Does copper-d-penicillamine catalyze the dismutation of O2−?

It has been reported (M. Younes and U. Weser, 1977, Biochem. Biophys. Res. Commun.78, 1247–1253; E. Lengfelder and E. F. Elstner, 1978, Hoppe-Seyler's Z. Physiol. Chem.359, 751–757) that the complex [Cu(I)₈Cu(II)₆(D-penicillamine)₁₂Cl]^5?-efficiently catalyzes the dismutation of O₂^? and that this activity is resistant to both EDTA and CN^?. However, careful study has demonstrated that this complex is unable to catalyze the dismutation of O₂^?, but that it slowly decomposes to simpler copper complexes which are active. Moreover, the activity which is observed is suppressed by EDTA or by Chelex 100 treatment.     

Resonance Raman studies of the peroxotitanate(IV) complexes K2(Ti(O2)(SO4)2)·5H2O and K2(Ti(O2)(C2O4)2)·3H2O

The resonance Raman spectra of K₂(Ti(O₂)(SO₄)₂)·5H₂O and K₂(Ti(O₂)(C₂O₄)₂)·3H₂O are recorded. The results are consistent with the triangular structure of the peroxotitanium unit, Ti(O₂), with C_2ν symmetry. The ν(OO), ν_s(TiO) and ν_as(TiO) are observed around 890, 610 and 535 cm⁻¹, respectively. The resonance effects are shown to be associated with the 425 nm absorption band. This band is assigned to the O₂²⁻ → Ti(IV) charge-transfer transition. The calculated force constant values for the O₂²⁻ and TiO bonds are 320 and 275 N m⁻¹, respectively.     

The effect of air containing O2 −,O2 +, CO2 − and CO2 + on the growth of seedlings ofHordeum Vulgaris

Equipment was devised which permitted the addition of specific gaseous ions to the atmosphere of plastic chambers in which seedlings of HORDEUM VULGARIS were grown in sand culture supplied with chemically defined nutrient solutions. Moderate densities of O₂ ^– or O₂ ⁺ ions (1.8×10⁴/cm³)in air containing an added 8% of O₂ accelerated the growth rate. A like number of CO₂ ^– or CO₂ ⁺ ions in air containing 8% of CO₂ inhibited growth, impeded the production of chlorophyll and devitalized the young seedlings. Evidence is presented that O₂ ^– and O₂ ⁺ stimulate the production of cytochromes and other Fe-containing enzymes through their action on the plant regulatory system responsible for the control of Fe metabolism. The toxic effect of CO₂ ^– and CO₂ ⁺ cannot be explained as yet.

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Zusammenfassung Eine Apparatur wurde entwickelt, die die Zufuhr von ionisiertem Gas der AtmosphÄre in Kammern gestattet. Darin wurden Keimlinge von HORDEUM VULGARIS in Sand mit chemisch definierten NÄhrlösungen gezüchtet. Konzentrationen von 1,8×10⁴/cm³ O₂ ^– und O₂ ⁺ in Luft mit zusÄtzlich 8% O₂ beschleunigten die Wachstumsrate. Die gleiche Menge CO₂ ^– und CO₂ ⁺ in Luft mit zusÄtzlich 8% CO₂ hemmte die Wachstumsrate, die Bildung von Chlorophyll und entkrÄftigte die Keimlinge. Es wird gezeigt,dass O₂ ^– und O₂ ⁺ die Bildung von Cytochrom und anderen eisenhaltigen Enzymen anregen durcn ihre Wirkung auf das den Fe-Stoffwechsel regulierende System der Pflanze. Die toxische Wirkung von CO₂ ^– und CO₂ ⁺ lÄsst sich noch nicht erklÄren.

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Resume On a construit un appareil permettant d'introduire dans 1'atmosphères des ions de gaz déterminés. On a alors effectué de telles adjonctions à l'air contenu dans des cellules de plastique dans lesquelles on cultivait HORDEUM VULGARIS sur du sable et dans une solution nutritive chimiquement définie. Des densités modérées d'ions O₂ ^– ou O₂ ⁺ (1,8×10⁴/cm³) dans de l'air additionné de 8% d'O₂ accélèrent la croissance. La meme concentration de CO₂ ^– et CO₂ ⁺ additionnée de 8% de CO₂ a ralenti la croissance et la formation de chlorophylle et a diminué la vitalite des plantes nouvellement germées. On démontre que O₂ ^– et O₂ ⁺ active la formation de cytochrome et d'autres enzymes ferreuses par suite de l'action de ces ions sur le système régularisant le métabolisme du fer dans la plante. L'effet toxique du CO₂ ^– et CO₂ ⁺ reste encore inexpliqué.

     

Theoretical study of the hydroxylation of phenolates by the Cu2O2(N,N′-dimethylethylenediamine)2 2+ complex

Tyrosinase catalyzes the ortho hydroxylation of monophenols and the subsequent oxidation of the diphenolic products to the resulting quinones. In efforts to create biomimetic copper complexes that can oxidize C–H bonds, Stack and coworkers recently reported a synthetic μ-η²:η²-peroxodicopper(II)(DBED)₂ complex (DBED is N,N′-di-tert-butylethylenediamine), which rapidly hydroxylates phenolates. A reactive intermediate consistent with a bis-μ-oxo-dicopper(III)-phenolate complex, with the O–O bond fully cleaved, is observed experimentally. Overall, the evidence for sequential O–O bond cleavage and C–O bond formation in this synthetic complex suggests an alternative mechanism to the concerted or late-stage O–O bond scission generally accepted for the phenol hydroxylation reaction performed by tyrosinase. In this work, the reaction mechanism of this peroxodicopper(II) complex was studied with hybrid density functional methods by replacing DBED in the μ-η²:η²-peroxodicopper(II)(DBED)₂ complex by N,N′-dimethylethylenediamine ligands to reduce the computational costs. The reaction mechanism obtained is compared with the existing proposals for the catalytic ortho hydroxylation of monophenol and the subsequent oxidation of the diphenolic product to the resulting quinone with the aim of gaining some understanding about the copper-promoted oxidation processes mediated by 2:1 Cu(I)O₂-derived species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Further quasi-classical trajectory studies on the C++ H2O reaction

Further trajectory studies on the C⁺ + H₂O reaction have been performed using a potential energy surface described through a finite element method in its p version. In former trajectory studies [Y. Ishikawa, T. Ikegami and R.C. Binning Jr., Direct ab initio molecular dynamics study of C⁺+H₂O: angular distribution of products and distribution of product kinetic energies, Chem. Phys. Lett. 370 (2003), pp. 490–495; J.R. Flores, Quasichemical trajectories on a finite element density functional potential energy surface: the C⁺+H₂O reaction revisited, J. Chem. Phys. 125 (2006), 164309], tunnelling was not taken into account. The present results together with the analysis of the electronic excited states [J.R. Flores and A.B. González, The role of the excited electronic states in the C⁺+H₂O reaction, J. Chem. Phys. 128 (2008), 144310] are useful to interpret the mechanism of the title reaction, which has been the subject of crossed beam experiments [D.M. Sonnenfroh, R.A. Curtiss and J.M. Farrar, Collision complex formation in the reaction of C⁺ with H₂O, J. Chem. Phys. 83 (1985), pp. 3958–3964] and can be considered a prototypical ion–molecule reaction.     

