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The building blocks of materials are the chemical elements. These can be identified by their atomic number Z, which is the number of protons in the nucleus. An element can have more than one value for N, the number of neutrons in the nucleus. The sum of these is the mass number, which is roughly equal to the atomic mass. Atoms with the same atomic number but different neutron numbers are called isotopes. A given isotope is identified by a letter for the element preceded by a superscript for the mass number. For example, two common isotopes of chlorine are Cl and Cl. There are about 1700 known combinations of Z and N, of which only about 260 are stable. However, most of the unstable isotopes do not occur in nature. In geochemistry, stable isotopes are used to trace chemical pathways and reactions, while radioactive isotopes are primarily used to date samples.
The chemical behavior of an atom – its affinity for other elements and the type of bonds it forms – is determined by the arrangement of electrons in orbitals, particularly the outermost (valence) electrons. These arrangements are reflected in the position of elements in the periodic table. Based on position, the elements fall into the broad groups of alkali metals, alkaline earth metals, transition metals, semi-metals (also known as metalloids), halogens, noble gases, lanthanides and actinides.
Another useful classification scheme for geochemistry is the Goldschmidt classification, which places the elements into four main groups. Lithophiles combine easily with oxygen. These elements, which include Na, K, Si, Al, Ti, Mg and Ca, dominate in the Earths crust, forming silicates and other oxides. Siderophile elements (Fe, Co, Ni, Pt, Re, Os) have an affinity for iron and tend to concentrate in the core. Chalcophile elements (Cu, Ag, Zn, Pb, S) form sulfides; and atmophile' elements (O, N, H and noble gases) dominate the atmosphere. Within each group, some elements are refractory, remaining stable at high temperatures, while others are volatile, evaporating more easily, so heating can separate them. | 9 | Geochemistry |
Schwab received honours throughout his lifetime in recognition of his scientific work. In 1952 he became one of the only 45 ordinary members of the Bavarian Academy of Sciences, and in 1956 he was also inducted as a member of the Heidelberg Academy of Sciences and the German National Academy of Sciences Leopoldina.
In 1960 he was awarded the Liebig Medal of the German Chemical Society; he had also been awarded the Order of the Crown of Belgium (Officer class) as well as the Golden Cross of the Greek Order of George I.
Additionally, he was conferred honorary doctorates from the Sorbonne, the Free University of Berlin and the University of Liège, as well as an honorary professorship at the Central University of Venezuela. | 7 | Physical Chemistry |
The optimization of the particle size distribution facilitates the pumping, mixing and transportation of foodstuff. Particle size analysis is usually done with any milled food, such as coffee, flour, cocoa powder. It is especially helpful with chocolate quality to ensure there is a consistent taste and feeling when eaten. Furthermore, in the case of food emulsions, particle size analysis is relevant to predict stability and shelf-life, and optimize homogenization. | 3 | Analytical Chemistry |
Household RO units use a lot of water because they have low back pressure. Household RO water purifiers typically produce one liter of usable water and 3-25 liters of wastewater. The remainder is discharged, usually into the drain. Because wastewater carries the rejected contaminants, recovering this water is not practical for household systems. Wastewater is typically delivered to house drains. A RO unit delivering of treated water per day also discharge between . This led India's National Green Tribunal to propose a ban on RO water purification systems in areas where the total dissolved solids (TDS) measure in water is less than 500 mg/liter. In Delhi, large-scale use of household RO devices has increased the total water demand of the already water-parched National Capital Territory of India. | 3 | Analytical Chemistry |
Fumagillin has been used in the treatment of microsporidiosis. It is also an amebicide.
Fumagillin can block blood vessel formation by binding to an enzyme methionine aminopeptidase 2 and for this reason, the compound, together with semisynthetic derivatives, are investigated as an angiogenesis inhibitor in the treatment of cancer.
The company Zafgen conducted clinical trials using the fumagillin analog beloranib for weight loss, but they were unsuccessful.
Fumagillin is toxic to erythrocytes in vitro at concentrations greater than 10 μM. | 0 | Organic Chemistry |
Obtaining samples for analysis is challenging. VOCs, even when at dangerous levels, are dilute, so preconcentration is typically required. Many components of the atmosphere are mutually incompatible, e.g. ozone and organic compounds, peroxyacyl nitrates and many organic compounds. Furthermore, collection of VOCs by condensation in cold traps also accumulates a large amount of water, which generally must be removed selectively, depending on the analytical techniques to be employed.
Solid-phase microextraction (SPME) techniques are used to collect VOCs at low concentrations for analysis. As applied to breath analysis, the following modalities are employed for sampling: gas sampling bags, syringes, evacuated steel and glass containers. | 0 | Organic Chemistry |
Besides the oxygen ligand, which binds to hemoglobin in a cooperative manner, hemoglobin ligands also include competitive inhibitors such as carbon monoxide (CO) and allosteric ligands such as carbon dioxide (CO) and nitric oxide (NO). The carbon dioxide is bound to amino groups of the globin proteins to form carbaminohemoglobin; this mechanism is thought to account for about 10% of carbon dioxide transport in mammals. Nitric oxide can also be transported by hemoglobin; it is bound to specific thiol groups in the globin protein to form an S-nitrosothiol, which dissociates into free nitric oxide and thiol again, as the hemoglobin releases oxygen from its heme site. This nitric oxide transport to peripheral tissues is hypothesized to assist oxygen transport in tissues, by releasing vasodilatory nitric oxide to tissues in which oxygen levels are low. | 7 | Physical Chemistry |
AFPs are thought to inhibit ice growth by an adsorption–inhibition mechanism. They adsorb to nonbasal planes of ice, inhibiting thermodynamically-favored ice growth. The presence of a flat, rigid surface in some AFPs seems to facilitate its interaction with ice via Van der Waals force surface complementarity. | 1 | Biochemistry |
Both the oral and patch forms come with strong warnings against combining selegiline with drugs that could produce serotonin syndrome, such as SSRIs and the cough medicine dextromethorphan. Selegiline in combination with the opioid analgesic pethidine is not recommended, as it can lead to severe adverse effects. Several other synthetic opioids such as tramadol and methadone, as well as various triptans, are contraindicated due to potential for serotonin syndrome.
Birth control pills containing ethinylestradiol and a progestin increase the bioavailability of selegiline by 10- to 20-fold. High levels can lead to loss of MAO-B selectivity, and selegiline may begin inhibiting MAO-A as well. This increases susceptibility to side effects of non-selective MAOIs, such as tyramine-induced hypertensive crisis and serotonin toxicity when combined with serotonergic medications.
Both forms of the drug carry warnings about food restrictions to avoid hypertensive crisis that are associated with MAO inhibitors. The patch form was created in part to overcome food restrictions; clinical trials showed that it was successful. Additionally, in post-marketing surveillance from April 2006 to October 2010, only 13 self-reports of possible hypertensive events or hypertension were made out of 29,141 exposures to the drug, and none were accompanied by objective clinical data. The lowest dose of the patch method of delivery, 6 mg/24 hours, does not require any dietary restrictions. Higher doses of the patch and oral formulations, whether in combination with the older non-selective MAOIs or in combination with the reversible MAO-A inhibitor moclobemide, require a low-tyramine diet. | 4 | Stereochemistry |
The beta 2,6 linkages of levan allow for it to be soluble in both water and oil; however, the water temperature varies the degree of solubility. Levan also is insoluble in many organic solvents such as methanol, ethanol, and isopropanol. The branching of levan allows it to have a high tensile and cohesive strength, while the hydroxyl groups contribute to adhesion with other molecules. The intrinsic viscosity n, a measure of the substance effect on viscosity of a solution, tends to be very low for levan. This allows levan to be utilized in a pharmaceutical setting. | 1 | Biochemistry |
The glyoxalase system is a set of enzymes that carry out the detoxification of methylglyoxal and the other reactive aldehydes that are produced as a normal part of metabolism. This system has been studied in both bacteria and eukaryotes. This detoxification is accomplished by the sequential action of two thiol-dependent enzymes; firstly glyoxalase І, which catalyzes the isomerization of the spontaneously formed hemithioacetal adduct between glutathione and 2-oxoaldehydes (such as methylglyoxal) into S-2-hydroxyacylglutathione. Secondly, glyoxalase ІІ hydrolyses these thiolesters and in the case of methylglyoxal catabolism, produces D-lactate and GSH from S-D-lactoyl-glutathione.
This system shows many of the typical features of the enzymes that dispose of endogenous toxins. Firstly, in contrast to the amazing substrate range of many of the enzymes involved in xenobiotic metabolism, it shows a narrow substrate specificity. Secondly, intracellular thiols are required as part of its enzymatic mechanism and thirdly, the system acts to recycle reactive metabolites back to a form which may be useful to cellular metabolism. | 1 | Biochemistry |
Synthetic chelates such as ethylenediaminetetraacetic acid (EDTA) proved too stable and not nutritionally viable. If the mineral was taken from the EDTA ligand, the ligand could not be used by the body and would be expelled. During the expulsion process the EDTA ligand randomly chelated and stripped other minerals from the body. According to the Association of American Feed Control Officials (AAFCO), a metal–amino acid chelate is defined as the product resulting from the reaction of metal ions from a soluble metal salt with amino acids, with a mole ratio in the range of 1–3 (preferably 2) moles of amino acids for one mole of metal. The average weight of the hydrolyzed amino acids must be approximately 150 and the resulting molecular weight of the chelate must not exceed 800 Da. Since the early development of these compounds, much more research has been conducted, and has been applied to human nutrition products in a similar manner to the animal nutrition experiments that pioneered the technology. Ferrous bis-glycinate is an example of one of these compounds that has been developed for human nutrition. | 7 | Physical Chemistry |
Thiosemicarbazide is the chemical compound with the formula HNC(S)NHNH. A white, odorless solid, it is related to thiourea (HNC(S)NH) by the insertion of an NH center. They are commonly used as ligands for transition metals. Many thiosemicarbazides are known. These feature an organic substituent in place of one or more H's of the parent molecule. 4-Methyl-3-thiosemicarbazide is a simple example.
