Flow Synthesis of Gigantic Porphyrinic Cages: Facile Synthesis of P12 L24 and Discovery of Kinetic Product P9 L18.

A continuous flow methodology for the facile and high-yielding synthesis of the porphyrin-based self-assembled organic cage, P12 L24 is reported, along with the serendipitous discovery of a kinetic product, P9 L18 cage, which has been characterized by MALDI-TOF MS, NMR, and AFM analysis. A theoretical study suggests a tricapped trigonal prismatic geometry for P9 L18 . Unlike P12 L24 , P9 L18 is unstable and readily decomposes into monomers and small oligomers. While the batch synthesis produces only the thermodynamic product P12 L24 , the continuous flow process generates not only the thermodynamic product but also kinetic products, such as P9 L18 , illustrating the advantages of the continuous flow process for the synthesis of self-assembled cages and the exploration of new non-equilibrium assemblies.

Dramatically Enhanced Reactivity of Fullerenes and Tetrazine towards the Inverse-Electron-Demand Diels-Alder Reaction inside a Porous Porphyrinic Cage.

Inverse-electron-demand Diels-Alder reaction (IEDDA) between fullerenes and 1,2,4,5-tetrazine generally requires harsh conditions and long reaction times due to their strong electron-accepting nature. Herein, we report a dramatic enhancement in the reactivity of the fullerenes (C60 /C70 )-tetrazine reaction inside a porous Zn-porphyrinic cage (Zn-PB) under sustainable conditions by installing a tetrazine-based axle (LA) via metal-ligand coordination bond, which modulates the cavity size to facilitate the encapsulation of fullerenes. Upon encapsulation, the close proximity of fullerenes and the tetrazine group of LA dramatically increase their reactivity towards the IEDDA reaction to form fullerene-tetrazine adducts. Furthermore, the C60 -tetrazine adduct is rearranged upon hydration to a bent-shaped C60 -pyrazoline adduct that can be released from the Zn-PB cavity in the presence of excess LA, thus catalyzing the formation of C60 -pyrazoline adduct inside Zn-PB without product inhibition.

Programmable Synthesis of Silver Wheels.

The synthesis of sandwich-shaped multinuclear silver complexes with planar penta- and tetranuclear wheel-shaped silver units and a central anion, [Agn(2-HPB)2(A-)](OTf-)n-1, nAgA, n = 4 or 5 and A- = OH- or F- or Cl-, is reported, along with complete spectroscopic and structural characterization. An NMR mechanistic study reveals that silver complexes were formed in the following order: 2Ag → 3AgH2O → 5AgOH → 4AgOH. The central hydroxides in 4AgOH and 5AgOH exhibit exotic physical properties due to the confined environment inside the complex. The size of these silver wheels can be tuned by changing the central anion or extracting/adding one silver atom. This study provides the facile way to synthesize discrete wheel-shaped multinuclear silver complexes and provides valuable insights into the dynamics of the self-assembly process.

Supramolecular Fullerene Tetramers Concocted with Porphyrin Boxes Enable Efficient Charge Separation and Delocalization.

Herein, we report a novel porphyrin/fullerene supramolecular cocrystal using a shape-persistent zinc-metalated porphyrin box (Zn-PB) and C60/C70. An unprecedented arrangement of a tightly packed square-planar core of four C60 or C70 surrounded by six cube-shaped Zn-PBs was observed. This unique packing promotes strong charge transfer (CT) interactions between the two components in the ground state and formation of charge-separated states with very long lifetimes in the excited state and enables unusually high photoconductivity. Quantum chemical calculations show that these features are enabled by delocalized orbitals that promote the CT, on one hand, and that are spatially separated from each other, on the other hand. This work may open a new avenue to design novel electron donor/acceptor architectures for artificial photosynthesis.

Hierarchical Self-Assembly of Poly-Pseudorotaxanes into Artificial Microtubules.

