Electrochemical study of self-assembled monolayers of a β-cyclodextrin methyl sulfide covalently linked to anthraquinone |
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Authors: | Keith J Stine Donna M Andrauskas Abdul R Khan Peter Forgo Valerian T D’Souza |
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Institution: | Department of Chemistry and Center for Molecular Electronics, University of Missouri-St. Louis, St. Louis, MO 63121, USA |
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Abstract: | Self-assembled monolayers of a β-cyclodextrin with methyl sulfides on the primary sites of the molecule and mono-functionalized with anthraquinone on a secondary site have been formed on gold electrodes. The surface coverages obtained by electrochemistry are consistent with values reported previously or calculated for similar non-electroactive β-CD derivatives. The electron transfer rate constants vary markedly with pH, increasing rapidly between pH 7 and 9 to values of approximately 700–900 s?1. These values are faster than reported previously for thiol derivatives of anthraquinone dispersed in an alkylthiol SAM matrix. Near pH 6, slow electron transfer is observed with a splitting into individual one-electron steps. Lowering the pH further results in very sluggish kinetics and indistinguishable peaks. Inclusion of naphthalene into the β-CD cavity appears to affect the anodic rate constant, and a small potential shift occurs. The efficient electron transfer of the anthraquinone spaced from the gold surface by a β-CD unit suggests promise for use of such molecules as ‘immobilized artificial enzymes’. |
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Keywords: | Anthraquinones Cyclodextrins Self-assembly Electron transfer |
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