Peroxide Dianion Research Articles

Magnetoelectricity-Mediated Tunable Absorption and Release of Peroxide Dianions

Peroxide dianion (O22-) has strong oxidizing activity and ease of proton abstraction and is extremely unstable. Direct and controllable adsorption and release of O22- has large application implication and is a large challenge so far. Here, we use a unique metal (Ni)-organic (diphenylalanine, DPA) framework (MOF), Ni(DPA)2, as adsorbents for absorption and release of O22-. This MOF structure has room-temperature magnetoelectricity via distortion of the Ni-centered octahedron {NiN2O4} and thus possesses a tunable ferroelectric polarization under applied electric/magnetic fields. Controllable adsorption and release of O22- are realized in such a MOF system via electrochemical redox measurements. Structural/spectroscopic characterization and calculations reveal that a number of NH active sites in the nanopores of MOF can effectively adsorb O22- by hydrogen bonds and then tunable ferroelectric polarization induces controllable release of O22- under applied magnetic fields. This work presents a constructive way for controllable adsorption and release of reactive oxygen species.

Chemical Challenges that the Peroxide Dianion Presents to Rechargeable Lithium–Air Batteries

Chemical Challenges that the Peroxide Dianion Presents to Rechargeable Lithium–Air Batteries

Cryo-EM structures of intermediates suggest an alternative catalytic reaction cycle for cytochrome c oxidase

Cytochrome c oxidases are among the most important and fundamental enzymes of life. Integrated into membranes they use four electrons from cytochrome c molecules to reduce molecular oxygen (dioxygen) to water. Their catalytic cycle has been considered to start with the oxidized form. Subsequent electron transfers lead to the E-state, the R-state (which binds oxygen), the P-state (with an already split dioxygen bond), the F-state and the O-state again. Here, we determined structures of up to 1.9 Å resolution of these intermediates by single particle cryo-EM. Our results suggest that in the O-state the active site contains a peroxide dianion and in the P-state possibly an intact dioxygen molecule, the F-state may contain a superoxide anion. Thus, the enzyme’s catalytic cycle may have to be turned by 180 degrees.

On the Interaction between Superatom Al12Be and DNA Nucleobases/Base Pairs: Bonding Nature and Potential Applications in O2 Activation and CO Oxidation.

The interaction between quasi-chalcogen superatom Al12Be and DNA nucleobases/base pairs has been explored by searching for the most stable Al12Be–X (X = DNA bases and base pairs) complexes. Our results reveal that Al12Be prefers to combine with guanine by two Al–O and Al–N bonds rather than the other DNA bases, no matter in free state or base pair. The formed Al–N and Al–O bonds between Al12Be and DNA bases proved to be strong polar covalent bonds by the Wiberg bond index, nature bond orbitals, atoms in molecules theory, localized molecular orbitals, and electron localization functions analyses. More importantly, it is found that the formed global minimum of Al12Be–G has the ability to activate an oxygen molecule into a peroxide dianion 1O22–, which can further catalyze the CO oxidation via the Eley–Rideal mechanism with a small energy barrier of 7.78 kcal/mol. We hope that this study could not only provide an in-depth understanding on the intermolecular interaction between metallic superatoms and DNA at the molecular level but also attract more interest in designing and synthesizing superatom-based heterogeneous catalysts with DNA/nucleobases as basic building blocks.

Copper(II)-Silver(I) Macrocyclic Metal-Organic Framework: A Highly Efficient Reusable Triplet Oxygen Collector and Singlet Oxygen Generator.

The generation of highly reactive oxygen (1O2) is very significant for a variety of applications such as degradation, bleaching, chemical synthesis, photodynamic therapy for tumor treatment, and others. Herein, we report a novel peroxide-dianion-embedded bimetallic macrocycle, [O22-@Ag4Cu4L4]2+ (2), that can completely release the inserted peroxide dianion as the singlet oxygen (1O2) via a H+-assisted disproportionation process in methanol. Notably, the resulting empty Ag4Cu4L4(ClO4)4 (3) is able to trap oxygen (3O2) from air and fixes it in the macrocycle host as a peroxide dianion; furthermore, it releases it as 1O2 again in the presence of H+. So, the bimetallic macrocycle [Ag4Cu4L4]4+ herein behaves as a highly efficient reusable triplet oxygen receptor and singlet oxygen generator.

On the incompatibility of lithium-O2 battery technology with CO2.

