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17 O‐NMR. of Enriched Acetic Acid, Glycine, Glutamic Acid and Aspartic Acid in Aqueous Solution. I. Chemical Shift Studies
Author(s) -
Gerothanassis Ioannis P.,
Hunston Roger,
Lauterwein Jürgen
Publication year - 1982
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19820650612
Subject(s) - chemistry , aspartic acid , glutamic acid , aqueous solution , intramolecular force , deprotonation , chemical shift , glycine , acetic acid , amino acid , carboxylate , titration curve , protonation , inorganic chemistry , medicinal chemistry , titration , stereochemistry , organic chemistry , ion , biochemistry
The 17 O‐NMR. chemical shifts of the enriched amino acids glycine, aspartic acid and glutamic acid were measured in aqueous solution as a function of pH. High magnetic fields are necessary to resolve the α, β‐ and α, γ‐carboxyl resonances of aspartic acid and glutamic acid, respectively. The chemical shifts of acetic acid were measured for comparative reasons. Ionization constants and titration shifts were obtained by nonlinear least‐squares fits to one‐proton titration curves. The average excitation energy approximation is discussed in terms of the observed changes in 17 O‐shielding on deprotonation. No intramolecular association between the α‐amino group and the α‐carboxyl group in the zwitterionic form is required to explain the high‐frequency shift of the carboxylate ion. Also no indication of an intramolecular association between the α‐amino group and the side‐chain carboxyl groups of aspartic acid or glutamic acid was found.