Potentiometric and spectroscopic studies on copper(II) complexes of non-proteinogenic histidine analogues.

Copper(II) complexes of the histidine analogues: ?-(2-pyridyl)-dl-alanine, ?-(2-thienyl)-dl-alanine, ?-(1,2,4-triazol-1-yl)-dl-alanine, ?-(2-thiazolyl)-dl-alanine ligands, and for comparison ?-(2-thienyl)glycine and 2-(2-aminoethyl)pyridine, were studied by potentiometric, UV-VIS, EPR and thermogravimetric techniques. The amino acid residues of the ligands were described as the main binding sites forming mono- and bis-(ligand) complexes, but the interaction between aromatic triazolyl and pyridyl nitrogen atoms and the copper(II) ion also was detected in the case of ?-(1,2,4-triazol-1-yl)-dl-alanine and ?-(2-pyridyl)-dl-alanine. The presence of heteroaromatic rings in the amino acid analogues influences the amino acid like coordination mode in the order imidazole > pyridyl ~ triazolyl > thiazolyl ~ thienyl rings.