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Lipids comprise a diverse range of molecules and to some extent is a catchall for relatively water-insoluble or nonpolar compounds of biological origin, including waxes, fatty acids, fatty-acid derived phospholipids, sphingolipids, glycolipids, and terpenoids (e.g., retinoids and steroids). Some lipids are linear, open-chain aliphatic molecules, while others have ring structures. Some are aromatic (with a cyclic [ring] and planar [flat] structure) while others are not. Some are flexible, while others are rigid.
Lipids are usually made from one molecule of glycerol combined with other molecules. In triglycerides, the main group of bulk lipids, there is one molecule of glycerol and three fatty acids. Fatty acids are considered the monomer in that case, and maybe saturated (no double bonds in the carbon chain) or unsaturated (one or more double bonds in the carbon chain).
Most lipids have some polar character and are largely nonpolar. In general, the bulk of their structure is nonpolar or hydrophobic ("water-fearing"), meaning that it does not interact well with polar solvents like water. Another part of their structure is polar or hydrophilic ("water-loving") and will tend to associate with polar solvents like water. This makes them amphiphilic molecules (having both hydrophobic and hydrophilic portions). In the case of cholesterol, the polar group is a mere –OH (hydroxyl or alcohol).
In the case of phospholipids, the polar groups are considerably larger and more polar, as described below.
Lipids are an integral part of our daily diet. Most oils and milk products that we use for cooking and eating like butter, cheese, ghee etc. are composed of fats. Vegetable oils are rich in various polyunsaturated fatty acids (PUFA). Lipid-containing foods undergo digestion within the body and are broken into fatty acids and glycerol, the final degradation products of fats and lipids. Lipids, especially phospholipids, are also used in various pharmaceutical products, either as co-solubilizers (e.g. in parenteral infusions) or else as drug carrier components (e.g. in a liposome or transfersome). | 1 | Biochemistry |
One of the critical needs for NMR structural ensemble validation is to distinguish well-determined regions (those that have experimental data) from regions that are highly mobile and/or have no observed data. There are several current or proposed methods for making this distinction such as Random Coil Index, but so far the NMR community has not standardized on one. | 1 | Biochemistry |
Chromatin Immuno-Precipitation, or (ChIP), is an alternative method to assay protein binding at specific loci of the genome. Unlike ChIP, DamID does not require a specific antibody against the protein of interest. On the one hand, this allows to map proteins for which no such antibody is available. On the other hand, this makes it impossible to specifically map posttranslationally modified proteins.
Another fundamental difference is that ChIP assays where the protein of interests is at a given time, whereas DamID assays where it has been. The reason is that m6A stays in the DNA after the Dam fusion protein goes away. For proteins that are either bound or unbound on their target sites this does not change the big picture. However, this can lead to strong differences in the case of proteins that slide along the DNA (e.g. RNA polymerase). | 1 | Biochemistry |
An early example of a supported metal–metal bond is cyclopentadienyliron dicarbonyl dimer, [(CH)Fe(CO)]. In the predominant isomers of this complex, the two Fe centers are joined not only by an Fe–Fe bond, but also by bridging CO ligands. The related cyclopentadienylruthenium dicarbonyl dimer features an unsupported Ru–Ru bond. Many metal clusters contain several supported M–M bonds. Some examples are Fe(CO) and Co(CO). | 7 | Physical Chemistry |
The compound has uses ranging from medicine to laboratory syntheses of chemically similar compounds. o-Cresophthalein has been used to derive polyamides and polyimides, colorimetrically estimate calcium in serum, and predict amount of time to wait before blood collection after a patient receives gadodiamide. | 3 | Analytical Chemistry |
Chelating agents, natural zeolite, activated carbon, resins, and liquid organics impregnated with chelating agents are all used to exchange cations or anions with the solution. Selectivity and recovery are a function of the reagents used and the contaminants present. | 8 | Metallurgy |
There currently are very few effective methods for expressing functional plant Rubisco in bacterial hosts for genetic manipulation studies. This is largely due to Rubiscos requirement of complex cellular machinery for its biogenesis and metabolic maintenance including the nuclear-encoded RbcS subunits, which are typically imported into chloroplasts as unfolded proteins. Furthermore, sufficient expression and interaction with Rubisco activase are major challenges as well. One successful method for expression of Rubisco in E. coli involves the co-expression of multiple chloroplast chaperones, though this has only been shown for Arabidopsis thaliana' Rubisco. | 5 | Photochemistry |
Fas ligand (FASL or CD95L) is a type-II transmembrane protein expressed on various types of cells, including cytotoxic T lymphocytes, monocytes, neutrophils, breast epithelial cells, vascular endothelial cells and natural killer (NK) cells. It binds with its receptor, called FAS receptor (also called CD95) and plays a crucial role in the regulation of the immune system and in induction of apoptosis, a programmed cell death. | 1 | Biochemistry |
Ocean acidification not only has impacts on aquatic life, but also on human communities and the overall livelihood of people living near these waters. For example, as a result of crustaceans being unable to produce their shells and skeletons due to reduced amounts of carbonate ions, populations such as crabs have significantly decreased in some areas in the Northern hemisphere. This has resulted in numerous fisheries in these areas to close down as a result of multi-million dollar losses. In addition, increased temperatures have caused a swift increase in toxic algal blooms, which are known to produce a neurotoxin called domoic acid that can accumulate inside the bodies of certain shellfish. If ingested by humans this toxin can cause severe health issues, which has forced many additional fisheries to close down. | 9 | Geochemistry |
The Grignard reaction is conducted under anhydrous conditions. Otherwise, the reaction will fail because the Grignard reagent will act as a base rather than a nucleophile and pick up a labile proton rather than attacking the electrophilic site. This will result in no formation of the desired product as the R-group of the Grignard reagent will become protonated while the MgX portion will stabilize the deprotonated species.
To prevent this, Grignard reactions are completed in an inert atmosphere to remove all water from the reaction flask and ensure that the desired product is formed. Additionally, if there are acidic protons in the starting material, as shown in the figure on the right, one can overcome this by protecting the acidic site of the reactant by turning it into an ether or a silyl ether to eliminate the labile proton from the solution prior to the Grignard reaction. | 0 | Organic Chemistry |
The archaeological record in Egypt, Peru and the Caucasus suggests that arsenical bronze was produced for a time alongside tin bronze. At Tepe Yahya its use continued into the Iron Age for the manufacture of trinkets and decorative objects, thus demonstrating that there was not a simple succession of alloys over time, with superior new alloys replacing older ones. There are few real advantages metallurgically for the superiority of tin bronze, and early authors suggested that arsenical bronze was phased out due to its health effects. It is more likely that it was phased out in general use because alloying with tin gave castings which had similar strength to arsenical bronze but did not require further work-hardening to achieve useful strength. It is also probable that more certain results could be achieved with the use of tin, because it could be added directly to the copper in specific amounts, whereas the precise amount of arsenic being added was much harder to gauge due to the manufacturing process. | 8 | Metallurgy |
The Hopkins-Cole reaction, also known as the glyoxylic acid reaction, is a chemical test used for detecting the presence of tryptophan in proteins. A protein solution is mixed with Hopkins Cole reagent, which consists of glyoxylic acid. Concentrated sulfuric acid is slowly added to form two layers. A purple ring appears between the two layers if the test is positive for tryptophan. Nitrites, chlorates, nitrates and excess chlorides prevent the reaction from occurring.
The reaction was first reported by Frederick Gowland Hopkins and Sydney W. Cole in 1901, as part of their work on the first isolation of tryptophan itself. | 3 | Analytical Chemistry |
Virtually any chemical may be found in water, but routine testing is commonly limited to a few chemical elements of unique significance. | 3 | Analytical Chemistry |
* Rh-catalyzed Trp and Cys alkylation
Using in situ generated Rh-carbenoid by activation of vinyl-substituted diazo compounds with Rh(OAc), tryptophans and cysteines were shown to be selectively alkylated in aqueous media.
However, this method is limited to surface tryptophans and cysteines possibly because of steric constraints.
* Ir-catalyzed Lys and N-terminus (reductive) alkylation
Imines formed from the condensation of aldehydes with lysines or the N-terminus can be reduced efficient by an water-stable [Cp*Ir(bipy)(HO)]SO complex in the presence of formate ions (serving as the hydride source). The reaction happens readily under physiologically relevant conditions and results in high conversion for various aromatic aldehydes.
* Pd-catalyzed Tyr O-alkylation
By using a pre-formed electrophilic π-allylpalladium(II) reagent derived from allylic acetate or carbamate precursors, selective allylic alkylation of tyrosines can be achieved in aqueous solution at room temperature and in the presence of cysteines.
* Au-catalyzed Cys alkylation
Cysteine-containing peptides have been shown to undergo 1,2-addition to allenes in the presence of gold(I) and/or silver(I) salts, producing hydroxyl substituted vinyl thioethers. The reaction with peptides proceeds with high yields and is selective for cysteines over other nucleophilic residues.
However, the reactivity towards proteins is much decreased, potentially due to the coordination of gold to the protein backbone. | 1 | Biochemistry |
The CHNO strychnine molecule contains 7 rings including an indoline system. It has a tertiary amine group, an amide, an alkene and an ether group. The naturally occurring compound is also chiral with 6 asymmetric carbon atoms including one quaternary one. | 0 | Organic Chemistry |
* Spinal neurons that pass over to the opposite side of the spinal cord.
* A protein complex that contains two or more different polypeptides. | 1 | Biochemistry |
The consideration of energy quality was a fundamental driver of industrialization from the 18th through 20th centuries. Consider for example the industrialization of New England in the 18th century. This refers to the construction of textile mills containing power looms for weaving cloth. The simplest, most economical and straightforward source of energy was provided by water wheels, extracting energy from a millpond behind a dam on a local creek. If another nearby landowner also decided to build a mill on the same creek, the construction of their dam would lower the overall hydraulic head to power the existing waterwheel, thus hurting power generation and efficiency. This eventually became an issue endemic to the entire region, reducing the overall profitability of older mills as newer ones were built. The search for higher quality energy was a major impetus throughout the 19th and 20th centuries. For example, burning coal to make steam to generate mechanical energy would not have been imaginable in the 18th century; by the end of the 19th century, the use of water wheels was long outmoded. Similarly, the quality of energy from electricity offers immense advantages over steam, but did not become economic or practical until the 20th century.
