Optical Activity Related to Ordered Aggregation in Some Biological Molecules: I. Poly(L-proline) and Collagen

Abstract

Optical activity, due to differential light scattering, is shown to produce large effects on the circular dichroism (CD) spectra of several biopolymers. It is suggested that helical association on aggregation is the causative factor. Thus, under the salt conditions for formation of native fibrils of collagen from solution, new CD bands are found to appear and intensify with time. Similarly, in the case of polyproline I, M = 13,500 (thought to associate in a side-to-side manner), large CD bands are observed throughout the visible and UV spectrum in addition to the normal CD bands of the unassociated form. These bands can be related to scattering phenomena. The new bands appear to be overtones of a fundamental frequency, similar, in some respects, to Bragg X-ray diffraction from crystals, and not to be confused with the ordinary Duysens absorption flattening effect on the CD spectra that is theoretically calculable from Mie scattering of spherical aggregates. It does, however, correspond to the optical activity observed in liquid crystals.