Orientation determination of interfacial bent α-helical structures using Sum Frequency Generation vibrational spectroscopy

- A formal SFG data analysis approach on bent α-helical structures was proposed.
- The twist angle of α-helical structures was shown to be important in the analysis.
- The interaction between melittin and DPPG was examined by this proposed approach.
- The transient pore model was validated by the data analysis proposed in this study.

Sum Frequency Generation (SFG) has been shown to be a powerful and versatile technique in studies of proteins/peptides at surfaces and interfaces. Recently SFG was successfully applied in studies of interfacial macro-molecules with increasing size and complexity. In this report we continued to employ bond additivity model and group theory to demonstrate the importance of both the inter-helical tilt angle and the lengths of the helical segments assembling the structures being studies. Specifically, a newly improved SFG data analysis of multiple α-helical structures on melittin was used to interpret the SFG experimental observation and also verified the findings with the recent insights brought by other spectroscopic techniques.