When solubilized in a hexacarboxamide cryptand anion receptor, the peroxide dianion reacts rapidly with CO2 in polar aprotic organic media to produce hydroperoxycarbonate (HOOCO2-) and peroxydicarbonate (-O2COOCO2-). Peroxydicarbonate is subject to thermal fragmentation into two equivalents of the highly reactive carbonate radical anion, which promotes hydrogen atom abstraction reactions responsible for the oxidative degradation of organic solvents. The activation and conversion of the peroxide dianion by CO2 is general. Exposure of solid lithium peroxide (Li2O2) to CO2 in polar aprotic organic media results in aggressive oxidation. These findings indicate that CO2 must not be introduced in conditions relevant to typical lithium-O2 cell configurations, as production of HOOCO2- and -O2COOCO2- during lithium-O2 cell cycling will lead to cell degradation via oxidation of organic electrolytes and other vulnerable cell components.

Anion-Receptor Mediated Oxidation of Carbon Monoxide to Carbonate by Peroxide Dianion.

The reactivity of peroxide dianion O2(2-) has been scarcely explored in organic media due to the lack of soluble sources of this reduced oxygen species. We now report the finding that the encapsulated peroxide cryptate, [O2⊂mBDCA-5t-H6](2-) (1), reacts with carbon monoxide in organic solvents at 40 °C to cleanly form an encapsulated carbonate. Characterization of the resulting hexacarboxamide carbonate cryptate by single crystal X-ray diffraction reveals that carbonate dianion forms nine complementary hydrogen bonds with the hexacarboxamide cryptand, [CO3⊂mBDCA-5t-H6](2-) (2), a conclusion that is supported by spectroscopic data. Labeling studies and (17)O solid-state NMR data confirm that two-thirds of the oxygen atoms in the encapsulated carbonate derive from peroxide dianion, while the carbon is derived from CO. Further evidence for the formation of a carbonate cryptate was obtained by three methods of independent synthesis: treatment of (i) free cryptand with K2CO3; (ii) monodeprotonated cryptand with PPN[HCO3]; and (iii) free cryptand with TBA[OH] and atmospheric CO2. This work demonstrates CO oxidation mediated by a hydrogen-bonding anion receptor, constituting an alternative to transition-metal catalysis.

Ultrafast Photoinduced Electron Transfer from Peroxide Dianion.

The encapsulation of peroxide dianion by hexacarboxamide cryptand provides a platform for the study of electron transfer of isolated peroxide anion. Photoinitiated electron transfer (ET) between freely diffusing Ru(bpy)3(2+) and the peroxide dianion occurs with a rate constant of 2.0 × 10(10) M(-1) s(-1). A competing electron transfer quenching pathway is observed within an ion pair. Picosecond transient spectroscopy furnishes a rate constant of 1.1 × 10(10) s(-1) for this first-order process. A driving force dependence for the ET rate within the ion pair using a series of Ru(bpy)3(2+) derivatives allows for the electronic coupling and reorganization energies to be assessed. The ET reaction is nonadiabatic and dominated by a large inner-sphere reorganization energy, in accordance with that expected for the change in bond distance accompanying the conversion of peroxide dianion to superoxide anion.

Combination of redox-active ligand and lewis acid for dioxygen reduction with π-bound molybdenum-quinonoid complexes.

A series of π-bound Mo-quinonoid complexes supported by pendant phosphines have been synthesized. Structural characterization revealed strong metal-arene interactions between Mo and the π system of the quinonoid fragment. The Mo-catechol complex (2a) was found to react within minutes with 0.5 equiv of O(2) to yield a Mo-quinone complex (3), H(2)O, and CO. Si- and B-protected Mo-catecholate complexes also react with O(2) to yield 3 along with (R(2)SiO)n and (ArBO)(3) byproducts, respectively. Formally, the Mo-catecholate fragment provides two electrons, while the elements bound to the catecholate moiety act as acceptors for the O(2) oxygens. Unreactive by itself, the Mo-dimethyl catecholate analogue reduces O(2) in the presence of added Lewis acid, B(C(6)F(5))(3), to generate a Mo(I) species and a bis(borane)-supported peroxide dianion, [[(F(5)C(6))(3)B](2)O(2)(2-)], demonstrating single-electron-transfer chemistry from Mo to the O(2) moiety. The intramolecular combination of a molybdenum center, redox-active ligand, and Lewis acid reduces O(2) with pendant acids weaker than B(C(6)F(5))(3). Overall, the π-bound catecholate moiety acts as a two-electron donor. A mechanism is proposed in which O(2) is reduced through an initial one-electron transfer, coupled with transfer of the Lewis acidic moiety bound to the quinonoid oxygen atoms to the reduced O(2) species.

