Hideaki Monjushiro

Optical chirality of protonated tetraphenylporphyrin J-aggregate formed at the liquid–liquid interface in a centrifugal liquid membrane cell

J-aggregation of an achiral hydrophobic porphyrin, 5,10,15,20-tetraphenylporphyrin (H2TPP), at a toluene–4 M sulfuric acid interface was studied by a centrifugal liquid membrane–circular dichroism (CLM-CD) method. It was found for the first time that the exciton chirality sign of the interfacial J-aggregate of H4TPP2+ was affected by the rotational direction of the cylindrical CLM cell: a negative sign for clockwise (CW) rotation and a positive sign for anticlockwise (ACW) rotation. The sign of the measured optical chirality also depended on the injection position of the H2TPP stock solution in the rotating cell. Furthermore, it was observed that the rotational linear velocity of the aqueous phase was faster than that of the toluene phase, when the CLM cell was rotated at 7000 rpm. The effects of rotational direction and sample injection position on the optical chirality were overcome by the effect of chiral counter-ions such as (+)- or (−)-camphorsulfonic anions. From the observed results, a possible mechanism for the generation of the optical chirality of the interfacial J-aggregate was proposed taking into account an interfacial shear force and the spreading direction of H2TPP in the toluene phase.

Ruthenium(II) complexes with the tetradentate 6,6′-bis(oxazolinyl or benzimidazolyl)-2,2′-bipyridine ligand: synthesis, electrochemical properties, and catalytic reactivities

Abstract New ruthenium complexes, trans-[RuX2(L)] (L = tetradentate 6,6′-bis(oxazolinyl or benzimidazolyl)-2,2′-bipyridine; X=halide or cyanide ion) have been synthesized. The present Ru complexes reveal a stable Ru(II/III) oxidation process and exhibit strong MLCT bands around 450–600 nm. The oxidation potential depends on the axial halogeno ligand; the potential increases in the order of X=Cl

Microgravity laser-photophoresis of high density microparticles in water

Abstract Laser-photophoresis is a new technique, which can be used to characterize and separate microparticles in liquids. The photophoretic migration of high density solid particles in water has been observed experimentally for the first time by experiments under microgravity conditions. The photophoretic velocity was measured under microgravity conditions, in order to minimize the effects of density difference and convection. Furthermore, by using an optical cylindrical cell, we could observe the precise photophoretic velocities without the wall-induced drag effect. The apparatus consisted of a cw Nd:YAG laser (532 nm), a microscope, a CCD system, and a remote controlled sample stage and was set in a capsule which was used for a free-fall experiment. All the experimental operations were made externally by using a personal computer. The photophoretic velocities for the particles of carbon, stainless steel, gold plated nickel, and polystyrene in water were determined under microgravity. It was found that the photophoretic efficiencies of the photo-absorbing carbon particles and the photo-reflecting metal particles were much larger than those of transparent particles. The order of magnitude of the observed photophoretic efficiency was carbon>stainless steel>gold plated nickel>polystyrene. The photophoretic efficiencies were compared with those calculated by a Mie scattering theory. It was proved that the Mie scattering theory was useful for the prediction of the photophoretic efficiency of various kinds of particles in water.

Linear dichroism of Zn(II)-tetrapyridylporphine aggregates formed at the toluene/water interface.

The apparent circular dichroism (CD) and the linear dichroism (LD) spectra of the aggregates of achiral zinc(II)-5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP), formed at the toluene/water interface in a centrifugal liquid membrane (CLM) cell, were investigated by comparison with the microscopic CD and LD spectra of a single interfacial aggregate of ZnTPyP about 100 mum in length, measured by a microscope-spectropolarimeter. The interfacial ZnTPyP aggregate showed two types of flat trapezoidal shapes, one had a seedlike core at an edge (type I) and another a needlelike core at an edge (type II). The microscopic CD and LD spectra were observed by varying the angle between the parallel axis of the trapezoidal aggregate and the perpendicular axis of a polarized light for LD. The plot of the CD intensity against the LD intensity for a single aggregate, observed at a given wavelength, showed a rotated elliptical shape with a long axis through the origin, when the orientation angle was changed. From these results, it was concluded that the apparent CD spectra observed by the CLM-CD method were mainly due to the large linear dichroism of the aggregate. Both type I and type II structures showed two transition dipole moments, parallel and perpendicular to the long axis of the structure, but suggesting a more developed J-aggregate in type II structure. AFM measurements showed that the interfacial ZnTPyP aggregate had a multilayer structure, in which the unit monolayer thickness was 1.58 +/- 0.23 nm. Finally, the orientation angle of the interfacial aggregate in the CLM cell was estimated as 41 degrees -44 degrees to the rotating axis of the cell.

