Laboratory of Physical Chemistry, Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2, 30100 Agrinio, Greece.
Environ Sci Technol. 2010 Sep 15;44(18):7011-6. doi: 10.1021/es101708f.
The interaction of indigenous radicals of humic acid (HA) with metal cations has been studied using high magnetic field (10.5T-285 GHz) electron paramagnetic resonance (HFEPR) spectroscopy. Strong [HA]-[metal] interaction was observed in the case of heavy metals, Cd(2+), Pb(2+), and Sr(2+), leading to formation of covalent bonds with the radicals of HA. On the contrary, alkaline earth metal ions, such as Mg(2+), generate only electrostatic interaction. The two types of indigenous radicals that exist in all HAs are influenced by the metal cations in a unified manner. This provides evidence that the two types of indigenous radicals in HAs originate from a unique, phenolic, moiety in HA. Mg(2+) ions dramatically changed the pH profile of the two radical types of HA, downshifting their interconversion pK(a) by ca. 3 pH units. This is the first experimental observation of the effect of metals on the H-dissociation of the radical centers in HAs.
使用高磁场（10.5T-285GHz）电子顺磁共振波谱（HFEPR）研究了腐殖酸（HA）的本征自由基与金属阳离子的相互作用。在重金属 Cd(2+)、Pb(2+)和 Sr(2+)的情况下，观察到强的[HA]-[金属]相互作用，导致与 HA 的自由基形成共价键。相反，碱土金属离子，如 Mg(2+)，仅产生静电相互作用。在所有 HA 中存在的两种本征自由基以统一的方式受到金属阳离子的影响。这证明了 HA 中的两种本征自由基来源于 HA 中独特的酚部分。Mg(2+)离子显著改变了 HA 中两种自由基类型的 pH 分布，使它们的互变异构 pK(a)向下移动约 3 个 pH 单位。这是首次观察到金属对 HA 中自由基中心 H 离解的影响。
