Figure 5.

X-band CW spectra measured at 10 K showing that the proximal [4Fe–3S] cluster is in its most reduced (3+) state (S = 1/2, g_av ∼ 1.85–2) under all conditions, for both Ni-L and Ni-C species. The Ni-C and Ni-L peaks are split due to spin-coupling between Ni and reduced proximal cluster. All stated potentials are relative to SHE. Conditions for measuring spectra: Microwave power = 7.7 μW, microwave frequency = 9.38 GHz, modulation amplitude = 5.0 G, receiver gain = 55 dB. Spectra have been scaled as for Figure 1.