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<p>The speciation of binary Nickel(II) complexes with pyridinecarboxylic acids—Nicotinic Acid (HNic), Picolinic Acid (HPic), and Dipicolinic Acid (H<sub>2</sub>Dipic)—as well as their ternary complexes with various amino acids (Glycine, Asparagine, Lysine, Serine, and Aspartic Acid) was investigated in aqueous solution. The study was conducted using potentiometric measurements (emf(H)) at 25&#xa0;°C and an ionic strength of 1.0&#xa0;mol·dm<sup>–3</sup> NaCl. The stability constants were determined by analyzing the potentiometric data with the LETAGROP software. For the binary systems, the formation of [Ni(Nic)]<sup>+</sup>, [Ni(Pic)<sub>n</sub>] (n = 1, 2, 3), and Ni(Dipic)<sub>n</sub> (n = 1, 2) species was established. In the ternary systems, the results indicate the formation of several mixed-ligand species, including protonated complexes such as [Ni(Pic)(HL)]<sup>+</sup> and hydrolyzed species like [Ni(Pic)(L)(OH)]<sup>−</sup> at higher pH values. The coordination behavior of the amino acids was found to be predominantly bidentate, with the side chains of bulky amino acids showing minimal involvement in metal coordination due to steric hindrance. Species distribution diagrams were generated to illustrate the prevalence of these complexes across a wide pH range (2.0–10.0), providing a comprehensive view of the chemical equilibria in these bioinorganic-relevant systems.</p>

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Speciation in Aqueous Solution of the Binary Nickel(II) Complexes with Pyridinecarboxylic Acids and Their Ternary Complexes with Amino Acids

  • 期刊论文

  • 发表日期：

    2026年7月12日

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  • Vito Lubes,
  • Mary Lorena Araujo,
  • Lino Hernández

摘要

The speciation of binary Nickel(II) complexes with pyridinecarboxylic acids—Nicotinic Acid (HNic), Picolinic Acid (HPic), and Dipicolinic Acid (H2Dipic)—as well as their ternary complexes with various amino acids (Glycine, Asparagine, Lysine, Serine, and Aspartic Acid) was investigated in aqueous solution. The study was conducted using potentiometric measurements (emf(H)) at 25 °C and an ionic strength of 1.0 mol·dm–3 NaCl. The stability constants were determined by analyzing the potentiometric data with the LETAGROP software. For the binary systems, the formation of [Ni(Nic)]+, [Ni(Pic)n] (n = 1, 2, 3), and Ni(Dipic)n (n = 1, 2) species was established. In the ternary systems, the results indicate the formation of several mixed-ligand species, including protonated complexes such as [Ni(Pic)(HL)]+ and hydrolyzed species like [Ni(Pic)(L)(OH)]− at higher pH values. The coordination behavior of the amino acids was found to be predominantly bidentate, with the side chains of bulky amino acids showing minimal involvement in metal coordination due to steric hindrance. Species distribution diagrams were generated to illustrate the prevalence of these complexes across a wide pH range (2.0–10.0), providing a comprehensive view of the chemical equilibria in these bioinorganic-relevant systems.