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The persistent organic pollutant chlordecone massively contaminates water resources of the French West Indies. Hemicryptophanes are cages capable of complexing chlordecone in organic solvents. Here we demonstrate that a hemicryptophane cage is not only able to recognize this pollutant in chloroform but is also efficient for the removal of chlordecone from water. This evidences that, beyond our previously reported proof of concept, this receptor could be apply as a direct and efficient depolluting agent, making it a promising system for applied supramolecular chemistry. A simple pH switch (basic washing) enables the release of chlordecone from the host, under its deprotonated form, allowing the empty supramolecular cage to be recycled and reused. This method for recycling the receptor, is to the best of our knowledge unprecedented. [ABSTRACT FROM AUTHOR]

The recognition of carbohydrate plays a key role in numerous biological processes. Thus, artificial receptors have been synthesized to mimic these biological systems. To date, most of the receptors reported for carbohydrate complexation present highly symmetrical cavities, probably because their syntheses require less synthetic efforts and are easier to achieve and control. However, carbohydrates display complex, asymmetrical structures suggesting that hosts with low symmetry might be more adapted to recognize these guests. Here, we described the strategies that have been used to complex carbohydrates with macrocycles and cages presenting low symmetry and the potential of this approach. Self‐assembled cages are first described, then covalent macrocycles and cages are presented and for each example the binding properties of low‐symmetry systems are compared to those of their higher‐symmetry counterparts. [ABSTRACT FROM AUTHOR]

Covalent cages with a well‐defined cavity located close to a reactive center are of increasing interest because of their outstanding ability to mimic the catalytic properties of enzymatic systems. The size and shape of such synthetic nanosized reactors strongly affect the behavior of the trapped reaction partners, which can adopt specific conformations and orientations. In particular, the use of molecular cages with confined reactive functions strongly modifies the outcome of catalytic transformations that are carried out therein. This review article describes covalent molecular cages presenting an endohedral functionalization of their inner space and reports on their catalytic activities compared with those of model systems that lack cavity. The confinement of endohedral‐functionalized cavities affects their stability as catalysts and the rate and selectivity of reactions they mediate. [ABSTRACT FROM AUTHOR]

A frustrated Lewis pair (FLP) system was obtained by confinement of the Lewis base partner, a Verkade's superbase, in a molecular cavity. Whereas the model superbase lacking cavity displayed no catalytic activity in Morita–Baylis–Hillman (MBH) reactions, when associated to titanium (IV) chloride, the encaged superbase turns out to be an efficient catalyst under the same conditions. The crucial role of the endohedral functionalized cage on catalytic performance was further demonstrated by the fact that model superbases with bulky substituents were much less efficient to produce active catalysts, as well as by inhibition and substrate selection experiments. 31P NMR spectroscopy and mass spectrometry experiments evidenced that no interaction between the Lewis acidic and basic partners occurred when the superbase was capped by a cycloveratrylene (CTV) unit, thus creating a true FLP active system. Switching on the catalytic activity: A frustrated Lewis pair (FLP) system has been designed, where the Lewis base partner is encapsulated in a cage structure. Endohedral functionalization of a well‐defined cavity allows for the formation of a FLP, restoring the catalytic activity of the Verkade's superbase. [ABSTRACT FROM AUTHOR]

A convenient and efficient gram-scale synthesis for enantiopure hemicryptophane-tren (tren=tris(2-aminoethyl)amine) derivatives has been developed. The four-step synthesis is based on the optical resolution of a key intermediate, cyclotriveratrylene, for which the energy barrier for racemization has been measured to ensure that no racemization occurs during the two last steps of the synthetic pathway. The assignments of the absolute configurations have been performed by electronic circular dichroism and the enantiopurity was determined by NMR spectroscopy in the presence of enantiopure camphor sulfonic acid. To highlight the interest of such compounds, the recognition of norephedrine neurotransmitter was investigated and showed a remarkable enantioselectivity towards the C3 symmetrical hosts. Finally, this highly modular synthetic pathway was used to provide eight enantiopure hemicryptophanes with different sizes, shapes, and functionalities. These results underline the high potential of this approach, which could lead to many applications in chiral recognition or asymmetric supramolecular catalysis. [ABSTRACT FROM AUTHOR]

ABSTRACT Enantiopure hemicryptophanes efficiently discriminate chiral ammonium neurotransmitters. The ephedrine and norephedrine molecules associate with hemicryptophane hosts to form 1:1 and 1:2 host-guest complexes. Binding constants are determined by fitting the 1H (NMR) titration curves to give β1 and β2 values, which are used to characterize the diastereomeric and enantiomeric discriminating potentials of the hosts. Chirality 25:47-479, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Hemicryptophane–oxidovanadium(V) complexes 1 and 2 were tested in the oxidation of sulfide to sulfoxide. They were found to be efficient supramolecular catalysts in the oxidation of thioanisol with yields up to 95%. Furthermore, turnover up to 180 was obtained by decreasing the amount of catalyst to 0.5% molar. A direct comparison between hemicryptophane complexes 1 and 2 and the model complex 3, which lacks a cavity, was made. The cage structure in 1 and 2 strongly enhanced the catalytic activity, and higher yields were obtained with 1 or 2 than with the model compound 3. Kinetic constants for the oxidation of thioanisol were estimated up to sixfold higher with the hemicryptophane complexes than with the model complex 3. [Copyright &y& Elsevier]

