Surface Curvature and Aminated Side-Chain Partitioning Affect Structure of Poly(oxonorbornenes) Attached to Planar Surfaces and Nanoparticles of Gold.

Cationic amphiphilic polymers are often used to coat nanoparticles as they increase chemical stability in solution and exhibit membrane disruption activities. Among these, poly(oxonorbornenes) (PONs) are tunable membrane disruptors. They can be constructed with either one amine-terminated side chain and one hydrophobic alkyl side chain (PON-50) or two amine-terminated side chains (PON-100) on each repeat unit and can then be conjugated to gold nanoparticles using O-(2-carboxyethyl)-O'-(2-mercaptoethyl) heptaethylene glycol (HEG) spacers. While the amine content and membrane disruption activity of PONs can be controlled, the detailed structural properties of PONs conjugated to gold nanoparticles remain less understood. To address this, we performed molecular dynamics simulations of PON-50 and PON-100 to determine the nonbonded energies of PON structures as a function of amine composition. We found increasing energetic stabilization with decreasing amine composition. These results were consistent with experimental observations obtained with X-ray photoelectron spectroscopy (XPS) in which PON-100 was found to have the lowest conjugation efficiency to gold surfaces out of a range of PON amination ratios. Computationally obtained energetics suggest that replacing the aliphatic amine groups with aromatic amine groups can reverse this behavior and lead to more stable PON structures with increasing amine content. We also found that the curvature of the gold nanoparticle surface affects interactions between the surface and the amine groups of PON-50. Increasing curvature decreased these interactions, resulting in a smaller effective footprint of the HEG-PON-50 structure.