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Two molecular cages have been tested as receptors for the persistent organic pollutant chlordecone. Whereas the host bearing amide functions displays a moderate binding constant (126 M−1), the receptor with a tris(2-aminoethyl)amine moiety exhibits a higher association constant (2.1 × 104 M−1). The recognition process was investigated by NMR experiments and DFT calculations. [ABSTRACT FROM AUTHOR]

The synthesis of a hemicryptophane cage combining a CTV unit with a C3 symmetrical moiety bearing three urea functions is reported. This host was found to bind anions with higher binding constants than other previously reported hemicryptophanes. Due to its heteroditopic character this cage proved to be an efficient ion‐pair receptor. The best cooperativity effect was observed for the tetramethylammonium bromide (TMABr) salt, which was confirmed and rationalized by DFT calculations. A tris‐urea unit was combined with CTV moiety, leading to a heteroditopic hemicryptophane capable of binding ion pairs efficiently and selectively. [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. [ABSTRACT FROM AUTHOR]

Two strategies have been explored towards the heterogenization of a host–guest catalytic system where either cavitand host [3iPO] or quaternary ammonium catalysts are grafted on silica supports. The bis-propargyl substituted triphosphonate cavitand [3iPO] was clicked onto an azido functionalized ultra-large pore SBA-15 type silica (UL-SBA-15). Ammonium hybrid materials were produced by grafting a propyltrimethylammonium chloride silane precursor onto silicas of varying porosities and textural properties (UL-SBA-15, SBA-15 and SiO2). Extensive characterization of each material is presented (XRD, N2 sorption, TGA, solid state NMR, elemental analyses, FT-IR). The effect of heterogenization was investigated in the coupling of CO2 with styrene oxide and was compared to all-soluble cavitand/ammonium homogeneous analogs. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and chiroptical properties of a new class of hemicryptophane cages combining a cyclotriveratrylene unit and a tris(2-pyridylmethyl)amine (TPA) moiety are reported. Changing the linkers between these two units allows for the modification of the size and shape of the cavity. The synthesis is straightforward and efficient, providing gram-scale of cage compounds. The racemic mixture of each hemicryptophane host can be readily resolved by chiral HPLC, giving an easy access to the enantiopure molecular cages of which absolute configurations have been assigned by ECD spectroscopy. These new hemicryptophanes are available chemical platforms ready to use for various purposes due to the versatile metal complexation properties of the TPA unit. A Zn(II)@hemicryptophane complex has been obtained and used as a heteroditopic host for the selective recognition of zwitterionic guests. [ABSTRACT FROM AUTHOR]

A class of hemicryptophane cages that adopt imploded conformations in solution and in the solid state has been described and studied by NMR spectroscopy and X-ray crystallography. It is reported that the degree of collapse of the molecular cavity can be controlled by changing the stereochemistry of the chiral elements of the hemicryptophanes, leading to a modulation of their physical and chemical properties. Upon the binding of an oxidovanadium unit, the collapsed molecular cavity can inflate to give an expanded conformation. Removal of the vanadium core by an ancillary complexing ligand restores the initial folded structure. Thus, coordination/de-coordination of the metal ion controls the dynamic motions of the cage, leading to a reversible nanomechanical process. This controlled motion between a collapsed and expanded cavity can be seen as that of a breathable molecular cage. [ABSTRACT FROM AUTHOR]

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]

The synthesis of eight enantiopure molecular cages (four diastereomeric pairs of enantiomers) comprising a helically chiral cyclotriveratrylene (CTV) unit, three axially chiral binaphthol linkages, and three centrally asymmetric carbon atoms of a trialkanolamine core, is described. These new cages constitute a novel family of hemicryptophanes, which combine three classes of chirality. Their absolute configuration was successfully assigned by a chemical correlation method to overcome the signals overlap in the ECD spectra of the binaphtol and CTV units. Stereoselective recognition of glucose and mannose derivatives was investigated with these new chiral cages. Excellent enantio- and diastereoselectivity were reached, since in some cases, both exclusive enantio- and diastereo-discrimination have been observed. In addition, compared with the most relevant hemicryptophanes, these new cages also exhibit improved binding affinities. [ABSTRACT FROM AUTHOR]