The recent results in the chemistry of cavitands have proved that they are very efficient molecular receptors and potential precursors of molecular devices. In this context, we have investigated the synthesis and binding properties of phosphorylated cavitands. The stereoselective synthesis and the structural studies of the new compounds showed that these bowl-shaped molecules possess a well defined aromatic cavity surrounded by four phosphoryl groups (P=O or P=S). They are very efficient ligands for metal and organic cations. They are able to encapsulate cationic species by cooperative effect of the preorganized aromatic cavity and the four phosphorylated groups. Moreover, the upper and lower rim functionalitics can lead to the formation of molecular capsules and supramolecular assemblies whose properties and structures have been investigated by X-ray diffraction and NMR studies in solution. [ABSTRACT FROM AUTHOR]

In the wide area of host-guest chemistry, hemicryptophanes, combining a cyclotribenzylene (or cyclotriveratrylene CTV) unit with another different C [sub 3]-symmetrical moiety, appears as a recent family of molecular cages. The synthesis and recognition properties of the first hemicryptophane were reported in 1982 by Collet and Lehn, but the very little attention received by this class of host compounds in the 20 years following this first promising result can account for their apparent novelty. Indeed, in the last 10 years hemicryptophanes have aroused growing interest, and new aspects have been developed. Thanks to the rigid shaping unit of the north part (CTV) and also the variable and easily functionalized south moiety, hemicryptophanes are revealed to be inherently chiral ditopic host compounds, able to encapsulate various guests, including charged and neutral species. They also enter the field of stimuli-responsive supramolecular systems exhibiting controlled functions. Moreover, endohedral functionalization of their inner cavity leads to supramolecular catalysts. The confinement of the catalytic center affords nanoreactors with improved catalytic activities or selectivities when compared to model systems without a cavity. The current trend shows that reactions in the confined space of synthetic hosts, mimicking enzyme behavior, will expand rapidly in the near future. [ABSTRACT FROM AUTHOR]

The iiii stereoisomer of the tetrathiophosphonate-calix[4]resorcinarene host 1 exhibited excellent extraction properties towards soft metal ions, with a better affinity for Ag+ (91%), than for Tl+ (38%) and Hg2+ (16%). The extraction of other picrate salts (Cu2+, Ni2+, Co2+, Zn2+, Cd2+, Pb2+) was not detected. The stoichiometry and the structure of the Hg2+, Tl+ and Ag+ complexes were studied by NMR in solution and gave respectively 1:1, 1:1 and 1:2 host–guest complexes. The formation of the self-assembled 12·(AgPic)4 complex was independent on the anion and only observed with silver(I) ion. [Copyright &y& Elsevier]

The use of tri- and tetraphosphonate cavitand hosts in conjunction with tetrabutylammonium halide catalysts led to improved activity in the coupling of 1,2-epoxyhexane and CO 2 . Catalytic efficiency of the supramolecular assembly strongly relies on both the structural features and binding properties of the cavitand host. Tetraphosphonate cavitand host (4 i PO 1 ) was shown to impact more markedly n- Bu 4 NCl reactivity than triphosphonate counterpart (3iPO 3 ) due to its greater binding strength toward the ammonium cation as evidenced by titration experiments. The participation of acidic functional groups within the cavitand structure to activity enhancement was also clearly demonstrated. The best result was obtained with n- Bu 4 NI/3iPO 2 supramolecular assembly affording hexene carbonate in quantitative yield after 18 h of reaction. The improved performance observed with the cavitand 3 i PO 2 relies on a double activation of both the nucleophile (halide) through efficient encapsulation of the ammonium cation and the substrate (epoxide) through hydrogen bonding. [ABSTRACT FROM AUTHOR]

Endohedral functionalization of the molecular cavity of host molecules is in high demand in many areas of supramolecular chemistry. When highly reactive species are incarcerated in the confined space of a molecular cavity, deep changes of their chemical properties are expected. Here, we show that the superbasic properties of proazaphosphatranes can be improved in the confined space of the molecular cavity of hemicryptophane hosts. A general and modular procedure is described to prepare supramolecular superbases with various cavity sizes. The rate of proton transfer is strongly dependent on the shape and size of the inner cavity of the designed superbasic structure. Kinetic and thermodynamic data are strongly correlated to the space available around the basic center as revealed by the X-ray molecular structures analyses [ABSTRACT FROM AUTHOR]

Abstract: For detection of biological events in vitro, sensors using hyperpolarized 129Xe NMR can become a powerful tool, provided the approach can bridge the gap in sensitivity. Here we propose constructs based on the non-selective grafting of cryptophane precursors on holo-transferrin. This biological system was chosen because there are many receptors on the cell surface, and endocytosis further increases this density. The study of these biosensors with K562 cell suspensions via fluorescence microscopy and 129Xe NMR indicates a strong interaction, as well as interesting features such as the capacity of xenon to enter the cryptophane even when the biosensor is endocytosed, while keeping a high level of polarization. Despite a lack of specificity for transferrin receptors, undoubtedly due to the hydrophobic character of the cryptophane moiety that attracts the biosensor into the cell membrane, these biosensors allow the first in-cell probing of biological events using hyperpolarized xenon. [Copyright &y& Elsevier]

Four tetraphosphorylated TiiiiPO cavitands 1 encapsulate the pyridinium heads of a tetrakis(N-methylpyridinium)porphyrin iodide to form a 4:1:4 (host)4/guest4+/4I- complex. The single-crystal X-ray diffraction analysis shows the arrangement of the four cavities bound to the CH3N+ groups of the porphyrin moiety and the four iodide anions nested between the phenethyl substituents of the hosts. ¹H NMR investigations show that the structure is preserved in chloroform solution and underscore the effect of the counteranions. [ABSTRACT FROM AUTHOR]

An abstract of the study "Helical, Axial, and Central Chirality Combined in a Single Cage: Synthesis, Absolute Configuration, and Recognition Properties" by D. Zhang and colleagues is presented.