dorsal/arxiv
View SchemaHydration and mobility of HO-(aq)
| Authors | D. Asthagiri, Lawrence R. Pratt, J. D. Kress, Maria A. Gomez |
|---|---|
| Categories | |
| ArXiv ID | physics/0211057 |
| URL | https://arxiv.org/abs/physics/0211057 |
Abstract
The hydroxide anion plays an essential role in many chemical and biochemical reactions. But a molecular-scale description of its hydration state, and hence also its transport, in water is currently controversial. The statistical mechanical quasi-chemical theory of solutions suggests that HO[H2O]3- is the predominant species in the aqueous phase under standard conditions. This result is in close agreement with recent spectroscopic studies on hydroxide water clusters, and with the available thermodynamic hydration free energies. In contrast, a recent ab initio molecular dynamics simulation has suggested that HO[H_2O]4- is the only dominant aqueous solution species. We apply adiabatic ab initio molecular dynamics simulations, and find good agreement with both the quasi-chemical theoretical predictions and experimental results. The present results suggest a picture that is simpler, more traditional, but with additional subtlety. These coordination structures are labile but the tri-coordinate species is the prominent case. This conclusion is unaltered with changes in the electronic density functional. No evidence is found for rate-determining activated inter-conversion of a HO[H2O]4- trap structure to HO[H2O]3-, mediating hydroxide transport. The view of HO- diffusion as the hopping of a proton hole has substantial validity, the rate depending largely on the dynamic disorder of the water hydrogen-bond network.
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"abstract": "The hydroxide anion plays an essential role in many chemical and biochemical\nreactions. But a molecular-scale description of its hydration state, and hence\nalso its transport, in water is currently controversial. The statistical\nmechanical quasi-chemical theory of solutions suggests that HO[H2O]3- is the\npredominant species in the aqueous phase under standard conditions. This result\nis in close agreement with recent spectroscopic studies on hydroxide water\nclusters, and with the available thermodynamic hydration free energies. In\ncontrast, a recent ab initio molecular dynamics simulation has suggested that\nHO[H_2O]4- is the only dominant aqueous solution species. We apply adiabatic ab\ninitio molecular dynamics simulations, and find good agreement with both the\nquasi-chemical theoretical predictions and experimental results. The present\nresults suggest a picture that is simpler, more traditional, but with\nadditional subtlety. These coordination structures are labile but the\ntri-coordinate species is the prominent case. This conclusion is unaltered with\nchanges in the electronic density functional. No evidence is found for\nrate-determining activated inter-conversion of a HO[H2O]4- trap structure to\nHO[H2O]3-, mediating hydroxide transport. The view of HO- diffusion as the\nhopping of a proton hole has substantial validity, the rate depending largely\non the dynamic disorder of the water hydrogen-bond network.",
"arxiv_id": "physics/0211057",
"authors": [
"D. Asthagiri",
"Lawrence R. Pratt",
"J. D. Kress",
"Maria A. Gomez"
],
"categories": [
"physics.chem-ph",
"physics.bio-ph"
],
"title": "Hydration and mobility of HO-(aq)",
"url": "https://arxiv.org/abs/physics/0211057"
},
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