Addition Of Methyl Viologen Research Articles

Mechanism of photoinduced redox reactions in aqueous solutions of [Fe(bpy)(CN) 4] 2−

The mechanism of redox reactions initiated by UV excitation of [Fe(bpy)(CN) 4] 2− in aqueous solutions has been investigated by continuous photolysis, laser kinetic spectroscopy and pulse radiolysis. Hydrated electrons formed in the light induced reaction are shown to react with ground state [Fe(bpy)(CN) 4] 2− to form [Fe(bpy)(CN) 4] 3− characterized by its absorption spectra and reactions. The back reaction between [Fe(bpy)(CN) 4] − and [Fe(bpy)(CN) 4] 3− takes place with kl.8±4x10 10 M −1 s −1. The quantum yield of solvated electron formation determined by using nitrate ions as electron scavenger is 0.14±0.01 and 0.068±0.007 at μ∼ 0.01 and μ∼ 1.0, respectively. Addition of methylviologen (MV 2+) to the solution of iron(II) complex leads to production of MV+ via direct electron scavenging and an electron transfer reaction from [Fe(bpy)(CN) 4] 3−. The latter process takes place with k = 9.0±0.6 x 10 9 M −1 s −1. The decay of MV + occurs in reactions with both iron(III) and iron(II) complexes.

Electrochemical investigation of dihexadecyl phosphate vesicle incorporated colloidal cadmium sulfide particles

Photocurrents, generated upon irradiation of dihexadecylphosphate (DHP) incorporated cadmium sulfide (CdS) solutions containing glucose, have been determined in a three-compartment electrochemical cell with a 3.0-mm{sup 2} platinum-disk working electrode in the absence of supporting electrolytes. Addition of methylviologen, MV{sup 2+}, as electron acceptor significantly increased the photocurrent. The onset of the photocurrent, pH{sub 0} = 10.1 {plus minus} 0.1, and the location of the quasi-Fermi level for electrons, nF{sub f}* = -0.85 V vs SCE, have been determined for DHP vesicle incorporated CdS particles containing glucose and MV{sup 2+} from pH-dependent photocurrent measurements. Substantially greater steady-state photocurrents were observed in irradiating 50-{angstrom}, instead of 100-{angstrom}, diameter DHP vesicle incorporated CdS particles. The electrochemical mechanism has been discussed in terms of (i) production of conduction-band electrons and valence-band holes, (ii) hole depletion by sacrificial electron transfer from glucose, (iii) MV{sup 2+} reduction to MV{sup {sm bullet}+} by conduction-band electrons, and (iv) reoxidation of MV{sup {sm bullet}+} at the anode.

Effects of sodium dodecyl sulfate and methyl viologen on the differential extinction coefficient of P-700 — a band shift of chlorophyll a associated with oxidation of P-700

The magnitude of flash-induced bleaching at 700 nm in the thylakoid membranes isolated from the thermophilic cyanobacterium Synechococcus sp. was affected neither by addition of 4 mM methyl viologen, nor by treatment of the membranes with 0.1% sodium dodecyl sulfate (SDS) for 1 h, but appreciably increased on addition of methyl viologen to the SDS-treated membranes. Detailed studies on the light-minus-dark difference spectrum of P-700 revealed that methyl viologen induces a shift-type change consisting of a bleaching at 695 nm and a positive band at 685 nm, and consequently increases the magnitude of the 700 nm bleaching without affecting P-700 photooxidation in the SDS-treated membranes. Other bipyridinium dyes, 1,1′-trimethylene-2,2′-bipyridinium dibromide and 1,1′-trimethylene-5,5′-dimethyl-2,2′-bipyridinium dibromide were equally effective as methyl viologen, and a prolonged treatment of the membranes with SDS caused a similar band shift in the difference spectrum of P-700. The band shift is closely associated with P-700 oxidation because, on redox titration, the magnitude of the band shift varied in parallel to the amount of P-700 oxidized by light. Methyl viologen also induced the band shift in the chemically oxidized-minus-reduced difference spectrum of P-700 in the SDS-treated membranes. Thus, the band shift is not related to reduction of a bound electron acceptor. As a consequence of the band shift, the oxidized-minus-reduced differential extinction coefficient of P-700 in the 700 nm region was increased by 40%. The extinction coefficient was 64 mM −1 · cm −1 at 701 nm in the thylakoid membranes, whereas the 1-h treated membranes with added methyl viologen, or a Photosystem I reaction center complex prepared by SDS-gel electrophoresis, showed the extinction value of 84–86 mM −1 · cm −1 at 698 nm. Two different models for the band shift are discussed.

