Proton magnetic resonance spectra of amino-acids and peptides relevant to wool structure. Part IV. Relative residence times of dipeptides and tripeptides of phenylalanine and tyrosine

Abstract

100 MHz High resolution 1H n.m.r. spectra have been recorded from acidic (pD 0.6–1.4) and basic (pD 12.3–13.1) D2O solutions of the dipeptides Gly-Phe, Ala-Phe, Val-Phe, Met-Phe, Leu-Phe, Phe-Leu, Phe-Val, Phe-Tyr, His-Phe, Gly-Tyr, Ala-Tyr, Val-Tyr, L-Leu-Tyr, D-Leu-Tyr, Trp-Tyr, Trp-Gly, and Tyr-Val, within the range 300–360 K. Iterative analyses of ABC/ABX systems have yielded coupling constants from which relative populations of Cα–Cβ rotamers have been derived. 100 and 220 MHz 1H spectra have similarly been analysed for the basic and acidic D2O solutions of the tripeptides Gly-Phe-Met, Met-Phe-Gly, Gly-Phe-Ala, Gly-Phe-Phe, Gly-Tyr-Gly, and Val-Tyr-Val, within the range 280–360 K. In acid, the trans-rotamer (ring opposed to carboxyl or C-terminal peptide group) is favoured for dipeptides of the types X-L-Phe and X-L-Tyr and for the tripeptides Gly-Phe-Ala and Gly-Tyr-Gly; in base, the trans-rotamer predominates in most peptides.