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Gaseous methylglyoxal has two carbonyl groups, an aldehyde and a ketone. In the presence of water, it exists as hydrates and oligomers. The formation of these hydrates is indicative of the high reactivity of MGO, which is relevant to its biological behavior. | 1 | Biochemistry |
Sputter damage is usually defined during transparent electrode deposition on optoelectronic devices, which is usually originated from the substrate's bombardment by highly energetic species. The main species involved in the process and the representative energies can be listed as (values taken from):
* Sputtered atoms (ions) from the target surface (~10 eV), the formation of which mainly depends on the binding energy of the target material;
* Negative ions (originating from the carrier gas) formed in the plasma (~5–15 eV), the formation of which mainly depends on the plasma potential;
* Negative ions formed at the target surface (up to 400 eV), the formation of which mainly depends on the target voltage;
* Positive ions formed in the plasma (~15 eV), the formation of which mainly depends on the potential fall in front of a substrate at floating potential;
* Reflected atoms and neutralized ions from the target surface (20–50 eV), the formation of which mainly depends on the background gas and the mass of the sputtered element.
As seen in the list above, negative ions (e.g., O and In for ITO sputtering) formed at the target surface and accelerated toward the substrate acquire the largest energy, which is determined by the potential between target and plasma potentials. Although the flux of the energetic particles is an important parameter, high-energy negative O ions are additionally the most abundant species in plasma in case of reactive deposition of oxides. However, energies of other ions/atoms (e.g., Ar, Ar, or In) in the discharge may already be sufficient to dissociate surface bonds or etch soft layers in certain device technologies. In addition, the momentum transfer of high-energy particles from the plasma (Ar, oxygen ions) or sputtered from the target might impinge or even increase the substrate temperature sufficiently to trigger physical (e.g., etching) or thermal degradation of sensitive substrate layers (e.g. thin film metal halide perovskites).
This can affect the functional properties of underlying charge transport and passivation layers and photoactive absorbers or emitters, eroding device performance. For instance, due to sputter damage, there may be inevitable interfacial consequences such as pinning of the Fermi level, caused by damage-related interface gap states, resulting in the formation of Schottky-barrier impeding carrier transport. Sputter damage can also impair the doping efficiency of materials and the lifetime of excess charge carriers in photoactive materials; in some cases, depending on its extent, such damage can even lead to a reduced shunt resistance. | 7 | Physical Chemistry |
Ynolates are chemical compounds with a negatively charged oxygen atom attached to an alkyne functionality. They were first synthesized in 1975 by Schöllkopf and Hoppe via the n-butyllithium fragmentation of 3,4-diphenylisoxazole.
Synthetically, they behave as ketene precursors or synthons. | 0 | Organic Chemistry |
It is uncertain whether the use of mechanical closure of the cervical canal following embryo transfer has any effect.
There is considerable evidence that prolonges bed rest (more than 20 minutes) after embryo transfer is associated with reduced chances of clinical pregnancy.
Using hyaluronic acid as an adherence medium for the embryo may increase live birth rates. There may be little or no benefit in having a full bladder, removal of cervical mucus, or flushing of the endometrial or endocervical cavity at the time of embryo transfer. Adjunctive antibiotics in the form of amoxicillin plus clavulanic acid probably does not increase the clinical pregnancy rate compared with no antibiotics. The use of Atosiban, G-CSF and hCG around the time of embryo transfer showed a trend towards increased clinical pregnancy rate.
For frozen-thawed embryo transfer or transfer of embryo from egg donation, no previous ovarian hyperstimulation is required for the recipient before transfer, which can be performed in spontaneous ovulatory cycles. Still, various protocols exist for frozen-thawed embryo transfers as well, such as protocols with ovarian hyperstimulation, protocols in which the endometrium is artificially prepared by estrogen and/or progesterone. There is some evidence that in cycles where the endometrium is artificially prepared by estrogen or progesterone, it may be beneficial to administer an additional drug that suppresses hormone production by the ovaries such as continuous administration of a gonadotropin releasing hormone agonist (GnRHa). For egg donation, there is evidence of a lower pregnancy rate and a higher cycle cancellation rate when the progesterone supplementation in the recipient is commenced prior to oocyte retrieval from the donor, as compared to commenced day of oocyte retrieval or the day after.
Seminal fluid contains several proteins that interact with epithelial cells of the cervix and uterus, inducing active gestational immune tolerance. There are significantly improved outcomes when women are exposed to seminal plasma around the time of embryo transfer, with statistical significance for clinical pregnancy, but not for ongoing pregnancy or live birth rates with the limited data available. | 1 | Biochemistry |
*Acidification − Browning enzymes, as other enzymes, are active at a specific range of pH. For example, PPO shows optimal activity at pH 5-7 and is inhibited below pH 3. Acidifying agents and acidity regulators are widely used as food additives to maintain a desired pH in food products. Acidulants, such as citric acid, ascorbic acid, and glutathione, are used as anti-browning agents. Many of these agents also show other anti-browning effects, such as chelating and antioxidant activities.
*Antioxidants − Many antioxidants are used in food industry as food additives. These compounds react with oxygen and suppress the initiation of the browning process. Also, they interfere with intermediate products of the following reactions and inhibit melanin formation. Ascorbic acid, N-acetylcysteine, L-cysteine, 4-hexylresorcinol, erythorbic acid, cysteine hydrochloride, glutathione are examples of antioxidants that have been studied for their anti-browning properties.
*Chelating agents − Polyphenol oxidase requires copper as a cofactor for its functionality, thus copper-chelating agents inhibit the activity of this enzyme. Many agents possessing chelating activity have been studied and used in different fields of food industry, such as citric acid, sorbic acid, polyphosphates, hinokitiol, kojic acid, EDTA, porphyrins, polycarboxylic acids, different proteins. Some of these compounds also have other anti-browning effects, such as acidifying or antioxidant. Hinokitiol is used in coating materials for food packaging. | 1 | Biochemistry |
Elizabeth A. Canuel is a chemical oceanographer known for her work on organic carbon cycling in aquatic environments. She is the Chancellor Professor of Marine Science at the College of William & Mary and is an elected fellow of the Geochemical Society and the European Association of Geochemistry. | 9 | Geochemistry |
Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty acids. They constitute about 0.25% of phospholipids in the bilayer. | 1 | Biochemistry |
Single fluorophores can be chemically attached to biomolecules, such as proteins or DNA, and the dynamics of individual molecules can be tracked by monitoring the fluorescent probe. Spatial movements within the Rayleigh limit can be tracked, along with changes in emission intensity and/or radiative lifetime, which often indicate changes in local environment. For instance, single-molecule labeling has yielded a vast quantity of information on how kinesin motor proteins move along microtubule strands in muscle cells. Single-molecule imaging in live cells reveals interesting information about protein dynamics under its physiological environment. Several biophysical parameters about protein dynamics can be quantified such as diffusion coefficient, mean squared displacements, residence time, the fraction of bound and unbound molecules, and target-search mechanism of protein binding to its target site in the live cell. | 7 | Physical Chemistry |
Siefert writes:
:Classical thermodynamics, at its heart, deals with general laws governing the transformations of a system, in particular, those involving the exchange of heat, work and matter with an environment. As a central result, total entropy production is identified that in any such process can never decrease, leading, inter alia, to fundamental limits on the efficiency of heat engines and refrigerators.
:The thermodynamic characterisation of systems in equilibrium got its microscopic justification from equilibrium statistical mechanics which states that for a system in contact with a heat bath the probability to find it in any specific microstate is given by the Boltzmann factor. For small deviations from equilibrium, linear response theory allows to express transport properties caused by small external fields through equilibrium correlation functions. On a more phenomenological level, linear irreversible thermodynamics provides a relation between such transport coefficients and entropy production in terms of forces and fluxes. Beyond this linear response regime, for a long time, no universal exact results were available.
:During the last 20 years fresh approaches have revealed general laws applicable to non-equilibrium system thus pushing the range of validity of exact thermodynamic statements beyond the realm of linear response deep into the genuine non-equilibrium region. These exact results, which become particularly relevant for small systems with appreciable (typically non-Gaussian) fluctuations, generically refer to distribution functions of thermodynamic quantities like exchanged heat, applied work or entropy production.
:Stochastic thermodynamics combines the stochastic energetics introduced by with the idea that entropy can consistently be assigned to a single fluctuating trajectory. | 7 | Physical Chemistry |
The two most common modes of nc-AFM operation, frequency modulation (FM) and amplitude modulation (AM), are described below. | 6 | Supramolecular Chemistry |
Reverse [2+2] photocycloaddition, decomposition of 1,2-dioxetanedione, is stated as the mechanism that produces light in glow sticks. | 5 | Photochemistry |
20α,22R-Dihydroxycholesterol, or (3β)-cholest-5-ene-3,20,22-triol is an endogenous, metabolic intermediate in the biosynthesis of the steroid hormones from cholesterol. Cholesterol ((3β)-cholest-5-en-3-ol) is hydroxylated by cholesterol side-chain cleavage enzyme (P450scc) to form 22R-hydroxycholesterol, which is subsequently hydroxylated again by P450scc to form 20α,22R-dihydroxycholesterol, and finally the bond between carbons 20 and 22 is cleaved by P450scc to form pregnenolone ((3β)-3-hydroxypregn-5-en-20-one), the precursor to the steroid hormones. | 1 | Biochemistry |
Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs (German "surface growth" or "overgrowth", ) refers to the collection of small animals and plants that adhere to open surfaces in aquatic environments, such as parts of rooted plants.
Periphyton serves as an important food source for invertebrates, tadpoles, and some fish. It can also absorb contaminants, removing them from the water column and limiting their movement through the environment. The periphyton is also an important indicator of water quality; responses of this community to pollutants can be measured at a variety of scales representing physiological to community-level changes. Periphyton has often been used as an experimental system in, e.g., pollution-induced community tolerance studies. | 2 | Environmental Chemistry |
The phenolphthalein used in this test has been modified from its conventional form, in that it has been reduced by two electrons and is pre-dissolved in alkaline solution. This is typically achieved by boiling an alkaline solution of phenolphthalein with powdered zinc, which reduces the phenolphthalein into phenolphthalin. Upon reduction, the very intense pink color of the cationic form of phenolphthalein fades to a faint yellow color. It is this form of phenolphthalein that is present in Kastle–Meyer test kits. In order to generate the intense pink color indicative of a positive test, the reduced phenolphthalein must be oxidized back to its normal, colored form.
