Catalytic Role of Calix 4 hydroquinone in Acetone-Water Proton Exchange: A Quantum Chemical Study of Proton Transfer via Keto-Enol Tautomerism

    Authors

    A. Zakharov; A. E. Masunov;A. Dreuw

    Comments

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    Abbreviated Journal Title

    J. Phys. Chem. A

    Keywords

    ELECTRONIC-STRUCTURE; ORGANIC NANOTUBES; GAS-PHASE; WAVE-FUNCTIONS; BASIS-SETS; ENERGIES; CLUSTERS; HYDROGEN; NMR; Chemistry, Physical; Physics, Atomic, Molecular & Chemical

    Abstract

    Calix[4]hydroquinone has recently attracted considerable interest since it forms stable tubular aggregates mediated solely by hydrogen bonding and pi-pi-stacking interactions. These aggregates trap specifically various small organic molecules and, in particular, catalyze the proton exchange of water with acetone. Using correlated quantum chemical methods, the mechanism of the observed proton exchange mediated by keto-enol tautomerism of acetone is investigated in detail. Starting with an investigation of keto-enol tautomerism of acetone-water clusters, it appears that four catalytic water molecules are optimal for the catalysis and that additional solvent water molecules lead to a decrease in efficiency. Analyses of the partial charges revealed a decrease of the polarization of the reactive hydrogen bonds due to the additional water molecules. As a next step, hydroquinone- acetone-water complexes were studied as models for the situation in the CHQ moieties. However, the computations revealed that the proton transfer reaction becomes less efficient when one catalytic water molecule is replaced by hydroquinone. Although concerted proton transfer via keto-enol tautomerism of acetone seems to be the predominant mechanism in supercritical water, it is no longer the rate-determining reaction mechanism for the catalyzed acetone-water proton exchange observed in tubular CHQ. Nevertheless, a key feature of the catalytic function of tubular CHQ has been identified to be the stiff hydrogen bonding network and the exclusion of additional solvent water molecules.

    Journal Title

    Journal of Physical Chemistry A

    Volume

    112

    Issue/Number

    41

    Publication Date

    1-1-2008

    Document Type

    Article

    Language

    English

    First Page

    10405

    Last Page

    10412

    WOS Identifier

    WOS:000259943100041

    ISSN

    1089-5639

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