An ab initio study of the effect of the 3d orbitals of phosphorus on the properties of the phosphate group

A large number of properties of the dimethylphosphate anion (DMP^?), model system for the phosphate group of the nucleic acids and the phospholipid components of membranes, has been investigated by the SCF ab initio procedure including the 3d orbitals of the phosphorus atom in the gaussian basis set and the results of the computations were compared with similar results obtained previously without taking these orbitals into account. The properties investigated include the conformational states of DMP with respect to the torsion about the P-O_ester bonds, the distribution of the electronic charges, the molecular electrostatic potentials generated by DMP^?, the characteristics of the molecular orbitals, particularly the electronic isodensity maps, the hydration scheme. Qualitatively, the introduction of the 3d orbitals modifies little the general aspects of the results obtained for most of the properties studied. On the quantitative level significant, although generally not great, modifications may be noticed with respect to some features of these properties. One of the strongest influences of the introduction of the 3d orbitals concerns the decrease of the net electronic charges in DMP^?.