Density Functional Theory studies on interactions of phosphoryl ligands with the Ca2+ cation: Affinity and associated parameters

DFT (B3LYP/6-31G(d)) and semi-empirical (PM6) calculations of Ca2+ affinities on a set of substituted phosphoryl ligands were performed with complete geometry optimization. Two types of ligands were calculated: a set of trivalent [OP(R)] and a set of pentavalent [OP(R)3] ones (R = H, F, Cl, Br, OH, OCH3, CH3, CN, NH2 and NO2), with R either directly bound to the phosphorus atom or to the para position of a phenyl ring. The affinity of the Ca2+ cation for the ligands was quantified in terms of interaction energy. Additionally, geometric and electronic parameters were correlated with the intensity of that interaction. Our results show that the electronic nature of the substituent mainly affects the interaction energy. Donor groups are associated with more negative interaction energies, while acceptor groups are associated with less negative interaction energies.