Driving Forces for Oppositely Charged Polyion Association in Aqueous Solutions: Enthalpic, Entropic, but Not Electrostatic
Driving Forces for Oppositely Charged Polyion Association in Aqueous Solutions: Enthalpic, Entropic, but Not Electrostatic
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DOI：
10.1021/jacs.5b11878
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发表时间：
2016-01-27
影响因子：
15
通讯作者：
Schlenoff, Joseph B.
中科院分区：
文献类型：
--
作者：
Fu, Jingcheng;Schlenoff, Joseph B.
长期以来，在水溶液中电荷相反的生物或合成聚合物之间的相互作用的驱动力一直被认为是静电的起源。由于反离子的损失，这种引力被分解为熵分量和因相反电荷之间的库仑引力而产生的焓分量。虽然熵和焓的贡献之间的平衡随着条件的变化而变化，但混合过程中放热或吸热的存在虽然很小，但被视为库仑相互作用的标志，这支持了植根于连续静电学的聚电解质缔合理论。在这里，对基于静电学的机制和基于特定离子配对或离子交换的机制进行了逐个比较。使用Hofmeister系列反离子对常见的聚阳离子聚(二烯丙基二甲基铵)，通过水O-H振动的拉曼散射研究表明，与聚苯乙烯磺酸盐缔合的焓变化源于水微扰的变化。在所有盐浓度范围内，络合自由能几乎完全是熵的。
Driving forces for association between oppositely charged biological or synthetic polymers in aqueous solution have long been identified as electrostatic in origin. This attraction is broken down into an entropic component, due to loss of counterions, and an enthalpic component, stemming from Coulombic attraction between opposite charges. While the balance between entropic and enthalpic contributions shifts according to the conditions, the presence of exotherms or endotherms on mixing, though small, are viewed as signatures of Coulombic interactions which support theories of polyelectrolyte association rooted in continuum electrostatics. Here, a head-to-head comparison is made between mechanisms based on electrostatics and those based on specific ion pairing, or ion exchange. Using a Hofmeister series of counterions for a common polycation, poly(diallyldimethylammonium), enthalpy changes on association with poly(styrenesulfonate) are shown to derive from changes in water perturbation, revealed by Raman scattering studies of water O-H vibrations. The free energy for complexation is almost completely entropic over all salt concentrations.