Microsolvation of dimethylphosphate: a molecular model for the interaction of cell membranes with water

We present an exhaustive stochastic search of the quantum conformational spaces of the (CH3O)(2)PO2- + nH(2)O (n = 1,2,3) systems. We uncover structural, conformational and energetic features of the problem. As in the isolated species, clusters containing the gauche-gauche (gg) conformation of dimethylphosphate (DMP-) are energetically preferred, however, contributions from hydrated gauche-anti (ga) and anti-anti (aa) monomers cannot be neglected because such structures are quite common and because they are close in energy to those containing the gg monomer. At least seven distinct types of O center dot center dot center dot H-O-H contacts lead to DMP- <-> water interactions that are always stabilizing, but not strong enough to induce significant changes in the geometries of either DMP- or water units. Our results lead us to postulate DMP- to be a suitable model to study explicit and detailed aspects of microsolvation of cell membranes.