Potential of Mean Force for Mg2+ at the Cleaved Mica-Water Interface

Monte Carlo simulations of Mg2+ on cleaved mica reveal that Mg2+ is preferentially adsorbed above a tetrahedral substitution at a distance of 1.2 angstrom from the surface. At the highest simulated water coverage, the free energy of Mg2+ at this position is lower by 108 kJ/mol than at 3.45 angstrom, which corresponds to an outer-sphere adsorption complex. In the dehydrated state, Mg2+ adsorption above a tetrahedral substitution is energetically much more favorable than that in a ditrigonal cavity, which has been proposed earlier to explain the ability of small divalent cations to bind DNA to mica.