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In 1912, Frederick Gowland Hopkins demonstrated that unknown accessory factors found in milk, other than carbohydrates, proteins, and fats were necessary for growth in rats. Hopkins received a Nobel Prize for this discovery in 1929. By 1913, one of these substances was independently discovered by Elmer McCollum and Marguerite Davis at the University of Wisconsin–Madison, and Lafayette Mendel and Thomas Burr Osborne at Yale University. McCollum and Davis ultimately received credit because they submitted their paper three weeks before Mendel and Osborne. Both papers appeared in the same issue of the Journal of Biological Chemistry in 1913. The "accessory factors" were termed "fat soluble" in 1918, and later "vitamin A" in 1920. In 1919, Harry Steenbock (University of Wisconsin–Madison) proposed a relationship between yellow plant pigments (beta-carotene) and vitamin A. In 1931, Swiss chemist Paul Karrer described the chemical structure of vitamin A. Retinoic acid and retinol were first synthesized in 1946 and 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens.
During World War II, German bombers would attack at night to evade British defenses. In order to keep the 1939 invention of a new on-board Airborne Intercept Radar system secret from Germany, the British Ministry of Information told newspapers an unproven claim that the nighttime defensive success of Royal Air Force pilots was due to a high dietary intake of carrots rich in beta-carotene, successfully convincing many people.
In 1967, George Wald shared the Nobel Prize in Physiology and Medicine for his work on chemical visual processes in the eye. Wald had demonstrated in 1935 that photoreceptor cells in the eye contain rhodopsin, a chromophore composed of the protein opsin and 11-cis-retinal. When struck by light, 11-cis-retinal undergoes photoisomerization to all-trans-retinal and via signal transduction cascade send a nerve signal to the brain. The all-trans-retinal is reduced to all-trans-retinol and travels back to the retinal pigment epithelium to be recycled to 11-cis-retinal and reconjugated to opsin. Wald's work was the culmination of nearly 60 years of research. In 1877, Franz Christian Boll identified a light-sensitive pigment in the outer segments of rod cells of the retina that faded/bleached when exposed to light, but was restored after light exposure ceased. He suggested that this substance, by a photochemical process, conveyed the impression of light to the brain. The research was taken up by Wilhelm Kühne, who named the pigment rhodopsin, also known as "visual purple." Kühne confirmed that rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions, and that it was this chemical decomposition that stimulated nerve impulses to the brain. Research stalled until after identification of "fat-soluble vitamin A" as a dietary substance found in milkfat but not lard, would reverse night blindness and xerophthalmia. In 1925, Fridericia and Holm demonstrated that vitamin A deficient rats were unable to regenerate rhodopsin after being moved from a light to a dark room. | 1 | Biochemistry |
High resolution melting assays typically involve qPCR amplification followed by a melting curve collected using a fluorescent dye. Due to the sensitivity of high-resolution melting analysis, it is necessary to carefully consider PCR cycling conditions, template DNA quality, and melting curve parameters. For accurate and repeatable results, PCR thermal cycling conditions must be optimized to ensure that the desired DNA region is amplified with high specificity and minimal bias between sequence variants. The melting curve is typically performed across a broad range of temperatures in small (~0.3 °C) increments that are long enough (~10 seconds) for the DNA to reach equilibrium at each temperature step.
In addition to typical primer design considerations, the design of primers for high-resolution melting assays involves maximizing the thermodynamic differences between PCR products belonging to different genotypes. Smaller amplicons generally yield greater melting temperature variation than longer amplicons, but the variability cannot be predicted by eye. For this reason, it is critical to accurately predict the melting curve of PCR products when designing primers that will distinguish sequence variants. Specialty software, such as uMelt and DesignSignatures, are available to help design primers that will maximize melting curve variability specifically for high-resolution melting assays. | 1 | Biochemistry |
In 2009, Erik Verlinde proposed a conceptual model that describes gravity as an entropic force. He argues (similar to Jacobsons result) that gravity is a consequence of the "information associated with the positions of material bodies". This model combines the thermodynamic approach to gravity with Gerard t Hoofts holographic principle. It implies that gravity is not a fundamental interaction, but an emergent phenomenon which arises from the statistical behavior of microscopic degrees of freedom encoded on a holographic screen. The paper drew a variety of responses from the scientific community. Andrew Strominger, a string theorist at Harvard said "Some people have said it cant be right, others that it's right and we already knew it – that it’s right and profound, right and trivial."
In July 2011, Verlinde presented the further development of his ideas in a contribution to the Strings 2011 conference, including an explanation for the origin of dark matter.
Verlinde's article also attracted a large amount of media exposure, and led to immediate follow-up work in cosmology, the dark energy hypothesis, cosmological acceleration, cosmological inflation, and loop quantum gravity. Also, a specific microscopic model has been proposed that indeed leads to entropic gravity emerging at large scales. Entropic gravity can emerge from quantum entanglement of local Rindler horizons. | 7 | Physical Chemistry |
Many useful organic reactions involve the formation of tetrahedral intermediates through nucleophilic attack of functional groups such as aldehydes, amides or imines. In these cases, catalysis with hydrogen-bond donors is an attractive strategy since the anionic tetrahedral intermediates are better hydrogen-bond acceptors than the starting compound. This means that relative to the initial catalyst-substrate complex, the transition state, bearing more negative charge, is stabilized.
For example, in a typical acyl substitution reaction, the starting carbonyl compound is coordinated to the catalyst through one, two or possibly more hydrogen bonds. During the attack of the nucleophile, negative charge builds on the oxygen until the tetrahedral intermediate is reached. Therefore, the formally negative oxygen engages in a much stronger hydrogen bond than the starting carbonyl oxygen because of its increased negative charge. Energetically, this has the effect of lowering the intermediate and the transition state, thus accelerating the reaction.
This mode of catalysis is found in the active sites of many enzymes, such as the serine proteases. In this example, the amide carbonyl is coordinated to two N–H donors. These sites of multiple coordination designed to promote carbonyl reactions in biology are termed "oxyanion holes". Delivery of serine nucleophile forms a tetrahedral intermediate, which is stabilized by the increase hydrogen bonding to the oxyanion hole.
Many synthetic catalysts have been able to successfully employ this strategy to activate a variety of electrophiles. Using a chiral BINOL catalyst, for instance, the Morita-Baylis-Hillman reaction involving the addition of enones to aldehydes can be effected with high enantioselectivity. The nucleophile is an enolate-type species generated from the conjugate addition of PEt to the enone, and adds enantioselectively to the aldehyde coordinated to catalyst.
In addition to carbonyls, other electrophiles such as imines can be successfully used. For example, using a simple chiral thiourea catalyst, the asymmetric Mannich reaction of aromatic imines with silyl ketene acetals can be catalyzed with high ee in near quantitative conversion. The mechanism of this reaction is not fully resolved and the reaction is very substrate-specific, only effective on certain aromatic electrophiles.
The scope of this mode of activation is immense, with constant new reports of different combinations of electrophiles, nucleophiles and catalyst structures. Furthermore, analogous reactions involving oxyanion intermediates such as enolate addition to nitroso compounds or opening of epoxides have also been successfully catalyzed with this strategy.
However, despite the number of different reactions known, general understanding of the mode of catalysis is limited, and almost all reactions discovered are extremely substrate specific. | 0 | Organic Chemistry |
Laser cooling includes several techniques where atoms, molecules, and small mechanical systems are cooled with laser light. The directed energy of lasers is often associated with heating materials, e.g. laser cutting, so it can be counterintuitive that laser cooling often results in sample temperatures approaching absolute zero. Laser cooling relies on the change in momentum when an object, such as an atom, absorbs and re-emits a photon (a particle of light). For example, if laser light illuminates a warm cloud of atoms from all directions and the lasers frequency is tuned below an atomic resonance, the atoms will be cooled. This common type of laser cooling relies on the Doppler effect where individual atoms will preferentially absorb laser light from the direction opposite to the atoms motion. The absorbed light is re-emitted by the atom in a random direction. After repeated emission and absorption of light the net effect on the cloud of atoms is that they will expand more slowly. The slower expansion reflects a decrease in the velocity distribution of the atoms, which corresponds to a lower temperature and therefore the atoms have been cooled. For an ensemble of particles, their thermodynamic temperature is proportional to the variance in their velocity. More homogeneous velocities between particles corresponds to a lower temperature. Laser cooling techniques combine atomic spectroscopy with the aforementioned mechanical effect of light to compress the velocity distribution of an ensemble of particles, thereby cooling the particles.
The 1997 Nobel Prize in Physics was awarded to Claude Cohen-Tannoudji, Steven Chu, and William Daniel Phillips "for development of methods to cool and trap atoms with laser light". | 7 | Physical Chemistry |
HNMT is a cytoplasmic protein, meaning that it operates within the cytoplasm of a cell. The cytoplasm fills the space between the outer cell membrane (also known as the cellular plasma membrane) and the nuclear membrane (which surrounds the cell's nucleus). HNMT helps regulate histamine levels by degrading histamine within the cytoplasm, ensuring proper cellular function.
Proteins consist of amino acid residues and form a three-dimensional structure. The crystallographic structure to depict the three-dimensional structure of human HNMT protein was first described in 2001 as a monomeric protein that has a mass of 33 kilodaltons and consists of two structural domains.
The first domain, called the "MTase domain", contains the active site where methylation occurs. It has a classic fold found in many other methyltransferases and consists of a seven-stranded beta-sheet surrounded by three helices on each side. This domain binds to its cofactor, S-adenosyl--methionine (SAM-e), which provides the methyl group for N-methylation reactions.
The second domain, called the "substrate binding domain", interacts with histamine, contributing to its binding to the enzyme molecule. This domain is connected to the MTase domain and forms a separate region. It includes an anti-parallel beta sheet along with additional alpha helices and 310 helices. | 1 | Biochemistry |
Most organisms synthesize NAD from simple components. The specific set of reactions differs among organisms, but a common feature is the generation of quinolinic acid (QA) from an amino acideither tryptophan (Trp) in animals and some bacteria, or aspartic acid (Asp) in some bacteria and plants. The quinolinic acid is converted to nicotinic acid mononucleotide (NaMN) by transfer of a phosphoribose moiety. An adenylate moiety is then transferred to form nicotinic acid adenine dinucleotide (NaAD). Finally, the nicotinic acid moiety in NaAD is amidated to a nicotinamide (Nam) moiety, forming nicotinamide adenine dinucleotide.
In a further step, some NAD is converted into NADP by NAD kinase, which phosphorylates NAD. In most organisms, this enzyme uses adenosine triphosphate (ATP) as the source of the phosphate group, although several bacteria such as Mycobacterium tuberculosis and a hyperthermophilic archaeon Pyrococcus horikoshii, use inorganic polyphosphate as an alternative phosphoryl donor. | 5 | Photochemistry |
In addition to fatty acid synthesis in the cytosol, mitochondria also have their own fatty acid synthesis (mtFASII). Mitochondrial fatty acid synthesis is essential for cellular respiration and mitochondrial biogenesis. A role as a mediator in intracellular signal transduction is also assumed, as the levels of bioactive lipids, such as lysophospholipids and sphingolipids, correlate with mtFASII.
