A metal-peptide capsule by multiple ring threading

Self-Assembly of an [M8 L24 ]16+ Intertwined Cube and a Giant [M12 L16 ]24+ Orthobicupola

Through coordination-driven self-assembly, aesthetically captivating structures can be formed by tuning the length or flexibility of various components. The self-assembly of an elongated rigid terphenyl-based tetra-pyridyl ligand (L1) with a cis-Pd(II) acceptor produces an [M12 L16 ]24+ triangular orthobicupola structure (1). When flexibility is introduced into the ligand by the incorporation of a -CH2 - group between the dipyridylamine and terphenyl rings in the ligand (L2), anunique [M8 L24 ]16+ water-soluble 'intertwined cubic structure' (2) results. The inherent flexibility of ligand L2 might be the key factor behind the formation of the thermodynamically stable and 'intertwined cubic structure' in this scenario. This research showcases the ability to design and fabricate novel, topologically distinctive molecular structures by a straightforward and efficient approach.

Unravelling the Roles of Solvophobic Effects and π⋅⋅⋅π Stacking Interactions in the Formation of [2]Catenanes Featuring Di-(N-Heterocyclic Carbene) Building Blocks

A series of [2]catenanes has been prepared from di-NHC building blocks by utilizing solvophobic effects and/or π⋅⋅⋅π stacking interactions. The dinickel naphthobiscarbene complex syn-[1] and the kinked biphenyl-bridged bipyridyl ligand L2 yield the [2]catenane [2-IL](OTf)4 by self-assembly. Solvophobic effects are pivotal for the formation of the interlocked species. Substitution of the biphenyl-linker in L2 for a pyromellitic diimide group gave ligand L3 , which yielded in combination with syn-[1] the [2]catenane [3-IL](OTf)4 . This assembly exhibits enhanced stability in diluted solution, aided by additional π⋅⋅⋅π stacking interactions. The π⋅⋅⋅π stacking was augmented by the introduction of a pyrene bridge between two NHC donors in ligand L4 . Di-NHC precursor H2 -L4 (PF6 )2 reacts with Ag2 O to give the [Ag2 L4 2 ]2 [2]catenane [4-IL](PF6 )4 , which shows strong π⋅⋅⋅π stacking interactions between the pyrene groups. This assembly was readily converted into the [Au2 L4 2 ]2 gold species [5-IL](PF6 )4 , which exhibits exceptional stability based on the strong π⋅⋅⋅π stacking interactions and the enhanced stability of the Au-CNHC bonds.

Biasing the Formation of Solution-Unstable Intermediates in Coordination Self-Assembly by Mechanochemistry

Due to the reversible nature of coordination bonds and solvation effect, coordination self-assembly pathways are often difficult to elucidate experimentally in solution, as intermediates and products are in constant equilibration. The present study shows that some of these transient and high-energy self-assembly intermediates can be accessed by means of ball-milling approaches. Among them, highly aqueous-unstable Pd3 L11 and Pd6 L14 open-cage intermediates of the framed Fujita Pd6 L14 cage and Pd2 L22 , Pd3 L21 and Pd4 L22 intermediates of Mukherjee Pd6 L24 capsule are successfully trapped in solid-state, where Pd=tmedaPd2+ , L1=2,4,6-tris(4-pyridyl)-1,3,5-triazine and L2=1,3,5-tris(1-imidazolyl)benzene). Their structures are assigned by a combination of solution-based characterization tools such as standard NMR spectroscopy, DOSY NMR, ESI-MS and X-ray diffraction. Collectively, these results highlight the opportunity of using mechanochemistry to access unique chemical space with vastly different reactivity compared to conventional solution-based supramolecular self-assembly reactions.

Redox-Controlled Self-Assembly of Vanadium-Seamed Hexameric Pyrogallol[4]Arene Nanocapsules

Here we report the controlled self-assembly of vanadium-seamed metal-organic nanocapsules with specific metal oxidation state distributions. Three supramolecular assemblies composed of the same numbers of components including 24 metal centers and six pyrogallol[4]arene ligands were constructed: a VIII24L6 capsule, a mixed-valence VIII18VIV6L6 capsule, and a VIV24L6 capsule. Crystallographic studies of the new capsules reveal their remarkable structural complexity and geometries, while marked differences in metal oxidation state distribution greatly affect the photoelectric conversion properties of these assemblies. This work therefore represents a significant step forward in the construction of intricate metal-organic architectures with tailored structure and functionality.

