Masanobu Naito

Large Cs adsorption capability of nanostructured Prussian Blue particles with high accessible surface areas

Very recently, we have reported preparation of several types of Prussian Blue (PB) particles with varying particle sizes by systematically tuning the synthetic conditions (Angew. Chem., Int. Ed., 2012, 51, 984–988). Here, the obtained PB particles are used for removal of Cs ions from aqueous solutions, which will be useful for remediation of nuclear waste. To evaluate the uptake ability of Cs ions into the PB particles, we utilize quartz crystal microbalance (QCM) for real-time monitoring of uptake behavior of Cs ions into the PB particles. The frequency of the QCM is promptly decreased after injection of Cs ions solution into the QCM cell. Hollow PB nanoparticles of 190 nm in diameter have very high surface area (338 m2 g−1), in comparison with other PB particles, leading to efficient Cs adsorption capability eight times larger than that of the commercial PB particles. The diffusion in terms of dissociation constant (Kd), maximum amount of adsorbed Cs in PB particles (mmax), and the adsorption kinetics (k) of Cs ions into the PB particles are also discussed. Due to the selective uptake for Cs ions based on Kd and k values, the PB particles can be proposed as good candidates in waste management consideration.

Circularly Polarized Luminescent CdS Quantum Dots Prepared in a Protein Nanocage

Semiconductor quantum dots (QDs) have attracted a great deal of attention because of their optically tunable light emissions, which are derived from the quantum confinement effect. Unlike bulk materials, QDs utilizing these unique optical properties have a wide range of potential applications, especially in light-emitting devices, sensory materials, and bioassays. More recently, several attempts to develop QDs with optical activity have been reported both experimentally and theoretically. AlthoughQDs prepared with chiral stabilizers, such as CdS or CdTe, showed significant circular dichroism (CD), their circularly polarized luminescence (CPL) was inactive. Density functional calculations revealed that the chiral stabilizer distorted the QD surface only, transmitting an enantiomeric structure to the surface layers. However, the QD core with hexagonal phase remained undistorted and achiral. Herein, we hypothesize that if the whole QD crystal adopted a chiral structure, emission from the QD would express CPL activity. Within this context, we focused on a QD prepared in a rhombic dodecahedral protein, horse spleen ferritin, as a hollow chiral template. The ferritin is composed of 24 a-helixrich subunits with exterior and interior diameters of 12 nm and 8 nm, respectively (Figure 1a). The ferritin ubiquitously regulates intracellular iron homeostasis, in which an iron ion is temporally stored as ferrihydride. Recently, sophisticated structural analysis has revealed that the ferrihydride in the ferritin was structurally distorted, reflecting a chiral nanosphere comprised of the a-helix-rich subunits. Along with the ferrihydride, a variety of QDs were prepared within the ferritin, in which the flow of ion precursors in the hollow core took place through specific channels at the interface of the apoferritin subunits. Here 72 glutamate residues on the interior surface of the apoferritin shell are thought to promote the formation of the QDs (Figure 1b). Therefore, we expected that the QD prepared in the hollow chiral template would adopt a chiral crystal structure, resulting in CPL activity. We first demonstrated that a water-soluble CdS QD prepared in ferritin (CdS@ferritin) exhibits significant lefthanded CPL emissions from direct transition and surfacetrapping sites of the CdS QDs. Furthermore, wavelengths of the photoluminescence (PL)/CPL were modulated by laser photoetching. Figure 2a,b shows PL and CPL spectra of the apoferritin and CdS@ferritin with an excitation wavelength at 325 nm. The apoferritin exhibited an intense PL band with lmax at 396 nm, which originated from post-translationally modified dityrosine in the ferritin shell (Figure 2a, blue line; Figure 2c), whereas its CPL signal was negligibly small (Figure 2b, blue line). On the other hand, CdS@ferritin afforded a broad PL band with lmax at 780 nm and a shoulder peak at ca. 498 nm, although the PL signal from ferritin disappeared, which was probably due to intramolecular energy migration from the ferritin shell to the CdS QD (Figure 2a, red line; Figure 2d). Furthermore, the CPL of CdS@ferritin showed an intense band at 498 nm and a broad band at 780 nm (Figure 2b, red line). To quantify these PL/ CPL spectra, Kuhn s anisotropy factor (gLum) was calculated: gLum is defined as gLum= 2(IL IR)/(IL+IR), where IL and IR indicate the signals for leftand right-handed CPL, respectively (Figure 2e). Consequently, the gLum values at 498 nm Figure 1. a) Illustration of apoferritin from a threefold channel (ribbon model) and b) a cross-sectional view (slab 65%). The 72 glutamate residues on the interior surface are depicted as a yellow space-filling model.

