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Walter White (Breaking Bad) On October 19, 2013, actor Jackamoe Buzzell organized a mock funeral procession (including a hearse and a replica of Walt's meth lab RV) and service for the character was held at Albuquerque's Sunset Memorial Park cemetery. A headstone was placed with a photo of Cranston as Walt, which is permanently located on an outside wall at the address 6855 4th St NW Los Ranchos de Albuquerque in New Mexico. While some residents were unhappy with the makeshift grave-site for closure with the show, tickets for the event raised over $30,000 for a local charity called Albuquerque Healthcare for the Homeless. Many fans of "Breaking Bad", including actor Norm Macdonald and "New Yorker" magazine writer Emily Nussbaum, proposed a theory, in which most of the series finale happened in Walt's mind, and he really died in the stolen Volvo in the beginning of it. While Nussbaum merely stated that it would be her preferred ending, Macdonald emphasized the seemingly unreal scenarios of Walt's final day, as well as what he deemed as unreliable acting. However, series creator Vince Gilligan debunked this theory, explaining that Walt could not possibly have known several things that happened, like Jesse being held in captivity by Jack's gang instead of being murdered by them, or that Todd had begun taking meetings with Lydia regarding the meth trade. This theory has also been disproven by "". In the 2015 country music song Fix, singer Chris Lane vows in the chorus, “I’ll be... your Walter White high.” | https://en.wikipedia.org/wiki?curid=22530352 |
Penny battery The penny battery is a voltaic pile which uses various coinage as the metal disks (pennies) of a traditional voltaic pile. The coins are stacked with pieces of electrolyte soaked paper in between (see diagram at right). The penny battery experiment is common during electrochemistry units in an educational setting. Each cell in a penny battery can produce up to 0.8 volt, and many can be stacked together to produce higher voltages. Since the battery is a wet cell, the effectiveness will be reduced when the electrolyte evaporates. As the name implies, Canadian pennies from 1997-1999 may serve the zinc electrode and 1942-1996 pennies as the copper. Alternatively, American pennies from 1982–present may be used as the zinc electrodes and 1944-1982 pennies as the copper electrodes. A variety of other coins may also be used, with varying results. A penny battery can be useful in producing a small amount of voltage. To make a penny battery it is crucial that there are two different kinds of metals with a substance in between them. To begin, scratch off the copper coating on one side of a penny exposing the metal zinc (silver color). This process will be difficult and will take some time. It is beneficial to have at least 5 pennies so that enough volts can be created. Then cut 5 circle pieces as big as the penny of matboard or cardboard. Soak the matboard in an acid solution. An acid as simple as vinegar and water, or lemon juice could be used | https://en.wikipedia.org/wiki?curid=22535079 |
Penny battery Stack the pennies on top of one another with a piece of matboard in between them. The zinc side should be facing upward. Use a penny that has not been scratched on either side and place it on top. Finally connect an LED with the longer lead attached to the top and shorter lead touching the bottom. The LED should light up proving that the battery works. It is also possible to use a voltmeter to test the amount of volts being produced by the battery cell. Take a AA battery and attach it to voltmeter to ensure that it is working properly before testing out the penny battery. For an alternate way of making this that is slightly weaker, click here. This method uses USA pennies from 1945-1980 or 10 cent euro coins, alongside aluminum foil. If the LED is not lighting up or if the voltmeter is not registering any electricity then a few problems could have occurred during set up. First, make sure that the matboard or cardboard pieces are moist. Less electrical energy will be produced if less electrolytes are available. Second, ensure that none of the pennies are touching one another and that each matboard only touches two pennies and does not overlap onto other pennies. This would create a short and little to no electrical energy will be produced. Third, check the acidity of the solution that is being used to soak the matboard. The greater the acidity, the greater number of electrolytes, and the greater amount of electricity that can be conducted | https://en.wikipedia.org/wiki?curid=22535079 |
Penny battery Fourth, it can be beneficial to sand down the coins instead of scratching off the copper to reach the zinc layer underneath. Batteries convert the chemical energy of the two metals (electrodes) interacting with the acid on the matboard (electrolyte) into electrical energy. In this situation, the metal surface serves as the electrode and an electric current (movement of electrons from one metal to the other) is created when the wire connects both metal surfaces. In the first hour, a five cell penny battery is able to provide about watts. Each cell is defined as a stack of a zinc penny, matboard, and a copper penny. Each cell can provide about 0.6 volts. Indicating that to power an LED light, needing 1.7 volts, only three cells need to be used. As time goes on the amount of energy that the battery can provide decreases. A five cell penny battery can last up to 6 1/2 hours providing minimal voltage. The stack of cells is also known as a voltaic pile. | https://en.wikipedia.org/wiki?curid=22535079 |
Hector Medal The Hector Medal, formerly known as the Hector Memorial Medal, is a science award given by the Royal Society of New Zealand in memory of Sir James Hector to researchers working in New Zealand. It is awarded annually in rotation for different sciences – currently there are three: chemical sciences; physical sciences; mathematical and information sciences. It is given to a researcher who "has undertaken work of great scientific or technological merit and has made an outstanding contribution to the advancement of the particular branch of science." It was previously rotated through more fields of science – in 1918 they were: botany, chemistry, ethnology, geology, physics (including mathematics and astronomy), zoology (including animal physiology). For a few years it was awarded biennially – it was not awarded in 2000, 2002 or 2004. In 1991 it was overtaken by the Rutherford Medal as the highest award given by the Royal Society of New Zealand. The obverse of the medal bears the head of James Hector and the reverse a Māori snaring a huia. The last confirmed sighting of a living huia predates the award of the medal by three years. | https://en.wikipedia.org/wiki?curid=22545239 |
PstI is a type II restriction endonuclease isolated from the Gram negative species, "Providencia stuartii". cleaves DNA at the recognition sequence 5′-CTGCA/G-3′ generating fragments with 3′-cohesive termini. This cleavage yields sticky ends 4 base pairs long. is catalytically active as a dimer. The two subunits are related by a 2-fold symmetry axis which in the complex with the substrate coincides with the dyad axis of the recognition sequence. It has a molecular weight of 69,500 and contains 54 positive and 41 negatively charged residues. The restriction/modification (R/M) system has two components: a restriction enzyme that cleaves foreign DNA, and a methyltransferase which protect native DNA strands via histone methylation. The combination of both provide a defense mechanism against invading viruses. The methyltransferase and endonuclease are encoded as two separate proteins and act independently. In the system, the genes are encoded on opposite strands and hence must be transcribed divergently from separate promoters. The transcription initiation sites are separated by only 70 base pairs. A delay in the expression of the endonuclease relative to methylase is due to the inherent differences of the two proteins. The endonuclease is a dimer, requiring a second step for assembly, whereas the methylase is a monomer. is functionally equivalent to BsuBI. Both enzymes recognize the target sequence 5'CTGCAG | https://en.wikipedia.org/wiki?curid=22555068 |
PstI The enzyme systems have similar methyltransferases (41% amino acid identity), restriction endonucleases (46% amino acid identity), and genetic makeup (58% nucleotide identity). These observations suggest a shared evolutionary history. When examining the preferential double strand cleavage of DNA, the restriction endonuclease bind to pSM1 plasmid DNA. is a useful enzyme for DNA cloning as it provides a selective system for generating hybrid DNA molecules. These hybrid DNA molecules can be then cleaved at the regenerated sites. Its use is not limited to molecular cloning; it is also used in restriction site mapping, genotyping, Southern blotting, restriction fragment length polymorphism (RFLP) and SNP. It is also an isoschizomer restriction enzyme SalPI from "Streptomyces albus P". preferentially cleaves purified pSM1 DNA without being influenced by the superhelicity of the substrate. However, it is not known whether the effects of this cleavage occurs upon binding to the recognition site or DNA scission. Its differential cleavage rates at different restriction sites is due to the five features of duplex structure. The proximity to the ends in linear DNA molecule, variation in DNA sequence within the recognition sites for enzymes, short distance between regions of unusual DNA sequences and recognition sites, and lastly the special structures such as loops and hairpins. The collective effect of these five factors could affect the accessibility of the restriction enzyme to its recognition sites. | https://en.wikipedia.org/wiki?curid=22555068 |
Post-combustion capture refers to the removal of "CO" from power station flue gas prior to its compression, transportation and storage in suitable geological formations, as part of carbon capture and storage. A number of different techniques are applicable, almost all of which are adaptations of acid gas removal processes used in the chemical and petrochemical industries. Many of these techniques existed before World War II and, consequently, post combustion capture is the most developed of the various carbon-capture methodologies. | https://en.wikipedia.org/wiki?curid=22558189 |
Very long chain fatty acid A very long chain fatty acid (VLCFA) is a fatty acid with 22 or more carbons. Their biosynthesis occurs in the endoplasmic reticulum. VLCFA's can represent up to a few percent of the total fatty acid content of a cell. Unlike most fatty acids, VLCFAs are too long to be metabolized in the mitochondria, and must be metabolized in peroxisomes. Certain peroxisomal disorders, such as adrenoleukodystrophy and Zellweger syndrome, can be associated with an accumulation of VLCFAs. Some of the more common saturated VLCFAs: lignoceric acid (C24), cerotic acid (C26), montanic acid (C28), melissic acid (C30), lacceroic acid (C32), ghedoic acid (C34), and the odd-chain fatty acid ceroplastic acid (C35). Several monounsaturated VLCFAs are also known: nervonic acid (Δ15-24:1), ximenic acid (Δ17-26:1), and llumequeic acid (Δ21-30:1). | https://en.wikipedia.org/wiki?curid=22561373 |
Purnell equation The is an equation used in analytical chemistry to calculate the resolution "R" between two peaks in a chromatogram. where The higher the resolution, the better the separation. | https://en.wikipedia.org/wiki?curid=22562598 |
Hexaarylbiimidazole (HABI) is an organic compound and an imidazole derivative. In its natural state, HABI is colorless, but when ultraviolet light breaks one of the bonds in the molecule, it produces a version that is dark blue. The transformation takes ten seconds or longer. By adding naphthalene to the compound, the color transition can be made in about 180 milliseconds. The cyclophane version of HABI reverts to colorless just as fast as the UV light is off. | https://en.wikipedia.org/wiki?curid=22571665 |
Arrow pushing or electron pushing is a technique used to describe the progression of organic chemistry reaction mechanisms. It was first developed by Sir Robert Robinson. In using arrow pushing, "curved arrows" or "curly arrows" are superimposed over the structural formulae of reactants in a chemical equation to show the reaction mechanism. The arrows illustrate the movement of electrons as bonds between atoms are broken and formed. is also used to describe how positive and negative charges are distributed around organic molecules through resonance. It is important to remember, however, that arrow pushing is a formalism and electrons (or rather, electron density) do not move around so neatly and discretely in reality. Recently, arrow pushing has been extended to inorganic chemistry, especially to the chemistry of s- and p-block elements. It has been shown to work well for hypervalent compounds. Organic chemists use two types of arrows within molecular structures to describe electron movements. Single electrons' trajectories are designated with single barbed arrows, whereas double-barbed arrows show movement of electron pairs. When a bond is broken, electrons leave where the bond was; this is represented by a curved arrow pointing away from the bond and an ending the arrow pointing towards the next unoccupied molecular orbital. Similarly, organic chemists represent the formation of a bond by a curved arrow pointing between two species | https://en.wikipedia.org/wiki?curid=22576085 |
Arrow pushing For clarity, when pushing arrows, it is best to draw the arrows starting from a lone pair of electrons or a σ or π bond and ending in a position that can accept a pair of electrons, allowing the reader to know exactly which electrons are moving and where they are ending. Bonds are broken in places where a corresponding antibonding orbital is filled. Some authorities allow the simplification that an arrow can originate at a formal negative charge that corresponds to a lone pair. However, not all formal negative charges correspond to the presence of a lone pair (e.g., the B in FB), and care needs to be taken with this usage. A covalent bond joining atoms in an organic molecule consists of a group of two electrons. Such a group is referred to as an electron pair. Reactions in organic chemistry proceed through the sequential breaking and formation of such bonds. Organic chemists recognize two processes for the breaking of a chemical bond. These processes are known as homolytic cleavage and heterolytic cleavage. Homolytic bond cleavage is a process where the electron pair comprising a bond is split, causing the bond to break. This is denoted by two single barbed curved arrows pointing away from the bond. The consequence of this process is the retention of a single unpaired electron on each of the atoms that were formerly joined by a bond. These single electron species are known as free radicals. For example, Ultraviolet light causes the chlorine-chlorine bond to break homolytically | https://en.wikipedia.org/wiki?curid=22576085 |
