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Trail pheromone deposition from an organism is correlated with its environment. In the event where a food source is identified and a trail pheromone is deposited, certain wildlife may flock towards or away from the trail causing temporary or dispersal of the population or individual. With relocation of wildlife, surrounding plant life may change as well; for example, pollen attached to the migrating organism is also relocating, thus may potentially regenerate in different patches. | 1 | Biochemistry |
A casting defect is an undesired irregularity in a metal casting process. Some defects can be tolerated while others can be repaired, otherwise they must be eliminated. They are broken down into five main categories: gas porosity, shrinkage defects, mould material defects, pouring metal defects, and metallurgical defects. | 8 | Metallurgy |
ICOS has currently 13 member states and is in operational mode, with stations being certified for the operation according to the strict protocols and quality parameters. By the end of 2020 ICOS had 68 out of the 148 stations certified (labelled as either Class 1,2 or associated station), with greenhouse gas concentrations and fluxes determined on a routine basis.
ICOS member states | 2 | Environmental Chemistry |
Binary subcomplexes in proteins database (BISC) is a protein–protein interaction database about binary subcomplexes. | 1 | Biochemistry |
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-containing compounds such as alkanes (e.g. methane ) and its derivatives are universally considered organic, but many others are sometimes considered inorganic, such as halides of carbon without carbon-hydrogen and carbon-carbon bonds (e.g. carbon tetrachloride ), and certain compounds of carbon with nitrogen and oxygen (e.g. cyanide ion , hydrogen cyanide , chloroformic acid , carbon dioxide , and carbonate ion ).
Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprise the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds (e.g., carbonate salts and cyanide salts), along with a few other exceptions (e.g., carbon dioxide, and even hydrogen cyanide despite the fact it contains a carbon-hydrogen bond), are generally considered inorganic. Other than those just named, little consensus exists among chemists on precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive.
Although organic compounds make up only a small percentage of Earth's crust, they are of central importance because all known life is based on organic compounds. Living things incorporate inorganic carbon compounds into organic compounds through a network of processes (the carbon cycle) that begins with the conversion of carbon dioxide and a hydrogen source like water into simple sugars and other organic molecules by autotrophic organisms using light (photosynthesis) or other sources of energy. Most synthetically-produced organic compounds are ultimately derived from petrochemicals consisting mainly of hydrocarbons, which are themselves formed from the high pressure and temperature degradation of organic matter underground over geological timescales. This ultimate derivation notwithstanding, organic compounds are no longer defined as compounds originating in living things, as they were historically.
In chemical nomenclature, an organyl group, frequently represented by the letter R, refers to any monovalent substituent whose open valence is on a carbon atom. | 0 | Organic Chemistry |
Many biologically active molecules are chiral, including the naturally occurring amino acids (the building blocks of proteins) and sugars.
The origin of this homochirality in biology is the subject of much debate. Most scientists believe that Earth life's "choice" of chirality was purely random, and that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality. However, there is some suggestion that early amino acids could have formed in comet dust. In this case, circularly polarised radiation (which makes up 17% of stellar radiation) could have caused the selective destruction of one chirality of amino acids, leading to a selection bias which ultimately resulted in all life on Earth being homochiral.
Enzymes, which are chiral, often distinguish between the two enantiomers of a chiral substrate. One could imagine an enzyme as having a glove-like cavity that binds a substrate. If this glove is right-handed, then one enantiomer will fit inside and be bound, whereas the other enantiomer will have a poor fit and is unlikely to bind.
-forms of amino acids tend to be tasteless, whereas -forms tend to taste sweet. Spearmint leaves contain the -enantiomer of the chemical carvone or R-(−)-carvone and caraway seeds contain the -enantiomer or S-(+)-carvone. The two smell different to most people because our olfactory receptors are chiral.
Chirality is important in context of ordered phases as well, for example the addition of a small amount of an optically active molecule to a nematic phase (a phase that has long range orientational order of molecules) transforms that phase to a chiral nematic phase (or cholesteric phase). Chirality in context of such phases in polymeric fluids has also been studied in this context. | 4 | Stereochemistry |
Apart from the very bulky substituents, a η-coordination of diphosphene to a metal is also possible to stabilize the P-P double bond. In 1982, K. R. Dixon et al. synthesized platinum and palladium complexes (with M=Pt or Pd and L=(PPh3) or ), which contained side-on coordination. Different from η coordination complex, where P-P still kept the double bond nature, P-P distance in side-on coordination complexes (2.121Å in ) was significantly longer than that in non-coordinated bis(2,4,6-tri-tert-butylphenyl)diphosphene. | 0 | Organic Chemistry |
It has been observed among natural RuBisCOs that an increased ability to distinguish between CO and O (larger values of S) corresponds with a decreased rate of carboxylation (lower values of V and K). The variation and trade-off between S and K has been observed across all photosynthetic organisms, from photosynthetic bacteria and algae to higher plants. Organisms using RuBisCOs with high values of V / K, and low values of S have localized RuBisCO to areas within the cell with artificially high local CO concentrations. In cyanobacteria, concentrations of CO are increased using a carboxysome, an icosahedral protein compartment about 100 nm in diameter that selectively uptakes bicarbonate and converts it to CO in the presence of RuBisCO. Organisms without a CCM, like certain plants, instead utilize RuBisCOs with high values of S and low values of V and K. It has been theorized that groups with a CCM have been able to maximize K at the expense of decreasing S, because artificially enhancing the concentration of CO would decrease the concentration of O and remove the need for high CO specificity. However, the opposite is true for organisms without a CCM, who must optimize S at the expense of K because O is readily present in the atmosphere.
This trade-off between S and V or K observed in extant organisms suggest that RuBisCO has evolved through geologic time to be maximally optimized in its current, modern environment. RuBisCO evolved over 2.5 billion years ago when atmospheric CO concentrations were 300 to 600 times higher than present day concentrations, and oxygen concentrations were only 5-18% of present-day levels. Therefore, because CO was abundant and O rare, there was no need for the ancestral RuBisCO enzyme to have high specificity. This is supported by the biochemical characterization of an ancestral RuBisCO enzyme, which has intermediate values of V and S between the extreme end-members.
It has been theorized that this ecological trade-off is due to the form that 2-carboxy-3-keto-D-arabinitol 1,5-bisphophate in its transient transition state before cleaving into two 3PGA molecules. The more closely the Mg-bound CO moiety resembles the carboxylate group in 2-carboxy-3-keto-D-arabinitol 1,5-bisphophate, the greater the structural difference between the transition states of carboxylation and oxygenation. The larger structural difference allows RuBisCO to better distinguish between CO and O, resulting in larger values of S. However, this increasing structural similarity between the transition state and the product state requires strong binding at the carboxyketone group, and this binding is so strong that the rate of cleavage into two product 3PGA molecules is slowed. Therefore, an increased specificity for CO over O necessitates a lower overall rate of carboxylation. This theory implies that there is a physical chemistry limitation at the heart of Rubisco's active site, and may preclude any efforts to engineer a simultaneously more selective and faster Rubisco. | 7 | Physical Chemistry |
When a neutral atom collides with an ion in a gas or a plasma, the ion can acquire an electron from the neutral atom as both electron shells overlap in the course of the collision. This can be used in various applications. | 7 | Physical Chemistry |
Side reactions of the alkenes are the isomerization and hydrogenation of the double bond. While the alkanes resulting from hydrogenation of the double bond do not participate further in the reaction, the isomerization of the double bond with subsequent formation of the n-alkyl complexes is a desired reaction. The hydrogenation is usually of minor importance; However, cobalt-phosphine-modified catalysts can have an increased hydrogenation activity, where up to 15% of the alkene is hydrogenated. | 0 | Organic Chemistry |
In 1985, MIM commissioned Jameson to undertake a project to improve the sparger design for flotation columns. Instead, he developed the concept of using a jet in a downcomer to create the bubbles and eliminate the need for a sparger in conventional flotation columns.
The concept of the Cell followed when further investigations showed that most of the bubble–particle interactions were occurring in the downcomer, rendering unnecessary the collection zone of flotation columns. The idea of the downcomer and short separation tank was developed and a provisional patent application was lodged in 1986. This patent was later assigned to TUNRA Limited ("TUNRA"), the technology transfer company of the University of Newcastle that is now known as "Newcastle Innovation".
A pilot two tonne per hour (t/h) Jameson Cell with a 100 mm downcomer and using an orifice plate to create the jet was tested in MIM's lead–zinc concentrator. Subsequently, in 1988, MIM tested the flotation of a stream of fine lead-bearing particles in a conventional mechanical flotation cell, a conventional column and the Jameson Cell. The Cell gave the best recoveries. This was thought to be a combination of the short residence time of the particles in the Cell and the fact that the hydrophobicity of the lead particles decreased over time.
As a result of this work, in 1989 MIM ordered four full-scale Cells, two for the Mount Isa lead–zinc concentrator and another two for the new Hilton lead–zinc concentrator to be built at the Hilton Mine, located about 20 kilometers north of Mount Isa. The Mount Isa cells had diameters of 1.9 m, with three downcomers each, while those at Hilton were 1.3 m in diameter and had two downcomers each. | 8 | Metallurgy |
An unnatural base pair (UBP) is a designed subunit (or nucleobase) of DNA that is created in a laboratory and does not occur in nature. In 2012, a group of American scientists led by Floyd Romesberg, a chemical biologist at the Scripps Research Institute in San Diego, California, published that his team had designed two unnatural base pairs
named d5SICS and dNaM. More technically, these artificial nucleotides bearing hydrophobic nucleobases feature two fused aromatic rings that form a d5SICS–dNaM complex or base pair in DNA. In 2014, the same team reported that they had synthesized a plasmid containing natural T-A and C-G base pairs along with the best-performing UBP Romesbergs laboratory had designed and inserted it into cells of the common bacterium E. coli, which successfully replicated the unnatural base pairs through multiple generations. This is the first known example of a living organism passing along an expanded genetic code to subsequent generations. This was in part achieved by the addition of a supportive algal gene that expresses a nucleotide triphosphate transporter which efficiently imports the triphosphates of both d5SICSTP and dNaMTP into E. coli' bacteria. Then, the natural bacterial replication pathways use them to accurately replicate the plasmid containing d5SICS–dNaM.
The successful incorporation of a third base pair is a significant breakthrough toward the goal of greatly expanding the number of amino acids which can be encoded by DNA, from the existing 20 amino acids to a theoretically possible 172, thereby expanding the potential for living organisms to produce novel proteins. Earlier, the artificial strings of DNA did not encode for anything, but scientists speculated they could be designed to manufacture new proteins which could have industrial or pharmaceutical uses. Transcription of DNA containing unnatural base pairs and translation of corresponding mRNA were actually achieved recently. In November 2017, the same team at the Scripps Research Institute that first introduced two extra nucleobases into bacterial DNA reported having constructed a semi-synthetic E. coli bacteria able to make proteins using such DNA. Its DNA contained six different nucleobases: four canonical and two artificially added, dNaM and dTPT3 (these two form a pair). The bacteria had two corresponding RNA bases included in two new codons, additional tRNAs recognizing these new codons (these tRNAs also contained two new RNA bases within their anticodons) and additional amino acids, enabling the bacteria to synthesize "unnatural" proteins.
