化学
腐植酸
质子化
膦酸盐
核磁共振波谱
氢键
腐殖质
有机质
溶解有机碳
疏水效应
无机化学
环境化学
有机化学
分子
土壤水分
离子
土壤科学
环境科学
肥料
作者
Pierluigi Mazzei,Alessandro Piccolo
摘要
Interactions of glyphosate (N-phosphonomethylglycine) herbicide (GLY) with soluble fulvic acids (FAs) and humic acids (HAs) at pH 5.2 and 7 were studied by 1H and 31P NMR spectroscopy. Increasing concentrations of soluble humic matter determined broadening and chemical shift drifts of proton and phosphorus GLY signals, thereby indicating the occurrence of weak interactions between GLY and humic superstructures. Binding was larger for FAs and pH 5.2 than for HAs and pH 7, thus suggesting formation of hydrogen bonds between GLY carboxyl and phosphonate groups and protonated oxygen functions in humic matter. Changes in relaxation and correlation times of 1H and 31P signals and saturation transfer difference NMR experiments confirmed the noncovalent nature of GLY–humic interactions. Diffusion-ordered NMR spectra allowed calculation of the glyphosate fraction bound to humic superstructures and association constants (Ka) and Gibbs free energies of transfer for GLY–humic complex formation at both pH values. These values showed that noncovalent interactions occurred most effectively with FAs and at pH 5.2. Our findings indicated that glyphosate may spontaneously and significantly bind to soluble humic matter by noncovalent interactions at slightly acidic pH and, thus, potentially pollute natural water bodies by moving through soil profiles in complexes with dissolved humus.
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