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The target of a gene gun is often a callus of undifferentiated plant cells or a group of immature embryos growing on gel medium in a Petri dish. After the DNA-coated gold particles have been delivered to the cells, the DNA is used as a template for transcription (transient expression) and sometimes it integrates into a plant chromosome (stable transformation)
If the delivered DNA construct contains a selectable marker, then stably transformed cells can be selected and cultured using tissue culture methods. For example, if the delivered DNA construct contains a gene that confers resistance to an antibiotic or herbicide, then stably transformed cells may be selected by including that antibiotic or herbicide in the tissue culture media.
Transformed cells can be treated with a series of plant hormones, such as auxins and gibberellins, and each may divide and differentiate into the organized, specialized, tissue cells of an entire plant. This capability of total re-generation is called totipotency. The new plant that originated from a successfully transformed cell may have new traits that are heritable. The use of the gene gun may be contrasted with the use of Agrobacterium tumefaciens and its Ti plasmid to insert DNA into plant cells. See transformation for different methods of transformation in different species. | 1 | Applied and Interdisciplinary Chemistry |
The total radiation intensity of a black body rises as the fourth power of the absolute temperature, as expressed by the Stefan–Boltzmann law. A kitchen oven, at a temperature about double room temperature on the absolute temperature scale (600 K vs. 300 K) radiates 16 times as much power per unit area. An object at the temperature of the filament in an incandescent light bulb—roughly 3000 K, or 10 times room temperature—radiates 10,000 times as much energy per unit area.
As for photon statistics, thermal light obeys Super-Poissonian statistics. | 0 | Theoretical and Fundamental Chemistry |
TCE is also used in the manufacture of a range of fluorocarbon refrigerants such as 1,1,1,2-tetrafluoroethane more commonly known as HFC 134a. TCE was also used in industrial refrigeration applications due to its high heat transfer capabilities and its low-temperature specification. | 1 | Applied and Interdisciplinary Chemistry |
Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper ores consists of a series of physical, chemical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors. | 1 | Applied and Interdisciplinary Chemistry |
In contrast to the rarity of Möbius aromatic ground state molecular systems, there are many examples of pericyclic transition states that exhibit Möbius aromaticity. The classification of a pericyclic transition state as either Möbius or Hückel topology determines whether 4N or 4N + 2 electrons are required to make the transition state aromatic or antiaromatic, and therefore, allowed or forbidden, respectively. Based on the energy level diagrams derived from Hückel MO theory, (4N + 2)-electron Hückel and (4N)-electron Möbius transition states are aromatic and allowed, while (4N + 2)-electron Möbius and (4N)-electron Hückel transition states are antiaromatic and forbidden. This is the basic premise of the Möbius-Hückel concept. | 0 | Theoretical and Fundamental Chemistry |
Single-strand conformation polymorphism (SSCP), or single-strand chain polymorphism, is defined as a conformational difference of single-stranded nucleotide sequences of identical length as induced by differences in the sequences under certain experimental conditions. This property allows sequences to be distinguished by means of gel electrophoresis, which separates fragments according to their different conformations. | 1 | Applied and Interdisciplinary Chemistry |
Deficiencies in vitamin A have been linked to an increased susceptibility to skin infection and inflammation. Vitamin A appears to modulate the innate immune response and maintains homeostasis of epithelial tissues and mucosa through its metabolite, retinoic acid (RA). As part of the innate immune system, toll-like receptors in skin cells respond to pathogens and cell damage by inducing a pro-inflammatory immune response which includes increased RA production. The epithelium of the skin encounters bacteria, fungi and viruses. Keratinocytes of the epidermal layer of the skin produce and secrete antimicrobial peptides (AMPs). Production of AMPs resistin and cathelicidin, are promoted by RA. | 1 | Applied and Interdisciplinary Chemistry |
Organic oxidations take place at the anode. Compounds are reduced at the cathode. Radical intermediates are often invoked. The initial reaction takes place at the surface of the electrode and then the intermediates diffuse into the solution where they participate in secondary reactions.
The yield of an electrosynthesis is expressed both in terms of the chemical yield and current efficiency. Current efficiency is the ratio of Coulombs consumed in forming the products to the total number of Coulombs passed through the cell. Side reactions decrease the current efficiency.
The potential drop between the electrodes determines the rate constant of the reaction. Electrosynthesis is carried out with either constant potential or constant current. The reason one chooses one over the other is due to a trade-off of ease of experimental conditions versus current efficiency. Constant potential uses current more efficiently because the current in the cell decreases with time due to the depletion of the substrate around the working electrode (stirring is usually necessary to decrease the diffusion layer around the electrode). This is not the case under constant current conditions, however. Instead, as the substrate's concentration decreases the potential across the cell increases in order to maintain the fixed reaction rate. This consumes current in side reactions produced outside the target voltage. | 0 | Theoretical and Fundamental Chemistry |
Induction shrink fitting refers to the use of induction heater technology to pre-heat metal components between and thereby causing them to expand and allow for the insertion or removal of another component. Typically the lower temperature range is used on metals such as aluminium and higher temperatures are used on metals such as low/medium carbon steels. The process avoids the changing of mechanical properties whilst allowing components to be worked. Metals typically expand in response to heating and contract on cooling; this dimensional response to temperature change is expressed as a coefficient of thermal expansion. | 1 | Applied and Interdisciplinary Chemistry |
In a review of earlier work on catecholamine biosynthesis, German-British biochemist Hermann Blaschko (1900–1993) wrote: "Our modern knowledge of the biosynthetic pathway for the catecholamines begins in 1939, with the publication of a paper by Peter Holtz and his colleagues: they described the presence in the guinea-pig kidneys of an enzyme that they called dopa decarboxylase, because it catalyzed the formation of dopamine and carbon dioxide from the amino acid L-dopa." The paper by Peter Holtz (1902–1970) and his coworkers referred to in that quote originated from the Institute of Pharmacology in Rostock. Already in that same year, both Blaschko at Cambridge and Holtz in Rostock predicted the entire sequence tyrosine → l-DOPA → oxytyramine = dopamine → noradrenaline → adrenaline. Edith Bülbring, who also had fled National Socialist racism in 1933, demonstrated methylation of noradrenaline to adrenaline in adrenal tissue in Oxford in 1949, and Julius Axelrod detected phenylethanolamine N-methyltransferase in Bethesda, Maryland in 1962. The two remaining enzymes, tyrosine hydroxylase and dopamine β-hydroxylase, were also characterized around 1960.
Even before contributing to the formation pathway, Blaschko had discovered a destruction mechanism. An enzyme tyramine oxidase described in 1928 also oxidized dopamine, noradrenaline and adrenaline. It was later named monoamine oxidase. This seemed to clarify the fate of the catecholamines in the body, but in 1956 Blaschko suggested that, because the oxidation was slow, “other mechanisms of inactivation … will be found to play an important part. Here is a gap in our knowledge which remains to be filled.” Within a year, Axelrod narrowed the gap by showing that dopamine, noradrenaline and adrenaline were O-methylated by catechol-O-methyl transferase. To fill the gap completely, however, the role of membranes had to be appreciated (). | 1 | Applied and Interdisciplinary Chemistry |
In polymer chemistry, reversible-deactivation polymerization (RDP) is a form of polymerization propagated by chain carriers, some of which at any instant are held in a state of dormancy through an equilibrium process involving other species.
An example of reversible-deactivation anionic polymerization (RDAP) is group transfer polymerization of alkyl methacrylates, where the initiator and the dormant state is a silyl ketene acetal.
In the case of reversible-deactivation radical polymerization (RDRP), a majority of the chain must be held in a dormant state to ensure that the concentration of active carriers is sufficiently low as to render chain termination reactions negligible.
Despite having some common features, RDP is distinct from living polymerization which requires a complete absence of termination and irreversible chain transfer. | 0 | Theoretical and Fundamental Chemistry |
Volume fraction is related to mass fraction,
by
where is the constituent density, and is the mixture density. | 0 | Theoretical and Fundamental Chemistry |
Recirculating aquaculture systems (RAS) are used in home aquaria and for fish production where water exchange is limited and the use of biofiltration is required to reduce ammonia toxicity. Other types of filtration and environmental control are often also necessary to maintain clean water and provide a suitable habitat for fish. The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish. To be operated economically commercial RAS must have high fish stocking densities, and many researchers are currently conducting studies to determine if RAS is a viable form of intensive aquaculture. | 1 | Applied and Interdisciplinary Chemistry |
Thermal barrier coatings (TBCs) are used extensively in gas turbine engines to increase component life and engine performance. A coating of about 1-200 µm can reduce the temperature at the superalloy surface by up to 200 K. TBCs are a system of coatings consisting of a bond coat, a thermally grown oxide (TGO), and a thermally insulating ceramic top coat. In most applications, the bond coat is either a MCrAlY (where M=Ni or NiCo) or a Pt modified aluminide coating. A dense bond coat is required to provide protection of the superalloy substrate from oxidation and hot corrosion attack and to form an adherent, slow-growing surface TGO. The TGO is formed by oxidation of the aluminum that is contained in the bond coat. The current (first generation) thermal insulation layer is composed of 7wt % yttria-stabilized zirconia (7YSZ) with a typical thickness of 100–300 µm. Yttria-stabilized zirconia is used due to its low thermal conductivity (2.6W/mK for fully dense material), relatively high coefficient of thermal expansion, and high temperature stability. The electron beam-directed vapor deposition (EB-DVD) process used to apply the TBC to turbine airfoils produces a columnar microstructure with multiple porosity levels. Inter-column porosity is critical to providing strain tolerance (via a low in-plane modulus), as it would otherwise spall on thermal cycling due to thermal expansion mismatch with the superalloy substrate. This porosity reduces the thermal coating's conductivity. | 1 | Applied and Interdisciplinary Chemistry |
Dexmedetomidine, sold under the trade name Precedex among others, is a drug used in humans for sedation. Veterinarians use dexmedetomidine for similar purposes in treating cats, dogs, and horses. It is also used in humans to treat acute agitation associated with schizophrenia or bipolar I or II disorder.
Similar to clonidine, it is a sympatholytic drug that acts as an agonist of α-adrenergic receptors in certain parts of the brain. It was developed by Orion Pharma. | 0 | Theoretical and Fundamental Chemistry |
There are a few common methods for filling the mold cavity: gravity, low-pressure, high-pressure, and vacuum.
