title: Influence of pH on the decay of β-carotene radical cation in aqueous Triton X-100: A laser flash photolysis study.
abstract: The identification of the spectral information of carotenoid neutral radicals is essential for studying their reactivities towards O2 and thereby evaluating their role in the antioxidant-prooxidant properties of the corresponding carotenoid. Recently, it was reported that β-carotene neutral radical (β-CAR) has an absorption maximum at 750 nm. This contradicts the results of many reports that show carotenoid neutral radicals (CAR) absorb in the same or near to the spectral region as their parent carotenoids. In this manuscript, the influence of pH on the decay of β-carotene radical cation (β-CAR-H(+)), generated in an aqueous solution of 2% Triton X-100 (TX-100), was investigated, employing laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy, to identify the absorption bands of the β-carotene neutral radicals. By increasing the pH value of the solution, the decay of β-CAR-H(+) is enhanced and this enhancement is not associated with the formation of any positive absorption bands over the range 550-900 nm. By comparing these results with the literature, it can be concluded that β-carotene neutral radicals most probably absorb within the same spectral range as that of β-carotene. The reaction pathways of the reaction of β-CAR-H(+) with (-)OH have been discussed.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan; Chemistry Department, Faculty of Science, Damietta University, New Damietta, Damietta, Egypt.
authors.forename: Ali
authors.initials: A
authors.lastname: El-Agamey
authors.affiliation: Chemistry Department, Faculty of Science, Damietta University, New Damietta, Damietta, Egypt.
authors.forename: Maha A
authors.initials: MA
authors.lastname: El-Hagrasy
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan.
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Suenobu
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
mesh_terms: D002412:Cations / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D007834:Lasers; D017830:Octoxynol / Q000737:chemistry*; D010782:Photolysis; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D002412:Cations; D005609:Free Radicals; D019207:beta Carotene; D017665:Hydroxyl Radical; D017830:Octoxynol