Photoacoustic Studies of Bundle Sheath Cell Photosynthesis in Zea mays

Summary Monitoring the photoacoustic signal from 400 to 750 nm provided new data on the energy storage spectra in bundle sheath chloroplasts. For this spectrum we found the following: the energy storage in bundle sheath chloroplasts was stimulated in the presence of 10 mM ascorbate or 4 mM ribose-5- phosphate, but it was diminished after the addition of 10 µM 3-(3′,4′-dichlorphenyl)-1, 1′-dimethylurea; the concentration of 20 µM dibromothymoquinone inhibited energy storage; the oxidized chloroplast electron transport carriers, introduced by the addition of methyl viologen to bundle sheath cells, inhibited the energy storage process; and the effect of malate was similar to that seen for methyl viologen. Our study confirms that PSII in bundle sheath cell chloroplasts is in a partially active state, while PSI is reduced with some endogen electron donor(s). The postulated electron donor(s) of PSI is (are) probably replacing low PSII activity in bundle sheat cell chloroplasts. Malate is inducing the oxidation of electron carriers in bundle sheath chloroplasts.

Involvement of Stromal ATP in the Light Activation of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase in Intact Isolated Chloroplasts

Light activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) and stromal ATP content were measured in intact isolated spinach chloroplasts. Treatments which decreased stromal ATP, such as incubation with the ATP analog beta,gamma-methylene adenosine triphosphate or with the energy transfer inhibitor phloridzin inhibited the light activation of rubisco. In the absence of added inorganic phosphate (Pi), light activation of rubisco was inhibited, coincident with low stromal ATP. Addition of methyl viologen restored both stromal ATP and rubisco activity to levels observed in the presence of Pi. Activation of rubisco was inhibited in the presence of 2 millimolar dihydroxyacetone phosphate or 3-phosphoglycerate and stromal ATP was also decreased under these conditions. Both were partially restored by increasing the Pi concentration. The strong correlation between activation state of rubisco and stromal ATP concentration in intact chloroplasts under a wide variety of experimental conditions indicates that light activation of rubisco is dependent on ATP and proportional to the ATP concentration. These observations can be explained in terms of the rubisco activase protein, which mediates activation of rubisco at physiological concentrations of CO(2) and ribulose-1,5-bisphosphate and is dependent upon ATP.

Reduction of n‐C5H11N3 Catalyzed by [Mo2Fe6S8(OMe)3(SC6H4‐p‐n‐C8H17)6]3– in an Aqueous Micellar Solution

AbstractReduction of n‐C5H11N3 by Na2S2O4 was performed in the presence of (n‐Bu4N)3 [Mo2Fe6S8(OMe)3(SC6H4‐p‐n‐C8H17)6] ((n‐Bu4N)3 [Mo‐Fe]) as a catalyst in aqueous Triton X‐100 micellar solutions. The rate of the reduction is enhanced efficiently by the addition of methyl viologen (MV2+). The methyl viologen radical cation (MV+) produced by the reaction of MV2+ with Na2S2O4 undergoes a disproportionation reaction to afford MV2+ and MV° in the micellar solution. The resultant MV° formed in the micelle transfers two electrons to [Mo‐Fe]3− effectively to give [Mo‐Fe]5−, which reduces n‐C5H11N3 with two electrons to produce n‐C5H11NH2 and N2.

