Phenyl-Extended Resorcin[4]arenes: Synthesis and Highly Efficient Iodine Adsorption.

The continuous exploration of new analogs of calixarenes and pillararenes unlocks infinite opportunities in supramolecular chemistry and materials. In this work, we introduce a new class of macrocycle, phenyl-extended resorcin[4]arenes (ExR4), a unique and innovative design that incorporates unsubstituted phenylene moieties into the resorcin[4]arene scaffold. Single-crystal analysis reveals a chair-like conformation for per-methylated ExR4 (Me-ExR4) and a twisted "Figure-of-eight" shaped conformation for per-hydroxylated ExR4 (OH-ExR4). Notably, OH-ExR4 demonstrates exceptional adsorption capability toward I3 - ions in an aqueous solution, with a rapid kinetic rate of 1.18×10-2 g ⋅ mg-1 ⋅ min-1. Furthermore, OH-ExR4 shows excellent recyclability and potential as a stationary phase in column setups. The discovery of ExR4 opens up new avenues for constructing new macrocycles and inspires further research in functional adsorption materials for water pollutant removal.

Solvent and Substituent Size Influence on the Cyclochiral Rigidity of Aminomethylene Derivatives of Resorcin[4]arene.

Resorcin[4]arenes (R[4]A) are a group of macrocyclic compounds whose peculiar feature is the presence of eight hydroxyl groups in their structure. The directional formation of intramolecular hydrogen bonds with their participation leads to the formation of a cyclochiral racemic mixture of these compounds. Their stability strongly depends on the substituent and especially the environment in which they are located. The paper discusses the cyclochiral nature of aminomethylene derivatives of R[4]A (AMD-R[4]A). Their cyclochiral rigidity in non-polar solvents has been shown. The influence of the size of the alkyl groups in the amino substituents of AMD-R[4]A on their cyclochiral nature was noted. To calculate the reaction paths for their racemization, the nudged elastic band (NEB) method was employed using the semi-empirical DFT (GFN1-xTB) approach. The calculated activation barrier energies for their racemization in chloroform, obtained through various semi-empirical quantum chemical methods (SE), Hartree-Fock (HF), and density functionals theory (DFT), show good correlation with experimental observations. Among the tested methods, the B38LYP-D4 method is highly recommended due to its fast computational speed and accuracy, which is comparable to the time-consuming double-hybrid DH-revDSD-PBEP86 approach.

Complexes of resorcin[4]arene with secondary amines: synthesis, solvent influence on "in-out" structure, and theoretical calculations of non-covalent interactions.

Resorcin[4]arenes (R[4]A) are macrocyclic compounds with a cavity structure. Despite a relatively small cavity, these compounds are capable of forming complexes with small organic molecules. The current paper focuses on the synthesis of complexes between R[4]A and secondary aliphatic amines (sec-amines). Through NMR spectroscopy, it was observed that "in-out" complexes are formed depending on the solvent. It was also found that the stoichiometry of the formed complexes depends on the size of the amine molecule. The automated interaction sites screening (aISS) made it possible to generate molecular ensembles of complexes. The geometry of the ensembles was first optimized with the r2scan-3c functional and, finally, the structure with the lowest energy, with the functional PBE0-D4/mTZVPP/CPCM. The Hartree-Fock plus London dispersion (HFLD) method was used for the study of non-covalent interactions (NCI). The calculations lead to the conclusion that a reduction in electrostatic interactions and an increase in exchange and dispersion interactions in CHCl3 in relation to DMSO are the driving forces behind the placement of sec-amine molecules into the R[4]A cavity and the formation of "in" type complexes.

Functionalized Hydrocarbon Belts: Synthesis, Structure and Properties.

Hydrocarbon belts have drawn great attention because of their unique structures and tantalizing properties. Although a few belts and heteroatom-doped analogs have been synthesized, belt molecules containing non-hexagonal rings remain rare. Herein we report the construction and application of unprecedented zigzag-type hydrocarbon belts which contain functionalized eight-membered rings. The synthesis features fourfold intramolecular acylation reactions of resorcin[4]arene-derived intermediates, which affords C4 -symmetric tetrabenzobelt[4]arene[4]cyclooctatrienones. Stereoselective ketone reduction with LiAlH4 and nucleophilic addition with alkynyllithiums provide the corresponding tetrahydroxylated belts. The tetraol and its methyl ether are powerful and selective hosts to form 2 : 1 and 1 : 1 complexes with cesium ion, respectively, with binding constants up to (1.71±0.33)×1011  M-2 and (1.50±0.16)×106  M-1 . In addition, enantiopure C4 -symmetric belts can emit CPL with |glum | being around 0.01.

