Ab initio studies on organophosphorus compounds. Part 3. Cationic calcium binding to phosphonate and phosphinate monoanions and their sulfur analogues

Abstract

Interactions between cationic calcium and 18 organophosphorus compounds, containing different numbers of oxygen and sulfur atoms, have been studied systematically. All the molecular backbones studied were of the phosphonate or phosphinate type. Molecular structures and calcium orientations through space were calculated by ab initio molecular orbital methods with the 3-21G (*) basis set. Different calcium binding sites were found for each molecule. The energetics of the calcium orientations were compared. The results give a quantum chemical reference for experimental studies of many phosphorus-containing biological systems inside living organisms, in which calcium(II) regulates cell functions. Examples of such systems are the bisphosphonate–osteoclast interactions in osteolytic bone diseases.