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The unit distance graph on the three-dimensional integer lattice has a vertex for each lattice point; each vertex has exactly six neighbors. It is possible to remove some of the points from the lattice, so that each remaining point has exactly three remaining neighbors, and so that the induced subgraph of these points has no cycles shorter than ten edges. There are four ways to do this, one of which is isomorphic as an abstract graph to the Laves graph. However, its vertices are in different positions than the more-symmetric, conventional geometric construction.
Another subgraph of the simple cubic net isomorphic to the Laves graph is obtained by removing half of the edges in a certain way. The resulting structure, called semi-simple cubic lattice, also has lower symmetry than the Laves graph itself. | 3 | Analytical Chemistry |
The reaction catalyzed by bacterial luciferase is also an oxidative process:
* FMNH + O + RCHO → FMN + RCOOH + HO + light
In the reaction, molecular oxygen oxidizes flavin mononucleotide and a long-chain aliphatic aldehyde to an aliphatic carboxylic acid. The reaction forms an excited hydroxyflavin intermediate, which is dehydrated to the product FMN to emit blue-green light.
Nearly all of the energy input into the reaction is transformed into light. The reaction is 80% to 90% efficient. In comparison, the incandescent light bulb only converts about 10% of its energy into light and a 150 lumen per Watt (lm/W) LED converts 20% of input energy to visible light. | 1 | Biochemistry |
Alkaloids are bitter-tasting chemicals, widespread in nature, and often toxic. There are several classes with different modes of action as drugs, both recreational and pharmaceutical. Medicines of different classes include atropine, scopolamine, and hyoscyamine (all from nightshade), the traditional medicine berberine (from plants such as Berberis and Mahonia), caffeine (Coffea), cocaine (Coca), ephedrine (Ephedra), morphine (opium poppy), nicotine (tobacco), reserpine (Rauvolfia serpentina), quinidine and quinine (Cinchona), vincamine (Vinca minor), and vincristine (Catharanthus roseus). | 1 | Biochemistry |
tert-butyl hydroperoxide is potentially dangerous, but explosions are rare.
A solution of tert-butyl hydroperoxide and water with a concentration of greater than 90% is forbidden to be shipped according to US Department of Transportation Hazardous Materials Table 49 CFR 172.101.
In some sources it also has an NFPA 704 rating of 4 for health, 4 for flammability, 4 for reactivity and is a potent oxidant, however other sources claim lower ratings of 3-2-2 or 1-4-4. | 0 | Organic Chemistry |
Pyridine can be prepared by dealkylation of alkylated pyridines, which are obtained as byproducts in the syntheses of other pyridines. The oxidative dealkylation is carried out either using air over vanadium(V) oxide catalyst, by vapor-dealkylation on nickel-based catalyst, or hydrodealkylation with a silver- or platinum-based catalyst. Yields of pyridine up to be 93% can be achieved with the nickel-based catalyst. Pyridine can also be produced by the decarboxylation of nicotinic acid with copper chromite. | 0 | Organic Chemistry |
Prismane is a colourless liquid at room temperature. The deviation of the carbon-carbon bond angle from 109° to 60° in a triangle leads to a high ring strain, reminiscent of that of cyclopropane but greater. The compound is explosive, which is unusual for a hydrocarbon. Due to this ring strain, the bonds have a low bond energy and break at a low activation energy, which makes synthesis of the molecule difficult; Woodward and Hoffmann noted that prismane's thermal rearrangement to benzene is symmetry-forbidden, comparing it to "an angry tiger unable to break out of a paper cage." On account of its strain energy and the aromatic stabilization of benzene, the molecule is estimated to be 90 kcal/mole less stable than benzene, but the activation of this highly exothermic transformation is a surprisingly high 33 kcal/mol, making it persistent at room temperature.
The substituted derivative hexamethylprismane (in which all six hydrogens are substituted by methyl groups) has a higher stability, and was synthesized by rearrangement reactions in 1966. | 4 | Stereochemistry |
Amyloid precursor protein has been shown to interact with:
* APBA1,
* APBA2,
* APBA3,
* APBB1,
* APPBP1,
* APPBP2,
* BCAP31,
* BLMH
* CLSTN1,
* CAV1,
* COL25A1,
* FBLN1,
* GSN,
* HSD17B10, and
* SHC1.
APP interacts with reelin, a protein implicated in a number of brain disorders, including Alzheimer's disease. | 1 | Biochemistry |
Currently, the stability of most ionic liquids under practical electrochemical conditions is unknown, and the fundamental choice of ionic fluid is still empirical as there is almost no data on metal ion thermodynamics to feed into solubility and speciation models. Also, there are no Pourbaix diagrams available, no standard redox potentials, and bare knowledge of speciation or pH-values. It must be noticed that most processes reported in the literature involving ionic fluids have a Technology Readiness Level (TRL) 3 (experimental proof-of-concept) or 4 (technology validated in the lab), which is a disadvantage for short-term implementation. However, ionometallurgy has the potential to effectively recover metals in a more selective and sustainable way, as it considers environmentally benign solvents, reduction of greenhouse gas emissions and avoidance of corrosive and harmful reagents. | 8 | Metallurgy |
Bioconversion, also known as biotransformation, is the conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms. One example is the industrial production of cortisone, which one step is the bioconversion of progesterone to 11-alpha-Hydroxyprogesterone by Rhizopus nigricans. Another example is the bioconversion of glycerol to 1,3-propanediol, which is part of scientific research for many decades.
Another example of bioconversion is the conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms, some detritivores or enzymes.
In the US, the Bioconversion Science and Technology group performs multidisciplinary R&D for the Department of Energys (DOE) relevant applications of bioprocessing, especially with biomass. Bioprocessing combines the disciplines of chemical engineering, microbiology and biochemistry. The Group s primary role is investigation of the use of microorganism, microbial consortia and microbial enzymes in bioenergy research. New cellulosic ethanol conversion processes have enabled the variety and volume of feedstock that can be bioconverted to expand rapidly. Feedstock now includes materials derived from plant or animal waste such as paper, auto-fluff, tires, fabric, construction materials, municipal solid waste (MSW), sludge, sewage, etc. | 2 | Environmental Chemistry |
FEBS publishes four scientific journals: The FEBS Journal, FEBS Letters, Molecular Oncology and FEBS Open Bio. The FEBS Journal was previously entitled the European Journal of Biochemistry. Molecular Oncology and FEBS Open Bio are open-access journals. | 1 | Biochemistry |
Phase-boundary catalytic (PBC) systems can be contrasted with conventional catalytic systems. PBC is primarily applicable to reactions at the interface of an aqueous phase and organic phase. In these cases, an approach such as PBC is needed due to the immiscibility of aqueous phases with most organic substrate. In PBC, the catalyst acts at the interface between the aqueous and organic phases. The reaction medium of phase boundary catalysis systems for the catalytic reaction of immiscible aqueous and organic phases consists of three phases; an organic liquid phase, containing most of the substrate, an aqueous liquid phase containing most of the substrate in aqueous phase and the solid catalyst.
In case of conventional catalytic system;
*When the reaction mixture is vigorously stirred, an apparently homogeneous emulsion is obtained, which segregates very rapidly into two liquid phases when the agitation ceases. Segregation occurs by formation of organic bubbles in the emulsion which move downwards to form the aqueous phase, indicating that emulsion consists of dispersed particles of the aqueous phase in the organic phase.
*Due to the triphasic reactions conditions, the overall reaction between aqueous phase and organic phase substrates on solid catalyst requires different transfer processes. The following steps are involved:
*# transfer of aqueous phase from organic phase to the external surface of solid catalyst;
*# transfer of aqueous phase inside the pore volume of solid catalyst;
*# transfer of the substrate from aqueous phase to the interphase between aqueous and organic phases
*# transfer of the substrate from the interphase to the aqueous phase;
*# mixing and diffusion of the substrate in the aqueous phase;
*# transfer of the substrate from the aqueous phase to the external surface of solid catalyst;
*# transfer of the substrate inside the pore volume of the solid catalyst;
*# catalytic reaction (adsorption, chemical reaction and desorption).
In some systems, without vigorous stirring, no reactivity of the catalyst is observed in conventional catalytic system. Stirring and mass transfer from the organic to the aqueous phase and vice versa are required for conventional catalytic system. Conversely, in PBC, stirring is not required because the mass transfer is not the rate determining step in this catalytic system. It is already demonstrated that this system works for alkene epoxidation without stirring or the addition of a co-solvent to drive liquid–liquid phase transfer. The active site located on the external surface of the zeolite particle were dominantly effective for the observed phase boundary catalytic system. | 7 | Physical Chemistry |
Antinuclear antibodies (ANAs, also known as antinuclear factor or ANF) are autoantibodies that bind to contents of the cell nucleus. In normal individuals, the immune system produces antibodies to foreign proteins (antigens) but not to human proteins (autoantigens). In some cases, antibodies to human antigens are produced.
There are many subtypes of ANAs such as anti-Ro antibodies, anti-La antibodies, anti-Sm antibodies, anti-nRNP antibodies, anti-Scl-70 antibodies, anti-dsDNA antibodies, anti-histone antibodies, antibodies to nuclear pore complexes, anti-centromere antibodies and anti-sp100 antibodies. Each of these antibody subtypes binds to different proteins or protein complexes within the nucleus. They are found in many disorders including autoimmunity, cancer and infection, with different prevalences of antibodies depending on the condition. This allows the use of ANAs in the diagnosis of some autoimmune disorders, including systemic lupus erythematosus, Sjögren syndrome, scleroderma, mixed connective tissue disease, polymyositis, dermatomyositis, autoimmune hepatitis and drug-induced lupus.
