Chiral Supramolecular Organogel Constructed Using Riboflavin and Melamine: Its Application in Photo-Catalyzed Colorimetric Chiral Sensing and Enantioselective Adsorption.

The synthesis of a chiral supramolecular organogel via the hierarchical helical self-assembly of optically active riboflavin and melamine derivatives is described herein. Owing to the photocatalysis of riboflavin and the supramolecular chirality induced in the helically stacked riboflavin/melamine complex, the gel is observed to act as a light-stimulated chiral sensor of optically active alcohols by detecting the change in color from yellow to green. The gel also served as an efficient chiral adsorbent, enabling optical resolution of a racemic compound with high chiral recognition ability.

Important Roles of Water Clusters Confined in a Nanospace as Revealed by a Synchrotron X-ray Diffraction Study.

States of water molecules confined in a nanospace designed by montmorillonite (negatively charged silicate layer) and charge compensating benzylammonium were investigated. Caffeine was used as a probe because of its compatibility for the fine structure of the interlayer water. Powder synchrotron radiation X-ray diffraction (SXRD) and adsorption isotherms of the water vapor revealed a metastable structure of bimolecular water layers (2WLs) in the interlayer space. Water molecules readily penetrated to expand the interlayer space to 0.56 nm. The interlayer space did not increase further even in the presence of excess water. According to the isosteric heat of water, the expansion was limited because of moderate hydration as forming 2WLs. Caffeine molecules replaced a part of the water molecules in the 2WLs to expand the interlayer space to 0.65 nm. Time-resolved SXRD with an accumulation time of 500 ms revealed that the interlayer expansion reached a steady state within a few minutes. The caffeine intercalation proceeded, involving a change in the molecular orientation that increased the contact area of the caffeine molecules. The interlayer expansion was limited in all the solvents examined (mixtures of water with methanol, ethanol, acetone, and tetrahydrofuran), while the packing density of the incorporated caffeine was maximized in the absence of an organic solvent. The water molecules confined in the interlayer space acted as an actuator to accommodate a large quantity of amphiphilic molecules by adapting the nanostructure, which was achieved by releasing the confined water molecules.

Why Do Carbonate Anions Have Extremely High Stability in the Interlayer Space of Layered Double Hydroxides? Case Study of Layered Double Hydroxide Consisting of Mg and Al (Mg/Al = 2).

Layered double hydroxides (LDHs) are promising compounds in a wide range of fields. However, exchange of CO32- anions with other anions is necessary, because the CO32- anions are strongly affixed in the LDH interlayer space. To elucidate the reason for the extremely high stability of CO32- anions intercalated in LDHs, we investigated in detail the chemical states of CO32- anions and hydrated water molecules in the LDH interlayer space by synchrotron radiation X-ray diffraction, solid-state NMR spectroscopy, and Raman spectroscopy. We found the rigidity of the network structure formed between the CO32- anions, hydrated water molecules, and the hydroxyl groups on the metal hydroxide layer surface to be a crucial factor underlying the stability of CO32- anions in the LDH interlayer space.

Optical Humidity Sensing Using Transparent Hybrid Film Composed of Cationic Magnesium Porphyrin and Clay Mineral.

A transparent hybrid film composed of cationic magnesium porphyrin and clay mineral was developed, and its chromic behavior depending on relative humidity (RH) was investigated. The hybrid film was obtained via intercalation of magnesium porphyrin into clay film; magnesium porphyrin was intercalated into the interlayer spaces of the clay mineral without aggregation. The absorption spectra of the hybrid film showed red shifts compared to the aqueous solution of magnesium porphyrin because of the π-conjugated system extension with coplanarization of the meso-substituted pyridinium group and porphyrin ring. The absorption maximum of the hybrid film was gradually shifted to a shorter wavelength, and the color of the hybrid film was changed with increasing RH. The X-ray diffraction measurement suggested that the basal space of clay was expanded with increasing RH, indicating that the interlayer space of clay was expanded by water adsorption, and the spectral shift was induced by the change in coplanarization degree between the porphyrin ring and meso-substituted pyridinium groups.

