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A cumulative or overall constant, given the symbol β, is the constant for the formation of a complex from reagents. For example, the cumulative constant for the formation of ML is given by
The stepwise constants, K and K refer to the formation of the complexes one step at a time.
It follows that
A cumulative constant can always be expressed as the product of stepwise constants. Conversely, any stepwise constant can be expressed as a quotient of two or more overall constants. There is no agreed notation for stepwise constants, though a symbol such as K is sometimes found in the literature. It is good practice to specify each stability constant explicitly, as illustrated above. | 7 | Physical Chemistry |
xDNA has many applications in chemical and biological research, including expanding upon applications of natural DNA, such as scaffolding. In order to create self-assembling nanostructures, a scaffold is needed as a sort of trellis to support the growth. DNA has been used as a means to this end in the past, but expanded scaffolds make larger scaffolds for more complex self-assembly an option. xDNAs electrical conduction properties also make it a prime candidate as a molecular wire, as its π-π interactions help it efficiently conduct electricity. Its 8-letter alphabet (A, T, C, G, xA, xT, xC, xG) gives it the potential to store 2 times more states per sequence than DNA, where n' is the number of bases in the sequence. For example, combining 6 nucleotides of with B-DNA yields 4096 possible sequences, whereas a combination of the same number of nucleotides created with xDNA yields 262,144 possible sequences. Additionally, xDNA can be used as a fluorescent probe at enzyme active sites, as was its original application by Leonard et al.
xDNA has also been applied to the study of protein-DNA interactions. Due to xDNA's natural fluorescing properties, it can easily be visualized in both lab and living conditions. xDNA is becoming more easy to create and oligomerize, and its high-affinity binding to complementary DNA and RNA sequences means that it can not only help locate these sequences floating around in the cell, but also when they are already interacting with other structures within the cell. xDNA also has potential applications in assays that employ TdT as it may improve reporters, and can be used as an affinity tag for interstrand bonding. | 1 | Biochemistry |
Simon retired from AVCO at the age of 65, moving to Pittsboro, North Carolina. She would operate her own consulting firm, Simon Associates, from her home until 1993. After concluding her research career, she served on numerous committees and advisory boards for government agencies, universities, and corporations. The most notable positions include the Department of Commerce Committee for the National Bureau of Standards, and the committee for the National Medal of Science during the Carter administration. Simon served as the first female trustee at Worcester Polytechnic Institute, where she set up the Dorothy M. Simon Endowed Fund for Fire Safety Studies.
Simon died on March 25, 2016, at the age of 96, in her home in Pittsboro, North Carolina. | 7 | Physical Chemistry |
In the wine/water mixing problem, one starts with two barrels, one holding wine and the other an equal volume of water. A cup of wine is taken from the wine barrel and added to the water. A cup of the wine/water mixture is then returned to the wine barrel, so that the volumes in the barrels are again equal. The question is then posed—which of the two mixtures is purer? The answer is that the mixtures will be of equal purity. The solution still applies no matter how many cups of any sizes and compositions are exchanged, or how little or much stirring at any point in time is done to any barrel, as long as at the end each barrel has the same amount of liquid.
The problem can be solved with logic and without resorting to computation. It is not necessary to state the volumes of wine and water, as long as they are equal. The volume of the cup is irrelevant, as is any stirring of the mixtures. | 7 | Physical Chemistry |
Sedimentation has been used to treat wastewater for millennia.
Primary treatment of sewage is removal of floating and settleable solids through sedimentation. Primary clarifiers reduce the content of suspended solids as well as the pollutant embedded in the suspended solids. Because of the large amount of reagent necessary to treat domestic wastewater, preliminary chemical coagulation and flocculation are generally not used, remaining suspended solids being reduced by following stages of the system. However, coagulation and flocculation can be used for building a compact treatment plant (also called a "package treatment plant"), or for further polishing of the treated water.
Sedimentation tanks called "secondary clarifiers" remove flocs of biological growth created in some methods of secondary treatment including activated sludge, trickling filters and rotating biological contactors. | 3 | Analytical Chemistry |
In many areas of science, Braggs law, Wulff–Braggs condition, or Laue–Bragg interference are a special case of Laue diffraction, giving the angles for coherent scattering of waves from a large crystal lattice. It describes how the superposition of wave fronts scattered by lattice planes leads to a strict relation between the wavelength and scattering angle. This law was initially formulated for X-rays, but it also applies to all types of matter waves including neutron and electron waves if there are a large number of atoms, as well as visible light with artificial periodic microscale lattices. | 3 | Analytical Chemistry |
A replication-competent vector called ONYX-015 is used in replicating tumor cells. It was found that in the absence of the E1B-55Kd viral protein, adenovirus caused very rapid apoptosis of infected, p53(+) cells, and this results in dramatically reduced virus progeny and no subsequent spread. Apoptosis was mainly the result of the ability of EIA to inactivate p300. In p53(-) cells, deletion of E1B 55kd has no consequence in terms of apoptosis, and viral replication is similar to that of wild-type virus, resulting in massive killing of cells.
A replication-defective vector deletes some essential genes. These deleted genes are still necessary in the body so they are replaced with either a helper virus or a DNA molecule. | 1 | Biochemistry |
Scaffold proteins act in at least four ways: tethering signaling components, localizing these components to specific areas of the cell, regulating signal transduction by coordinating positive and negative feedback signals, and insulating correct signaling proteins from competing proteins. | 1 | Biochemistry |
Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785. Antoine Lavoisier in 1787 proposed the name acide malique, which is derived from the Latin word for apple, mālum—as is its genus name Malus.
In German it is named Äpfelsäure (or Apfelsäure) after plural or singular of a sour thing from the apple fruit, but the salt(s) are called Malat(e).
Malic acid is the main acid in many fruits, including apricots, blackberries, blueberries, cherries, grapes, mirabelles, peaches, pears, plums, and quince and is present in lower concentrations in other fruits, such as citrus. It contributes to the sourness of unripe apples. Sour apples contain high proportions of the acid. It is present in grapes and in most wines with concentrations sometimes as high as 5 g/L. It confers a tart taste to wine; the amount decreases with increasing fruit ripeness. The taste of malic acid is very clear and pure in rhubarb, a plant for which it is the primary flavor. It is also the compound responsible for the tart flavor of sumac spice. It is also a component of some artificial vinegar flavors, such as "salt and vinegar" flavored potato chips.
The process of malolactic fermentation converts malic acid to much milder lactic acid. Malic acid occurs naturally in all fruits and many vegetables, and is generated in fruit metabolism.
Malic acid, when added to food products, is denoted by E number E296. It is sometimes used with or in place of the less sour citric acid in sour sweets. These sweets are sometimes labeled with a warning stating that excessive consumption can cause irritation of the mouth. It is approved for use as a food additive in the EU, US and Australia and New Zealand (where it is listed by its INS number 296).
Malic acid contains 10 kJ (2.39 kilocalories) of energy per gram. | 1 | Biochemistry |
The leuco form of malachite green was first prepared by Hermann Fischer in 1877 by condensing benzaldehyde and dimethylaniline in the molecular ratio 1:2 in the presence of sulfuric acid. | 3 | Analytical Chemistry |
Splicing events can be experimentally altered by binding steric-blocking antisense oligos, such as Morpholinos or Peptide nucleic acids to snRNP binding sites, to the branchpoint nucleotide that closes the lariat, or to splice-regulatory element binding sites.
The use of antisense oligonucleotides to modulate splicing has shown great promise as a therapeutic strategy for a variety of genetic diseases caused by splicing defects.
Recent studies have shown that RNA splicing can be regulated by a variety of epigenetic modifications, including DNA methylation and histone modifications. | 1 | Biochemistry |
An increased plasma transferrin level is often seen in patients with iron deficiency anemia, during pregnancy, and with the use of oral contraceptives, reflecting an increase in transferrin protein expression. When plasma transferrin levels rise, there is a reciprocal decrease in percent transferrin iron saturation, and a corresponding increase in total iron binding capacity in iron deficient states
A decreased plasma transferrin level can occur in iron overload diseases and protein malnutrition. An absence of transferrin results from a rare genetic disorder known as atransferrinemia, a condition characterized by anemia and hemosiderosis in the heart and liver that leads to heart failure and many other complications as well as to H63D syndrome.
Studies reveal that a transferrin saturation (serum iron concentration ÷ total iron binding capacity) over 60 percent in men and over 50 percent in women identified the presence of an abnormality in iron metabolism (Hereditary hemochromatosis, heterozygotes and homozygotes) with approximately 95 percent accuracy. This finding helps in the early diagnosis of Hereditary hemochromatosis, especially while serum ferritin still remains low. The retained iron in Hereditary hemochromatosis is primarily deposited in parenchymal cells, with reticuloendothelial cell accumulation occurring very late in the disease. This is in contrast to transfusional iron overload in which iron deposition occurs first in the reticuloendothelial cells and then in parenchymal cells. This explains why ferritin levels remain relative low in Hereditary hemochromatosis, while transferrin saturation is high.
Transferrin and its receptor have been shown to diminish tumour cells when the receptor is used to attract antibodies. | 1 | Biochemistry |
Structures for lossless ion manipulations (SLIM) are a form of ion optics to which various radio frequency and dc electric potentials can be applied and used to enable a broad range of ion manipulations, such as separations based upon ion mobility spectrometry, reactions (unimolecular, ion-molecule, and ion-ion), and storage (i.e. ion trapping). SLIM was developed by Richard D. Smith and coworkers at Pacific Northwest National Laboratory (PNNL) and are generally fabricated from arrays of electrodes on evenly spaced planar surfaces. In 2017, Erin S. Baker, Sandilya Garimella, Yehia Ibrahim, Richard D. Smith and Ian Webb from the Interactive Omics Group of PNNL received the R&D 100 Award for the development of SLIM.
