Superoxo Group Research Articles

H2O2-sensitized titania with activity under visible light and in the dark

The development of visible-light photoactive materials decomposing pollutants and removing bacteria is a frequent motivation for scientific research. However, the reliance on light to sustain the degradation process restricts the practical application of photocatalysts. In this paper, titania was sensitized with H2O2 to overcome this problemand exhibit photocatalytic and dark activity. Efficiency of degradation of standard pollutant (methylene blue) and antibacterial properties (tested on two strains of bacteria: Enterococcus faecalis and Escherichia coli) were asessed. The comprehensive effect of this material is a result of the peroxide-assisted sol-gel method, without heat treatment, which allows obtaining titanium dioxide with hydroxy and adoxygen groups on the surface and in the volume. The presence of the peroxo and superoxo groups was confirmed using Raman, IR and EPR spectroscopies. The thermal stability of the adoxygen groups was analysed by TG/DSC analysis. X-ray diffraction indicated the formation of an amorphous layered structure. The Tauc plot revealed midgap states which reduced the band gaps towards visible light. The H2O2-sensitized TiO2 was characterized by negative surface potential (pHPZC=3.2) which improved adsorption.The study provides insight for the development of self-cleaning and antibacterial surfaces.

QM/MM Study Into the Mechanism of Oxidative C=C Double Bond Cleavage by Lignostilbene-α,β-Dioxygenase.

The enzymatic biosynthesis of fragrance molecules from lignin fragments is an important reaction in biotechnology for the sustainable production of fine chemicals. In this work we investigated the biosynthesis of vanillin from lignostilbene by a nonheme iron dioxygenase using QM/MM and tested several suggested proposals via either an epoxide or dioxetane intermediate. Binding of dioxygen to the active site of the protein results in the formation of an iron(II)-superoxo species with lignostilbene cation radical. The dioxygenase mechanism starts with electrophilic attack of the terminal oxygen atom of the superoxo group on the central C=C bond of lignostilbene, and the second-coordination sphere effects in the substrate binding pocket guide the reaction towards dioxetane formation. The computed mechanism is rationalized with thermochemical cycles and valence bond schemes that explain the electron transfer processes during the reaction mechanism. Particularly, the polarity of the protein and the local electric field and dipole moments enable a facile electron transfer and an exergonic dioxetane formation pathway.

The Chemical Nature of Ti4O10-: Vibrational Predissociation Spectroscopy Combined with Global Structure Optimization.

The gas-phase infrared spectrum of Ti4O10- is studied in the spectral range from 400 cm-1 to 1250 cm-1 using cryogenic ion trap vibrational spectroscopy, in combination with density functional theory (DFT). The infrared photodissociation (IRPD) spectrum of D2-tagged Ti4O10- provides evidence for a structure of lower symmetry that contains a superoxo group (1121 cm-1) and two terminal Ti=O moieties. DFT combined with a genetic algorithm for global structure optimization predicts two isomers which feature a superoxo group: the Cs symmetric global minimum-energy structure and a similar isomer (C1) that is slightly higher in energy. Coupled cluster calculations confirm the relative stability. Comparison of the harmonic DFT spectra (different functionals) with the IRPD spectrum suggests that both of these isomers contribute. Earlier assignments to the adamantane-like C3v isomer with three terminal Ti-O• - groups in a quartet state are not confirmed. They were based on the infrared multiple photon photodissociation (IRMPD) spectrum of bare Ti4O10- and local DFT structure optimizations.

