Mitsunori Sukigara

Photoinduced charge separation in liposomes containing chlorophyll a. I. Photoreduction of copper(II) by potassium ascorbate through liposome bilayer containing purified chlorophylla a

Photosensitivity of dispersion of phosphatidylcholine bilayer liposomes containing purified chlorophyll alpha was examined. The reduction of Cu(II) in the solution outside liposomes was observed upon illumination with visible light under anaerobic condition by means of ESR. The rate of photoreduction was significantly increased by a reductant, potassium ascorbate, localized in the solution of the opposite side of the membrane. The aciton spectrum of the reduction agreed with the absorption spectrum of chlorphyll a in the dispersion. The amount of bleach chlorophyll a was negligible compared with that of reduced (Cu(II). These facts lead to the conclusion that the potoinduced redox reactions at both the membrane-solution interfaces are coupled with each other through the bilayer of each liposome. Kinetic analysis of the reactions based on a possible reaction scheme was carried out and some of the kinetic parameters were determined.

Effect of the Electrical Field on the Phase Transition in Solutions of Rod-Like Particles I: Optical Observations

Abstract Effect of electrical field on the temperature of phase transition between the isotropic liquid phase and liquid crystal phase in dioxane solution of poly-γ-benzyl-L-glutamate (PBLG), ranging in concentration from 11.0 to 15.0 wt % was examined by means of polarizing microscope measurements. Shift of the transition temperature, δT was found to be essentially proportional to square of the field strength applied in the range of less than 500 volts/cm. A semi-empirical equation which gives a linear relationship between the transition temperature and square of the field strength is derived taking the structure of the solution into consideration and compared with the experiments.

Photoinduced charge separation in liposomes containing chlorophyll a. II the effect of ion transport across membrane on the photoreduction of Fe(CN)63

Abstract The reduction of Fe(CN)63− in the solution of outside liposome incorporating chlorophyll a was observed upon illumination with visible light under unaerobic condition. The photoreduction of Fe(CN)63− was enhanced by the presence of ion carrier, such as carbonylcyanide m-chlorophenylhydrazone, in the dispersion. The action spectrum of the photoreduction agreed with the absorption spectrum of chlorophyll a in liposome bilayer. The carrier-mediated proton transport was also observed upon illumination, occuring in the direction to compensate the excess charge produced by the photoinduced electron transport through the bilayer.

AC impedance theory for surface states at a semiconductor—liquid junction

Abstract The ac impedance theory at a semiconductor—liquid junction indicates that the addition of redox couples to an electrolyte solution makes it impossible to determine properties of the surface states from capacitance and conductance measurements. In particular, the surface-state capacitance disappears when the electron exchange between the surface states and redox couples is dominant compared with the electron exchange between the surface states and the conduction band.

Surface states at semiconductor‐liquid junction

Surface states at a junction of n‐TiO2 and aqueous solution were studied by means of the capacitance measurement. It appeared that, from the relation between surface‐state capacitance and electrode potential, surface states with state density of 8×1012 cm−2 were located at 0.5 eV below the bottom of the conduction band. The electron capture cross section of 2.0×10−19 cm2 was obtained from the frequency dependence of surface‐state capacitance. The effect of the UV irradiation of TiO2 on the surface‐state capacitance suggested that this surface state originated from adsorbates.

Surface states at the TiO2/H2O interface under UV illumination

Abstract The donor-like surface states at the TiO 2 /H 2 O interface were detected by measuring the capacitance under UV illumination. The surface states were located 0.65 eV below the bottom of the conduction band of TiO 2 . The density of surface states increased by increasing the light intensity. The surface states were observed under UV illumination but disappeared in the dark

Electrochemil uminescence of pyrene in acetonitrile

Summary The e.c.l. of pyrene in acetonitrile has been studied using a controlledpotential double-step method, and the following results were obtained: (1) the electrode potential regions where the emission was observed were in agreement with those of cation and anion formation; (2) the e.c.l. spectrum had two main bands at 400 nm and 470 nm and a subsidiary band at the longer wavelength; (3) the peak wavelengths of the two main bands concided with those of the monomer and excimer fluorescences of pyrene; (4) the intensity ratio of the two main bands is linearly dependent on the concentration of pyrene. From these results, we conclude that the e.c.l. of pyrene is most probably composed of the emission bands of monomer and excimer fluorescences of pyrene including some impurity emission at longer wavelengths, and that a considerable amount of the excimer is produced directly by the electron transfer reaction between cation and anion radicals of pyrene.

Electrochemiluminescence of 9,10-diphenylanthracene-halogen ion systems

Influence of halide ions (Cl−, Br−, I−) on the electrochemiluminescence (ecl) of 9,10-diphenplanthracene (DPA) is studied by using controlled-potential double-step method. It is confirmed that the ecl begins to appear at the anodic potential corresponding to the potential of the first anodic half-wave potential of each halide ion and that, passing through an intensity maximum, it disappears at more positive potential. Similarly, when the cathodic potential is changed, the ecl appears at the first cathodic half-wave potential of DPA and disappears at more negative potential than the second half-wave potential of DPA. These facts indicate that the ecl must be due to the reaction between oxidised species of halide ions (presumably trihalide ions) and monovalent DPA anion radicals. The mechanism for the formation of the excited singlet state of DPA is reasonably explained by assuming a reaction scheme containing a mono-halogenated DPA radical as an intermediate.

Effect of Electrical Field on the Phase Transition of Rod-like Polymer Solution

Abstract The effect of external electrical field on the phase transition from isotropic to liquid crystalline phase in rod-like polymer solution was discussed by applying the lattice model. Free energy of each phase and the chemical potential of rod-like molecule and that of solvent in each phase were calculated. With these results a phase diagram was obtained. Application of an electrical field resulted in narrowing the region of phase separation and shifting the phase transition concentration at a lower value.

A capacitance relaxation method for studying surface states at the semiconductor-liquid junction

Abstract For the investigation of surface states at the semiconductor-liquid junction, we have newly developed a “Capacitance relaxation method” in which the frequency dependence of −ωd C p /dω is analyzed where C p and ω are the parallel equivalent capacitance of the space charge layer and an angular frequency, respectively. By employing this method, one can detect surface states with a state density larger than 5×10 9 eV −1 cm −2 . The advantage of this method is that the high sensitivity is not lowered by the leakage current.