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______________________________________________________________________The molar amounts of defective sites (M d ) in several titanium(IV) oxide (TiO 2 ) powders were determined using photoinduced reaction of electron accumulation in deaerated aqueous solutions containing sacrificial hole scavengers and subsequent reduction of methylviologen to its cation radical. The measurements of pH dependence of typical anatase and rutile TiO 2 powders showed that these defective sites were of electronic energy just below the conduction band edge of TiO 2 in ranges of 0-0.35 V for anatase and 0-0.25 V for rutile. A linear relation of M d with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that M d could be a quantitative parameter of recombination between a 2 photoexcited electron and a positive hole. The tendency for M d to increase, but not proportionally, with increase in the specific surface area suggested that these defective sites are mainly located near the external surfaces of TiO 2 particles. A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and M d revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO 2 powders in this reaction system. ______________________________________________________________________ IntroductionPolycrystalline titanium(IV) oxide (TiO 2 ) has been widely used as semiconductor photocatalysts in liquid-solid as well as in gas-liquid regimes 1-9 because of its sufficient photostability in various circumstances, nontoxicity for environments, and potent ability to induce various types of redox reactions. 10,11 It is well known that photocatalytic activity strongly depends on bulk and surface physicochemical properties of the TiO 2 powder, such as the kind of crystal structure, 12-15 surface area and particle size, [16][17][18][19][20] Experimental SectionMaterials. Several kinds of titanium oxide (TiO 2 ) powders, those from commercial sources (Degussa P-25, Merck, Ishihara CR-EL, and Hombikat UV-100), reference catalysts supplied from the Catalysis Society of Japan (JRC-TIO-1, -2, -3, and -5), and powders synthesized by the HyCOM method 6,28,29 followed by a calcination at 1073 K under O 2 (designated as HyCOM (1073)), were used. In a separate experiment to quantify the amount of accumulated electrons by another chemical reaction, a deaerated aqueous solution containing colloidal platinum particles was added to the photoirradiated suspension under Ar instead of the addition of MV 2+ . After shaking the mixture for a few minutes, the gas phase was analyzed using a gas chromatograph (GC, Shimadzu, GC-8A, equipped with an MS-5A column (GL Sciences) and a TCD detector). Measurement of the amount of accumulated electrons in photoirradiated TiOPP-DR spectroscopy. Details of PP-DR spectroscopy were reported previously 40,41 and are briefly summarized as follows. The light source consisted of a mode-lo...

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SummaryUsing transgenic rice seedlings expressing a ®re¯y luciferase (luc) gene under the control of a rice CAB (chlorophyll a/b binding protein) promoter, we demonstrated how light affects circadian clocks in the transcription of the CAB gene. Rhythmic luc expression was observed for more than 5 d under constant light and dark (DD) conditions after light/dark entrainment. After a light pulse was applied at different time points in DD various temporal patterns of CAB gene expression were individually observed. We ®rst examined two distinct properties related to the entrainment mechanism of the circadian clock:¯uence-rate dependence of free-running periods (FRPs) and phase resetting by a light pulse. Although¯uence-rate dependent shortening of FRP was demonstrated, the FRP in DD was almost equal to that in constant light of a middle¯uence-rate, indicating that this¯uence-rate dependence may not fully describe the entrainment of the circadian clock in rice. Typical phase responses of the circadian clock by a single light pulse were also observed at the transcriptional level in rice seedlings. Thus, the phase resettings upon the light/dark transitions of daily cycles may be suf®cient to explain the entrainment mechanisms of rice. We have further demonstrated that, in addition to having a gating effect to acute response, a light pulse can activate the circadian clock-controlled CAB1R gene expression at the ®rst circadian peak in a phase-dependent manner. This suggests that light activates circadian clock activity in the diurnal CAB gene expression under daily light/dark cycles.