Facile Synthesis of Nb2O5 as a Visible Light-Sensitive Photocatalyst

Niobium pentoxide (Nb2O5) is a promising semiconductor in catalysis due to its chemical and physical properties, availability, and non-toxicity. However, because of its large bandgap energy (Eg= 3.1 – 4.0 eV), Nb2O5 does not work as a photocatalyst under visible light, which makes its use of solar light limited. Even though Nb2O5 presents this drawback, its photocatalytic activity under visible light radiation can be enhanced due to the presence of surface groups, known as niobium peroxo complexes, formed by the treatment with hydrogen peroxide. In general, the modified niobia is synthetized in multi-step processes which allow the generation of strongly reactive oxygen species (ROS) (i.e. peroxo and superoxo) on its surface. In contrast, in this study, the peroxo-niobium oxide was prepared by a facile combination of the oxidant peroxide method (OPM) and hydrothermal treatment. The ability of Nb2O5 to form the ROS using this method was investigated in respect to the different Nb:H2O2 molar ratio (1:2 or 1:10) added in the metal oxide synthesis. For this purpose, ammonium niobium oxalate was dissolved in distilled water and hydrogen peroxide was then added to the reaction medium. The niobium precursor in contact with H2O2 forms instantaneously the niobium peroxo complex that was crystallized at 120 ⁰C with a heating ramp of 1 oC/min, for 12h in a home-made teflon lined autoclave. When the desired temperature was reached, the internal pressure of the reactor varied from ca. 10 to 27 atm, depending upon the amount of hydrogen peroxide used to prepare each material. The oxidative properties of the reactive oxygen species formed on the surface of metal oxides were tested in photodegradation of caffeic acid (CA) under visible light. In addition, reuse tests were performed in order to investigate the loss of photoactivity of the best photocatalyst in the CA degradation. XRD patterns revealed that the crystallographic structures of the samples Nb2H and Nb10H contain the Nb2O5 pseudohexagonal-type phase (JCPDS 28-317) and hydrated niobium oxide. Although no changes in the crystalline structure of both materials were observed, the presence of peroxo and superoxo species in the photocatalysts was confirmed by XPS and FTIR. The composites Nb2H and Nb10H presented band gap energies of 3.20 and 3.16 eV, respectively. However, Nb10H sample absorbs visible light at more than 400 nm, suggesting that the synthesis of the Nb2O5 with excess of H2O2 shifts the absorption edge of this material to the visible range, as well as reduces the energy required to the photoactivation of the catalyst. It was found that the photocatalytic activity increased with increasing oxidant concentration in the synthesis medium due to formation of a higher amount of oxygen reactive species on the surface of niobia. The peroxo-niobium groups on the Nb2O5 surface allowed the photocatalysts to be activated by visible light, and the superoxo groups formed can be also be responsible to improve its photocatalytic efficiency. The reuse tests of the Nb10H oxide indicated that the CA removal capacity remained practically constant even after four consecutive cycles. Therefore, the possibility of using solar irradiation to supply energy to active the photocatalyst make this material promising for use in low-cost photocatalytic systems for treatment of wastewater.

DFT study reveals geometric and electronic synergisms of palladium-mercury alloy catalyst used for hydrogen peroxide formation

One of the main obstacles confronting the direct synthesis of hydrogen peroxide (H2O2) is how to maintain the unbroken OO bonding of the intermediate species on the catalytic surface. To address this challenge Pd-Hg alloys have been used with initial reports suggesting their performance offers advantages when compared to monometallic Pd and Pd-Au alloys; however, the interactions of O2 with Pd-Hg alloys are not well characterised. In this study, density functional theory (DFT) calculations, employed to investigate O2 adsorption on the Pd and Pd-Hg alloy surfaces, suggested O2 adsorption can occur via either a superoxo or a peroxo pathway and that when Hg is alloyed to Pd there are more surface adsorbed superoxo groups compared to adsorption on a monometallic Pd surface. The Hg in Pd6Hg3/Pd(111) results in an electronic surface structure different to that of Pd(111) and a reduced O2 adsorption energy. The stronger O2 surface interactions, when combined with weaker OO bonding (of the adsorbed O2), which result from the presence of Hg on the Pd-Hg surface leads to synergistic geometric and electronic effects that result in an increased selectivity during of the synthesis of H2O2.

Kinetics and mechanism of oxidation of thiourea by a bridging superoxide in the presence of Ellman’s reagent

In aqueous acetate buffer, reaction between the superoxo complex [(dien)(en)CoIII(O2)CoIII(en)(dien)]5+ (1) and thiourea (Tu, SC(NH2)2) proceeds through a complex kinetic pathway and the change of the absorbance of 1 with time follows a sigmoidal trace. Only in the presence of Ellman’s reagent (5,5′-dithio-bis-(2-nitrobenzoic acid), DTNB), the reaction becomes quantitative and Tu reduces the bound superoxo group (––) of 1 to the corresponding peroxo group (––) in [(dien)(en)CoIII(O2)CoIII(en)(dien)]4+ (2). In the presence of DTNB, with large excess of Tu over [1], the reaction follows first-order kinetics and the observed rate constant, ko, increases linearly with the increase in [1], [TTu] ([TTu] is the analytical concentration of Tu), [H+], and the media ionic strength (I). The presence of an intercept in the plot of ko versus [H+] suggests that both tautomeric forms of thiourea, i.e. TuZ and its protonated form TuZH+, are kinetically reactive reductants. The calculated rate constant values for k1 (~102) and k2 (~104) indicate that TuZH+ plays the leading role in the redox reaction. The present work also reveals the prospective involvement of Ellman’s reagent as a radical scavenger.

