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In mammals, CPSF is a protein complex, consisting of six subunits: CPSF-160 (CPSF1), CPSF-100 (CPSF2), CPSF-73 (CPSF3), and CPSF-30 (CPSF4) kDa subunits, WDR33 and Fip1 (FIP1L1).
The subunits form two components: mammalian polyadenylation specificity factors (mPSF) and mammalian cleavage factor (mCF). The mPSF is made up of CPSF-160, WDR33, CPSF-30, and Fip1. It is necessary for PAS recognition and polyadenylation. The mCF is made up of CPSF-73, CPSF-100, and symplekin. It catalyzes the cleavage reaction by recognizing the histone mRNA 3' processing site.
CPSF-73 is a zinc-dependent hydrolase which cleaves the mRNA precursor between a CA dinucleotide just downstream the polyadenylation signal sequence AAUAAA.
CPSF-100 contributes to the endonuclease activity of CPSF-73.
CPSF-160 (160 kDa) is the largest subunit of CPSF and directly binds to the AAUAAA polyadenylation signal. 160 kDa has three β-propeller domains and a C-terminal domain.
CPSF-30 (30 kDa) has five Cys-Cys-Cys-His (CCCH) zinc-finger motifs near the N terminus and a CCCH zinc knuckle at the C terminus. Two isoforms of CPSF-30 exist and can be found in CPSF complexes. The RNA binding activity of CPSF-30 is mediated by its zinc-fingers 2 and 3. WD repeat domain 33 (146 kDa) has a WD40 domain near the N terminus. The WD40 domain interacts with RNA. WDR33 and CPSF-30 recognize the polyadenylation signal (PAS) in pre-mRNA, which aids in defining the position of RNA cleavage. CPSF-30 recognizes the AU-rich hexamer region by a cooperative, metal-dependent binding mechanism.
Although CPSF-160 is the largest subunit of CPSF, a study conducted by Schönemann et al., debate that WDR33 is responsible for recognizing the PAS and not CPSF-160 as previously believed. The study concluded that the reason that CPSF-160 was believed to be responsible for recognizing the PAS was due to the fact that the WDR33 subunit had not been discovered at the time of the claim.
Fip1 binds to U-rich RNAs by its arginine-rich C-terminus. It binds to RNA sequences upstream of the AAUAAA hexamer region in vitro. Fip1 and CPSF-160 recruit poly(A) polymerase (PAP) to the 3' processing site. PAP is stimulated by Poly(A) binding protein nuclear one to add the poly(A) tail, a non-templated adenosine residues, at the cleavage site.
Only CPSF-160, CPSF-30, Fip1, and WDR33 are necessary and sufficient to form an active CPSF subcomplex in AAUAAA-dependent polyadenylation. CPSF-73 and CPSF-100 are disposable.
CPSF recruits proteins to the 3' region. Identified proteins that are coordinated by CPSF activity include: cleavage stimulatory factor and the two poorly understood cleavage factors. The binding of the polynucleotide adenylyltransferase responsible for actually synthesizing the tail is a necessary prerequisite for cleavage, thus ensuring that cleavage and polyadenylation are tightly coupled processes. | 1 | Biochemistry |
The E3 ubiquitin ligase enzyme is a main component that provides specificity in protein degradation pathways, including immune signaling pathways. The E3 enzyme components can be grouped by which domains they contain and include several types.
These include the Ring and U-box single subunit, HECT, and CRLs. Plant signaling pathways including immune responses are controlled by several feedback pathways, which often include negative feedback; and they can be regulated by De-ubiquitination enzymes, degradation of transcription factors and the degradation of negative regulators of transcription. | 1 | Biochemistry |
A presumed blood sample is first collected with a swab. A drop of phenolphthalein reagent is added to the sample, and after a few seconds, a drop of hydrogen peroxide is applied to the swab. If the swab turns pink rapidly, it is said to test presumptive positive for blood. Waiting for periods over 30 seconds will result in most swabs turning pink naturally as they oxidize on their own in the air.
Optionally, the swab can first be treated with a drop of ethanol in order to lyse the cells present and gain increased sensitivity and specificity. This test is nondestructive to the sample, which can be kept and used in further tests at the lab; however, few labs would use the swab used for the Kastle–Meyer test in any further testing, opting instead to use a fresh swab of the original stain. | 3 | Analytical Chemistry |
Melzers reagent is an aqueous solution of chloral hydrate, potassium iodide, and iodine. Depending on the formulation, it consists of approximately 2.50-3.75% potassium iodide and 0.75–1.25% iodine, with the remainder of the solution being 50% water and 50% chloral hydrate. Melzers is toxic to humans if ingested due to the presence of iodine and chloral hydrate. Due to the legal status of chloral hydrate, Melzer's reagent is difficult to obtain in the United States.
In response to difficulties obtaining chloral hydrate, scientists at Rutgers formulated Visikol (compatible with Lugol's iodine) as a replacement. In 2019, research showed that Visikol behaves differently to Melzer’s reagent in several key situations, noting it should not be recommended as a viable substitute.
Melzers reagent is part of a class of iodine/potassium iodide (IKI)-containing reagents used in biology; Lugols iodine is another such formula. | 3 | Analytical Chemistry |
Different configurations can be used to perform Raman-SEC experiments. Raman scattering provides spectra with very weak Raman bands, therefore, a very well aligned optical configuration is required. Laser has to be focused on the electrode surface and an efficient collection of the scattered photons is mandatory. Many of the instruments used for Raman-SEC are based on the combination of a spectrometer, a potentiostat and a confocal microscope, since it is possible to focus and collect the scattered photons in a highly efficient way. Low resolution Raman spectrometers can be also used, providing suitable results. Using this setup, the sampling area is larger and average information about the electrode surface is obtained.
Typical configurations in Raman-SEC:
* Normal configuration. The laser beam samples the electrode/solution interface in a normal way respect to the electrode surface. The scattered radiation is collected, and the monochromator allows passing only the light beam with wavelengths different from that of the laser used.
* Inverted microscope. In this configuration the electrode/solution is sampled from behind the electrode, using optically transparent electrodes (OTE).
* Angular configuration. This configuration is usually selected when electrochemical techniques are combined with TERS.
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Bhushan is a member of editorial board of
* Biomedical Chromatography, (John Wiley & Sons, UK, since Jan 1996);
* Bioanalysis (Future Science Group, UK, since 2011), and
* Acta Chromatographica (Akademiai Kiado, Hungary, since 2012). | 3 | Analytical Chemistry |
Jean-Claude Bradley was a chemist who actively promoted Open Science in chemistry, including at the White House, for which he was awarded the Blue Obelisk award in 2007. He coined the term "Open Notebook science". He died in May 2014. A memorial symposium was held July 14, 2014 at Cambridge University, UK.
One outcome of his Open Notebook work is the collection of physicochemical properties of organic compounds he was studying. All of this data he made available as Open data under the CCZero license. For example, in 2009 Bradley et al. published their work on making solubility data of organic compounds available as Open data. Later, the melting point data set he collaborated on with Andrew Lang and Antony Williams was published with Figshare. Both data sets were also made available as books via the Lulu.com self-publishing platform.
He blogged extensively and contributed to at least 25 individual blogs. In an interview in 2008 with Bora Zivkovic titled "Doing Science Publicly", he spoke of his work and online presence. In 2010, he gave an extensive interview about the impact of Open Notebook science with Richard Poynder. | 0 | Organic Chemistry |
Building on his earlier pioneering research on the surface passivation and thermal oxidation processes, Atalla developed the metal–oxide–semiconductor (MOS) process. Atalla then proposed that a field effect transistor–a concept first envisioned in the 1920s and confirmed experimentally in the 1940s, but not achieved as a practical device—be built of metal-oxide-silicon. Atalla assigned the task of assisting him to Dawon Kahng, a Korean scientist who had recently joined his group. That led to the invention of the MOSFET (metal–oxide–semiconductor field-effect transistor) by Atalla and Kahng, in November 1959. Atalla and Kahng first demonstrated the MOSFET in early 1960. With its high scalability, and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuit (IC) chips. | 7 | Physical Chemistry |
The total synthesis of solenopsin has been described by several methods. A proposed method of synthesis(Figure 1) starts with alkylation of 4-chloropyridine with a Grignard reagent derived from 1-bromoundecane, followed by reaction with phenyl chloroformate to form 4-chloro-1-(phenoxycarbonyl)-2-n-undecyl-1,2-dihydropyridine. The phenylcarbamate is converted to the BOC protecting group, and then pyridine is methylated at the 6 position. The pyridine ring is then reduced to a tetrahydropyridine via catalytic hydrogenation with Pd/C and then further reduced with sodium cyanoborohydride to a piperidine ring. The BOC group is finally removed to yield solenopsin. A number of analogs have been synthesized using modifications of this procedure.
A shorter method of synthesis stemming from commercially-available lutidine has been more recently proposed. | 0 | Organic Chemistry |
Hartshorn was appointed as a lecturer in the Department of Chemistry at the University of Canterbury in Christchurch in 1960, and rose to become a professor in 1972. When he retired in 1996 he was made a professor emeritus.
Hartshorn's research centred on reaction mechanisms. He investigated the chemical rearrangement of steroids, cyclic sulfites, monoterpenes and acetylenic alcohols. His research included the ipso nitration of aromatic hydrocarbons and phenols, and their reactions with fuming nitric acid and nitrogen dioxide, as well as the chlorination of polysubstituted phenols. He also studied the reactions of cation radicals arising from the photolysis of aromatic hydrocarbons.
Hartshorn was elected a fellow of the New Zealand Institute of Chemistry in 1969, and a fellow of the Royal Society of New Zealand the following year. In 1973, he received the Hector Memorial Medal, at that time the highest honour for scientific excellence awarded by the Royal Society of New Zealand. | 0 | Organic Chemistry |
Halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is a dense, highly volatile, clear, colourless, nonflammable liquid with a chloroform-like sweet odour. It is very slightly soluble in water and miscible with various organic solvents. Halothane can decompose to hydrogen fluoride, hydrogen chloride and hydrogen bromide in the presence of light and heat.
