Novel insights on the physicochemical properties of eumelanins and their DMSO derivatives

Abstract

The biopigment eumelanin, ubiquitous in flora and fauna, is made up of chemically heterogeneous macromolecules based on the 5,6‐dihydroxyindole and 5,6‐dihydroxyindole‐2‐carboxylic acid building blocks. The exciting possibility of designing eumelanin‐based technologies for bioelectronics and sustainable electronics has to be properly assessed by gaining insights on the charge transfer and charge carrier transport in the pigment, preferably in film form, easily amenable to devices. In this work, we report a study on the electrochemical behaviour of films of eumelanin and its derivatives synthesized in dimethyl sulfoxide (DMSO eumelanins) in different aqueous electrolytes, with different chemical compositions and pH. DMSO eumelanins feature an improved solubility in the solvent DMSO, of relevance for processing purposes. The voltammetric currents are higher at relatively low pH (5.5), as expected considering the well‐established proton transport properties of the biopigment. Raman spectroscopy and atomic force microscopy performed on eumelanin films were combined with thermogravimetry with the aim of advancing knowledge on the molecular and supramolecular features of synthetic commercially available eumelanin, DMSO eumelanins as well as natural eumelanin (Sepia melanin). The results collected permit unprecedented insights on the physicochemical properties of eumelanin. © 2016 Society of Chemical Industry

Anomalous evolution of broadband optical absorption reveals dynamic solid state reorganization during eumelanin build-up in thin films

“…Moreover a shoulder around 1200 cm −1 is also present, further confirming the eumelanin signature 29 .…”

Structural and optical properties of soluble melanin analogues with enhanced photoluminescence quantum efficiency

“…Notice that DMel‐4P has the lowest grain size, which can be related to the higher DHICA/DHI ratio since it is known that DHICA monomers form smaller and more elongated aggregates . Previous AFM results reported a similar effect in DMel . The higher values of d and D for DMel‐8P on the other hand can be assigned to SO 4 2− trapped inside the macromolecule.…”

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

“…Crucial features of melanogenesis, such as the rate of formation of eumelanin [49] and the relative percentage of the two indolic building blocks present (DHI versus DHICA), [50,51] are influenced by the presence of metal ions. Whether their influence on self-assembly and structure is significant [52,53] or not [54] is still a matter of debate. Neuromelanin, another class of melanins, is a black insoluble pigment found in some (but not all) dopaminergic neurons of three regions of the brain: the "substantia nigra" of the midbrain (where it derives from dopamine), the "locus coeruleus" in the pons and small regions of the "medulla oblongata" (where it derives from noradrenaline) (Fig.…”