Kinetics and Mechanism of Oxidation of Tryptophan by Ferrate(VI) (original) (raw)
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Ferrates (iron(VI) and iron(V)): Environmentally friendly oxidants and disinfectants
Journal of Water and Health, 2005
Iron(VI) and iron(V), known as ferrates, are powerful oxidants and their reactions with pollutants are typically fast with the formation of non-toxic by-products. Oxidations performed by Fe(VI) and Fe(V) show pH dependence; faster rates are observed at lower pH. Fe(VI) shows excellent disinfectant properties and can inactivate a wide variety of microorganisms at low Fe(VI) doses. Fe(VI) also possesses efficient coagulation properties and enhanced coagulation can also be achieved using Fe(VI) as a preoxidant. The reactivity of Fe(V) with pollutants is approximately 3–5 orders of magnitude faster than that of Fe(VI). Fe(V) can thus be used to oxidize pollutants and inactivate microorganisms that have resistance to Fe(VI). The final product of Fe(VI) and Fe(V) reduction is Fe(III), a non-toxic compound. Moreover, treatments by Fe(VI) do not give any mutagenic/carcinogenic by-products, which make ferrates environmentally friendly ions. This paper reviews the potential role of iron(VI) a...
Overlooked Role of Fe(IV) and Fe(V) in Organic Contaminant Oxidation by Fe(VI
Fe(VI) has received increasing attention since it can decompose a wide range of trace organic contaminants (TrOCs) in water treatment. However, the role of short-lived Fe(IV) and Fe(V) in TrOC decomposition by Fe(VI) has been overlooked. Using methyl phenyl sulfoxide (PMSO), carbamazepine, and caffeine as probe TrOCs, we observed that the apparent second-order rate constants (k app) between TrOCs and Fe(VI) determined with the initial kinetics data were strongly dependent on the initial molar ratios of TrOCs to Fe(VI). Furthermore, the k app value increases gradually as the reaction proceeds. Several lines of evidence suggested that these phenomena were ascribed to the accumulation of Fe(IV) and Fe(V) arising from Fe(VI) decay. Kinetic models were built and employed to simulate the kinetics of Fe(VI) self-decay and the kinetics of PMSO degradation by Fe(VI). The modeling results revealed that PMSO was mainly degraded by Fe(IV) and Fe(V) rather than by Fe(VI) per se and Fe(V) played a dominant role, which was also supported by the density functional theory calculation results. Given that Fe(IV) and Fe(V) have much greater oxidizing reactivity than Fe(VI), this work urges the development of Fe(V)/Fe(IV)-based oxidation technology for efficient degradation of TrOCs.
Ferrate(VI) oxidation of endocrine disruptors and antimicrobials in water
Journal of Water Supply: Research and Technology—AQUA, 2008
2 ASTRACT Potassium ferrate(VI) (K 2 FeO 4 ) has advantageous properties such as a dual function as an oxidant and disinfectant with a non-toxic byproduct, iron(III), which makes it an environmentally friendly chemical for water treatment. This paper presents an assessment of the potential of ferrate(VI) to oxidize representative endocrine disruptors (EDs) and antimicrobials during water treatment using information about reaction kinetics and products. Selected EDs were bisphenol A (BPA) and 17α-ethynylestradiol (EE2), estrone (E1), 17β-estradiol (E2), and estriol (E3), and sulfonamides and tetracycline were representative pharamaceuticals. The second-order rate constants, k, of the oxidation reactions at neutral pH were in the range from 6.50 -11.8 x 10 2 M -1 s -1 and 0.79 -15.0x10 2 M -1 s -1 for EDs and sulfonamides, respectively. At a 10 mg/L K 2 FeO 4 dose, half-lives of the oxidation reaction would be in seconds at a neutral pH. The values of k, and the reaction half-lives, varied with pH. Oxidation products from the reaction with BPA and sulamethoxazole (SMX) at molar ratios of 5:1 were found to be relatively less toxic. Overall, ferrate(VI) oxidation could be an effective treatment method for the purification of waters containing these particular EDs and antimicrobials.
Biological trace element research
Quin2, a fluorescent calcium probe, has a low affinity for calcium in comparison to its affinities for transition metal ions. Chelation of ferric ion with quin2 strongly enhanced the formation of oxidizing species in the presence of bolus H2O2 as detected with four assays, electron spin resonance with the spin-trap DMPO, the deoxyribose assay, the DMSO assay, and plasmid DNA strand breakage. In comparison, Fe(III)-EDTA reacted with bolus H2O2 only as detected with electron spin resonance and deoxyribose assay, but not as detected with the two latter assays. The addition of reductants, like ascorbate or superoxide generated by hypoxanthine/xanthine oxidase, to Fe(III)-EDTA in the presence of H2O2 produced plasmid DNA strand breakage and strong reactivity in both the DMSO and the deoxyribose assays. Our findings suggest that the main oxidizing species produced in Fenton-type reactions is hydroxyl radical. However, the reaction between Fe(III)-EDTA and bolus H2O2 appears to be exceptio...
