Response of holosymbiont pigments from the scleractinian coral Montipora monasteriata to short-term heat stress

Heating the scleractinian coral, Montipora monasteriata (Forskal 1775) to 32 degrees C under < 650 mu mol quanta m(-2) s(-1) led to bleaching in the form of a reduction in Peridinin, xanthophyll pool, chlorophyll c(2) and chlorophyll a, but areal dinoflagellates densities did not decline. Associated with this bleaching, chlorophyll (Chl) allomerization and dinoflagellate xanthophyll cycling increased. Chl allomerization is believed to result from the interaction of Chl with singlet oxygen (O-1(2)) or other reactive oxygen species. Thermally induced increases in Chl allomerization are consistent with other studies that have demonstrated that thermal stress generates reactive oxygen species in symbiotic dinoflagellates. Xanthophyll cycling requires the establishment of a pH gradient across the thylakoid membrane. Our results indicate that, during the early stages of thermal stress, thylakoid membranes are intact. Different morphs of M. monasteriata responded differently to the heat stress applied: heavily pigmented coral hosts taken from a high-light environment showed significant reductions in green fluorescent protein (GFP)-like homologues, whereas nonhost pigmented high-light morphs experienced a significant reduction in water-soluble protein content. Paradoxically, the more shade acclimated cave morph were, based on Chl fluorescence data, less thermally stressed than either of the high-light morphs. These results Support the importance of coral pigments for the regulation of the light environment within the host tissue.

In situ electron paramagnetic resonance (EPR) study of surface oxygen species on Au/ZnO catalyst for low-temperature carbon monoxide oxidation

Some paramagnetic superoxide ions detectable by electron paramagnetic resonance (EPR) can be generated on Au/ZnO catalyst by oxygen adsorption at room temperature as well as at 553 K. In both the cases, the O-2(-) ions are present on the catalyst surface. The disappearance of the O-2(-) signal by the introduction of carbon monoxide over the catalyst surface implies that the O-2(-) ions are either the active oxygen species or the precursors of the active oxygen species. The CO3- species produced are also detected by EPR. (C) 2001 Elsevier Science B.V. All rights reserved.

Soil carbon determination by high temperature combustion - A comparison with dichromate oxidation procedures and the influence of charcoal and carbonate carbon on the measured value

The measurement of organic carbon in soils has traditionally used dichromate oxidation procedures including the Wakley and Black and the Heanes methods. The measurement of carbon in soils by high temperature combustion is now widely used providing a rapid automated procedure without the use of toxic chemicals. This procedure however measures total carbon thus requiring some means of correction for soil samples containing carbonate and charcoal forms of carbon. This paper examines the effects of known additions of charcoal to a range of soil types on the results obtained by the Walkley and Black, Heanes and combustion methods. The results show, that while the charcoal carbon does not react under Walkley and Black conditions, some proportion does so with the Heanes method. A comparison of six Australian Soil and Plant Analysis Council reference soil samples by the three methods showed good agreement between the Heanes method, the combustion method and only slightly lower recoveries by the Walkley and Black procedure. Carbonate carbon will cause an overestimation of soil organic carbon by the combustion method thus requiring a separate determination of carbonate carbon to be applied as a correction. This work shows that a suitable acid pre-treatment of alkaline soils in the sample boats followed by a drying step eliminates the carbonate carbon prior to combustion and the need for an additional measurement. The measurement of carbon in soils by high temperature combustion in an oxygen atmosphere has been shown to be a rapid and reliable method capable of producing results in good agreement with one of the established dichromate oxidation procedures.

Reply to comments on "Oxidation mechanism of Si3N4-bonded SiC ceramics by CO, CO2 and steam," by Balat et al.

First of all, we would like to clarify that the passive to active transition was determined not by using Solgasmix [1], but by combining thermodynamic equilibrium and mass balance for the oxidation of SiC under pure CO2 and pure CO. The model used in our paper [2]was an extension ofWagner’s model [3], in a similar way as Balat et al. [4] did for the oxidation of SiC in oxygen.

Determination of activation energy distributions for chemisorption of oxygen on carbon: an improved approach

The present paper proposes an approach to obtaining the activation energy distribution for chemisorption of oxygen onto carbon surfaces, while simultaneously allowing for the activation energy dependence of the pre-exponential factor of the rate constant. Prior studies in this area have considered this factor to be uniform, thereby biasing estimated distributions. The results show that the derived activation energy distribution is not sensitive to the chemisorption mechanism because of the step function like property of the coverage. The activation energy distribution is essentially uniform for some carbons, and has two or possibly more discrete stages, suggestive of at least two types of sites, each with its own uniform distribution. The pre-exponential factors of the reactions are determined directly from the experimental data, and are found not to be constant as assumed in earlier work, but correlated with the activation energy. The latter results empirically follow an exponential function, supporting some earlier statistical and experimental work. The activation energy distribution obtained in the present paper permits improved correlation of chemisorption data in comparison to earlier studies. (C) 2000 Elsevier Science Ltd. All rights reserved.

