Lignin- and tannin-like phenolic compounds are shown to be the major compositions of electron donating moieties (EDM) of aquatic natural organic matter (NOM). However, little is known about the compositions of EDMs within effluent organic matter (EfOM). In the present study, chlorine dioxide (ClO2) was used as a selectively oxidative probe to investigate the difference in the molecular composition of EDM between NOM and EfOM due to its high selectivity towards electron-rich compounds. The results showed that there was a large difference in the bulk and molecular properties of ClO2-reactive moieties between EfOM and NOM. Specifically, ClO2-reactive moieties of EfOM are distributed in a narrower molecular weight range (i.e., 0.9 kDa to 3.0 kDa) compared to NOM (i.e., 1.0 kDa to 20 kDa). The molecular-level analysis demonstrated that highly aromatic, reduced formulas (O/C = 0.33 ± 0.16; H/C = 1.10 ± 0.34) referring the lignin- and tannin-like compounds within both NOM and EfOM were susceptible to oxidation by ClO2, while more saturated formulas including the peptide-like formulas (H/C = 1.59 ± 0.36) within EfOM were reactive towards ClO2. Furthermore, the nitrogen (N)-containing formulas in EfOM are suggested to be the major EDMs compared to the CHO-only formulas dominating the EDM in NOM. This study has important implications for understanding of the origin and chemical nature of EDM in DOM from various sources and provides molecular-level evidence for the selectivity of ClO2 as an oxidant towards DOM.

中文翻译：

---

二氧化氯探测天然有机物与流出有机物的电子供体分子组成差异


木质素和单宁样酚类化合物被证明是水生天然有机物 （NOM） 的电子供体部分 （EDM） 的主要组成。然而，人们对流出有机物 （EfOM） 中 EDM 的成分知之甚少。在本研究中，二氧化氯 （ClO2） 用作选择性氧化探针，以研究 NOM 和 EfOM 之间 EDM 分子组成的差异，因为它对富电子化合物具有高选择性。结果表明，EfOM 和 NOM 之间 ClO2 反应性部分的体积和分子性质存在很大差异。具体而言，与 NOM（即 1.0 kDa 至 20 kDa）相比，EfOM 的 ClO2 反应性部分分布在更窄的分子量范围内（即 0.9 kDa 至 3.0 kDa）。分子水平分析表明，高度芳香族、还原的配方 （O/C = 0.33 ± 0.16;H/C = 1.10 ± 0.34） 表示 NOM 和 EfOM 中的木质素和单宁样化合物易被 ClO 2 氧化，而 EfOM 中包括肽样分子式 （H/C = 1.59 ± 0.36） 在内的更饱和分子式对 ClO 2 有反应。此外，与 NOM 中主导 EDM 的纯 CHO 公式相比，EfOM 中含氮 （N） 的公式被认为是主要的 EDM。这项研究对于从各种来源理解 DOM 中 EDM 的来源和化学性质具有重要意义，并为 ClO2 作为氧化剂对 DOM 的选择性提供了分子水平证据。