The ANA test detects the autoantibodies present in an individual's blood serum. The common tests used for detecting and quantifying ANAs are indirect immunofluorescence and enzyme-linked immunosorbent assay (ELISA). In immunofluorescence, the level of autoantibodies is reported as a titre. This is the highest dilution of the serum at which autoantibodies are still detectable. Positive autoantibody titres at a dilution equal to or greater than 1:160 are usually considered as clinically significant. Positive titres of less than 1:160 are present in up to 20% of the healthy population, especially the elderly. Although positive titres of 1:160 or higher are strongly associated with autoimmune disorders, they are also found in 5% of healthy individuals. Autoantibody screening is useful in the diagnosis of autoimmune disorders and monitoring levels helps to predict the progression of disease. A positive ANA test is seldom useful if other clinical or laboratory data supporting a diagnosis are not present. | 1 | Biochemistry |
The identification of synexpression groups has affected the way some scientists view evolutionary change in higher eukaryotes. Since groups of genes involved in the same biological process often share one or more common control elements, it has been suggested that the differential expression of these synexpression groups in different tissues of organisms can contribute to co-evolution tissues, organs, and appendages. Today it is commonly believed that it is not primarily the gene products themselves that evolve, but that it is the control networks for groups of genes that contribute most to the evolution of higher eukaryotes. | 1 | Biochemistry |
#Anthocyanin pigments are assembled like all other flavonoids from two different streams of chemical raw materials in the cell:
#* One stream involves the shikimate pathway to produce the amino acid phenylalanine, (see phenylpropanoids)
#* The other stream produces three molecules of malonyl-CoA, a C unit from a C unit (acetyl-CoA),
#These streams meet and are coupled together by the enzyme chalcone synthase, which forms an intermediate chalcone-like compound via a polyketide folding mechanism that is commonly found in plants,
#The chalcone is subsequently isomerized by the enzyme chalcone isomerase to the prototype pigment naringenin,
#Naringenin is subsequently oxidized by enzymes such as flavanone hydroxylase, flavonoid 3-hydroxylase, and flavonoid 3,5'-hydroxylase,
#These oxidation products are further reduced by the enzyme dihydroflavonol 4-reductase to the corresponding colorless leucoanthocyanidins,
#Leucoanthocyanidins once were believed to be the immediate precursors of the next enzyme, a dioxygenase referred to as anthocyanidin synthase, or, leucoanthocyanidin dioxygenase. Flavan-3-ols, the products of leucoanthocyanidin reductase (LAR), recently have been shown to be their true substrates,
#The resulting unstable anthocyanidins are further coupled to sugar molecules by enzymes such as UDP-3-O-glucosyltransferase, to yield the final relatively-stable anthocyanins.
Thus, more than five enzymes are required to synthesize these pigments, each working in concert. Even a minor disruption in any of the mechanisms of these enzymes by either genetic or environmental factors, would halt anthocyanin production. While the biological burden of producing anthocyanins is relatively high, plants benefit significantly from the environmental adaptation, disease tolerance, and pest tolerance provided by anthocyanins.
In anthocyanin biosynthetic pathway, -phenylalanine is converted to naringenin by phenylalanine ammonialyase, cinnamate 4-hydroxylase, 4-coumarate CoA ligase, chalcone synthase, and chalcone isomerase. Then, the next pathway is catalyzed, resulting in the formation of complex aglycone and anthocyanin through composition by flavanone 3-hydroxylase, flavonoid 3'-hydroxylase, dihydroflavonol 4-reductase, anthocyanidin synthase, UDP-glucoside: flavonoid glucosyltransferase, and methyl transferase. | 3 | Analytical Chemistry |
In genetics, a promoter is a sequence of DNA to which proteins bind to initiate transcription of a single RNA transcript from the DNA downstream of the promoter. The RNA transcript may encode a protein (mRNA), or can have a function in and of itself, such as tRNA or rRNA. Promoters are located near the transcription start sites of genes, upstream on the DNA (towards the 5' region of the sense strand).
Promoters can be about 100–1000 base pairs long, the sequence of which is highly dependent on the gene and product of transcription, type or class of RNA polymerase recruited to the site, and species of organism.
Promoters control gene expression in bacteria and eukaryotes. RNA polymerase must attach to DNA near a gene for transcription to occur. Promoter DNA sequences provide an enzyme binding site. The -10 sequence is TATAAT. -35 sequences are conserved on average, but not in most promoters.
Artificial promoters with conserved -10 and -35 elements transcribe more slowly. All DNAs have "Closely spaced promoters". Divergent, tandem, and convergent orientations are possible. Two closely spaced promoters will likely interfere. Regulatory elements can be several kilobases away from the transcriptional start site in gene promoters (enhancers).
In eukaryotes, the transcriptional complex can bend DNA, allowing regulatory sequences to be placed far from the transcription site. The distal promoter is upstream of the gene and may contain additional regulatory elements with a weaker influence. RNA polymerase II (RNAP II) bound to the transcription start site promoter can start mRNA synthesis. It also typically contains CpG islands, a TATA box, and TFIIB recognition elements.
Hypermethylation downregulates both genes, while demethylation upregulates them. Non-coding RNAs are linked to mRNA promoter regions. Subgenomic promoters range from 24 to 100 nucleotides (Beet necrotic yellow vein virus). Gene expression depends on promoter binding. Unwanted gene changes can increase a cell's cancer risk.
MicroRNA promoters often contain CpG islands. DNA methylation forms 5-methylcytosines at the 5' pyrimidine ring of CpG cytosine residues. Some cancer genes are silenced by mutation, but most are silenced by DNA methylation. Others are regulated promoters. Selection may favor less energetic transcriptional binding.
Variations in promoters or transcription factors cause some diseases. Misunderstandings can result from using a canonical sequence to describe a promoter. | 1 | Biochemistry |
Goss specialises in the biosynthesis of natural products at the chemical and genetic level.
Goss joined the University of Cambridge in 2000 to study the chemistry and molecular biology of polyketide biosynthesis in the research group of Professors Jim Staunton (FRS) and Peter Leadlay (FRS). She held a one-year teaching fellowship at the School of Chemistry, University of Nottingham between 2002 and 2003 before obtaining a lectureship at the School of Biological and Chemical Science, University of Exeter in 2003. Between 2005 and 2010 Goss held a lectureship at the University of East Anglia before being promoted to senior lecturer in 2010 and then reader in organic chemistry in 2012. Goss moved to the University of St. Andrews in 2012 to become a reader in biomolecular and organic chemistry. In 2018 she became the first woman to be appointed professor of organic chemistry in St Andrews' 600-year history.
She was awarded the Royal Society of Chemistry Meldola prize for her work to understand the interface of organic chemistry and molecular biology. In 2013 she was awarded the Royal Society of Chemistry Natural Product Report Emerging Researcher Lectureship for her pioneering approach to Genochemetics, which combines synthetic biology and chemistry for medicinal purposes. In 2014 she was awarded an ERC consolidator grant.
Goss is on the advisory board for the peer-reviewed journals Chemical Communications and Natural Product Reports. | 0 | Organic Chemistry |
A Norrish type II reaction is the photochemical intramolecular abstraction of a γ-hydrogen (a hydrogen atom three carbon positions removed from the carbonyl group) by the excited carbonyl compound to produce a 1,4-biradical as a primary photoproduct. Norrish first reported the reaction in 1937.
Secondary reactions that occur are fragmentation (β-scission) to form an alkene and an enol (which will rapidly tautomerise to a carbonyl), or intramolecular recombination of the two radicals to a substituted cyclobutane (the Norrish–Yang reaction). | 5 | Photochemistry |
One general form of cell engineering involves altering natural cell production to achieve a more desirable yield or shorter production time. A possible method for changing natural cell production includes boosting or repressing genes that are involved in the metabolism of the product. For example, researchers were able to overexpress transporter genes in hamster ovary cells to increase monoclonal antibody yield. Another approach could involve incorporating biologically foreign genes into an existing cell line. For example, E.Coli, which synthesizes ethanol, can be modified using genes from Zymomonas mobilis to make ethanol fermentation the primary cell fermentation product. | 1 | Biochemistry |
Small RNA sequencing can be useful for:
* studying the expression profile of miRNA and other small RNAs
* increasing the understanding of how cells are regulated or misregulated under pathological conditions
* small RNA clustering
* novel small RNA discovery
* small RNA prediction
* differential expression of all small RNAs in any sample | 1 | Biochemistry |
Human artificial chromosome may be potentially useful as a gene transfer vectors for gene delivery into human cells, and a tool for expression studies and determining human chromosome function. It can carry very large DNA fragment (there is no upper limit on size for practical purposes), therefore it does not have the problem of limited cloning capacity of other vectors, and it also avoids possible insertional mutagenesis caused by integration into host chromosomes by viral vector. | 1 | Biochemistry |
Thermobarometry uses equilibrium constants to calculate information about the environmental conditions present during the rocks' formation. While each rock is forming, it reacts with the surrounding elements until it cools down enough to become inert. Each mineral within the rock will cool and crystalize at different points; a petrogenetic grid is a useful way to visualize each mineral crystalizing in sequence.
Individual reactions of specific minerals can be used to calculate either the temperature or pressure. Therefore, two different reactions are needed to calculate both the temperature and pressure of the magma for a single rock. Some reactions are better for pressure and others are better for temperature, based on thermodynamics and Le Chatelier's Principle.
