Detection of chiral sum frequency generation vibrational spectra of proteins and peptides at interfaces in situ.

In this work, we demonstrate the feasibility to collect off-electronic resonance chiral sum frequency generation (SF6) vibrational spectra from interfacial proteins and peptides at the solid/liquid inter- face in situ. It is difficult to directly detect a chiral SF6 vibrational spectrum from interfacial fibrinogen molecules. By adopting an interference enhancement method, such a chiral SF6 vibrational spectrum can be deduced from interference spectra between the normal achiral spectrum and the chiral spectrum. We found that the chiral SF6 vibrational spectrum of interfacial fibrinogen was mainly contributed by the β-sheet structure. For a β-sheet peptide tachyplesin 1, which may be quite ordered at the solid/liquid interface, chiral SF6 vibrational spectra can be collected directly. We believe that these chiral signals are mainly contributed by electric dipole contributions, which can dominate the chiroptical responses of uniaxial systems. For the first time, to our knowledge, this work indicates that the off-electronic resonance SF6 technique is sensitive enough to collect chiral SFG vibrational spectra of interfacial proteins and peptides, providing more structural information to elucidate interfacial protein and peptide structures. [ABSTRACT FROM AUTHOR]