Infrared and NMR Spectroscopic Fingerprints of the Asymmetric H7+O3 Complex in Solution. Issue 8 (23rd March 2021)

• Record Type: Journal Article
• Authors: Kozari, Eve; Sigalov, Mark; Pines, Dina; Fingerhut, Benjamin P.; Pines, Ehud
• Is Part Of: Chemphyschem. Volume 22:Issue 8(2021)
• Page Start: 716
• Page End: 725
• Publication Date: 2021-03-23
• Subjects: hydrated proton -- trimer -- Zundel cation -- CN stretch -- molecular dynamics simulations; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.202001046
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: Infrared (IR) absorption in the 1000–3700 cm −1 range and 1 H NMR spectroscopy reveal the existence of an asymmetric protonated water trimer, H7 + O3, in acetonitrile. The core H7 + O3 motif persists in larger protonated water clusters in acetonitrile up to at least 8 water molecules. Quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations reveal irreversible proton transport promoted by propagating the asymmetric H7 + O3 structure in solution. The QM/MM calculations allow for the successful simulation of the measured IR absorption spectra of H7 + O3 in the OH stretch region, which reaffirms the assignment of the H7 + O3 spectra to a hybrid‐complex structure: a protonated water dimer strongly hydrogen‐bonded to a third water molecule with the proton exchanging between the two possible shared‐proton Zundel‐like centers. The H7 + O3 structure lends itself to promoting irreversible proton transport in presence of even one additional water molecule. We demonstrate how continuously evolving H7 + O3 structures may support proton transport within larger water solvates. Abstract : Spectroscopic fingerprints : We identify H7 + O3 as the core protonated‐water unit in water/acetonitrile solutions using IR and NMR spectroscopies. QM/MM MD simulations reinforce the experimental assignment and reveal the asymmetric structure of solvated H7 + O3 : a protonated water‐dimer strongly H‐bonded to a 3 rd water molecule in a chain arrangement around the H7 + O3 unit. Translocation of the H7 + O3 motif driven by 1 st shell H‐bonds fluctuations around the H7 + O3 unit lends itself to promoting the Grotthuss mechanism.