The mechanism of water photooxidation reaction at atomically flat n-TiO(2) (rutile) surfaces was investigated in aqueous solutions of various pH values, using photoluminescence (PL) measurements. The PL bands, which peaked at around 810 and 840 nm for the (110) and (100) surfaces, respectively, were assigned to radiative transitions between conduction-band electrons and surface-trapped holes (STH), [Ti-O=Ti(2)](s)+, formed at triply coordinated (normal) O atoms at the surface lattice. The PL intensity (I(PL)) decreased stepwise with increasing solution pH, namely, it sharply decreased at around pH 4, near the point of zero charge of TiO(2) (about 5), and then rapidly decreased to zero near pH 13. The first sharp decrease around pH 4 is attributed to the increased rate of nucleophilic attack of a water molecule to a hole at a site of surface bridging oxygen (Ti-O-Ti), the density of which increases with increasing pH. The nucleophilic attack is regarded as the main initiating step of the water oxidation reaction in low and intermediate pH. The high PL intensity at low pH is ascribed to slow nucleophilic attack owing to a very low density of Ti-O-Ti by its protonation at the low pH. The second sharp decrease near pH 13 is attributed to formation of surface anionic species like Ti-O- which can be readily oxidized by photogenerated holes. Interrelations between reaction intermediates proposed in this work and those reported by time-resolved laser spectroscopy are discussed.

Multiple internal reflection infrared spectroscopy was applied to in situ investigations of surface intermediates of photocatalytic reactions on nanocrystalline TiO(2) films in contact with aqueous solutions. UV irradiation in the presence of dissolved O(2) caused the appearance of new bands peaked at 943, 838, and 1250-1120 cm(-)(1) together with intensity changes in other bands. Investigations of influences of the solution pH, the presence or absence of hole and electron scavengers, and isotopic H(2)O --> D(2)O exchange on the spectral changes have revealed that the primary step of photocatalytic O(2) reduction is the formation of the surface peroxo species, Ti(O(2)), giving the 943 cm(-)(1) band, probably with the surface superoxo species, TiOO., as a precursor, in neutral and acidic solutions. The surface peroxo species is then transformed to the surface hydroperoxo, TiOOH, giving the 838 and 1250-1120 cm(-)(1) bands, by protonation in the dark. This is, to our knowledge, the first direct in situ spectroscopic detection of primary intermediates for the photocatalytic O(2) reduction in aqueous solutions. On the basis of the assignment, a possible reaction scheme for various processes of the photocatalytic O(2) reduction is proposed, which is in harmony with other spectral changes induced by the UV irradiation.

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Proton pump inhibitors (PPIs) are widely used in the treatment of acid-related diseases. However, several unmet medical needs, such as suppression of night-time acid secretion and rapid symptom relief, remain. In this study, we investigated the pharmacological effects of 1-[5-(2-fluorophenyl)-1-(pyridin-3-ylsulfonyl)-1H-pyrrol-3-yl]-N-methylmethanamine monofumarate (TAK-438), a novel potassium-competitive acid blocker (P-CAB), on gastric acid secretion in comparison with lansoprazole, a typical PPI, and SCH28080 [3-(cyanomethyl)-2-methyl,8-(phenylmethoxy)imidazo(1,2-a)pyridine], a prototype of P-CAB. TAK-438, SCH28080, and lansoprazole inhibited H ϩ ,K ϩ -ATPase activity in porcine gastric microsomes with IC 50 values of 0.019, 0.14, and 7.6 M, respectively, at pH 6.5. The inhibitory activity of TAK-438 was unaffected by ambient pH, whereas the inhibitory activities of SCH28080 and lansoprazole were weaker at pH 7.5. The inhibition by TAK-438 and SCH28080 was reversible and achieved in a K ϩ -competitive manner, quite different from that by lansoprazole. TAK-438, at a dose of 4 mg/kg (as the free base) orally, completely inhibited basal and 2-deoxy-D-glucose-stimulated gastric acid secretion in rats, and its effect on both was stronger than that of lansoprazole. TAK-438 increased the pH of gastric perfusate to a higher value than did lansoprazole or SCH28080, and the effect of TAK-438 was sustained longer than that of lansoprazole or SCH28080. These results indicate that TAK-438 exerts a more potent and longer-lasting inhibitory action on gastric acid secretion than either lansoprazole or SCH28080. TAK-438 is a novel antisecretory drug that may provide a new option for the patients with acid-related disease that is refractory to, or inadequately controlled by, treatment with PPIs.

The influence of the atomic-level structure of electrode surfaces on electrochemical oscillations has been studied in a system of H2O2 reduction on Pt electrodes in acidic solutions. A current oscillation of another type, named oscillation E, has been found to appear for an atomically flat single-crystal Pt(111) electrode, in addition to previously reported oscillations, named oscillations A and B. Oscillation E does not appear for atomically flat Pt(100), Pt(110), polycrystalline Pt, and Pt(111) with atomically nonflat surfaces. Mathematical simulation by use of a model including an autocatalytic effect of adsorbed OH for dissociative adsorption of H2O2, as a possible explanation, has reproduced the appearance of oscillation E, as well as observed correlations between the appearance of oscillation E and the magnitudes of H2O2-reduction current and “negative” resistance. It is discussed that an efficient autocatalytic mechanism works at the atomically flat Pt(111) surface, which is responsible for the appearance of oscillation E at this surface.

Essentially atomically smooth (100) and (110) n-TiO(2) (rutile) surfaces were prepared by immersion of commercially available single-crystal wafers in 20% HF, followed by annealing at 600 degrees C in air. The obtained surfaces were stable in aqueous solutions of pH 1-13, showing no change in the surface morphology on an atomic level, contrary to atomically flat surfaces prepared by ion sputtering and annealing under UHV. The success in preparation of the atomically smooth and stable n-TiO(2) surfaces enabled us to reveal clear crystal-face dependences of the surface band edges and hole reactivity in aqueous solutions.

The work functions for atomic-level regulated (HF-treated and annealed) n-TiO 2 (110) and (100) surfaces with a clear step and terrace structure, together with photoetched ones, were investigated with a scanning auger microprobe (SAM) using 0.05 wt % Nb-doped TiO 2 . Analysis of the threshold region of the secondary electron spectra has revealed that the work function of the atomic-level regulated TiO 2 (100) surface (about 4.13 eV) is 0.07 eV lower than that of the (110) surface. The photoetching of the atomic-level regulated TiO 2 (110) surface in 0.05 M H 2 SO 4 decreased the work function by 0.07 eV, but that of the atomic-level regulated (100) surface did not cause any change. Both results were in harmony with previously reported results that the flat-band potential for the (110) surface is about 0.09 V more positive than that for the (100) surface and that the (100) face was selectively exposed by the photoetching, irrespective of original surfaces. The investigation of the work function at local areas of the atomically flat TiO 2 (110) surface after a half of it was photoetched showed that the work function continuously changed from the value for the (110) face to that of the (100) face as the photoetching proceeded. It was suggested that the SAM was a powerful method to investigate the work function of the solid surface with complex morphology.

A novel method to synthesize Au nanoparticles via a reductive reaction in an ionic liquid containing Au3+ ions was demonstrated using a low-energy electron beam irradiation technique; Au nanoparticles (approximately 122 nm) formed by the incident electron beam were well dispersed and crystallized; this finding opens up the possibility that the use of electron beams and ionic liquids is of key importance in the development of new fabrication techniques for nanomaterials.