Iron catalyzed formation of methyl radicals as a common source of environmentally important volatile organic compounds

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Organic and inorganic volatile compounds containing one carbon atom (C1), such as carbon dioxide, methane, methanol, formaldehyde, carbon monoxide and chloromethane are ubiquitous in the environment and play an important role in atmospheric physics and chemistry as they act as greenhouse gases, destroy stratospheric and tropospheric ozone and control the atmospheric oxidation capacity. Furthermore, these compounds play an important role in global carbon cycling. Up to now, most C1 compounds in the environment were associated to complex metabolic and enzymatic pathways in organisms or combustion processes of organic matter. So far, it was not recognized that many C1 compounds in the geobiosphere might also have a common origin in methyl groups from methyl-substituted substrates that are cleaved by the iron-catalyzed formation of methyl radicals. In this interdisciplinary proposal, we aim to combine the expertise of our two research groups that ideally complement each other in the environmental field and laboratory work, and experimental as well as computational/theoretical mechanistic work, to investigate the iron catalyzed formation of methyl radicals as a common source of environmentally important C1 compounds, and to determine the precise chemistry behind these processes. Based on our preliminary results we hypothesize that formation of methyl radicals by abiotic and possibly also by biochemical processes is ubiquitous in the environment with various heteroatom-methylated substrates. We propose that by generating methyl radicals formation of the entire set of C1 compounds with carbon oxidation states of -IV to +IV but also formation of short chain n-alkanes and alkenes is possible. The relative amounts of the formed individual C1 species might depend on the redox milieu and biogeochemical conditions such as the availability of methyl radical donors, iron species, oxygen, pH and possibly a range of other parameters. In this project, we will investigate systematically the formation of C1 compounds in the laboratory, using different iron species and biogeochemically relevant methyl-substituted substrates and applying stable isotope techniques. Furthermore, to thoroughly understand the chemistry behind these processes, we will identify the mechanistic steps of methyl radical and C1 formation and verify mechanistic scenarios using computational modeling based on density functional theory and ab-initio quantum-chemical studies, also in combination with reaction kinetics, spectroscopy of intermediates and product distributions. Finally, we will put our assembled knowledge into practice and study these reactions in water and soil samples collected from the field. The results from our project will help to improve our knowledge about formation processes of C1 compounds in the geobiosphere and help to design future studies investigating these processes under field-like conditions involving the application of both biological and geochemical tools.