Abstract
Desolvation barriers are present for solute-solvent exchange events, such as ligand binding to an enzyme active site, during protein folding, and at battery electrodes. For solution-grown crystals, desolvation at kink sites can be the rate-limiting step for growth. However, desolvation and the associated kinetic barriers are poorly understood. In this work, we use rare-event simulation techniques to investigate attachment/detachment events at kink sites of a NaCl crystal in water. We elucidate the desolvation mechanism and present an optimized reaction coordinate, which involves one solute collective variable and one solvent collective variable. The attachment/detachment pathways for Na+ and Cl- are qualitatively similar, with quantitative differences that we attribute to different ion sizes and solvent coordination. The attachment barriers primarily result from kink site desolvation, while detachment barriers largely result from breaking ion-crystal bonds. We compute ion detachment rates from kink sites and compare with results from an independent study. We anticipate that the reaction coordinate and desolvation mechanism identified in this work may be applicable to other alkali halides.
Highlights
Ion dissolution mechanism and kinetics at kink sites on NaCl surfacesADepartment of Chemical Engineering, University of California, Santa Barbara, CA 93106; and bDepartment of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106
Desolvation barriers are present for solute–solvent exchange events, such as ligand binding to an enzyme active site, during protein folding, and at battery electrodes
Ionic crystal growth and dissolution rates near saturation in aqueous solution are limited by desolvation and attachment of solute growth units at kink sites
Summary
ADepartment of Chemical Engineering, University of California, Santa Barbara, CA 93106; and bDepartment of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106. We compute ion detachment rates from kink sites and compare with results from an independent study. A few computational studies focus on attachment/detachment of a solute at a crystal surface [12, 14,15,16,17,18,19,20,21], and only recently have kink sites been examined [22, 23]. Accurate rates can be computed using only ion positions without a complete understanding of the attachment/detachment mechanism [15, 22] [e.g., via trajectory-based rate calculations [24]], but these calculations provide only numerical rate estimates. We compute ion detachment rates from kink sites and make comparisons with other studies
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