Issue 11, 2009
From the journal:

Physical Chemistry Chemical Physics

Anthraquinone catalysis in the glucose-driven reduction of indigo to leuco-indigo

Anne Vuorema,a   Philip John,b   Marjo Keskitalo,a   Mary F. Mahon,c   M. Anbu Kulandainathand  and  Frank Marken*c  

* Corresponding authors

a MTT Agrifood Research Finland, Plant Production Research, Crop Science and Technology, Jokioinen, Finland

b School of Biological Sciences, The University of Reading, PO Box 221, Reading, UK

c Department of Chemistry, University of Bath, Bath, UK
E-mail: f.marken@bath.ac.uk

d Electro-organic Division, Central Electrochemical Research Institute, Karaikudi, India

Abstract

Anthraquinone immobilised onto the surface of indigo microcrystals enhances the reductive dissolution of indigo to leuco-indigo. Indigo reduction is driven by glucose in aqueous NaOH and a vibrating gold disc electrode is employed to monitor the increasing leuco-indigo concentration with time. Anthraquinone introduces a strong catalytic effect which is explained by invoking a molecular “wedge effect” during co-intercalation of Na+ and anthraquinone into the layered indigo crystal structure. The glucose-driven indigo reduction, which is ineffective in 0.1 M NaOH at 65 °C, becomes facile and goes to completion in the presence of anthraquinone catalyst. Electron microscopy of indigo crystals before and after reductive dissolution confirms a delamination mechanism initiated at the edges of the plate-like indigo crystals. Catalysis occurs when the anthraquinone–indigo mixture reaches a molar ratio of 1 : 400 (at 65 °C; corresponding to 3 μM anthraquinone) with excess of anthraquinone having virtually no effect. A strong temperature effect (with a composite EA≈ 120 kJ mol−1) is observed for the reductive dissolution in the presence of anthraquinone. The molar ratio and temperature effects are both consistent with the heterogeneous nature of the anthraquinone catalysis in the aqueous reaction mixture.

Graphical abstract: Anthraquinone catalysis in the glucose-driven reduction of indigo to leuco-indigo

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Article information

DOI
https://doi.org/10.1039/B814149E
Article type
Paper
Submitted
14 Aug 2008
Accepted
01 Dec 2008
First published
14 Jan 2009

Phys. Chem. Chem. Phys., 2009,11, 1816-1824

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Anthraquinone catalysis in the glucose-driven reduction of indigo to leuco-indigo

A. Vuorema, P. John, M. Keskitalo, M. F. Mahon, M. A. Kulandainathan and F. Marken, Phys. Chem. Chem. Phys., 2009, 11, 1816 DOI: 10.1039/B814149E

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