Electron-transfer studies of a peroxide dianion.

A peroxide dianion (O2(2-)) can be isolated within the cavity of hexacarboxamide cryptand, [(O2)⊂mBDCA-5t-H6](2-), stabilized by hydrogen bonding but otherwise free of proton or metal-ion association. This feature has allowed the electron-transfer (ET) kinetics of isolated peroxide to be examined chemically and electrochemically. The ET of [(O2)⊂mBDCA-5t-H6](2-) with a series of seven quinones, with reduction potentials spanning 1 V, has been examined by stopped-flow spectroscopy. The kinetics of the homogeneous ET reaction has been correlated to heterogeneous ET kinetics as measured electrochemically to provide a unified description of ET between the Butler-Volmer and Marcus models. The chemical and electrochemical oxidation kinetics together indicate that the oxidative ET of O2(2-) occurs by an outer-sphere mechanism that exhibits significant nonadiabatic character, suggesting that the highest occupied molecular orbital of O2(2-) within the cryptand is sterically shielded from the oxidizing species. An understanding of the ET chemistry of a free peroxide dianion will be useful in studies of metal-air batteries and the use of [(O2)⊂mBDCA-5t-H6](2-) as a chemical reagent.

Interaction of Tris(2-aminoethyl)amine-based Ureas and Thiourea with Superoxide Anion and Peroxide Dianion through Multiple Hydrogen Bonding

Abstract Tris(2-aminoethyl)amine-based urea and thiourea derivatives interacted with a superoxide anion (O2−) and peroxide dianion (O22−): The redox potential of oxygen was positively shifted with the molecules through their multiple-hydrogen-bond donor ability.

A combined quantum chemical and crystallographic study on the oxidized binuclear center of cytochrome c oxidase

Cytochrome c oxidase (C cO) is the terminal enzyme of the respiratory chain. By reducing oxygen to water, it generates a proton gradient across the mitochondrial or bacterial membrane. Recently, two independent X-ray crystallographic studies ((Aoyama et al. Proc. Natl. Acad. Sci. USA 106 (2009) 2165–2169) and (Koepke et al. Biochim. Biophys. Acta 1787 (2009) 635–645)), suggested that a peroxide dianion might be bound to the active site of oxidized C cO. We have investigated this hypothesis by combining quantum chemical calculations with a re-refinement of the X-ray crystallographic data and optical spectroscopic measurements. Our data suggest that dianionic peroxide, superoxide, and dioxygen all form a similar superoxide species when inserted into a fully oxidized ferric/cupric binuclear site (BNC). We argue that stable peroxides are unlikely to be confined within the oxidized BNC since that would be expected to lead to bond splitting and formation of the catalytic P intermediate. Somewhat surprisingly, we find that binding of dioxygen to the oxidized binuclear site is weakly exergonic, and hence, the observed structure might have resulted from dioxygen itself or from superoxide generated from O 2 by the X-ray beam. We show that the presence of O 2 is consistent with the X-ray data. We also discuss how other structures, such as a mixture of the aqueous species (H 2O + OH − and H 2O) and chloride fit the experimental data.

Identification of a Discrete Peroxide Dianion, O22−, in a Two Sodium–(1,6-Anhydro-β-maltose)2–Peroxide Complex

Abstract A complex formed by two 1,6-anhydro-β-maltoses with peroxide and two sodium ions has been isolated and determined to be [Na2(1,6-anhydro-β-maltose)2(H2O)3]O2 by X-ray crystallography. The O2 moiety, 1.496(2) Å for the O–O distances in the complex was identified as a discrete peroxide dianion, whereas two sodium and two carbohydrate molecules constitute a binuclear complex counter cation.The complex containing the discrete peroxide dianion was proven to be a useful oxidizing agent, which successfully oxidized α,β-unsaturated ketone to epoxyketone.

A heterocyclic organogallium peroxide with two dialkylgallium groups bridged by a peroxide dianion

Treatment of Li[H2GaR2] [R=CH(SiMe3)2] with the hydrogen peroxide adduct (H2O2)2.DABCO (DABCO=diazabicyclooctane) afforded a heterocyclic digallium peroxide, [R2Ga(micro,eta1,eta1-O2)(micro-OH)GaR2]Li(DABCO) (2), in which two dialkylgallium groups are bridged by an oxidizing peroxo and a hydroxo ligand.

