text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
The ELP can be conjugated to a functional group that can bind to a protein of interest. At temperatures below the T the ELP will bind to the ligand in its linear form. In this linear state, the ELP-protein complex cannot easily be distinguished from the extraneous proteins in the solution. However, once the solution is heated to a temperature exceeding the T the ELP will form spherical clumps. These clumps will then settle to the bottom of the solution tube following centrifugation, carrying the protein of interest. The proteins that are not needed will be found in the supernatant, which can be physically separated from the spherical aggregates. To ensure that there are few impurities in the ELP-protein complex isolated, the solution can be cooled below the T enabling the ELPs to once again assume their linear structure. From this point, hot and cold centrifugation cycles can be repeated, and then the protein of interest can be eluted from the ELPs via the addition of a salt. | 7 | Physical Chemistry |
Ibuprofen is sometimes used for the treatment of acne because of its anti-inflammatory properties, and has been sold in Japan in topical form for adult acne. As with other NSAIDs, ibuprofen may be useful in the treatment of severe orthostatic hypotension (low blood pressure when standing up). NSAIDs are of unclear utility in the prevention and treatment of Alzheimer's disease.
Ibuprofen has been associated with a lower risk of Parkinsons disease and may delay or prevent it. Aspirin, other NSAIDs, and paracetamol (acetaminophen) had no effect on the risk for Parkinsons. In March 2011, researchers at Harvard Medical School announced in Neurology that ibuprofen had a neuroprotective effect against the risk of developing Parkinsons disease. People regularly consuming ibuprofen were reported to have a 38% lower risk of developing Parkinsons disease, but no such effect was found for other pain relievers, such as aspirin and paracetamol. Use of ibuprofen to lower the risk of Parkinson's disease in the general population would not be problem-free, given the possibility of adverse effects on the urinary and digestive systems.
Some dietary supplements might be dangerous to take along with ibuprofen and other NSAIDs, but more research needs to be conducted to be certain. These supplements include those that can prevent platelet aggregation, including ginkgo, garlic, ginger, bilberry, dong quai, feverfew, ginseng, turmeric, meadowsweet (Filipendula ulmaria), and willow (Salix spp.); those that contain coumarin, including chamomile, horse chestnut, fenugreek and red clover; and those that increase the risk of bleeding, like tamarind. | 4 | Stereochemistry |
Another example is the unimolecular nucleophilic substitution (S1) reaction in organic chemistry, where it is the first, rate-determining step that is unimolecular. A specific case is the basic hydrolysis of tert-butyl bromide () by aqueous sodium hydroxide. The mechanism has two steps (where R denotes the tert-butyl radical ):
# Formation of a carbocation R−Br → + .
# Nucleophilic attack by hydroxide ion + → ROH.
This reaction is found to be first-order with r = k[R−Br], which indicates that the first step is slow and determines the rate. The second step with OH is much faster, so the overall rate is independent of the concentration of OH.
In contrast, the alkaline hydrolysis of methyl bromide () is a bimolecular nucleophilic substitution (S2) reaction in a single bimolecular step. Its rate law is second-order: r = k[R−Br][]. | 7 | Physical Chemistry |
Transition metal-based bioconjugation had been challenging due to the nature of biological conditions – aqueous solution, room temperature, mild pH, and low substrate concentrations – which are generally challenging for organometallic reactions. However, recently, besides [[CuAAC|copper-catalyzed [3 + 2] azide alkyne cycloaddition]] reaction, more and more diverse transition metal-mediated chemical transformations have been applied for bioconjugation reactions, introducing olefin metathesis, alkylation, C–H arylation, C–C, C–S, and C–N cross-coupling reactions. | 1 | Biochemistry |
The heat distortion temperature is determined by the following test procedure outlined in ASTM D648. The test specimen is loaded in three-point bending in the edgewise direction. The outer fiber stress used for testing is either 0.455 MPa or 1.82 MPa, and the temperature is increased at 2 °C/min until the specimen deflects 0.25 mm. This is similar to the test procedure defined in the ISO 75 standard.
Limitations that are associated with the determination of the HDT is that the sample is not thermally isotropic and, in thick samples in particular, will contain a temperature gradient. The HDT of a particular material can also be very sensitive to stress experienced by the component which is dependent on the component’s dimensions. The selected deflection of 0.25 mm (which is 0.2% additional strain) is selected arbitrarily and has no particular physical significance. | 7 | Physical Chemistry |
In sediments, oceans, and rivers, distinct trace metal isotope ratios exist due to biological processes such as metal ion uptake and abiotic processes such as adsorption to particulate matter that preferentially remove certain isotopes. The trace metal isotopic composition of a given organism results from a combination of the isotopic compositions of source material (i.e., food and water) and any fractionations imparted during metal ion uptake, translocation and processing inside cells. | 9 | Geochemistry |
Fabre-salts are composed of tetramethyltetrathiafulvalene (TMTTF) and Bechgaard salts of tetramethyltetraselenafulvalene (TMTSF). These two organic molecules are similar except for the sulfur-atoms of TMTTF being replaced by selenium-atoms in TMTSF. The molecules are stacked in columns (with a tendency to dimerization) which are separated by anions. Typical anions are, for example, octahedral PF, AsF or tetrahedral ClO or ReO.
Both material classes are quasi-one-dimensional at room-temperature, only conducting along the molecule stacks, and share a very rich phase diagram containing antiferromagnetic ordering, charge order, spin-density wave state, dimensional crossover and superconductivity.
Only one Bechgaard salt was found to be superconducting at ambient pressure which is (TMTTF)ClO with a transition temperature of T = 1.4 K. Several other salts become superconducting only under external pressure. The external pressure required to drive most Fabre-salts to superconductivity is so high, that under lab conditions superconductivity was observed only in one compound. A selection of the transition temperature and corresponding external pressure of several one-dimensional organic superconductors is shown in the table below. | 0 | Organic Chemistry |
Metabolic disorder is one of the causes of liver cancer. Mitochondria is responsible for oxidation using NAD, which is produced in Step 4 of the citrate–malate shuttle system. In high obesity or insulin resistance (diabetes) patients, their body contains large amounts of fatty acid, the shuttle system might not generate sufficient NAD to metabolize the fat efficiently. They also exhibit a low NAD level. Thus, it is more likely for obesity or diabetes patients to develop liver cancer.
Moreover, overloading of mitochondria may occur. There is an increase in reactive oxygen species level in the liver. Those species are highly reactive and would attack liver cells. They can damage the DNA strands. Cells with DNA damage may divide abnormally. They might grow into cancer cells, resulting in HCC.
Another risk factor is mutations and overexpressed citrate–malate shuttle. A high frequency mutated gene in a wide range of cancers, Ras oncogene, has a significantly close association to HCC. Many HCC patients carry this gene. They also have abnormal citrate–malate shuttle. The research of Dalian Medical University shows that there is a noticeable increase in the HCC patients’ citrate and malate levels, suggesting the possibility of higher activity of citrate–malate shuttle. This mechanism is effective when TCA cycle activity is low. The shuttle also helps the production of fatty acid and lactic acid.
In liver cancer cells, the TCA cycle is blocked, causing accumulation of excess pyruvate. It is a signal of the body defense mechanism. Normally, the cancer cells would die under a high pyruvate level. However, the overexpressed citrate–malate shuttle can remove the excessive pyruvate. In this situation, the natural cell death of liver tumor will not occur. The cancer cells can keep growing.
In addition, high shuttle activity is linked to increase in fatty acid generation. It is also a risk factor of HCC. | 1 | Biochemistry |
Malachite green is an organic compound that is used as a dyestuff and controversially as an antimicrobial in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper. Despite its name the dye is not prepared from the mineral malachite; the name just comes from the similarity of color. | 3 | Analytical Chemistry |
Atmospheric methane removal is a category of potential approaches being researched to accelerate the breakdown of methane that is in the atmosphere, for the purpose of mitigating some of the impacts of climate change.
Atmospheric methane has increased since pre-industrial times from 0.7 ppm to 1.9 ppm. From 2010 to 2019, methane emissions caused 0.5 °C (about 30%) of observed global warming. Global methane emissions approached a record 600 Tg CH per year in 2017. | 2 | Environmental Chemistry |
The Mountain Pass deposit is in a 1.4 billion-year-old Precambrian carbonatite intruded into gneiss. It contains 8% to 12% rare-earth oxides, mostly contained in the mineral bastnäsite. Gangue minerals include calcite, barite, and dolomite. It is regarded as a world-class rare-earth mineral deposit. The metals that can be extracted from it include: cerium, lanthanum, neodymium, and europium.
At 1 July 2020, Proven and Probable Reserves, using a 3.83% total rare-earth oxide (REO) cutoff grade, were 18.9 million tonnes of ore containing 1.36 million tonnes of REO at an average grade of 7.06% REO. | 8 | Metallurgy |
Liebig–Pasteur dispute is the dispute between Justus von Liebig and Louis Pasteur on the processes and causes of fermentation. | 1 | Biochemistry |
In organic chemistry, the Mallory reaction is a photochemical-cyclization–elimination reaction of diaryl-ethylene structures to form phenanthrenes and other polycyclic form polycyclic aromatic hydrocarbons and heteroaromatics. This name reaction is named for Frank Mallory, who discovered it while a graduate student.
Under UV irradiation, stilbene and its derivatives undergo intramolecular cyclization to form dihydrophenanthrenes. In the presence of an oxidant, the dihydrophenanthrenes aromatize to give polycyclic aromatics. Typically, the dihydrophenanthrenes themselves are relatively unstable, and revert to cis-stilbenes in the absence of a hydrogen-trapping agent. Suitably substituted stilbenes may undergo irreversible, rearomatizing elimination or [1,n]-shift processes in the absence of an oxidant. Aryl enynes, heteroatomic stilbene derivatives (e.g. amides), and substrates containing a single heteroatom in place of the stilbene double bond also undergo the reaction. | 5 | Photochemistry |
In August 2009, scientists in Israel raised serious doubts concerning the use of DNA by law enforcement as the ultimate method of identification. In a paper published in the journal Forensic Science International: Genetics, the Israeli researchers demonstrated that it is possible to manufacture DNA in a laboratory, thus falsifying DNA evidence. The scientists fabricated saliva and blood samples, which originally contained DNA from a person other than the supposed donor of the blood and saliva.
The researchers also showed that, using a DNA database, it is possible to take information from a profile and manufacture DNA to match it, and that this can be done without access to any actual DNA from the person whose DNA they are duplicating. The synthetic DNA oligos required for the procedure are common in molecular laboratories.
