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Global radiative equilibrium can be defined for an entire passive celestial system that does not supply its own energy, such as a planet.
Liou (2002, page 459) and other authors use the term global radiative equilibrium to refer to radiative exchange equilibrium globally between Earth and extraterrestrial space; such authors intend to mean that, in the theoretical, incoming solar radiation absorbed by Earths surface and its atmosphere would be equal to outgoing longwave radiation from Earths surface and its atmosphere. Prevost would say then that the Earth's surface and its atmosphere regarded as a whole were in absolute radiative equilibrium. Some texts, for example Satoh (2004), simply refer to "radiative equilibrium" in referring to global exchange radiative equilibrium. | 7 | Physical Chemistry |
Hypothermia continues to be a major limitation to swimming or diving in cold water. The reduction in finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries.
Other factors predisposing to immersion hypothermia include dehydration, inadequate rewarming between repetitive dives, starting a dive while wearing cold, wet dry suit undergarments, sweating with work, inadequate thermal insulation, and poor physical conditioning.
Heat is lost much more quickly in water than in air. Thus, water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia in survivors, although this is not usually the direct clinical cause of death for those who are not rescued. A water temperature of can lead to death in as little as one hour, and water temperatures near freezing can cause death in as little as 15 minutes. During the sinking of the Titanic, most people who entered the water died in 15–30 minutes.
The actual cause of death in cold water is usually the bodily reactions to heat loss and to freezing water, rather than hypothermia (loss of core temperature) itself. For example, plunged into freezing seas, around 20% of victims die within two minutes from cold shock (uncontrolled rapid breathing, and gasping, causing water inhalation, massive increase in blood pressure and cardiac strain leading to cardiac arrest, and panic); another 50% die within 15–30 minutes from cold incapacitation: inability to use or control limbs and hands for swimming or gripping, as the body "protectively" shuts down the peripheral muscles of the limbs to protect its core. Exhaustion and unconsciousness cause drowning, claiming the rest within a similar time. | 1 | Biochemistry |
The program may run with fixed input data for the number of years determined by the user. This option can be used to predict future developments based on long-term average input values, e.g. rainfall, as it will be difficult to assess the future values of the input data year by year.
The program also offers the possibility to follow historic records with annually changing input values (e.g. rainfall, irrigation, agricultural practices), the calculations must be made year by year. If this possibility is chosen, the program creates transfer files by which the final conditions of the previous year (e.g. water table and salinity) are automatically used as the initial conditions for the subsequent period. This facility makes it possible to use various generated rainfall sequences drawn randomly from a known rainfall probability distribution and obtain a stochastic prediction of the resulting output parameters.
If the computations are made with annual changes, not all input parameters can be changed, notably the thickness of the soil reservoirs and their total porosities as these would cause illogical shifts in the water and salt balances. | 9 | Geochemistry |
Self-heating cans of military food rations developed during WWII used a thermite-like mixture of 1:1 iron(II,III) oxide and calcium silicide. Such mixture, when ignited, generates moderate amount of heat and no gaseous products. | 8 | Metallurgy |
Protective forms of chemical mimicry work to benefit the mimicking species by preventing harm. In most cases this achieved by acting as a deterrent to other organisms by mimicking the chemicals emitted by another species that has a mechanism to deter predators. This can be either Batesian Mimicry or Müllerian mimicry. | 1 | Biochemistry |
Metal smiths demonstrated increasing technical sophistication, producing both utilitarian and status-linked items. During the latter phase, Michoacán emerged as a technological hub, with metal artifacts also appearing at the adjacent zones of Guerrero and Jalisco.
Alloys became more prevalent during the second phase, as metal workers experimented with color, strength and fluidity. Formerly utilitarian assemblages transformed, with new focus placed upon metallic status objects. Further, the appearance of a copper-tin bronze alloy suggests contact between West Mexico and Peru during this period. However, many of the alloys/alloy concentrations used in West Mexico appear to reflect local innovation.
Scholars such as Dorothy Hosler suggest that ancient Mesoamericans were unique in their attention to the peculiar aesthetic properties of metals, such as the brilliant sounds and colors evoked through the movement of metallic objects. The rather late emergence of metallurgy in ancient Mesoamerica likely contributed to its novelty and subsequent role as a marker of elite status.
It has been suggested that Mesoamerican metal smiths produced particular alloys with the chief aim of exploiting the alloys’ emergent color properties, particularly the vivid gold tones produced through infusion of tin, and the silver shades that develop at high arsenic concentrations. Notably, certain artifacts from West Mexico contain tin or arsenic at concentrations as high as 23 weight percent, while concentrations of alloying elements at roughly 2 to 5 weight percent are typically adequate for augmented strength and mechanical utility.
Metal smiths in pre-Columbian West Mexico particularly exploited the brilliance inherent in metallic sound and sheen, suggesting that their creations tended to occupy a sacred and symbolic space. Metallic colors, gold and silver, might have been connected with solar and lunar deities while bell sounds have been associated with fertility rituals and protection in warfare. | 8 | Metallurgy |
A key physical factor which distinguishes the LCST from other mixture behavior is that the LCST phase separation is driven by unfavorable entropy of mixing. Since mixing of the two phases is spontaneous below the LCST and not above, the Gibbs free energy change (ΔG) for the mixing of these two phases is negative below the LCST and positive above, and the entropy change ΔS = – (dΔG/dT) is negative for this mixing process. This is in contrast to the more common and intuitive case in which entropies drive mixing due to the increased volume accessible to each component upon mixing.
In general, the unfavorable entropy of mixing responsible for the LCST has one of two physical origins. The first is associating interactions between the two components such as strong polar interactions or hydrogen bonds, which prevent random mixing. For example, in the triethylamine-water system, the amine molecules cannot form hydrogen bonds with each other but only with water molecules, so in solution they remain associated to water molecules with loss of entropy. The mixing which occurs below 19 °C is not due to entropy but due to the enthalpy of formation of the hydrogen bonds.
The second physical factor which can lead to an LCST is compressibility effects, especially in polymer-solvent systems. For nonpolar systems such as polystyrene in cyclohexane, phase separation has been observed in sealed tubes (at high pressure) at temperatures approaching the liquid-vapor critical point of the solvent. At such temperatures the solvent expands much more rapidly than the polymer, whose segments are covalently linked. Mixing therefore requires contraction of the solvent for compatibility of the polymer, resulting in a loss of entropy. | 7 | Physical Chemistry |
In the most simplified quorum sensing systems, bacteria only need two components to make use of autoinducers. They need a way to produce a signal and a way to respond to that signal. These cellular processes are often tightly coordinated and involve changes in gene expression. The production of autoinducers generally increases as bacterial cell densities increase. Most signals are produced intracellularly and are subsequently secreted in the extracellular environment. Detection of autoinducers often involves diffusion back into cells and binding to specific receptors. Usually, binding of autoinducers to receptors does not occur until a threshold concentration of autoinducers is achieved. Once this has occurred, bound receptors alter gene expression either directly or indirectly. Some receptors are transcription factors themselves, while others relay signals to downstream transcription factors. In many cases, autoinducers participate in forward feedback loops, whereby a small initial concentration of an autoinducer amplifies the production of that same chemical signal to much higher levels. | 1 | Biochemistry |
Desalting spin columns are widely available with various volumes and MWCO limits:
* [http://www.piercenet.com/cat/desalting-columns Thermo Scientific Pierce Products]
* [http://www.bio-rad.com/en-us/category/bio-spin-micro-bio-spin-size-exclusion-columns Bio-Rad Laboratories, Inc.]
* [https://www.cytivalifesciences.com/en/us/shop/chromatography/prepacked-columns/desalting-and-buffer-exchange/ Cytiva ] | 3 | Analytical Chemistry |
SPIDR (scaffold protein involved in DNA repair) regulates the stability or assembly of RAD51 and DMC1 on single-stranded DNA. RAD51 and DMC1 are recombinases that act during mammalian meiosis to mediate strand exchange during the repair of DNA double-strand breaks by homologous recombination. | 1 | Biochemistry |
Chlorination of organic isothiocyanates is also well established:
:RN=C=S + 2Cl → RN=CCl + SCl
Alkylisocyanates are chlorinated by phosphorus pentachloride:
:RN=C=O + PCl → RN=CCl + POCl
Cyanogen chloride also chlorinates to give the isocyanide dichloride:
:ClCN + Cl → ClN=CCl | 0 | Organic Chemistry |
Paramyxoviruses are a diverse family of non-segmented negative strand RNA viruses that include many highly pathogenic viruses affecting humans, animals, and birds. These include canine distemper virus (dogs), phocine distemper virus (seals), cetacean morbillivirus (dolphins and porpoises) Newcastle disease virus (birds) and rinderpest virus (cattle). Some paramyxoviruses such as the henipaviruses are zoonotic pathogens, occurring primarily in an animal hosts, but also able to infect humans. | 1 | Biochemistry |
In China, a number of incidents have occurred where state limits were exceeded by large amounts or where the wrong pesticide was used. In August 1994, a serious incident of pesticide poisoning of sweet potato crops occurred in Shandong province, China. Because local farmers were not fully educated in the use of insecticides, they used the highly-toxic pesticide named parathion instead of trichlorphon. It resulted in over 300 cases of poisoning and 3 deaths. Also, there was a case where a large number of students were poisoned and 23 of them were hospitalized because of vegetables that contained excessive pesticide residues. | 2 | Environmental Chemistry |
An improvement on optical mapping, called "Nanocoding", has potential to boost throughput by trapping elongated DNA molecules in nanoconfinements. | 1 | Biochemistry |
SMA actuators are typically actuated electrically by Joule heating. If the SMA is used in an environment where the ambient temperature is uncontrolled, unintentional actuation by ambient heating may occur. | 8 | Metallurgy |
In South Africa, modafinil is Schedule V substance, which means that it is legal to use modafinil in South Africa, but only with a valid prescription from a licensed medical practitioner. | 4 | Stereochemistry |
Consistent with Coulomb's law, There is a very strong relationship between the energetic stabilization associated with a sigma hole interaction and the product of the electrostatic potentials associated with the sigma hole and lone pair sites. Therefore, factors that increase the electrostatic potential of the sigma hole and decrease the electrostatic potential of the lone pair result in stronger interactions. The main structural factors contributing to the electrostatic potential of the sigma hole are the electronegativity of the host atom, the polarizability of the host atom, and the electron donating or withdrawing character of the group bonded to the host atom, with less electronegative and more polarizable host atoms bound to more electron withdrawing groups associated with the highest electrostatic potential.
