. 2014 Feb 25;4(1):252–267. doi: 10.3390/biom4010252

Table 1.

Dissociation equilibrium constants of monodentate metal complexes.

	K_d’ at pH 7 *			Approximate pK_a in proteins
	Cd²⁺	Hg²⁺	Pb²⁺	Approximate pK_a in proteins
Thiol group	2.5 µM	0.063 nM	13 µM	9.4
Imidazole group	2.0 mM	200 µM	6.3 mM	6.5
Carboxyl group	16 mM	2.5 µM	13 mM	4.6

* K_d’is the apparent dissociation equilibrium constant at pH 7 of the reaction ML Inline graphic M + L, where ML is the 1:1 complex of the metal ion (M) and ligand (L) [45].