The above example focused on the economic impacts of the exploitation of energy. A similar scenario plays out in nature and biology, where living organisms can extract energy of varying quality from nature, ultimately driven by solar energy as the primary driver of thermodynamic disequilibrium on Earth. The ecological balance of ecosystems is predicated on the energy flows through the system. For example, rainwater drives the erosion of rocks, which liberates chemicals that can be used as nutrients; these are taken up by plankton, using solar energy to grow and thrive; whales obtain energy by eating plankton, thus indirectly using solar energy as well, but this time in a much more concentrated and higher quality form.
Water wheels are also driven by rainwater, via the solar evaporation-condensation water cycle; thus ultimately, industrial cloth-making was driven by the day-night cycle of solar irradiation. This is a holistic view of energy sources as a system-in-the-large. Thus, discussions of energy quality can sometimes be found in the Humanities, such as dialectics, Marxism and postmodernism. This is effectively because disciplines such as economics failed to recognize the thermodynamic inputs into the economy (now recognized as thermoeconomics), while disciplines such as physics and engineering were unable to address either the economic impacts of human activity, or the impacts of thermodynamic flows in biological ecosystems. Thus, the broad-stroke, global system-in-the-large discussions were taken up by those best trained for the nebulous, non-specific reasoning that such complex systems require. The resulting mismatch of vocabulary and outlook across disciplines can lead to considerable contention. | 7 | Physical Chemistry |
Members of the signal transducer and activator of transcription (STAT) protein family are intracellular transcription factors that mediate many aspects of cellular immunity, proliferation, apoptosis and differentiation. They are primarily activated by membrane receptor-associated Janus kinases (JAK). Dysregulation of this pathway is frequently observed in primary tumors and leads to increased angiogenesis which enhances the survival of tumors and immunosuppression. Gene knockout studies have provided evidence that STAT proteins are involved in the development and function of the immune system and play a role in maintaining immune tolerance and tumor surveillance. | 1 | Biochemistry |
An optical filter can be used to block out visible light and near-ultraviolet light. It is important to have a high transmittance within the solar-blind spectrum, but to strongly block the other wavelengths.
Interference filters can pass 25% of the wanted rays, and reduce others by 1000 to 10,000 times. However they are unstable and have a narrow field of view.
Absorption filters may only pass 10% of wanted UV, but can reject by a ratio of 10. They can have a wide field of view and are stable. | 5 | Photochemistry |
Early studies showed that individuals who swam in waters with geometric mean coliform densities above 2300/100 mL for three days had higher illness rates. In the 1960s, these numbers were converted to fecal coliform concentrations assuming 18 percent of total coliforms were fecal. Consequently, the National Technical Advisory Committee in the US recommended the following standard for recreational waters in 1968: 10 percent of total samples during any 30-day period should not exceed 400 fecal coliforms/100 mL or a log mean of 200/100 mL (based on a minimum of 5 samples taken over not more than a 30-day period).
Despite criticism, EPA recommended this criterion again in 1976, however, the Agency initiated numerous studies in the 1970s and 1980s to overcome the weaknesses of the earlier studies. In 1986, EPA revised its bacteriological ambient water quality criteria recommendations to include E. coli and enterococci.
Canadas National Agri-Environmental Standards Initiatives approach to characterizing risks associated with fecal water pollution bacterial water quality at agricultural sites is to compare these sites with those at reference sites away from human or livestock sources. This approach generally results in lower levels if E. coli being used as a standard or “benchmark” based on a study that indicated pathogens were detected in 80% of water samples with less than 100 cfu E. coli per 100 mL. | 3 | Analytical Chemistry |
In 1898, Scientific American published an article called Bessemer Steel and its Effect on the World explaining the significant economic effects of the increased supply in cheap steel. They noted that the expansion of railroads into previously sparsely inhabited regions of the country had led to settlement in those regions, and had made the trade of certain goods profitable, which had previously been too costly to transport.
The Bessemer process revolutionized steel manufacture by decreasing its cost, from £40 per long ton to £6–7 per long ton, along with greatly increasing the scale and speed of production of this vital raw material. The process also decreased the labor requirements for steel-making. Before it was introduced, steel was far too expensive to make bridges or the framework for buildings and thus wrought iron had been used throughout the Industrial Revolution. After the introduction of the Bessemer process, steel and wrought iron became similarly priced, and some users, primarily railroads, turned to steel. Quality problems, such as brittleness caused by nitrogen in the blowing air, prevented Bessemer steel from being used for many structural applications. Open-hearth steel was suitable for structural applications.
Steel greatly improved the productivity of railroads. Steel rails lasted ten times longer than iron rails. Steel rails, which became heavier as prices fell, could carry heavier locomotives, which could pull longer trains. Steel rail cars were longer and were able to increase the freight to car weight from 1:1 to 2:1. | 8 | Metallurgy |
Pyrimidines are ultimately catabolized (degraded) to CO, HO, and urea. Cytosine can be broken down to uracil, which can be further broken down to N-carbamoyl-β-alanine, and then to beta-alanine, CO, and ammonia by beta-ureidopropionase. Thymine is broken down into β-aminoisobutyrate which can be further broken down into intermediates eventually leading into the citric acid cycle.
β-aminoisobutyrate acts as a rough indicator for rate of DNA turnover. | 1 | Biochemistry |
Lithium is widely believed to prevent suicide, and often used in clinical practice towards that end. However, meta-analyses, faced with evidence-base limitations, have yielded differing results, and it therefore remains unclear whether or not lithium is efficacious in the prevention of suicide. | 1 | Biochemistry |
Hyperspectral data is often used to determine what materials are present in a scene. Materials of interest could include roadways, vegetation, and specific targets (i.e. pollutants, hazardous materials, etc.). Trivially, each pixel of a hyperspectral image could be compared to a material database to determine the type of material making up the pixel. However, many hyperspectral imaging platforms have low resolution (>5m per pixel) causing each pixel to be a mixture of several materials. The process of unmixing one of these mixed pixels is called hyperspectral image unmixing or simply hyperspectral unmixing.
A solution to hyperspectral unmixing is to reverse the mixing process. Generally, two models of mixing are assumed: linear and nonlinear.
Linear mixing models the ground as being flat and incident sunlight on the ground causes the materials to radiate some amount of the incident energy back to the sensor. Each pixel then, is modeled as a linear sum of all the radiated energy curves of materials making up the pixel. Therefore, each material contributes to the sensor's observation in a positive linear fashion. Additionally, a conservation of energy constraint is often observed thereby forcing the weights of the linear mixture to sum to one in addition to being positive. The model can be described mathematically as follows:
where represents a pixel observed by the sensor, is a matrix of material reflectance signatures (each signature is a column of the matrix), and is the proportion of material present in the observed pixel. This type of model is also referred to as a simplex.
With satisfying the two constraints:
1. Abundance Nonnegativity Constraint (ANC) - each element of x is positive.
2. Abundance Sum-to-one Constraint (ASC) - the elements of x must sum to one.
Non-linear mixing results from multiple scattering often due to non-flat surface such as buildings and vegetation.
There are many algorithms to unmix hyperspectral data each with their own strengths and weaknesses. Many algorithms assume that pure pixels (pixels which contain only one materials) are present in a scene.
Some algorithms to perform unmixing are listed below:
* Pixel Purity Index Works by projecting each pixel onto one vector from a set of random vectors spanning the reflectance space. A pixel receives a score when it represent an extremum of all the projections. Pixels with the highest scores are deemed to be spectrally pure.
* N-FINDR
* Gift Wrapping Algorithm
* Independent Component Analysis Endmember Extraction Algorithm - works by assuming that pure pixels occur independently than mixed pixels. Assumes pure pixels are present.
* Vertex Component Analysis - works on the fact that the affine transformation of a simplex is another simplex which helps to find hidden (folded) vertices of the simplex. Assumes pure pixels are present.
* Principal component analysis - could also be used to determine endmembers, projection on principal axes could permit endmember selection [Smith, Johnson et Adams (1985), Bateson et Curtiss (1996)]
* Multi endmembers spatial mixture analysis based on the SMA algorithm
* Spectral phasor analysis based on Fourier transformation of spectra and plotting them on a 2D plot.
Non-linear unmixing algorithms also exist: support vector machines or analytical neural network.
Probabilistic methods have also been attempted to unmix pixel through Monte Carlo unmixing algorithm.
Once the fundamental materials of a scene are determined, it is often useful to construct an abundance map of each material which displays the fractional amount of material present at each pixel. Often linear programming is done to observed ANC and ASC. | 7 | Physical Chemistry |
Recombinant DNA (rDNA) molecules are DNA molecules formed by laboratory methods of genetic recombination (such as molecular cloning) that bring together genetic material from multiple sources, creating sequences that would not otherwise be found in the genome.
Recombinant DNA is the general name for a piece of DNA that has been created by combining two or more fragments from different sources. Recombinant DNA is possible because DNA molecules from all organisms share the same chemical structure, differing only in the nucleotide sequence. Recombinant DNA molecules are sometimes called chimeric DNA because they can be made of material from two different species like the mythical chimera. rDNA technology uses palindromic sequences and leads to the production of sticky and blunt ends.
The DNA sequences used in the construction of recombinant DNA molecules can originate from any species. For example, plant DNA can be joined to bacterial DNA, or human DNA can be joined with fungal DNA. In addition, DNA sequences that do not occur anywhere in nature can be created by the chemical synthesis of DNA and incorporated into recombinant DNA molecules. Using recombinant DNA technology and synthetic DNA, any DNA sequence can be created and introduced into living organisms.
Proteins that can result from the expression of recombinant DNA within living cells are termed recombinant proteins. When recombinant DNA encoding a protein is introduced into a host organism, the recombinant protein is not necessarily produced. Expression of foreign proteins requires the use of specialized expression vectors and often necessitates significant restructuring by
foreign coding sequences.
Recombinant DNA differs from genetic recombination in that the former results from artificial methods while the latter is a normal biological process that results in the remixing of existing DNA sequences in essentially all organisms. | 1 | Biochemistry |
The symbol for pressure is usually or which may use a subscript to identify the pressure, and gas species are also referred to by subscript. When combined, these subscripts are applied recursively.
Examples:
* or = pressure at time 1
* or = partial pressure of hydrogen
* or or PO = arterial partial pressure of oxygen
* or or PO = venous partial pressure of oxygen | 7 | Physical Chemistry |
In grain-boundary strengthening, the grain boundaries act as pinning points impeding further dislocation propagation. Since the lattice structure of adjacent grains differs in orientation, it requires more energy for a dislocation to change directions and move into the adjacent grain. The grain boundary is also much more disordered than inside the grain, which also prevents the dislocations from moving in a continuous slip plane. Impeding this dislocation movement will hinder the onset of plasticity and hence increase the yield strength of the material.
