Resorcinarene Cavitand Research Articles

Inherently chiral resorcinarene cavitands through ionic catalyst-controlled cross-coupling

Inherently chiral resorcinarene cavitands through ionic catalyst-controlled cross-coupling

Synthesis of 6-Methyluracilpentylviologen Resorcinarene Cavitand

Resorcinarenes, as macrocyclic compounds, are widely used to recognize substrates and create supramolecular assemblies. Their bowl-like form organizes functional groups at the upper and lower rims, which has a substantial impact on the molecular recognition of various substrates. As a result, resorcinarenes make good drug nanocarrier candidates. This paper presents the synthesis of a new resorcinarene cavitand functionalized along the upper rim with methyluracil and viologen fragments for its potential use in drug delivery. Methyluracils and viologens are well-known receptor-targeted compounds capable of facilitating the vector transfer of drugs and increasing the effectiveness of their action on cells. The paper describes the synthesis of resorcinarene modified with methyluracil and viologen groups along with its structure determined by 1H-, 13C-NMR and IR spectroscopy.

A glutathione responsive nanocarrier based on viologen resorcinarene cavitand and 1-allylthymine

A glutathione-sensitive nanocarrier for doxorubicin to improve cellular penetration and selective cytotoxic effects on T98G human glioblastoma cells.

Separation and preconcentration of perrhenate from ionic solutions by ion exchange chromatography

Technetium poses an environmental hazard because of its radioactivity and long half-life. It exists in the form of pertechnetate in the environment and can be modeled by the nonradioactive ion perrhenate, since pertechnetate and perrhenate have the same geometry and similar chemical properties. In this research, a new zinc cyclen resorcinarene cavitand (ZCR) column was used in ion chromatography (IC) to efficiently separate perrhenate. Ion chromatography has the advantage of requiring almost no sample preparation for water samples. The ZCR column demonstrated the ability to separate anions: fluoride, chloride, nitrate, sulfate, phosphate, perchlorate, and perrhenate by gradient 2–60 mM NaOH. Unlike other columns, the new column material was selective in retaining perrhenate. The ZCR column also gave a linear range from 2.0 to 1000 mg L−1 for perrhenate with R2 > 0.997. There was a logarithmic relationship between the concentration of perrhenate and its retention time. Excellent perrhenate recovery was achieved on the ZCR column when river water was spiked with perrhenate and perrhenate was preconcentrated. The efficient separations of perrhenate by the ZCR column will potentially assist in pertechnetate separations.

Multicomponent Metallo-Supramolecular Nanocapsules Assembled from Calix[4]resorcinarene-Based Terpyridine Ligands.

Tetrafunctionalized calix[4]resorcinarene cavitands commonly serve as supramolecular scaffolds for construction of coordination-driven self-assembled capsules. However, due to the calix-like shape, the structural diversity of assemblies is mostly restricted to dimeric and hexameric capsules. Previously, we reported a spontaneous heteroleptic complexation strategy based on a pair of self-recognizable terpyridine-based ligands and CdII ions. Building on this complementary ligand pairing system, herein three types of nanocapsules, including a dimeric capsule, a Sierpiński triangular prism, and a cubic star, could be readily obtained through dynamic complexation reactions between a tetratopic cavitand-based ligand and various multitopic counterparts in the presence of CdII ions. The dimeric capsular assemblies display the spacer-length-dependent self-sorting behavior in a four-component system. Moreover, the precise multicomponent self-assembly of a Sierpiński triangular prism and a cubic star possessing three and six cavitand-based motifs, respectively, demonstrates that such self-assembly methodology is able to efficiently enhance architectural complexity for calix[4]resorcinarene-containing metallo-supramolecules.

Embedding calix[4]resorcinarenes in liposomes: Experimental and computational investigation of the effect of resorcinarene inclusion on liposome properties and stability

Two calix[4]resorcinarenes, which differ in the length of the alkyl chain on the methylene bridge between the aromatic rings, have been embedded in unilamellar liposomes prepared from 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine in three host/guest ratios, following two different procedures. The effect of the insertion of the guests has been evaluated through the measurements of the viscosity and the kinetic stability of the liposomal systems by means of the fluorescent probes pyrene and 5(6)-carboxyfluorescein. The presence of the guests reduces the viscosity of the liposomes, suggesting a modification of the bilayer structure. However, this does not affect liposome stability. A calix[4]resorcinarene cavitand with a more rigid conformation compared to the parent resorcinarene, has been also synthetized and embedded in liposomes. The free energy of the insertion of the substrates in the lipid bilayer has been evaluated through Molecular Dynamics simulations.

