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Like liquid crystals, plastic crystals can be considered a transitional stage between real solids and real liquids and can be considered soft matter. Another common denominator is the simultaneous presence of order and disorder. Both types of phases are usually observed between the true solid and liquid phases on the temperature scale:
The difference between liquid and plastic crystals is easily observed in X-ray diffraction. Plastic crystals possess strong long range order and therefore show sharp Bragg reflections. Liquid crystals show none or very broad Bragg peaks because the order is not long range. The molecules that give rise to liquid crystalline behavior often have a strongly elongated or disc like shape. Plastic crystals consist usually of almost spherical objects. In this respect one could see them as opposites.
Certain liquid crystals go through plastic crystal phase before melting. In general, liquid crystals are closer to liquids while plastic crystals are closer to true crystals. | 7 | Physical Chemistry |
Fig. 3 shows an AFM, which typically consists of the following features. Numbers in parentheses correspond to numbered features in Fig. 3. Coordinate directions are defined by the coordinate system (0).
The small spring-like cantilever (1) is carried by the support (2). Optionally, a piezoelectric element (typically made of a ceramic material) (3) oscillates the cantilever (1). The sharp tip (4) is fixed to the free end of the cantilever (1). The detector (5) records the deflection and motion of the cantilever (1). The sample (6) is mounted on the sample stage (8). An xyz drive (7) permits to displace the sample (6) and the sample stage (8) in x, y, and z directions with respect to the tip apex (4). Although Fig. 3 shows the drive attached to the sample, the drive can also be attached to the tip, or independent drives can be attached to both, since it is the relative displacement of the sample and tip that needs to be controlled. Controllers and plotter are not shown in Fig. 3.
According to the configuration described above, the interaction between tip and sample, which can be an atomic-scale phenomenon, is transduced into changes of the motion of cantilever, which is a macro-scale phenomenon. Several different aspects of the cantilever motion can be used to quantify the interaction between the tip and sample, most commonly the value of the deflection, the amplitude of an imposed oscillation of the cantilever, or the shift in resonance frequency of the cantilever (see section Imaging Modes). | 6 | Supramolecular Chemistry |
Apart from uses in coatings and adhesives they are also used to enhance the performance of polyester tire cord. Other uses include Powder coatings, Coil Coatings, Cationic Electrocoating and primers. Blocked isocyanates have also been used in tertiary oilfield recovery techniques. A blocked isocyanate is pumped into the rock/geological formation and then an organic compound with an active hydrogen is also pumped down. The result is a polymeric gel assisting with oil recovery. The use of sodium bisulfite as a blocking agent has also allowed them to be used in waterborne resins such as PUDs. Similarly, vanillin maybe used as an isocyanate blocker and is actively being researched. It is then used in single component waterborne coatings. | 0 | Organic Chemistry |
There are six operational steam traction engines on the grounds, with a 1913 Buffalo-Pitts steamroller and a 1909 20 horsepower Case undergoing restoration. The operational steam tractors are an 1895 Russell & Co. 15-30 steam tractor, a 1902 Advance 16-30 steam tractor, a 1912 J.I. Case steam tractor, a 1920 Minneapolis steam tractor, and a 1916 15-30 Russell & Co. Most, if not all, of these tractors can be seen steaming around the grounds during the show days. | 8 | Metallurgy |
For sum-frequency generation to occur efficiently, phase-matching conditions must be satisfied:
where are the angular wavenumbers of the three waves as they travel through the medium. (Note that the equation resembles the equation for conservation of momentum.) As this condition is satisfied more and more accurately, the sum-frequency generation becomes more and more efficient. | 7 | Physical Chemistry |
Combination therapy with paricalcitol and trandolapril has been found to reduce fibrosis in obstructive uropathy. | 4 | Stereochemistry |
Coal-tar creosote is greenish-brown liquid, with different degrees of darkness, viscosity, and fluorescence depending on how it is made. When freshly made, the creosote is a yellow oil with a greenish cast and highly fluorescent, and the fluorescence is increased by exposure to air and light. After settling, the oil is dark green by reflected light and dark red by transmitted light. To the naked eye, it generally appears brown. The creosote (often called "creosote oil") consists almost wholly of aromatic hydrocarbons, with some amount of bases and acids and other neutral oils. The flash point is 70–75 °C and burning point is 90–100 °C, and when burned it releases a greenish smoke. The smell largely depends on the naphtha content in the creosote. If there is a high amount, it will have a naphtha-like smell, otherwise it will smell more of tar.
In the process of coal-tar distillation, the distillate is collected into four fractions; the "light oil", which remains lighter than water, the "middle oil" which passes over when the light oil is removed; the "heavy oil", which sinks; and the "anthracene oil", which when cold is mostly solid and greasy, of a buttery consistence. Creosote refers to the portion of coal tar which distills as "heavy oil", typically between 230 and 270 °C, also called "dead oil"; it sinks into water but still is fairly liquid. Carbolic acid is produced in the second fraction of distillation and is often distilled into what is referred to as "carbolic oil".
Commercial creosote contains substances from six groups. The two groups occur in the greatest amounts and are the products of the distillation process—the "tar acids", which distill below 205 °C and consist mainly of phenols, cresols, and xylenols, including carbolic acid—and aromatic hydrocarbons, which divide into naphthalenes, which distill approximately between 205 and 255 °C, and constituents of an anthracene nature, which distill above 255 °C. The quantity of each varies based on the quality of tar and temperatures used, but generally, the tar acids wont exceed 5%, the naphthalenes make up 15 to 50%, and the anthracenes make up 45% to 70%. The hydrocarbons are mainly aromatic; derivatives of benzene and related cyclic compounds such as naphthalene, anthracene, phenanthrene, acenaphthene, and fluorene. Creosotes from vertical-retort and low temperature tars contain, in addition, some paraffinic and olefinic hydrocarbons. The tar-acid content also depends on the source of the tar—it may be less than 3% in creosote from coke-oven tar and as high as 32% in creosote from vertical retort tar. All of these have antiseptic properties. The tar acids are the strongest antiseptics but have the highest degree of solubility in water and are the most volatile; so, like with wood-tar creosote, phenols are not the most valued component, as by themselves they would lend to being poor preservatives. In addition, creosote contains several products naturally occurring in coal—nitrogen-containing heterocycles, such as acridines, carbazoles, and quinolines, referred to as the "tar bases" and generally make up about 3% of the creosote—sulfur-containing heterocycles, generally benzothiophenes—and oxygen-containing heterocycles, dibenzofurans. Lastly, creosote contains a small number of aromatic amines produced by the other substances during the distillation process and likely resulting from a combination of thermolysis and hydrogenation. The tar bases are often extracted by washing the creosote with aqueous mineral acid, although theyre also suggested to have antiseptic ability similar to the tar acids.
Commercially used creosote is often treated to extract the carbolic acid, naphthalene, or anthracene content. The carbolic acid or naphthalene is generally extracted to be used in other commercial products. American produced creosote oils typically have low amounts of anthracene and high amounts of naphthalene, because when forcing the distillate at a temperature that produces anthracene the soft pitch will be ruined and only the hard pitch will remain; this ruins it for use in roofing purposes, and only leaves a product which isn't commercially useful. | 7 | Physical Chemistry |
In many supramolecular catalytic systems designed to work with bimolecular addition reactions like the Diels-Alder, the product of the reaction binds more strongly to the supramolecular host than the two substrates do, consequently leading to inhibition by the product. As a result, these catalysts has a turnover number of one and are not truly catalytic. A stoichiometric quantity of the catalysts is needed for a full conversion. | 6 | Supramolecular Chemistry |
Trifluoroacetic acid, often used in these reductions, is a strong, corrosive acid. Some hydrosilanes are pyrophoric. | 0 | Organic Chemistry |
Molten salt is salt which is solid at standard temperature and pressure but liquified due to elevated temperature. A salt that is liquid even at standard temperature and pressure is usually called a room-temperature ionic liquid, and molten salts are technically a class of ionic liquids. | 8 | Metallurgy |
In viruses this phenomenon may be programmed to occur at particular sites and allows the virus to encode multiple types of proteins from the same mRNA. Notable examples include HIV-1 (human immunodeficiency virus), RSV (Rous sarcoma virus) and the influenza virus (flu), which all rely on frameshifting to create a proper ratio of 0-frame (normal translation) and "trans-frame" (encoded by frameshifted sequence) proteins. Its use in viruses is primarily for compacting more genetic information into a shorter amount of genetic material.
In eukaryotes it appears to play a role in regulating gene expression levels by generating premature stops and producing nonfunctional transcripts. | 1 | Biochemistry |
Two Soviet scientists, B. R. Lazarenko and N. I. Lazarenko, were tasked in 1943 to investigate ways of preventing the erosion of tungsten electrical contacts due to sparking. They failed in this task but found that the erosion was more precisely controlled if the electrodes were immersed in a dielectric fluid. This led them to invent an EDM machine used for working difficult-to-machine materials such as tungsten. The Lazarenkos' machine is known as an R-C-type machine, after the resistor–capacitor circuit (RC circuit) used to charge the electrodes.
Simultaneously but independently, an American team, Harold Stark, Victor Harding, and Jack Beaver, developed an EDM machine for removing broken drills and taps from aluminium castings. Initially constructing their machines from under-powered electric-etching tools, they were not very successful. But more powerful sparking units, combined with automatic spark repetition and fluid replacement with an electromagnetic interrupter arrangement produced practical machines. Stark, Harding, and Beaver's machines produced 60 sparks per second. Later machines based on their design used vacuum tube circuits that produced thousands of sparks per second, significantly increasing the speed of cutting. | 8 | Metallurgy |
The construction of more complex molecular machines is an active area of theoretical and experimental research. Though a diverse variety of AMMs are known today, experimental studies of these molecules are inhibited by the lack of methods to construct these molecules. In this context, theoretical modeling has emerged as a pivotal tool to understand the self-assembly or -disassembly processes in these systems.
A wide range of applications have been demonstrated for AMMs, including those integrated into polymeric, liquid crystal, and crystalline systems for varied functions. Homogenous catalysis is a prominent example, especially in areas like asymmetric synthesis, utilizing noncovalent interactions and biomimetic allosteric catalysis. AMMs have been pivotal in the design of several stimuli-responsive smart materials, such as 2D and 3D self-assembled materials and nanoparticle-based systems, for versatile applications ranging from 3D printing to drug delivery.
AMMs are gradually moving from the conventional solution-phase chemistry to surfaces and interfaces. For instance, AMM-immobilized surfaces (AMMISs) are a novel class of functional materials consisting of AMMs attached to inorganic surfaces forming features like self-assembled monolayers; this gives rise to tunable properties such as fluorescence, aggregation and drug-release activity.
