title: NMR resonance splitting of urea in stretched hydrogels: proton exchange and (1)H/(2)H isotopologues.
abstract: Urea at ∼12 M in concentrated gelatin gel, that was stretched, gave (1)H and (2)H NMR spectral splitting patterns that varied in a predictable way with changes in the relative proportions of (1)H2O and (2)H2O 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 (1)H 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 (1)H and (2)H 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.
authors.affiliation: School of Molecular Bioscience, University of Sydney, NSW 2006, Australia. Electronic address: philip.kuchel@sydney.edu.au.
authors.forename: Philip W
authors.initials: PW
authors.lastname: Kuchel
authors.affiliation: School of Molecular Bioscience, University of Sydney, NSW 2006, Australia.
authors.forename: Christoph
authors.initials: C
authors.lastname: Naumann
authors.affiliation: School of Molecular Bioscience, University of Sydney, NSW 2006, Australia.
authors.forename: Bogdan E
authors.initials: BE
authors.lastname: Chapman
authors.affiliation: School of Molecular Bioscience, University of Sydney, NSW 2006, Australia.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Shishmarev
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ, United Kingdom.
authors.forename: Pär
authors.initials: P
authors.lastname: Håkansson
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia.
authors.forename: George
authors.initials: G
authors.lastname: Bacskay
authors.affiliation: School of Molecular Bioscience, University of Sydney, NSW 2006, Australia; School of Chemistry, University of Sydney, NSW 2006, Australia.
authors.forename: Noel S
authors.initials: NS
authors.lastname: Hush
mesh_terms: D000577:Amides / Q000737:chemistry; D003903:Deuterium; D017666:Deuterium Oxide; D004574:Electromagnetic Fields; D005780:Gelatin / Q000737:chemistry; D020100:Hydrogels / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011522:Protons; D014508:Urea / Q000737:chemistry*
chemical_list: D000577:Amides; D020100:Hydrogels; D011522:Protons; D014508:Urea; D005780:Gelatin; D003903:Deuterium; D017666:Deuterium Oxide
keywords: (1)H NMR spectroscopy; (2)H NMR spectroscopy; Chirality; Gelatin gel; Isotopomers; Residual dipolar coupling; Residual quadrupolar coupling; Stretched gel; [1,3-(15)N]urea