Melanin is ubiquitous in living organisms across different biological kingdoms of life, making it an important, natural biomaterial. Its presence in nature from microorganisms to higher animals and plants is attributed to the many functions of melanin, including pigmentation, radical scavenging, radiation protection, and thermal regulation. Generally, melanin is classified into five typeseumelanin, pheomelanin, neuromelanin, allomelanin, and pyomelaninbased on the various chemical precursors used in their biosynthesis. Despite its long history of study, the exact chemical makeup of melanin remains unclear, and it moreover has an inherent diversity and complexity of chemical structure, likely including many functions and properties that remain to be identified. Synthetic mimics have begun to play a broader role in unraveling structure and function relationships of natural melanins. In the past decade, polydopamine, which has served as the conventional form of synthetic eumelanin, has dominated the literature on melaninbased materials, while the synthetic analogues of other melanins have received far less attention. In this perspective, we will discuss the synthesis of melanin materials with a special focus beyond polydopamine. We will emphasize efforts to elucidate biosynthetic pathways and structural characterization approaches that can be harnessed to interrogate specific structure−function relationships, including electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. We believe that this timely Perspective will introduce this class of biopolymer to the broader chemistry community, where we hope to stimulate new opportunities in novel, melanin-based poly-functional synthetic materials.

The first examples of Co(ii) mesoionic carbene complexes (CoX2DippMIC2; X = Cl−, Br−, I−) demonstrate a new electronic perturbation on tetrahedral Co(ii) complexes.

High catalytic activity and substrate specificity make enzymes a rich source of inspiration for catalyst development. Co-opting the advantages of natural materials while tuning them to a modified form and purpose, however, is not a straightforward synthetic task. Polymerization of L-3,4-dihydroxyphenylalanine (L-DOPA) results in amorphous polymer nanoparticles that are similar in many ways to natural eumelanin. Herein, the authors introduce mesoporosity and iron ion chelation to synthesize a variant of the L-DOPA polymer with high peroxidase-like activity. Our results indicate catalytic reaction with peroxide under mildly acidic conditions (pH 5.4 and 6) with a greater maximum reaction velocity (V max ) than horseradish peroxidase (HRP) at optimal pH 3.5-4.5. Comparison between Fe(III) and Fe(II) loading indicates that either can be used as a starting point to trigger reactivity, though Fe(II) loading leads to materials with twice the V max of the Fe(III)-loaded sample. The lack of catalyst degradation despite the redox changes and presence of radical species is consistent with the robust nature and redox versatility of polydopamine-based materials and demonstrates strong potential as a versatile redox-catalysis platform.