1D‐ and 2D‐NMR study of a nonapeptide, a fragment of collagen, in its free state and complexed with aluminium (III)

Abstract 1H NMR studies at 250 MHz and 13C NMR studies at 62.8 MHz on the synthetic nonapeptide fragment of type III collagen, Gly‐Lys‐Hyp‐Gly‐Glu‐Hyp‐Gly‐Pro‐Lys (CP9), have been carried out in aqueous solution and DMSO‐d6. The resonances are assigned with the help of 2D correlated spectroscopy, pH titrations by following the characteristic pK values exhibited by protons adjacent to ionization sites and one‐dimensional (1D) spin decoupling techniques. Chemical shifts of the proline and hydroxylproline carbon atoms indicate that the trans configuration about the three X—Pro and XHyp peptide bonds is strongly favoured in all cases, although the minor cis resonances accounting for about 10% of the Pro and Hyp intensity can also be observed. In addition, there appears to be no significant pH sensitivity of the cis ⇌ trans equilibrium. Addition of aluminium causes changes in the spectra, indicating specific interactions with carboxylates of the glutamyl and lysyl residues, as well as a change for both hydroxylproline residues. These data are interpreted by the formation of a 1:2 stoichiometric complex (AlIII‐CP9). the implication of these results with respect to the effect of aluminium in the tanning process is discussed.