This technique requires each reaction to be calibrated, which is done through experimentation and data analysis. Experimentation involves simulating the temperatures and pressures at which these rocks form and observing how the reaction proceeds at those conditions, while data analysis relies on amassing a large database of rock samples with pressure and temperature information. Experimental data tends to have significant variation, so using data from natural formations is more accurate, if it's available. | 9 | Geochemistry |
In botany, a light curve shows the photosynthetic response of leaf tissue or algal communities to varying light intensities. The shape of the curve illustrates the principle of limiting factors; in low light levels, the rate of photosynthesis is limited by the concentration of chlorophyll and the efficiency of the light-dependent reactions, but in higher light levels it is limited by the efficiency of RuBisCo and the availability of carbon dioxide. The point on the curve where these two differing slopes meet is called the light saturation point and is where the light-dependent reactions are producing more ATP and NADPH than can be utilized by the light-independent reactions. Since photosynthesis is also limited by ambient carbon dioxide levels, light curves are often repeated at several different constant carbon dioxide concentrations. | 5 | Photochemistry |
All metal castings experience segregation to some extent, and a distinction is made between macrosegregation and microsegregation. Microsegregation refers to localized differences in composition between dendrite arms, and can be significantly reduced by a homogenizing heat treatment. This is possible because the distances involved (typically on the order of 10 to 100 μm) are sufficiently small for diffusion to be a significant mechanism. This is not the case in macrosegregation. Therefore, macrosegregation in metal castings cannot be remedied or removed using heat treatment. | 7 | Physical Chemistry |
This process was patented and sold to Hoffmann-La Roche in 1934. The first commercially sold vitamin C product was either Cebion from Merck or Redoxon from Hoffmann-La Roche.
Even today industrial methods for the production of ascorbic acid can be based on the Reichstein process. In modern methods however, sorbose is directly oxidized with a platinum catalyst (developed by Kurt Heyns (1908–2005) in 1942). This method avoids the use of protective groups. A side product with particular modification is 5-Keto-D-gluconic acid.
A shorter biotechnological synthesis of ascorbic acid was announced in 1988 by Genencor International and Eastman Chemical. Glucose is converted to 2-keto-L-gulonic acid in two steps (via 2,4-diketo-L-gulonic acid intermediate) as compared to five steps in the traditional process.
Though many organisms synthesize their own vitamin C, the steps can be different in plants and mammals. Smirnoff concluded that “..little is known about many of the enzymes involved in ascorbate biosynthesis or about the factors controlling flux through the pathways". There is interest in finding alternatives to the Reichstein process. Experiments suggest that genetically modified bacteria might be commercially usable. | 0 | Organic Chemistry |
(+)-discodermolide has a linear polypropionate backbone, punctuated by Z-olefinic linkages at C(8,9) and C(13,14), a terminal Z-diene substituent at C(21–24), 13 stereogenic centers (including four secondary hydroxyls and seven methyl substituents), a carbamate, and a fully substituted D-lactone. The relative stereochemistry was determined by X-ray crystallography. The absolute stereochemistry of (+)-discodermolide was reported by Schreiber and his co-workers in 1993. Discodermolide adopts a U-shaped conformation, where the internal (Z)-alkenes act as conformational locks by minimizing allylic strain and syn-pentane interactions along the backbone. The D-lactone is held in a boat-like conformation. | 0 | Organic Chemistry |
Octafluoropropane can be produced either by electrochemical fluorination or by the Fowler process using cobalt fluoride. | 2 | Environmental Chemistry |
In solid-state physics, an orientational glass is a molecular solid in which crystalline long-range order coexists with quenched disorder in some rotational degree of freedom.
An orientational glass is either obtained by quenching a plastic crystal, (e.g. cyclohexane, levoglucosan), or it is a mixed crystal in which positional disorder causes additional disorder of molecular orientations, e.g. CN orientations in KCN:KBr. | 3 | Analytical Chemistry |
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group. Aldehydes are a common motif in many chemicals important in technology and biology. | 0 | Organic Chemistry |
Malonyl-CoA, in a series of reactions, is further split into acetyl-CoA and glyoxylate. Glyoxylate is incorporated into beta-methylmalyl-coA which is then split, again through a series of reactions, to release pyruvate as well as acetate, which is used to replenish the cycle. | 1 | Biochemistry |
The B-B bond adds across alkenes and alkynes to give the 1,2-diborylated alkanes and alkenes. Using various organorhodium or organoiridium catalysts, it can also be installed onto saturated hydrocarbons:
:CH(CH)CH + [pinB] → pinBH + CH(CH)Bpin
These reactions proceed via boryl complexes.
Bis(pinacolato)diboron can also be used as reducing agent for example in transition metal catalyzed hydrogenations of alkenes and alkynes. | 0 | Organic Chemistry |
We consider a polymer as a chain of monomers, each with its position vector and scattering amplitude . For simplicity, it is worthwhile considering identical monomers in the chain, such that all .
An incoming ray (of light/neutrons/X-ray etc.) has a wave vector (or momentum) , and is scattered by the polymer to the vector . This enables us to define the scattering vector .
By coherently summing the contributions of all monomers, we get the scattering intensity from a single polymer, as a function of : | 7 | Physical Chemistry |
In froth flotation, the crushed ore is wetted, suspended in a slurry, and mixed with reagents that render the sulfide particles hydrophobic. Typical reagents ("collectors") include potassium ethylxanthate and sodium ethylxanthate, but dithiophosphates and dithiocarbamates are also used. The slurry is introduced to a water-filled aeration tank containing a surfactant such as methylisobutyl carbinol (MIBC). Air is constantly forced through the slurry. The air bubbles attach to the hydrophobic copper sulfide particles, which are conveyed to the surface where the froth is skimmed off. These skimmings are generally subjected to a cleaner-scavenger cell to remove excess silicates and to remove other sulfide minerals that can deleteriously impact the concentrate quality (typically, galena), and the final concentrate sent for smelting. The rock that has not floated off in the flotation cell is either discarded as tailings or further processed to extract other metals such as lead (from galena) and zinc (from sphalerite), should they exist. A variety of measures are taken to improve the efficiency of the froth flotation. Lime is used to raise the pH of the water bath, causing the collector to bond more efficiently to the copper sulfides. The process can produce a concentrates with 27–29% and 37–40% copper contents from chalcopyrite and chalcocite, respectively. | 8 | Metallurgy |
In organosulfur chemistry, a thioketal is the sulfur analogue of a ketal (), with one of the oxygen replaced by sulfur (as implied by the thio- prefix), giving the structure . A dithioketal has both oxygens replaced by sulfur ().
Thioketals can be obtained by reacting ketones () or aldehydes () with thiols ().
An oxidative cleavage mechanism has been proposed for dithioketals, which involves thioether oxidation, the formation of thionoiums, and hydrolysis, resulting in the formation of aldehyde and ketone products.
Thioketal moieties are found to be responsive to reactive oxygen species (ROS). In the presence of ROS, thioketals can be selectively cleaved. ROS successfully cleave heterobifunctional thioketal linkers, which have been found to have therapeutic potential, as they can produce ROS-responsive agents with two different functionalities.
Ketones can be reduced at neutral pH via conversion to thioketals; the thioketal prepared from the ketone can be easily reduced by catalytic hydrogenation using Raney nickel in a reaction known as the Mozingo reduction. | 0 | Organic Chemistry |
In the 1996 report of the method, thin films were coated with yttrium and lanthanum topped with a layer of palladium for the diffusion of hydrogen. The rate of absorption of hydrogen resulted in typical optical properties. In the 2008 report magnesium, titanium and nickel are eroded and sputtering deposited in different ratios onto a transparent film in a thin layer of 100 nanometres following exposure to hydrogen in different amounts resulting in optical differences. | 3 | Analytical Chemistry |
Terahertz spectroscopy detects and controls properties of matter with electromagnetic fields that are in the frequency range between a few hundred gigahertz and several terahertz (abbreviated as THz). In many-body systems, several of the relevant states have an energy difference that matches with the energy of a THz photon. Therefore, THz spectroscopy provides a particularly powerful method in resolving and controlling individual transitions between different many-body states. By doing this, one gains new insights about many-body quantum kinetics and how that can be utilized in developing new technologies that are optimized up to the elementary quantum level.
Different electronic excitations within semiconductors are already widely used in lasers, electronic components and computers. At the same time, they constitute an interesting many-body system whose quantum properties can be modified, e.g., via a nanostructure design. Consequently, THz spectroscopy on semiconductors is relevant in revealing both new technological potentials of nanostructures as well as in exploring the fundamental properties of many-body systems in a controlled fashion. | 7 | Physical Chemistry |
The boronic acid organic residue is a nucleophile in conjugate addition also in conjunction with a metal. In one study the pinacol ester of allylboronic acid is reacted with dibenzylidene acetone in such a conjugate addition:
:The catalyst system in this reaction is tris(dibenzylideneacetone)dipalladium(0) / tricyclohexylphosphine.
Another conjugate addition is that of gramine with phenylboronic acid catalyzed by cyclooctadiene rhodium chloride dimer: | 0 | Organic Chemistry |
Carbon dioxide in the Earth's atmosphere is essential to life and to most of the planetary biosphere. The average rate of energy capture by photosynthesis globally is approximately 130 terawatts, which is about six times larger than the current power consumption of human civilization. Photosynthetic organisms also convert around 100–115 billion metric tonnes of carbon into biomass per year.
Photosynthetic organisms are photoautotrophs, which means that they are able to synthesize food directly from and water using energy from light. However, not all organisms that use light as a source of energy carry out photosynthesis, since photoheterotrophs use organic compounds, rather than , as a source of carbon. In plants, algae and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis. Although there are some differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms. Some types of bacteria, however, carry out anoxygenic photosynthesis, which consumes but does not release oxygen.
Carbon dioxide is converted into sugars in a process called carbon fixation. Carbon fixation is an endothermic redox reaction, so photosynthesis needs to supply both the source of energy to drive this process and the electrons needed to convert into a carbohydrate. This addition of the electrons is a reduction reaction. In general outline and in effect, photosynthesis is the opposite of cellular respiration, in which glucose and other compounds are oxidized to produce and water, and to release exothermic chemical energy to drive the organism's metabolism. The two processes take place through a different sequence of chemical reactions, however, and in different cellular compartments. | 2 | Environmental Chemistry |
Passive daytime radiative cooling is referred to as more stable, adaptable, and reversible when compared to stratospheric aerosol injection, which proposes injecting particles into the atmosphere to increase radiative forcing to reduce temperatures. Studies have warned against stratospheric aerosol injections potential to contribute to further ozone loss and heat the Earths lower stratosphere further, stating that the injection of sulfate particles "would reflect more of the incoming solar radiation back into space, but it would also capture more of the outgoing thermal radiation back to the Earth" and therefore accelerate warming.