In the relevant reaction, hydrogen peroxide reacts with the hemoglobin in the blood. Phenolphthalein does not directly participate in this process; instead, it acts as an external source of electrons. In its reaction with hydrogen peroxide, the heme center of hemoglobin behaves as a peroxidase, reducing the peroxide to water. This activity depletes hemoglobin of electrons that are, in turn, re-supplied by the phenolphthalein. Donating electrons to hemoglobin converts the phenolphthalin back into the intensely colored phenolphthalein. As long as the enzyme survives, the reaction of heme with peroxide is catalytic, making this test very sensitive to small quantities of blood present on the test swab. The hemoglobin-catalyzed reduction of peroxide that occurs is shown in the reaction below. The two electrons are supplied by phenolphthalein:
: HOOH + 2 e + 2 H → 2 HO
The consumption of protons during the course of the reaction has the effect of raising the pH of the solution, but the amount of base produced is negligible compared to the amount of base already present in the reagent mixture. | 3 | Analytical Chemistry |
Cholesterol 7 alpha-hydroxylase is a cytochrome P450 heme enzyme that oxidizes cholesterol in the position 7 using molecular oxygen. It is an oxidoreductase. CYP7A1 is located in the endoplasmic reticulum (ER) and is important for the synthesis of bile acid and the regulation of cholesterol levels. | 1 | Biochemistry |
SLC18A2 is believed to possess at least two distinct binding sites, which are characterized by tetrabenazine (TBZ) and reserpine binding to the transporter. Amphetamine (TBZ site) and methamphetamine (reserpine site) bind at distinct sites on SLC18A2 to inhibit its function. SLC18A2 inhibitors like tetrabenazine and reserpine reduce the concentration of monoamine neurotransmitters in the synaptic cleft by inhibiting uptake through SLC18A2; the inhibition of SLC18A2 uptake by these drugs prevents the storage of neurotransmitters in synaptic vesicles and reduces the quantity of neurotransmitters that are released through exocytosis. Although many substituted amphetamines induce the release of neurotransmitters from vesicles through SLC18A2 while inhibiting uptake through SLC18A2, they may facilitate the release of monoamine neurotransmitters into the synaptic cleft by simultaneously reversing the direction of transport through the primary plasma membrane transport proteins for monoamines (i.e., the dopamine transporter, norepinephrine transporter, and serotonin transporter) in monoamine neurons. Other SLC18A2 inhibitors such as GZ-793A inhibit the reinforcing effects of methamphetamine, but without producing stimulant or reinforcing effects themselves.
Researchers have found that inhibiting the dopamine transporter (but not SLC18A2) will block the effects of amphetamine and cocaine; while, in another experiment, observing that disabling SLC18A2 (but not the dopamine transporter) prevents any notable action in test animals after amphetamine administration yet not cocaine administration. This suggests that amphetamine may be an atypical substrate with little to no ability to prevent dopamine reuptake via binding to the dopamine transporter but, instead, uses it to enter a neuron where it then interacts with SLC18A2 to induce efflux of dopamine from their vesicles into the cytoplasm whereupon dopamine transporters with amphetamine substrates attached move this recently liberated dopamine into the synaptic cleft. | 1 | Biochemistry |
The heavy-metal binding abilities of humic acids have been exploited to develop remediation technologies for removing lead from waste water. To this end, Yurishcheva et al. coated magnetic nanoparticles with humic acids. After capturing lead ions, the nanoparticles can then be captured using a magnet. | 9 | Geochemistry |
The importance of ocean acidification is reflected in its inclusion as one of seven Global Climate Indicators. These Indicators are a set of parameters that describe the changing climate without reducing climate change to only rising temperature. The Indicators include key information for the most relevant domains of climate change: temperature and energy, atmospheric composition, ocean and water as well as the cryosphere. The Global Climate Indicators have been identified by scientists and communication specialists in a process led by Global Climate Observing System (GCOS). The Indicators have been endorsed by the World Meteorological Organization (WMO). They form the basis of the annual WMO Statement of the State of the Global Climate, which is submitted to the Conference of Parties (COP) of the United Nations Framework Convention on Climate Change (UNFCCC). Additionally, the Copernicus Climate Change Service (C3S) of the European Commission uses the Indicators for their annual "European State of the Climate". | 9 | Geochemistry |
Thalidomide causes birth defects. The U.S. Food and Drug Administration (FDA) and other regulatory agencies have approved marketing of the drug only with an auditable risk evaluation and mitigation strategy that ensures that people using the drug are aware of the risks and avoid pregnancy; this applies to both men and women, as the drug can be transmitted in semen.
There is a high risk that thalidomide can cause excessive blood clots. There is also a high risk that thalidomide can interfere with production of several types of new blood cells, creating a risk of infection via neutropenia, leukopenia, and lymphopenia, and risks that blood will not clot via thrombocytopenia. There is also a risk of anemia via lack of red blood cells. The drug can also damage nerves, causing potentially irreversible peripheral neuropathy.
Thalidomide has several adverse cardiovascular effects, including risk of heart attacks, pulmonary hypertension, and changes in heart rhythm, such as syncope, bradycardia, and atrioventricular block.
Thalidomide can cause liver damage and severe skin reactions like Stevens–Johnson syndrome. It tends to make people sleepy, which creates risk when driving and operating other machinery. As it kills cancer cells, it can cause tumor lysis syndrome. Thalidomide can prevent menstruation.
In addition, very common (reported in more than 10% of people) adverse effects include tremor, dizziness, tingling, numbness, constipation, and peripheral edema.
Common adverse effects (reported by 1–10% of people) include confusion, depressed mood, reduced coordination, heart failure, difficulty breathing, interstitial lung disease, lung inflammation, vomiting, dry mouth, rashes, dry skin, fever, weakness, and a sense of unwellness. | 4 | Stereochemistry |
* Roberto Todeschini, Viviana Consonni, Raimund Mannhold, Hugo Kubinyi & Hendrik Timmerman, 2008, "Entry: Electronic substituent constants (Hammet substituent constants, σ electronic constants)," in Handbook of Molecular Descriptors, Vol. 11 of Methods and Principles in Medicinal Chemistry (book series), pp. 144–157, New York, NY, US: John Wiley & Sons, , see [https://books.google.com/books?isbn=3527613110], accessed 22 June 2015.
* N. Chapman, 2012, Correlation Analysis in Chemistry: Recent Advances, New York, NY, US: Springer Science & Business, , see [https://books.google.com/books?isbn=1461588316], accessed 22 June 2015. | 7 | Physical Chemistry |
In photolysis cancer therapy, light is used to selectively break bonds which releases and activates a target drug molecule. The drug molecule can be released near or in tumour sites to combat the disease. TTA-UC materials that can be excited by near-infrared light are desirable for this application since near-infrared light penetrates tissue well. | 7 | Physical Chemistry |
Phenol red is a weak estrogen mimic, and in cell cultures can enhance the growth of cells that express the estrogen receptor. It has been used to induce ovarian epithelial cells from post-menopausal women to differentiate into cells with properties of oocytes (eggs), with potential implications for both fertility treatment and stem cell research. | 3 | Analytical Chemistry |
A relatively recent analytical tool that has been used for the separation of UCMs is comprehensive two-dimensional GC (GCxGC). This powerful technique, introduced by Liu and Phillips combines two GC columns with different separation mechanisms: typically a primary column that separates compounds based on volatility coupled to a second short column that separates by polarity. The two columns are connected by a modulator, a device that traps, focuses and re-injects the peaks that elute from the first column into the second column. Each peak eluting from the first column (which may be a number of co-eluting peaks) is further separated on the second column. The second separation is rapid, allowing the introduction of subsequent fractions from the first column without mutual interference. Dallüge et al. reviewed the principles, advantages and main characteristics of this technique. One of the main advantages is the very high separation power, making the technique ideal for unravelling the composition of complex mixtures. Another important feature of GC×GC is that chemically related compounds show up as ordered structures within the chromatograms, i.e. isomers appear as distinct groups in the chromatogram as a result of their similar interaction with the second dimension column phase. The use of GC×GC for the characterization of complex petrochemical mixtures has been extensively reviewed. Most research into petrochemical hydrocarbons using GC×GC has utilised flame ionisation detection (FID) but mass spectrometry (MS) is necessary to obtain the structural information necessary to identify unknown compounds. Currently, only time-of-flight MS (ToF-MS) can deliver the high acquisition rates required to analyse GC×GC. | 3 | Analytical Chemistry |
Gaseous scintillators consist of nitrogen and the noble gases helium, argon, krypton, and xenon, with helium and xenon receiving the most attention. The scintillation process is due to the de-excitation of single atoms excited by the passage of an incoming particle. This de-excitation is very rapid (~1 ns), so the detector response is quite fast. Coating the walls of the container with a wavelength shifter is generally necessary as those gases typically emit in the ultraviolet and PMTs respond better to the visible blue-green region. In nuclear physics, gaseous detectors have been used to detect fission fragments or heavy charged particles. | 5 | Photochemistry |
One of the earliest steps towards atomic physics was the recognition that matter was composed
of atoms. It forms a part of the texts written in 6th century BC to 2nd century BC, such as those of Democritus or written by . This theory was later developed in the modern sense of the basic unit of a chemical element by the British chemist and physicist John Dalton in the 18th century. At this stage, it wasn't clear what atoms were, although they could be described and classified by their properties (in bulk). The invention of the periodic system of elements by Dmitri Mendeleev was another great step forward.
The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The study of these lines led to the Bohr atom model and to the birth of quantum mechanics. In seeking to explain atomic spectra, an entirely new mathematical model of matter was revealed. As far as atoms and their electron shells were concerned, not only did this yield a better overall description, i.e. the atomic orbital model, but it also provided a new theoretical basis for chemistry
(quantum chemistry) and spectroscopy.
Since the Second World War, both theoretical and experimental fields have advanced at a rapid pace. This can be attributed to progress in computing technology, which has allowed larger and more sophisticated models of atomic structure and associated collision processes. Similar technological advances in accelerators, detectors, magnetic field generation and lasers have greatly assisted experimental work. | 7 | Physical Chemistry |
* 2023 President-elect Cell Stress Society International
* 2019 Fellow of Cell Stress Society International
*2017 Society for Basic Urological Research Young Investigator
* 2017 American Urological Association Research Scholar
* 2013 Early Career Award, Cell Stress Society International
* 2011 2011 Lasker~Bloomberg Public Service Award, as member of the recipient team at The Clinical Center of the National Institutes of Health
* 2010 Intramural National Cancer Institute (NCI) Fellow and Young Investigator of the Year
* 2010 Scholar-in-training award, American Association for Cancer Research (AACR)
* 2006 Federation of European Biochemical Societies Research Fellowship (FEBS) | 1 | Biochemistry |
A Stirling cycle is like an Otto cycle, except that the adiabats are replaced by isotherms. It is also the same as an Ericsson cycle with the isobaric processes substituted for constant volume processes.
