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In 2005, a mode of desorption was discovered by John Weaver et al. that has elements of both thermal and electron stimulated desorption. This mode is of particular interest as desorption can occur in a closed system without external stimulus. The mode was discovered whilst investigating bromine absorbed on silicone using scanning tunnelling microscopy. In the experiment, the Si-Br wafers were heated to temperatures ranging from 620 to 775 K. However, it was not simple thermal desorption bond breaking that was observed as the activation energies calculated from Arrhenius plots were found to be lower than the Si-Br bond strength. Instead, the optical phonons of the Silicon weaken the surface bond through vibrations and also provide the energy for electron to excite to the antibonding state. | 7 | Physical Chemistry |
The protein content of peroxisomes varies across species or organism, but the presence of proteins common to many species has been used to suggest an endosymbiotic origin; that is, peroxisomes evolved from bacteria that invaded larger cells as parasites, and very gradually evolved a symbiotic relationship. However, this view has been challenged by recent discoveries. For example, peroxisome-less mutants can restore peroxisomes upon introduction of the wild-type gene.
Two independent evolutionary analyses of the peroxisomal proteome found homologies between the peroxisomal import machinery and the ERAD pathway in the endoplasmic reticulum, along with a number of metabolic enzymes that were likely recruited from the mitochondria. The peroxisome may have had an Actinomycetota origin; however, this is controversial. | 1 | Biochemistry |
The Szyszkowski Equation has been used by Meissner and Michaels to describe the decrease in surface tension of aqueous solutions of carboxylic acids, alcohols and esters at varying mole fractions. It describes the exponential decrease of the surface tension at low concentrations reasonably but should be used only at concentrations below 1 mole%. | 7 | Physical Chemistry |
This idea, drug to metabolite switching, is an extension of the chiral switch concept. The purpose of the switching is to develop an active metabolite which will be devoid of the side-effects and have an improved therapeutic profile compared to the parent chiral drug. Some examples of chiral drug to metabolite switches, (those in the market and others under investigation) include terfenadine to fexofenadine, halofantrine to desbutylhalofantrine, and cisapride to norcisapride. A summary is presented in the table below. | 4 | Stereochemistry |
Genes of all organisms, except bacteria, consist of short protein-coding regions (exons) interrupted by long sequences (introns). When a gene is expressed, its DNA sequence is copied into a “primary RNA” sequence by the enzyme RNA polymerase. Then the “spliceosome” machinery physically removes the introns from the RNA copy of the gene by the process of splicing, leaving only a contiguously connected series of exons, which becomes messenger RNA (mRNA). This mRNA is now read by the ribosome, which produces the encoded protein. Thus, although introns are not physically removed from a gene, a gene's sequence is read as if introns were not present.
Exons are usually short, with an average length of about 120 bases (e.g. in human genes). Intron lengths vary widely from 10 to 500,000, but exon lengths have an upper bound of about 600 bases in most eukaryotes. Because exons code for protein sequences, they are important for the cell, yet constitute only ~2% of the sequences. Introns, in contrast, constitute 98% of the sequences but seem to have few crucial functions, except for enhancer sequences and developmental regulators in rare instances.
Until Philip Sharp and Richard Roberts discovered introns within eukaryotic genes in 1977, it was believed that the coding sequence of all genes was always in one single stretch, bounded by a single long ORF. The discovery of introns was a profound surprise, which instantly brought up the questions of how, why and when the introns came into the eukaryotic genes.
It soon became apparent that a typical eukaryotic gene was interrupted at many locations by introns, dividing the coding sequence into many short exons. Also surprising was that the introns were long, as long as hundreds of thousands of bases. These findings prompted the questions of why many introns occur within a gene (for example, ~312 introns occur in the human gene TTN), why they are long, and why exons are short.
It was also discovered that the spliceosome machinery was large and complex with ~300 proteins and several SnRNA molecules. The questions extended to the origin of the spliceosome. Soon after the discovery of introns, it became apparent that the junctions between exons and introns on either side exhibited specific sequences that directed the spliceosome machinery to the exact base position for splicing. How and why these splice junction signals came into being was another important question. | 1 | Biochemistry |
The kinesis strategy controlled by the locally and instantly evaluated well-being (fitness) can be described in simple words: Animals stay longer in good conditions and leave bad conditions more quickly. If the well-being is measured by the local reproduction coefficient then the minimal reaction-diffusion model of kinesis can be written as follows:
For each population in the biological community,
where:
is the population density of ith species,
represents the abiotic characteristics of the living conditions (can be multidimensional),
is the reproduction coefficient, which depends on all and on s,
is the equilibrium diffusion coefficient (defined for equilibrium ). The coefficient characterises dependence of the diffusion coefficient on the reproduction coefficient.
The models of kinesis were tested with typical situations. It was demonstrated that kinesis is beneficial for assimilation of both patches and fluctuations of food distribution. Kinesis may delay invasion and spreading of species with the Allee effect. | 1 | Biochemistry |
In guenons, selection is responsible for the evolution of predator-specific alarm calls from loud calls. Loud calls travel long distances, greater than that of the home range, and can be used as beneficial alarm calls to warn conspecifics or showcase their awareness of and deter a predator. A spectrogram of a subadult male call shows that the call is a composition of elements from a female alarm call and male loud call, suggesting the transition from the latter to the former during puberty and suggesting that alarm calls gave rise to loud calls through sexual selection. Evidence of sexual selection in loud calls includes structural adaptations for long-range communication, co-incidence of loud calls and sexual maturity, and sexual dimorphism in loud calls. | 1 | Biochemistry |
SBPase is involved in the regeneration of 5-carbon sugars during the Calvin cycle. Although SBPase has not been emphasized as an important control point in the Calvin cycle historically, it plays a large part in controlling the flux of carbon through the Calvin cycle. Additionally, SBPase activity has been found to have a strong correlation with the amount of photosynthetic carbon fixation. Like many Calvin cycle enzymes, SBPase is activated in the presence of light through a ferredoxin/thioredoxin system. In the light reactions of photosynthesis, light energy powers the transport of electrons to eventually reduce ferredoxin. The enzyme ferredoxin-thioredoxin reductase uses reduced ferredoxin to reduce thioredoxin from the disulfide form to the dithiol. Finally, the reduced thioredoxin is used to reduced a cysteine-cysteine disulfide bond in SBPase to a dithiol, which converts the SBPase into its active form.
SBPase has additional levels of regulation beyond the ferredoxin/thioredoxin system. Mg2+ concentration has a significant impact on the activity of SBPase and the rate of the reactions it catalyzes. SBPase is inhibited by acidic conditions (low pH). This is a large contributor to the overall inhibition of carbon fixation when the pH is low inside the stroma of the chloroplast. Finally, SBPase is subject to negative feedback regulation by sedoheptulose-7-phosphate and inorganic phosphate, the products of the reaction it catalyzes. | 5 | Photochemistry |
Phillips' contributions to computational biology include advanced techniques for interpreting experimental data in complex chemical and biological systems. He focused on the interaction between troponin T (TnT) and tropomyosin, shedding light on the molecular mechanisms in muscle contractions. Additionally, he explored protein dynamics in crystals by using the Gaussian network model (GNM) and a crystallographic model to calculate Cα atom fluctuations in 113 proteins emphasizing the improved results obtained by considering neighboring molecules in the crystal. In a book chapter discussing ongoing advancements in experimental methods for complex chemical and biological systems, he highlighted the growing need for creative approaches and delved into the exploration of Normal Mode Analysis as a technique to address these challenges. | 1 | Biochemistry |
A concern usually addressed in catalyst design is efficiency, in particular how much of the incident light can be used in a system in practice. This is comparable with photosynthetic efficiency, where light-to-chemical-energy conversion is measured. Photosynthetic organisms are able to collect about 50% of incident solar radiation, however the theoretical limit of photosynthetic efficiency is 4.6 and 6.0% for C3 and C4 plants respectively. In reality, the efficiency of photosynthesis is much lower and is usually below 1%, with some exceptions such as sugarcane in tropical climate. In contrast, the highest reported efficiency for artificial photosynthesis lab prototypes is 22.4%. However, plants are efficient in using CO at atmospheric concentrations, something that artificial catalysts still cannot perform. | 5 | Photochemistry |
* Gonyaulax
* Karenia
* Gymnodinium
* Dinophysis
* Noctiluca
* Chattonella
* Ceratium
* Amoebophyre
* Alexandrium
* Cochlodinium | 3 | Analytical Chemistry |
In thermodynamics, the Gibbs free energy or Helmholtz free energy is essentially the energy of a chemical reaction "free" or available to do external work. Historically, the "free energy" is a more advanced and accurate replacement for the thermochemistry term “affinity” used by chemists of olden days to describe the “force” that caused chemical reactions. The term dates back to at least the time of Albertus Magnus in 1250.
According to Nobelist and chemical engineering professor Ilya Prigogine: “as motion was explained by the Newtonian concept of force, chemists wanted a similar concept of ‘driving force’ for chemical change? Why do chemical reactions occur, and why do they stop at certain points? Chemists called the ‘force’ that caused chemical reactions affinity, but it lacked a clear definition.
During the entire 18th century, the dominant view in regard to heat and light was that put forward by Isaac Newton, called the “Newtonian hypothesis”, which stated that light and heat are forms of matter attracted or repelled by other forms of matter, with forces analogous to gravitation or to chemical affinity.
In the 19th century, the French chemist Marcellin Berthelot and the Danish chemist Julius Thomsen had attempted to quantify chemical affinity using heats of reaction. In 1875, after quantifying the heats of reaction for a large number of compounds, Berthelot proposed the “principle of maximum work” in which all chemical changes occurring without intervention of outside energy tend toward the production of bodies or of a system of bodies which liberate heat. | 7 | Physical Chemistry |
the health effects of using hash oil were poorly documented. Cannabis extracts have less plant matter and create less harmful smoke. However, trace amounts of impurities are not generally regarded as safe (GRAS). In 2019 following an outbreak of illnesses additives added to vape pen mixtures were found to be causing breathing problems, lung damage, and deaths. | 7 | Physical Chemistry |
Snieckus' research interests in organic synthesis focused on metalation and particularly lithiation. He is best known for his work on the directed ortho metalation family of reactions. His work has had practical applications in both academic and industrial settings, particularly in the industrial-scale synthesis of pharmaceuticals and in an agricultural antifungal. | 0 | Organic Chemistry |
Gold(III) bromide is used as a catalyst in a variety of reactions, but one of its most interesting uses is found in the Diels-Alder reaction. Specifically, the compound catalyzes the reaction between an enynal unit and carbonyl compounds to form a six-membered cyclic compound.
