Reaction of hydroxyl radicals with the ferrous and ferric iron chelates of diethylenetriamine-N,N,N',N",N"- pentaacetate

Photodegradation and ozonation of ibuprofen derivatives in the water environment: Kinetics approach and assessment of mineralization and biodegradability

This article presents the results of studies on the degradation of ibuprofen transformation products: 1-hydroxyibuprofen (1OHIBF), 4-ethylbenzaldehyde (4EBA), 1-[4-(2-methylpropyl)phenyl]ethan-1-ol (MPPE) in water. To the best of our knowledge, this is the first paper where the ozonation and photodegradation (VIS and UV photolysis, degradation in H₂O₂/UV system, photosensitized oxidation) of 1OHIBF, 4EBA and MPPE are reported. The processes were performed in demineralized and natural river water. The influence of various reaction parameters on the removal degree was checked. Both, photolysis under VIS light and photosensitized oxidation of target compounds are very low-efficient processes. Ozonation and degradation in H₂O₂/UV system are effective methods for ibuprofen derivatives degradation. Components present in river water reduced removal degree of investigated compounds during ozonation and degradation in H₂O₂/UV system. The biodegradability assessment using the Average Oxidation State (AOS) and COD/TOC ratio proved the formation of more oxidized by-products during both processes. The determined second-order rate constants for ozone reaction with 1OHIBF, 4EBA and MPPE are 0.1 ± 0.01, 10.95 ± 1.36 and 3.04 ± 0.33 M^-1 s^-1, respectively. The calculated reaction rate constants of hydroxyl radicals with MPPE, 4EBA and 1OHIBF are 3.57 × 10⁹, 6.83 × 10⁹ and 1.06 × 10⁹ M^-1 s^-1, respectively.

Pulse Radiolysis Investigation of Radicals Derived from Water-Soluble Cyanine Dyes: Implications for Super-resolution Microscopy

Light-induced blinking, an inherent feature of many forms of super-resolution microscopy, has been linked to transient reduction of the fluorescent cyanine dye used as an imaging agent. There is, however, only scant literature information related to one-electron reduced cyanine dyes, especially in an aqueous environment. Here, we examine a small series of cyanine dyes, possessing disparate π-conjugation lengths, under selective reducing or oxidizing conditions. The experiment allows recording of both differential absorption spectra and decay kinetics of the resultant one-electron reduced or oxidized transient species in water. Relative to the ground state, absorption transitions for the various radicals are weak and somewhat broadened but do allow correlation with the π-conjugation length. In all cases, absorption maxima lie to the blue of the main ground-state transition. Under anaerobic conditions, the transient species decay on the microsecond to millisecond time scale, with the mean lifetime depending on molecular structure, radiation dose, and dye concentration. The experimental absorption spectra recorded for the one-electron reduced radicals and the presumed dimer cation radical compare well to spectra obtained from time-dependent density functional theory calculations. The results allow conclusions to be drawn regarding the plausibility of the reduced species being responsible for light-induced blinking in direct stochastic optical reconstruction microscopy.

Proteomic mechanisms for the stimulatory effects of antibiotics on Microcystis aeruginosa during hydrogen peroxide treatment

Application of low dosage of H₂O₂ at early stage of cyanobacterial life cycle is a promising route for cyanobacterial bloom mitigation, which could minimize adverse effects on non-target organisms. Besides, influence of co-existing contaminants on cyanobacterial bloom mitigation under combined pollution conditions remains unclear. This study assessed the influence of a mixture of four frequently detected antibiotics (tetracycline, sulfamethoxazole, ciprofloxacin and amoxicillin) during H₂O₂ treatment of Microcystis aeruginosa at early growth stage. H₂O₂ significantly (p < 0.05) inhibited growth rate, chlorophyll a content, F_v/F_m and rETR_max in a dose-dependent manner at low doses of 0.25-1 mg L^-1, through downregulating proteins involved in cell division, cellular component organization, gene expression and photosynthesis. Although H₂O₂ increased microcystin content in each cyanobacterial cell through the upregulation of microcystin synthetases (mcyC and mcyF), total microcystin concentration in H₂O₂ treated groups was significantly (p < 0.05) reduced due to the decrease of cell density. Existence of 80 and 200 ng L^-1 mixed antibiotics during H₂O₂ treatment facilitated the scavenging of ROS by antioxidant enzymes and significantly (p < 0.05) stimulated growth, photosynthesis, microcystin synthesis and microcystin release in H₂O₂ treated cells, through the upregulation of proteins involved in photosynthesis, oxidation-reduction process, biosynthesis, gene expression and transport. Mixed antibiotics increased the hazard of M. aeruginosa during H₂O₂ treatment, through the stimulation of microcystin synthesis and release at the proteomic level. Each target antibiotic should be controlled below 5 ng L^-1 before the application of H₂O₂ for eliminating the interference of antibiotics on cyanobacterial bloom mitigation.

