Far‐infrared spectra of sequential copolymers of amino acids with alkyl group side chains

Far‐infrared spectra were measured for the sequential copolymers of amino acids with alkyl group side chains. The analysis of the spectra showed that (L‐Ala‐L‐Ala‐Gly)n, (L‐Ala‐Gly)n, (L‐Ala‐Gly‐Gly)n, (L‐Val‐L‐Ala‐L‐Ala)n, and (L‐Val‐L‐Ala)n, have the antiparallel pleated sheet structures and that the backbone conformations of (L‐Val‐L‐Val‐L‐Ala)n and (L‐Val‐L‐Val‐Gly)n are the same as that of poly‐L‐valine. The far‐infrared bands characteristic of the antiparallel pleated sheet structure were assigned on the basis of the result of the normal coordinate analysis of poly‐L‐alanine with this structure. The intersheet and interchain spacings of the sequential copolymers with the antiparallel pleated sheet structure were determined from the x‐ray powder‐diffraction patterns of these samples.