Ab initio modelling of basal plane oxidation of graphenes and implications for modelling char combustion

Ab initio calculations have been performed to determine the energetics of oxygen atoms adsorbed onto graphene planes and the possible reaction path extracting carbon atorns in the form of carbon monoxide. Front the energetics it is confirmed that this reaction path will not significantly contribute to the gasification of well ordered carbonaceous chars. Modelling results which explore this limit Lire presented. (C) 2002 Elsevier Science Ltd, All rights reserved.

Anaerobic ammonium oxidation by marine and freshwater planctomycete-like bacteria

Recently, two fresh water species, 'Candidatus Brocadia anammoxidans' and 'Candidatus Kuenenia stuttgartiensis', and one marine species, 'Candidatus Scalindua sorokinii', of planctomycete anammox bacteria have been identified. 'Candidatus Scalindua sorokinii' was discovered in the Black Sea, and contributed substantially to the loss of fixed nitrogen. All three species contain a unique organelle-the anammoxosome-in their cytoplasm. The anammoxosome contains the hydrazine/hydroxylamine oxidoreductase enzyme, and is thus the site of anammox catabolism. The anammoxosome is surrounded by a very dense membrane composed almost exclusively of linearly concatenated cyclobutane-containing lipids. These so-called 'ladderanes' are connected to the glycerol moiety via both ester and ether bonds. In natural and man-made ecosystems, anammox bacteria can cooperate with aerobic ammonium-oxidising bacteria, which protect them from harmful oxygen, and provide the necessary nitrite. The cooperation of these two groups of ammonium-oxidising bacteria is the microbial basis for a sustainable one reactor system, CANON (completely autotrophic nitrogen-removal over nitrite) to remove ammonia from high strength wastewater.

Anodic behaviour of arsenopyrite and cathodic reduction of ferrate(VI) and oxygen in alkaline solutions

This paper presents the results of an electrochemical study of the anodic characteristics of arsenopyrite in strongly alkaline solutions and of the cathodic reduction of ferrate( VI) and of dissolved oxygen at an arsenopyrite surface at potentials which are relevant to the oxidation reactions. Cyclic voltammetry at both arsenopyrite disc and arsenopyrite disc/platinum ring electrodes has shown that arsenic(III) is the main product of the anodic process at potentials in the region of the rest potential during oxidation by either ferrate( VI) or oxygen. Evidence for partial passivation of both the anodic and cathodic reactions has been obtained from potentiostatic current - time transients. The initial stage of oxidation by ferrate( VI) has been shown to be mass-transport controlled and this is also true of the oxidation by oxygen in dilute solutions of sodium hydroxide.

Walking performance, oxygen uptake kinetics and resting muscle pyruvate dehydrogenase complex activity in peripheral arterial disease

In the present study, we tested the hypothesis that walking intolerance in intermittent claudication (IC) is related to both slowed whole body oxygen uptake (Vo(2)) kinetics and altered activity of the active fraction of the pyruvate dehydrogenase complex (PDCa) in skeletal muscle. Ten patients with IC and peripheral arterial disease [ankle/brachial index (ABI) = 0.73 +/- 0.13] and eight healthy controls (ABI = 1. 17 +/- 0.13) completed three maximal walking tests. From these tests, averaged estimates of walking time, peak Vo(2) and the time constant of Vo(2) (tau) during submaximal walking were obtained. A muscle sample was taken from the gastrocnemius medialis muscle at rest and analysed for PDCa and several other biochemical variables. Walking time and peak Vo(2) were approx. 50 % lower in patients with IC than controls, and tau was 2-fold higher (P < 0.05). r was significantly correlated with walking time (r = -0.72) and peak Vo(2) (r = -0.66) in patients with IC, but not in controls. PDCa was not significantly lower in patients with IC than controls; however, PDCa tended to be correlated with tau (r = -0.56, P = 0.09) in patients with IC, but not in controls (r = -0.14). A similar correlation was observed between resting ABI and tau (r = -0.63, P = 0.05) in patients with IC. These data suggest that the impaired Vo(2) kinetics contributes to walking intolerance in IC and that, within a group of patients with IC, differences in Vo(2) kinetics might be partly linked to differences in muscle carbohydrate oxidation.

