Exploring the Role of N-hydroxy Heterocycles in Synthetic Eumelanin Formation

Eumelanin, a black to brown pigment, is one of the chemically distinct forms of melanin. Small molecule modulators can be used to fine-tune the properties of synthetic eumelanin for different applications and provide information about the biological process of melanin formation. Following initial screening results from the Spring 2015 Bioorganic Chemistry (CHEM 254) lab, we decided to focus on four nitrogen-containing heterocyclic compounds: N-hydroxyphthalimide, N-hydroxysuccinimide, succinimide and TEMPO. We are running kinetic assays on a UV-Vis spectrophotometer and a microplate spectrophotometer to interrogate these compounds in synthetic eumelanin polymerizations. Our preliminary results showed three wavelengths of interest: 475nm, which corresponds to the eumelanin precursor dopachrome, and initially decreases as dopachrome is consumed but increases as the pathway continues, and 375nm and 650nm, where the absorbance increases throughout the polymerization. Our experiments focused on the changes in the presence and absence of the heterocyclic compounds, under different conditions such as shaking and the initial L-dopa and oxidant concentrations. Three of the four heterocyclic compounds tested influence the polymerization in diverse ways. We believe these compounds are reacting through the formation of an N-O radical, however TEMPO, an N-O radical containing compound, seems to have little effect on the rate of dopachrome formation and appears to impact later steps in the pathway. The extent of shaking and amount of excess L-dopa also seem to affect these later steps. These studies will inform the lab’s development of an easy and cheap water filtration device based on synthetic eumelanin.