According to X-ray crystallography, the CSN core of the molecule is planar as are the three H's nearest the thiocarbonyl group. | 0 | Organic Chemistry |
Some coactivators indirectly regulate gene expression by binding to an activator and inducing a conformational change that then allows the activator to bind to the DNA enhancer or promoter sequence. Once the activator-coactivator complex binds to the enhancer, RNA polymerase II and other general transcription machinery are recruited to the DNA and transcription begins. | 1 | Biochemistry |
Thorin (also called thoron or thoronol) is an indicator used in the determination of barium, beryllium, lithium, uranium and thorium compounds. Being a compound of arsenic, it is highly toxic. | 3 | Analytical Chemistry |
RNA-Seq (named as an abbreviation of RNA sequencing) is a technique that uses next-generation sequencing to reveal the presence and quantity of RNA molecules in a biological sample, providing a snapshot of gene expression in the sample, also known as transcriptome.
Specifically, RNA-Seq facilitates the ability to look at alternative gene spliced transcripts, post-transcriptional modifications, gene fusion, mutations/SNPs and changes in gene expression over time, or differences in gene expression in different groups or treatments. In addition to mRNA transcripts, RNA-Seq can look at different populations of RNA to include total RNA, small RNA, such as miRNA, tRNA, and ribosomal profiling. RNA-Seq can also be used to determine exon/intron boundaries and verify or amend previously annotated 5 and 3 gene boundaries. Recent advances in RNA-Seq include single cell sequencing, bulk RNA sequencing, in situ sequencing of fixed tissue, and native RNA molecule sequencing with single-molecule real-time sequencing. Other examples of emerging RNA-Seq applications due to the advancement of bioinformatics algorithms are copy number alteration, microbial contamination, transposable elements, cell type (deconvolution) and the presence of neoantigens.
Prior to RNA-Seq, gene expression studies were done with hybridization-based microarrays. Issues with microarrays include cross-hybridization artifacts, poor quantification of lowly and highly expressed genes, and needing to know the sequence a priori. Because of these technical issues, transcriptomics transitioned to sequencing-based methods. These progressed from Sanger sequencing of Expressed sequence tag libraries, to chemical tag-based methods (e.g., serial analysis of gene expression), and finally to the current technology, next-gen sequencing of complementary DNA (cDNA), notably RNA-Seq. | 1 | Biochemistry |
Emerin has been shown to interact with:
* ACTA1,
* ACTG2,
* BANF1,
* BCLAF1,
* CTNNB1,
* GMCL1,
* LMNA,
* PSME1,
* SYNE1,
* SYNE2,
* TMEM43, and
* YTHDC1. | 1 | Biochemistry |
Ratsimamanga married Suzanne Urverg-Ratsimamanga on 23 March 1963. She was a French Ashkenazi Jewish biochemist, a Fellow of the World Academy of Sciences (1989), and the African Academy of Sciences (1987), and IMRAs Chair and Alberts closest collaborator. With Albert, she co-founded "Albert and Suzanne Rakoto Ratsimamanga Foundation" within IMRA.
Ratsimamanga died on 16 September 2001, aged 93, in Antananarivo, Madagascar. A state funeral was held for him. | 1 | Biochemistry |
Recent research has shown that AAV can successfully restore color vision to treat color blindness in adult monkeys. Although this treatment has not yet entered clinical trials for humans, this work was considered a breakthrough for the ability to target cone photoreceptors. | 1 | Biochemistry |
The association of phosphorylation and the reduction of an electron acceptor such as ferricyanide increase similarly with the addition of phosphate, magnesium (Mg), and ADP. The existence of these three components is important for maximal reductive and phosphorylative activity. Similar increases in the rate of ferricyanide reduction can be stimulated by a dilution technique. Dilution does not cause a further increase in the rate in which ferricyanide is reduced with the accumulation of ADP, phosphate, and Mg to a treated chloroplast suspension. ATP inhibits the rate of ferricyanide reduction. Studies of light intensities revealed that the effect was largely on the light-independent steps of the Hill reaction. These observations are explained in terms of a proposed method in which phosphate esterifies during electron transport reactions, reducing ferricyanide, while the rate of electron transport is limited by the rate of phosphorylation. An increase in the rate of phosphorylation increases the rate by which electrons are transported in the electron transport system. | 5 | Photochemistry |
Escitalopram appears to be effective in treating generalized anxiety disorder, with relapse on escitalopram at 20% rather than placebo at 50%, which translates to a number needed to treat of 3.33. Escitalopram appears effective in treating social anxiety disorder as well. | 4 | Stereochemistry |
In 2009, Zurek et al. predicted that the alloy would be a stable metal at only one quarter of the pressure required to metallize hydrogen, and that similar effects should hold for alloys of type LiH and possibly "other alkali high-hydride systems", i.e. alloys of type XH, where X is an alkali metal. This was later verified in AcH and LaH with T approaching 270 K leading to speculation that other compounds may even be stable at mere MPa pressures with room-temperature superconductivity. | 7 | Physical Chemistry |
This technique either uses a camera to detect many speckle grains (see speckle pattern) or a ground glass to create a large number of speckle realizations (Echo-DWS). In both cases an average over a large number of statistically independent intensity values is obtained, allowing a much faster data acquisition time.
MSDWS is particularly adapted for the study of slow dynamics and non ergodic media. Echo-DWS allows seamless integration of MSDWS in a traditional DWS-scheme with superior temporal resolution down to 12 ns. Camera based adaptive image processing allows online measurement of particle dynamics for example during drying. | 7 | Physical Chemistry |
This is an example of an esterification reaction where one molecule acetic acid (also called ethanoic acid) reacts with one molecule ethanol, yielding one molecule ethyl acetate (a bimolecular second-order reaction of the type A + B → C):
: 120 g acetic acid (60 g/mol, 2.0 mol) was reacted with 230 g ethanol (46 g/mol, 5.0 mol), yielding 132 g ethyl acetate (88 g/mol, 1.5 mol). The yield was 75%.
# The molar amount of the reactants is calculated from the weights (acetic acid: 120 g ÷ 60 g/mol = 2.0 mol; ethanol: 230 g ÷ 46 g/mol = 5.0 mol).
# Ethanol is used in a 2.5-fold excess (5.0 mol ÷ 2.0 mol).
# The theoretical molar yield is 2.0 mol (the molar amount of the limiting compound, acetic acid).
# The molar yield of the product is calculated from its weight (132 g ÷ 88 g/mol = 1.5 mol).
# The % yield is calculated from the actual molar yield and the theoretical molar yield (1.5 mol ÷ 2.0 mol × 100% = 75%). | 0 | Organic Chemistry |
Manfred Schidlowski (13 November 1933 – 3 October 2012) was a German Professor of Geochemistry at the Max-Planck-Institut for Chemistry (Otto-Hahn-Institut) in Mainz. His research was concerned with the biochemistry of the Early Earth with a focus on isotope-biogeochemistry and the evidence of the earliest life processes in Precambrian. Schidlowski is considered the founder of this research direction in Germany and he also shaped international research in isotope biogeochemistry of Precambrian sediments for more than two decades. | 9 | Geochemistry |
Polyanionic and featuring a potentially chelating polyphosphate group, ATP binds metal cations with high affinity. The binding constant for is (). The binding of a divalent cation, almost always magnesium, strongly affects the interaction of ATP with various proteins. Due to the strength of the ATP-Mg interaction, ATP exists in the cell mostly as a complex with bonded to the phosphate oxygen centers.
A second magnesium ion is critical for ATP binding in the kinase domain. The presence of Mg regulates kinase activity. It is interesting from an RNA world perspective that ATP can carry a Mg ion which catalyzes RNA polymerization. | 1 | Biochemistry |
In free-radical chain-growth polymerization, chain termination can occur by a disproportionation step in which a hydrogen atom is transferred from one growing chain molecule to another one, which produces two dead (non-growing) chains.
:: Chain—CH–CHX + Chain—CH–CHX → Chain—CH=CHX + Chain—CH–CHX
in which, Chain— represents the already formed polymer chain, and indicates a reactive free radical. | 0 | Organic Chemistry |
An allomone is any chemical substance released by an individual of one species that affects the behavior of a member of another species to the benefit of the originator but not the receiver. Production of allomones is a common form of defense, such as by plant species against insect herbivores or prey species against predators. Sometimes species produce the sex pheromones of the organisms they exploit as prey or pollinators (such as bolas spiders and some orchids). Male sex pheromone of Dacini fruit flies, besides acting as aggregation pheromone to form lek, also acts as an allomone to deter lizard predation. The term "Allomone" was proposed by Brown, Eisner, and Whittaker to denote those substances which confer an advantage upon the emitter. | 1 | Biochemistry |
Recent evidence suggests that similar chemical cycles to Earth's occur on a lesser scale on Mars, facilitated by the thin atmosphere, including carbon dioxide (and possibly carbon), water, sulphur, methane, oxygen, ozone, and nitrogen cycles. Many studies point to significantly more active chemical cycles on Mars in the past, however the faint young Sun paradox has proved problematic in determining chemical cycles involved in early climate models of the planet. | 9 | Geochemistry |
The chemical composition of a mixture can be defined as the distribution of the individual substances that constitute the mixture, called "components". In other words, it is equivalent to quantifying the concentration of each component. Because there are different ways to define the concentration of a component, there are also different ways to define the composition of a mixture. It may be expressed as molar fraction, volume fraction, mass fraction, molality, molarity or normality or mixing ratio.
