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Abstract
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was later found to be effective against other RNA viruses, including arenaviruses, bunyaviruses, Zika, Ebola,
Lassa, and COVID-19 viruses, in addition to influenza A and B. Due to the global prevalence of SARS-COV-2 in
2019, Favipiravir was used as an antiviral drug for treating COVID-19, but the challenges facing it, including its
solubility, tablet ability, and bioavailability, remain. It is critical and challenging to develop a drug with
appropriate bioavailability, improved oral absorption, and increased solubility without interfering with other
functions and preventing the consumption of high daily doses. For this purpose, in the present study, the interactions
of Favipiravir-Favipiravir and Favipiravir-H2O and the association of the Favipiravir molecules were
investigated experimentally and theoretically. The theoretical results showed that under normal conditions, all
structures were stable, but the most stable structure based on calculations of electronic energy, Gibbs, and
solvation Gibbs free energies (minimum value), both in the gas phase and in the aqueous phase, is related to the
B-enol isomer. Also, the change in dipole moment in the solvation process for this isomer was less than others.
Also, the intense intermolecular hydrogen bonds O-H…O and N-H…O between the Favipiravir and water molecules
showed that Favipiravir…Favipiravir interactions are stronger than Favipiravir…H2O interactions in
aqueous solutions. These interactions indicate that Favipiravir can participate in the aggregation phenomena in
high concentrations. Also, Stokeʼs shift values slightly increased with the decreasing the drug concentration in
water (intramolecular charge transfer phenomenon).
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