Accurate Determination of the Quantity and Spatial Distribution of Counterions around a Spherical Macroion
Accurate Determination of the Quantity and Spatial Distribution of Counterions around a Spherical Macroion
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准确测定球形宏离子周围反离子的数量和空间分布
DOI：
10.1002/ange.202013806
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发表时间：
2021
影响因子：
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通讯作者：
Chuang, Steven S. C.
中科院分区：
文献类型：
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作者：
Chen, Jiahui;Bera, Mrinal K.;Li, Hui;Yang, Yuqing;Sun, Xinyu;Luo, Jiancheng;Baughman, Jessi;Liu, Cheng;Yao, Xuesi;Chuang, Steven S. C.
反阳离子（Rb+和Sr 2+）在刚性、球形、2.9 nm大小的聚氧乙烯簇{Mo 132}42−周围的精确分布是通过异常小角X射线散射确定的。Rb+和Sr 2+离子导致{Mo 132}的扩散长度比预测的短。大部分Rb+离子通过停留在{Mo 132}的骨架附近或Stern层中与{Mo 132}紧密缔合，而更多的Sr 2+离子在扩散层中与{Mo 132}松散缔合。Rb+离子对{Mo 132}的亲合力比Sr 2+离子的亲合力强，这解释了{Mo 132}与Rb+的凝聚临界浓度比Sr 2+低的反常现象。{Mo 132}的反常行为可归因于大部分负电荷位于其空腔的内表面。阴-阳离子间距的增大削弱了库仑相互作用，使得阳离子水化层破裂引起的焓变在调节反离子-{Mo 132}相互作用中更为重要。
The accurate distribution of countercations (Rb+and Sr2+) around a rigid, spherical, 2.9‐nm size polyoxometalate cluster, {Mo132}42−, is determined by anomalous small‐angle X‐ray scattering. Both Rb+and Sr2+ions lead to shorter diffuse lengths for {Mo132} than prediction. Most Rb+ions are closely associated with {Mo132} by staying near the skeleton of {Mo132} or in the Stern layer, whereas more Sr2+ions loosely associate with {Mo132} in the diffuse layer. The stronger affinity of Rb+ions towards {Mo132} than that of Sr2+ions explains the anomalous lower critical coagulation concentration of {Mo132} with Rb+compared to Sr2+. The anomalous behavior of {Mo132} can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion–cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion–{Mo132} interaction.