Fe3O4‐Decorated Co9S8 Nanoparticles In Situ Grown on Reduced Graphene Oxide: A New and Efficient Electrocatalyst for Oxygen Evolution Reaction

Cobalt sulfide materials have attracted enormous interest as low‐cost alternatives to noble‐metal catalysts capable of catalyzing both oxygen reduction and oxygen evolution reactions. Although recent advances have been achieved in the development of various cobalt sulfide composites to expedite their oxygen reduction reaction properties, to improve their poor oxygen evolution reaction (OER) activity is still challenging, which significantly limits their utilization. Here, the synthesis of Fe3O4‐decorated Co9S8 nanoparticles in situ grown on a reduced graphene oxide surface (Fe3O4@Co9S8/rGO) and the use of it as a remarkably active and stable OER catalyst are first reported. Loading of Fe3O4 on cobalt sulfide induces the formation of pure phase Co9S8 and highly improves the catalytic activity for OER. The composite exhibits superior OER performance with a small overpotential of 0.34 V at the current density of 10 mA cm−2 and high stability. It is believed that the electron transfer trend from Fe species to Co9S8 promotes the breaking of the Co–O bond in the stable configuration (Co–O–O superoxo group), attributing to the excellent catalytic activity. This development offers a new and effective cobalt sulfide‐based oxygen evolution electrocatalysts to replace the expensive commercial catalysts such as RuO2 or IrO2.

Unusual formations of superoxo heptaoxomolybdates from peroxo molybdates

Two novel dioxygen heptaoxomolybdates K5[Mo7O22(O2)(OH)]Cl·6H2O (1) and K5[Mo7O22(O2)(O2)]·8H2O (2) were isolated from the solution of peroxo molybdate accidently. The solids were characterized by IR, EPR and X-ray single crystal analysis. Complex 1 contains a superoxo group with a short bond distance 1.27(1) Å, while 2 is a mixed complex with peroxo and superoxo groups [1.43(1), 1.27(1) Å]. All of the dioxygen groups coordinate to molybdenum atoms in side-on (η2) fashion. The two complexes are short-lived and will decompose into peroxo molybdates K5[Mo7O21(O2)2(OH)]·6H2O (3) and K6[Mo7O22(O2)2]·9H2O (4) very quickly.

Reaction Mechanism of Homoprotocatechuate 2,3-Dioxygenase with 4-Nitrocatechol: Implications for the Role of Substrate

The reaction mechanism of the dioxygen activation by homoprotocatechuate 2,3-dioxygenase (HPCD) with the substrate 4-nitrocatechol was investigated by quantum mechanical/molecular mechanical calculations. Our results demonstrated that the experimentally determined side-on iron-oxygen complex in crystallo is a semiquinone substrate radical (SQ(•))-Fe(III)-hydroperoxo species, which could not act as the reactive species. In fact, the Fe(III)-superoxo species with a hydrogen bond between His200 and the proximal oxygen is the reactive oxygen species. The second-sphere His200 residue was found to play an important role in manipulating the orientation of the superoxide in the Fe-O2 adduct for the further reaction. The rate-limiting step is the attack of the superoxo group on the substrate with a barrier of 17.2 kcal/mol, in good agreement with the experimental value of 16.8 kcal/mol. The reaction mechanism was then compared with the one for HPCD with its native substrate homoprotocatechuate studied recently by the same methods, in which a hybrid SQ(•)-Fe(II)-O2(•-)/Fe(III)-O2(•-) was suggested to be the reactive species. Therefore, our studies suggested that the substrate plays important roles in the dioxygen activation by HPCD.