Another demonstration of UBPs were achieved by Ichiro Hiraos group at RIKEN institute in Japan. In 2002, they developed an unnatural base pair between 2-amino-8-(2-thienyl)purine (s) and pyridine-2-one (y) that functions in vitro in transcription and translation, for the site-specific incorporation of non-standard amino acids into proteins. In 2006, they created 7-(2-thienyl)imidazo[4,5-b]pyridine (Ds) and pyrrole-2-carbaldehyde (Pa) as a third base pair for replication and transcription. Afterward, Ds and 4-[3-(6-aminohexanamido)-1-propynyl]-2-nitropyrrole (Px) was discovered as a high fidelity pair in PCR amplification. In 2013, they applied the Ds-Px pair to DNA aptamer generation by in vitro' selection (SELEX) and demonstrated the genetic alphabet expansion significantly augment DNA aptamer affinities to target proteins. | 1 | Biochemistry |
Mathematically, the atomic percent is
where N are the number of atoms of interest and N are the total number of atoms, while the atomic ratio is
For example, the atomic percent of hydrogen in water (HO) is , while the atomic ratio of hydrogen to oxygen is . | 7 | Physical Chemistry |
Long strands of repetitive DNA can be found at each end of a LTR retrotransposon. These are termed long terminal repeats (LTRs) that are each a few hundred base pairs long, hence retrotransposons with LTRs have the name long terminal repeat (LTR) retrotransposon. LTR retrotransposons are over 5 kilobases long. Between the long terminal repeats there are genes that can be transcribed equivalent to retrovirus genes gag and pol. These genes overlap so they encode a protease that processes the resulting transcript into functional gene products. Gag gene products associate with other retrotransposon transcripts to form virus-like particles. Pol gene products include enzymes reverse transcriptase, integrase and ribonuclease H domains. Reverse transcriptase carries out reverse transcription of retrotransposon DNA. Integrase integrates retrotransposon DNA into eukaryotic genome DNA. Ribonuclease cleaves phosphodiester bonds between RNA nucleotides.
LTR retrotransposons encode transcripts with tRNA binding sites so that they can undergo reverse transcription. The tRNA-bound RNA transcript binds to a genomic RNA sequence. Template strand of retrotransposon DNA can hence be synthesised. Ribonuclease H domains degrade eukaryotic genomic RNA to give adenine- and guanine-rich DNA sequences that flag where the complementary noncoding strand has to be synthesised. Integrase then integrates the retrotransposon into eukaryotic DNA using the hydroxyl group at the start of retrotransposon DNA. This results in a retrotransposon flagged by long terminal repeats at its ends. Because the retrotransposon contains eukaryotic genome information it can insert copies of itself into other genomic locations within a eukaryotic cell. | 1 | Biochemistry |
In photosynthesis, singlet oxygen can be produced from the light-harvesting chlorophyll molecules. One of the roles of carotenoids in photosynthetic systems is to prevent damage caused by produced singlet oxygen by either removing excess light energy from chlorophyll molecules or quenching the singlet oxygen molecules directly.
In mammalian biology, singlet oxygen is one of the reactive oxygen species, which is linked to oxidation of LDL cholesterol and resultant cardiovascular effects. Polyphenol antioxidants can scavenge and reduce concentrations of reactive oxygen species and may prevent such deleterious oxidative effects.
Ingestion of pigments capable of producing singlet oxygen with activation by light can produce severe photosensitivity of skin (see phototoxicity, photosensitivity in humans, photodermatitis, phytophotodermatitis). This is especially a concern in herbivorous animals (see Photosensitivity in animals).
Singlet oxygen is the active species in photodynamic therapy. | 7 | Physical Chemistry |
While the bays salinity is ideal for oysters and the oyster fishery was at one time the bays most commercially viable, the population has in the last fifty years been devastated. Maryland once had roughly of oyster reefs. In 2008 there were about . It has been estimated that in pre-colonial times, oysters could filter the entirety of the bay in about 3.3 days; by 1988 this time had increased to 325 days. The harvest's gross value decreased 88% from 1982 to 2007. One report suggested the bay had fewer oysters in 2008 than 25 years earlier.
The primary problem is overharvesting. Lax government regulations allow anyone with a license to remove oysters from state-owned beds, and although limits are set, they are not strongly enforced. The overharvesting of oysters has made it difficult for them to reproduce, which requires close proximity to one another. A second cause for the oyster depletion is that the drastic increase in human population caused a sharp increase in pollution flowing into the bay. The bay's oyster industry has also suffered from two diseases: MSX and Dermo.
The depletion of oysters has had a particularly harmful effect on the quality of the bay. Oysters serve as natural water filters, and their decline has further reduced the water quality of the bay. Water that was once clear for meters is now so turbid that a wader may lose sight of his feet while his knees are still dry. | 2 | Environmental Chemistry |
Cymene describes organic compounds with the formula . Three isomers exist: 1,2- 1,3-, and 1,4-. All are colorless liquids, immiscible in water, with similar boiling points. They are classified are aromatic hydrocarbons. The bearing two substituents: an isopropyl () group and a methyl group. | 0 | Organic Chemistry |
A melanotroph (or melanotrope) is a cell in the pituitary gland that generates melanocyte-stimulating hormone (α‐MSH) from its precursor pro-opiomelanocortin. Chronic stress can induce the secretion of α‐MSH in melanotrophs and lead to their subsequent degeneration. | 1 | Biochemistry |
Thiocarboxylic acids (RC(O)SH) and dithiocarboxylic acids (RC(S)SH) are well known. They are structurally similar to carboxylic acids but more acidic. Thioamides are analogous to amides. | 9 | Geochemistry |
In general, the luminous intensity of a point on a surface varies by direction; for a Lambertian surface, that distribution is defined by the cosine law, with peak luminous intensity in the normal direction. Thus when the Lambertian assumption holds, we can calculate the total luminous flux, , from the peak luminous intensity, , by integrating the cosine law:
and so
where is the determinant of the Jacobian matrix for the unit sphere, and realizing that is luminous flux per steradian. Similarly, the peak intensity will be of the total radiated luminous flux. For Lambertian surfaces, the same factor of relates luminance to luminous emittance, radiant intensity to radiant flux, and radiance to radiant emittance. Radians and steradians are, of course, dimensionless and so "rad" and "sr" are included only for clarity.
Example: A surface with a luminance of say 100 cd/m (= 100 nits, typical PC monitor) will, if it is a perfect Lambert emitter, have a luminous emittance of 100π lm/m. If its area is 0.1 m (~19" monitor) then the total light emitted, or luminous flux, would thus be 31.4 lm. | 7 | Physical Chemistry |
Siddiquis first breakthrough in research came when he successfully isolated an antiarrhythmic agent in 1931 from the roots of Rauvolfia serpentina. He named the newly discovered chemical compound as Ajmaline, after his mentor Hakim Ajmal Khan who was one of the illustrious practitioners of Unani system of medicine in South Asia. Later on, Siddiqui also extracted other alkaloids from Rauvolfia serpentina that included Ajmalinine, Ajmalicine (CHNO), Isoajmaline, Neoajmaline, Serpentine and Serpentinine'. Many of these are still used worldwide for treatment of mental disorders and cardiovascular ailments, especially as antiarrhythmic agents in Brugada syndrome. | 0 | Organic Chemistry |
Interplanetary contamination occurs when a planetary body is biologically contaminated by a space probe or spacecraft, either deliberately or unintentionally. This can work both on arrival to the foreign planetary body and upon return to Earth. | 9 | Geochemistry |
The first explanation of the attraction between noble gas atoms was given by Fritz London in 1930. He used a quantum-mechanical theory based on second-order perturbation theory. The perturbation is because of the Coulomb interaction between the electrons and nuclei of the two moieties (atoms or molecules). The second-order perturbation expression of the interaction energy contains a sum over states. The states appearing in this sum are simple products of the stimulated electronic states of the monomers. Thus, no intermolecular antisymmetrization of the electronic states is included, and the Pauli exclusion principle is only partially satisfied.
London wrote a Taylor series expansion of the perturbation in , where is the distance between the nuclear centers of mass of the moieties.
This expansion is known as the multipole expansion because the terms in this series can be regarded as energies of two interacting multipoles, one on each monomer. Substitution of the multipole-expanded form of V into the second-order energy yields an expression that resembles an expression describing the interaction between instantaneous multipoles (see the qualitative description above). Additionally, an approximation, named after Albrecht Unsöld, must be introduced in order to obtain a description of London dispersion in terms of polarizability volumes, , and ionization energies, , (ancient term: ionization potentials).
In this manner, the following approximation is obtained for the dispersion interaction between two atoms and . Here and are the polarizability volumes of the respective atoms. The quantities and are the first ionization energies of the atoms, and is the intermolecular distance.
Note that this final London equation does not contain instantaneous dipoles (see molecular dipoles). The "explanation" of the dispersion force as the interaction between two such dipoles was invented after London arrived at the proper quantum mechanical theory. The authoritative work contains a criticism of the instantaneous dipole model and a modern and thorough exposition of the theory of intermolecular forces.
The London theory has much similarity to the quantum mechanical theory of light dispersion, which is why London coined the phrase "dispersion effect". In physics, the term "dispersion" describes the variation of a quantity with frequency, which is the fluctuation of the electrons in the case of the London dispersion. | 6 | Supramolecular Chemistry |
Sodium methylsulfinylmethylide (also called NaDMSO or dimsyl sodium) is the sodium salt of the conjugate base of dimethyl sulfoxide. This unusual salt has some uses in organic chemistry as a base and nucleophile.
Since the first publication in 1965 by Corey et al., a number of additional uses for this reagent have been identified. | 0 | Organic Chemistry |
All SK channels can be pharmacologically blocked by quaternary ammonium salts of a plant-derived neurotoxin bicuculline. In addition, SK channels (SK1-SK3) but not SK4 (IK) are sensitive to blockade by the bee toxin apamin, and the scorpion venoms tamapin and charybdotoxin (ChTx), all via competitive antagonism for access to the mouth of the pore formation. All known blockers compete for roughly the same binding site, the pore, in all subtypes. This provides a physical blockage to the channel pore. Since all blockers are universal to all three types of SK channels, there is an incredibly narrow therapeutic window that does not allow for blocking of a specific SK channel subtype. Quaternary ammonium salts like bicuculline and tetraethylammonium (TEA) enter the pore via the selectivity filter by acting as a potassium mimic in the dehydration step of pore permeation.
