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Cordon MJ, Harris JW, Vega-Vila JC, et al. Dominant Role of Entropy in Stabilizing Sugar Isomerization Transition States within Hydrophobic Zeolite Pores. J Am Chem Soc. 2018;140(43):14244-14266doi: 10.1021/jacs.8b08336.
Cordon, M. J., Harris, J. W., Vega-Vila, J. C., Bates, J. S., Kaur, S., Gupta, M., Witzke, M. E., Wegener, E. C., Miller, J. T., Flaherty, D. W., Hibbitts, D. D., & Gounder, R. (2018). Dominant Role of Entropy in Stabilizing Sugar Isomerization Transition States within Hydrophobic Zeolite Pores. Journal of the American Chemical Society, 140(43), 14244-14266. https://doi.org/10.1021/jacs.8b08336
Cordon, Michael J, et al. "Dominant Role of Entropy in Stabilizing Sugar Isomerization Transition States within Hydrophobic Zeolite Pores." Journal of the American Chemical Society vol. 140,43 (2018): 14244-14266. doi: https://doi.org/10.1021/jacs.8b08336
Cordon MJ, Harris JW, Vega-Vila JC, Bates JS, Kaur S, Gupta M, Witzke ME, Wegener EC, Miller JT, Flaherty DW, Hibbitts DD, Gounder R. Dominant Role of Entropy in Stabilizing Sugar Isomerization Transition States within Hydrophobic Zeolite Pores. J Am Chem Soc. 2018 Oct 31;140(43):14244-14266. doi: 10.1021/jacs.8b08336. Epub 2018 Oct 19. PMID: 30265002.
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J Am Chem Soc. 2018 Oct 31;140(43):14244-14266. doi: 10.1021/jacs.8b08336. Epub 2018 Oct 19.

Dominant Role of Entropy in Stabilizing Sugar Isomerization Transition States within Hydrophobic Zeolite Pores.

Journal of the American Chemical Society

Michael J Cordon, James W Harris, Juan Carlos Vega-Vila, Jason S Bates, Sukhdeep Kaur, Mohit Gupta, Megan E Witzke, Evan C Wegener, Jeffrey T Miller, David W Flaherty, David D Hibbitts, Rajamani Gounder

Affiliations

  1. Charles D. Davidson School of Chemical Engineering , Purdue University , 480 Stadium Mall Drive , West Lafayette , Indiana 47907 , United States.
  2. Department of Chemical Engineering , University of Florida , 1030 Center Drive , Gainesville , Florida 32611 , United States.
  3. Department of Chemical and Biomolecular Engineering , University of Illinois Urbana-Champaign , Urbana , Illinois 61801 , United States.

PMID: 30265002 DOI: 10.1021/jacs.8b08336

Abstract

Lewis acid sites in zeolites catalyze aqueous-phase sugar isomerization at higher turnover rates when confined within hydrophobic rather than within hydrophilic micropores; however, relative contributions of competitive water adsorption at active sites and preferential stabilization of isomerization transition states have remained unclear. Here, we employ a suite of experimental and theoretical techniques to elucidate the effects of coadsorbed water on glucose isomerization reaction coordinate free energy landscapes. Transmission IR spectra provide evidence that water forms extended hydrogen-bonding networks within hydrophilic but not hydrophobic micropores of Beta zeolites. Aqueous-phase glucose isomerization turnover rates measured on Ti-Beta zeolites transition from first-order to zero-order dependence on glucose thermodynamic activity, as Lewis acidic Ti sites transition from water-covered to glucose-covered, consistent with intermediates identified from modulation excitation spectroscopy during in situ attenuated total reflectance IR experiments. First-order and zero-order isomerization rate constants are systematically higher (by 3-12×, 368-383 K) when Ti sites are confined within hydrophobic micropores. Apparent activation enthalpies and entropies reveal that glucose and water competitive adsorption at Ti sites depend weakly on confining environment polarity, while Gibbs free energies of hydride-shift isomerization transition states are lower when confined within hydrophobic micropores. DFT calculations suggest that interactions between intraporous water and isomerization transition states increase effective transition state sizes through second-shell solvation spheres, reducing primary solvation sphere flexibility. These findings clarify the effects of hydrophobic pockets on the stability of coadsorbed water and isomerization transition states and suggest design strategies that modify micropore polarity to influence turnover rates in liquid water.

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