Bis–Calix[4]pyrroles: Preparation, structure, complexation properties and beyond

Recent Progress of Supramolecular Chemotherapy Based on Host-Guest Interactions

Chemotherapy is widely recognized as an effective approach for treating cancer due to its ability to eliminate cancer cells using chemotherapeutic drugs. However, traditional chemotherapy suffers from various drawbacks, including limited solubility and stability of drugs, severe side effects, low bioavailability, drug resistance, and challenges in tracking treatment efficacy. These limitations greatly hinder its widespread clinical application. In contrast, supramolecular chemotherapy, which relies on host-guest interactions, presents a promising alternative by offering highly efficient and minimally toxic anticancer drug delivery. In this review, an overview of recent advancements in supramolecular chemotherapy based on host-guest interactions is provided. The significant role it plays in guiding cancer therapy is emphasized. Drawing on a wealth of cutting-edge research, herein, a timely and valuable resource for individuals interested in the field of supramolecular chemotherapy or cancer therapy, is presented. Furthermore, this review contributes to the progression of the field of supramolecular chemotherapy toward clinical application.

Dual Brønsted acidic-basic function immobilized on the 3D mesoporous polycalix [4]resorcinarene: As a highly recyclable catalyst for the synthesis of spiro acenaphthylene/indene heterocycles

In this study, a novel dual Brønsted acidic-basic nano-scale porous organic polymer catalyst, PC4RA@SiPr-Pip-BuSO3H, was synthesized through various steps: preparation of a 3D network of polycalix, modification with (3-chloropropyl)-trimethoxysilane, then functionalization of polymer with piperazine and n-butyl sulfonic acid under the provided conditions. The catalyst characterization was performed by FT-IR, TGA, EDS, elemental mapping, PXRD, TEM, and FE-SEM analyses, confirming high chemical stability, activity, recoverability, and excellent covalent anchoring of functional groups. So, the designed catalyst was utilized for preparing spiro-acenaphthylene and amino-spiroindene heterocycles, providing good performance with a high yield of the corresponding products. Accordingly, this catalyst can be used in different organic transformations. Necessary experiments were conducted for the recyclability test of the polymeric catalyst, and the results showed the PC4RA@SiPr-Pip-BuSO3H catalyst can be reused 10 times without any decrease in its activity or quality with excellent stability. The structure of resultant spiro heterocycles was confirmed using 1H NMR, 13C NMR, and FT-IR.

Friedel-Crafts Acylation for Accessing Multi-Bridge-Functionalized Large Pillar[n]arenes

Pillar[n]arenes can be constructed using a Friedel-Crafts alkylation process. However, due to the reversible nature of the alkylation, mixture of large pillar[n]arenes (n≥7) are obtained as minor products, and thus laborious purification are necessary to isolate the larger pillar[n]arenes. Moreover, inert methylene bridges are introduced during the alkylation process, and the multi-functionalization of the bridges has never been investigated. Herein, an irreversible Friedel-Crafts acylation is used to prepare pillar[n]arenes. Due to the irreversible nature of the acylation, the reaction of precursors bearing carboxylic acids and electron-rich arene rings results in a size-exclusive formation of pillar[n]arenes, in which the ring-size is determined by the precursor length. Because of this size-selective formation, laborious separation of undesired macrocycles is not necessary. Moreover, the bridges of pillar[n]arenes are selectively installed with reactive carbonyl groups using the acylation method, whose positions are determined by the precursor used. The carbonyl bridges can be easily converted into versatile functional groups, leading to various laterally modified pillar[n]arenes, which cannot be accessed by the alkylation strategy.