Asymmetric Induction in the Preparation of Helical Receptor–Anion Complexes: Ion‐Pair Formation with Chiral Cations

A number of helical structures have been reported. Foldamers form helical structures in response to chemical stimuli such as neutral molecules, metal cations, and anions. The ability to prepare enantiomerically enriched helical foldamers is crucial for applying helical structures to functional materials with chiroptical properties. One strategy for preparing enantiomerically enriched helices is the direct attachment of chiral moieties to the foldamers. In addition, the introduction of a chiral guest species can also induce the preferential formation of one diastereomer of the resulting complex through specific noncovalent interactions between the guest and the host system. Electrostatic interactions between oppositely charged species can occur in the absence of specific interactions. Therefore, a challenging way to make a compound fold into an enantiomerically pure chiral structure is to use electrostatic interactions between an achiral ion and an enantiomerically pure chiral counterion. In fact, chiral anions have been used for the preparation of enantiomerically pure metal helicates. 8] Conversely, the association of chiral cations with helixforming compounds that contain receptor and anionic moieties has led to the formation of enantiomerically pure helical structures. The chiroptical properties of receptor– anion helical complexes that form through hydrogen bonding can be difficult to examine because they can undergo more facile interconversion between enantiomeric helical forms compared to metal-based helices that form through coordination bonds. This fast interconversion is not a problem when one diastereomer of an ion pair consisting of a helical receptor–anion complexes and chiral counter cations is more stable than the other because then only one enantiomeric helix structure predominates in solution. p-Conjugated molecules that form helical structures in the presence of anions include boron complexes of 1,3-dipyrrolyl1,3-propanediones. These complexes, an example being 1a (Scheme 1a), bind anions through dynamic conformational changes involving rotation of the bond between the carbonyl group and the pyrrole moiety, thus resulting in helical oligomers (e.g., 2a and 2b, Scheme 1b). 11b, c,e] These helical oligomers were observed in the solid state and were comprised of alternately stacking negatively and positively charged species, that is, oligomer–anion complexes and counter cations, respectively. Anion complexes of the receptor-containing oligomers could be formed in enantiomerically enriched state in solution through ion pairing with optically active cations. In this paper, we report the preparation of enantiomerically enriched anionic helices that form electrostatic interactions with chiral counter cations; we also describe the chiroptical properties of these helices such as their circularly polarized luminescence (CPL). 13] Chiral p-conjugated cations are suitable candidates for inducing asymmetry in helix formation owing to their ability to form interactions with p-conjugated receptor–anion complexes. Therefore, we focused on the chiral binaphthylammonium Cl and Br salts, RR·X and SS·X (X = Cl and Br) (Scheme 1c), which Ooi, Kameda, and Maruoka reported as being efficient phase-transfer catalysts in enantioselective reactions. The formation of 1:1 receptor–anion complexes in solution can be followed by analyzing electronic spectra. Upon the addition of RR·Cl (1.5 equivalents) to 2b in CH2Cl2 (1 mm) at 20 and 70 8C, the UV/Vis absorption bands associated with 2 b at 514 and 523 nm decreased and those at [*] Dr. Y. Haketa, Y. Bando, Prof. Dr. H. Maeda College of Pharmaceutical Sciences, Ritsumeikan University Kusatsu 525–8577 (Japan) E-mail: maedahir@ph.ritsumei.ac.jp

Circularly Polarized Luminescence in Supramolecular Assemblies of Chiral Bichromophoric Perylene Bisimides

Chiral bichromophoric perylene bisimides are demonstrated as active materials of circularly polarized emission. The bichromophoric system exhibited circularly polarized luminescence with dissymmetry factors typical of that of similar organic chiral chromophoric systems in the monomeric state. Variation in solvent composition led to the formation of stably soluble helical aggregates through intermolecular interactions. A large enhancement in the dissymmetry of circularly polarized luminescence was exhibited by the aggregated structures both in the solution and solid states. The sum of excitonic couplings between the individual chromophoric units in the self-assembled state results in relatively large dissymmetry in the circularly polarized luminescence, thereby giving rise to enhanced dissymmetry factors for the aggregated structures. The spacer between chiral center and chromophoric units played a crucial role in the effective enhancement of chiroptical properties in the self-assembled structures. These materials might provide opportunities for the design of a new class of functional bichromophoric organic nanoarchitectures that can find potential applications in the field of chiroptical memory and light-emitting devices based on supramolecular electronics.

