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The Scenedesmus obliquus mitochondrial code (translation table 22) is a genetic code found in the mitochondria of Scenedesmus obliquus, a species of green algae. | 1 | Biochemistry |
Nanaerobes are organisms that cannot grow in the presence of micromolar concentrations of oxygen, but can grow with and benefit from the presence of nanomolar concentrations of oxygen (e.g. Bacteroides fragilis). Like other anaerobes, these organisms do not require oxygen for growth. This growth benefit requires the expression of an oxygen respiratory chain that is typically associated with microaerophilic respiration. Recent studies suggest that respiration in low concentrations of oxygen is an ancient process which predates the emergence of oxygenic photosynthesis. | 1 | Biochemistry |
Prior to its widespread use in the past three decades radioactivity was the most common label.
The advantages of fluorescence over radioactive labels are as follows:
* Fluorescence is safer to use and does not require radiological controls.
* Several fluorescent molecules can be used simultaneously given that they do not overlap, cf. FRET, whereas with radioactivity two isotopes can be used (tritium and a low energy isotope such as P due to different intensities) but require special machinery (a tritium screen and a regular phosphor-imaging screen or a specific dual channel detector).
Note: a channel is similar to "colour" but distinct, it is the pair of excitation and emission filters specific for a dye, e.g. agilent microarrays are dual channel, working on cy3 and cy5, these are colloquially referred to as green and red.
Fluorescence is not necessarily more convenient to use because it requires specialized detection equipment of its own. For non-quantitative or relative quantification applications it can be useful but it is poorly suited for making absolute measurement because of fluorescence quenching, whereas measuring radioactively labeled molecules is always direct and highly sensitive.
Disadvantages of fluorophores include:
* Significantly changes the properties of a fluorescently-labeled molecule
* Interference with normal biological processes
* Toxicity | 1 | Biochemistry |
Sulfoxides undergo deoxygenation to give sulfides. Typically metal complexes are used to catalyze the reaction, using hydrosilanes as the stoichiometric reductant. The deoxygenation of dimethylsulfoxide is catalyzed by DMSO reductase, a molybdoenzyme:
:OSMe + 2e + 2 H → SMe + HO | 0 | Organic Chemistry |
These models based on data are black box systems, using mathematical and statistical concepts to link a certain input (for instance rainfall) to the model output (for instance runoff). Commonly used techniques are regression, transfer functions, neural networks and system identification. These models are known as stochastic hydrology models. Data based models have been used within hydrology to simulate the rainfall-runoff relationship, represent the impacts of antecedent moisture and perform real-time control on systems. | 2 | Environmental Chemistry |
Green fluorescent protein may be used as a reporter gene.
For example, GFP can be used as a reporter for environmental toxicity levels. This protein has been shown to be an effective way to measure the toxicity levels of various chemicals including ethanol, p-formaldehyde, phenol, triclosan, and paraben. GFP is great as a reporter protein because it has no effect on the host when introduced to the host's cellular environment. Due to this ability, no external visualization stain, ATP, or cofactors are needed. With regards to pollutant levels, the fluorescence was measured in order to gauge the effect that the pollutants have on the host cell. The cellular density of the host cell was also measured. Results from the study conducted by Song, Kim, & Seo (2016) showed that there was a decrease in both fluorescence and cellular density as pollutant levels increased. This was indicative of the fact that cellular activity had decreased. More research into this specific application in order to determine the mechanism by which GFP acts as a pollutant marker. Similar results have been observed in zebrafish because zebrafish that were injected with GFP were approximately twenty times more susceptible to recognize cellular stresses than zebrafish that were not injected with GFP. | 1 | Biochemistry |
Sulfoquinovose is rarely found in its free form in nature; rather it occurs predominantly as a glycoside, SQDG. SQDG can be deacylated to form lyso-SQDG and sulfoquinovosylglycerol (SQGro). Sulfoquinovose is obtained from SQ glycosides by the action of sulfoquinovosidases, which are glycoside hydrolases that can hydrolyse the glycosidic linkage in SQDG, or its deacylated form, sulfoquinovosyl glycerol (SQGro).
There are two main classes of sulfoquinovosidases. The first are classical glycoside hydrolases (which belong to CAZy family GH31), and is exemplified by the sulfoquinovosidase YihQ from Escherichia coli. Family GH31 sulfoquinovosidases cleave SQ glycosides with retention of configuration, initially forming α-sulfoquinovose. YihQ sulfoquinovosidase exhibits a preference for the naturally occurring 2’R-SQGro. The second class of sulfoquinovosidases are NAD-dependent enzymes (which belong to CAZy family GH188) that use an oxidoreductive mechanism to cleave both α- and β-glycosides of sulfoquinovose.
Sulfoglycolysis encoding operons often contain gene sequences encoding aldose-1-epimerases that act as sulfoquinovose mutarotases, catalyzing the interconversion of the α and β anomers of sulfoquinovose. | 1 | Biochemistry |
The conversion of ammonium to nitrate is performed primarily by soil-living bacteria and other nitrifying bacteria. In the primary stage of nitrification, the oxidation of ammonium () is performed by bacteria such as the Nitrosomonas species, which converts ammonia to nitrites (). Other bacterial species such as Nitrobacter, are responsible for the oxidation of the nitrites () into nitrates (). It is important for the ammonia () to be converted to nitrates or nitrites because ammonia gas is toxic to plants.
Due to their very high solubility and because soils are highly unable to retain anions, nitrates can enter groundwater. Elevated nitrate in groundwater is a concern for drinking water use because nitrate can interfere with blood-oxygen levels in infants and cause methemoglobinemia or blue-baby syndrome. Where groundwater recharges stream flow, nitrate-enriched groundwater can contribute to eutrophication, a process that leads to high algal population and growth, especially blue-green algal populations. While not directly toxic to fish life, like ammonia, nitrate can have indirect effects on fish if it contributes to this eutrophication. Nitrogen has contributed to severe eutrophication problems in some water bodies. Since 2006, the application of nitrogen fertilizer has been increasingly controlled in Britain and the United States. This is occurring along the same lines as control of phosphorus fertilizer, restriction of which is normally considered essential to the recovery of eutrophied waterbodies. | 1 | Biochemistry |
In the 1980s, most of the dioxane produced was used as a stabilizer for 1,1,1-trichloroethane for storage and transport in aluminium containers. Normally aluminium is protected by a passivating oxide layer, but when these layers are disturbed, the metallic aluminium reacts with trichloroethane to give aluminium trichloride, which in turn catalyses the dehydrohalogenation of the remaining trichloroethane to vinylidene chloride and hydrogen chloride. Dioxane "poisons" this catalysis reaction by forming an adduct with aluminium trichloride. | 6 | Supramolecular Chemistry |
As a reagent in organic chemistry, DBU is used as a ligand and base. As a base, protonation occurs at the imine nitrogen. Lewis acids also attach to the same nitrogen.
These properties recommend DBU for use as a catalyst, for example as a curing agent for epoxy resins and polyurethane.
It is used in the separation of fullerenes in conjunction with trimethylbenzene. It reacts with C and higher fullerenes, but not with C.
It is useful for dehydrohalogenations. | 0 | Organic Chemistry |
One suitable definition of organic matter is biological material in the process of decaying or decomposing, such as humus. A closer look at the biological material in the process of decaying reveals so-called organic compounds (biological molecules) in the process of breaking up (disintegrating).
The main processes by which soil molecules disintegrates are by bacterial or fungal enzymatic catalysis. If bacteria or fungi were not present on Earth, the process of decomposition would have proceeded much slower. | 0 | Organic Chemistry |
The electrolyte is a solution of some other solvent different from water. Solvents like methanol, acetone, dimethyl sulphoxide and dimethyl formamide have been successfully employed in thermogalvanic cells running on copper sulfate. | 7 | Physical Chemistry |
Inside eukaryotic cells, there is a balance between the processes of translation and mRNA decay. Messages that are being actively translated are bound by ribosomes, the eukaryotic initiation factors eIF-4E and eIF-4G, and poly(A)-binding protein. eIF-4E and eIF-4G block the decapping enzyme (DCP2), and poly(A)-binding protein blocks the exosome complex, protecting the ends of the message. The balance between translation and decay is reflected in the size and abundance of cytoplasmic structures known as P-bodies. The poly(A) tail of the mRNA is shortened by specialized exonucleases that are targeted to specific messenger RNAs by a combination of cis-regulatory sequences on the RNA and trans-acting RNA-binding proteins. Poly(A) tail removal is thought to disrupt the circular structure of the message and destabilize the cap binding complex. The message is then subject to degradation by either the exosome complex or the decapping complex. In this way, translationally inactive messages can be destroyed quickly, while active messages remain intact. The mechanism by which translation stops and the message is handed-off to decay complexes is not understood in detail. | 1 | Biochemistry |
Photolysis is part of the light-dependent reaction or light phase or photochemical phase or Hill reaction of photosynthesis. The general reaction of photosynthetic photolysis can be given in terms of photons as:
The chemical nature of "A" depends on the type of organism. Purple sulfur bacteria oxidize hydrogen sulfide () to sulfur (S). In oxygenic photosynthesis, water () serves as a substrate for photolysis resulting in the generation of diatomic oxygen (). This is the process which returns oxygen to Earth's atmosphere. Photolysis of water occurs in the thylakoids of cyanobacteria and the chloroplasts of green algae and plants. | 5 | Photochemistry |
As well as the electronic transitions discussed above, the energy of a molecule can also change via rotational, vibrational, and vibronic (combined vibrational and electronic) transitions. These energy transitions often lead to closely spaced groups of many different spectral lines, known as spectral bands. Unresolved band spectra may appear as a spectral continuum. | 7 | Physical Chemistry |
The yeast homing endonuclease PI-Sce is a LAGLIDADG-type endonuclease encoded as an intein that splices itself out of another protein (). The high-resolution structure reveals two domains: an endonucleolytic centre resembling the C-terminal domain of Hedgehog proteins, and a Hint domain (Hedgehog/Intein) containing the protein-splicing active site. | 1 | Biochemistry |
CKIα or CKIδ is essential in modulating the nuclear export of eukaryotic translation initiation factor 6 (eIF6), a protein with essential nuclear and cytoplasmic roles in biogenesis of the 60S subunit of the eukaryotic ribosome. Phosphorylation of Ser-174 and Ser-175 by CKI promotes nuclear export of eIF6 while dephosphorylation by calcineurin promotes nuclear accumulation of eIF6. It is unclear whether the same mechanism is responsible for eIF6 cycling in yeast and if other kinases also play roles in these processes.
