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Tripodal chiral ligands containing amino acid residues and salicyl-acylhydrazone units were synthesized and used to obtain coordination cages through deprotonation and coordination to gallium. These coordination cages have Ga

Macrocyclic polyphenolic compounds such as resorcin[4]arenes can be considered as multidentate anion receptors. In the current work, we combine new experimental data and reports from the previous literature (solution data and deposited crystal structures from the CCDC) to systematically analyze binding motifs between resorcin[4]arene derivatives and anions, determine the role of supporting interactions from CH donors, ion pairing and estimate their relative strength. We have found that in medium polarity solvents (THF) anion binding is a main driving force for the formation of complexes between resorcinarenes and Alk

Core-fluorescent cavitands based on 2-(2'-resorcinol)benzimidazole fluorophores (RBIs) merged with the resorcin[4]arene skeleton were designed and synthesized. The cavitands, due to the presence of intramolecular hydrogen bonds and increased acidity, show excited state intramolecular proton transfer (ESIPT) and readily undergo deprotonation to form dianionic cavitands, capable of strong binding to organic cations. The changes in fluorescence are induced by deprotonation and binding events and involve huge Stokes shifts (due to emission from anionic double keto tautomers) and cation-selective enhancement of emission originating from the restriction of intramolecular motion (RIR) upon recognition in the cavity. Ab initio calculations indicate that the macrocyclic scaffold stabilizes the ground state tautomeric forms of the fluorophores that are not observed for non-macrocyclic analogs. In the excited state, the emitting forms for both macrocyclic scaffolds and non-macrocyclic analogs are anionic double keto tautomers, which are the result of excited state intramolecular proton transfer (ESIPT) or excited state double proton transfer (ESDPT).

Spatial sequestration of molecules is a prerequisite for the complexity of biological systems, enabling the occurrence of numerous, often non-compatible chemical reactions and processes in one cell at the same time. Inspired by this compartmentalization concept, chemists design and synthesize artificial nanocontainers (capsules and cages) and use them to mimic the biological complexity and for new applications in recognition, separation, and catalysis. Here, we report the formation of large closed-shell species by interactions of well-known polyphenolic macrocycles with anions. It has been known since many years that C-alkyl resorcin[4]arenes (

A molecular container with C60 cargo was crystallized and studied by X-ray diffraction revealing a complicated dis­order of the ligand caused by the incompatibility with its site symmetry. The tumbling of the C60 cargo was studied by solid-state NMR which suggested possible phase transitions, positively verified at high temperature by DSC., A supramolecular complex, formed by encapsulation of C60 fullerene in a molecular container built from two resorcin[4]arene rims zipped together by peptidic arms hydrogen bonded into a cylindrical β-sheet, was studied by X-ray crystallography, solid-state and solution NMR, EPR spectroscopy and differential scanning calorimetry (DSC). The crystal structure, determined at 100 K, reveals that the complex occupies 422 site symmetry, which is compatible with the molecular symmetry of the container but not of the fullerene molecule, which has only 222 symmetry. The additional crystallographic symmetry leads to a complicated but discrete dis­order, which could be resolved and modelled using advanced features of the existing refinement software. Solid-state NMR measurements at 184–333 K indicate that the thermal motion of C60 in this temperature range is fast but has different activation energies at different temperatures, which was attributed to a phase transition, which was confirmed by DSC. Intriguingly, the activation energy for reorientations of C60 in the solid state is very similar for the free and encaged molecules. Also, the rotational diffusion coefficients seem to be very similar or even slightly higher for the encaged fullerene compared to the free molecule. We also found that chemical shift anisotropy (CSA) is not the main relaxation mechanism for the 13C spins of C60 in the studied complex.

Electronic circular dichroism (ECD) can be used to study various aspects of self-assembly (definition of stoichiometric ratios, chirality amplification during self-assembly, host-guest complexation). In this work, we show that ECD is a valuable tool for monitoring the self-assembly of chiral peptide-based capsules. By analyzing the signs, intensities, and temperature dependences of ECD bands, the effects of the non-specific processes can be separated from the restriction of intramolecular motion (RIM) caused by discrete self-assembly. Analysis of experimental and theoretical ECD spectra show that the differences between assembled and non-assembled species originate from induction of inherently chiral conformation and restriction of conformational freedom that leads to amplification of ECD signals during self-assembly of discrete species.