The following molecules are other toxins and organic compounds that also inhibit all three small SK channel subtypes to any (even minimal) degree:
*Dequalinium
*d-Tubocurarine
*UCL-1684
*UCL-1848
*Cyproheptadine
*Fluoxetine, the active ingredient in Prozac
*NS8593
*Scyllatoxin (Leiurotoxin-I)
*Lei-Dab7
*N-methyl-laudanosine
*N-Me-bicuculline
*Pancuronium
*Atracurium
*1-ethyl-1H-benzo[d]imidazol-2(3H)-on
*6,7-dichloro-3-(hydroxyimino)indolin-2-one
*N-cyclohexyl-2-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylpyrimidin-4-amine
*(R)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1H-benzo[d]imidazol-2-amine | 1 | Biochemistry |
DIC has largely replaced the older oblique illumination (OI) technique, which was available on reflected light microscopes prior to about 1975. In OI, the vertical illuminator is offset from perpendicular, producing shading effects that reveal height differences. This procedure reduces resolution and yields uneven illumination across the field of view. Nevertheless, OI was useful when people needed to know if a second phase particle was standing above or was recessed below the plane-of-polish, and is still available on a few microscopes. OI can be created on any microscope by placing a piece of paper under one corner of the mount so that the plane-of-polish is no longer perpendicular to the optical axis. | 8 | Metallurgy |
Acetals, imines, and enamines can be converted back into ketones by treatment with excess water under acid-catalyzed conditions: ; ; . | 7 | Physical Chemistry |
One of the major potential applications of aluminum-based nanogalvanic alloys is hydrogen production for fuel cells. Due to their high energy efficiency, non-toxic nature, and transportation ease, the alloy powders have also been considered as an alternative energy source for batteries (when coupled with fuel cells) during reconnaissance for soldiers on the battlefield. Additionally, the alloy powder may also be 3D-printed into self-cannibalizing drone components that could recharge the drone's hydrogen supply by making contact with water whenever it runs low on power. ARL researchers also discovered that the hydrogen generation rate increases by almost two-fold when the aluminum based nanogalvanic alloy powder comes in contact with urine, when compared with pure water. Because of this unique property, scientists have considered applying the aluminum powder in austere environments where power and water are scarce, such as deserts or space, where urine could be repurposed as a fuel source. | 2 | Environmental Chemistry |
In humans, anandamide is biosynthesized from N-arachidonoyl phosphatidylethanolamine (NAPE). In turn, NAPE arises by transfer of arachidonic acid from lecithin to the free amine of cephalin through an N-acyltransferase enzyme. Anandamide synthesis from NAPE occurs via multiple pathways and includes enzymes such as phospholipase A2, phospholipase C and N-acetylphosphatidylethanolamine-hydrolysing phospholipase D (NAPE-PLD).
The crystal structure of NAPE-PLD in complex with phosphatidylethanolamine and deoxycholate shows how the cannabinoid anandamide is generated from membrane N-acylphosphatidylethanolamines (NAPEs), and reveals that bile acids – which are mainly involved in the absorption of lipids in the small intestine – modulate its biogenesis.
Endogenous anandamide is present at very low levels and has a very short half-life due to the action of the enzyme fatty acid amide hydrolase (FAAH), which breaks it down into free arachidonic acid and ethanolamine. Studies of piglets show that dietary levels of arachidonic acid and other essential fatty acids affect the levels of anandamide and other endocannabinoids in the brain. High fat diet feeding in mice increases levels of anandamide in the liver and increases lipogenesis. Anandamide may be relevant to the development of obesity, at least in rodents.
Paracetamol (called acetaminophen in the US and Canada) is metabolically combined with arachidonic acid by FAAH to form AM404. This metabolite of paracetamol is a potent agonist at the TRPV1 vanilloid receptor, a weak agonist at both CB and CB receptors, and an inhibitor of anandamide reuptake. As a result, anandamide levels in the body and brain are elevated. In this fashion, paracetamol acts as a pro-drug for a cannabimimetic metabolite. This action may be partially or fully responsible for the analgesic effects of paracetamol.
Endocannabinoid transporters for anandamide and 2-arachidonoylglycerol include the heat shock proteins (Hsp70s) and fatty acid binding proteins (FABPs).
It is found that anandamide prefers cholesterol and ceramide more than other membrane lipids, and cholesterol can behave as a binding partner for it, and following an initial interaction mediated by the establishment of a hydrogen bond, the endocannabinoid is attracted towards the membrane interior, where it forms a molecular complex with cholesterol after a functional conformation adaptation to the apolar membrane milieu, and from there, the complex is further directed to the cannabinoid receptor (CB1) and out. | 1 | Biochemistry |
MVR is thought to affect signal strength in postsynaptic neurons that typically have low receptor occupancy; this number can vary widely throughout the nervous system. This means that for however many receptors are found on a postsynaptic cell in the area of presynaptic cell vesicle release, only a small number of them would typically be occupied by neurotransmitter released from one vesicle (each vesicle can contain up to approximately 10,000 molecules of neurotransmitter). MVR increases the likelihood that an action potential in a presynaptic cell will result in a postsynaptic cell chance in action potential likelihood. This could be either more or fewer action potentials, depending upon if the neurotransmitter / receptor combo is excitatory or inhibitory. | 1 | Biochemistry |
Expression in various retinal cell types can be determined by the promoter sequence. In order to restrict expression to a specific cell type, a tissue-specific or cell-type specific promoter can be used.
For example, in rats the murine rhodopsin gene drive the expression in AAV2, GFP reporter product was found only in rat photoreceptors, not in any other retinal cell type or in the adjacent RPE after subretinal injection. On the other hand, if ubiquitously expressed immediate-early cytomegalovirus (CMV) enhancer-promoter is expressed in a wide variety of transfected cell types. Other ubiquitous promoters such as the CBA promoter, a fusion of the chicken-actin promoter and CMV immediate-early enhancer, allows stable GFP reporter expression in both RPE and photoreceptor cells after subretinal injections. | 1 | Biochemistry |
In 2000, EPA drafted plans to phase out the use of MTBE nationwide over four years.. Some states enacted MTBE prohibitions without waiting for federal restrictions. California banned MTBE as a gasoline additive in 2002. The State of New York banned the use of MTBE as a "fuel additive", effective in 2004. MTBE use is still legal in the state for other industrial uses.
The federal Energy Policy Act of 2005 removed the oxygenate requirement for reformulated gasoline and established a renewable fuel standard. The lack of MTBE liability protection in the law also prompted refiners to substitute ethanol for MTBE as a gasoline additive. | 2 | Environmental Chemistry |
In molecular spectroscopy, the Birge–Sponer method or Birge–Sponer plot is a way to calculate the dissociation energy of a molecule. By observing transitions between as many vibrational energy levels as possible, for example through electronic or infrared spectroscopy, the difference between the energy levels, can be calculated. This sum will have a maximum at , representing the point of bond dissociation; summing over all the differences up to this point gives the total energy required to dissociate the molecule, i.e. to promote it from the ground state to an unbound state. This can be written:
where is the dissociation energy. If a Morse potential is assumed, plotting against should give a straight line, from which it is easy to extract from the intercept with the x-axis. In practice, such plots often give curves because of unaccounted anharmonicity in the potential; furthermore, the low population of the higher states (or the Franck–Condon principle) makes it difficult to experimentally obtain data at high values of . Thus the extrapolation can be inaccurate and only an upper limit for the value of the dissociation energy can be obtained.
This method takes its name from Raymond Thayer Birge and Hertha Sponer, the two physical chemists that developed it.
A detailed example may be found here. | 7 | Physical Chemistry |
The Gibbs–Thomson equation may be written in a compact form:
where the Gibbs–Thomson coefficient assumes different values for different liquids and different interfacial geometries (spherical/cylindrical/planar).
In more detail:,
where:
* is a geometric constant dependent on the interfacial shape,
* is a constant involving parameters specific to the crystalline solid of solid–liquid system, and
* is an interfacial energy term. | 7 | Physical Chemistry |
Several GC–MS systems have left earth. Two were brought to Mars by the Viking program. Venera 11 and 12 and Pioneer Venus analysed the atmosphere of Venus with GC–MS. The Huygens probe of the Cassini–Huygens mission landed one GC–MS on Saturns largest moon, Titan. The MSL Curiosity rovers Sample analysis at Mars (SAM) instrument contains both a gas chromatograph and quadrupole mass spectrometer that can be used in tandem as a GC–MS. The material in the comet 67P/Churyumov–Gerasimenko was analysed by the Rosetta mission with a chiral GC–MS in 2014. | 3 | Analytical Chemistry |
Radiation is produced owing to the spontaneous transition of an excimer molecule from an excited electronic state to the ground state. Excimer and exciplex molecules are not long-living formations. They rapidly decompose, typically within a few nanoseconds, releasing their excitation energy in the form of a UV photon:
: emission by an excimer molecule:
: emission by an exciplex molecule:
where Rg* is an excimer molecule, RgX* is an exciplex molecule, Rg is an atom of rare gas, and X is an atom of halogen. | 5 | Photochemistry |
Ethanol (CHOH) is not an essential nutrient, but it does supply approximately of food energy per gram. For spirits (vodka, gin, rum, etc.) a standard serving in the United States is , which at 40%ethanol (80proof) would be 14 grams and . At 50%alcohol, 17.5 g and . Wine and beer contain a similar amount of ethanol in servings of , respectively, but these beverages also contribute to food energy intake from components other than ethanol. A serving of wine contains . A serving of beer contains . According to the U.S. Department of Agriculture, based on NHANES 2013–2014 surveys, women ages 20 and up consume on average 6.8grams of alcohol per day and men consume on average 15.5 grams per day. Ignoring the non-alcohol contribution of those beverages, the average ethanol contributions to daily food energy intake are , respectively. Alcoholic beverages are considered empty calorie foods because, while providing energy, they contribute no essential nutrients.
By definition, phytochemicals include all nutritional and non-nutritional components of edible plants. Included as nutritional constituents are provitamin A carotenoids, whereas those without nutrient status are diverse polyphenols, flavonoids, resveratrol, and lignans that are present in numerous plant foods. Some phytochemical compounds are under preliminary research for their potential effects on human diseases and health. However, the qualification for nutrient status of compounds with poorly defined properties in vivo is that they must first be defined with a Dietary Reference Intake level to enable accurate food labeling, a condition not established for most phytochemicals that are claimed to be antioxidant nutrients. | 9 | Geochemistry |
Methylene blue is a formal derivative of phenothiazine. It is a dark green powder that yields a blue solution in water. The hydrated form has 3 molecules of water per unit of methylene blue. | 3 | Analytical Chemistry |
Common donors in oligosaccharide synthesis are glycosyl halides, glycosyl acetates, thioglycosides, trichloroacetimidates, pentenyl glycosides, and glycals. Of all these donors, glycosyl halides are classic donors, which played a historical role in the development of glycosylation reactions. Thioglycoside and trichloroacetimidate donors are used more than others in contemporary glycosylation methods. When it comes to the trichloroacetimidate method, one of the advantages is that there is no need to introduce heavy metal reagents in the activation process. Moreover, using different bases can selectively lead to different anomeric configurations. (Scheme 2) As to the thioglycosides, the greatest strength is that they can offer temporary protection to the anomeric centre because they can survive after most of the activation processes. Additionally, a variety of activation methods can be employed, such as NIS/ AgOTf, NIS/ TfOH, IDCP (Iodine Dicollidine Perchlorate), iodine, and PhSO/ TfO. Furthermore, in the preparation of 1, 2-trans glycosidic linkage, using thioglycosides and imidates can promote the rearrangement of the orthoester byproducts, since the reaction mixtures are acidic enough. | 0 | Organic Chemistry |
The van der Waals volume, V, also called the atomic volume or molecular volume, is the atomic property most directly related to the van der Waals radius. It is the volume "occupied" by an individual atom (or molecule).