In SLIM, ions move in the space between the two surfaces, in directions controlled using electric fields, and also moved between different of multi-level SLIM, as can be constructed from a stack of printed circuit boards (PCBs). The lossless nature of SLIM is derived from the use of rf electric fields, and particularly the pseudo potential derived from the inhomogeneous electric fields resulting from rf of appropriate frequency applied to multiple adjacent electrodes, and that serves to prevent ions from closely approaching the electrodes and surface where loss would conventionally be expected. SLIM are generally used in conjunction with mass spectrometry for analytical applications. | 7 | Physical Chemistry |
As PA is rapidly converted to DAG, it is very short-lived in the cell. This means that it is difficult to measure PA production and therefore to study the role of PA in the cell. However, PLD activity can be measured by the addition of primary alcohols to the cell. PLD then carries out a transphosphatidylation reaction, instead of hydrolysis, producing phosphatidyl alcohols in place of PA. The phosphatidyl alcohols are metabolic dead-ends, and can be readily extracted and measured. Thus PLD activity and PA production (if not PA itself) can be measured, and, by blocking the formation of PA, the involvement of PA in cellular processes can be inferred. | 1 | Biochemistry |
In chemistry, catalytic resonance theory was developed to describe the kinetics of reaction acceleration using dynamic catalyst surfaces. Catalytic reactions occurring on surfaces that undergo variation in surface binding energy and/or entropy exhibit overall increase in reaction rate when the surface binding energy frequencies are comparable to the natural frequencies of the surface reaction, adsorption, and desorption. | 7 | Physical Chemistry |
Coupon holders are used to fix corrosion coupons inside a pipe or tank and attaches itself to a solid plug or hollow plug. They are usually made from stainless steel 316/316L or Monel and inconel or other corrosion resistant materials. | 8 | Metallurgy |
Emission coefficient is a coefficient in the power output per unit time of an electromagnetic source, a calculated value in physics. The emission coefficient of a gas varies with the wavelength of the light. It has units of mssr. It is also used as a measure of environmental emissions (by mass) per MWh of electricity generated, see: Emission factor. | 7 | Physical Chemistry |
The NV center has a ground-state triplet (A), an excited-state triplet (E) and two intermediate-state singlets (A and E). Both A and E contain m = ±1 spin states, in which the two electron spins are aligned (either up, such that m = +1 or down, such that m = -1), and an m = 0 spin state where the electron spins are antiparallel. Due to the magnetic interaction, the energy of the m = ±1 states is higher than that of the m = 0 state. A and E only contain a spin state singlet each with m = 0.
If an external magnetic field is applied along the defect axis (the axis which aligns with the nitrogen atom and the vacancy) of the NV center, it does not affect the m = 0 states, but it splits the m = ±1 levels (Zeeman effect). Similarly the following other properties of the environment influence the energy level diagram :
# Amplitude and orientation of a static magnetic field splits the m = ±1 levels in the ground and excited states.
# Amplitude and orientation of elastic (strain) or electric fields have a much smaller but also more complex effects on the different levels.
# Continuous-wave microwave radiation (applied in resonance with the transition between m = 0 and (one of the) m = ±1 states) changes the population of the sublevels within the ground and excited state.
# A tunable laser can selectively excite certain sublevels of the ground and excited states.
# Surrounding spins and spin–orbit interaction will modulate the magnetic field experienced by the NV center.
# Temperature and pressure affect different parts of the spectrum including the shift between ground and excited states.
The above-described energy structure is by no means exceptional for a defect in diamond or other semiconductor. It was not this structure alone, but a combination of several favorable factors (previous knowledge, easy production, biocompatibility, simple initialisation, use at room temperature etc.) which suggested the use of the NV center as a qubit and quantum sensor. | 7 | Physical Chemistry |
Flow-FISH (fluorescence in-situ hybridization) is a cytogenetic technique to quantify the copy number of RNA or specific repetitive elements in genomic DNA of whole cell populations via the combination of flow cytometry with cytogenetic fluorescent in situ hybridization staining protocols.
Flow-FISH is most commonly used to quantify the length of telomeres, which are stretches of repetitious DNA (hexameric TTAGGG repeats) at the distal ends of chromosomes in human white blood cells, and a semi-automated method for doing so was published in Nature Protocols. Telomere length in white blood cells has been a subject of interest because telomere length in these cell types (and also of other somatic tissues) declines gradually over the human lifespan, resulting in cell senescence, apoptosis, or transformation. This decline has been shown to be a surrogate marker for the concomitant decline in the telomere length of the hematopoietic stem cell pool, with the granulocyte lineage giving the best indication, presumably due to the absence of a long lived memory subtype and comparatively rapid turnover of these cells.
Flow-FISH is also suitable for the concomitant detection of RNA and protein. This allows for the identification of cells that not only express a gene, but also translate it into protein. This type of Flow-FISH has been used to study latent infection of viruses such as HIV-1 and EBV, but also to track single cell gene expression and translation into protein. | 1 | Biochemistry |
The polymerase chain reaction method is used to quantify nucleic acids by amplifying a nucleic acid molecule with the enzyme DNA polymerase. Conventional PCR is based on the theory that amplification is exponential. Therefore, nucleic acids may be quantified by comparing the number of amplification cycles and amount of PCR end-product to those of a reference sample. However, many factors complicate this calculation, creating uncertainties and inaccuracies. These factors include the following: initial amplification cycles may not be exponential; PCR amplification eventually plateaus after an uncertain number of cycles; and low initial concentrations of target nucleic acid molecules may not amplify to detectable levels. However, the most significant limitation of PCR is that PCR amplification efficiency in a sample of interest may be different from that of reference samples.
Instead of performing one reaction per well, dPCR involves partitioning the PCR solution into tens of thousands of nano-liter sized droplets, where a separate PCR reaction takes place in each one. A PCR solution is made similarly to a TaqMan assay, which consists of template DNA (or RNA), fluorescence-quencher probes, primers, and a PCR master mix, which contains DNA polymerase, dNTPs, MgCl, and reaction buffers at optimal concentrations. Several different methods can be used to partition samples, including microwell plates, capillaries, oil emulsion, and arrays of miniaturized chambers with nucleic acid binding surfaces. The PCR solution is partitioned into smaller units, each with the necessary components for amplification. The partitioned units are then subjected to thermocycling so that each unit may independently undergo PCR amplification. After multiple PCR amplification cycles, the samples are checked for fluorescence with a binary readout of “0” or “1”. The fraction of fluorescing droplets is recorded. The partitioning of the sample allows one to estimate the number of different molecules by assuming that the molecule population follows the Poisson distribution, thus accounting for the possibility of multiple target molecules inhabiting a single droplet. Using Poissons law of small numbers, the distribution of target molecule within the sample can be accurately approximated allowing for a quantification of the target strand in the PCR product. This model simply predicts that as the number of samples containing at least one target molecule increases, the probability of the samples containing more than one target molecule increases. In conventional PCR, the number of PCR amplification cycles is proportional to the starting copy number. Different from many peoples belief that dPCR provides absolute quantification, digital PCR uses statistical power to provide relative quantification. For example, if Sample A, when assayed in 1 million partitions, gives one positive reaction, it does not mean that the Sample A has one starting molecule.
The benefits of dPCR include increased precision through massive sample partitioning, which ensures reliable measurements in the desired DNA sequence due to reproducibility. Error rates are larger when detecting small-fold change differences with basic PCR, while error rates are smaller with dPCR due to the smaller-fold change differences that can be detected in DNA sequence. The technique itself reduces the use of a larger volume of reagent needed, which inevitably will lower experiment cost. Also, dPCR is highly quantitative as it does not rely on relative fluorescence of the solution to determine the amount of amplified target DNA. | 1 | Biochemistry |
Planktonic foraminiferal species diversity depends on available niches, which are in turn related to ocean circulation. By correlation with stable isotope records, maximum diversity has been found to occur after the initiation of a glaciation period. | 9 | Geochemistry |
The crystal structure describes the three-dimensional periodic arrangement of atoms, ions, or molecules in a crystal. The unit cell represents the simplest repeating unit of the crystal structure. It is a parallelepiped containing a certain spatial arrangement of atoms, ions, molecules, or molecular fragments. From the unit cell the crystal structure can be fully reconstructed via translations.
The visualization of a crystal structure can be reduced to the arrangement of atoms, ions, or molecules in the unit cell, with or without cell outlines. Structure elements extending beyond single unit cells, such as isolated molecular or polyhedral units as well as chain, net, or framework structures, can often be better understood by extending the structure representation into adjacent cells.
The space group of a crystal is a mathematical description of the symmetry inherent in the structure. The motif of the crystal structure is given by the asymmetric unit, a minimal subset of the unit cell contents. The unit cell contents can be fully reconstructed via the symmetry operations of the space group on the asymmetric unit. Visualization interfaces usually allow for switching between asymmetric unit and full structure representations.
Bonds between atoms or ions can be identified by characteristic short distances between them. They can be classified as covalent, ionic, hydrogen, or other bonds including hybrid forms. Bond angles can be deduced from the bond vectors in groups of atoms or ions. Bond distances and angles can be made available to the user in tabular form or interactively, by selecting pairs or groups of atoms or ions. In ball-and-stick models of crystal structures, balls represent atoms and sticks represent bonds.
Since organic chemists are particularly interested in molecular structures, it might be useful to be able to single out individual molecular units interactively from the drawing. Organic molecular units need to be given both as 2D structural formulae and full 3D molecular structures. Molecules on special-symmetry positions need to be reconstructed from the asymmetric unit. Protein crystallographers are interested in molecular structures of biological macromolecules, so that provisions need to be made to be able to represent molecular subunits as helices, sheets, or coils, respectively.
Crystal structure visualization can be integrated into a crystallographic database. Alternatively, the crystal structure data are exchanged between the database and the visualization software, preferably using the CIF format. Web-based crystallographic databases can integrate crystal structure visualization capability. Depending on the complexity of the structure, lighting, and 3D effects, crystal structure visualization can require a significant amount of processing power, which is why the actual visualization is typically run on the client.