Air oxidation of carbon soot generated by laser ablation

Abstract Carbon soot was generated by laser ablation under oxygen-free and regulated-temperature conditions at 300 K and 1500 K. The soot was significantly oxidised by being exposed to air in darkness. The degree of oxidation was determined to be 0.038±0.012 and 0.093±0.009 for the high temperature (HT) soot and the low temperature (LT) soot, respectively, on the basis of elemental analysis, XPS and Karl-Fischer titration. Water physically absorbs on the soot in proportion to the degree of oxidation. TG, TPD and 13C-NMR revealed that there were at least 2 kinds of oxidised states. One of them mainly contributes to CO and CO2 emissions at 420–970 K, while another contributes to CO emission above 770 K. The former is a dominant oxide in the LT soot. On the basis of FT-IR and 13C-NMR spectra, carbonyl groups were confirmed to be one of the major oxidised species in the soot. FT-IR and acid-base titration revealed that the LT soot adsorbed more CO2 than the HT soot did. The adsorbed CO2 contributes to the acidic property of the soot. The soot is paramagnetic as well as conductive. C1s and Auger photoelectron spectra of the soot were neither graphite-like nor diamond-like. The air oxidation is discussed in relation to unique structures and formation mechanisms of the soot.

Measurement of dielectrophoretic mobility of single micro-particles in a flow channel

A new device to measure the dielectrophoretic mobility alpha of a single micro-particle in a micro-flow system has been proposed. From the velocity analysis of the micro-particle flowing between a pair of parabolic electrodes, the value of alpha could be obtained.

Electrochemical properties of dinuclear Ru complex Langmuir-Blodgett films towards molecular electronics

Abstract A novel amphiphilic Ru dinuclear complex, [(L 18)Ru(tppz)Ru(L18)]4+, was synthesized and was introduced as a redox-active complex in Langmuir-Blodgett (LB) films, where L18= 2,6-bis(2′-(1′-octadecylbenzimidazolyl))pyridine and 2,3,5,6-tetrakis(2′-pyridyl)pyrazine (tppz). This Ru complex leads to a stable LB film formation and monolayers of this complex were transferred on glass and indium-tin oxide (ITO) substrates. The π-A isotherm indicates an orientation of the complex with Ru-Ru axis nearly parallel to the substrate surface. Two succesive one-electron oxidation processes were observed for the LB monolayer on ITO electrode.

Total internal reflection second-harmonic generation spectrometer system optimized for the liquid/liquid interface

An apparatus for optical second-harmonic generation (SHG) spectroscopy at the liquid/liquid interface has been constructed. The fundamental laser beam of 780–920nm was irradiated to the interface under the total internal reflection condition, and the interfacial second-harmonic spectrum was obtained during 390–460nm. An automatically wavelength-tuned Ti:Sapphire laser was employed in this study, and it was simultaneously controlled with other peripheral instruments, such as monochromator. The acquisition time per spectrum with 2nm interval was less than 30min. The measurement of SHG spectrum of water-soluble porphyrin adsorbed at the heptane/water interface was demonstrated. The solvatochromic shift of the SHG maximum of the adsorbed porphyrin was ascribed to the less polar environment around the porphyrin molecule at the interface in comparison with the aqueous phase.

Micro-particle sorting by Newton-ring device.

A Newton-ring micro-particle sorter was constructed from a small convex lens and a flat glass. The sub-micrometer gap between them was controlled by a piezo-actuator and utilized for the fractionation of very small amounts of micro-particles in liquid.

Identification of uranium(V) in photoreduced uranyl compounds by photoacoustic spectroscopy

Abstract The photoacoustic spectra of uranium(V) in powdered samples have been measured and assigned on the basis of both the time-course of the spectra and comparison with the absorption spectra of photochemically or electrochemically reduced uranyl ions in solution. Uranium(V) is relatively stable in the photoreduced uranyl complex in the crystalline state.