Capsular Assemblies Research Articles

A Pillararene-Based Cavitand: Synthesis and Solid-State Capsular Assemblies Induced by Linear Alkanes with Specific Lengths.

Herein, a novel pillararene-based cavitand with fixed planar chirality was synthesized by the SuFEx reaction. As demonstrated by single crystal X-ray analysis, host-guest capsules involving this cavitand and linear alkanes with specific lengths are observed in the solid state. The formation of each capsule is driven by hydrogen bonding interactions between a linear alkane molecule and two cavitand molecules, as well as noncovalent interactions between the two cavitand molecules in this capsule.

Supramolecular and molecular capsules, cages and containers.

Stemming from early seminal notions of molecular recognition and encapsulation, three-dimensional, cavity-containing capsular compounds and assemblies have attracted intense interest due to the ability to modulate chemical and physical properties of species encapsulated within these confined spaces compared to bulk environments. With such a diverse range of covalent motifs and non-covalent (supramolecular) interactions available to assemble building blocks, an incredibly wide-range of capsular-type architectures have been developed. Furthermore, synthetic tunability of the internal environments gives chemists the opportunity to engineer systems for uses in sensing, sequestration, catalysis and transport of molecules, just to name a few. In this tutorial review, an overview is provided into the design principles, synthesis, characterisation, structural facets and properties of coordination cages, porous organic cages, supramolecular capsules, foldamers and mechanically interlocked molecules. Using seminal and recent examples, the advantages and limitations of each system are explored, highlighting their application in various tasks and functions.

Influence of H-bond competitors on the solvent-dependent structures of an octaurea-calix[4]tube.

A novel octaurea-calix[4]tube (UC4T) has been synthesized in three steps from the original Beer's p-tert-butylcalix[4]tube ionophore. In a polar solvent (DMSO-d6), UC4T rapidly interconverts between two identical conformations with C2v symmetry for the two calix[4]arene subunits. However, in a less polar solvent mixture (CDCl3/DMSO-d6, 98 : 2), UC4T adopts a highly distorted asymmetric structure, which hinders the formation of typical tetraurea calix[4]arene capsular assemblies. The complexation of potassium (or barium) cations inside the dioxyethylene ionophoric binding site of UC4T triggers a C2v to C4v symmetry rearrangement of the two calix[4]arene subunits. This rearrangement leads to the formation of a transient capsular dimeric species observed in solution upon the addition of KI or BaCl2·2H2O to a solution (CDCl3/DMSO-d6, 98 : 2) of the macrocycle. X-ray studies confirm UC4T's ability to adopt different asymmetric conformations, depending on its interactions with solvent molecules. Two distinct crystal forms (α and β) of UC4T have been obtained, each displaying divergent calix[4]arene subunits with pinched-cone conformations. These conformations exhibit distinctive head-to-tail (α) or head-to-head/tail-to-tail (β) orientations of the ureido groups, which are involved in hydrogen bonding with solvent molecules. Notably, the pseudo-capsular 1D supramolecular polymeric arrays observed in the β form of UC4T assemble to create large parallel solvent channels.

Dynamic Cages—Towards Nanostructured Smart Materials

AbstractThe interest in capsular assemblies such as dynamic organic and coordination cages has blossomed over the last decade. Given their chemical and structural variability, these systems have found applications in diverse fields of research, including energy conversion and storage, catalysis, separation, molecular recognition, and live‐cell imaging. In the exploration of the potential of these discrete architectures, they are increasingly being employed in the formation of more complex systems and smart materials. This Review highlights the most promising pathways to overcome common drawbacks of cage systems (stability, recovery) and discusses the most promising strategies for their hybridization with systems featuring various dimensionalities. Following the description of the most recent advances in the fabrication of zero to three‐dimensional cage‐based systems, this Review will provide the reader with the structure‐dependent relationship between the employed cages and the properties of the materials.

Dynamic Cages-Towards Nanostructured Smart Materials.

The interest in capsular assemblies such as dynamic organic and coordination cages has blossomed over the last decade. Given their chemical and structural variability, these systems have found applications in diverse fields of research, including energy conversion and storage, catalysis, separation, molecular recognition, and live-cell imaging. In the exploration of the potential of these discrete architectures, they are increasingly being employed in the formation of more complex systems and smart materials. This Review highlights the most promising pathways to overcome common drawbacks of cage systems (stability, recovery) and discusses the most promising strategies for their hybridization with systems featuring various dimensionalities. Following the description of the most recent advances in the fabrication of zero to three-dimensional cage-based systems, this Review will provide the reader with the structure-dependent relationship between the employed cages and the properties of the materials.

