Improved selectivity to orthophosphate, pyrophosphate and triphosphate by adding metal ions to a tripodal ligand

Abstract

The strong and selective binding of phosphate (PO), pyrophosphate (PP) and triphosphate (tP) by tripodal ligand N, N, N-tri((2-aminoethyl)thioethyl)-amine (L) has been studied in

aqueous solution at <i>I </i>= 0.1 mol dm^-3 KNO₃ and 25°C. The interactions between L and the inorganic substrates are described and equilibrium constants for each species formed have been determined. The stability constants of 1 : 1: 1 M (M = Cu²⁺ or Zn²⁺):L:S (S = PO, PP, tP) are determined by potentiometric <i>p</i>H titrations. The interactions of Zn(II)/L/phosphate systems and Cu(II)/L/phosphate systems are investigated by ³¹P NMR and EPR spectra respectively. The results show that metal ion acts as "messenger" or bridge between the receptor and the substrate, and the existence of metal ion in the ternary systems leads to

competition between the mixed ligands. The metal ion improves the selectivity and recog nition of the substrates by protonated tripodal ligand.