Autoxidation and Photosensitized Oxidation of Methyl Eicosapentaenoate: Secondary Oxidation Products

Methyl eicosapentaenoate (methyl 5,8,11,14,17-eicosapentaenoate) was subjected to autoxidation and methylene blue-sensitized photooxidation. The secondary oxidation products were separated, and characterized by gas chromatography-mass spectrometry. The autoxidation products included hydroperoxy endoperoxide isomers, prostaglandin-like hydroperoxy bicyclic endoperoxide isomers and 5,18-dihydroperoxide. The photosensitized oxidation products included only dihydroperoxide isomers as the secondary products.     

Nitrate-Dependent Ferrous Iron Oxidation by Anaerobic Ammonium Oxidation (Anammox) Bacteria

We examined nitrate-dependent Fe²⁺ oxidation mediated by anaerobic ammonium oxidation (anammox) bacteria. Enrichment cultures of “Candidatus Brocadia sinica” anaerobically oxidized Fe²⁺ and reduced NO₃⁻ to nitrogen gas at rates of 3.7 ± 0.2 and 1.3 ± 0.1 (mean ± standard deviation [SD]) nmol mg protein⁻¹ min⁻¹, respectively (37°C and pH 7.3). This nitrate reduction rate is an order of magnitude lower than the anammox activity of “Ca. Brocadia sinica” (10 to 75 nmol NH₄⁺ mg protein⁻¹ min⁻¹). A ¹⁵N tracer experiment demonstrated that coupling of nitrate-dependent Fe²⁺ oxidation and the anammox reaction was responsible for producing nitrogen gas from NO₃⁻ by “Ca. Brocadia sinica.” The activities of nitrate-dependent Fe²⁺ oxidation were dependent on temperature and pH, and the highest activities were seen at temperatures of 30 to 45°C and pHs ranging from 5.9 to 9.8. The mean half-saturation constant for NO₃⁻ ± SD of “Ca. Brocadia sinica” was determined to be 51 ± 21 μM. Nitrate-dependent Fe²⁺ oxidation was further demonstrated by another anammox bacterium, “Candidatus Scalindua sp.,” whose rates of Fe²⁺ oxidation and NO₃⁻ reduction were 4.7 ± 0.59 and 1.45 ± 0.05 nmol mg protein⁻¹ min⁻¹, respectively (20°C and pH 7.3). Co-occurrence of nitrate-dependent Fe²⁺ oxidation and the anammox reaction decreased the molar ratios of consumed NO₂⁻ to consumed NH₄⁺ (ΔNO₂⁻/ΔNH₄⁺) and produced NO₃⁻ to consumed NH₄⁺ (ΔNO₃⁻/ΔNH₄⁺). These reactions are preferable to the application of anammox processes for wastewater treatment.     

Peroxidase Oxidation of Phenols

Partially purified preparations of horseradish peroxidase were able to catalyze the effective transformation of such phenol compounds as phenol, o-chlorophenol, 2,4,6-trichlorophenol, pentachlorophenol (giving rise to the formation of polymer products insoluble in water), resorcinol, and thymol (giving rise to the formation of low-molecular-weight products). The following conditions were found to be optimal for peroxidase oxidation and provide the maximum extent of elimination of phenol compounds: temperature, 15–25 and 25–30°C for phenol and chlorophenol compounds, respectively; molar ratio H₂O₂/phenol, 1 : 1; and transformation time, 1–3 h. Although effective transformation was observed within a broad range of pH, the efficiency of the process slightly increased at a pH from 6.0 to 7.5. It was suggested to carry out multiple peroxidase oxidations of phenols using partially purified peroxidase enclosed in a dialysis membrane bag placed into a solution of a phenol compound containing hydrogen peroxide.     

Oxidation states of peroxidase

Summary Five oxidation states of horseradish peroxidase, ferrous, ferric, Compounds I and II, oxy-ferrous, are known. Various reactions and plausible structures of these states are reported. Mechanisms of peroxidase-oxidase reactions are discussed in terms of the five oxidation states of the enzyme.an invited article     

Oxidation of anthracycline antibiotics

The quantum-chemical estimation of the highest occupied molecular orbital energy for the aglycons of carminomycin, rubomycin, adriamycin and aclacinomycin A in the neutral and ionized states was performed with a semiempirical method. It was shown that the aglycon ionization amplified the electron donor properties of the antibiotics. On the basis of the difference in the absorption spectra of the neutral and ionized chromophores their ionization constants were determined spectrophotometrically. For comparison of the electron donor properties of the anthracyclines at the physiological pH value the reaction of their oxidation with potassium ferricyanide accompanied by decoloration of the solutions was studied. On the basis of the quantum-chemical and experimental data it was concluded that the electron donor properties amplified as follows: aclacinomycin A less than adriamycin-rubomycin less than carminomycin. At the same time their acute toxicity increased (a decrease in the LD50). Therefore, the toxicity of the anthracycline antibiotics could be also due to formation of the radicals with high reactivity on the monoelectronic oxidation.     

Atmospheric Oxidation of Hydrocarbons

Hydrocarbon oxidation in the atmosphere proceeds generally by the following sequence of reactions: hydrocarbon + OH → alkyl radical + H₂O, alkyl radical + O,(³I) → alkylperoxy radical, alkylperoxy radical + NO → alkoxy radical + NO₂, alkoxy radical + O₂(³X) -→ aldehyde + HO,. The atmospheric lifetimes of hydrocarbons are determined by their reactivity towards OH as well as by the average OH concentration level. They are compound specific and vary from several hours to several years. Hydrocarbon oxidation chains couple with other trace gases (O_v, HO_x, and NO_v). For the conditions of the average continental atmosphere an increase of the oxidative potential (HO_v, O_x) is predicted through hydrocarbon oxidation.