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The magnetic nanoparticles are typically made from iron oxide, which is fully biodegradable, using methods such as coprecipitation or microemulsion.
The nanoparticles are then combined with gene vectors (DNA, siRNA, ODN, virus, etc.). One method involves linking viral particles to magnetic particles using an avidin-biotin interaction. Viruses can also bind to the nanoparticles via hydrophobic interaction.
Another synthesis method involves coating magnetic nanoparticles with cationic lipids or polymers via salt-induced aggregation. For example, nanoparticles may be conjugated with the polyethylenimine (PEI), a positively charged polymer used commonly as a transfection agent. The PEI solution must have a high pH during synthesis to encourage high gene expression. The positively charged nanoparticles can then associate with negatively charged nucleic acids via electrostatic interaction. | 1 | Biochemistry |
In addition to Tafts steric parameter E, other steric parameters that are independent of kinetic data have been defined. Charton has defined values v that are derived from van der Waals radii. Using molecular mechanics, Meyers has defined V' values that are derived from the volume of the portion of the substituent that is within 0.3 nm of the reaction center. | 7 | Physical Chemistry |
In a high-temperature, classical paramagnet phase, the magnetic susceptibility is given by the Curie–Weiss law
Fitting experimental data to this equation determines a phenomenological Curie–Weiss temperature, . There is a second temperature, , where magnetic order in the material begins to develop, as evidenced by a non-analytic feature in . The ratio of these is called the frustration parameter
In a classic antiferromagnet, the two temperatures should coincide and give . An ideal quantum spin liquid would not develop magnetic order at any temperature and so would have a diverging frustration parameter . A large value is therefore a good indication of a possible spin liquid phase. Some frustrated materials with different lattice structures and their Curie–Weiss temperature are listed in the table below. All of them are proposed spin liquid candidates. | 7 | Physical Chemistry |
AFM-IR (atomic force microscope-infrared spectroscopy) or infrared nanospectroscopy is one of a family of techniques that are derived from a combination of two parent instrumental techniques. AFM-IR combines the chemical analysis power of infrared spectroscopy and the high-spatial resolution of scanning probe microscopy (SPM). The term was first used to denote a method that combined a tuneable free electron laser with an atomic force microscope (AFM, a type of SPM) equipped with a sharp probe that measured the local absorption of infrared light by a sample with nanoscale spatial resolution.
Originally the technique required the sample to be deposited on an infrared-transparent prism and be less than 1μm thick. This early setup improved the spatial resolution and sensitivity of photothermal AFM-based techniques from microns to circa 100 nm. Then, the use of modern pulsed optical parametric oscillators and quantum cascade lasers, in combination with top-illumination, have enabled to investigate samples on any substrate and with increase sensitivity and spatial resolution. As most recent advances, AFM-IR has been proved capable to acquire chemical maps and nanoscale resolved spectra at the single-molecule scale from macromolecular self-assemblies and biomolecules with circa 10 nm diameter, as well as to overcome limitations of IR spectroscopy and measure in aqueous liquid environments.
Recording the amount of infrared absorption as a function of wavelength or wavenumber, AFM-IR creates an infrared absorption spectra that can be used to chemically characterize and even identify unknown samples. Recording the infrared absorption as a function of position can be used to create chemical composition maps that show the spatial distribution of different chemical components. Novel extensions of the original AFM-IR technique and earlier techniques have enabled the development of bench-top devices capable of nanometer spatial resolution, that do not require a prism and can work with thicker samples, and thereby greatly improving ease of use and expanding the range of samples that can be analysed. AFM-IR has achieved lateral spatial resolutions of ca. 10 nm, with a sensitivity down to the scale of molecular monolayer and single protein molecules with molecular weight down to 400-600 kDa.
AFM-IR is related to techniques such as tip-enhanced Raman spectroscopy (TERS), scanning near-field optical microscopy (SNOM), nano-FTIR and other methods of vibrational analysis with scanning probe microscopy. | 3 | Analytical Chemistry |
A quasistatic process is an idealized or fictive model of a thermodynamic "process" considered in theoretical studies. It does not occur in physical reality. It may be imagined as happening infinitely slowly so that the system passes through a continuum of states that are infinitesimally close to equilibrium. | 7 | Physical Chemistry |
In chemistry, the Möbius–Hückel treatment is a methodology used to predict whether a reaction is allowed or forbidden. It is often used along with the Woodward–Hoffmann approach. The description in this article uses the plus-minus sign notation for parity as shorthand while proceeding around a cycle of orbitals in a molecule or system, while the Woodward–Hoffmann methodology uses a large number of rules with the same consequences. | 7 | Physical Chemistry |
Single-molecule RNA FISH, also known as Stellaris® RNA FISH or smFISH, is a method of detecting and quantifying mRNA and other long RNA molecules in a thin layer of tissue sample. Targets can be reliably imaged through the application of multiple short singly labeled oligonucleotide probes. The binding of up to 48 fluorescent labeled oligos to a single molecule of mRNA provides sufficient fluorescence to accurately detect and localize each target mRNA in a wide-field fluorescent microscopy image. Probes not binding to the intended sequence do not achieve sufficient localized fluorescence to be distinguished from background.
Single-molecule RNA FISH assays can be performed in simplex or multiplex, and can be used as a follow-up experiment to quantitative PCR, or imaged simultaneously with a fluorescent antibody assay. The technology has potential applications in cancer diagnosis, neuroscience, gene expression analysis, and companion diagnostics. | 1 | Biochemistry |
As for any other physical separation process, liberation is pre-requisite for possible separation. Liberation characteristics are well known and relatively easy to study for particulate lots in smaller size ranges, e.g. flotation feed and products. The analysis is essential for understanding the possible results of physical separation and relatively easy to conduct in laboratory on a couple of dozens of grams of sample which can be studied using optical methods or such as the QEMSCAN.
For larger particles above it is widely known for applications that are treated using density separation methods, such as coal or iron ore. Here, the washability analysis can be conducted on sample masses up to 10 tonnes in equipped laboratories. For sensor-based sorting, where laboratory methods can only tell about the liberation characteristics where the describing feature is the density (e.g. iron ore, coal), hand counting, single-particle tests and bulk tests can reveal the liberation characteristics of a bulk material: Hereby, only single particle tests reveal the true liberation, while hand counting and bulk testing give a result which also incorporates the separation efficiency of the type of analysis. More information on the testing procedures used in technical feasibility evaluation can be found in the respective chapter. | 3 | Analytical Chemistry |
Synthetic screen media is used where wear life is an issue. Large producers such as mines or huge quarries use them to reduce the frequency of having to stop the plant for screen deck maintenance. Rubber is also used as a very resistant high-impact screen media material used on the top deck of a scalper screen. To compete with rubber screen media fabrication, polyurethane manufacturers developed screen media with lower Shore Hardness. To compete with self-cleaning screen media that is still primarily available in tensioned cloth, synthetic screen media manufacturers also developed membrane screen panels, slotted opening panels and diamond opening panels. Due to the 7-degree demoulding angle, polyurethane screen media users can experience granulometry changes of product during the wear life of the panel. | 8 | Metallurgy |
The average grade of copper ores in the 21st century is below 0.6% copper, with a proportion of economic ore minerals being less than 2% of the total volume of the ore rock. Thus, all mining operations, the ore must usually be beneficiated (concentrated). The concentrate is typically sold to distant smelters, although some large mines have smelters located nearby. Such colocation of mines and smelters was more typical in the 19th and early 20th centuries, when smaller smelters could be economic. The subsequent processing techniques depend on the nature of the ore.
In the usual case when it is primarily sulfide copper minerals (such as chalcopyrite, FeCuS), the ore is treated by comminution, where the rock is crushed to produce small particles (<100 μm) consisting of individual mineral phases. These particles are then ready to be separated to remove gangue (silicate rocks residues) using froth flotation. | 8 | Metallurgy |
is a bis-nido edge-shared polyhedron. Here, m + n + o + p − q = 2 + 18 + 0 + 2 − 0 = 22; 16 BH units provide 16 pairs, 4 bridging hydrogen atoms provide 2 pairs, two shared boron atoms provide 3 pairs, along with the two negative charges which provide 1 pair. | 7 | Physical Chemistry |
Sometimes a distinction is made between sequence coverage and physical coverage. Where sequence coverage is the average number of times a base is read, physical coverage is the average number of times a base is read or spanned by mate paired reads. | 1 | Biochemistry |
Magnesium is essential as part of the process that generates adenosine triphosphate.
Mitochondria are often referred to as the "powerhouses of the cell" because their primary role is generating energy for cellular processes. They achieve this by breaking down nutrients, primarily glucose, through a series of chemical reactions known as cellular respiration. This process ultimately produces adenosine triphosphate (ATP), the cell's main energy currency. | 1 | Biochemistry |
LAGP belongs to phosphate-based solid electrolytes and, in spite of showing a moderate ionic conductivity compared to other families of solid ionic conductors, it possesses some intrinsic advantages with respect to sulfides and oxides:
* Extremely high chemical stability in humid air;
* Wide electrochemical stability window;
* Low to negligible electronic conductivity.
One of the main advantages of LAGP is its chemical stability in the presence of oxygen, water vapour, and carbon dioxide, which simplifies the manufacture process preventing the use of a glovebox or protected environments. Unlike sulfide-based solid electrolytes, which react with water releasing poisonous gaseous hydrogen sulfide, and garnet-type lithium lanthanum zirconium oxide (LLZO), which react with water and CO to form passivating layers of LiOH and LiCO, LAGP is practically inert in humid air.
