Fe2+/EDTA

Benzoate oxidation by Fenton reagent Benzoate Fenton reagent (Fe2+-EDTA/H202) Colorimetric K13... 

The result of Fe +Cl O) 5(NO) is in good agreement with that determined by Kastin et al. (15) using the same experimental technique. For both Fe2+(EDTA)(NO) and Fe2+(NTA)(NO), the relaxation times due to the temperature jump were too fast to be measured. However, an upper limit of 10 /is was established for the relaxation times for both complexes. By use of this value with the equilibrium constants determined for Fe2+(EDTA)(NO) (16) and Fe2+(NTA)(NO) (10), the lower limits of formation rate constants were calculated to be 7 x 10 and 6 x 107 Z/nol -sec at 35 °C, which is in good agreement with that determined by the temperature-jump technique. From the results listed in Table I, we can conclude that the formation rate of Fe2+(EDTA)(NO) is at least 85 times faster than that of Fe2+(H20)5(N0), whereas, the dissociation rate of Fe2+(EDTA)(NO) is about 250 times slower than that of Fe2+(H20)5(N0) at 25 °C. 

Measurements of the absorption of nitric oxide by Fe2+(EDTA) solutions done by Teramoto et al. (17) allowed them to estimate k to be on the order of 10 M-1 sec for the EDTA complex. This indicates that NO does not need to become hydrated to bind to the ferrous chelate. This explains why Sada et al. (22) saw much more toO from the Fe2+(EDTA) + S032 solutions than from solutions of S032 alone. In the limited time available to extract NO from a gas bubble, the... 

In addition to oxidation by 02, Fe2+(L) can be converted to Fe +(L) in an aqueous system containing only Fe2+(L) + NO + S032 . Preliminary experiments from our laboratory, performed by mixing Fe2+(NTA) or Fe2+(EDTA) with NHAS, have shown the formation of Fe + and the liberation of N20. The kinetic study of this reaction is in progress. 

Reduction of Ferric Chelates by HSO3 and Formation of Dithionate. FeJ+(EDTA) is reduced by HSO3, producing dithionate and a small amount of S0/2 (24). The rate of reduction of Fe +(EDTA) is first order in [HSO3] and [Fe +(EDTA)], and inversely first order in [Fe2+(EDTA)]. 

Using formate, Sutton and Winterbourn [111,132,133] also presented evidence that the reaction of Fe2+-edta and aqueous, unchelated, iron(II) with hydrogen peroxide involves in part a higher oxidation state of iron. This experiment involves a chain of reactions, which on the basis of the known rate constants, would have a very large number of cycles before it would come to an end. Instead, fewer than 10 cycles were observed, see below. These experiments have been extended to other ligands. In rapid-mix experiments a solution of iron(II) complex [or iron(II)], formate and PQ + is mixed with hydrogen peroxide and the ratio of carbon dioxide produced per paraquat oxidised (the number of cycles) is determined. Alternatively, paraquat radicals are generated... 

Neuere, bei pH = 7 mit dem Redoxsystem Fe2+/EDTA/tert.-Butyl-hydroperoxid durchgefuhrte Versuche (772) lieferten wie bei der Acrylsaure sehr gut aufgeloste Spektren (Abb. 17) und erlauben folgende sichere Aussagen ... 

Chemistry at the 4 -position of 2 -deoxyribose has been extensively studied due to the availability of reagents producing radical formation at this site (bleomycin, calicheamicin, peroxynitrite, and Fe2+-EDTA) [25-28]. 4 -Free radical formation... 

The relative chelating capacity of a series of flavonoids was studied spectrophotometrically by measuring the ability to release Fe2+ ions from a Fe2+-EDTA complex and to chelate Fe2+ ions [27]. The flavonoids were classified into four groups (1) flavonoids, such as apigenin, that could release Fe2+ from this complex were ranked as good chelators, (2) flavonoids, such as quercetin, that could not remove Fe2+ from the... 

Fig. 9.9 Luminescence spectrum of a young fruiting body of Fanellus stipticus (1) the chemiluminescence spectra of PM-1 in the presence of CTAB (2) hexadecanoyl-choline iodide (3) and tetradecanoylcholine chloride (4). Chemiluminescence was elicited with Fe2+ and H2O2 in 50mM Tris buffer, pH 8.0, containing 0.18mM EDTA.

EDTA-Fe3 + ascorbate -> EDTA-Fe2+ +"Asc + H+ Regeneration with ascorbate... 

Inhibition and stimulation of LOX activity occurs as a rule by a free radical mechanism. Riendeau et al. [8] showed that hydroperoxide activation of 5-LOX is product-specific and can be stimulated by 5-HPETE and hydrogen peroxide. NADPH, FAD, Fe2+ ions, and Fe3+(EDTA) complex markedly increased the formation of oxidized products while NADH and 5-HETE were inhibitory. Jones et al. [9] also demonstrated that another hydroperoxide 13(5)-hydroperoxy-9,ll( , Z)-octadecadienoic acid (13-HPOD) (formed by the oxidation of linoleic acid by soybean LOX) activated the inactive ferrous form of the enzyme. These authors suggested that 13-HPOD attached to LOX and affected its activation through the formation of a protein radical. Werz et al. [10] showed that reactive oxygen species produced by xanthine oxidase, granulocytes, or mitochondria activated 5-LOX in the Epstein Barr virus-transformed B-lymphocytes. 

Figure 12-8 Seven-coordinate geometry of Fe(EDTA)(H20). Other metal ions that form seven-coordinate EDTA complexes include Fe2. Mg2, Cd2, Co2. Mn2, Ru3, Cr3+. Co3, V3, Ti3+, In3, Sn4, Os4, and Ti4. Some of these same ions also form six-coordinate EDTA complexes. Eight-coordinate complexes are formed by Ca2, Er3 , Yb3r, and Zr4. p Mizuta.

To measure hardness, the sample is treated with ascorbic acid (or hydroxylamine) to reduce Fe3+ to Fe2+ and with cyanide to mask Fe2+, Cu+, and several other minor metal ions. Titration with EDTA at pH 10 in NH3 buffer then gives the total concentrations of Ca2+ and Mg2+. Ca2+ can be determined separately if the titration is carried out at pH 13 without ammonia. At this pH, Mg(OH)2 precipitates and is inaccessible to EDTA. Interference by many metal ions can be reduced by the right choice of indicators.21... 

The values of the formation constants for chelates of Fe2+ typically lie between those of Mn2+ and Co2+ (Fig. 6-6, Table 6-9). For example, K, = 1014 3 M-1 for formation of the Fe2+ chelate of EDTA. The smaller and more highly charged Fe3+ is bonded more strongly (Kj = 1025 M 1). These binding constants are independent of pH. However, the binding of any metal ion is affected by pH, as discussed in Chapter 6. A fact of... 

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