Vacuum filling, also known as counter-gravity filling, is more metal efficient than gravity pouring because less material solidifies in the gating system. Gravity pouring only has a 15 to 50% metal yield as compared to 60 to 95% for vacuum pouring. There is also less turbulence, so the gating system can be simplified since it does not have to control turbulence. Plus, because the metal is drawn from below the top of the pool the metal is free from dross and slag, as these are lower density (lighter) and float to the top of the pool. The pressure differential helps the metal flow into every intricacy of the mold. Finally, lower temperatures can be used, which improves the grain structure. The first patented vacuum casting machine and process dates to 1879.
Low-pressure filling uses 5 to 15 psig (35 to 100 kPag) of air pressure to force liquid metal up a feed tube into the mold cavity. This eliminates turbulence found in gravity casting and increases density, repeatability, tolerances, and grain uniformity. After the casting has solidified the pressure is released and any remaining liquid returns to the crucible, which increases yield. | 1 | Applied and Interdisciplinary Chemistry |
Marketing is the wholesale and retail distribution of refined petroleum products to business, industry, government, and public consumers. | 1 | Applied and Interdisciplinary Chemistry |
A phagemid or phasmid is a DNA-based cloning vector, which has both bacteriophage and plasmid properties. These vectors carry, in addition to the origin of plasmid replication, an origin of replication derived from bacteriophage. Unlike commonly used plasmids, phagemid vectors differ by having the ability to be packaged into the capsid of a bacteriophage, due to their having a genetic sequence that signals for packaging. Phagemids are used in a variety of biotechnology applications; for example, they can be used in a molecular biology technique called "Phage Display".
The term (and new word) "phagemid" or "phagemids" was offered to the world science community by a group of Soviet scientists, who discovered them, named them, and published the article in April 1984 in Gene magazine. After that, the world community started using this term. | 1 | Applied and Interdisciplinary Chemistry |
To improve its biophysical properties, derivatives of coelenterazine have been synthesized by means of different procedures including multicomponent strategies. | 1 | Applied and Interdisciplinary Chemistry |
CRISPR gene editing technology in humans has the potential to cause profound social impacts, such as in the long-term prevention of diseases in humans. However, Hes human experiments raised ethical concerns the effect are unknown on future generations. Ethical concerns have been raised relative to the four ethical criteria of autonomy, justice, beneficence, and non-maleficence, first postulated by Tom Beauchamp and James Childress in Principles of Biomedical Ethics'.
The ethical principle of autonomy requires that individuals have the ability and comprehensive information to make their own decisions based on their values and beliefs. He violated this by failing to inform patients of potential risks, including off-target mutations that might be a threat to the twins' lives.
Since He had forged the approval certificate from the hospitals Director of Direct Genomics, the procedure was likely "unlawful", which is against the principle of non-maleficence. Off-target mutations are likely to start at undesired sites, causing cell death or cell transformation. Sonia Ouagrham-Gormley, an associate professor in the Schar School of Policy and Government at George Mason University, and Kathleen Vogel, a professor in the School for the Future of Innovation in Society at Arizona State University, stated that the procedure was "unnecessary" and "risks the safety of the patients". The researchers criticized Hes unethical action by presenting the fact that the prevention of HIV transmission from parents to newborn babies can be safely achieved with existing standard methods, such as sperm washing and caesarian section delivery.
The principle of justice argues that individuals should have the right to receive the same amount of care from medical providers regardless of their social and economic background. Beneficence requires healthcare providers to maximize benefits and put the benefit of the patients first. Hes intervention in the twins genes cannot be justified, and the risk-benefit is unacceptable. He paid the couple $40,000 to ensure that they would keep his operation confidential. This action can be viewed as an inducement and violates China's regulations on the prohibition of genetic manipulation of human gametes, zygotes, and embryos for reproductive purposes; HIV carriers being not allowed to have assisted reproductive technologies, and the manipulation of a human embryo for research being only permitted within 14 days.
Thus, while genome editing in humans has potential as an effective and cost-efficient method for manipulating genes within living cells, it requires more research and transparent procedures to be ethically justified. | 1 | Applied and Interdisciplinary Chemistry |
The noncanonical Wnt/Ca pathway regulates intracellular calcium levels. Again Wnt binds and activates to Frizzled. In this case however activated Frizzled causes a coupled G-protein to activate a phospholipase (PLC), which interacts with and splits PIP into DAG and IP. IP can then bind to a receptor on the endoplasmic reticulum to release intracellular calcium stores, to induce calcium-dependent gene expression. | 1 | Applied and Interdisciplinary Chemistry |
Although available commercially, diethyl azodicarboxylate can be prepared fresh in the laboratory, especially if required in pure, non-diluted form. A two-step synthesis starts from hydrazine, first by alkylation with ethyl chloroformate, followed by treating the resulting diethyl hydrazodicarboxylate with chlorine (bubbling through the solution), hypochlorous acid, concentrated nitric acid or red fuming nitric acid. The reaction is carried out in an ice bath, and the reagents are added dropwise so that the temperature does not rise above 20 °C. Diethyl hydrazodicarboxylate is a solid with melting temperature of 131–133 °C which is collected as a residue; it is significantly more stable to heating than DEAD and is conventionally dried at a temperature of about 80 °C. | 0 | Theoretical and Fundamental Chemistry |
*ADRBK1 can downregulate response to epinephrine
*AGPAT1 acyl 3 phosphoglycerol acyl transferase
*ARF1
*ARF3
*ARF4
*ARF5
*ARL2 RAS Superfamily
*CSF1 Colony stimulating factor not highly expressed constitutively at 5-12
*CSK C-src tyrosine kinase
*DCT dopachrome tautomerase
*EFNA3
*FKBP1A
*GDI1 GDP Dissociation inhibitor (Rab family)
*GNAS1 ubiquitously expressed, but differentially imprinted
*GNAI2
*HAX1 associated with tyrosine kinases
*ILK Integrin linked kinase
*MAPKAPK2
*MAP2K2
*MAP3K11
*PITPNM Phosphatidylinositol transfer protein
*RAC1 Ro GTPase involved with many signaling pathways
*RAP1B GTPase involved with cell adhesion
*RAGA Ras-related GTP Binding
*STK19
*STK24 Serine/Threonine Kinase
*STK25
*YWHAB Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, beta polypeptide
*YWHAH Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, h polypeptide
*YWHAQ Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, theta polypeptide
*YWHAZ Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, zeta polypeptide | 1 | Applied and Interdisciplinary Chemistry |
About half of Richards's scientific research concerned atomic weights, starting in 1886 with his graduate studies. On returning to Harvard in 1889, this was his first line of research, continuing up to his death. According to Forbes, by 1932 the atomic weights of 55 elements had been studied by Richards and his students. Among the potential sources of error Richards uncovered in such determinations was the tendency of certain salts to occlude gases or foreign solutes on precipitation. As an example of the care Richards used in his work, Emsley reports that he carried out 15,000 recrystallizations of thulium bromate in order to obtain the pure element thulium for an atomic weight measurement.
Richards was the first to show, by chemical analysis, that an element could have different atomic weights. He was asked to analyze samples of naturally occurring lead and lead produced by radioactive decay. His measurements showed that the two samples had different atomic weights, supporting the concepts of isotopes.
Although Richardss chemical determinations of atomic weights were highly significant for their time, they have largely been superseded. Modern scientists use electronic instrumentation, such as mass spectrometers, to determine both the masses and the abundances of an elements isotopes. From this information, an average atomic mass can be calculated, and compared to the values measured by Richards. The modern methods are faster and more sensitive than those on which Richards had to rely, but not necessarily less expensive.
Other scientific work of Theodore Richards included investigations of the compressibilities of atoms, heats of solution and neutralization, and the electrochemistry of amalgams. His investigation of electrochemical potentials at low temperatures was among the work that led, in the hands of others, to the Nernst heat theorem and the Third law of thermodynamics, although not without heated debate between Nernst and Richards.
Richards also is credited with the invention of the adiabatic calorimeter as well as the nephelometer, which was devised for his work on the atomic weight of strontium. | 1 | Applied and Interdisciplinary Chemistry |
Pyroelectric biosensors generate an electric current as a result of a temperature change. This differential induces a polarization in the substance, producing a dipole moment in the direction of the temperature gradient. The result is a net voltage across the material. This net voltage can be calculated by the following equation.
where V = Voltage,
ω = angular frequency of the modulated incident,
P = pyroelectric coefficient,
L = film thickness,
ε = film dielectric constant,
A = area of film,
r = resistance of the film,
C = capacitance of the film,
τE = electrical time constant of the detector output. | 1 | Applied and Interdisciplinary Chemistry |
The theorem of Torricelli was employed by many succeeding writers, but particularly by Edme Mariotte (1620–1684), whose Traité du mouvement des eaux, published after his death in the year 1686, is founded on a great variety of well-conducted experiments on the motion of fluids, performed at Versailles and Chantilly. In the discussion of some points he committed considerable mistakes. Others he treated very superficially, and in none of his experiments apparently did he attend to the diminution of efflux arising from the contraction of the liquid vein, when the orifice is merely a perforation in a thin plate; but he appears to have been the first who attempted to ascribe the discrepancy between theory and experiment to the retardation of the water's velocity through friction. His contemporary Domenico Guglielmini (1655–1710), who was inspector of the rivers and canals at Bologna, had ascribed this diminution of velocity in rivers to transverse motions arising from inequalities in their bottom. But as Mariotte observed similar obstructions even in glass pipes where no transverse currents could exist, the cause assigned by Guglielmini seemed destitute of foundation. The French philosopher, therefore, regarded these obstructions as the effects of friction. He supposed that the filaments of water which graze along the sides of the pipe lose a portion of their velocity; that the contiguous filaments, having on this account a greater velocity, rub upon the former, and suffer a diminution of their celerity; and that the other filaments are affected with similar retardations proportional to their distance from the axis of the pipe. In this way the medium velocity of the current may be diminished, and consequently the quantity of water discharged in a given time must, from the effects of friction, be considerably less than that which is computed from theory. | 1 | Applied and Interdisciplinary Chemistry |
Grating monochromators disperse ultraviolet, visible, and infrared radiation typically using replica gratings, which are manufactured from a master grating. A master grating consists of a hard, optically flat, surface that has a large number of parallel and closely spaced grooves. The construction of a master grating is a long, expensive process because the grooves must be of identical size, exactly parallel, and equally spaced over the length of the grating (3–10 cm). A grating for the ultraviolet and visible region typically has 300–2000 grooves/mm, however 1200–1400 grooves/mm is most common. For the infrared region, gratings usually have 10–200 grooves/mm. When a diffraction grating is used, care must be taken in the design of broadband monochromators because the diffraction pattern has overlapping orders. Sometimes broadband preselector filters are inserted in the optical path to limit the width of the diffraction orders so they do not overlap. Sometimes this is done by using a prism as one of the monochromators of a dual monochromator design.
