Molecular Face-Rotating Cube with Emergent Chiral and Fluorescence Properties.

Chiral cage compounds are mainly constructed from chiral precursors or based on the symmetry breaking during coordination-driven self-assembly. Herein, we present a strategy to construct chiral organic cages by restricting the P or M rotational configuration of tetraphenylethylene (TPE) faces through dynamic covalent chemistry. The combination of graph theory, experimental characterizations and theoretical calculations suggests emergent chirality of cages is originated from complex arrangements of TPE faces with different orientational and rotational configurations. Accompanied by the generation of chirality, strong fluorescence also emerged during cage formation, even in dilute solutions with various solvents. In addition, the circularly polarized luminescence of the cages is realized as a synergy of their dual chiral and fluorescence properties. Chirality and fluorescence of cages are remarkably stable, because intramolecular flipping of phenyl rings in TPE faces is restricted, as indicated by calculations. This study provides insight into construct chiral cages by the rational design through graph theory, and might facilitate further design of cages and other supramolecular assemblies from aggregation-induced emission active building blocks.

Supramolecular copolymerization through self-correction of non-polymerizable transient intermediates.

Kinetic control over structures and functions of complex assembly systems has aroused widespread interest. Understanding the complex pathway and transient intermediates is helpful to decipher how multiple components evolve into complex assemblies. However, for supramolecular polymerizations, thorough and quantitative kinetic analysis is often overlooked. Challenges remain in collecting the information of structure and content of transient intermediates in situ with high temporal and spatial resolution. Here, the unsolved evolution mechanism of a classical self-sorting supramolecular copolymerization system was addressed by employing multidimensional NMR techniques coupled with a microfluidic technique. Unexpected complex pathways were revealed and quantitatively analyzed. A counterintuitive pathway involving polymerization through the 'error-correction' of non-polymerizable transient intermediates was identified. Moreover, a 'non-classical' step-growth polymerization process controlled by the self-sorting mechanism was unraveled based on the kinetic study. Realizing the existence of transient intermediates during self-sorting can encourage the exploitation of this strategy to construct kinetic steady state assembly systems. Moreover, the strategy of coupling a microfluidic technique with various characterization techniques can provide a kinetic analysis toolkit for versatile assembly systems. The combined approach of coupling thermodynamic and kinetic analyses is indispensable for understanding the assembly mechanisms, the rules of emergence, and the engineering of complex assembly systems.

Optimization of twin parallel microstrips based nuclear magnetic resonance probe for measuring the kinetics in molecular assembly in ultra-small samples.

We present the design, fabrication, characterization, and optimization of a TPM (twin parallel microstrip)-based nuclear magnetic resonance (NMR) probe, produced by using a low-loss Teflon PTFE F4B high frequency circuit board. We use finite element analysis to optimize the radio frequency (RF) homogeneity and sensitivity of the TPM probe jointly for various sample volumes. The RF homogeneity of this TPM planar probe is superior to that of only a single microstrip probe. The optimized TPM probe properties such as RF homogeneity and field strength are characterized experimentally and discussed in detail. By combining this TPM based NMR probe with microfluidic technology, the sample amount required for kinetic study using NMR spectroscopy was minimized. This is important for studying costly samples. The TPM NMR probes provide high sensitivity to analysis of 5 µl samples with 2 mM concentrations within 10 min. The miniaturized microfluidic NMR probe plays an important role in realizing down to seconds timescale for kinetic monitoring.

Chaperone-like chiral cages for catalyzing enantio-selective supramolecular polymerization.

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.

Elucidation of the origin of chiral amplification in discrete molecular polyhedra.

Chiral amplification in molecular self-assembly has profound impact on the recognition and separation of chiroptical materials, biomolecules, and pharmaceuticals. An understanding of how to control this phenomenon is nonetheless restricted by the structural complexity in multicomponent self-assembling systems. Here, we create chiral octahedra incorporating a combination of chiral and achiral vertices and show that their discrete nature makes these octahedra an ideal platform for in-depth investigation of chiral transfer. Through the construction of dynamic combinatorial libraries, the unique possibility to separate and characterise each individual assembly type, density functional theory calculations, and a theoretical equilibrium model, we elucidate that a single chiral unit suffices to control all other units in an octahedron and how this local amplification combined with the distribution of distinct assembly types culminates in the observed overall chiral amplification in the system. Our combined experimental and theoretical strategy can be applied generally to quantify discrete multi-component self-assembling systems.

Interconversion of molecular face-rotating polyhedra through turning inside out.

