Models, for hemerythrin

Binuclear iron(II) complexes in which a hydroxide bridge is supported by the dinucleating bis-carboxylate ligand dibenzofuran-4,6-bis(diphenylacetate), (217), have proved useful models for hemerythrin. The nature of the binuclear iron center in hemerythrin itself, and in other metalloproteins, has been reviewed, the binding of O2, NO, N3, and NCS to the iron of hemerythrin discussed, " and the volume profile for hemerythrin reacting with O2 established. Bulky tolyl-substituted carboxylate ligands, both bridging and terminal, and... 

Arii, H. Nagatomo, S. Kitagawa, T. Miwa, T. Jitsukawa, K. Einaga. H. Masuda, H. A novel diiron complex as a functional model for hemerythrin. J. Inorg. Biochem. 2000. 

A suitable model for the oxygen carrier protein hemerythrin is [Fe2(Et-HPTB)(OBz)](BF4)2 (Et-HPTB = AWAT,iV -tetrakis[(N-ethyl-2-benzimidazolyl)methyl]-2-hydroxy-l,3-diaminopropane, OBz = benzoate). It can mimic the formation of a binuclear peroxo iron complex in the natural system (101). The measured value of -12.8 cm3 mol1 for the activation volume of the oxidation reaction together with the negative value of the activation entropy confirm the highly structured nature of the transition state. 

A (/t-oxo)bis(t<-carboxylato)diiron(III) core in a model for met hemerythrin has been prepared by spontaneous self-assembly in aqueous solutions of iron(III) perchlorate, sodium acetate and sodium tri-1 -pyrazolylborate.384 The resulting binuclear complex was shown to be very similar in structure and properties to that of met hemerythrin. Thus, the two Fe111 atoms are linked via a n-oxo... 

The complex HB(pz)3Fe(p-CH3C00)2(p-0)Fe(pz)3BH, prepared in one step as a model for the binuclear iron center in hemerythrin, contains two CH3COO and one O bridge between the two Fe(III) atoms. The same holds true for the similarly synthesized diformato and dibenzoato analogs The oxygen bridge in these compounds... 

Comparison of Structural Data for Hemerythrins and Model Complexes (L = MesOlaneNs)... 

Fig. 9. Models for the central core complexes of native octameric hemerythrin (182). Besides being complexed to the protein through amino acid side chains, each iron atom is coordinated to an external, variable ligand X which can be Cl , Bv, F-, CN , NCS-, N3, etc., when bridging the two Fe(III) centers or H2O, OH , F , etc., when two ligands bind. B stands for either OH or an amino acid side chain derived from the protein...

Figure 17. Oxidative addition model for 02 binding by hemerythrin...

We propose that the two-electron oxidative addition 02-binding model developed for hemerythrin can be generalized to hemoglobin, as shown in Figure 20. The deoxy form is presumed to have weak axial... 

A second relevant aspect here is the consideration of models for the various dimetal species that could be important in the reactions at the ferroxidase centers. The area of di-iron metallosites has received a great deal of attention from the early 1980s since the identification of such sites in hemerythrin and the production of the first coordination chemistry model compounds for these (Chapters 8.12 and 8.13). Subsequently several other systems with this motif have been studied and the ones of most relevance to the ferroxidase centers would appear to be those involved in oxygen activation rather than transport. ... 

Binuclear metal complexes are interesting from several points of view, in particular if it is possible to keep the two metal ions not to far from each other [1]. Under such conditions metal-metal interactions are expected and they should reflect themselves in their magnetic and electrochemical properties. In addition two metal ions kept at a fixed distance often allow the specifical binding of a bridging ligand and thus recognition of a molecule and sometimes also its activation. Thus they can be used as models for the study of the structure and reactivity of metalloproteins such as laccase, hemocyanin, hemerythrin and urease. 

N and O donors typically hexacoordinate, these can have extended carboxylate bridged stractures. The stracture and reactivity of such complexes have been examined as model systems in the search for explanations of the biological activation and transport of oxygen. The oxygen carrying proteins hemerythrins contain active centers " " in which two iron atoms are linked by both /x-oxo and carboxylate bridges provided by amino acid groups - these are discussed elsewhere in this Encyclopedia. 

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