all nuclei of the same nuclide (and hence the same γ) would resonate at exactly the same frequency. This is not the case. The most important perturbation of the NMR frequency for applications of NMR is the "shielding" effect of the surrounding shells of electrons. Electrons, similar to the nucleus, are also charged and rotate with a spin to produce a magnetic field opposite to the applied magnetic field. In general, this electronic shielding reduces the magnetic field at the nucleus (which is what determines the NMR frequency). As a result, the frequency required to achieve resonance is also reduced. This shift in the NMR frequency due to the electronic molecular orbital coupling to the external magnetic field is called chemical shift, and it explains why NMR is able to probe the chemical structure of molecules, which depends on the electron density distribution in the corresponding molecular orbitals. If a nucleus in a specific chemical group is shielded to a higher degree by a higher electron density of its surrounding molecular orbital, then its NMR frequency will be shifted "upfield" (that is, a lower chemical shift), whereas if it is less shielded by such surrounding electron density, then its NMR frequency will be shifted "downfield" (that is, a higher chemical shift).
Unless the local symmetry of such molecular orbitals is very high (leading to "isotropic" shift), the shielding effect will depend on the orientation of the molecule with respect to the external field (B). In solid-state NMR spectroscopy, magic angle spinning is required to average out this orientation dependence in order to obtain frequency values at the average or isotropic chemical shifts. This is unnecessary in conventional NMR investigations of molecules in solution, since rapid "molecular tumbling" averages out the chemical shift anisotropy (CSA). In this case, the "average" chemical shift (ACS) or isotropic chemical shift is often simply referred to as the chemical shift. | 0 | Theoretical and Fundamental Chemistry |
Pentamethylcyclopentadiene gives rise to pentamethylcyclopentadienyl (Cp*) complexes. These ligands are more basic and more lipophilic. Replacing methyl groups with larger substituents results in cyclopentadienes that are so encumbered that pentaalkyl derivatives are no longer possible. Well-studied ligands of this type include CRH (R = iso-Pr) and 1,2,4-CRH (R = tert-Bu). | 0 | Theoretical and Fundamental Chemistry |
Liquid chromatography is a method of physical separation in which the components of a liquid mixture are distributed between two immiscible phases, i.e., stationary and mobile. The practice of LC can be divided into five categories, i.e., adsorption chromatography, partition chromatography, ion-exchange chromatography, size-exclusion chromatography, and affinity chromatography. Among these, the most widely used variant is the reverse-phase (RP) mode of the partition chromatography technique, which makes use of a nonpolar (hydrophobic) stationary phase and a polar mobile phase. In common applications, the mobile phase is a mixture of water and other polar solvents (e.g., methanol, isopropanol, and acetonitrile), and the stationary matrix is prepared by attaching long-chain alkyl groups (e.g., n-octadecyl or C) to the external and internal surfaces of irregularly or spherically shaped 5 μm diameter porous silica particles.
In HPLC, typically 20 μl of the sample of interest are injected into the mobile phase stream delivered by a high pressure pump. The mobile phase containing the analytes permeates through the stationary phase bed in a definite direction. The components of the mixture are separated depending on their chemical affinity with the mobile and stationary phases. The separation occurs after repeated sorption and desorption steps occurring when the liquid interacts with the stationary bed. The liquid solvent (mobile phase) is delivered under high pressure (up to 400 bar or 5800 psi) into a packed column containing the stationary phase. The high pressure is necessary to achieve a constant flow rate for reproducible chromatography experiments. Depending on the partitioning between the mobile and stationary phases, the components of the sample will flow out of the column at different times. The column is the most important component of the LC system and is designed to withstand the high pressure of the liquid. Conventional LC columns are 100–300 mm long with outer diameter of 6.4 mm (1/4 inch) and internal diameter of 3.0–4.6 mm. For applications involving LC–MS, the length of chromatography columns can be shorter (30–50 mm) with 3–5 μm diameter packing particles. In addition to the conventional model, other LC columns are the narrow bore, microbore, microcapillary, and nano-LC models. These columns have smaller internal diameters, allow for a more efficient separation, and handle liquid flows under 1 ml/min (the conventional flow-rate). In order to improve separation efficiency and peak resolution, ultra performance liquid chromatography (UHPLC) can be used instead of HPLC. This LC variant uses columns packed with smaller silica particles (~1.7 μm diameter) and requires higher operating pressures in the range of 310000 to 775000 torr (6000 to 15000 psi, 400 to 1034 bar). | 0 | Theoretical and Fundamental Chemistry |
For infinitesimal wave height the results of cnoidal wave theory are expected to converge towards those of Airy wave theory for the limit of long waves λ ≫ h. First the surface elevation, and thereafter the phase speed, of the cnoidal waves for infinitesimal wave height will be examined. | 1 | Applied and Interdisciplinary Chemistry |
There are numerous companies that offer calibration for spectrometers, but not all are equal. It is important to find a traceable, certified laboratory to perform calibration. The calibration certificate should state the light source used (ex: Halogen, Deuterium, Xenon, LED), and the uncertainty of the calibration for each band (UVC, UVB, VIS..), each wavelength in nm, or for the full spectrum measured. It should also list the confidence level for the calibration uncertainty. | 0 | Theoretical and Fundamental Chemistry |
S-Nitrosothiols, also known as thionitrites, are compounds containing a nitroso group attached to the sulfur atom of a thiol, e.g. R−S−N=O. They have received considerable attention in biochemistry because they serve as donors of the nitrosonium ion, NO, and nitric oxide, NO, which may serve as signaling molecules in living systems, especially related to vasodilation. | 0 | Theoretical and Fundamental Chemistry |
Genome mining describes the exploitation of genomic information for the discovery of biosynthetic pathways of natural products and their possible interactions. It depends on computational technology and bioinformatics tools. The mining process relies on a huge amount of data (represented by DNA sequences and annotations) accessible in genomic databases. By applying data mining algorithms, the data can be used to generate new knowledge in several areas of medicinal chemistry, such as discovering novel natural products. | 1 | Applied and Interdisciplinary Chemistry |
Transitions between rotational states can be observed in molecules with a permanent electric dipole moment. A consequence of this rule is that no microwave spectrum can be observed for centrosymmetric linear molecules such as (dinitrogen) or HCCH (ethyne), which are non-polar. Tetrahedral molecules such as (methane), which have both a zero dipole moment and isotropic polarizability, would not have a pure rotation spectrum but for the effect of centrifugal distortion; when the molecule rotates about a 3-fold symmetry axis a small dipole moment is created, allowing a weak rotation spectrum to be observed by microwave spectroscopy.
