Potentiometric titration results for ZAC307 and ZAC989. (A) Potentiometric equilibrium curves of ZAC307 in the absence or presence of 0.5 mol equivalent of Zn(NO3)2, CaCl2, or MgCl2 in DMSO-water (70:30, vol/vol). (B) Potentiometric equilibrium curves of ZAC989 in the absence or presence of 0.5 mol equivalent of Zn(CF3SO3)2, CuSO4, CaCl2, or MgCl2 in DMSO-water (70:30, vol/vol). (C, D, and E) Species distribution diagram as a function of pH for a system containing 0.5 mM Zn(II) and 1 mM ZAC307 (C), 0.5 mM Zn(II) and 1 mM ZAC989 (D), and 0.5 mM Cu(II) and 1 mM ZAC989 (E).