Vibrational spectroscopic studies of L,D-alternating phenylalanine peptides

Infrared and Raman spectra of Boc-(D-Phe-L-Phe)n-OMe, with n = 4 and 5, and Boc-L-Phe-(D-Phe-L-Phe)7-OMe, have been obtained in crystalline and solution states. Based on the earlier spectroscopic studies on Boc-(L-Val-D-Val)n-OMe, with n = 4, 6 and 8, and the predictions from the normal-mode calculations of double-stranded beta-helix conformations, structures have been assigned for the three oligopeptides. In the crystalline state, all three oligopeptides have a double-stranded increases decreases beta 5.6 structure. Spectra from chloroform solution indicate that the solid-state conformation is retained in this solvent for all three oligopeptides.