Open AccessNovel free radicals in synthetic and natural pheomelanins: distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy.
Author(s) -
Roger C. Sealy,
James S. Hyde,
Christopher C. Felix,
I. A. Me,
Giuseppe Prota,
Harold M. Swartz,
Suruj D. Persad,
Herbert F. Haberman
Publication year - 1982
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.79.9.2885
Subject(s) - melanin , chemistry , pigment , radical , photochemistry , unpaired electron , spectroscopy , dihydroxyphenylalanine , chelation , biochemistry , organic chemistry , biology , physics , quantum mechanics , neuroscience , dopamine
Synthetic pheomelanins from enzymic oxidation of the 3,4-dihydroxyphenylalanine (dopa) derivative 5-S-cysteinyldopa have been examined by ESR spectroscopy. These alkalisoluble polymers contain a novel kind of free radical that is spectroscopically distinct from that found in eumelanins. Delocalization of the unpaired electron onto a nitrogen atom and the ability of the radical to chelate complexing metal ions strongly suggest an o-semiquinonimine structure. The synthetic pheomelanin was compared with natural red pigments extracted from human red hair and from red chicken feathers. Spectroscopically, the chicken feather pheomelanin is almost identical to synthetic cysteinyldopa pheomelanin. In contrast, the pigment from red hair has a major spectral component very similar to that found in dopa melanin, with a smaller component corresponding to that found in cysteinyldopa melanin.