A Chromium(III)–Superoxo Complex in Oxygen Atom Transfer Reactions as a Chemical Model of Cysteine Dioxygenase

Metal-superoxo species are believed to play key roles in oxygenation reactions by metalloenzymes. One example is cysteine dioxygenase (CDO) that catalyzes the oxidation of cysteine with O(2), and an iron(III)-superoxo species is proposed as an intermediate that effects the sulfoxidation reaction. We now report the first biomimetic example showing that a chromium(III)-superoxo complex bearing a macrocyclic TMC ligand, [Cr(III)(O(2))(TMC)(Cl)](+), is an active oxidant in oxygen atom transfer (OAT) reactions, such as the oxidation of phosphine and sulfides. The electrophilic character of the Cr(III)-superoxo complex is demonstrated unambiguously in the sulfoxidation of para-substituted thioanisoles. A Cr(IV)-oxo complex, [Cr(IV)(O)(TMC)(Cl)](+), formed in the OAT reactions by the chromium(III)-superoxo complex, is characterized by X-ray crystallography and various spectroscopic methods. The present results support the proposed oxidant and mechanism in CDO, such as an iron(III)-superoxo species is an active oxidant that attacks the sulfur atom of the cysteine ligand by the terminal oxygen atom of the superoxo group, followed by the formation of a sulfoxide and an iron(IV)-oxo species via an O-O bond cleavage.

Mechanism of S-Oxygenation by a Cysteine Dioxygenase Model Complex

In this work, we present the first computational study on a biomimetic cysteine dioxygenase model complex, [Fe(II)(LN(3)S)](+), in which LN(3)S is a tetradentate ligand with a bis(imino)pyridyl scaffold and a pendant arylthiolate group. The reaction mechanism of sulfur dioxygenation with O(2) was examined by density functional theory (DFT) methods and compared with results obtained for cysteine dioxygenase. The reaction proceeds via multistate reactivity patterns on competing singlet, triplet, and quintet spin state surfaces. The reaction mechanism is analogous to that found for cysteine dioxygenase enzymes (Kumar, D.; Thiel, W.; de Visser, S. P. J. Am. Chem. Soc. 2011, 133, 3869-3882); hence, the computations indicate that this complex can closely mimic the enzymatic process. The catalytic mechanism starts from an iron(III)-superoxo complex and the attack of the terminal oxygen atom of the superoxo group on the sulfur atom of the ligand. Subsequently, the dioxygen bond breaks to form an iron(IV)-oxo complex with a bound sulfenato group. After reorganization, the second oxygen atom is transferred to the substrate to give a sulfinic acid product. An alternative mechanism involving the direct attack of dioxygen on the sulfur, without involving any iron-oxygen intermediates, was also examined. Importantly, a significant energetic preference for dioxygen coordinating to the iron center prior to attack at sulfur was discovered and serves to elucidate the function of the metal ion in the reaction process. The computational results are in good agreement with experimental observations, and the differences and similarities of the biomimetic complex and the enzymatic cysteine dioxygenase center are highlighted.

A systematic study of neutral and charged 3d-metal trioxides and tetraoxides

Using density functional theory with generalized gradient approximation, we have performed a systematic study of the structure and properties of neutral and charged trioxides (MO(3)) and tetraoxides (MO(4)) of the 3d-metal atoms. The results of our calculations revealed a number of interesting features when moving along the 3d-metal series. (1) Geometrical configurations of the lowest total energy states of neutral and charged trioxides and tetraoxides are composed of oxo and∕or peroxo groups, except for CuO(3)(-) and ZnO(3)(-) which possess a superoxo group, CuO(4)(+) and ZnO(4)(+) which possess two superoxo groups, and CuO(3)(+), ZnO(3)(+), and ZnO(4)(-) which possess an ozonide group. While peroxo groups are found in the early and late transition metals, all oxygen atoms bind chemically to the metal atom in the middle of the series. (2) Attachment or detachment of an electron to∕from an oxide often leads to a change in the geometry. In some cases, two dissociatively attached oxygen atoms combine and form a peroxo group or a peroxo group transforms into a superoxo group and vice versa. (3) The adiabatic electron affinity of as many as two trioxides (VO(3) and CoO(3)) and four tetraoxides (TiO(4), CrO(4), MnO(4), and FeO(4)) are larger than the electron affinity of halogen atoms. All these oxides are hence superhalogens although only VO(3) and MnO(4) satisfy the general superhalogen formula.

