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The front-end optics of a spectroradiometer includes the lenses, diffusers, and filters that modify the light as it first enters the system. For Radiance an optic with a narrow field of view is required. For total flux an integrating sphere is required. For Irradiance cosine correcting optics are required. The material used for these elements determines what type of light is capable of being measured. For example, to take UV measurements, quartz rather than glass lenses, optical fibers, Teflon diffusers, and barium sulphate coated integrating spheres are often used to ensure accurate UV measurement. | 0 | Theoretical and Fundamental Chemistry |
It is the integration-based method (technique). More precisely it is based on the discrete line integral on uniform grids. Discrete numerical integration is performed along a line (more precisely curve). Line here means field line of vector field. | 1 | Applied and Interdisciplinary Chemistry |
Kuftin was invited to Central Asia to carry out explorations in 1949. He first reconnoitered Turkmenistan and selected a very large tepe (hill), the Altyndepe (in Turkmen language meaning: the "Golden Hill" ). This tepe overlooks the Tedzen delta at the foot of Kopetdag. He found a Neolithic settlement extending into Bronze Age in southern Turkmenistan near the village of Miana, a settlement of 25 ha area with a total stratification thickness of with an strip of human habitation. This excavated tepe turned out to be a large settlement, in length and in width, and was identified as a major Bronze Age town. From the highest point of this tepe, a trench was dug to a depth of and the section was logged, which revealed layers of the Bronze Age, of neolithic and Eneolithic periods. Ceramics collected from the different layers of the trench enabled Kuftin to establish the sequence and chronology of the findings. One year after he started sequencing the site, he died suddenly and was replaced by Vadim Mikhailovich Masson who published a book on the Bronze Age sequence of this site. The settlement of Ilgynly had also shifted to Altyndepe. Early Bronze period fort walls with decorated towers and a huge entrance had encircled this settlement, though when found, they were in ruins. Discoveries by Soviet archeologists dated the finds at this place, in a chronological order, to the later half of the third millennium BC. Altyn-Depe also provided a link to the several Bronze Age cultures of Eurasia.
The most notable findings in the burial ground of the elite, located in the outskirts of Altyndepe, were "a disk-like stone weight, a miniature column, more than 1500 beads, a steatite plate with an image of cross and half-moon, a moulded clay wolf, as well as a golden head of a bull with a turquoise sickle inlaid in the forehead".
Excavations revealed bone and copper artifacts of the fifth millennium BC (Neolithic period), female figurines painted with ornaments, and necklaces of the fourth million BC.
Brick walls of thickness with brick kilns and a hearth in the middle of the house dated to early third millennium, and small temple buildings and rectangular hearths of Namazga V type of the middle third millennium were also found.
In the period from late third millennium to early second millennium, the antiquaries revealed an urban habitation with artisans' houses. Also unearthed were 62 double-tiered kilns, beads and seals.
Four stepped ziggurats were found. Further were revealed female terracotta figurines with plaited hair, stone vessels, hafted bronze and copper daggers with flat blades, tabbed silver and bronze seals.
The further findings were,
* Paintings of animals such as goats, eagles, and panthers.
* Three headed composite animal.
* A priest's tomb with gold heads of a wolf and a bull.
* Other tombs with silver ornaments, precious stones and seals.
*One quarter of a ‘nobility’ seal with two signs in Indus script conjectured to be that of Bronze Age settlers in Altyndepe.
However, the settlement gradually disappeared (it was deserted around 1600 BC) as a result of climatic changes; people migrated to the Mugrab region, another area of South Uzbekistan (Sapali), and Northern Afghanistan (Dashli). Further, these findings confirmed the Middle Asian interaction from the north to the Oxus civilization. | 1 | Applied and Interdisciplinary Chemistry |
Outdoors, DLI values vary depending on latitude, time of year, and cloud cover. Occasionally, values over 70 mol·m·d can be reached at bright summer days at some locations. Monthly-averaged DLI values range between 20-40 in the tropics, 15-60 at 30° latitude and 1-40 at 60° latitude. For plants growing in the shade of taller plants, such as on the forest floor, DLI may be less than 1 mol·m·d, even in summer.
In greenhouses, 30-70% of the outside light will be absorbed or reflected by the glass and other greenhouse structures. DLI levels in greenhouses therefore rarely exceed 30 mol·m·d. In growth chambers, values between 10 and 30 mol·m·d are most common. New light modules are now available for the horticultural industry, where light intensity of the lamps used in glasshouses is regulated such that plants receive a set value of DLI, independent of outside weather conditions. | 0 | Theoretical and Fundamental Chemistry |
If the two solvents can form a negative azeotrope, then distillation of any mixture of those constituents will result in the residue being closer to the composition at the azeotrope than the original mixture.
For example, if a hydrochloric acid solution contains less than 20.2% hydrogen chloride, boiling the mixture will leave behind a solution that is richer in hydrogen chloride than the original. If the solution initially contains more than 20.2% hydrogen chloride, then boiling will leave behind a solution that is poorer in hydrogen chloride than the original. Boiling of any hydrochloric acid solution long enough will cause the solution left behind to approach the azeotropic ratio. On the other hand, if two solvents can form a positive azeotrope, then distillation of any mixture of those constituents will result in the residue away from the composition at the azeotrope than the original mixture. For example, if a 50/50 mixture of ethanol and water is distilled once, the distillate will be 80% ethanol and 20% water, which is closer to the azeotropic mixture than the original, which means the solution left behind will be poorer in ethanol. Distilling the 80/20% mixture produces a distillate that is 87% ethanol and 13% water. Further repeated distillations will produce mixtures that are progressively closer to the azeotropic ratio of 95.5/4.5%. No numbers of distillations will ever result in a distillate that exceeds the azeotropic ratio. Likewise, when distilling a mixture of ethanol and water that is richer in ethanol than the azeotrope, the distillate (contrary to intuition) will be poorer in ethanol than the original but still richer than the azeotrope.
Distillation is one of the primary tools that chemists and chemical engineers use to separate mixtures into their constituents. Because distillation cannot separate the constituents of an azeotrope, the separation of azeotropic mixtures (also called azeotrope breaking) is a topic of considerable interest. Indeed, this difficulty led some early investigators to believe that azeotropes were actually compounds of their constituents. But there are two reasons for believing that this is not the case. One is that the molar ratio of the constituents of an azeotrope is not generally the ratio of small integers. For example, the azeotrope formed by water and acetonitrile contains 2.253 moles (or 9/4 with a relative error of just 2%) of acetonitrile for each mole of water. A more compelling reason for believing that azeotropes are not compounds is, as discussed in the last section, that the composition of an azeotrope can be affected by pressure. Contrast that with a true compound, carbon dioxide for example, which is two moles of oxygen for each mole of carbon no matter what pressure the gas is observed at. That azeotropic composition can be affected by pressure suggests a means by which such a mixture can be separated. | 1 | Applied and Interdisciplinary Chemistry |
Mammalian cell expression systems are essential for the transient production of recombinant proteins and their complementary post-translational modifications. In fact, approximately half of the current commercially available therapeutic proteins are produced in mammalian cells. However, mammalian cell systems' slow growth, precise growth requirements, and potential risk of infection by animal viruses present a number of challenges. As a result, a growing number of mammalian cell lines have been established to serve as hosts for transient recombinant protein production. | 1 | Applied and Interdisciplinary Chemistry |
Metal formyl complexes are often prepared by the reaction of metal carbonyls with hydride reagents:
:[Re(CO)] + H → (CO)ReCHO
The CO ligand is the electrophile and the hydride (provided typically from a borohydride) is the nucleophile.
Some metal formyls are produced by reaction of metal carbonyl anions with reagents that donate the equivalent of a formyl cation, such a mixed formate anhydrides.
Metal formyls participate in many reactions, many of which are motivated by interest in Fischer-Tropsch chemistry. O-alkylation gives carbenoid complexes. The formyl ligand also functions as a base, allowing the formation of M-CH=O-M' linkages. Decarbonylation leads to de-insertion of the carbonyl, yielding hydride complexes. | 0 | Theoretical and Fundamental Chemistry |
The Latin term in vitro, meaning "in glass", is used because early biological experiments involving cultivation of tissues outside the living organism were carried out in glass containers, such as beakers, test tubes, or Petri dishes. Today, the scientific term "in vitro" is used to refer to any biological procedure that is performed outside the organism in which it would normally have occurred, to distinguish it from an in vivo procedure (such as in vivo fertilisation), where the tissue remains inside the living organism in which it is normally found.
A colloquial term for babies conceived as the result of IVF, "test tube babies", refers to the tube-shaped containers of glass or plastic resin, called test tubes, that are commonly used in chemistry and biology labs. However, IVF is usually performed in Petri dishes, which are both wider and shallower and often used to cultivate cultures.
IVF is a form of assisted reproductive technology. | 1 | Applied and Interdisciplinary Chemistry |
The Journal of Medicinal Chemistry is a biweekly peer-reviewed medical journal covering research in medicinal chemistry. It is published by the American Chemical Society. It was established in 1959 as the Journal of Medicinal and Pharmaceutical Chemistry and obtained its current name in 1963. Philip S. Portoghese served as editor-in-chief from 1972 to 2011. In 2012, Gunda Georg (University of Minnesota) and Shaomeng Wang (University of Michigan) succeeded Portoghese (University of Minnesota). In 2021, Craig W. Lindsley (Vanderbilt University) became editor-in-chief. According to the Journal Citation Reports, the journal has a 2022 impact factor of 7.3. | 1 | Applied and Interdisciplinary Chemistry |
Loss on ignition (LOI) is a test used in inorganic analytical chemistry and soil science, particularly in the analysis of minerals and the chemical makeup of soil. It consists of strongly heating ("igniting") a sample of the material at a specified temperature, allowing volatile substances to escape, until its mass ceases to change. This may be done in air or in some other reactive or inert atmosphere. The simple test typically consists of placing a few grams of the material in a tared, pre-ignited crucible and determining its mass, placing it in a temperature-controlled furnace for a set time, cooling it in a controlled (e.g., water-free, CO2-free) atmosphere, and re-determining the mass. The process may be repeated to show that the mass change is complete. A variant of the test in which mass change is continually monitored as the temperature changes is called thermogravimetry. | 0 | Theoretical and Fundamental Chemistry |
Cell–cell interaction refers to the direct interactions between cell surfaces that play a crucial role in the development and function of multicellular organisms.
These interactions allow cells to communicate with each other in response to changes in their microenvironment. This ability to send and receive signals is essential for the survival of the cell. Interactions between cells can be stable such as those made through cell junctions. These junctions are involved in the communication and organization of cells within a particular tissue. Others are transient or temporary such as those between cells of the immune system or the interactions involved in tissue inflammation. These types of intercellular interactions are distinguished from other types such as those between cells and the extracellular matrix. The loss of communication between cells can result in uncontrollable cell growth and cancer. | 1 | Applied and Interdisciplinary Chemistry |
Diastereomers are stereoisomers not related through a reflection operation. They are not mirror images of each other. These include meso compounds, cis–trans isomers, E-Z isomers, and non-enantiomeric optical isomers. Diastereomers seldom have the same physical properties. In the example shown below, the meso form of tartaric acid forms a diastereomeric pair with both levo- and dextro-tartaric acids, which form an enantiomeric pair.
The - and - labeling of the isomers above is not the same as the d- and l- labeling more commonly seen, explaining why these may appear reversed to those familiar with only the latter naming convention.
A Fischer projection can be used to differentiate between L- and D- molecules Chirality (chemistry). For instance, by definition, in a Fischer projection the penultimate carbon of D-sugars are depicted with hydrogen on the left and hydroxyl on the right. L-sugars will be shown with the hydrogen on the right and the hydroxyl on the left.
The other refers to Optical rotation, when looking at the source of light, the rotation of the plane of polarization may be either to the right (dextrorotary — d-rotary, represented by (+), clockwise), or to the left (levorotary — l-rotary, represented by (−), counter-clockwise) depending on which stereoisomer is dominant. For instance, sucrose and camphor are d-rotary whereas cholesterol is l-rotary. | 0 | Theoretical and Fundamental Chemistry |
NMH is formed by N-methylation of histamine, catalyzed by the enzyme Histamine N-methyltransferase.
NMH is excreted in the urine and can be measured as a biomarker of histamine activity. While NMH has some biological activity on its own, it is much weaker than histamine. It can bind to histamine receptors, still, NMH has a lower affinity and efficacy than histamine for these receptors, meaning that it binds less strongly and activates them less effectively. Depending on the receptor subtype and the tissue context, NMH may act as a partial agonist or an antagonist for some histamine receptors. NMH may have some modulatory effects on histamine signalling, but it is unlikely to cause significant allergic or inflammatory reactions by itself. NMH may also serve as a feedback mechanism to regulate histamine levels and prevent excessive histamine release.
In clinical settings, urinary NMH can be measured when systemic mastocytosis is suspected. Systemic mastocytosis and anaphylaxis are typically associated with at least a two-fold increase in urinary NMH levels, which are also increased in patients taking monoamine oxidase inhibitors and in patients on histamine-rich diets. | 1 | Applied and Interdisciplinary Chemistry |
Dichloromethyl methyl ether (HClCOCH) is an organic compound that belongs to the class of ethers with a dichloromethyl group and a methyl group. It can be synthesized from methyl formate and a mixture of phosphorus pentachloride and phosphorus oxychloride or by chlorination of chlorodimethyl ether.
The compound is used in the formylation of aromatic compounds (Rieche formylation) and as a chlorination agent in the formation of acid chlorides. | 0 | Theoretical and Fundamental Chemistry |
Compost windrow turners were developed to produce compost on a large scale by Fletcher Sims Jr. of Canyon, Texas. They are traditionally a large machine that straddles a windrow of or more high, by as much as across. Although smaller machines exist for small windrows, most operations use large machines for volume production. Turners drive through the windrow at a slow rate of forward movement. They have a steel drum with paddles that are rapidly turning. As the turner moves through the windrow, fresh air (oxygen) is injected into the compost by the drum/paddle assembly, and waste gases produced by bacterial decomposition are vented. The oxygen feeds the aerobic bacteria and thus speeds the composting process.
;Utilization
To properly use a compost windrow turner, it is ideal to compost on a hard surfaced pad. Heavy-duty compost windrow turners allow the user to obtain optimum results with the aerobic hot composting process. By using four wheel drive or tracks the windrow turner is capable of turning compost in windrows located in remote locations. With a self-trailering option this allows the compost windrow turner to convert itself into a trailer to be pulled by a semi-truck tractor. These two options combined allow the compost windrow turner to be easily hauled anywhere and to work compost windrows in muddy and wet locations. | 1 | Applied and Interdisciplinary Chemistry |
Recommendations on recommended 25(OH)D serum levels vary across authorities, and vary based on factors like age. US labs generally report 25(OH)D levels in ng/mL. Other countries often use nmol/L. Oneng/mL is approximately equal to 2.5nmol/L.
A 2014 review concluded that the most advantageous serum levels for 25(OH)D for all outcomes appeared to be close to 30ng/mL (75nmol/L). The optimal vitamin D levels are still controversial and another review concluded that ranges from 30 to 40ng/mL (75 to 100nmol/L) were to be recommended for athletes. Part of the controversy is because numerous studies have found differences in serum levels of 25(OH)D between ethnic groups; studies point to genetic as well as environmental reasons behind these variations. Supplementation to achieve these standard levels could cause harmful vascular calcification.
A 2012 meta-analysis showed that the risk of cardiovascular diseases increases when blood levels of vitamin D are lowest in a range of 8 to 24ng/mL (20 to 60nmol/L), although results among the studies analyzed were inconsistent.
In 2011 an IOM committee concluded a serum 25(OH)D level of 20ng/mL (50nmol/L) is needed for bone and overall health. The dietary reference intakes for vitamin D are chosen with a margin of safety and overshoot the targeted serum value to ensure the specified levels of intake achieve the desired serum 25(OH)D levels in almost all persons. No contributions to serum 25(OH)D level are assumed from sun exposure and the recommendations are fully applicable to people with dark skin or negligible exposure to sunlight. The Institute found serum 25(OH)D concentrations above 30ng/mL (75nmol/L) are "not consistently associated with increased benefit". Serum 25(OH)D levels above 50ng/mL (125nmol/L) may be cause for concern. However, some people with serum 25(OH)D between 30 and 50ng/mL (75nmol/L-125nmol/L) will also have inadequate vitamin D. | 1 | Applied and Interdisciplinary Chemistry |
Mixed oxide, or MOX fuel, is a blend of plutonium and natural or depleted uranium which behaves similarly (though not identically) to the enriched uranium feed for which most nuclear reactors were designed. MOX fuel is an alternative to low enriched uranium (LEU) fuel used in the light water reactors which predominate nuclear power generation.
Some concern has been expressed that used MOX cores will introduce new disposal challenges, though MOX is itself a means to dispose of surplus plutonium by transmutation.
Reprocessing of commercial nuclear fuel to make MOX was done in the Sellafield MOX Plant (England). As of 2015, MOX fuel is made in France (see Marcoule Nuclear Site), and to a lesser extent in Russia (see Mining and Chemical Combine), India and Japan. China plans to develop fast breeder reactors (see CEFR) and reprocessing.
The Global Nuclear Energy Partnership, was a U.S. proposal in the George W. Bush administration to form an international partnership to see spent nuclear fuel reprocessed in a way that renders the plutonium in it usable for nuclear fuel but not for nuclear weapons. Reprocessing of spent commercial-reactor nuclear fuel has not been permitted in the United States due to nonproliferation considerations. All of the other reprocessing nations have long had nuclear weapons from military-focused "research"-reactor fuels except for Japan. Normally, with the fuel being changed every three years or so, about half of the is burned in the reactor, providing about one third of the total energy. It behaves like and its fission releases a similar amount of energy. The higher the burn-up, the more plutonium in the spent fuel, but the lower the fraction of fissile plutonium. Typically about one percent of the used fuel discharged from a reactor is plutonium, and some two thirds of this is fissile (c. 50% , 15% ). Worldwide, some 70 tonnes of plutonium contained in used fuel is removed when refueling reactors each year. | 0 | Theoretical and Fundamental Chemistry |
Cytochrome c belongs to class I of the c-type cytochrome family and contains a characteristic CXXCH (cysteine-any-any-cysteine-histidine) amino acid motif that binds heme. This motif is located towards the N-terminus of the peptide chain and contains a histidine as the 5th ligand of the heme iron. The 6th ligand is provided by a methionine residue found towards the C-terminus. The protein backbone is folded into five α-helices that are numbered α1-α5 from N-terminus to C-terminus. Helices α3, α4 and α5 are referred to as 50s, 60s and 70s helices, respectively, when referring to mitochondrial cytochrome c. | 1 | Applied and Interdisciplinary Chemistry |
G activates the cAMP-dependent pathway by stimulating the production of cyclic AMP (cAMP) from ATP. This is accomplished by direct stimulation of the membrane-associated enzyme adenylate cyclase. cAMP can then act as a second messenger that goes on to interact with and activate protein kinase A (PKA). PKA can phosphorylate a myriad downstream targets.
The cAMP-dependent pathway is used as a signal transduction pathway for many hormones including:
* ADH – Promotes water retention by the kidneys (created by the magnocellular neurosecretory cells of the posterior pituitary)
* GHRH – Stimulates the synthesis and release of GH (somatotropic cells of the anterior pituitary)
* GHIH – Inhibits the synthesis and release of GH (somatotropic cells of anterior pituitary)
* CRH – Stimulates the synthesis and release of ACTH (anterior pituitary)
* ACTH – Stimulates the synthesis and release of cortisol (zona fasciculata of the adrenal cortex in the adrenal glands)
* TSH – Stimulates the synthesis and release of a majority of T4 (thyroid gland)
* LH – Stimulates follicular maturation and ovulation in women; or testosterone production and spermatogenesis in men
* FSH – Stimulates follicular development in women; or spermatogenesis in men
* PTH – Increases blood calcium levels. This is accomplished via the parathyroid hormone 1 receptor (PTH1) in the kidneys and bones, or via the parathyroid hormone 2 receptor (PTH2) in the central nervous system and brain, as well as the bones and kidneys.
* Calcitonin – Decreases blood calcium levels (via the calcitonin receptor in the intestines, bones, kidneys, and brain)
* Glucagon – Stimulates glycogen breakdown in the liver
* hCG – Promotes cellular differentiation, and is potentially involved in apoptosis.
* Epinephrine – released by the adrenal medulla during the fasting state, when body is under metabolic duress. It stimulates glycogenolysis, in addition to the actions of glucagon. | 1 | Applied and Interdisciplinary Chemistry |
Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental component that determines the physicochemical properties of a biofilm. EPS in the matrix of biofilms provides compositional support and protection of microbial communities from the harsh environments. Components of EPS can be of different classes of polysaccharides, lipids, nucleic acids, proteins, lipopolysaccharides, and minerals. | 1 | Applied and Interdisciplinary Chemistry |
In a normal helium atom, two electrons are found in the 1s orbital. However, if sufficient energy is added, one electron can be elevated to a higher energy level. This high energy electron can become a valence electron, and the electron that remains in the 1s orbital is a core electron. Two excited helium atoms can react with a covalent bond to form a molecule called dihelium that lasts for short times of the order of a microsecond up to second or so. Excited helium atoms in the 2S state can last for up to an hour, and react like alkali metal atoms.