Another catalytic use of gold tribromide is in the nucleophilic substitution reaction of propargylic alcohols. In this reaction, the gold complex acts as an alcohol-activating agent to facilitate the substitution. | 3 | Analytical Chemistry |
Bis(trimethylsilyl)acetamide (BSA) is an organosilicon compound with the formula (Me = CH). It is a colorless liquid that is soluble in diverse organic solvents, but reacts rapidly with moisture and solvents containing OH and NH groups. It is used in analytical chemistry to increase the volatility of analytes, e.g., for gas chromatography. It is also used to introduce the trimethylsilyl protecting group in organic synthesis. A related reagent is N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). | 0 | Organic Chemistry |
Histatins are antimicrobial and antifungal proteins, and have been found to play a role in wound-closure. A significant source of histatins is found in the serous fluid secreted by Ebner's glands, salivary glands at the back of the tongue, and produced by acinus cells. Here they offer some early defense against incoming microbes.
The three major histatins are 1, 3, and 5, which contains 38, 32, and 24 amino acids, respectively. Histatin 2 is a degradation product of histatin 1, and all other histatins are degradation products of Histatin 3 through the process of post-translational proteolysis of the HTN3 gene product. Therefore there are only two genes, HTN1 and HTN3.
The N-terminus of Histatin 5 allows it to bind with metals, and this can result in the production of reactive oxygen species.
Histatins disrupt the fungal plasma membrane, resulting in release of the intracellular content of the fungal cell. They also inhibit the growth of yeast, by binding to the potassium transporter and facilitating in the loss of azole-resistant species.
The antifungal properties of histatins have been seen with fungi such as Candida glabrata, Candida krusei, Saccharomyces cerevisiae, and Cryptococcus neoformans.
Histatins also precipitate tannins from solution, thus preventing alimentary adsorption. | 1 | Biochemistry |
In many kinds of breast cancer, aberrations in the PI3K/AKT/mTOR pathway are the most common genomic abnormalities. The most common known aberrations include the PIK3CA gene mutation and the loss-of-function mutations or epigenetic silencing of PTEN. The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway is activated in approximately 30–40% of BC cases. In triple-negative breast cancer (TNBC), oncogenic activation of the PI3K/AKT/mTOR pathway can happen as a function of overexpression of upstream regulators like EGFR, activating mutations of PIK3CA, loss of function or expression of phosphatase and tensin homolog (PTEN), and the proline-rich inositol polyphosphatase, which are downregulators of PI3K. It is consistent with the hypothesis that PI3K inhibitors can overcome resistance to endocrine therapy when it is acquired | 1 | Biochemistry |
SuperSAGE is a derivative of SAGE that uses the type III-endonuclease EcoP15I of phage P1, to cut 26 bp long sequence tags from each transcript's cDNA, expanding the tag-size by at least 6 bp as compared to the predecessor techniques SAGE and LongSAGE. The longer tag-size allows for a more precise allocation of the tag to the corresponding transcript, because each additional base increases the precision of the annotation considerably.
Like in the original SAGE protocol, so-called ditags are formed, using blunt-ended tags. However, SuperSAGE avoids the bias observed during the less random LongSAGE 20 bp ditag-ligation. By direct sequencing with high-throughput sequencing techniques (next-generation sequencing, i.e. pyrosequencing), hundred thousands or millions of tags can be analyzed simultaneously, producing very precise and quantitative gene expression profiles. Therefore, tag-based gene expression profiling also called "digital gene expression profiling" (DGE) can today provide most accurate transcription profiles that overcome the limitations of microarrays. | 1 | Biochemistry |
Organic and inorganic anions are produced from fluoride, including:
*Bifluoride, used as an etchant for glass
*Tetrafluoroberyllate
*Hexafluoroplatinate
*Tetrafluoroborate used in organometallic synthesis
*Hexafluorophosphate used as an electrolyte in commercial secondary batteries.
*Trifluoromethanesulfonate | 1 | Biochemistry |
While the lead ISASMELT 5 t/h pilot plant was being designed in 1982–1983, MIM continued to use the 120 kg/h test rig to develop other processes, including the dross treatment process previously mentioned, and the treatment of lead-acid battery paste for lead recycling.
The MIM Holdings Board of Directors approved the construction of an ISASMELT plant at Britannia Refined Metals, the company's lead refinery at Northfleet in the United Kingdom, for commercial recovery of lead from battery paste to supplement the existing plant, which used a short rotary furnace to produce 10,000 t/y of lead. The new plant increased annual production to 30,000 t/y of recycled lead, and was commissioned in 1991. The ISASMELT furnace was used to produce low-antimony lead bullion from the battery paste and an antimony-rich slag that contained 55–65% lead oxide. While it was possible to recover the lead from the slag in the ISASMELT furnace by a reduction step, the total throughput of the plant was increased by treating the slag in the short rotary furnace when sufficient quantities of the slag had been generated. The plant was designed to treat 7.7 t/h of battery paste, but routinely treated 12 t/h. The plant was shut down in 2004 when Xstrata Zinc, which took over the MIM Holdings lead operations, decided to leave the lead recycling business.
A second lead ISASMELT plant for recovering lead from recycled batteries was commissioned in 2000 in Malaysia at Metal Reclamation Industries’ Pulau Indah plant. This ISASMELT plant has a design capacity of 40,000 t/y of lead bullion. | 8 | Metallurgy |
In his 2016 Handbook of Synthetic Organic Chemistry, Michael Pirrung wrote that yield is one of the primary factors synthetic chemists must consider in evaluating a synthetic method or a particular transformation in "multistep syntheses." He wrote that a yield based on recovered starting material (BRSM) or (BORSM) does not provide the theoretical yield or the "100% of the amount of product calculated", that is necessary in order to take the next step in the multistep systhesis.
Purification steps always lower the yield, through losses incurred during the transfer of material between reaction vessels and purification apparatus or imperfect separation of the product from impurities, which may necessitate the discarding of fractions deemed insufficiently pure. The yield of the product measured after purification (typically to >95% spectroscopic purity, or to sufficient purity to pass combustion analysis) is called the isolated yield of the reaction. | 0 | Organic Chemistry |
The title, Mappae clavicula, is absurd, translating approximately as the little key to the small cloth. The best explanation is that it is a mis-translation from a Greek original, in which χειρόκμητον kheirókmēton (knack or trick of the trade) was mis-read as χειρόμακτρον kheirómaktron (hand-towel). This is consistent with the observation that certain recipes derive from the Greek technical papyri, the Leyden papyrus X and the Stockholm papyrus. | 8 | Metallurgy |
In electrochemistry, a valve metal is a metal which passes current in only one direction. Usually, in an electrolytic cell, it can function generally as a cathode, but not generally as an anode because a (highly resistive) oxide of the metal forms under anodic conditions. Valve metals include commonly aluminium, titanium, tantalum, and niobium. Other metals may also be considered as valve metals, such as tungsten, chromium, zirconium, hafnium, zinc, vanadium, bismuth or antimony. | 7 | Physical Chemistry |
This strategy is based around the use of locally available plants, not costly industrial inputs, thus making it both more economically feasible and more culturally appropriate as this method is in many ways similar to traditional African practices of intercropping. For this reason, this method is anticipated to be a popular solution to food insecurity in Sub-Saharan Africa. While this strategy is less resource-intensive, it is more knowledge-intensive. For this reason, mass media campaigns have been launched, public meetings held, printed materials disseminated, and farmer-to-farmer and farmer field school programs established in order to overcome knowledge barriers to the implementation of push-pull technology. The most efficient, influential, and cost-effective methods of disseminating information and encouraging farmers to adopt push-pull methods have been identified to be field days (lead to approximately 26.8% increase in adoption), farmer field schools (22.2% chance of swaying farmers' decisions), and farmer teachers (18.1% chance of convincing farmers to adopt the technology). Additionally, it has been found that over 80% of farmers who participate in field days adopt the technology on their land.
Another measure that has been taken to boost adoption rates of push-pull technology is to distribute desmodium seeds and other inputs that are required to begin this practice. Distribution of seeds and other required inputs has been made possible through partnerships with seed companies and local farmer groups. In order to combat the former shortage and high cost of desmodium seeds that were limiting the spread of push-pull technology, intensive seed production initiatives have been launched and farmer groups have been encouraged to propagate the seeds themselves. As a result of these measures, the market for desmodium seeds has been stimulated and the seeds have become more accessible to smallholder farmers looking to implement push-pull methods in their fields.
In Kenya, Tanzania, and Uganda alone, push-pull technology has been adopted by 68,800 smallholder farmers; however, these numbers may be higher in reality because of gaps in reporting. Because these areas in Sub-Saharan Africa often suffer from unreliable crop production as a result of stemborers and striga, soil infertility, and unsustainable supplies of fodder, the push-pull solution to these problems is expected to be adopted by more smallholder farmers in the future at an annual adoption rate of 30% and a potential annual adoption rate of 50% because of intensive education campaigns that have been launched. | 1 | Biochemistry |
When ground state energies are different but transition state energies are similar, selectivity will be degraded in the transition state, and poor overall selectivity may be observed. For instance, high selectivity for one ground state conformer is observed in the following radical methylation reaction.
The conformer in which A(1,3) strain is minimized is at an energy minimum, giving 99:1 selectivity in the ground state. However, transition state energies depend both on the presence of A(1,3) strain and on steric hindrance associated with the incoming methyl radical. In this case, these two factors are in opposition, and the difference in transition state energies is small compared to the difference in ground state energies. As a result, poor overall selectivity is observed in the reaction. | 7 | Physical Chemistry |
Mitochondrial replacement therapy (MRT), sometimes called mitochondrial donation, is the replacement of mitochondria in one or more cells to prevent or ameliorate disease. MRT originated as a special form of in vitro fertilisation in which some or all of the future baby's mitochondrial DNA (mtDNA) comes from a third party. This technique is used in cases when mothers carry genes for mitochondrial diseases. The therapy is approved for use in the United Kingdom. A second application is to use autologous mitochondria to replace mitochondria in damaged tissue to restore the tissue to a functional state. This has been used in clinical research in the United States to treat cardiac-compromised newborns. | 1 | Biochemistry |
Coelenterazine is a luciferin, a molecule that emits light after reaction with oxygen, found in many aquatic organisms across eight phyla. It is the substrate of many luciferases such as Renilla reniformis luciferase (Rluc), Gaussia luciferase (Gluc), and photoproteins, including aequorin, and obelin. All these proteins catalyze the oxidation of this substance, a reaction catalogued EC 1.13.12.5. | 1 | Biochemistry |
* The French writer René Daumal intoxicated himself by inhalation of carbon tetrachloride which he used to kill the beetles he collected, to "encounter other worlds" by voluntarily plunging himself into intoxications close to comatose states.
