pH Dependence of 15N NMR Shifts and Coupling Constants in Aqueous Imidazole and 1-Methylimidazole. Comments on Estimation of Tautomeric Equilibrium Constants for Aqueous Histidine

Article abstract of DOI:10.1021/ja00529a002

15N, 1H, and 13C NMR spectra for <15N2>imidazole and <15N2>-1-methylimidazole in aqueous solution as functions of pH provide shift and coupling constant information useful in characterizing the protonated and unprotonated forms of these compounds and as background for determining N binding to other species, such as metal ions.When combined with similar data for the imidazole-ring atoms in histidine, these data give more reliable estimates of tautomeric equilibrium constants for the amphionic and anionic forms of histidine than were possible from the histidine data alone.