Theoretical calculations of formation and reactivity of o-quinomethide derivatives of resorcin[4]arene with reference to empirical data.

This paper describes theoretical reaction pathways of alkoxybenzyl derivatives of resorcin[4]arene leading to the formation of o-quinomethide derivatives of resorcin[4]arene (o-QMR[4]A). For each case, the activation energies for the formation of one o-QMR[4]A unit and the activation energies for the backward reaction were calculated. Based on the calculated reaction pathways, the reaction mechanism of o-QMR[4]A formation was proposed. Using the example of o-QMR[4]A generated from a methoxy derivative of resorcin[4]arene, the activation energies with selected nucleophiles were calculated and the reaction mechanisms discussed. Reaction path calculations were performed using the nudged elastic band method and semiempirical extended tight-binding method (GFN2-xTB). Using hydroxybenzyl derivatives of resorcin[4]arene as an example, a comparison of calculated activation energies by selected density-functional theory methods with GFN2-xTB and B97-3c geometries was performed. B97-3c and wB97XD methods were used to calculate the energies of the reactants (R), transition states (TS) and products (P) of the analysed reactions. Theoretical reaction mechanisms were discussed with respect to the orbital-weighted Fukui dual descriptor (Δfw ) and experimental data.

A resorcin[4]arene hexameric capsule as a supramolecular catalyst in elimination and isomerization reactions.

The hexameric resorcin[4]arene capsule as a self-assembled organocatalyst promotes a series of reactions like the carbonyl-ene cyclization of (S)-citronellal preferentially to isopulegol, the water elimination from 1,1-diphenylethanol, the isomerization of α-pinene and ß-pinene preferentially to limonene and minor amounts of camphene. The role of the supramolecular catalyst consists in promoting the protonation of the substrates leading to the formation of cationic intermediates that are stabilized within the cavity with consequent peculiar features in terms of acceleration and product selectivity. In all cases the catalytic activity displayed by the hexameric capsule is remarkable if compared to many other strong Brønsted or Lewis acids.

Self-Assembly of Polyoxometalate-Resorcin[4]arene-Based Inorganic-Organic Complexes: Metal Ion Effects on the Electrochemical Performance of Lithium Ion Batteries.

With their adjustable structures and diverse functions, polyoxometalate (POM)-resorcin[4]arene-based inorganic-organic complexes are a kind of potential multifunctional material. They have potential applications for lithium ion batteries (LIBs). However, the relationship between different coordinated metal ions and electrochemical performance has rarely been investigated. Here, three functionalized POM-resorcin[4]arene-based inorganic-organic materials, [Co2 (TMR4 A)2 (H2 O)10 ][SiW12 O40 ]⋅2 EtOH⋅4.5 H2 O (1), [Ni2 (TMR4 A)2 (H2 O)10 ][SiW12 O40 ]⋅4 EtOH⋅13 H2 O (2), and [Zn2 (TMR4 A)2 (H2 O)10 ][SiW12 O40 ]⋅2 EtOH⋅2 H2 O (3), have been synthesized. Furthermore, to enhance the conductivities of these compounds, 1-3 were doped with reduced graphene oxide (RGO) to give composites 1@RGO-3@RGO, respectively. As anode materials for LIBs, 1@RGO-3@RGO can deliver very high discharge capacities (1445.9, 1285.0 and 1095.3 mAh g-1 , respectively) in the initial run, and show discharge capacities of 898, 665 and 651 mAh g-1 , respectively, at a current density of 0.1 A g-1 over 100 runs. More importantly, the discharge capacities of 319, 283 and 329 mAh g-1 were maintained for 1@RGO-3@RGO even after 400 cycles at large current density (1 A g-1 ).

Enaminone Substituted Resorcin[4]arene-Sealing of an Upper-Rim with a Directional System of Hydrogen-Bonds.

