Side Chain and Flexibility Contributions to the Raman Optical Activity Spectra of a Model Cyclic Hexapeptide
Abstract
A model peptide, cyclo-(Phe-D-Pro-Gly-Arg-Gly-Asp), with a distinct folded structure containing short beta-hairpin and beta-sheet patterns was studied by Raman and Raman optical activity (ROA) spectroscopies. Unlike for previously analyzed vibrational circular dichroism of the same compound (Chirality 2008, 20, 1104), the Raman spectrum is dominated by side chain contributions and is more sensitive to their geometry fluctuations.
The spectra and molecular motion were analyzed with the aid of the density functional theory simulations combined with molecular dynamics (MD). The side chain geometry fluctuations were found to significantly contribute to the broadening of the spectral bands, while dynamics of the backbone is rather restricted.
The ROA spectroscopic technique thus provides important local structural information that needs, however, to be extracted by multiscale (QM/MM) simulation techniques.