Arrow pushing This is the initiation stage of free radical halogenation. Heterolytic bond cleavage is a process where the electron pair that comprised a bond moves to one of the atoms that was formerly joined by a bond. The bond breaks, forming a negatively charged species (an anion) and a positively charged species (a cation). The anion is the species that retains the electrons from the bond while the cation is stripped of the electrons from the bond. The anion usually forms on the most electronegative atom, in this example atom A. All heterolytic organic chemistry reactions can be described by a sequence of fundamental mechanistic subtypes. The elementary mechanistic subtypes taught in introductory organic chemistry are S1, S2, E1, E2, addition and addition-elimination. Using arrow pushing, each of these mechanistic subtypes can be described. An S1 reaction occurs when a molecule separates into a positively charged component and a negatively charged component. This generally occurs in highly polar solvents through a process called solvolysis. The positively charged component then reacts with a nucleophile forming a new compound. In the first stage of this reaction (solvolysis), the C-L bond breaks and both electrons from that bond join L (the leaving group) to form L and RC ions. This is represented by the curved arrow pointing away from the C-L bond and towards L. The nucleophile Nu, being attracted to the RC, then donates a pair of electrons forming a new C-Nu bond | https://en.wikipedia.org/wiki?curid=22576085 |
Arrow pushing Because an S1 reaction proceeds with the Substitution of a leaving group with a Nucleophile, the S designation is used. Because the initial solvolysis step in this reaction involves a single molecule dissociating from its leaving group, the initial stage of this process is considered a uni-molecular reaction. The involvement of only 1 species in the initial phase of the reaction enhances the mechanistic designation to S1. An S2 reaction occurs when a nucleophile displaces a leaving group residing on a molecule from the backside of the leaving group. This displacement or substitution results in the formation of a substitution product with inversion of stereochemical configuration. The nucleophile forms a bond with its lone pair as the electron source. The electron sink which ultimately accepts the electron density is the nucleofuge (leaving group), with bond forming and bond breaking occurring simultaneously at the transition state (marked with a double-dagger). Because an S2 reaction proceeds with the substitution of a leaving group with a nucleophile, the S designation is used. Because this mechanism proceeds with the interaction of two species at the transition state, it is referred to as a bimolecular process, resulting in the S2 designation. An E1 elimination occurs when a proton adjacent to a positive charge leaves and generates a double bond. Because initial formation of a cation is necessary for E1 reactions to occur, E1 reactions are often observed as side reactions to S1 mechanisms | https://en.wikipedia.org/wiki?curid=22576085 |
Arrow pushing E1 eliminations proceed with the Elimination of a leaving group leading to the E designation. Because this mechanism proceeds with the initial dissociation of a single starting material forming a carbocation, this process is considered a uni-molecular reaction. The involvement of only 1 species in the initial phase of the reaction enhances the mechanistic designation to E1. An E2 elimination occurs when a proton adjacent to a leaving group is extracted by a base with simultaneous elimination of a leaving group and generation of a double bond. Similar to the relationship between E1 eliminations and S1 mechanisms, E2 eliminations often occur in competition with S2 reactions. This observation is most often noted when the base is also a nucleophile. In order to minimize this competition, non-nucleophilic bases are commonly used to effect E2 eliminations. E2 eliminations proceed through initial extraction of a proton by a base or nucleophile leading to Elimination of a leaving group justifying the E designation. Because this mechanism proceeds through the interaction of two species (substrate and base/nucleophile), E2 reactions are recognized as bi-molecular. Thus, the involvement of 2 species in the initial phase of the reaction enhances the mechanistic designation to E2. Addition reactions occur when nucleophiles react with carbonyls. When a nucleophile adds to a simple aldehyde or ketone, the result is a 1,2-addition. When a nucleophile adds to a conjugated carbonyl system, the result is a 1,4-addition | https://en.wikipedia.org/wiki?curid=22576085 |
Arrow pushing The designations 1,2 and 1,4 are derived from numbering the atoms of the starting compound where the oxygen is labeled “1” and each atom adjacent to the oxygen are sequentially numbered out to the site of nucleophilic addition. A 1,2-addition occurs with nucleophilic addition to position 2 while a 1,4-addition occurs with nucleophilic addition to position 4. Addition-elimination reactions are addition reactions immediately followed by elimination reactions. In general, these reactions take place when esters (or related functional groups) react with nucleophiles. In fact, the only requirement for an addition-elimination reaction to proceed is that the group being eliminated is a better leaving group than the incoming nucleophile. | https://en.wikipedia.org/wiki?curid=22576085 |
Linear ion trap The linear ion trap (LIT) is a type of ion trap mass spectrometer. In a linear ion trap, ions are confined radially by a two-dimensional radio frequency (RF) field, and axially by stopping potentials applied to end electrodes. Linear ion traps have high injection efficiencies and high ion storage capacities. One of the first linear traps was constructed in 1969, by Church who bent linear quadrupoles into closed circle and racetrack geometries and demonstrated storage of He and H ions for several minutes. Earlier, Drees and Paul described a circular quadrupole. However, it was used to produce and confine a plasma, not to store ions. In 1989, Prestage, Dick, and Malecki described that ions could be trapped in the linear quadrupole trap system to enhance ion-molecule reactions, thus it can be used to study spectroscopy of stored ions. The linear ion trap uses a set of quadrupole rods to confine ions radially and a static electrical potential on the end electrodes to confine the ions axially. The linear ion trap can be used as a mass filter or as a trap by creating a potential well for the ions along the axis of the trap. The mass of trapped ions may be determined if the m/z lies between defined parameters. Advantages of the linear trap design are high ion storage capacity, high scan rate, and simplicity of construction. Although quadrupole rod alignment is critical, adding a quality control constraint to their production, this constraint is additionally present in the machining requirements of the 3D trap | https://en.wikipedia.org/wiki?curid=22579952 |
Linear ion trap Ions are either injected into or created within the interior of the ion trap. They are confined by application of appropriate RF and DC voltages with their final position maintained within the center section of the ion trap. The RF voltage is adjusted and multi-frequency resonance ejection waveforms are applied to the trap to eliminate all but the desired ions in preparation for subsequent fragmentation and mass analysis. The voltages applied to the ion trap are adjusted to stabilize the selected ions and to allow for collisional cooling in preparation for excitation. The energy of the selected ions is increased by application of a supplemental resonance excitation voltage applied to all segments of two rods located on the X-axis. This increase of energy causes dissociation of the selected ions due to collisions with damping gas. The product ions formed are retained in the trapping field. Scanning the contents of the trap to produce a mass spectrum is accomplished by linearly increasing the RF voltage applied to all sections of the trap and utilizing a supplemental resonance ejection voltage. These changes sequentially move ions from within the stability diagram to a position where they become unstable in the x-direction and leave the trapping field for detection. Ions are accelerated into two high voltage dynodes where ions produce secondary electrons. This signal is subsequently amplified by two electron multipliers and the analog signals are then integrated together and digitized | https://en.wikipedia.org/wiki?curid=22579952 |
Linear ion trap Linear ion traps can be used as stand alone mass analyzers, and they can be combined with other mass analyzers, such as 3D Paul ion traps, TOF mass spectrometers, FTMS, and other kind of mass analyzers. 3D ion trap (or Paul trap) mass spectrometers are widely used but have limitations. With a continuous source, such as one utilizing electrospray ionization (ESI), ions generated while the 3D trap is processing other ions are not used, thereby limiting the duty cycle. Furthermore, the total number of ions that can be stored in a 3D ion trap is limited by space charge effects. Combining a linear trap with a 3D trap can help overcome these limitations. Recently, Hardman and Makarov have described the use of a linear quadrupole trap to store ions formed by ESI for injection into an orbitrap mass analyzer. Ions passed through an orifice and skimmer, a quadrupole ion guide for ion cooling and then entered the quadrupole storage trap. The quadrupole trap has two rod sets; short rods near the exit were biased so that most ions accumulated in this region. Because the orbitrap requires that ions be injected in very short pulses, kilovolt ion extraction potentials were applied to the exit aperture. Flight times of ions to the orbitrap were mass dependent, but for a given mass, ions were injected in bunches less than 100 nanoseconds wide (fwhm). A TOF mass spectrometer can also have a low-duty cycle when coupled with a continuous ion source. Combining an ion trap with a TOF mass analyzer can improve the duty cycle | https://en.wikipedia.org/wiki?curid=22579952 |
Linear ion trap Both 3D and linear traps have been combined with TOF mass analyzers. A trap can also add MSn capabilities to the system. Linear traps can be used to improve the performance of FTICR (or FTMS) systems. As with 3D ion traps, the duty cycle can be increased to nearly 100% if ions are accumulated in a linear trap, while the FTMS performs other functions. Unwanted ions that can cause space charge problems in the FTMS can be ejected in the linear trap to improve the resolution, sensitivity, and dynamic range of the system. The combination of triple quadrupole MS with LIT technology in the form of an instrument of configuration QqLIT, using axial ejection, is particularly interesting, because this instrument retains the classical triple quadrupole scan functions such as selected reaction monitoring (SRM), product ion (PI), neutral loss (NL) and precursor ion (PC) while also providing access to sensitive ion trap experiments. For small molecules, quantitative and qualitative analysis can be performed using the same instrument. In addition, for peptide analysis, the enhanced multiply charged (EMC) scan allows an increase in selectivity, while the time-delayed fragmentation (TDF) scan provides additional structural information. In the case of the QqLIT, the uniqueness of the instrument is that the same mass analyzer Q3 can be run in two different modes. This allows very powerful scan combinations when performing information-dependent data acquisition. | https://en.wikipedia.org/wiki?curid=22579952 |
Hotbed A hotbed is a biological term for an area of decaying organic matter that is warmer than its surroundings. The heat gradient is generated by the decomposition of organic substituents within the pile by microorganism metabolization. A hotbed covered with a small glass cover (also called a hotbox) is used as a small version of a hothouse (heated greenhouse). Oftentimes, this bed is made of manure from animals such as horses, which pass undigested plant cellulose in their droppings, creating a good environment for microorganisms to come and break down the cellulose and create a hotbed. (The digestive systems of ruminants such as cattle and sheep destroy and use all cellulose in their food, and their droppings remain cold and do not heat up.) Some egg-laying animals, such as the brush turkey, make or use hotbeds to incubate their eggs. By extension, the term "hotbed" is used metaphorically to describe an environment that is ideal for the growth or development of something, especially of something undesirable. | https://en.wikipedia.org/wiki?curid=22584796 |
Vortex stretching In fluid dynamics, vortex stretching is the lengthening of vortices in three-dimensional fluid flow, associated with a corresponding increase of the component of vorticity in the stretching direction—due to the conservation of angular momentum. is associated with a particular term in the vorticity equation. For example, vorticity transport in an incompressible inviscid flow is governed by where "D/Dt" is the material derivative. The source term on the right hand side is the vortex stretching term. It amplifies the vorticity formula_2 when the velocity is diverging in the direction parallel to formula_2. A simple example of vortex stretching in a viscous flow is provided by the Burgers vortex. is at the core of the description of the turbulence energy cascade from the large scales to the small scales in turbulence. In general, in turbulence fluid elements are more lengthened than squeezed, on average. In the end, this results in more vortex stretching than vortex squeezing. For incompressible flow—due to volume conservation of fluid elements—the lengthening implies thinning of the fluid elements in the directions perpendicular to the stretching direction. This reduces the radial length scale of the associated vorticity. Finally, at the small scales of the order of the Kolmogorov microscales, the turbulence kinetic energy is dissipated into heat through the action of molecular viscosity. | https://en.wikipedia.org/wiki?curid=22586949 |
Polymer ratio In a given formulation or recipe of a polymer compound, the total amount/parts per hundred of polymer added to prepare certain compound is called polymer ratio. It basically refers to the aggregated amount of polymer content within the formulation that may undergo any physical or chemical change during the course of post polymerization or physical heat treatment. | https://en.wikipedia.org/wiki?curid=22591659 |
Process simulation is used for the design, development, analysis, and optimization of technical processes such as: chemical plants, chemical processes, environmental systems, power stations, complex manufacturing operations, biological processes, and similar technical functions. is a model-based representation of chemical, physical, biological, and other technical processes and unit operations in software. Basic prerequisites are a thorough knowledge of chemical and physical properties of pure components and mixtures, of reactions, and of mathematical models which, in combination, allow the calculation of a process in computers. software describes processes in flow diagrams where unit operations are positioned and connected by product or educt streams. The software has to solve the mass and energy balance to find a stable operating point. The goal of a process simulation is to find optimal conditions for an examined process. This is essentially an optimization problem which has to be solved in an iterative process. always use models which introduce approximations and assumptions but allow the description of a property over a wide range of temperatures and pressures which might not be covered by real data. Models also allow interpolation and extrapolation - within certain limits - and enable the search for conditions outside the range of known properties. The development of models for a better representation of real processes is the core of the further development of the simulation software | https://en.wikipedia.org/wiki?curid=22594732 |
