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When encapsulating hydrophobic or potentially toxic materials it is important that the encapsulant remain intact while inside the body. Studying the rheological properties of the micelles permits identification and selection of the polymer that is most appropriate for use in long-term biological applications. R-PEG exhibits superior rheological properties when used in vivo. | 7 | Physical Chemistry |
Viruses can be spread by direct transfer of sap by contact of a wounded plant with a healthy one. Such contact may occur during agricultural practices, as by damage caused by tools or hands, or naturally, as by an animal feeding on the plant. Generally TMV, potato viruses and cucumber mosaic viruses are transmitted via sap. | 1 | Biochemistry |
The steam reforming, shift conversion, carbon dioxide removal, and methanation steps each operate at absolute pressures of about 25 to 35 bar, while the ammonia synthesis loop operates at temperatures of and pressures ranging from 60 to 180 bar depending upon the method used. The resulting ammonia must then be separated from the residual hydrogen and nitrogen at temperatures of . | 7 | Physical Chemistry |
GPCRs become desensitized when exposed to their ligand for a long period of time. There are two recognized forms of desensitization: 1) homologous desensitization, in which the activated GPCR is downregulated; and 2) heterologous desensitization, wherein the activated GPCR causes downregulation of a different GPCR. The key reaction of this downregulation is the phosphorylation of the intracellular (or cytoplasmic) receptor domain by protein kinases. | 1 | Biochemistry |
There exist many different conformations for cyclohexane, such as chair, boat, and twist-boat, but the chair conformation is the most commonly observed state for cyclohexanes because it requires the least amount of energy. The chair conformation minimizes both angle strain and torsional strain by having all carbon-carbon bonds at 110.9° and all hydrogens staggered from one another.
The molecular motions involved in a chair flip are detailed in the figure on the right: The half-chair conformation (D, 10.8 kcal/mol, C symmetry) is the energy maximum when proceeding from the chair conformer (A, 0 kcal/mol reference, D symmetry) to the higher energy twist-boat conformer (B, 5.5 kcal/mol, D symmetry). The boat conformation (C, 6.9 kcal/mol, C symmetry) is a local energy maximum for the interconversion of the two mirror image twist-boat conformers, the second of which is converted to the other chair confirmation through another half-chair. At the end of the process, all axial positions have become equatorial and vice versa. The overall barrier of 10.8 kcal/mol corresponds to a rate constant of about 10 s at room temperature.
Note that the twist-boat (D) conformer and the half-chair (C) transition state are in chiral point groups and are therefore chiral molecules. In the figure, the two depictions of B and two depictions of D are pairs of enantiomers.
As a consequence of the chair flip, the axially-substituted and equatorially-substituted conformers of a molecule like chlorocyclohexane cannot be isolated at room temperature. However, in some cases, the isolation of individual conformers of substituted cyclohexane derivatives has been achieved at low temperatures (–150 °C). | 4 | Stereochemistry |
Early African miners used copper oxides and carbonates rather than sulfides, because they were able to reduce oxides and carbonates to copper metal, but not sulfides. Sulfides were more complex to reduce to metal and required multiple stages. Complex deep-mining methods and special tools were not needed, because oxides were structurally weakened by decomposition processes and contained the most desirable ores, and although the techniques used seemed to be simple, Africans were very successful in extracting large quantities of high-grade ore.
The copper mines themselves were most frequently open stopes or open stopes with shafts. Shafts were rare in African copper mining. There are several ethnographic accounts of African copper mining techniques, and they all seem to be on the same technological level. Any variation depended upon different geological circumstances and capabilities of the miners.
There are more variations of copper smelting than there are of mining, and most of the observations and photos that were taken are in major copper producing areas. There is a lack of evidence of smelting in West Africa; however casting continued to be present and is well documented. The most common ore in Africa is malachite and it was used mainly with hardwood charcoal the smelting process. | 8 | Metallurgy |
An opioidergic agent (or drug) is a chemical which functions to directly modulate the opioid neuropeptide systems (i.e., endorphin, enkephalin, dynorphin, nociceptin) in the body or brain. Examples include opioid analgesics such as morphine and opioid antagonists such as naloxone. Opioidergics also comprise allosteric modulators and enzyme affecting agents like enkephalinase inhibitors. | 1 | Biochemistry |
Burks is a popular science communicator, using pop culture as an anchor to explore chemistry. She appeared on the Science Channels Outrageous Acts of Science and Reactions, the video series for the American Chemical Society. She has appeared on Mother Jones Inquiring Minds podcast to share how chemistry can save you from a zombie apocalypse and on The Story Collider podcast with a story from her time working in a crime lab. In early 2020, she appeared on the NPR [https://www.npr.org/podcasts/510351/short-wave Short Wave] podcast on the episode "A Short Wave Guide to Good - and Bad - TV Forensics". Burks has also contributed to scientific interest pieces for St. Andrew University on using chemistry in every day life. Her writing has been featured in Slate, The Washington Post, UNDARK, and Chemistry World.
Burks is also an advocate for women and underrepresented groups in science, speaking from her experiences as a black woman in STEM. In 2018, Burks was a co-principal investigator for a $1.5 million NSF STEM grant to fund the establishment of the St. Andrew's Institute for Interdisciplinary Science (I4), which would promote internships and research opportunities for underrepresented groups in STEM. She founded the DIYSciZone at [https://geekgirlcon.com/ GeekGirlCon], bringing scientists and science educators together to give convention attendees hands-on experiences with science experiments. The citation for her American Chemical Society [https://www.acs.org/content/acs/en/pressroom/newsreleases/2019/october/raychelle-burks-phd-wins-acs-grady-stack-award-for-science-communication.html#:~:text=1%2C%202019%20%E2%80%94%20Raychelle%20Burks%2C,News%20Service%20Directors%20James%20T. Grady-Stack award] read, “Raychelle is a public-scientist extraordinaire... She inspires a love of chemistry by bringing chemistry directly to where her audience is. This direct engagement — her commitment to finding chemistry that can entertain and enlighten people who wouldn’t normally think of science — is nothing short of phenomenal". Burks is active on social media to promote her field and fellow scientists.
In 2020, Burks appeared in the Tribeca Film Festival in the film "Picture a Scientist." | 3 | Analytical Chemistry |
In 1990, Asemota moved to Jamaica to take up a position as Associate Honorary Lecturer at the University of the West Indies. She was appointed Lecturer in 1996, and promoted to Senior Lecturer in Biochemistry and Biotechnology in 1998. In 2003, Asemota was promoted to Professor of Biochemistry and Molecular Biology. She was Full Professor at the Shaw University, North Carolina from 2005 to 2012. During this time she was Head of the Nanobiology Division of the Shaw Nanotechnology Initiative at the Nanoscience and Nanotechnology Research Centre (NNRC) from 2005 to 2009, Nature Sciences Biological Sciences' Program Coordinator from 2009 to 2010, and Chairman for the Shaw University Institutional Review Board (IRB) from 2006 to 2009, Senator for the Shaw Faculty Senate between 2007 and 2012, Core Director of the Faculty Research Development at the NIH- Research Infrastructure for Minority Institutions and as IRB Administrator between 2010 and 2012.
In 2013, Asemota was appointed Director of the Biotechnology Centre, a research unit at the University of the West Indies with a focus on biotechnology-based enterprises.
At the time of her promotion to Professor in 2003, Asemota was a member of the Caribbean Biotechnology Network, the Biochemical Society of Nigeria, the Third World Organisation for Women in Science, and the Nigerian Association of Women in Science, Technology & Mathematics. She was a Fellow of the American Biographical Institute, a member of the National Geographic Society, the Nigerian Institute of Food Science and Technology, and the New York Academy of Science. | 1 | Biochemistry |
Floral scent is often composed of hundreds of VOCs, in very variable proportions. The method used is a tradeoff between accurately detecting quantifying minor compounds and avoiding detector saturation by major compounds. For most analysis methods routinely used, the detection threshold of many VOCs is still higher than the perception threshold of insects, which reduces our capacity to understand plant-insect interactions mediated by floral scent.
Further, the chemical diversity in floral scent samples is challenging. The time of analysis is proportional to the range in molecular weight of VOCs present in the sample, hence a high diversity will increase analysis time. Floral scent may also be composed of very similar molecules, such as isomers and especially enantiomers, which tend to co-elute and then to be very hardly separated. Unambiguously detecting and quantifying them is of importance though, as enantiomers may trigger very different responses in pollinators. | 1 | Biochemistry |
The Russian Journal of Physical Chemistry A: Focus on Chemistry () is an English-language translation of the eponymous Russian-language peer-reviewed scientific journal published by Springer Science+Business Media on behalf of Pleiades Publishing. It was established in 1930 and focuses on review articles pertaining to global coverage of all theory and experiment in physical chemistry. The editor-in-chief is Aslan Yu. Tsivadze (Russian Academy of Sciences). | 7 | Physical Chemistry |
Amphetamine and its enantiomers have been identified as potent full agonists of trace amine-associated receptor 1 (TAAR1), a GPCR, discovered in 2001, that is important for regulation of monoaminergic systems in the brain. Activation of TAAR1 increases cAMP production via adenylyl cyclase activation and inhibits the function of the dopamine transporter, norepinephrine transporter, and serotonin transporter, as well as inducing the release of these monoamine neurotransmitters (effluxion). Amphetamine enantiomers are also substrates for a specific neuronal synaptic vesicle uptake transporter called VMAT2. When amphetamine is taken up by VMAT2, the vesicle releases (effluxes) dopamine, norepinephrine, and serotonin, among other monoamines, into the cytosol in exchange.
Dextroamphetamine (the dextrorotary enantiomer) and levoamphetamine (the levorotary enantiomer) have identical pharmacodynamics, but their binding affinities to their biomolecular targets vary. Dextroamphetamine is a more potent agonist of TAAR1 than levoamphetamine. Consequently, dextroamphetamine produces roughly three to four times more central nervous system (CNS) stimulation than levoamphetamine; however, levoamphetamine has slightly greater cardiovascular and peripheral effects. | 4 | Stereochemistry |
Ocean acidification threatens the Great Barrier Reef by reducing the viability and strength of coral reefs. The Great Barrier Reef, considered one of the seven natural wonders of the world and a biodiversity hotspot, is located in Australia. Similar to other coral reefs, it is experiencing degradation due to ocean acidification. Ocean acidification results from a rise in atmospheric carbon dioxide, which is taken up by the ocean. This process can increase sea surface temperature, decrease aragonite, and lower the pH of the ocean. The more humanity consumes fossil fuels, the more the ocean absorbs released CO₂, furthering ocean acidification.
