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•Defined coordination cages (CCs) with metal-pyridine coordination bonds.•Defined metal-organic cages (MOCs) bearing tetracarboxylates paddlewheel complexes.•Meta-analyzed ...experimental information of 197 CCs and 83 MOCs. • Unveiled roles of ligand, metal ion, temperature and solvent for cage formation. • Discussed challenges and future perspectives of CCs and MOCs in unexplored areas.
Cage-like molecules, assembled by the coordination of multiple metal ions and organic links, are pushing new frontiers in science due to their design flexibility and the resulting diverse and unique chemical properties. This field has been advanced by two close but distinct chemistry communities. Consequently, the family of molecules referred to as coordination cages (CCs) constituted of metal-pyridine coordination bonds or metal–organic cages (MOCs) based on dinuclear tetracarboxylates paddlewheel complexes in each community had not been reviewed cross-sectionally, even though they are conceptually similar. This review article extracted and compared experimental information on a total of 197 CCs and 83 MOCs from 185 reports to identify their synthetic and structural signatures. We did not merely enumerate the reports we collected; we meta-analyzed the data extracted from the reports and highlighted both the similarities and dissimilarities between CCs and MOCs. As a result, we clarified the key parameters governing the synthetic conditions. Furthermore, we identified a new research direction by visualizing unexplored features and properties of CCs and MOCs. This review article provides a good tutorial both for researchers attempting to cross the boundary between CCs and MOCs and those who are new to the field.
One-to-one capture and confinement of a molecule within a finely designed synthetic scaffold is a highly topical field of research that aims to control the functions, properties, and stabilities of ...trapped molecules. In this account, a brief history of molecular encapsulation, for the design and synthesis of suitable molecular cages for large molecules, summarizes the daunting synthetic challenge associated with increasing molecular weight, and the attendant challenge to encapsulate macromolecules like proteins by synthetic hosts. Recent approaches toward the overall objective of large molecular encapsulation are discussed, and a personal account is given of the design and assembly of an advanced scaffolding system, which offers the promise of unprecedented progress toward this goal.
The self‐assembly of a cuboctahedral M12L24 complex is traced by time‐dependent NMR spectroscopy and mass spectrometry. The metastable intermediate structures that exist during the self‐assembly ...process are not a chaotic mixture of numerous species, but instead are geometrically restricted. Short‐lived M8L16 (D4d) and relatively long‐lived M9L18 (D3h) are fully characterized as major intermediates. Employing a ligand with a smaller bend angle (112°) allows these two species to be kinetically trapped and more clearly observed by NMR spectroscopy. X‐ray crystallography shows that M9L18 has the framework topology predicted by geometric discussion.
Geometrically dictated: Due to the geometrically restricted number of possible structures, the intermediates of self‐assembly are rather relatively ordered than a chaotic mixture of numerous species. Two prominent metastable intermediates, M8L16 and M9L18, are well characterized during the self‐assembly of an M12L24 cuboctahedral complex.
Thermodynamically controlled platinum(II) spherical complexes were synthesized via temporary labilization of inert Pt(II)–pyridine bonds by the addition of the strong hydrogen-bond donor ...2,2,2-trifluoroethanol (TFE), which weakens the pyridine–metal interaction. The platinum complex was stably trapped after removal of TFE and showed higher acid durability than its palladium counterpart.
Mesenchymal stem cells (MSCs) are multipotent stem cells that reside in various organs. They have the capacity to differentiate into various cell types, including cardiomyocytes, vascular endothelial ...cells, and vascular smooth muscle cells. Among the various MSCs, bone marrow-derived MSCs (BMMSCs) have been widely used for treating acute myocardial infarction (AMI) and ischemic heart failure (IHF) in preclinical and clinical studies. Although the beneficial effects of BMMSCs in treating AMI and IHF were originally attributed to their capacity to differentiate into cardiac cell types, recent evidence suggests that the differentiation capacity of BMMSCs appears to be minimal and that BMMSCs exert cardioprotective effects by secreting paracrine factors. In this context, MSC-derived exosomes have recently gained much attention. In this chapter, we introduce preclinical studies in which MSC-derived exosomes are used for treating cardiovascular diseases (CVDs) such as AMI, stroke, pulmonary hypertension, and septic cardiomyopathy. Future clinical studies are required to confirm the efficacy of exosome administration in treating CVDs.
