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

The 1H‐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 D2O and H2O, 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 pKa values obtained in D2O, 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 pKa values in H2O. This suggests that the present data are suitable “random‐coil” 1H‐nmr parameters for conformational studies of polypeptide chains in D2O and H2O solutions.