Synergistic effect of Si-doping and Fe(2)O(3)-encapsulation on drug delivery and sensor applications of γ-graphyne nanotube toward favipiravir as an antiviral for COVID-19: A DFT study

In this work, the behavior of favipiravir (FAV) adsorption on the pristine (2,2) graphyne-based γ-nanotube (GYNT) was theoretically studied. Also, the Si-doped form (Si-GYNT) and its composite with encapsulated Fe(2)O(3) (Fe(2)O(3)@Si-GYNT) were investigated within density functional theory (DFT) calculations, using M05 functionals and B3LYP. It was found that FAV is weakly to moderately adsorb on the bare GYNT and Si-GYNT tube, releasing the energy of 2.2 to 19.8 kcal/mol. After FAV adsorption, the bare tube's electronic properties are changed. Localized impurity is induced at the valence and conduction levels by encapsulating a tiny Fe(2)O(3) cluster. As such, the target composite becomes a magnetic material. The binding energy between the Fe(2)O(3)@Si-GYNT and the FAV molecule becomes substantially stronger (E(ad) = -25.2 kcal/mol). We developed a drug release system in target parts of body, during protonation in the low pH of injured cells, detaching the FAV from the tube surface. The drug's reaction mechanism with Fe(2)O(3)@Si-GYNT shifts from covalence in the normal environment to hydrogen bonding in an acidic matrix. The optimized structure's natural bond orbital, quantum molecular descriptors, LUMO, HOMO and energy gap were also investigated. The recovery time can be reduced to less than 10 s by increasing the working temperature properly during the experimental test.