Quantum-chemical and empirical calculations on phospholipids, III. Hydration of the dimethylphosphate anion

The binding of water to the dimethylphosphate anion (DMP-) was calculated using the PCILO method. We found binding energies of 25.95 kcal-mol-1 in the O1-P-O3 plane bridgeing the anionic oxygen atoms and 19.3 kacl-mol-1 for the one-site association of a water molecule to an anionic oxygen atom of DMP-. In this range on water molecule added to DMP- in the O1...O3 bridged configuration has a significantly higher binding energy to DMP- than water molecules added to other binding sites. The total binding energy of 5 water molecules to DMP- is 92 kcal-mol-1, a quantity which is about 10% less than the sum of the binding energies of the corresponding monohydrates.