Efficient synthesis and host-guest properties of a new class of calix[6]azacryptands.

Two members of a new class of calix[6]azacryptands, namely, calix[6]tampo and calix[6]tamb, have been synthesized through an efficient [1 + 1] macrocyclization reaction--reduction sequence. One of them has been obtained in a remarkably high overall yield from the known X(6)H(3)Me(3). In comparison to all the other calix[6]azacryptands, they possess unique conformational properties since they present a rigidified cone conformation with a partial filling of the cavity by the methoxy groups. In contrast to calix[6]tampo, the fully protonated derivative of calix[6]tamb behaves as a remarkable molecular receptor toward polar neutral guests. NMR studies have shown that the intracavity binding process is governed by a conformational flip of the aromatic walls of the calixarene core.Journal ArticleSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Development and characterization of a copper ion-selective optical sensor based on a novel calix[4]dicyano-diimidazole thin film

International audienceA novel optical sensor for sensitive and selective determination of copper ions in aqueous solution based on a novel calix[4]dicyano-diimidazole ionophore was prepared. The newly synthesized calix[4]dicyano-diimidazole exhibited obvious absorbance enhancement at 284 nm in the presence of copper ions. At pH 6.8, the measuring range of the optode membrane for Cu2+ ions was from 1.0 × 10−8 to 1.0 × 10−4 M with a detection limit of 7.0 × 10−9 M. Furthermore, the response time of the proposed optical device was within 10 min. With the optimum condition described, the optical sensor revealed good selectivity toward Cu2+ ions in comparison with common coexisting cations (Hg2+, Pb2+, Cd2+, Ni2+ and Zn2+). Finally, the reproducibility, regeneration, reversibility and repeatability of this optical sensor were discussed

Synthesis of the first calix[6]crypturea via a versatile tris-azide precursor.

Various nitrogenous calix[6]arene based receptors have been synthesized in one step from a new C3v symmetrical calix[6]arene intermediate decorated with azido groups. Hence, the first calix[6]crypturea has been obtained in high yield through a unique one-pot process consisting of a domino Staudinger/aza-Wittig reaction followed by a [1 + 1] macrocyclization reaction with a tripodal amine. The conformational properties and some of the host-guest properties of the new calix[6]arene derivatives have been studied by NMR spectroscopy.Journal ArticleSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Second generation of calix[6]aza-Cryptands: synthesis of heteroditopic receptors for organic ion pairs.

The efficient syntheses of calix[6]azacryptands decorated with anion-binding groups on the narrow rim have been achieved from an 1,3,5-tris-protected calix[6]hexa-amine. These heteroditopic receptors can bind ammonium ions or organic ion pair salts with a positive cooperativity. In regard to their functionalization at the 1,3,5-phenolic positions, these compounds constitute the first examples of a second generation of C3 v symmetrical calix[6]azacryptands.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Mimicking the protein access channel to a metal center: effect of a funnel complex on dissociative versus associative copper redox chemistry.

The control of metal-ligand exchange in a confined environment is of primary importance for understanding thermodynamics and kinetics of the electron transfer process governing the reactivity of enzymes. This study reveals an unprecedented change of the Cu(II)/Cu(I) binding and redox properties through a subtle control of the access to the labile site by a protein channel mimic. The cavity effect was estimated from cyclic voltammetry investigations by comparison of two complexes displaying the same coordination sphere (tmpa) and differing by the presence or absence of a calix[6]arene cone surrounding the metal labile site L. Effects on thermodynamics are illustrated by important shifts of E(1/2) toward higher values for the calix complexes. This is ascribable to the protection of the labile site of the open-shell system from the polar medium. Such a cavity control also generates specific stabilizations. This is exemplified by an impressively exalted affinity of the calixarene system for MeCN, and by the detection of a kinetic intermediate, a noncoordinated DMF guest molecule floating inside the cone. Kinetically, a unique dissymmetry between the Cu(I) and Cu(II) ligand exchange capacity is highlighted. At the CV time scale, the guest interconversion is only feasible after reduction of Cu(II) to Cu(I). Such a redox-switch mechanism results from the blocking of the associative process at the Cu(II) state, imposed by the calixarene funnel. All of this suggests that the embedment of a reactive redox metal ion in a funnel-like cavity can play a crucial role in catalysis, particularly for metallo-enzymes associating electron transfer and ligand exchange.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Calix[6]tris(thio)ureas: heteroditopic receptors for the cooperative binding of organic ion pairs.

The straightforward syntheses of C3v symmetrical calix[6]trisureas and -thiourea have been achieved. NMR studies have shown that these flexible compounds possess a major cone conformation. While these neutral hosts can strongly bind anions such as AcO(-) or HSO4(-) through induced fit processes, they can also behave as unique heteroditopic receptors for organic ion pairs with a remarkable positive cooperativity in the complexation process, the anion acting as an allosteric effector.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe