Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy
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...
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| Format: | Article |
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MDPI AG
2021-12-01
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| Series: | Polymers |
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| Online Access: | https://www.mdpi.com/2073-4360/13/24/4403 |
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| author | Zakhar V. Bedran Sergey S. Zhukov Pavel A. Abramov Ilya O. Tyurenkov Boris P. Gorshunov A. Bernardus Mostert Konstantin A. Motovilov |
| author_facet | Zakhar V. Bedran Sergey S. Zhukov Pavel A. Abramov Ilya O. Tyurenkov Boris P. Gorshunov A. Bernardus Mostert Konstantin A. Motovilov |
| author_sort | Zakhar V. Bedran |
| collection | DOAJ |
| 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” C𝌁O bonds, typical for <i>o</i>-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. |
| first_indexed | 2024-03-10T03:15:22Z |
| format | Article |
| id | doaj.art-424a171f298a4be9916b735a02f38a3b |
| institution | Directory Open Access Journal |
| issn | 2073-4360 |
| language | English |
| last_indexed | 2024-03-10T03:15:22Z |
| publishDate | 2021-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Polymers |
| spelling | doaj.art-424a171f298a4be9916b735a02f38a3b2023-11-23T10:15:50ZengMDPI AGPolymers2073-43602021-12-011324440310.3390/polym13244403Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared SpectroscopyZakhar V. Bedran0Sergey S. Zhukov1Pavel A. Abramov2Ilya O. Tyurenkov3Boris P. Gorshunov4A. Bernardus Mostert5Konstantin A. Motovilov6Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Institute Lane 9, 141701 Dolgoprudny, RussiaCenter for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Institute Lane 9, 141701 Dolgoprudny, RussiaCenter for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Institute Lane 9, 141701 Dolgoprudny, RussiaCenter for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Institute Lane 9, 141701 Dolgoprudny, RussiaCenter for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Institute Lane 9, 141701 Dolgoprudny, RussiaDepartment of Chemistry, Swansea University, Singleton Park, Swansea SA2 8PP, UKCenter for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Institute Lane 9, 141701 Dolgoprudny, RussiaEumelanin 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” C𝌁O bonds, typical for <i>o</i>-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.https://www.mdpi.com/2073-4360/13/24/4403melaninFTIR spectroscopywatercomproportionation |
| spellingShingle | Zakhar V. Bedran Sergey S. Zhukov Pavel A. Abramov Ilya O. Tyurenkov Boris P. Gorshunov A. Bernardus Mostert Konstantin A. Motovilov Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy Polymers melanin FTIR spectroscopy water comproportionation |
| title | 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_short | 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 |
| topic | melanin FTIR spectroscopy water comproportionation |
| url | https://www.mdpi.com/2073-4360/13/24/4403 |
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