Evidence of Porphyrin‐Like Structures in Natural Melanin Pigments Using Electrochemical Fingerprinting

Abstract

Eumelanins are extended heterogeneous biopolymers composed of molecular subunits with ambiguous macromolecular topology. Here, an electrochemical fingerprinting technique is described, which suggests that natural eumelanin pigments contain indole-based tetramers that are arranged into porphyrin-like domains. Spectroscopy and density functional theory calculations suggest that sodium ions undergo occupancy-dependent stepwise insertion into the core of porphyrin-like tetramers in natural eumelanins at discrete potentials.

Polydopamine and eumelanin molecular structures investigated with ab initio calculations

“…45 These tetramers are made through 2,7′- & 2,7′- & 2,7′-position, creating an interior ring where all the nitrogen atoms are in the center, in an arrangement similar to porphyrin. Such arrangement was first proposed by Kaxiras 25,26 and have been adopted to study the structural, mechanical, and optical properties of PDA and eumelanin in our previous computational work.…”

Natural melanin pigments and their interfaces with metal ions and oxides: emerging concepts and technologies

“…Tetramers have been proposed as molecular units to explain a number of functional properties of eumelanin. [13][14][15][16][17] The π-π-stacked eumelanin protomolecules with different sizes, randomly oriented, leading to peculiar excitonic interactions among them, have been proposed to explain the broadband optical absorption of eumelanin (see "Photophysical behavior of eumelanin: absorption spectrum, chromophoric species" section and Fig. 3).…”

Materialien und Strukturen für schluckbare elektromechanische medizinische Funktionseinheiten

“…[38][39][40] Melanin kann sowohl als Anode wie auch als Kathode fungieren, je nach Reduktionspotenzial der Gegenelektrode.Z um Beispiel kçnnen wässrige Natriumionen-Primärzellen mit voroxidierten Melanin-Kathoden gekoppelt mit keramikbasierten Anoden bei 0.5 Vb etrieben werden und zeigen nominal-spezifische Energiekapazitäten von 25 mWhg À1 (Abbildung 3). Natürliche Melanin-Pigmente und synthetische Analoga (zur Einfachheit hier als Melanine bezeichnet) kçnnen als Elektrodenmaterial in verschiedenen Konfigurationen wasserbasierter Batterien dienen.…”