Proton Transfer in Phosphoric Acid-Based Protic Ionic Liquids: Effects of the Base

Zhenghao Zhu, Xubo Luo, Alexei P. Sokolov, Alexei P. Sokolov, Stephen J. Paddison

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Electronic structure calculations were performed to understand highly decoupled conductivities recently reported in protic ionic liquids (PILs). To develop a molecular-level understanding of the mechanisms of proton conductivity in PILs, minimum-energy structures of trimethylamine, imidazole, lidocaine, and creatinine (CRT) with the addition of one to three phosphoric acid (PA) molecules were determined at the B3LYP/6-311G*∗ level of theory with the inclusion of an implicit solvation model (SMD with ϵ = 61). The proton affinity of the bases and zero-point energy corrected binding energies were computed at a similar level of theory. Proton dissociation from PA occurs in all systems, resulting in the formation of ion pairs due to the relatively strong basicity of the bases (proton acceptors) and the effect of the high dielectric constant solvent in stabilizing the charge separation. The second and third PA molecules preferentially form "ring-like"hydrogen bonds with one another instead of forming hydrogen bonds at the donor and acceptor sites of the bases. Potential energy scans reveal that the bases with stronger proton affinity exert greater influence on the energetics of proton transfer between the individual PA molecules. However, the effects are minimal when shifted into a single-well from a double-well potential. Barrierless proton transfer was observed to occur in the CRT system with several PA molecules present, implying that the CRT may be a promising PA-based PIL.

Original languageEnglish
Pages (from-to)4141-4149
Number of pages9
JournalJournal of Physical Chemistry A
Volume124
Issue number20
DOIs
StatePublished - May 21 2020

Funding

This work was supported by the National Science Foundation under CHE 1764409: “Mechanisms of Proton Transport in Ionic Liquids: Grotthuss versus Vehicular”. Computing resource was provided through an XSEDE allocation award: DMR130078.

FundersFunder number
National Science Foundation1764409, CHE 1764409

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