Kinetic trapping of 2,4,6-tris(4-pyridyl)benzene and ZnI2 into M12L8 poly-[n]-catenanes using solution and solid-state processes

Here, we show that in a supramolecular system with more than 20 building blocks forming large icosahedral M₁₂L₈ metal-organic cages (MOCs), using the instant synthesis method, it is possible to kinetically trap and control the formation of interlocking M₁₂L₈ nanocages, giving rare M₁₂L₈ TPB-ZnI₂ poly-[n]-catenane. The catenanes are obtained in a one-pot reaction, selectively as amorphous (a1) or crystalline states, as demonstrated by powder X-ray diffraction (powder XRD), thermogravimetric (TG) analysis and ¹H NMR. The 300 K M₁₂L₈ poly-[n]-catenane single crystal X-ray diffraction (SC-XRD) structure including nitrobenzene (1) indicates strong guest binding with the large M₁₂L₈ cage (i.e., internal volume ca. 2600 ų), allowing its structural resolution. Conversely, slow self-assembly (5 days) leads to a mixture of the M₁₂L₈ poly-[n]-catenane and a new TPB-ZnI₂ (2) coordination polymer (i.e., thermodynamic product), as revealed by SC-XRD. The neat grinding solid-state synthesis also yields amorphous M₁₂L₈ poly-[n]-catenane (a1'), but not coordination polymers, selectively in 15 min. The dynamic behavior of the M₁₂L₈ poly-[n]-catenanes demonstrated by the amorphous-to-crystalline transformation upon the uptake of ortho-, meta- and para-xylenes shows the potential of M₁₂L₈ poly-[n]-catenanes as functional materials in molecular separation. Finally, combining SC-XRD of 1 and DFT calculations specific for the solid-state, the role of the guests in the stability of the 1D chains of M₁₂L₈ nanocages is reported. Energy interactions such as interaction energies (E), lattice energies (E*), host-guest energies (E_host-guest) and guest-guest energies (E_guest-guest) were analysed considering the X-ray structure with and without the nitrobenzene guest. Not only the synthetic control achieved in the synthesis of the M₁₂L₈ MOCs but also their dynamic behavior either in the crystalline or amorphous phase are sufficient to raise scientific interest in areas ranging from fundamental to applied sides of chemistry and material sciences.

Crystalline Metal-Peptide Networks: Structures, Applications, and Future Outlook

Metal-peptide networks (MPNs), which are assembled from short peptides and metal ions, are considered one of the most fascinating metal-organic coordinated architectures because of their unique and complicated structures. Although MPNs have considerable potential for development into versatile materials, they have not been developed for practical applications because of several underlying limitations, such as designability, stability, and modifiability. In this review, we summarise several important milestones in the development of crystalline MPNs and thoroughly analyse their structural features, such as peptide sequence designs, coordination geometries, cross-linking types, and network topologies. In addition, potential applications such as gas adsorption, guest encapsulation, and chiral recognition are introduced. We believe that this review is a useful survey that can provide insights into the development of new MPNs with more sophisticated structures and novel functions.

Bioinorganic supramolecular coordination complexes and their biomedical applications

The field of Bioinorganic Supramolecular Chemistry is an emerging research area including metal-based supramolecules resulting from coordination-driven self-assembly (CDSA), whereby metal ions and organic ligands can be easily linked by metal-ligand bonds via Lewis' acid/base interactions. The focus of this 'In a Nutshell' review will be on the family of supramolecular coordination complexes, discrete entities formed by CDSA, which have recently captured widespread attention as a new class of versatile multifunctional materials with broad biological applications including molecular recognition, biosensing, therapy, imaging and drug delivery. Herein, we provide a summary of the state-of-the-art use of these systems in biomedicine, with some selected representative examples, as well as our visions of the challenges and possible directions in the field.

Synthetic approaches to metal-coordination-directed macrocyclic complexes

Metal-coordination-directed macrocyclic complexes, in which macrocyclic architectures are formed by metal-ligand coordination interactions, have emerged as attractive supramolecular scaffolds for the creation of materials for applications in biosensing and therapeutics. Despite recent progress, uncontrolled multicyclic cages and linear oligomers/polymers is the most likely outcome from metal-ligands assembly, representing a challenge to current synthetic methods. Herein we outlined the state-of-art synthetic approaches to the metal-coordination-directed macrocyclic complexes by using foldable ligands or through assembly of amphiphilic ligands. This mini-review offers a guideline for the efficient preparation of metal-coordination-directed macrocyclic complexes with predictable and controllable structures, which may find applications in many biology-related areas.

