Theoretical studies of metal complexes of anhydrotetracycline:: interaction with ZnII

A quantum mechanical semiempirical study (AML) of the interaction of anhydrotetracycline (AHTC) with zinc(II) has been reported. All possible complexation sites were examined and structures of complexes containing two and four water molecules were fully optimized. The solvent effect was included using macroscopic dielectric models for calculating solvation energies in aqueous solution. It was predicted that the four-co-ordinated complexes are favored in solution and the six-co-ordinated complexes are predominant in the gas phase. Comparison with recent experimental investigations, conducted in aqueous solution, is made. The theoretical results agree well with the sparse experimental information that is available on the molecular structure of the Zn-II-AHTC complex, allowing predictions to be made on the structures of related complexes not yet determined.