Structure and Dynamics of Proton Transfer in Liquid Imidazole. A Molecular Dynamics Simulation

Abstract

Proton transfer (PT) via the Grotthuss mechanism in liquid imidazole (im) at 393 K is studied with molecular dynamics simulation using a reactive multistate empirical valence bond (MS-EVB) model. It is found that the proton is tightly binded to an imidazole to form an imidazolium (imH(+)), which is solvated in a distorted Eigen-like complex (im-imH(+)-im), whereas the Zundel-like complex (im-H(+)-im) is rare. PT occurs via an Eigen-Zundel-Eigen scenario for switching the identity of imH(+) from an Eigen-like complex to another, intermediated by a Zundel-like complex. Structural and dynamical analyses demonstrate that PT in imidazole can be considered as a local event with very short spatial/temporal correlation, characterized by a few "rattling" or recurrent PT events. At long time scale, the trend of the PT correlation function may be recast with the diffusion model of reversible geminate recombination toward the power-law decay. The formation of the hydrogen bonds (HBs) for the imidazole molecules between the first and second solvation shell of imH(+) is crucial to pave the PT pathway. The above features may be understood by the flexibility of the HBs in liquid imidazole, as a stable HB network is essential for the Grotthuss mechanism.

Dynamics of structural diffusion in phosphoric acid hydrogen-bond clusters

“…The formation of Zundel-like and Eigenlike complexes leads to a positive charge displacement from H-bond (1) to (2), as shown in Fig. 5a, which is in accordance with the Eigen-Zundel-Eigen mechanism in protonated imidazole (Im) H-bond chains, 52 in which breaking and forming H-bonds in the c crystallographic axis of a unit cell represent the most important elementary steps in the structural diffusion process. 31 Effects of local-dielectric environment.…”

Applying neutron diffraction with isotopic substitution to the structure and proton-transport pathways in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

“…Li et al 38 modelled proton transfer in liquid imidazole, identifying [Im-imid-Im]+ cation formation through solvation of protonated imidazolium cations (generated by reaction with injected protons) by imidazole. Within the simulations, proton transfer was considered as a local event with only very short spatial/temporal correlation whereas slower imidazole reorientation was identified as the rate limiting step.…”

Proton transfer mechanism of 1,3,5-tri(2-benzimidazolyl) benzene with a unique triple-stranded hydrogen bond network as studied by DFT-MD simulations

“…In the product, R NI-NII increased to stabilize the product and retain the proton from I-layer (N I ). To further understand the effect of the external electric field on the intrinsic charge delocalization because of the hydrogen bond, the Hirshfeld charge distribution (Geldof et al, 2011;Van Damme et al, 2009;Marenich et al, 2012;Krishtal et al, 2006) was analyzed. The partial negative charges on N I (N I … H) decreased while the partial negative charges on N II (H … N II ) increased at the transition state (TS) as higher electric field strengths were applied.…”