Issue 24, 2018

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

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

Supplementary files

Article information

Article type
Edge Article
Submitted
09 Mar 2018
Accepted
29 May 2018
First published
29 May 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2018,9, 5479-5487

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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