A model of O·2 - generation in the complex III of the electron transport chain

Oxidation of semiquinone by O₂ in the Q cycle is known to be one of the sources of superoxide anion (O·₂ ^-) in aerobic cells. In this paper, such a phenomenon was analyzed using the chemical kinetics model of electron transfer from succinate to cytochrome c, including coenzyme Q, the complex III non-heme iron protein FeS_III and cytochromes b₁, b_h and c₁. Electron transfers from QH₂ to FeS_III and cytochrome b₁ were assumed to occur according to direct transfer mechanism (dynamic channelling) involving the formation of FeS^red _III -Q·^- and Q·^--cytochrome b₁ complexes. For oxidation/reduction reactions involving cytochromes b_h and b₁, the dependence of the equilibrium and elementary rate constants on the membrane potential () was taken into consideration. The rate of O·₂ ^- generation was found to increase dramatically with increase in above the values found in State 3. On the other hand, the rate of cytochrome c reduction decreased sharply at the same values of the membrane potential. This explains experimental data that the O·2^- generation at State 4 appears to be very much faster than at State 3. A mild uncoupling in State 4 can markedly decrease the superoxide generation due to a decrease in below the above mentioned critical level. pH appears to be equally effective as in stimulation of superoxide production which depends, in fact, upon the ^- _H + level.     

Do copper ions influence the reduction of ferricytochrome C by O−2?

Recently, it was suggested that the measured rate of reduction of ferricyto chrome $\text{C}$ by O^?₂ below pH 8, was too high in the presence of high concentrations of formate (Koppenol, W.H., Van Buuren, K.J.H., Butler J. and Braams, R. (1976) Biochim. Biophys. Acta 449, 157–168).The high values were attributed to the presence of impurities of copper, which compete for O^?₂. This assumption is consistent with either a decrease in the reduction yield of ferricytochrome $\text{C}$ in the presence of copper, or with a very fast reaction of Cu(I) with ferricytochrome $\text{C}$.It was previously shown by us and by others that the reduction yield of ferricytochrome $\text{C}$ by O^?₂ is 100%. We measured the rate of reduction of ferricytochrome $\text{C}$ by Cu(I), and found that this reaction is slow: $\text{k = (1.5±0.5) · 10}{}^3\text{M}{}^{\mathrm{?1}}\text{) ·}\text{s}{}^{\mathrm{?1}}$.Therefore, our results rule out the possibility that below pH 8 copper impurities affect the measured rate constant of the reduction of ferricytochrome $\text{C}$ by O^?₂.     

In vitro effects of reactive O2 species on the β-receptor-adenylyl cyclase system

The irreversible loss of activity of the sarcolemma-localized β-receptor-adenylyl cyclase system (β-RAS) in myocardial ischemia is a well documented phenomenon. Alterations in the sarcolemma (SL) induced by reactive O₂ species could be responsible for this loss. Therefore the influence of oxidation of SH-groups and lipid peroxidation induced by Fe²⁺/Vit. C on the β-RAS activity was studied. During incubation of SL with Fe²⁺/Vit. C a transient enhancement followed by a continuous loss of the β-RAS activity (isoprenaline-, NaF-, Gpp(NH)p-, forskolin-stimulated and basal activity) was observed. In contrast there occurred a continuous loss of SH-groups and lipid peroxidation, beginning immediately after the start of incubation. Loss of SH-groups and lipid peroxidation as well as changes in the β-RAS did not take place in the presence of the antioxidant t-Butyl-4-hydroxyanisole (BHA) or the Fe²⁺-chelator EGTA. In view of the known ischemia-induced formation of reactive O₂ species our results show that these powerful oxidants could contribute to the modulation of the β-RAS during myocardial ischemia.     

Optical analysis of RE3+ (RE = Nd or Er):B2O3–P2O5–CaF2–ZnO–(Li2O/Na2O/K2O) glasses

Calcium boro fluoro zinc phosphate glasses modified using alkali oxide and doped with Nd³⁺ and Er³⁺ ions with the chemical composition of 69.5 (B₂O₃) + 10 (P₂O₅) + 10 (CaF₂) + 5 (ZnO) + 5 (Na₂O/Li₂O/K₂O) + 0.5 (Er₂O₃/Nd₂O₃) were prepared using a conventional melt quenching technique. The results of X-ray diffraction patterns indicated the amorphous nature of all the prepared glasses. The visible–near-infrared red (NIR) absorption spectra of these glasses were analyzed systematically. The NIR emission spectra of Er³⁺ and Nd³⁺:calcium boro fluoro zinc phosphate glasses showed prominent emission bands at 1536 nm (⁴I_13/2→⁴I_15/2) and 1069 nm (⁴F_3/2→⁴I_11/2) respectively with λ_exci = 514.5 nm (Ar⁺ laser) as the excitation source.     