# TOP and BOTTOM of the loop: a pair of quasi-parallel isothermal processes
# LEFT and RIGHT sides of the loop: a pair of parallel isochoric processes
Heat flows into the loop through the top isotherm and the left isochore, and some of this heat flows back out through the bottom isotherm and the right isochore, but most of the heat flow is through the pair of isotherms. This makes sense since all the work done by the cycle is done by the pair of isothermal processes, which are described by Q=W. This suggests that all the net heat comes in through the top isotherm. In fact, all of the heat which comes in through the left isochore comes out through the right isochore: since the top isotherm is all at the same warmer temperature and the bottom isotherm is all at the same cooler temperature , and since change in energy for an isochore is proportional to change in temperature, then all of the heat coming in through the left isochore is cancelled out exactly by the heat going out the right isochore. | 7 | Physical Chemistry |
Bisulfite sequencing (also known as bisulphite sequencing) is the use of bisulfite treatment of DNA before routine sequencing to determine the pattern of methylation. DNA methylation was the first discovered epigenetic mark, and remains the most studied. In animals it predominantly involves the addition of a methyl group to the carbon-5 position of cytosine residues of the dinucleotide CpG, and is implicated in repression of transcriptional activity.
Treatment of DNA with bisulfite converts cytosine residues to uracil, but leaves 5-methylcytosine residues unaffected. Therefore, DNA that has been treated with bisulfite retains only methylated cytosines. Thus, bisulfite treatment introduces specific changes in the DNA sequence that depend on the methylation status of individual cytosine residues, yielding single-nucleotide resolution information about the methylation status of a segment of DNA. Various analyses can be performed on the altered sequence to retrieve this information. The objective of this analysis is therefore reduced to differentiating between single nucleotide polymorphisms (cytosines and thymidine) resulting from bisulfite conversion (Figure 1). | 1 | Biochemistry |
Expression of genetic code in all life forms consists of two major processes, synthesis of copies of the genetic code recorded in DNA into the form of mRNA (transcription), and protein synthesis itself (translation), whereby the code copies in mRNA are decoded into amino acid sequences of the respective proteins. Both transcription and translation are highly regulated processes essentially controlling everything of what happens in live cells (and multicellular organisms, consequently).
Control of translation is especially important in eukaryotic cells where it forms part of post-transcriptional regulatory networks of genes expression. This additional functionality is reflected in the increased complexity of the translation process, making it a hard object to investigate. Yet details on when and what mRNA is translated and what mechanisms are responsible for this control are key to understanding of normal and pathological cell functionality. TCP-seq can be used to obtain this information. | 1 | Biochemistry |
An interest in the natural world, combined with the logic of science and math, attracted Lynch-Stieglitz to science and after a summer at the Duke University Marine Laboratory she decided on a career in physical oceanography. In 1986, she earned B.S. degrees in physics and geology from Duke University and for two years she worked as an oceanographer at the Pacific Marine Environmental Laboratory. From 1988 until 1989 she worked at the Maryland Science Center and as a programmer at Johns Hopkins University before moving to Columbia University where she earned an M.A. (1991) and Ph.D. (1995) in geological sciences. After two years as a postdoctoral scholar at Woods Hole Oceanographic Institution, in 1996 she returned to New York where she joined the faculty of the Lamont–Doherty Earth Observatory. In 2004, Lynch-Stieglitz moved to the Georgia Institute of Technology where she was promoted to professor in 2010.
From 2012 to 2015, Lynch-Stieglitz was the Editor of Earth and Planetary Science Letters.
In 2015 Lynch-Stieglitz was elected a fellow of the American Association for the Advancement of Science "for bringing physical oceanography approaches to the study of transient circulation changes during ice ages, providing a window into the ocean’s interaction with today’s climate change." | 9 | Geochemistry |
A wide variety of absorption band and line shapes exist, and the analysis of the band or line shape can be used to determine information about the system that causes it. In many cases it is convenient to assume that a narrow spectral line is a Lorentzian or Gaussian, depending respectively on the decay mechanism or temperature effects like Doppler broadening. Analysis of the spectral density and the intensities, width and shape of spectral lines sometimes can yield a lot of information about the observed system like it is done with Mössbauer spectra.
In systems with a very large number of states like macromolecules and large conjugated systems the separate energy levels can't always be distinguished in an absorption spectrum. If the line broadening mechanism is known and the shape of then spectral density is clearly visible in the spectrum, it is possible to get the desired data. Sometimes it is enough to know the lower or upper limits of the band or its position for an analysis.
For condensed matter and solids the shape of absorption bands are often determined by transitions between states in their continuous density of states distributions. For crystals, the electronic band structure determines the density of states. In fluids, glasses and amorphous solids, there is no long range correlation and the dispersion relations are isotropic. For charge-transfer complexes and conjugated systems, the band width is complicated by a variety of factors, compared to condensed matter. | 7 | Physical Chemistry |
The conditional entropy,
is the number of bits which would have to be transmitted to identify from equally likely possibilities, less the relative entropy of the product distribution from the true joint distribution — i.e. less the expected number of bits saved which would have had to be sent if the value of were coded according to the uniform distribution rather than the conditional distribution of given . | 7 | Physical Chemistry |
Layered sedimentary deposits are widespread on Mars. These deposits probably consist of both sedimentary rock and poorly indurated or unconsolidated sediments. Thick sedimentary deposits occur in the interior of several canyons in Valles Marineris, within large craters in Arabia and Meridiani Planum (see Henry Crater for example), and probably comprise much of the deposits in the northern lowlands (e.g., Vastitas Borealis Formation). The Mars Exploration Rover Opportunity landed in an area containing cross-bedded (mainly eolian) sandstones (Burns formation). Fluvial-deltaic deposits are present in Eberswalde Crater and elsewhere, and photogeologic evidence suggests that many craters and low lying intercrater areas in the southern highlands contain Noachian-aged lake sediments.
While the possibility of carbonates on Mars has been of great interest to astrobiologists and geochemists alike, there was little evidence for significant quantities of carbonate deposits on the surface. In the summer of 2008, the TEGA and WCL experiments on the 2007 Phoenix Mars lander found between 3–5wt% (percent by weight) calcite (CaCO) and an alkaline soil. In 2010, analyses by the Mars Exploration Rover Spirit identified outcrops rich in magnesium-iron carbonate (16–34 wt%) in the Columbia Hills of Gusev crater. The magnesium-iron carbonate most likely precipitated from carbonate-bearing solutions under hydrothermal conditions at near-neutral pH in association with volcanic activity during the Noachian Period.
Carbonates (calcium or iron carbonates) were discovered in a crater on the rim of Huygens Crater, located in the Iapygia quadrangle. The impact on the rim exposed material that had been dug up from the impact that created Huygens. These minerals represent evidence that Mars once had a thicker carbon dioxide atmosphere with abundant moisture, since these kind of carbonates only form when there is a lot of water. They were found with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. Earlier, the instrument had detected clay minerals. The carbonates were found near the clay minerals. Both of these minerals form in wet environments. It is supposed that billions of years ago Mars was much warmer and wetter. At that time, carbonates would have formed from water and the carbon dioxide-rich atmosphere. Later the deposits of carbonate would have been buried. The double impact has now exposed the minerals. Earth has vast carbonate deposits in the form of limestone. | 9 | Geochemistry |
The Earth’s gravitational field acts upon colloidal particles. Therefore, if the colloidal particles are denser than the medium of suspension, they will sediment (fall to the bottom), or if they are less dense, they will cream (float to the top). Larger particles also have a greater tendency to sediment because they have smaller Brownian motion to counteract this movement.
The sedimentation or creaming velocity is found by equating the Stokes drag force with the gravitational force:
where
: is the Archimedean weight of the colloidal particles,
: is the viscosity of the suspension medium,
: is the radius of the colloidal particle,
and is the sedimentation or creaming velocity.
The mass of the colloidal particle is found using:
where
: is the volume of the colloidal particle, calculated using the volume of a sphere ,
and is the difference in mass density between the colloidal particle and the suspension medium.
By rearranging, the sedimentation or creaming velocity is:
There is an upper size-limit for the diameter of colloidal particles because particles larger than 1 μm tend to sediment, and thus the substance would no longer be considered a colloidal suspension.
The colloidal particles are said to be in sedimentation equilibrium if the rate of sedimentation is equal to the rate of movement from Brownian motion. | 7 | Physical Chemistry |
Siddiqui was a founder-member of the Indian and Pakistan Academies of Sciences, and later a founder member of the international body the Third World Academy of Sciences. The following are the honours he received, in reverse chronological order:
* Gold medal of the Soviet Academy of Sciences
* Third World Academy of Sciences – TWAS Prize, 1985
* Hilal-e-Imtiaz, (Crescent of Excellence) 1980 by the Government of Pakistan
* President of Pakistan's Pride of Performance Medal, 1966
* Sitara-e-Imtiaz, 1962 (Star of Excellence) by the Government of Pakistan
* Fellow of the Royal Society, 1961
* President, Pan-Indian Ocean Science Association, 1960
* Tamgha-e-Pakistan, 1958 (Medal of Pakistan)
* D. Med. Honoris causa from the Frankfurt University, 1958
* Foundation Fellow, Pakistan Academy of Sciences, 1953
* Order of the British Empire in 1946 | 0 | Organic Chemistry |
The only first-principles calculational tool currently available is lattice QCD, i.e. brute-force computer calculations. Because of a technical obstacle known as the fermion sign problem, this method can only be used at low density and high temperature (μ < T), and it predicts that the crossover to the quark–gluon plasma will occur around T = 150 MeV However, it cannot be used to investigate the interesting color-superconducting phase structure at high density and low temperature. | 7 | Physical Chemistry |
A diverse range of biomolecules exist, including:
* Small molecules:
** Lipids, fatty acids, glycolipids, sterols, monosaccharides
** Vitamins
** Hormones, neurotransmitters
** Metabolites
* Monomers, oligomers and polymers: | 0 | Organic Chemistry |
Based on the results of the pilot plant work, the MIM Holdings Board of Directors approved the construction of an A$65 million demonstration plant, capable of producing 60,000 t/y of lead bullion. This plant operated from early 1991 until 1995. It was initially designed to treat 20 t/h of lead concentrate using lance air enriched to 27%. However, the oxygen originally designated for its use was diverted to the more profitable copper smelting operations, and the feed rate to the lead ISASMELT demonstration plant was severely restricted. When there was sufficient oxygen available in 1993 to increase the enrichment level to 33–35%, treatment rates of up to 36 t/h of concentrate were achieved, with residual lead in the final reduction furnace slag being in the range of 2–5%.