CKI homologs are also implicated in cytoplasmic shuttling of nuclear factor of activated T-cells (NFAT) through observation that the transcription factor Crz1p is phosphorylated by a CKI homolog in yeast. | 1 | Biochemistry |
The RNA polymerase holoenzyme binds to a promoter of an exposed DNA strand and begins to synthesize the new strand of RNA. The double helix DNA is unwound and a short nucleotide sequence is accessible on each strand. The transcription bubble is a region of unpaired bases on one of the exposed DNA strands. The starting transcription point is determined by the place where the holoenzyme binds to a promoter. The DNA is unwound and single-stranded at the start site. The DNA promoter interaction is interrupted as the RNA polymerase moves down the template DNA strand and the sigma factor is released. The σ factor is required for the initiation but not for the remaining steps of the DNA transcription. Once the σ factor dissociates from the RNA polymerase, the transcription continues. About 10 synthesized nucleotides of a new RNA strand are required for this to proceed to the elongation step. The process of transcribing during elongation is very fast. Elongation takes place until the RNA polymerase comes across a termination signal (terminator) which arrests the process and causes the release of both the DNA template and the new RNA molecule. The DNA usually encodes the termination signal. | 1 | Biochemistry |
The journal is abstracted and indexed in:
According to the Journal Citation Reports, the journal has a 2020 impact factor of 0.946. | 7 | Physical Chemistry |
Genetically Modified Organisms (GMOs) are plants or living things that have been altered at a genomic level by scientists to improve the organisms characteristics. These characteristics include providing new vaccines for humans, increasing nutrients supplies, and creating unique plastics. They may also be able to grow in climates that are typically not suitable for the original organism to grow in. Examples of GMOs include virus resistant tobacco and squash, delayed ripening tomatoes, and herbicide resistant soybeans.
GMO's came with an increased interest in using biotechnology to produce fertilizer and pesticides. Due to an increased market interest in biotechnology in the 1970s, there was more technology and infrastructure developed, a decreased cost, and an advance in research. Since the early 1980s, genetically-modified crops have been incorporated. Increased biotechnological work calls for the union of biology and chemistry to produce improved crops, a main reason behind this being the increasing amount of food needed to feed a growing population.
That being said, concerns with GMOs include potential antibiotic resistance from eating a GMO. There are also concerns about the long term effects on the human body since many GMOs were recently developed.
Much controversy surrounds GMOs. In the United States, all foods containing GMOs must be labeled as such. | 1 | Biochemistry |
Usually, but not universally, the numbers indicate:
* the first digit corresponds to the furnace number
* the second digit indicates the year in which the material was melted
* the last three (and sometimes four) indicate the melt number. | 8 | Metallurgy |
At lower temperatures, about 400–450 °C, an interdiffusion process takes place at the junction, leading to formation of layers of different gold-aluminum intermetallic compounds with different growth rates. Gaps are formed as the denser and faster-growing layers consume the slower-growing layers. This process is known as the Kirkendall voiding, which leads to both increased electrical resistance and mechanical weakening of the wire bond. When the voids forms along the diffusion front, this process is aided by contaminants present in the lattice, and is known as the Horsting voiding, which is a similar process to the Kirkendall voiding. | 8 | Metallurgy |
The Association for Materials Protection and Performance (AMPP), is a professional association focused on the protection of assets and performance of materials. AMPP was created when NACE International and SSPC the Society for Protective Coatings merged in 2021. AMPP is active in more than 130 countries and has more than 40,000 members. AMPP is headquartered in the U.S. with offices in Houston, Texas and Pittsburgh, Pennsylvania. Additional offices are located in the U.K., China, Malaysia, Brazil, and Saudi Arabia with a training center in Dubai. | 8 | Metallurgy |
Genetic polymorphisms of genes that encode subunits of TFH are known to be associated with increased cancer susceptibility in many tissues, e.g.; skin tissue, breast tissue and lung tissue. Mutations in the subunits (such as XPD and XPB) can lead to a variety of diseases, including xeroderma pigmentosum (XP) or XP combined with Cockayne syndrome. In addition to genetic variations, virus-encoded proteins also target TFH. | 1 | Biochemistry |
The human CCR4-Not complex is composed of structural (non-catalytic) subunits and those that have exonuclease and E3 ligase activity. Some but not all of the human subunits are conserved in budding yeast. In yeast the complex has nine core subunits, comprising Ccr4 (carbon catabolite repression), Caf proteins (Ccr4 associated factor) (Caf1, Caf40, Caf130) and Not proteins (Not1, Not2, Not3, Not4, and Not5).
Molecular weight of human subunits from Uniprot. | 1 | Biochemistry |
The IUPAC has designated the symbols for nucleotides. Apart from the five (A, G, C, T/U) bases, often degenerate bases are used especially for designing PCR primers. These nucleotide codes are listed here. Some primer sequences may also include the character "I", which codes for the non-standard nucleotide inosine. Inosine occurs in tRNAs and will pair with adenine, cytosine, or thymine. This character does not appear in the following table, however, because it does not represent a degeneracy. While inosine can serve a similar function as the degeneracy "D", it is an actual nucleotide, rather than a representation of a mix of nucleotides that covers each possible pairing needed. | 1 | Biochemistry |
Triatomic molecules are molecules composed of three atoms, of either the same or different chemical elements. Examples include HO, CO (pictured), HCN, O (ozone) and NO. | 7 | Physical Chemistry |
Returning to his native Korea, he began studies of the staple Korean diet and its effects on metabolism as a research assistant at Kyŏngsŏng Medical College in February 1928. He was appointed an instructor of physiology in the department of biochemistry of Severance Union Medical College (now Yonsei University College of Medicine) and an adjunct instructor of dietetics at Ewha Womans University College of Medicine.
In 1932, Suksin Lee was the first Korean to earn a Ph.D. in biochemistry for his thesis, A Study on the Eating Habits of Koreans, presented to Kyoto Imperial University on the nutrition and metabolism of prisoners in Korea. Among his advisers at the time was Professor Sato of Keijo Imperial University.
He was then appointed full-time professor of biochemistry in 1933 at Severance Union Medical College, the first Korean to hold such a position. He continued to lead the department, later serving as Severance's Dean of Student Affairs, until his death aged approximately 47 of a cerebral hemorrhage on 12 December 1944. | 1 | Biochemistry |
In-situ leaching is also called "solution mining". This process initially involves drilling of holes into the ore deposit. Explosives or hydraulic fracturing are used to create open pathways within the deposit for solution to penetrate into. Leaching solution is pumped into the deposit where it makes contact with the ore. The solution is then collected and processed. The Beverley uranium deposit is an example of in-situ leaching. | 8 | Metallurgy |
Microscope-based diagnostics are widely performed and served as a gold standard in histological analysis. However this procedure generally requires a series time-consuming lab-based procedures including fixation, paraffin embedment, sectioning, and staining to produce microscope slides with optically thin tissue slides (4–6 µm). While in developed regions histology is commonly used, people who live in areas with limited resources can hardly access it and consequently are in need for a low-cost, more efficient way to access pathological diagnosis. The main significance of MUSE system comes from its capacity to produce high-resolution microscopic image with subcellular features in a time-efficient manner with less costs and less lab-expertises requirements.
With 280 nm deep UV excitation and simple but robust hardware design, MUSE system can collect fluorescence signals without the need for fluorescence filtering techniques or complex mathematical image reconstruction. It has potential for generate high quality images containing more information than microscope slides in terms of its 2.5 dimensional features. MUSE images have been validated with diagnostic values. The system is capable to produce images from various tissue type in different sizes, either fresh or fixed. | 5 | Photochemistry |
The body of a ChemFET is generally found to be robust. However, the unavoidable requirement for a separate reference electrode makes the system more bulky overall and potentially more fragile. | 7 | Physical Chemistry |
(See also Bridgman's thermodynamic equations for the use of exact differentials in the theory of thermodynamic equations)
Suppose we have five state functions , and . Suppose that the state space is two-dimensional and any of the five quantities are differentiable. Then by the chain rule
but also by the chain rule:
and
so that (by substituting (2) and (3) into (1)):
which implies that (by comparing (4) with (1)):
Letting in (5) gives:
Letting in (5) gives:
Letting and in (7) gives:
using ( gives the triple product rule: | 7 | Physical Chemistry |
Gas electron diffraction (GED) can be used to determine the geometry of molecules in gases. A gas carrying the molecules is exposed to the electron beam, which is diffracted by the molecules. Since the molecules are randomly oriented, the resulting diffraction pattern consists of broad concentric rings, see Figure 24. The diffraction intensity is a sum of several components such as background, atomic intensity or molecular intensity.
In GED the diffraction intensities at a particular diffraction angle is described via a scattering variable defined asThe total intensity is then given as a sum of partial contributions:where results from scattering by individual atoms, by pairs of atoms and by atom triplets. Intensity corresponds to the background which, unlike the previous contributions, must be determined experimentally. The intensity of atomic scattering is defined aswhere , is the distance between the scattering object detector, is the intensity of the primary electron beam and is the scattering amplitude of the atom of the molecular structure in the experiment. is the main contribution and easily obtained for known gas composition. Note that the vector used here is not the same as the excitation error used in other areas of diffraction, see earlier.
The most valuable information is carried by the intensity of molecular scattering , as it contains information about the distance between all pairs of atoms in the molecule. It is given bywhere is the distance between two atoms, is the mean square amplitude of vibration between the two atoms, similar to a Debye–Waller factor, is the anharmonicity constant and a phase factor which is important for atomic pairs with very different nuclear charges. The summation is performed over all atom pairs. Atomic triplet intensity is negligible in most cases. If the molecular intensity is extracted from an experimental pattern by subtracting other contributions, it can be used to match and refine a structural model against the experimental data.
Similar methods of analysis have also been applied to analyze electron diffraction data from liquids. | 7 | Physical Chemistry |
Mefloquine is contraindicated in those with a previous history of seizures or a recent history of psychiatric disorders. | 4 | Stereochemistry |
In an experiment in 1995, display of Glutathione S-transferase was attempted on both pVII and pIX and failed. However, phage display of this protein was completed successfully after the addition of a periplasmic signal sequence (pelB or ompA) on the N-terminus. In a recent study, it has been shown that AviTag, FLAG and His could be displayed on pVII without the need of a signal sequence. Then the expression of single chain Fv's (scFv), and single chain T cell receptors (scTCR) were expressed both with and without the signal sequence.
PelB (an amino acid signal sequence that targets the protein to the periplasm where a signal peptidase then cleaves off PelB) improved the phage display level when compared to pVII and pIX fusions without the signal sequence. However, this led to the incorporation of more helper phage genomes rather than phagemid genomes. In all cases, phage display levels were lower than using pIII fusion. However, lower display might be more favorable for the selection of binders due to lower display being closer to true monovalent display. In five out of six occasions, pVII and pIX fusions without pelB was more efficient than pIII fusions in affinity selection assays. The paper even goes on to state that pVII and pIX display platforms may outperform pIII in the long run.