The original high-resolution diffraction gratings were ruled. The construction of high-quality ruling engines was a large undertaking (as well as exceedingly difficult, in past decades), and good gratings were very expensive. The slope of the triangular groove in a ruled grating is typically adjusted to enhance the brightness of a particular diffraction order. This is called blazing a grating. Ruled gratings have imperfections that produce faint "ghost" diffraction orders that may raise the stray light level of a monochromator. A later photolithographic technique allows gratings to be created from a holographic interference pattern. Holographic gratings have sinusoidal grooves and so are not as bright, but have lower scattered light levels than blazed gratings. Almost all the gratings actually used in monochromators are carefully made replicas of ruled or holographic master gratings. | 0 | Theoretical and Fundamental Chemistry |
The Vietnam War was fought between North Vietnam (with support from Communist countries such as Soviet Union and China) and South Vietnam (with support from the United States and its allies). The conflicts began in 1954 and became large-scale battles by 1961. Although in a better warfare position, the Peoples Army of Vietnam (North Vietnamese Army) and its allies in the South, Viet Cong, suffered increasing mortality because of malaria epidemics. In some battlefields, the disease would reduce military strengths by half and in severe cases, disable 90% of the troops. North Vietnamese Prime Minister Ho Chih Minh asked Chinese Premier Zhou Enlai for medical help. The year before, party Chairman Mao Zedong had introduced the Cultural Revolution, during which he would close schools and universities and banish scientists and intellectuals. Mao took Hos plea seriously and approved a military project. On 23 May 1967, about six hundred scientists convened. These included military personnel, scientists, and medical practitioners of Western and traditional Chinese medicine. The meeting marked the start of the military-research programme, which received the code name Project 523, after the date (23 May) it launched. The project was divided into three main streams, one for developing synthetic compounds, one for clinical studies (or infection control) and another for investigating traditional Chinese medicine. Classified as a top secret state mission, the project itself saved many scientists from the atrocities of the Cultural Revolution. | 1 | Applied and Interdisciplinary Chemistry |
Manganese is an essential human dietary element. It is present as a coenzyme in several biological processes, which include macronutrient metabolism, bone formation, and free radical defense systems. It is a critical component in dozens of proteins and enzymes. The human body contains about 12 mg of manganese, mostly in the bones. The soft tissue remainder is concentrated in the liver and kidneys. In the human brain, the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes. | 1 | Applied and Interdisciplinary Chemistry |
Shape-memory alloys are typically made by casting, using vacuum arc melting or induction melting. These are specialist techniques used to keep impurities in the alloy to a minimum and ensure the metals are well mixed. The ingot is then hot rolled into longer sections and then drawn to turn it into wire.
The way in which the alloys are "trained" depends on the properties wanted. The "training" dictates the shape that the alloy will remember when it is heated. This occurs by heating the alloy so that the dislocations re-order into stable positions, but not so hot that the material recrystallizes. They are heated to between and for 30 minutes, shaped while hot, and then are cooled rapidly by quenching in water or by cooling with air. | 1 | Applied and Interdisciplinary Chemistry |
*Nitrosyl (NO) binds to metals in one of two extreme geometries - bent where NO is treated as a pseudohalide (NO), and linear, where NO is treated as NO.
*Dioxygen can be non-innocent, since it exists in two oxidation states, superoxide (O) and peroxide (O).
Ligands with extended pi-delocalization such as porphyrins, phthalocyanines, and corroles and ligands with the generalised formulas [D-CR=CR-D] (D = O, S, NR’ and R, R' = alkyl or aryl) are often non-innocent. In contrast, [D-CR=CR-CR=D] such as NacNac or acac are innocent.
*catecholates and related 1,2-dioxalenes.
*dithiolenes, such as maleonitriledithiolate (see example of [Ni(SCPh)] above).
*1,2-diimines such as derivatives of 1,2-diamidobenzene, 2,2-bipyridine, and dimethylglyoxime. The complex Cr(2,2-bipyridine) is a derivative of Cr(III) bound to three bipyridine ligands. On the other hand, one-electron oxidation of [[Ruthenium tris(bipyridine) chloride|Ru(2,2'-bipyridine)]] is localized on Ru and the bipyridine is behaving as a normal, innocent ligand in this case.
*ligands containing ferrocene can have oxidation events centered on the ferrocene iron center rather than the catalytically active metal center.
*pyridine-2,6-diimine ligands can be reduced by one and two electrons. | 0 | Theoretical and Fundamental Chemistry |
The name "mycofactocin" is derived from three words, the genus name "Mycobacterium" (across which it is nearly universal), "cofactor" because its presence in a genome predicts the co-occurrence of certain families of enzymes as if it is a cofactor they require, and "bacteriocin" because a radical SAM enzyme critical to its biosynthesis, MftC, is closely related to the key enzyme for the biosynthesis of subtilosin A, a bacteriocin, from its precursor peptide. | 1 | Applied and Interdisciplinary Chemistry |
Charles Kettering, vice president of General Motors Research Corporation, was seeking a refrigerant replacement that would be colorless, odorless, tasteless, nontoxic, and nonflammable. He assembled a team that included Thomas Midgley, Jr., Albert Leon Henne, and Robert McNary. From 1930 to 1935, they developed dichlorodifluoromethane (CClF or R12), trichlorofluoromethane (CClF or R11), chlorodifluoromethane (CHClF or R22), trichlorotrifluoroethane (CClFCClF or R113), and dichlorotetrafluoroethane (CClFCClF or R114), through Kinetic Chemicals which was a joint venture between DuPont and General Motors. | 1 | Applied and Interdisciplinary Chemistry |
Benzoyl chloride is produced from benzotrichloride using either water or benzoic acid:
As with other acyl chlorides, it can be generated from the parent acid and other chlorinating agents phosphorus pentachloride or thionyl chloride.
Representative laboratory routes to aromatic acyl halides are comparable to those for aliphatic acyl halides. For example, chloroformylation, a specific type of Friedel-Crafts acylation which uses formaldehyde as a reagent, or by the direct chlorination of benzaldehyde derivatives. | 0 | Theoretical and Fundamental Chemistry |
In the mitochondrion, pyruvate is oxidized by the pyruvate dehydrogenase complex to the acetyl group, which is fully oxidized to carbon dioxide by the citric acid cycle (also known as the Krebs cycle). Every "turn" of the citric acid cycle produces two molecules of carbon dioxide, one equivalent of ATP guanosine triphosphate (GTP) through substrate-level phosphorylation catalyzed by succinyl-CoA synthetase, as succinyl-CoA is converted to succinate, three equivalents of NADH, and one equivalent of FADH. NADH and FADH are recycled (to NAD and FAD, respectively) by oxidative phosphorylation, generating additional ATP. The oxidation of NADH results in the synthesis of 2–3 equivalents of ATP, and the oxidation of one FADH yields between 1–2 equivalents of ATP. The majority of cellular ATP is generated by this process. Although the citric acid cycle itself does not involve molecular oxygen, it is an obligately aerobic process because O is used to recycle the NADH and FADH. In the absence of oxygen, the citric acid cycle ceases.
The generation of ATP by the mitochondrion from cytosolic NADH relies on the malate-aspartate shuttle (and to a lesser extent, the glycerol-phosphate shuttle) because the inner mitochondrial membrane is impermeable to NADH and NAD. Instead of transferring the generated NADH, a malate dehydrogenase enzyme converts oxaloacetate to malate, which is translocated to the mitochondrial matrix. Another malate dehydrogenase-catalyzed reaction occurs in the opposite direction, producing oxaloacetate and NADH from the newly transported malate and the mitochondrion's interior store of NAD. A transaminase converts the oxaloacetate to aspartate for transport back across the membrane and into the intermembrane space.
In oxidative phosphorylation, the passage of electrons from NADH and FADH through the electron transport chain releases the energy to pump protons out of the mitochondrial matrix and into the intermembrane space. This pumping generates a proton motive force that is the net effect of a pH gradient and an electric potential gradient across the inner mitochondrial membrane. Flow of protons down this potential gradient – that is, from the intermembrane space to the matrix – yields ATP by ATP synthase. Three ATP are produced per turn.
Although oxygen consumption appears fundamental for the maintenance of the proton motive force, in the event of oxygen shortage (hypoxia), intracellular acidosis (mediated by enhanced glycolytic rates and ATP hydrolysis), contributes to mitochondrial membrane potential and directly drives ATP synthesis.
Most of the ATP synthesized in the mitochondria will be used for cellular processes in the cytosol; thus it must be exported from its site of synthesis in the mitochondrial matrix. ATP outward movement is favored by the membrane's electrochemical potential because the cytosol has a relatively positive charge compared to the relatively negative matrix. For every ATP transported out, it costs 1 H. Producing one ATP costs about 3 H. Therefore, making and exporting one ATP requires 4H The inner membrane contains an antiporter, the ADP/ATP translocase, which is an integral membrane protein used to exchange newly synthesized ATP in the matrix for ADP in the intermembrane space. | 1 | Applied and Interdisciplinary Chemistry |
Vitamin A toxicity (hypervitaminosis A) occurs when too much vitamin A accumulates in the body. It comes from consumption of preformed vitamin A but not of carotenoids, as conversion of the latter to retinol is suppressed by the presence of adequate retinol. | 1 | Applied and Interdisciplinary Chemistry |
In Denmark, modafinil is a prescription drug but not listed as a controlled substance. According to the Danish Medicines Agency, modafinil is approved for use in the treatment of narcolepsy, still, importing modafinil to Denmark is considered illegal without a valid prescription.
In Finland, modafinil is a prescription drug but not listed as a controlled substance. Finland is a member of the European Union, and it is illegal to import prescription medicine from outside the European Union unless the person has a valid prescription.
In the Republic of Moldova, modafinil is classified as a psychotropic drug (included in table III list 3 which is the list of psychotropic substances as defined by the Government) and is available by prescription. Importation of modafinil may be considered illegal and subject to severe penalties, even if you have a prescription. For example, on June 29, 2017, postal officers discovered 60 tablets of Modalert (200 mg modafinil tablets) in a parcel sent from India to a resident in Chișinău, Moldova. The prohibited substance was detected during a routine scan and was seized as illegal. The authorities were notified of the incident and the recipient was charged with criminal penalties. In the Transnistria region of Moldova, modafinil is completely prohibited, due to application of the legislation similar to that of Russia where modafinil is completely prohibited and is in the same list as narcotics. Possession or an attempt to bring modafinil to Transnistria potentially leads to imprisonment.
