Co-ordination abilities of thioamide analogues of amino acids and peptides. Copper(II) and nickel (II) complexes

Abstract

Potentiometric and spectroscopic results for CuII and NiII complexes with leucine-N-methylamide, methionine-N-methylamide, their thiocarbonyl analogues, and for (phenylalanyl)methionine-N-methylamide are reported. For solubility reasons only spectroscopic results in ethanol solutions are presented for CuII complexes with the last of these. Thiocarbonyl was found to be much more effective in metal ion binding than carbonyl donor and the complexes formed with metal–sulphur bonds are several orders of magnitude more stable than the respective species with carbonyl binding. The sulphur donation, however, does not prevent thioamide nitrogen deprotonation and co-ordination at high pH.