Systems containing Fe

The measurement of dissolved Fe(III) and calculation of the activities of aqueous ferric species have challenged geochemists and others in their efforts to understand the chemistry of iron in natural waters (i-5). A new method for determining the activities of dissolved Fe(IlI) species in anaerobic systems containing Fe(II) is described in this paper (see also Q, along with conclusions about the behavior of redox electrodes in such systems and solubilities of associated ferric-oxyhydroxide solids. Redox conditions in dramatically different anaerobic aquifers, at Otis Air Force Base, MA and near Leadville, CO are also discussed. 

In systems containing no anion other than fluoride, mixed aqua-fluorometalates mainly with [MF5 (H20)] and [MF4(H2 0)2] are frequently formed. Therefore the possibility of H-bond formation plays an important role (see Hydrogen Bonding Dihydrogen Bonding. The most investigated systems contain Fe (surveys in... 

The non-competitive SCM (equation 9) can be used to estimate the equilibrium association of RX with the surface (Xrx), and the surface rate constant ( Rx) hy modeling previously published site saturation data for systems containing Fe (Figure 4). To do this, we estimated the total number of sites using... 

Fig. 6.15. Mossbauer absorption spectra in various biological systems containing Fe. The solid curves are theoretical least square fits. The parameters D (in units of 10" mVs) and a (in units of 10 s ) are respectivdy (a) 4, 2.5, (i) 40, 10, (c) 26, 5, and (d) 87, 13. (Nowik et a ., 1983.)...

The excess chemiccil potential is thus determined from the average of exp[—lT (r )/fe In ensembles other than the canonical ensemble the expressions for the excess chem potential are slightly different. The ghost particle does not remain in the system and the system is unaffected by the procedure. To achieve statistically significant results m Widom insertion moves may be required. However, practical difficulties are encounte when applying the Widom insertion method to dense fluids and/or to systems contain molecules, because the proportion of insertions that give rise to low values of y f, dramatically. This is because it is difficult to find a hole of the appropriate size and sha... 

In the nickel—carbon and cobalt—carbon systems, the nickel carbide (3 1) [12012-02-1], Ni C, and cobalt carbide (3 1) [12011-59-5] C03C, are isomorphous with Fe C and exist only at low temperatures. The manganese—carbon system contains manganese carbide (3 1) [12121 -90-3] Mn C, isomorphous with Fe C, and manganese carbide (23 6) [12266-65-8] isomorphous with chromium carbide (23 6) [12105-81 -6] These... 

Relative width of region of unreliable reaction (5) was estimated as the ratio of difference between maximum and minimal concentrations to minimal concentration in this region. The test-system containing Co [Fe(CN)g] is the most resistant to uncontrolled factors, the lowest detection limit characterizes a film with Ni,[Fe(CN)J. The possibility of test-films application for quantitative determination of nitroxoline is testified. 

This example shows that dipolar interactions can produce unexpected effects in systems containing polynuclear clusters, so that their complete quantitative description requires a model in which the dipolar interactions between all the paramagnetic sites of the system are explicitly taken into account. Local spin models of this kind can provide a description of the relative arrangement of the interacting centers at atomic resolution and have been worked out for systems containing [2Fe-2S] and [4Fe-4S] clusters (112, 192). In the latter case, an additional complication arises due to the delocalized character of the [Fe(III), Fe(II)] mixed-valence pair, so that the magnetic moments carried by the two sites A and B of Fig. 8B must be written... 

These results may be viewed in the wider context of interactions between potential ligands of multifunctional xenobiotics and metal cations in aquatic environments and the subtle effects of the oxidation level of cations such as Fe. The Fe status of a bacterial culture has an important influence on synthesis of the redox systems of the cell since many of the electron transport proteins contain Fe. This is not generally evaluated systematically, although the degradation of tetrachloromethane by a strain of Pseudomonas sp. under denitrifying conditions clearly illustrated the adverse effect of Fe on the biotransformation of the substrate (Lewis and Crawford 1993 Tatara et al. 1993). This possibility should therefore be taken into account in the application of such organisms to bioremediation programs. 

Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid.

Fig. 4. Substrate first binds to the complete system containing all three protein components. Addition of NADH next effects two-electron reduction of the hydroxylase from the oxidized Fe(III)Fe(III) to the fully reduced Fe(II)Fe(II) form, bypassing the inactive Fe(II)Fe(III) state. The fully reduced hydroxylase then reacts with dioxygen in a two-electron step to form the first known intermediate, a diiron(III) peroxo complex. The possibility that this species itself is sufficiently activated to carry out the hydroxylation reaction for some substrates cannot be ruled out. The peroxo intermediate is then converted to Q as shown in Fig. 3. Substrate reacts with Q, and product is released with concomitant formation of the diiron(III) form of the hydroxylase, which enters another cycle in the catalysis.

Abstract The behaviour of many metal ions which are stable in more than one oxidation states in their aqueous solutions has been studied under sonochemical reaction conditions. Fe(II) is oxidized to Fe(III) and Fe(III) is reduced to Fe(II) with equal ease under sonochemical conditions. Besides, the oxidizing power of Cr2072 is found to be less than the MnO ions, therefore, in a system containing both species, Cr3+ is susceptible to oxidation to Cr61 and the MnO to reduction to Mn2+. 

As an example of an equilibrium calculation accounting for surface complexation, we consider the sorption of mercury, lead, and sulfate onto hydrous ferric oxide at pH 4 and 8. We use ferric hydroxide [Fe(OH)3] precipitate from the LLNL database to represent in the calculation hydrous ferric oxide (FeOOH /1H2O). Following Dzombak and Morel (1990), we assume a sorbing surface area of 600 m2 g-1 and site densities for the weakly and strongly binding sites, respectively, of 0.2 and 0.005 mol (mol FeOOH)-1. We choose a system containing 1 kg of solvent water (the default) in contact with 1 g of ferric hydroxide. 

Fig. 15.8. Results of reacting 02 at 100 °C into a system containing pyrite. Pyrite dissolves (top) with addition of 02. The reaction (bottom) produces bisulfate ions and ferric species (FeCl+ and Fe++), which in turn are consumed at the end of the path to form hematite.

The [Fe(diimine)2X2] system has been modified by replacing the diimines by unidentate nitrogen donors. [Fe(diimine)(py)2(NCS)2] is a crossover system when the diimine is 2,2 -bipyrimidine or phen [99] but [Fe(py)4(NCS)2] is purely high spin [100]. However, [Fe(py)4(NCS)2] systems containing substituted pyridine derivatives have been shown to exhibit thermal SCO [101], while 4,4 -bipyridine derivatives are able to bridge Fe(II) centres and form polynuclear structures containing SCO [Fe(py)4(NCS)2] centres [102]. SCO is maintained in certain instances when the diimines are replaced by an N4 quadridentate [103,104]. 

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