The first clues that dihelium exists were noticed in 1900 when W. Heuse observed a band spectrum in a helium discharge. However, no information about the nature of the spectrum was published. Independently E. Goldstein from Germany and W. E. Curtis from London published details of the spectrum in 1913. Curtis was called away to military service in World War I, and the study of the spectrum was continued by Alfred Fowler. Fowler recognised that the double headed bands fell into two sequences analogous to principal and diffuse series in line spectra.
The emission band spectrum shows a number of bands that degrade towards the red, meaning that the lines thin out and the spectrum weakens towards the longer wavelengths. Only one band with a green band head at 5732 Å degrades towards the violet. Other strong band heads are at 6400 (red), 4649, 4626, 4546, 4157.8, 3777, 3677, 3665, 3356.5, and 3348.5 Å. There are also some headless bands and extra lines in the spectrum. Weak bands are found with heads at 5133 and 5108.
If the valence electron is in a 2s 3s, or 3d orbital, a Σ state results; if it is in 2p 3p or 4p, a Σ state results. The ground state is XΣ.
The three lowest triplet states of He have designations aΣ, bΠ and cΣ. The aΣ state with no vibration (v=0) has a long metastable lifetime of 18 s, much longer than the lifetime for other states or inert gas excimers. The explanation is that the aΣ state has no electron orbital angular momentum, as all the electrons are in S orbitals for the helium state.
The lower lying singlet states of He are AΣ, BΠ and CΣ. The excimer molecules are much smaller and more tightly bound than the van der Waals bonded helium dimer. For the AΣ state the binding energy is around 2.5 eV, with a separation of the atoms of 103.9 pm. The CΣ state has a binding energy 0.643 eV and the separation between atoms is 109.1 pm. These two states have a repulsive range of distances with a maximum around 300 pm, where if the excited atoms approach, they have to overcome an energy barrier. The singlet state AΣ is very unstable with a lifetime only nanoseconds long.
The spectrum of the He excimer contains bands due to a great number of lines due to transitions between different rotation rates and vibrational states, combined with different electronic transitions. The lines can be grouped into P, Q and R branches. But the even numbered rotational levels do not have Q branch lines, due to both nuclei being spin 0. Numerous electronic states of the molecule have been studied, including Rydberg states with the number of the shell up to 25.
Helium discharge lamps produce vacuum ultraviolet radiation from helium molecules. When high energy protons hit helium gas it also produces UV emission at around 600 Å by the decay of excited highly vibrating molecules of He in the AΣ state to the ground state. The UV radiation from excited helium molecules is used in the pulsed discharge ionization detector (PDHID) which is capable of detecting the contents of mixed gases at levels below parts per billion.
The Hopfield continuum is a band of ultraviolet light between 600 and 1000 Å in wavelength formed by photodissociation of helium molecules.
One mechanism for formation of the helium molecules is firstly a helium atom becomes excited with one electron in the 2S orbital. This excited atom meets two other non excited helium atoms in a three body association and reacts to form a AΣ state molecule with maximum vibration and a helium atom.
Helium molecules in the quintet state Σ can be formed by the reaction of two spin polarised helium atoms in He(2S) states. This molecule has a high energy level of 20 eV. The highest vibration level allowed is v=14.
In liquid helium the excimer forms a solvation bubble. In a d state a He molecule is surrounded by a bubble 12.7 Å in radius at atmospheric pressure. When pressure is increased to 24 atmospheres the bubble radius shrinks to 10.8 Å. This changing bubble size causes a shift in the fluorescence bands. | 0 | Theoretical and Fundamental Chemistry |
The most effective self-assembly director is a combination of external force fields. If the fields and conditions are optimized, self-assembly can be permanent and complete. When a field combination is used with nanoparticles that are tailored to be intrinsically responsive, the most complete assembly is observed. Combinations of fields allow the benefits of self-assembly, such as scalability and simplicity, to be maintained while being able to control orientation and structure formation. Field combinations possess the greatest potential for future directed self-assembly work. | 0 | Theoretical and Fundamental Chemistry |
Reuterin (3-hydroxypropionaldehyde) is the organic compound with the formula HOCHCHCHO. It is a bifunctional molecule, containing both a hydroxy and aldehyde functional groups.
The name reuterin is derived from Lactobacillus reuteri, which produces the compound biosynthetically from glycerol as a broad-spectrum antibiotic (bacteriocin). L. reuteri itself is named after the microbiologist Gerhard Reuter, who did early work in distinguishing it as a distinct species. | 1 | Applied and Interdisciplinary Chemistry |
The Joback method uses a four-parameter polynomial to describe the temperature dependency of the ideal-gas heat capacity. These parameters are valid from 273 K to about 1000 K. But you are able to extend it to 1500K if you don't mind a bit of uncertainty here and there. | 0 | Theoretical and Fundamental Chemistry |
DNA purification in 1869 by Dr. Friedrich Miescher’s, from salmon sperm and pus cells guided the scientists towards the presence of additional molecules in the cell except for proteins. Miescher identified the presence of a highly acidic molecule that he isolated from the pus cells and labeled it “nuclein”. The term was coined as the DNA isolated by Miescher was not protein and was derived from the nucleus of the cell. It wasn’t until 1944, when Oswald Avery proposed the DNA as a genetic carrier of information that the Miescher discovery was brought back to light.
Following the X-ray crystallography, by Rosalind Franklin and the determination of DNA double helix by Watson and Crick in 1953, further enhanced the understanding of DNA structure and allowed for the establishment of central dogma of molecular biology. However, one of the flaws with central dogma was the postulation that information flow proceeds from DNA to RNA to protein, which hinders the understanding of different regulatory mechanisms.
In 1955, George Palade identified the first ncRNA as a part of the large ribonucleoprotein complex (RNP). The second class of ncRNA to be discovered was transfer RNA (tRNA) in 1957. However, the first regulatory ncRNA was a microRNA discovered in 1988 from E.coli and was labeled as micF. On other hand, the first eukaryotic microRNA was discovered in C.elegans in 1993. It was derived from gene lin-4 and was identified as a small RNA molecule (as compared to longer mRNA molecules) forming stem-loop structures. This structure gets further modified to generate a shorter RNA that is complementary to the 3’UTR region of lin-14 transcript. This pathway allowed for a better understanding of different post translational gene silencing pathways. Since then, many other miRNAs have been discovered.
Detailed understanding of the mechanism behind this post translational silencing pathway was established in 2001 by Thomas Tuschl. It was discovered that the double stranded RNA gets processed into a shorter 25 nucleotides long fragment which is then modified into a short hairpin like structure by Drosha complex. The molecule is then diced by dicer enzymes into a functional double stranded RNA (dsRNA). These are then loaded onto the RISC complex which then finds and cleaves the targeted mRNA of interest in the cytoplasm.
It wasn’t until 1989 that the imprinting genes were discovered and the genome imprinting was established. The first two genomic imprinting genes were paternally expressed Igf2r and H19. These were both discovered independently in mice and were localized to chromosome 7. H19 is peculiar as it functions as a lncRNA but undergoes modifications similar to that of pre-mRNA processing such as splicing, 3’ polyadenylation and is transcribed by RNA polymerase II. This lncRNA plays a significant role in mice embryonic development and can be lethal if expressed during prenatal stages. More lncRNAs have been discovered in eukaryotes overtime. One such discovery that allowed for better understanding between H19 functions was a lncRNA called XIST (X inactive-specific transcript). | 1 | Applied and Interdisciplinary Chemistry |
The alcoholysis of acyl halides (the alkoxy-dehalogenation) is believed to proceed via an S2 mechanism (Scheme 10). However, the mechanism can also be tetrahedral or S1 in highly polar solvents (while the S2 reaction involves a concerted reaction, the tetrahedral addition-elimination pathway involves a discernible intermediate).
Bases, such as pyridine or N,N-dimethylformamide, catalyze acylations. These reagents activate the acyl chloride via a nucleophilic catalysis mechanism. The amine attacks the carbonyl bond and presumably first forms a transient tetrahedral intermediate, then forms a quaternary acylammonium salt by the displacement of the leaving group. This quaternary acylammonium salt is more susceptible to attack by alcohols or other nucleophiles.
The use of two phases (aqueous for amine, organic for acyl chloride) is called the Schotten-Baumann reaction. This approach is used in the preparation of nylon via the so-called nylon rope trick. | 0 | Theoretical and Fundamental Chemistry |
After tin and lead, the next metal smelted appears to have been copper. How the discovery came about is debated. Campfires are about 200 °C short of the temperature needed, so some propose that the first smelting of copper may have occurred in pottery kilns. (The development of copper smelting in the Andes, which is believed to have occurred independently of the Old World, may have occurred in the same way.)
The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia. A mace head found in Turkey and dated to 5000 BC, once thought to be the oldest evidence, now appears to be hammered, native copper.
Combining copper with tin and/or arsenic in the right proportions produces bronze, an alloy that is significantly harder than copper. The first copper/arsenic bronzes date from 4200 BC from Asia Minor. The Inca bronze alloys were also of this type. Arsenic is often an impurity in copper ores, so the discovery could have been made by accident. Eventually, arsenic-bearing minerals were intentionally added during smelting.
Copper–tin bronzes, harder and more durable, were developed around 3500 BC, also in Asia Minor.
How smiths learned to produce copper/tin bronzes is unknown. The first such bronzes may have been a lucky accident from tin-contaminated copper ores. However, by 2000 BC, people were mining tin on purpose to produce bronze—which is remarkable as tin is a semi-rare metal, and even a rich cassiterite ore only has 5% tin. However early peoples learned about tin, they understood how to use it to make bronze by 2000 BC.
The discovery of copper and bronze manufacture had a significant impact on the history of the Old World. Metals were hard enough to make weapons that were heavier, stronger, and more resistant to impact damage than wood, bone, or stone equivalents. For several millennia, bronze was the material of choice for weapons such as swords, daggers, battle axes, and spear and arrow points, as well as protective gear such as shields, helmets, greaves (metal shin guards), and other body armor. Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as chisels, saws, adzes, nails, blade shears, knives, sewing needles and pins, jugs, cooking pots and cauldrons, mirrors, and horse harnesses. Tin and copper also contributed to the establishment of trade networks that spanned large areas of Europe and Asia and had a major effect on the distribution of wealth among individuals and nations. | 1 | Applied and Interdisciplinary Chemistry |
Calcitonin, as salmon calcitonin (sCT), is available in the pharmaceutical market as an injectable preparation for intravenous, intramuscular or subcutaneous application. Noninvasive sCT preparation as a nasal spray is commercially produced and received US FDA approval under the proprietary name Miacalcin® in 1975 for the treatment of postmenopausal osteoporosis. The bioavailability of Miacalcin® nasal spray relative to the injectable form is between 3% and 5%.