This decreased health of coral reefs, particularly the Great Barrier Reef, can result in reduced biodiversity. Organisms can become stressed due to ocean acidification and the disappearance of healthy coral reefs, such as the Great Barrier Reef, is a loss of habitat for several taxa. | 9 | Geochemistry |
The principle of this method is based on the nucleic acid-binding properties of silica particles or diatoms in the presence of a chaotropic agent, which follows the chaotropic effect.
Put simply, the chaotropic effect is where a chaotropic anion in an aqueous solution disturbs the structure of water, and weakens the hydrophobic interaction.
According to the chaotropic effect,
in the presence of the chaotropic agent, hydration water of nucleic acids are taken from the phosphodiester bond of the phosphate group of the backbone of a nucleic acid. Thus, the phosphate group becomes "exposed" and hydrophobic interaction between silica and exposed phosphate group are formed. | 1 | Biochemistry |
Actinic inspection of masks in computer chip manufacture refers to inspecting the mask with the same wavelength of light that the lithography system will use. | 7 | Physical Chemistry |
Cell–cell fusogens have several different applications. These chemical agents can play a significant part in sexual and asexual reproduction by promoting the fusion of the membrane bilayers. With sexual reproduction, evidence found to prove that in mice, some mandatory sperm-egg fusogens are responsible for fusion; two particular proteins were IZUMO1 and CD9. After comparing the data of experiments done with plants, fungi, and invertebrates, it was seen that several crucial genes could have been responsible for fertilization. However, like yeasts, there were no genes found to be adequate for the fertilization process. As of late, another protein has been classified as a gamete fusogen (HAP2 or GCS1). Like the previous example, this protein is present in plants, protists, and invertebrates. This fusogen resembles the eukaryotic somatic fusogen mentioned earlier, EFF-1. The presence of HAP2 induces hemifusion and the mixing of cell content. Yet when considering asexual reproduction, somatic cells can also undergo cell-cell fusion or self-fusion. Two particular fusogens observed were SO and MAK-2. Evidence supports that these proteins control and regulate efficient protein concentration and localization. | 1 | Biochemistry |
Another approach to improving media sensitivity has been to employ resonant two-photon absorption (also known as "1+1" or "sequential" two–photon absorbance). Nonresonant two-photon absorption (as is generally used) is weak since in order for excitation to take place, the two exciting photons must arrive at the chromophore at almost exactly the same time. This is because the chromophore is unable to interact with a single photon alone. However, if the chromophore has an energy level corresponding to the (weak) absorption of one photon then this may be used as a stepping stone, allowing more freedom in the arrival time of photons and therefore a much higher sensitivity. However, this approach results in a loss of nonlinearity compared to nonresonant two–photon absorbance (since each two-photon absorption step is essentially linear), and therefore risks compromising the 3D resolution of the system. | 5 | Photochemistry |
Gill remodelling happens in only a few species of fish, and it involves the buildup or removal of an inter-lamellar cell mass (ILCM). As a response to hypoxia, some fish are able to remodel their gills to increase respiratory surface area, with some species such as goldfish doubling their lamellar surface areas in as little as 8 hours. The increased respiratory surface area comes as a trade-off with increased metabolic costs because the gills are a very important site for many important processes including respiratory gas exchange, acid-base regulation, nitrogen excretion, osmoregulation, hormone regulation, metabolism, and environmental sensing.
The crucian carp is one species able to remodel its gill filaments in response to hypoxia. Their inter-lamellar cells have high rates of mitotic activity which are influenced by both hypoxia and temperature. In cold (15 °C) water the crucian carp has more ILCM, but when the temperature is increased to 25 °C the ILCM is removed, just as it would be in hypoxic conditions. This same transition in gill morphology occurs in the goldfish when the temperature was raised from 7.5 °C to 15 °C. This difference may be due to the temperature regimes that these fish are typically found in, or there could be an underlying protective mechanism to prevent a loss of ion balance in stressful temperatures. Temperature also affects the speed at which the gills can be remodelled: for example, at 20 °C in hypoxia, the crucian carp can completely remove its ILCM in 6 hours, whereas at 8 °C, the same process takes 3–7 days. The ILCM is likely removed by apoptosis, but it is possible that when the fish is faced with the double stress of hypoxia at high temperature, the lamellae may be lost by physical degradation. Covering the gill lamellae may protect species like the crucian carp from parasites and environmental toxins during normoxia by limiting their surface area for inward diffusion while still maintaining oxygen transport due to an extremely high hemoglobin oxygen binding affinity.
The naked carp, a closely related species native to the high-altitude Lake Qinghai, is also able to remodel their gills in response to hypoxic conditions. In response to oxygen levels 95% lower than normoxic conditions, apoptosis of ILCM increases lamellar surface area by up to 60% after just 24 hours. However, this comes at a significant osmoregulatory cost, reducing sodium and chloride levels in the cytoplasm by over 10%. The morphological response to hypoxia by scaleless carp is the fastest respiratory surface remodelling reported in vertebrates thus far. | 9 | Geochemistry |
MAO is prepared by the incomplete hydrolysis of trimethylaluminium, as indicated by this idealized equation
:n Al(CH) + n HO → (Al(CH)O) + 2n CH
Diverse mechanisms have been proposed for the formation of MAO. Well defined analogues of MAO can be generated with tert-butyl substituents. | 7 | Physical Chemistry |
Dr. Norbert Bischofberger (born 10 January 1956 in Mellau, Austria) is an Austrian scientist and one of the inventors of the antiviral drug Tamiflu generically known as oseltamivir, which is, as of 2009, the only oral medication on the market to treat influenza A and B as well as the 2009 Pandemic H1N1 (swine flu), the spread of which caused an ongoing pandemic in 2009. Bischofberger is currently the President & Chief Executive Officer of Kronos Bio, and previously was the Executive Vice President, Research and Development and Chief Scientific Officer at Gilead Sciences, a biopharmaceutical company specializing in antivirals. | 0 | Organic Chemistry |
Low-volume/high-velocity (LVHV) capture systems are specialised types of LEV that use an extractor hood designed as an integral part of the tool or positioned very close to the operating point of the cutting tool. The hood is designed to provide high capture velocities, often greater than 50 m/s (10,000 fpm) at the contaminant release point. This high velocity is accompanied by airflows often less than 0.02m3/s (50 cfm) resulting from the small face area of the hood that is used. These systems have come into favour for portable power tools, although adoption of the technology is not widespread. Festool is one manufacturer of portable power tools using LVHV ventilation integrated into the tool design. | 2 | Environmental Chemistry |
The hardness of local water supplies depends on the source of water. Water in streams flowing over volcanic (igneous) rocks will be soft, while water from boreholes drilled into porous rock is normally very hard. | 3 | Analytical Chemistry |
One of the major concerns associated with telomere lengthening is the potential for increased cancer risk. Telomeres naturally shorten with each cell division and act as a tumor suppressor mechanism. Extending telomeres can allow cells to divide more and increase the risk of uncontrolled cell growth and cancer development. A study conducted by Johns Hopkins University challenged the idea that long telomeres prevent aging. Rather than protecting cells from aging, long telomeres help cells with age-related mutations last longer. This problem prepares the conditions for the occurrence of various types of cancer, and people with longer cell telomeres showed more signs of suffering from types of cancer such as Melanoma and Lymphoma. | 1 | Biochemistry |
The Kröhnke synthesis for making pyridines possesses a number of succinct advantages over other methods. Unlike the Hantzsch synthesis, the Kröhnke method does not require oxidation to generate the desired product since the α-pyridinium methyl ketone already possesses the correct oxidation state.
Another advantage of the Kröhnke synthesis is its high atom economy. For example, the Chichibabin synthesis requires 2 equivalents of unsaturated starting material. Additionally, the byproducts of the Kröhnke synthesis is water and pyridine, which allow for easy workup and purification protocols. Unlike comparable methods for pyridine synthesis, the Kröhkne synthesis benefits from being a high-yielding one pot synthesis, which ultimately allows for abbreviation of synthetic pathways and further simplifies combinatorial library cataloging. | 0 | Organic Chemistry |
The ages of domestic cats and dogs are often referred to in terms of "cat years" or "dog years", representing a conversion to human-equivalent years. One formula for cat years is based on a cat reaching maturity in approximately 1 year, which could be seen as 16 in human terms, then adding about 4 years for every year the cat ages. A 5-year-old cat would then be (5 − 1) × 4 + 16 = 32 "cat years" (i.e. human-equivalent years), and a 10-year-old cat (10 − 1) × 4 + 16 = 52 in human terms. | 1 | Biochemistry |
Untreated organic matter that contains fecal coliform can be harmful to the environment. Aerobic decomposition of this material can reduce dissolved oxygen levels if discharged into rivers or waterways. This may reduce the oxygen level enough to kill fish and other aquatic life. Reduction of fecal coliform in wastewater may require the use of chlorine and other disinfectant chemicals, or UV disinfection treatment. Such materials may kill the fecal coliform and disease bacteria. They also kill bacteria essential to the proper balance of the aquatic environment, endangering the survival of species dependent on those bacteria. So higher levels of fecal coliform require higher levels of chlorine, threatening those aquatic organisms. | 3 | Analytical Chemistry |
The lost-wax casting process may also be used in the production of cast glass sculptures. The original sculpture is made from wax. The sculpture is then covered with mold material (e.g., plaster), except for the bottom of the mold which must remain open. When the mold has hardened, the encased sculpture is removed by applying heat to the bottom of the mold. This melts out the wax (the wax is lost) and destroys the original sculpture. The mold is then placed in a kiln upside down with a funnel-like cup on top that holds small chunks of glass. When the kiln is brought up to temperature (1450-1530 degrees Fahrenheit), the glass chunks melt and flow down into the mold. Annealing time is usually 3–5 days, and total kiln time is 5 or more days. After the mold is removed from the kiln, the mold material is removed to reveal the sculpture inside. | 8 | Metallurgy |
Booth designed an electromechanical computer, the ARC (Automatic Relay Computer), in the late 1940s (1947-1948). Later on, they built an experimental electronic computer named SEC (Simple Electronic Computer, designed around 1948-1949) - and finally, the APE(X)C (All-Purpose Electronic Computer) series.
The computers were programmed by Kathleen. | 3 | Analytical Chemistry |
In quantum mechanics, the Hellmann–Feynman theorem relates the derivative of the total energy with respect to a parameter to the expectation value of the derivative of the Hamiltonian with respect to that same parameter. According to the theorem, once the spatial distribution of the electrons has been determined by solving the Schrödinger equation, all the forces in the system can be calculated using classical electrostatics.
The theorem has been proven independently by many authors, including Paul Güttinger (1932), Wolfgang Pauli (1933), Hans Hellmann (1937) and Richard Feynman (1939).
The theorem states
where
* is a Hermitian operator depending upon a continuous parameter ,
*, is an eigenstate (eigenfunction) of the Hamiltonian, depending implicitly upon ,
* is the energy (eigenvalue) of the state , i.e. .
