Molecular mechanics and semiempirical molecular orbital calculations on zinc complexes with amino acid derivatives

Geometry optimisation calculations using semiempirical molecular orbital and molecular mechanics methods on tetrahedral zinc complexes with derivatives of the amino acids cysteine, histidine and glutamic acid have been performed. Charge interaction terms, based on a semiempirical calculation of partial atomic charges, are found to dominate the molecular mechanical steric energy. Geometries optimised by molecular mechanics show better agreement with crystallographic results than do those obtained by the modified neglect of differential overlap method. The final steric energy values show a large variation between the complexes of the derivatives of cysteine, histidine and glutamic acid.