Hydration and Ion Pairing in Aqueous Mg 2+ and Zn 2+ Solutions: Force-Field Description Aided by Neutron Scattering Experiments and Ab Initio Molecular Dynamics Simulations

• Published in: The journal of physical chemistry. B Vol. 122; no. 13; pp. 3296 - 3306
• Main Authors: Duboué-Dijon, Elise, Mason, Philip E, Fischer, Henry E, Jungwirth, Pavel
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 05.04.2018
• Subjects: Chemical Sciences; or physical chemistry; Theoretical and
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/acs.jpcb.7b09612

Magnesium and zinc dications possess the same charge and have an almost identical size, yet they behave very differently in aqueous solutions and play distinct biological roles. It is thus crucial to identify the origins of such different behaviors and to assess to what extent they can be captured by force-field molecular dynamics simulations. In this work, we combine neutron scattering experiments in a specific mixture of H O and D O (the so-called null water) with ab initio molecular dynamics simulations to probe the difference in the hydration structure and ion-pairing properties of chloride solutions of the two cations. The obtained data are used as a benchmark to develop a scaled-charge force field for Mg that includes electronic polarization in a mean field way. We show that using this electronic continuum correction we can describe aqueous magnesium chloride solutions well. However, in aqueous zinc chloride specific interaction terms between the ions need to be introduced to capture ion pairing quantitatively.