Directing the Self-Assembly of Aromatic Foldamer Helices using Acridine Appendages and Metal Coordination

Folded molecules provide complex interaction interfaces amenable to sophisticated self-assembly motifs. Because of their high conformational stability, aromatic foldamers constitute suitable candidates for the rational elaboration of self-assembled architectures. Several multiturn helical aromatic oligoamides have been synthesized that possess arrays of acridine appendages pointing in one or two directions. The acridine units were shown to direct self-assembly in the solid state via aromatic stacking leading to recurrent helix-helix association patterns under the form of discrete dimers or extended arrays. In the presence of Pd(II), metal coordination of the acridine units overwhelms other forces and generates new metal-mediated multihelical self-assemblies, including macrocycles. These observations demonstrate simple access to different types of foldamer-containing architectures, ranging from discrete objects to 1D and, by extension, 2D and 3D arrays.

On the Classification of Polyhedral Links

Knots and links are ubiquitous in chemical systems. Their structure can be responsible for a variety of physical and chemical properties, making them very important in materials development. In this article, we analyze the topological structures of interlocking molecules composed of metal-peptide rings using the concept of polyhedral links. To that end, we discuss the topological classification of alternating polyhedral links.

A Peptide Nanocage Constructed by Self-Assembly of Oligoproline Conjugates

Cage-like supramolecular assemblies called molecular cages, which possess attractive functions, have been prepared. Although biomolecule-based nanocages are required for biological/medical applications such as drug delivery systems, the majority of nanocages are constructed using aromatic compounds with lower biocompatibility and biodegradability. In this study, the construction of a peptide nanocage consisting of an oligoproline conjugate is demonstrated. The conjugate was easy to prepare and had high biocompatibility. The oligoproline moiety of the conjugate had a rigid, rod-like structure suitable for the backbone of the supramolecular nanocage. The conjugates self-assembled to form peptide nanocages with a huge inner cavity.

Experimental X-ray and DFT Structural Analyses of M12L8 Poly-[n]-catenanes Using exo-Tridentate Ligands

Despite their potential applications in host-guest chemistry, there are only five reported structures of poly-[n]-catenanes self-assembled by elusive M₁₂L₈ icosahedral nanocages. This small number of structures of M₁₂L₈ poly-[n]-catenanes is because self-assembly of large metal-organic cages (MOCs) with large windows allowing catenation by means of mechanical bonds is very challenging. Structural reports of M₁₂L₈ poly-[n]-catenanes are needed to increase our knowledge about the self-assembly and genesis of such materials. Poly-[n]-catenane (1·p-CT) self-assembly of interlocked M₁₂L₈ icosahedral cages (M = Zn(II) and L = 2,4,6-tris-(4-pyridyl)benzene (TPB)) including a new aromatic guest (p-chlorotoluene (p-CT)) is reported by single-crystal XRD. Despite the huge internal M₁₂L₈ voids (> 2500 ų), p-CT is ordered, allowing a clear visualization of the relative host-guest positions. DFT calculations have been used to compute the electrostatic potential of the TPB ligand, and various aromatic guests (i.e., o-dichlorobenzene (o-DCB), p-chloroanisole (p-CA), and nitrobenzene (NBz)) included (ordered) within the M₁₂L₈ cages were determined by single-crystal XRD. The computed maps of electrostatic potential (MEPs) allow for the rationalization of the guest's inclusion seen in the 3D X-ray structures. Although more crystallographic X-ray structures and DFT analysis are needed to gain insights of guest inclusion in the large voids of M₁₂L₈ poly-[n]-catenanes, the reported combined experimental/DFT structural analyses approach can be exploited to use isostructural M₁₂L₈ poly-[n]-catenanes as hosts for molecular separation and could find applications in the crystalline sponge method developed by Fujita and co-workers. We also demonstrate, exploiting the instant synthesis method, in solution (i.e., o-DCB), and in the solid-state by neat grinding (i.e., without solvent), that the isostructural M₁₂L₈ poly-[n]-catenane self-assembled with 2,4,6-tris-(4-pyridyl)pyridine (TPP) ligand and ZnX₂ (where X = Cl, Br, and I) can be kinetically synthesized as crystalline (yields ≈ 60%) and amorphous phases (yields ≈ 70%) in short time and large quantities. Despite the change in the aromatic nature at the center of the rigid exo-tridentate pyridine-based ligand (TPP vs TPB), the kinetic control gives the poly-[n]-catenanes selectively. The dynamic behavior of the TPP amorphous phases upon the uptake of aromatic guest molecules can be used in molecular separation applications like benzene derivatives.

