Zahra Nikfar - Department of Chemistry, Amirkabir University of Technology (Tehran Polytechnic),
Zahra Shariatinia - Department of Chemistry, Amirkabir University of Technology (Tehran Polytechnic),

The structures of boron-doped fullerene B-C59 (1) as a drug delivery system, two phosphoramides with formula [NH(CH2)3O]P(O)[N(CH2)3X2]2 where X = F (1) and Br (2) which are analogous to the cyclophosphamide anticancer prodrug as well as their covalently bonded structures to B-C59 (4 and 5) were optimized by DFT computations using B3LYP/6-31G(d) approach. Comparing compounds 4 and 5 reveals that the (-22.9869 kcal/mol) is slightly more stable than its bromo analogue (-22.6778 kcal/mol). The ΔGinteraction value is slightly more negative for compound 5 (-8.5892 kcal/mol) relative to that of 4 (-8.3087 kcal/mol) and the attachment of both drugs on the surface of B-fullerene is exergonic (ΔGinteraction < 0) that means formation of compounds 4 and 5 are both spontaneous. Similarly, the ΔHinteraction values are negative for both compounds 4 and 5 (-21.5207 and -21.2252 kcal/mol, respectively) reflecting these interactions are exothermic (ΔHinteraction < 0). In molecules 2 and 3, the P–N1 and P–N2 (N1 and N2 are endocyclic and exocyclic atoms, respectively) bond lengths are about 1.69, 1.67 Å while they are near 1.65, 1.64 Å for compounds 4 and 5, respectively, that are close to the P–N single bond length (1.77 Å). The C–X bonds are near 1.39, 1.98 Å for X = F, Br, respectively, displaying smaller C–X bond for a smaller, more electronegative halogen atom. The distance measured from the phosphoryl oxygen and B atom of B-C59 in compounds 4 and 5 are 1.5883, 1.5904 Å, respectively, reflecting a strong interaction (chemisorption) occurs between each drug and B-C59 in all thermodynamically favourable compounds. The HOMO-1 and LUMO-2 of compounds 4 and 5 are mainly concentrated on the B and C atoms of the B-fullerene which are closer to the boron atom but the carbon atoms on the B-C59 semi-sphere which are farther than B do not share or have a little partition in the HOMO-1 and LUMO-2 but in case of HOMO-2 and LUMO-1, the orbitals are principally placed on some carbon atoms of B-C59 particle but there is not any orbital on the B atom. The HOMO-2 orbital of structure 5 is only located on the Br and C-Br parts of the phosphoramide drug

DFT computation, B-C59 nanoparticle, Phosphoramide, NBO, Drug delivery