Edgar Del Carpio

Potentiometric studies on the formation equilibria of ternary complexes of vanadium(III) with cysteine and some amino acids

In this work, we present the results of the speciation of the ternary vanadium(III)–cysteine (H2Cys) complexes with the amino acids glycine (HGly), proline (HPro), α-alanine (HαAla), β-alanine (HβAla), histidine (HHis), aspartic acid (H2Asp), and glutamic acid (H2Glu), studied by the measurements of electromotive forces, emf(H), using 3.0 mol dm−3 KCl as the ionic medium at 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid base reactions of the amino acids, which were kept fixed during the analysis. In the vanadium(III)–cysteine-amino acid (HB) systems, where HB represents the bidentate ligands, the formations of the ternary complexes [V(Cys)(HB)]+, V(Cys)(B), [V(Cys)(B)(OH)]−, and [V(Cys)(B)(OH)2]2− were observed. In the vanadium(III)-H2Cys-HHis system, the formations of the complexes [V(HCys)(HHis)]2+, [V(HCys)(His)]+, V(Cys)(His), and [V(Cys)(His)(OH)]− were detected; in the vanadium(III)-H2Cys-H2Asp system, the complexes [V(H2Cys)(HAsp)]2+, [V(HCys)(HAsp)]+, V(HCys)(Asp), [V(Cys)(Asp)]−,and [V(Cys)(Asp)(OH)]2− were detected; and finally, in the vanadium(III)-H2Cys-H2Glu system, the complexes [V(H2Cys)(HGlu)]2+, [V(HCys)(HGlu)]+, V(Cys)(HGlu), and [V(Cys)(HGlu)(OH)]− were observed. The species distribution diagrams as a function of pH are briefly discussed.

Mixed-ligand complex formation equilibria of vanadium(III) with picolinic and dipicolinic acids with some dicarboxylic acids (oxalic, malonic, and phthalic acids) studied in 3.0 M KCl at 25 °C

The ternary complexes formed between vanadium(III) and picolinic acid (Hpic) and dipicolinic acid (H2dipic) with the dicarboxylic oxalic, malonic, and phthalic acids (H2ox), (H2mal), and (H2phtha) briefly (H2L) were studied in aqueous solution by means of electromotive forces’ measurements emf(H) at 25 °C and 3.0 mol dm−3 KCl as ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, considering the hydrolysis products of the V(III), the acidity constants of the ligands employed, and the formation constants of the binary complexes, obtaining the complexes V(pic)(ox), log β1,1,1,−3 = 5.39(7) and [V(pic)2(ox)]−, log β1,2,1,−4 = 4.3(1); V(pic)(ma), log β1,1,1,−3 = 5.58(5) and [V(pic)2(ox)]−, log β1,2,1,−4 = 5.00(8); V(pic)(phtha), log β1,1,1,−3 = 5.66(6) and [V(pic)2(phtha)]− log β1,2,1,−4 = 4.5(2) in the vanadium(III)-Hpic-H2L system. In the case of the vanadium(III)-H2dipic-H2L system, the complexes [V(dipic)(ox)]−, log1,1,1,−4 β = 9.3(2), [V(dipic)(Hox)(ox)]2−, log β1,1,2,−5 = 11.2(2) and [V(dipic)(ox)2]3−, log β1,1,2,.6 = 5.7 max 7.0; [V(dipic)(ma)]−, log β1,1,1,−4 = 8.7(2), [V(dipic)(Hma)(ma)]2−, log β1,1,2,−5 = 10.3(1) and [V(dipic)(ma)2]3−, log β1,1,2,.6 = 6.9(1); [V(dipic)(phtha)]−, log β1,1,1,−4 = 10.9(1), [V(dipic)(Hphtha)(phtha)]2−, log β1,1,2,−5 = 9.2 max 10.4 and [V(dipic)(phtha)2]3−, log β1,1,2,.6 = 6.9(3) were observed.