Molecular dynamics simulations of adsorption of long pyrene-PEG chains on a thin carbon nanotube

Carbon nanotubes have emerged as highly promising theranostic agents due to their unique structural/physical features, high surface area, and high drug-loading capacity. The high cytotoxicity of carbon nanotubes can be eliminated by noncovalent coating using hydrophilic polymers. We investigated the adsorption of long pyrene functionalized polyethylene glycol (PEG) chains, PEG 2000 and PEG 5000, on a single-walled carbon nanotube (SWNT) from a crowded solution. Full-atom molecular dynamics simulations in explicit water were used to mimic the experimental conditions of noncovalent PEGylation with a stoichiometry of one SWNT to ten pyrene-PEG. Although the diffusional behavior of the pyrene molecules still attached to the polymers did not change according to chain length, the adsorption rate for pyrene-PEG 2000 to the SWNT was higher than that for pyrene-PEG 5000 chains. Here longer chains sterically hindered the adsorption of pyrene groups on the SWNT surface. Once adsorbed, pyrene molecules stayed on the SWNT surface even though they frequently adopted different orientations that may weaken their π − π stacking interactions with the nanotube surface.