Photoluminescence by Intercalation of a Fluorescent ß-Diketone Dye into a Layered Silicate.

A ß-diketone dye was packed into the two-dimensional nanospace of a synthetic smectite (Sumecton SA), which is a cation-exchangeable layered silicate, to induce strong emission owing to molecular packing of the dye. An emissive dye, 1-(4-methoxyphenyl)-3-(4-pyridyl)-1,3-propandione, was prepared through a Claisen condensation reaction; the dye exhibited aggregation-induced emission, which is enhanced emission owing to clustering of molecules to form aggregates in poor solvents or in the solid state. The dye was nonemissive in solution. However, strong green emission was observed because of the restriction of molecular motion when the protonated dye was accommodated into the interlayer nanospace of the silicate layers through cation-exchange reactions. The restricted motion was confirmed by the smaller nonradiative relaxation rate constant obtained by time-resolved luminescence and quantum yield measurements. A moderate dye packing (0.11 mmol/g) in the interlayer space is important to obtain enhanced emission, whereas the intercalation of a large amount of dye (0.27 mmol/g) resulted in concentration quenching. Therefore, the interlayer space of the layered silicate used here was responsible for the strong emission because of moderate packing of the accommodated ß-diketones.

Dielectric Mismatch Mediates Carrier Mobility in Organic-Intercalated Layered TiS2.

The dielectric constant is a key parameter that determines both optical and electronic properties of materials. It is desirable to tune electronic properties though dielectric engineering approach. Here, we present a systematic approach to tune carrier mobilities of hybrid inorganic/organic materials where layered two-dimensional transition-metal dichalcogenide TiS2 is electrochemically intercalated with polar organic molecules. By manipulating the dielectric mismatch using polar organic molecules with different dielectric constants, ranging from 10 to 41, the electron mobility of the TiS2 layers was changed three times due to the dielectric screening of the Coulomb-impurity scattering processes. Both the overall thermal conductivity and the lattice thermal conductivity were also found to decrease with an increasing dielectric mismatch. The enhanced electrical mobility along with the decreased thermal conductivity together gave rise to a significantly improved thermoelectric figure of merit of the hybrid inorganic/organic materials at room temperature, which might find applications in wearable electronics.

Intercalation of a surfactant with a long polyfluoroalkyl chain into a clay mineral: unique orientation of polyfluoroalkyl groups in clay layers.

Eight novel polyfluorinated surfactants (C(n)F(2n+1)CONH(CH2)2 N(+)(CH3)2C16H33 Br(-); abbreviated as CnF-S, where n = 1, 2, 3, 4, 5, 6, 8, 10) were synthesized and their intercalation into cation-exchangeable clay was investigated. All of the polyfluorinated surfactants intercalated in amounts exceeding the cation exchange capacity (CEC) of the clay. The C4F-S and C5F-S surfactants exhibited intercalation up to 480% of the CEC as a saturated adsorption limit. On the basis of X-ray analysis, CnF-S surfactants intercalated between clay nanosheets to form a bilayer structure in which the surfactant molecules tilt at an angle of ∼60° with respect to the clay surface. The saturated adsorption limits and layer distances differed between surfactants with short (n = 1, 2) and long (n = 3-10) perfluoroalkyl chains. For long-chain surfactants, their saturated adsorption limits were independent of the perfluoroalkyl chain length and the layer distances systematically increased with increasing perfluoroalkyl chain length. These results suggest that the microscopic orientation differed between the short and long chains. X-ray analysis showed that the long-chain surfactants orient the perfluoroalkyl chains at a tilt of 41 ± 5° with respect to the clay layer. This value was in good agreement with polarized IR measurements of 42 ± 2° for this angle.

High density intercalation of porphyrin into transparent clay membrane without aggregation.

