text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Freshly-distilled trichloroacetonitrile is a colorless liquid with a pungent odor that discolours rapidly yellowish to light brown. It is sensitive towards water, acids and bases.
The bond lengths are 146.0 pm (C–C), 116.5 pm (C≡N) and 176.3 pm (C–Cl). The bond angle is 110.0° (Cl–C–Cl). | 0 | Organic Chemistry |
There is evidence that immunological mechanisms may injure hypothermically perfused kidneys after reimplantation if the perfusate contained specific antibody. Cross described two pairs of human cadaver kidneys that were perfused simultaneously with cryoprecipitated plasma containing type specific HLA antibody to one of the pairs. Both these kidneys suffered early arterial thrombosis. Light described similar hyperacute rejection following perfusion storage and showed that the cryoprecipitated plasma used contained cytotoxic IgM antibody. This potential danger of using cryoprecipitated plasma was demonstrated experimentally by Filo who perfused dog kidneys for 24 hours with specifically sensitised cryoprecipitated dog plasma and found that he could induce glomerular and vascular lesions with capillary engorgement, endothelial swelling, infiltration by polymorphonuclear leucocytes and arterial thrombosis. Immunofluorescent microscopy demonstrated specific binding of IgG along endothelial surfaces, in glomeruli, and also in vessels. After reimplantation, complement fixation and tissue damage occurred in a similar pattern. There was some correlation between the severity of the histological damage and subsequent function of the kidneys.
Many workers have attempted to prevent kidneys rewarming during reimplantation but only Cohen has described using a system of active cooling. Measurements of lysosomal enzyme release from kidneys subjected to sham anastomoses, when either in or out of the cooling system, demonstrated how sensitive kidneys were to rewarming after a period of cold storage, and confirmed the effectiveness of the cooling system in preventing enzyme release. A further factor in minimising injury at the reimplantation operations may have been that the kidneys were kept at 7 °C within the cooling coil, which was within a degree of the temperature used during perfusion storage, so that the kidneys were not subjected to the greater changes in temperature that would have occurred if ice cooling had been used.
Dempster described using slow release of the vascular clamps at the end of kidney reimplantation operations to avoid injuring the kidney, but other workers have not mentioned whether or not they used this manoeuvre. After Cohen found vascular injury with intra renal bleeding after 3 days of perfusion storage, a technique of slow revascularisation was used for all subsequent experiments, with the aim of giving the intra- renal vessels time to recover their tone sufficiently to prevent full systolic pressure being applied to the fragile glomerular vessels. The absence of gross vascular injury in his later perfusions may be attributable to the use of this manoeuvre. | 1 | Biochemistry |
* [https://www.youtube.com/watch?v=iIXI_pl-Akk&feature=emb_logo Solar power from space] 5-minute video about space-based solar power plants by the European Space Agency
* [https://web.archive.org/web/20091020135852/http://www.thefutureschannel.com/dockets/realworld/space_based_solar_power/ Powering the Planet] 20-minute streaming video from The Futures Channel that provides a "101" on space-based solar power
* [https://www.youtube.com/watch?v=eTdJw30Pg4Q Space Solar Power] NewSpace 2010 Panel, 72 minutes
* [https://www.youtube.com/watch?v=kMW64hqipGI Space Solar Power and Space Energy Systems] SSI – Space Manufacturing 14 Panel – 2010 – 27 min
* [https://www.youtube.com/watch?v=og9UvxrHA9E NASA DVD in 16 Parts] Exploring New Frontiers for Tomorrow's Energy Needs
* [https://www.youtube.com/watch?v=2E_z6L9Hn0Q Space Solar Power] Press Conference September 12, 2008 (71 minutes) National Space Society
* [https://www.bbc.co.uk/programmes/p00yjt99 BBC One - Bang Goes the Theory, Series 6, Episode 5, Transmitting power without wires] BBC/Lighthouse DEV Eye-safe Laser Based Power Beaming Demo | 7 | Physical Chemistry |
* [https://vimeo.com/132472772 Towards a metabolism for synthetic cells] (video KNAW-symposium: Op jacht naar de minimale cel, 24 juni 2015 op Vimeo)
* [https://www.youtube.com/watch?v=O8BpEiYEvAU De mens als schepper] (The human being as creator. Unifocus on YouTube. Subtitles in English) | 0 | Organic Chemistry |
Methane chlorination is a chain reaction. If only the products and reactants are analyzed, the result is:
However, this reaction has 3 intermediate reactants which are formed during a sequence of 4 irreversible second order reactions until we arrive at the final product. This is why it is called a chain reaction. Following only the carbon containing species in series:
Reactants:
Products:
The other species are reaction intermediates:
These are the set of irreversible second-order reactions:
These intermediate species' concentrations can be calculated by integrating the system of kinetic equations. The full reaction is a free radical propagation reaction which is filled out in detail below.
Initiation: This reaction can occur by thermolysis (heating) or photolysis (absorption of light) leading to the breakage of a molecular chlorine bond.
When the bond is broken it produces two highly reactive chlorine atoms.
Propagation: This stage has two distinct reaction classes. The first is the stripping of a hydrogen from the carbon species by the chlorine radicals. This occurs because chlorine atoms alone are unstable, and these chlorine atoms react with one the carbon species' hydrogens. The result is the formation of hydrochloric acid and a new radical methyl group.
These new radical carbon containing species now react with a second molecule. This regenerates the chlorine radical and the cycle continues. This reaction occurs because while the radical methyl species are more stable than the radical chlorines, the overall stability of the newly formed chloromethane species more than makes up the energy difference.
During the propagation of the reaction, there are several highly reactive species that will be removed and stabilized at the termination step.
Termination: This kind of reaction takes place when the radical species interact directly. The products of the termination reactions are typically very low yield in comparison to the main products or intermediates as the highly reactive radical species are in relatively low concentration in relation to the rest of the mixture. This kind of reaction produces stable side products, reactants, or intermediates and slows the propagation reaction by lowering the number of radicals available to propagate the chain reaction.
There are many different termination combinations, some examples are:
Union of methyl radicals from a C-C bond leading to ethane (a side product).
Union of one methyl radical to a Cl radical forming chloromethane (another reaction forming an intermediate).
Union of two Cl radicals to reform chlorine gas (a reaction reforming a reactant). | 7 | Physical Chemistry |
Thermopiles are used for measuring the intensity of incident radiation, typically visible or infrared light, which heats the hot junctions, while the cold junctions are on a heat sink. It is possible to measure radiative intensities of only a few μW/cm with commercially available thermopile sensors. For example, some laser power meters are based on such sensors; these are specifically known as thermopile laser sensor.
The principle of operation of a thermopile sensor is distinct from that of a bolometer, as the latter relies on a change in resistance. | 8 | Metallurgy |
Evelyn B. Man was born in Lawrence, New York, but she grew up in North Stonington, Connecticut. Man's father, Edward Man, was an attorney from New York City and her mother was Mary Hewitt Man.
Man graduated from Wheeler High School, and then, in 1925, she graduated from Wellesley College with a degree in chemistry. Man graduated from Yale with a doctorate degree in physiological chemistry in 1932. | 1 | Biochemistry |
When used as a food additive, ractopamine added to feed can be distributed by the blood to the muscle tissues, where it serves as a full agonist to murine (mouse or rat) TAAR1, a receptor protein (not necessarily in humans). It is also an agonist to beta-adrenergic receptors. A cascade of events will then be initiated to increase protein synthesis, which results in increased muscle fiber size. Ractopamine is known to increase the rate of weight gain, improve feed efficiency, and increase carcass leanness in finishing swine. Its use in finishing swine yields about of additional lean pork per animal, and improves feed efficiency by 10%. In cattle on 28 January 2004 Elanco Animal Health
made Optaflexx commercially available in the US. Optaflexx is a "medicated feed additive that is labeled only for use in steers or market heifers (not breeding heifers or bulls) during the last 28–42 days on feed." | 4 | Stereochemistry |
These density differences caused by temperature and salinity ultimately separate ocean water into distinct water masses, such as the North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). These two waters are the main drivers of the circulation, which was established in 1960 by Henry Stommel and Arnold B. Arons. They have chemical, temperature and isotopic ratio signatures (such as Pa / Th ratios) which can be traced, their flow rate calculated, and their age determined. NADW is formed because North Atlantic is a rare place in the ocean where precipitation, which adds fresh water to the ocean and so reduces its salinity, is outweighed by evaporation, in part due to high windiness. When water evaporates, it leaves salt behind, and so the surface waters of the North Atlantic are particularly salty. North Atlantic is also an already cool region, and evaporative cooling reduces water temperature even further. Thus, this water sinks downwards in the Norwegian Sea, fills the Arctic Ocean Basin and spills southwards through the Greenland-Scotland-Ridge - crevasses in the submarine sills that connect Greenland, Iceland and Great Britain. It cannot flow towards the Pacific Ocean due to the narrow shallows of the Bering Strait, but it does slowly flow into the deep abyssal plains of the south Atlantic.
In the Southern Ocean, strong katabatic winds blowing from the Antarctic continent onto the ice shelves will blow the newly formed sea ice away, opening polynyas in locations such as Weddell and Ross Seas, off the Adélie Coast and by Cape Darnley. Without sea ice acting a Meanwhile, sea ice starts reforming, so the surface waters also get saltier, hence very dense. In fact, the formation of sea ice contributes to an increase in surface seawater salinity; saltier brine is left behind as the sea ice forms around it (pure water preferentially being frozen). Increasing salinity lowers the freezing point of seawater, so cold liquid brine is formed in inclusions within a honeycomb of ice. The brine progressively melts the ice just beneath it, eventually dripping out of the ice matrix and sinking. This process is known as brine rejection. The resulting Antarctic bottom water sinks and flows north and east. It is denser than the NADW, and so flows beneath it. AABW formed in the Weddell Sea will mainly fill the Atlantic and Indian Basins, whereas the AABW formed in the Ross Sea will flow towards the Pacific Ocean. At the Indian Ocean, a vertical exchange of a lower layer of cold and salty water from the Atlantic and the warmer and fresher upper ocean water from the tropical Pacific occurs, in what is known as overturning. In the Pacific Ocean, the rest of the cold and salty water from the Atlantic undergoes haline forcing, and becomes warmer and fresher more quickly.
The out-flowing undersea of cold and salty water makes the sea level of the Atlantic slightly lower than the Pacific and salinity or halinity of water at the Atlantic higher than the Pacific. This generates a large but slow flow of warmer and fresher upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesian Archipelago to replace the cold and salty Antarctic Bottom Water. This is also known as haline forcing (net high latitude freshwater gain and low latitude evaporation). This warmer, fresher water from the Pacific flows up through the South Atlantic to Greenland, where it cools off and undergoes evaporative cooling and sinks to the ocean floor, providing a continuous thermohaline circulation. | 9 | Geochemistry |
Grignard reagents serve as a base for non-protic substrates (this scheme does not show workup conditions, which typically includes water). Grignard reagents are basic and react with alcohols, phenols, etc. to give alkoxides (ROMgBr). The phenoxide derivative is susceptible to formylation by paraformaldehyde to give salicylaldehyde. | 0 | Organic Chemistry |
Plant immune system activity is regulated in part by signaling hormones such as:
* Salicylic acid
* Jasmonic acid
* Ethylene
There can be substantial cross-talk among these pathways. | 1 | Biochemistry |
Before modern PCR methods existed, it was almost impossible to analyze degraded DNA samples. Methods like restriction fragment length polymorphism or RFLP Restriction fragment length polymorphism, which was the first technique used for DNA analysis in forensic science, required high molecular weight DNA in the sample in order to get reliable data. High molecular weight DNA, however, is lacking in degraded samples, as the DNA is too fragmented to carry out RFLP accurately. It was only when PCR techniques were invented that analysis of degraded DNA samples were able to be carried out Polymerase chain reaction. Multiplex PCR in particular made it possible to isolate and to amplify the small fragments of DNA that are still left in degraded samples. When multiplex PCR methods are compared to the older methods like RFLP, a vast difference can be seen. Multiplex PCR can theoretically amplify less than 1 ng of DNA, but RFLP had to have a least 100 ng of DNA in order to carry out an analysis. | 1 | Biochemistry |
Applications of phase change materials include, but are not limited to:
* Thermal energy storage, such as the FlexTherm Eco by Flamco.
