Takeaki Iida

Selective electroacatalysis for CO2 reduction in the aqueous phase using cobalt phthalocyanine/poly-4-vinylpyridine modified electrodes

Abstract The electrocatalytic reduction of CO 2 in aqueous electrolytes by a cobalt phthalocyanine (CoPc)/poly-4-vinylpyridine (PVP) membrane coated on a graphite electrode was studied. Enhanced catalysis for CO 2 electroreduction at more positive potential and of greater efficiency was achieved with the present system than with the system using pure CoPc as catalyst, whereas both coatings were found to catalyze proton reduction as well. The electrochemical behavior of the PVP-bound CoPc was examined at different pH, taking the normally adsorbed CoPc as reference. The greatly enhanced and sustained catalytic activity of the CoPc/PVP membrane for CO 2 electroreduction in water is discussed in terms of electron donation of the pyridine group to the central cobalt by an axial coordination and a proton-exchanging property of the PVP and the increased local concentration of CO 2 in the PVP layer owing to their hydrophobic and/or acid-base interaction. A reaction scheme for the electrocatalytic reduction of CO 2 by CoPc is proposed.

Synthesis of secondary face-to-face cyclodextrin dimers linked at each 2-position

Abstract A useful method for the synthesis of secondary face-to-face cyclodextrin dimers retaining the glucoside form was achieved.

Integration of bienzymatic disaccharide sensors for simultaneous determination of disaccharides by means of light addressable potentiometric sensor

Abstract Three saccharides such as sucrose, maltose and glucose were simultaneously determined by the use of the light addressable potentiometric sensor (LAPS). One-chip integration of three saccharide sensors was performed by means of a glucose sensor using glucokinase. By the addition of oligosaccharide hydrolases such as invertase and α- d -glucosidase to the glucose sensors, the disaccharide concentrations were determined by variation of glucose concentrations. All the enzymes employed were thermostable enzymes because of their durability for repeated measurements. Clear distinctions of the response patterns were obtained among the three saccharide samples. Since the simplified LAPS system was limited in number of sensing spots, the complicated chemometrics such as partial least squares (PLS) was not always indispensable. Therefore, a simpler method such as multiple linear regression (MLR) was able to be applied to the mixture analysis under a low-concentrated sample in order to simplify the analysis. Thus, we treated the glucose as a key product in the regression equation optimized for the bienzymatic biosensensing process. The multivariate calibrations of the samples were simultaneously illustrated by using the estimated local glucose concentration. Finally, more than 0.7 of correlation coefficients were obtained between the true and the predicted sample concentrations although the linear approximation was not able to correct a few kinds of inhibition.

Novel type cholinesterase sensor based on SPV measurement technique

Abstract The surface photovoltage (SPV) technique was applied to the fabrication of a novel type biosensor based on immobilized cholinesterase. Two types of cholinesterase were utilized, acetylcholinesterase and butyrylcholinesterase, depending on the types of substrates. On the surface of the silicon wafer the cholinesterase layers were immobilized by using 3-aminopropyltriethoxysilane and glutaraldehyde. Characteristics of the sensor were studied in phosphate-buffered saline containing 15 mM NaCl and 1 mM phosphate buffer, pH 7.0. The detection limits of the substrates were 9.0×10−7 M, 2.7×10−6 M, and 4.1×10−6 M for butyrylthiocholine iodide, acetylcholine iodide, and acetylcholine chloride, respectively. The activity of the cholinesterase was inhibited by the presence of alkaloids such as physostigmine and neostigmine.

Regio- and stereoselective reduction of intramolecular N-strapped porphyrins to phlorins

Abstract Intramolecular N -strapped porphyrins were successfully reduced to N -alkyl phlorins regio- and stereoselectively.

Stability of tetragonal zirconia in Molten fluoride salts

The phase stability of tetragonal zirconia specimens in various molten salts was studied by a corrosion test. The corrosion test was examined using 3 mol% Y2O3-partially stabilized ZrO2(3 Y-PSZ) with high thermal phase stability. XRD results indicated that the phase transformation of 3 Y-PSZ from tetragonal (t) to monoclinic (m) phase (t→m transformation) was observed only in molten fluoride salts. when 3 Y-PSZ was dipped into molten Na2SiF6 salt, more than 90% tetragonal phase on the surface of 3 Y-PSZ transformed into monoclinic one in 5 min-dipping. The corrosion depth accompanied by the t→y m transformation reached 300μm for 200 min-dipping. From the results of corrosion tests with alkaline metal fluorides, the rate of t→m transformation on the surface of a sintered body and the rate of depth increase from surface to inside depended on the ionic radius of univalent rations. In the same test with PbF2, the sintered body was heavily attacked, but no remarkable t→m transformation was observed on the surface of the sintered body. Raman spectra for the surface of test samples gave dispersed bands characteristic of the tetragonal phase. The result indicated that Pb restrains tetragonal particles. The corrosion depth for 3 Y-PSZ-Al2O3 was the same as that for 3 Y-PSZ. EPMA results indicated that the region enriched with Si or Na was equivalent to the t→m transformation range over 90% by XRD analysis. Remarkable t→m transformation is considered to be influenced by these Cations. The activation energy was measured to estimate the t→m transformation rates The activation energies of 3 Y-PSZ, 3 Y-PSZ-Al2O3 and 3 Y-PSZ-Cr2O3 were 12, 44 and 154kJ/mol, respectively. The t→m transformation depth of 3 Y-PSZ-Cr2O3 was the smallest among the three 3 Y-PSZ complexes. 3 Y-PSZ-Cr2O3 had high phase stability in molten fluoride salts.

The relationship between the photocurrent of the chloroplast - methyl viologen photoelectrochemical system and its activities of photosystems I and II.

gations1) that the inactivation of the photosynthetic electron transport systems (PETS) of the isolated chloroplasts is mainly attributable both to photochemical inactivation and to thermal destabilization. The study reported here is the relationship between the decrease of the photocurrent for the photoelectrochemical cell, of which the anolyte was madeup of isolated chloroplasts and methyl viologen, and the changes in the activities of photosystem I (PS-I) and photosystem II (PS-II) in PETS of the chloroplasts. The procedures for the preparation of Class II chloroplasts from fresh spinach leaves6* and the determination of the chlorophyll concentration7) were essentially similar to those previously described.5) Glucose oxidase (EC 1. 1.3.4) was purchased from Sigma and 3-(3,4-dichlorophenyl)1,4-dimethylurea (DCMU) was a generous gift from