Shoichiro Yoshida

Optical effect of the substrate on the anomalous absorption of aggregated silver films

The optical effect of the substrate on the anomalous absorption of aggregated silver films is taken into account in terms of the dipole interaction between an island particle and its mirror image in the substrate. The previously reported relation 2F|+F⊥<1, which holds for the observed values of the apparent depolarizing factors of island particles for an electric field parallel to (F|) and perpendicular to (F|) the substrate surface, is explained by the effect. The parameters characterizing the film structure are optically evaluated by stretching the substrate, and are compared with those evaluated from electron micrographs.

Anomalous optical absorption of aggregated silver films

A simple equation for the anisotropic dielectric constant of a metal island film is derived and applied to the ellipsometric measurement for an aggregated silver film. The experimental result can be explained when the inter-island dielectric constant is around unity. It is concluded that, in spite of the theoretical prediction that 2F∥+F⊥ = 1, the relation 2F∥+F⊥<1 holds for the observed values of the apparent depolarizing factors for electric fields parallel (F) and perpendicular (F⊥) to the substrate surface.

Bifunctional Langmuir-Blodgett film for enzyme immobilization and amperometric biosensor sensitization

Abstract A Langmuir-Blodgett (LB) film consisting of octadecylamine as the binding site for the enzyme molecule, an amphiphilic ferrocene derivative as the electron mediator, and octadecanol as the matrix for these molecules was deposited on a hydrophobized tin oxide (SnO 2 ) electrode. Glucose oxidase (GOx) was then covalently immobilized on the film via glutaraldehyde, and the GOx electrode thus obtained worked as an amperometric glucose sensor based on the oxidation of hydrogen peroxide liberated by the enzymatic reaction. The sensitivity of this sensor was about twice as high as that of a GOx electrode prepared with the same LB film as above but without the ferrocene. The sensitizing effect of ferrocene was attributed to its capability of electron mediation between hydrogen peroxide and the SnO 2 electrode.

Effect of the dipole interaction between island particles on the optical properties of an aggregated silver film

Abstract If an aggregated metal film is assumed to consist of ellipsoidal particles of the same shape, the complex dielectric constant e of the film is represented by the equation e−e = q e i −e a 1+ ƒ(e i −e a ) e a ƒ=ƒ 0 +β where ea and ei are the dielectric constants of the medium and the island material, respectively, q is the packing factor, ƒ0 the depolarizing factor of the particles and β the term that arises from the dipole interaction. Assuming that the island particles are distributed in a square array of lattice parameter α with mean thickness dw, β is estimated approximately to be −0.36 d w α for an electric field parallel to the substrate. If e1 ( = e1 − ie2) is known as a function of wavelength, ƒ can be determined from the transmittance spectrum, because Im(e), the absorption, shows a sharp maximum when ƒ = (−e 1 + e a )e a [(e 1 − e a ) 2 + e 2 2 ] . However, it is usually impossible to determine ƒ0 and β separately. In our work separation was attempted by changing α by isotropic expansion of the substrate. When the rate of square expansion is denoted by r, ƒ is expressed by ƒ 0 − ( 0.36d w α )r − 3 2 . Using the value of bulk silver as ei, ƒ was calculated for two values of ea. Since the ƒ versus r − 3 2 relation was approximated well by a straight line, ƒ0 and α could be determined from the intercept on the ordinate and the slope of the straight line, respectively.

The strain effect on the electrical conduction in discontinuous gold films

Abstract Discontinuous gold films prepared by vacuum evaporation were strained and the strain coefficient γ of the electrical resistance was measured. It was observed that γ increases with resistance, which suggests that the activated tunnelling model is an appropriate one for explaining the conduction mechanism in discontinuous metal films.

Characterization of adsorption gels prepared from plant biomaterials

The adsorption of Pb(II), Cu(II), Cd(II), and Zn(II) by new biomaterial gels synthesized in cross-linked reactions from agricultural wastes such as lemon, yuzu (Citrus junos), and coffee was investigated. Experimental data of adsorption equilibrium from the heavy metal solutions correlate well with Freundlich isotherm equations. The adsorption mechanism involved acid ion-exchange reactions between the heavy metal and the carboxylic acid of pectic acid in the lemon and yuzu gels, improving the amounts of Pb(II), Cu(II), Cd(II), and Zn(II) adsorbed onto the lemon and yuzu gels by approximately 5- and 6-fold, respectively. The maximum adsorption capacities of the yuzu and lemon gels for Pb(II) and Cu(II) were high. Among the biomaterial gels investigated, the lemon gel possessed the highest complexation ability with these heavy metals. In addition, the adsorption of nitrate ion (NO3−) was especially strong by the Pb(II)-adsorbed lemon gel, as shown by IR absorption spectrophotometry. These results indicate that lemon and yuzu gels can function, as new “green chemistry” adsorbents, which can be generated from recycled wastes, involve zero emissions, and provide effective recovery of precious resources.