Chemical composition of a mixture can be represented graphically in plots like ternary plot and quaternary plot. | 3 | Analytical Chemistry |
Single 20 to 40mg oral doses generally give rise to peak plasma esomeprazole concentrations of 0.5-1.0mg/L within 1–4 hours, but after several days of once-daily administration, these levels may increase by about 50%. A 30-minute intravenous infusion of a similar dose usually produces peak plasma levels on the order of 1–3mg/L. The drug is rapidly cleared from the body, largely by urinary excretion of pharmacologically inactive metabolites such as 5-hydroxymethylesomeprazole and 5-carboxyesomeprazole. Esomeprazole and its metabolites are analytically indistinguishable from omeprazole and the corresponding omeprazole metabolites unless chiral techniques are employed. | 4 | Stereochemistry |
Epoxides are typically prepared by oxidation of alkenes. The most important epoxide in terms of industrial scale is ethylene oxide, which is produced by oxidation of ethylene with oxygen. Other epoxides are produced by one of two routes:
* By the oxidation of alkenes with a peroxyacid such as m-CPBA.
* By the base intramolecular nucleophilic substitution of a halohydrin.
Many ethers, ethoxylates and crown ethers, are produced from epoxides. | 0 | Organic Chemistry |
Because of their mechanism of action, phorbol esters can be used to study tumor proliferation and pain response. TPA is most commonly used in the laboratory to induce a cellular response. For example, TPA can be used to measure response to pain and test compounds that may mitigate the inflammatory response. TPA and other phorbol esters can also be used to induce tumor formation and to study mechanism of action. TPA, together with ionomycin, can also be used to stimulate T-cell activation, proliferation, and cytokine production, and is used in protocols for intracellular staining of these cytokines. | 0 | Organic Chemistry |
Chlorinated or fluorinated alkenes undergo polymerization. Important halogenated polymers include polyvinyl chloride (PVC), and polytetrafluoroethene (PTFE, or teflon).
;Alkyl fluorides: An estimated one fifth of pharmaceuticals contain fluorine, including several of the top drugs. Most of these compounds are alkyl fluorides. Examples include 5-fluorouracil, flunitrazepam (Rohypnol), fluoxetine (Prozac), paroxetine (Paxil), ciprofloxacin (Cipro), mefloquine and fluconazole. Fluorine-substituted ethers are volatile anesthetics, including the commercial products methoxyflurane, enflurane, isoflurane, sevoflurane and desflurane.
;Alkyl chlorides: Some low molecular weight chlorinated hydrocarbons such as chloroform, dichloromethane, dichloroethene, and trichloroethane are useful solvents. Several million tons of chlorinated methanes are produced annually. Chloromethane is a precursor to chlorosilanes and silicones. Chlorodifluoromethane (CHClF) is used to make teflon.
;Alkyl bromides: Large scale applications of alkyl bromides exploit their toxicity, which also limits their usefulness. Methyl bromide is also an effective fumigant, but its production and use are controversial.
;Alkyl iodides: No large scale applications are known for alkyl iodides. Methyl iodide is a popular methylating agent in organic synthesis.
;Chlorofluorocarbons: Chlorofluorocarbons were used almost universally as refrigerants and propellants due to their relatively low toxicity and high heat of vaporization. Starting in the 1980s, as their contribution to ozone depletion became known, their use was increasingly restricted, and they have now largely been replaced by HFCs. | 0 | Organic Chemistry |
The European Union has a searchable database with the Maximum Residue Limits (MRLs) for 716 pesticides. Under the previous system, revised in 2008, certain pesticide residues were regulated by the commission; others were regulated by Member States, and others were not regulated at all. | 2 | Environmental Chemistry |
Papakostas et al. observed in 2003 that planar chirality affects the polarization of light diffracted by arrays of planar chiral microstructures, where large polarization changes of opposite sign were detected in light diffracted from planar structures of opposite handedness. | 4 | Stereochemistry |
Since the industrial revolution 30% of the anthropogenic CO has been absorbed by the oceans, resulting in ocean acidification, which is a threat to calcifying alga. As a result, there has been profound interest in these calcifying algae, boosted by their major role in the global carbon cycle. Globally, coccolithophores, particularly Emiliania huxleyi, are considered to be the most dominant calcifying algae, which blooms can even be seen from outer space. Calcifying algae create an exoskeleton from calcium carbonate platelets (coccoliths), providing ballast which enhances the organic and inorganic carbon flux to the deep sea. Organic carbon is formed by means of photosynthesis, where CO is fixed and converted into organic molecules, causing removal of CO from the seawater. Counterintuitively, the production of coccoliths leads to the release of CO in the seawater, due to removal of carbonate from the seawater, which reduces the alkalinity and causes acidification. Therefore, the ratio between particulate inorganic carbon (PIC) and particulate organic carbon (POC) is an important measure for the net release or uptake of CO. In short, the PIC:POC ratio is a key characteristic required to understand and predict the impact of climate change on the global ocean carbon cycle. | 9 | Geochemistry |
The transesterification reaction is base catalyzed. Any strong base capable of deprotonating the alcohol will work (e.g. NaOH, KOH, sodium methoxide, etc.), but the sodium and potassium hydroxides are often chosen for their cost. The presence of water causes undesirable base hydrolysis, so the reaction must be kept dry.
In the transesterification mechanism, the carbonyl carbon of the starting ester (RCOOR) undergoes nucleophilic attack by the incoming alkoxide (RO) to give a tetrahedral intermediate, which either reverts to the starting material, or proceeds to the transesterified product (RCOOR). The various species exist in equilibrium, and the product distribution depends on the relative energies of the reactant and product. | 0 | Organic Chemistry |
TDS spectrum 1 and 2 are typical examples of a TPD measurement. Both are examples of NO desorbing from a single crystal in high vacuum. The crystal was mounted on a titanium filament and heated with current. The desorbing NO was measured using a mass spectrometer monitoring the atomic mass of 30.
Before 1990 analysis of a TPD spectrum was usually done using a so-called simplified method; the "Redhead" method, assuming the exponential prefactor and the desorption energy to be independent of the surface coverage. After 1990 and with use of computer algorithms TDS spectra were analyzed using the "complete analysis method" or the "leading edge method". These methods assume the exponential prefactor and the desorption energy to be dependent of the surface coverage. Several available methods of analyzing TDS are described and compared in an article by A.M. de JONG and J.W. NIEMANTSVERDRIET. During parameter optimization/estimation, using the integral has been found to create a more well behaved objective function than the differential. | 7 | Physical Chemistry |
Levomethamphetamine is an active metabolite of the antiparkinson's drug selegiline. Selegiline, a selective monoamine oxidase B (MAO) inhibitor at low doses, is also metabolized into levomethamphetamine and levoamphetamine. This has caused users to test positive for amphetamines.
Selegiline itself has neuroprotective and neuro-rescuing effects, but concern over the resulting levomethamphetamine's neurotoxicity led to development of alternative MAO inhibitors, such as rasagiline, that do not produce toxic metabolites. | 4 | Stereochemistry |
Safranin (Safranin O or basic red 2) is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring cell nuclei red. This is the classic counterstain in both Gram stains and endospore staining. It can also be used for the detection of cartilage, mucin and mast cell granules.
Safranin typically has the chemical structure shown at right (sometimes described as dimethyl safranin). There is also trimethyl safranin, which has an added methyl group in the ortho- position (see Arene substitution pattern) of the lower ring. Both compounds behave essentially identically in biological staining applications, and most manufacturers of safranin do not distinguish between the two. Commercial safranin preparations often contain a blend of both types.
Safranin is also used as redox indicator in analytical chemistry. | 3 | Analytical Chemistry |
Chemical mimicry exists in many forms and for a variety of uses. It may be classified by the function it performs for the mimicking species and the effect that the mimic will have on the species that is deceived. It can be used for such functions as deterring predators, drawing prey, to allow a parasite to deceive a host species, or to help assist in the reproduction of an organism. | 1 | Biochemistry |
Sonoelectrochemistry is the application of ultrasound in electrochemistry. Like sonochemistry, sonoelectrochemistry was discovered in the early 20th century. The effects of power ultrasound on electrochemical systems and important electrochemical parameters were originally demonstrated by Moriguchi and then by Schmid and Ehert when the researchers investigated the influence of ultrasound on concentration polarisation, metal passivation and the production of electrolytic gases in aqueous solutions. In the late 1950s, Kolb and Nyborg showed that the electrochemical solution (or electroanalyte) hydrodynamics in an electrochemical cell was greatly increased in the presence of ultrasound and described this phenomenon as acoustic streaming. In 1959, Penn et al. demonstrated that sonication had a great effect on the electrode surface activity and electroanalyte species concentration profile throughout the solution. In the early 1960s, the electrochemist Allen J. Bard showed in controlled potential coulometry experiments that ultrasound significantly enhances mass transport of electrochemical species from the bulk solution to the electroactive surface.
In the range of ultrasonic frequencies [20 kHz – 2 MHz], ultrasound has been applied to many electrochemical systems, processes and areas of electrochemistry (to name but a few: electroplating, electrodeposition, electropolymerisation, electrocoagulation, organic electrosynthesis, materials electrochemistry, environmental electrochemistry, electroanalytical chemistry, hydrogen energy and fuel cell technology) both in academia and industry, as this technology offers several benefits over traditional technologies. The advantages are as follows: significant thinning of the diffusion layer thickness (δ) at the electrode surface; increase in electrodeposit/electroplating thickness; increase in electrochemical rates, yields and efficiencies; increase in electrodeposit porosity and hardness; increase in gas removal from electrochemical solutions; increase in electrode cleanliness and hence electrode surface activation; lowering in electrode overpotentials (due to metal depassivation and gas bubble removal generated at the electrode surface induced by cavitation and acoustic streaming); and suppression in electrode fouling (depending on the ultrasonic frequency and power).
