NMR investigations on alanyl‐[15% 13C, 95% 15N]‐proline: 15N chemical shifts and 13C-15N coupling constants
- 1 December 1978
- journal article
- research article
- Published by Wiley in Magnetic Resonance in Chemistry
- Vol. 11 (12) , 598-602
- https://doi.org/10.1002/mrc.1270111204
Abstract
The dipeptide alanylproline has been prepared with the proline residue both 13C (15%) and 15N (95%) enriched. 15N NMR spectra of alanylproline reveal signals for both possible conformations—cis and trans—of the dipeptide backbone in solution. Different pK values for both conformers are obtained from the pH dependence of the 15N 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 15N NMR signal intensities of the two conformers. One, two or three bonded 13C15N coupling constants measured in the 13C NMR high resolution spectra have different values in the cis and trans isomers of alanylproline and thus indicate different geometry in the pyrrolidine ring.Keywords
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