Penta-glycine copper(II) complexes in slightly alkaline solutions

The kinetics of the reaction of Cu^II(GGG), Cu^II(GGGGG) and Cu^II(GGGGS), where G = glycine and S = sarcosine, with 4-nitrophenyl-acetate were measured. The results point out that at pH 9.0 hydroxide is an axial, or equatorial ligand to a significant amount of these complexes. The source of the different mechanisms of reaction of the analogous nickel complexes is attributed to the axial water ligand of the copper complexes. The biological implications of axial hydroxide binding to copper peptides is discussed.