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Using density functional theory, noncovalent interactions and two mechanisms of covalent functionalization of drug tirapazamine with pristine, COOH and COCl functionalized carbon nanotube (NT, NTCOOH and NTCOCl) have been investigated. Quantum molecular descriptors of noncovalent configurations were studied. It was specified that binding of drug tirapazamine with NTCOOH has more binding energy than NTCOCl and NT, so NTCOOH can act as a favorable system for tirapazamine drug delivery within biological and chemical systems (noncovalent). NTCOOH and NTCOCl can bond to the amino group of tirapazamine through OH (COOH mechanism) and Cl (COCl mechanism) groups, respectively. The activation parameters of two 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.

Magnetic nanoparticles are among the most important carriers for the delivery of anticancer drugs. Four important noncovalent interactions between tirapazamine anticancer drug (TPZ) and magnetic nanoparticle Fe 6 (OH) 18 (H 2 O) 6 (MNP) have been examined by using density functional theory (DFT). Important interactions are those where the drug approaches the magnetic nanocarrier via NH 2 (MNP/TPZ1), NO (MNP/TPZ2-3) and intraring N-atom (MNP/TP4) functional groups. The negative values of binding energies and quantum molecular descriptor showed that these interactions contribute to the stability of the system. By increasing the temperature, TPZ can bond to MNP through NH 2 (NH 2 mechanism), NO (NO mechanisms) and intraring N-atom (N mechanism) functional groups. The activation parameters of four mechanisms were evaluated using quadratic synchronous transit method. Relative energies indicate that the product of the NH 2 mechanism is more stable but is produced more slowly (thermodynamic product). In contrast, the products of the NO mechanisms are kinetic products.