Another important advantage of LAGP is its wide electrochemical stability window, up to 6 V, which allows the use of such electrolyte in contact with high-voltage cathodes, thus enabling high energy densities. However, the stability at very low voltages and against lithium metal is controversial: even if LAGP is more stable than LATP because of the absence of titanium, some literature works report on the reduction of Ge by lithium as well, with formation of Ge and metallic germanium at the electrode-electrolyte interface and dramatic increase of interfacial resistance.
The possible decomposition mechanism of LAGP in contact with metallic lithium is reported in the equation below: | 7 | Physical Chemistry |
The geometry and bonding of a Zintl ion cannot be easily described by classical two electron two center bonding theories; however the geometries Zintl ions can be well described by Wade’s rules of boranes. Wade’s rules offer an alternative model for the relationship between geometry and electron count in delocalized electron deficient systems. The rules were developed to predict the geometries of boranes from the number of electrons and can be applied to these polyanions by replacing the BH unit with a lone pair. Some unique clusters of Ge occur in non-deltahedral shapes that cannot be described by Wade’s rules. The rules also become more convoluted in intermetallic clusters with transition metals and consideration needs to be taken for the location of the additional electrons. | 7 | Physical Chemistry |
The Fridge Gate method is a theoretical application of using a single logic gate to drive a refrigerator in the most energy efficient way possible without violating the laws of thermodynamics. It operates on the fact that there are two energy states in which a particle can exist: the ground state and the excited state. The excited state carries a little more energy than the ground state, small enough so that the transition occurs with high probability. There are three components or particle types associated with the fridge gate. The first is on the interior of the refrigerator, the second on the outside and the third is connected to a power supply which heats up every so often that it can reach the E state and replenish the source. In the cooling step on the inside of the refrigerator, the g state particle absorbs energy from ambient particles, cooling them, and itself jumping to the e state. In the second step, on the outside of the refrigerator where the particles are also at an e state, the particle falls to the g state, releasing energy and heating the outside particles. In the third and final step, the power supply moves a particle at the e state, and when it falls to the g state it induces an energy-neutral swap where the interior e particle is replaced by a new g particle, restarting the cycle. | 7 | Physical Chemistry |
By the 1760s (or earlier) German artisans had invented a so-called "pulse hammer" (Pulshammer). In 1767 Benjamin Franklin visited Germany, saw a pulse hammer, and in 1768, improved it. Franklins pulse hammer consisted of two glass bulbs connected by a U-shaped tube; one of the bulbs was partially filled with water in equilibrium with its vapor. Holding the partially filled bulb in ones hand would cause the water to flow into the empty bulb. In 1872, the Italian physicist and engineer Enrico Bernardi combined three Franklin tubes to build a simple heat motor that was powered by evaporation in a way similar to the drinking bird.
In 1881 Israel L. Landis got a patent for a similar oscillating motor.
A year later (1882), the Iske brothers got a patent for a similar motor.
Unlike the drinking bird, the lower tank was heated and the upper tank just air-cooled in this engine. Other than that, it used the same principle. The Iske brothers during that time got various patents on a related engine which is now known as Minto wheel.
A Chinese drinking bird toy dating back to 1910s~1930s named insatiable birdie is described in Yakov Perelmans Physics for Entertainment. The book explained the "insatiable" mechanism: "Since the headtubes temperature becomes lower than that of the tail reservoir, this causes a drop in the pressure of the saturated vapours in the head-tube ..." It was said in Shanghai, China, that when Albert Einstein and his wife, Elsa, arrived in Shanghai in 1922, they were fascinated by the Chinese "insatiable birdie" toy.
In addition, the Japanese professor of toys, Takao Sakai, from Tohoku University, also introduced this Chinese toy.
Arthur M. Hillery got a US patent in 1945. Arthur M. Hillery suggested the use of acetone as working fluid.
It was again patented in the US by Miles V. Sullivan in 1946.
He was a Ph.D. inventor-scientist at Bell Labs in Murray Hill, NJ, USA. Robert T. Plate got a US Design patent in 1947, that cities Arthur M. Hillerys patent. | 7 | Physical Chemistry |
This is a list of instruments used in general in laboratories, including:
*Biochemistry
*Microbiology
*Pharmacology
__FORCETOC__ | 1 | Biochemistry |
ZMAb is a mixture of three mouse mAbs: m1H3, m2G4, and m4G7. A study published in November 2013 found that EBOV-infected macaque monkeys survived after being given a therapy with a combination of three EBOV surface glycoprotein (EBOV-GP)-specific monoclonal antibodies (ZMAb) within 24 hours of infection. The authors concluded that post-exposure treatment resulted in a robust immune response, with good protection for up to 10 weeks and some protection at 13 weeks. ZMab was created by the NML and licensed to Defyrus, a Toronto-based biodefense company, with further funding by the Public Health Agency of Canada. | 1 | Biochemistry |
Damage to buildings, equipment and people can result from a large-scale, short-duration deflagration. The potential damage is primarily a function of the total amount of fuel burned in the event (total energy available), the maximum reaction velocity that is achieved, and the manner in which the expansion of the combustion gases is contained. Vented deflagrations tend to be less violent or damaging than contained deflagrations.
In free-air deflagrations, there is a continuous variation in deflagration effects relative to the maximum flame velocity. When flame velocities are low, the effect of a deflagration is to release heat, such as in a flash fire. At flame velocities near the speed of sound, the energy released is in the form of pressure, and the resulting high pressure can damage equipment and buildings. | 7 | Physical Chemistry |
This formulation for a 2 component reaction is equivalent to the selection rules for a [p + q]-cycloaddition reactions shown in the following table:
If the total number of electrons is 4n + 2, then one is in the bottom row of the table. The reaction is thermally allowed if it is suprafacial with respect to both components or antarafacial with respect to both components. That is to say the number of antarafacial components is even (it is 0 or 2). Similarly if the total number of electrons is 4n, then one is in the top row of the table. This is thermally allowed if it is suprafacial with respect to one component and antarafacial with respect to the other. Thus the total number of antarafacial components is always odd as it is always 1.
The following are some common ground state (i.e. thermal) reaction classes analyzed in light of the generalized Woodward–Hoffmann rules. | 7 | Physical Chemistry |
Growing understanding of small RNA gene-silencing mechanisms involving dsRNA-mediated sequence-specific mRNA degradation has directly impacted the fields of functional genomics, biomedicine, and experimental biology. The following section describes various applications involving the effects of RNA silencing. These include uses in biotechnology, therapeutics, and laboratory research. Bioinformatics techniques are also being applied to identify and characterize large numbers of small RNAs and their targets. | 1 | Biochemistry |
In order to determine the fate of natural carbon containing substances deep in the Earth, experiments have been conducted to see what happens when high pressure, and or temperatures are applied. Such substances include carbon dioxide, carbon monoxide, graphite, methane, and other hydrocarbons such as benzene, carbon dioxide water mixtures and carbonate minerals such as calcite, magnesium carbonate, or ferrous carbonate. Under super high pressures carbon may take on a higher coordination number than the four found in sp compounds like diamond, or the three found in carbonates. Perhaps carbon can substitute into silicates, or form a silicon oxycarbide. Carbides may be possible. | 9 | Geochemistry |
The polymerase chain reaction (PCR) is a commonly used molecular biology tool for amplifying DNA, and various techniques for PCR optimization which have been developed by molecular biologists to improve PCR performance and minimize failure. | 1 | Biochemistry |
Optical properties are tested for optical sensing-related applications. This can include light attenuation, refractive index, transmission, etc. These optical properties are significantly influenced by the composition of the hydrogel. | 7 | Physical Chemistry |
This family of clusters includes the closo cages . This family of clusters are also lightly studied owing to synthetic difficulties. Also reflecting synthetic challenges, many of these compounds are best known as their alkyl derivatives. 1,5- is the only known isomer of the five-vertex cage. It is prepared from the reaction of pentaborane(9) with acetylene in two operations beginning with condensation with acetylene followed by pyrolysis (cracking) of the product:
: nido-2,3-
: closo-2,3- | 7 | Physical Chemistry |
In order to simultaneously manipulate and image samples that exhibit fluorescence, optical tweezers can be built alongside a fluorescence microscope. Such instruments are particularly useful when it comes to studying single or small numbers of biological molecules that have been fluorescently labelled, or in applications in which fluorescence is used to track and visualize objects that are to be trapped.
This approach has been extended for simultaneous sensing and imaging of dynamic protein complexes using long and strong tethers generated by a highly efficient multi-step enzymatic approach and applied to investigations of disaggregation machines in action. | 1 | Biochemistry |
The Lowry protein assay is a biochemical assay for determining the total level of protein in a solution. The total protein concentration is exhibited by a color change of the sample solution in proportion to protein concentration, which can then be measured using colorimetric techniques. It is named for the biochemist Oliver H. Lowry who developed the reagent in the 1940s. His 1951 paper describing the technique is the most-highly cited paper ever in the scientific literature, cited over 300,000 times. | 1 | Biochemistry |
Gamma TiAl has excellent mechanical properties and oxidation and corrosion resistance at elevated temperatures (over 600°C), which makes it a possible replacement for traditional Ni based superalloy components in aircraft turbine engines.
