Selective C70 encapsulation by a robust octameric nanospheroid held together by 48 cooperative hydrogen bonds

Window[1]resorcin[3]arenes: A Novel Macrocycle Able to Self-Assemble to a Catalytically Active Hexameric Cage

The hexameric resorcin[4]arene capsule has been utilized as one of the most versatile supramolecular capsule catalysts. Enlarging its size would enable expansion of the substrate size scope. However, no larger catalytically active versions have been reported. Herein, we introduce a novel class of macrocycles, named window[1]resorcin[3]arene (wRS), that assemble to a cage-like hexameric host. The new host was studied by NMR, encapsulation experiments, and molecular dynamics simulations. The cage is able to bind tetraalkylammonium ions that are too large for encapsulation inside the hexameric resorcin[4]arene capsule. Most importantly, it retained its catalytic activity, and the accelerated conversion of a large substrate that does not fit the closed hexameric resorcin[4]arene capsule was observed. Thus, it will help to expand the limited substrate size scope of the closed hexameric resorcin[4]arene capsule.

Molecular vessels from preorganised natural building blocks

Supramolecular vessels emerged as tools to mimic and better understand compartmentalisation, a central aspect of living matter. However, many more applications that go beyond those initial goals have been documented in recent years, including new sensory systems, artificial transmembrane transporters, catalysis, and targeted drug or gene delivery. Peptides, carbohydrates, nucleobases, and steroids bear great potential as building blocks for the construction of supramolecular vessels, possessing complexity that is still difficult to attain with synthetic methods - they are rich in functional groups and well-defined stereogenic centers, ready for noncovalent interactions and further functions. One of the options to tame the functional and dynamic complexity of natural building blocks is to place them at spatially designed positions using synthetic scaffolds. In this review, we summarise the historical and recent advances in the construction of molecular-sized vessels by the strategy that couples synthetic predictability and durability of various scaffolds (cyclodextrins, porphyrins, crown ethers, calix[n]arenes, resorcin[n]arenes, pillar[n]arenes, cyclotriveratrylenes, coordination frameworks and multivalent high-symmetry molecules) with functionality originating from natural building blocks to obtain nanocontainers, cages, capsules, cavitands, carcerands or coordination cages by covalent chemistry, self-assembly, or dynamic covalent chemistry with the ultimate goal to apply them in sensing, transport, or catalysis.

Post-Assembly Polymerization of Discrete Anion-Coordinated Triple Helicate

Hierarchical self-assembly has been recently employed in the construction of anion-coordination-driven gel materials. However, the post-assembly modification strategy, which may be a highly efficient strategy to realize the functionalization of discrete 'aniono' supramolecular architectures, has not been employed yet. Herein we report the first example of anion-coordination-driven gel material cross-linked by well-defined 'aniono' triple helicate through post-assembly polymerization. The obtained gel shows self-healing property and excellent compatibility with various surfaces, including glass, rubber, leaf, PP, and metal. The viscoelastic gel constructed through the post-assembly modification strategy enriches the method to construct the anion-coordination-driven smart materials.

Dynamic covalent synthesis

Dynamic covalent synthesis aims to precisely control the assembly of simple building blocks linked by reversible covalent bonds to generate a single, structurally complex, product. In recent years, considerable progress in the programmability of dynamic covalent systems has enabled easy access to a broad range of assemblies, including macrocycles, shape-persistent cages, unconventional foldamers and mechanically-interlocked species (catenanes, knots, etc.). The reversibility of the covalent linkages can be either switched off to yield stable, isolable products or activated by specific physico-chemical stimuli, allowing the assemblies to adapt and respond to environmental changes in a controlled manner. This activatable dynamic property makes dynamic covalent assemblies particularly attractive for the design of complex matter, smart chemical systems, out-of-equilibrium systems, and molecular devices.

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Intermolecular hydrogen bonding in calix[5]arene derived cavitands regulates the molecular recognition of fullerenes

We present a readily available calix[5]arene derived cavitand receptor that is stabilized in the closed cone conformer through intermolecular hydrogen bonding with methanol molecules. The receptor features a highly spherical aromatic surface that binds C60 and C70 fullerenes effectively, and the binding event can be regulated allosterically by the addition of methanol.