The use of pVII and pIX instead of pIII might also be an advantage because virion rescue may be undertaken without breaking the virion-antigen bond if the pIII used is wild type. Instead, one could cleave in a section between the bead and the antigen to elute. Since the pIII is intact it does not matter whether the antigen remains bound to the phage. | 1 | Biochemistry |
Some examples of macromolecules are synthetic polymers (plastics, synthetic fibers, and synthetic rubber), graphene, and carbon nanotubes. Polymers may be prepared from inorganic matter as well as for instance in inorganic polymers and geopolymers. The incorporation of inorganic elements enables the tunability of properties and/or responsive behavior as for instance in smart inorganic polymers. | 7 | Physical Chemistry |
Together with 1,3,5-trioxane, hexamethylenetetramine is a component of hexamine fuel tablets used by campers, hobbyists, the military and relief organizations for heating camping food or military rations. It burns smokelessly, has a high energy density of 30.0 megajoules per kilogram (MJ/kg), does not liquify while burning, and leaves no ashes, although its fumes are toxic.
Standardized 0.149 g tablets of methenamine (hexamine) are used by fire-protection laboratories as a clean and reproducible fire source to test the flammability of carpets and rugs. | 0 | Organic Chemistry |
Potential associations have been found between low vitamin D levels and the risk of developing several types of cancer. Meta-analyses of observational studies have found reduced risk of cancer incidence related to vitamin D intake and 25(OH)D levels, particularly for colorectal cancer, although the strength of the associations was classified as weak. Vitamin D receptor and SNAI2 are found to be involved in the metastastic process of osteosarcoma. While randomized controlled trials have not confirmed that vitamin D supplements reduce the risk of cancer incidence, the relative risk of cancer deaths was lower by up to 16% in several meta-analyses. | 1 | Biochemistry |
Manufactured foods fortified with vitamin D include some fruit juices and fruit juice drinks, meal replacement energy bars, soy protein-based beverages, certain cheese and cheese products, flour products, infant formulas, many breakfast cereals, and milk.
In 2016 in the United States, the Food and Drug Administration (FDA) amended food additive regulations for milk fortification, stating that vitamin D levels not exceed 42IU vitamin D per 100g (400IU per US quart) of dairy milk, 84IU of vitamin D per 100g (800IU per quart) of plant milks, and 89IU per 100g (800IU per quart) in plant-based yogurts or in soy beverage products. Plant milks are defined as beverages made from soy, almond, rice, among other plant sources intended as alternatives to dairy milk.
While some studies have found that vitamin D raises 25(OH)D blood levels faster and remains active in the body longer, others contend that vitamin D sources are equally bioavailable and effective as D for raising and sustaining 25(OH)D. | 1 | Biochemistry |
Directed-, chelation-assisted-, or "guided" C-H activation involves directing groups that influence regio- and stereochemistry. This is the most useful style of C-H activation in organic synthesis. N,N-dimethylbenzylamine undergoes cyclometalation readily by many transition metals. A semi-practical implementations involve weakly coordinating directing groups, as illustrated by the Murai reaction.
The mechanism for the Pd-catalyzed C-H activation reactions of 2-phenylpyridine involves a metallacycle intermediate. The intermediate is oxidized to form a Pd species, followed by reductive elimination to form the C-O bond and release the product. | 0 | Organic Chemistry |
The PiggyBac (PB) transposon from the cabbage looper moth Trichoplusia ni was engineered to be highly active in mammalian cells, and is capable of genome-wide mutagenesis. Transposons contained both PB and Sleeping Beauty inverted repeats, in order to be recognized by both transposases and increase the frequency of transposition. In addition, the transposon contained promoter and enhancer elements, a splice donor and acceptors to allow gain- or loss-of-function mutations depending on the transposons orientation, and bidirectional polyadenylation signals. The transposons were transformed into mouse cells in vitro' and mutants containing tumours were analyzed. The mechanism of the mutation leading to tumour formation determined if the gene was classified as an oncogene or a tumour-suppressor gene. Oncogenes tended to be characterized by insertions in regions leading to overexpression of a gene, whereas tumour-suppressor genes were classified as such based on loss-of-function mutations. Since the mouse is a model organism for the study of human physiology and disease, this research will help lead to an increased understanding of cancer-causing genes and potential therapeutic targets. | 1 | Biochemistry |
Present-day (2021) atmospheric carbon dioxide (CO) levels of around 415 ppm are around 50% higher than preindustrial concentrations. The current elevated levels and rapid growth rates are unprecedented in the past 55 million years of the geological record. The sources of this excess CO are clearly established as human driven: they include anthropogenic fossil fuel, industrial, and land-use/land-change emissions. The ocean acts as a carbon sink for anthropogenic CO and takes up roughly a quarter of total anthropogenic CO emissions. However, the additional CO in the ocean results in a wholesale shift in seawater acid-base chemistry toward more acidic, lower pH conditions and lower saturation states for carbonate minerals used in many marine organism shells and skeletons.
Accumulated since 1850, the ocean sink holds up to 175 ± 35 gigatons of carbon, with more than two-thirds of this amount (120 GtC) being taken up by the global ocean since 1960. Over the historical period, the ocean sink increased in pace with the exponential anthropogenic emissions increase. From 1850 until 2022, the ocean has absorbed 26 % of total anthropogenic emissions. Emissions during the period 1850–2021 amounted to 670 ± 65 gigatons of carbon and were partitioned among the atmosphere (41 %), ocean (26 %), and land (31 %).
The carbon cycle describes the fluxes of carbon dioxide () between the oceans, terrestrial biosphere, lithosphere, and atmosphere. The carbon cycle involves both organic compounds such as cellulose and inorganic carbon compounds such as carbon dioxide, carbonate ion, and bicarbonate ion, together referenced as dissolved inorganic carbon (DIC). These inorganic compounds are particularly significant in ocean acidification, as they include many forms of dissolved present in the Earth's oceans.
When dissolves, it reacts with water to form a balance of ionic and non-ionic chemical species: dissolved free carbon dioxide (), carbonic acid (), bicarbonate () and carbonate (). The ratio of these species depends on factors such as seawater temperature, pressure and salinity (as shown in a Bjerrum plot). These different forms of dissolved inorganic carbon are transferred from an oceans surface to its interior by the oceans solubility pump. The resistance of an area of ocean to absorbing atmospheric is known as the Revelle factor. | 9 | Geochemistry |
Deuterium is most commonly used in hydrogen nuclear magnetic resonance spectroscopy (proton NMR) in the following way. NMR ordinarily requires compounds of interest to be analyzed as dissolved in solution. Because of deuterium's nuclear spin properties which differ from the light hydrogen usually present in organic molecules, NMR spectra of hydrogen/protium are highly differentiable from that of deuterium, and in practice deuterium is not "seen" by an NMR instrument tuned for light-hydrogen. Deuterated solvents (including heavy water, but also compounds like deuterated chloroform, CDCl) are therefore routinely used in NMR spectroscopy, in order to allow only the light-hydrogen spectra of the compound of interest to be measured, without solvent-signal interference.
Nuclear magnetic resonance spectroscopy can also be used to obtain information about the deuteron's environment in isotopically labelled samples (Deuterium NMR). For example, the configuration of hydrocarbon chains in lipid bilayers can be quantified using solid state deuterium NMR with deuterium-labelled lipid molecules.
Deuterium NMR spectra are especially informative in the solid state because of its relatively small quadrupole moment in comparison with those of bigger quadrupolar nuclei such as chlorine-35, for example. | 9 | Geochemistry |
* Contributions to the synthetic and structural chemistry of acetals, especially cyclic acetals.
* Studies of hydrogels containing UV-absorbing agents. Correlating the concentration, absorptive properties and extractability of the agents.
* Interaction of polymers with IR laser radiation – demonstrating that the monomer release following the irradiation of IOL materials with surgical IR lasers is too low to cause deleterious effects in the eye.
* First investigation of interaction between poly(2-hydroxyethyl methacrylate) (PHEMA) and UV laser radiation. First use of X-ray photoelectron spectroscopy to investigate the process of ablation of ophthalmic hydrogels with excimer lasers. General studies on the interaction between high-energy laser radiation and polymers.
* Invention and development of melanin-containing synthetic hydrogels able to absorb UV and blue radiation and their application as IOL materials. First polymer-biopolymer combinations to be reported as interpenetrating polymer networks (IPNs).
* Invention and development of an artificial cornea. Initially known as "Chirila keratoprosthesis", this device has been commercially developed as AlphaCor and received approvals from FDA and other regulatory bodies and is used in human patients.
* Development of hydrogels with very high water content as potential substitutes for the vitreous body, including a methodology for their evaluation in vitro.
* Evaluation of porous hydrogel scaffolds for nerve repair.
* Development and study of polymer matrices for the sustained release of bioactive agents, including therapeutic oligonucleotides.
* Development of an orbital implant, currently commercialised as AlphaSphere.
* Contributions to the history of ophthalmology and biomaterials.
* Development of tissue-engineered corneal constructs for the restoration of ocular surface.
His research has resulted to date in 175 journal publications and 13 patents. He has contributed over 175 presentations at scientific meetings and he has been invited to present lectures in China, the United States, Japan, Romania, Italy, France, Switzerland, Korea, Germany and The Netherlands. | 0 | Organic Chemistry |
Specific surface area (SSA) is a property of solids defined as the total surface area (SA) of a material per unit mass, (with units of m/kg or m/g). Alternatively, it may be defined as SA per solid or bulk volume (units of m/m or m).
It is a physical value that can be used to determine the type and properties of a material (e.g. soil or snow). It has a particular importance for adsorption, heterogeneous catalysis, and reactions on surfaces. | 7 | Physical Chemistry |
This section applies specifically to imaging in . For other imaging modes, the process is similar, except that "deflection" should be replaced by the appropriate feedback variable.
When using the AFM to image a sample, the tip is brought into contact with the sample, and the sample is raster scanned along an x–y grid (fig 4). Most commonly, an electronic feedback loop is employed to keep the probe-sample force constant during scanning. This feedback loop has the cantilever deflection as input, and its output controls the distance along the z axis between the probe support (2 in fig. 3) and the sample support (8 in fig 3). As long as the tip remains in contact with the sample, and the sample is scanned in the x–y plane, height variations in the sample will change the deflection of the cantilever. The feedback then adjusts the height of the probe support so that the deflection is restored to a user-defined value (the setpoint). A properly adjusted feedback loop adjusts the support-sample separation continuously during the scanning motion, such that the deflection remains approximately constant. In this situation, the feedback output equals the sample surface topography to within a small error.