The table below shows the computed strength (in kcal/mol) of three selected sigma hole interactions at a variety of angles. At any angle, it can be observed that the interaction is stronger when the Bromine atom hosting the sigma hole is bound to a strongly electron withdrawing cyano group than when this atom is bound to a trifluoromethyl group, which is only moderately electron withdrawing. On the other hand, the interaction is stronger when an ammonia molecule provides the lone pair, as the electrostatic potential associated with this site is more negative than the corresponding site on hydrogen cyanide. In all cases, the interaction is becomes stronger at more linear angles. | 6 | Supramolecular Chemistry |
Purinergic signalling has an essential role at interactions between neurons and glia cells, allowing these to detect action potentials and modulate neuronal activity, contributing for intra and extracellular homeostasis regulation. Besides purinergic neurotransmitter, ATP acts as a trophic factor at cellular development and growth, being involved on microglia activation and migration, and also on axonal myelination by oligodendrocytes. There are two main types of purinergic receptors, P1 binding to adenosine, and P2 binding to ATP or ADP, presenting different signalling cascades.
The Nrf2/ARE signalling pathway has a fundamental role at fighting against oxidative stress, to which neurons are especially vulnerable due to its high oxygen consumption and high lipid content. This neuroprotective pathway involves control of neuronal activity by perisynaptic astrocytes and neuronal glutamate release, with the establishment of tripartite synapses. The Nrf2/ARE activation leads to a higher expression of enzymes involved in glutathione syntheses and metabolism, that have a key role in antioxidant response.
The LKB1/NUAK1 signalling pathway regulates terminal axon branching at cortical neurons, via local immobilized mitochondria capture. Besides NUAK1, LKB1 kinase acts under other effectors enzymes as SAD-A/B and MARK, therefore regulating neuronal polarization and axonal growth, respectively. These kinase cascades implicates also Tau and others MAP.
An extended knowledge of these and others neuronal pathways could provide new potential therapeutic targets for several neurodegenerative chronic diseases as Alzheimers, Parkinsons and Huntington's disease, and also amyotrophic lateral sclerosis. | 7 | Physical Chemistry |
Although the concept of molecular-weight markers has been retained, techniques of development have varied throughout the years. New inventions of molecular-weight markers are distributed in kits specific to the marker's type.
An early problem in the development of markers was achieving high resolution throughout the entire length of the marker. Depending on the running conditions of gel electrophoresis, fragments may have been compressed, disrupting clarity. To address this issue, a kit for Southern Blot analysis was developed in 1990, providing the first marker to combine target DNA and probe DNA. This technique took advantage of logarithmic spacing, and could be used to identify target bands ranging over a length of 20,000 nucleotides. | 1 | Biochemistry |
Most VOCs in Earth's atmosphere are biogenic, largely emitted by plants.
Biogenic volatile organic compounds (BVOCs) encompass VOCs emitted by plants, animals, or microorganisms, and while extremely diverse, are most commonly terpenoids, alcohols, and carbonyls (methane and carbon monoxide are generally not considered). Not counting methane, biological sources emit an estimated 760 teragrams of carbon per year in the form of VOCs. The majority of VOCs are produced by plants, the main compound being isoprene. Small amounts of VOCs are produced by animals and microbes. Many VOCs are considered secondary metabolites, which often help organisms in defense, such as plant defense against herbivory. The strong odor emitted by many plants consists of green leaf volatiles, a subset of VOCs. Although intended for nearby organisms to detect and respond to, these volatiles can be detected and communicated through wireless electronic transmission, by embedding nanosensors and infrared transmitters into the plant materials themselves.
Emissions are affected by a variety of factors, such as temperature, which determines rates of volatilization and growth, and sunlight, which determines rates of biosynthesis. Emission occurs almost exclusively from the leaves, the stomata in particular. VOCs emitted by terrestrial forests are often oxidized by hydroxyl radicals in the atmosphere; in the absence of NO pollutants, VOC photochemistry recycles hydroxyl radicals to create a sustainable biosphere-atmosphere balance. Due to recent climate change developments, such as warming and greater UV radiation, BVOC emissions from plants are generally predicted to increase, thus upsetting the biosphere-atmosphere interaction and damaging major ecosystems. A major class of VOCs is the terpene class of compounds, such as myrcene.
Providing a sense of scale, a forest in area, the size of the US state of Pennsylvania, is estimated to emit of terpenes on a typical August day during the growing season. Researchers investigating mechanisms of induction of genes producing volatile organic compounds, and the subsequent increase in volatile terpenes, has been achieved in maize using (Z)-3-hexen-1-ol and other plant hormones. | 0 | Organic Chemistry |
The word transcriptome is a portmanteau of the words transcript and genome. It appeared along with other neologisms formed using the suffixes -ome and -omics to denote all studies conducted on a genome-wide scale in the fields of life sciences and technology. As such, transcriptome and transcriptomics were one of the first words to emerge along with genome and proteome. The first study to present a case of a collection of a cDNA library for silk moth mRNA was published in 1979. The first seminal study to mention and investigate the transcriptome of an organism was published in 1997 and it described 60,633 transcripts expressed in S. cerevisiae using serial analysis of gene expression (SAGE). With the rise of high-throughput technologies and bioinformatics and the subsequent increased computational power, it became increasingly efficient and easy to characterize and analyze enormous amount of data. Attempts to characterize the transcriptome became more prominent with the advent of automated DNA sequencing during the 1980s. During the 1990s, expressed sequence tag sequencing was used to identify genes and their fragments. This was followed by techniques such as serial analysis of gene expression (SAGE), cap analysis of gene expression (CAGE), and massively parallel signature sequencing (MPSS). | 1 | Biochemistry |
Although shotgun sequencing can in theory be applied to a genome of any size, its direct application to the sequencing of large genomes (for instance, the human genome) was limited until the late 1990s, when technological advances made practical the handling of the vast quantities of complex data involved in the process. Historically, full-genome shotgun sequencing was believed to be limited by both the sheer size of large genomes and by the complexity added by the high percentage of repetitive DNA (greater than 50% for the human genome) present in large genomes. It was not widely accepted that a full-genome shotgun sequence of a large genome would provide reliable data. For these reasons, other strategies that lowered the computational load of sequence assembly had to be utilized before shotgun sequencing was performed.
In hierarchical sequencing, also known as top-down sequencing, a low-resolution physical map of the genome is made prior to actual sequencing. From this map, a minimal number of fragments that cover the entire chromosome are selected for sequencing. In this way, the minimum amount of high-throughput sequencing and assembly is required.
The amplified genome is first sheared into larger pieces (50-200kb) and cloned into a bacterial host using BACs or P1-derived artificial chromosomes (PAC). Because multiple genome copies have been sheared at random, the fragments contained in these clones have different ends, and with enough coverage (see section above) finding the smallest possible scaffold of BAC contigs that covers the entire genome is theoretically possible. This scaffold is called the minimum tiling path. Once a tiling path has been found, the BACs that form this path are sheared at random into smaller fragments and can be sequenced using the shotgun method on a smaller scale.
Although the full sequences of the BAC contigs is not known, their orientations relative to one another are known. There are several methods for deducing this order and selecting the BACs that make up a tiling path. The general strategy involves identifying the positions of the clones relative to one another and then selecting the fewest clones required to form a contiguous scaffold that covers the entire area of interest. The order of the clones is deduced by determining the way in which they overlap. Overlapping clones can be identified in several ways. A small radioactively or chemically labeled probe containing a sequence-tagged site (STS) can be hybridized onto a microarray upon which the clones are printed. In this way, all the clones that contain a particular sequence in the genome are identified. The end of one of these clones can then be sequenced to yield a new probe and the process repeated in a method called chromosome walking.
Alternatively, the BAC library can be restriction-digested. Two clones that have several fragment sizes in common are inferred to overlap because they contain multiple similarly spaced restriction sites in common. This method of genomic mapping is called restriction or BAC fingerprinting because it identifies a set of restriction sites contained in each clone. Once the overlap between the clones has been found and their order relative to the genome known, a scaffold of a minimal subset of these contigs that covers the entire genome is shotgun-sequenced.
Because it involves first creating a low-resolution map of the genome, hierarchical shotgun sequencing is slower than whole-genome shotgun sequencing, but relies less heavily on computer algorithms than whole-genome shotgun sequencing. The process of extensive BAC library creation and tiling path selection, however, make hierarchical shotgun sequencing slow and labor-intensive. Now that the technology is available and the reliability of the data demonstrated, the speed and cost efficiency of whole-genome shotgun sequencing has made it the primary method for genome sequencing. | 1 | Biochemistry |
Reactive compatibilization is the process of modifying a mixed immiscible blend of polymers to arrest phase separation and allow for the formation of a stable, long-term continuous phase. It is done via the addition of a reactive polymer, miscible with one blend component and reactive towards functional groups on the second component, which result in the "in-situ" formation of block or grafted copolymers.
