INQUIMAE, Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, pabellon II, C1428EHA Buenos Aires, Argentina.
Langmuir. 2010 Mar 2;26(5):3134-44. doi: 10.1021/la903086s.
A new model for the electrostatic contribution to ion binding to humic substances is proposed and applied to published data for proton binding to fulvic and humic acids. The elastic polyelectrolyte network model treats humic substance particles as composed by two parts, an external one directly in contact with the solution, and an internal part or gel fraction which is considered, from a statistical point of view, as a charged polymer network swelled by the electrolyte solution, in the framework of the Flory polymer network theory. The electrostatic effect is given by a Donnan-like potential, which can be regarded as an average value over the gel fraction of the humic particle. The gel fraction expands as the pH and humic charge are increased, determining the Donnan potential and consequently the ion activity inside the gel. The model was fitted to published experimental data with good agreement. The model predictions are discussed, and the behavior suggests, for some cases, the presence of a transition between closed and open structures attributed to the presence, at low pH, of intramolecular hydrogen bonds which are removed as the carboxylic sites become deprotonated.
提出了一种新的静电贡献模型，用于将离子与腐殖质结合，应用于已发表的质子与富里酸和腐殖酸结合的数据。弹性聚电解质网络模型将腐殖质颗粒视为由两部分组成，一部分直接与溶液接触，另一部分为内部部分或凝胶部分，从统计角度来看，在 Flory 聚合物网络理论的框架内，凝胶部分被视为由电解质溶液溶胀的带电聚合物网络。静电效应由类似 Donnan 的势给出，该势可以被视为腐殖质颗粒的凝胶部分的平均值。随着 pH 值和腐殖质电荷的增加，凝胶部分会膨胀，从而确定 Donnan 势，进而确定凝胶内部的离子活度。该模型与已发表的实验数据拟合良好。讨论了模型预测，并表明在某些情况下，存在从封闭结构到开放结构的转变，这归因于在低 pH 值下存在分子内氢键，随着羧酸位点去质子化，氢键被去除。
