PNNL

Abstract

The switching of the protonation sites in hydrated nicotine, probed by experimental infrared (IR) spectroscopy and theoretical ab-initio calculations, is facilitated via a Grotthuss over a vehicle mechanism at the experimental temperature (T=130K) as unambiguously confirmed by 25 experiments with deuterated water. In contrast, the vehicle mechanism was found to be the preferred one at higher temperatures (T=300K). The Grotthuss mechanism for the concerted proton transfer, the first one reported in the ground state of a finite aqueous cluster, results in the production of nicotine’s bioactive and addictive Pyrrolidine protonated (Pyrro-H+) protomer with just 5 water molecules. Theoretical analysis suggests that the concerted proton transfer occurs via 30 hydrogen bonded bridges consisting of a 3-water molecule “core” that connects the Pyridine protonated (Pyri-H+) with the Pyrrolidine protonated (Pyrro-H+) protomers. Additional water molecules, attached as acceptors to the hydrogen bonded “core” bridge result in lowering the reaction barrier of the concerted proton transfer to