Process simulation Model development is done on the chemical engineering side but also in control engineering and for the improvement of mathematical simulation techniques. is therefore one of the few fields where scientists from chemistry, physics, computer science, mathematics, and several engineering fields work together. A lot of efforts are made to develop new and improved models for the calculation of properties. This includes for example the description of Two main different types of models can be distinguished: The equations and correlations are normally preferred because they describe the property (almost) exactly. To obtain reliable parameters it is necessary to have experimental data which are usually obtained from factual data banks or, if no data are publicly available, from measurements. Using predictive methods is much cheaper than experimental work and also than data from data banks. Despite this big advantage predicted properties are normally only used in early steps of the process development to find first approximate solutions and to exclude wrong pathways because these estimation methods normally introduce higher errors than correlations obtained from real data. also encouraged the further development of mathematical models in the fields of numerics and the solving of complex problems. The history of process simulation is strongly related to the development of the computer science and of computer hardware and programming languages | https://en.wikipedia.org/wiki?curid=22594732 |
Process simulation Early working simple implementations of partial aspects of chemical processes were introduced in the 1970s when suitable hardware and software (here mainly the programming languages FORTRAN and C) became available. The modelling of chemical properties began much earlier, notably the cubic equation of states and the Antoine equation were precursory developments of the 19th century. Initially process simulation was used to simulate steady state processes. Steady-state models perform a mass and energy balance of a stationary process (a process in an equilibrium state) it does not depend on time. Dynamic simulation is an extension of steady-state process simulation whereby time-dependence is built into the models via derivative terms i.e. accumulation of mass and energy. The advent of dynamic simulation means that the time-dependent description, prediction and control of real processes in real time has become possible. This includes the description of starting up and shutting down a plant, changes of conditions during a reaction, holdups, thermal changes and more. Dynamic simulations require increased calculation time and are mathematically more complex than a steady state simulation. It can be seen as a multiply repeated steady state simulation (based on a fixed time step) with constantly changing parameters. Dynamic simulation can be used in both an online and offline fashion | https://en.wikipedia.org/wiki?curid=22594732 |
Process simulation The online case being model predictive control, where the real-time simulation results are used to predict the changes that would occur for a control input change, and the control parameters are optimised based on the results. Offline process simulation can be used in the design, troubleshooting and optimisation of process plant as well as the conduction of case studies to assess the impacts of process modifications. Dynamic simulation is also used for operator training. | https://en.wikipedia.org/wiki?curid=22594732 |
Structure-based combinatorial protein engineering (SCOPE) is a synthetic biology technique for creating gene libraries (lineages) of defined composition designed from structural and probabilistic constraints of the encoded proteins. The development of this technique was driven by fundamental questions about protein structure, function, and evolution, although the technique is generally applicable for the creation of engineered proteins with commercially desirable properties. Combinatorial travel through sequence spacetime is the goal of SCOPE. At its inception, SCOPE was developed as a homology-independent recombination technique to enable the creation of multiple crossover libraries from distantly related genes. In this application, an “exon plate tectonics” design strategy was devised to assemble “equivalent” elements of structure (continental plates) with variability in the junctions linking them (fault lines) to explore global protein space. To create the corresponding library of genes, the breeding scheme of Gregor Mendel was adapted into a PCR strategy to selectively cross hybrid genes, a process of iterative inbreeding to create all possible combinations of coding segments with variable linkages. Genetic complementation in temperature-sensitive E. coli was used as the selection system to successfully identify functional hybrid DNA polymerases of minimal architecture with enhanced phenotypes | https://en.wikipedia.org/wiki?curid=22596736 |
Structure-based combinatorial protein engineering SCOPE was then used to construct a synthetic enzyme lineage, which was biochemically characterized to recapitulate the evolutionary divergence of two modern day enzymes. The rapid evolvability of chemical diversity in terpene synthases were demonstrated through processes akin to both Darwinian gradualism and saltation: some mutational pathways show steady, additive changes, whereas others show drastic jumps between contrasting product specificities with single mutational steps. Further, a metric was devised to describe the chemical distance of mutational steps to derive a chemical-based phylogeny relating sequence variation to chemical output. These examples establish SCOPE as a standardized method for the construction of synthetic gene libraries from close or distantly related parental sequences to identify functional novelty among the encoded proteins. | https://en.wikipedia.org/wiki?curid=22596736 |
In situ polymerization In polymer chemistry, "in situ" polymerization is a preparation method that occurs "in the polymerization mixture" and is used to develop polymer nanocomposites from nanoparticles. There are numerous unstable oligomers (molecules) which must be synthesized "in situ" (i.e. in the reaction mixture but cannot be isolated on their own) for use in various processes. The "in situ" polymerization process consists of an initiation step followed by a series of polymerization steps, which results in the formation of a hybrid between polymer molecules and nanoparticles. Nanoparticles are initially spread out in a liquid monomer or a precursor of relatively low molecular weight. Upon the formation of a homogenous mixture, initiation of the polymerization reaction is carried out by addition of an adequate initiator, which is exposed to a source of heat, radiation, etc. After the polymerization mechanism is completed, a nanocomposite is produced, which consists of polymer molecules bound to nanoparticles. In order to perform the "in situ" polymerization of precursor polymer molecules to form a polymer nanocomposite, certain conditions must be fulfilled which include the use of low viscosity pre-polymers (typically less than 1 pascal), a short period of polymerization, the use of polymer with advantageous mechanical properties, and no formation of side products during the polymerization process | https://en.wikipedia.org/wiki?curid=22597036 |
In situ polymerization There are several advantages of the "in situ" polymerization process, which include the use of cost-effective materials, being easy to automate, and the ability to integrate with many other heating and curing methods. Some downsides of this preparation method, however, include limited availability of usable materials, a short time period to execute the polymerization process, and expensive equipment is required. The next sections will cover the various examples of polymer nanocomposites produced using the "in situ" polymerization technique, and their real life applications. Towards the end of the 20th century, Toyota Motor Corp devised the first commercial application of the clay-polyamide-6 nanocomposite, which was prepared via "in situ" polymerization. Once Toyota laid the groundwork for polymer layered silicate nanocomposites, extensive research in this particular area was conducted afterwards. Clay nanocomposites can experience a significant increase in strength, thermal stability, and ability to penetrate barriers upon addition of a minute portion of nanofiller into the polymer matrix. A standard technique to prepare clay nancomposites is "in situ" polymerization, which consists of intercalation of the monomer with the clay surface, followed by initiation by the functional group in the organic cation and then polymerization. A study by Zeng and Lee investigated the role of the initiator in the "in situ" polymerization process of clay nanocomposites | https://en.wikipedia.org/wiki?curid=22597036 |
In situ polymerization One of the major findings was that the more favorable nanocomposite product was produced with a more polar monomer and initiator. "In situ" polymerization is an important method of preparing polymer grafted nanotubes using carbon nanotubes. Due to their remarkable mechanical, thermal and electronic properties, including high conductivity, large surface area, and excellent thermal stability, carbon nanotubes (CNT) have been heavily studied since their discovery to develop various real world applications. Two particular applications that carbon nanotubes have made major contributions to include strengthening composites as filler material and energy production via thermally conductive composites. Currently, the two principal types of carbon nanotubes are single walled nanotubes (SWNT) and multi-walled nanotubes (MWNT). "In situ" polymerization offers several advantages in the preparation of polymer grafted nanotubes compared to other methods. First and foremost, it allows polymer macromolecules to attach to CNT walls. Additionally, the resulting composite is miscible with most types of polymers. Unlike solution or melt processing, "in situ" polymerization can prepare insoluble and thermally unstable polymers. Lastly, "in situ" polymerization can achieve stronger covalent interactions between polymer and CNTs earlier in the process. Recent improvements in the "in situ" polymerization process have led to the production of polymer-carbon nanotube composites with enhanced mechanical properties | https://en.wikipedia.org/wiki?curid=22597036 |
In situ polymerization With regards to their energy-related applications, carbon nanotubes have been used to make electrodes, with one specific example being the CNT/PMMA composite electrode. "In situ" polymerization has been studied to streamline the construction process of such electrodes. Huang, Vanhaecke, and Chen found that in situ polymerization can potentially produce composites of conductive CNTs on a grand scale. Some aspects of "in situ" polymerization that can help achieve this feat are that it is cost effective with regards to operation, requires minimal sample, has high sensitivity, and offers many promising environmental and bioanlaytical applications. Proteins, DNAs, and RNAs are just a few examples of biopharmaceuticals that hold the potential to treat various disorders and diseases, ranging from cancer to infectious diseases. However, due to certain undesirable properties such as poor stability, susceptibility to enzyme degradation, and insufficient capability to penetrate biological barriers, the application of such biopharmaceuticals in delivering medical treatment has been severely hindered. The formation of polymer-biomacromolecule nanocomposites via "in situ" polymerization offers an innovative means of overcoming these obstacles and improving the overall effectiveness of biopharmaceuticals. Recent studies have demonstrated how "in situ" polymerization can be implemented to improve the stability, bioactivity, and ability to cross biological barriers of biopharmaceuticals | https://en.wikipedia.org/wiki?curid=22597036 |
In situ polymerization The two main types of nanocomposites formed by "in situ" polymerization are 1) biomolecule-linear polymer hybrids, which are linear or have a star-like shape, and contain covalent bonds between individual polymer chains and the biomolecular surface and 2) biomolecule-crosslinked polymer nanocapsules, which are nanocapsules with biomacromolecules centered within the polymer shells. Biomolecule-linear polymer hybrids are formed via “grafting-from” polymerization, which is an "in situ" approach that differs from the standard “grafting to” polymerization. Whereas “grafting to” polymerization involves the straightforward attachment of polymers to the biomolecule of choice, the “grafting from” method takes place on proteins that are pre-modified with initiators. Some examples of “grafting to” polymerization include atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT). These methods are similar in that they both lead to narrow molecular weight distributions and can make block copolymer. On the other hand, they each have distinct properties that need to be analyzed on a case-by-case basis. For example, ATRP is sensitive to oxygen whereas RAFT is insensitive to oxygen; in addition, RAFT has a much greater compatibility with monomers than ATRP. Radical polymerization with crosslinkers is the other "in situ" polymerization method, and this process leads to the formation of biomolecule-crosslinked polymer nanocapsules | https://en.wikipedia.org/wiki?curid=22597036 |
In situ polymerization This process produces nanogels/nanocapsules via a covalent or non-covalent approach. In the covalent approach, the two steps are the conjugation of acryloyl groups to protein followed by in situ free radical polymerization. In the non-covalent approach, proteins are entrapped within nanocapsules. Nanogels, which are microscopic hydrogel particles held together by a cross-linked polymer network, offer a desirable mode of drug delivery that has a variety of biomedical applications. "In situ" polymerization can be used to prepare protein nanogels that help facilitate the storage and delivery of protein. The preparation of such nanogels via the "in situ" polymerization method begins with free proteins dispersed in an aqueous solution along with cross-linkers and monomers, followed by addition of radical initiators, which leads to the polymerization of a nanogel polymer shell that encloses a protein core. Additional modification of the polymeric nanogel enables delivery to specific target cells. Three classes of "in situ" polymerized nanogels are 1) direct covalent conjugation via chemical modifications, 2) noncovalent encapsulation, and 3) cross-linking of preformed crosslinkable polymers. Protein nanogels have tremendous applications for cancer treatment, vaccination, diagnosis, regenerative medicine, and therapies for loss-of-function genetic diseases | https://en.wikipedia.org/wiki?curid=22597036 |
