Second Harmonic Generation, a new approach for analyzing the interfacial properties of a short tryptophan-rich peptide

The involvement of the tryptophan residues in the interactions of peptides or proteins with lipid membranes justifies our characterization of the interfacial properties of a synthetic tryptophan-rich peptide by a new approach using the nonlinear optic properties of this amino acid. The positively-charged peptide (KWWKWWK) at pH 8.5, alone or in the presence of a negatively-charged phospholipid monolayer, was detected at the air-water interface by combined optical Second Harmonic Generation (SHG), a nonlinear spectroscopy, and surface tension measurements. Further polarized SHG experiments showed that the short peptide was oriented at the negatively-charged phospholipid interface.