Aggregation of Chlorophyll a′ in Aqueous Methanol

An aggregate of chlorophyll a′ (Chi a′, C132‐epimer of ChI a) formed in a methanovwater (40160, vol/vol) mixed solvent was examined by visible absorption, circular dichro‐ism (CD), fluorescence and resonance Raman spectrosco‐pies in relation to its possible involvement in the core of photosystem I reaction center. The Chl a′ aggregate exhibited a sharp, double‐peaked absorption spectrum (690 and 715 nm) accompanied by an intense, conservative CD signal. The fluorescence excitation polarization spectrum showed that the doublet results from the exciton splitting in a single aggregate species. Time‐dependent changes in the spectroscopic properties clearly point to a simple transformation process from one molecular species to another, though a minor component appears to coexist. This conclusion was supported also by the principal multicom‐ponent spectral estimation analysis of the transients of absorption spectra. The species formed at the initial stage is most probably a T‐shaped dimer or oligomer, which is then gradually converted into the final major product, presumably a stacked dimer. In both of these states, the Chl molecules are linked together via direct coordination of the C13’keto carbonyl oxygen onto the Mg atom of neighboring molecules, as suggested by almost identical resonance Raman spectra in ordinary and deuterated methanovwater mixed solvents. The stacked dimers probably further associate to form a colloidal state in this solvent system. Based on these results, a model for the Chl a′ aggregation is proposed.

Kinetics of partition between aqueous solutions of salts and bulk liquid membranes containing neutral carriers

The relationship between the rates of transport of alkali metal cations through a bulk chloroform liquid membrane containing polynactin or dibenzo-18-crown-6 as neutral carrier and the rates of uptake and release of cation at the interfaces between aqueous phase and membrane phase were investigated. The fluxes of cations through the membranes and cation-distribution ratios between aqueous solution and membrane were strongly dependent on the anions present. The distribution ratio increased in the following order: Cl− < NO3− < SCN− < ClO4−, and the flux increased in the same order as the distribution ratio, except for the fluxes of KSCN and KClO4 with polynactin. In the case of polynactin, the flux of KSCN was comparable to that of KClO4 in spite of the fact that KSCN was less soluble in the membrane than was KClO4. In order to clarify the cause of this apparently contradictory behavior, the apparent rate constants of uptake and release of potassium were determined independently using an equation derived from Ficks first law of diffusion. From the rates of uptake and release, it was suggested that the overall rate of cation transport through the membrane was dependent on the rate of release rather than that of uptake.

Kinetics of Ion Transport by Macrocyclic Carriers in Liquid Membrane Systems

Abstract The relationship between the extractability of a metal ion (K+ or Pb2+) and the rate of its transfer by neutral macrocyclic carriers (dibenzo-18-crown-6, dicyclo-hexano-18-crown-6, 18-crown-6, and polynactin) was investigated in chloroform membrane systems. The experimentally determined apparent rate constants are compatible with the diffusion-limited process. Both the rate of ion uptake and the rate of ion transport depend crucially on the extractability of the metal ion rather than on the apparent rate constant.

The effect of complex stability on the rates of transport, uptake, and release of ions by macrocyclic carriers in liquid membrane systems

Abstract Several macrocyclic carriers were used in the measurements of the rates of transport, uptake, and release of potassium picrate in a chloroform membrane system. For the carrier cryptand 2.2.2, the rates were determined for each of the other alkali metal picrates (Na+, Rb+ and Cs+). With an increase in the stability constant of the metal—carrier complex, the rate of ion uptake, Ju, increased and the rate of ion release, Jr, decreased. Among the carriers studied, 18-crown-6 (18C6), whose Ju and Jr values were not small, gave a maximum rate of transport of potassium picrate through the liquid membrane. The rate of transport decreased with stability constant values higher or lower than that for the K+—18C6 complex. For cryptand 2.2.2 complexes with high stability, the Jr value was very small compared with the Ju value and decreased in the reverse order to that for the uptake, Na+ > Rb+ > K+, in which the rate of transport decreased. These results suggest that the rate of transport is controlled by the rate of uptake in the region of low stability constant and by the rate of release in that of high stability constant.