Spontaneous assembly of a nine-vertex lithium framework encapsulating the peroxide dianion

Investigation of the structure of the lithiated bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) has led to the reproducible isolation of compounds containing the 'Li9(hpp)7(O2)' core, in which a peroxide dianion has been encapsulated within a mono-capped, cubic array of lithium ions.

Activation of the Proton Transfer Pathway in Catalysis by Iron Superoxide Dismutase

Catalysis by Escherichia coli and Porphyromonas gingivalis iron superoxide dismutase was activated by addition of primary amines, as measured by pulse radiolysis and stopped-flow spectrophotometry. This activation was saturable for most amines investigated, and a free energy plot of the apparent second-order rate constant of activation was linear as a function of the pK(a) of the amine, indicating activation by proton transfer. Amines provide an alternate rather than the only pathway for proton transfer, and catalysis was appreciable in the absence of amines. Solvent hydrogen isotope effects were near unity for amine activation, which is consistent with rate-contributing proton transfer if the pK(a) of the proton acceptor on the enzyme is not in the region of the pK(a) values of the amines studied, from 7.8 to 10.6. The activation of catalysis by these amines was uncompetitive with respect to superoxide, interpreted as proton transfer in a ternary complex of amine with the enzyme-bound peroxide dianion.

Kinetic analysis of product inhibition in human manganese superoxide dismutase.

Manganese superoxide dismutase (MnSOD) cycles between the Mn(II) and Mn(III) states during the catalyzed disproportionation of O(2)(*-), a catalysis that is limited at micromolar levels of superoxide by a peroxide-inhibited complex with the metal. We have investigated the role in catalysis and inhibition of the conserved residue Trp161 which forms a hydrophobic side of the active site cavity of MnSOD. Crystal structures of mutants of human MnSOD in which Trp161 was replaced with Ala or Phe showed significant conformational changes on adjacent residues near the active site, particularly Gln143 and Tyr34 which in wild-type MnSOD participate in a hydrogen bond network believed to support proton transfer during catalysis. Using pulse radiolysis and observing the UV absorbance of superoxide, we have determined rate constants for the catalytic dismutation of superoxide. In addition, the rates of formation and dissociation of the product-inhibited complex of these mutants were determined by direct observation of the characteristic visible absorption of the oxidized and inhibited states. Catalysis by W161A and W161F MnSOD was associated with a decrease of at least 100-fold in the catalytic rate of reduction of superoxide, which then promotes a competing pathway leading to product inhibition. The structural changes caused by the mutations at position 161 led to small changes, at most a 6-fold decrease, in the rate constant for formation of the inhibited complex. Solvent hydrogen isotope effects support a mechanism in which formation of this complex, presumably the peroxide dianion bound to the manganese, involves no rate-contributing proton transfer; however, the dissociation of the complex requires proton transfer to generate HO(2)(-) or H2O2.

Cytochrome P450: substrate and prosthetic-group free radicals generated during the enzymatic cycle.

During the enzymatic cycle of the cytochromes P450, dioxygen binds to the ferrous haemprotein when the resting ferric haemprotein has undergone a one-electron oxidation after substrate binding. A further one-electron reduction generates an intermediate that is isoelectronic with a peroxide dianion coordinated to a ferric iron. Heterolytic cleavage of the omicron--omicron bond generates water and a species which is formally an oxene (oxygen atom) coordinated by iron(III). However, on the basis of model reactions and by analogy to the catalases and peroxidases, this active oxidizing intermediate is formulated as an oxo-FeIV porphyrin pi-cation radical. The radical is stabilized by delocalization on the porphyrin macrocycle and the high oxidation state is achieved by oxidizing both the metal and the porphyrin ring of the haemprotein. Hydrogen atom abstraction from a saturated hydrocarbon substrate generates a substrate free radical, constrained by the protein binding site, and the equivalent of a hydroxyl radical bound to iron(III). Coupling of the 'hydroxy' and substrate radicals generates hydroxylated product and resting protein. For olefins an initial electron transfer to oxidized haemprotein gives a substrate cation radical. Further reaction of this radical can give the epoxide, the principal product; an aldehyde or ketone by rearrangement; or an alkylated haemprotein resulting in suicide inhibition.