Solvents effects on organisms

Applications to solvent effects on organic equilibria and reactions, J. Phys. Chem. B 102 1787(1998). 

In recent years there have been many studies of organic reactions in cavities that exist in crystalline materials such as zeolites or in large macrocycles such as cyclodextrins. The relationship between the structure of these cavities, their microscopic environments, and the rates and products of organic reactions may be characterized in much the same way as solvent effects on organic reactivity. Murray Rosenberg and Udo Brinker summarize here what has been learned about the mechanism for formation and reaction of carbenes within cyclodextrins and zeolites. 

Acevedo, O., Jorgensen, W.L. Solvent effects on organic reactions from QM/MM simulations. Annu. Rep. Comput. Chem. 2006, 2, 263-78. 

Kaminski, G.A., Jorgensen, W.L. A quantum mechanical and molecular mechanical method based on CMIA charges Applications to solvent effects on organic equilibria and reactions. J. Phys. Chem. B 1998,102(10), 1787-96. 

Solvents exert their influence on organic reactions through a complicated mixture of all possible types of noncovalent interactions. Chemists have tried to unravel this entanglement and, ideally, want to assess the relative importance of all interactions separately. In a typical approach, a property of a reaction (e.g. its rate or selectivity) is measured in a laige number of different solvents. All these solvents have unique characteristics, quantified by their physical properties (i.e. refractive index, dielectric constant) or empirical parameters (e.g. ET(30)-value, AN). Linear correlations between a reaction property and one or more of these solvent properties (Linear Free Energy Relationships - LFER) reveal which noncovalent interactions are of major importance. The major drawback of this approach lies in the fact that the solvent parameters are often not independent. Alternatively, theoretical models and computer simulations can provide valuable information. Both methods have been applied successfully in studies of the solvent effects on Diels-Alder reactions. 

Solvent effects on chemical equilibria and reactions have been an important issue in physical organic chemistry. Several empirical relationships have been proposed to characterize systematically the various types of properties in protic and aprotic solvents. One of the simplest models is the continuum reaction field characterized by the dielectric constant, e, of the solvent, which is still widely used. Taft and coworkers [30] presented more sophisticated solvent parameters that can take solute-solvent hydrogen bonding and polarity into account. Although this parameter has been successfully applied to rationalize experimentally observed solvent effects, it seems still far from satisfactory to interpret solvent effects on the basis of microscopic infomation of the solute-solvent interaction and solvation free energy. 

In the following text, examples of solvent effects on enzyme selectivity, referred either to systems based (i) on water-miscible organic cosolvents added to aqueous buffers or (ii) on organic media with low water activity, are discussed. 

A brief discussion of the systematics of solvent effects on the p/, pr, and values of Tables II and III is presented in the discussion section. However, it is worthy of note here that sets 7, 37, 38, 39, 40, and 41, which involve nonhydroxylic solvents, are fitted with comparable precision to that for reaction series in aqueous or mixed aqueous organic solvents. The present analysis does not support the previous assignment (7b) of ion-pair formation of benzoic acids... 

Resources, Conservation Recycling 23,Nos.l-2, 1998,p.47-56 ORGANIC SOLVENT EFFECTS ON WASTE PLASTICS-LIGNITE COLIQUEFACTION... 

Since around 1950, in studies of solvent effects for organic reactions, empirical solvent parameters have been used these parameters represent the capabilities of solvents for the solute-solvent interactions (especially Lewis acid-base interactions). Though the solute-solvent interactions should depend on the solute as well as on the solvent, the empirical solvent parameters are considered to be irrelevant to solutes in other words, the use of only these parameters enables us to evaluate the solvation energies. Strictly... 

Finally, in the sense that the imposition of conformational restrictions or specific solvent effects on an organic molecule are forms of strain, non-covalent catalysis by the cycloamyloses may provide a simple model for the investigation of strain and distortion effects in enzymatic reactions. 

The several theoretical and/or simulation methods developed for modelling the solvation phenomena can be applied to the treatment of solvent effects on chemical reactivity. A variety of systems - ranging from small molecules to very large ones, such as biomolecules [236-238], biological membranes [239] and polymers [240] -and problems - mechanism of organic reactions [25, 79, 223, 241-247], chemical reactions in supercritical fluids [216, 248-250], ultrafast spectroscopy [251-255], electrochemical processes [256, 257], proton transfer [74, 75, 231], electron transfer [76, 77, 104, 258-261], charge transfer reactions and complexes [262-264], molecular and ionic spectra and excited states [24, 265-268], solvent-induced polarizability [221, 269], reaction dynamics [28, 78, 270-276], isomerization [110, 277-279], tautomeric equilibrium [280-282], conformational changes [283], dissociation reactions [199, 200, 227], stability [284] - have been treated by these techniques. Some of these... 

The activation of various reactions by Lewis acids is now an everyday practice in synthetic organic chemistry. In contrast, solvent effects on Lewis acid catalysed Diels-Alder reactions have received much less attention. A change in the solvent can affect the association step leading to the transition structure. Ab initio calculations on the Diels-Alder reaction of cyclopentadiene and methyl vinyl ketone in aqueous media showed that there is a complex of the reactants which also involves one water molecule119. In an extreme case solvents can even impede catalysis120. The use of inert solvents such as dichloromethane and chloroform for synthetic applications of Lewis acid catalysed Diels-Alder reactions is thus well justified. General solvent effects, in particular those of water, will be discussed in the following section. 

The dissociation constant of an analyte can be calculated mathematically from Hammet s equation.27 The organic solvent effect on the pA a has also been examined 26... 

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