In the first step of mtFASII, malonyl-CoA is formed from malonic acid by ACSF3. This occurs in tandem with a mitochondrial isoform of ACC1 (mtACC1), which can still provide malonyl-CoA from acetyl-CoA. The fatty acids, such as octanoyl-ACP (C8), which forms the starting substrate of lipoic acid biosynthesis, are formed via further intermediate steps and chain extensions. Through lipoic acid as a cofactor respectively the degree of lipoylation, mtFASII has an influence on mitochondrial enzyme complexes in energy metabolism, such as the pyruvate dehydrogenase complex, the α-ketoglutarate dehydrogenase complex, the BCKDH complex and the glycine cleavage system (GCS), among others. | 1 | Biochemistry |
The company Pyrosequencing AB in Uppsala, Sweden was founded with venture capital provided by HealthCap in order to commercialize machinery and reagents for sequencing short stretches of DNA using the pyrosequencing technique. Pyrosequencing AB was listed on the Stockholm Stock Exchange in 1999. It was renamed to Biotage in 2003. The pyrosequencing business line was acquired by Qiagen in 2008. Pyrosequencing technology was further licensed to 454 Life Sciences. 454 developed an array-based pyrosequencing technology which emerged as a platform for large-scale DNA sequencing, including genome sequencing and metagenomics.
Roche announced the discontinuation of the 454 sequencing platform in 2013. | 1 | Biochemistry |
Despite the promising outcomes of the two techniques, pronuclear transfer and spindle transfer, mitochondrial gene replacement raises ethical and social concerns.
Mitochondrial donation involves modification of the germline, and hence such modifications would be passed on to subsequent generations. Using human embryos for in vitro research is also controversial, as embryos are created specifically for research and egg donors are induced to undergo the procedure by financial compensation.
Mitochondrial donation also has the potential for psychological and emotional impacts on an offspring through an effect on the person's sense of identity. Ethicists question whether the genetic make-up of children born as a result of mitochondrial replacement might affect their emotional well-being when they become aware that they are different from other healthy children conceived from two parents.
Opponents argue that scientists are "playing God" and that children with three genetic parents may suffer both psychological and physical damage.
On the other hand, New York University researcher James Grifo, a critic of the American ban, has argued that society "would never have made the advances in treating infertility that we have if these bans had been imposed 10 years" earlier.
On February 3, 2016, the Institute of Medicine of the National Academies of Sciences, Engineering, and Medicine issued a report, commissioned by the U.S. Food and Drug Administration, addressing whether it is ethically permissible for clinical research into mitochondrial replacement techniques (MRT) to continue. The report, titled Mitochondrial Replacement Techniques: Ethical, Social, and Policy Considerations, analyzes multiple facets of the arguments surrounding MRT and concludes that it is ethically permissible to continue clinical investigations of MRT, so long as certain conditions are met. It recommended that initially the technique should only be used for male embryos to ensure that DNA with potential mitochondrial disease would not be passed on.
In 2018 Carl Zimmer compared the reaction to He Jiankui's human gene editing experiment to the debate over MRT. | 1 | Biochemistry |
Currently, SiRNA are currently chemically synthesized and so, are legally categorized inside EU and in USA as simple medicinal products. But as bioengineered siRNA (BERAs) are in development, these would be classified as biological medicinal products, at least in EU. The development of the BERAs technology raises the question of the categorization of drugs having the same mechanism of action but being produced chemically or biologically. This lack of consistency should be addressed. | 1 | Biochemistry |
Mathur's researches were focused on the organometallic chemistry of mixed metal cluster compounds and he has developed synthetic strategies for introducing chalcogen bridges. At IIT Mumbai, he handled projects related to the investigation of unusual metal mediated transformations and the interactions between the metal atoms and unsaturated organic species. He has published his researches by way of chapters contributed to books authored by others and over 180 peer-reviewed articles; ResearchGate and Google Scholar, two online repositories have listed several of them. He has also guided 22 doctoral scholars in their studies.
Mathur was a Fulbright scholar in 1995 and the Indian Academy of Sciences elected him as a fellow in 1996. The Council of Scientific and Industrial Research awarded him the Shanti Swarup Bhatnagar Prize, one of the highest Indian science awards, in 2000. He has also been honoured with an honorary D.Sc. degree by the University of Keele in the U.K. | 0 | Organic Chemistry |
* by organic reduction at an electrode
* by mild reducing agents such as ascorbic acid (vitamin C)
* by gamma radiation from solvated electrons generated in water
* photoinduced electron transfer
* reduction by metal cations, most commonly a cuprous salt.
* anion-induced dediazoniation: a counterion such as iodine gives electron transfer to the diazonium cation forming the aryl radical and an iodine radical
* solvent-induced dediazoniation with solvent serving as electron donor | 0 | Organic Chemistry |
The two terminal N–O bonds are nearly equivalent and relatively short, at 1.20 and 1.21 Å. This can be explained by theories of resonance; the two major canonical forms show some double bond character in these two bonds, causing them to be shorter than N–O single bonds. The third N–O bond is elongated because its O atom is bonded to H atom, with a bond length of 1.41 Å in the gas phase. The molecule is slightly aplanar (the nitro group| and NOH planes are tilted away from each other by 2°) and there is restricted rotation about the N–OH single bond. | 3 | Analytical Chemistry |
In 1800, William Nicholson and Johann Wilhelm Ritter succeeded in decomposing water into hydrogen and oxygen by electrolysis using Volta's battery. Soon thereafter Ritter discovered the process of electroplating. He also observed that the amount of metal deposited and the amount of oxygen produced during an electrolytic process depended on the distance between the electrodes. By 1801, Ritter observed thermoelectric currents and anticipated the discovery of thermoelectricity by Thomas Johann Seebeck.
By the 1810s, William Hyde Wollaston made improvements to the galvanic cell.
Sir Humphry Davy's work with electrolysis led to the conclusion that the production of electricity in simple electrolytic cells resulted from chemical action and that chemical combination occurred between substances of opposite charge. This work led directly to the isolation of metallic sodium and potassium by electrolysis of their molten salts, and of the alkaline earth metals from theirs, in 1808.
Hans Christian Ørsteds discovery of the magnetic effect of electric currents in 1820 was immediately recognized as an epoch-making advance, although he left further work on electromagnetism to others. André-Marie Ampère quickly repeated Ørsteds experiment, and formulated them mathematically.
In 1821, Estonian-German physicist Thomas Johann Seebeck demonstrated the electrical potential between the juncture points of two dissimilar metals when there is a temperature difference between the joints.
In 1827, the German scientist Georg Ohm expressed his law in this famous book "Die galvanische Kette, mathematisch bearbeitet" (The Galvanic Circuit Investigated Mathematically) in which he gave his complete theory of electricity.
In 1832, Michael Faraday's experiments led him to state his two laws of electrochemistry. In 1836, John Daniell invented a primary cell which solved the problem of polarization by introducing copper ions into the solution near the positive electrode and thus eliminating hydrogen gas generation. Later results revealed that at the other electrode, amalgamated zinc (i.e., zinc alloyed with mercury) would produce a higher voltage.
William Grove produced the first fuel cell in 1839. In 1846, Wilhelm Weber developed the electrodynamometer. In 1868, Georges Leclanché patented a new cell which eventually became the forerunner to the world's first widely used battery, the zinc–carbon cell.
Svante Arrhenius published his thesis in 1884 on Recherches sur la conductibilité galvanique des électrolytes (Investigations on the galvanic conductivity of electrolytes). From his results the author concluded that electrolytes, when dissolved in water, become to varying degrees split or dissociated into electrically opposite positive and negative ions.
In 1886, Paul Héroult and Charles M. Hall developed an efficient method (the Hall–Héroult process) to obtain aluminium using electrolysis of molten alumina.
In 1894, Friedrich Ostwald concluded important studies of the conductivity and electrolytic dissociation of organic acids.
Walther Hermann Nernst developed the theory of the electromotive force of the voltaic cell in 1888. In 1889, he showed how the characteristics of the voltage produced could be used to calculate the free energy change in the chemical reaction producing the voltage. He constructed an equation, known as Nernst equation, which related the voltage of a cell to its properties.
In 1898, Fritz Haber showed that definite reduction products can result from electrolytic processes if the potential at the cathode is kept constant. In 1898, he explained the reduction of nitrobenzene in stages at the cathode and this became the model for other similar reduction processes. | 7 | Physical Chemistry |
Biomarkers of exposure are the actual chemicals, or chemical metabolites, that can be measured in the body or after excretion from the body to determine different characteristics of an organism’s exposure. For example, a person or fish’s blood can be tested to see the levels of lead and therefore determine the exposure. | 2 | Environmental Chemistry |
In an X-ray tube, electrons are accelerated in a vacuum by an electric field towards a piece of metal called the "target". X-rays are emitted as the electrons slow down (decelerate) in the metal. The output spectrum consists of a continuous spectrum of X-rays, with additional sharp peaks at certain energies. The continuous spectrum is due to bremsstrahlung, while the sharp peaks are characteristic X-rays associated with the atoms in the target. For this reason, bremsstrahlung in this context is also called continuous X-rays.
The shape of this continuum spectrum is approximately described by Kramers' law.
The formula for Kramers' law is usually given as the distribution of intensity (photon count) against the wavelength of the emitted radiation:
The constant is proportional to the atomic number of the target element, and is the minimum wavelength given by the Duane–Hunt law.
The spectrum has a sharp cutoff at which is due to the limited energy of the incoming electrons. For example, if an electron in the tube is accelerated through 60 kV, then it will acquire a kinetic energy of 60 keV, and when it strikes the target it can create X-rays with energy of at most 60 keV, by conservation of energy. (This upper limit corresponds to the electron coming to a stop by emitting just one X-ray photon. Usually the electron emits many photons, and each has an energy less than 60 keV.) A photon with energy of at most 60 keV has wavelength of at least 21 pm, so the continuous X-ray spectrum has exactly that cutoff, as seen in the graph. More generally the formula for the low-wavelength cutoff, the Duane–Hunt law, is:
where is Planck's constant, is the speed of light, is the voltage that the electrons are accelerated through, is the elementary charge, and is picometres. | 7 | Physical Chemistry |
Hydrogen–deuterium exchange of fast-exchanging species (e.g. hydroxyl groups) can be measured at atomic resolution quantitatively by neutron crystallography, and in real time if exchange is conducted during the diffraction experiment.
High intensity neutron beams are generally generated by spallation at linac particle accelerators such as the Spallation Neutron Source. Neutrons diffract crystals similarly to X-rays and can be used for structural determination. Hydrogen atoms, with between one and zero electrons in a biological setting, diffract X-rays poorly and are effectively invisible under normal experimental conditions. Neutrons scatter from atomic nuclei, and are therefore capable of detecting hydrogen and deuterium atoms.