The New York Times quoted the lead author, Daniel Frumkin, saying, "You can just engineer a crime scene ... any biology undergraduate could perform this". Frumkin perfected a test that can differentiate real DNA samples from fake ones. His test detects epigenetic modifications, in particular, DNA methylation. Seventy percent of the DNA in any human genome is methylated, meaning it contains methyl group modifications within a CpG dinucleotide context. Methylation at the promoter region is associated with gene silencing. The synthetic DNA lacks this epigenetic modification, which allows the test to distinguish manufactured DNA from genuine DNA.
It is unknown how many police departments, if any, currently use the test. No police lab has publicly announced that it is using the new test to verify DNA results.
Researchers at the University of Tokyo integrated an artificial DNA replication scheme with a rebuilt gene expression system and micro-compartmentalization utilizing cell-free materials alone for the first time. Multiple cycles of serial dilution were performed on a system contained in microscale water-in-oil droplets.
Chances of making DNA change on purpose
Overall, this study's artificial genomic DNA, which kept copying itself using self-encoded proteins and made its sequence better on its own, is a good starting point for making more complex artificial cells. By adding the genes needed for transcription and translation to artificial genomic DNA, it may be possible in the future to make artificial cells that can grow on their own when fed small molecules like amino acids and nucleotides. Using living organisms to make useful things, like drugs and food, would be more stable and easier to control in these artificial cells.
On July 7, 2008, the American chemical society reported that Japanese chemists have created the world's first DNA molecule comprised nearly completely of synthetic components.
A nano-particle based artificial transcription factor for gene regulation:
Nano Script is a nanoparticle-based artificial transcription factor that is supposed to replicate the structure and function of TFs. On gold nanoparticles, functional peptides and tiny molecules referred to as synthetic transcription factors, which imitate the various TF domains, were attached to create Nano Script. We show that Nano Script localizes to the nucleus and begins transcription of a reporter plasmid by an amount more than 15-fold. Moreover, Nano Script can successfully transcribe targeted genes onto endogenous DNA in a nonviral manner.
Three different fluorophores—red, green, and blue—were carefully fixed on the DNA rod surface to provide spatial information and create a nanoscale barcode. Epifluorescence and total internal reflection fluorescence microscopy reliably deciphered spatial information between fluorophores. By moving the three fluorophores on the DNA rod, this nanoscale barcode created 216 fluorescence patterns. | 1 | Biochemistry |
Investigations of planktonic foraminiferal population indicate that tropical species attain their largest test sizes in tropical waters, and polar species reach maximum sizes in polar waters. Species living in subtropical and subpolar waters decrease in test size with both increasing and decreasing temperature.
The proloculus (the first chamber) sizes of benthic forams are affected by sea water temperature and their mean has been used as proxy for paleoclimatic investigations.
Mean test diameters of the planktonic foraminifer Orbulina universa have been used to interpret sea surface temperature history in Somali Basin. R-mode factor and Q-mode cluster analyses define five significant factor assemblages and five clusters reflecting different environmental characteristics, including increased oxygenation, high surface productivity. | 9 | Geochemistry |
The Bioconductor project curates a variety of R packages aimed at integrating omic data:
*[http://bioconductor.org/packages/release/bioc/html/omicade4.html omicade4], for multiple co-inertia analysis of multi omic datasets
*[http://bioconductor.org/packages/release/bioc/html/MultiAssayExperiment.html MultiAssayExperiment], offering a bioconductor interface for overlapping samples
*[http://bioconductor.org/packages/release/bioc/html/IMAS.html IMAS], a package focused on using multi omic data for evaluating alternative splicing
*[http://bioconductor.org/packages/release/bioc/html/bioCancer.html bioCancer], a package for visualization of multiomic cancer data
*[http://bioconductor.org/packages/release/bioc/html/mixOmics.html mixOmics], a suite of multivariate methods for data integration
*[http://bioconductor.org/packages/release/bioc/html/MultiDataSet.html MultiDataSet], a package for encapsulating multiple data sets
The [https://cran.r-project.org/web/packages/RGCCA/ RGCCA package] implements a versatile framework for data integration. This package is freely available on the [https://cran.r-project.org/ Comprehensive R Archive Network (CRAN)].
The OmicTools database further highlights R packages and othertools for multi omic data analysis:
* [http://www.paintomics.org/ PaintOmics], a web resource for visualization of multi-omics datasets
* SIGMA, a Java program focused on integrated analysis of cancer datasets
* iOmicsPASS, a tool in C++ for multiomic-based phenotype prediction
* [https://github.com/mkanai/grimon Grimon], an R graphical interface for visualization of multiomic data
* [https://pypi.org/project/omics_pipe/ Omics Pipe], a framework in Python for reproducibly automating multiomic data analysis | 1 | Biochemistry |
The drawbacks of the SMB are higher investment cost compared to single column operations, a higher complexity, as well as higher maintenance costs. But these drawbacks are effectively compensated by the better yield and a much lower solvent consumption as well as a much higher productivity compared to simple batch separations.
For purifications, in particular the isolation of an intermediate single component or a fraction out of a multicomponent mixture, the SMB is not as ideally suited. Normally, a single SMB will separate only two fractions from each other, but a series or "train" of SMBs can perform multiple cuts and purify one or more products from a multi-component mixture. SMB is not readily suited for solvent gradients. Solvent gradient purification may be preferred for the purification of some biomolecules. A continuous chromatography technique to overcome the two fraction limit and to apply gradients is multicolumn countercurrent solvent gradient purification (MCSGP). | 3 | Analytical Chemistry |
In chemistry, the valence (US spelling) or valency (British spelling) of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Valence is generally understood to be the number of chemical bonds that each atom of a given chemical element typically forms. Double bonds are considered to be two bonds, triple bonds to be three, quadruple bonds to be four, quintuple bonds to be five and sextuple bonds to be six. In most compounds, the valence of hydrogen is 1, of oxygen is 2, of nitrogen is 3, and of carbon is 4. Valence is not to be confused with the related concepts of the coordination number, the oxidation state, or the number of valence electrons for a given atom. | 3 | Analytical Chemistry |
This form of corrosion is usually caused by a combination of corrosion and cyclic stress. Measuring and controlling this is difficult because of the many factors at play including the nature or form of the stress cycle. The stress cycles cause localized work hardening. So avoiding stress concentrators such as holes etc would be good corrosion engineering design. | 8 | Metallurgy |
AFM has several advantages over the scanning electron microscope (SEM). Unlike the electron microscope, which provides a two-dimensional projection or a two-dimensional image of a sample, the AFM provides a three-dimensional surface profile. In addition, samples viewed by AFM do not require any special treatments (such as metal/carbon coatings) that would irreversibly change or damage the sample, and does not typically suffer from charging artifacts in the final image. While an electron microscope needs an expensive vacuum environment for proper operation, most AFM modes can work perfectly well in ambient air or even a liquid environment. This makes it possible to study biological macromolecules and even living organisms. In principle, AFM can provide higher resolution than SEM. It has been shown to give true atomic resolution in ultra-high vacuum (UHV) and, more recently, in liquid environments. High resolution AFM is comparable in resolution to scanning tunneling microscopy and transmission electron microscopy. AFM can also be combined with a variety of optical microscopy and spectroscopy techniques such as fluorescent microscopy of infrared spectroscopy, giving rise to scanning near-field optical microscopy, nano-FTIR and further expanding its applicability. Combined AFM-optical instruments have been applied primarily in the biological sciences but have recently attracted strong interest in photovoltaics and energy-storage research, polymer sciences, nanotechnology and even medical research. | 6 | Supramolecular Chemistry |
Estimating lake metabolism requires approximating processes that influence the production and consumption of organic carbon by organisms within the lake. Cyclical changes on a daily scale occur in most lakes on Earth because sunlight is available for photosynthesis and production of new carbon only for a portion of the day. Researchers can take advantage of this diel pattern to measure rates of change in carbon itself or changes in dissolved gases such as carbon dioxide or oxygen that occur on a daily scale. Although daily estimates of metabolism are most common, whole-lake metabolism can be integrated over longer time periods such as seasonal or annual rates by estimating a whole-lake carbon budget. The following sections highlight the most common ways to estimate lake metabolism across a variety of temporal and spatial scales and go over some of the assumptions of each of these methods. | 1 | Biochemistry |
2,3-butanediol fermentation produces smaller amounts of acid than mixed acid fermentation, and butanediol, ethanol, CO and H are the end products. While equal amounts of CO and H are created during mixed acid fermentation, butanediol fermentation produces more than twice the amount of CO because the gases are not produced only by formate hydrogen lyase as they are in mixed acid fermentation.
2,3 Butanediol is produced at varying levels in aerated fermentations as long as the dissolved oxygen level is limiting (i.e., the culture is trying to consume more oxygen than is available). The degree of oxygen limitation dictates the ratios of 2,3-butanediol to by-products produced. | 1 | Biochemistry |
Vectorette PCR is a variation of polymerase chain reaction (PCR) designed in 1988. The original PCR was created and also patented during the 1980s. Vectorette PCR was first noted and described in an article in 1990 by John H. Riley and his team. Since then, multiple variants of PCR have been created. Vectorette PCR focuses on amplifying a specific sequence obtained from an internal sequence that is originally known until the fragment end. Multiple researches have taken this method as an opportunity to conduct experiments in order to uncover the potential uses that can be derived from Vectorette PCR. | 1 | Biochemistry |
In inorganic chemistry, the sulfuryl group is a functional group consisting of a sulfur atom covalently bound to two oxygen atoms ().
It occurs in compounds such as sulfuryl chloride, and sulfuryl fluoride, .
In organic chemistry, this group is found in sulfones () and sulfonyl halides (), where it is called the sulfonyl group. | 0 | Organic Chemistry |
Helium-3 was trapped in the planet when it formed. Some He is being added by meteoric dust, primarily collecting on the bottom of oceans (although due to subduction, all oceanic tectonic plates are younger than continental plates). However, He will be degassed from oceanic sediment during subduction, so cosmogenic He is not affecting the concentration or noble gas ratios of the mantle.
Helium-3 is created by cosmic ray bombardment, and by lithium spallation reactions which generally occur in the crust. Lithium spallation is the process by which a high-energy neutron bombards a lithium atom, creating a He and a He ion. This requires significant lithium to adversely affect the He/He ratio.
All degassed helium is lost to space eventually, due to the average speed of helium exceeding the escape velocity for the Earth. Thus, it is assumed the helium content and ratios of Earth's atmosphere have remained essentially stable.
It has been observed that He is present in volcano emissions and oceanic ridge samples. How He is stored in the planet is under investigation, but it is associated with the mantle and is used as a marker of material of deep origin.
Due to similarities in helium and carbon in magma chemistry, outgassing of helium requires the loss of volatile components (water, carbon dioxide) from the mantle, which happens at depths of less than 60 km. However, He is transported to the surface primarily trapped in the crystal lattice of minerals within fluid inclusions.
