Theoretical study of adsorption behaviour of Thioguanine anticancer drug on the surface of fullerene C60 nanocage

At present work, the adsorption properties of the Thioguanine (TG) interacting with (fullerene C60) are investigated by density functional theory (DFT) calculations. Thioguanine is a chemotherapeutic drug which has significantly curative effect for acute lymphoblastic leukemia and other tumors [1]. Fullerenes are of great interest due to their unique properties, which makes them very attractive for a wide range of applications [2].The interaction mechanism of TG with C60 was investigated by using DFT calculation of the special level of B3LYP/6-31G*. Several possible configurations were selected for TG approaching the side-wall of fullerene. The corresponding adsorption energy value in the most stable structure is -1.61 kJ/mol in the water phase, showing that process of drug adsorption is exothermic.This weak interaction indicates the existence of physisorption between TG and C60. The results of NBO analysis on studied configurations indicated that The important charge transfer in the most stable configuration related to electron donating from lone pair of N atom of TG to the anti‐bonding acceptors σ*(C-C) of C60. In other words, drug molecule acts as donor NBO and C60 acts as acceptor NBO. After TG is adsorbed, in the most stable complex, the HOMO is positioned on the drug molecule, while the LUMO is located on the surface of fullerene, indicating that electron transfer from TG molecule to C60. It is found that the Eg of C60 by interacting with TG altered very slightly, so that we can claim that it is an electronically harmless interaction and the nanocarrier would not significantly alter the drug properties.