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 |
a
All measurements were at 25 °C and 2.5 μM protein, 100 mM KCl, and 10 mM PIPES, pH 6.0.
b
Binding free energies for 1 M standard state concentration (ΔGB = RT In KD)
c
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).
d
Determined by equilibrium dialysis.