Modeling Proton Dissociation and Transfer Using Dissipative Particle Dynamics Simulation

We suggest a coarse-grained model for dissipative particle dynamics (DPD) simulations of solutions with dissociated protons. The model uses standard short-range soft repulsion and smeared charge electrostatic potentials between the beads, representing solution components. The proton is introduced as a separate charged bead that forms dissociable bonds with proton receptor base beads, such as water or deprotonated acid anions. The proton-base bonds are described by Morse potentials. When the proton establishes the Morse bonds with two bases, they form an intermediate complex, and the proton is able to "hop" between the bases artificially mimicking the Grotthuss diffusion mechanism. By adjusting the Morse potential parameters, one can regulate the potential barrier associated with intermediate complex formation and breakup and control the hopping frequency. This makes the proposed model applicable to simulations of proton mobility and reaction equilibria between protonated and deprotonated acid forms in aqueous solutions. The proposed model provides quantitative agreement with experiments for the proton self-diffusion coefficient and hopping frequency, as well as for the degree of dissociation of benzenesulfonic acid.