Authors: Konaka, R.¹; Kasahara, E.¹; Dunlap, W.C.²; Yamamoto, Y.³; Chien, K.C.¹; Inoue, M.¹

Source: Redox Report, Volume 6, Number 5, October 2001 , pp. 319-325(7)

Publisher: Maney Publishing

Abstract:

We previously reported that irradiation of titanium dioxide (TiO₂) in ethanol generates both singlet oxygen (¹O₂) and superoxide anion (O₂ ^·-) as measured by EPR spectroscopy. The present study describes the production of reactive oxygen species upon irradiation of TiO₂ in aqueous suspension as determined by EPR spectroscopy using 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TMP) and 5,5- dimethyl-pyrroline-N-oxide (DMPO). Photoproduction of ¹O₂ by suspended TiO₂, detected as 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (4-oxo-TEMPO), was measured in water and deuterium oxide (D₂O) in the presence or absence of sodium azide (NaN₃) and under air or argon atmospheres. Production of a DMPO-OH adduct was examined in 4-oxo-TMP containing medium in the presence or absence of dimethyl sulfoxide (DMSO). The signal for the DMPO spin adduct of superoxide anion was not observed in aqueous conditions. Kinetic analysis revealed that ¹O₂ was produced at the surface of irradiated TiO₂ in aqueous suspension as was observed in ethanol. Kinetic analysis revealed that the formation of DMPO-OH adduct reflects oxidation of DMPO by ¹O₂ rather than the trapping of the hydroxyl radical produced by the reaction of photo-exited TiO₂ and water. The production of large amounts of ¹O₂ by TiO₂ in aqueous suspension as compared to those in ethanol and possible formation of hydroxyl radical in aqueous suspension but not in alcohol, suggest that irradiation of TiO₂ in aqueous environments is biologically more important than that in non-aqueous media.

Document Type: Research Article

DOI: http://dx.doi.org/10.1179/135100001101536463

Affiliations: 1: Department of Biochemistry and Molecular Pathology, Osaka City University Medical School, Abeno, Osaka, Japan 2: Australian Institute of Marine Science, Townsville, Queensland, Australia 3: Department of Chemistry and Biotechnology, University of Tokyo, Hongo, Tokyo, Japan

Publication date: 2001-10-01

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