Iron complexes biology

In addition to nonheme iron complexes also heme systems are able to catalyze the oxidation of benzene. For example, porphyrin-like phthalocyanine structures were employed to benzene oxidation (see also alkane hydroxylation) [129], Mechanistic investigations of this t3 pe of reactions were carried out amongst others by Nam and coworkers resulting in similar conclusions like in the nonheme case [130], More recently, Sorokin reported a remarkable biological aromatic oxidation, which occurred via formation of benzene oxide and involves an NIH shift. Here, phenol is obtained with a TON of 11 at r.t. with 0.24 mol% of the catalyst. 

Results discussed above show in several lines a distinct biomimetic-type activity of iron complexes stabilized in the ZSM-S matrix. The most important feature is their unique ability to coordinate a very reactive a-oxygen form which is similar to the active oxygen species of MMO. At room temperature a-oxygen provides various oxidation reactions including selective hydroxylation of methane to methanol. Like in biological oxidation, the rate determining step of this reaction involves the cleavage of C-H bond. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

Recently, a new natural product linking sulfur, oxygen and iron has been isolated from bacterial sources. These substances, the thiohydroxa-mic adds, are worthy of discussion in the present context even though their biological significance has yet to be defined. The copper and iron complexes of N-methyl thioformylhydroxamic acid were obtained from the culture broth of Pseudomonas fluorescens and named fluopsins C and... 

Unfortunately, the iron complexes of both chelators desferal and LI are able to catalyze the formation of oxygen radicals [394,395]. Cragg et al. [395] also showed that LI exposure markedly enhanced free radical-mediated DNA damage in iron-loaded liver cells. It has been suggested that the prooxidantrantioxidant ratio of LI activity depends on the composition of complexes formed a 1 3 Fe/Ll is supposed to be inactive in the production of free radicals while the generation of radicals is possible at lower Fe/Ll ratios [395], But it should be noted that in real biological systems there is always equilibrium between iron-chelator complexes of different composition. 

Drapier, J. C., Pellat, C., and Henry, Y. (1992). Characterization of the nitrosyl-iron complexes generated in tumour cells after co-culture with activated macrophages. In The Biology of Nitric Oxide. 2. Enzymology, Biochemistry and Immunology. (S. Moncada, M. A. Marietta, J. B. Hibbs, Jr., and E. A. Higgs, eds.), pp. 72-76, Portland Press, London. 

Vanin, A. F. (1967). Identification of divalent iron complexes with cysteine in biological systems by the EPR method. Biochemistry (USSR) 32, 228-232. 

Sodium nitroprusside was first prepared and investigated in the middle of the nineteenth century, and a comprehensive summary of the earlier chemical investigations has been published (17). Up to 1910-1930, the addition reactions of bases to NP were explored, involving the characterization of colored intermediates (e.g., with SH-, SR-, and SO3 ), useful for analytical purposes. The hypotensive action of NP was first demonstrated in 1929, and a considerable research effort has attempted to establish the mode of action of NP and its metabolic fate. Questions still arise on the mechanism of NO release from NP in the biological fluids, and we refer to them below. New accounts dealing with modern structural and reactivity issues associated with the coordination of nitrosyl in NP and other complexes have appeared (18-20). From the bioinorganic and environmental viewpoint, nitrosyl iron complexes have been studied with... 

Iron as a cofactor in catalysis is receiving increasing attention. The most common oxidation states of iron are Fe2+ and Fe3+. Iron complexes are nearly all octahedral, and practically all are paramagnetic (as a result of unpaired electrons in the 3d orbital). The most common form of iron in biological systems is heme. Heme groups (Fe2+) and hema-tin (Fe3+) most frequently involve a complex with protoporphyrin IX (fig. 10.19). They are the coenzymes (prosthetic... 

The actual biological concentrations of the reactants (ligands, iron, complexes, H202) are also important and need to be considered when assessing the redox properties of the formed complex. 

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