Chain polyphosphates diphosphates

Condensed phosphates are derived by dehydration of acid orthophosphates. The resulting polymeric stmctures are based on a backbone of P—O—P linkages where PO tetrahedra are joined by shared oxygen atoms. The range of materials within this classification is extremely broad, extending from the simple diphosphate, also known as pyrophosphate, to indefinitely long-chain polyphosphates and ultraphosphates (see Table 1). Both weU-defined crystalline and amorphous materials occur among the condensed phosphates. 

A rather different structure-motif is observed in the chain polyphosphates these feature comer-shared PO4 tetrahedra as in the polyphosphoric acids (p. 522). The general formula for such anions is [Pn03 4.i] + , of which the diphosphates, P2O7 ", and tripolyphosphates, PsOjo , constitute the first two members. Chain polyphosphates have been isolated with n up to 10 and with n infinite , but those of intermediate chain length (10 < n < 50) can only be obtained as glassy or amorphous mixtures. As the chain length increases, the ratio (3n + l)/n approaches 3.00 and the formula approaches that of the polymetaphosphates [P03 ]oo-... 

Hydrolysis of triphosphate at pH 9 results in the formation of diphosphate (pyrophosphate) and monophosphate (orthophosphate). In a parallel step, the diphosphate is split, at a slower rate, into monophosphate. A tetraphosphate is thus cleaved into one triphosphate and one monophosphate anion, followed by cleavage of the triphosphate as just described (5.151). In general, hydrolytic degradation of long-chain polyphosphates proceeds primarily by scission of the end PO4 groups and there is a rapid buildup of monophosphate during such reactions. 

More complicated structures that form with longer chains or rings also exist. The biochemically most important polyphosphate is adenosine triphosphate, ATP, which contains three phosphorus tetrahedral units linked by -O-P-0- bonds. The hydrolysis of ATP to adenosine diphosphate, ADP, by the rupture of an 0-P bond releases energy that is used by cells to drive biochemical reactions within the cell. ATP + H2O ADP + HP04 " A//= - 41 kJ... 

S (phosphate)n + D-glucose <1-13> (<1> i.e. poly(P)n, no substrates are monophosphate, diphosphate or triphosphate [2] <1>, no utilization of triphosphate or tetrapolyphosphate [1] <11> the enzyme utilizes polyphosphate much more efficiently than it does ATP, with a turnover num-ber/Kpolyphosphate to turnover number/KATP ratio of 2800 [8] <8> polyphosphate is utilized nonprocessively with a preference for longer chains [9]) (Reversibility ir <12,13> [11,12] <1-11> [1-10]) [1-12]... 

The phosphorus content in some foods can be raised above the natural level using food additives based on polyphosphoric acid salts or salts of phosphoric acid. Polyphosphates are either sodium or potassium salts of polyphosphoric acids with straight chains and different degrees of polymerisation, M +2P 03 +i (6-30) or salts of cyclic polyphosphoric acids, (M POj) (6-31), which are actually oligomers of hydrogenphosphoric acid (m-phosphoric acid), HPO3. The most commonly used materials are sodium and potassium phosphates, especially disodium dihydrogendiphos-phate, tetrasodium diphosphate, sodium triphosphate and the so-called sodium hexametaphosphate. 

Ammonium diphosphate cannot be made by thermal dehydration of ammonium phosphates because both water and ammonia are split off, and the resulting product is a mixture of short-chain ammonium polyphosphates and short-chain polyphosphoric acids. Ammonium diphosphate usually is prepared from pure diphosphoric acid. The diphosphoric acid is crystallized from a polyphosphoric acid mixture containing 80% PjOs or made by running a solution of sodium diphosphate through an ion exchange column. The resulting diphosphoric acid then is treated with ammonia. Ammonium diphosphate also has been made by heating a mixture of urea and phosphoric acid, but by-products such as cyanuric acid are tedious to remove. The present method is based on the reac-... 

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