In Romania, modafinil is classified as a stimulant doping agent and is prohibited in sports competitions. In 2022, laws were passed making its importation or sale a felony, punishable by three to seven years in jail. Simple possession for personal use may result in a fine and confiscation.
In Sweden, modafinil is classified as a schedule IV substance, which means that it is considered to have low potential for abuse and low risk of dependence. Still, possession is illegal without prescription.
In the United Kingdom, it is not listed in Misuse of Drugs Act, so possession is not illegal, but a prescription is required. | 0 | Theoretical and Fundamental Chemistry |
Several groups have applied atomic manipulation techniques for artistic purposes to demonstrate control over the adatom positions. These include various institutional logos and a movie called “A Boy and His Atom” composed of individual STM scans by IBM researchers.
Several notable condensed matter physics experiments have been realized with atomic manipulation techniques. These include the demonstration of electron confinement in so-called quantum corrals by Michael F. Crommie et al., and the subsequent Quantum mirage experiment, where the Kondo signature of an adatom was reflected from one focus to another in an elliptical quantum corral.
Atomic manipulation has also sparked interest as a computation platform. Andreas J. Heinrich et al. built logic gates out of molecular cascades of CO adsorbates, and Kalff et al. demonstrated a rewritable kilobyte memory made of individual atoms.
Recent experiments on artificial lattice structures have utilized atomic manipulation techniques to study the electronic properties of Lieb lattices, artificial graphene and Sierpiński triangles. | 0 | Theoretical and Fundamental Chemistry |
The optically pumped caesium vapour magnetometer is a highly sensitive (300 fT/Hz) and accurate device used in a wide range of applications. It is one of a number of alkali vapours (including rubidium and potassium) that are used in this way.
The device broadly consists of a photon emitter, such as a laser, an absorption chamber containing caesium vapour mixed with a "buffer gas" through which the emitted photons pass, and a photon detector, arranged in that order. The buffer gas is usually helium or nitrogen and they are used to reduce collisions between the caesium vapour atoms.
The basic principle that allows the device to operate is the fact that a caesium atom can exist in any of nine energy levels, which can be informally thought of as the placement of electron atomic orbitals around the atomic nucleus. When a caesium atom within the chamber encounters a photon from the laser, it is excited to a higher energy state, emits a photon and falls to an indeterminate lower energy state. The caesium atom is "sensitive" to the photons from the laser in three of its nine energy states, and therefore, assuming a closed system, all the atoms eventually fall into a state in which all the photons from the laser pass through unhindered and are measured by the photon detector. The caesium vapour has become transparent. This process happens continuously to maintain as many of the electrons as possible in that state.
At this point, the sample (or population) is said to have been optically pumped and ready for measurement to take place. When an external field is applied it disrupts this state and causes atoms to move to different states which makes the vapour less transparent. The photo detector can measure this change and therefore measure the magnitude of the magnetic field.
In the most common type of caesium magnetometer, a very small AC magnetic field is applied to the cell. Since the difference in the energy levels of the electrons is determined by the external magnetic field, there is a frequency at which this small AC field makes the electrons change states. In this new state, the electrons once again can absorb a photon of light. This causes a signal on a photo detector that measures the light passing through the cell. The associated electronics use this fact to create a signal exactly at the frequency that corresponds to the external field.
Another type of caesium magnetometer modulates the light applied to the cell. This is referred to as a Bell-Bloom magnetometer, after the two scientists who first investigated the effect. If the light is turned on and off at the frequency corresponding to the Earth's field, there is a change in the signal seen at the photo detector. Again, the associated electronics use this to create a signal exactly at the frequency that corresponds to the external field. Both methods lead to high performance magnetometers. | 0 | Theoretical and Fundamental Chemistry |
The Martin Medal is an award given for outstanding contributions to the advancement of separation science. The award is presented by The Chromatographic Society, a UK-based organization promoting all aspects of chromatography and related separation techniques. The award is named after Professor Archer J.P Martin, who contributed to the invention of partition chromatography, and shared the 1952 Nobel Prize in Chemistry. | 0 | Theoretical and Fundamental Chemistry |
Targeting PDE3 with optimal doses and timing, enoximone prevents allergic inflammation in HDM-driven models of allergic airway inflammation. PDE3 inhibitors enoximone and milrinone can be used as a rescue drug in life-threatening bronchial asthma/acute severe asthma. | 1 | Applied and Interdisciplinary Chemistry |
Plutonium selenide is a binary inorganic compound of plutonium and selenium with the chemical formula PuSe. The compound forms black crystals and does not dissolve in water. | 0 | Theoretical and Fundamental Chemistry |
Thevetins are a group of poisonous cardiac glycosides. They are obtained especially from the seeds of a West Indian shrub or small tree (Cascabela thevetia syn. Thevetia nereifolia) of the dogbane family (Apocynaceae). Hydrolysis products include glucose, digitalose, and a sterol. | 1 | Applied and Interdisciplinary Chemistry |
The most effusive solar flares emit across the entire EM spectrum, including γ-rays. The first confident observation occurred in 1972. | 0 | Theoretical and Fundamental Chemistry |
CaCrO is a frustrated kagome bilayer magnet, which does not develop long-range order even below 1 K, and has a diffuse spectrum of gapless excitations. | 0 | Theoretical and Fundamental Chemistry |
Explosive yields can be affected by the introduction of mechanical loads or the application of temperature; such damages are called insults. The mechanism of a thermal insult at low temperatures on an explosive is primarily thermomechanical, at higher temperatures it is primarily thermochemical. | 0 | Theoretical and Fundamental Chemistry |
This isotherm takes into account indirect adsorbate–adsorbate interactions on adsorption isotherms. Temkin noted experimentally that heats of adsorption would more often decrease than increase with increasing coverage.
The heat of adsorption ΔH is defined as
He derived a model assuming that as the surface is loaded up with adsorbate, the heat of adsorption of all the molecules in the layer would decrease linearly with coverage due to adsorbate–adsorbate interactions:
where α is a fitting parameter. Assuming the Langmuir adsorption isotherm still applied to the adsorbed layer, is expected to vary with coverage as follows:
Langmuir's isotherm can be rearranged to
Substituting the expression of the equilibrium constant and taking the natural logarithm: | 0 | Theoretical and Fundamental Chemistry |
Administration of levamlodipine (2.5 mg) as a single dose gives maximum plasma concentration (C) of 8.3 to 9.3 ng/mL in 2 to 3 hrs (T). It is extensively (about 90%) converted to inactive metabolites via hepatic metabolism with 10% of the parent compound and 60% of the metabolites excreted in the urine. Levamlodipine shows approximately 93% plasma protein binding in hypertensive patients. The mean AUC value (t = 48 hrs) of levamlodipine tablets (2.5 mg) is . The plasma elimination half-life of levamlodipine has been found to be . | 0 | Theoretical and Fundamental Chemistry |
A field prototype of SOLID was first tested in 2005 in a simulated Mars drilling expedition called MARTE (Mars Analog Rio Tinto Experiment) where the researchers tested a drill in depth, sample-handling systems, and immunoassays relevant to the search for life in the Martian subsurface. MARTE was funded by the NASA Astrobiology Science and Technology for Exploring Planets (ASTEP) program. Using the sample cores, SOLID successfully detected several biological polymers in extreme environments in different parts of the world, including a deep South African mine, Antarctica's McMurdo Dry Valleys, Yellowstone, Iceland, Atacama Desert in Chile, and in the acid water of Rio Tinto.
Extracts obtained from Mars analogue sites on Earth were added to various perchlorate concentrations at −20 °C for 45 days and then the samples were analyzed with SOLID. The results showed no interference from acidity or from the presence of 50 mM perchlorate which is 20 times higher than that found at the Phoenix landing site. SOLID demonstrated that the chosen antibodies are unaffected by acidity, heat and oxidants such as perchlorates, and it has emerged as a viable choice for an astrobiology mission directly searching for biosignatures.
In 2018, another field test took place at the Atacama Desert with a rover called ARADS (Atacama Rover Astrobiology Drilling Studies) that carried a core drill, SOLID instrument, and another life detection system called Microfluidic Life Analyzer (MILA). MILA processes minuscule volumes of fluid samples to isolate amino acids, which are building blocks of proteins. The rover tested different strategies for searching for potential evidence of life in the soil, and established that roving, drilling and life detection can take place in concert. | 1 | Applied and Interdisciplinary Chemistry |
Steel with an ultimate tensile strength of less than 1000 MPa (~145,000 psi) or hardness of less than HRC 32 on the Hardness Rockwell Scale is not generally considered susceptible to hydrogen embrittlement. As an example of severe hydrogen embrittlement, the elongation at failure of 17-4PH precipitation hardened stainless steel was measured to drop from 17% to only 1.7% when smooth specimens were exposed to high-pressure hydrogen
As the strength of steels increases, the fracture toughness decreases, so the likelihood that hydrogen embrittlement will lead to fracture increases. In high-strength steels, anything above a hardness of HRC 32 may be susceptible to early hydrogen cracking after plating processes that introduce hydrogen. They may also experience long-term failures anytime from weeks to decades after being placed in service due to accumulation of hydrogen over time from cathodic protection and other sources. Numerous failures have been reported in the hardness range from HRC 32-36 and more above; therefore, parts in this range should be checked during quality control to ensure they are not susceptible.
Testing the fracture toughness of hydrogen-charged, embrittled specimens is complicated by the need to keep charged specimens very cold, in liquid nitrogen, to prevent the hydrogen diffusing away. | 0 | Theoretical and Fundamental Chemistry |
hnRNPs also play a role in DNA damage response in coordination with p53. hnRNP K is rapidly induced after DNA damage by ionizing radiation. It cooperates with p53 to induce the activation of p53 target genes, thus activating cell-cycle checkpoints. p53 itself is an important tumor-suppressor gene sometimes known by the epithet “the guardian of the genome.” hnRNP K’s close association with p53 demonstrates its importance in DNA damage control.
p53 regulates a large group of RNAs that are not translated into protein, called large intergenic noncoding RNAs (lincRNAs). p53 suppression of genes is often carried out by a number of these lincRNAs, which in turn have been shown to act though hnRNP K. Through physical interactions with these molecules, hnRNP K is targeted to genes and transmits p53 regulation, thus acting as a key repressor within the p53-dependent transcriptional pathway. | 1 | Applied and Interdisciplinary Chemistry |
Manfred Schidlowski was born in Stettin on 13 November 1933. His family left his homeland during the Second World War and moved to Greifswald. From 1952-1955 he studied at the Humboldt University of Berlin, and from 1956 at the Free University of Berlin, where he received his diploma in geology in 1960 and one year later his doctorate with the "Contribution to the Geology of the Eastern Alps between the Small Walser Valley and the Upper Lech (Vorarlberg, Austria)". His desire for a change in geoscientific content led him to South Africa, first as a postdoctoral researcher at the University of Pretoria and then as a mine geologist for the Anglo-Transvaal Consolidated Investment Co. Ltd. at the Loraine Gold Mine to Allanridge in the Orange Free State. In 1962 he met his future wife Ingrid Piegler, a great-great-granddaughter of Heinrich Gottfried Piegler, he married her in 1964.