The many lives of resorcinarene cavitands: from molecular recognition to crystal engineering

The many lives of resorcinarene cavitands: from molecular recognition to crystal engineering

The Use of Resorcinarene Cavitands in Metal‐Based Catalysis

Catalytic chemistry involving coordination complexes based on resorcinarene cavitands has been little explored in comparison to the many studies concerning the use of such ligands in classical coordination chemistry or host–guest chemistry. The potential utility of resorcinarene cavitands in catalysis arises essentially from two features: (1) their ability to function as ligands suitable for metal confinement and thus to make reactions either shape selective or to enhance their rates through supramolecular assistance by the receptor subunit; (2) their ability to enforce steric interactions with a coordinated metal center and thereby favor carbon–carbon bond forming reactions. To date, limited use has been made of cavitands as platforms for the attachment of different ligating sites, in particular for the generation of multifunctional ligands giving rise to anchimeric assistance in catalytic reactions. This review is intended to show the promise that exists in this area. As generic cavitands can be easily expanded to result in large bowl‐shaped structures as well as capsular containers, it may be anticipated that future work in this field will focus on the synthesis of sophisticated, metallated microreactors (possibly made water‐soluble) for highly selective transformations, including polymerizations.

Organization of diglycolamides on resorcinarene cavitand and its effect on the selective extraction and separation of HREEs

Abstract Two calix(4)resorcinarene based cavitands, one that contains four triazole units, calix(4)resorcinarene-tetra(hexyltriazole) CR4-Tz LI , and another that contains four triazole diglycolamide units, calix(4)resorcinarene-tetra(didecyldiglycolamidetriazole) CR4-Tz-DDDGA LII , were synthesized and fully characterized by IR, NMR, and MS. The efficiency of the two cavitands were compared toward the extraction of 7 lanthanides (Ce(III), Nd(III), Sm(III), Gd(III), Dy(III), Er(III), Yb(III)) in chloroform from 5 M HNO 3 . The extraction study showed that LI , which contains only the triazole units, is unable to extract any of the targeted metals. The effects of the organization and diluents on the distribution coefficients and the selectivity of LII were also studied toward the same lanthanide series at the same acidity. The obtained results showed that the cavitand is selective toward heavy lanthanides irrespective of the diluents. The extraction and stripping experiments of the 7 Ln(III) and the separation of Nd and Dy from a Fe-B-Nd-Dy leaching solution were performed.

Versatile Assembly of Metal-Coordinated Calix[4]resorcinarene Cavitands and Cages through Ancillary Linker Tuning.

We propose a design strategy for assembly of metal-coordinated calix[4]resorcinarene cavitands and cages by tuning of the ancillary linkers. Assembly of newly functionalized cavitand with angular isophthalic acid analogs affords three intriguing metal-coordinated cavitands with deep cavities, 1a-1c. Further, by mediating appropriate spacers between two isophthalic acids, two bowl-shaped cavitands are successfully joined together to produce three elegant coordination cages with tunable sizes and shapes, 2a-2c. The cavitand and cage crystals possess considerable amount of accessible porosities, as clearly established by gas adsorption measurements. Remarkably, 1a-1c also exhibit high structural flexibilities, reversibly transforming between the open-pore and the narrow-pore structures, upon removal and sorption of guest molecules, as evidenced by diffraction and gas adsorption measurements. By combining experimental studies with density functional theory (DFT) calculations, we thoroughly elucidated the mechanism of the structural transformations in response to external stimuli in this new class of flexible porous solids.

Rapid selective colorimetric sensing of polyphosphates by ionic resorcinarene cavitand interdigitated gold nanoparticles

In this article, we show that resorcinarene tetratrimethylammonium tetrabromide cavitand interdigitated gold nanoparticles can be prepared by appropriate choice of solvent and that they can act as efficient colorimetric sensors for the selective detection of polyphosphates such as pyrophosphate, ADP and ATP in aqueous medium. Remarkably, this electrostatically mediated sensing occurs in a minute in biologically relevant HEPES medium and anions such as closely related monobasic- and tribasic-phosphate, various halides including fluoride, acetate, carbonates, nitrate, and sulfate don’t show any colorimetric response. NMR titration showed that the resorcinarene cavitand surfactant binds to pyrophosphate with a binding constant of 4190M−1. Further, we show that PPi can be colorimetrically detected even in the presence of tribasic phosphate, which also binds to the resorcinarene cavitand surfactant with a binding constant of 850M−1. Given the dimensions of the resorcinarene cavitand and the calculated initial interparticle distances of 7.3nm, we believe that the aggregation based sensing of PPi, ADP and ATP occurs by the crosslinking of two resorcinarene cavitand interdigitated nanoparticles by these anions. We show the ratio of absorbance at 700nm and 529nm (A700/A529) and the LSPR of the resorcinarene cavitand interdigitated nanoparticles varied significantly over a wide range of pyrophosphate concentrations with a limit of detection of 140nM.

