Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California94720, United States.
Cluster of Excellence Physics of Life, Technische Universität Dresden, 01307Dresden, Germany.
J Am Chem Soc. 2023 Jan 25;145(3):1826-1834. doi: 10.1021/jacs.2c11331. Epub 2023 Jan 12.
Transport mechanisms of solvated protons of 1 M HCl acid pools, confined within reverse micelles (RMs) containing the negatively charged surfactant sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) or the positively charged cetyltrimethylammonium bromide (CTABr), are analyzed with reactive force field simulations to interpret dynamical signatures from TeraHertz absorption and dielectric relaxation spectroscopy. We find that the forward proton hopping events for NaAOT are further suppressed compared to a nonionic RM, while the Grotthuss mechanism ceases altogether for CTABr. We attribute the sluggish proton dynamics for both charged RMs as due to headgroup and counterion charges that expel hydronium and chloride ions from the interface and into the bulk interior, thereby increasing the pH of the acid pools relative to the nonionic RM. For charged NaAOT and CTABr RMs, the localization of hydronium near a counterion or conjugate base reduces the Eigen and Zundel configurations that enable forward hopping. Thus, localized oscillatory hopping dominates, an effect that is most extreme for CTABr in which the proton residence time increases dramatically such that even oscillatory hopping is slow.
通过反应力场模拟分析了 1 M HCl 酸池溶剂化质子在含有带负电荷的表面活性剂双(2-乙基己基)磺基琥珀酸钠(NaAOT)或带正电荷的十六烷基三甲基溴化铵(CTABr)的反胶束(RM)中的传输机制，以解释太赫兹吸收和介电弛豫光谱的动态特征。我们发现，与非离子 RM 相比，NaAOT 的质子正向跳跃事件进一步受到抑制，而 CTABr 的质子协同扩散机制完全停止。我们将这两种带电 RM 中质子动力学的缓慢归因于头基和抗衡离子电荷，它们将氢离子和氯离子从界面排斥到本体内部，从而使酸池的 pH 值相对于非离子 RM 升高。对于带电荷的 NaAOT 和 CTABr RM，氢离子在抗衡离子或共轭碱附近的定位减少了使正向跳跃发生的 Eigen 和 Zundel 结构。因此，局部振荡跳跃占主导地位，对于 CTABr 来说，这种效应最为极端，其中质子停留时间大大增加，以至于即使是振荡跳跃也很慢。