With symmetric tops, the selection rule for electric-dipole-allowed pure rotation transitions is , . Since these transitions are due to absorption (or emission) of a single photon with a spin of one, conservation of angular momentum implies that the molecular angular momentum can change by at most one unit. Moreover, the quantum number K is limited to have values between and including +J to -J. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, the Hammett plot provides a means to assess substituent effects on a reaction equilibrium or rate using the Hammett equation (1):
Hammett developed this equation from equilibrium constants from the dissociation of benzoic acid and derivatives (Fig. 1):
Hammett defined the equation based on two parameters: the reaction constant (ρ) and the substituent parameter (σ). When other reactions were studied using these parameters, a correlation was not always found due to the specific derivation of these parameters from the dissociation equilibrium of substituted benzoic acids and the original negligence of resonance effects. Therefore, the effects of substituents on an array of compounds must be studied on an individual reaction basis using the equation Hammett derived either for field or resonance effects, but not both. | 0 | Theoretical and Fundamental Chemistry |
Overshot titrations are a common phenomenon, and refer to a situation where the volume of titrant added during a chemical titration exceeds the amount required to reach the equivalence point. This excess titrant leads to an outcome where the solution becomes slightly more alkaline or over-acidified.
Overshooting the equivalence point can occur due to various factors, such as errors in burette readings, imperfect reaction stoichiometry, or issues with endpoint detection. The consequences of overshot titrations can affect the accuracy of the analytical results, particularly in quantitative analysis.
Researchers and analysts often employ corrective measures, such as back-titration and using more precise titration techniques, to mitigate the impact of overshooting and obtain reliable and precise measurements. Understanding the causes, consequences, and solutions related to overshot titrations is crucial in achieving accurate and reproducible results in the field of chemistry. | 0 | Theoretical and Fundamental Chemistry |
In 1887, Heinrich Rudolf Hertz discovered but could not explain the photoelectric effect, which was later explained in 1905 by Albert Einstein (Nobel Prize in Physics 1921). Two years after Einsteins publication, in 1907, P.D. Innes experimented with a Röntgen tube, Helmholtz coils, a magnetic field hemisphere (an electron kinetic energy analyzer), and photographic plates, to record broad bands of emitted electrons as a function of velocity, in effect recording the first XPS spectrum. Other researchers, including Henry Moseley, Rawlinson and Robinson, independently performed various experiments to sort out the details in the broad bands. After WWII, Kai Siegbahn and his research group in Uppsala (Sweden) developed several significant improvements in the equipment, and in 1954 recorded the first high-energy-resolution XPS spectrum of cleaved sodium chloride (NaCl), revealing the potential of XPS. A few years later in 1967, Siegbahn published a comprehensive study of XPS, bringing instant recognition of the utility of XPS and also the first hard X-ray photoemission experiments, which he referred to as Electron Spectroscopy for Chemical Analysis (ESCA). In cooperation with Siegbahn, a small group of engineers (Mike Kelly, Charles Bryson, Lavier Faye, Robert Chaney) at Hewlett-Packard in the US, produced the first commercial monochromatic XPS instrument in 1969. Siegbahn received the Nobel Prize for Physics in 1981, to acknowledge his extensive efforts to develop XPS into a useful analytical tool. In parallel with Siegbahns work, David Turner at Imperial College London (and later at Oxford University) developed ultraviolet photoelectron spectroscopy (UPS) for molecular species using helium lamps. | 0 | Theoretical and Fundamental Chemistry |
For polystyrene the complete mechanism of photo-oxidation is still a matter of debate, as different pathways may operate concurrently and vary according to the wavelength of the incident light.
Regardless, there is agreement on the major steps.
Pure polystyrene should not be able to absorb light with a wavelength below ~280 nm and initiation is explained though photo-labile impurities (hydroperoxides) and charge transfer complexes, all of which are able to absorb normal sunlight. Charge-transfer complexes of oxygen and polystyrene phenyl groups absorb light to form singlet oxygen, which acts as a radical initiator. Carbonyl impurities in the polymer (c.f. acetophenone) also absorb light in the near ultraviolet range (300 to 400 nm), forming excited ketones able to abstract hydrogen atoms directly from the polymer. Hyroperoxide undergoes photolysis to form hydroxyl and alkoxyl radicals.
These initiation steps generate macroradicals at tertiary sites, as these are more stabilised. The propagation steps are essentially identical to those seen for polyolefins; with oxidation, hydrogen abstraction and photolysis leading to beta scission reactions and increasing numbers of radicals.
These steps account for the majority of chain-breaking, however in a minor pathway the hydroperoxide reacts directly with polymer to form a ketone group (acetophenone) and a terminal alkene without the formation of additional radicals.
Polystyrene is observed to yellow during photo-oxidation, which is attributed to the formation of polyenes from these terminal alkenes. | 0 | Theoretical and Fundamental Chemistry |
In fluid mechanics, specific weight represents the force exerted by gravity on a unit volume of a fluid. For this reason, units are expressed as force per unit volume (e.g., N/m or lbf/ft). Specific weight can be used as a characteristic property of a fluid. | 0 | Theoretical and Fundamental Chemistry |
The effect is named after the German physicist Johannes Stark, who discovered it in 1913. It was independently discovered in the same year by the Italian physicist Antonino Lo Surdo, and in Italy it is thus sometimes called the Stark–Lo Surdo effect. The discovery of this effect contributed importantly to the development of quantum theory and Stark was awarded with the Nobel Prize in Physics in the year 1919.