Highly selective synthesis and near-infrared photothermal conversion of metalla-Borromean ring and [2]catenane assemblies

Although the selective synthesis of complicated supramolecular architectures has seen significant progress in recent years, the exploration of the properties of these complexes remains a fascinating challenge. Herein, a series of new supramolecular topologies, metalla[2]catenanes and Borromean ring assemblies, were constructed based on appropriate Cp*Rh building blocks and two rigid alkynyl pyridine ligands (L1, L2) via coordination-driven self-assembly. Interestingly, minor differences between the two rigid alkynyl pyridine ligands with/without organic substituents led to products with dramatically different topologies. Careful structural analysis showed that π–π stacking interactions play a crucial role in stabilizing these [2]catenanes and Borromean ring assemblies, while also promoting nonradiative transitions and triggering photothermal conversion in both the solution and the solid states. These results were showcased through comparative studies of the NIR photothermal conversion efficiencies of the Borromean ring assemblies, [2]catenanes and metallarectangles, which exhibited a wide range of photothermal conversion efficiencies (12.64–72.21%). The influence of the different Cp*Rh building blocks on the NIR photothermal conversion efficiencies of their assemblies was investigated. Good photothermal conversion properties of the assemblies were also found in the solid state. This study provides a new strategy to construct valuable half-sandwich-based NIR photothermal conversion materials while also providing promising candidates for the further development of materials science.

The selective synthesis of three kinds of supermolecular topologies, molecular Borromean ring, [2]catenane and metallarectangle based on two alkynyl ligands is presented. Remarkably, the NIR photothermal conversion efficiency was found to improve as the π–π stacking increases.

Incorporation of a Phosphino(pyridine) Subcomponent Enables the Formation of Cages with Homobimetallic and Heterobimetallic Vertices

Biological systems employ multimetallic assemblies to achieve a range of functions. Here we demonstrate the preparation of metal–organic cages that contain either homobimetallic or heterobimetallic vertices. These vertices are constructed using 2-formyl-6-diphenylphosphinopyridine, which forms ligands that readily bridge between a pair of metal centers, thus enforcing the formation of bimetallic coordination motifs. Two pseudo-octahedral homometallic M^I₁₂L₄ cages (M^I = Cu^I or Ag^I) were prepared, with a head-to-head configuration of their vertices confirmed by X-ray crystallography and multinuclear NMR for Ag^I. The phosphino-pyridine subcomponent also enabled the formation of a class of octanuclear Cd^II₄Cu^I₄L₄ tetrahedral cages, representing an initial example of self-assembled cages containing well-defined heterobimetallic vertices.

Distinctive features and challenges in catenane chemistry

From being an aesthetic molecular object to a building block for the construction of molecular machines, catenanes and related mechanically interlocked molecules (MIMs) continue to attract immense interest in many research areas. Catenane chemistry is closely tied to that of rotaxanes and knots, and involves concepts like mechanical bonds, chemical topology and co-conformation that are unique to these molecules. Yet, because of their different topological structures and mechanical bond properties, there are some fundamental differences between the chemistry of catenanes and that of rotaxanes and knots although the boundary is sometimes blurred. Clearly distinguishing these differences, in aspects of bonding, structure, synthesis and properties, between catenanes and other MIMs is therefore of fundamental importance to understand their chemistry and explore the new opportunities from mechanical bonds.

Syntheses of three-dimensional catenanes under kinetic control

SignificanceDuring the past decades, the development of efficient methodologies for the creation of mechanically interlocked molecules (MIMs), such as catenanes and rotaxanes, has not only laid the foundation for the design and syntheses of artificial molecular machines (AMMs) but also opened up new research opportunities in multiple disciplines, ranging from contemporary chemistry to materials science. In this study, we describe a suitane-based strategy for the construction of three-dimensional (3D) catenanes, a subset of MIMs that are far from easy to make. Together with synthetic methodologies based on the metal coordination and dynamic covalent chemistry, this approach brings us one step closer to realizing routine syntheses of 3D catenanes.