Chemically, halothane is an alkyl halide (not an ether like many other anesthetics). The structure has one stereocenter, so (R)- and (S)-optical isomers occur. | 4 | Stereochemistry |
Recent research has suggested a number of roles for the LNGFR, including in development of the eyes and sensory neurons, and in repair of muscle and nerve damage in adults. Two distinct subpopulations of Olfactory ensheathing glia have been identified with high or low cell surface expression of low-affinity nerve growth factor receptor (p75). | 1 | Biochemistry |
The sperm and the egg are incubated together at a ratio of about 75,000:1 in a culture media in order for the actual fertilisation to take place. A review in 2013 came to the result that a duration of this co-incubation of about 1 to 4 hours results in significantly higher pregnancy rates than 16 to 24 hours. In most cases, the egg will be fertilised during co-incubation and will show two pronuclei. In certain situations, such as low sperm count or motility, a single sperm may be injected directly into the egg using intracytoplasmic sperm injection (ICSI). The fertilised egg is passed to a special growth medium and left for about 48 hours until the embryo consists of six to eight cells.
In gamete intrafallopian transfer, eggs are removed from the woman and placed in one of the fallopian tubes, along with the mans sperm. This allows fertilisation to take place inside the womans body. Therefore, this variation is actually an in vivo fertilisation, not in vitro. | 1 | Biochemistry |
Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and lost-foam casting. It uses an expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact. | 8 | Metallurgy |
A further subclass of catalytic triad variants are pseudoenzymes, which have triad mutations that make them catalytically inactive, but able to function as binding or structural proteins. For example, the heparin-binding protein Azurocidin is a member of the PA clan, but with a glycine in place of the nucleophile and a serine in place of the histidine. Similarly, RHBDF1 is a homolog of the S54 family rhomboid proteases with an alanine in the place of the nucleophilic serine. In some cases, pseudoenzymes may still have an intact catalytic triad but mutations in the rest of the protein remove catalytic activity. The CA clan contains catalytically inactive members with mutated triads (calpamodulin has lysine in place of its cysteine nucleophile) and with intact triads but inactivating mutations elsewhere (rat testin retains a Cys-His-Asn triad). | 1 | Biochemistry |
A widely used coordinate system is the Cartesian coordinate system, which consists of orthonormal basis vectors. This means that,
and
However, when describing objects with crystalline or periodic structure a Cartesian coordinate system is often not the most useful as it does not often reflect the symmetry of the lattice in the simplest manner. | 3 | Analytical Chemistry |
Surfaces of solids can be cleaned from contaminants by using physical sputtering in a vacuum. Sputter cleaning is often used in surface science, vacuum deposition and ion plating. In 1955 Farnsworth, Schlier, George, and Burger reported using sputter cleaning in an ultra-high-vacuum system to prepare ultra-clean surfaces for low-energy electron-diffraction (LEED) studies. Sputter cleaning became an integral part of the ion plating process. When the surfaces to be cleaned are large, a similar technique, plasma cleaning, can be used. Sputter cleaning has some potential problems such as overheating, gas incorporation in the surface region, bombardment (radiation) damage in the surface region, and the roughening of the surface, particularly if over done. It is important to have a clean plasma in order to not continually recontaminate the surface during sputter cleaning. Redeposition of sputtered material on the substrate can also give problems, especially at high sputtering pressures. Sputtering of the surface of a compound or alloy material can result in the surface composition being changed. Often the species with the least mass or the highest vapor pressure is the one preferentially sputtered from the surface. | 7 | Physical Chemistry |
At length-scales larger than the persistence length, the entropic flexibility of DNA is remarkably consistent with standard polymer physics models, such as the Kratky-Porod worm-like chain model. Consistent with the worm-like chain model is the observation that bending DNA is also described by Hooke's law at very small (sub-piconewton) forces. For DNA segments less than the persistence length, the bending force is approximately constant and behaviour deviates from the worm-like chain predictions.
This effect results in unusual ease in circularising small DNA molecules and a higher probability of finding highly bent sections of DNA. | 4 | Stereochemistry |
In the 2008 pilot of the crime drama television series Breaking Bad, Walter White poisons two rival gangsters by adding red phosphorus to boiling water to produce phosphine gas. However, this reaction in reality would require white phosphorus instead, and for the water to contain sodium hydroxide. An episode of Homicide: Life on the Street depicted a murder suspect who adulterated beverages, including Sacramental wine, with a poison called "Phosphozine." | 0 | Organic Chemistry |
Until 1951, it was not possible to obtain the absolute configuration of chiral compounds. It was at some time decided that (+)-glyceraldehyde was the -enantiomer. The configuration of other chiral compounds was then related to that of (+)-glyceraldehyde by sequences of chemical reactions. For example, oxidation of (+)-glyceraldehyde (1) with mercury oxide gives (−)-glyceric acid (2), a reaction that does not alter the stereocenter. Thus the absolute configuration of (−)-glyceric acid must be the same as that of (+)-glyceraldehyde. Nitric acid oxidation of (+)-isoserine (3) gives (–)-glyceric acid, establishing that (+)-isoserine also has the same absolute configuration. (+)-Isoserine can be converted by a two-stage process of bromination and zinc reduction to give (–)-lactic acid, therefore (–)-lactic acid also has the same absolute configuration. If a reaction gave the enantiomer of a known configuration, as indicated by the opposite sign of optical rotation, it would indicate that the absolute configuration is inverted.
In 1951, Johannes Martin Bijvoet for the first time used in X-ray crystallography the effect of anomalous dispersion, which is now referred to as resonant scattering, to determine absolute configuration. The compound investigated was (+)-sodium rubidium tartrate and from its configuration (R,R) it was deduced that the original guess for (+)-glyceraldehyde was correct.
Despite the tremendous and unique impact on access to molecular structures, X-ray crystallography poses some challenges. The process of crystallization of the target molecules is time- and resource-intensive, and can not be applied to relevant systems of interest such as many biomolecules (some proteins are an exception) and in situ catalysts. Another important limitation is that the molecule must contain "heavy" atoms (for example, bromine) to enhance the scattering. Furthermore, crucial distorsions of the signal arise from the influence of the nearest neighbors in any crystal structure and of solvents used during the crystallization process.
Just recently, novel techniques have been introduced to directly investigate the absolute configuration of single molecules in gas-phase, usually in combination with ab initio quantum mechanical theoretical calculations, therefore overcoming some of the limitations of the X-ray crystallography. | 4 | Stereochemistry |
In crystallography, polymorphism describes the phenomenon where a compound or element can crystallize into more than one crystal structure. The preceding definition has evolved over many years and is still under discussion today. Discussion of the defining characteristics of polymorphism involves distinguishing among types of transitions and structural changes occurring in polymorphism versus those in other phenomena.
It is also useful to note that materials with two polymorphic phases can be called dimorphic, those with three polymorphic phases, trimorphic, etc. | 3 | Analytical Chemistry |
Snf3 is a protein which regulates glucose uptake in yeast. It senses glucose in the environment with high affinity. | 1 | Biochemistry |
Shark skin is another example of antifouling, self-cleaning and low adhesion surfaces. This hydrophobic surface allows sharks to maneuvers fast in water. Shark skin is composed of periodically arranged diamond-shape dermal denticles, superimposed with triangular riblets. | 7 | Physical Chemistry |
Acid chlorides can be used as a chloride source. Thus acetyl chloride can be distilled from a mixture of benzoyl chloride and acetic acid:
Other methods that do not form HCl include the Appel reaction:
Another is the use of cyanuric chloride: | 0 | Organic Chemistry |
On June 28, 2007, a team at the J. Craig Venter Institute published an article in Science Express, saying that they had successfully transplanted the natural DNA from a Mycoplasma mycoides bacterium into a Mycoplasma capricolum cell, creating a bacterium which behaved like a M. mycoides.
On Oct 6, 2007, Craig Venter announced in an interview with UKs The Guardian newspaper that the same team had synthesized a modified version of the single chromosome of Mycoplasma genitalium artificially. The chromosome was modified to eliminate all genes which tests in live bacteria had shown to be unnecessary. The next planned step in this minimal genome project is to transplant the synthesized minimal genome into a bacterial cell with its old DNA removed; the resulting bacterium will be called Mycoplasma laboratorium. The next day the Canadian bioethics group, ETC Group issued a statement through their representative, Pat Mooney, saying Venters "creation" was "a chassis on which you could build almost anything". The synthesized genome had not yet been transplanted into a working cell.
On May 21, 2010, Science reported that the Venter group had successfully synthesized the genome of the bacterium Mycoplasma mycoides from a computer record, and transplanted the synthesized genome into the existing cell of a Mycoplasma capricolum bacterium that had its DNA removed. The "synthetic" bacterium was viable, i.e. capable of replicating billions of times. The team had originally planned to use the M. genitalium bacterium they had previously been working with, but switched to M. mycoides because the latter bacterium grows much faster, which translated into quicker experiments. Venter describes it as "the first species.... to have its parents be a computer". The transformed bacterium is dubbed "Synthia" by ETC. A Venter spokesperson has declined to confirm any breakthrough at the time of this writing. | 1 | Biochemistry |
Zinc oxide is used as a weak antiseptic and in paints as a white pigment and mold-growth inhibitor. Zinc chloride is a common ingredient in mouthwashes and deodorants, and zinc pyrithione is an ingredient in antidandruff shampoos. Galvanized (zinc-coated) fittings on roofs impede the growth of algae. Copper- and zinc-treated shingles are available. Zinc iodide and zinc sulfate are used as topical antiseptics. | 1 | Biochemistry |
Jacob Nissim Israelachvili, (19 August 1944 – 20 September 2018) was an Israeli physicist who was a professor at the University of California, Santa Barbara (UCSB). | 6 | Supramolecular Chemistry |
The total synthesis of ouabain was achieved in 2008 by Deslongchamps laboratory in Canada. It was synthesized under the hypothesis that a polyanionic cyclization (double Michael addition followed by aldol condensation) would allow access to a tetracyclic intermediate with the desired functionality. The figure below shows the key steps in the synthesis of ouabain.
In their synthesis, Zhang et al. from the Deslongchamps laboratory condensed cyclohexenone A with Nazarov substitute B in a double Michael addition to produce tricycle C. At the indicated position, C was reduced to the aldehyde and the alcohol group was protected with p-methoxybenzyl ether (PMB) to form the aldol precursor needed to produce D. After several steps, intermediate E was produced. E contained all the required functionalities and stereochemistry needed to produce ouabain. The structure of E was confirmed by comparison against the degradation product of ouabain. Methylation of E, catalyzed by rhodium, produced F. The dehydroxylation and selective oxidation of the secondary hydroxy group of F produced G. G reacted with triphenyl phosphoranylidene ketene and the ester bonds in G were hydrolyzed to produce ouabagenin, a precursor to ouabain. The glycosylation of ouabagenin with rhamnose produced ouabain. | 0 | Organic Chemistry |
para-Dimethylaminobenzaldehyde is the main ingredient in Ehrlich's reagent. It acts as a strong electrophile which reacts with the electron-rich α-carbon (2-position) of indole rings to form a blue-colored adduct. It can be used to detect the presence of indole alkaloids. Not all indole alkaloids give a colored adduct as result of steric hindrance which does not allow the reaction to proceed.