Cationic porphyrin was successfully intercalated into transparent clay membrane by developing the new strategy for the sample preparation conditions. When water:ethanol = 1:2 (v:v) was used as solvent for porphyrin penetration process, high density intercalation of porphyrin into the clay membrane was achieved. In the interlayer space, porphyrin molecules do not aggregate owing to intercharge distance matching effect (size-matching effect), even at high density condition. Judging from XRD and absorption measurements, the orientations of the porphyrins in the clay layers should be almost parallel to the clay nanosheet as monolayer. Because the fluorescence quantum yield did not depend on its loading level, it is turned out that intercalated TMPyP in the clay film keeps the photoactivity even under the high density conditions.

Behavior of chiral induction from polysilsesquioxanes bearing chiral and ammonium groups to anionic pyrene derivatives.

The behavior of chiral induction from ladder-like polysilsesquioxanes (R60- and S60-PSQs) bearing chiral and ammonium side-chain groups (compositional ratio = ca. 60:40) to the anionic pyrene derivative, 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PTSNa4), was investigated. The circular dichroism (CD) spectra of PTSNa4/(R60- and S60-PSQs) mixtures in methanol exhibited reverse peaks at 230-250, 280-290, and 310-370 nm, which were assigned to PTSNa4 and indicated that the achiral PTSNa4 molecule had chirality induced from the chiral PSQs. In addition, it was found that an eximer of PTSNa4 was formed by hybridization with the chiral PSQs, i.e., the emission peaks not only due to a monomer state at 385 and 408 nm but also due to an eximer at 460-520 nm were observed in the fluorescence spectrum excited at 377 nm. This result suggests that the negatively charged PTSNa4 formed an eximer along the positively charged side-chain ammonium groups of PSQs. To investigate the influence of the structures of the pyrene derivatives on chiral induction behavior, the CD measurements of the mixtures of R60- and S60-PSQs in methanol with different pyrene derivative, 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine), were also performed. It was found that the intensities of the absorptions for the pyanine solutions were lower than those for PTSNa4 solutions. These results suggest that the point-symmetry of the pyrene derivatives influences the level of chiral induction. Therefore, the point-symmetry of pyrene derivatives is an important factor for determining the behavior of chiral induction from chiral PSQs to these compounds.

Creation of a Highly Active Small Cu-Based Catalyst Derived from Copper Aluminium Layered Double Hydroxide Supported on α-Al2 O3 for Acceptorless Alcohol Dehydrogenation.

A highly dispersed carbonate-intercalated Cu2+ -Al3+ layered double hydroxide (CuAl LDH) was created on an unreactive α-Al2 O3 surface (CuAl LDH@α-Al2 O3 ) via a simple coprecipitation method of Cu2+ and Al3+ under alkaline conditions in the presence of α-Al2 O3 . A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl2 O4 on the surface of α-Al2 O3 (CuAlO@α-Al2 O3 ) after calcination at 1073 K in air, as confirmed by powder X-ray diffraction (XRD) and Cu K-edge X-ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in-situ temperature-programmed synchrotron XRD (tp-SXRD). The layered structure of CuAl LDH@α-Al2 O3 completely disappeared at 473 K, and CuO or CuAl2 O4 phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α-Al2 O3 catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1-phenylethanol dehydrogenation. The results suggested that Cu0 was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species.

Ultra-sensitive detection of pyridine in water using zinc porphyrin incorporated in a transparent hydrophobic film.

In this study, we investigated the axial coordination reaction between pyridine and zinc meso-tetra(4-sulfonatophenyl)porphyrin (ZnTPPS) incorporated in a transparent layered double hydroxide (LDH) film modified with 1-decanesulfonate (C10S) in an aqueous solution. The apparent equilibrium constant ([Formula: see text]) of the axial coordination reaction between pyridine and ZnTPPS incorporated in the transparent ZnTPPS/C10S/LDH film was approximately 260 times that of the corresponding reaction in an aqueous solution. The hydrophobisation of the LDH interlayer space by C10S, which led to the elimination of water molecules surrounding ZnTPPS and enabled the accumulation of pyridine molecules, was responsible for such a significant increase in the apparent [Formula: see text] value. The developed film can detect pyridine in aqueous solutions with ultra-high sensitivity in the order of 10-5 mol/L through changes in the colour tone, which is comparable to the molecular detection ability of insect antennae. The sensing response was also observed at pyridine concentrations as low as 10-9 mol/L.