Wang et al. states that stratospheric aerosol injection "might cause potentially dangerous threats to the Earth’s basic climate operations" that may not be reversible, and thus put forth a preference for passive radiative cooling. Munday noted that although "unexpected effects will likely occur" with the global implementation of PDRC, that "these structures can be removed immediately if needed, unlike methods that involve dispersing particulate matter into the atmosphere, which can last for decades."
When compared to the reflective surfaces approach of increasing the reflectivity or albedo of surfaces, such as through painting roofs white, or the space mirror proposals of "deploying giant reflective surfaces in space," Munday states that "the increased reflectivity likely falls short of what is needed and comes at a high financial cost." PDRC differs from the reflective surfaces approach by "increasing the radiative heat emission from the Earth rather than merely decreasing its solar absorption." | 7 | Physical Chemistry |
An ion trap mass spectrometer may incorporate a Penning trap (Fourier-transform ion cyclotron resonance), Paul trap or the Kingdon trap. The Orbitrap, introduced in 2005, is based on the Kingdon trap. Other types of mass spectrometers may also use a linear quadrupole ion trap as a selective mass filter. | 7 | Physical Chemistry |
* Evaporation
* Sublimation
* Cracking of alkanes
* Thermal decomposition
* Hydrolysis
* Nucleosynthesis of elements heavier than nickel in stellar cores
* High-energy neutrons can produce tritium from lithium-7 in an endothermic process, consuming 2.466 MeV. This was discovered when the 1954 Castle Bravo nuclear test produced an unexpectedly high yield.
* Nuclear fusion of elements heavier than iron in supernovae
*Dissolving together barium hydroxide and ammonium chloride
*Dissolving together citric acid and baking soda | 7 | Physical Chemistry |
*Atkins, P.W. (1978). Physical Chemistry Oxford University Press
*Trevor Palmer (2001) Enzymes: biochemistry, biotechnology and clinical chemistry Chichester Horwood Publishing | 7 | Physical Chemistry |
Acid–base homeostasis is the homeostatic regulation of the pH of the body's extracellular fluid (ECF). The proper balance between the acids and bases (i.e. the pH) in the ECF is crucial for the normal physiology of the body—and for cellular metabolism. The pH of the intracellular fluid and the extracellular fluid need to be maintained at a constant level.
The three dimensional structures of many extracellular proteins, such as the plasma proteins and membrane proteins of the body's cells, are very sensitive to the extracellular pH. Stringent mechanisms therefore exist to maintain the pH within very narrow limits. Outside the acceptable range of pH, proteins are denatured (i.e. their 3D structure is disrupted), causing enzymes and ion channels (among others) to malfunction.
An acid–base imbalance is known as acidemia when the pH is acidic, or alkalemia when the pH is alkaline. | 7 | Physical Chemistry |
Linear azole(in)e-containing peptides (LAPs) contain thiazoles and oxazoles, or their reduced thiazoline and oxazoline forms. Thiazol(in)es are the result of cyclization of Cys residues in the precursor peptide, while (methyl)oxazol(in)es are formed from Thr and Ser. Azole and azoline formation also modifies the residue in the -1 position, or directly C-terminal to the Cys, Ser, or Thr. A dehydrogenase in the LAP gene cluster is required for oxidation of azolines to azoles.
Plantazolicin is a LAP with extensive cyclization. Two sets of five heterocycles endow the natural product with structural rigidity and unusually selective antibacterial activity. Streptolysin S (SLS) is perhaps the most well-studied and most famous LAP, in part because the structure is still unknown since the discovery of SLS in 1901. Thus, while the biosynthetic gene cluster suggests SLS is a LAP, structural confirmation is lacking. | 1 | Biochemistry |
The Britton–Robinson buffer (aka BRB aka PEM) is a "universal" pH buffer used for the pH range from 2 to 12. It has been used historically as an alternative to the McIlvaine buffer, which has a smaller pH range of effectiveness (from 2 to 8).
Universal buffers consist of mixtures of acids of diminishing strength (increasing pK), so that the change in pH is approximately proportional to the amount of alkali added. It consists of a mixture of 0.04 M boric acid, 0.04 M phosphoric acid and 0.04 M acetic acid that has been titrated to the desired pH with 0.2 M sodium hydroxide. Britton and Robinson also proposed a second formulation that gave an essentially linear pH response to added alkali from pH 2.5 to pH 9.2 (and buffers to pH 12). This mixture consists of 0.0286 M citric acid, 0.0286 M monopotassium phosphate, 0.0286 M boric acid, 0.0286 M veronal and 0.0286 M hydrochloric acid titrated with 0.2 M sodium hydroxide.
The buffer was invented in 1931 by the English chemist Hubert Thomas Stanley "Kevin" Britton (1892–1960) and the New Zealand chemist Robert Anthony Robinson (1904–1979). | 3 | Analytical Chemistry |
Sekeris was a direct descendant of Panagiotis Sekeris, a merchant and ship owner who lived in Constantinople in the early 19th century and co-founded the Filiki Eteria (a secret society aiming to overthrow the Ottoman rule in Greece), and who spent his entire wealth financing this process. Sekeris married Lioka (Kalliope), born Platsouka (passed away in 1997) and then Evi, born Protopappa. He was survived by one son, Evangelos a member of the Hellenic Diplomatic Corps, three grandchildren (Kalliope, Katherine and Constantine) and his three siblings, two brothers (Giorgos and Thanassis) and one sister (Kalliope). | 1 | Biochemistry |
There are a number of software tools that can directly compute elasticities and control coefficients:
* COPASI (GUI)
* PySCeS (Python)
* SBW (GUI)
* libroadrunner (Python)
* VCell | 1 | Biochemistry |
An essential nutrient is a nutrient required for normal physiological function that cannot be synthesized in the body – either at all or in sufficient quantities – and thus must be obtained from a dietary source. Apart from water, which is universally required for the maintenance of homeostasis in mammals, essential nutrients are indispensable for various cellular metabolic processes and for the maintenance and function of tissues and organs. The nutrients considered essential for humans comprise nine amino acids, two fatty acids, thirteen vitamins, fifteen minerals and choline. In addition, there are several molecules that are considered conditionally essential nutrients since they are indispensable in certain developmental and pathological states. | 9 | Geochemistry |
A methylene blue active substances assay, or MBAS assay, is a colorimetric analysis test method that uses methylene blue to detect the presence of anionic surfactants (such as a detergent or foaming agent) in a sample of water. An anionic surfactant detected by the color reaction is called a methylene blue active substance (MBAS).
After first acidifying a water sample (with boric acid, for example), one adds to it chloroform and a solution of methylene blue et al. Methylene blue is a cationic dye. The biphasic solution is then agitated to distribute these reagents throughout the aqueous and organic phases. If an anionic surfactant is present, then the cationic methylene blue and the anionic surfactant forms an ion pair, which is extracted into the organic phase. The color saturation of the chloroform increases with the concentration of anionic surfactants.
MBAS assay is an ASTM International standard technique for detecting anionic surfactants. These include carboxylates, phosphates, sulfates, and sulfonates. An MBAS assay alone does not, however, identify specific surfactants. ASTM withdrew the standard (ASTM D2330-02) in 2011 pending a review and update of the method, which was last approved in 2003.
The publication Standard Methods for the Examination of Water and Wastewater lists the following methods used by certified laboratories testing wastewater in the United States.
* Method 5540B describes surfactant separation by sublation.
* Method 5540C discusses anionic surfactants as methylene blue active substances (MBAS).
* Method 5540D discusses nonionic surfactants as cobalt thiocyanate active substances (CTAS). | 3 | Analytical Chemistry |
The Buchner-Curtius-Schlotterbeck reaction yields ketones from aldehydes and aliphatic diazo compounds:
The reaction type is nucleophilic addition. | 0 | Organic Chemistry |
Milky seas (Somali: Kaluunka iftiima; English: Milky seas), also called mareel, is a luminous phenomenon in the ocean in which large areas of seawater (up to ) appear to glow translucently (in varying shades of blue). Such occurrences glow brightly enough at night to be visible from satellites orbiting Earth.
Mariners and other seafarers have reported that the ocean often emits a visible glow which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow. It is most likely caused by bioluminescence. | 1 | Biochemistry |
The Egyptians were practicing cire perdue from the mid 3rd millennium BC, shown by Early Dynastic bracelets and gold jewellery. Inserted spouts for ewers (copper water vessels) from the Fourth Dynasty (Old Kingdom) were made by the lost-wax method. Hollow castings, such as the Louvre statuette from the Fayum find appeared during the Middle Kingdom, followed by solid cast statuettes (like the squatting, nursing mother, in Brooklyn) of the Second Intermediate/Early New Kingdom. The hollow casting of statues is represented in the New Kingdom by the kneeling statue of Tuthmosis IV (British Museum, London) and the head fragment of Ramesses V (Fitzwilliam Museum, Cambridge). Hollow castings become more detailed and continue into the Eighteenth Dynasty, shown by the black bronze kneeling figure of Tutankhamun (Museum of the University of Pennsylvania). Cire Perdue is used in mass-production during the Late Period to Graeco-Roman times when figures of deities were cast for personal devotion and votive temple offerings. Nude female-shaped handles on bronze mirrors were cast by the lost-wax process. | 8 | Metallurgy |
Chloromethane was a widely used refrigerant, but its use has been discontinued. It was particularly dangerous among the common refrigerants of the 1930s due to its combination of toxicity, flammability and lack of odor as compared with other toxic refrigerants such as sulfur dioxide and ammonia. Chloromethane was also once used for producing lead-based gasoline additives (tetramethyllead). | 2 | Environmental Chemistry |
Oxygen-17 (O) is a low-abundance, natural, stable isotope of oxygen (0.0373% in seawater; approximately twice as abundant as deuterium).
