Probing eumelanin photoprotection using a catechol:quinone heterodimer model system
Probing eumelanin photoprotection using a catechol:quinone heterodimer model system
复制标题
使用儿茶酚：醌异二聚体模型系统探测真黑素光保护
DOI：
10.1039/c8fd00231b
复制
发表时间：
2019
影响因子：
3.4
通讯作者：
Kohler, Bern
中科院分区：
文献类型：
--
作者：
Grieco, Christopher;Empey, Jennifer M.;Kohl, Forrest R.;Kohler, Bern
真黑素是一种天然色素，具有光保护和清除自由基的特性，这对许多生物来说是至关重要的。然而，这些功能背后的分子机制仍然不清楚，部分原因是真黑素是一种由复杂的结构和化学结构域组成的多相聚合物。尽管真黑素的精确结构不确定，但人们认为真黑素的功能单元包括各种氧化态的苯醌。在这里，我们研究了邻苯二酚邻苯二酚杂二聚体的光化学，作为揭示真黑素光保护根的模型系统。在紫外近红外光谱区的超快瞬时吸收测量被用来识别在395 nm的光下选择性地激发异二聚体中的邻苯二酚的光化学过程。我们发现，邻苯二酚的单重态和三重态激发态都能引起邻苯二酚的氢原子转移，形成持续时间超过2.5 ns的半醌自由基对，这是我们的仪器所能达到的时间上限。此外，通过单重态通道，氢原子转移反应的速度提高了1000倍。这样的激发态途径在真黑素中可能很重要，在真黑素中，邻苯二酚和邻苯二酚官能团之间被认为存在类似的氢键界面。
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.