12-Phosphotungstic acid

Phosphotungstic acid was first used for biological staining of structures about 1945. Hayat [126] described that early work and what is known about the mechanism of staining. Phosphotungstic acid (PTA) is an anionic stain with a high 

Phosphotungstic acid staining was used to show the fine structure in nylon 6 fibers [127] by soaking the fibers in 9-11% aqueous salt solutions and staining with 1.5 and 4.8% PTA. Longitudinal periodicities were shown for the stained fibers by TEM. However, the lamellae showed a change in size, depending on the concentration. 

8% PTA the lamellae were about 7nm. These authors reported [128] that 9-11% HCl treatment bound 15% of the weight of PTA in the unoriented or amorphous regions of nylon. TEM and electron diffraction showed a range of periodicities in nylon from the ordered, oriented and unoriented regions. 

PTA is known to react with monomer epoxy resins which extract the stain [73], precluding its use prior to epoxy embedding. Therefore, PTA stained material is usually either embedded in glycol methacrylate or polyester resins, or sections are post-stained in cured epoxies. PTA penetration is slow and about 100 pm penetration into a block of material can be expected. Sections on grids are immersed into the solution or placed on a droplet. Pretreatment in absolute ethanol increases exposure to the stain. Martinez-Salazar and Cannon [136] reported a new method of PTA staining of nylon 6 and nylon 6,6 using 2% PTA and 2% benzyl alcohol. Thin films on a specimen grid were floated on a drop of the mixed solution for 10 min and then washed in water several times. 

Of the many phosphotungstic acids, the so-called 12-phos-photungstic acid is the most common and important. According to the Rosenheim-Miolati theory, this acid is heptabasic, and the heptaguanidine salt has been reported.3 Pauling1 and others have criticized their theory, however, and have suggested other formulae. The large amount of water contained in the acid is evidently partly water of constitution and partly water of hydration. 

Phosphotungstic acid finds use in the precipitation of proteins, alkaloids, and certain amino acids. The solubility of sodium phosphotungstate, contrasted with the comparative insolubility of the potassium and ammonium salts, has suggested its use as a reagent in qualitative analysis. 

Phosphotungstic acid crystallizes from water (in which it is extremely soluble) in very heavy white octahedra. The water solution is not stable toward light but slowly turns blue as a result of reduction. Re-oxidation is easily effected by heating with chlorine water. In spite of its great solubility in water, the acid may be completely extracted from water solution by ether. It forms with ether a dense liquid layer of a complex compound which is insoluble both in ether and in water, so that three liquid layers are formed when the water solution is extracted with an excess of ether. In addition to being very soluble in water and ether, phosphotungstic acid is readily soluble in the lower alcohols and esters. 

Rosenheim and Jaenicke Zeit. anorg. allgem. Chem., 101, 251 (1917). 

Spit [152, 153] showed detailed spherulitic structures in solvent cast nylon 6 and nylon 6,6 films cast from formic acid onto water and stained with 2% PTA. Spherulitic textures with white and dark bands or lines were observed. 

The dark bands contained the electron dense stain while the white, crystalline areas did not absorb the stain, enhancing the contrast in the 5 nm wide lamellae. The fine structures of nylon 

PTA is known to react with monomer epoxy resins which extract the stain [93], precluding its use prior to epoxy embedding. Therefore, PTA stained material is usually either embedded in glycol methacrylate or polyester resins, or sec- 

6 using 2% PTA and 2% benzyl alcohol. Thin films on a specimen grid were floated on a drop of the mixed solution for 10 min and then washed in water several times. 

The staining of polypropylene was not as straightforward as that of the polyamides and polyesters. Hock [270] developed a method for staining melt crystallized PP and showed it to be eomposed of spherulites containing lamellae. The melt crystallized polymer was boiled for 4h in 70% HNO3 at 120°C, and then chips 

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Ben2enesulfonate compounds yield very iasoluble salts which have been used for separation and identification of amino acids (89). Similarly, phosphotungstic acid forms iasoluble salts with basic amino acids such as lysiae, arginine, and cysteiae. 

Cesium isotopes can be recovered from fission products by digestion in nitric acid, and after filtration of waste the radioactive cesium phosphotungstate is precipitated using phosphotungstic acid. This technique can be used to prepare radioactive cesium metal or compounds. Various processes for removal of Cs isotopes from radioactive waste have been developed including solvent extraction using macrocycHc polyethers (62) or crown ethers (63) and coprecipitation with sodium tetraphenylboron (64). 

In biological materials, various nonspecific precipitants have been used in the gravimetric deterrnination of choline, including potassium triiodide, platinum chloride, gold chloride, and phosphotungstic acid (28). Choline may also be determined spectrophotometricaHy and by microbiological, enzymatic, and physiological assay methods. 