Under an applied stress, existing dislocations and dislocations generated by Frank–Read sources will move through a crystalline lattice until encountering a grain boundary, where the large atomic mismatch between different grains creates a repulsive stress field to oppose continued dislocation motion. As more dislocations propagate to this boundary, dislocation pile up occurs as a cluster of dislocations are unable to move past the boundary. As dislocations generate repulsive stress fields, each successive dislocation will apply a repulsive force to the dislocation incident with the grain boundary. These repulsive forces act as a driving force to reduce the energetic barrier for diffusion across the boundary, such that additional pile up causes dislocation diffusion across the grain boundary, allowing further deformation in the material. Decreasing grain size decreases the amount of possible pile up at the boundary, increasing the amount of applied stress necessary to move a dislocation across a grain boundary. The higher the applied stress needed to move the dislocation, the higher the yield strength. Thus, there is then an inverse relationship between grain size and yield strength, as demonstrated by the Hall-Petch equation. However, when there is a large direction change in the orientation of the two adjacent grains, the dislocation may not necessarily move from one grain to the other but instead create a new source of dislocation in the adjacent grain. The theory remains the same that more grain boundaries create more opposition to dislocation movement and in turn strengthens the material.
Obviously, there is a limit to this mode of strengthening, as infinitely strong materials do not exist. Grain sizes can range from about (large grains) to (small grains). Lower than this, the size of dislocations begins to approach the size of the grains. At a grain size of about , only one or two dislocations can fit inside a grain (see Figure 1 above). This scheme prohibits dislocation pile-up and instead results in grain boundary diffusion. The lattice resolves the applied stress by grain boundary sliding, resulting in a decrease in the material's yield strength.
To understand the mechanism of grain boundary strengthening one must understand the nature of dislocation-dislocation interactions. Dislocations create a stress field around them given by:
where G is the material's shear modulus, b is the Burgers vector, and r is the distance from the dislocation. If the dislocations are in the right alignment with respect to each other, the local stress fields they create will repel each other. This helps dislocation movement along grains and across grain boundaries. Hence, the more dislocations are present in a grain, the greater the stress field felt by a dislocation near a grain boundary:
Interphase boundaries can also contribute to grain boundary strengthening, particularly in composite materials and precipitation-hardened alloys. Coherent IPBs, in particular, can provide additional barriers to dislocation motion, similar to grain boundaries. In contrast, non-coherent IPBs and partially coherent IPBs can act as sources of dislocations, which can lead to localized deformation and affect the mechanical properties of the material. | 8 | Metallurgy |
Photobiologically Active Radiation (PBAR) is a range of light energy beyond and including PAR. Photobiological Photon Flux (PBF) is the metric used to measure PBAR. | 5 | Photochemistry |
Water is said to "boil" when bubbles of water vapor grow without bound, bursting at the surface. For a vapor bubble to expand, the temperature must be high enough that the vapor pressure exceeds the ambient pressure (the atmospheric pressure, primarily). Below that temperature, a water vapor bubble will shrink and vanish.
Superheating is an exception to this simple rule; a liquid is sometimes observed not to boil even though its vapor pressure does exceed the ambient pressure. The cause is an additional force, the surface tension, which suppresses the growth of bubbles.
Surface tension makes the bubble act like an elastic balloon. The pressure inside is raised slightly by the "skin" attempting to contract. For the bubble to expand, the temperature must be raised slightly above the boiling point to generate enough vapor pressure to overcome both surface tension and ambient pressure.
What makes superheating so explosive is that a larger bubble is easier to inflate than a small one; just as when blowing up a balloon, the hardest part is getting started. It turns out the excess pressure due to surface tension is inversely proportional to the diameter of the bubble. That is, .
This can be derived by imagining a plane cutting a bubble into two halves. Each half is pulled towards the middle with a surface tension force , which must be balanced by the force from excess pressure . So we obtain , which simplifies to .
This means if the largest bubbles in a container are small, only a few micrometres in diameter, overcoming the surface tension may require a large , requiring exceeding the boiling point by several degrees Celsius. Once a bubble does begin to grow, the surface tension pressure decreases, so it expands explosively in a positive feedback loop. In practice, most containers have scratches or other imperfections which trap pockets of air that provide starting bubbles, and impure water containing small particles can also trap air pockets. Only a smooth container of purified liquid can reliably superheat. | 7 | Physical Chemistry |
Parasympatholytic drugs are sometimes used to treat slow heart rhythms (bradycardias or bradydysrhythmias) caused by myocardial infarctions or other pathologies, as well as to treat conditions that cause bronchioles in the lung to constrict, such as asthma. By blocking the parasympathetic nervous system, parasympatholytic drugs can increase heart rate in patients with bradycardic heart rhythms, and open up airways and reduce mucous production in patients with asthma. | 1 | Biochemistry |
In 1801, John Dalton published the law of partial pressures from his work with ideal gas law relationship: The pressure of a mixture of non reactive gases is equal to the sum of the pressures of all of the constituent gases alone. Mathematically, this can be represented for n species as:
: Pressure = Pressure + Pressure + ... + Pressure
The image of Dalton's journal depicts symbology he used as shorthand to record the path he followed. Among his key journal observations upon mixing unreactive "elastic fluids" (gases) were the following:
*Unlike liquids, heavier gases did not drift to the bottom upon mixing.
*Gas particle identity played no role in determining final pressure (they behaved as if their size was negligible). | 7 | Physical Chemistry |
The vapor pressure of a liquid, which varies with its temperature, is a measure of how much the vapor of the liquid tends to concentrate in the surrounding atmosphere as the liquid evaporates. Vapor pressure is a major determinant of the flash point and flame point, with higher vapor pressures leading to lower flash points and higher flammability ratings. | 7 | Physical Chemistry |
One type of organelle can turn nitrogen gas into a biologically available form. This nitroplast was discovered in algae. | 1 | Biochemistry |
* "A Study of Grain Shape", Journal of Metals, July 1952, 775.
* "Stereoscopic Microradiography", Metallurgia, 63, 95, 1961.
* "Careers in the Canadian Minerals Industry", Northern Miner, December 1980.
* “An Historical Sketch of the Canadian Steel Industry.” In All That Glitters: Readings in Historical Metallurgy, edited by Michael L. Wayman, 143-146. Montreal: Canadian Institute of Mining and Metallurgy, 1989
* "Observations on an Old Broad Axe - An Example of Steeling", Bulletin of the Canadian Institute of Mining and Metallurgy, Vol. 83, No. 934, pp. 93–95, January 1990. | 8 | Metallurgy |
Deuterium HCL or even hydrogen HCL and deuterium discharge lamps are used in LS AAS for background correction purposes. The radiation intensity emitted by these lamps decreases significantly with increasing wavelength, so that they can be only used in the wavelength range between 190 and about 320 nm. | 3 | Analytical Chemistry |
After pelleting, the pellets are cooled with a cooler to bring the temperature of the feed down. Other post pelleting applications include post-pelleting conditioning, sorting via a screen, and maybe coating if required. | 8 | Metallurgy |
The concentration of HCFC-142b in the atmosphere grew to over 20 parts per trillion by year 2010. It has an ozone depletion potential (ODP) of 0.07. This is low compared to the ODP=1 of trichlorofluoromethane (CFC-11, R-11), which also grew about ten times more abundant in the atmosphere by year 1985 (prior to introduction of HFC-142b and the Montreal Protocol).
HFC-142b is also a minor but potent greenhouse gas. It has an estimated lifetime of about 17 years and a 100-year global warming potential ranging 2300 to 5000. This compares to the GWP=1 of carbon dioxide, which had a much greater atmospheric concentration near 400 parts per million in year 2020. | 2 | Environmental Chemistry |
The mammalian target of rapamycin (mTOR), also referred to as the mechanistic target of rapamycin, and sometimes called FK506-binding protein 12-rapamycin-associated protein 1 (FRAP1), is a kinase that in humans is encoded by the MTOR gene. mTOR is a member of the phosphatidylinositol 3-kinase-related kinase family of protein kinases.
mTOR links with other proteins and serves as a core component of two distinct protein complexes, mTOR complex 1 and mTOR complex 2, which regulate different cellular processes. In particular, as a core component of both complexes, mTOR functions as a serine/threonine protein kinase that regulates cell growth, cell proliferation, cell motility, cell survival, protein synthesis, autophagy, and transcription. As a core component of mTORC2, mTOR also functions as a tyrosine protein kinase that promotes the activation of insulin receptors and insulin-like growth factor 1 receptors. mTORC2 has also been implicated in the control and maintenance of the actin cytoskeleton. | 1 | Biochemistry |
Molecularity in chemistry is the number of colliding molecular entities that are involved in a single reaction step.
* A reaction step involving one molecular entity is called unimolecular.
* A reaction step involving two molecular entities is called bimolecular.
* A reaction step involving three molecular entities is called trimolecular or termolecular.
In general, reaction steps involving more than three molecular entities do not occur, because is statistically improbable in terms of Maxwell distribution to find such a transition state. | 7 | Physical Chemistry |
A crystal cluster is a group of crystals which are formed in an open space environment and exhibit euhedral crystal form determined by their internal crystal structure. A cluster of small crystals coating the walls of a cavity are called druse. | 3 | Analytical Chemistry |
The earliest mention came in 1911, when German chemist Dr. Alexander Eibner integrated the concept in his research of the illumination of zinc oxide (ZnO) on the bleaching of the dark blue pigment, Prussian blue. Around this time, Bruner and Kozak published an article discussing the deterioration of oxalic acid in the presence of uranyl salts under illumination, while in 1913, Landau published an article explaining the phenomenon of photocatalysis. Their contributions led to the development of actinometric measurements, measurements that provide the basis of determining photon flux in photochemical reactions. After a hiatus, in 1921, Baly et al. used ferric hydroxides and colloidal uranium salts as catalysts for the creation of formaldehyde under visible light.