Historically, a different operation method has been used, in which the sample-probe support distance is kept constant and not controlled by a feedback (servo mechanism). In this mode, usually referred to as "constant-height mode," the deflection of the cantilever is recorded as a function of the sample x–y position. As long as the tip is in contact with the sample, the deflection then corresponds to surface topography. This method is now less commonly used because the forces between tip and sample are not controlled, which can lead to forces high enough to damage the tip or the sample. It is, however, common practice to record the deflection even when scanning in "constant force mode," with feedback. This reveals the small tracking error of the feedback, and can sometimes reveal features that the feedback was not able to adjust for.
The AFM signals, such as sample height or cantilever deflection, are recorded on a computer during the x–y scan. They are plotted in a pseudocolor image, in which each pixel represents an x–y position on the sample, and the color represents the recorded signal. | 6 | Supramolecular Chemistry |
Two isozymes are encoded by the PKM gene: PKM1 and PKM2. The M-gene consists of 12 exons and 11 introns. PKM1 and PKM2 are different splicing products of the M-gene (exon 9 for PKM1 and exon 10 for PKM2) and solely differ in 23 amino acids within a 56-amino acid stretch (aa 378–434) at their carboxy terminus. | 1 | Biochemistry |
Selegiline is a selective inhibitor of MAO-B, irreversibly inhibiting it by binding to it covalently. It is generally believed to exert its effects by blocking the breakdown of dopamine, thus increasing its activity; however, recent evidence suggests that MAO-A is solely or almost entirely responsible for the metabolism of dopamine. Its possible neuroprotective properties may be due to protecting nearby neurons from the free oxygen radicals that are released by MAO-B activity. At higher doses, selegiline loses its selectivity for MAO-B and inhibits MAO-A as well.
Selegiline potentiates the release of catecholamines independent of its MAO-B inhibiting action. As such, it has been called the "first synthetic catecholaminergic activity enhancer substance".
Selegiline also inhibits CYP2A6 and can increase the effects of nicotine as a result. Selegiline also appears to activate σ receptors, having a relatively high affinity for these receptors of approximately 400 nM. | 4 | Stereochemistry |
Crystal violet can be used as an alternative to Coomassie brilliant blue (CBB) in staining of proteins separated by SDS-PAGE, reportedly showing a 5x improved sensitivity vs CBB. | 3 | Analytical Chemistry |
Accelerated testing may induce reaction kinetics that is not applicable to the actual service environment of an adhesive, which could cause greater concern than is necessary for certain adhesives. High temperatures are often avoided because it frequently causes new reactions to occur. | 3 | Analytical Chemistry |
Early records of the discovery of polymorphism credit Eilhard Mitscerlich and Jöns Jacob Berzelius for their studies of phosphates and arsenates in the early 1800s. The studies involved measuring the interfacial angles of the crystals to show that chemically identical salts could have two different forms. Mitscerlich originally called this discovery isomorphism. The measurement of crystal density was also used by Wilhelm Ostwald and expressed in Ostwald's Ratio.
The development of the microscope enhanced observations of polymorphism and aided Moritz Ludwig Frankenheim’s studies in the 1830s. He was able to demonstrate methods to induce crystal phase changes and formally summarized his findings on the nature of polymorphism. Soon after, the more sophisticated polarized light microscope came into use, and it provided better visualization of crystalline phases allowing crystallographers to distinguish between different polymorphs. The hot stage was invented and fitted to a polarized light microscope by Otto Lehmann in about 1877. This invention helped crystallographers determine melting points and observe polymorphic transitions.
While the use of hot stage microscopes continued throughout the 1900s, thermal methods also became commonly used to observe the heat flow that occurs during phase changes such as melting and polymorphic transitions. One such technique, differential scanning calorimetry (DSC), continues to be used for determining the enthalpy of polymorphic transitions.
In the 20th century, X-ray crystallography became commonly used for studying the crystal structure of polymorphs. Both single crystal x-ray diffraction and powder x-ray diffraction techniques are used to obtain measurements of the crystal unit cell. Each polymorph of a compound has a unique crystal structure. As a result, different polymorphs will produce different x-ray diffraction patterns.
Vibrational spectroscopic methods came into use for investigating polymorphism in the second half of the twentieth century and have become more commonly used as optical, computer, and semiconductor technologies improved. These techniques include infrared (IR) spectroscopy, terahertz spectroscopy and Raman spectroscopy. Mid-frequency IR and Raman spectroscopies are sensitive to changes in hydrogen bonding patterns. Such changes can subsequently be related to structural differences. Additionally, terahertz and low frequency Raman spectroscopies reveal vibrational modes resulting from intermolecular interactions in crystalline solids. Again, these vibrational modes are related to crystal structure and can be used to uncover differences in 3-dimensional structure among polymorphs. | 3 | Analytical Chemistry |
By definition, internal transmittance is related to optical depth and to absorbance as
where
*τ is the optical depth;
*A is the absorbance.
The Beer–Lambert law states that, for N attenuating species in the material sample,
or equivalently that
where
*σ is the attenuation cross section of the attenuating species i in the material sample;
*n is the number density of the attenuating species i in the material sample;
*ε is the molar attenuation coefficient of the attenuating species i in the material sample;
*c is the amount concentration of the attenuating species i in the material sample;
*ℓ is the path length of the beam of light through the material sample.
Attenuation cross section and molar attenuation coefficient are related by
and number density and amount concentration by
where N is the Avogadro constant.
In case of uniform attenuation, these relations become
or equivalently
Cases of non-uniform attenuation occur in atmospheric science applications and radiation shielding theory for instance. | 7 | Physical Chemistry |
A carbyne can occur as a short-lived reactive intermediate. For instance, fluoromethylidyne (CF) can be detected in the gas phase by spectroscopy as an intermediate in the flash photolysis of CHFBr.
Carbynes can act as trivalent ligands in complexes with transition metals, in which they are connected to a metal by the three non-bonded electrons in the –C group. Examples of such coordination compounds are , WBr(CO)(2,2'-bipyridine)≡C-aryl and WBr(CO)(PPh)≡C-NR. Such a compound can be obtained by the reaction of tungsten hexacarbonyl W(CO) with lithium diisopropylamide to form (PrN)(OLi)C=W(CO). This salt is then oxidized with either oxalyl bromide or triphenylphosphine dibromide, followed by addition of triphenylphosphine. Another method is to treat a methoxy metal carbene with a Lewis acid. | 0 | Organic Chemistry |
Pheromones are used in the detection of oestrus in sows. Boar pheromones are sprayed into the sty, and those sows that exhibit sexual arousal are known to be currently available for breeding. | 1 | Biochemistry |
In molecular biology, a library is a collection of genetic material fragments that are stored and propagated in a population of microbes through the process of molecular cloning. There are different types of DNA libraries, including cDNA libraries (formed from reverse-transcribed RNA), genomic libraries (formed from genomic DNA) and randomized mutant libraries (formed by de novo gene synthesis where alternative nucleotides or codons are incorporated). DNA library technology is a mainstay of current molecular biology, genetic engineering, and protein engineering, and the applications of these libraries depend on the source of the original DNA fragments. There are differences in the cloning vectors and techniques used in library preparation, but in general each DNA fragment is uniquely inserted into a cloning vector and the pool of recombinant DNA molecules is then transferred into a population of bacteria (a Bacterial Artificial Chromosome or BAC library) or yeast such that each organism contains on average one construct (vector + insert). As the population of organisms is grown in culture, the DNA molecules contained within them are copied and propagated (thus, "cloned"). | 1 | Biochemistry |
The cross-flow or tangential fan, sometimes known as a tubular fan, was patented in 1893 by Paul Mortier, and is used extensively in heating, ventilation, and air conditioning (HVAC), especially in ductless split air conditioners. The fan is usually long relative to its diameter, so the flow remains approximately two-dimensional away from the ends. The cross-flow fan uses an impeller with forward-curved blades, placed in a housing consisting of a rear wall and a vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.
The flow within a cross-flow fan may be broken up into three distinct regions: a vortex region near the fan discharge, called an eccentric vortex, the through-flow region, and a paddling region directly opposite. Both the vortex and paddling regions are dissipative, and as a result, only a portion of the impeller imparts usable work on the flow. The cross-flow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in HVAC comes from its compactness, shape, quiet operation, and ability to provide a high pressure coefficient. Effectively a rectangular fan in terms of inlet and outlet geometry, the diameter readily scales to fit the available space, and the length is adjustable to meet flow rate requirements for the particular application.
Common household tower fans are also cross-flow fans. Much of the early work focused on developing the cross-flow fan for both high- and low-flow-rate conditions and resulted in numerous patents. Key contributions were made by Coester, Ilberg and Sadeh, Porter and Markland, and Eck. One interesting phenomenon particular to the cross-flow fan is that, as the blades rotate, the local air incidence angle changes. The result is that in certain positions the blades act as compressors (pressure increase), while at other azimuthal locations the blades act as turbines (pressure decrease).
Since the flow both enters and exits the impeller radially, the crossflow fan has been studied and prototyped for potential aircraft applications. Due to the two-dimensional nature of the flow, the fan can be integrated into a wing for use in both thrust production and boundary-layer control. A configuration that utilizes a crossflow fan is located at the wing leading edge is the FanWing design concept initially developed around 1997 and under development by a company of the same name. This design creates lift by deflecting the wake downward due to the rotational direction of the fan, causing a large Magnus force, similar to a spinning leading-edge cylinder. Another configuration utilizing a crossflow fan for thrust and flow control is the propulsive wing, another experimental concept prototype initially developed in the 1990s and 2000s. In this design, the crossflow fan is placed near the trailing edge of a thick wing and draws the air of the wing's suction (top) surface. By doing this, the propulsive wing is nearly stall-free, even at extremely high angles of attack, producing very high lift. However, the fanwing and propulsive wing concepts remain experimental and have only been used for unmanned prototypes.
A cross-flow fan is a centrifugal fan in which the air flows straight through the fan instead of at a right angle. The rotor of a cross-flow fan is covered to create a pressure differential. Cross-flow fans are made to have a double circular arc rear wall with a thick vortex wall that decreases in radial gap. The gap decreases in the direction of the fans impeller rotation. The rear wall has a log-spiral profile while the vortex stabilizer is a horizontal thin wall with rounded edge. The resultant pressure difference allows air to flow straight through the fan, even though the fan blades counter the flow of air on one side of the rotation. Cross-flow fans give airflow along the entire width of the fan; however, they are noisier than ordinary centrifugal fans. Cross-flow fans are often used in ductless air conditioners, air doors, in some types of laptop coolers, in automobile ventilation systems, and for cooling in medium-sized equipment such as photocopiers. | 7 | Physical Chemistry |
Transfer of genes makes possible the horizontal transfer of genes from one organism to another. Thus plants can receive genes from humans or algae or any other organism. This provides limitless opportunities in breeding crop plants. | 1 | Biochemistry |
The most common types of π-interactions involve:
*Metal–π interactions: involves interaction of a metal and the face of a π system, the metal can be a cation (known as cation–π interactions) or neutral
*Polar–π interactions: involves interaction of a polar molecule and quadrupole moment a π system.
