Metaphosphates, determination

Metaphosphoric Acid. Reactions jor Determining Metaphosphoric Acid and Its Salts. 1. Pour about 1 ml of an aqueous protein solution into a test tube and add to it approximately the same amount of a sodium metaphosphate solution acidified with acetic acid. What do you observe See whether the protein solution is affected in the same way by sodium metaphosphate and acetic acid solutions taken separately. 

The whole question of the specificity was reopened with the discovery that E. coli phosphatase, contrary to an earlier statement (114), hydrolyzed a variety of polyphosphates including metaphosphate of average chain length 8 (97). It was subsequently reported that partially purified phosphatases from several mammalian tissues had appreciable PPi-ase activity at pH 8.5 (115). This was confirmed (116) and extended to include ATPase and fluorophosphatase activities (117). Proof that the same enzyme is responsible for the monoesterase and PPi-ase activities was afforded by heat inactivation studies, cross inhibition experiments, and inhibition of PPi-ase activity by L-phenylalanine, a specific inhibitor of intestinal phosphatase. It was also found that calf intestinal phosphatase couid be phosphorylated by 32P-PP and the number of sites so labeled agreed with the number of active sites determined with a monoester substrate using a stopped-flow technique (118). It would seem that the main reason for the confusion with regard to the PPi-ase activity results from the inclusion of Mg2+ in the assay. This stimulates the monoesterase activity but almost completely inhibits PPi-ase activity (117). 

Scheme 2. Conformational changes of the y-phosphate in a) phosphoryl-transfer reaction transition state K), and various species of AlFx b) AlF41, c) A1C13. Dotted lines indicate that the degree of bond making and bond breaking determines whether the transition is more dissociative, with a metaphosphate-like intermediate, or associative, with a pentavalent intermediate. Charges have been omitted for clarity. N = adenosine or guanosine. According to [16, 17, 21]...

At a temperature of 78° C. the velocity constant whether referred to a unimolecular or a bimolecular reaction diminished with time after an hour rather less than three-quarters of the original metaphosphate remains.6 The product is mainly orthophosphate, as was proved by titration with methyl orange and phenolphthalein, although small quantities of pyrophosphate were formed by a side reaction. The pyro-acid was determined by titration to bromophenol blue in the presence of zinc sulphate, which leads to a complete precipitation of pyrophosphate, the ortho-acid being unaffected, thus... 

SatnpCe Preparation. Seventy grams of sample, previously calcined at 538°C, was dispersed in about 125 mL of sodium metaphosphate solution and "wet screened" using a sieve stack of 250, 270 and 325 mesh, 8-inch diameter sieves. The sieves were washed with water until the effluent was free of any particulate and then rinsed with acetone to de-water. After air drying, the contents of each sieve were transferred to a porcelain dish and the material was recalcined at 538°C. Appropriate weights taken during this procedure allowed for the determination of percent moisture in the starting material and sieve analysis relative to the appropriate sieve fractions. The total +325 mesh material was recombined and mixed for the test. 

As cyclophosphates and the catenaphosphate anion (together termed metaphosphates) share the basic composition (PO3 ) , crystal-structure analysis is often the only way to determine which species is present, although IR spectroscopy may be useful (see Section 3.2.1). Different isomers of the same metaphosphate composition are often found. Six crystal forms (A-F) of M(P03)3 (M = Al, Cr, Mn, Fe, Ga) have been identified, three of which have been structurally characterized and found to contain cyclotetraphosphate (form A), cyclohexaphosphate (B), and catenaphosphate (C) anions. 

The rate-determining step for the sodium salt has been identified [73] as a surface process below 470 K ( , = 158 kJ mol" ) and, above 470 K, the diffiision of H2O becomes controlling. Sodium metaphosphate, NaPOj, is formed only above 510 K. 

Further progress has been reported in the chemistry of CT X, -p -bonded systems. Full details of such systems stabilised by intramolecular coordination, as in, e.g., 334, have been described. The kinetically stable system 335 has been prepared and its solid state structure determined . The P-halobis(imino)-CT -phosphoranes 336 have also been prepared, and detailed NMR studies of bis(imino) phosphoranes reported . Quin s group has continued studies of the generation and characterisation of reactive a X -systems, e.g., 337 ". Methods for the generation of monomeric metaphosphate esters in solution have been investigated. A theoretical approach has been used to probe the mechanism of the reaction between phosphanylnitrenes 338 and boranes. The thiophosphonic anhydride 339 behaves as a source of the dithioxophosphorane... 

In physical and theoretical methods there has been a notable increase in the use of recently developed techniques - most of which have trendy acronyms. Thus DRAMA P NMR has been used to determine internuclear P-P distance in a phosphine sulfide 4,8-residue substituted decapeptide, and XANES has been applied to structural studies of phosphine selenides. In the mass spectral field MALDI-TOF has been found to be better than FAB for the determination of the mass spectra of nucleotide triphosphates, LA-FTICR has been used to study tris(cyanoethyl)phosphine and metaphosphates have been detected for the first time by laser photoionisation MS. ERMS was shown to be a powerful technique for the analysis of structurally similar organophosphate insecticides (OPs) and trace quantities of OPs can be determined by Cl using water as the ionising agent. 

This is not necessarily the case in less nucleophilic media, and we — the scientific community — will try our best to determine whether the environment of enzymes resembles aqueous solution or a much less polar medium. Such investigations are of real scientific interest, but must not obscure the important fact that the role of monomeric metaphosphate in biochemistry is as an electrophile. Like the proton, its electrophilicity is sharply diminished by water and, at least in aqueous solution, it is transferred from one molecule to another without becoming free. Unlike the proton, which is never free in any liquid medium, monomeric metaphosphate is probably free in apolar solution like the proton, its role is that of an electrophile. 

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