Comparative binding energetics of Mg2+, Ca2+, Zn2+, and Cd2+ to biologically relevant ligands: Combined ab initio SCF supermolecule and molecular mechanics investigation

A combined ab initio SCF supermolecule and molecular mechanics investigation is carried out on the binding energetics of the divalent cations Mg²⁺, Ca²⁺, Zn²⁺, and Cd²⁺ to a series of the most common ligand functional groups found in biomolecules. The SCF binding energy components are resolved using the restricted variational space method.¹ The results show that the SIBFA molecular mechanics (SMM) procedure² reproduces the ab initio binding energies and total energy variations as a function of intermolecular variables. The model also reproduces the selectivity energetics for exchange reactions. Thus, the SMM procedure can be used without reparametrization to describe the coordination energetics of complex molecules including those subject to coordination changes. The energetic properties of divalent cation-hexahydrate complexes are compared as examples of a complete, realistic coordination system. The hexahydrates exhibit strong nonadditive effects typical of dication coordination. Nevertheless, these energetics are satisfactorily reproduced by the SMM procedure. © 1996 John Wiley & Sons, Inc.