It has already been shown that the helix senses of poly(p-benzyl L-aspartate) and poly(D-methyl L-aspartate) are left-handed, while the poly esters of n-propyl, isopropyl, n-butyl, and phenethyl L-asparate are all right-handed. The effect of changes in helix sense from the left-handed to the right-handed a-helical form on the infrared spectra of copolymers of benzyl L-aspartate with ethyl, n-butyl, isopropyl, n-propyl, and phenethyl L-aspartate have been studied. These show that for the right-handed heliral form the amide band frequencies fall within the range given by Elliott,? while for the left-handed form the frequenries are higher The frequenry ranges for the two helix senses are given and have been used to show that poly(p-n-propyl L-aspartate) in rhloroform solution undergoes a transition from the right-handed to the left-handed helix form on heating. Polarized infrared studies of the different copolymers show that the disposition of the sidechain ester groups is different for the two forms. Although methyl L-aspartate forms a left-handed a-helix similar to benzyl L-aspartate, the introduction of methyl L-aspartate residues into poly(pbenzy1 L-aspartate) prevents the formation of the w-helix. The fartors involved in the formation of this helix form are discussed.
CH stretching region the accuracy was to within 10 em-'. Spectra of unoriented films and solutions were recorded on a Grubb Parsons double-beam grating spectrometer, the Spectromaster. Each Infrared spectra were recorded on three spectrometers.