Chemical, Biological and Medical Controversies Surrounding the Fenton Reaction

A critical evaluation is made of the role of the Fenton reaction (Fe2+ + H2O2 → Fe3+ + •OH + OH-) in the promotion of oxidative damage in mammalian systems. Following a brief, historical overview of the Fenton reaction, including the formulation of the Haber–Weiss cycle as a mechanism for the catalysis of hydroxyl radical production, an appraisal is made of the biological relevance of the reaction today, following recognition of the important role played by nitric oxide and its congers in the promotion of biomolecular damage. In depth coverage is then given of the evidence (largely from EPR studies) for and against the hydroxyl radical as the active oxidant produced in the Fenton reaction and the role of metal chelating agents (including those of biological importance) and ascorbic acid in the modulation of its generation. This is followed by a description of the important developments that have occurred recently in the molecular and cellular biology of iron, including evidence for the presence of ‘free’ iron that is available in vivo for the Fenton reaction. Particular attention here is given to the role of the iron-regulatory proteins in the modulation of cellular iron status and how their functioning may become dysregulated during oxidative and nitrosative stress, as well as in hereditary haemochromatosis, a common disorder of iron metabolism. Finally, an assessment is made of the biological relevance of ascorbic acid in the promotion of hydroxyl radical generation by the Fenton reaction in health and disease.

Hydroxyl radical production by H2O2-mediated oxidation of Fe(II) complexed by Suwannee River fulvic acid under circumneutral freshwater conditions

The Fenton reaction, the oxidation of ferrous iron by hydrogen peroxide (H(2)O(2)), is typically assumed to be a source of hydroxyl radical (HO(•)) in natural systems, however, formation of HO(•) in this process is strongly dependent upon solution pH and the ligand environment, with HO(•) only formed when Fe(II) is organically complexed. In this study we examine the formation of HO(•) when Fe(II)-NOM complexes are oxidized by H(2)O(2) using phthalhydrazide as a probe for HO(•). We demonstrate that HO(•) formation can be quantitatively described using a kinetic model that assumes HO(•) formation occurs solely from the reaction of Fe(II)-NOM complexes with H(2)O(2), even though this reaction is sufficiently slow to play only a negligible role in the overall oxidation rate of total Fe(II). As such, NOM is seen to play a dual role in circumneutral natural systems in stabilizing Fe(II) toward oxidation by H(2)O(2) while enabling the formation of HO(•) through this oxidation process.

DTPA Fe(III) decreases cytokines and hypotension but worsens survival with Escherichia coli sepsis in rats

OBJECTIVE

Nonselective inhibition of nitric oxide (NO) with NO synthase antagonists decreases hypotension but worsens outcome clinically. We investigated whether iron (III) complex of diethylenetriaminepentaacetic acid [DTPA Fe(III)], a scavenger of NO as well as other oxidant mediators, has similar divergent effects in E. coli challenged rats.

METHODS

Animals with venous and arterial catheters and challenged with intrabronchial or intravenous E. coli were randomized to treatment with DTPA Fe(III) in doses from 3 to 800 mg/kg or placebo. Mean blood pressure (MBP) was measured in all animals and plasma NO, cytokines, and blood and lung leukocyte and bacteria counts in animals administered intrabronchial E. coli and DTPA Fe(III) 50 mg/kg or placebo. Animals received antibiotics and were observed 168 h.