Peptides are commonly perceived as inapplicable components for construction of porous structures. Due to their flexibility the design is difficult and shape persistence of such putative structures is diminished. Notwithstanding these limitations, the advantages of peptides as building blocks are numerous: they are functional and functionalizable, widely available, diverse and biocompatible. We aimed at the construction of discrete porous structures that exploit the inherent functionality of peptides by an approach that is inspired by nature: structural pockets are defined by the backbones of peptides while functionality is introduced by their side chains. In this work peptide ribbons were preorganized on a macrocyclic scaffold using azapeptide-aldehyde reactions. The resulting cavitands with semicarbazone linkers arrange the peptide backbones at positions that are suitable for self-assembly of dimeric capsules by formation of binding motifs that resemble eight-stranded β-barrels. Self-assembly properties and inside/outside positions of the side chains depend crucially on the chirality of peptides. By rational optimization of successive generations of capsules we have found that azapeptides containing three amino acids in a (l, d, d) sequence give well-defined dimeric capsules with side chains inside their cavities. Taking advantage of the reversibility of the reaction of semicarbazone formation we have also employed the dynamic covalent chemistry (DCC) for a combinatorial discovery of capsules that could not be rationally designed. Indeed, the results show that stable capsules with side chains positioned internally can be obtained even for shorter sequences but only for combination peptides of (l, l) and (d, l) chirality. The hybrid (l, l)(d, l) capsule is amplified directly from a reaction mixture containing two different peptides. All capsules gain substantial ordering upon self-assembly, which is manifested by a two orders of magnitude increase of the intensity of CD spectra of capsules compared with non-assembled analogs. Temperature-dependent CD measurements indicate that the capsules remain stable over the entire temperature range tested (20-100 °C). Circular dichroism coupled with TD DFT calculations, DOSY measurements and X-ray crystallography allow for elucidation of the structures in the solid state and in solution and guide their iterative evolution for the current goals.

Electron flow through proteins is a crucial factor, which decides about their multiple functions in living organisms. Incorporating polypeptides as bridges in donor-bridge-acceptor (DBA) conjugates allows for examining how various structural features in proteins affect the kinetics of the CT processes they mediate. Based on the premise that hydrogen-bonds formation could serve to modify geometry and special orientation of donor and acceptor scaffolds in covalently linked bichromophoric system we designed and synthesized series of dyads comprised of perylene-bisimide and free-base corrole. Specifically, the object of the study was hydrogen-bonded discrete assemblies of corroles possessing core-NH as hydrogen bond donor and amide groups located at position meso-10 as hydrogen bond acceptor. The three dyads differ in type and number of bridging aminoacids’ moieties: L-alanine and L-phenylalanine and one or four respectively. These complex corroles were prepared via synthesis of perylenebisimide-amino acid conjugate possessing free NH2 group followed by amidation of COOH-corrole. Combined steady-state and time-resolved photophysical studies identified that electron-transfer occurs in all four bichromophoric systems. Our focus was on alanine tetramer that is long enough not to mediate too efficiently through-bond CT. A corrole moiety serves as an electron donor, and a perylenediimide as an acceptor. The picosecond rates of electron transfer suggests that the electronic-coupling pathways cannot be through-bond and most likely involve through-hydrogen bond interaction. References Orłowski, R.; Vakuliuk, O.; Gullo, M. P.; Danylyuk, O.; Ventura, B.; Koszarna, B.; Tarnowska, A.; Jaworska, N.; Barbieri, A.; Gryko, D. T. Commun. 2015, 51, 8284-8287. Orłowski, R.; Cichowicz, G.; Staszewska-Krajewska, O.; Schilf, W.; Cyrański, M. K.; Gryko, D. T. Eur. J. 2019, 25, 9658-9664. Figure 1

