Allosterically coupled double induced fit for 1+1+1+1 self-assembly of a calix[6]trisamine, a calix[6]trisacid, and their guests.

Journal ArticleResearch Support, Non-U.S. Gov'tFLWINinfo:eu-repo/semantics/publishe

Nouveaux récepteurs moléculaires chiraux dérivés de calix[6]arènes

LE HAVRE-BU Centrale (763512101) / SudocTOULOUSE-ENSIACET (315552325) / SudocSudocFranceF

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

Highly selective synthesis of a 1,3,5-tris-protected calix[6]arene-type molecular platform through coordination and host-guest chemistry.

An elegant methodology based on the synergistic combination of coordination and host-guest chemistry led to the highly efficient synthesis of a unique C(3v)-symmetrical, calix[6]arene-based molecular platform with three protected amino arms in alternating positions. The key step involves the formation of a stable supramolecular host-guest Zn(II) complex from a C(6v)-symmetrical calix[6]hexaamine. Indeed, in the presence of a polar neutral guest and a strong donor that acts as an exogenous ligand, three alternating amino groups of this calix[6]hexaamine are selectively coordinated to the Zn(II) ion while the three others remain free and are thus much more reactive toward chemical reagents. In addition to this protective role, the metal centre preorganises the C(3v)-symmetrical complex in such a way that the uncoordinated NH(2) groups are directed toward the outside of the cavity; they are then accessible for a chemical transformation. Hence, reaction of these alternating free amino groups with a protective reagent (i.e. Boc(2)O) followed by zinc decoordination quantitatively and selectively yielded the 1,3,5-tris-Boc-protected calixarene derivative on a gram scale. It was shown that the presence of all the partners of the key intermediate Zn complex (i.e. the metal centre, the exogenous ligand and the included guest) is crucial for a high selectivity. Finally, a two step sequence that led to a C(3v)-symmetrical 1,3,5-tris-acetylated calix[6]hexaamine through the removal of the Boc groups illustrates that the 1,3,5-tris-protected calix[6]hexaamine is a promising molecular platform. Examples of such readily available C(3v)-symmetrical calixarene-based building blocks are extremely rare in the literature.Journal ArticleSCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

A novel C3v-symmetrical calix[6](aza)cryptand with a remarkably high and selective affinity for small ammoniums.

The three-step synthesis of a calix[6]arene capped with a TAC unit is presented. The novel C(3v)-symmetrical calix[6](aza)cryptand displayed an exceptionally high affinity for small ammoniums. NMR and X-ray diffraction analyses demonstrated the formation of endo-complexes. These complexes are stabilized thanks to (i) hydrogen bonding to both the aza cap and one phenolic unit of the calixarene and to (ii) cationic and CH-pi interactions between the ammonium and the aromatic walls of the host. Combined extraction and competitive binding experiments yielded the free energies of bindings DeltaG degrees in chloroform. The values are the highest ever obtained with a calixarene-type host. Calix[6]TAC displayed the best affinity for EtNH(3)(+). Comparison with other small ammoniums emphasizes the high selectivity of the recognition process.Journal ArticleArticle faisant la couverture du numéro du 23 juillet 2004info:eu-repo/semantics/publishe

Optically pure calix[6]tris-ammoniums: syntheses and host-guest properties toward neutral guests.

[reaction: see text] Optically pure calix[6]arenes bearing chiral amino arms 4, 7, and 10 have been synthesized in high yields from the known symmetrically 1,3,5-trismethylated calix[6]arene. For both compounds 7 and 10, the key step consists of an efficient selective alkylation on the narrow rim of the calix[6]arene with Ba(OH)2 as the base. All of these chiral calix[6]tris-amines possess a similar flattened cone conformation with the cavity occupied by the methoxy groups. In contrast to 4 and 7, upon protonation, the enantiopure calix[6]arene 10 can switch to the opposite flattened cone conformation through self-assembly of its ammonium arms in an ion-paired cap which closes the cavity. As shown by NMR host-guest studies and an X-ray structure, the obtained polarized host (10 x 3H+) behaves as a remarkable endo-receptor for small polar neutral molecules. Thanks to the tris-cationic chiral binding site of 10 x 3H+, it was shown that the guests experience a chiral environment upon inclusion. Finally, the first example of enantioselective molecular recognition inside the cavity of a calix[6]arene has been evidenced with a racemic 1,2-diol guest.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Synthesis and study of calix[6]cryptamides: A new class of heteroditopic receptors that display versatile host-guest properties toward neutral species and organic associated ion-pair salts.

The synthesis of a new family of molecular receptors, namely the calix[6]cryptamides, was achieved through an original [1+1] macrocyclization step that consists of a peptide-coupling reaction between tripodal triscarboxylic acids and a calix[6]trisamine subunit. Several C3- or C3v-symmetrical calix[6]arene-based compounds capped by a trisamido cryptand unit on the narrow rim have been obtained, with the more flexible partners leading to the best yields. These calix[6]cryptamides exhibit two favorably positioned binding sites for the complexation of organic-associated ion pairs in close proximity: a well-defined calix[6]arene cavity suitable for the inclusion of ammonium ions and a cryptamide unit for the coordination of anions. We demonstrate one example, chiral calix[6]cryptamide 12, that constitutes a heteroditopic receptor capable of cooperatively binding both a primary ammonium ion and its chloride counterion, thanks to a combination of polarization and induced-fit effects. In addition, the hydrophobic calixarene cavity of 12 can strongly bind neutral guests through hydrogen bonding and is capable of discriminating between different enantiomers. All these versatile host-guest properties differ greatly from those observed in the parent calix[6]azacryptands.Journal ArticleSCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Enantioselective recognition of amino acids by chiral peptido-calix[4]arenes and thiacalix[4]arene

International audienc

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