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(A) Schematic illustration of dihydroxyphenylalanine (DOPA) oxidative polymerization to melanin (highlighted is the generation of L-3,4-dihydroxyphenylalanine (L-DOPA) by redox cycling between leucodopachrome and dopaquinone). (B) Molecular structures of porphyrinoids used, 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin tetrachloride salt (H2T4) and copper(II) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin tetrasodium salt (CuTPPS).