Elucidating the factors that control charge transfer rates in relatively flexible conjugates is of importance for understanding energy flows in biology as well as assisting the design and construction of electronic devices. Here, we report ultrafast electron transfer (ET) and hole transfer (HT) between a corrole (Cor) donor linked to a perylene-diimide (PDI) acceptor by a tetrameric alanine (Ala)(4). Selective photoexcitation of the donor and acceptor triggers subpicosecond and picosecond ET and HT. Replacement of the (Ala)(4) linker with either a single alanine or phenylalanine does not substantially affect the ET and HT kinetics. We infer that electronic coupling in these reactions is not mediated by tetrapeptide backbone nor by direct donor–acceptor interactions. Employing a combination of NMR, circular dichroism, and computational studies, we show that intramolecular hydrogen bonding brings the donor and the acceptor into proximity in a “scorpion-shaped” molecular architecture, thereby accounting for the unusually high ET and HT rates. Photoinduced charge transfer relies on a (Cor)NH(…)O=C–NH(…)O=C(PDI) electronic-coupling pathway involving two pivotal hydrogen bonds and a central amide group as a mediator. Our work provides guidelines for construction of effective donor–acceptor assemblies linked by long flexible bridges as well as insights into structural motifs for mediating ET and HT in proteins.

Easy scalable and eco-friendly syntheses of resorcin[5]arene, pyrogallol[5]arene, (2-nitro)resorcin[5]arene, (2-carboxyl)resorcin[5]arene, and resorcin[7]arene are presented and a wide range of upper-rim modifications is demonstrated. The macrocycles open the door toward expanding the rich covalent and supramolecular chemistry of [4]arenes with analogues having unique 5-fold and 7-fold symmetry.

A missing, inherently chiral member of the calix[4]arene family denoted "catechol[4]arene" was synthesized. Its properties were studied and compared to the ones of its close relatives resorcin[4]arene and pyrogallol[4]arene. This novel supramolecular host exhibits binding capabilities that are superior to its sister molecules in polar media. The enantiomerically pure forms of the macrocycle display modest recognition of chiral ammonium salts.

Numerous applications of Stoddart's 'blue-box', a pyridinium containing macrocycle of rectangular shape, encouraged us to seek successors of this amazing molecule. Using a one-step cyclization reaction we synthesized a square-shaped cyclic tetramer consisting of 4-methylenepyridinium units - pillar[4]pyridinium (P[4]P). Pillar[4]pyridinium is a quadruply positively charged water-soluble macrocycle with a highly symmetric, strained structure and an electron-deficient cavity. These features impel the macrocycle to assemble into channel networks in the solid state and render it an effective fluoride receptor in water.

We present the synthesis of hybrid[4]arenes via a one-pot reaction of 1,4,5,8-tetramethoxyanthracene and 1,3-dimethoxybenzene with formaldehyde catalyzed by TFA. Two new C2h-symmetric macrocycles having different substitution patterns at anthracene units were obtained. Both X-ray structure analysis and molecular modelling reveal a parallel arrangement of the anthracene units with an interplane distance of 4.8 A. A comparison of UV and fluorescence spectra of hybrid[4]arene and a monomeric anthracene unit indicates that the energies and intensities of the absorption bands (scaled to the same number of chromophores) remain similar. However, for the macrocycle the quantum yield of emission is increased, which may originate from its rigid structure. Hybrid[4]arene was post-macrocyclization modified by the Diels–Alder reaction with benzyne and a macrocycle with an expanded cavity was obtained. The expanded cavity macrocycle is able to selectively complex and solubilize pyridinium iodide in chloroform.

Mechanical grinding/milling can be regarded as historically the first technology for changing the properties of matter. Mechanically activated molecular units (mechanophores) can be present in various structures: polymers, macromolecules, or small molecules. However, only polymers have been reported to effectively transduce energy to mechanophores, which induces breakage of covalent bonds. In this paper, a second possibility is presented-molecular capsules as stress-sensitive units. Mechanochemical encapsulation of fullerenes in cystine-based covalent capsules indicates that complexation takes place in the solid state, despite the fact that the capsules do not possess large enough entrance portals. By using a set of solvent-free MALDI (sf-MALDI) and solid-state NMR (ss-NMR) experiments, it has been proven that encapsulation proceeds during milling and in this process hydrazones and disulfides get activated for breakage, exchange, and re-forming. The capsules are porous and therefore prone to collapse under solvent-free conditions and their conformational rigidity promotes the collapse by the breaking of covalent bonds.

Directional self-assembly of uncharged molecules in water is a major challenge in supramolecular chemistry. Herein, it is demonstrated that peptide-based cavitands wrap around a hydrophobic core (fullerene C60 ) by a combination of the hydrophobic effect and hydrogen-bonding interactions to form highly ordered three-component complexes in water that resemble the molten-globule stage of protein folding. The complexes were characterized by DOSY NMR spectroscopy, small-angle X-ray scattering, and circular dichroism, and their structures were confirmed by X-ray crystallography. Enhancement of the CD signals by nearly one order of magnitude and increased hydrolytic stability of hydrazone bonds of the complexes relative to the nonassembled species were observed. In contrast, DMSO and DMSO/water mixtures were found to be highly disintegrative for these complexes. Interestingly, some cavitands can only be synthesized in the presence of the hydrophobic template followed by disassembly of the complexes.

