Biomimetic and self-assembled calix[6]arene-based receptors for neutral molecules

Abstract

The selective recognition of substrates or cofactors is a key feature of biological processes. It involves coordination bonds, hydrogen bonding, charge/charge and charge/dipole interactions. In this Perspective, we describe how the calix[6]arene core can be functionalized and shaped to act as a biomimetic molecular receptor. The strategy relies on the selective introduction of three amino arms on alternate phenolic positions. Upon metal ion binding or self-assembly via multiple ion-pairing and H-bonding, these amino arms are projected towards each other, thus closing the calixarene small rim. The resulting cone-shaped receptors act as molecular funnels displaying high affinities for a variety of neutral guests. Their hosting properties can be finely tuned by changing the small or the large rim or by allosteric effects. Induced-fit processes are also often observed as the cavity can expand for large guests or shrink for small ones. Hence, the different families of calix[6]arene-based receptors presented here highlight the importance of having a flexible and polarized hydrophobic structure to accommodate the guest.

Supramolecular Control of Biomimetic Coordination – ZnII Cavity Complexes Presenting Two Differentiated Labile Sites in cis Positions

“…As a result, the Xim 3 Zn II complexes display remarkable affinities for a variety of neutral donors as weak as acetaldehyde. [7,8] However, the funnel provides a very different second coordination sphere compared to that of the bowl: its oxygen-rich small rim acts as a repellent for anions at the endo position. [11] This leads to drastically different behaviors: acetic acid and acetamide coordinate within funnels, [7] stabilized by H bonding at the small rim, whereas acetate and deprotonated acetamide anions coordinate within the bowl.…”

“…[8] (3) Whereas the small rim of the calixarene precludes bidentate coordination modes, the bowl readily allows it.…”

“…These cavity complexes display a nitrogen coordination core that mimics the poly-(histidine) site present in many metalloenzymes and coordinates to biologically occurring metal ions such as copper and zinc. [8,19,20] In this system, the simultaneous embedment of two guest ligands is totally precluded by the small rim of the cone cavity. Hence, the only site that allows interaction with a second exogenous ligand [10,21] (or an anion) [11] is situated in a trans position as shown in Figure 1c.…”

“…[6] These two systems display common and different features ( Figure 1). The calix [6]arene-based Cu I complex (and subsequently described Zn II complexes, [7] also called "funnel complexes") [8] displays a single exogenous [9] ligand (an organonitrile) bound to the metal center in the cavity within a tetrahedral geome-tion in the endo position, the exo position, or both. The coordination of diketonates unambiguously demonstrates the relative cis position of the two labile sites present in the tris-(imidazole)zinc(II) bowl complex.…”

Proteïnes com a microreactors en fotoquímica supramolecular

“…Segons els substituents dels anells aromàtics, l"estructura supramolecular pot tenir distintes conformacions i això li dóna versatilitat en les seues utilitats. interessants aplicacions biomimètiques relacionades amb aquest aspecte [56,57] ), per a encapsular nanopartícules [58] , catalitzar reaccions químiques [59] , etc.…”