* Carbon tetrachloride is listed (along with salicylic acid, toluene, sodium tetraborate, silica gel, methanol, potassium carbonate, ethyl acetate and "BHA") as an ingredient in Peter Parkers (Spider-Man) custom web fluid formula in the book The Wakanda Files: A Technological Exploration of the Avengers and Beyond'.
* Australian YouTuber Tom of Explosions&Fire and Extractions&Ire made a video on extracting carbon tetrachloride from an old fire extinguisher in 2019, and later experimenting with it by mixing it with sodium, and the chemical gained a fan base called "Tet Gang" on social media (especially on Reddit). The channel owner later used carbon tetrachloride-themed designs in the channel's merch.
* In the Ramones song "Carbona Not Glue" released in 1977, the narrator says that huffing the vapours of Carbona, a carbon tetrachloride-based stain remover, was better than huffing glue. They later removed the song from the album as Carbona was a corporate trademark. | 2 | Environmental Chemistry |
An important factor in the antiperiplanar conformer is the interaction between molecular orbitals. Anti-periplanar geometry will put a bonding orbital and an anti-bonding orbital approximately parallel to each other, or syn-periplanar. Figure 6 is another representation of 2-chloro-2,3-dimethylbutane (Figure 5), showing the C–H bonding orbital, σ, and the C–Cl anti-bonding orbital, σ*, syn-periplanar. The parallel orbitals can overlap and become involved in hyperconjugation. If the bonding orbital is an electron donor and the anti-bonding orbital is an electron acceptor, then the bonding orbital will be able to donate electronegativity into the anti-bonding orbital. This filled-to-unfilled donor-acceptor interaction has an overall stabilizing effect on the molecule. However, donation from a bonding orbital into an anti-bonding orbital will also result in the weakening of both of those bonds. In Figure 6, 2-chloro-2,3-dimethylbutane is stabilized through hyperconjugation from electron donation from σ into σ*, but both C–H and C–Cl bonds are weakened. A molecular orbital diagram shows that the mixing of σ and σ* in 2-chloro-2,3-dimethylbutane lowers the energy of both the orbitals (Figure 7). | 0 | Organic Chemistry |
In 1986, Novotny was given the Award in Chromatography from the American Chemical Society. Novotny received the ANACHEM award in 1992. This award is given to outstanding analytical chemists for teaching, research, administration or other activities which have advanced of the field.
Novotny was also selected as the LCGC Lifetime Achievement award recipient in 2019. | 3 | Analytical Chemistry |
The micelle packing parameter equation is utilized to help "predict molecular self-assembly in surfactant solutions":
where is the surfactant tail volume, is the tail length, and is the equilibrium area per molecule at the aggregate surface. | 6 | Supramolecular Chemistry |
The thermodynamics of an ideal Bose gas is best calculated using the grand canonical ensemble. The grand potential for a Bose gas is given by:
where each term in the sum corresponds to a particular single-particle energy level ε; g is the number of states with energy ε; z is the absolute activity (or "fugacity"), which may also be expressed in terms of the chemical potential μ by defining:
and β defined as:
where k is Boltzmanns constant and T is the temperature. All thermodynamic quantities may be derived from the grand potential and we will consider all thermodynamic quantities to be functions of only the three variables z , β (or T ), and V '. All partial derivatives are taken with respect to one of these three variables while the other two are held constant.
The permissible range of z is from negative infinity to +1, as any value beyond this would give an infinite number of particles to states with an energy level of 0 (it is assumed that the energy levels have been offset so that the lowest energy level is 0). | 7 | Physical Chemistry |
There are various forms of mutations that can occur in coding regions. One form is silent mutations, in which a change in nucleotides does not result in any change in amino acid after transcription and translation. There also exist nonsense mutations, where base alterations in the coding region code for a premature stop codon, producing a shorter final protein. Point mutations, or single base pair changes in the coding region, that code for different amino acids during translation, are called missense mutations. Other types of mutations include frameshift mutations such as insertions or deletions. | 1 | Biochemistry |
Oil-in-water emulsions are common in food products:
* Mayonnaise and Hollandaise sauces – these are oil-in-water emulsions stabilized with egg yolk lecithin, or with other types of food additives, such as sodium stearoyl lactylate
* Homogenized milk – an emulsion of milk fat in water, with milk proteins as the emulsifier
* Vinaigrette – an emulsion of vegetable oil in vinegar, if this is prepared using only oil and vinegar (i.e., without an emulsifier), an unstable emulsion results
Water-in-oil emulsions are less common in food, but still exist:
* Butter – an emulsion of water in butterfat
* Margarine
Other foods can be turned into products similar to emulsions, for example meat emulsion is a suspension of meat in liquid that is similar to true emulsions. | 7 | Physical Chemistry |
In Japan, "clarke" is translated as . The word is always added, which happens to make the term appear similar in form with scientific constants such as . The term may have a narrower sense than Fersman's. Several of the following constraints may apply:
* Only of Earth's crust
* Lithosphere approximated as a 10 mile-deep layer from sea level
* Must include all of three layers: lithosphere (93.06%), hydrosphere (0.91%) and atmosphere (0.03%)
* Only mass ratio)
* Denote in percents) (not in ppm or ppb)
* (What the quoter believes to be) data from Clarke and Washington(1924)
Another peculiarity in Japan is the existence of a popular version of data, which was tabulated in reference books such as the annual "Chronological Scientific Tables" (RCST1939(1938)), the "Dictionary of Physics and Chemistry" (IDPC(1939)) and other prominent books on geochemistry and chemistry. This version Kimura(1938) was devised by chemist . It was often quoted as The "Clarke numbers" (unsourced examples:,). The numbers differed from any versions by Clarke / Clarke&Washington (1889–1924), or anything listed in foreign (non-Japanese) articles such as the USGS compilation , thus unknown outside of Japan. Yet the numbers were sometimes quoted in English articles without citation (example:).
As geological definition of "Earths crust" evolved, the "10 mile-deep" approximation were deemed out-of-date, and some people considered the term "clarke number" obsolete too. Yet other people may have meant broader senses, not limiting to Earths crust, leading to confusion. RCST1961(1961) switched their "clarke number" table from Kimura(1938) to Mason(1958) based, and the label "clarke number" on table was removed in RCST1963(1962). IDPC(1971) removed the "clarke number" table which was a Kimura(1938)s variant. IDPC(1981) said the term is mostly abandoned, and the dictionary entry for "clarke number" itself was removed from IDPC(1998). So "clarke numbers" became associated almost solely with Kimura(1938)s data, but Kimuras name forgotten. Incidentally, in major reference books, there was no data table titled "clarke numbers" which showed Clarkes original tables.
Despite being removed from major reference books, data from Kimura(1938) and phrases such as "the Clarke number of iron is 4.70", unsourced, continue to circulate, even in the 2010s (example:). | 9 | Geochemistry |
Acid–base titration plays a crucial role in environmental monitoring by providing a quantitative analytical method for assessing the acidity or alkalinity of water samples. The measurement of parameters such as pH, total alkalinity, and acidity is essential in evaluating the environmental impact of industrial discharges, agricultural runoff, and other sources of water contamination.
Acid–base titration allows for the determination of the buffering capacity of natural water systems, aiding in the assessment of their ability to resist changes in pH. Monitoring pH levels is important for preserving aquatic ecosystems and ensuring compliance with environmental regulations.
Acid–base titration is also utilized in the analysis of acid rain effects on soil and water bodies, contributing to the overall understanding and management of environmental quality. The method's prevision and reliability make it a valuable tool in safeguarding ecosystems and assessing the impact of human activities on natural water resources. | 3 | Analytical Chemistry |
Sharpless was a professor at the Massachusetts Institute of Technology (1970–1977, 1980–1990) and Stanford University (1977–1980). While at Stanford, Sharpless discovered Sharpless asymmetric epoxidation, which was used to make (+)-disparlure. , Sharpless led a laboratory at Scripps Research. | 4 | Stereochemistry |
The risk of opioid-related adverse effects such as respiratory depression, falls, cognitive impairment and sedation is increased. Tramadol may interact with other medications and increase the risk for adverse events. | 4 | Stereochemistry |
*Bailyn, M. (1994). A Survey of Thermodynamics, American Institute of Physics Press, New York, .
*Beattie, J.A., Oppenheim, I. (1979). Principles of Thermodynamics, Elsevier, Amsterdam, .
*Born, M. (1921). Kritische Betrachtungen zur traditionellen Darstellung der Thermodynamik, Physik. Zeitschr. 22: 218–224.
*Bryan, G.H. (1907). Thermodynamics. An Introductory Treatise dealing mainly with First Principles and their Direct Applications, B.G. Teubner, Leipzig.
*Buchdahl, H.A. (1957/1966). The Concepts of Classical Thermodynamics, Cambridge University Press, London.
*Callen, H.B. (1960/1985). Thermodynamics and an Introduction to Thermostatistics, second edition, John Wiley & Sons, New York, .
* A translation may be found [http://neo-classical-physics.info/uploads/3/0/6/5/3065888/caratheodory_-_thermodynamics.pdf here] . A partly reliable translation is to be found at Kestin, J. (1976). The Second Law of Thermodynamics, Dowden, Hutchinson & Ross, Stroudsburg PA.
*Haase, R. (1971). Survey of Fundamental Laws, chapter 1 of Thermodynamics, pages 1–97 of volume 1, ed. W. Jost, of Physical Chemistry. An Advanced Treatise, ed. H. Eyring, D. Henderson, W. Jost, Academic Press, New York, lcn 73–117081.
*Kirkwood, J.G., Oppenheim, I. (1961). Chemical Thermodynamics, McGraw–Hill, New York. | 7 | Physical Chemistry |
The charge of proteins is determined by the pKa of its amino acid side chains, and the terminal amino acid and carboxylic acid. Proteins with isoelectric point (pI) above physiological conditions have a positive charge and proteins with pI below physiological conditions have a negative charge. The net charge of the protein, determined by the sum charge of its constituents, results in electrophoretic migration in a physiologic electric field. These effects are short-range because of the high di-electric constant of water, however, once the protein is close to a charged surface, electrostatic coupling becomes the dominant force. | 1 | Biochemistry |
Methods of determining pH include:
*Observation of soil profile: certain profile characteristics can be indicators of either acid, saline, or sodic conditions. Examples are:
**Poor incorporation of the organic surface layer with the underlying mineral layer – this can indicate strongly acidic soils;
**The classic podzol horizon sequence, since podzols are strongly acidic: in these soils, a pale eluvial (E) horizon lies under the organic surface layer and overlies a dark B horizon;
**Presence of a caliche layer indicates the presence of calcium carbonates, which are present in alkaline conditions;
**Columnar structure can be an indicator of sodic condition.
*Observation of predominant flora. Calcifuge plants (those that prefer an acidic soil) include Erica, Rhododendron and nearly all other Ericaceae species, many birch (Betula), foxglove (Digitalis), gorse (Ulex spp.), and Scots Pine (Pinus sylvestris). Calcicole (lime loving) plants include ash trees (Fraxinus spp.), honeysuckle (Lonicera), Buddleja, dogwoods (Cornus spp.), lilac (Syringa) and Clematis species.