Theoretical Study on the Mechanism of the Oxygen Activation Process in Cysteine Dioxygenase Enzymes

Cysteine dioxygenase (CDO) is a vital enzyme for human health involved in the biodegradation of toxic cysteine and thereby regulation of the cysteine concentration in the body. The enzyme belongs to the group of nonheme iron dioxygenases and utilizes molecular oxygen to transfer two oxygen atoms to cysteinate to form cysteine sulfinic acid products. The mechanism for this reaction is currently disputed, with crystallographic studies implicating a persulfenate intermediate in the catalytic cycle. To resolve the dispute we have performed quantum mechanics/molecular mechanics (QM/MM) calculations on substrate activation by CDO enzymes using an enzyme monomer and a large QM active region. We find a stepwise mechanism, whereby the distal oxygen atom of the iron(II)-superoxo complex attacks the sulfur atom of cysteinate to form a ring structure, followed by dioxygen bond breaking and the formation of a sulfoxide bound to an iron(IV)-oxo complex. A sulfoxide rotation precedes the second oxygen atom transfer to the substrate to give cysteine sulfinic acid products. The reaction takes place on several low-lying spin-state surfaces via multistate reactivity patterns. It starts in the singlet ground state of the iron(II)-superoxo reactant and then proceeds mainly on the quintet and triplet surfaces. The initial and rate-determining attack of the superoxo group on the cysteinate sulfur atom involves a spin-state crossing from singlet to quintet. We have also investigated an alternative mechanism via a persulfenate intermediate, with a realignment of hydrogen bonding interactions in the substrate binding pocket. However, this alternative mechanism of proximal oxygen atom attack on the sulfur atom of cysteinate is computed to be a high-energy pathway, and therefore, the persulfenate intermediate is unlikely to participate in the catalytic cycle of CDO enzymes.

Structure and Spectroscopic Properties of Iron Oxides with the High Content of Oxygen: FeOn and FeOn− (n = 5−12)

The electronic and geometrical structures of oxygen-rich neutral and negatively charged FeO(5), FeO(6), FeO(7), FeO(8), FeO(9), FeO(10), FeO(11), and FeO(12) clusters were obtained using density functional theory with generalized gradient approximation. With the exception of FeO(11) and FeO(12), all clusters are found to possess a large number of isomers composed of oxo, peroxo, superoxo, and ozonide fragments that are closely spaced in total energy, especially for n = 7 and 8. The preferable structures of FeO(12) are composed of superoxo groups with different orientations. All the neutral species possess rather large electron affinities, which range from 3.24 eV (FeO(8)) to 3.95 eV (FeO(5)). Although all of the lowest energy states were found to possess positive vibrational frequencies and thus are geometrically stable, the states are thermodynamically unstable against dissociation to FeO(4) + (n - 4)/2 O(2) for n = 6, 8, 10, and 12 and FeO(5) + (n - 5)/2 O(2) for n = 7, 9, and 11. In particular, the decay of FeO(12) is exothermic by 34 kcal/mol.

Metal‐catalyzed reversible conversion between chemical and electrical energy designed towards a sustainable society

Proton dissociation of an aqua-Ru-quinone complex, [Ru(trpy)(q)(OH2)]2+ (trpy = 2,2' : 6',2''-terpyridine, q = 3,5-di-t-butylquinone) proceeded in two steps (pK(a) = 5.5 and ca. 10.5). The first step simply produced [Ru(trpy)(q)(OH)]+, while the second one gave an unusual oxyl radical complex, [Ru(trpy)(sq)(O-*)]0 (sq = 3,5-di-t-butylsemiquinone), owing to an intramolecular electron transfer from the resultant O2- to q. A dinuclear Ru complex bridged by an anthracene framework, [Ru2(btpyan)(q)2(OH)2]2+ (btpyan = 1,8-bis(2,2'-terpyridyl)anthracene), was prepared to place two Ru(trpy)(q)(OH) groups at a close distance. Deprotonation of the two hydroxy protons of [Ru2(btpyan)(q)2(OH)2]2+ generated two oxyl radical Ru-O-* groups, which worked as a precursor for O2 evolution in the oxidation of water. The [Ru2(btpyan)(q)2(OH)2](SbF6)2 modified ITO electrode effectively catalyzed four-electron oxidation of water to evolve O2 (TON = 33500) under electrolysis at +1.70 V in H2O (pH 4.0). Various physical measurements and DFT calculations indicated that a radical coupling between two Ru(sq)(O-*) groups forms a (cat)Ru-O-O-Ru(sq) (cat = 3,5-di-t-butylcathechol) framework with a mu-superoxo bond. Successive removal of four electrons from the cat, sq, and superoxo groups of [Ru2(btpyan)(cat)(sq)(mu-O2-)]0 assisted with an attack of two water (or OH-) to Ru centers, which causes smooth O2 evolution with regeneration of [Ru2(btpyan)(q)2(OH)2]2+. Deprotonation of an Ru-quinone-ammonia complex also gave the corresponding Ru-semiquinone-aminyl radical. The oxidized form of the latter showed a high catalytic activity towards the oxidation of methanol in the presence of base. Three complexes, [Ru(bpy)2(CO)2]2+, [Ru(bpy)2(CO)(C(O)OH)]+, and [Ru(bpy)2(CO)(CO2)]0 exist as an equilibrium mixture in water. Treatment of [Ru(bpy)2(CO)2]2+ with BH4- gave [Ru(bpy)2(CO)(C(O)H)]+, [Ru(bpy)2(CO)(CH2OH)]+, and [Ru(bpy)2(CO)(OH2)]2+ with generation of CH3OH in aqueous conditions. Based on these results, a reasonable catalytic pathway from CO2 to CH3OH in electro- and photochemical CO2 reduction is proposed. A new pbn (pbn = 2-pyridylbenzo[b]-1,5-naphthyridine) ligand was designed as a renewable hydride donor for the six-electron reduction of CO2. A series of [Ru(bpy)(3-n)(pbn)n]2+ (n = 1, 2, 3) complexes undergoes photochemical two- (n = 1), four- (n = 2), and six-electron reductions (n = 3) under irradiation of visible light in the presence of N(CH2CH2OH)3.

