Theoretical insights into the intermolecular and mechanisms of covalent interaction of Flutamide drug with COOH and COCl functionalized carbon nanotubes: A DFT approach

In this study, it is attempted to scrutinize the noncovalent interaction and two mechanisms of covalent between Flutamide anti-cancer drug (FLU) and functionalized carbon nanotubes (f-CNT) employing density functional theory (DFT) calculations regarding their geometries, binding energies and topological features of the electron density in the water solution. For designed noncovalent interactions, binding energies, natural bond orbital (NBO), atom in molecule (AIM) and quantum molecular descriptors analyses were applied for further understanding of the adsorption process. The computed theoretical results confirmed that binding of Flutamide molecule with functionalized CNT is thermodynamically suitable and among two considered systems containing COOH functionalized CNT (NTCOOH) and COCl functionalized CNT (NTCOCl), the NTCOOH revealed more binding energy value which suggests it as a favorable system as a drug delivery within biological and chemical systems (noncovalent). NTCOOH and NTCOCl can bond to the NH group of flutamide through OH (COOH mechanism) and Cl (COCl mechanism) groups, respectively. Finally, to obtain the values of activation energies, the activation enthalpies and the activation Gibbs free energies of two considered pathways different calculations were performed and the results have been compared with each other. Numerical studies for calculating activation parameters related to the COOH mechanism show higher values than those related to the COCl mechanism and therefore COOH mechanism can be suitable for noncovalent functionalization. These results could be generalized to other similar drugs.