Hydrogen atoms are routinely replaced with deuterium, which introduce a strong and positive scattering factor. It is often sufficient to replace only the solvent and labile hydrogen atoms in a protein crystal by vapor diffusion. In such a structure the occupancy of an exchangeable deuterium atom in a crystal will refine from 0-100%, directly quantifying the amount of exchange. | 7 | Physical Chemistry |
The multiplicity function for a two state paramagnet, W(n,N), is the number of spin states such that n of the N spins point in the z-direction. This function is given by the combinatoric function C(N,n). That is:
It is primarily used in introductory statistical mechanics and thermodynamics textbooks to explain the microscopic definition of entropy to students. If the spins are non-interacting, then the multiplicity function counts the number of states which have the same energy in an external magnetic field. By definition, the entropy S is then given by the natural logarithm of this number: | 7 | Physical Chemistry |
Passive transport of ions across a membrane can take place by three main mechanisms: by ferrying, through defects in a disrupted membrane, or through a defined trajectory; these corresponds to ionophore, detergent, and ion channel transporters. While synthetic ion channel research attempts to prepare compounds that show conductance via a defined path, the elucidation of mechanism is difficult and seldom unambiguous. The two main methods of characterization both have their drawbacks, and as a consequence, often function is defined but mechanism presumed. | 6 | Supramolecular Chemistry |
This compound is used for bioconjugation. The target, which contains a terminal alkyne functional group, is treated with the organic azide in the presence of a Cu(I) catalyst. The resulting 1,2,3-triazole is fluorescent. The coumarin backbone is chosen to be used as the profluorophore due to its small size, biocompatibility, and its ability to be easily manipulated synthetically. Illustrative of this is the labeling of biological compounds such as the protein calmodulin. Neither the azidocoumarin nor the alkyne substrate fluoresce. Azidocoumarin is also inert in biological systems and insensitive to pH and solvent. A variety of azidocoumarin compounds have been evaluated. | 1 | Biochemistry |
Soon after Hagemann, Emil Knoevenagel described a modified procedure to produce the same intermediate diethyl ester of 2,4-diacetyl pentane using
formaldehyde and two equivalents of ethyl acetoacetate which undergo condensation in the presence of a catalytic amount of piperidine. | 0 | Organic Chemistry |
A plastid is a membrane-bound organelle found in plants, algae and other eukaryotic organisms that contribute to the production of pigment molecules. Most plastids are photosynthetic, thus leading to color production and energy storage or production. There are many types of plastids in plants alone, but all plastids can be separated based on the number of times they have undergone endosymbiotic events. Currently there are three types of plastids; primary, secondary and tertiary. Endosymbiosis is reputed to have led to the evolution of eukaryotic organisms today, although the timeline is highly debated. | 5 | Photochemistry |
Early in her career, Soderholm focused on the characterizing the magnetic and electronic behavior of compounds containing f-ions (lanthanides and actinides) with a focus on high-T materials, compounds that are superconducting under usually high temperatures. She was part of the research group that first determined the structure of YBaCuO. Their discovery formed the foundation for the further developments in the broad field of superconductivity. | 7 | Physical Chemistry |
Sodium dithionite finds widespread use in industry as a reducing agent. It is for example used in bleaching of pulp and some dyes. | 8 | Metallurgy |
Hypothermia can happen in most mammals in cold weather and can be fatal. Baby mammals such as kittens are unable to regulate their body temperatures and have a risk of hypothermia if they are not kept warm by their mothers.
Many animals other than humans often induce hypothermia during hibernation or torpor.
Water bears (Tardigrade), microscopic multicellular organisms, can survive freezing at low temperatures by replacing most of their internal water with the sugar trehalose, preventing the crystallization that otherwise damages cell membranes. | 1 | Biochemistry |
Similar to DNA markers, these markers are typically composed of purified proteins whose molecular masses are already known. The list below outlines some of the proteins, as well as the molecular mass, that are commonly used when constructing a protein marker. | 1 | Biochemistry |
In the United States in 1996 embryologist Jacques Cohen and others at the Institute for Reproductive Medicine and Science, Saint Barnabas Medical Center in Livingston, New Jersey first used cytoplasmic transfer in a human assisted reproduction procedure. In 1997 the first baby was born using this procedure. In 2001, Cohen and others reported that ten single babies, twins, and a quadruplet at his New Jersey clinic and a further six children in Israel had been born using his technique. Using modifications of his procedure, a baby had been born at Eastern Virginia Medical School, five children at the Lee Women's Hospital Infertility Clinic in Taichung, Taiwan. twins in Naples, Italy and a twins in India. In total as of 2016, 30–50 children worldwide had been reported to have been born using cytoplasmic transfer.
In 2002, the US Food and Drug Administration (FDA) asked a Biological Response Modifiers Advisory Committee Meeting to advise on the technique of cytoplasmic transfer to treat infertility. This committee felt that there were risks at the time of inadvertent transfer of chromosomes and enhanced survival of abnormal embryos. The FDA informed clinics that they considered the cytoplasmic transfer technique as a new treatment, and, as such, it would require an Investigational New Drug (IND) application. Cohen's clinic started the pre-IND application, but the clinic then went private, funding for the application dried up, the application was abandoned, the research team disbanded, and the cytoplasmic transfer procedure fell out of favor. In 2016, 12 (out of the 13) parents of children born using cytoplasmic transfer at the Saint Barnabas Center participated in a limited follow-up inquiry via online questionnaire. Children whose ages then were 13–18 reported no major problems.
In 2009, a team in Japan published studies of mitochondrial donation. In the same year, a team led by scientists at Oregon Health & Science University published results of mitochondrial donation in monkeys; that team published an update reporting on the health of the monkeys born with the technique, as well as further work it had done on human embryos.
Human trials with oocytes in 2010 by Craven et al. were successful in reducing transmission of mutated mtDNA. The results of the study found the mean transfer DNA (tDNA) carryover to stay under 2% in all of the experimental embryos. This was true for both the MI-SCC and PN transfer methods of MTR. This research did not extend past the blastocyst stage because of ethical concerns, and there are still concerns about whether results retrieved from the blastocyst stage are viable representations of whole embryos. Because of these speculations and to further the viability of MTR as a safe and effective technique, further research and clinical trials would need to be initiated to test the efficacy of MTR in the long term in human patients. | 1 | Biochemistry |
Armodafinil is readily absorbed after oral administration. The absolute oral bioavailability was not determined due to the aqueous insolubility of armodafinil, which precluded intravenous administration. Peak plasma concentrations are attained at approximately 2 hours in the fasted state. Food effect on the overall bioavailability of armodafinil is considered minimal; however, time to reach peak concentration may be delayed 2–4 hours in the fed state. Since the delay in T is also associated with elevated plasma concentration later in time, food can potentially affect the onset and time course of pharmacologic action of armodafinil. | 4 | Stereochemistry |
TFIIB is a single 33kDa polypeptide consisting of 316 amino acids. TFIIB is made up of four functional regions: the C-terminal core domain; the B linker; the B reader and the amino terminal zinc ribbon.
TFIIB makes protein-protein interactions with the TATA-binding protein (TBP) subunit of transcription factor IID, and the RPB1 subunit of RNA polymerase II.
TFIIB makes sequence-specific protein-DNA interactions with the B recognition element (BRE), a promoter element flanking the TATA element. | 1 | Biochemistry |
When it is time for a cell to enter S phase, complexes of cyclin-dependent kinases (CDK) and cyclins phosphorylate pRb, allowing E2F-DP to dissociate from pRb and become active. When E2F is free it activates factors like cyclins (e.g. cyclin E and cyclin A), which push the cell through the cell cycle by activating cyclin-dependent kinases, and a molecule called proliferating cell nuclear antigen, or PCNA, which speeds DNA replication and repair by helping to attach polymerase to DNA. | 1 | Biochemistry |
Copper is the eighth most abundant metal in the Earth's crust, is available all over the world, and is one of the few that can appear in a pure state. It is not complicated to work with, and a bare hammering can be enough to transform a nugget into a bead. The eye-catching look of native copper makes it easy to recognize, and even flashier if converted into jewelry, a possible motivation for humankind to start metallurgy with it. An evolutive technological process has been described, although there are authors like Javinovic, who think that it is not necessary to pass through the first stages to reach the last one. | 8 | Metallurgy |
A development of transition state theory in which the position of the dividing surface is varied so as to minimize the rate constant at a given temperature. | 7 | Physical Chemistry |
Azomethine ylides can be generated from ring opening of aziridines. In accordance with the Woodward–Hoffmann rules, the thermal four-electron ring opening proceeds via a conrotatory process, whereas the photochemical reaction is disrotatory.
In this ring opening reaction, there is an issue of torquoselectivity. Electronegative substituents prefer to rotate outwards, to the same side as the R substituent on the nitrogen, whereas electropositive substituents prefer to rotate inwards.
Note that with aziridines, ring opening can result in a different 1,3-dipole, in which a C–N bond (rather than the C–C bond) breaks. | 0 | Organic Chemistry |
The nucleosome core particle (shown in the figure) consists of about 146 base pair of DNA wrapped in 1.67 left-handed superhelical turns around the histone octamer, consisting of 2 copies each of the core histones H2A, H2B, H3, and H4. Adjacent nucleosomes are joined by a stretch of free DNA termed linker DNA (which varies from 10 - 80 bp in length depending on species and tissue type).The whole structure generates a cylinder of diameter 11 nm and a height of 5.5 nm.
Nucleosome core particles are observed when chromatin in interphase is treated to cause the chromatin to unfold partially. The resulting image, via an electron microscope, is "beads on a string". The string is the DNA, while each bead in the nucleosome is a core particle. The nucleosome core particle is composed of DNA and histone proteins.
Partial DNAse digestion of chromatin reveals its nucleosome structure. Because DNA portions of nucleosome core particles are less accessible for DNAse than linking sections, DNA gets digested into fragments of lengths equal to multiplicity of distance between nucleosomes (180, 360, 540 base pairs etc.). Hence a very characteristic pattern similar to a ladder is visible during gel electrophoresis of that DNA. Such digestion can occur also under natural conditions during apoptosis ("cell suicide" or programmed cell death), because autodestruction of DNA typically is its role. | 1 | Biochemistry |
Other methods of laser cooling include:
* Sisyphus cooling
* Resolved sideband cooling
* Raman sideband cooling
* Velocity selective coherent population trapping (VSCPT)
* Gray molasses
* Optical molasses
* Cavity-mediated cooling
* Use of a Zeeman slower
* Electromagnetically induced transparency (EIT) cooling
* Anti-Stokes cooling in solids
* Polarization gradient cooling | 7 | Physical Chemistry |
Compared to the elemental form, potassium iodide has a median lethal dose (LD) that is relatively high in several animals: in rabbits, it is 10 g/kg; in rats, 14 g/kg, and in mice, 22 g/kg. The tolerable upper intake level for iodine as established by the Food and Nutrition Board is 1,100 µg/day for adults. The safe upper limit of consumption set by the Ministry of Health, Labor and Welfare in Japan is 3,000 µg/day.
The biological half-life of iodine differs between the various organs of the body, from 100 days in the thyroid, to 14 days in the kidneys and spleen, to 7 days in the reproductive organs. Typically the daily urinary elimination rate ranges from 100 to 200 µg/L in humans. However, the Japanese diet, high in iodine-rich kelp, contains 1,000 to 3,000 µg of iodine per day, and research indicates the body can readily eliminate excess iodine that is not needed for thyroid hormone production. The literature reports as much as 30,000 µg/L (30 mg/L) of iodine being safely excreted in the urine in a single day, with levels returning to the standard range in a couple of days, depending on seaweed intake. One study concluded the range of total body iodine content in males was 12.1 mg to 25.3 mg, with a mean of 14.6 mg. It is presumed that once thyroid-stimulating hormone is suppressed, the body simply eliminates excess iodine, and as a result, long-term supplementation with high doses of iodine has no additional effect once the body is replete with enough iodine. It is unknown if the thyroid gland is the rate-limiting factor in generating thyroid hormone from iodine and tyrosine, but assuming it is not, a short-term loading dose of one or two weeks at the tolerable upper intake level may quickly restore thyroid function in iodine-deficient patients.
Excessive iodine intake presents symptoms similar to those of iodine deficiency. Commonly encountered symptoms are abnormal growth of the thyroid gland and disorders in functioning, as well as in growth of the organism as a whole. Iodide toxicity is similar to (but not the same as) toxicity to ions of the other halogens, such as bromides or fluorides. Excess bromine and fluorine can prevent successful iodine uptake, storage and use in organisms, as both elements can selectively replace iodine biochemically.