Gas phase vibrational spectroscopy of mass-selected vanadium oxide anions

The vibrational spectra of vanadium oxide anions ranging from V(2)O(6)(-) to V(8)O(20)(-) are studied in the region from 555 to 1670 cm(-1) by infrared multiple photon photodissociation (IRMPD) spectroscopy. The cluster structures are assigned and structural trends identified by comparison of the experimental IRMPD spectra with simulated linear IR absorption spectra derived from density functional calculations, aided by energy calculations at higher levels of theory. Overall, the IR absorption of the V(m)O(n)(-) clusters can be grouped in three spectral regions. The transitions of (i) superoxo, (ii) vanadyl and (iii) V-O-V and V-O single bond modes are found at approximately 1100 cm(-1), 1020 to 870 cm(-1), and 950 to 580 cm(-1), respectively. A structural transition from open structures, including at least one vanadium atom forming two vanadyl bonds, to caged structures, with only one vanadyl bond per vanadium atom, is observed in-between tri- and tetravanadium oxide anions. Both the closed shell (V(2)O(5))(2,3)VO(3)(-) and open shell (V(2)O(5))(2-4)(-) anions prefer cage-like structures. The (V(2)O(5))(3,4)(-) anions have symmetry-broken minimum energy structures (C(s)) connected by low-energy transition structures of C(2v) symmetry. These double well potentials for V-O-V modes lead to IR transitions substantially red-shifted from their harmonic values. For the oxygen rich clusters, the IRMPD spectra prove the presence of a superoxo group in V(2)O(7)(-), but the absence of the expected peroxo group in V(4)O(11)(-). For V(4)O(11)(-), use of a genetic algorithm was necessary for finding a non-intuitive energy minimum structure with sufficient agreement between experiment and theory.

Electrochemical oxidation of La 2CuO 4 in fused nitrates

La 2CuO 4 has been electrochemically oxidized in fused alkali nitrates, a medium that stabilizes peroxo and superoxo groups. The oxidation takes place either in neutral (NaClO 4 electrolyte) or basic (KOH, Na 2O electrolytes) media, in the presence or absence of protons, and in the presence or absence of added oxo groups (e.g. NaClO 4). The oxidation potentials are lower as the basicity of the medium increases (NaClO 4 > KOH > Na 2O). The resulting La 2CuO 4 + δ materials have large superconductivity fractions when the oxidation is performed at 150°C, and very small fractions (along with phase decomposition into CuO) when it is performed at 235°C. The oxidized materials are totally unreactive versus iodide. That, along with the reported existence of peroxo and superoxo groups in this media, suggests that intercalation of oxygen in intermediate −1 and/or − 1 2 oxidation states takes place. However, the existence of such reaction in the absence of protons eliminates the possibility of a mechanism by which OH − groups are being intercalated. Potentiostatic experiments yield a phase-segregated material with phases of T c 45 and 35 K, while galvanostatic experiments allow to prepare the 35 K phase by itself.