title: Degree of polymerization of 5,6-dihydroxyindole-derived eumelanin from chemical degradation study.
abstract: Eumelanin is a brown-black pigment comprising 5,6-dihydroxyindole (DHI) and its 2-carboxy derivative (DHICA), but the detailed structure of eumelanin is unclear. Chemical degradation is a powerful tool for analyzing melanin. H2 O2 oxidation degradation of eumelanin affords pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA). The ratio of PDCA to PTCA provides information about the eumelanin structure. In this article, we propose simple equations on the basis of previous experimental results on dimer yields for evaluating the yields of PTCA and PDCA from any DHI oligomers. Assuming the chemical disorder model of DHI-melanin, we solve an equation where a theoretical expression for the ratio of PDCA to PTCA is set to the corresponding experimental value to obtain a plausible Poisson distribution of DHI oligomers. The results demonstrate that the main contributors to DHI-melanin are tetramers and pentamers as shown by the mass spectrometry.
authors.affiliation: Research Institute for Science and Engineering, Waseda University, Tokyo, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Okuda
authors.forename: Kyoji
authors.initials: K
authors.lastname: Yoshino
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Wakamatsu
authors.forename: Shosuke
authors.initials: S
authors.lastname: Ito
authors.forename: Takayuki
authors.initials: T
authors.lastname: Sota
mesh_terms: D007211:Indoles / Q000737:chemistry*; D008543:Melanins / Q000737:chemistry*
chemical_list: D007211:Indoles; D008543:Melanins; C041877:eumelanin; C033871:5,6-dihydroxyindole
keywords: 5,6-dihydroxyindole; chemical disorder model; degree of polymerization; eumelanin; hydrogen peroxide oxidation