Fast and Long‐Lasting Iron(III) Reduction by Boron Toward Green and Accelerated Fenton Chemistry

Generation of hydroxyl radicals in the Fenton system (Fe^II/H₂O₂) is seriously limited by the sluggish kinetics of Fe^III reduction and fast Fe^III precipitation. Here, boron crystals (C‐Boron) remarkably accelerate the Fe^III/Fe^II circulation in Fenton‐like systems (C‐Boron/Fe^III/H₂O₂) to produce a myriad of hydroxyl radicals with excellent efficiencies in oxidative degradation of various pollutants. The surface B?B bonds and interfacial suboxide boron in the surface B₁₂ icosahedra are the active sites to donate electrons to promote fast Fe^III reduction to Fe^II and further enhance hydroxyl radical production via Fenton chemistry. The C‐Boron/Fe^III/H₂O₂ system outperforms the benchmark Fenton (Fe^II/H₂O₂) and Fe^III‐based sulfate radical systems. The reactivity and stability of crystalline boron is much higher than the popular molecular reducing agents, nanocarbons, and other metal/metal‐free nanomaterials.     

Highly Efficient FeIII-initiated Self-cycled Fenton System in Piezo-catalytic Process for Organic Pollutants Degradation

Piezo-catalytic self-Fenton (PSF) system has been emerging as a promising technique for wastewater treatment, while the competing O₂ reductive hydrogen peroxide (H₂O₂) production and Fe^III reduction seriously limited the reaction kinetics. Here, we develop a two-electron water oxidative H₂O₂ production (WOR−H₂O₂) coupled with Fe^III reduction over a Fe^III/BiOIO₃ piezo-catalyst for highly efficient PSF. It is found that the presence of Fe^III can simultaneously initiate the WOR−H₂O₂ and reduction of Fe^III to Fe^II, thereby enabling a rapid reaction kinetics towards subsequent Fenton reaction of H₂O₂/Fe^II. The Fe^III initiating PSF system offers exceptional self-recyclable degradation of pollutants with a degradation rate constant for sulfamethoxazole (SMZ) over 3.5 times as that of the classic Fe^II-PSF system. This study offers a new perspective for constructing efficient PSF systems and shatters the preconceived notion of Fe^III in the Fenton reaction.     

New Mechanistic Aspects of the Fenton Reaction

The kinetics of the Fenton reaction was studied in detail. A second reaction step in the presence of excess H₂O₂ is attributed to formation of the complex Fe^III(^?O₂H)_aq. Therefore, the reaction of Fe(H₂O)₆²⁺ with Fe^III(^?O₂H)_aq in the presence of Fe^II to form Fe^III_aq (k=(7.7±1.5)×10⁵ M ^?1 s^?1) may contribute to the overall Fenton reaction, and could account for some of the debate in the literature concerning its detailed mechanism. If this is correct for LFe^III(^?O₂H)_aq also, then it might be of significant biological importance. The activation parameters ΔH^≠, ΔS^≠, and ΔV^≠ for the Fenton reaction were measured under various experimental conditions, and are used in the mechanistic interpretation.     

Elimination of 4‐chlorophenol in aqueous solution by the Novel Pd/MIL‐101(Cr)‐Hydrogen‐Accelerated catalytic fenton system

Excessive consumption of Fe (II) and massive generation of sludge containing Fe (III) from classic Fenton process remains a major obstacle for its poor recycling of Fe (III) to Fe (II). Therefore, the MHACF‐MIL‐101(Cr) system, by introducing H₂, Pd⁰ and MIL‐101(Cr) into Fenton reaction system, was developed at normal temperature and pressure. In this system, the reduction of Fe^III back to Fe^II by solid catalyst Pd/MIL‐101(Cr) for the storage and activation of H₂, was accelerated significantly by above 10‐fold and 5‐fold controlled with the H₂‐MIL‐101(Cr) system and H₂‐Pd⁰ system, respectively. However, the concentration of Fe (II) generated by the reduction of Fe (III) could not be detected with the only input of H₂ and without the addition of MOFs material. In addition, the apparent consumption of Fe (II) in MHACF‐MIL‐101(Cr) system was half of that in classical Fenton system, while more Fe (II) might be reused infinitely in fact. Accordingly, only trace amount of Fe (II) vs H₂O₂ concentration was needed and hydroxyl radicals through the detection of para‐hydroxybenzoic acid (p‐HBA) as the oxidative product of benzoic acid (BA) by·OH could be continuously generated for the effective degradation of 4‐chlorophenol(4‐CP). The effects of initial pH, concentration of 4‐CP, dosage of Fe²⁺, H₂O₂ and Pd/MIL‐101(Cr) catalyst, Pd content and H₂ flow were investigated, combined with systematic controlled experiments. Moreover, the robustness and morphology change of Pd/MIL‐101(Cr) were thoroughly analyzed. This study enables better understanding of the H₂‐mediated Fenton reaction enhanced by Pd/MIL‐101(Cr) and thus, will shed new light on how to accelerate Fe (III)/Fe (II) redox cycle and develop more efficient Fenton system.     

