Polyphosphate ligands

If the polyelectrolyte can coordinate strongly to a metal ion, marked deceleration effects can be noted, as, for example, in the reactions of Ni + and Co + with pad in the presence of polyphosphates. Modifications of equilibria constants in these micelles must also be recognized as contributing to rate change, e. g., ligand pK or keto-enol equilibria may be altered. 

This Group IIA (or Group 2) element (atomic symbol, Ca atomic number, 20 atomic weight, 40.078 electronic configuration = ls 2s 2p 3s 3p 4s ) loses both As electrons to form a divalent cation of 0.99A ionic radius. Ionic calcium combines readily with oxygen ligands (chiefly water, phosphates, polyphosphates, and carbox-ylates) to form stable metal ion complexes. Ca under-... 

After a carboxylate, the next most significant biological ligand for Mg + is a phosphate. Phosphates, in addition to being present as inorganic phosphate (Pi), also happily polymerize to form not only diphosphates (for example, PPi and ADP) but also triphosphates (nucleoside triphosphates such as ATP). Many of these polyphosphates have fundamental biochemical importance as evidenced by the ATP ADP - - Pi reaction. 

In spite of much information available for the interactions of various metal ions with small oxoanions of phosphorus, relatively little information has been obtained for the complex formation of long-chain polyphosphate ion. This may be due to the fact that the conventional methods useful for the study of the complex formation of a relatively small ligand are not always applicable to the polyanion complex formation system. Since a gel chromatographic method based on the same principle as the equilibrium dialysis method has been proved to be applicable in the field of inorganic complex chemistry (1), this method has been applied to the study of the binding of long-chain polyphosphate ions to magnesium ion. 

In aqueous solution many other types of polyoxo ligands effectively complex the Ln3+ ions, including polyphosphates, mixed phosphoryl-carbonyl species, and crown ethers. 

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