Given the pK_a1 of H₃PO₄ (phosphoric acid) of 2.2 and pK_a2 of 7.2, inorganic phosphate at physiological values of pH 7–7.4 is a mix of monoanions and dianions. In the P^V oxidation state, the central phosphorus atom in inorganic phosphate and biological derivatives is electrophilic, capturable by cellular nucleophiles. Complementarily, the peripheral oxyanions can behave as nucleophiles, imparting bifunctional reactivity to PO₄²⁻ ions. Most notable are phosphoric anhydrides, such as inorganic pyrophosphate, and inorganic triphosphate: kinetically stable but thermodynamically activated tetra-anionic and penta-anionic species in neutral aqueous solutions. These anionic kinetically stable anhydride linkages prefigure most of phosphorus chemical biology.