Cabrerizo Franco M, Lorente Carolina, Vignoni Mariana, Cabrerizo Romina, Thomas Andrés H, Capparelli Alberto L
Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina.
Photochem Photobiol. 2005 Jul-Aug;81(4):793-801. doi: 10.1562/2004-11-29-RA-383.
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 (1O2) production and quenching in aqueous solution. The quantum yields of 1O2 production (phi(delta)) was determined by measurements of the 1O2 luminescence in the near-infrared upon continuous excitation of the sensitizer. Values of phi(delta) were found to be 0.10 +/- 0.02 and 0.14 +/- 0.02 in acidic and alkaline media, respectively. Studies of the photooxidation 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 H2O2 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) x 10(-4) and 8.1 (+/-0.8) x 10(-4) were obtained in acidic and alkaline media, respectively. H2O2 was detected and quantified in irradiated solutions of MPT. The rate constant of the chemical reaction between 1O2 and MPT (k(r)) was determined to be 4.9 x 10(6) M(-1) s(-1) in alkaline medium and the role of 1O2 in the photooxidation of MPT is discussed.
蝶呤是一类杂环化合物，存在于广泛的生命系统中，参与相关生物学功能，并涉及不同的光生物学过程。对6-甲基蝶呤（MPT）在水溶液中产生和猝灭单线态氧（1O2）的效率进行了研究。通过在敏化剂连续激发下测量近红外区域的1O2发光来确定1O2产生的量子产率（phi(delta)）。发现在酸性和碱性介质中phi(delta)的值分别为0.10±0.02和0.14±0.02。在350nm和室温下，对MPT在酸性（pH = 5.0 - 6.0）和碱性（pH = 10.2 - 10.8）水溶液中的光氧化进行了研究。通过紫外 - 可见分光光度法、高效液相色谱法和测定H2O2的酶法跟踪光化学反应。MPT在无氧条件下对光不敏感，但在有氧条件下会发生光氧化反应，产生几种非蝶呤类产物。测定了MPT消失的量子产率，在酸性和碱性介质中分别得到的值为2.4（±0.5）×10(-4)和8.1（±0.8）×10(-4)。在MPT的辐照溶液中检测并定量了H2O2。在碱性介质中确定1O2与MPT之间化学反应的速率常数（k(r)）为4.9×10(6) M(-1) s(-1)，并讨论了1O2在MPT光氧化中的作用。
