Advances in QM/MM molecular dynamics simulations of chemical processes at aqueous interfaces

Abstract

We review recent studies carried out in our group on the modeling of aqueous interfaces using Molecular Dynamics simulations with a combined Quantum Mechanics and Molecular Mechanics force-field (QM/MM ). We first present the methodology and we comment on some ongoing developments. Since in the QM/MM approach the adsorbed molecule is described quantum mechanically, this computational scheme has allowed us to get insights on interface solvation effects on molecular properties. In particular, we have shown that polarization phenomena at the air–water interface may produce larger effects than polarization in bulk water. This finding contrasts with the usual assumption that polarity at liquid interfaces is close to the arithmetic average of the polarity of the two bulk phases, and that solvation effects at the air–water interface should be similar to the effects in a low polar solvent such as butyl ether. A summary of previous results is presented with some selected examples that are briefly discussed, and which include systems of atmospheric interest at the air–water interface, as well as systems of biological relevance at a water-organic interface. Then, we report some new results for a series of small volatile organic compounds at the air–water interface, namely methyl chloride, acetonitrile and methanol. These molecules share a similar structure but display quite different behaviors at the interface; the discussion focuses on the orientational dynamics and the solvation effects on reactivity indices. Finally, some conclusions and future directions in this exciting field are presented.