Using the NZ–DNDC model to estimate agricultural N2O emissions in the Manawatu–Wanganui region

Nitrous oxide (N₂O) emissions are difficult to quantify at regional and national scales. There is considerable spatial and temporal variability in N₂O emissions from soil, partly because of variability in the underlying biogenic processes responsible for soil N₂O production. The process-based NZ–DNDC (New Zealand Denitrification-Decomposition) model was used, with georeferenced input data on soils, climate and land use, to map and predict net N₂O emissions from farming in the Manawatu–Wanganui region. The Manawatu–Wanganui region has a temperate, maritime climate and the major agricultural land use is pastoral grazing. We created databases of regional soil, climate and farm management information from various available data sources including national databases of climate, soil type and land use, and national agricultural production statistics. The error introduced by upscaling the model was assessed by comparing results using measured site data with the corresponding predictions using the regional approximations. We also examined the effect of climate conditions by rerunning the 2003 simulation using the climate data for the years ended June 1990 and 2004. The modelled net N₂O emissions for this region for the year ended June 2003 were 4.6?±?1.5 Gg N₂O–N per year. The total fertiliser and excretal N inputs for the region were approximately 224,140 tonnes, so the percentage emitted as N₂O was 2.0?±?0.7%. The modelled net N₂O emissions for the region for the year ended June 1990 were 3.8?±?2.1 Gg N₂O–N per year, indicating annual net N₂O emissions in the Manawatu–Wanganui region between 1990 and 2003 had increased by 0.8?±?0.6 Gg N₂O–N (an increase of about 20%). This change can be attributed to both changes in weather conditions and land use and farm management between 1990 and 2003.     

Fe^2＋-H2O2体系降解壳聚糖

Fe2 -H2O2体系能够有效地降解壳聚糖,反应介质的pH值、反应时间、反应温度、Fe2 浓度及H2O2浓度等实验因素对壳聚糖的降解效果都有程度不同的影响,其中以反应介质的pH值和H2O2浓度对降解反应的影响为最大.在pH值为3～5时Fe2 -H2O2体系降解壳聚糖的活性最高.适当增大H2O2的用量可以增大壳聚糖的降解程度,但当其用量增大至一定程度后,壳聚糖降解产物分子量的下降趋势明显变缓.合理的Fe2 -H2O2体系降解壳聚糖的实验条件为:介质pH值3～5;温度,室温;时间60～90 min;壳聚糖:H2O2:Fe2 =240:12～24:1～2(摩尔比).     

C3−C4 Intermediate species in the genus Flaveria: leaf anatomy,ultrastructure, and the effect of O2 on the CO2 compensation concentration

Leaf anatomical, ultrastructural, and CO₂-exchange analyses of three closely related species of Flaveria indicate that they are C₃–C₄ intermediate plants. The leaf mesophyll of F. floridana J.R. Johnston, F. linearis Lag., and F. chloraefolia A. Gray is typical of that in dicotyledonous C₃ plants, but the bundle sheath cells contain granal, starch-containing chloroplasts. In F. floridana and F. chloraefolia, the chloroplasts and numerous associated mitochondria are arranged largely centripetally, as in the closely related C₄ species, F. brownii A.M. Powell. In F. linearis, fewer mitochondria are present and the chloroplasts are more evenly distributed throughout the bundle sheath cytosol. There is no correlation between the bundle sheath ultrastructure and CO₂ compensation concentration. () values of these C₃–C₄ intermediate Flaveria species. At 21% O₂ and 25°C, for F. chloraefolia, F. linearis, and F. floridana is 23–26, 14–19, and 8–10 l CO₂ l^-1, respectively. The O₂ dependence of is the greatest for F. chloraefolia and F. linearis (similar to that for C₃–C₄ intermediate Panicum and Moricandia species) and the least for F. floridana, whose O₂ response is identical to that for F. brownii from 1.5 to 21% O₂, but greater at higher pO₂. The variation in leaf anatomy, bundle sheath ultrastructure, and O₂ dependence of among these Flaveria species may indicate an active evolution in the pathway of photosynthetic carbon metabolism within this genus.Abbreviations CO₂ compensation concentration - IRGA infrared gas analysis Published as Paper No. 7068, Journal Series, Nebraska Agricultural Experiment Station     