*Use of an inexpensive pH testing kit, where in a small sample of soil is mixed with indicator solution which changes colour according to the acidity.
*Use of litmus paper. A small sample of soil is mixed with distilled water, into which a strip of litmus paper is inserted. If the soil is acidic the paper turns red, if basic, blue.
*Certain other fruit and vegetable pigments also change color in response to changing pH. Blueberry juice turns more reddish if acid is added, and becomes indigo if titrated with sufficient base to yield a high pH. Red cabbage is similarly affected.
*Use of a commercially available electronic pH meter, in which a glass or solid-state electrode is inserted into moistened soil or a mixture (suspension) of soil and water; the pH is usually read on a digital display screen.
* In the 2010s, spectrophotometric methods were developed to measure soil pH involving addition of an indicator dye to the soil extract. These compare well to glass electrode measurements but offer substantial advantages such as lack of drift, liquid junction and suspension effects.
Precise, repeatable measures of soil pH are required for scientific research and monitoring. This generally entails laboratory analysis using a standard protocol; an example of such a protocol is that in the USDA Soil Survey Field and Laboratory Methods Manual. In this document the three-page protocol for soil pH measurement includes the following sections: Application; Summary of Method; Interferences; Safety; Equipment; Reagents; and Procedure. | 9 | Geochemistry |
Since the 1920s, beryllium has been used in electronics, ceramics, research and development labs, aircraft, and the atomic energy and defense industry. Cases of bronchitis and pneumonia-like symptoms were reported in Germany and Russia in the 1930s among workers mining and refining beryllium. By 1946, a cluster of cases associated with fluorescent lamp manufacturers were apparent in the United States, and the lamp industry stopped using beryllium in 1949. At that time, most construction trades and industries were unaware of the potential risks associated with beryllium exposure.
It occasionally killed early workers in nuclear weapons design, such as Herbert L. Anderson.
Beryllium sensitivity testing was first performed as a cutaneous beryllium patch test in the early 1950s, but was discontinued due to the test stimulating sensitization or aggravating existing chronic beryllium disease.
In the 1990s, the DOE began screening employees using the BeLPT test in facilities where beryllium was used, to take preventive measures against beryllium exposure. Somewhat alarmingly, clerical staff who were never involved in handling the material had developed asymptomatic sensitivities. | 1 | Biochemistry |
Cognitive studies frequently rely on the detection of neuronal activity during cognition. The use of fMRS for this purpose is at present mainly at an experimental level but is rapidly increasing. Cognitive tasks where fMRS has been used and the major findings of the research are summarized below. | 7 | Physical Chemistry |
Cytocidal infections are often associated with changes in cell morphology, physiology and are thus important for the complete viral replication and transformation. Cytopathic Effects, often include a change in cells morphology such as fusion with adjacent cells to form polykaryocytes as well as the synthesis of nuclear and cytoplasmic inclusion bodies. Physiological changes include the insufficient movement of ions, formation of secondary messengers, and activation of cellular cascades to continue cellular activity. Biochemically, many viruses inhibit the synthesis of host DNA, RNA, proteins directly or even interfere with protein-protein, DNA-protein, RNA-protein interactions at the subcellular level. Genotoxicity involves breaking, fragmenting, or rearranging chromosomes of the host. Lastly, biologic effects include the viruses ability to affect the activity of antigens and immunologlobulins in the host cell.
There are two types of cytocidal infections, productive and abortive. In productive infections, additional infectious viruses are produced. Abortive infections do not produce infectious viruses. One example of a productive cytocidal infection is the herpes virus. | 1 | Biochemistry |
While there are myriad sites that have been analyzed to date within the United States, the following list will serve as examples of the subject matter:
*Auke Bay U.S. Postal Facility, Juneau, Alaska
*Esso Canada Ltd. Former Bulk Fuels Facility, Owen Sound, Ontario, Canada
*Dakin Building, Brisbane, California
*East Elk Grove Specific Plan, Elk Grove, California
*Mariners Marsh Park, Staten Island, New York
*Richmond State Hospital Farm Industrial Park, Wayne County, Indiana
*Sydney Steel Plant Lands, Sydney, Nova Scotia
*Weyerhauser Technology Center, Federal Way, Washington | 2 | Environmental Chemistry |
Soil vapor extraction (SVE) is a physical treatment process for in situ remediation of volatile contaminants in vadose zone (unsaturated) soils (EPA, 2012). SVE (also referred to as in situ soil venting or vacuum extraction) is based on mass transfer of contaminant from the solid (sorbed) and liquid (aqueous or non-aqueous) phases into the gas phase, with subsequent collection of the gas phase contamination at extraction wells. Extracted contaminant mass in the gas phase (and any condensed liquid phase) is treated in aboveground systems. In essence, SVE is the vadose zone equivalent of the pump-and-treat technology for groundwater remediation. SVE is particularly amenable to contaminants with higher Henry’s Law constants, including various chlorinated solvents and hydrocarbons. SVE is a well-demonstrated, mature remediation technology and has been identified by the U.S. Environmental Protection Agency (EPA) as presumptive remedy. | 2 | Environmental Chemistry |
An RBS instrument generally includes three essential components:
* An ion source, usually alpha particles (He ions) or, less commonly, protons.
* A linear particle accelerator capable of accelerating incident ions to high energies, usually in the range 1-3 MeV.
* A detector capable of measuring the energies of backscattered ions over some range of angles.
Two common source/acceleration arrangements are used in commercial RBS systems, working in either one or two stages. One-stage systems consist of a He source connected to an acceleration tube with a high positive potential applied to the ion source, and the ground at the end of the acceleration tube. This arrangement is simple and convenient, but it can be difficult to achieve energies of much more than 1 MeV due to the difficulty of applying very high voltages to the system.
Two-stage systems, or "tandem accelerators", start with a source of He ions and position the positive terminal at the center of the acceleration tube. A stripper element included in the positive terminal removes electrons from ions which pass through, converting He ions to He ions. The ions thus start out being attracted to the terminal, pass through and become positive, and are repelled until they exit the tube at ground. This arrangement, though more complex, has the advantage of achieving higher accelerations with lower applied voltages: a typical tandem accelerator with an applied voltage of 750 kV can achieve ion energies of over 2 MeV.
Detectors to measure backscattered energy are usually silicon surface barrier detectors, a very thin layer (100 nm) of P-type silicon on an N-type substrate forming a p-n junction. Ions which reach the detector lose some of their energy to inelastic scattering from the electrons, and some of these electrons gain enough energy to overcome the band gap between the semiconductor valence and conduction bands. This means that each ion incident on the detector will produce some number of electron-hole pairs which is dependent on the energy of the ion. These pairs can be detected by applying a voltage across the detector and measuring the current, providing an effective measurement of the ion energy. The relationship between ion energy and the number of electron-hole pairs produced will be dependent on the detector materials, the type of ion and the efficiency of the current measurement; energy resolution is dependent on thermal fluctuations. After one ion is incident on the detector, there will be some dead time before the electron-hole pairs recombine in which a second incident ion cannot be distinguished from the first.
Angular dependence of detection can be achieved by using a movable detector, or more practically by separating the surface barrier detector into many independent cells which can be measured independently, covering some range of angles around direct (180 degrees) back-scattering. Angular dependence of the incident beam is controlled by using a tiltable sample stage. | 7 | Physical Chemistry |
Robert Marc Mazo is a theoretical physical chemist who specialized in statistical mechanics. Educated at Harvard and Yale, he was a research associate at the University of Chicago, and he taught at the California Institute of Technology prior to joining the University of Oregon faculty in 1962. He was designated a professor emeritus in 1996. He is a member of the American Association of University Professors and a Fellow of the American Physical Society. | 7 | Physical Chemistry |
In this formalism, a liquid crystal material is treated as a continuum; molecular details are entirely ignored. Rather, this theory considers perturbations to a presumed oriented sample. The distortions of the liquid crystal are commonly described by the Frank free energy density. One can identify three types of distortions that could occur in an oriented sample: (1) twists of the material, where neighboring molecules are forced to be angled with respect to one another, rather than aligned; (2) splay of the material, where bending occurs perpendicular to the director; and (3) bend of the material, where the distortion is parallel to the director and molecular axis. All three of these types of distortions incur an energy penalty. They are distortions that are induced by the boundary conditions at domain walls or the enclosing container. The response of the material can then be decomposed into terms based on the elastic constants corresponding to the three types of distortions. Elastic continuum theory is an effective tool for modeling liquid crystal devices and lipid bilayers. | 7 | Physical Chemistry |
Salts of thioacetic acid such as potassium thioacetate can be used convert nitroarenes to aryl acetamides in one step. This is particularly useful in the preparation of pharmaceuticals, e.g., paracetamol. | 0 | Organic Chemistry |
A copolymer is formed from more than one monomeric species. Advanced polymerization techniques have been established for the preparation of covalent copolymers, however supramolecular copolymers are still in its infancy and is slowly progressing. In recent years, all plausible category of supramolecular copolymers such as random, alternating, block, blocky, or periodic has been demonstrated in a broad sense. | 6 | Supramolecular Chemistry |
Aldehydes are commonly generated by alcohol oxidation. Industry oxidizes methanol to formaldehyde on a large scale, and, in the Wacker process, ethylene to acetaldehyde in the presence of copper and palladium catalysts (acetaldehyde is also produced on a large scale by acetylene hydration). "Green" and cheap oxygen is the oxidant of choice. For sensitive substrates, Oppenauer transfer oxidation avoids overoxidation to a carboxylic acid. When a mixture of products may be acceptable, hydroformylation directly adds a carbonyl to a olefin.
Laboratories may instead apply a wide variety of specialized oxidizing agents; chromium(VI) reagents are popular. Oxidation can be achieved by heating the alcohol with an acidified solution of potassium dichromate. In this case, excess dichromate will further oxidize the aldehyde to a carboxylic acid, so either the aldehyde is distilled out as it forms (if volatile) or milder reagents such as PCC are used.
A variety of reagent systems achieve aldehydes under chromium-free conditions. One such are the hypervalent organoiodine compounds (i.e., IBX acid, Dess–Martin periodinane), although these often also oxidize the α position. A Lux-Flood acid will activate other pre-oxidized substrates: various sulfoxides (e.g. the Swern oxidation), or amine oxides (e.g., the Ganem oxidation). Sterically-hindered nitroxyls (i.e., TEMPO) can catalyze aldehyde formation with a cheaper oxidant.