Most of these applications remain at the proof-of-concept level, and need major modifications to be adapted to the industrial scale. Challenges in streamlining macroscale applications include autonomous operation, the complexity of the machines, stability in the synthesis of the machines and the working conditions. | 6 | Supramolecular Chemistry |
In chemistry, the square antiprismatic molecular geometry describes the shape of compounds where eight atoms, groups of atoms, or ligands are arranged around a central atom, defining the vertices of a square antiprism. This shape has D symmetry and is one of the three common shapes for octacoordinate transition metal complexes, along with the dodecahedron and the bicapped trigonal prism.
Like with other high coordination numbers, eight-coordinate compounds are often distorted from idealized geometries, as illustrated by the structure of NaTaF. In this case, with the small Na ions, lattice forces are strong. With the diatomic cation NO, the lattice forces are weaker, such as in (NO)XeF, which crystallizes with a more idealized square antiprismatic geometry. | 4 | Stereochemistry |
In a chemical structural formula, an organic substituent such as methyl, ethyl, or aryl can be written as R (or R, R, etc.) It is a generic placeholder, the R derived from radical or rest, which may replace any portion of the formula as the author finds convenient. The first to use this symbol was Charles Frédéric Gerhardt in 1844.
The symbol X is often used to denote electronegative substituents such as the halides. | 0 | Organic Chemistry |
The configuration index consists of two segments separated by a hyphen. The first segment consists of two digits which are the priority numbers of the ligands on the five, six or sevenfold rotation axis. The lowest numerical value is cited first.
The second segment consists of 5, 6 or 7 digits respectively. The lowest priority number is the first digit followed by the digits of the other atoms in the plane. The clockwise and anticlockwise sequences are compared and the one that yields the lowest numerical sequence is chosen. | 4 | Stereochemistry |
Moreover, because the assembly of the full-length gene product relies on the efficient and specific alignment of long single stranded oligonucleotides, critical parameters for synthesis success include extended sequence regions comprising secondary structures caused by inverted repeats, extraordinary high or low GC-content, or repetitive structures. Usually these segments of a particular gene can only be synthesized by splitting the procedure into several consecutive steps and a final assembly of shorter sub-sequences, which in turn leads to a significant increase in time and labor needed for its production.
The result of a gene synthesis experiment depends strongly on the quality of the oligonucleotides used. For these annealing based gene synthesis protocols, the quality of the product is directly and exponentially dependent on the correctness of the employed oligonucleotides. Alternatively, after performing gene synthesis with oligos of lower quality, more effort must be made in downstream quality assurance during clone analysis, which is usually done by time-consuming standard cloning and sequencing procedures.
Another problem associated with all current gene synthesis methods is the high frequency of sequence errors because of the usage of chemically synthesized oligonucleotides. The error frequency increases with longer oligonucleotides, and as a consequence the percentage of correct product decreases dramatically as more oligonucleotides are used.
The mutation problem could be solved by shorter oligonucleotides used to assemble the gene. However, all annealing based assembly methods require the primers to be mixed together in one tube. In this case, shorter overlaps do not always allow precise and specific annealing of complementary primers, resulting in the inhibition of full length product formation.
Manual design of oligonucleotides is a laborious procedure and does not guarantee the successful synthesis of the desired gene. For optimal performance of almost all annealing based methods, the melting temperatures of the overlapping regions are supposed to be similar for all oligonucleotides. The necessary primer optimisation should be performed using specialized oligonucleotide design programs. Several solutions for automated primer design for gene synthesis have been presented so far. | 1 | Biochemistry |
The selectivity in the reaction is due to the stronger electron withdrawing power of the esters compared to the ethers. A stronger electron withdrawing substituent leads to a greater destabilization of the oxocarbenium ion. This slows this reaction pathway, and allows for disaccharide formation to occur with the benzylated sugar. Other effective electron withdrawing groups that have shown selectivity are halogens and azido groups, while deoxygenation has been proven an effective tool in “arming” sugars. | 0 | Organic Chemistry |
In chemistry, a sample's oxygen–argon ratio (or oxygen/argon ratio) is a comparison between the concentrations of oxygen (O) and the noble gas argon (Ar), either in air or dissolved in a liquid such as seawater. The two gases have very similar physical properties such as solubility and diffusivity, as well as a similar temperature dependence, making them easy to compare. | 3 | Analytical Chemistry |
Ortho lithiation followed by methylation with methyl iodide is a convenient method for the synthesis of starting materials for lateral lithiations. Elaboration of the benzylic carbon through lateral lithiation and treatment with an electrophile provides a powerful synthetic alternative to direct electrophilic aromatic substitution (EAS). Although yields over the entire sequence are moderate, site selectivity is generally higher than analogous EAS reactions. | 0 | Organic Chemistry |
In cellular biology, proteins act as intracellular signaling molecules by activating another protein in a signaling pathway. In order to do this, proteins can switch between active and inactive states, thus acting as molecular switches in response to another signal. For example, phosphorylation of proteins can be used to activate or inactivate proteins. The external signal flipping the molecular switch could be a protein kinase, which adds a phosphate group to the protein, or a protein phosphatase, which removes phosphate groups. | 6 | Supramolecular Chemistry |
It is a common observation that when oil and water are poured into the same container, they separate into two phases or layers, because they are immiscible. In general, aqueous (or water-based) solutions, being polar, are immiscible with non-polar organic solvents (cooking oil, chloroform, toluene, hexane etc.) and form a two-phase system. However, in an ABS, both immiscible components are water-based.
The formation of the distinct phases is affected by the pH, temperature and ionic strength of the two components, and separation occurs when the amount of a polymer present exceeds a certain limiting concentration (which is determined by the above factors). | 3 | Analytical Chemistry |
There are 3 types of tumor suppressor genes:
* Genes that affect cell growth
* Genes that limit the cell cycle and induce apoptosis
* Genes that repair damaged DNA
SFRP1 appears to fall in the first category of genes, those that affect cell growth.
The role of SFRP1 as a tumor suppressor has been proposed in many cancers, based on its loss in patient tumors. Its frequent inactivation by methylation-induced silencing is consistent with it behaving as a tumor suppressor. Also, the SFRP1 gene is located in a region on chromosome 8 that is frequently lost in many cancer types. Expression levels of several targets of the Wnt signaling pathways are increased in tumor tissue compared with normal, and the expression of SFRP1 is lost in patient tumor samples. The role for the Wnt/β-catenin signaling in cancer has been well defined: β-catenin drives transcription of genes that contribute to the tumor phenotype by regulating processes such as proliferation, survival and invasion.
Gumz et al. showed that SFRP1 expression in UMRC3 cells (clear cell renal cell carcinoma cell line) resulted in a growth-inhibited phenotype. SFRP1 expression not only reduced the expression of Wnt target genes, but also markedly inhibited tumor cell growth in culture, soft agar and xenografts in athymic nude mice. Growth in culture and anchorage-independent growth were inhibited in SFRP1-expressing UMRC3 cells. The growth-inhibitory effects of SFRP1 were due primarily to decreased cell proliferation rather than an increase in apoptosis. This was consistent with the effect of SFRP1 on cellular proliferation as seen in prostate cancer, where retroviral-mediated expression of SFRP1 resulted in inhibited cellular proliferation but had no effect on apoptosis. Also, restoration of SFRP1 expression attenuated the malignant phenotype of cRCC; moreover, other studies showed reexpression of SFRP1 resulted in decreased colony formation in colon and lung cancer models. | 1 | Biochemistry |
Prokaryotic cells have various shapes; the four basic shapes of bacteria are:
* Cocci – A bacterium that is spherical or ovoid is called a coccus (Plural, cocci). e.g. Streptococcus, Staphylococcus.
* Bacilli – A bacterium with cylindrical shape called rod or a bacillus (Plural, bacilli).
* Spiral bacteria – Some rods twist into spiral shapes and are called spirilla (singular, spirillum).
* Vibrio – comma-shaped
The archaeon Haloquadratum has flat square-shaped cells. | 1 | Biochemistry |
KAP1 can regulate genomic transcription through a variety of mechanisms, many of which remain somewhat unclear. Studies have shown that KAP1 can repress transcription by binding directly to the genome (which can be sufficient in and of itself) or through the induction of heterochromatin formation via the Mi2α-SETB1-HP1 macromolecular complex. KAP1 can also interact with histone methyltransferases and deacetylases via the C-terminal PHD and Bromodomain to control transcription epigenetically. | 1 | Biochemistry |
The first high-volume product (> 5Mio actuators / year) is an automotive valve used to control low pressure pneumatic bladders in a car seat that adjust the contour of the lumbar support / bolsters. The overall benefits of SMA over traditionally-used solenoids in this application (lower noise/EMC/weight/form factor/power consumption) were the crucial factor in the decision to replace the old standard technology with SMA.
The 2014 Chevrolet Corvette became the first vehicle to incorporate SMA actuators, which replaced heavier motorized actuators to open and close the hatch vent that releases air from the trunk, making it easier to close. A variety of other applications are also being targeted, including electric generators to generate electricity from exhaust heat and on-demand air dams to optimize aerodynamics at various speeds. | 8 | Metallurgy |
The C metabolic pathway is a valuable recent evolutionary innovation in plants, involving a complex set of adaptive changes to physiology and gene expression patterns. About 7600 species of plants use carbon fixation, which represents about 3% of all terrestrial species of plants. All these 7600 species are angiosperms.
C plants evolved carbon concentrating mechanisms. These work by increasing the concentration of around RuBisCO, thereby facilitating photosynthesis and decreasing photorespiration. The process of concentrating around RuBisCO requires more energy than allowing gases to diffuse, but under certain conditions – i.e. warm temperatures (>25 °C), low concentrations, or high oxygen concentrations – pays off in terms of the decreased loss of sugars through photorespiration.
One type of C metabolism employs a so-called Kranz anatomy. This transports through an outer mesophyll layer, via a range of organic molecules, to the central bundle sheath cells, where the is released. In this way, is concentrated near the site of RuBisCO operation. Because RuBisCO is operating in an environment with much more than it otherwise would be, it performs more efficiently. In C photosynthesis, carbon is fixed by an enzyme called PEP carboxylase, which, like all enzymes involved in C photosynthesis, originated from non-photosynthetic ancestral enzymes.
A second mechanism, CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. The most important benefit of CAM to the plant is the ability to leave most leaf stomata closed during the day. This reduces water loss due to evapotranspiration. The stomata open at night to collect , which is stored as the four-carbon acid malate, and then used during photosynthesis during the day. The pre-collected is concentrated around the enzyme RuBisCO, increasing photosynthetic efficiency. More is then harvested from the atmosphere when stomata open, during the cool, moist nights, reducing water loss.
