Induced Circular Dichroism of Benzyl Chromophores Bound to Helical Polypeptides

Extrinsic optical activity was observed for symmetric side chain chromophores in helical polypeptides. Poly-β-benzyl-l-aspartate, poly-β-p-nitrobenzyl-l-aspartate and poly-γ-p-nitrobenzyl-l-glutamate gave induced circular dichroism in the wavelength regions corresponding to the absorption bands of the benzyl and the p-nitrobenzyl chromophores of the side chains in their dilute solutions. Moreover, poly-γ-benzyl-d-glutamate gave induced circular dichroism due to the benzyl chromophore in its concentrated solutions which formed a liquid crystalline phase. The extrinsic optical activity thus observed was explained as the consequence of the loss of the rotational freedom of the chromophores relative to the α-helical structure and to the cholesteric helical structure of the polypeptides.