Modeling electrostatic and heterogeneity effects on proton dissociation from humic substances
Modeling electrostatic and heterogeneity effects on proton dissociation from humic substances
复制标题
模拟静电和异质性对腐殖质质子解离的影响
DOI：
10.1021/es00081a012
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发表时间：
1990
影响因子：
11.4
通讯作者：
M. Hurley
中科院分区：
文献类型：
--
作者：
E. Tipping;Michael M Reddy;M. Hurley
腐殖质的表观酸解离常数随着腐殖质羧酸基的电离而增加2-4个pK单位。这种表观酸强度的变化部分是由于质子脱落时腐殖质分子上电荷的增加。此外，质子解离反应是复杂的，因为腐殖质在质子解离基团和分子大小方面是不均匀的。本文用Debye-Hueckel理论描述了静电相互作用对腐殖质质子解离的影响。模拟结果表明，对于大小不一的分子系统，平均分子量比平均数分子量更适合于平均静电相互作用的效应。对Suwannee河中黄腐酸质子解离的已发表数据的分析表明，静电相互作用可以用一个假设的分子量为1000的均相化合物（类似于实验确定的重量平均值）来令人满意地描述。
The apparent acid dissociation constant of humic substances increases by 2-4 pK units as ionization of the humic carboxylate groups proceeds. This change in apparent acid strength is due in part to the increase in electrical charge on the humic molecules as protons are shed. In addition, proton dissociation reactions are complicated because humic substances are heterogeneous with respect to proton dissociating groups and molecular size. In this paper, the authors use the Debye-Hueckel theory to describe the effects of electrostatic interactions on proton dissociation of humic substances. Simulations show that, for a size-heterogeneous system of molecules, the weight-average molecular weight is preferable to the number-average value for averaging the effects of electrostatic interactions. Analysis of published data on the proton dissociation of fulvic acid from the Suwannee River shows that the electrostatic interactions can be satisfactorily described by a hypothetical homogeneous compound having a molecular weight of 1,000 (similar to the experimentally determined weight-average value).