CAM has evolved convergently many times. It occurs in 16,000 species (about 7% of plants), belonging to over 300 genera and around 40 families, but this is thought to be a considerable underestimate. It is found in quillworts (relatives of club mosses), in ferns, and in gymnosperms, but the great majority of plants using CAM are angiosperms (flowering plants). | 5 | Photochemistry |
5-guanosyl-methylene-triphosphate (GDPCP) and 5-adenosyl-methylene-triphosphate (ADPCP) are analogues of guanosine 5-triphosphate (GTP) and adenosine 5-triphosphate (ATP), which store chemical energy from metabolism in the cell. Hydrolysis of nucleoside triphosphates (NTPs) such as ATP and GTP yields energy, inorganic phosphate (P or PP), and either NDP or NMP. GDPCP and ADPCP are not subject to hydrolysis under the same conditions as NTPs; it is this property which makes them useful in experiments in biochemistry and molecular biology.
NTPs can be hydrolyzed at the phosphodiester bonds between phosphates, releasing energy and one or more of the three phosphate groups. Additionally, NTPs are inextricable components of some proteins, where their role may be structural and need not involve hydrolysis. In some cases, the presence of an NTP may be required for association of one protein with another, while hydrolysis is necessary for dissociation. GDPCP and ADPCP could be used in such a case, since association can still occur, but hydrolysis-dependent dissociation cannot.
GDPCP was used to examine the prokaryotic elongation factor EF-Tu. EF-Tu is required for the elongation phase of protein synthesis (translation). EF-Tu requires GTP in order for the ribosome to bind it, necessary for recruiting an aminoacyl-tRNA. The later dissociation of EF-Tu from the ribosome, however, requires that the GTP first be hydrolyzed to GDP and P. GDPCP was used in place of GTP to differentiate between these two steps: the elongation factor could associate, but without hydrolysis, it was effectively stuck. | 1 | Biochemistry |
The first attempt for the total synthesis of hydrastine was reported by Sir Robert Robinson and co-workers in 1931. Following studies where the synthesis of the key lactonic amide intermediate (structure 4 in figure) was the most troublesome, the major breakthrough was achieved in 1981 when J. R. Falck and co-workers reported a four-step total synthesis of hydrastine from simple starting materials. The key step in the Falck synthesis was using a Passerini reaction to construct the lactonic amide intermediate 4.
Starting from a simple phenylbromide variant 1, alkylation reaction with lithium methylisocyanide gives the isocyanide intermediate 2. Reacting isocyanide intermediate 2 with opianic acid 3 initiated the intramolecular Passerini reaction to give the key lactonic amide intermediate 4. The tetrahydro-isoquinolin ring was formed by first a ring-closure reaction under dehydration conditions using POCl3 and then a catalyzed hydrogenation using PtO2 as the catalyst. Finally, hydrastine was synthesized by installing the N-methyl group via reductive amination reaction with formaldehyde. | 0 | Organic Chemistry |
Sonoporation is performed with a dedicated sonoporator. Sonoporation may also be performed with custom-built piezoelectric transducers connected to bench-top function generators and acoustic amplifiers. Standard ultrasound medical devices may also be used in some applications.
Measurement of the acoustics used in sonoporation is listed in terms of mechanical index, which quantifies the likelihood that exposure to diagnostic ultrasound will produce an adverse biological effect by a non-thermal action based on pressure. | 1 | Biochemistry |
The nucleosome contains over 120 direct protein-DNA interactions and several hundred water-mediated ones. Direct protein - DNA interactions are not spread evenly about the octamer surface but rather located at discrete sites. These are due to the formation of two types of DNA binding sites within the octamer; the α1α1 site, which uses the α1 helix from two adjacent histones, and the L1L2 site formed by the L1 and L2 loops. Salt links and hydrogen bonding between both side-chain basic and hydroxyl groups and main-chain amides with the DNA backbone phosphates form the bulk of interactions with the DNA. This is important, given that the ubiquitous distribution of nucleosomes along genomes requires it to be a non-sequence-specific DNA-binding factor. Although nucleosomes tend to prefer some DNA sequences over others, they are capable of binding practically to any sequence, which is thought to be due to the flexibility in the formation of these water-mediated interactions. In addition, non-polar interactions are made between protein side-chains and the deoxyribose groups, and an arginine side-chain intercalates into the DNA minor groove at all 14 sites where it faces the octamer surface.
The distribution and strength of DNA-binding sites about the octamer surface distorts the DNA within the nucleosome core. The DNA is non-uniformly bent and also contains twist defects. The twist of free B-form DNA in solution is 10.5 bp per turn. However, the overall twist of nucleosomal DNA is only 10.2 bp per turn, varying from a value of 9.4 to 10.9 bp per turn. | 1 | Biochemistry |
Another approach is low-pressure high-recovery multistage RO (LPHR). It produces concentrated brine and freshwater by cycling the output repeatedly through a relatively porous membrane at relatively low pressure. Each cycle removes additional impurities. Once the output is relatively pure, it is sent through a conventional RO membrane at conventional pressure to complete the filtration step. LPHR was found to be economically feasible, recovering more than 70% with an OPD between 58 and 65 bar and leaving no more than 350 ppm TDS from a seawater feed with 35,000 ppm TDS. | 3 | Analytical Chemistry |
Water vapor is a greenhouse gas in the Earth's atmosphere, responsible for 70% of the known absorption of incoming sunlight, particularly in the infrared region, and about 60% of the atmospheric absorption of thermal radiation by the Earth known as the greenhouse effect. It is also an important factor in multispectral imaging and hyperspectral imaging used in remote sensing because water vapor absorbs radiation differently in different spectral bands. Its effects are also an important consideration in infrared astronomy and radio astronomy in the microwave or millimeter wave bands. The South Pole Telescope was constructed in Antarctica in part because the elevation and low temperatures there mean there is very little water vapor in the atmosphere.
Similarly, carbon dioxide absorption bands occur around 1400, 1600 and 2000 nm, but its presence in the Earths atmosphere accounts for just 26% of the greenhouse effect. Carbon dioxide gas absorbs energy in some small segments of the thermal infrared spectrum that water vapor misses. This extra absorption within the atmosphere causes the air to warm just a bit more and the warmer the atmosphere the greater its capacity to hold more water vapor. This extra water vapor absorption further enhances the Earths greenhouse effect.
In the atmospheric window between approximately 8000 and 14000 nm, in the far-infrared spectrum, carbon dioxide and water absorption is weak. This window allows most of the thermal radiation in this band to be radiated out to space directly from the Earth's surface. This band is also used for remote sensing of the Earth from space, for example with thermal Infrared imaging.
As well as absorbing radiation, water vapour occasionally emits radiation in all directions, according to the Black Body Emission curve for its current temperature overlaid on the water absorption spectrum. Much of this energy will be recaptured by other water molecules, but at higher altitudes, radiation sent towards space is less likely to be recaptured, as there is less water available to recapture radiation of water-specific absorbing wavelengths. By the top of the troposphere, about 12 km above sea level, most water vapor condenses to liquid water or ice as it releases its heat of vapourization. Once changed state, liquid water and ice fall away to lower altitudes. This will be balanced by incoming water vapour rising via convection currents.
Liquid water and ice emit radiation at a higher rate than water vapour (see graph above). Water at the top of the troposphere, particularly in liquid and solid states, cools as it emits net photons to space. Neighboring gas molecules other than water (e.g. Nitrogen) are cooled by passing their heat kinetically to the water. This is why temperatures at the top of the troposphere (known as the tropopause) are about -50 degrees Celsius. | 7 | Physical Chemistry |
In molecular biology, SNP array is a type of DNA microarray which is used to detect polymorphisms within a population. A single nucleotide polymorphism (SNP), a variation at a single site in DNA, is the most frequent type of variation in the genome. Around 335 million SNPs have been identified in the human genome, 15 million of which are present at frequencies of 1% or higher across different populations worldwide. | 1 | Biochemistry |
Pulse electrolysis is an alternate electrolysis method that utilises a pulsed direct current to initiate non-spontaneous chemical reactions. Also known as pulsed direct current (PDC) electrolysis, the increased number of variables that it introduces to the electrolysis method can change the application of the current to the electrodes and the resulting outcome. This varies from direct current (DC) electrolysis, which only allows the variation of one value, the voltage applied. By utilising conventional pulse width modulation (PMW), multiple dependent variables can be altered, including the type of waveform, typically a rectangular pulse wave, the duty cycle, and the frequency.
Currently, there has been a focus on theoretical and experimental research into PDC electrolysis in terms of the electrolysis of water to produce hydrogen. Past research has demonstrated that there is a possibility it can result in a higher electrical efficiency in comparison to DC electrolysis. This would allow electrolysis procedures to produce greater volumes of hydrogen with a reduced electrical energy consumption. Although theoretical research has made large promise for the efficiencies and benefits of utilising pulse electrolysis, it has many contradictions including a common issue that it is difficult to replicate the successes of patents experimentally and produces its own negative effects on the electrolyser.
PDC electrolysis is not only confined to the electrolysis of water. Uses in industry such as electroplating and electrocrystallisation are also undergoing research due to the wider range of properties that can be achieved.
The various and alterable effects of using intermittent pulses in PDC electrolysis has resulted in an area of interest that could benefit industry. However, as it is still being researched and has produced conflicting results, a consistent and reliable answer to how dependent electrolysis efficiency is on the properties of an electrical pulse has not been determined, hence, other forms of electrolysis such as polymer electrolyte membrane and alkaline water electrolysis are being used in industry. | 7 | Physical Chemistry |
Nocturnal passive radiative cooling has been recognized for thousands of years, with records showing awareness by the ancient Iranians, demonstrated through the construction of Yakhchāls, since 400 B.C.E.
Passive daytime radiative cooling was hypothesized by Félix Trombe in 1967. The first experimental setup was created in 1975, but was only successful for nighttime cooling. Further developments to achieve daytime cooling using different material compositions were not successful.
In the 1980s, Lushiku and Granqvist identified the infrared window as a potential way to access the ultracold outer space as a way to achieve passive daytime cooling.
Early attempts at developing passive radiative daytime cooling materials took inspiration from nature, particularly the Saharan silver ant and white beetles, noting how they cooled themselves in extreme heat.
Research and development in passive daytime radiative cooling evolved rapidly in the 2010s with the discovery of the ability to suppress solar heating using photonic metamaterials, which widely expanded research and development in the field. This is largely credited to the landmark study by Aaswath P. Raman, Marc Abou Anoma, Linxiao Zhu, Eden Raphaeli, and Shanhui Fan published in 2014. | 7 | Physical Chemistry |
The conformation assumed by a polymer chain in dilute solution can be modeled as a random walk of monomer subunits using a freely jointed chain model. However, this model does not account for steric effects. Real polymer coils are more closely represented by a self-avoiding walk because conformations in which different chain segments occupy the same space are not physically possible. This excluded volume effect causes the polymer to expand.