In 1938 Doodeve and Kitchener discovered that , a highly-stable and non-toxic oxide, in the presence of oxygen could act as a photosensitizer for bleaching dyes, as ultraviolet light absorbed by led to the production of active oxygen species on its surface, resulting in the blotching of organic chemicals via photooxidation. This was the first observation of the fundamental characteristics of heterogeneous photocatalysis. | 5 | Photochemistry |
Satellite images show that storms over Australian, African, and Asian deserts create dust plumes which can carry dust to altitudes of over 5 kilometers above the Earth's surface. This mechanism transports the material thousands of kilometers away, even moving it between continents. Multiple studies have supported the theory that bioaerosols can be carried along with dust. One study concluded that a type of airborne bacteria present in a particular desert dust was found at a site 1,000 kilometers downwind.
Possible global scale highways for bioaerosols in dust include:
* Storms over Northern Africa picking up dust, which can then be blown across the Atlantic to the Americas, or north to Europe. For transatlantic transport, there is a seasonal shift in the destination of the dust: North America during the summer, and South America during the winter.
* Dust from the Gobi and Taklamakan deserts is transported to North America, mainly during the Northern Hemisphere spring.
* Dust from Australia is carried out into the Pacific Ocean, with the possibility of being deposited in New Zealand. | 7 | Physical Chemistry |
An enyne is an organic compound containing a double bond (alkene) and a triple bond (alkyne). It is called a conjugated enyne when the double and triple bonds are conjugated.
The term is a contraction of the terms alkene and alkyne.
The simplest enyne is vinylacetylene. | 0 | Organic Chemistry |
Each year, approximately 0.3 gigatons of elemental sulfur is converted into organic matter by photosynthetic organisms. This organic sulfur is allocated into a diversity of compounds such as amino acids – namely cysteine (Cys) and methionine (Met) – proteins, cofactors, antioxidants, sulfate groups, Fe-S centers and secondary metabolites. The three main sources of sulfur are atmospheric, soil, and aquatic.
Most vegetation can acquire sulfur from gaseous atmospheric compounds or various ions either in soil solutions or water bodies. Uptake of gaseous and dissolved sulfur compounds apparently occurs with little accompanying isotopic selectivity. Dissolved sulfate (SO) is considered to be the central pool which is metabolized by microorganisms and plants as most forms of atmospheric sulfur is oxidized into sulfate. Atmospheric sulfur is eventually returned to the soil when it is scrubbed from the atmosphere during precipitation or through dryfall. | 9 | Geochemistry |
Defective function of the survival of motor neuron (SMN) protein in snRNP biogenesis, caused by a genetic defect in the SMN1 gene which codes for SMN, may account for the motor neuron pathology observed in the genetic disorder spinal muscular atrophy. | 1 | Biochemistry |
The formation of a hydroxo complex is a typical example of a hydrolysis reaction. A hydrolysis reaction is one in which a substrate reacts with water, splitting a water molecule into hydroxide and hydrogen ions. In this case the hydroxide ion then forms a complex with the substrate.
In water the concentration of hydroxide is related to the concentration of hydrogen ions by the self-ionization constant, K.
The expression for hydroxide concentration is substituted into the formation constant expression
In general, for the reaction
In the older literature the value of log K is usually cited for an hydrolysis constant. The log β value is usually cited for an hydrolysed complex with the generic chemical formula ML(OH). | 7 | Physical Chemistry |
Sepiapterin reductase deficiency is an inherited pediatric disorder characterized by movement problems, and most commonly displayed as a pattern of involuntary sustained muscle contractions known as dystonia. Symptoms are usually present within the first year of age, but diagnosis is delayed due to physicians lack of awareness and the specialized diagnostic procedures. Individuals with this disorder also have delayed motor skills development including sitting, crawling, and need assistance when walking. Additional symptoms of this disorder include intellectual disability, excessive sleeping, mood swings, and an abnormally small head size. SR deficiency is a very rare condition. The first case was diagnosed in 2001, and since then there have been approximately 30 reported cases. At this time, the condition seems to be treatable, but the lack of overall awareness and the need for a series of atypical procedures used to diagnose this condition pose a dilemma. | 1 | Biochemistry |
Entropy is a function of state, and therefore the entropy change can be computed directly from the knowledge of the final and initial equilibrium states. For an ideal gas, the change in entropy is the same as for isothermal expansion where all heat is converted to work:
For an ideal monatomic gas, the entropy as a function of the internal energy , volume , and number of moles is given by the Sackur–Tetrode equation:
In this expression is the particle mass and Planck's constant. For a monatomic ideal gas , with the molar heat capacity at constant volume.
A second way to evaluate the entropy change is to choose a route from the initial state to the final state where all the intermediate states are in equilibrium. Such a route can only be realized in the limit where the changes happen infinitely slowly. Such routes are also referred to as quasistatic routes. In some books one demands that a quasistatic route has to be reversible, here we don't add this extra condition. The net entropy change from the initial state to the final state is independent of the particular choice of the quasistatic route, as the entropy is a function of state.
Here is how we can effect the quasistatic route. Instead of letting the gas undergo a free expansion in which the volume is doubled, a free expansion is allowed in which the volume expands by a very small amount . After thermal equilibrium is reached, we then let the gas undergo another free expansion by and wait until thermal equilibrium is reached. We repeat this until the volume has been doubled. In the limit to zero, this becomes an ideal quasistatic process, albeit an irreversible one. Now, according to the fundamental thermodynamic relation, we have:
As this equation relates changes in thermodynamic state variables, it is valid for any quasistatic change, regardless of whether it is irreversible or reversible. For the above defined path we have that and thus , and hence the increase in entropy for the Joule expansion is
A third way to compute the entropy change involves a route consisting of reversible adiabatic expansion followed by heating. We first let the system undergo a reversible adiabatic expansion in which the volume is doubled. During the expansion, the system performs work and the gas temperature goes down, so we have to supply heat to the system equal to the work performed to bring it to the same final state as in case of Joule expansion.
During the reversible adiabatic expansion, we have . From the classical expression for the entropy it can be derived that the temperature after the doubling of the volume at constant entropy is given as:
for the monoatomic ideal gas. Heating the gas up to the initial temperature increases the entropy by the amount
We might ask what the work would be if, once the Joule expansion has occurred, the gas is put back into the left-hand side by compressing it. The best method (i.e. the method involving the least work) is that of a reversible isothermal compression, which would take work given by
During the Joule expansion the surroundings do not change, i.e. the entropy of the surroundings is constant. Therefore the entropy change of the so-called "universe" is equal to the entropy change of the gas which is . | 7 | Physical Chemistry |
The IscR stability element is a conserved secondary structure found in the intergenic regions of iscRSUA polycistronic mRNA. This secondary structure prevents the degradation of the iscR mRNA.
The iscRSUA operon encodes for the proteins required in iron–sulfur cluster biosynthesis where the expression of this operon is regulated by RyhB and iscR, a transcription repressor. Under sufficient iron conditions RyhB binds to iscRSUA mRNA and promotes the degradation of the mRNA located downstream of iscR. Scanning the intergenic regions of this polycistronic mRNA and using Mfold software a secondary structure was predicted within the intergenic region between iscR and iscS and later confirmed by lead acetate probing. Mutations that disrupt this secondary structure resulted in the degradation of iscR mRNA after RyhB binding. 3′ RACE analysis of the iscR mRNA fragment identified the intergenic RNA at the 3′ end. These results suggest that this intergenic RNA element acts as an iscR mRNA stability element by protecting iscR from exonuclease degradation. | 1 | Biochemistry |
The growth rate hypothesis, also known as the resource availability hypothesis, states that defense strategies are determined by the inherent growth rate of the plant, which is in turn determined by the resources available to the plant. A major assumption is that available resources are the limiting factor in determining the maximum growth rate of a plant species. This model predicts that the level of defense investment will increase as the potential of growth decreases. Additionally, plants in resource-poor areas, with inherently slow-growth rates, tend to have long-lived leaves and twigs, and the loss of plant appendages may result in a loss of scarce and valuable nutrients.
One test of this model involved a reciprocal transplants of seedlings of 20 species of trees between clay soils (nutrient rich) and white sand (nutrient poor) to determine whether trade-offs between growth rate and defenses restrict species to one habitat. When planted in white sand and protected from herbivores, seedlings originating from clay outgrew those originating from the nutrient-poor sand, but in the presence of herbivores the seedlings originating from white sand performed better, likely due to their higher levels of constitutive carbon-based defenses. These finding suggest that defensive strategies limit the habitats of some plants. | 1 | Biochemistry |
Henri Moissan was the first to isolate the element, observing its gaseous phase. Solid fluorine received significant study in the 1920s and 30s, but relatively less until the 1960s. The crystal structure of alpha-fluorine given, which still has some uncertainty, dates to a 1970 paper by Linus Pauling. | 7 | Physical Chemistry |
New knowledge about the chemistry of soils often comes from studies in the laboratory, in which soil samples taken from undisturbed soil horizons in the field are used in experiments that include replicated treatments and controls. In many cases, the soil samples are air dried at ambient temperatures (e.g., ) and sieved to a 2 mm size prior to storage for further study. Such drying and sieving soil samples markedly disrupts soil structure, microbial population diversity, and chemical properties related to pH, oxidation-reduction status, manganese oxidation state, and dissolved organic matter; among other properties. Renewed interest in recent decades has led many soil chemists to maintain soil samples in a field-moist condition and stored at under aerobic conditions before and during investigations.
Two approaches are frequently used in laboratory investigations in soil chemistry. The first is known as batch equilibration. The chemist adds a given volume of water or salt solution of known concentration of dissolved ions to a mass of soil (e.g., 25–mL of solution to 5–g of soil in a centrifuge tube or flask). The soil slurry then is shaken or swirled for a given amount of time (e.g., 15 minutes to many hours) to establish a steady state or equilibrium condition prior to filtering or centrifuging at high speed to separate sand grains, silt particles, and clay colloids from the equilibrated solution. The filtrate or centrifugate then is analyzed using one of several methods, including ion specific electrodes, atomic absorption spectrophotometry, inductively coupled plasma spectrometry, ion chromatography, and colorimetric methods. In each case, the analysis quantifies the concentration or activity of an ion or molecule in the solution phase, and by multiplying the measured concentration or activity (e.g., in mg ion/mL) by the solution-to-soil ratio (mL of extraction solution/g soil), the chemist obtains the result in mg ion/g soil. This result based on the mass of soil allows comparisons between different soils and treatments. A related approach uses a known volume to solution to leach (infiltrate) the extracting solution through a quantity of soil in small columns at a controlled rate to simulate how rain, snow meltwater, and irrigation water pass through soils in the field. The filtrate then is analyzed using the same methods as used in batch equilibrations.