Ehrlich's reagent is also used as a stain in thin layer chromatography and as a reagent to detect urobilinogen in fresh, cool urine. If a urine sample is left to oxidize in air to form urobilin the reagent will not detect the urobilinogen. By adding few drops of reagent to 3 mL of urine in a test tube one can see a change of color, to dark pink or red. The degree of color change is proportional to the amount of urobilinogen in the urine sample. | 3 | Analytical Chemistry |
A shuttle vector is a vector (usually a plasmid) constructed so that it can propagate in two different host species. Therefore, DNA inserted into a shuttle vector can be tested or manipulated in two different cell types. The main advantage of these vectors is they can be manipulated in E. coli, then used in a system which is more difficult or slower to use (e.g. yeast).
Shuttle vectors include plasmids that can propagate in eukaryotes and prokaryotes (e.g. both Saccharomyces cerevisiae and Escherichia coli) or in different species of bacteria (e.g. both E. coli and Rhodococcus erythropolis). There are also adenovirus shuttle vectors, which can propagate in E. coli and mammals.
Shuttle vectors are frequently used to quickly make multiple copies of the gene in E. coli (amplification). They can also be used for in vitro experiments and modifications (e.g. mutagenesis, PCR).
One of the most common types of shuttle vectors is the yeast shuttle vector. Almost all commonly used S. cerevisiae vectors are shuttle vectors. Yeast shuttle vectors have components that allow for replication and selection in both E. coli cells and yeast cells. The E. coli component of a yeast shuttle vector includes an origin of replication and a selectable marker, e.g. antibiotic resistance, beta lactamase, beta galactosidase. The yeast component of a yeast shuttle vector includes an autonomously replicating sequence (ARS), a yeast centromere (CEN), and a yeast selectable marker (e.g. URA3, a gene that encodes an enzyme for uracil synthesis, Lodish et al. 2007). | 1 | Biochemistry |
Nuclear DNA is injured during cold storage of kidneys. Lazarus showed that single stranded DNA breaks occurred within 16 hours in hypothermically stored mice kidneys, with the injury being inhibited a little by storage in Collins or Sacks solutions. This nuclear injury differed from that seen in warm injury when double stranded DNA breaks occurred. | 1 | Biochemistry |
High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures. The mixtures can originate from food, chemicals, pharmaceuticals, biological, environmental and agriculture, etc, which have been dissolved into liquid solutions.
It relies on high pressure pumps, which deliver mixtures of various solvents, called the mobile phase, which flows through the system, collecting the sample mixture on the way, delivering it into a cylinder, called the column, filled with solid particles, made of adsorbent material, called the stationary phase.
Each component in the sample interacts differently with the adsorbent material, causing different migration rates for each component. These different rates lead to separation as the species flow out of the column into a specific detector such as UV detectors. The output of the detector is a graph, called a chromatogram. Chromatograms are graphical representations of the signal intensity versus time or volume, showing peaks, which represent components of the sample. Each sample appears in its respective time, called its retention time, having area proportional to its amount.
HPLC is widely used for manufacturing (e.g., during the production process of pharmaceutical and biological products), legal (e.g., detecting performance enhancement drugs in urine), research (e.g., separating the components of a complex biological sample, or of similar synthetic chemicals from each other), and medical (e.g., detecting vitamin D levels in blood serum) purposes.
Chromatography can be described as a mass transfer process involving adsorption and/or partition. As mentioned, HPLC relies on pumps to pass a pressurized liquid and a sample mixture through a column filled with adsorbent, leading to the separation of the sample components. The active component of the column, the adsorbent, is typically a granular material made of solid particles (e.g., silica, polymers, etc.), 1.5–50 μm in size, on which various reagents can be bonded. The components of the sample mixture are separated from each other due to their different degrees of interaction with the adsorbent particles. The pressurized liquid is typically a mixture of solvents (e.g., water, buffers, acetonitrile and/or methanol) and is referred to as a "mobile phase". Its composition and temperature play a major role in the separation process by influencing the interactions taking place between sample components and adsorbent. These interactions are physical in nature, such as hydrophobic (dispersive), dipole–dipole and ionic, most often a combination. | 3 | Analytical Chemistry |
In the search for a clean, renewable energy source to replace fossil fuels, hydrogen has gained much attention as a possible fuel for the future. One of the challenges that must be overcome if this is to become a reality is an efficient way to produce and consume hydrogen. Currently, we have the technology to generate hydrogen from coal, natural gas, biomass and water. The majority of hydrogen currently produced comes from natural gas reformation, and hence does not help remove fossil fuel as an energy source. A variety of sustainable methods for hydrogen production are currently being researched, including solar, geothermal and catalytic hydrogen production.
Platinum is currently used to catalyze hydrogen production, but as Pt is expensive, found in limited supply, and easily poisoned by carbon monoxide during H production, it is not a practical for large-scale use. Catalysts inspired by the Fe–Ni active site of many hydrogen producing enzymes are particularly desirable due to the readily available and inexpensive metals.
The synthesis of Fe–Ni biomimetic catalytic complexes has proved difficult, primarily due to the extreme oxygen-sensitivity of such complexes. To date, only one example of a Fe–Ni model complex that is stable enough to withstand the range of electronic potential required for catalysis has been published.
When designing model complexes, it is crucial to preserve the key features of the active site of the Fe–Ni hydrogenases: the iron organometallic moiety with CO or CN ligands, nickel coordinated to terminal sulfur ligands, and the thiolate bridge between the metals. By preserving these traits of the enzyme active site, it is hoped that the synthetic complexes will operate at the electrochemical potential necessary for catalysis, have a high turnover frequency and be robust. | 7 | Physical Chemistry |
Flotation is used for the purification of potassium chloride from sodium chloride and clay minerals. The crushed mineral is suspended in brine in the presence of fatty ammonium salts. Because the ammonium head group and K have very similar ionic radii (ca. 0.135, 0.143 nm respectively), the ammonium centers exchange for the surface potassium sites on the particles of KCl, but not on the NaCl particles. The long alkyl chains then confer Hydrophobicity to the particles, which enable them to form foams. | 8 | Metallurgy |
Reactions used in DCvC must generate thermodynamically stable products to overcome the entropic cost of self-assembly. The reactions must form covalent linkages between building blocks. Finally, all possible intermediates must be reversible, and the reaction ideally proceeds under conditions that are tolerant of functional groups elsewhere in the molecule.
Reactions that can be used in DCvC are diverse and can be placed into two general categories. Exchange reactions involve the substitution of one reaction partner in an intermolecular reaction for another with an identical type of bonding. Some examples of this are shown in schemes 5 and 8, in an ester exchange, and disulfide exchange reactions. The second type, formation reactions, rely on the formation of new covalent bonds. Some examples include Diels–Alder and aldol reactions. In some cases, a reaction can pertain to both categories. For example, Schiff base formation can be categorized as a forming new covalent bonds between a carbonyl and primary amine. However, in the presence of two different amines the reaction becomes an exchange reaction where the two imine derivatives compete in equilibrium.
Exchange and formation reactions can be further broken down into three categories:
# Bonding between carbon–carbon
# Bonding between carbon–heteroatom
# Bonding between heteroatom–heteroatom | 6 | Supramolecular Chemistry |
A coating is a covering that is applied to the surface of an object, or substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. powder coatings.
Paints and lacquers are coatings that mostly have dual uses, which are protecting the substrate and being decorative, although some artists paints are only for decoration, and the paint on large industrial pipes is for identification (e.g. blue for process water, red for fire-fighting control) in addition to preventing corrosion. Along with corrosion resistance, functional coatings may also be applied to change the surface properties of the substrate, such as adhesion, wettability, or wear resistance. In other cases the coating adds a completely new property, such as a magnetic response or electrical conductivity (as in semiconductor device fabrication, where the substrate is a wafer), and forms an essential part of the finished product.
A major consideration for most coating processes is controlling coating thickness. Methods of achieving this range from a simple brush to expensive precision machinery in the electronics industry. Limiting coating area is crucial in some applications, such as printing.
"roll-to-roll" or "web-based" coating is the process of applying a thin film of functional material to a substrate on a roll, such as paper, fabric, film, foil, or sheet stock. | 8 | Metallurgy |
A selector gene can be used to distinguish successfully genetically modified cells from unmodified ones. The selector gene is integrated into the plasmid along with the desired target gene, providing the cells with resistance to an antibiotic, such as kanamycin, ampicillin, spectinomycin or tetracycline. The desired cells, along with any other organisms growing within the culture, can be treated with an antibiotic, allowing only the modified cells to survive. The antibiotic gene is not usually transferred to the plant cell but instead remains within the bacterial cell. | 1 | Biochemistry |
Isomers having distinct biological properties are common; for example, the placement of methyl groups. In substituted xanthines, theobromine, found in chocolate, is a vasodilator with some effects in common with caffeine; but, if one of the two methyl groups is moved to a different position on the two-ring core, the isomer is theophylline, which has a variety of effects, including bronchodilation and anti-inflammatory action. Another example of this occurs in the phenethylamine-based stimulant drugs. Phentermine is a non-chiral compound with a weaker effect than that of amphetamine. It is used as an appetite-reducing medication and has mild or no stimulant properties. However, an alternate atomic arrangement gives dextromethamphetamine, which is a stronger stimulant than amphetamine.
In medicinal chemistry and biochemistry, enantiomers are a special concern because they may possess distinct biological activity. Many preparative procedures afford a mixture of equal amounts of both enantiomeric forms. In some cases, the enantiomers are separated by chromatography using chiral stationary phases. They may also be separated through the formation of diastereomeric salts. In other cases, enantioselective synthesis have been developed.
