X-RAY CHARACTERIZATION OF MELANINS .2.

Structural modeling of amorphous eumelanin has been carried out by com paring calculated data, S(q) and RDF(r), in reciprocal and real space, respectively, for limited random network models with the experimental X-ray scattering data of tyrosine melanin (Cheng et al., 1994). A bas ic picture of the atomic arrangements in amorphous eumelanin, which ac counts for the short and intermediate range order, has been formulated . This reveals domains of a fundamental ''particle'' dimension of R si milar to 15 Angstrom, consisting of a paracrystalline array of disorde red planar networks polymerized by 4-8 DHI monomers with a graphite-li ke stacking spacing of similar to 3.45 Angstrom, 4-5 layers thick.