To date, over 3,500 publications inc. patents, technical, research and review articles have been written on the subject with the vast majority being published post-1990 after a review paper from Mason et al. entitled Sonoelectrochemistry highlighting the extraordinary effects of sonication on enhancing mass transport, aiding solution degassing, improving electrode surface cleaning, producing radical species (via sonolysis) and increasing electrochemical products and yields. | 7 | Physical Chemistry |
The Polycomb-group (PcG) regulatory complexes are known for their influence in the epigenetic regulation of stem cells,
especially in hematopoietic stem cells. The Polycomb Repressive Complex 1 (PRC 1) is directly involved in the process of hematopoiesis, and functions together with, for example, the PcG gene “Bmi1”. Studies in mice indicate that organisms with mutated “Bmi1” demonstrate deficient mitochondrial functioning, and also hindered the ability of hematopoietic cells to self-renew. Likewise, mutations in PRC2 genes were related to hematological conditions such as acute lymphoblastic leukemia (ALL), which is a form of leukemia. Hence, Polycomb-group genes and proteins are involved in the proper maintenance of hematopoiesis in the body. | 1 | Biochemistry |
The basic metabolic rate varies between individuals. One study of 150 adults representative of the population in Scotland reported basal metabolic rates from as low as per day to as high as ; with a mean BMR of per day. Statistically, the researchers calculated that 62% of this variation was explained by differences in fat free mass. Other factors explaining the variation included fat mass (7%), age (2%), and experimental error including within-subject difference (2%). The rest of the variation (27%) was unexplained. This remaining difference was not explained by sex nor by differing tissue size of highly energetic organs such as the brain.
A cross-sectional study of more than 1400 subjects in Europe and the US showed that once adjusted for differences in body composition (lean and fat mass) and age, BMR has fallen over the past 35 years. The decline was also observed in a meta-analysis of more than 150 studies dating back to the early 1920s, translating into a decline in total energy expenditure of about 6%. | 1 | Biochemistry |
Hydrogen sulfide - a component of crude oil and natural gas and a by-product in anaerobic digestion of biomass - is also suitable for plasma-catalytic decomposition to produce hydrogen and elemental sulfur due to its weak binding energy.
The energy requirement for the production of hydrogen from HS is approx. 5 kWh/kg. | 7 | Physical Chemistry |
Certain perfusates have been shown to have toxic effects on kidneys as a result of the inadvertent inclusion of particular chemicals in their formulation. Collins showed that the procaine included in the formulation of his flush fluids could be toxic, and Pegg has commented how toxic materials, such as PVC plasticizers, may be washed out of perfusion circuit tubing. Dvorak showed that the methyl-prednisolone addition to the perfusate that was thought to be essential by Woods might in some circumstances be harmful. He showed that with over g of methyl-prednisolone in 650 mL of perfusate (compared with 250 mg in 1 litre used by Woods) irreversible haemodynamic and structural changes were produced in the kidney after 20 hours of perfusion. There was necrosis of capillary loops, occlusion of Bowman's spaces, basement membrane thickening and endothelial cell damage. | 1 | Biochemistry |
Consider two energy eigenstates of a quantum system with Hamiltonian (for example, this could be the Hamiltonian of a particle in a potential, like the Hydrogen atom or the Alkali atoms):
We want to consider the time dependent Hamiltonian
where is the potential of the electromagnetic field. Treating the potential as a perturbation, we can expect the eigenstates of the perturbed Hamiltonian to be some mixture of the eigenstates of the original Hamiltonian with time dependent coefficients:
Plugging this into the time dependent Schrödinger equation
taking the inner product with each of and , and using the orthogonality condition of eigenstates , we arrive at two equations in the coefficients and :
where . The two terms in parentheses are dipole matrix elements dotted into the polarization vector of the electromagnetic field. In considering the spherically symmetric spatial eigenfunctions of the Hydrogen atom potential, the diagonal matrix elements go to zero, leaving us with
or
Here , where is the Rabi Frequency. | 7 | Physical Chemistry |
4-(γ-Glutamylamino)butanoic acid is molecule that consists of -glutamate conjugated to γ-aminobutyric acid (GABA). It is the substrate of the enzyme γ-glutamyl-γ-aminobutyrate hydrolase, which is involved in the biosynthesis of polyamines. | 1 | Biochemistry |
Although a plain metallic cathode will exhibit photoelectric properties, the specialized coating greatly increases the effect. A photocathode usually consists of alkali metals with very low work functions.
The coating releases electrons much more readily than the underlying metal, allowing it to detect the low-energy photons in infrared radiation. The lens transmits the radiation from the object being viewed to a layer of coated glass. The photons strike the metal surface and transfer electrons to its rear side. The freed electrons are then collected to produce the final image. | 7 | Physical Chemistry |
Liquid-liquid extractions in the laboratory usually make use of a separatory funnel, where two immiscible phases are combined to separate a solute from one phase into the other, according to the relative solubility in each of the phases. Typically, this will be to extract organic compounds out of an aqueous phase and into an organic phase, but may also include extracting water-soluble impurities from an organic phase into an aqueous phase.
Common extractants may be arranged in increasing order of polarity according to the Hildebrand solubility parameter:
ethyl acetate < acetone < ethanol < methanol < acetone:water (7:3) < ethanol:water (8:2) < methanol:water (8:2) < water
Solid-liquid extractions at laboratory scales can use Soxhlet extractors. A solid sample containing the desired compound along with impurities is placed in the thimble. An extracting solvent is chosen in which the impurities are insoluble and the desired compound has at least limited solubility. The solvent is refluxed and condensed solvent falls into the thimble and dissolves the desired compound which then passes back through the filter into the flask. After extraction is complete the solvent can be removed and the desired product collected. | 3 | Analytical Chemistry |
In crystallography, mosaicity is a measure of the spread of crystal plane orientations. A mosaic crystal is an idealized model of an imperfect crystal, imagined to consist of numerous small perfect crystals (crystallites) that are to some extent randomly misoriented. Empirically, mosaicities can be determined by measuring rocking curves. Diffraction by mosaics is described by the Darwin–Hamilton equations.
The mosaic crystal model goes back to a theoretical analysis of X-ray diffraction by C. G. Darwin (1922). Currently, most studies follow Darwin in assuming a Gaussian distribution of crystallite orientations centered on some reference orientation. The mosaicity is commonly equated with the standard deviation of this distribution. | 3 | Analytical Chemistry |
The first known use of liquation on a large scale was in Germany in the mid-15th century. Metal workers had long known that Central European copper ore was rich in silver, so it was only a matter of time until a method was discovered that could separate the two metals.
Liquation is first documented in the archives of the municipal foundry in Nuremberg in 1453. Nuremberg was one of Germany's main centres of metal refining and fabrication, and was a leader in metallurgical techniques. Five liquation plants soon sprang up around the city, and within 15 years had spread throughout Germany, Poland and the Italian Alps.
This is often regarded as the beginning of liquation, but evidence suggests liquation may have existed in smaller-scale use centuries earlier. The sophisticated nature of the 15th century liquation plants with custom-made furnaces would be surprising for a new technology. There was also a far simpler but more labour-intensive version of the method brought to Japan by the Portuguese in 1591; this is possibly the remnants of an earlier European method.
Agricola discusses various types of copper produced from the liquation process; one of these is caldarium or ‘cauldron copper’ which contains a high level of lead and was used to make medieval cauldrons. Analysis of 13th century cauldrons shows that they are made out of copper with a low level of silver and high levels of lead which would match that produced by liquation.
Liquation may even have existed as early as the 12th century; in Theophilus’ On Divers Arts he makes a possible reference to liquation. However, he was not an expert in metallurgy, so his writings may not be accurate, and though there were similar cauldrons in the 12th century, no compositional analysis has been published that supports this theory.
Against the idea that this process was used significantly before it became widespread in the mid-15th century, is the fact that it had to be done on a large-scale to be financially viable. There is no evidence of large-scale liquation before Nuremberg. Also, efficient liquation requires an extremely skilled practitioner. Anyone with that much skill is unlikely to spend much time on something unprofitable.
Some suggest liquation existed even earlier. Babylonian texts from Mari mention that ‘mountain copper’ was ‘washed’ to produce ‘washed copper’ and that lead was used with silver to produce ‘washed silver’. Some say this shows liquation was being carried out in the Near East as early as the second millennium BC. Crucially, however, these texts do not specifically mention lead being used with copper to produce silver, as would be expected for liquation. | 8 | Metallurgy |
Due to the paternal inheritance, Y-haplotypes provide information about the genetic ancestry of the male population. To investigate this population history, and to provide estimates for haplotype frequencies in criminal casework, the "Y haplotype reference database (YHRD)" has been created in 2000 as an online resource. It currently comprises more than 300,000 minimal (8 locus) haplotypes from world-wide populations. | 1 | Biochemistry |
The members of genus Orbivirus within the Reoviridae family are arthropod borne viruses and are responsible for high morbidity and mortality in ruminants. Bluetongue virus (BTV) which causes disease in livestock (sheep, goat, cattle) has been in the forefront of molecular studies for the last three decades and now represents the best understood orbivirus at the molecular and structural levels. BTV, like other members of the family, is a complex non-enveloped virus with seven structural proteins and a RNA genome consisting of 10 variously sized dsRNA segments. | 1 | Biochemistry |
Knock-in technology is different from knockout technology in that knockout technology aims to either delete part of the DNA sequence or insert irrelevant DNA sequence information to disrupt the expression of a specific genetic locus. Gene knock-in technology, on the other hand, alters the genetic locus of interest via a one-for-one substitution of DNA sequence information or by the addition of sequence information that is not found on said genetic locus. A gene knock-in therefore can be seen as a gain-of-function mutation and a gene knockout a loss-of-function mutation, but a gene knock-in may also involve the substitution of a functional gene locus for a mutant phenotype that results in some loss of function. | 1 | Biochemistry |
Empirical scales are based on the measurement of physical parameters that express the property of interest to be measured through some formal, most commonly a simple linear, functional relationship. For the measurement of temperature, the formal definition of thermal equilibrium in terms of the thermodynamic coordinate spaces of thermodynamic systems, expressed in the zeroth law of thermodynamics, provides the framework to measure temperature.
