Chiral properties of proteins at interfaces play important roles in structure and function at membrane surfaces, but a molecular-level understanding of protein chirality at interfaces has remained elusive. Here, we report our experimental and theoretical development of chiral sum frequency generation (SFG) spectroscopy to characterize vibrational chirality of protein secondary structures at interfaces in situ. We obtained chiral SFG spectra and found that the peptide amide I and N-H stretch provide unique vibrational signatures for various secondary structures. We also performed ab initio calculation to interpret these chiroptical responses. We found that the highly coupled amide I vibration has chiral responses for parallel and anti-parallel beta-sheets, but not alpha-helices; whereas, the localized N-H stretch has strong chiral SFG signal in alpha-helices and antiparallel beta-sheet, but not parallel beta-sheet. These results provide fundamental understanding of relations between vibrational coupling and chiroptical response of proteins at interfaces.

Vibrational chirality of protein secondary structures studied by sum frequency generation spectroscopy and ab initio calculation

244th National Meeting (2012)

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