In situ polymerization "In situ" polymerized nanogels are capable of delivering the appropriate amount of protein to the site of treatment; certain chemical and physical factors including pH, temperature, and redox potential manage the protein delivery process of nanogels. Urea-formaldehyde (UF) and melamine formaldehyde (MF) encapsulation systems are other examples that utilize "in situ" polymerization. In such type of "in situ" polymerization a chemical encapsulation technique is involved very similar to interfacial coating. The distinguishing characteristic of "in situ" polymerization is that no reactants are included in the core material. All polymerization occurs in the continuous phase, rather than on both sides of the interface between the continuous phase and the core material. "In situ" polymerization of such formaldehyde systems usually involves the emulsification of an oil-phase in water. Then, water-soluble urea/melamine formaldehyde resin monomers are added, which are allowed to disperse. The initiation step occurs when acid is added to lower the pH of the mixture. Crosslinking of the resins completes the polymerization process and results in a shell of polymer-encapsulated oil droplets. | https://en.wikipedia.org/wiki?curid=22597036 |
Cadmium cyanide is an inorganic compound with the formula Cd(CN). It is a white crystalline compound that is used in electroplating. It is very toxic, along with other cadmium and cyanide compounds. is prepared commercially by treating cadmium hydroxide with hydrogen cyanide: It can also be generated from tetracyanocadmate: and zinc cyanide adopt similar structures. As such, each metal has tetrahedral coordination sphere. Cyanide ligands interconnect pairs of metal centers. Two of the resulting diamondoid structures are interpenetrated. The structure is related to that of cristobalite, a polymorphs of SiO. This structural similarity of cadmium dicyanide and cristobalite was foundational in the development of mineralomimetic chemistry: "the build-up of mineral-like structures using materials that never give stable minerals." It is used as an electrolyte for electrodeposition of thin metallic cadmium coatings on metal to protect against corrosion. Like zinc cyanide, cadmium cyanide is fairly soluble in water, which is unusual for transition metal cyanides. The solubility increases with the additional cyanide, this reaction proceeding via "[Cd(CN)]" and [Cd(CN)]. With acids, its solutions evolve hydrogen cyanide. When it is crystallizes in the presence of certain small molecules, it forms clathrates. | https://en.wikipedia.org/wiki?curid=22599311 |
TSE buffer TSE or Tris/Saline/EDTA, is a buffer solution containing a mixture of Tris base, Sodium chloride and EDTA. In molecular biology, TSE buffers are often used in procedures involving nucleic acids. Tris-acid solutions are effective buffers for slightly basic conditions, which keep DNA deprotonated and soluble in water. The concentration of tris in the solution is kept near 25 mM. EDTA is a chelator of divalent cations, particularly of magnesium (Mg). As these ions are necessary co-factors for many enzymes, including contaminant nucleases, the role of the EDTA is to protect the nucleic acids against enzymatic degradation. But since Mg is also a co-factor for many useful DNA-modifying enzymes such as restriction enzymes and DNA polymerases, its concentration in TSE buffers is generally kept low (typically at around 2.5 mM). The sodium chloride is generally kept at a concentration of 0.05 M. | https://en.wikipedia.org/wiki?curid=22600725 |
Jugyeom To make , sea salt is packed into bamboo canisters and sealed with yellow clay. The mixture is baked in an iron oven and roasted in a pine fire. A bamboo stem is filled with bay salt produced from the west coast, sealed with red clay, and baked in a kiln with pine tree firewood. The baked salt lumps, hardening after baking. It is taken out, crushed, and repacked in the bamboo stem for the next cycle. During baking the salt absorbs the bamboo constituents that bring a distinctive sweetness, which is called Gamrojung flavor. Baking darkens the salt. The ninth baking process uses the highest temperature, over 1,000℃. Afterwards the bamboo salt contains blue, yellow, red, white and black. Well-baked bamboo salt, with a temperature above 1,500℃, is called “purple bamboo salt” because of its unique purple color, which indicates the best quality. While the quality of bamboo salt cannot be solely determined by color, its crystal structure and hardiness is definitive. In Korean folk medicine, trace elements in the yellow clay and bamboo are thought to make this form of salt more healthy. Historically, has been used as a digestive aid, styptic, disinfectant or dentifrice. Studies have reported "in vitro" and "in vivo" anti-cancer effects. A study published in "Experimental and Therapeutic Medicine" suggests that Purple Bamboo Salt may prevent the growth of oral cancers in mice | https://en.wikipedia.org/wiki?curid=22603189 |
Jugyeom According to "The Universe and God's Medicine" by Il-hoon (In-san) Kim in 1981, can be used to treat: In the 2012 film "Masquerade", bamboo salt caused a silver spoon in a bowl of soup to turn black, but before this explanation was discovered, the event caused the king to believe people were trying to poison him. | https://en.wikipedia.org/wiki?curid=22603189 |
Chain shuttling polymerization is a dual-catalyst method for producing block copolymers with alternating or variable tacticity. The desired effect of this method is to generate hybrid polymers that bear the properties of both polymer chains, such as a high melting point accompanied by high elasticity. It is a relatively new method, the first instance of its use being reported by Arriola et al. in May 2006. Olefin polymers (such as polypropylene and polyethylene) have seen widespread use in the plastics industry in the past 50 years. A way to enhance the properties of these olefin polymers was first discovered by the scientists Karl Ziegler and Giulio Natta. Ziegler discovered the original Titanium based catalyst essential for olefin polymerization, while Natta used the catalyst to alter and control the stereochemistry (tacticity) of the olefin polymers (hence Ziegler–Natta catalyst). By controlling the tacticity of the polymer, a chain can, for example, either be semi crystalline or amorphous, rigid or elastic, heat resistant or have a low glass transition temperature. Much research since has been dedicated to predicting and creating polymers based on this work. Living polymerization is the term coined to describe the use of specially made catalysts (often involving transition metal centers) in olefin polymerization, since the polymer chains self-propagate in the presence of the catalyst until intentionally terminated. Living polymerization, however, produces only one type of tacticity per catalyst | https://en.wikipedia.org/wiki?curid=22606070 |
Chain shuttling polymerization While the specific tacticity can be controlled by altering the type of catalyst used, creating a block copolymer requires that the polymerization be terminated, the catalyst destroyed, and that the chain re-propagate using another catalyst that produces the desired stereochemistry. Such manipulations are usually difficult, however. makes use of two catalysts and a chain shuttling agent (CSA) to generate copolymers of alternating tacticity. Catalyst 1 (Cat1) propagates a polyolefin of a desired tacticity. Catalyst 2 (Cat2) generates another chain of a different tacticity. The two chains are allowed to co-propagate in a single reactor in the same living polymer fashion as before. To alternate the tacticity, a CSA will transfer the polymer chain from its respective catalyst. The CSA can then bind to Cat2 and attach the chain to Cat2. When the chain attaches to Cat2, the polymerization of that chain continues, except it now propagates with the tacticity dictated by Cat2, not Cat1. The general result is that the chain will alternate between two different tacticities. As the forward and reverse reactions occur, the polymer chain is “shuttled” back and forth between the two catalysts and a block copolymer is formed. The shuttling of chains back and forth from catalysts via a CSA can be viewed as a competing chemical equilibrium. Note that the forward and reverse reactions of CSA binding and leaving either Cat1 or Cat2 are possible | https://en.wikipedia.org/wiki?curid=22606070 |
Chain shuttling polymerization This competition means that a chain can leave Cat1 via a CSA and the reattach to Cat1, polymerizing the same tacticity. The rate at which the reattachment of Cat1 occurs can be controlled by altering the relative concentrations of Cat1, Cat2 and CSA. For example, if one wanted to produce a polymer with the properties mainly resulting from the use of Cat1 and only wanted to influence its properties slightly by the presence of Cat2, a greater concentration of Cat1 would be used than for Cat2. The rate of alternation between tacticity can be controlled by altering the concentration of CSA relative to Cat1 and Cat2; having a higher concentration of CSA means that the chains will shuttle back and forth more rapidly, creating shorter units of alternating tacticity. The first clear advantage of chain shuttling is that one can design copolymers with more desirable traits. A polymer that is normally semi crystalline and rigid can be altered so that it has a lower glass transition temperature. An amorphous, elastic polymer membrane can be altered to have a higher melting point. The technique opens the door for tailor-made polymers to be widely accessible and simple to make inexpensively. | https://en.wikipedia.org/wiki?curid=22606070 |
Cross-coupling reaction A cross-coupling reaction in organic chemistry is a reaction where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R = organic fragment, M = main group center) reacts with an organic halide of the type R'-X with formation of a new carbon-carbon bond in the product R-R'. are a subset of coupling reactions. It is often used in arylations. Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki were awarded the 2010 Nobel Prize in Chemistry for developing palladium-catalyzed cross coupling reactions. The mechanism generally involves reductive elimination of the organic substituents R and R' on a metal complex of the type LMR(R') (where L is some arbitrary spectator ligand). The crucial intermediate LMR(R') is formed in a two step process from a low valence precursor L. The oxidative addition of an organic halide (RX) to LM gives LMR(X). Subsequently, the second partner undergoes transmetallation with a source of R'. The final step is reductive elimination of the two coupling fragments to regenerate the catalyst and give the organic product. Unsaturated organic groups couple more easily in part because they add readily. The intermediates are also less prone to beta-hydride elimination. Catalysts are often based on palladium, which is frequently selected due to high functional group tolerance. Organopalladium compounds are generally stable towards water and air | https://en.wikipedia.org/wiki?curid=22610613 |
Cross-coupling reaction Palladium catalysts can be problematic for the pharmaceutical industry, which faces extensive regulation regarding heavy metals. Many pharmaceutical chemists attempt to use coupling reactions early in production to minimize metal traces in the product. Heterogeneous catalysts based on Pd are also well developed. Copper-based catalysts are also common, especially for coupling involving heteroatom-C bonds. Iron-, cobalt-, and nickel-based nickel. catalysts have been investigated. The leaving group X in the organic partner is usually a halide, although triflate, tosylate and other pseudohalide have been used. Chloride is an ideal group due to the low cost of organochlorine compounds. Frequently, however, C-Cl bonds are too inert, and bromide or, worse, iodide leaving groups are required for acceptable rates. The main group metal in the organometallic partner usually is an electropositive element such as tin, zinc, silicon, or boron. Many cross-couplings entail forming carbon-carbon bonds. Many cross-couplings entail forming carbon-heteroatom bonds (heteroatom = S, N, O). A popular method is the Buchwald–Hartwig reaction: One method for palladium-catalyzed cross-coupling reactions of aryl halides with fluorinated arenes was reported by Keith Fagnou and co-workers. It is unusual in that it involves C-H functionalisation at an electron deficient arene. Cross-coupling reactions are important for the production of pharmaceuticals, examples being montelukast, eletriptan, naproxen, varenicline, and resveratrol | https://en.wikipedia.org/wiki?curid=22610613 |
Cross-coupling reaction Some polymers and monomers are also prepared in this way. | https://en.wikipedia.org/wiki?curid=22610613 |
Lindhard theory Lindhard theory, named after Danish professor Jens Lindhard, is a method of calculating the effects of electric field screening by electrons in a solid. It is based on quantum mechanics (first-order perturbation theory) and the random phase approximation. Thomas–Fermi screening can be derived as a special case of the more general Lindhard formula. In particular, Thomas–Fermi screening is the limit of the Lindhard formula when the wavevector (the reciprocal of the length-scale of interest) is much smaller than the Fermi wavevector, i.e. the long-distance limit. This article uses cgs-Gaussian units. The Lindhard formula for the longitudinal dielectric function is given by Here, formula_1 is a positive infinitesimal constant, formula_2 is formula_3 and formula_4 is the carrier distribution function which is the Fermi–Dirac distribution function for electrons in thermodynamic equilibrium. However this Lindhard formula is valid also for nonequilibrium distribution functions. To understand the Lindhard formula, consider some limiting cases in 2 and 3 dimensions. The 1-dimensional case is also considered in other ways. First, consider the long wavelength limit (formula_5). For the denominator of the Lindhard formula, we get and for the numerator of the Lindhard formula, we get Inserting these into the Lindhard formula and taking the formula_8 limit, we obtain where we used formula_10, formula_11 and formula_12. This result is the same as the classical dielectric function | https://en.wikipedia.org/wiki?curid=22613078 |
Lindhard theory Second, consider the static limit (formula_15). The Lindhard formula becomes Inserting the above equalities for the denominator and numerator, we obtain Assuming a thermal equilibrium Fermi–Dirac carrier distribution, we get here, we used formula_19 and formula_20. Therefore, Here, formula_22 is the 3D screening wave number (3D inverse screening length) defined as formula_23. Then, the 3D statically screened Coulomb potential is given by And the Fourier transformation of this result gives known as the Yukawa potential. Note that in this Fourier transformation, which is basically a sum over "all" formula_26, we used the expression for small formula_27 for "every" value of formula_26 which is not correct. For a degenerated Fermi gas ("T"=0), the Fermi energy is given by So the density is At "T"=0, formula_31, so formula_32. Inserting this into the above 3D screening wave number equation, we obtain This is the 3D Thomas–Fermi screening wave number. For reference, Debye–Hückel screening describes the nondegenerate limit case. The result is formula_33, the 3D Debye–Hückel screening wave number. First, consider the long wavelength limit (formula_5). For the denominator of the Lindhard formula, and for the numerator, Inserting these into the Lindhard formula and taking the limit of formula_8, we obtain where we used formula_39, formula_40 and formula_41. Second, consider the static limit (formula_15) | https://en.wikipedia.org/wiki?curid=22613078 |