Currently, a number of sCT oral preparations are under clinical trials and at least one of them has reached Phase III of clinical approval. | 1 | Applied and Interdisciplinary Chemistry |
The after effects can be defined as any residual effects which may remain after the experience has reached its conclusion. After effects depend on the substance and usage. This is colloquially known as a "hangover" for negative after effects of substances, such as alcohol, cocaine, and MDMA or an "afterglow" for describing a typically positive, pleasant effect, typically found in substances such as cannabis, LSD in low to high doses, and ketamine. | 1 | Applied and Interdisciplinary Chemistry |
UV water treatment devices can be used for well water and surface water disinfection. UV treatment compares favourably with other water disinfection systems in terms of cost, labour and the need for technically trained personnel for operation. Water chlorination treats larger organisms and offers residual disinfection, but these systems are expensive because they need special operator training and a steady supply of a potentially hazardous material. Finally, boiling of water is the most reliable treatment method but it demands labour and imposes a high economic cost. UV treatment is rapid and, in terms of primary energy use, approximately 20,000 times more efficient than boiling. | 0 | Theoretical and Fundamental Chemistry |
β-Catenin also acts as a morphogen in later stages of embryonic development. Together with TGF-β, an important role of β-catenin is to induce a morphogenic change in epithelial cells. It induces them to abandon their tight adhesion and assume a more mobile and loosely associated mesenchymal phenotype. During this process, epithelial cells lose expression of proteins like E-cadherin, Zonula occludens 1 (ZO1), and cytokeratin. At the same time they turn on the expression of vimentin, alpha smooth muscle actin (ACTA2), and fibroblast-specific protein 1 (FSP1). They also produce extracellular matrix components, such as type I collagen and fibronectin. Aberrant activation of the Wnt pathway has been implicated in pathological processes such as fibrosis and cancer. In cardiac muscle development, β-catenin performs a biphasic role. Initially, the activation of Wnt/β-catenin is essential for committing mesenchymal cells to a cardiac lineage; however, in later stages of development, the downregulation of β-catenin is required. | 1 | Applied and Interdisciplinary Chemistry |
From the 7th to 3rd Century BC, the Scythian people of the Pontic–Caspian steppe engaged in the widespread practice of metallurgy. Though Scythian society was heavily based around a nomadic, mobile lifestyle, the culture was capable of practicing metallurgy and of producing metal objects. Many works of Scythian metalworking have subsequently been found throughout the range of the people. | 1 | Applied and Interdisciplinary Chemistry |
In 1998, he founded the journal Accountability in Research, and has served as its editor-in-chief since its inception. He is on the editorial boards of several other journals, including the Drug Information Journal. From 2000 to 2002, he served on the advisory committee for National Human Research Protections. Although he has an extensive list of publications in the fields of biochemistry and microbiology, he is currently busied by his work as an analyst for Foreign Policy In Focus, a project of the Institute for Policy Studies, a think tank, to which he has been contributing since 2005. Shamoo has also authored and co-authored many op-eds on U.S. foreign policy that have been published in newspapers across the country.
Shamoo is also currently occupied with his work in the field of ethics. Since 1991, he has taught a graduate course at the University of Maryland entitled "Responsible Conduct of Research". In 1995, he co-founded the human rights organization, Citizens for Responsible Care and Research (CIRCARE). In 2003, he chaired a Special Issue GlaxoSmithKline Pharmaceuticals Ethics Advisory Group. Shamoo was then appointed to the Armed Forces Epidemiological Board (AFEB) of the United States Department of Defense as ethics consultant (2003–2004). Because he served as chairman on nine international conferences in ethics in research and human research protection, he was asked to testify before a congressional committee and the National Bioethics Advisory Commission. Since 2006, he has served on the Defense Health Board. And from 2006 to 2007,Shamoo was a member of the new Maryland Governors Higher Education Transition Working Group. He was an invited participant and presenter in the 2007 New Year Renaissance Weekend.
Shamoo has held visiting professorships at the Institute for Political Studies in Paris, France and at East Carolina University.
Shamoo has been cited and/or appeared frequently in local and national media both print and television. He has published numerous articles and books. | 1 | Applied and Interdisciplinary Chemistry |
The DNA double helix was discovered in 1953 (with further details in 1954) based on X-ray diffraction images of DNA (most notably photo 51, taken by Raymond Gosling and Rosalind Franklin) as well as base-pairing chemical and biochemical information. Prior to this, X-ray data being gathered in the 1950s indicated that DNA formed some sort of helix, but it had not yet been discovered what the exact structure of that helix was. There were therefore several proposed structures that were later overturned by the data supporting a DNA duplex. The most famous of these early models was by Linus Pauling and Robert Corey in 1953 in which they proposed a triple helix with the phosphate backbone on the inside, and the nucleotide bases pointing outwards. A broadly similar, but detailed structure was also proposed by Bruce Fraser that same year. However, Watson and Crick soon identified several problems with these models:
* Negatively charged phosphates near the axis repel each other, leaving the question of how the three-chain structure stays together.
* In a triple-helix model (specifically Pauling and Corey's model), some of the van der Waals distances appear to be too small.
The initial double helix model discovered, now termed B-form DNA is by far the most common conformation in cells. Two additional rarer helical conformations that also naturally occur were identified in the 1970s: A-form DNA, and Z-form DNA. | 1 | Applied and Interdisciplinary Chemistry |
Adkins' study found that global salinity increased with a global sea level drop of 120 m. Analyzing O data they also found that deep waters were within error of the freezing point, with oceanic waters exhibiting a greater degree of homogeneity in temperatures. In contrast, variations in salinity were much greater than they are today. Modern day salinities are all within 0.5 psu of the global average salinity of 34.7 psu, whereas salinities during the last glacial maximum (LGM) ranged from 35.8 psu in the North Atlantic to 37.1 in the Southern Ocean.
There are some notable differences in the hydrography at the LGM and present day. Today the North Atlantic Deep Water (NADW) is observed to be more saline than Antarctic Bottom Water (AABW), whereas at the last glacial maximum it was observed that the AABW was in fact more saline; a complete reversal. Today the NADW is more salty because of the Gulf Stream; this could thus indicate a reduction of flow through the Florida Straits due to lowered sea level.
Another observation is that the Southern Ocean was vastly more salty at the LGM than today. This is particularly intriguing given the assumed importance of the Southern Ocean in oceanic dynamical regulation of ice ages. The extreme value of 37.1 psu is assumed to be a consequence of an increased degree of sea ice formation and export. This would account for the increased salinity, but would also account for the lack of oxygen isotopic fractionation; brine rejection without oxygen isotopic fractionation is thought to be highly characteristic of sea ice formation. | 0 | Theoretical and Fundamental Chemistry |
Glyceraldehyde-3-phosphate can double up to form larger sugar molecules like glucose and fructose. These molecules are processed, and from them, the still larger sucrose, a disaccharide commonly known as table sugar, is made, though this process takes place outside of the chloroplast, in the cytoplasm.
Alternatively, glucose monomers in the chloroplast can be linked together to make starch, which accumulates into the starch grains found in the chloroplast.
Under conditions such as high atmospheric CO concentrations, these starch grains may grow very large, distorting the grana and thylakoids. The starch granules displace the thylakoids, but leave them intact.
Waterlogged roots can also cause starch buildup in the chloroplasts, possibly due to less sucrose being exported out of the chloroplast (or more accurately, the plant cell). This depletes a plant's free phosphate supply, which indirectly stimulates chloroplast starch synthesis.
While linked to low photosynthesis rates, the starch grains themselves may not necessarily interfere significantly with the efficiency of photosynthesis, and might simply be a side effect of another photosynthesis-depressing factor. | 0 | Theoretical and Fundamental Chemistry |
Sharpless married Jan Dueser in 1965 and they have three children. He was blinded in one eye during a lab accident in 1970 where an NMR tube exploded, shortly after he arrived at MIT as an assistant professor. After this accident, Sharpless stresses "theres simply never an adequate excuse for not wearing safety glasses in the laboratory at all times'." | 0 | Theoretical and Fundamental Chemistry |
Macrocyclic chiral stationary phases consist of a silica support, on which macrocyclic antibiotic molecules are bonded. The commonly used macrocyclic antibiotics include rifamycin, glycopeptides (for example, avoparcin, teicoplanin, ristocetin A, vancomycin, and their analogs), polypeptide antibiotic thiostrepton, and aminoglycosides (for example, fradiomycin, kanamycin, and streptomycin). The macrocyclic antibiotics interact with the analyte through hydrogen bonds, dipole-dipole interactions with the polar groups of the analyte, ionic interactions and π-π interactions. | 0 | Theoretical and Fundamental Chemistry |
* HYDROELAS : International conference on Hydroelasticity in marine technology.
* FSI : International conference on fluid-structure interaction.
* OT : Offshore Technology Conference.
* ISOPE : International Society of Offshore and Polar Engineers conference. | 1 | Applied and Interdisciplinary Chemistry |
A cascade refrigeration cycle is a multi-stage thermodynamic cycle. An example two-stage process is shown at right. (Bottom on mobile) The cascade cycle is often employed for devices such as ULT freezers.
In a cascade refrigeration system, two or more vapor-compression cycles with different refrigerants are used. The evaporation-condensation temperatures of each cycle are sequentially lower with some overlap to cover the total temperature drop desired, with refrigerants selected to work efficiently in the temperature range they cover. The low temperature system removes heat from the space to be cooled using an evaporator, and transfers it to a heat exchanger that is cooled by the evaporation of the refrigerant of the high temperature system. Alternatively, a liquid to liquid or similar heat exchanger may be used instead. The high temperature system transfers heat to a conventional condenser that carries the entire heat output of the system and may be passively, fan, or water-cooled.
Cascade cycles may be separated by either being sealed in separated loops, or in what is referred to as an "auto-cascade" where the gases are compressed as a mixture but separated as one refrigerant condenses into a liquid while the other continues as a gas through the rest of the cycle. Although an auto-cascade introduces several constraints on the design and operating conditions of the system that may reduce the efficiency it is often used in small systems due to only requiring a single compressor, or in cryogenic systems as it reduces the need for high efficiency heat exchangers to prevent the compressors leaking heat into the cryogenic cycles. Both types can be used in the same system, generally with the separate cycles being the first stage(s) and the auto-cascade being the last stage.
Peltier coolers may also be cascaded into a multi-stage system to achieve lower temperatures. Here the hot side of the first Peltier cooler is cooled by the cold side of the second Peltier cooler, which is larger in size, whose hot side is in turn cooled by the cold side of an even larger Peltier cooler, and so on. Efficiency drops very rapidly as more stages are added but for very small heat loads down to near-cryogenic temperatures this can often be an effective solution due to being compact and low cost, such as in mid-range thermographic cameras. A two stage Peltier cooler can achieve around -30°C, -75°C with three stages, -85°C with four stages, -100°C with six stages, and -123°C with seven stages. Refrigeration power and efficiency are low but Peltier coolers can be small, for small cooling loads resulting in overall low power consumption for a Peltier cooler with three stages.
