Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology , SE-10044 Stockholm, Sweden.
J Phys Chem B. 2017 Mar 9;121(9):2179-2188. doi: 10.1021/acs.jpcb.6b12381. Epub 2017 Feb 24.
The binding of K and Ba cations to short poly(ethylene oxide) (PEO) chains with ca. 4-25 monomeric units in methanol was studied by determining the effective charge of the polymer through a combination of electrophoretic NMR and diffusion NMR experiments. These cations were previously found to bind to long PEO chains in a similar strong manner. In addition, H chemical shift and longitudinal spin relaxation rate changes upon binding were quantified. For both systems, binding was stronger for the short chains than that for the longer chains, which is attributed mainly to interactions between bound ions. For K ions, the equilibrium binding constant of a cation to a binding site was measured. For both cations, the binding site was estimated to consist of ca. six monomeric units that coordinated with the respective ions. For the systems with barium, a significant fraction of the bound ions are (BaAnion) ion pairs. This leads to a strong anion effect in the effective charge of the oligomers acquired upon barium ion binding. For K, the coordinating oligomer segment remains rather mobile and individual oligomers exchange rapidly (≪s) between their free and ion-complexing states. In contrast, segmental dynamics slows significantly for the oligomer section that coordinates with the barium species, and for individual oligomers, binding and nonbinding sections do not exchange on the time scale of seconds. Hence, oligomers also exchange slowly (>s) between their free and barium complexing states.
在甲醇中，通过电泳 NMR 和扩散 NMR 实验相结合，研究了约 4-25 个单体单元的短聚（氧化乙烯）（PEO）链与 K 和 Ba 阳离子的结合。这些阳离子先前被发现以类似的强方式与长 PEO 链结合。此外，还量化了结合时 H 化学位移和纵向自旋弛豫率的变化。对于这两种体系，短链的结合比长链更强，这主要归因于结合离子之间的相互作用。对于 K 离子，测量了一个阳离子与一个结合位点的平衡结合常数。对于两种阳离子，估计结合位点由大约六个单体单元组成，这些单元与相应的离子配位。对于钡体系，大量的结合离子是（BaAnion）离子对。这导致钡离子结合后获得的低聚物有效电荷中的强阴离子效应。对于 K，配位的低聚物段仍然相当移动，各个低聚物在其游离和离子络合状态之间快速交换（≪s）。相比之下，与钡物种配位的低聚物段的片段动力学显著减慢，对于各个低聚物，结合和非结合段不会在秒的时间尺度上交换。因此，低聚物也在其游离和钡络合状态之间缓慢交换（>s）。
