Electrostatic potential is widely used in characterizing molecules, especially for biomolecules, and takes special effect in the biomolecular recognition and in the prediction of the functional sites [62] . Nam et al. reported their discovery that electrostatic interactions accounted for the majority of the rate acceleration in the mechanism of RNA transphosphorylation in solutions catalyzed by the hairpin ribozyme [63] . Daga and Doerksen have stated the binding mode and the role of stereoelectronic properties in binding of spiroquinazolinones showing phosphodiesterase 7 (PDE7) inhibitory activities [64] . Recently, the electrostatic funnel illuminated from three-dimensional mapping of the electrostatic potential was reported by Dehez et al., driving the diphosphate nucleotide rapidly toward the bottom of the internal cavity of membrane-protein mitochondrial ADP/ATP carrier by forming a privileged passageway [65] . Considering these discoveries comprehensively, we supposed that the electrostatic potential of the inhibitor also played a significant role in the binding and interaction with chymase together with orbital energy and consequently influenced the inhibition effect. The 3D isosurface maps of MESP were interpolated on the electron density surfaces of constant electron charge density (0.0004 e/au 3 ). As is well known, the electrostatic potential is defined as the interacted energy of a positively remote charge point with the nuclei and the electrons of a molecule. The 3D plots of electron density (ED) and the MESP for compounds 1, 20, BTB and HTS are shown in Figure 12 . The red and the blue color represent the electronegative and electropositive potentials whereas the green represents a potential halfway between the two extremes.