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

含有一个碳原子（C1）的有机和无机挥发性化合物，如二氧化碳、甲烷、甲醇、甲醛、一氧化碳和氯甲烷等，普遍存在于环境中，它们作为温室气体，破坏平流层和对流层臭氧，控制大气氧化能力，在大气物理和化学中起着重要作用。此外，这些化合物在全球碳循环中发挥着重要作用。到目前为止，环境中的大多数C1化合物与生物体中复杂的代谢和酶促途径或有机物的燃烧过程有关。到目前为止，人们还没有认识到，地球生物圈中的许多C1化合物也可能有一个共同的起源，即甲基取代的基质被铁催化形成甲基自由基所裂解。在这个跨学科的建议，我们的目标是联合收割机的专业知识，我们的两个研究小组，理想地相互补充，在环境领域和实验室工作，以及实验和计算/理论的机械工作，调查铁催化形成的甲基自由基作为一个共同的来源，对环境有重要意义的C1化合物，并确定这些过程背后的精确化学。根据我们的初步结果，我们假设，形成甲基自由基的非生物和可能也由生物化学过程是普遍存在的环境中的各种杂原子甲基化的基板。我们建议，通过生成甲基自由基形成的整套C1化合物的碳氧化态-IV至+IV，但也形成短链正构烷烃和烯烃是可能的。所形成的单个C1物质的相对量可能取决于氧化还原环境和生物地球化学条件，例如甲基自由基供体、铁物质、氧、pH和可能的一系列其他参数的可用性。在这个项目中，我们将在实验室中系统地研究C1化合物的形成，使用不同的铁物种和地球化学相关的甲基取代底物，并应用稳定同位素技术。此外，为了彻底了解这些过程背后的化学，我们将确定甲基自由基和C1形成的机械步骤，并使用基于密度泛函理论和从头算量子化学研究的计算建模来验证机械方案，同时结合反应动力学，中间体光谱和产物分布。最后，我们将把我们组装的知识付诸实践，并研究这些反应的水和土壤样品从外地收集。从我们的项目的结果将有助于提高我们的知识C1化合物在地球生物圈的形成过程，并有助于设计未来的研究调查这些过程中涉及的应用领域的条件下，生物和地球化学工具。

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.