Characterization of protein secondary structures at interfaces is central in solving fundamental and engineering problems in biomedical and material sciences. However, it remains challenging because it requires a technique selective to both interfaces and secondary structures. Here, we use surface-specific chiral sum frequency generation (SFG) spectroscopy to obtain amide I and N-H stretch spectra of peptide backbone in various secondary structures at interfaces. We found that the spectra are unique to parallel beta-sheets, anti-parallel beta-sheets, alpha-helices, 3-10 helices, and random-coils, thus providing signatures to characterize these structures at interfaces. Moreover, the N-H/H-D stretch of peptide backbone is not interfered by the achiral water O-H/O-D stretch, which allows probing kinetics of H-D exchange of protein backbone at interfaces in real time and in situ. Our results support that chiral SFG can identify secondary structures at interfaces, similar to the use of circular dichroism spectroscopy for characterizing secondary structures in bulk solution.

Chiral sum frequency generation spectroscopy: A probe for protein secondary structures and proton exchange at interfaces

243rd National Meeting (2012)

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