Exploring the Charge Transport of a Natural Eumelanin for Sustainable Technologies.

Eumelanin, the main quinone-based biomaterial of the melanin family of compounds, is emerging as a model for medical and sustainable electronic interfaces due to its biocompatibility, biodegradability, and transducing abilities. The study utilizes current-voltage measurements and impedance/dielectric spectroscopy under a controlled hydration atmosphere to investigate the charge transport of eumelanin produced from the S. parvus BSB49 strain. We show no differences in the electrical response in highly hydrated conditions compared to the standard synthetic eumelanin. Hence, our findings provide the groundwork to assess the potential use of this natural eumelanin in sustainable organic (bio)electronic applications.

Sulfonated melanin derivatives: theoretical evaluation of local reactivities and chemical structures.

Melanins are natural macromolecules present in several organisms responsible for photoprotection, photosensitivity, ion chelation, and thermoregulation. Such materials have attracted attention due to their interesting electronic properties, which suggest their possible application in biocompatible devices. However, the low typical solubility of traditional melanins does not allow the production of good quality thin films. In this sense, soluble compounds obtained via alternative synthetic routes, for instance, via levodopa (L-DOPA) oxidation in sulfonated solvents (S-melanins), can be considered interesting technological materials. Despite this, the structural and electronic features of these compounds are not fully understood. In this context, here we present a theoretical study on the local reactivities of S-melanin building blocks to better understand possible mechanisms involved in its synthesis and propose extended structures of this material. For this purpose, condensed-to-atoms Fukui indices were evaluated in the framework of the density functional theory (DFT). The obtained results show that the different side groups present in S-melanins do not significantly influence the reactivity of the compound in relation to non-functionalized melanins, indicating that both materials can present similar macroscopic structures.

Identification of Common Resonant Lines in the EPR Spectra of Melanins.

Melanins are natural pigments with promising bioelectronic applications. Among their unique properties, the existence of a persistent paramagnetic signal can be considered one of the most intriguing and controversial features. Additionally, the possible influence of such centers on charge transport accentuates the need for a better understanding of their origin and specific characteristics. In this report, electron paramagnetic resonance spectra of melanin samples obtained at different experimental conditions were systematically studied. From the fitting procedure, three distinct resonant lines are proposed, two associated with carbon-centered radicals and one with semiquinone free radicals.