Proton magnetic resonance of the triple helix of poly(prolylprolylglycyl) n with defined degree of polymerization

Abstract

Proton magnetic resonance spectra at 220 MHz were obtained for deuterium oxide and aqueous solutions of the polytripeptides (Pro-Pro-Gly) n , which were synthesized as collagen models by the modified solid phase method. At higher temperatures, the signals of the proline C a -protons for the peptides with n ≦ 5 and for those with n = 10 and 15 demonstrate the presence of cis and trans isomers with respect to the Gly-Pro or Pro-Pro C-N bonds. Glycine C a -protons give typical AB type patterns. At lower temperatures, as the peptides with n = 5, 10 and 15 form triple helices, all of the resonance peaks become broad, but the whole form of the spectrum is quite similar to that of poly(l-proline) form II. The glycine C a -proton resonances become barely detectable and the upfield peak of the two proline C a -proton resonances fade away. At the same time, a new glycine NH resonance appears at a field slightly higher than that of a random coil. It seems to suggest that the formation of triple helices accompanies the conversion of cis proline peptide bonds into all trans bonds, and that the glycine residue environment completely changes in the helix.