Another approach to quantifying soil processes and phenomena uses in situ methods that do not disrupt the soil. as occurs when the soil is shaken or leached with an extracting soil solution. These methods usually use surface spectroscopic techniques, such as Fourier transform infrared spectroscopy, nuclear magnetic resonance, Mössbauer spectroscopy, and X-ray spectroscopy. These approaches aim to obtain information on the chemical nature of the mineralogy and chemistry of particle and colloid surfaces, and how ions and molecules are associated with such surfaces by adsorption, complexation, and precipitation.
These laboratory experiments and analyses have an advantage over field studies in that chemical mechanisms on how ions and molecules react in soils can be inferred from the data. One can draw conclusions or frame new hypotheses on similar reactions in different soils with diverse textures, organic matter contents, types of clay minerals and oxides, pH, and drainage condition. Laboratory studies have the disadvantage that they lose some of the realism and heterogeneity of undisturbed soil in the field, while gaining control and the power of extrapolation to unstudied soil. Mechanistic laboratory studies combined with more realistic, less controlled, observational field studies often yield accurate approximations of the behavior and chemistry of the soils that may be spatially heterogeneous and temporally variable. Another challenge faced by soil chemists is how microbial populations and enzyme activity in field soils may be changed when the soil is disturbed, both in the field and laboratory, particularly when soils samples are dried prior to laboratory studies and analysis. | 9 | Geochemistry |
To describe the Hund's coupling cases, we use the following angular momenta (where boldface letters indicate vector quantities):
*, the electronic orbital angular momentum
*, the electronic spin angular momentum
*, the total electronic angular momentum
*, the rotational angular momentum of the nuclei
*, the total angular momentum of the system (exclusive of nuclear spin)
*, the total angular momentum exclusive of electron (and nuclear) spin
These vector quantities depend on corresponding quantum numbers whose values are shown in molecular term symbols used to identify the states. For example, the term symbol Π denotes a state with S = 1/2, Λ = 1 and J = 3/2. | 7 | Physical Chemistry |
Corrosion engineering is an engineering specialty that applies scientific, technical, engineering skills, and knowledge of natural laws and physical resources to design and implement materials, structures, devices, systems, and procedures to manage corrosion.
From a holistic perspective, corrosion is the phenomenon of metals returning to the state they are found in nature. The driving force that causes metals to corrode is a consequence of their temporary existence in metallic form. To produce metals starting from naturally occurring minerals and ores, it is necessary to provide a certain amount of energy, e.g. Iron ore in a blast furnace. It is therefore thermodynamically inevitable that these metals when exposed to various environments would revert to their state found in nature. Corrosion and corrosion engineering thus involves a study of chemical kinetics, thermodynamics, electrochemistry and materials science. | 8 | Metallurgy |
The carboalumination reaction is most commonly catalyzed by zirconocene dichloride (or related catalyst). Some carboaluminations are performed with titanocene complexes. This reaction is sometimes referred to as the Zr- catalyzed asymmetric carboalumination of alkenes (ZACA) or the Zr-catalyzed methylalumination of alkynes (ZMA).
The most common trialkyl aluminum reagents for this transformation are trimethylaluminium, triethylaluminium, and sometimes triisobutylaluminium. When using trialkylaluminum reagents that have beta-hydrides, eliminations and hydroaluminum reactions become competing processes. The general mechanism of the ZMA reaction can be described as first the formation of the active catalytic species from the pre-catalyst zirconocene dichloride through its reaction with trimethyl aluminum. First transmetalation of a methyl from the aluminum to the zirconium occurs. Next, chloride abstraction by aluminum creates a cationic zirconium species that is closely associated with an anionic aluminum complex. This zirconium cation can coordinate an alkene or alkyne where migratory insertion of a methyl then takes place. The resultant vinyl or alkyl zirconium species can undergo a reversible, but stereoretentive transmetalation with an organoaluminum to provide the carboalumination product and regeneration of the zirconcene dichloride catalyst. This process generally provides the syn-addition product; however, conditions exist to provide the anti-addition product though a modified mechanism.
Trimethylsilyl (TMS) protected alkynes, trimethyl germanium alkynes, and terminal alkynes can produce anti-carboalumination products at room temperature or elevated temperatures if a coordinating group is nearby on the substrate. In these reactions, first syn-carboalumination takes place under the previously outlined mechanism. Then, another equivalent of aluminum that is coordinated to the directing group can displace the vinyl aluminum, inverting the geometry at the carbon where displacement takes place.
This forms a thermodynamically favorable metallacycle to prevent subsequent inversions. Formally, this process provides anti-carboalumination products that can be quenched with electrophiles. A limitation of this methodology is that the directing group must be sufficiently close to the carbon-carbon π-bond to form a thermodynamically favorable ring or else mixtures of geometric isomers will form.
The carboalumination of alkenes to form substituted alkanes can be rendered enantioselective if prochiral alkenes are used. In these reactions, a chiral indenyl zirconium catalyst is used to induce enantioselectivity. In these reactions, high enantioselectivities were obtained for several trialkyl aluminum reagents, however, the yield decreases dramatically with each additional carbon of the alkyl chain on the trialkyl aluminum reagent. | 0 | Organic Chemistry |
Because of their sequence similarity and operon structure, many two-component systems – particularly histidine kinases – are relatively easy to identify through bioinformatics analysis. (By contrast, eukaryotic kinases are typically easily identified, but they are not easily paired with their substrates.) A database of prokaryotic two-component systems called P2CS has been compiled to document and classify known examples, and in some cases to make predictions about the cognates of "orphan" histidine kinase or response regulator proteins that are genetically unlinked to a partner. | 1 | Biochemistry |
Indirect immunoperoxidase assay (IPA) is a laboratory technique used to detect and titrate viruses that do not cause measurable cytopathic effects and cannot be measured by classical plaque assays. These viruses include human coronavirus 229E and OC43. | 1 | Biochemistry |
:These are used for high-temperature FT synthesis (nearly 340 °C) to produce low-molecular-weight unsaturated hydrocarbons on alkalized fused iron catalysts. The fluid-bed technology (as adapted from the catalytic cracking of heavy petroleum distillates) was introduced by Hydrocarbon Research in 1946–50 and named the Hydrocol process. A large scale Fischer–Tropsch Hydrocol plant (350,000 tons per annum) operated during 1951–57 in Brownsville, Texas. Due to technical problems, and impractical economics due to increasing petroleum availability, this development was discontinued. Fluid-bed FT synthesis has been reinvestigated by Sasol. One reactor with a capacity of 500,000 tons per annum is in operation. The process has been used for C and C alkene production. A high-temperature process with a circulating iron catalyst (circulating fluid bed, riser reactor, entrained catalyst process) was introduced by the Kellogg Company and a respective plant built at Sasol in 1956. It was improved by Sasol for successful operation. At Secunda, South Africa, Sasol operated 16 advanced reactors of this type with a capacity of approximately 330,000 tons per annum each. The circulating catalyst process can be replaced by fluid-bed technology. Early experiments with cobalt catalyst particles suspended in oil have been performed by Fischer. The bubble column reactor with a powdered iron slurry catalyst and a CO-rich syngas was particularly developed to pilot plant scale by Kölbel at the Rheinpreuben Company in 1953. Since 1990, low-temperature FT slurry processes are under investigation for the use of iron and cobalt catalysts, particularly for the production of a hydrocarbon wax, or to be hydrocracked and isomerized to produce diesel fuel, by Exxon and Sasol. Slurry-phase (bubble column) low-temperature FT synthesis is efficient. This technology is also under development by the Statoil Company (Norway) for use on a vessel to convert associated gas at offshore oil fields into a hydrocarbon liquid. | 0 | Organic Chemistry |
A variational principle in physics, such as the principle of least action or Fermat's principle in optics, allows one to describe the system in a global manner and to solve it using the calculus of variations. In thermodynamics, such a principle would allow a Lagrangian formulation. The Gouy-Stodola theorem can be used as the basis for such a variational principle, in thermodynamics. It has been proven to satisfy the necessary conditions.
This is fundamentally different from most of the theorems other uses - here, it isnt being applied in order to locate components with irreversibilities or loss of exergy, but rather helps give some more general information about the system. | 7 | Physical Chemistry |
Radon has been produced commercially for use in radiation therapy, but for the most part has been replaced by radionuclides made in particle accelerators and nuclear reactors. Radon has been used in implantable seeds, made of gold or glass, primarily used to treat cancers.
The gold seeds were produced by filling a long tube with radon pumped from a radium source, the tube being then divided into short sections by crimping and cutting. The gold layer keeps the radon within, and filters out the alpha and beta radiation, while allowing the gamma rays to escape (which kill the diseased tissue). The activities might range from 2 to 200 MBq/seed. The gamma rays are produced by radon and the first short-lived elements of its decay chain (Po, Pb, Bi, Po).
Radon and its first decay products being very short-lived, the seed is left in place. After 11 half-lives (42 days), radon radioactivity is at 1/2 000 of its original level. At this stage, the predominant residual activity is due to the radon decay product Pb, whose half-life (22.3 years) is 2 000 times that of radon, and its descendants Bi and Po, totalling 0.03% of the initial seed activity. | 2 | Environmental Chemistry |
The journal is abstracted and indexed in:
*Biological Abstracts
*BIOSIS Previews
*CAB Abstracts
*Chemical Abstracts Service
*Current Contents/Agriculture, Biology & Environmental Sciences
*Current Contents/Physical Chemical & Earth Sciences
*Science Citation Index Expanded
*Scopus
According to the Journal Citation Reports, the journal has a 2017 impact factor of 2.923. | 9 | Geochemistry |
The CBS catalyst can be prepared from diphenylprolinol, condensed with a phenylboronic acid, or with borane (as shown below). The CBS catalyst then complexes in situ with borane to give the active catalyst. | 0 | Organic Chemistry |
The vertebrate neural retina composed of several layers and distinct cell types (see anatomy of the human retina). A number of these cell types are implicated in retinal diseases, including retinal ganglion cells, which degenerate in glaucoma, the rod and cone photoreceptors, which are responsive to light and degenerate in retinitis pigmentosa, macular degeneration, and other retinal diseases, and the retinal pigment epithelium (RPE), which supports the photoreceptors and is also implicated in retinitis pigmentosa and macular degeneration.
