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Issue 43, 2018
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Gating the electron transfer at a monocopper centre through the supramolecular coordination of water molecules within a protein chamber mimic

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Abstract

Functionality of enzymes is strongly related to water dynamic processes. The control of the redox potential for metallo-enzymes is intimately linked to the mediation of water molecules in the first and second coordination spheres. Here, we report a unique example of supramolecular control of the redox properties of a biomimetic monocopper complex by water molecules. It is shown that the copper complex based on a calix[6]arene covalently capped with a tetradentate [tris(2-methylpyridyl)amine] (tmpa) core, embedding the metal ion in a hydrophobic cavity, can exist in three different states. The first system displays a totally irreversible redox behaviour. It corresponds to the reduction of the 5-coordinate mono-aqua-CuII complex, which is the thermodynamic species in the +II state. The second system is detected at a high redox potential. It is ascribed to an “empty cavity” or “water-free” state, where the CuI ion sits in a 4-coordinate trigonal environment provided by the tmpa cap. This complex is the thermodynamic species in the +I state under “dry conditions”. Surprisingly, a third redox system appears as the water concentration is increased. Under water-saturation conditions, it displays a pseudo-reversible behaviour at a low scan rate at the mid-point from the water-free and aqua species. This third system is not observed with the Cu-tmpa complex deprived of a cavity. In the calix[6]cavity environment, it is ascribed to a species where a pair of water molecules is hosted by the calixarene cavity. A molecular mechanism for the CuII/CuI redox process with an interplay of (H2O)x (x = 0, 1, 2) hosting is proposed on the basis of computational studies. Such an unusual behaviour is ascribed to the unexpected stabilization of the CuI state by inclusion of the pair of water molecules. This phenomenon strongly evidences the drastic influence of the interaction between water molecules and a hydrophobic cavity on controlling the thermodynamics and kinetics of the CuII/CuI electron transfer process.

Graphical abstract: Gating the electron transfer at a monocopper centre through the supramolecular coordination of water molecules within a protein chamber mimic

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Supplementary files

Article information


Submitted
14 Jul 2018
Accepted
29 Aug 2018
First published
30 Aug 2018

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2018,9, 8282-8290
Article type
Edge Article

Gating the electron transfer at a monocopper centre through the supramolecular coordination of water molecules within a protein chamber mimic

N. Le Poul, B. Colasson, G. Thiabaud, D. J. Dit Fouque, C. Iacobucci, A. Memboeuf, B. Douziech, J. Řezáč, T. Prangé, A. D. L. Lande, O. Reinaud and Y. Le Mest, Chem. Sci., 2018, 9, 8282
DOI: 10.1039/C8SC03124J

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