Zinc complexation of cyclic dipeptides containing cysteine and/or histidine

摘要

the cyclic dipeptides c-HisHis, c-GlyCys, c-HisCys and c-CysCys were prepared in an analytically pure form. Potentiometric titrations in the presence of zinc nitrate showed that they all form a species of composition ZnL in solution, which in case of c-CysCys is dimeric. Except for c-CysCys they also form the complex ZnL_2, which in case of c-GlyCys is poymeric. Contrary to the expectation the preorganization of the peptide donors does not enhance the complex stabilities in comparison to those of the non-cyclic peptides. Preparative reactions have yielded the compounds Zn(c-HisHis)Cl_2, Zn(c-GlyCys)_2, Zn(c-GlyCys)_2 centre dot neocuproin, Zn_2(c-HisCys)_3I, and Zn(c-CysCys)(N-methylimidazole)_2.