The two-stage approach to ISASMELT lead smelting was partly driven by the relatively low lead content of Mount Isa lead concentrates (typically in the range of 47–52% lead during the lead ISASMELT development period). Trying to produce lead bullion in a single furnace with such low concentrate grades would result in excessive fuming of lead oxide with a huge amount of material that would have to be returned to the furnace to recover the lead and, consequently, a higher energy demand as that material had to be reheated to the furnace temperatures.
Concentrates with higher lead contents can be smelted directly into lead metal in a single furnace without excess fuming. This was demonstrated on the large scale in 1994, when 4000 t of concentrate containing 67% lead were treated at rates up to 32 t/h with lance air enriched to 27%. During these trials, 50% of the lead in the concentrate was converted to lead bullion in the smelting furnace, while most of the rest ended up as lead oxide in the smelting furnace slag.
Like the lead ISASMELT pilot plant, the lead ISASMELT demonstration plant suffered from constraints imposed by the waste gas handling system. In the case of the demonstration plant, the problem was caused by sticky fume that formed an insulating layer on the convection tube bundles of the waste heat boilers, significantly reducing the heat transfer rates and thus the ability of the boilers to reduce the waste gas temperature. As the plant used baghouses to filter lead fume from the waste gas, it was necessary to reduce the temperature of the gas below the point at which the bags would be damaged by high temperatures. The problem was solved by allowing cool air to mix with the hot waste gas to lower the temperature to a level at which the baghouse could operate. This reduced the ISASMELT plant's capacity because it was again limited by the volume of gas that could be filtered by the baghouse.
The lead ISASMELT demonstration plant was mothballed in 1995 because there was insufficient concentrate to keep both it and the rest of the lead smelter operating. It was too small to treat all the Mount Isa lead concentrate by itself. | 8 | Metallurgy |
Ramipril is marketed as Prilace by Arrow Pharmaceuticals in Australia, Ramipro by Westfield Pharma in the Philippines, Triatec by Sanofi-Aventis in Italy and United States and Altace by King Pharmaceuticals in the United States, Novapril by Pharmanova in Ghana, Ramitens by PharmaSwiss, Ampril by Krka in Slovenia, Corpril by Cemelog-BRS in Hungary, Piramil and Prilinda by Hemofarm in Serbia, by Lek in Poland and by Novartis and Opsonin Pharma Limited as Ramace in Bangladesh, and in Canada as Altace (Sanofi-Aventis) and Ramipril (Pharmascience).
Ramipril is marketed in India under the brand names Cardace, Zigpril, Ramistar, Odipril and Zorem . Ramipril is marketed in Myanmar under brand name Endpril . | 4 | Stereochemistry |
Half sandwich compounds, also known as piano stool complexes, are organometallic complexes that feature a cyclic polyhapto ligand bound to an ML center, where L is a unidentate ligand. Thousands of such complexes are known. Well-known examples include cyclobutadieneiron tricarbonyl and (CH)TiCl. Commercially useful examples include (CH)Co(CO), which is used in the synthesis of substituted pyridines, and methylcyclopentadienyl manganese tricarbonyl, an antiknock agent in petrol. | 0 | Organic Chemistry |
Cooperativity is a phenomenon displayed by systems involving identical or near-identical elements, which act dependently of each other, relative to a hypothetical standard non-interacting system in which the individual elements are acting independently. One manifestation of this is enzymes or receptors that have multiple binding sites where the affinity of the binding sites for a ligand is apparently increased, positive cooperativity, or decreased, negative cooperativity, upon the binding of a ligand to a binding site. For example, when an oxygen atom binds to one of hemoglobin's four binding sites, the affinity to oxygen of the three remaining available binding sites increases; i.e. oxygen is more likely to bind to a hemoglobin bound to one oxygen than to an unbound hemoglobin. This is referred to as cooperative binding.
We also see cooperativity in large chain molecules made of many identical (or nearly identical) subunits (such as DNA, proteins, and phospholipids), when such molecules undergo phase transitions such as melting, unfolding or unwinding. This is referred to as subunit cooperativity. However, the definition of cooperativity based on apparent increase or decrease in affinity to successive ligand binding steps is problematic, as the concept of "energy" must always be defined relative to a standard state. When we say that the affinity is increased upon binding of one ligand, it is empirically unclear what we mean since a non-cooperative binding curve is required to rigorously define binding energy and hence also affinity. A much more general and useful definition of positive cooperativity is: A process involving multiple identical incremental steps, in which intermediate states are statistically underrepresented relative to a hypothetical standard system (null hypothesis) where the steps occur independently of each other.
Likewise, a definition of negative cooperativity would be a process involving multiple identical incremental steps, in which the intermediate states are overrepresented relative to a hypothetical standard state in which individual steps occur independently. These latter definitions for positive and negative cooperativity easily encompass all processes which we call "cooperative", including conformational transitions in large molecules (such as proteins) and even psychological phenomena of large numbers of people (which can act independently of each other, or in a co-operative fashion). | 1 | Biochemistry |
The endocannabinoid system has been shown to have a homeostatic role by controlling several metabolic functions, such as energy storage and nutrient transport. It acts on peripheral tissues such as adipocytes, hepatocytes, the gastrointestinal tract, the skeletal muscles and the endocrine pancreas. It has also been implied in modulating insulin sensitivity. Through all of this, the endocannabinoid system may play a role in clinical conditions, such as obesity, diabetes, and atherosclerosis, which may also give it a cardiovascular role. | 1 | Biochemistry |
Nucleic acid analogues are used in molecular biology for several purposes:
* Investigation of possible scenarios of the origin of life: By testing different analogs, researchers try to answer the question of whether life's use of DNA and RNA was selected over time due to its advantages, or if they were chosen by arbitrary chance;
* As a tool to detect particular sequences: XNA can be used to tag and identify a wide range of DNA and RNA components with high specificity and accuracy;
* As an enzyme acting on DNA, RNA and XNA substrates - XNA has been shown to have the ability to cleave and ligate DNA, RNA and other XNA molecules similar to the actions of RNA ribozymes;
* As a tool with resistance to RNA hydrolysis;
* Investigation of the mechanisms used by enzyme; and
* Investigation of the structural features of nucleic acids. | 1 | Biochemistry |
Like other organolithium compounds, tert-butyllithium is a cluster compound. Whereas n-butyllithium exists both as a hexamer and a tetramer, tert-butyllithium exists exclusively as a tetramer with a cubane structure. Bonding in organolithium clusters involves sigma delocalization and significant Li−Li bonding. Despite its complicated structure, tert-butyllithium is usually depicted in equations as a monomer.
The lithium–carbon bond in tert-butyllithium is highly polarized, having about 40 percent ionic character. The molecule reacts like a carbanion, as is represented by these two resonance structures: | 0 | Organic Chemistry |
A phase-change material (PCM) is a substance which releases/absorbs sufficient energy at phase transition to provide useful heat or cooling. Generally the transition will be from one of the first two fundamental states of matter - solid and liquid - to the other. The phase transition may also be between non-classical states of matter, such as the conformity of crystals, where the material goes from conforming to one crystalline structure to conforming to another, which may be a higher or lower energy state.
The energy released/absorbed by phase transition from solid to liquid, or vice versa, the heat of fusion is generally much higher than the sensible heat. Ice, for example, requires 333.55 J/g to melt, but then water will rise one degree further with the addition of just 4.18 J/g. Water/ice is therefore a very useful phase change material and has been used to store winter cold to cool buildings in summer since at least the time of the Achaemenid Empire.
By melting and solidifying at the phase-change temperature (PCT), a PCM is capable of storing and releasing large amounts of energy compared to sensible heat storage. Heat is absorbed or released when the material changes from solid to liquid and vice versa or when the internal structure of the material changes; PCMs are accordingly referred to as latent heat storage (LHS) materials.
There are two principal classes of phase-change material: organic (carbon-containing) materials derived either from petroleum, from plants or from animals; and salt hydrates, which generally either use natural salts from the sea or from mineral deposits or are by-products of other processes. A third class is solid to solid phase change.
PCMs are used in many different commercial applications where energy storage and/or stable temperatures are required, including, among others, heating pads, cooling for telephone switching boxes, and clothing.
By far the biggest potential market is for building heating and cooling. In this application area, PCMs hold potential in light of the progressive reduction in the cost of renewable electricity, coupled with the intermittent nature of such electricity. This can result in a misfit between peak demand and availability of supply. In North America, China, Japan, Australia, Southern Europe and other developed countries with hot summers, peak supply is at midday while peak demand is from around 17:00 to 20:00. This creates opportunities for thermal storage media.
Solid-liquid phase-change materials are usually encapsulated for installation in the end application, to contain in the liquid state. In some applications, especially when incorporation to textiles is required, phase change materials are micro-encapsulated. Micro-encapsulation allows the material to remain solid, in the form of small bubbles, when the PCM core has melted. | 7 | Physical Chemistry |
The Hedgehog protein family is involved in induction of cell types and the creation of tissue boundaries and patterning and are found in all bilateral organisms. Hedgehog proteins were first discovered and studied in Drosophila. Hedgehog proteins produce key signals for the establishment of limb and body plan of fruit flies as well as homeostasis of adult tissues, involved in late embryogenesis and metamorphosis. At least three "Drosophila" hedgehog homologs have been found in vertebrates: sonic hedgehog, desert hedgehog, and Indian hedgehog. Sonic hedgehog (SHH) has various roles in vertebrae development, mediating signaling and regulating the organization of central nervous system, limb, and somite polarity. Desert hedgehog (DHH) is expressed in the Sertoli cells involved in spermatogenesis. Indian hedgehog (IHH) is expressed in the gut and cartilage, important in postnatal bone growth. | 1 | Biochemistry |
Unlike ultraviolet–visible spectroscopy which measures absorbance, charge modulation spectroscopy measures the charge introduced optical transmission variation. In other words, it reveals the new features in optical transmission introduced by charges. In this setup, there are mainly four components: lamp, monochromator, photodetector and lock-in amplifier. Lamp and monochromator are used for generating and selecting the wavelength. The selected wavelength passes through the transistor, and the transmitted light is recorded by the Photodiode. When the signal to noise ratio is very low, the signal can be modulated and recovered with a Lock-in amplifier.
