Ferric complex

Pulcherrimin, the red pigment from Candida pulcherrima, is a polymeric ferric complex of pulcherriminic acid (9). The structure of... 

The majority of octahedral ferric complexes exhibit simple Curie or Curie-Weiss magnetic behavior (i.e., magnetic susceptibility 1/7. They can be classified as either "high spin or "low spin. In high-spin complexes, the lowest term (ground state) is Aig, which corresponds to the tag eg2 configuration. The low-spin complexes have the Tgg term as... 

Fig. 5.8 Molecular radial wavefunctions for the ferric complex FeCLt compared to the radial wavefunctions of the free ions Fe ", Fe ", and Fe " (taken from [79])...

A comparison of anisotropic Fe HFCs with the experimental results shows good agreement between theory and experiment for the ferryl complexes and reasonable agreement for ferrous and ferric complexes. Inspection reveals that the ZORA corrections are mostly small ( 0.1 MHz) but can approach 2 MHz and improve the agreement with the experiment. The SOC contributions are distinctly larger than the scalar-relativistic corrections for the majority of the investigated iron complexes. They can easily exceed 20%. 

Coordination compounds of dianionic dithiolene (S2C2 R2) and benzene-1,2-dithiolene (bdt = (S2C6H4) and their derivatives have been studied since the 1960s by Mossbauer spectroscopy [87] and other techniques. Nevertheless, many aspects of their electronic structure remained uncertain for a long time. The five-coordinate ferric complexes with two equatorial dithiolene ligands exhibit intermediate spin and show the Mossbauer parameters = 0.25-0.38 mm s and A q = 1.6-3.2 mm s For example, [Fe° mnt)2/ y] with two mnt ligands (=S2C2(CN)2) and an... 

Iron or copper complexes will catalyse Fenton chemistry only if two conditions are met simultaneously, namely that the ferric complex can be reduced and that the ferrous complex has an oxidation potential such that it can transfer an electron to H2O2. However, we must also add that this reasoning supposes that we are under standard conditions and at equilibrium, which is rarely the case for biological systems. A simple example will illustrate the problem whereas under standard conditions reaction (2) has a redox potential of —330 mV (at an O2 concentration of 1 atmosphere), in vivo with [O2] = 3.5 x 10 5 M and [O2 ] = 10 11 M the redox potential is +230 mV (Pierre and Fontecave, 1999). 

Figure 8.3 A model of iron transport across the intestine. Reduction of ferric complexes to the ferrous form is achieved by the action of the brush border ferric reductase. The ferrous form is transported across the brush border membrane by the proton-coupled divalent cation transporter (DCT1) where it enters an unknown compartment in the cytosol. Ferrous iron is then transported across the basolateral membrane by IREG1, where the membrane-bound copper oxidase hephaestin (Hp) promotes release and binding of Fe3+ to circulating apotransferrin. Except for hephaestin the number of transmembrane domains for each protein is not shown in full. Reprinted from McKie et al., 2000. Copyright (2000), with permission from Elsevier Science.

Synthetic linear dihydroxamic acids may be considered as models of rhodotorulic acid (3) to investigate steric effects on the formation of mono- or di-iron(III) species (127,128). pH-dependent electrospray ionization-mass spectrometry (ESI-MS) methods show that ferric complexes with dihydroxamates with short linker chains (37 and 38 in Fig. 15) will prefer the dimeric... 

Table V shows redox potentials (Ey2) for ferric complexes of a series of natural and synthetic siderophores. The first coordination shell of the complex formed between iron and siderophore...

Using linear regression, it is possible to estimate the protonation constants of the Fe(II) complexes of siderophore complexes where the redox potentials have been measured over a range of pH values (59). This also explains the variation in reversibility of reduction as the pH changes, as the stability of the ferro-siderophore complex is much lower than the ferric complex, and the increased lability of ligand exchange and increased binding site competition from H+ may result in dissociation of the complex before the iron center can be reoxidized. 

Composi- Ferric oxide hydrate bonded to Complex of ferric Complex of polynuclear... 

TOA were determined, in the supernatant prepared as described by Hissett et al (25), by the method of Montgomery et al (26). The organic acids were esterified with acidified ethylene glycol. The esters were then reacted with hydroxylamine and the hydroxamic acids thus formed were converted to their ferric complexes and their concentrations were determined by optical density measurements at 500u. 

For iron and tin the magnitude of 8 has been found to be related to the oxidation state of the metal (15, 28) (Table I). In iron complexes, the spin of the 3d electrons of the iron atoms can be paired (low spin) or unpaired (high spin). In low spin ferrous and ferric complexes, 8 and AEq values are similar, but the value of AEq differs greatly for the high spin complexes (Figure 1). Mossbauer spectroscopy has been used to... 

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