Hierarchical self-assembly of building blocks over multiple length scales is ubiquitous in living organisms. Microtubules are one of the principal cellular components formed by hierarchical self-assembly of nanometer-sized tubulin heterodimers into protofilaments, which then associate to form micron-length-scale, multi-stranded tubes. This peculiar biological process is now mimicked with a fully synthetic molecule, which forms a 1:1 host-guest complex with cucurbit[7]uril as a globular building block, and then polymerizes into linear poly-pseudorotaxanes that associate laterally with each other in a self-shape-complementary manner to form a tubular structure with a length over tens of micrometers. Molecular dynamic simulations suggest that the tubular assembly consists of eight poly-pseudorotaxanes that wind together to form a 4.5 nm wide multi-stranded tubule.

Fuel-Driven Transient Crystallization of a Cucurbit[8]uril-Based Host-Guest Complex.

Transient self-assembling systems often suffer from accumulation of chemical wastes that interfere with the formation of pristine self-assembled products in subsequent cycles. Herein, we report the transient crystallization of a cucurbit[8]uril-based host-guest complex, preventing the accumulation of chemical wastes. Base-catalyzed thermal decarboxylation of trichloroacetic acid that chemically fuels the crystallization process dissolves the crystals, and produces volatile chemical wastes that are spontaneously removed from the solution. With such self-clearance process, no significant damping in the formation of the crystals was observed. The morphology and structural integrity of the crystals was also maintained in subsequent cycles. The concept may be further extended to obtain other temporally functional materials, quasicrystals, etc., based on stimuli-responsive guest molecules.

Rational Design and Construction of Hierarchical Superstructures Using Shape-Persistent Organic Cages: Porphyrin Box-Based Metallosupramolecular Assemblies.

We report a new approach to building hierarchical superstructures using a shape-persistent porous organic cage, which acts as a premade secondary building unit, and coordination chemistry. To illustrate the principle, a zinc-metalated porphyrin box (Zn-PB), a corner-truncated cubic porous cage, was connected by suitable dipyridyl terminated bridging ligands to construct PB-based hierarchical superstructures (PSSs). The PSSs were stabilized not only by the coordination bonds between Zn ions and bipyridyl-terminated ligands but also by π-π interactions between the corners of the Zn-PB units. By varying the length of the linker, we identified an optimum range of the linker length for construction of PSSs. The PSSs have large void volumes and an extrinsic surface area compared to the parent PBs, which can be exploited for the selective encapsulation and interior functionalization of the PSSs for various applications, including catalysis. We observed that singlet oxygen induced synthesis of the natural product, juglone, is more efficiently catalyzed by PSS-1 than its constituent component Zn-PB.

High-temperature in situ crystallographic observation of reversible gas sorption in impermeable organic cages.

Crystallographic observation of adsorbed gas molecules is a highly difficult task due to their rapid motion. Here, we report the in situ single-crystal and synchrotron powder X-ray observations of reversible CO2 sorption processes in an apparently nonporous organic crystal under varying pressures at high temperatures. The host material is formed by hydrogen bond network between 1,3,5-tris-(4-carboxyphenyl)benzene (H3BTB) and N,N-dimethylformamide (DMF) and by π-π stacking between the H3BTB moieties. The material can be viewed as a well-ordered array of cages, which are tight packed with each other so that the cages are inaccessible from outside. Thus, the host is practically nonporous. Despite the absence of permanent pathways connecting the empty cages, they are permeable to CO2 at high temperatures due to thermally activated molecular gating, and the weakly confined CO2 molecules in the cages allow direct detection by in situ single-crystal X-ray diffraction at 323 K. Variable-temperature in situ synchrotron powder X-ray diffraction studies also show that the CO2 sorption is reversible and driven by temperature increase. Solid-state magic angle spinning NMR defines the interactions of CO2 with the organic framework and dynamic motion of CO2 in cages. The reversible sorption is attributed to the dynamic motion of the DMF molecules combined with the axial motions/angular fluctuations of CO2 (a series of transient opening/closing of compartments enabling CO2 molecule passage), as revealed from NMR and simulations. This temperature-driven transient molecular gating can store gaseous molecules in ordered arrays toward unique collective properties and release them for ready use.

Iodide-Selective Synthetic Ion Channels Based on Shape-Persistent Organic Cages.

