Theoretical studies solvation reactions

In contrast, the hairpin ribozyme (HPR) [107, 108], which catalyzes the reversible, site-specific phosphodiester bond cleavage of an RNA substrate, is unique in that the chemical steps of the reaction do not require involvement of a divalent metal ion [107-111]. This lack of an explicit metal ion requirement [112] makes the hairpin ribozyme an ideal target for theoretical studies aimed to characterize the contribution of generalized solvation provided by the solvated ribozyme on catalysis. 

Hu and Truhlar have recently reported a modeling transition state solvation at a single-water representation [295]. Recent experimental advances leading to the study of SN2 reactions of gas-phase microsolvated clusters which can advantageously been studied with ab initio electronic theory. These experiments and theoretical studies are quite relevant to chemical reactions in supercritical water. 

Tapia, O., Lluch, J. M., Cardenas, R. and Andres, J. Theoretical study of solvation effects in chemical reactions. A combined quantum chemical/Monte Carlo study ofthe Meyer-Schuster reaction mechanism in water, J. Am. Chem.Soc., Ill (1989), 829-835... 

Theoretical studies of the ester enolate-imine reaction <98MI1826>, the effects of solvation on barriers of reaction <99JPC8628>, interactions of P-lactams in aqueous solution <99MI1401> and their ammonolysis and aminolysis <99JOC3281,99MI1045> are available. 

Theoretical Study of Electron Transfer Reactions of Solvated Electrons... 

Both experimental and theoretical studies have been reported of fluoro-denitration and fluoro-dechlorination reactions using anhydrous tetrabutylammonium fluoride in DMSO. The absences of ion pairing and strong solvation are critical in contributing to the reactivity of the fluorinating agent24 Quaternary ammonium salts derived from cinchona alkaloids have been shown to be effective catalysts in an improved asymmetric substitution reaction of /1-dicarbonyl compounds with activated fluoroarenes. The products may be functionalized to yield spiro-oxindoles.25... 

Our book is about the emerging field of Superelectrophiles and Their Reactions. It deals first with the differentiation of usual electrophiles from superelectrophiles, which show substantially increased reactivity. Ways to increase electrophilic strength, the classification into gitionic, vicinal, and distonic superelectrophiles, as well as the differentiation of superelec-trophilic solvation from involvement of de facto dicationic doubly electron deficient intermediates are discussed. Methods of study including substituent and solvent effects as well as the role of electrophilic solvation in chemical reactions as studied by kinetic investigations, spectroscopic and gas-phase studies, and theoretical calculations are subsequently reviewed. Subsequently, studied superelectrophilic systems and their reactions are discussed with specific emphasis on involved gitionic, vicinal, and distonic superelectrophiles. A brief consideration of the significance of superelectrophilic chemistry and its future outlook concludes this book. 

The mechanism of the addition of aldehydes and ketones to group 14 dimetallenes has been examined through a theoretical study. It was found that for reactions in which a Si-O bond is formed, both diradical and zwitterionic intermediates are possible. However, the presence of diradical intermediates was not found for Ge-O bond-forming reactions. Solvation simulations were performed to examine the effect of solvent polarity on the reaction energetics <2002JA13306>. 

M. Seth, H. M. Senn and T. Ziegler, The influence of solvation and finite temperatures on the Wittig reaction A theoretical study, J. Phys. Chem. A, 109 (2005) 5136-5143. 

It is an open question as to which is simpler for theoretical study—reactions in gas phase where wall effects can complicate the situation or reactions in solution where solvation may be an important factor. 

In conclusion, these gas-phase measurements provide new elues to the role of solvation in ion-moleeule reaetions. For the first time, it is possible to study intrinsie reactivities and the extent to which the properties of gas-phase ion-moleeule reaetions relate to those of the eorresponding reactions in solution. It is clear, however, that gas-phase solvated-ion/moleeule reaetions in which solvent moleeules are transferred into the intermediate elusters by the nucleophile cannot be exaet duplieates of solvated-ion/ molecule reactions in solution in which solvated reactants exchange solvent molecules with the surrounding bulk solvent [743]. For a selection of more recent experimental [772] and theoretical studies of Sn2 reactions in gas phase and solution by classical trajectory simulations [773], molecular dynamics simulations [774, 775], ab initio molecular orbital calculations [776, 777], and density functional theory calculations [778, 779], see the references given. For studies of reactions other than Sn2 ion-molecule processes in the gas phase and in solution, see reviews [780, 781]. 

Recent studies have suggested that coordination with a lithium cation may be responsible for the stereochemical outcome in Meyers-type enolate alkylations . In fact, the hypothesis that the diastereofacial selectivity observed in these reactions might result from specific interactions with a solvated lithium cation was already proposed in 1990 . Nevertheless, the potential influence exerted by solvation and lithium cation coordination was not supported by a series of experimental results reported by Romo and Meyers , who stated that it would appear that neither the aggregation state of the enolate nor the coordination sphere about lithium plays a major role in the observed selectivity. This contention is further supported by recent theoretical studies of Ando , who carried out a detailed analysis of the potential influence of solvated lithium cation on the stereoselective alkylation of enolates of y-butyrolactones. The results showed conclusively that complexation with lithium cation had a negligible effect on the relative stability of the transition states leading to exo and endo addition. The stereochemical outcome in the alkylation of y -butyrolactones is determined by the different torsional strain in the endo and exo TSs. 

A theoretical study based on MP2/6-31+G(d,p) and HF/6-31G(d) ab initio quantum mechanical calculations coupled with Langevin dipoles (LD) and polarised continuum (PCM) solvation models have been carried out by Florian and Warshel [387] to achieve a first systematic study of the free energy surfaces for the hydrolysis of methylphosphate in aqueous solution. The important biological implication of this work is the fact that since the energetics of both the associative and the dissociative mechanics are not too different, the active sites of enzymes can select either mechanism depending on the particular electrostatic environment. This conclusion basically means that both mechanisms should be considered, and this fact seems to contradict some previous studies which have focused on phosphoryl transfer reactions. 

Theoretical calculations by Siegbahn and Crabtree [4] found the barrier for the reaction via the [PP (R)(H)] intermediate to be a little lower in energy compared with a one-step mechanism, while a study by Hill and Puddephatt favors type interactions [5]. The most recent theoretical study was conducted by Hush and co-workers using density functional theory (B3LYP functional) calculations with double-f to polarized double- basis sets [6]. They also studied solvation effects by a dielectric continuum method. 

Moliner, V., Castillo, R., Safont, V. S., Oliva, M., Bohn, S., Tunon, I., Andres, J. A theoretical study of the Favorskii rearrangement, calculation of gas-phase reaction paths and solvation effects on the molecular mechanism for the transposition of the a-chlorocyclobutanone. J. Am. Chem. Soc. 1997,119,1941-1947. 

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