Chain conformation is also affected by solvent quality. The intermolecular interactions between polymer chain segments and coordinated solvent molecules have an associated energy of interaction which can be positive or negative. For a good solvent, interactions between polymer segments and solvent molecules are energetically favorable, and will cause polymer coils to expand. For a poor solvent, polymer-polymer self-interactions are preferred, and the polymer coils will contract. The quality of the solvent depends on both the chemical compositions of the polymer and solvent molecules and the solution temperature. | 7 | Physical Chemistry |
Surface diffusion kinetics can be thought of in terms of adatoms residing at adsorption sites on a 2D lattice, moving between adjacent (nearest-neighbor) adsorption sites by a jumping process. The jump rate is characterized by an attempt frequency and a thermodynamic factor that dictates the probability of an attempt resulting in a successful jump. The attempt frequency ν is typically taken to be simply the vibrational frequency of the adatom, while the thermodynamic factor is a Boltzmann factor dependent on temperature and E, the potential energy barrier to diffusion. Equation 1 describes the relationship:
Where ν and E are as described above, Γ is the jump or hopping rate, T is temperature, and k is the Boltzmann constant. E must be smaller than the energy of desorption for diffusion to occur, otherwise desorption processes would dominate. Importantly, equation 1 tells us how strongly the jump rate varies with temperature. The manner in which diffusion takes place is dependent on the relationship between E and kT as is given in the thermodynamic factor: when E T the thermodynamic factor approaches unity and E ceases to be a meaningful barrier to diffusion. This case, known as mobile diffusion, is relatively uncommon and has only been observed in a few systems. For the phenomena described throughout this article, it is assumed that E >> kT and therefore Γ from an Arrhenius plot of the logarithm of the diffusion coefficient, D, versus 1/T. For cases where more than one diffusion mechanism is present (see below), there may be more than one E such that the relative distribution between the different processes would change with temperature.
Random walk statistics describe the mean squared displacement of diffusing species in terms of the number of jumps N and the distance per jump a. The number of successful jumps is simply Γ multiplied by the time allowed for diffusion, t. In the most basic model only nearest-neighbor jumps are considered and a corresponds to the spacing between nearest-neighbor adsorption sites. The root mean squared displacement goes as:
The diffusion coefficient is given as:
where for 1D diffusion as would be the case for in-channel diffusion, for 2D diffusion, and for 3D diffusion. | 7 | Physical Chemistry |
Chalconatronite is a carbonate mineral and rare secondary copper mineral that contains copper, sodium, carbon, oxygen, and hydrogen, its chemical formula is NaCu(CO)•3(HO). Chalconatronite is partially soluble in water, and only decomposes, although chalconatronite is soluble while cold, in dilute acids. The name comes from the minerals compounds, copper ("chalcos'" in Greek) and natron, naturally forming sodium carbonate. The mineral is thought to be formed by water carrying alkali carbonates (possibly from soil) reacting with bronze. Similar minerals include malachite, azurite, and other copper carbonates. Chalconatronite has also been found and recorded in Australia, Germany, and Colorado. | 8 | Metallurgy |
The most common radical in the lower atmosphere is molecular dioxygen. Photodissociation of source molecules produces other radicals. In the lower atmosphere, important radical are produced by the photodissociation of nitrogen dioxide to an oxygen atom and nitric oxide (see below), which plays a key role in smog formation—and the photodissociation of ozone to give the excited oxygen atom O(1D) (see below). The net and return reactions are also shown ( and , respectively).
In the upper atmosphere, the photodissociation of normally unreactive chlorofluorocarbons (CFCs) by solar ultraviolet radiation is an important source of radicals (see eq. 1 below). These reactions give the chlorine radical, Cl, which catalyzes the conversion of ozone to O, thus facilitating ozone depletion (– below).
Such reactions cause the depletion of the ozone layer, especially since the chlorine radical is free to engage in another reaction chain; consequently, the use of chlorofluorocarbons as refrigerants has been restricted. | 2 | Environmental Chemistry |
and other lanthanide phthalocyanines are of interest in the development of organic thin-film field-effect transistors.
derivatives can be selected to change color in the presence of certain molecules, such as in gas detectors; for example, the thioether derivative changes from green to brownish-purple in the presence of NADH. | 3 | Analytical Chemistry |
A persistent carbene (also known as stable carbene) is an organic molecule whose natural resonance structure has a carbon atom with incomplete octet (a carbene), but does not exhibit the tremendous instability typically associated with such moieties. The best-known examples and by far largest subgroup are the N-heterocyclic carbenes (NHC) (sometimes called Arduengo carbenes), in which nitrogen atoms flank the formal carbene.
Modern theoretical analysis suggests that the term "persistent carbene" is in fact a misnomer. Persistent carbenes do not in fact have a carbene electronic structure in their ground state, but instead an ylide stabilized by aromatic resonance or steric shielding. Excitation to a carbene structure then accounts for the carbene-like dimerization that some persistent carbenes undergo over the course of days.
Persistent carbenes in general, and Arduengo carbenes in particular, are popular ligands in organometallic chemistry. | 0 | Organic Chemistry |
Inverse photoemission spectroscopy (IPES) is a surface science technique used to study the unoccupied electronic structure of surfaces, thin films, and adsorbates. A well-collimated beam of electrons of a well defined energy (< 20 eV) is directed at the sample. These electrons couple to high-lying unoccupied electronic states and decay to low-lying unoccupied states, with a subset of these transitions being radiative. The photons emitted in the decay process are detected and an energy spectrum, photon counts vs. incident electron energy, is generated. Due to the low energy of the incident electrons, their penetration depth is only a few atomic layers, making inverse photoemission a particularly surface sensitive technique. As inverse photoemission probes the electronic states above the Fermi level of the system, it is a complementary technique to photoemission spectroscopy. | 7 | Physical Chemistry |
Methyl chloroformate hydrolyzes in water to form methanol, hydrochloric acid, and carbon dioxide. This decomposition happens violently in the presence of steam, causing foaming. The compound decomposes in heat, which can liberate hydrogen chloride, phosgene, chlorine, or other toxic gases. | 0 | Organic Chemistry |
Disphenoidal or seesaw (also known as sawhorse) is a type of molecular geometry where there are four bonds to a central atom with overall C molecular symmetry. The name "seesaw" comes from the observation that it looks like a playground seesaw. Most commonly, four bonds to a central atom result in tetrahedral or, less commonly, square planar geometry.
The seesaw geometry occurs when a molecule has a steric number of 5, with the central atom being bonded to 4 other atoms and 1 lone pair (AXE in AXE notation). An atom bonded to 5 other atoms (and no lone pairs) forms a trigonal bipyramid with two axial and three equatorial positions, but in the seesaw geometry one of the atoms is replaced by a lone pair of electrons, which is always in an equatorial position. This is true because the lone pair occupies more space near the central atom (A) than does a bonding pair of electrons. An equatorial lone pair is repelled by only two bonding pairs at 90°, whereas a hypothetical axial lone pair would be repelled by three bonding pairs at 90° which would make it stable. Repulsion by bonding pairs at 120° is much smaller and less important. | 4 | Stereochemistry |
In chronic toxicity, people have primarily neurological symptoms which include nystagmus, tremor, hyperreflexia, ataxia, and change in mental status. During chronic toxicity, the gastrointestinal symptoms seen in acute toxicity are less prominent. The symptoms are often vague and nonspecific. | 1 | Biochemistry |
In the brain, cholesterol is synthesized in astrocytes and transported to neurons with the cholesterol transport protein apolipoprotein E (apoE). The cholesterol controls the clustering of amyloid precursor protein with gamma secretase in GM1 lipid domains. High cholesterol induces APP hydrolysis and the eventual accumulation of amyloid plaques tau phosphorylation. The ApoE isotype4 is the greatest risk factor for sporadic Alzheimer's and this allele was shown to increase cholesterol in mice. | 1 | Biochemistry |
Flutamide has been found to be effective in the treatment of hirsutism (excessive body/facial hair growth) in numerous studies. It possesses moderate effectiveness for this indication, and the overall quality of the evidence is considered to be moderate. The medication shows equivalent or superior effectiveness to other antiandrogens including spironolactone, cyproterone acetate, and finasteride in the treatment of hirsutism, although its relatively high risk of hepatotoxicity makes it unfavorable compared to these other options. It has been used to treat hirsutism at dosages ranging from 62.5 mg/day to 750 mg/day. A study found that multiple dosages of flutamide significantly reduced hirsutism in women with polycystic ovary syndrome and that there were no significant differences in the effectiveness for dosages of 125 mg/day, 250 mg/day, and 375 mg/day. In addition, a study found that combination of 125 mg/day flutamide with finasteride was no more effective than 125 mg/day flutamide alone in the treatment of hirsutism. These findings support the use of flutamide at lower doses for hirsutism without loss of effectiveness, which may help to lower the risk of hepatotoxicity. However, the risk has been found to remain even at very low doses. | 4 | Stereochemistry |
The Meixner test (also known as the Wieland test) uses concentrated hydrochloric acid and newspaper to test for the deadly amatoxins found in some species of Amanita, Lepiota, and Galerina. The test yields false positives for some compounds, such as psilocin. | 3 | Analytical Chemistry |
The BioCyc database collection is an assortment of organism specific Pathway/Genome Databases (PGDBs) that provide reference to genome and metabolic pathway information for thousands of organisms. As of July 2023, there were over 20,040 databases within BioCyc. SRI International, based in Menlo Park, California, maintains the BioCyc database family. | 1 | Biochemistry |
Most species have a negligible vapour pressure at such low temperatures, and this means that they quickly condense on the sides of the apparatus. Essentially, the CRESU technique provides a "wall-less flow tube", which allows the kinetics of gas-phase reactions to be investigated at much lower temperatures than otherwise possible.
Chemical kinetics experiments can then be carried out in a pump–probe fashion, using a laser to initiate the reaction (for example, by preparing one of the reagents by photolysis of a precursor), followed by observation of that same species (for example, by laser-induced fluorescence) after a known time delay. The fluorescence signal is captured by a photomultiplier a known distance downstream of the de Laval nozzle. The time delay can be varied up to the maximum corresponding to the flow time over that known distance. By studying how quickly the reagent species disappears in the presence of differing concentrations of a (usually stable) co-reagent species, the reaction rate constant at the low temperature of the CRESU flow can be determined.
Reactions studied by the CRESU technique typically have no significant activation energy barrier. In the case of neutral–neutral reactions (i.e., not involving any charged species, ions), these type of barrier-free reactions usually involve free radical species, such as molecular oxygen (O), the cyanide radical (CN) or the hydroxyl radical (OH). The energetic driving force for these reactions is typically an attractive long-range intermolecular potential.
CRESU experiments have been used to show deviations from Arrhenius kinetics at low temperatures: as the temperature is reduced, the rate constant actually increases. They can explain why chemistry is so prevalent in the interstellar medium, where many different polyatomic species have been detected (by radio astronomy). | 7 | Physical Chemistry |
One use of PIDA is in the preparation of similar reagents by substitution of the acetate groups. For example, it can be used to prepare (bis(trifluoroacetoxy)iodo)benzene (phenyliodine(III) bis(trifluoroacetate), PIFA) by heating in trifluoroacetic acid:
PIFA can be used to carry out the Hofmann rearrangement under mildly acidic conditions, rather than the strongly basic conditions traditionally used. The Hofmann decarbonylation of an N-protected asparagine has been demonstrated with PIDA, providing a route to β-amino--alanine derivatives.
