oa Quantum Tunneling Effect Reflected by Isotopic Fractionation During Aerobic Methanotrophy

Microbial oxidation of methane (methanotrophy) occurs under either aerobic or anaerobic conditions. While both pathways involve hydrogen abstraction as the activation step for methane, their active sites differ. In aerobic methanotrophy, the active sites are typically copper-oxygen complexes, whereas in anaerobic methanotrophy, they are often sulfur-metal complexes. These pathways exhibit distinct energy barriers, quantum tunneling effects, and isotopic fractionation patterns. We conducted simulations based on density-functional theory (DFT) and discovered that quantum tunneling governs the reaction rate of methane activation in aerobic methanotrophy, accelerating hydrogen abstraction by over 400 times and deuterium abstraction by over 35 times at 300.15 K. The results accurately explained isotopic fractionation patterns observed in laboratory experiments. These findings demonstrate the practicality and necessity of first-principles simulations for interpreting isotopic data in biogeochemistry, especially with advancements in quantum chemical tools.