Coordination-Driven Tetragonal Prismatic Cage and the Investigation on Host-Guest Complexation

A coordination-driven host has been reported to encapsulate guests by noncovalent interactions. Herein, we present the design and synthesis of a new type of prism combining porphyrin and terpyridine moieties with a long cavity. The prism host can contain bisite or monosite guests through axial coordination binding of porphyrin and aromatic π interactions of terpyridine. The ligands and prismatic complexes were characterized by electrospray ionization mass spectrometry (ESI-MS), TWIM-MS, NMR spectrometry, and single-crystal X-ray diffraction analysis. The guest encapsulation was investigated through ESI-MS, NMR spectrometry, and transient absorption spectroscopy analysis. The binding constant and stability were determined by UV-Vis spectrometry and gradient tandem MS (gMS²) techniques. Based on the prism, a selectively confined condensation reaction was also performed and detected by NMR spectrometry. This study provides a new type of porphyrin- and terpyridine-based host that could be used for the detection of pyridyl- and amine-contained molecules and confined catalysis.

Stereoselective Assembly of Hydrogen-Bonded Anionic Cages Dictated by Organophosphate-Based Chiral Nodes

Inspired by the signal transduction function of organophosphates in biological systems, bioactive organophosphates were utilized for the first time as chiral nodes to dictate the stereoselective assembly of hydrogen-bonded anionic cages. Phosphonomycin (antibiotics), tenofovir (antivirals), adenosine monophosphate (natural product, AMP) and clindamycin phosphate (antibiotics) were assembled with an achiral bis-monourea ligand, thereby leading to the stereoselective formation of quadruple or triple helicates. The extent of the stereoselectivity could be enhanced by either lowering the temperature or adding stronger-binding cations as templates. With the chiral anionic cages as the host, some enantioselectivity was achieved when binding chiral quaternary ammonium cations.

Chiral Supramolecular Polymers Assembled from Conformationally Flexible Amino-Acid-Substituted Biphenyldiimides

Hydrogen-bonded polymers are a class of highly dynamic supramolecular aggregates, whose self-assembly may be tuned by very mild external or internal stimuli. However, the rational design of chiral supramolecules remains challenging especially when flexible components are involved. The combination of the inherent weakness and dynamic nature of the intermolecular bonds that hold together such assemblies with unrestricted molecular motions introduces additional factors which may affect the self-assembly process. In this report, the self-assembly of four amino acid-derived chiral biphenyldiimides into open-chain 1D supramolecular polymers is presented. While the primary driving force, COOH···HOOC hydrogen bonding, is responsible for the polymer growth in all cases, the amino acid side chains play an important role in either stabilizing or destabilizing the assemblies obtained, as deduced from studies of the thermodynamics of the self-assembly process. Furthermore, substantial differences in the structural factors governing the polymerization process between dynamic liquid and static solid are found. This work demonstrates the potential of the rather unexplored class of diimide-based organic dyes in the formation of well-organized chiral supramolecular assemblies with tunable properties.

Fullerene Complexation in a Hydrogen-Bonded Porphyrin Receptor via Induced-Fit: Cooperative Action of Tautomerization and C-H···π Interactions

A supramolecular chiral hydrogen-bonded tetrameric aggregate possessing a large cavity and tetraarylporphyrin substituents was assembled using alternating 4H- and 2H-bonds between ureidopyrimidinone and isocytosine units, respectively. The aggregation mode was rationally shifted from social to narcissistic self-sorting by changing urea substituent size only. The H-bonded tetramer forms a strong complex with C₆₀ guest, at the same time undergoing remarkable structural changes. Namely, the cavity adjusts to the guest via keto-to-enol tautomerization of the ureidopyrimidinone unit and as a result, porphyrin substituents move apart from each other in a scissor blade-like opening fashion. The rearrangement is accompanied by C-H···π interaction between the alkyl solubilizing groups and the nearby placed porphyrin π-systems. The latter interaction was found to be crucial for the guest complexation event, providing energetic compensation for otherwise costly tautomerization. We showed that only the systems possessing sufficiently long alkyl chains capable of interacting with a porphyrin ring are able to form a complex with C₆₀. The structural rearrangement of the tetramer was quantitatively characterized by electron paramagnetic resonance pulsed dipolar spectroscopy measurements using photogenerated triplets of porphyrin and C₆₀ as spin probes. Further exploring the C-H···π interaction as a decisive element for the C₆₀ recognition, we investigated the guest-induced self-sorting phenomenon using scrambled tetramer assemblies composed of two types of monomers possessing alkyl chains of different lengths. The presence of the fullerene guest has enabled the selective scavenging of monomers capable of C-H···π interaction to form homo-tetrameric aggregates.

Purely Covalent Molecular Cages and Containers for Guest Encapsulation

Cage compounds offer unique binding pockets similar to enzyme-binding sites, which can be customized in terms of size, shape, and functional groups to point toward the cavity and many other parameters. Different synthetic strategies have been developed to create a toolkit of methods that allow preparing tailor-made organic cages for a number of distinct applications, such as gas separation, molecular recognition, molecular encapsulation, hosts for catalysis, etc. These examples show the versatility and high selectivity that can be achieved using cages, which is impossible by employing other molecular systems. This review explores the progress made in the field of fully organic molecular cages and containers by focusing on the properties of the cavity and their application to encapsulate guests.

