Iron complexes imidazole

The third group of studies involves attachment of the iron complexes to solid substrates in order to inhibit formation of bridged species. In a very early study, dioxygen was found to bind reversibly to haem diethyl ester embedded in a mixture of polystyrene and l-(2-phenylethyl)imidazole (Wang, 1958). 

Figure 12.9 Structural model for deoxymyoglobin based on the formation of a five-coordinate iron complex of tetraphenylporphyrin (12.23, R = Ph), stabilised by 2-methyl imidazole.

The hyperfine-shifted proton resonance of metmyoglobin and methemoglobin complexes with imidazoles, in particular, 4-nitroimidazole, was studied in order to obtain an insight into the structural features of the iron-bound imidazole [352], The structure of l-(l,3-dihydroxy-2-propyl)-4-nitroimidazoles, so called acyclic nucleosides, has been established by II and 13C NMR [327],... 

Cobalt Complexes. A fair number of complexes of cobalt have been studied theoretically. Veillard and co-workers have studied the Schiff base adduct Co(acacen)L02 (L = none, H2O, CO, CN", imidazole) and the porphyrin complex Co(porph)(NH3)02 using ab initio LCAO SCF methods. The calculations show the structure to be more stable than the if a linear structure is also found to be unstable. The most important interaction is that between the cobalt d a orbital and the in- plane rg orbital. The interactions of the in-plane jig orbital with the dyz orbital and TTg (i) with dxz, although present, are much less than in the analogous iron complexes as a result of the tighter binding of the d-orbitals in cobalt. The unpaired electron is localised essentially in the Tig (1) orbital of dioxygen. 

In this section, the question raised above will be addressed by applying the local control methodology to a two-dimensional quantum model of the active site of hemoglobin. This system has been studied extensively for many years, both theoretically and experimentally, using a wide range of theoretical methods or experimental techniques. For a recent review of the theoretical approaches, see Ref. 144 and references therein. Here, we choose the six-coordinated iron-porphyrin-imidazole-CO (FeP(Im)-CO) as active site model, which recently has also been used for the study of the excited states [145]. In this complex, the imidazole mimics the proximal histidine, which binds to the central Fe atom and a second imidazole is placed in the proximity of the complex, to include the influence of the distal histidine. The respective configuration is sketched in Fig. 8. 

Figure 3.20. Ligand-induced conformational changes in CYP119. Compared to the phenylimidazole complex (dark shading), the C-terminal end of the F-helix in the imidazole complex unfolds which lengthens the F/G loop thus allowing the F/G loop to dip into the active site and interact with the iron-linked imidazole. Since phenylimidazole is larger than imidazole, the F/G loop cannot remain positioned in the active site complex. Therefore, the F/G helical region and loop shapes itself around the ligand bound in the active site.

In 2011, Sortais and Darcel described the activity of the related nonlinked half-sandwich iron complex [CpFe(IMes)(CO)2]I [IMes = l,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] (Fig. 10.15c) in the hydrosilylation of aldehydes and ketones [73], and more recently, they extended these studies to the reduction of amides [74], nitriles [74], imines... 

Hsieh C-H, Pulukkody R, Darensbourg MY. A dinitrosyl iron complex as a platform for metal-bound imidazole to N-heterocyclic carbene conversion. Chem Commun. 2013 49 9326-9328. 

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