For a Peltier cooler with seven stages, power consumption can be 65 W with a cooling capacity of 80 mW. | 0 | Theoretical and Fundamental Chemistry |
Most imides are cyclic compounds derived from dicarboxylic acids, and their names reflect the parent acid. Examples are succinimide, derived from succinic acid, and phthalimide, derived from phthalic acid. For imides derived from amines (as opposed to ammonia), the N-substituent is indicated by a prefix. For example, N-ethylsuccinimide is derived from succinic acid and ethylamine. Isoimides are isomeric with normal imides and have the formula RC(O)OC(NR′)R″. They are often intermediates that convert to the more symmetrical imides. Organic compounds called carbodiimides have the formula RN=C=NR. They are unrelated to imides. | 0 | Theoretical and Fundamental Chemistry |
Cefroxadine (INN, trade names Oraspor and Cefthan-DS) is a cephalosporin antibiotic. It is structurally related to cefalexin, and both drugs share a similar spectrum of activity.
It is available in Italy. | 0 | Theoretical and Fundamental Chemistry |
The process of isolating a natural product from its source can be costly in terms of committed time and material expense, and it may challenge the availability of the relied upon natural resource (or have ecological consequences for the resource). For instance, it has been estimated that the bark of an entire yew tree (Taxus brevifolia) would have to be harvested to extract enough paclitaxel for just a single dose of therapy. Furthermore, the number of structural analogues obtainable for structure–activity analysis (SAR) simply via harvest (if more than one structural analogue is even present) is limited by the biology at work in the organism, and so outside of the experimentalist's control.
In such cases where the ultimate target is harder to come by, or limits SAR, it is sometimes possible to source a middle-to-late stage biosynthetic precursor or analogue from which the ultimate target can be prepared. This is termed semisynthesis or partial synthesis. With this approach, the related biosynthetic intermediate is harvested and then converted to the final product by conventional procedures of chemical synthesis.
This strategy can have two advantages. Firstly, the intermediate may be more easily extracted, and in higher yield, than the ultimate desired product. An example of this is paclitaxel, which can be manufactured by extracting 10-deacetylbaccatin III from T. brevifolia needles, then carrying out a four-step synthesis. Secondly, the route designed between semisynthetic starting material and ultimate product may permit analogues of the final product to be synthesized. The newer generation semisynthetic penicillins are an illustration of the benefit of this approach. | 1 | Applied and Interdisciplinary Chemistry |
The first experimental account and analysis of gene expression noise in prokaryotes is from Becskei & Serrano and from Alexander van Oudenaardens lab. The first experimental account and analysis of gene expression noise in eukaryotes is from James J. Collinss lab. | 1 | Applied and Interdisciplinary Chemistry |
The Faraday Lectureship Prize, previously known simply as the Faraday Lectureship, is awarded once every two years (approximately) by the Royal Society of Chemistry for "exceptional contributions to physical or theoretical chemistry". Named after Michael Faraday, the first Faraday Lecture was given in 1869, two years after Faraday's death, by Jean-Baptiste Dumas. As of 2009, the prize was worth £5000, with the recipient also receiving a medal and a certificate. As the name suggests, the recipient also gives a public lecture describing his or her work. | 1 | Applied and Interdisciplinary Chemistry |
Molecular breeding resources (including multiomics data) are available for:
* Some of the millets
* Wheat | 1 | Applied and Interdisciplinary Chemistry |
Serious galvanic corrosion has been reported on the latest US Navy attack littoral combat vessel the USS Independence caused by steel water jet propulsion systems attached to an aluminium hull. Without electrical isolation between the steel and aluminium, the aluminium hull acts as an anode to the stainless steel, resulting in aggressive galvanic corrosion. | 1 | Applied and Interdisciplinary Chemistry |
α-Halo carboxylic acids and esters are organic compounds with the respective formulas where R and R' are organic substituents. The X in these compounds is a halide, usually chloride and bromide. These compounds are often used as intermediates in the preparation of more elaborate derivatives. They are often potent alkylating agents. The mono halide derivatives are chiral. | 0 | Theoretical and Fundamental Chemistry |
A non-competitive antagonist is a type of insurmountable antagonist that may act in one of two ways: by binding to an allosteric site of the receptor, or by irreversibly binding to the active site of the receptor. The former meaning has been standardised by the IUPHAR, and is equivalent to the antagonist being called an allosteric antagonist. While the mechanism of antagonism is different in both of these phenomena, they are both called "non-competitive" because the end-results of each are functionally very similar. Unlike competitive antagonists, which affect the amount of agonist necessary to achieve a maximal response but do not affect the magnitude of that maximal response, non-competitive antagonists reduce the magnitude of the maximum response that can be attained by any amount of agonist. This property earns them the name "non-competitive" because their effects cannot be negated, no matter how much agonist is present. In functional assays of non-competitive antagonists, depression of the maximal response of agonist dose-response curves, and in some cases, rightward shifts, is produced. The rightward shift will occur as a result of a receptor reserve (also known as spare receptors) and inhibition of the agonist response will only occur when this reserve is depleted.
An antagonist that binds to the active site of a receptor is said to be "non-competitive" if the bond between the active site and the antagonist is irreversible or nearly so. This usage of the term "non-competitive" may not be ideal, however, since the term "irreversible competitive antagonism" may also be used to describe the same phenomenon without the potential for confusion with the second meaning of "non-competitive antagonism" discussed below.
The second form of "non-competitive antagonists" act at an allosteric site. These antagonists bind to a distinctly separate binding site from the agonist, exerting their action to that receptor via the other binding site. They do not compete with agonists for binding at the active site. The bound antagonists may prevent conformational changes in the receptor required for receptor activation after the agonist binds. Cyclothiazide has been shown to act as a reversible non-competitive antagonist of mGluR1 receptor. Another example of a non-competitive is phenoxybenzamine which binds irreversibly (with covalent bonds) to alpha-adrenergic receptors, which in turn reduces the fraction of available receptors and reduces the maximal effect that can be produced by the agonist. | 1 | Applied and Interdisciplinary Chemistry |
Copper-free click chemistry is a bioorthogonal reaction as a variant of an azide-alkyne Huisgen cycloaddition. By eliminating cytotoxic copper catalysts, the reaction proceeds without live-cell toxicity. It was developed as a faster alternative to the Staudinger ligation with the first generation of Cu-free click chemistry, producing rate constants over 63 times faster.
Although the reaction produces a regioisomeric mixture of triazoles, the lack of regioselectivity in the reaction is not a major concern for its applications in bioorthogonal chemistry. More regiospecific and less bioorthogonal requirements are best served by the traditional Huisgen cycloaddition, especially given the low yield and synthetic difficulty of synthesizing a strained cyclooctyne (compared to the addition of a terminal alkyne).
The bioorthogonality of the reaction has allowed the Cu-free click reaction to be applied within cultured cells, live zebrafish, and mice.
The absence of exogenous metal catalysts makes the Cu-free chemical reactions suitable for the in vivo applications of bioorthogonal chemistry or bioorthogonal click chemistry. | 0 | Theoretical and Fundamental Chemistry |
Due to the essential role of NADPH in lipid and DNA biosynthesis and the hyperproliferative nature of most cancers, NADK is an attractive target for cancer therapy. Furthermore, NADPH is required for the antioxidant activities of thioredoxin reductase and glutaredoxin. Thionicotinamide and other nicotinamide analogs are potential inhibitors of NADK, and studies show that treatment of colon cancer cells with thionicotinamide suppresses the cytosolic NADPH pool to increase oxidative stress and synergizes with chemotherapy.
While the role of NADK in increasing the NADPH pool appears to offer protection against apoptosis, there are also cases where NADK activity appears to potentiate cell death. Genetic studies done in human haploid cell lines indicate that knocking out NADK may protect from certain non-apoptotic stimuli. | 1 | Applied and Interdisciplinary Chemistry |
Biorheological research aims to determine and characterize the dynamics of physiological processes at all levels of biological organization, and the inter-relationships between rheological properties of various biological systems. Biorheological studies can include both animal and plant systems, and can be in broad contexts like the rheology of macromolecules and macromolecular arrays, or in narrower contexts like the rheology in cells, tissues or organs. | 1 | Applied and Interdisciplinary Chemistry |
The hyperbolic response between photosynthesis and irradiance, depicted by the PI curve, is important for assessing phytoplankton population dynamics, which influence many aspects of the marine environment. | 0 | Theoretical and Fundamental Chemistry |
Space-based measurements of carbon dioxide are also a recent addition to atmospheric X measurements. SCIAMACHY aboard ESAs ENVISAT made global column X measurements from 2002 to 2012. AIRS aboard NASAs Aqua satellite makes global X measurements and was launched shortly after ENVISAT in 2012. More recent satellites have significantly improved the data density and precision of global measurements. Newer missions have higher spectral and spatial resolutions. JAXAs GOSAT was the first dedicated GHG monitoring satellite to successfully achieve orbit in 2009. NASAs OCO-2 launched in 2014 was the second. Various other satellites missions to measure atmospheric X are planned. | 1 | Applied and Interdisciplinary Chemistry |
Several routes exist for the synthesis of Dextromethorphan. Even though many of the syntheses have been known since the middle of the 20th century, researchers are still working today to further develop the synthesis of Dextromethorphan and, for example, to make it more environmentally friendly.
This includes the synthesis by means of ionic liquids. | 0 | Theoretical and Fundamental Chemistry |
There are four main types of making to localize the artificial metal cofactor to make an ArM, including covalent, supramolecular, metal substitution and dative. | 0 | Theoretical and Fundamental Chemistry |
The Gladstone–Dale relation can be expressed as an equation of state by re-arranging the terms to .
where n is the index of refraction, D = density and constant = Gladstone-Dale constant.
The macroscopic values (n) and (V) determined on bulk material are now calculated as a sum of atomic or molecular properties. Each molecule has a characteristic mass (due to the atomic weights of the elements) and atomic or molecular volume that contributes to the bulk density, and a characteristic refractivity due to a characteristic electric structure that contributes to the net index of refraction.
The refractivity of a single molecule is the refractive volume k(MW)/N in nm, where MW is the molecular weight and N is the Avogadro constant. To calculate the optical properties of materials using the polarizability or refractivity volumes in nm, the Gladstone–Dale relation competes with the Kramers–Kronig relation and Lorentz–Lorenz relation but differs in optical theory.
The index of refraction (n) is calculated from the change of angle of a collimated monochromatic beam of light from vacuum into liquid using Snells law for refraction. Using the theory of light as an electromagnetic wave, light takes a straight-line path through water at reduced speed (v) and wavelength (λ). The ratio v/λ is a constant equal to the frequency (ν) of the light, as is the quantized (photon) energy using the Planck constant and . Compared to the constant speed of light in vacuum (c'), the index of refraction of water is .