New host compounds combining a cyclotriveratrylene (CTV) unit and three binaphthol moieties have been synthesized enantiomerically and diastereomerically pure. The use of a chemical correlation allows for the assignment of their absolute configuration. The energy barrier of epimerization was measured, suggesting that no intramolecular hydrogen bonding occurs between the hydroxyl groups of the binaphthols. These open-shell host compounds were then tested in the recognition of carbohydrates; a preferential binding of mannose toward glucose was observed, and good diastereoselectivities were reached (up to 1:10). This recognition of sugar derivatives by open-shell CTV-based host compounds is unprecedented and opens up the way for a wider use of this easily accessible class of molecules as chiral sensors. [ABSTRACT FROM AUTHOR]

The hydrogen-bonding activation of C=O bonds by azaphosphatranes was explored in a model reaction, i.e., the ring-opening polymerization of lactide. The polymerization process was controlled, and allowed the preparation of polylactides with narrow dispersity under mild conditions (20 °C, 24 h, 10 mol-% catalyst loading). Interestingly, the steric hindrance of azaphosphatranes, as globular rigid structures, prevents any undesired interaction with the tertiary amine cocatalysts, as shown by X-ray analysis and semi-empirical calculations. In contrast to their organocatalytic activity in the CO2/epoxide reaction, all of the phosphonium derivatives tested were found to be efficient catalysts in this ROP benchmark reaction. [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]

Four new enantiopure hemicryptophanes were synthesized and their absolute configuration was determined from experimental and calculated ECD spectra. Complexation properties of these receptors were studied toward six carbohydrate stereoisomers derived from glucose, galactose and mannose. All the receptors showed a better affinity for α-mannoside with association constants up to 2.5 × 103 M−1. One of the receptor can complex almost exclusively α-mannoside facing to α-galactoside. [ABSTRACT FROM AUTHOR]

In this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F- in DMSO or more competitive media (DMSO containing 10% water). In the presence of F-, the yellow and non-fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards F- was attributed to the formation of N-heterocyclic carbene deprotonated by F-, which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments. [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]

A new sensor for in situ, real time methane (CH4) measurements in aqueous environments is based on the refractive index (RI) modulation of a sensitive film composed of a polydimethylsiloxane (PDMS) layer incorporating molecules of cryptophane-A. The RI varies according to the amount of CH4 bound to the cryptophane-A in the film and is determined using surface plasmon resonance (SPR). Tests of the sensor in the summer of 2012 reveal the expansive range of conditions of the Central Baltic Sea with CH4 concentrations varying from 5 nM up to a few hundred nanomolar. The sensor showed detection limits down to 3 nM, sensitivity of 6 to 7 × 10-6 RIU/nM, and response times of 1 to 2 min. Best responses were obtained for concentrations up to 200 nM. Side effects (temperature, cross-sensitivity) are reviewed for future improvements to the sensor design. CH4 values are highest in the Landsort Deep up to 1.2 μM at 400 m depth and lowest in the Gotland Deep with 900 nM at 220 m depth. However, variable values in the upper layers indicate higher mixing rates due to currents and wind driven forces in the Gotland Basin compared with almost constant CH4 values in the Landsort Deep. [ABSTRACT FROM AUTHOR]

