A Hybrid Molecular Dynamics/Multiconformer Continuum Electrostatics (MD/MCCE) Approach for the Determination of Surface Charge of Nanomaterials

The surface charge of nanomaterials determines their stability in solution and interaction with other molecules and surfaces, yet experimental determination of surface charge of complex nanomaterials is not straightforward. We propose a hybrid approach that iteratively integrates explicit solvent molecular dynamics simulations and a multiconformer continuum electrostatic model (MCCE) to efficiently sample the configurational and titration spaces of surface ligands of nanomaterials. Test calculations of model systems indicate that the iterative approach converges rapidly even for systems that contain hundreds of titratable sites, making the approach complementary to more elaborate methods such as explicit solvent based constant-pH molecular dynamics. The hybrid method is applied to analyze the pK(a) distribution of alkylamines attached to a carbon-based nanoparticle as a function of ligand density, nanoparticle surface curvature, and ligand heterogeneity. The results indicate that functionalization strategies can modulate the pK(a) of surface ligands and therefore charge properties of nanomaterials (e.g., surface charge, charge capacitance). The hybrid computational approach makes a major step toward guiding the design of nanomaterials with desired charge properties.