Alternatively, vicinal diols or their oxidized sequelae (acyloins or α-hydroxy acids) can be oxidized with cleavage to two aldehydes or an aldehyde and carbon dioxide. | 0 | Organic Chemistry |
A general second messenger system mechanism can be broken down into four steps. First, the agonist activates a membrane-bound receptor. Second, the activated G-protein produces a primary effector. Third, the primary effect stimulates the second messenger synthesis. Fourth, the second messenger activates a certain cellular process.
The G-protein coupled receptors for the PIP messenger system produces two effectors, phospholipase C (PLC) and phosphoinositide 3-kinase (PI3K). PLC as an effector produces two different second messengers, inositol triphosphate (IP) and Diacylglycerol (DAG).
IP is soluble and diffuses freely into the cytoplasm. As a second messenger, it is recognized by the inositol triphosphate receptor (IP3R), a Ca channel in the endoplasmic reticulum (ER) membrane, which stores intracellular Ca. The binding of IP to IP3R releases Ca from the ER into the normally Ca-poor cytoplasm, which then triggers various events of Ca signaling. Specifically in blood vessels, the increase in Ca concentration from IP releases nitric oxide, which then diffuses into the smooth muscle tissue and causes relaxation.
DAG remains bound to the membrane by its fatty acid "tails" where it recruits and activates both conventional and novel members of the protein kinase C family. Thus, both IP and DAG contribute to activation of PKCs.
Phosphoinositide 3-kinase (PI3K) as an effector phosphorylates phosphatidylinositol bisphosphate (PIP) to produce phosphatidylinositol (3,4,5)-trisphosphate (PIP). PIP has been shown to activate protein kinase B, increase binding to extracellular proteins and ultimately enhance cell survival. | 1 | Biochemistry |
Some efforts have been made to extract systematically interaction networks directly from the scientific literature. Such approaches range in terms of complexity from simple co-occurrence statistics of entities that are mentioned together in the same context (e.g. sentence) to sophisticated natural language processing and machine learning methods for detecting interaction relationships. | 1 | Biochemistry |
Before introduction of platinum catalysts by Speier, hydrosilylation was not practiced widely. A peroxide-catalyzed process was reported in academic literature in 1947, but the introduction of Speier's catalyst (HPtCl) was a big breakthrough.
Karstedts catalyst was later introduced. It is a lipophilic complex that is soluble in the organic substrates of industrial interest. Complexes and compounds that catalyze hydrogenation are often effective catalysts for hydrosilylation, e.g. Wilkinsons catalyst. | 7 | Physical Chemistry |
Because of the way ESTs are sequenced, many distinct expressed sequence tags are often partial sequences that correspond to the same mRNA of an organism. In an effort to reduce the number of expressed sequence tags for downstream gene discovery analyses, several groups assembled expressed sequence tags into EST contigs. Example of resources that provide EST contigs include: TIGR gene indices, Unigene, and STACK
Constructing EST contigs is not trivial and may yield artifacts (contigs that contain two distinct gene products). When the complete genome sequence of an organism is available and transcripts are annotated, it is possible to bypass contig assembly and directly match transcripts with ESTs. This approach is used in the TissueInfo system (see below) and makes it easy to link annotations in the genomic database to tissue information provided by EST data. | 1 | Biochemistry |
Corrosion mapping by ultrasonics is a nonintrusive (noninvasive) technique which maps material thickness using ultrasonic techniques.
Variations in material thickness due to corrosion can be identified and graphically portrayed as an image.
The technique is widely used in the oil and gas industries for the in-service detection and characterization of corrosion in pipes and vessels.
The data is stored on a computer and may be color coded to show differences in thickness readings.
Corrosion may be mapped using Zero degree ultrasonic probes, an Eddy current array and/or Time of flight detection methods.
The book Nondestructive Examination of Underwater Welded Structures by Victor S. Davey describes a "fully automated dual axis robotic scanner used for corrosion mapping normally using a single zero degree compression probe scanned in a raster pattern over the area of interest."
He also goes on to explain that "typically a 4 mm by 4 mm raster" is used. | 8 | Metallurgy |
The set of databases includes data from International Tables of Crystallography, Vol. A: Space-Group Symmetry, and the data of maximal subgroups of space groups as listed in International Tables of Crystallography, Vol. A1: Symmetry relations between space groups. A k-vector database with Brillouin zone figures and classification tables of the k-vectors for space groups is also available via the [http://www.cryst.ehu.es/cryst/get_kvec.html KVEC] tool. | 3 | Analytical Chemistry |
The activity of some enzymes is regulated by ADP-ribosylation. For instance, the activity of Rodospirillum rubrum di-nitrogenase-reductase is turned off by ADP-ribosylation of an arginine residue, and reactivated by the removal of the ADP-ribosyl group. | 1 | Biochemistry |
Coenzyme Q (CoQ ) also known as ubiquinone, is a naturally occurring biochemical cofactor (coenzyme) and an antioxidant produced by the human body. It can also be obtained from dietary sources, such as meat, fish, seed oils, vegetables, and dietary supplements. CoQ is found in many organisms, including animals and bacteria.
CoQ plays a role in mitochondrial oxidative phosphorylation, aiding in the production of adenosine triphosphate (ATP), which is involved in energy transfer within cells. The structure of CoQ consists of a benzoquinone moiety and an isoprenoid side chain, with the "10" referring to the number of isoprenyl chemical subunits in its tail.
Although a ubiquitous molecule in human tissues, CoQ is not a dietary nutrient, does not have a recommended intake level, and its use as a supplement is not associated with or approved for any health or anti-disease effect. | 1 | Biochemistry |
The organization is led by a steering committee elected from its members. The steering committee represents the EBF in international forums and sets the agenda for the closed and open meetings. | 3 | Analytical Chemistry |
In high-density oligonucleotide SNP arrays, hundreds of thousands of probes are arrayed on a small chip, allowing for many SNPs to be interrogated simultaneously. Because SNP alleles only differ in one nucleotide and because it is difficult to achieve optimal hybridization conditions for all probes on the array, the target DNA has the potential to hybridize to mismatched probes. This is addressed somewhat by using several redundant probes to interrogate each SNP. Probes are designed to have the SNP site in several different locations as well as containing mismatches to the SNP allele. By comparing the differential amount of hybridization of the target DNA to each of these redundant probes, it is possible to determine specific homozygous and heterozygous alleles. Although oligonucleotide microarrays have a comparatively lower specificity and sensitivity, the scale of SNPs that can be interrogated is a major benefit. The Affymetrix Human SNP 5.0 GeneChip performs a genome-wide assay that can genotype over 500,000 human SNPs (Affymetrix 2007).. | 1 | Biochemistry |
George Simms Hammond (May 22, 1921 – October 5, 2005) was an American scientist and theoretical chemist who developed "Hammonds postulate", and fathered organic photochemistry,–the general theory of the geometric structure of the transition state in an organic chemical reaction. Hammonds research is also known for its influence on the philosophy of science. His research garnered him the Norris Award in 1968, the Priestley Medal in 1976, the National Medal of Science in 1994, and the Othmer Gold Medal in 2003. He served as the executive chairman of the Allied Chemical Corporation from 1979 to 1989.
He was a chemist at the California Institute of Technology, and subsequently headed both the Departments of Chemistry and Chemical Engineering at the university. He conducted research at the University of Oxford and University of Basel as a Guggenheim Fellow and National Science Foundation Fellow, respectively. He served as the foreign secretary of the National Academy of Sciences from 1974 to 1978.
A native of Maine, he was born and raised in Auburn; he attended nearby Bates College in Lewiston, Maine, where he graduated magna cum laude with a B.S. in chemistry in 1943. He completed his doctorate at Harvard University in 1947, under the mentorship of Paul Doughty Bartlett, and a postdoctorate at University of California, Los Angeles with Saul Winstein in 1948. | 7 | Physical Chemistry |
Lichenometry is a technique used to determine the age of exposed rock surfaces based on the size of lichen thalli. Introduced by Beschel in the 1950s, the technique has found many applications. it is used in archaeology, palaeontology, and geomorphology. It uses the presumed regular but slow rate of lichen growth to determine the age of exposed rock. Measuring the diameter (or other size measurement) of the largest lichen of a species on a rock surface indicates the length of time since the rock surface was first exposed. Lichen can be preserved on old rock faces for up to 10,000 years, providing the maximum age limit of the technique, though it is most accurate (within 10% error) when applied to surfaces that have been exposed for less than 1,000 years. Lichenometry is especially useful for dating surfaces less than 500 years old, as radiocarbon dating techniques are less accurate over this period. The lichens most commonly used for lichenometry are those of the genera Rhizocarpon (e.g. the species Rhizocarpon geographicum, map lichen) and Xanthoria. | 2 | Environmental Chemistry |
The proposed mechanism for cationic photopolymerization begins with the photoexcitation of the initiator. Once excited, both homolytic cleavage and dissociation of a counter anion takes place, generating a cationic radical (R), an aryl radical (R') and an unaltered counter anion (X). The abstraction of a lewis acid by the cationic radical produces a very weakly bound hydrogen and a free radical. The acid is further deprotonated by the anion (X) in solution, generating a lewis acid with the starting anion (X) as a counter ion. It is thought that the acidic proton generated is what ultimately initiates the polymerization. | 5 | Photochemistry |
The plate count method relies on bacteria growing a colony on a nutrient medium so that the colony becomes visible to the naked eye and the number of colonies on a plate can be counted. To be effective, the dilution of the original sample must be arranged so that on average between 30 and 300 colonies of the target bacterium are grown. Fewer than 30 colonies makes the interpretation statistically unsound whilst greater than 300 colonies often results in overlapping colonies and imprecision in the count. To ensure that an appropriate number of colonies will be generated several dilutions are normally cultured. This approach is widely utilised for the evaluation of the effectiveness of water treatment by the inactivation of representative microbial contaminants such as E. coli following ASTM D5465.
The laboratory procedure involves making serial dilutions of the sample (1:10, 1:100, 1:1000, etc.) in sterile water and cultivating these on nutrient agar in a dish that is sealed and incubated. Typical media include plate count agar for a general count or MacConkey agar to count Gram-negative bacteria such as E. coli. Typically one set of plates is incubated at 22 °C and for 24 hours and a second set at 37 °C for 24 hours. The composition of the nutrient usually includes reagents that resist the growth of non-target organisms and make the target organism easily identified, often by a colour change in the medium. Some recent methods include a fluorescent agent so that counting of the colonies can be automated. At the end of the incubation period the colonies are counted by eye, a procedure that takes a few moments and does not require a microscope as the colonies are typically a few millimetres across. | 3 | Analytical Chemistry |
Heterogeneous gold catalysis refers to the use of elemental gold as a heterogeneous catalyst. As in most heterogeneous catalysis, the metal is typically supported on metal oxide. Furthermore, as seen in other heterogeneous catalysts, activity increases with a decreasing diameter of supported gold clusters. Several industrially relevant processes are also observed such as H activation, Water-gas shift reaction, and hydrogenation. One or two gold-catalyzed reactions may have been commercialized.