Excess iodine may also be more cytotoxic in combination with selenium deficiency. Iodine supplementation in selenium-deficient populations is theoretically problematic, partly for this reason. Selenocysteine (abbreviated as Sec or U, in older publications also as Se-Cys) is the 21st proteinogenic amino acid, and is the root of iodide ion toxicity when there is a simultaneous insufficiency of biologically available selenium. Selenocysteine exists naturally in all kingdoms of life as a building block of selenoproteins. | 1 | Biochemistry |
The synergy between the atmospheric concentration measurements, the knowledge of local ecosystem fluxes on the other hand, has shown effective in reducing the uncertainties on carbon assessments. However, in Europe, observatories are all managed differently for each country and data is not homogeneously processed.
The value added impact of the infrastructure allows an enhanced visibility and dissemination of European greenhouse gas data and products that are both long-term and carefully calibrated. ICOS meets the data needs of carbon cycle and climate researchers as well as those of politicians and the general public. ICOS serves as the backbone to users engaged in developing data assimilation models of greenhouse gas sources and sinks, namely reverse modelling, which allows the deduction of surface carbon flux pattern.
A common data centre, the ICOS Carbon Portal, provides free access to all ICOS data, as well as to links with inventory data, and outreach material. This portal allows the production of web based tools for the survey of sources and sinks in near real-time. ICOS delivers the information in near real-time with a quantification of the uncertainty associated with the results due to the use of several different models using different methodologies.
ICOS enables Europe to be a key global player for in-situ observations of greenhouse gases, data processing and user-friendly access to data products for validation of remote sensing products, scientific assessments, modelling and data assimilation. | 2 | Environmental Chemistry |
The germanium-vacancy center (Ge-V) is an optically active defect in diamond, which can be created by doping germanium into diamond during its growth or by implanting germanium ions into diamond after its growth. Its properties are similar to those of the silicon-vacancy center in diamond (SiV). Ge-V can behave as a single-photon source and shows potential for quantum and nanoscience applications due to its narrow zero-phonon line (ZPL) and minimal phononic-sideband (compared to that of the nitrogen-vacancy center (NV)). | 7 | Physical Chemistry |
Butyrates effects on the immune system are mediated through the inhibition of class I histone deacetylases and activation of its G-protein coupled receptor targets: Hydroxycarboxylic acid receptor 2| (GPR109A), FFAR2 (GPR43), and FFAR3 (GPR41). Among the short-chain fatty acids, butyrate is the most potent promoter of intestinal regulatory T cells in vitro' and the only one among the group that is an ligand. It has been shown to be a critical mediator of the colonic inflammatory response. It possesses both preventive and therapeutic potential to counteract inflammation-mediated ulcerative colitis and colorectal cancer.
Butyrate has established antimicrobial properties in humans that are mediated through the antimicrobial peptide LL-37, which it induces via HDAC inhibition on histone H3. In vitro, butyrate increases gene expression of FOXP3 (the transcription regulator for ) and promotes colonic regulatory T cells (Tregs) through the inhibition of class I histone deacetylases; through these actions, it increases the expression of interleukin 10, an anti-inflammatory cytokine. Butyrate also suppresses colonic inflammation by inhibiting the IFN-γ–STAT1 signaling pathways, which is mediated partially through histone deacetylase inhibition. While transient IFN-γ signaling is generally associated with normal host immune response, chronic IFN-γ signaling is often associated with chronic inflammation. It has been shown that butyrate inhibits activity of HDAC1 that is bound to the Fas gene promoter in T cells, resulting in hyperacetylation of the Fas promoter and up-regulation of Fas receptor on the T-cell surface.
Similar to other agonists studied, butyrate also produces marked anti-inflammatory effects in a variety of tissues, including the brain, gastrointestinal tract, skin, and vascular tissue. Butyrate binding at FFAR3 induces neuropeptide Y release and promotes the functional homeostasis of colonic mucosa and the enteric immune system. | 1 | Biochemistry |
Indigo carmine in a 0.2% aqueous solution is blue at pH 11.4 and yellow at 13.0. Indigo carmine is also a redox indicator, turning yellow upon reduction. Another use is as a dissolved ozone indicator through the conversion to isatin-5-sulfonic acid. This reaction has been shown not to be specific to ozone, however: it also detects superoxide, an important distinction in cell physiology. It is also used as a dye in the manufacturing of capsules. | 3 | Analytical Chemistry |
Lisinopril is a medication belonging to the drug class of angiotensin-converting enzyme (ACE) inhibitors and is used to treat hypertension (high blood pressure), heart failure, and heart attacks. For high blood pressure it is usually a first-line treatment. It is also used to prevent kidney problems in people with diabetes mellitus. Lisinopril is taken orally (swallowed by mouth). Full effect may take up to four weeks to occur.
Common side effects include headache, dizziness, feeling tired, cough, nausea, and rash. Serious side effects may include low blood pressure, liver problems, hyperkalemia (high blood potassium), and angioedema. Use is not recommended during the entire duration of pregnancy as it may harm the baby. Lisinopril works by inhibiting the renin–angiotensin–aldosterone system.
Lisinopril was patented in 1978 and approved for medical use in the United States in 1987. It is available as a generic medication. In 2021, it was the fourth most commonly prescribed medication in the United States, with more than 88million prescriptions. In July 2016, an oral solution formulation of lisinopril was approved for use in the United States. | 4 | Stereochemistry |
Acridine has been obtained as eight polymorphs and aripiprazole has nine. The record for the largest number of well-characterised polymorphs is held by a compound known as ROY. Glycine crystallizes as both monoclinic and hexagonal crystals. Polymorphism in organic compounds is often the result of conformational polymorphism. | 3 | Analytical Chemistry |
The Hedgehog Signaling pathway is critical in proper tissue patterning and orientation during normal development of most animals. Hedgehog proteins induce cell proliferation in certain cells and differentiations in others. Aberrant activation of the Hedgehog pathway has been implicated in several types of cancers, Basal Cell Carcinoma in particular. This uncontrolled activation of the Hedgehog proteins can be caused by mutations to the signal pathway, which would be ligand independent, or a mutation that causes overexpression of the Hedgehog protein, which would be ligand dependent. In addition, therapy-induced Hedgehog pathway activation has been shown to be necessary for progression of Prostate Cancer tumors after androgen deprivation therapy. This connection between the Hedgehog signaling pathway and human cancers may provide for the possible of therapeutic intervention as treatment for such cancers. The Hedgehog signaling pathway is also involved in normal regulation of stem-cell populations, and required for normal growth and regeneration of damaged organs. This may provide another possible route for tumorigenesis via the Hedgehog pathway. | 1 | Biochemistry |
Isotopic substitution can lead to changes in the values of equilibrium constants, especially if hydrogen is replaced by deuterium (or tritium). This equilibrium isotope effect is analogous to the kinetic isotope effect on rate constants, and is primarily due to the change in zero-point vibrational energy of H–X bonds due to the change in mass upon isotopic substitution. The zero-point energy is inversely proportional to the square root of the mass of the vibrating hydrogen atom, and will therefore be smaller for a D–X bond that for an H–X bond.
An example is a hydrogen atom abstraction reaction R + H–R R–H + R with equilibrium constant K, where R and R are organic radicals such that R forms a stronger bond to hydrogen than does R. The decrease in zero-point energy due to deuterium substitution will then be more important for R–H than for R–H, and R–D will be stabilized more than R–D, so that the equilibrium constant K for R + D–R R–D + R is greater than K. This is summarized in the rule the heavier atom favors the stronger bond.
Similar effects occur in solution for acid dissociation constants (K) which describe the transfer of H or D from a weak aqueous acid to a solvent molecule: HA + HO = HO + A or DA + DO DO + A. The deuterated acid is studied in heavy water, since if it were dissolved in ordinary water the deuterium would rapidly exchange with hydrogen in the solvent.
The product species HO (or DO) is a stronger acid than the solute acid, so that it dissociates more easily, and its H–O (or D–O) bond is weaker than the H–A (or D–A) bond of the solute acid. The decrease in zero-point energy due to isotopic substitution is therefore less important in DO than in DA so that K , and the deuterated acid in DO is weaker than the non-deuterated acid in HO. In many cases the difference of logarithmic constants pK – pK is about 0.6, so that the pD corresponding to 50% dissociation of the deuterated acid is about 0.6 units higher than the pH for 50% dissociation of the non-deuterated acid.
For similar reasons the self-ionization of heavy water is less than that of ordinary water at the same temperature. | 7 | Physical Chemistry |
The first example of molecular imprinting is attributed to M. V. Polyakov in 1931 with his studies in the polymerization of sodium silicate with ammonium carbonate. When the polymerization process was accompanied by an additive such as benzene, the resulting silica showed a higher uptake of this additive. By 1949, the concept of instructional theory molecular imprinting was used by Dickey; his research precipitated silica gels in the presence of organic dyes and showed imprinted silica had high selectivity towards the template dye.
Following Dickey’s observations, Patrikeev published a paper of his ‘imprinted’ silica with the method of incubating bacteria with gel silica. The process of drying and heating the silica promoted growth of bacteria better than other reference silicas and exhibited enantioselectivity. He later used this imprinted silica method in further applications such as thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). In 1972, Wulff and Klotz introduced molecular imprinting to organic polymers. They found that molecular recognition was possible by covalently introducing functional groups within the imprinted cavity of polymers. The Mosbach group then proved it was possible to introduce functional groups into imprinted cavities through non-covalent interactions, thus leading to non-covalent imprinting. Many approaches regarding molecular imprinting have since been extended to different purposes. | 6 | Supramolecular Chemistry |
Methylotrophic yeast metabolism differs from bacteria primarily on the basis of the enzymes used and the carbon assimilation pathway. Unlike bacteria which use bacterial MDH, methylotrophic yeasts oxidize methanol in their peroxisomes with a non-specific alcohol oxidase. This produces formaldehyde as well as hydrogen peroxide. Compartmentalization of this reaction in peroxisomes likely sequesters the hydrogen peroxide produced. Catalase is produced in the peroxisomes to deal with this harmful by-product. | 0 | Organic Chemistry |
Relative to other SNRIs, levomilnacipran, as well as milnacipran, differ in that they are much more balanced reuptake inhibitors of serotonin and norepinephrine. To demonstrate, the serotonin:norepinephrine ratios of SNRIs are as follows: venlafaxine = 30:1, duloxetine = 10:1, desvenlafaxine = 14:1, milnacipran = 1.6:1, and levomilnacipran = 1:2. The clinical implications of more balanced elevations of serotonin and norepinephrine are unclear, but may include improved effectiveness, though also increased side effects.
Levomilnacipran is selective for the serotonin and norepinephrine transporters, lacking significant affinity for over 23 off-target sites. However, it does show some affinity for the dizocilpine (MK-801/) site of the NMDA receptor (K = 1.7 μM), and has been found to inhibit NR2A and NR2B subunit-containing NMDA receptors with respective IC values of 5.62 and 4.57 μM. As such, levomilnacipran is an NMDA receptor antagonist at high concentrations.
