Theoretical study of chemical reactivity descriptors of some repurposed drugs for COVID-19.

This study focuses on computational studies of chemical reactivity descriptors of some proposed drugs for COVID-19. Density functional theory calculations were used to optimize the structure and investigate the frontier orbitals and the chemical reactivity descriptors of these drugs. The frontier orbitals, which include both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), play an essential role in molecular interactions and chemical reactivity of molecule. Polarizability, which determines the response of the susceptibility of a molecule to an approaching charge, is higher in the more complex drugs such as Hydroxychloroquine, Remdesivir, and Ivermectin compare to the smaller drugs. The HOMO and LUMO orbital energies were calculated to obtain the energy gap of the studied drugs, which is in the following order: Favipiravir < Hydroxychloroquine, Remdesivir < Ivermectin < Artesunate < Artemether < Artemisinin. Generally, molecules with a larger energy gap have lower chemical reactivity and higher kinetic stability.