Diverse Self-Assembly and Xenon Binding from a Single Mesomeric Macrocycle Component

Xenon binding has received considerable interest, but effective hosts remain rare, and the majority of assembly-type hosts are barely explored. Here, we report the synthesis, self-assembly, and xenon inclusion behavior with a homemade mesomeric bisurea–bisthiourea macrocycle. Compared to its racemic counterparts as recently investigated, the single mesomeric macrocycle forms even more comprehensive dimerization assemblies. From the single macrocycle component, up to two pairs of enantiomeric homochiral dimeric assemblies are formed. In the presence of xenon, the assembly diversity was pushed further, and an additional pair of enantiomeric heterochiral assemblies is induced. The diverse assembly comes from the macrocycle component adopting a folded, dissymmetric chiral conformation and undergoing spontaneous symmetry breaking upon cross-buckling together. The formed capsular assemblies possess a sealed, adaptive cavity for accommodating xenon. The cumulative xenon binding constant with the induced heterochiral capsule is about two times higher than the prior one assembled from racemic counterparts. The xenon-induced heterochiral capsule formation with the mesomeric macrocycle again demonstrates that xenon can find its own preferred host from a dynamic self-assembly system and likes to be accommodated by a more spherical van der Waals surrounding.

Inherently Chiral 6,7-Diphenyldibenzo[ e,g ][1,4]diazocine: Enantioselective Synthesis and Application as a Ligand Platform

Inherently Chiral 6,7-Diphenyldibenzo[ <i>e,g</i> ][1,4]diazocine: Enantioselective Synthesis and Application as a Ligand Platform

A “nucleophilic” iodine in a halogen-bonded iodonium complex manifests an unprecedented I+···Ag+ interaction

Summary When an electron is removed from a halogen atom, it forms a halenium ion X+ (X = I, Br, Cl). In halogen bonding (XB), X+ is considered as a strong XB donor, and when interacting with two XB acceptors (e.g., pyridine), it forms a halonium XB complex with a [N–I–N] three-center-four-electron bond with the two XB acceptors. An unprecedented I+···Ag+ interaction occurs between a [L1–I–L1]+ halogen-bonded complex and a [L2–Ag–L2]+ complex in which the iodonium ion acts like a nucleophile and donates electrons to the silver(I) cation. The X-ray diffraction analysis reveals a short contact [3.4608(3) A] between the I+ and Ag+ cations, and ITC measurements give a ΔG of −6.321 kcal/mol and Ka∼37,000 M−1 for the 1:1 complex. The DFT computational study on the nature of the I+···Ag+ interaction indicates that the I+ is nucleophilic in character, manifesting an unusual and strongly attractive interaction between the I+ and Ag+ cations.

Recent Advances in Halogen Bonded Assemblies with Resorcin[4]arenes.

Resorcinarenes are cavity-containing compounds when in the crown conformation, from the calixarene family of concave compounds. These easy to synthesize macrocycles can be decorated at the upper rim through the eight hydroxyl groups and/or the 2-position of the aromatic ring. They are good synthons in supramolecular chemistry leading to appealing assemblies such as open-inclusion complexes, capsules and tubes through multiple weak interactions with various guests. Halogen bonding (XB) is a highly directional non-covalent interaction by an electron-deficient halogen atom as a donor that interacts with a Lewis base, the XB acceptor. This tutorial review provides an overview of recent advances in halogen-bonded assemblies based on resorcinarenes and their derivatives, specifically focusing on discrete and capsular assemblies.

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

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

Structural basis for Fullerene geometry in a human endogenous retrovirus capsid

The HML2 (HERV-K) group constitutes the most recently acquired family of human endogenous retroviruses, with many proviruses less than one million years old. Many maintain intact open reading frames and provirus expression together with HML2 particle formation are observed in early stage human embryo development and are associated with pluripotency as well as inflammatory disease, cancers and HIV-1 infection. Here, we reconstruct the core structural protein (CA) of an HML2 retrovirus, assemble particles in vitro and employ single particle cryogenic electron microscopy (cryo-EM) to determine structures of four classes of CA Fullerene shell assemblies. These icosahedral and capsular assemblies reveal at high-resolution the molecular interactions that allow CA to form both pentamers and hexamers and show how invariant pentamers and structurally plastic hexamers associate to form the unique polyhedral structures found in retroviral cores.