* Solar cooking
* Cold Energy Battery
* Conditioning of buildings, such as ice-storage
* Cooling of heat and electrical engines
* Cooling: food, beverages, coffee, wine, milk products, green houses
*Delaying ice and frost formation on surfaces
* Medical applications: transportation of blood, operating tables, hot-cold therapies, treatment of birth asphyxia
* Human body cooling under bulky clothing or costumes.
* Waste heat recovery
* Off-peak power utilization: Heating hot water and Cooling
* Heat pump systems
* Passive storage in bioclimatic building/architecture (HDPE, paraffin)
* Smoothing exothermic temperature peaks in chemical reactions
* Solar power plants
* Spacecraft thermal systems
* Thermal comfort in vehicles
* Thermal protection of electronic devices
* Thermal protection of food: transport, hotel trade, ice-cream, etc.
* Textiles used in clothing
* Computer cooling
* Turbine Inlet Chilling with thermal energy storage
* Telecom shelters in tropical regions. They protect the high-value equipment in the shelter by keeping the indoor air temperature below the maximum permissible by absorbing heat generated by power-hungry equipment such as a Base Station Subsystem. In case of a power failure to conventional cooling systems, PCMs minimize use of diesel generators, and this can translate into enormous savings across thousands of telecom sites in tropics. | 7 | Physical Chemistry |
John William Draper (May 5, 1811 – January 4, 1882) was an English scientist, philosopher, physician, chemist, historian and photographer. He is credited with pioneering portrait photography (1839–40) and producing the first detailed photograph of the moon in 1840. He was also the first president of the American Chemical Society (1876–77) and a founder of the New York University School of Medicine.
One of Drapers books, the History of the Conflict between Religion and Science', popularised the conflict thesis proposing intrinsic hostility in the relationship between religion and science. It was widely read and was translated into several languages.
His son, Henry Draper, and his granddaughter, Antonia Maury, were astronomers. His granddaughter, Carlotta Maury (Antonia's younger sister), was a paleontologist. His eldest son, John Christopher Draper, was a chemist; and son Daniel Draper, a meteorologist. | 5 | Photochemistry |
Modern biological research has revealed strong evidence that the enzymes of the mitochondrial respiratory chain assemble into larger, supramolecular structures called supercomplexes, instead of the traditional fluid model of discrete enzymes dispersed in the inner mitochondrial membrane. These supercomplexes are functionally active and necessary for forming stable respiratory complexes.
One supercomplex of complex I, III, and IV make up a unit known as a respirasome. Respirasomes have been found in a variety of species and tissues, including rat brain, liver, kidney, skeletal muscle, heart, bovine heart, human skin fibroblasts, fungi, plants, and C. elegans. | 1 | Biochemistry |
The BOD is used in measuring waste loadings to treatment plants and in evaluating the BOD-removal efficiency of such treatment systems. | 3 | Analytical Chemistry |
Stereoisomers have the same atoms or isotopes connected by bonds of the same type, but differ in their shapes – the relative positions of those atoms in space – apart from rotations and translations.
In theory, one can imagine any arrangement in space of the atoms of a molecule or ion to be gradually changed to any other arrangement in infinitely many ways, by moving each atom along an appropriate path. However, changes in the positions of atoms will generally change the internal energy of a molecule, which is determined by the angles between bonds in each atom and by the distances between atoms (whether they are bonded or not).
A conformational isomer is an arrangement of the atoms of the molecule or ion for which the internal energy is a local minimum; that is, an arrangement such that any small changes in the positions of the atoms will increase the internal energy, and hence result in forces that tend to push the atoms back to the original positions. Changing the shape of the molecule from such an energy minimum to another energy minimum will therefore require going through configurations that have higher energy than and . That is, a conformation isomer is separated from any other isomer by an energy barrier: the amount that must be temporarily added to the internal energy of the molecule in order to go through all the intermediate conformations along the "easiest" path (the one that minimizes that amount).
A classic example of conformational isomerism is cyclohexane. Alkanes generally have minimum energy when the angles are close to 110 degrees. Conformations of the cyclohexane molecule with all six carbon atoms on the same plane have a higher energy, because some or all the angles must be far from that value (120 degrees for a regular hexagon). Thus the conformations which are local energy minima have the ring twisted in space, according to one of two patterns known as chair (with the carbons alternately above and below their mean plane) and boat (with two opposite carbons above the plane, and the other four below it).
If the energy barrier between two conformational isomers is low enough, it may be overcome by the random inputs of thermal energy that the molecule gets from interactions with the environment or from its own vibrations. In that case, the two isomers may as well be considered a single isomer, depending on the temperature and the context. For example, the two conformations of cyclohexane convert to each other quite rapidly at room temperature (in the liquid state), so that they are usually treated as a single isomer in chemistry.
In some cases, the barrier can be crossed by quantum tunneling of the atoms themselves. This last phenomenon prevents the separation of stereoisomers of fluorochloroamine or hydrogen peroxide , because the two conformations with minimum energy interconvert in a few picoseconds even at very low temperatures.
Conversely, the energy barrier may be so high that the easiest way to overcome it would require temporarily breaking and then reforming one or more bonds of the molecule. In that case, the two isomers usually are stable enough to be isolated and treated as distinct substances. These isomers are then said to be different configurational isomers or "configurations" of the molecule, not just two different conformations. (However, one should be aware that the terms "conformation" and "configuration" are largely synonymous outside of chemistry, and their distinction may be controversial even among chemists.)
Interactions with other molecules of the same or different compounds (for example, through hydrogen bonds) can significantly change the energy of conformations of a molecule. Therefore, the possible isomers of a compound in solution or in its liquid and solid phases many be very different from those of an isolated molecule in vacuum. Even in the gas phase, some compounds like acetic acid will exist mostly in the form of dimers or larger groups of molecules, whose configurations may be different from those of the isolated molecule. | 4 | Stereochemistry |
* Calmodulin 1 ()
* Calmodulin 2 ()
* Calmodulin 3 ()
* calmodulin 1 pseudogene 1 ()
* Calmodulin-like 3 ()
* Calmodulin-like 4 ()
* Calmodulin-like 5 ()
* Calmodulin-like 6 () | 1 | Biochemistry |
The concept of using a post-column catalytic reactor to enhance the response of the FID was described by Kenneth Porter & D.H. Volman, for the reduction of carbon dioxide and carbon monoxide to methane using a nickel catalyst. This process was later refined by Johns & Thompson, and is now commonplace in many laboratories, colloquially referred to as a methanizer. This device is limited to the conversion of carbon dioxide and carbon monoxide to methane, and the nickel catalysts are poisoned by species such as sulfur and ethylene.
The use of two reactors in series for the subsequent combustion and then reduction of organic molecules is described by Takuro Watanabes group and Paul Dauenhauers group using separate reactors for oxidation and reduction. The authors demonstrate the effectiveness of this technique in qualifying traceable standards and the analysis of mixtures without calibrations.
The PolyArc reactor combines the combustion and reduction zones into a single microreactor using proprietary catalyst blends that efficiently convert organic molecules to methane. | 3 | Analytical Chemistry |
In plumbing systems fluxes are used to keep the mating surfaces clean during soldering operations. The fluxes often consist of corrosive chemicals such as ammonium chloride and zinc chloride in a binder such as petroleum jelly. If too much flux is applied to the joint then the excess will melt and run down the bore of a vertical tube or pool in the bottom of a horizontal tube. Where the bore of the tube is covered in a layer of flux it may be locally protected from corrosion but at the edges of the flux pits often initiate. If the tube is put into service in a water that supports Type 1 pitting then these pits will develop and eventually perforate the sides of the tube. | 8 | Metallurgy |
Gustavs Vanags was born in "Rungas" house of the Schnicken (Sniķeru) manor (now in Ukri Parish, Auce Municipality). He received primary education in the Mitau Classic Gymnasium, and in 1910 enrolled Riga Polytechnic Institute. During the First World War, he, among many, went in evacuation to the inner regions of Russian Empire; after returning from it in 1921, he completed his education in the new-founded University of Latvia and worked at the Faculty of Chemistry, raising to the position of the chair of the Department of organic chemistry. He received his habilitation in 1932.
After Riga Polytechnic Institute was reestablished in 1958, G. Vanags moved to it, serving in the same position as the department chair until 1965. Simultaneously he also worked in the State Institute of Organic Synthesis, where he carried out his research in the chemistry of cyclic β-diketones. He was founder of Riga scholl of organic chemists specializing on β-diketones, which continues up to day (2020). Gustavs Vanags, along with his students, designed and synthesized several compounds of notable application in medicine, agriculture and chemical analysis (omefin, bindon, nitroindandione, rhodenticide diphenadione or ratindan).
Gustavs Vanags died in a sudden death on May 8, 1965, in Riga. He was buried in the Forest Cemetery. | 0 | Organic Chemistry |
ELSDs analyze solutes eluting out of the chromatographic column, both in LC and SFC. As the eluent exits the columns outlet into the detector inlet, it is mixed with an inert carrier gas (usually nitrogen) and forced through a nebulizer, which separates the liquid into fine aerosolized droplets. These droplets then pass into a heated drift tube, where the mobile phase solvent is evaporated off. As the mobile phase evaporates, the droplets become smaller and smaller until all that is left is minute particles of dried analyte. These particles are pushed through the drift tube by the carrier gas to the detection region. In this region, a beam of light crosses the column of analyte and the scattering of light is measured by a photodiode or photomultiplier tube. The detectors output is non-linear across more than one order of magnitude and proper calibration is required for quantitative analysis. | 3 | Analytical Chemistry |
TIRAP (TIR domain containing adaptor protein) is an adapter molecule associated with toll-like receptors. The innate immune system recognizes microbial pathogens through Toll-like receptors (TLRs), which identify pathogen-associated molecular patterns. Different TLRs recognize different pathogen-associated molecular patterns and all TLRs have a Toll-interleukin 1 receptor (TIR) domain, which is responsible for signal transduction. The protein encoded by this gene is a TIR adaptor protein involved in the TLR4 signaling pathway of the immune system. It activates NF-kappa-B, MAPK1, MAPK3 and JNK, which then results in cytokine secretion and the inflammatory response. Alternative splicing of this gene results in several transcript variants; however, not all variants have been fully described. | 1 | Biochemistry |
The rotary vacuum drum filter designs available vary in physical aspects and their characteristics. The filtration area ranges from 0.5 m to 125 m. Disregarding the size of the design, filter cloth washing is a priority as it ensures efficiency of cake washing and acting vacuum. However, a smaller design would be more economical as the maintenance, energy usage and investment cost would be less than a bigger rotary vacuum drum filter.
Over the years, the technology drive has pushed development to further heights revolving around rotary vacuum drum filter in terms of design, performance, maintenance and cost. This has also led to the development of smaller rotary drum vacuum filters, ranging from laboratory scale to pilot scale, both of which can be used for smaller applications (such as at a lab in a university) High performance capacity, optimised filtrate drainage with low flow resistance and minimal pressure loss are just a few of the benefits.