Inspired by the magnetic Zeeman effect, and especially by Hendrik Lorentz's explanation of it, Woldemar Voigt performed classical mechanical calculations of quasi-elastically bound electrons in an electric field. By using experimental indices of refraction he gave an estimate of the Stark splittings. This estimate was a few orders of magnitude too low. Not deterred by this prediction, Stark undertook measurements on excited states of the hydrogen atom and succeeded in observing splittings.
By the use of the Bohr–Sommerfeld ("old") quantum theory, Paul Epstein and Karl Schwarzschild were independently able to derive equations for the linear and quadratic Stark effect in hydrogen. Four years later, Hendrik Kramers derived formulas for intensities of spectral transitions. Kramers also included the effect of fine structure, with corrections for relativistic kinetic energy and coupling between electron spin and orbital motion. The first quantum mechanical treatment (in the framework of Werner Heisenberg's matrix mechanics) was by Wolfgang Pauli. Erwin Schrödinger discussed at length the Stark effect in his third paper on quantum theory (in which he introduced his perturbation theory), once in the manner of the 1916 work of Epstein (but generalized from the old to the new quantum theory) and once by his (first-order) perturbation approach.
Finally, Epstein reconsidered the linear and quadratic Stark effect from the point of view of the new quantum theory. He derived equations for the line intensities which were a decided improvement over Kramers's results obtained by the old quantum theory.
While the first-order-perturbation (linear) Stark effect in hydrogen is in agreement with both the old Bohr–Sommerfeld model and the quantum-mechanical theory of the atom, higher-order corrections are not. Measurements of the Stark effect under high field strengths confirmed the correctness of the new quantum theory. | 0 | Theoretical and Fundamental Chemistry |
Stacking is the stabilizing interaction between the flat surfaces of adjacent bases. Stacking can happen with any face of the base, that is 5-5, 3-3, and vice versa.
Stacking in "free" nucleic acid molecules is mainly contributed by intermolecular force, specifically electrostatic attraction among aromatic rings, a process also known as pi stacking. For biological systems with water as a solvent, hydrophobic effect contributes and helps in formation of a helix. Stacking is the main stabilizing factor in the DNA double helix.
Contribution of stacking to the free energy of the molecule can be experimentally estimated by observing the bent-stacked equilibrium in nicked DNA. Such stabilization is dependent on the sequence. The extent of the stabilization varies with salt concentrations and temperature. | 1 | Applied and Interdisciplinary Chemistry |
In aquatic toxicology, the sediment quality triad (SQT) approach has been used as an assessment tool to evaluate the extent of sediment degradation resulting from contaminants released due to human activity present in aquatic environments (Chapman, 1990). This evaluation focuses on three main components: 1.) sediment chemistry, 2.) sediment toxicity tests using aquatic organisms, and 3.) the field effects on the benthic organisms (Chapman, 1990). Often used in risk assessment, the combination of three lines of evidence can lead to a comprehensive understanding of the possible effects to the aquatic community (Chapman, 1997). Although the SQT approach does not provide a cause-and-effect relationship linking concentrations of individual chemicals to adverse biological effects, it does provide an assessment of sediment quality commonly used to explain sediment characteristics quantitatively. The information provided by each portion of the SQT is unique and complementary, and the combination of these portions is necessary because no single characteristic provides comprehensive information regarding a specific site (Chapman, 1997) | 1 | Applied and Interdisciplinary Chemistry |
3,4,5,14,15,16-hexamethoxy-9,10-dimethyltricyclo[10.4.0.02,7]hexadeca-1(16),2,4,6,12,14-hexaen-9-ol
Computed by Lexichem TK 2.7.0 (PubChem release 2021.05.07) | 0 | Theoretical and Fundamental Chemistry |
Through studies using mammalian model organisms, there are two main hypotheses for the location of oxygen sensing in chemoreceptor cells: the membrane hypothesis and the mitochondrial hypothesis. The membrane hypothesis was proposed for the carotid body in mice, and it predicts that oxygen sensing is an ion balance initiated process. The mitochondrial hypothesis was also proposed for the carotid body of mice, but it relies on the levels of oxidative phosphorylation and/or reactive oxygen species (ROS) production as a cue for hypoxia. Specifically, the oxygen sensitive K currents are inhibited by HO and NADPH oxidase activation. There is evidence for both of these hypotheses depending on the species used for the study. For the neuroepithelial cells in the zebrafish gills, there is strong evidence supporting the "membrane hypothesis" due to their capacity to respond to hypoxia after removal of the contents of the cell. However, there is no evidence against multiple sites for oxygen sensing in organisms. | 0 | Theoretical and Fundamental Chemistry |
In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices. Space groups are classified into crystal systems according to their point groups, and into lattice systems according to their Bravais lattices. Crystal systems that have space groups assigned to a common lattice system are combined into a crystal family.
The seven crystal systems are triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic. Informally, two crystals are in the same crystal system if they have similar symmetries (albeit there are many exceptions). | 0 | Theoretical and Fundamental Chemistry |
In coordination chemistry, a binucleating ligand binds two metals. Much attention has been directed toward such ligands that hold metals side-by-side, such that the pair of metals can bind substrates cooperatively.
A variety of metalloenzymes feature bimetallic active sites. Examples include superoxide dismutase, urease, nickel-iron hydrogenase. Many Non-heme iron proteins have diiron active sites, e.g. ribonucleotide reductase and hemerythrin. | 0 | Theoretical and Fundamental Chemistry |
Carboranes have been prepared by many routes, the most common being addition of alkynyl reagents to boron hydride clusters to form dicarbon carboranes. For this reason, the great majority of carborane have two carbon vertices. | 0 | Theoretical and Fundamental Chemistry |
An orbifold can be viewed as a polygon with face, edges, and vertices which can be unfolded to form a possibly infinite set of polygons which tile either the sphere, the plane or the hyperbolic plane. When it tiles the plane it will give a wallpaper group and when it tiles the sphere or hyperbolic plane it gives either a spherical symmetry group or Hyperbolic symmetry group. The type of space the polygons tile can be found by calculating the Euler characteristic, χ = V − E + F, where V is the number of corners (vertices), E is the number of edges and F is the number of faces. If the Euler characteristic is positive then the orbifold has an elliptic (spherical) structure; if it is zero then it has a parabolic structure, i.e. a wallpaper group; and if it is negative it will have a hyperbolic structure. When the full set of possible orbifolds is enumerated it is found that only 17 have Euler characteristic 0.
