Functionalization of 5-hydroxyindole-based i-melanin pigment for hair dyeing and UV-protective applications

Abstract

In this study, 5-hydroxyindole-based i-melanin was biosynthesized through enzymatic reactions catalyzed by flavin monooxygenase (FMO) and sequential MelC tyrosinase. The monomer underwent intracellular random polymerization, resulting in a novel symmetric melanin. The synthesized i-melanin exhibited a significantly darker black coloration compared to conventional melanin and demonstrated enhanced biological activities, including antioxidant and antibacterial properties. The physical and biological characteristics of i-melanin were analyzed using UV/Vis spectroscopy, ABTS assays, and growth inhibition studies. Notably, i-melanin displayed antifungal activity against Candida albicans. For functional applications, i-melanin was formulated as a hair dye and incorporated into a UV-protection cream through complexation with ZnO. Both formulations exhibited excellent dyeing efficacy and UV-blocking performance. Given the high production yield of i-melanin, its scalability for industrial applications appears promising. These findings suggest that this novel melanin has potential for integration into various functional products in the future.