Does Larger Cavity-Size Really Help Bigger Anions to Bind? A Scrutiny on Core-Expanded Calix[4]pyrroles and Their Properties

Calix[4]pyrroles are an important class of oligopyrrolic macrocycles and have found applications in many diverse fields including anion recognition. To modulate the properties of the calix[4]pyrrole, several structural modifications are realized. The core-expansion has attracted extra attention as it provides larger cavity-size compared to parent calix[4]pyrrole(s). This review highlights the synthetic development of various core-expanded calix[4]pyrroles and their applications in anion-binding properties. Emphasis is given to the changes in the binding properties observed with expanded versions of calix[4]pyrrole(s) in both solution and the solid states. The expanded versions of calix[4]pyrrole do not always show higher binding affinities for larger anions as anticipated. Rather, they display reduced affinities with the anions. The truncated form or asymmetric nature of the expanded versions of calix[4]pyrrole does not probably allow to access all the available binding sites for the anions and hence reduced binding affinities are observed. The receptors which contain a greater number of binding sites and are somehow rigid or preorganized apparently show enhanced binding affinities for anions. The relative binding constants for halide series indicate that the enlarged molecules are more beneficial for largest iodide among others. However, most of the receptors show selectivity towards smallest fluoride over other anions studied.

Tying a knot between crown ethers and porphyrins

Porphyrins and crown ether hybrids have emerged as a promising class of molecules composed of elements of a tetrapyrrole macrocycle and an oligo(ethylene glycol) segment. These hybrid systems constitute a broad group of compounds, including crowned porphyrins, crownphyrins, and calixpyrrole-crown ether systems forming Pacman complexes with transition metals. Their unique nature accustoms them as excellent ligands and hosts capable of binding guest molecules/ions, but also to undergo unusual transformations, such as metal-induced expansion/contraction. Depending on the design of the particular hybrid, they present unique features involving intriguing redox chemistry, interesting optical properties, and reactivity towards transition metals. In this perspective article, the overview of both the early designs of porphyrin-crown ether hybrids, as well as the most recent advances in the synthesis and characterisation of this remarkable group of macrocyclic systems, are addressed. The discussion covers the strategies employed in synthesising these systems, including cyclisation reactions, self-assembly, and their remarkable reactivity. The potential applications of porphyrin-crown ether hybrids are also highlighted. Moreover, the discussion identifies the challenges associated with synthesising and characterising hybrids, outlining the possible future directions.

Bismacrocycle: Structures and Applications

In the past half-century, macrocycles with different structures and functions, have played a critical role in supramolecular chemistry. Two macrocyclic moieties can be linked to form bismacrocycle molecules. Compared with monomacrocycle, the unique structures of bismacrocycles led to their specific recognition and assembly properties, also a wide range of applications, including molecular recognition, supramolecular self-assembly, advanced optical material construction, etc. In this review, we focus on the structure of bismacrocycle and their applications. Our goal is to summarize and outline the possible future development directions of bismacrocycle research.

Tungstic acid-functionalized polycalix[4]resorcinarene as a cavity-containing hyper-branched supramolecular and recoverable acidic catalyst in 4H-pyran synthesis

In this study, tungstic acid immobilized on polycalix[4]resorcinarene, PC4RA@SiPr-OWO₃H, as a mesoporous acidic solid catalyst was synthesized and investigated for its catalytic activity. Polycalix[4]resorcinarene was prepared via a reaction between formaldehyde and calix[4]resorcinarene, and then the resulting polycalix[4]resorcinarene was modified using (3-chloropropyl)trimethoxysilane (CPTMS) to obtain polycalix[4]resorcinarene@(CH₂)₃Cl that was finally functionalized with tungstic acid. The designed acidic catalyst was characterized by various methods including FT-IR spectroscopy, energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), elemental mapping analysis and transmission electron microscopy (TEM). The catalyst efficiency was evaluated via the preparation of 4H-pyran derivatives using dimethyl/diethyl acetylenedicarboxylate, malononitrile, and beta-carbonyl compounds, confirmed by FT-IR spectroscopy and ¹H and ¹³C NMR spectroscopy. The synthetic catalyst was introduced as a suitable catalyst with high recycling power in 4H-pyran synthesis.

