Table I.
Summary of Metal Dissociation Constants
metal ion | effective ionic radius (Å) | KD (M)a | ±SE (M) | calcd ΔGB (kcal/mol)b |
---|---|---|---|---|
group IA | ||||
Li(I) | 0.84c | ≥0.9 | ≥−0.1 | |
Na(I) | 1.12 | ≥2.4 | ≥0.5 | |
K(I) | 1.46 | ≥0.8 | ≥−0.1 | |
Rb(I) | 1.56 | ≥1.9 | ≥0.3 | |
group IIA | ||||
Mg(II) | 0.81c | 0.20 | 0.06 | −1.0 |
Ca(II) | 1.06 | 2.5 × 10−5 | 1.1 × 10−5 | −6.3 |
Sr(II) | 1.21 | 5.4 × 10−3 | 0.2 × 10−3 | −3.1 |
Ba(II) | 1.38 | ≥0.6 | ≥−0.3 | |
group IIIA | ||||
Sc(III) | 0.81c | 1.91 × 10−4 | 0.01 × 10−4 | −5.1 |
Y(III) | 0.96 | 3.8 × 10−5 | 0.1 × 10−5 | −6.0 |
La(III) | 1.10 | 7.29 × 10−4 | 0.04 × 10−4 | −4.3 |
lanthanides | ||||
Ce(III) | 1.07 | 4.6 × 10−4 | 0.6 × 10−4 | −4.6 |
Pr(III) | 1.06 | 3 × 10−4 | 1 × 10−4 | −4.8 |
Nd(III) | 1.05c | 2.3 × 10−4 | 0.4 × 10−4 | −5.0 |
Sm(III) | 1.02 | 1.3 × 10−4 | 0.2 × 10−4 | −5.3 |
Eu(III) | 1.01 | 9.5 × 10−5 | 0.5 × 10−5 | −5.5 |
Gd(III) | 1.00 | 8.2 × 10−5 | 0.1 × 10−5 | −5.6 |
Tb(III) | 0.98 | 9 × 10−6d | 4 × 10−6 | −6.9 |
Dy(III) | 0.97 | 2.5 × 10−5 | 0.8 × 10−5 | −6.3 |
Ho(III) | 0.96c | 3.3 × −610−5 | 0.1 × 10−5 | −6.1 |
Er(III) | 0.945 | 2.6 × 10−5 | 0.1 × 10−5 | −6.3 |
Tm(III) | 0.94c | 1.3 × 10−5 | 0.2 × 10−5 | −6.6 |
Yb(III) | 0.925 | 0.8 × 10−6 | 0.2 × 10−6 | −8.3 |
Lu(III) | 0.92c | 1.1 × 10−6 | 0.2 × 10−6 | −8.1 |
All measurements were at 25 °C and 2.5 μM protein, 100 mM KCl, and 10 mM PIPES, pH 6.0.
Binding free energies for 1 M standard state concentration (ΔGB = RT In KD)
Effective ionic radius for coordination number = 7 was obtained by averaging EIR for CN = 6 and CN = 8. In other cases EIR are those measured for CN = 7. EIR are from Shannon (1976).
Determined by equilibrium dialysis.