Phosphotungstate

The effect is more than just a matter of pH. As shown in Fig. XV-14, phospholipid monolayers can be expanded at low pH values by the presence of phosphotungstate ions [123], which disrupt the stmctival order in the lipid film [124]. Uranyl ions, by contrast, contract the low-pH expanded phase presumably because of a type of counterion condensation [123]. These effects caution against using these ions as stains in electron microscopy. Clearly the nature of the counterion is very important. It is dramatically so with fatty acids that form an insoluble salt with the ion here quite low concentrations (10 M) of divalent ions lead to the formation of the metal salt unless the pH is quite low. Such films are much more condensed than the fatty-acid monolayers themselves [125-127]. 

Safrole can be oxidized to safrole epoxide with H2O2 in a two-phase system, using a quaternary phosphotungstic PTC. The formed safrole epoxide is then isomerized to MDP2P with Lil. 

Fig. 4J2 Adsorption isotherms of carbon tetrachloride (at 298 K) on ammonium phosphotungstate compact, (1) before, (2) after preadsorption of n-nonane. (3) is the isotherm of nitrogen, after preadsorption, for reference. Open symbols, adsorption solid symbols,...

The history of the discovery of amino acids is closely related to advances ia analytical methods. Initially, quantitative and qualitative analysis depended exclusively upon crystallization from proteia hydrolysates. The quantitative precipitation of several basic amino acids including phosphotungstates, the separation of amino acid esters by vacuum distillation, and precipitation by sulfonic acid derivatives were developed successively duriag the last century. 

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. 

According to this mechanism, the reaction rate is proportional to the concentration of hydronium ion and is independent of the associated anion, ie, rate = / [CH3Hg][H3 0 ]. However, the acid anion may play a marked role in hydration rate, eg, phosphomolybdate and phosphotungstate anions exhibit hydration rates two or three times that of sulfate or phosphate (78). Association of the polyacid anion with the propyl carbonium ion is suggested. Protonation of propylene occurs more readily than that of ethylene as a result of the formation of a more stable secondary carbonium ion. Thus higher conversions are achieved in propylene hydration. 

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. 

Silver nitrate -f triglycerides, saturated and heat to 230 to 250 °C phosphotungstic monounsaturated alcohols acid + cobalt nitrate [205, 206]... 

S-Formylpropionic acid) 2,4-dinitrophenylhydrazine (Bromolysine) phosphotungstic-pnosphomolybdic... 

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)... 

Its stability then decreases progressively until we reach curium where aqueous solutions containing the tetra-positive state must be complexed by ligands such as fluoride or phosphotungstate. Even then, they oxidize water and revert to cur-ium(lll). The expected drop in I4 between curium and berkelium provides Bk" (aq) with a stability similar to that of Ce (aq), but the decrease in stability is then renewed, and beyond californium, the +4 oxidation state has not yet been prepared [2, 10, 15]. 

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].

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