TiAl-based alloys have potential to increase the thrust-to-weight ratio in aircraft engines. This is especially the case with the engine's low-pressure turbine blades and the high-pressure compressor blades. These are traditionally made of Ni-based superalloy, which is nearly twice as dense as TiAl-based alloys. Some gamma titanium aluminide alloys retain strength and oxidation resistance to 1000 °C, which is 400 °C higher than the operating temperature limit of conventional titanium alloys.
General Electric uses gamma TiAl for the low-pressure turbine blades on its GEnx engine, which powers the Boeing 787 and Boeing 747-8 aircraft. This was the first large-scale use of this material on a commercial jet engine when it entered service in 2011. The TiAl LPT blades are cast by Precision Castparts Corp. and Avio s.p.a. Machining of the Stage 6, and Stage 7 LPT blades is performed by Moeller Manufacturing. An alternate pathway for production of the gamma TiAl blades for the GEnx and GE9x engines using additive manufacturing is being explored.
In 2019 a new 55g lightweight version of the Omega Seamaster wristwatch was made, using gamma titanium aluminide for the case, backcase and crown, and a titanium dial and mechanism in Ti 6/4 (grade 5). The retail price of this watch at £37,240 was nine times that of the basic Seamaster and comparable to the top of the range platinum-cased version with a moonphase complication. | 8 | Metallurgy |
Salinosporamide A (Marizomib) is a potent proteasome inhibitor being studied as a potential anticancer agent. It entered phase I human clinical trials for the treatment of multiple myeloma, only three years after its discovery in 2003. This marine natural product is produced by the obligate marine bacteria Salinispora tropica and Salinispora arenicola, which are found in ocean sediment. Salinosporamide A belongs to a family of compounds, known collectively as salinosporamides, which possess a densely functionalized γ-lactam-β-lactone bicyclic core. | 0 | Organic Chemistry |
Organic radicals are inherently electron deficient thus the greater the electronegativity of the atom on which the unpaired electron resides the less stable the radical. Between carbon, nitrogen, and oxygen, for example, carbon is the most stable and oxygen the least stable.
Electronegativity also factors into the stability of carbon atoms of different hybridizations. Greater s-character correlates to higher electronegativity of the carbon atom (due to the close proximity of s orbitals to the nucleus), and the greater the electronegativity the less stable a radical. sp-hybridized carbons (50% s-character) form the least stable radicals compared to sp-hybridized carbons (25% s-character) which form the most stable radicals. | 2 | Environmental Chemistry |
The National Center for Functional Glycomics has developed GlycoPattern, a web-based bioinformatics resource to assist in analysis of glycan array data. The GlycoPattern website offers tools and algorithms to discover structural motifs, heatmap visualizations for multiple experiment comparisons, clustering of Glycan Binding Proteins. | 0 | Organic Chemistry |
ECS Meeting Abstracts contain extended abstracts of the technical papers presented at the ECS biannual meetings and ECS-sponsored meetings. This publication offers a first look into current research in the field. ECS Meeting Abstracts are freely available to all visitors to the ECS Digital Library. | 7 | Physical Chemistry |
In pharmacology, an indirect agonist or indirect-acting agonist is a substance that enhances the release or action of an endogenous neurotransmitter but has no specific agonist activity at the neurotransmitter receptor itself. Indirect agonists work through varying mechanisms to achieve their effects, including transporter blockade, induction of transmitter release, and inhibition of transmitter breakdown. | 1 | Biochemistry |
Many woody plants produce resins and antimicrobial chemicals to limit the spread of pathogens after an injury. | 1 | Biochemistry |
PEA, as an N-acylethanolamine, has physico-chemical properties comparable to anandamide, and, while it is not strictly an endocannabinoid, it is often studied in conjunction with anandamide because of their overlapping synthetic and metabolic pathways. N-acylethanolamines such as PEA often act as signaling molecules, activating receptors and regulating a variety of physiological functions. PEA is known to activate intracellular, nuclear and membrane-associated receptors, and to regulate many physiological functions related to the inflammatory cascade and chronic pain states. Endocannabinoid lipids like PEA are widely distributed in nature, in a variety of plant, invertebrate, and mammalian tissues.
PEAs mechanism of action sometimes is described as Autacoid Local Injury Antagonism (acronym ALIA), and PEA under this nomenclature is an ALIAmide. Levi-Montalcini and coworkers presented evidence in 1993 that lipid amides of the N-acylethanolamine type, such as PEA, are potential prototypes of naturally occurring molecules capable of modulating mast cell activation, and her group used the acronym ALIA in that report. An autocoid is a regulating molecule, locally produced. An ALIAmide is an autocoid synthesized on-demand in response to injury, and acts locally to counteract such pathology. Soon after the breakthrough paper of Levi-Montalcini, the mast cell appeared to be an important target for the anti-inflammatory activity of PEA. Since 1993, at least 25 papers have been published on the various effects of PEA on mast cells. These cells are often found in proximity to sensory nerve endings, and their degranulation can enhance the nociceptive signal, the reason why peripheral mast cells are considered to be pro-inflammatory and pro-nociceptive. PEAs activity is currently seen as a new inroad in the treatment of neuropathic pain and related disorders based on overactivation of glia and glia-related cells, such as in diabetes and glaucoma. Microglia plays a key role in the winding up phenomenon and central sensitization. | 1 | Biochemistry |
Interaction networks can be analyzed using the tools of graph theory. Network properties include the degree distribution, clustering coefficients, betweenness centrality, and many others. The distribution of properties among the proteins of an interactome has revealed that the interactome networks often have scale-free topology where functional modules within a network indicate specialized subnetworks. Such modules can be functional, as in a signaling pathway, or structural, as in a protein complex. In fact, it is a formidable task to identify protein complexes in an interactome, given that a network on its own does not directly reveal the presence of a stable complex. | 1 | Biochemistry |
3β-Etiocholanediol, or epietiocholanediol, also known as 3β,5β-androstanediol or as etiocholane-3β,17β-diol, is a naturally occurring etiocholane (5β-androstane) steroid and an endogenous metabolite of testosterone. It is formed from 5β-dihydrotestosterone (after 5β-reduction of testosterone) and is transformed into epietiocholanolone. | 1 | Biochemistry |
Cryptands enjoy some commercial applications (e.g. in homogenous-time-resolved-fluorescence, HTRF, technologies using Eu3+ as central ion). More importantly, they are reagents for the synthesis of inorganic and organometallic salts. Although more expensive and more difficult to prepare than crown ethers, cryptands bind alkali metals more strongly. They are especially used to isolate salts of highly basic anions. They convert solvated alkali metal cations into lipophilic cations, thereby conferring solubility in organic solvents to the resulting salts.
Referring to achievements that have been recognized in textbooks, cryptands enabled the synthesis of the alkalides and electrides. For example, addition of 2,2,2-cryptand to a solution of sodium in ammonia affords the salt [Na(2,2,2-crypt)]e, isolated a blue-black paramagnetic solid. Cryptands have also been used in the crystallization of Zintl ions such as .
Although rarely practical, cryptands can serve as phase transfer catalysts since their cationic complexes are lipophilic. | 6 | Supramolecular Chemistry |
Thermal rearrangements of aromatic hydrocarbons are generally carried out through flash vacuum pyrolysis (FVP). In a typical FVP apparatus, a sample is sublimed under high vacuum (0.1-1.0 mmHg), heated in the range of 500-1100 °C by an electric furnace as it passes through a horizontal quartz tube, and collected in a cold trap. Sample is carried through the apparatus by nitrogen carrier gas.
FVP has numerous limitations:
*First, it requires a slow rate of sublimation to minimize bimolecular reactions in the gas phase, limiting the amount of material that can be reacted in a given amount of time.
*Second, the high temperatures used in FVP often lead to reactant or product degradation. Combined, these first two limitations restrict FVP yields to the range of 25-30%.
*Third, the high temperatures used in FVP do not allow for the presence of functional groups, thereby limiting possible products.
*Fourth, as FVP is a gas-phase process, difficulties are frequently encountered when scaling above the milligram level.
*Fifth, the FVP synthesis of strained systems mandates temperatures exceeding 1100 °C, which can lead to the degradation and softening of the expensive quartz apparati. | 5 | Photochemistry |
Copper alloys which contain oxygen can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of , forming 2 metallic Cu atoms and (water), which then forms pressurized bubbles at the grain boundaries. This process can cause the grains to literally be forced away from each other, and is known as steam embrittlement (because steam is directly produced inside the copper crystal lattice, not because exposure of copper to external steam causes the problem). | 7 | Physical Chemistry |
The first stable carbenes to be isolated were based on an imidazole ring, with the hydrogen in carbon 2 of the ring (between the two nitrogen atoms) removed, and other hydrogens replaced by various groups. These imidazol-2-ylidenes are still the most stable and the most well studied and understood family of persistent carbenes.
A considerable range of imidazol-2-ylidenes have been synthesised, including those in which the 1,3-positions have been functionalised with alkyl, aryl, alkyloxy, alkylamino, alkylphosphino and even chiral substituents:
In particular, substitution of two chlorine atoms for the two hydrogens at ring positions 4 and 5 yielded the first air-stable carbene. Its extra stability probably results from the electron-withdrawing effect of the chlorine substituents, which reduce the electron density on the carbon atom bearing the lone pair, via induction through the sigma-backbone.
