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In this paper we report a comparison on the sequestering ability of some polycarboxylic ligands towards dioxouranium(VI) (UO(2)(2+), uranyl). Ligands taken into account are mono- (acetate), di- (oxalate, malonate, succinate and azelate), tri- (1,2,3-propanetricarboxylate) and hexa-carboxylate (1,2,3,4,5,6-benzenehexacarboxylate). The sequestering ability of polycarboxylic ligands towards UO(2)(2+) was quantified by a new approach expressed by means of a sigmoid Boltzman type equation and of a empirical parameters (pL(50)) which defines the amount of ligand necessary to sequester 50% of the total UO(2)(2+) concentration. A fairly linear correlation was obtained between pL(50) or log K(110) (log K(110) refers to the equilibrium: UO(2)(2+)+L(z-)=UO(2)L((2-z)); L=generic ligand) and the polyanion charges. In order to complete the picture, a tetra-carboxylate ligand (1,2,3,4-butanetetracarboxylate) was studied in NaCl aqueous solutions at 0potentiometry, ISE-[H(+)] glass electrode. The formation of ML(2-), MLH(-), MLH(2)(0) and MLOH(3-) species (M=UO(2)(2+) and L=1,2,3,4-butanetetracarboxylate) was found, with log beta(110)=7.937+/-0.028, log beta(111)=13.066+/-0.027, log beta(112)=17.401+/-0.013, log beta(11-1)=2.062+/-0.040 at I=0 mol L(-1) and t=25 degrees C [beta(pqr) refer to reaction: pUO(2)(2+)+qL(4-)+rH(+)=(UO(2)(2+))(p)L(q)H(r)((2p-4q+r))]. The dependence on ionic strength of all ligand protonation constants and of the complex formation constants of UO(2)(2+)-polycarboxylate systems was modelled by the SIT (specific ion interaction theory) approach and by the Pitzer equations.


Francesco Crea, Claudia Foti, Silvio Sammartano. Sequestering ability of polycarboxylic ligands towards dioxouranium(VI). Talanta. 2008 May 15;75(3):775-85

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PMID: 18585146

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