Unraveling the Structure and Function of Melanin through Synthesis

Abstract

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.

Melanin, the What, the Why and the How: An Introductory Review for Materials Scientists Interested in Flexible and Versatile Polymers

“…The melanins are a class of compounds, defined as pigments, of diverse structure and origin derived by the oxidation and polymerization of tyrosine in animals or phenolic compounds in lower organisms [11]. Generally, within this class there are three main compounds, though this could be extended to five compounds if considering non-nitrogen containing systems [13]. Keeping with the more traditional, nitrogen containing materials, the first compound is called eumelanin and is what is usually associated with the term melanin.…”

Optimization of extractions of eumelanin from cuttlefish ink and the hypoglycemic effects: In vitro enzyme inhibitory activity and glucose consumption in HepG2 cells

“…acid (Lea, 1952). There are five main types of melanin found in nature: eumelanin, pheomelanin, allomelanin, neuromelanin, and pyomelanin (Cao et al, 2021). The difference between pheomelanin and eumelanin is whether it contains a sulfur atom (Galvan & Jorge, 2015).…”

Fungal Melanins and Applications in Healthcare, Bioremediation and Industry

“…Although a synthesis pathway has not been fully outlined, it is thought to occur as GHB is transformed by a polyphenol oxidase (typically tyrosinase) into 2-hydroxy- p -iminobenzoquinone (2-HpIBQ) and polymerized [ 42 , 44 ]. The diversity of pathways that organisms use to synthesize melanin explains in part why these polymers are not as well understood as other biopolymers such as proteins or nucleic acids [ 45 ].…”