The conformation and aggregation of some block copolymers (L-alanine)_n-(L-glutamate)_m in aqueous media

Abstract

A series of low molecular weight $(\bar M_n < 10,000)$ block copolymers of composition (L-alanine)_n-(L-glutamate)_m covering a range of values of m/n from 0.56 to 4.4 have been prepared and characterised. Samples with m/n < 1.3 were shown by low angle laser light scattering to be very highly aggregated in aqueous solutions of ionic strength 0.5 whereas above this ratio the copolymers were monomeric. Circular dichroic spectra of the samples in aqueous media can be interpreted in terms of a conformation consisting of β-sheet structure plus extended structure with a greater proportion of β-sheet structure in the aggregated state most probably associated with the alanine residues. On the addition of methanol the longer chain copolypeptides exhibit a transition to an α-helical conformation.