Knowledge Bank

Raman spectra of aqueous solutions of some peptides show spectral features in certain vibrations which can be interpreted in terms of a coupled oscillator model, that is, degenerate vibrations on separate groups form symmetric and antisymmetric combinations. These symmetric and antisymmetric components show expected polarizations behaviour, and the splitting between these components was shown to be geometry (conformation) dependent. The observed spectral features were correlated to molecular geometries using the two-group model developed by $Barron1$: $(Iz-/Iz+)=3(1-cos2\theta )/(5+3cos2\theta )$ where $Iz-$ and $Iz+$ denote the Raman intensity scattered parallel to the scattering plane for the antisymmetric and the symmetric combinations. and o is the dihedral angle between the coupled groups. The observed results indicate the sensitivity of long range vibrational coupling toward molecular conformation.