Showing papers on "Redox published in 1971"

Vertical advection diffusion and redox potentials as controls on the distribution of manganese and other trace metals Dissolved in waters of the Black Sea

Abstract: Profiles of dissolved manganese, copper, iron, and zinc show that the distributions of these elements are markedly affected by redox reactions at the boundary between oxygenated surface waters and the sulfide-containing deep waters. Copper and zinc are depleted in the deep water by precipitation as insoluble sulfides. The concentrations of manganese and iron in the deep water greatly exceed those of the surface water principally because of the greater solubility of the sulfides and hydroxides of the reduced species as compared with the solubility of hydroxides and oxides of the oxidized species. The distribution of dissolved nickel and cobalt does not appear to be greatly affected by redox reactions. The profile of dissolved manganese, which shows a pronounced mid-water maximum about 40 meters below the oxygen zero boundary, has been explained with the aid of a vertical advection-diffusion model. We suggest that the Black Sea basin is currently acting as a very efficient trap for manganese. A flux of manganese, from surface particulates, of about 200 mg m−2 year−1, which is reduced and dissolved immediately upon penetrating to the sulfide-containing waters, builds up a mid-water maximum until the concentration gradient between the maximum and the deep water is sufficient to drive an equivalent diffusive flux of manganese into the deep water. Manganese is not lost by upward diffusion and advection because the reduced species is oxidized and precipitated just above the oxygen zero boundary and hence adds to the total flux of particulate manganese into the deep water. Currently the total flux of particulate manganese that is going into solution in the deep water is about 875 mg m−2 year−1 of which 675 mg m−2 year−1 is derived from the precipitation of dissolved manganese. The latter amount will increase in the future until the concentration of dissolved manganese at the midwater maximum exceeds the solubility product of some salt. Although we have performed no calculations, the shape of the dissolved iron profile indicates that a mechanism similar to that described for manganese is controlling the distribution. In addition it is likely that sulfide precipitation limits the iron concentration in the deep water.

The Isolation and Characterization of a Photochemically Active Complex from Chloropseudomonas ethylica

Abstract: A photochemically active subcellular fraction has been isolated from the green bacterium Chloropseudomonas ethylica. It is enriched in bacteriochlorophyll a and contains only a small amount of Chlorobium chlorophyll. Both a reaction-center bleaching (P840) and a cytochrome oxidation (C553) are observed to occur in the fraction. Particles that are contained in the fraction are larger than 1.5 × 106 daltons and exhibit a range of sizes consistent with some form of polymeric association of similar subunits. Around 80 bacteriochlorophyll a molecules are present per P840. In an intact photosynthetic apparatus there are about 1000-1500 total chlorophylls (including Chlorobium chlorophyll) per reaction center. The redox potentials of the reaction center P840 and C553 were found to be 0.24 and 0.17 V, respectively, in one-electron reactions. The potentials of these components are around 0.2 V lower than comparable components found in other photosynthetic organisms.

Quinones and Nicotinamide Nucleotides Associated with Electron Transfer

Abstract: Publisher Summary This chapter concentrates on the principles of function of nicotinamide nucleotides (NAN) and of menaquinone and ubiquinone in terminal substrate oxidation In mitochondria, NAN and quinones have been considered as members of the respiratory chain In particular for the NAN, this association is too limited because by the pool function the NAN is linked to the majority of cellular redox reactions In animal cells one may concentrate on the mitochondrial NAN system, whereas in protists and plants, the extramitochondrial NAD also is directly linked to the respiratory chain In prekaryotic cells, this compartmentation of NAN does not exist In this chapter, particularly interesting principles of function for the quinones are revealed In view of these various associations, the function of the coenzymes is considered both in terminal oxidation and in the substrate–substrate hydrogen transfer The molar relations between coenzymes, respiratory carriers, and dehydrogenases in mitochondria are elaborated Topochemical organization of the hydrogen-transferring coenzymes and enzymes in the mitochondrial membrane is described The redox state of nicotinamide nucleotides in mitochondria is also discussed

A study of the reduction and oxidation of human ceruloplasmin. Evidence that a diamagnetic chromophore in the enzyme participates in the oxidase mechanism.

