Correlation between Raman and X-ray crystallography data of (Pro-Pro-Gly)10

Model biopolymers are powerful tools to guide the interpretation of physical properties in complex systems. (Pro-Pro-Gly)10, (PPG)10, is a collagen-model peptide, whose structure is known at high resolution. Herein, Raman microscopy data of (PPG)10 powders and single crystals are reported. The spectra interpretation leads to an accurate assignment of three well-resolved amide bands corresponding to the three peptide bonds (PP, PG and GP) present in the (PPG)10 structure. These data together with the availability of torsional angles φ and ψ derived from the high-resolution crystal structure, provide the opportunity to test the validity of theoretical equations for the calculation of non-canonical amide III bands and represent a reference for theoretical calculations of vibrational spectra and for polyproline II detection in complex proteins. Spectroscopic data do not support the indication of two distinct and equally populated up and down conformations of the pyrrolidine rings observed in the (PPG)10 crystal structure.