ABSTRACT The hemicryptophane racemate (±)- M-1 P-1 was optically resolved by semipreparative HPLC on Chiralpak IC column. The absolute configuration of each isolated enantiomer was established from the analysis of their electronic circular dichroism spectra. Enantiodifferentiation of the chiral cationic cage (±)- M-1 P-1 was evidenced in solution using Δ-TRISPHAT as chiral solvating agent, and the diastereomeric associations were observed in 1H and 31P NMR spectra. Chirality 24:1077-1081, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Triphosphonate cavitand, 3iPO, has been designed for the recognition of ammonium in solution. This Letter presents a study of the selective guest–host recognition between Acetylcholine and Choline ions, ACh+ and Ch+, and the host. We are able to observe that the ACh+ ion replaces the Ch+ ion in the 3iPO-Ch+ complexes with a concomitant exchange/substitution constant of 7×104 M−1. Conversely a replacement of the ACh+ ions by the Ch+ ions in the 3iPO-ACh+ complexes has been also observed with a concomitant exchange constant of 5.8×103 M−1. The structure of the 3iPO-ACh+ complex is determined by single crystal X-ray crystallography. [Copyright &y& Elsevier]

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]

ABii diphosphonatocavitands self-assemble in chloroform solution to form dimeric molecular capsules. The molecular capsules can incarcerate an N-methylpyridinium or N-methylpicolinium guest. We have demonstrated that the supramolecular assembly acts as a molecular rotor as a result of the restricted motion of the guest inside the molecular cavity. In the solid state, X-ray diffraction analysis of the free host showed that two cavitands interact through strong hydrogen bonds to give the supramolecular self-assembled capsule. The solid-state structure of the N-methylpicolinium complex is comparable to that of the free host and indicates that the guest is not a prerequisite for the formation of the capsule. DOSY NMR studies provided a definitive argument for the formation of the free and complexed supramolecular capsule in CDCl3 solution. In solution, the tumbling of the N-methylpyridinium and N-methylpicolinium guests about the equatorial axes of the host can be frozen and differs by the respective energy barriers, with the larger picolinium substrate having a larger value (ΔG‡ = 69.7 kJ mol-1) than the shorter pyridinium guest (ΔG‡ = 44.8 kJ mol-1). This behavior corresponds to the restricted rotation of a rotator in a supramolecular rotor. [ABSTRACT FROM AUTHOR]

Abstract: An inherently chiral ABii diphosphonato cavitand (±)-4 bearing a single quinoxaline bridging moiety was synthesized and resolved by chiral HPLC. Its chiroptical properties were investigated and VCD experiments allowed the determination of its absolute configuration. Distinguishable diastereomeric complexes in solution with l-adrenaline were observed by 1H and 31P NMR together with a noticeable enantio-discrimination at 253K (dr ∼2:1) in favor of the dextrorotatory cavitand (+)-4. [ABSTRACT FROM AUTHOR]

New gallium(III) and iron(III) endohedral complexes were obtained from a hemicryptophane ligand bearing suitable binding sites for octahedral metal coordination. The solid-state structures of the free host and of the complexes were determined by single-crystal X-ray diffraction analysis. The metal ion is linked to the hydrazone nitrogen and the phenolate oxygen atoms, yielding a distorted octahedral geometry around the encapsulated metal. The two isomorphous structures of the metal complexes reveal the exclusive formation of PΔ/MΛ enantiomeric pairs. [ABSTRACT FROM AUTHOR]

iii-Phosphorylated cavitands incorporating an N-methylpyridinium guest moiety as the fourth bridging unit form supramolecular associations by inclusion of the charged CH3N+-pyridinium head into a neighboring host cavity. The dimeric association is favored in solution and was characterized by NMR, mass spectrometry, DOSY experiments, and single crystal X-ray analysis. [ABSTRACT FROM AUTHOR]