In the experiment, a direct current plus an alternating current bias are applied to the organic field-effect transistor. Charge carries accumulate at the interface between the dielectric and the semiconductor (usually a few nanometers). With the appearance of the accumulation charge, the intensity of the transmitted light changes. The variation of the light intensity () is then collected though the photodetector and lock-in amplifier. The charge modulation frequency is given to Lock-in amplifier as the reference. | 7 | Physical Chemistry |
In genetics and cell biology, repression is a mechanism often used to decrease or inhibit the expression of a gene. Removal of repression is called derepression. This mechanism may occur at different stages in the expression of a gene, with the result of increasing the overall RNA or protein products. Dysregulation of derepression mechanisms can result in altered gene expression patterns, which may lead to negative phenotypic consequences such as disease. | 1 | Biochemistry |
Vienna Standard Mean Ocean Water (VSMOW) is an isotopic standard for water, that is, a particular sample of water whose proportions of different isotopes of hydrogen and oxygen are accurately known. VSMOW is distilled from ocean water and does not contain salt or other impurities. Published and distributed by the Vienna-based International Atomic Energy Agency in 1968, the standard and its essentially identical successor, VSMOW2, continue to be used as a reference material.
Water samples made up of different isotopes of hydrogen and oxygen have slightly different physical properties. As an extreme example, heavy water, which contains two deuterium (H) atoms instead of the usual, lighter hydrogen-1 (H), has a melting point of and boiling point of . Different rates of evaporation cause water samples from different places in the water cycle to contain slightly different ratios of isotopes. Ocean water (richer in heavy isotopes) and rain water (poorer in heavy isotopes) roughly represent the two extremes found on Earth. With VSMOW, the IAEA simultaneously published an analogous standard for rain water, Standard Light Antarctic Precipitation (SLAP), and eventually its successor SLAP2. SLAP contains about 5% less oxygen-18 and 42.8% less deuterium than VSMOW.
A scale based on VSMOW and SLAP is used to report oxygen-18 and deuterium concentrations. From 2005 until its redefinition in 2019, the kelvin was specified to be of the temperature of specifically VSMOW at its triple point. | 9 | Geochemistry |
The European Association of Geochemistry (EAG) is a pan-European organization founded to promotes geochemical research. The EAG organizes conferences, meetings and educational courses for geochemists in Europe, including the Goldschmidt Conference which it co-sponsors with the North American Geochemical Society. | 9 | Geochemistry |
As explained by Gibbs and appreciated by Maxwell, the advantage of a U-V-S (energy-volume-entropy) surface over the usual P-V-T (pressure-volume-temperature) surface was that it allowed to geometrically explain sharp, discontinuous phase transitions as emerging from a purely continuous and smooth state function ; Maxwell's surface demonstrated the generic behaviour for a substance that can exist in solid, liquid, and gaseous phases. The basic geometrical operation involved simply placing a tangent plane (such as a flat sheet of glass) on the surface and rolling it around, observing where it touches the surface. Using this operation, it was possible to explain phase coexistence, the triple point, to identify the boundary between absolutely stable and metastable phases (e.g., superheating and supercooling), the spinodal boundary between metastable and unstable phases, and to illustrate the critical point.
Maxwell drew lines of equal pressure (isopiestics) and of equal temperature (isothermals) on his plaster cast by placing it in the sunlight, and "tracing the curve when the rays just grazed the surface." He sent sketches of these lines to a number of colleagues. For example, his letter to Thomas Andrews of 15 July 1875 included sketches of these lines. Maxwell provided a more detailed explanation and a clearer drawing of the lines (pictured) in the revised version of his book Theory of Heat, and a version of this drawing appeared on a 2005 US postage stamp in honour of Gibbs.
As well as being on display in two countries, Maxwells model lives on in the literature of thermodynamics, and books on the subject often mention it, though not always with complete historical accuracy. For example, the thermodynamic surface represented by the sculpture is often reported to be that of water, contrary to Maxwells own statement. | 7 | Physical Chemistry |
Experimentally verified and predicted telomere sequence motifs from more than 9000 species are collected in research community curated database [http://cfb.ceitec.muni.cz/telobase/ TeloBase]. Some of the experimentally verified telomere nucleotide sequences are also listed in [http://telomerase.asu.edu/sequences_telomere.html Telomerase Database] website (see nucleic acid notation for letter representations). | 1 | Biochemistry |
The compound is prepared in the lab by treating benzyl alcohol with phosgene:
: PhCHOH + COCl → PhCHOC(O)Cl + HCl
Phosgene is used in excess to minimise the production of the carbonate (PhCHO)C=O.
The use of phosgene gas in the lab preparation carries a very large health hazard, and has been implicated in the chronic pulmonary disease of pioneers in the usage of the compound such as Zervas. | 0 | Organic Chemistry |
The free Maxwell equations imply that
The precedent equation implies that the quantity is constant. This time-independent quantity is one of the ten zilches discovered by Lipkin. Nowadays, the quantity is widely known as optical chirality (up to a factor of 1/2).
The quantity is the spatial density of optical chirality, while is the optical chirality flux. Generalizing the aforementioned differential conservation law for , Lipkin found other nine conservation laws, all unrelated to the stress–energy tensor. He collectively named these ten conserved quantities the zilch (nowadays, they are also called the zilches) because of the apparent lack of physical significance. | 4 | Stereochemistry |
* University Faculty Scholar
* Premier's Research Excellence Award
* Marilyn Robinson Award for Excellence in Teaching
* Alumni Western, Bank of Nova Scotia, University Students' Council Award for Excellence in Undergraduate Teaching (1997–98, 2001–02)
* Canadian National Congress-International Union Pure and Applied Chemistry (CNC-IUPAC) Award
* Ontario Confederation of University Faculty Associations Award for Excellence in University Teaching
* USC Teaching Honour Roll (2001–2005)
* NRC Research Associateship (1992–1994)
* NSERC Postdoctoral Scholarship (1992) – declined to take position at NRC
* NSERC Doctoral Prize finalist (1993)
* NSERC Postgraduate Scholarships (1988–1992)
* McMaster University Centennial Scholarships for Academic Excellence (1988–1992) | 0 | Organic Chemistry |
In 1964, William Zisman published an article in the ACS publications on the "Relation of the Equilibrium Contact Angle to Liquid and Solid Constitution". It was in this article where he used what we call today as the Zisman plot. The Zisman plot is used to very quickly give a quantitative measurement of wettability, also known as the critical surface tension, γ , of a solid surface by measuring the liquid contact angle as shown in Figure 1. Taking the cosine of said angle and then graphing it against the surface tension of the liquid wetting the solid substrate yields the critical surface tension. Wettability is a measure of how well a liquid spreads and how complete the contact of the liquid is across the surface of a solid interface. A small contact angle indicates good wettability, while a large contact angle indicates poor wettability. The critical surface tension is the highest liquid surface tension that can completely wet a specific solid surface. For adhesive bonding complete wetting is used to maximize the adhesive joint strength.
Even though this relationship is empirical and less precise than the surface tension of a homologous series of liquids, it is very useful considering it is a parameter of the solid surface. This method is especially used to compare and measure the critical surface tension of low-energy solids (mainly plastics) very quickly and easily. Figure 4 in ZIsmans published article from 1964 shows the critical surface tension as a measure of wettability of Polyethylene. Zisman published this analysis in 1964 and used a variety of nonhomologous liquids to measure the critical surface tension of Polyethylene to be around 35 dynes per centimeter as shown by the intercept at x=1 in Figure 4. Figure 12 in Zismans 1964 article shows that different solids can also be plotted on the same graph to easily compare the critical solid surface tensions of a variety of plastic substrates including very different polymers such as teflon, acid monolayers, and esters. The ZIsman Plot proved to be a breakthrough which allowed for a very efficient way to measure wettability of a solid which helped to spawn the work of Dann in the late 1960s. Dann characterized the critical surface tensions of a variety of polymeric materials using the Zisman Plot. In modern days, David and Neumann in an investigation of contact angle on low-energy surfaces. However, today some different variations of the Zisman plot exist because the dependent variable is unitless being since it is cosine of the contact angle for the liquid. | 7 | Physical Chemistry |
Oxaziridines are intermediates in the peroxide process for the production of hydrazine. Many millions of kilograms of hydrazine are produced annually by this method that involves a step wherein ammonia is oxidized in the presence of methyl ethyl ketone to give the oxaziridine:
:Me(Et)C=O + NH + HO → Me(Et)CONH + HO
In subsequent steps the oxaziridine is converted to the hydrazone, which is the immediate in the way to hydrazine:
:Me(Et)CONH + NH → Me(Et)C=NNH + HO | 0 | Organic Chemistry |
Oxide fluxes are often combined to reduce volatility, viscosity, and reactivity towards the crucibles. Metallic fluxes aren't typically combined, as they do not suffer from the same volatility, viscosity, and reactivity issues. An ideal flux should have the following properties:
* Good solubility for desired compound at growth temperatures.
* Low melting point.
* Large gap between melting and boiling point.
* Easily removed from crystals.
* Unreactive with crucible and starting materials at growth temperatures. | 3 | Analytical Chemistry |
Birds not usually considered predators of mice do take voles; examples include gulls (Larus sp.), northern shrikes (Larius borealis), black-billed magpies (Pica hudsonica), common ravens (Corvus corax), American crows (C. brachyrhynchos), great blue herons (Ardea herodias), and American bitterns (Botaurus lentiginosus).
Major mammalian predators include the badger (Taxidea taxus), striped skunk (Mephitis mephitis), weasels (Mustela and Neogale sp.), martens (Martes americana and M. caurina), domestic dogs (Canis familiaris), domestic cats (Felis catus) and mountain lions (Puma concolor). Other animals reported to have ingested voles include trout (Salmo sp.), Pacific giant salamanders (Dicampton ensatus), garter snakes (Thamnophis sp.), yellow-bellied racers (Coluber constrictor flaviventris), gopher snakes (Pituophis melanoleucas), plains rattlesnakes (Crotalus viridis), and rubber boas (Charina bottae).
In northern prairie wetlands, meadow voles are a large portion of the diets of red foxes (Vulpes vulpes), American mink (Neogale vison), short-eared owls (Asio flammeus), and northern harriers (Circus cyaneus). Voles are frequently taken by racers (Coluber sp.) since both often use the same burrows. | 2 | Environmental Chemistry |
* Gamma (γ): This phase composes the matrix of Ni-based superalloy. It is a solid solution fcc austenitic phase of the alloying elements. The alloying elements most found in commercial Ni-based alloys are, C, Cr, Mo, W, Nb, Fe, Ti, Al, V, and Ta. During the formation of these materials, as they cool from the melt, carbides precipitate, and at even lower temperatures γ' phase precipitates.
* Gamma prime (γ): This phase constitutes the precipitate used to strengthen the alloy. It is an intermetallic phase based on Ni(Ti,Al) which have an ordered FCC L1 structure. The γ phase is coherent with the matrix of the superalloy having a lattice parameter that varies by around 0.5%. Ni(Ti,Al) are ordered systems with Ni atoms at the cube faces and either Al or Ti atoms at the cube edges. As particles of γ precipitates aggregate, they decrease their energy states by aligning along the <100> directions forming cuboidal structures. This phase has a window of instability between 600 °C and 850 °C, inside of which γ will transform into the HCP η phase. For applications at temperatures below 650 °C, the γ" phase can be utilized for strengthening.
