(557g) Isomerization and Epimerization of Sugars Using Homogeneous and Heterogeneous Catalysts in Aqueous Media: A Multiscale Molecular Modeling Investigation

Isomerization and epimerization reactions are of great relevance to the conversion of sugars, as biomass components, to fuels and chemicals and to the production of rare sugars. The economics of the conversion of biomass–derived sugars into furanic intermediates and that of the production of rare sugars based sweeteners and pharmaceuticals depend heavily on sugars transformation. Enzymatic transformation of sugars is expensive and there is a pressing need to develop novel inorganic catalysts that can selectively isomerize/epimerize sugars in a more economical fashion. Recent developments in this field have revealed several potential homogeneous and heterogeneous catalysts that can selectively transform sugars in aqueous media.^1-3 Physico–chemical interactions amongst the sugar, the catalyst and the solvent govern the catalytic mechanism of sugars transformation reactions. In the present work, we investigate the isomerization and epimerization of a model sugar molecule, glucose, using different homogeneous and heterogeneous catalysts in aqueous media. Calculations are performed in condensed phase, adopting the Car–Parrinello molecular dynamics scheme with metadynamics acceleration.⁴ Speciation and coordination of different catalysts with glucose, in the presence of solvent, and the corresponding reaction mechanisms and energetics are compared. Solvent dynamics are taken into account while simulating reaction mechanisms and its effect on rate limiting steps of the reactions is studied in detail. Molecular details obtained from the present work will serve as an input for developing and designing novel catalytic materials for sugars transformations in aqueous media, thus providing a bottom-up approach for developing materials for sugars chemistry.

1. Choudhary et al., J. Amer. Chem. Soc., 135, 2013, 3997.
2. Moliner et al., Proc. Natl. Acad. Sci, 107, 2010, 6164.
3. Gunther et al., Nat. Commun., 3, 2012, 1109.
4. Laio and Gervasio, Rep. Prog. Phys., 71, 2008, 126601.