Dark Oxidation Research Articles

Temperature dependence of the reactions of HO2 with NO and NO2

Abstract Mixtures of N2O, H2, O2, and trace amounts of NO and NO2 were photolyzed at 213.9 nm, at 245°–328°K, and at about 1 atm total pressure (mostly H2). HO2 radicals are produced from the photolysis and they react as follows: equation image Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k1a/k31/2 = 6.4 × 10−6 exp { z−(1400 ± 500)/RT} cm3/2/sec1/2. If k3 is taken to be 3.3 × 10−12 cm3/sec independent of temperature, k1a = 1.2 × 10−11 exp {−(1400 ± 500)/RT} cm3/sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k2b/k1 = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k1a given above leads to k2b = 4.2 × 10−13 cm3/sec, which is assumed to be independent of temperature. The intermediate HO2NO2 is unstable and induces the dark oxidation of NO through reaction (−2b), which was found to have a rate coefficient k−2b = 6 × 1017 exp {−26,000/RT} sec−1 based on the value of k1a given above. The intermediate can also decompose via equation image Reaction (10b) is at least partially heterogeneous.

PH dependent changes in the reactivity of the primary electron acceptor of System II in spinach chloroplasts to external oxidant and reductant

pH dependent changes in the reactivity of the primary electron acceptor of System II in spinach chloroplasts to external oxidant and reductant

FLAVIN‐MEDIATED PHOTOREACTIONS IN ARTIFICIAL SYSTEMS: A POSSIBLE MODEL FOR THE BLUE‐LIGHT PHOTORECEPTOR PIGMENT IN LIVING SYSTEMS*

Abstract— The photoreduction of cytochrome c and the photostimulation of oxygen uptake were studied in solutions of flavin and cytochrome as a possible model system for similar photoreactions which have been observed in vivo. Light causes the photoreduction of the flavin. Under aerobic conditions the photoreduced flavin reacts with oxygen to form the superoxide anion which in turn can reduce cytochrome c. Dismutation of the superoxide anions forms hydrogen peroxide which mediates the dark oxidation of the photoreduced cytochrome. Superoxide formation and dismutation also account for the light‐induced oxygen uptake. Action spectra confirm the role of flavin in the photoreduction of cytochrome c and the photostimulation of oxygen uptake. Under anaerobic conditions the photoreduced flavin reduces cytochrome c directly. In the presence of an electron donor only catalytic amounts of flavin are required. In the absence of an added electron donor flavin itself can act as the electron donor if substrate amounts are present. Azide inhibits all of these flavin‐mediated photoresponses. Azide also inhibits the photoreduction of cytochrome b which occurs in the mycelium of Newospora.

Dark and photochemical oxidation reaction of 1-ethoxy-2-ethylthioethene stereoisomers

1. We were the first to identify the oxidation product of 1-ethoxy-2-ethylthioethene as being the diethyl monothioacetal of glyoxal; it proved that the dark oxidation of 1-ethoxy-2-ethylthioethene with molecular oxygen to glyoxal diethyl monothioacetal is possible only for the cis-isomer. 2. A method was developed for the photochemical oxidation of the trans-isomer of 1-ethoxy-2-ethylthioethene, adsorbed on porous glass, to the diethyl monothioacetal. 3. Based on the kinetic and stereochemical characteristics of the reaction, a mechanism was proposed for the oxidation process, which includes the formation of an intermediate complex from two molecules of the oxidized substrate and one molecule of oxygen. 4. It was established by the EPR method that the O2− ion-radical is formed in the photochemical oxidation of trans-1-ethoxy-2-ethylthioethene, which takes part in the oxidation process.

A Study of the Control of Glycolate Excretion in Chlorella

Chlorella pyrenoidosa cells grown on 5% CO(2) excreted glycolate when incubated in light with 10 mm bicarbonate, but excreted no glycolate under the same conditions when they were maintained on air for 7 hours prior to the assay. Incubation of 5% CO(2)-grown and air-grown cells with 10 mm isonicotinyl hydrazide or 10 mm alpha-hydroxypyridinemethane sulfonate during the assay stimulated the excretion of glycolate by CO(2)-grown cells severalfold that of air-grown cells.Adaptation of CO(2)-grown Chlorella to growth on air did not affect the levels of glycolate dehydrogenase in the cells and did not affect the rate of dark oxidation and metabolism of exogeneous (14)C-glycolate by the cells. These results indicate that the lack of glycolate excretion by air-grown or air-adapted cells of Chlorella cannot be explained by a concomitant change in the level of glycolate dehydrogenase.

