TABLE 2.
Properties and effects of tested metal ions
| Iona | Charge | Radius (Å)b | Eo (V)b,c | Effect on enzymatic cellulolysisd |
|---|---|---|---|---|
| Mg(II) | 2+ | 0.72 | ∼20% gain in initial rate, ∼20% gain in extended hydrolysis extent | |
| Ca(II) | 2+ | 1.00 | ∼20% gain in initial rate, ∼20% gain in extended hydrolysis extent | |
| Cr(III) | 3+ | 0.62 | −0.407 | ∼40% loss in initial rate, ∼40% loss in extended hydrolysis extent |
| Mn(II) | 2+ | 0.67 | ∼10% loss in initial rate, no change on extended hydrolysis extent | |
| Fe(II) | 2+ | 0.61 | ∼70% loss in initial rate, ∼70% loss in extended hydrolysis extent | |
| Fe(III) | 3+ | 0.55 | 0.771 | ∼90% loss in initial rate, ∼90% loss in extended hydrolysis extent |
| Co(II) | 2+ | 0.65 | ∼10% loss in initial rate, no change on extended hydrolysis extent | |
| Ni(II) | 2+ | 0.69 | ∼20% loss in initial rate, ∼10% loss in extended hydrolysis extent | |
| Cu(II) | 2+ | 0.73 | 0.153 | ∼90% loss in initial rate, ∼80% loss in extended hydrolysis extent |
| Ru(III) | 3+ | 0.68 | 0.249 | ∼90% loss in initial rate, ∼80% loss in extended hydrolysis extent |
| Zn(II) | 2+ | 0.74 | ∼20% loss in initial rate, ∼20% loss in extended hydrolysis extent |
a
The counteranions of these metal ion compounds, SO42− and Cl−, were inert under the hydrolysis conditions of this study.
b
Ionic radii in crystals for six-ligand coordination (19).
c
Single-electron oxidation potential versus a normal hydrogen electrode. Metal ions without Eo entry are stable against either reduction or oxidation under the conditions of this study.
d
One-milliliter-scale hydrolysis of 23 g/liter Avicel by 0.25 g/liter cellulase mix in 50 mM Na-acetate at pH 5 and at 50°C for 4 days.