As an inorganic example, cisplatin (see structure above) is an important drug used in cancer chemotherapy, whereas the trans isomer (transplatin) has no useful pharmacological activity. | 4 | Stereochemistry |
The pack mill process begins with a tin bar, which is a drawn flat bar that was usually purchased from an ironworks or steel works. The tin bar could be wrought iron or mild steel. The cross-section of the bar needed to be accurate in size as this dictates the length and thickness of the final plates. The bar was cut to the correct length to make the desired size plate. For instance, if a plate is desired the tin bar is cut to a length and width that is divisible by 14 and 20. The bar is then rolled and doubled over, with the number of times being doubled over dependent on how large the tin bar is and what the final thickness is. If the starting tin bar is then it must be at least finished on the fours, or doubled over twice, and if a thin gauge is required then it may be finished on the eights, or doubled over three times. The tin bar is then heated to a dull red heat and passed five or six times through the roughing rolls. Between each pass the plate is passed over (or round) the rolls, and the gap between the rolls is narrowed by means of a screw. The plate is then reheated and run through the finishing rolls.
If the plate is not finished on singles, or without doubling the plate over, it is doubled over in a squeezer. The squeezer was like a table where one half of the surface folds over on top of the other and a press flattens the doubled over plate so the rolled end will fit in the rollers. It is then reheated for another set of rolling. This is repeated until the desired geometry is reached. Note that if the plate needs to be doubled over more than once the rolled end is sheared off. The pack is then allowed to cool. When cool, the pack is sheared slightly undersized from the final dimensions and the plates separated by openers.
At this point, the plates are covered in scale and must be pickled. This involves dipping the plates in sulfuric acid for five minutes. The pickling turns the scales into a greenish-black slime which is removed via annealing. The plates are annealed for approximately 10 hours and then allowed to slowly cool. At this point the plates are known as pickled and annealed black plates. These plates were commonly sold for stamping and enameling purposes.
After this, the plates are rough and not straight, so they are cold rolled several times. The rolling lengthens the plates to their final dimension. They are then annealed again to remove any strain hardening. These plates are called black plate pickled, cold rolled, and close annealed (black plate p. cr. and ca.). To attain perfect cleanliness the plates are pickled again in a weak sulfuric acid. Finally they are rinsed and stored in water until ready to be tinned.
The tinning set consists of at least one pot of molten tin, with a zinc chloride flux on top, and a grease pot. The flux dries the plate and prepares it for the tin to adhere. If a second tin pot is used, called the wash pot, it contains tin at a lower temperature. This is followed by the grease pot, which contains oil and a tinning machine. The tinning machine has two small rollers that are spring-loaded together so that when the tinned plate is inserted the rolls squeeze off any excess tin. The springs on the tinning machine can be set to different forces to give different thicknesses of tin. Finally, the oil is cleaned off with fine bran and dusted clean.
What is described here is the process as employed during the 20th century. The process grew somewhat in complexity over time, as it was found that the inclusion of additional procedures improved quality. The practice of hot rolling and then cold rolling evidently goes back to the early days, as the Knight family's tinplate works had (from its foundation in about 1740) two rolling mills, one at Bringewood (west of Ludlow) which made blackplate, and the other the tin mill at Mitton (now part of Stourport, evidently for the later stages. | 8 | Metallurgy |
A recent technique called non-thermal irreversible electroporation (N-TIRE) has proven successful in treating many different types of tumors and other unwanted tissue. This procedure is done using small electrodes (about 1mm in diameter), placed either inside or surrounding the target tissue to apply short, repetitive bursts of electricity at a predetermined voltage and frequency. These bursts of electricity increase the resting transmembrane potential (TMP), so that nanopores form in the plasma membrane. When the electricity applied to the tissue is above the electric field threshold of the target tissue, the cells become permanently permeable from the formation of nanopores. As a result, the cells are unable to repair the damage and die due to a loss of homeostasis. N-TIRE is unique to other tumor ablation techniques in that it does not create thermal damage to the tissue around it. | 1 | Biochemistry |
In the early history of thermodynamics, a positive amount of work done by the system on the surroundings leads to energy being lost from the system. This historical sign convention has been used in many physics textbooks and is used in the present article.
According to the first law of thermodynamics for a closed system, any net change in the internal energy U must be fully accounted for, in terms of heat Q entering the system and work W done by the system:
An alternate sign convention is to consider the work performed on the system by its surroundings as positive. This leads to a change in sign of the work, so that . This convention has historically been used in chemistry, and has been adopted by most physics textbooks.
This equation reflects the fact that the heat transferred and the work done are not properties of the state of the system. Given only the initial state and the final state of the system, one can only say what the total change in internal energy was, not how much of the energy went out as heat, and how much as work. This can be summarized by saying that heat and work are not state functions of the system. This is in contrast to classical mechanics, where net work exerted by a particle is a state function. | 7 | Physical Chemistry |
As mentioned before, scientists Monika Suchanek, Anna Radzikowski, and Christoph Thiele wanted to study protein-protein interaction in their natural environment. Specifically, the membrane proteins (in a complex and are SCAP, Insig-1, and SREBP) that regulate cholesterol homeostasis so they wanted to know what their function was and the complex structure. What they had found was that using this photo-reactive amino acid was incorporated efficiently into the protein by mammalian cells, but did not need to use modified tRNAs (transfer RNAs) or AARSs (aminoacyl tRNA syntheses) which that allowed the specific cross-linking needed. This cross-linking could be determined by western blotting and they had discovered a direct interaction between Insig-1 and PGRMC1 (a progesterone-binding membrane protein). All four of the membrane proteins are found in the endoplasmic reticulum and the complex responds to low cholesterol levels. Cells (COS7) that had HA (hemagglutinin tagged PGRMC1) and Myc tagged Insig-1 were grown with and without photo-Met. In the presence of photo-Met, Insig-1 and SCAP had cross-linked with PGRMC1; specifically, Insig-1 cross-linked had a strong band. The cross-linking was detected by immunoprecipitating detergent-extracts with an antibody to HA then the precipitant was tested for Insig-1 using western blotting with the antibody for Myc. An identical band was found doing the reverse order of the detection; meaning Myc antibody was immunoprecipitated then followed by blotting with the HA antibody. So, the method had proven to work that photo-Met could cross-link proteins, but the physiological implications of this cross-linking has yet to be determined. | 5 | Photochemistry |
Professor Paul Karrer FRS FRSE FCS (21 April 1889 – 18 June 1971) was a Swiss organic chemist best known for his research on vitamins. He and Norman Haworth won the Nobel Prize for Chemistry in 1937. | 0 | Organic Chemistry |
* Orthodontic items, such as wires and foams for endovascular procedures.
* Microelements for intelligent suturing.
* Intravenous needles that soften in the body and laparoscopy devices
* Drug delivery systems.
* In-body degradable implants for minimally invasive surgeries.
* Inner soles of orthopedic or special needs shoes and utensils for people with disabilities.
* Intravenous catheters. | 7 | Physical Chemistry |
In chemistry, the Fischer projection, devised by Emil Fischer in 1891, is a two-dimensional representation of a three-dimensional organic molecule by projection. Fischer projections were originally proposed for the depiction of carbohydrates and used by chemists, particularly in organic chemistry and biochemistry. The use of Fischer projections in non-carbohydrates is discouraged, as such drawings are ambiguous and easily confused with other types of drawing. The main purpose of Fischer projections is to show the chirality of a molecule and to distinguish between a pair of enantiomers. Some notable uses include drawing sugars and depicting isomers. | 4 | Stereochemistry |
Although bitumen typically makes up only 4 to 5 percent (by weight) of the pavement mixture, as the pavement's binder, it is also the most expensive part of the cost of the road-paving material.
During bitumen's early use in modern paving, oil refiners gave it away. However, bitumen is a highly traded commodity today. Its prices increased substantially in the early 21st Century. A U.S. government report states:
:"In 2002, asphalt sold for approximately $160 per ton. By the end of 2006, the cost had doubled to approximately $320 per ton, and then it almost doubled again in 2012 to approximately $610 per ton."
The report indicates that an "average" 1-mile (1.6-kilometer)-long, four-lane highway would include "300 tons of asphalt," which, "in 2002 would have cost around $48,000. By 2006 this would have increased to $96,000 and by 2012 to $183,000... an increase of about $135,000 for every mile of highway in just 10 years." | 7 | Physical Chemistry |
William Martin and Michael Russell suggest that the first cellular life forms may have evolved inside alkaline hydrothermal vents at seafloor spreading zones in the deep sea. These structures consist of microscale caverns that are coated by thin membraneous metal sulfide walls. Therefore, these structures would resolve several critical points germane to Wächtershäuser's suggestions at once:
# the micro-caverns provide a means of concentrating newly synthesised molecules, thereby increasing the chance of forming oligomers;
# the steep temperature gradients inside the hydrothermal vent allow for establishing "optimum zones" of partial reactions in different regions of the vent (e.g. monomer synthesis in the hotter, oligomerisation in the cooler parts);
# the flow of hydrothermal water through the structure provides a constant source of building blocks and energy (chemical disequilibrium between hydrothermal hydrogen and marine carbon dioxide);
# the model allows for a succession of different steps of cellular evolution (prebiotic chemistry, monomer and oligomer synthesis, peptide and protein synthesis, RNA world, ribonucleoprotein assembly and DNA world) in a single structure, facilitating exchange between all developmental stages;
# synthesis of lipids as a means of "closing" the cells against the environment is not necessary, until basically all cellular functions are developed.
This model locates the "last universal common ancestor" (LUCA) within the inorganically formed physical confines of an alkaline hydrothermal vent, rather than assuming the existence of a free-living form of LUCA. The last evolutionary step en route to bona fide free-living cells would be the synthesis of a lipid membrane that finally allows the organisms to leave the microcavern system of the vent. This postulated late acquisition of the biosynthesis of lipids as directed by genetically encoded peptides is consistent with the presence of completely different types of membrane lipids in archaea and bacteria (plus eukaryotes). The kind of vent at the foreground of their suggestion is chemically more similar to the warm (ca. 100 °C) off ridge vents such as Lost City than to the more familiar black smoker type vents (ca. 350 °C).
In an abiotic world, a thermocline of temperatures and a chemocline in concentration is associated with the pre-biotic synthesis of organic molecules, hotter in proximity to the chemically rich vent, cooler but also less chemically rich at greater distances. The migration of synthesized compounds from areas of high concentration to areas of low concentration gives a directionality that provides both source and sink in a self-organizing fashion, enabling a proto-metabolic process by which acetic acid production and its eventual oxidization can be spatially organized.
