ABSTRACT: Predictable stereoselective formation of supramolecular assembly is generally believed to be an important but complicated process. Here, we show that point chirality of a ligand decisively influences its supramolecular assembly behavior. We designed three closely related chiral ligands with different point chiralities, and observe their self-assembly into europium (Eu) tetrametallic tetrahedral cages. One ligand exhibits a highly diastereoselective assembly into homochiral (either ???? or ????) Eu tetrahedral cages whereas the two other ligands, with two different approaches of loosened point chirality, lead to a significant breakdown of the diastereoselectivity to generate a mixture of (???? and ????) isomers. The cages are highly emissive (luminescence quantum yields of 16(1) to 18(1)%) and exhibit impressive circularly polarized luminescence properties (|g lum|: up to 0.16). With in-depth studies, we present an example that correlates the nonlinear enhancement of the chiroptical response to the nonlinearity dependence on point chirality.
Project description:Supramolecular chirality may emerge from self-assembly processes to yield architectures that differ only in the topological arrangement of their constituent parts. Since the properties of the resulting enantiomeric assemblies are identical, purification and characterisation can be challenging. Here, we have examined the hypothesis that the intrinsic chirality of a protein nanopore can be exploited to detect supramolecular chirality. Transient blockages in the ion current flowing through a single membrane-spanning ?-haemolysin nanopore were shown to discriminate between M4L6 tetrahedral coordination cages of opposing chiralities. The single-molecule nature of the approach facilitated direct access to the rates of association and dissociation with the nanopore, which allowed the concentrations of the enantiomeric supramolecular assemblies to be determined in situ. Thus, we have established that a protein nanopore can be used to discriminate the chiral topologies of supramolecular assemblies, even when they are too large to fully enter the nanopore.
Project description:Cage catalysis has emerged as an important approach for mimicking enzymatic reactions by increasing the reaction rate and/or product selectivity of various types of covalent reactions. Here, we extend the catalytic application of cage compounds to the field of non-covalent molecular assembly. Acid-stable chiral imine cages are found to catalyze the supramolecular polymerization of porphyrins with an accelerated assembling rate and increased product enantioselectivity. Because the imine cages have a stronger interaction with porphyrin monomers and a weaker interaction with porphyrin assemblies, they can fully automatically detach from the assembled products without being consumed during the catalytic process. We reveal the kinetics of the auto-detachment of cages and the chirality growth of the assemblies using spectroscopic characterization studies. We find that the passivation groups attached to the cages are important for maintaining the structural stability of the cages during catalyzed assembly, and that the steric geometries of the cages can profoundly affect the efficiency of chiral regulation. This strategy demonstrates a new type of catalytic application of cage compounds in the field of molecular assembly, and paves the way to controlling supramolecular polymerization through a catalytic pathway.
Project description:Multivalent cooperativity plays an important role in the supramolecular self-assembly process. Herein, we report a remarkable cooperative enhancement of both structural integrity and metal ion selectivity on metal-organic M4L4 tetrahedral cages self-assembled from a tris-tridentate ligand (L1) with a variety of metal ions spanning across the periodic table, including alkaline earth (CaII), transition (CdII), and all the lanthanide (LnIII) metal ions. All these M4L14 cages are stable to excess metal ions and ligands, which is in sharp contrast with the tridentate (L2) ligand and bis-tridentate (L3) ligand bearing the same coordination motif as L1. Moreover, high-precision metal ion self-sorting is observed during the mixed-metal self-assembly of tetrahedral M4L4 cages, but not on the M2L3 counterparts. Based on the strong cooperative metal ion self-recognition behavior of M4L4 cages, a supramolecular approach to lanthanide separation is demonstrated, offering a new design principle of next-generation extractants for highly efficient lanthanide separation.
Project description:Transfer of both chirality and energy information plays an important role in biological systems. Here we show a chiral donor ?-gelator and assembled it with an achiral ?-acceptor to see how chirality and energy can be transferred in a composite donor-acceptor system. It is found that the individual chiral gelator can self-assemble into nanohelix. In the presence of the achiral acceptor, the self-assembly can also proceed and lead to the formation of the composite nanohelix. In the composite nanohelix, an energy transfer is realized. Interestingly, in the composite nanohelix, the achiral acceptor can both capture the supramolecular chirality and collect the circularly polarized energy from the chiral donor, showing both supramolecular chirality and energy transfer amplified circularly polarized luminescence (ETACPL).
Project description:Porous molecular solids composed of discrete macrocycles/cages have great potential for catalysis, separation and sensing techniques. Dynamic structural transformation of the host building blocks, especially a helicity inversion responsive to chemical triggers, is central to upgrading the spatial functions. Here we have achieved the syntheses of homochiral porous molecular solids composed of helical metal macrocycles through supramolecular chirality induction to both enantiomorphic forms with the aid of two different enantiopure sugar-derived lactones in the crystallization process. Moreover, we found that the helicity of the macrocyclic skeletons can be inverted in the crystalline state only by changing the type of solvent. This finding would lead to dynamic control of space chirality in connection with optical resolution, chiral amplification and asymmetric reactions.
