In the current study, the compound 4,4-dimethoxychalcone (DMC) was structurally studied and analyzed by in silico approach against M^pro to investigate its inhibitory potential. The molecular structure of the compound was confirmed by the single crystal X-ray diffraction studies. The crystal structure packing is characterized by various hydrogen bonds, C-H…π and π…π stacking. Intermolecular interactions are quantified by Hirshfeld surface analysis and the electronic structure was optimized by DFT calculations; results are in agreement with the experimental studies. Further, DMC was virtually screened against SARS-CoV-2 main protease (PDB-ID: 6LU7) using molecular docking, and molecular dynamics (MD) simulations to identify its inhibitory potential. A significant binding affinity exists between DMC and M^pro with a -6.00 kcal/mol binding energy. A MD simulation of 30ns was carried out; the results predict DMC possessing strong binding affinity and hydrogen-bonding interactions within the active site during the simulation period. Therefore, based on the results of the current investigation, it can be inferred that a DMC molecule may be able to inhibit M^pro of COVID-19.

Single crystal X-ray diffraction is the only experimental technique available to elucidate the complete three-dimensional structure of the samples at molecular and atomic levels. But this technique demands defect-free single crystals. Growing good quality single crystals which are suitable to collect X-ray intensity data is an art rather than science. Among the various crystal growth methods, the most effective and commonly used is the slow evaporation method. Using this method, defect-free single crystals of the ground mixture of gallic acid (GA) and butyramide (BU) taken in a 1:1 molar ratio are obtained. The compound was subjected to experimental characterizations like; PXRD, FTIR, SCXRD, and TGA. Further, these results were utilized in the computational characterizations namely, Hirshfeld surface analysis, interaction energy calculations, DFT studies, and docking studies. Structural characterization revealed that the GA-BU compound was crystallized as a cocrystal hydrate with 2:1:1 stoichiometry in a monoclinic crystal system and P21/n space group. Structural studies exposed the presence of various inter and intramolecular hydrogen bond interactions, ring synthons, DDAA environment of the water molecule, and π ... π stacking interactions. The contribution of the several close contacts to the crystal structure, the influence of different interaction energies in the packing, the HOMO-LUMO energy gap, and the location of reactive sites were realized through computational studies. Further, a molecular docking study has been performed to check the antiviral activity of the title compound against COVID-19.