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Photochemical Behavior of 6‐Methylpterin in Aqueous Solutions: Generation of Reactive Oxygen Species ¶
Author(s) -
Cabrerizo Franco M.,
Lorente Carolina,
Vigl Mariana,
Cabrerizo Romina,
Thomas Andrés H.,
Capparelli Alberto L.
Publication year - 2005
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2005.tb01445.x
Subject(s) - chemistry , singlet oxygen , aqueous solution , quenching (fluorescence) , oxygen , photochemistry , luminescence , quantum yield , spectrophotometry , inorganic chemistry , fluorescence , organic chemistry , chromatography , quantum mechanics , physics , optoelectronics
Pterins are a family of heterocyclic compounds present in a wide range of living systems that participate in relevant biological functions and are involved in different photobiological processes. 6‐Methylpterin (MPT) was investigated for its efficiency of singlet‐oxygen ( 1 O 2 ) production and quenching in aqueous solution. The quantum yields of 1 O 2 production (φ Δ ) was determined by measurements of the 1 O 2 luminescence in the near‐infrared upon continuous excitation of the sensitizer. Values of φ Δ were found to be 0.10 ± 0.02 and 0.14 ± 0.02 in acidic and alkaline media, respectively. Studies of the photo‐oxidation of MPT in acidic (pH = 5.0–6.0) and alkaline (pH = 10.2–10.8) aqueous solutions at 350 nm and room temperature have been performed. The photochemical reactions were followed by UV‐visible spectrophotometry, high‐performance liquid chromatography and an enzymatic method for H 2 O 2 determination. MPT is not light sensitive in the absence of oxygen, but it undergoes a photooxidation reaction in the presence of oxygen, yielding several nonpteridinic products. The quantum yields of MPT disappearance were determined and values of 2.4 (±0.5) × 10 −4 and 8.1 (±0.8) × 10 −4 were obtained in acidic and alkaline media, respectively. H 2 O 2 was detected and quantified in irradiated solutions of MPT. The rate constant of the chemical reaction between 1 O 2 and MPT ( k r ) was determined to be 4.9 × 10 6 M −1 s −1 in alkaline medium and the role of 1 O 2 in the photooxidation of MPT is discussed.