A large number of commercial polymeric products are derived from the blending of two or more polymers to achieve a favorable balance of physical properties. However, since most polymer blends are immiscible, it is rare to find a pair of polymers that both are miscible and have desired characteristics. An example of such pair is the miscible resin NORYL™, a mix of poly(phenylene oxide) and polystyrene. Immiscible blends will phase separate and form a dispersed phase, which may improve physical properties (figure 1). DuPont’s rubber toughened Nylon consists of small particles of poly(cis-isoprene) (natural rubber) in a Nylon matrix that toughen the material by arresting crack propagation. | 7 | Physical Chemistry |
Organic molecules containing knots may fall into the categories of slipknots or pseudo-knots. They are not considered mathematical knots because they are not a closed curve, but rather a knot that exists within an otherwise linear chain, with termini at each end. Knotted proteins are thought to form molecular knots during their tertiary structure folding process, and knotted nucleic acids generally form molecular knots during genomic replication and transcription, though details of knotting mechanism continue to be disputed and ambiguous. Molecular simulations are fundamental to the research on molecular knotting mechanisms.
Knotted DNA was found first by Liu et al. in 1981, in single-stranded, circular, bacterial DNA, though double-stranded circular DNA has been found to also form knots. Naturally knotted RNA has not yet been reported.
A number of proteins containing naturally occurring molecular knots have been identified. The knot types found to be naturally occurring in proteins are the and knots, as identified in the KnotProt database of known knotted proteins. | 6 | Supramolecular Chemistry |
* Promoter - commonly used inducible promoters are promoters derived from lac operon and the T7 promoter. Other strong promoters used include Trp promoter and Tac-Promoter, which are a hybrid of both the Trp and Lac Operon promoters.
* Ribosome binding site (RBS) - follows the promoter, and promotes efficient translation of the protein of interest.
* Translation initiation site - Shine-Dalgarno sequence enclosed in the RBS, 8 base-pairs upstream of the AUG start codon. | 1 | Biochemistry |
Zinc metal is inserted into the carbon-halogen bond of the α-haloester by oxidative addition 1. This compound dimerizes and rearranges to form two zinc enolates 2. The oxygen on an aldehyde or ketone coordinates to the zinc to form the six-member chair like transition state 3. A rearrangement occurs in which zinc switches to the aldehyde or ketone oxygen and a carbon-carbon bond is formed 4. Acid workup 5,6 removes zinc to yield zinc(II) salts and a β-hydroxy-ester 7. | 0 | Organic Chemistry |
kainic acid receptor - kallidin - kappa opioid receptor - kappa-chain immunoglobulin - karyoplasm - karyotype - kelvin - keratin - kinase - kinesin - kinetic energy - kinetic exclusion assay - kinetics - knock-out mouse - Krebs cycle | 1 | Biochemistry |
The surface-area-to-volume ratio has physical dimension inverse length (L) and is therefore expressed in units of inverse metre (m) or its prefixed unit multiples and submultiples. As an example, a cube with sides of length 1 cm will have a surface area of 6 cm and a volume of 1 cm. The surface to volume ratio for this cube is thus
For a given shape, SA:V is inversely proportional to size. A cube 2 cm on a side has a ratio of 3 cm, half that of a cube 1 cm on a side. Conversely, preserving SA:V as size increases requires changing to a less compact shape. | 7 | Physical Chemistry |
The discovery of mineral acids such as nitric acid is generally believed to go back to 13th-century European alchemy. The conventional view is that nitric acid was first described in pseudo-Gebers De inventione veritatis' ("On the Discovery of Truth", after ).
However, according to Eric John Holmyard and Ahmad Y. al-Hassan, the nitric acid also occurs in various earlier Arabic works such as the ("Chest of Wisdom") attributed to Jabir ibn Hayyan (8th century) or the attributed to the Fatimid caliph al-Hakim bi-Amr Allah (985–1021).
The recipe in the attributed to Jabir has been translated as follows:
Nitric acid is also found in post-1300 works falsely attributed to Albert the Great and Ramon Llull (both 13th century). These works describe the distillation of a mixture containing niter and green vitriol, which they call "eau forte" (aqua fortis). | 3 | Analytical Chemistry |
In nature, the incorporation of a deoxyribonucleoside triphosphate (dNTP) into a growing DNA strand involves the formation of a covalent bond and the release of pyrophosphate and a positively charged hydrogen ion. A dNTP will only be incorporated if it is complementary to the leading unpaired template nucleotide. Ion semiconductor sequencing exploits these facts by determining if a hydrogen ion is released upon providing a single species of dNTP to the reaction.
Microwells on a semiconductor chip that each contain many copies of one single-stranded template DNA molecule to be sequenced and DNA polymerase are sequentially flooded with unmodified A, C, G or T dNTP. If an introduced dNTP is complementary to the next unpaired nucleotide on the template strand it is incorporated into the growing complementary strand by the DNA polymerase. If the introduced dNTP is not complementary there is no incorporation and no biochemical reaction. The hydrogen ion that is released in the reaction changes the pH of the solution, which is detected by an ISFET. The unattached dNTP molecules are washed out before the next cycle when a different dNTP species is introduced. | 1 | Biochemistry |
* Biochemistry of phenolic compounds, by J. B. Harborne, 1964, Academic Press ([https://books.google.com/books?id=_-lqAAAAMAAJ Google Books])
* Plant phenolics, by Pascal Ribéreau-Gayon, 1972, Oliver and Boyd Editions ([https://books.google.com/books?id=EHzwAAAAMAAJ Google Books], , )
* The Biochemistry of plant phenolics, by C. F. van Sumere and P. J. Lea, Phytochemical Society of Europe, 1985, Clarendon Press ([https://books.google.com/books?id=YwmLAAAAIAAJ Google Books], )
* Biochemistry of Phenolic Compounds, by Wilfred Vermerris and Ralph Nicholson, 2006, Springer ([https://books.google.com/books?id=uLzdv8fsRxYC&dq=Biochemistry+of+Phenolic+Compounds&pg=PA3 Google book]) | 0 | Organic Chemistry |
These elements are bound by specific uncharged tRNAs and modulate the expression of corresponding aminoacyl-tRNA synthetase operons. High levels of uncharged tRNA promote the anti-terminator sequence leading to increased concentrations of charged tRNA. These are considered by some to be a separate family of riboswitches but are significantly more complex than the previous class of attenuators. | 1 | Biochemistry |
A consensus site is a term in molecular biology that refers to a site on a protein that is often modified in a particular way. Modifications may be N- or O- linked glycosylation, phosphorylation, tyrosine sulfation or other. | 1 | Biochemistry |
In organic chemistry, a nitrate ester is an organic functional group with the formula , where R stands for any organyl group. They are the esters of nitric acid and alcohols. A well-known example is nitroglycerin, which is not a nitro compound, despite its name. | 0 | Organic Chemistry |
One of the highest, at least in Western Europe, is in Loos-en-Gohelle in the former mining area of Pas-de-Calais, France. It comprises a range of five cones, of which two reach , surpassing the highest peak in Flanders, Mont Cassel. One of the regions of Europe most "littered" with (mountainous) spoil heaps is the Donbas, in Ukraine, especially around the city of Donetsk, which alone boasts about 130 of them.
In Ukrainian, they are called (; singular ) because of their shape.
In Heringen, Hesse, Germany, is the popularly called "Monte Kali", made of spoil from potash mining and rising some 200 meters above the surrounding terrain. "La Muntanya de Sal" (The Salt Mountain), another potash mine spoil heap, lies in Cardona, Catalonia, at about 120 meters in height. A larger and higher pile is that of "El runam del Cogulló" (The Spoil Heap of El Cogulló), also known as "El runam de la democràcia" (The Slag Heap of Democracy) or "Montsalat" (Salty Mountain), in Sallent, which has already grown higher than the small mountain it was named after (El Cogulló, 474 meters above sea level). | 8 | Metallurgy |
An oxyhydrogen torch (also known as hydrogen torch) is an oxy-gas torch that burns hydrogen (the fuel) with oxygen (the oxidizer). It is used for cutting and welding metals, glasses, and thermoplastics.
Due to competition from arc welding and other oxy-fuel torches such as the acetylene-fueled cutting torch, the oxyhydrogen torch is seldom used today, but it remains the preferred cutting tool in some niche applications.
Oxyhydrogen was once used in working platinum, because at the time, only it could burn hot enough to melt the metal . These techniques have been superseded by the electric arc furnace. | 7 | Physical Chemistry |
Gene symbols generally are italicised, with only the first letter in uppercase and the remaining letters in lowercase (Shh). Italics are not required on web pages. Protein designations are the same as the gene symbol, but are not italicised and all are upper case (SHH). | 1 | Biochemistry |
Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics and chemical equilibria.
Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a supra-molecular science, as the majority of the principles on which it was founded relate to the bulk rather than the molecular or atomic structure alone (for example, chemical equilibrium and colloids).
Some of the relationships that physical chemistry strives to resolve include the effects of:
# Intermolecular forces that act upon the physical properties of materials (plasticity, tensile strength, surface tension in liquids).
# Reaction kinetics on the rate of a reaction.
# The identity of ions and the electrical conductivity of materials.
# Surface science and electrochemistry of cell membranes.
# Interaction of one body with another in terms of quantities of heat and work called thermodynamics.
# Transfer of heat between a chemical system and its surroundings during change of phase or chemical reaction taking place called thermochemistry
# Study of colligative properties of number of species present in solution.
# Number of phases, number of components and degree of freedom (or variance) can be correlated with one another with help of phase rule.
