Table 1. Overall Stability Constants (logβ) of the Cu²⁺ Complexes Formed by DO4S, DO3S, DO3SAm, and DO2A2S at I = 0.15 mol/L NaCl and T = 25 °C^a.

ligand	equilibrium reactionb	logβ
DO4S	Cu2+ + L ⇋ CuL2+	19.8 ± 0.1c
		19.6 ± 0.4d
DO3S	Cu2+ + L ⇋ CuL2+	20.34 ± 0.06c
		20.10 ± 0.08d
DO3SAm	Cu2+ + L ⇋ CuL2+	19.8 ± 0.2c
		19.7 ± 0.2d
DO2A2S	Cu2+ + H+ + L2– ⇋ CuHL+	24.22 ± 0.09c
	Cu2+ + L2– ⇋ CuL	22.0 ± 0.3d
		21.9 ± 0.2c
DOTA	Cu2+ + 2H+ + L4– ⇋ CuH2L	30.8e
	Cu2+ + H+ + L4– ⇋ CuHL–	26.60e
	Cu2+ + L4– ⇋ CuL2–	22.30e

^aThe literature data for DOTA are reported for comparison.

^bL denotes the ligand in its totally deprotonated form.

^cObtained by UV–vis spectrophotometric titrations.

^dObtained by Ag⁺–Cu²⁺ competition (no ionic strength control).

^eFrom ref (44).