A Tale of Two Complexes: Electro-Assisted Oxidation of Thioanisole by an “O2 Activator/Oxidizing Species” Tandem System of Non-Heme Iron Complexes

We report two new Fe^III complexes [L¹Fe^III(H₂O)](OTf)₂ and [L²Fe^III(OTf)] , obtained by replacing pyridines by phenolates in a known non-heme aminopyridine iron complex. While the original, starting aminopyridine [(L₅ ² )Fe^II(MeCN)](PF₆) complex is stable in air, the potentials of the new Fe^III/II couples decrease to the point that [L²Fe^II] spontaneously reduces O₂ to superoxide. We used it as an O₂ activator in an electrochemical setup, as its presence allows to generate superoxide at a much more accessible potential (>500 mV gain). Our aim was to achieve substrate oxidation via the reductive activation of O₂. While L²Fe^III(OTf) proved to be a good O₂ activator but a poor oxidation system, its association with another complex (TPEN)Fe^II(PF₆)₂ generates a complementary tandem couple for electro-assisted oxidation of substrates, working at a very accessible potential: upon reduction, L²Fe^III(OTf) activates O₂ to superoxide and transfers it to (TPEN)Fe^II(PF₆)₂ leading in fine to the oxidation of thioanisole.     

Oxidation of fast green FCF by the solar photo-Fenton process

This study was conducted to assess the removal efficiency of fast green FCF (a dye) from aqueous medium using the photo-Fenton process. Fenton’s reagent, a mixture of hydrogen peroxide (H₂O₂) and ferric ions (Fe^3t+), used to generate hydroxyl radicals (·OH), was used to attack the target contaminant and degrade it. A visible light source was used to provide the radiation needed in the photo-Fenton method (i.e. H₂O₂/Fe³⁺). The effects of varying the parameters of ferric ion, fast green FCF and hydrogen peroxide concentrations, as well as pH, and light intensity on the reaction rate were determined. More effective and faster than Fenton’s reagent in removing fast green FCF, the results show that the photo-Fenton method completely oxidizes and degrades fast green FCF into CO₂ and H₂O. A tentative mechanism for photobleaching of the dye is proposed.     

On‐surface Fenton and Fenton‐like reactions appraised by paper spray ionization mass spectrometry

On‐surface degradation of sildenafil (an adequate substrate as it contains assorted functional groups in its structure) promoted by the Fenton (Fe²⁺/H₂O₂) and Fenton‐like (Mⁿ⁺/H₂O₂; Mⁿ⁺ = Fe³⁺, Co²⁺, Cu²⁺, Mn²⁺) systems was investigated by using paper spray ionization mass spectrometry (PS‐MS). The performance of each system was compared by measuring the ratio between the relative intensities of the ions of m/z 475 (protonated sildenafil) and m/z 235 (protonated lidocaine, used as a convenient internal standard and added to the paper just before the PS‐MS analyzes). The results indicated the following order in the rates of such reactions: Fe²⁺/H₂O₂ ≫ H₂O₂ ≫ Cu²⁺/H₂O₂ > Mⁿ⁺/H₂O₂ (Mⁿ⁺ = Fe³⁺, Co²⁺, Mn²⁺) ~ Mⁿ⁺ (Mⁿ⁺ = Fe²⁺, Fe³⁺, Co²⁺, Cu²⁺, Mn²). The superior capability of Fe²⁺/H₂O₂ in causing the degradation of sildenafil indicates that Fe²⁺ efficiently decomposes H₂O₂ to yield hydroxyl radicals, quite reactive species that cause the substrate oxidation. The results also indicate that H₂O₂ can spontaneously decompose likely to yield hydroxyl radicals, although in a much smaller extension than the Fenton system. This effect, however, is strongly inhibited by the presence of the other cations, ie, Fe³⁺, Co²⁺, Cu²⁺, and Mn²⁺. A unique oxidation by‐product was detected in the reaction between Fe²⁺/H₂O₂ with sildenafil, and a possible structure for it was proposed based on the MS/MS data. The on‐surface reaction of other substrates (trimethoprim and tamoxifen) with the Fenton system was also investigated. In conclusion, PS‐MS shows to be a convenient platform to promptly monitor on‐surface oxidation reactions.     

