title: Proton-Transfer-Driven Water Exchange Mechanism in the Na+Solvation Shell.
abstract: Ligand exchange plays an important role for organic and inorganic chemical reactions. We demonstrate the existence of a novel water exchange mechanism, the "proton transfer pathway" (PTP), around Na+(aq) in basic (high pH) solution, using reactive molecular dynamics simulations employing a high-dimensional neural network potential. An aqua ligand in the first solvation (hydration) shell around a sodium ion is only very weakly acidic, but if a hydroxide ion is present in the second solvation shell, thermal fluctuations can cause the aqua ligand to transfer a proton to the neighboring OH-, resulting in a transient direct-contact ion pair, Na+-OH-, which is only weakly bound and easily dissociates. The extent to which water exchange events follow the PTP is pH-dependent: in dilute NaOH(aq) solutions, only very few exchanges occur, whereas in saturated NaOH(aq) solutions up to a third of water self-exchange events are induced by proton transfer. The principles and results outlined here are expected to be relevant for chemical synthesis involving bases and alkali metal cations.
authors.affiliation: Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum , 44780 Bochum, Germany.
authors.forename: Matti
authors.identifier: 0000-0003-3053-5658
authors.initials: M
authors.lastname: Hellström
authors.affiliation: Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum , 44780 Bochum, Germany.|Universität Göttingen , Institut für Physikalische Chemie, Tammannstr. 6, 37077 Göttingen, Germany.
authors.forename: Jörg
authors.identifier: 0000-0002-1220-1542
authors.initials: J
authors.lastname: Behler