Enhanced Host-Guest Association and Fluorescence in Copolymers from Copper Salphen Complexes by Supramolecular Internalization of Anions

We describe the synthesis, crystallographic characterization of a new Cu-Salphen compound and its use as a host Lewis-acid against guest anions in two versions: a) free molecule, b) copolymerized with methyl methacrylate:n-butyl acrylate (1 : 4-wt.) as protective co-monomers. Higher contents in Cu-Salphen yielded larger and more homogeneous polymer sizes. Polymer size together with glass transitions, heat capacity, thermal degradation, guest-saturation degrees and host-guest species distribution profiles from spectrophotometric titrations explained growths of up to 630-fold in K₁₁ and 180000-fold in K₁₂ for the host's binding site attributable to a solvophobic protection from the macromolecular structure. Spectrofluorimetry revealed blue-shifted×13-16 larger luminescence for Cu-Salphen in the polymers (λ_em =488-498 nm) than that of the non-polymerized counterpart (λ_em =510-543 nm) and "turn-on" blue-shifted enhanced fluorescence upon guest association. We propose a cooperative incorporation of the guests occurring from the outer medium toward internally protected binding site pockets in the random coil polymer conformations.

Aryl-Extended and Super Aryl-Extended Calix[4]pyrroles: Design, Synthesis, and Applications

ConspectusProteins exhibit high-binding affinity and selectivity, as well as remarkable catalytic performance. Their binding pockets are hydrophobic but also contain polar and charged groups to contribute to the binding of polar organic molecules in aqueous solution. In the past decades, the synthesis of biomimetic receptors featuring sizable aromatic cavities equipped with converging polar groups has received considerable attention. "Temple" cages, naphthotubes, and aryl-extended calix[4]pyrroles are privileged examples of synthetic scaffolds displaying functionalized hydrophobic cavities capable of binding polar substrates. In particular, calix[4]pyrroles are macrocycles containing four pyrrole rings connected through their pyrrolic 2- and 5-positions by tetra-substituted sp³ carbon atoms (meso-substituents). In 1996, Sessler introduced the meso-octamethyl calix[4]pyrrole as an outstanding receptor for anion binding. Independently, Sessler and Floriani also showed that the introduction of aryl substituents in the meso-positions produced aryl-extended calix[4]pyrroles as a mixture of configurational isomers. In addition, aryl-extended calix[4]pyrroles bearing two and four meso-aryl substituents (walls) were reported. The cone conformation of "two-wall" αα-aryl-extended calix[4]pyrroles features an aromatic cleft with a polar binding site defined by four converging pyrrole NHs. On the other hand, "four-wall" αααα-calix[4]pyrrole isomers possess a deep polar aromatic cavity closed at one end by the converging pyrrole NHs. Because of their functionalized interior, aryl-extended calix[4]pyrroles are capable of binding anions, ion-pairs, and electron-rich neutral molecules in organic solvents. However, in water, they are restricted to the inclusion of neutral polar guests.Since the early 2000s, our research group has been involved in the design and synthesis of "two-wall" and "four-wall" aryl-extended calix[4]pyrroles and their derivatives, such as aryl-extended calix[4]pyrrole cavitands and super aryl-extended calix[4]pyrroles. In this Account, we mainly summarize our own results on the binding of charged and neutral polar guests with these macrocyclic receptors in organic solvents and in water. We also describe the applications of calix[4]pyrrole derivatives in the sensing of creatinine, the facilitated transmembrane transport of anions and amino acids, and the monofunctionalization of bis-isonitriles. Moreover, we explain the use of calix[4]pyrrole receptors as model systems for the quantification of anion-π interactions and the hydrophobic effect. Finally, we discuss the self-assembly of dimeric capsules and unimolecular metallo-cages based on calix[4]pyrrole scaffolds. We comment on their binding properties, as well as on those of bis-calix[4]pyrroles having a fully covalent structure.In molecular recognition, aryl-extended calix[4]pyrroles and their derivatives are considered valuable receptors owing to their ability to interact with a wide variety of electron-rich, neutral, and charged guests. Calix[4]pyrrole scaffolds have also been applied in the development of molecular sensors, ionophores, transmembrane carriers, supramolecular protecting groups and molecular containers modulating chemical reactivity, among others. We believe that the design of new calix[4]pyrrole receptors and the investigation of their binding properties may lead to promising applications in many research areas, such as supramolecular catalysis, chemical biology and materials science. We hope that this Account will serve to spread the knowledge of the supramolecular chemistry of calix[4]pyrroles among supramolecular and nonsupramolecular chemists alike.