The van der Waals volume may be calculated if the van der Waals radii (and, for molecules, the inter-atomic distances, and angles) are known. For a single atom, it is the volume of a sphere whose radius is the van der Waals radius of the atom:
For a molecule, it is the volume enclosed by the van der Waals surface.
The van der Waals volume of a molecule is always smaller than the sum of the van der Waals volumes of the constituent atoms: the atoms can be said to "overlap" when they form chemical bonds.
The van der Waals volume of an atom or molecule may also be determined by experimental measurements on gases, notably from the van der Waals constant b, the polarizability α, or the molar refractivity A.
In all three cases, measurements are made on macroscopic samples and it is normal to express the results as molar quantities.
To find the van der Waals volume of a single atom or molecule, it is necessary to divide by the Avogadro constant N.
The molar van der Waals volume should not be confused with the molar volume of the substance.
In general, at normal laboratory temperatures and pressures, the atoms or molecules of gas only occupy about of the volume of the gas, the rest is empty space.
Hence the molar van der Waals volume, which only counts the volume occupied by the atoms or molecules, is usually about times smaller than the molar volume for a gas at standard temperature and pressure. | 6 | Supramolecular Chemistry |
The Phage-ligand technology is a technology to detect, bind and remove bacteria and bacterial toxins by using highly specific bacteriophage derived proteins. | 1 | Biochemistry |
The Management Committee is responsible for the general management of the IIR in between Executive Committee meetings. It includes:
* the President of the Executive Committee
* three members elected every four years by the Executive Committee
* three members elected every four years by the Science and Technology Council | 7 | Physical Chemistry |
A fundamental flaw of transition state theory is that it counts any crossing of the transition state as a reaction from reactants to products or vice versa. In reality, a molecule may cross this "dividing surface" and turn around, or cross multiple times and only truly react once. As such, unadjusted TST is said to provide an upper bound for the rate coefficients. To correct for this, variational transition state theory varies the location of the dividing surface that defines a successful reaction in order to minimize the rate for each fixed energy. The rate expressions obtained in this microcanonical treatment can be integrated over the energy, taking into account the statistical distribution over energy states, so as to give the canonical, or thermal rates. | 7 | Physical Chemistry |
Eoxin D4, also known as 14,15-leukotriene D4, is an eoxin. Cells make eoxins by metabolizing arachidonic acid with a 15-lipoxygenase enzyme to form 15(S)-hydroperoxyeicosapentaenoic acid (i.e. 15(S)-HpETE). This product is then converted serially to eoxin A4 (i.e. EXA4), EXC4, EXD4, and EXE4 by LTC4 synthase, an unidentified gamma-glutamyltransferase, and an unidentified dipeptidase, respectively, in a pathway which appears similar if not identical to the pathway which forms leukotreines, i.e. LTA4, LTC4, LTD4, and LTE4. This pathway is schematically shown as follows:
EXA is viewed as an intracellular-bound, short-lived intermediate which is rapidly metabolized to the down-stream eoxins. The eoxins down stream of EXA4 are secreted from their parent cells and, it is proposed but not yet proven, serve to regulate allergic responses and the development of certain cancers (see Eoxins). | 1 | Biochemistry |
Hydrogen bonding is of persistent theoretical interest. According to a modern description integrates both the intermolecular O:H lone pair ":" nonbond and the intramolecular polar-covalent bond associated with repulsive coupling.
Quantum chemical calculations of the relevant interresidue potential constants (compliance constants) revealed large differences between individual H bonds of the same type. For example, the central interresidue hydrogen bond between guanine and cytosine is much stronger in comparison to the bond between the adenine-thymine pair.
Theoretically, the bond strength of the hydrogen bonds can be assessed using NCI index, non-covalent interactions index, which allows a visualization of these non-covalent interactions, as its name indicates, using the electron density of the system.
Interpretations of the anisotropies in the Compton profile of ordinary ice claim that the hydrogen bond is partly covalent. However, this interpretation was challenged.
Most generally, the hydrogen bond can be viewed as a metric-dependent electrostatic scalar field between two or more intermolecular bonds. This is slightly different from the intramolecular bound states of, for example, covalent or ionic bonds. However, hydrogen bonding is generally still a bound state phenomenon, since the interaction energy has a net negative sum. The initial theory of hydrogen bonding proposed by Linus Pauling suggested that the hydrogen bonds had a partial covalent nature. This interpretation remained controversial until NMR techniques demonstrated information transfer between hydrogen-bonded nuclei, a feat that would only be possible if the hydrogen bond contained some covalent character. | 6 | Supramolecular Chemistry |
Antifreeze glycoproteins or AFGPs are found in Antarctic notothenioids and northern cod. They are 2.6-3.3 kD. AFGPs evolved separately in notothenioids and northern cod. In notothenioids, the AFGP gene arose from an ancestral trypsinogen-like serine protease gene.
*Type I AFP is found in winter flounder, longhorn sculpin and shorthorn sculpin. It is the best documented AFP because it was the first to have its three-dimensional structure determined. Type I AFP consists of a single, long, amphipathic alpha helix, about 3.3-4.5 kD in size. There are three faces to the 3D structure: the hydrophobic, hydrophilic, and Thr-Asx face.
**Type I-hyp AFP (where hyp stands for hyperactive) are found in several righteye flounders. It is approximately 32 kD (two 17 kD dimeric molecules). The protein was isolated from the blood plasma of winter flounder. It is considerably better at depressing freezing temperature than most fish AFPs. The ability is partially derived from its many repeats of the Type I ice-binding site.
*Type II AFPs (e.g. ) are found in sea raven, smelt and herring. They are cysteine-rich globular proteins containing five disulfide bonds. Type II AFPs likely evolved from calcium dependent (c-type) lectins. Sea ravens, smelt, and herring are quite divergent lineages of teleost. If the AFP gene were present in the most recent common ancestor of these lineages, it is peculiar that the gene is scattered throughout those lineages, present in some orders and absent in others. It has been suggested that lateral gene transfer could be attributed to this discrepancy, such that the smelt acquired the type II AFP gene from the herring.
*Type III AFPs are found in Antarctic eelpout. They exhibit similar overall hydrophobicity at ice binding surfaces to type I AFPs. They are approximately 6kD in size. Type III AFPs likely evolved from a sialic acid synthase (SAS) gene present in Antarctic eelpout. Through a gene duplication event, this gene—which has been shown to exhibit some ice-binding activity of its own—evolved into an effective AFP gene by loss of the N-terminal part.
*Type IV AFPs () are found in longhorn sculpins. They are alpha helical proteins rich in glutamate and glutamine. This protein is approximately 12KDa in size and consists of a 4-helix bundle. Its only posttranslational modification is a pyroglutamate residue, a cyclized glutamine residue at its N-terminus. | 1 | Biochemistry |
When World War II ended with the use of atomic weapons which had been developed in secret by the Manhattan Project, Hecht was concerned that the American public was uninformed about the development of this new source of energy. He wrote a book Explaining the Atom (1947), to educate the public. He wrote,
:So long as one supposes this business is mysterious and secret, one cannot have a just evaluation of our possessions and security. Only by understanding the basis and development of atomic energy can one judge the legislation and foreign policy that concern it.
In a review in the New York Times (4/27/1947), Stephen Wheeler wrote that it was "by all odds the best book on atomic energy so far to be published for the ordinary reader." Similarly, James J. Jelinek wrote that it was an "invaluable contribution to the layman." He credits Hecht with "conveying to the layman the intellectual drama" of the development. Jelinek asserts that the book is "profoundly provocative in its political and sociological implications."
After Hecht died, a second edition was issued in 1959 by Eugene Rabinowitch. Both editions were recommended by George Gamow. | 5 | Photochemistry |
The study of the tumor metabolism, also known as tumor metabolome describes the different characteristic metabolic changes in tumor cells. The characteristic attributes of the tumor metabolome are high glycolytic enzyme activities, the expression of the pyruvate kinase isoenzyme type M2, increased channeling of glucose carbons into synthetic processes, such as nucleic acid, amino acid and phospholipid synthesis, a high rate of pyrimidine and purine de novo synthesis, a low ratio of Adenosine triphosphate and Guanosine triphosphate to Cytidine triphosphate and Uridine triphosphate, low Adenosine monophosphate levels, high glutaminolytic capacities, release of immunosuppressive substances and dependency on methionine.
Although the link between the cancer and metabolism was observed in the early days of cancer research by Otto Heinrich Warburg, which is also known as Warburg hypothesis, not much substantial research was carried out until the late 1990s because of the lack of in vitro tumor models and the difficulty in creating environments that lack oxygen. Recent research has revealed that metabolic reprogramming occurs as a consequence of mutations in cancer genes and alterations in cellular signaling. Therefore, the alteration of cellular and energy metabolism has been suggested as one of The Hallmarks of Cancer. | 1 | Biochemistry |
Various methods have been proposed to achieve the suitable alignment of monomers in the crystal. These methods can be divided into two categories:
An obvious method is to introduce supramolecular interactions to the monomer. Popular choices include π - π stacking interactions, hydrogen/halogen bonding interactions, and Coulomb interactions. These interactions are sometimes inherent properties of reaction groups, such as π-π interaction between azide and acetylene group, or stacking force between biphenylethylene unit. Sometimes the side groups are introduced to form a network within the crystal.
The other strategy is to take advantage of the so-called "host-guest" assembly. In this case, the monomer is designed to link to a "host" molecule, while the host molecule is in charge of forming the ordered network. The host molecule stays intact during the polymerization. Such strategies simplify the synthesis of monomer. | 7 | Physical Chemistry |
It is well known that at low temperature many metals become superconductors. A metal can be viewed in part as a Fermi liquid of electrons, and below a critical temperature, an attractive phonon-mediated interaction between the electrons near the Fermi surface causes them to pair up and form a condensate of Cooper pairs, which via the Anderson–Higgs mechanism makes the photon massive, leading to characteristic behaviors of a superconductor: infinite conductivity and the exclusion of magnetic fields (Meissner effect). The crucial ingredients for this to occur are:
# a liquid of charged fermions.
# an attractive interaction between the fermions
# low temperature (below the critical temperature)
These ingredients are also present in sufficiently dense quark matter, leading physicists to expect that something similar will happen in that context:
# quarks carry both electric charge and color charge;
# the strong interaction between two quarks is powerfully attractive;
# the critical temperature is expected to be given by the QCD scale, which is of order 100 MeV, or 10 kelvins, the temperature of the universe a few minutes after the Big Bang, so quark matter that we may currently observe in compact stars or other natural settings will be below this temperature.
