Table 1.
Calculated Fe-Fe and Fe-ligand distances (Å), the net spin populations (NSP) of Fe1(III), Fe2(IV) and Trp48+·, the broken-symmetry state energies E (eV), and the pKa value of the bridging O2 site for models X(di-μ-oxo)-Trp48+· and X(μ-oxo)(μ-hydroxo)-Trp48+· and similar calculated properties for Fe1(IV)(di-μ-oxo)Fe2(IV)a
| X(di-μ-oxo)-Trp48+· | X(μ-oxo)(μ-hydroxo)-Trp48+· | Fe1(IV)(di-μ-oxo)Fe2(IV) | ||
|---|---|---|---|---|
| Stotal = 0 | Stotal = 1 | Stotal = 0 | Stotal = 0 | |
| Fe1-Fe2 | 2.792 | 2.794 | 2.959 | 2.731 (2.744) b |
| Fe1-O1 | 1.886 | 1.926 | 1.934 | 1.765 (1.772) |
| Fe2-O1 | 1.748 | 1.732 | 1.708 | 1.815 (1.808) |
| Fe1-O2 | 1.937 | 1.968 | 2.153 | 1.832 (1.809) |
| Fe2-O2 | 1.758 | 1.753 | 1.960 | 1.769 (1.786) |
| Fe1-O3 | 2.119 | 2.130 | 2.092 | 2.125 (2.095) |
| Fe1-N-His118 | 2.345 | 2.368 | 2.196 | 2.180 (2.212) |
| Fe2-N-His241 | 2.180 | 2.192 | 2.154 | 2.102 (2.155) |
| Fe1-O-Asp84 | 2.081 | 2.117 | 2.019 | 1.958 (2.001) |
| Fe1-O-Glu115 | 1.985 | 1.995 | 1.980 | 2.020 (2.012) |
| Fe2-O-Glu115 | 2.592 | 2.598 | 2.350 | 2.349 (2.344) |
| Fe2-O-Glu204 | 1.964 | 1.986 | 1.922 | 1.923 (1.910) |
| Fe2-O-Glu238 | 2.065 | 2.075 | 2.013 | 2.049 (2.037) |
| NSP(Fe1) | 3.83 | 4.04 | 4.09 | 3.15 (3.14) |
| NSP(Fe2) | −3.24 | −3.23 | −3.28 | −3.17 (−3.16) |
| NSP(C1-Trp48+·) | −0.24 | 0.24 | −0.43 | 0.00 |
| NSP(C2-Trp48+·) | −0.07 | 0.07 | −0.14 | 0.00 |
| NSP(N3-Trp48+·) | −0.09 | 0.09 | −0.14 | 0.00 |
| NSP(C4-Trp48+·) | −0.01 | 0.01 | −0.03 | 0.00 |
| NSP(C5-Trp48+·) | −0.04 | 0.04 | −0.05 | 0.00 |
| NSP(C6-Trp48+·) | −0.08 | 0.09 | −0.16 | 0.00 |
| NSP(C7-Trp48+·) | 0.03 | −0.03 | 0.06 | 0.00 |
| NSP(C8-Trp48+·) | −0.12 | 0.13 | −0.22 | 0.00 |
| NSP(C9-Trp48+·) | 0.05 | −0.05 | 0.10 | 0.00 |
| E | −880.6840 | −880.5995 | −880.4384 | −880.9702 (−880.8538) |
| pKa c | 6.06 | |||
Model of X(di-μ-oxo)-Trp48+·and Fe1(IV)(di-μ-oxo)Fe2(IV) was shown in Figure 2. The difference between X(di-μ-oxo)-Trp48+· and X(μ-oxo)(μ-hydroxo)-Trp48+·is that the bridging site O2 is protonated in X(μ-oxo)(μ-hydroxo)-Trp48+·.
Data in parenthesis are for the geometry which was optimized starting from the Stotal = 0 state X(di-μ-oxo)-Trp48+· optimized geometry, and all the H-linking atoms were fixed according to the initial geometry during the optimization process.