In retinal gene therapy, AAV is capable of "transducing" these various cell types by entering the cells and expressing the therapeutic DNA sequence. Since the cells of the retina are non-dividing, AAV continues to persist and provide expression of the therapeutic DNA sequence over a long time period that can last several years. | 1 | Biochemistry |
Imprint nanolithography also utilizes templates, pressing a hard mold into a polymer above the polymer glass transition temperature (Tg). Thus, the driving forces for this type of fabrication are heat and high pressure. Porous templates consisting of aluminum with anodized aluminum oxide (a hard mold) were used to imprint polystyrene. To achieve this, the polystyrene was heated well above its Tg to 130 degrees Celsius and pressed against the template. The template was then removed by dissolving the aluminum and producing either nanoemboss or nanofiber surfaces. Increasing the aspect ratio of the nanofibers disrupted the uniform hexagonal pattern and caused the fibers to form bundles. Ultimately, the longest nanofibers resulted in the greatest surface roughness, which significantly decreased surface wettability. | 7 | Physical Chemistry |
There are several on-line software and databases available for glycomic research. This includes:
* GlyCosmos
* GlyTouCan
* GlycomeDB
* UniCarb-DB | 0 | Organic Chemistry |
In 1977 J.M Whatley proposed a plastid development cycle which said that plastid development is not always unidirectional but is instead a complicated cyclic process. Proplastids are the precursor of the more differentiated forms of plastids, as shown in the diagram to the right. | 5 | Photochemistry |
Esters are widespread in nature and are widely used in industry. In nature, fats are, in general, triesters derived from glycerol and fatty acids. Esters are responsible for the aroma of many fruits, including apples, durians, pears, bananas, pineapples, and strawberries. Several billion kilograms of polyesters are produced industrially annually, important products being polyethylene terephthalate, acrylate esters, and cellulose acetate. | 0 | Organic Chemistry |
Plasma processing, corona treatment, and flame treatment can all be classified as surface oxidation mechanisms. These methods all involve cleavage of polymer chains in the material and the incorporation of carbonyl, and hydroxyl functional groups. The incorporation of oxygen into the surface creates a higher surface energy allowing the substrate to be coated. | 7 | Physical Chemistry |
The first studies measuring drugs in biological fluids were carried out to determine possible overdosing as part of the new science of forensic medicine/toxicology.
Initially, nonspecific assays were applied to measuring drugs in biological fluids. These were unable to discriminate between the drug and its metabolites; for example, aspirin () and sulfonamides (developed in the 1930s) were quantified by the use of colorimetric assays. Antibiotics were quantified by their ability to inhibit bacterial growth. The 1930s also saw the rise of pharmacokinetics, and as such the desire for more specific assays. Modern drugs are more potent, which has required more sensitive bioanalytical assays to accurately and reliably determine these drugs at lower concentrations. This has driven improvements in technology and analytical methods. | 3 | Analytical Chemistry |
The Unruh temperature, sometimes called the Davies–Unruh temperature, was derived separately by Paul Davies and William Unruh and is the effective temperature experienced by a uniformly accelerating detector in a vacuum field. It is given by
where is the reduced Planck constant, is the proper uniform acceleration, is the speed of light, and is the Boltzmann constant. Thus, for example, a proper acceleration of corresponds approximately to a temperature of . Conversely, an acceleration of corresponds to a temperature of .
The Unruh temperature has the same form as the Hawking temperature with denoting the surface gravity of a black hole, which was derived by Stephen Hawking in 1974. In the light of the equivalence principle, it is, therefore, sometimes called the Hawking–Unruh temperature.
Solving the Unruh temperature for the uniform acceleration, it can be expressed as
where is Planck acceleration and is Planck temperature. | 7 | Physical Chemistry |
Sticky end links are different in their stability. Free energy of formation can be measured to estimate stability. Free energy approximations can be made for different sequences from data related to oligonucleotide UV thermal denaturation curves. Also predictions from molecular dynamics simulations show that some sticky end links are much stronger in stretch than the others. | 1 | Biochemistry |
Some catastrophins affect catastrophe by binding to the ends of microtubules and promoting the dissociation of tubulin dimers.
Different mathematical models of microtubule development are being developed to take into account in vitro and in vivo observations. Meanwhile, there are new in vitro models of microtubule polymerization dynamics, of which catastrophins take a part in, being tested to emulate in vivo behaviors of microtubules. | 1 | Biochemistry |
The finding of a potential sperm donor and motivating them to actually donate sperm is typically called recruitment. A sperm bank can recruit donors by advertising, often in colleges, in local newspapers, and also on the internet.
A donor must be a fit and healthy male, normally between 18 and 45 years of age, and willing to undergo frequent and rigorous testing. The donor must also be willing to donate their sperm so that it can be used to impregnate people who are unrelated to and unknown by them. Some sperm banks require two screenings and a laboratory screening before a donor is eligible. The donor must agree to relinquish all legal rights to all children which result from their donations. The donor must produce their sperm at the sperm bank thus enabling the identity of the donor, once proven, always to be ascertained, and also enabling fresh samples of sperm to be produced for immediate processing. Some sperm banks have been accused of heightism due to minimum height requirements. | 1 | Biochemistry |
The same triad geometries been converged upon by serine proteases such as the chymotrypsin and subtilisin superfamilies. Similar convergent evolution has occurred with cysteine proteases such as viral C3 protease and papain superfamilies. These triads have converged to almost the same arrangement due to the mechanistic similarities in cysteine and serine proteolysis mechanisms.
Families of cysteine proteases
Families of serine proteases | 1 | Biochemistry |
Work on aequorin began with E. Newton Harvey in 1921. Though Harvey was unable to demonstrate a classical luciferase-luciferin reaction, he showed that water could produce light from dried photocytes and that light could be produced even in the absence of oxygen. Later, Osamu Shimomura began work into the bioluminescence of Aequorea in 1961. This involved tedious harvesting of tens of thousands of jellyfish from the docks in Friday Harbor, Washington. It was determined that light could be produced from extracts with seawater, and more specifically, with calcium. It was also noted during the extraction the animal creates green light due to the presence of the green fluorescent protein, which changes the native blue light of aequorin to green.
While the main focus of his work was on the bioluminescence, Shimomura and two others, Martin Chalfie and Roger Tsien, were awarded the Nobel Prize in 2008 for their work on green fluorescent proteins. | 1 | Biochemistry |
Once the oligonucleotide library has been incubated with target for sufficient time, unbound oligonucleotides are washed away from immobilized target, often using the incubation buffer so that specifically bound oligonucleotides are retained. With unbound sequences washed away, the specifically bound sequences are then eluted by creating denaturing conditions that promote oligonucleotide unfolding or loss of binding conformation including flowing in deionized water, using denaturing solutions containing urea and EDTA, or by applying high heat and physical force. Upon elution of bound sequences, the retained oligonucleotides are reverse-transcribed to DNA in the case of RNA or modified base selections, or simply collected for amplification in the case of DNA SELEX. These DNA templates from eluted sequences are then amplified via PCR and converted to single stranded DNA, RNA, or modified base oligonucleotides, which are used as the initial input for the next round of selection. | 1 | Biochemistry |
In physics, the reciprocal lattice emerges from the Fourier transform of another lattice. The direct lattice or real lattice is a periodic function in physical space, such as a crystal system (usually a Bravais lattice). The reciprocal lattice exists in the mathematical space of spatial frequencies, known as reciprocal space or k space, where refers to the wavevector.
In quantum physics, reciprocal space is closely related to momentum space according to the proportionality , where is the momentum vector and is the reduced Planck constant. The reciprocal lattice of a reciprocal lattice is equivalent to the original direct lattice, because the defining equations are symmetrical with respect to the vectors in real and reciprocal space. Mathematically, direct and reciprocal lattice vectors represent covariant and contravariant vectors, respectively.
The reciprocal lattice is the set of all vectors , that are wavevectors of plane waves in the Fourier series of a spatial function whose periodicity is the same as that of a direct lattice . Each plane wave in this Fourier series has the same phase or phases that are differed by multiples of at each direct lattice point (so essentially same phase at all the direct lattice points).
The reciprocal lattice plays a fundamental role in most analytic studies of periodic structures, particularly in the theory of diffraction. In neutron, helium and X-ray diffraction, due to the Laue conditions, the momentum difference between incoming and diffracted X-rays of a crystal is a reciprocal lattice vector. The diffraction pattern of a crystal can be used to determine the reciprocal vectors of the lattice. Using this process, one can infer the atomic arrangement of a crystal.
The Brillouin zone is a Wigner–Seitz cell of the reciprocal lattice. | 3 | Analytical Chemistry |
The ASTM D 6002 method for determining the compostability of a plastic defined the word compostable as follows:
This definition drew much criticism because, contrary to the way the word is traditionally defined, it completely divorces the process of "composting" from the necessity of it leading to humus/compost as the end product. The only criterion this standard does describe is that a compostable plastic must look to be going away as fast as something else one has already established to be compostable under the traditional definition. | 7 | Physical Chemistry |
The product scope of this reaction is extremely broad with the use of different substrates; however development of different functionalities has required accompanied studies to determine the proper catalyst system. The most typical class of reactions involves coupling between C–COOH and C–X bonds, however C–COOH and C–M cross-coupling, homo-coupling of carboxylic acids, heck coupling, and dehydrogenative cross-coupling can also be including in this class as they release CO. Heteroatom cross coupling reactions involving formation of C–N, C–S, C–P, and C–X bonds have also been demonstrated. | 0 | Organic Chemistry |
Mainline CSIs are those in which a conserved insert or deletion is shared by several major phyla, but absent from other phyla.
Figure 2 shows an example of 5aa CSI found in a conserved region that is commonly present in the species belonging to phyla X, Y and Z, but it is absent in other phyla (A, B and C). This signature indicates a specific relationship of taxa X, Y and Z and also A, B and C. Based upon the presence or absence of such an indel, in out-group species (viz. Archaea), it can be inferred whether the indel is an insert or a deletion, and which of these two groups A, B, C or X, Y, Z is ancestral.
