Synthesis and structural analysis of copper(II) cysteine complexes

This report describes the synthesis and structural analysis of stable copper(II) cysteine complexes. Pale pink copper(II) cysteine complexes were synthesized in mole ratios of 1:2, 1:4, and 1:6 of copper(II):cysteine in ethanol. Infrared spectroscopy and X-ray absorption spectroscopy confirmed that copper(II) binding occurred via the thiol ligand of cysteine. XANES analysis showed that the oxidation state of copper remained as copper(II) and the local atomic geometry was similar in all of the cysteine complexes. The EXAFS data indicate that the copper(II) cysteine complexes are forming ring type structures with sulfur ligands from the cysteines acting as bridging ligands. X-ray diffraction revealed that the copper(II) cysteine complexes formed monoclinic cells with maximum crystallinity found in the 1:4 copper(II):cysteine complex.

Graphical abstractCopper(II) reacted with 2 mole equivalents of cysteine revealed a coordination of three sulfur atoms in the first shell at approximately 2.28 Å indicating that the copper is present as copper(II). In addition, an interaction between copper and copper atoms was observed at 2.61 Å, indicating that the sulfur ligands are bridging ligands.Figure optionsDownload full-size imageDownload as PowerPoint slide