Amphetamine binding to synthetic melanin and scatchard analysis of binding data

Previous research into drug-hair binding shows that hair color affects drug-hair binding. There are no structural disparities in hair of different colors other than the type and content of melanin present. For this reason, this investigation focuses on synthetic eumelanin as a site for drug interaction using amphetamine as the candidate drug. The binding study was carried out at room temperature. The interaction between synthetic eumelanin and amphetamine was monitored using UV-Vis spectrophotometry at 257.2 nm. As the molecular weight of melanin is unknown, the number of binding sites could not be calculated directly. Hence the ratio of the number of mumoles of drug bound and the dry weight of melanin in mug was considered. Equilibrium was reached when approximately 32% of the drug was bound to melanin. Hence this study proves that amphetamine binds to synthetic eumelanin in vitro. Data interpretation using Scatchard analysis yielded a curvilinear plot with upward concavity indicating multiple binding sites on melanin and negative cooperativity.