Programmable Hierarchical Construction of Mixed/Multilayered Polysaccharide Nanocapsules through Simultaneous/Sequential Nanoprecipitation Steps.

We report here on a one-pot construction of oil-filled hierarchical capsular assemblies using the nanoprecipitation technique. Relying on multicomponent phase diagrams, we show that simultaneous and/or sequential nanoprecipitations involving polymer combinations can be precisely programmed to design a new class of mixed/multilayered multicomponent nanocapsules, with a precise control of the dimensions, shell thickness/composition, and spatial distribution of the building blocks. The simplicity and tunability of this approach are exemplified here with a library of neutral and ionic polysaccharides giving access to a range of functional multilayered nanocarriers of interest for biomedical applications.

Fixation of atmospheric CO2 and recognition of anions/hydrated anions: Differential binding mode in protonated vs. neutral tripodal urea/thiourea receptors

Tris-(2-aminoethyl) amine (Tren) based tripodal thiourea (L1 and L2) and urea (L3) receptors are reported. L1 efficiently fix atmospheric CO2 as CO32– in presence of the hydroxide ion. Both L1 and L2 encapsulate SO42− anion by forming 2:1 host–guest capsular assemblies through hydrogen-bond activated proton transfer. Both L1 and L2 show strong anion binding in their neutral form through strong non-covalent interactions. On contrary, tris-urea ligand L3 recognizes SiF62− and Br− trapped cyclic/acyclic anion-water network assemblies outside the protonated receptor cavities in presence of corresponding inorganic acids HF and HBr respectively.

Synthesis and Dimerization Studies of a Lipophilic Photoresponsive Aryl-Extended Tetraurea-Calix[4]pyrrole.

We describe the syntheses of the lipophilic aryl-extended α,α,α,α-tetraurea-phenyl-calix[4]pyrrole 1, featuring four appended azo-phenyl groups with two tert-butoxy carbonyl meta-substituents and its photo-inactive counterpart 2. In CD2 Cl2 solutions, both tetraurea-calix[4]pyrroles self-assemble into dimeric capsules by encapsulating one molecule of a suitable bis-N-oxide or two molecules of a mono-N-oxide. The dimeric capsules are mainly stabilized by a cyclic array of sixteen hydrogen bonds established between the eight unidirectionally oriented urea groups. Photoirradiation experiments demonstrated the trans-to-cis isomerization of the azo-phenyl groups and the formation of a plethora of stereo isomeric cis-azo-enriched capsular assemblies. The highly cis-azo enriched capsular assemblies seem to show a reduced stability and their involvement in equilibria with non-capsular counterparts that also bind the N-oxides. The thermally induced cis-to-trans interconversion processes demonstrated the reversibility of the photoisomerization and the photostability of most binding partners. An equimolar mixture of the two tetraureas produced two homodimeric capsules and the heterodimeric counterpart in a ratio close to statistical distribution.

Neutral host–guest capsular associations by a homologous halophenyl-substituted organic tris-urea receptor series: solid and solution state studies

Efficient and regular construction of unimolecular fluoride-encapsulated complexes and oxyanion-bound dimeric capsular assemblies by three electron-deficient neutral tris-urea receptors is observed corroborated by solution-state analysis.

Resolving the Magnetic Asymmetry of the Inner Space in Self-assembled Dimeric Capsules Based on Tetraurea-calix[4]pyrrole Components.

