Free-Energy Simulations of Hydrogen Bonding versus Stacking of Nucleobases on a Graphene Surface

It has been demonstrated by molecular modeling and experiments that free nucleic acid bases form hydrogen-bonded complexes in vacuum but prefer pi-pi stacking in partially and fully solvated systems. Here we show using molecular dynamics simulations and metadynamics that the addition of a surface (in this case a nanographene monolayer) reverts the situation from stacking back to hydrogen bonding. Watson-Crick as well as several non-Watson-Crick base pairs lying on a graphene surface are significantly more stable in a water environment than a pi-pi-pi-stacked graphene-base-base assembly. It illustrates that the thermodynamics of nucleobase interactions results from a fine balance among hydrogen bonding, stacking, and solvation, and that these effects must be considered in molecular design.