Exploration of DFT and TD-DFT computation to investigate the interaction between paracetamol and lithium or its compounds

Paracetamol is a commonly used antipyretic drug and its consumption drastically was increased during the COVID-19 times as fever was one of the symptoms. The excessive usage of paracetamol could harm humans, as the unused accumulated paracetamol can involve in the reaction with many small molecules as well as can interact with several biomolecules. Lithium chloride in its hydrated form is used as an antimanic drug and a geroprotector. It is needed in very small quantities by humans. Tetrahydrated form of lithium ion is the most stable hydrated form. Herein, the authors have investigated the interaction of paracetamol with tetrahydrated lithium chloride (1:1 and 1:2) using the DFT and TD-DFT calculations at 298 K and 310 K. The interaction of paracetamol with lithium chloride P1 (1:1), P2 (2:1), P3 (3:1) and P4 (4:1) are also studied by DFT calculations in default and CPCM model. The authors have calculated the free energy, optimization energy, dipole moment and other thermodynamic parameters of all the systems. Based on enthalpy and change in Gibbs free energy, the interaction was maximum between the paracetamol and tetrahydrated lithium chloride at 298 K as well as 310 K which indicates that the hydrated lithium chloride is being consumed by unused paracetamol. In P1 and P3, lithium showed interaction with oxygen of phenolic group and other atoms of all the paracetamol molecules present, while in P2 and P4, lithium showed these interactions with only one paracetamol molecule.