Melanin polymers, properties

Stabilizing agents are used to maintain drilling fluid rheological properties at highly elevated downhole temperatures. Chromium and chromium-free lignosulfonates, polyglycol ethers, sodium polystyrene sulfonate-co-maleic anhydride), and a melanin polymer have been used in this application. Additives such as sodium diethyldi-thiocarbamate have been used to stabilize aqueous polysaccharides such as xanthan gum (18). 

Melanins have photoprotective properties. Paramagnetic changes occur upon ultraviolet or visible irradiation and have been studied by ESR. Two types of reactions have been identified [161] production of melanin free radicals and reduction of oxygen to O2. Oxygen consumption in the polymer solution is strongly wavelength dependent, as shown by spin-probe measurements of oxygen concentration [167],... 

The chemistry of melanins reveals that it is difficult to study these pigment polymers using conventional chemical and physical methods. On the other hand, by using known precursors biosynthetic studies under biologically relevant conditions can be used successfully to understand the chemistry of melanin, i.e. the identification of the intermediates, their reactivities, the formation of melanin, and its properties. 

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