Cryptophanes bearing OCH2COOH groups in place of the methoxy groups represent a new class of xenon-carrier molecules soluble in water at biological pH. By using ¹H and 129Xe NMR (thermally- and laser-polarized dissolved gas), the structural and dynamical behaviors of these host molecules as well as their interaction with xenon are studied. They are shown to exist in aqueous solution under different conformations in very slow exchange. A saddle form present for one of these conformations could explain the ¹H NMR spectra. Whereas the cryptophanes in such a conformation are unable to complex xenon, unprecedented high binding constants are found for cryptophanes in the other canonical crown-crown conformation. These host molecules could therefore be valuable candidates for biosensing using 129Xe MRI. [ABSTRACT FROM AUTHOR]

The known xenon-binding (±)-cryptophane-111(1) has been functionalized with six [(η5-C5Me5)RuII]+ ([Cp*Ru]+) moieties to give, in 89% yield, the first water-soluble cryptophane-111 derivative, namely [(Cp*Ru)61]Cl6 ([2]Cl6). [2]Cl6 exhibits a very high affinity for xenon in water, with a binding constant of 2.9(2) × 104 M-1 as measured by hyperpolarized 129Xe NMR spectros- copy. The 129Xe NMR chemical shift of the aqueous Xe@[2]6+ species (308 ppm) resonates over 275 ppm downfield of the parent Xe@1 species in (CDCl2)2 and greatly broadens the practical 129Xe NMR chemical shift range made available by xenon-binding molecular hosts. Single crystal structures of [2][CF3SO3]6·xsolvent and 0.75H2O@1·2CHCl3 reveal the ability of the cryptophane-111 core to adapt its conformation to guests. [ABSTRACT FROM AUTHOR]

The article presents a study that asserts the cryptophane optimization for xenon (Xe) encapsulation. The smallest cryptophane synthesis was used in the study which served as a molecular host to the transport of agents. The study was carried by creating molecular hosts and comparing Xe nuclear magnetic resonance spectroscopy from the results of the chemical shift and coupling reactions. It shows that host 1 possesses binding properties in the organic solution, implying cryptophane complexity.

Hereby, we describe the synthesis of a self-assembled syn -cryptophane using dynamic nucleophilic aromatic substitution of tetrazines. 1 H NMR cage titrations reveal that the tetramethylammonium cation binds under slow exchange conditions while counter-anions show a fast exchange regime. Finally, the cryptophane can be disassembled by the addition of thiols allowing guest release.

Polycyclic aromatic hydrocarbons including heteroatoms have found a wide range of applications, for instance, in supramolecular chemistry or material science. Phosphangulene derivatives are P-containing polycyclic aromatic hydrocarbons presenting a concave aromatic surface suitable for building supramolecular receptors. However, the applications of this convenient building block have been strongly hampered by a difficult and multistep preparation requiring several protection-deprotection sequences along with the use of harmful reagents. Here, we report a straightforward, protecting-group-free, three-step, and hundred-milligram-scale synthesis of a chiral phosphangulene oxide derivative via a triple phospho-Fries rearrangement. This compound was easily resolved by chiral HPLC and further functionalized, giving rise to versatile chiral phosphangulene derivatives. Following this strategy, chiral phosphangulene oxides with low symmetry were synthesized. Molecular crystal structures revealed a variety of molecular organization in the solid. This opens the way to wider use of this compound as a building block for cages or new materials.

A new hemicryptophane host with a ditopic molecular cavity combining a cyclotriveratrylene (CTV) unit with a tris-urea moiety was synthesized. The complexation of halides, tetramethylammonium (TMA + ) cation, and ion pairs was investigated. A positive cooperativity was observed, since halides display a higher binding constant when a TMA + cation is already present inside the cage. When TMA + was complexed alone, a decrease of temperature from 298 K to 230 K was required to switch from a fast to a slow exchange regime on the NMR time scale. Nevertheless, the prior complexation of a halide guest in the lower part of the host resulted in significant decrease of the exchange rate of the subsequent complexation of the TMA + cation. Under these conditions, the 1 H NMR signals characteristic of a slow exchange regime were observed at 298 K. Addition of an excess of salts, increases the ionic strength of the solution, restoring the fast exchange dynamics. This result provides insight on how the exchange rate of a cation guest can be modulated by the complexation of a co-guest anion., (© 2023 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