Scientifically, he worked on the mineralogy of the gold-bearing Witwatersrand sequence. The discovery of detrital, i.e. sedimentary rearranged pyrites and uraninites as well as the frequently occurring carbonaceous material in these layers founded his scientific interest in the early evolution of the Earth and provided the data for his first Nature publication in 1965 with the title "Probable Life-forms from the Precambrian of the Witwatersrand System (South Africa)".
In 1963 Schidlowski returned to Germany to work on the ores of the Witwatersrand succession in Paul Ramdohrs group in the Heidelberg. Here the idea of a relationship between the presence of detrital pyrites and the oxygen content of the Earths atmosphere was born. He spent the years 1965-1967 at the University of Göttingen. Evidence for a biological origin of the carbonaceous material in the Witwatersrand sediments was consolidated during this time by carbon isotope investigations in cooperation with Jochen Hoefs. Afterwards, Schidlowski habilitated at the University of Heidelberg. In 1969 he moved to the newly founded Institute for Air Chemistry at the Max Planck Institute for Chemistry in Mainz in 1969. Its director, Christian Junge, sent him back to South Africa on a large sampling campaign. The focus was on the carbonates of early Earth history as archives of ocean-atmosphere evolution. Among these were carbonates of the Lomagundi succession from Rhodesia (now Zimbabwe) with their unusually positive carbon isotopy. Initially classified as a local feature, it quickly became clear that this was a global phenomenon, one of the most massive changes in global carbon cycle. There is still intense debate about the reasons for this global phenomenon, the basis of which was researched by him. His 1976 publication on this subject (Schidlowski et al., Geochim.Cosmochim. Acta 40: 449-455) is still cited several times in 2012. The move to the Max Planck Institute set the course for Schidlowski's future scientific career: research into the Earth system during the Precambrian. The time in Mainz was interrupted by stays at Harvard University, the University of California Los Angeles and the Weizman Institute in Rehovot, Israel.
From 1979 to 1989, he was chairman of the UNESCO-sponsored IGCP Project 157 (Early Organic Evolution and Mineral and Energy Resources). He established close contacts with geological and geochemical research centres such as the institutes of the Academy of Sciences of the USSR, the Academia Sinica (Lanzhou, Beijing). Since 1996, he was a member of the exobiology science team of the European Space Agency (ESA). He spent his scientific life researching the development of the atmosphere, the ocean and life on the early Earth. He wrote more than 100 scientific papers in journals and book chapters as well as edited special volumes and books on the topic of the early development of the Earth system.
Schidlowski retired in 1998. In 2005 he moved with his wife to Altusried. Here he died on October 3, 2012. | 0 | Theoretical and Fundamental Chemistry |
In applied mathematics, objective Eulerian coherent structures (OECSs) are the instantaneously most influential surfaces or curves that exert a major influence on nearby trajectories in a dynamical system over short time-scales, and are the short-time limit of Lagrangian coherent structures (LCSs). Such influence can be of different types, but OECSs invariably create a short-term coherent trajectory pattern for which they serve as a theoretical centerpiece. While LCSs are intrinsically tied to a specific finite time interval, OECSs can be computed at any time instant regardless of the multiple and generally unknown time scales of the system.
In observations of tracer patterns in nature, one readily identifies short-term variability in material structures such as emerging and dissolving coherent features. However, it is often the underlying structure creating these features that is of interest. While individual tracer trajectories forming coherent patterns are generally sensitive with respect to changes in their initial conditions and the system parameters, OECSs are robust and reveal the instantaneous time-varying skeleton of complex dynamical systems. Despite OECSs are defined for general dynamical systems, their role in creating coherent patterns is perhaps most readily observable in fluid flows. Therefore, OECSs are suitable in a number of applications ranging from flow control to environmental assessment such as now-casting or short-term forecasting of pattern evolution, where quick operational decisions need to be made. Examples include floating debris, oil spills, surface drifters, and control of unsteady flow separation. | 1 | Applied and Interdisciplinary Chemistry |
The phrase "cell engineering" was first used in a published paper in 1968 to describe the process of improving fuel cells. The term was then adopted by other papers until the more specific "fuel-cell engineering" was used.
The first use of the term in a biological context was in 1971 in a paper which describes methods to graft reproductive caps between algae cells. Despite the rising popularity of the phrase, there remains unclear boundaries between cell engineering and other forms of biological engineering. | 1 | Applied and Interdisciplinary Chemistry |
Chloropentammineplatinum chloride is the inorganic compound with the formula . It is the chloride salt of the coordination complex . It is a white, water soluble solid.
The compound is prepared by treating potassium hexachloroplatinate with aqueous ammonia: | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, an ortho ester is a functional group containing three alkoxy groups attached to one carbon atom, i.e. with the general formula . Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids and it is from these that the name ortho ester is derived. An example is ethyl orthoacetate, , more correctly known as 1,1,1-triethoxyethane. | 0 | Theoretical and Fundamental Chemistry |
The Boltzmann constant k (alternatively k) may be used in place of the molar gas constant by working in pure particle count, N, rather than amount of substance, n, since:
where N is the Avogadro constant.
For example, the ideal gas law in terms of the Boltzmann constant is:
where N is the number of particles (molecules in this case), or to generalize to an inhomogeneous system the local form holds:
where ρ = N/V is the number density. | 0 | Theoretical and Fundamental Chemistry |
The transduction of the signal through the membrane by the receptor is not completely understood. It is known that in the inactive state, the GPCR is bound to a heterotrimeric G protein complex. Binding of an agonist to the GPCR results in a conformational change in the receptor that is transmitted to the bound G subunit of the heterotrimeric G protein via protein domain dynamics. The activated G subunit exchanges GTP in place of GDP which in turn triggers the dissociation of G subunit from the G dimer and from the receptor. The dissociated G and G subunits interact with other intracellular proteins to continue the signal transduction cascade while the freed GPCR is able to rebind to another heterotrimeric G protein to form a new complex that is ready to initiate another round of signal transduction.
It is believed that a receptor molecule exists in a conformational equilibrium between active and inactive biophysical states. The binding of ligands to the receptor may shift the equilibrium toward the active receptor states. Three types of ligands exist: Agonists are ligands that shift the equilibrium in favour of active states; inverse agonists are ligands that shift the equilibrium in favour of inactive states; and neutral antagonists are ligands that do not affect the equilibrium. It is not yet known how exactly the active and inactive states differ from each other. | 1 | Applied and Interdisciplinary Chemistry |
Metal cluster compounds are a molecular ion or neutral compound composed of three or more metals and featuring significant metal-metal interactions. | 0 | Theoretical and Fundamental Chemistry |
Following the excitation of P700, one of its electrons is passed on to an electron acceptor, A, triggering charge separation producing an anionic A and cationic P700. Subsequently, electron transfer continues from A to a phylloquinone molecule known as A, and then to three iron-sulfur clusters.
Type I photosystems use iron-sulfur cluster proteins as terminal electron acceptors. Thus, the electron is transferred from F to another iron sulfur cluster, F, and then passed on to the last iron-sulfur cluster serving as an electron acceptor, F. Eventually, the electron is transferred to the protein ferredoxin, causing it to transform into its reduced form, which subsequently finalizes the process by reducing NADP to NADPH. | 0 | Theoretical and Fundamental Chemistry |
The extracellular polysaccharide colanic acid is produced by species of the family Enterobacteriaceae. In Escherichia coli strain K12 the colanic acid cluster comprises 19 genes. The wzx gene encodes a protein with multiple transmembrane segments that may function in export of the colanic acid repeat unit from the cytoplasm into the periplasm in a process analogous to O-unit export. The colanic acid gene clusters may be involved in the export of polysaccharide from the cell. | 1 | Applied and Interdisciplinary Chemistry |
The concentration of HCFC-141b in the atmosphere grew to near 25 parts per trillion by year 2016. It has an ozone depletion potential (ODP) of 0.12. This is low compared to the ODP=1 of trichlorofluoromethane (CFC-11, R-11), which also grew about ten times more abundant in the atmosphere prior to introduction of HFC-141b and subsequent adoption of the Montreal Protocol.
HFC-141b is also a minor but potent greenhouse gas. It has an estimated lifetime of about 10 years and a 100-year global warming potential ranging 725 to 2500. This compares to the GWP=1 of carbon dioxide, which had a much greater atmospheric concentration near 400 parts per million in year 2020. | 1 | Applied and Interdisciplinary Chemistry |
Space-based solar power (SBSP, SSP) is the concept of collecting solar power in outer space with solar power satellites (SPS) and distributing it to Earth. Its advantages include a higher collection of energy due to the lack of reflection and absorption by the atmosphere, the possibility of very little night, and a better ability to orient to face the Sun. Space-based solar power systems convert sunlight to some other form of energy (such as microwaves) which can be transmitted through the atmosphere to receivers on the Earth's surface.
Various SBSP proposals have been researched since the early 1970s, but none is economically viable with the space launch costs. Some technologists propose lowering launch costs with space manufacturing or with radical new space launch technologies other than rocketry.
Besides cost, SBSP also introduces several technological hurdles, including the problem of transmitting energy from orbit. Since wires extending from Earths surface to an orbiting satellite are not feasible with current technology, SBSP designs generally include the wireless power transmission with its associated conversion inefficiencies, as well as land use concerns for antenna stations to receive the energy at Earths surface. The collecting satellite would convert solar energy into electrical energy, power a microwave transmitter or laser emitter, and transmit this energy to a collector (or microwave rectenna) on Earths surface. Contrary to appearances in fiction, most designs propose beam energy densities that are not harmful if human beings were to be inadvertently exposed, such as if a transmitting satellites beam were to wander off-course. But the necessarily vast size of the receiving antennas would still require large blocks of land near the end users. The service life of space-based collectors in the face of long-term exposure to the space environment, including degradation from radiation and micrometeoroid damage, could also become a concern for SBSP.