Levomilnacipran has recently been found to act as an inhibitor of beta-site amyloid precursor protein cleaving enzyme-1 (BACE-1), which is responsible for β-amyloid plaque formation, and hence may be a potentially useful drug in the treatment of Alzheimer's disease. | 4 | Stereochemistry |
The dramatic increase in genome sequencing technology has caused the number of protein sequences deposited into public databases to grow apparently exponentially. To cope with the influx of sequences, databases use computational predictions to auto-annotate individual proteins functions. While these computational methods offer the advantages of being extremely high-throughput and generally provide accurate broad classifications, exclusive use has led to a significant level of misannotation of enzyme function in protein databases. Thus although the information now available represents an unprecedented opportunity to understand cellular metabolism across a wide variety of organisms, which includes the ability to identify molecules and/or reactions that may benefit human quality of life, the potential has not been fully actualized. The biological communitys ability to characterize newly discovered proteins has been outstripped by the rate of genome sequencing, and the task of assigning function is now considered the rate-limiting step in understanding biological systems in detail. | 1 | Biochemistry |
FCCS is an extension of the fluorescence correlation spectroscopy (FCS) method that uses two fluorescent molecules instead of one that emits different colours. The technique measures coincident green and red intensity fluctuations of distinct molecules that correlate if green and red labelled particles move together through a predefined confocal volume. FCCS utilizes two species that are independently labeled with two different fluorescent probes of different colours. These fluorescent probes are excited and detected by two different laser light sources and detectors typically labeled as "green" and "red". By combining FCCS with a confocal microscope, the technique's capabilities are highlighted, as it becomes possible to detect fluorescence molecules in femtoliter volumes within the nanomolar range, with a high signal-to-noise ratio, and at a microsecond time scale.
The normalized cross-correlation function is defined for two fluorescent species, G and R, which are independent green and red channels, respectively:
where differential fluorescent signals at a specific time, and at a delay time, later is correlated with each other. In the absence of spectral bleed-through – when the fluorescence signal from an adjacent channel is visible in the channel being observed – the cross-correlation function is zero for non-interacting particles. In contrast to FCS, the cross-correlation function increases with increasing numbers of interacting particles.
FCCS is mainly used to study bio-molecular interactions both in living cells and in vitro. It allows for measuring simple molecular stoichiometries and binding constants. It is one of the few techniques that can provide information about protein–protein interactions at a specific time and location within a living cell. Unlike fluorescence resonance energy transfer, FCCS does not have a distance limit for interactions making it suitable for probing large complexes. However, FCCS requires active diffusion of the complexes through the microscope focus on a relatively short time scale, typically seconds. | 7 | Physical Chemistry |
Consider two coupled ultrasensitive modules, disregarding effects of sequestration of molecular components between layers. In this case, the expression for the system's dose-response curve, , results from the mathematical composition of the functions, , which describe the input/output relationship of isolated modules :
Brown et al. (1997) have shown that the local ultrasensitivity of the different layers combines multiplicatively:
In connection with this result, Ferrell et al. (1997) showed, for Hill-type modules, that the overall cascade global ultrasensitivity had to be less than or equal to the product of the global ultrasensitivity estimations of each cascade's layer,
where and are the Hill coefficient of modules 1 and 2 respectively.
Altszyler et al. (2017) have shown that the cascade's global ultrasensitivity can be analytically calculated:
where and delimited the Hill inputs working range of the composite system, i.e. the input values for the i-layer so that the last layer (corresponding to in this case) reached the 10% and 90% of it maximal output level. It followed this equation that the systems Hill coefficient could be written as the product of two factors, and , which characterized local average sensitivities over the relevant input region for each layer: , with in this case.
For the more general case of a cascade of modules, the Hill Coefficient can be expressed as: | 1 | Biochemistry |
Drugs or toxic chemicals are useful in killing pathogenic bacteria or tumor cells, and studying how they mechanistically develop tolerance to a wide range of drugs can improve anti-bacterial and cancer therapeutics. Pdr5p has a similar mechanism of actions and functions to human multidrug resistance protein, whose overexpression is shown to provide chemical tolerance to cancer cells. Studying Pdr5p and how it is regulated by Pdr1p in yeast can give insights into how multi drug resistance occurs in mammals.
By using pdr1-3 and fusing the promoter of Pdr5p to genes that code for membrane proteins of interests, yeast membrane proteins such as Pdr5p, Yor1, and Drs2 can be expressed highly so that they can be efficiently cloned and purified for further studies. | 1 | Biochemistry |
Simmons-Smith cyclopropanation, which employs carbenes derived from diiodomethane, is a popular alternative to rhodium-catalyzed cyclopropanation. In the presence of a chiral diamine, Simmons-Smith cyclopropanation is enantioselective; however, selectivities are not as high as the corresponding rhodium-catalyzed reactions.
Substituted zinc carbenoids can be prepared from the corresponding ketones or aldehydes through a sequence analogous to the mechanism of the Clemmensen reduction. Cyclopropanation of olefins with these intermediates occurs with moderate diastereoselectivity and yield.
Other diazo compounds besides diazocarbonyl compounds have been used for rhodium-catalyzed cyclopropanations; however, these substrates are much more difficult to handle and unstable than diazocarbonyl compounds. Thus, they have not been extensively adopted for organic synthesis. | 0 | Organic Chemistry |
Plasmas are by far the most common phase of ordinary matter in the universe, both by mass and by volume.
Above the Earths surface, the ionosphere is a plasma, and the magnetosphere contains plasma. Within our Solar System, interplanetary space is filled with the plasma expelled via the solar wind, extending from the Suns surface out to the heliopause. Furthermore, all the distant stars, and much of interstellar space or intergalactic space is also filled with plasma, albeit at very low densities. Astrophysical plasmas are also observed in accretion disks around stars or compact objects like white dwarfs, neutron stars, or black holes in close binary star systems. Plasma is associated with ejection of material in astrophysical jets, which have been observed with accreting black holes or in active galaxies like M87's jet that possibly extends out to 5,000 light-years. | 7 | Physical Chemistry |
The similarity to histone H1 explains how fork head factors are able to bind chromatin by interacting with the major groove of only the one available side of DNA wrapped around a nucleosome. Fork head domains also have a helix that confers sequence specificity unlike linker histone. The C terminus is associated with higher mobility around the nucleosome than linker histone, displacing it and rearranging nucleosomal landscapes effectively. This active re-arrangement of the nucleosomes allows for other transcription factors to bind the available DNA. In thyroid cell differentiation FoxE binds to compacted chromatin of the thyroid peroxidase promoter and opens it for NF1 binding. | 1 | Biochemistry |
After labeling of the surface with the selected F bioactives, the constructs will be present and oriented at the membrane surface. It is expected that the FSL will be highly mobile within the membrane and the choice of lipid tail will effect is relative partitioning within the membrane. The construct unless it has flip-flop behavior is expected to remain surface presented. However, the modification is not permanent in living cells and constructs will be lost (consumed) at a rate proportional to the activity at the membrane and division rate of the cell (with dead cells remaining highly labeled). Additionally, when present in vivo with serum lipids FSLs will elute from the membrane into the plasma at a rate of about 1% per hour. In fixed cells or inactive cells (e.g. red cells) stored in serum free media the constructs are retained normally.
Liposomes are easy koded by simply adding FSL Kode constructs into the preparation. Contacting koded liposomes with microplates or other surfaces can cause the labeling of the microplate surface. | 1 | Biochemistry |
Countercurrent chromatography (CCC, also counter-current chromatography) is a form of liquid–liquid chromatography that uses a liquid stationary phase that is held in place by inertia of the molecules composing the stationary phase accelerating toward the center of a centrifuge due to centripetal force and is used to separate, identify, and quantify the chemical components of a mixture. In its broadest sense, countercurrent chromatography encompasses a collection of related liquid chromatography techniques that employ two immiscible liquid phases without a solid support. The two liquid phases come in contact with each other as at least one phase is pumped through a column, a hollow tube or a series of chambers connected with channels, which contains both phases. The resulting dynamic mixing and settling action allows the components to be separated by their respective solubilities in the two phases. A wide variety of two-phase solvent systems consisting of at least two immiscible liquids may be employed to provide the proper selectivity for the desired separation.
Some types of countercurrent chromatography, such as dual flow CCC, feature a true countercurrent process where the two immiscible phases flow past each other and exit at opposite ends of the column. More often, however, one liquid acts as the stationary phase and is retained in the column while the mobile phase is pumped through it. The liquid stationary phase is held in place by gravity or inertia of the molecules composing the stationary phase accelerating toward the center of a centrifuge due to centripetal force. An example of a gravity method is called droplet counter current chromatography (DCCC). There are two modes by which the stationary phase is retained by centripetal force: hydrostatic and hydrodynamic. In the hydrostatic method, the column is rotated about a central axis. Hydrostatic instruments are marketed under the name centrifugal partition chromatography (CPC). Hydrodynamic instruments are often marketed as high-speed or high-performance countercurrent chromatography (HSCCC and HPCCC respectively) instruments which rely on the Archimedes' screw force in a helical coil to retain the stationary phase in the column.
The components of a CCC system are similar to most liquid chromatography configurations, such as high-performance liquid chromatography (HPLC). One or more pumps deliver the phases to the column which is the CCC instrument itself. Samples are introduced into the column through a sample loop filled with an automated or manual syringe. The outflow is monitored with various detectors such as ultraviolet–visible spectroscopy or mass spectrometry. The operation of the pumps, CCC instrument, sample injection, and detection may be controlled manually or with a microprocessor. | 3 | Analytical Chemistry |
As many quantities of cell biological interest are present in discrete copy number within the cell (single DNAs, dozens of mRNAs, hundreds of proteins), tools from discrete stochastic mathematics are often used to analyse and model cellular noise. In particular, master equation treatments – where the probabilities of observing a system in a state at time are linked through ODEs – have proved particularly fruitful. A canonical model for noise gene expression, where the processes of DNA activation, transcription and translation are all represented as Poisson processes with given rates, gives a master equation which may be solved exactly (with generating functions) under various assumptions or approximated with stochastic tools like Van Kampen's system size expansion.
Numerically, the Gillespie algorithm or stochastic simulation algorithm is often used to create realisations of stochastic cellular processes, from which statistics can be calculated.
The problem of inferring the values of parameters in stochastic models (parametric inference) for biological processes, which are typically characterised by sparse and noisy experimental data, is an active field of research, with methods including Bayesian MCMC and approximate Bayesian computation proving adaptable and robust. Regarding the two-state model, a moment-based method was described for parameters inference from mRNAs distributions. | 1 | Biochemistry |
August Wilhelm von Hofmann, Auguste Laurent and Charles Frédéric Gerhardt challenged Frankland and Kolbe by suggesting that the ethyl radical was in fact a dimer called dimethyl. Frankland and Kolbe countered that ethyl hydride was also a possibility and in 1864 Carl Schorlemmer proved that dimethyl and ethyl hydride were in fact one and the same compound.
Radical theory was eventually replaced by a number of theories each advocating specific entities. One adaptation of radical theory was called theory of types (theory of residues), advocated by Charles-Adolphe Wurtz, August Wilhelm von Hofmann and Charles Frédéric Gerhardt. Another was water type as promoted by Alexander William Williamson. Jean-Baptiste Dumas and Auguste Laurent (an early supporter of radical theory) challenged radical theory in 1840 with a Law of Substitution (or Theory of Substitution). This law acknowledged that any hydrogen atom even as part of a radical could be substituted by a halogen.
Eventually Frankland in 1852 and August Kekulé in 1857 introduced valence theory with the tetravalency of carbon as its central theme, making trivalent carbon obsolete for the time being. | 0 | Organic Chemistry |
ITS-90 is designed to represent the thermodynamic temperature scale (referencing absolute zero) as closely as possible throughout its range. Many different thermometer designs are required to cover the entire range. These include helium vapor pressure thermometers, helium gas thermometers, standard platinum resistance thermometers (known as SPRTs, PRTs or Platinum RTDs) and monochromatic radiation thermometers.
