Abstract Natural organic matter (NOM) is an important component in many near-surface geochemical environments, and its properties are greatly affected by the incorporation of water. Because of its importance, the macroscopic behavior and effects of water in NOM and soil organic matter (SOM) have been extensively studied using a wide range of experimental and computational methods. The molecular scale structural and dynamical behavior of water in these materials, however, is less well understood. This paper presents a variable temperature 2H NMR and XRD study of water in Suwannee River NOM and its fulvic acid (FA) and humic acid (HA) fractions that provides new insight into the dynamical behavior of structurally different types of water and exchangeable hydrogen environments in NOM. The results provide a basis for future studies of more complex natural organic materials and the interaction of organic materials with mineral surfaces. Room temperature 2H NMR spectra of samples hydrated in 2H2O and then dehydrated, distinguish 2H2O molecules that are in rapid reorientational motion (correlation times, νc, > 105 Hz), 2H exchanged onto carboxylic sites of the NOM that do not undergo rapid reorientation at frequencies >∼103 Hz, and 2H exchanged onto phenolic and possibly other alcohol sites of the NOM that undergoes rapid, but anisotropic, dynamical reorientation. For samples exposed to water and not dried, the XRD results collected at temperatures from 173 to 298 K show the formation of ice-1h in samples exposed to 100% relative humidity (R.H.) but not in samples exposed to 43% R.H. 2H NMR of those samples collected at temperatures from 313 K to 173 K show the presence of multiple sites. Near room temperature, the spectra contain a narrow resonance for mobile water undergoing rapid isotropic motion, and a broader symmetrical resonance probably due to a combination of more dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups undergoing rapid anisotropic motion. The 43% R.H. samples also yield a broader, quadrupole-dominated, resonance for 2H exchanged onto functional groups of the NOM. With decreasing temperature the resonances for dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups become broader, reflecting a decreasing rate of exchange between the water molecules and functional groups and a decreasing rate of reorientation of the 2H2O molecules. The formation of ice-1h is directly reflected in the 2H spectra of the 100% R.H. samples as a resonance with a quadrupole coupling constant (QCC) of ∼180 kHz. For the 43% R.H. samples, there is also a broad, poorly resolved resonance with typical QCCs of ∼180 kHz for which the relative signal intensity increases with decreasing temperature. This signal represents 2H2O molecules that are not crystallized in ice-1h but have greatly reduced reorientation frequencies at low temperature and a hydrogen bonding network with hydrogen bond strengths similar to, but somewhat weaker than, ice-1h. Such molecules are also likely to be present in the 100% R.H. samples. At both R.H.s, some of the 2H2O molecules do not freeze and retain their isotropic motion down to 173 K, the lowest temperature investigated.

中文翻译：

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水在天然有机物质中的结构和动力学作用：2 H NMR 和 XRD 研究

摘要 天然有机质（NOM）是许多近地表地球化学环境中的重要组成部分，其性质受水的掺入影响很大。由于其重要性，水在 NOM 和土壤有机质 (SOM) 中的宏观行为和影响已使用各种实验和计算方法进行了广泛研究。然而，对这些材料中水的分子尺度结构和动力学行为了解较少。本文介绍了对 Suwannee 河 NOM 中的水及其富里酸 (FA) 和腐植酸 (HA) 馏分的变温 2H NMR 和 XRD 研究，为了解结构不同类型的水和可交换氢环境中的动力学行为提供了新的见解。名额。该结果为未来研究更复杂的天然有机材料以及有机材料与矿物表面的相互作用提供了基础。在 2H2O 中水合然后脱水的样品的室温 2H NMR 光谱，区分快速重新定向运动的 2H2O 分子（相关时间，vc，> 105 Hz），2H 交换到 NOM 的羧基位点上，在频率下不会发生快速重新定向>~103 Hz 和 2H 交换到 NOM 的酚类和可能的其他醇位点上，这些位点经历快速但各向异性的动力学重新定向。对于暴露于水且未干燥的样品，在 173 至 298 K 的温度下收集的 XRD 结果表明，暴露于 100% 相对湿度 (RH) 的样品中形成了冰-1h，但暴露于 43% RH 的样品中没有 在 313 K 至 173 K 的温度下收集的那些样品的 2 H NMR 显示存在多个位点。在接近室温时，光谱包含对经历快速各向同性运动的流动水的窄共振，以及更宽的对称共振，这可能是由于更多动态限制的水分子和 2H 交换到经历快速各向异性运动的酚类和醇官能团上的组合。43% RH 样品还产生了更广泛的、四极杆主导的共振，用于交换到 NOM 的官能团上的 2H。随着温度的降低，动态限制的水分子和交换到酚和醇官能团上的 2H 的共振变得更广泛，反映了水分子和官能团之间交换速率的降低以及 2H2O 分子重新定向的速率的降低。ice-1h 的形成直接反映在 100% RH 样品的 2H 光谱中，作为与约 180 kHz 的四极耦合常数 (QCC) 的共振。对于 43% RH 样品，也有一个广泛的、分辨率较差的共振，典型的 QCC 约为 180 kHz，其相对信号强度随着温度的降低而增加。该信号表示 2H2O 分子在冰 1h 中未结晶，但在低温下重新定向频率大大降低，氢键网络的氢键强度与冰 1h 相似，但略弱于冰 1h。此类分子也可能存在于 100% RH 样品中。在两个 RH，