Photo-Fenton and Riboflavin-photosensitized Processes of the Isoxaflutole Herbicide

Photocatalytic evaluation and characterization of TiO2-riboflavin phosphate film: analysis of reactive oxygen species

The effect of Riboflavin-5'-phosphate (RFPO₄) sensitization on photocatalytic properties of TiO₂ film was studied. RFPO₄ was adsorbed on film surface to investigate the photophysical properties of TiO₂ upon blue-light photoexcitation. The film was characterized through scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and diffuse reflectance spectroscopy. The efficiency of the TiO₂/RFPO₄ film was tested for pollutant elimination in aqueous media in a visible-light-driven system. The phenol paradigmatic model was employed in an aqueous solution as a contaminant target. TiO₂/RFPO₄ sensitized photodegradation of phenol, which produces catechol, hydroquinone, and benzophenone, was monitored by absorption spectroscopy and HPLC. The results indicated that phenol degradation with TiO₂/RFPO₄ film was due to the photogeneration of two reactive oxygen species, singlet molecular oxygen (O₂(¹Δ_g)) and superoxide radical anion (O₂^·-) identified through specific detection techniques. The presence of O₂(¹Δ_g) is reported here for the first time as generated from a sensitized TiO₂ film upon visible-light photoirradiation. Based on the photophysical determinations, a photocatalytic mechanism for TiO₂/RFPO₄ was established.

Bisretinoids of the Retina: Photo-Oxidation, Iron-Catalyzed Oxidation, and Disease Consequences

The retina and, in particular, retinal pigment epithelial cells are unusual for being encumbered by exposure to visible light, while being oxygen-rich, and also amassing photoreactive molecules. These fluorophores (bisretinoids) are generated as a byproduct of the activity of vitamin A aldehyde-the chromophore necessary for vision. Bisretinoids form in photoreceptor cells due to random reactions of two molecules of vitamin A aldehyde with phosphatidylethanolamine; bisretinoids are subsequently transferred to retinal pigment epithelial (RPE) cells, where they accumulate in the lysosomal compartment with age. Bisretinoids can generate reactive oxygen species by both energy and electron transfer, and they become photo-oxidized and photolyzed in the process. While these fluorescent molecules are accrued by RPE cells of all healthy eyes, they are also implicated in retinal disease.

A vicious cycle of bisretinoid formation and oxidation relevant to recessive Stargardt disease

The ability of iron to transfer electrons enables the contribution of this metal to a variety of cellular activities even as the redox properties of iron are also responsible for the generation of hydroxyl radicals (^•OH), the most destructive of the reactive oxygen species. We previously showed that iron can promote the oxidation of bisretinoid by generating highly reactive hydroxyl radical (^•OH). Now we report that preservation of iron regulation in the retina is not sufficient to prevent iron-induced bisretinoid oxidative degradation when blood iron levels are elevated in liver-specific hepcidin knockout mice. We obtained evidence for the perpetuation of Fenton reactions in the presence of the bisretinoid A2E and visible light. On the other hand, iron chelation by deferiprone was not associated with changes in postbleaching recovery of 11-cis-retinal or dark-adapted ERG b-wave amplitudes indicating that the activity of Rpe65, a rate-determining visual cycle protein that carries an iron-binding domain, is not affected. Notably, iron levels were elevated in the neural retina and retinal pigment epithelial (RPE) cells of Abca4^−/− mice. Consistent with higher iron content, ferritin-L immunostaining was elevated in RPE of a patient diagnosed with ABCA4-associated disease and in RPE and photoreceptor cells of Abca4^−/− mice. In neural retina of the mutant mice, reduced Tfrc mRNA was also an indicator of retinal iron overload. Thus iron chelation may defend retina when bisretinoid toxicity is implicated in disease processes.

Complete benzothiazole elimination by the solar photo-Fenton process in aqueous and β-cyclodextrin solutions

Benzothiazole (BTH), a ubiquitous contaminant, was degraded by the solar photo-Fenton process using a solar reactor with a cylindrical-parabolic solar collector and by a classical photo-Fenton system with UV irradiation lamps.