Investigation of thermodynamic properties of favipiravir and ribavirin molecular structures used in the treatment of Covid-19 and their interaction with dna bases by DFT

Different properties of the molecular structures of favipiravir and ribavirin, which are used in the treatment of SARS-CoV-2 and also needed in the treatment of coronavirus disease (COVID-19) in recent years, have been investigated using Density Functional Theory (DFT) B3LYP/6-311G(d, p) and 6-311+G(d, p) methods. The geometrical optimization of the molecular structures of favipiravir and ribavirin was made in the ground state, gas, and water solvent environments, the bond parameters were obtained and the theoretical results were compared with the values in the literature. By obtaining molecular orbital energy values from energy calculations, global reactivity parameters such as electron affinity, electronegativity, chemical potential, chemical hardness, softness, and electrophilicity index were obtained for both environments. The interactions between adenine, guanine, cytosine, and thymine DNA bases and the molecular structures of favipiravir and ribavirin were investigated in water with the help of two parameters such as ΔN (charge transfer) and ECT (electrophilicity-based charge transfer) using global reactivity values. By using the optimized molecular structures of favipiravir and ribavirin, ground state frequency calculations were made for both environments, and thermodynamic properties of molecular structures such as entropy, enthalpy, heat capacity, zero point vibration energy, and Gibbs free energy were investigated.