Currently, web-integrated crystal structure visualization is based on Java applets from open-source projects such as Jmol. Web-integrated crystal structure visualization is tailored for examining crystal structures in web browsers, often supporting wide color spectra (up to 32 bit) and window size adaptation. However, web-generated crystal structure images are not always suitable for publishing due to issues such as resolution depth, color choice, grayscale contrast, or labeling (positioning, font type, font size). | 7 | Physical Chemistry |
Bartolomé de Medina was a successful Spanish merchant who became fascinated with the problem of decreasing silver yields from ores mined in Spanish America. By the mid-sixteenth century, it was well known in Spain that American silver production was in decline due to the depletion of high-grade ores and increasing production costs. The New Laws, prohibiting the enslavement of Indians, had resulted in higher labor costs as miners turned to wage labor and expensive African slaves. These higher production costs made mining and smelting anything but the highest grade silver ores prohibitively expensive, just as the availability of high grade ores was in decline. Bartolomé de Medina initially focused his attentions on learning about new smelting methods from smelters in Spain. He was approached during his research by an unknown German man, known only as "Maestro Lorenzo," who told him that silver could be extracted from ground ores using mercury and a salt-water brine. With this knowledge, Medina left Spain for New Spain (Mexico) in 1554 and established a model patio refinery in order to prove the effectiveness of the new technology. Medina is generally credited with adding "magistral" (a type of copper sulfate CuSO derived from pyrites) to the mercury and salt-water (HO · NaCl) solution in order to catalyze the amalgamation reaction. Some historians assert that there were already sufficient copper sulfates in the local ores and that no additional magistral was needed, though others argue that while naturally occurring copper sulfates allowed for potential amalgamation sans magistral, the erratic results of this method made magistral a key component of the effective refinement of ore on a large scale. Regardless of whether or not Medina's contribution was entirely original, he promoted his process to local miners and was able to obtain a patent from the Viceroy of New Spain. As a result, he is generally credited with the invention of silver amalgamation in the form of the patio process.
The effectiveness of this method was such that when German experts arrived in America in the late 1700s to teach the newest amalgamation technology, they admitted they did not believe they could improve upon the American method in its context. Friedrich Sonneschmidt, a German refiner, stated: "It is not to be expected that there will ever be found a method by which all varieties of ore can be refined, having expenses lower than or even equal to those required by the patio beneficiation." The amalgamation was so efficient that a refiner could turn a profit even if the ores were poor enough to yield only 1.5 oz of silver per 100 lbs of original material. | 8 | Metallurgy |
Standards are used in analytical chemistry. Here, a primary standard is typically a reagent which can be weighed easily, and which is so pure that its weight is truly representative of the number of moles of substance contained. Features of a primary standard include:
# High purity
# Stability (low reactivity)
# Low hygroscopicity (to minimize weight changes due to humidity)
# High equivalent weight (to minimize weighing errors)
# Long lasting molar solution i.e. concentration remains unchanged for long periods of time
# Non-toxicity
# Ready and cheap availability
(The last two are not as essential as the first four.)
Some examples of primary standards for titration of solutions, based on their high purity, are provided:
*Arsenic trioxide for making sodium arsenite solution for standardisation of sodium periodate solution (until Ph. Eur. 3, Appendix 2001 also for iodine and cerium(IV) sulfate solutions, since Ph. Eur. 4, 2002 standardised by sodium thiosulfate)
*Benzoic acid for standardisation of waterless basic solutions: ethanolic sodium and potassium hydroxide, TBAH, and alkali methanolates in methanol, isopropanol, or DMF
*Potassium bromate (KBrO) for standardisation of sodium thiosulfate solutions
*Potassium hydrogen phthalate (usually called KHP) for standardisation of aqueous base and perchloric acid in acetic acid solutions
*Sodium carbonate for standardisation of aqueous acids: hydrochloric, sulfuric acid and nitric acid solutions (but not acetic acid)
*Sodium chloride for standardisation of silver nitrate solutions
*Sulfanilic acid for standardisation of sodium nitrite solutions
*Zinc powder, after being dissolved in sulfuric or hydrochloric acid, for standardization of EDTA solutions
Such standards are often used to make standard solutions. These primary standards are used in titration and are essential for determining unknown concentrations or preparing working standards. | 3 | Analytical Chemistry |
This compound is commercially available. It may be prepared by oxidation of to the sulfoxide, followed by reaction with palladium acetate. | 0 | Organic Chemistry |
Tollens reagent (chemical formula ) is a chemical reagent used to distinguish between aldehydes and ketones along with some alpha-hydroxy ketones which can tautomerize into aldehydes. The reagent consists of a solution of silver nitrate, ammonium hydroxide and some sodium hydroxide (to maintain a basic pH of the reagent solution). It was named after its discoverer, the German chemist Bernhard Tollens. A positive test with Tollens reagent is indicated by the precipitation of elemental silver, often producing a characteristic "silver mirror" on the inner surface of the reaction vessel. | 3 | Analytical Chemistry |
The biopolymers that comprise DNA, RNA and (poly)peptides are linear polymers (i.e.: each monomer is connected to at most two other monomers). The sequence of their monomers effectively encodes information. The transfers of information from one molecule to another are faithful, deterministic transfers, wherein one biopolymers sequence is used as a template for the construction of another biopolymer with a sequence that is entirely dependent on the original biopolymers sequence. When DNA is transcribed to RNA, its complement is paired to it. DNA codes A, G, T, and C are transferred to RNA codes U, C, A, and G, respectively. The encoding of proteins is done in groups of three, known as codons. The standard codon table applies for humans and mammals, but some other lifeforms (including human mitochondria) use different translations. | 1 | Biochemistry |
Neuromodulation also refers to an emerging class of medical therapies that target the nervous system for restoration of function (such as in cochlear implants), relief of pain, or control of symptoms, such as tremor seen in movement disorders like Parkinson's disease. The therapies consist primarily of targeted electrical stimulation, or infusion of medications into the cerebrospinal fluid using intrathecal drug delivery, such as baclofen for spasticity. Electrical stimulation devices include deep brain stimulation systems (DBS), colloquially referred to as "brain pacemakers", spinal cord stimulators (SCS) and vagus nerve stimulators (VNS), which are implanted using minimally invasive procedures, or transcutaneous electrical nerve stimulation and scrambler therapy devices, which are fully external, among others. | 1 | Biochemistry |
A saponifiable lipid is part of the ester functional group. They are made up of long chain carboxylic (of fatty) acids connected to an alcoholic functional group through the ester linkage which can undergo a saponification reaction. The fatty acids are released upon base-catalyzed ester hydrolysis to form ionized salts. The primary saponifiable lipids are free fatty acids, neutral glycerolipids, glycerophospholipids, sphingolipids, and glycolipids.
By comparison, the non-saponifiable class of lipids is made up of terpenes, including fat-soluble A and E vitamins, and certain steroids, such as cholesterol. | 1 | Biochemistry |
Decomposition products of dead plant materials form intimate associations with minerals, making it difficult to isolate and characterize soil organic constituents. 18th century soil chemists successfully used alkaline extraction to isolate a portion of the organic constituents in soil. This led to the theory that a humification process created humic substances; most commonly humic acid, fulvic acid, and humin. However, these humic substances have not been observed in soil. Although humification theory is unsupported by evidence, "the underlying theory persists in the contemporary literature, including current textbooks." Attempts to redefine humic substances in valid terms have resulted in a proliferation of incompatible definitions, "with far-reaching implications beyond our ability to communicate scientifically accurate soil processes and properties." | 9 | Geochemistry |
London dispersion forces (LDF, also known as dispersion forces, London forces, instantaneous dipole–induced dipole forces, fluctuating induced dipole bonds or loosely as van der Waals forces) are a type of intermolecular force acting between atoms and molecules that are normally electrically symmetric; that is, the electrons are symmetrically distributed with respect to the nucleus. They are part of the van der Waals forces. The LDF is named after the German physicist Fritz London. They are the weakest intermolecular force. | 6 | Supramolecular Chemistry |
All cells are coated in either glycoproteins or glycolipids, both of which help determine cell types. Lectins, or proteins that bind carbohydrates, can recognize specific oligosaccharides and provide useful information for cell recognition based on oligosaccharide binding.
An important example of oligosaccharide cell recognition is the role of glycolipids in determining blood types. The various blood types are distinguished by the glycan modification present on the surface of blood cells. These can be visualized using mass spectrometry. The oligosaccharides found on the A, B, and H antigen occur on the non-reducing ends of the oligosaccharide. The H antigen (which indicates an O blood type) serves as a precursor for the A and B antigen. Therefore, a person with A blood type will have the A antigen and H antigen present on the glycolipids of the red blood cell plasma membrane. A person with B blood type will have the B and H antigen present. A person with AB blood type will have A, B, and H antigens present. And finally, a person with O blood type will only have the H antigen present. This means all blood types have the H antigen, which explains why the O blood type is known as the "universal donor".
How do transport vesicles know the final destination of the protein that they are transporting?
Vesicles are directed by many ways, but the two main ways are:
# The sorting signals encoded in the amino acid sequence of the proteins.
# The Oligosaccharide attached to the protein.
The sorting signals are recognised by specific receptors that reside in the membranes or surface coats of budding vesicles, ensuring that the protein is transported to the appropriate destination. | 0 | Organic Chemistry |
There are many applications in which viral transformation can be artificially induced in a cell culture in order to treat an illness or other condition. A cell culture is infected with a virus causing the transformation; transformed cells can then be used to either produce treatments or be directly introduced into the body. | 1 | Biochemistry |
Gold clusters can be obtained in colloid form. Such colloids often occur with a surface coating of alkanethiols or proteins. Such clusters can be used in immunohistochemical staining. Gold metal nanoparticles (NPs) are characterized by an intense absorption in the visible region, which enhances the utility of these species for the development of completely optical devices. The wavelength of this surface plasmon resonance (SPR) band depends on the size and shape of the nanoparticles as well as their interactions with the surrounding medium. The presence of this band enhances the utility of gold nanoparticle as building blocks for devices for data storage, ultrafast switching, and gas sensors. Whilst plasmonic gold nanoparticles only exhibit electric moments, clusters of such particles can exhibit magnetic moments making them of great interest for use in optical metamaterials | 7 | Physical Chemistry |
Xylene was first isolated and named in 1850 by the French chemist Auguste Cahours (1813–1891), having been discovered as a constituent of wood tar. | 2 | Environmental Chemistry |
-Formylkynurenine is an intermediate in the catabolism of tryptophan. It is a formylated derivative of kynurenine. The formation of -formylkynurenine is catalyzed by heme dioxygenases. | 1 | Biochemistry |
As an azo dye, methyl red may be prepared by diazotization of anthranilic acid, followed by reaction with dimethylaniline: | 3 | Analytical Chemistry |
In powder samples there is a tendency for plate- or rod-like crystallites to align themselves along the axis of a cylindrical sample holder. In solid polycrystalline samples the production of the material may result in greater volume fraction of certain crystal orientations (commonly referred to as texture). In such cases the reflex intensities will vary from that predicted for a completely random distribution. Rietveld allowed for moderate cases of the former by introducing a correction factor:
where is the intensity expected for a random sample, is the preferred orientation parameter and is the acute angle between the scattering vector and the normal of the crystallites. | 3 | Analytical Chemistry |
The typical EDI installation has the following components: electrodes, anion exchange membranes, cation exchange membranes, and resin. The simplest configurations comprise three compartments. To increase production intensity or efficiency, the number of compartments or cells can be increased as desired.
