The yellow and the black of synthetic melanins

The observations reported here are a continuation and expansion of observations described earlier: the typical conditions to synthesize melanin-like materials from catecholic precursors (air-oxidation in an alkaline environment) leads to the generation of a light-colored substance in addition to the typical dark substances. This light-colored substance appears to be associated with the dark-colored materials through non-covalent interactions. We employed a novel co-precipitation process that allows for a simple separation of this light-colored substance from the dark-colored materials. We studied some of the physic-chemical properties (color, fluorescence, FT-IR absorbance) of some of the fractions we obtained and discussed these properties in the context of what has been discussed for eumelanin, pheomelanin or neuromelanin. Overall, the current observations strengthen our hypothesis that synthetic melanins may be built from at least two types of substances: 1) a soluble, yellow-to-orange colored component, possibly rich in unoxidized precursors and 2) an insoluble, dark component. Our observations do suggest that when studying the chemistry or physiology of melanins one should look beyond the dark colors typically displayed by melanin-like materials.