Project description:Self-assembly of a Gemini-shaped, chiral amphiphilic hexa-peri-hexabenzocoronene having two chiral oxyalkylene side chains, along with two lipophilic side chains, yields graphitic nanotubes with one-handed helical chirality. The nanotubes are characterized by an extremely high aspect ratio of >1,000 and have a uniform diameter of 20 nm and a wall thickness of 3 nm. The nanotubes with right- and left-handed helical senses were obtained from the (S)- and (R)-enantiomers of the amphiphile, respectively, due to an efficient translation of point chirality into supramolecular helical chirality. The (S)- and (R)-enantiomers coassemble at varying mole ratios to give nanotubes, whose circular dichroism profiles are almost unchanged over a wide range of the enantiomeric excess of the amphiphile (100-20%). The high level of chirality amplification thus observed indicates a long-range cooperativity in the self-assembling process. In sharp contrast, a hexabenzocoronene amphiphile with chiral lipophilic side chains did not form nanotubular assemblies. The present work demonstrates the majority rule in noncovalent systems and also may provide a synthetic strategy toward realization of molecular solenoids.
Project description:Recently, porous framework materials with various network-type structures have been constructed via several different approaches, such as coordination interactions, reversible covalent bonds, and non-covalent interactions. Here, we have combined the concepts of supramolecular coordination complex (SCC) and metal-organic framework to offer a new strategy to construct a diamondoid supramolecular coordination framework (SCF) from an adamantanoid supramolecular coordination cage as the tetrahedral node and a difunctional Pt(II) ligand as the linear linker via stepwise orientation-induced supramolecular coordination. The adamantanoid supramolecular coordination cage has four uncoordinated pyridyl groups, which serve as the four vertexes of the tetrahedral geometry in the diamondoid framework. As a result, this diamondoid SCF exhibits an adamantanoid-to-adamantanoid substructure with two sets of pores, including the interior cavity of the adamantanoid cage and the extended adamantanoid space between the individual cages in the framework. In addition, the shape-controllable and highly ordered self-assembly of nanometer-sized diamondoid SCF is observed as micrometer-sized regular octahedrons by evaporation under heating in DMSO. This study demonstrates the potential application of supramolecular coordination complexes in the precise construction of highly regulated porous framework materials.
Project description:The chiral dissymmetric tetradentate ligand (S)-6'-(4-phenyloxazolin-2-yl)-2,2'-bipyridine-6-carboxylate (S-Phbipox) leads to the diastereoselective assembly of a homochiral Eu(3+) triangle and a highly emissive (quantum yield = 27%) heptanuclear wheel that is the largest example of a chiral luminescent complex of Eu(3+) reported to date. The nuclearity of the assembly is controlled by the solvent and the Eu(3+) cation. All of the compounds show large circularly polarized luminescence with an activity that varies with the nature of the assembly (highest for the homochiral trimer).
Project description:The luminescence and circularly polarized luminescence (CPL) spectra of M(I)[Eu((+)-hfbc)(4)] show a similar behavior to the exciton CD in the intraligand ?-?* transitions when the alkali metal ions and solvents are manipulated. There is a difference in susceptibility in solvation toward the alkali metal ions but not toward the Eu(III) ion, as in the case of axially symmetric DOTA-type compounds. The remarkable CPL in the 4f-4f transitions provide much more information on the stereospecific formation of chiral Eu(III) complexes, since CPL spectroscopy is limited to luminescent species and reflects selectively toward helicity of the local structural environment around the lanthanide(III). While in comparison, exciton CD reveals the chiral structural information from the helical arrangement of the four bladed chelates. Of special importance, the observation of the highest CPL activities measured to date for lanthanide(III)-containing compounds (i.e., Eu and Sm) in solution supports the theory that the chirality of lanthanide(III) in the excited state corresponds to that in the ground state, which was derived from the exciton CD.
Project description:The presence of anomalous chirality in a roll of graphitic carbon sheets has been recognized since the discovery of carbon nanotubes, which are becoming available in higher quantities through the isolation of chiral single-wall congeners with high purity. Exploration of the properties arising from cylinder chirality is expected to expand the scope of tubular entities in the future. By studying molecular fragments of helical carbon nanotubes, we herein reveal interesting properties that arise from this chirality. The chirality of nanoscale cylinders resulted in chirality of larger dimensions in the form of a double-helix assembly. Cylinder chirality in solution gave rise to a large dissymmetry factor of metal-free entities in circular polarized luminescence. Theoretical investigations revealed the pivotal role of cylindrical shapes in enhancing magnetic dipole transition moments to yield extreme rotatory strength. Unique effects of cylinder chirality in this study may prompt the development of tubular entities, for instance, toward chiroptical applications.