For decades, chemists have strived to mimic the intricate design and diverse functions of naturally occurring systems through the bioinspired synthesis of programmable inorganic nanomaterials. The ...development of thiol-capped gold nanoparticles (AuNPs) has driven advancement in this area; however, although versatile and readily accessible, hybrid AuNPs are rarely atomically precise, which limits control over their surface topology and therefore the study of complex structure–function relationships. Here, we present a bottom-up approach to the systematic assembly of atomically precise hybrid nanoclusters employing a strategy that mimics the synthetic ease with which thiol-capped AuNPs are normally constructed, while producing well-defined covalent nanoscale assemblies with diverse surface topologies. For the first time, using a structurally characterized cluster-based organometallic building block, we demonstrate the systematic synthesis of nanoclusters with multivalent binding capabilities to complex protein targets.
“Molecular flasks” are well-defined supramolecular cages that can encapsulate one or more molecular guests within their cavities and, in so doing, change the physical properties and reactivities of ...the guests. Although molecular flasks are powerful tools for manipulating matter on the nanoscale, most of them are limited in their scope because of size restrictions. Recently, however, increasingly large and diverse supramolecular cages have become available with enough space in their cavities for larger chemical systems such as polymers, nanoparticles, and biomolecules. Here we report how a class of metallosupramolecular cages known as M12L24 polyhedra have been adapted to serve as nanometer-scale containers for solutions of a pseudorotaxane host–guest complex based on a tetracationic cyclophane host, cyclobis(paraquat-p-phenylene) (CBPQT4+), and a 1,5-dioxynaphthalene (DNP) guest. Remarkably, the hierarchical integration of pseudorotaxanes and M12L24 superhosts causes the system to express stimulus-responsive behavior, a property which can be described as emergent because neither the DNP⊂CBPQT4+ nor the M12L24 assemblies exhibit this behavior independently. The DNP-containing M12L24 molecular flasks are effectively “sealed off” to CBPQT4+ until ions are added as a stimulus to “open” them. The electrolyte stimulus reduces the electrostatic screening distance in solution, allowing favorable DNP⊂CBPQT4+ host–guest interactions to overcome repulsive Coulombic interactions between the cationic M12L24 cages and CBPQT4+ rings. This unusual example of ion-gated transport into chemical nanocontainers is reminiscent of transmembrane ion channels which act as gates to the cell, with the important difference that this system is reversible and operates at equilibrium.
Characterization of complex natural product mixtures to the absolute structural level of their components often requires significant amounts of starting materials and lengthy purification process, ...followed by arduous structure elucidation efforts. The crystalline sponge (CS) method has demonstrated utility in the absolute structure elucidation of isolated organic compounds at miniscule quantities compared to conventional methods. In this work, we developed a new CS‐based workflow that greatly expedites the in‐depth structural analysis of crude natural product extracts. Using a crude extract of the red alga Laurencia pacifica, we showed that CS affinity screening prior to compound isolation enables prioritization of analytes present in the extract, and we subsequently resolved the molecular structures of six sesquiterpenes with stereochemical clarity from around 10 mg crude extract. This study demonstrates a new chemotyping workflow that can greatly accelerate natural product discovery from complex samples.
Crystal clear: A crystalline sponge (CS)‐based method was developed for the prioritization of target analytes present in a methanolic crude extract from a red alga. Subsequent analysis by the CS method enabled the clarification of the structures of six sesquiterpenoid natural products, starting from only around 10 mg of the crude extract.
Protein encapsulation has long attracted many chemists and biologists because of its potential to control the structure and functions of proteins, but has been a daunting challenge because of their ...incommensurably larger size compared with common synthetic hosts. Here we report the encapsulation of a small protein, ubiquitin, within giant coordination cages. The protein was attached to one bidentate ligand and, upon addition of Pd(II) ions (M) and additional ligands (L), M(12)L(24) coordination nanocages self-assembled around the protein. Because of the well-defined host framework, the protein-encapsulated structure could be analysed by NMR spectroscopy, ultracentrifugation and X-ray crystallography.
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