A light-initiated, dark oxidation of bacteriochlorophyll from reaction center particles

A light-initiated, dark oxidation of bacteriochlorophyll from reaction center particles

The role of cytochrome b6 in cyclic electron transport: Evidence for an energy-coupling site in the pathway of cytochrome b6 oxidation in spinach chloroplasts

The role of cytochrome b6 in cyclic electron transport: Evidence for an energy-coupling site in the pathway of cytochrome b6 oxidation in spinach chloroplasts

アルミニウムの電解発色皮膜の研究

Integrally colored anodic coating of aluminum was obtained by electrolysis in aqueous solution of sulfo-salicylic acid. The properties and micro-structure of the coating were studied by X-ray diffraction and micro-analyses.The color difference was measured as a function of electrolysis time.The results obtained were as follows:1) The oxide coating of sulfo-salicylic acid was observed amorphous by X-ray analysis, but it turned to the structure of γ-Al2O3 by heating to about 700°C.2) The dark brown colored oxide coating of sulfo-salicylic acid turned to pale pink by heating at 700-900°C. Therefore, it was supposed that the color component would consist of some substance changing its color tone by heating at 700-900°C.The relation between the color difference and the time of electrolysis was expressed by the following equation:y=17.5 log T-11.5where y: Color difference (NBS)T: Time of electrolysis (min.)The depth of color of the coating increased with time of electrolysis and finally reached saturated state.

Multiple light-induced reactions of cytochromes b and c in Rhodopseudomonas spheroides.

Illumination of chromatophore preparations from Rhodopseudomonas spheroides causes the oxidation of a cytochrome c and a slight oxidation of a cytochrome b with a maximum at 560nm. When illuminated in the presence of antimycin A the oxidation of cytochrome c was more pronounced and cytochrome b(560) was reduced; the dark oxidation of cytochrome b(560) was biphasic in the presence of succinate, but not in the presence of NADH, a less effective reductant. Split-beam spectroscopy showed that, in addition to the reduction of cytochrome b(560), another pigment with maxima at 565 and 537nm. was reduced and was more rapidly oxidized in the dark than cytochrome b(560). This pigment, tentatively identified as cytochrome b(565), was also detected in spectra at 77 degrees k, after brief illumination at room temperature; the maxima at 77 degrees k were at 562 and 536nm. In the absence of antimycin A, light caused a transient reduction of cytochrome b(565) and an oxidation of cytochrome b(560). Dark oxidation of b(565) was rapid, even in the presence of antimycin A and succinate. Difference spectra, at 77 degrees k, of ascorbate-reduced minus succinate-reduced chromatophores or of anaerobic succinate-reduced minus aerobic succinate-reduced chromatophores suggested that two cytochromes c were present, with maxima at 547 and 549nm. When chromatophores frozen at 77 degrees k were illuminated both these cytochromes c were oxidized, indicating a close association with the photochemical reaction centre. A scheme involving two reaction centres is proposed to explain these results.

Studies on the respiratory system of aerobically (dark) and anaerobically (light) grown Rhodospirillum rubrum.

1. A major part of the respiratory activity of light grown cells of Rhodospirillum rubrum is associated with a system identical with that found in dark grown cells. 2. The specific activity of NADH and succinate dehydrogenase and cytochrome c reductase on a protein basis is the same in the particulate fraction from photosynthetic and aerobic cells. In contrast, the NADH and succinate oxidase is more than four times higher in the aerobic cells. Since the amount of particulate protein per cell is almost four-fold less in the aerobic cells, the total particle bound capacity for NADH and succinate oxidation per cell is approximately the same regardless of whether the cells were grown photosynthetically or aerobically. 3. The effect of various inhibitors of NADH oxidation was compared in the particulate fraction from aerobically and anaerobically grown cells. 4,5,6,7-Tetrachloro-2-trifluoromethylbenzimidazole (TTFB) was found to be a potent inhibitor of NADH and succinate oxidation; one-half maximal inhibition was observed at 0.5 μM. Rotenone and amytal inhibited about 80%. 4. In particles from photosynthetically grown cells respiration was inhibited to a maximum of 45–70% by KCN and TTFB; whereas in aerobically grown cells these inhibitors consistently inhibited maximally by more than 70%. 5. NADH oxidation was inhibited 35–50% by light in chromatophore preparations. Antimycin a relieved the light inhibition. In the presence of antimycin a and m-chlorocarbonyl cyanide phenylhydrazone, light stimulated NADH oxidation and the oxidation was not sensitive to KCN. 6. 2-Hydroxy-3-(ω-cyclohexyloctyl)-1,4-naphthoquinone which had little effect on dark NADH oxidation inhibited the light stimulated oxidation. 7. These results indicate that at least three pathways exist for NADH oxidation in chromatophores: a) KCN sensitive which is characteristic of aerobically grown cells; b) KCN insensitive which appears to be part of the cyclic photochemical pathway; and c) the rotenone insensitive pathway.