The high activity of supported gold clusters has been proposed to arise from a combination of structural changes, quantum-size effects and support effects that preferentially tune the electronic structure of gold such that optimal binding of adsorbates during the catalytic cycle is enabled. The selectivity and activity of gold nanoparticles can be finely tuned by varying the choice of support material, with e.g. titania (TiO), hematite (α-FeO), cobalt(II/III) oxide (CoO) and nickel(II) oxide (NiO) serving as the most effective support materials for facilitating the catalysis of CO combustion. Besides enabling an optimal dispersion of the nanoclusters, the support materials have been suggested to promote catalysis by altering the size, shape, strain and charge state of the cluster. A precise shape control of the deposited gold clusters has been shown to be important for optimizing the catalytic activity, with hemispherical, few atomic layers thick nanoparticles generally exhibiting the most desirable catalytic properties due to maximized number of high-energy edge and corner sites. | 7 | Physical Chemistry |
CH has been measured directly in the environment since the 1970s. The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century.
Long term atmospheric measurements of methane by NOAA show that the build up of methane nearly tripled since pre-industrial times since 1750. In 1991 and 1998 there was a sudden growth rate of methane representing a doubling of growth rates in previous years. The June 15, 1991 eruption of Mount Pinatubo, measuring VEI-6was the second-largest terrestrial eruption of the 20th century. In 2007 it was reported that unprecedented warm temperatures in 1998the warmest year since surface records were recordedcould have induced elevated methane emissions, along with an increase in wetland and rice field emissions and the amount of biomass burning.
Data from 2007 suggested methane concentrations were beginning to rise again. This was confirmed in 2010 when a study showed methane levels were on the rise for the 3 years 2007 to 2009. After a decade of near-zero growth in methane levels, "globally averaged atmospheric methane increased by [approximately] 7 nmol/mol per year during 2007 and 2008. During the first half of 2009, globally averaged atmospheric CH was [approximately] 7 nmol/mol greater than it was in 2008, suggesting that the increase will continue in 2009." From 2015 to 2019 sharp rises in levels of atmospheric methane have been recorded.
In 2010, methane levels in the Arctic were measured at 1850 nmol/mol which is over twice as high as at any time in the last 400,000 years. According to the IPCC AR5, since 2011 concentrations continued to increase. After 2014, the increase accelerated and by 2017, it reached 1,850 (parts per billion) ppb. The annual average for methane (CH) was 1866 ppb in 2019 and scientists reported with "very high confidence" that concentrations of CH were higher than at any time in at least 800,000 years. The largest annual increase occurred in 2021 with current concentrations reaching a record 260% of pre-industrialwith the overwhelming percentage caused by human activity.
In 2013, IPCC scientists said with "very high confidence", that concentrations of atmospheric methane CH "exceeded the pre-industrial levels by about 150% which represented "levels unprecedented in at least the last 800,000 years." The globally averaged concentration of methane in Earth's atmosphere increased by about 150% from 722 ± 25 ppb in 1750 to 1803.1 ± 0.6 ppb in 2011. As of 2016, methane contributed radiative forcing of 0.62 ± 14% Wm, or about 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases. The atmospheric methane concentration has continued to increase since 2011 to an average global concentration of 1911.8 ± 0.6 ppb as of 2022. The May 2021 peak was 1891.6 ppb, while the April 2022 peak was 1909.4 ppb, a 0.9% increase. The Global Carbon Project consortium produces the Global Methane Budget. Working with over fifty international research institutions and 100 stations globally, it updates the methane budget every few years.
In 2013, the balance between sources and sinks of methane was not yet fully understood. Scientists were unable to explain why the atmospheric concentration of methane had temporarily ceased to increase.
The focus on the role of methane in anthropogenic climate change has become more relevant since the mid-2010s. | 2 | Environmental Chemistry |
Filtration is a unit operation that is commonly used both in laboratory and production conditions. This apparatus, adapted for laboratory work, is often used to isolate the product of synthesis of a reaction when the product is a solid in suspension. The product of synthesis is then recovered faster, and the solid is drier than in the case of a simple filtration. Other than isolating a solid, filtration is also a stage of purification: the soluble impurities in the solvent are eliminated in the filtrate (liquid).
This apparatus is often used to purify a liquid. When a synthesised product is filtered, the insolubles (catalysers, impurities, sub-products of the reaction, salts, ...) remain in the filter. In this case, vacuum filtration is also more efficient that a simple filtration: there is more liquid recovered, and the yield is therefore better. | 3 | Analytical Chemistry |
*SK1
*PDE4A1
*Raf1
*mTOR
*PP1
*SHP1
*Spo20p
*p47phox
*PKCε
*PLCβ
*PIP5K
*[https://www.yeastgenome.org/locus/S000001012 Opi1]
*TREK-1
*K
*K2.2 | 1 | Biochemistry |
The dendrimer is assembled from a multifunctional core, which is extended outward by a series of reactions, commonly a Michael reaction. Each step of the reaction must be driven to full completion to prevent mistakes in the dendrimer, which can cause trailing generations (some branches are shorter than the others). Such impurities can impact the functionality and symmetry of the dendrimer, but are extremely difficult to purify out because the relative size difference between perfect and imperfect dendrimers is very small. | 6 | Supramolecular Chemistry |
The presence of these two genes was first suspected when Nelson and Kennedy (1972) showed that there were Mg-repressible and non-repressible Mg uptake systems in E. coli. The non-repressible uptake of Mg is mediated by the CorA protein. In S. typhimurium the repressible Mg uptake was eventually shown to be via the MgtA and MgtB proteins.
Both MgtA and MgtB are regulated by the PhoPQ system and are actively transcribed during the process of infection of human patients by S. typhimurium. Although neither gene is required for pathogenicity, the MgtB protein does enhance the long-term survival of the pathogen in the cell. The genes are also upregulated in vitro when the Mg concentration falls below 50 μM (Snavely et al., 1991a). Although the proteins have km values similar to CorA and transport rates approximately 10 times less, the genes may be part of a Mg scavenging system. Chamnongpol and Groisman (2002) presents evidence that the role of these proteins may be to compensate for the inactivation of the CorA protein by the PhoPQ regulon. The authors suggest that the CorA protein is inactivated to allow the avoidance of metal toxicity via the protein in the low Mg environments S. typhimurium is subjected to by cells after infection.
The proteins are both P-type ATPases
and neither gene shows any similarity to CorA. The MgtA and MgtB proteins are 75% similar (50% identical), although it seems that MgtB may have been acquired by horizontal gene transfer as part of Salmonella Pathogenicity Island 3. The TM topology of the MgtB protein has been experimentally determined, showing that the protein has ten TM-spanning helices with the termini of the protein in the cytoplasm (see figure
). MgtA is present in widely divergent bacteria, but is not nearly as common as CorA, while MgtB appears to have a quite restricted distribution. No hypotheses for the unusual distribution have been suggested.
The figure, adapted from Smith et al. (1993b), shows the experimentally determined membrane topology of the MgtB protein in S. typhimurium. The TM domains are shown in light blue and the orientation in the membrane and the positions of the N- and C-termini are indicated. The figure is not drawn to scale.
While the MgtA and MgtB proteins are very similar, they do show some minor differences in activity. MgtB is very sensitive to temperature, losing all activity (with regard to Mg transport) at a temperature of 20 °C. Additionally, MgtB and MgtA are inhibited by different ranges of cations (Table A10.1).
The table lists cation transport characteristics of the MgtA and MgtB proteins in S. typhimurium as well as the kinetic data for the MgtA and MgtB transport proteins at 37 °C. The Vmax numbers listed in parentheses are those for uptake at 20 °C. The inhibition of Mg transport by Mn via MgtA showed unusual kinetics (see Figure 1 of Snavely et al., 1989b)
The MgtA and MgtB proteins are ATPases, using one molecule of ATP per transport cycle, whereas the Mg uptake via CorA is simply electrochemically favourable. Chamnongpol and Groisman (2002) have suggested that the MgtA and MgtB proteins form part of a metal toxicity avoidance system. Alternatively, as most P-type ATPases function as efflux mediating transporters, it has been suggested that the MgtA and MgtB proteins act as efflux proteins for a currently unidentified cation, and Mg transport is either non-specific or exchanged to maintain the electro-neutrality of the transport process. Further experiments will be required to define the physiological function of these proteins. | 1 | Biochemistry |
Chimpanzees emit alarm calls in response to predators, such as leopards and snakes. They produce three types of alarm calls: acoustically-variable hoos, barks, and SOS screams. Alarm signalling is impacted by receiver knowledge and caller age, can be coupled with receiver monitoring, and is important to the understanding of the evolution of hominoid communication. | 1 | Biochemistry |
In 1897, protargol, a silver salt of a protein mixture, developed by Eichengrün at Bayer, was introduced as a new drug against gonorrhea. Protargol stayed in use until sulfa drugs and then antibiotics became available in the 1940s. | 5 | Photochemistry |
Alexander Nikolayevich Nesmeyanov (; – 17 January 1980) was a Soviet chemist and academician (1943) specializing in organometallic chemistry. | 0 | Organic Chemistry |
Positive feedback loops can cause ultrasensitive responses. An example of this is seen in the transcription of certain eukaryotic genes in which non-cooperative transcription factor binding changes positive feedback loops of histone modification that results in an ultrasensitive activation of transcription. The binding of a transcription factor recruits histone acetyltransferases and methyltransferases. The acetylation and methylation of histones recruits more acetyltransferases and methyltransferases that results in a positive feedback loop. Ultimately, this results in activation of transcription.
Additionally, positive feedback can induce bistability in Cyclin B1- by the two regulators Wee1 and Cdc25C, leading to the cells decision to commit to mitosis. The system cannot be stable at intermediate levels of Cyclin B1, and the transition between the two stable states is abrupt when increasing levels of Cyclin B1 switches the system from low to high activity. Exhibiting hysteresis, for different levels of Cyclin B1, the switches from low to high and high to low states vary. However, the emergence of a bistable system is highly influenced by the sensitivity of its feedback loops. It has been shown in Xenopus' egg extracts that Cdc25C hyperphosphorylation is a highly ultrasensitive function of Cdk activity, displaying a high value of the Hill coefficient (approx. 11), and the dephosphorylation step of Ser 287 in Cdc25C (also involved in Cdc25C activation) is even more ultrasensitive, displaying a Hill coefficient of approximately 32. | 1 | Biochemistry |
Alloy systems that are liquid at room temperature have thermal conductivity far superior to ordinary non-metallic liquids, allowing liquid metal to efficiently transfer energy from the heat source to the liquid. They also have a higher electrical conductivity that allows the liquid to be pumped more efficiently, by electromagnetic pumps. This results in the use of these materials for specific heat conducting and/or dissipation applications.
