Table 1.

Protonation Constants of Various Chelators and the Thermodynamic Stability Constants of Corresponding La³⁺ Complexes Determined by pH Potentiometry (25 °C and I = 0.1 M KCl).

	H2macropa	H2BZmacropa	H2BZ2macropa	H4DOTA	H5DTPA	H4EDTA
log K1	7.41(1)c	7.06(2)	6.89(7)	11.14d	10.45e	10.17e
log K2	6.85(1)c	6.41(1)	6.11(3)	9.69d	8.53e	6.11e
log K3	3.32(1)c	3.35(2)	3.36(3)	4.84d	4.28e	2.68e
log K4	2.36(1)c	2.41(9)	2.26(9)	3.95d	2.65e	2.00e
log K5	1.69(1)c		-		1.82e	1.5e
log KLaL	14.99(2) c	13.99(5)	12.04(6)	21.7(1) d	19.48 e	15.46 e
log KLaHL	2.28(3) c	-	-	2.5(2) d	-	2.24 e
log K´Laa	14.63	13.81	11.92	15.67	15.27	12.67
pLab	15.58	14.77	12.87	16.62	16.22	13.62

^aConditional stability constants (log K’_M) at pH 7.4, 25 °C, and I = 0.1 M KCl

^bpM values calculated from −log [M]_free ([M]_total = 10⁻⁶ M, [L]_total = 10⁻⁵ M, pH 7.4, 25 °C, and I = 0.1 M KCl)

^c0.1 M KCl, ref ²¹.

^d0.1 M KCl, ref ²².

^e0.1 M, ref ²³.