Once the system is installed and feedwater begins to flow through it, cations flow toward the cathode and anions flow toward the anode. Only anions can go through the anion exchange membrane, and only cations can go through the cation exchange membrane. This configuration allows anions and cations to flow in only one direction because of the selectivity of the membranes and the electrical forces, rendering the feedwater relatively free of ions. It also allows for the separate collection of cation and anion concentration flows, creating the opportunity for more selective waste disposal, recycling, or reuse; this is especially useful in the removal of heavy metal cations. | 7 | Physical Chemistry |
A decrease in pH (increase in ion concentration) shifts the standard curve to the right, while an increase shifts it to the left. This occurs because at greater ion concentration, various amino acid residues, such as Histidine 146 exist predominantly in their protonated form allowing them to form ion pairs that stabilize deoxyhemoglobin in the T state. The T state has a lower affinity for oxygen than the R state, so with increased acidity, the hemoglobin binds less O for a given P (and more H). This is known as the Bohr effect. A reduction in the total binding capacity of hemoglobin to oxygen (i.e. shifting the curve down, not just to the right) due to reduced pH is called the root effect. This is seen in bony fish. The binding affinity of hemoglobin to O is greatest under a relatively high pH. | 1 | Biochemistry |
Attempts at standardized temperature measurement prior to the 17th century were crude at best. For instance in 170 AD, physician Claudius Galenus mixed equal portions of ice and boiling water to create a "neutral" temperature standard. The modern scientific field has its origins in the works by Florentine scientists in the 1600s including Galileo constructing devices able to measure relative change in temperature, but subject also to confounding with atmospheric pressure changes. These early devices were called thermoscopes. The first sealed thermometer was constructed in 1654 by the Grand Duke of Tuscany, Ferdinand II. The development of todays thermometers and temperature scales began in the early 18th century, when Gabriel Fahrenheit produced a mercury thermometer and scale, both developed by Ole Christensen Rømer. Fahrenheits scale is still in use, alongside the Celsius and Kelvin scales. | 7 | Physical Chemistry |
The candidate editing sites were determined experimentally by comparison of cDNA sequences and genomically encoded DNA from the same individual to avoid single nucleotide polymorphisms (SNPs). Two of the three editing sites found in mouse gene were found in the human transcript.
However, only the Q/R site was detected in all RNA, with the T/A site detected just once. Both sites are found within exon 1.
Q/R site
This site is found in exon 1 at position 66. Editing results in a codon change from a Glutamine codon to an Arginine codon.
T/A site
This site is also found in exon 1, at position 63. It was only detected in one genomic sample indicating that the edited residue may be an SNP. However, the secondary structure of the RNA is predicted, around the editing site, to be highly conserved in mice and humans. This indicates that the T/A site may still be shown to be a site of A to I RNA editing. Editing at this site would result in an amino acid change from a Threonine to an Alanine.
The ECS is also predicted to be found within exon 1 at a location 5' to the editing region. | 1 | Biochemistry |
In humans, two isoforms of glycogenin can be expressed: glycogenin-1, with a molecular weight of 37 kDa and codified by GYG1 gen, which is expressed mostly in muscles; and glycogenin-2, with a molecular weight of 66 kDa and codified by GYG2 gen, which is expressed mainly in liver, cardiac muscle and other types of tissue, but not in skeletal muscle.
Glycogenin-1 was described by analyzing the glycogen of skeletal muscle. It was determined that this molecule was united by a covalent bond to each mature molecule of muscular glycogen. | 1 | Biochemistry |
A high-frequency approximation (or "high energy approximation") for scattering or other wave propagation problems, in physics or engineering, is an approximation whose accuracy increases with the size of features on the scatterer or medium relative to the wavelength of the scattered particles.
Classical mechanics and geometric optics are the most common and extreme high frequency approximation, where the wave or field properties of, respectively, quantum mechanics and electromagnetism are neglected entirely.
Less extreme approximations include, the WKB approximation, physical optics, the geometric theory of diffraction, the uniform theory of diffraction, and the physical theory of diffraction. When these are used to approximate quantum mechanics, they are called semiclassical approximations. | 7 | Physical Chemistry |
The perovskite structure is adopted at high pressure by bridgmanite, a silicate with the chemical formula , which is the most common mineral in the Earth's mantle. As pressure increases, the SiO tetrahedral units in the dominant silica-bearing minerals become unstable compared with SiO octahedral units. At the pressure and temperature conditions of the lower mantle, the second most abundant material is likely the rocksalt-structured oxide, periclase.
At the high pressure conditions of the Earths lower mantle, the pyroxene enstatite, MgSiO, transforms into a denser perovskite-structured polymorph; this phase may be the most common mineral in the Earth. This phase has the orthorhombically distorted perovskite structure (GdFeO-type structure) that is stable at pressures from ~24 GPa to ~110 GPa. However, it cannot be transported from depths of several hundred km to the Earths surface without transforming back into less dense materials. At higher pressures, MgSiO perovskite, commonly known as silicate perovskite, transforms to post-perovskite. | 3 | Analytical Chemistry |
For altering moss genes in a targeted way, the DNA-construct needs to be incubated together with moss protoplasts and with polyethylene glycol (PEG). Because mosses are haploid organisms, the regenerating moss filaments (protonemata) can be directly assayed for gene targeting within six weeks when utilizing PCR methods. | 1 | Biochemistry |
Cholesterol 7 alpha-hydroxylase is the rate-limiting enzyme in the synthesis of bile acid from cholesterol via the classic pathway, catalyzing the formation of 7α-hydroxycholesterol. The unique detergent properties of bile acids are essential for the digestion and intestinal absorption of hydrophobic nutrients.
Bile acids have powerful toxic properties like membrane disruption and there are a wide range of mechanisms to restrict their accumulation in tissues and blood. The discovery of farnesoid X receptor (FXR) which is located in the liver, has opened new insights. Bile acid activation of FXR represses the expression of CYP7A1 via, raising the expression of small heterodimer partner (SHP, NR0B2), a non-DNA binding protein.
The increased abundance of SHP causes it to associate with liver receptor homolog (LRH)-1, an obligate factor required for the transcription of CYP7A1. Furthermore, there is an "FXR/SHP-independent" mechanism that also represses CYP7A1 expression. This "FXR/SHP-independent" pathway involves the interaction of bile acids with liver macrophages, which finally induces the expression and secretion of cytokines. These inflammatory cytokines, which include tumor necrosis factor alpha and interleukin-1beta, act upon the liver parenchymal cells causing a rapid repression of the CYP7A1 gene. | 1 | Biochemistry |
Another commonly considered model is the heat pump or refrigerator. Again there are four bodies: the working body, the hot reservoir, the cold reservoir, and the work reservoir. A single cycle starts with the working body colder than the cold reservoir, and then energy is taken in as heat by the working body from the cold reservoir. Then the work reservoir does work on the working body, adding more to its internal energy, making it hotter than the hot reservoir. The hot working body passes heat to the hot reservoir, but still remains hotter than the cold reservoir. Then, by allowing it to expand without passing heat to another body, the working body is made colder than the cold reservoir. It can now accept heat transfer from the cold reservoir to start another cycle.
The device has transported energy from a colder to a hotter reservoir, but this is not regarded as by an inanimate agency; rather, it is regarded as by the harnessing of work . This is because work is supplied from the work reservoir, not just by a simple thermodynamic process, but by a cycle of thermodynamic operations and processes, which may be regarded as directed by an animate or harnessing agency. Accordingly, the cycle is still in accord with the second law of thermodynamics. The efficiency of a heat pump (which exceeds unity) is best when the temperature difference between the hot and cold reservoirs is least.
Functionally, such engines are used in two ways, distinguishing a target reservoir and a resource or surrounding reservoir. A heat pump transfers heat to the hot reservoir as the target from the resource or surrounding reservoir. A refrigerator transfers heat, from the cold reservoir as the target, to the resource or surrounding reservoir. The target reservoir may be regarded as leaking: when the target leaks heat to the surroundings, heat pumping is used; when the target leaks coldness to the surroundings, refrigeration is used. The engines harness work to overcome the leaks. | 7 | Physical Chemistry |
* Butyl butyrate
* Butyryl-CoA
* Cellulose acetate butyrate (aircraft dope)
* Estradiol benzoate butyrate
* Ethyl butyrate
* Methyl butyrate
* Pentyl butyrate
* Tributyrin | 1 | Biochemistry |
Bathochromic shift is typically demonstrated using a spectrophotometer, colorimeter, or spectroradiometer. | 7 | Physical Chemistry |
Nitrolic acids are organic compounds with the functional group RC(NO)=NOH. They are prepared by the reaction of nitroalkanes with base and nitrite sources:
:RCHNO + HNO → RC(NO)=NOH + HO
The conversion was first demonstrated by Victor Meyer using nitroethane. The reaction proceeds via the intermediacy of the nitronate anion. | 0 | Organic Chemistry |
Base degradation of ortho carborane gives the anionic 11-vertex derivative, precursor to dicarbollide complexes:
:CBH + NaOEt + 2 EtOH → NaCBH + H + B(OEt)
:NaCBH + NaH → NaCBH + H
Dicarbollides (CBH) function as ligands for transition metals and f-elements. The dianion forms sandwich compounds, bis(dicarbollides). Dicarbollides, being strong electron donors, stabilize higher oxidation states, e.g. Ni(IV). | 7 | Physical Chemistry |
Berend (Bert) Poolman is a Dutch biochemist, as specialist in bioenergetics of microorganisms and membrane transport. He is a professor of Biochemistry at the University of Groningen and an elected member of the Royal Netherlands Academy of Arts and Sciences (KNAW) since 2009. Poolman is a pioneer in the field of bottom-up synthetic biology, that is, the construction from molecular building blocks of functional metabolic networks and autonomously operating functional systems, which are typical of living cells. Poolman is a lecturer in membrane biology and synthetic biology. | 0 | Organic Chemistry |
Partially digested food starts to arrive in the small intestine as semi-liquid chyme, one hour after it is eaten. The stomach is half empty after an average of 1.2 hours. After four or five hours the stomach has emptied.
