Phosphation reduction

Ke and Regier [71] have described a direct potentiometric determination of fluoride in seawater after extraction with 8-hydroxyquinoline. This procedure was applied to samples of seawater, fluoridated tap-water, well-water, and effluent from a phosphate reduction plant. Interfering metals, e.g., calcium, magnesium, iron, and aluminium were removed by extraction into a solution of 8-hydroxyquinoline in 2-butoxyethanol-chloroform after addition of glycine-sodium hydroxide buffer solution (pH 10.5 to 10.8). A buffer solution (sodium nitrate-l,2-diamino-cyclohexane-N,N,N. AT-tetra-acetic acid-acetic acid pH 5.5) was then added to adjust the total ionic strength and the fluoride ions were determined by means of a solid membrane fluoride-selective electrode (Orion, model 94-09). Results were in close agreement with and more reproducible than those obtained after distillation [72]. Omission of the extraction led to lower results. Four determinations can be made in one hour. 

The oxidized form of As, arsenate, As(V), which is present as HAs04 at neutral pH (p f values in Table 7.8), is sorbed on soil surfaces in a similar way to orthophosphate. The reduced form arsenite, As(lll), which is present in solution largely as H3As03(p fi = 9.29), is only weakly sorbed, hence mobility tends to increase under reducing conditions. Mobility will also increase without reduction of As(V) because, as for phosphate, reductive dissolution of iron oxides results in desorption of HAs04 into the soil solution. Under prolonged submergence As(lll) may be co-precipitated with sulfides. 

Enzymes can also undergo other side reactions under conditions that divert a chemically reactive intermediate from its usual catalytic function. Again, glutamine synthetase is an excellent example (see figure above), because its side reactions include acyl-phosphate reduction by borohydride, pyroglutamate formation, and the formation of y-glutamyl hydroxamate in the presence of hydroxylamine and arsenate. 

The spiked filters were placed in a 50-mL beaker with the spiked side up and 1 mL of water was added. The beaker was shaken so that all of the filter area had been washed by the water. One mL of the reduction-buffer solution without the sodium hydrosulfite was added to the filter and water. The beaker was shaken a second time. The filter was then turned over (spiked side down) and the beaker placed in an ultrasonic bath for 15 minutes. At the end of this period, the solution in the beaker was colored. A 1-mL aliquot of this solution was transferred to a 4-mL vial. One mL of a freshly prepared solution of 100-mg sodium hydrosulfite in 10-mL phosphate reduction buffer was then added to the vial. The vial was then capped and shaken several times during the course of an hour. During this time, the original color of the solution disappeared or changed to a different color, depending on the dye present. This solution was then injected into the liquid chromatograph. A 10-yL aliquot was used, giving a measurement limit of 0.38 ng benzidine/yL. The analytical reproducibility at this limit was 10% coefficient of variation (CV). 

C.I. Direct Black 38, C.I. Direct Brown 95 and C.I. Direct Blue 6 were studied individually in the visible spectrum. A baseline was recorded using the phosphate reduction buffer in both cells. Subsequent additions of known amounts of dye and scanning allowed absorption maxima and molar absorptivity to be determined. Then 3 mg of sodium hydrosulfite was added to the dye-containing cell. The concentration of dye remaining after reduction was calculated using Beer s Law. The remaining dye varied from 0 to 6% of the original amount of dye added (Table I). Reduction was complete within 30 minutes. 

Pathway Amount of ATP for synthesis of one triose phosphate Reductants for synthesis of one triose phosphate C02-fixing enzymes Active C02 species C02 fixation products which may be used for biosynthesis Key enzymes... 

JemelovA. 1971. Phosphate reduction in lakes by precipitation with aluminum sulphate. In Jenkins SH, ed. Advances in water pollution. 1-15/1 to 1-15/6. 

Tsubota, G., 1959. Phosphate reduction in the paddy field. Soil Plant Food, 5 10—15. 

During electrothermal phosphate reduction, 80 to 90% of the fluoride contained in the rock remains with the slag as its calcium salt [21] (Eq. 10.12). 

Respiration Photosynthesis Denitrification Nitrification Ammonia volatilization Sulfate reduction Fermentation Nitrogen fixation Methanogenesis Phosphate reduction... 

Despite these physicochemical limitations, phosphate reduction has often been postulated in the literature in analogy to sulfate reduction or nitrate reduction, although the average redox potentials of these reduction processes are substantially more positive, at -218 or -1-363 mV, respectively [78]. It is obvious from this comparison that phosphate reduction to phosphine can never proceed as an energy-conserving respiratory process [79]. 

Nonetheless, traces of phosphine (in the nanomolar range) have been detected in certain anoxic environments such as sediments [80,81], paddy fields [82,83], and manure samples [84], but it was never proven that its formation was caused by biological phosphate reduction. Some of these phosphine findings are interpreted today as the result of a biologically enhanced hydrolysis of... 

Glindemann, D., M. Edwards and P. Morgenstern (2005b) Phosphine from rocks Mechanically driven phosphate reduction Environmental Science and Technology 39, 8295-8299... 

Eutrophied lakes can often be reclaimed if the phosphate content of the inflowing water or sewage is drastically reduced. This allows the existing phosphate level to slowly reduce itself by natural precipitation and sedimentation. Since agricultural drainage waters are more difficult to control, efforts at phosphate reduction have been concentrated mostly on sewage treatment. 

Tin pyrophosphate (SnP207) was synthesised and tested as an anode in lithium ion batteries. P MAS NMR indicates a single species near in position to that expected for Li3P04 but this species would be inconsistent with the observed phosphate reduction. Li MAS NMR shows no presence of Li20. To advance the work on the characterisation of Ti02 hetero-assemblies formed by surface modification with functional molecular materials, solid-state NMR study was carried out on the molecules chemisorption on the surface of the semiconductor by P solid-state NMR. ... 

Usage of polymers with carbonate can more than compensate for the phosphate reduction. The sodium carbonate helps the stain removal, whereas the polymer avoids the negative consequences of using a precipitating builder. 

The forward and reverse reactions were verified by showing a stoichiometric relation between decrease of 3-aspartyl phosphate and TPNH and the increase of aspartyl semialdehyde in the forward reaction and an equivalent formation of /3-aspartyl phosphate and TPN when the components of the reverse reaction were incubated. Participation of phosphate in the reverse reaction was demonstrated by the dependence of the equilibrium level of TPNH on the phosphate concentration. The product of aspartyl phosphate reduction was established to be L-aspartyl /3-semialdehyde by its subsequent reaction with DPNH and homoserine dehydrogenase to yield homoserine. /3-Aspartyl phosphate formed by aspartyl semi-aldehyde oxidation was identified by its reaction with ADP in the (8-aspartokinase system. 

Several anaerobic bacteria are now known to contain ferredoxins with potentials that are low enough (e.g. - 0.4 V) to make them candidates for phosphate reduction. Therefore it seems thermodynamically possible that anaerobic microorganisms could synthesise reduced P compounds, for example, PH3. The literature on this appears to be sparse, however there are hints and debates that this may be the case. 

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