Abstract: | The effects of eight divalent metal ions on fully neutralized poly(S-carboxyethyl-l-cysteine) have been studied by means of circular dichroism. Four ionic species (Cd2+, Cu2+, Zn2+ and Ni2+) effectively induce the β-form, while the other four species (Co2+, Ba2+, Ca2+ and Mg2+) are not effective. Specifically, Mg(ClO4)2 is ineffective, even at 1.86 m. The effect of Cu2+ ions on the polypeptide conformation is significant at pH values other than in the neural range. Comparison of the present results with previous ones from the lower side chain homologue, poly(S-carboxymethyl-l-cysteine), shows that Cd2+ and Zn2+ ions are more effetive but Co2+ ions are much less effective in the polypeptide studied here. Random coils of poly(S-carboxyethyl-l-cysteine) are more soluble while the β-form is less soluble compared with the respective conformations of the lower side-chain homologue. |