When an orbifold replicates by symmetry to fill the plane, its features create a structure of vertices, edges, and polygon faces, which must be consistent with the Euler characteristic. Reversing the process, one can assign numbers to the features of the orbifold, but fractions, rather than whole numbers. Because the orbifold itself is a quotient of the full surface by the symmetry group, the orbifold Euler characteristic is a quotient of the surface Euler characteristic by the order of the symmetry group.
The orbifold Euler characteristic is 2 minus the sum of the feature values, assigned as follows:
*A digit n without or before a * counts as .
*A digit n after a * counts as .
*Both * and × count as 1.
*The "no symmetry" o counts as 2.
For a wallpaper group, the sum for the characteristic must be zero; thus the feature sum must be 2.
;Examples
Now enumeration of all wallpaper groups becomes a matter of arithmetic, of listing all feature strings with values summing to 2.
Feature strings with other sums are not nonsense; they imply non-planar tilings, not discussed here. (When the orbifold Euler characteristic is negative, the tiling is hyperbolic; when positive, spherical or bad). | 0 | Theoretical and Fundamental Chemistry |
A tetrose diphosphate molecule, D-threose 2,4-diphosphate, was discovered to be an inhibitor of glyceraldehyde 3-phosphate dehydrogenase. Glyceraldehyde 3-phosphate dehydrogenase is the sixth enzyme used in the glycolysis pathway, and its function is to convert glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate. This tetrose diphosphate molecule inhibits the G3P dehydrogenase from performing catalysis because it oxidizes the enzyme by binding to it at the active site. When tetrose diphosphate is bound to the enzyme, the active site of the enzyme is blocked; therefore phosphorolysis of G3P is unable to occur. High concentrations of tetrose diphosphate must be used to outcompete the substrate, G3P, and block the function of G3P dehydrogenase. With the function of glyceraldehyde 3-phosphate dehydrogenase lost, glycolysis cannot proceed.
D-erythrose 4-phosphate was found to be an inhibitor of phosphoglucose isomerase. Phosphoglucose isomerase is the second enzyme in the glycolysis pathway, and its role is to convert glucose 6-phosphate into fructose 6-phosphate.
In both of these cases, the tetrose is an inhibitor of an enzyme in the glycolysis pathway, preventing it from proceeding onward. | 1 | Applied and Interdisciplinary Chemistry |
Pervious concrete is widely available, can bear frequent traffic, and is universally accessible. Pervious concrete quality depends on the installer's knowledge and experience. | 1 | Applied and Interdisciplinary Chemistry |
The bacterial photosynthetic reaction center has been an important model to understand the structure and chemistry of the biological process of capturing light energy. In the 1960s, Roderick Clayton was the first to purify the reaction center complex from purple bacteria. However, the first crystal structure (upper image at right) was determined in 1984 by Hartmut Michel, Johann Deisenhofer and Robert Huber for which they shared the Nobel Prize in 1988. This was also significant for being the first 3D crystal structure of any membrane protein complex.
Four different subunits were found to be important for the function of the photosynthetic reaction center. The L and M subunits, shown in blue and purple in the image of the structure, both span the lipid bilayer of the plasma membrane. They are structurally similar to one another, both having 5 transmembrane alpha helices. Four bacteriochlorophyll b (BChl-b) molecules, two bacteriopheophytin b molecules (BPh) molecules, two quinones (Q and Q), and a ferrous ion are associated with the L and M subunits. The H subunit, shown in gold, lies on the cytoplasmic side of the plasma membrane. A cytochrome subunit, not shown here, contains four c-type hemes and is located on the periplasmic surface (outer) of the membrane. The latter sub-unit is not a general structural motif in photosynthetic bacteria. The L and M subunits bind the functional and light-interacting cofactors, shown here in green.
Reaction centers from different bacterial species may contain slightly altered bacterio-chlorophyll and bacterio-pheophytin chromophores as functional co-factors. These alterations cause shifts in the colour of light that can be absorbed. The reaction center contains two pigments that serve to collect and transfer the energy from photon absorption: BChl and Bph. BChl roughly resembles the chlorophyll molecule found in green plants, but, due to minor structural differences, its peak absorption wavelength is shifted into the infrared, with wavelengths as long as 1000 nm. Bph has the same structure as BChl, but the central magnesium ion is replaced by two protons. This alteration causes both an absorbance maximum shift and a lowered redox potential. | 0 | Theoretical and Fundamental Chemistry |
The reaction mechanism for the industrial Wacker process (olefin oxidation via palladium(II) chloride) has received significant attention for several decades. Aspects of the mechanism are still debated. A modern formulation is described below:
The initial stoichiometric reaction was first reported by Phillips. The net reaction can also be described as follows:
:[PdCl] + CH + HO → CHCHO + Pd + 2 HCl + 2 Cl
This conversion is followed by reactions that regenerate the Pd(II) catalyst:
: Pd + 2 CuCl + 2 Cl → [PdCl] + 2 CuCl
: 2 CuCl + O + 2 HCl → 2 CuCl + HO
Only the alkene and oxygen are consumed. Without copper(II) chloride as an oxidizing agent, Pd(0) metal (resulting from beta-hydride elimination of Pd(II) in the final step) would precipitate, stopping the reaction after one cycle. This stoichiometric reaction was discovered in 1894. Air, pure oxygen, or a number of other reagents can then oxidise the resultant CuCl-chloride mixture back to CuCl, allowing the cycle to continue. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, the Murai reaction is an organic reaction that uses C-H activation to create a new C-C bond between a terminal or strained internal alkene and an aromatic compound using a ruthenium catalyst. The reaction, named after Shinji Murai, was first reported in 1993. While not the first example of C-H activation, the Murai reaction is notable for its high efficiency and scope. Previous examples of such hydroarylations required more forcing conditions and narrow scope. | 0 | Theoretical and Fundamental Chemistry |
To identify the putative functions and annotations of the genes, MG-RAST follows a multi-step process. Initially, it builds clusters of proteins at a 90% identity level using the UCLUST implementation in QIIME. The longest sequence within each cluster is then selected for further analysis.
