St. Arroyo et al., Study of the N-H center dot center dot center dot O=C proton transfer reaction in aqueous solution using classical free energy curves, CHEM PHYS, 265(2), 2001, pp. 207-215
The classical free energy surfaces of the reactive and product states invol
ved in the proton transfer reaction of the N-H . . . O=C molecular associat
ion in aqueous solution were obtained by means of molecular dynamics simula
tions using ab initio MP2-CP potentials. The values of the reaction free en
ergy (DeltaG = -1.53 kJ mol(-1), which is opposed to the non-spontaneous ch
aracter of the reaction in the gas phase) and the rate constant (k(TST) = 7
.92 x 10(11) s(-1)) of the process show the viability of this proton transf
er in aqueous medium. The change in spontaneity due to the surrounding wate
r reflects a major redistribution of the solvent (DeltaG(r) = 14.18 kJ mol(
-1)), which leads to a decrease of the energy barrier to a value of DeltaG(
#) = 5.05 kJ mol(-1). Also, the higher solvent force constant and solvent f
requency derived from the free energy curve associated with the non-transfe
rred proton system (k(R) = 4.01 x 10(-4) cm and v(R) = 10.13 ps(-1)) reflec
t a weakening of the water-water interactions when the solute has the trans
ferred proton. (C) 2001 Elsevier Science B.V. All rights reserved.