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., (© 2023 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

Chlordecone (CLD), a Persistent Organic Pollutant, is still present in water and food chain of the French West Indies (FWI), leading to dramatical public health problems. One of the major issues is the lack of an easy, non-expensive, sensitive and robust method for the detection of chlordecone to ensure chlordecone-free water and foods for the residents of the FWI. This study reports on the development of a fluorescent molecular cage that allows a simple and convenient detection of chlordecone in water at environmental concentration. The specific structural features of chlordecone prompted the choice of hemicryptophanes as receptor. First, the size, shape of the cavity, as well as the recognition units, were optimized to identify the most efficient non fluorescent host for CLD complexation. Then, this selected compound was equipped with fluorophores at different positions in order to find the most efficient system for CLD detection by fluorescence. Among the two most promising fluorescent cages, the newly synthesized hemicryptophane with biphenyl moieties allowed the development of a fast, easy, reproducible and cheap procedure to detect CLD in water. Based on its sensitivity and scalability, with modulation of hemicryptophane, concentration, CLD concentrations were estimated over five orders of magnitude (10 -2 -10 3  μg/L) including the environmental levels of contamination and the permissible limit for drinking water in the FWI., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Haloazaphosphatranes are the halogenated parents of proazaphosphatranes, also known as Verkade's superbase. While the synthesis of iodo-, bromo- and chloroazaphosphatranes was reported more than thirty years ago by J. G. Verkade, the first synthesis of fluoroazaphosphatranes was only described in 2018 by Stephan et al. Currently, no common and versatile procedure exists to access fluoroazaphosphatranes platform with different structural characteristics. In this report, a new and simple synthesis of this class of compounds was developed based on the nucleophilic attack of the fluoride anion on chloroazaphosphatrane derivatives with good to high isolated yields for the corresponding fluoroazaphosphatranes (70-92%). The scope of the reaction was widened to fluoroazaphosphatranes bearing various substituents and X-ray molecular structures of two of them are reported. The stability of fluoroazaphosphatranes toward nucleophilic solvents like water has been investigated. As they revealed much more robust cations than their chloroazaphosphatrane parents, their chloride salts were tested as organocatalysts for the formation of cyclic carbonates from epoxides and CO 2 . Fluoroazaphosphatranes proved to be both efficient and stable catalytic systems for CO 2 conversion with catalytic activities similar to those of azaphosphatranes, and no decomposition of the cation was observed at the end of reaction., (© 2022 Wiley-VCH GmbH.)

Two new hemicryptophanes combining a cyclotriveratrylene unit with either an aminotrisamide or a tris(2-aminoethyl)amine (tren) moiety have been synthesized. Although a conventional synthesis approach was used, the molecular cages obtained are devoid of the expected C 3 symmetry. NMR analyses and X-ray crystal structure determination showed that these hemicryptophanes exhibited C 1 symmetry due to the unusual arrangement of the substituents of the cyclotriveratrylene unit. This unprecedented arrangement is related to a change in the regioselectivity of the Friedel-Crafts reactions that led to the CTV cap. This constitutes an original approach to access enantiopure chiral molecular cages with low symmetry.

Chloroazaphosphatranes, the corresponding halogenophosphonium cations of the Verkade superbases, were evaluated as a new motif for halogen bonding (XB). Their modulable synthesis allowed for synthetizing chloroazaphosphatranes with various substituents on the nitrogen atoms. The binding constants determined from NMR titration experiments for Cl - , Br - , I - , AcO - , and CN - anions are comparable to those obtained with conventional iodine-based monodentate XB receptors. Remarkably, the protonated azaphosphatrane counterparts display no affinity for anions under the same conditions. The strength of the XB interaction is, to some extent, related to the basicity of the corresponding Verkade superbase. The halogen bonding abilities of this new class of halogen donor motif were also revealed by the Δδ( 31 P) NMR shift observed in CD 2 Cl 2 solution in the presence of triethylphosphine oxide (TEPO). Thus, chloroazaphosphatranes constitute a new class of halogen bond donors, expanding the repertory of XB motifs mainly based on C Ar -I bonds.