Another advantage of liquid alloy systems is their inherent high densities. | 8 | Metallurgy |
Sea salt aerosols can alter the Earth radiation budget through directly scattering solar radiation (direct effect), and indirectly changing the cloud albedo by serving as CCN (indirect effect). Different models give different predictions of annual mean radiative forcing induced by sea salt direct effect, but most of the previous studies give a number around 0.6-1.0 W m. Radiative forcing caused by indirect effects show even greater variations in model prediction because of the parameterization of aerosol indirect effect. However, model results present a stronger indirect effect on the Southern Hemisphere. | 9 | Geochemistry |
The number of RNAPs in bacterial cells (e.g., E. coli) have been shown to be smaller than the number of sigma factors. Consequently, if a certain sigma factor is overexpressed, not only will increase the expression levels of genes whose promoters have preference for that sigma factor, but it will also reduce the probability that genes with promoters with preference for other sigma factors.
Meanwhile, transcription initiation has two major rate limiting steps: the closed and the open complex formation. However, only the dynamics of the first step depends on the concentration of sigma factors. Interestingly, the fastest is the closed complex formation relative to the open complex formation, the less responsive is a promoter to changes in sigma factors’ concentration (see for a model and empirical data of this phenomenon). | 1 | Biochemistry |
The pressure cell is connected to a source of compressed gas (such as Argon, Helium or Nitrogen). A capillary is placed through a ferrule in the cap so that one end is in contact with the liquid in the tube or vial. The distal end of the capillary is fritted to retain the particles while packing. Pressure from the compressed gas can be regulated to adjust the flow rate of the sample into the capillary. | 3 | Analytical Chemistry |
In general, in prokaryotes the lifetime of mRNA is much shorter than in eukaryotes. Prokaryotes degrade messages by using a combination of ribonucleases, including endonucleases, 3 exonucleases, and 5 exonucleases. In some instances, small RNA molecules (sRNA) tens to hundreds of nucleotides long can stimulate the degradation of specific mRNAs by base-pairing with complementary sequences and facilitating ribonuclease cleavage by RNase III. It was recently shown that bacteria also have a sort of 5 cap consisting of a triphosphate on the 5 end. Removal of two of the phosphates leaves a 5 monophosphate, causing the message to be destroyed by the exonuclease RNase J, which degrades 5 to 3'. | 1 | Biochemistry |
The term optical activity is derived from the interaction of chiral materials with polarized light. In a solution, the (−)-form, or levorotatory form, of an optical isomer rotates the plane of a beam of linearly polarized light counterclockwise. The (+)-form, or dextrorotatory form, of an optical isomer does the opposite. The rotation of light is measured using a polarimeter and is expressed as the optical rotation.
Enantiomers can be separated by chiral resolution. This often involves forming crystals of a salt composed of one of the enantiomers and an acid or base from the so-called chiral pool of naturally occurring chiral compounds, such as malic acid or the amine brucine. Some racemic mixtures spontaneously crystallize into right-handed and left-handed crystals that can be separated by hand. Louis Pasteur used this method to separate left-handed and right-handed sodium ammonium tartrate crystals in 1849. Sometimes it is possible to seed a racemic solution with a right-handed and a left-handed crystal so that each will grow into a large crystal.
Liquid chromatography (HPLC and TLC) may also be used as an analytical method for the direct separation of enantiomers and the control of enantiomeric purity, e.g. active pharmaceutical ingredients (APIs) which are chiral. | 4 | Stereochemistry |
Sultams are cyclic sulfonamides. Bioactive sultams include the antiinflammatory ampiroxicam and the anticonvulsant sulthiame. Sultams are prepared analogously to other sulfonamides, allowing for the fact that sulfonic acids are deprotonated by amines. They are often prepared by one-pot oxidation of disulfides or thiols linked to amines. An alternative synthesis of sultams involves initial preparation of a linear sulfonamide, followed by intramolecular C-C bond formation (i.e. cyclization), a strategy that was used in the synthesis of a sultam-based deep-blue emitter for organic electronics. | 0 | Organic Chemistry |
Nitroalkenes are useful intermediates for various chemical functionalities.
* A nitroalkene behaving as a Michael acceptor in the synthesis of Lycoricidine:
* Nitroalkene acting as an activated dienophile toward butadiene in a Diels-Alder cycloaddition:
* The synthesis of pyrrole derivatives via the Barton–Zard reaction:
* Pericyclic reaction of a nitroalkene yielding an indole:
* Partial hydrogenation to an alkene baring a hydroxylamine functional group:
* Reduction to primary amines:
* Asymmetric Stetter reaction: | 0 | Organic Chemistry |
Gel electrolytes – closely resemble liquid electrolytes. In essence, they are liquids in a flexible lattice framework. Various additives are often applied to increase the conductivity of such systems. | 7 | Physical Chemistry |
In biology, much of what we understand to be protein-based molecular motors may also in fact be Brownian motors. These molecular motors facilitate critical cellular processes in living organisms and, indeed, are fundamental to life itself.
Researchers have made significant advances in terms of examining these organic processes to gain insight into their inner workings. For example, molecular Brownian motors in the form of several different types of protein exist within humans. Two common biomolecular Brownian motors are ATP synthase, a rotary motor, and myosin II, a linear motor. The motor protein ATP synthase produces rotational torque that facilitates the synthesis of ATP from Adenosine diphosphate (ADP) and inorganic phosphate (P) through the following overall reaction:
ADP + P + 3H ⇌ ATP + HO + 3H
In contrast, the torque produced by myosin II is linear and is a basis for the process of muscle contraction. Similar motor proteins include kinesin and dynein, which all convert chemical energy into mechanical work by the hydrolysis of ATP. Many motor proteins within human cells act as Brownian motors by producing directed motion on the nanoscale, and some common proteins of this type are illustrated by the following computer-generated images. | 7 | Physical Chemistry |
Membrane proteins and self-assembly properties of certain proteins can be studied under this technique, due to being a label-free calorimeter. Membrane proteins are known to have difficulties with selection of proper solubilization and purification protocols. As ITC is a non-destructive calorimetric tool, it can be used as a detector to locate the fraction of protein with desired binding sites, by binding a known binding ligand to the protein. This feature also applies in studies of self-assembling proteins, especially in use of measuring thermodynamics of their structural transformation. | 7 | Physical Chemistry |
It is desirable to ferment D-xylose to ethanol. This can be accomplished either by native xylose fermenting yeasts such as Scheffersomyces Pichia stipitis or by metabolically engineered strains of Saccharomyces cerevisiae. Pichia stipitis is not as ethanol tolerant as the traditional ethanol producing yeast Saccharomyces cerevisiae. S. cerevisiae on the other hand can not ferment D-xylose to ethanol. In attempts to generate S. cerevisiae strains that are able to ferment D-xylose the XYL1 and XYL2 genes of P. stipitis coding for the D-xylose reductase (XR) and xylitol dehydrogenase (XDH), respectively were introduced in S. cerevisiae by means of genetic engineering. XR catalyze the formation of xylitol from D-xylose and XDH the formation of D-xylulose from xylitol. Saccharomyces cerevisiae can naturally ferment D-xylulose through the pentose phosphate pathway.
In another approach, bacterial xylose isomerases have been introduced into S. cerevisiae. This enzyme catalyze the direct formation of D-xylulose from D-xylose. Many attempts at expressing bacterial isomerases were not successful due to misfolding or other problems, but a xylose isomerase from the anaerobic fungus Piromyces Sp. has proven effective. One advantage claimed for S. cerevisiae engineered with the xylose isomerase is that the resulting cells can grow anaerobically on xylose after evolutionary adaptation.
Studies on flux through the oxidative pentose phosphate pathway during D-xylose metabolism have revealed that limiting the rate of this step may be beneficial to the efficiency of fermentation to ethanol. Modifications to this flux that may improve ethanol production include deleting the GND1 gene, or the ZWF1 gene. Since the pentose phosphate pathway produces additional NADPH during metabolism, limiting this step will help to correct the already evident imbalance between NAD(P)H and NAD+ cofactors and reduce xylitol byproduct formation.
Another experiment comparing the two D-xylose metabolizing pathways revealed that the XI pathway was best able to metabolize D-xylose to produce the greatest ethanol yield, while the XR-XDH pathway reached a much faster rate of ethanol production.
Overexpression of the four genes encoding non-oxidative pentose phosphate pathway enzymes Transaldolase, Transketolase, Ribulose-5-phosphate epimerase and Ribose-5-phosphate ketol-isomerase led to both higher D-xylulose and D-xylose fermentation rate.
The aim of this genetic recombination in the laboratory is to develop a yeast strain that efficiently produces ethanol. However, the effectiveness of D-xylose metabolizing laboratory strains do not always reflect their metabolism abilities on raw xylose products in nature. Since D-xylose is mostly isolated from agricultural residues such as wood stocks then the native or genetically altered yeasts will need to be effective at metabolizing these less pure natural sources.
Varying expression of the XR and XDH enzyme levels have been tested in the laboratory in the attempt to optimize the efficiency of the D-xylose metabolism pathway. | 1 | Biochemistry |
Only two elements are liquid at standard conditions for temperature and pressure: mercury and bromine. Four more elements have melting points slightly above room temperature: francium, caesium, gallium and rubidium. In addition, certain mixtures of elements are liquid at room temperature, even if the individual elements are solid under the same conditions (see eutectic mixture). An example is the sodium-potassium metal alloy NaK. Other metal alloys that are liquid at room temperature include galinstan, which is a gallium-indium-tin alloy that melts at , as well as some amalgams (alloys involving mercury).
Pure substances that are liquid under normal conditions include water, ethanol and many other organic solvents. Liquid water is of vital importance in chemistry and biology, and it is necessary for all known forms of life.
Inorganic liquids include water, magma, inorganic nonaqueous solvents and many acids.
Important everyday liquids include aqueous solutions like household bleach, other mixtures of different substances such as mineral oil and gasoline, emulsions like vinaigrette or mayonnaise, suspensions like blood, and colloids like paint and milk.
Many gases can be liquefied by cooling, producing liquids such as liquid oxygen, liquid nitrogen, liquid hydrogen and liquid helium. Not all gases can be liquified at atmospheric pressure, however. Carbon dioxide, for example, can only be liquified at pressures above 5.1 atm.