We report here a synthetic ion channel developed from a shape-persistent porphyrin-based covalent organic cage. The cage was synthesized by employing a synthetically economical dynamic covalent chemistry (DCC) approach. The organic cage selectively transports biologically relevant iodide ions over other inorganic anions by a dehydration-driven, channel mechanism as evidenced by vesicle-based fluorescence assays and planar lipid bilayer-based single channel recordings. Furthermore, the organic cage appears to facilitate iodide transport across the membrane of a living cell, suggesting that the cage could be useful as a biological tool that may replace defective iodide channels in living systems.

Effect of metal doping, doped structure, and annealing under argon on the properties of 30 nm thick ultrathin hematite photoanodes.

The doping of the whole hematite layer with W (9.4%) and the additional doping of the bottom half of the W-doped hematite layer with Sn (8.6%), and the subsequent annealing under argon at 600 °C give rise to large increases in the Fe(2+) concentration (by >∼200 times), carrier density (Cd, by ∼48 times) and current density (i(d), by ∼8 times at 1.23 V vs. RHE, under 1 sun) with respect to those of bare hematite photoanodes. The measured i(d) (0.9 mA cm(-2)) is the highest among those of the ultrathin hematite photoanodes and the measured Cd (3.8 × 10(22) cm(-3)) is the highest among those ever observed for hematite.

A novel vanadosilicate with hexadeca-coordinated Cs(+) ions as a highly effective Cs(+) remover.

The effective removal of (137) Cs(+)  ions from contaminated groundwater and seawater and from radioactive nuclear waste solutions is crucial for public health and for the continuous operation of nuclear power plants. Various (137) Cs(+)  removers have been developed, but more effective (137) Cs(+)  removers are still needed. A novel microporous vanadosilicate with mixed-valence vanadium (V(4+) and V(5+) ) ions is now reported, which shows an excellent ability for Cs(+)  capture and immobilization from groundwater, seawater, and nuclear waste solutions. This material is superior to other known materials in terms of selectivity, capacity, and kinetics, and at very low Cs(+)  concentrations, it was found to be the most effective material for the removal of radioactive Cs(+)  ions under the test conditions. This novel vanadosilicate also contains hexadeca-coordinated Cs(+)  ions, which corresponds to the highest coordination number ever described.

The pH Response of a Peptoid Oligomer.

Polypeptoids are N-substituted glycine polymers, which differ from peptides in the placement of the side chain on the amide nitrogen rather than the Cα carbon. A peptoid with a chiral side chain containing both an aromatic group and carboxylic acid has a structure that responds to pH changes. All-atom molecular dynamics simulations using a force field specifically tuned for peptoids were carried out with an advanced sampling method for the peptoid (S)-N-(1-carboxy-2-phenylethyl)glycine in the high and low pH limits. The simulations show that the structure changes from mostly cis amide bonds at low pH to mostly trans bonds at high pH. The structural changes are driven by side chain-backbone hydrogen bonds at low pH and side chain repulsions and increased water contact at high pH.

Fluorogenic sensing of CH3CO2- and H2PO4- by ditopic receptor through conformational change.

Cyclo-bis-(urea-3,6-dichlorocarbazole) (1) forms a 1 : 2 complex with CH(3)CO(2)(-) and H(2)PO(4)(-) through hydrogen bonding with the two urea moieties, resulting in fluorescence enhancement via a combined photoinduced electron transfer (PET) and energy transfer mechanism. The binding mechanism involves a conformational change of the two urea receptors to a trans orientation after binding of the first anion, which facilitates the second interaction.

One-pot Synthesis of a Truncated Cone-shaped Porphyrin Macrocycle and Its Self-assembly into Permanent Porous Material.

Here, we report the synthesis of a truncated cone-shaped triangular porphyrinic macrocycle, P3 L3 , via a single step imine condensation of a cis-diaminophenylporphyrin and a bent dialdehyde-based linker as building units. X-ray diffraction analysis reveals that the truncated cone-shaped P3 L3 molecules are stacked on top of each other by π⋯π and CH⋯π interactions, to form 1.7 nm wide hollow columns in the solid state. The formation of the triangular macrocycle is corroborated by quantum chemical calculations. The permanent porosity of the P3 L3 crystals is demonstrated by several gas sorption experiments and powder X-ray diffraction analysis.