Electrochemical study of a nonheme Fe(ii) complex in the presence of dioxygen. Insights into the reductive activation of O2 at Fe(ii) centers

Recent efforts to model the reactivity of iron oxygenases have led to the generation of nonheme Fe^III(OOH) and Fe^IV(O) intermediates from Fe^II complexes and O₂ but using different cofactors. This diversity emphasizes the rich chemistry of nonheme Fe(ii) complexes with dioxygen. We report an original mechanistic study of the reaction of [(TPEN)Fe^II]²⁺ with O₂ carried out by cyclic voltammetry. From this Fe^II precursor, reaction intermediates such as [(TPEN)Fe^IV(O)]²⁺, [(TPEN)Fe^III(OOH)]²⁺ and [(TPEN)Fe^III(OO)]⁺ have been chemically generated in high yield, and characterized electrochemically. These electrochemical data have been used to analyse and perform simulation of the cyclic voltammograms of [(TPEN)Fe^II]²⁺ in the presence of O₂. Thus, several important mechanistic informations on this reaction have been obtained. An unfavourable chemical equilibrium between O₂ and the Fe^II complex occurs that leads to the Fe^III-peroxo complex upon reduction, similarly to heme enzymes such as P450. However, unlike in heme systems, further reduction of this latter intermediate does not result in O–O bond cleavage.     

High Sensitive Microsensor Based on Organic‐Inorganic Composite for Two‐Dimensional Mapping of H2O2 by SECM

The present work describes the development of a selective, sensitive and stable sensing microsensor for scanning electrochemical microscopy (SECM) to measure H₂O₂ during electrochemical reduction of oxygen. The microsensor is based on graphene and Poly(3,4‐ethylenedioxythiophene) composite as support to iron (III) hexacyanoferrate (II) (PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor). The electrochemical properties of the PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor were investigated by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor showed an excellent electrocatalytic activity toward hydrogen peroxide (H₂O₂) reduction with a diminution of the overpotential of about 500 mV in comparison to the process at a bare gold microelectrode. The microsensor presented excellent performance for two dimensional mapping of H₂O₂ by SECM in 0.1 mol L^?1 phosphate buffer solution (pH 7.0). Under optimized conditions, a linear response range from 1 up to 1000 µmol L^?1 was obtained with a sensitivity of 0.08 nA L µmol^?1 and limit of detection of 0.5 µmol L^?1.     

Accelerated FeIII/FeII redox cycle of Fenton reaction system using Pd/NH2-MIL-101(Cr) and hydrogen

In this paper, a novel improvement in the catalytic Fenton reaction system named MHACF-NH₂-MIL-101(Cr) was constructed based on H₂ and Pd/NH₂-MIL-101(Cr). The improved system would result in an accelerated reduction in Fe^III, and provide a continuous and fast degradation efficiency of the 10 mg L^-1 4-chlorophenol which was the model contaminant by using only trace level Fe^II. The activity of Pd/NH₂-MIL-101(Cr) decreased from 100% to about 35% gradually during the six consecutive reaction cycles of 18 h. That could be attributed to the irreversible structural damage of NH₂-MIL-101(Cr).     

FerriIridium: A Lysosome-Targeting Iron(III)-Activated Iridium(III) Prodrug for Chemotherapy in Gastric Cancer Cells

Reported is the Fe^III-activated lysosome-targeting prodrug FerriIridium for gastric cancer theranostics. It contains a meta-imino catechol group that can selectively bond to, and be oxidized by, free Fe^III inside the cell. Subsequent oxidative rearrangement releases Fe^II and hydrolyses the amine bond under acidic conditions, forming an aminobipyridyl Ir complex and 2-hydroxybenzoquinone. Thus, Fe^II catalyzes the Fenton reaction, transforming hydrogen peroxide into hydroxyl radicals, the benzoquinone compounds interfere with the respiratory chain, and conversion of the prodrug into the Ir complex leads to an increase in phosphorescence and toxicity. These properties, combined with the high Fe^III content and acidity of cancer cells, make FerriIridium a selective and efficient theranostic agent (IC₅₀=9.22 μm for AGS cells vs. >200 μm for LO2 cells). FerriIridium is the first metal-based compound that has been developed for chemotherapy using Fe^III to enhance both selectivity and potency.     

Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

An insight into the overoxidation of polypyrrole materials

In aqueous solution, under anodic potentials at which water oxidation occurs, the polypyrrole is irreversibly oxidized leading progressively to an insulating material. In this paper, it is evidenced that this overoxidation process is due to the hydroxyl radicals formed during solvent oxidation. Indeed, it is shown that, at open-circuit potential, polypyrrole films are overoxidized in the presence of hydroxyl radicals produce by Fenton’s reagent (H₂O₂/Fe²⁺). On the contrary, the use of hydroxyl radical scavengers, such as methanol and dimethylthiourea, allows one to increase the stability of polypyrrole films under anodic potentials.     

The FeII-FeIV and FeIII-FeV manifolds in an expanded world of Gif chemistry

The Gif systems for the selective functionalization of saturated hydrocarbons based on the reactions of Superoxide with Fe^II and of hydrogen peroxide with Fe^III are described. Both systems are relatively efficient, but not nearly so efficient as the electrochemical system developed in collaboration with Prof. G. Balavoine and Dr. Aurore Gref (Université de Paris-Sud-Orsay, France). All of the systems afford mainly ketones. This is an unusual selectivity, which implies a non-radical mechanism. It has been proven for the Fe^III-H₂O₂ system that the activation of the Fe^III is independent of the formation of ketone, which involves a hydroperoxide (derived from oxygen) as an intermediate. This intermediate controls the formation of ketone and of secondary alcohol. The addition of a number of trapping reagents such as BrCCl₃ diverts the reaction from oxygenation to bromide formation. Although BrCCl₃ is indeed a good trap for carbon radicals, the pattern of selectivity across a range of saturated hydrocarbons is completely different for Gif chemistry when compared with normal radical bromination. The chemistry is explained in terms of an Fe^V oxenoid species that inserts itself into secondary C-H bonds (a compromise between bond strength and steric hindrance). This gives an Fe^V intermediateA with an iron-carbon bond, which is probably rapidly reduced to the Fe^III state by hydrogen peroxide. Then oxygen is inserted into the Fe^III-C bond. Hydrolysis affords the isolateable intermediate hydroperoxide (intermediateB). A system based ontert-butyl hydroperoxide (TBHP) is described. This is similar to the above Gif systems, but the kinetic isotope effect is very different and the selectivity for adamantane substitution is different. However, Fe^III is activated by TBHP to an Fe^V oxenoid which, after reaction with a hydrocarbon, reacts with oxygen to give a hydroperoxide. So the pattern of intermediatesA andB is maintained with TBHP. Radical chemistry is involved in some of the reactions that involve ionic coupling to saturated hydrocarbons. The importance of the Fe^II-Fe^IV manifold in providing a mechanism that permits the selective functionalization of saturated hydrocarbons by ionic trapping with chloride, azide, and other anions is made manifest. Comparison is made with the Fe^III-Fe^V manifold where ionic trapping is never seen. Traditional Fenton chemistry (hydroxyl radical formation) is not operative here, but the trapping does involve the formation of carbon radicals. These react very efficiently with anions bonded to Fe^III.D. R. H. Barton is a Nobel Prize winner in chemistry in 1969. Since 1994, he is a foreign member of the Russian Academy of Sciences.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 595–604, April, 1995.We thank all our colleagues cited in the various References for their contributions to this fascinating subject. We also thank Prof. Minisci for his helpful comments. This work was supported by Quest Intl. and by the Welch Foundation.     

FerriIridium: A Lysosome‐Targeting Iron(III)‐Activated Iridium(III) Prodrug for Chemotherapy in Gastric Cancer Cells

Reported is the Fe^III‐activated lysosome‐targeting prodrug FerriIridium for gastric cancer theranostics. It contains a meta‐imino catechol group that can selectively bond to, and be oxidized by, free Fe^III inside the cell. Subsequent oxidative rearrangement releases Fe^II and hydrolyses the amine bond under acidic conditions, forming an aminobipyridyl Ir complex and 2‐hydroxybenzoquinone. Thus, Fe^II catalyzes the Fenton reaction, transforming hydrogen peroxide into hydroxyl radicals, the benzoquinone compounds interfere with the respiratory chain, and conversion of the prodrug into the Ir complex leads to an increase in phosphorescence and toxicity. These properties, combined with the high Fe^III content and acidity of cancer cells, make FerriIridium a selective and efficient theranostic agent (IC₅₀=9.22 μm for AGS cells vs. >200 μm for LO2 cells). FerriIridium is the first metal‐based compound that has been developed for chemotherapy using Fe^III to enhance both selectivity and potency.     