Expanding structural diversity in a library of disulfide macrocycles through in-situ imide hydrolysis

We describe here an unorthodox approach to dynamic covalent chemistry in which the initially-unexpected in-situ hydrolysis of a bis-imide is employed to control the composition of a library of structurally diverse macrocycles. A single building block is used to generate a library of numerous disulfide-based architectures in a one-pot single-step process. The dual-stimuli method is based on simultaneous changes in pH and DMSO concentration to expand the structural diversity of the macrocyclic products. Mechanistic details of this complex process are investigated by the kinetics analysis. We delivered a facile strategy for the synthesis of water-soluble, multicomponent and dynamic macrocycles equipped with number of different functional groups, thus giving a prospect of their application in guest-driven phase transfer.

Synthesis of a chiral metallo-capsule composed of concave molecules and chirogenesis upon fullerene binding

An enantiopure molecular capsule was synthesized quantitatively using complexation of four phosphangulenes as concave molecules with four Zn²⁺ ions and applied to fullerene binding and chirogenesis. The capsule encapsulated selectively fullerene and its derivatives based on the size of cavity. The fullerene C₆₀ incorporated in the capsule exhibited induced-CD signals at the transitions of C₆₀.

Thioderivatives of Resorcin[4]arene and Pyrogallol[4]arene: Are Thiols Tolerated in the Self-Assembly Process?

Three novel thiol bearing resorcin[4]arene and pyrogallol[4]arene derivatives were synthesized. Their properties were studied with regards to self-assembly, disulfide chemistry, and Brønsted acid catalysis. This work demonstrates that (1) one aromatic thiol on the resorcin[4]arene framework is tolerated in the self-assembly process to a hexameric hydrogen bond-based capsule, (2) thio-derivatized resorcin[4]arene analogs can be covalently linked through disulfides, and (3) the increased acidity of aromatic thio-substituent is not sufficient to replace HCl as cocatalyst for capsule catalyzed terpene cyclizations.

Strong intramolecular hydrogen bonding in confined amino acids

Intramolecular hydrogen bonding is evaluated in three different amino acids encapsulated in C₆₀ fullerene in the context of electron density analysis. While conventional intramolecular hydrogen bonding in isolated amino acids are dominated by electrostatic character, it is shown that strong intramolecular hydrogen bonding can be formed in confined amino acids so that in two cases covalent intramolecular hydrogen bonding is appeared in the confined species. Also, results show that zwitterionic amino acids are stable in confined state, where no implicit or explicit solvation is applied. Covalent character for intramolecular hydrogen bonding in amino acids have not yet been reported.

Concentration-Dependent Self-Assembly of an Unusually Large Hexameric Hydrogen-Bonded Molecular Cage

The sizes of available self-assembled hydrogen-bond-based supramolecular capsules and cages are rather limited. The largest systems have volumes of approximately 1400-2300 ų . Herein, we report a large, hexameric cage based on intermolecular amide-amide dimerization. The unusual structure with openings, reminiscent of covalently linked cages, is held together by 24 hydrogen bonds. With a diameter of 2.3 nm and a cavity volume of ∼2800 ų , the assembly is larger than any previously known capsule/cage structure relying exclusively on hydrogen bonds. The self-assembly process in chlorinated, organic solvents was found to be strongly concentration dependent, with the monomeric form prevailing at low concentrations. Additionally, the formation of host-guest complexes with fullerenes (C₆₀ and C₇₀ ) was observed.

Glucose Binding Drives Reconfiguration of a Dynamic Library of Urea-Containing Metal-Organic Assemblies

A bis-urea-functionalized ditopic subcomponent assembled with 2-formylpyridine and Fe^II , resulting in a dynamic library of metal-organic assemblies: an irregular Fe^II ₄ L₆ structure and three Fe^II ₂ L₃ stereoisomers: left- and right-handed helicates and a meso-structure. This library reconfigured in response to the addition of monosaccharide derivatives, which served as guests for specific library members, and the rate of saccharide mutarotation was also enhanced by the library. The (P) enantiomer of the Fe^II ₂ L₃ helical structure bound β-D-glucose selectively over α-D-glucose. As a consequence, the library collapsed into the (P)-Fe^II ₂ L₃ helicate following glucose addition. The α-D-glucose was likewise transformed into the β-D-anomer during equilibration and binding. Thus, β-D-glucose and (P)-3 amplified each other in the product mixture, as metal-organic and saccharide libraries geared together into a single equilibrating system.

