Hydrolysis of polyphosphates

These ideas are readily testable and therefore can constitute a research enterprise. For example, the hydrolysis of polyphosphates to monomeric phosphate is relatively fast in weak aqueous acid and warm temperatures. [129, 205] Curiously, however, the same acidity would promote thermal polyphosphate synthesis under the dehydrating conditions of the heated subterranean mineral pores within a hydrothermal system. Measurement of the stability of polyphosphates in microscopic environments where the activity of water might be low would test the phosphate-polyphosphate conjecture made above. If polyphosphates are not stabilized relative to bulk water solutions, as dissolved within micron-sized mineral pores or within vesicles, perhaps in the presence of dissolved organics, then this hypothesis is in danger. Additionally, the proposed production and delivery of polyphosphates by hydrothermal systems can be tested in an appropriate laboratory setting. 

This enzyme [EC 3.6.1.10] (also known as polyphosphate depolymerase, metaphosphatase, and polyphosphatase) catalyzes the hydrolysis of polyphosphate to yield oligo-phosphate products containing four or five phosphate residues. 

As in the hydrolysis of polyphosphates (Sections IV,B, and IV,E,1), hydrolysis of the trimetaphosphate anion is eatalytically accelerated by added cations. Their effect is attributed, as in the ease of the polyphosphates, to the formation of complex ions of the type CafPsOs)- or Ba(P309)- and Na PsOs)3 (130, I44, 146). 

Catalytic Action of Various Cations on the Rate of Hydrolysis of Polyphosphates... 

The effect of cations on the rate of hydrolysis of cycio-tri- and cvc/o-tetra-phosphates has also been studied.260 Alkali metal cations retarded the hydrolysis of both cyclo-phosphates in acidic solution but accelerated the reaction in basic solution. The catalytic activity followed the sequence Li+ > Na+> K+. Mg11, Ca11 and Ni11 retarded the hydrolysis of the cyclo-phosphates in the pH range 1.0-2.0 or 1.0-2.7, but accelerated the reaction at pH>3. Catalysis by Cu11 is observed above pH 2, while Alni has a marked catalytic effect at pH 1 and 2. A variety of other papers have appeared dealing with metal ion-promoted hydrolysis of polyphosphates.261-264 However, the mechanistic details of these reactions remain unclear and the catalytically active complexes remain undefined. 

In addition, they are anodic inhibitors, depositing iron metaphosphate, and forming y-Fe2C>3, thus stifling the anodic reaction. High and low pH or high temperatures will hasten the reversion (hydrolysis) of polyphosphate to orthophosphate. 

Figure 23. Hypothetical metal ion effect on the hydrolysis of polyphosphate (26).

J. D. Keasling (1997). Regulation of intracellular toxic metals and other cations by hydrolysis of polyphosphate. Annu. New York Acad. Sci., 829, 243-249. 

The effect of metal ions on the rates of hydrolysis of polyphosphates is of great biochemical interest. Calcium and magnesium ions probably form six-membered chelate rings with a long-chain polyphosphate, although it... 

Lanthanide hydroxide gels have been known for about 50 years to catalyze the hydrolysis of polyphosphates and phosphate esters (20). However, the study of these systems is fraught with similar difficulties to those mentioned previously, that is, the inability to be able to identify the complexes responsible for the activation. Butcher and Westheimer (20) in 1955 investigated the hydrolysis of a variety of phosphate esters by La(OH)3 gels. The gel promotes the hydrolysis of the esters by up to 10 -fold. The reaction is at the P-center as shown by tracer studies. In that communication, the mechanism by which the metal ion promotes hydrolysis could not be specified although a mechanism involving the intermediacy of the metaphosphate anion was suggested as a possibility. 

The ascorbic acid reduction method of Murphy and Riley (18) can also be used for orthophosphate analyses in estuarine waters since hydrolysis of polyphosphates and salt effects are absent in this technique. 

Products and kinetics of hydrolysis of polyphosphates have been reported for several systems. Transition-metal cations can have an accelerating or... 

Metal ions have been known for many years to promote the hydrolysis of polyphosphates and phosphate esters [12]. A major problem with these systems is that die divalent metal ions are substitutionally labile and form a variety of complexes, many of which are in rapid equilibrium. As a result it has been quite difficult to define any... 

The hydrolysis of polyphosphate chains is catalysed by heavy metal cations, the effect being most pronounced with cations of high charge and small radius. The effect is believed to be connected with chelation of the cations by the oxygen atoms, which probably increases the susceptibility of the P atom to nucleophilic attack. 

As usual there have been a number of papers on the hydrolysis of polyphosphates. Complexes of [VO] + or [VO] + with polyphosphates give species in which phosphate hydrolysis is much more rapid than for the uncomplexed species. We may also note the appearance of further evidence that the oxidation reactions of peroxodiphosphate involve hydrolysis in the rate-determining stage. Studies on the oxidation of antimony(iii), hydrazine, nitrite, and hypophosphite have appeared. ... 

Rates of decomposition of the phosphododecavanadate ion [H4PVi2036] depend on the concentration of acid or of alkali present. The vanadium is stated to end up in the form of [VO2] in acid solution, [HV04] and [HV207] in alka-line. Vanadium(v) is known to catalyse hydrolysis of polyphosphates. The maximum catalytic effect corresponds to the participation of a [V2P30io] anion (or some appropriately protonated form thereof), whose enthalpy of activation for dissociation must be unusually low. ... 

This procedure is based on the method of Strickland and Solorzano (Limnol. Oceanogr. 13 515, 1968). It relies on the fact that organic phosphate can be converted to orthophosphate without the hydrolysis of polyphosphates by the action of ultraviolet radiation (Armstrong, Williams, and Strickland, Nature, 211 481, 1966) and then any polyphosphate can be converted to orthophosphate by acid hydrolysis. The method measures inorganic and organic polyphosphates. 

---