Figure 4.

Thermodynamic cycle of the complex formation between a receptor (R) and a protonated ( ${\text{HL}}^{+}$)/a deprotonated (L) ligand. $K_{\mathrm{b}}^{+}$ and $K_{\mathrm{b}}^0$ are the binding constants of the protonated and deprotonated ligands. $K_{\mathrm{a}}^F$ and $K_{\mathrm{a}}^C$ represent the equilibrium constants between protonated and deprotonated states of the free ligand and the complex.