Adsorption and diffusion of the antiparkinsonian drug amantadine in carbon nanotubes

Abstract

Using molecular simulations, we study the adsorption and diffusion of an antiparkinsonian drug known as amantadine (or 1-aminoadamantane) in different single-walled carbon nanotubes (SWCNs) with diameters ranging from 10.9 to 27.1 Å. First, we compute the adsorption isotherm for each SWCN at using the recently developed expanded Wang–Landau (EWL) simulations. This method allows for a direct computation of the grand canonical partition function of the system studied which, in turn, gives access to thermodynamics properties important for the adsorption process. The EWL approach is especially well suited to study the adsorption of large molecules in nanoporous materials since it combines the advantages of the expanded ensemble, in which the insertion and deletion of molecules is divided into a large number of steps, and of the Wang–Landau sampling scheme, which ensures uniform sampling of the number of molecules adsorbed in the porous material. Second, to characterise transport in these systems, we use molecular dynamics simulations to determine how self-diffusivity varies with the loading in amantadine. This allows us to shed light on the interplay between structure and transport in the nanoconfined fluid. In particular, we identify a sharp change in the rate at which the self-diffusivity decreases with the loading and relate it to a transition of the confined fluid from a single cylindrical layer to a bilayer, when additional adamantine molecules are adsorbed in the central region of the pore.