With advanced control systems prompting automation, this has reduced the operation of attention needed hence, reducing the operational cost. Advancements in technology also means that precoat can be cut to 1/20th the thickness of human hair, thus making the use of precoat more efficient Lowered operational and capital cost can also be achieved nowadays due to easier maintenance and cleaning. Complete cell emptying can be done quickly with the installation of leading and trailing pipes.
Given that the filter cloth is usually one of the more expensive component in the rotary vacuum drum filter build up, priority on its maintenance must be kept quite high. A longer lifetime, protection from damage and consistent performance are the few criteria that must not be overlooked.
Besides considering production cost and quality, cake washing and cake thickness are essential issues that are important in the process. Methods have been performed to ensure a minimal amount of cake moisture while undergoing good cake washing with large cake dewatering angle. An even thickness of filter cake besides having a complete cake discharge is also possible. | 3 | Analytical Chemistry |
After time is allowed for binding with the oligonucleotide probes, the hope is that some of the proteins on the membrane filter have bound to the probes. Any probe that was not able to bind a protein needs to be removed. Once unbound probe removal has been taken care of, to better visualize the membrane filter, it is subjected to further varying procedures. By corresponding the resulting membrane filter to the second membrane filter that the gel was sandwiched between, the position of the protein in comparison to the molecular weight ladder gives information about the weight of the protein that bound to the probe. | 1 | Biochemistry |
The term "triangle of death" was first used with regard to the region in a September 2004 scientific publication in the Lancet Oncology. | 2 | Environmental Chemistry |
Sponge iron is not useful by itself, but can be processed to create wrought iron or steel. The sponge is removed from the furnace, called a bloomery, and repeatedly beaten with heavy hammers and folded over to remove the slag, oxidize any carbon or carbide, and weld the iron together. This treatment usually creates wrought iron with about three percent slag and a fraction of a percent of other impurities. Further treatment may add controlled amounts of carbon, allowing various kinds of heat treatment (e.g. "steeling").
Today, sponge iron is created by reducing iron ore without melting it. This makes for an energy-efficient feedstock for specialty steel manufacturers which used to rely upon scrap metal. | 8 | Metallurgy |
A non-stick surface is engineered to reduce the ability of other materials to stick to it. Non-stick cookware is a common application, where the non-stick coating allows food to brown without sticking to the pan. Non-stick is often used to refer to surfaces coated with polytetrafluoroethylene (PTFE), a well-known brand of which is Teflon. In the twenty-first century, other coatings have been marketed as non-stick, such as anodized aluminium, silica, enameled cast iron, and seasoned cookware. | 7 | Physical Chemistry |
A number of adhesion GPCRs may have important roles within the immune system. In particular, members the EGF-TM7 subfamily which possess N-terminal EGF-like domains are predominantly restricted to leukocytes suggesting a putative role in immune function. The human EGF‑TM7 family is composed of CD97, EMR1 (F4/80 receptor orthologue) EMR2, EMR3 and EMR4 (a probable pseudogene in humans). The human-restricted EMR2 receptor, is expressed by myeloid cells including monocytes, dendritic cells and neutrophils has been shown to be involved in the activation and migration of human neutrophils and upregulated in patients with systemic inflammatory response syndrome (SIRS). Details of EMR1, CD97 needed. The adhesion‑GPCR brain angiogenesis inhibitor 1 (BAI1) acts as a phosphatidylserine receptor playing a potential role in the binding and clearance of apoptotic cells, and the phagocytosis of Gram-negative bacteria. GPR56 has been shown to a marker for inflammatory NK cell subsets and to be expressed by cytotoxic lymphocytes. | 1 | Biochemistry |
The thermodynamic potentials also satisfy
where is the chemical potential defined as (for constant n</sub> with j≠i):
This last partial derivative is the same as , the partial molar Gibbs free energy. This means that the partial molar Gibbs free energy and the chemical potential, one of the most important properties in thermodynamics and chemistry, are the same quantity. Under isobaric (constant P) and isothermal (constant T ) conditions, knowledge of the chemical potentials, , yields every property of the mixture as they completely determine the Gibbs free energy. | 7 | Physical Chemistry |
In April 1989, MIM Holdings Limited acquired the world rights to the Jameson Cell from TUNRA, with TUNRA retaining the rights to use the Cell for waste water treatment.
After the initial applications within the MIM Holdings group of companies, the years to 1994 saw Jameson Cells installed by various base and precious metals companies in Asia, South Africa, Canada and the United States, mainly in concentrate cleaning duties, but also in SX–EW electrolyte cleaning duties. The installation by Phelps Dodge (now Freeport-McMoRan) for electrolyte cleaning at its Morenci operation in Arizona was notable for having a large cell 6.5 m in diameter with 30 downcomers. The Morenci Jameson Cell consistently recovered over 82% of the organic extractant.
Toward the end of the period, Cells were installed in coal preparation plants operated by the BHP Mitsubishi Alliance and by Peabody for fines recovery. | 8 | Metallurgy |
The reaction is catalyzed by a base and a divalent metal such as calcium. The intermediary steps taking place are aldol reactions, reverse aldol reactions, and aldose-ketose isomerizations. Intermediates are glycolaldehyde, glyceraldehyde, dihydroxyacetone, and tetrose sugars. In 1959, Breslow proposed a mechanism for the reaction, consisting of the following steps:
The reaction exhibits an induction period, during which only the nonproductive Cannizzaro disproportionation of formaldehyde (to methanol and formate) occurs. The initial dimerization of formaldehyde to give glycolaldehyde (1) occurs via an unknown mechanism, possibly promoted by light or through a free radical process and is very slow. However, the reaction is autocatalytic: 1 catalyzes the condensation of two molecules of formaldehyde to produce an additional molecule of 1. Hence, even a trace (as low as 3 ppm) of glycolaldehyde is enough to initiate the reaction. The autocatalytic cycle begins with the aldol reaction of 1 with formaldehyde to make glyceraldehyde (2). An aldose-ketose isomerization of 2 forms dihydroxyacetone (3). A further aldol reaction of 3 with formaldehyde produces tetrulose (6), which undergoes another ketose-aldose isomerization to form aldotetrose 7 (either threose or erythrose). The retro-aldol reaction of 7 generates two molecules of 1, resulting in the net production of a molecule of 1 from two molecules of formaldehyde, catalyzed by 1 itself (autocatalysis). During this process, 3 can also react with 1 to form ribulose (4), which can isomerize to give rise to ribose (5), an important building block of ribonucleic acid. The reaction conditions must be carefully controlled, otherwise the alkaline conditions will cause the aldoses to undergo the Cannizzaro reaction.
The aldose-ketose isomerization steps are promoted by chelation to calcium. However, these steps have been shown to proceed through a hydride shift mechanism by isotope labeling studies, instead of via an intermediate enediolate, as previously proposed. | 0 | Organic Chemistry |
In biology, actinic light denotes light from solar or other sources that can cause photochemical reactions such as photosynthesis in a species. | 7 | Physical Chemistry |
There's evidence of very early metallurgy at Aratashen, going back to the first half of the sixth millennium BCE. According to A. Courcier,
At Aratashen and Khatunakh/Aknashen, there are similarities to the contemporary sites of Kultepe I, and Alikemek-Tepesi. Another prehistoric site that is close to Aratashen is Masis Blur. | 8 | Metallurgy |
Dynamic reserve, in the context of the dynamic energy budget theory, refers to the set of metabolites (mostly polymers and lipids) that an organism can use for metabolic purposes. These chemical compounds can have active metabolic functions, however. They are not just "set apart for later use." Reserve differs from structure in the first place by its dynamics. Reserve has an implied turnover, because it is synthesized from food (or other substrates in the environment) and used by metabolic processes occurring in cells. The turnover of structure depends on the maintenance of an organism. Maintenance is not required for reserve. A freshly laid egg consists almost exclusively of reserve, and hardly respires. The chemical compounds in the reserve have the same turnover, while that in the structure can have a different turnover, and so it depends on the compound. | 1 | Biochemistry |
The term GM ("genetically modified") is often used as a synonym of transgenic to refer to plants modified using recombinant DNA technologies. Plants with transgenic/GM disease resistance against insect pests have been extremely successful as commercial products, especially in maize and cotton, and are planted annually on over 20 million hectares in over 20 countries worldwide (see also genetically modified crops). Transgenic plant disease resistance against microbial pathogens was first demonstrated in 1986. Expression of viral coat protein gene sequences conferred virus resistance via small RNAs. This proved to be a widely applicable mechanism for inhibiting viral replication. Combining coat protein genes from three different viruses, scientists developed squash hybrids with field-validated, multiviral resistance. Similar levels of resistance to this variety of viruses had not been achieved by conventional breeding.
A similar strategy was deployed to combat papaya ringspot virus, which by 1994 threatened to destroy Hawaii's papaya industry. Field trials demonstrated excellent efficacy and high fruit quality. By 1998 the first transgenic virus-resistant papaya was approved for sale. Disease resistance has been durable for over 15 years. Transgenic papaya accounts for ~85% of Hawaiian production. The fruit is approved for sale in the U.S., Canada and Japan.
Potato lines expressing viral replicase sequences that confer resistance to potato leafroll virus were sold under the trade names NewLeaf Y and NewLeaf Plus, and were widely accepted in commercial production in 1999–2001, until McDonald's Corp. decided not to purchase GM potatoes and Monsanto decided to close their NatureMark potato business. NewLeaf Y and NewLeaf Plus potatoes carried two GM traits, as they also expressed Bt-mediated resistance to Colorado potato beetle.
No other crop with engineered disease resistance against microbial pathogens had reached the market by 2013, although more than a dozen were in some state of development and testing. | 1 | Biochemistry |
* Quinine total synthesis
* Vitamin B total synthesis
* Strychnine total synthesis
* Paclitaxel (Taxol) total synthesis
* Cholesterol total synthesis | 0 | Organic Chemistry |
As described above, the use of N-terminal and side chain protecting groups is essential during peptide synthesis to avoid undesirable side reactions, such as self-coupling of the activated amino acid leading to (polymerization). This would compete with the intended peptide coupling reaction, resulting in low yield or even complete failure to synthesize the desired peptide.
Two principle protecting group schemes are typically used in solid phase peptide synthesis: so-called Boc/benzyl and Fmoc/tert-butyl approaches. The Boc/Bzl strategy utilizes TFA-labile N-terminal Boc protection alongside side chain protection that is removed using anhydrous hydrogen fluoride during the final cleavage step (with simultaneous cleavage of the peptide from the solid support). Fmoc/tBu SPPS uses base-labile Fmoc N-terminal protection, with side chain protection and a resin linkage that are acid-labile (final acidic cleavage is carried out via TFA treatment).
Both approaches, including the advantages and disadvantages of each, are outlined in more detail below. | 1 | Biochemistry |
At boiling and higher temperatures the sum of the individual component partial pressures becomes equal to the overall pressure, which can symbolized as .
Under such conditions, Dalton's law would be in effect as follows:
:P = P + P + ...
Then for each component in the vapor phase:
:y = P / P, y = P / P, ... etc.
where P = partial pressure of component 1, = partial pressure of component 2, etc.
Raoults law is approximately valid for mixtures of components between which there is very little interaction other than the effect of dilution by the other components. Examples of such mixtures includes mixtures of alkanes, which are non-polar, relatively inert compounds in many ways, so there is little attraction or repulsion between the molecules. Raoults law states that for components 1, 2, etc. in a mixture:
:P = x P, P = x P, ... etc.
where P, P, etc. are the vapor pressures of components 1, 2, etc. when they are pure, and x, x, etc. are mole fractions of the corresponding component in the liquid.
