Blackness is an index of redox complexity in melanin polymers

Disclosed herein is the first experimental evidence for a direct correlation between the broadband visible light absorption ("blackness") and the coexistence of reduced and oxidized substructures in a set of model polymers from isomeric dihydroxynaphthalenes structurally related to fungal melanin (mycomelanin) from 1,8-dihydroxynaphthalene. Excellent linear plots (r(2)= 0.97 and 0.94) were determined between the integrals of featureless absorbance curves over the 400-800 nm range, the electron spin density values in the EPR spectra and the width of selected oligomer peak clusters in the MALDI-MS spectra. Blackness, which is shown to be strongly interrelated with electron spin density, is thus proposed herein as a robust index of redox inhomogeneity and electron complexity reflecting the shift of oligomer populations toward highest oxidation states.