RESULTS

Independent of drug regimen or infection site, compared to placebo, DTPA Fe(III) increased MBP although this was greater with high vs. lower doses. Despite increased MBP, DTPA Fe(III) worsened the hazards ratio of survival . At 6 and 24 h DTPA Fe(III) decreased NO but not significantly and decreased four cytokines (tumor necrosis factor-alpha, interleukins 1 and 10, and macrophage inflammatory protein 3alpha) and lung lavage neutrophils. From 6 to 24 h DTPA Fe(III) increased blood bacteria.

CONCLUSIONS

DTPA Fe(III) while increasing blood pressure has the potential to worsen outcome in sepsis. Further preclinical testing is required before this agent is applied clinically.

Iron chelates bind nitric oxide and decrease mortality in an experimental model of septic shock

The hydroxamic acid siderophore ferrioxamine B [FeIII(HDFB)+] and the iron complex of diethylenetri-aminepentaacetic acid [FeIII(DTPA)2-] protected mice against death by septic shock induced by Corynebacterium parvum + lipopolysaccharide. Although FeIII(DTPA)2- was somewhat more effective than FeIII(HDFB)+, the iron-free ligand H4DFB+ was significantly more effective than DTPA. The hydroxamic acid chelator has a much higher iron affinity than the amine carboxylate, allowing for more efficient formation of the FeIII(HDFB)+ complex upon administration of the iron-free ligand. Electrochemical studies show that FeIII(DTPA)2- binds NO stoichiometrically upon reduction to iron(II) at biologically relevant potentials to form a stable NO adduct. In contrast, FeIII(HDFB)+ is a stable and efficient electrocatalyst for the reduction of NO to N2O at biologically relevant potentials. These results suggest that the mechanism of protection against death by septic shock involves NO scavenging and that particularly effective drugs that operate a low dosages may be designed based on the principle of redox catalysis. These complexes constitute a new family of drugs that rely on the special ability of transition metals to activate small molecules. In addition, the wealth of information available on siderophore chemistry and biology provides an intellectual platform for further development.

Efficacy of treatment with the iron (III) complex of diethylenetriamine pentaacetic acid in mice and primates inoculated with live lethal dose 100 Escherichia coli

The iron (III) complex of diethylenetriamine pentaacetic acid (DTPA iron [III]) protected mice and baboons from the lethal effects of an infusion with live LD100 Escherichia coli. In mice, optimal results were obtained when DTPA iron (III) was administered two or more hours after infection. Prevention of death occurred in spite of the fact that the adverse effects of TNF-alpha were well underway in the mouse model. The half-life of DTPA iron (III) was 51 +/- 9 min in normal baboons; primary clearance was consistent with glomerular filtration. In septic baboons, survival was observed after administration of two doses of DTPA iron (III) at 2.125 mg/kg, the first one given before, or as late as 2 h after, severe hypotension. Administration of DTPA iron (III) did not alter mean systemic arterial pressure, but did protect baboons in the presence of high levels of TNF-alpha and free radical overproduction. Furthermore, exaggerated production of nitric oxide was attenuated. The mechanism of protection with DTPA iron (III) is not obvious. Because of its ability to interact in vitro with free radicals, its poor cell permeability, and its short half-life, we postulate that DTPA iron (III) and/or its reduced form may have protected the mice and baboons by sequestration and subsequent elimination of free radicals (including nitric oxide) from their systems.

ESR spin trapping studies into the nature of the oxidizing species formed in the Fenton reaction: pitfalls associated with the use of 5,5-dimethyl-1-pyrroline-N-oxide in the detection of the hydroxyl radical