Helium-4 is created by radiogenic production (by decay of uranium/thorium-series elements). The continental crust has become enriched with those elements relative to the mantle and thus more He is produced in the crust than in the mantle.
The ratio (R) of He to He is often used to represent He content. R usually is given as a multiple of the present atmospheric ratio (Ra).
Common values for R/Ra:
* Old continental crust: less than 1
* mid-ocean ridge basalt (MORB): 7 to 9
* Spreading ridge rocks: 9.1 plus or minus 3.6
* Hotspot rocks: 5 to 42
* Ocean and terrestrial water: 1
* Sedimentary formation water: less than 1
* Thermal spring water: 3 to 11
He/He isotope chemistry is being used to date groundwaters, estimate groundwater flow rates, track water pollution, and provide insights into hydrothermal processes, igneous geology and ore genesis.
* [http://www.geotrack.com.au/uthhe/u-th-he-techinfo.htm (U-Th)/He dating of apatite as a thermal history tool]
* [https://web.archive.org/web/20050210172919/http://lvo.wr.usgs.gov/helium.html USGS: Helium Discharge at Mammoth Mountain Fumarole (MMF)] | 9 | Geochemistry |
The English word "chitin" comes from the French word chitine, which was derived in 1821 from the Greek word χιτών (khitōn) meaning covering.
A similar word, "chiton", refers to a marine animal with a protective shell. | 1 | Biochemistry |
Bacterial initiation factor 1 associates with the 30S ribosomal subunit in the A site and prevents an aminoacyl-tRNA from entering. It modulates IF2 binding to the ribosome by increasing its affinity. It may also prevent the 50S subunit from binding, stopping the formation of the 70S subunit. It also contains a β-domain fold common for nucleic acid-binding proteins. It is a homolog of eIF1A. Initiation factor IF-1 is the smallest translation factor at only 8.2kDa. Beyond blocking the A-site, it affects the dynamics of ribosome association and dissociation. IF-1 enhances dissociation with IF-3, likely by inducing conformational changes in the 30S subunit. It also increases the binding affinity of IF-2 to the 30S subunit, possibly by altering the subunit configuration. Though IF-1 occupies the A-site, it does so in a way that is distinct from tRNA binding. Structural studies show IF-1 inserts a loop into the minor groove of helix 44 of 16S rRNA, flipping out bases A1492 and A1493. This insertion repositions nucleotides of helix 44, transmitting a conformational change over a 70Å distance and rotating the head of the 30S subunit. IF-1 mutants can exhibit cold-sensitive phenotypes, indicating a role for the factor in cold shock adaptation. Certain mutations also lead to o of genes at low temperatures, suggesting IF-1 is involved in gene regulation. IF-1 actively modifies ribosome structure and dynamics during initiation, in addition to just blocking the A-site. | 1 | Biochemistry |
YeTFaSCo (The Yeast Transcription Factor Specificity Compendium) is a database of transcription factors for Saccharomyces cerevisiae. | 1 | Biochemistry |
The term "molecular tweezers" was first used by Whitlock. The class of hosts was developed and popularized by Zimmerman in the mid-1980s to early 1990s and later by Klärner. | 6 | Supramolecular Chemistry |
Apart from some production of puddled steel, English steel continued to be made by the cementation process, sometimes followed by remelting to produce crucible steel. These were batch-based processes whose raw material was bar iron, particularly Swedish oregrounds iron.
The problem of mass-producing cheap steel was solved in 1855 by Henry Bessemer, with the introduction of the Bessemer converter at his steelworks in Sheffield, England. (An early converter can still be seen at the city's Kelham Island Museum). In the Bessemer process, molten pig iron from the blast furnace was charged into a large crucible, and then air was blown through the molten iron from below, igniting the dissolved carbon from the coke. As the carbon burned off, the melting point of the mixture increased, but the heat from the burning carbon provided the extra energy needed to keep the mixture molten. After the carbon content in the melt had dropped to the desired level, the air draft was cut off: a typical Bessemer converter could convert a 25-ton batch of pig iron to steel in half an hour.
In the 1860s development of regenerative furnaces and higher temperature refractory lining allowed to melt steel in an open hearth. That was slow and energy intensive, but allowed to better control the chemical makeup of the product and recycle iron scrap.
The acidic refractory lining of Bessemer converters and early open hearths didn't allow to remove phosphorus from steel with lime, which prolonged the life of puddling furnaces in order to utilize phosphorous iron ores abundant in Continental Europe. However in the 1870s Gilchrist–Thomas process was developed, and later basic lining was adopted for the open hearths as well.
Finally, the basic oxygen process was introduced at the Voest-Alpine works in 1952; a modification of the basic Bessemer process, it lances oxygen from above the steel (instead of bubbling air from below), reducing the amount of nitrogen uptake into the steel. The basic oxygen process is used in all modern steelworks; the last Bessemer converter in the U.S. was retired in 1968. Furthermore, the last three decades have seen a massive increase in the mini-mill business, where scrap steel only is melted with an electric arc furnace. These mills only produced bar products at first, but have since expanded into flat and heavy products, once the exclusive domain of the integrated steelworks.
Until these 19th-century developments, steel was an expensive commodity and only used for a limited number of purposes where a particularly hard or flexible metal was needed, as in the cutting edges of tools and springs. The widespread availability of inexpensive steel powered the Second Industrial Revolution and modern society as we know it. Mild steel ultimately replaced wrought iron for almost all purposes, and wrought iron is no longer commercially produced. With minor exceptions, alloy steels only began to be made in the late 19th century. Stainless steel was developed on the eve of World War I and was not widely used until the 1920s. | 8 | Metallurgy |
Diisopinocampheylborane is an organoborane that is useful for asymmetric synthesis of secondary alcohols. It is derived by hydroboration of α-pinene, a common diterpene member of the chiral pool. | 0 | Organic Chemistry |
1,3,5-Triheptylbenzene (also called sym-triheptylbenzene) is an aromatic organic compound with a chemical formula and molar mass 372.67 g/mol. It can be prepared by the hydrogenation reduction reaction of 1,1,1-(benzene-1,3,5-triyl)tris(heptan-1-one). Alternatively, 1-nonyne trimerizes to 1,3,5-triheptylbenzene when catalyzed by rhodium trichloride. | 0 | Organic Chemistry |
Copper roofs are extremely durable in most environments. They have performed well for over 700 years, primarily because of the protective patina that forms on copper surfaces. Tests conducted on 18th Century copper roofs in Europe showed that, in theory, they could last for one thousand years. | 8 | Metallurgy |
Transcription can be repressed in a variety of ways, and therefore can be derepressed in different ways as well. A common mechanism is allosteric regulation. This is when a substrate binds a repressor protein and causes it to undergo a conformational change. If the repressor is bound upstream of a gene, such as in an operator sequence, then it would be repressing the gene's expression. This conformational change would take away the repressor’s ability to bind DNA, thus removing its repressive effect on transcription.
Another form of transcriptional derepression uses chromatin remodeling complexes. For transcription to occur, RNA polymerase needs to have access to the promoter sequence of the gene or it cannot bind the DNA. Sometimes these sequences are wrapped around nucleosomes or are in condensed heterochromatin regions, and are therefore inaccessible. Through different chromatin remodeling mechanisms these promoter sequences can become accessible to the RNA polymerase, and transcription becomes derepressed.
Transcriptional derepression may also occur at the level of transcription factor activation. Certain families of transcription factors are non-functional on their own because their active domains are blocked by another part of the protein. Substrate binding to this second, regulatory domain causes a conformational change in the protein to allows access to the active domain. This lets the transcription factor bind to DNA and serve its function, thus derepressing the transcription factor. | 1 | Biochemistry |
Pulsed FT spectrometry gives the advantage of requiring a single, time-dependent measurement which can easily deconvolute a set of similar but distinct signals. The resulting composite signal, is called a free induction decay, because typically the signal will decay due to inhomogeneities in sample frequency, or simply unrecoverable loss of signal due to entropic loss of the property being measured. | 7 | Physical Chemistry |
A very convenient way to get a quantitative understanding of the throttling process is by using diagrams such as h-T diagrams, h-P diagrams, and others. Commonly used are the so-called T-s diagrams. Figure 2 shows the T-s diagram of nitrogen as an example. Various points are indicated as follows:
As shown before, throttling keeps h constant. E.g. throttling from 200 bar and 300K (point a in fig. 2) follows the isenthalpic (line of constant specific enthalpy) of 430kJ/kg. At 1 bar it results in point b which has a temperature of 270K. So throttling from 200 bar to 1 bar gives a cooling from room temperature to below the freezing point of water. Throttling from 200 bar and an initial temperature of 133K (point c in fig. 2) to 1 bar results in point d, which is in the two-phase region of nitrogen at a temperature of 77.2K. Since the enthalpy is an extensive parameter the enthalpy in d (h) is equal to the enthalpy in e (h) multiplied with the mass fraction of the liquid in d (x) plus the enthalpy in f (h) multiplied with the mass fraction of the gas in d (1 − x). So
With numbers: 150 = x 28 + (1 − x) 230 so x is about 0.40. This means that the mass fraction of the liquid in the liquid–gas mixture leaving the throttling valve is 40%. | 7 | Physical Chemistry |
Mutants are viable, but may be distinguished from normal plants by FeCl staining: plants able to synthesize benzoxinoids have pale blue color when crushed and treated with FeCl solutions (Hamilton 1964, Simcox 1993 ). Mutations in the bx1 gene reduce the resistance to first generation European corn borer (Ostrinia nubilalis) that is conferred by benzoxazinoids (Klun et al. 1970 ). Bx1 mutant maize deposited less callose in response to chitosan elicitation than isogenic wildtype plants (Ahmad et al. 2011 ). Genetic mapping using recombinant inbred lines derived from maize inbred lines B73 and Mo17 showed that a 3.9 kb cis-regulatory element that is located approximately 140 kb upstream of Bx1 causes higher 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) accumulation in Mo17 than in B73 seedlings (Zheng et al. 2015 ). This genetic variation is also associated with higher corn leaf aphid (Rhopalosiphum maidis) reproduction on B73 compared to Mo17 maize seedlings (Betsiashvili et al. 2014 ). Relative to maize inbred line W22, Bx1::Ds mutant maize plants are more sensitive to corn leaf aphids (Rhopalosiphum maidis) (Betsiashvili et al. 2014) and beet armyworms (Spodoptera exigua) (Tzin et al. 2017 ). Highly localized induction of benzoxazinoid accumulation in response to Egyptian cotton leafworm (Spodoptera littoralis) feeding is abolished in a maize bx1 mutant (Maag et al. 2016 ). | 1 | Biochemistry |
#Isolate the fly genome.