Molecules containing two and even three imidazol-2-ylidene groups have also been synthesised.
Imidazole-based carbenes are thermodynamically stable and generally have diagnostic C NMR chemical shift values between 210 and 230 ppm for the carbenic carbon. Typically, X-ray structures of these molecules show N–C–N bond angles of 101–102°. | 0 | Organic Chemistry |
There appear to be two main kinds of methodology used for the calculation of energy quality. These can be classed as either receiver or donor methods. One of the main differences that distinguishes these classes is the assumption of whether energy quality can be upgraded in an energy transformation process.
Receiver methods: view energy quality as a measure and indicator of the relative ease with which energy converts from one form to another. That is, how much energy is received from a transformation or transfer process. For example, A. Grubler [http://www.iiasa.ac.at/Research/TNT/WEB/Publications/Transition_in_Energy_Use/transitions-euse-ene_encyclop_2004.pdf] used two types of indicators of energetic quality pars pro toto: the hydrogen/carbon (H/C) ratio, and its inverse, the carbon intensity of energy. Grubler used the latter as an indicator of relative environmental quality. However Ohta says that in multistage industrial conversion systems, such as a hydrogen production system using solar energy, the energy quality is not upgraded (1994, p. 125).
Donor methods: view energy quality as a measure of the amount of energy used in an energy transformation, and that goes into sustaining a product or service (H.T.Odum 1975, p. 3). That is how much energy is donated to an energy transformation process. These methods are used in ecological physical chemistry, and ecosystem evaluation. From this view, in contrast with that outlined by Ohta, energy quality is upgraded in the multistage trophic conversions of ecological systems. Here, upgraded energy quality has a greater capacity to feedback and control lower grades of energy quality. Donor methods attempt to understand the usefulness of an energetic process by quantifying the extent to which higher quality energy controls lower quality energy. | 7 | Physical Chemistry |
With the use of Green's function, the Lippmann–Schwinger equation has counterparts in homogenization theory (e.g. mechanics, conductivity, permittivity). | 7 | Physical Chemistry |
NADH is oxidized into NAD, H ions, and electrons by an enzyme. FADH is also oxidized into H ions, electrons, and FAD. As those electrons travel farther through the electron transport chain in the inner membrane, energy is gradually released and used to pump the hydrogen ions from the splitting of NADH and FADH into the space between the inner membrane and the outer membrane (called the intermembrane space), creating an electrochemical gradient.
This electrochemical gradient creates potential energy (see ) across the inner mitochondrial membrane known as the proton-motive force. As a result, chemiosmosis occurs, and the enzyme ATP synthase produces ATP from ADP and a phosphate group. This harnesses the potential energy from the concentration gradient formed by the amount of H ions. H ions passively pass into the mitochondrial matrix by the ATP synthase, and later help to re-form HO (water).
The electron transport chain requires a varying supply of electrons in order to properly function and generate ATP. However, the electrons that have entered the electron transport chain would eventually pile up like cars traveling down a blocked one-way street. Those electrons are finally accepted by oxygen (O). As a result, they form two molecules of water (HO). By accepting the electrons, oxygen allows the electron transport chain to continue functioning. The chain is organized in the cristae lumen membrane, i.e. the membrane inside the junction.
The electrons from each NADH molecule can form a total of 3 ATP's from ADPs and phosphate groups through the electron transport chain, while each FADH molecule can produce a total of 2 ATPs.
As a result, 10 NADH molecules (from glycolysis and the Krebs cycle), along with 2 FADH molecules, can form a total of 34 ATPs during aerobic respiration (from a single electron transport chain). This means that combined with the Krebs Cycle and glycolysis, the efficiency for the electron transport chain is about 65%, as compared to only 3.5% efficiency for glycolysis alone. | 1 | Biochemistry |
Blockages in repolarization can arise due to modifications of the voltage-gated K channels. This is demonstrated with selectively blocking voltage gated K channels with the antagonist tetraethylammonium (TEA). By blocking the channel, repolarization is effectively stopped. Dendrotoxins are another example of a selective pharmacological blocker for voltage gated K channels. The lack of repolarization means that neuron stays at a high voltage, which slows sodium channel deactivation to a point where there is not enough inwards Na current to depolarize and sustain firing. | 7 | Physical Chemistry |
In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices. Space groups are classified into crystal systems according to their point groups, and into lattice systems according to their Bravais lattices. Crystal systems that have space groups assigned to a common lattice system are combined into a crystal family.
The seven crystal systems are triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic. Informally, two crystals are in the same crystal system if they have similar symmetries (albeit there are many exceptions). | 3 | Analytical Chemistry |
Chiral purity is a measure of the purity of a chiral drug. Other synonyms employed include enantiomeric excess, enantiomer purity, enantiomeric purity, and optical purity. Optical purity is an obsolete term since today most of the chiral purity measurements are done using chromatographic techniques (not based on optical principles). Enantiomeric excess tells the extent (in %) to which the chiral substance contains one enantiomer over the other. For a racemic drug the enantiomeric excess will be 0%. There are number of chiral analysis tools such as polarimetry, NMR spectroscopy with the use of chiral shift reagents, chiral GC (gas chromatography), chiral HPLC (high performance liquid chromatography), chiral TLC (thin-layer chromatography) and other chiral chromatographic techniques, that are employed to evaluate chiral purity. Assessing the purity of a unichiral drug or enantiopure drug is of great importance from a drug safety and efficacy perspective. | 4 | Stereochemistry |
NRTL binary interaction parameters have been published in the Dechema data series and are provided by NIST and DDBST. In 2023 the DDBST database of VLE-data in combination with the smiles notation for molecules has been used as input to generate via a machine learning algorithm a giant database of 100 million NRTL binary interaction parameter sets. It covers a list of 10 thousand compounds. | 7 | Physical Chemistry |
FCS almost always refers to the single point, single channel, temporal autocorrelation measurement, although the term "fluorescence correlation spectroscopy" out of its historical scientific context implies no such restriction. FCS has been extended in a number of variations by different researchers, with each extension generating another name (usually an acronym). | 7 | Physical Chemistry |
Scheme 3: The scheme illustrates the first displacement, the rate determining step and slowest step, where the starting material is converted to the iodo-intermediate. The intermediate is not detectable as it is rapidly converted to the unsaturated sugar. Experiments with azide instead of the iodide confirmed attack occurs at the C-3 as nitrogen-intermediates were isolated. The order of reactivity from most reactive to least reactive is: β-glucopyranosides > β-mannopyranosides > α-glucopyranosides> α-mannopyranosides.
The reaction of β–mannopyranosides gives low yields and required longer reaction times than with β-glucopyranosides due to the presence of a neighboring axial substituent (sulfonyloxy) relative to C-3 sulfonyloxy group in the starting material. The axial substituent increases the steric interactions in the transition state, causing unfavorable eclipsing of the two sulfonyloxy groups. α-Glucopyranosides possess a β-trans-axial substituent relative to C-3 sulfonyloxy (anomeric OCH group) in the starting material. The β-trans-axial substituent influences the transition state by also causing an unfavorable steric interaction between the two groups. In the case of α-mannopyranosides, both a neighboring axial substituent (2-sulfonyloxy group) and a β-trans-axial substituent (anomeric OCH group) are present, therefore significantly increasing the reaction time and decreasing the yield. | 0 | Organic Chemistry |
New mTOR-specific inhibitors came forth from screening and drug discovery efforts. These compounds block activity of both mTOR complexes and are called mTORC1/mTORC2 dual inhibitors. Compounds with this characteristics such as sapanisertib (codenamed INK128), AZD8055, and AZD2014 have entered clinical trials.
A series of these mTOR kinase inhibitors have been studied. Their structure is derived from morpholino pyrazolopyrimidine scaffold.
Improvements of this type of inhibitors have been made by exchanging the morpholines with bridged morpholines in pyrazolopyrimidine inhibitors and results showed increased selectivity to mTOR by 26000 fold. | 1 | Biochemistry |
Ferrosilicon is produced by reduction of silica or sand with coke in the presence of iron. Typical sources of iron are scrap iron or millscale. Ferrosilicons with silicon content up to about 15% are made in blast furnaces lined with acid fire bricks.
Ferrosilicons with higher silicon content are made in electric arc furnaces. The usual formulations on the market are ferrosilicons with 15%, 45%, 75%, and 90% silicon. The remainder is iron, with about 2% consisting of other elements like aluminium and calcium. An overabundance of silica is used to prevent formation of silicon carbide. Microsilica is a useful byproduct.
A mineral perryite is similar to ferrosilicon, with its composition FeSi. In contact with water, ferrosilicon may slowly produce hydrogen. The reaction, which is accelerated in the presence of base, is used for hydrogen production. The melting point and density of ferrosilicon depends on its silicon content, with two nearly-eutectic areas, one near FeSi and second spanning FeSi-FeSi composition range. | 8 | Metallurgy |
When dealing with a heterogeneous surface, the Wenzel model is not sufficient. A more complex model is needed to measure how the apparent contact angle changes when various materials are involved. This heterogeneous surface, like that seen in Figure 8, is explained using the Cassie–Baxter equation (Cassie's law):
Here the r is the roughness ratio of the wet surface area and f is the fraction of solid surface area wet by the liquid. It is important to realize that when f = 1 and r = r, the Cassie–Baxter equations becomes the Wenzel equation. On the other hand, when there are many different fractions of surface roughness, each fraction of the total surface area is denoted by .
