Iron clusters oxygen

Wang L S, Wu FI and Desai S R 1996 Sequential oxygen atom chemisorption on surfaces of small iron clusters Phys. Rev. Lett. 76 4853... 

Iron clusters exhibit facile chemisorption toward methanol, the reaction proceeding with little or no cluster-size selectivity. An interesting feature of this system is that the chemisorption rate constants are nearly identical toward various isotopic sjjecies (CH3OH, CH30D,CD3 0H). If dissociation of a C—H or O—H bond was the initial step, then this should be manifested in an observable kinetic isotope effect. Thus the initial chemisorption step most likely involves the lone-pair orbital localized on the oxygen atom. More extensive studies of the chemistry of the Fe methanol system have been explored using infrared multiple-photon dissociation spectroscopy. These results are discussed in detail in Section Vlll. 

The metal clusters are not the only similarity in the diiron-oxygen protein group. Another common denominator is that all can react with dioxygen, albeit in different states of oxidation. RNR-R2 (30) and MMOH (31) proteins have in common that both cleave an oxygen-oxygen bond, with the iron cluster as an active participant. Hemerythrin is different from these others with five histidines (1-7) in the cluster... 

Fig. 1. Diferric iron clusters form hemer3fthrin, ribonucleotide reductase R2 subunit, and methane monooxygenase hydroxylase. The figure was made with the RasMol 2.0 program, and the protein coordinates as PDB files were obtained from Brookhaven Protein Data Bank. Only the amino acids (histidines, green carboxylates, black oxygen, red nitrogen, yellow acetate, blue iron, violet) coordinated to the iron cluster are shown, coordinated waters are not indicated. The first subunit containing the cluster is shown. Diferric Hr is from sipunculid worm Themiste dyscritra). The RNR-R2 is from E. coli. The MMOH is from Methvlococcus caosulatus (Bath).

Figure 5. Modeling the Fischer-Tropsch reaction on tetranuclear iron clusters. Formation of oxygenated products is not shown.

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