As of 2020, SBSP is being actively pursued by Japan, China, Russia, India, the United Kingdom, and the US.
In 2008, Japan passed its Basic Space Law which established space solar power as a national goal. JAXA has a roadmap to commercial SBSP.
In 2015, the China Academy for Space Technology (CAST) showcased its roadmap at the International Space Development Conference. In February 2019, Science and Technology Daily (科技日报, Keji Ribao), the official newspaper of the Ministry of Science and Technology of the Peoples Republic of China, reported that construction of a testing base had started in Chongqings Bishan District. CAST vice-president Li Ming was quoted as saying China expects to be the first nation to build a working space solar power station with practical value. Chinese scientists were reported as planning to launch several small- and medium-sized space power stations between 2021 and 2025. In December 2019, Xinhua News Agency reported that China plans to launch a 200-tonne SBSP station capable of generating megawatts (MW) of electricity to Earth by 2035.
In May 2020, the US Naval Research Laboratory conducted its first test of solar power generation in a satellite. In August 2021, the California Institute of Technology (Caltech) announced that it planned to launch a SBSP test array by 2023, and at the same time revealed that Donald Bren and his wife Brigitte, both Caltech trustees, had been since 2013 funding the institute's Space-based Solar Power Project, donating over $100 million. A Caltech team successfully demonstrated beaming power to earth in 2023. | 0 | Theoretical and Fundamental Chemistry |
Na/glucose cotransporter (SGLT1) – is also known as sodium-glucose cotransporter 1 and is encoded by the SLC5A1 gene. SGLT1 is an electrogenic transporter as the sodium electrochemical gradient drives glucose uphill into the cells. SGLT1 is a high affinity Na /glucose cotransporter that has an important role in transferring sugar across the epithelial cells of renal proximal tubules and of the intestine, in particular the small intestine.
Na/phosphate cotransporter (NaPi) – Sodium-phosphate cotransporters are from the SLC34 and SLC20 protein families. They are also found across the epithelial cells of renal proximal tubule and of the small intestine. It transfers inorganic phosphate into cells through active transport with the help of a Na gradient. Similar to SGTL1, they are classified as electrogenic transporters. NaPi coupled with 3 Na ions and 1 divalent Pi, are classified as NaPi IIa and NaPi IIb. NaPi that couples with 2 Na and 1 divalent Pi are classified as NaPi IIc.
Na/I symporter (NIS) – Sodium-Iodide is a type of symporter that is responsible for transferring iodide in the thyroid gland. NIS is primarily found in cells of the thyroid gland and also in the mammary glands. They are located on the basolateral membrane of thyroid follicular cells where 2 Na ions and 1 I ion is coupled to transfer the iodide. NIS activity helps in the diagnosis and treatment of thyroid disease, including the highly successful treatment of thyroid cancer with radioiodide after thyroidectomy.
Na-K-2Cl symporter – This specific cotransporter regulates the cell volume by controlling the water and electrolyte content within the cell. The Na-K-2Cl Cotransporter is vital in salt secretion in secretory epithelia cells along with renal salt reabsorption. Two variations of the Na-K-2Cl symporter exist and are known as NKCC1 and NKCC2. The NKCC1 cotransport protein is found throughout the body but NKCC2 is found only in the kidney and removes the sodium, potassium, and chloride found in the body's urine, so it can be absorbed into the blood.
GABA transporter (GAT) – neurotransmitter γ-aminobutyric acid (GABA) transporters are members of the solute carrier family 6 (SLC6) of sodium- and chloride-dependent neurotransmitter receptor transporters that are located in the plasma membrane and regulate the concentration of GABA in the synaptic cleft. The SLC6A1 gene encodes GABA transporters. The transporters are electrogenic and couples 2 Na, 1 Cl and 1 GABA for inward translocation.
KCl Symporter – The K-Cl cotransporter family consists of four specific symporters known as KCC1, KCC2, KCC3, and KCC4. The KCC2 isoform is specific to neuronal tissue and the other three can be found in various tissues throughout the body. This cotransporter family controls the concentration levels of potassium and chloride within cells through the combined movement of K/H and Cl/HCO3 exchangers or through combined movement of both ions due to concentration activated channels. The four known KCC proteins team up to form two separate subfamilies with KCC1 and KCC3 pairing together and KCC2 and KCC4 becoming a pair to facilitate ion movement. | 1 | Applied and Interdisciplinary Chemistry |
Exemestane has been used in doping to raise luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels, which in turn increases the ratio of male over female sexual hormones and so improves performance. The drug also counteracts gynecomastia as well as fat and water retention following excessive aromatase production due to testosterone doping.
Along with other aromatase inhibitors, exemestane is on the World Anti-Doping Agency's list of prohibited substances. | 0 | Theoretical and Fundamental Chemistry |
Henry Kolm constructed an elementary TPV system at MIT in 1956. However, Pierre Aigrain is widely cited as the inventor based on lectures he gave at MIT between 1960–1961 which, unlike Kolm's system, led to research and development.
In the 1980s, efficiency reached around 30%.
In 1997 a prototype TPV hybrid car was built, the "Viking 29" (TPV) powered automobile, designed and built by the Vehicle Research Institute (VRI) at Western Washington University.
In 2022, MIT/NREL announced a device with 41% efficiency. The absorber employed multiple III-V semiconductor layers tuned to absorb variously, ultraviolet, visible, and infrared photons. A gold reflector recycled unabsorbed photons. The device operated at 2400 °C, at which temperature the tungsten emitter reaches maximum brightness. | 0 | Theoretical and Fundamental Chemistry |
In AFM, feedback loops control the operation of the microscope by keeping a fixed value a parameter of the tip's oscillation. If the main feedback loop operates with the amplitude, the AFM mode is called amplitude modulation (AM). If it operates with the frequency shift, the AFM mode is called frequency modulation (FM). Bimodal AFM might be operated with several feedback loops. This gives rise to a variety of bimodal configurations. The configurations are termed AM-open loop, AM-FM, FM-FM. For example, bimodal AM-FM means that the first mode is operated with an amplitude modulation loop while the 2nd mode is operated with a frequency modulation loop. The configurations might not be equivalent in terms of sensitivity, signal-to-noise ratio or complexity.
Let's consider the AM-FM configuration. The first mode is excited to reach free amplitude (no interaction) and the changes of its amplitude and phase shift are tracked by a lock-in amplifier. The main feedback loop keeps constant the amplitude, at a certain set-point by modifying the tip vertical position (AM). In a nanomechanical mapping experiment, must be kept below 90°, i.e., the AFM is operated in the repulsive regime. At the same time, an FM loop acts on the second eigenmode. A phase-lock-loop regulates the excitation frequency by keeping the phase shift of the second mode at 90°. An additional feedback loop might be used to maintain the amplitude constant. | 0 | Theoretical and Fundamental Chemistry |
Rayleigh scattering is defined by a mathematical formula that requires the light-scattering particles to be far smaller than the wavelength of the light. For a dispersion of particles to qualify for the Rayleigh formula, the particle sizes need to be below roughly 40 nanometres (for visible light), and the particles may be individual molecules. Colloidal particles are bigger and are in the rough vicinity of the size of a wavelength of light. Tyndall scattering, i.e. colloidal particle scattering, is much more intense than Rayleigh scattering due to the bigger particle sizes involved. The importance of the particle size factor for intensity can be seen in the large exponent it has in the mathematical statement of the intensity of Rayleigh scattering. If the colloid particles are spheroid, Tyndall scattering can be mathematically analyzed in terms of Mie theory, which admits particle sizes in the rough vicinity of the wavelength of light. Light scattering by particles of complex shape are described by the T-matrix method. | 0 | Theoretical and Fundamental Chemistry |
is a bis-nido edge-shared polyhedron. Here, m + n + o + p − q = 2 + 18 + 0 + 2 − 0 = 22; 16 BH units provide 16 pairs, 4 bridging hydrogen atoms provide 2 pairs, two shared boron atoms provide 3 pairs, along with the two negative charges which provide 1 pair. | 0 | Theoretical and Fundamental Chemistry |
Oxidizing conditions are common in some environments of deposition and diagenesis of sedimentary rocks. The fugacity of oxygen at the MH buffer (magnetite-hematite) is only about 10 at 25 °C, but it is about 0.2 atmospheres in the Earth's atmosphere, so some sedimentary environments are far more oxidizing than those in magmas. Other sedimentary environments, such as the environments for formation of black shale, are relatively reducing. | 0 | Theoretical and Fundamental Chemistry |
Atomic energy-level and Grotrian diagrams by Stanley Bashkin and John O. Stoner, Jr.
* [https://www.osti.gov/etdeweb/biblio/7245253 Volume I: Hydrogen - Phosphorus]
* [https://www.osti.gov/etdeweb/biblio/5726087 Volume I: Hydrogen - Phosphorus (Addenda)]
* [https://www.osti.gov/etdeweb/biblio/5286863 Volume III]
* [https://www.osti.gov/etdeweb/biblio/7095470 Volume IV] | 0 | Theoretical and Fundamental Chemistry |
Superelectrophiles are defined as cationic electrophilic reagents with greatly enhanced reactivities in the presence of superacids. These compounds were first described by George A. Olah. Superelectrophiles form as a doubly electron deficient superelectrophile by protosolvation of a cationic electrophile. As observed by Olah, a mixture of acetic acid and boron trifluoride is able to remove a hydride ion from isobutane when combined with hydrofluoric acid via the formation of a superacid from BF and HF. The responsible reactive intermediate is the [CHCOH] dication. Likewise, methane can be nitrated to nitromethane with nitronium tetrafluoroborate NOBF only in presence of a strong acid like fluorosulfuric acid via the protonated nitronium dication.
In gitionic (gitonic) superelectrophiles, charged centers are separated by no more than one atom, for example, the protonitronium ion O=N=O—H (a protonated nitronium ion). And, in distonic superelectrophiles, they are separated by 2 or more atoms, for example, in the fluorination reagent F-TEDA-BF. | 0 | Theoretical and Fundamental Chemistry |
A polyprotic acid is a compound which may lose more than 1 proton. Stepwise dissociation constants are each defined for the loss of a single proton. The constant for dissociation of the first proton may be denoted as K and the constants for dissociation of successive protons as K, etc. Phosphoric acid, , is an example of a polyprotic acid as it can lose three protons.
When the difference between successive pK values is about four or more, as in this example, each species may be considered as an acid in its own right; In fact salts of may be crystallised from solution by adjustment of pH to about 5.5 and salts of may be crystallised from solution by adjustment of pH to about 10. The species distribution diagram shows that the concentrations of the two ions are maximum at pH 5.5 and 10.