The fact that a Cooper pair of quarks carries a net color charge, as well as a net electric charge, means that some of the gluons (which mediate the strong interaction just as photons mediate electromagnetism) become massive in a phase with a condensate of quark Cooper pairs, so such a phase is called a "color superconductor". Actually, in many color superconducting phases the photon itself does not become massive, but mixes with one of the gluons to yield a new massless "rotated photon". This is an MeV-scale echo of the mixing of the hypercharge and W bosons that originally yielded the photon at the TeV scale of electroweak symmetry breaking. | 7 | Physical Chemistry |
According to Frankel (1998) who performed a review on pitting corrosion, it develops in three successive steps: (or nucleation) by breakdown of the passive film protecting the metal surface from oxidation, (2) growth of metastable pits (growing up to the micron scale and then repassivating), and (3) the growth of larger and stable pits.
The evolution of the pit density (number of pits per surface area) as a function of time follows a sigmoid curve with the characteristic shape of a logistic function curve, or a hyperbolic tangent. Guo et al. (2018), after a statistical analysis of hundreds of individual pits observed on carbon steel surfaces at the nano-to-micro- scales, distinguish three stages of pitting corrosion: induction, propagation, and saturation. | 8 | Metallurgy |
The internal energy is given by the energetic equation of state,
where is an arbitrary constant of integration.
Now in order for to be an exact differential, namely that be continuous with continuous partial derivatives, its second mixed partial derivatives must also be equal, . Then with this condition can be written simply as . Differentiating for the vdW equation gives , so . Consequently for a vdW fluid exactly as it is for an ideal gas. To keep things simple it is regarded as a constant here, with a number. Then both integrals can be easily evaluated and the result is
This is the energetic equation of state for a perfect vdW fluid. By making a dimensional analysis (what might be called extending the principle of corresponding states to other thermodynamic properties) it can be written simply in reduced form as
where and C is a dimensionless constant. | 7 | Physical Chemistry |
Nebulized meropenem (inhaled route) is researched, but is not approved, for prevention of bronchiectasis exacerbation. | 4 | Stereochemistry |
siRNAs have been chemically modified to enhance their therapeutic properties, Short interfering RNA (siRNA) must be delivered to the site of action in the cells of target tissues in order for RNAi to fulfill its therapeutic promise. A detailed database of all such chemical modifications is manually curated as [http://crdd.osdd.net/servers/sirnamod siRNAmod] in scientific literature. Chemical modification of siRNA can also inadvertently result in loss of single-nucleotide specificity. | 1 | Biochemistry |
Firefly luciferin is the luciferin found in many Lampyridae species. It is the substrate of beetle luciferases (EC 1.13.12.7) responsible for the characteristic yellow light emission from fireflies, though can cross-react to produce light with related enzymes from non-luminous species. The chemistry is unusual, as adenosine triphosphate (ATP) is required for light emission, in addition to molecular oxygen. | 1 | Biochemistry |
The major source of hydrogen is methane. Steam reforming extracts hydrogen from methane in a high-temperature and pressure tube inside a reformer with a nickel catalyst. Other fossil fuel sources include coal, heavy fuel oil and naphtha.
Green hydrogen is produced without fossil fuels or carbon dioxide emissions from biomass, water electrolysis and thermochemical (solar or another heat source) water splitting. However, these hydrogen sources are not economically competitive with steam reforming.
Starting with a natural gas () feedstock, the steps are as follows;
* Remove sulfur compounds from the feedstock, because sulfur deactivates the catalysts used in subsequent steps. Sulfur removal requires catalytic hydrogenation to convert sulfur compounds in the feedstocks to gaseous hydrogen sulfide (hydrodesulfurization, hydrotreating):
* Hydrogen sulfide is adsorbed and removed by passing it through beds of zinc oxide where it is converted to solid zinc sulfide:
* Catalytic steam reforming of the sulfur-free feedstock forms hydrogen plus carbon monoxide:
* Catalytic shift conversion converts the carbon monoxide to carbon dioxide and more hydrogen:
* Carbon dioxide is removed either by absorption in aqueous ethanolamine solutions or by adsorption in pressure swing adsorbers (PSA) using proprietary solid adsorption media.
* The final step in producing hydrogen is to use catalytic methanation to remove residual carbon monoxide or carbon dioxide: | 7 | Physical Chemistry |
Liver of sulfur is mainly used in metalworking to form a brown or black patina on copper and silver as well as many (though not all) copper alloys and silver alloys (brass, for example— a copper alloy— does not react with sulfur compounds). It is sold as a yellow brittle solid (a "lump" which must be mixed with water before use) as well as a pre-mixed liquid and a gel form. The solid is believed to have the longest shelf life, though all liver of sulfur tends to decompose with time. Modern gel forms contain stabilizers that allow the reactivity to last much longer. Liver of sulfur that is kept dry, sealed from air, out of the light, and in a freezer will last many times longer than that kept in any other condition.
The highest quality liver of sulfur in solid form is a dark yellow, almost "liver" colored substance. As it ages and is exposed to air, its potency decreases, it will turn lighter yellow and finally white, at which point its reactivity is negligible. Liver of sulfur decomposes to sulfate of potash and carbonate of potash, neither of which has any value as an oxidizer of metal.
The reactivity of liver of sulfur with silver and copper quickly creates a dark or colored patina on the metal. This is done by immersing the metal object in a solution of liver of sulfur and water. When treating silver, the solution must be hot, though if the bath is brought to its boiling point the liver of sulfur will quickly decompose and become ineffective. Also, if the concentration of the solution is too strong, the oxidation process will proceed too quickly and the layer of patina thus created will tend to flake away. The best results are usually obtained by using more dilute solutions and allowing the patina to build more slowly but more securely, and, for silver, keeping the solution just under its boiling point. Lastly, it is critical that the metal surface be extremely clean, as clean as would be necessary to electroplate the same surface. Even small amounts of oil on the metal such as that produced by handling without gloves will be sufficient to protect the metal surface from oxidation. | 7 | Physical Chemistry |
In selective ion monitoring (SIM) certain ion fragments are entered into the instrument method and only those mass fragments are detected by the mass spectrometer. The advantages of SIM are that the detection limit is lower since the instrument is only looking at a small number of fragments (e.g. three fragments) during each scan. More scans can take place each second. Since only a few mass fragments of interest are being monitored, matrix interferences are typically lower. To additionally confirm the likelihood of a potentially positive result, it is relatively important to be sure that the ion ratios of the various mass fragments are comparable to a known reference standard. | 3 | Analytical Chemistry |
Analysis of RFLP variation in genomes was formerly a vital tool in genome mapping and genetic disease analysis. If researchers were trying to initially determine the chromosomal location of a particular disease gene, they would analyze the DNA of members of a family afflicted by the disease, and look for RFLP alleles that show a similar pattern of inheritance as that of the disease (see genetic linkage). Once a disease gene was localized, RFLP analysis of other families could reveal who was at risk for the disease, or who was likely to be a carrier of the mutant genes. RFLP test is used in identification and differentiation of organisms by analyzing unique patterns in genome. It is also used in identification of recombination rate in the loci between restriction sites.
RFLP analysis was also the basis for early methods of genetic fingerprinting, useful in the identification of samples retrieved from crime scenes, in the determination of paternity, and in the characterization of genetic diversity or breeding patterns in animal populations. | 1 | Biochemistry |
Concomitant with the displacement of two N-H protons, porphyrins bind metal ions in the N4 "pocket". The metal ion usually has a charge of 2+ or 3+. A schematic equation for these syntheses is shown:
:Hporphyrin + [ML] → M(porphyrinate)L + 4 L + 2 H, where M = metal ion and L = a ligand | 1 | Biochemistry |
Let us assume that a particle supports only electric and magnetic dipole modes with polarizabilities and (here we use the notation of magnetic polarizability in the manner of Bekshaev et al. rather than the notation of Nieto-Vesperinas et al.) expressed through the Mie coefficients as
Then the cross sections are given by and
For the case of a no-inside-gain particle, i.e. no energy is emitted by the particle internally (), we have a particular case of the Optical theorem <math display="block">
\frac{1}{4\pi \varepsilon \varepsilon_0} \Im(\alpha^e) + \frac{1}{4\pi \mu \mu_0} \Im(\alpha^m) \geq \frac{2 k^3}{3} \left[ \frac{|\alpha^e|^2}{(4\pi \varepsilon \varepsilon_0)^2} + \frac{|\alpha^m|^2}{(4\pi \mu \mu_0)^2} \right] | 7 | Physical Chemistry |
The most common application of passive daytime radiative cooling currently is on building envelopes, including PDRC cool roofs, which can significantly lower indoor space temperatures within buildings. A PDRC roof application can double the energy savings of a white roof. This makes PDRCs a sustainable and low-cost alternative or supplement to air conditioning by decreasing energy demand, alleviating energy grids in peak periods, and reducing emissions caused by air conditioning's release of hydrofluorocarbons into the atmosphere which can be thousands of times more potent that .
Air conditioning alone accounts for 12%-15% of global energy usage, while emissions from air conditioning account for "13.7% of energy-related emissions, approximately 52.3 EJ yearly" or 10% of emissions total. Air conditioning applications are expected to rise, despite their negative impacts on energy sectors, costs, and global warming, which has been described as a "vicious cycle." However, this can be significantly reduced with the mass production of low-cost PDRCs for indoor space cooling. A multilayer PDRC surface covering 10% of a building's roof can replace 35% of air conditioning used during the hottest hours of daytime.
In suburban single-family residential areas, PDRCs can lower energy costs by 26% to 46% in the United States and lower temperatures on average by 5.1ᵒC. With the addition of "cold storage to utilize the excess cooling energy of water generated during off-peak hours, the cooling effects for indoor air during the peak-cooling-load times can be significantly enhanced" and air temperatures may be reduced by 6.6–12.7 °C.
In cities, PDRCs can result in significant energy and cost savings. In a study on US cities, Zhou et al. found that "cities in hot and arid regions can achieve high annual electricity consumption savings of >2200 kWh, while <400 kWh is attainable in colder and more humid cities," being ranked from highest to lowest by electricity consumption savings as follows: Phoenix (~2500 kWh), Las Vegas (~2250 kWh), Austin (~2100 kWh), Honolulu (~2050 kWh), Atlanta (~1500 kWh), Indianapolis (~1200 kWh), Chicago (~1150 kWh), New York City (~900 kWh), Minneapolis (~850 kWh), Boston (~750 kWh), Seattle (~350 kWh). In a study projecting energy savings for Indian cities in 2030, Mumbai and Kolkata had a lower energy savings potential, Jaisalmer, Varansai, and Delhi had a higher potential, although with significant variations from April to August dependent on humidity and wind cover.
