title: Development of a Singlet Oxygen Absorption Capacity (SOAC) Assay Method. Measurements of the SOAC Values for Carotenoids and α-Tocopherol in an Aqueous Triton X-100 Micellar Solution.
abstract: Recently, a new assay method for the quantification of the singlet oxygen absorption capacity (SOAC) of antioxidants (AOs) and food extracts in homogeneous organic solvents was proposed. In this study, second-order rate constants (kQ) for the reaction of singlet oxygen (1O2) with eight different carotenoids (Cars) and α-tocopherol (α-Toc) were measured in an aqueous Triton X-100 (5.0 wt %) micellar solution (pH 7.4, 35 °C), which was used as a simple model of biomembranes. The kQand relative SOAC values were measured using ultraviolet-visible (UV-vis) spectroscopy. The UV-vis absorption spectra of Cars and α-Toc were measured in both a micellar solution and chloroform, to investigate the effect of solvent on the kQand SOAC values. Furthermore, decay rates (kd) of1O2were measured in 0.0, 1.0, 3.0, and 5.0 wt % micellar solutions (pH 7.4), using time-resolved near-infrared fluorescence spectroscopy, to determine the absolute kQvalues of the AOs. The results obtained demonstrate that the kQvalues of AOs in homogeneous and heterogeneous solutions vary notably depending on (i) the polarity [dielectric constant (ε)] of the reaction field between AOs and1O2, (ii) the local concentration of AOs, and (iii) the mobility of AOs in solution. In addition, the kQand relative SOAC values obtained for the Cars in a heterogeneous micellar solution differ remarkably from those in homogeneous organic solvents. Measurements of kQand SOAC values in a micellar solution may be useful for evaluating the1O2quenching activity of AOs in biological systems.
authors.affiliation: Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan.
authors.forename: Kazuo
authors.identifier: http://orcid.org/0000-0003-4118-9607
authors.initials: K
authors.lastname: Mukai
authors.affiliation: Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Ouchi
authors.affiliation: Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan.
authors.forename: Nagao
authors.initials: N
authors.lastname: Azuma
authors.affiliation: Research & Development Division, Kagome Company Ltd. , Nasushiobara-shi, Tochigi 329-2762, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Takahashi
authors.affiliation: Research & Development Division, Kagome Company Ltd. , Nasushiobara-shi, Tochigi 329-2762, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Aizawa
authors.affiliation: Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan.
authors.forename: Shin-Ichi
authors.identifier: http://orcid.org/0000-0003-1564-7328
authors.initials: SI
authors.lastname: Nagaoka
mesh_terms: D000975:Antioxidants / Q000737:chemistry; D002338:Carotenoids / Q000737:chemistry*; D007700:Kinetics; D008823:Micelles; D017830:Octoxynol / Q000737:chemistry; D026082:Singlet Oxygen / Q000737:chemistry*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D024502:alpha-Tocopherol / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D008823:Micelles; D026082:Singlet Oxygen; D002338:Carotenoids; D017830:Octoxynol; D024502:alpha-Tocopherol
keywords: SOAC value; carotenoids; endoperoxide; kinetic study; micellar solution; quenching rate; singlet oxygen; α-tocopherol