#Undergo a light digest (using an enzyme [enzyme 1] known NOT to cut in the reporter gene), giving fragments of a few kilobases, a few with the insertion and its flanking DNA.
#Self ligate the digest (low DNA concentration to ensure self ligation) giving a selection of circular DNA fragments, a few with the insertion and its flanking DNA.
#Cut the plasmids at some point in the reporter gene (with an enzyme [enzyme 2] known to cut very rarely in genomic DNA, but is known to in the reporter gene).
#Using primers for the reporter gene sections, the DNA can be amplified for sequencing.
The process of cutting, self ligation and re cutting allows the amplification of the flanking regions of DNA without knowing the sequence. The point at which the ligation occurred can be seen by identifying the cut site of [enzyme 1]. | 1 | Biochemistry |
A (by no means exhaustive) selection of models of biological systems involving multi-state molecules and using some of the tools discussed here is give in the table below. | 1 | Biochemistry |
Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal can flow like a liquid, but its molecules may be oriented in a common direction as in solid. There are many types of LC phases, which can be distinguished by their optical properties (such as textures). The contrasting textures arise due to molecules within one area of material ("domain") being oriented in the same direction but different areas having different orientations. An LC material may not always be in an LC state of matter (just as water may be ice or water vapor).
Liquid crystals can be divided into three main types: thermotropic, lyotropic, and metallotropic. Thermotropic and lyotropic liquid crystals consist mostly of organic molecules, although a few minerals are also known. Thermotropic LCs exhibit a phase transition into the LC phase as temperature changes. Lyotropic LCs exhibit phase transitions as a function of both temperature and concentration of molecules in a solvent (typically water). Metallotropic LCs are composed of both organic and inorganic molecules; their LC transition additionally depends on the inorganic-organic composition ratio.
Examples of LCs exist both in the natural world and in technological applications. Lyotropic LCs abound in living systems; many proteins and cell membranes are LCs, as well as the tobacco mosaic virus. LCs in the mineral world include solutions of soap and various related detergents, and some clays. Widespread liquid-crystal displays (LCD) use liquid crystals. | 7 | Physical Chemistry |
Geopolymer bonded wood composite (GWC) are similar and a green alternatives to cement bonded wood composites. These products are composed of geopolymer binder, wood fibers/ wood particles. Depending on the wood and geopolymer ratio in the material, the properties of the wood-geopolymer composite material vary. The main functions of wood in the composite material are weight reduction, reduction of thermal conductivity and the fixture function whereas the main functions of geopolymer are bonding of wood particles, improvement of fire resistance, providing mechanical strength, improvement of humidity resistance and protection against fungal and insect damages.
They serve similar functions and purposes like all other mineral bonded wood composites. The fact that the binder agent (geopolymer) are mostly produced from industrial residue and waste puts these materials at a greater advantage over other mineral bonded wood composites. However, most of the works under this topic remains at the research and development phase. Some of the core difficulties in production and commercialization of standardize product is the variation in the sources of the aluminosilicate binder and the cost involve in activating the binder. Currently, metakaolin binder remains as the one key source to produce or bind these products with huge variations in other sources of the binder such as slag, fly ash etc. | 9 | Geochemistry |
In a bimolecular reaction, two molecules collide and exchange energy, atoms or groups of atoms.
This can be described by the equation
which corresponds to the second order rate law: .
Here, the rate of the reaction is proportional to the rate at which the reactants come together. An example of a bimolecular
reaction is the S2-type nucleophilic substitution of methyl bromide by hydroxide ion: | 7 | Physical Chemistry |
When disposed, PHBV degrades into carbon dioxide and water. PHBV undergo bacterial degradation. PHBV, just like fats to human, is an energy source to microorganisms. Enzymes produced by them degrade it and are consumed.
PHBV has a low thermal stability and the cleavage occurs at the ester bond by β elimination reaction.
Hydrolytic degradation occurs only slowly making it usable in medical applications. | 1 | Biochemistry |
Plasma electrochemistry is a new field of research where the interaction of plasma with an electrolyte solution is studied. It uses plasma to drive chemical reactions in liquid. | 7 | Physical Chemistry |
The first photovoltaic cell ever designed was also the first photoelectrochemical cell. It was created in 1839, by Alexandre-Edmond Becquerel, at age 19, in his father's laboratory.
The mostly commonly researched modern photoelectrochemical cell in recent decades has been the Grätzel cell, although much attention has recently shifted away from this topic to perovskite solar cells, due to relatively high efficiency of the latter and the similarity in vapor assisted deposition techniques commonly used in their creation.
Dye-sensitized solar cells or Grätzel cells use dye-adsorbed highly porous nanocrystalline titanium dioxide (nc-) to produce electrical energy. | 5 | Photochemistry |
The reagent appears as a clear, yellow liquid without odour. It is harmful if inhaled, a recognised carcinogen and can cause eye burns. | 3 | Analytical Chemistry |
During the 1970s the BNF became the BNF Metals Technology Centre and moved out of London to Grove Laboratories, Denchworth Road, Wantage, Oxfordshire. Recognising globalisation, membership was then opened to companies based overseas. In 1990 the BNF bought Fulmer Research Laboratories from the Institute of Physics and was renamed the BNF-Fulmer, then BNF (Fulmer Materials Centre). The laboratories were closed in 1992. | 8 | Metallurgy |
Ion funnels are frequently used in mass spectroscopy devices to collect ions from an ionization source. Previous devices lacking an ion funnel often lost ions during the transition from ionization source to the detector of the mass spectrometer. This loss was due to the increasing number of collisions undergone by ions with other gas molecules present in the atmosphere. The introduction of the ion funnel greatly reduced the amount of ions lost during experiments by guiding ions towards a desired destination, and through modification of the number of inlets is also able to increases sensitivity of measurements taken by the mass spectrometer. Multiple inlets allow multiple electrospray emitters, reducing the flow through each individual emitter. This creates many highly efficient electrosprays at low flow rates. Multiple inlets also improve sensitivity, with a linearly arranged 19 electrospray emitter coupled to 19 inlets operating at 18 Torr giving a nine-fold increase compared to a single inlet. | 7 | Physical Chemistry |
Explained briefly, NASBA works as follows:
#RNA template added to the reaction mixture, the first primer with the T7 promoter region on its 5 end attaches to its complementary site at the 3 end of the template.
#Reverse transcriptase synthesizes the opposite complementary DNA strand extending the 3' end of the primer, moving upstream along the RNA template.
#RNAse H destroys the RNA template from the DNA-RNA compound (RNAse H only destroys RNA in RNA-DNA hybrids, but not single-stranded RNA).
#The second primer attaches to the 5' end of the (antisense) DNA strand.
#Reverse transcriptase again synthesizes another DNA strand from the attached primer resulting in double stranded DNA.
#T7 RNA polymerase binds to the promoter region on the double strand. Since T7 RNA polymerase can only transcribe in the 3 to 5 direction the sense DNA is transcribed and an anti-sense RNA is produced. This is repeated, and the polymerase continuously produces complementary RNA strands of this template which results in amplification.
#Now a cyclic phase can begin similar to the previous steps. Here, however, the second primer first binds to the (-)RNA
#The reverse transcriptase now produces a (+)cDNA/(-)RNA duplex.
#RNAse H again degrades the RNA and the first primer binds to the now single stranded +(cDNA)
#The reverse transcriptase now produces the complementary (-)DNA, creating a dsDNA duplex
#Exactly like step 6, the T7 polymerase binds to the promoter region to produce (-)RNA, and the cycle is complete. | 1 | Biochemistry |
The clipping method is similar to the capping reaction except that in this case the dumbbell shaped molecule is complete and is bound to a partial macrocycle. The partial macrocycle then undergoes a ring closing reaction around the dumbbell-shaped molecule, forming the rotaxane. | 6 | Supramolecular Chemistry |
Push–pull perfusion is an in vivo sampling method most commonly used for measuring neurotransmitters in the brain. Developed by J.H. Gaddum in 1960,
this technique replaced the cortical cup technique for observing neurotransmitters. The advent of concentric microdialysis probes in the 1980s resulted in push-pull sampling falling out of favor, as such probes require less monitoring, and are less invasive than the higher flow rate push-pull probes (>10 microliter/min), which could result in lesions if flow is unbalanced.
With the advent of microfluidics and miniaturized probes, low-flow push–pull sampling was developed in 2002. By using flow rates of ~50 nL/min, this technique minimizes tissue damage while providing finer spatial resolution than microdialysis sampling. | 1 | Biochemistry |
TGFβ signaling at the cell membrane results in 2 different intracellular pathways. One of them depends on MED15, while the other is independent of MED15. In both human cells and Caenorhabditis elegans MED15 is involved in lipid homeostasis through the pathway involving SREBPs In the model plant Arabidopsis thaliana the ortholog of MED15 is required for signaling by the plant hormone Salicylic acid, while MED25 is required for the transcriptional activation of jasmonate and shade signalling responses. Two components of the CDK module (MED12 and MED13) are involved in the Wnt signaling pathway MED23 is involved in RAS/MAPK/ERK pathway This abbreviated review shows the versatility of individual mediator subunits, and leads to the idea that mediator is an end-point of signaling pathways. | 1 | Biochemistry |
The Hamiltonian describing a spinor condensate is most frequently written using the language of
second quantization. Here the field operator
creates a boson in Zeeman level at position . These
operators satisfy bosonic commutation relations:
The free (non-interacting) part of the Hamiltonian is
where denotes the mass of the constituent particles and
is an external potential.
For a spin-one spinor condensate, the interaction Hamiltonian is
In this expression,
is the operator corresponding to the density,
is the local spin operator (
is a vector composed of the spin-one matrices),
and :: denotes normal ordering. The parameters
can be expressed in terms of the s-wave scattering lengths of the constituent particles.
Higher spin versions of the
interaction Hamiltonian are slightly more involved, but
can generally be expressed by using Clebsch–Gordan coefficients.