Will elevated CO2 concentrations protect the yield of wheat from O3 damage?

This study investigated the interacting effects of carbon dioxide and ozone concentrations on the growth and yield of spring whet (Triticum aestivum L. cv. Wembley). Plants were exposed from time of sowing to harvest to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO₂] at 350 or 700 μmol mol^?1, and [O₃] at < 5 or 60 nmol mol^?1. Records of leaf emergence, leaf duration and tillering were taken throughout leaf development. At harvest, biomass, yield and partitioning were analysed. Our data showed that elevated [CO₂] fully protected against the detrimental effect of elevated [O₃] on biomass, but not yield.     

Putative role of the malate valve enzyme NADP–malate dehydrogenase in H2O2 signalling in Arabidopsis

In photosynthetic organisms, sudden changes in light intensity perturb the photosynthetic electron flow and lead to an increased production of reactive oxygen species. At the same time, thioredoxins can sense the redox state of the chloroplast. According to our hypothesis, thioredoxins and related thiol reactive molecules downregulate the activity of H₂O₂-detoxifying enzymes, and thereby allow a transient oxidative burst that triggers the expression of H₂O₂ responsive genes. It has been shown recently that upon light stress, catalase activity was reversibly inhibited in Chlamydomonas reinhardtii in correlation with a transient increase in the level of H₂O₂. Here, it is shown that Arabidopsis thaliana mutants lacking the NADP–malate dehydrogenase have lost the reversible inactivation of catalase activity and the increase in H₂O₂ levels when exposed to high light. The mutants were slightly affected in growth and accumulated higher levels of NADPH in the chloroplast than the wild-type. We propose that the malate valve plays an essential role in the regulation of catalase activity and the accumulation of a H₂O₂ signal by transmitting the redox state of the chloroplast to other cell compartments.     

Myoglobin-H2O2 catalyzes the oxidation of β-ketoacids to α-dicarbonyls: mechanism and implications in ketosis

Acetoacetate (AA) and 2-methylacetoacetate (MAA) are accumulated in metabolic disorders such as diabetes and isoleucinemia. Here we examine the mechanism of AA and MAA aerobic oxidation initiated by myoglobin (Mb)/H₂O₂. We propose a chemiluminescent route involving a dioxetanone intermediate whose thermolysis yields triplet α-dicarbonyl species (methylglyoxal and diacetyl). The observed ultraweak chemiluminescence increased linearly on raising the concentration of either Mb (10-500 μM) or AA (10-100 mM). Oxygen uptake studies revealed that MAA is almost a 100-fold more reactive than AA. EPR spin-trapping studies with MNP/MAA revealed the intermediacy of an α-carbon-centered radical and acetyl radical. The latter radical, probably derived from triplet diacetyl, is totally suppressed by sorbate, a well-known quencher of triplet carbonyls. Furthermore, an EPR signal assignable to MNP-AA^• adduct was observed and confirmed by isotope effects. Oxygen consumption and α-dicarbonyl yield were shown to be dependent on AA or MAA concentrations (1-50 mM) and on H₂O₂ or tert-butOOH added to the Mb-containing reaction mixtures. That ferrylMb is involved in a peroxidase cycle acting on the substrates is suggested by the reaction pH profiles and immunospin-trapping experiments. The generation of radicals and triplet dicarbonyl products by Mb/H₂O₂/β-ketoacids may contribute to the adverse health effects of ketogenic unbalance.