The paper presents the synthesis of an enaminone resorcin[4]arene via a thermally activated o-quinomethide. The crystal structure indicates that in the solid state all enaminone units participate in a unidirectional seam of 12 intramolecular hydrogen bonds that are formed around the cavity. The molecule exhibits C2 symmetry, with two opposite-laying enaminone units directed inside the cavity ("in"), and the other two units outside the cavity ("out"). In the solution the enaminone resorcin[4]arene exists as a mixture of conformers with distribution controlled by temperature and solvent. The experimental data are compared with the results of theoretical calculations using DFT B3LYP/6-31G(d,p) and fast semi-empirical DFTB/GFN2-xTB method in various solvents.

Intramolecular Hydrogen Bond Driven Conformational Selectivity of Coumarin Derivatives of Resorcin[4]arene.

In this study, the synthesis and structure of 4-aminocoumarin derivatives of resorcin[4]arene were investigated. Spectroscopic analysis and quantum mechanical calculations showed that this molecule undertakes a crown-in conformation in chloroform. The conformations of the aminocoumarin derivative of resorcin[4]arene were compared with a hydroxycoumarin derivative of resorcin[4]arene, and the effect of the substituent on the conformational selectivity of the coumarin derivatives of resorcin[4]arene was demonstrated. Both UV-VIS and fluorescence spectroscopy for the coumarin derivative of resorcin[4]arene (3) were performed, and a strong fluorescence quenching of derivative 3 compared to 4-aminocoumarin was observed.

Synthesis and Structure of Functionalized Zigzag Hydrocarbon Belts.

Described in this paper are the synthesis and structure of novel and edge-functionalized zigzag hydrocarbon belts. A stepwise "fjord-stitching" strategy featuring repetitive intramolecular acylation reactions of a resorcin[4]arene derivative as the key steps afforded a biscarbonyl-functionalized octahydrobelt[8]arene product. Facile ketone reduction with NaBH4 and nucleophilic addition with n-butyllithium produced secondary and tertiary alcohol-containing molecular belts, respectively. Selective oxidation reactions of biscarbonyl-bearing octahydrobelt[8]arene with m-CPBA and (PhSeO)2 O furnished the corresponding lactone- and 1,4-quinone-embedded molecular belts. Depending on the functional groups on the edges, the acquired belt molecules adopt different shapes such as square prism, truncated cone, and elliptical cylinder.

Design of N-Methyl-d-Glucamine-Based Resorcin[4]arene Nanoparticles for Enhanced Apoptosis Effects.

The addition of specific chemical groups in a macrocycle structure influences its functional properties and, consequently, can provide new possibilities, among which are aggregation properties, water solubility, biocompatibility, stimuli response, biological activity, etc. Herein, we report synthesis of new resorcin[4]arene with N-methyl-d-glucamine groups on the upper rim and n-decyl chains on the lower rim, an investigation of its self-assembly behavior in aqueous media, and its use as a building block for the formation of drug nanocontainer. N-methyl-d-glucamine fragments in the resorcin[4]arene structure promote higher stability in solutions, simplification of self-aggregation, and increased biological activity. Antimicrobial and hemolytic activity assessment revealed that this resorcin[4]arene obtained is nontoxic. The study of cell penetration was carried out with both free and encapsulated doxorubicin (DOX). Surprisingly, DOX-loaded macrocycle aggregates are more efficient in causing apoptosis in human cancer cell line. Conceivably, this knowledge will help in the rational design of DOX combination for novel drug-administration strategies in cancer treatment.

Complexation of chiral amines by resorcin[4]arene sulfonic acids in polar media - circular dichroism and diffusion studies of chirality transfer and solvent dependence.

Directional self-assembly of conformationally well-defined complexes in polar environment is still a major challenge in supramolecular chemistry. In the present study we demonstrate that resorcin[4]arene sulfonic acid (RSA) interacts with chiral amines (amino acid derivatives and aminocavitands) to form inclusion complexes and capsules based on electrostatic interactions. The complexes were characterized by circular dichroism and DOSY NMR spectroscopy. Chirality transfer from amines onto a resorcinarene skeleton was manifested by the appearance of signals in CD spectra and diastereotopic splitting in NMR spectra. The complexes proved to be thermodynamically stable in methanol, but DMSO and methanol/water mixtures were found to be highly disintegrative for these complexes. This result is quite non-intuitive and worth attention in the context of formation of supramolecular complexes in polar environment, for which DMSO is most often a first-choice solvent.