Recall from the first section that vapor pressures of liquids are very dependent on temperature. Thus the P pure vapor pressures for each component are a function of temperature (T): For example, commonly for a pure liquid component, the Clausius–Clapeyron relation may be used to approximate how the vapor pressure varies as a function of temperature. This makes each of the partial pressures dependent on temperature also regardless of whether Raoults law applies or not. When Raoults law is valid these expressions become:
:PT = x PT, PT = x PT, ... etc.
At boiling temperatures if Raoult's law applies, the total pressure becomes:
:P = x PT + x PT + ... etc.
At a given P such as 1 atm and a given liquid composition, T can be solved for to give the liquid mixtures boiling point or bubble point, although the solution for T may not be mathematically analytical (i.e., may require a numerical solution or approximation). For a binary mixture at a given P, the bubble point T can become a function of x (or x') and this function can be shown on a two-dimensional graph like a binary boiling point diagram.
At boiling temperatures if Raoult's law applies, a number of the preceding equations in this section can be combined to give the following expressions for vapor mole fractions as a function of liquid mole fractions and temperature:
:y = x PT / P, y = x PT / P, ... etc.
Once the bubble point Ts as a function of liquid composition in terms of mole fractions have been determined, these values can be inserted into the above equations to obtain corresponding vapor compositions in terms of mole fractions. When this is finished over a complete range of liquid mole fractions and their corresponding temperatures, one effectively obtains a temperature T function of vapor composition mole fractions. This function effectively acts as the dew point T' function of vapor composition.
In the case of a binary mixture, x = 1 − x and the above equations can be expressed as:
:y = x PT / P, and
:y = (1 − x) PT / P
For many kinds of mixtures, particularly where there is interaction between components beyond simply the effects of dilution, Raoults law does not work well for determining the shapes of the curves in the boiling point or VLE diagrams. Even in such mixtures, there are usually still differences in the vapor and liquid equilibrium concentrations at most points, and distillation is often still useful for separating components at least partially. For such mixtures, empirical data is typically used in determining such boiling point and VLE diagrams. Chemical engineers have done a significant amount of research trying to develop equations for correlating and/or predicting VLE data for various kinds of mixtures which do not obey Raoults law well. | 7 | Physical Chemistry |
Drugs can profoundly affect thyroid function tests. Listed below is a selection of important effects.
↓: reduced serum concentration or structure parameter; ↑: increased serum concentration or structure parameter; ↔: no change; TSH: Thyroid-stimulating hormone; T: Total triiodothyronine; T: Total thyroxine; fT: Free thyroxine; fT: Free triiodothyronine; rT: Reverse triiodothyronine | 1 | Biochemistry |
A dentine conditioning agent is used initially, to remove the smear layer resulting from the preparation of a cavity and, to alter the dentine surface by partially demineralising the intertubulary dentine. This partially demineralised dentine acts as a hollow scaffolding which can be perfused with the primer. Over-etching (as well as over-drying) of the dentine can lead to collapse of the collagen network, making infiltration of the primer more challenging. However, sclerosed dentine requires a longer time of exposure to the dentine conditioner compared to healthy dentine. Some dentine conditioners contain a chemical called glutaraldehyde, which reinforces the collagen matrix, preventing its collapse.
Some common dentine conditioners include:
* phosphoric acid
* nitric acid
* maleic acid
* citric acid
* ethylene diamine tetra-acetic acid (EDTA) | 7 | Physical Chemistry |
The Nanodragster, dubbed the worlds smallest hot rod, is a molecular nanocar. The design improves on previous nanocar designs and is a step towards creating molecular machines. The name comes from the nanocars resemblance to a dragster, as its staggered wheel fitment has a shorter axle with smaller wheels in the front and a larger axle with larger wheels in the back.
The nanocar was developed at Rice University’s Richard E. Smalley Institute Nanoscale Science and Technology by the team of James Tour, Kevin Kelly and other colleagues involved in its research. The previous nanocar developed was 3 to 4 nanometers which was a little a strand of DNA and was around 20,000 times thinner than a human hair. These nanocars were built with carbon buckyballs as their four wheels, and the surface on which they were placed required a temperature of to get it moving. On the other hand, a nanocar which utilized p-carborane wheels moves as if sliding on ice, rather than rolling. Such observations led to the production of nanocars which had both wheel designs.
The nanodragster is 50,000 times thinner than a human hair and has a top speed of 0.014 millimeters per hour (0.0006 in/h or 3.89×10 m/s). The rear wheels are spherical fullerene molecules, or buckyballs, composed of sixty carbon atoms each, which are attracted to a dragstrip that is made up of a very fine layer of gold. This design also enabled Tour’s team to operate the device at lower temperatures.
The nanodragster and other nano-machines are designed for use in transporting items. The technology can be used in manufacturing computer circuits and electronic components, or in conjunction with pharmaceuticals inside the human body. Tour also speculated that the knowledge gained from the nanocar research would help build efficient catalytic systems in the future. | 6 | Supramolecular Chemistry |
Mongo foot refers to the use of the rider's front foot for pushing. Normally, a skateboarder will feel more comfortable using their back foot to push, while their front foot remains on the board. In the minority case of mongo-footed skateboarders, the opposite is true. Some skateboarders who do not push mongo in their regular stance may still push mongo when riding in switch stance, rather than push with their weaker back foot. Some well-known skaters who change between mongo and normal when pushing switch include Jacob Vance, Stevie Williams, and Eric Koston.
Although its origins remain uncertain, it is widely believed that the term derives from the pejorative use of "mongoloid". | 4 | Stereochemistry |
As studies of the consequences of ocean acidification for marine organisms and ecosystems expanded rapidly over the past decade, the methods employed to evaluate the effects of expected future changes in ocean chemistry have become more sophisticated. Initial studies frequently involved measurements of the survival or physiological response of individuals of marine species to large changes in pCO2 or pH, while held in small containers under laboratory conditions. This approach increased the level of understanding of the effects of these environmental changes on individual species but provided little information concerning the response of natural assemblages of interacting species, in which the direct impacts of ocean acidification as well as their cascading indirect consequences (e.g. changes in the intensity of interaction strengths among predators or competitors) may be evident. Pelagic mesocosm experiments that examined the response of natural plankton communities to controlled pH perturbations helped move methods of ocean acidification research toward more comprehensive studies of whole communities and embedded processes under mostly natural conditions. The FOCE approach represents an analogous advance for benthic assemblages, by allowing examination of the direct effects of acidification on particular species, but also potential changes in interactions among species. Moreover, FOCE methods provide precise control of pH, while allowing many other parameters to vary naturally. Like mesocosm studies, FOCE methods exploit the advantages of studying a natural community under mostly natural ranges of environmental variability. | 9 | Geochemistry |
The idea of affinity is extremely old. Many attempts have been made at identifying its origins. The majority of such attempts, however, except in a general manner, end in futility since "affinities" lie at the basis of all magic, thereby pre-dating science. Physical chemistry, however, was one of the first branches of science to study and formulate a "theory of affinity". The name affinitas was first used in the sense of chemical relation by German philosopher Albertus Magnus near the year 1250. Later, those as Robert Boyle, John Mayow, Johann Glauber, Isaac Newton, and Georg Stahl put forward ideas on elective affinity in attempts to explain how heat is evolved during combustion reactions.
The term affinity has been used figuratively since c. 1600 in discussions of structural relationships in chemistry, philology, etc., and reference to "natural attraction" is from 1616. "Chemical affinity", historically, has referred to the "force" that causes chemical reactions. as well as, more generally, and earlier, the ″tendency to combine″ of any pair of substances. The broad definition, used generally throughout history, is that chemical affinity is that whereby substances enter into or resist decomposition.
The modern term chemical affinity is a somewhat modified variation of its eighteenth-century precursor "elective affinity" or elective attractions, a term that was used by the 18th century chemistry lecturer William Cullen. Whether Cullen coined the phrase is not clear, but his usage seems to predate most others, although it rapidly became widespread across Europe, and was used in particular by the Swedish chemist Torbern Olof Bergman throughout his book (1775). Affinity theories were used in one way or another by most chemists from around the middle of the 18th century into the 19th century to explain and organise the different combinations into which substances could enter and from which they could be retrieved. Antoine Lavoisier, in his famed 1789 Traité Élémentaire de Chimie (Elements of Chemistry), refers to Bergman's work and discusses the concept of elective affinities or attractions.
According to chemistry historian Henry Leicester, the influential 1923 textbook Thermodynamics and the Free Energy of Chemical Reactions by Gilbert N. Lewis and Merle Randall led to the replacement of the term "affinity" by the term "free energy" in much of the English-speaking world.
According to Prigogine, the term was introduced and developed by Théophile de Donder.
Goethe used the concept in his novel Elective Affinities (1809). | 7 | Physical Chemistry |
It is now widely accepted that atherosclerosis is a result of cellular and molecular events characteristic of inflammation. Vascular inflammation can be caused by upregulation of Ang-II, which is produced locally by inflamed vessels and induces synthesis and secretion of IL-6, a cytokine responsible for induction of angiotensinogen synthesis in liver through JAK/STAT3 pathway, which gets activated through high affinity membrane protein receptors on target cells, termed IL-6R-chain recruiting gp-130 that is associated with tyrosine kinases (Jaks 1/2, and TYK2 kinase). Cytokines IL-4 and IL-13 gets elevated in lungs of chronically suffered asthmatics. Signalling through IL-4/IL-13 complexes is thought to occur through IL-4Rα-chain, which is responsible for activation of JAK-1 and TYK2 kinases. A role of TYK2 in rheumatoid arthritis is directly observed in TYK2-deficient mice that were resistant to experimental arthritis. TYK2 mice displayed a lack of responsiveness to a small amount of IFN-α, but they respond normally to a high concentration of IFN-α/β. In addition, these mice respond normally to IL-6 and IL-10, suggesting that TYK2 is dispensable for mediating for IL-6 and IL-10 signaling and does not play a major role in IFN-α signaling. Although TYK2 mice are phenotypically normal, they exhibit abnormal responses to inflammatory challenges in a variety of cells isolated from TYK2 mice. The most remarkable phenotype observed in TYK2-deficient macrophages was lack of nitric oxide production upon stimulation with LPS. Further elucidation of molecular mechanisms of LPS signaling, showed that TYK2 and IFN-β deficiency leads resistance to LPS-induced endotoxin shock, whereas STAT1-deficient mice are susceptible. Development of a TYK2 inhibitor appears to be a rational approach in the drug discovery. | 1 | Biochemistry |
In 1763, James Watt was working as instrument maker at the University of Glasgow when he was assigned the job of repairing a model Newcomen engine and noted how inefficient it was.
In 1765, Watt conceived the idea of equipping the engine with a separate condensation chamber, which he called a "condenser". Because the condenser and the working cylinder were separate, condensation occurred without significant loss of heat from the cylinder. The condenser remained cold and below atmospheric pressure at all times, while the cylinder remained hot at all times.
Steam was drawn from the boiler to the cylinder under the piston. When the piston reached the top of the cylinder, the steam inlet valve closed and the valve controlling the passage to the condenser opened. The condenser being at a lower pressure, drew the steam from the cylinder into the condenser where it cooled and condensed from water vapour to liquid water, maintaining a partial vacuum in the condenser that was communicated to the space of the cylinder by the connecting passage. External atmospheric pressure then pushed the piston down the cylinder.
The separation of the cylinder and condenser eliminated the loss of heat that occurred when steam was condensed in the working cylinder of a Newcomen engine. This gave the Watt engine greater efficiency than the Newcomen engine, reducing the amount of coal consumed while doing the same amount of work as a Newcomen engine.
