The first solvation shell of magnesium and calcium ions in a model nucleic acid environment: an ab initio study.

The interaction of organophosphate anions with divalent metal ions is central to many biological catalytic events. While experimental structural studies can give insight into the likely geometries that can be adopted, quantum mechanics allows for a more complete exploration of the competing forms. Ab initio quantum mechanical calculations have been performed on a series of complexes comprised of dimethyl phosphate, a divalent metal ion (either Mg(II) or Ca(II)) and water of hydration. An additional series of complexes were studied that included a Cl(I) ion to provide for charge neutrality. The most stable orientation of the hydrated metal ion complexed with the phosphate anion occurs when the metal ion is in a unidentate, rather than bidentate, orientation. The question of whether the divalent metal ion is located in the phosphinyl (-PO2(-)-) plane depends on the identity of the divalent metal ion and on the charge state of the complex.