Synthesis of ultra‐high molecular weight polymers by controlled production of initiating radicals

This study demonstrates that the gradual and slow production of initiating radicals (i.e., hydroxyl radicals here) is the key point for the synthesis of ultra‐high molecular weight (UHMW) polymers via controlled radical polymerization. Hydrogen peroxide (H₂O₂) and ferrous iron (Fe²⁺) react via Fenton redox chemistry to initiate RAFT polymerization. This work presents two enzymatic‐mediated (i.e., Bio‐Fenton‐RAFT and Semi Bio‐Fenton‐RAFT) and one syringe pump‐driven Fenton‐RAFT polymerization processes in which the initiating radicals are carefully and gradually dosed into the reaction solution. The “livingness” of the synthesized UHMW polymers is demonstrated by chain extension and aminolysis experiments. Zimm plots obtained from static light scattering (SLS) technique are used to characterize the UHMW polymers. This Fenton‐RAFT polymerization provides access to polymers of unprecedented UHMW (M_w ~ 20 × 10⁶ g mol^?1) with potential in diverse applications. The UHMW polymers made via the controlled Fenton‐RAFT polymerization by using a syringe pump shows that it is possible to produce such materials through an easy‐to‐set up and scalable process. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1922–1930     

Synthesis,characterization and magnetic properties of mixed-valence iron complexes with 2-pyridyl oximes

Abstract

Two new mixed-valence iron complexes with 2-pyridyl oximes, [Fe(mpko)₃Fe(H₂O)₂(NO₃)](NO₃)·2H₂O (1) (mpko^? = methyl(2-pyridyl)ketone oximate) and [{Fe(dpko)₃}₂Fe](ClO₄)·4H₂O (2) (dpko^? = bis(2-pyridyl)ketone oximate), have been prepared by reaction of Fe^III with mpkoH in methanol (1) and Fe^II with dpkoH in methanol/water (2). Dinuclear Fe^II(low-spin)Fe^III(high-spin) and trinuclear Fe^II(low-spin)Fe^III(high-spin)Fe^II(low-spin) cations are present in the crystal structure of 1 and 2, respectively. Intermolecular hydrogen bonds in 1 lead to weak antiferromagnetic interactions between pairs of neighboring Fe^III centers, which allows observation of single-ion zero-field splitting effects.     

Boron Cluster Anions [BnHn]2– (n = 10, 12) in Reactions of Iron(II) and Iron(III) Complexation with 2, 2′‐Bipyridyl and 1, 10‐Phenanthroline

Complexation of Fe^II and Fe^III with azaheterocyclic ligands L (L = phen or bipy) were studied in the presence and in the absence of boron cluster anions [B_nH_n]^2– (n = 10, 12). The reactions were carried out in air at room temperature in organic solvents and/or water. In all the solvents used, well known [FeL₃]An (An = 2Cl^– or SO₄^2–) ferrous complexes were formed from Fe^II salts. Composition of ferric complexes with L ligands depends on the nature of solvent: either dinuclear oxo‐iron(III) chlorides [L₂ClFe^III–O–Fe^IIIL₂Cl]Cl₂ or ferric ferrates(III) [Fe^IIIL₂Cl₂][Fe^IIICl₄], or [Fe^IIIL₂Cl₂][Fe^IIICl₄L] were isolated from Fe^III salts. Introduction of the closo‐borate anions to a Fe³⁺(or Fe²⁺)/L/solv. mixture stabilizes ferrous cationic complexes [FeL₃]²⁺ in all the solvents used: only ferrous [FeL₃][B_nH_n] (n = 10, 12) complexes were isolated from all the reaction mixtures in the presence of boron cluster anions.     

Superoxide Dismutase Activity of the Naturally Occurring Human Serum Albumin–Copper Complex without Hydroxyl Radical Formation

The superoxide radical anion (O₂^.?) is biologically toxic and contributes to the pathogenesis of various diseases. Here we describe the superoxide dismutase (SOD) activity of human serum albumin (HSA) complexed with a single Cu^II ion at the N‐terminal end (HSA–Cu complex). The structure of this naturally occurring copper‐coordinated blood serum protein has been characterized by several physicochemical measurements. The O₂^.? dismutation ability of the HSA–Cu (1:1) complex is almost the same as that of the well‐known SOD mimics, such as Mn^III‐tetrakis(N‐methylpyridinium)porphyrin. Interestingly, the HSA–Cu complex does not induce a subsequent Fenton reaction to produce the hydroxyl radical (OH^.), which is one of the most harmful reactive oxygen species.