The full Hamiltonian then is . | 7 | Physical Chemistry |
Condensation polymerization is an important class of step-growth polymerization, which is formed simply by the reaction of two monomers and results in the release of a water molecule. Since these polymers are typically made up of two or more monomers, the resulting end groups are from the monomer functionality. Examples of condensation polymers can be seen with polyamides, polyacetals and polyesters. An example of polyester is polyethylene terephthalate (PET), which is made from the monomers terephthalic acid and ethylene glycol. If one of the components in the polymerization is in excess, then that polymers functionality will be at the ends of the polymers (a carboxylic acid or alcohol group respectively). | 7 | Physical Chemistry |
* NADPH-cytochrome P450 reductase
Cytochrome P450 reductase, also known as NADPH:ferrihemoprotein oxidoreductase, NADPH:hemoprotein oxidoreductase, NADPH:P450 oxidoreductase, P450 reductase, POR, CPR, CYPOR, is a membrane-bound enzyme required for electron transfer to cytochrome P450 in the microsome of the eukaryotic cell from a FAD- and FMN-containing enzyme NADPH:cytochrome P450 reductase
The general scheme of electron flow in the POR/P450 system is:
NADPH
FAD
FMN
P450
O
* Reduced (ferrous) cytochrome P450
During reduction reactions, a chemical can enter futile cycling, in which it gains a free-radical electron, then promptly loses it to oxygen (to form a superoxide anion). | 1 | Biochemistry |
EPS is found in the matrix of other microbial biofilms such as microalgal biofilms. The formation of biofilm and structure of EPS share a lot of similarities with bacterial ones. The formation of biofilm starts with reversible absorption of floating cells to the surface. Followed by production of EPS, the adsorption will get irreversible. EPS will colonize the cells at the surface with hydrogen bonding. Replication of early colonizers will be facilitated by the presence of organic molecules in the matrix which will provide nutrients to the algal cells. As the colonizers are reproducing, the biofilm grows and becomes a 3-dimensional structure. Microalgal biofilms consist of 90% EPS and 10% algal cells. Algal EPS has similar components to the bacterial one; it is made up of proteins, phospholipids, polysaccharides, nucleic acids, humic substances, uronic acids and some functional groups, such as phosphoric, carboxylic, hydroxyl and amino groups. Algal cells consume EPS as their source of energy and carbon. Furthermore, EPS protects them from dehydration and reinforces the adhesion of the cells to the surface. In algal biofilms, EPS has two sub-categories; soluble EPS (sEPS) and the bounded EPS (bEPS) with former being distributed in the medium and the latter being attached to the algal cells. Bounded EPS can be further subdivided to tightly bounded EPS (TB-EPS) and loosely bounded EPS (LB-EPS). Several factors contribute to the composition of EPS including species, substrate type, nutrient availability, temperature, pH and light intensity. | 1 | Biochemistry |
For equilibria in a gas phase, fugacity, f, is used in place of activity. However, fugacity has the dimension of pressure, so it must be divided by a standard pressure, usually 1 bar, in order to produce a dimensionless quantity, . An equilibrium constant is expressed in terms of the dimensionless quantity. For example, for the equilibrium 2NO NO,
Fugacity is related to partial pressure, , by a dimensionless fugacity coefficient ϕ: . Thus, for the example,
Usually the standard pressure is omitted from such expressions. Expressions for equilibrium constants in the gas phase then resemble the expression for solution equilibria with fugacity coefficient in place of activity coefficient and partial pressure in place of concentration. | 7 | Physical Chemistry |
In the process of photosynthesis, green plants use the energy of sunlight to split water into free oxygen (which is released) and free hydrogen. Rather than attempt to store the hydrogen, plants immediately capture carbon dioxide from the air to allow the hydrogen to reduce it to storable fuels such as hydrocarbons (plant oils and terpenes) and polyalcohols (glycerol, sugars and starches). In the methanol economy, any process which similarly produces free hydrogen, proposes to immediately use it "captively" to reduce carbon dioxide into methanol, which, like plant products from photosynthesis, has great advantages in storage and transport over free hydrogen itself.
Methanol is a liquid under normal conditions, allowing it to be stored, transported and dispensed easily, much like gasoline and diesel fuel. It can also be readily transformed by dehydration into dimethyl ether, a diesel fuel substitute with a cetane number of 55.
Methanol is water-soluble: An accidental release of methanol in the environment would cause much less damage than a comparable gasoline or crude oil spill. Unlike these fuels, methanol is biodegradable and totally soluble in water, and would be rapidly diluted to a concentration low enough for microorganism to start biodegradation. This effect is already exploited in water treatment plants, where methanol is already used for denitrification and as a nutrient for bacteria. Accidental release causing groundwater pollution has not been thoroughly studied yet, though it is believed that it might undergo relatively rapid. | 2 | Environmental Chemistry |
Racemic drugs are not drug combinations in the accepted sense of two or more co-formulated therapeutic agents, but combinations of isomeric substances whose pharmacological activity may reside predominantly in one specific enantiomeric form. In case of stereoselectivity in action only one of the components in the racemic mixture is truly active. The other isomer, the distomer, should be regarded as impurity or isomeric ballast, a term coined by Ariëns, not contributing to the effects aimed at. In contrast to the pharmacokinetic properties of an enantiomeric pair, differences in pharmacodynamic activity tend to be more obvious. There is a wide spectrum of possibilities of distomer actions, many of which are confirmed experimentally. Selected examples of the distomer actions (viz. equipotent, less active, inactive, antagonistic, chiral inversion) are presented in the table below. | 4 | Stereochemistry |
Hess's law states that the change of enthalpy in a chemical reaction is the same regardless of whether the reaction takes place in one step or several steps, provided the initial and final states of the reactants and products are the same. Enthalpy is an extensive property, meaning that its value is proportional to the system size. Because of this, the enthalpy change is proportional to the number of moles participating in a given reaction.
In other words, if a chemical change takes place by several different routes, the overall enthalpy change is the same, regardless of the route by which the chemical change occurs (provided the initial and final condition are the same). If this were not true, then one could violate the first law of thermodynamics.
Hesss law allows the enthalpy change (ΔH') for a reaction to be calculated even when it cannot be measured directly. This is accomplished by performing basic algebraic operations based on the chemical equations of reactions using previously determined values for the enthalpies of formation.
Combination of chemical equations leads to a net or overall equation. If the enthalpy changes are known for all the equations in the sequence, their sum will be the enthalpy change for the net equation. If the net enthalpy change is negative (), the reaction is exothermic and is more likely to be spontaneous; positive ΔH values correspond to endothermic reactions. (Entropy also plays an important role in determining spontaneity, as some reactions with a positive enthalpy change are nevertheless spontaneous due to an entropy increase in the reaction system.) | 7 | Physical Chemistry |
People who survive an intoxication episode may develop persistent health problems. This group of persistent health symptoms are called syndrome of irreversible lithium-effectuated neurotoxicity (SILENT). The syndrome presents with irreversible neurological and neuro-psychiatric effects. The neurological signs are cerebellar dysfunction, extrapyramidal symptoms, and brainstem dysfunction. The neuro-psychiatric findings present with memory deficits, cognitive deficits, and sub-cortical dementia. For a diagnosis, the syndrome requires the absence of prior symptoms and persistence of symptoms for greater than 2 months after cessation of lithium. | 1 | Biochemistry |
Hydrogen-bond catalysis is a type of organocatalysis that relies on use of hydrogen bonding interactions to accelerate and control organic reactions. In biological systems, hydrogen bonding plays a key role in many enzymatic reactions, both in orienting the substrate molecules and lowering barriers to reaction. However, chemists have only recently attempted to harness the power of using hydrogen bonds to perform catalysis, and the field is relatively undeveloped compared to research in Lewis acid catalysis.
Catalytic amounts of hydrogen-bond donors can promote reactions through a variety of different mechanisms. During the course of a reaction, hydrogen bonding can be used to stabilize anionic intermediates and transition states. Alternatively, some catalysts can bind small anions, enabling the formation of reactive electrophilic cations. More acidic donors can act as general or specific acids, which activate electrophiles by protonation. A powerful approach is the simultaneous activation of both partners in a reaction, e.g. nucleophile and electrophile, termed "bifunctional catalysis". In all cases, the close association of the catalyst molecule to substrate also makes hydrogen-bond catalysis a powerful method of inducing enantioselectivity.
Hydrogen-bonding catalysts are often simple to make, relatively robust, and can be synthesized in high enantiomeric purity. New reactions catalyzed by hydrogen-bond donors are being discovered at an increasing pace, including asymmetric variants of common organic reactions useful for synthesis, such as aldol additions, Diels-Alder cycloadditions and Mannich reactions.
However, there are several challenges that must be overcome before hydrogen-bond catalysis can achieve its full potential in terms of synthetic utility. Current known reactions are very substrate specific and generally exhibit low rate acceleration and turnover, thus requiring high catalyst loading. Catalysts are often discovered and optimized by trial and error, and chemists have a poor understanding of the relationship between catalyst structure and reactivity. Additionally, the field suffers from a lack of general mechanistic understanding, which has been greatly outpaced by the discovery of new reactions. With more detailed studies of structure and mechanism in the future, hydrogen-bond catalysis has great potential for enabling new, efficient, selective reactions and promising applications in asymmetric synthesis. | 0 | Organic Chemistry |
Catenin beta-1, also known as β-catenin (beta-catenin), is a protein that in humans is encoded by the CTNNB1 gene.
β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcription. In humans, the CTNNB1 protein is encoded by the CTNNB1 gene. In Drosophila, the homologous protein is called armadillo. β-catenin is a subunit of the cadherin protein complex and acts as an intracellular signal transducer in the Wnt signaling pathway. It is a member of the catenin protein family and homologous to γ-catenin, also known as plakoglobin. β-Catenin is widely expressed in many tissues. In cardiac muscle, β-catenin localizes to adherens junctions in intercalated disc structures, which are critical for electrical and mechanical coupling between adjacent cardiomyocytes.