All temperature scales, including the modern thermodynamic temperature scale used in the International System of Units, are calibrated according to thermal properties of a particular substance or device. Typically, this is established by fixing two well-defined temperature points and defining temperature increments via a linear function of the response of the thermometric device. For example, both the old Celsius scale and Fahrenheit scale were originally based on the linear expansion of a narrow mercury column within a limited range of temperature, each using different reference points and scale increments.
Different empirical scales may not be compatible with each other, except for small regions of temperature overlap. If an alcohol thermometer and a mercury thermometer have the same two fixed points, namely the freezing and boiling point of water, their readings will not agree with each other except at the fixed points, as the linear 1:1 relationship of expansion between any two thermometric substances may not be guaranteed.
Empirical temperature scales are not reflective of the fundamental, microscopic laws of matter. Temperature is a universal attribute of matter, yet empirical scales map a narrow range onto a scale that is known to have a useful functional form for a particular application. Thus, their range is limited. The working material only exists in a form under certain circumstances, beyond which it no longer can serve as a scale. For example, mercury freezes below 234.32 K, so temperatures lower than that cannot be measured in a scale based on mercury. Even ITS-90, which interpolates among different ranges of temperature, has a range of only 0.65 K to approximately 1358 K (−272.5 °C to 1085 °C). | 7 | Physical Chemistry |
Comparative genomic hybridization can be described as a method that uses FISH in a parallel manner with the comparison of the hybridization strength to recall any major disruptions in the duplication process of the DNA sequences in the genome of the nucleus. | 1 | Biochemistry |
Hafnium or zirconium added to niobium–tin increases the maximum current density in a magnetic field. This may allow it to be used at 16 tesla for CERN's planned Future Circular Collider. | 8 | Metallurgy |
The company sells a special soap – available to authorities but not the general public – that neutralises the smell of skunk water if officers are accidentally sprayed. It has been suggested that rubbing a surface contaminated with skunk with ketchup, similar to treating a real skunk spray with tomato juice, and then washing it off, may diminish perception of the odor (due to the effects of olfactory fatigue). In 1993, American chemist Paul Krebaum developed a compound that chemically neutralizes natural skunk spray by changing the odor-causing thiols into odorless acids. This compound can be prepared as a mixture of: 1 quart of 3% hydrogen peroxide, ¼ cup of baking soda, and 1-2 teaspoons of liquid dish soap. | 1 | Biochemistry |
While A, T, C, and G represent a particular nucleotide at a position, there are also letters that represent ambiguity which are used when more than one kind of nucleotide could occur at that position. The rules of the International Union of Pure and Applied Chemistry (IUPAC) are as follows:
For example, W means that either an adenine or a thymine could occur in that position without impairing the sequence's functionality.
These symbols are also valid for RNA, except with U (uracil) replacing T (thymine).
Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytidine (m5C). In RNA, there are many modified bases, including pseudouridine (Ψ), dihydrouridine (D), inosine (I), ribothymidine (rT) and 7-methylguanosine (m7G). Hypoxanthine and xanthine are two of the many bases created through mutagen presence, both of them through deamination (replacement of the amine-group with a carbonyl-group). Hypoxanthine is produced from adenine, and xanthine is produced from guanine. Similarly, deamination of cytosine results in uracil.
;Example of comparing and determining the % difference between two nucleotide sequences
* AATCCGCTAG
* AAACCCTTAG
Given the two 10-nucleotide sequences, line them up and compare the differences between them. Calculate the percent difference by taking the number of differences between the DNA bases divided by the total number of nucleotides. In this case there are three differences in the 10 nucleotide sequence. Thus there is a 30% difference. | 1 | Biochemistry |
One distinct section of cell engineering involves the alteration and tuning of stem cells. Much of the recent research on stem cell therapies and treatments falls under the aforementioned cell engineering methods. Stem cells are unique in that they may differentiate into various other types of cells which may then be altered to produce novel therapeutics or provide a foundation for further cell engineering efforts. One example of directed stem cell engineering includes partially differentiating stem cells into myocytes to enable production of pro-myogenic factors for the treatment of sarcopenia or muscle disuse atrophy. | 1 | Biochemistry |
* A miniature binary weapon is used in an assassination in the Frederick Forsyth novel The Devils Alternative'. It consists of two half-capsules, a non-resistant one containing potassium cyanide and an acid-resistant one containing hydrochloric acid. The substances mix after the halves are assembled and the seal between them is broken, and form hydrogen cyanide. The surplus acid eats through the capsule walls of the non-resistant half, and after a delay of several hours, the lethal content is released into the intestinal tract of whoever ingested it. While technically possible, the assassination tool as discussed in the novel is presumably fictional. However, there are claims that in September 2003, the SVR (Russian Foreign Intelligence Service) prepared to assassinate Boris Berezovsky with a similar device.
* In the 10th and 11th episodes of the 6th season of TV-series Dexter are shown preparation and application of binary weapon consisting of two containers filled with DF and isopropyl alcohol. When mixed, the two substances form sarin.
* The 2002 movie xXx features a Soviet-made binary chemical weapon codenamed "Silent Night", after its supposed ability to render an area silent by killing its inhabitants. In the movie, the chemical was acquired by the terrorist group Anarchy-99, and their leader, Yorgi, plans to launch missiles containing Silent Night from an autonomous solar-powered submarine called Ahab, with the intent to sow chaos among civilized nations as they all blame each other for the attacks.
* Michael Crichtons 1972 novel Binary' uses a binary nerve agent "VZ" as the main plot device intended to kill the President of the United States, and indirectly most of the inhabitants of San Diego. | 1 | Biochemistry |
A hydrogen bond is an extreme form of dipole-dipole bonding, referring to the attraction between a hydrogen atom that is bonded to an element with high electronegativity, usually nitrogen, oxygen, or fluorine. The hydrogen bond is often described as a strong electrostatic dipole–dipole interaction. However, it also has some features of covalent bonding: it is directional, stronger than a van der Waals force interaction, produces interatomic distances shorter than the sum of their van der Waals radii, and usually involves a limited number of interaction partners, which can be interpreted as a kind of valence. The number of Hydrogen bonds formed between molecules is equal to the number of active pairs. The molecule which donates its hydrogen is termed the donor molecule, while the molecule containing lone pair participating in H bonding is termed the acceptor molecule. The number of active pairs is equal to the common number between number of hydrogens the donor has and the number of lone pairs the acceptor has.
Though both not depicted in the diagram, water molecules have four active bonds. The oxygen atom’s two lone pairs interact with a hydrogen each, forming two additional hydrogen bonds, and the second hydrogen atom also interacts with a neighbouring oxygen. Intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C) compared to the other group 16 hydrides, which have little capability to hydrogen bond. Intramolecular hydrogen bonding is partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids. It also plays an important role in the structure of polymers, both synthetic and natural. | 6 | Supramolecular Chemistry |
The modification of A to I is effected by adenosine deaminases that act on RNA (ADARs), of which in mice there are three. The knockdown of these in the cell, therefore, and the subsequent cell–cell comparison of ADAR+ and ADAR- RNA content would be anticipated to provide a basis for A-to-I modification profiling. However, there are further functions of ADAR enzymes within the cell — for example, they have further roles in RNA processing, and in miRNA biogenesis — which would also be likely to change the landscape of cellular mRNA. Recently a map of A-to-I editing in mice was generated using editing-deficient ADAR1 and ADAR2 double-knockout mice as a negative control. Thereby, A-to-I editing was detected with high confidence. | 1 | Biochemistry |
Progesterone has key effects via non-genomic signalling on human sperm as they migrate through the female tract before fertilization occurs, though the receptor(s) as yet remain unidentified. Detailed characterisation of the events occurring in sperm in response to progesterone has elucidated certain events including intracellular calcium transients and maintained changes, slow calcium oscillations, now thought to possibly regulate motility. It is produced by the ovaries. Progesterone has also been shown to demonstrate effects on octopus spermatozoa.
Progesterone is sometimes called the "hormone of pregnancy", and it has many roles relating to the development of the fetus:
* Progesterone converts the endometrium to its secretory stage to prepare the uterus for implantation. At the same time progesterone affects the vaginal epithelium and cervical mucus, making it thick and impenetrable to sperm. Progesterone is anti-mitogenic in endometrial epithelial cells, and as such, mitigates the tropic effects of estrogen. If pregnancy does not occur, progesterone levels will decrease, leading to menstruation. Normal menstrual bleeding is progesterone-withdrawal bleeding. If ovulation does not occur and the corpus luteum does not develop, levels of progesterone may be low, leading to anovulatory dysfunctional uterine bleeding.
* During implantation and gestation, progesterone appears to decrease the maternal immune response to allow for the acceptance of the pregnancy.
* Progesterone decreases contractility of the uterine smooth muscle. This effect contributes to prevention of preterm labor. Studies have shown that in women who are pregnant with a single fetus, asymptomatic in the prenatal stage, and at a high risk of giving pre-term birth spontaneously, vaginal progesterone medication has been found to be effective in preventing spontaneous pre-term birth. Women who are at a high risk of giving pre-term birth spontaneously are those who have a short cervix of less than 25 mm or have previously given pre-term birth spontaneously. Although pre-term births are generally considered to be less than 37 weeks, these studies found that vaginal progesterone is associated with fewer pre-term births of less than 34 weeks.