As the only stable isotope of oxygen possessing a nuclear spin (+5/2) and a favorable characteristic of field-independent relaxation in liquid water, O enables NMR studies of oxidative metabolic pathways through compounds containing O (i.e. metabolically produced HO water by oxidative phosphorylation in mitochondria) at high magnetic fields.
Water used as nuclear reactor coolant is subjected to intense neutron flux. Natural water starts out with 373 ppm of O; heavy water starts out incidentally enriched to about 550 ppm of oxygen-17. The neutron flux slowly converts O in the cooling water to O by neutron capture, increasing its concentration. The neutron flux slowly converts O (with much greater cross section) in the cooling water to carbon-14, an undesirable product that can escape to the environment:
: O (n,α) → C
Some tritium removal facilities make a point of replacing the oxygen of the water with natural oxygen (mostly O) to give the added benefit of reducing C production. | 9 | Geochemistry |
There is an operational blacksmith shop with an operating line shaft setup powered by a 15-horsepower 1917 Mogul gasoline engine. During the show days, there are multiple forges lit, and multiple blacksmiths can be found working pieces of iron into many different things. | 8 | Metallurgy |
The PCR method is extremely sensitive, requiring only a few DNA molecules in a single reaction for amplification across several orders of magnitude. Therefore, adequate measures to avoid contamination from any DNA present in the lab environment (bacteria, viruses, or human sources) are required. Because products from previous PCR amplifications are a common source of contamination, many molecular biology labs have implemented procedures that involve dividing the lab into separate areas. One lab area is dedicated to preparation and handling of pre-PCR reagents and the setup of the PCR reaction, and another area to post-PCR processing, such as gel electrophoresis or PCR product purification. For the setup of PCR reactions, many standard operating procedures involve using pipettes with filter tips and wearing fresh laboratory gloves, and in some cases a laminar flow cabinet with UV lamp as a work station (to destroy any extraneomultimer formation). PCR is routinely assessed against a negative control reaction that is set up identically to the experimental PCR, but without template DNA, and performed alongside the experimental PCR. | 1 | Biochemistry |
In spectroscopy, an isosbestic point is a specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample. The word derives from two Greek words: "iso", meaning "equal", and "sbestos", meaning "extinguishable". | 7 | Physical Chemistry |
Nearly all materials could be seen as hierarchically structured, since the changes in spatial scale bring about different mechanisms of deformation and damage. However, in biological materials, this hierarchical organization is inherent to the microstructure. One of the first examples of this, in the history of structural biology, is the early X-ray scattering work on the hierarchical structure of hair and wool by Astbury and Woods. In bone, for example, collagen is the building block of the organic matrix, a triple helix with diameter of 1.5 nm. These tropocollagen molecules are intercalated with the mineral phase (hydroxyapatite, calcium phosphate) forming fibrils that curl into helicoids of alternating directions. These "osteons" are the basic building blocks of bones, with the volume fraction distribution between organic and mineral phase being about 60/40.
In another level of complexity, the hydroxyapatite crystals are mineral platelets that have a diameter of approximately 70 to 100 nm and thickness of 1 nm. They originally nucleate at the gaps between collagen fibrils.
Similarly, the hierarchy of abalone shell begins at the nanolevel, with an organic layer having a thickness of 20 to 30 nm. This layer proceeds with single crystals of aragonite (a polymorph of CaCO) consisting of "bricks" with dimensions of 0.5 and finishing with layers approximately 0.3 mm (mesostructure).
Crabs are arthropods, whose carapace is made of a mineralized hard component (exhibits brittle fracture) and a softer organic component composed primarily of chitin. The brittle component is arranged in a helical pattern. Each of these mineral "rods" (1 μm diameter) contains chitin–protein fibrils with approximately 60 nm diameter. These fibrils are made of 3 nm diameter canals that link the interior and exterior of the shell. | 1 | Biochemistry |
Polytypes are a special case of polymorphs, where multiple close-packed crystal structures differ in one dimension only. Polytypes have identical close-packed planes, but differ in the stacking sequence in the third dimension perpendicular to these planes. Silicon carbide (SiC) has more than 170 known polytypes, although most are rare. All the polytypes of SiC have virtually the same density and Gibbs free energy. The most common SiC polytypes are shown in Table 1.
Table 1: Some polytypes of SiC.
A second group of materials with different polytypes are the transition metal dichalcogenides, layered materials such as molybdenum disulfide (MoS). For these materials the polytypes have more distinct effects on material properties, e.g. for MoS, the 1T polytype is metallic in character, while the 2H form is more semiconducting.
Another example is tantalum disulfide, where the common 1T as well as 2H polytypes occur, but also more complex mixed coordination types such as 4Hb and 6R, where the trigonal prismatic and the octahedral geometry layers are mixed. Here, the 1T polytype exhibits a charge density wave, with distinct influence on the conductivity as a function of temperature, while the 2H polytype exhibits superconductivity.
ZnS and CdI are also polytypical. It has been suggested that this type of polymorphism is due to kinetics where screw dislocations rapidly reproduce partly disordered sequences in a periodic fashion. | 3 | Analytical Chemistry |
Serious galvanic corrosion has been reported on the latest US Navy attack littoral combat vessel the USS Independence caused by steel water jet propulsion systems attached to an aluminium hull. Without electrical isolation between the steel and aluminium, the aluminium hull acts as an anode to the stainless steel, resulting in aggressive galvanic corrosion. | 8 | Metallurgy |
Campbell was born in Waimate on 27 May 1925, the son of Mona Sevicke Campbell (née Jones) and David Brown Campbell. He was educated at Waimate High School, and then proceeded to study chemistry at the University of Otago, graduating Master of Science with second-class honours in 1948, and PhD in 1953. His doctoral thesis was titled Some applications of acrylonitrile.
In 1950, Campbell married Ruth Florence Smith, and the couple went on to have three children. | 3 | Analytical Chemistry |
The cyclooctane derivative OCT was the first one developed for Cu-free click chemistry; it had only ring strain to drive the reaction forward, and the kinetics were barely improved over the Staudinger ligation. After OCT and MOFO (monofluorinated cyclooctyne), the difluorinated cyclooctyne (DIFO) was developed. An improved synthetic approach to a monofluorosubstituted cyclooctyne (MFCO) was introduced that could easily be converted to a useful reactive intermediate for bioconjugation applications, although the reactivity was somewhat slower than DIFO. The MFCO demonstrated excellent stability characteristics for long-term storage.
The substituted cyclooctyne is activated for a 1,3-dipolar cycloaddition by its ring strain and electron-withdrawing fluorine substituents, which allows the reaction to take place with kinetics comparable to the Cu-catalyzed Huisgen cycloaddition. Ring strain (~18 kcal/mol) arises from the deviation of the bond angles from the ideal 180° to form an eight-membered ring, the smallest of all cycloalkynes. The electron-withdrawing fluorine substituents were chosen due to their synthetic ease and compatibility with living biological systems. Additionally, the group cannot produce cross-reacting Michael acceptors that could act as alkylating agents toward nucleophilic species within cells.
Like most cyclooctynes, DIFO prefers the chair conformation in both the ground state and the minimum energy traction path, although boat transition states may also be involved. Gas phase regioselectivity is calculated to favor 1,5 addition over 1,4 addition by up to 2.9 kcal/mol in activation energy in the gas phase; solvation corrections give the same energy barriers for both regioisomers, explaining the regioisomeric mix that results from DIFO cycloadditions. While the 1,4 isomer is disfavored by its larger dipole moment (all electron-rich substituents on one side), solvation stabilizes it more strongly than the 1,5 isomer, eroding regioselectivity. Experimental studies by Carolyn R. Bertozzi report a nearly 1:1 ratio of regioisomers, confirming the predicted lack of regioselectivity in the addition.
Furthermore, nearly all of the distortion energy (92%) arises from the distortion of the 1,3 dipole rather than the cyclooctyne, which has a pre-distorted ground state geometry that increases its reactivity. Fluorination decreases the distortion energy by allowing the transition state to be achieved with a lesser distortion of the 1,3-dipole during a reaction, resulting in a larger dipole angle. | 0 | Organic Chemistry |
Chloroplasts alone make almost all of a plant cell's amino acids in their stroma except the sulfur-containing ones like cysteine and methionine. Cysteine is made in the chloroplast (the proplastid too) but it is also synthesized in the cytosol and mitochondria, probably because it has trouble crossing membranes to get to where it is needed. The chloroplast is known to make the precursors to methionine but it is unclear whether the organelle carries out the last leg of the pathway or if it happens in the cytosol. | 5 | Photochemistry |
In humans endoglin may be involved in the autosomal dominant disorder known as hereditary hemorrhagic telangiectasia (HHT) type 1. HHT is actually the first human disease linked to the TGF beta receptor complex. This condition leads to frequent nose bleeds, telangiectases on skin and mucosa and may cause arteriovenous malformations in different organs including brain, lung, and liver. | 1 | Biochemistry |
Physicochemical distance is a measure that assesses the difference between replaced amino acids. The value of distance is based on properties of amino acids. There are 134 physicochemical properties that can be used to estimate similarity between amino acids. Each physicochemical distance is based on different composition of properties. | 1 | Biochemistry |
Selected reactivity of diphosphenes is summarized in the following picture, including oxidation, reduction, sulfurization, polymerization, carbene addition, halogenation, photolysis, and coordination to the transition-metal: | 0 | Organic Chemistry |
The Hepatitis C virus requires the CD81 co-receptor for infection. Studies suggest that the tight junction protein Claudin-1 (CLDN1) may also play a part in HCV entry. Claudin family abnormalities are also common in hepatocellular carcinoma, which can result from HPV infection. | 1 | Biochemistry |
Closed fullerenes encapsulating small molecules have been synthesized. Representative are the synthesis of the dihydrogen endofullerene H@C, the water endofullerene HO@C, the hydrogen fluoride endofullerene HF@C, and the methane endofullerene CH@C. The encapsulated molecules display unusual physical properties which have been studied by a variety of physical methods. As shown theoretically, compression of molecular endofullerenes (e.g., H@C) may lead to dissociation of the encapsulated molecules and reaction of their fragments with interiors of the fullerene cage. Such reactions should result in endohedral fullerene adducts, which are currently unknown. | 6 | Supramolecular Chemistry |
Joseph Joshua Weiss (30 August 1905 – 9 April 1972) was a Jewish-Austrian chemist and Professor at the Newcastle University. He was a pioneer in the field of radiation chemistry and photochemistry. | 5 | Photochemistry |
Problems with mRNA stability have been identified in viral genomes, cancer cells, and various diseases. Research shows that many of these problems arise because of faulty ARE function. Some of these problems have been listed below:
* The c-fos gene produces a transcription factor that is activated in several cancers, and it lacks the ARE elements.