Although the Kelvin and Celsius scales are defined using absolute zero (0 K) and the triple point of water (273.16 K and 0.01 °C), it is impractical to use this definition at temperatures that are very different from the triple point of water. Accordingly, ITS–90 uses numerous defined points, all of which are based on various thermodynamic equilibrium states of fourteen pure chemical elements and one compound (water). Most of the defined points are based on a phase transition; specifically the melting/freezing point of a pure chemical element. However, the deepest cryogenic points are based exclusively on the vapor pressure/temperature relationship of helium and its isotopes whereas the remainder of its cold points (those less than room temperature) are based on triple points. Examples of other defining points are the triple point of hydrogen (−259.3467 °C) and the freezing point of aluminum (660.323 °C).
Thermometers calibrated per ITS–90 use complex mathematical formulas to interpolate between its defined points. ITS–90 specifies rigorous control over variables to ensure reproducibility from lab to lab. For instance, the small effect that atmospheric pressure has upon the various melting points is compensated for (an effect that typically amounts to no more than half a millikelvin across the different altitudes and barometric pressures likely to be encountered). The standard even compensates for the pressure effect due to how deeply the temperature probe is immersed into the sample. ITS–90 also draws a distinction between "freezing" and "melting" points. The distinction depends on whether heat is going into (melting) or out of (freezing) the sample when the measurement is made. Only gallium is measured while melting, all the other metals are measured while the samples are freezing.
There are often small differences between measurements calibrated per ITS–90 and thermodynamic temperature. For instance, precise measurements show that the boiling point of VSMOW water under one standard atmosphere of pressure is actually 373.1339 K (99.9839 °C) when adhering strictly to the two-point definition of thermodynamic temperature. When calibrated to ITS–90, where one must interpolate between the defining points of gallium and indium, the boiling point of VSMOW water is about 10 mK less, about 99.974 °C. The virtue of ITS–90 is that another lab in another part of the world will measure the very same temperature with ease due to the advantages of a comprehensive international calibration standard featuring many conveniently spaced, reproducible, defining points spanning a wide range of temperatures. | 7 | Physical Chemistry |
Developing technologies include:
* Ion-trap mass spectrometry
* Laser-induced immunofluorometric biosensors
* Magnetic levitation
* Nuclear magnetic resonance spectroscopy | 3 | Analytical Chemistry |
Mg is the coordinating metal ion in the chlorophyll molecule, and in plants where the ion is in high supply about 6% of the total Mg is bound to chlorophyll. Thylakoid stacking is stabilised by Mg and is important for the efficiency of photosynthesis, allowing phase transitions to occur.
Mg is probably taken up into chloroplasts to the greatest extent during the light-induced development from proplastid to chloroplast or etioplast to chloroplast. At these times, the synthesis of chlorophyll and the biogenesis of the thylakoid membrane stacks absolutely require the divalent cation.
Whether Mg is able to move into and out of chloroplasts after this initial developmental phase has been the subject of several conflicting reports. Deshaies et al. (1984) found that Mg did move in and out of isolated chloroplasts from young pea plants, but Gupta and Berkowitz (1989) were unable to reproduce the result using older spinach chloroplasts. Deshaies et al. had stated in their paper that older pea chloroplasts showed less significant changes in Mg content than those used to form their conclusions. The relative proportion of immature chloroplasts present in the preparations may explain these observations.
The metabolic state of the chloroplast changes considerably between night and day. During the day, the chloroplast is actively harvesting the energy of light and converting it into chemical energy. The activation of the metabolic pathways involved comes from the changes in the chemical nature of the stroma on the addition of light. H is pumped out of the stroma (into both the cytoplasm and the lumen) leading to an alkaline pH. Mg (along with K) is released from the lumen into the stroma, in an electroneutralisation process to balance the flow of H. Finally, thiol groups on enzymes are reduced by a change in the redox state of the stroma. Examples of enzymes activated in response to these changes are fructose 1,6-bisphosphatase, sedoheptulose bisphosphatase and ribulose-1,5-bisphosphate carboxylase. During the dark period, if these enzymes were active a wasteful cycling of products and substrates would occur.
Two major classes of the enzymes that interact with Mg in the stroma during the light phase can be identified. Firstly, enzymes in the glycolytic pathway most often interact with two atoms of Mg. The first atom is as an allosteric modulator of the enzymes' activity, while the second forms part of the active site and is directly involved in the catalytic reaction. The second class of enzymes includes those where the Mg is complexed to nucleotide di- and tri-phosphates (ADP and ATP), and the chemical change involves phosphoryl transfer. Mg may also serve in a structural maintenance role in these enzymes (e.g., enolase). | 1 | Biochemistry |
Primary cilia, present in many types of mammalian cells, serve as cellular antennae. The motile function of these cilia is lost in favour of their sensory specialization. | 3 | Analytical Chemistry |
A critical parameter affecting the performance of proton exchange membranes is the water content. Water is typically supplied to the fuel cell by humidifying the gas feed stream. The level of hydration within the proton exchange membrane is vital to its performance: if the hydration level is too low, the polymers exhibit greatly reduced ionic conductivity; if hydration level is too high, excess water can flood the pores in the gas diffusion layer and impede mass transport within the electrode structure. For these reasons, DVS has been used to study the water sorption and transport properties of proton exchange membranes. | 7 | Physical Chemistry |
Diels–Alder reactions occur between a conjugated diene and an alkene (commonly known as the dienophile). This cycloaddition process allows for the stereoselective formation of cyclohexene rings capable of possessing as many as four contiguous stereogenic centers.
Diels–Alder reactions can lead to the formation of a variety of structural isomers and stereoisomers. Molecular orbital theory considers that the endo transition state, instead of the exo transition state, is favored (endo addition rule). Also, augmented secondary orbital interactions have been postulated as the source of enhanced endo diastereoselection.
Usually, CLAs are employed to activate the dienophile. A typical CLA catalyst is derived from a Mg center made chiral by attachment of a binol- phosphate ester. CLAs have been applied to a number of intramolecular Diels–Alder reactions.
A complex derived from diethylaluminium chloride and a “vaulted” biaryl ligand below catalyzes the enantioselective Diels–Alder reaction between cyclopentadiene and methacrolein. The chiral ligand is recovered quantitatively by silica gel chromatography.
The chiral (acyloxy) borane (CAB) complex is effective in catalyzing a number of aldehyde Diels–Alder reactions. NMR spectroscopic experiments have indicated close proximity of the aldehyde and the aryl ring. Pi stacking between the aryl group and aldehyde has been suggested as an organizational feature that imparts high enantioselectivity to the cycloaddition.
Bronsted acid-assisted chiral Lewis acid (BLA) catalyzes a number of diene-aldehyde cycloaddition reactions. | 4 | Stereochemistry |
Many types of battery have been commercialized and represent an important practical application of electrochemistry. Early wet cells powered the first telegraph and telephone systems, and were the source of current for electroplating. The zinc-manganese dioxide dry cell was the first portable, non-spillable battery type that made flashlights and other portable devices practical. The mercury battery using zinc and mercuric oxide provided higher levels of power and capacity than the original dry cell for early electronic devices, but has been phased out of common use due to the danger of mercury pollution from discarded cells.
The lead–acid battery was the first practical secondary (rechargeable) battery that could have its capacity replenished from an external source. The electrochemical reaction that produced current was (to a useful degree) reversible, allowing electrical energy and chemical energy to be interchanged as needed. Common lead acid batteries contain a mixture of sulfuric acid and water, as well as lead plates. The most common mixture used today is 30% acid. One problem, however, is if left uncharged acid will crystallize within the lead plates of the battery rendering it useless. These batteries last an average of 3 years with daily use but it is not unheard of for a lead acid battery to still be functional after 7–10 years. Lead-acid cells continue to be widely used in automobiles.
All the preceding types have water-based electrolytes, which limits the maximum voltage per cell. The freezing of water limits low temperature performance. The lithium metal battery, which does not (and cannot) use water in the electrolyte, provides improved performance over other types; a rechargeable lithium-ion battery is an essential part of many mobile devices.
The flow battery, an experimental type, offers the option of vastly larger energy capacity because its reactants can be replenished from external reservoirs. The fuel cell can turn the chemical energy bound in hydrocarbon gases or hydrogen and oxygen directly into electrical energy with a much higher efficiency than any combustion process; such devices have powered many spacecraft and are being applied to grid energy storage for the public power system. | 7 | Physical Chemistry |
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about , rather than the present average of .
The five most abundant greenhouse gases in Earth's atmosphere, listed in decreasing order of average global mole fraction, are: water vapor, carbon dioxide, methane, nitrous oxide, ozone. Other greenhouse gases of concern include chlorofluorocarbons (CFCs and HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons, sulfur hexafluoride|, and nitrogen trifluoride|. Water vapor causes about half of the greenhouse effect, but humans are not directly adding to its amount, so it is not a driver of climate change.
Carbon dioxide is causing about three-quarters of global warming and can take thousands of years to be fully absorbed by the carbon cycle. Methane causes most of the remaining warming and lasts in the atmosphere for an average of 12 years. Human activities since the beginning of the Industrial Revolution (around 1750) have increased carbon dioxide by over 50%, up to a level not seen in over 3 million years. The atmospheric methane concentrations have increased by over 150% during the same time period.
Without human influence, the natural flows of carbon between the atmosphere, terrestrial ecosystems, the ocean, and sediments would be fairly balanced. The vast majority of carbon dioxide emissions by humans come from the burning of fossil fuels. Further contributions come for example from cement manufacturing and deforestation. Methane emissions originate from agriculture, fossil fuel production, waste, and other sources. If current emission rates continue then temperature rises will surpass sometime between 2040 and 2070. This is a level which the Intergovernmental Panel on Climate Change (IPCC) says is "dangerous". | 2 | Environmental Chemistry |
* Christopher Longuet-Higgins (Founding Editor)
* Joan van der Waals (Founding Editor)
* John Shipley Rowlinson
* A. David Buckingham
* Lawrence D. Barron
* Martin Quack
* Dominic Tildesley
* Henry F. Schaefer III
* Nicholas C. Handy
* Ruth Lynden-Bell
* Jean-Pierre Hansen
* Timothy Softley
* Martin Head-Gordon
* Trygve Helgaker | 7 | Physical Chemistry |
The idea of sequence quality scores can be traced back to the original description of the SCF file format by Staden's group in 1992. In 1995, Bonfield and Staden proposed a method to use base-specific quality scores to improve the accuracy of consensus sequences in DNA sequencing projects.
However, early attempts to develop base-specific quality scores had only limited success.
The first program to develop accurate and powerful base-specific quality scores was the program Phred. Phred was able to calculate highly accurate quality scores that were logarithmically linked to the error probabilities. Phred was quickly adopted by all the major genome sequencing centers as well as many other laboratories; the vast majority of the DNA sequences produced during the Human Genome Project were processed with Phred.
After Phred quality scores became the required standard in DNA sequencing, other manufacturers of DNA sequencing instruments, including Li-Cor and ABI, developed similar quality scoring metrics for their base calling software. | 1 | Biochemistry |
Introns were first discovered in protein-coding genes of adenovirus, and were subsequently identified in genes encoding transfer RNA and ribosomal RNA genes. Introns are now known to occur within a wide variety of genes throughout organisms, bacteria, and viruses within all of the biological kingdoms.
The fact that genes were split or interrupted by introns was discovered independently in 1977 by Phillip Allen Sharp and Richard J. Roberts, for which they shared the Nobel Prize in Physiology or Medicine in 1993. The term intron was introduced by American biochemist Walter Gilbert:
The term intron also refers to intracistron, i.e., an additional piece of DNA that arises within a cistron.
