Precipitation with phosphotungstic acid

It is also possible to titrate biochemical species. Antibodies have been titrated with antigen, and enzyme-substrate mixtures have been titrated with appropriate coenzymes. Proteins are readily titrated with acid or base, or precipitated with phosphotungstic acid, yielding very informative thermometric titration curves [7, 8]. 

Histidine hydrochloride (2 g.) is suspended in concentrated hydrochloric acid and slowly treated with silver nitrite (3 g.). After removal of excess nitrous acid and silver chloride, the liquid is concentrated to a sirup, which is taken up in alcohol, treated with an excess of alcoholic trimethylamine solution, and kept at 80° for 8 hours. After removal of the alcohol the product is precipitated with phosphotungstic acid. The phosphotungstate is decomposed with barium hydroxide in the usual manner, and the solution of the base thus obtained is strongly concentrated to remove trimethylamine, treated with hydrochloric acid, and the resulting chloride is taken up in alcohol and precipitated with chloroplatinic acid. It is finally converted into the chloroaurate, m.p. 183° with decomposition (14). 

PTA n. (1) Abbreviation for phosphotungstic acid. (2) Applied also to toners and pigments which have been precipitated with phosphotungstic acid to give it permanence and insolubility. 

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). 

The separation and estimation of the two main groups of amino acids can be carried out in one experiment, instead of separately as described. The protein is hydrolysed by sulphuric acid, the tyrosine, cystine and diaminotrioxydodecanic acid are removed by crystallisation, and the diamino acids are precipitated by phosphotungstic acid. From this precipitate they are obtained by decomposition with baryta, and they are then separated by means of their silver compounds by Kossel, Kustcher and Patten s method. The filtrate from the phosphotungstic acid precipitate is freed from the excess of phosphotungstic acid by means of baryta, and the solution is treated by Fischer s ester method for the monoamino acids. 

In addition to concerns over the incomplete solubility of some of the H-coal vacuum-still bottom materials in toluene, the precipitation experiments just discussed are subject to problems associated with two-phase reactions in general. Incomplete contact between the organic compounds in toluene solution and the aqueous acids can lead to inconsistent precipitation results. With this in mind, a different approach was developed in which various H-coal vacuum-still bottoms were treated with phosphotungstic acid, which is soluble in tetrahydrofuran. This reagent allows precipitation to be accomplished from an initially one-phase system, and gives rise to crisp, easily collected salts. 

Table IV. Precipitation of Coal-Derived Bases with Phosphotungstic Acid...

This product, though it had many points of resemblance, such as precipitation by phosphotungstic acid, tannic acid, hydrolysis by tiyp-sin, with the natural tetrapeptide, was not, however, identical with it it differed mainly in its behaviour to ammonium sulphate, by which it was only salted out with great difficulty. 

Although it contains two nitrogen atoms, vasicine is a monoacidic base numerous salts have been described (see Section 5). It forms precipitates with phosphotungstic, phosphomolybdic, picric and picro-Ionic acids, platinic, auric and mercuric chlorides, potassium mercuric... 

To summarize, the final products of peptic digestion are composed of deutero-albumose C, products not precipitable by phosphotungstic acid, and peptones. The different results which have just been set forth relate to serum-albumin. Zunz has found that egg-albumin, casein or globulin, treated in a similar way, act in a similar manner. Yet the progress of digestion of these various materials does not show entirely the same course. In general, extensive hydrolysis is reached with these bodies with more difficulty than with serum-albumin. 

In the table above, as Witte peptone comes from a transformation of fibrin, we have given the composition of the products obtained after hydrolysis of the latter with acid. These ana lytical data show beyond doubt that plastein is a very complex substance, approaching closely the albiuninoids in composition. Moreover, of all the products which are found in peptone, only the fraction precipitable by phosphotungstic acid can give rise to a plastein of composition analogous to that given above. 

Several methods are available to measure lactose content. As lactose is optically active and rotates the plane of polarized light in proportion to its concentration, polarimetry may be used to quantify it. The proteins are first removed by precipitating them with phosphotungstic acid. This method is much less used now. 

The basic group, precipitated by phosphotungstic acid. This group includes the three diamino acids arginine, histidine, lysine, along with cystine and the imino acids, proline and hydroxyproline. 

When distilled with soda Ijme, vapors were obtained which gave a strong pine-splinter reaction. Among the hydrolytic products, there was found a substance which gave a green copper salt and was precipitable by phosphotungstic acid. 

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