Electrostatic potentials of humic acid: Fluorescence quenching measurements and comparison with model calculations
Electrostatic potentials of humic acid: Fluorescence quenching measurements and comparison with model calculations
复制标题
DOI：
10.1016/j.colsurfa.2008.10.038
复制
发表时间：
2009-09
期刊：
影响因子：
--
通讯作者：
Takumi Saito;L. Koopal;S. Nagasaki;Satoru Tanaka
中科院分区：
文献类型：
--
作者：
Takumi Saito;L. Koopal;S. Nagasaki;Satoru Tanaka
基于具有相似结构的中性和阳离子猝灭剂分子对腐殖酸荧光的猝灭，测量了纯化的奥德里奇腐殖酸（PAHA）的平均静电势。所获得的负电位增加，在给定的盐浓度的pH值的增加，并在给定的pH值的盐浓度的增加，弱下降。的趋势和幅度的电位对应于文献中的几个实验结果。与由PAHA的电荷计算的静电模型的电位比较表明，从离子渗透球模型和Donnan-EDL模型得到的平均电位与测量的平均电位一致。与这两个模型，它是假设的PAHA电荷的一部分被中和的PAHA颗粒周围的双电层（EDL）的观点，腐殖酸是一个纳米尺寸的颗粒，部分渗透到小离子和溶剂分子。由这两个模型计算的电势是粒子“内部”电势（其控制质子结合）和EDL中的电势的平均值。Donnan模型中，固定电荷和反电荷都分布在大于颗粒体积本身的体积上，导致比PAHA的测量平均电势更负的电势。这些观察结果表明，猝灭剂位于靠近官能团，但扩散结合。
Average electrostatic potentials of purified Aldrich humic acid (PAHA) are measured, based on quenching of the PAHA fluorescence by neutral and cationic quencher molecules with similar structures. The obtained negative potentials increased with increasing pH at a given salt concentration and weakly decreased with increasing salt concentration at given pH. The trends and the magnitudes of the potentials correspond with the few experimental results available in the literature. Comparison with potentials calculated by the electrostatic models from the charge of PAHA revealed that the average potentials obtained from the ion permeable sphere model and Donnan-EDL model agreed with the measured average potentials. With these two models it is assumed that a part of the PAHA charge is neutralized by the electrical double layer (EDL) around the PAHA particle in line with the view that humic acid is a nano-size particle partly permeable to small ions and solvent molecules. The potentials calculated by these two models are averages of the potential “inside” the particle (which governs the proton binding) and that in the EDL. The Donnan models, with both the fixed charges and the counter charges distributed over a volume that is greater than the particle volume itself, result in more negative potentials than the measured average potentials of PAHA. These observations suggest that the quenchers are located close to the functional groups but diffusely bound.