Ryuhei Nishiyabu

Supramolecular sensor for cancer-associated nitrosamines.

A supramolecular assay based on two fluorescent cucurbit[n]uril probes enables the recognition and quantification of nitrosamines, including cancer-associated nitrosamines, compounds that are difficult to recognize. The cross-reactive sensor leverages weak interactions and competition among the probe, metal, and guest, yielding high information density in the signal output (variance) and enabling the recognition of structurally similar guests.

Near-Infrared Absorbing Boron-dibenzopyrromethenes that Serve As Light-Harvesting Sensitizers for Polymeric Solar Cells

Hexylthiophene-conjugated boron-dibenzopyrromethenes with benzo[1,3,2]oxazaborinine rings, 1, that absorb near-infrared light with relatively high molecular extinction coefficients have been synthesized. The incorporation of 3-hexylthiophene-conjugated dye 1a at a blend ratio of 5 wt % into a polymeric solar cell based on a P3HT/indene-C(70) bisadduct (IC(70)BA) bulk heterojunction structure improved power conversion efficiency from 3.7 to 4.3%. The present work suggests that well-defined near-infrared absorbing BODIPY analogues can potentially be used as photosensitizers in polymeric solar cells.

Sensing of carboxylate drugs in urine by a supramolecular sensor array.

A supramolecular sensor array consisting of eight chemosensors embedded in a hydrogel matrix was used to sense carboxylate drugs. The discriminatory power of the array has been evaluated using principal component analysis and linear discriminant analysis. The eight-member sensor array has been shown to accurately identify 14 carboxylates in water with 100% classification accuracy. To demonstrate the potential for practical utility in the physiological environment, analysis of carboxylate drugs in human urine was also performed achieving 100% correct classification. In addition, the array performance in semiquantitative identification of nonsteroidal anti-inflammatory drugs has been investigated, and the results show that the sensor array is able to differentiate six typical nonsteroidal anti-inflammatory drugs at concentrations of 0.5-100 ppm. This illustrates the potential utility of the designed sensor array for diagnostic and environmental monitoring applications.

Boron–dibenzopyrromethene-based organic dyes for application in dye-sensitized solar cells

Novel boron–dibenzopyrromethene dyes with thienyl-cyanoacrylic acid units were synthesized and characterized for application in dye-sensitized solar cells (DSSCs); the dyes feature intense absorption bands in the longer wavelength region with λmax values of 647 nm (e = 1.57 × 105 M−1 cm−1) for 1, which has two anchoring units, 660 nm (e = 1.09 × 105 M−1 cm−1) for regioisomer 2, and 644 nm (e = 1.39 × 105 M−1 cm−1) for 3, which has a single anchoring unit. Density functional theory (DFT) analysis revealed that these absorption properties are mainly characterized by intramolecular charge transfer from the dibenzopyrromethene core to the thienyl-cyanoacrylic acid unit that depend on both the number of anchoring groups and the position of the thienyl-cyanoacrylic acid unit on the isoindole ring. The relationship between the chemical structures and cell properties of these dyes was investigated. Although the short circuit photocurrent density (Jsc) value of a 1-loaded cell is larger than that of a 3-loaded cell, which reflects the results of the incident photon-to-charge carrier efficiency (IPCE) spectra, the 1-loaded cell has a lower open circuit voltage (Voc) and fill factor (FF). Accordingly, overall power-to-current conversion efficiencies of 5.24 and 5.48% were obtained for a 1-loaded cell and 3-loaded cell, respectively, under 100 mW cm−2 AM1.5G simulated light. On the other hand, the cell containing butterfly-shaped regioisomer 2, which showed improved intramolecular charge transfer, has an overall power-to-current conversion efficiency of 6.06%; this value is the highest published for BODIPY dyes even though the sensitizer does not contain any strong donor units, such as arylamines.

Boronate self-assemblies with embedded Au nanoparticles: preparation, characterization and their catalytic activities for the reduction of nitroaromatic compounds

Sequential boronate esterification of benzene-1,4-diboronic acid with pentaerythritol induced hierarchical molecular self-assembly to produce mono-dispersed flower-like microparticles. ATR-FT-IR, PXRD, 13C-CP-MAS and 11B-DD-MAS NMR spectra indicate that the particles consist of zigzag-shaped packing structures of polymeric 2,4,8,10-tetraoxa-3,9-diboraspiro[5.5]undecane. Au nanoparticles (Au NPs) with a mean diameter of 2.7 nm were successfully deposited on the microparticles by the deposition reduction (DR) method. It is noteworthy that the resulting novel hybrids exhibited an efficient catalytic activity for the reduction of nitroaromatic compounds; in particular, high chemoselectivity in the hydrogenation of 4-nitrostyrene to the corresponding aniline was attained without reduction of the vinyl bond. Careful investigation of the catalyst suggested a synergistic effect between Au NPs and the boronate support in the selective hydrogenation. These findings strongly suggest that boronate self-assemblies are advantageous as support materials for preparation of heterogeneous catalysts based on polymer–Au hybrids.

Leveraging material properties in fluorescence anion sensor arrays: a general approach.