The Gladstone–Dale term is the non-linear optical path length or time delay. Using Isaac Newton's theory of light as a stream of particles refracted locally by (electric) forces acting between atoms, the optic path length is due to refraction at constant speed by displacement about each atom. For light passing through 1 m of water with , light traveled an extra 0.33 m compared to light that traveled 1 m in a straight line in vacuum. As the speed of light is a ratio (distance per unit time in m/s), light also took an extra 0.33 s to travel through water compared to light traveling 1 s in vacuum. | 1 | Applied and Interdisciplinary Chemistry |
It has been stated that one of the biggest challenges in the United Kingdom railway industry is corrosion. The biggest problem is that corrosion can affect the structural integrity of passenger carrying railway carriages thus affecting their crashworthiness. Other railway structures and assets can also be affected. The Permanent Way Institution give lectures on the subject periodically. In January 2018 corrosion of a metal structure caused the emergency closure of Liverpool Lime Street railway station. | 1 | Applied and Interdisciplinary Chemistry |
Investigation on dinoflagellate cyst in the Mediterranean Sea has identified warm and cold temperate dinocyst species and these species have been used to reconstruct the paleoclimate changes during the past 30,000 years. | 0 | Theoretical and Fundamental Chemistry |
Fluorescence in situ hybridization (FISH) is a molecular cytogenetic technique that uses fluorescent probes that bind to only particular parts of a nucleic acid sequence with a high degree of sequence complementarity. It was developed by biomedical researchers in the early 1980s to detect and localize the presence or absence of specific DNA sequences on chromosomes. Fluorescence microscopy can be used to find out where the fluorescent probe is bound to the chromosomes. FISH is often used for finding specific features in DNA for use in genetic counseling, medicine, and species identification. FISH can also be used to detect and localize specific RNA targets (mRNA, lncRNA and miRNA) in cells, circulating tumor cells, and tissue samples. In this context, it can help define the spatial-temporal patterns of gene expression within cells and tissues. | 1 | Applied and Interdisciplinary Chemistry |
Asteroid mining has also been seriously considered. A NASA design study evaluated a 10,000-ton mining vehicle (to be assembled in orbit) that would return a 500,000-ton asteroid fragment to geostationary orbit. Only about 3,000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine, which could be arranged to be the spent rocket stages used to launch the payload. Assuming that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition. One proposal is to capture the asteroid Apophis into Earth orbit and convert it into 150 solar power satellites of 5 GW each or the larger asteroid 1999 AN10, which is 50 times the size of Apophis and large enough to build 7,500 5-gigawatt solar power satellites | 0 | Theoretical and Fundamental Chemistry |
The primary function of lysosomal lipase is to hydrolyze lipids such as triglycerides and cholesterol. These fats are transported and degraded into free fatty acids. Lysosomal lipases function optimally at an acidic pH which are complementary with the environment found in the lysosomal lumen. These enzymes were believed to only hydrolyze the lipids found in organelle membranes and extracellular lipids. However, recent studies suggest that lysosomal lipases also play a significant role in the degradation of cytosolic lipids, a characteristic that was previously limited to neutral lipases. The ability of the lysosome to degrade a diverse set of cargo is attributed to the lysosomal lipase and other soluble hydrolases. These enzymes include sulphatases, phosphatases, peptidases, glycosidases, and nucleases.
The biochemical role of these enzymes are observed in various pathways, specifically in lipid catabolism. At the intracellular level, the byproducts released by the lysosomal lipase are recycled for membrane assembly and energy production. In addition, these enzymes participate in the production of specific fatty acids necessary for the metabolic reprogramming of CD8+ memory T cells, macrophage alternative activation, and lipid mediator synthesis. As observed, the degradation of these lipids are essential to maintain homeostasis within the body. The absence or decreased activity of this enzyme could lead to various metabolic disorders. | 1 | Applied and Interdisciplinary Chemistry |
Heme A differs from heme B in that a methyl side chain at ring position 8 is oxidized to a formyl group and a hydroxyethylfarnesyl group, an isoprenoid chain, has been attached to the vinyl side chain at ring position 2 of the iron tetrapyrrole heme. Heme A is similar to heme o, in that both have this farnesyl addition at position 2 but heme O does not have the formyl group at position 8, still containing the methyl group. The correct structure of heme A, based upon NMR and IR experiments of the reduced, Fe(II) form of the heme, was published in 1975. The structure was confirmed by synthesis of the dimethyl ester of the iron-free form. | 1 | Applied and Interdisciplinary Chemistry |
Dynamic heteroatom bond formation, presents useful reactions in the dynamic covalent reaction toolbox. Boronic acid condensation (BAC) and disulfide exchange constitute the two main reactions in this category. | 0 | Theoretical and Fundamental Chemistry |
X-ray crystallography is a technique that measures the angles and intensities of crystalline atoms in order to determine the atomic and molecular structure of the crystal of interest. Crystallographers are then able to produce and three-dimensional picture where the positions of the atoms, chemical bonds as well as other important characteristics can be determined. Klimasaukas and colleagues used this technique to observe the first base flipping phenomenon, in which their experimental procedure involved several steps:
# Purification
# Crystallization
# Data Collection
# Structure determination and refinement
During purification, Haemophilus haemolyticus methyltransferase was overexpressed and purified using a high salt back-extraction step to selectively solubilize M.HhaI, followed by fast protein liquid chromatography (FPLC) as done previously by Kumar and colleagues. Authors utilized a Mono-Q anion exchange column to remove the small quantity of proteinaceous materials and unwanted DNA prior to the crystallization step. Once M.HhaI was successfully purified, the sample was then grown using a method that mixes the solution containing the complex at a temperature of 16 °C and the hanging-drop vapor diffusion technique to obtain the crystals. Authors were then able to collect the x-ray data according to a technique used by Cheng and colleagues in 1993. This technique involved the measurement of the diffraction intensities on a FAST detector, where the exposure times for 0.1° rotation were 5 or 10 seconds. For the structure determination and refinement, Klimasaukas and colleagues used the molecular replacement of the refined apo structure described by Cheng and colleagues in 1993 where the search models X-PLOR, MERLOT, and TRNSUM were used to solve the rotation and translation functions. This part of the study involves the use of a variety of software and computer algorithms to solve the structures and characteristics of the crystal of interest. | 1 | Applied and Interdisciplinary Chemistry |
Gadolinium-based pharmaceuticals alter the relaxation time, and hence spectral line shape, of those protons that are in water molecules that are transiently attached to the paramagnetic atoms, resulting contrast enhancement of the MRI image. This allows better visualisation of some brain tumours. | 0 | Theoretical and Fundamental Chemistry |
The raw sequencing data is then processed through bioinformatics (e.g., the GemCode analysis software developed by 10x Genomics) to remove low-quality reads and to assign reads to their respective barcodes. Reads can be aligned to a reference genome or assembled de novo to generate long-range contigs. The read alignment step is important for determining the order and orientation of the long DNA fragments, and for identifying genomic variations, such as insertions or deletions. | 1 | Applied and Interdisciplinary Chemistry |
* Zur Kenntnis der thermischen Zersetzung der Salpetersäure, 1926.
* Zur Erklärung der abnormen Osmose an nichtquellbaren Membranen, I.-III. Teil, 1933.
* The Structure of the Colladion Membrane and Its Electrical Behavior, an Experimental Test of Some Aspects of the Teorell and Meyer-sievers Theories of Electrical Membrane Behavior, 1944. | 0 | Theoretical and Fundamental Chemistry |
To better understand the challenges for building full-thickness engineered oral mucosa it is important to first understand the structure of normal oral mucosa. Normal oral mucosa consists of two layers, the top stratified squamous epithelial layer and the bottom lamina propria. The epithelial layer consists of four layers:
* Stratum basale (basal layer)
* Stratum spinosum (spinous layer)
* Stratum granulosum (granular layer)
* Stratum corneum (keratinized/superficial layer)
Depending on the region of the mouth the epithelium may be keratinized or non-keratinized. Non-keratinized squamous epithelium covers the soft palate, lips, cheeks and the floor of the mouth. Keratinized squamous epithelium is present in the gingiva and hard palate. Keratinization is the differentiation of keratinocytes in the granular layer into dead surface cells to form the stratum corneum. The cells terminally differentiate as they migrate to the surface (from the basal layer where the progenitor cells are located to the dead superficial surface).
The lamina propria is a fibrous connective tissue layer that consists of a network of type I and III collagen and elastin fibers. The main cells of the lamina propria are the fibroblasts, which are responsible for the production of the extracellular matrix. The basement membrane forms the border between the epithelial layer and the lamina propria. | 1 | Applied and Interdisciplinary Chemistry |
*phosphorus • sulfur (sulphur) • arsenic • antimony
*vitriol • quartz • cinnabar • pyrites • orpiment • galena
*magnesia • lime • potash • natron • saltpetre • kohl
*ammonia • ammonium chloride • alcohol • camphor
*sulfuric acid (sulphuric acid) • hydrochloric acid • nitric acid • acetic acid • formic acid • citric acid • tartaric acid
*aqua regia • gunpowder
*blue vitriol • green vitriol • vinegar • salt
more... | 1 | Applied and Interdisciplinary Chemistry |
Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of crystal structure beneath the surface. This will generally leave some material stuck or even friction welded to the adjacent surface, whereas the galled material may appear gouged with balled-up or torn lumps of material stuck to its surface.
Galling is most commonly found in metal surfaces that are in sliding contact with each other. It is especially common where there is inadequate lubrication between the surfaces. However, certain metals will generally be more prone to galling, due to the atomic structure of their crystals. For example, aluminium is a metal that will gall very easily, whereas annealed (softened) steel is slightly more resistant to galling. Steel that is fully hardened is very resistant to galling.
Galling is a common problem in most applications where metals slide in contact with other metals. This can happen regardless of whether the metals are the same or different. Alloys such as brass and bronze are often chosen for bearings, bushings, and other sliding applications because of their resistance to galling, as well as other forms of mechanical abrasion. | 0 | Theoretical and Fundamental Chemistry |
FASTpp has been used to probe:
* Lysate effect on protein stability
* Thermal proteome stability
* Coupled folding and binding
* Ligand effects on fraction folded & stability
* Effects of mutations on fraction folded & stability (e.g. point mutation/missense mutations)
* Kinetic protein stability | 1 | Applied and Interdisciplinary Chemistry |
Vauquelin was born at Saint-André-d'Hébertot in Normandy, France, the son of Nicolas Vauquelin, an estate manager, and his wife, Catherine Le Charterier.
His first acquaintance with chemistry was gained as laboratory assistant to an apothecary in Rouen (1777–1779), and after various vicissitudes he obtained an introduction to A. F. Fourcroy, in whose laboratory he was an assistant from 1783 to 1791.