* Gamma double prime (γ"): This phase typically is NiNb or NiV and is used to strengthen Ni-based superalloys at lower temperatures (<650 °C) relative to γ'. The crystal structure of γ" is body-centered tetragonal (BCT), and the phase precipitates as 60 nm by 10 nm discs with the (001) planes in γ" parallel to the {001} family in γ. These anisotropic discs form as a result of lattice mismatch between the BCT precipitate and the FCC matrix. This lattice mismatch leads to high coherency strains which, together with order hardening, are the primary strengthening mechanisms. The γ" phase is unstable above approximately 650 °C.
* Carbide phases: Carbide formation is usually deleterious although in Ni-based superalloys they are used to stabilize the structure of the material against deformation at high temperatures. Carbides form at the grain boundaries, inhibiting grain boundary motion.
*Topologically close-packed (TCP) phases: The term "TCP phase" refers to any member of a family of phases (including the σ phase, the χ phase, the μ phase, and the Laves phase), which are not atomically close-packed but possess some close-packed planes with HCP stacking. TCP phases tend to be highly brittle and deplete the γ matrix of strengthening, solid solution refractory elements (including Cr, Co, W, and Mo). These phases form as a result of kinetics after long periods of time (thousands of hours) at high temperatures (>750 °C). | 8 | Metallurgy |
The biochemical systems equation makes two key assumptions:
# Species exist in a well-stirred reactor, so there are no spatial gradients.
# Species concentrations are high enough so that stochastic effects are negligible | 1 | Biochemistry |
Modification of human genes in order to treat genetic diseases is referred to as gene therapy. Gene therapy is a medical procedure that involves inserting genetic material into a patients cells to repair or fix a malfunctioning gene in order to treat hereditary illnesses. Between 1989 and December 2018, over 2,900 clinical trials of gene therapies were conducted, with more than half of them in phase I. Since that time, many gene therapy based drugs became available, such as Zolgensma and Patisiran. Most of these approaches utilize viral vectors, such as adeno-associated viruses (AAVs), adenoviruses (AV) and lentiviruses (LV), for inserting or replacing transgenes in vivo or ex vivo'.
In 2023, nanoparticles that act similarly to viral vectors were created. These nanoparticles, called bioorthgonal engineered virus-like recombinant biosomes, display strong and rapid binding capabilities to LDL receptors on cell surfaces, allowing them to enter cells efficiently and deliver genes to specific target areas, such as tumor and arthritic tissues.
RNA interference-based agents, such as zilebesiran, contain siRNA which binds with mRNA of the target cells, modifying gene expression. | 1 | Biochemistry |
Chemical weapons are said to "make deliberate use of the toxic properties of chemical substances to inflict death". At the start of World War II it was widely reported in newspapers that "entire regions of Europe" would be turned into "lifeless wastelands". However, chemical weapons were not used to the extent predicted by the press.
An unintended chemical weapon release occurred at the port of Bari. A German attack on the evening of December 2, 1943, damaged U.S. vessels in the harbour and the resultant release from their hulls of mustard gas inflicted a total of 628 casualties.
The U.S. Government was highly criticized for exposing American service members to chemical agents while testing the effects of exposure. These tests were often performed without the consent or prior knowledge of the soldiers affected. Australian service personnel were also exposed as a result of the "Brook Island trials" carried out by the British Government to determine the likely consequences of chemical warfare in tropical conditions; little was known of such possibilities at that time.
Some chemical agents are designed to produce mind-altering changes; rendering the victim unable to perform their assigned mission. These are classified as incapacitating agents, and lethality is not a factor of their effectiveness. | 1 | Biochemistry |
Esketamine is the generic name of the drug and its and , while esketamine hydrochloride is its . It is also known as S(+)-ketamine, (S)-ketamine, or (–)-ketamine ((-)[+] ketamine), as well as by its developmental code name JNJ-54135419.
Esketamine is sold under the brand name Spravato for use as an antidepressant and the brand names Eskesia, Ketanest, Ketanest S, Ketanest-S, Keta-S for use as an anesthetic (veterinary), among others. | 4 | Stereochemistry |
Since only some plants need sodium and those in small quantities, a completely plant-based diet will generally be very low in sodium. This requires some herbivores to obtain their sodium from salt licks and other mineral sources. The animal need for sodium is probably the reason for the highly conserved ability to taste the sodium ion as "salty." Receptors for the pure salty taste respond best to sodium; otherwise, the receptors respond only to a few other small monovalent cations (, and somewhat to ). The calcium ion (Ca) also tastes salty and sometimes bitter to some people but, like potassium, can trigger other tastes.
Sodium ions play a diverse and important role in many physiological processes, acting to regulate blood volume, blood pressure, osmotic equilibrium and pH. | 1 | Biochemistry |
"Euhedral" is derived from the Greek eu meaning "well, good" and hedron meaning a seat or a face of a solid. | 3 | Analytical Chemistry |
Quantum dot solar cells (QDSCs) are based on the Gratzel cell, or dye-sensitized solar cell architecture, but employ low band gap semiconductor nanoparticles, fabricated with crystallite sizes small enough to form quantum dots (such as CdS, CdSe, Stibnite|, PbS, etc.), instead of organic or organometallic dyes as light absorbers. Due to the toxicity associated with Cd and Pb based compounds there are also a series of "green" QD sensitizing materials in development (such as CuInS CuInSe and CuInSeS). QD's size quantization allows for the band gap to be tuned by simply changing particle size. They also have high extinction coefficients and have shown the possibility of multiple exciton generation.
In a QDSC, a mesoporous layer of titanium dioxide nanoparticles forms the backbone of the cell, much like in a DSSC. This layer can then be made photoactive by coating with semiconductor quantum dots using chemical bath deposition, electrophoretic deposition or successive ionic layer adsorption and reaction. The electrical circuit is then completed through the use of a liquid or solid redox couple. The efficiency of QDSCs has increased to over 5% shown for both liquid-junction and solid state cells, with a reported peak efficiency of 11.91%. In an effort to decrease production costs, the Prashant Kamat research group demonstrated a solar paint made with and CdSe that can be applied using a one-step method to any conductive surface with efficiencies over 1%. However, the absorption of quantum dots (QDs) in QDSCs is weak at room temperature. The plasmonic nanoparticles can be utilized to address the weak absorption of QDs (e.g., nanostars). Adding an external infrared pumping source to excite intraband and interband transition of QDs is another solution. | 7 | Physical Chemistry |
In 2013 a cell with 2 nanometers of nickel on a silicon electrode, paired with a stainless steel electrode, immersed in an aqueous electrolyte of potassium borate and lithium borate operated for 80 hours without noticeable corrosion, versus 8 hours for titanium dioxide. In the process, about 150 ml of hydrogen gas was generated, representing the storage of about 2 kilojoules of energy. | 5 | Photochemistry |
The "black box" in the title refers to the conceptual tool in which, for one reason or another, the internal workings of a device are taken for granted, so that its function may be discussed. The philosophical tool is commonly used in scientific discourse, and Behe notes that understandings of cellular structure and other aspects of microbiology were not much understood when Charles Darwin was alive. He then states that he plans to delve into the issue.
Behe begins by reminding the general reader of paradigm shifts in the history of science, in which the foundations and assumptions of theories are examined, sometimes resulting in the rejection of an entire past theory. Behe suggests that such a paradigm shift in biology (and particularly in evolution) is imminent due to recent discoveries (circa 1996) in biochemistry. Behe acknowledges acceptance of the theory of evolution by "the great majority" of scientists, and he states that "most (though not all) do so based on authority."
Behe states that elucidations of the evolutionary history of various biological features typically assume the existence of certain abilities as their starting point, such as Charles Darwins example of a cluster of light-sensitive spots evolving into an eye via a series of intermediate steps. He then points out that Darwin dismissed the need to explain the origin of the simple' light-sensitive spot, summarizes the modern understanding of the biochemistry of vision and claims that many other evolutionary explanations face a similar challenge.
Behe next introduces and defines the concept of irreducible complexity as a system with a series of parts in which the removal of any part causes the entire system to cease functioning, offering a spring-loaded bar mousetrap as a familiar example. In the following chapters, Behe discusses the apparent irreducible complexity of several biological systems, including the cilium, the bacterial flagellum, blood clotting, the immune system, and vesicular transport. Behe claims the underlying complexity and biochemical mechanisms of the systems are vastly under-appreciated, and identifies other, similar systems.
Behe identifies one of the primary counter-arguments of irreducible complexity, gradual adaptation—that certain systems may have been co-opted from an original, unrelated role to assume a new function as an irreducibly complex system. He counter-argues that though it is impossible to consider all possible roles for any component, it is extremely implausible that components can fortuitously change function within a complex system and that the focus of the theory changes from making to modifying components and recounts unsuccessful attempts to discover evolutionary pathways for complex systems within scientific journals. Behe states that though he did identify assertions that evolution had occurred, he found none that had been supported by experiment or calculation, and concludes the book by offering intelligent design as a solution to irreducible complexity. | 1 | Biochemistry |
Vanadyl ribonucleoside is produced by combining vanadyl sulphate with various ribonucleosides (such as guanosine) in a 1:10 molar ratio. | 1 | Biochemistry |
Diazomethane is toxic by inhalation or by contact with the skin or eyes (TLV 0.2 ppm). Symptoms include chest discomfort, headache, weakness and, in severe cases, collapse. Symptoms may be delayed. Deaths from diazomethane poisoning have been reported. In one instance a laboratory worker consumed a hamburger near a fumehood where he was generating a large quantity of diazomethane, and died four days later from fulminating pneumonia. Like any other alkylating agent it is expected to be carcinogenic, but such concerns are overshadowed by its serious acute toxicity.
CHN may explode in contact with sharp edges, such as ground-glass joints, even scratches in glassware. Glassware should be inspected before use and preparation should take place behind a blast shield. Specialized kits to prepare diazomethane with flame-polished joints are commercially available.
The compound explodes when heated beyond 100 °C, exposed to intense light, alkali metals, or calcium sulfate. Use of a blast shield is highly recommended while using this compound.
