Tracking Aqueous Proton Transfer by Two-Dimensional Infrared Spectroscopy and ab Initio Molecular Dynamics Simulations

Abstract

Proton transfer in water is ubiquitous and a critical elementary event that, via proton hopping between water molecules, enables protons to diffuse much faster than other ions. The problem of the anomalous nature of proton transport in water was first identified by Grotthuss over 200 years ago. In spite of a vast amount of modern research effort, there are still many unanswered questions about proton transport in water. An experimental determination of the proton hopping time has remained elusive due to its ultrafast nature and the lack of direct experimental observables. Here, we use two-dimensional infrared spectroscopy to extract the chemical exchange rates between hydronium and water in acid solutions using a vibrational probe, methyl thiocyanate. Ab initio molecular dynamics (AIMD) simulations demonstrate that the chemical exchange is dominated by proton hopping. The observed experimental and simulated acid concentration dependence then allow us to extrapolate the measured single step proton hopping time to the dilute limit, which, within error, gives the same value as inferred from measurements of the proton mobility and NMR line width analysis. In addition to obtaining the proton hopping time in the dilute limit from direct measurements and AIMD simulations, the results indicate that proton hopping in dilute acid solutions is induced by the concerted multi-water molecule hydrogen bond rearrangement that occurs in pure water. This proposition on the dynamics that drive proton hopping is confirmed by a combination of experimental results from the literature.

First principles study of electronic and optical properties and photocatalytic performance of GaN–SiS van der Waals heterostructure

“…1(c and d). These results are in good agreement with the available literature, [60][61][62][63] indicating the reliability of the present study (Table 1).…”

First-principles study of the electronic structures and optical and photocatalytic performances of van der Waals heterostructures of SiS, P and SiC monolayers

“…In this paper, comprehensive insight is gained into the physical properties of the SiS, P and SiC monolayers and their vdW heterostructures. The thermal stabilities of the heterostructures and corresponding monolayers are investigated by ab initio molecular dynamics (AIMD) simulations 37 with an 8 Â 8 Â 1 supercell through the Nose thermostat algorithm at a temperature of 300 K for a total of 6 ps with a time interval of 1 fs. Density functional theory (DFT) 38 calculations with Grimme's (DFT-D2) empirical dispersion correction 39 in the Vienna ab initio simulation package [40][41][42] are used to investigate the electronic structures and optical and photocatalytic performances of the SiS, P and SiC van der Waals heterostructures.…”

Highly Dynamic Polynuclear Metal Cluster Revealed in a Single Metallothionein Molecule

“…Pathways and a Plastic Metal Cluster. To identify the M-S bonds broken upon mechanical stress, we employed molecular modeling and simulated the forced unfolding of the αMT protein using a hybrid QM/MM potential and the constrained geometry emulating force procedure (COGEF, see Supplementary Methods for details) [42][43][44][45][46]. These simulations employ a quantum-chemical model and naturally describe the formation and rupture of M-S bonds.…”