title: Energetics of Radical Formation in Eumelanin Building Blocks: Implications for Understanding Photoprotection Mechanisms in Eumelanin.
abstract: 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.
authors.affiliation: Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa , 1749-016 Lisboa, Portugal.
authors.forename: Filipe
authors.initials: F
authors.lastname: Agapito
authors.affiliation: Departamento de Química e Bioquímica and Grupo de Física Matemática, Faculdade de Ciências, Universidade de Lisboa , 1749-016 Lisboa, Portugal.
authors.forename: Benedito J Costa
authors.identifier: http://orcid.org/0000-0003-4824-3530
authors.initials: BJ
authors.lastname: Cabral
mesh_terms: D005609:Free Radicals / Q000138:chemical synthesis / Q000737:chemistry; D008543:Melanins / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D055668:Photochemical Processes; D011789:Quantum Theory
chemical_list: D005609:Free Radicals; D008543:Melanins; C041877:eumelanin