In Watts design, the cold water was injected only into the condensation chamber. This type of condenser is known as a jet condenser'. The condenser is located in a cold water bath below the cylinder. The volume of water entering the condenser as spray absorbed the latent heat of the steam, and was determined as seven times the volume of the condensed steam. The condensate and the injected water was then removed by the air pump, and the surrounding cold water served to absorb the remaining thermal energy to retain a condenser temperature of 30 °C to 45 °C and the equivalent pressure of 0.04 to 0.1 bar
At each stroke the warm condensate was drawn off from the condenser and sent to a hot well by a vacuum pump, which also helped to evacuate the steam from under the power cylinder. The still-warm condensate was recycled as feedwater for the boiler.
Watt's next improvement to the Newcomen design was to seal the top of the cylinder and surround the cylinder with a jacket. Steam was passed through the jacket before being admitted below the piston, keeping the piston and cylinder warm to prevent condensation within it. The second improvement was the utilisation of steam expansion against the vacuum on the other side of the piston. The steam supply was cut during the stroke, and the steam expanded against the vacuum on the other side. This increased the efficiency of the engine, but also created a variable torque on the shaft which was undesirable for many applications, in particular pumping. Watt therefore limited the expansion to a ratio of 1:2 (i.e. the steam supply was cut at half stroke). This increased the theoretical efficiency from 6.4% to 10.6%, with only a small variation in piston pressure. Watt did not use high pressure steam because of safety concerns.
These improvements led to the fully developed version of 1776 that actually went into production. | 7 | Physical Chemistry |
A number of lactose derivatives or analogs have been described that are useful for work with the lac operon. These compounds are mainly substituted galactosides, where the glucose moiety of lactose is replaced by another chemical group.
* Isopropyl-β-D-thiogalactopyranoside (IPTG) is frequently used as an inducer of the lac operon for physiological work. IPTG binds to repressor and inactivates it, but is not a substrate for β-galactosidase. One advantage of IPTG for in vivo studies is that since it cannot be metabolized by E. coli. Its concentration remains constant and the rate of expression of lac p/o-controlled genes is not a variable in the experiment. IPTG intake is dependent on the action of lactose permease in P. fluorescens, but not in E. coli.
* Phenyl-β-D-galactose (phenyl-Gal) is a substrate for β-galactosidase, but does not inactivate repressor and so is not an inducer. Since wild type cells produce very little β-galactosidase, they cannot grow on phenyl-Gal as a carbon and energy source. Mutants lacking repressor are able to grow on phenyl-Gal. Thus, minimal medium containing only phenyl-Gal as a source of carbon and energy is selective for repressor mutants and operator mutants. If 10 cells of a wild type strain are plated on agar plates containing phenyl-Gal, the rare colonies which grow are mainly spontaneous mutants affecting the repressor. The relative distribution of repressor and operator mutants is affected by the target size. Since the lacI gene encoding repressor is about 50 times larger than the operator, repressor mutants predominate in the selection.
* Thiomethyl galactoside [TMG] is another lactose analog. These inhibit the lacI repressor. At low inducer concentrations, both TMG and IPTG can enter the cell through the lactose permease. However at high inducer concentrations, both analogs can enter the cell independently. TMG can reduce growth rates at high extracellular concentrations.
* Other compounds serve as colorful indicators of β-galactosidase activity.
** ONPG is cleaved to produce the intensely yellow compound, orthonitrophenol and galactose, and is commonly used as a substrate for assay of β-galactosidase in vitro.
** Colonies that produce β-galactosidase are turned blue by X-gal (5-bromo-4-chloro-3-indolyl-β-D-galactoside) which is an artificial substrate for B-galactosidase whose cleavage results in galactose and 4-Cl,3-Br indigo thus producing a deep blue color.
* Allolactose is an isomer of lactose and is the inducer of the lac operon. Lactose is galactose-β(1→4)-glucose, whereas allolactose is galactose-β(1→6)-glucose. Lactose is converted to allolactose by β-galactosidase in an alternative reaction to the hydrolytic one. A physiological experiment which demonstrates the role of LacZ in production of the "true" inducer in E. coli cells is the observation that a null mutant of lacZ can still produce LacY permease when grown with IPTG, a non-hydrolyzable analog of allolactose, but not when grown with lactose. The explanation is that processing of lactose to allolactose (catalyzed by β-galactosidase) is needed to produce the inducer inside the cell. | 1 | Biochemistry |
AR4 is expressed in Halobacterium species xz 515. The organism was first identified in a salt lake in Tibet. The gene encoding it was identified by H. Wang and colleagues in 2000. In most bacteriorhodopsin homologs, H release to the extracellular medium takes place before a replacement ion is taken up from the cytosolic side of the membrane. Under the acidic conditions found in the organism's native habitat, the order of these stages in the AR4 photocycle is reversed. | 5 | Photochemistry |
Real-time PCR technique can be classified by the chemistry used to detect the PCR product, specific or non-specific fluorochromes. | 1 | Biochemistry |
Molecular imprinting describes a process by which a host is constructed from small molecules using a suitable molecular species as a template. After construction, the template is removed leaving only the host. The template for host construction may be subtly different from the guest that the finished host binds to. In its simplest form, imprinting uses only steric interactions, but more complex systems also incorporate hydrogen bonding and other interactions to improve binding strength and specificity. | 6 | Supramolecular Chemistry |
Solomon's considerable contributions to science have been recognised by his peers through election to the following Academies:
* Fellow of the Institution of Chemical Engineers (FIChemE, 2007)
* Fellow of the Royal Society (FRS, 2004).
* Foundation Fellow of the Australian Academy of Technological Sciences and Engineering (FTSE, 1976).
* Fellow of the Australian Academy of Science (FAA, 1975).
* Fellow of the Royal Australian Chemical Institute (FRACI, 1966)
Solomon has always been active in these societies, in particular the Royal Australian Chemical Institute (RACI). In 2001 the RACI established the Solomon Lecture Series in recognition of his contribution to the field and to the RACI. A biennial series presented by an invited leading international polymer researcher, this Lecture Series recognizes the importance of promoting the exchange of ideas and expertise and to expose young scientists to the best in their field internationally. | 7 | Physical Chemistry |
Another problem with plotting this (or any) type of count data is [http://en.wiktionary.org/wiki/overplotting overplotting] which is solved in the RA plot by jittering the points out away from each other but no so far as to merge with other coordinates. The result of this feature is a patchwork-like appearance to the plot that fades away as the A increases. | 1 | Biochemistry |
Electrochemical impedance spectroscopy is used in a wide range of applications.
In the paint and coatings industry, it is a useful tool to investigate the quality of coatings and to detect the presence of corrosion.
It is used in many biosensor systems as a label-free technique to measure bacterial concentration and to detect dangerous pathogens such as Escherichia coli O157:H7 and Salmonella, and yeast cells.
Electrochemical impedance spectroscopy is also used to analyze and characterize different food products. Some examples are the assessment of food–package interactions, the analysis of milk composition, the characterization and the determination of the freezing end-point of ice-cream mixes, the measure of meat ageing, the investigation of ripeness and quality in fruits and the determination of free acidity in olive oil.
In the field of human health monitoring is better known as bioelectrical impedance analysis (BIA) and is used to estimate body composition as well as different parameters such as total body water and free fat mass.
Electrochemical impedance spectroscopy can be used to obtain the frequency response of batteries and electrocatalytic systems at relatively high temperatures.
Biomedical sensors working in the microwave range relies on dielectric spectroscopy to detect changes in the dielectric properties over a frequency range, such as non-invasive continuous blood glucose monitoring. The IFAC database can be used as a resource to get the dielectric properties for human body tissues.
For heterogenous mixtures like suspensions impedance spectroscopy can be used to monitor the particle sedimentation process. | 7 | Physical Chemistry |
Palmitoylethanolamide (PEA) is an endogenous fatty acid amide, and lipid modulator PEA has been studied in in vitro and in vivo systems using exogenously added or dosed compound; there is evidence that it binds to a nuclear receptor, through which it exerts a variety of biological effects, some related to chronic inflammation and pain.
A main target of PEA is proposed to be the peroxisome proliferator-activated receptor alpha (PPAR-α). PEA also has affinity to cannabinoid-like G-coupled receptors GPR55 and GPR119. PEA cannot strictly be considered a classic endocannabinoid because it lacks affinity for the cannabinoid receptors CB1 and CB2. However, primary research supports the conclusion that the presence of PEA (or other structurally related N-acylethanolamines) enhances anandamide activity by an "entourage effect".
Some primary research reports support the conclusion that PEA levels are altered and that the endocannabinoid system (ECS) is "imbalanced" in acute and chronic inflammation. A primary research article, for instance, has reported that the deregulation of cannabinoid receptors and their endogenous ligands accompanies the development and progression of β-amyloid-induced neuroinflammation.
In some primary research studies, PEA has been shown to have anti-inflammatory, anti-nociceptive, neuroprotective, and anticonvulsant properties. | 1 | Biochemistry |
The German Institute for Standardization publishes a standard for pH measurement using pH meters, DIN 19263.
Very precise measurements necessitate that the pH meter is calibrated before each measurement. More typically calibration is performed once per day of operation. Calibration is needed because the glass electrode does not give reproducible electrostatic potentials over longer periods of time.
Consistent with principles of good laboratory practice, calibration is performed with at least two standard buffer solutions that span the range of pH values to be measured. For general purposes, buffers at pH 4.00 and pH 10.00 are suitable. The pH meter has one calibration control to set the meter reading equal to the value of the first standard buffer and a second control to adjust the meter reading to the value of the second buffer. A third control allows the temperature to be set. Standard buffer sachets, available from a variety of suppliers, usually document the temperature dependence of the buffer control. More precise measurements sometimes require calibration at three different pH values. Some pH meters provide built-in temperature-coefficient correction, with temperature thermocouples in the electrode probes. The calibration process correlates the voltage produced by the probe (approximately 0.06 volts per pH unit) with the pH scale. Good laboratory practice dictates that, after each measurement, the probes are rinsed with distilled water or deionized water to remove any traces of the solution being measured, blotted with a scientific wipe to absorb any remaining water, which could dilute the sample and thus alter the reading, and then immersed in a storage solution suitable for the particular probe type. | 7 | Physical Chemistry |
The liver, gastrointestinal tract (GIT), lungs, kidney, and brain are among the tissues that participate in the chiral inversion of medicines. The liver has been shown to be the most crucial organ in the development of this mechanism. Although some studies contend that rat liver homogenates lack the enzymatic mechanisms necessary to invert the R-enantiomers of flurbiprofen, naproxen, suprofen, and ibuprofen, the liver may also be involved in the inversion of R-ibuprofen in rats. On the other hand, it was noted that certain medicines underwent chiral inversion without the involvement of the liver (hepatocytes). Although liver did not play a substantial role in the inversion of benoxaprofen, studies using benoxaprofen and ketoprofen show that one of the primary sites of inversion in rats is the GI tract. | 4 | Stereochemistry |
No heterogeneous catalyst has been commercialized for asymmetric hydrogenation.
The first asymmetric hydrogenation focused on palladium deposited on a silk support. Cinchona alkaloids have been used as chiral modifiers for enantioselectivity hydrogenation.
An alternative technique and one that allows more control over the structural and electronic properties of active catalytic sites is the immobilization of catalysts that have been developed for homogeneous catalysis on a heterogeneous support. Covalent bonding of the catalyst to a polymer or other solid support is perhaps most common, although immobilization of the catalyst may also be achieved by adsorption onto a surface, ion exchange, or even physical encapsulation. One drawback of this approach is the potential for the proximity of the support to change the behaviour of the catalyst, lowering the enantioselectivity of the reaction. To avoid this, the catalyst is often bound to the support by a long linker though cases are known where the proximity of the support can actually enhance the performance of the catalyst.