An efficient method for the synthesis of resorcinarene phosphonium salts, obtained from benzyl derivatives of resorcinarene, has been described. An effect of anion on the stability and structure of phosphonium salts of resorcinarenes has been discussed.

This paper presents a novel approach to highly diastereoselective synthesis of resorcinarenes having enlarged cavities. Inherently chiral heterocyclic resorcinarenes have been obtained with unusually high diastereoselecivity by a “one pot” sequence involving thermal generation of o-quinomethide resorcinarene derivatives and the subsequent Diels–Alder reaction with dienophiles (exemplified by α-methylstyrene). The diastereoselectivity of this reaction is explained based on the thermodynamic stability of the products. The enantiomers of rac-4 have been separated by HPLC and their absolute configuration was assigned by comparison of their experimental and theoretical CD spectra.

Macrocycles consisting of naphthalene units connected via methylene bridges offer certain advantages as macrocylic scaffolds as compared with parent calixarenes. These advantages originate from their electron rich and enlarged cavities. Additionally, macrocycles containing 1,3-bridged naphthalene units are dissymmetric and therefore they present interesting stereochemical features, including inherent chirality. We describe here a facile, one-step synthesis of two new calix[4]naphthalenes, by the condensation of 1,6-dimethoxynaphthalene with formaldehyde catalyzed by Bronsted acid (TFA). Additionally, we show the first example of hybrid[n]arene containing a 1,6-dimethoxynaphthalene unit and 1,3-dimethoxybenzene units obtained by a simple, one-pot condensation. The conformational and complexation properties were also studied for the resulting hybrid macrocycles.

Several new conjugates of tert-butylcalix[4]arenes bearing different 1-substituted triazoles at the lower rim were synthesized via click chemistry. The products were tested towards complexation of metal ions exhibiting pronounced selectivity towards Hg2+. The 1H NMR titration results for ligand 12a show formation of L:Hg2+ complexes with various stoichiometries, logβ(1:1)=6.8, logβ(2:1)=11.9, logβ(2:2)=15.1 in CDCl3:CD3CN 1:1.

2-naphthol derivatives of resorcinarenes were synthesized by solvent-free 1,4 Michael addition reactions in yields up to 76%. This result is significantly better than in case of reactions in solution. Based on experimental results and previously known similar reactions a mechanism is proposed involving an in situ generated o-quino methide derivative of resorcinarene.

Sublimation of p-iso-propylcalix[4]arene under reduced pressure results in the concomitant formation of two new polymorphs (forms IIP and IIIP). Both forms consist of interdigitated dimers of calixarene molecules, as does the known form IP. Despite similar inclusion behaviour to that of p-tert-butylcalix[4]arene, p-iso-propylcalix[4]arene does not appear to favour the formation of a transiently porous material.

Peptide-based cavitands (resorcin[4]arenes substituted with histidine and glutamine hydrazides) exist as monomeric species in polar solvents (DMSO and methanol). Upon complexation of fullerenes, the cavitands wrap around the hydrophobic guests forming dimeric capsular shells (as evidenced by DOSY). The self-assembly of the cavitands is based on the formation of beta-sheet-like binding motifs around the hydrophobic core. In a polar environment, these hydrogen bonded structures are kinetically stable and highly ordered as manifested by a 100-fold increase of intensity of circular dichroism bands, as well as a separate set of signals and substantial differences in chemical shifts in NMR spectra. This behavior resembles a protein folding process at the molten globule stage with non-specific hydrophobic interactions creating a protective and favourable local environment for the formation of secondary structures of proteins.

Molecular encapsulation of C60 inside a hydrogen-bond-sealed semi-flexible peptidic capsule is hindered in solution, yet it proceeds effectively after mechanical milling of a solid sample. We show that the molecular mechanism involves the generation of non-covalently disordered forms that are active in guest uptake. We also show that the solvent-free mechanochemical covalent synthesis of capsules directly results in obtaining disordered, active forms.