Naked-eye discrimination of methanol from ethanol using composite film of oxoporphyrinogen and layered double hydroxide.

Methanol is a highly toxic substance, but it is unfortunately very difficult to differentiate from other alcohols (especially ethanol) without performing chemical analyses. Here we report that a composite film prepared from oxoporphyrinogen (OxP) and a layered double hydroxide (LDH) undergoes a visible color change (from magenta to purple) when exposed to methanol, a change that does not occur upon exposure to ethanol. Interestingly, methanol-induced color variation of the OxP-LDH composite film is retained even after removal of methanol under reduced pressure, a condition that does not occur in the case of conventional solvatochromic dyes. The original state of the OxP-LDH composite film could be recovered by rinsing it with tetrahydrofuran (THF), enabling repeated usage of the composite film. The mechanism of color variation, based on solid-state (13)C-CP/MAS NMR and solution-state (13)C NMR studies, is proposed to be anion transfer from LDH to OxP triggered by methanol exposure.

Achiral guest-induced chiroptical changes of a planar-chiral pillar[5]arene containing one π-conjugated unit

A planar-chiral pillar[5]arene derivative containing one π-conjugated unit was prepared. Chiroptical changes were observed upon addition of the achiral guest 1,4-dicyanobutane.

Chirality Induction by Formation of Assembled Structures Based on Anion-Responsive π-Conjugated Molecules

Anion-responsive π-conjugated compounds having chiral alkyl chains were synthesized. Circular dichroism (CD) and circularly polarized luminescence (CPL) were observed in the solution-state assemblies of the chiral anion receptors and those of their anion complexes as salts of a planar triazatriangulenium cation. The CD and CPL spectral patterns of the ion-pair-based assemblies were completely opposite to those of the anion-free assemblies, and this suggests that anion binding and subsequent ion pairing change the chirality of the assembly modes.

Highly Crystallized Nanometer‐Sized Zeolite A with Large Cs Adsorption Capability for the Decontamination of Water

Nanometer-sized zeolite A with a large cesium (Cs) uptake capability is prepared through a simple post-milling recrystallization method. This method is suitable for producing nanometer-sized zeolite in large scale, as additional organic compounds are not needed to control zeolite nucleation and crystal growth. Herein, we perform a quartz crystal microbalance (QCM) study to evaluate the uptake ability of Cs ions by zeolite, to the best of our knowledge, for the first time. In comparison to micrometer-sized zeolite A, nanometer-sized zeolite A can rapidly accommodate a larger amount of Cs ions into the zeolite crystal structure, owing to its high external surface area. Nanometer-sized zeolite is a promising candidate for the removal of radioactive Cs ions from polluted water. Our QCM study on Cs adsorption uptake behavior provides the information of adsorption kinetics (e.g., adsorption amounts and rates). This technique is applicable to other zeolites, which will be highly valuable for further consideration of radioactive Cs removal in the future.

Molecular cavity nanoarchitectonics for biomedical application and mechanical cavity manipulation

The design, synthesis, and functions of cavity structures have been paid much attention in supramolecular chemistry and related nanotechnology. Not limited to simple inclusion phenomena, the manipulation of cavity structures and functions are essential for stimuli-responsive functions. In addition, more advanced functions require regulation of mutual interaction, cooperative actions and harmonized actions between cavity units. With this background, a novel concept of cavity nanoarchitectonics is explained here with recent research examples. In the initial parts of this highlight, molecular cavity manipulations, mainly using modified cyclodextrins for biomedical applications, are exemplified. In these examples, molecular-level architectonics (molecular decoration) and small-scale supramolecular nanoarchitectonics are used to improve properties for pharmaceutical applications and cancer therapy. The later part of this highlight introduces future challenges in cavity nanoarchitectonics. Based on designed constructions of cavity networks and arrays, macroscopic mechanical motions can lead to cavity manipulations for drug delivery and molecular capture. From biomedical applications to mechanical cavity manipulation, the great potential and possibilities of cavity nanoarchitectonics are demonstrated in this highlight.

Chiroptical Control in Helical Receptor–Anion Complexes

Dimers of appropriately arranged anion-responsive π-conjugated moieties form helical structures by interaction with chiral anions. Terphenyl-bridged dimers of dipyrrolyldiketone boron complexes show chirality induced by binding l-amino acid anions, as observed by circular dichroism (CD) and circularly polarized luminescence (CPL). The preferred configurations of helical structures depend on the geometries of the terphenyl spacer moieties.