Aryl- and Superaryl-Extended Calix[4]pyrroles: From Syntheses to Potential Applications

The incorporation of aryl substituents at the meso-positions of calix[4]pyrrole (C4P) scaffolds produces aryl-extended (AE) and super-aryl-extended (SAE) calix[4]pyrroles. The cone conformation of the all-α isomers of "multi-wall" AE-C4Ps and SAE-C4Ps displays deep aromatic clefts or cavities. In particular, "four-wall" receptors feature an aromatic polar cavity closed at one end with four convergent pyrrole rings and fully open at the opposite end. This makes AE- and SAE-C4P scaffolds effective receptors for the molecular recognition of negatively charged ions and neutral guest molecules with donor-acceptor and hydrogen bonding motifs. In addition, adequately functionalized all-α isomers of multi wall AE- and SAE-C4P scaffolds self-assemble into uni-molecular and supra-molecular aggregates displaying capsular and cage-like structures. The self-assembly process requires the presence of template ions or molecules that lock the C4P cone conformation and complementing the inner polar functions and volumes of their cavities. We envisioned performing an in-depth revision of AE- and SAE-C4P scaffolds owing to their importance in different domains such as supramolecular chemistry, biology, material sciences and pharmaceutical chemistry. Herewith, besides the synthetic details on the elaboration of their structures, we also draw attention to their diverse applications. The organization of this review is mainly based on the number of "walls" present in the AE-C4P derivatives and their structural modifications. The sections are further divided based on the C4P functions and applications. The authors are convinced that this review will be of interest to researchers working in the general area of supramolecular chemistry as well as those involved in the study of the binding properties and applications of C4P derivatives.

Calix[4]pyrrole-Based Molecular Capsule: Dihydrogen Phosphate-Promoted 1:2 Fluoride Anion Complexation

A molecular capsule (1) consisting of two calix[4]pyrroles connected via ethylene diamide linkers has been prepared as an anion receptor. ¹H NMR spectroscopic studies carried out in CD₂Cl₂ revealed that receptor 1 recognizes a variety of anions with different binding modes and stoichiometries. For instance, receptor 1 binds fluoride and acetate with 1:2 receptor/anion stoichiometry and other test anions with 1:1 stoichiometry in solution when their respective tetrabutylammonium (TBA⁺) salts were used. In contrast, with tetraethylammnium (TEA⁺) salts, receptor 1 forms 1:2 complexes with chloride and bromide in addition to fluoride, overcoming expected Columbic repulsions between the anions co-bound in close proximity. Receptor 1 is also able to bind oxoanions, such as oxalate (C₂O₄^2-), dihydrogen phosphate (H₂PO₄^-), sulfate (SO₄^2-), and hydrogen pyrophosphate (HP₂O₇^3-), in the form of 1:1 complexes as the result of presumed cooperation between the two calix[4]pyrrole subunits. The selectivity of receptor 1 for fluoride versus dihydrogen phosphate varies depending on their relative concentrations. For instance, in the presence of less than 1.0 equiv of an equimolar mixture of fluoride and dihydrogen phosphate, receptor 1 shows high selectivity for dihydrogen phosphate. In contrast, in the presence of ≥2.0 anion equiv, receptor 1 binds fluoride preferentially, forming a 1:2 complex. Moreover, when treated with F^-, the preformed 1:1 H₂PO₄^- complex of receptor 1 is converted to the corresponding 1:2 receptor/fluoride complex with the release of the prebound dihydrogen phosphate anion. As inferred from gas-phase computations, this seemingly counterintuitive behavior is rationalized in terms of the precomplexed dihydrogen phosphate serving to reduce the reorganization energy required to bind two fluoride anions. The presence of a water molecule in addition to the bound fluoride anions may also favor the formation of the 1:2 F^- complex. The present study provides a new approach for fine-tuning the binding selectivity of polytopic anion receptors.

Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

Synthesis of Novel One-Walled meso-Phenylboronic Acid-Functionalized Calix[4]pyrrole: A Highly Sensitive Electrochemical Sensor for Dopamine

Facile access to new one-walled meso-substituted phenylboronic acid-functionalized calix[4]pyrrole (C4P) has been revealed for the first time, starting from cost-effective and easily accessible materials. The structures of both the intermediate dipyrromethane (DPM) and the targeted functionalized C4P have been confirmed by means of ¹H-NMR, ¹³C-NMR, IR, and HRMS spectral data. The voltammetric investigations of the functionalized C4P films cast over a glassy carbon electrode (C4P-GCE) clearly establish the redox stability and redox accessibility of the boronic acid functional moiety present in the C4P framework. We demonstrate that the presence of the unique boronic acid functionality in the C4P endows it with an excellent potential for the highly sensitive electrochemical sensing of the neurotransmitter dopamine (DA). A linear correlation between the strength of the Faradaic signals corresponding to the electro-oxidation of DA over C4P-GCE and the concentration of DA was observed in a concentration range as wide as 0.165-2.302 μM. The C4P-GCE has revealed exceptional stability and reproducibility in the electrochemical sensing of DA, with a nanomolar level limit of detection as low as 15 nM.

Oligopyrrolic Cages: From Classic Molecular Constructs to Chemically Responsive Polytopic Receptors

Conspectus"Functional molecular systems", discrete and self-assembled constructs where control over molecular recognition, structure, bonding, transport, release, catalytic activity, etc., is readily achieved, are a topic of current interest. Within this broad paradigm, oligopyrrolic cages have garnered attention due to their responsive recognition features. Due to the presence of slightly polar pyrrole subunits which can also behave as hydrogen-bonding donors, these oligopyrrolic cages are potential receptors for various polarized species. In this Account, we summarize recent advances involving the syntheses and study of (1) covalent oligopyrrolic macrobicyclic cages, (2) oligopyrrolic metallacages, and (3) oligopyrrolic noncovalently linked cages. Considered in concert, these molecular constructs have allowed advances in applied supramolecular chemistry; to date, they have been exploited for selective guest encapsulation studies, anion binding and ion-channel formation, and gas absorption, among other applications. While key findings from others will be noted, in this Account will focus on our own contributions to the chemistry of discrete oligopyrrolic macrocycles and their use in supramolecular host-guest chemistry and sensing applications. In terms of specifics, we will detail how oligopyrrole cages with well-defined molecular geometries permit reversible guest binding under ambient conditions and how the incorporation of pyrrole subunits within larger superstructures allows effective control over anion/conjugate acid binding activity under ambient conditions. We will also provide examples that show how derivatization of these rudimentary macrocyclic cores with various sterically congested β-substituted oligopyrroles can provide entry into more complex supramolecular architectures. In addition, we will detail how hybrid systems that include heterocycles other than pyrrole, such as pyridine and naphthyridine, can be used to create self-assembled materials that show promise as gas-absorbing materials and colorimetric reversible sensors. Studies involving oligopyrrolic polymetallic cages and oligopyrrolic supramolecular cages will also be reviewed. First, we will discuss all-carbon-linked oligopyrrolic bicycles and continue on to present systems linked via amines and imines linkages. Finally, we will summarize recent work on pyrrolic cages created through the use of metal centers or various noncovalent interactions. We hope that this Account will provide researchers with an initial foundation for understanding oligopyrrolic cage chemistry, thereby allowing for further advances in the area. It is expected that the fundamental design and recognition principles made in the area of oligopyrrole cages, as exemplified by our contributions, will be of general use to researchers targeting the design of functional molecular systems. As such, we have structured this Account so as to summarize the past while setting the stage for the future.