In this way many of the individual reactions that are today found in central metabolism could initially have occurred independent of any developing cell membrane. Each vent microcompartment is functionally equivalent to a single cell. Chemical communities having greater structural integrity and resilience to wildly fluctuating conditions are then selected for; their success would lead to local zones of depletion for important precursor chemicals. Progressive incorporation of these precursor components within a cell membrane would gradually increase metabolic complexity within the cell membrane, whilst leading to greater environmental simplicity in the external environment. In principle, this could lead to the development of complex catalytic sets capable of self-maintenance.
Russell adds a significant factor to these ideas, by pointing out that semi-permeable mackinawite (an iron sulfide mineral) and silicate membranes could naturally develop under these conditions and electrochemically link reactions separated in space, if not in time. | 1 | Biochemistry |
Concentrations of VOCs in indoor air may be 2 to 5 times greater than in outdoor air, sometimes far greater. During certain activities, indoor levels of VOCs may reach 1,000 times that of the outside air. Studies have shown that emissions of individual VOC species are not that high in an indoor environment, but the total concentration of all VOCs (TVOC) indoors can be up to five times higher than that of outdoor levels.
New buildings experience particularly high levels of VOC off-gassing indoors because of the abundant new materials (building materials, fittings, surface coverings and treatments such as glues, paints and sealants) exposed to the indoor air, emitting multiple VOC gases. This off-gassing has a multi-exponential decay trend that is discernible over at least two years, with the most volatile compounds decaying with a time-constant of a few days, and the least volatile compounds decaying with a time-constant of a few years.
New buildings may require intensive ventilation for the first few months, or a bake-out treatment. Existing buildings may be replenished with new VOC sources, such as new furniture, consumer products, and redecoration of indoor surfaces, all of which lead to a continuous background emission of TVOCs, and requiring improved ventilation.
Numerous studies show strong seasonal variations in indoors VOC emissions, with emission rates increasing in summer. This is largely due to the rate of diffusion of VOC species through materials to the surface, increasing with temperature. Most studies have shown that this leads to generally higher concentrations of TVOCs indoors in summer. | 0 | Organic Chemistry |
The key to the two-hybrid screen is that in most eukaryotic transcription factors, the activating and binding domains are modular and can function in proximity to each other without direct binding. This means that even though the transcription factor is split into two fragments, it can still activate transcription when the two fragments are indirectly connected.
The most common screening approach is the yeast two-hybrid assay. In this approach the researcher knows where each prey is located on the used medium (agar plates). Millions of potential interactions in several organisms have been screened in the latest decade using high-throughput screening systems (often using robots) and over thousands of interactions have been detected and categorized in databases as [https://thebiogrid.org BioGRID]. This system often utilizes a genetically engineered strain of yeast in which the biosynthesis of certain nutrients (usually amino acids or nucleic acids) is lacking. When grown on media that lacks these nutrients, the yeast fail to survive. This mutant yeast strain can be made to incorporate foreign DNA in the form of plasmids. In yeast two-hybrid screening, separate bait and prey plasmids are simultaneously introduced into the mutant yeast strain or a mating strategy is used to get both plasmids in one host cell.
The second high-throughput approach is the library screening approach. In this set up the bait and prey harboring cells are mated in a random order. After mating and selecting surviving cells on selective medium the scientist will sequence the isolated plasmids to see which prey (DNA sequence) is interacting with the used bait. This approach has a lower rate of reproducibility and tends to yield higher amounts of false positives compared to the matrix approach.
Plasmids are engineered to produce a protein product in which the DNA-binding domain (BD) fragment is fused onto a protein while another plasmid is engineered to produce a protein product in which the activation domain (AD) fragment is fused onto another protein. The protein fused to the BD may be referred to as the bait protein, and is typically a known protein the investigator is using to identify new binding partners. The protein fused to the AD may be referred to as the prey protein and can be either a single known protein or a library of known or unknown proteins. In this context, a library may consist of a collection of protein-encoding sequences that represent all the proteins expressed in a particular organism or tissue, or may be generated by synthesising random DNA sequences. Regardless of the source, they are subsequently incorporated into the protein-encoding sequence of a plasmid, which is then transfected into the cells chosen for the screening method. This technique, when using a library, assumes that each cell is transfected with no more than a single plasmid and that, therefore, each cell ultimately expresses no more than a single member from the protein library.
If the bait and prey proteins interact (i.e., bind), then the AD and BD of the transcription factor are indirectly connected, bringing the AD in proximity to the transcription start site and transcription of reporter gene(s) can occur. If the two proteins do not interact, there is no transcription of the reporter gene. In this way, a successful interaction between the fused protein is linked to a change in the cell phenotype.
The challenge of separating cells that express proteins that happen to interact with their counterpart fusion proteins from those that do not, is addressed in the following section. | 1 | Biochemistry |
The auxiliary can be removed from the desired amine by treatment with hydrochloric acid in protic solvents.
<br /> | 4 | Stereochemistry |
Acyl chlorides are reduced by lithium aluminium hydride and diisobutylaluminium hydride to give primary alcohols. Lithium tri-tert-butoxyaluminium hydride, a bulky hydride donor, reduces acyl chlorides to aldehydes, as does the Rosenmund reduction using hydrogen gas over a poisoned palladium catalyst. | 0 | Organic Chemistry |
may be used in combination with vibrational spectroscopy techniques to understand the origins of vibrations within crystals. The combination of techniques provides detailed information about crystal structures, similar to what can be achieved with x-ray crystallography. In addition to using computational methods for enhancing the understanding of spectroscopic data, the latest development in identifying polymorphism in crystals is the field of . This technique uses computational chemistry to model the formation of crystals and predict the existence of specific polymorphs of a compound before they have been observed experimentally by scientists. | 3 | Analytical Chemistry |
PMCA has been applied to replicate the misfolded protein from diverse species. The newly generated protein exhibits the same biochemical, biological, and structural properties as brain-derived PrP and strikingly it is infectious to wild type animals, producing a disease with similar characteristics as the illness produced by brain-isolated prions. | 1 | Biochemistry |
From an operational point of view the Hill coefficient can be calculated as:
where and are the input values needed to produce the 10% and 90% of the maximal response, respectively. | 1 | Biochemistry |
* Railway - gearboxes, wheels, transmissions
* Machine tools - lathe gearboxes, mills
* Steel works - roll bearings, roll neck rings
* Power generation - various generator components
Due to the need to insert a core and also that to be effective, the core has to be in relatively close proximity to the bore of the part to be heated, there are many application in which the above bearing heater type approach is not feasible. | 8 | Metallurgy |
The Arens–van Dorp synthesis is a name reaction in organic chemistry. It describes the addition of lithiated ethoxyacetylenes to ketones to give propargyl alcohols, which can undergo further reaction to form α,β-unsaturated aldehydes, or esters. There is also a variation of this reaction called the Isler modification, where the acetylide anion is generated in situ from β-chlorovinyl ether using lithium amide. | 0 | Organic Chemistry |
The European FOCE ([http://efoce.eu eFOCE]) comprises two open-top chambers (control and experimental) as well as a surface buoy housing the electronics and pumps to produce CO-enriched water. The system is powered by solar and wind energy. Data packets are wirelessly sent to the nearby laboratory and can be monitored on the internet. The eFOCE system is currently deployed in the bay of Villefranche-sur-mer (France) at about 12 m depth and 300 m offshore. The eFOCE project has been developed to investigate the long-term effects of acidification on benthic marine communities of the North West Mediterranean Sea, especially Posidonia seagrass beds. Over a 3-year period, the aim of the project is to develop relatively long (> 6 month) experiments. | 9 | Geochemistry |
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group (these may respectively be called alkylamines and arylamines; amines in which both types of substituent are attached to one nitrogen atom may be called alkylarylamines). Important amines include amino acids, biogenic amines, trimethylamine, and aniline. Inorganic derivatives of ammonia are also called amines, such as monochloramine ().
The substituent is called an amino group.
Compounds with a nitrogen atom attached to a carbonyl group, thus having the structure , are called amides and have different chemical properties from amines. | 0 | Organic Chemistry |
ATP synthase is the simplest known form of ATP synthase, with 8 different subunit types.
Bacterial F-ATPases can occasionally operate in reverse, turning them into an ATPase. Some bacteria have no F-ATPase, using an A/V-type ATPase bidirectionally. | 5 | Photochemistry |
The precursors of ketone bodies include fatty acids from adipose tissue or the diet and ketogenic amino acids. The formation of ketone bodies occurs via ketogenesis in the mitochondrial matrix of liver cells.
Fatty acids can be released from adipose tissue by adipokine signaling of high glucagon and epinephrine levels and low insulin levels. High glucagon and low insulin correspond to times of low glucose availability such as fasting. Fatty acids bound to coenzyme A allow penetration into mitochondria. Once inside the mitochondrion, the bound fatty acids are used as fuel in cells predominantly through beta oxidation, which cleaves two carbons from the acyl-CoA molecule in every cycle to form acetyl-CoA. Acetyl-CoA enters the citric acid cycle, where it undergoes an aldol condensation with oxaloacetate to form citric acid; citric acid then enters the tricarboxylic acid cycle (TCA), which harvests a very high energy yield per carbon in the original fatty acid.
Acetyl-CoA can be metabolized through the TCA cycle in any cell, but it can also undergo ketogenesis in the mitochondria of liver cells. When glucose availability is low, oxaloacetate is diverted away from the TCA cycle and is instead used to produce glucose via gluconeogenesis. This utilization of oxaloacetate in gluconeogenesis can make it unavailable to condense with acetyl-CoA, preventing entrance into the TCA cycle. In this scenario, energy can be harvested from acetyl-CoA through ketone production.
In ketogenesis, two acetyl-CoA molecules condense to form acetoacetyl-CoA via thiolase. Acetoacetyl-CoA briefly combines with another acetyl-CoA via HMG-CoA synthase to form hydroxy-β-methylglutaryl-CoA. Hydroxy-β-methylglutaryl-CoA form the ketone body acetoacetate via HMG-CoA lyase. Acetoacetate can then reversibly convert to another ketone body—D-β-hydroxybutyrate—via D-β-hydroxybutyrate dehydrogenase. Alternatively, acetoacetate can spontaneously degrade to a third ketone body (acetone) and carbon dioxide, which generates much greater concentrations of acetoacetate and D-β-hydroxybutyrate. The resulting ketone bodies cannot be used for energy by the liver so are exported from the liver to supply energy to the brain and peripheral tissues.
