College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.; The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China.
Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195-2700, United States.
Water Res. 2023 Oct 1;244:120522. doi: 10.1016/j.watres.2023.120522. Epub 2023 Aug 24.
Natural organic matter (NOM) is critical for the biogeochemical cycles of energy and many elements in terrestrial and aquatic ecosystems, and protonation-active functional groups in NOM molecules, notably carboxylic and phenolic groups often mediate these critical environmental functions. Molecular heterogeneity, polydispersity and dynamic behavior of NOM complicate achieving an unambiguous description of its molecular properties and reactivity. This study demonstrates that differential ultraviolet-visible (UV/VIS) absorbance spectra (DAS) of NOM acquired at varying pH values exhibit several distinct features associated with the deprotonation of NOM molecules, independent of the environmental provenance of NOM (e.g., surface water, seawater, sediment, and wastewater). The protonation-active functionalities that contribute to the Gaussian distribution bands present in the DAS were identified here by comparing characteristic properties of the bands with the stoichiometries of NOM molecules ascertained by Ultrahigh-Resolution Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). The protonation-active individual chromophores universally present in NOM molecules were identified by a genetic molecular network analysis. The observed DAS features were closely modeled via superimposing DAS spectra of 51 individual protonation-active chromophores. Molecular orbital theory was applied to further interpret the deprotonation of these chromophores, their molecular structure, electron distribution, and electron transitions measured using DAS. The high sensitivity and easy implementation of the DAS approach allows using it as a powerful tool to quantify the molecular properties and reactivity of NOM at environmental concentrations.
天然有机物 (NOM) 对陆地和水生生态系统的能量和许多元素的生物地球化学循环至关重要，NOM 分子中的质子化活性官能团，特别是羧酸和酚基团，通常介导这些关键的环境功能。NOM 的分子异质性、多分散性和动态行为使得难以明确描述其分子特性和反应性。本研究表明，在不同 pH 值下获得的天然有机物的差示紫外可见（UV/VIS）吸收光谱（DAS）表现出与 NOM 分子去质子化相关的几个明显特征，而与 NOM 的环境来源（例如地表水、海水、沉积物和废水）无关。通过将带的特征性质与超高效分辨率傅里叶变换离子回旋共振质谱 (FT-ICR-MS) 确定的 NOM 分子的化学计量进行比较，确定了对 DAS 中存在的高斯分布带做出贡献的质子化活性官能团。通过遗传分子网络分析鉴定了普遍存在于 NOM 分子中的质子化活性单体发色团。通过叠加 51 个单体发色团的 DAS 光谱，对观察到的 DAS 特征进行了紧密建模。应用分子轨道理论进一步解释了这些发色团的去质子化、它们的分子结构、电子分布以及使用 DAS 测量的电子跃迁。DAS 方法具有高灵敏度和易于实施的特点，使其成为在环境浓度下定量 NOM 分子特性和反应性的有力工具。