# Reactions of electrochemical cells.
# Behaviour of microscopic systems using quantum mechanics and macroscopic systems using statistical thermodynamics.
# Calculation of the energy of electron movement in a metal complexes. | 7 | Physical Chemistry |
The attractive forces between polymer chains play a large part in determining the polymer's properties. Because polymer chains are so long, they have many such interchain interactions per molecule, amplifying the effect of these interactions on the polymer properties in comparison to attractions between conventional molecules. Different side groups on the polymer can lend the polymer to ionic bonding or hydrogen bonding between its own chains. These stronger forces typically result in higher tensile strength and higher crystalline melting points.
The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing amide or carbonyl groups can form hydrogen bonds between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to the partially negatively charged oxygen atoms in C=O groups on another. These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Dipole bonding is not as strong as hydrogen bonding, so a polyesters melting point and strength are lower than Kevlars (Twaron), but polyesters have greater flexibility. Polymers with non-polar units such as polyethylene interact only through weak Van der Waals forces. As a result, they typically have lower melting temperatures than other polymers.
When a polymer is dispersed or dissolved in a liquid, such as in commercial products like paints and glues, the chemical properties and molecular interactions influence how the solution flows and can even lead to self-assembly of the polymer into complex structures. When a polymer is applied as a coating, the chemical properties will influence the adhesion of the coating and how it interacts with external materials, such as superhydrophobic polymer coatings leading to water resistance. Overall the chemical properties of a polymer are important elements for designing new polymeric material products. | 7 | Physical Chemistry |
Static light scattering assumes that each detected photon has only been scattered exactly once. Therefore, analysis according to the calculations stated above will only be correct if the sample has been diluted sufficiently to ensure that photons are not scattered multiple times by the sample before being detected. Accurate interpretation becomes exceedingly difficult for systems with non-negligible contributions from multiple scattering. In many commercial instruments where analysis of the scattering signal is automatically performed, the error may never be noticed by the user. Particularly for larger particles and those with high refractive index contrast, this limits the application of standard static light scattering to very low particle concentrations. On the other hand, for soluble macromolecules that exhibit a relatively low refractive index contrast versus the solvent, including most polymers and biomolecules in their respective solvents, multiple scattering is rarely a limiting factor even at concentrations that approach the limits of solubility.
However, as shown by Schaetzel, it is possible to suppress multiple scattering in static light scattering experiments via a cross-correlation approach. The general idea is to isolate singly scattered light and suppress undesired contributions from multiple scattering in a static light scattering experiment. Different implementations of cross-correlation light scattering have been developed and applied. Currently, the most widely used scheme is the so-called 3D-dynamic light scattering method,. The same method can also be used to correct dynamic light scattering data for multiple scattering contributions. | 7 | Physical Chemistry |
Signaling action in neurons by sigma-2 receptors and their associated ligands results in modulation of action potential firing by regulation of calcium and potassium channels. They also are involved in synaptic vesicular release and modulation of dopamine, serotonin, and glutamate, with activation and increase of the dopaminergic, serotonergic, and noradrenergic activity of neurons. | 1 | Biochemistry |
For efficient ridged mirrors, both estimates above should predict high reflectivity. This implies reduction of both, width, of the ridges and the period, . The width of the ridges cannot be smaller than the size of an atom; this sets the limit of performance of the ridged mirrors. | 7 | Physical Chemistry |
The synthesis of Pd-NHC complexes follows the methods used for the synthesis of transition metal NHC complexes. The synthesis of Pd-NHC complexes can also be achieved through substitution of a labile ligand L in a Pd-L complex. Labile ligands typically include cyclooctadiene, dibenzylideneacetone, bridging halides, or phosphines. This process can be used in conjunction with the in situ generation of free carbenes. Pd-NHC complexes can also be synthesized through transmetalation with silver-NHC complexes. The transmetallated NHCs can either be isolated for subsequent reaction with palladium in a two-step method, or generated in the presence of palladium in a one-pot reaction. However, generation of Pd-NHC complexes by Ag transmetallation is cost-prohibitive and hampered by Ag complexes’ light sensitivity. | 0 | Organic Chemistry |
Rayleigh scattering is defined by a mathematical formula that requires the light-scattering particles to be far smaller than the wavelength of the light. For a dispersion of particles to qualify for the Rayleigh formula, the particle sizes need to be below roughly 40 nanometres (for visible light), and the particles may be individual molecules. Colloidal particles are bigger and are in the rough vicinity of the size of a wavelength of light. Tyndall scattering, i.e. colloidal particle scattering, is much more intense than Rayleigh scattering due to the bigger particle sizes involved. The importance of the particle size factor for intensity can be seen in the large exponent it has in the mathematical statement of the intensity of Rayleigh scattering. If the colloid particles are spheroid, Tyndall scattering can be mathematically analyzed in terms of Mie theory, which admits particle sizes in the rough vicinity of the wavelength of light. Light scattering by particles of complex shape are described by the T-matrix method. | 7 | Physical Chemistry |
For the pinhole configuration the width of the beam (which we aim to minimise) is largely given by geometrical optics. The size of the beam at the sample plane is given by the lines connecting the skimmer edges with the pinhole edges. When the Fresnel number is very small (), the beam width is also affected by Fraunhofer diffraction (see equation below).
In this equation is the Full Width at Half Maximum of the beam, is the geometrical projection of the beam and is the Airy diffraction term. is the Heaviside step function used here to indicate that the presence of the diffraction term depends on the value of the Fresnel number. Note that there are variations of this equation depending on what is defined as the "beam width" (for details compare and ). Due to the small wavelength of the helium beam, the Fraunhofer diffraction term can usually be omitted.
The intensity of the beam (which we aim to maximise) is given by the following equation (according to the Sikora and Andersen model):
Where is the total intensity stemming from the supersonic expansion nozzle (taken as a constant in the optimisation problem), is the radius of the pinhole, S is the speed ratio of the beam, is the radius of the skimmer, is the radius of the supersonic expansion quitting surface (the point in the expansion from which atoms can be considered to travel in a straight line), is the distance between the nozzle and the skimmer and is the distance between the skimmer and the pinhole. There are several other versions of this equation that depend on the intensity model, but they all show a quadratic dependency on the pinhole radius (the bigger the pinhole, the more intensity) and an inverse quadratic dependency with the distance between the skimmer and the pinhole (the more the atoms spread, the less intensity).
By combining the two equations shown above, one can obtain that for a given beam width for the geometrical optics regime the following values correspond to intensity maxima:
In here, represents the working distance of the microscope and is a constant that stems from the definition of the beam width. Note that both equations are given with respect to the distance between the skimmer and the pinhole, a. The global maximum of intensity can then be obtained numerically by replacing these values in the intensity equation above. In general, smaller skimmer radii coupled with smaller distances between the skimmer and the pinhole are preferred, leading in practice to the design of increasingly smaller pinhole microscopes. | 7 | Physical Chemistry |
Co-translational and post-translational covalent modifications enable proteins to develop higher levels of complexity in cellular function, further adding diversity to the proteome. The addition of myristoyl-CoA to a protein can occur during protein translation or after. During co-translational addition of the myristoyl group, the N-terminal glycine is modified following cleavage of the N-terminal methionine residue in the newly forming, growing polypeptide. Post-translational myristoylation typically occurs following a caspase cleavage event, resulting in the exposure of an internal glycine residue, which is then available for myristic acid addition. | 1 | Biochemistry |
A glycinergic agent (or drug) is a chemical which functions to directly modulate the glycine system in the body or brain. Examples include glycine receptor agonists, glycine receptor antagonists, and glycine reuptake inhibitors. | 1 | Biochemistry |
Deoxidization is a method used in metallurgy to remove the oxygen content during steel manufacturing. In contrast, antioxidants are used for stabilization, such as in the storage of food. Deoxidation is important in the steelmaking process as oxygen is often detrimental to the quality of steel produced. Deoxidization is mainly achieved by adding a separate chemical species to neutralize the effects of oxygen or by directly removing the oxygen. | 8 | Metallurgy |
The re-evaluation of single enantiomers not without problems. The chiral switches of fluoxetine and fenfluramine are classical examples. The development of (R )-fluoxetine was terminated after patients developed abnormal heart rhythms. The chiral switch of fenfluramine, dexfenfluramine was withdrawn from world marker due to pulmonary hypertension. The table below enumerates couple of chiral switches aborted or withdrawn due stereochemically engineered toxicity. | 4 | Stereochemistry |
For plants to absorb nitrogen from urea it must first be broken down:
Urease is a naturally occurring enzyme that catalyzes the hydrolysis of urea to unstable carbamic acid. Rapid decomposition of carbamic acid occurs without enzyme catalysis to form ammonia and carbon dioxide. The ammonia will likely escape to the atmosphere unless it reacts with water to form ammonium (NH) according to the following reaction:
This is important because ammonium is a plant available source of nitrogen while ammonia is not. Additionally, the formation of the hydroxide ion may cause soils around the applied urea particle to have a pH around 9.0 which increases ammonia volatilization. This area is also highly toxic due to elevated ammonia concentration for several hours so it is recommended that urea based fertilizers not be applied or banded with planted seed at a rate that exceeds 10–20 kg/ha, depending on the crop species. It is important that there is adequate moisture because up to thirty percent of the available nitrogen can be lost through atmospheric volatilization within seventy-two hours of application. | 9 | Geochemistry |
Several compounds are known to promote the opening or activation of specific ion channels. These are classified by the channel on which they act:
*Calcium channel openers, such as Bay K8644
*Chloride channel openers, such as phenanthroline
*Potassium channel openers, such as minoxidil
*Sodium channel openers, such as DDT | 1 | Biochemistry |
In the 1600s, the Moon was divided into two terranes, terra and maria. The terra terrane was thought to be landmass, and the maria terrane was thought to be the Moon's ocean, although this is now known to be false. The maria terrane is lower in elevation and younger in age than the terra terrane, and was formed by lava. The terra terrane is higher and older, and hence more cratered. Visually, the maria correspond to the dark regions of the Moon, and the terra to the light. | 9 | Geochemistry |
A melanomorph is a substance related to the pigment melanin. Melanomorphs originate from the aromatic amino acids tyrosine, tryptophan, and phenylalanine. They tend to absorb ultraviolet-B light, with peaks around 280 nanometers. See also Beer's Law. | 1 | Biochemistry |
Following excitation, the loosened electron of P680* is taken up by the primary electron acceptor, a pheophytin molecule located within photosystem II near P680. During this transfer, P680* is ionized and oxidized, producing cationic P680. | 5 | Photochemistry |
In molecular biology, a hybridization probe (HP) is a fragment of DNA or RNA, usually 15–10000 nucleotides long, which can be radioactively or fluorescently labeled. HPs can be used to detect the presence of nucleotide sequences in analyzed RNA or DNA that are complementary to the sequence in the probe. The labeled probe is first denatured (by heating or under alkaline conditions such as exposure to sodium hydroxide) into single stranded DNA (ssDNA) and then hybridized to the target ssDNA (Southern blotting) or RNA (northern blotting) immobilized on a membrane or in situ.