Superoxide dismutase activities in Rhizobium phaseoli bacteria and bacteroids

Superoxide dismutase activity in free-living Rhizobium phaseoli is due to the presence of two different enzymes containing manganese or iron. Under usual culture conditions, the manganese-enzyme appears largely predominant but the induction of the iron-superoxide dismutase can be obtained by addition of methyl viologen to the culture media. The corresponding bacteroid, extracted from French-bean nodules, contains only a manganese-superoxide dismutase whose characteristics are similar to those of the bacterial enzyme. However, the activity of the microsymbiont is slightly lower than that of free-living cells. The presence of an active superoxide dismutase in the bacteroids suggests a significant formation of superoxide anion by their metabolism; this can be correlated with the existence of a large oxygen demand by the microsymbionts within the nodule, as suggested by their important oxygen uptake in vitro.

Photochemistry of porphyrins: a model for the origin of photosynthesis.

A series of porphyrins and catalysts has been prepared as a model for the origin of photosynthesis on the primordial earth. These compounds have been used to test the hypotheses that (1) the biosynthetic pathway to chlorophyll recapitulates the evolutionary history of photosynthesis, and (2) the proto-photosythetic function of biogenetic porphyrins (biosynthetic chlorophyll precursors) was the oxidation of organic molecules by photoexcited porphyrins with the attendant emission of molecular hydrogen. This paper describes experiments in which photoexcited biogenetic porphyrins oxidize ethylenediamine tetraacetic acid (EDTA). The concomitant reduction of protons to hydrogen gas occurs in the presence of a colloidal platinum catalyst. The addition of methyl viologen, a one-electron shuttle, increases the amount of molecular hydrogen generated during long irradiations and the quantum yield of hydrogen production. When the porphyrin and catalyst are held in association by molecular complexes, the increased efficiency of electron transfer produces higher yields of hydrogen gas.

Measurement of the ascorbate content of spinach leaf protoplasts and chloroplasts during illumination

Protoplasts prepared from spinach leaves in May and June contained substantial amounts of ascorbate (1.33±0.28 μmol mg(-1) chlorophyll), of which 30-40% was localised in the chloroplasts. During illumination, the ascorbate content was maintained at approximately the same concentration as in the dark in both protoplasts and chloroplasts, even in the absence of CO2 when pseudocyclic electron flow would be expected to be maximal. The addition of the Mehler reagent, methyl viologen, to isolated chloroplasts caused a rapid oxidation of stromal ascorbate in the light such that less than 95% of the ascorbate was oxidised after illumination for 1 min. Similarly the stromal ascorbate pool was rapidly oxidised upon the addition of H2O2. We conclude that when the intracellular ascorbate concentration is high, photosynthetically generated H2O2 can be reduced at rates comparable to its synthesis via the ascorbate-glutathione cycle. The addition of methyl viologen which catalyses rapid production of the superoxide anion, O 2 (-) or the addition of excess H2O2, overwhelms the reductive cycle and the ascorbate system becomes partially or totally oxidised.

Electrochemical investigation of the energetics of particulate titanium dioxide photocatalysts. The methyl viologen-acetate system

Addition of methyl viologen (MV/sup 2 +/) enhances the anodic currents observed for TiO/sub 2/ suspensions under illumination by trapping of photogenerated electrons with formation of MV/sup +/. The magnitude of the photocurrent depends upon the relative location of the semiconductor Fermi level and E/sub redox/ of the MV/sup 2 +//MV/sup +/.couple. The location of the Fermi level in the anatase powders was estimated as -0.05 V vs. NHE (pH 0) based on the observed variation of photocurrent with pH. The shift in the quasi-Fermi level with light intensity is also discussed.