A summation of all equals 1 or the total surface. Cassie–Baxter can also be recast in the following equation:
Here is the Cassie–Baxter surface tension between liquid and vapor, is the solid vapor surface tension of every component, and is the solid liquid surface tension of every component. A case that is worth mentioning is when the liquid drop is placed on the substrate and creates small air pockets underneath it. This case for a two-component system is denoted by:
Here the key difference to notice is that there is no surface tension between the solid and the vapor for the second surface tension component. This is because of the assumption that the surface of air that is exposed is under the droplet and is the only other substrate in the system. Subsequently, the equation is then expressed as (1 – f). Therefore, the Cassie equation can be easily derived from the Cassie–Baxter equation. Experimental results regarding the surface properties of Wenzel versus Cassie–Baxter systems showed the effect of pinning for a Young angle of 180 to 90°, a region classified under the Cassie–Baxter model. This liquid/air composite system is largely hydrophobic. After that point, a sharp transition to the Wenzel regime was found where the drop wets the surface, but no further than the edges of the drop. Actually, the Young, Wenzel and Cassie-Baxter equations represent the transversality conditions of the variational problem of wetting. | 7 | Physical Chemistry |
A15 phases are intermetallic alloys with an average coordination number (ACN) of 13.5 and eight AB stoichiometry atoms per unit cell where two B atoms are surrounded by CN12 polyhedral (icosahedra), and six A atoms are surrounded by CN14 polyhedral. NbGe is a superconductor with A15 structure. | 8 | Metallurgy |
Levetiracetam is effective for treatment of generalized tonic-clonic epilepsy. It has been approved in the United States as add-on treatment for myoclonic, and tonic-clonic seizures. Levetiracetam has been approved in the European Union as a monotherapy treatment for epilepsy in the case of partial seizures or as an adjunctive therapy for partial, myoclonic, and tonic-clonic seizures.
Levetiracetam is sometimes used off label to treat status epilepticus. | 4 | Stereochemistry |
Many stationary phases are porous to provide greater surface area. Small pores provide greater surface area while larger pore size has better kinetics, especially for larger analytes. For example, a protein which is only slightly smaller than a pore might enter the pore but does not easily leave once inside. | 3 | Analytical Chemistry |
Early models to explain the origin of the index of refraction treated an electron in an atomic system classically according to the model of Paul Drude and Hendrik Lorentz. The theory was developed to attempt to provide an origin for the wavelength-dependent refractive index n of a material. In this model, incident electromagnetic waves forced an electron bound to an atom to oscillate. The amplitude of the oscillation would then have a relationship to the frequency of the incident electromagnetic wave and the resonant frequencies of the oscillator. The superposition of these emitted waves from many oscillators would then lead to a wave which moved more slowly. | 7 | Physical Chemistry |
The early work of the scientists J. Arthur Harris and Francis G. Benedict showed that approximate values for BMR could be derived using body surface area (computed from height and weight), age, and sex, along with the oxygen and carbon dioxide measures taken from calorimetry. Studies also showed that by eliminating the sex differences that occur with the accumulation of adipose tissue by expressing metabolic rate per unit of "fat-free" or lean body mass, the values between sexes for basal metabolism are essentially the same. Exercise physiology textbooks have tables to show the conversion of height and body surface area as they relate to weight and basal metabolic values.
The primary organ responsible for regulating metabolism is the hypothalamus. The hypothalamus is located on the diencephalon and forms the floor and part of the lateral walls of the third ventricle of the cerebrum. The chief functions of the hypothalamus are:
# control and integration of activities of the autonomic nervous system (ANS)
#* The ANS regulates contraction of smooth muscle and cardiac muscle, along with secretions of many endocrine organs such as the thyroid gland (associated with many metabolic disorders).
#* Through the ANS, the hypothalamus is the main regulator of visceral activities, such as heart rate, movement of food through the gastrointestinal tract, and contraction of the urinary bladder.
# production and regulation of feelings of rage and aggression
# regulation of body temperature
# regulation of food intake, through two centers:
#* The feeding center or hunger center is responsible for the sensations that cause us to seek food. When sufficient food or substrates have been received and leptin is high, then the satiety center is stimulated and sends impulses that inhibit the feeding center. When insufficient food is present in the stomach and ghrelin levels are high, receptors in the hypothalamus initiate the sense of hunger.
#* The thirst center operates similarly when certain cells in the hypothalamus are stimulated by the rising osmotic pressure of the extracellular fluid. If thirst is satisfied, osmotic pressure decreases.
All of these functions taken together form a survival mechanism that causes us to sustain the body processes that BMR measures. | 1 | Biochemistry |
The next generation of SNP annotation webservers can take advantage of the growing amount of data in core bioinformatics resources and use intelligent agents to fetch data from different sources as needed. From a user’s point of view, it is more efficient to submit a set of SNPs and receive results in a single step, which makes meta-servers the most attractive choice. However, if SNP annotation tools deliver heterogeneous data covering sequence, structure, regulation, pathways, etc., they must also provide frameworks for integrating data into a decision algorithms, and quantitative confidence measures so users can assess which data are relevant and which are not. | 1 | Biochemistry |
Radioactive isotope labeling experiments provide a powerful tool for determining the structure of organic molecules. By systematically decomposing the 2-norbornyl cation and analyzing the amount of radioactive isotope in each decomposition product, researchers were able to show further evidence for the non-classical picture of delocalized bonding (see Figure 9). Proponents of the nonclassical picture would expect 50% of the generated CO in the decomposition in Figure 9 to contain C, while proponents of the classical picture would expect more of the generated CO to be radioactive due to the short-lived nature of the cation. 40% of the carbon dioxide produced via decomposition has been observed to be radioactive, suggesting that the non-classical picture is more correct.
Further distinction between non-classical and classical structures of the 2-norbornyl cation is possible by combining NMR experiments with isotope-labeling experiments. Isotopic substitution of one of two deuterium atoms for a hydrogen atom causes the environment of nearby NMR-active atoms to change dramatically. Asymmetric deuterium isotope labeling (substitution) will cause a set of carbons that were all equivalent in the all-hydrogen species to be split into two or more sets of equivalent carbons in the deutero-labeled species; this will be manifested in the NMR spectrum as one peak in the all-hydrogen species' spectrum becoming at least two "split" peaks in the deutero-labeled species. If a system is undergoing a rapid equilibrium at a rate faster than the timescale of a C NMR experiment, the relevant peak will be split dramatically (on the order of 10-100 ppm). If the system is instead static, the peak will be split very little. The C NMR spectrum of the 2-norbornyl cation at -150 °C shows that the peaks corresponding to carbons 1 and 2 are split by less than 10 ppm (parts per million) when this experiment is carried out, indicating that the system is not undergoing a rapid equilibrium as in the classical picture. | 7 | Physical Chemistry |
Charles Roger Slack (22 April 1937 – 24 October 2016) was a British-born plant biologist and biochemist who lived and worked in Australia (1962–1970) and New Zealand (1970–2000). In 1966, jointly with Marshall Hatch, he discovered C4 photosynthesis (also known as the Hatch Slack Pathway). | 1 | Biochemistry |
In the following formulas G denotes a group contribution. G are counted for every single available group. If a group is present multiple times, each occurrence is counted separately. | 7 | Physical Chemistry |
An oxocarbenium ion (or oxacarbenium ion) is a chemical species characterized by a central sp-hybridized carbon, an oxygen substituent, and an overall positive charge that is delocalized between the central carbon and oxygen atoms. An oxocarbenium ion is represented by two limiting resonance structures, one in the form of a carbenium ion with the positive charge on carbon and the other in the form of an oxonium species with the formal charge on oxygen. As a resonance hybrid, the true structure falls between the two. Compared to neutral carbonyl compounds like ketones or esters, the carbenium ion form is a larger contributor to the structure. They are common reactive intermediates in the hydrolysis of glycosidic bonds, and are a commonly used strategy for chemical glycosylation. These ions have since been proposed as reactive intermediates in a wide range of chemical transformations, and have been utilized in the total synthesis of several natural products. In addition, they commonly appear in mechanisms of enzyme-catalyzed biosynthesis and hydrolysis of carbohydrates in nature. Anthocyanins are natural flavylium dyes, which are stabilized oxocarbenium compounds. Anthocyanins are responsible for the colors of a wide variety of common flowers such as pansies and edible plants such as eggplant and blueberry. | 0 | Organic Chemistry |
The solution containing the relevant substance to be analysed is drawn into the burner and dispersed into the flame as a fine spray. The solvent evaporates first, leaving finely divided solid particles which move to the hottest region of the flame where gaseous atoms and ions are produced through the dissociation of molecules. Here electrons are excited as described above, and the spontaneously emit photon to decay to lower energy states. It is common for a monochromator to be used to allow for easy detection.
On a simple level, flame emission spectroscopy can be observed using just a flame and samples of metal salts. This method of qualitative analysis is called a flame test. For example, sodium salts placed in the flame will glow yellow from sodium ions, while strontium (used in road flares) ions color it red. Copper wire will create a blue colored flame, however in the presence of chloride gives green (molecular contribution by CuCl). | 7 | Physical Chemistry |
Instruments accept small (mm range) and large samples (cm range), e.g. wafers. The limiting factor is the design of the sample holder, the sample transfer, and the size of the vacuum chamber. Large samples are laterally moved in x and y direction to analyze a larger area. | 7 | Physical Chemistry |
There are two distinctive features of ion channels that differentiate them from other types of ion transporter proteins:
#The rate of ion transport through the channel is very high (often 10 ions per second or greater).