In addition to fatty acids, deaminated ketogenic amino acids can also be converted into intermediates in the citric acid cycle and produce ketone bodies. | 1 | Biochemistry |
The 2016 ExoMars Trace Gas Orbiter (TGO) is a Mars telecommunications orbiter and atmospheric gas analyzer mission. It delivered the Schiaparelli EDM lander and then began to settle into its science orbit to map the sources of methane on Mars and other gases, and in doing so, will help select the landing site for the Rosalind Franklin rover to be launched in 2022. The primary objective of the Rosalind Franklin rover mission is the search for biosignatures on the surface and subsurface by using a drill able to collect samples down to a depth of , away from the destructive radiation that bathes the surface. | 2 | Environmental Chemistry |
Androstenediol sulfate, also known as androst-5-ene-3β,17β-diol 3β-sulfate, is an endogenous, naturally occurring steroid and a urinary metabolites of androstenediol. It is a steroid sulfate which is formed from sulfation of androstenediol by steroid sulfotransferase and can be desulfated back into androstenediol by steroid sulfatase. | 1 | Biochemistry |
Due to the electronegativity difference between carbon and oxygen / nitrogen, there will be a slight electron withdrawing effect through inductive effect (known as the –I effect). However, the other effect called resonance add electron density back to the ring (known as the +M effect) and dominate over that of inductive effect. Hence the result is that they are EDGs and ortho/para directors.
Phenol is an ortho/para director, but in a presence of base, the reaction is more rapid. It is due to the higher reactivity of phenolate anion. The negative oxygen was forced to give electron density to the carbons (because it has a negative charge, it has an extra +I effect). Even when cold and with neutral (and relatively weak) electrophiles, the reaction still occurs rapidly. | 0 | Organic Chemistry |
RoXaN (Rotavirus X-associated non-structural protein) also known as ZC3H7B (zinc finger CCCH-type containing 7B), is a protein that in humans is encoded by the ZC3H7B gene. RoXaN is a protein that contains tetratricopeptide repeat and leucine-aspartate repeat as well as zinc finger domains. This protein also interacts with the rotavirus non-structural protein NSP3. | 1 | Biochemistry |
For his work in the area of applying laser spectroscopic techniques to study of properties and behavior on the nanoscale, El-Sayed was elected to the National Academy of Sciences in 1980. In 1989 he received the Tolman Award, and in 2002, he won the Irving Langmuir Award in Chemical Physics. He has been the recipient of the 1990 King Faisal International Prize ("Arabian Nobel Prize") in Sciences, Georgia Techs highest award, "The Class of 1943 Distinguished Professor", an honorary doctorate of philosophy from the Hebrew University, and several other awards including some from the different American Chemical Society local sections. He was a Sherman Fairchild Distinguished Scholar at the California Institute of Technology and an Alexander von Humboldt Senior U.S. Scientist Awardee. He served as editor-in-chief of the Journal of Physical Chemistry from 1980 to 2004 and has also served as the U.S. editor of the International Reviews in Physical Chemistry'. He is a Fellow of the American Academy of Arts and Sciences, a member of the American Physical Society, the American Association for the Advancement of Science and the Third World Academy of Science. Mostafa El-Sayed was awarded the 2007 US National Medal of Science "for his seminal and creative contributions to our understanding of the electronic and optical properties of nanomaterials and to their applications in nanocatalysis and nanomedicine, for his humanitarian efforts of exchange among countries and for his role in developing the scientific leadership of tomorrow." Mostafa was also announced to be the recipient of the 2009 Ahmed Zewail prize in molecular sciences. In 2011, he was listed #17 in Thomson-Reuters listing of the Top Chemists of the Past Decade. Professor El-Sayed also received the 2016 Priestley Medal, the American Chemical Society’s highest honor, for his decades-long contributions to chemistry. | 1 | Biochemistry |
The flux control coefficient connectivity theorem is the easiest to understand. Starting with a simple two step pathway:
where and are fixed species so that the pathway can reach a steady-state. and are the reaction rates for the first and second steps.
We can write the flux connectivity theorem for this simple system as follows:
where is the elasticity of the first step with respect to the species and is the elasticity of the second step with respect to the species . It is easier to interpret the equation with a slight rearrangement to the following form:
The equation indicates that the ratio of the flux control coefficients is inversely proportional to the elasticities. That is, a high flux control coefficient on step one is associated with a low elasticity and vice versa. Likewise a high value for the flux control coefficient on step two is associated with a low elasticity .
This can be explained as follows: If is high (in absolute terms, since it is negative) then a change at will be resisted by the elasticity, hence the flux control coefficient on step one will be low. | 1 | Biochemistry |
Data resulting from toxicity studies that is integrated in to the ECOTOX database is subjected to a screening and quality assurance criteria developed by the EPA and the Office of Pesticide Programs (OPP). In order for study results to be accepted by the EPA and OPP the toxicity study must follow or consist of the following:
* The toxic effects are related to single chemical exposure;
* The toxic effects are on an aquatic or terrestrial plant or animal species;
* There is a biological effect on live, whole organisms;
* A concurrent environmental chemical concentration/dose or application rate is reported; and
* There is an explicit duration of exposure.
In addition to the criteria listed above, the following criteria, which are discussed in further detail in Attachment I, are applied by OPP as a further screen of acceptability:
* Toxicology information is reported for a chemical of concern to OPP;
* The article is published in the English language;
* The study is presented as a full article;
* The paper is a publicly available document;
* The paper is the primary source of the data
* A calculated endpoint is reported;
* Treatment(s) are compared to an acceptable control;
* The location of the study (e.g., laboratory vs. field) is reported; and
* The tested species is reported and verified. | 1 | Biochemistry |
Since almost all adsorptive separation processes are dynamic -meaning, that they are running under flow - testing porous materials for those applications for their separation performance has to be tested under flow as well. Since separation processes run with mixtures of different components, measuring several breakthrough curves results in thermodynamic mixture equilibria - mixture sorption isotherms, that are hardly accessible with static manometric sorption characterization. This enables the determination of sorption selectivities in gaseous and liquid phase.
The determination of breakthrough curves is the foundation of many other processes, like the pressure swing adsorption. Within this process, the loading of one adsorber is equivalent to a breakthrough experiment. | 7 | Physical Chemistry |
Soil organic matter is the largest source of nutrients and energy in a soil. Its inputs strongly influence key soil factors such as types of biota, pH, and even soil order. Soil organic matter is often strategically applied by plant growers because of its ability to improve soil structure, supply nutrients, manage pH, increase water retention, and regulate soil temperature (which directly affects water dynamics and biota).
The chief elements found in humus, the product of organic matter decomposition in soil, are carbon, hydrogen, oxygen, sulphur and nitrogen. The important compound found in humus are carbohydrates, phosphoric acid, some organic acids, resins, urea etc. Humus is a dynamic product and is constantly changing because of its oxidation, reduction and hydrolysis; hence, it has much carbon content and less nitrogen. This material can come from a variety of sources, but often derives from livestock manure and plant residues.
Though there are many other variables, such as texture, soils that lack sufficient organic matter content are susceptible to soil degradation and drying, as there is nothing supporting the soil structure. This often leads to a decline in soil fertility and an increase in erodibility.
Other associated concepts:
* Anion and cation exchange capacity
* Soil pH
* Mineral formation and transformation processes and pedogenesis
* Clay mineralogy
* Sorption and precipitation reactions in soil
* Chemistry of problem soils
* C/N ratio
* Erosion and soil degradation | 9 | Geochemistry |
Ružička married twice: to Anna Hausmann in 1912, and 1951 to Gertrud Acklin. From 1929, he lived at Freudenbergstrasse 101 until the last years of his life. He died in Mammern, Switzerland, a village on Lake Constance at the age of 89. | 0 | Organic Chemistry |
Jin-Quan Yu () is a Chinese-born American chemist. He is the Frank and Bertha Hupp Professor of Chemistry at Scripps Research, where he also holds the Bristol Myers Squibb Endowed Chair in Chemistry. He is a 2016 recipient of the MacArthur Fellowship, and is a member of the American Academy of Arts and Sciences, American Association for the Advancement of Science, and the Royal Society of Chemistry. Yu is a leader in the development of C–H bond activation reactions in organic chemistry, and has reported many C–H activation reactions that could be applicable towards the synthesis of drug molecules and other biologically active compounds. He also co-founded Vividion Therapeutics in 2016 with fellow Scripps chemists Benjamin Cravatt and Phil Baran, and is a member of the scientific advisory board of Chemveda Life Sciences. | 0 | Organic Chemistry |
Soil retains a degree of moisture after a rainfall. This residual water moisture affects the soil's infiltration capacity. During the next rainfall event, the infiltration capacity will cause the soil to be saturated at a different rate. The higher the level of antecedent soil moisture, the more quickly the soil becomes saturated. Once the soil is saturated, runoff occurs. Therefore, surface runoff is a significantly factor in the controlling of soil moisture after medium and low intensity storms. | 2 | Environmental Chemistry |
Dosage quotient analysis is the usual method of interpreting MLPA data. If a and b are the signals from two amplicons in the patient sample, and A and B are the corresponding amplicons in the experimental control, then the dosage quotient DQ = (a/b) / (A/B). Although dosage quotients may be calculated for any pair of amplicons, it is usually the case that one of the pair is an internal reference probe. | 1 | Biochemistry |
Of all commercialized pharmaceutical drugs, twenty percent contain fluorine, including important drugs in many different pharmaceutical classes. Fluorine is often added to drug molecules during drug design, as even a single atom can greatly change the chemical properties of the molecule in desirable ways.
Because of the considerable stability of the carbon–fluorine bond, many drugs are fluorinated to delay their metabolism, which is the chemical process in which the drugs are turned into compounds that allows them to be eliminated. This prolongs their half-lives and allows for longer times between dosing and activation. For example, an aromatic ring may prevent the metabolism of a drug, but this presents a safety problem, because some aromatic compounds are metabolized in the body into poisonous epoxides by the organisms native enzymes. Substituting a fluorine into a para' position, however, protects the aromatic ring and prevents the epoxide from being produced.
Adding fluorine to biologically active organic compounds increases their lipophilicity (ability to dissolve in fats), because the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond. This effect often increases a drug's bioavailability because of increased cell membrane penetration. Although the potential of fluorine being released in a fluoride leaving group depends on its position in the molecule, organofluorides are generally very stable, since the carbon–fluorine bond is strong.
