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Issue 24, 2018
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The 3rd degree of biomimetism: associating the cavity effect, ZnII coordination and internal base assistance for guest binding and activation

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Abstract

The synthesis and characterization of a resorcinarene-based tetra(imidazole) ligand is reported. The properties of the corresponding ZnII complex are studied in depth, notably by NMR spectroscopy. In MeCN, acid–base titration reveals that one out of the four imidazole arms is hemi-labile and can be selectively protonated, thereby opening a coordination site in the exo position. Quite remarkably, the 4th imidazole arm promotes binding of an acidic molecule (a carboxylic acid, a β-diketone or acetamide), by acting as an internal base, which allows guest binding as an anion to the metal center in the endo position. Most importantly, the presence of this labile imidazole arm makes the ZnII complex active for the catalyzed hydration of acetonitrile. It is proposed that it acts as a general base for activating a water molecule in the vicinity of the metal center during its nucleophilic attack to the endo-bound MeCN substrate. This system presents a unique degree of biomimetism when considering zinc enzymes: a pocket for guest binding, a similar first coordination sphere, a coordination site available for water activation in the cis position relative to the substrate and finally an internal imidazole residue that plays the role of a general base.

Graphical abstract: The 3rd degree of biomimetism: associating the cavity effect, ZnII coordination and internal base assistance for guest binding and activation

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Publication details

The article was received on 09 Mar 2018, accepted on 29 May 2018 and first published on 29 May 2018


Article type: Edge Article
DOI: 10.1039/C8SC01129J
Citation: Chem. Sci., 2018,9, 5479-5487
  • Open access: Creative Commons BY-NC license
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    The 3rd degree of biomimetism: associating the cavity effect, ZnII coordination and internal base assistance for guest binding and activation

    A. Parrot, S. Collin, G. Bruylants and O. Reinaud, Chem. Sci., 2018, 9, 5479
    DOI: 10.1039/C8SC01129J

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