Photosensitized Amino Acid Degradation in the Presence of Riboflavin and Its Derivatives

• Published in: Environmental science & technology Vol. 45; no. 12; pp. 5230 - 5237
• Main Authors: Remucal, Christina K, McNeill, Kristopher
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.06.2011
• Subjects: Amino acids; Amino Acids - chemistry; Applied sciences; Chemical compounds; Drinking water and swimming-pool water. Desalination; Environmental Processes; Exact sciences and technology; Flavins - chemistry; Furans - chemistry; Light; Oxidation; Photodegradation; Photosensitizing Agents - chemistry; Pollution; Riboflavin - analogs & derivatives; Riboflavin - chemistry; Singlet Oxygen - analysis; Spectrum Analysis; Ultraviolet radiation; Vitamin B; Water treatment and pollution; Drinking water treatment; Water treatment; Microbiology; Riboflavin; Disinfection; B-Vitamins; Aminoacid; Model compound; Pathogenic; Metabolic inactivation; Biological contamination; Photosensitizer; Organic compounds; Photochemical degradation
• DOI: 10.1021/es200411a
• ISSN: 0013-936X

The addition of photosensitizers to water can accelerate disinfection in sunlight-based systems by enhancing oxidation of target compounds through direct reaction with the excited sensitizer or through production of another oxidant, such as singlet oxygen (1O2). The kinetics of the oxidation of selected amino acids in the presence of the sensitizer riboflavin (Vitamin B2), its primary photoproduct lumichrome, and its derivative riboflavin tetraacetate (2′,3′,4′,5′-tetraacetylriboflavin; RTA) were quantified and the mechanisms of reaction were determined during exposure to 365 ± 9 nm light. 1O2-mediated reactions contributed to the rapid photodegradation of the four amino acids, but its contribution was sensitizer-dependent and varied from 5.4−10.2% for tyrosine, 7.1–12.4% for tryptophan, 18.7–69.0% for methionine, and 64.7–100.2% for histidine. Riboflavin was subject to rapid photodegradation (t 1/2 <8 min), while the half-lives of lumichrome and RTA were 100 and 30 times longer, respectively. Lumichrome and RTA also were more efficient 1O2 sensitizers (quantum yield (Φ) = 0.63 and 0.66) compared to riboflavin (Φ = 0.48). Of the three flavin-based compounds, RTA shows the most promise as a sensitizer in sunlight-based disinfection systems because it absorbs both visible and UV light, is an efficient 1O2 sensitizer, is a strong oxidant in its triplet state, and exhibits greater photostability.