*3.3. Electrostatic Surface Potential Map*

Investigating the electrostatic surface potential (ESP) map is a key activity in drug design as it determines the chemical reactivity of the compound and its ability to produce important molecular interactions. It is an effective way to visualize the molecular reactivity and evaluate the nature of ligand-binding with a targeted protein. The ESP map is depicted by different colored regions depending upon the electronegativity of the compound. The highly electronegative part is represented by the color red, whereas the electropositive part is represented by the color blue. The QM calculations were performed using DFTs at the B3LYP/6-31G\* level of theory. Figure 8 depicts the ESP potential and the nature of ligandbinding with the targeted protein. In this study, the contribution of the electronegative oxygen atom in all interactions is indicated by the color red, whereas the contribution of the nitrogen atom is provided in the color blue. Considering the electrostatic surface potential map, the contribution of oxygen atoms toward interaction potential is higher than that of nitrogen atoms. It was observed that in the case of compound 208, the electronegative oxygen atom was acting as a hydrogen acceptor and was producing strong hydrogen bonding with GLY117. Similarly, in compound **248**, **255** and **762**, electronegative oxygen atoms were involved in stronger intermolecular interactions. In contrast, nitrogen atom was involved in hydrogen bonding by donating the hydrogen bond for example, in case of compound **208**, nitrogen was donating hydrogen bond to ASP118 residue. In addition, the docked conformation of ligands on the protein surface is also represented by different colored regions (Figure 8). The red surface indicates the hydrogen bond acceptor region, while the blue surface indicates the hydrogen bond donor locations. Whereas the grey color areas indicate the hydrophobic interactions, including van der Waals interactions. The red-colored surface area of protein is buried by nitrogen atoms as they act as proton donors, whereas the blue-colored protein surface is buried by electronegative atoms such as oxygen, fluorine and chlorine, which acts as a hydrogen bond acceptor. It can be observed

that the grey surface area of protein is mostly involved in hydrophobic interactions, and these regions are buried by alkyl, phenyl rings and other hydrophobic groups present in all compounds.

**Figure 8.** Electrostatic surface potential map of all ligand complexes.