PIDA is also used in Suárez oxidation, where photolysis of hydroxy compounds in the presence of PIDA and iodine generates cyclic ethers. This has been used in several total syntheses, such as the total synthesis of (−)-majucin, (−)-Jiadifenoxolane A, and cephanolide A. | 0 | Organic Chemistry |
The first pass through the hepatic portal vein results in some of the drug being metabolized by O-demethylation into an active metabolite of dextromethorphan called dextrorphan, the 3-hydroxy derivative of dextromethorphan. The therapeutic activity of dextromethorphan is believed to be caused by both the drug and this metabolite. Dextromethorphan also undergoes N-demethylation (to 3-methoxymorphinan or MEM), and partial conjugation with glucuronic acid and sulfate ions. Hours after dextromethorphan therapy, (in humans) the metabolites (+)-3-hydroxy-N-methylmorphinan, (+)-3-morphinan, and traces of the unchanged drug are detectable in the urine.
A major metabolic catalyst involved is the cytochrome P450 enzyme known as 2D6, or CYP2D6. A significant portion of the population has a functional deficiency in this enzyme and are known as poor CYP2D6 metabolizers. O-demethylation of dextromethorphan to dextrorphan contributes to at least 80% of the dextrorphan formed during dextromethorphan metabolism. As CYP2D6 is a major metabolic pathway in the inactivation of dextromethorphan, the duration of action and effects of dextromethorphan can be increased by as much as three times in such poor metabolizers. In one study on 252 Americans, 84.3% were found to be "fast" (extensive) metabolizers, 6.8% to be "intermediate" metabolizers, and 8.8% were "slow" metabolizers of dextromethorphan. A number of alleles for CYP2D6 are known, including several completely inactive variants. The distribution of alleles is uneven amongst ethnic groups.
A large number of medications are potent inhibitors of CYP2D6. Some types of medications known to inhibit CYP2D6 include certain SSRIs and tricyclic antidepressants, some antipsychotics, and the commonly available antihistamine diphenhydramine. Therefore, the potential of interactions exists between dextromethorphan and medications that inhibit this enzyme, particularly in slow metabolizers.
Dextromethorphan is also metabolized by CYP3A4. N-demethylation is primarily accomplished by CYP3A4, contributing to at least 90% of the MEM formed as a primary metabolite of dextromethorphan.
A number of other CYP enzymes are implicated as minor pathways of dextromethorphan metabolism. CYP2D6 is more effective than CYP3A4 at N-demethylation of dextromethorphan, but since the average individual has a much lower CYP2D6 content in the liver compared to CYP3A4, most N-demethylation of dextromethorphan is catalyzed by CYP3A4. | 4 | Stereochemistry |
In the Black Sea, sapropels are distributed at a depth of 500 to 2200 m, and in different morpholithological zones they have different thicknesses. Deep sea sediments are called the sediments formed outside the zone of influence of hydrogenic factors such as wind-driven waves and internal waves as well as of the transgressive and regressive cycles of the Black Sea basin. Here, under the conditions of relative stagnation, can be observed uninterrupted cross-sections because this area was under the sea level during the entire Pleistocene and Holocene. Deep sea organogenic mineral sediments (DSOMS) are those sediments that contain more than 3% organic carbon. The sapropels form a single horizon with constant thickness typical of the Black Sea basin. Analogues of the sapropels on the continental shelf and the upper part of the continental slope are the green aleurite-pelite, oozes with accumulation of plant detritus and decomposed shells of Mytilus galloprovincialis. The transition from aleurite-pelitic oozes to sapropels is facial. The organic matter in the sapropels is of heterogeneous origin. They are composed primarily of planktogenic organisms (about 80%) and continental organic matter (20%). The planktonic organisms are well preserved in most cases under the conditions of the hydrogen sulfide zone. The main components of the sapropels are the dinoflagellate cysts, diatom algae, coccolithophorids, peridiniales. The mineral part of sapropel muds is represented by a poly-component mixture of clay minerals. The minerals illite and montmorillonite predominate, chlorite and kaolinite occur in subordinate quantities. Individual grains of quartz, feldspar, volcanic glass and others are rarely found among them. Carbonate minerals are mainly represented by calcite and dolomite. It is generally accepted that the main source of hydrogen sulfide in the Black Sea today are the processes of anaerobic decomposition of organic matter by sulfate-reducing bacteria (SRB). The organic substance that is fixed at the bottom of the basin in the form of organogenic-mineral sediments (sapropels) is a product of the mass extinction of the plankton biomass as a result of the Black Sea flood. There is an excess of a huge amount of organic matter, which creates favorable conditions for the development of bacterial sulfate reduction. | 9 | Geochemistry |
In the 1960s it was headquartered at 17 Belgrave Square in the City of Westminster. In the 1970s it moved to Northway House on the A1000 (High Road) in north London. | 8 | Metallurgy |
Typical dispersities vary based on the mechanism of polymerization and can be affected by a variety of reaction conditions. In synthetic polymers, it can vary greatly due to reactant ratio, how close the polymerization went to completion, etc. For typical addition polymerization, Đ can range around 5 to 20. For typical step polymerization, most probable values of Đ are around 2 —Carothers' equation limits Đ to values of 2 and below.
Living polymerization, a special case of addition polymerization, leads to values very close to 1. Such is the case also in biological polymers, where the dispersity can be very close or equal to 1, indicating only one length of polymer is present. | 7 | Physical Chemistry |
Via the process of hydrogenation, unsaturated N-containing functional groups are reduced to amines using hydrogen in the presence of a nickel catalyst. Suitable groups include nitriles, azides, imines including oximes, amides, and nitro. In the case of nitriles, reactions are sensitive to acidic or alkaline conditions, which can cause hydrolysis of the group. Lithium aluminium hydride| is more commonly employed for the reduction of these same groups on the laboratory scale.
Many amines are produced from aldehydes and ketones via reductive amination, which can either proceed catalytically or stoichiometrically.
Aniline () and its derivatives are prepared by reduction of the nitroaromatics. In industry, hydrogen is the preferred reductant, whereas, in the laboratory, tin and iron are often employed. | 0 | Organic Chemistry |
Energy transmission with a rotating shaft is very common in engineering practice. Often the torque T applied to the shaft is constant which means that the force F applied is constant. For a specified constant torque, the work done during n revolutions is determined as follows: A force F acting through a moment arm r generates a torque T
This force acts through a distance s, which is related to the radius r by
The shaft work is then determined from:
The power transmitted through the shaft is the shaft work done per unit time, which is expressed as | 7 | Physical Chemistry |
A carbon-to-nitrogen ratio (C/N ratio or C:N ratio) is a ratio of the mass of carbon to the mass of nitrogen in organic residues. It can, amongst other things, be used in analysing sediments and soil including soil organic matter and soil amendments such as compost. | 9 | Geochemistry |
Phenols represent a kind of enol. For some phenols and related compounds, the keto tautomer plays an important role. Many of the reactions of resorcinol involve the keto tautomer, for example. Naphthalene-1,4-diol exists in observable equilibrium with the diketone tetrahydronaphthalene-1,4-dione. | 0 | Organic Chemistry |
* [https://web.archive.org/web/20071209060605/http://cus.cam.ac.uk/~jld1/lists/ Cambridge University Officers] | 8 | Metallurgy |
Evaporation is a phase transition from the liquid phase to vapor (a state of substance below critical temperature) that occurs at temperatures below the boiling temperature at a given pressure. Evaporation occurs on the surface. Evaporation only occurs when the partial pressure of vapor of a substance is less than the equilibrium vapor pressure. For example, due to constantly decreasing pressures, vapor pumped out of a solution will eventually leave behind a cryogenic liquid. | 7 | Physical Chemistry |
In the United States, Valeant raised the cost of the medication from about US$500 to US$24,000 per month in 2016. | 4 | Stereochemistry |
CDI can be prepared straightforwardly by the reaction of phosgene with four equivalents of imidazole under anhydrous conditions. Removal of the side product, imidazolium chloride, and solvent results in the crystalline product in ~90% yield.
:4 CHN + C(O)Cl → (CHN)CO + 2 [CHNH]Cl
In this conversion, the imidazole serves both as the nucleophile and the base. An alternative precursor 1-(trimethylsilyl)imidazole requires more preparative effort with the advantage that the coproduct trimethylsilyl chloride is volatile.
CDI hydrolyzes readily to give back imidazole:
:(CHN)CO + HO → 2 CHN + CO
The purity of CDI can be determined by the amount of CO that is formed upon hydrolysis. | 0 | Organic Chemistry |
Drospirenone is available in the following formulations, brand names, and indications:
* Drospirenone 4 mg (Slynd) – progestogen-only birth control pill
* Drospirenone 3 mg and estetrol 14.2 mg (Nextstellis (US)) – combined birth control pill
* Ethinylestradiol 30 μg and drospirenone 3 mg (Ocella, Syeda, Yasmin, Zarah, Zumandimine) – combined birth control pill
* Ethinylestradiol 20 μg and drospirenone 3 mg (Gianvi, Jasmiel, Loryna, Lo-Zumandimine, Nikki, Vestura, Yaz) – combined birth control pill, acne, PMS, PMDD, dysmenorrhea
* Ethinylestradiol 30 μg, drospirenone 3 mg, and levomefolate calcium 0.451 mg (Beyaz, Tydemy) – combined birth control pill with vitamin B supplementation, acne, PMS
* Estetrol 15 mg and drospirenone 3 mg (Nextstellis (CA)) – combined birth control pill
* Estradiol 0.5 or 1 mg and drospirenone 0.25 or 0.5 mg (Angeliq) – menopausal hormone therapy (menopausal syndrome, postmenopausal osteoporosis) | 4 | Stereochemistry |
Lichens cover about 7% of the planet's surface and grow on and in a wide range of substrates and habitats, including some of the most extreme conditions on earth. They are abundant growing on bark, leaves, and hanging from epiphyte branches in rain forests and in temperate woodland. They grow on bare rock, walls, gravestones, roofs, and exposed soil surfaces. They can survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, and toxic slag heaps. They can live inside solid rock, growing between the grains, and in the soil as part of a biological soil crust in arid habitats such as deserts. Some lichens do not grow on anything, living out their lives blowing about the environment.
When growing on mineral surfaces, some lichens slowly decompose their substrate by chemically degrading and physically disrupting the minerals, contributing to the process of weathering by which rocks are gradually turned into soil. While this contribution to weathering is usually benign, it can cause problems for artificial stone structures. For example, there is an ongoing lichen growth problem on Mount Rushmore National Memorial that requires the employment of mountain-climbing conservators to clean the monument.
