Molecular Dynamics Simulation of the Effect of Hydrophobic Cosolutes on the Neutral Hydrolysis of an Activated Ester
2004; American Chemical Society; Volume: 108; Issue: 17 Linguagem: Inglês
10.1021/jp037120o
ISSN1520-6106
AutoresTheo Rispens, Marc F. Lensink, Herman J. C. Berendsen, Jan B. F. N. Engberts,
Tópico(s)Chemical Reaction Mechanisms
ResumoWe have studied, by means of molecular dynamics (MD) simulations, the effect of two hydrophobic cosolutes, tert-butanol (t-BuOH) and ethanol (EtOH), on the neutral hydrolysis of p-methoxyphenyl dichloroacetate (MPDA) in water. Shifts were calculated in a pre-equilibrium, defined as a spatial distribution of the reacting molecules satisfying specific geometric constraints. The criteria applied represent the configurations from which the reaction can take place (reactive conformation, RC). The shifts induced by the presence of cosolute, as determined from the simulations, correspond well to the experimentally found rate retardations. In accord with experiments, an almost linear correlation between the concentration of added cosolute and the logarithm of the rate constant was found. This is in agreement with a simple mechanistic model. The percentage of RCs in pure water was calculated to be ∼15%, complementing earlier work performed in this group (Lensink, M. F.; Mavri, J.; Berendsen, H. J. C. J. Comput. Chem. 1999, 20, 886), leading to a calculated rate constant of kcalc = 3.9 × 10-3 s-1 (exptl: kobs = 2.78 × 10-3 s-1). The molecular structure of the RC was examined more extensively, investigating correlations between the positions of participating molecules.
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