*Aromatic–aromatic interactions (π stacking): involves interactions of aromatic molecules with each other.
**Arene–perfluoroarene interaction: electron-rich benzene ring interacts with electron-poor hexafluorobenzene.
*π donor–acceptor interactions: interaction between low energy empty orbital (acceptor) and a high-energy filled orbital (donor).
*Anion–π interactions: interaction of anion with π system
*Cation–π interactions: interaction of a cation with a π system
*C–H–π interactions: interaction of C-H with π system: These interactions are well studied using experimental as well as computational techniques. | 6 | Supramolecular Chemistry |
Okazaki fragments are short sequences of DNA nucleotides (approximately 150 to 200 base pairs long in eukaryotes) which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication. They were discovered in the 1960s by the Japanese molecular biologists Reiji and Tsuneko Okazaki, along with the help of some of their colleagues.
During DNA replication, the double helix is unwound and the complementary strands are separated by the enzyme DNA helicase, creating what is known as the DNA replication fork. Following this fork, DNA primase and DNA polymerase begin to act in order to create a new complementary strand. Because these enzymes can only work in the 5’ to 3’ direction, the two unwound template strands are replicated in different ways. One strand, the leading strand, undergoes a continuous replication process since its template strand has 3’ to 5’ directionality, allowing the polymerase assembling the leading strand to follow the replication fork without interruption. The lagging strand, however, cannot be created in a continuous fashion because its template strand has 5’ to 3’ directionality, which means the polymerase must work backwards from the replication fork. This causes periodic breaks in the process of creating the lagging strand. The primase and polymerase move in the opposite direction of the fork, so the enzymes must repeatedly stop and start again while the DNA helicase breaks the strands apart. Once the fragments are made, DNA ligase connects them into a single, continuous strand. The entire replication process is considered "semi-discontinuous" since one of the new strands is formed continuously and the other is not.
During the 1960s, Reiji and Tsuneko Okazaki conducted experiments involving DNA replication in the bacterium Escherichia coli. Before this time, it was commonly thought that replication was a continuous process for both strands, but the discoveries involving E. coli led to a new model of replication. The scientists found there was a discontinuous replication process by pulse-labeling DNA and observing changes that pointed to non-contiguous replication. | 1 | Biochemistry |
With regard to the theory of CVI and ESA, there was an important observation made by O'Brien, who linked these measured parameters with dynamic electrophoretic mobility μ.
where
: A is calibration constant, depending on frequency, but not particles properties;
: ρ is particle density,
: ρ density of the fluid,
: φ is volume fraction of dispersed phase,
Dynamic electrophoretic mobility is similar to electrophoretic mobility that appears in electrophoresis theory. They are identical at low frequencies and/or for sufficiently small particles.
There are several theories of the dynamic electrophoretic mobility. Their overview is given in the Ref.5. Two of them are the most important.
The first one corresponds to the Smoluchowski limit. It yields following simple expression for CVI for sufficiently small particles with negligible CVI frequency dependence:
where:
: ε is vacuum dielectric permittivity,
: ε is fluid dielectric permittivity,
: ζ is electrokinetic potential
: η is dynamic viscosity of the fluid,
: K is conductivity of the system,
: K is conductivity of the fluid,
: ρ is density of the system.
This remarkably simple equation has same wide range of applicability as Smoluchowski equation for electrophoresis. It is independent on shape of the particles, their concentration.
Validity of this equation is restricted with the following two requirements.
First, it is valid only for a thin double layer, when the Debye length is much smaller than particle's radius a:
Secondly, it neglects the contribution of the surface conductivity. This assumes a small Dukhin number:
Restriction of the thin double layer limits applicability of this Smoluchowski type theory only to aqueous systems with sufficiently large particles and not very low ionic strength. This theory does not work well for nano-colloids, including proteins and polymers at low ionic strength. It is not valid for low- or non-polar fluids.
There is another theory that is applicable for the other extreme case of a thick double layer, when
This theory takes into consideration the double layer overlap that inevitably occurs for concentrated systems with thick double layer. This allows introduction of so-called "quasi-homogeneous" approach, when overlapped diffuse layers of particles cover the complete interparticle space. The theory becomes much simplified in this extreme case, as shown by Shilov and others. Their derivation predicts that surface charge density σ is a better parameter than ζ-potential for characterizing electroacoustic phenomena in such systems. An expression for CVI simplified for small particles follows: | 7 | Physical Chemistry |
Surface runoff can cause erosion of the Earth's surface; eroded material may be deposited a considerable distance away. There are four main types of soil erosion by water: splash erosion, sheet erosion, rill erosion and gully erosion. Splash erosion is the result of mechanical collision of raindrops with the soil surface: soil particles which are dislodged by the impact then move with the surface runoff. Sheet erosion is the overland transport of sediment by runoff without a well defined channel. Soil surface roughness causes may cause runoff to become concentrated into narrower flow paths: as these incise, the small but well-defined channels which are formed are known as rills. These channels can be as small as one centimeter wide or as large as several meters. If runoff continue to incise and enlarge rills, they may eventually grow to become gullies. Gully erosion can transport large amounts of eroded material in a small time period.
Reduced crop productivity usually results from erosion, and these effects are studied in the field of soil conservation. The soil particles carried in runoff vary in size from about 0.001 millimeter to 1.0 millimeter in diameter. Larger particles settle over short transport distances, whereas small particles can be carried over long distances suspended in the water column. Erosion of silty soils that contain smaller particles generates turbidity and diminishes light transmission, which disrupts aquatic ecosystems.
Entire sections of countries have been rendered unproductive by erosion. On the high central plateau of Madagascar, approximately ten percent of that country's land area, virtually the entire landscape is devoid of vegetation, with erosive gully furrows typically in excess of 50 meters deep and one kilometer wide. Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. Erosion causes loss of the fertile top soil and reduces its fertility and quality of the agricultural produce.
Modern industrial farming is another major cause of erosion. Over a third of the U.S. Corn Belt has completely lost its topsoil. Switching to no-till practices would reduce soil erosion from U.S. agricultural fields by more than 70 percent. | 2 | Environmental Chemistry |
Indium gallium arsenide antimonide (InGaAsSb) is a compound III-V semiconductor. (InGaAsSb) The addition of GaAs allows for a narrower bandgap (0.5 to 0.6 eV), and therefore better absorption of long wavelengths. Specifically, the bandgap was engineered to 0.55 eV. With this bandgap, the compound achieved a photon-weighted internal quantum efficiency of 79% with a fill factor of 65% for a black body at 1100 °C. This was for a device grown on a GaSb substrate by organometallic vapour phase epitaxy (OMVPE). Devices have been grown by molecular beam epitaxy (MBE) and liquid phase epitaxy (LPE). The internal quantum efficiencies (IQE) of these devices approach 90%, while devices grown by the other two techniques exceed 95%. The largest problem with InGaAsSb cells is phase separation. Compositional inconsistencies throughout the device degrade its performance. When phase separation can be avoided, the IQE and fill factor of InGaAsSb approach theoretical limits in wavelength ranges near the bandgap energy. However, the V/E ratio is far from the ideal. Current methods to manufacture InGaAsSb PVs are expensive and not commercially viable. | 7 | Physical Chemistry |
Crude oil is traded as a future on both the NYMEX and ICE exchanges. Futures contracts are agreements in which buyers and sellers agree to purchase and deliver specific amounts of physical crude oil on a given date in the future. A contract covers any multiple of 1000 barrels and can be purchased up to nine years into the future. | 7 | Physical Chemistry |
Poly(phthalaldehyde), abbreviated as PPA, is a metastable stimuli-responsive polymer first synthesized in 1967. It has garnered significant attention during the past couple of years due to its ease of synthesis and outstanding transient and mechanical properties. for this reason, It has been exploited for a variety of applications including sensing, drug delivery, and EUV lithography. As of 2023, it is considered the only aromatic aldehyde polymerized through a living chain growth polymerization. | 7 | Physical Chemistry |
A common problem to X-ray crystallography and electron crystallography is radiation damage, by which especially organic molecules and proteins are damaged as they are being imaged, limiting the resolution that can be obtained. This is especially troublesome in the setting of electron crystallography, where that radiation damage is focused on far fewer atoms. One technique used to limit radiation damage is electron cryomicroscopy, in which the samples undergo cryofixation and imaging takes place at liquid nitrogen or even liquid helium temperatures. Because of this problem, X-ray crystallography has been much more successful in determining the structure of proteins that are especially vulnerable to radiation damage. Radiation damage was recently investigated using MicroED of thin 3D crystals in a frozen hydrated state. | 3 | Analytical Chemistry |
Many antagonists are reversible antagonists that, like most agonists, will bind and unbind a receptor at rates determined by receptor-ligand kinetics.
Irreversible antagonists covalently bind to the receptor target and, in general, cannot be removed; inactivating the receptor for the duration of the antagonist effects is determined by the rate of receptor turnover, the rate of synthesis of new receptors. Phenoxybenzamine is an example of an irreversible alpha blocker—it permanently binds to α adrenergic receptors, preventing adrenaline and noradrenaline from binding. Inactivation of receptors normally results in a depression of the maximal response of agonist dose-response curves and a right shift in the curve occurs where there is a receptor reserve similar to non-competitive antagonists. A washout step in the assay will usually distinguish between non-competitive and irreversible antagonist drugs, as effects of non-competitive antagonists are reversible and activity of agonist will be restored.