Lichens are not parasites on the plants they grow on, but only use them as a substrate. The fungi of some lichen species may "take over" the algae of other lichen species. Lichens make their own food from their photosynthetic parts and by absorbing minerals from the environment. Lichens growing on leaves may have the appearance of being parasites on the leaves, but they are not. Some lichens in Diploschistes parasitise other lichens. Diploschistes muscorum starts its development in the tissue of a host Cladonia species.
In the arctic tundra, lichens, together with mosses and liverworts, make up the majority of the ground cover, which helps insulate the ground and may provide forage for grazing animals. An example is "reindeer moss", which is a lichen, not a moss.
There are only two species of known permanently submerged lichens; Hydrothyria venosa is found in fresh water environments, and Verrucaria serpuloides is found in marine environments.
A crustose lichen that grows on rock is called a saxicolous lichen. Crustose lichens that grow on the rock are epilithic, and those that grow immersed inside rock, growing between the crystals with only their fruiting bodies exposed to the air, are called endolithic lichens. A crustose lichen that grows on bark is called a corticolous lichen. A lichen that grows on wood from which the bark has been stripped is called a lignicolous lichen. Lichens that grow immersed inside plant tissues are called endophloidic lichens or endophloidal lichens. Lichens that use leaves as substrates, whether the leaf is still on the tree or on the ground, are called epiphyllous or foliicolous. A terricolous lichen grows on the soil as a substrate. Many squamulous lichens are terricolous. Umbilicate lichens are foliose lichens that are attached to the substrate at only one point. A vagrant lichen is not attached to a substrate at all, and lives its life being blown around by the wind. | 2 | Environmental Chemistry |
Appointed to a teaching position at Birkbeck College, University of London, Ferrier's focus turned from polysaccharides to monosaccharides. New laboratory tools and methods enabled their reactions and mechanisms to be studied like normal organic compounds, rather than a separate field, and he pioneered this approach. In the early 1960s as a NATO Post Doctoral Fellow, he worked in Professor Melvin Calvin’s group at the University of California, Berkeley. They were exciting times. While Ferrier was there, Calvin was awarded the Nobel Prize for Chemistry, and he also met Carolyn Tompkins, the pair marrying in Edinburgh in 1962.
Arriving in New Zealand in 1970 as Victoria University’s first Chair of Organic Chemistry, Ferrier continued to lead work on the monosaccharides, specialising in their use as starting materials for the synthesis of non-carbohydrate compounds of pharmaceutical interest. He had previously clarified the mechanism of the Fischer glycosidation and discovered an allylic rearrangement reaction of glycals, now known as the Ferrier rearrangement – the first of two reactions that bear his name. Many of Ferrier's best discoveries were made by following up unexpected chemical observations, which often led him into uncharted territory. His second ‘name’ reaction, the Ferrier carbocyclization, was the result of this approach.
He served on the Toxic Substances Board in the 1980s and the leadership of the RSNZ report Lead in the Environment that confirmed the toxic effects of lead and began the phase-out of leaded petrol.
After his retirement from Victoria University in 1998, he became an emeritus professor. Ferrier then entered what he referred to as his supposed retirement, working with the carbohydrate chemists at Industrial Research Ltd. Here he continued to foster the next generation of carbohydrate chemists in New Zealand – his grandchildren, instilling his rigorous approach to chemistry with mentoring and assistance with the group's publications. | 0 | Organic Chemistry |
Volatilization methods can be either direct or indirect. Water eliminated in a quantitative manner from many inorganic substances by ignition is an example of a direct determination. It is collected on a solid desiccant and its mass determined by the gain in mass of the desiccant.
Another direct volatilization method involves carbonates which generally decompose to release carbon dioxide when acids are used. Because carbon dioxide is easily evolved when heat is applied, its mass is directly established by the measured increase in the mass of the absorbent solid used.
Determination of the amount of water by measuring the loss in mass of the sample during heating is an example of an indirect method. It is well known that changes in mass occur due to decomposition of many substances when heat is applied, regardless of the presence or absence of water. Because one must make the assumption that water was the only component lost, this method is less satisfactory than direct methods.
This often faulty and misleading assumption has proven to be wrong on more than a few occasions. There are many substances other than water loss that can lead to loss of mass with the addition of heat, as well as a number of other factors that may contribute to it. The widened margin of error created by this all-too-often false assumption is not one to be lightly disregarded as the consequences could be far-reaching.
Nevertheless, the indirect method, although less reliable than direct, is still widely used in commerce. For example, it's used to measure the moisture content of cereals, where a number of imprecise and inaccurate instruments are available for this purpose. | 3 | Analytical Chemistry |
When a photon hits a piece of semiconductor, one of three things can happen:
# The photon can pass straight through the semiconductor — this (generally) happens for lower energy photons.
# The photon can reflect off the surface.
# The photon can be absorbed by the semiconductor if the photon energy is higher than the band gap value. This generates an electron-hole pair and sometimes heat depending on the band structure.
When a photon is absorbed, its energy is given to an electron in the crystal lattice. Usually this electron is in the valence band. The energy given to the electron by the photon "excites" it into the conduction band where it is free to move around within the semiconductor. The network of covalent bonds that the electron was previously a part of now has one fewer electron. This is known as a hole, and it has positive charge. The presence of a missing covalent bond allows the bonded electrons of neighboring atoms to move into the "hole", leaving another hole behind, thus propagating holes throughout the lattice in the opposite direction to the movement of the negatively electrons. It can be said that photons absorbed in the semiconductor create electron-hole pairs.
A photon only needs to have energy greater than that of the band gap in order to excite an electron from the valence band into the conduction band. However, the solar frequency spectrum approximates a black body spectrum at about 5,800 K, and as such, much of the solar radiation reaching the Earth is composed of photons with energies greater than the band gap of silicon (1.12eV), which is near to the ideal value for a terrestrial solar cell (1.4eV). These higher energy photons will be absorbed by a silicon solar cell, but the difference in energy between these photons and the silicon band gap is converted into heat (via lattice vibrations — called phonons) rather than into usable electrical energy. | 7 | Physical Chemistry |
Bitumen was used starting in the 1960s as a hydrophobic matrix aiming to encapsulate radioactive waste such as medium-activity salts (mainly soluble sodium nitrate and sodium sulfate) produced by the reprocessing of spent nuclear fuels or radioactive sludges from sedimentation ponds. Bituminised radioactive waste containing highly radiotoxic alpha-emitting transuranic elements from nuclear reprocessing plants have been produced at industrial scale in France, Belgium and Japan, but this type of waste conditioning has been abandoned because operational safety issues (risks of fire, as occurred in a bituminisation plant at Tokai Works in Japan) and long-term stability problems related to their geological disposal in deep rock formations. One of the main problems is the swelling of bitumen exposed to radiation and to water. Bitumen swelling is first induced by radiation because of the presence of hydrogen gas bubbles generated by alpha and gamma radiolysis. A second mechanism is the matrix swelling when the encapsulated hygroscopic salts exposed to water or moisture start to rehydrate and to dissolve. The high concentration of salt in the pore solution inside the bituminised matrix is then responsible for osmotic effects inside the bituminised matrix. The water moves in the direction of the concentrated salts, the bitumen acting as a semi-permeable membrane. This also causes the matrix to swell. The swelling pressure due to osmotic effect under constant volume can be as high as 200 bar. If not properly managed, this high pressure can cause fractures in the near field of a disposal gallery of bituminised medium-level waste. When the bituminised matrix has been altered by swelling, encapsulated radionuclides are easily leached by the contact of ground water and released in the geosphere. The high ionic strength of the concentrated saline solution also favours the migration of radionuclides in clay host rocks. The presence of chemically reactive nitrate can also affect the redox conditions prevailing in the host rock by establishing oxidizing conditions, preventing the reduction of redox-sensitive radionuclides. Under their higher valences, radionuclides of elements such as selenium, technetium, uranium, neptunium and plutonium have a higher solubility and are also often present in water as non-retarded anions. This makes the disposal of medium-level bituminised waste very challenging.
Different types of bitumen have been used: blown bitumen (partly oxidized with air oxygen at high temperature after distillation, and harder) and direct distillation bitumen (softer). Blown bitumens like Mexphalte, with a high content of saturated hydrocarbons, are more easily biodegraded by microorganisms than direct distillation bitumen, with a low content of saturated hydrocarbons and a high content of aromatic hydrocarbons.
Concrete encapsulation of radwaste is presently considered a safer alternative by the nuclear industry and the waste management organisations. | 7 | Physical Chemistry |
In humans, L-2-Hydroxyglutaric aciduria was the first disease linked to a missing metabolite repair enzyme. Mutations in the L2HGDH gene cause accumulation of L-2-hydroxyglutarate, which is a structural analog to glutamate and alpha-ketoglutarate and presumably inhibits other enzymes or transporters. | 1 | Biochemistry |
In E2 elimination reactions, a base abstracts a proton that is beta to a leaving group, such as a halide. The removal of the proton and the loss of the leaving group occur in a single, concerted step to form a new double bond. When a small, unhindered base – such as sodium hydroxide, sodium methoxide, or sodium ethoxide – is used for an E2 elimination, the Zaytsev product is typically favored over the least substituted alkene, known as the Hofmann product. For example, treating 2-Bromo-2-methyl butane with sodium ethoxide in ethanol produces the Zaytsev product with moderate selectivity.
Due to steric interactions, a bulky base – such as potassium tert-butoxide, triethylamine, or 2,6-lutidine – cannot readily abstract the proton that would lead to the Zaytsev product. In these situations, a less sterically hindered proton is preferentially abstracted instead. As a result, the Hofmann product is typically favored when using bulky bases. When 2-Bromo-2-methyl butane is treated with potassium tert-butoxide instead of sodium ethoxide, the Hofmann product is favored.
Steric interactions within the substrate also prevent the formation of the Zaytsev product. These intramolecular interactions are relevant to the distribution of products in the Hofmann elimination reaction, which converts amines to alkenes. In the Hofmann elimination, treatment of a quaternary ammonium iodide salt with silver oxide produces hydroxide ions, which act as a base and eliminate the tertiary amine to give an alkene.