Fluorines also find their uses in common mineralocorticoids, a class of drugs that increase the blood pressure. Adding a fluorine increases both its medical power and anti-inflammatory effects. Fluorine-containing fludrocortisone is one of the most common of these drugs. Dexamethasone and triamcinolone, which are among the most potent of the related synthetic corticosteroid class of drugs, contain fluorine as well.
Several inhaled general anesthetic agents, including the most commonly used inhaled agents, also contain fluorine. The first fluorinated anesthetic agent, halothane, proved to be much safer (neither explosive nor flammable) and longer-lasting than those previously used. Modern fluorinated anesthetics are longer-lasting still and almost insoluble in blood, which accelerates the awakening. Examples include sevoflurane, desflurane, enflurane, and isoflurane, all hydrofluorocarbon derivatives.
Prior to the 1980s, antidepressants altered not only serotonin uptake but also the uptake of altered norepinephrine; the latter caused most of the side effects of antidepressants. The first drug to alter only the serotonin uptake was Prozac; it gave birth to the extensive selective serotonin reuptake inhibitor (SSRI) antidepressant class and is the best-selling antidepressant. Many other SSRI antidepressants are fluorinated organics, including Celexa, Luvox, and Lexapro. Fluoroquinolones are a commonly used family of broad-spectrum antibiotics. | 1 | Biochemistry |
Detonation spraying produces coatings of very high chemical bond strength and hardness. Coatings are of low porosity, oxygen content and have a low to medium surface roughness. This is achieved due to the extremely high temperatures and velocities produced by the detonation gun during surface coating application. These properties make detonation spraying the standard of comparison for all other thermal spray coatings (wire arc, plasma, flame, HVAF, HVOF, Warm, Cold).
There are many factors that determine the final detonation gun coating properties. Primarily, surface properties are determined by the type and properties of the powdered feedstock used (composition and particle size) but they are also affected by the settings used on the D-gun. These are powder flow rate, firing rate, distance from gun to target, how the D-gun is moved around to apply the coating, size of barrel, amount and composition of fuel and oxygen mixture.
Detonation spraying is able to apply protective coatings to relatively sensitive and delicate materials. This is due to the nature of the application of detonation gun coatings, being very quick and having the heat source removed from the target material. This allows for a large range of suitable applications for detonation spraying. | 8 | Metallurgy |
The social, political, and economic stagnation that followed the Roman Empire affected Europe throughout the early medieval period and had a critical impact on technological progress, trade, and social organization. Technological developments that affected the course of metal production were only feasible within a stable political environment, and this was not the case until the 9th century (Martinon-Torres & Rehren in press, a).
During the first medieval centuries, the output of metal was in a steady decline with constraints in small-scale activities. Miners adopted methods much less efficient than those of Roman times. Ores were extracted only from shallow depths or from remnants of formerly abandoned mines. The vicinity of the mine to villages or towns was also a determining factor when due to the high cost of material transportation (Martinon-Torres & Rehren in press, b). Only the output of iron diminished less in relation to the other base and precious metals until the 8th century. This fact, correlated with the dramatic decrease in copper production, may indicate a possible displacement of copper and bronze artifacts by iron ones (Forbes 1957, 64; Bayley et al. 2008, 50).
By the end of the 9th century, economic, and social conditions dictated a greater need for metal for agriculture, arms, stirrups, and decoration. Consequently, conditions began to favor metallurgy and a slow but steady general progress developed. Starting from the reign of the emperor Otto I in the 960s, smelting sites were multiplied. New mines were discovered and exploited, like the well-known Mines of Rammelsberg, close to the town of Goslar in the Harz Mountains. Open-cast mining and metallurgical activities were mostly concentrated in the Eastern Alps, Saxony, Bohemia, Tuscany, Rhineland, Gaul, and Spain (Nef 1987). It was mainly German miners and metallurgists who were the generators of metal production, but the French and Flemish made contributions to the developments. | 8 | Metallurgy |
For intense beams of light (e.g. laser) traveling in a medium or in a waveguide, such as an optical fiber, the variations in the electric field of the beam itself may induce acoustic vibrations in the medium via electrostriction or radiation pressure. The beam may display Brillouin scattering as a result of those vibrations, usually in the direction opposite the incoming beam, a phenomenon known as stimulated Brillouin scattering (SBS). For liquids and gases, the frequency shifts typically created are of the order of 1–10 GHz resulting in wavelength shifts of ~1–10 pm in the visible light. Stimulated Brillouin scattering is one effect by which optical phase conjugation can take place. | 7 | Physical Chemistry |
The thermodynamic equilibrium constant, K, for the equilibrium
can be defined as
where {ML} is the activity of the chemical species ML etc. K is dimensionless since activity is dimensionless. Activities of the products are placed in the numerator, activities of the reactants are placed in the denominator. See activity coefficient for a derivation of this expression.
Since activity is the product of concentration and activity coefficient (γ) the definition could also be written as
where [ML] represents the concentration of ML and Γ is a quotient of activity coefficients. This expression can be generalized as
To avoid the complications involved in using activities, stability constants are determined, where possible, in a medium consisting of a solution of a background electrolyte at high ionic strength, that is, under conditions in which Γ can be assumed to be always constant. For example, the medium might be a solution of 0.1 mol dm sodium nitrate or 3 mol dm sodium perchlorate. When Γ is constant it may be ignored and the general expression in theory, above, is obtained.
All published stability constant values refer to the specific ionic medium used in their determination and different values are obtained with different conditions, as illustrated for the complex CuL (L = glycinate). Furthermore, stability constant values depend on the specific electrolyte used as the value of Γ is different for different electrolytes, even at the same ionic strength. There does not need to be any chemical interaction between the species in equilibrium and the background electrolyte, but such interactions might occur in particular cases. For example, phosphates form weak complexes with alkali metals, so, when determining stability constants involving phosphates, such as ATP, the background electrolyte used will be, for example, a tetralkylammonium salt. Another example involves iron(III) which forms weak complexes with halide and other anions, but not with perchlorate ions.
When published constants refer to an ionic strength other than the one required for a particular application, they may be adjusted by means of specific ion theory (SIT) and other theories. | 7 | Physical Chemistry |
The spines of sea urchins are composed of mesocrystals of calcite nano-crystals (92%) in a matrix of non-crystalline calcium carbonate (8%). This structure makes the spines hard but also shock-absorbing, which special property makes them effective defences against predators. Mesocrystals also appear in the shells of some eggs, coral, chitin, and the shells of mussels. | 7 | Physical Chemistry |
A qPlus sensor is used in many ultra-high vacuum nc-AFMs. The sensor was originally made from a quartz tuning fork from a wristwatch. In contrast to a quartz tuning fork sensor that consists of two coupled tines that oscillate opposed to each other, a qPlus sensor has only one tine that oscillates. The tuning fork is glued to a mount such that one tine of the tuning fork is immobilised, a tungsten wire, etched to have a sharp apex, is then glued to the free prong. The sensor was invented in 1996 by physicist Franz J. Giessibl. The AFM deflection signal is generated by the piezoelectric effect, and can be read from the two electrodes on the tuning fork.
As the tungsten tip wire is conductive, the sensor can be used for combined STM/nc-AFM operation. The tip can either be electrically connected to one of tuning fork electrodes, or to a separate thin (~30μm diameter) gold wire. The advantage of the separate wire is that it can reduce crosstalk between the tunnel current and the deflection channels, however the wire will have its own resonance, which can affect the resonant properties of the sensor. New versions of the qPlus sensor with one or several integrated service electrodes as proposed in reference and implemented in solve that problem. The Bergman reaction has recently been imaged by the IBM group in Zurich using such a qPlus sensor with integrated STM electrode.
The sensor has a much higher stiffness than silicon microcantilevers, ~1800 N/m (tip placement further down the tine can lead to higher stiffness's ~2600 N/m). This higher stiffness allows higher forces before snap to contact instabilities. The resonant frequency of a qPlus sensor is typically lower than that of a silicon microcantilever, ~25 kHz (Watch tuning forks have a resonant frequency of 32,768 Hz before tip placement). Several factors (in particular detector noise and eigenfrequency) affect the speed of operation. qPlus sensors with long tip wires that approach the length of the sensor display a movement of the apex which is no longer perpendicular to the surface, thus probing the forces in a different direction to expected. | 6 | Supramolecular Chemistry |
*David R. Bundle, former postdoctoral fellow with Prof. Lemieux, currently professor of chemistry, the Raymond U. Lemieux Chair in Carbohydrate Chemistry, and a distinguished university professor at the University of Alberta, founder and former director of the Alberta Glycomics Centre (formerly known as Alberta Ingenuity Centre for Carbohydrate Science). http://www.chem.ualberta.ca/~glyco/who/index.htm
*Ole Hindsgaul, former PhD student with Prof. Lemieux, currently a distinguished professor at the Carlsberg Laboratory, Copenhagen, Denmark, and an adjunct professor, Department of Chemistry, University of Alberta, Canada. http://www.crc.dk/carbochem/oledraft2.htm | 0 | Organic Chemistry |
Mass-analyzed ion kinetic-energy spectrometry (MIKES) is a mass spectrometry technique by which mass spectra are obtained from a sector instrument that incorporates at least one magnetic sector plus one electric sector in reverse geometry (the beam first enters the magnetic sector). The accelerating voltage V, and the magnetic field B, are set to select the precursor ions of a particular m/z. The precursor ions then dissociate or react in an electric field-free region between the two sectors. The ratio of the kinetic energy to charge of the product ions are analyzed by scanning the electric sector field E. The width of the product ion spectrum peaks is related to the kinetic energy release distribution for the dissociation process. | 7 | Physical Chemistry |
The outer thermal protection layer of NASA's LOFTID inflatable heat shield incorporates a woven ceramic made from silicon carbide, with fiber of such small diameter that it can be bundled and spun into a yarn. | 8 | Metallurgy |
As with other members of the penicillin family, the chemical structure of oxacillin features a 6-aminopenicillanic acid nucleus with a substituent attached to the amino group. The 6-aminopenicillanic acid nucleus consists of a thiazolidine ring attached to a β-lactam ring, which is the active moiety responsible for the antibacterial activity of the penicillin family. The substituent present on oxacillin is thought to impart resistance to degradation via bacterial β-lactamases. | 4 | Stereochemistry |
Chemical additives are small chemical compounds that are added to the crystallization process to increase the yield of crystals. The role of small molecules in protein crystallization had not been well thought of in the early days since they were thought of as contaminants in most case. Smaller molecules crystallize better than macromolecules such as proteins, therefore, the use of chemical additives had been limited prior to the study by McPherson. However, this is a powerful aspect of the experimental parameters for crystallization that is important for biochemists and crystallographers to further investigate and apply. | 3 | Analytical Chemistry |
In non-photosynthetic eukaryotes such as animals, insects, fungi, and protozoa, as well as the α-proteobacteria group of bacteria, the committed step for porphyrin biosynthesis is the formation of δ-aminolevulinic acid (δ-ALA, 5-ALA or dALA) by the reaction of the amino acid glycine with succinyl-CoA from the citric acid cycle. In plants, algae, bacteria (except for the α-proteobacteria group) and archaea, it is produced from glutamic acid via glutamyl-tRNA and glutamate-1-semialdehyde. The enzymes involved in this pathway are glutamyl-tRNA synthetase, glutamyl-tRNA reductase, and glutamate-1-semialdehyde 2,1-aminomutase. This pathway is known as the C5 or Beale pathway.