Lindhard theory The Lindhard formula becomes Inserting the above equalities for the denominator and numerator, we obtain Assuming a thermal equilibrium Fermi–Dirac carrier distribution, we get here, we used formula_19 and formula_20. Therefore, formula_22 is 2D screening wave number(2D inverse screening length) defined as formula_50. Then, the 2D statically screened Coulomb potential is given by It is known that the chemical potential of the 2-dimensional Fermi gas is given by and formula_53. So, the 2D screening wave number is Note that this result is independent of "n". This time, consider some generalized case for lowering the dimension. The lower the dimension is, the weaker the screening effect. In lower dimension, some of the field lines pass through the barrier material wherein the screening has no effect. For the 1-dimensional case, we can guess that the screening affects only the field lines which are very close to the wire axis. In real experiment, we should also take the 3D bulk screening effect into account even though we deal with 1D case like the single filament. The Thomas–Fermi screening has been applied to an electron gas confined to a filament and a coaxial cylinder. For a KPt(CN)Cl·2.6H0 filament, it was found that the potential within the region between the filament and cylinder varies as formula_54 and its effective screening length is about 10 times that of metallic platinum. | https://en.wikipedia.org/wiki?curid=22613078 |
Placebo in history The word placebo was used in a medicinal context in the late 18th century to describe a "commonplace method or medicine" and in 1811 it was defined as "any medicine adapted more to please than to benefit the patient". Although this definition contained a derogatory implication, it did not necessarily imply that the remedy had no effect. Placebos have featured in medical use until well into the twentieth century. In 1955 Henry K. Beecher published an influential paper entitled "The Powerful Placebo" which proposed idea that placebo effects were clinically important. Subsequent re-analysis of his materials, however, found in them no evidence of any "placebo effect". "Placebo" is Latin for "I shall be pleasing." It was used as a name for the Vespers in the Office of the Dead, taken from a phrase used in it, a quote from the Vulgate's Psalm 116:9. From that, a "singer of placebo" became associated with someone who falsely claimed a connection to the deceased to get a share of the funeral meal, and hence a flatterer, and so a deceptive act to please. In the practice of medicine it had been long understood that, as Ambroise Paré (1510–1590) had expressed it, the physician's duty was to "cure occasionally, relieve often, console always" ("Guérir quelquefois, soulager souvent, consoler toujours"). Accordingly, placebos were widespread in medicine until the 20th century, and were often endorsed as necessary deceptions | https://en.wikipedia.org/wiki?curid=22613807 |
Placebo in history According to Nicholas Jewson, eighteenth century English medicine was gradually moving away from a model in which the patient had considerable interaction with the physician – and, through this consultative relationship, had an equal influence on the physician's therapeutic approach. It was moving towards a paradigm in which the patient became the recipient of a more standardized form of intervention that was determined by the prevailing opinions of the medical profession of the day. Jewson characterized this as parallel to the changes that were taking place in the manner in which medical knowledge was being produced; namely, a transition from "bedside medicine", through to "hospital medicine", and finally to "laboratory medicine". The last vestiges of the "consoling" approach to treatment were the prescription of "morale-boosting" and "pleasing" remedies, such as the "sugar pill", electuary or pharmaceutical syrup; all of which had no known pharmacodynamic action, even at the time. Those doctors who provided their patients with these sorts of morale-boosting therapies (which, while having no pharmacologically active ingredients, provided reassurance and comfort) did so either to reassure their patients while the "Vis medicatrix naturae" (i.e., "the healing power of nature") performed its normalizing task of restoring them to health, or to gratify their patients' need for an active treatment | https://en.wikipedia.org/wiki?curid=22613807 |
Placebo in history In 1811, Hooper's "Quincy's Lexicon–Medicum" defined placebo as "an epithet given to any medicine adapted more to please than benefit the patient". In 1903 Richard Cabot said that he was brought up to use placebos, but he ultimately concluded by saying that "I have not yet found any case in which a lie does not do more harm than good." Early implementations of placebo controls date back to 16th-century Europe with Catholic efforts to discredit exorcisms. Individuals who claimed to be possessed by demonic forces were given false holy objects. If the person reacted with violent contortions, it was concluded that the possession was purely imagination. Use of the placebo effect as a medical treatment has been controversial throughout history, and was common until the mid twentieth century. In 1903 Richard Cabot concluded that it should be avoided because it is deceptive. Newman points out the "placebo paradox" – it may be unethical to use a placebo, but also unethical ""not" to use something that heals". He suggests to solve this dilemma by appropriating the meaning response in medicine, that is make use of the placebo effect, as long as the "one administering... is honest, open, and believes in its potential healing power". John Haygarth was the first to investigate the efficacy of the placebo effect in the 18th century | https://en.wikipedia.org/wiki?curid=22613807 |
Placebo in history He tested a popular medical treatment of his time, called "Perkins tractors", and concluded that the remedy was ineffectual by demonstrating that the results from a "dummy" remedy were just as useful as from the alleged "active" remedy. Émile Coué, a French pharmacist, working as an apothecary at Troyes between 1882 and 1910, also advocated the effectiveness of the "Placebo Effect". He became known for reassuring his clients by praising each remedy's efficiency and leaving a small positive notice with each given medication. His book "Self-Mastery Through Conscious Autosuggestion" was published in England (1920) and in the United States (1922). Placebos remained widespread in medicine until the 20th century, and they were sometimes endorsed as necessary deceptions. In 1903, Richard Cabot said that he was brought up to use placebos, but he ultimately concluded by saying that "I have not yet found any case in which a lie does not do more harm than good". T. C. Graves first defined the "placebo effect" in a published paper in "The Lancet" in 1920. He spoke of "the placebo effects of drugs" being manifested in those cases where "a real psychotherapeutic effect appears to have been produced". The placebo effect of new drugs was known anecdotally in the 18th century, as demonstrated by Michel-Philippe Bouvart's 1780s quip to a patient that she should "take [a remedy] ... and hurry up while it [still] cures." The first to recognize and demonstrate the placebo effect was English physician John Haygarth in 1799 | https://en.wikipedia.org/wiki?curid=22613807 |
Placebo in history He tested a popular medical treatment of his time, called "Perkins tractors", which were metal pointers supposedly able to 'draw out' disease. They were sold at the extremely high price of five guineas, and Haygarth set out to show that the high cost was unnecessary. He did this by comparing the results from "dummy" wooden tractors with a set of allegedly "active" metal tractors, and published his findings in a book "On the Imagination as a Cause & as a Cure of Disorders of the Body". The wooden pointers were just as useful as the expensive metal ones, showing "to a degree which has never been suspected, what powerful influence upon diseases is produced by mere imagination". While the word placebo had been used since 1772, this is the first real demonstration of the placebo effect. In modern times the first to define and discuss the "placebo effect" was T.C Graves, in a published paper in "The Lancet" in 1920. He spoke of "the placebo effects of drugs" being manifested in those cases where "a real psychotherapeutic effect appears to have been produced". At the Royal London Hospital in 1933, William Evans and Clifford Hoyle experimented with 90 subjects and published studies which compared the outcomes from the administration of an active drug and a dummy simulator ("placebo") in the same trial. The experiment displayed no significant difference between drug treatment and placebo treatment, leading the researchers to conclude that the drug exerted no specific effects in relation to the conditions being treated | https://en.wikipedia.org/wiki?curid=22613807 |
Placebo in history In 1946, the Yale biostatistician and physiologist E. Morton Jellinek described the "placebo reaction" or "response". He probably used the terms "placebo response" and "placebo reaction" as interchangeable. Henry K. Beecher's 1955 paper "The Powerful Placebo" was the first to use the term "placebo effect", which he contrasts with drug effects. In 1961, Beecher reported that patients of 'enthusiastic' surgeons experienced greater levels of chest pain relief than those receiving treatment from skeptic surgeons. In 1961 Walter Kennedy introduced the word nocebo to refer to a neutral substance that creates harmful effects in a patient who takes it. In 1961 Henry K. Beecher concluded that surgeons he categorized as enthusiasts relieved their patients' chest pain and heart problems more than skeptic surgeons. Beginning in the 1960s, the placebo effect became widely recognized and placebo-controlled trials became the norm in the approval of new medications. Dylan Evans argues that placebos are linked with activation of the acute-phase response so will work only on subjective conditions such as pain, swelling, stomach ulcers, depression, and anxiety that are linked to this. A 2001 systematic review of clinical trials concluded that there was no evidence of clinically important effects, except perhaps in the treatment of pain and continuous subjective outcomes. The authors later published a Cochrane review with similar conclusions (updated ) | https://en.wikipedia.org/wiki?curid=22613807 |
Placebo in history Most studies have attributed the difference from baseline until the end of the trial to a placebo effect, but the reviewers examined studies which had both placebo and untreated groups in order to distinguish the placebo effect from the natural progression of the disease. Placebo observations differ between individuals. In the 1950s, there was considerable research to find whether there was a specific personality to those that responded to placebos. The findings could not be replicated and it is now thought to have no effect. The word "obecalp", "placebo" spelled backwards, was coined by an Australian doctor in 1998 when he recognised the need for a freely available placebo. The word is sometimes used to make the use or prescription of fake medicine less obvious to the patient. It has been suggested that a distinction exists between the placebo effect (which applies to a group) and the placebo response (which is individual). Some statements about the role of placebos in doctor patient relationship are: | https://en.wikipedia.org/wiki?curid=22613807 |
Sodium in biology Sodium ions (Na) are necessary in small amounts for some types of plants, but sodium as a nutrient is more generally needed in larger amounts by animals, due to their use of it for generation of nerve impulses and for maintenance of electrolyte balance and fluid balance. In animals, sodium ions are necessary for the aforementioned functions and for heart activity and certain metabolic functions. The health effects of salt reflect what happens when the body has too much or too little sodium. Characteristic concentrations of sodium in model organisms are: 10mM in "E. coli", 30mM in budding yeast, 10mM in mammalian cell and 100mM in blood plasma. The minimum physiological requirement for sodium is between 115 and 500 milligrams per day depending on sweating due to physical activity, and whether the person is adapted to the climate. Sodium chloride is the principal source of sodium in the diet, and is used as seasoning and preservative, such as for pickling and jerky; most of it comes from processed foods. The Adequate Intake for sodium is 1.2 to 1.5 grams per day, but on average people in the United States consume 3.4 grams per day, the minimum amount that promotes hypertension. (Note that salt contains about 39.3% sodium by massthe rest being chlorine and other trace chemicals; thus the UL of 2.3g sodium would be about 5.9g of saltabout 1 teaspoon) Normal serum sodium levels are between approximately 135 and 145 mEq/liter (135 - 145 mmol/L) | https://en.wikipedia.org/wiki?curid=22615598 |
Sodium in biology A serum sodium level of less than 135 mEq/L qualifies as hyponatremia, which is considered severe when the serum sodium level is below 125 mEq/L. The renin–angiotensin system and the atrial natriuretic peptide indirectly regulate the amount of signal transduction in the human central nervous system, which depends on sodium ion motion across the nerve cell membrane, in all nerves. Sodium is thus important in neuron function and osmoregulation between cells and the extracellular fluid; the distribution of sodium ions are mediated in all animals by sodium–potassium pumps, which are active transporter solute pumps, pumping ions against the gradient, and sodium-potassium channels. Sodium channels are known to be less selective in comparison to potassium channels. Sodium is the most prominent cation in extracellular fluid: in the 15 liters of extracellular fluid in a 70 kg human there is around 50 grams of sodium, 90% of the body's total sodium content. Some potent neurotoxins, such as batrachotoxin, increase the sodium ion permeability of the cell membranes in nerves and muscles, causing a massive and irreversible depolarization of the membranes, with potentially fatal consequences. However, drugs with smaller effects on sodium ion motion in nerves may have diverse pharmacological effects which range from anti-depressant to anti-seizure actions. Since only some plants need sodium and those in small quantities, a completely plant-based diet will generally be very low in sodium | https://en.wikipedia.org/wiki?curid=22615598 |
