The calculated ultraviolet optical properties of poly- l-proline I and II

Abstract

Application of the current theory of optical activity of polymers to poly- l -proline I and poly- l -proline II reproduces the major features experimentally observed for these substances and allows a tentative assignment of the observed circular dichroism bands. In both structures, the π-π * amide absorption band is expected to be split into low energy and high energy branches, polarized parallel and perpendicular to the helix axis, respectively. Exciton interactions are the dominant source of the optical rotation in the tightly wound poly- l -proline I helix, as in the α-helix. The low and high energy π-π * branches have large positive and negative rotational strengths, respectively, with most of the π-π * absorption intensity being found in the low energy band. In poly- l -proline II most of the rotational strength and absorption intensity will be found in the high energy band. Preliminary calculations on collagen show that π-π * band splitting is expected.