Photoluminescence Gas Sensing by Fluorescein-Dye Anions/1-Butanesulfonate/Layered Double Hydroxide Hybrid Materials under Humid Environment Conditions.

In this study, we investigated the photoluminous spectroscopic behavior of hybrid powder incorporating both anionic fluorescein dye (AFD) and 1-butanesulfonate (C4S) with layered double hydroxide (LDH) in the presence of NH3 or NO2 gas under various relative humidity conditions. In the presence of NH3 gas, drastic photoluminescence enhancement from the LDH/AFD/C4S hybrid was observed at relative humidity (RH) ≥ 40% when the NH3 reached a certain concentration. Meanwhile, the LDH/AFD/C4S hybrid was exposed to NO2 gas at various relative humidity conditions, and the following behavior was observed: At RH ≥ 60%, the photoluminescence (PL) intensity from the hybrid gradually decreased as NO2 concentration increased. Therefore, the LDH/AFD/C4S hybrid investigated in this study is inferred to be suitable for optical NH3/NO2 sensor devices, which can be used in humid air.

Photocatalytic Hydrogen Evolution over Exfoliated Rh-Doped Titanate Nanosheets.

Various amounts of Rh-doped titanate nanosheets (Ti3NS:Rh(x), where x is doped amount) were prepared to develop a new nanostructured photocatalyst based on metal oxide compounds that can split water to produce H2 under sunlight. Ti3NS:Rh(x) was obtained by acid exchange, intercalation, and exfoliation of Rh-doped layered sodium titanate compound (Na2Ti3-x Rh x O7). A new energy gap was found in the diffuse reflection spectrum of the Ti3NS:Rh(x) colloidal suspension solution; this new energy gap corresponds to electrons in the 4d level of Rh3+ or Rh4+, which are doped in the Ti4+ site. A photocatalyst activity of Ti3NS:Rh(x) for H2 evolution in water with triethylamine (TEA) as an electron donor was investigated. The appropriate amount of Rh doping can improve the photocatalytic activity of Ti3NS for H2 evolution from water using triethylamine (TEA) as a sacrifice agent. The reason was related to the rich state of Rh3+ or Rh4+ doped in the Ti4+ site of Ti3NS. Doping Rh 1 mol % of Ti, Ti3NS:Rh(0.03) shows the H2 evolution rates up to 1040 nmol/h, which is about 25 times larger than that of nondoped Ti3NS under UV irradiation (>220 nm) and 302 nmol/h under near-UV irradiation (>340 nm). These results show that the development of new nanostructured photocatalyst based on Rh-doped titanate compounds that can produce H2 under near-UV irradiation present in sunlight was a success.

Synthesis, photodynamic activities, and cytotoxicity of new water-soluble cationic gallium(III) and zinc(II) phthalocyanines.

The cationic Ga(III) and Zn(II) phthalocyanines carrying N-methyl-pyridinium groups at eight peripheral ß-positionshave been synthesized. These complexes are highly soluble in dimethyl sulfoxide (DMSO) and moderately soluble in water and phosphate buffered saline (PBS); both Ga(III)Cl and Zn(II) complexes have shown no aggregation in water up to 1.2 × 10-4 and 1.5 × 10-5 M, respectively. A higher water-solubility of Ga(III)Cl complex as compared to Zn(II) complex is ascribed to the presence of an axially coordinated chloride. The spectroscopic properties, photogeneration of singlet oxygen (1O2), and cytotoxicity of these complexes have been investigated. The absolute quantum yields (ΦΔabsolute) for the photogeneration of singlet oxygen using Ga(III)Cl and Zn(II) complexes have been determined to be 4.4 and 5.3%, respectively, in DMSO solution. The cytotoxicity and intracellular sites of localization of Ga(III)Cl and Zn(II) complexes have been evaluated in human HEp2 cells. Both complexes, localized intracellularly in multiple organelles, have shown no cytotoxicity in the dark. Upon exposure to a low light dose (1.5 J/cm2), however, Zn(II) complex has exhibited a high photocytotoxicity. The result suggests that Zn(II) complex can be considered as a potential photosensitizer for Photodynamic therapy (PDT).