When the difference between successive pK values is less than about four there is overlap between the pH range of existence of the species in equilibrium. The smaller the difference, the more the overlap. The case of citric acid is shown at the right; solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5.
According to Paulings first rule, successive pK values of a given acid increase . For oxyacids with more than one ionizable hydrogen on the same atom, the pK' values often increase by about 5 units for each proton removed, as in the example of phosphoric acid above.
It can be seen in the table above that the second proton is removed from a negatively charged species. Since the proton carries a positive charge extra work is needed to remove it, which is why pK is greater than pK. pK is greater than pK because there is further charge separation. When an exception to Pauling's rule is found, it indicates that a major change in structure is also occurring. In the case of (aq), the vanadium is octahedral, 6-coordinate, whereas vanadic acid is tetrahedral, 4-coordinate. This means that four "particles" are released with the first dissociation, but only two "particles" are released with the other dissociations, resulting in a much greater entropy contribution to the standard Gibbs free energy change for the first reaction than for the others. | 0 | Theoretical and Fundamental Chemistry |
Modafinil is researched as a remedy to improve abstinence in people with cocaine addiction. Morning-dosed modafinil has been shown to normalize sleep parameters in individuals experiencing cocaine withdrawal. | 0 | Theoretical and Fundamental Chemistry |
Pulmonary surfactant protein D (SP-D), has an important role in acting as a lung host defence protein. SP-D has a significant roles in immune and inflammatory regulation of the lung as it regulates of the level of surfactant in the lungs by a process named surfactant homeostasis. | 0 | Theoretical and Fundamental Chemistry |
In the general case, for a free surface and where there is an applied "over-pressure", Δp, at the interface in equilibrium, there is a balance between the applied pressure, the hydrostatic pressure and the effects of surface tension. The Young–Laplace equation becomes:
The equation can be non-dimensionalised in terms of its characteristic length-scale, the capillary length:
and characteristic pressure
For clean water at standard temperature and pressure, the capillary length is ~2 mm.
The non-dimensional equation then becomes:
Thus, the surface shape is determined by only one parameter, the over pressure of the fluid, Δp and the scale of the surface is given by the capillary length. The solution of the equation requires an initial condition for position, and the gradient of the surface at the start point. | 1 | Applied and Interdisciplinary Chemistry |
Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars (also, disaccharides of six-carbon sugars, e.g. sucrose or lactose) are converted into cellular energy and the metabolite lactate, which is lactic acid in solution. It is an anaerobic fermentation reaction that occurs in some bacteria and animal cells, such as muscle cells.
If oxygen is present in the cell, many organisms will bypass fermentation and undergo cellular respiration; however, facultative anaerobic organisms will both ferment and undergo respiration in the presence of oxygen. Sometimes even when oxygen is present and aerobic metabolism is happening in the mitochondria, if pyruvate is building up faster than it can be metabolized, the fermentation will happen anyway.
Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD.
In homolactic fermentation, one molecule of glucose is ultimately converted to two molecules of lactic acid. Heterolactic fermentation, by contrast, yields carbon dioxide and ethanol in addition to lactic acid, in a process called the phosphoketolase pathway. | 1 | Applied and Interdisciplinary Chemistry |
The Kitchen gear is closed to direct an increasing proportion of thrust forward. As the balance changes the vessel will move astern. | 1 | Applied and Interdisciplinary Chemistry |
As Pol I escapes and clears the promoter, UBF and SL1 remain-promoter bound, ready to recruit another Pol I. Indeed, each active rDNA gene can be transcribed multiple times simultaneously, as opposed to Pol II-transcribed genes, which associate with only one complex at a time. While elongation proceeds unimpeded in vitro, it is unclear at this point whether this process happens in a cell, given the presence of nucleosomes. Pol I does seem to transcribe through nucleosomes, either bypassing or disrupting them, perhaps assisted by chromatin-remodeling activities. In addition, UBF might also act as positive feedback, enhancing Pol I elongation through an anti-repressor function. An additional factor, TIF-IC, can also stimulate the overall rate of transcription and suppress pausing of Pol I. As Pol I proceeds along the rDNA, supercoils form both ahead of and behind the complex. These are unwound by topoisomerase I or II at regular intervals, similar to what is seen in Pol II-mediated transcription.
Elongation is likely to be interrupted at sites of DNA damage. Transcription-coupled repair occurs similarly to Pol II-transcribed genes and requires the presence of several DNA repair proteins, such as TFIIH, CSB, and XPG. | 1 | Applied and Interdisciplinary Chemistry |
LAAM was approved in 1993 by the U.S. Food and Drug Administration for use in the treatment of opioid dependence. In 2001, LAAM was removed from the European market due to reports of life-threatening ventricular rhythm disorders. In 2003, Roxane Laboratories, Inc. discontinued Orlaam in the US. | 0 | Theoretical and Fundamental Chemistry |
The first record of the pyroelectric effect was made in 1707 by Johann Georg Schmidt, who noted that the "[hot] tourmaline could attract the ashes from the warm or burning coals, as the magnet does iron, but also repelling them again [after the contact]". In 1717 Louis Lemery noticed, as Schmidt had, that small scraps of non-conducting material were first attracted to tourmaline, but then repelled by it once they contacted the stone. In 1747 Linnaeus first related the phenomenon to electricity (he called tourmaline Lapidem Electricum, "the electric stone"), although this was not proven until 1756 by Franz Ulrich Theodor Aepinus.
Research into pyroelectricity became more sophisticated in the 19th century. In 1824 Sir David Brewster gave the effect the name it has today. Both William Thomson in 1878 and Woldemar Voigt in 1897 helped develop a theory for the processes behind pyroelectricity. Pierre Curie and his brother, Jacques Curie, studied pyroelectricity in the 1880s, leading to their discovery of some of the mechanisms behind piezoelectricity.
It is mistakenly attributed to Theophrastus (c. 314 BC) the first record of pyroelectricity. The misconception arose soon after the discovery of the pyroelectric properties of tourmaline, which made mineralogists of the time associate the legendary stone Lyngurium with it. Lyngurium is described in the work of Theophrastus as being similar to amber, without specifying any pyroelectric properties. | 0 | Theoretical and Fundamental Chemistry |
In a controversial 2009 article in the New England Journal of Medicine, "Lost in Transmission — FDA Drug Information That Never Reaches Clinicians", it was reported that the largest of three Lunesta trials found that compared to placebo Lunesta "was superior to placebo" while it only shortened initial time falling asleep by 15 minutes on average. "Clinicians who are interested in the drug’s efficacy cannot find efficacy information in the label: it states only that Lunesta is superior to placebo. The FDA’s medical review provides efficacy data, albeit not until page 306 of the 403-page document. In the longest, largest phase 3 trial, patients in the Lunesta group reported falling asleep an average of 15 minutes faster and sleeping an average of 37 minutes longer than those in the placebo group. However, on average, Lunesta patients still met criteria for insomnia and reported no clinically meaningful improvement in next-day alertness or functioning." | 0 | Theoretical and Fundamental Chemistry |
Methemoglobin (British: methaemoglobin, shortened MetHb) (pronounced "met-hemoglobin") is a hemoglobin in the form of metalloprotein, in which the iron in the heme group is in the Fe (ferric) state, not the Fe (ferrous) of normal hemoglobin. Sometimes, it is also referred to as ferrihemoglobin. Methemoglobin cannot bind oxygen, which means it cannot carry oxygen to tissues. It is bluish chocolate-brown in color. In human blood a trace amount of methemoglobin is normally produced spontaneously, but when present in excess the blood becomes abnormally dark bluish brown. The NADH-dependent enzyme methemoglobin reductase (a type of diaphorase) is responsible for converting methemoglobin back to hemoglobin.
Normally one to two percent of a person's hemoglobin is methemoglobin; a higher percentage than this can be genetic or caused by exposure to various chemicals and depending on the level can cause health problems known as methemoglobinemia. A higher level of methemoglobin will tend to cause a pulse oximeter to read closer to 85% regardless of the true level of oxygen saturation. | 1 | Applied and Interdisciplinary Chemistry |
Partition chromatography theory and practice was introduced through the work and publications of Archer Martin and Richard Laurence Millington Synge during the 1940s. They would later receive the 1952 Nobel Prize in Chemistry "for their invention of partition chromatography". | 0 | Theoretical and Fundamental Chemistry |
Blocking antibodies have a variety of functions on the merozoite form of parasitic malaria. While in the merozoite form, malaria parasites invade erythrocytes and reproduce in them. Some blocking antibodies may inhibit the invasion of erythrocytes, while other blocking antibodies prevent the binding of inhibitory antibodies, allowing merozoite invasion of erythrocytes despite the presence of inhibitory antibodies. The monoclonal antibodies that prevent the invasion of merozoites bind to the parasitic antigen MSP-1 (merozoite surface protein 1). The binding of blocking antibodies to MSP-1 is shown to result in the inhibition of secondary processing, resulting in the inability for merozoites to invade host erythrocytes. Secondary processing involves a single proteolytic cleavage on the merozoite surface of the carboxy-terminal component of MSP-1. The blocking of MSP-1 has been proposed to be a method of creating a vaccine against malaria by preventing its invasion and multiplication. | 1 | Applied and Interdisciplinary Chemistry |
Azide has become a popular target for chemoselective protein modification, because they are small in size and have a favorable thermodynamic reaction potential. One such azide reactions is the [3+2] cycloaddition reaction with alkyne, but the reaction requires high temperature and often gives mixtures of regioisomers.
An improved reaction developed by chemist Karl Barry Sharpless involves the copper (I) catalyst, which couples azide with terminal alkyne that only give 1,4 substituted 1,2,3 triazoles in high yields (shown below in Figure 11). The mechanistic study suggests a stepwise reaction. The Cu (I) first couples with acetylenes, and then it reacts with azide to generate a six-membered intermediate. The process is very robust that it occurs at pH ranging from 4 to 12, and copper (II) sulfate is often used as a catalyst in the presence of a reducing agent. | 1 | Applied and Interdisciplinary Chemistry |
*Gadd45a was discovered and characterized in the laboratory of Dr. Albert J. Fornace Jr. in 1988.
*Gadd45b (MyD118) was discovered and characterized in the laboratories of Drs. Dan A. Liebermann and Barbara Hoffman in 1991.
