2.5. Free radical scavenging assay using EPR spectroscopy

EPR spectroscopy was used to monitor the scavenging of DPPH radicals by the TA extracts. 20 µl of TA extracts were mixed with 100 µl of methanolic solution of DPPH to a total volume of 3 ml, and the EPR spectrum was measured using VARIAN E-112 ESR spectrometer at different time points. 3 ml of 100 mM DPPH in ethanol was taken as blank. The decrease in the intensity of the DPPH peak, which was indicative of a decrease in the concentration of DPPH radical, was monitored by an EPR spectrometer for a period of 30 min during which the radical was stable (Adevaiton et al., 2009). The DPPH radical was generated in ethanol solution and considered as a control (Figure S5). The DPPH radical scavenging activity was estimated as a ratio of individual DPPH signal peak height to that of control.

Molecular docking studies of SARS-CoV-2 protease with Lopinavir (a) 3D interaction of 3CL + Lopinavir, (b) 3D interaction of PL + Lopinavir, (c) Structure of Lopinavir, (d) Binding energy values of SARS-CoV-2 protease with Lopinavir.

The DPPH radical scavenging activity of each sample was calculated by comparison of relative peak height for control (sample free) DPPH solution. DPPH radical reducing activity of each test sample was expressed as the percentage of DPPH residue