Irreversible competitive antagonists also involve competition between the agonist and antagonist of the receptor, but the rate of covalent bonding differs and depends on affinity and reactivity of the antagonist. For some antagonists, there may be a distinct period during which they behave competitively (regardless of basal efficacy), and freely associate to and dissociate from the receptor, determined by receptor-ligand kinetics. But, once irreversible bonding has taken place, the receptor is deactivated and degraded. As for non-competitive antagonists and irreversible antagonists in functional assays with irreversible competitive antagonist drugs, there may be a shift in the log concentration–effect curve to the right, but, in general, both a decrease in slope and a reduced maximum are obtained. | 1 | Biochemistry |
CDP Cities provides a platform for cities to measure, manage and disclose their environmental data. More than 500 cities are now measuring and disclosing environmental data annually. The potential and need for this program is enormous since over 56% of the world's population now live in cities. CDP Cities provides a global platform based upon a simple questionnaire that allows city governments to disclose their greenhouse gas emission data publicly. One of the greatest values of the annual report, first released in June 2011, is to city leaders who can identify peers who are addressing similar risks and issues with new and innovative strategies for reducing carbon emissions and for mitigating risk from climate change. | 2 | Environmental Chemistry |
To adapt the footprinting technique to updated detection methods, the labelled DNA fragments are detected by a capillary electrophoresis device instead of being run on a polyacrylamide gel. If the DNA fragment to be analyzed is produced by polymerase chain reaction (PCR), it is straightforward to couple a fluorescent molecule such as carboxyfluorescein (FAM) to the primers. This way, the fragments produced by DNaseI digestion will contain FAM, and will be detectable by the capillary electrophoresis machine. Typically, carboxytetramethyl-rhodamine (ROX)-labelled size standards are also added to the mixture of fragments to be analyzed. Binding sites of transcription factors have been successfully identified this way. | 1 | Biochemistry |
The most commonly used and commercially available fluorescent base analogue, 2-aminopurine (2-AP), has a high-fluorescence quantum yield free in solution (0.68) that is considerably reduced (appr. 100 times but highly dependent on base sequence) when incorporated into nucleic acids. The emission sensitivity of 2-AP to immediate surroundings is shared by other promising and useful fluorescent base analogues like 3-MI, 6-MI, 6-MAP, pyrrolo-dC (also commercially available), modified and improved derivatives of pyrrolo-dC, furan-modified bases and many other ones (see recent reviews). This sensitivity to the microenvironment has been utilized in studies of e.g. structure and dynamics within both DNA and RNA, dynamics and kinetics of DNA-protein interaction and electron transfer within DNA.
A newly developed and very interesting group of fluorescent base analogues that has a fluorescence quantum yield that is nearly insensitive to their immediate surroundings is the tricyclic cytosine family. 1,3-Diaza-2-oxophenothiazine, tC, has a fluorescence quantum yield of approximately 0.2 both in single- and in double-strands irrespective of surrounding bases. Also the oxo-homologue of tC called tC (both commercially available), 1,3-diaza-2-oxophenoxazine, has a quantum yield of 0.2 in double-stranded systems. However, it is somewhat sensitive to surrounding bases in single-strands (quantum yields of 0.14–0.41). The high and stable quantum yields of these base analogues make them very bright, and, in combination with their good base analogue properties (leaves DNA structure and stability next to unperturbed), they are especially useful in fluorescence anisotropy and FRET measurements, areas where other fluorescent base analogues are less accurate. Also, in the same family of cytosine analogues, a FRET-acceptor base analogue, tC, has been developed. Together with tC as a FRET-donor this constitutes the first nucleic acid base analogue FRET-pair ever developed. The tC-family has, for example, been used in studies related to polymerase DNA-binding and DNA-polymerization mechanisms. | 1 | Biochemistry |
* Australian Capital Territory: Pepper spray is a "prohibited weapon", making it an offence to possess or use it.
* New South Wales: Possession of pepper spray by unauthorized persons is illegal, under schedule 1 of the Weapons Prohibition Act 1998, being classified as a "prohibited weapon".
* Northern Territory: Prescribed by regulation to be a prohibited weapon under the Weapons Control Act.
** This legislation makes it an offense for someone without a permit, normally anyone who is not an officer of Police/Correctional Services/Customs/Defence, to carry a prohibited weapon.
* Tasmania: Possession of pepper spray by unauthorized persons is illegal, under an amendment of the Police Offences Act 1935, being classified as an "offensive weapon". Likewise, possession of knives, batons, and any other instrument that may be considered, "Offensive Weapons" if they are possessed by an individual, in a Public Place, "Without lawful excuse", leading to confusion within the police force over what constitutes "lawful excuse". Self-defense as a lawful excuse to carry such items varies from one officer to the next.
** Pepper spray is commercially available without a license. Authority to possess and use Oleoresin Capsicum devices remains with Tasmania Police Officers (As part of general-issue operational equipment), and Tasmanian Justice Department (H.M. Prisons) Officers.
* South Australia: in South Australia, possession of pepper spray without lawful excuse is illegal.
* Western Australia: The possession of pepper spray by individuals for self-defense subject to a "reasonable excuse" test has been legal in Western Australia following the landmark Supreme Court decision in Hall v Collins [2003] WASCA 74 (4 April 2003).
* Victoria: Schedule 3 of the Control of Weapons Regulations 2011 designates "an article designed or adapted to discharge oleoresin capsicum spray" as a prohibited weapon.
* Queensland: in Queensland, pepper spray is considered an offensive weapon and can not be used for self-defence. | 1 | Biochemistry |
The first total synthesis was accomplished in 2000 by the Danishefsky group at Columbia University, with a number of other syntheses following shortly thereafter by Williams, Ganesan, Fuji, Carreira, Horne, Overman, and most recently Trost.
From a synthetic point of view, the most challenging structural features of the molecule are the C3 spirocyclic ring juncture and the adjacent prenyl-substituted carbon. Approaches toward preparing the skeleton of spirotryprostatin B have varied considerably.
Danishefsky spirotryprostatin B synthesis
In the Danishefsky synthesis, an amine derived from tryptophan was condensed with an aldehyde, triggering a Mannich-type reaction wherein the pendant oxindole acted as a nucleophile toward the intermediate iminium species.
Williams spirotryprostatin B synthesis
The synthesis by the Williams group utilized a 3-component coupling reaction. A secondary amine was combined with an aldehyde to form an intermediate azomethine ylide, which underwent a 1,3-dipolar cycloaddition with an unsaturated oxindole also present in the reaction mixture.
Ganesan spirotryprostatin B synthesis
Ganesan made use of a biomimetic strategy in his synthesis of spirotryprostatin B. An indole was treated with N-bromosuccinimide to trigger an oxidative rearrangement, forming the quaternary stereocenter in a diastereoselective manner.
Fuji spirotryprostatin B synthesis
In the synthesis developed by the Fuji group, the stereochemistry at the spirocyclic carbon was established by a nitroolefination reaction. An oxindole with pendant prenyl group was reacted with a nitroolefin bearing a chiral leaving group.
Carreira spirotryprostatin B synthesis
The Carreira group made use of a magnesium iodide promoted annulation reaction in their approach toward spirotryprostatin B. An oxindole bearing a cyclopropane was reacted with an imine in the presence of the magnesium iodide, triggering the ring-expansion reaction.
Horne spirotryprostatin B synthesis
Horne's synthesis of spirotryprostatin B also made use of a Mannich-type process, wherein a chloro-indole served as the pro-nucleophile. The cyclization was triggered by treating the pendant imine with the acyl chloride derived from proline. The resulting iminium species was attacked by the chloro-indole, forming the spirocyclic bond.
Overman spirotryprostatin B synthesis
The Overman group utilized a Heck reaction to prepare the molecule. An iodo-aniline with a tethered alkene was subjected to palladium catalysis. The intermediate palladium-allyl species was intercepted by the pendant amide nitrogen to generate the prenyl stereocenter in the same reaction.
Trost spirotryprostatin B synthesis
In the synthesis developed by the Trost group, the stereochemistry at the spirocyclic ring juncture is established by a decarboxylation-prenylation sequence, reminiscent of the Carroll reaction. Here, a prenyl ester serves as both the nucleophile and electrophile precursor. Upon treatment with a chiral palladium catalyst the prenyl group ionizes and decarboxylates. The resulting ion pair subsequently recombines to generate the prenylated product. Notably, double bond migration occurs and the prenyl group is attacked at the oxindole carbon. | 0 | Organic Chemistry |
Good single crystal X-ray diffraction experiments in diamond anvil cells require sample stage to rotate on the vertical axis, omega. Most diamond anvil cells do not feature a large opening that would allow the cell to be rotated to high angles, a 60 degrees opening is considered sufficient for most crystals but larger angles are possible. The first cell to be used for single crystal experiments was designed by a graduate student at the University of Rochester, Leo Merrill. The cell was triangular with beryllium seats that the diamonds were mounted on; the cell was pressurized with screws and guide pins holding everything in place. | 7 | Physical Chemistry |
A native antigen is an antigen that is not yet processed by an APC to smaller parts. T cells cannot bind native antigens, but require that they be processed by APCs, whereas B cells can be activated by native ones. | 1 | Biochemistry |
Cyanophages are viruses that infect cyanobacteria. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. The size of the head and tail vary among species of cyanophages.
Cyanophages, like other bacteriophages, rely on Brownian motion to collide with bacteria, and then use receptor binding proteins to recognize cell surface proteins, which leads to adherence. Viruses with contractile tails then rely on receptors found on their tails to recognize highly conserved proteins on the surface of the host cell.
Cyanophages infect a wide range of cyanobacteria and are key regulators of the cyanobacterial populations in aquatic environments, and may aid in the prevention of cyanobacterial blooms in freshwater and marine ecosystems. These blooms can pose a danger to humans and other animals, particularly in eutrophic freshwater lakes. Infection by these viruses is highly prevalent in cells belonging to Synechococcus spp. in marine environments, where up to 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles.
The first cyanophage, LPP-1, was discovered in 1963. Cyanophages are classified within the bacteriophage families Myoviridae (e.g. AS-1, N-1), Podoviridae (e.g. LPP-1) and Siphoviridae (e.g. S-1). | 5 | Photochemistry |
In electrochemistry, ITIES (interface between two immiscible electrolyte solutions) is an electrochemical interface that is either polarisable or polarised. An ITIES is polarisable if one can change the Galvani potential difference, or in other words the difference of inner potentials between the two adjacent phases, without noticeably changing the chemical composition of the respective phases (i.e. without noticeable electrochemical reactions taking place at the interface). An ITIES system is polarised if the distribution of the different charges and redox species between the two phases determines the Galvani potential difference.