Porphyrin bearing phenothiazine pincers as hosts for fullerene binding via concave–convex complementarity: synthesis and complexation study

Free base porphyrin hosts, m-(PTZ)4-H2P and p-(PTZ)4-H2P, tethered with four phenothiazine moieties at the meso-position via a flexible ethoxy phenyl linker were synthesized and used for the selective complexation of fullerenes, C60 and C70.

Coordination cages as permanently porous ionic liquids

Porous materials are widely used in industry for applications that include chemical separations and gas scrubbing. These materials are typically porous solids, although the liquid state can be easier to manipulate in industrial settings. The idea of combining the size and shape selectivity of porous domains with the fluidity of liquids is a promising one and porous liquids composed of functionalized organic cages have recently attracted attention. Here we describe an ionic-liquid, porous, tetrahedral coordination cage. Complementing the gas binding observed in other porous liquids, this material also encapsulates non-gaseous guests-shape and size selectivity was observed for a series of isomeric alcohols. Three gaseous chlorofluorocarbon guests, trichlorofluoromethane, dichlorodifluoromethane and chlorotrifluoromethane, were also shown to be taken up by the liquid coordination cage with an affinity that increased with their size. We hope that these findings will lead to the synthesis of other porous liquids whose guest-uptake properties may be tailored to fulfil specific functions.

Tuning the Solubility of Self-Assembled Fluorescent Aromatic Cages Using Functionalized Amino Acid Building Blocks

We previously reported novel fluorescent aromatic cages that are self-produced using a set of orthogonal dynamic covalent reactions, operating simultaneously in one-pot, to assemble up to 10 components through 12 reactions into a single cage-type structure. We now introduce N-functionalized amino acids as new building blocks that enable tuning the solubility and analysis of the resulting cages. A convenient divergent synthetic approach was developed to tether different side chains on the N-terminal of a cysteine-derived building block. Our studies show that this chemical functionalization does not prevent the subsequent self-assembly and effective formation of desired cages. While the originally described cages required 94% DMSO, the new ones bearing hydrophobic side chains were found soluble in organic solvents (up to 75% CHCl3), and those grafted with hydrophilic side chains were soluble in water (up to 75% H2O). Fluorescence studies confirmed that despite cage functionalization the aggregation-induced emission properties of those architectures are retained. Thus, this work significantly expands the range of solvents in which these self-assembled cage compounds can be generated, which in turn should enable new applications, possibly as fluorescent sensors.

Dynamic polyimine macrobicyclic cryptands - self-sorting with component selection

Self-assembling macrobicyclic cryptand-type organic cages display remarkable self-sorting behavior with efficient component selection.

Self-assembling macrobicyclic cryptand-type organic cages display remarkable self-sorting behavior with efficient component selection. Making use of the dynamic covalent chemistry approach, eight different cages were synthesized by condensation of tris(2-aminopropyl)amine with structurally different dialdehydes. A series of self-sorting experiments were first carried out on simple dynamic covalent libraries. They reveal the influence of different structural features of the aldehyde components on the condensation with two triamine capping units. Subsequently, self-sorting experiments were performed on more complex systems involving several dialdehyde building blocks. Altogether, the results obtained describe the effect of the presence of a heteroatom, of electrostatic interactions, of delocalization and of the flexibility/stiffness of the propensity of a component to undergo formation of a macrobicyclic cage. In the presence of a catalytic amount of acid, the macrobicyclic structure undergoes dynamic component exchange.

Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of "High-Energy" Water

The cavity of an M8 L12 cubic coordination cage can accommodate a cluster of ten water molecules in which the average number of hydrogen bonds per water molecule is 0.5 H-bonds less than it would be in the bulk solution. The presence of these "hydrogen-bond frustrated" or "high-energy" water molecules in the cavity results in the hydrophobic effect associated with guest binding being predominantly enthalpy-based, as these water molecules can improve their hydrogen-bonding environment on release. This contrasts with the classical form of the hydrophobic effect in which the favourable entropy change associated with release of ordered molecules from hydrophobic surfaces dominates. For several guests Van't Hoff plots showed that the free energy of binding in water is primarily enthalpy driven. For five homologous pairs of guests related by the presence or absence of a CH2 group, the incremental changes to ΔH and TΔS for guest binding-that is, ΔΔH and TΔΔS, the difference in contributions arising from the CH2 group-are consistently 5(±1) kJ mol-1 for ΔΔH and 0(±1) kJ mol-1 for TΔΔS. This systematic dominance of ΔH in the binding of hydrophobic guests is consistent with the view that guest binding is dominated by release of "high energy" water molecules into a more favourable solvation environment, as has been demonstrated recently for some members of the cucurbituril family.

The templation effect as a driving force for the self-assembly of hydrogen-bonded peptidic capsules in competitive media

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.