Chloramine-T also functions as a nitrene source in the presence of heteropoly acids (HPAs) such as phosphomolybdic and phosphotungstic acids. The aziridination of alkenes by treatment with the combination of HPA and chloramine-T is... 

For light microscopic examination, liver tissue was fixed in 10 % buffered formalin, embedded in paraffin, sectioned and stained with hematoxylin and eosin. In some cases, preparations were stained with PTAH (phosphotungstic acid-haematoxylin), by the Van Gieson method and the PAS (periodic acid-Schiff)... 

In this work, various Ru-BINAP catalysts immobilized on the phosphotungstic acid(PTA) modified alumina were prepared and the effects of the reaction variables (temperature, H2 pressure, solvent and content of triethylamine) on the catalytic performance of the prepared catalysts were investigated in the asymmetric hydrogenation of dimethyl itaconate (DMIT). 

SINGLETON V L and ROSSI J A J (1965) Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid regents , Am JEnol Vitic, 16, 144-58. 

Fig. 1. Negative staining by phosphotungstic acid of Na,K-ATPase purified in membrane-bound form. The membrane surfaces are covered by particles arranged in clusters between smooth areas. From [2] procedure as described by Deguchi et al. [30].

The standard method used to prepare these AHC s was by anchoring a preformed complex onto an alumina support which had been treated with a heteropoly acid such as phosphotungstic acid (PTA). Alternately, the AHC can be prepared by treating an anchored Rh(COD)2 precursor with an appropriate ligand (8). We report here the use of AHC s which have been prepared by this... 

Figure 6.4 TEM image of the dispersion of nanoparticles obtained after evaporation of the solvent of a nanoemulsion with an O/S of 70 30 and a water content of 90wt% and negative staining with a phosphotungstic acid solution. Reproduced with permission from [54].

Desulfurization using purified enzymes Investigations into enzymatic desulfurization as an alternative to microbial desulfurization has revealed several enzymes capable of the initial oxidation of sulfur. A study reported use of laccase with azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator for oxidation of DBT [181]. The rate of this reaction was compared to hydrogen peroxide-based phosphotungstic acid-catalyzed oxidation and the latter was found to be about two orders of magnitude higher. The authors also oxidized diesel oil sulfur to no detectable levels via extraction of the oxidized sulfur compounds from diesel. In Table 9, the enzymes used in oxidation of DBT to DBTO are reported. 

The Folin-Denis assay is used as a procedure for the quantification of total phenolics in plant materials, food, and beverages. Reduction of phosphomolybdic-phosphotungstic acid (Folin-Denis reagent) to a blue-colored complex in an alkaline solution occurs in the presence of phenolic compounds (Folin and Denis 1912). 

Lowry method uses a combination of the Biuret copper-based reagent and the Folin-Ciocalteau reagent, which contains phosphomolybdic-phosphotungstic acid. Reagents react with protein, yielding a blue colour that displays an absorbance maximum at 750 nm... 

The preparation of this type of catalyst is quite simple. HPAs such as phos-photungstic acid were adsorbed onto inorganic supports such as clays, alumina, and active carbon. Subsequently, the metal complex was added to form the immobilized catalyst. If necessary, the catalyst can be pre-reduced. These types of catalysts were developed mainly for enantioselective hydrogenations. For instance, a supported chiral catalyst that was based on a cationic Rh(DIPAMP) complex, phosphotungstic acid and alumina showed an ee-value of 93% with a TOF of about 100 IT1 in the hydrogenation of 2-acetamidoacrylic acid methyl ester (Fig. 42.4 Table 42.2). 

Phosphotungstic acid (PTA) 1 g STA or PTA in 100 mL of 10% aqueous Plasma membrane Golgi complex-... 

Phosphotungstic acid 2% aqueous, pH 6.5-7.5 (note some investigators employ 4%) Virus particles, proteins molecules, liposomes Harris and Home (43)... 

The process of infection of lupine nodule cells by Rhizobia was examined by the thin-section electron microscopic technique, as well as the freeze-fracture technique. Different membranes such as infection thread membranes, peribacterioid membranes, plasma membranes, membranes of cytoplasmic vesicles, and membranes of the Golgi bodies and ER were stained with uranium-lead, silver, phosphotungstic acid, and ZIO (31). ZIO stained the membranes of the proximal face of the Golgi bodies and endoplasmic reticulum. ZIO staining has given good contrast in thick sections such as a cotyledon cell, a root cell, and an aleurone layer for ER, dictyosomes cisternae, mitochondria, and nuclear envelopes (17,32-37). 

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