Revisiting the influence of pH on (1)J(C)(α)(H) and chemical shifts of glycine and alanine short oligopeptides

The pH dependence of several NMR parameters of glycine and alanine short oligopeptides has been reported previously in different studies. Here we have thoroughly examined, summarized and demonstrated the dependences of (1)H, (13)C and (15)N chemical shifts and protonation states of amino acids using two-dimensional NMR experiments. Nevertheless, (1)J(C)(α)(H) one bond spin–spin coupling constants are more informative and convenient for determination of the position and protonation state of glycine and alanine residue in the oligopeptide chain. In particular, for various oligopeptides (up to six residues), it was shown that the pH dependence of (1)J(C)(α)(H) of N-terminal glycine and alanine residues is larger than that of C-terminal groups, and in backbone residues, it is not influenced by pH and only slightly depends on the position of the amino acid residue in the chain.