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A semiempirical molecular orbital calculation (MOPAC-PM3) was applied to investigate the effects of crystal arrangement, phenyl capping, and dimer formation for CdS nanoparticles. Molecular structures of possible polynuclear cadmium complexes were classified into four categories, zinc blende (ZB) tetrahedron, ZB cuboctahedron, wurtzite (W), and ZB−W mixture, and the last one is found to be the most favorable formation. The first excitation energies for these cluster complexes were calculated as the HOMO−LUMO energy difference and compared with the absorption peak energy reported in the literature. The electronic effect in polynuclear Cd thiophenolate complexes was discussed in terms of the fractionated density of states as an anti-π-bond interaction between the benzene π-orbital and the S 3p-orbitals. The dimer formation did not affect significantly the excited state of the nanoparticle dimer based on the estimation of intramolecular electron interaction.

We have investigated the effect of H2O2 on the behavior of O2^•- and OH^• produced in photocatalysis of aqueous TiO2 suspensions by means of luminol chemiluminescence probing and terephthalic acid fluorescence probing, respectively. The reduction of O2 by photoinduced conduction band electrons (e^-) was increased by the addition of H2O2, since the consumption of photoinduced valence band holes (h⁺) in the oxidation of H2O2 caused the repression of e^-−h⁺ recombination. After the end of the light irradiation, the amount of O2^•- decreased based on the fractal-like kinetics at the heterogeneous surface of the TiO2 particle. The decay process might be caused by trapped h⁺, which cannot react with water and then remains on the TiO2 particle after the irradiation. The energy level of the trapped h⁺ was estimated to be above the redox potential of SCN^-, since it could react with the adsorbed H2O2 and I^- ions but not with other ions such as SCN^-, Br^-, and Cl^-. The formation rate of OH^• was increased by the addition of H2O2, indicating the direct reduction of adsorbed H2O2 on the TiO2 surface. The quantum efficiencies of the formation of O2^•- and OH^• were increased by 3.0 and 3.6 times by the addition of 0.2 mM H2O2.

The effect of calcination on photocatalytic activities was studied for highly crystalline TiO2 powder, which was synthesized by the method of hydrothermal crystallization in organic media (HyCOM). The productions of O2^•-and H2O2 under ambient condition were monitored by means of luminol chemiluminescence probing. The amount of produced O2^•- was decreased with the calcination at lower temperatures in parallel to the decrease of inner Ti³⁺ signal observed at 77 K by ESR spectroscopy. The formation route for H2O2 under aerated condition is mainly two-step O2 reduction in the presence of oxidizable organic molecules such as luminol. Oxidization activity was significantly high when HyCOM-TiO2 was calcined at higher temperatures, 973−1173 K, as monitored by the amount of oxidized luminol. The observation in ESR measurements and other evidences indicated that the luminol is oxidized via hydroxyl radicals rather than the direct oxidation by photoinduced surface trapped holes.

The ratio of the amount of carboxymethyl radicals to that of methyl radicals was measured in situ for the photocatalytic decomposition of acetic acid over platinized TiO2 powder in deoxygenated aqueous solution at room temperature and discussed in connection with the contribution of ·OH radicals in the oxidation process. Since carboxymethyl radicals are formed only by indirect oxidation, the radical ratio was used to measure the indirect oxidation via ·OH radicals. Thus, ratios of the indirect oxidation were estimated for five commercially available TiO2 photocatalysts, in addition to the several properties of the powders. The ratios were found to be sensitive to the characteristics of the TiO2 catalysts. The larger the amount of surface OH group, the more likely the indirect oxidation via ·OH radicals occurs. This could be attributed to the difference in the structures of the surface trapped holes elucidated by the ESR measurements of the corresponding TiO2 powder at 77 K.