* A drop in progesterone levels is possibly one step that facilitates the onset of labor.
* In addition, progesterone inhibits lactation during pregnancy. The fall in progesterone levels following delivery is one of the triggers for milk production.
The fetus metabolizes placental progesterone in the production of adrenal steroids. | 0 | Organic Chemistry |
In organic chemistry, a moiety ( ) is a part of a molecule that is given a name because it is identified as a part of other molecules as well.
Typically, the term is used to describe the larger and characteristic parts of organic molecules, and it should not be used to describe or name smaller functional groups of atoms that chemically react in similar ways in most molecules that contain them. Occasionally, a moiety may contain smaller moieties and functional groups.
A moiety that acts as a branch extending from the backbone of a hydrocarbon molecule is called a substituent or side chain, which typically can be removed from the molecule and substituted with others.
The term is also used in pharmacology, where an active moiety is the part of a molecule responsible for the physiological or pharmacological action of a drug. | 0 | Organic Chemistry |
According to Reetz, the Cram-chelate model for 1,2-inductions can be extended to predict the chelated complex of a β-alkoxy aldehyde and metal. The nucleophile is seen to attack from the less sterically hindered side and anti- to the substituent R, leading to the anti-adduct as the major product.
To make such chelates, the metal center must have at least two free coordination sites and the protecting ligands should form a bidentate complex with the Lewis acid. | 4 | Stereochemistry |
Two-photon absorption (TPA) is a third-order process in which two photons are nearly simultaneously absorbed by the same molecule. If a second photon is absorbed by the same electron within the same quantum event, the electron enters an excited state.
This is the same phenomenon used in two-photon microscopy (TPM), but there are two key features that distinguish pump–probe microscopy from TPM. First, since the molecule is not necessarily fluorescent, a photodetector measures the probe intensity. Therefore, the signal decreases as two-photon absorption occurs, the reverse of TPM.
Second, pump–probe microscopy uses spectrally separated sources for each photon, whereas conventional TPM uses one source of a single wavelength. This is referred to as degenerate two-photon excitation. | 7 | Physical Chemistry |
Parkinsons disease is caused by the loss of dopamine stimulation to the basal ganglia of the midbrain, resulting in tremor at rest and bradykinesia. In some rare forms, protein aggregation of alpha-synuclein and parkin can elicit symptoms of Parkinsons disease. For a variety of drugs, restoring dopamine to the central nervous system remains the target therapy. Because dopamine cannot pass the blood brain barrier on its own, the dopamine precursor L-DOPA is used in its stead. However, synaptic plasticity renders this treatment decreasingly effective with time. Another treatment option is bromocriptine, which directly stimulates D Dopamine Receptors. Bromocriptine is less effective than L-Dopa in reducing symptoms, but provides less dyskinesia. Often, the two drugs are used in concert with one another.
New approaches to treatment include deep brain simulation and cell transplantation with stem cells. Deep brain stimulation offsets symptoms rather than cures, and stem cell studies have been extremely disappointing, despite relative success with animal models. Gene therapy may provide a novel route to introduce new dopamine production via viral-medicated gene transfection, but clinical trials are yet to be completed. | 1 | Biochemistry |
The scholarship surrounding Mosul Metalwork has been ongoing for a very long time, since it became the first Islamic objects dart studied in Europe, due to its early arrival on the continent. The diverse opinions on what constitutes as Mosul Metalwork arise due to the styles dispersion across lands and through the component of signatures which identify creators as "al Mawsili", meaning "of Mosul". Within the section of metalwork with signatures, twenty-seven out of the thirty-five state themselves as "al- Mawsili". Out of those, eight state their provenance through the name of the people for which they were created along with statements declaring their engendering within Mosul. Some notable scholars that have helped shape the basis of this study include: Joseph Toussaint Reinaud, Henri Lavoix, Gaston Migeon, Max Van Berchem, Mehmed Aga-Oglu, David Storm Rice.
In the early years of Mosul Metalwork, around 1828, Joseph Toussaint Reinaud, published a collection that included the first item to clearly state its creation in Mosul, the Blacas ewer, an artifact consistently scrutinized by scholars when exploring Mosul style. Then in the 1860s the credibility of Mosul was being questioned by scholars, it was during that century that Henry Lavoix declared that Damascus, Aleppo, Mosul, and Egypt all created inlaid metalwork, but specifically singled out Mosul as a source for a unique style unseen throughout the medium.
A critical point in the scholarship came in the beginning of the 20th, through Gaston Migeon, whose claims over the precedency of Mosul caused objection and an urgency for reliability. Migeon also wrote the first comprehensive article introducing the inlaid Islamic metalwork. In the following years, the fluctuation of precedence of Mosul and the lack of it continued, leading up to David Storm Rice, who released the first series of articles exploring the complexities of multiple objects, a process similar to that of Max Van Brehmen and Mehmed Aga-Oglu, two scholars that impacted the relevance and viability of Mosul Metalwork, some of which included the Blacas Ewer, Louvre basin and the Munich Tray.
Present day, Mosul Metalwork is still elusive, and lacks a sustaining amount of scholarship, but scholars continue to construct a field that utilizes substantiated evidence through designs, inscription, and other items engendered specifically in Mosul around the 13th century. An example of this is represented in an article written by Ruba Kana' An who utilizes its iconography and description to construct the argument stating the Freer Ewer as one of many metalworks constructed in Mosul. | 8 | Metallurgy |
In 1979, teams at Harvard and Caltech extended the basic idea of making DNA copies of mRNAs in vitro to amplifying a library of such in bacterial plasmids.
In 1982, the idea of selecting random or semi-random clones from such a cDNA library for sequencing was explored by Greg Sutcliffe and coworkers.
In 1983, Putney et al. sequenced 178 clones from a rabbit muscle cDNA library.
In 1991, Adams and co-workers coined the term EST and initiated more systematic sequencing as a project (starting with 600 brain cDNAs). | 1 | Biochemistry |
The methods to prevent and treat lipotoxicity are divided into three main groups.
The first strategy focuses on decreasing the lipid content of non-adipose tissues. This can be accomplished by either increasing the oxidation of the lipids, or increasing their secretion and transport. Current treatments involve extreme weight loss and leptin treatment.
Another strategy is focusing on diverting excess lipids away from non-adipose tissues, and towards adipose tissues. This is accomplished with thiazolidinediones, a group of medications that activate nuclear receptor proteins responsible for lipid metabolism.
The final strategy focuses on inhibiting the apoptotic pathways and signaling cascades. This is accomplished by using drugs that inhibit production of specific chemicals required for the pathways to be functional. While this may prove to the most effective protection against cell death, it will also require the most research and development due to the specificity required of the medications. | 1 | Biochemistry |
Bioorganic chemistry is a scientific discipline that combines organic chemistry and biochemistry. It is that branch of life science that deals with the study of biological processes using chemical methods. Protein and enzyme function are examples of these processes.
Sometimes biochemistry is used interchangeably for bioorganic chemistry; the distinction being that bioorganic chemistry is organic chemistry that is focused on the biological aspects. While biochemistry aims at understanding biological processes using chemistry, bioorganic chemistry attempts to expand organic-chemical researches (that is, structures, synthesis, and kinetics) toward biology. When investigating metalloenzymes and cofactors, bioorganic chemistry overlaps bioinorganic chemistry. | 1 | Biochemistry |
There are three types of magnetic effects in electrochemistry:
* on electrolytes
* on mass transfer
* on metal deposition | 7 | Physical Chemistry |
The Gibbs free energy is so combining the previous results gives
This is the Gibbs free energy for a perfect vdW fluid, or in reduced form | 7 | Physical Chemistry |
Hysteresis, in this case, refers to the restructuring of the adhesive interface over some period of time, with the result being that the work needed to separate two surfaces is greater than the work that was gained by bringing them together (W > γ + γ). For the most part, this is a phenomenon associated with diffusive bonding. The more time is given for a pair of surfaces exhibiting diffusive bonding to restructure, the more diffusion will occur, the stronger the adhesion will become. The aforementioned reaction of certain polymer-on-polymer surfaces to ultraviolet radiation and oxygen gas is an instance of hysteresis, but it will also happen over time without those factors.
In addition to being able to observe hysteresis by determining if W > γ + γ is true, one can also find evidence of it by performing “stop-start” measurements. In these experiments, two surfaces slide against one another continuously and occasionally stopped for some measured amount of time. Results from experiments on polymer-on-polymer surfaces show that if the stopping time is short enough, resumption of smooth sliding is easy. If, however, the stopping time exceeds some limit, there is an initial increase of resistance to motion, indicating that the stopping time was sufficient for the surfaces to restructure. | 6 | Supramolecular Chemistry |
Methoxy groups heavily decorate the biopolymer lignin. Much interest has been shown in converting this abundant form of biomass into useful chemicals (aside from fuel). One step in such processing is demethylation.
The demethylation of vanillin, a derivative of lignin, requires and strong base. Pulp and paper industry]] digests lignin using aqueous sodium sulfide, which partially depolymerizes the lignin. Delignification is accompanied by extensive O-demethylation, yielding methanethiol, which is emitted by paper mills. | 0 | Organic Chemistry |
Exemestane, sold under the brand name Aromasin among others, is a medication used to treat breast cancer. It is a member of the class of antiestrogens known as aromatase inhibitors. Some breast cancers require estrogen to grow. Those cancers have estrogen receptors (ERs), and are called ER-positive. They may also be called estrogen-responsive, hormonally-responsive, or hormone-receptor-positive. Aromatase is an enzyme that synthesizes estrogen. Aromatase inhibitors block the synthesis of estrogen. This lowers the estrogen level, and slows the growth of cancers. | 4 | Stereochemistry |
A solid in contact with a liquid, in the presence of an electric field, forms an electric double layer. This layer is present at the interface of the solid and liquid and it shields the charged surface of the solid. This electric double layer has an effect on the optical reflectivity of the solid as it changes the elastic light scattering properties. The formation of the electric double layer involves different timescales, such as the relaxation time and the charging time.
