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Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin

A. Bernardus Mostert, Graeme R. Hanson, Tadeusz Sarna, Ian R. Gentle, Benjamin J. Powell, Paul Meredith Orcid Logo, Bernard Mostert Orcid Logo

The Journal of Physical Chemistry B, Volume: 117, Issue: 17, Pages: 4965 - 4972

Swansea University Authors: Paul Meredith Orcid Logo, Bernard Mostert Orcid Logo

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DOI (Published version): 10.1021/jp401615e

Abstract

Melanin, the human skin pigment, is found everywhere in nature. Recently it has gained significant attention for its potential bioelectronic properties. However, there remain significant obstacles in realizing its electronic potential, in particular, the identity of the solid-state free radical in e...

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Published in: The Journal of Physical Chemistry B
ISSN: 1520-6106 1520-5207
Published: 2013
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URI: https://cronfa.swan.ac.uk/Record/cronfa38483
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spelling 2018-02-09T12:49:30.9385029 v2 38483 2018-02-09 Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin 31e8fe57fa180d418afd48c3af280c2e 0000-0002-9049-7414 Paul Meredith Paul Meredith true false a353503c976a7338c7708a32e82f451f 0000-0002-9590-2124 Bernard Mostert Bernard Mostert true false 2018-02-09 SPH Melanin, the human skin pigment, is found everywhere in nature. Recently it has gained significant attention for its potential bioelectronic properties. However, there remain significant obstacles in realizing its electronic potential, in particular, the identity of the solid-state free radical in eumelanin, which has been implicated in charge transport. We have therefore undertaken a hydration-controlled continuous-wave electron paramagnetic resonance study on solid-state eumelanin. Herein we show that the EPR signal from solid-state eumelanin arises predominantly from a carbon-centered radical but with an additional semiquinone free radical component. Furthermore, the spin densities of both of these radicals can be manipulated using water and pH. In the case of the semiquinone radical, the comproportionation reaction governs the pH- and hydration-dependent behavior. In contrast, the mechanism underlying the carbon-centered radical’s pH- and hydration-dependent behavior is not clear; consequently, we have proposed a new destacking model in which the intermolecular structure of melanin is disordered due to π–π destacking, brought about by the addition of water or increased pH, which increases the proportion of semiquinone radicals via the comproportionation reaction. Journal Article The Journal of Physical Chemistry B 117 17 4965 4972 1520-6106 1520-5207 Melanin, electron paramagnetic resonance, semiquinone, carbon centered radicalm, comproportionation reaction, destacking 2 5 2013 2013-05-02 10.1021/jp401615e COLLEGE NANME Physics COLLEGE CODE SPH Swansea University 2018-02-09T12:49:30.9385029 2018-02-09T12:49:30.9697020 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Physics A. Bernardus Mostert 1 Graeme R. Hanson 2 Tadeusz Sarna 3 Ian R. Gentle 4 Benjamin J. Powell 5 Paul Meredith 0000-0002-9049-7414 6 Bernard Mostert 0000-0002-9590-2124 7
title Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin
spellingShingle Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin
Paul Meredith
Bernard Mostert
title_short Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin
title_full Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin
title_fullStr Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin
title_full_unstemmed Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin
title_sort Hydration-Controlled X-Band EPR Spectroscopy: A Tool for Unravelling the Complexities of the Solid-State Free Radical in Eumelanin
author_id_str_mv 31e8fe57fa180d418afd48c3af280c2e
a353503c976a7338c7708a32e82f451f
author_id_fullname_str_mv 31e8fe57fa180d418afd48c3af280c2e_***_Paul Meredith
a353503c976a7338c7708a32e82f451f_***_Bernard Mostert
author Paul Meredith
Bernard Mostert
author2 A. Bernardus Mostert
Graeme R. Hanson
Tadeusz Sarna
Ian R. Gentle
Benjamin J. Powell
Paul Meredith
Bernard Mostert
format Journal article
container_title The Journal of Physical Chemistry B
container_volume 117
container_issue 17
container_start_page 4965
publishDate 2013
institution Swansea University
issn 1520-6106
1520-5207
doi_str_mv 10.1021/jp401615e
college_str Faculty of Science and Engineering
hierarchytype
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 Biosciences, Geography and Physics - Physics{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Physics
document_store_str 0
active_str 0
description Melanin, the human skin pigment, is found everywhere in nature. Recently it has gained significant attention for its potential bioelectronic properties. However, there remain significant obstacles in realizing its electronic potential, in particular, the identity of the solid-state free radical in eumelanin, which has been implicated in charge transport. We have therefore undertaken a hydration-controlled continuous-wave electron paramagnetic resonance study on solid-state eumelanin. Herein we show that the EPR signal from solid-state eumelanin arises predominantly from a carbon-centered radical but with an additional semiquinone free radical component. Furthermore, the spin densities of both of these radicals can be manipulated using water and pH. In the case of the semiquinone radical, the comproportionation reaction governs the pH- and hydration-dependent behavior. In contrast, the mechanism underlying the carbon-centered radical’s pH- and hydration-dependent behavior is not clear; consequently, we have proposed a new destacking model in which the intermolecular structure of melanin is disordered due to π–π destacking, brought about by the addition of water or increased pH, which increases the proportion of semiquinone radicals via the comproportionation reaction.
published_date 2013-05-02T03:48:40Z
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score 11.037056

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