COMPREHENSIVE QUANTUM MECHANICAL STUDY ON THE MECHANISTIC, ENERGETIC AND STRUCTURAL PROPERTIES OF ADSORPTION OF DRUG 6-THIOGUANINE ONTO FUNCTIONALIZED CARBON NANOTUBES

Using density functional theory, the six noncovalent interactions and possible mechanisms of covalent functionalization of drug 6-thioguanine with COOH and COCl functionalized carbon nanotube (NTCOOH and NTCOCl) have been investigated. Quantum molecular descriptors of noncovalent configurations were studied. It was specified that binding of drug 6-thioguanine with NTCOOH has more binding energy than NTCOCl and can act as a favorable system for 6-thioguanine drug delivery within biological and chemical systems (noncovalent). NTCOOH and NTCOCl can bond to the amino groups of 6-thioguanine through OH (COOH mechanism) and Cl (COCl mechanism) groups, respectively. The activation energies, the activation enthalpies and the activation Gibbs free energies of six pathways were calculated and compared with each other. The activation parameters related to COOH mechanism are higher than those related to COCl mechanism and therefore COCl mechanism is suitable for covalent functionalization. These results could be generalized to other similar drugs.