A Simulation Model for the Non-Electrogenic Uniport Carrier-Assisted Transport of Ions across Lipid Membranes

Impressive work has been completed in recent decades on the transmembrane anion transport capability of small synthetic transporters from many different structural classes. However, very few predicting models have been proposed for the fast screening of compound libraries before spending time and resources on the laboratory bench for their synthesis. In this work, a new approach is presented which aims at describing the transport process by taking all the steps into explicit consideration, and includes all possible experiment-derived parameters. The algorithm is able to simulate the macroscopic experiments performed with lipid vesicles to assess the ion-transport ability of the synthetic transporters following a non-electrogenic uniport mechanism. While keeping calculation time affordable, the final goal is the curve-fitting of real experimental data—so, to obtain both an analysis and a predictive tool. The role and the relative weight of the different parameters is discussed and the agreement with the literature is shown by using the simulations of a virtual benchmark case. The fitting of real experimental curves is also shown for two transporters of different structural type.

Preparation of tricationic tris(pyridylpalladium(II)) metallacyclophane as an anion receptor

A tricationic tris(pyridylpalladium(II)) metallacyclophane was prepared from 3,5-dibromopyridine by a successive treatment with tetrakis(triphenylphosphine)palladium(0), diphosphine, and silver salt. Single-crystal X-ray diffraction analysis revealed that the metallacyclophane incorporated one of three counter anions into its hole-shaped cavity to form multidentate C-H⋯anion interactions. Solution-phase ¹H NMR experiments in DMSO-d₆ indicated that the metallacyclophane exhibited selective binding behavior toward nitrate, tetrafluoroborate, p-toluenesulfonate, perchlorate, and hydrogen sulfate ions, whereas the hexafluoroantimonate ion exhibited only weak interaction toward the metallacyclophane. This anion recognition behavior was further demonstrated by an extraction experiment of water-soluble sulfonate dyes.

Recent developments in calix[4]pyrrole (C4P)-based supramolecular functional systems

Recent advances with calix[4]pyrrole-based supramolecular functional entities in the fields of molecular recognition (receptors, sensors, and metal ion caged systems), self-assembly (polymers), photo/pH-responsive molecular switches and catalysis are reviewed.

[1]Rotaxanes based on phosphorylated pillar[5]arenes

[1]Rotaxanes based on monosubstituted phosphorus-containing pillar[5]arenes have been synthesized by the Kabachnik–Fields reaction for the first time in good yields.

An expeditious and highly efficient synthesis of substituted pyrroles using a low melting deep eutectic mixture

An expeditious green method for the synthesis of diverse valued substituted pyrroles through a Paal-Knorr condensation reaction, using a variety of amines and 2,5-hexanedione/2,5-dimethoxytetrahydrofuran in the presence of a low melting mixture of N,N'-dimethylurea and L-(+)-tartaric acid (which acts as a dual catalyst/solvent system), has fruitfully been revealed. Herein, we have disclosed the applicability of this simple yet effective strategy for the generation of mono- and dipyrroles in good to excellent yields. Moreover, C₃-symmetric tripyrrolo-truxene derivatives have also been assembled by means of cyclotrimerization, Paal-Knorr and Clauson-Kaas reactions as crucial steps. Interestingly, the melting mixture was recovered and reused with only a gradual decrease in the catalytic activity (over four cycles) without any significant drop in the yield of the product. This particular methodology is simple, rapid, environmental friendly, and high yielding for the generation of a variety of pyrroles. To the best of our knowledge, the present work reveals the fastest greener method reported up to this date for the construction of substituted pyrroles by utilizing the Paal-Knorr synthetic protocol, achieving impressive yields under operationally simple reaction conditions without involving any precarious/dangerous catalysts or unsafe volatile organic solvents.

