Structural determinations using vibrational Raman optical activity: from a single peptide group to β-turns
Vibrational Raman optical activity (ROA) spectra, predicted using an ab initio VROA method, are presented. Agreement between the predicted and experimental VROA spectra for amino acids is generally satisfactory. The predictions obtained for different conformers of N-acetyl-N′-methyl-L-alaninamide are used as model peptide spectra and are compared with the experimental VROA spectra of L-alanyl-L-alanyl-L-alanine, α-chymotrypsin and poly(L-lysine) whose structures are established in the literature. It appears that most of the VROA sign patterns in these molecules are determined by the relative orientations of the peptide groups.