Surface-bound iron species

From all these observations and relative behaviors it can be concluded that formation of a precursor complex or regeneration of reactive sites is important in determining the overall rate of NAC reduction by surface-bound iron(II) species. Therefore, in this reaction scenario, a much weaker correlation between log kre] and h(AtN02)/0.059 V can be expected and is actually obtained (e.g., Fig. 14.10apparent correlation of the 3- and 4-substituted nitrobenzenes (slope = 0.5) may be due to a co-correlation between (r(ArN02) and the tendency of the... 

Addition of base to aqueous solutions of Fe(III) in the presence ofthe ligandN(CH2C00H)2(CH2CH20H) ( heidi ), produced 19-iron and 17-iron species, neither of which have a 3-D framework of Fe(ni) ions. These species contain close-packed iron hydroxide cores bound, via oxide and hydroxide bridges, to Fe(III) located on the inner surface of the heidi coat. The inner core, which is common to both Fen and Fei9 compounds and consists of an [Fe7(/U3-OH)6(/tr2-0H)4 (/u-3-0)Fe 2] + unit, derives from a portion of an infinite 2-D [Fe(OH)2+] framework. This suggests that the ligand shell, [Feio(heidi)io(H20)i2(/(r3-0)4(/U2-OH)4] , traps the iron in an unusual, for Fe(IIl), hydroxide mineral structure, and poses the question of whether the core of ferritin is a similarly trapped structure. ... 

Surface Density of Fe(II)-Species. Figure 6 shows the rate constants for the reduction of dibromodichloromethane in suspensions containing goethite and Fe(II) as a function of total ferrous iron present and pre-equilibration time of Fe(II) with the surface. A strong dependence of pseudo-first-order reaction rates on total ferrous iron concentrations was observed for long pre-equilibration times (teq > 30 h) which provides further evidence that surface species of Fe(II) formed after prolonged contact of ferrous iron with iron(hydr)oxide surfaces are most reactive. Experiments such as shown in Figure 6 do not allow one to calculate second-order rate constants as it is remains unclear which species or fraction(s) of surface-bound Fe(II) is involved in the reaction. 

Different ethylene-derived species, such as vinyl or acetylene, have been observed on other metals. On the (100) surface of iron, for example, the di-<7-bound C2H4 dehydrogenates to acetylene around 200 K, while at about 400 K the triple C=C bond breaks to yield CH and CH2 fragments, which eventually release their hydrogen to form carbidic or even graphitic carbon at elevated temperatures. 

Fds with conventional [Fe2-S2] clusters can undergo a one-electron transfer to a deeply valence-trapped FemFen species. For proteins of known structure (and presumably others) one iron atom is closer to the surface (by about 0.5 nm) and it has been established that the added electron resides on that atom. No instances are known where an [Fe2-S2] centre acts as a physiological two-electron donor or acceptor. In addition to the conventional [Fe2-S2] ferredoxins, the electron-transfer chains of mitochondria and photosynthetic bacteria contain Rieske proteins which have a cluster with the composition [(Cys.S)2FeS2Fe(N.His)2], in which the two imidazole groups are bound to the same iron atom (Figure 2.9). This atom is the site... 

As shown in Figure 5.3, chemicals, such as iron, can be present in a rariety of species and phases that span a large size spectrum. The dissolved fraction can include inorganic complexes, organometallic molecules, and the uncomplexed ions. In the case of iron, two oxidation states are possible, so the free ion can be in the form of Fe (aq) or Fe " (aq). In the colloidal and particulate phases, iron can be present as part of a mineral (inorganic) or an organic molecule. Within the particulate phase, a distinction is often made between the fraction that is adsorbed, usually electrostatically as an ion, onto the surface and the fraction that is covalently bound into the crystal lattice. 

The shorter-term exposure experiments show that some portion of the organically-bound chlorine, such as trichlorethane or its decomposition products, remains absorbed on a 304 stainless steel surface, even after heating at 35-40°C in a high vacuum. Conversion to an ionic species begins after a short contact period and can be detected using XPS. Formation of the ionic chloride is likely the result of hydrolysis by water also absorbed on the surface, and is perhaps catalyzed by the surface metal oxides. Further atmospheric exposure up to a few months increases the relative amount of the ionic form of chlorine. The composition of the surface oxide layer was altered, with chromium oxide replacing iron oxide as the major species. There was further evidence that chlorine was present as iron chloride, perhaps up to 5% of the surface film. The conditions under which oxidation of such surfaces occurred are quite comparable to those which could occur on steel surfaces in industrial usage. 

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