Calix[4]pyrroles as ligands: recent progress with a focus on the emerging p-block element chemistry

Calix[4]pyrroles are readily synthesized in one step from pyrroles and ketones. For several decades, these macrocycles have been exploited as powerful anion receptors or ligands for transition and rare-earth metals. In contrast, calix[4]pyrrolates as ligands for p-block elements were established only in 2018. The present feature article reviews these developments, together with the recent progress on s-, d-, and f-block element complexes of the calix[4]pyrroles. Particular focus is given on the calix[4]pyrrolato aluminate and the corresponding silane, both featuring square planar-coordinated p-block elements in their highest oxidation states. These unique "anti-van't-Hoff-Le-Bel" structures introduce valuable characteristics into main-group element chemistry, such as agostic interactions or ligand-to-metal charge transfer absorptions. The most vital reactivities are highlighted, which rely on properties ranging from amphoterism, redox-activity, and a small HOMO-LUMO gap up to the ability to provide a platform for additional external stimuli. Overall, these developments underscore the beneficial impact of structural constraint of p-block elements and element-ligand cooperativity to enhance the functionality of the most abundant elements in their native oxidation states.

4-Phosphoryl Pyrazolones for Highly Selective Lithium Separation from Alkali Metal Ions

Effective receptors for the separation of Li⁺ from a mixture with other alkali metal ions under mild conditions remains an important challenge that could benefit from new approaches. In this study, it is demonstrated that the 4-phosphoryl pyrazolones, HL² -HL⁴ , in the presence of the typical industrial organophosphorus co-ligands tributylphosphine oxide (TBPO), tributylphosphate (TBP) and trioctylphosphine oxide (TOPO), are able to selectively recognise and extract lithium ions from aqueous solution. Structural investigations in solution as well as in the solid state reveal the existence of a series of multinuclear Li⁺ complexes that include dimers (TBPO, TBP) as well as rarely observed trimers (TOPO) and represent the first clear evidence for the synergistic role of the co-ligands in the extraction process. Our findings are supported by detailed NMR, MS and extraction studies. Liquid-liquid extraction in the presence of TOPO revealed an unprecedented high Li⁺ extraction efficiency (78 %) for HL⁴ compared to the use of the industrially employed acylpyrazolone HL¹ (15 %) and benzoyl-1,1,1-trifluoroacetone (52 %) extractants. In addition, a high selectivity for Li⁺ over Na⁺ , K⁺ and Cs⁺ under mild conditions (pH ∼8.2) confirms that HL² -HL⁴ represent a new class of ligands that are very effective extractants for use in lithium separation.

Thallium(I) Salts: New Partners for Calix[4]pyrroles

Calix[4]pyrrole 1 can form host-guest complexes with certain thallium salts, for example, TlF, not only in the gas phase but also in solution and in the solid state. The complexation of TlF by calix[4]pyrrole 1 was found to promote self-assembly and the formation of well-defined and highly ordered fibrous supramolecular morphologies, as revealed by polarizing microscopy and scanning electron microscopy. The findings reported here serve to broaden the scope of cationic substrates that may be complexed as ion pairs by calix[4]pyrrole receptors while setting the stage for the development of new hosts for thallium(I) salts.

Suppression of Malachite Green-Induced Toxicity to Human Liver Cells Utilizing Host-Guest Chemistry of Cucurbit[7]uril

We investigated a host-guest complex between cucurbit[7]uril and malachite green, and its effect on the toxicity to human liver cells. The host-guest complexation was evaluated by a UV/vis titration and electrospray-ionization mass spectrometry. Interestingly, the host-guest complex resulted in remarkable suppression of the toxicity of malachite green in its practical concentration range (ca. ∼6 μM). This study is one step forward to the active control of the biological effects of potent toxicants utilizing host-guest chemistry.