The reactivity of [Fe (tpena)] (tpena=N,N,N'-tris(2-pyridylmethyl)ethylenediamine-N'-acetate) as a catalyst for oxidation reactions depends on its ratio to the terminal oxidant H O and presence or absence of sacrificial substrates. The outcome can be switched between: 1) catalysed H O disproportionation, 2) selective catalytic oxidation of methanol or benzyl alcohol to the corresponding aldehyde, or 3) oxidative decomposition of the tpena ligand. A common mechanism is proposed involving homolytic O-O cleavage in the detected transient purple low-spin (S=1/2 ) [(tpenaH)Fe O-OH] . The resultant iron(IV) oxo and hydroxyl radical both participate in controllable hydrogen-atom transfer (HAT) reactions. Consistent with the presence of a weaker σ-donor carboxylate ligand, the most pronounced difference in the spectroscopic properties of [Fe(OOH)(tpenaH)] and its conjugate base, [Fe(OO)(tpenaH)] , compared to non-heme iron(III) peroxide analogues supported by neutral multidentate N-only ligands, are slightly blue-shifted maxima of the visible absorption band assigned to ligand-to-metal charge-transfer (LMCT) transitions and, corroborating this, lower Fe /Fe redox potentials for the pro-catalysts.

Oxygen (O(2)) availability and diffusivity in wetlands are controlling factors for the production and consumption of both carbon dioxide (CO(2)) and methane (CH(4)) in the subsoil and thereby potential emission of these greenhouse gases to the atmosphere. To examine the linkage between high-resolution spatiotemporal trends in O(2) availability and CH(4)/CO(2) dynamics in situ, we compare high-resolution subsurface O(2) concentrations, weekly measurements of subsurface CH(4)/CO(2) concentrations and near continuous flux measurements of CO(2) and CH(4). Detailed 2-D distributions of O(2) concentrations and depth-profiles of CO(2) and CH(4) were measured in the laboratory during flooding of soil columns using a combination of planar O(2) optodes and membrane inlet mass spectrometry. Microsensors were used to assess apparent diffusivity under both field and laboratory conditions. Gas concentration profiles were analyzed with a diffusion-reaction model for quantifying production/consumption profiles of O(2), CO(2), and CH(4). In drained conditions, O(2) consumption exceeded CO(2) production, indicating CO(2) dissolution in the remaining water-filled pockets. CH(4) emissions were negligible when the oxic zone was >40 cm and CH(4) was presumably consumed below the depth of detectable O(2). In flooded conditions, O(2) was transported by other mechanisms than simple diffusion in the aqueous phase. This work demonstrates the importance of changes in near-surface apparent diffusivity, microscale O(2) dynamics, as well as gas transport via aerenchymous plants tissue on soil gas dynamics and greenhouse gas emissions following marked changes in water level.

Aims: Staphylococcus xylosus is an important starter culture in the production of flavours from the branched-chain amino acids leucine, valine and isoleucine in fermented meat products. The sensorially most important flavour compounds are the branched-chain aldehydes and acids derived from the corresponding amino acids and this paper intends to perspectivate these flavour compounds in the context of leucine metabolism. Methods and Results: GC and GC/MS analysis combined with stable isotope labelling was used to study leucine catabolism. This amino acid together with valine and isoleucine was used as precursors for the production of branched-chain fatty acids for cell membrane biosynthesis during growth. A 83AE3% of the cellular fatty acids were branched. The dominating fatty acid was anteiso-C 15:0 that constituted 55% of the fatty acids. A pyridoxal 5¢-phosphate and a-ketoacid dependent reaction catalysed the deamination of leucine, valine and isoleucine into their corresponding a-ketoacids. As a-amino group acceptor a-keto-b-methylvaleric acid and a-ketoisovaleric acid was much more efficient than a-ketoglutarate. The sensorially and metabolic key intermediate on the pathway to the branched-chain fatty acids, 3-methylbutanoic acid was produced from leucine at the onset of the stationary growth phase and then, when the growth medium became scarce in leucine, from the oxidation of glucose via pyruvate. Conclusions: This paper demonstrates that the sensorially important branched-chain aldehydes and acids are important intermediates on the metabolic route leading to branched-chain fatty acids for cell membrane biosynthesis. Significance and Impact of the Study: The metabolic information obtained is extremely important in connection with a future biotechnological design of starter cultures for production of fermented meat.

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A complex mixture of methyl-branched alkyl-substituted pyrazines was found in the growth medium of the polymyxin-producing bacterium Paenibacillus polymyxa, and of these, seven are new natural compounds. A total of 19 pyrazine metabolites were identified. The dominant metabolite was 2,5-diisopropylpyrazine as identified using a combination of high-resolution mass spectrometry, (1)H- and (13)C-nuclear magnetic resonance, gas chromatography-mass spectrometry as well as co-elution with an authentic standard. Its biosynthesis was correlated with growth and production was strongly stimulated by valine supplementation. The other pyrazine metabolites, all related pyrazines with either one, two or three alkyl substituents, were identified by means of their mass spectral data and/or co-elution with authentic standards.