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B: Liquids, Chemical and Dynamical Processes in Solution, Spectroscopy in Solution 42-
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Hydrated Sulfate Clusters SO (HO)(n=1-40): Charge Distribution Through Solvation Shells and Stabilization Maksim Kulichenko, Nikita S. Fedik, Konstantin V Bozhenko, and Alexander I. Boldyrev J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.9b01744 • Publication Date (Web): 17 Apr 2019 Downloaded from http://pubs.acs.org on April 22, 2019
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The Journal of Physical Chemistry
Hydrated Sulfate Clusters SO42(H2O)n(n=1-40): Charge Distribution Through Solvation Shells and Stabilization Maksim Kulichenkoa, Nikita Fedika, Konstantin V. Bozhenko b,c, and Alexander I. Boldyreva* a Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, Utah,
84322-0300, United States b Department of Physical and Colloid Chemistry, Рeoples’ Friendship University of Russia (RUDN
University), 6 Miklukho-Maklaya St, Moscow 117198, Russian Federation c Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432,
Moscow Region, Russian Federation * E-mail:
[email protected] * Phone: +1 435 7971630
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Abstract Investigations of inorganic anion SO42- interactions with water are crucial for understanding the chemistry of its aqueous solutions. It is known that isolated SO42- dianion is unstable and three H2O molecules are required for its stabilization. In the current work we report our ab initio study of hydrated sulfate clusters SO42-(H2O)n (n=1 – 40) in order to understand the nature of stabilization of this important anion by water molecules. We showed that the most significant charge transfer from dianion SO42- to H2O takes place at number of H2O molecules n≤7. The SO42- directly donates its charge only to the first solvation shell and surprisingly small amount of electron density of 0.15 |e| is enough to be transferred in order to stabilize the dianion. Upon further addition of H2O molecules we observed that the cage effect played an essential role at n≤12 where the first solvation shell closes. During this process SO42- continues to lose density up to 0.25 |e| at n=12. From this point additional water molecules do not take any significant amount of electron density from dianion. These results can help in development of understanding how other solvent molecules could stabilize SO42- anion as well as other multicharged unstable anions. Introduction Hydrates of the sulfate dianion SO42- play significant role in chemistry and biochemistry where they appear as units of solutions and molten substances. This textbook compound occurs in drinking water, soils and atmospheric aerosols1. While sulfate aggregates participate in Erath processes such as cloud formation2, hydrated sulfate minerals were even detected on the Martian surface3 meaning sulfate ubiquity through the Solar System. Moreover, sulfate dianion is also known as strong kosmotropic molecule in terms of Hofmeister series4. Due to the strong intramolecular Coulomb repulsion of the two excess charges, an isolated sulfate dianion was shown to be unstable5,6,7, whereas it is stabilized in the condensed phase by solvation in
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The Journal of Physical Chemistry
solution or counterions in solid. As for the gas phase, Blades and Kebarle6 observed stable hydrated sulfate clusters with the four additional water molecules. Then, Wang and co-authors made a game changing discovery revealing that only three water molecules are necessary for sulfate dianion stabilization7. Further study was continued in series of recent experimental and theoretical works on the structure and stability of solvated sulfate dianion.8–24 These intriguing systems deserved much attention in scientific community and, no doubt, they bear interesting chemical and physical properties and many of them are not studied yet. In the present work, we report our ab initio study of charge distribution in SO42(H2O)n (n=1-40) clusters. We show that the most significant charge transfer takes place at n=
