Iron complexes redox properties

The MoFe proteins exhibit complex redox properties. Each tetra-meric a2/32 molecule of MoFe protein contains two P clusters and two FeMoco centers and, as normally isolated in the presence of sodium dithionite, the FeMoco centers are EPR-active, exhibiting an S = spin state with g values near 4.3 and 3.7 and 2.01 (Fig. 6). The P clusters are EPR silent and there is a wealth of evidence (39) using a variety of techniques that indicates that the iron atoms in these clusters are all reduced to the Fe state. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

The characterization, redox properties, and pulse radiolysis study of manganese(III) complexes of type [MnLCy (where L = cyclam, meso-, and rac-5,7,7,12,14,14-hexamethylcyclam (tet a and tet b, respectively)) have been reported." An X-ray crystal structure of the meso-5,l,l, 2, A, A-hexamethyl-l,4,8,ll-tetraazacyclotetradecane complex shows that the coordination geometry of the tet a complex is close to octahedral with the macrocycle coordinated equatorially and the chlorides occupying irons axial sites. 

From the point of view of the redox properties of the formed complex, Merkofer et al. [2006] have studied the Fenton reaction 18 catalyzed by different iron chelators and concluded that a Fe-complex can participate in cell redox cycling only when two conditions are fulfilled (i) the oxidized complex (ligand-M(" + 1 +) can be reduced by a physiologically relevant compound [e.g., NAD(P)H] [Pierre et al., 2002], then the 0 (Ligand M( +i)+/Ligand M +) is higher... 

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. 

The role of transition metals as counter-cations in polyoxometaUates used as oxidation catalysts has been reviewed [75]. Transition metals have important and complex effects on textural, acid-base and redox properties of the heteropolyanions, as described in a number of studies. The interaction of the molybdophos-phoric Keggin heteropolyanion with the iron counter-ion has been studied and... 

The insertion into porphyrins of central metals capable of easy oxidation or reduction can shift the site of redox chemistry from the macrocycle n-electron system to the metal. While this substitution allows large changes in the redox properties of a porphyrin, it may introduce changes in the photophysics if a transition metal is employed. For example, iron (III) porphyrins are particularly good electron acceptor moieties, and have been used as components of porphyrin dyad and more complex systems that show photoinduced electron transfer behavior [11, 18, 19, 26, 31, 32, 34, 43, 44]. McLendon and coworkers used this strategy with dyad 3, in... 

The redox properties of macrobicyclic iron(II) mono- and binuclear oximehydrazonates and a-dioximates formed by capping with antimony(V) and germanium(IV) triorganyles were studied by cyclic voltammetry [73, 74]. The electrochemical behaviour of these compounds is similar to that of analogous boron- and tin-capped clathrochelates. Oxidation of all mononuclear complexes involves a one-electron process, assigned to the oxidation of encapsulated iron(II) ion to iron(III) ion. This process is electrochemically... 

COX-1 inhibition up to 100 yM in human blood (152,153). (Cyclic voltammetry and iron chelation measurements confirmed that this (methoxyalkyl)thiazole series is free from redox and iron-complexing properties. The series differs from redox and theiV-hydroxyurea series in that it demonstrates enantioselective inhibition of 5-LO both in vitro and in vivo (154). This was the first evidence of 5-LO inhibitors forming enantiospecific interactions with the enzyme. Thus, unlike the a-methyl-ene center in the Abbott N-hydroxyurea series, the stereoselectivity of these ligands indicates a close contact of the stereogenic center and active site of the protein. 

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