CINETIQUE DES ECHANGES D'OXYGENE ET DE LA FLUORESCENCE DES CHLOROPLASTES ISOLES

Abstract Oxygen evolution and fluorescence have been studied with isolated chloroplasts illuminated, in the absence of Hill reagents, by flashes or continuous light. As in whole cells, at least two substances are involved in the primary process leading to the oxygen evolution. The first, called E, probably is the photochemical “complex” of System II. After a long period of darkness, E is not active. It is activated in two steps. Step one is a photochemical reaction, induced by a quantum of light absorbed by pigment‐system II, which results in the production of E in a reduced state. Step two is a dark oxidation of the reduced E by the second substance, A. The oxidized E can then enter the normal photochemical cycle of system II. Reduced E might alternatively be oxidized by oxygen, this reaction being responsible for a very rapid and brief light‐induced oxygen uptake. Substance A is measured by the oxygen burst and is present in the chloroplasts at the approximate ratio of 1 molecule for 70 molecules of total chlorophyll while E is at the ratio of about 1/2800. This gives a E over A value of 1/35 which is much smaller than the one found in whoe cells (ca. 1/10). This independent behavior of E and A suggests that chloroplast extraction destroys some photochemical centers without having a direct impact on A, which might diffuse from one center to another. Besides the brief light‐induced oxygen uptake above mentioned, there is another one which is related to System I functioning.The kinetics of the oxygen evolution and of the fluorescence have been compared. During the activation process of the oxygen evolving ability, rate of oxygen evolution and fluorescence yield increase in a parallel way. After the maximum velocity of the oxygen burst is reached (i.e. after activation), the fluorescence yield keeps growing up until the steady‐state is attained (with an intermediary plateau), whereas the rate of oxygen emission slows down. The time‐course curves of fluorescence obtained with inactivated or activated chloroplasts are essentially different in that the initial yield is higher in the latter case.

The formation of a quencher of the fluorescence of chromatophores from photosynthetic bacteria.

The formation of a quencher of the fluorescence of chromatophores from photosynthetic bacteria.

Some Observations on the Oxidation of Rubber in Light

Abstract An apparatus is described for measuring the oxygen absorption of vulcanized rubber, either in darkness or under illumination from a controlled light source. The light and dark oxidation curves of four vulcanizates at temperatures of 60°, 65°, and 70° C are examined. Three of the four vulcanizates were protected by the incorporation, respectively, of 2 per cent phenyl-β-naphthylamine, 2 per cent mercaptobenzimidazole, and a mixture of 1 per cent each of the above substances. The dark reaction over 60 hours' duration was in all cases similar and could be represented by a standard equation. It is shown that the effects of PBN and MBI on the dark oxidation are clearly different throughout the temperature ranges. From a consideration of the initial reaction, the decay during storage of the initial oxidizability of the vulcanizates is shown. In oxidation under light from a relatively weak source at a given temperature, the total absorption is considered as the sum of the dark thermal oxidation appropriate to the temperature, and a light-activated absorption. The effect of the light is then shown to be similar in all cases, the rate of absorption due to light starting from zero and increasing through a maximum to a constant value. By comparison of these constant light rates, it is shown that PBN and MBI have little effect on the light-activated absorption of the control, but that the mixture (PBN, MBI) effectively reduces this absorption. The persistence or development of an enhanced dark rate after illumination is shown to depend on the period of illumination and the length of dark storage of the vulcanizate.