CrkL is an SH2 and SH3 domain-containing adaptor protein implicated in pathogenesis of chronic myelogenous leukemia. Here, we demonstrate that overexpression of CrkL enhances the erythropoietin (Epo)- or interleukin (IL)-3-induced activation of Elk-1 and the c-fos gene promoter activity in 32D/EpoR-Wt cells. Moreover, the Epo-induced activation of ERK1 and ERK2 was augmented and prolonged in cells inducibly overexpressing CrkL. A moderate increase in Epo-induced activation of JNK was also observed in cells overexpressing CrkL. Overexpression of C3G enhanced the Elk-1 activation synergistically with CrkL, while a C3G mutant lacking the guanine nucleotide exchange domain showed an inhibitory effect. Studies using a dominant negative Ha-Ras mutant demonstrated that the Elk-1 and ERK2 activation enhanced by CrkL and C3G was dependent on Ras. Consistent with this, the Epo-induced activation of Ras was augmented in cells inducibly overexpressing CrkL. Most importantly, a CrkL mutant defective in the SH2 or N-terminal SH3 domain showed an inhibitory effect on the Epo-induced activation of ERK2. These data indicate that the CrkL-C3G complex plays a role in Epo- or IL-3-induced, Ras-dependent activation of the Raf/ERK pathway leading to the activation of Elk-1 and the c-fos gene transcription.

Photocatalytic properties of TiO2 aqueous suspension were analyzed by means of the chemiluminescent probe method, which enables us to monitor superoxide ions (^•O2^-) and hydrogen peroxide (H2O2) in the reaction system. The amount of produced ^•O2^- is independent of the surface properties of TiO2, while H2O2 is formed significantly for smaller particles with large amount of surface hydroxyl groups. The amount of produced ^•OH radicals was estimated from the effect of Cl^- ions on the ^•O2^- formation and found to be large for the TiO2 having a large amount of surface hydroxyl groups. This difference is explained to originate from the different structure of hole intermediates, based on the ESR measurements for these powders at 77 K.

Active oxygen species formed on TiO2 film photocatalysts in air were examined by use of a chemiluminescence method. Under relatively strong UV light irradiation, 15 mW cm^-2, two types of active oxygen species formed on the TiO2 surface were observed after the interception of the excitation light, i.e., one with a shorter lifetime, ca. 3 s, and another with a longer lifetime, ca. 50 s, which may correspond to superoxide (O2^-). On the contrary, under relatively weak UV light irradiation, 1 μW cm^-2, only the long-lived species, O2^-, was observed. The concentration of O2^- on the TiO2 surface was saturated even under weak UV illumination, while the short-lived species was not. We suggest that O2^- is deactivated mainly by an electron transfer to surface defects or vacancy sites on the TiO2 surface. This deactivation reaction proceeds almost independently of coexisting active species.

Quantized ZnS particles were prepared and isolated from aqueous solution with a capping agent, thioglycerol. The absorption peak of the particles was located at 259−260 nm, and the diameter was estimated to be 1.5−1.6 nm from X-ray diffractograms. Their excitation energy agrees well with that calculated with the finite depth potential well model. ESR spectra were measured for the quantized and bulk ZnS particles at 77 K under photoirradiation. For the quantized ZnS, only surface hole radicals were observed, while several kinds of radicals consisting of trapped electron, inner, and surface holes were observed for the bulk ZnS. A high activity of photocatalytic reactions for quantized semiconductor particles may arise from a large number of radicals photoproduced at the surface.

A chemiluminescent probe, luminol, was successfully applied to monitoring superoxide ions (O2^•-) and hydrogen peroxide (H2O2) produced on photocatalytic reaction in aqueous TiO2 suspension. Two chemiluminescent reactions were distinguished from the decay profile after the end of the irradiation, and the reaction mechanism was analyzed. The fast decay component gives information about O2^•- and the slow one provides the amount of H2O2. The rate constant for the reaction of O2^•- with luminol was found to be 1 × 10⁴ M^-1 s^-1. The amount of O2^•- during the irradiation on TiO2 in alkaline solution could be estimated to be on the order of 10^-13 M. Detection of H2O2 in concentrations as small as 10^-9 M was demonstrated in the photocatalytic water oxidation.

The adsorption and photodecomposition of ethanol that was employed as a model substrate of organic pollutants were investigated in the presence of adsorbed water with TiO2 by solid-state ¹H NMR spectroscopy in order to obtain information about the actual photocatalytic reaction sites of organic pollutants on TiO2 photocatalysts. Consequently it was revealed that ethanol molecules in practical conditions as contaminants were firmly captured in mobile physisorbed water layers to be photodecomposed to CO2 and water after photoillumination, suggesting that actual photocatalytic reactions should proceed in physisorbed water layers.