Fig. 1. Eumelanin presents multiple levels of structural diversity. The first, 1, arises through different levels of oxidation represented by X1 and Y1 (yellow). The second arises in the monomers connectivity, as noted by the comparison of 1 to 2 (red). The third is the degree of monomer connectivity, such as mono-linked 1/2 to di-linked 3/4. Further complexity can come from different functional linkages, as shown in pheomelanin 5 (orange, green and blue).