Moving to Paris, he became a laboratory assistant at the Jardin du Roi and was befriended by a professor of chemistry. In 1791 he was made a member of the Academy of Sciences and from that time he helped to edit the journal Annales de Chimie (Chemical annals), although he left the country for a while during the height of the French Revolution. In 1798 Vauquelin discovered beryllium oxide by extracting it from an emerald (a beryl variety); Klaproth isolated the element from the oxide. | 1 | Applied and Interdisciplinary Chemistry |
Falk's main research area is the structural analysis, synthesis, stereochemistry and photochemistry of plant and animal photosensitizing and photosensory pigments. The main group of compounds covered in his work are pigments derived from the fundamental phenanthro[1,10,9,8-opqra]perylene-7,14-dione chromophore with natural pigments like hypericin, stentorin, the fringelites, the gymnochromes, and blepharismin. In addition, he is focusing on hemin-analogous corrphycene derivatives (e.g. as potential blood substitutes and heme oxygenase blocker) as well as on other natural compounds such as the natural sun blocker urocanic acid. Furthermore, research on applied problems of industrial relevance, like oxidation, ozonization, non natural amino acids and catalysis have been pursued. | 0 | Theoretical and Fundamental Chemistry |
Figure 3 shows the line of contact where three phases meet. In equilibrium, the net force per unit length acting along the boundary line between the three phases must be zero. The components of net force in the direction along each of the interfaces are given by:
where α, β, and θ are the angles shown and γ is the surface energy between the two indicated phases. These relations can also be expressed by an analog to a triangle known as Neumanns triangle, shown in Figure 4. Neumanns triangle is consistent with the geometrical restriction that , and applying the law of sines and law of cosines to it produce relations that describe how the interfacial angles depend on the ratios of surface energies.
Because these three surface energies form the sides of a triangle, they are constrained by the triangle inequalities, γ + γ meaning that not one of the surface tensions can exceed the sum of the other two. If three fluids with surface energies that do not follow these inequalities are brought into contact, no equilibrium configuration consistent with Figure 3 will exist. | 0 | Theoretical and Fundamental Chemistry |
In most industrial wastewater and biosolids applications jet aerators exhibit superior oxygen transfer efficiency compared to other aeration technologies. The hydrodynamic conditions within the jet and fine bubble cloud produces continuous surface renewal at the gas/liquid interface resulting in higher alpha factors. This results in superior process oxygen transfer performance in the presence of surfactants, extracellular enzymes and high MLS concentrations. | 1 | Applied and Interdisciplinary Chemistry |
Secondary amines can be alkylated with cuprates. The reaction is based on the oxidative coupling of lithium alkyl copper amide which is reported to form in situ during the reaction between lithium dialkylcuprates and primary or secondary amides. | 0 | Theoretical and Fundamental Chemistry |
Clay-water interaction is an all-inclusive term to describe various progressive interactions between clay minerals and water. In the dry state, clay packets exist in face-to-face stacks like a deck of playing cards, but clay packets begin to change when exposed to water. Five descriptive terms describe the progressive interactions that can occur in a clay-water system, such as a water mud.
(1) Hydration occurs as clay packets absorb water and swell.
(2) Dispersion (or disaggregation) causes clay platelets to break apart and disperse into the water due to loss of attractive forces as water forces the platelets farther apart.
(3) Flocculation begins when mechanical shearing stops and platelets previously dispersed come together due to the attractive force of surface charges on the platelets.
(4) Deflocculation, or peptization, the opposite effect, occurs by addition of chemical deflocculant to flocculated mud; the positive edge charges are covered and attraction forces are greatly reduced.
(5) Aggregation, a result of ionic or thermal conditions, alters the hydrational layer around clay platelets, removes the deflocculant from positive edge charges and allows platelets to assume a face-to-face structure. | 0 | Theoretical and Fundamental Chemistry |
Nines are an informal logarithmic notation for proportions very near to one or, equivalently, percentages very near 100%. Put simply, "nines" are the number of consecutive nines in a percentage such as 99% (two nines) or a decimal fraction such as 0.999 (three nines). Their common uses include grading the purity of materials. | 1 | Applied and Interdisciplinary Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V) | 1 | Applied and Interdisciplinary Chemistry |
Testosterone glucuronide is an endogenous, naturally occurring steroid and minor urinary metabolite of testosterone. | 1 | Applied and Interdisciplinary Chemistry |
The force required to separate two colloid particles can be measured using optical tweezers. This method uses a focused laser beam to apply an attractive or repulsive force on dielectric micro and nanoparticles. This technique is used with dispersion particles by applying a force which resists depletion forces. The displacement of the particles is then measured and used to find the attractive force between the particles. | 0 | Theoretical and Fundamental Chemistry |
Propargyl methanesulfinates are useful substrates for the synthesis of allenes from stoichiometric organocopper complexes. In this case, the complexes were generated in situ through the combination of a Grignard reagent, copper(I) bromide, and lithium bromide. Organocopper complexes very often need Lewis acid activation in order to react efficiently; magnesium bromide generated in situ serves as an activating Lewis acid in this case.
Alkenylcopper complexes, easily generated through carbocupration, are useful for the introduction of a vinyl group in the β position of a carbonyl compound. In this case, as above, magnesium bromide is serving as an activating Lewis acid.
Epoxide opening with organocuprates is highly selective for the less hindered position. Substitution takes place with complete inversion of configuration at the electrophilic carbon.
Generally, organocuprates react with allylic electrophiles in an anti S2 fashion. In the reaction below, nearly complete inversion of configuration was observed despite the presence of a second stereocenter in the ring.
Conjugate addition of organocuprates is widely used in organic synthesis. Vinyl ether cuprates serve as convenient acyl anion equivalents in conjugate addition reactions to enones. The resulting enol ethers can be hydrolyzed to 1,4-diketones, which are difficult to access using conventional carbonyl chemistry.
The use of additives in conjunction with a stoichiometric amount of organocopper complexes enhances the rate and yield of many reactions. Organocopper complexes in particular react sluggishly in the absence of a Lewis acid. Although magnesium bromide generated in situ from the reaction of Grignard reagents and copper(I) halides can serve this role (see above), external Lewis acids are also useful. In the presence of boron trifluoride etherate, organocopper complexes are able to add to sterically congested enones in moderate yield (effecting the same transformation with an organocuprate would be difficult).
Boron trifluoride etherate is also useful as an additive in reactions of higher-order cyanocuprates. The use of the 2-thienyl group as a "dummy" substituent in the cyanocuprate conserves the potentially valuable organolithium reagent used to generate the cyanocuprate (as only the dummy group is present in copper-containing byproducts). In the absence of boron trifluoride etherate, no reaction was observed in this case.
Conjugate addition reactions of higher-order cyanocuprates represent another useful application for boron trifluoride etherate. The vinyl group is transferred selectively in this reaction (there is a mistake in a scheme); this is in contrast to substitution reactions employing the same reagent, which result in selective transfer of the methyl group. | 0 | Theoretical and Fundamental Chemistry |
Thermobarometry uses equilibrium constants to calculate information about the environmental conditions present during the rocks' formation. While each rock is forming, it reacts with the surrounding elements until it cools down enough to become inert. Each mineral within the rock will cool and crystalize at different points; a petrogenetic grid is a useful way to visualize each mineral crystalizing in sequence.
Individual reactions of specific minerals can be used to calculate either the temperature or pressure. Therefore, two different reactions are needed to calculate both the temperature and pressure of the magma for a single rock. Some reactions are better for pressure and others are better for temperature, based on thermodynamics and Le Chatelier's Principle.
This technique requires each reaction to be calibrated, which is done through experimentation and data analysis. Experimentation involves simulating the temperatures and pressures at which these rocks form and observing how the reaction proceeds at those conditions, while data analysis relies on amassing a large database of rock samples with pressure and temperature information. Experimental data tends to have significant variation, so using data from natural formations is more accurate, if it's available. | 0 | Theoretical and Fundamental Chemistry |
Ferrosilicon is produced by reduction of silica or sand with coke in the presence of iron. Typical sources of iron are scrap iron or millscale. Ferrosilicons with silicon content up to about 15% are made in blast furnaces lined with acid fire bricks.
Ferrosilicons with higher silicon content are made in electric arc furnaces. The usual formulations on the market are ferrosilicons with 15%, 45%, 75%, and 90% silicon. The remainder is iron, with about 2% consisting of other elements like aluminium and calcium. An overabundance of silica is used to prevent formation of silicon carbide. Microsilica is a useful byproduct.
A mineral perryite is similar to ferrosilicon, with its composition FeSi. In contact with water, ferrosilicon may slowly produce hydrogen. The reaction, which is accelerated in the presence of base, is used for hydrogen production. The melting point and density of ferrosilicon depends on its silicon content, with two nearly-eutectic areas, one near FeSi and second spanning FeSi-FeSi composition range. | 1 | Applied and Interdisciplinary Chemistry |
The electronic density functional is explicitly used in the calculation of the electronic ground state. Packages such as VASP have an option to calculate the electronic density of states per eV to facilitate the prediction of conduction bands and band gaps. | 0 | Theoretical and Fundamental Chemistry |
The Lumière–Barbier method is a method of acetylating aromatic amines in aqueous solutions. Illustrative is the acetylation of aniline. First aniline is dissolved in water using one equivalent of hydrochloric acid. This solution is subsequently treated, sequentially, with acetic anhydride and aqueous sodium acetate. Aniline attacks acetic anhydride followed by deprotonation of the ammonium ion:
Acetate then acts as a leaving group:
The acetanilide product is insoluble in water and can therefore be filtered off as crystals. | 0 | Theoretical and Fundamental Chemistry |
Isolation of the toxin using cyanobacteria cultured from the original Palm Island strain was achieved by gel filtration of an aqueous extract, followed by reverse-phase HPLC. Structure elucidation was achieved via mass spectrometry (MS) and nuclear magnetic resonance (NMR) experiments, and a structure (later proven slightly incorrect) was proposed (Figure 1).
