The photo-oxidation of water by sodium persulfate, and other electron acceptors, sensitised by TiO2

A number of different electron acceptors are tested for efficacy in the oxidation of water to oxygen, photocatalysed by titanium dioxide. The highly UV-absorbing metal ion electron acceptors, Ce4+ and Fe3+, appear ineffective at high concentration (10(-2) M), due to UV-screening, but more effective at lower concentrations (10(-3) M). The metal-depositing electron acceptor, Ag+, is initially effective, but loses activity upon prolonged irradiation due to metal deposition which promotes electron-hole recombination as well as UV-screening the titania particles. Most striking of the electron acceptors tested is persulfate, particularly in alkaline solution (0.1 M NaOH). The kinetics of the photo-oxidation of water by persulfate, photocatalysed by titania are studied as a function of pH, [S2O82-] and incident light intensity (I). The initial rate of water oxidation increases with pH, is directly proportional to the concentration of persulfate present and depends upon I-0.6. The TiO2/alkaline persulfate photosystem is robust and shows very little evidence of photochemical wear upon repeated irradiation. The results of this work are discussed with regard to previous work in this area and current mechanistic thinking. The formal quantum efficiency of the TiO2/alkaline persulfate photosystem was estimated as ca. 2%. (C) 2004 Elsevier B.V. All rights reserved.

Photo-oxidation of water sensitized by TiO2 and WO3 in presence of different electron acceptors

The photo-oxidation of water is studied in presence of UV-light (lambda

Different sugar residues of the lipopolysaccharide outer core are required for early interactions of Salmonella enterica serovars Typhi and Typhimurium with epithelial cells

The role of lipopolysaccharide (LPS) in entry of Salmonella Typhimurium into epithelial cells remains unclear. In this study, we tested the ability of a series of mutants with deletions in genes for the synthesis and assembly of the O antigen and the outer core of LPS to adhere to and invade HeLa, BHK, and IB3 epithelial cells lines. Mutants devoid of O antigen, or that synthesized only one O antigen unit, or with altered O antigen chain lengths were as able as the wild type to enter epithelial cells, indicating that this polysaccharide is not required for invasion of epithelial cells in vitro. In contrast, the LPS core plays a role in the interaction of S. Typhimurium with epithelial cells. The minimal core structure required for adherence and invasion comprised the inner core and residues Glc I Gal I of the outer core. A mutant of S. Typhimurium that produced a truncated LPS core lacking the terminal galactose residue had a significant lower level of adherence to and ingestion by the three epithelial cell lines than did strains with this characteristic. Complementation of the LPS production defect recovered invasion to parental levels. Heat-killed bacteria with a core composed of Glc 1 Gal I. but not bacteria with a core composed of Glc 1, inhibited uptake of the wild type by HeLa cells. A comparison of the chemical structure of the S. Typhi core with the published chemical structure of that of S. Typhimurium indicated that the Glc I Gal 1 Glc 11 backbone is conserved in both serovars. However, S. Typhi requires a terminal glucose for maximal invasion. Therefore, our data indicate that critical saccharide residues of the outer core play different roles in the early interactions of serovars Typhi and Typhimurium with epithelial cells. (C) 2010 Elsevier Ltd. All rights reserved.