Dipartimento di Scienze di Base e Applicate per l'Ingegneria SBAI, Sapienza Università di Roma, via del Castro Laurenziano 7, I-00161 Rome, Italy.
Dipartimento di Scienze di Base e Applicate per l'Ingegneria SBAI, Sapienza Università di Roma, via del Castro Laurenziano 7, I-00161 Rome, Italy.
Biochim Biophys Acta Gen Subj. 2018 Aug;1862(8):1781-1789. doi: 10.1016/j.bbagen.2018.05.011. Epub 2018 May 13.
Antioxidant properties have been recently suggested for caffeine that seems showing protective effects against damages caused by oxidative stress. In particular, a HO scavenging activity has been ascribed to caffeine. Even if the oxidation of caffeine has been widely studied, the antioxidant mechanism is still far to be understood.
The electrochemical behavior of caffeine, theobromine and theophylline was studied in aprotic medium by cyclic voltammetry and electrolysis in UV-vis cell; a computational analysis of the molecular structures based on the Density Functional Theory was performed; the reactivity of all substrates towards lead dioxide, superoxide and galvinoxyl radical was followed by UV-vis spectrophotometry.
Results supported the mono-electronic oxidation of the CC bond for all substrates at high oxidation potentials, the electron-transfer process leading to a radical cation or a neutral radical according to the starting methylxanthine N-substituted (caffeine and theobromine) or N-unsubstituted (theophylline), respectively. A different following chemical fate might be predicted for the radical cation or the neutral radical. No interaction was evidenced towards the tested reactive oxygen species.
No reactivity via H-atom transfer was evidenced for all studied compounds, suggesting that an antiradical activity should be excluded. Some reactivity only with strong oxidants could be predicted via electron-transfer. The acclaimed HO scavenging activity should be interpreted in these terms. The study suggested that CAF might be hardly considered an antioxidant.
Beyond the experimental methods used, the discussion of the present results might provide food for thought to the wide audience working on antioxidants.
最近有研究表明咖啡因具有抗氧化特性，似乎能对抗氧化应激引起的损伤。特别是，咖啡因具有清除羟自由基（HO）的活性。尽管咖啡因的氧化已得到广泛研究，但抗氧化机制仍远未被理解。
通过循环伏安法和紫外可见池中的电解研究了咖啡因、可可碱和茶碱在非质子介质中的电化学行为；基于密度泛函理论对分子结构进行了计算分析；通过紫外可见分光光度法跟踪所有底物对二氧化铅、超氧自由基和半醌自由基的反应性。
结果支持所有底物在高氧化电位下的 CC 键单电子氧化，电子转移过程根据起始甲基黄嘌呤的 N-取代（咖啡因和可可碱）或 N-未取代（茶碱）分别生成自由基阳离子或中性自由基。自由基阳离子或中性自由基可能会预测出不同的后续化学命运。对测试的活性氧物种没有证据表明存在相互作用。
对于所有研究的化合物，没有证据表明存在通过 H 原子转移的反应性，这表明应该排除其作为自由基清除剂的活性。通过电子转移可能预测到仅与强氧化剂的一些反应性。应该根据这些术语来解释对咖啡因清除羟自由基（HO）活性的认可。该研究表明，CAF 可能很难被认为是一种抗氧化剂。
除了使用的实验方法外，对现有结果的讨论可能会为广泛从事抗氧化剂研究的读者提供一些启示。
