Spectro- electrochemical reverse engineering applied to probe redox and radical scavenging property of melanin

Melanin is proposed to perform various functions in biology. The conventional approach to understand a material’s functions is to start by characterizing its structure, but this approach has been difficult to apply to melanin because of its complexity. We are developing an alternative, reverse engineering approach that focuses on properties. Importantly, our reverse engineering uses electrochemistry to probe melanin’s redox and radical- scavenging properties that are believed to be integral to many of melanin’s proposed protective functions. In this reverse engineering method we: entrap melanin in a hydro-gel film adjacent to an electrode surface; add diffusible mediator(s) that can shuttle electrons between the electrode and the melanin; impose a complex sequence of voltages to the electrode to oxidize/reduce the mediators; and measure/analyze the resulting currents to understand if, and under what voltages the melanin donates or ac-cepts electrons. This electrochemical approach can also be coupled to spectral analysis to allow observation of the generation/quenching of free radicals.Through a series of (spectro)electrochemical reverse engineering studies, we have shown:• All melanins tested are redox-active and can be repeatedly oxidized and reduced.• Pheomelanin appears to have a more oxidative redox potential (vs eumelanin) which may explain its pro-oxidant activities.• The agricultural chemical paraquat can transfer electrons to melanin through redox-cycling reactions. While the medical sig-nificance is uncertain, it is important to note that exposure to paraquat is linked to Parkinson’s disease through a proposed redox-cycling, oxidative-stress-inducing mechanism, while the neurons selectively vulnerable in Parkinson’s disease are rich in melanin.• All melanins tested are able to scavenge free radicals either by do-nating or accepting electrons, and the radical-scavenging activity is linked to melanin’s redox state.In summary, (spectro)electrochemical reverse engineering allows melanin’s redox and radical- scavenging activities to be readily charac-terized and this could assist in discerning melanin’s complex and diverse biological functions.