Note that there is a breakdown of the Hellmann-Feynman theorem close to quantum critical points in the thermodynamic limit. | 6 | Supramolecular Chemistry |
* "Alloy White Cast Iron" U.S. Patent 3623922, November 10, 1971.
* "Annealing Process Control Method and Apparatus", U.S. Patent 4595427, June 17, 1986.
* "Annealing Process Control Method and Apparatus", Canadian Patent 1,225,522, August 18, 1987. | 8 | Metallurgy |
Exemestane is quickly absorbed from the gut, but undergoes a strong first-pass effect in the liver. Highest blood plasma concentrations are reached after 1.2 hours in breast cancer patients and after 2.9 hours in healthy subjects. Maximal aromatase inhibition occurs after two to three days. 90% of the absorbed substance are bound to plasma proteins. The liver enzyme CYP3A4 oxidizes the methylidene group in position 6, and the 17-keto group (on the five-membered ring) is reduced by aldo-keto reductases to an alcohol. Of the resulting metabolites, 40% are excreted via the urine and 40% via the feces within a week. The original substance accounts for only 1% of excretion in the urine. The terminal half-life is 24 hours. | 4 | Stereochemistry |
In 1946, Leo Sommer and Frank C. Whitmore reported that radically chlorinating liquid ethyltrichlorosilane gave an isomeric mixture with exhibited unexpected reactivity in aqueous base. All chlorides pendant to silicon hydrolyze, but the geminal chlorine on carbon failed to hydrolyze, and the vicinal chlorine eliminated to ethene: The same behavior appeared with n-propyltrichlorosilane. The α and γ isomers resisted hydrolysis, but a hydroxyl group replaced the β chlorine: They concluded that silicon inhibits electrofugal activity at the α carbon.
The silicon effect also manifests in certain compound properties. Trimethylsilylmethylamine (MeSiCHNH) is a stronger base (conjugate pK 10.96) than neopentylamine (conjugate pK 10.21); trimethylsilylacetic acid (pKa 5.22) is a poorer acid than trimethylacetic acid (pKa 5.00).
In 1994, Yong and coworkers compared the free-energy effects of α- and β-Si(CH) moieties on C–H homo- and heterolysis. They, too, concluded that the β silicon atom could stabilize carbocations and the α silicon destabilize carbocations. | 7 | Physical Chemistry |
Persons are generally warned not to enter or drink water from algal blooms, or let their pets swim in the water since many pets have died from algal blooms. In at least one case, people began getting sick before warnings were issued. There is no treatment available for animals, including livestock cattle, if they drink from algal blooms where such toxins are present. Pets are advised to be kept away from algal blooms to avoid contact.
In some locations visitors have been warned not to even touch the water. Boaters have been told that toxins in the water can be inhaled from the spray from wind or waves. Ocean beaches, lakes and rivers have been closed due to algal blooms. After a dog died in 2015 from swimming in a bloom in California's Russian River, officials likewise posted warnings for parts of the river. Boiling the water at home before drinking does not remove the toxins.
In August 2014 the city of Toledo, Ohio advised its 500,000 residents to not drink tap water as the high toxin level from an algal bloom in western Lake Erie had affected their water treatment plant's ability to treat the water to a safe level. The emergency required using bottled water for all normal uses except showering, which seriously affected public services and commercial businesses. The bloom returned in 2015 and was forecast again for the summer of 2016.
In 2004, a bloom in Kisumu Bay, which is the drinking water source for 500,000 people in Kisumu, Kenya, suffered from similar water contamination. In China, water was cut off to residents in 2007 due to an algal bloom in its third largest lake, which forced 2 million people to use bottled water. A smaller water shut-down in China affected 15,000 residents two years later at a different location. Australia in 2016 also had to cut off water to farmers.
Alan Steinman of Grand Valley State University has explained that among the major causes for the algal blooms in general, and Lake Erie specifically, is because blue-green algae thrive with high nutrients, along with warm and calm water. Lake Erie is more prone to blooms because it has a high nutrient level and is shallow, which causes it to warm up more quickly during the summer.
Symptoms from drinking toxic water can show up within a few hours after exposure. They can include nausea, vomiting, and diarrhea, or trigger headaches and gastrointestinal problems. Although rare, liver toxicity can cause death. Those symptoms can then lead to dehydration, another major concern. In high concentrations, the toxins in the algal waters when simply touched can cause skin rashes, irritate the eyes, nose, mouth or throat. Those with suspected symptoms are told to call a doctor if symptoms persist or they can't hold down fluids after 24 hours.
In studies at the population level bloom coverage has been significantly related to the risk of non-alcoholic liver disease death. | 3 | Analytical Chemistry |
Bioluminescence is produced by the dinoflagellate Pyrodinium bahamense, which glows blue when agitated. Although the phytoplankton responsible for the phenomenon of bioluminescence is found throughout the Antilles, Puerto Mosquito is one of the seven year-round bioluminescent bays in the Caribbean. The bioluminescence is the product of a number of factors: the water conditions and ecosystem created by the surrounding mangrove forest (mostly Rhizophora mangle), the complete lack of modern development in the lagoon, the temperature of the water and the depth of the bay. | 1 | Biochemistry |
Pol I is a 590 kDa enzyme that consists of 14 protein subunits (polypeptides), and its crystal structure in the yeast Saccharomyces cerevisiae was solved at 2.8Å resolution in 2013. Twelve of its subunits have identical or related counterparts in RNA polymerase II (Pol II) and RNA polymerase III (Pol III). The other two subunits are related to Pol II initiation factors and have structural homologues in Pol III.
Ribosomal DNA transcription is confined to the nucleolus, where about 400 copies of the 42.9-kb rDNA gene are present, arranged as tandem repeats in nucleolus organizer regions. Each copy contains a ~13.3 kb sequence encoding the 18S, the 5.8S, and the 28S RNA molecules, interlaced with two internal transcribed spacers, ITS1 and ITS2, and flanked upstream by a 5 external transcribed spacer and a downstream 3 external transcribed spacer. These components are transcribed together to form the 45S pre-rRNA. The 45S pre-rRNA is then post-transcriptionally cleaved by C/D box and H/ACA box snoRNAs, removing the two spacers and resulting in the three rRNAs by a complex series of steps. The 5S ribosomal RNA is transcribed by Pol III. Because of the simplicity of Pol I transcription, it is the fastest-acting polymerase and contributes up to 60% of cellular transcription levels in exponentially growing cells.
In Saccharomyces cerevisiae, the 5S rDNA has the unusual feature of lying inside the rDNA repeat. It is flanked by non-transcribed spacers NTS1 and NTS2, and is transcribed backwards by Pol III, separately from the rest of the rDNA. | 1 | Biochemistry |
NANOG is a transcription factor in embryonic stem cells (ESCs) and is thought to be a key factor in maintaining pluripotency. NANOG is thought to function in concert with other factors such as POU5F1 (Oct-4) and SOX2 to establish ESC identity. These cells offer an important area of study because of their ability to maintain pluripotency. In other words, these cells have the ability to become virtually any cell of any of the three germ layers (endoderm, ectoderm, mesoderm). It is for this reason that understanding the mechanisms that maintain a cell's pluripotency is critical for researchers to understand how stem cells work, and may lead to future advances in treating degenerative diseases.
NANOG has been described to be expressed in the posterior side of the epiblast at the onset of gastrulation. There, NANOG has been implicated in inhibiting embryonic hematopoiesis by repressing the expression of the transcription factor Tal1. In this embryonic stage, NANOG represses Pou3f1, a transcription factor crucial for the anterior-posterior axis formation.
Analysis of arrested embryos demonstrated that embryos express pluripotency marker genes such as POU5F1, NANOG and Rex1. Derived human ESC lines also expressed specific pluripotency markers:
*TRA-1-60
*TRA-1-81
*SSEA4
*alkaline phosphatase
*TERT
*Rex1
These markers allowed for the differentiation in vitro and in vivo conditions into derivatives of all three germ layers.
POU5F1, TDGF1 (CRIPTO), SALL4, LECT1, and BUB1 are also related genes all responsible for self-renewal and pluripotent differentiation.
The NANOG protein has been found to be a transcriptional activator for the Rex1 promoter, playing a key role in sustaining Rex1 expression. Knockdown of NANOG in embryonic stem cells results in a reduction of Rex1 expression, while forced expression of NANOG stimulates Rex1 expression.
Besides the effects of NANOG in the embryonic stages of life, ectopic expression of NANOG in the adult stem cells can restore the proliferation and differentiation potential that is lost due to organismal aging or cellular senescence. | 1 | Biochemistry |
The added complexity of generating a eukaryotic cell carries with it an increase in the complexity of transcriptional regulation. Eukaryotes have three RNA polymerases, known as Pol I, Pol II, and Pol III. Each polymerase has specific targets and activities, and is regulated by independent mechanisms. There are a number of additional mechanisms through which polymerase activity can be controlled. These mechanisms can be generally grouped into three main areas:
*Control over polymerase access to the gene. This is perhaps the broadest of the three control mechanisms. This includes the functions of histone remodeling enzymes, transcription factors, enhancers and repressors, and many other complexes
*Productive elongation of the RNA transcript. Once polymerase is bound to a promoter, it requires another set of factors to allow it to escape the promoter complex and begin successfully transcribing RNA.
*Termination of the polymerase. A number of factors which have been found to control how and when termination occurs, which will dictate the fate of the RNA transcript.
All three of these systems work in concert to integrate signals from the cell and change the transcriptional program accordingly.
While in prokaryotic systems the basal transcription state can be thought of as nonrestrictive (that is, “on” in the absence of modifying factors), eukaryotes have a restrictive basal state which requires the recruitment of other factors in order to generate RNA transcripts. This difference is largely due to the compaction of the eukaryotic genome by winding DNA around histones to form higher order structures. This compaction makes the gene promoter inaccessible without the assistance of other factors in the nucleus, and thus chromatin structure is a common site of regulation. Similar to the sigma factors in prokaryotes, the general transcription factors (GTFs) are a set of factors in eukaryotes that are required for all transcription events. These factors are responsible for stabilizing binding interactions and opening the DNA helix to allow the RNA polymerase to access the template, but generally lack specificity for different promoter sites. A large part of gene regulation occurs through transcription factors that either recruit or inhibit the binding of the general transcription machinery and/or the polymerase. This can be accomplished through close interactions with core promoter elements, or through the long distance enhancer elements.
