Vibrational spectroscopic studies of -alternating valine peptides

Abstract

Raman and infrared spectra of Boc-(Val--Val)n-OMe [(-Val)n], with n = 4, 6 and 8, were obtained in crystalline and solution states. Based on predictions from normal-mode calculations of a number of relevant single- and double-stranded [beta]-helix conformations, structures were assigned for the three oligopeptides under the above-mentioned conditions. In the crystalline state, all three oligopeptides have a double-stranded [short up arrow][downwards arrow] [beta]5.6 structure. In cyclohexane and in chloroform, the [short up arrow][downwards arrow] [beta]5.6 structure predominates for (-Val)4. In chloroform the (-Val)6 has a [beta]4.4 structure. (-Val)8 in cyclohexane and in chloroform exists predominantly in a [short up arrow][downwards arrow] [beta]5.6 structure together with some [beta]4.4.