To detect hybridization of the probe to its target sequence, the probe is tagged (or "labeled") with a molecular marker of either radioactive or (more recently) fluorescent molecules. Commonly used markers are P (a radioactive isotope of phosphorus incorporated into the phosphodiester bond in the probe DNA), digoxigenin, a non-radioactive, antibody-based marker, biotin or fluorescein. DNA sequences or RNA transcripts that have moderate to high sequence similarity to the probe are then detected by visualizing the hybridized probe via autoradiography or other imaging techniques. Normally, either X-ray pictures are taken of the filter, or the filter is placed under UV light. Detection of sequences with moderate or high similarity depends on how stringent the hybridization conditions were applied—high stringency, such as high hybridization temperature and low salt in hybridization buffers, permits only hybridization between nucleic acid sequences that are highly similar, whereas low stringency, such as lower temperature and high salt, allows hybridization when the sequences are less similar.
Hybridization probes used in DNA microarrays refer to DNA covalently attached to an inert surface, such as coated glass slides or gene chips, to which a mobile cDNA target is hybridized. Depending on the method, the probe may be synthesized using the phosphoramidite method, or it can be generated and labeled by PCR amplification or cloning (both are older methods). In order to increase the in vivo stability of the probe RNA is not used. Instead, RNA analogues may be used, in particular morpholino- derivatives. Molecular DNA- or RNA-based probes are routinely used in screening gene libraries, detecting nucleotide sequences with blotting methods, and in other gene technologies, such as nucleic acid and tissue microarrays. | 1 | Biochemistry |
SRAS (spatially resolved acoustic spectroscopy) a non-destructive acoustic microscopy microstructural-crystallographic characterization technique commonly used in the study of crystalline or polycrystalline materials. The technique can provide information about the structure and crystallographic orientation of the material. Traditionally, the information provided by SRAS has been acquired by using diffraction techniques in electron microscopy - such as EBSD. The technique was patented in 2005, .
SRAS measures the surface acoustic wave velocity across a specimen, the surface acoustic wave (SAW) velocity is in turn a function of the material state, including parameters such as crystallographic orientation, elastic constants, temperature and stress. | 7 | Physical Chemistry |
Other dyes used in connection with Van Gieson staining include:
* Alcian blue
* Amido black 10B
* Verhoeff's stain | 1 | Biochemistry |
The three-dimensional isotropic and non-relativistic uniform Fermi gas case is known as the Fermi sphere.
A three-dimensional infinite square well, (i.e. a cubical box that has a side length L) has the potential energy
The states are now labelled by three quantum numbers n, n, and n. The single particle energies are
where n, n, n are positive integers. In this case, multiple states have the same energy (known as degenerate energy levels), for example . | 7 | Physical Chemistry |
Primary alkyl halides react with aqueous NaOH or KOH to alcohols in nucleophilic aliphatic substitution. (Secondary and especially tertiary alkyl halides will give the elimination (alkene) product instead). Grignard reagents react with carbonyl groups to secondary and tertiary alcohols. Related reactions are the Barbier reaction and the Nozaki-Hiyama reaction. | 0 | Organic Chemistry |
Multilocus sequence typing (MLST) is a technique in molecular biology for the typing of multiple loci, using DNA sequences of internal fragments of multiple housekeeping genes to characterize isolates of microbial species.
The first MLST scheme to be developed was for Neisseria meningitidis, the causative agent of meningococcal meningitis and septicaemia. Since its introduction for the research of evolutionary history, MLST has been used not only for human pathogens but also for plant pathogens. | 1 | Biochemistry |
He is known for the so-called Zinin reaction or Zinin reduction, in which nitro aromates like nitrobenzene are converted to amines by reduction with ammonium sulfides.
In 1842 Zinin played an important role in identifying aniline. | 0 | Organic Chemistry |
Hammond was born on April 4, 1833, in Grafton, Massachusetts, to Josiah and Anna Warren. One of his siblings, William Henry (1841–1908), followed him to Maine. He worked in Portland until his death, a few months after George, at the age of 67. His body was returned to the family's hometown of Grafton for interment.
He received an honorary degree of Master of Arts degree from Bowdoin College in 1900. | 8 | Metallurgy |
Historically, sediments with the highest organic carbon contents were frequently found in areas with high surface water productivity or those with low bottom-water oxygen concentrations. 90% of organic carbon burial occurs in deposits of deltas and continental shelves and upper slopes; this is due partly to short exposure time because of a shorter distance to the seafloor and the composition of the organic matter that is already deposited in those environments. Organic carbon burial is also sensitive to climate patterns: the accumulation rate of organic carbon was 50% larger during the glacial maximum compared to interglacials. | 9 | Geochemistry |
Chloroplasts have their own ribosomes, which they use to synthesize a small fraction of their proteins. Chloroplast ribosomes are about two-thirds the size of cytoplasmic ribosomes (around 17 nm vs 25 nm). They take mRNAs transcribed from the chloroplast DNA and translate them into protein. While similar to bacterial ribosomes, chloroplast translation is more complex than in bacteria, so chloroplast ribosomes include some chloroplast-unique features.
Small subunit ribosomal RNAs in several Chlorophyta and euglenid chloroplasts lack motifs for Shine-Dalgarno sequence recognition, which is considered essential for translation initiation in most chloroplasts and prokaryotes. Such loss is also rarely observed in other plastids and prokaryotes. An additional 4.5S rRNA with homology to the 3' tail of 23S is found in "higher" plants. | 5 | Photochemistry |
In the experiment, proflavin-induced mutations of the T4 bacteriophage gene, rIIB, were isolated. Proflavin causes mutations by inserting itself between DNA bases, typically resulting in insertion or deletion of a single base pair.
Through the use of proflavin, the experimenters were able to insert or delete base pairs into their sequence of interest. When nucleotides were inserted or deleted, the gene would often be nonfunctional. However, if three base pairs were added or deleted, the gene would remain functional. This proved that the genetic code uses a codon of three nucleotide bases that corresponds to an amino acid. The mutants produced by Crick and Brenner that could not produce functional rIIB protein were the results of frameshift mutations, where the triplet code was disrupted.
Brenner and Crick et al. were also able to correct their frameshift mutations through the use of proflavin. If they had a nonfunctional gene due to a deleted base pair, by inserting a base pair into the general area of the deleted one, they were able to rescue the function of the gene. This is because the bases were shifted back into the correct reading frame. | 1 | Biochemistry |
A clinical application of DCS is for use in diagnosis of cancers. An example of this is measuring red blood cell flow in breast tumors. In this experiment, both healthy patients and patients with breast tumors were recruited. Researchers scanned the tumor with a hand-held optical probe with 4 sources and detectors 2.5 cm apart from each other. Then, the resultant correlation functions were fit to the solution of the correlation diffusion equation to obtain the blood flow index. The average relative blood flow was reported at each position. Blood flow increased in both horizontal and vertical scans as the probe crossed over the tumor. These findings were consistent with previous Doppler ultrasound and PET results. | 7 | Physical Chemistry |
Particulate inorganic carbon (PIC) can be contrasted with dissolved inorganic carbon (DIC), the other form of inorganic carbon found in the ocean. These distinctions are important in chemical oceanography. Particulate inorganic carbon is sometimes called suspended inorganic carbon. In operational terms, it is defined as the inorganic carbon in particulate form that is too large to pass through the filter used to separate dissolved inorganic carbon.
Most PIC is calcium carbonate, CaCO, particularly in the form of calcite, but also in the form of aragonite. Calcium carbonate makes up the shells of many marine organisms. It also forms during whiting events and is excreted by marine fish during osmoregulation. | 9 | Geochemistry |
Moshers acid, via its acid chloride derivative, reacts readily with alcohols and amines to give esters and amides, respectively. The lack of an alpha-proton on the acid prevents loss of stereochemical fidelity under the reaction conditions. Thus, using an enantiomerically pure Moshers acid allows for determination of the configuration of simple chiral amines and alcohols. For example, the (R)- and (S)-enantiomers of 1-phenylethanol react with (S)-Mosher acid chloride to yield (R,S)- and (S,S)-diastereomers, respectively, that are distinguishable in NMR. | 4 | Stereochemistry |
DNA testing has been used to establish the right of succession to British titles.