Once a polymerase is successfully bound to a DNA template, it often requires the assistance of other proteins in order to leave the stable promoter complex and begin elongating the nascent RNA strand. This process is called promoter escape, and is another step at which regulatory elements can act to accelerate or slow the transcription process. Similarly, protein and nucleic acid factors can associate with the elongation complex and modulate the rate at which the polymerase moves along the DNA template. | 1 | Biochemistry |
Scar sequences are common in multiple segment DNA assembly. In the multisegment assembly method Gateway, segments are added into the donor with additional ATT sequences, which overlap in those added segments, and this results in the segments separated by the ATT sequences. In BioBrick assembly, an eight-nucleotide scar sequence, which codes for a tyrosine and a stop codon, is left between every segment added into the plasmid.
Golden Gate assembly uses Type IIS restriction enzymes cutting outside their recognition sequences. Also, the same Type IIS restriction enzyme can generate copious different overhangs on the inserts and the vector; for instance, BsaI creates 256 four-basepair overhangs. If the overhangs are carefully designed, the segments are ligated without scar sequences between them, and the final construct can be quasi-scarless, where the restriction enzyme sites remain on both sides of the insert. As additional segments can be inserted into the vectors without scars within an open reading frame, Golden Gate is widely used in protein engineering. | 1 | Biochemistry |
Similar to copper oxide heap leaching, also using dilute sulfuric acid. Rio Tinto is commercializing this technology in Namibia and Australia; the French nuclear fuel company Orano, in Niger with two mines and Namibia; and several other companies are studying its feasibility.
The final product is yellowcake and requires significant further processing to produce fuel-grade feed. | 8 | Metallurgy |
Gluten & Food Allergens (GFA) program focuses on coordinating all future consensus-driven need for development, validation, and implementation of methods for the analysis of a wide range of food-associated allergens and gluten. | 3 | Analytical Chemistry |
James Murray worked at the University of Otago in Dunedin as a senior lecturer in chemistry.
Murray began research with lichens in the 1950s, applying his knowledge and skills in plant secondary compounds as well as morphology. This was the first systematic work on the lichens of New Zealand since the 1890s. He revised the New Zealand lichens within the Coniocarpineae, Peltigeraceae, Teloschistaceae among others, as well as lichens from the Antarctic and Subantarctic regions.
He spent 1959 on sabbatical working with the chemist Derek Barton at Imperial College, University of London. During this visit Murray also met with Peter James, a lichen specialist at the Natural History Museum, London. There were extensive nineteenth-century specimens of New Zealand lichens at both this museum and at Royal Botanic Gardens, Kew. Murray was able to work with these specimens and with James. They began to define the genus Sticta more precisely, distinguishing it from Pseudocyphellaria and also other groups such as Menegazzia, Nephroma, the Pannariaceae and the Parmeliaceae that contained more species in the Southern Hemisphere. Murray also visited several other lichenologists in France and Sweden including Henri Des Abbayes, Michael Mitchell, Greta Du Rietz, Adolf Hugo Magnusson, Gunnar Degelius, Rolf Santesson and Einar Timdall. He returned to New Zealand in February 1961.
After his death, his lichen specimens (over 10,000), notes and papers were donated to University of Otago and Peter James was seconded in 1962 to curate the collection. Murrays work on the natural products of lichens contributed to developments in this area and also became important to definition of genera in the Lobariaceae'. He developed keys to New Zealand lichen genera, some published posthumously. | 0 | Organic Chemistry |
It is possible to synthesize COFs using both dynamic covalent and non-covalent chemistry. The kinetic approach involves a stepwise process of polymerizing pre-assembled 2D-monomer while thermodynamic control exploits reversible covalent chemistry to allow simultaneous monomer assembly and polymerization. Under thermodynamic control, bond formation and crystallization also occur simultaneously. Covalent organic frameworks formed by dynamic covalent bond formation involves chemical reactions carried out reversibly under conditions of equilibrium control. Because the formation of COFs in dynamic covalent formation occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. Covalent assembly to form 2D COFs has been previously done using boronate esters from catechol acetonides in the presence of a lewis acid (BF*OEt).
2D polymerization under kinetic control relies on non-covalent interactions and monomer assembly prior to bond formation. The monomers can be held together in a pre-organized position by non-covalent interactions, such as hydrogen bonding or van der Waals. | 7 | Physical Chemistry |
He has published over 400 papers and 25 books over the course of his career.
Notable publications include:
*Tamejiro Hiyama and Koichiro Oshima, “有機合成化学” [Organic Synthetic Chemistry], Tokyo Kagaku Dojin, 2012,
*G. S. Zweifel, M. H. Nantz, Tamejiro Hiyama, “最新有機合成法 設計と戦略 – Modern Organic Synthesis: An Introduction”, Kagaku Dojin, 2009,
*Tamejiro Hiyama, coedited by Kyoko Nozaki, “有機合成のための触媒反応103” [103 Catalytic Reactions for Organic Synthesis], Tokyo Kagaku Dojin, 2004,
*Tamejiro Hiyama, “Organofluorine Compounds: Chemistry and Applications”, Springer, 2000,
*Tamejiro Hiyama, coedited with Martin Oestreich, “Organosilicon Chemistry: Novel Approaches and Reactions”, Wiley-VCH, 2019,
*Tamejiro Hiyama, coedited by Kyoko Nozaki, Yoshiaki Nakao, and Koji Nakano, “有機合成のための新触媒反応101” [101 New Catalytic Reactions for Organic Synthesis], Tokyo Kagaku Dojin, 20021, | 0 | Organic Chemistry |
There are multiple conventions for naming polymer substances. Many commonly used polymers, such as those found in consumer products, are referred to by a common or trivial name. The trivial name is assigned based on historical precedent or popular usage rather than a standardized naming convention. Both the American Chemical Society (ACS) and IUPAC have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not identical. Examples of the differences between the various naming conventions are given in the table below:
In both standardized conventions, the polymers names are intended to reflect the monomer(s) from which they are synthesized (source based nomenclature) rather than the precise nature of the repeating subunit. For example, the polymer synthesized from the simple alkene ethene is called polyethene, retaining the -ene' suffix even though the double bond is removed during the polymerization process:
:→
However, IUPAC structure based nomenclature is based on naming of the preferred constitutional repeating unit. | 7 | Physical Chemistry |
CTCF physically binds to itself to form homodimers,
which causes the bound DNA to form loops. CTCF also occurs frequently at the boundaries of sections of DNA bound to the nuclear lamina. Using chromatin immuno-precipitation (ChIP) followed by ChIP-seq, it was found that CTCF localizes with cohesin genome-wide and affects gene regulatory mechanisms and the higher-order chromatin structure. It is currently believed that the DNA loops are formed by the "loop extrusion" mechanism, whereby the cohesin ring is actively being translocated along the DNA until it meets CTCF. CTCF has to be in a proper orientation to stop cohesin. | 1 | Biochemistry |
Under the framework of valence bond theory, resonance is an extension of the idea that the bonding in a chemical species can be described by a Lewis structure. For many chemical species, a single Lewis structure, consisting of atoms obeying the octet rule, possibly bearing formal charges, and connected by bonds of positive integer order, is sufficient for describing the chemical bonding and rationalizing experimentally determined molecular properties like bond lengths, angles, and dipole moment. However, in some cases, more than one Lewis structure could be drawn, and experimental properties are inconsistent with any one structure. In order to address this type of situation, several contributing structures are considered together as an average, and the molecule is said to be represented by a resonance hybrid in which several Lewis structures are used collectively to describe its true structure. For instance, in NO, nitrite anion, the two N–O bond lengths are equal, even though no single Lewis structure has two N–O bonds with the same formal bond order. However, its measured structure is consistent with a description as a resonance hybrid of the two major contributing structures shown above: it has two equal N–O bonds of 125 pm, intermediate in length between a typical N–O single bond (145 pm in hydroxylamine, HN–OH) and N–O double bond (115 pm in nitronium ion, [O=N=O]). According to the contributing structures, each N–O bond is an average of a formal single and formal double bond, leading to a true bond order of 1.5. By virtue of this averaging, the Lewis description of the bonding in NO is reconciled with the experimental fact that the anion has equivalent N–O bonds.
The resonance hybrid represents the actual molecule as the "average" of the contributing structures, with bond lengths and partial charges taking on intermediate values compared to those expected for the individual Lewis structures of the contributors, were they to exist as "real" chemical entities. The contributing structures differ only in the formal apportionment of electrons to the atoms, and not in the actual physically and chemically significant electron or spin density. While contributing structures may differ in formal bond orders and in formal charge assignments, all contributing structures must have the same number of valence electrons and the same spin multiplicity.
Because electron delocalization lowers the potential energy of a system, any species represented by a resonance hybrid is more stable than any of the (hypothetical) contributing structures. Electron delocalization stabilizes a molecule because the electrons are more evenly spread out over the molecule, decreasing electron-electron repulsion. The difference in potential energy between the actual species and the (computed) energy of the contributing structure with the lowest potential energy is called the resonance energy or delocalization energy. The magnitude of the resonance energy depends on assumptions made about the hypothetical "non-stabilized" species and the computational methods used and does not represent a measurable physical quantity, although comparisons of resonance energies computed under similar assumptions and conditions may be chemically meaningful.
Molecules with an extended π system such as linear polyenes and polyaromatic compounds are well described by resonance hybrids as well as by delocalised orbitals in molecular orbital theory. | 7 | Physical Chemistry |
An auxiliary protein unique to most eukaryotes is the E3 binding protein (E3BP), which serves to bind the E3 subunit to the PDC complex. In the case of human E3BP, hydrophobic proline and leucine residues in the BP interact with the surface recognition site formed by the binding of two identical E3 monomers. | 1 | Biochemistry |
Crystallization is largely over when reaches values close to 1, which will be at a crystallization time defined by , as then the exponential term in the above expression for will be small. Thus crystallization takes a time of order
i.e., crystallization takes a time that decreases as one over the one-quarter power of the nucleation rate per unit volume, , and one over the three-quarters power of the growth velocity . Typical crystallites grow for some fraction of the crystallization time and so have a linear dimension , or
i.e., the one quarter power of the ratio of the growth velocity to the nucleation rate per unit volume. Thus the size of the final crystals only depends on this ratio, within this model, and as we should expect, fast growth rates and slow nucleation rates result in large crystals. The average volume of the crystallites is of order this typical linear size cubed.
This all assumes an exponent of , which is appropriate for the uniform (homogeneous) nucleation in three dimensions. Thin films, for example, may be effectively two-dimensional, in which case if nucleation is again uniform the exponent . In general, for uniform nucleation and growth, , where is the dimensionality of space in which crystallization occurs. | 3 | Analytical Chemistry |
In analytical chemistry, Karl Fischer titration is a classic titration method that uses coulometric or volumetric titration to determine trace amounts of water in a sample. It was invented in 1935 by the German chemist Karl Fischer. Today, the titration is done with an automated Karl Fischer titrator. | 3 | Analytical Chemistry |
Central to the MaxEnt thesis is the principle of maximum entropy. It demands as given some partly specified model and some specified data related to the model. It selects a preferred probability distribution to represent the model. The given data state "testable information" about the probability distribution, for example particular expectation values, but are not in themselves sufficient to uniquely determine it. The principle states that one should prefer the distribution which maximizes the Shannon information entropy,
This is known as the Gibbs algorithm, having been introduced by J. Willard Gibbs in 1878, to set up statistical ensembles to predict the properties of thermodynamic systems at equilibrium. It is the cornerstone of the statistical mechanical analysis of the thermodynamic properties of equilibrium systems (see partition function).