* c-myc gene, also responsible for producing transcription factors found in several cancers, has also been reported to lack the ARE elements.
* The Cox-2 gene catalyses the production of prostaglandins—it overexpresses in several cancers, and is stabilized by the binding of CUGBP2 RNA-binding protein to ARE | 1 | Biochemistry |
In chemistry, halogenation is a chemical reaction which introduces of one or more halogens into a chemical compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (). Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride. | 0 | Organic Chemistry |
A common way ordinary consumers are exposed to nitrosamines is through tobacco use and cigarette smoke. Tobacco-specific nitrosamines also can be found in American dip snuff, chewing tobacco, and to a much lesser degree, snus (127.9 ppm for American dip snuff compared to 2.8 ppm in Swedish snuff or snus). | 0 | Organic Chemistry |
Following their development of Au-catalyzed Conia-ene reactions, Toste and coworkers employed such a transformation toward the alkaloid natural product lycopladine A. Starting from chiral cyclohexenone 1, a series of enone functionalizations gave silyl enol ether 2 as the Conia-ene precursor. To effect cyclization, 2 was treated with catalytic AuCl(PPh) and AgBF to furnish vinyl iodide 3 in high yield as a single diastereomer. The remainder of the molecule was completed in three steps to give (+)-lycopladine A in eight steps and 17% overall yield.
In 2012, Carreira et al. synthesized , a halogenated terpene isolated from the red algae Laurencia majuscula, and employed Au-catalyzed Conia-ene cyclization as the penultimate step. Having obtained silyl enol ether 7 in 11 steps from bicycle 6, itself the product of a Diels–Alder cycloaddition between 4 and enone 5, the authors subject 7 to 50 mol% Echavarren’s catalyst to deliver tricycle 8 in 65% yield. This compound is then elaborated to by chlorination of the exo-methylene.
In 2020, Yang and coworkers employed a diastereoselective Conia-ene reaction during their asymmetric synthesis of (+)-waihoensene, a structurally dense terpenoid from Podocarpus totara var. waihoensis, first synthesized by the Lee group in 2017. Vinylogous ester 9 was first functionalized in six steps to chiral Conia-ene precursor 10. Subsequent treatment of 10 with tBuOK in DMSO gave bicycle 11 in 83% yield as a single diastereomer. This compound then required eight additional transformations to reach (+)-waihoensene in 15 steps and 4% overall yield. | 0 | Organic Chemistry |
Shotgun lipidomics was developed by Richard W. Gross and Xianlin Han, by employing ESI intrasource separation techniques. Individual molecular species of most major and many minor lipid classes can be fingerprinted and quantitated directly from biological lipid extracts without the need for chromatographic purification. | 1 | Biochemistry |
In special relativity, an observer moving with uniform proper acceleration through Minkowski spacetime is conveniently described with Rindler coordinates, which are related to the standard (Cartesian) Minkowski coordinates by
The line element in Rindler coordinates, i.e. Rindler space is
where , and where is related to the observer's proper time by (here ).
An observer moving with fixed traces out a hyperbola in Minkowski space, therefore this type of motion is called hyperbolic motion. The coordinate is related to the Schwarzschild spherical coordinate by the relation
An observer moving along a path of constant is uniformly accelerating, and is coupled to field modes which have a definite steady frequency as a function of . These modes are constantly Doppler shifted relative to ordinary Minkowski time as the detector accelerates, and they change in frequency by enormous factors, even after only a short proper time.
Translation in is a symmetry of Minkowski space: it can be shown that it corresponds to a boost in x, t coordinate around the origin. Any time translation in quantum mechanics is generated by the Hamiltonian operator. For a detector coupled to modes with a definite frequency in , we can treat as "time" and the boost operator is then the corresponding Hamiltonian. In Euclidean field theory, where the minus sign in front of the time in the Rindler metric is changed to a plus sign by multiplying to the Rindler time, i.e. a Wick rotation or imaginary time, the Rindler metric is turned into a polar-coordinate-like metric. Therefore any rotations must close themselves after 2 in a Euclidean metric to avoid being singular. So
A path integral with real time coordinate is dual to a thermal partition function, related by a Wick rotation. The periodicity of imaginary time corresponds to a temperature of in thermal quantum field theory. Note that the path integral for this Hamiltonian is closed with period 2. This means that the modes are thermally occupied with temperature . This is not an actual temperature, because is dimensionless. It is conjugate to the timelike polar angle , which is also dimensionless. To restore the length dimension, note that a mode of fixed frequency in at position has a frequency which is determined by the square root of the (absolute value of the) metric at , the redshift factor. This can be seen by transforming the time coordinate of a Rindler observer at fixed to an inertial, co-moving observer observing a proper time. From the Rindler-line-element given above, this is just . The actual inverse temperature at this point is therefore
It can be shown that the acceleration of a trajectory at constant in Rindler coordinates is equal to , so the actual inverse temperature observed is
Restoring units yields
The temperature of the vacuum, seen by an isolated observer accelerating at the Earth's gravitational acceleration of = , is only . For an experimental test of the Unruh effect it is planned to use accelerations up to , which would give a temperature of about .
The Rindler derivation of the Unruh effect is unsatisfactory to some, since the detector's path is super-deterministic. Unruh later developed the Unruh–DeWitt particle detector model to circumvent this objection. | 7 | Physical Chemistry |
The original sequence is reconstructed from the reads using sequence assembly software. First, overlapping reads are collected into longer composite sequences known as contigs. Contigs can be linked together into scaffolds by following connections between mate pairs. The distance between contigs can be inferred from the mate pair positions if the average fragment length of the library is known and has a narrow window of deviation. Depending on the size of the gap between contigs, different techniques can be used to find the sequence in the gaps. If the gap is small (5-20kb) then the use of polymerase chain reaction (PCR) to amplify the region is required, followed by sequencing. If the gap is large (>20kb) then the large fragment is cloned in special vectors such as bacterial artificial chromosomes (BAC) followed by sequencing of the vector. | 1 | Biochemistry |
Oxoammonium cations are isoelectronic with carbonyls and structurally related to aldoximes (hydroxylamines), and aminoxyl (nitroxide) radicals, with which they can interconvert via a series of redox steps. According to X-ray crystallography, the N–O distance in [TEMPO]BF is 1.184 Å, 0.1 Å shorter than the N–O distance of 1.284 Å in the charge-neutral TEMPO. Similarly, the N in [TEMPO] is nearly planar, but the O moves 0.1765 Å out of the plane in the neutral TEMPO.
The N-oxoammonium salts are used for oxidation of alcohols to carbonyl groups, as well as other forms of oxoammonium-catalyzed oxidations. The nitroxyl TEMPO reacts via its N-oxoammonium salt. | 0 | Organic Chemistry |
In 1995 high levels of MTBE were unexpectedly discovered in the water wells of Santa Monica, California, and the U.S. Geological Survey reported detections. Subsequent U.S. findings indicate tens of thousands of contaminated sites in water wells distributed across the country. As per toxicity alone, MTBE is not classified as a hazard for the environment, but it imparts an unpleasant taste to water even at very low concentrations. The maximum contaminant level of MTBE in drinking water has not yet been established by the United States Environmental Protection Agency (EPA). The leakage problem is partially attributed to the lack of effective regulations for underground storage tanks, but spillage from overfilling is also a contributor. As an ingredient in unleaded gasoline, MTBE is the most water-soluble component. When dissolved in groundwater, MTBE will lead the contaminant plume with the remaining components such as benzene and toluene following. Thus the discovery of MTBE in public groundwater wells indicates that the contaminant source was a gasoline release. Its criticism and subsequent decreased usage, some claim, is more a product of its easy detectability (taste) in extremely low concentrations (ppb) than its toxicity. The MTBE concentrations used in the EU (usually 1.0–1.6%) and allowed (maximum 5%) in Europe are lower than in California.