*Gadd45g (CR6) was discovered and characterized in the laboratories of Drs. Kenneth Smith, Dan A. Liebermann, and Barbara Hoffman in 1993 and 1999. | 1 | Applied and Interdisciplinary Chemistry |
Owing to the vacant orbital present in Z-ligands, many have incomplete octets which allow them to readily accept a pair of electrons from other atoms. A Z‑function ligand interacts with a metal center via a dative covalent bond, differing from the L‑function in that both electrons are donated by the metal rather than the ligand. As such, Z-ligands donate zero electrons to a metal center because they tend to be strong electron acceptors.
Although many Z-ligands are Lewis acids, they behave as neutral ligands in the complex without contributing to the overall charge present on the complex. But since the metal uses two of its electrons in forming the metal-ligand bond, the Z-ligand raises the valence of the metal center by two units. This means that presence of the Z-ligands change the d configuration of the complex without changing the total e count.
A Z-ligand is usually accompanied by an L-ligand, as the presence of the L-ligand adds stability to the complex. As the electrons are being donated from the central metal atom to the Z-ligand, the L-ligand donates its pair of electrons to the metal atom. This unique type of bonding existing between two different ligands and the metal atom renders the complexes stable when present with a strong sigma donor ligand. In such complexes, the L and Z ligands can be written in terms of X. For example, if one Z-ligand is accompanied by one L type ligand, it can be written as a complex containing two X type ligands; i.e. MLZ type complex becomes an MX type. | 0 | Theoretical and Fundamental Chemistry |
Polyolefins such as polyethylene and polypropylene are susceptible to photo-oxidation and around 70% of light stabilizers produced world-wide are used in their protection, despite them representing only around 50% of global plastic production. Aliphatic hydrocarbons can only adsorb high energy UV-rays with a wavelength below ~250 nm, however the Earth’s atmosphere and ozone layer screen out such rays, with the normal minimum wavelength being 280–290 nm.
The bulk of the polymer is therefore photo-inert and degradation is instead attributed to the presence of various impurities, which are introduced during the manufacturing or processing stages. These include hydroperoxide and carbonyl groups, as well as metal salts such as catalyst residues.
All of these species act as photoinitiators.
The organic hydroperoxide and carbonyl groups are able to absorb UV light above 290 nm whereupon they undergo photolysis to generate radicals. Metal impurities act as photocatalysts, although such reactions can be complex. It has also been suggested that polymer-O charge-transfer complexes are involved. Initiation generates radical-carbons on the polymer chain, sometimes called macroradicals (P•).
Chain initiation
Chain propagation
Chain branching
Termination
Classically the carbon-centred macroradicals (P•) rapidly react with oxygen to form hydroperoxyl radicals (POO•), which in turn abstract an H atom from the polymer chain to give a hydroperoxide (POOH) and a fresh macroradical. Hydroperoxides readily undergo photolysis to give an alkoxyl macroradical radical (PO•) and a hydroxyl radical (HO•), both of which may go on to form new polymer radicals via hydrogen abstraction. Non-classical alternatives to these steps have been proposed. The alkoxyl radical may also undergo beta scission, generating a acyl-ketone and macroradical. This is considered to be the main cause of chain breaking in polypropylene.
Secondary hydroperoxides can also undergo an intramolecular reaction to give a ketone group, although this is limited to polyethylene.
The ketones generated by these processes are themselves photo-active, although much more weakly. At ambient temperatures they undergo Type II Norrish reactions with chain scission. They may also absorb UV-energy, which they can then transfer to O, causing it to enter its highly reactive singlet state. Singlet oxygen is a potent oxidising agent can go on to form cause further degradation. | 0 | Theoretical and Fundamental Chemistry |
Soon after Hagemann, Emil Knoevenagel described a modified procedure to produce the same intermediate diethyl ester of 2,4-diacetyl pentane using
formaldehyde and two equivalents of ethyl acetoacetate which undergo condensation in the presence of a catalytic amount of piperidine. | 0 | Theoretical and Fundamental Chemistry |
In the study of turbulence in fluids, a common practical strategy is to ignore the small-scale vortices (or eddies) in the motion and to calculate a large-scale motion with an effective viscosity, called the "eddy viscosity", which characterizes the transport and dissipation of energy in the smaller-scale flow (see large eddy simulation). In contrast to the viscosity of the fluid itself, which must be positive by the second law of thermodynamics, the eddy viscosity can be negative. | 1 | Applied and Interdisciplinary Chemistry |
Network motifs are recurrent and statistically significant subgraphs or patterns of a larger graph. All networks, including biological networks, social networks, technological networks (e.g., computer networks and electrical circuits) and more, can be represented as graphs, which include a wide variety of subgraphs.
Network motifs are sub-graphs that repeat themselves in a specific network or even among various networks. Each of these sub-graphs, defined by a particular pattern of interactions between vertices, may reflect a framework in which particular functions are achieved efficiently. Indeed, motifs are of notable importance largely because they may reflect functional properties. They have recently gathered much attention as a useful concept to uncover structural design principles of complex networks. Although network motifs may provide a deep insight into the network's functional abilities, their detection is computationally challenging. | 1 | Applied and Interdisciplinary Chemistry |
All fish species have a preferred temperature above and below which that fish will experience negative health effects and eventually death. Warm water species such as Tilapia and Barramundi prefer 24 °C water or warmer, where as cold water species such as trout and salmon prefer water temperature below 16 °C. Temperature also plays an important role in dissolved oxygen (DO) concentrations, with higher water temperatures having lower values for DO saturation. Temperature is controlled through the use of submerged heaters, heat pumps, chillers, and heat exchangers. All four may be used to keep a system operating at the optimal temperature for maximizing fish production. | 1 | Applied and Interdisciplinary Chemistry |
This section provides a kinetic derivation for a single-adsorbate case. The kinetic derivation applies to gas-phase adsorption. However, it has been mistakenly applied to solutions. The multiple-adsorbate case is covered in the competitive adsorption sub-section.
The model assumes adsorption and desorption as being elementary processes, where the rate of adsorption r and the rate of desorption r are given by
where p is the partial pressure of A over the surface, [S] is the concentration of free sites in number/m, [A] is the surface concentration of A in molecules/m (concentration of occupied sites), and k and k are constants of forward adsorption reaction and backward desorption reaction in the above reactions.
At equilibrium, the rate of adsorption equals the rate of desorption. Setting r = r and rearranging, we obtain
The concentration of sites is given by dividing the total number of sites (S) covering the whole surface by the area of the adsorbent (a):
We can then calculate the concentration of all sites by summing the concentration of free sites [S] and occupied sites:
Combining this with the equilibrium equation, we get
We define now the fraction of the surface sites covered with A as
This, applied to the previous equation that combined site balance and equilibrium, yields the Langmuir adsorption isotherm: | 0 | Theoretical and Fundamental Chemistry |
Additionally, pH levels control specificity of substrate binding by malate dehydrogenase due to proton transfer in the catalytic mechanism. A histidine moiety with a pK value of 7.5 has been suggested to play a role in the pH-dependency of the enzyme. Studies have indicated that the binding of the enol form oxaloacetate with the malate dehydrogenase:NADH complex forms much more rapidly at higher pH values. Additionally, L-malate binding to malate dehydrogenase is promoted at alkaline conditions. Consequently, the non-protonated form malate dehydrogenase binds preferentially to L-malate and the enol form of oxaloacetate. In contrast, D-malate, hydroxymalonate, and the keto form of oxaloacetate have been found to bind exclusively to the protonated form of the enzyme. Specifically, when the histidine is protonated, the His residue can form a hydrogen bond with the substrate's carbonyl oxygen, which shifts electron density away from the oxygen and makes it more susceptible to nucleophilic attack by hydride. This promotes the binding of malate dehydrogenase to these substrates. As a result, at lower pH values malate dehydrogenase binds preferentially to D-malate, hydroxymalonate, and keto-oxaloacetate. | 1 | Applied and Interdisciplinary Chemistry |
In marine hydrodynamic applications, the Froude number is usually referenced with the notation and is defined as:
where is the relative flow velocity between the sea and ship, is in particular the acceleration due to gravity, and is the length of the ship at the water line level, or in some notations. It is an important parameter with respect to the ship's drag, or resistance, especially in terms of wave making resistance.
In the case of planing craft, where the waterline length is too speed-dependent to be meaningful, the Froude number is best defined as displacement Froude number and the reference length is taken as the cubic root of the volumetric displacement of the hull: | 1 | Applied and Interdisciplinary Chemistry |
Neurodegeneration is classified as a massive death of neurons, and encompasses diseases such as Alzheimers, Parkinsons, and Huntingtons. Although many cells die due to necrosis, many cells in neurodegenerative disorders are killed via the apoptotic pathway. Excitotoxicity, which involves overstimulation of a cell via its glutamate receptors, is one of the major processes which can initiate cell death. Other inducers include mitochondrial dysfunction, oxidative stress, and abnormal protein aggregation. Surprisingly, both necrotic and apoptotic processes utilize a similar intracellular signaling cascade which uses caspase proteins to induce cell death. Abnormal protein accumulation causes Alzheimers, Parkinsons, and Huntingtons diseases. | 1 | Applied and Interdisciplinary Chemistry |
The essence of Brønsted–Lowry theory is that an acid is only such in relation to a base, and vice versa. Water is amphoteric as it can act as an acid or as a base. In the image shown at the right one molecule of acts as a base and gains to become while the other acts as an acid and loses to become .
Another example is illustrated by substances like aluminium hydroxide, . | 0 | Theoretical and Fundamental Chemistry |
Compounds that contain the cyanate functional group, −O−C≡N, are known as cyanates or cyanate esters. Aryl cyanates such are phenyl cyanate, can be formed by a reaction of phenol with cyanogen chloride, ClCN, in the presence of a base.
Organic compounds that contain the isocyanate functional group −N=C=O are known as isocyanates. It is conventional in organic chemistry to write isocyanates with two double bonds, which accords with a simplistic valence bond theory of the bonding. In nucleophilic substitution reactions cyanate usually forms an isocyanate. Isocyanates are widely used in the manufacture of polyurethane products and pesticides; methyl isocyanate, used to make pesticides, was a major factor in the Bhopal disaster. | 0 | Theoretical and Fundamental Chemistry |
Check dams require regular maintenance as typically temporary structures not designed to withstand long-term use. Dams should be inspected every week and after heavy rainfall. It is important that rubble, litter, and leaves are removed from the upstream side of the dam. This is typically done when the sediment has reached a height of one-half the original height of the dam.
When the site is permanently stabilized and the check dam is no longer needed, it is fully removed, including components washed downstream, and bare spots are stabilized. | 1 | Applied and Interdisciplinary Chemistry |
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