Orthophosphate ion

The first example of a tetrakisimido analogue of the orthophosphate ion, PO, the solvent-separated ion pair [(THF)4Li][(THF)4Li2P(Nnaph)4] (16), was reported by Russell et al. [21]. This complex was isolated in low yield from the reaction of P2I4 with a-naphthylamine in THF/NEt3, followed by the addition of "BuLi. The mechanism of this remarkable redox process is not understood. 

Calcium phosphate precipitation may also be involved in the fixation of phosphate fertilizer in soils. Studies of the uptake of phosphate on calcium carbonate surfaces at low phosphate concentrations typical of those in soils, reveal that the threshold concentration for the precipitation of the calcium phosphate phases from solution is considerably increased in the pH range 8.5 -9.0 (3). It was concluded that the presence of carbonate ion from the calcite inhibits the nucleation of calcium phosphate phases under these conditions. A recent study of the seeded crystal growth of calcite from metastable supersaturated solutions of calcium carbonate, has shown that the presence of orthophosphate ion at a concentration as low as 10-6 mol L" and a pH of 8.5 has a remarkable inhibiting influence on the rate of crystallization (4). A seeded growth study of the influence of carbonate on hydroxyapatite crystallization has also shown an appreciable inhibiting influence of carbonate ion.(5). 

This calcium ion-dependent enzyme [EC 3.6.1.5] (also known as ATP-diphosphatase, adenosine diphosphatase, and ATP-diphosphohydrolase) catalyzes the hydrolysis (with two H2O) of ATP to generate AMP and two orthophosphate ions. The enzyme will also utilize ADP as a substrate as well as other nucleoside triphosphates and diphosphates. 

Persson, P., Nillson, N. Sjoberg, S. (1996) Structure and bonding of orthophosphate ions at the iron oxide interface. J. Coll. Interf Sd. 177 263-275... 

Elemental composition P 37.78%, H 3.69%, 0 58.54%. The acid in solid form may be identified by its physical properties. Aqueous solution may be heated and phosphorus acid is converted to phosphoric acid which is measured for orthophosphate ion by ion chromatography or colorimetry (see Phosphoric Acid). A cold aqueous solution may be analyzed for phosphite ion by ion chromatography, following appropriate dilution. Strength of the acid in an aqueous solution may be measured by acid-base titration using a standard solution of alkali. Also, titration against a standard solution of silver nitrate using potassium chromate as indicator may serve as an additional confirmatory test. 

Elemental composition P 20.20%, O 10.43%, Cl 69.36%. The compound is hydrolyzed in water and the products phosphoric and hydrochloric acids are measured by a colorimetric method for orthophosphate ion (see Phosphoric Acid, Analysis), and titration with silver nitrate for the chloride ion. Also, phosphate and chloride ions can be measured by ion chromatography. 

Phosphoric acid (orthophosphoric acid), as well as the different phosphoric acids, can ionize to form corresponding phosphates. When phosphoric acid loses its three hydrogen ions, it becomes the phosphate or orthophosphate ion, P043. Likewise, when the polyphosphoric acids lose their hydrogen ions, the corresponding polyphosphate ion is produced. For example,... 

In order to measure, by the methods of isotopic dilution the mass concentration of the orthophosphate ion PO4-, in an aqueous solution. 3 mg of labelled phosphate ion 32PC>4 (32P being a /3-emitter whose half-life is 14 days), is added to 1 g of the sample solution. 

Mucci A. (1986) Growth kinetics and composition of magnesian calcite overgrowths precipitated from seawater Quantitative influence of orthophosphate ions. Geochim. Cosmochim. Acta 50, 2255-2265. 

The nature of the calcium orthophosphate precipitated from an aqueous solution containing calcium and orthophosphate ions depends on the pH of the solution. The solubility products of the different calcium orthophosphates at room temperature1 indicate that the pH must be less than 4 in order to obtain calcium hydrogen orthophosphate... 

Just as P043- is known as the orthophosphate ion, the tetrahedral Si044- ion is called orthosilicate. This tetrahedral monomeric unit is found in several minerals (e.g., phenacite, Be2Si04, and willemite, Zn2Si04). In both of these minerals, the metal is surrounded by four oxygen atoms in Si04 units arranged tetrahedrally around the metal ... 

Organophosphoric esters are very effective and degradable pesticides [304], which makes them preferable to their chlorine-based counterparts. Their hydrolysis behavior is well known [305], the final product being the orthophosphate ion. But these compounds are very toxic to humans because of their inhibiting effect on acetylcolinesterase as little as a few ppm can be lethal [306]. 

Fig. 6.2.1. Regulation of assimilatory sulfate metabolism in Saccharomyces cerevisiae. (Cherest et al., 1969 Siegel, 1975 de Vito and Dreyfuss, 1964). Abbreviations as follows ADP adenosine 5 -diphosphate AMP adenosine 5 -phosphate (adenylic acid) APS adenylyl sulphate ATP adenosine 5 -triphosphate NADP, NADPH nicotinamide-adenine dinucleotide phosphate (oxidised and reduced) PAP adenosine 3, 5 -diphos-phate PAPS 3 -phosphoadenylyl sulphate Pj orthophosphate ion PPj pyrophosphate ion.

After extraction, in the filtered extract, phosphorus is estimated colorimetrically by adding ammonium molybdate and thereafter reducing the molybdenum-phosphate complex in acidic medium with a reducing agent for which stannous chloride is used. The intensity of the blue colour molybdenum blue is directly related to the quantity of orthophosphate ion and thus provides a measure for the concentration of P in test solution. The absorbance or transmittance is measured spectrophotometrically at 660 mp,. wavelength. 

Phosphorus compounds occur in wastewater under various forms, among which the reduced ones are predominant. The phosphorus compounds of wastewater concern not only some organic forms (natural or anthropic) but also orthophosphate ion and acid hydrolysable phosphate (condensed phosphate) (Fig. 10). 

A few inhibitors of these several enzymes are provided in Voet and Voet (1990). These include glucose-6-phosphate as an inhibitor for hexokinase, as it is a reaction product. Also, ATP and citrate are listed as inhibitors of PFK, and ATP is an inhibitor for pyruvate kinase, as it is a conversion product. Other inhibitors are tabulated in Appendix A of Hoffman s Cancer and the Search for Selective Biochemical Inhibitors (1999). On the other hand, Voet and Voet (1990) list a few activators or promoters for PFK, including ADP, fructose 6-phosphate (which is a reactant), fructose 1,6-bisphosphate (which is a product), the ammonium ion, and the orthophosphate ion Pj. The situation can get complicated. 

Certain dipositive metal ions not only accelerate the hydrolysis of ATP, as mentioned above, but also assist in the transfer of a phosphoryl group from one molecule to another. Such a nonenzymatic transphosphorylation takes place between ATP and an orthophosphate ion or its monoester in the presence of calcium(II), cadmium(II), and manganese(II). This type of nonenzymatic process can serve as a model for the biologically important enzymatic transphosphorylations that involve ATP, although... 

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