Donor-Bridge-Acceptor Proton Transfer in Aqueous Solution.

We use ab initio molecular dynamics to study proton transfer in a donor-bridge-acceptor system in which the bridge is a single water molecule and the entire system is embedded in aqueous solution. The results, based on a large number of proton transfer trajectories, demonstrate that the dominant charge-transfer pathway is a subpicosecond "through bridge" event in which the bridge adopts an Eigen-like (hydronium) structure. We also identify another state in which the bridge forms a Zundel-like configuration with the acceptor that appears to be a dead end for the charge transfer.

Moderately strong phenols dissociate by forming an ion-pair kinetic intermediate.

We show computational evidence that ground-state moderately strong hydroxyarenes (Ar-OH, pKa ∼ 0) dissociate by forming an ion-pair intermediate that lives for 3-5 ps. The concentration of this intermediate is approximately 2 times smaller than that of the un-ionized acid at pH ∼ 0.6 and is characterized by average C-O bond lengths (1.

Concerted and Sequential Proton Transfer Mechanisms in Water-Separated Acid-Base Encounter Pairs.

The proton transfer mechanisms involved inside aqueous, solvent-separated encounter complexes between phenol and carboxyl moieties are studied using ab initio molecular dynamics and computational time-resolved vibrational spectroscopy. This model framework can be viewed as a ground-state analog of the excited-state proton transfer reactions that have been actively investigated using ultrafast spectroscopy. Three qualitatively distinct proton transfer pathways are observed in the simulations.

A computational study of ultrafast acid dissociation and acid-base neutralization reactions. I. The model.

Ultrafast, time-resolved investigations of acid-base neutralization reactions have recently been performed using systems containing the photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and various Bronsted bases. Two conflicting neutralization mechanisms have been formulated by Mohammed et al. [Science 310, 83 (2005)] and Siwick et al.