Cases:
* Baron Moynihan
* Pringle baronets | 1 | Biochemistry |
Lexitropsins are members of a family of semi-synthetic DNA-binding ligands. They are structural analogs of the natural antibiotics netropsin and distamycin. Antibiotics of this group can bind in the minor groove of DNA with different sequence-selectivity. Lexitropsins form a complexes with DNA with stoichiometry 1:1 and 2:1. Based on the 2:1 complexes were obtained ligands with high sequence-selectivity. | 1 | Biochemistry |
For the flux density received from a remote unresolvable "point source", the measuring instrument, usually telescopic, though not able to resolve any detail of the source itself, must be able to optically resolve enough details of the sky around the point source, so as to record radiation coming from it only, uncontaminated by radiation from other sources. In this case, spectral flux density is the quantity that describes the rate at which energy transferred by electromagnetic radiation is received from that unresolved point source, per unit receiving area facing the source, per unit wavelength range.
At any given wavelength λ, the spectral flux density, F, can be determined by the following procedure:
*An appropriate detector of cross-sectional area 1 m is pointed directly at the source of the radiation.
*A narrow band-pass filter is placed in front of the detector so that only radiation whose wavelength lies within a very narrow range, Δλ, centred on λ, reaches the detector.
*The rate at which EM energy is detected by the detector is measured.
*This measured rate is then divided by Δλ to obtain the detected power per square metre per unit wavelength range.
Spectral flux density is often used as the quantity on the y-axis of a graph representing the spectrum of a light-source, such as a star. | 7 | Physical Chemistry |
In Crigler Najjar disease, there is an inherited deficiency of glucuronyl transferase resulting in high concentrations of unconjugated bilirubin appear in the plasma. Furthermore, those affected may develop kernicterus (deposits of pigment in the brain) that can cause nerve degeneration. | 1 | Biochemistry |
In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron.
With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes.
A notable example of a radical is the hydroxyl radical (HO·), a molecule that has one unpaired electron on the oxygen atom. Two other examples are triplet oxygen and triplet carbene (꞉) which have two unpaired electrons.
Radicals may be generated in a number of ways, but typical methods involve redox reactions, Ionizing radiation, heat, electrical discharges, and electrolysis are known to produce radicals. Radicals are intermediates in many chemical reactions, more so than is apparent from the balanced equations.
Radicals are important in combustion, atmospheric chemistry, polymerization, plasma chemistry, biochemistry, and many other chemical processes. A majority of natural products are generated by radical-generating enzymes. In living organisms, the radicals superoxide and nitric oxide and their reaction products regulate many processes, such as control of vascular tone and thus blood pressure. They also play a key role in the intermediary metabolism of various biological compounds. Such radicals can even be messengers in a process dubbed redox signaling. A radical may be trapped within a solvent cage or be otherwise bound. | 2 | Environmental Chemistry |
Fatty acids, stored as triglycerides in an organism, are a concentrated source of energy because they contain little oxygen and are anhydrous. The energy yield from a gram of fatty acids is approximately 9 kcal (37 kJ), much higher than the 4 kcal (17 kJ) for carbohydrates. Since the hydrocarbon portion of fatty acids is hydrophobic, these molecules can be stored in a relatively anhydrous (water-free) environment. Carbohydrates, on the other hand, are more highly hydrated. For example, 1 g of glycogen binds approximately 2 g of water, which translates to 1.33 kcal/g (4 kcal/3 g). This means that fatty acids can hold more than six times the amount of energy per unit of stored mass. Put another way, if the human body relied on carbohydrates to store energy, then a person would need to carry 31 kg (67.5 lb) of hydrated glycogen to have the energy equivalent to 4.6 kg (10 lb) of fat.
Hibernating animals provide a good example for utilization of fat reserves as fuel. For example, bears hibernate for about 7 months, and during this entire period, the energy is derived from degradation of fat stores. Migrating birds similarly build up large fat reserves before embarking on their intercontinental journeys.
The fat stores of young adult humans average between about 10–20 kg, but vary greatly depending on gender and individual disposition. By contrast, the human body stores only about 400 g of glycogen, of which 300 g is locked inside the skeletal muscles and is unavailable to the body as a whole. The 100 g or so of glycogen stored in the liver is depleted within one day of starvation. Thereafter the glucose that is released into the blood by the liver for general use by the body tissues has to be synthesized from the glucogenic amino acids and a few other gluconeogenic substrates, which do not include fatty acids. Nonetheless, lipolysis releases glycerol which can enter the pathway of gluconeogenesis. | 1 | Biochemistry |
As fusion time begins, there is an incubation period where no strength develops. Once enough time has passed for the molten material to begin solidifying, the joint strength begins to develop before plateauing at the maximum strength. If power is applied after full joint strength is achieved, the strength will start to decline slowly. | 7 | Physical Chemistry |
Particle-induced X-ray emission or proton-induced X-ray emission (PIXE) is a technique used for determining the elemental composition of a material or a sample. When a material is exposed to an ion beam, atomic interactions occur that give off EM radiation of wavelengths in the x-ray part of the electromagnetic spectrum specific to an element. PIXE is a powerful yet non-destructive elemental analysis technique now used routinely by geologists, archaeologists, art conservators and others to help answer questions of provenance, dating and authenticity.
The technique was first proposed in 1970 by Sven Johansson of Lund University, Sweden, and developed over the next few years with his colleagues Roland Akselsson and Thomas B Johansson.
Recent extensions of PIXE using tightly focused beams (down to 1 μm) gives the additional capability of microscopic analysis. This technique, called microPIXE, can be used to determine the distribution of trace elements in a wide range of samples. A related technique, particle-induced gamma-ray emission (PIGE) can be used to detect some light elements. | 7 | Physical Chemistry |
GPCRs downstream signals have been shown to possibly interact with integrin signals, such as FAK. Integrin signaling will phosphorylate FAK, which can then decrease GPCR G activity. | 1 | Biochemistry |
The first Congress of Biochemistry was held in 1949 in Cambridge, UK, and was inspired by German-born British biochemist Sir Hans Adolf Krebs as a means of bringing together biochemists who had been separated by World War II. At the time, biochemistry was blossoming as a discipline and was seeking its own recognition as a union within the International Council for Science (ICSU). The congress was a first step to recognize biochemistry as a separate discipline and entity. At the final session of this congress, the International Committee of Biochemistry was set up with 20 members from fourteen countries with the goal obtaining from the ICSU recognition as the international body representative of biochemistry, with a view to the formal constitution of an International Union of Biochemistry as soon as possible. Discussions continued over the next few years, and by the third Congress of Biochemistry, which took place in Brussels in 1955, the International Union of Biochemistry (IUB) was formed and officially admitted to the ICSU. In 1991, the IUB changed its name to the International Union of Biochemistry and Molecular Biology (IUBMB). | 1 | Biochemistry |
The Broken Hill Associated Smelters Proprietary Limited (“BHAS”) lead smelter, now owned by Nyrstar NV, has been the world’s largest lead smelter. Its staff was responsible for many significant technical developments in the lead smelting industry, including the updraft sinter plant and continuous lead refining.
Until 1990, BHAS recovered silver in a two-stage reverberatory cupellation process. This process suffered from low recoveries (80–83%), a long cycle time (4–5 days) that caused large in-process inventories, inefficient use of labor and energy, and poor workplace hygiene. After a test work program undertaken at Ausmelt’s facilities in Melbourne, BHAS switched to using a process based on the Sirosmelt top-submerged lance in June 1990.
The change to the lance-based furnace increased oxygen utilization to 95% and the cycle time was reduced to a little less than eight hours, “but the grade of the doré which could be economically produced was poor.” The doré from the new furnace still contained about 0.8% lead and 0.4% copper. It was also found impractical to cast anode plates of doré directly from the Sirosmelt furnace, so the Sirosmelt doré had to undergo a further refining step in a reverberatory furnace, together with a sodium nitrate flux.
Then, in 1996, BHAS decided to modernize the refining circuit and replaced the Sirosmelt silver refining furnace with a BBOC furnace. Commissioning of the modernized refining circuit was completed in 1999, and the lead throughput was increased by 11%, with the silver refining capacity increasing to over 400 t/y.
The BBOC process proved to be “generally successful”, although it did suffer some problems with the lance jamming that were attributed to higher than expected levels of zinc in the feed, due to problems removing the zinc in earlier stages of the refinery circuit. The higher levels of zinc also caused higher than expected refractory wear and excessive lance consumption, because the heat generated by oxidizing the zinc was greater than that of oxidizing lead.
The BBOC furnace proved to be capable of producing doré containing as little as 0.01% lead and less than 0.1% copper at a temperature around 1050 °C, but BHAS wanted to cast the doré directly into anode plates using an existing doré casting conveyor. Casting using the existing conveyor proved impossible at an operating temperature of 1050 °C, because the high thermal conductivity of the silver resulted in it freezing before it reached the molds. Consequently, BHAS decided to increase the operating temperature to 1100–1150 °C so that the silver remained liquid until cast into the anode molds. A side effect of this is that the lead and copper content of the product doré are higher than if the furnace is operated at 1050 °C, at 0.2% lead and 0.6% copper. Thermodynamic calculations have shown that this is unavoidable at this higher operating temperature. | 8 | Metallurgy |
Microarrays are not limited to DNA analysis; protein microarrays, antibody microarray, chemical compound microarray can also be produced using biochips. Randox Laboratories Ltd. launched Evidence, the first protein Biochip Array Technology analyzer in 2003. In protein Biochip Array Technology, the biochip replaces the ELISA plate or cuvette as the reaction platform. The biochip is used to simultaneously analyze a panel of related tests in a single sample, producing a patient profile. The patient profile can be used in disease screening, diagnosis, monitoring disease progression or monitoring treatment. Performing multiple analyses simultaneously, described as multiplexing, allows a significant reduction in processing time and the amount of patient sample required. Biochip Array Technology is a novel application of a familiar methodology, using sandwich, competitive and antibody-capture immunoassays. The difference from conventional immunoassays is that, the capture ligands are covalently attached to the surface of the biochip in an ordered array rather than in solution.