Structural Chemistry of Giant Metal Based Supramolecules

The review presents a bird-eye view on the state of research in the field of giant nonbiological discrete metal complexes and ions of nanometer size, which are structurally characterized by means of single-crystal X-ray diffraction, using the crystal structure as a common key feature. The discussion is focused on the main structural features of the metal clusters, the clusters containing compact metal oxide/hydroxide/chalcogenide core, ligand-based metal-organic cages, and supramolecules as well as on the aspects related to the packing of the molecules or ions in the crystal and the methodological aspects of the single-crystal neutron and X-ray diffraction of these compounds.

Metal-Peptide Nonafoil Knots and Decafoil Supercoils

Despite the frequent occurrence of knotted frameworks in protein structures, the latent potential of peptide strands to form entangled structures is rarely discussed in peptide chemistry. Here we report the construction of highly entangled molecular topologies from Ag(I) ions and tripeptide ligands. The efficient entanglement of metal-peptide strands and the wide scope for design of the amino acid side chains in these ligands enabled the construction of metal-peptide 9₁ torus knots and 10₁² torus links. Moreover, steric control of the peptide side chain induced ring opening and twisting of the torus framework, which resulted in an infinite toroidal supercoil nanostructure.

Conformational Adaptation of β-Peptide Foldamers for the Formation of Metal-Peptide Frameworks

Metal-coordinated frameworks derived from small peptidic ligands have received much attention thanks to peptides' vast structural and functional diversity. Various peptides with partial conformational preferences have been used to build metal-peptide frameworks, however, the use of conformationally constrained β-peptide foldamers has not been explored yet. Herein we report the first metal-coordination-mediated assembly of β-peptide foldamers with 12-helical folding propensity. The coordination of Ag⁺ to the terminal pyridyl moieties afforded a set of metal-peptide frameworks with unique entangled topologies. Interestingly, formation of the network structures was accompanied by notable conformational distortions of the foldamer ligands. As the first demonstration of new metal-peptide frameworks built from modular β-peptide foldamers, we anticipate that this work will be an important benchmark for further structural evolution and mechanistic investigation.

Dynamic covalent self-assembly of mechanically interlocked molecules solely made from peptides

Mechanically interlocked molecules (MIMs), such as rotaxanes and catenanes, have captured the attention of chemists both from a synthetic perspective and because of their role as simple prototypes of molecular machines. Although examples exist in nature, most synthetic MIMs are made from artificial building blocks and assembled in organic solvents. Synthesis of MIMs from natural biomolecules remains highly challenging. Here we report on a synthesis strategy for interlocked molecules solely made from peptides—mechanically interlocked peptides (MIPs). Fully peptidic, cysteine-decorated building blocks were self-assembled in water to generate disulfide-bonded dynamic combinatorial libraries consisting of multiple different rotaxanes, catenanes and daisy chains as well as more exotic structures. Detailed NMR spectroscopy and mass spectrometry characterization of a [2]catenane comprised of two peptide macrocycles revealed that this structure has rich conformational dynamics reminiscent of protein folding. Thus, MIPs can serve as a bridge between fully synthetic MIMs and those found in nature.

Constructing multicomponent cooperative functional systems using metal complexes of short flexible peptides

The construction of cooperative systems comprising several units is an essential challenge for artificial systems toward the development of sophisticated functions comparable to those found in biological systems. Flexible frameworks possessing various functional groups that can form weak intra/intermolecular interactions similar to those observed in biological systems have promising design features for artificial systems used to control cooperative systems. However, it is difficult to construct multiple component systems >1 nm using these flexible units by controlling the arrangement of functional units, beginning with the precise control of the cooperative switching of multiple units. In general, it is difficult for oligopeptides to form stable conformations by themselves, although they have designability and structural features suitable for the development of cooperative systems. Increasing the number of coordination bonds in peptides, which are stronger than hydrogen bonds, can be used to control the assembled peptide structures and stabilize their structures owing to the variety of coordination bonds and selective binding affinity. Thus, metal complexes of artificial short peptides have great potential for the development of multicomponent cooperative systems. Based on this concept, we have developed a series of novel metal complexes of flexible peptides and have achieved, to date, cooperative systems, the formation of giant structures, and precise control over the functional units that are the essential bases for designable multifunctional systems that can be regarded as artificial enzymes. In this feature article, we summarize these results and discuss the principal/essential design of artificial systems.

