Absorption and circular dichroism spectra of CuCl 2 complexed with poly(S‐carboxymethyl‐ L ‐cysteine) and poly(S‐carboxyethyl‐ L ‐cysteine)

The interaction of CuCl 2 with poly(S‐carboxymethyl‐ L ‐cysteine) (poly[Cys(CH 2 COOH)]) and poly(S‐carboxyethyl‐ L ‐cysteine) (poly[Cys(C 2 H 4 COOH)]) were studied by absorption spectra and circular dichroism (CD). On mixing CuCl 2 with polypeptide solutions, absorption bands appeared at 320–325 nm in both polypeptides, and at 255–260 nm in the case of poly[Cys(CH 2 COOH)]. A stable bound species was formed in the case of poly[Cys(CH 2 COOH)], since the apparent molar absorption coefficient of the bound species did not depend on the mixing ratio. From the absorption data, it was inferred that Cu 2+ ions were complexed with the side chains, most probably with sulfur atoms and carboxyl groups. Induced optical activities were observed for the two polypeptides. The CD spectra of poly[Cys(CH 2 COOH)] + CuCl 2 gave simpler aspects than those of poly[Cys(C 2 H 4 COOH)] + CuCl 2 .