Preparation of Stable Silver Nanoparticles Having Wide Red-To-Near-Infrared Extinction.

The synthesis of silver nanoparticles (AgNPs) within the interlayer space of transparent layered titania nanosheet (TNS) films is investigated. A considerable number of silver ions (≈70% against the cation exchange capacity of the TNS) are intercalated in the TNS films using methyl-viologen-containing TNSs as a precursor. The silver ion (Ag+)-containing TNS films are treated with aqueous sodium tetrahydroborate (NaBH4), resulting in a gradual color change to bright blue. Various structural analyses clearly show that crystalline AgNPs are generated within the interlayer space of the TNSs. The NaBH4-treated films show intense and characteristic near-infrared (NIR) extinction spectra up to 1800 nm. The stability of the AgNPs within the TNS against oxygen and moisture is also investigated, and 96% and 82% of the AgNPs remain after standing in air for 1 month and 1 year, respectively. The NIR extinctions of the AgNP-containing TNS films are further extended by employing different preparation procedures, for example, using sintered TNS films as starting materials and irradiating the Ag+-containing TNSs with ultraviolet (UV) light. The obtained AgNP-containing TNS films exhibit photochemical activities in the production of hydrogen from ammonia borane under visible-light irradiation and the decomposition of nitrogen monoxide under UV-light irradiation.

Arsenic recovery from water containing arsenite and arsenate ions by hydrothermal mineralization.

Recovery of arsenic as precipitate of natural mineral from model wastewater containing various initial concentrations and oxidation states of inorganic arsenic oxoanions was investigated by hydrothermal mineralization treatment. The treatment is an earth-mimetic method to produce natural minerals by hydrothermal treatment using Ca(OH)2 as a mineralizer. The treatment of model wastewater containing arsenate ion or mixed aqueous solution of arsenate and arsenite ions by using Ca(OH)2 mineralizer and H2O2 oxidizer was found to precipitate arsenate apatite which is a natural mineral containing high concentration of arsenic. The feature of this treatment was independent on the initial concentration and the oxidation state of arsenic regardless of mixed ratio of arsenate and arsenite ions. Arsenic concentration in the treated-water at the optimum treatment conditions was 0.02 mg/dm3, when treated for the aqueous solution containing 1-2000 mg/dm3 of arsenate or arsenite ions. The precipitate obtained by this treatment was a kind of natural mineral (Johnbaumite), which could be easily reused as resources of arsenic compounds. Therefore, the present hydrothermal mineralization treatment with the Ca(OH)2 mineralizer is an effective technique to recover arsenic from aqueous media.

Electrooptics of beta-FeOOH particle in aqueous media 2. Field-strength dependence of decay and steady-state birefringence, and the hydrodynamic and electrooptic properties.

