Satoshi Tsukahara

Acid-catalyzed interfacial complexation in the extraction kinetics of palladium(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

The extraction kinetic mechanism of palladium(II) in acidic aqueous solution with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in toluene was investigated by the high-speed stirring method, along with the complexation kinetics in the aqueous phase by the stopped-flow method. The rate-determining step in the extraction at pH<3 was the complexation between the Pd(II) complexes, PdCl(n−2)−n (n=2–4), and the protonated 5-Br-PADAP adsorbed at the interface. The rate constants at the interfacial complexation were the same order of magnitude as those in the aqueous phase. The extraction rate was accelerated by a decrease in pH causing an increase in the interfacial concentration of the protonated 5-Br-PADAP. The acid-catalyzed interfacial reaction revealed the advantageous property of 5-Br-PADAP; it could be adsorbed at the interface by protonation at the diethylamino group under the acidic condition of pH<2, but did not lose reactivity to the metal ion since its pyridyl group was not protonated.

Chirality induction and amplification in methylene blue H-aggregates viaD- and L-phenylalanine pre-adsorbed on the tungsten oxide nanocolloid surface

In the methylene blue (MB)–phenylalanine (Phe)–tungsten(VI) oxide (WO3) colloid ternary aqueous solution, the MB H-aggregates, which could recognize the chirality of D- and L-Phe, were formed and investigated by means of UV-Vis absorption and CD spectroscopy. These results demonstrate a chirality transfer and amplification from only the pre-adsorbed Phe molecules to MB aggregates formed on the WO3 colloid surface via non-covalent interactions.

Microscope measurements for the transient formation of W/O emulsions of sodium bis(2-ethylhexyl) sulfosuccinate in the dodecane/water interfacial region.

The present study investigated the transient formation of water-in-oil (W/O) emulsions of sodium bis(2-ethylhexyl) sulfosuccinate (aerosol OT, AOT) in a dodecane/water interfacial region and the anomalous uptake of water in the dodecane phase by in situ bright-field optical microscopy and water concentration measurements in detail. The hydrodynamic radius of the individual W/O emulsions in the dodecane phase was determined to be 0.1-1.2 μm from the analysis of their diffusion behavior; they are much larger than common W/O microemulsions (a few nanometers in radius). At first, they were formed spontaneously in the dodecane/water interfacial region without shaking, and they diffused away into the dodecane phase. Then, almost all of them vanished at the interface by fusion. Their number and the water concentration in the dodecane phase increased first and then decreased gradually. The formation mechanism was discussed with estimated concentration profiles of AOT and water molecules, which suggests that larger W/O emulsions of 0.01-0.44 μm in radius can be formed in the dodecane phase near the interface (within 2 μm) because the concentration of AOT becomes lower than that of water there.

Isomer recognizing adsorption of palladium(II)-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol with diazine derivatives at the toluene-water interface

Abstract The isomer recognizing reaction of palladium(II)–2-(5-bromo-2-pyridylazo)-5-diethylaminophenol–chloride complex (PdLCl) with diazine derivatives at the toluene–water interface was investigated by a high-speed stirring method. The chloride ion in PdLCl was substituted by a neutral diazine and the PdL+–diazine complex was completely adsorbed at the interface without extraction into the toluene phase. PdL+-pyridazine derivative complexes showed much higher stability at the interface than pyrimidine and pyrazine derivative complexes. This result could be correlated with the change in the dipole moment of the diazine derivative after bonding to PdL+. A linear relationship was obtained between the logarithmic interfacial formation constants (log βi) for PdL+–diazine derivative complexes and the logarithmic ratio of the distribution constant (KD) to the acid-dissociation constant (Ka) for the diazine derivatives.

Faraday rotation dispersion microscopy imaging of diamagnetic and chiral liquids with pulsed magnetic field.

