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Long-Range Hofmeister Effects of Anionic and Cationic Amphiphiles

机译:阴离子和阳离子两亲物的远程霍夫迈斯特效应

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摘要

Specific ion effects at aqueous interfaces play key roles in many important phenomena. We recently reported that ions interact specifically over unexpectedly long distances on the surface of sub-micromolar electrolyte solutions (Enami et al. J. Chem. Phys. 2012, 136, 1S4707). Whether the anionic and cationic headgroups of the organic amphiphiles present at most water/ hydrophobe interfaces act similarly or display new behaviors, however, is not known. Here we report the results of experiments in which we apply online electrospray ionization mass spectrometry (ESI-MS) to investigate how carboxylate, RCOO~- (R = CH3, C5H_(11), C7H_(15)), and alkylammonium, R'(CH3)3N~+ (R' = CH3, C_(14)H_(29)), ions affect the ratio χ - I~-/Br~- at the aerial interface of 1 μM (Nal + NaBr) aqueous solutions. We found that χ is systematically but selectively depressed by these ionic amphiphiles and minimally affected by the neutral surfactant 1-octanol. The depressing effects induced by cationic headgroups are stronger than those caused by anionic surfactants and always increase with the length of the alkyi chains.
机译:水界面的特定离子效应在许多重要现象中起着关键作用。我们最近报道,离子在亚微摩尔电解质溶液的表面上发生了意想不到的长距离相互作用(Enami等人,J。Chem。Phys。2012,136,1S4707)。然而,目前尚不清楚大多数水/疏水界面处存在的有机两亲物的阴离子和阳离子头基是否起类似作用或表现出新的行为。在这里,我们报告了使用在线电喷雾电离质谱(ESI-MS)进行实验以研究羧酸盐RCOO〜-(R = CH3,C5H_(11),C7H_(15))和烷基铵R'的实验结果。 (CH3)3N〜+(R'= CH3,C_(14)H_(29)),离子会影响1μM(Nal + NaBr)水溶液空中接口处的比例χ-I〜-/ Br〜-。我们发现,χ被这些离子两亲物系统地但有选择地抑制,而受中性表面活性剂1-辛醇的影响最小。阳离子头基引起的抑制作用比阴离子表面活性剂引起的抑制作用更强,并且总是随着烷基链的长度而增加。

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