The synthesis of two new fluorescent hemicryptophanes is reported. They were found to be efficient and selective receptors for acetylcholine over choline. When compared to other hemicryptophane hosts previously reported for the selective recognition of acetylcholine, they display improved fluorescent properties: their maximum emission wavelengths are red-shifted and the quantum yields are higher. NMR titration experiments and density functional theory (DFT) calculations support the results obtained from fluorescence spectroscopy and give insights into the interactions involved in the host/guest complexes and into the selectivity for acetylcholine over choline.

Proazaphosphatranes (also named Verkade's superbases) and their azaphosphatrane conjugated acids have been recently been shown to be confined in either covalent or self-assembled molecular cages, or immobilized in nanopores of hybrid materials. The encapsulation of these phosphorus moieties turns out to strongly affect both their acid-base, catalytic, and recognition properties. The thermodynamics and kinetics of the proton transfer as well as the selectivity and catalytic activities of Verkade's superbases were strongly changed upon their confinement in a hemicryptophane cavity. Moreover, self-assembled cages, including azaphosphatrane moieties, were found to display remarkable anion recognition properties in water. In this Minireview, these new aspects of the chemistry of aza- and proaza-phosphatranes are presented, in order to highlight the great potential of such an approach., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A highly selective recognition of fluoride was achieved through the design of a small hemicryptophane cage ( 3 ) presenting a southern tris-urea hosting moiety. The resulting host-guest complex has been characterized by electrospray ionization-high-resolution mass spectrometry, 1 H and 19 F NMR, and X-ray diffraction techniques. In particular, X-ray diffraction analysis of [ 3 ·F - ] reveals that the encapsulation of one fluoride, within 3 , occurs through NH···F - H-bonding with the six NH residues of the tris-urea ligand. An association constant of 1200 M -1 was extracted from 1 H NMR titration experiments, indicating that efficient fluoride binding also occurs in solution. Finally, in sharp contrast with previously reported urea-based hemicryptophane hosts, the small preorganized cavity found in 3 allows for an exclusive selectivity for fluoride over other competing halides.

We report on the synthesis of C 3 -symmetric enantiopure cage molecules 1 , which exhibit remarkable to exclusive enantioselective recognition properties toward chiral ammonium neurotransmitters. Strong changes in the substrate selectivity are also observed when different stereoisomers of 1 are used. Furthermore, protonation/deprotonation induces a reversible modification of the conformation of 1 , which switches from an imploded to an inflated form, leading to ejection and reuptake of the guest initially encaged inside the cavity.

The five-steps synthesis of a hemicryptophane cage combining a benzene-1,3,5-tricarboxamide unit and a cyclotriveratrylene (CTV) moiety is described. Chiral high-performance liquid chromatography (HPLC) was used to resolve the racemic mixture. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental electronic circular dichroism (ECD) spectra with the calculated ones. X-ray molecular structures reveal that the capped benzene-1,3,5-tricarboxamide unit adopts a structurally chiral conformation in solid state: the chirality of CTV moiety controls the Λ or Δ orientation of the three amides., (© 2019 Wiley Periodicals, Inc.)