Although introns are sometimes called intervening sequences, the term "intervening sequence" can refer to any of several families of internal nucleic acid sequences that are not present in the final gene product, including inteins, untranslated regions (UTR), and nucleotides removed by RNA editing, in addition to introns. | 1 | Biochemistry |
Double-stranded nucleic acids are made up of complementary sequences, in which extensive Watson-Crick base pairing results in a highly repeated and quite uniform Nucleic acid double-helical three-dimensional structure. In contrast, single-stranded RNA and DNA molecules are not constrained to a regular double helix, and can adopt highly complex three-dimensional structures that are based on short stretches of intramolecular base-paired sequences including both Watson-Crick and noncanonical base pairs, and a wide range of complex tertiary interactions.
Nucleic acid molecules are usually unbranched and may occur as linear and circular molecules. For example, bacterial chromosomes, plasmids, mitochondrial DNA, and chloroplast DNA are usually circular double-stranded DNA molecules, while chromosomes of the eukaryotic nucleus are usually linear double-stranded DNA molecules. Most RNA molecules are linear, single-stranded molecules, but both circular and branched molecules can result from RNA splicing reactions. The total amount of pyrimidines in a double-stranded DNA molecule is equal to the total amount of purines. The diameter of the helix is about 20 Å. | 1 | Biochemistry |
Epothilone A and B are reported to be highly effective anticancer drugs. Several of their structural derivatives show very promising inhibition against breast cancer with only mild side effect and some of them are now under trials. In 1997, K. C. Nicolaou and coworkers reported the first total synthesis of both Epothilone A and B. Ender's alkylation reaction was utilized at the very beginning of the synthesis to install the stereogenic center at C8. The reaction proceeded with both high yield and high diastereoselectivity. | 0 | Organic Chemistry |
The perovskite structure, ABO, is the most widespread ternary phase. The perovskite structure is frequently found for ternary oxides formed with one large (A) and one small cation (B). In this structure, there is a simple cubic array of B cations, with the A cations occupying the center of the cube, and the oxide atoms are sited at the center of the 12 edges of the simple cube. | 7 | Physical Chemistry |
In some clinical circumstances, succinylcholine may be administered before and after a nondepolarising NMBA or two different nondepolarising NMBAs are administered in sequence. Combining different NMBAs can result in different degrees of neuromuscular block and management should be guided with the use of a neuromuscular function monitor.
The administration of nondepolarising neuromuscular blocking agent has an antagonistic effect on the subsequent depolarising block induced by succinylcholine. If a nondepolarising NMBA is administered prior to succinycholine, the dose of succinylcholine must be increased.
The administration of succinylcholine on the subsequent administration of a nondepolarising neuromuscular block depends on the drug used. Studies have shown that administration of succinylcholien before a nondepolarising NMBA does not affect the potency of mivacurium or rocuronium. But for vecuronium and cisatracurium, it speeds up the onset, increases the potency and prolongs the duration of action.
Combining two nondepolarising NMBAs of the same chemical class (e.g. rocuronium and vecuronium) produces an additive effect, while combining two nondepolarising NMBAs of different chemical class (e.g. rocuronium and cisatracurium) produces a synergistic response. | 1 | Biochemistry |
In oceanic biogeochemistry, the f-ratio is the fraction of total primary production fuelled by nitrate (as opposed to that fuelled by other nitrogen compounds such as ammonium). The ratio was originally defined by Richard Eppley and Bruce Peterson in one of the first papers estimating global oceanic production. This fraction was originally believed significant because it appeared to directly relate to the sinking (export) flux of organic marine snow from the surface ocean by the biological pump. However, this interpretation relied on the assumption of a strong depth-partitioning of a parallel process, nitrification, that more recent measurements has questioned. | 9 | Geochemistry |
Compounds that contain sulfur exhibit unique chemistry due to sulfur's ability to form more bonds than oxygen, its lighter analogue on the periodic table. Substitutive nomenclature (marked as prefix in table) is preferred over functional class nomenclature (marked as suffix in table) for sulfides, disulfides, sulfoxides and sulfones. | 0 | Organic Chemistry |
Zinc is rarely anodized, but a process was developed by the International Lead Zinc Research Organization and covered by MIL-A-81801. A solution of ammonium phosphate, chromate and fluoride with voltages of up to 200 V can produce olive green coatings up to 80 μm thick. The coatings are hard and corrosion resistant.
Zinc or galvanized steel can be anodized at lower voltages (20–30 V) as well as using direct currents from silicate baths containing varying concentration of sodium silicate, sodium hydroxide, borax, sodium nitrite and nickel sulphate. | 8 | Metallurgy |
It was in Munich (1928–1938) that Schwab started systematic work on heterogeneous catalysis which marked the rest of his career. Among the catalysis-related topics he studied in Munich were the kinetics of heterogeneously catalysed reactions, the nature of the heat of adsorption, the poisoning of catalysts and the spatial distribution of active catalytic sites. He also collaborated with his future wife Elly on her research about the influence of free radicals on parahydrogen, a work which they completed in Greece.
In the Kanellopoulos Institute (1939–1950), with the academic freedom he was given Schwab produced research on various occasional topics such as inorganic chromatography (which he is credited with inventing), turn-over transitions, carbon adsorption and properties of parahydrogen. He also built on his previous work with a series of kinetic studies, which eventually led to his theory on the electronic mechanisms of metal catalysis.
In later years, after returning to Munich as professor of physical chemistry, Schwab discovered the surface catalytic influence of a metal in contact with a semiconductor catalyst or an insulator in contact with a metal catalyst (occasionally referred to as Schwab effects of the 1st and of the 2nd type, respectively). | 7 | Physical Chemistry |
The concept of an acid–base reaction was first proposed in 1754 by Guillaume-François Rouelle, who introduced the word "base" into chemistry to mean a substance which reacts with an acid to give it solid form (as a salt). Bases are mostly bitter in nature. | 7 | Physical Chemistry |
The oxidized structure of CoQ is shown below. The various kinds of coenzyme Q may be distinguished by the number of isoprenoid subunits in their side-chains. The most common coenzyme Q in human mitochondria is CoQ. Q refers to the quinone head and "10" refers to the number of isoprene repeats in the tail. The molecule below has three isoprenoid units and would be called Q.
In its pure state, it is an orange-colored lipophile powder, and has no taste nor odor. | 1 | Biochemistry |
The same technique has been used to construct process maps for sintering, diffusion bonding, hot isostatic pressing, and indentation. | 8 | Metallurgy |
Chemotaxis assays are experimental tools for evaluation of chemotactic ability of prokaryotic or eukaryotic cells.
A wide variety of techniques have been developed. Some techniques are qualitative - allowing an investigator to approximately determine a cell's chemotactic affinity for an analyte - while others are quantitative, allowing a precise measurement of this affinity. | 1 | Biochemistry |
Caustic ingestion occurs when someone accidentally or deliberately ingests a caustic or corrosive substance. Depending on the nature of the substance, the duration of exposure and other factors it can lead to varying degrees of damage to the oral mucosa, the esophagus, and the lining of the stomach.
The severity of the injury can be determined by endoscopy of the upper digestive tract, although CT scanning may be more useful to determine whether surgery may be required.
During the healing process, strictures of the oesophagus may form, which may require therapeutic dilatation and insertion of a stent. | 8 | Metallurgy |
Cyanate esters are chemical compounds in which the hydrogen atom of the cyanic acid is replaced by an organyl group (for example aryl group). The resulting compound is termed a cyanate ester, with the formula , where R is an organyl group. Cyanate esters contain a monovalent cyanate group . | 0 | Organic Chemistry |
The deprotonation of carbon acids can proceed with either kinetic or thermodynamic reaction control. Kinetic controlled deprotonation requires a base that is sterically hindered and strong enough to remove the proton irreversibly. For example, in the case of phenylacetone, deprotonation can produce two different enolates. LDA has been shown to deprotonate the methyl group, which is the kinetic course of the deprotonation. To ensure the production of the kinetic product, a slight excess (1.1 equiv) of lithium diisopropylamide is used, and the ketone is added to the base at –78 °C. Because the ketone is quickly and quantitatively converted to the enolate and base is present in excess at all times, the ketone is unable to act as a proton shuttle to catalyze the gradual formation of the thermodynamic product. A weaker base such as an alkoxide, which reversibly deprotonates the substrate, affords the more thermodynamically stable benzylic enolate. An alternative to the weaker base is to use a strong base which is present at a lower concentration than the ketone. For instance, with a slurry of sodium hydride in THF or dimethylformamide (DMF), the base only reacts at the solution-solid interface. A ketone molecule might be deprotonated at the kinetic site. This enolate may then encounter other ketones and the thermodynamic enolate will form through the exchange of protons, even in an aprotic solvent which does not contain hydronium ions.
LDA can, however, act as a nucleophile under certain conditions. | 0 | Organic Chemistry |
More recently, it has been proposed as a near-carbon-neutral construction material. Its waterless and less energy-intensive production (in comparison with ordinary cement and regular concrete) makes it a potential alternative for high--emission portland-cement-based materials. Due to improvements in fabrication techniques, it can be produced in high quality and large quantities. Recyclable sulfur concrete sleepers are used in Belgium for the railways infrastructure, and are mass-produced locally. THIOTUBE is the brand name for certified acid-resistant DWF (dry weather flow) discharge pipes used in Belgium. | 8 | Metallurgy |
The binding and cyclizing of adenosine 5’ triphosphate (ATP) to the catalytic active site of the enzyme is coordinated by two metal cations. The catalytic activity of sAC is increase by the presence of manganese [Mn]. sAC magnesium [Mg] activity is regulated by calcium [Ca] which increases the affinity for ATP of mammalian sAC. In addition, bicarbonate [HCO] releases ATP-Mg substrate inhibition and increases V of the enzyme.
The open conformation state of sAC is reached when ATP, with Ca bound to its γ-phosphate binds with specific residues in the catalytic center of the enzyme. When the second metal – a Mg ion – binds to the α-phosphate of ATP leads to a conformational change of the enzyme: the close state. The change in conformation from open to close state induces esterification of the α-phosphate with the ribose in adenosine and the release of the β- and γ-phosphates, this leads to cyclizing. Hydrogencarbonate stimulates the enzyme’s V by promoting the allosteric change that leads to active site closure, recruitment of the catalytic Mg ion, and readjustment of the phosphates in the bound ATP. The activator bicarbonate binds to a site pseudo-symmetric to the active site and triggers conformational changes by recruiting Arg176 from the active site (see above - "structure"). Calcium increases substrate affinity by replacing the magnesium in the ion B site, which provides an anchoring point for the beta- and gamma-phosphates of the ATP substrate. | 1 | Biochemistry |
Walter Cox McCrone Jr. (June 9, 1916July 10, 2002) was an American chemist who worked extensively on applications of polarized light microscopy and is sometimes characterized as the "father of modern microscopy". He was also an expert in electron microscopy, crystallography, ultra-microanalysis, and particle identification. In 1960 he founded the McCrone Research Institute, a non-profit educational and research organization for microscopy based in Chicago.
McCrones crystallographic work on polymorphism and its pharmaceutical applications played a central role in the subsequent development of the field. To the general public, McCrone was best known for his work in forensic science, especially his analyses of the Vinland Map and the Shroud of Turin. In 2000 he received the American Chemical Societys National Award in Analytical Chemistry. | 3 | Analytical Chemistry |
It is common in E1 and S1 reactions for a poor leaving group to be transformed into a good one by protonation or complexation with a Lewis acid. Thus, it is by protonation before departure that a molecule can formally lose such poor leaving groups as hydroxide.