In the Hofmann elimination, the least substituted alkene is typically favored due to intramolecular steric interactions. The quaternary ammonium group is large, and interactions with alkyl groups on the rest of the molecule are undesirable. As a result, the conformation necessary for the formation of the Zaytsev product is less energetically favorable than the conformation required for the formation of the Hofmann product. As a result, the Hofmann product is formed preferentially. The Cope elimination is very similar to the Hofmann elimination in principle but occurs under milder conditions. It also favors the formation of the Hofmann product, and for the same reasons. | 7 | Physical Chemistry |
The ancestry of each present day cell presumably traces back, in an unbroken lineage for over 3 billion years to the origin of life. It is not actually cells that are immortal but multi-generational cell lineages. The immortality of a cell lineage depends on the maintenance of cell division potential. This potential may be lost in any particular lineage because of cell damage, terminal differentiation as occurs in nerve cells, or programmed cell death (apoptosis) during development. Maintenance of cell division potential over successive generations depends on the avoidance and the accurate repair of cellular damage, particularly DNA damage. In sexual organisms, continuity of the germline depends on the effectiveness of processes for avoiding DNA damage and repairing those DNA damages that do occur. Sexual processes in eukaryotes, as well as in prokaryotes, provide an opportunity for effective repair of DNA damages in the germ line by homologous recombination. | 1 | Biochemistry |
Collision in diluted gas or liquid solution is regulated by diffusion instead of direct collisions, which can be calculated from Fick's laws of diffusion. Theoretical models to calculate the collision frequency in solutions have been proposed by Marian Smoluchowski in a seminal 1916 publication at the infinite time limit, and Jixin Chen in 2022 at a finite-time approximation. A scheme of comparing the rate equations in pure gas and solution is shown in the right figure.
For a diluted solution in the gas or the liquid phase, the collision equation developed for neat gas is not suitable when diffusion takes control of the collision frequency, i.e., the direct collision between the two molecules no longer dominates. For any given molecule A, it has to collide with a lot of solvent molecules, let's say molecule C, before finding the B molecule to react with. Thus the probability of collision should be calculated using the Brownian motion model, which can be approximated to a diffusive flux using various boundary conditions that yield different equations in the Smoluchowski model and the JChen Model.
For the diffusive collision, at the infinite time limit when the molecular flux can be calculated from the Fick's laws of diffusion, in 1916 Smoluchowski derived a collision frequency between molecule A and B in a diluted solution:
where:
* is the collision frequency, unit #collisions/s in 1 m of solution.
* is the radius of the collision cross-section, unit m.
* is the relative diffusion constant between A and B, unit m/s, and .
* and are the number concentrations of molecules A and B in the solution respectively, unit #molecule/m.
or
where:
* is in unit mole collisions/s in 1 L of solution.
* is the Avogadro constant.
* is the radius of the collision cross-section, unit m.
* is the relative diffusion constant between A and B, unit m/s.
* and are the molar concentrations of A and B respectively, unit mol/L.
* is the diffusive collision rate constant, unit L mol s.
There have been a lot of extensions and modifications to the Smoluchowski model since it was proposed in 1916.
In 2022, Chen rationales that because the diffusive flux is evolving over time and the distance between the molecules has a finite value at a given concentration, there should be a critical time to cut off the evolution of the flux that will give a value much larger than the infinite solution Smoluchowski has proposed. So he proposes to use the average time for two molecules to switch places in the solution as the critical cut-off time, i.e., first neighbor visiting time. Although an alternative time could be the mean free path time or the average first passenger time, it overestimates the concentration gradient between the original location of the first passenger to the target. This hypothesis yields a fractal reaction kinetic rate equation of diffusive collision in a diluted solution:
where:
* is in unit mole collisions/s in 1 L of solution.
* is the Avogadro constant.
* is the area of the collision cross-section in unit m.
* is the product of the unitless fractions of reactive surface area on A and B. is the effective adsorption cross-section area.
* is the relative diffusion constant between A and B, unit m/s, and .
* and are the molar concentrations of A and B respectively, unit mol/L.
* is the diffusive collision rate constant, unit L mol s. | 7 | Physical Chemistry |
Measurement of VOCs from the indoor air is done with sorption tubes e. g. Tenax (for VOCs and SVOCs) or DNPH-cartridges (for carbonyl-compounds) or air detector. The VOCs adsorb on these materials and are afterwards desorbed either thermally (Tenax) or by elution (DNPH) and then analyzed by GC-MS/FID or HPLC. Reference gas mixtures are required for quality control of these VOC-measurements. Furthermore, VOC emitting products used indoors, e.g. building products and furniture, are investigated in emission test chambers under controlled climatic conditions. For quality control of these measurements round robin tests are carried out, therefore reproducibly emitting reference materials are ideally required. Other methods have used proprietary Silcosteel-coated canisters with constant flow inlets to collect samples over several days. These methods are not limited by the adsorbing properties of materials like Tenax. | 0 | Organic Chemistry |
As one of the primary segments of the guidelines, there are several essential parts on the checklist for the qPCR process itself. This includes the full set of conditions used for the reaction, the volume of both the reaction and the cDNA, the concentrations for the probes, magnesium ions, and dNTPs, what kind of polymerase was used and its concentration, what kit was used and its manufacturer, what additives to the reaction were used, who manufactured the qPCR machine, and what parameters were set for the thermocycling process. The only additional desired pieces of information are the chemical composition of the buffer used, who manufactured the plates and tubes used and what their catalog number is, and whether the reaction was set up manually or by a machine. | 1 | Biochemistry |
In chemistry, an enantiomer (/ɪˈnænti.əmər, ɛ-, -oʊ-/ ih-NAN-tee-ə-mər; from Ancient Greek ἐναντίος (enantíos) opposite, and μέρος (méros) part) – also called optical isomer, antipode, or optical antipode – is one of two stereoisomers that are nonsuperposable onto their own mirror image. Enantiomers are much like one's right and left hands; without mirroring one of them, hands cannot be superposed onto each other. No amount of reorientation in three spatial dimensions will allow the four unique groups on the chiral carbon (see chirality) to line up exactly. The number of stereoisomers a molecule has can be determined by the number of chiral carbons it has.
A molecule with chirality rotates plane-polarized light. A mixture of equal amounts of each enantiomer, a racemic mixture or a racemate, does not rotate light.
Stereoisomers include both enantiomers and diastereomers. Diastereomers, like enantiomers, share the same molecular formula and are also nonsuperposable onto each other; however, they are not mirror images of each other. | 4 | Stereochemistry |
Release of other organisms that fight the pest is another example of an alternative to pesticide use. These organisms can include natural predators or parasites of the pests. Biological pesticides based on entomopathogenic fungi, bacteria and viruses causing disease in the pest species can also be used. | 2 | Environmental Chemistry |
The overall process of corrosion can be represented by a bimodal function, where the type of corrosion varies with time, including both oxygen-driven and anaerobic mechanisms. The dominant process will depend on the given conditions. During oxygen-driven corrosion, layers of rust form, creating various non-homogenous anoxic niches throughout the metal's surface. Within the niches the diffusion of oxygen is inhibited, leading to the ideal conditions for anaerobic corrosion to occur. | 8 | Metallurgy |
In ecology, base-richness is the level of chemical bases in water or soil, such as calcium or magnesium ions. Many organisms<nowiki/> prefer base-rich environments. Chemical bases are alkalis, hence base-rich environments are either neutral or alkaline. Because acid-rich environments have few bases, they are dominated by environmental acids (usually organic acids). However, the relationship between base-richness and acidity is not a rigid one – changes in the levels of acids (such as dissolved carbon dioxide) may significantly change acidity without affecting base-richness.
Base-rich terrestrial environments are characteristic of areas where underlying rocks (below soil) are limestone. Seawater is also base-rich, so maritime and marine environments are themselves base-rich.
Base-poor environments are characteristic of areas where underlying rocks (below soil) are sandstone or granite, or where the water is derived directly from rainfall (ombrotrophic). | 9 | Geochemistry |
The problem of close-packing of spheres was first mathematically analyzed by Thomas Harriot around 1587, after a question on piling cannonballs on ships was posed to him by Sir Walter Raleigh on their expedition to America.
Cannonballs were usually piled in a rectangular or triangular wooden frame, forming a three-sided or four-sided pyramid. Both arrangements produce a face-centered cubic lattice – with different orientation to the ground. Hexagonal close-packing would result in a six-sided pyramid with a hexagonal base.
The cannonball problem asks which flat square arrangements of cannonballs can be stacked into a square pyramid. Édouard Lucas formulated the problem as the Diophantine equation or and conjectured that the only solutions are and . Here is the number of layers in the pyramidal stacking arrangement and is the number of cannonballs along an edge in the flat square arrangement. | 3 | Analytical Chemistry |
ZMPSTE24 is a human gene. The protein encoded by this gene is a metallopeptidase. It is involved in the processing of lamin A. Defects in the ZMPSTE24 gene lead to similar laminopathies as defects in lamin A, because the latter is a substrate for the former. In humans, a mutation abolishing the ZMPSTE24 cleavage site in prelamin A causes a progeroid disorder. Failure to correctly process prelamin A leads to deficient ability to repair DNA double-strand breaks.
As shown by Liu et al., lack of Zmpste24 prevents lamin A formation from its precursor farnesyl-prelamin A. Lack of ZMPSTE24 causes progeroid phenotypes in mice and humans. This lack increases DNA damage and chromosome aberrations and sensitivity to DNA-damaging agents that cause double-strand breaks. Also, lack of ZMPSTE24 allows an increase in non-homologous end joining, but a deficiency in steps leading to homologous recombinational DNA repair. | 1 | Biochemistry |
Jiří Drahoš was born on 20 February 1949 in Český Těšín to a Czech father originally from Skuteč in Vysočina, and a Polish mother from Jablunkov. He spent most of his childhood in Jablunkov, where his mother Anna lived and worked as a nurse. His father, also named Jiří, was a teacher in a local Czech school.
Drahoš studied at the University of Chemistry and Technology in Prague and qualified as a scientist in 1972. He joined the Institute of Chemical Process Fundamentals at the Czech Academy of Sciences, and was later head of the institute from 1996 to 2003. On 13 March 2009, Drahoš was elected President of the Czech Academy of Sciences, defeating Eva Syková. During his tenure, he successfully opposed 50% budget cuts to the Academy proposed by the governments of Prime Ministers Mirek Topolánek and Jan Fischer as a consequence of the 2008 financial crisis. Drahoš later called it an "attempt to destroy my motherly institution". In 2012, President Václav Klaus awarded him the Medal of Merit in the field of science. His second term as head of the academy ended on 24 March 2017. He is co-author of 14 patents. | 7 | Physical Chemistry |
The capacity of some compounds to change in function of the pH was known since the sixteenth century. This effect was even known before the development of acid-base theory. Those are found in a wide range of plants like roses, cornflowers, primroses and violets. Robert Boyle was the first person to describe this effect, employing plant juices (in the forms of solution and impregnated paper).
