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Switching of Protonation Sites in Hydrated Nicotine via a Grotthuss Mechanism.

Yuika OkuraGarrett D SantisKeisuke HirataVasilios S MelissasShun-Ichi IshiuchiMasaaki FujiiSotiris S Xantheas
Published in: Journal of the American Chemical Society (2024)
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 instead of a bimolecular proton transfer (vehicle) mechanism at the experimental temperature ( T = 130 K) as unambiguously confirmed by experiments with deuterated water. In contrast, the bimolecular vehicle mechanism is preferred at higher temperatures ( T = 300 K) as determined by theory. The Grotthuss mechanism for the concerted proton transfer 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 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 down to less than 6 kcal/mol, which is consistent with the experimental observations.
Keyphrases
  • electron transfer
  • smoking cessation
  • molecular dynamics simulations
  • magnetic resonance
  • magnetic resonance imaging
  • solar cells
  • data analysis