In the small intestine, the pH becomes crucial; it needs to be finely balanced in order to activate digestive enzymes. The chyme is very acidic, with a low pH, having been released from the stomach and needs to be made much more alkaline. This is achieved in the duodenum by the addition of bile from the gall bladder combined with the bicarbonate secretions from the pancreatic duct and also from secretions of bicarbonate-rich mucus from duodenal glands known as Brunner's glands. The chyme arrives in the intestines having been released from the stomach through the opening of the pyloric sphincter. The resulting alkaline fluid mix neutralises the gastric acid which would damage the lining of the intestine. The mucus component lubricates the walls of the intestine.
When the digested food particles are reduced enough in size and composition, they can be absorbed by the intestinal wall and carried to the bloodstream. The first receptacle for this chyme is the duodenal bulb. From here it passes into the first of the three sections of the small intestine, the duodenum (the next section is the jejunum and the third is the ileum). The duodenum is the first and shortest section of the small intestine. It is a hollow, jointed C-shaped tube connecting the stomach to the jejunum. It starts at the duodenal bulb and ends at the suspensory muscle of duodenum. The attachment of the suspensory muscle to the diaphragm is thought to help the passage of food by making a wider angle at its attachment.
Most food digestion takes place in the small intestine. Segmentation contractions act to mix and move the chyme more slowly in the small intestine allowing more time for absorption (and these continue in the large intestine). In the duodenum, pancreatic lipase is secreted together with a co-enzyme, colipase to further digest the fat content of the chyme. From this breakdown, smaller particles of emulsified fats called chylomicrons are produced. There are also digestive cells called enterocytes lining the intestines (the majority being in the small intestine). They are unusual cells in that they have villi on their surface which in turn have innumerable microvilli on their surface. All these villi make for a greater surface area, not only for the absorption of chyme but also for its further digestion by large numbers of digestive enzymes present on the microvilli.
The chylomicrons are small enough to pass through the enterocyte villi and into their lymph capillaries called lacteals. A milky fluid called chyle, consisting mainly of the emulsified fats of the chylomicrons, results from the absorbed mix with the lymph in the lacteals. Chyle is then transported through the lymphatic system to the rest of the body.
The suspensory muscle marks the end of the duodenum and the division between the upper gastrointestinal tract and the lower GI tract. The digestive tract continues as the jejunum which continues as the ileum. The jejunum, the midsection of the small intestine contains circular folds, flaps of doubled mucosal membrane which partially encircle and sometimes completely encircle the lumen of the intestine. These folds together with villi serve to increase the surface area of the jejunum enabling an increased absorption of digested sugars, amino acids and fatty acids into the bloodstream. The circular folds also slow the passage of food giving more time for nutrients to be absorbed.
The last part of the small intestine is the ileum. This also contains villi and vitamin B12; bile acids and any residue nutrients are absorbed here. When the chyme is exhausted of its nutrients the remaining waste material changes into the semi-solids called feces, which pass to the large intestine, where bacteria in the gut flora further break down residual proteins and starches.
Transit time through the small intestine is an average of 4 hours. Half of the food residues of a meal have emptied from the small intestine by an average of 5.4 hours after ingestion. Emptying of the small intestine is complete after an average of 8.6 hours. | 1 | Biochemistry |
-Hb dissociation curve is a sigmoidal curve that represents the relationship between O concentration and the percentage saturation of Hb. As the concentration increases from about 90% there is a plateau in the curve that has several important biological implications.|right|thumb|300px||
The oxygen–hemoglobin dissociation curve, also called the oxyhemoglobin dissociation curve or oxygen dissociation curve (ODC), is a curve that plots the proportion of hemoglobin in its saturated (oxygen-laden) form on the vertical axis against the prevailing oxygen tension on the horizontal axis. This curve is an important tool for understanding how our blood carries and releases oxygen. Specifically, the oxyhemoglobin dissociation curve relates oxygen saturation (S) and partial pressure of oxygen in the blood (P), and is determined by what is called "hemoglobin affinity for oxygen"; that is, how readily hemoglobin acquires and releases oxygen molecules into the fluid that surrounds it. | 1 | Biochemistry |
Although the Montreal Protocol regulates the phasing out of HCFCs, there was no international agreement on the regulation of HFCs until late 2016 when the Kigali Amendment under the Montreal Protocol was signed, which has put compulsory phase wise phasing out of CFC gases. Efforts are ongoing to develop a global approach for the control of HFCs. Most recently, this has taken the form of a declaration of support for a global phase-down as part of the outcomes of the "Rio+20" United Nations Conference on Sustainable Development. | 2 | Environmental Chemistry |
The first recorded use of the term automated mineralogy in technical journals can be traced back to seminal papers in the late eighties early nineties describing QEMSCAN technology and applications. The term gained significant popularity after it was used to name a new international conference in July 2006. | 7 | Physical Chemistry |
Since thermal bumps can either cool or heat the chip depending on the current direction, they can be used to provide precision control of temperature for chips that must operate within specific temperature ranges irrespective of ambient conditions. For example, this is a common problem for many optoelectronic components. | 7 | Physical Chemistry |
An increase in certain hormones such as oestrogen, progesterone, human placental lactogen, human placental growth hormone and cortisol during the second and third trimester of pregnancy cause an increase in insulin resistance. This increase in insulin resistance and following increase in insulin secretion ensures that the foetus develops a normal glucose tolerance. Gestational Diabetes Mellitus (GDM) arises when beta cells do not secrete enough insulin to adopt to the insulin resistance triggered by pregnancy, which leads to mild hyperglycaemia.
Although the mechanisms are still largely unknown, foetus exposure to GDM and maternal diabetes has been shown to lead to lifelong metabolic complications because of metabolic imprinting. The risk of Type II diabetes developing in offspring is significantly higher in offspring where the mother was diagnosed with Type II diabetes before pregnancy rather than after. In addition, the age at which offspring are diagnosed with Type 2 diabetes is significantly younger in offspring exposed to maternal diabetes/GDM than those who are not. It is suggested that this is a result of DNA methylation during foetal development. | 1 | Biochemistry |
UTP also has roles in mediating responses by extracellular binding to the P2Y receptors of cells. UTP and its derivatives are still being investigated for their applications in human medicine. However, there is evidence from various model systems to suggest it has applications in pathogen defense and injury repair. In mice UTP has been found to interact with P2Y4 receptors to mediate an enhancement in antibody production. In Schwannoma cells, UTP binds to the P2YP receptors in the event of damage. This leads to the downstream signal cascade that leads to the eventual injury repair. | 1 | Biochemistry |
A dispersion is a system in which distributed particles of one material are dispersed in a continuous phase of another material. The two phases may be in the same or different states of matter.
Dispersions are classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not precipitation occurs, and the presence of Brownian motion. In general, dispersions of particles sufficiently large for sedimentation are called suspensions, while those of smaller particles are called colloids and solutions. | 7 | Physical Chemistry |
* (German) Richard van Basshuysen: Handbuch Verbrennungsmotor, Fred Schäfer; 3. Auflage; 2005; Vieweg Verlag | 7 | Physical Chemistry |
Hormones have the following effects on the body:
* stimulation or inhibition of growth
* wake-sleep cycle and other circadian rhythms
* mood swings
* induction or suppression of apoptosis (programmed cell death)
* activation or inhibition of the immune system
* regulation of metabolism
* preparation of the body for mating, fighting, fleeing, and other activity
* preparation of the body for a new phase of life, such as puberty, parenting, and menopause
* control of the reproductive cycle
* hunger cravings
A hormone may also regulate the production and release of other hormones. Hormone signals control the internal environment of the body through homeostasis. | 1 | Biochemistry |
Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNA at first non-coding RNA molecules, typically 20–24 (normally 21) base pairs in length, similar to miRNA, and operating within the RNA interference (RNAi) pathway. It interferes with the expression of specific genes with complementary nucleotide sequences by degrading mRNA after transcription, preventing translation.
It was discovered in 1998, by Andrew Fire at Carnegie Institution for Science in Washington DC and Craig Mello at University of Massachusetts in Worcester. | 1 | Biochemistry |
Ammonia exhibits a quantum tunnelling due to a narrow tunneling barrier, and not due to thermal excitation. Superposition of two states leads to energy level splitting, which is used in ammonia masers. | 4 | Stereochemistry |
Nucleophilic/electrophilic cascades are
defined as the cascade sequences in which the key step constitutes a nucleophilic
or electrophilic attack.
An example of such a cascade is seen in the short enantioselective synthesis of the broad-spectrum antibiotic (–)-chloramphenicol, reported by Rao et al. (Scheme 1). Herein, the chiral epoxy-alcohol 1 was first treated with dichloroacetonitrile in the presence of NaH. The resulting intermediate 2 then underwent a BF·EtO-mediated cascade reaction. Intramolecular opening of the epoxide ring yielded intermediate 3, which, after an in situ hydrolysis facilitated by excess BF·EtO, afforded (–)-chloramphenicol (4) in 71% overall yield.