Some materials cannot be classified within the classical three states of matter. For example, liquid crystals (used in liquid-crystal displays) possess both solid-like and liquid-like properties, and belong to their own state of matter distinct from either liquid or solid. | 7 | Physical Chemistry |
Accumulation of excess homogentisic acid and its oxide, named alkapton, is a result of the failure of the enzyme homogentisic acid 1,2-dioxygenase (typically due to a mutation) in the degradative pathway of tyrosine, consequently associated with alkaptonuria. | 1 | Biochemistry |
The evolution of photosynthesis refers to the origin and subsequent evolution of photosynthesis, the process by which light energy is used to assemble sugars from carbon dioxide and a hydrogen and electron source such as water. The process of photosynthesis was discovered by Jan Ingenhousz, a Dutch-born British physician and scientist, first publishing about it in 1779.
The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen rather than water. There are three major metabolic pathways by which photosynthesis is carried out: C photosynthesis, C photosynthesis, and CAM photosynthesis. C photosynthesis is the oldest and most common form. A C3 plant uses the Calvin cycle for the initial steps that incorporate into organic material. A C4 plant prefaces the Calvin cycle with reactions that incorporate into four-carbon compounds. A CAM plant uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. C4 and CAM plants have special adaptations that save water. | 5 | Photochemistry |
The investigation of the TRPM genes and proteins in human cells is an area of intense recent study and, at times, debate. Montell et al. (2002) have reviewed the research into the TRP genes, and a second review by Montell (2003) has reviewed the research into the TRPM genes.
The TRPM family of ion channels has members throughout the metazoa. The TRPM6 and TRPM7 proteins are highly unusual, containing both an ion channel domain and a kinase domain (Figure 1.7), the role of which brings about the most heated debate.
The activity of these two proteins has been very difficult to quantify. TRPM7 by itself appears to be a Ca channel but in the presence of TRPM6 the affinity series of transported cations places Mg above Ca. The differences in reported conductance were caused by the expression patterns of these genes. TRPM7 is expressed in all cell types tested so far, while TRPM6 shows a more restricted pattern of expression. An unfortunate choice of experimental system by Voets et al., (2004) led to the conclusion that TRPM6 is a functional Mg transporter. However, later work by Chubanov et al. (2004) clearly showed that TRPM7 is required for TRPM6 activity and that the results of Voets et al. are explained by the expression of TRPM7 in the experimental cell line used by Voets et al. in their experiments. Whether TRPM6 is functional by itself is yet to be determined.
The predicted TM topology of the TPRM6 and TRPM7 proteins has been adapted from Nadler et al. (2001), Runnels et al. (2001) and Montell et al. (2002), this figure shows the computer predicted membrane topology of the TRPM6 and TRPM7 proteins in Homo sapiens. At this time, the topology shown should be considered a tentative hypothesis. The TM domains are shown in light blue, the pore loop in purple, the TRP motif in red and the kinase domain in green. The orientation in the membrane and the positions of the N- and C-termini are indicated and the figure is not drawn to scale.
The conclusions of the Voets et al. (2004) paper are probably incorrect in attributing the Mg dependent currents to TRPM7 alone, and their kinetic data are likely to reflect the combined TRPM7/ TRPM6 channel. The report presents a robust collection of data consistent with a channel-like activity passing Mg, based on both electrophysiological techniques and also mag-fura 2 to determine changes in cytoplasmic free Mg. | 1 | Biochemistry |
Survivin is known to be expressed during fetal development and across most tumour cell types, but is rarely present in normal, non-malignant adult cells. Tamm et al. showed that survivin was expressed in all 60 different human tumour lines used in the National Cancer Institute's cancer drug-screening program, with the highest levels of expression in breast and lung cancer lines and the lowest levels in renal cancers. Knowing the relative expression levels of survivin in different tumour types may prove helpful as survivin-related therapy may be administered depending on the expression level and reliance of the tumour type on survivin for resistance to apoptosis. | 1 | Biochemistry |
Sepro Mineral Systems Corp. is a Canadian company founded in 1987 and headquartered in British Columbia, Canada. The outcome of the acquisition of Sepro Mineral Processing International by Falcon Concentrators in 2008, the company's key focus is the production of mineral processing equipment for the mining and aggregate industries. Sepro Mineral Systems Corp. also provides engineering and process design services. Products sold by Sepro include grinding mills, ore scrubbers, vibrating screens, centrifugal gravity concentrators, agglomeration drums, and dense media separators. The company is also a supplier of single source modular pre-designed and custom designed plants and circuits.
Today, Sepro Mineral Systems Corp. is represented by global agents in over 15 countries and has equipment operating in over 31 countries around the world. | 8 | Metallurgy |
According to Mendelian inheritance, variations in an organism's phenotype (observable physical and behavioral characteristics) are due in part to variations in its genotype (particular set of genes). Each gene specifies a particular trait with a different sequence of a gene (alleles) giving rise to different phenotypes. Most eukaryotic organisms (such as the pea plants Mendel worked on) have two alleles for each trait, one inherited from each parent.
Alleles at a locus may be dominant or recessive; dominant alleles give rise to their corresponding phenotypes when paired with any other allele for the same trait, whereas recessive alleles give rise to their corresponding phenotype only when paired with another copy of the same allele. If you know the genotypes of the organisms, you can determine which alleles are dominant and which are recessive. For example, if the allele specifying tall stems in pea plants is dominant over the allele specifying short stems, then pea plants that inherit one tall allele from one parent and one short allele from the other parent will also have tall stems. Mendel's work demonstrated that alleles assort independently in the production of gametes, or germ cells, ensuring variation in the next generation. Although Mendelian inheritance remains a good model for many traits determined by single genes (including a number of well-known genetic disorders) it does not include the physical processes of DNA replication and cell division. | 1 | Biochemistry |
Imipenem is rapidly degraded by the renal enzyme dehydropeptidase 1 when administered alone, and is almost always coadministered with cilastatin to prevent this inactivation. | 4 | Stereochemistry |
Zeolites are natural or synthetic crystalline aluminosilicates, which have a repeating pore network and release water at high temperature. Zeolites are polar in nature.
They are manufactured by hydrothermal synthesis of sodium aluminosilicate or another silica source in an autoclave followed by ion exchange with certain cations (Na, Li, Ca, K, NH). The channel diameter of zeolite cages usually ranges from 2 to 9 Å. The ion exchange process is followed by drying of the crystals, which can be pelletized with a binder to form macroporous pellets.
Zeolites are applied in drying of process air, CO removal from natural gas, CO removal from reforming gas, air separation, catalytic cracking, and catalytic synthesis and reforming.
Non-polar (siliceous) zeolites are synthesized from aluminum-free silica sources or by dealumination of aluminum-containing zeolites. The dealumination process is done by treating the zeolite with steam at elevated temperatures, typically greater than . This high temperature heat treatment breaks the aluminum-oxygen bonds and the aluminum atom is expelled from the zeolite framework. | 7 | Physical Chemistry |
Many methods have been developed for measuring temperature. Most of these rely on measuring some physical property of a working material that varies with temperature. One of the most common devices for measuring temperature is the glass thermometer. This consists of a glass tube filled with mercury or some other liquid, which acts as the working fluid. Temperature increase causes the fluid to expand, so the temperature can be determined by measuring the volume of the fluid. Such thermometers are usually calibrated so that one can read the temperature simply by observing the level of the fluid in the thermometer. Another type of thermometer that is not really used much in practice, but is important from a theoretical standpoint, is the gas thermometer.
Other important devices for measuring temperature include:
* Thermocouples
* Thermistors
* Resistance temperature detector (RTD)
* Pyrometer
* Langmuir probes (for electron temperature of a plasma)
*Infrared thermometer
* Other thermometers
One must be careful when measuring temperature to ensure that the measuring instrument (thermometer, thermocouple, etc.) is really the same temperature as the material that is being measured. Under some conditions heat from the measuring instrument can cause a temperature gradient, so the measured temperature is different from the actual temperature of the system. In such a case the measured temperature will vary not only with the temperature of the system, but also with the heat transfer properties of the system.
What thermal comfort humans, animals and plants experience is related to more than temperature shown on a glass thermometer. Relative humidity levels in ambient air can induce more or less evaporative cooling. Measurement of the wet-bulb temperature normalizes this humidity effect. Mean radiant temperature also can affect thermal comfort. The wind chill factor makes the weather feel colder under windy conditions than calm conditions even though a glass thermometer shows the same temperature. Airflow increases the rate of heat transfer from or to the body, resulting in a larger change in body temperature for the same ambient temperature.
The theoretical basis for thermometers is the zeroth law of thermodynamics which postulates that if you have three bodies, A, B and C, if A and B are at the same temperature, and B and C are at the same temperature then A and C are at the same temperature. B, of course, is the thermometer.
The practical basis of thermometry is the existence of triple point cells. Triple points are conditions of pressure, volume and temperature such that three phases are simultaneously present, for example solid, vapor and liquid. For a single component there are no degrees of freedom at a triple point and any change in the three variables results in one or more of the phases vanishing from the cell. Therefore, triple point cells can be used as universal references for temperature and pressure (see Gibbs phase rule).
Under some conditions it becomes possible to measure temperature by a direct use of the Planck's law of black-body radiation. For example, the cosmic microwave background temperature has been measured from the spectrum of photons observed by satellite observations such as the WMAP. In the study of the quark–gluon plasma through heavy-ion collisions, single particle spectra sometimes serve as a thermometer. | 7 | Physical Chemistry |
There is an inverse relationship between delta yield strength and grain size to some power, x.
where k is the strengthening coefficient and both k and x are material specific. Assuming a narrow monodisperse grain size distribution in a polycrystalline material, the smaller the grain size, the smaller the repulsion stress felt by a grain boundary dislocation and the higher the applied stress needed to propagate dislocations through the material.
The relation between yield stress and grain size is described mathematically by the Hall–Petch equation:
where σ is the yield stress, σ is a materials constant for the starting stress for dislocation movement (or the resistance of the lattice to dislocation motion), k is the strengthening coefficient (a constant specific to each material), and d is the average grain diameter. It is important to note that the H-P relationship is an empirical fit to experimental data, and that the notion that a pileup length of half the grain diameter causes a critical stress for transmission to or generation in an adjacent grain has not been verified by actual observation in the microstructure.
Theoretically, a material could be made infinitely strong if the grains are made infinitely small. This is impossible though, because the lower limit of grain size is a single unit cell of the material. Even then, if the grains of a material are the size of a single unit cell, then the material is in fact amorphous, not crystalline, since there is no long range order, and dislocations can not be defined in an amorphous material. It has been observed experimentally that the microstructure with the highest yield strength is a grain size of about , because grains smaller than this undergo another yielding mechanism, grain boundary sliding. Producing engineering materials with this ideal grain size is difficult because only thin films can be reliably produced with grains of this size. In materials having a bi-disperse grain size distribution, for example those exhibiting abnormal grain growth, hardening mechanisms do not strictly follow the Hall–Petch relationship and divergent behavior is observed. | 8 | Metallurgy |
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