For the similarity analysis, MG-RAST employs sBLAT, a parallelized version of the BLAT algorithm using OpenMP. The search is conducted against a protein database derived from the M5nr, which integrates nonredundant sequences from various databases such as GenBank, SEED, IMG, UniProt, KEGG, and eggNOGs.
In the case of reads associated with rRNA sequences, a clustering step is performed at a 97% identity level. The longest sequence from each cluster is chosen as the representative and is used for a BLAT search against the M5rna database. This database integrates sequences from SILVA, Greengenes, and RDP, providing a comprehensive reference for the analysis of ribosomal RNA sequences. | 1 | Applied and Interdisciplinary Chemistry |
β-TG is a chemoattractant, strongly for fibroblasts and weakly for neutrophils. It is a stimulator of mitogenesis, extracellular matrix synthesis, glucose metabolism, and plasminogen activator synthesis in human fibroblasts.
β-TG also affects megakaryocyte maturation, and thus helps in regulating platelet production. | 1 | Applied and Interdisciplinary Chemistry |
Metastasis is a major cause of cancer deaths, and strategies to prevent or halt invasion are lacking. One study showed that autocrine PDGFR signaling plays an essential role in epithelial-mesenchymal transition (EMT) maintenance in vitro, which is known to correlate well with metastasis in vivo. The authors showed that the metastatic potential of oncogenic mammary epithelial cells required an autocrine PDGF/PDGFR signaling loop, and that cooperation of autocrine PDGFR signaling with oncogenic was required for survival during EMT. Autocrine PDGFR signaling also contributes to maintenance of EMT, possibly through activation of STAT1 and other distinct pathways. In addition, expression of PDGFRα and -β correlated with invasive behavior in human mammary carcinomas. This indicates the numerous pathways through which autocrine signaling can regulate metastatic processes in a tumor. | 1 | Applied and Interdisciplinary Chemistry |
Biomarkers validated by genetic and molecular biology methods can be classified into three types.
* Type 0 — Natural history markers
* Type 1 — Drug activity markers
* Type 2 — Surrogate markers | 1 | Applied and Interdisciplinary Chemistry |
The HUGO Gene Nomenclature Committee is responsible for providing human gene naming guidelines and approving new, unique human gene names and symbols (short identifiers typically created by abbreviating). All human gene names and symbols can be searched online at the HGNC website, and the guidelines for their formation are available there. The guidelines for humans fit logically into the larger scope of vertebrates in general, and the HGNCs remit has recently expanded to assigning symbols to all vertebrate species without an existing nomenclature committee, to ensure that vertebrate genes are named in line with their human orthologs/paralogs. Human gene symbols generally are italicised, with all letters in uppercase (e.g., SHH, for sonic hedgehog). Italics are not necessary in gene catalogs. Protein designations are the same as the gene symbol except that they are not italicised. Like the gene symbol, they are in all caps because human (human-specific or human homolog). mRNAs and cDNAs use the same formatting conventions as the gene symbol. For naming families of genes, the HGNC recommends using a "root symbol" as the root for the various gene symbols. For example, for the peroxiredoxin family, PRDX is the root symbol, and the family members are PRDX1, PRDX2, PRDX3, PRDX4, PRDX5, and PRDX6'. | 1 | Applied and Interdisciplinary Chemistry |
Ribulose-1,5-bisphosphate carboxylase/oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in light-independent (or "dark") part of photosynthesis, including the carbon fixation by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose. It emerged approximately four billion years ago in primordial metabolism prior to the presence of oxygen on Earth. It is probably the most abundant enzyme on Earth. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate (also known as RuBP). | 0 | Theoretical and Fundamental Chemistry |
Advantages cited for the IsaKidd technology include:
* long life – the operational life of the permanent cathodes without repair is said to be over seven years under correct operating conditions for electrowinning applications and over 15 years for electrorefining applications
* reduced labour costs – due to the elimination of the starter-sheet production process and the automation of cathode stripping. The average labour requirement for refineries based on the IsaKidd technology is 0.9 man-hours per tonne of cathode, compared to 2.4 man-hours/t for tank houses using starter sheets. Atlantic Copper personnel reported a figure of 0.43 man-hours/t for the Huelva refinery in Spain in 1998
* no suspension loops – the suspension loops of starter sheets can corrode and thus cause cutting of the electrolytic cell liners. The lack of suspension loops also makes crane handling easier
* improved cathode quality – due to the straight cathode plates, which eliminates short-circuiting, and the lack of bends and other surface irregularities reduces the capture of contaminants such as floating arsenic, antimony and bismuth and other slimes compounds. The elimination of the starter-sheet suspension loops also improved cathode quality. In SX–EW operations, the use of stainless-steel cathode plates eliminates lead flakes and other debris from the cathode copper.
* improved current efficiency – this arises both from eliminating short circuits caused by bent and irregular electrodes and from the shorter cathode cycles possible with the use of the reusable cathode plates. Current efficiencies of over 98% are claimed
* increased refining intensity – this reduces the number of electrolytic cells needed in a refinery and its capital cost because the gap between the anodes and the cathodes can be narrower due to the lower risk of short circuits and because the current density can be increased, making the refining process faster. Refineries operating with the IsaKidd technology can achieve current densities of 330 amperes per square meter (“A/m”) of cathode area, whereas a refinery using starter sheets can only operate at around 240 A/m
* shorter cathode cycles – shorter cathode cycles are possible using the IsaKidd technology, which reduces the metal inventory and means that the refinery or SX–EW operator is paid more quickly
* shorter anode cycles – the higher intensity of the refining also results in about a 12% reduction in anode cycle time, also reducing the metal inventory
* uniform cathode copper sheets for ease of transport – the control over the dimensions of the copper sheets made possible by the IsaKidd technology, provides uniform cathode bundles that can be securely strapped and easily transported (see Figure 7)
* improved safety – elimination of much of the manual handling leads to improved safety conditions in the workplace.