A nucleophilic cascade was also employed in the total synthesis of the natural product pentalenene (Scheme 2). In this procedure, squarate ester 5 was treated with (5-methylcyclopent-1-en-1-yl)lithium and propynyllithium. The two nucleophilic attacks occurred predominantly with trans addition to afford intermediate 6, which spontaneously underwent a 4π-conrotatory electrocyclic opening of the cyclobutene ring. The resulting conjugated species 7 equilibrated to conformer 8, which more readily underwent an 8π-conrotatory electrocyclization to the highly strained intermediate 9. The potential to release strain directed protonation of 9 such that species 10 was obtained selectively. The cascade was completed by an intramolecular aldol condensation that afforded product 11 in 76% overall yield. Further elaboration afforded the target (±)-pentalenene (12). | 0 | Organic Chemistry |
Atmospheric corrosion generally refers to general corrosion in a non-specific environment. Prevention of atmospheric corrosion is typically handled by use of materials selection and coatings specifications. The use of zinc coatings also known as galvanization on steel structures is a form of cathodic protection where the zinc acts as a sacrificial anode and also a form of coating. Small scratches are expected to occur in the galvanized coating over time. The zinc being more active in the galvanic series corrodes in preference to the underlying steel and the corrosion products fil the scratch preventing further corrosion. As long as the scratches are fine, condensation moisture should not corrode the underlying steel as long as both the zinc and steel are in contact. As long as there is moisture, the zinc corrodes and eventually disappears. Impressed current cathodic protection is also used. | 8 | Metallurgy |
In the sulfite process for paper-making, lignin is removed from the lignocellulose by treating wood chips with solutions of sulfite and bisulfite ions. These reagents cleave the bonds between the cellulose and lignin components and especially within the lignin itself. The lignin is converted to lignosulfonates, useful ionomers, which are soluble and can be separated from the cellulose fibers. | 0 | Organic Chemistry |
In geological applications, detecting the presence of calcite or other forms of calcium carbonate in alkaline soils or during lithological analysis involves using dilute hydrochloric acid and observing effervescence. | 3 | Analytical Chemistry |
Nujol is a brand of mineral oil by Plough Inc., cas number 8012-95-1, and density 0.838 g/mL at 25 °C, used in infrared spectroscopy. It is a heavy paraffin oil so it is chemically inert and has a relatively uncomplicated IR spectrum, with major peaks between 2950-2800, 1465-1450, and 1380–1300 cm. The empirical formula of Nujol is hard to determine exactly because it is a mixture but it is essentially the alkane formula where n is very large.
To obtain an IR spectrum of a solid, a sample is combined with Nujol in a mortar and pestle or some other device to make a mull (a very thick suspension), and is usually sandwiched between potassium- or sodium chloride plates before being placed in the spectrometer. For very reactive samples, the layer of Nujol can provide a protective coating, preventing sample decomposition during acquisition of the IR spectrum. When preparing the sample it is important to keep the sample from being saturated with Nujol, this will result in erroneous spectra since the Nujol peaks will dominate, silencing the actual sample's peaks. | 0 | Organic Chemistry |
The Victor Meyer apparatus is the standard laboratory method for determining the molecular weight of a volatile liquid. It was developed by Viktor Meyer, who spelled his name Victor in publications at the time of its development. In this method, a known mass of a volatile solid or liquid under examination is converted into its vapour form by heating in a Victor Meyers tube. The vapour displaces its own volume of air. The volume of air displaced at experimental temperature and pressure is calculated. Then volume of air displaced at standard temperature and pressure is calculated. Using this, mass of air displaced at 2.24 × 10 m of vapour at STP is calculated. This value represents the molecular mass of the substance. The apparatus consists of an inner Victor Meyers tube, lower end of which is in form of a bulb. The upper end of tube has a side tube that leads to a trough filled with water. The Victor Meyers tube is surrounded by an outer jacket. In the outer jacket, a liquid is placed, which boils at a temperature at least 30 K higher than the substance under examination. A small quantity of glass-wool or asbestos pad covers the lower end of the Victor Meyers tube to prevent breakage, when a glass bottle containing the substance under examination is dropped to it | 7 | Physical Chemistry |
Real-time PCR permits the identification of specific, amplified DNA fragments using analysis of their melting temperature (also called T value, from melting temperature). The method used is usually PCR with double-stranded DNA-binding dyes as reporters and the dye used is usually SYBR Green. The DNA melting temperature is specific to the amplified fragment. The results of this technique are obtained by comparing the dissociation curves of the analysed DNA samples.
Unlike conventional PCR, this method avoids the previous use of electrophoresis techniques to demonstrate the results of all the samples. This is because, despite being a kinetic technique, quantitative PCR is usually evaluated at a distinct end point. The technique therefore usually provides more rapid results and/or uses fewer reactants than electrophoresis. If subsequent electrophoresis is required it is only necessary to test those samples that real time PCR has shown to be doubtful and/or to ratify the results for samples that have tested positive for a specific determinant. | 1 | Biochemistry |
Harry Clary Jones (11 November 1865 – 9 April 1916) was an American physical chemist and a professor of chemistry at Johns Hopkins University. He worked extensively on the chemistry of solutions. His textbook Elements of Physical Chemistry was influential in its day. In 1913, he published a vision of chemistry in his book A new era in chemistry in which he noted the gaps of contemporary chemistry and indicated directions for work. | 7 | Physical Chemistry |
Photoinhibition follows simple first-order kinetics if measured from a lincomycin-treated leaf, cyanobacterial or algal cells, or isolated thylakoid membranes in which concurrent repair does not disturb the kinetics. Data from the group of W. S. Chow indicate that in leaves of pepper (Capsicum annuum), the first-order pattern is replaced by a pseudo-equilibrium even if the repair reaction is blocked. The deviation has been explained by assuming that photoinhibited PSII centers protect the remaining active ones.
Both visible and ultraviolet light cause photoinhibition, ultraviolet wavelengths being much more damaging. Some researchers consider ultraviolet and visible light induced photoinhibition as a two different reactions, while others stress the similarities between the inhibition reactions occurring under different wavelength ranges. | 5 | Photochemistry |
For the reaction
the observed rate equation (or rate expression) is:
As for many reactions, the experimental rate equation does not simply reflect the stoichiometric coefficients in the overall reaction: It is third order overall: first order in H and second order in NO, even though the stoichiometric coefficients of both reactants are equal to 2.
In chemical kinetics, the overall reaction rate is often explained using a mechanism consisting of a number of elementary steps. Not all of these steps affect the rate of reaction; normally the slowest elementary step controls the reaction rate. For this example, a possible mechanism is:
Reactions 1 and 3 are very rapid compared to the second, so the slow reaction 2 is the rate-determining step. This is a bimolecular elementary reaction whose rate is given by the second-order equation:
where is the rate constant for the second step.
However NO is an unstable intermediate whose concentration is determined by the fact that the first step is in equilibrium, so that where is the equilibrium constant of the first step. Substitution of this equation in the previous equation leads to a rate equation expressed in terms of the original reactants
This agrees with the form of the observed rate equation if it is assumed that . In practice the rate equation is used to suggest possible mechanisms which predict a rate equation in agreement with experiment.
The second molecule of H does not appear in the rate equation because it reacts in the third step, which is a rapid step after the rate-determining step, so that it does not affect the overall reaction rate. | 7 | Physical Chemistry |
In free-radical additions, a radical adds to a spin-paired substrate. When applied to organic compounds, the reaction usually entails addition to an alkene. This addition generates a new radical, which can add to yet another alkene, etc. This behavior underpins radical polymerization, technology that produces many plastics. | 2 | Environmental Chemistry |
The transformation was discovered in 1979 by Pierre Crabbé and coworkers at the Université Scientifique et Médicale (currently merged into Université Grenoble Alpes) in Grenoble, France. As initially discovered, the reaction was a one-carbon homologation reaction (the Crabbé homologation) of a terminal alkyne into a terminal allene using formaldehyde as the carbon source, with diisopropylamine as base and copper(I) bromide as catalyst.
Despite the excellent result for the substrate shown, yields were highly dependent on substrate structure and the scope of the process was narrow. The author noted that iron salts were completely ineffective, while cupric and cuprous chloride and bromide, as well as silver nitrate provided the desired product, but in lower yield under the standard conditions.
Shengming Ma (麻生明) and coworkers at the Shanghai Institute of Organic Chemistry (SIOC, Chinese Academy of Sciences) investigated the reaction in detail, including clarifying the critical role of the base, and developed conditions that exhibited superior functional-group compatibility and generally resulted in higher yields of the allene. One of the key changes was the use of dicyclohexylamine as the base. In another important advance, the Ma group found that the combination of zinc iodide and morpholine allowed aldehydes besides formaldehyde, including benzaldehyde derivatives and a more limited range of aliphatic aldehydes, to be used as coupling partners, furnishing 1,3-disubstituted allenes via an alkyne-aldehyde coupling method of substantial generality and utility. A separate protocol utilizing copper catalysis and a fine-tuned amine base was later developed to obtain better yields for aliphatic aldehydes.
The Crabbé reaction is applicable to a limited range of ketone substrates for the synthesis of trisubstituted allenes; however, a near stoichiometric quantity (0.8 equiv) of cadmium iodide (CdI) is needed to promote the reaction. Alternatively, the use of cuprous bromide and zinc iodide sequentially as catalysts is also effective, provided the copper catalyst is filtered before zinc iodide is added. | 0 | Organic Chemistry |
Systematic evolution of ligands by exponential enrichment (SELEX), also referred to as in vitro selection or in vitro evolution, is a combinatorial chemistry technique in molecular biology for producing oligonucleotides of either single-stranded DNA or RNA that specifically bind to a target ligand or ligands. These single-stranded DNA or RNA are commonly referred to as aptamers.
Although SELEX has emerged as the most commonly used name for the procedure, some researchers have referred to it as SAAB (selected and amplified binding site) and CASTing (cyclic amplification and selection of targets) SELEX was first introduced in 1990. In 2015, a special issue was published in the Journal of Molecular Evolution in the honor of quarter century of the discovery of SELEX.
