Purity of Biosynthesized Eumelanin via Solid-State Nuclear Magnetic Resonance

Eumelanins are a family of biomolecules with a wide range of functionality in nature and tremendous potential for commercial and industrial applications, provided that they can be produced in large quantities. Our group has developed a method to biosynthesize eumelanin with high yield using the marine bacterium Vibrio natriegens. In this work, we use high-resolution ¹H, ¹³C, and ¹⁵N magic angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the purity of the extracted solid eumelanin as a function of the quality control methods. A key observation is that biomass eumelanin contains a higher level of biocontaminant compared to supernatant eumelanin. Additional insights into the efficiency of the biosynthetic pathway of eumelanin synthesis were obtained by incorporating ¹³C- and ¹⁵N-enriched precursors into the growth medium and subsequent MAS NMR spectra of the eumelanins. These results highlight the usefulness of solid-state NMR for assessing the quality of the eumelanins produced biosynthetically, which is critical for their further application.