Hydrated Anions: From Clusters to Bulk Solution with Quasi-Chemical Theory

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dc.citation.firstpage2201en_US
dc.citation.issueNumber16en_US
dc.citation.journalTitleAccounts of Chemical Researchen_US
dc.citation.lastpage2212en_US
dc.citation.volumeNumber55en_US
dc.contributor.authorGomez, Diego T.en_US
dc.contributor.authorPratt, Lawrence R.en_US
dc.contributor.authorAsthagiri, Dilipkumar N.en_US
dc.contributor.authorRempe, Susan B.en_US
dc.date.accessioned2022-09-08T14:40:00Zen_US
dc.date.available2022-09-08T14:40:00Zen_US
dc.date.issued2022en_US
dc.description.abstractConspectusThe interactions of hydrated ions with molecular and macromolecular solution and interface partners are strong on a chemical energy scale. Here, we recount the foremost ab initio theory for the evaluation of the hydration free energies of ions, namely, quasi-chemical theory (QCT). We focus on anions, particularly halides but also the hydroxide anion, because they have been outstanding challenges for all theories. For example, this work supports understanding the high selectivity for F– over Cl– in fluoride-selective ion channels despite the identical charge and the size similarity of these ions. QCT is built by the identification of inner-shell clusters, separate treatment of those clusters, and then the integration of those results into the broader-scale solution environment. Recent work has focused on a close comparison with mass-spectrometric measurements of ion-hydration equilibria. We delineate how ab initio molecular dynamics (AIMD) calculations on ion-hydration clusters, elementary statistical thermodynamics, and electronic structure calculations on cluster structures sampled from the AIMD calculations obtain just the free energies extracted from the cluster experiments. That theory–experiment comparison has not been attempted before the work discussed here, but the agreement is excellent with moderate computational effort. This agreement reinforces both theory and experiment and provides a numerically accurate inner-shell contribution to QCT. The inner-shell complexes involving heavier halides display strikingly asymmetric hydration clusters. Asymmetric hydration structures can be problematic for the evaluation of the QCT outer-shell contribution with the polarizable continuum model (PCM). Nevertheless, QCT provides a favorable setting for the exploitation of PCM when the inner-shell material shields the ion from the outer solution environment. For the more asymmetrically hydrated, and thus less effectively shielded, heavier halide ions clustered with waters, the PCM is less satisfactory. We therefore investigate an inverse procedure in which the inner-shell structures are sampled from readily available AIMD calculations on the bulk solutions. This inverse procedure is a remarkable improvement; our final results are in close agreement with a standard tabulation of hydration free energies, and the final composite results are independent of the coordination number on the chemical energy scale of relevance, as they should be. Finally, a comparison of anion hydration structure in clusters and bulk solutions from AIMD simulations emphasize some differences: the asymmetries of bulk solution inner-shell structures are moderated compared with clusters but are still present, and inner hydration shells fill to slightly higher average coordination numbers in bulk solution than in clusters.en_US
dc.identifier.citationGomez, Diego T., Pratt, Lawrence R., Asthagiri, Dilipkumar N., et al.. "Hydrated Anions: From Clusters to Bulk Solution with Quasi-Chemical Theory." <i>Accounts of Chemical Research,</i> 55, no. 16 (2022) American Chemical Society: 2201-2212. https://doi.org/10.1021/acs.accounts.2c00078.en_US
dc.identifier.digitalacs-accounts-2c00078en_US
dc.identifier.doihttps://doi.org/10.1021/acs.accounts.2c00078en_US
dc.identifier.urihttps://hdl.handle.net/1911/113191en_US
dc.language.isoengen_US
dc.publisherAmerican Chemical Societyen_US
dc.rightsLicensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)en_US
dc.rights.urihttps://creativecommons.org/licenses/by-nc-nd/4.0/en_US
dc.titleHydrated Anions: From Clusters to Bulk Solution with Quasi-Chemical Theoryen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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