Proof-of-concept work has been done with microfluidics, in which continuous point-of-use synthesis from N-methyl-N-nitrosourea and 0.93 M potassium hydroxide in water was followed by point-of-use conversion with benzoic acid, resulting in a 65% yield of the methyl benzoate ester within seconds at temperatures ranging from 0 to 50 °C. The yield was better than under capillary conditions; the microfluidics were credited with "suppression of hot spots, low holdup, isothermal conditions, and intensive mixing." | 0 | Organic Chemistry |
For blood tests, clinical chemists must process the specimen to obtain plasma and serum before testing for targeted analytes. This is most easily done by centrifugation, which packs the denser blood cells and platelets to the bottom of the centrifuge tube, leaving the liquid serum fraction resting above the packed cells. This initial step before analysis has recently been included in instruments that operate on the "integrated system" principle. Plasma is obtained by centrifugation before clotting occurs. | 1 | Biochemistry |
Sephadex is used to separate molecules by molecular weight. Sephadex is a faster alternative to dialysis (de-salting), requiring a low dilution factor (as little as 1.4:1), with high activity recoveries. Sephadex is also used for buffer exchange and the removal of small molecules during the preparation of large biomolecules, such as ampholytes, detergents, radioactive or fluorescent labels, and phenol (during DNA purification).
A special hydroxypropylated form of Sephadex resin, named Sephadex LH-20, is used for the separation and purification of small organic molecules such as steroids, terpenoids, lipids. An example of use is the purification of cholesterol. | 1 | Biochemistry |
Erosion corrosion, also known as impingement damage, is the combined effect of corrosion and erosion caused by rapid flowing turbulent water. It is probably the second most common cause of copper tube failures behind Type 1 pitting which is also known as Cold Water Pitting of Copper Tube.
Copper Water Tubes
Copper tubes have been used to distribute drinking water within buildings for many years, and hundreds of miles are installed throughout Europe every year. The long life of copper when exposed to natural waters is a result of its thermodynamic stability, its high resistance to reacting with the environment, and the formation of insoluble corrosion products that insulate the metal from the environment. The corrosion rate of copper in most drinkable waters is less than 2.5 µm/year, at this rate a 15 mm tube with a wall thickness of 0.7 mm would last for about 280 years. In some soft waters the general corrosion rate may increase to 12.5 µm/year, but even at this rate it would take over 50 years to perforate the same tube. | 8 | Metallurgy |
Although small in terms of power, the disposal of waste heat from microchips and other electronic components, represents a significant engineering challenge. This necessitates the use of fans, heatsinks, etc. to dispose of the heat.
For example, data centers use electronic components that consume electricity for computing, storage and networking. The French CNRS explains a data center is like a resistor and most of the energy it consumes is transformed into heat and requires cooling systems. | 7 | Physical Chemistry |
An alternative method is to use liquid scintillation counting (LSC), where the sample is directly mixed with a scintillation cocktail. When the individual light emission events are counted, the LSC instrument records the amount of light energy per radioactive decay event. The alpha spectra obtained by liquid scintillation counting are broaden because of the two main intrinsic limitations of the LSC method: (1) because the random quenching reduces the number of photons emitted per radioactive decay, and (2) because the emitted photons can be absorbed by cloudy or coloured samples (Lambert-Beer law). The liquid scintillation spectra are subject to Gaussian broadening, rather than to the distortion caused by the absorption of alpha-particles by the sample when the layer of active material deposited onto a disk is too thick. | 7 | Physical Chemistry |
In 1856, Rudolf Clausius, referring to closed systems, in which transfers of matter do not occur, defined the second fundamental theorem (the second law of thermodynamics) in the mechanical theory of heat (thermodynamics): "if two transformations which, without necessitating any other permanent change, can mutually replace one another, be called equivalent, then the generations of the quantity of heat Q from work at the temperature T, has the equivalence-value:"
In 1865, he came to define the entropy symbolized by S, such that, due to the supply of the amount of heat Q at temperature T the entropy of the system is increased by
In a transfer of energy as heat without work being done, there are changes of entropy in both the surroundings which lose heat and the system which gains it. The increase, , of entropy in the system may be considered to consist of two parts, an increment, that matches, or compensates, the change, , of entropy in the surroundings, and a further increment, that may be considered to be generated or produced in the system, and is said therefore to be uncompensated. Thus
This may also be written
The total change of entropy in the system and surroundings is thus
This may also be written
It is then said that an amount of entropy has been transferred from the surroundings to the system. Because entropy is not a conserved quantity, this is an exception to the general way of speaking, in which an amount transferred is of a conserved quantity.
From the second law of thermodynamics it follows that in a spontaneous transfer of heat, in which the temperature of the system is different from that of the surroundings:
For purposes of mathematical analysis of transfers, one thinks of fictive processes that are called reversible, with the temperature of the system being hardly less than that of the surroundings, and the transfer taking place at an imperceptibly slow rate.
Following the definition above in formula (), for such a fictive reversible process, a quantity of transferred heat (an inexact differential) is analyzed as a quantity , with (an exact differential):
This equality is only valid for a fictive transfer in which there is no production of entropy, that is to say, in which there is no uncompensated entropy.
If, in contrast, the process is natural, and can really occur, with irreversibility, then there is entropy production, with . The quantity was termed by Clausius the "uncompensated heat", though that does not accord with present-day terminology. Then one has
This leads to the statement
which is the second law of thermodynamics for closed systems.
In non-equilibrium thermodynamics that makes the approximation of assuming the hypothesis of local thermodynamic equilibrium, there is a special notation for this. The transfer of energy as heat is assumed to take place across an infinitesimal temperature difference, so that the system element and its surroundings have near enough the same temperature . Then one writes
where by definition
The second law for a natural process asserts that | 7 | Physical Chemistry |
Reporter genes can be used to assay for the activity of a particular promoter in a cell or organism. In this case there is no separate "gene of interest"; the reporter gene is simply placed under the control of the target promoter and the reporter gene product's activity is quantitatively measured. The results are normally reported relative to the activity under a "consensus" promoter known to induce strong gene expression. | 1 | Biochemistry |
Prior to 1907, nearly all the copper mined in the US came from underground vein deposits, averaging 2.5 percent copper. By 1991, the average grade of copper ore mined in the US had fallen to only 0.6 percent. | 8 | Metallurgy |
The simplest way to understand the origin of RUMs is to consider the balance between the numbers of constraints and degrees of freedom of the network, an engineering analysis that dates back to James Clerk Maxwell and which was introduced to amorphous materials by Jim Phillips and Mike Thorpe. If the number of constraints exceeds the number of degrees of freedom, the structure will be rigid. On the other hand, if the number of degrees of freedom exceeds the number of constraints, the structure will be floppy.
For a structure that consists of corner-linked tetrahedra (such as the SiO tetrahedra in silica, SiO) we can count the numbers of constraints and degrees of freedom as follows. For a given tetrahedron, the position of any corner has to have its three spatial coordinates (x,y,z) match the spatial coordinates of the corresponding corner of a linked tetrahedron. Thus each corner has three constraints. These are shared by the two linked tetrahedra, so contribute 1.5 constraints to each tetrahedron. There are 4 corners, so we have a total of 6 constraints per tetrahedron. A rigid three-dimensional object has 6 degrees of freedom, 3 translations and 3 rotations. Thus there is an exact balance between the numbers of constraints and degrees of freedom.
(Note that we can get an identical result by considering the atoms to be the basic units. There are 5 atoms in the structural tetrahedron, but 4 of there are shared by two tetrahedra, so that there are 3 + 4*3/2 = 9 degrees of freedom per tetrahedron. The number of constraints to hold together such a tetrahedron is 9 (4 distances and 5 angles)).
What this balance means is that a structure composed of structural tetrahedra joined at corners is exactly on the border between being rigid and floppy. What appears to happen is that symmetry reduces the number of constraints so that structures such as quartz and cristobalite are slightly floppy and thus support some RUMs.
The above analysis can be applied to any network structure composed of polyhedral groups of atoms. One example is the perovskite family of structures, which consist of corner-linked BX octahedra such as TiO or ZrO. A simple counting analysis would in fact suggest that such structures are rigid, but in the ideal cubic phase symmetry allows some degree of flexibility. Zirconium tungstate, the archetypal material showing negative thermal expansion, contains ZrO octahedra and WO tetrahedra, with one of the corners of each WO tetrahedra having no linkage. The counting analysis shows that, like silica, zirconium tungstate has an exact balance between the numbers of constraints and degrees of freedom, and further analysis has shown the existence of RUMs in this material. | 3 | Analytical Chemistry |
pH affects the reaction rate due to a variety of reasons. At a low pH, complexation of also occurs, leading to lower availability of to form reactive oxidative species (OH). Lower pH also results in the scavenging of OH by excess , hence reducing its reaction rate. Whereas at high pH, the reaction slows down due to precipitation of Fe(OH), lowering the concentration of the species in solution. Solubility of iron species is directly governed by the solution's pH. is about 100 times less soluble than in natural water at near-neutral pH, the ferric ion concentration is the limiting factor for the reaction rate. Under high pH conditions, the stability of the HO is also affected, resulting in its self-decomposition. Higher pH also decreased the redox potential of OH thereby reducing its effectiveness. pH plays a crucial role in the formation of free radicals and hence the reaction performance. Thus ongoing research has been done to optimize pH and amongst other parameters for greater reaction rates. | 2 | Environmental Chemistry |
In 2023, the Oregon Department of Environmental Quality (DEQ) and Oregon Health Authority issued a cyanobacteria advisory for much of the Willamette River as it runs through Portland. The advisory affected the Willamette from the Ross Island Lagoon through Cathedral Park. Testing by the DEQ showed microcystin levels at 549 ppb. | 2 | Environmental Chemistry |
The distance is typically ≈110 pm, whereas the distance is ≈160 to 200 pm. The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. The following hydrogen bond angles between a hydrofluoric acid donor and various acceptors have been determined experimentally: | 6 | Supramolecular Chemistry |
Ghatak's contributions were primarily on stereochemically controlled organic synthesis and he was known developing methodologies for the synthesis of polycarbocyclic diterpenoids and bridged-ring compounds. His work on the four possible racemates of deoxypodocarpic acid, deisopropyl dehydroabietic acid and the corresponding 5-epimers reportedly clarified some of the stereochemical uncertainties existed till then. He demonstrated total synthesis of compounds related to gibberellins, a group of growth-regulating plant hormones. The regio- and stereo-specific intramolecular alkylation rearrangements through diazoketones as well as new annulation reactions involving cationic and radical processes he developed widened the understanding of free radical cyclization chemistry.
Ghatak documented his researches by way of a book, A Century, 1876-1976 and a number of articles published in peer-reviewed journals; ResearchGate, an online article repository, has listed 148 of them. He mentored several doctoral scholars in their researches and his works have been cited by several authors. He was associated with journals such as Indian Journal of Chemistry (Sec B), Proceedings of Indian Academy of Sciences (Chem Sci) and Proceedings of the Indian National Science Academy as a member of their editorial boards and served as a member of the Indian National Science Academy Council from 1994 to 1996. | 4 | Stereochemistry |
His wide-ranging studies of protein structure have contributed insights to viral architecture, DNA–protein recognition, and cellular signaling.