Mutations and overexpression of β-catenin are associated with many cancers, including hepatocellular carcinoma, colorectal carcinoma, lung cancer, malignant breast tumors, ovarian and endometrial cancer. Alterations in the localization and expression levels of β-catenin have been associated with various forms of heart disease, including dilated cardiomyopathy. β-Catenin is regulated and destroyed by the beta-catenin destruction complex, and in particular by the adenomatous polyposis coli (APC) protein, encoded by the tumour-suppressing APC gene. Therefore, genetic mutation of the APC gene is also strongly linked to cancers, and in particular colorectal cancer resulting from familial adenomatous polyposis (FAP). | 1 | Biochemistry |
NMR spectroscopy is often the method of choice for monitoring reaction progress, where substrate consumption and/or product formation may be observed over time from the change of peak integration relative to a non-reactive standard. From the concentration data, the rate of reaction over time may be obtained by taking the derivative of a polynomial fit to the experimental curve. Reaction progress NMR may be classified as an integral technique as the primary data collected are proportional to concentration vs. time. While this technique is extremely convenient for clearly defined systems with distinctive, isolated product and/or reactant peaks, it has the drawback of requiring a homogeneous system amenable to reaction in an NMR tube. While NMR observation may allow for the identification of a reaction intermediates, the presence of any given species over the course of the reaction does not necessarily implicate it in a productive process. Reaction progress NMR may, however, often be run at variable temperature, allowing the rate of reaction to be adjusted to a level convenient for observation. Examples of utilization of reaction progress NMR abound, with notable examples including investigation of Buchwald–Hartwig amination (One might note that considerable debate surrounded the best approach to mechanistic development of the Buchwald-Hartwig amination as indicated by a number of contradictory and competing reports published over a short period of time. See the designated article and references therein.) | 7 | Physical Chemistry |
An amorphism, in chemistry, crystallography and, by extension, to other areas of the natural sciences is a substance or feature that lacks an ordered form. In the specific case of crystallography, an amorphic material is one that lacks long range (significant) crystalline order at the molecular level. In the history of chemistry, amorphism was recognised even before the discovery of the nature of the exact atomic crystalline lattice structure. The concept of amorphism can also be found in the fields of art, biology, archaeology and philosophy as a characterisation of objects without form, or with random or unstructured form. | 7 | Physical Chemistry |
Primary standards are compounds with known stoichiometry, high purity, and high stability. Standard solutions can be prepared using primary standards by accurately weighing a known quantity of the compound, followed by dilution to a precise volume. For example, a weighed sample of 0.15 g sodium chloride contains 2.6 x 10 moles of sodium chloride. The following dilution of this sample in a 50-mL volumetric flask will result in a concentration of 0.51 M. | 3 | Analytical Chemistry |
The Kuhn length is a theoretical treatment, developed by Werner Kuhn, in which a real polymer chain is considered as a collection of Kuhn segments each with a Kuhn length . Each Kuhn segment can be thought of as if they are freely jointed with each other. Each segment in a freely jointed chain can randomly orient in any direction without the influence of any forces, independent of the directions taken by other segments. Instead of considering a real chain consisting of bonds and with fixed bond angles, torsion angles, and bond lengths, Kuhn considered an equivalent ideal chain with connected segments, now called Kuhn segments, that can orient in any random direction.
The length of a fully stretched chain is for the Kuhn segment chain. In the simplest treatment, such a chain follows the random walk model, where each step taken in a random direction is independent of the directions taken in the previous steps, forming a random coil. The average end-to-end distance for a chain satisfying the random walk model is .
Since the space occupied by a segment in the polymer chain cannot be taken by another segment, a self-avoiding random walk model can also be used. The Kuhn segment construction is useful in that it allows complicated polymers to be treated with simplified models as either a random walk or a self-avoiding walk, which can simplify the treatment considerably.
For an actual homopolymer chain (consists of the same repeat units) with bond length and bond angle θ with a dihedral angle energy potential, the average end-to-end distance can be obtained as
::where is the average cosine of the dihedral angle.
The fully stretched length . By equating the two expressions for and the two expressions for from the actual chain and the equivalent chain with Kuhn segments, the number of Kuhn segments and the Kuhn segment length can be obtained.
For worm-like chain, Kuhn length equals two times the persistence length. | 7 | Physical Chemistry |
Primary and secondary consumers in lakes require organic matter (either from plants or animals) to maintain organismal function. Organic matter including tree leaves, dissolved organic matter, and algae provide essential resources to these consumers and in the process increase lake ecosystem respiration rates in the conversion of organic matter to cellular growth and organismal maintenance. Some sources of organic matter may impact the availability of other constituents. For example, dissolved organic matter often darkens lake water which reduces the amount of light available in the lake, thus reducing primary production. However, increases in organic matter loading to a lake can also increase nutrients that are associated with the organic matter, which can stimulate primary production and respiration. Increased dissolved organic matter loading can create tradeoffs between increasing light limitation and release from nutrient limitation. This tradeoff can create non-linear relationships between lake primary production and dissolved organic matter loading based on how much nutrients are associated with the organic matter and how quickly the dissolved organic matter blocks out light in the water column. This is because at low dissolved organic matter concentrations as dissolved organic matter concentration increases, increased associated nutrients enhances GPP. But as dissolved organic matter continues to increase, the reduction in light from the darkening of the lake water suppresses GPP as light becomes the limiting resource for primary productivity. Differences in the magnitude and location of maximum GPP in response to increased DOC load are hypothesized to arise based on the ratio of DOC to nutrients coming into the lake as well as the effect of DOC on lake light climate. The darkening of the lake water can also change thermal regimes within the lake as darker waters typically mean that warmer waters remain at the top of the lake while cooler waters are at the bottom. This change in heat energy distribution can impact the rates of pelagic and benthic productivity (see Temperature above), and change water column stability, with impacts on vertical distribution of nutrients, therefore having effects on vertical distribution of metabolic rates. | 1 | Biochemistry |
In many substitution reactions, well-defined intermediates are not observed, when the rate of such processes are influenced by the nature of the entering ligand, the pathway is called associative interchange, abbreviated I. Representative is the interchange of bulk and coordinated water in [V(HO)]. In contrast, the slightly more compact ion [Ni(HO)] exchanges water via the I. | 0 | Organic Chemistry |
Ionic additives, such as ammonium acetate and ammonium formate, are usually used to control the mobile phase pH and ion strength. In HILIC they can also contribute to the polarity of the analyte, resulting in differential changes in retention. For extremely polar analytes (e.g. aminoglycoside antibiotics (gentamicin) or adenosine triphosphate), higher concentrations of buffer (c. 100 mM) are required to ensure that the analyte will be in a single ionic form. Otherwise, asymmetric peak shape, chromatographic tailing, and/or poor recovery from the stationary phase will be observed. For the separation of neutral polar analytes (e.g. carbohydrates), no buffer is necessary.
Other salts, such as 100–300 mM sodium perchlorate, that are soluble in high-organic solvent mixtures (c. 70–90% acetonitrile), can be used to increase the mobile phase polarity to affect elution These salts are not volatile, so this technique is less useful with a mass spectrometer as the detector. Usually a gradient (to increasing amounts of water) is enough to promote elution.
All ions partition into the stationary phase to some degree, so an occasional "wash" with water is required to ensure a reproducible stationary phase. | 1 | Biochemistry |
*1896–1932 Wilder Dwight Bancroft, Joseph E. Trevor
*1933–1951 S. C. Lind
*1952–1964 William A. Noyes
*1965–1969 F. T. Wall
*1970–1980 Bryce Crawford
*1980–2004 Mostafa El-Sayed
*2005–2019 George C. Schatz
*2020–present Joan-Emma Shea | 7 | Physical Chemistry |
Cryo-adsorption is a method used for hydrogen storage where gaseous hydrogen at cryogenic temperatures (150—60 K) is physically adsorbed on porous material, mostly activated carbon. The achievable storage density is between liquid-hydrogen (LH) storage systems and compressed-hydrogen (CGH) storage systems. | 3 | Analytical Chemistry |
A variety of synthetic routes to acid have been developed. The first reported chemical syntheses approached HMB by oxidation of alkene, vicinal diol, and alcohol precursors:
* in 1877, Russian chemists Michael and Alexander Zaytsev reported the preparation of HMB by oxidation of 2-methylpent-4-en-2-ol with chromic acid (HCrO);
* in 1880 and 1889, Schirokoff and Reformatsky (respectively) reported that the oxidative cleavage of the vicinal diol 4-methylpentane-1,2,4-triol with acidified potassium permanganate (KMnO) yields HMB – this result is closest related to the first synthesis as cold dilute KMnO oxidises alkenes to vicinal cis-diols which hot acid KMnO further oxidises to carbonyl-containing compounds, and the diol intermediate is not obtained when hot acidic conditions are used for alkene oxidation. In other words, racemic 4-methylpentane-1,2,4-triol is a derivative of 2-methylpent-4-en-2-ol and β-hydroxy β-methylbutyric acid is a derivative of both; and,
* in 1892, Kondakow reported the preparation of HMB by permanganate oxidation of 3-methylbutane-1,3-diol.
Depending on the experimental conditions, cycloaddition of acetone and ketene produces either or 4,4-dimethyloxetan-2-one, both of which hydrolyze under basic conditions to yield the conjugate base of HMB. The haloform reaction provides another pathway to HMB involving the exhaustive halogenation of the methyl-ketone region of diacetone alcohol with sodium hypobromite or sodium hypochlorite; Diacetone alcohol is readily available from the aldol condensation of acetone. An organometallic approach to HMB involves the carboxylation of tert-butyl alcohol with carbon monoxide and Fentons reagent (hydrogen peroxide and ferrous iron). Alternatively, HMB can be prepared through microbial oxidation of acid by the fungus Galactomyces reessii'. | 1 | Biochemistry |
Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximately of dissolved salts (predominantly sodium () and chloride () ions). The average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water (density 1.0 kg/L at ) because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about . The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an Antarctic glacier: the measured temperature was .
Seawater pH is typically limited to a range between 7.5 and 8.4. However, there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units. | 9 | Geochemistry |
The Dortmund Data Bank is distributed by DDBST GmbH as in-house software. Many parts of the Dortmund Data Bank are also distributed as part of the DETHERM data bank which is also available online. | 7 | Physical Chemistry |
Upon first arriving in the Philippine archipelago, landing specifically in the visayas, Spanish colonizers noted astonishing amounts of gold in common use, including earrings, armbands legbands, gold chains, collars of beads, wristlets, armlets, finger rings, and so on. They were also integrated into clothing as sequins, as clasps or buttons for cloaks or as broaches. | 8 | Metallurgy |
In the study of the structure of mercury b- , lead- and organotin derivatives of nitrosophenols, Nesmeyanov discovered the phenomenon of metallotropy, that is, a special tautomerism in which a reversible transfer of an organometallic group occurs. Joint studies by A. N. Nesmeyanov and I. F. Lutsenko discovered heteroatomic tautomerism (between carbon and oxygen atoms) in keto-enol systems of tin , o- and germanium compounds. Nesmeyanov, together with Yu. A. and N. A. Ustynyuk, discovered a new type of metallotropy: it was found that in fluorenylchromium tricarbonyl anions, η 6 -complexes are equilibrium and reversibly isomerized into η 5 -complexes. | 0 | Organic Chemistry |
In addition to linking primary producers to higher trophic levels in marine food webs, zooplankton also play an important role as “recyclers” of carbon and other nutrients that significantly impact marine biogeochemical cycles, including the biological pump. This is particularly the case with copepods and krill, and is especially important in oligotrophic waters of the open ocean. Through sloppy feeding, excretion, egestion, and leaching of fecal pellets, zooplankton release dissolved organic matter (DOM) which controls DOM cycling and supports the microbial loop. Absorption efficiency, respiration, and prey size all further complicate how zooplankton are able to transform and deliver carbon to the deep ocean.
