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|Section2= }} A phosphate (PO43−) is an inorganic chemical and a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Of the various phosphoric acids and phosphates, organic phosphates are important in biochemistry and biogeochemistry (ecology), and inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry. At elevated temperatures in the solid state, phosphates can condense to form pyrophosphates. The addition and removal of phosphates from proteins in all cells is a pivotal strategy in the regulation of metabolic processes. Phosphorylation and dephosphorylation are important ways that energy is stored and released in living systems. ==Chemical properties== The phosphate ion is a polyatomic ion with the empirical formula PO43− and a molar mass of 94.97 g/mol. It consists of one central phosphorus atom surrounded by four oxygen atoms in a tetrahedral arrangement. The phosphate ion carries a negative-three formal charge and is the conjugate base of the hydrogen phosphate ion, HPO42−, which is the conjugate base of H2PO4−, the dihydrogen phosphate ion, which in turn is the conjugate base of , phosphoric acid. A phosphate salt forms when a positively charged ion attaches to the negatively charged oxygen atoms of the ion, forming an ionic compound. Many phosphates are not soluble in water at standard temperature and pressure. The sodium, potassium, rubidium, caesium, and ammonium phosphates are all water-soluble. Most other phosphates are only slightly soluble or are insoluble in water. As a rule, the hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates. The pyrophosphates are mostly water-soluble. Aqueous phosphate exists in four forms. In strongly basic conditions, the phosphate ion (PO43−) predominates, whereas in weakly basic conditions, the hydrogen phosphate ion (HPO42−) is prevalent. In weakly acid conditions, the dihydrogen phosphate ion (H2PO4−) is most common. In strongly acidic conditions, trihydrogen phosphate () is the main form. Image:3-phosphoric-acid-3D-balls.png| Image:2-dihydrogenphosphate-3D-balls.png| Image:1-hydrogenphosphate-3D-balls.png| Image:0-phosphate-3D-balls.png| More precisely, considering these three equilibrium reactions: : H+ + H2PO4− :H2PO4− H+ + HPO42− :HPO42− H+ + PO43− the corresponding constants at 25 °C (in mol/L) are (see phosphoric acid): : (pKa1 2.12) : (pKa2 7.21) : (pKa3 12.67) The speciation diagram obtained using these p''K'' values shows three distinct regions. In effect, , and behave as separate weak acids. This is because the successive p''K'' values differ by more than 4. For each acid, the pH at half-neutralization is equal to the p''K'' value of the acid. The region in which the acid is in equilibrium with its conjugate base is defined by pH ≈ p''K'' ± 2. Thus, the three pH regions are approximately 0–4, 5–9 and 10–14. This is idealized, as it assumes constant ionic strength, which will not hold in reality at very low and very high pH values. For a neutral pH as in the cytosol, pH=7.0 : so that only and ions are present in significant amounts (62% , 38% . Note that in the extracellular fluid (pH=7.4), this proportion is inverted (61% , 39% ). Phosphate can form many polymeric ions such as pyrophosphate), , and triphosphate, . The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of and are found in many compounds. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「phosphate」の詳細全文を読む スポンサード リンク
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