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Direct Identification of Diverse Alicyclic Terpenoids in Suwannee River Fulvic Acid

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journal contribution
posted on 07.04.2015, 00:00 by Neal Arakawa, Lihini Aluwihare
The chemical complexity of dissolved organic matter (DOM) obstructs our ability to definitively recover source compounds from within DOM, an objective which has the capacity to alter our understanding of carbon sequestration on a global scale. To advance compositional studies of DOM we have applied a previously published reduction method to an environmental standard, Suwannee River Fulvic Acid (SRFA). The reduction products, comprising 12% of the prereduced carbon, were then separated by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF-MS). Results indicate that the majority of observed reduced compounds corresponded to alicyclic hydrocarbons in the size range C10 to C17. Cyclic terpenoids are the only biomolecule class with contiguous, alicyclic carbon backbones of this size. These terpenoid reduction products contain series offset by CH2 and exhibit great isomeric diversity, features previously inferred from ultrahigh resolution mass spectrometry and NMR studies of unreduced SRFA. Reduction of Taxodium leaf litter as a source material to SRFA confirmed the prevalence of terpenoids in SRFA and provided insight into the parent compounds that must be diagenetically modified on relatively short time scales. These data corroborate several recent studies that suggest alicyclic hydrocarbons to be important components of longer-lived DOM.