Mainline CSIs have been used in the past to determine the phylogenetic relationship of a number of bacterial phyla. The large CSI of about 150-180 amino acids within a conserved region of Gyrase B (between amino acids 529-751), is commonly shared between various Pseudomonadota, Chlamydiota, Planctomycetota and Aquificota species. This CSI is absent in other ancestral bacterial phyla as well as Archaea. Similarly a large CSI of about 100 amino acids in RpoB homologs (between amino acids 919-1058) is present in various species belonging to Pseudomonadota, Bacteroidota, Chlorobiota, Chlamydiota, Planctomycetota, and Aquificota. This CSI is absent in other ancestral bacterial phyla as well as Archaea. In both cases one can infer that the groups lacking the CSI are ancestral. | 1 | Biochemistry |
Ion-exchange chromatography separates molecules based on their respective charged groups. Ion-exchange chromatography retains analyte molecules on the column based on coulombic (ionic) interactions. The ion exchange chromatography matrix consists of positively and negatively charged ions. Essentially, molecules undergo electrostatic interactions with opposite charges on the stationary phase matrix. The stationary phase consists of an immobile matrix that contains charged ionizable functional groups or ligands. The stationary phase surface displays ionic functional groups (R-X) that interact with analyte ions of opposite charge. To achieve electroneutrality, these immobilized charges couple with exchangeable counterions in the solution. Ionizable molecules that are to be purified, compete with these exchangeable counterions, for binding to the immobilized charges on the stationary phase. These ionizable molecules are retained or eluted based on their charge. Initially, molecules that do not bind or bind weakly to the stationary phase are first to be washed away. Altered conditions are needed for the elution of the molecules that bind to the stationary phase. The concentration of the exchangeable counterions, which competes with the molecules for binding, can be increased, or the pH can be changed to affect the ionic charge of the eluent or the solute. A change in pH affects the charge on the particular molecules and, therefore, alter their binding. When reducing the net charge of the solute's molecules, they start eluting out. This way, such adjustments can be used to release the proteins of interest. Additionally, concentration of counterions can be gradually varied to affect the retention of the ionized molecules, thus separate them. This type of elution is called gradient elution. On the other hand, step elution can be used, in which the concentration of counterions are varied in steps. This type of chromatography is further subdivided into cation exchange chromatography and anion-exchange chromatography. Positively charged molecules bind to cation exchange resins, while negatively charged molecules bind to anion exchange resins. The ionic compound consisting of the cationic species M+ and the anionic species B− can be retained by the stationary phase.
Cation exchange chromatography retains positively charged cations because the stationary phase displays a negatively charged functional group:
Anion exchange chromatography retains anions using positively charged functional group:
Note that the ion strength of either C+ or A− in the mobile phase can be adjusted to shift the equilibrium position, thus retention time.
The ion chromatogram shows a typical chromatogram obtained with an anion exchange column. | 3 | Analytical Chemistry |
First write down the equilibrium expression
This shows that when the acid dissociates, equal amounts of hydrogen ion and anion are produced. The equilibrium concentrations of these three components can be calculated in an ICE table (ICE standing for "initial, change, equilibrium").
The first row, labelled I, lists the initial conditions: the concentration of acid is C, initially undissociated, so the concentrations of A and H would be zero; y is the initial concentration of added strong acid, such as hydrochloric acid. If strong alkali, such as sodium hydroxide, is added, then y will have a negative sign because alkali removes hydrogen ions from the solution. The second row, labelled C for "change", specifies the changes that occur when the acid dissociates. The acid concentration decreases by an amount −x, and the concentrations of A and H both increase by an amount +x. This follows from the equilibrium expression. The third row, labelled E for "equilibrium", adds together the first two rows and shows the concentrations at equilibrium.
To find x, use the formula for the equilibrium constant in terms of concentrations:
Substitute the concentrations with the values found in the last row of the ICE table:
Simplify to
With specific values for C, K and y, this equation can be solved for x. Assuming that pH = −log[H], the pH can be calculated as pH = −log(x + y). | 7 | Physical Chemistry |
Isocyanates can be converted to carbodiimides with loss of carbon dioxide:
:2 RN=C=O → (RN)C + CO
The reaction is catalyzed by phosphine oxides. This reaction is reversible. | 0 | Organic Chemistry |
The concept of a thermodynamic template is demonstrated in scheme 1. A thermodynamic template is a reagent that can stabilize the form of one product over others by lowering its Gibbs free energy (ΔG°) in relation to other products. cyclophane C2 can be prepared by the irreversible highly diluted reaction of a diol with chlorobromomethane in the presence of sodium hydride. The dimer however is part of series of equilibria between polyacetal macrocycles of different size brought about by acid catalyzed (triflic acid) transacetalization. Regardless of the starting material, C2, C4 or a high molar mass product, the equilibrium will eventually produce a product distribution across many macrocycles and oligomers. In this system it is possible to amplify' the presence of C2 in the mixture when the transacetalisation catalyst is silver triflate because the silver ion fits ideally and irreversibly in the C2 cavity. | 6 | Supramolecular Chemistry |
The Serine octamer cluster in physical chemistry is an unusually stable cluster consisting of eight serine molecules (Ser) implicated in the origin of homochirality. This cluster was first discovered in mass spectrometry experiments. Electrospray ionization of an aerosol of serine in methanol results in a mass spectrum with a prominent ion peak of 841 corresponding to the Ser+H cation. The smaller and larger clusters are virtually absent in the spectrum and therefore the number 8 is called a magic number. The same octamer ions are also produced by rapid evaporation of a serine solution on a hot (200-250 °C) metal surface or by sublimation of solid serine. After production, detection again is by mass-spectroscopic means. For the discussion of homochirality, these laboratory production methods are designed to mimic prebiotic conditions.
The cluster is not only unusually stable but also unusual because the clusters have a strong homochiral preference. A racemic serine solution produces a minimum amount of cluster and with solutions of both enantiomers a maximum amount is formed of both homochiral D-Ser and L-Ser. In another experiment cluster formation of a racemic mixture with deuterium enriched L-serine results in a product distribution with hardly any 50/50 D/L clusters but a preference for either D or L enantioenriched clusters.
A model for chiral amplification is proposed whereby enantioenriched clusters are formed from a non-racemic mixture already enriched by L-serine as a result of a mirror-symmetry breaking process. Cluster formation is followed by isolation and on subsequent dissociation of the cluster a serene solution forms with a higher concentration of L-serine than in the original mixture. A cycle can be maintained in which each turn results in an incremental enrichment in L-serine. Many such cycles eventually result in enantiopure L-serine. This model has been experimentally verified.
Chiral transmission is assumed to take place through so-called substitution reactions of serine clusters. In these reactions, a serine monomer in a cluster can be replaced by another small biologically relevant molecule. For instance Ser reacts with glucose (Glc) to the Ser + Glc + Na cluster. Moreover, the cluster of synthetic L-glucose with Ser is less abundant than that with the biological D-glucose. | 4 | Stereochemistry |
The phenomena of superfluidity of a Bose gas and superconductivity of a strongly-correlated Fermi gas (a gas of Cooper pairs) are tightly connected to Bose–Einstein condensation. Under corresponding conditions, below the temperature of phase transition, these phenomena were observed in helium-4 and different classes of superconductors. In this sense, the superconductivity is often called the superfluidity of Fermi gas. In the simplest form, the origin of superfluidity can be seen from the weakly interacting bosons model. | 7 | Physical Chemistry |
The line coefficient (Fig 5) suggests that this is a fairly accurate result, however this is only the case for the pairing of that particular solid with those particular liquids. In other cases, the fit may not be so great (such is the case if we replace polyethylene with poly(methyl methacrylate), wherein the line coefficient of the plot results using the same list of liquids would be significantly lower). This shortcoming is a result of the fact that the Zisman theory treats the surface energy as one single parameter, rather than accounting for the fact that, for example, polar interactions are much stronger than dispersive ones, and thus the degree to which one is happening versus the other greatly affects the necessary calculations. As such, it is a simple but not particularly robust theory. Since the premise of this procedure is to determine the hypothetical properties of a liquid, the precision of the result depends on the precision to which the surface energy values of the probe liquids are known. | 7 | Physical Chemistry |
Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from other reagents or catalysts present in the reaction. This allows spatial information (what chemists refer to as chirality) to transfer from one molecule to the target, forming the product as a single enantiomer. The chiral information is most commonly contained in a catalyst and, in this case, the information in a single molecule of catalyst may be transferred to many substrate molecules, amplifying the amount of chiral information present. Similar processes occur in nature, where a chiral molecule like an enzyme can catalyse the introduction of a chiral centre to give a product as a single enantiomer, such as amino acids, that a cell needs to function. By imitating this process, chemists can generate many novel synthetic molecules that interact with biological systems in specific ways, leading to new pharmaceutical agents and agrochemicals. The importance of asymmetric hydrogenation in both academia and industry contributed to two of its pioneers — William Standish Knowles and Ryōji Noyori — being collectively awarded one half of the 2001 Nobel Prize in Chemistry. | 0 | Organic Chemistry |
*Ellagic acid (Hexahydroxydiphenic acid dilactone)
*Flavogallonic acid dilactone can be found in Rhynchosia volubilis seeds and in Shorea laeviforia
*Lactide
*Tergallic acid dilactone can be found in Rhynchosia volubilis seeds
*Valoneic acid dilactone can be isolated from the heartwood of Shorea laeviforia
*Ethylene brassylate (Musk T), a widely used synthetic musk | 0 | Organic Chemistry |
Thiomers are able to reversibly inhibit efflux pumps. Because of this property the mucosal uptake of various efflux pump substrates such as anticancer drugs, antimycotic drugs and antiinflammatory drugs can be tremendously improved. The postulated mechanism of efflux pump inhibition is based on an interaction of thiolated polymers with the channel forming transmembrane domain of various efflux pumps such as P-gp and multidrug resistance proteins (MRPs). P-gp, for instance, exhibits 12 transmembrane regions forming a channel through which substrates are transported outside of the cell. Two of these transmembrane domains – namely 2 and 11 – exhibit on position 137 and 956, respectively, a cysteine subunit. Thiomers seem to enter in the channel of P-gp and likely form subsequently one or two disulfide bonds with one or both cysteine subunits located within the channel. Due to this covalent interaction the allosteric change of the transporter being essential to move drugs outside of the cell might be blocked. | 7 | Physical Chemistry |
Trichloroethylene is a good analgesic at 0.35 to 0.5% concentrations. Trichloroethylene was used in the treatment of trigeminal neuralgia beginning in 1916.
From the 1940s through the 1980s, both in Europe and North America, trichloroethylene was used as a volatile anesthetic almost invariably administered with nitrous oxide. Marketed in the UK by Imperial Chemical Industries under the trade name Trilene it was coloured blue (with a dye called waxoline blue in 1:200,000 concentration) to avoid confusion with the similar-smelling chloroform. Trilene was stabilised with 0.01% thymol.
