使用邻苯二酚：醌异二聚体模型系统探测Eumelanin的光保护作用。,Faraday Discussions

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使用邻苯二酚：醌异二聚体模型系统探测Eumelanin的光保护作用。
Faraday Discussions ( IF 3.3 ) Pub Date : 2019-07-11 , DOI: 10.1039/c8fd00231b
Christopher Grieco ₁ , Jennifer M Empey ₁ , Forrest R Kohl ₁ , Bern Kohler ₁

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Eumelanin是一种天然色素，具有光保护和清除自由基的特性，对多种生物至关重要。但是，这些功能背后的分子机制仍然不清楚，部分原因是因为Eumelanin是由结构和化学结构域的复杂分类组成的异质聚合物。尽管不确定其精确的结构，但认为其具有多种氧化态的醌类功能。在这里，我们研究儿茶酚的光化学：邻醌异二聚体作为模型系统，用于揭示真木兰的光保护根。紫外至近红外光谱区域的超快速瞬态吸收测量用于确定光化学过程，该过程遵循使用395 nm光选择性激发异二聚体中邻醌的现象。我们发现，单重态和三重态的邻醌激发态均会引起邻苯二酚的氢原子转移，形成对醌自由基对，其持续时间超过2.5 ns，这是仪器可达到的上限。此外，发现经由单线态通道氢原子转移反应发生快1000倍。诸如此类的兴奋状态途径可能在Eumelanin中很重要，因为邻苯二酚和邻苯二酚官能团之间存在相似的氢键界面。通过单线态通道发现氢原子转移反应的速度快了1000倍。诸如此类的兴奋状态途径可能在Eumelanin中很重要，而邻苯二酚和邻醌功能基团之间存在相似的氢键界面。通过单线态通道发现氢原子转移反应的速度快了1000倍。诸如此类的兴奋状态途径可能在Eumelanin中很重要，因为邻苯二酚和邻苯二酚官能团之间存在相似的氢键界面。

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Probing eumelanin photoprotection using a catechol:quinone heterodimer model system.

Eumelanin is a natural pigment with photoprotective and radical scavenging characteristics, which are vital for a multitude of living organisms. However, the molecular mechanisms behind these functions remain obscure, in part because eumelanin is a heterogeneous polymer composed of a complex assortment of structural and chemical domains. Despite uncertainty about its precise structure, the functional units of eumelanin are thought to include quinones in various oxidation states. Here, we investigate the photochemistry of a catechol : o-quinone heterodimer as a model system for uncovering the photoprotective roots of eumelanin. Ultrafast transient absorption measurements in the UV to near-IR spectral regions are used to identify the photochemical processes that follow selective excitation of the o-quinone in the heterodimer using 395 nm light. We find that both singlet and triplet o-quinone excited states induce hydrogen atom transfer from the catechol, forming semiquinone radical pairs that persist beyond 2.5 ns, which is the upper time limit accessible by our instrument. Furthermore, the hydrogen atom transfer reaction was found to occur 1000 times faster via the singlet channel. Excited state pathways such as these may be important in eumelanin, where similar hydrogen-bonded interfaces are believed to exist between catechol and o-quinone functional groups.

更新日期：2019-07-11

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