Molecular switches are most commonly used as pH indicators, which are molecules with acidic or basic properties. Their acidic and basic forms have different colors. When an acid or a base is added, the equilibrium between the two forms is displaced. | 6 | Supramolecular Chemistry |
Virokines are proteins encoded by some large DNA viruses that are secreted by the host cell and serve to evade the host's immune system. Such proteins are referred to as virokines if they resemble cytokines, growth factors, or complement regulators; the term viroceptor is sometimes used if the proteins resemble cellular receptors. A third class of virally encoded immunomodulatory proteins consists of proteins that bind directly to cytokines. Due to the immunomodulatory properties of these proteins, they have been proposed as potentially therapeutically relevant to autoimmune diseases. | 1 | Biochemistry |
K. C. Nicolaou has received numerous awards and honors including:
* 2021 Robert Koch Gold Medal (Germany)
* 2016 Wolf Prize in Chemistry (Israel)
* 2011 Benjamin Franklin Medal in Chemistry (Franklin Institute USA)
* 2005 Arthur C. Cope Award (USA)
* 2003 Nobel Laureate Signature Award in Graduate Education (with Phil S. Baran)
* 2002 Tetrahedron Prize
* 2001 Ernst Schering Prize (Germany)
* 2000 Paul Karrer Gold Medal (Switzerland)
* 1998 Esselen Award (USA)
* 1996 Linus Pauling Award (USA)
* 1996 William H. Nichols Medal (USA)
* Aspirin Prize (Spain)
* Max Tishler Prize Lecture (Harvard)
* Yamada Prize (Japan)
* Janssen Prize (Belgium)
* Nagoya Medal (Japan)
* Centenary Medal (Royal Society UK)
* Inhoffen Medal (Germany)
* ACS Award for Creative Work in Synthetic Organic Chemistry (USA)
* ACS Guenther Award in Natural Products Chemistry (USA)
* Fellow of the American Academy of Arts and Sciences
* Member of the National Academy of Sciences
*Member of the American Philosophical Society
* Foreign Member of the Royal Society (2013)
* Several honorary degrees | 0 | Organic Chemistry |
In the United States, modafinil is classified as a schedule IV controlled substance under US federal law. This means that the drug has a low potential for abuse and dependence compared to other controlled substances. However, it still requires a prescription from a licensed healthcare provider to obtain.
It is illegal to import modafinil to the United States without a Drug Enforcement Administration (DEA)-registered importer and a prescription. Individuals may legally bring modafinil into the US from a foreign country for personal use, limited to 50 dosage units, with a prescription and proper declaration at the border. Under the Pure Food and Drug Act, marketing drugs for off-label uses is prohibited. Cephalon, the manufacturer of Provigil, faced legal issues for promoting off-label uses and paid significant fines in 2008. | 4 | Stereochemistry |
Competing with the generation of electrons is the downconversion of optical phonons into multiple acoustic phonons. The coupling arises from the crystal Hamiltonian (H) expanded in terms of the ionic displacement () from the equilibrium position () of atom i in direction in direction, i.e.,
where is the ground-state Hamiltonian, the linear term vanishes (as the ground state is found by minimizing the energy in terms of the ionic position), and and are the second- and third-order force constants between atoms i, j, and k when moved in along coordinate , , and . The second order term is primarily responsible for the phonon dispersion, while the anharmonic (third order and higher) terms are responsible for thermal expansion as well as the phonon up- (multiple low-energy optical phonons combine to form a high-energy phonon) and downconversion (a high-energy phonon splits into multiple low-energy phonons).
Typically, up- and down-conversion is dominated by the third-order interaction. Thus, the perturbation Hamiltonian used in Fermi's golden rule for phonon up- and downconversion is
where is the direction of displacement for atom i due to the phonon. The resulting downconversion rate, from Fermi's golden rule, is
where two phonons are produced with polarization and and momentum and . | 7 | Physical Chemistry |
The human gastrointestinal tract is around long. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal, and the process of digestion normally takes between 24 and 72 hours.
Digestion begins in the mouth with the secretion of saliva and its digestive enzymes. Food is formed into a bolus by the mechanical mastication and swallowed into the esophagus from where it enters the stomach through the action of peristalsis. Gastric juice contains hydrochloric acid and pepsin which would damage the walls of the stomach and mucus and bicarbonates are secreted for protection. In the stomach further release of enzymes break down the food further and this is combined with the churning action of the stomach. Mainly proteins are digested in stomach. The partially digested food enters the duodenum as a thick semi-liquid chyme. In the small intestine, the larger part of digestion takes place and this is helped by the secretions of bile, pancreatic juice and intestinal juice. The intestinal walls are lined with villi, and their epithelial cells are covered with numerous microvilli to improve the absorption of nutrients by increasing the surface area of the intestine. Bile helps in emulsification of fats and also activates lipases.
In the large intestine, the passage of food is slower to enable fermentation by the gut flora to take place. Here, water is absorbed and waste material stored as feces to be removed by defecation via the anal canal and anus. | 1 | Biochemistry |
The officers of the IDDRG are the current President, Vice-Presidents, General Secretary, Treasurer, and active Past-Presidents. The officers of the IDDRG comprise the Executive Committee. The vice-presidents are selected for their expertise and to represent, as far as possible, the geographic distribution of the member countries. Specific responsibilities of vice-presidents are to contact and represent the National delegations in their geographic area and to chair technical sessions at conferences. | 8 | Metallurgy |
A number of methods exist in the literature for the preparation of diazirines, which begin from a variety of reagents. | 5 | Photochemistry |
Aberrant promoter hypermethylation of SFRP1 occurs frequently during the pathogenesis of human cancers and has been found to be one of the primary mechanisms in SFRP1 down-regulation. Methylation-specific PCR (MSP) is able to detect this epigenetic change and could be used for cancer detection. Detection and quantification of promoter CpG methylation in body fluid is both feasible and noninvasive. Combined MSP analyses of multiple genes in voided urine could provide a reliable way to improve cancer diagnosis.
Urakami et al. were able to detect cancers cells using conventional MSP analysis of Wnt-antagonist genes (including SFRP1) in voided urine of patients with bladder tumor. Their results showed a high percentage of identical methylation with tumor-tissue DNA. Conversely, no aberrant methylation was detected in >90% of urine DNA from normal controls. This demonstrates that methylation detection of SFRP1 is both feasible and reliable and that the urine methylation score (M score) of Wnt antagonist genes could be used as an excellent noninvasive diagnostic biomarker for bladder tumor. Furthermore, the M score of Wnt-antagonist genes may reflect the presence of bladder tumor that progresses to invasive disease that would signal for future aggressive treatment. An optimal hypermethylation panel of Wnt-antagonist genes could contribute significantly to early detection of bladder tumor and predict bladder tumor aggressiveness. In fact, the methylation of SFRP1 genes in fecal DNA isolated from stool samples has been used to screen for colorectal cancer. | 1 | Biochemistry |
In organic chemistry, aminobenzal is a functional group which is composed of a cyclic ketal of a diol with 4-dimethylaminobenzylidene. It is seen in triamcinolone aminobenzal benzamidoisobutyrate. | 0 | Organic Chemistry |
The screw axis is noted by a number, n, where the angle of rotation is . The degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. For example, 2 is a 180° (twofold) rotation followed by a translation of of the lattice vector. 3 is a 120° (threefold) rotation followed by a translation of of the lattice vector.
The possible screw axes are: 2, 3, 3, 4, 4, 4, 6, 6, 6, 6, and 6.
There are 4 enantiomorphic pairs of axes: (3 – 3), (4 – 4), (6 – 6), and (6 – 6). This enantiomorphism results in 11 pairs of enantiomorphic space groups, namely | 3 | Analytical Chemistry |
Cytokines are somnogenic and are likely key mediators of sleep responses to infection and food. Some proinflammatory cytokines correlate with daytime sleepiness. | 1 | Biochemistry |
Many specialized methods also yield amides. A variety of reagents, e.g. tris(2,2,2-trifluoroethyl) borate have been developed for specialized applications. | 0 | Organic Chemistry |
In phase-II metabolizing includes glucuronidation and sulfation of the mycoestrogen compound. Glucuronidation is the major phase II metabolic pathway. The transferase UGT (5-diphosphate glucuronosyltransferase) adds a glucuronic acid group sourced from uridine 5-diphosphate glucuronic acid (UDPGA). | 1 | Biochemistry |
Glycosylation reactions are very important reactions in carbohydrate chemistry, leading to the synthesis of oligosaccharides, preferably in a stereoselective manner. The stereoselectivity of these reactions has been shown to be affected by both the nature and the configuration of the protecting group at C-2 on the glycosyl donor ring. While 1,2-trans-glycosides (e.g. α-mannosides and β-glucosides) can be synthesised easily in the presence of a participating group (such as OAc, or NHAc) at the C-2 position in the glycosyl donor ring, 1,2-cis-glycosides are more difficult to prepare. 1,2-cis-glycosides with the α configuration (e.g. glucosides or galactosides) can often be prepared using a non-participating protecting group (such as Bn, or All) on the C-2 hydroxy group. However, 1,2-cis-glycosides with the β configuration are the most difficult to achieve, and present the greatest challenge in glycosylation reactions.
One of the most recent approaches to prepare 1,2-cis-β-glycosides in a stereospecific manner is termed ‘Intramolecular Aglycon Delivery’, and various methods have been developed based on this approach.
In this approach, the glycosyl acceptor is tethered onto the C-2-O-protecting group (X) in the first step. Upon activation of the glycosyl donor group (Y) (usually SR, OAc, or Br group) in the next step, the tethered aglycon traps the developing oxocarbenium ion at C-1, and is transferred from the same face as OH-2, forming the glycosidic bond stereospecifically. The yield of this reaction drops as the bulkiness of the alcohol increases. | 0 | Organic Chemistry |
ATP is a molecule found only in and around living cells, and as such it gives a direct measure of biological concentration and health. ATP is quantified by measuring the light produced through its reaction with the naturally-occurring firefly enzyme luciferase using a luminometer. The amount of light produced is directly proportional to the amount of biological energy present in the sample.
Within a water sample containing microorganisms, there are two types of ATP:
* Intracellular ATP – ATP contained within living biological cells.
* Extracellular ATP – ATP located outside of biological cells that has been released from dead or stressed organisms.
Accurate measurement of these two types of ATP is critical to utilizing ATP-based measurements. Being able to accurately measure these different types of ATP offers the ability to assess biological health and activity, and subsequently control water and wastewater processes. | 2 | Environmental Chemistry |
Depending on the field of literature being surveyed, one might encounter the same compound referred to with different chemical formulas. An example of the most common difference is XYZ versus XYZ, where the labels of the two transition metals X and Y in the compound are swapped. The traditional convention XYZ arises from the interpretation of Heuslers as intermetallics and is used predominantly in literature studying magnetic applications of Heuslers compounds. The XYZ convention on the other hand is used mostly in thermoelectric materials and transparent conducting applications literature where semiconducting Heuslers (most half-Heuslers are semiconductors) are used. This convention, in which the left-most element on the periodic table comes first, uses the Zintl interpretation of semiconducting compounds where the chemical formula XYZ is written in order of increasing electronegativity. In well-known compounds such as FeVAl which were historically thought of as metallic (semi-metallic) but were more recently shown to be small-gap semiconductors one might find both styles being used. In the present article semiconducting compounds might sometimes be mentioned in the XYZ style. | 8 | Metallurgy |
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