A cubic nanocage (O symmetry) that exhibits inherent chirality and has a covalent, rigid skeleton with molecule-sized entrance portals was obtained by means of dynamic covalent chemistry using a reaction between aldehyde-functionalized resorcin[4]arene and hydrazine.

This review discusses chiral self-sorting-the process of choosing an interaction partner with a given chirality from a complex mixture of many possible racemic partners. Chiral self-sorting (also known as chiral self-recognition or chiral self-discrimination) is fundamental for creating functional structures in nature and in the world of chemistry because interactions between molecules of the same or the opposite chirality are characterized by different interaction energies and intrinsically different resulting structures. However, due to the similarity between recognition sites of enantiomers and common conformational lability, high fidelity homochiral or heterochiral self-sorting poses a substantial challenge. Chiral self-sorting occurs among natural and synthetic molecules that leads to the amplification of discrete species. The review covers a variety of complex self-assembled structures ranging from aggregates made of natural and racemic peptides and DNA, through artificial functional receptors, macrocyles, and cages to catalytically active metal complexes and helix mimics. The examples involve a plethora of reversible interactions: electrostatic interactions, π-π stacking, hydrogen bonds, coordination bonds, and dynamic covalent bonds. A generalized view of the examples collected from different fields allows us to suggest suitable geometric models that enable a rationalization of the observed experimental preferences and establishment of the rules that can facilitate further design.

A strategy that utilizes macrocyclic resorcin[4]arenes for the pre-positioning of peptides to form cavitands that subsequently self-assemble through hydrogen bonds was used for the formation of molecular capsules. Hydrophobic tri- and tetrapeptides were attached via their C-termini to tetraformylresorcin[4]arene using acylhydrazone linkers. The resulting cavitands self-assemble in relatively non-polar environments (chloroform or chloroform-methanol) forming non-covalent dimers through hydrogen bonding motifs resembling beta-sheets. NMR studies (ROESY and DOSY) indicate that the binding motif involves C-terminal amino acids from the peptide strands, while the N-terminal parts are positioned outside of the cavity. The capsules possess stable porous structures and they are able to quantitatively complex fullerenes C60 and C70.

The Diels–Alder reaction enables introduction of new functionalities onto the resorcinarene skeleton with simultaneous generation of new stereogenic centers and expansion of the internal cavity. We present highly regio- and diastereoselective inverse electron demand oxa-Diels–Alder reactions of resorcinarene ortho-quinone methide with benzofuran and indene, each generating 12 new stereogenic centers. The mechanism and reasons for regioselectivity and diastereoselectivity were analyzed using theoretical calculations (NBO charges, Fukui functions, transition state energies, and thermodynamic stability of the products). Enantiomers were separated, and their configurations were determined by comparison of experimental and theoretical electronic circular dichroism spectra.

The title compounds are prepared with unusually high diastereoselectivity in one-pot via thermal generation of o-quinomethide resorcinarene derivatives and subsequent Diels—Alder reaction with dienophiles, such as α-methylstyrene.

Since the first synthesis of chiral calixarenes in 1979 by Gutsche enormous progress has been made in preparation techniques and applications. Many chiral calixarenes (including resorcinarenes and homocalixarenes) modified with peptides, carbohydrates, chiral amines or axially chiral groups are known. Due to their diverse conformational features, introduction of chirality into a calixarene platform is not only limited to classical chirality based on carbon stereogenic centers but also can be introduced by asymmetric/dissymmetric substitution pattern or in a non-covalent way. The main driving force for the development of chiral calixarenes is the possibility to use them as enantioselective synthetic receptors. Effective chiral receptors based on calixarenes have found applications in recognition of chiral guests in solution, as chromatography stationary phases, enantioselective membrane carriers and catalysts. Their potential has also been demonstrated in interactions with biological molecules, including protein recognition, formation of gels and antimicrobial activity. The chapter summarizes the current achievements in the field with the special emphasis on unique features of calixarenes and resorcinarenes leading to “non-classical” chirality and functionality based on chiral recognition.

