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

Abstract

Abstract We report the measurement of backscattering in‐phase dual circular polarization (DCP I ) 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 DCP I ROA spectra for L‐Ala‐Gly and Gly‐L‐Ala is nearly the same as the corresponding ROA spectrum for (L‐Ala) 2 . Additionally, the DCP I ROA 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 (ICP u ) 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.