The relaxation time we can write as with being the Diffusion constant and the Debye length.
The charging time can be expressed by where is the representative system size.
The Debye length is often used as a measure of electric double layer thickness. Measuring the electric double layer with electroreflectance is challenging due to separation caused by conduction electrons. | 7 | Physical Chemistry |
In this biological process, which is a redox comproportionation reaction, nitrite and ammonium ions are converted directly into a diatomic molecule of nitrogen and water.
: (ΔG° = ).
Globally, this process may be responsible for 30–50% of the gas produced in the oceans. It is thus a major sink for fixed nitrogen and so limits oceanic primary productivity.
The bacteria that perform the anammox process belong to the bacterial phylum Planctomycetota. Currently, five anammox genera have been discovered: Brocadia, Kuenenia, Anammoxoglobus, Jettenia (all fresh water species), and Scalindua (marine species). The anammox bacteria are characterized by several striking properties:
* They all possess one anammoxosome, a membrane bound compartment inside the cytoplasm which is the locus of anammox catabolism. Further, the membranes of these bacteria mainly consist of ladderane lipids so far unique in biology.
* Of special interest is the conversion to hydrazine (normally used as a high-energy rocket fuel, and poisonous to most living organisms) as an intermediate.
* A final striking feature of the organism is the extremely slow growth rate; the doubling time is anywhere from 7–22 days.
The anammox bacteria are geared towards converting their substrates at very low concentrations; in other words, they have a very high affinity to their substrates ammonium and nitrite (sub-micromolar range). Anammox cells are packed with cytochrome c type proteins (≈30% of the protein complement), including the enzymes that perform the key catabolic reactions of the anammox process, making the cells remarkably red. The anammox process was originally found to occur only from 20 °C to 43 °C but more recently, anammox has been observed at temperatures from 36 °C to 52 °C in hot springs and 60 °C to 85 °C at hydrothermal vents located along the Mid-Atlantic Ridge. | 1 | Biochemistry |
Amoxicillin is occasionally used for the treatment of skin infections, such as acne vulgaris. It is often an effective treatment for cases of acne vulgaris that have responded poorly to other antibiotics, such as doxycycline and minocycline. | 4 | Stereochemistry |
Chymotrypsin is a serine endopeptidase that is present in pancreatic juice and helps the hydrolysis of proteins and peptide. It catalyzes the hydrolysis of peptide bonds in L-isomers of tyrosine, phenylalanine, and tryptophan. In the active site of this enzyme, three amino acid residues work together to form a catalytic triad which makes up the catalytic site. In chymotrypsin, these residues are Ser-195, His-57 and Asp-102.
The mechanism of chymotrypsin can be divided into two phases. First, Ser-195 nucleophilically attacks the peptide bond carbon in the substrate to form a tetrahedral intermediate. The nucleophilicity of Ser-195 is enhanced by His-57, which abstracts a proton from Ser-195 and is in turn stabilised by the negatively charged carboxylate group (RCOO) in Asp-102. Furthermore, the tetrahedral oxyanion intermediate generated in this step is stabilised by hydrogen bonds from Ser-195 and Gly-193.
In the second stage, the RNH group is protonated by His-57 to form RNH and leaves the intermediate, leaving behind the acylated Ser-195. His-57 then acts as a base again to abstract one proton from a water molecule. The resulting hydroxide anion nucleophilically attacks the acyl-enzyme complex to form a second tetrahedral oxyanion intermediate, which is once again stabilised by H bonds. In the end, Ser-195 leaves the tetrahedral intermediate, breaking the CO bond that connected the enzyme to the peptide substrate. A proton is transferred to Ser-195 through His-57, so that all three amino acid return to their initial state. | 1 | Biochemistry |
Due to the high activity of the enzyme, expression of untethered Dam results in methylation of all regions of accessible chromatin. This approach can be used as an alternative to ATAC-seq or DNAse-seq. When combined with cell-type specific DamID methods, expression of untethered Dam can be used to identify cell-type specific promoter or enhancer regions. | 1 | Biochemistry |
The Class IIB HDACs include HDAC6 and HDAC10. These two HDACs are most closely related to each other in overall sequence. However, HDAC6's catalytic domain is most similar to HDAC9. A unique feature of HDAC6 is that it contains two catalytic domains in tandem of one another. Another unique feature of HDAC6 is the HDAC6-, SP3, and Brap2-related zinc finger motif (HUB) domain in the C-terminus which shows some functions related to ubiquitination, meaning this HDAC is prone to degradation. HDAC10 has two catalytic domains as well. One active domain is located in the N-terminus and a putative catalytic domain is located in the C-terminus along with an NES domain. Two putative Rb-binding domains have also been found on HDAC10 which shows it may have roles in the regulation of the cell cycle. Two variants of HDAC10 have been found, both having slight differences in length. HDAC6 is the only HDAC to be shown to act on tubulin, acting as a tubulin deacetylase which helps in the regulation of microtubule-dependent cell motility. It is mostly found in the cytoplasm but has been known to be found in the nucleus, complexed together with HDAC11. HDAC10 has been seen to act on HDACs 1, 2, 3 (or SMRT), 4, 5 and 7. Some evidence has been shown that it may have small interactions with HDAC6 as well. This leads researchers to believe that HDAC10 may function more as a recruiter rather than a factor for deacetylation. However, experiments conducted with HDAC10 did indeed show deacetylation activity. | 0 | Organic Chemistry |
* The spectral centroid of a signal is the midpoint of its spectral density function, i.e. the frequency that divides the distribution into two equal parts.
* The spectral edge frequency (SEF), usually expressed as "SEF x", represents the frequency below which x percent of the total power of a given signal are located; typically, x is in the range 75 to 95. It is more particularly a popular measure used in EEG monitoring, in which case SEF has variously been used to estimate the depth of anesthesia and stages of sleep.
* A spectral envelope is the envelope curve of the spectrum density. It describes one point in time (one window, to be precise). For example, in remote sensing using a spectrometer, the spectral envelope of a feature is the boundary of its spectral properties, as defined by the range of brightness levels in each of the spectral bands of interest.
* The spectral density is a function of frequency, not a function of time. However, the spectral density of a small window of a longer signal may be calculated, and plotted versus time associated with the window. Such a graph is called a spectrogram. This is the basis of a number of spectral analysis techniques such as the short-time Fourier transform and wavelets.
* A "spectrum" generally means the power spectral density, as discussed above, which depicts the distribution of signal content over frequency. For transfer functions (e.g., Bode plot, chirp) the complete frequency response may be graphed in two parts: power versus frequency and phase versus frequency—the phase spectral density, phase spectrum, or spectral phase. Less commonly, the two parts may be the real and imaginary parts of the transfer function. This is not to be confused with the frequency response of a transfer function, which also includes a phase (or equivalently, a real and imaginary part) as a function of frequency. The time-domain impulse response cannot generally be uniquely recovered from the power spectral density alone without the phase part. Although these are also Fourier transform pairs, there is no symmetry (as there is for the autocorrelation) forcing the Fourier transform to be real-valued. See Ultrashort pulse#Spectral phase, phase noise, group delay.
* Sometimes one encounters an amplitude spectral density (ASD), which is the square root of the PSD; the ASD of a voltage signal has units of V Hz. This is useful when the shape of the spectrum is rather constant, since variations in the ASD will then be proportional to variations in the signal's voltage level itself. But it is mathematically preferred to use the PSD, since only in that case is the area under the curve meaningful in terms of actual power over all frequency or over a specified bandwidth. | 7 | Physical Chemistry |
Senftleben was born in Bremen. After graduating from the König-Wilhelm-Gymnasium in Breslau, Senftleben studied physics at the University of Breslau and received his doctorate with Rudolf Ladenburg. The dissertation was about the glow of flames, which he attributed in part to light scattering from small particles in the flame. He was then an assistant in Breslau (with Carl Hintze, Arnold Eucken and Otto Lummer) and Marburg (with Clemens Schaefer), where he habilitated in 1924 and became a privatdozent at University of Marburg. From 1935 until his retirement in 1958 he was a full professor at the University of Münster. He also conducted research there from 1946 to 1961 as an employee at the Marl Chemical Park.
Stimulated by Eucken, he turned to physical chemistry in the 1930s. Among other things, he researched on the direct proof of the dissociation of molecules by collisions of the second kind, the course of the reaction in the production of hydrogen and the electron affinity of oxygen. In particular, however, he investigated the conduction of heat in gases.
The Senftleben-Beenakker effects are named after him and Jan Beenakker, the influence of electric and magnetic fields on the transport properties (thermal conductivity, viscosity) of molecular gases. | 7 | Physical Chemistry |
Passage of hydrogen chloride through molten MsO yields MsCl.
Similar to MsCl, MsO can perform mesylation of alcohols to form sulfonates. Use of MsO avoids the alkyl chloride, which often appears as a side-product when MsCl is used. Unlike MsCl, MsO may not be suitable for mesylation of the unsaturated alcohols.
Examples of mesylation of alcohols with MsO:
* Octadecyl methanesulfonate was prepared from octadecanol in pyridine.
* Secondary alcohol at the anomeric carbon of 2,3,4,5-O-Benzyl-protected glucose reacted to form a glycosyl mesylate, which was found to be more stable than its triflate counterpart, in 2,4,6-collidine.
