Nitrogenase spin states

Table 3.4 lists values for A Eq and for some important oxidation and spin states found in bioinorganic molecules. Data are taken from reference 24 and from Table 1 of reference 25 for hemoglobin, myoglobin, and the picket-fence porphyrin model compound, FeTpivPP(l-Melm).25 The myoglobin and hemoglobin model compounds are discussed in Section 4.8.2. Reference 26 provides the Table 3.4 data on iron sulfur clusters found in many bioinorganic species.26 The unusual iron-sulfur and iron-molybdenum-sulfur clusters found in the enzyme nitrogenase are discussed more fully below and in Chapter 6. 

Table 6.3 Oxidation and Spin States for Nitrogenase P-Cluster Iron Atoms...

There are cases in which the total spin of the system under study is S > and the analysis of the hyperfine coupling in such systems must take into account the spin state of the system. Notable examples of this include ENDOR measurements on the Fe-Mo cluster of nitrogenase, whose EPR signal arises from the ms = doublet of an S = t system and ENDOR experiments on Mn centers, whose EPR signal can include contributions from all transitions within the manifold of spin states in the 5 = 1 system. 

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