1 H‐nmr parameters of the common amino acid residues measured in aqueous solutions of the linear tetrapeptides H‐Gly‐Gly‐ X ‐ L ‐Ala‐OH

The 1 H‐nmr chemical shifts and the spin–spin coupling constants of the common amino acid residues were measured in solutions of the linear tetrapeptides H‐Gly‐Gly‐ X ‐ L ‐Ala‐OH in D 2 O and H 2 O, the influence of X on the nmr parameters of the neighboring residues Gly 2 and Ala 4 was investigated. The titration parameters for the side chains of Asp, Glu, Lys, Tyr, and His were determined. The p K a values obtained in D 2 O, with the use of pH‐meter readings with a combination glass electrode uncorrected for istope effects, were 0.06 pH units higher in the acidic range and 0.10 pH units higher in the basic range than the corresponding p K a values in H 2 O. This suggests that the present data are suitable “random‐coil” 1 H‐nmr parameters for conformational studies of polypeptide chains in D 2 O and H 2 O solutions.