Steady-state and decay birefringence, expressed in terms of the optical phase retardation per cell length delta/d, was measured on beta-FeOOH in aqueous ionic media at 633 nm and at 25 degrees C by an electric square-pulse technique over a wide range of field strength E to ca. 6 kV/cm. The field-strength dependence of both delta/d and field-free rotational relaxation time tau was determined at the sample concentrations between 0.0011 and 0.055 g/L and in the 0.02-2.0 mM NaCl concentration range. Extrapolation of both delta/d and tau values to infinitely high fields (E(2)-->infinity) could yield birefringence- and weight-average quantities, respectively. Observed tau values were decreased at weak fields but leveled off to ca. 0.3 ms at very high fields due to a slight polydispersity regarding the length and volume of particles. The weight-average relaxation time tau(w) was calculated with Perrin's expressions theoretically from the length, width, and volume of beta-FeOOH particles estimated in the dried state from electron micrograph. These quantities were variously averaged. The size distribution was discussed in terms of observed discrete histogram and theoretical (Weibull and Lansing-Kraemer) distribution functions. The sign of observed delta/d value was always positive. The infinitely high-field (delta/d)(infinity) values and the reduced optical anisotropy factor Delta g/n were evaluated by fitting to theoretical orientation functions. The intrinsic birefringence (n3-n1) could be estimated with the mean refractive index n(p) reported in the literature. For the spindle-shaped particle with an axial ratio of ca. 4, the sign of Delta g/n is always positive, whereas the quantity (n3-n1) was either negative (n(p) > 2.35) or positive (n(p) < 2.05) in sign or nearly zero (ca. n(p) = 2.26), depending critically on the n(p) values.

Lead recovery from PbZrO3 using wet ball-mill technique and hydrothermal synthesis of alpha-zirconium phosphate from wastewater for resource recovery.

Lead recovery from lead zirconate (PbZrO(3)) ceramics was investigated using a wet ball-mill treatment in H(2)SO(4) aqueous solution. Subsequently crystalline alpha-zirconium phosphate (alpha-Zr(HPO(4))(2).H(2)O) was synthesized using a hydrothermal technique in order for the resource recovery of zirconium in the wastewater after the wet ball-mill treatment. A wet ball-mill treatment in 4.5M H(2)SO(4) aqueous solution for 24h was capable of converting more than 99.9% of the Pb initially included in the PbZrO(3) to solid state PbSO(4) with a purity of 98%. On the other hand, the Zr in the PbZrO(3) was dissolved into the acidic solution during the treatment. The Pb and Zr metal elements coexisting in PbZrO(3) were successfully separated by the wet ball-mill technique. Then, resource recovery of zirconium in the wastewater was examined. Crystalline alpha-Zr(HPO(4))(2).H(2)O was synthesized by hydrothermal treatments in 3.1-12.5M H(3)PO(4) aqueous solutions at temperatures of 120-240 degrees C for a duration of 70h. The hydrothermally prepared powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and then they were also evaluated in terms of cation exchange capacity (CEC) measurement and thermogravimetric (TG) analysis.

Precipitation recovery of boron from wastewater by hydrothermal mineralization.

It is well known that boric acid exhibits various toxic effects on plant, animal and human beings even at very low concentrations. Thus, the development of boron-removal technique from wastewater has been intensively investigated. In this study, a new hydrothermal treatment technique was developed to recover boron as recyclable precipitate Ca(2)B(2)O(5).H(2)O from aqueous solutions. As a result, it was found that the hydrothermal treatment using calcium hydroxide as a mineralizer converted boron in the aqueous media effectively into calcium borate, Ca(2)B(2)O(5).H(2)O. In the optimal hydrothermal condition, more than 99% of boron was collected from the synthetic wastewater of 500 ppm. Thus, the present hydrothermal treatment in the presence of calcium hydroxide is recommended as one of the effective techniques to recover boron from aqueous media.

Effect of layer charge density on orientation and aggregation of a cationic laser dye incorporated in the interlayer space of montmorillonites.

Effect of layer charge density of clay on the orientation and aggregation state of a laser dye, oxazine 4, in dye/clay complexes was investigated using a series of layer-charge-controlled montmorillonites as host materials. By the combination of polarized UV-vis spectroscopy and powder X-ray diffraction methods, it was revealed that the higher layer charge caused the formation of higher-order H-aggregates with the molecular axis nearly perpendicular to the silicate layer, and that the basal spacing was mostly governed by the degree of dye aggregation.