Photoactivated racemization catalyst for dynamic kinetic resolution of secondary alcohols.

Household fluorescent light activates a diruthenium complex to generate catalytic species highly active for the racemization of secondary alcohols under ambient conditions. This catalyst system is applicable for the chemoenzymatic dynamic kinetic resolution of racemic alcohols to give optically pure acetates under mild conditions.

Transient Self-assembly Processes Operated by Gaseous Fuels under Out-of-Equilibrium Conditions.

Herein we report transient out-of-equilibrium self-assembly of molecules operated by gaseous fuel mixtures. The combination of an active gaseous chemical fuel and an inert gas or compressed air, which assists the degassing of the gaseous fuel from the solution, drives the transient self-assembly process. The gaseous nature of the fuel as well as the exhaust helps in their easy removal and thereby prevents their accumulation within the system and helps in maintaining the efficiency of the transient self-assembly process. The strategy is executed with a rather simple experimental set up and operates at ambient temperatures. Our approach may find use in the development of smart materials suitable for applications such as temporally active gas sensing and sequestration.

Controlling metal nanotoppings on the tip of silicide nanostructures.

Utilizing the difference in surface tension between SiO2 and metal catalysts (Mn2+, Ni2+), we show how metals form nanoshells, nanodiscs and nanospheres at the tips of the SiO2 nanostructures of nanocones, nanorods and nanowires. For the Mn2+ catalyst (i), SiO2-nanocones are formed with the hemispherical convex cap of the MnO/SiO2 composite. For the Ni2+ catalyst (ii), SiO2 nanowires are grown due to the concave shape of SiO2 surrounding the multi-faceted NiSi particles at their tip. For the Mn2+/Ni2+ catalyst (iii), SiO2 nanorods are formed with large-sized spherical ferromagnetic single Ni nanocrystals (50-200 nm in diameter) surrounded by the concave MnO2/SiO2 composite at the tip of the SiO2 nanorods. This large-sized spherical formation of the single Ni crystal is possible because Ni is able to be chemically reduced by Mn at 950 degrees C, well below the melting point of Ni (1455 degrees C) due to the alloying effect.

4,11-Diaza-1,8-diazo-niacyclo-tetra-decane dichloride hemihydrate.

In the title compound, C(10)H(26)N(4) (2+)·2Cl(-)·0.5H(2)O, the cyclam (1,4,8,11-tetra-azacyclo-tetra-decane) dication adopts an endodentate conformation which my be inflenced by intra-molecular N-H⋯N hydrogen bonding. In the crystal structure, the components are linked by N-H⋯Cl and O-H⋯Cl hydrogen bonds into chains along [100]. The water molecule is disordered over two sites in a 50:50 ratio.

Cyclo-hexane-1,2-diammonium bis-(pyridine-2-carboxyl-ate).

In the dication of the title salt, C(6)H(16)N(2) (2+)·2C(6)H(4)NO(2) (-), the two ammonium groups are in the equatorial positions of the chair-shaped cyclo-hexyl ring. In the crystal, the cations and anions are linked by N-H⋯O and N-H⋯N hydrogen bonds, forming a layer network parallel to the ac plane. Weak π-π inter-actions between adjacent pyridine rings with a centroid-centroid distance of 3.589 (2) Šare also present.

Bis(2,2'-bipyridine-κN,N')dichlorido-platinum(IV) dichloride monohydrate.

In the title complex, [PtCl(2)(C(10)H(8)N(2))(2)]Cl(2)·H(2)O, the Pt(4+) ion is six-coordinated in a distorted octa-hedral environment by four N atoms from the two 2,2'-bipyridine ligands and two Cl atoms. As a result of the different trans influences of the N and Cl atoms, the Pt-N bonds trans to the Cl atom are slightly longer than those trans to the N atom. The compound displays inter-molecular hydrogen bonding between the water mol-ecule and the Cl anions. There are inter-molecular π-π inter-actions between adjacent pyridine rings, with a centroid-centroid distance of 3.962 Å.