A new, very efficient, and selective preparation method of peralkylated pillar[5]arenes is presented. By replacing typical Lewis acids with trifluoroacetic acid (TFA) we were able to eliminate the need of anhydrous conditions without a loss of effectiveness. The method is highly practical: a) it is moisture-insensitive, b) starting from simple and cheap reagents and reactants, and c) allows for chromatography-free isolation of the products. The results indicate that the interactions with solvent molecules can modulate stability of the products and influence the reaction outcome. Dichloromethane (DCM) and dichloroethane (DCE) are complexed within the cyclopentamer cavity with association constants of 120 M−1 and 600 M−1, respectively (CDCl3). The interactions involve a combination of hydrogen–pi and halogen–pi bonds.

The complexation of chiral guests in the cavity of dimeric self-assembled chiral capsule 1(2) was studied by using NMR spectroscopy and X-ray crystallography. Capsule 1(2) has walls composed of amino acid backbones forming numerous directional binding sites that are arranged in a chiral manner. The polar character of the interior dictates the encapsulation preferences towards hydrophilic guests and the ability of the capsule to extract guests from water into an organic phase. Chiral discrimination towards hydroxy acids was evaluated by using association constants and competition experiments, and moderate de values were observed (up to 59 %). Complexes with one or two guest molecules in the cavity were formed. For 1:1 complexes, solvent molecules are coencapsulated; this influences guest dynamics and makes the chiral recognition solvent dependent. Reversal of the preferences can be induced by coencapsulation of a nonchiral solvent in the chiral internal environment. For complexes with two guests, filling of the capsule's internal space can be very effective and packing coefficients of up to 70 % can be reached. The X-ray crystal structure of complex 1(2) superset((S)-6)(2) with well-resolved guest molecules reveals a recognition motif that is based on an extensive system of hydrogen bonds. The optimal arrangement of interactions with the alternating positively and negatively charged groups of the capsule's walls is fulfilled by the guest carboxylic groups acting simultaneously as hydrogen-bond donors and acceptors. An additional guest molecule interacting externally with the capsule reveals a possible entrance mechanism involving a polar gate. In solution, the structural features and dynamic behavior of the D(4)-symmetric homochiral capsule were analyzed by variable-temperature NMR spectroscopy and the results were compared with those for the S(8)-symmetric heterochiral capsule.

Chiral C4-symmetric resorcinarenes, substituted with l-amino acid derivatives at upper rims, were synthesized by the modified Mannich reaction and subsequent N-substitution reactions. Compounds of that type (5a–e) can exist in two relatively stable inherently chiral C4-symmetric conformations, (M) and (P), stabilized by the formation of seams of hydrogen bonds. However, because of diastereomeric preferences the amino acid substituted resorcinarenes exhibit considerable diastereomeric excesses for the induced conformational inherent chirality (up to ≥95 %). The relatively slow exchange allowed the determination of the directions of the hydrogen bond ring closures through the combined application of NMR (ROESY) and X-ray analysis. It was also possible to correlate the absolute conformation with the sign of the Cotton effects observed for the transitions within the resorcinol chromophore in the CD spectra (solution and solid state). The ab initio calculations (TDDFT/B3LYP/DZVP and TDDFT/CAMB3LYP/6-31++G*) for model compounds showed that the chiral arrangement of the hydrogen bonding in resorcinarenes can produce substantial CD effects, which are amplified by exciton coupling. However, it was also shown that the neighboring urea, amide, or phenyl groups have crucial effects on the direction of electric transition dipoles and, as the result, on the signs of the exciton-coupled bands.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Dynamic chirality of iminoresorcin[4]arenes that originates from regioselective and diastereoselective keto-enol tautomerisation was switched by non-covalent interactions with achiral molecules, as demonstrated by experimental electronic circular dichroism (ECD) spectra supported by TD DFT calculations.

Hybrid [n]arenes, the class of medium-sized macrocyclic compounds consisting of different alkoxybenzene units, were obtained by a simple, one-pot, direct condensation of two different alkoxybenzenes with formaldehyde catalyzed by a Bronsted acid (trifluoroacetic acid). We have shown that, under Bronsted acid catalysis, this reaction is reversible and therefore governed by the relative stability of the products. The main macrocyclic products are hybrid [n]arenes consisting of four alkoxybenzene units of [2 + 2] or [3 + 1] stoichiometry. However, an unusual [3 + 2] hybrid macrocycle was also obtained as a main product of the condensation between 1,4-dimethoxybenzene, 1,3,5-trimethoxybenzene, and formaldehyde. The stability of the hybrid products and the reversibility of the reaction were further confirmed by a scrambling experiment, involving pillar[5]arene and per-O-methylated resorcin[4]arene. The scrambling experiment has given hybrid macrocycles in yields comparable with those obtained in condensation reactions. NMR spectra and X-ray structures of hybrid [n]arenes indicate that 1,2- and 1,3-dialkoxybenzene units are flexible parts of macrocyclic rings. However, the 1,4-dialkoxybenzene units present considerable steric hindrance, resulting in the formation of isomers and inherently chiral macrocycles due to inhibited rotation. The recognition properties toward various organic cations were also determined. Highly selective recognition of the N-methylpyridinium cation was observed for the [3 + 2] hybrid macrocycle.

