An experimental charge density distribution of 2-nitroimidazole was determined from high-resolution X-ray diffraction and the Hansen-Coppens multipole model. The 2-nitroimidazole compound was crystallized and a high-angle X-ray diffraction intensity data set has been collected at low temperature (110 K). The structure was solved and further, an aspherical multipole model refinement was performed up to octapole level; the results were used to determine the structure, bond topological and electrostatic properties of the molecule. In the crystal, the molecule exhibits a planar structure and forms weak and strong intermolecular hydrogen-bonding interactions with the neighbouring molecules. The Hirshfeld surface of the molecule was plotted, which explores different types of intermolecular interactions and their strength. The topological analysis of electron density at the bond critical points (b.c.p.) of the molecule was performed, from that the electron density ρ(r) and the Laplacian of electron density ∇ρ(r) at the b.c.p.s of the molecule have been determined; these parameters show the charge concentration/depletion of the nitroimidazole bonds in the crystal. The electrostatic parameters like atomic charges and the dipole moment of the molecule were calculated. The electrostatic potential surface of the molecule has been plotted, and it displays a large electronegative region around the nitro group. All the experimental results were compared with the corresponding theoretical calculations performed using CRYSTAL09.

The unprecedented coronavirus SARS-CoV-2 outbreak at Wuhan, China, caused acute respiratory infection to humans. There is no precise vaccine/therapeutic agents available to combat the COVID-19 disease. Some repurposed drugs are saving the life of diseased, but the complete cure is relatively less. Several drug targets have been reported to inhibit the SARS-CoV-2 virus infection, in that TMPRSS2 (transmembrane protease serine 2) is one of the potential targets; inhibiting this protease stops the virus entry into the host human cell. Camostat mesylate, nafamostat, and leupeptin are the drugs, in which the first two drugs are being used for COVID-19 and leupeptin also tested. To consider these drugs as the repurposed drug for COVID-19, it is essential to understand their binding affinity and stability with TMPRSS2. In the present study, we performed the molecular docking and molecular dynamics (MD) simulation of these molecules with the TMPRSS2. The docking study reveals that leupeptin molecule strongly binds with TMPRSS2 protein than the other two drug molecules. The RMSD and RMSF values of MD simulation confirm that leupeptin and the amino acids of TMPRSS2 are very stable than the other two molecules. Furthermore, leupeptin forms interactions with the key amino acids of TMPRSS2 and the same have been maintained during the MD simulations. This structural and dynamical information is useful to evaluate these drugs to be used as repurposed drugs, however, the strong binding profile of leupeptin with TMPRSS2, suggests, it may be considered as a repurposed drug for COVID-19 disease after clinical trial.

Andrographolide (AGH) is a hepatitis C anti-viral agent which targets the host cell by covalently binding with the NF-Breceptor. The experimental electron density distribution study of AGH has been carried out from high-resolution X-ray diffraction data collected at 110.2 (3) K. The unit-cell packing of AGH was stabilized by strong O-HÁ Á ÁO and weak C-HÁ Á ÁO types of intermolecular interactions. The dissociation energy of the strong hydrogen bond O2-H22Á Á ÁO1 is very high, 32 kJ mol À1 . The percentage occupancy of HÁ Á ÁH interactions is found to be maximum (68.5%) when it comparing with the other types of interactions occurring in the AGH crystalline phase. The atomic valance index (V topo ) of the C16 atom is low compared with other carbon atoms; this shows that C16 could be the possible reactive location of the AGH molecule. All atoms in the OH groups have very low V topo values; this indicates their role in strong hydrogen bonding interactions. The electrostatic potential (ESP) surface of AGH shows the polarization of the C16 C17 bond and ESP contour map shows several maxima at the vicinity of the C16 atom; these results strongly demonstrate that the C16 atom is the reactive location of the AGH molecule. The molecular covalent docking analysis of AGH with the NF-B receptor has been performed and confirmed this result. The highly electronegative region around -butyrolactone can be helpful for initial alignment of the AGH molecule in NF-B receptor active site. The atomic volumes of the hydrogen atoms which participate in the HÁ Á ÁH interaction are found to be low.

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