Understanding the Molecular Properties of Doxorubicin Filling Inside and Wrapping Outside Single-Walled Carbon Nanotubes

Molecular dynamics (MD) simulations were applied in order to examine the molecular properties of the anticancer drug, doxorubicin (DOX), carried by single-walled carbon nanotubes (SWCNT) in an aqueous solution. The models evaluated were the two DOX-SWCNT complexes based upon DOX being inside (DOXin-SWCNT) or outside (DOXout-SWCNT) the pristine SWCNT, and these were compared to that for the aqueous free form (DOXfree). It was found that DOX in the DOXin-SWCNT complex was less flexible than DOXfree and DOXout-SWCNT, which was expected due to its collaborative interaction with the surface of the tube. Interestingly, in both complexes with SWCNT, DOX was found to move from one end of the SWCNT to the other in the pi-pi stacking conformation between the three aromatic hydroxyanthraquinonic rings of the DOX and the surface of the SWCNT. This configuration is better established in the DOXout-SWCNT complex than in the DOXin-SWCNT complex, with their respective distances from the DOX center of mass to the nearest carbon atom of the SWCNT being 4.0 angstrom and 4.5 angstrom. Due to the curvature effect and the volume constraints, the ordering of water accessibility around DOX was observed in the following order: DOXfree >> DOXout-SWCNT > DOXin-SWCNT.