Constructing π-Stacked Supramolecular Cage Based Hierarchical Self-Assemblies via π···π Stacking and Hydrogen Bonding

Constructing supramolecular cages with multiple subunits via weak intermolecular interactions is a long-standing challenge in chemistry. So far, π-stacked supramolecular cages still remain unexplored. Here, we report a series of π-stacked cage based hierarchical self-assemblies. The π-stacked cage (π-MX-cage) is assembled from 16 [MXL]⁺ ions (M = Mn²⁺, Co²⁺; X = Br^-, SCN^-, Cl^-; and L = tris(2-benzimidazolylmethyl)amine) via 18 intermolecular π-stacking interactions. The tetrahedral cage, consisting of four [MXL]⁺ ions as the vertexes and six pairs of [MXL]⁺ ions as the edges, features 48 exterior N-H hydrogen bond donors for hydrogen bond formation with guest molecules. By variation of the M²⁺/X^- pair, the π-MX-cage demonstrates unique versatility for incorporating a wide variety of species via different hydrogen-bonding modes during the assembly of hierarchical superstructures. In specific, the π-MnBr-cages encapsulate acetonitrile (CH₃CN) or cis-1,3,5-cyclohexanetricarbonitrile (cis-HTN) molecules in the central voids, while a core-shell tetrahedral inorganic cluster [Mn(H₂O)₆]@([Mn(H₂O)₄]₄[Br₄^2-]₆) (Mn@Mn₄-cage) is captured within the interstitial regions between cages. The π-CoSCN-cages are capable of stabilizing reactive sulfur-containing species, such as S₂O₄^2-, S₂O₆^2-, and HSO₃^- ions, in the hierarchical superstructure. Finally, H₂PO₄^- ions are incorporated between π-CoCl-cages, resulting in an inorganic mesoporous framework. These results provide insights into further exploring the chemistry and hierarchical assembly of supramolecular cages based on π-π stacking intermolecular interactions.

Selective Anion Binding Drives the Formation of AgI8L6 and AgI12L6 Six-Stranded Helicates

Here we describe the formation of an unexpected and unique family of hollow six-stranded helicates. The formation of these structures depends on the coordinative flexibility of silver and the 2-formyl-1,8-napthyridine subcomponent. Crystal structures show that these assemblies are held together by Ag4I, Ag4Br, or Ag6(SO4)2 clusters, where the templating anion plays an integral structure-defining role. Prior to the addition of the anionic template, no six-stranded helicate was observed to form, with the system instead consisting of a dynamic mixture of triple helicate and tetrahedron. Six-stranded helicate formation was highly sensitive to the structure of the ligand, with minor modifications inhibiting its formation. This work provides an unusual example of mutual stabilization between metal clusters and a self-assembled metal-organic cage. The selective preparation of this anisotropic host demonstrates new modes of guiding selective self-assembly using silver(I), whose many stable coordination geometries render design difficult.

Emergent Self-Assembly of a Multicomponent Capsule via Iodine Capture

Described here is a three-component self-assembly system that displays emergent behavior that differs from that of its constituents. The system comprises an all-hydrocarbon octaaryl macrocycle cyclo[8](1,3-(4,6-dimethyl)benzene (D_4d-CDMB-8), corannulene (Cora), and I₂. No appreciable interaction is seen between any pair of these three-components, either in cyclohexane or under various crystallization conditions. On the other hand, when all three-components are mixed in cyclohexane and allowed to undergo crystallization, a supramolecular iodine-containing capsule, ((D_4d-CDMB-8)₃⊃(Cora)₂)⊃I₂, is obtained. This all-hydrocarbon capsule consists of three D_4d-CDMB-8 and two Cora subunits and contains a centrally bound I₂ molecule as inferred from single-crystal and powder X-ray diffraction studies as well as solid-state ¹³C NMR and Raman spectroscopy. These analyses were complemented by solution-phase ¹H NMR and UV-vis spectroscopic studies. No evidence of I₂ escape from the capsule is seen, even at high temperatures (e.g., up to 418 K). The bound I₂ is likewise protected from reaction with alkali or standard reductants in aqueous solution (e.g., saturated NaOH(aq) or aqueous Na₂S₂O₃). It was also found that a mixed powder containing D_4d-CDMB-8 and Cora in a 3:2 molar ratio could capture saturated I₂ vapor or iodine from aqueous sources (e.g., 1.0 mM I₂ in NaCl (35 wt %) or I₂ + NaI(aq) (1.0 mM each)). The present system displays structural and functional features that go beyond what would be expected on the basis of a simple sum-of-the-components analysis. As such, it illustrates a new approach to creating self-assembled ensembles with emergent features.

