Humic substances (HSs) are collections of diverse organic compounds with broad redox capacities, which directly or indirectly affect the biogeochemical behaviors and fates of almost all the pollutants in the environment. The present study investigates the relationships between the molecular characteristics of HSs and their reducing capacities or electron-donating capacities (EDCs) by electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), total phenolic assay, and mediated electrochemical oxidation analysis. For decreasing the molecular heterogeneity of bulk HSs, HSs were first separated into three fractions according to their polarities. The results demonstrated that compounds in HS fractions with moderate polarity possessed a high content of total phenols and consistently had high EDCs. A strong linear correlation (R² = 0.97) existed between EDCs and the total phenolic content, which confirmed that phenols contributed to the EDCs of HSs. Further analysis of molecular components confirmed that polyphenol-like compounds with medium oxygen content were the major moieties acting as electron donors in HSs. This study provides a linkage between the molecular components of HSs and their EDCs, which will help us to understand the molecular-dependent reducing properties of HSs or other dissolved organic matters under oxic conditions.

中文翻译：

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分子成分与腐殖质还原能力的关系

腐殖质（HSs）是具有广泛氧化还原能力的多种有机化合物的集合，这些化合物直接或间接影响环境中几乎所有污染物的生物地球化学行为和命运。本研究通过电喷雾电离结合傅里叶变换离子回旋共振质谱（FT-ICR-MS），总酚分析和介导方法研究了HS的分子特性与其还原能力或给电子能力（EDC）之间的关系。电化学氧化分析。为了降低本体HS的分子异质性，首先根据其极性将HS分为三个部分。结果表明，具有中等极性的HS馏分中的化合物具有较高的总酚含量，并且始终具有较高的EDC。在EDC与总酚含量之间存在R ² = 0.97），这证实了酚对HS的EDC有贡献。分子成分的进一步分析证实，具有中等氧含量的多酚样化合物是HSs中充当电子给体的主要部分。这项研究提供了HS和其EDC的分子成分之间的联系，这将有助于我们了解在有氧条件下HS或其他溶解的有机物的分子依赖性还原性质。