Isotope effect-mapping of the ionization of glucose demonstrates unusual charge sharing

Brett E. Lewis, Vern L. Schramm

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Isotopic substitution is known to affect kinetic rate constants and equilibrium constants in chemistry. In this study, we have used tritium substitution and high pH to probe the glucose ⇋ glucose- + H+ equilibrium. Passing partially ionized mixtures of [3H]- and [14C]glucose over anionic exchange resin has permitted the detection of subtle differences in pKa. We have found that, at pH 11.7 in an anionic exchange system, [3H]glucose always elutes ahead of the [14C]glucose, and we report isotope effects of 1.051 ± 0.0007, 1.012 ± 1.0005, 1.014 ± 0.0004, 1.024 ± 0.0003, 1.014 ± 0.0004, and 1.015 ± 0.0014 for [1-3H]-, [2-3H]-, [3-3H]-, [4-3H]-, [5-3H]-, and [6,6-3H2]glucose, respectively, as compared to either [2-14C]- or [6-14C]glucose. The elevated isotope effects at H1 and H4 imply unusual charge sharing in anionic aqueous glucose. Base titration of 13C-chemical shift changes demonstrates the dominance of pyranose forms at elevated pH, and ab initio isotope effect computations on gas-phase glucose anions are presented.

Original languageEnglish (US)
Pages (from-to)7872-7877
Number of pages6
JournalJournal of the American Chemical Society
Volume125
Issue number26
DOIs
StatePublished - Jul 2 2003

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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