Chevron, BP, and other oil companies agreed to settle with Santa Monica for $423 million on May 7, 2008. | 2 | Environmental Chemistry |
Conventional cryoprotectants are glycols (alcohols containing at least two hydroxyl groups), such as ethylene glycol , propylene glycol and glycerol. Ethylene glycol is commonly used as automobile antifreeze; while propylene glycol has been used to reduce ice formation in ice cream. Dimethyl sulfoxide (DMSO) is also regarded as a conventional cryoprotectant. Glycerol and DMSO have been used for decades by cryobiologists to reduce ice formation in sperm, oocytes, and embryos that are cold-preserved in liquid nitrogen. Cryoconservation of animal genetic resources is a practice that involves conventional cryoprotectants to store genetic material with the intention of future revival. Trehalose is non-reducing sugar produced by yeasts and insects in copious amounts. Its use as a cryoprotectant in commercial systems has been patented widely. | 1 | Biochemistry |
* Effects of Pyrazinamide on Fatty Acid Synthesis by Whole Mycobacterial Cells and Purified Fatty Acid Synthase I. Helena I. Boshoff, Valerie Mizrahi, Clifton E. Barry. Journal of Bacteriology, 2002
* The impact of drug resistance on Mycobacterium tuberculosis physiology: what can we learn from rifampicin?. Anastasia Koch, Valerie Mizrahi, Digby F Warner. Emerging Microbes & Infections, 2014 | 1 | Biochemistry |
The treatment given so far is for a system not subject to an external electric field. When conductivity is measured the system is subject to an oscillating external field due to the application of an AC voltage to electrodes immersed in the solution. Debye and Hückel modified their theory in 1926 and their theory was further modified by Lars Onsager in 1927. All the postulates of the original theory were retained. In addition it was assumed that the electric field causes the charge cloud to be distorted away from spherical symmetry. After taking this into account, together with the specific requirements of moving ions, such as viscosity and electrophoretic effects, Onsager was able to derive a theoretical expression to account for the empirical relation known as Kohlrausch's Law, for the molar conductivity, Λ.
is known as the limiting molar conductivity, K is an empirical constant and c is the electrolyte concentration. Limiting here means "at the limit of the infinite dilution").
Onsager's expression is
where A and B are constants that depend only on known quantities such as temperature, the charges on the ions and the dielectric constant and viscosity of the solvent. This is known as the Debye–Hückel–Onsager equation. However, this equation only applies to very dilute solutions and has been largely superseded by other equations due to Fuoss and Onsager, 1932 and 1957 and later. | 7 | Physical Chemistry |
In contrast to most other neuroleptics which block both D and D receptors, levosulpiride is more selective and acts primarily as a D antagonist. Levosulpiride appears to lack effects on norepinephrine, acetylcholine, serotonin, histamine, and gamma-aminobutyric acid (GABA) receptors. | 4 | Stereochemistry |
* 1941: Isaac Asimov published the science fiction short story "Reason," in which a space station transmits energy collected from the sun to various planets using microwave beams. "Reason" was published in the "Astounding Science Fiction" magazine.
*1968: Peter Glaser introduces the concept of a "solar power satellite" system with square miles of solar collectors in high geosynchronous orbit for collection and conversion of sun's energy into a microwave beam to transmit usable energy to large receiving antennas (rectennas) on Earth for distribution.
* 1973: Peter Glaser is granted United States patent number 3,781,647 for his method of transmitting power over long distances using microwaves from a large (one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
* 1978–1981: The United States Department of Energy and NASA examine the solar power satellite (SPS) concept extensively, publishing design and feasibility studies.
* 1987: Stationary High Altitude Relay Platform a Canadian experiment
* 1995–1997: NASA conducts a "Fresh Look" study of space solar power (SSP) concepts and technologies.
* 1998: The Space Solar Power Concept Definition Study (CDS) identifies credible, commercially viable SSP concepts, while pointing out technical and programmatic risks.
* 1998: Japan's space agency begins developing a space solar power system (SSPS), a program that continues to the present day.
* 1999: NASAs Space Solar Power Exploratory Research and Technology program (SERT, see below') begins.
* 2000: John Mankins of NASA testifies in the U.S. House of Representatives, saying "Large-scale SSP is a very complex integrated system of systems that requires numerous significant advances in current technology and capabilities. A technology roadmap has been developed that lays out potential paths for achieving all needed advances — albeit over several decades. | 7 | Physical Chemistry |
Methylmercury is formed from inorganic mercury by the action of microbes that live in aquatic systems including lakes, rivers, wetlands, sediments, soils and the open ocean. This methylmercury production has been primarily attributed to anaerobic bacteria in the sediment. Significant concentrations of methylmercury in ocean water columns are strongly associated with nutrients and organic matter remineralization, which indicate that remineralization may contribute to methylmercury production. Direct measurements of methylmercury production using stable mercury isotopes have also been observed in marine waters, but the microbes involved are still unknown. Increased methylmercury concentrations in water and fish have been detected after flooding of soils associated with reservoir creation (e.g. for hydroelectric power generation) and in thermokarst wetlands that form after permafrost thaw.
There are various sources of inorganic mercury that may indirectly contribute to the production of methylmercury from microbes in the environment. Natural sources of mercury released to the atmosphere include volcanoes, forest fires, volatilization from the ocean and weathering of mercury-bearing rocks. Anthropogenic sources of mercury include the burning of wastes containing inorganic mercury and from the burning of fossil fuels, particularly coal. Although inorganic mercury is only a trace constituent of such fuels, their large scale combustion in utility and commercial/industrial boilers in the United States alone results in release of some 80.2 tons (73 metric tons) of elemental mercury to the atmosphere each year, out of total anthropogenic mercury emissions in the United States of 158 tons (144 metric tons)/year.
In the past, methylmercury was produced directly and indirectly as part of several industrial processes such as the manufacture of acetaldehyde. However, currently there are few direct anthropogenic sources of methylmercury pollution in the United States.
Whole-lake ecosystem experiments at IISD-ELA in Ontario, Canada, showed that mercury falling directly on a lake had the fastest impacts on aquatic ecosystems as opposed to mercury falling on the surrounding land. This inorganic mercury is converted to methylmercury by bacteria. Different stable isotopes of mercury were added to lakes, wetlands, and uplands, simulating rain, and then mercury concentrations in fish were analyzed to find their source. The mercury applied to lakes was found in young-of-the-year yellow perch within two months, whereas the mercury applied to wetlands and uplands had a slower but longer influx.
Acute methylmercury poisoning can occur either directly from the release of methylmercury into the environment or indirectly from the release of inorganic mercury that is subsequently methylated in the environment. For example, methylmercury poisoning occurred at Grassy Narrows in Ontario, Canada (see Ontario Minamata disease), as a result of mercury released from the mercury-cell Chloralkali process, which uses liquid mercury as an electrode in a process that entails electrolytic decomposition of brine, followed by mercury methylation in the aquatic environment. An acute methylmercury poisoning tragedy occurred also in Minamata, Japan, following release of methylmercury into Minamata Bay and its tributaries (see Minamata disease). In the Ontario case, inorganic mercury discharged into the environment was methylated in the environment; whereas, in Minamata, Japan, there was direct industrial discharge of methylmercury. | 0 | Organic Chemistry |
Though nitrogen fixation is the primary source of plant-available nitrogen in most ecosystems, in areas with nitrogen-rich bedrock, the breakdown of this rock also serves as a nitrogen source. Nitrate reduction is also part of the iron cycle, under anoxic conditions Fe(II) can donate an electron to and is oxidized to Fe(III) while is reduced to , and depending on the conditions and microbial species involved. The fecal plumes of cetaceans also act as a junction in the marine nitrogen cycle, concentrating nitrogen in the epipelagic zones of ocean environments before its dispersion through various marine layers, ultimately enhancing oceanic primary productivity. | 1 | Biochemistry |
Gel electrophoresis of nucleic acids is an analytical technique to separate DNA or RNA fragments by size and reactivity. Nucleic acid molecules are placed on a gel, where an electric field induces the nucleic acids (which are negatively charged due to their sugar-phosphate backbone) to migrate toward the positively charged anode. The molecules separate as they travel through the gel based on the each molecule's size and shape. Longer molecules move more slowly because they the gel resists their movement more forcefully than it resists shorter molecules. After some time, the electricity is turned off and the positions of the different molecules are analyzed.
The nucleic acid to be separated can be prepared in several ways before separation by electrophoresis. In the case of large DNA molecules, the DNA is frequently cut into smaller fragments using a DNA restriction endonuclease (or restriction enzyme). In other instances, such as PCR amplified samples, enzymes present in the sample that might affect the separation of the molecules are removed through various means before analysis. Once the nucleic acid is properly prepared, the samples of the nucleic acid solution are placed in the wells of the gel and a voltage is applied across the gel for a specified amount of time.
The DNA fragments of different lengths are visualized using a fluorescent dye specific for DNA, such as ethidium bromide. The gel shows bands corresponding to different nucleic acid molecules populations with different molecular weight. Fragment size is usually reported in "nucleotides", "base pairs" or "kb" (for thousands of base pairs) depending upon whether single- or double-stranded nucleic acid has been separated. Fragment size determination is typically done by comparison to commercially available DNA markers containing linear DNA fragments of known length.
The types of gel most commonly used for nucleic acid electrophoresis are agarose (for relatively long DNA molecules) and polyacrylamide (for high resolution of short DNA molecules, for example in DNA sequencing). Gels have conventionally been run in a "slab" format such as that shown in the figure, but capillary electrophoresis has become important for applications such as high-throughput DNA sequencing. Electrophoresis techniques used in the assessment of DNA damage include alkaline gel electrophoresis and pulsed field gel electrophoresis.
For short DNA segments such as 20 to 60 bp double stranded DNA, running them in polyacrylamide gel (PAGE) will give better resolution (native condition). Similarly, RNA and single-stranded DNA can be run and visualised by PAGE gels containing denaturing agents such as urea. PAGE gels are widely used in techniques such as DNA foot printing, EMSA and other DNA-protein interaction techniques.
The measurement and analysis are mostly done with a specialized gel analysis software. Capillary electrophoresis results are typically displayed in a trace view called an electropherogram. | 1 | Biochemistry |
The Sir William Dunn Professorship of Biochemistry is the senior professorship in biochemistry at the University of Cambridge. The position was established in 1914 by the trustees of the will of Sir William Dunn, banker, merchant and philanthropist.