A direct connection is thus made between the equilibrium thermodynamic entropy S, a state function of pressure, volume, temperature, etc., and the information entropy for the predicted distribution with maximum uncertainty conditioned only on the expectation values of those variables:
k, the Boltzmann constant, has no fundamental physical significance here, but is necessary to retain consistency with the previous historical definition of entropy by Clausius (1865) (see Boltzmann constant).
However, the MaxEnt school argue that the MaxEnt approach is a general technique of statistical inference, with applications far beyond this. It can therefore also be used to predict a distribution for "trajectories" Γ "over a period of time" by maximising:
This "information entropy" does not necessarily have a simple correspondence with thermodynamic entropy. But it can be used to predict features of nonequilibrium thermodynamic systems as they evolve over time.
For non-equilibrium scenarios, in an approximation that assumes local thermodynamic equilibrium, with the maximum entropy approach, the Onsager reciprocal relations and the Green–Kubo relations fall out directly. The approach also creates a theoretical framework for the study of some very special cases of far-from-equilibrium scenarios, making the derivation of the entropy production fluctuation theorem straightforward. For non-equilibrium processes, as is so for macroscopic descriptions, a general definition of entropy for microscopic statistical mechanical accounts is also lacking.
Technical note: For the reasons discussed in the article differential entropy, the simple definition of Shannon entropy ceases to be directly applicable for random variables with continuous probability distribution functions. Instead the appropriate quantity to maximize is the "relative information entropy",
H is the negative of the Kullback–Leibler divergence, or discrimination information, of m(x) from p(x), where m(x) is a prior invariant measure for the variable(s). The relative entropy H is always less than zero, and can be thought of as (the negative of) the number of bits of uncertainty lost by fixing on p(x) rather than m(x). Unlike the Shannon entropy, the relative entropy H has the advantage of remaining finite and well-defined for continuous x, and invariant under 1-to-1 coordinate transformations. The two expressions coincide for discrete probability distributions, if one can make the assumption that m(x) is uniform – i.e. the principle of equal a-priori probability, which underlies statistical thermodynamics. | 7 | Physical Chemistry |
Because of the large size of the α-pinenyl substituents, diisopinocampheylborane only hydroborates unhindered alkenes. These reactions proceed with high enantioselectivity. 2-Butene, 2-pentene, 3-hexene are converted to the respective chiral alcohols in high ees. Norbornene under the same conditions gave an 83% ee. Heterocycles (dihydrofuran, dihydrothiophene, dihydropyrrole, tetrahydropyran) give the alcohols in ≥99% ee; the high ees reflect their constrained conformations.
It adds to alkynes to form the corresponding vinyldiisopinocampheylboranes
In a highly stereoselective reaction, allyldiisopinocampheylboranes converts aldehydes to the homologated alcohols, rapidly even at -100 °C. The alkyldiisopinocampheylboranes, which result from the addition to alkenes, usefully react with a range of different reagents. Hydroxylamine-O-sulfonic acid provides 3-pinanamine.
Also useful is the reaction of diisopinocampheylborane with an aldehyde (RCHO) to give the chiral boronic ester, (isopinocampheyl)BOCH(R), which can be further used is a number of reactions e.g. Suzuki reaction. | 0 | Organic Chemistry |
Initially, More O’Ferrall introduced this type of analysis to discuss the continuity between concerted and step-wise β-elimination reaction mechanisms. The model also provided a framework within which to explain the effects of substituents and reaction conditions on the mechanism. The appropriate lower energy species were placed at the corners of the two dimensional plot (Figure 2). These were the reactants (top left), the products (bottom right) and the intermediates of the two possible stepwise reactions: the carbocation for E1 (bottom left) and the carbanion for E1cB (top-right). Thus, the horizontal axes represent the extent of deprotonation (C-H bond distance) and the vertical axes represent the extent of leaving group departure (C-LG distance). By applying the Hammond and anti-Hammond effects, he predicted the effects of various changes in the reactants or reaction conditions. For example, the effects of introducing a better leaving group on a substrate that initially eliminates via an E2 mechanism are illustrated in Figure 2. A better leaving group increases the energy of the reactants and of the carbanion intermediate. Thus, the transition state moves towards the reactants and away from the carbanion intermediate.
The model does not predict any change in leaving group departure at the transition state. Instead the extent of deprotonation is expected to decrease. This can be explained by the fact that a better leaving group needs less assistance from a developing neighbouring negative charge in order to depart. The true change predicts more carbocation character at the transition state and a mechanism that is more E1-like. These observations can be correlated with Hammett ρ-values. Poor leaving groups correlate with large positive ρ-values. Gradually increasing the leaving group ability decreases the ρ-value until it becomes large and negative, indicating the development of positive charge in the transition state. | 7 | Physical Chemistry |
It was not long until several executives of large banks persuaded him to develop security systems for the Internet to work. They were worried about the fact that no useful framework for electronic commerce would have been possible at that time without innovation in the computer and network security industry. Following a request from former Wells Fargo Bank president William Zuendt in 1993, Atalla began developing a new Internet security technology, allowing companies to scramble and transmit secure computer files, e-mail, and digital video and audio, over the internet.
As a result of these activities, he founded the company TriStrata Security in 1996. In contrast to most conventional computer security systems at the time, which built walls around a company's entire computer network to protect the information within from thieves or corporate spies, TriStrata took a different approach. Its security system wrapped a secure, encrypted envelope around individual pieces of information (such as a word processing file, a customer database, or e-mail) that can only be opened and deciphered with an electronic permit, allowing companies to control which users have access to this information and the necessary permits. It was considered a new approach to enterprise security at the time. | 7 | Physical Chemistry |
By the process of silylation, polar functional groups such as alcohols and amines readily undergo reaction with trimethylsilyl chloride, giving trimethylsilyl ethers and trimethylsilyl amines. These new groups "protect" the original functional group by removing the labile protons and decreasing the basicity of the heteroatom. The lability of the and groups allow them to be easily removed afterwards ("deprotected"). Trimethylsilylation can also be used to increase the volatility of a compound, enabling gas chromatography of normally nonvolatile substances such as glucose.
Trimethylsilyl chloride also reacts with carbanions to give trimethylsilyl derivatives. Lithium acetylides react to give trimethylsilylalkynes such as bis(trimethylsilyl)acetylene. Such derivatives are useful protected forms of alkynes.
In the presence of triethylamine and lithium diisopropylamide, enolisable aldehydes, ketones and esters are converted to trimethylsilyl enol ethers. Despite their hydrolytic instability, these compounds have found wide application in organic chemistry; oxidation of the double bond by epoxidation or dihydroxylation can be used to return the original carbonyl group with an alcohol group at the alpha carbon. The trimethylsilyl enol ethers can also be used as masked enolate equivalents in the Mukaiyama aldol addition. | 0 | Organic Chemistry |
The timing electronics is needed to losslessly reconstruct the histogram of the distribution of time of flight of photons. This is done by using the technique of time-correlated single photon counting (TCSPC), where the individual photon arrival times are marked with respect to a start/stop signal provided by the periodic laser cycle. These time-stamps can then be used to build up histograms of photon arrival times.
The two main types of timing electronics are based on a combination of time-to-analog converter (TAC) and an analog-to-digital converter (ADC), and time-to-digital converter (TDC), respectively. In the first case, the difference between the start and the stop signal is converted into an analog voltage signal, which is then processed by the ADC. In the second method, the delay is directly converted into a digital signal. Systems based on ADCs generally have a better timing resolution and linearity while being expensive and the capability of being integrated. TDCs, on the other hand, can be integrated into a single chip and hence are better suited in multi-channel systems. However, they have a worse timing performance and can handle much lower sustained count-rates. | 7 | Physical Chemistry |
RT-PCR can be used to diagnose genetic disease such as Lesch–Nyhan syndrome. This genetic disease is caused by a malfunction in the HPRT1 gene, which clinically leads to the fatal uric acid urinary stone and symptoms similar to gout. Analyzing a pregnant mother and a fetus for mRNA expression levels of HPRT1 will reveal if the mother is a carrier and if the fetus will likely to develop Lesch–Nyhan syndrome. | 1 | Biochemistry |
In thermodynamics, heat is the thermal energy transferred between systems due to a temperature difference. In colloquial use, heat sometimes refers to thermal energy itself. Thermal energy is the kinetic energy of vibrating and colliding atoms in a substance.
An example of formal vs. informal usage may be obtained from the right-hand photo, in which the metal bar is "conducting heat" from its hot end to its cold end, but if the metal bar is considered a thermodynamic system, then the energy flowing within the metal bar is called internal energy, not heat. The hot metal bar is also transferring heat to its surroundings, a correct statement for both the strict and loose meanings of heat. Another example of informal usage is the term heat content, used despite the fact that physics defines heat as energy transfer. More accurately, it is thermal energy that is contained in the system or body, as it is stored in the microscopic degrees of freedom of the modes of vibration.
Heat is energy in transfer to or from a thermodynamic system by a mechanism that involves the microscopic atomic modes of motion or the corresponding macroscopic properties. This descriptive characterization excludes the transfers of energy by thermodynamic work or mass transfer. Defined quantitatively, the heat involved in a process is the difference in internal energy between the final and initial states of a system, and subtracting the work done in the process. This is the formulation of the first law of thermodynamics.
Calorimetry is measurement of quantity of energy transferred as heat by its effect on the states of interacting bodies, for example, by the amount of ice melted or by change in temperature of a body.
In the International System of Units (SI), the unit of measurement for heat, as a form of energy, is the joule (J). | 7 | Physical Chemistry |
I-type lectin named from the immunoglobulin-like domain. Sialoadhesin is one of the I-type lectin, which binds specifically to sialic acid. | 0 | Organic Chemistry |
The gene gun was originally a Crosman air pistol modified to fire dense tungsten particles. It was invented by John C Sanford, Ed Wolf, and Nelson Allen at Cornell University along with Ted Klein of DuPont between 1983 and 1986. The original target was onions (chosen for their large cell size), and the device was used to deliver particles coated with a marker gene which would relay a signal if proper insertion of the DNA transcript occurred. Genetic transformation was demonstrated upon observed expression of the marker gene within onion cells.
