CC BY
0The influence of copper ions on eumelanin hydration examined by
mid-infrared spectroscopy
P.A. Abramov1*, A.B. Mostert2, K.A. Motovilov1
1-Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141700 Russia 2- Swansea University, Department of Chemistry, Singleton Park, Wales, UK
* pbrmv@phystech. edu
Melanins are promising natural materials for applications in bioelectronic devices such as organic electrochemical transistors [1], memristors [2], supercapacitors [3], and pH sensors [4]. Similar to bioorganics the properties of melanins are highly influenced by water and naturally occurring d-elements. Being a critical part of tyrosinase synthesis machinery, copper ions are widely presented in biologically derived melanins. In the current study we examine water and Cu2+ ions effects on eumelanin by infrared spectroscopy for the first time. Our findings reveal that copper ions significantly alter the properties of both melanin and hydration layers. Notably, with an increase of copper content, the fraction of 4-hydrogen bonded water molecules also increases, rendering general water behavior more ice-like. Copper ions shift the comproportionation reaction between quinone and hydroquinone moieties towards the formation of semiquinone radicals even in the dry system. Also, we demonstrate that these ions tend to decrease the contribution of some signatures of aqueous proton cations. The general picture explains the mechanisms of conductivity inhibition induced in melanin by copper ions via both trapping electron density of semiquinone radicals in corresponding complexes and by decreasing the proton diffusion efficiency via the transformation of water into a more ice-like structure.
The work was supported by the RSF grant 19-73-10154.
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