Ab Initio Molecular Dynamics Simulations of the Hydration of Zwitterions

Biofouling is a global problem caused by the gradual accumulation of biomolecules and microorganisms, such as barnacles and algae, on a surface. For example, it increases the hydrodynamic drag on vessels' sailing and causes pitting and crevice corrosion of vessels' metal surfaces. Developing a non-toxic and eco-friendly biofouling-resistant coating—which is also effective in different marine environments—is essential to minimize the biofouling effects. Zwitterionic polymers are promising candidates to this end due to their electrostatically driven strong hydration. Experimentally, it is found that the antibiofouling property of zwitterions increases as the zwitterionic separation decreases. Employing ab initio molecular dynamics, we investigate hydration of multiple zwitterions of varied molecular structures. We further study their strong hydration's assumed origin, the non-covalent interactions between the zwitterions and their solvent waters, using symmetry-adapted perturbation theory. Our simulations show that the zwitterionic-hydration is varied with the separation distance of oppositely charged moieties, and the induction interaction with hydrogen-bonded water plays a critical role.