We report the post-synthesis interconversion of two enantiomeric organic cages through turning inside out. By scrutinizing the thermodynamics and kinetics, we are able to control the racemization rate by various reaction conditions and reveal that the turning-inside-out interconversion is realized through a partial disassembly pathway. The kinetics investigation also provides insight into the dynamic essence of imine chemistry using different solvents and catalysts.

Assembled molecular face-rotating polyhedra to transfer chirality from two to three dimensions.

In nature, protein subunits on the capsids of many icosahedral viruses form rotational patterns, and mathematicians also incorporate asymmetric patterns into faces of polyhedra. Chemists have constructed molecular polyhedra with vacant or highly symmetric faces, but very little is known about constructing polyhedra with asymmetric faces. Here we report a strategy to embellish a C3h truxene unit with rotational patterns into the faces of an octahedron, forming chiral octahedra that exhibit the largest molar ellipticity ever reported, to the best of our knowledge. The directionalities of the facial rotations can be controlled by vertices to achieve identical rotational directionality on each face, resembling the homo-directionality of virus capsids. Investigations of the kinetics and mechanism reveal that non-covalent interaction among the faces is essential to the facial homo-directionality.

[Studies on the alkaloids from stem of Artabotrys hainanensis].

OBJECTIVE: To investigate the alkaloids from the stem of Artabotrys hainanensis. METHOD: Compounds in plant extracts were separated by silica gel and sephadex LH-20 column chromatography. Chemical structures were elucidated by chemical and spectral analyses including UV, 1H-NMR, 13C-NMR, ESIMS and ESI-MS-MS. RESULT: Eight alkaloids were isolated and identified as spinosine (1), 3-hydroxynornuciferine (2), juzirine (3), artabotrine (4), liridine (5), assimilobine (6), isococlaurine (7), N-demethylarmepavine (8). CONCLUSION: All alkaloids were isolated from this plant for the first time and compounds 1, 3, 7 and 8 were isolated from genus Artabotrys for the first time.

Corannulene derivatives with low LUMO levels and dense convex-concave packing for n-channel organic field-effect transistors.

Electron-deficient corannulene derivatives incorporating cyano and imide groups into the corannulene core were synthesized, which showed low LUMO (lowest unoccupied molecular orbital) levels and dense convex-concave packing structures in single crystals. These two features help to realize the first n-channel organic field-effect transistors (OFETs) in air based on corannulene derivatives.

Molecular mechanism of granulocytic differentiation of human promyelocytic leukemia HL-60 cells induced by all-trans retinoic acid.

AIM: To elucidate the molecular mechanism of granulocytic differentiation of human promyelocytic leukemia HL-60 cells induced by all-trans-retinoic acid (ATRA). METHODS: Flow cytometry was used to determine the cell cycle changes of HL-60 cells upon ATRA treatment. Gene expression profiles of HL-60 cells induced by 1 mumol.L-1 ATRA were obtained by using cDNA microarrays containing 9,984 genes and expressed sequence tags (ESTs). RESULTS: Cell cycle analysis showed that 48%-73% of cells were arrested at G1/G0 phase upon ATRA treatment; cDNA microarray results demonstrated that the expression of genes encoding adhesion molecules, tissue remodeling proteins, transporters and ribosomal proteins were up-regulated in ATRA treated of HL-60 cells. Several genes involved in oxidase activation pathway were also differentially expressed. CONCLUSION: ATRA treatment induced growth arrest and differentiation in HL-60 cells, which is associated with regulation of the oxidase activation pathway and the expression of tissue remodeling proteins.

Molecularly imprinted photonic polymer based on ß-cyclodextrin for amino acid sensing.

A novel molecularly imprinted photonic polymer (MIPP) using maleic anhydride modified ß-cyclodextrin (ß-CD) and acrylic acid as functional monomers has been presented for amino acid sensing. Reactive ß-CD monomer carrying vinyl carboxylic acid functional groups was first synthesized. MIPP was fabricated by filling precursor solution into the interstitial spaces of polystyrene photonic crystal templates, followed by a thermal polymerization at 55 °C. Characterization showed that the MIPP possessed an opal photonic crystal structure. This ß-CD-based MIPP could undergo a swelling change from 590 nm to 704 nm and still retain the molecular imprinting recognition ability during the sensing of L-phenylalanine (L-Phe). A function relationship was found between the diffraction wavelength shift and the logarithm of L-Phe concentration in the range of 10(-8)M to 10(-4)M at pH 6. A wavelength shift of 114 nm for L-Phe was observed within 30s, whereas there were no obvious shifts for d-Phe, L-tyrosine and L-tryptophan, indicating that the ß-CD-based MIPP had high specificity and rapid response to L-Phe. The developed MIPP sensor has been applied to detect L-Phe in compound amino acid injection sample.