The earliest custom manufactured gene guns (fabricated by Nelson Allen) used a 22 caliber nail gun cartridge to propel a polyethylene cylinder (bullet) down a 22 caliber Douglas barrel. A droplet of the tungsten powder coated with genetic material was placed onto the bullet and shot down into a Petri dish below. The bullet welded to the disk below the Petri plate, and the genetic material blasted into the sample with a doughnut effect involving devastation in the middle of the sample with a ring of good transformation around the periphery. The gun was connected to a vacuum pump and was placed under a vacuum while firing. The early design was put into limited production by a Rumsey-Loomis (a local machine shop then at Mecklenburg Road in Ithaca, NY, USA).
Biolistics, Inc sold Dupont the rights to manufacture and distribute an updated device with improvements including the use of helium as a non-explosive propellant and a multi-disk collision delivery mechanism to minimize damage to sample tissues. Other heavy metals such as gold and silver are also used to deliver genetic material with gold being favored due to lower cytotoxicity in comparison to tungsten projectile carriers. | 1 | Biochemistry |
Reproductive cloning generally uses "somatic cell nuclear transfer" (SCNT) to create animals that are genetically identical. This process entails the transfer of a nucleus from a donor adult cell (somatic cell) to an egg from which the nucleus has been removed, or to a cell from a blastocyst from which the nucleus has been removed. If the egg begins to divide normally it is transferred into the uterus of the surrogate mother. Such clones are not strictly identical since the somatic cells may contain mutations in their nuclear DNA. Additionally, the mitochondria in the cytoplasm also contains DNA and during SCNT this mitochondrial DNA is wholly from the cytoplasmic donor's egg, thus the mitochondrial genome is not the same as that of the nucleus donor cell from which it was produced. This may have important implications for cross-species nuclear transfer in which nuclear-mitochondrial incompatibilities may lead to death.
Artificial embryo splitting or embryo twinning, a technique that creates monozygotic twins from a single embryo, is not considered in the same fashion as other methods of cloning. During that procedure, a donor embryo is split in two distinct embryos, that can then be transferred via embryo transfer. It is optimally performed at the 6- to 8-cell stage, where it can be used as an expansion of IVF to increase the number of available embryos. If both embryos are successful, it gives rise to monozygotic (identical) twins. | 1 | Biochemistry |
All cells need energy to survive. Mitochondria is a double-membrane structure in the body cell that generates and transports essential metabolic products. The three layers of this structure are the outer membrane, intermembrane space, and inner membrane. The space inside the mitochondria is called the mitochondrial matrix, while the region outside is the cytosol. The outer membrane allows most small molecules to pass through. In contrast, the inner membrane transports specific molecules only, which is impermeable to many substances. Therefore, a shuttle is required for the transportation of molecules across the inner membrane. It acts as a pump to drive the substances from the inner membrane to the outside. | 1 | Biochemistry |
Inorganic atoms form cyclic compounds as well. Examples include sulfur and nitrogen (e.g. heptasulfur imide , trithiazyl trichloride , tetrasulfur tetranitride ), silicon (e.g., cyclopentasilane ), phosphorus and nitrogen (e.g., hexachlorophosphazene ), phosphorus and oxygen (e.g., metaphosphates and other cyclic phosphoric acid derivatives), boron and oxygen (e.g., sodium metaborate , borax), boron and nitrogen (e.g. borazine ). When carbon in benzene is "replaced" by other elements, e.g., as in borabenzene, silabenzene, germanabenzene, stannabenzene, and phosphorine, aromaticity is retained, and so aromatic inorganic cyclic compounds are also known and well-characterized. | 4 | Stereochemistry |
Trimethylsilyl iodide is used to introduce the trimethylsilyl group onto alcohols (ROH):
:R-OH + TMSI → R-OTMS + HI
This type of reaction may be useful for gas chromatography analysis; the resultant silyl ether is more volatile than the underivatized original materials. However, for the preparation of bulk trimethylsilylated material, trimethylsilyl chloride may be preferred due to its lower cost.
TMSI reacts with alkyl ethers (ROR′), forming silyl ethers (ROSiMe) and iodoalkanes (RI) that can be hydrolyzed to alcohols (ROH).
Trimethylsilyl iodide is also used for the removing of the Boc protecting group, especially where other deprotection methods are too harsh for the substrate. | 0 | Organic Chemistry |
The ores are treated by a sulfatizing roast in a fluidized bed furnace to convert copper and cobalt sulfides into soluble sulfates and iron into insoluble hematite. The calcine is subsequently leached with sulfuric acid from the spent copper recovery electrolyte. Oxide concentrates are introduced at this leaching step to maintain the acid balance in the circuit. Iron and aluminum are removed from the leach solution by the addition of lime, and copper is electrowon on copper cathodes. A part of the spent electrolyte enters the cobalt recovery circuit and is purified by the removal of iron, copper, nickel, and zinc prior to the precipitation of cobalt as its hydroxide. This is accomplished by the addition of more lime to raise the pH until the remaining copper precipitates. This copper is sent back to the copper circuit. As more lime is then added, a copper-cobaltite precipitates and is fed back to the leaching process. Sodium hydrosulfide (NaHS) is added (along with some metallic cobalt as a catalyst) to precipitate nickel sulfide (NiS). Hydrogen sulfide (HS) and sodium carbonate (NaCO) are then added to precipitate zinc sulfide (ZnS).). In the final stages, this cobalt hydroxide is redissolved and the metal is refined by electrolysis. The resulting cobalt cathodes are crushed and vacuum degassed to obtain a pure cobalt metal. | 8 | Metallurgy |
Introduction of too many siRNA can result in nonspecific events due to activation of innate immune responses. Most evidence to date suggests that this is probably due to activation of the dsRNA sensor PKR, although retinoic acid-inducible gene I (RIG-I) may also be involved. The induction of cytokines via toll-like receptor 7 (TLR7) has also been described. Chemical modification of siRNA is employed to reduce in the activation of the innate immune response for gene function and therapeutic applications. One promising method of reducing the nonspecific effects is to convert the siRNA into a microRNA. MicroRNAs occur naturally, and by harnessing this endogenous pathway it should be possible to achieve similar gene knockdown at comparatively low concentrations of resulting siRNAs. This should minimize nonspecific effects. | 1 | Biochemistry |
Semiconductors are usually studied in a photoelectrochemical cell. Different configurations exist with a three electrode device. The phenomenon to study happens at the working electrode WE while the differential potential is applied between the WE and a reference electrode RE (saturated calomel, Ag/AgCl). The current is measured between the WE and the counter electrode CE (carbon vitreous, platinum gauze). The working electrode is the semiconductor material and the electrolyte is composed of a solvent, an electrolyte and a redox specie.
A UV-vis lamp is usually used to illuminate the working electrode. The photoelectrochemical cell is usually made with a quartz window because it does not absorb the light. A monochromator can be used to control the wavelength sent to the WE. | 5 | Photochemistry |
The independent coordinate has sense of time. Indeed, it may be proportional to time with some relation like , where is constant.
The derivative may have sense of velocity of particle with coordinate ; then can be interpreted as acceleration; and the mass of such a particle is equal to unity.
The dissipative function may have sense of coefficient of the speed-proportional friction.
Usually, both parameters and are supposed to be positive; then this speed-proportional friction coefficient grows exponentially at large positive values of coordinate .
The potential is a fixed function, which also shows exponential growth at large positive values of coordinate .
In the application in laser physics, may have a sense of logarithm of number of photons in the laser cavity, related to its steady-state value. Then, the output power of such a laser is proportional to and may show pulsation at oscillation of .
Both analogies, with a unity mass particle and logarithm of number of photons, are useful in the analysis of behavior of the Toda oscillator. | 7 | Physical Chemistry |
Meropenem rapidly reduces serum concentrations of valproic acid. As a result, people who use valproic acid for epilepsy are at increased risk of seizures during treatment with meropenem. In situations where the use of meropenem cannot be avoided, prescription of an additional anticonvulsant should be considered. | 4 | Stereochemistry |
In computational chemistry a chicken wire model or chicken wire surface plot is a way to visualize molecular models by drawing the polygon mesh of their surface (defined e.g. as the van der Waals radius or a certain electron density). | 4 | Stereochemistry |
Radiogenic isotopes provide powerful tracers for studying the ages and origins of Earth systems. They are particularly useful to understand mixing processes between different components, because (heavy) radiogenic isotope ratios are not usually fractionated by chemical processes.
Radiogenic isotope tracers are most powerful when used together with other tracers: The more tracers used, the more control on mixing processes. An example of this application is to the evolution of the Earths crust and Earths mantle through geological time. | 9 | Geochemistry |
Aromaticity is found in ions as well: the cyclopropenyl cation (2e system), the cyclopentadienyl anion (6e system), the tropylium ion (6e), and the cyclooctatetraene dianion (10e). Aromatic properties have been attributed to non-benzenoid compounds such as tropone. Aromatic properties are tested to the limit in a class of compounds called cyclophanes.
A special case of aromaticity is found in homoaromaticity where conjugation is interrupted by a single sp³ hybridized carbon atom.
When carbon in benzene is replaced by other elements in borabenzene, silabenzene, germanabenzene, stannabenzene, phosphorine or pyrylium salts the aromaticity is still retained. Aromaticity also occurs in compounds that are not carbon-based at all. Inorganic 6-membered-ring compounds analogous to benzene have been synthesized. Hexasilabenzene (SiH) and borazine (BNH) are structurally analogous to benzene, with the carbon atoms replaced by another element or elements. In borazine, the boron and nitrogen atoms alternate around the ring. Quite recently, the aromaticity of planar Si rings occurring in the Zintl phase LiSi was experimentally evidenced by Li solid state NMR.
Metal aromaticity is believed to exist in certain metal clusters of aluminium.
Möbius aromaticity occurs when a cyclic system of molecular orbitals, formed from p atomic orbitals and populated in a closed shell by 4n (n is an integer) electrons, is given a single half-twist to correspond to a Möbius strip. A π system with 4n electrons in a flat (non-twisted) ring would be anti-aromatic, and therefore highly unstable, due to the symmetry of the combinations of p atomic orbitals. By twisting the ring, the symmetry of the system changes and becomes allowed (see also Möbius–Hückel concept for details). Because the twist can be left-handed or right-handed, the resulting Möbius aromatics are dissymmetric or chiral.
As of 2012, there is no proof that a Möbius aromatic molecule was synthesized.
Aromatics with two half-twists corresponding to the paradromic topologies were first suggested by Johann Listing. In carbo-benzene the ring bonds are extended with alkyne and allene groups. | 7 | Physical Chemistry |
Cylindrospermopsin (abbreviated to CYN, or CYL) is a cyanotoxin produced by a variety of freshwater cyanobacteria. CYN is a polycyclic uracil derivative containing guanidino and sulfate groups. It is also zwitterionic, making it highly water soluble. CYN is toxic to liver and kidney tissue and is thought to inhibit protein synthesis and to covalently modify DNA and/or RNA. It is not known whether cylindrospermopsin is a carcinogen, but it appears to have no tumour initiating activity in mice.