Metal-Assembled, Resorcin[4]arene-Based Molecular Trimer for Efficient Removal of Toxic Dichromate Pollutants and Knoevenagel Condensation Reaction.

Self-assembly of resorcin[4]arene-based coordination cages involving more than two resorcin[4]arenes poses significant challenges for the requirements of suitable functionalized resorcin[4]arene ligands and metals. Here, we report an unusual example of a metal-coordinated, resorcin[4]arene-based molecular trimer (1-NO3), composed of three resorcin[4]arenes and three Cd(II) cations. In particular, 1-NO3 features efficient and selective removal of environmentally toxic dichromate (Cr2O72-) anions. Moreover, the Knoevenagel condensation reaction was also explored by using 1-NO3 as an efficient heterogeneous catalyst.

Highly Stable Copper(I)-Based Metal-Organic Framework Assembled with Resorcin[4]arene and Polyoxometalate for Efficient Heterogeneous Catalysis of Azide-Alkyne "Click" Reaction.

A new highly stable copper(I)-based metal-organic framework (MOF), namely, [CuI4(SiW12O40)(L)]·6H2O·2DMF (1), was synthesized by incorporating Keggin-type polyoxometalate (POM) anions and a functionalized wheel-like resorcin[4]arene-based ligand (L) under sovothermal condition. 1 exhibits a charming 3D supramolecular architecture sandwiched by the POM anions. Noticeably, 1 has exceptional chemical stability, especially in organic solvents or aqueous solutions with a wide range of pH values. Considering the catalytically active Cu(I) sites in 1, the azide-alkyne cycloaddition (AAC) reaction was studied by employing 1 as the heterogeneous catalyst. Most strikingly, 1 exhibits excellent catalytic activity as well as recyclability for the AAC reaction.

Resorcin[4]arene-Based Microporous Metal-Organic Framework as an Efficient Catalyst for CO2 Cycloaddition with Epoxides and Highly Selective Luminescent Sensing of Cr2O72.

A stable microporous anionic metal-organic framework (MOF), [(CH3)2NH2]6[Cd3L(H2O)2]·12H2O (1), has been synthesized via solvothermal assembly of a new resorcin[4]arene-functionalized dodecacarboxylic acid (H12L) and Cd(II) cations. The constructed MOF (1) was characterized by single-crystal X-ray diffraction and other physicochemical analyses. 1 exhibits a fascinating 3D microporous framework structure, in which the free water molecules and the [(CH3)2NH2]+ cations were located. Remarkably, the exposed Lewis acid Cd(II) sites of activated 1 make it an efficient heterogeneous catalyst for the cycloaddition of CO2 with epoxides at 1 and 20 atm. Importantly, the activated samples of 1 can be reused at least five circles with excellent catalytic performance. Moreover, the fluorescence detection of Cr2O72- and Fe3+ was studied by using 1 as a potential luminescent sensor.

Conversion of Pregabalin to 4-Isobutylpyrrolidone-2.

Solid-state studies of C-butyl-resorcin[4]arene with pregabalin (Lyrica, Nervalin) in nitrobenzene yielded a cocrystal of C-butyl-resorcin[4]arene with 4-isobutylpyrrolidone-2. A combined experimental and quantum chemical investigation was implemented to further our understanding of the factors affecting the conversion process.

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system.

This review describes the state-of-art in the field of the gas-phase reactivity of diastereomeric complexes formed between a chiral artificial receptor and a biologically active molecule. The presented experimental approach is a ligand-displacement reaction carried out in a nano ESI-FT-ICR instrument, supported by a thermodynamic MS-study and molecular-mechanics and molecular-dynamics (MM/MD) computational techniques. The noncovalent ion-molecule complexes are ideal for the study of chiral recognition in the absence of complicating solvent and counterion effects.

Size selective recognition of small esters by a negative allosteric hemicarcerand.

A bis(resorcinarene) substituted 2,2'-bipyridine was found to bind weakly to small esters like ethyl acetate whereas more bulky esters were not recognized by this hemicarcerand. This size selective molecular recognition could be controlled by a negative cooperative allosteric effect: coordination of a triscarbonyl rhenium chloride fragment to the bipyridine causes a conformational rearrangement that orientates the resorcinarene moieties in different directions so that they cannot act cooperatively in the binding of the substrate.