Iron -imidazole interactions

We have investigated the picosecond photodissociation of the 2 and CO forms of a number of synthetic and natural heme complexes that differ in the geometry and strain associated with the imidazole-iron (porphyrin) interaction using the standard Nd 61ass laser pump-probe absorption method. Our results indicate that it takes some picoseconds for these complexes to dissociate and further suggest that a pseudo four coordinate complex may be present as a photointermediate in the synthetic compounds with the strained imidazole geometry. 

The bleomycins (50) are hardly simple amines, but they do have two NH2 groups and a CONH2 group at the N-terminal domain, as well as potential donor nitrogens in pyrimidine and imidazole, which can complex metal ions." " The complexing of iron to bleomycin" " " has a significant effect on bleomycin-DNA interactions—metal complexes can mediate strand scission—and on alkene oxidation. Both may involve hydroperoxide intermediates." " " " ... 

Four spin-labelled derivatives of sperm whale metmyoglobin were prepared by site-directed mutagenesis.101 Cyanide anion or imidazole was added to prepare low-spin Fe(III). Iron relaxation rates were measured by saturation recovery or inversion recovery between 5 and 17 K and by analysis of the temperature-dependent contribution to the CW line widths of the iron signal at 20 to 160 K. The nitroxyl 7i values in spin-labelled Zn-substituted myoglobin were measured to provide values in the absence of interaction with the more rapidly-relaxing Fe(III). The full shapes of the nitroxyl saturation-recovery curves for the spin-... 

Figures 5.10 and 5.11 show a histidyl F8 residue interacting with the heme iron on deoxy- and oxyhemoglobin. Would you expect the imidazole nitrogen of the histidyl group to be protonated or unproton-ated during this interaction Why ... 

On the structure of Hb02 two models are presented (Fe(II)-02, Fe(IH)-02 ) (12-14). Iron in Hb02 is in a low spin state. However, when imidazole coordinates as the sixth legand both high spin state and low spin state of Fe(III) are observed. These states relate to the interaction of oxygen with Hb, and analyses using NMR technique have recently been done (15-17). 

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