CYN was first discovered after an outbreak of a mystery disease on Palm Island, Queensland, Australia. The outbreak was traced back to a bloom of Cylindrospermopsis raciborskii in the local drinking water supply, and the toxin was subsequently identified. Analysis of the toxin led to a proposed chemical structure in 1992, which was revised after synthesis was achieved in 2000. Several analogues of CYN, both toxic and non-toxic, have been isolated or synthesised.
C. raciborskii has been observed mainly in tropical areas, however has also recently been discovered in temperate regions of Australia, North, South America, New Zealand and Europe. However, CYN-producing strain of C. raciborskii has not been identified in Europe, several other cyanobacteria species occurring across the continent are able to synthesize it. | 0 | Organic Chemistry |
The successful operation and development of the demonstration copper ISASMELT, and the degree of interest shown in the new process by the global smelting community, gave MIM Holdings sufficient confidence to license the ISASMELT technology to external companies, so an agreement under which MIM could incorporate the Sirosmelt lance into ISASMELT technology was signed with the CSIRO in 1989. | 8 | Metallurgy |
Photoelectrolysis of water, also known as photoelectrochemical water splitting, occurs in a photoelectrochemical cell when light is used as the energy source for the electrolysis of water, producing dihydrogen which can be used as a fuel. This process is one route to a "hydrogen economy", in which hydrogen fuel is produced efficiently and inexpensively from natural sources without using fossil fuels. In contrast, steam reforming usually or always uses a fossil fuel to obtain hydrogen. Photoelectrolysis is sometimes known colloquially as the hydrogen holy grail for its potential to yield a viable alternative to petroleum as a source of energy; such an energy source would supposedly come without the sociopolitically undesirable effects of extracting and using petroleum.
Some researchers have practiced photoelectrolysis by means of a nanoscale process. Nanoscale photoelectrolysis of water could someday reach greater efficiency than that of "traditional" photoelectrolysis. Semiconductors with bandgaps smaller than 1.7 eV would ostensibly be required for efficient nanoscale photoelectrolysis using light from the Sun.
Devices based on hydrogenase have also been investigated. | 5 | Photochemistry |
Solvophoresis is a spontaneous motion of dispersed particles in a mixed solvent induced by a gradient of solvent concentration. Solvophoresis was experimentally established by Marek Kosmulski and Egon Matijevic. Solvophoresis is similar to diffusiophoresis. | 7 | Physical Chemistry |
The Tsuji-Wacker oxidation oxidizes terminal olefin to the corresponding methyl ketone under the Wacker process condition. Almost identical to that of Wacker Process, the proposed catalytic cycle(Figure 1) begins with complexation of PdCl and two chloride anions to PdCl, which then undergoes subsequent ligand exchange of two chloride ligand for water and alkene to form Pd(Cl)(HO)(alkene) complex. A water molecule then attacks the olefin regioselectively through an outer sphere mechanism in a Markovnikov fashion, to form the more thermodynamically stable Pd(Cl)(OH)(-CH-CHOH-R) complex. Dissociation of a chloride ligand to the three coordinate palladium complex promotes β-hydride elimination, then subsequent 1,2-hydride migratory insertion generates Pd(Cl)(OH)(-CHOHR-CH) complex. This undergoes β-hydride elimination to release the ketone, and subsequent reductive elimination produces HCl, water, and palladium(0). Finally palladium(0) is reoxidized to PdCl with two equivalents of Cu(II)Cl, which in turn can be reoxidized by O.
The oxidation of terminal olefins generally provide the Markovnikov ketone product, however in cases where substrate favors the aldehyde (discussed below), different ligands can be used to enforce the Markovnikov regioselectivity. The use of sparteine as a ligand (Figure 2, A) favors nucleopalladation at the terminal carbon to minimize steric interaction between the palladium complex and substrate. The Quinox-ligated palladium catalyst is used to favor ketone formation when substrate contains a directing group (Figure 2, B). When such substrate bind to Pd(Quinox)(OOtBu), this complex is coordinately saturated which prevents the binding of the directing group, and results in formation of the Markovnikov product. The efficiency of this ligand is also attributed to its electronic property, where anionic TBHP prefers to bind trans to the oxazoline and olefin coordinate trans to the quinoline. | 0 | Organic Chemistry |
The tandem affinity purification (TAP) method allows the high-throughput identification of proteins interactions. In contrast with the Y2H approach, the accuracy of the method can be compared to those of small-scale experiments (Collins et al., 2007) and the interactions are detected within the correct cellular environment as by co-immunoprecipitation. However, the TAP tag method requires two successive steps of protein purification, and thus can not readily detect transient protein–protein interactions. Recent genome-wide TAP experiments were performed by Krogan et al., 2006, and Gavin et al., 2006, providing updated protein interaction data for yeast organisms.
Chemical crosslinking is often used to "fix" protein interactions in place before trying to isolate/identify interacting proteins. Common crosslinkers for this application include the non-cleavable [NHS-ester] crosslinker, [bis-sulfosuccinimidyl suberate] (BS3); a cleavable version of BS3, [dithiobis(sulfosuccinimidyl propionate)](DTSSP); and the [imidoester] crosslinker [dimethyl dithiobispropionimidate] (DTBP) that is popular for fixing interactions in ChIP assays. | 1 | Biochemistry |
The ICBM cooperates closely with the Max Planck Institute for Marine Microbiology und MARUM, both located in Bremen; with the Alfred Wegener Institute in Bremerhaven, as well as with the Senckenberg Institute by the Sea and the Jade University of Applied Sciences, both located in Wilhelmshaven. The ICBM is a member of the German Marine Research Consortium (KDM) and of the Northwest Marine Research Association (NWMV). | 9 | Geochemistry |
* Bioassays. Test organisms are exposed to an environment and their response is measured. Typical organisms used in bioassays are certain species of plants, bacteria, fish, water fleas (Daphnia), and frogs.
* Community assessments. Also called biosurveys. An entire community of organisms is sampled to see what types of taxa remain. In aquatic ecosystems, these assessments often focus on invertebrates, algae, macrophytes (aquatic plants), fish, or amphibians. Rarely, other large vertebrates (reptiles, birds, and mammals) may be considered.
* Online biomonitoring devices. One example uses chemoreceptor cells of molluscs and similar animals to monitor their coastal and fresh water habitats. Different types of animals are used for this purpose either in the lab or in the field. The study of the opening and closing activity of clams valves is an example of one possible way to monitor in-situ' the quality of fresh and coastal waters. | 2 | Environmental Chemistry |
Phosphoranes of the type RP=CR are more common and more important. Phosphoranes are also considered to be one of the resonance structures of ylides, these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the Wittig reaction, for instance methylenetriphenylphosphorane or PhP=CH. | 0 | Organic Chemistry |
Consider the reaction
:A ⇌ 2 B + 3 C
Suppose an infinitesimal amount of the reactant A changes into B and C. This requires that all three mole numbers change according to the stoichiometry of the reaction, but they will not change by the same amounts. However, the extent of reaction can be used to describe the changes on a common footing as needed. The change of the number of moles of A can be represented by the equation , the change of B is , and the change of C is .
The change in the extent of reaction is then defined as
where denotes the number of moles of the reactant or product and is the stoichiometric number of the reactant or product. Although less common, we see from this expression that since the stoichiometric number can either be considered to be dimensionless or to have units of moles, conversely the extent of reaction can either be considered to have units of moles or to be a unitless mole fraction.
The extent of reaction represents the amount of progress made towards equilibrium in a chemical reaction. Considering finite changes instead of infinitesimal changes, one can write the equation for the extent of a reaction as
The extent of a reaction is generally defined as zero at the beginning of the reaction. Thus the change of is the extent itself. Assuming that the system has come to equilibrium,
Although in the example above the extent of reaction was positive since the system shifted in the forward direction, this usage implies that in general the extent of reaction can be positive or negative, depending on the direction that the system shifts from its initial composition. | 7 | Physical Chemistry |
Pan Britannica Industries Ltd (PBI) was a household and agrochemical formulation company incorporated in 1932 and based at Britannica House, Stewardstone Road, Waltham Abbey and with a distribution presence in Wisbech in Cambridgeshire. PBI was, in common with many other UK household names, both a manufacturer and marketing organisation for both agricultural and horticultural products.
PBI produced many agro-chemical formulations for farmers, however it was perhaps best known for its product Baby Bio, a liquid plant food that came in a small perfume-shaped bottle. PBI was also the original publisher of the Expert range of gardening books, starting with Be Your Own Gardening Expert written in 1958 by Dr D.G. Hessayon, who later became the company's chairman.
The company was sold to Sumitomo Corporation on 28 September 1990, and rebranded as PBI Home & Garden in 1998. In March 1999 the company was acquired by global conglomerate Bayer. The company has ceased production at Waltham Abbey, the works have been demolished and the site redeveloped for a Tesco supermarket. The rebranded company, PBI Home and Garden, was dissolved in 2015. | 2 | Environmental Chemistry |
In 1945, Folch married Willa Babcock, who was also a scholar in her own right (in the field of Romance languages) and would later become the academic dean of Tufts University. The couple had three children. Folch died in Boston, Massachusetts on October 3, 1979 at 69 years of age. | 1 | Biochemistry |
Both TERS and SERS rely on a localized surface plasmon for increasing the ought-to-be weak Raman signal. The only difference between them is that the sample in SERS has a rough surface that hinders application of a sharp AFM-like tip. TERS, on the other hand, uses a metal-coated tip having some roughness at nanoscale. The “hot spot” theory is very popular in explaining the large enhancement in the signal. That is, the signal from “hot spots” on the surface of the sample dominates the total signal from the sample. This is also reinforced by the fact that the distance between nanoparticles and sample is an important factor in obtaining high Raman signal. | 7 | Physical Chemistry |
The simplest thiophosphates have the formula [PSO]. These trianions are only observed at very high pH, instead they exist in protonated form with the formula [HPSO] (x = 0, 1, 2, or 3 and (n = 1, 2, or 3). | 0 | Organic Chemistry |
The C and N contents of feedstocks is generally known from lookup tables listing common types of feedstock. It is important to deduct the moisture content if the listed value is for dry material.
For foodstuffs with a nutrition analysis, the N content may be estimated from the protein content as , reversing the crude protein calculation. The C content may be estimated from crude ash content (often reported in animal feed) or from reported macronutrient levels as .