This almost-correct molecule possesses a tricyclic guanidine group (rings A, B & C), along with a uracil ring (D). The zwitterionic nature of the molecule makes this highly water-soluble, as the presence of charged areas within the molecule creates a dipole effect, suiting the polar solvent. Sensitivity of key signals in the NMR spectrum to small changes in pH suggested that the uracil ring exists in a keto/enol tautomeric relationship, where a hydrogen transfer results in two distinct structures (Figure 2). It was originally proposed that a hydrogen bond between the uracil and guanidine groups in the enol tautomer would make this the dominant form. | 0 | Theoretical and Fundamental Chemistry |
With the development of the first two laws of thermodynamics in the 1850s and 60s, heats of reaction and the work associated with these processes were given a more accurate mathematical basis. In 1876, Willard Gibbs unified all of this in his 300-page "On the Equilibrium of Heterogeneous Substances". Suppose, for example, we have a general thermodynamic system, called the "primary" system and that we mechanically connect it to a "reversible work source". A reversible work source is a system which, when it does work, or has work done to it, does not change its entropy. It is therefore not a heat engine and does not suffer dissipation due to friction or heat exchanges. A simple example would be a frictionless spring, or a weight on a pulley in a gravitational field. Suppose further, that we thermally connect the primary system to a third system, a "reversible heat source". A reversible heat source may be thought of as a heat source in which all transformations are reversible. For such a source, the heat energy δQ added will be equal to the temperature of the source (T) times the increase in its entropy. (If it were an irreversible heat source, the entropy increase would be larger than δQ/T)
Define:
We may now make the following statements
Eliminating , , and gives the following equation:
When the primary system is reversible, the equality will hold and the amount of work delivered will be a maximum. Note that this will hold for any reversible system which has the same values of dU and dS . | 0 | Theoretical and Fundamental Chemistry |
An expression vector has features that any vector may have, such as an origin of replication, a selectable marker, and a suitable site for the insertion of a gene like the multiple cloning site. The cloned gene may be transferred from a specialized cloning vector to an expression vector, although it is possible to clone directly into an expression vector. The cloning process is normally performed in Escherichia coli. Vectors used for protein production in organisms other than E.coli may have, in addition to a suitable origin of replication for its propagation in E. coli, elements that allow them to be maintained in another organism, and these vectors are called shuttle vectors. | 1 | Applied and Interdisciplinary Chemistry |
(R)-2-Methyl-CBS-oxazaborolidine is an organoboron catalyst that is used in organic synthesis. This catalyst, developed by Itsuno and Elias James Corey, is generated by heating (R)-(+)-2-(diphenylhydroxymethyl) pyrrolidine along with trimethylboroxine or methylboronic acid. It is an excellent tool for the synthesis of alcohols in high enantiomeric ratio. Generally, 2-10 mol% of this catalyst is used along with borane-tetrahydrofuran (THF), borane-dimethylsulfide, borane-N,N-diethylaniline, or diborane as the borane source. Enantioselective reduction using chiral oxazaborolidine catalysts has been used in the synthesis of commercial drugs such as ezetimibe and aprepitant. | 0 | Theoretical and Fundamental Chemistry |
Theresa M. Reineke (born January 1, 1972) is an American chemist and Distinguished McKnight University Professor at the University of Minnesota. She designs sustainable, environmentally friendly polymer-based delivery systems for targeted therapeutics. She is the associate editor of ACS Macro Letters. | 1 | Applied and Interdisciplinary Chemistry |
The chelate effect is the greater affinity of chelating ligands for a metal ion than that of similar nonchelating (monodentate) ligands for the same metal.
The thermodynamic principles underpinning the chelate effect are illustrated by the contrasting affinities of copper(II) for ethylenediamine (en) vs. methylamine.
In () the ethylenediamine forms a chelate complex with the copper ion. Chelation results in the formation of a five-membered CuCN ring. In () the bidentate ligand is replaced by two monodentate methylamine ligands of approximately the same donor power, indicating that the Cu–N bonds are approximately the same in the two reactions.
The thermodynamic approach to describing the chelate effect considers the equilibrium constant for the reaction: the larger the equilibrium constant, the higher the concentration of the complex.
Electrical charges have been omitted for simplicity of notation. The square brackets indicate concentration, and the subscripts to the stability constants, β, indicate the stoichiometry of the complex. When the analytical concentration of methylamine is twice that of ethylenediamine and the concentration of copper is the same in both reactions, the concentration [Cu(en)] is much higher than the concentration [Cu(MeNH)] because β ≫ β.
An equilibrium constant, K, is related to the standard Gibbs free energy, by
where R is the gas constant and T is the temperature in kelvins. is the standard enthalpy change of the reaction and is the standard entropy change.
Since the enthalpy should be approximately the same for the two reactions, the difference between the two stability constants is due to the effects of entropy. In equation () there are two particles on the left and one on the right, whereas in equation () there are three particles on the left and one on the right. This difference means that less entropy of disorder is lost when the chelate complex is formed with bidentate ligand than when the complex with monodentate ligands is formed. This is one of the factors contributing to the entropy difference. Other factors include solvation changes and ring formation. Some experimental data to illustrate the effect are shown in the following table.
These data confirm that the enthalpy changes are approximately equal for the two reactions and that the main reason for the greater stability of the chelate complex is the entropy term, which is much less unfavorable. In general it is difficult to account precisely for thermodynamic values in terms of changes in solution at the molecular level, but it is clear that the chelate effect is predominantly an effect of entropy.
Other explanations, including that of Schwarzenbach, are discussed in Greenwood and Earnshaw (loc.cit). | 0 | Theoretical and Fundamental Chemistry |
A second Fe species apart from the ferrate(VI) ion, [(Mecy-ac)FeN](PF), has been reported. This species, is formed by oxidation followed by photolysis to yield the Fe(VI) species. Characterization of the Fe(VI) complex was done by Mossbauer, EXAFS, IR, and DFT calculations. Unlike the ferrate(VI) ion, compound 5 is diamagnetic. | 0 | Theoretical and Fundamental Chemistry |
The development of laser heating began only 8 years after Charles Weir, of the National Bureau of Standards (NBS), made the first diamond anvil cell and Alvin Van Valkenburg, NBS, realized the potential of being able to see the sample while under pressure. William Bassett and his colleague Taro Takahashi focused a laser beam on the sample while under pressure. The first laser heating system used a single 7 joule pulsed ruby laser that heated the sample to 3000 °C while at 260 kilobars. This was sufficient to convert graphite to diamond. The major flaws within the first system related to control and temperature measurement.
Temperature measurement was initially done by Basset using an optical pyrometer to measure the intensity of the incandescent light from the sample. Colleagues at UC Berkeley were better able to utilize the black-body radiation and more accurately measure the temperature. The hot spot produced by the laser also created large thermal gradients in between the portions of sample that were hit by the focused laser and those that were not. The solution to this problem is ongoing but advances have been made with the introduction of a double-sided approach. | 0 | Theoretical and Fundamental Chemistry |
The MyD88-dependent response occurs on dimerization of TLRs, and is used by every TLR except TLR3. Its primary effect is activation of NFκB and Mitogen-activated protein kinase. Ligand binding and conformational change that occurs in the receptor recruits the adaptor protein MyD88, a member of the TIR family. MyD88 then recruits IRAK4, IRAK1 and IRAK2. IRAK kinases then phosphorylate and activate the protein TRAF6, which in turn polyubiquinates the protein TAK1, as well as itself to facilitate binding to IKK-β. On binding, TAK1 phosphorylates IKK-β, which then phosphorylates IκB causing its degradation and allowing NFκB to diffuse into the cell nucleus and activate transcription and consequent induction of inflammatory cytokines. | 1 | Applied and Interdisciplinary Chemistry |
In Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of several greenhouse gases in the atmosphere of Earth. The current global average concentration of carbon dioxide (CO) in the atmosphere is 421 ppm as of May 2022 (0.04%). This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century. The increase is due to human activity. Burning fossil fuels is the main cause of these increased CO concentrations and also the main cause of climate change. Other large sources of CO from human activities include cement production, deforestation, and biomass burning.
Carbon dioxide is a greenhouse gas. It absorbs and emits infrared radiation at its two infrared-active vibrational frequencies. The two wavelengths are 4.26 μm (2,347 cm) (asymmetric stretching vibrational mode) and 14.99 μm (667 cm) (bending vibrational mode). CO plays a significant role in influencing Earths surface temperature through the greenhouse effect. Light emission from the Earths surface is most intense in the infrared region between 200 and 2500 cm, as opposed to light emission from the much hotter Sun which is most intense in the visible region. Absorption of infrared light at the vibrational frequencies of atmospheric traps energy near the surface, warming the surface of Earth and its lower atmosphere. Less energy reaches the upper atmosphere, which is therefore cooler because of this absorption.
The increase in atmospheric concentrations of and other long-lived greenhouse gases such as methane increase the absorption and emission of infrared radiation by the atmosphere. This has led to a rise in average global temperature and ocean acidification. Another direct effect is the CO fertilization effect. The increase in atmospheric concentrations of causes a range of further effects of climate change on the environment and human living conditions.
The present atmospheric concentration of is the highest for 14 million years. Concentrations of in the atmosphere were as high as 4,000 ppm during the Cambrian period about 500 million years ago, and as low as 180 ppm during the Quaternary glaciation of the last two million years. Reconstructed temperature records for the last 420 million years indicate that atmospheric concentrations peaked at approximately 2,000 ppm. This peak happened during the Devonian period (400 million years ago). Another peak occurred in the Triassic period (220–200 million years ago). | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, a glycosyl group is a univalent free radical or substituent structure obtained by removing the hydroxyl () group from the hemiacetal () group found in the cyclic form of a monosaccharide and, by extension, of a lower oligosaccharide.
Glycosyl also reacts with inorganic acids, such as phosphoric acid, forming an ester such as glucose 1-phosphate. | 0 | Theoretical and Fundamental Chemistry |
Taurates were first obtained by the Schotten-Baumann method which is the reaction of long-chain carboxylic acid chlorides with aqueous solutions of the sodium salt of N-methyltaurine.
The formation of (at least) equimolar amounts of sodium chloride is problematic, as they worsen the properties of surfactant mixtures with such taurates. The high salt content also makes the resulting taurates hygroscopic and corrosive. Another disadvantage of the Schotten-Baumann method is the hazardousness of the raw materials (such as phosphorus trichloride) and the intermediates (the acyl chlorides) and the accumulation of large amounts of waste materials, such as phosphonic acids. This synthesis pathway for taurates is therefore complicated and expensive. An advantage of the Schotten-Baumann method, however, is the very low content of free fatty acids in the end product. Taurates are also accessible by direct amidation of N-methyltaurine or its sodium salt with the corresponding fatty acid for 10 hours at 220 °C under nitrogen.
The excess fatty acid (added for a favorable equilibrium) usually remain in the product, which can interfere with some applications. The decomposition of N-methyltaurine already begins At temperatures above 200 °C and the resulting taurates darken and develop an unpleasant smell. Therefore, more recent variants of the direct amidation aim at gentler process conditions using suitable catalysts, such as sodium borohydride, boric acid or zinc oxide. | 0 | Theoretical and Fundamental Chemistry |
In the dressed micelle model, the total Gibbs energy is broken down into several components accounting for the hydrophobic tail, the electrostatic repulsion of the head groups, and the interfacial energy on the surface of the micelle.
where the components of the total Gibbs micellization energy are hydrophobic, electrostatic, and interfacial. | 0 | Theoretical and Fundamental Chemistry |
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