Excretion and sloppy feeding (the physical breakdown of food source) make up 80% and 20% of crustacean zooplankton-mediated DOM release respectively. In the same study, fecal pellet leaching was found to be an insignificant contributor. For protozoan grazers, DOM is released primarily through excretion and egestion and gelatinous zooplankton can also release DOM through the production of mucus. Leaching of fecal pellets can extend from hours to days after initial egestion and its effects can vary depending on food concentration and quality. Various factors can affect how much DOM is released from zooplankton individuals or populations. | 9 | Geochemistry |
The mechanism by which molecules cross cellular membrane barriers during sonoporation remains unclear. Different theories exist that may potentially explain barrier permeabilization and molecular delivery. The dominant hypotheses include pore formation, endocytosis, and membrane wounds. | 1 | Biochemistry |
The FDA approved Phase I clinical trials on thalassemia major patients in the US for 10 participants in July. The study was expected to continue until 2015.
In July 2012, the European Medicines Agency recommended approval of a gene therapy treatment for the first time in either Europe or the United States. The treatment used Alipogene tiparvovec (Glybera) to compensate for lipoprotein lipase deficiency, which can cause severe pancreatitis. The recommendation was endorsed by the European Commission in November 2012, and commercial rollout began in late 2014. Alipogene tiparvovec was expected to cost around $1.6 million per treatment in 2012, revised to $1 million in 2015, making it the most expensive medicine in the world at the time. , only the patients treated in clinical trials and a patient who paid the full price for treatment have received the drug.
In December 2012, it was reported that 10 of 13 patients with multiple myeloma were in remission "or very close to it" three months after being injected with a treatment involving genetically engineered T cells to target proteins NY-ESO-1 and LAGE-1, which exist only on cancerous myeloma cells. | 1 | Biochemistry |
Several physical properties of superconductors vary from material to material, such as the critical temperature, the value of the superconducting gap, the critical magnetic field, and the critical current density at which superconductivity is destroyed. On the other hand, there is a class of properties that are independent of the underlying material. The Meissner effect, the quantization of the magnetic flux or permanent currents, i.e. the state of zero resistance are the most important examples. The existence of these "universal" properties is rooted in the nature of the broken symmetry of the superconductor and the emergence of off-diagonal long range order. Superconductivity is a thermodynamic phase, and thus possesses certain distinguishing properties which are largely independent of microscopic details. Off diagonal long range order is closely connected to the formation of Cooper pairs. | 7 | Physical Chemistry |
Determining the point group is a useful way to predict polarity of a molecule. In general, a molecule will not possess dipole moment if the individual bond dipole moments of the molecule cancel each other out. This is because dipole moments are euclidean vector quantities with magnitude and direction, and a two equal vectors that oppose each other will cancel out.
Any molecule with a centre of inversion ("i") or a horizontal mirror plane ("σ") will not possess dipole moments.
Likewise, a molecule with more than one C axis of rotation will not possess a dipole moment because dipole moments cannot lie in more than one dimension. As a consequence of that constraint, all molecules with dihedral symmetry (D) will not have a dipole moment because, by definition, D point groups have two or multiple C axes.
Since C, C,C C and C point groups do not have a centre of inversion, horizontal mirror planes or multiple C axis, molecules in one of those point groups will have dipole moment. | 7 | Physical Chemistry |
Joule effect and Joule's law are any of several different physical effects discovered or characterized by English physicist James Prescott Joule. These physical effects are not the same, but all are frequently or occasionally referred to in the literature as the "Joule effect" or "Joule law" These physical effects include:
* "Joule's first law" (Joule heating), a physical law expressing the relationship between the heat generated and the current flowing through a conductor.
* Joule's second law states that the internal energy of an ideal gas is independent of its volume and pressure, depending only on its temperature.
* Magnetostriction, a property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field.
* The Joule effect (during Joule expansion), the temperature change of a gas (usually cooling) when it is allowed to expand freely.
* The Joule–Thomson effect, the temperature change of a gas when it is forced through a valve or porous plug while keeping it insulated so that no heat is exchanged with the environment.
* The Gough–Joule effect or the Gow–Joule effect, which is the tendency of elastomers to contract if heated while they are under tension. | 7 | Physical Chemistry |
In 2014 and 2016 the Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, hosted academic symposiums to commemorate his life's work.
A Special Memorial Exhibition was also held in 2015 at the Dong-Eun Museum of Medical Science in Seoul, Korea. The exhibit included a collection of papers left by the late Suksin Lee. | 1 | Biochemistry |
Applications in macroscopic engineering have been suggested, building quasi-crystal-like large scale engineering structures, which could have interesting physical properties. Also, aperiodic tiling lattice structures may be used instead of isogrid or honeycomb patterns. None of these seem to have been put to use in practice. | 3 | Analytical Chemistry |
In E. coli, the biosynthesis begins with phosphorylation of 5-phosphoribosyl-pyrophosphate (PRPP), catalyzed by ATP-phosphoribosyl transferase. Phosphoribosyl-ATP converts to phosphoribosyl-AMP (PRAMP). His4 then catalyzes the formation of phosphoribosylformiminoAICAR-phosphate, which is then converted to phosphoribulosylformimino-AICAR-P by the His6 gene product. His7 splits phosphoribulosylformimino-AICAR-P to form -erythro-imidazole-glycerol-phosphate. After, His3 forms imidazole acetol-phosphate releasing water. His5 then makes -histidinol-phosphate, which is then hydrolyzed by His2 making histidinol. His4 catalyzes the oxidation of -histidinol to form -histidinal, an amino aldehyde. In the last step, -histidinal is converted to -histidine.
In general, the histidine biosynthesis is very similar in plants and microorganisms.
HisG → HisE/HisI → HisA → HisH → HisF → HisB → HisC → HisB → HisD (HisE/I and HisB are both bifunctional enzymes)
The enzymes are coded for on the His operon. This operon has a distinct block of the leader sequence, called block 1:
Met-Thr-Arg-Val-Gln-Phe-Lys-His-His-His-His-His-His-His-Pro-Asp
This leader sequence is important for the regulation of histidine in E. coli. The His operon operates under a system of coordinated regulation where all the gene products will be repressed or depressed equally. The main factor in the repression or derepression of histidine synthesis is the concentration of histidine charged tRNAs. The regulation of histidine is actually quite simple considering the complexity of its biosynthesis pathway and, it closely resembles regulation of tryptophan. In this system the full leader sequence has 4 blocks of complementary strands that can form hairpin loops structures. Block one, shown above, is the key to regulation. When histidine charged tRNA levels are low in the cell the ribosome will stall at the string of His residues in block 1. This stalling of the ribosome will allow complementary strands 2 and 3 to form a hairpin loop. The loop formed by strands 2 and 3 forms an anti-terminator and translation of the his genes will continue and histidine will be produced. However, when histidine charged tRNA levels are high the ribosome will not stall at block 1, this will not allow strands 2 and 3 to form a hairpin. Instead strands 3 and 4 will form a hairpin loop further downstream of the ribosome. The hairpin loop formed by strands 3 and 4 is a terminating loop, when the ribosome comes into contact with the loop, it will be “knocked off” the transcript. When the ribosome is removed the His genes will not be translated and histidine will not be produced by the cell. | 1 | Biochemistry |
Type-II superconductivity is characterized by two critical fields called B and B. At a magnetic field B the applied magnetic field starts to penetrate the sample, but the sample is still superconducting. Only at a field of B the sample is completely normal. For fields in between B and B magnetic flux penetrates the superconductor in well-organized patterns, the so-called Abrikosov vortex lattice similar to the pattern shown in Fig. 2. A cross section of the superconducting plate is given in Fig. 7. Far away from the plate the field is homogeneous, but in the material superconducting currents flow which squeeze the field in bundles of exactly one flux quantum. The typical field in the core is as big as 1 tesla. The currents around the vortex core flow in a layer of about 50 nm with current densities on the order of 15 A/m. That corresponds with 15 million ampère in a wire of one mm. | 7 | Physical Chemistry |
As mentioned in the introduction, -photo-leucine is a synthetic derivative of the -Leucine amino acid. -photo-leucine is characterized by the presence of a diazirine ring linked to the R radical of the original amino acid. This cyclopropene ring-shaped molecule is constituted of a carbon atom attached to two nitrogen atoms through a covalent single bond. These two nitrogen atoms are simultaneously connected to each other by a double covalent bond. The diazirine carbon is located in the position where theoretically the 2nd carbon atom of the R radical of -leucine would be, linked up with the 1st and 3rd carbon of this theoretical R radical.
The diazirine ring confers to the photo-leucine its photoreactive property. When irradiated with UV light, it splits releasing nitrogen in gas form and leaving an unbound carbon atom (see Diazirine). In protein-protein interactions (PPI), this atom is attached to the complex formed by the two proteins susceptible of being under study.
The rest of the amino acid has indeed the same structure as the original -leucine molecule, which includes, as every amino acid, an amino group and a carboxyl group bonded to an α-carbon, and a radical that is attached to this carbon atom. The R chain, contains, in this case, a diazirine ring and two extra carbon atoms connected each to the diazirine carbon as it has been previously mentioned.
For use in biology experiments, only the -enantiomer of the photo-leucine amino acid is synthesized, so that it can substitute for natural -leucine. (Natural proteins consist only of -amino acids; see homochirality.) | 5 | Photochemistry |
In shallower waters, evidence supports that activity of local fisherman and marine life such as fish and certain shark species can disturb bottom sediments containing calcium carbonate particles and lead to their suspension. In addition, as microorganisms impact water chemistry in observable ways and require certain nutrient levels to thrive, whiting events found occurring in nutrient-poor waters where no significant alkalinity difference exists between whiting and non-whiting waters support the idea of sediment re-suspension as a primary cause. | 9 | Geochemistry |
Fluorescence in situ hybridization (FISH), is an example of a genetic labeling technique that utilizes probes that are specific for chromosomal sites along the length of a chromosome, also known as chromosome painting. Multiple fluorescent dyes that each have a distinct excitation and emission wavelength are bound to a probe which is then hybridized to chromosomes. A fluorescence microscope can detect the dyes present and send it to a computer that can reveal the karyotype of a cell. This technique allows abnormalities such as deletions and duplications to be revealed. | 1 | Biochemistry |
Modification had also been extended past hydrophobic and hydrophilic attachments, charged compounds have also been introduced to TRPs. Kobayashi et al. had previously performed successful modifications to separate bioactive ionic compounds, and continued on that success to improve separation efficiency of bioactive compounds. Common methods of separating angiotensin peptides had involved reverse-phased high-performance liquid chromatography (RP-HPLC) and cation-exchange chromatography. RP-HPLC requires the use of organic solvents, which is not favored and current trends are moving away from that. Hydrophobic interaction chromatography requires high concentration salt elutions and eluent cleaning to remove the salt. To address the shortcomings of the previous methods, Kobayashi’s group grafted acrylic acid (anionic acrylate under neutral conditions) and tert-butylacrylamide (hydrophobic) monomers onto PNIPAAm, resulting in PNIPAAm-co-AAc-co-tBAAm (IAtB) onto silica beads as a stationary phase medium. The reason for incorporating both ionic and hydrophobic compounds is multifaceted. The ionic compound improves interactivity with the ionic species, but raises the LCST significantly. The hydrophobic addition counteracts against the raise in LCST and lowers it to a more standard value, but also interacts with the hydrophobic surfaces of biological compounds. This resulted in successful and resolved elution of angiotensin peptides. Additionally, they were able to tune the retention factor for the analytes through isocratic temperature gradient elution. Ideal elutions occurred at 35 °C, but decreasing the temperature to 10 °C or raising it to 50 °C caused faster elutions either way. This is a strong indication that electrostatic and hydrophobic interactions can be similarly affected by changes in temperature. The major advantages from applying these success of this study include stationary phase versatility and maintaining bioactivity of the analytes.
