Dendrimers are a class of branched macromolecules with generational growth that have been explored for applications in fields including water purification, drug delivery and light harvesting. Dendrimers offer desirable properties, such as precise control of the size, shape, and chemical functionality of the molecule. Applications such as oil dispersion and water purification extensively involve dendrimers interactions with aromatic and linear hydrocarbons. A detailed description of the interactions between dendrimers and hydrocarbons can assist researchers in selecting and tuning dendrimer properties for specific applications.<br/><br/>We used a combination of all-atom and coarse-grained (CG) molecular dynamics (MD) simulations to investigate the interactions between dendrimers and hydrocarbons. All-atom MD simulations with explicit water were used to investigate the mechanistic details of association of a model aromatic hydrocarbon guest molecule, naphthalene (NPH), with 3rd – 6th generation (G3–G6) PAMAM dendrimers. The simulations total several microseconds of simulation time for 70,000+ atom systems. We observe NPH–NPH interactions which appear to promote NPH association with the dendrimers. NPH associates at a distance from the dendrimer center that is accessible to the water solvent. However, dendrimer branches form local pocket-like structures around NPH molecules associated with the dendrimers. These pockets provide a local environment protected from water. Increasing the NPH concentration, did not shown any clear saturation point, but instead observed a transition to NPH molecules aggregating together on the dendrimers.<br/><br/>Motivated by our observations of NPH aggregation on the dendrimers and experiments that report large aggregates of dendrimers in solution with linear hydrocarbons, we performed CG simulations of two dendrimers in solution with octane. The two dendrimers aggregate via the hydrophobic interactions between droplets of octane inside each of the dendrimers. We calculate the dendrimer–dendrimer potential of mean force for two dendrimers in water both with and without octane molecules to show the extent to which the dendrimer aggregation is driven by the hydrophobic interactions. Since the dendrimer aggregates observed in experiments are much larger than a few dendrimers, we also performed simulations of the dendrimers at the octane–water interface. We will discuss the comprehensive view of dendrimer-guest interactions emerging from our results.

Dendrimers for water purification and oil dispersion: Atomistic and coarse-grained molecular dynamics investigations of dendrimer–hydrocarbon interactions

251st National Meeting (2016)

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