Mixed Ligand Copper(II) Complexes of Amino Acids and Related Compounds with Possible Ligand-Ligand Interactions

Ternary systems composed of copper(II) and two ligands, each with an oppositely charged uncoordinated group in the side chain, have been investigated by synthetic and spectral methods. The absorption and circular dichroism(CD) spectra in the d-d region were measured at various pH values for the binary and ternary systems, Cu(B)2 and Cu(A)(B), where A refers to ethylenediamine-N-monoacetic acid(EDMA), glycylglycine(Gly·Gly), glycyl-β-alanine(Gly·β-Ala), ethylenediamine(en), or glycine(Gly), and B to d- and l-arginine (d- and l-Arg), l-ornithine(l-Orn), l-lysine(l-Lys), l-alanine(l-Ala), or l-valine(l-Val), and the following complexes containing ligands with polar side chains were isolated as crystals: [Cu(EDMA)(l-Arg)]C1O4·H2O; [Cu(EDMA)(l-Orn)]ClO4·1/2H2O; [Cu(EDMA)(l-Lys)]ClO4; [Cu(Gly·Gly) (l-Arg)]·3/2H2O. From comparison of the CD magnitudes expressed in terms of the relative magnitude which assumes half the value for Cu(B)2 as unity, the magnitude enhancements observed for the systems Cu(EDMA)(d- and l-Arg), Cu(EDMA)(l-Orn), Cu(EDMA)-(l-Lys), and Cu(Gly·β-Ala)(d- and l-Arg) in water and in 50% aqueous ethanol have been inferred to be due to the intramolecular electrostatic interactions between the charged groups in the side chains of ligands A and B.