Usually, one electrolyte is an aqueous electrolyte composed of hydrophilic ions such as NaCl dissolved in water and the other electrolyte is a lipophilic salt such as tetrabutylammonium tetraphenylborate dissolved in an organic solvent immiscible with water such as nitrobenzene, or 1,2-dichloroethane. | 7 | Physical Chemistry |
Up to now, seven meetings have been held:
* ACEPS-1, November 15–17, 2006, Kyoto, Japan
* ACEPS-2, October 21–23, 2007, Fudan University, Shanghai, China
* ACEPS-3, November, 2008, Korea University, Seoul, South Korea
* ACEPS-4, November 8–12, 2009, National Taiwan University of Science and Technology, Taipei, Taiwan
* ACEPS-5, September 17–20, 2010, Singapore
* ACEPS-6, January 5–8, 2012, Indian Institute of Science and Central Electro Chemical Research Institute, India
* ACEPS-7, November 24–27, 2013, Co-Sponsored by Electrochemical Society of Japan and Chemical Society of Japan,
* ACEPS-8, August 21–25, 2015, Kai Wah Plaza Hotel, Kunming, Co-Sponsored by Fudan University, Shanghai, China,
* ACEPS-9, August 20–23, 2017, Gyeongju, South Korea,
* ACEPS-10, November 24–27, 2019, Kaohsiung, Taiwan,
* ACEPS-11, December 11–14, 2022, National University of Singapore, Singapore
* ACEPS-12, scheduled in 2024, Nara or Kyoto, Japan | 7 | Physical Chemistry |
Plain RNAs may be poor immunogens, but antibodies can easily be created against RNA-protein complexes. Many autoimmune diseases see these types of antibodies. There haven't yet been reports of antibodies against siRNA bound to proteins. Some methods for siRNA delivery adjoin polyethylene glycol (PEG) to the oligonucleotide reducing excretion and improving circulating half-life. However recently a large Phase III trial of PEGylated RNA aptamer against factor IX had to be discontinued by Regado Biosciences because of a severe anaphylactic reaction to the PEG part of the RNA. This reaction led to death in some cases and raises significant concerns about siRNA delivery when PEGylated oligonucleotides are involved. | 1 | Biochemistry |
Histamine intolerance is a presumed set of adverse reactions to ingested histamine in food believed to be associated with flawed activity of DAO and HNMT enzymes. This set of reactions include cutaneous reactions (such as itching, flushing and edema), gastrointestinal symptoms (such as abdominal pain and diarrhea), respiratory symptoms (such as runny nose and nasal congestion), and neurological symptoms (such as dizziness and headache). However, this link between DAO and HNMT enzymes and adverse reactions to ingested histamine in food is not shared by mainstream science due to insufficient evidence. The exact underlying mechanisms by which deficiency in these enzymes can cause these adverse reactions are not fully understood but are hypothesized to involve genetic factors. Despite extensive research, there are no definitive, objective measures or indicators that could unambiguously define histamine intolerance as a distinct medical condition. | 1 | Biochemistry |
Many of the same people who created Rosetta@home worked on Foldit. The public beta version was released in May 2008 and has 240,000 registered players.
Since 2008, Foldit has participated in Critical Assessment of Techniques for Protein Structure Prediction (CASP) experiments, submitting its best solutions to targets based on unknown protein structures. CASP is an international program to assess methods of protein structure prediction and identify those that are most productive. | 1 | Biochemistry |
A bloomery consists of a pit or chimney with heat-resistant walls made of earth, clay, or stone. Near the bottom, one or more pipes (made of clay or metal) enter through the side walls. These pipes, called tuyeres, allow air to enter the furnace, either by natural draught or forced with bellows or a trompe. An opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the top.
The first step taken before the bloomery can be used is the preparation of the charcoal and the iron ore. Charcoal is nearly pure carbon, which, when burned, both produces the high temperature needed for the smelting process and provides the carbon monoxide needed for reduction of the metal.
The ore is broken into small pieces and usually roasted in a fire, to make rock-based ores easier to break up, bake out some impurities, and (to a lesser extent) to remove any moisture in the ore. Any large impurities (as silica) in the ore can be removed as it is crushed. The desired particle size depends primarily on which of several ore types may be available, which will also have a relationship to the layout and operation of the furnace, of which a number of regional, historic/traditional forms exist. Natural iron ores can vary considerably in oxide form ( / / ), and importantly in relative iron content. Since slag from previous blooms may have a high iron content, it can also be broken up and may be recycled into the bloomery with the new ore.
In operation, after the bloomery is heated typically with a wood fire, shifting to burning sized charcoal, iron ore and additional charcoal are introduced through the top. Again, traditional methods vary, but normally smaller charges of ore are added at the start of the main smelting sequence, increasing to larger amounts as the smelt progresses. Overall, a typical ratio of total charcoal to ore added is in a roughly one-to-one ratio. Inside the furnace, carbon monoxide from the incomplete combustion of the charcoal reduces the iron oxides in the ore to metallic iron without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. As the desired product of a bloomery is iron that is easily forgeable, it requires a low carbon content. The temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing too much carbon and thus becoming unforgeable. Cast iron occurs when the iron absorbs 2% to 4% carbon. Because the bloomery is self-fluxing, the addition of limestone is not required to form a slag.
The small particles of iron produced in this way fall to the bottom of the furnace, where they combine with molten slag, often consisting of fayalite, a compound of silicon, oxygen, and iron mixed with other impurities from the ore. The hot liquid slag, running to the bottom of the furnace, cools against the base and lower side walls of the furnace, effectively forming a bowl still containing fluid slag. As the individual iron particles form, they fall into this bowl and sinter together under their own weight, forming a spongy mass referred to as the bloom. Because the bloom is typically porous, and its open spaces can be full of slag, the extracted mass must be beaten with heavy hammers to both compress voids and drive out any molten slag remaining. This process may require several additional heating and compaction cycles, working at high welding temperatures. Iron treated this way is said to be wrought (worked), and the resulting iron, with reduced amounts of slag, is called wrought iron or bar iron. Because of the creation process, individual blooms can often have differing carbon contents between the original top and bottom surfaces, differences that will also be somewhat blended together through the flattening, folding, and hammer-welding sequences. Intentionally producing blooms that are coated in steel (i.e. iron with a higher carbon content) by manipulating the charge of and air flow to the bloomery is also possible.
As the era of modern commercial steelmaking began, the word "bloom" was extended to another sense referring to an intermediate-stage piece of steel, of a size comparable to many traditional iron blooms, that was ready to be further worked into billet. | 8 | Metallurgy |
With GM corn being a common feedstock, it is unsurprising that some bioplastics are made from this.
Under the bioplastics manufacturing technologies there is the "plant factory" model, which uses genetically modified crops or genetically modified bacteria to optimise efficiency. | 7 | Physical Chemistry |
Catalysts also have a role in the unblocking of blocked isocyanates. As with regular isocyanates organometallic compounds and tertiary amines may lower the unblocking temperature. Tin compounds, such as dibutyltin dilaurate, dibutyltin diacetate and other metal compounds are effective deblocking catalysts. | 0 | Organic Chemistry |
The visual cycle can be regulated by the retinal G-protein-coupled Receptor (RGR-opsin) system. When light activates the RGR-opsin, the recycling of chromophore in the RPE is accelerated. This mechanism provides additional chromophore after intense bleaches, and can be seen as an important mechanism in the early phases of dark adaptation and chromophore replenishment. | 1 | Biochemistry |
An insulator is a type of cis-regulatory element known as a long-range regulatory element. Found in multicellular eukaryotes and working over distances from the promoter element of the target gene, an insulator is typically 300 bp to 2000 bp in length. Insulators contain clustered binding sites for sequence specific DNA-binding proteins and mediate intra- and inter-chromosomal interactions.
Insulators function either as an enhancer-blocker or a barrier, or both. The mechanisms by which an insulator performs these two functions include loop formation and nucleosome modifications. There are many examples of insulators, including the CTCF insulator, the gypsy insulator, and the β-globin locus. The CTCF insulator is especially important in vertebrates, while the gypsy insulator is implicated in Drosophila. The β-globin locus was first studied in chicken and then in humans for its insulator activity, both of which utilize CTCF.
The genetic implications of insulators lie in their involvement in a mechanism of imprinting and their ability to regulate transcription. Mutations to insulators are linked to cancer as a result of cell cycle disregulation, tumourigenesis, and silencing of growth suppressors. | 1 | Biochemistry |
The FDA estimated that in 2011, over 23 million outpatient prescriptions for fluoroquinolones, of which levofloxacin made up 28%, were filled in the United States. | 4 | Stereochemistry |
Born in Leith, Thomas Anderson graduated from the University of Edinburgh with a medical doctorate in 1841. Having developed an interest in chemistry during his medical studies, he then spent several years studying chemistry in Europe, including spells under Jöns Jakob Berzelius in Sweden and Justus von Liebig in Germany. Returning to Edinburgh, he worked at the University of Edinburgh and at the Highland and Agricultural Society of Scotland. In 1852, he was appointed Regius Professor of Chemistry at the University of Glasgow and remained in that post for the remainder of his career. In 1854, he became one of the editors of the Edinburgh New Philosophical Journal. In 1872, Anderson was awarded a Royal Medal from the Royal Society "for his investigations on the organic bases of Dippells animal oil; on codeine; on the crystallized constituents of opium; on piperin and on papaverin; and for his researches in physiological and animal chemistry."
His later years were marred by a progressive neurological disease which may have been syphilis. He resigned his chair in early 1874, and died later that year in Chiswick.
He was succeeded by John Ferguson. | 0 | Organic Chemistry |
As a result of the Manhattan Project, the United States government needed ready access to uranium. Many different techniques in leaching were quickly employed at a large scale. Both synthetic resins and organic solvents were used early on to extract uranium. Ultimately, the use of organic solvents was less tedious compared to ion exchange through synthetic resins, and further production of uranium and other rare earth metals moved towards solvent extraction. | 8 | Metallurgy |
The occurrence of amorphous phases turned out to be a phenomenon of particular interest for the studying of thin-film growth. The growth of polycrystalline films is often used and preceded by an initial amorphous layer, the thickness of which may amount to only a few nm. The most investigated example is represented by the unoriented molecules of thin polycrystalline silicon films. Wedge-shaped polycrystals were identified by transmission electron microscopy to grow out of the amorphous phase only after the latter has exceeded a certain thickness, the precise value of which depends on deposition temperature, background pressure, and various other process parameters. The phenomenon has been interpreted in the framework of Ostwald's rule of stages that predicts the formation of phases to proceed with increasing condensation time towards increasing stability. | 7 | Physical Chemistry |
First, the model tries to predict where an atom would land on a surface and its rate at particular environmental conditions, such as temperature and vapor pressure. In order to land on a surface, atoms have to overcome the so-called activation energy barrier. The frequency of passing through the activation barrier can by calculated by the Arrhenius equation:
where A is the thermal frequency of molecular vibration, is the activation energy, k is the Boltzmann constant and T is the absolute temperature. | 7 | Physical Chemistry |
Rho-related GTPases from plants, otherwise known as ROPs, are involved in cell polarity through the regulation of cytoskeleton components like actin and microtubules. Unlike mammalian cells, plant cells do not contain heterotrimeric G proteins like Cdc42, Rac, and Rho that are known to regulate cellular polarity.
