A survey of methoxyl and methyl isotopic clumping in a variety of biologic and synthetic materials

Stable isotope measurements are important tracers of sample origins and formational conditions, including distinguishing between samples formed via synthetic vs. biological pathways. Here we present results that establish the ability of multiply substituted isotopologues, colloquially termed clumped isotopes, of methoxyl and methyl groups (Δ¹³CH₂D and Δ¹²CHD₂) can be used to distinguish biologically- from synthetically- generated materials and related to these (bio)chemical formational pathways. Specifically, we demonstrate that there is a large distinction between Δ¹³CH₂D values of plant-derived methoxyl groups vs. synthetic groups, including in the same molecule (e.g., vanillin). These distinctions are independent of bulk methoxyl and methyl hydrogen and carbon isotopic compositions. We discuss the processes that can generate these differences as well as implications for the study of methane clumped isotopes in the environment.