Importance of Iron Complexation for Fenton-Mediated Hydroxyl Radical Production at Circumneutral pH

Abstract

The reaction between Fe(II) and H 2 O 2 to yield hydroxyl radicals (HO • ), the Fenton reaction, is of interest due to its role in trace metal and natural organic matter biogeochemistry, its utility in water treatment and its role in oxidative cell degradation and associated human disease. There is significant dispute over whether HO • , the most reactive of the so-called reactive oxygen species (ROS), is formed in this reaction, particularly under circumneutral conditions relevant to natural systems. In this work we have studied the oxidation kinetics of Fe(II) complexed by L = citrate, ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) and also measured HO • production using phthalhydrazide as a probe compound at pH 8.2. A kinetic model has been developed and utilized to confirm that HO • is the sole product of the Fe(II)L-H 2 O 2 reaction for L = EDTA and DTPA. Quantitative HO • production also appears likely for L = citrate, although uncertainties with the speciation of Fe(II)-citrate complexes as well as difficulties in modeling the oxidation kinetics of these complexes has prevented a definitive conclusion. In the absence of ligands at circumneutral pH, inorganic Fe(II) reacts with H 2 O 2 to yield a species other than HO • , contrary to the well-established production of HO • from inorganic Fe(II) at low pH. Our results suggest that at high pH Fe(II) must be complexed for HO • production to occur.

Protective Role of Sphingomyelin in Eye Lens Cell Membrane Model against Oxidative Stress

“…Therefore, they provide a powerful platform to study the membrane properties and interaction of reactive species with lipid bilayer [ 34 , 35 , 36 ]. Various methods have been developed for generating reactive species, such as Fenton reaction [ 37 , 38 ], photolysis [ 39 , 40 ] and cold physical plasma (CPP) [ 41 , 42 ]. CPP as ionized gas with temperature close to human body temperature can be produced by different sources such as plasma jets or dielectric barrier discharges [ 42 , 43 ], and beneficial effects have been shown in several medical applications, including wound healing [ 44 , 45 ], cancer treatment [ 46 , 47 , 48 , 49 ] and dental care [ 50 ].…”

Organic exudates promote Fe(II) oxidation in Fe limited cultures of <i>Trichodesmium erythraeum</i>

“…For analysis of Fe(II) oxidation kinetics, it was assumed that Fe(II) is mainly oxidised by O2 due to its presence at a much higher concentration than other potential oxidants such as reactive oxygen species. This is a reasonable assumption given that with the relatively low (at most 20 nmol (Miller et al 2009;Miller et al 2016). This means that micromolar concentrations of H2O2 are needed to outcompete O2 and affect the oxidation rate; therefore only the reaction between Fe(II) and O2…”

Potential Advantages of Peroxoborates and Their Ester Adducts Over Hydrogen Peroxide as Therapeutic Agents in Oral Healthcare Products: Chemical/Biochemical Reactivity Considerations In Vitro, Ex Vivo And In Vivo

“…Despite this, Miller et al [ 66 ] found that, in view of an ill-defined speciation status and oxidation mechanism, predictions of ● OH radical production from Fe(II)/Fe(III)-citrate complex(es) were poor, unlike results they obtained for these metal ions’ well-characterized 1:1 EDTA and diethylenetriamine-penta-acetate (DTPA) complexes; 1:1 iron(III)-citrate complexes are well known to be heterogeneous, including a range of oligomeric/polymeric adducts with co-complexing oxo/hydroxo ligands [ 67 ]. Indeed, for these EDTA-/DTPA-chelated Fe(II)/Fe(III) systems, they found that at circumneutral (soil) pH values (6.5-7.5), ● OH radical was the only species formed, and kinetic modelling suggested that ‘between-ligand’ differences found in the levels of its production were largely explicable by full considerations of all possible reactions between the redox-active Fe(II)-chelate/Fe(III)-chelate system and reactive oxygen species (ROS).…”