. 2009 Sep 19;15(2):203–212. doi: 10.1007/s00775-009-0585-6

Table 3.

Results of the quantum-refinement calculations with w _A = 0.1

	Fe^…Fe	Distance to Fe1 (Å)				Distance to Fe2 (Å)				R _free	Residue R	ΔE _QM1(kJ/mol)	Δr ₁(Å)
	Å	N	S1	S2	S3	S2	S3	S4	S5	R _free	Residue R	ΔE _QM1(kJ/mol)	Δr ₁(Å)
Small QM system, oxidised state, intact cluster
1	2.58	3.29	2.24	2.21	2.19	2.25	2.22	2.25	2.25	0.3042	0.236	60.8	0.27
2	2.69	2.09	2.32	2.23	2.21	2.26	2.22	2.33	2.31	0.3028	0.197	41.6	0.13
3	2.69	2.28	2.30	2.20	2.21	2.24	2.23	2.33	2.30	0.3032	0.212	95.3	0.29
4	2.69	2.37	2.31	2.18	2.21	2.22	2.24	2.33	2.30	0.3035	0.213	127.1	0.36
Large QM system, oxidised state, intact cluster
1	2.60	3.34	2.22	2.22	2.18	2.29	2.21	2.23	2.23	0.3044	0.243	178.5	0.91
2	2.74	2.10	2.29	2.25	2.20	2.31	2.20	2.31	2.29	0.3028	0.199	89.8	0.20
3	2.72	2.33	2.26	2.20	2.21	2.27	2.23	2.31	2.28	0.3031	0.228	130.9	0.31
4	2.67	3.18	2.24	2.19	2.17	2.26	2.23	2.28	2.29	0.3048	0.285	133.0	0.87
Large QM system, reduced state, intact cluster
1	2.77	3.55	2.27	2.36	2.17	2.49	2.31	2.28	2.35	0.3042	0.250	125.0	0.65
2	2.67	2.09	2.31	2.27	2.24	2.34	2.28	2.38	2.34	0.3029	0.206	75.2	0.11
3	2.77	3.08	2.29	2.23	2.21	2.32	2.30	2.33	2.36	0.3043	0.265	204.9	0.96
4	2.66	3.25	2.25	2.19	2.33	2.36	2.33	2.33	2.40	0.3038	0.276	191.1	1.03
Large QM system, without one S atom
1	2.88	2.41	2.23	2.22		2.27		2.27	2.24	0.3034	0.212	192.4	0.26
2	2.85	2.06	2.29	2.22		2.24		2.30	2.27	0.3040	0.196	161.6	0.20
3	2.99	2.24	2.24	2.20		2.25		2.30	2.26	0.3030	0.193	195.3	0.33
4	2.98	2.20	2.25	2.18		2.25		2.32	2.27	0.3030	0.196	156.4	0.14
Crystal structure re-refined without quantum mechanics
i	2.99	2.33	2.37	2.19	2.10	2.11	2.16	2.19	2.25	0.3004	0.138		1.18
ii	2.97	2.33	2.38	2.19	2.13	2.12	2.17	2.19	2.27	0.3004	0.140		1.11
Crystal structure
A	3.24	2.35	2.32	2.23	2.22	2.22	2.23	2.28	2.30	0.3003	0.140	244.4	1.00
B	3.28	2.40	2.30	2.26	2.23	2.22	2.23	2.25	2.27				1.17

Distances between the iron ions and the ligands (Å) are given, as well as the R _free, residue R factors, ΔE _QM1 and Δr _QM, which are the differences in the energy and iron–ligand distances of the QM system optimised in the crystal and in a vacuum. Four sets of calculations are presented: with the small QM system or with the QM system enlarged by Ser⁴³ and Arg⁹⁵, for the oxidised state (Fe^III₂) or for the two-electron-reduced state (Fe^II₂), and for the intact [2Fe–2S] cluster or for the cluster with one sulphide ion removed. In addition, the data from the crystal structure (both subunits) are presented, as well as a standard crystallographic re-refinement of the [2Fe–2S] cluster with two different treatments of the Fe–S interactions (see the text)