Identification of Binding Sites in Copper(II)-Peptide Complexes Using Infrared Spectroscopy

Complex formation of the copper(II) ion (Cu^II) with histidine (H) and H-containing peptides plays a crucial role in various metallo-enzymatic reactions. To elucidate the nature of coordinate bonding in Cu^II complexes, Fourier-transform infrared spectroscopy and 2D IR spectroscopy were employed to investigate the coordination geometries of Cu^II with diglycine, l-histidylglycine (HG), glycyl-l-histidine (GH), and glycylglycyl-l-histidine. The coordination of Cu^II to different peptide groups, including the peptide N- and C-termini, the amide group, and the imidazole of the H side chain, exhibits distinct spectral features. The derived molecular structure of the Cu^II-HG complex based on these spectral features significantly differs from that of Cu^II-GH, suggesting a preference of the N-terminus and the steric hindrance of the H side chain in Cu^II chelation.