Staff of the Cyprus Miami copper refinery wrote after their installation of the Isa Process technology that: “It is now well proven that tankhouses applying stainless steel cathode technology can consistently produce high quality cathodes while operating at higher cathode current density and at a lower cathode spacing than those used in conventional tankhouses.” | 1 | Applied and Interdisciplinary Chemistry |
β-Catenin has a central role in directing several developmental processes, as it can directly bind transcription factors and be regulated by a diffusible extracellular substance: Wnt. It acts upon early embryos to induce entire body regions, as well as individual cells in later stages of development. It also regulates physiological regeneration processes. | 1 | Applied and Interdisciplinary Chemistry |
The classical types of quantum systems, superconductors and superfluid helium, were discovered in the beginning of the 20th century. Near the end of the 20th century, scientists discovered how to create very dilute atomic or molecular gases, cooled first by laser cooling and then by evaporative cooling. They are trapped using magnetic fields or optical dipole potentials in ultrahigh vacuum chambers. Isotopes which have been used include rubidium (Rb-87 and Rb-85), strontium (Sr-87, Sr-86, and Sr-84) potassium (K-39 and K-40), sodium (Na-23), lithium (Li-7 and Li-6), and hydrogen (H-1). The temperatures to which they can be cooled are as low as a few nanokelvin. The developments have been very fast in the past few years. A team of NIST and the University of Colorado has succeeded in creating and observing vortex quantization in these systems. The concentration of vortices increases with the angular velocity of the rotation, similar to the case of superfluid helium and superconductivity. | 0 | Theoretical and Fundamental Chemistry |
Derived structure parameters that describe constant properties of the overall feedback control system may add useful information for special purposes, e.g. in diagnosis of nonthyroidal illness syndrome or central hypothyroidism. | 1 | Applied and Interdisciplinary Chemistry |
In astronomy, hyperspectral imaging is used to determine a spatially-resolved spectral image. Since a spectrum is an important diagnostic, having a spectrum for each pixel allows more science cases to be addressed. In astronomy, this technique is commonly referred to as integral field spectroscopy, and examples of this technique include FLAMES and SINFONI on the Very Large Telescope, but also the Advanced CCD Imaging Spectrometer on Chandra X-ray Observatory uses this technique. | 0 | Theoretical and Fundamental Chemistry |
Just as relative entropy of "actual from ambient" measures thermodynamic availability, relative entropy of "reality from a model" is also useful even if the only clues we have about reality are some experimental measurements. In the former case relative entropy describes distance to equilibrium or (when multiplied by ambient temperature) the amount of available work, while in the latter case it tells you about surprises that reality has up its sleeve or, in other words, how much the model has yet to learn.
Although this tool for evaluating models against systems that are accessible experimentally may be applied in any field, its application to selecting a statistical model via Akaike information criterion are particularly well described in papers and a book by Burnham and Anderson. In a nutshell the relative entropy of reality from a model may be estimated, to within a constant additive term, by a function of the deviations observed between data and the model's predictions (like the mean squared deviation) . Estimates of such divergence for models that share the same additive term can in turn be used to select among models.
When trying to fit parametrized models to data there are various estimators which attempt to minimize relative entropy, such as maximum likelihood and maximum spacing estimators. | 0 | Theoretical and Fundamental Chemistry |
One major use of genomic libraries is hierarchichal shotgun sequencing, which is also called top-down, map-based or clone-by-clone sequencing. This strategy was developed in the 1980s for sequencing whole genomes before high throughput techniques for sequencing were available. Individual clones from genomic libraries can be sheared into smaller fragments, usually 500bp to 1000bp, which are more manageable for sequencing. Once a clone from a genomic library is sequenced, the sequence can be used to screen the library for other clones containing inserts which overlap with the sequenced clone. Any new overlapping clones can then be sequenced forming a contig. This technique, called chromosome walking, can be exploited to sequence entire chromosomes.
Whole genome shotgun sequencing is another method of genome sequencing that does not require a library of high-capacity vectors. Rather, it uses computer algorithms to assemble short sequence reads to cover the entire genome. Genomic libraries are often used in combination with whole genome shotgun sequencing for this reason. A high resolution map can be created by sequencing both ends of inserts from several clones in a genomic library. This map provides sequences of known distances apart, which can be used to help with the assembly of sequence reads acquired through shotgun sequencing. The human genome sequence, which was declared complete in 2003, was assembled using both a BAC library and shotgun sequencing. | 1 | Applied and Interdisciplinary Chemistry |
This compound is commercially available. It is prepared by exhaustive free radical chlorination of dimethyl carbonate:
:CHOCOCH + 6 Cl → CClOCOCCl + 6 HCl
Triphosgene can be easily recrystallized from hot hexanes. | 0 | Theoretical and Fundamental Chemistry |
Typical rain garden plants are herbaceous perennials and grasses, which are chosen for their porous root structure and high growth rate. Trees and shrubs can also be planted to cover larger areas on the bioretention site. Although specific plants are selected and designed for respective soils and climates, plants that can tolerate both saturated and dry soil are typically used for the rain garden. They need to be maintained for maximum efficiency, and be compatible with adjacent land uses. Native and adapted plants are commonly selected for rain gardens because they are more tolerant of the local climate, soil, and water conditions; have deep and variable root systems for enhanced water infiltration and drought tolerance; increase habitat value, diversity for local ecological communities, and overall sustainability once established. Vegetation with dense and uniform root structure depth helps to maintain consistent infiltration throughout the bioretention system. There can be trade-offs associated with using native plants, including lack of availability for some species, late spring emergence, short blooming season, and relatively slow establishment.
