title: Two-dimensional sum-frequency generation reveals structure and dynamics of a surface-bound peptide.
abstract: Surface-bound polypeptides and proteins are increasingly used to functionalize inorganic interfaces such as electrodes, but their structural characterization is exceedingly difficult with standard technologies. In this paper, we report the first two-dimensional sum-frequency generation (2D SFG) spectra of a peptide monolayer, which are collected by adding a mid-IR pulse shaper to a standard femtosecond SFG spectrometer. On a gold surface, standard FTIR spectroscopy is inconclusive about the peptide structure because of solvation-induced frequency shifts, but the 2D line shapes, anharmonic shifts, and lifetimes obtained from 2D SFG reveal that the peptide is largely α-helical and upright. Random coil residues are also observed, which do not themselves appear in SFG spectra due to their isotropic structural distribution, but which still absorb infrared light and so can be detected by cross-peaks in 2D SFG spectra. We discuss these results in the context of peptide design. Because of the similar way in which the spectra are collected, these 2D SFG spectra can be directly compared to 2D IR spectra, thereby enabling structural interpretations of surface-bound peptides and biomolecules based on the well-studied structure/2D IR spectra relationships established from soluble proteins.
authors.affiliation: Department of Chemistry and ‡Department of Materials Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Laaser
authors.forename: David R
authors.initials: DR
authors.lastname: Skoff
authors.forename: Jia-Jung
authors.initials: JJ
authors.lastname: Ho
authors.forename: Yongho
authors.initials: Y
authors.lastname: Joo
authors.forename: Arnaldo L
authors.initials: AL
authors.lastname: Serrano
authors.forename: Jay D
authors.initials: JD
authors.lastname: Steinkruger
authors.forename: Padma
authors.initials: P
authors.lastname: Gopalan
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Gellman
authors.forename: Martin T
authors.initials: MT
authors.lastname: Zanni
mesh_terms: D000595:Amino Acid Sequence; D006046:Gold / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013499:Surface Properties
chemical_list: D010455:Peptides; D006046:Gold