In sandwich assays an enzyme-labelled antibody is used; in competitive assays an enzyme-labelled antigen is used. On antibody-antigen binding a chemiluminescence reaction produces light. Detection is by a charge-coupled device (CCD) camera. The CCD camera is a sensitive and high-resolution sensor able to accurately detect and quantify very low levels of light. The test regions are located using a grid pattern then the chemiluminescence signals are analysed by imaging software to rapidly and simultaneously quantify the individual analytes.
Biochips are also used in the field of microphysiometry e.g. in skin-on-a-chip applications.
For details about other array technologies, see Antibody microarray. | 1 | Biochemistry |
The first medical application of electroporation was used for introducing poorly permeant anticancer drugs into tumor nodules. Soon also gene electrotransfer became of special interest because of its low cost, easiness of realization and safety. Namely, viral vectors can have serious limitations in terms of immunogenicity and pathogenicity when used for DNA transfer.
Irreversible electroporation is being used and evaluated as cardiac ablation therapy to kill very small areas of heart muscle. This is done to treat irregularities of heart rhythm. A cardiac catheter delivers trains of high-voltage ultra-rapid electrical pulses that form irreversible pores in cell membranes, resulting in cell death. It is thought to allow better selectivity than the previous techniques, which used heat or cold to kill larger volumes of muscle.
A higher voltage of electroporation was found in pigs to irreversibly destroy target cells within a narrow range while leaving neighboring cells unaffected, and thus represents a promising new treatment for cancer, heart disease and other disease states that require removal of tissue. Irreversible electroporation (IRE) has since proven effective in treating human cancer, with surgeons at Johns Hopkins and other institutions now using the technology to treat pancreatic cancer previously thought to be unresectable.
Also first phase I clinical trial of gene electrotransfer in patients with metastatic melanoma was reported. Electroporation mediated delivery of a plasmid coding gene for interleukin-12 (pIL-12) was performed and safety, tolerability and therapeutic effect were monitored. Study concluded, that gene electrotransfer with pIL-12 is safe and well tolerated. In addition partial or complete response was observed also in distant non treated metastases, suggesting the systemic treatment effect. Based on these results they are already planning to move to Phase II clinical study. There are currently several ongoing clinical studies of gene electrotransfer where safety, tolerability and effectiveness of immunization with DNA vaccine, which is administered by the electric pulses is monitored.
Although the method is not systemic, but strictly local one, it is still the most efficient non-viral strategy for gene delivery. | 1 | Biochemistry |
ISO standard 1133-1 governs the procedure for measurement of the melt flow rate. The procedure for determining MFI is as follows:
# A small amount of the polymer sample (around 4 to 5 grams) is taken in the specially designed MFI apparatus. A die with an opening of typically around 2 mm diameter is inserted into the apparatus.
# The material is packed properly inside the barrel to avoid formation of air pockets.
# A piston is introduced which acts as the medium that causes extrusion of the molten polymer.
# The sample is preheated for a specified amount of time: 5 min at 190 °C for polyethylene and 6 min at 230 °C for polypropylene.
# After the preheating a specified weight is introduced onto the piston. Examples of standard weights are 2.16 kg, 5 kg, etc.
# The weight exerts a force on the molten polymer and it immediately starts flowing through the die.
# A sample of the melt is taken after the desired period of time and is weighed accurately.
# MFI is expressed in grams of polymer per 10 minutes of duration of the test.
Synonyms of Melt Flow Index are Melt Flow Rate and Melt Index. More commonly used are their abbreviations: MFI, MFR and MI.
Confusingly, MFR may also indicate "melt flow ratio", the ratio between two melt flow rates at different gravimetric weights. More accurately, this should be reported as FRR (flow rate ratio), or simply flow ratio. FRR is commonly used as an indication of the way in which rheological behavior is influenced by the molecular mass distribution of the material.
formerly: (MFI = Melt Flow Index) → currently: (MFR = Melt mass-Flow Rate)
formerly: (MVI = Melt Volume Index) → currently: (MVR = Melt Volume-flow Rate)
formerly: (MFR = Melt Flow Ratio) → currently: (FRR = Flow Rate Ratio)
The flow parameter that is readily accessible to most processors is the MFI. MFI is often used to determine how a polymer will process. However, MFI takes no account of the shear, shear rate or shear history and as such is not a good measure of the processing window of a polymer. It is a single-point viscosity measurement at a relatively low shear rate and temperature. Earlier, it was often said that MFI give a ‘dot’ when actually what is needed is a ‘plot’ for the polymer processors. However, this is not true now because of a unique approach developed for estimating the rheogram merely from the knowledge of the MFI.
The MFI device is not an extruder in the conventional polymer processing sense in that there is no screw to compress, heat and shear the polymer. MFI additionally does not take account of long chain branching nor the differences between shear and elongational rheology. Therefore, two polymers with the same MFI will not behave the same under any given processing conditions.
The relationship between MFI and temperature can be used to obtain the activation energies for polymers. The activation energies developed from MFI values has the advantage of simplicity and easy availability. The concept of obtaining activation energy from MFI can be extended to copolymers as well wherein there exists an anomalous temperature dependence of melt viscosity leading to the existence of two distinct values of activation energies for each copolymer.
For a detailed numerical simulation of the melt flow index, see or. | 7 | Physical Chemistry |
Some assembly methods also make use of type IIs restriction endonucleases. These differ from other type II endonucleases as they cut several base pairs away from the recognition site. As a result, the overhang sequence can be modified to contain the desired sequence. This provides Type IIs assembly methods with two advantages – it enables "scar-less" assembly, and allows for one-pot, multi-part assembly. Assembly methods that use type IIs endonucleases include Golden Gate and its associated variants. | 1 | Biochemistry |
Novec 1230 is used as gaseous fire suppression agent in scenarios where water-based fire suppression (for example, from a fire sprinkler) would be impractical or where it could damage expensive equipment or property, such as museums, server rooms, banks, clean rooms and hospitals. It functions by rapidly removing heat to extinguish a fire before it starts; also, its density enables it to displace air and thereby deprive the fire of oxygen. Novec 1230 can be used in both total/partial/localized flooding systems, and directional spray-type applications; it is also used in portable extinguishers for specialized applications. The Patent for Novec 1230 as fire extinguishant ended on July 19, 2020. Since the expiry of the patent, multiple companies have brought equivalent products to market under the chemical name FK-5-1-12.
Recently, it has found active use in microencapsulated form in the manufacture of fire-extinguishing composite materials. Samsung SDI is using this product to extinguish fires in the early stages of modular high-capacity storage systems (ESS) based on lithium-ion batteries for solar panels and electric vehicles. In August 2019, Samsung SDI officially announced its investment of $ 169 million into fire-extinguishing composite materials based on microencapsulated Novec 1230. The firm later reported that UL9540A testing for this product was passed. | 2 | Environmental Chemistry |
A cumulative equilibrium constant, denoted by is related to the product of stepwise constants, denoted by For a dibasic acid the relationship between stepwise and overall constants is as follows
Note that in the context of metal-ligand complex formation, the equilibrium constants for the formation of metal complexes are usually defined as association constants. In that case, the equilibrium constants for ligand protonation are also defined as association constants. The numbering of association constants is the reverse of the numbering of dissociation constants; in this example | 7 | Physical Chemistry |
The TCF7L2 gene, encoding the TCF7L2 protein, is located on chromosome 10q25.2-q25.3. The gene contains 19 exons. Of the 19 exons, 5 are alternative. The TCF7L2 protein contains 619 amino acids and its molecular mass is 67919 Da. TCF7L2's secondary structure is a helix-turn-helix structure. | 1 | Biochemistry |
Polanyi's theory has historical significance whose work has been used a foundation for other models, such as the theory of volume filling micropores (TVFM) and the Dubinin–Radushkevich theory.
Other research have been performed loosely involving the potential theory of Polanyi such as the capillary condensation phenomenon discovered by Zsigmondy. Unlike Poylanis theory which involves a flat surface, Zsigmondys research involves a porous structure like silica materials. His research proved that condensation of vapors can occur in narrow pores below the standard saturated vapour pressure. | 7 | Physical Chemistry |
After oral administration, peak serum concentration is reached after 12 hours, and up to 99% of the drug is bound to plasma proteins. The majority of ibuprofen is metabolized and eliminated within 24 hours in the urine; however, 1% of the unchanged drug is removed through biliary excretion. | 4 | Stereochemistry |
Starting with the work of Carl Woese from 1977, genomics studies have placed the last universal common ancestor (LUCA) of all modern life-forms between Bacteria and a clade formed by Archaea and Eukaryota in the phylogenetic tree of life. It lived over 4 Gya. A minority of studies have placed the LUCA in Bacteria, proposing that Archaea and Eukaryota are evolutionarily derived from within Eubacteria; Thomas Cavalier-Smith suggested in 2006 that the phenotypically diverse bacterial phylum Chloroflexota contained the LUCA.