The final approach involves the construction of MOFs that incorporate chiral reaction sites from a number of different components, potentially including chiral and achiral organic ligands, structural metal ions, catalytically active metal ions, and/or preassembled catalytically active organometallic cores. One of these involved ruthenium-based catalysts. As little as 0.005 mol% of such catalysts proved sufficient to achieve the asymmetric hydrogenation of aryl ketones, although the usual conditions featured 0.1 mol % of catalyst and resulted in an enantiomeric excess of 90.6–99.2%.
<br /> | 0 | Organic Chemistry |
Feringa received his MSc degree with distinction from the University of Groningen in 1974. He subsequently obtained a PhD degree at the same university in 1978, with the thesis titled "Asymmetric oxidation of phenols. Atropisomerism and optical activity". Following a short period at Shell in the Netherlands and the United Kingdom, he was appointed as lecturer at the University of Groningen in 1984 and Full Professor, succeeding Prof Wijnberg, in 1988. His early career was focused on homogenous catalysis and oxidation catalysis, and especially on stereochemistry with major contributions in the field of enantioselective catalysis, including monophos ligand used in asymmetric hydrogenation, asymmetric conjugate additions of organometallic reagents, including the highly reactive organolithium reagents and organic photochemistry and stereochemistry. In the 1990s, Feringa's work in stereochemistry led to major contributions in photochemistry, resulting in the first monodirectional light driven molecular rotary motor and later a molecular car (a so-called nanocar) driven by electrical impulses.
Ben Feringa holds over 30 patents and has published over 650 peer reviewed research papers to date, cited more than 30,000 times and has an h-index in excess of 90. He has guided over 100 PhD students over his career. | 4 | Stereochemistry |
Consider the reaction below:
The two elements involved, iron and chlorine, each change oxidation state; iron from +2 to +3, chlorine from 0 to −1. There are then effectively two half reactions occurring. These changes can be represented in formulas by inserting appropriate electrons into each half reaction:
Given two half reactions it is possible, with knowledge of appropriate electrode potentials, to arrive at the complete (original) reaction the same way. The decomposition of a reaction into half reactions is key to understanding a variety of chemical processes. For example, in the above reaction, it can be shown that this is a redox reaction in which Fe is oxidised, and Cl is reduced. Note the transfer of electrons from Fe to Cl. Decomposition is also a way to simplify the balancing of a chemical equation. A chemist can atom balance and charge balance one piece of an equation at a time.
For example:
* becomes
* is added to
* and finally becomes
It is also possible and sometimes necessary to consider a half reaction in either basic or acidic conditions, as there may be an acidic or basic electrolyte in the redox reaction. Due to this electrolyte it may be more difficult to satisfy the balance of both the atoms and charges. This is done by adding , and/or to either side of the reaction until both atoms and charges are balanced.
Consider the half reaction below:
, and can be used to balance the charges and atoms in basic conditions, as long as it is assumed that the reaction is in water.
Again consider the half reaction below:
, and can be used to balance the charges and atoms in acidic conditions, as long as it is assumed that the reaction is in water.
Notice that both sides are both charge balanced and atom balanced.
Often there will be both and present in acidic and basic conditions but that the resulting reaction of the two ions will yield water, (shown below): | 7 | Physical Chemistry |
Retromer is a complex of proteins that has been shown to be important in recycling transmembrane receptors from endosomes to the trans-Golgi network (TGN) and directly back to the plasma membrane. Mutations in retromer and its associated proteins have been linked to Alzheimers and Parkinsons diseases.
Retromer is a heteropentameric complex, which in humans is composed of a less defined membrane-associated sorting nexin dimer (SNX1, SNX2, SNX5, SNX6), and a vacuolar protein sorting (Vps) heterotrimer containing Vps26, Vps29, and Vps35. Although the SNX dimer is required for the recruitment of retromer to the endosomal membrane, the cargo binding function of this complex is contributed by the core heterotrimer through the binding of Vps26 and Vps35 subunits to various cargo molecules including M6PR, wntless, SORL1 (which is also a receptor for other cargo proteins such as APP), and sortilin. Early study on sorting of acid hydrolases such as carboxypeptidase Y (CPY) in S. cerevisiae mutants has led to the identification of retromer in mediating the retrograde trafficking of the pro-CPY receptor (Vps10) from the endosomes to the TGN. Age-related loss of OXR1 causes retromer decline. | 1 | Biochemistry |
All magneto-optical traps require at least one trapping laser plus any necessary repumper lasers (see above). These lasers need stability, rather than high power, requiring no more than the saturation intensity, but a linewidth much less than the Doppler width, usually several megahertz. Because of their low cost, compact size and ease of use, laser diodes are used for many of the standard MOT species while the linewidth and stability of these lasers is controlled using servo systems, which stabilises the lasers to an atomic frequency reference by using, for example, saturated absorption spectroscopy and the Pound-Drever-Hall technique to generate a locking signal.
By employing a 2-dimensional diffraction grating it is possible to generate the configuration of laser beams required for a magneto-optical trap from a single laser beam and thus have a very compact magneto-optical trap. | 7 | Physical Chemistry |
Hydrocarbons are a class of molecule that is defined by functional groups called hydrocarbyls that contain only carbon and hydrogen, but vary in the number and order of double bonds. Each one differs in type (and scope) of reactivity.
There are also a large number of branched or ring alkanes that have specific names, e.g., tert-butyl, bornyl, cyclohexyl, etc. Hydrocarbons may form charged structures: positively charged carbocations or negative carbanions. Carbocations are often named -um. Examples are tropylium and triphenylmethyl cations and the cyclopentadienyl anion. | 0 | Organic Chemistry |
Dynamic kinetic resolution (DKR) occurs when the starting material racemate is able to epimerize easily, resulting in an essentially racemic starting material mix at all points during the reaction. Then, the enantiomer with the lower barrier to activation can form in, theoretically, up to 100% yield. This is in contrast to standard kinetic resolution, which necessarily has a maximum yield of 50%. For this reason, dynamic kinetic resolution has extremely practical applications to organic synthesis. The observed dynamics are based on the Curtin-Hammett principle. The barrier to reaction of either enantiomer is necessarily higher than the barrier to epimerization, resulting in a kinetic well containing the racemate. This is equivalent to writing, for k>k,
A number of excellent reviews have been published, most recently in 2008, detailing the theory and practical applications of DKR. | 4 | Stereochemistry |
In 1884, Jacobus van t Hoff proposed the Van t Hoff equation describing the temperature dependence of the equilibrium constant for a reversible reaction:
where ΔU is the change in internal energy, K is the equilibrium constant of the reaction, R is the universal gas constant, and T is thermodynamic temperature. Based on experimental work, in 1889, Svante Arrhenius proposed a similar expression for the rate constant of a reaction, given as follows:
Integration of this expression leads to the Arrhenius equation
where k is the rate constant. A was referred to as the frequency factor (now called the pre-exponential coefficient), and E is regarded as the activation energy. By the early 20th century many had accepted the Arrhenius equation, but the physical interpretation of A and E remained vague. This led many researchers in chemical kinetics to offer different theories of how chemical reactions occurred in an attempt to relate A and E to the molecular dynamics directly responsible for chemical reactions.
In 1910, French chemist René Marcelin introduced the concept of standard Gibbs energy of activation. His relation can be written as
At about the same time as Marcelin was working on his formulation, Dutch chemists Philip Abraham Kohnstamm, Frans Eppo Cornelis Scheffer, and Wiedold Frans Brandsma introduced standard entropy of activation and the standard enthalpy of activation. They proposed the following rate constant equation
However, the nature of the constant was still unclear. | 7 | Physical Chemistry |
Aluminium, like its congener boron, is less electronegative than carbon (Al, 1.61; C, 2.55); thus, aluminium-bound carbons in organoalanes possess partial negative charge and are nucleophilic as a result. Generally, however, organoalanes are not nucleophilic enough to transfer an organic group on their own (the exception being when carbonyl and enone acceptors are used, due to the high oxophilicity of aluminium). In most cases, nucleophilic activation of organoalanes is necessary for group transfer to take place. Like organoboranes, organoalanes possess an empty p orbital on the aluminium center that can receive electron density from an added nucleophile. The resulting negatively charged aluminate is much more nucleophilic than the neutral alane.
This concept has been applied to methods for the synthesis of organic compounds from alkenyl- and alkynylalanes. The most notable applications are methods for the stereospecific synthesis of olefins. Alkenylalanes, which are easily synthesized with complete stereocontrol through alkyne hydroalumination, transfer the alkenyl unit to a variety of electrophiles. Alkynylalanes are less commonly used because alkali metal acetylides can be used for many of the same transformations as alkynylalanes. However, alkynylalanes are useful for the coupling of tertiary halides and alkynes (a reaction difficult to effect with alkali metal alkynes) and for conjugate addition and epoxide opening reactions. | 0 | Organic Chemistry |
Isotopocule is a shorthand for an isotopically substituted molecule. Isotopocules are molecules that differ only in their isotopic composition or the intramolecular position of the isotopes. It is an umbrella term for the more specific terms isotopologue and isotopomer, coined by Jan Kaiser and Thomas Röckmann in 2008. | 7 | Physical Chemistry |
Gestonorone caproate was first described in 1960. It was developed by Schering and has been marketed since at least 1968. | 4 | Stereochemistry |
The antibiotic is produced under many brand names across the world.
* Bangladesh: Ancef, Ancef forte, Aphrin, Avlosef, Cefadin, Cephadin, Cephran, Cephran-DS, Cusef, Cusef DS, Dicef , Dicef forte, Dolocef, Efrad, Elocef, Extracef, Extracef-DS, Intracef, Kefdrin, Lebac, Lebac Forte, Medicef, Mega-Cef, Megacin, Polycef, Procef, Procef, Procef forte, Rocef, Rocef Forte DS, Sefin, Sefin DS, Sefnin, Sefrad, Sefrad DS, Sefril, Sefril-DS, Sefro, Sefro-HS, Sephar, Sephar-DS, Septa, Sinaceph, SK-Cef, Sk-Cef DS, Supracef and Supracef-F, Torped, Ultrasef, Vecef, Vecef-DS, Velogen, Sinaceph, Velox
* China: Cefradine, Cephradine, Kebili, Saifuding, Shen You, Taididing, Velosef, Xianyi, and Xindadelei
* Colombia: Cefagram, Cefrakov, Cefranil , Cefrex, and Kliacef
* Egypt: Cefadrin, Cefadrine, Cephradine, Cephraforte, Farcosef, Fortecef, Mepadrin, Ultracef, and Velosef
* France: Dexef
* Hong Kong: Cefradine and ChinaQualisef-250
* Indonesia: Dynacef, Velodine, and Velodrom
* Lebanon: Eskacef, Julphacef, and Velosef
* Lithuania: Tafril
* Myanmar: Sinaceph
* Oman: Ceframed, Eskasef, Omadine, and Velocef
* Pakistan: Abidine, Ada-Cef, Ag-cef, Aksosef, Amspor, Anasef, Antimic, Atcosef, Bactocef, Biocef, Biodine, Velora, Velosef
* Peru: Abiocef, Cefradinal, Cefradur, Cefrid, Terbodina II, Velocef, Velomicin
* Philippines: Altozef, Racep, Senadex, Solphride, Yudinef, Zefadin, Zefradil, and Zolicef
* Poland: Tafril
* Portugal: Cefalmin, Cefradur
* South Africa: Cefril A
* South Korea: Cefradine and Tricef
* Taiwan: Cefadin, Cefamid, Cefin, Cekodin, Cephradine, Ceponin, Lacef, Licef-A, Lisacef, Lofadine, Recef, S-60, Sefree, Sephros, Topcef, Tydine, Unifradine, and U-Save
* UK: Cefradune (Kent)
* Vietnam: Eurosefro and Incef | 4 | Stereochemistry |
In cell culture, a monolayer refers to a layer of cells in which no cell is growing on top of another, but all are growing side by side and often touching each other on the same growth surface. | 7 | Physical Chemistry |
Although isomerization of proteins has been known about since 1968 when it was discovered by C. Tanford, proline isomerization and its use as a noncovalent histone tail modification was not discovered until 2006 by Nelson and his colleagues. | 4 | Stereochemistry |
Physalaemin is a tachykinin peptide obtained from the Physalaemus frog, closely related to substance P. Its structure was first elucidated in 1964.