Sodium in biology This requires some herbivores to obtain their sodium from salt licks and other mineral sources. The animal need for sodium is probably the reason for the highly conserved ability to taste the sodium ion as "salty." Receptors for the pure salty taste respond best to sodium, otherwise only to a few other small monovalent cations (Li, NH, and somewhat to K). Calcium ion (Ca) also tastes salty and sometimes bitter to some people but, like potassium, can trigger other tastes. Sodium ions play a diverse and important role in many physiological processes, acting to regulate blood volume, blood pressure, osmotic equilibrium and pH. In C4 plants, sodium is a micronutrient that aids in metabolism, specifically in regeneration of phosphoenolpyruvate (involved in the biosynthesis of various aromatic compounds, and in carbon fixation) and synthesis of chlorophyll. In others, it substitutes for potassium in several roles, such as maintaining turgor pressure and aiding in the opening and closing of stomata. Excess sodium in the soil limits the uptake of water due to decreased water potential, which may result in wilting; similar concentrations in the cytoplasm can lead to enzyme inhibition, which in turn causes necrosis and chlorosis. To avoid these problems, plants developed mechanisms that limit sodium uptake by roots, store them in cell vacuoles, and control them over long distances; excess sodium may also be stored in old plant tissue, limiting the damage to new growth | https://en.wikipedia.org/wiki?curid=22615598 |
Sodium in biology Sodium is the primary cation (positive ion) in extracellular fluids in animals and humans. These fluids, such as blood plasma and extracellular fluids in other tissues, bathe cells and carry out transport functions for nutrients and wastes. Sodium is also the principal cation in seawater, although the concentration there is about 3.8 times what it is normally in extracellular body fluids. Although the system for maintaining optimal salt and water balance in the body is a complex one, one of the primary ways in which the human body keeps track of loss of body water is that osmoreceptors in the hypothalamus sense a balance of sodium and water concentration in extracellular fluids. Relative loss of body water will cause sodium concentration to rise higher than normal, a condition known as hypernatremia. This ordinarily results in thirst. Conversely, an excess of body water caused by drinking will result in too little sodium in the blood (hyponatremia), a condition which is again sensed by the hypothalamus, causing a decrease in vasopressin hormone secretion from the posterior pituitary, and a consequent loss of water in the urine, which acts to restore blood sodium concentrations to normal. Severely dehydrated persons, such as people rescued from ocean or desert survival situations, usually have very high blood sodium concentrations | https://en.wikipedia.org/wiki?curid=22615598 |
Sodium in biology These must be very carefully and slowly returned to normal, since too-rapid correction of hypernatremia may result in brain damage from cellular swelling, as water moves suddenly into cells with high osmolar content. In humans, a high-salt intake was demonstrated to attenuate nitric oxide production. Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium Because the hypothalamus/osmoreceptor system ordinarily works well to cause drinking or urination to restore the body's sodium concentrations to normal, this system can be used in medical treatment to regulate the body's total fluid content, by first controlling the body's sodium content. Thus, when a powerful diuretic drug is given which causes the kidneys to excrete sodium, the effect is accompanied by an excretion of body water (water loss accompanies sodium loss). This happens because the kidney is unable to efficiently retain water while excreting large amounts of sodium. In addition, after sodium excretion, the osmoreceptor system may sense lowered sodium concentration in the blood and then direct compensatory urinary water loss in order to correct the hyponatremic (low blood sodium) state. | https://en.wikipedia.org/wiki?curid=22615598 |
ITIES In electrochemistry, (interface between two immiscible electrolyte solutions) is an electrochemical interface that is either polarisable or polarised. An is polarisable if one can change the Galvani potential difference, or in other words the difference of inner potentials between the two adjacent phases, without noticeably changing the chemical composition of the respective phases (i.e. without noticeable electrochemical reactions taking place at the interface). An system is polarised if the distribution of the different charges and redox species between the two phases determines the Galvani potential difference. Usually, one electrolyte is an aqueous electrolyte composed of hydrophilic ions such as NaCl dissolved in water and the other electrolyte is a lipophilic salt such as tetrabutylammonium tetraphenylborate dissolved in an organic solvent immiscible with water such as nitrobenzene, or 1,2-dichloroethane. Three major classes of charge transfer reactions can be studied at an ITIES: The Nernst equation for an ion transfer reaction reads where formula_2 is the standard transfer potential defined as the Gibbs energy of transfer expressed in a voltage scale. The Nernst equation for a single heterogeneous electron transfer reaction reads where formula_5 is the standard redox potential for the interfacial transfer of electrons defined as the difference the standard redox potentials of the two redox couples but referred to the aqueous standard hydrogen electrode (SHE) | https://en.wikipedia.org/wiki?curid=22616026 |
ITIES To study charge transfer reactions of an ITIES, a four-electrode cell is used. Two reference electrodes are used to control the polarisation of the interface, and two counter electrodes made of noble metals are used to pass the current. The aqueous supporting electrolyte must be hydrophilic, such as LiCl, and the organic electrolyte must be lipophilic, such as tetraheptylammonium tetra-pentafluorophenyl borate. Contrary to a neutral solute, the partition coefficient of an ion depends of the Galvani potential difference between the two phases: When a salt is distributed between two phases, the Galvani potential difference is called the distribution potential and is obtained from the respective Nernst equations for the cation C and the anion A to read where γ represents the activity coefficient. | https://en.wikipedia.org/wiki?curid=22616026 |
PowerGenix PowerGenix, was a San Diego-based company developing and manufacturing Nickel-zinc (NiZn) rechargeable batteries, prior to being acquired by ZincFive, Inc. in 2016. ZincFive manufacturers cell and monobloc nickel-zinc batteries and is the world leader in innovation and delivery of nickel-zinc battery-based uninterruptible power supplies for mission critical applications in Data Centers and Intelligent Transportation and offer batteries for stationary, motive and start-stop applications. With 95 patents awarded, ZincFive leverages nickel-zinc chemistry within its solutions to provide high power density and performance simultaneous with superior safety and environmental advantages. ZincFive has global operations in the US and China. The location near Portland, OR serves as corporate headquarters and UPS solutions design and manufacturing. The two China locations provide nickel-zinc battery design, development, testing and high volume battery manufacturing operations. As of 2018, ZincFive has commercially available products using nickel-zinc batteries in the intelligent transportation and mission critical IT/data center markets in the form of uninterruptible power supplies. Also available is nickel-zinc batteries for stationary, motive and start-stop applications. | https://en.wikipedia.org/wiki?curid=22619349 |
Barium sulfite is the barium salt of sulfurous acid with the chemical formula BaSO. It is a white powder which is used in paper manufacturing. Like other barium compounds, it is toxic. It may be formed by the action of sulfur dioxide on barium oxide or barium hydroxide. It can also be formed by treating barium with sulfurous acid. | https://en.wikipedia.org/wiki?curid=22623943 |
European Calcium Society The is a non-profit society that aims to develop relationships between different generations of scientists in Europe working in the field of calcium signaling and the proteins involved in the Calcium Toolkit. The First European Symposium took place in 1989 and covered calcium binding proteins in normal and transformed cells. The symposium resulted from a 30-month gestation. The symposium filled a gap given the lack of European fora in which young European researchers could participate (the International Symposium was held in Asilomar, CA 1986, in Nagoya in 1988, in Banff, Canada, etc.) A European Union grant called Stimulation Action was awarded to Roland Pochet in November 1986. Long discussions in 1988 between Pochet and Jacques Haiech at Mont Sainte-Odile who pointed out the importance of European researchers in calcium binding proteins (Hamoir, Liége, 1955, Pechere, Montpellier, 1965, Drabikowski, Varsovie, 1970) and the strong support received from Claus Heizmann. 1997 was important because the “European Calcium Society” was registered under E.U. guidelines, which had earlier rejected a proposal to finance the fourth symposium because of lack of structure. In 1997 they created the group's first ECS Web site, logo, newsletter and a set of statutes published in the “Moniteur belge” as an “Arrêté Royal du 22 septembre 1997” signed by King Albert II. 1998-2005 was a consolidation period | https://en.wikipedia.org/wiki?curid=22625701 |
European Calcium Society Since 2000, ECS has been selected as an EU High-level Scientific Conference allowing it to offer grants to young European researchers. The board was enlarged to include Volker Gerke and Steve Moss. ECS provided posters, prizes and recently special grants for young researchers. Since its creation, 30 to 35% of the participants at ECS symposia were young researchers (below 35 years old). Encouraging young researchers to participate has always been one of the main objectives. Since 1992 Heizmann has sponsored the publication of significant articles in the scientific journal Biochimica et Biophysica Acta. A newsletter is also produced twice a year (May and November). In 2007, ECS launched its first workshop, in Ariège (France). The second took place in June 2009 in Smolenice (Slovakia). | https://en.wikipedia.org/wiki?curid=22625701 |
Rhodium(IV) oxide (or rhodium dioxide) is the chemical compound with the formula RhO. RhO is highly insoluble even in hot aqua regia. RhO has the tetragonal rutile structure. RhO has metallic resistivity with values <10 Ohm·cm. It transforms in air to RhO at 850 °C and then to metal and oxygen at 1050 °C. | https://en.wikipedia.org/wiki?curid=22626054 |
Rhodium oxide can refer to: | https://en.wikipedia.org/wiki?curid=22626067 |
Frontier molecular orbital theory In chemistry, frontier molecular orbital theory is an application of MO theory describing HOMO/LUMO interactions. In 1952, Kenichi Fukui published a paper in the "Journal of Chemical Physics" titled "A molecular theory of reactivity in aromatic hydrocarbons." Though widely criticized at the time, he later shared the Nobel Prize in Chemistry with Roald Hoffmann for his work on reaction mechanisms. Hoffman's work focused on creating a set of four pericyclic reactions in organic chemistry, based on orbital symmetry, which he coauthored with Robert Burns Woodward, entitled "The Conservation of Orbital Symmetry." Fukui's own work looked at the frontier orbitals, and in particular the effects of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) on reaction mechanisms, which led to it being called Frontier Molecular Orbital Theory (FMO Theory). He used these interactions to better understand the conclusions of the Woodward–Hoffmann rules. Fukui realized that a good approximation for reactivity could be found by looking at the frontier orbitals (HOMO/LUMO). This was based on three main observations of molecular orbital theory as two molecules interact: In general, the total energy change of the reactants on approach of the transition state is described by the Klopman-Salem equation, derived from perturbational MO theory | https://en.wikipedia.org/wiki?curid=22629003 |
Frontier molecular orbital theory The first and second observations correspond to taking into consideration the filled-filled interaction and Coulombic interaction terms of the equation, respectively. With respect to the third observation, primary consideration of the HOMO-LUMO interaction is justified by the fact that the largest contribution in the filled-unfilled interaction term of the Klopman-Salem equation comes from molecular orbitals "r" and "s" that are closest in energy (i.e., smallest formula_1 value). From these observations, frontier molecular orbital (FMO) theory simplifies prediction of reactivity to analysis of the interaction between the more energetically matched HOMO-LUMO pairing of the two reactants. In addition to providing a unified explanation of diverse aspects of chemical reactivity and selectivity, it agrees with the predictions of the Woodward–Hoffmann orbital symmetry and Dewar-Zimmerman aromatic transition state treatments of thermal pericyclic reactions, which are summarized in the following selection rule: ""A ground-state pericyclic change is symmetry-allowed when the total number of (4q+2) and (4r) components is odd"" (4q+2) refers to the number of aromatic, suprafacial electron systems; likewise, (4r) refers to antiaromatic, antarafacial systems. It can be shown that if the total number of these systems is odd then the reaction is thermally allowed. A cycloaddition is a reaction that simultaneously forms at least two new bonds, and in doing so, converts two or more open-chain molecules into rings | https://en.wikipedia.org/wiki?curid=22629003 |
Frontier molecular orbital theory The transition states for these reactions typically involve the electrons of the molecules moving in continuous rings, making it a pericyclic reaction. These reactions can be predicted by the Woodward–Hoffmann rules and thus are closely approximated by FMO Theory. The Diels–Alder reaction between maleic anhydride and cyclopentadiene is allowed by the Woodward–Hoffmann rules because there are six electrons moving suprafacially and no electrons moving antarafacially. Thus, there is one (4"q" + 2) component and no (4"r") component, which means the reaction is allowed thermally. FMO theory also finds that this reaction is allowed and goes even further by predicting its stereoselectivity, which is unknown under the Woodward-Hoffmann rules. Since this is a [4 + 2], the reaction can be simplified by considering the reaction between butadiene and ethene. The HOMO of butadiene and the LUMO of ethene are both antisymmetric (rotationally symmetric), meaning the reaction is allowed. In terms of the stereoselectivity of the reaction between maleic anhydride and cyclopentadiene, the "endo"-product is favored, a result best explained through FMO theory. The maleic anhydride is an electron-withdrawing species that makes the dieneophile electron deficient, forcing the regular Diels–Alder reaction. Thus, only the reaction between the HOMO of cyclopentadiene and the LUMO of maleic anhydride is allowed | https://en.wikipedia.org/wiki?curid=22629003 |
Frontier molecular orbital theory Furthermore, though the "exo"-product is the more thermodynamically stable isomer, there are secondary (non-bonding) orbital interactions in the "endo"- transition state, lowering its energy and making the reaction towards the "endo"- product faster, and therefore more kinetically favorable. Since the "exo"-product has primary (bonding) orbital interactions it can still form, but since the "endo"-product forms faster it is the major product. "Note: The HOMO of ethene and the LUMO of butadiene are both symmetric, meaning the reaction between these species is allowed as well. This is referred to as the "inverse electron demand Diels–Alder."" A sigmatropic rearrangement is a reaction in which a sigma bond moves across a conjugated pi system with a concomitant shift in the pi bonds. The shift in the sigma bond may be antarafacial or suprafacial. In the example of a [1,5] shift in pentadiene, if there is a suprafacial shift, there is 6 e moving suprafacially and none moving antarafacially, implying this reaction is allowed by the Woodward–Hoffmann rules. For an antarafacial shift, the reaction is not allowed. These results can be predicted with FMO theory by observing the interaction between the HOMO and LUMO of the species. To use FMO theory, the reaction should be considered as two separate ideas: (1) whether or not the reaction is allowed, and (2) which mechanism the reaction proceeds through. In the case of a [1,5] shift on pentadiene, the HOMO of the sigma bond (i.e | https://en.wikipedia.org/wiki?curid=22629003 |