#Ions pass through channels down their electrochemical gradient, which is a function of ion concentration and membrane potential, "downhill", without the input (or help) of metabolic energy (e.g. ATP, co-transport mechanisms, or active transport mechanisms).
Ion channels are located within the membrane of all excitable cells, and of many intracellular organelles. They are often described as narrow, water-filled tunnels that allow only ions of a certain size and/or charge to pass through. This characteristic is called selective permeability. The archetypal channel pore is just one or two atoms wide at its narrowest point and is selective for specific species of ion, such as sodium or potassium. However, some channels may be permeable to the passage of more than one type of ion, typically sharing a common charge: positive (cations) or negative (anions). Ions often move through the segments of the channel pore in a single file nearly as quickly as the ions move through the free solution. In many ion channels, passage through the pore is governed by a "gate", which may be opened or closed in response to chemical or electrical signals, temperature, or mechanical force.
Ion channels are integral membrane proteins, typically formed as assemblies of several individual proteins. Such "multi-subunit" assemblies usually involve a circular arrangement of identical or homologous proteins closely packed around a water-filled pore through the plane of the membrane or lipid bilayer. For most voltage-gated ion channels, the pore-forming subunit(s) are called the α subunit, while the auxiliary subunits are denoted β, γ, and so on. | 1 | Biochemistry |
The copolymerization of ethylene with polar monomers has been heavily studied. The high oxophilicity of the early metals precluded their use in this application.
Efforts to copolymerize polar comonomers led to catalysts based upon nickel and palladium, inspired by the success of the Shell Higher Olefin Process. Typical post-metallocene catalysts feature bulky, neutral, alpha-diimine ligands. DuPont commercialized the Versipol olefin polymerization system. Eastman commercialized the related Gavilan technology. These complexes catalyze the homopolymerize ethylene to a variety of structures that range from high density polyethylene through hydrocarbon plastomers and elastomers by a mechanism referred to as “chain-walking”. By modifying the bulk of the alpha-diimine, the product distribution of these systems can be tuned to consist of hydrocarbon oils (alpha-olefins), similar to those produced by more tradition nickel(II) oligo/polymerization catalysts. As opposed to metallocenes, they can also randomly copolymerize ethylene with polar comonomers such as methyl acrylate.
A second class of catalysts feature mono-anionic bidentate ligands related to salen ligands. and DuPont.
The concept of bulky bis-imine ligands was extended to iron complexes Representative catalysts feature diiminopyridine ligands. These catalysts are highly active but do not promote chain walking. The give very linear high-density polyethylene when bulky and when the steric bulk is removed, they are very active for ethylene oligomerization to linear alpha-olefins.
A salicylimine catalyst system based on zirconium exhibits high activity for ethylene polymerization. The catalysts can also produce some novel polypropylene structures. Despite intensive efforts, few catalysts have been successfully commercialized for the copolymerization of polar monomers. | 7 | Physical Chemistry |
If carbon dioxide, carbonic acid, hydrogen ions, bicarbonate and carbonate are all dissolved in water, and at chemical equilibrium, their equilibrium concentrations are often assumed to be given by:
where the subscript eq denotes that these are equilibrium concentrations, K is the equilibrium constant for the reaction + H + (i.e. the first acid dissociation constant for carbonic acid), K is the equilibrium constant for the reaction H + (i.e. the second acid dissociation constant for carbonic acid), and DIC is the (unchanging) total concentration of dissolved inorganic carbon in the system, i.e. [] + [] + []. K, K and DIC each have units of a concentration, e.g. mol/L.
A Bjerrum plot is obtained by using these three equations to plot these three species against , for given K, K and DIC. The fractions in these equations give the three species' relative proportions, and so if DIC is unknown, or the actual concentrations are unimportant, these proportions may be plotted instead.
These three equations show that the curves for and intersect at , and the curves for and intersect at . Therefore, the values of K and K that were used to create a given Bjerrum plot can easily be found from that plot, by reading off the concentrations at these points of intersection. An example with linear Y axis is shown in the accompanying graph. The values of K and K, and therefore the curves in the Bjerrum plot, vary substantially with temperature and salinity. | 7 | Physical Chemistry |
The convective heat transfer between a uniformly heated wall and the working fluid is described by Newton's law of cooling:
where represents the heat flux, represents the proportionally constant called the heat transfer coefficient, represents the wall temperature and represents the fluid temperature. If decreases significantly due to the occurrence of the CHF condition, will increase for fixed and while will decrease for fixed . | 7 | Physical Chemistry |
The concept of a transition state has been important in many theories of the rates at which chemical reactions occur. This started with the transition state theory (also referred to as the activated complex theory), which was first developed around 1935 by Eyring, Evans and Polanyi, and introduced basic concepts in chemical kinetics that are still used today. | 7 | Physical Chemistry |
In his first scientific works carried out under the guidance of Chugaev, Pigulevsky studied the chemistry of terpenes. Subsequently, essential oils and resins of coniferous plants became the main subject of his research. In addition to studying their formation and reactions, Pigulevsky also studied the optical properties of terpene compounds isolated from these oils. A number of articles were devoted to direct studies of plant materials from which essential oils and resins were extracted. His research of essential oils were of great practical importance, some of the substances discovered by Pigulevsky were applied in the perfume industry.
An important part of his research was the study of vegetable fats. Pigulevsky discovered the correlation between the degree of unsaturation of fats and the climate in which plants grew. Some of his works were devoted to the chemical properties of unsaturated acids.
In 1937, Pigulevsky was one of the first organic chemists in the USSR who began using the phenomenon of Raman scattering of light (the Raman effect) to study the physical properties of organic substances. By 1961, large number of Raman spectra had been collected for compounds found in essential oils of coniferous plants.
While working as the head of the laboratory of the labor protection department of the People's Commissariat of Labour, Pigulevsky published a number of works on the use of various devices in industry, as well as on the identification of harmful substances in the air. | 0 | Organic Chemistry |
The Platinum Metal Review journal was established in 1957 and was published by Johnson Mattley and Co. From April 1998, it was published as open access and from the July 2004 issue in electronic format only. In 2014 the name of the journal was changed to Johnson Matthey Technology Review. | 8 | Metallurgy |
The Thyrotroph Thyroid Hormone Sensitivity Index (TTSI, also referred to as Thyrotroph T4 Resistance Index or TT4RI) was developed to enable fast screening for resistance to thyroid hormone. Somewhat similar to the TSH Index it is calculated from equilibrium values for TSH and FT4, however with a different equation. | 1 | Biochemistry |
Oxygen has three stable isotopes, O, O, and O. Oxygen ratios are measured relative to Vienna Standard Mean Ocean Water (VSMOW) or Vienna Pee Dee Belemnite (VPDB). Variations in oxygen isotope ratios are used to track both water movement, paleoclimate, and atmospheric gases such as ozone and carbon dioxide. Typically, the VPDB oxygen reference is used for paleoclimate, while VSMOW is used for most other applications. Oxygen isotopes appear in anomalous ratios in atmospheric ozone, resulting from mass-independent fractionation. Isotope ratios in fossilized foraminifera have been used to deduce the temperature of ancient seas. | 9 | Geochemistry |
FAS receptor gene is located on the long arm of chromosome 10 (10q24.1) in humans and on chromosome 19 in mice. The gene lies on the plus (Watson strand) and is 25,255 bases in length organized into nine protein encoding exons. Similar sequences related by evolution (orthologs) are found in most mammals. | 1 | Biochemistry |
Two mole of is split into 1 mole and 2 mole using light in the process shown below.
A photon with an energy greater than 1.23 eV is needed to generate an electron–hole pairs, which react with water on the surface of the photocatalyst. The photocatalyst must have a bandgap large enough to split water; in practice, losses from material internal resistance and the overpotential of the water splitting reaction increase the required bandgap energy to 1.6–2.4 eV to drive water splitting.
The process of water-splitting is a highly endothermic process (ΔH > 0). Water splitting occurs naturally in photosynthesis when the energy of four photons is absorbed and converted into chemical energy through a complex biochemical pathway (Dolais or Koks S-state diagrams).
O–H bond homolysis in water requires energy of 6.5 - 6.9 eV (UV photon). Infrared light has sufficient energy to mediate water splitting because it technically has enough energy for the net reaction. However, it does not have enough energy to mediate the elementary reactions leading to the various intermediates involved in water splitting (this is why there is still water on Earth). Nature overcomes this challenge by absorbing four visible photons. In the laboratory, this challenge is typically overcome by coupling the hydrogen production reaction with a sacrificial reductant other than water.
Materials used in photocatalytic water splitting fulfill the band requirements and typically have dopants and/or co-catalysts added to optimize their performance. A sample semiconductor with the proper band structure is titanium dioxide () and is typically used with a co-catalyst such as platinum (Pt) to increase the rate of production. A major problem in photocatalytic water splitting is photocatalyst decomposition and corrosion. | 5 | Photochemistry |
Intrastrand DNA crosslinks have strong effects on organisms because these lesions interfere with transcription and replication. These effects can be put to good use (addressing cancer) or they can be lethal to the host organism. The drug cisplatin functions by formation of intrastrand crosslinks in DNA. Other crosslinking agents include mustard gas, mitomycin, and psoralen. | 7 | Physical Chemistry |
To introduce a reporter gene into an organism, scientists place the reporter gene and the gene of interest in the same DNA construct to be inserted into the cell or organism. For bacteria or prokaryotic cells in culture, this is usually in the form of a circular DNA molecule called a plasmid. For viruses, this is known as a viral vector. It is important to use a reporter gene that is not natively expressed in the cell or organism under study, since the expression of the reporter is being used as a marker for successful uptake of the gene of interest.
