The NBO Analyses of Two Complexes Formed Between Cyclophosphamide Derivatives and Fullerene C60

The natural bond orbital (NBO) analyses were performed on the optimized structures of two cyclophosphamide drug derivatives physically adsorbed on the surface of fullerene C60 using density functional theory (DFT) at B3LYP level. The carbon atoms bonded to Cl and Br atoms reveal positive charges. The negative charges on Cl (~ -0.09 e) atoms are slightly greater than those on Br nuclei (~ -0.04 e). The carbon atom of C60 to which the phosphoryl oxygen is bonded display positive charge (~0.02 e). The presence of small positive charge on the carbon atom of C60 connected to the O1 suggests physical interaction between the drugs and C60. The NBO perturbation theory energy analysis for the charge transfer transitions in complexes 1 and 2 illustrate that the Lp1 (O1) → * (P1–N1), Lp1 (O1) → * (P1–N2) and Lp1 (O2) → * (P1–N1), Lp1 (O2) → * (P1–N2) are the most significant interactions that are charge transfer transitions from the lone pairs of oxygen atoms O1, O2 to the P–N bonds.