The oxidation state of a chemical species is often responsible for its environmental behavior. Natural or anthropogenic processes can often change an oxidation state. For example, the redox state of iron depends on the presence of oxygen. In the following experiments the influence of pH upon the oxidation of Fe(II) is investigated by bubbling air through an Fe(II) solution at different pH values. In the first part, a qualitative experiment is aimed at showing the influence of pH upon the production of an Fe(III) precipitate. In the second part, a quantitative experiment is performed by bubbling air simultaneously through a series of Fe(II) solutions at different pH values. The Fe(II) remaining at the end of the experiment is then analyzed by potentiometric titration. It is made clear that high pH values favor the oxidation of Fe(II), whereas low pH values retard it.
Chemosphere, 2007
The spontaneous chemical oxidation of Fe(II) to Fe(III) by O 2 is a complex process involving meta-stable partially oxidized intermediate species such as green rusts, which ultimately transform into a variety of stable iron oxide end-products such as hematite, magnetite, goethite and lepidocrocite. Although in many practical situations the nature of the end-products is of less interest than the oxidation kinetics, it is difficult to find in the literature a description of all the basic steps and principles governing the kinetics of these reactions. This paper uses basic aquatic-chemistry equilibrium theory as the framework upon which to present a heuristic model of the oxidation kinetics of Fe(II) species to ferric iron by O 2 . The oxidation rate can be described by the equation (in units of mol Fe(II)/(l min)): Àd½Fe 2þ =dt ¼ 6 Â 10 À5 ½Fe 2þ þ 1:7½FeðOHÞ þ þ 4:3 Â 10 5 ½FeðOHÞ 0 2 . This rate equation yields a sigmoid-shaped curve as a function of pH; at pH values below 4,theFe2+concentrationdominatesandtherateisindependentofpH.AtpH>4, the Fe 2+ concentration dominates and the rate is independent of pH. At pH > 4,theFe2+concentrationdominatesandtherateisindependentofpH.AtpH>5, ½FeðOHÞ 0 2 determines the rate because it is far more readily oxidized than both Fe 2+ and FeOH + . Between pH 5 and 8 the FeðOHÞ 0 2 concentration rises steeply with pH and the overall oxidation rate increases accordingly. At pH values > $8 ½FeðOHÞ 0 2 no longer varies with pH and the oxidation rate is again independent of pH. The paper presents a heuristic overview of the pH dependent kinetics of aqueous ferrous oxidation by O 2(aq) which we believe will be useful to professionals at both research and technical levels.
2015
Oxidation of hexacyanoferrate(ll) with peroxodiphosphate(pdp) in aqueous perchloric acid solutions occurs through the catalysis by Fe(llI) present in traces in the reagents and distilled water involving the equilibrium. Fe(llI)+Fe(CN)~-~Fe(ll)+Fe(CN)~-. Fe(ll) is oxidised back to Fe(llI) by pdp in the fast step. The rate law is d[Fe(CN)~-Vdt=((k, + kd/[H+]) [Fe(Ill)][Fe(CN)~-].The values of k, and kd have been found to be 5.7 x 103dm3mol-I s-I and 36 s-I respectively at 1=0.5 mol dm 3and 30°. The equilibrium constant for the above equilibrium determined spectrophotometrically is 34 ± 4 at 28°, 1=0.05 mol dm-3 and [H+]= 0.01 mol dm -3. Aquo copper(II) retards the rate of oxidation of Fe(CN)tby pdp. Spectrophotometrically too the equilibrium is shifted to the left in the presence of Cu(II).
Kinetic assessment of the potassium ferrate(VI) oxidation of antibacterial drug sulfamethoxazole
Chemosphere, 2006
Sulfamethoxazole (SMX), a worldwide-applied antibacterial drug, was recently found in surface waters and in secondary wastewater effluents, which may result in ecotoxical effects in the environment. Herein, removal of SMX by environmentally-friendly oxidant, potassium ferrate(VI) (K 2 FeO 4 ), is sought by studying the kinetics of the reaction between Fe(VI) and SMX as a function of pH (6.93-9.50) and temperature (15-45°C). The rate law for the oxidation of SMX by Fe(VI) is first-order with respect to each reactant. The observed second-order rate constant decreased nonlinearly from 1.33 ± 0.08 · 10 3 M À1 s À1 to 1.33 ± 0.10 · 10 0 M À1 s À1 with an increase of pH from 7.00 to 9.50. This is related to protonation of Fe(VI) (HFeO À 4 () H þ þ FeO 2À 4 ; pK a,HFeO 4 = 7.23) and sulfamethoxazole (SH () H + + S À ; pK a,SH = 5.7). The estimated rate constants were k 11 ðHFeO À 4 þ SHÞ ¼ 3.0 Â 10 4 M À1 s À1 , k 12 ðHFeO À 4 þ S À Þ ¼ 1.7Â 10 2 M À1 s À1 , and k 13 ðFeO 2À 4 þ SHÞ ¼ 1.2 Â 10 0 M À1 s À1 . The energy of activation at pH 7.0 was found to be 1.86 ± 0.04 kJ mol À1 . If excess potassium ferrate(VI) concentration (10 lM) is used than the SMX in water, the halflife of the reaction using a rate constant obtained in our study would be approximately 2 min at pH 7. The reaction rates are pH dependent; thus, so are the half-lives of the reactions. The results suggest that K 2 FeO 4 has the potential to serve as an oxidative treatment chemical for removing SMX in water.