Commonly used reporter genes that induce visually identifiable characteristics usually involve fluorescent and luminescent proteins. Examples include the gene that encodes jellyfish green fluorescent protein (GFP), which causes cells that express it to glow green under blue or ultraviolet light, the enzyme luciferase, which catalyzes a reaction with luciferin to produce light, and the red fluorescent protein from the gene . The GUS gene has been commonly used in plants but luciferase and GFP are becoming more common.
A common reporter in bacteria is the E. coli lacZ gene, which encodes the protein beta-galactosidase. This enzyme causes bacteria expressing the gene to appear blue when grown on a medium that contains the substrate analog X-gal. An example of a selectable marker which is also a reporter in bacteria is the chloramphenicol acetyltransferase (CAT) gene, which confers resistance to the antibiotic chloramphenicol. | 1 | Biochemistry |
Ferredoxin can also be reduced by using NADH (-320 mV) or (-414 mV), but these processes are coupled to the consumption of the membrane potential to power the "boosting" of electrons to the higher energy state. The Rnf complex is a widespread membrane protein in bacteria that reversibly transfers electrons between NADH and ferredoxin while pumping or ions across the membrane. The chemiosmotic potential of the membrane is consumed to power the unfavorable reduction of by NADH. This reaction is an essential source of in many autotrophic organisms. If the cell is growing on substrates that provide excess , the Rnf complex can transfer these electrons to and store the resultant energy in the membrane potential. The energy converting hydrogenases (Ech) are a family of enzymes that reversibly couple the transfer of electrons between and while pumping ions across the membrane to balance the energy difference. | 5 | Photochemistry |
In the early 1970s, the traditional blast furnace and sinter plant technology that was the mainstay of the lead smelting industry was coming under sustained pressure from more stringent environmental requirements, increased energy costs, decreasing metal prices and rising capital and operating costs.
Many smelting companies were seeking new processes to replace sinter plants and blast furnaces. Possibilities included the QSL lead smelting process, the Kivcet process, the Kaldo top-blown rotary converter, and adapting Outokumpu's successful copper and nickel flash furnace to lead smelting.
MIM was seeking ways to safeguard the future of its Mount Isa lead smelting operations. It did this in two ways:
# working to improve the environmental and operational performance of its existing operations
# investigating new technologies.
MIM investigated new technologies by arranging plant testing of large parcels of Mount Isa lead concentrates for all the then process options except for the Kivcet process. At the same time, it had been aware of the use of top-jetting lances in the Mitsubishi and Kaldo processes, and of top-entry submerged combustion lance investigations undertaken by Asarco (which had a long association with MIM, including being a shareholder in MIM Holdings) in the 1960s. This stimulated MIM's interest in the Sirosmelt lance, which was seen as a way to produce a robust submerged lance.
Following the copper slag trials of 1976–1978, MIM initiated a joint project with the CSIRO in 1978 to investigate the possibility of applying Sirosmelt lances to lead smelting.
The work began with computer modelling the equilibrium thermodynamics (1978) and was followed by laboratory bench-scale test work using large alumina silicate crucibles (1978–1979). The results were sufficiently encouraging that MIM built a 120 kg/h test rig in Mount Isa. It began operation in September 1980. This was used to develop a two-stage process to produce lead bullion from Mount Isa lead concentrate. The first stage was an oxidation step that removed virtually all the sulfur from the feed, oxidising the contained lead to lead oxide (PbO) that was largely collected in the slag (some was carried out of the furnace as lead oxide fume that was returned for lead recovery). The second stage was a reduction step in which the oxygen was removed from the lead to form lead metal. | 8 | Metallurgy |
Mayeda worked initially as a laboratory assistant to Harold Urey at the University of Chicago, where she was hired initially to wash glassware. They used mass spectrometry to measure oxygen isotopes in the shells of marine molluscs which gave information on the prehistoric temperatures of ocean waters and hence paleoclimates. Urey developed the field of cosmochemistry and with Mayeda studied primitive meteorites, also by using oxygen isotope analysis. Later, she worked with Cesare Emiliani on isotopic evaluation of the ice age. When Urey retired from the university in 1958, Mayeda was persuaded to remain there by Robert N. Clayton, and collaborate with him on applications of mass spectroscopy. She was described as an indomitable research assistant.
Mayeda and Clayton's first research paper considered the use of Bromine pentafluoride to extract Isotopes of oxygen from rocks and minerals. It remains their most cited work. From the 1970s until the late 1990s Mayeda and Clayton became famous for their use of oxygen isotopes to classify meteorites. They developed several tests that were used across the field of meteorite and lunar sample analysis. They studied variations in the abundances of the stable isotopes of oxygen, oxygen-16, oxygen-17 and oxygen-18, and deduced differences in the formation temperatures of the meteorites. They also worked on the mass spectroscopy and chemistry of the Allende meteorite. They published many scientific papers on the "oxygen thermometer" and analysed approximately 300 lunar samples that had been collected during NASAs Apollo Program.
In 1992, a new type of meteorite, the Brachinite, was identified. Clayton and Mayeda studied the Achondrite meteorites and showed that variations in the oxygen-17 isotope ratios within a planet are due to inhomogeneities in the Solar Nebula. They analysed Shergotty meteorites, proposing that there could have been a water-rich atmosphere on Mars and studied the Bocaiuva meteorite, finding that the Eagle Station meteorite was formed due to impact heating.
In 2002 Mayeda was awarded the Society Merit Prize from the Geochemical Society of Japan. In the same year, an asteroid was named after her. Mayedas husband, Harry, died in 2003. Mayeda suffered from cancer and died on February 13, 2004. In 2008, the book Oxygen in the Solar System' was dedicated to Clayton and Mayeda. | 9 | Geochemistry |
Prior to 1925, the materials used in implant surgery were primarily relatively pure metals. The success of these materials was surprising considering the relatively primitive surgical techniques. The 1930s marked the beginning of the era of better surgical techniques as well as the first use of alloys such as vitallium.
In 1969, L. L. Hench and others discovered that various kinds of glasses and ceramics could bond to living bone. Hench was inspired by the idea on his way to a conference on materials. He was seated next to a colonel who had just returned from the Vietnam War. The colonel shared that after an injury the bodies of soldiers would often reject the implant. Hench was intrigued and began to investigate materials that would be biocompatible. The final product was a new material which he called bioglass. This work inspired a new field called bioceramics. With the discovery of bioglass, interest in bioceramics grew rapidly.
On April 26, 1988, the first international symposium on bioceramics was held in Kyoto, Japan. | 7 | Physical Chemistry |
Electroplasticity, describes the enhanced plastic behavior of a solid material under the application of an electric field. This electric field could be internal, resulting in current flow in conducting materials, or external. The effect of electric field on mechanical properties ranges from simply enhancing existing plasticity, such as reducing the flow stress in already ductile metals, to promoting plasticity in otherwise brittle ceramics. The exact mechanisms that control electroplasticity vary based on the material and the exact conditions (e.g., temperature, strain rate, grain size, etc.). Enhancing the plasticity of materials is of great practical interest as plastic deformation provides an efficient way of transforming raw materials into final products. The use of electroplasticity to improve processing of materials is known as electrically assisted manufacturing. | 7 | Physical Chemistry |
There are four main limiting factors leading to no initiation of replication in iterons:
*Transcriptional autorepression
*Initiator dimerization
*Initiator titration
*Handcuffing
Transcriptional auto-repression is thought to reduce initiator synthesis by repressing the formation of the Rep proteins. Since these proteins work to promote binding of replication machinery, replication can be halted in this form. Another factor used to stop replication is known as dimerization. It works to dimerize these Rep proteins and as a result monomers of these proteins are no longer in a high enough concentration to initiate replication. Another limiting factor, titration, occurs after replication and works to prevent saturation by distributing monomers to daughter origins so that no are fully saturated. Finally, handcuffing refers to pairing origins leading to inactivation. This is mediated by monomers and inactivation is due to steric hindrance between the origins.
Another less prevalent limitation thought to be present in these iterons is the presence of extra repeats. If a plasmid contains an extra supply of iterons outside of the saturation site it has been shown this can decrease plasmid copy number. In contrast, removing these extra iterons will increase copy number. | 1 | Biochemistry |
Rain can generally help clean PDRC surfaces that have been covered with dust, dirt, or other debris and improve their reflectivity. However, in humid areas, consistent rain can result in heavy water accumulation on PDRC surfaces which can hinder performance. In response, porous PDRCs have been developed. Another response is to make hydrophobic PDRCs which are "self-cleaning." Scalable and sustainable hydrophobic PDRCs that avoid VOCs have been developed that repel rainwater and other liquids. | 7 | Physical Chemistry |
"Litigation science" describes analysis or data developed or produced expressly for use in a trial versus those produced in the course of independent research. This distinction was made by the U.S. 9th Circuit Court of Appeals when evaluating the admissibility of experts.