Abstract: The stopped-flow technique was utilized to measure the 610 and 340 nm absorbances of human ceruloplasmin during oxidation and reduction reactions. The results confirm earlier observations that the chromophores giving rise to these absorbances are different electron acceptors. Under steady state conditions both chromophores were partially reduced which indicates that they participate in the oxidase reaction. Oxidation rates for the 610 and 340 nm chromophores of completely reduced ceruloplasmin were too high to be compatible with the respective steady state absorbances. These results, together with a comparison of the oxidation rates for Type 1 copper of partially and completely reduced protein, showed that the oxidation rate for one chromophore is influenced by the oxidation states of the other and/or the nonchromophoric paramagnetic copper (Type 2). Therefore, the oxidase mechanism appears to involve concerted transfer of electrons from the 610 and 340 nm chromophores and possibly Type 2 copper.

Oxidation and Reduction of Amino Acids by Ionizing Radiation

Abstract: The effects of ionizing radiation on the amino acids β‐alanine and e‐aminocaproic acid were studied in single crystals irradiated at 4.2°K. The paramagnetic species resulting from radiation‐induced oxidation and reduction processes were investigated using electron spin resonance and electron—nuclear double‐resonance (ENDOR) spectroscopy. The reduced species is a free radical formed by the addition of an electron to the carbonyl oxygen of the carboxyl group. The ENDOR measurements indicate the oxidation product is a free radical derived from oxidized amino acid by the dissociation of CO2.

Bis(trimethylsilyl)diimine: Preparation, Structure, and Reactivity

Abstract: The highly reactive compound bis(trimethylsilyl)diimine (BSD), which was first prepared by oxidation of lithium tris(trimethylsilyl)hydrazide, is light blue, sensitive to thermolysis and hydrolysis, and ignites spontaneously in air. On the basis of electron transfer, acid-base, or free-radical reactions, it acts in particular as a (preparatively useful) redox system and as an agent for the introduction of azo groups. Redox reactions lead by oxidation or reduction of the other reactant through two oxidation stages to hydrazine derivatives or molecular nitrogen, and in the case of electrochemical reduction, to BSD radical-anions. Azo-group transfers, on the other hand, yield new inorganic azo compounds with no change in the oxidation state of the diimine group.

A Lipid Requirement for Photosystem I Activity in Heptane-extracted Spinach Chloroplasts

Abstract: A lipid requirement for photosystem I activity in Spinacia oleracea chloroplasts has been characterized. The transfer of electrons from tetramethyl-p-phenylenediamine through the chloroplast photosystem to viologen dye was used as an assay of photosystem I activity. Activity is diminished by prolonged heptane extraction and is partially restored by readdition of the extracted lipid. Extracted chloroplasts require plastocyanin for maximal restoration of activity. The effect of lipid extract in restoration is partially replaced by triglycerides containing unsaturated, C(18) fatty acids. Various potential redox carriers which occur naturally in chloroplasts do not substitute for extracted lipid. Galacto-lipids, sulfolipids, and phospholipids are not involved in the restoration of activity.

Some observations on growth and hydrogen uptake by Desulfovibrio vulgaris.

Abstract: 1. Calculation showed that rates of sulphate reduction by the Hildenborough strain of Desulfovibrio vulgaris in non-nutrient buffer with gaseous hydrogen as electron donor were as high as, or higher than, the maximum possible rate of sulphate reduction during growth. 2. Respirometry showed that H2 oxidation was completely suppressed during growth unless the whole electron transport system was bypassed with a redox dye or the sulphate reductase system (terminal electron acceptor) was bypassed with FMN. 3. Growth experiments with intermittent sulphate feeds showed that cells under H2 “wasted” most of the sulphate by a reaction unconnected with growth, and thus made much less growth than did similar cultures under N2. 4. H2 exerted no discernible “lactate-sparing” action (that is, it did not serve as an alternative energy source) in low-lactate medium.

Oxidation of Methyl Radicals Studied in Reflected Shock Waves using the Time-of-Flight Mass Spectrometer

Abstract: The oxidation of methyl radicals has been investigated using a shock tube coupled to a time-of-flight mass spectrometer between 1100 and 1400°K. The effect of varying the temperature and oxygen concentration is reported. Formaldehyde was observed as a product of the oxidation reaction. For a 10-fold excess of O2 at 1350°K the concentration—time profiles for the following principal species: CH3, C2H6, C2H4, CH4, CH2O, H2O, and CO have been obtained over the reaction time scale of 350 μsec. Numerical integration calculations have been performed using a mechanism and rate data compounded from two earlier studies in this laboratory to describe the present methyl radical oxidation data. Good agreement between all the experimental and calculated profiles is obtained, with the inclusion of one additional reaction in the integrated mechanism, O+C2H4→CH3+H+CO, with a rate coefficient k13=8.3× 10−12 cc/particle·sec at 1350°K as quoted in the literature, and if the following reactions: CH3+O2→CH2O+OH, CH3+O→CH2O+H, ...