Formation of Copper(II)-Wool Keratin Complexes

The effect of the binding of Cu(II) ions on the dissociation of the side chain carboxyl groups in wool keratin has been measured using a modified Bjerrum's method. Data taken at various ionic strengths indicate that in the presence of much NaNO 3 , the formation curves fall on the same curve regardless of Cu(II) ion concentration, and the stability constants b 1 and b 2 decrease with increasing NaNO 3 concentration. This phenomenon might be due to the fact that complexing reactions become increasingly difficult because of the screening effect of NaNO 3 . The variation of the value of b 2 was more significant than that of b 1 , confirming that the increase of the ratio of the concentrations of Cu(II) to glutamyl and aspartyl residues ( T Cu / T HL ) and of the NaNO 3 concentration resulted in an increase in the fraction of CuL 2 species.