Frontier molecular orbital theory a constructive bond) and the LUMO of butadiene on the remaining 4 carbons is observed. Assuming the reaction happens suprafacially, the shift results with the HOMO of butadiene on the 4 carbons that are not involved in the sigma bond of the product. Since the pi system changed from the LUMO to the HOMO, this reaction is allowed (though it would not be allowed if the pi system went from LUMO to LUMO). To explain why the reaction happens suprafacially, first notice that the terminal orbitals are in the same phase. For there to be a constructive sigma bond formed after the shift, the reaction would have to be suprafacial. If the species shifted antarafacially then it would form an antibonding orbital and there would not be a constructive sigma shift. It is worth noting that in propene the shift would have to be antarafacial, but since the molecule is very small that twist is not possible and the reaction is not allowed. An electrocyclic reaction is a pericyclic reaction involving the net loss of a pi bond and creation of a sigma bond with formation of a ring. This reaction proceeds through either a conrotatory or disrotatory mechanism. In the conrotatory ring opening of cyclobutene, there are two electrons moving suprafacially (on the pi bond) and two moving antarafacially (on the sigma bond). This means there is one 4"q" + 2 suprafacial system and no 4r antarafacial system; thus the conrotatory process is thermally allowed by the Woodward–Hoffmann rules. The HOMO of the sigma bond (i.e | https://en.wikipedia.org/wiki?curid=22629003 |
Frontier molecular orbital theory a constructive bond) and the LUMO of the pi bond are important in the FMO theory consideration. If the ring opening uses a conrotatory process then the reaction results with the HOMO of butadiene. As in the previous examples the pi system moves from a LUMO species to a HOMO species, meaning this reaction is allowed. | https://en.wikipedia.org/wiki?curid=22629003 |
Cerium anomaly The cerium anomaly, in geochemistry, is the phenomenon whereby cerium (Ce) concentration is either depleted or enriched in a rock relative to the other rare-earth elements (REEs). A Ce anomaly is said to be "negative" if Ce is depleted relative to the other REEs and is said to be "positive" if Ce is enriched relative to the other REEs. Cerium is a rare-earth element (lanthanide) characterized by two different redox states: III and IV. Contrary to other lanthanide elements, which are only trivalent (with the notable exception of Eu), Ce can be oxidized by atmospheric oxygen (O) to Ce under alkaline conditions. The cerium anomaly relates to the decrease in solubility, which accompanies the oxidation of Ce(III) to Ce(IV). Under reducing conditions, Ce is relatively soluble, while under oxidizing conditions CeO precipitates. Sediments deposited under oxic or anoxic conditions can preserve on the long term the geochemical signature of Ce or Ce upon reserve that no early diagenetic transformation altered it. Cerium can occur in nature as a 3+ or 4+ ion and is a compatible element (at 4+ valency) in zircon and less commonly in silica. Thomas "et al.", (2003) state that “terrestrial zircons commonly show a positive Ce anomaly due to the incorporation of Ce into zircon, which is because Ce has the same charge and a similar ionic radius than Zr (Ce = 0.97 Å; Zr = 0.84 Å)”. As such, Ce is incorporated into zircon much more easily than the larger Ce (ionic radius = 1.143 Å) | https://en.wikipedia.org/wiki?curid=22629902 |
Cerium anomaly This shows that both Ce and Ce are present and that the Ce being compatible in zircon is causing the anomaly. | https://en.wikipedia.org/wiki?curid=22629902 |
Cobalt(II) cyanide is the inorganic compound with the formula Co(CN). It is coordination polymer that has attracted intermittent attention over many years in the area of inorganic synthesis and homogeneous catalysis. has been used as a precursor to cobalt carbonyl. The trihydrate salt is obtained as a reddish-brown precipitate by adding potassium cyanide to a cobalt salt solution.: Hydrated Co(CN) dissolves in the presence of excess potassium cyanide, forming a red solution of KCo(CN). This material further oxidizes to yellow KCo(CN). | https://en.wikipedia.org/wiki?curid=22633997 |
Hydrindantin is an organic chemical thought to be involved with the ninhydrin test for amines. | https://en.wikipedia.org/wiki?curid=22635133 |
Wetting transition A wetting transition (Cassie–Wenzel transition) may occur during the process of wetting of a solid (or liquid) surface with a liquid. The transition corresponds to a certain change in contact angle, the macroscopic parameter characterizing wetting. Various contact angles can co-exist on the same solid substrate. Wetting transitions may occur in a different way depending on whether the surface is flat or rough. When a liquid drop is put onto a flat surface, two situations may result. If the contact angle is zero, the situation is referred to as complete wetting. If the contact angle is between 0 and 180°, the situation is called partial wetting. A wetting transition is a surface phase transition from partial wetting to complete wetting. The situation on rough surfaces is much more complicated. The main characteristic of the wetting properties of rough surfaces is the so-called apparent contact angle (APCA). It is well known that the APCA usually measured are different from those predicted by the Young equation. Two main hypotheses were proposed in order to explain this discrepancy, namely the Wenzel and Cassie wetting models. According to the traditional Cassie model, air can remain trapped below the drop, forming "air pockets". Thus, the hydrophobicity of the surface is strengthened because the drop sits partially on air. On the other hand, according to the Wenzel model the roughness increases the area of a solid surface, which also geometrically modifies the wetting properties of this surface | https://en.wikipedia.org/wiki?curid=22639515 |
Wetting transition Transition from Cassie to Wenzel regime is also called wetting transition. Under certain external stimuli, such as pressure or vibration, the Cassie air trapping wetting state could be converted into the Wenzel state. It is well accepted that the Cassie air trapping wetting regime corresponds to a higher energetic state, and the Cassie–Wenzel transition is irreversible. However, the mechanism of the transition remains unclear. It was suggested that the Cassie–Wenzel transition occurs via a nucleation mechanism starting from the drop center. On the other hand, recent experiments showed that the Cassie–Wenzel transition is more likely to be due to the displacement of a triple line under an external stimulus. The existence of so-called impregnating Cassie wetting state also has to be considered. Understanding wetting transitions is of a primary importance for design of superhydrophobic surfaces. | https://en.wikipedia.org/wiki?curid=22639515 |
Ascalaph Designer is a computer program for general purpose molecular modelling for molecular design and simulations. It provides a graphical environment for the common programs of quantum and classical molecular modelling ORCA, NWChem, Firefly, CP2K and MDynaMix . The molecular mechanics calculations cover model building, energy optimizations and molecular dynamics. Firefly (formerly named PC GAMESS) covers a wide range of quantum chemistry methods. is free and open-source software, released under the GNU General Public License, version 2 (GPLv2). | https://en.wikipedia.org/wiki?curid=22640378 |
Electrocapillarity or electrocapillary phenomena are the phenomena related to changes in the surface energy (or interfacial tension) of the dropping mercury electrode (DME), or in principle, any electrode, as the electrode potential changes or the electrolytic solution composition and concentration change. The term "electro-capillary" is used to describe the change in mercury (Hg) electrode potential as a function of the change in the surface or interfacial tension of the Hg determined by the capillary rise method. The phenomena are the historic main contributions for understanding and validating the models of the structure of the electrical double layer. The phenomena are related to the electrokinetic phenomena and consequently to the colloid chemistry. The interfacial (surface) tension, St, (dyne cm), can be calculated by applying the equation of capillary rise method (when the contact angle Ө → 0): formula_1 where: The circuit contains Hg electrode as the ideally polarizable electrode and a reference electrode as the non-polarizable electrode. Thus, when an external voltage is applied, only EM/S of Hg/solution fluid interface is changed. | https://en.wikipedia.org/wiki?curid=22649696 |
Ion association In chemistry, ion association is a chemical reaction whereby ions of opposite electrical charge come together in solution to form a distinct chemical entity. Ion associates are classified, according to the number of ions that associate with each other, as ion pairs, ion triplets, etc. Ion pairs are also classified according to the nature of the interaction as contact, solvent-shared or solvent-separated. The most important factor to determine the extent of ion association is the dielectric constant of the solvent. Ion associates have been characterized by means of vibrational spectroscopy. The concept was introduced by Niels Bjerrum. "Ion pairs" are formed when a cation and anion, which are present in a solution of an ionizable substance, come together to form a discrete chemical species. There are three distinct types of "ion pairs", depending on the extent of solvation of the two ions. For example, magnesium sulphate exists as both contact and solvent-shared ion-pairs in seawater. In the schematic representation above, the circles represent spheres. The sizes are arbitrary and not necessarily similar as illustrated. The cation is coloured red and the anion is coloured blue. The green area represents solvent molecules in a primary solvation shell; secondary solvation is ignored. When both ions have a complete primary solvation sphere, the ion pair may be termed "fully solvated". When there is about one solvent molecule between cation and anion, the ion pair may be termed "solvent-shared" | https://en.wikipedia.org/wiki?curid=22649721 |
Ion association Lastly, when the ions are in contact with each other, the ion pair is termed a "contact" ion pair. Even in a contact ion pair, however, the ions retain most of their solvation shell. The nature of this solvation shell is generally not known with any certainty. In aqueous solution and in other donor solvents, metal cations are surrounded by between 4 and 9 solvent molecules in the primary solvation shell, An alternative name for a solvent-shared ion pair is an "outer-sphere complex". This usage is common in co-ordination chemistry and denotes a complex between a solvated metal cation and an anion. Similarly, a contact ion pair may be termed an "inner-sphere complex". The essential difference between the three types is the closeness with which the ions approach each other: fully solvated > solvent-shared > contact. With fully solvated and solvent-shared ion pairs the interaction is primarily electrostatic, but in a contact ion pair some covalent character in the bond between cation and anion is also present. An "ion triplet" may be formed from one cation and two anions or from one anion and two cations. Higher aggregates, such as a tetramer (AB), may be formed. Ternary ion associates involve the association of three species. Another type, named "intrusion ion pair", has also been characterized. Ions of opposite charge are naturally attracted to each other by the electrostatic force | https://en.wikipedia.org/wiki?curid=22649721 |
Ion association This is described by Coulomb's law: where "F" is the force of attraction, "q" and "q" are the magnitudes of the electrical charges, ε is the dielectric constant of the medium and "r" is the distance between the ions. For ions in solution this is an approximation because the ions exert a polarizing effect on the solvent molecules that surround them, which attenuates the electric field somewhat. Nevertheless, some general conclusions can be inferred. The equilibrium constant "K" for ion-pair formation, like all equilibrium constants, is related to the standard free-energy change: where "R" is the gas constant and "T" is the temperature in kelvins. Free energy is made up of an enthalpy term and an entropy term: The coulombic energy released when ions associate contributes to the enthalpy term, . In the case of contact ion pairs, the covalent interaction energy also contributes to the enthalpy, as does the energy of displacing a solvent molecule from the solvation shell of the cation or anion. The tendency to associate is opposed by the entropy term, which results from the fact that the solution containing unassociated ions is more disordered than a solution containing associates. The entropy term is similar for electrolytes of the same type, with minor differences due to solvation effects. Therefore, it is the magnitude of the enthalpy term that mostly determines the extent of ion association for a given electrolyte type. This explains the general rules given above | https://en.wikipedia.org/wiki?curid=22649721 |
Ion association Dielectric constant is the most important factor in determining the occurrence of ion association. A table of some typical values can be found under Dielectric constant. Water has a relatively high dielectric constant value of 78.7 at 298K (25 °C), so in aqueous solutions at ambient temperatures 1:1 electrolytes such as NaCl do not form ion pairs to an appreciable extent except when the solution is very concentrated. 2:2 electrolytes ("q" = 2, "q" = 2) form ion pairs more readily. Indeed, the solvent-shared ion pair [Mg(HO)]SO was famously discovered to be present in seawater, in equilibrium with the contact ion pair [Mg(HO)(SO)] Trivalent ions such as Al, Fe and lanthanide ions form weak complexes with monovalent anions. The dielectric constant of water decreases with increasing temperature to about 55 at 100 °C and about 5 at the critical temperature (217.7 °C). Thus ion pairing will become more significant in superheated water. Solvents with a dielectric constant in the range, roughly, 20–40, show extensive ion-pair formation. For example, in acetonitrile both contact and solvent-shared ion pairs of Li(NCS) have been observed. In methanol the 2:1 electrolyte Mg(NCS) is partially dissociated into a contact ion pair, [Mg(NCS)] and the thiocyanate ion. The dielectric constant of liquid ammonia decreases from 26 at its freezing point (−80 °C) to 17 at 20 °C (under pressure). Many simple 1:1 electrolytes form contact ion pairs at ambient temperatures. The extent of ion pairing decreases as temperature decreases | https://en.wikipedia.org/wiki?curid=22649721 |
