Melanin Biopolymers: Tailoring Chemical Complexity for Materials Design

Abstract

Melanins, a group of dark insoluble pigments found widespread in nature, have become the focus of growing interest in materials science for various biomedical and technological applications, including opto‐bioelectronics, nanomedicine and mussel‐inspired surface coating. Recent progress in the understanding of melanin optical, paramagnetic redox, and conductivity properties, including photoconductivity, would point to a revision of the traditional concept of structural disorder in terms of more sophisticated and interrelated levels of chemical complexity which however have never been defined and codified. Herein, we bring to focus the various levels of structural disorder that emerged from spectral and chemical signatures over the past decade. A revised approach to structure–property relationships in terms of intermolecular interactions is also provided that may pave the way towards the rational design of next‐generation melanin‐based functional materials.

Insoluble organic matter in chondrites: Archetypal melanin-like PAH-based multifunctionality at the origin of life?

“…[234] Studies over the last decades have clarified some important chemical and physical properties of allomelanins [207] that are common to all members of this class of polymers regardless of structural and biosynthetic differences [235]. These properties include, among others: a) a black or dark coloration due to broadband, often featureless, absorption spectra covering the entire UV-visible range [236]; b) a marked structural heterogeneity; c) almost complete insolubility in water and organic solvents; d) an intrinsic paramagnetic character responsible for a broad stable EPR signal [237]; e) semiconductor-type electrical conductivity properties [238]; f) efficient non-radiative excited state deactivation; g) a redox behavior associated with antioxidant activity; h) a strong metal cation binding and drug affinity, and i) efficient gas adsorption properties.…”

“…Most of these properties, especially a) and d-g), are evidently associated with the unusual chemical complexity of all melanin-type polymers at the level of the conjugated -system. Such a complexity stems from various interrelated levels of structural disorder, including monomer disorder, molecular weight disorder, isomerism-related disorder, redox disorder and supramolecular disorder [236,237].…”

A Melanin-Related Phenolic Polymer with Potent Photoprotective and Antioxidant Activities for Dermo-Cosmetic Applications

“…Melanins are the primary determinants of skin, hair and exoskeletal pigmentation in mammals, birds and insects [1][2][3][4][5][6], and their importance has been growing over the past few years not only from a biological point of view, related to their role in the human body, but also for the exploitation of their unique properties in biomedicine or in the cosmetic and health sectors [7][8][9][10][11][12][13][14][15][16]. These pigments are biosynthesized in melanocytes, starting with the oxidation of tyrosine to dopaquinone catalyzed by the enzyme tyrosinase ( Figure 1) [1,17,18].…”

Unconventional Constituents and Shared Molecular Architecture of the Melanized Cell Wall of C. neoformans and Spore Wall of S. cerevisiae

“…Melanins are a class of structurally diverse pigments that are produced via the oxidation and polymerization of aromatic ring compounds. They share a multitude of remarkable properties such as the ability to absorb ultraviolet (UV) light, transduce electricity, and protect against ionizing radiation [ 11 , 12 , 13 ]. Unlike most melanotic microorganisms that produce 1,8-dihydroxynaphthalene (DHN) melanin from endogenously synthesized substrates, C. neoformans synthesizes 3,4-dihydroxyphenylalanine (DOPA) melanin (also called eumelanin) exclusively from exogenous precursors, particularly from catecholamines and other phenolic compounds found in its environment [ 14 ].…”