NMR resonance splitting of urea in stretched hydrogels

Abstract

Urea at ∼12 M in concentrated gelatin gel, that was stretched, gave 1H and 2H NMR spectral splitting patterns that varied in a predictable way with changes in the relative proportions of 1H2O and 2H2O in the medium. This required consideration of the combinatorics of the two amide groups in urea that have a total of four protonation/deuteration sites giving rise to 16 different isotopologues, if all the atoms were separately identifiable. The rate constant that characterized the exchange of the protons with water was estimated by back-transformation analysis of 2D-EXSY spectra. There was no 1H NMR spectral evidence that the chiral gelatin medium had caused in-equivalence in the protons bonded to each amide nitrogen atom. The spectral splitting patterns in 1H and 2H NMR spectra were accounted for by intra-molecular scalar and dipolar interactions, and quadrupolar interactions with the electric field gradients of the gelatin matrix, respectively. Show more