Vibrational spectroscopy of L‐valyl‐glycyl‐glycine, a parallel‐chain β‐structure

Bands in the ir and Raman spectra of L ‐valyl‐glycyl‐glycine (VGG) and VGG‐ND have been assigned on the basis of a normal mode analysis of the known parallel‐chain β‐structure of this tripeptide. Amide I, II, III, and V mode shifts are obtained by the interactions of dipole derivatives in symmetry coordinates, referred to as dipole derivative coupling. These derivatives, obtained from ab initio studies, are also used to calculate ir intensities of amide I, II, and V modes. The agreement between predicted and observed frequencies and intensities is very good, providing confidence in the application of our force fields to the calculation of the vibrational modes of the general parallel‐chain β‐sheet structure (following paper).