Transition states for glucopyranose interconversion.
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TLDR
The transition states for anomerization are found, and it is concluded that it is forbidden for the water molecule to form a hydrogen bond bridge to both OH1 and O5 of glucose simultaneously in either transition state.Abstract:
Glucose is a central molecule in biology and chemistry, and the anomerization reaction has been studied for more than 150 years. Transition-state structure is the last impediment to an in-depth understanding of its solution chemistry. We have measured kinetic isotope effects on the rate constants for approach of R-glucopyranose to its equilibrium with ‚-glucopyranose, and these were converted into unidirectional kinetic isotope effects using equilibrium isotope effects. Saturation transfer 13 C NMR spectroscopy has yielded the relative free energies of the transition states for the ring-opening and ring- closing reactions, and both transition states contribute to the experimental kinetic isotope effects. Both transition states of the anomerization process have been modeled with high-level computational theory with constraints from the primary, secondary, and solvent kinetic isotope effects. We have found the transition states for anomerization, and we have also concluded that it is forbidden for the water molecule to form a hydrogen bond bridge to both OH1 and O5 of glucose simultaneously in either transition state.read more
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References
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Study of Moderately Rapid Chemical Exchange Reactions by Means of Nuclear Magnetic Double Resonance
Sture Forsén,Ragnar A. Hoffman +1 more
TL;DR: In this paper, a nuclear magnetic double resonance method for the determination of chemical exchange rates has been developed, which is applicable to systems in which a nuclear spin is reversibly transferred between two nonequivalent sites, A and B, and is obtained through the study of the decay to a new equilibrium value of Signal A upon the sudden saturation of Signal B.
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Complete kinetic isotope effect description of transition states for acid-catalyzed hydrolyses of methyl .alpha.- and .beta.-glucopyranosides
TL;DR: In this paper, the isotope effects of methyl aldopyranosyl derivatives were measured by the isotopic quasi-racemate method for the hydrolyses of methyl A * and A * derivatives, respectively in 2.0 M HClO/sub 4/ at 80/sup 0/C.