The infrared and Raman spectra of solid tridehydropeptides: Influence of ΔAla and ΔPhe on the spectral profile

A series of solid tripeptides Boc-Gly-X-Gly-OMe (X = dehydroalanine (ΔAla), dehydrophenylalanine (ΔPhe)) was investigated by Raman scattering and Fourier transform infrared spectra to examine the conformational marker bands of the unsaturated residue. The observed fundamental modes gave us the opportunity to analyze structural features that change due to the substitution of Ala by ΔAla and due to the different spatial arrangement of ΔPhe (Z and E isomers). In addition, we showed the alteration of the spectral profile when the large size residue (Phe) is introduced into the backbone of the peptide with ΔPhe (in Boc-Gly-Δ(Z)Phe-Phe-OMe). The frequency ranges of interest included the NH stretching, carbonyl stretching, and amide deformation modes as well as vibrations of the investigated dehydroresidues. The observed differences of positions and intensities of IR and Raman bands provided an insight into the structural and spectroscopic properties of the selected dehydropeptides.