Several investigators have challenged the widely held view that the hydroxyl radical is the primary oxidant formed in the reaction between the ferrous ion and hydrogen peroxide. In recent studies, using the ESR spin trapping technique. Yamazaki and Piette found that the stoichiometry of oxidant formation in the reaction between Fe2+ and H2O2 often shows a marked deviation from the expected value of 1:1 (I. Yamazaki and L. H. Piette (1990) J. Am. Chem. Soc. 113, 7588-7593). In order to account for these observations, it was suggested that additional oxidizing species are formed, such as the ferryl ion (FeO2+), particularly when iron is present at high concentration and chelated to EDTA. In this paper it is shown that secondary reactions, involving the redox cycling of iron and the oxidation of the hydroxyl radical adduct of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) by iron, operate under the reaction conditions employed by Yamazaki and Piette. Consequently, the stoichiometry of oxidant formation can be rationalized without the need to envisage the formation of oxidizing species other than the hydroxyl radical. It is also demonstrated that the iron(III) complex of DETAPAC can react directly with DMPO to form the DMPO hydroxyl radical adduct (DMPO/OH) in the absence of hydrogen peroxide. Therefore, to avoid the formation of (DMPO/OH) as an artefact, it is suggested that DETAPAC should not be used as a reagent to inactivate containing adventitious iron in experiments using DMPO.

Fenton reagents may not initiate lipid peroxidation in an emulsified linoleic acid model system

This study includes two parts. First, the Fe2+ autooxidation and chelation processes in the presence of the chelators ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine pentaacetic acid (DTPA) were studied by measuring UV light absorbance alterations. Competition for Fe3+ between chelators and water or phosphate buffer (PB) ions was confirmed. The addition of EDTA or DTPA to Fe3+ in water or PB only slowly turned the water/PB-Fe3+ complexes to EDTA-Fe3+ or DTPA-Fe3+ complexes. In the second part of this study, the initiation mechanisms of Tween 20 emulsified linoleic acid peroxidation under stimulation by chelator-Fe-O2 complexes were studied by measuring changes in UV light absorbance following diene conjugation. Fe3+ in the presence of EDTA or DTPA did not stimulate diene conjugation. Fe2+ (0.10 mM) and EDTA (0.11 mM) stimulated diene conjugation of the linoleic acid emulsion, but only after apparent Fe2+ autooxidation. Fe2+ and DTPA, as well as premixed DTPA-Fe2+ complex, resulted in very fast diene conjugation in a wide range of concentrations. A nonlinear, mainly square root relation between Fe2+ concentration and peroxidation rate was noted. Superoxide dismutase (SOD), catalase, and mannitol did not prevent the lipid peroxidation. H2O2 substantially decreased the DTPA-Fe2+ stimulated, otherwise rapid, diene conjugation but slightly enhanced the slower one stimulated by EDTA-Fe2+. Without ambient oxygen, Fenton reagents did not result in .H abstraction-related diene conjugation. The findings suggest that .OH resulting from Fenton reagents may not be the main cause for the initiation of peroxidation in this model system. Furthermore, a study with different combinations of Fe2+ and Fe3+ did not support the Fe2+/Fe3+ (1:1) optimum ratio hypothesis. We therefore conclude that perferryl ions or chelator-Fe-O2 complexes may be responsible for the first-chain initiation of lipid peroxidation, at least in this model system.

Maintenance of left ventricular function (90%) after twenty-four-hour heart preservation with deferoxamine

During 24-h in vitro heart preservation and reperfusion, irreversible tissue damage occurs caused by reactive oxygen intermediates, such as superoxide radicals, singlet oxygen, hydrogen peroxide, hydroperoxyl, hydroxyl radicals, as well as the peroxynitrite radical. Reduction of the related oxidative damage of reperfused ischemic tissue by free radical scavengers and metal chelators is of primary importance in maintaining heart function. We assessed whether deferoxamine (DFR) added to a cardioplegia solution decreased free radical formation during 24-h cold (5 degrees C) heart preservation and normothermic reperfusion (37 degrees C) in the Langendorff isolated perfused rat heart. The deferoxamine treated hearts were significantly (p less than .001) better preserved than the control hearts after 24 h of preservation with regard to recovery of left ventricular diastolic pressure, contractility (+dP/dt), relaxation (-dP/dt), creatine kinase release, and lipid peroxidation. DFR preserved cell membrane integrity and maintained 93% of left ventricular contractility. The evidence suggests that DFR reduces lipid peroxidation damage by reducing free radical formation and thereby maintaining normal coronary perfusion flow and myocardial function.