Thermodynamic origin of the increased rate of hydrolysis of phosphate and phosphorothioate esters in DMSO/water mixtures.

ABSTRACT: The hydrolysis rates of the dianions of phosphate and phosphorothioate esters are substantially accelerated by the addition of polar aprotic solvents such as DMSO and acetonitrile. The activation barrier DeltaG is smaller due to a lower enthalpy of activation. The enthalpy of transfer of p-nitrophenyl phosphate (pNPP) and p-nitrophenyl phosphorothioate (pNPPT), from water to 0.6 (mol) aq DMSO (60 mol % water in DMSO) were measured calorimetrically. The enthalpies of activation for the hydrolysis reactions in the two solvents permitted the calculation of the enthalpy of transfer of the transition states. This transfer is thermodynamically favorable for both the reactants and the transition states but is more favorable for the transition states. In the case of pNPP, the enthalpy of transfer

SUBMITTER: Sorensen-Stowell K 

PROVIDER: S-EPMC2519604 | biostudies-literature | 2006 Sep

REPOSITORIES: biostudies-literature