It is important to plant a wide variety of species so the rain garden is functional during all climatic conditions. It is likely that the garden will experience a gradient of moisture levels across its functional lifespan, so some drought tolerant plantings are desirable. There are four categories of a vegetative species’ moisture tolerance that can be considered when choosing plants for a rain garden. Wet soil is constantly full of water with long periods of pooling surface water; this category includes swamp and marsh sites. Moist soil is always slightly damp, and plants that thrive in this category can tolerate longer periods of flooding. Mesic soil is neither very wet nor very dry; plants that prefer this category can tolerate brief periods of flooding. Dry soil is ideal for plants that can withstand long dry periods. Plantings chosen for rain gardens must be able to thrive during both extreme wet and dry spells, since rain gardens periodically swing between these two states. A rain garden in temperate climates will unlikely dry out completely, but gardens in dry climates will need to sustain low soil moisture levels during periods of drought. On the other hand, rain gardens are unlikely to suffer from intense waterlogging, since the function of a rain garden is that excess water is drained from the site. Plants typically found in rain gardens are able to soak up large amounts of rainfall during the year as an intermediate strategy during the dry season. Transpiration by growing plants accelerates soil drying between storms. Rain gardens perform best using plants that grow in regularly moist soils, because these plants can typically survive in drier soils that are relatively fertile (contain many nutrients).
Chosen vegetation needs to respect site constraints and limitations, and especially should not impede the primary function of bioretention. Trees under power lines, or that up-heave sidewalks when soils become moist, or whose roots seek out and clog drainage tiles can cause expensive damage. Trees generally contribute to bioretention sites the most when they are located close enough to tap moisture in the rain garden depression, yet do not excessively shade the garden and allow for evaporation. That said, shading open surface waters can reduce excessive heating of vegetative habitats. Plants tolerate inundation by warm water for less time than they tolerate cold water because heat drives out dissolved oxygen, thus a plant tolerant of early spring flooding may not survive summer inundation. | 1 | Applied and Interdisciplinary Chemistry |
Some types of separation require complete purification of a certain component. An example is the production of aluminum metal from bauxite ore through electrolysis refining. In contrast, an incomplete separation process may specify an output to consist of a mixture instead of a single pure component. A good example of an incomplete separation technique is oil refining. Crude oil occurs naturally as a mixture of various hydrocarbons and impurities. The refining process splits this mixture into other, more valuable mixtures such as natural gas, gasoline and chemical feedstocks, none of which are pure substances, but each of which must be separated from the raw crude.
In both complete separation and incomplete separation, a series or cascade of separations may be necessary to obtain the desired end products. In the case of oil refining, crude is subjected to a long series of individual distillation steps, each of which produces a different product or intermediate. | 0 | Theoretical and Fundamental Chemistry |
* Recipient of the Royal Family Order of Perak (DK) (6 May 2015).
* Superior Class of the Perak Family Order of Sultan Azlan Shah (DKSA) (18 May 2007)
* Member First Class of the Azlanii Royal Family Order (DKA) | 1 | Applied and Interdisciplinary Chemistry |
Since the discovery of merrilactone A, many methods of total synthesis have been proposed, of which four produce racemic material, and two produce the natural enantiomer. | 0 | Theoretical and Fundamental Chemistry |
Mosander married Hulda Philippina Forsström on 20 December 1832. They had four children, two sets of twins.
Mosander suffered from cataracts in later life. He died in 1858, at his summer house on the island of Lovön, Stockholm County. | 1 | Applied and Interdisciplinary Chemistry |
Methylotrophy refers to the ability of an organism to use C1-compounds as energy sources. These compounds include methanol, methyl amines, formaldehyde, and formate. Several other less common substrates may also be used for metabolism, all of which lack carbon-carbon bonds. Examples of methylotrophs include the bacteria Methylomonas and Methylobacter. Methanotrophs are a specific type of methylotroph that are also able to use methane () as a carbon source by oxidizing it sequentially to methanol (), formaldehyde (), formate (), and carbon dioxide initially using the enzyme methane monooxygenase. As oxygen is required for this process, all (conventional) methanotrophs are obligate aerobes. Reducing power in the form of quinones and NADH is produced during these oxidations to produce a proton motive force and therefore ATP generation. Methylotrophs and methanotrophs are not considered as autotrophic, because they are able to incorporate some of the oxidized methane (or other metabolites) into cellular carbon before it is completely oxidized to (at the level of formaldehyde), using either the serine pathway (Methylosinus, Methylocystis) or the ribulose monophosphate pathway (Methylococcus), depending on the species of methylotroph.
In addition to aerobic methylotrophy, methane can also be oxidized anaerobically. This occurs by a consortium of sulfate-reducing bacteria and relatives of methanogenic Archaea working syntrophically (see below). Little is currently known about the biochemistry and ecology of this process.
Methanogenesis is the biological production of methane. It is carried out by methanogens, strictly anaerobic Archaea such as Methanococcus, Methanocaldococcus, Methanobacterium,
Methanothermus, Methanosarcina, Methanosaeta and Methanopyrus. The biochemistry of methanogenesis is unique in nature in its use of a number of unusual cofactors to sequentially reduce methanogenic substrates to methane, such as coenzyme M and methanofuran. These cofactors are responsible (among other things) for the establishment of a proton gradient across the outer membrane thereby driving ATP synthesis. Several types of methanogenesis occur, differing in the starting compounds oxidized. Some methanogens reduce carbon dioxide () to methane () using electrons (most often) from hydrogen gas () chemolithoautotrophically. These methanogens can often be found in environments containing fermentative organisms. The tight association of methanogens and fermentative bacteria can be considered to be syntrophic (see below) because the methanogens, which rely on the fermentors for hydrogen, relieve feedback inhibition of the fermentors by the build-up of excess hydrogen that would otherwise inhibit their growth. This type of syntrophic relationship is specifically known as interspecies hydrogen transfer. A second group of methanogens use methanol () as a substrate for methanogenesis. These are chemoorganotrophic, but still autotrophic in using as only carbon source. The biochemistry of this process is quite different from that of the carbon dioxide-reducing methanogens. Lastly, a third group of methanogens produce both methane and carbon dioxide from acetate () with the acetate being split between the two carbons. These acetate-cleaving organisms are the only chemoorganoheterotrophic methanogens. All autotrophic methanogens use a variation of the reductive acetyl-CoA pathway to fix and obtain cellular carbon. | 1 | Applied and Interdisciplinary Chemistry |
