Institute for Condensed Matter Physics, Svientsitskii 1, 79011 Lviv, Ukraine.
J Phys Chem B. 2009 Oct 29;113(43):14270-6. doi: 10.1021/jp906727h.
Ionenes are alkyl polymer chains in which different numbers of methylene groups separate quaternary ammonium groups. They are ideal molecules for studying the balance between hydrophobic and charge effects in water. Implicit-solvent models predict osmotic coefficients that are too high (too low water vapor pressures), compared to experiments. We present a molecular dynamics simulation, in explicit SPC/E water, of a solution of aliphatic 6,6 ionene oligocations with sodium co-ions and fluorine, chlorine, bromine, or iodine counterions. In the 6,6 ionene solution, the latter polyion has more hydrophobic groups than its 3,3 counterpart, the waters are displaced more from the oligoion surface. Also, we find that the large ions, such as iodine, act like hydrophobic groups insofar as they bind to ionene's methylene groups. The water-mediated attraction between fluorine ions is enhanced in presence of weakly charged 6,6 ionene molecules. This effect may additionally reduce the osmotic pressure in such systems. Our results can explain some experimental trends in ionene solutions and weakly charged polyelectrolytes in general.
离子聚合物是其中不同数量的亚甲基基团隔开季铵基团的烷基聚合物链。它们是研究水的疏水性和电荷效应之间平衡的理想分子。隐溶剂模型预测的渗透压过高（水蒸气压力过低），与实验结果不符。我们在 SPC/E 显式水中进行了脂肪族 6,6 离子聚合物齐聚物与钠离子和氟、氯、溴或碘抗衡离子的溶液的分子动力学模拟。在 6,6 离子聚合物溶液中，后一种聚离子比其 3,3 对应物具有更多的疏水性基团，水分子从齐聚物表面被排挤得更远。此外，我们发现大离子，如碘，在与离子聚合物的亚甲基基团结合时，其行为类似于疏水分子。在存在带弱电荷的 6,6 离子聚合物分子的情况下，氟离子之间的水介导吸引力增强。这种效应可能会进一步降低此类系统中的渗透压。我们的结果可以解释离子聚合物溶液和一般带弱电荷的聚电解质的一些实验趋势。
