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Proton affinity of proline and modified prolines using the kinetic method: role of the conformation investigated by ab initio calculations
Author(s) -
Mezzache S.,
Afonso C.,
Pepe C.,
Karoyan P.,
Fournier F.,
Tabet J.C.
Publication year - 2003
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1096
Subject(s) - chemistry , protonation , affinities , proton affinity , proline , ab initio , kinetic energy , ab initio quantum chemistry methods , proton , computational chemistry , ring (chemistry) , hydrogen bond , hydrogen atom , ion , crystallography , stereochemistry , group (periodic table) , amino acid , molecule , organic chemistry , biochemistry , physics , quantum mechanics
The proton affinities of proline, cis ‐3‐methylproline and cis ‐3‐ethylproline have been measured by the kinetic method using an ion trap instrument; the values obtained are 936, 940.5, and 943 kJ mol −1 , respectively. The experimental values are consistent with those obtained by high‐level ab initio calculations (B3LYP/6−31+G*//B3LYP/6−31G* and B3P86/6−31+G*//B3LYP/6−31G*). Several conformations of neutral and protonated proline were considered, in particular the endo and exo ring structure and the position of the carboxyl group. These results show the importance of the position of the hydrogen atom of the carboxyl group in determining the most stable protonated proline structure. Copyright © 2003 John Wiley & Sons, Ltd.