Given the C:N ratio and one of C and N contents, the other content may be calculated using the very definition of the ratio. When only the ratio is known, one must estimate the total C+N% or one of the contents to get both values. | 9 | Geochemistry |
In a potential application in nanotechnology, the diazonium salts 4-chlorobenzenediazonium tetrafluoroborate very efficiently functionalizes single wall nanotubes. In order to exfoliate the nanotubes, they are mixed with an ionic liquid in a mortar and pestle. The diazonium salt is added together with potassium carbonate, and after grinding the mixture at room temperature the surface of the nanotubes are covered with chlorophenyl groups with an efficiency of 1 in 44 carbon atoms. These added subsituents prevent the tubes from forming intimate bundles due to large cohesive forces between them, which is a recurring problem in nanotube technology.
It is also possible to functionalize silicon wafers with diazonium salts forming an aryl monolayer. In one study, the silicon surface is washed with ammonium hydrogen fluoride leaving it covered with silicon–hydrogen bonds (hydride passivation). The reaction of the surface with a solution of diazonium salt in acetonitrile for 2 hours in the dark is a spontaneous process through a free radical mechanism:
So far grafting of diazonium salts on metals has been accomplished on iron, cobalt, nickel, platinum, palladium, zinc, copper and gold surfaces. Also grafting to diamond surfaces has been reported. One interesting question raised is the actual positioning on the aryl group on the surface. An in silico study demonstrates that in the period 4 elements from titanium to copper the binding energy decreases from left to right because the number of d-electrons increases. The metals to the left of iron are positioned tilted towards or flat on the surface favoring metal to carbon pi bond formation and those on the right of iron are positioned in an upright position, favoring metal to carbon sigma bond formation. This also explains why diazonium salt grafting thus far has been possible with those metals to right of iron in the periodic table. | 0 | Organic Chemistry |
Spice, spiciness, or spicity, symbol τ, is a term in oceanography referring to variations in the temperature and salinity of seawater over space or time, whose combined effects leave the water's density unchanged. For a given spice, any change in temperature is offset by a change in salinity to maintain unchanged density. An increase in temperature decreases density, but an increase in salinity increases density. Such density-compensated thermohaline variability is ubiquitous in the upper ocean. Warmer, saltier water is more spicy while cooler, less salty water is more minty. For a density ratio of 1, all the thermohaline variability is spice, and there are no density fluctuations. | 7 | Physical Chemistry |
As long ago as 1890, Hiorns observed as follows:
:"Noble Metals. Gold, Platinum, Silver, and a few rare metals. The members of this class have little or no tendency to unite with oxygen in the free state, and when placed in water at a red heat do not alter its composition. The oxides are readily decomposed by heat in consequence of the feeble affinity between the metal and oxygen."
Smith, writing in 1946, continued the theme:
:"There is no sharp dividing line [between noble metals and base metals] but perhaps the best definition of a noble metal is a metal whose oxide is easily decomposed at a temperature below a red heat."
:"It follows from this that noble metals...have little attraction for oxygen and are consequently not oxidised or discoloured at moderate temperatures."
Such nobility is mainly associated with the relatively high electronegativity values of the noble metals, resulting in only weakly polar covalent bonding with oxygen. The table lists the melting points of the oxides of the noble metals, and for some of those of the non-noble metals, for the elements in their most stable oxidation states. | 8 | Metallurgy |
Sea salt aerosols are mainly constituted of sodium chloride (NaCl), but other chemical ions which are common in sea water, such as K, Mg, Ca, SO and so on, can also be found. A recent study revealed that sea salt aerosols also contain a substantial amount of organic matter. Mostly, organic materials are internally mixed due to the drying of air bubbles at the organic-rich sea surface. The fraction of organic components increases with the decreasing particle size. The contained organic materials change the optical properties of sea salt as well as the hygroscopicity, especially when some insoluble organic matter is induced. | 9 | Geochemistry |
Three minerals exist that are industrially relevant sources of fluorine: fluorite, fluorapatite, and cryolite. | 9 | Geochemistry |
In analytical chemistry, crossed molecular beam experiments involve two beams of atoms or molecules which are collided together to study the dynamics of the chemical reaction, and can detect individual reactive collisions. | 7 | Physical Chemistry |
Oncometabolites are metabolites whose abundance increases markedly in cancer cells through loss-of-function or gain-of-function mutations in specific enzymes involved in their production, the accumulation of these endogenous metabolites initiates or sustains tumor growth and metastasis. Cancer cells rely on aerobic glycolysis, which is reached through defects in enzymes involved in normal cell metabolism, this allows the cancer cells to meet their energy needs and divert acetyl-CoA from the TCA cycle to build essential biomolecules such as amino acids and lipids. These defects cause an overabundance of endogenous metabolites, which are frequently involved in critical epigenetic changes and signaling pathways that have a direct impact on cancer cell metabolism. | 1 | Biochemistry |
Experimentally, it is hard to map the phase diagram of quark matter because it has been rather difficult to learn how to tune to high enough temperatures and density in the laboratory experiment using collisions of relativistic heavy ions as experimental tools. However, these collisions ultimately will provide information about the crossover from hadronic matter to QGP. It has been suggested that the observations of compact stars may also constrain the information about the high-density low-temperature region. Models of the cooling, spin-down, and precession of these stars offer information about the relevant properties of their interior. As observations become more precise, physicists hope to learn more.
One of the natural subjects for future research is the search for the exact location of the chiral critical point. Some ambitious lattice QCD calculations may have found evidence for it, and future calculations will clarify the situation. Heavy-ion collisions might be able to measure its position experimentally, but this will require scanning across a range of values of μ and T. | 7 | Physical Chemistry |
Helmut Cölfen discovered and named mesocrystals in 2005 during his studies on biominerals. He suggested that their growth was due to a non-classical, self-assembly based process. | 7 | Physical Chemistry |
In simple cases there is only one grain or one type of material in the area used for collecting a diffraction pattern. However, often there is more than one. If they are in different areas then the diffraction pattern will be a combination. In addition there can be one grain on top of another, in which case the electrons that go through the first are diffracted by the second. Electrons have no memory (like many of us), so after they have gone through the first grain and been diffracted, they traverse the second as if their current direction was that of the incident beam. This leads to diffraction spots which are the vector sum of those of the two (or even more) reciprocal lattices of the crystals, and can lead to complicated results. It can be difficult to know if this is real and due to some novel material, or just a case where multiple crystals and diffraction is leading to odd results. | 7 | Physical Chemistry |
Corepressor proteins also bind to the surface of the ligand binding domain of nuclear receptors, but through a LXXXIXXX(I/L) motif of amino acids (where L = leucine, I = isoleucine and X = any amino acid). In addition, compressors bind preferentially to the apo (ligand free) form of the nuclear receptor (or possibly antagonist bound receptor).
* CtBP 602618 (associates with class II histone deacetylases)
* LCoR (ligand-dependent corepressor)
* Nuclear receptor CO-Repressor (NCOR)
** NCOR1 ()
** NCOR2 ()/SMRT (Silencing Mediator (co-repressor) for Retinoid and Thyroid-hormone receptors) (associates with histone deacetylase-3)
* Rb (retinoblastoma protein) (associates with histone deacetylase-1 and -2)
* RCOR (REST corepressor)
** RCOR1 ()
** RCOR2 ()
** RCOR3 ()
* Sin3
** SIN3A ()
** SIN3B ()
* TIF1 (transcriptional intermediary factor 1)
** TRIM24 Tripartite motif-containing 24 ()
** TRIM28 Tripartite motif-containing 28 ()
** TRIM33 Tripartite motif-containing 33 () | 1 | Biochemistry |
CNS is a mixture of chloroacetophenone, chloropicrin and chloroform that is used as a chemical warfare agent. CNS has the lachrymatory effects of chloroacetophenone and choking effects of chloropicrin. It has a flypaper-like odor.
CNS was used as a riot control agent, but it's no longer used now. | 1 | Biochemistry |
From the very early stages of structural studies of DNA by X-ray diffraction and biochemical means, molecular models such as the Watson-Crick nucleic acid double helix model were successfully employed to solve the puzzle of DNA structure, and also find how the latter relates to its key functions in living cells. The first high quality X-ray diffraction patterns
of A-DNA were reported by Rosalind Franklin and Raymond Gosling in 1953. Rosalind Franklin made the critical observation that DNA exists in two distinct forms, A and B, and produced the sharpest pictures of both through X-ray diffraction technique. The first calculations of the Fourier transform of an atomic helix were reported one year earlier by Cochran, Crick and Vand, and were followed in 1953 by the computation of the Fourier transform of a coiled-coil by Crick.
Structural information is generated from X-ray diffraction studies of oriented DNA fibers with the help of molecular models of DNA that are combined with crystallographic and mathematical analysis of the X-ray patterns.
The first reports of a double helix molecular model of B-DNA structure were made by James Watson and Francis Crick in 1953. That same year, Maurice F. Wilkins,
A. Stokes and H.R. Wilson, reported the first X-ray patterns
of in vivo B-DNA in partially oriented salmon sperm heads.
The development of the first correct double helix molecular model of DNA by Crick and Watson may not have been possible without the biochemical evidence for the nucleotide base-pairing ([A---T]; [C---G]), or Chargaffs rules. Although such initial studies of DNA structures with the help of molecular models were essentially static, their consequences for explaining the in vivo functions of DNA were significant in the areas of protein biosynthesis and the quasi-universality of the genetic code. Epigenetic transformation studies of DNA in vivo' were however much slower to develop despite their importance for embryology, morphogenesis and cancer research. Such chemical dynamics and biochemical reactions of DNA are much more complex than the molecular dynamics of DNA physical interactions with water, ions and proteins/enzymes in living cells. | 4 | Stereochemistry |
Apart from being as a general tumor suppressor gene, p53 also plays an important part in regulating of metabolism. p53 activates hexokinase 2 (HK2) that converts glucose to glucose-6-phosphate (G6P) which enters glycolysis to produce ATP, or enters the pentose phosphate pathway (PPP). It therefore, supports macromolecular biosynthesis by producing reducing potential in the form of reduced Nicotinamide adenine dinucleotide phosphate (NADPH) and/or ribose that are used for nucleotide synthesis. p53 inhibits the glycolytic pathway by upregulating the expression of TP53-induced glycolysis and apoptosis regulator. Wild-type p53 supports the expression of PTEN (gene), which inhibits the PI3K pathway, thereby suppressing glycolysis. POU2F1 also cooperate with p53 in regulating the balance between oxidative and glycolytic metabolism. It provides resistance to oxidative stress that would regulates a set of genes that increase glucose metabolism and reduce mitochondrial respiration. This will provide additive force when the p53 is lost. Mutated Ras also enhances glycolysis, partly through increasing the activity of Myc and hypoxia-inducible factors. Although HIF-1 inhibits Myc, HIF-2 activates Myc causing the multiplicity of the tumor cells. | 1 | Biochemistry |
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