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Anomalous surface behavior of hydrated guanidinium ions due to ion pairing
The Journal of Chemical Physics ( IF 4.4 ) Pub Date : 2018-04-13 , DOI: 10.1063/1.5024348
Victor Ekholm 1 , Mario Vazdar 2 , Philip E. Mason 3 , Erik Bialik 4 , Marie-Madeleine Walz 5 , Gunnar Öhrwall 6 , Josephina Werner 1, 7 , Jan-Erik Rubensson 1 , Pavel Jungwirth 3 , Olle Björneholm 1
Affiliation  

Surface affinity of aqueous guanidinium chloride (GdmCl) is compared to that of aqueous tetrapropylammonium chloride (TPACl) upon addition of sodium chloride (NaCl) or disodium sulfate (Na2SO4). The experimental results have been acquired using the surface sensitive technique X-ray photoelectron spectroscopy on a liquid jet. Molecular dynamics simulations have been used to produce radial distribution functions and surface density plots. The surface affinities of both TPA+ and Gdm+ increase upon adding NaCl to the solution. With the addition of Na2SO4, the surface affinity of TPA+ increases, while that of Gdm+ decreases. From the results of MD simulations it is seen that Gdm+ and SO42 ions form pairs. This finding can be used to explain the decreased surface affinity of Gdm+ when co-dissolved with SO42 ions. Since SO42 ions avoid the surface due to the double charge and strong water interaction, the Gdm+-SO42 ion pair resides deeper in the solutions’ bulk than the Gdm+ ions. Since TPA+ does not form ion pairs with SO42, the TPA+ ions are instead enriched at the surface.

中文翻译:

离子配对导致水合胍离子的异常表面行为

在添加氯化钠(NaCl)或硫酸钠(Na 2 SO 4)后,将氯化胍水溶液(GdmCl)的表面亲和力与氯化四丙基铵水溶液(TPACl)的表面亲和力进行比较。实验结果已经在液体喷射器上使用表面敏感技术X射线光电子能谱获得。分子动力学模拟已用于产生径向分布函数和表面密度图。在溶液中添加NaCl后,TPA +和Gdm +的表面亲和力都会增加。通过添加Na 2 SO 4,TPA +的表面亲和力增加,而Gdm +的表面亲和力增加。减少。从MD模拟的结果可以看出,Gdm +小号Ø42个-离子成对形成。该发现可用于解释当与Gdm +共溶时Gdm +的表面亲和力降低小号Ø42个-离子。自从小号Ø42个- 由于双电荷和强水相互作用,离子避开了表面 Gdm+--小号Ø42个-离子对比Gdm +离子更深地存在于溶液中。由于TPA +不会与小号Ø42个-,TPA +离子反而在表面富集。
更新日期:2018-04-14
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