Cavitand Chemistry – Towards Metallocapsular Catalysts

Two diphosphanes with widely separated P centres and cores that consists of two covalently linked resorcinarene cavitands were synthesised. Their ability to bind transition‐metal ions in a chelating fashion with the concomitant formation of capsular complexes was shown in their reactions with metal centres with two available binding sites. The solid‐state structure of one of the complexes, a capsule with a partially embedded “trans‐PtCl2” unit, was determined by single‐crystal X‐ray diffraction. Upon reaction with SnCl2, this complex developed good activity for the hydroformylation of styrene. Its activity and selectivity towards the branched aldehyde were significantly superior to those observed for the reference complex trans‐PtCl2L2, in which L is a monophosphane monocavitand ligand. The higher activity is likely to reflect the initial formation of a hydrido intermediate with a somewhat distorted trigonal‐bipyramidal structure that facilitates the intracapsular olefin/PtH insertion step. The observed aldehyde selectivity is probably controlled by the shape of the capsule, which is sterically better suited for hosting a branched Pt–alkyl unit than a linear one.

Rim, Side Arms, and Cavity: Three Sites for the Recognition of Anions by Tetraazolium Resorcinarene Cavitands.

Two tetrabenzoimidazolium-resorcinarene cavitands were prepared and used for the recognition of chloride, bromide, iodide, cyanide, nitrate, perchlorate, hexanoate, benzenesulfonate, and p-toluenesulfonate. Binding affinities of the two cavitands were determined by 1 H NMR titration and computational analysis. The observed spectral changes were related to specific interaction sites, which were supported by the computational studies. In the case of the C2-H tetrabenzoimidazolium-resorcinarene, the recognition region of the inorganic anions and hexanoate was located at the rim of the cavitand, although chloride and bromide also interacted with the aromatic C-H bonds located between adjacent arms of the cavitand. By contrast, the recognition of the two anions with an aromatic ring (benzenesulfonate and p-toluenesulfonate) results from encapsulation of the aromatic part of the anions inside the hydrophobic cavity of the host. In the case of the C2-Me tetrabenzoimizazolium-resorcinarene receptor, the ability of the molecule to bind all inorganic anions and hexanoate was suppressed, but the receptor maintained its ability to strongly bind benzenesulfonate and p-toluenesulfonate. This is interpreted in terms of suppression of the ability of the cavitand to form hydrogen bonds at the rim of the molecule due to replacement of the C2-H proton by a methyl group, while the hydrophobic pocket of the molecule maintains its binding abilities.

Highly fluorescent resorcinarene cavitand nanocapsules with efficient renal clearance

Nanomaterial based imaging approaches hold substantial promise in addressing current diagnostic and therapeutic challenges. One of the key requirements for the successful clinical translation of nanomaterials is their complete clearance from the body within a reasonable time period preferably via the renal filtration route. This article describes the synthesis of highly fluorescent, water soluble, resorcinarene cavitand nanocapsules and demonstrates their effective renal clearance in mice. The synthesis and functionalization of nanocapsules was accomplished in a one-pot operation via thiol-ene reactions without involving self-assembly, sacrificial templates or emulsions. Water soluble resorcinarene cavitand nanocapsules obtained by this approach were covalently functionalized with Alexa Fluor 750. Highly fluorescent nanocapsules with hydrodynamic diameters of 122 nm and 68 nm and extinction coefficients of 1.3 × 109 M−1 cm−1 and 1.5 × 108 M−1 cm−1 respectively were prepared by varying the reaction conditions. The in vivo biodistribution and clearance of these nanocapsules in mice followed by whole-body fluorescence imaging showed that they were both cleared renally within a few hours. Given the inherent encapsulation capabilities of nanocapsules, the renal clearance demonstrated in this work opens up new opportunities for their theranostic applications especially for targeting and treating the urinary tract.

The Origin of Selectivity in the Complexation of N-Methyl Amino Acids by Tetraphosphonate Cavitands.

