Ion-mediated hydrogen-bond rearrangement through tunnelling in the iodide–dihydrate complex


A microscopic picture of hydrogen-bond structure and dynamics in ion hydration shells remains elusive. Small ion–dihydrate molecular complexes are ideal systems with which to investigate the interplay and competition between ion–water and water–water interactions. Here, state-of-the-art quantum dynamics simulations provide evidence for tunnelling in hydrogen-bond rearrangements in the iodide–dihydrate complex and show that it can be controlled through isotopic substitutions. We find that the iodide ion weakens the neighbouring water–water hydrogen bond, leading to faster water reorientation than in the analogous water trimer. These faster dynamics, which are apparently at odds with the slowdown observed in the first hydration shell of iodide in solution, can be traced back to the presence of a free OH bond in the iodide–dihydrate complex, which effectively triggers the overall structural rearrangements within it. Besides providing indirect support for cooperative hydrogen-bond dynamics in iodide solutions, the analysis presented here suggests that iodide ions may accelerate hydrogen-bond rearrangements at aqueous interfaces, where neighbouring water molecules can be undercoordinated.

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Fig. 1: Ground-state geometry and OH-stretch vibrational frequencies of the iodide–dihydrate complex.
Fig. 2: Ground-state tunnelling pathways and splitting pattern in the iodide–dihydrate complex.
Fig. 3: Tunnelling timescales in the isotopologues of the iodide–dihydrate complex.
Fig. 4: Temperature-dependent free energies along the tunnelling pathways.
Fig. 5: Determining local free energies associated with different hydrogen-bonding environments in the I(HOD)(D2O) isotopologue of the iodide–dihydrate complex.

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The computer codes used in this study are available from the authors upon request.

Data availability

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The authors thank M.A. Johnson and N. Yang for stimulating discussions about the vibrational spectroscopy and dynamics of the I(H2O)2 complex and its isotopologues. This research was supported by the National Science Foundation Center for Chemical Innovation ‘Center for Aerosol Impacts on Chemistry of the Environment’ (grant no. CHE-1305427) and by the Swiss National Science Foundation (project no. 175696). Calculations were performed using the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the National Science Foundation (grant no. ACI-1053575, allocation TG-CHE110009), the High Performance Computing Modernization Program (HPCMP), which is supported by the Air Force Office of Scientific Research (grant no. FA9550-16-1-0327), as well as the Triton Shared Computing Cluster (TSCC) at the San Diego Supercomputer Center.

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P.B. performed all simulations, contributed to data analysis and co-wrote the paper. J.O.R. guided the RPI calculations, contributed to data analysis and co-wrote the paper. F.P. initiated the project, guided the simulation design and data analysis, and co-wrote the paper.

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Correspondence to Francesco Paesani.

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Supplementary Information

Supplementary Figures 1–3, Supplementary Tables 1–9, Supplementary Methods, Supplementary Data and Analysis.

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Bajaj, P., Richardson, J.O. & Paesani, F. Ion-mediated hydrogen-bond rearrangement through tunnelling in the iodide–dihydrate complex. Nat. Chem. 11, 367–374 (2019).

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