Harrison has made important contributions to structural biology, most notably by determining and analyzing the structures of viruses and viral proteins, by crystallographic analysis of protein–DNA complexes, and by structural studies of protein-kinase switching mechanisms. The initiator of high-resolution virus crystallography, he has moved from his early work on tomato bushy stunt virus (1978) to the study of more complex human pathogens, including the capsid of human papillomavirus, the envelope of dengue virus, and several components of HIV. He has also turned some of his research attention to even more complex assemblies, such as clathrin-coated vesicles. He led the Structural Biology team at the Center for HIV/AIDS Vaccine Immunology (CHAVI) when it received National Institute of Allergy and Infectious Diseases (NIAID) funding of around $300 million to address key immunological roadblocks to HIV vaccine development and to design, develop and test novel HIV vaccine candidates. | 1 | Biochemistry |
Dithiocarbamates are described by invoking resonance structures that emphasize the pi-donor properties of the amine group. This bonding arrangement is indicated by a short C–N distance and the coplanarity of the NCS core as well as the atoms attached to N.
Because of the pi-donation from nitrogen, dithiocarbamates are more basic than structurally related anions such as dithiocarboxylates and xanthates. Consequently, they tend to bind as bidentate ligands. Another consequence of the C–N multiple bonding is that rotation about that bond is subject to a high barrier. | 0 | Organic Chemistry |
The luciferases of fireflies – of which there are over 2000 species – and of the other Elateroidea (click beetles and relatives in general) are diverse enough to be useful in molecular phylogeny. In fireflies, the oxygen required is supplied through a tube in the abdomen called the abdominal trachea. One well-studied luciferase is that of the Photinini firefly Photinus pyralis, which has an optimum pH of 7.8. | 1 | Biochemistry |
random primed synthesis - reading frame - recessive - recognition sequence - recombinant DNA - recombination - recombination-repair - relaxed DNA - repetitive DNA - replica plating - reporter gene - repression - repressor - residue - response element - restriction - restriction endonuclease - restriction enzyme - restriction fragment - restriction fragment length polymorphism (RFLP) - restriction fragments - restriction map - restriction site - reticulocyte lysate - retrovirus - reverse transcriptase - reverse transcription - revertant - ribonuclease - ribonuclease - ribonucleic acid - riboprobe - ribosomal-protein-alanine N-acetyltransferase - ribosomal binding sequence - ribosome - ribosyldihydronicotinamide dehydrogenase (quinone) - ribozyme - risk communication - RNA polymerase - RNA splicing - RNAi - RNase - RNase protection assay - rRNA - rRNA (guanine-N2-)-methyltransferase - RT-PCR - Run-on - runoff transcript | 1 | Biochemistry |
Lichens are eaten by many different cultures across the world. Although some lichens are only eaten in times of famine, others are a staple food or even a delicacy. Two obstacles are often encountered when eating lichens: lichen polysaccharides are generally indigestible to humans, and lichens usually contain mildly toxic secondary compounds that should be removed before eating. Very few lichens are poisonous, but those high in vulpinic acid or usnic acid are toxic. Most poisonous lichens are yellow.
In the past, Iceland moss (Cetraria islandica) was an important source of food for humans in northern Europe, and was cooked as a bread, porridge, pudding, soup, or salad. Bryoria fremontii (edible horsehair lichen) was an important food in parts of North America, where it was usually pitcooked. Northern peoples in North America and Siberia traditionally eat the partially digested reindeer lichen (Cladina spp.) after they remove it from the rumen of caribou or reindeer that have been killed. Rock tripe (Umbilicaria spp. and Lasalia spp.) is a lichen that has frequently been used as an emergency food in North America, and one species, Umbilicaria esculenta, (iwatake in Japanese) is used in a variety of traditional Korean and Japanese foods. | 2 | Environmental Chemistry |
Construction of RSN is ongoing. As of September 19, 2014, the primary infrastructure and most of the secondary infrastructure was successfully in place, and OOI RSN and UW APL crews were working to complete the vertical moorings for the shallow profiler. | 9 | Geochemistry |
The alloys of tantalum–tungsten have high corrosion resistance, and refractory properties. The crystalline structure of the material is body-centered cubic with a substitutional solid solution with atoms of tungsten. The alloy also has a high melting point and can reach high elastic modulus and high tensile strength. | 8 | Metallurgy |
Similar assays can be performed for research purposes, detecting concentrations of potential clinical candidates like anti-fungal and asthma drugs. This technique is obviously useful in observing multiple species in collected samples, as well, but requires the use of standard solutions when information about species identity is sought out. It is used as a method to confirm results of synthesis reactions, as purity is essential in this type of research. However, mass spectrometry is still the more reliable way to identify species. | 3 | Analytical Chemistry |
In the acetalisation reaction, under acidic or basic conditions, an alcohol adds to the carbonyl group and a proton is transferred to form a hemiacetal. Under acidic conditions, the hemiacetal and the alcohol can further react to form an acetal and water. Simple hemiacetals are usually unstable, although cyclic ones such as glucose can be stable. Acetals are stable, but revert to the aldehyde in the presence of acid. Aldehydes can react with water to form hydrates, . These diols are stable when strong electron withdrawing groups are present, as in chloral hydrate. The mechanism of formation is identical to hemiacetal formation. | 0 | Organic Chemistry |
Ff phages (for F specific filamentous phages) is a group of almost identical filamentous phage (genus Inovirus) including phages f1, fd, M13 and ZJ/2, which infect bacteria bearing the F fertility factor. The virion (virus particle) is a flexible filament measuring about 6 by 900 nm, comprising a cylindrical protein tube protecting a single-stranded circular DNA molecule at its core. The phage codes for only 11 gene products, and is one of the simplest viruses known. It has been widely used to study fundamental aspects of molecular biology. George Smith and Greg Winter used f1 and fd for their work on phage display for which they were awarded a share of the 2018 Nobel Prize in Chemistry. Early experiments on Ff phages used M13 to identify gene functions, and M13 was also developed as a cloning vehicle, so the name M13 is sometimes used as an informal synonym for the whole group of Ff phages. | 1 | Biochemistry |
Kai Simons (born 24 May 1938) is a Finnish professor of biochemistry and cell biology and physician living and working in Germany. He introduced the concept of lipid rafts, as well as coined the term trans-Golgi network and proposed its role in protein and lipid sorting. The co-founder and co-organizer of EMBO, ELSO, Simons initiated the foundation of MPI-CBG, where he acted as a director (1998–2006) and a group-leader (until 2012). He is the co-founder and co-owner of Lipotype GmbH. | 1 | Biochemistry |
In molecular biology, the NAD+ five-prime cap (NAD+ 5’ cap) refers to a molecule of nicotinamide adenine dinucleotide (NAD+), a nucleoside-containing metabolite, covalently bonded the 5’ end of cellular mRNA. While the more common methylated guanosine (m7G) cap is added to RNA by a capping complex that associates with RNA polymerase II (RNAP II), the NAD cap is added during transcriptional initiation by the RNA polymerase itself, acting as a non-canonical initiating nucleotide (NCIN). As such, while m7G capping can only occur in organisms possessing specialized capping complexes, because NAD capping is performed by RNAP itself, it is hypothesized to occur in most, if not all, organisms.
The NAD+ 5’ cap has been observed in bacteria, contrary to the long-held belief that prokaryotes lacked 5’-capped RNA, as well as on the 5’ cap of eukaryotic mRNA, in place of the m7G cap. This modification also potentially allows for selective degradation of RNA]within prokaryotes as different pathways are involved in the degradation of NAD+-capped and uncapped 5′-triphosphate-RNAs.
In eukaryotic cells, while the more commonly observed m7G cap promotes the stability of the mRNA and supports translation, the NAD+ cap targets the RNA transcript for decay, facilitated by the non-canonical decapping enzyme, DXO. Considering the centrality of NAD in redox chemistry and post-translational protein modification, its attachment to RNA represents potentially undiscovered pathways in RNA metabolism and regulation. | 1 | Biochemistry |
In aromatic amines ("anilines"), nitrogen is often nearly planar owing to conjugation of the lone pair with the aryl substituent. The C-N distance is correspondingly shorter. In aniline, the C-N distance is the same as the C-C distances. | 0 | Organic Chemistry |
Prior to Kaminsky, titanium chlorides supported on various materials were widely used (and still are) as heterogeneous catalysts for alkene polymerization. These halides are typically activated by treatment with trimethylaluminium. Kaminsky discovered that titanocene and related complexes emulated some aspects of these Ziegler–Natta catalysts but with low activity. He subsequently found that high activity could be achieved upon activation of these metallocenes with methylaluminoxane (MAO). The MAO serves two roles: (i) alkylation of the metallocene halide and (ii) abstraction of an anionic ligand (chloride or methyl) to give an electrophilic catalyst with a labile coordination site. | 7 | Physical Chemistry |
S-block compounds with low oxidation states can be short lived. There are various techniques available for use. However, the generation and detection of these molecules rely on frozen inert gas matrices, low pressures, high temperatures in the gas phase, or a combination of these. This can then be combined with theoretical studies to gain more information regarding the complex. Matrix isolation techniques were carried out for gaining spectroscopic insight on how the Mg(I) dimer may behave.
By heating magnesium diboride, MgB, at 700 Celsius (°C) with a pressure of 0.1 mbar, and passing HCl gas over it several products are formed, such as magnesium chloride, MgCl. The generation of •MgCl and subsequent compounds from the reaction then underwent further study. At 10 Kelvin (K), the solution was combined with an inert gas, undergoing IR and Raman spectroscopic techniques, combined with Density Functional Theory (DFT) calculations. This showed the monomeric and dimeric Mg(I) Halides, •MgCl and ClMgMgCl, a linear molecule. While these studies were useful in gaining more insight on the Mg-Mg bond characteristics, it failed to yield a stable Mg(I) dimer in ambient conditions. | 7 | Physical Chemistry |
The a-keto stabilized ylides derived from bisphosphines like dppe, dppm, etc., viz., [PhPCHPPh]C(H)C(O)R and [PhPCHCHPPh]C(H)C(O)R (R = Me, Ph or OMe) constitute an important class of hybrid ligands containing both phosphine and ylide functionalities, and can exist in ylidic and enolate forms. These ligands can therefore be engaged in different kinds of bonding with metal ions like palladium and platinum. | 0 | Organic Chemistry |
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