Agapito Filipe, Cabral Benedito J Costa
Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa , 1749-016 Lisboa, Portugal.
Departamento de Química e Bioquímica and Grupo de Física Matemática, Faculdade de Ciências, Universidade de Lisboa , 1749-016 Lisboa, Portugal.
J Phys Chem A. 2016 Dec 22;120(50):10018-10022. doi: 10.1021/acs.jpca.6b10122. Epub 2016 Dec 8.
The supramolecular structure of melanin pigments is characterized by a high concentration of radical species. Therefore, the energetics of the radical formation in melanin building blocks is key for understanding the structure and the electronic properties of the pigments at the molecular level. Nevertheless, the radical energetics of even the simplest melanin building blocks are largely unknown. In order to address this fundamental issue, the bond dissociation enthalpies (BDEs) for the melanin monomers 5,6-dihydroxy-1H-indole-2-carboxylic acid (DHICA), 1H-indole-5,6-diol (DHI), and 1H-indole-5,6-dione (IQ) were determined through high-accuracy ab initio quantum chemistry methods. Our results provide strong evidence of the importance on BDEs for explaining the experimentally observed dependence of the antioxidant properties of eumelanin pigments on the DHICA/DHI ratio, and the role that these two species play on the photoprotection mechanism.
黑色素的超分子结构以高浓度的自由基为特征。因此，黑色素结构单元中自由基形成的能量学对于在分子水平上理解色素的结构和电子性质至关重要。然而，即使是最简单的黑色素结构单元的自由基能量学也很大程度上未知。为了解决这个基本问题，通过高精度的从头算量子化学方法确定了黑色素单体5,6-二羟基-1H-吲哚-2-羧酸（DHICA）、1H-吲哚-5,6-二醇（DHI）和1H-吲哚-5,6-二酮（IQ）的键解离焓（BDE）。我们的结果提供了有力证据，证明BDE对于解释实验观察到的真黑素色素抗氧化性能对DHICA/DHI比率的依赖性以及这两种物质在光保护机制中所起的作用具有重要性。
