Natural abiotic iron-oxido-mediated formation of C1 and C2 compounds from environmentally important methyl-substituted substrates

Organic and inorganic volatile compounds containing one carbon atom (C1), such as carbon dioxide, methane, methanol, formaldehyde and chloromethane are ubiquitous in the environment and play an important role in atmospheric physics and chemistry as they act as greenhouse gases, destroy ozone and control the atmospheric oxidation capacity. Up to now, most C1 compounds in the environment were associated to complex metabolic and enzymatic pathways in organisms or to combustion processes of organic matter. So far, it was not recognized that many C1 and C2 compounds might also have a common origin in methyl groups of methyl-substituted substrates that are cleaved by the iron-catalyzed formation of methyl radicals. Here, using stable isotope techniques we present a mechanism for the formation of all major C1 and various C2 compounds from methyl radicals derived from methyl-substituted substrates such as dimethyl sulfoxide (DMSO). We applied isotopic labeling experiments (²H, ¹³C and ¹⁸O labeling) in order to investigate (using GC-MS and GC-IRMS) the source of the carbon, hydrogen and oxygen groups in the formed products C1 and C2 compounds. Our combined approach (experimental, computational, and based on field studies) implies that the iron-oxido-mediated process is a common abiotic source for environmentally important gases and of potential relevance for the global carbon cycling.