dorsal/arxiv
View SchemaLiquid-vapor oscillations of water in hydrophobic nanopores
| Authors | Oliver Beckstein, Mark S. P. Sansom |
|---|---|
| Categories | |
| ArXiv ID | physics/0303096 |
| URL | https://arxiv.org/abs/physics/0303096 |
| DOI | 10.1073/pnas.1136844100 |
| Journal | Proceedings of the National Academy of Sciences, 100:7063-7068, 2003 |
Abstract
Water plays a key role in biological membrane transport. In ion channels and water-conducting pores (aquaporins), one dimensional confinement in conjunction with strong surface effects changes the physical behavior of water. In molecular dynamics simulations of water in short (0.8 nm) hydrophobic pores the water density in the pore fluctuates on a nanosecond time scale. In long simulations (460 ns in total) at pore radii ranging from 0.35 nm to 1.0 nm we quantify the kinetics of oscillations between a liquid-filled and a vapor-filled pore. This behavior can be explained as capillary evaporation alternating with capillary condensation, driven by pressure fluctuations in the water outside the pore. The free energy difference between the two states depends linearly on the radius. The free energy landscape shows how a metastable liquid state gradually develops with increasing radius. For radii larger than ca. 0.55 nm it becomes the globally stable state and the vapor state vanishes. One dimensional confinement affects the dynamic behavior of the water molecules and increases the self diffusion by a factor of two to three compared to bulk water. Permeabilities for the narrow pores are of the same order of magnitude as for biological water pores. Water flow is not continuous but occurs in bursts. Our results suggest that simulations aimed at collective phenomena such as hydrophobic effects may require simulation times longer than 50 ns. For water in confined geometries, it is not possible to extrapolate from bulk or short time behavior to longer time scales.
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"abstract": "Water plays a key role in biological membrane transport. In ion channels and\nwater-conducting pores (aquaporins), one dimensional confinement in conjunction\nwith strong surface effects changes the physical behavior of water. In\nmolecular dynamics simulations of water in short (0.8 nm) hydrophobic pores the\nwater density in the pore fluctuates on a nanosecond time scale. In long\nsimulations (460 ns in total) at pore radii ranging from 0.35 nm to 1.0 nm we\nquantify the kinetics of oscillations between a liquid-filled and a\nvapor-filled pore. This behavior can be explained as capillary evaporation\nalternating with capillary condensation, driven by pressure fluctuations in the\nwater outside the pore. The free energy difference between the two states\ndepends linearly on the radius. The free energy landscape shows how a\nmetastable liquid state gradually develops with increasing radius. For radii\nlarger than ca. 0.55 nm it becomes the globally stable state and the vapor\nstate vanishes. One dimensional confinement affects the dynamic behavior of the\nwater molecules and increases the self diffusion by a factor of two to three\ncompared to bulk water. Permeabilities for the narrow pores are of the same\norder of magnitude as for biological water pores. Water flow is not continuous\nbut occurs in bursts. Our results suggest that simulations aimed at collective\nphenomena such as hydrophobic effects may require simulation times longer than\n50 ns. For water in confined geometries, it is not possible to extrapolate from\nbulk or short time behavior to longer time scales.",
"arxiv_id": "physics/0303096",
"authors": [
"Oliver Beckstein",
"Mark S. P. Sansom"
],
"categories": [
"physics.bio-ph",
"physics.chem-ph"
],
"doi": "10.1073/pnas.1136844100",
"journal_ref": "Proceedings of the National Academy of Sciences, 100:7063-7068,\n 2003",
"title": "Liquid-vapor oscillations of water in hydrophobic nanopores",
"url": "https://arxiv.org/abs/physics/0303096"
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