As the demand for probes suitable for sensor development increases, investigation of approaches that utilize known successful receptors gains in general importance. This study describes a two-prong approach that can be used as a guide to developing sensors from known receptors. First, the conversion of a simple receptor, calix[4]pyrrole, into a fluorescent probe to establish a ratiometric signal is described. Secondly, the sensors that employ an output from a single ratiometric calix[4]pyrrole probe are fabricated by using poly(ether-urethane) hydrogel copolymers. These hydrogels are designed to absorb, internalize and transport aqueous electrolytes. A sensor array of ten different poly(ether-urethane) matrices with varying comonomer proportions were doped with a single probe and were exposed to eight different anions: acetate, benzoate, fluoride, chloride, phosphate, pyrophosphate, hydrogen sulfide, and cyanide, eight urine samples and anti-inflammatory drugs (NSAIDs). The poly(ether-urethane) matrices comprise different proportions of anion-binding urethane moieties and different hydrophilicity given by the ratio between ethylene glycol ether and butylene glycol ether. This diversity in the hydration behavior provides different environment polarity, in which the recognition and self-assembly processes display enough diverse behavior to allow for unique response of the probe to the analytes. Furthermore, a single probe is shown to recognize eight different aqueous anions and eight urine samples when embedded in ten different polyurethanes in an array that displays 100 % classification accuracy. To demonstrate the potential of the concept for quantitative studies, an estimation of non-steroidal anti-inflammatory drugs ibuprofen and diclofenac in water and in saliva was performed. A limit of detection of 0.1 ppm and a dynamic range of 0.1-0.6 and 0.05-60 ppm was observed, respectively. Given the general difficulty of chemosensors to recognize aqueous anions, the fact that one probe recognizes eight different analytes attests to an enormous effect of the polymer environment on the recognition process. This method could be used to generate a variety of sensor arrays for various analyses including species that are difficult to recognize, such as small-molecule- and inorganic anions.

2,3-Naphtho-Fused BODIPYs as Near-Infrared Absorbing Dyes

2,3-Naphtho-fused boron-dipyrromethenes (BODIPYs) 1a and 1b, which absorb near-infrared light at 740-770 nm with molar extinction coefficients above 10(5) M(-1) cm(-1) in THF, have been synthesized through a palladium(II)-catalyzed direct acylation of N-BOC hydrazones and subsequent Paal-Knorr pyrrole synthesis. Simple benzo-annulation of dibenzo-BODIPY caused a significant red-shift in the absorption. Subsequent intramolecular B,O-cyclization of 1b gave 2, which exhibited an intense absorption band at 830 nm. The structure-optical property relationship has been investigated using theoretical calculations and cyclic voltammetry.

Dansyl-containing boronate hydrogel film as fluorescent chemosensor of copper ions in water

A new type of boronate hydrogel with covalently bound dansyldiethylenetriamine as an indicator has been developed; the gel networks are based on boronate esterification of poly(vinylalcohol) with benzene-1,4-diboronic acid. In this approach, phenylboronic acid-appended N-dansyldiethylenetriamine 1 was newly synthesized to be incorporated into the gel matrix. The resulting gel film showed an absorption band at 336 nm and fluorescence at 511 nm when excited at 340 nm in water. The fluorescence measurements indicated that at neutral conditions using a HEPES buffer, the gel film was selectively quenched after immersion in an aqueous solution of Cu2+ for 30 min. The response had minimal interference from other metal ions such as Na+, K+, Mg2+, Ca2+, Fe3+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, Al3+, and Pb2+, which was noteworthy because dansyldiethylenetriamine alone responds to Hg2+ and Ni2+ in addition to Cu2+ in water. The reversible sensing capability was also evaluated by rinsing the film with an aqueous solution of ethylenediaminetetraacetic acid (EDTA). The gel was found to be a reusable and free-standing film capable of visually detecting Cu2+, providing a simple and expedient tool for on-site monitoring of Cu2+ in environmental applications such as water analysis.

Boronate microparticle-supported nano-palladium and nano-gold catalysts for chemoselective hydrogenation of cinnamaldehyde in environmentally preferable solvents

Dispersible self-assembled boronate polymers can serve as support materials for metal nanoparticle catalysts. As a proof-of-concept, catalytic systems for the chemoselective hydrogenation of cinnamaldehyde (CA) were prepared by the NaBH4 reduction of PdCl42− and AuCl4− in methanol, in the presence of polyethyleneimine (PEI)-coated boronate particles (BPs) composed of polymeric 3-benzo-2,4,8,10-tetraoxa-3,9-diboraspiro[5.5]undecane. The Pd-deposited BP (Pd/BP) showed highly selective catalytic activity for the hydrogenation of CA to hydrocinnamaldehyde (HCA) under 0.1 MPa of H2 at 25 °C in environmentally preferable solvents such as water and methanol. Of particular note is the recyclability of the hydrogenation catalyst in methanol; repeated 4 h reactions afforded HCA in >90% selectivity with a reaction conversion of 100%. On another front, when the corresponding Au catalyst (Au/BP) was used in the hydrogenation in water, a favorable selective reduction of CO to cinnamyl alcohol (CAL) (selectivity ≈ 80%) was obtained with 78% reaction conversion under 0.8 MPa of H2 at 80 °C for 12 h. The potential use of BP-supported metal nanoparticles as green catalysts is discussed.

White-light emitting boronate microparticles for potential use as reusable bright chemosensors in water

The facile surface functionalization of surfactant-free organic microparticles composed of polymeric 2,4,8,10-tetraoxa-3,9-diboraspiro[5.5]undecane allowed us to develop white-light emissive chemosensors for the real-time visual detection of Cu(2+) in HEPES buffer (pH 7.0) due to a synergistic response of fluorophores grafted onto the particles. A detection limit of 15.4 ppb for Cu(2+) in aqueous media and excellent recyclability were also observed.