Unveiling Redox-Active Quinones in Pyrogenic Carbon by Nontargeted Metabolomics and Dual Chemical Tagging

Quinones in natural organic matter mediate key biogeochemical processes, including methane oxidation, iron reduction, and contaminant degradation. However, pinpointing their molecular identities in the environment remains a formidable challenge due to extreme compositional complexity. Here, we developed a workflow combining dual chemical tagging with high-resolution tandem mass spectrometry to profile quinones in a complex matrix. Applying this approach, we identified previously undisclosed quinones in a representative pyrogenic sample, including benzoquinones, alkylated chromene-diones, and hydroxylated naphthoquinone. Meta-analysis across public spectral repositories (>40,000 spectra) revealed that these quinones occur widely in 33 to 819 environmental samples spanning temperate to polar ecosystems. With estimated reduction-oxidation potential of 0.21-0.41 V (pH 7), these quinones fall within the range for natural electron shuttles, contributing 2.3%-11.5% of the redox capacity in natural and pyrogenic organic matter. This dual-tagging strategy overcomes a long-standing analytical barrier, providing unprecedented molecular-level insight and enabling accurate modeling of quinone-mediated biogeochemical and contaminant dynamics in complex systems.