The encapsulation of N,N, N',N'-tetramethyl-1,5-pentanediamine-N,N'-dioxide 2 in a non-chiral capsular assembly formed by dimerization of tetraurea-calix[4]pyrrole 1a produced the observation of the N-methyl groups of the encapsulated guest as two separated singlets resonating highly upfield in the (1)H NMR spectrum. In order to clarify the origin of the observed signal splitting we assembled and studied a series of structurally related dimeric capsules. We used the tetraurea-calix[4]pyrrole 1a , the enantiomerically pure tetraurea-calix[4] pyrrole R-1b and the tetraurea-bisloop calix[4]pyrrole 1c as components of the produced assemblies. The (1)H NMR spectra of the assembled encapsulation complexes with bis-N-oxide 2 evidenced diverse splitting patterns of the N-methyl groups. In addition, 2D EXSY/ROESY NMR experiments revealed the existence of chemical exchange processes involving the separated methyl signals of the encapsulated guest. The capsular assemblies were mainly stabilized by a belt of eight head-to-tail hydrogen-bonded urea groups. The interconversion between the two senses of rotation of the unidirectionally oriented urea groups was slow on the (1)H NMR timescale. These characteristics determined the appearance of a new asymmetry element (supramolecular conformational chirality) in the assemblies that accounted for some of the magnetic asymmetries featured by the capsule's inner space. The racemization of the supramolecular chirality element was fast on the EXSY timescale and produced the chemical exchange processes detected for the encapsulation complexes.

Encapsulation of secondary and tertiary ammonium salts by resorcinarenes and pyrogallarenes: the effect of size and charge concentration

Multiple weak interactions are manifested in the complexation of different categories of secondary and tertiary alkyl ammonium salts with resorcinarenes and pyrogallarene leading to open inclusion and dimeric capsular assemblies with varying binding affinities, and analyzed in solid, liquid and gas phases.

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

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

Aromatic N-oxide templates open inclusion and dimeric capsular assemblies with methylresorcinarene

Multiple weak interactions are manifested in the complexation of pyridine N-oxide and quinoline N-oxide by methylresorcinarene resulting to 1 : 1 assemblies in solution, with 2 : 3 and 2 : 2 host–guest dimeric capsules respectively in the solid state.

Aerial CO2 Trapped as CO32– Ions in a Dimeric Capsule That Efficiently Extracts Chromate, Sulfate, and Thiosulfate from Water by Anion‐Exchange Metathesis

AbstractThe tris(2‐aminoethyl)amine‐based (tren‐based) 3‐cyanophenyl‐substituted tripodal urea L1, one of the familiar urea‐based anion receptors, has shown encapsulation of CO32– ions as the carbonate capsule [(L1)2·(CO3)·(TBA)2] (1, TBA = tetrabutylammonium) by the fixation of aerial carbon dioxide from basic dimethyl sulfoxide (DMSO) solution. Single‐crystal X‐ray structural analysis confirmed the encapsulation of CO32– ions in the cavity of a dimeric capsular assembly of L1 (9.62 Å) through the formation of twelve strong N–H···O hydrogen‐bonding interactions. The excellent CHCl3 and CH2Cl2 solubility of 1 has been exploited for the liquid–liquid (L–L) extraction of CrO42–, SO42–, and S2O32– ions from water by anion‐exchange metathesis. The extraction of these anions from water was unambiguously confirmed by 1H NMR spectroscopy, IR spectroscopy, powder XRD (PXRD), and single‐crystal X‐ray diffraction analysis. The 1H NMR spectroscopic analysis of the bulk extracts supports the formation of 2:1 (host–guest) complexes. For the CrO42– ion, the 53Cr NMR spectrum of the bulk extract shows a characteristic peak at δ = –99.98 ppm. The complexes of CrO42–, S2O32–, and SO42– ions with L1 (i.e., 2–4, respectively) were obtained from crystallization of the bulk extracts and show anion‐assisted dimeric capsular assemblies of L1 through multiple N–H···X (X = O, S) interactions. The dimensions of the anion‐encapsulated capsular assemblies are quite similar to that of the carbonate capsule and are 9.70 Å for [(L1)2·(CrO4)·(TBA)2] (2), 9.61 Å for [(L1)2·(S2O3)·(TBA)2] (3), and 9.71 Å for [(L1)2·(SO4)·(TBA)2] (4). Quantification by weighing the bulk extract shows that 1 can separately extract ca. 90 % of the above three anions from water by anion‐exchange metathesis. The quantitative estimations of the extractions of SO42– and CrO42– ions were further verified by gravimetric analysis by BaSO4 and BaCrO4 precipitation techniques, respectively. The extraction of SO42– ions from water was also demonstrated under alkaline conditions (pH 12.5) and in the presence of an excess of nitrate ions. Further, the quantification of CrO42– extraction was established by solution‐state UV/Vis studies.