__TOC__ | 1 | Biochemistry |
Several different theories have been proposed to explain the formation of Liesegang rings. The chemist Wilhelm Ostwald in 1897 proposed a theory based on the idea that a precipitate is not formed immediately upon the concentration of the ions exceeding a solubility product, but a region of supersaturation occurs first. When the limit of stability of the supersaturation is reached, the precipitate forms, and a clear region forms ahead of the diffusion front because the precipitate that is below the solubility limit diffuses into the precipitate. This was argued to be a critically flawed theory when it was shown that seeding the gel with a colloidal dispersion of the precipitate (which would arguably prevent any significant region of supersaturation) did not prevent the formation of the rings.
Another theory focuses on the adsorption of one or the other of the precipitating ions onto the colloidal particles of the precipitate which forms. If the particles are small, the absorption is large, diffusion is "hindered" and this somehow results in the formation of the rings.
Still another proposal, the "coagulation theory" states that the precipitate first forms as a fine colloidal dispersion, which then undergoes coagulation by an excess of the diffusing electrolyte and this somehow results in the formation of the rings.
Some more recent theories invoke an auto-catalytic step in the reaction that results in the formation of the precipitate. This would seem to contradict the notion that auto-catalytic reactions are, actually, quite rare in nature.
The solution of the diffusion equation with proper boundary conditions, and a set of good assumptions on supersaturation, adsorption, auto-catalysis, and coagulation alone, or in some combination, has not been done yet, it appears, at least in a way that makes a quantitative comparison with experiment possible. However, a theoretical approach for the Matalon-Packter law predicting the position of the precipitate bands when the experiments are performed in a test tube, has been provided
A general theory based on Ostwald's 1897 theory has recently been proposed. It can account for several important features sometimes seen, such as revert and helical banding. | 7 | Physical Chemistry |
The equivalence point, or stoichiometric point, of a chemical reaction is the point at which chemically equivalent quantities of reactants have been mixed. For an acid-base reaction the equivalence point is where the moles of acid and the moles of base would neutralize each other according to the chemical reaction. This does not necessarily imply a 1:1 molar ratio of acid:base, merely that the ratio is the same as in the chemical reaction. It can be found by means of an indicator, for example phenolphthalein or methyl orange.
The endpoint (related to, but not the same as the equivalence point) refers to the point at which the indicator changes color in a colorimetric titration. | 3 | Analytical Chemistry |
Glycosyltransferases (GTFs, Gtfs) are enzymes (EC 2.4) that establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar (also known as the "glycosyl donor") to a nucleophilic glycosyl acceptor molecule, the nucleophile of which can be oxygen- carbon-, nitrogen-, or sulfur-based.
The result of glycosyl transfer can be a carbohydrate, glycoside, oligosaccharide, or a polysaccharide. Some glycosyltransferases catalyse transfer to inorganic phosphate or water. Glycosyl transfer can also occur to protein residues, usually to tyrosine, serine, or threonine to give O-linked glycoproteins, or to asparagine to give N-linked glycoproteins. Mannosyl groups may be transferred to tryptophan to generate C-mannosyl tryptophan, which is relatively abundant in eukaryotes. Transferases may also use lipids as an acceptor, forming glycolipids, and even use lipid-linked sugar phosphate donors, such as dolichol phosphates in eukaryotic organism, or undecaprenyl phosphate in bacteria.
Glycosyltransferases that use sugar nucleotide donors are Leloir enzymes, after Luis F. Leloir, the scientist who discovered the first sugar nucleotide and who received the 1970 Nobel Prize in Chemistry for his work on carbohydrate metabolism. Glycosyltransferases that use non-nucleotide donors such as dolichol or polyprenol pyrophosphate are non-Leloir glycosyltransferases.
Mammals use only 9 sugar nucleotide donors for glycosyltransferases: UDP-glucose, UDP-galactose, UDP-GlcNAc, UDP-GalNAc, UDP-xylose, UDP-glucuronic acid, GDP-mannose, GDP-fucose, and CMP-sialic acid. The phosphate(s) of these donor molecules are usually coordinated by divalent cations such as manganese, however metal independent enzymes exist.
Many glycosyltransferases are single-pass transmembrane proteins, and they are usually anchored to membranes of Golgi apparatus | 0 | Organic Chemistry |
Type II MAPs are found exclusively in nerve cells in mammals. These are the most well studied MAPs—MAP2 and tau (MAPT)—which participate in determining the structure of different parts of nerve cells, with MAP2 being found mostly in dendrites and tau in the axon. These proteins have a conserved C-terminal microtubule-binding domain and variable N-terminal domains projecting outwards, probably interacting with other proteins. MAP2 and tau stabilize microtubules, and thus shift the reaction kinetics in favor of addition of new subunits, accelerating microtubule growth. Both MAP2 and tau have been shown to stabilize microtubules by binding to the outer surface of the microtubule protofilaments. A single study has suggested that MAP2 and tau bind on the inner microtubule surface on the same site in tubulin monomers as the drug Taxol, which is used in treating cancer, but this study has not been confirmed. MAP2 binds in a cooperative manner, with many MAP2 proteins binding a single microtubule to promote stabilization. Tau has the additional function of facilitating bundling of microtubules within the nerve cell.
The function of tau has been linked to the neurological condition Alzheimers disease. In the nervous tissue of Alzheimers patients, tau forms abnormal aggregates. This aggregated tau is often severely modified, most commonly through hyperphosphorylation. As described above, phosphorylation of MAPs causes them to detach from microtubules. Thus, the hyperphosphorylation of tau leads to massive detachment, which in turn greatly reduces the stability of microtubules in nerve cells. This increase in microtubule instability may be one of the main causes of the symptoms of Alzheimer's disease.
In contrast to the MAPs described above, MAP4 (MAP4) is not confined to just nerve cells, but rather can be found in nearly all types of cells. Like MAP2 and tau, MAP4 is responsible for stabilization of microtubules. MAP4 has also been linked to the process of cell division. | 1 | Biochemistry |
The combination of piperacillin and tazobactam, commonly branded as Zosyn, improves their overall bactericidal activity as amino-benzylpenicillins and ureidopencillins work synergistically with β-lactamase inhibitors. Concurrent use or unregulated dosages of piperacillin results in increasing levels of piperacillin within the body, prolonging neuromuscular transmission blockages created by non-depolarizing muscle relaxants, and disruptions in urine tests for glucose. Some compounds that may interfere with the bactericidal activity of piperacillin include chloramphenicol, macrolides, and sulfonamides.
Following two studies conducted in 1986 and 2006, piperacillin was found to inhibit the removal of methotrexate in animal kidneys. Furthermore, in the presence of piperacillin-tazobactam, the decay time for methotrexate triples in comparison to the normal half-life, leaving the patient exposed to cytotoxic effects produced by the chemical agent. While penicillin antibiotics generally work synergistically with aminoglycosides by enhancing their penetration of bacterial membranes, they can also work adversely by inactivating them. A reformulation of ethylenediaminetetraacetic acid and piperacillin-tazobactam has produced results showing an increase in their affinity with amikacin and gentamicin in vitro, enabling the process of simultaneous Y-site infusion to occur. However, tobramycin was found to be incompatible as a combination through Y-site infusion. | 4 | Stereochemistry |
More precise measurement techniques developed in the late 1990s have allowed for a good understanding of how dissolved organic carbon is distributed in marine environments both vertically and across the surface. It is now understood that dissolved organic carbon in the ocean spans a range from very labile to very recalcitrant (refractory). The labile dissolved organic carbon is mainly produced by marine organisms and is consumed in the surface ocean, and consists of sugars, proteins, and other compounds that are easily used by marine bacteria. Recalcitrant dissolved organic carbon is evenly spread throughout the water column and consists of high molecular weight and structurally complex compounds that are difficult for marine organisms to use such as the lignin, pollen, or humic acids. As a result, the observed vertical distribution consists of high concentrations of labile DOC in the upper water column and low concentrations at depth.
In addition to vertical distributions, horizontal distributions have been modeled and sampled as well. In the surface ocean at a depth of 30 meters, the higher dissolved organic carbon concentrations are found in the South Pacific Gyre, the South Atlantic Gyre, and the Indian Ocean. At a depth of 3,000 meters, highest concentrations are in the North Atlantic Deep Water where dissolved organic carbon from the high concentration surface ocean is removed to depth. While in the northern Indian Ocean high DOC is observed due to high fresh water flux and sediments. Since the time scales of horizontal motion along the ocean bottom are in the thousands of years, the refractory dissolved organic carbon is slowly consumed on its way from the North Atlantic and reaches a minimum in the North Pacific. | 2 | Environmental Chemistry |
A novel input representation has been developed consisting of a combination of sparse encoding, Blosum encoding, and input derived from hidden Markov models. this method predicts T-cell epitopes for the genome of hepatitis C virus and discuss possible applications of the prediction method to guide the process of rational vaccine design. | 1 | Biochemistry |
The Combined gas law or General Gas Equation is obtained by combining Boyles Law, Charless law, and Gay-Lussac's Law. It shows the relationship between the pressure, volume, and temperature for a fixed mass of gas:
This can also be written as:
With the addition of Avogadro's law, the combined gas law develops into the ideal gas law:
:where P is the pressure, V is volume, n is the number of moles, R is the universal gas constant and T is the absolute temperature.
:The proportionality constant, now named R, is the universal gas constant with a value of 8.3144598 (kPa∙L)/(mol∙K).
An equivalent formulation of this law is:
:where P is the pressure, V is the volume, N is the number of gas molecules, k is the Boltzmann constant (1.381×10J·K in SI units) and T is the absolute temperature.
These equations are exact only for an ideal gas, which neglects various intermolecular effects (see real gas). However, the ideal gas law is a good approximation for most gases under moderate pressure and temperature.
This law has the following important consequences:
# If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
# If the temperature and volume remain constant, then the pressure of the gas changes is directly proportional to the number of molecules of gas present.
# If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.
# If the temperature changes and the number of gas molecules are kept constant, then either pressure or volume (or both) will change in direct proportion to the temperature. | 7 | Physical Chemistry |
If suitably designed, general ventilation can also be used as a control of airborne dust. General ventilation can often help reduce skin and clothing contamination, and dust deposition on surfaces. | 2 | Environmental Chemistry |
*Bio: Shortened form of Biology; refers to usage of bacteria.
*Hydro: Term referring to the usage of water; process occurs in aqueous environments
*Metallurgy: A process involving the separating and refining of metals from other substances;
*Bioleaching: Using biological agents (bacteria) to extract metals or soils; general term used to encompass all forms biotechnological forms of extraction (hydrometallurgy, biohydrometallurgy, biomining, etc) | 8 | Metallurgy |
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