Endurance exercise, plasma oxidation and cardiovascular risk

Objective-Although physical activity is beneficial to health, people who exercise at high intensities throughout their lifetime may have increased cardiovascular risk. Aerobic exercise increases oxidative stress and may contribute to atherogenesis by augmented oxidation of plasma lipoproteins. The aim of this study was to examine the relationship between aerobic power and markers of oxidative stress, including the susceptibility of plasma to oxidation. Methods and results-Aerobic power was measured in 24 healthy men aged 29 9 years (mean +/- SD). Plasma was analysed from subjects of high aerobic power (HAP; VO(2)max, 64.6 +/- 6.1 ml/kg/min) and lower aerobic power (LAP;VO(2)max, 45.1 +/- 6.3 ml/kg/min) for total antioxidant capacity (TAC), malondialdehyde (MDA) and susceptibility to oxidation. Three measures were used to quantify plasma oxidizability: (1) lag time to conjugated diene formation (lag time); (2) change in absorbance at 234 nm and; (3) slope of the oxidation curve during propagation (slope). The HAP subjects had significantly lowerTAC (1.38 +/- 0.04 versus 1.42 +/- 0.06 TEAC units; P < 0.05), significantly higher change in absorbance (1.55 +/- 0.21 versus 1.36 +/- 0.17 arbitrary units; P < 0.05), but no difference in MDA (P = 0.6), compared to LAP subjects. There was a significant inverse association between TAC and slope (r = -0.49; P < 0.05). Lipoprotein profiles and daily intake of nutrients did not differ between the groups. Conclusions-These findings suggest that people with high aerobic power, due to extreme endurance exercise, have plasma with decreased antioxidant capacity and higher susceptibility to oxidation, which may increase their cardiovascular risk.

Calibration of the channel that determines the omega-hydroxylation regiospecificity of cytochrome P4504A1 - Catalytic oxidation of 12-halododecanoic acids

The fatty acid omega-hydroxylation regiospecificity of CYP4 enzymes may result from presentation of the terminal carbon to the oxidizing species via a narrow channel that restricts access to the other carbon atoms. To test this hypothesis, the oxidation of 12-iodo-, 12-bromo-, and 12-chlorododecanoic acids by recombinant CYP4A1 has been examined. Although all three 12-halododecanoic acids bind to CYP4A1 with similar dissociation constants, the 12-chloro and 12-bromo fatty acids are oxidized to 12-hydroxydodecanoic acid and 12-oxododecanoic acid, whereas the 12-iodo analogue is very poorly oxidized. Incubations in (H2O)-O-18 show that the 12-hydroxydodecanoic acid oxygen derives from water, whereas that in the aldehyde derives from O-2. The alcohol thus arises from oxidation of the halide to an oxohalonium species that is hydrolyzed by water, whereas the aldehyde arises by a conventional carbon hydroxylation-elimination mechanism. No irreversible inactivation of CYP4A1 is observed during 12-halododecanoic acid oxidation. Control experiments show that CYP2E1, which has an omega-1 regiospecificity, primarily oxidizes 12-halododecanoic acids to the omega-aldehyde rather than alcohol product. Incubation of CYP4A1 with 12,12-[H-2](2)-12-chlorododecanoic acid causes a 2-3-fold increase in halogen versus carbon oxidation. The fact that the order of substrate oxidation (Br > Cl >> I) approximates the inverse of the intrinsic oxidizability of the halogen atoms is consistent with presentation of the halide terminus via a channel that accommodates the chloride and bromide but not iodide atoms, which implies an effective channel diameter greater than 3.90 angstrom but smaller than 4.30 angstrom.

Oxidation mechanism of Si3N4-bonded SiC ceramics by CO, CO2 and steam

This paper presents a theoretical and experimental investigation into the oxidation reactions of Si3N4-bonded SiC ceramics. Such ceramics which contain a small amount of silicon offer increased oxidation and wear resistance and are widely used as lining refractories in blast furnaces. The thermodynamics of oxidation reactions were studied using the JANAF tables. The weight gain was measured using a thermogravimetric analysis technique to study the kinetics. The temperature range of oxidation measurements is from 1073 to 1573 K and the oxidation atmosphere is water vapour, pure CO and CO-CO2 gas mixtures with various CO-to-CO2 ratios. Thermodynamic simulations showed that the oxidation mechanism of Si3N4-bonded SiC ceramics is passive oxidation and all components contribute to the formation of a silica film. The activated energies of the reactions follow the sequence Si3N4>SiC>Si. The kinetic study revealed that the oxidation of Si3N4-bonded SiC ceramics occurred in a mixed regime controlled by both interface reaction and diffusion through the silica film. Under the atmosphere conditions prevailing in the blast furnace, this ceramic is predicted to be passively oxidized with the chemical reaction rate becoming more dominant as the CO concentration increases. (C) 1998 Chapman & Hall.