TCE replaced earlier anesthetics chloroform and ether in the 1940s due to its lower toxicity than chloroform and being relatively non-flammable (unlike ether which is extremely flammable), but was itself replaced in the 1960s in developed countries with the introduction of halothane, which allowed much faster induction and recovery times and was considerably easier to administer. Trilene was also used as an inhaled analgesic, mainly during childbirth, often self-applied by the patient. Trichloroethylene was introduced for obstetrical anaesthesia in 1943, and used until the 1980s. Its anaesthetic use was banned in the United States in 1977 but the anaesthetic use in the United Kingdom remained until the late 1980s.
TCE was used with halothane in the tri-service field anaesthetic apparatus used by the UK armed forces under field conditions. As of 2000, TCE was still in use as an anesthetic in Africa.
Trichloroethylene has been used in the production of halothane. | 2 | Environmental Chemistry |
The use of particle bombardment, or the gene gun, is another physical method of DNA transfection. In this technique, DNA is coated onto gold particles and loaded into a device which generates a force to achieve penetration of the DNA into the cells, leaving the gold behind on a "stopping" disk. | 1 | Biochemistry |
At its most comprehensive definition, biochemistry can be seen as a study of the components and composition of living things and how they come together to become life. In this sense, the history of biochemistry may therefore go back as far as the ancient Greeks. However, biochemistry as a specific scientific discipline began sometime in the 19th century, or a little earlier, depending on which aspect of biochemistry is being focused on. Some argued that the beginning of biochemistry may have been the discovery of the first enzyme, diastase (now called amylase), in 1833 by Anselme Payen, while others considered Eduard Buchners first demonstration of a complex biochemical process alcoholic fermentation in cell-free extracts in 1897 to be the birth of biochemistry. Some might also point as its beginning to the influential 1842 work by Justus von Liebig, Animal chemistry, or, Organic chemistry in its applications to physiology and pathology', which presented a chemical theory of metabolism, or even earlier to the 18th century studies on fermentation and respiration by Antoine Lavoisier. Many other pioneers in the field who helped to uncover the layers of complexity of biochemistry have been proclaimed founders of modern biochemistry. Emil Fischer, who studied the chemistry of proteins, and F. Gowland Hopkins, who studied enzymes and the dynamic nature of biochemistry, represent two examples of early biochemists.
The term "biochemistry" was first used when Vinzenz Kletzinsky (1826–1882) had his "Compendium der Biochemie" printed in Vienna in 1858; it derived from a combination of biology and chemistry. In 1877, Felix Hoppe-Seyler used the term ( in German) as a synonym for physiological chemistry in the foreword to the first issue of Zeitschrift für Physiologische Chemie (Journal of Physiological Chemistry) where he argued for the setting up of institutes dedicated to this field of study. The German chemist Carl Neuberg however is often cited to have coined the word in 1903, while some credited it to Franz Hofmeister.
It was once generally believed that life and its materials had some essential property or substance (often referred to as the "vital principle") distinct from any found in non-living matter, and it was thought that only living beings could produce the molecules of life. In 1828, Friedrich Wöhler published a paper on his serendipitous urea synthesis from potassium cyanate and ammonium sulfate; some regarded that as a direct overthrow of vitalism and the establishment of organic chemistry. However, the Wöhler synthesis has sparked controversy as some reject the death of vitalism at his hands. Since then, biochemistry has advanced, especially since the mid-20th century, with the development of new techniques such as chromatography, X-ray diffraction, dual polarisation interferometry, NMR spectroscopy, radioisotopic labeling, electron microscopy and molecular dynamics simulations. These techniques allowed for the discovery and detailed analysis of many molecules and metabolic pathways of the cell, such as glycolysis and the Krebs cycle (citric acid cycle), and led to an understanding of biochemistry on a molecular level.
Another significant historic event in biochemistry is the discovery of the gene, and its role in the transfer of information in the cell. In the 1950s, James D. Watson, Francis Crick, Rosalind Franklin and Maurice Wilkins were instrumental in solving DNA structure and suggesting its relationship with the genetic transfer of information. In 1958, George Beadle and Edward Tatum received the Nobel Prize for work in fungi showing that one gene produces one enzyme. In 1988, Colin Pitchfork was the first person convicted of murder with DNA evidence, which led to the growth of forensic science. More recently, Andrew Z. Fire and Craig C. Mello received the 2006 Nobel Prize for discovering the role of RNA interference (RNAi) in the silencing of gene expression. | 1 | Biochemistry |
The principal environmental issues associated with runoff are the impacts to surface water, groundwater and soil through transport of water pollutants to these systems. Ultimately these consequences translate into human health risk, ecosystem disturbance and aesthetic impact to water resources. Some of the contaminants that create the greatest impact to surface waters arising from runoff are petroleum substances, herbicides and fertilizers. Quantitative uptake by surface runoff of pesticides and other contaminants has been studied since the 1960s, and early on contact of pesticides with water was known to enhance phytotoxicity. In the case of surface waters, the impacts translate to water pollution, since the streams and rivers have received runoff carrying various chemicals or sediments. When surface waters are used as potable water supplies, they can be compromised regarding health risks and drinking water aesthetics (that is, odor, color and turbidity effects). Contaminated surface waters risk altering the metabolic processes of the aquatic species that they host; these alterations can lead to death, such as fish kills, or alter the balance of populations present. Other specific impacts are on animal mating, spawning, egg and larvae viability, juvenile survival and plant productivity. Some research shows surface runoff of pesticides, such as DDT, can alter the gender of fish species genetically, which transforms male into female fish.
Surface runoff occurring within forests can supply lakes with high loads of mineral nitrogen and phosphorus leading to eutrophication. Runoff waters within coniferous forests are also enriched with humic acids and can lead to humification of water bodies Additionally, high standing and young islands in the tropics and subtropics can undergo high soil erosion rates and also contribute large material fluxes to the coastal ocean. Such land derived runoff of sediment nutrients, carbon, and contaminants can have large impacts on global biogeochemical cycles and marine and coastal ecosystems.
In the case of groundwater, the main issue is contamination of drinking water, if the aquifer is abstracted for human use. Regarding soil contamination, runoff waters can have two important pathways of concern. Firstly, runoff water can extract soil contaminants and carry them in the form of water pollution to even more sensitive aquatic habitats. Secondly, runoff can deposit contaminants on pristine soils, creating health or ecological consequences. | 2 | Environmental Chemistry |
Diphosphenes can bind to transition metal either in a η mode by donating a lone pair on phosphorus, or in a η behavior via a interaction. If the bulky groups are aryl- groups, arene-coordinated products of η-type coordination are also possible. | 0 | Organic Chemistry |
The first reported kinetic resolution was achieved by Louis Pasteur. After reacting aqueous racemic ammonium tartrate with a mold from Penicillium glaucum, he reisolated the remaining tartrate and found it was levorotatory. The chiral microorganisms present in the mold catalyzed the metabolization of (R,R)-tartrate selectively, leaving an excess of (S,S)-tartrate.
Kinetic resolution by synthetic means was first reported by Marckwald and McKenzie in 1899 in the esterification of racemic mandelic acid with optically active (−)-menthol. With an excess of the racemic acid present, they observed the formation of the ester derived from (+)-mandelic acid to be quicker than the formation of the ester from (−)-mandelic acid. The unreacted acid was observed to have a slight excess of (−)-mandelic acid, and the ester was later shown to yield (+)-mandelic acid upon saponification. The importance of this observation was that, in theory, if a half equivalent of (−)-menthol had been used, a highly enantioenriched sample of (−)-mandelic acid could have been prepared. This observation led to the successful kinetic resolution of other chiral acids, the beginning of the use of kinetic resolution in organic chemistry. | 4 | Stereochemistry |
Birds have bony beaks that are specialised according to the bird's ecological niche. For example, macaws primarily eat seeds, nuts, and fruit, using their beaks to open even the toughest seed. First they scratch a thin line with the sharp point of the beak, then they shear the seed open with the sides of the beak.
The mouth of the squid is equipped with a sharp horny beak mainly made of cross-linked proteins. It is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species. The beak is the only indigestible part of the squid. | 1 | Biochemistry |
Living polymerization was first described by Michael Szwarc in 1956. It is defined as a chain polymerization from which chain transfer and chain termination are absent. In the absence of chain-transfer and chain termination, the monomer in the system is consumed and the polymerization stops but the polymer chain remains active. If new monomer is added, the polymerization can proceed.
Due to the low PDI and predictable molecular weight, living polymerization is at the forefront of polymer research. It can be further divided into living free radical polymerization, living ionic polymerization and living ring-opening metathesis polymerization, etc. | 7 | Physical Chemistry |
PDRCs can be broadband in their thermal emittance capacity, meaning they possess high emittance in both the solar spectrum and atmospheric LWIR window (8 to 14 μm), or selective emitters, meaning they narrowband emit longwave infrared radiation only in the infrared window.
In theory, selective thermal emitters can achieve higher cooling power. However, selective emitters also face additional challenges in real-world applications that can weaken their performance, such as from dropwise condensation, which is common even in semi-arid environments, that can accumulate on the PDRC surface even when it has been made hydrophobic and alter the narrowband emission. Broadband emitters also outperform selective materials when "the material is warmer than the ambient air, or when its sub-ambient surface temperature is within the range of several degrees."
Both emitters can be advantageous for different types of applications. Broadband emitters may be less problematic for horizontal applications, such as on roofs, whereas selective emitters may be more useful if implemented on vertical surfaces like building facades, where dropwise condensation is inconsequential and their stronger cooling power can be actualized.
Broadband emitters can be made angle-dependent to potentially enhance their cooling performance. Polydimethylsiloxane (PDMS) is a common broadband emitter used for PDRC. Most PDRC materials are broadband primarily credited to their lower cost and higher performance at above-ambient temperatures. | 7 | Physical Chemistry |
Amino acid metabolism in plants has been deemed a controversial topic, due to the lack of concrete evidence for any particular pathway. However, it has been suggested that enzymes related to the production and use of propionyl-CoA are involved. Associated with this is the metabolism of isobutyryl-CoA. These two molecules are deemed to be intermediates in valine metabolism. As propionate consists in the form of propionyl-CoA, it was discovered that propionyl-CoA is converted to β-hydroxypropionate through a peroxisomal enzymatic β-oxidation pathway. Nevertheless, in the plant Arabidopsis, key enzymes in the conversion of valine to propionyl-CoA were not observed. Through different experiments performed by Lucas et al., it has been suggested that in plants, through peroxisomal enzymes, propionyl-CoA (and isobutyryl-CoA) are involved in the metabolism of many different substrates (currently being evaluated for identity), and not just valine. | 1 | Biochemistry |
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