Non-heme iron, vanadium, and copper complexes bearing hemicryptophane cavities were evaluated in the oxidation of methane in water by hydrogen peroxide. According to 1 H nuclear magnetic resonance studies, a hydrophobic hemicryptophane cage accommodates a methane molecule in the proximity of the oxidizing site, leading to an improvement in the efficiency and selectivity for CH 3 OH and CH 3 OOH compared to those of the analogous complexes devoid of a hemicryptophane cage. While copper complexes showed low catalytic efficiency, their vanadium and iron counterparts exhibited higher turnover numbers, ≤13.2 and ≤9.2, respectively, providing target primary oxidation products (CH 3 OH and CH 3 OOH) as well as over-oxidation products (HCHO and HCOOH). In the case of caged vanadium complexes, the confinement effect was found to improve either the selectivity for CH 3 OH and CH 3 OOH (≤15%) or the catalytic efficiency. The confined space of the hydrophobic pocket of iron-based supramolecular complexes plays a significant role in the improvement of both the selectivity (≤27% for CH 3 OH and CH 3 OOH) and the turnover number of methane oxidation. These results indicate that the supramolecular approach is a promising strategy for the development of efficient and selective bioinspired catalysts for the mild oxidation of methane to methanol.

A fluorescent hemicryptophane has been synthesized and can be used as a turn on receptor of acetylcholine. A binding constant of 2.4 × 104 M-1 was measured for this neurotransmitter, and its selective and sensitive detection over choline and choline phosphate was achieved. NMR and DFT calculations provide insight into the interactions involved in this selective recognition process.

The polytopic hemicryptophane cage HC1 combining a cyclotriveratrylene (CTV) unit and a tris(2-aminoethyl)amine (tren) moiety connected by three 2-hydroxyisophthalamide linkers was synthesized in 12 steps. The resulting highly functionalized covalent host is soluble in aqueous medium and has been used to complex Gd(III) ion. The Gd(III)@HC1 complex presents promising relaxivity properties when compared to the clinically used Dotarem MRI agent.

Cyclotriveratrylene (CTV) is a macrocyclic cyclophane presenting a bowl-shaped conformation, used as building block to construct cryptophane and hemicryptophane capsules. A method to synthesize new enantiopure CTV derivatives with an unprecedented spatial arrangement of their substituents, exhibiting C 1 symmetry, is described. The absolute configuration was assigned by ECD spectroscopy coupled with modeling. A statistical model has allowed for optimization of the proportion of C 1 CTV, and the modularity of this approach is also highlighted.

A hemicryptophane cage bearing amine and amide functions in its three linkers was synthesized in five steps. The X-ray molecular structure of the cage shows a triple-stranded helical arrangement of the linkers stabilized by intramolecular hydrogen bonds between amide and amine groups. The chirality of the cyclotriveratrylene unit controls the propeller arrangement of the three aromatic rings in the opposite part of the cage. 1 H NMR studies suggest that this structure is retained in solution.

A new chiral hemicryptophane cage combining an electron-rich cyclotriveratrylene (CTV) unit and polar amine functions has been synthesized. The resolution of the racemic mixture has been performed by chiral HPLC, and the assignment of the absolute configuration of the two enantiomers has been achieved using ECD spectroscopy. In contrast with other hemicryptophane receptors, the two enantiomeric hosts display both remarkable enantioselectivities in the recognition of carbohydrates and good binding constants. Moreover, by switching the chirality of the CTV unit from M to P, a strong preference shift from glucose to mannose derivatives is observed.

The synthesis, characterization, and chiroptical properties of a new class of hemicryptophane cages combining a cyclotriveratrylene unit and a tris(2-pyridylmethyl)amine (TPA) moiety are reported. Changing the linkers between these two units allows for the modification of the size and shape of the cavity. The synthesis is straightforward and efficient, providing gram-scale of cage compounds. The racemic mixture of each hemicryptophane host can be readily resolved by chiral HPLC, giving an easy access to the enantiopure molecular cages of which absolute configurations have been assigned by ECD spectroscopy. These new hemicryptophanes are available chemical platforms ready to use for various purposes due to the versatile metal complexation properties of the TPA unit. A Zn(II)@hemicryptophane complex has been obtained and used as a heteroditopic host for the selective recognition of zwitterionic guests.