Hawkes Jeffrey A, Flygare Agnes D, Moodie Lindon W K, Craig Alexander J
Department of Chemistry BMC, Uppsala University, Uppsala 752 37, Sweden.
Department of Medicinal Chemistry, Uppsala University, Uppsala 752 37, Sweden.
Anal Chem. 2025 Sep 2;97(34):18612-18620. doi: 10.1021/acs.analchem.5c02665. Epub 2025 Aug 21.
Dissolved organic matter (DOM) is one of the most complex chemical mixtures known, with its chemical composition having long puzzled biogeochemists. Identifying the chemical structures within DOM is essential for unraveling its origins and environmental fate. However, DOM's complexity has impeded structural elucidation, and molecules with accurate functional group compositions for recalcitrant DOM are poorly represented in the synthetic and isolative literature. Consequently, hypothesized DOM compounds are derived from models that inadequately represent true structures. To address this, carboxylic-acid-only CRAM analogues were previously synthesized but failed to replicate the extensive fragmentation observed in marine DOM during tandem mass spectrometry (MS2). Here, we prepared CRAM analogues with varied oxygen functionalities to enable more diverse fragmentation pathways. Liquid chromatography (LC) studies showed that functional group composition better predicted LC polarity than the O/C ratio and that alcohols represented early eluting DOM profiles, while ethers, ketones, and lactones better represented mid-eluting isomers. MS2 studies revealed that the incorporation of α-hydroxy ketones and 1,2-diols led to the most extensive fragmentation. Ether and ester functionalities were labile even at low fragmentation energy, indicating that such groups are likely contributors to core marine DOM carbon backbones and contribute to the extensive fragmentation observed for natural DOM in all MS2 experiments. The data gathered within this work suggest that the widely discussed all carbon-backbone alicyclic model of CRAM is incompatible with the MS2 fragmentation data of DOM.
溶解有机物（DOM）是已知的最复杂的化学混合物之一，其化学组成长期以来一直困扰着生物地球化学家。确定DOM中的化学结构对于揭示其来源和环境归宿至关重要。然而，DOM的复杂性阻碍了结构解析，并且在合成和分离文献中，具有准确官能团组成的难降解DOM分子的代表性不足。因此，假设的DOM化合物来自不能充分代表真实结构的模型。为了解决这个问题，之前合成了仅含羧酸的CRAM类似物，但未能重现串联质谱（MS2）过程中在海洋DOM中观察到的广泛碎片化。在这里，我们制备了具有不同氧官能团的CRAM类似物，以实现更多样化的碎片化途径。液相色谱（LC）研究表明，官能团组成比O/C比能更好地预测LC极性，醇类代表早期洗脱的DOM谱图，而醚、酮和内酯能更好地代表中期洗脱的异构体。MS2研究表明，α-羟基酮和1,2-二醇的引入导致了最广泛的碎片化。即使在低碎片化能量下，醚和酯官能团也不稳定，这表明这些基团可能是海洋DOM核心碳骨架的组成部分，并导致在所有MS2实验中天然DOM观察到的广泛碎片化。这项工作中收集的数据表明，广泛讨论的CRAM全碳骨架脂环族模型与DOM的MS2碎片化数据不相符。
