Proton magnetic resonance spectra of amino-acids and peptides relevant to wool structure. Part VI. Relative residence times of peptides of histidine, tryptophan, and valine

Abstract

100 and 220 MHz ¹H n.m.r. spectra have been recorded, over the temperature range 291–358 K, for acidic and basic D₂O solutions of nine dipeptides and three tripeptides containing histidyl, tryptophyl, and valyl groups. Analysis of the spectra enabled the populations of the side-chain (C_α–C_β bond) rotamers to be calculated from the vicinal coupling constants. For the histidyl and tryptophyl peptides in acid and base, all rotamers are appreciably populated. In the range studied, the rotamer populations of the histidyl residues are almost unaffected by increase of temperature, while for Gly-Tyr and Gly-Trp-Gly there is a slight tendency for the preponderance of rotamer (I) to lessen. In the valyl peptides examined, the population of the rotamer with the vicinal hydrogens trans was greatest for acidic solutions of peptides with the valyl residue carbon terminal.