The growing interest and rise in PDRC application to buildings has been attributed to cost savings related to "the sheer magnitude of the global building surface area, with a market size of ~$27 billion in 2025," as estimated in a 2020 study. | 7 | Physical Chemistry |
The phase diagram of quark matter is not well known, either experimentally or theoretically. A commonly conjectured form of the
phase diagram is shown in the figure to the right. It is applicable to matter in a compact star, where the only relevant thermodynamic potentials are quark chemical potential μ and temperature T.
For guidance it also shows the typical values of μ and T in heavy-ion collisions and in the early universe. For readers who are not familiar with the concept of a chemical potential, it is helpful to think of μ as a measure of the imbalance between quarks and antiquarks in the system. Higher μ means a stronger bias favoring quarks over antiquarks. At low temperatures there are no antiquarks, and then higher μ generally means a higher density of quarks.
Ordinary atomic matter as we know it is really a mixed phase, droplets of nuclear matter (nuclei) surrounded by vacuum, which exists at the low-temperature phase boundary between vacuum and nuclear matter, at μ = 310 MeV and T close to zero. If we increase the quark density (i.e. increase μ) keeping the temperature low, we move into a phase of more and more compressed nuclear matter. Following this path corresponds to burrowing more and more deeply into a neutron star.
Eventually, at an unknown critical value of μ, there is a transition to quark matter. At ultra-high densities we expect to find the color-flavor-locked (CFL) phase of color-superconducting quark matter. At intermediate densities we expect some other phases (labelled "non-CFL quark liquid" in the figure) whose nature is presently unknown. They might be other forms of color-superconducting quark matter, or something different.
Now, imagine starting at the bottom left corner of the phase diagram, in the vacuum where μ = T = 0. If we heat up the system without introducing any preference for quarks over antiquarks, this corresponds to moving vertically upwards along the T axis. At first, quarks are still confined and we create a gas of hadrons (pions, mostly). Then around T = 150 MeV there is a crossover to the quark gluon plasma: thermal fluctuations break up the pions, and we find a gas of quarks, antiquarks, and gluons, as well as lighter particles such as photons, electrons, positrons, etc. Following this path corresponds to travelling far back in time (so to say), to the state of the universe shortly after the big bang (where there was a very tiny preference for quarks over antiquarks).
The line that rises up from the nuclear/quark matter transition and then bends back towards the T axis, with its end marked by a star, is the conjectured boundary between confined and unconfined phases. Until recently it was also believed to be a boundary between phases where chiral symmetry is broken (low temperature and density) and phases where it is unbroken (high temperature and density). It is now known that the CFL phase exhibits chiral symmetry breaking, and other quark matter phases may also break chiral symmetry, so it is not clear whether this is really a chiral transition line. The line ends at the "chiral critical point", marked by a star in this figure, which is a special temperature and density at which striking physical phenomena, analogous to critical opalescence, are expected. (Reference for this section:).
For a complete description of phase diagram it is required that one must have complete understanding of dense, strongly interacting hadronic matter and strongly interacting quark matter from some underlying theory e.g. quantum chromodynamics (QCD). However, because such a description requires the proper understanding of QCD in its non-perturbative regime, which is still far from being completely understood, any theoretical advance remains very challenging. | 7 | Physical Chemistry |
Chinese researchers have utilized LEAPER to restore functional enzyme activity in cells from patients with Hurler syndrome. They have claimed that LEAPER could have the potential to treat almost half of all known hereditary disorders.
Highly specific editing efficiencies of up to 80% can be achieved when LEAPER editing using arRNA151 is delivered via a plasmid or viral vector or as a synthetic oligonucleotide, though this efficiency varied significantly across cell types. Based on these preliminary results, LEAPER may have the most therapeutic promise with no production of functional protein but if a partial restoration of protein expression would provide therapeutic benefit. For example, in human cells with defective α-L-iduronidase (IDUA) expression in cells from patients with IDUA-defective Hurler syndrome, LEAPER resulted in a W53X truncation mutant of p53 being edited using arRNA151 to achieve a "normal" p53 translation and functional p53-mediated transcriptional responses. | 1 | Biochemistry |
In order to understand how life arose, knowledge is required of the chemical pathways that permit formation of the key building blocks of life under plausible prebiotic conditions. The RNA world hypothesis holds that in the primordial soup there existed free-floating pyrimidine and purine ribonucleotides, the fundamental molecules that combine in series to form RNA. Complex molecules such as RNA must have emerged from relatively small molecules whose reactivity was governed by physico-chemical processes. RNA is composed of pyrimidine and purine nucleotides, both of which are necessary for reliable information transfer, and thus natural selection and Darwinian evolution. Becker et al. showed how pyrimidine nucleosides can be synthesized from small molecules and ribose, driven solely by wet-dry cycles. | 1 | Biochemistry |
Disruption of TAD boundaries can affect the expression of nearby genes, and this can cause disease.
For example, genomic structural variants that disrupt TAD boundaries have been reported to cause developmental disorders such as human limb malformations. Additionally, several studies have provided evidence that the disruption or rearrangement of TAD boundaries can provide growth advantages to certain cancers, such as T-cell acute lymphoblastic leukemia (T-ALL), gliomas, and lung cancer. | 1 | Biochemistry |
CK1δ and CK1ε have been shown to be relevant in human disease. Recent findings indicate that pharmaceutical inhibition of CK1 may be a promising therapeutic for aberrant circadian rhythm. Mutations and variants of the CK1ε phosphorylation site of PER2 are associated with cases of Familial Advanced Sleep Phase Syndrome (FASPS). Similarly, length variations in the CK1ε phosphorylation site of PER3 have been found to correlate with morningness and eveningness; longer alleles are associated with early risers while shorter alleles are associated with late risers. Additionally, 75% of patients with Delayed sleep phase syndrome are homozygous for the shorter allele.
Mutations in CK1 have been shown to alter circadian behavior in other mammals, as well. In 1988, the golden hamster tau mutant, which has a freerunning period of 22hrs, was the first mammalian circadian mutant discovered. Twelve years later in 2000, the tau mutation was mapped to CK1ε. Since its discovery, the tau mutant has proven to be a valuable research tool in circadian biology. CK1ɛ, a T178C substitution, is a gain-of function mutation that causes an increase in degradation of PER, but not CRY. This creates a disruption in the PER-regulated feedback loop and consequently an acceleration of molecular oscillations. Homozygous mutants (CK1ε(tau/tau)) show a significant decrease in period, both in vivo (behaviorally) and in vitro (measured by firing rates of the suprachiasmatic nucleus). Recent research has also identified a link between mutations in the CK1δ gene and familial migraine and advanced sleep phase, a finding that was replicated in mice migraine models. | 1 | Biochemistry |
Examples of response elements include:
* Nuclear receptor response elements – two 6-meric repeats for dimeric binding
** Type 2 NR response elements: direct repeat RGKTCA motifs, canonically AGGTCA
*** Vitamin D response element (VDRE)
*** Retinoic acid response elements (RAREs)
*** ROR-response element
*** Thyroid hormone response element
*** Growth hormone response element (GHRE)
*** Peroxisome proliferator hormone response elements (PPREs)
** Type 1 NR response elements (typical of hormone response elements) – inverted repeat
*** estrogen response elements (EREs)
*** androgen response elements (AREs)
*** glucocorticoid response elements (GREs)
*cAMP response element (CRE)
*B recognition element
*AhR-, dioxin- or xenobiotic- responsive element
*Hypoxia-responsive elements
*Serum response element (SRE)
*Metal-responsive element (MRE)
*DNA damage response element (DRE)
*IFN-stimulated response elements (ISREs)
*[https://www.ebi.ac.uk/interpro/entry/IPR029309 Calcium-response element CaRE1]
*Antioxidant response element (ARE)
*[http://p53.iarc.fr/TargetGenes.aspx p53 response element]
*Sterol regulatory element
*Polycomb Response Elements (PREs)
*Rev response element (RRE)
*Wnt response element (WRE), core CTTTG | 1 | Biochemistry |
It is one of the most commonly used volatile anesthetic agents, particularly for outpatient anesthesia, across all ages, as well as in veterinary medicine. Together with desflurane, sevoflurane is replacing isoflurane and halothane in modern anesthesia practice. It is often administered in a mixture of nitrous oxide and oxygen. | 2 | Environmental Chemistry |
Since the emitted light can be easily detected with a luminometer, aequorin has become a useful tool in molecular biology for the measurement of intracellular Ca levels. The early successful purification of aequorin led to the first experiments involving the injection of the protein into the tissues of living animals to visualize the physiological release of calcium in the muscle fibers of a barnacle. Since then, the protein has been widely used in many model biological systems, including zebrafish, rats, mice, and cultured cells.
Cultured cells expressing the aequorin gene can effectively synthesize apoaequorin; however, recombinant expression yields only the apoprotein. Therefore it is necessary to add coelenterazine into the culture medium of the cells to obtain a functional protein and thus use its blue light emission to measure Ca concentration. Coelenterazine is a hydrophobic molecule, and therefore is easily taken up across plant and fungal cell walls, as well as the plasma membrane of higher eukaryotes, making aequorin suitable as a Ca reporter in plants, fungi, and mammalian cells.
Aequorin has a number of advantages over other Ca indicators. Because the protein is large, it has a low leakage rate from cells compared to lipophilic dyes such as DiI. It lacks phenomena of intracellular compartmentalization or sequestration as is often seen for Voltage-sensitive dyes, and does not disrupt cell functions or embryo development. Moreover, the light emitted by the oxidation of coelenterazine does not depend on any optical excitation, so problems with auto-fluorescence are eliminated. The primary limitation of aequorin is that the prosthetic group coelenterazine is irreversibly consumed to produce light, and requires continuous addition of coelenterazine into the media. Such issues led to developments of other genetically encoded calcium sensors including the calmodulin-based sensor cameleon, developed by Roger Tsien and the troponin-based sensor, TN-XXL, developed by Oliver Griesbeck. | 1 | Biochemistry |
Microbial biodegradation is the use of bioremediation and biotransformation methods to harness the naturally occurring ability of microbial xenobiotic metabolism to degrade, transform or accumulate environmental pollutants, including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), heterocyclic compounds (such as pyridine or quinoline), pharmaceutical substances, radionuclides and metals.
Interest in the microbial biodegradation of pollutants has intensified in recent years, and recent major methodological breakthroughs have enabled detailed genomic, metagenomic, proteomic, bioinformatic and other high-throughput analyses of environmentally relevant microorganisms, providing new insights into biodegradative pathways and the ability of organisms to adapt to changing environmental conditions.