We have constructed an experimental setup for Faraday rotation dispersion imaging and demonstrated the performance of a novel imaging principle. By using a pulsed magnetic field and a polarized light synchronized to the magnetic field, quantitative Faraday rotation images of diamagnetic organic liquids in glass capillaries were observed. Nonaromatic hydrocarbons, benzene derivatives, and naphthalene derivatives were clearly distinguished by the Faraday rotation images due to the difference in Verdet constants. From the wavelength dispersion of the Faraday rotation images in the visible region, it was found that the resonance wavelength in the UV region, which was estimated based on the Faraday B-term, could be used as characteristic parameters for the imaging of the liquids. Furthermore, simultaneous acquisition of Faraday rotation image and natural optical rotation image was demonstrated for chiral organic liquids.

Single-molecule lactonization of octadecylrhodamine B at a liquid-liquid interface.

The total internal reflection laser fluorescence microscope method was used to observe the lateral diffusion of a single octadecylrhodamine B (C(18)RB) molecule at the toluene-water interface. The interfacial diffusion constant of single fluorescent cation C(18)RB(+) was obtained from the maximum residence time in a small observation area with pH <2. For pH >3, the maximum residence time was remarkably shortened, indicating that single fluorescent zwitterion C(18)RB(±) rapidly converted to the nonfluorescent lactone at the interface. The lactonization rate was completed within 0.13 ms at the toluene-water interface but slowed to 67 ms at an interface saturated with dimyristoylphosphatidylcholine.

Single Molecule Diffusion and Metal Complex Formation at Liquid/Liquid Interfaces

Honaker and Freiser reported the first fundamental kinetic mechanism of chelate extraction in 1962 [1]. They elucidated that the rate-determining step for the extraction of divalent metal ions with dithizone was the formation of their 1:1 complexes in the aqueous phase. They proposed that a simple batch extraction method could be used as an alternative method of the complicated stopped-flow method, which was the only method available at the time, to measure such a fast reaction rate. Since the 1970s, hydrometallurgy has been developed in many countries, and extensive kinetic studies on the metal extraction have been conducted in an effort to improve the extraction rate as well as to develop effective and reusable extractants. The extractants used in hydrometallurgy are required to be highly hydrophobic and readily coordinative with various metal ions. On the basis of the interfacial adsorptivity of the extractant, Flett et al. [2] expected an interfacial reaction mechanism in the chelate extraction process. There was, however, no experimental evidence to prove the interfacial mechanism directly [3]. The solvent extraction process of metal ions inherently depends on the mass transfer across the interface and the reaction that occurs at the interfacial region. Therefore, the elucidation of the kinetic role of the interface was very important in order to clarify the extraction mechanism and to control the extraction rates. In 1982, Watarai and Freiser invented the high-speed stirring (HSS) method [4,5]. Figure 10.1 shows the schematic drawing of the HSS method [6]. When a two-phase system is vigorously stirred in a

Kinetics for acid-dissociation of tetraphenylporphinetetrasulfonate in the ground state measured by laser photolysis relaxation method

Transient absorption spectra (TAS) for tetraphenylporphinetetrasulfonate (tpps4−) and its diprotonated form (H2tpps2−; protonated at the two N-atoms of the porphyrin-ring) after laser photolysis (532 nm, pulse width 6 ns) showed the generation of their respective triplet states in aqueous solutions. From the analysis of TAS for tpps4− and H2tpps2− at pH 2.05 and 7.41 (I, 0.01; 25u2006°C), molar absorption coefficients of tpps4− and H2tpps2− in their triplet states were obtained. On the other hand, as the triplet tpps4− was deactivated, H2tpps2− in the triplet state was generated through the protonation of the triplet tpps4− in the pH range of 5.0–6.0 (I, 0.01; 25u2006°C). This indicated nthat the triplet tpps4− was more basic than the ground state. As H2tpps2− in the triplet state was deactivated, an excess amount of H2tpps2− in the ground state was successively generated. The excess H2tpps2− faded to attain the acid-dissociation equilibrium in the ground state again. The total decay curves were successfully fitted to triple-exponential decay functions, and the rate constant for acid-dissociation of H2tpps2− in the ground state was determined as (3.3u2006±u20060.4)u2006×u2006105 s−1, independent of pH. From this value and the acid-dissociation constants of H2tpps2−, the overall acid-dissociation kinetics of tpps4− was proposed.