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Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups

[Image: see text] Carbon monoxide (CO) is the second most abundant identified product of dissolved organic matter (DOM) photodegradation after CO(2), but its formation mechanism remains unknown. Previous work showed that aqueous photodegradation of methoxy-substituted aromatics (ArOCH(3)) produces C...

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Autores principales: Ossola, Rachele, Gruseck, Richard, Houska, Joanna, Manfrin, Alessandro, Vallieres, Morgan, McNeill, Kristopher
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2022
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9494748/
https://www.ncbi.nlm.nih.gov/pubmed/36054115
http://dx.doi.org/10.1021/acs.est.2c03762
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author Ossola, Rachele
Gruseck, Richard
Houska, Joanna
Manfrin, Alessandro
Vallieres, Morgan
McNeill, Kristopher
author_facet Ossola, Rachele
Gruseck, Richard
Houska, Joanna
Manfrin, Alessandro
Vallieres, Morgan
McNeill, Kristopher
author_sort Ossola, Rachele
collection PubMed
description [Image: see text] Carbon monoxide (CO) is the second most abundant identified product of dissolved organic matter (DOM) photodegradation after CO(2), but its formation mechanism remains unknown. Previous work showed that aqueous photodegradation of methoxy-substituted aromatics (ArOCH(3)) produces CO considerably more efficiently than aromatic carbonyls. Following on this precedent, we propose that the methoxy aromatic groups of lignin act as the C source for the photochemical formation of CO from terrestrial DOM via a two-step pathway: formal hydrolytic demethylation to methanol and methanol oxidation to CO. To test the reasonableness of this mechanism, we investigated the photochemistry of eight lignin model compounds. We first observed that initial CO production rates are positively correlated with initial substrate degradation rates only for models containing at least one ArOCH(3) group, regardless of other structural features. We then confirmed that all ArOCH(3)-containing substrates undergo formal hydrolytic demethylation by detecting methanol and the corresponding phenolic transformation products. Finally, we showed that hydroxyl radicals, likely oxidants to initiate methanol oxidation to CO, form during irradiation of all models. This work proposes an explicit mechanism linking ubiquitous, abundant, and easily quantifiable DOM functionalities to CO photoproduction. Our results further hint that methanol may be an abundant (yet overlooked) DOM photoproduct and a likely precursor of formaldehyde, formic acid, and CO(2) and that lignin photodegradation may represent a source of hydroxyl radicals.
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spelling pubmed-94947482022-09-23 Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups Ossola, Rachele Gruseck, Richard Houska, Joanna Manfrin, Alessandro Vallieres, Morgan McNeill, Kristopher Environ Sci Technol [Image: see text] Carbon monoxide (CO) is the second most abundant identified product of dissolved organic matter (DOM) photodegradation after CO(2), but its formation mechanism remains unknown. Previous work showed that aqueous photodegradation of methoxy-substituted aromatics (ArOCH(3)) produces CO considerably more efficiently than aromatic carbonyls. Following on this precedent, we propose that the methoxy aromatic groups of lignin act as the C source for the photochemical formation of CO from terrestrial DOM via a two-step pathway: formal hydrolytic demethylation to methanol and methanol oxidation to CO. To test the reasonableness of this mechanism, we investigated the photochemistry of eight lignin model compounds. We first observed that initial CO production rates are positively correlated with initial substrate degradation rates only for models containing at least one ArOCH(3) group, regardless of other structural features. We then confirmed that all ArOCH(3)-containing substrates undergo formal hydrolytic demethylation by detecting methanol and the corresponding phenolic transformation products. Finally, we showed that hydroxyl radicals, likely oxidants to initiate methanol oxidation to CO, form during irradiation of all models. This work proposes an explicit mechanism linking ubiquitous, abundant, and easily quantifiable DOM functionalities to CO photoproduction. Our results further hint that methanol may be an abundant (yet overlooked) DOM photoproduct and a likely precursor of formaldehyde, formic acid, and CO(2) and that lignin photodegradation may represent a source of hydroxyl radicals. American Chemical Society 2022-09-02 2022-09-20 /pmc/articles/PMC9494748/ /pubmed/36054115 http://dx.doi.org/10.1021/acs.est.2c03762 Text en © 2022 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by-nc-nd/4.0/Permits non-commercial access and re-use, provided that author attribution and integrity are maintained; but does not permit creation of adaptations or other derivative works (https://creativecommons.org/licenses/by-nc-nd/4.0/).
spellingShingle Ossola, Rachele
Gruseck, Richard
Houska, Joanna
Manfrin, Alessandro
Vallieres, Morgan
McNeill, Kristopher
Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups
title Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups
title_full Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups
title_fullStr Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups
title_full_unstemmed Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups
title_short Photochemical Production of Carbon Monoxide from Dissolved Organic Matter: Role of Lignin Methoxyarene Functional Groups
title_sort photochemical production of carbon monoxide from dissolved organic matter: role of lignin methoxyarene functional groups
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9494748/
https://www.ncbi.nlm.nih.gov/pubmed/36054115
http://dx.doi.org/10.1021/acs.est.2c03762
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