Aggregation and disaggregation of humic supramolecular assemblies by NMR diffusion ordered spectroscopy (DOSY-NMR).
Aggregation and disaggregation of humic supramolecular assemblies by NMR diffusion ordered spectroscopy (DOSY-NMR).
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DOI：
10.1021/es071828p
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发表时间：
2008-02
影响因子：
11.4
通讯作者：
D. Šmejkalová;A. Piccolo
中科院分区：
文献类型：
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作者：
D. Šmejkalová;A. Piccolo
扩散有序核磁共振波谱 (DOSY-NMR) 应用于多种不同来源的黄腐酸 (FA) 和腐殖酸 (HA)。 DOSY 基于扩散系数 (D) 实现的光谱分离，并通过校准标准与分子大小相关，表明碳水化合物在 FA 中具有最大的分子大小，而烷基或芳香族成分是 HA 中扩散最慢的部分。随着浓度的增加，这些成分在所有腐殖质样品的 DOSY 光谱中总是具有较低的 D 值，从而表明聚集成明显更大的组合，其增加的流体动力学半径通过粘度测量得到证实。当腐殖质溶液的 pH 值从碱性变为酸性（3.6）时，DOSY 检测到的组分扩散率显着增加，表明聚集和分子尺寸减小。通过多变量统计分析实现了 HA 和 FA 分子大小的总体比较。虽然观察到 HA 的聚集和解聚程度比 FA 更大，但在类似条件下，对于真正的大聚合物标准品，没有检测到聚集。聚合物分子和腐殖质样品之间的这种扩散差异与腐殖质的超分子性质一致。还通过 DOSY 谱中扩散率的变化和 1 H NMR 信号的移动研究了腐殖质胶束的可能形成。除了泥炭和土壤来源的HA在4 mg·mL(-1)浓度下显示出胶束状结构的自组装外，没有其他腐殖质样品显示出临界胶束浓度(cmc)高达20 mg·mL(-1)的证据。这些结果表明 DOSY-NMR 波谱是评估天然腐殖质超结构中不同分子大小成分的有用技术。
Diffusion ordered nuclear magnetic resonance spectroscopy (DOSY-NMR) was applied to a number of fulvic (FA) and humic (HA) acids of different origin. Spectral separation achieved by DOSY based on diffusion coefficients (D), and correlated to molecular sizes by calibration standards, showed that carbohydrates had the largest molecular size in FA, whereas alkyl or aromatic components were the most slowly diffusing moieties in HA. At increasing concentrations, these components had invariably lower D values in DOSY spectra for all humic samples,thereby indicating an aggregation into apparently larger associations, whose increased hydrodynamic radius was confirmed by viscosity measurements. When humic solutions were broughtfrom alkaline to acidic pH (3.6), components diffusivity detected by DOSY increased significantly, suggesting a decrease of aggregation and molecular size. A general comparison of HA and FA molecular sizes was achieved by multivariate statistical analysis. While a larger extent of aggregation and disaggregation was observed for HA than for FA, no aggregation was detected, under similar conditions, for a true macropolymeric standard. Such difference in diffusion between a polymeric molecule and humic samples, is in line with the supramolecular nature of humic matter. The possible formation of humic micelles was also investigated by both changes of diffusivity in DOSY spectra and shift of 1H NMR signals. Except for HA of peat and soil origin, revealing a self-assembling in micelle-like structures at the 4 mg mL(-1) concentration, no other humic sample showed evidence of critical micelle concentration (cmc) up to 20 mg mL(-1). These results indicated that DOSY-NMR spectroscopy is a useful technique to evaluate components of different molecular size in natural humic superstructures.