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NMR investigations on alanyl‐[15% 13 C, 95% 15 N]‐proline: 15 N chemical shifts and 13 C 15 N coupling constants
Author(s) -
Blomberg F.,
Rüterjans H.,
Lintner K.,
Toma F.,
Fermandjian S.
Publication year - 1978
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270111204
Subject(s) - conformational isomerism , dipeptide , chemistry , chemical shift , carboxylate , nmr spectra database , coupling constant , pyrrolidine , crystallography , hydrogen bond , proton nmr , spectral line , stereochemistry , oxygen 17 , molecule , nuclear magnetic resonance , amino acid , organic chemistry , physics , biochemistry , particle physics , astronomy
The dipeptide alanylproline has been prepared with the proline residue both 13 C (15%) and 15 N (95%) enriched. 15 N NMR spectra of alanylproline reveal signals for both possible conformations— cis and trans —of the dipeptide backbone in solution. Different p K values for both conformers are obtained from the pH dependence of the 15 N chemical shifts using a least square programme based on the Henderson–Hasselbach equation. These different values are discussed in terms of interaction between the α‐amino group and the carboxylate group and between the carboxylate oxygen and the carbonyl oxygen of the dipeptide via hydrogen bonding. Further evidence for these interactions is obtained from the pH dependence of the ratio of the 15 N NMR signal intensities of the two conformers. One, two or three bonded 13 C 15 N coupling constants measured in the 13 C NMR high resolution spectra have different values in the cis and trans isomers of alanylproline and thus indicate different geometry in the pyrrolidine ring.