Raman optical activity of simple alanyl peptides: Backscattering in‐phase dual circular polarization measurements in aqueous solution

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Abstract
We report the measurement of backscattering in‐phase dual circular polarization (DCPI) Raman optical activity (ROA) for the simple alanyl peptides L‐alanyl‐L‐alanine ([L‐Ala]2), L‐alanylglycine (L‐Ala‐Gly), glycyl‐L‐alanine (Gly‐L‐Ala), and L‐alanyl‐L‐alanyl‐L‐alanine ([L‐Ala]3) in aqueous solutions. Empirical correlations between ROA features and the amino acid composition of the peptides are described. It is shown that the sum of the DCPIROA spectra for L‐Ala‐Gly and Gly‐L‐Ala is nearly the same as the corresponding ROA spectrum for (L‐Ala)2. Additionally, the DCPIROA spectrum for (L‐Ala)2 is very close to that of (L‐Ala)3, as has been observed previously using backscattering unpolarized incident circular polarization (ICPu) ROA. The ROA contributions of the different L‐Ala groups, which occur separately in the two glycyl peptides of alanine and jointly in (L‐Ala)2, are described in terms of the extent of vibrational coupling between peptide subunits. From these results, it appears that ROA has a more local sensitivity to vibrational coupling than is found in VCD or electronic circular dichroism. © 1995 John Wiley & Sons, Inc.