Photochemical reactivity in organized assemblies. 24. Solute partitioning in aqueous surfactant assemblies: comparison of hydrophobic-hydrophilic interactions in micelles, alcohol-swollen micelles, microemulsions, and synthetic vesicles

The structures of anionic assemblies including sodium lauryl sulfate (SLS) micelles, alcohol-swollen SLS micelles, microemulsions, and vesicles of a mixture of dipalmitoyllecithin and dicetyl phosphate are investigated by using the ground-state complexation of a hydrophilic quencher (methyl viologen) with several hydrophobic fluorescent probes, including surfactant stilbenes and 1,4-diphenylbutadiene. In SLS micelles this complexation can be decreased nearly an order of magnitude by addition of 1-heptanol, indicating that the structure of the micelle can be adjusted from the highly open structure of the pure micelle to a much more closed structure in which hydrophobic solubilizates can be sequestered from hydrophilic reagents bound to the surface. The fluorescence quenching process in anionic vesicles is strongly dependent on temperature; at low temperatures quenching occurs, while at higher temperatures addition of methyl viologen appears to increase the stilbene fluorescence, indicating that the dicationic quencher binds to the vesicle surface, increasing the order of the system. These results indicate that the degree of organization of surfactant systems can be adjusted by simple changes in composition. 33 references.

ELECTROCHROMIC BAND SHIFTS OF CAROTENOID IN A BLUE-GREEN ALGA

— The excitation with a short flash of cells of a blue-green alga, Synechococcus sp., induced, besides photooxidation of cytochrome c-553 and P-700, small absorption changes of complex kinetics in the wavelength region between 450 and 570 nm. The absorption changes were resolved into two kinetic components different in their sensitivity to gramicidin D. The ionophore-sensitive component (Gs), which rose very rapidly on flash illumination and decayed with a half-time of 3 ms, has spectral features indicating a red shift of carotenoid absorption bands. Gs was sensitive to valonomycin but not to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). The relaxation rate of Gs was markedly slowed down in the presence of tri-n-butyltin chloride. Phenazine methosulfate induced a secondary slow rise following the initial rapid rise. A similar slow rise appeared in the dark-starved cells but disappeared on the addition of methyl viologen. It is concluded from these results that Gs is an electrochromic band shift of carotenoid responding to the electric field formed by the primary charge separation of the photosystem I reaction center and its decay is related to the proton translocation through a proton channel of the membrane. The ionophore-resistant component rose and decayed with the half-times of 0.2 and 2 ms, respectively. Its difference spectrum suggests a blue band shift of carotenoid. The ionophore-resistant component was also insensitive to DCMU. However, this component may be related in some way to flash-induced electron flow, because the photoresponse was altered by dibromothymoquinone, bathophenanthroline and 2-n-heptyl-hydroxyquinoline-N-oxide or the dark starvation of cells, which were all effective in inhibiting the cytochrome c-553 reduction.

An inducible iron-containing superoxide dismutase in Rhizobium japonicum

Crude extracts of Rhizobium japonicum contained a single superoxide dismutase (SOD) as revealed by polyacrylamide gel electrophoresis. Rhizobium japonicum SOD was determined to be iron-containing by criteria of sensitivity to 5 mM H2O2 and 1 mM NaN3. Growth media strongly influenced SOD activity. The addition of methyl viologen to cultures of R. japonicum 61A76NS, growing in complex medium, caused induction of the enzyme. Yeast extract was essential for induction of SOD. Puromycin blocked the induction of the enzyme. Rhizobium spp. were surveyed for SOD activity, electrophoretic mobility on polyacrylamide gels, and metal content.