We report on the eligibility of tetraphosphonate resorcinarene cavitands for the molecular recognition of amino acids. We determined the crystal structure of 13 complexes of the tetraphosphonate cavitand Tiiii[H, CH3, CH3] with amino acids. (1)H NMR and (31)P NMR experiments and ITC analysis were performed to probe the binding between cavitand Tiiii[C3H7, CH3, C2H5] or the water-soluble counterpart Tiiii[C3H6Py(+)Cl(-), CH3, C2H5] and a selection of representative amino acids. The reported studies and results allowed us (i) to highlight the noncovalent interactions involved in the binding event in each case; (ii) to investigate the ability of tetraphosphonate cavitand receptors to discriminate between the different amino acids; (iii) to calculate the Ka values of the different complexes formed and evaluate the thermodynamic parameters of the complexation process, dissecting the entropic and enthalpic contributions; and (iv) to determine the solvent influence on the complexation selectivity. By moving from methanol to water, the complexation changed from entropy driven to entropy opposed, leading to a drop of almost three orders in the magnitude of the Ka. However, this reduction in binding affinity is associated with a dramatic increase in selectivity, since in aqueous solutions only N-methylated amino acids are effectively recognized. The thermodynamic profile of the binding does not change in PBS solution. The pivotal role played by cation-π interactions is demonstrated by the linear correlation found between the log Ka in methanol solution and the depth of (+)N-CH3 cavity inclusion in the molecular structures. These findings are relevant for the potential use of phosphonate cavitands as synthetic receptors for the detection of epigenetic modifications of histones in physiological media.

An Introverted Bis‐Au Cavitand and Its Catalytic Dimerization of Terminal Alkynes

AbstractA preparative synthesis of an inwardly oriented phosphoramidite‐Au dinuclear resorcinarene cavitand complex is described, including a description of potent catalytic abilities. The cavitand structure was determined by crystallographic analysis, which revealed that the phosphoramidite P–N bonds point outside placing the two Au atoms inside. We explored the catalytic proclivity of the cavitand and found that it effeciently catalyzes selective and direct dimerization of terminal alkynes to afford conjugated enynes. Mixed dimerizations give rise to chemoselective products, and macrocyclization by intramolecular dimerization are both trademark capabilities of the method.

Interfacial interactions of hard polyelectrolyte-stabilized luminescent colloids with substrates

Abstract The present work introduces an origin of sensing function of polyelectrolyte-coated colloids based on Tb(III) complexes with calix[4]resorcinarene cavitand bearing four 1,3 -diketone groups at the upper rim. The Tb(III)-centered luminescence of the colloids remains unchanged at pH 3–9, although the Tb(III) complexes are highly pH-dependent in DMF solutions. Both colloidal and luminescent properties of the colloids are stable within one month at least, which reveals stability of complex-based hard nanotemplates and soft polyelectrolyte deposition. The chelating substrates (catechol, tetracycline and fluoroquinolone derivatives) induce quick and reproducible luminescent response of the complex-based colloids without any detectable changes of their colloidal properties. The ternary complex formation at the interface of the colloids is the reason for their luminescent response on the substrates in aqueous solutions. Both the insolubility of the Tb(III)-containing cores and the shielding and/or buffer effect of the polyelectrolyte coating affect the interfacial complex formation, which results in more selective luminescent response of the colloids on the tetracycline and fluoroquinolone antibiotics in comparison with the complexes in solutions.

Self-assembled capsules based on tetrafunctionalized calix[4]resorcinarene cavitands.

Calix[4]resorcinarene-based cavitands with a bowl-shaped aromatic cavity are widely used as scaffolds for covalently bound and self-assembled capsules. There are two main categories of calix[4]resorcinarene-based cavitands that are tetrafunctionalized at the upper (wider) rim: one category includes derivatives that have functionalized bridges between pairs of hydroxy groups of the calix[4]resorcinarene, and the second category includes derivatives with functional groups at the 2-position on the resorcinol ring and the methylene bridge between pairs of hydroxy groups. This review describes capsular self-assemblies of the latter type of methylene-bridge cavitands, which are formed through hydrogen bonds, metal-coordination bonds, and dynamic covalent bonds.

Fluorescent mono- and tetra-dansylated cavitands: synthesis and acid sensitivity

Two fluorescent tetra- and mono-dansylated resorcinarene cavitands were prepared and fully characterized. The X-ray structure of mono-dansylated resorcinarene cavitand was obtained. Their intrinsic absorption and fluorescence properties were studied. These properties were strongly sensitive to the presence of perchloric acid, as evidenced by the appearance of isobestic points upon protonation of the dansyl dimethylamino functions. The decreasing of the fluorescence emission intensity upon titration with perchloric acid was explained by the excited state interactions between the dansyl groups of the resorcinarene. Fluorescence quantum yields (\Phi _F) of mono- and tetra-dansylated cavitands and the reference compound were determined using dansyl chloride as reference in acetonitrile.

Tetraiodoethynyl resorcinarene cavitands as multivalent halogen bond donors.

The syntheses and halogen bonded (XB) complexes of tetrahalogenated ethynyl cavitands are presented. These cavitands act as quite rigid 3D multivalent halogen bond donors and show strong XB with oxygen, nitrogen and bromide XB acceptors.