Quenching of Singlet Oxygen by Gadusol in Micellar Solutions

ERNESTO M. ARBELOA; SONIA G. BERTOLOTTI; M. SANDRA CHURIO

Mendoza

Conferencia; 21st I-APS Conference; 2011

Inter-American Photochemical Society

Gadusol (3,5,6-trihydroxy-5-hydroxymethyl-2-methoxycyclohex-2-en-1-one) is structurally related to the mycosporine-like amino acids (MAAs), a family of substances occurring in a wide variety of marine and terrestrial organisms. The high photostability of the metabolite under physiological conditions is consistent with the proposed UV-sunscreening role of the molecule in the earlier stages of life. Gadusolate, the enolate form of gadusol, efficiently quenches singlet oxygen and reduces triplet sensitizers in aqueous solution. This reactivity is in line with the results of in vitro determinations of the antioxidant capacity of gadusol and supports its potential role against oxidative stress in living organisms.[1,2] With the general goal of assessing the effect of microheterogeneous media on these properties, here we report on the quenching of singlet oxygen by gadusol and gadusolate in SDS and CTAC direct micelles as simple models of the biological environments. Singlet oxygen was generated by photosensitization with perinaphtenone. The total quenching rate constant was determined by time resolved phosphorescence detection at 1270 nm in D2O solutions above the critical micelle concentration for each surfactant. The contribution of chemical reaction to the quenching rate was evaluated by following the substrate consumption in the micellar solution and taking the reactive quenching by gadusolate in homogeneous aqueous solution as the reference process. The results indicate that the total quenching constants decrease between 20 to 50% in the micellar media in comparison to aqueous solution. The effect is more pronounced in the case of SDS micelles. Besides, the reactive quenching rate values also diminish relatively to aqueous solutions and with surfactant concentration. Physical quenching seems to be less favoured in polar environments as indicated by the estimated photo-oxidation quantum yields for gadusolate: 0.50, 0.27 and 0.14 in aqueous, CTAC and SDS solutions, respectively. Thus, gadusolate appears to be more efficient in the biological-like media than in homogeneous solution where it mainly behaves as a sacrifice antioxidant. The observations are rationalized in terms of the association of quencher to the micelle surface and the charge-transfer character of the encounter complex that it forms with singlet oxygen molecules. [1] E. M. Arbeloa, M. J. Uez, S. G. Bertolotti, M. S. Churio. Antioxidant activity of Gadusol and occurrence in fish roes from Argentine Sea. Food Chem. (2010), 119, pp. 586–591. [2] E. M. Arbeloa, S. G. Bertolotti, M. S. Churio. Photophysics and reductive quenching reactivity of gadusol in solution. Photochem. Photobiol. Sci. (2011), 10, pp. 133–142. in vitro determinations of the antioxidant capacity of gadusol and supports its potential role against oxidative stress in living organisms.[1,2] With the general goal of assessing the effect of microheterogeneous media on these properties, here we report on the quenching of singlet oxygen by gadusol and gadusolate in SDS and CTAC direct micelles as simple models of the biological environments. Singlet oxygen was generated by photosensitization with perinaphtenone. The total quenching rate constant was determined by time resolved phosphorescence detection at 1270 nm in D2O solutions above the critical micelle concentration for each surfactant. The contribution of chemical reaction to the quenching rate was evaluated by following the substrate consumption in the micellar solution and taking the reactive quenching by gadusolate in homogeneous aqueous solution as the reference process. The results indicate that the total quenching constants decrease between 20 to 50% in the micellar media in comparison to aqueous solution. The effect is more pronounced in the case of SDS micelles. Besides, the reactive quenching rate values also diminish relatively to aqueous solutions and with surfactant concentration. Physical quenching seems to be less favoured in polar environments as indicated by the estimated photo-oxidation quantum yields for gadusolate: 0.50, 0.27 and 0.14 in aqueous, CTAC and SDS solutions, respectively. Thus, gadusolate appears to be more efficient in the biological-like media than in homogeneous solution where it mainly behaves as a sacrifice antioxidant. The observations are rationalized in terms of the association of quencher to the micelle surface and the charge-transfer character of the encounter complex that it forms with singlet oxygen molecules. [1] E. M. Arbeloa, M. J. Uez, S. G. Bertolotti, M. S. Churio. Antioxidant activity of Gadusol and occurrence in fish roes from Argentine Sea. Food Chem. (2010), 119, pp. 586–591. [2] E. M. Arbeloa, S. G. Bertolotti, M. S. Churio. Photophysics and reductive quenching reactivity of gadusol in solution. Photochem. Photobiol. Sci. (2011), 10, pp. 133–142. 2O solutions above the critical micelle concentration for each surfactant. The contribution of chemical reaction to the quenching rate was evaluated by following the substrate consumption in the micellar solution and taking the reactive quenching by gadusolate in homogeneous aqueous solution as the reference process. The results indicate that the total quenching constants decrease between 20 to 50% in the micellar media in comparison to aqueous solution. The effect is more pronounced in the case of SDS micelles. Besides, the reactive quenching rate values also diminish relatively to aqueous solutions and with surfactant concentration. Physical quenching seems to be less favoured in polar environments as indicated by the estimated photo-oxidation quantum yields for gadusolate: 0.50, 0.27 and 0.14 in aqueous, CTAC and SDS solutions, respectively. Thus, gadusolate appears to be more efficient in the biological-like media than in homogeneous solution where it mainly behaves as a sacrifice antioxidant. The observations are rationalized in terms of the association of quencher to the micelle surface and the charge-transfer character of the encounter complex that it forms with singlet oxygen molecules. [1] E. M. Arbeloa, M. J. Uez, S. G. Bertolotti, M. S. Churio. Antioxidant activity of Gadusol and occurrence in fish roes from Argentine Sea. Food Chem. (2010), 119, pp. 586–591. [2] E. M. Arbeloa, S. G. Bertolotti, M. S. Churio. Photophysics and reductive quenching reactivity of gadusol in solution. Photochem. Photobiol. Sci. (2011), 10, pp. 133–142.