The first holder of the chair was Frederick Gowland Hopkins, winner of the 1929 Nobel Prize in Medicine for his work on the discovery of vitamins. | 1 | Biochemistry |
HDAC11 has been shown to be related to HDACs 3 and 8, but its overall sequence is quite different from the other HDACs, leading it to be in its own category. HDAC11 has a catalytic domain located in its N-terminus. It has not been found incorporated in any HDAC complexes such as Nurd or SMRT which means it may have a special function unique to itself. It has been found that HDAC11 remains mainly in the nucleus. | 0 | Organic Chemistry |
The Dufour effect is the energy flux due to a mass concentration gradient occurring as a coupled effect of irreversible processes, named after L. Dufour. It is the reciprocal phenomenon to the Soret effect. The concentration gradient results in a temperature change. For binary liquid mixtures, the Dufour effect is usually considered negligible, whereas in binary gas mixtures the effect can be significant. | 7 | Physical Chemistry |
Some wastes contain chemicals capable of suppressing microbiological growth or activity. Potential sources include industrial wastes, antibiotics in pharmaceutical or medical wastes, sanitizers in food processing or commercial cleaning facilities, chlorination disinfection used following conventional sewage treatment, and odor-control formulations used in sanitary waste holding tanks in passenger vehicles or portable toilets. Suppression of the microbial community oxidizing the waste will lower the test result. | 3 | Analytical Chemistry |
The structure of Zintl ions can be confirmed through x-ray crystallography. Corbett has also improved the crystallization of Zintl ions by demonstrating the use of chelating ligands such as cryptands, as cation sequestering agents.
Many of the main group elements have NMR active nuclei, thus NMR experiments are also valuable for gaining structural and electronic information; they can reveal information about the flexibility of clusters. For example, differently charged species can be present in solution because the polyanions are highly reduced and may be oxidized by solvent molecules. NMR experiments have shown a low barrier to change and thus similar energies for different states. NMR is also useful for gaining information about the coupling between individual atoms of the polyanion and with the counter-ion, a coordinated transition metal, or ligand. Nucleus independent chemical shifts can also be an indicator for 3D aromaticity, which causes magnetic shielding at special points.
Additionally, EPR can be used to measure paramagnetic in relevant clusters, of which there are a number of examples of the [E] type, among others. | 7 | Physical Chemistry |
The Ružička large-ring synthesis or Ružička reaction or Ružička cyclization is an organic reaction in which a dicarboxylic acid is converted to a cyclic ketone via heating with a thorium oxide catalyst. The reaction is named after Lavoslav Ružička, who invented it in 1926.
The reaction has been applied in the synthesis of Exaltone, a low-toxicity synthetic musk. | 0 | Organic Chemistry |
In 1998, Andrew Fire at Carnegie Institution for Science in Washington DC and Craig Mello at University of Massachusetts in Worcester discovered the RNAi mechanism while working on the gene expression in the nematode, Caenorhabditis elegans. They won the Nobel prize for their research with RNAi in 2006. siRNAs and their role in post-transcriptional gene silencing (PTGS) was discovered in plants by David Baulcombes group at the Sainsbury Laboratory in Norwich, England and reported in Science in 1999. Thomas Tuschl and colleagues soon reported in Nature' that synthetic siRNAs could induce RNAi in mammalian cells. In 2001, the expression of a specific gene was successfully silenced by introducing chemically synthesized siRNA into mammalian cells (Tuschl et al.) These discoveries led to a surge in interest in harnessing RNAi for biomedical research and drug development. Significant developments in siRNA therapies have been made with both organic (carbon based) and inorganic (non-carbon based) nanoparticles, which have been successful in drug delivery to the brain, offering promising methods to deliver therapeutics into human subjects. However, human applications of siRNA have had significant limitations to its success. One of these being off-targeting. There is also a possibility that these therapies can trigger innate immunity. Animal models have not been successful in accurately representing the extent of this response in humans. Hence, studying the effects of siRNA therapies has been a challenge.
In recent years, siRNA therapies have been approved and new methods have been established to overcome these challenges. There are approved therapies available for commercial use and several currently in the pipeline waiting to get approval. | 1 | Biochemistry |
When genotypes grown together in a diverse population have different profiles of resource use they complement each other in the exploitation of the limiting resource and therefore are subject to smaller between-plant competition.
In case of disease or environmental change some plants will take over when others fail. Yield stability over years and environments can be better than pure lines due to compensation.
Participatory plant breeding (PPB) methods represent alternatives aimed to improve local adaptation breeding, to promote genetic diversity, to empower farmers and rural communities. In PPB farmers are actively participating in developing new cultivars or populations, e.g. by performing selection. | 1 | Biochemistry |
Chiral molecules have two forms (at each point of asymmetry), which differ in their optical characteristics: The levorotatory form (the (−)-form) will rotate counter-clockwise on the plane of polarization of a beam of light, whereas the dextrorotatory form (the (+)-form) will rotate clockwise on the plane of polarization of a beam of light. The two forms, which are non-superposable when rotated in 3-dimensional space, are said to be enantiomers. The notation is not to be confused with and naming of molecules which refers to the similarity in structure to -glyceraldehyde and -glyceraldehyde. Also, (R)- and (S)- refer to the chemical structure of the molecule based on Cahn–Ingold–Prelog priority rules of naming rather than rotation of light. R/S notation is the primary notation used for +/- now because D and L notation are used primarily for sugars and amino acids.
Racemization occurs when one pure form of an enantiomer is converted into equal proportion of both enantiomers, forming a racemate. When there are both equal numbers of dextrorotating and levorotating molecules, the net optical rotation of a racemate is zero. Enantiomers should also be distinguished from diastereomers which are a type of stereoisomer that have different molecular structures around a stereocenter and are not mirror images.
Partial to complete racemization of stereochemistry in solutions are a result of SN1 mechanisms. However, when complete inversion of stereochemistry configuration occurs in a substitution reaction, an SN2 reaction is responsible. | 4 | Stereochemistry |
Triazenes derived from primary amines engage in tautomerism. In the case of symmetric triazenes, the tautomers are identical.
Triazenes can be converted to diazonium salts.
Triazenes decompose in the presence of protonating or alkylating agents into quaternary amines and diazonium salts; as such triazenes have been used as an in situ source of diazonium that reacted with sodium sulfide to give the corresponding thiophenols. A strategy for the protection and deprotection of sensitive secondary amines is based on this principle.
Polymeric triazenes are applied as conductive and absorbent materials. Triazenes have been used in the synthesis of cinnoline, functionalized lactams, and coumarins. | 0 | Organic Chemistry |
From early studies an initial model of PDE, active site topography was derived. This early model can be summarized into the following steps concerning cAMP active site topography:
# cAMP substrate with its adenine and ribose moieties in an "anti" relationship
# The phosphate atom in cAMP binds to PDE active site, using an arginine residue and a water molecule, which was initially associated with Mg. A second arginine residue and the Mg may also play roles during binding and/or play roles in the next step
# S2 attack of phosphorus by HO with formation of a trigonal bipyramid transition state
# 5´-AMP is formed as an "inverted" product. Electronic charges conserve the net charge overall and across the transition state | 1 | Biochemistry |
Leaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous (falling off or dying for the inclement season). This mechanism to shed leaves is called abscission. When the leaf is shed, it leaves a leaf scar on the twig. In cold autumns, they sometimes change color, and turn yellow, bright-orange, or red, as various accessory pigments (carotenoids and xanthophylls) are revealed when the tree responds to cold and reduced sunlight by curtailing chlorophyll production. Red anthocyanin pigments are now thought to be produced in the leaf as it dies, possibly to mask the yellow hue left when the chlorophyll is lost—yellow leaves appear to attract herbivores such as aphids. Optical masking of chlorophyll by anthocyanins reduces risk of photo-oxidative damage to leaf cells as they senesce, which otherwise may lower the efficiency of nutrient retrieval from senescing autumn leaves. | 5 | Photochemistry |
Supramolecular complexes are held together by hydrogen bonding, hydrophobic forces, van der Waals forces, π-π interactions, and electrostatic effects, all of which can be described as noncovalent bonding. Applications include molecular recognition, host–guest chemistry and anion sensors.
A typical application in molecular recognition involved the determination of formation constants for complexes formed between a tripodal substituted urea molecule and various saccharides. The study was carried out using a non-aqueous solvent and NMR chemical shift measurements. The object was to examine the selectivity with respect to the saccharides.
An example of the use of supramolecular complexes in the development of chemosensors is provided by the use of transition-metal ensembles to sense for ATP.
Anion complexation can be achieved by encapsulating the anion in a suitable cage. Selectivity can be engineered by designing the shape of the cage. For example, dicarboxylate anions could be encapsulated in the ellipsoidal cavity in a large macrocyclic structure containing two metal ions. | 7 | Physical Chemistry |
Phytoplankton supports all life in the ocean as it converts inorganic compounds into organic constituents. This autotrophically produced biomass presents the foundation of the marine food web. In the diagram immediately below, the arrows indicate the various production (arrowhead pointing toward DOM pool) and removal processes of DOM (arrowhead pointing away), while the dashed arrows represent dominant biological processes involved in the transfer of DOM. Due to these processes, the fraction of labile DOM decreases rapidly with depth, whereas the refractory character of the DOM pool considerably increases during its export to the deep ocean. DOM, dissolved organic matter. | 9 | Geochemistry |
Facilitating drug absorption by increasing its solubility in water is a common pharmaceutical strategy and also has been shown to be successful for CoQ. Various approaches have been developed to achieve this goal, with many of them producing significantly better results over oil-based softgel capsules in spite of the many attempts to optimize their composition. Examples of such approaches are use of the aqueous dispersion of solid CoQ with the polymer tyloxapol, formulations based on various solubilising agents, such as hydrogenated lecithin, and complexation with cyclodextrins; among the latter, the complex with β-cyclodextrin has been found to have highly increased bioavailability and also is used in pharmaceutical and food industries for CoQ-fortification. | 1 | Biochemistry |
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