Solvent research

By using a mixture of ethyl acetate and D2O as solvent for hydrogenation, up to 75% deuterium is incorporated in the reduced product.13 This result indicates that the role of water here is not only as a solvent. Research on asymmetric hydrogenation in an aqueous medium is still actively being pursued. The method has been applied extensively in the synthesis of various amino acid derivatives.14... 

The use of a deuterium tracer in this research makes it possible to obtain new information regarding the reactions involved in the formation of these compounds. Since reactions of this type result in a loss of hydrogen donor capability of the solvent, research in this area is important to improve the efficiency of coal hydroliquefaction and the recycleability of the solvent. 

In the material that follows we describe high solvent use areas. It will be these areas where green solvent research and solvent substitution will have the greatest impact... 

While by far the greater portion of the electrochemical studies on solutions have been made using water as solvent, researches have also been carried out in which the water has been replaced by other solvents, or mixtures of non-aqueous solvents with water. Until very recently such studies yielded little of value because of their scattered nature and, usually, lack of accuracy, to which was added a lack of an adequate theory for their interpretation. It will be shown in the following chapter that some headway has been made in the, difficult field of study of the thermodynamic properties of such solutions of electrolytes. The Debye-Hiickel theory is, if anything, more valuable in the interpretation of the results in this field than in that of aqueous solutions. 

Although the aforementioned methods are generally applicable for the incorporation of group 10 metals into metal-acetylide polymers, these approaches could not be extended to metals from groups 8 and 9 due to the instability of the starting complexes in amine solvents. Research efforts into the molecular chemistry of hydrido-acetylide complexes of rhodium have resulted in a facile route to group 9 polymers 169 and This method involves... 

Intense efforts are being undertaken both to overcome detection limits and to increase the number of determinable compounds, also for the purpose of developing alternative analytical methods that are simpler, cheaper, and require less solvent. Researchers are currently experimenting new methods for purifying samples and new extraction systems specially tailored to the bee s body that rely on techniques such as gel permeation [68] and solid phase extraction. A particular focus is placed on the study of enzymatic and immunoenzymatic assays for classes of compounds these methods may allow samples to be passed through a fast prehminary qualitative screening and thus drastically reduce the number of analyses to be performed. 

In solvent research, dielectric constant has a special place as aparameter characteristic of solvent polarity. The dielectric constant, s, is used to calculate dipole moment, p. ... 

The book is aimed not only at the practitioner who is knowledgeable in the use of solvents and requires a one-stop source of reliable and up-to-date information, but also at the newcomer, for whom it provides an accessible review of major topics and a databank of key information, from which an initial selection of solvent can be made. The volume will be of interest to those engaged in solvents research, technical service and sales, and to operational chemists and engineers. Companies involved in formulating products which use or are based on solvents will find this an invaluable guide to current issues and products. The academic researcher will find much useful information in the range of solvents available and in the reviews of key issues. 

To separate approximately this contribution to A jj [Eq- (3.1)], the smdies of (mixed solvent)/(pure solvent) junctions [3] are rather informative. Under more or less ideal conditions (no hydrogen bonds, etc.), the dipole-dipole interactions at the boundary are expected to result in a linear dependence of A< s(,iy on the molar composition of the mixed solvent. Correspondingly, the same trend is expected for measurable emf s of the model cells with the above-mentioned junction, and it was really observed for usual aprotic solvents with not too low polarity. The quafitative models of smooth and stepped dipoles distributicai in the diffusion layer [3, 4] were suggested in relation to these experiments (see also discussion in review [2]). These models can be further improved if the molecular structure of the solvents is involved. The topic is surely under construction, as well as more bulky mixed solvent research. 

