Clue to Understanding the Janus Behavior of Eumelanin: Investigating the Relationship between Hierarchical Assembly Structure of Eumelanin and Its Photophysical Properties

The contradictory biological functionof eumelanin ( photoprotectionvs photosensitization) has long been a topic of debate in a wide range of disciplines such as chemistry, physics and biology. For understanding full spectrum of eumelanin’s photobiologicalaspect, revealing how eumelanin’s complex structural organization dictates its photophysical properties is critical step. Here, we report a practical approach to controlling the hierarchically assembled structure of natural eumelanin, which leads to disassembly of its structure into subunits and oxidized subunits, respectively. Based on the well-characterized model system, it was possible to systematically determine how the photophysical properties of eumelanin are ruled by its hierarchical assembly organization. Particularly, our experiments reveal that the chemical oxidation of eumelanin’s subunits, which leads to delamination of their stacked layer structure, is critical to significantly increase their photochemical reactivity to generate ROS under U...