Ductile iron pipe is highly resistant to internal corrosion in potable water and less aggressive forms of sewage because of the linings applied during manufacturing. Tuberculation, or the deposition of corrosion products on the internal pipe wall has largely been eliminated by the cement mortar lining which provides a physical and chemical barrier to the corrosive water. The first cement lined iron pipe was installed in Charleston, South Carolina, in 1922 and provided 100 years of free-flowing service until the mains were replaced during a routine upgrade to the city's infrastructure in 2022. | 1 | Applied and Interdisciplinary Chemistry |
aOFM (Figure 4) allows continuous on-line monitoring of metabolic processes in the subcutaneous adipose tissue, e.g. glucose and lactate, as well as larger analytes such as insulin (5.9 kDa). The role of polypeptides for metabolic signaling (leptin, cytokine IL-6, TNFα) has also been studied with aOFM. aOFM allows the quantification of proteins (e.g. albumin size: 68 kDa) in adipose tissue and thus opens up the possibility to investigate protein-bound drugs directly in peripheral target tissues, such as highly protein-bound insulin analogues designed for a prolonged, retarded insulin action. Most recently, aOFM has been used to sample agonists to study obesity, lipid metabolism and immune-inflammation. Applications of aOFM include ex vivo studies with tissue explants and preclinical and clinical in vivo studies. | 1 | Applied and Interdisciplinary Chemistry |
The sample surface must be extremely clean for effective RHEED experiments. Contaminants on the sample surface interfere with the electron beam and degrade the quality of the RHEED pattern. RHEED users employ two main techniques to create clean sample surfaces. Small samples can be cleaved in the vacuum chamber prior to RHEED analysis. The newly exposed, cleaved surface is analyzed. Large samples, or those that are not able to be cleaved prior to RHEED analysis can be coated with a passive oxide layer prior to analysis. Subsequent heat treatment under the vacuum of the RHEED chamber removes the oxide layer and exposes the clean sample surface. | 0 | Theoretical and Fundamental Chemistry |
Manfred Schidlowski (13 November 1933 – 3 October 2012) was a German Professor of Geochemistry at the Max-Planck-Institut for Chemistry (Otto-Hahn-Institut) in Mainz. His research was concerned with the biochemistry of the Early Earth with a focus on isotope-biogeochemistry and the evidence of the earliest life processes in Precambrian. Schidlowski is considered the founder of this research direction in Germany and he also shaped international research in isotope biogeochemistry of Precambrian sediments for more than two decades. | 0 | Theoretical and Fundamental Chemistry |
Tumor angiogenesis rely on interactions between endothelial vascular growth factors which can all activate the PI3K/AKT/mTOR in endothelial cells, pericytes, or cancer cells. Example of these growth factors are angiopoietin 1 (ANG1), ANG 2, basic fibroblast growth factor (bFGF), ephrin-B2, vascular endothelial growth factor (VEGF), and members of the tumor growth factor-β (TGFβ) superfamily. One of the major stimuli of angiogenesis is hypoxia, resulting in activation of hypoxia-inducible transcription factors (HIFs) and expression of ANG2, bFGF, PDGF, VEGF, and VEGFR. Inhibition of HIF1α translation by preventing PDGF/PDGFR and VEGF/VEGFR can result from mTOR inhibition. A G0-G1 cell-cycle blockage can be the consequence of inactivation of mTOR in hypoxia-activated pericytes and endothelial cells.
There is some evidence that extended therapy with rapamycin may have effect on AKT and mTORC2 as well. | 1 | Applied and Interdisciplinary Chemistry |
When two carbonyl groups are coupled and undergo a McMurry reaction, there is a possibility of the formation of cycloalkenes under specific conditions. When both carbonyls are within the same molecule and not sufficiently separated from each other, a cycloalkene can be formed through an intramolecular McMurry reaction. | 0 | Theoretical and Fundamental Chemistry |
The signal of mass-independent fractionation of sulfur isotopes, known as MIF-S, correlates with the end of Xe isotope fractionation. During the Great Oxidation Event (GOE), the ozone layer formed when O rose, accounting for the end of the MIF-S signature. The disappearance of the MIF-S signal has been regarded as changing the redox ratio of Earth's surface reservoirs. However, potential memory effects of MIF-S due to oxidative weathering can lead to large uncertainty on the process and chronology of GOE. Compared to the MIF-S signals, hydrodynamic escape of Xe is not affected by the ozone formation and may be even more sensitive to O availability, promising to provide more details about the oxidation history of Earth. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, a selone (also known as a selenoketone) is the structural analog of a ketone where selenium replaces oxygen. Selenium-77 is one of the isotopes of selenium that is stable and naturally occurring, so selenoketone-containing chemicals can be analyzed by nuclear magnetic resonance spectroscopy (NMR). Selones can be used as chiral derivatizing agents for Se-NMR. Chiral oxazolidineselones can be used for stereoselective control of aldol reactions, analogous to the Evans aldol reaction that uses oxazolidinones, which allows Se-NMR to be used to determine the diastereomeric ratio of the aldol product.
Selenobenzophenone reversibly dimerizes. It is known to undergo cycloaddition with 1,3-dienes in a reaction similar to the Diels-Alder reaction. | 0 | Theoretical and Fundamental Chemistry |
Earlier converters, with a false bottom that can be detached and repaired, are still in use. Modern converters have a fixed bottom with plugs for argon purging. The energy optimization furnace (EOF) is a BOF variant associated with a scrap preheater where the sensible heat in the off-gas is used for preheating scrap, located above the furnace roof.
The lance used for blowing has undergone changes. Slagless lances, with a long tapering copper tip, have been employed to avoid jamming of the lance during blowing. Post-combustion lance tips burn the CO generated during blowing into carbon dioxide| and provide additional heat. For slag-free tapping, darts, refractory balls, and slag detectors are employed. Modern converters are fully automated with automatic blowing patterns and sophisticated control systems. | 1 | Applied and Interdisciplinary Chemistry |
Distonic ions are chemical species that contain ionic charges and radical sites in different locations (on separate atoms), unlike regular radicals where the formal charge and unpaired electron are in the same location. These molecular species are created by ionization of either zwitterions or diradicals; ultimately, a neutral molecule loses an electron. Through experimental research distonic radicals have been found to be extremely stable gas phase ions and can be separated into different classes depending on the inherent features of the charged portion of the ion. | 0 | Theoretical and Fundamental Chemistry |
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