A DFT study on the high-density assembly of doxorubicin drug delivery by single-walled carbon nanotubes

We assembled 1, 4, or 20 doxorubicin (DOX) molecules on the surface of (9, 9) carbon nanotubes (CNTs) as well as 1, 4, 12, or 24 DOX molecules on the surface of -COOH functionalized (9, 9) CNTs (f-CNT) by the density functional tight binding method. The stable assembled structural properties and the interaction energies, such as the total interaction energy, the interaction energy between the CNT/f-CNT and DOX, and the interaction energy between DOX molecules, were analyzed in detail for the complexes. We found that the complex become more stable as the number of DOX molecules increased; the high density adsorption of DOX molecules on the surface of the CNT/f-CNT is more advantageous. To further understand the interactions, the hydrogen bonds, the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals were analyzed. We further investigated the stability and thermodynamic characteristics of the 20DOX/CNT and 24DOX/f-CNT complexes at room temperature via molecular dynamic simulations. The root mean squared displacement and the total energy variations were studied. This work offers a new strategy to assemble a high density of DOX molecules on the surfaces of CNTs.