Vibrational spectroscopy of self-assembling aromatic peptide derivates

Peptides can assemble to supramolecular structures, of which fibers are of special biochemical and medical relevance. We employed Raman and infrared spectroscopy to elucidate the chemical integrity of fibers built from peptides and peptide derivates that contain the aromatic side groups fluorenyl and phenyl. Because the observed spectra compare very well with simulation results of the respective single molecules in vacuum, we were able to assign all observed vibrations. We found the main differences between solid phase and single molecule for O-H and N-H stretching and bending vibrations, owing to hydrogen bonding in solids. The fluorenyl and phenyl residues cause p-stacking of the molecules, which barely manifests in the spectra, but clearly in the structures. Whereas hydrogen bonds provide the principal stability of the fiber backbone, aromatic p-stacking supports the assembly to fibers, especially when electrospinning assists the molecular alignment. Copyright (c) 2012 John Wiley & Sons, Ltd.