Table 4.

Protonation constants of 8O₂-bridged-DOTAM, DOTAM and DOTA and their stability constants with some lanthanide ions. The constants were determined at 25 °C in an ionic background (I) of 1.0 M KCl (in the case of DOTA I = 0.1 Me₄NCl). The standard deviations are given in parentheses.

Equilibrium Constant	1	DOTAMa	DOTAb
log K1H	8.44 (0.02)	9.08	12.60
log K2H	5.51 (0.03)	6.44	9.70
log K3H	–	–	4.50
log K4H	–	–	4.14
log K5H	–	–	2.32
log KCeL	4.85 (0.06)	11.93	23.4c
log KEuL	6.44 (0.08)	13.54	23.5c
log KYbL	9.58 (0.06)	–	25.0c
log KLuL	–	13.53	–

^aValues taken from reference ⁴¹

^bValues taken from reference ⁴²

^cValues taken from reference ⁴³