Geochemical mass-balance and oxygen-isotope constrains on silcrete formation and its paleoclimatic implications in Southern Australia

Two geographically distinct silcrete associations are present in southern Australia, inland and eastern; these were sampled in central South Australia and central Victoria, respectively, At each site, both silicified and immediately adjacent unsilicified parent material were collected. Analytical data from these pairs were used to construct isocons, assuming Zr immobility, and to calculate the volume change and amount of silica introduced during silicification, These results, together with whole-rock oxygen isotope compositions, were used to determine the delta(18)O of th, introduced silica, The results show that the eastern silcretes in central Victoria are probably linked genetically to the associated basalts, weathering of which supplied the introduced silica, This conclusion is based on the close spatial connection between the two, as well as the substantial amount of introduced silica in the silcretes (greater than in the inland silcretes), resulting in volume increases in some eastern silcretes, Oxygen isotopic calculations for the silcretes indicate that the silica precipitated from groundwaters at temperatures slightly higher than present conditions. Silcrete formation apparently occurred during the Miocene and Pliocene (basalts in Victoria younger than Pliocene lack associated silcrete) and may reflect the much wetter climate in southeastern Australia at that time. The inland silcretes of central South Australia can be divided into pedogenic (the most common) and groundwater varieties. The pedogenic silcretes, which show typical soil features like columnar and nodular textures, contain moderate amounts of introduced silica that precipitated by evaporation from saline groundwaters, For the groundwater silcretes, which have massive textures and formed at or close to the water table, insufficient data are available to determine the mode of formation. The inland pedogenic silcretes have probably been farming from the Eocene-Miocene to the present, implying that conditions of seasonally high evaporation have occurred in central Australia during this time period. Thus silcrete formation depends on a complex interplay between climate and silica supply, and it is impossible to generalize that the presence of silcrete is indicative of a particular climate. Likewise, the elemental composition of silcretes, particularly Ti content, is not necessarily of climatic significance, Nevertheless, detailed geochemical and oxygen isotopic studies of a silcrete and its parent material can elucidate the mechanisms of silcrete formation, and if evaporation is indicated as a major factor in silcrete formation, then the climate at the time was likely to have been at least seasonally arid.

Solution structure of methionine-oxidized amyloid beta-peptide (1-40). Does oxidation affect conformational switching?

The solution structure of A beta(1-40)Met(O), the methionine-oxidized form of amyloid beta-peptide A beta(1-40), has been investigated by CD and NMR spectroscopy. Oxidation of Met35 may have implications in the aetiology of Alzheimer's disease. Circular dichroism experiments showed that whereas A beta(1-40) and A beta(1-40)Met(O) both adopt essentially random coil structures in water (pH 4) at micromolar concentrations, the former aggregates within several days while the latter is stable for at least 7 days under these conditions. This remarkable difference led us to determine the solution structure of A beta(1-40)Met(O) using H-1 NMR spectroscopy. In a water-SDS micelle medium needed to solubilize both peptides at the millimolar concentrations required to measure NMR spectra, chemical shift and NOE data for A beta(1-40)Met(O) strongly suggest the presence of a helical region between residues 16 and 24. This is supported by slow H-D exchange of amide protons in this region and by structure calculations using simulated annealing with the program XPLOR. The remainder of the structure is relatively disordered. Our previously reported NMR data for A beta(1-40) in the same solvent shows that helices are present over residues 15-24 (helix 1) and 28-36 (helix 2), Oxidation of Met35 thus causes a local and selective disruption of helix 2. In addition to this helix-coil rearrangement in aqueous micelles, the CD data show that oxidation inhibits a coil-to-beta-sheet transition in water. These significant structural rearrangements in the C-terminal region of A beta may be important clues to the chemistry and biology of A beta(1-40) and A beta(1-42).

The chemistry of copper patination

The chemistry of copper patination was investigated by two series of experiments. The chemistry of an aqueous copper-sulphate solution was studied at concentrations and pH values near those predicted in an electrolyte on copper exposed to the atmosphere. The electrochemical reactions in an electrolyte in contact with cuprite were investigated in a reaction vessel which used cuprite powder in artificial rainwater to study the electrochemistry of the atmospheric corrosion and patination of copper. Typical sulphate concentrations in rainwater are sufficient to precipitate posnjakite (Cu4SO4(OH)(6)2H(2)O)), a possible precursor to brochantite, within an hour of wetting a cuprite surface. Brochantite (Cu4SO4(OH)(6)), the most commonly found copper salt in natural patinas is responsible for their green appearance. Precipitation of brochantite from the electrolyte resulted from an increase in pH due to the cathodic reduction of oxygen and an increase in cupric ion concentrations by cuprite oxidation. (C) 1998 Elsevier Science Ltd. All rights reserved.