Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
Langmuir. 2010 Jun 15;26(12):9449-56. doi: 10.1021/la100467p.
The interaction between water-soluble Keplerate polyoxometalate {Mo(72)Fe(30)} macroions and small countercations is explored by laser light scattering, anomalous small-angle X-ray scattering (ASAXS), and isothermal titration calorimetry (ITC) techniques. The macroions are found to be able to select the type of associated counterions based upon the counterions' valence state and hydrated size, when multiple types of additional cations are present in solution (even among different monovalent cations). The preference goes to the cations with higher valences or smaller hydrated sizes if the valences are identical. This counterion exchange process changes the magnitude of the macroion-counterion interaction and, thus, is reflected in the dimension of the self-assembled {Mo(72)Fe(30)} blackberry supramolecular structures. The hydrophilic macroions exhibit a competitive recognition of various monovalent counterions in dilute solutions. A critical salt concentration (CSC) for each type of cation exists for the blackberry formation of {Mo(72)Fe(30)} macroions, above which the blackberry size increases significantly with the increasing total ionic strength in solution. The CSC values are much smaller for cations with higher valences and also decrease with the cations' hydrated size for various monovalent cations. The change of blackberry size corresponding to the change of ionic strength in solution is reversible.
通过激光光散射、小角非弹性 X 射线散射（ASAXS）和等温热滴定技术研究了水溶性 Keplerate 多金属氧酸盐{Mo(72)Fe(30)}大分子离子与小抗衡离子之间的相互作用。发现当溶液中存在多种类型的额外阳离子（甚至是不同的单价阳离子）时，根据抗衡离子的价态和水合大小，大分子离子能够选择与之结合的抗衡离子类型。如果价态相同，则具有较高价态或较小水合大小的阳离子更优先。这种抗衡离子交换过程改变了大分子离子-抗衡离子相互作用的大小，因此反映在自组装{Mo(72)Fe(30)}黑莓超分子结构的尺寸上。亲水性大分子离子在稀溶液中表现出对各种单价抗衡离子的竞争性识别。对于{Mo(72)Fe(30)}大分子离子的黑莓形成，存在每种类型阳离子的临界盐浓度（CSC），在该浓度以上，黑莓尺寸随着溶液中总离子强度的增加而显著增加。对于具有较高价态的阳离子，CSC 值要小得多，对于各种单价阳离子，CSC 值也随着阳离子水合大小的减小而减小。溶液中离子强度变化对应的黑莓尺寸变化是可逆的。
