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Chen M , Zheng L , Santra B , Ko HY , DiStasio RA Jr , Klein ML , Car R , Wu X
Hydroxide diffuses slower than hydronium in water because its solvated structure inhibits correlated proton transfer
Nat Chem. 2018 Apr;10(4) :413-419
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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.
1755-4349 Chen, Mohan ORCID: http://orcid.org/0000-0002-8071-5633 Zheng, Lixin ORCID: http://orcid.org/0000-0001-5778-8028 Santra, Biswajit ORCID: http://orcid.org/0000-0003-3609-2106 Ko, Hsin-Yu ORCID: http://orcid.org/0000-0003-1619-6514 DiStasio, Robert A Jr ORCID: http://orcid.org/0000-0003-2732-194X Klein, Michael L Car, Roberto ORCID: http://orcid.org/0000-0001-5243-2647 Wu, Xifan ORCID: http://orcid.org/0000-0001-6561-8942 Journal Article England Nat Chem. 2018 Apr;10(4):413-419. doi: 10.1038/s41557-018-0010-2. Epub 2018 Mar 12.