The process begins with the synthesis of a very large oligonucleotide library, consisting of randomly generated sequences of fixed length flanked by constant 5 and 3 ends. The constant ends serve as primers, while a small number of random regions are expected to bind specifically to the chosen target. For a randomly generated region of length n, the number of possible sequences in the library using conventional DNA or RNA is 4 (n positions with four possibilities (A,T,C,G) at each position). The sequences in the library are exposed to the target ligand - which may be a protein or a small organic compound - and those that do not bind the target are removed, usually by affinity chromatography or target capture on paramagnetic beads. The bound sequences are eluted and amplified by PCR to prepare for subsequent rounds of selection in which the stringency of the elution conditions can be increased to identify the tightest-binding sequences. A caution to consider in this method is that the selection of extremely high, sub-nanomolar binding affinity entities may not in fact improve specificity for the target molecule. Off-target binding to related molecules could have significant clinical effects.
SELEX has been used to develop a number of aptamers that bind targets interesting for both clinical and research purposes. Nucleotides with chemically modified sugars and bases have been incorporated into SELEX reactions to increase the chemical diversity at each base, expanding the possibilities for specific and sensitive binding, or increasing stability in serum or in vivo. | 1 | Biochemistry |
The theories developed in the early 20th century to integrate Mendelian genetics with Darwinian evolution are called the modern synthesis, a term introduced by Julian Huxley.
This view of evolution was emphasized by George C. Williams' gene-centric view of evolution. He proposed that the Mendelian gene is a unit of natural selection with the definition: "that which segregates and recombines with appreciable frequency." Related ideas emphasizing the centrality of Mendelian genes and the importance of natural selection in evolution were popularized by Richard Dawkins.
The development of the neutral theory of evolution in the late 1960s led to the recognition that random genetic drift is a major player in evolution and that neutral theory should be the null hypothesis of molecular evolution. This led to the construction of phylogenetic trees and the development of the molecular clock, which is the basis of all dating techniques using DNA sequences. These techniques are not confined to molecular gene sequences but can be used on all DNA segments in the genome. | 1 | Biochemistry |
A biological half-life or elimination half-life is the time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or radiological activity. In a medical context, the half-life may also describe the time that it takes for the concentration of a substance in blood plasma to reach one-half of its steady-state value (the "plasma half-life").
The relationship between the biological and plasma half-lives of a substance can be complex, due to factors including accumulation in tissues, active metabolites, and receptor interactions.
While a radioactive isotope decays almost perfectly according to so-called "first order kinetics" where the rate constant is a fixed number, the elimination of a substance from a living organism usually follows more complex chemical kinetics.
For example, the biological half-life of water in a human being is about 9 to 10 days, though this can be altered by behavior and other conditions. The biological half-life of caesium in human beings is between one and four months.
The concept of a half-life has also been utilized for pesticides in plants, and certain authors maintain that pesticide risk and impact assessment models rely on and are sensitive to information describing dissipation from plants.
In epidemiology, the concept of half-life can refer to the length of time for the number of incident cases in a disease outbreak to drop by half, particularly if the dynamics of the outbreak can be modeled exponentially. | 7 | Physical Chemistry |
In addition to the specialisation factories have for the type of RNA polymerase they contain, there is a further level of specialisation present. There are some factories that only transcribe a certain set of related genes, this further strengthens the concept that the main function of a transcription factory is for transcriptional efficiency. | 1 | Biochemistry |
Boronate affinity electrophoresis utilizes boronic acid infused acrylamide gels to purify NAD-RNA. This purification allows for researchers to easily measure the kinetic activity of NAD-RNA decapping enzymes. | 1 | Biochemistry |
After 1.5 years in space, samples were retrieved, rehydrated and spread on different culture media. The only two organisms able to grow were isolated from a sample exposed to simulated Mars conditions beneath a 0.1% T Suprasil neutral density filter and from a sample exposed to space vacuum without solar radiation exposure, respectively. The two surviving organisms were identified as Stichococcus sp. (green algae) and Acarospora sp. (lichenized fungal genus). Among other fungal spores tested were Cryomyces antarcticus and Cryomyces minteri, and although 60% of the cells' DNA studied remained intact after the Mars-like conditions, less than 10% of the fungi were able to proliferate and form colonies after their return to Earth. According to the researchers, the studies provide experimental information on the possibility of eukaryotic life transfer from one planet to another by means of rocks and of survival in Mars environment.
Cryptoendolithic microbial communities and epilithic lichens have been considered as appropriate candidates for the scenario of lithopanspermia, which proposes a natural interplanetary exchange of organisms by means of rocks that have been impact ejected from their planet of origin. A 1.5 years exposure experiment in space was performed with a variety of rock-colonizing eukaryotic organisms. Selected organisms are known to cope with the environmental extremes of their natural habitats. It was found that some — but not all — of those most robust microbial communities from extremely hostile regions on Earth are also partially resistant to the even more hostile environment of outer space, including high vacuum, temperature fluctuation, the full spectrum of extraterrestrial solar electromagnetic radiation, and cosmic ionizing radiation. Although the reported experimental period of 1.5 years in space is not comparable with the time spans of thousands or millions of years believed to be required for lithopanspermia, the data provide first evidence of the differential hardiness of cryptoendolithic communities in space. | 1 | Biochemistry |
Urea can be irritating to skin, eyes, and the respiratory tract. Repeated or prolonged contact with urea in fertilizer form on the skin may cause dermatitis.
High concentrations in the blood can be damaging. Ingestion of low concentrations of urea, such as are found in typical human urine, are not dangerous with additional water ingestion within a reasonable time-frame. Many animals (e.g. camels, rodents or dogs) have a much more concentrated urine which may contain a higher urea amount than normal human urine.
Urea can cause algal blooms to produce toxins, and its presence in the runoff from fertilized land may play a role in the increase of toxic blooms.
The substance decomposes on heating above melting point, producing toxic gases, and reacts violently with strong oxidants, nitrites, inorganic chlorides, chlorites and perchlorates, causing fire and explosion. | 0 | Organic Chemistry |
Though the specific mechanisms by which paramutation acts vary from organism to organism, all well-documented cases point towards epigenetic modification and RNA-silencing as the underlying mechanism for paramutation.
In the case of the r1 locus in maize, DNA methylation of a region of tandem repeats near the coding region of the gene is characteristic of the paramutagenic B’ allele, and when the paramutable B-I allele becomes paramutagenic, it too takes on the same DNA methylation pattern. In order for this methylation to be successfully transferred, a number of genes coding for RNA-dependent RNA polymerases and other components of RNA-silencing pathways are required, suggesting that paramutation is mediated via endogenous RNA-silencing pathways. The transcription of short interfering RNAs from the tandem repeat regions corroborates this. In animal systems such as Drosophila, piRNAs have also been implicated in mediating paramutation. In addition to the characteristic DNA methylation state changes, changes in histone modification patterns in the methylated DNA regions, and/or the requirement of histone modifying proteins to mediate paramutation have also been noted in multiple systems. It has been suggested that these histone modifications play a role in maintaining the paramutated state. The previously mentioned tandem repeat region in the r1 locus is also typical of other loci showing paramutation or paramutation-like phenomena.
However, it has been noted that it is not possible to explain all occurrences and features of paramutation with what is known about RNAi-mediated transcriptional silencing, suggesting that other pathways and/or mechanisms are also at play. | 1 | Biochemistry |
m6A-LAIC-seq (m6A-level and isoform-characterization sequencing) is a high-throughput approach to quantify methylation status on a whole-transcriptome scale. Full-length RNA samples are used in this method. RNAs are first subjected to immunoprecipitation with an anti-m6A antibody. Excess antibody is added to the mixture to ensure all m6A-containing RNAs are pulled down. The mixture is separated into eluate (m6A+ RNAs) and supernatant (m6A- RNAs) pools. External RNA Controls Consortium (ERCC) spike ins are added to the eluate and supernatant, as well as an independent control arm consisting of just ERCC spike in. After antibody cleavage in the eluate pool, each of the three mixtures are sequenced on a next generation sequencing platform. The m6A levels per site or gene could be quantified by the ERCC-normalized RNA abundances in different pools. Since full-length RNA is used, it is possible to directly compare alternatively spliced isoforms between the m6A+ and m6A- fractions as well as comparing isoform abundance within the m6A+ portion.
Despite the advances in m6A-sequencing, several challenges still remain: (1) A method has yet to be developed that characterizes the stoichiometry between different sites in the same transcript; (2) Analysis results are heavily dependent on the bioinformatics algorithm used to call the peaks; (3) Current methods all use m6A-specific antibodies to tag m6A sites, but it has been reported that the antibodies contain intrinsic bias for RNA sequences. | 1 | Biochemistry |
The first plastid is highly accepted within the scientific community to be derived from the engulfment of cyanobacteria ancestor into a eukaryotic organism. Evidence supporting this belief is found in many morphological similarities such as the presence of a two plasma membranes. It is thought that the first membrane belonged to the cyanobacteria ancestor. During phagocytosis, a vesicle engulfs a molecule with its plasma membrane to allow safe import. When the cyanobacteria became engulfed, the bacterium avoided digestion and led to the double membrane found in primary plastids. However, in order to live in symbiosis, the eukaryotic cell that engulfed the cyanobacterium must now provide proteins and metabolites to maintain the functions of the bacteria in exchange for energy. Thus, an engulfed cyanobacterium must give up some of its genetic material to allow for endosymbiotic gene transfer to the eukaryote, a phenomenon that is thought to be extremely rare due to the "learned nature" of the interactions that must occur between the cells to allow for processes such as; gene transfer, protein localization, excretion of highly reactive metabolites, and DNA repair. This would mean, a reduction in genome size, for the cyanobacteria, but also an increase in cytobacterial genes within the eukaryotic genome. The genus of Synechocystis sp., strain PCC6803 is a unicellular fresh water cyanobacteria that encodes 3725 genes, and a 3.9 Mb sized genome. However, most plastids rarely exceed 200 protein coding genes. A recent study sequenced the genome of a cyanobacterium that was living extracellularly in endosymbiosis with the water-fern Azolla filiculoides. Endosymbiosis was supported by the fact that the cyanobacterium was unable to grow autonomously, and the observance of the cyanobacterium being vertically transferred between succeeding generations. After cyanobacterium genome analysis, the researchers found that over 30% of the genome was made up of pseudogenes. In addition, roughly 600 transposable elements were found within the genome. The pseudogenes were found in genes such as dnaA, DNA repair genes, glycolysis and nutrient uptake genes. dnaA is essential to initiation of DNA replication in prokaryotic organisms, thus Azolla filiculoides is thought to provide nutrients, and transcriptional factors for DNA replication in exchange for fixed nitrogen that is not readily available in water. Although the cyanobacterium had not been completely engulfed in the eukaryotic organism, the relationship is thought to demonstrate the precursor to endosymbiotic primary plastids. | 5 | Photochemistry |
Water is an excellent solvent due to its high dielectric constant. Substances that mix well and dissolve in water are known as hydrophilic ("water-loving") substances, while those that do not mix well with water are known as hydrophobic ("water-fearing") substances. The ability of a substance to dissolve in water is determined by whether or not the substance can match or better the strong attractive forces that water molecules generate between other water molecules. If a substance has properties that do not allow it to overcome these strong intermolecular forces, the molecules are precipitated out from the water. Contrary to the common misconception, water and hydrophobic substances do not "repel", and the hydration of a hydrophobic surface is energetically, but not entropically, favorable.