MsO also converts amines to sulfonamides. | 0 | Organic Chemistry |
In Conia-ene reactions proceeding via alkyne activation, a suitable late transition metal (Au, Ag, Pt, Pd) coordinates to the alkyne and increases its electrophilicity; thus, the enol tautomer of the carbonyl can attack more readily. Toste et al. pioneered two of the first examples of alkyne activation in 2004. Using a cationic Au(I) complex, the authors formed a wide variety of cyclized products from linear β-ketoester starting materials. Notably, the reactions are run under mild conditions and give high diastereoselectivity. Moreover, by shortening the alkyne tether from three carbons to two, substituted cyclopentenes can also be accessed. | 0 | Organic Chemistry |
A combination of ethinylestradiol, drospirenone, and prasterone is under development by Pantarhei Bioscience as a combined birth control pill for prevention of pregnancy in women. It includes prasterone (dehydroepiandrosterone; DHEA), an oral androgen prohormone, to replace testosterone and avoid testosterone deficiency caused by suppression of testosterone by ethinylestradiol and drospirenone. As of August 2018, the formulation is in phase II/III clinical trials.
Drospirenone has been suggested for potential use as a progestin in male hormonal contraception.
Drospirenone has been studied in forms for parenteral administration. | 4 | Stereochemistry |
Currently there are six known structural families. Their conserved structural motifs are:
* LAGLIDADG: Every polypeptide has 1 or 2 LAGLIDADG motifs. The sequence LAGLIDADG is a conserved sequence of amino acids where each letter is a code that identifies a specific residue. This sequence is directly involved in the DNA cutting process. Those enzymes that have only one motif work as homodimers, creating a saddle that interacts with the major groove of each DNA half-site. The LAGLIDADG motifs contribute amino acid residues to both the protein-protein interface between protein domains or subunits, and to the enzyme's active sites. Enzymes that possess two motifs in a single protein chain act as monomers, creating the saddle in a similar way. The first structures to be determined of homing endonucleases (of PI-SceI and I-CreI, both reported in 1997) were both from the LAGLIDADG structural family., The following year, the first structure of a homing endonuclease (I-CreI) bound to its DNA target site was also reported.
* GIY-YIG: These have only one GIY-YIG motif, in the N-terminal region, that interacts with the DNA in the cutting site. The prototypic enzyme of this family is I-TevI which acts as a monomer. Separate structural studies have been reported of the DNA-binding and catalytic domains of I-TevI, the former bound to its DNA target and the latter in the absence of DNA.
* His-Cys box (): These enzymes possess a region of 30 amino acids that includes 5 conserved residues: two histidines and three cysteins. They co-ordinate the metal cation needed for catalysis. I-PpoI is the best characterized enzyme of this family and acts as a homodimer. Its structure was reported in 1998. It is possibly related to the H-N-H family, as they share common features.
* H-N-H: (): These have a consensus sequence of approximately 30 amino acids. It includes two pairs of conserved histidines and one asparagine that create a zinc finger domain. I-HmuI () is the best characterized enzyme of this family, and acts as a monomer. Its structure was reported in 2004 ().
* PD-(D/E)xK (): These enzymes contain a canonical nuclease catalytic domain typically found in type II restriction endonucleases. The best characterized enzyme in this family, I-Ssp6803I (), acts as a tetramer. Its structure was reported in 2007 (). The overall fold is conserved in many endonuclease families, all of which belong to the PD-(D/E)xK superfamily.
* Vsr-like/EDxHD (DUF559, ): These enzymes were discovered in the Global Ocean Sampling Metagenomic Database and first described in 2009. The term Vsr-like refers to the presence of a C-terminal nuclease domain that displays recognizable homology to bacterial Very short patch repair (Vsr) endonucleases. The structure has been solved in 2011, confirming the Vsr homology. Is considered part of the PD-(D/E)xk superfamily. | 1 | Biochemistry |
In July 1987, Lower Saxony’s minister of Science and Art approved the establishment of the ICBM as a cooperation of the university departments of mathematics, biology, physics and chemistry. In 1991, the ICBM was approved as a central organisation of the University of Oldenburg. The registered association „Centre for Research on Shallow seas, Coastal Zones and the Marine Environment – Research Centre Terramare” (Zentrum für Flachmeer-, Küsten- und Meeresumweltforschung e.V. – Forschungszentrum Terramare) which was founded in 1990 in Wilhelmshaven and financed through federal state resources was incorporated into the ICBM in 2008.
The former directors of the ICBM are Wolfgang Krumbein, Ulrich Kattmann, Hans Joachim Schellnhuber, Bruno Eckhardt, Wolfgang Ebenhöh, Heribert Cypionka, Meinhard Simon, Hans-Jürgen Brumsack, Ulrike Feudel, Jürgen Rullkötter, Helmut Hillebrand, Bernd Blasius and Oliver Zielinski. At present, the institute is headed by Heinz Wilkes. | 9 | Geochemistry |
* Dragomir Vitorović, Snežana Bojović, Živorad Čeković: “Vukić M. Mićović 1896-1981, life and work", Faculty of Chemistry, Belgrade, 1996, 142 pages. | 0 | Organic Chemistry |
Axially chiral biaryl compounds are prepared by coupling reactions, e.g., Ullmann coupling, Suzuki–Miyaura reaction, or palladium-catalyzed arylation of arenes. Subsequent to the synthesis, the racemic biaryl is resolved by classical methods. Diastereoselective coupling can be achieved through the use of a chiral bridge that links the two aryl groups or through the use of a chiral auxiliary at one of the positions proximal to axial bridge. Enantioselective coupling can be achieved through the use of a chiral leaving group on one of the biaryls or under oxidative conditions that utilize chiral amines to set the axial configuration.
Individual atropisomers can be isolated by seed-directed crystallization of racemates. Thus, 1,1'-Binaphthyl crystallizes from the melt as individual enantiomers. | 4 | Stereochemistry |
An endothermic process is a chemical or physical process that absorbs heat from its surroundings. In terms of thermodynamics and thermochemistry, it is a thermodynamic process with an increase in the enthalpy (or internal energy ) of the system. In an endothermic process, the heat that a system absorbs is thermal energy transfer into the system. Thus, an endothermic reaction generally leads to an increase in the temperature of the system and a decrease in that of the surroundings.
The term was coined by 19th-century French chemist Marcellin Berthelot. The term endothermic comes from the Greek ἔνδον (endon) meaning within and θερμ- (therm) meaning hot or warm.
An endothermic process may be a chemical process, such as dissolving ammonium nitrate () in water (), or a physical process, such as the melting of ice cubes.
The opposite of an endothermic process is an exothermic process, one that releases or "gives out" energy, usually in the form of heat and sometimes as electrical energy. Thus, endo in endothermic refers to energy or heat going in, and exo in exothermic refers to energy or heat going out. In each term (endothermic and exothermic) the prefix refers to where heat (or electrical energy) goes as the process occurs. | 7 | Physical Chemistry |
The covalent pair-wise interaction between boronic acids and hydroxy groups as found in alcohols and acids is rapid and reversible in aqueous solutions. The equilibrium established between boronic acids and the hydroxyl groups present on saccharides has been successfully employed to develop a range of sensors for saccharides. One of the key advantages with this dynamic covalent strategy lies in the ability of boronic acids to overcome the challenge of binding neutral species in aqueous media. If arranged correctly, the introduction of a tertiary amine within these supramolecular systems will permit binding to occur at physiological pH and allow signalling mechanisms such as photoinduced electron transfer mediated fluorescence emission to report the binding event.
Potential applications for this research include blood glucose monitoring systems to help manage diabetes mellitus. As the sensors employ an optical response, monitoring could be achieved using minimally invasive methods, one such example is the investigation of a contact lens that contains a boronic acid based sensor molecule to detect glucose levels within ocular fluids. | 0 | Organic Chemistry |
* Gas chromatography/mass spectrometry-olfactometry (GC/MS-O)
* GC-recomposition-olfactometry (GC-R)
* Multi-gas chromatography-olfactometry | 3 | Analytical Chemistry |
Calcium carbide is used:
* in the desulfurization of iron (pig iron, cast iron and steel)
* as a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on economics.
* as a powerful deoxidizer at ladle treatment facilities. | 8 | Metallurgy |
The overall organisation of prokaryotic genes is markedly different from that of the eukaryotes. The most obvious difference is that prokaryotic ORFs are often grouped into a polycistronic operon under the control of a shared set of regulatory sequences. These ORFs are all transcribed onto the same mRNA and so are co-regulated and often serve related functions. Each ORF typically has its own ribosome binding site (RBS) so that ribosomes simultaneously translate ORFs on the same mRNA. Some operons also display translational coupling, where the translation rates of multiple ORFs within an operon are linked. This can occur when the ribosome remains attached at the end of an ORF and simply translocates along to the next without the need for a new RBS. Translational coupling is also observed when translation of an ORF affects the accessibility of the next RBS through changes in RNA secondary structure. Having multiple ORFs on a single mRNA is only possible in prokaryotes because their transcription and translation take place at the same time and in the same subcellular location.
The operator sequence next to the promoter is the main regulatory element in prokaryotes. Repressor proteins bound to the operator sequence physically obstructs the RNA polymerase enzyme, preventing transcription. Riboswitches are another important regulatory sequence commonly present in prokaryotic UTRs. These sequences switch between alternative secondary structures in the RNA depending on the concentration of key metabolites. The secondary structures then either block or reveal important sequence regions such as RBSs. Introns are extremely rare in prokaryotes and therefore do not play a significant role in prokaryotic gene regulation. | 1 | Biochemistry |
Endre Qvie Berner (24 September 1893 – 30 January 1983) was a Norwegian organic chemist, author and educator. | 0 | Organic Chemistry |
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