Preparation and Structure of Zinc Complexes of Cysteine Derivatives

Sodium bis(L-cysteinato)zincate(II) hexahydrate (1) and bis(0-ethvl-L-cysteinato)zinc(II) (2) have been prepared from respectively alkaline (pH > 1 1 ) and neutral aqueous solutions and their structures determined by X-ray structural analysis. N ,S-coordination of the Zn atoms with the formation of two five-membered chelate rings is observed for both com plexes. The deprotonated carboxylate groups in 1 do not coordinate the Zn atom. D ibrom o-bis(DL-penicillam ine)zinc(II) (3) and dibromo-bis(D-penicillamine)zinc(II) have been isolated from acid solu­ tions with a pH of 2. The penicillamine moieties which are present in the zwitterionic form HS — C(C H 3)2—C H (N H 3+) — C O O behave as monodentate ligands with the deprotonated car­ boxylate group as binding site. The role of solution pH in determining the binding properties of cysteine and penicillamine with zinc(II) is discussed.