X-ray Crystallographic Observation of Chiral Transformations within a Metal-Peptide Pore

Porous metal complexes enable single-crystal X-ray crystallographic observation of included guests or reaction intermediates through simple soaking with the guests/substrates. Previous studies on this technique have often encountered difficulties in the observation of chiral structures because the host frameworks had no chirality. We synthesized a new metal-peptide porous complex through a folding-and-assembly strategy and utilized the chiral pore for trapping chiral guests. Chiral alcohols and ketones were successfully included within the pore. Crystallographic analyses clearly revealed not only their chemical structures but also chiral transformation events within the pore such as fixed conformations or an unstable hemiacetal formation.

Isogonal weavings on the sphere: knots, links, polycatenanes

Mathematical knots and links are described as piecewise linear - straight, non-intersecting sticks meeting at corners. Isogonal structures have all corners related by symmetry (`vertex'-transitive). Corner- and stick-transitive structures are termed regular. No regular knots are found. Regular links are cubic or icosahedral and a complete account of these (36 in number) is given, including optimal (thickest-stick) embeddings. Stick 2-transitive isogonal structures are again cubic and icosahedral and also encompass the infinite family of torus knots and links. The major types of these structures are identified and reported with optimal embeddings. The relevance of this work to materials chemistry and biochemistry is noted.

Selective synthesis and structural transformation between a molecular ring-in-ring architecture and an abnormal trefoil knot

The synthesis of complicated supramolecular architectures and the study of their reversible structural transformations remains a fascinating challenge in the field of supramolecular chemistry. Herein, two types of novel coordination compounds, a non-intertwined ring-in-ring assembly and an abnormal trefoil knot were constructed from a strategically selected Cp*Rh building block and a semi-rigid N,N'-bis(4-pyridylmethyl)diphthalic diimide ligand via coordination-driven self-assembly. Remarkably, the reversible transformation between the abnormal trefoil knot and the ring-in-ring assembly or the corresponding tetranuclear macrocycle could be achieved by the synergistic effects of Ag+ ion coordination and alteration of the solvent. Single-crystal X-ray crystallographic data and NMR spectroscopic experiments support the structural assignments.

Coordination-Directed Construction of Molecular Links

Since the emergence of the concept of chemical topology, interlocked molecular assemblies have graduated from academic curiosities and poorly defined species to become synthetic realities. Coordination-directed synthesis provides powerful, diverse, and increasingly sophisticated protocols for accessing interlocked molecules. Originally, metal ions were employed solely as templates to gather and position building blocks in entwined or threaded arrangements. Recently, metal centers have increasingly featured within the backbones of the integral structural elements, which in turn use noncovalent interactions to self-assemble into intricate topologies. By outlining ingenious recent examples as well as seminal classic cases, this Review focuses on the role of metal-ligand paradigms in assembling molecular links. In addition, the ever-evolving approaches to efficient assembly, the structural features of the resulting architectures, and their prospects for the future are also presented.

An approach to generate DNA polyhedral links of one/two strands

Scientists can change programmed DNA strands to adjust edge length and vertex junction to control the 3D structures with precision space signatures. The number of strands plays an important role in sequence design, synthesis and constitutive property. However, the majority of DNA branched polyhedra comprise a number of single strands. Therefore, it is crucial to make the number of strands to be calculated as less as possible. DNA polyhedral links are regarded as ideal templates of DNA polyhedra. In this research, we introduce odd-half turn edges and pseudo-surrounded vertexes to build DNA polyhedral links and reduce the strands number of them to one or two. Compare to the known strategies, our strategy is well established to generate the DNA polyhedral links of one/two DNA strands easier and faster. All Platonic, pyramid and prism polyhedral links may provide candidates for DNA polyhedra synthesis.

A giant hybrid organic–inorganic octahedron from a narrow rim carboxylate calixarene

Here we discovered an unprecedented giant octahedral coordination compound bearing 16 Zn²⁺, 12 Na⁺, 8 O²⁻, 4 OH⁻, 13 H₂O and 6 L⁴⁻ ligands [L⁴⁻ = fully deprotonated tetra(carboxymethoxy)calix[4]arene].