Uncouplers Stimulate Photosynthesis in Intact Chloroplasts by Enhancing Light-Activation of Enzymes Regulated by the Ferredoxin-Thioredoxin System

Some uncouplers stimulate CO(2)-dependent O(2) evolution by intact spinach chloroplasts at pH 8.6. This effect is not due to alkalinization of the stroma. The stimulation is observed only when photosynthesis has been partly inhibited by the presence of H(2)O(2), generated in a Mehler-type reaction by the broken chloroplasts which always contaminate the intact chloroplast preparations. The addition of methyl viologen increases the Mehler-type reaction and results in greater inhibition of photosynthesis. The addition of excess catalase stimulates photosynthesis by preventing accumulation of H(2)O(2). The uncouplers stimulate photosynthesis primarily by enhancing the light-activation of enzymes that are regulated by the ferredoxin-thioredoxin system, and this effect results from the influence of the uncouplers on the redox poising of the ferredoxin in the intact chloroplasts.

The apparent loss of cytochrome P-450 associated with metabolic activation of carbon tetrachloride.

Carbon monoxide inhibited the carbon tetrachloride-induced NADPH oxidation rate. The addition of methylviologen to the incubation mixture under the atmosphere of nitrogen resulted in the enhancement of the reductase activity of microsomes for carbon tetrachloride, as determined by chloroform formation. The addition of methylviologen also enhanced the carbon tetrachloride-induced loss of cytochrome P-450, while the apparent content of cytochrome b5 and the activity of NADPH-cytochrome c reductase remained unchanged. Under a strong inhibition of lipid peroxidation by addition of EDTA, carbon tetrachloride induced a clear loss of cytochrome P-450 to the extent similar to that seen in the absence of EDTA. These results indicate that cytochrome P-450 is directly degraded in association with the reductive metabolism of carbon tetrachloride by cytochrome P-450.

The Apparent Loss of Cytochrome P-450 Associated with Metabolic Activation of Carbon Tetrachloride

Carbon monoxide inhibited the carbon tetrachloride-induced NADPH oxidation rate. The addition of methylviologen to the incubation mixture under the atmosphere of nitrogen resulted in the enhancement of the reductase activity of microsomes for carbon tetrachloride, as determined by chloroform formation. The addition of methylviologen also enhanced the carbon tetrachloride-induced loss of cytochrome P-450, while the apparent content of cytochrome b5 and the activity of NADPH-cytochrome c reductase remained unchanged. Under a strong inhibition of lipid peroxidation by addition of EDTA, carbon tetrachloride induced a clear loss of cytochrome P-450 to the extent similar to that seen in the absence of EDTA. These results indicate that cytochrome P-450 is directly degraded in association with the reductive metabolism of carbon tetrachloride by cytochrome P-450.

Photooxidative Damage in Photosynthetic Activities of Chromatium vinosum

The capacity of photosynthetic CO(2) fixation in the anaerobic purple-sulfur bacterium, Chromatium vinosum is markedly impaired by strong illumination (9 x 10(4) lux) in the presence of 100% O(2). In the absence of HCO(3) (-), decline in activity occurred gradually, with about 40% of the initial activity remaining after a 1-hour incubation. The addition of 50 millimolar HCO(3) (-) to the incubation medium resulted in a measurable delay (about 30 minutes) of the inactivation process. Ribulose-1,5-bisphosphate carboxylase activity and light-dependent O(2) uptake (electron flow) or crude extracts prepared after pretreatment of the bacterial cells with O(2) and light were not affected but the photophosphorylation capacity of either bacterial cells or chromatophores was drastically reduced. The inhibition of photophos-phorylation in the chromatophore preparations was significantly reduced by the addition of either an O(2) (-) scavenger, Tiron, or an (1)O(2) scavenger, alpha-tocopherol. These results suggest that the active O(2) species, O(2) (-) or (1)O(2), might take part in the observed inactivation.The pretreatment of the bacteria with O(2) and light inhibited CO(2) assimilation through the Calvin-Benson cycle, while relatively stimulating the formation of aspartate and glutamate. It also inhibited the conversion of glycolate to glycine, resulting in a sustained extracellular excretion of glycolate. The inactivation of photosynthetic CO(2) fixation by intact cells was enhanced by low temperature, KCN, or methylviologen addition during the pretreatment with O(2) and light. The mechanism(s) of O(2)-dependent photoinactivation of photosynthetic activities in Chromatium are discussed in relation to the possible role of photorespiration as a means of producing CO(2) in the photosynthetic system.

