Allosteric Tuning of the Intra-Cavity Binding Properties of a Calix[6]arene through External Binding to a ZnII Center Coordinated to Amino Side Chains

Authors

  • Ulrich Darbost Dr.,

    1. Unité de Recherche en Chimie Organique et Macromoléculaire (URCOM), Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre cedex, France, Fax: (+33) 232-744-391
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  • Olivier Sénèque Dr.,

    1. Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR CNRS 8601, Université René Descartes, 45 rue des Saints Pères, 75270 Paris cedex 06, France, Fax: (+33) 142-868-387
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  • Yun Li Dr.,

    1. Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR CNRS 8601, Université René Descartes, 45 rue des Saints Pères, 75270 Paris cedex 06, France, Fax: (+33) 142-868-387
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  • Gildas Bertho Dr.,

    1. Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR CNRS 8601, Université René Descartes, 45 rue des Saints Pères, 75270 Paris cedex 06, France, Fax: (+33) 142-868-387
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  • Jérôme Marrot,

    1. Institut Lavoisier, UMR CNRS 8180, Université de Versailles St-Quentin en Yvelines, 45 av. des Etats-Unis, 78035 Versailles cedex, France
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  • Marie-Noëlle Rager,

    1. Service de RMN, Ecole Nationale Supérieure de Chimie de Paris (ENSCP), 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
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  • Olivia Reinaud Prof.,

    1. Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR CNRS 8601, Université René Descartes, 45 rue des Saints Pères, 75270 Paris cedex 06, France, Fax: (+33) 142-868-387
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  • Ivan Jabin Dr.

    1. Unité de Recherche en Chimie Organique et Macromoléculaire (URCOM), Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre cedex, France, Fax: (+33) 232-744-391
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Abstract

Molecular recognition by calix[6]arene-based receptors bearing three primary alkylamino side chain arms (1) is described. Complexation of ZnII ion provides the dinuclear μ-hydroxo complex equation image, XRD characterization of which, together with solution studies, provided evidence of its hosting of neutral polar organic guests G. Treatment of this complex with a carboxylic acid or a sulfonamide (XH) results in the formation of mononuclear species equation image, one of which (X = Cl) has been characterized by XRD. A dicationic complex equation image is obtained upon treatment of equation image with a mixture of an alkylamine and a strong acid. Each of these ZnII complexes features a tetrahedral metal ion bound to the three amino arms of ligand 1 and to an exogenous ligand (either HO, X, or RNH2) sitting outside of the cavity. As a result, the metal ion structures the calixarene core, constraining it in a cone conformation suitable for guest hosting. The receptor properties of these compounds have been explored in detail and are compared with those of the trisammonium receptor equation image, based on the same calixarene core, as well as those of the trisimidazole-based dicationic Zn funnel complexes. This study reveals very different host properties, in spite of the common hydrophobic, π-basic, and hydrogen-bonding acceptor properties of the calixarene cores. A harder external ligand produces a less polarized receptor that is consequently particularly sensitive to the hydrogen-bonding ability of its guest. The less electron-rich the apical ligand, and a fortiori the trisammonium host, the more sensitive the receptor to the dipole moment of the guest. All this stands in contrast with the funnel Zn complexes, in which the coordination link plays a dominant role. It is also shown that the asymmetry of an exo-coordinated enantiopure amino ligand is sensed by the guest. This supramolecular system nicely illustrates how the receptor properties of a hydrophobic cavity can be allosterically tuned by the environment.

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