Long-Range Hofmeister Effects of Anionic and Cationic Amphiphiles
Long-Range Hofmeister Effects of Anionic and Cationic Amphiphiles
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DOI：
10.1021/jp401285f
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发表时间：
2013-05-23
影响因子：
3.3
通讯作者：
Colussi, Agustin J.
中科院分区：
文献类型：
--
作者：
Enami, Shinichi;Colussi, Agustin J.
水相界面的特殊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以出乎意料的长距离相互作用(Enami等人)。J·化学。太棒了。2012年，136,154707)。然而，存在于大多数水/疏水界面的有机两亲分子的阴离子和阳离子头基是否具有类似的作用或表现出新的行为尚不清楚。本文报道了我们应用在线电喷雾电离质谱仪(ESI-MS)研究了羧酸盐，RCOO-(R=CH3，C5H11，C7H15)和烷基铵，R‘(CH3)(3)N+(R’=CH3，C14H29)离子对1mU M(NaI+NaBR)水溶液空中界面比值chi=I-/Br2-的影响。我们发现，CHI被这些离子两亲分子系统地但选择性地抑制，而受中性表面活性剂1-辛醇的影响很小。阳离子基团的抑制作用强于阴离子表面活性剂，且随着烷基链长的增加而增强。
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, 154707). 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, C5H11, C7H15), and alkylammonium, R'(CH3)(3)N+ (R' = CH3, C14H29), ions affect the ratio chi = I-/Br- at the aerial interface of 1 mu M (NaI + NaBr) aqueous solutions. We found that chi 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 alkyl chains.