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Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy

Zakhar V. Bedran, Sergey S. Zhukov, Pavel A. Abramov, Ilya O. Tyurenkov, Boris P. Gorshunov, Bernard Mostert Orcid Logo, Konstantin A. Motovilov

Polymers, Volume: 13, Issue: 24, Start page: 4403

Swansea University Author: Bernard Mostert Orcid Logo

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DOI (Published version): 10.3390/polym13244403

Abstract

Eumelanin is a widespread biomacromolecule pigment in the biosphere and has been widely investigated for numerous bioelectronics and energetic applications. Many of these applications depend on eumelanin's ability to conduct proton current at various levels of hydration. The origin of this beha...

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Published in: Polymers
ISSN: 2073-4360
Published: MDPI AG 2021
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URI: https://cronfa.swan.ac.uk/Record/cronfa59165
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spelling 2022-01-12T15:41:11.1792559 v2 59165 2022-01-12 Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy a353503c976a7338c7708a32e82f451f 0000-0002-9590-2124 Bernard Mostert Bernard Mostert true false 2022-01-12 BGPS Eumelanin is a widespread biomacromolecule pigment in the biosphere and has been widely investigated for numerous bioelectronics and energetic applications. Many of these applications depend on eumelanin's ability to conduct proton current at various levels of hydration. The origin of this behavior is connected to a comproportionation reaction between oxidized and reduced monomer moieties and water. A hydration-dependent FTIR spectroscopic study on eumelanin is presented herein, which allows for the first time tracking the comproportionation reaction via the gradual increase of the overall aromaticity of melanin monomers in the course of hydration. We identified spectral features associated with the presence of specific "one and a half" CO bonds, typical for -semiquinones. Signatures of semiquinone monomers with internal hydrogen bonds and that carboxylic groups, in contrast to semiquinones, begin to dissociate at the very beginning of melanin hydration were indicated. As such, we suggest a modification to the common hydration-dependent conductivity mechanism and propose that the conductivity at low hydration is dominated by carboxylic acid protons, whereas higher hydration levels manifest semiquinone protons. Journal Article Polymers 13 24 4403 MDPI AG 2073-4360 melanin; FTIR spectroscopy; water; comproportionation 15 12 2021 2021-12-15 10.3390/polym13244403 COLLEGE NANME Biosciences Geography and Physics School COLLEGE CODE BGPS Swansea University This work was supported by the Russian Science Foundation, Grant 19-73-10154. A.B.M. is a Sêr Cymru II fellow, and the results incorporated in this work are supported by the Welsh Government through the European Union’s Horizon 2020 Research and Innovation Program under Marie Skłodowska-Curie Grant Agreement No. 663830 2022-01-12T15:41:11.1792559 2022-01-12T15:34:16.0202331 Faculty of Science and Engineering School of Engineering and Applied Sciences - Chemistry Zakhar V. Bedran 1 Sergey S. Zhukov 2 Pavel A. Abramov 3 Ilya O. Tyurenkov 4 Boris P. Gorshunov 5 Bernard Mostert 0000-0002-9590-2124 6 Konstantin A. Motovilov 7 59165__22132__b88973919a4f4c5eb3cf970e88305714.pdf 59165.pdf 2022-01-12T15:36:58.3600568 Output 4087941 application/pdf Version of Record true © 2021 by the authors. This is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license true eng https://creativecommons.org/licenses/by/4.0/
title Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
spellingShingle Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
Bernard Mostert
title_short Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
title_full Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
title_fullStr Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
title_full_unstemmed Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
title_sort Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
author_id_str_mv a353503c976a7338c7708a32e82f451f
author_id_fullname_str_mv a353503c976a7338c7708a32e82f451f_***_Bernard Mostert
author Bernard Mostert
author2 Zakhar V. Bedran
Sergey S. Zhukov
Pavel A. Abramov
Ilya O. Tyurenkov
Boris P. Gorshunov
Bernard Mostert
Konstantin A. Motovilov
format Journal article
container_title Polymers
container_volume 13
container_issue 24
container_start_page 4403
publishDate 2021
institution Swansea University
issn 2073-4360
doi_str_mv 10.3390/polym13244403
publisher MDPI AG
college_str Faculty of Science and Engineering
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hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Chemistry{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Chemistry
document_store_str 1
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description Eumelanin is a widespread biomacromolecule pigment in the biosphere and has been widely investigated for numerous bioelectronics and energetic applications. Many of these applications depend on eumelanin's ability to conduct proton current at various levels of hydration. The origin of this behavior is connected to a comproportionation reaction between oxidized and reduced monomer moieties and water. A hydration-dependent FTIR spectroscopic study on eumelanin is presented herein, which allows for the first time tracking the comproportionation reaction via the gradual increase of the overall aromaticity of melanin monomers in the course of hydration. We identified spectral features associated with the presence of specific "one and a half" CO bonds, typical for -semiquinones. Signatures of semiquinone monomers with internal hydrogen bonds and that carboxylic groups, in contrast to semiquinones, begin to dissociate at the very beginning of melanin hydration were indicated. As such, we suggest a modification to the common hydration-dependent conductivity mechanism and propose that the conductivity at low hydration is dominated by carboxylic acid protons, whereas higher hydration levels manifest semiquinone protons.
published_date 2021-12-15T08:08:39Z
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