OPTS (Optim i/.ed Potentials for Liquid Simulations) is based on a force field developed by the research group of Bill Jorgensen now at Yale University and previously at Purdue University. Like AMBER, the OPLS force field is designed for calculations on proteins an d nucleic acids. It in troduces non bonded in leraclion parameters that have been carefully developed from extensive Monte Carlo liquid sim u lation s of small molecules. These n on-bonded interactions have been added to the bonding interactions of AMBER to produce a new force field that is expected to be better than AMBER at describing simulations w here the solvent isexplic-... 

Recrystallisation. The process of purification by recrystallisation is undoubtedly the most frequent operation in practical organic chemistry, and it is one which, when cleanly and efficiently performed, should give great pleasure to the chemist, particularly if the original crude material is in a very impure and filthy condition. Yet no operation is carried out so badly, wastefully (and thoughtlessly) by students in general, not only by elementary students, but often by research students of several years experience. The student who intends later to do advanced work must master the process, for unless he can choose a suitable solvent and then successfully recrystallise often minute quantities of material, he will frequently find his work completely arrested. 

A combination of the promoting effects of Lewis acids and water is a logical next step. However, to say the least, water has not been a very popular medium for Lewis-acid catalysed Diels-Alder reactions, which is not surprising since water molecules interact strongly with Lewis-acidic and the Lewis-basic atoms of the reacting system. In 1994, when the research described in this thesis was initiated, only one example of Lewis-acid catalysis of a Diels-Alder reaction in water was published Lubineau and co-workers employed lanthanide triflates as a catalyst for the Diels-Alder reaction of glyoxylate to a relatively unreactive diene . No comparison was made between the process in water and in organic solvents. 

The Dk parameter is based on the solvent effect, on the reaction of tetracyanoethylene with diazodiphenylmethane with benzene as a reference solvent. For details see Osbima, T. Arikata, S. Nagai, T. J. Chem. Research (S), 1981, 204... 

This thesis describes a study of catalysis of Diels-Alder reactions in water. No studies in this field had been reported at the start of the research, despite the well known beneficial effects of acpieous solvents as well as of Lewis-add catalysts on rate and endo-exo selectivity of Diels-Alder reactions in organic solvents. We envisaged that a combination of these two effects might well result in extremely large rate enhancements and improvements of the endo-exo selectivity. 

Over a decade of research, we were able to show that practically all conceivable carbocations could be prepared under what became known as stable ion conditions using various very strong acid systems (see discussion of superacids) and low nucleophilicity solvents (SO2, SO2CIF, SO2F2, etc.). A variety of precursors could be used under appropriate conditions, as shown, for example, in the preparation of the methylcyclopentyl cation. 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

YETI is a force held designed for the accurate representation of nonbonded interactions. It is most often used for modeling interactions between biomolecules and small substrate molecules. It is not designed for molecular geometry optimization so researchers often optimize the molecular geometry with some other force held, such as AMBER, then use YETI to model the docking process. Recent additions to YETI are support for metals and solvent effects. 

It is sometimes desirable to include the effect of the rest of the system, outside of the QM and MM regions. One way to do this is using periodic boundary conditions, as is done in liquid-state simulations. Some researchers have defined a potential that is intended to reproduce the effect of the bulk solvent. This solvent potential may be defined just for this type of calculation, or it may be a continuum solvation model as described in the next chapter. For solids, a set of point charges, called a Madelung potential, is often used. 

The primary problem with explicit solvent calculations is the significant amount of computer resources necessary. This may also require a significant amount of work for the researcher. One solution to this problem is to model the molecule of interest with quantum mechanics and the solvent with molecular mechanics as described in the previous chapter. Other ways to make the computational resource requirements tractable are to derive an analytic equation for the property of interest, use a group additivity method, or model the solvent as a continuum. 

Focuses on force field calculations for understanding the dynamic properties of proteins and nucleic acids. Provides a useful introduction to several computational techniques, including molecular mechanics minimization and molecular dynamics. Includes discussions of research involving structural changes and short time scale dynamics of these biomolecules, and the influence of solvent in these processes. 

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