Steric structure of <scp>L</scp>‐proline oligopeptides. II. Far‐ultraviolet absorption spectra and optical rotations of <scp>L</scp>‐proline oligopeptides

Abstract

Abstract The results of the measurement of the far‐ultraviolet absorption spectra of L ‐proline oligomers in water and acetonitrile are summarized as follows. The monomer has an absorption maximum at 182.5 mμ in acetonitrile. The absorption maximum of the dimer is found at 185 mμ and a shoulder appears around 200 mμ, that is, splitting of the absorption spectrum is observed in the dimer. As the degree of polymerization increases, the position of the shoulder shifts toward the wavelength of the absorption maximum of poly‐ L ‐proline II, with an accompanying increase in intensity. We may describe the absorption peak around 203 mμ of poly‐ L ‐proline II as identical with the shoulder with an increased intensity. By measurements of optical rotatory dispersion and circular dichroic spectra, it was also confirmed that the appearance of the helical conformation commences at the tetramer. When the number of residues is five or greater, the conformation of the helical structure of poly‐ L ‐proline II seems to be completed.