Ion association With lithium salts there is evidence to show that both inner-sphere and outer-sphere complexes exist in liquid-ammonia solutions. Of the solvents with dielectric constant of 10 or less, tetrahydrofuran (THF) is particularly relevant in this context, as it solvates cations strongly with the result that simple electrolytes have sufficient solubility to make the study of ion association possible. In this solvent ion association is the rule rather than the exception. Indeed, higher associates such as tetramers are often formed. Triple cations and triple anions have also been characterized in THF solutions. is an important factor in phase-transfer catalysis, since a species such as RPCl is formally neutral and so can dissolve easily in a non-polar solvent of low dielectric constant. In this case it also helps that the surface of the cation is hydrophobic. In S1 reactions the carbocation intermediate may form an ion pair with an anion, particularly in solvents of low dielectric constant, such as diethylether. This can affect both the kinetic parameters of the reaction and the stereochemistry of the reaction products. Vibrational spectroscopy provides the most widely used means for characterizing ion associates. Both infrared spectroscopy and Raman spectroscopy have been used. Anions containing a CN group, such as cyanide, cyanate and thiocyanide have a vibration frequency a little above 2000 cm, which can be easily observed, as the spectra of most solvents (other than nitriles) are weak in this region | https://en.wikipedia.org/wiki?curid=22649721 |
Ion association The anion vibration frequency is "shifted" on formation of ion pairs and other associates, and the extent of the shift gives information about the nature of the species. Other monovalent anions that have been studied include nitrate, nitrite and azide. Ion pairs of monatomic anions, such as halide ions, cannot be studied by this technique. NMR spectroscopy is not very useful, as association/dissociation reactions tend to be fast on the NMR time scale, giving time-averaged signals of the cation and/or anion. Nearly the same shift of vibration frequency is observed for solvent-shared ion pairs of LiCN, Be(CN) and Al(CN) in liquid ammonia. The extent of this type of ion pairing decreases as the size of the cation increases. Thus, solvent-shared ion pairs are characterized by a rather small shift of vibration frequency with respect to the "free" solvated anion, and the value of the shift is not strongly dependent on the nature of the cation. The shift for contact ion pairs is, by contrast, strongly dependent on the nature of the cation and decreases linearly with the ratio of the cations charge to the squared radius: The extent of contact ion pairing can be estimated from the relative intensities of the bands due to the ion pair and free ion. It is greater with the larger cations. This is counter to the trend expected if coulombic energy were the determining factor | https://en.wikipedia.org/wiki?curid=22649721 |
Ion association Instead, the formation of a contact ion pair is seen to depend more on the energy needed to displace a solvent molecule from the primary solvation sphere of the cation. This energy decreases with the size of the cation, making ion pairing occur to a greater extent with the larger cations. The trend may be different in other solvents. Higher ion aggregates, sometimes triples MXM, sometimes dimers of ion pairs (MX), or even larger species can be identified in the Raman spectra of some liquid-ammonia solutions of Na salts by the presence of bands that cannot be attributed to either contact- or solvent-shared ion pairs. Evidence for the existence of fully solvated ion pairs in solution is mostly indirect, as the spectroscopic properties of such ion pairs are indistinguishable from those of the individual ions. Much of the evidence is based on the interpretation of conductivity measurements. | https://en.wikipedia.org/wiki?curid=22649721 |
Boron monoxide (BO) is a chemical compound of boron and oxygen. Two experimental studies have proposed existence of diamond-like and graphite-like BO, as for boron nitride and carbon solids. However, a later, systematic, experimental study of boron oxide phase diagram suggests that BO is unstable. The instability of the graphite-like BO phase was also predicted theoretically. | https://en.wikipedia.org/wiki?curid=22650244 |
Magnetolithography (ML) is a method for pattern surfaces. ML based on applying a magnetic field on the substrate using paramagnetic metal masks named "magnetic mask". Magnetic masks are analogous to a photomask in photolithography, in that they define the spatial distribution and shape of the applied magnetic field. The second component of the process is ferromagnetic nanoparticles (analogous to the photoresist in photolithography) that are assembled onto the substrate according to the field induced by the magnetic mask. ML can be used for applying either a positive or negative approach. In the positive approach, the magnetic nanoparticles react chemically or interact via chemical recognition with the substrate. Hence, the magnetic nanoparticles are immobilized at selected locations, where the mask induces a magnetic field, resulting in a patterned substrate. In the negative approach, the magnetic nanoparticles are inert to the substrate. Hence, once they pattern the substrate, they block their binding site on the substrate from reacting with another reacting agent. After the adsorption of the reacting agent, the nanoparticles are removed, resulting in a negatively patterned substrate. ML is a backside lithography, which has the advantage of ease in producing multilayer with high accuracy of alignment and with the same efficiency for all layers. | https://en.wikipedia.org/wiki?curid=22682042 |
Zippe-type centrifuge The is a gas centrifuge designed to enrich the rare fissile uranium isotope Uranium-235 out of the mixture of isotopes found in naturally occurring uranium compounds. The isotopic separation is based on the slight difference in mass of the isotopes. The Zippe design was originally developed in the Soviet Union by a team led by 60 Austrian and German scientists and engineers captured after World War II, working in detention. In the West (and now generally) the type is known by the name of the man who recreated the technology after his return to the West in 1956, based on his recollection of his work in (and contributions to) the Soviet program, Gernot Zippe. To the extent that it might be referred to in Soviet/Russian usage by any one person's name, it was known (at least at a somewhat earlier stage of development) as a Kamenev centrifuge (after Evgeni Kamenev.) Natural uranium consists of three isotopes; the majority (99.274%) is U-238, while approximately 0.72% is fissile U-235 and the remaining 0.0055% is U-234. If natural uranium is enriched to contain 3% U-235, it can be used as fuel for light water nuclear reactors. If it is enriched to contain 90% uranium-235, it can be used for nuclear weapons. Enriching uranium is difficult because the isotopes are practically identical in chemistry and very similar in weight: U-235 is only 1.26% lighter than U-238. Separation efficiency in a centrifuge depends on weight difference | https://en.wikipedia.org/wiki?curid=22685481 |
Zippe-type centrifuge Separation of uranium isotopes requires a centrifuge that can spin at 1,500 revolutions per second (90,000 RPM). If we assume a rotor diameter of 20 cm (actual rotor diameter is likely to be less), this corresponds to a linear speed of greater than Mach 2 (Mach 1 = 340 m/s). For comparison, automatic washing machines operate at only about 12 to 25 revolutions per second (720–1500 RPM) during the spin cycle, while turbines in automotive turbochargers can run up to around 2500–3333 revolutions per second (150,000–200,000 RPM). A has a hollow, cylindrical rotor filled with gaseous uranium in the form of its hexafluoride. A rotating magnetic field at the bottom of the rotor, as used in an electric motor, is able to spin it quickly enough that the U-238 is thrown towards the edge. The lighter U-235 collects near the center. The bottom of the gaseous mix is heated, producing convection currents that move the U-238 down. The U-235 moves up, where scoops collect it. Each centrifuge has one inlet and two output lines (corresponding to the heavy and the light fractions). At the high speed of rotation, the gas is compressed close to the wall of the rotor. The rotor can be several meters in length (diameter is likely to be less than 10 cm) and a temperature gradient of between the top and bottom of the rotor produces a very strong convection current. In addition, the very strong Coriolis forces produced add to the separation efficiency. To reduce friction, the rotor spins in a vacuum | https://en.wikipedia.org/wiki?curid=22685481 |
Zippe-type centrifuge A magnetic bearing holds the top of the rotor steady, and the only physical contact is the conical jewel bearing on which the rotor sits. The three gas lines must be concentric with the fixed axis as the outer rim is spinning very quickly, and the seal is very important. After the scientists were released from Soviet captivity in 1956, Gernot Zippe was surprised to find that engineers in the West were years behind in their centrifuge technology. He was able to reproduce his design at the University of Virginia in the United States, publishing the results, even though the Soviets had confiscated his notes. Zippe left the United States when he was effectively barred from continuing his research: The Americans classified the work as secret, requiring him either to become an American citizen (he refused), return to Europe, or abandon his research. He returned to Europe where, during the 1960s, he and his colleagues made the centrifuge more efficient by changing the material of the rotor from aluminum to maraging steel, an alloy with a longer fatigue life, which allowed higher speed. This improved centrifuge design is used by the commercial company Urenco to produce enriched uranium fuel for nuclear power stations. The exact details of advanced Zippe-type centrifuges are closely guarded secrets, but the efficiency of the centrifuges is improved by making them longer, and increasing their speed of rotation | https://en.wikipedia.org/wiki?curid=22685481 |
Zippe-type centrifuge To do so, even stronger materials, such as carbon fiber-reinforced composite materials, are used; and various techniques are used to avoid forces causing destructive vibrations, including the use of flexible "bellows" to allow controlled flexing of the rotor, as well as careful speed control to ensure that the centrifuge does not operate for very long at speeds where resonance is a problem. The is difficult to build successfully and requires carefully machined parts. However, compared to other enrichment methods, it is much cheaper and more energy-efficient, and can be used in relative secrecy. This makes it ideal for covert nuclear-weapons programs and possibly increases the risk of nuclear proliferation. Centrifuge cascades also have much less material held in the machine at any time, unlike gaseous diffusion plants. Pakistan's atomic bomb program developed the P1 and P2 centrifuges—the first two centrifuges that Pakistan deployed in large numbers. The P1 centrifuge uses an aluminum rotor, and the P2 centrifuge uses a maraging steel rotor, which is stronger, spins faster, and enriches more uranium per machine than the P1. Russian and Soviet sources dispute the account of Soviet centrifuge development given by Gernot Zippe. They cite Prof. Max Steenbeck as the actual German scientist in charge of the German part of the Soviet centrifuge effort, which was started by German refugee Fritz Lange in the 1930s | https://en.wikipedia.org/wiki?curid=22685481 |
Zippe-type centrifuge The Soviets credit Steenbeck, Isaac Kikoin and Evgeni Kamenev with originating different valuable aspects of the design. They state Zippe was engaged in building prototypes for the project for two years from 1953. Since the centrifuge project was top secret the Soviets did not challenge any of Zippe's claims at the time. | https://en.wikipedia.org/wiki?curid=22685481 |
Concurrent tandem catalysis (CTC) is a technique in chemistry where multiple catalysts (usually two) produce a product otherwise not accessible by a single catalyst. It is usually practiced as homogeneous catalysis. Scheme 1 illustrates this process. Molecule A enters this catalytic system to produce the comonomer, B, which along with A enters the next catalytic process to produce the final product, P. This one-pot approach can decrease product loss from isolation or purification of intermediates. Reactions with relatively unstable products can be generated as intermediates because they are only transient species and are immediately used in a consecutive reaction. The major advantage of using CTC is it requires a single molecule; however, the required reaction conditions and catalyst compatibility are major hurdles. The system must be thoroughly studied to find the optimal conditions for both the catalysis and reactant to produce the desired product. Occasionally, a trade-off must be made between several competing effects. The desire of getting better yields and selectivity is of interest to many in academia and the industry. In this one-pot system, intermediate purification is unnecessary, so the risk of unwanted products and side reactions are more probable. Matching compatible catalysts would eliminate the likelihood of a catalyst starving or saturating the system, which may cause the catalyst to decompose or generate unwanted side reactions | https://en.wikipedia.org/wiki?curid=22686225 |
Concurrent tandem catalysis If side products were to be generated, it may be capable of interfering with the catalytic system. Thus in-depth knowledge is required of the mechanistic characteristics of both catalytic processes and the activity of the catalysts. Kinetic measurements are a crucial instrument in the development of CTC processes. One of the simplest and most thoroughly studied polymers arises from the polymerization of ethylene. Linear low-density polyethylene, LLDPE, is of industrial importance and is currently produced on the macro- scale; millions of tons per year. Branching of polyethylene involves the oligomerization of ethylene into alpha-olefins, carried out by one catalyst, followed by ethylene polymerization using the α-olefins as co-monomer, carried out by a second catalyst. This system suffers in practice. Electrophilic boranes activate the chelated nickel catalyst to oligomerize ethylene into α-butylene. In the same pot a titanium catalyst polymerizes ethylene and the α-olefin to form LLDPE. The degree of branching was found to increase linearly with the increase in concentration of the nickel catalyst. Metathesis has been a powerful tool in the coupling of olefins for several decades. The ability to rearrange carbon-carbon double bonds has provided great utility in all aspects of organic chemistry. Cossy et al. report a simple synthesis to form substituted five and six membered lactones from the cross metathesis of an allylic or homoallylic alcohol and acrylic acid using a ruthenium based metathesis catalyst | https://en.wikipedia.org/wiki?curid=22686225 |
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