When an ionic or polar compound enters water, it is surrounded by water molecules (hydration). The relatively small size of water molecules (~ 3 angstroms) allows many water molecules to surround one molecule of solute. The partially negative dipole ends of the water are attracted to positively charged components of the solute, and vice versa for the positive dipole ends.
In general, ionic and polar substances such as acids, alcohols, and salts are relatively soluble in water, and nonpolar substances such as fats and oils are not. Nonpolar molecules stay together in water because it is energetically more favorable for the water molecules to hydrogen bond to each other than to engage in van der Waals interactions with non-polar molecules.
An example of an ionic solute is table salt; the sodium chloride, NaCl, separates into cations and anions, each being surrounded by water molecules. The ions are then easily transported away from their crystalline lattice into solution. An example of a nonionic solute is table sugar. The water dipoles make hydrogen bonds with the polar regions of the sugar molecule (OH groups) and allow it to be carried away into solution. | 2 | Environmental Chemistry |
The only SI derived unit with a special name derived from the mole is the katal, defined as one mole per second of catalytic activity. Like other SI units, the mole can also be modified by adding a metric prefix that multiplies it by a power of 10:
One femtomole is exactly 602,214,076 molecules; attomole and smaller quantities cannot be exactly realized. The yoctomole, equal to around 0.6 of an individual molecule, did make appearances in scientific journals in the year the yocto- prefix was officially implemented. | 3 | Analytical Chemistry |
The Zisman theory is the simplest commonly used theory, as it is a one-component theory, and is best used for non-polar surfaces. This means that polymer surfaces that have been subjected to heat treatment, corona treatment, plasma cleaning, or polymers that contain heteroatoms do not lend themselves to this particular theory, as they tend to be at least somewhat polar. The Zisman theory also tends to be more useful in practice for surfaces with lower energies.
The Zisman theory simply defines the surface energy as being equal to the surface energy of the highest surface energy liquid that wets the solid completely. That is to say, the droplet will disperse as much as possible, i.e. completely wetting the surface, for this liquid and any liquids with lower surface energies, but not for liquids with higher surface energies. Since this probe liquid could hypothetically be any liquid, including an imaginary liquid, the best way to determine the surface energy by the Zisman method is to acquire data points of contact angles for several probe liquids on the solid surface in question, and then plot the cosine of that angle against the known surface energy of the probe liquid. By constructing the Zisman plot, one can extrapolate the highest liquid surface energy, real or hypothetical, that would result in complete wetting of the sample with a contact angle of zero degrees. | 7 | Physical Chemistry |
GAI or Gibberellic-Acid Insensitive is a gene in Arabidopsis thaliana which is involved in regulation of plant growth. GAI represses the pathway of gibberellin-sensitive plant growth. It does this by way of its conserved DELLA motif. | 1 | Biochemistry |
D designates compounds of arbitrary stoichiometry. Originally, D1-D10 were set aside for stoichiometry AB, D11-D20 for stoichiometry AB for n > 3, D31-D50 for (AB), and D51 up for the AB for arbitrary m and n. | 3 | Analytical Chemistry |
* Microsoft and Running Tide signed Two-Year agreement in 2023 to remove up to 12,000 tons of carbon through an ocean-based carbon removal system.
* In Canada, a North Atlantic Carbon Observatory (NACO) project is underway to establish an accurate measurement of the ocean's ability to continue to absorb carbon with particular emphasis on deep blue capacity.
* In Denmark, the "Greensand" project is underway to capture carbon at source and deposit it in the deep blue regions of the North Sea, creating a CO graveyard. The project is expected to store up to eight million tonnes of CO per year by 2030.
* A restoration project in South Australia will cover of mangroves, salt marsh and sea grasses extending in the St Vincents Gulf and Spencer Gulf in South Australia. The project will also look at various possibilities of insuring the huge expanse of existing blue carbon ecosystems.
* In South Korea, macroalgae have been utilized as part of a climate change mitigation program. The country has established the Coastal CO Removal Belt (CCRB) which is composed of artificial and natural ecosystems. The goal is to capture carbon using large areas of kelp forest.
* Marine permaculture also fixes carbon in seaweed forest projects offshore in Tasmania and the Philippines, with potential use from the tropics to temperate oceans. | 9 | Geochemistry |
When pans are overheated beyond approximately 260°C (500°F) the PTFE coating begins to dissociate, releasing hydrofluoric acid and a variety of organofluorine compounds which can cause polymer fume fever in humans and can be lethal to birds. Concerns have been raised over the possible negative effects of using PTFE-coated cooking pans.
Processing of PTFE in the past used to include PFOA as an emulsifier; however, PFOA is a persistent organic pollutant and poses both environmental and health concerns, and is now being phased out of use in PTFE processing.
PFOA is now replaced by the GenX product manufactured by the DuPont spin-off Chemours, which seems to pose similar health issues as the now banned PFOA. | 7 | Physical Chemistry |
-A simple example of the Evelyn effect is the sophomore level chemistry lab experiment involving two popular examples that are listed below.
a) Dehydration of 4-methylcyclohexanol
b) Dehydration of 2-Methylcyclohexanol
c) Mechanism for the dehydration of 2-methylcyclohexanol | 7 | Physical Chemistry |
Raman spectroscopy is similar to FTIR in using a focused laser on the glass phase of the melt inclusion or a vapor bubble that may be contained in the melt inclusion to identify wavelengths associated with the Raman vibrating bands of volatiles, such as HO and CO. Raman spectroscopy can also be used to determine the density of CO contained in a vapor bubble if present at a high enough concentration within a melt inclusion. | 9 | Geochemistry |
Tyrosine phosphorylation sites in growth factor receptors serve two major purposes—to control the state of activity of the kinase and to create binding sites for downstream signal transduction molecules, which in many cases also are substrates for the kinase. The second part of the tyrosine kinase domain in the PDGFβ receptor is phosphorylated at Tyr-857, and mutant receptors carrying phenylalanine at this position have reduced kinase activity. Tyr-857 has therefore been assigned a role in positive regulation of kinase activity. Sites of tyrosine phosphorylation involved in binding signal transduction molecules have been identified in the juxtamembrane domain, the kinase insert, and in the C-terminal tail in the PDGFβ receptor. The phosphorylated tyrosine residue and in general three adjacent C-terminal amino acid residues form specific binding sites for signal transduction molecules. Binding to these sites involves a common conserved stretches, denoted the Src homology (SH) 2 domain and/or Phosphotyrosine Binding Domains (PTB). The specificity of these interactions appears to be very high, since mutant receptors carrying phenylalanine residues in one or several of the different phosphorylation sites generally lack the capacity to bind the targeted signal transduction molecule. The signal transduction molecules are either equipped with different enzymatic activities, or they are adaptor molecules, which in some but not all cases are found in complexes with subunits that carry a catalytic activity. Upon interaction with the activated receptor, the catalytic activities become up-regulated, through tyrosine phosphorylation or other mechanisms, generating a signal that may be unique for each type of signal transduction molecule.
Examination of the different signaling cascades induced by RTKs established Ras/mitogen-activated protein kinase (MAPK), PI-3 kinase, and phospholipase-γ (PLCγ) pathways as key downstream mediators of PDGFR signaling. In addition, reactive oxygen species (ROS)-dependent STAT3 activation has been established to be a key downstream mediator of PDGFR signaling in vascular smooth muscle cells. | 1 | Biochemistry |
Bromothymol blue (also known as bromothymol sulfone phthalein and BTB) is a pH indicator. It is mostly used in applications that require measuring substances that would have a relatively neutral pH (near 7). A common use is for measuring the presence of carbonic acid in a liquid. It is typically sold in solid form as the sodium salt of the acid indicator. | 3 | Analytical Chemistry |
Transfer of thermal energy through direct contact between a closed system and its surroundings, is by the microscopic thermal motions of particles and their associated inter-molecular potential energies. The microscopic description of such processes are the province of statistical mechanics, not of macroscopic thermodynamics. Another kind of energy transfer is by radiation, performing work on the system. Radiative transfer of energy is irreversible in the sense that it occurs only from a hotter to a colder system. There are several forms of dissipative transduction of energy that can occur internally within a system at a microscopic level, such as friction including bulk and shear viscosity chemical reaction, unconstrained expansion as in Joule expansion and in diffusion, and phase change. | 7 | Physical Chemistry |
Natural enemies must survive long enough and respond quickly enough to plant volatiles in order to benefit the plant through predatory behavior. Certain plant structures, called domatia, can selectively reinforce mutualisms with natural enemies and increase the fitness benefit they receive from that mutualism by ensuring the survival and proximity of natural enemies. Domatia provide a kind of housing or refuge for predators from both abiotic stressors, such as desiccation, and biotic stressors, such as predation from higher-order predators. Therefore, they not only ensure better survival, but eliminate the time required for natural enemies to locate and travel to the damaged plant. Natural enemies that make use of domatia are often said to serve as "bodyguards" for the plant on or in which they live. Domatia may be as well-developed as acacia tree thorns or as simple and incidental as a depression or crevice in a leaf stem, but they are distinguishable from galls and other similar structures in that they are not induced by the insect but formed constitutively by the plant. | 1 | Biochemistry |
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