This uses demonstrative evidence, which is evidence created in preparation of trial by attorneys or paralegals. | 3 | Analytical Chemistry |
In geometry, a point group is a mathematical group of symmetry operations (isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every point group in dimension d is then a subgroup of the orthogonal group O(d). Point groups are used to describe the symmetries of geometric figures and physical objects such as molecules.
Each point group can be represented as sets of orthogonal matrices M that transform point x into point y according to . Each element of a point group is either a rotation (determinant of ), or it is a reflection or improper rotation (determinant of ).
The geometric symmetries of crystals are described by space groups, which allow translations and contain point groups as subgroups. Discrete point groups in more than one dimension come in infinite families, but from the crystallographic restriction theorem and one of Bieberbach's theorems, each number of dimensions has only a finite number of point groups that are symmetric over some lattice or grid with that number of dimensions. These are the crystallographic point groups. | 4 | Stereochemistry |
The strength and directionality of halogen bonds are a key tool in the discipline of crystal engineering, which attempts to shape crystal structures through close control of intermolecular interactions. Halogen bonds can stabilize copolymers or induce mesomorphism in otherwise isotropic liquids. Indeed, halogen bond-induced liquid crystalline phases are known in both alkoxystilbazoles and silsesquioxanes (pictured). Alternatively, the steric sensitivity of halogen bonds can cause bulky molecules to crystallize into porous structures; in one notable case, halogen bonds between iodine and aromatic π-orbitals caused molecules to crystallize into a pattern that was nearly 40% void. | 6 | Supramolecular Chemistry |
As SPR biosensors facilitate measurements at different temperatures, thermodynamic analysis can be performed
to obtain a better understanding of the studied interaction. By performing measurements at different temperatures,
typically between 4 and 40 °C, it is possible to relate association and dissociation rate constants with activation
energy and thereby obtain thermodynamic parameters including binding enthalpy, binding entropy,
Gibbs free energy and heat capacity. | 7 | Physical Chemistry |
Protein crystallization is governed by the same physics that governs the formation of inorganic crystals. For crystallization to occur spontaneously, the crystal state must be favored thermodynamically. This is described by Gibb's free energy (∆G), defined as ∆G = ∆H- T∆S, which captures how the energetics of a process, ∆H, trades off with the corresponding change in entropy, ∆S. Entropy, roughly, describes the disorder of a system. Highly ordered states, such as protein crystals, are disfavored thermodynamically compared to more disordered states, such as solutions of proteins in solvent, because the transition to a more ordered state would decrease the total entropy of the system (positive ∆S). For crystals to form spontaneously, the ∆G of crystal formation must be negative. In other words, the entropic penalty must be paid by a corresponding decrease in the total energy of the system (∆H). Familiar inorganic crystals such as sodium chloride spontaneously form at ambient conditions because the crystal state decreases the total energy of the system. However, crystallization of some proteins under ambient conditions would both decrease the entropy (positive ∆S) and increase the total energy (positive ∆H) of the system, and thus does not occur spontaneously. To achieve crystallization of such proteins conditions are modified to make crystal formation energetically favorable. This is often accomplished by creation of a supersaturated solution of the sample. | 3 | Analytical Chemistry |
Several methods exist to rank electrophiles in order of reactivity and one of them is devised by Robert Parr with the electrophilicity index ω given as:
with the electronegativity and chemical hardness. This equation is related to the classical equation for electrical power:
where is the resistance (Ohm or Ω) and is voltage. In this sense the electrophilicity index is a kind of electrophilic power. Correlations have been found between electrophilicity of various chemical compounds and reaction rates in biochemical systems and such phenomena as allergic contact dermititis.
An electrophilicity index also exists for free radicals. Strongly electrophilic radicals such as the halogens react with electron-rich reaction sites, and strongly nucleophilic radicals such as the 2-hydroxypropyl-2-yl and tert-butyl radical react with a preference for electron-poor reaction sites. | 7 | Physical Chemistry |
Electro–optics is a branch of electrical engineering, electronic engineering, materials science, and material physics involving components, electronic devices such as lasers, laser diodes, LEDs, waveguides, etc. which operate by the propagation and interaction of light with various tailored materials. It is closely related to photonics, the branch of optics that involves the application of the generation of photons. It is not only concerned with the "electro–optic effect", since it deals with the interaction between the electromagnetic (optical) and the electrical (electronic) states of materials. | 7 | Physical Chemistry |
Conductometric titration is a type of titration in which the electrolytic conductivity of the reaction mixture is continuously monitored as one reactant is added. The equivalence point is the point at which the conductivity undergoes a sudden change. Marked increase or decrease in conductance are associated with the changing concentrations of the two most highly conducting ions—the hydrogen and hydroxyl ions. The method can be used for titrating coloured solutions or homogeneous suspension (e.g.: wood pulp suspension), which cannot be used with normal indicators.
Acid-base titrations and redox titrations are often performed in which common indicators are used to locate the end point e.g., methyl orange, phenolphthalein for acid base titrations and starch solutions for iodometric type redox process. However, electrical conductance measurements can also be used as a tool to locate the end point.
Example: titration of an HCl solution with the strong base NaOH. As the titration progresses, the protons are neutralized to form water by the addition of NaOH. For each amount of NaOH added equivalent amount of hydrogen ions is removed. Effectively, the mobile H cation is replaced by the less-mobile Na ion, and the conductivity of the titrated solution as well as the measured conductance of the cell fall. This continues until the equivalence point is reached, at which one obtains a solution of sodium chloride, NaCl. If more base is added, an increase in conductivity or conductance is observed, since more ions Na and OH are being added and the neutralization reaction no longer removes an appreciable amount of H. Consequently, in the titration of a strong acid with a strong base, the conductance has a minimum at the equivalence point. This minimum can be used, instead of an indicator dye, to determine the endpoint of the titration. The conductometric titration curve is a plot of the measured conductance or conductivity values as a function of the volume of the NaOH solution added. The titration curve can be used to graphically determine the equivalence point.
For reaction between a weak acid and a weak base in the beginning conductivity decreases a bit as the few available H ions are used up. Then conductivity increases slightly up to the equivalence point volume, due to contribution of the salt cation and anion.(This contribution in case of a strong acid-strong base is negligible and is not considered there.) After the equivalence point is achieved the conductivity increases rapidly due to the excess OH ions. | 3 | Analytical Chemistry |
Jelly-falls are primarily made up of the decaying corpses of Cnidaria and Thaliacea (Pyrosomida, Doliolida, and Salpida). Several circumstances can trigger the death of gelatinous organisms which would cause them to sink. These include high levels of primary production that can clog the feeding apparatuses of the organisms, a sudden temperature change, when an old bloom runs out of food, when predators damage the bodies of the jellies, and parasitism. In general, however, jelly-falls are linked to jelly-blooms and primary production, with over 75% of the jelly falls in subpolar and temperate regions occurring after spring blooms, and over 25% of the jelly-falls in the tropics occurring after upwelling events.
With global climates shifting towards creating warmer and more acidic oceans, conditions not favored by non-resilient species, jellies are likely to grow in population sizes. Eutrophic areas and dead zones can become jelly hot spots with substantial blooms. As the climate changes and ocean waters warm, jelly blooms become more prolific and the transport of jelly-carbon to the lower ocean increases. With a possible slowing of the classic biological pump, the transport of carbon and nutrients to the deep sea through jelly-falls may become more and more important to deep ocean. | 9 | Geochemistry |
CDPs climate change program aims to reduce companies greenhouse gas emissions and mitigate climate change risk. CDP requests information on climate risks and low carbon opportunities from the world's largest companies on behalf of over 800 institutional investor signatories with a combined US$100 trillion in assets. | 2 | Environmental Chemistry |
In 2015, 251 million tubes of toothpaste were sold in the United States. A single tube holds roughly 170 grams of toothpaste, so approximately 43 kilotonnes of toothpaste get washed into the water systems annually. Toothpaste contains silver nanoparticle<nowiki/>s, also known as nanosilver or AgNPs, among other compounds.
Each tube of toothpaste contains approximately 91 mg of silver nanoparticles, with approximately 3.9 tonnes of silver nanoparticles entering the environment annually. Silver nanoparticles are not entirely cleared from the water during the wastewater treatment process, possibly leading to detrimental environmental effects. | 2 | Environmental Chemistry |
Vargulin is oxidized by the Vargula luciferase, a 62 kDa enzyme, to produce blue light at 462 nm (max emission, detected with a 425 to 525 nm filter).
The vargulin does not cross react with luciferases using coelenterazine or Firefly luciferin. | 1 | Biochemistry |
Nanocar Race is an international scientific competition with the aim of testing the performance of getting a large molecule suspended over a solid surface to cover the largest distance with the use of a scanning tunneling microscope.
The first race consisted of overcoming a distance of 100 nanometer and was held for the first time in Toulouse on 28 and 29 April 2017. A second race was held in 2022 with the winners covering multiple hundreds of nanometers. | 6 | Supramolecular Chemistry |
Butyric acid (; from , meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl carboxylic acid with the chemical formula . It is an oily, colorless liquid with an unpleasant odor. Isobutyric acid (2-methylpropanoic acid) is an isomer. Salts and esters of butyric acid are known as butyrates or butanoates. The acid does not occur widely in nature, but its esters are widespread. It is a common industrial chemical and an important component in the mammalian gut. | 1 | Biochemistry |
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