Biological processes play a major role in the removal of contaminants and take advantage of the catabolic versatility of microorganisms to degrade or convert such compounds. In environmental microbiology, genome-based global studies are increasing the understanding of metabolic and regulatory networks, as well as providing new information on the evolution of degradation pathways and molecular adaptation strategies to changing environmental conditions. | 2 | Environmental Chemistry |
The chief advantage over direct amperometry is that the magnitude of the measured current is of interest only as an indicator. Thus, factors that are of critical importance to quantitative amperometry, such as the surface area of the working electrode, completely disappear from amperometric titrations.
The chief advantage over other types of titration is the selectivity offered by the electrode potential, as well as by the choice of titrant. For instance, lead ion is reduced at a potential of -0.60 V (relative to the saturated calomel electrode), while zinc ions are not; this allows the determination of lead in the presence of zinc. Clearly this advantage depends entirely on the other species present in the sample. | 3 | Analytical Chemistry |
Although some control exists at the transcriptional level, the regulation of cellular iron levels is ultimately controlled at the translational level by iron-responsive element-binding proteins IRP1 and especially IRP2. When iron levels are low, these proteins are able to bind to iron-responsive elements (IREs). IREs are stem loop structures in the untranslated regions (UTRs) of mRNA.
Both ferritin and ferroportin contain an IRE in their 5 UTRs, so that under iron deficiency their translation is repressed by IRP2, preventing the unnecessary synthesis of storage protein and the detrimental export of iron. In contrast, TFR1 and some DMT1 variants contain 3 UTR IREs, which bind IRP2 under iron deficiency, stabilizing the mRNA, which guarantees the synthesis of iron importers. | 1 | Biochemistry |
Peripheral blood samples were obtained and processed to isolate plasma following standard protocols. Upon centrifugation, plasma specimens were preserved at −80 °C, awaiting the extraction of ctDNA. The extraction of cfDNA from plasma volumes ranging from 2 to 16 ml was carried out using established laboratory procedures. Following isolation, the concentration of cfDNA was determined using fluorescence-based quantification methods. | 1 | Biochemistry |
As of 2016, challenges including optimizing sample treatment, optimizing disk surfaces, developing readers that can deploy multiple colors of light delivery and sensing for multiplexing, and for clinical use, obtaining regulatory approvals. The field is similar to lab-on-a-chip platforms.
As of 2010 companies including Gyros AB, Tecan, and Burstein Technologies were working on bringing CD/DVD based immunoassays and equipment to market. | 1 | Biochemistry |
Photodynamic therapy utilizes Type II photosensitizers to harvest light to degrade tumors or cancerous masses. This discovery was first observed back in 1907 by Hermann von Tappeiner when he utilized eosin to treat skin tumors. The photodynamic process is predominantly a noninvasive technique wherein the photosensitizers are put inside a patient so that it may accumulate on the tumor or cancer. When the photosensitizer reaches the tumor or cancer, wavelength specific light is shined on the outside of the patients affected area. This light (preferably near infrared frequency as this allows for the penetration of the skin without acute toxicity) excites the photosensitizers electrons into the triplet state. Upon excitation, the photosensitizer begins transferring energy to neighboring ground state triplet oxygen to generate excited singlet oxygen. The resulting excited oxygen species then selectively degrades the tumor or cancerous mass.
In February 2019, medical scientists announced that iridium attached to albumin, creating a photosensitized molecule, can penetrate cancer cells and, after being irradiated with light (a process called photodynamic therapy), destroy the cancer cells. | 5 | Photochemistry |
In molecular biology, STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) is a biological database and web resource of known and predicted protein–protein interactions.
The STRING database contains information from numerous sources, including experimental data, computational prediction methods and public text collections. It is freely accessible and it is regularly updated. The resource also serves to highlight functional enrichments in user-provided lists of proteins, using a number of functional classification systems such as GO, Pfam and KEGG. The latest version 11b contains information on about 24,5 million proteins from more than 5000 organisms. STRING has been developed by a consortium of academic institutions including CPR, EMBL, KU, SIB, TUD and UZH. | 1 | Biochemistry |
The bis-nido- is formed by the edge-sharing condensation of a nido- unit and a nido- unit. The m + n + o + p − q count of 16 SEPs are satisfied by ten BH units which provide 10 pairs, two shared boron atoms which provide 3 pairs, and six bridging H atoms which provide 3 pairs. | 7 | Physical Chemistry |
While aerobic organisms during respiration use oxygen as a terminal electron acceptor, anaerobic organisms use other electron acceptors. These inorganic compounds release less energy in cellular respiration, which leads to slower growth rates than aerobes. Many facultative anaerobes can use either oxygen or alternative terminal electron acceptors for respiration depending on the environmental conditions.
Most respiring anaerobes are heterotrophs, although some do live autotrophically. All of the processes described below are dissimilative, meaning that they are used during energy production and not to provide nutrients for the cell (assimilative). Assimilative pathways for many forms of anaerobic respiration are also known. | 1 | Biochemistry |
The discovery of PKM2 began with laboratory observations made by Otto Heinrich Warburg, a German physiologist and Nobel Laureate in Physiology or Medicine in 1931. Warburg's experiments show that the cells exhibit dependence on glucose and are capable of fermentation, even under aerobic conditions. These observations are known as the Warburg effect. Subsequent research on the metabolic demands of cancer cells, studies have been directed towards the investigation of specific subtypes of pyruvate kinase, notably M1 and M2. | 1 | Biochemistry |
Zinc is extracted from the purified zinc sulfate solution by electrowinning, which is a specialized form of electrolysis. The process works by passing an electric current through the solution in a series of cells. This causes the zinc to deposit on the cathodes (aluminium sheets) and oxygen to form at the anodes. Sulfuric acid is also formed in the process and reused in the leaching process. Every 24 to 48 hours, each cell is shut down, the zinc-coated cathodes are removed and rinsed, and the zinc is mechanically stripped from the aluminium plates.
Electrolytic zinc smelters contain as many as several hundred cells. A portion of the electrical energy is converted into heat, which increases the temperature of the electrolyte. Electrolytic cells operate at temperature ranges from and at atmospheric pressure. A portion of the electrolyte is continuously circulated through the cooling towers both to cool and concentrate the electrolyte through evaporation of water. The cooled and concentrated electrolyte is then recycled to the cells. This process accounts for approximately one-third of all the energy usage when smelting zinc.
There are two common processes for electrowinning the metal: the low current density process, and the Tainton high current density process. The former uses a 10% sulfuric acid solution as the electrolyte, with current density of 270–325 amperes per square meter. The latter uses 22–28% sulfuric acid solution as the electrolyte with a current density of about 1,000 amperes per square metre. The latter gives better purity and has higher production capacity per volume of electrolyte, but has the disadvantage of running hotter and being more corrosive to the vessel in which it is done. In either of the electrolytic processes, each metric ton of zinc production expends about of electric power. | 8 | Metallurgy |
Diphenylchloroarsine (DA) is the organoarsenic compound with the formula (CH)AsCl. It is highly toxic and was once used in chemical warfare. It is also an intermediate in the preparation of other organoarsenic compounds. The molecule consists of a pyramidal As(III) center attached to two phenyl rings and one chloride. It was also known as sneezing oil during World War I by the Allies. | 1 | Biochemistry |
Many azo pigments are non-toxic, although some, such as dinitroaniline orange, ortho-nitroaniline orange, or pigment orange 1, 2, and 5 have been found to be mutagenic. Likewise, several case studies have linked azo pigments with basal cell carcinoma. | 0 | Organic Chemistry |
Figure 3 shows the line of contact where three phases meet. In equilibrium, the net force per unit length acting along the boundary line between the three phases must be zero. The components of net force in the direction along each of the interfaces are given by:
where α, β, and θ are the angles shown and γ is the surface energy between the two indicated phases. These relations can also be expressed by an analog to a triangle known as Neumann’s triangle, shown in Figure 4. Neumann’s triangle is consistent with the geometrical restriction that , and applying the law of sines and law of cosines to it produce relations that describe how the interfacial angles depend on the ratios of surface energies.
Because these three surface energies form the sides of a triangle, they are constrained by the triangle inequalities, γ + γ meaning that no one of the surface tensions can exceed the sum of the other two. If three fluids with surface energies that do not follow these inequalities are brought into contact, no equilibrium configuration consistent with Figure 3 will exist. | 7 | Physical Chemistry |
Octafluoropropane (CF) is the perfluorocarbon counterpart to the hydrocarbon propane. This non-flammable and non-toxic synthetic substance has applications in semiconductor production and medicine. It is also an extremely potent greenhouse gas. | 2 | Environmental Chemistry |
* The carbylamine reaction tests for primary amines
* The esterification reaction tests for the presence of alcohol and/or carboxylic acids
* The Griess test tests for organic nitrite compounds
* The 2,4-dinitrophenylhydrazine tests for carbonyl compounds
* The iodoform reaction tests for the presence of methyl ketones, or compounds which can be oxidized to methyl ketones
* The Schiff test detects aldehydes
* Tollens' reagent tests for aldehydes (known as the silver mirror test)
* The Zeisel determination tests for the presence of esters or ethers
*Lucas' reagent is used to distinguish between primary, secondary and tertiary alcohols.
* The bromine test is used to test for the presence of unsaturation and phenols. | 3 | Analytical Chemistry |
One response to added amounts of nutrients in aquatic ecosystems is the rapid growth of microscopic algae, creating an algal bloom. In freshwater ecosystems, the formation of floating algal blooms are commonly nitrogen-fixing cyanobacteria (blue-green algae). This outcome is favored when soluble nitrogen becomes limiting and phosphorus inputs remain significant. Nutrient pollution is a major cause of algal blooms and excess growth of other aquatic plants leading to overcrowding competition for sunlight, space, and oxygen. Increased competition for the added nutrients can cause potential disruption to entire ecosystems and food webs, as well as a loss of habitat, and biodiversity of species.
When overproduced macrophytes and algae die in eutrophic water, their decompose further consumes dissolved oxygen. The depleted oxygen levels in turn may lead to fish kills and a range of other effects reducing biodiversity. Nutrients may become concentrated in an anoxic zone, often in deeper waters cut off by stratification of the water column and may only be made available again during autumn turn-over in temperate areas or in conditions of turbulent flow. The dead algae and organic load carried by the water inflows into a lake settle to the bottom and undergo anaerobic digestion releasing greenhouse gases such as methane and CO. Some of the methane gas may be oxidised by anaerobic methane oxidation bacteria such as Methylococcus capsulatus, which in turn may provide a food source for zooplankton. Thus a self-sustaining biological process can take place to generate primary food source for the phytoplankton and zooplankton depending on the availability of adequate dissolved oxygen in the water body.
Enhanced growth of aquatic vegetation, phytoplankton and algal blooms disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen which is needed for fish and shellfish to survive. The growth of dense algae in surface waters can shade the deeper water and reduce the viability of benthic shelter plants with resultant impacts on the wider ecosystem. Eutrophication also decreases the value of rivers, lakes and aesthetic enjoyment. Health problems can occur where eutrophic conditions interfere with drinking water treatment.
Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes subjected to "point source" pollution from sewage pipes. The concentration of algae and the trophic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Later stages of eutrophication lead to blooms of nitrogen-fixing cyanobacteria limited solely by the phosphorus concentration. Phosphorus-base eutrophication in fresh water lakes has been addressed in several cases. | 2 | Environmental Chemistry |
Bimolecular nucleophilic substitution (SN2) reactions are concerted reactions where both the nucleophile and substrate are involved in the rate limiting step. Since this reaction is concerted, the reaction occurs in one step, where the bonds are broken, while new bonds are formed. Therefore, to interpret this reaction, it is important to look at the transition state, which resembles the concerted rate limiting step. In the "Depiction of S2 Reaction" figure, the nucleophile forms a new bond to the carbon, while the halide (L) bond is broken. | 7 | Physical Chemistry |
Some phase change materials are suspended in water, and are relatively nontoxic. Others are hydrocarbons or other flammable materials, or are toxic. As such, PCMs must be selected and applied very carefully, in accordance with fire and building codes and sound engineering practices. Because of the increased fire risk, flamespread, smoke, potential for explosion when held in containers, and liability, it may be wise not to use flammable PCMs within residential or other regularly occupied buildings. Phase change materials are also being used in thermal regulation of electronics. | 7 | Physical Chemistry |
The “shuttling” kinetics of Pd mass transfer (from solid phase to solution phase and back to solid phase) have been verified by three-phase test experiments, while the solution-phase catalytic activity which characterizes most heterogeneous cross-coupling has been verified by TEM, hot filtration, and poisoning experiments. However, truly heterogeneous cross-coupling systems may exist. Poyatos et al. immobilized a Pd pincer carbene complex (Figure 3) on MK-10 clay and observed that while high TON (ca. 10) and TOF was maintained relative to the soluble catalyst, no activity was found in the solution for the supported catalyst – a strong indicator of a fully heterogeneous catalytic mechanism. | 0 | Organic Chemistry |
In bacteria and fungi, the sulfur assimilation pathway is similar to that in plants, where inorganic sulfate is reduced to sulfide, and then incorporated into cysteine and other sulfur-containing compounds.
Bacteria and fungi can absorb inorganic sulfate from the environment through a sulfate transporter, which is regulated by the presence of sulfate in the medium. Once inside the cell, sulfate is activated by ATP sulfurylase to form adenosine 5'-phosphosulfate (APS), which is then reduced to sulfite by APS reductase. Sulfite is further reduced to sulfide by sulfite reductase, which is then incorporated into cysteine by enzyme.
Cysteine, once synthesized, can be used for the biosynthesis of methionine and other important biomolecules. In addition, microorganisms also use sulfur-containing compounds for various other purposes, such as the synthesis of antibiotics.
Sulfur assimilation in microorganisms is regulated by a variety of environmental factors, including the availability of sulfur in the medium and the presence of other nutrients. The activity of key enzymes in the sulfur assimilation pathway is also regulated by feedback inhibition from downstream products, similar to the regulation seen in plants. | 1 | Biochemistry |
Some major bacterial strains identified as being able to ferment lactose are in the genera Escherichia, Citrobacter, Enterobacter and Klebsiella . All four of these groups fall underneath the family of Enterobacteriaceae. These four genera are able to be separated from each other by using biochemical testing, and simple biological tests are readily available. Apart from whole-sequence genomics, common tests include H2S production, motility and citrate use, indole, methyl red and Voges-Proskauer tests. | 1 | Biochemistry |
In 2009, Hayashi et al. successfully produced an efficient, low cost synthetic route to prepare (-)-oseltamivir (1). Their goal was to design a procedure that would be suitable for large-scale production. Keeping cost, yield, and number of synthetic steps in mind, an enantioselective total synthesis of (1) was accomplished through three one-pot operations. Hayashi et al.'s use of one-pot operations allowed them to perform several reactions steps in a single pot, which ultimately minimized the number of purification steps needed, waste, and saved time.
In the first one-pot operation, Hayashi et al. begins by using diphenylprolinol silyl ether (4) as an organocatalyst, along with alkoxyaldehyde (2) and nitroalkene (3) to perform an asymmetric Michael reaction, affording an enantioselective Michael adduct. Upon addition of a diethyl vinylphosphate derivative (5) to the Michael adduct, a domino Michael reaction and Horner-Wadsworth-Emmons reaction occurs due to the phosphonate group produced from (5) to give an ethyl cyclohexenecarboxylate derivative along with two unwanted by-products. To transform the undesired by-products into the desired ethyl cyclohexencarboxylate derivative, the mixture of the product and by-products was treated with CsCO in ethanol. This induced a retro-Michael reaction on one by-product and a retro-aldol reaction accompanied with a Horner-Wadsworth-Emmons reaction for the other. Both by-products were successfully converted to the desired derivative. Finally, the addition of p-toluenethiol with CsCO gives (6) in a 70% yield after being purified by column chromatography, with the desired isomer dominating.
In the second one-pot operation, trifluoroacetic acid is employed first to deprotect the tert-butyl ester of (6); any excess reagent was removed via evaporation. The carboxylic acid produced as a result of the deprotection was then converted to an acyl chloride by oxalyl chloride and a catalytic amount of DMF. Finally, addition of sodium azide, in the last reaction of the second one-pot operation, produce the acyl azide (7) without any purification needed.
The final one-pot operation begins with a Curtius Rearrangement of acyl azide (7) to produce an isocyanate functional group at room temperature. The isocyanate derivative then reacts with acetic acid to yield the desired acetylamino moiety found in (1). This domino Curtius rearrangement and amide formation occurs in the absence of heat, which is extremely beneficial for reducing any possible hazard. The nitro moiety of (7) is reduced to the desired amine observed in (1) with Zn/HCl. Due to the harsh conditions of the nitro reduction, ammonia was used to neutralize the reaction. Potassium carbonate was then added to give (1), via a retro-Michael reaction of the thiol. (1) was then purified by an acid/base extraction. The overall yield for the total synthesis of (-)-oseltamivir is 57%. Hayashi et al. use of inexpensive, non-hazardous reagents has allowed for an efficient, high yielding synthetic route that can allow for vast amount of novel derivatives to be produced in hopes of combatting against viruses resistant to (-)-oseltamivir. | 0 | Organic Chemistry |
Dimercaprol and dimercaptosuccinic acid are chelating agents that sequester the arsenic away from blood proteins and are used in treating acute arsenic poisoning. The most important side effect is hypertension. Dimercaprol is considerably more toxic than succimer. Dimercaptosuccinic acid monoesters, e.g. MiADMSA, are promising antidotes for arsenic poisoning. | 1 | Biochemistry |
From the second order susceptibility, it is possible to ascertain information about the orientation of molecules at the surface. describes how the molecules at the interface respond to the input beam. A change in the net orientation of the polar molecules results in a change of sign of . As a rank 3 tensor, the individual elements provide information about the orientation. For a surface that has azimuthal symmetry, i.e. assuming rod symmetry, only seven of the twenty seven tensor elements are nonzero (with four being linearly independent), which are
: and
The tensor elements can be determined by using two different polarizers, one for the electric field vector perpendicular to the plane of incidence, labeled S, and one for the electric field vector parallel to the plane of incidence, labeled P. Four combinations are sufficient: PPP, SSP, SPS, PSS, with the letters listed in decreasing frequency, so the first is for the sum frequency, the second is for the visible beam, and the last is for the infrared beam. The four combinations give rise to four different intensities given by
: and
where index is of the interfacial -plane, and and are the linear and nonlinear Fresnel factors.
By taking the tensor elements and applying the correct transformations, the orientation of the molecules on the surface can be found. | 7 | Physical Chemistry |
By Taylor series expansion, the potential energy, , of any molecule can be expressed as:
: (eq. 1)
where is a column vector of arbitrary and fully determined displacement coordinates, and and are the corresponding gradient (first derivative of ) and Hessian (second derivative of ), respectively. The point of interest is the stationary point on a potential energy surface (PES), so is treated as zero, and by considering the relative energy, as well becomes zero. By assuming harmonic potential and regarding the third derivative term and forth as negligible, the potential energy formula then simply becomes:
: (eq. 2)
Transitioning from cartesian coordinates to internal coordinates , which are more commonly used for the description of molecular geometries, gives rise to equation 3:
: (eq. 3)
where is the corresponding Hessian for internal coordinates (commonly referred to as force constants), and it is in principle determined by the frequencies of a sufficient set of isotopic molecules. Since the Hessian is the second derivative of the energy with respect to displacements and that is the same as the first derivative of the force, evaluation of this property as shown in equation 4 is often used to describe chemical bonds.
: (eq. 4)
Nevertheless, there are several issues with this method as explained by Grunenberg, including the dependence of force constants on the choice of internal coordinates and the presence of the redundant Hessian which has no physical meaning and consequently engenders ill-defined description of bond strength. | 6 | Supramolecular Chemistry |
Solar cells started in 1876 with William Grylls Adams along with an undergraduate student of his. A French scientist, by the name of Edmond Becquerel, first discovered the photovoltaic effect in the summer of 1839. He theorized that certain elements on the periodic table, such as silicon, reacted to the exposure of sunlight in very unusual ways. Solar power is created when solar radiation is converted to heat or electricity. English electrical engineer Willoughby Smith, between 1873 and 1876, discovered that when selenium is exposed to light, it produced a high amount of electricity. The use of selenium was highly inefficient, but it proved Becquerel's theory that light could be converted into electricity through the use of various semi-metals on the periodic table, that were later labelled as photo-conductive material. By 1953, Calvin Fuller, Gerald Pearson, and Daryl Chapin discovered the use of silicon to produce solar cells was extremely efficient and produced a net charge that far exceeded that of selenium. Today solar power has many uses, from heating, electrical production, thermal processes, water treatment and storage of power that is highly prevalent in the world of renewable energy. | 7 | Physical Chemistry |
1-Chloro-1,1-difluoroethane is a highly flammable, colorless gas under most atmospheric conditions. It has a boiling point of -10 °C. Its critical temperature is near 137 °C. | 2 | Environmental Chemistry |
There are other omega-3 fish-oil based drugs on the market that have similar uses and mechanisms of action:
* Omega-3-acid ethyl esters (brand names Omacor [renamed Lovaza in the U.S. to avoid confusion with Amicar and Omtryg]), and as of March 2016, four generic versions
* Omega-3 carboxylic acids (Epanova); the Epanova brand name was discontinued in the United States. | 1 | Biochemistry |
Indoor tanning is prohibited for under-18s in British Columbia, Alberta, Manitoba, Saskatchewan, Ontario, Quebec, and Prince Edward Island; and for under-19s in New Brunswick, Nova Scotia, Newfoundland and Labrador, and the Northwest Territories. Health Canada recommends against the use of tanning equipment. | 5 | Photochemistry |
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