In 2016, a set of 355 genes likely present in the LUCA was identified. A total of 6.1 million prokaryotic genes from Bacteria and Archaea were sequenced, identifying 355 protein clusters from among 286,514 protein clusters that were probably common to the LUCA. The results suggest that the LUCA was anaerobic with a Wood–Ljungdahl (reductive Acetyl-CoA) pathway, nitrogen- and carbon-fixing, thermophilic. Its cofactors suggest dependence upon an environment rich in hydrogen, carbon dioxide, iron, and transition metals. Its genetic material was probably DNA, requiring the 4-nucleotide genetic code, messenger RNA, transfer RNA, and ribosomes to translate the code into proteins such as enzymes. LUCA likely inhabited an anaerobic hydrothermal vent setting in a geochemically active environment. It was evidently already a complex organism, and must have had precursors; it was not the first living thing. The physiology of LUCA has been in dispute.
Leslie Orgel argued that early translation machinery for the genetic code would be susceptible to error catastrophe. Geoffrey Hoffmann however showed that such machinery can be stable in function against "Orgel's paradox". Metabolic reactions that have also been inferred in LUCA are the incomplete reverse Krebs cycle, gluconeogenesis, the pentose phosphate pathway, glycolysis, reductive amination, and transamination. | 9 | Geochemistry |
In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate, the binding site, and residues that catalyse a reaction of that substrate, the catalytic site. Although the active site occupies only ~10–20% of the volume of an enzyme, it is the most important part as it directly catalyzes the chemical reaction. It usually consists of three to four amino acids, while other amino acids within the protein are required to maintain the tertiary structure of the enzymes.
Each active site is evolved to be optimised to bind a particular substrate and catalyse a particular reaction, resulting in high specificity. This specificity is determined by the arrangement of amino acids within the active site and the structure of the substrates. Sometimes enzymes also need to bind with some cofactors to fulfil their function. The active site is usually a groove or pocket of the enzyme which can be located in a deep tunnel within the enzyme, or between the interfaces of multimeric enzymes. An active site can catalyse a reaction repeatedly as residues are not altered at the end of the reaction (they may change during the reaction, but are regenerated by the end). This process is achieved by lowering the activation energy of the reaction, so more substrates have enough energy to undergo reaction. | 1 | Biochemistry |
In chemistry an eclipsed conformation is a conformation in which two substituents X and Y on adjacent atoms A, B are in closest proximity, implying that the torsion angle X–A–B–Y is 0°. Such a conformation can exist in any open chain, single chemical bond connecting two sp-hybridised atoms, and it is normally a conformational energy maximum. This maximum is often explained by steric hindrance, but its origins sometimes actually lie in hyperconjugation (as when the eclipsing interaction is of two hydrogen atoms).
In order to gain a deeper understanding of eclipsed conformations in organic chemistry, it is first important to understand how organic molecules are arranged around bonds, as well as how they move and rotate.
In the example of ethane, two methyl groups are connected with a carbon-carbon sigma bond, just as one might connect two Lego pieces through a single “stud” and “tube”. With this image in mind, if the methyl groups are rotated around the bond, they will remain connected; however, the shape will change. This leads to multiple possible three-dimensional arrangements, known as conformations, conformational isomers (conformers), or sometimes rotational isomers (rotamers). | 4 | Stereochemistry |
Material may be separated by means of air elutriation, which employs an apparatus with a vertical tube through which fluid is passed at a controlled velocity. When the particles are introduced, often through a side tube, the smaller particles are carried over in the fluid stream while the large particles settle against the upward current. If we start with low flow rates small less dense particle attain terminal velocities, and flow with the stream, the particle from the stream is collected in overflow and hence will be separated from the feed. Flow rates can be increased to separate higher size ranges. Further size fractions may be collected if the overflow from the first tube is passed vertically upwards through a second tube of greater cross-section, and any number of such tubes can be arranged in series.
Advantages: a bulk sample is analyzed using centrifugal classification and the technique is non-destructive. Each cut-point can be recovered for future size-respective chemical analyses. This technique has been used for decades in the air pollution control industry (data used for design of control devices). This technique determines particle size as a function of settling velocity in an air stream (as opposed to water, or some other liquid).
Disadvantages: a bulk sample (about ten grams) must be obtained. It is a fairly time-consuming analytical technique. The actual test method has been withdrawn by ASME due to obsolescence. Instrument calibration materials are therefore no longer available. | 7 | Physical Chemistry |
*Honor by the Sudanese Ambassador / Ahmed alsadeeq Abdulhai – Sudan Ambassador in UAE – On celebrations of Sudan's 56th Independence Day.2012
*Honor from Sudanese Consulate in Dubai and Sudanese Club On celebrations of Sudan's 56th Independence Day- Sudanese Club in Dubai.2012
*Honor from the higher Council for the Sudanese community in the UAE – On celebrations of Sudan's 56th Independence Day.2012
*Honor from Al-Merrikh sport club On celebrations of Sudan's 56th Independence Day- Sudanese Club in Dubai.2012
*Award by Vice President of Ajman University for Commendable achievement for the year.2011 | 7 | Physical Chemistry |
The method avoids DNA cloning (with the exception of NAPPA) and can quickly convert genetic information into functional proteins by using PCR DNA. The reduced steps in production and the ability to miniaturize the system saves on reagent consumption and cuts production costs. | 1 | Biochemistry |
Carbon dioxide, a key reactant in photosynthesis, is present in the atmosphere at a concentration of about 400 ppm. Most plants require the stomata to be open during daytime. The air spaces in the leaf are saturated with water vapour, which exits the leaf through the stomata in a process known as transpiration. Therefore, plants cannot gain carbon dioxide without simultaneously losing water vapour. | 5 | Photochemistry |
An acoustic slowness surface can be determined for each pixel by propagating the acoustic wave in several directions. Having measured the SAW velocity in multiple directions the challenge is then to convert this information into the measurement of crystallographic orientation. The direct calculation of the orientation from velocity is a difficult problem. However, the numerical calculation of the SAW velocity as a function of SAW velocity is relatively simple, as first outlined by Farnell. Therefore, a database of possible slowness surfaces can be pre-calculated and compared to the measurement values. For each measurement pixel the orientation is given by the orientation of the pre-calculated velocity surface which best matches the measured data. These maps can spatially describe the crystal orientation of the material being interrogated and can be used to examine microtexture and sample morphology. The technique is applicable to any crystal structure, however transverse isotropy means the full orientation cannot be determined in hexagonal materials, such as titanium.
In order to calculate the predicted SAW velocity of the sample, the materials density and elastic constants must be known. Elastic constants are typically measured by ultrasonic techniques such as resonant ultrasound spectroscopy, with well-established values for most common engineering materials. However, it is possible to attempt the full inverse problem to determine both the elastic constants and crystallographic orientation from only the measured SAW velocity.
From orientation data, a wealth of information can be devised that aids in the understanding of the sample's microstructure and processing history. Recent developments include understanding: the prior texture of parent phases at elevated temperature; the storage and residual deformation after mechanical testing; the population of various microstructural features, including precipitates and grain boundary character. | 7 | Physical Chemistry |
Early work in the development of liquid-liquid separation techniques was undertaken by Cornish et al. with a process called "systematic fractional distribution" as well as Randall and Longtin, however, the central figure is certainly Lyman C. Craig. Lyman Craigs development of countercurrent distribution began with studying the distribution of a pharmaceutical, mepacrine (atabrine), between the two layers of an ethylene dichloride, methanol, and aqueous buffer biphasic solvent system. The distribution coefficient (K which coincides with partition coefficient) of atabrine varied by the composition of the solvent system and the pH of the buffer. In the next article, Craig was inspired by the work of Martin and Synge with partition chromatography to develop an apparatus that would separate compounds based on their distribution constant (K which coincides with partition coefficient). It was shown that a solvent system composed of benzene, n'-hexane, methanol and water would separate mixtures of organic acids. It is remarkable that the mathematical theory developed hand-in-hand with the progression of applications. Craig continued to pursue this method of separation by testing different compounds, formulating biphasic solvent systems, and most importantly developing a commercially viable instrument.
The CCD technique was employed in many notable separations such as penicillin, polycyclic aromatic hydrocarbons, insulin, bile acids, ribonucleic acids, taxol, Streptomyces antibiotics. and many other antibiotics. | 3 | Analytical Chemistry |
Microcystinase is a protease that selectively degrades Microcystin, an extremely potent cyanotoxin that results in marine pollution and human and animal food chain poisoning. The enzyme is naturally produced by a number of bacteria isolated in Japan and New Zealand. As of 2012, the chemical structure of this enzyme has not been scientifically determined. The enzyme degrades the cyclic peptide toxin microcystin into a linear peptide, which is 160 times less toxic. Other bacteria then further degrade the linear peptide. | 1 | Biochemistry |
The instrumentation needed in order to conduct the data acquisition include a multimode optical fiber, single-mode or few-mode fibers, photon-counting avalanche photodiodes (APDs), multi-tau correlator board, and a computer.
The first step of data acquisition is probing the tissue with multimode optical fibers that deliver a long coherence length laser light to the tissue. The second step of data acquisition is collecting photons emitted from the tissue surface with single-mode or few-mode fibers. The third step of data acquisition is the APDs detect the photons from the single-mode or few-mode fibers. The APDs act like detectors. The APDs will have a transistor-transistor logic output or binary outputs with the use of transistors. These outputs will be fed into the multi-tau correlator board which will calculate the temporal intensity auto-correlation functions of the detected signal. Then, the function outputs onto the computer where the functions are fitted to the diffusion equation in the previous section in order to determine optical properties about the tissue as well as properties of the scatters or red blood cells such as blood flow index and many more. | 7 | Physical Chemistry |
The word ester was coined in 1848 by a German chemist Leopold Gmelin, probably as a contraction of the German , "acetic ether". | 0 | Organic Chemistry |
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