Speciation of the ternary complexes of vanadium(III)-dipicolinic acid and the amino acids cysteine, histidine, aspartic and glutamic acids in 3.0 mol·dm-3 KCl at 25 °C

摘要

In this work we present results for the speciation of the ternary complexes formed in the aqueous vanadium(III)-dipicolinic acid and the amino acids cysteine (H2cys), histidine (Hhis), aspartic acid (H2asp) and glutamic acid (H2glu) systems (25 °C; 3.0 mol·dm -3 KCl as ionic medium), determined by means of potentiometric measurements. The potentiometric data were analyzed with the least-squares program LETAGROP, taking into account the hydrolysis of vanadium(III), the acid-base reactions of the ligands, and the binary complexes formed. Under the experimental conditions (vanadium(III) concentration = 2-3 mmol·dm -3 and vanadium(III): dipicolinic acid: amino acid molar ratio 1:1:1, 1:1:2 and 1:2:1), the following species [V(dipic)(H2asp)] +, [V(dipic)(Hasp)], [V(dipic)(asp)]-, [V(dipic)(asp)(OH)]~(2-), and [V(dipic)(asp)(OH)_2] ~(3-) were found in the vanadium(III)-dipicolinic acid-aspartic acid system. In the vanadium(III)-dipicolinic acid-glutamic acid system [V(Hdipic)(H2glu)]2+, [V(dipic)(H_2glu)] +, [V(dipic)(Hglu)], [V(dipic)(Hglu)(OH)]-, and [V(dipic)(Hglu)(OH)_2]~(2-) were observed. In the vanadium (III)-dipicolinic acid-cysteine system the complexes [V(dipic)(H 2cys)]+, [V(dipic)(Hcys)], [V(dipic)(cys)]-, and [V(dipic)(cys)(OH)]~(2-) were present. And finally, in the vanadium(III)-dipicolinic acid-histidine system the complexes [V(Hdipic)(Hhis)]2+, [V(dipic) (Hhis)]+, [V(dipic)(his)], [V(dipic)(his)(OH)]-, and [V(dipic)(his)(OH)_2] ~(2-) were observed. The stability constants of these complexes were determined. The species distribution diagrams as a function of pH are briefly discussed.