Characterization of protein secondary structures at interfaces is important for understanding fundamental biological processes and guiding molecular design in biotechnologies. However, in situ and real-time characterization is challenging as it requires surface-sensitive methods that are also selective to protein secondary structures. We show that chiral sum frequency generation spectroscopy (SFG) can provide peptide amide I and N-H stretching vibrational signals that are characteristic to various secondary structures (parallel beta-sheet, anti-parallel beta-sheet, alpha-helix, 3-10 helix and disordered structures). These characteristic signals enable chiral SFG to distinguish protein secondary structures at interfaces, similar to circular dichroism signals for characterizing protein secondary structures in solution. Using chiral SFG, we monitor misfolding of an amyloid protein, measure protein orientation at interfaces, develop methods for probing proton exchange kinetics in proteins, and examine two-dimensional crowding effects on protein folding. Moreover, we observe chiral SFG stretching modes of water molecules associated with a beta-sheet peptide. This observation reveals that achiral water molecules can be organized by the protein into a chiral supermolecular structures, implying that chiral SFG can potentially be a powerful tool for probing water structures in protein hydration. These results suggest chiral SFG can provide new tools for addressing a wide range of fundamental and engineering problems.

Protein characterizations by chiral vibrational sum frequency generation spectroscopy

2019 Fall National Meeting

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