Like all tachykinins, physalaemin is a sialagogue (increases salivation) and a potent vasodilator with hypotensive effects. | 1 | Biochemistry |
High precision isotope-ratio mass spectrometry (IRMS) is another method for measuring kinetic fractionation of isotopes for natural abundance KIE measurements. Widlanski and coworkers demonstrated KIE at natural abundance measurements for the hydrolysis of sulfate monoesters. Their observation of a large KIE suggests S-O bond cleavage is rate controlling and likely rules out an associate reaction mechanism.
The major limitation for determining KIE's at natural abundance using IRMS is the required site selective degradation without isotopic fractionation into an analyzable small molecule, a non-trivial task. | 7 | Physical Chemistry |
Two basic sets of theorems exists, one for flux and another for concentrations. The concentration connectivity theorems are divided again depending on whether the system species is different from the local species . | 1 | Biochemistry |
In polymer systems, the general definition () holds; the elementary constituents are now the monomers making up the chains. However, the structure factor being a measure of the correlation between particle positions, one can reasonably expect that this correlation will be different for monomers belonging to the same chain or to different chains.
Let us assume that the volume contains identical molecules, each composed of monomers, such that ( is also known as the degree of polymerization). We can rewrite () as:
where indices label the different molecules and the different monomers along each molecule. On the right-hand side we separated intramolecular () and intermolecular () terms. Using the equivalence of the chains, () can be simplified:
where is the single-chain structure factor. | 3 | Analytical Chemistry |
In spite of the stepwise, radical mechanism, both stereoselective intra- and intermolecular variants have emerged. Cyclic enones are employed, otherwise competitive cis-trans isomerization ensues.
The mechanism of [2+2] photocyclization is proposed to begin with photoexcitation of the enone to a singlet excited state. The singlet state is typically very short lived, and decays by intersystem crossing to the triplet state. At this point, the enone forms an exciplex with the ground state alkene, eventually giving the triplet diradical. Spin inversion to the singlet diradical allows closure to the cyclobutane. As an alternative a pericyclic reaction mechanism is proposed, in which after intersystem crossing a radical cation and a radical anion are formed, which then recombine to the cyclobutane. | 5 | Photochemistry |
The first SLIM were fabricated using PCB technology to demonstrate a range of simple ion manipulations in gases at low pressures (a few torr). This SLIM technology has conceptual similarities with integrated electronic circuits, but instead of moving electrons, electric fields were used to create pathways, switches, etc. to manipulate ions in the gas phase.
SLIM devices can enable complex sequences of ion separations, transfers and trapping to occur in the space between two surfaces positioned (e.g., ~4 mm apart) and each patterned with conductive electrodes. The SLIM devices use the inhomogeneous electric fields created by arrays of closely spaced electrodes to which readily generated peak-to-peak RF voltages (e.g., Vp-p ~ 100 V; ~ 1 MHz) are applied with opposite polarity on adjacent electrodes to create effective potential fields that prevent ions from approaching the surfaces. The operating pressure for SLIM devices has initially been reported to be in the 1-10 torr range which allows ions to be effectively confined using the previously defined RF potentials. At higher pressures, the capacity to confine ions diminishes without additional forces being placed on the ion populations.
The confinement functions over a range of pressures (<0.1 torr to ~50 torr), and over an adjustable mass-to-charge ratio (m/z) range (e.g., m/z 200 to >2000). This effective potential works in conjunction with DC potentials applied to side electrodes to prevent ion losses, and allows creating ion traps and conduits in the gap between the two surfaces for the effectively lossless storage and movement of ions as a result of any gradient in the applied DC fields.
The two mirrored halves of a SLIM system are shown in the example to the left. Compared to the longer pathlength systems developed at PNNL, this board is considerably shorter but serves as a rapid prototype. When folded together and spaced ~3 mm apart, the co-planar electrode surfaces create the fields needed for ion confinement and separation. | 7 | Physical Chemistry |
* United States: California, Minnesota, Delaware, Washington DC and Wisconsin restrict use of less than lethal projectiles and devices using them.
* United Kingdom: Citizens may not use PAVA, under Section 5 of the Firearms Act 1968; however, police, prison officers and other officials are allowed to use PAVA to uphold the law. | 1 | Biochemistry |
Protecting a substrate with a PPG is commonly referred to as "photocaging." This term is especially popular in biological systems. For example, Ly et al. developed a p-iodobenzoate-based photocaged reagent, which would experience a homolytic photoclevage of the C-I bond. They found that the reaction could occur with excellent yields, and with a half-life of 2.5 minutes when a 15 W 254 nm light source was used. The resulting biomolecular radicals are necessary in many enzymatic processes. As a second example, researchers synthesized a cycloprene-modified glutamate photocaged with a 2-nitroveratrol-based PPG. As it is an excitatory amino acid neurotransmitter, the aim was to develop a bioorthagonal probe for glutamate in vivo. In a final example, Venkatesh et al. demonstrated the use of a PPG-based photocaged therapeutic. Their prodrug, which released one equivalent of caffeic acid and chlorambucil upon phototriggering, showed reasonable biocompatibility, cellular uptake and photoregulared drug release in vitro. | 5 | Photochemistry |
The Parkes process, patented in 1850 uses molten zinc. Zinc is not miscible with lead and when the two molten metals are mixed the zinc separates and floats to the top carrying only some 2% lead. However silver preferentially dissolves in zinc, so the zinc that floats to the top carries a significant proportion of the silver. The melt is then cooled until the zinc solidifies and the zinc crust is skimmed off. The silver is then recovered by volatalising the zinc. The Parkes process largely replaced the Pattinson process, except where the lead contained insufficient silver, in which case the Pattinson process provided a method to enrich it in silver to about 40 to 60 ounces per ton, at which concentration it could be treated using the Parkes' process. | 8 | Metallurgy |
In intramolecular organic reactions, two reaction sites are contained within a single molecule. This configuration elevates the effective concentration of the reacting partners resulting in high reaction rates. Many intramolecular reactions are observed where the intermolecular version does not take place.
Intramolecular reactions, especially ones leading to the formation of 5- and 6-membered rings, are rapid compared to an analogous intermolecular process. This is largely a consequence of the reduced entropic cost for reaching the transition state of ring formation and the absence of significant strain associated with formation of rings of these sizes. For the formation of different ring sizes via cyclization of substrates of varying tether length, the order of reaction rates (rate constants k for the formation of an n-membered ring) is usually k > k > k > k > k as shown below for a series of ω-bromoalkylamines. This somewhat complicated rate trend reflects the interplay of these entropic and strain factors:
For the <nowiki/>small rings<nowiki/> (3- and 4- membered), the slow rates is a consequence of angle strain experienced at the transition state. Although three-membered rings are more strained, formation of aziridine is faster than formation of azetidine due to the proximity of the leaving group and nucleophile in the former, which increases the probability that they would meet in a reactive conformation. The same reasoning holds for the <nowiki/>unstrained rings<nowiki/> (5-, 6-, and 7-membered). The formation of <nowiki/>medium-sized rings<nowiki/> (8- to 13-membered) is particularly disfavorable due to a combination of an increasingly unfavorable entropic cost and the additional presence of transannular strain arising from steric interactions across the ring. Finally, for <nowiki/>large rings (14-membered or higher), the rate constants level off, as the distance between the leaving group and nucleophile is now so large the reaction is now effectively intermolecular.
Although the details may change somewhat, the general trends hold for a variety of intramolecular reactions, including radical-mediated and (in some cases) transition metal-catalyzed processes. | 0 | Organic Chemistry |
Several biomolecules, including PUFAs and some amino acids, cannot be made by human beings and must be supplied in the diet. These molecules are termed “essential dietary components” and serve as building blocks that are incorporated into larger structures such as proteins and cell membranes. PUFA membrane components are particularly vulnerable to damage (oxidation) by reactive oxygen species (ROS) as part of both normal and pathological
metabolism. Unlike catabolic oxidation of drugs, or oxidative damage to DNA or proteins (which occurs stoichiometrically), oxidation of PUFAs is particularly pernicious, proceeding through a non-enzymatic lipid peroxidation chain reaction (LPO), whereby a single ROS species can initiate a runaway autoxidation process that does not need any additional ROS to propagate.
LPO may damage hundreds to thousands of PUFA residues in PUFA-rich neuronal, mitochondrial and retinal membranes. The chain oxidation proceeds inexorably through multiple steps, destroying lipid membranes and generating highly reactive toxic secondary products that damage numerous biomolecules, such as proteins and DNA, irreversibly. This makes LPO one of the most detrimental processes that occur in the body. LPO is not controlled by enzymes, so evolution could not have provided a straightforward solution. Antioxidants cannot efficiently stop the incipient chain reaction because their maximal achievable concentration in lipid membranes is orders of magnitude lower than the PUFA concentration (typically, 1 tocopherol moiety per 2000 PUFA residues in a bilayer). Numerous neuronal and retinal diseases have LPO in their etiology. To put things in perspective, the brain makes up 1.5–2% of body weight yet consumes about a fifth of the body’s total energy output. A quarter of this 20%, i.e. 5% of the total body energy expenditure, is used by the brain to recycle damaged lipids in neuronal membranes. | 7 | Physical Chemistry |
Radical Polymerization is used in the curing of acrylic resins in the presence of UV in the industry. Light energy from UV breaks apart photoinitiaters, forming radicals. The radical then react with the polymers, forming polymers with radical groups that then react with additional monomers. The monomer chain extends until it reaches another polymer and reacts with the polymer. Polymers will form with monomer bridges between them, thus leading to a cross-linked network. | 5 | Photochemistry |
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme hydrolysis, which causes the sugar part to be broken off, making the chemical available for use. Many such plant glycosides are used as medications. Several species of Heliconius butterfly are capable of incorporating these plant compounds as a form of chemical defense against predators. In animals and humans, poisons are often bound to sugar molecules as part of their elimination from the body.
In formal terms, a glycoside is any molecule in which a sugar group is bonded through its anomeric carbon to another group via a glycosidic bond. Glycosides can be linked by an O- (an O-glycoside), N- (a glycosylamine), S-(a thioglycoside), or C- (a C-glycoside) glycosidic bond. According to the IUPAC, the name "C-glycoside" is a misnomer; the preferred term is "C-glycosyl compound". The given definition is the one used by IUPAC, which recommends the Haworth projection to correctly assign stereochemical configurations.
Many authors require in addition that the sugar be bonded to a non-sugar for the molecule to qualify as a glycoside, thus excluding polysaccharides. The sugar group is then known as the glycone and the non-sugar group as the aglycone or genin part of the glycoside. The glycone can consist of a single sugar group (monosaccharide), two sugar groups (disaccharide), or several sugar groups (oligosaccharide).