Ayano et al. modified PNIPAAm with cationic N,N-dimethylaminopropylacrylamide (DMAPAAm) and hydrophobic BMA and grafted it onto silica beads to form IDB. They used pH changes to adjust the LCST. The effect of pH on the LCST is as follows, from a plateau value between pH 4.5 and pH 6.0, the LCST decreased up to pH 9 and below pH 4.5. This can be interpreted as requiring slightly basic or moderately acidic conditions, as the 4.5–6.0 pH region holds a maximum value of the LCST, an unfavorable condition. They used these properties to separate several non-steroidal anti-inflammatory drugs (NSAIDs). The analysis of acidic drugs (salicylic acid: BA; SA; MS; and As) was performed below pH 4.5. MS is hydrophobic only its retention time was affected by an increase in temperature on the column without a terminally modified anion-exchanger (IB column). However, with an anion-exchanger present, dissociated acidic drugs were retained longer at temperatures below LCST, and shorter at temperatures above LCST. When the IBD column compared to recently established PNIPAAm columns, electrostatic forces show remarkably higher retention ability of charged compounds than its hydrophilic predecessor. A single stationary phase can accomplish pharmaceutical separations based on hydrophobic interactions, hydrophilic interactions, and electrostatic interactions merely by adjusting the temperature (while adjusting pH to tweak the LCST). | 3 | Analytical Chemistry |
Phosphate-buffered saline (PBS) is a buffer solution (pH ~ 7.4) commonly used in biological research. It is a water-based salt solution containing disodium hydrogen phosphate, sodium chloride and, in some formulations, potassium chloride and potassium dihydrogen phosphate. The buffer helps to maintain a constant pH. The osmolarity and ion concentrations of the solutions match those of the human body (isotonic). | 1 | Biochemistry |
Phenolic acids can be found in mushroom basidiomycetes species. For example, protocatechuic acid and pyrocatechol are found in Agaricus bisporus as well as other phenylated substances like phenylacetic and phenylpyruvic acids. Other compounds like atromentin and thelephoric acid can also be isolated from fungi in the Agaricomycetes class. Orobol, an isoflavone, can be isolated from Aspergillus niger.
; In yeasts
Aromatic alcohols (example: tyrosol) are produced by the yeast Candida albicans. They are also found in beer. These molecules are quorum sensing compounds for Saccharomyces cerevisiae.
; Metabolism
Aryl-alcohol dehydrogenase uses an aromatic alcohol and NAD to produce an aromatic aldehyde, NADH and H.
Aryl-alcohol dehydrogenase (NADP+) uses an aromatic alcohol and NADP to produce an aromatic aldehyde, NADPH and H.
Aryldialkylphosphatase (also known as organophosphorus hydrolase, phosphotriesterase, and paraoxon hydrolase) uses an aryl dialkyl phosphate and HO to produce dialkyl phosphate and an aryl alcohol. | 0 | Organic Chemistry |
A high-resolution imaging (HRI) black-and-white, or panchromatic, camera is mounted adjacent to the HSI camera to enable both cameras to capture the same reflected light. The HRI camera uses a pushbroom approach just like the HSI camera with a similar lens and slit arrangement to limit the incoming light to a thin, wide beam. However, the HRI camera does not have a diffraction grating to disperse the incoming reflected light. Instead, the light is directed to a wider CCD to capture more image data. Because it captures a single line of the ground image per frame, it is called a line scan camera. The HRI CCD is 6,144 pixels wide and one pixel high. It operates at a frame rate of 720 Hz. At ARCHER search speed and altitude (100 knots over the ground at 2,500 ft AGL) each pixel in the black-and-white image represents a 3 inch by 3 inch area of the ground. This high resolution adds the capability to identify some objects. | 7 | Physical Chemistry |
Directional transmittance of a surface, denoted T, is defined as
where
*L is the radiance transmitted by that surface;
*L is the radiance received by that surface. | 7 | Physical Chemistry |
In June 2010, it was revealed that a phase II study of armodafinil as an adjunctive therapy in adults with schizophrenia had failed to meet the primary endpoints, and the clinical program was subsequently terminated. However, a study published later that year showed that patients with schizophrenia treated with armodafinil showed fewer of the negative symptoms of schizophrenia. | 4 | Stereochemistry |
*Lorraine Mercer MBE of the United Kingdom, born with phocomelia of both arms and legs, is the only thalidomide survivor to carry the Olympic Torch.
*Thomas Quasthoff, an internationally acclaimed bass-baritone, who describes himself: "1.34 meters tall, short arms, seven fingers — four right, three left — large, relatively well-formed head, brown eyes, distinctive lips; profession: singer".
*Niko von Glasow produced a documentary called NoBodys Perfect', based on the lives of 12 people affected by the drug, which was released in 2008.
*Mercédes Benegbi, born with phocomelia of both arms, drove the successful campaign for compensation from her government for Canadians who were affected by thalidomide.
*Mat Fraser, born with phocomelia of both arms, is an English rock musician, actor, writer and performance artist. He produced a 2002 television documentary "Born Freak", which looked at this historical tradition and its relevance to modern disabled performers. This work has become the subject of academic analysis in the field of disability studies.
*Sue Kent, born in 1963 with phocomelia of both arms, eight inches long, no thumbs, and seven fingers – three on one hand, four on the other - has appeared as a presenter on the BBC TV show Gardeners World' since 2020, demonstrating her ability to garden using her feet and toes where others would use their hands.
*Christian Lohr, born in 1962 with phocomelia of both arms and both legs, is a Swiss politician who served for 14 years in the legislature in the Canton Thurgau including 2 years as its president and has been a member of the national legislature since 2011. | 4 | Stereochemistry |
Consider a growth-optimizing investor in a fair game with mutually exclusive outcomes
(e.g. a “horse race” in which the official odds add up to one).
The rate of return expected by such an investor is equal to the relative entropy
between the investor's believed probabilities and the official odds.
This is a special case of a much more general connection between financial returns and divergence measures.
Financial risks are connected to via information geometry. Investors views, the prevailing market view, and risky scenarios form triangles on the relevant manifold of probability distributions. The shape of the triangles determines key financial risks (both qualitatively and quantitatively). For instance, obtuse triangles in which investors views and risk scenarios appear on “opposite sides” relative to the market describe negative risks, acute triangles describe positive exposure, and the right-angled situation in the middle corresponds to zero risk. | 7 | Physical Chemistry |
As sea ice freezes, it rejects increasingly salty water, which drains through narrow brine channels that thread through the ice. The brine flowing through the brine channels and out of the bottom of the ice is very cold and salty, so it sinks in the warmer, fresher seawater under the ice, forming a plume. The plume is colder than the freezing point of sea water under the ice, so the seawater can freeze where it touches the plume. Ice freezing around the edges of the plume gradually builds a hollow icicle-like tube, called a brinicle. These frozen stalactite-like forms are fragile during early stages, but if brine drainage ceases, they may freeze solid. In calm waters, brinicles can reach the sea floor, freezing it fairly abruptly. | 9 | Geochemistry |
The process of water sampling introduces two significant problems:
* The first problem is the extent to which the sample may be representative of the water source of interest. Water sources vary with time and with location. The measurement of interest may vary seasonally or from day to night or in response to some activity of man or natural populations of aquatic plants and animals. The measurement of interest may vary with distances from the water boundary with overlying atmosphere and underlying or confining soil. The sampler must determine if a single time and location meets the needs of the investigation, or if the water use of interest can be satisfactorily assessed by averaged values of sampling over time and location, or if critical maxima and minima require individual measurements over a range of times, locations or events. The sample collection procedure must assure correct weighting of individual sampling times and locations where averaging is appropriate. Where critical maximum or minimum values exist, statistical methods must be applied to observed variation to determine an adequate number of samples to assess the probability of exceeding those critical values.
* The second problem occurs as the sample is removed from the water source and begins to establish chemical equilibrium with its new surroundings – the sample container. Sample containers must be made of materials with minimal reactivity with substances to be measured; pre-cleaning of sample containers is important. The water sample may dissolve part of the sample container and any residue on that container, and chemicals dissolved in the water sample may sorb onto the sample container and remain there when the water is poured out for analysis. Similar physical and chemical interactions may take place with any pumps, piping, or intermediate devices used to transfer the water sample into the sample container. Water collected from depths below the surface will normally be held at the reduced pressure of the atmosphere; so gas dissolved in the water will collect at the top of the container. Atmospheric gas above the water may also dissolve into the water sample. Other chemical reaction equilibria may change if the water sample changes temperature. Finely divided solid particles formerly suspended by water turbulence may settle to the bottom of the sample container, or a solid phase may form from biological growth or chemical precipitation. Microorganisms within the water sample may biochemically alter concentrations of oxygen, carbon dioxide, and organic compounds. Changing carbon dioxide concentrations may alter pH and change solubility of chemicals of interest. These problems are of special concern during measurement of chemicals assumed to be significant at very low concentrations.
Sample preservation may partially resolve the second problem. A common procedure is keeping samples cold to slow the rate of chemical reactions and phase change, and analyzing the sample as soon as possible; but this merely minimizes the changes rather than preventing them. A useful procedure for determining influence of sample containers during delay between sample collection and analysis involves preparation for two artificial samples in advance of the sampling event. One sample container is filled with water known from previous analysis to contain no detectable amount of the chemical of interest. This sample, called a "blank", is opened for exposure to the atmosphere when the sample of interest is collected, then resealed and transported to the laboratory with the sample for analysis to determine if sample collection or holding procedures introduced any measurable amount of the chemical of interest. The second artificial sample is collected with the sample of interest, but then "spiked" with a measured additional amount of the chemical of interest at the time of collection. The blank (negative control) and spiked sample (positive control) are carried with the sample of interest and analyzed by the same methods at the same times to determine any changes indicating gains or losses during the elapsed time between collection and analysis. | 3 | Analytical Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.