▎ 摘　　要

Density functional theory calculations at the M06-2X/6-31G** level have been carried out to examine the adsorption behavior of Cladribine drug on the graphene and graphene nanosheets functionalized with different functional groups in water solution. The influence of molecular orientation on the structural properties, adsorption energies, quantum molecular descriptors, and the equilibrium distances has been investigated for studied nanosheets. Considering the results, the nature of drug adsorption on the surface of nanosheets is physical and it turned out that the adsorption energy of the considered complexes has increased by functionalization of the nanosheet. It is observed that the intermolecular hydrogen bonds between Cladribine and the functionalized graphene nanosheets have an influential role in the stability of the physisorption configurations. The negative values of solvation energies illustrate that the solvation of complexes is a spontaneous process and water stabilizes the considered complexes. The quantum theory of atoms has been also applied to investigate the properties of the bond critical points and illustrate closed shell interactions between the Cladribine drug molecule and the nanosheets. The analysis of natural bond orbital revealed that the Cladribine drug is able to be adsorbed on the surface of nanosheets with a charge transfer from the drug molecule to the nanosheets. Consequently, the functionalized graphene nanosheet with epoxide group has improved the interaction between drug molecules and graphene nanosheet with considerable adsorption energy. Therefore, it is concluded that the modified graphene nanosheets can be used as an appropriate carrier for the Cladribine drug molecule.