Induction of a Mehler reaction in chloroplast preparations by methyl viologen and by ferredoxin: Effects on photosynthesis by intact chloroplasts

CO 2-dependent oxygen evolution in illuminated spinach chloroplast preparations was found to be inhibited by addition of methyl viologen or ferredoxin. Under the conditions described, and in the absence of ribose-5-phosphate, the K i for inhibition by methyl viologen was 0.4 μM and the K i for inhibition by ferredoxin was 13 μM. The effect of osmotic shock on chloroplast oxygen uptake in the Mehler reaction implies that at the concentrations used neither methyl viologen nor ferredoxin freely penetrates the envelope of intact chloroplasts. The observed inhibition of CO 2-dependent oxygen evolution is therefore attributed in each case to a Mehler reaction in the broken chloroplasts of the preparations. Inhibition by methyl viologen (0.8 μM) and by ferredoxin (20 μM) could be reversed by ascorbate and by catalase. As reported [1] for flavin mononucleotide H 2O 2 is likely to be the chief inhibitory agent. The difference in mechanism of autoxidation between methyl viologen and ferredoxin is therefore less important in this system than is their common production of H 2O 2.

Studies on some characteristics of hydrogen production by cell-free extracts of rumen anaerobic bacteria.

Hydrogen production was studied in the following rumen anaerobes: Bacteroides clostridiiformis, Butyrivibrio fibrisolvens, Enbacterium limosum, Fusobacterium necrophorum, Megasphaera elsdenii, Ruminococcus albus, and Ruminococcus flavefaciens. Clostridium pasteurianum and Escherichia coli were included for comparative purposes. Hydrogen production from dithionite, dithionite-reduced methyl viologen, pyruvate, and formate was determined. All species tested produced hydrogen from dithionite-reduce methyl viologen, but only C. pasteurianum, B. clostridiiformis, E. limosum, and M. elsdenii produced hydrogen from dithionite. All species except E. coli produced hydrogen from pyruvate, but activity was low or absent in extracts of E. limosum, F. necrophorum, R. albus, and R. flavefaciens unless methyl viologen was added. Hydrogen was produced from formate only by E. coli, B. clostridiiformis, E. limosum, F. necrophorum, and R. flavefaciens. Extracts were subjected to ultracentrifugation in an effort to determine the solubility of hydrogenase. The hydrogenase of all species except E. coli appeared to be soluble, although variable amounts of hydrogenase activity were detected in the pellet. Treatment of extracts of the rumen microbial species with DEAE-cellulose resulted in loss ofhydrogen production from pyruvate. Activity was restored by the addition of methyl viologen. It is concluded that hydrogen production in these rumen microorganisms is similar to that in the saccharolytic clostridia.

The regulation of glucose-6-phosphate dehydrogenase in chloroplasts.

Glucose-6-phosphate dehydrogenase from intact pea chloroplasts is partially membrane bound and inactivated upon illumination. The inhibitory effect of light can be abolished by addition of methylviologen. Kinetic experiments with glucose-6-phosphate dehydrogenase reveal that, in the dark, the enzyme activity is strongly inhibited by the accumulation of NADPH. The inhibition of NADPH can be reversed by the addition of excess NADP+. The non-Michaelis-Menten-type kinetics suggest that the enzyme is stringently regulated by the ratio of NADPH to NADP+ plus NADPH, i.e., the "reduction charge". These observations seem to indicate that in the light the inhibition of glucose-6-phosphate dehydrogenase is due to a high reduction charge, whereas in the dark the enzyme is controlled by the metabolic demand for reducing equivalents.