The synthesis and structures of nickel (II) complexes of chiral cyclams originating from l -proline are presented. Upon addition of nickel acteate, oxocyclams having amide groups underwent deprotonation forming distorted square-planar complexes. In the case of the all-amine analogue a six-coordinate octahedral complex is formed.

The Mannich reaction between selectively tetratosylated resorcin[4]arene, formaldehyde and (S)-phenylalanine (or (S)-phenylglycine) methylamide gave cyclochiral mono- or dibenzoxazines with high diastereoselection as revealed by NMR and X-ray structural studies. X-ray structures of the products show the variety of intramolecular interactions that can be responsible for the diastereoselection of this acid-catalyzed reaction.

Based on an analysis of previously reported structures and a potential geometry fit with substrates, a new family of chiral dioxocyclam derivatives have been designed. The synthesis of those ligands was accomplished starting from l -proline and α- d -amino acids (converted to β-amino acids) with a key step of macrocyclization reaction of amino esters. All ligands were converted into neutral copper(II) complexes (amide groups underwent deprotonation of upon treatment of ligands with copper(II) acetate). The complexes exhibit the desired shape of their active surfaces, as proved by X-ray analysis.

Isophthalic acid-based macrocyclic tetraamide 4 shows considerable conformational change during anion binding. In the solid state and in solution the free receptor exists in nonbonding, closed conformation stabilized by two intramolecular hydrogen bonds. Upon anion complexation, the receptor switches to a conformation with convergent arrangement of hydrogen bond donors. The conformational switch is evidenced by 2D NMR and X-ray analyses of the free ligand and its Cl − complex.

The synthesis of a novel class of functionalized benzophanes in which a (2′-hydroxy)ethoxy pendant arm is attached to the phenyl ring is reported. The reported approach, utilizes simple starting materials, and skillful organization of the synthetic steps allows for simultaneous transforms of the macrocyclic ring and the pendant arm. Binding studies of these systems with Pd2+ and Cd2+ cations is described. A chromatographic stationary phase containing the benzodiazacoronand moiety was also synthesized, and found to interact specifically with isomeric nitrobenzene derivatives.

The interaction of the neutral form of resorcin[4]arene 1 (R=i-Bu) with tetraalkylammonium cations (Me4N+, Et4N+, Pr4N+and Bu4N+) was analyzed in the solid state and in methanol solutions. In methanol, NMR titration results indicate almost no differentiation between Me4N+ and Et4N+ cations (Kass(Me4N+)=93 M−1 and Kass(Et4N+)=81 M−1) and a relatively low association constant for Pr4N+( Kass(Pr4N+)=25 M−1). In the solid state, for the Me4NCl complex, the resorcinarene assumes the C2v boat conformation and is surrounded by as many as four Me4NCl moieties. The structure of the Et4NCl complex indicates that ethyl group can be conveniently placed in the resocin[4]arene cavity. The larger Bu4N+ cation was found completely external to the cavity.

Owing to their versatility and biocompatibility, peptide-based self-assembled structures constitute valuable targets for complex functional designs. It is now shown that artificial capsules based on β-barrel binding motifs can be obtained by means of dynamic covalent chemistry (DCC) and self-assembly. Short peptides (up to tetrapeptides) are reversibly attached to resorcinarene scaffolds. Peptidic capsules are thus selectively formed in either a heterochiral or a homochiral way by simultaneous and spontaneous processes, involving chiral sorting, tautomerization, diastereoselective induction of inherent chirality, and chiral self-assembly. Self-assembly is shown to direct the regioselectivity of reversible chemical reactions. It is also responsible for shifting the tautomeric equilibrium for one of the homochiral capsules. Two different tautomers (keto-enamine hemisphere and enol-imine hemisphere) are observed in this capsule, allowing the structure to adapt for self-assembly.