The same principle is at work in the Friedel-Crafts reaction. Here, a strong Lewis acid is required to generate either a carbocation from an alkyl halide in the Friedel-Crafts alkylation reaction or an acylium ion from an acyl halide.
In the vast majority of cases, reactions that involve leaving group activation generate a cation in a separate step, before either nucleophilic attack or elimination. For example, S1 and E1 reactions may involve an activation step, whereas S2 and E2 reactions generally do not. | 0 | Organic Chemistry |
In 2007, an MIT team successfully laser-cooled a macro-scale (1 gram) object to 0.8 K. In 2011, a team from the California Institute of Technology and the University of Vienna became the first to laser-cool a (10 μm x 1 μm) mechanical object to its quantum ground state. | 7 | Physical Chemistry |
Aerial respiration is the gulping of air at the surface of water to directly extract oxygen from the atmosphere. Aerial respiration evolved in fish that were exposed to more frequent hypoxia; also, species that engage in aerial respiration tend to be more hypoxia tolerant than those which do not air-breath during the hypoxia.
There are two main types of air breathing fish—facultative and non-facultative. Under normoxic conditions facultative fish can survive without having to breathe air from the surface of the water. However, non-facultative fish must respire at the surface even in normal dissolved oxygen levels because their gills cannot extract enough oxygen from the water.
Many air breathing freshwater teleosts use ABOs to effectively extract oxygen from air while maintaining functions of the gills. ABOs are modified gastrointestinal tracts, gas bladders, and labyrinth organs; they are highly vascularized and provide additional method of extracting oxygen from the air. Fish also use ABO for storing the retained oxygen. | 9 | Geochemistry |
After postdoctoral studies with Orville L. Chapman at the University of California, Los Angeles (UCLA) and habilitation at the Max Planck Institute for Medical Research in Heidelberg, he became Full Professor of Organic and Bioorganic Chemistry at UCLA in 1989. In 1992 he was appointed Professor of Organic Chemistry at ETH Zurich. He retired on 31 July 2017, and remained a research-active professor at ETH Zurich. On 16 March 2019, the German Chemical Society (Gesellschaft Deutscher Chemiker, GDCh) bestowed him with their highest recognition, Honorary Membership.
Diederich died on 23 September 2020 after a battle with cancer.
His research interests cover a wide range of topics:
* Molecular recognition in chemistry and biology.
* Modern medicinal chemistry: molecular recognition studies with biological receptors and X-ray structure-based design of nonpeptidic enzyme inhibitors. Examples of targets: plasmepsin II, IspE and IspF in the non-mevalonate pathway of isoprenoid biosynthesis (malaria); t-RNA guanine transglycosylase (shigellosis); trypanothione reductase (African sleeping sickness).
* Supramolecular nanosystems and nano-patterned surfaces.
* Advanced materials based on carbon-rich acetylenic molecular architecture: new organic super-acceptors and their inter- and intramolecular charge-transfer complexes, opto-electronic materials for molecular electronic circuitry, chiral macrocyclic and acyclic alleno-acetylenes, amplification of chirality and its transfer from the molecular to the macroscopic scale. | 0 | Organic Chemistry |
In the era when metals were analysed by spectrophotometry, many chelating ligands were developed that selectively formed brightly coloured complexes with particular metal ions. This methodology has been eclipsed with the introduction of inductively coupled plasma methodology. Salicylaldoxime can be used to selectively precipitate metal ions for gravimetric determination. It forms a greenish-yellow precipitate with copper at a pH of 2.6 in the presence of acetic acid. Under these conditions, this is the only metal that precipitates; at pH 3.3, nickel also precipitates. Iron (III) will interfere.
It has been used as an ionophore in ion selective electrodes, with good response to Pb and Ni. | 3 | Analytical Chemistry |
Muon spin spectroscopy is an atomic, molecular and condensed matter experimental technique that exploits nuclear detection methods. In analogy with the acronyms for the previously established spectroscopies NMR and ESR, muon spin spectroscopy is also known as µSR. The acronym stands for muon spin rotation, relaxation, or resonance, depending respectively on whether the muon spin motion is predominantly a rotation (more precisely a precession around a still magnetic field), a relaxation towards an equilibrium direction, or a more complex dynamic dictated by the addition of short radio frequency pulses. µSR does not require any radio-frequency technique to align the probing spin.
More generally speaking, muon spin spectroscopy includes any study of the interactions of the muons magnetic moment with its surroundings when implanted into any kind of matter. Its two most notable features are its ability to study local environments, due to the short effective range of muon interactions with matter, and the characteristic time-window (10 – 10 s) of the dynamical processes in atomic, molecular and condensed media. The closest parallel to µSR is "pulsed NMR", in which one observes time-dependent transverse nuclear polarization or the so-called "free induction decay" of the nuclear polarization. However, a key difference is that in µSR one uses a specifically implanted spin (the muons) and does not rely on internal nuclear spins.
Although particles are used as a probe, µSR is not a diffraction technique. A clear distinction between the µSR technique and those involving neutrons or X-rays is that scattering is not involved. Neutron diffraction techniques, for example, use the change in energy and/or momentum of a scattered neutron to deduce the sample properties. In contrast, the implanted muons are not diffracted but remain in a sample until they decay. Only a careful analysis of the decay product (i.e. a positron) provides information about the interaction between the implanted muon and its environment in the sample.
As with many of the other nuclear methods, µSR relies on discoveries and developments made in the field of particle physics. Following the discovery of the muon by Seth Neddermeyer and Carl D. Anderson in 1936, pioneer experiments on its properties were performed with cosmic rays. Indeed, with one muon hitting each square centimeter of the earth's surface every minute, the muons constitute the foremost constituent of cosmic rays arriving at ground level. However, µSR experiments require muon fluxes of the order of muons per second per square centimeter. Such fluxes can only be obtained in high-energy particle accelerators which have been developed during the last 50 years. | 7 | Physical Chemistry |
The fermentation reaction only involves two steps. Pyruvate is converted to acetaldehyde by Pdc and then acetaldehyde is converted to ethanol by alcohol dehydrogenase (Adh). There is no significant increase in the number of Pdc genes in Crabtree-positive compared to Crabtree-negative species and no correlation between number of Pdc genes and efficiency of fermentation. There are five Adh genes in S. cerevisiae. Adh1 is the major enzyme responsible for catalyzing the fermentation step from acetaldehyde to ethanol. Adh2 catalyzes the reverse reaction, consuming ethanol and converting it to acetaldehyde. The ancestral, or original, Adh had a similar function as Adh1 and after a duplication in this gene, Adh2 evolved a lower K for ethanol. Adh2 is believed to have increased yeast species tolerance for ethanol and allowed Crabtree-positive species to consume the ethanol they produced after depleting sugars. However, Adh2 and consumption of ethanol is not essential for aerobic fermentation. Sch. pombe and other Crabtree positive species do not have the ADH2' gene and consumes ethanol very poorly. | 1 | Biochemistry |
At least partly because TNFR2 has no intracellular death domain, TNFR2 is neuroprotective.
Patients with schizophrenia have increased levels of soluble tumor necrosis factor receptor 2 (sTNFR2). | 1 | Biochemistry |
In congestive heart failure, the ability of the heart to pump enough blood to satisfy the physiological needs of the body is reduced. This condition has a variety of causes, including damaged heart valves, myocardial infarction, hypertension, vitamin B deficiency, and genetic mutations. When subsequent blood flow to the kidneys is reduced, the kidneys respond by increasing the secretion of renin from the juxtaglomerular apparatus. Renin converts the inactive angiotensinogen into angiotensin I, which is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE). AII can have negative effects on the cardiovascular system after events such as heart failure and myocardial infarction. AII causes arterial vasoconstriction and hypertension, resulting in an increase in afterload, increasing the resistance against which the heart works. Additionally, chronic increase in production of AII is associated with structural changes to the myocardium which reduces the functionality of the heart.
In heart failure patients, fosinopril increases exercise tolerance and lowers the frequency of events associated with worsening heart failure, such as dyspnea, the need for supplemental diuretics, fatigue, and hospitalizations. | 4 | Stereochemistry |
Hydrophobic insecticides and herbicides tend to be more active. Hydrophobic agrochemicals in general have longer half-lives and therefore display increased risk of adverse environmental impact. | 7 | Physical Chemistry |
Two coils in an anti-Helmholtz configuration are used to generate a weak quadrupolar magnetic field; here, we will consider the coils as being separated along the -axis. In the proximity of the field zero, located halfway between the two coils along the -direction, the field gradient is uniform and the field itself varies linearly with position. For this discussion, consider an atom with ground and excited states with and , respectively, where is the magnitude of the total angular momentum vector. Due to the Zeeman effect, these states will each be split into sublevels with associated values of , denoted by (note that the Zeeman shift for the ground state is zero and that it will not be split into sublevels by the field). This results in spatially-dependent energy shifts of the excited-state sublevels, as the Zeeman shift is proportional to the field strength and in this configuration the field strength is linear in position. As a note, the Maxwell equation implies that the field gradient is twice as strong along the -direction than in the and -directions, and thus the trapping force along the -direction is twice as strong.
In combination with the magnetic field, pairs of counter-propagating circularly-polarized laser beams are sent in along three orthogonal axes, for a total of six MOT beams (there are exceptions to this, but a minimum of five beams is required to make a 3D MOT). The beams are red-detuned from the transition by an amount such that , or equivalently, , where is the frequency of the laser beams and is the frequency of the transition. The beams must be circularly polarized to ensure that photon absorption can only occur for certain transitions between the ground state and the sublevels of the excited state , where . In other words, the circularly-polarized beams enforce selection rules on the allowed electric dipole transitions between states.
At the center of the trap, the magnetic field is zero and atoms are "dark" to incident red-detuned photons. That is, at the center of the trap, the Zeeman shift is zero for all states and so the transition frequency from remains unchanged. The detuning of the photons from this frequency means that there will not be an appreciable amount of absorption (and therefore emission) by atoms in the center of the trap, hence the term "dark". Thus, the coldest, slowest moving atoms accumulate in the center of the MOT where they scatter very few photons.
Now consider an atom which is moving in the -direction. The Zeeman effect shifts the energy of the state lower in energy, decreasing the energy gap between it and the state; that is, the frequency associated with the transition decreases. Red-detuned photons, which only drive transitions, propagating in the -direction thus become closer to resonance as the atom travels further from the center of the trap, increasing the scattering rate and scattering force. When an atom absorbs a photon, it is excited to the state and gets a "kick" of one photon recoil momentum, , in the direction opposite to its motion, where . The atom, now in an excited state, will then spontaneously emit a photon in a random direction and after many absorption-spontaneous emission events, the atom will have, on average, been "pushed" back towards the field-zero of the trap. This trapping process will also occur for an atom moving in the -direction if photons are traveling in the -direction, the only difference being that the excitation will be from to <math>|J=1,m_J
=+1\rangle. Since the magnetic field gradient near the trap center is uniform, the same phenomenon of trapping and cooling occurs along the and -directions as well.
Mathematically, the radiation pressure force that atoms experience in a MOT is given by:
where is the damping coefficient, is the Landé g-factor and is the Bohr magneton. | 7 | Physical Chemistry |
Restriction enzymes likely evolved from a common ancestor and became widespread via horizontal gene transfer. In addition, there is mounting evidence that restriction endonucleases evolved as a selfish genetic element. | 1 | Biochemistry |
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