First ZnII Bowl-Complexes Modeling the Tris(histidine) Metallo-Site of Enzymes

Impact of positive charge and ring-size on interactions of calixarenes with DNA, RNA and nucleotides

Comparison of various calix[6]arene and calix[4]arene derivatives revealed that only analogues bearing permanent positive charge non-covalently bind to ds-DNA and ds-RNA, by insertion into DNA minor groove or RNA major...

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

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.

Chemoselective guest-triggered shaping of a polynuclear CuII calix[6]complex into a molecular host

A new calix[6]arene scaffold bearing a tris-imidazole binding site at the small rim and three tetradentate aza ligands at the large rim was synthesized. The system binds three Cu^II ions at the large rim sites and is unable to bind a fourth one, which remains in solution. The charge repulsion between the complexes, together with the flexibility of the scaffold, disorganizes the small rim site for binding and prevents its use for host-guest studies. Although the presence of MeCN or DMF guests does not alter this state, the addition of a heptylamine guest, which further displays Brønsted basicity, restores its receptor ability by stabilizing the extra Cu^II ion at the tris-imidazole site with concomitant guest encapsulation and binding of an exo hydroxo ligand. This chemoselective nuclearity switch yields a tetranuclear complex in which the guest backbone is preorganized in front of three potentially reactive Cu(ii) complexes, reminiscent of polynuclear Cu^II enzyme active sites.

Inherently chiral heterocyclic resorcinarenes using a Diels–Alder reaction

This paper presents a novel approach to highly diastereoselective synthesis of resorcinarenes having enlarged cavities.

Novel triazole-based ligands and their zinc(ii) and nickel(ii) complexes with a nitrogen donor environment as potential structural models for mononuclear active sites

A tridentate N,N,N-1,2,3-triazole-based ligand successfully coordinated to nickel ions through the less Lewis basic N2 atom of the triazole ring.

The first water-soluble bowl complex: molecular recognition of acetate by the biomimetic tris(imidazole) Zn(ii) system at pH 7.4

The bowl-shaped cavity-ligand based on resorcinarene has been successfully transposed into a water-soluble version that readily binds Zn(ii) and acetate at physiological pH.

Supramolecular control of transition metal complexes in water by a hydrophobic cavity: a bio-inspired strategy

Different strategies for obtaining water-soluble cavity-appended metal complexes are described, and their resulting interlocked assets are discussed in relationship with the very specific properties of water as a solvent.

Biomimetic cavity-based metal complexes

The biomimetic association of a metal ion with a cavity allows selective recognition, unusual redox properties and new reactivity patterns.