Proton transfer via hydronium and hydroxide ions in water is ubiquitous. It underlies acid–base chemistry, certain enzyme reactions, and even infection by the flu. Despite two centuries of investigation, the mechanism underlying why hydroxide diffuses slower than hydronium in water is still not well understood. Herein, we employ state-of-the-art density-functional-theory-based molecular dynamics—with corrections for non-local van der Waals interactions, and self-interaction in the electronic ground state—to model water and hydrated water ions. At this level of theory, we show that structural diffusion of hydronium preserves the previously recognized concerted behaviour. However, by contrast, proton transfer via hydroxide is less temporally correlated, due to a stabilized hypercoordination solvation structure that discourages proton transfer. Specifically, the latter exhibits non-planar geometry, which agrees with neutron-scattering results. Asymmetry in the temporal correlation of proton transfer leads to hydroxide diffusing slower than hydronium.

经由水合氢离子和氢氧根离子在水中的质子转移是普遍存在的。它是酸碱化学，某些酶反应乃至流感感染的基础。尽管进行了两个世纪的研究，但氢氧根在水中的扩散速度比水合氢盐扩散慢的根本机理仍未得到很好的理解。在本文中，我们采用了基于最新的密度泛函理论的分子动力学模型（对非局部范德华相互作用和电子基态下的自相互作用进行了校正）来对水和水合水离子进行建模。在此理论水平上，我们表明水合氢盐的结构扩散保留了先前公认的一致行为。然而，相比之下，由于稳定​​的超配位溶剂化结构会阻止质子转移，因此经由氢氧化物的质子转移在时间上的相关性较低。具体而言，后者表现出非平面几何形状，这与中子散射结果一致。质子传递的时间相关性的不对称导致氢氧根的扩散比水合氢慢。