Two molecules of dALA are then combined by porphobilinogen synthase to give porphobilinogen (PBG), which contains a pyrrole ring. Four PBGs are then combined through deamination into hydroxymethyl bilane (HMB), which is hydrolysed to form the circular tetrapyrrole uroporphyrinogen III. This molecule undergoes a number of further modifications. Intermediates are used in different species to form particular substances, but, in humans, the main end-product protoporphyrin IX is combined with iron to form heme. Bile pigments are the breakdown products of heme.
The following scheme summarizes the biosynthesis of porphyrins, with references by EC number and the OMIM database. The porphyria associated with the deficiency of each enzyme is also shown: | 1 | Biochemistry |
For the derivation of the Maxwell Garnett equation we start with an array of polarizable particles. By using the Lorentz local field concept, we obtain the Clausius-Mossotti relation:
Where is the number of particles per unit volume. By using elementary electrostatics, we get for a spherical inclusion with dielectric constant and a radius a polarisability :
If we combine with the Clausius Mosotti equation, we get:
Where is the effective dielectric constant of the medium, of the inclusions; is the volume fraction of the inclusions.<br />
As the model of Maxwell Garnett is a composition of a matrix medium with inclusions we enhance the equation: | 7 | Physical Chemistry |
The Grignard reaction () is an organometallic chemical reaction in which, according to the classical definition, carbon alkyl, allyl, vinyl, or aryl magnesium halides (Grignard reagent) are added to the carbonyl groups of either an aldehyde or ketone under anhydrous conditions. This reaction is important for the formation of carbon–carbon bonds.
(R or R could be hydrogen) | 0 | Organic Chemistry |
The main reason to use microspectrophotometry is the ability to measure the optical spectra of samples with a spatial resolution on the micron scale. Optical spectra may be acquired of either microscopic samples or larger samples with a micron-scale spatial resolution. Another reason microspectrophotometry is useful is that measurements are made without destroying the samples. This is important when dealing with stained/unstained histological or cytochemical biological sections, when measuring film thickness in semi-conductor integrated circuits, when matching paints and fibers (forensic science), when studying gems and coal (geology), and in paint/ink/color analysis in paint chemistry or art-work. | 7 | Physical Chemistry |
1,1-Dichloro-1-fluoroethane can be a non-flammable, colourless liquid under room-temperature atmospheric conditions. The compound is very volatile with a boiling point of 32°C. Its critical temperature is near 204°C. Its smell has been described as "usually ethereal" (like ether). | 2 | Environmental Chemistry |
In cell biology and protein biochemistry, heterologous expression means that a protein is experimentally put into a cell that does not normally make (i.e., express) that protein. Heterologous (meaning derived from a different organism) refers to the fact that often the transferred protein was initially cloned from or derived from a different cell type or a different species from the recipient.
Typically the protein itself is not transferred, but instead the correctly edited genetic material coding for the protein (the complementary DNA or cDNA) is added to the recipient cell. The genetic material that is transferred typically must be within a format that encourages the recipient cell to express the cDNA as a protein (i.e., it is put in an expression vector).
Methods for transferring foreign genetic material into a recipient cell include transfection and transduction. The choice of recipient cell type is often based on an experimental need to examine the proteins function in detail, and the most prevalent recipients, known as heterologous expression systems, are chosen usually because they are easy to transfer DNA into or because they allow for a simpler assessment of the proteins function. | 1 | Biochemistry |
Levobetaxolol is a drug used to lower the pressure in the eye in treating conditions such as glaucoma. It is marketed as a 0.25 or 0.5% ophthalmic solution of levobetaxolol hydrochloride under the trade name Betaxon. Levobetaxolol is a beta-adrenergic receptor inhibitor (beta blocker). | 4 | Stereochemistry |
* Brody, David. Labor in Crisis: The Steel Strike of 1919 (1965)
* Mary Margaret Fonow; Union Women: Forging Feminism in the United Steelworkers of America (University of Minnesota Press, 2003)
* [https://web.archive.org/web/20110717180737/http://www.ussteel.com/corp/about.htm#The%20History%20of%20United%20States%20Steel U.S. Steel's History of U.S. Steel]
* Urofsky, Melvin I. Big Steel and the Wilson Administration: A Study in Business-Government Relations (1969) | 8 | Metallurgy |
Bufothionine is a sulfur-containing compound which is present in the bufotoxins secreted by the parotoid gland of certain toads of the genera Bufo and Chaunus. This specific compound can be found in the skin of certain species of toad such as the Asiatic Toad, Chaunus arunco, Chaunus crucifer, Chaunus spinulosus, and Chaunus arenarum. | 1 | Biochemistry |
Phage display was first described by George P. Smith in 1985, when he demonstrated the display of peptides on filamentous phage (long, thin viruses that infect bacteria) by fusing the virus's capsid protein to one peptide out of a collection of peptide sequences. This displayed the different peptides on the outer surfaces of the collection of viral clones, where the screening step of the process isolated the peptides with the highest binding affinity. In 1988, Stephen Parmley and George Smith described biopanning for affinity selection and demonstrated that recursive rounds of selection could enrich for clones present at 1 in a billion or less. In 1990, Jamie Scott and George Smith described creation of large random peptide libraries displayed on filamentous phage. Phage display technology was further developed and improved by groups at the Laboratory of Molecular Biology with Greg Winter and John McCafferty, The Scripps Research Institute with Richard Lerner and Carlos Barbas and the German Cancer Research Center with Frank Breitling and Stefan Dübel for display of proteins such as antibodies for therapeutic protein engineering. Smith and Winter were awarded a half share of the 2018 Nobel Prize in chemistry for their contribution to developing phage display. A patent by George Pieczenik claiming priority from 1985 also describes the generation of peptide libraries. | 1 | Biochemistry |
The two first partial derivatives of the vdW equation are
The first equation is , while the second is , where , the isothermal compressibility, is a measure of the relative increase of volume from an increase of pressure, at constant temperature, while , the coefficient of thermal expansion, is a measure of the relative increase of volume from an increase of temperature, at constant pressure. Therefore
In the limit while . Since the vdW equation in this limit becomes , finally . Both of these are the ideal gas values, which is consistent because, as noted earlier, the vdW fluid behaves like an ideal gas in this limit.
The specific heat at constant pressure, is defined as the partial derivative . However, it is not independent of , they are related by the Mayer equation, . Then the two partials of the vdW equation can be used to express as
Here in the limit , , which is also the ideal gas result as expected; however the limit gives the same result, which does not agree with experiments on liquids.
In this liquid limit we also find , namely that the vdW liquid is incompressible. Moreover, since , it is also mechanically incompressible, that is faster than .
Finally , and are all infinite on the curve . This curve, called the spinodal curve, is defined by , and is discussed at length in the next section. | 7 | Physical Chemistry |
It was discovered that bioluminescent snails are able to exercise a great deal of control over light emission, but the way in which they exercise control over it is still unknown. Phuphania have even been shown to be able to preserve their ability to produce light even after long periods of hibernation. It is currently unknown how these snails are able to maintain their ability to produce light for long periods of time, but theories have been proposed possibly relating it to the way certain fungi are able to maintain their bioluminescence. | 1 | Biochemistry |
Werner also described a second achiral hexol (a minor byproduct from the production of Fremy's salt) that he incorrectly identified as a linear tetramer. The second hexol is hexanuclear (contains six cobalt centres in each ion), not tetranuclear. Its point group is C, and its formula is , whereas that of hexol is . | 4 | Stereochemistry |
Chemical imaging has been implemented for mid-infrared, near-infrared spectroscopy and Raman spectroscopy. As with their bulk spectroscopy counterparts, each imaging technique has particular strengths and weaknesses, and are best suited to fulfill different needs. | 7 | Physical Chemistry |
The electrodes in an electrochemical cell are each classified as either an anode or a cathode. An anode is an electrode at which electrons leave the cell and oxidation occurs, while a cathode is an electrode at which electrons enter the cell and reduction occurs. Each electrode may become either an anode or a cathode depending on the voltage applied to the cell.
Each deionization cell consists of an electrode and an electrolyte with ions that undergo either oxidation or reduction. Because they commonly consist of ions in solution, the electrolytes are often known as "ionic solutions", but molten and solid electrolytes are also possible.
Water passes between an anode and a cathode. Ion-selective membranes allow positive ions to separate from the water toward the negative electrode and negative ions toward the positive electrode. As a result, the ions cannot escape the cell and deionized water is produced.
When using a current that is higher than necessary for the movement of the ions, a portion of the incident water will be split, forming hydroxide (OH) anions and hydrogen (H) cations. These species will replace the impurity anions and cations in the resin. This process is called "in situ regeneration" of the resin. Because this replacement occurs alongside the deionization process it allows for continuous purification, as opposed to deionization techniques that require a pause in operation to chemically regenerate ion exchange resins.
The purpose of the ion exchange resin is to maintain a stable conductance across the feedwater. Without the resin, ions could be removed initially, but the conductance would drop dramatically as the concentration of ions decreases. With lower conductance, the electrodes would become less able to efficiently direct the flow of electrons across the cell, whereas with the addition of resin and thus a steady conductance, electron flow remains steady and ensures a steady rate of ion removal. With a resin, therefore, the final remaining ion concentrations in the processed water can be lower by orders of magnitude. | 7 | Physical Chemistry |
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