The first glycoside ever identified was amygdalin, by the French chemists Pierre Robiquet and Antoine Boutron-Charlard, in 1830. | 0 | Organic Chemistry |
A typical L1 element is approximately 6,000 base pairs (bp) long and consists of two non-overlapping open reading frames (ORFs) which are flanked by untranslated regions (UTRs) and target site duplications. In humans, ORF2 is thought to be translated by an unconventional termination/reinitiation mechanism, while mouse L1s contain an internal ribosome entry site (IRES) upstream of each ORF. | 1 | Biochemistry |
Some ferredoxins have a sufficiently high redox potential that they can be directly reduced by NADPH. One such ferredoxin is adrenoxin (-274mV) which takes part in the biosynthesis of many mammalian steroids. The ferredoxin Fd3 in the roots of plants that reduces nitrate and sulfite has a midpoint potential of -337mV and is also reduced by NADPH. | 5 | Photochemistry |
This is not the usual form in which the equation is used. Instead, the equation is set to zero, meaning , indicating we are at equilibrium and the concentrations and are now equilibrium concentrations, hence:
Rearranging this gives the so-called Haldane relationship:
The advantage of this is that one of the four constants can be eliminated and replaced with the equilibrium constant which is more likely to be known. In addition, it allows one to make a useful interpretation in terms of the thermodynamic and saturation effects (see next section). Most often the reverse maximum rate is eliminated to yield the final equation: | 7 | Physical Chemistry |
As a result of the surface tension inherent to liquids, curved surfaces are formed in order to minimize the area. This phenomenon arises from the energetic cost of forming a surface. As such the Gibbs free energy of the system is minimized when the surface is curved.
The Kelvin equation is based on thermodynamic principles and is used to describe changes in vapor pressure caused by liquids with curved surfaces. The cause for this change in vapor pressure is the Laplace pressure. The vapor pressure of a drop is higher than that of a planar surface because the increased Laplace pressure causes the molecules to evaporate more easily. Conversely, in liquids surrounding a bubble, the pressure with respect to the inner part of the bubble is reduced, thus making it more difficult for molecules to evaporate. The Kelvin equation can be stated as:
where is the vapor pressure of the curved surface, is the vapor pressure of the flat surface, is the surface tension, is the molar volume of the liquid, is the universal gas constant, is temperature (in kelvin), and and are the principal radii of curvature of the surface. | 7 | Physical Chemistry |
Bare gold clusters, i.e., clusters without stabilizing ligand shells can be synthesized and studied in vacuum using molecular beam techniques. Their structures have been experimentally studied using, e.g., anion photoelectron spectroscopy, far-infrared spectroscopy, as well as measurements of their ion mobility and electron diffraction studies in conjunction with quantum chemical calculations. The structures of such clusters differ strongly from those of the ligand-stabilized ones, indicating an pivotal influence of the chemical environment on the cluster structure. A notable example is Au which forms a perfect tetrahedron in which the Au atom packing closely resembles the atomic arrangement in the fcc bulk structure of metallic gold. Evidence has been presented for the existence of hollow golden cages with the partial formula with n = 16 to 18. These clusters, with diameter of 550 picometres, are generated by laser vaporization and characterized by photoelectron spectroscopy. | 7 | Physical Chemistry |
Fumagillin is a complex biomolecule and used as an antimicrobial agent. It was isolated in 1949 from the microbial organism Aspergillus fumigatus. | 0 | Organic Chemistry |
Referring to conduction, Partington writes: "If a hot body is brought in conducting contact with a cold body, the temperature of the hot body falls and that of the cold body rises, and it is said that a quantity of heat has passed from the hot body to the cold body."
Referring to radiation, Maxwell writes: "In Radiation, the hotter body loses heat, and the colder body receives heat by means of a process occurring in some intervening medium which does not itself thereby become hot."
Maxwell writes that convection as such "is not a purely thermal phenomenon". In thermodynamics, convection in general is regarded as transport of internal energy. If, however, the convection is enclosed and circulatory, then it may be regarded as an intermediary that transfers energy as heat between source and destination bodies, because it transfers only energy and not matter from the source to the destination body.
In accordance with the first law for closed systems, energy transferred solely as heat leaves one body and enters another, changing the internal energies of each. Transfer, between bodies, of energy as work is a complementary way of changing internal energies. Though it is not logically rigorous from the viewpoint of strict physical concepts, a common form of words that expresses this is to say that heat and work are interconvertible.
Cyclically operating engines that use only heat and work transfers have two thermal reservoirs, a hot and a cold one. They may be classified by the range of operating temperatures of the working body, relative to those reservoirs. In a heat engine, the working body is at all times colder than the hot reservoir and hotter than the cold reservoir. In a sense, it uses heat transfer to produce work. In a heat pump, the working body, at stages of the cycle, goes both hotter than the hot reservoir, and colder than the cold reservoir. In a sense, it uses work to produce heat transfer. | 7 | Physical Chemistry |
A Fischer carbene can undergo nucleophilic abstraction where a methyl group is removed. With the addition of a small abstracting agent, the abstracting agent would normally add to the carbene carbon. In this case however, the steric bulk of the abstracting agent that is added causes the abstraction of the methyl group. If the methyl group is replaced with ethyl, the reaction proceeds 70 times slower which is to be expected with a S2 displacement mechanism. | 0 | Organic Chemistry |
Although thermal degradation is defined as an oxygen free process it is difficult in practise to completely exclude oxygen. Where this is the case thermal oxidation is to be expected, leading to the formation of free radicals by way of hydroperoxides. These may then participate in thermal degradation reactions, accelerating the rate of breakdown. | 7 | Physical Chemistry |
The first article relating to continuous flow peptide synthesis was published in 1986, but due to technical limitations, it was not until the early 2010's when more academic groups started using continuous flow for the rapid synthesis of peptides. The advantages of continuous flow over traditional batch methods is the ability to heat reagents with good temperature control, allowing the speed of reaction kinetics while minimising side reactions. cycles times vary from 30 seconds, up to 6 minutes, depending on reaction conditions and excess of reagent.
Thanks to inline analytics, such as UV/Vis spectroscopy and the use of Variable Bed Flow reactor (VBFR) that monitor the resin volume, on-resin aggregation can be identified and coupling efficiency can be evaluated. | 1 | Biochemistry |
The systematic name of pyridine, within the Hantzsch–Widman nomenclature recommended by the IUPAC, is . However, systematic names for simple compounds are used very rarely; instead, heterocyclic nomenclature follows historically established common names. IUPAC discourages the use of in favor of pyridine. The numbering of the ring atoms in pyridine starts at the nitrogen (see infobox). An allocation of positions by letter of the Greek alphabet (α-γ) and the substitution pattern nomenclature common for homoaromatic systems (ortho, meta, para) are used sometimes. Here α (ortho), β (meta), and γ (para) refer to the 2, 3, and 4 position, respectively. The systematic name for the pyridine derivatives is pyridinyl, wherein the position of the substituted atom is preceded by a number. However, the historical name pyridyl is encouraged by the IUPAC and used instead of the systematic name. The cationic derivative formed by the addition of an electrophile to the nitrogen atom is called pyridinium. | 0 | Organic Chemistry |
Radical theory is an obsolete scientific theory in chemistry describing the structure of organic compounds. The theory was pioneered by Justus von Liebig, Friedrich Wöhler and Auguste Laurent around 1830 and is not related to the modern understanding of free radicals. In this theory, organic compounds were thought to exist as combinations of radicals that could be exchanged in chemical reactions just as chemical elements could be interchanged in inorganic compounds. | 0 | Organic Chemistry |
Translational regulation of MITF is still an unexplored area with only two peer-reviewed papers (as of 2019) highlighting the importance. During glutamine starvation of melanoma cells ATF4 transcripts increases as well as the translation of the mRNA due to eIF2α phosphorylation. This chain of molecular events leads to two levels of MITF suppression: first, ATF4 protein binds and suppresses MITF transcription and second, eIF2α blocks MITF translation possibly through the inhibition of eIF2B by eIF2α.
MITF can also be directly translationally modified by the RNA helicase DDX3X. The 5 UTR of MITF contains important regulatory elements (IRES) that is recognized, bound and activated by DDX3X. Although, the 5 UTR of MITF only consists of a nucleotide stretch of 123-nt, this region is predicted to fold into energetically favorable RNA secondary structures including multibranched loops and asymmetric bulges that is characteristics of IRES elements. Activation of this cis-regulatory sequences by DDX3X promotes MITF expression in melanoma cells. | 1 | Biochemistry |
London dispersion forces, named after the German-American physicist Fritz London, are weak intermolecular forces that arise from the interactive forces between instantaneous multipoles in molecules without permanent multipole moments. In and between organic molecules the multitude of contacts can lead to larger contribution of dispersive attraction, particularly in the presence of heteroatoms. London dispersion forces are also known as dispersion forces, London forces, or instantaneous dipole–induced dipole forces. The strength of London dispersion forces is proportional to the polarizability of the molecule, which in turn depends on the total number of electrons and the area over which they are spread. Hydrocarbons display small dispersive contributions, the presence of heteroatoms lead to increased LD forces as function of their polarizability, e.g. in the sequence RI>RBr>RCl>RF. In absence of solvents weakly polarizable hydrocarbons form crystals due to dispersive forces; their sublimation heat is a measure of the dispersive interaction. | 6 | Supramolecular Chemistry |
The effect has mainly been observed on alkaline atoms which have nuclear properties particularly suitable for working with traps. As of 2012, using ultra-low temperatures of or below, Bose–Einstein condensates had been obtained for a multitude of isotopes, mainly of alkali metal, alkaline earth metal,
and lanthanide atoms (, , , , , , , , , , , , , , and ). Research was finally successful in hydrogen with the aid of the newly developed method of evaporative cooling. In contrast, the superfluid state of below is not a good example, because the interaction between the atoms is too strong. Only 8% of atoms are in the ground state of the trap near absolute zero, rather than the 100% of a true condensate.
The bosonic behavior of some of these alkaline gases appears odd at first sight, because their nuclei have half-integer total spin. It arises from a subtle interplay of electronic and nuclear spins: at ultra-low temperatures and corresponding excitation energies, the half-integer total spin of the electronic shell and half-integer total spin of the nucleus are coupled by a very weak hyperfine interaction. The total spin of the atom, arising from this coupling, is an integer lower value. The chemistry of systems at room temperature is determined by the electronic properties, which is essentially fermionic, since room temperature thermal excitations have typical energies much higher than the hyperfine values. | 7 | Physical Chemistry |
The properties of a compound relating to human olfactory perception includes its odour quality, threshold and intensity as a function of its concentration.
The odour quality of a (odour-active) compound is assessed using odour descriptors in sensory descriptive analyses. It shows the sensory–chemical relationship in volatile compounds. The odour quality of a compound may change with its concentration.
The absolute threshold of a compound is the minimum concentration at which it can be detected. In a mixture of volatile compounds, only the proportion of compounds present at concentrations above their threshold contribute to the odour. This property can be represented by the odour threshold (OT), the minimum concentration at which the odour is perceived by 50% of a human panel without determining its quality, or the recognition threshold, the minimum concentration at which the odour is perceived and can be described by 50% of a human panel.
The intensity of perception of a compound is positively correlated with its concentration. It is represented by the unique psychometric or concentration-response function of the compound. A psychometric function with a log concentration–perceived intensity plot is characterised by its sigmoidal shape, with its initial baseline representing the compound at concentrations below its threshold, a slow rise in response around the inflection point representing the threshold, an exponential rise in response as the concentration exceeds the threshold, a deceleration of the response to a flat region as the zone of saturation or the point at which the change in intensity is no longer perceived is reached. On the other hand, a log concentration–log perceived intensity plot, using Steven's power law, forms a linear line with the exponent characterising the relationship between the two variables. | 3 | Analytical Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.