Vibrational Circular Dichroism of β-Hairpin Peptides

Analysis of vibrational absorption and vibrational circular dichroism (VCD) for synthetic peptides designed to adopt β-hairpin conformations reveals characteristic well-resolved amide I absorption and VCD bands. All β-hairpins with a type II‘ β-turn segment yield an intense negative VCD band in the ∼1643−1659 cm - 1 region, and a weak positive VCD band at ∼1693 cm - 1 . These spectral features are diagnostic of β-hairpins and distinct from those observed for other secondary structures. Comparison of the electronic CD spectra of the β-hairpin peptides Boc-Leu-Val-Val- D Pro-Gly-Leu-Val-Val-OMe ( 1 ) and Boc-Leu-Phe-Val- D Pro-Gly-Leu-Phe-Val-OMe ( 2 ) reveals that cross-strand aromatic interactions result in anomalous CD spectra in the region 200−240 nm for peptide 2 . Similar anomalous electronic CD are observed in the three-stranded β-sheet peptide Boc-Leu-Phe-Val- D Pro-Gly-Leu-Val-Leu-Ala- D Pro-Gly-Phe-Val-Leu-OMe ( 3 ), while the VCD spectrum is characteristic of β-hairpin conformations. The identical VCD spectra obtained for the peptides 1 and 2 emphasize the utility of VCD, as compared to electronic CD, in the conformational analysis of peptides containing aromatic residues.