Speciation of the Ternary Cobalt(II) Picolinic and Dipicolinic Acid Complexes with Small Bioligands

Abstract

This study reports on the determination of stability constants for ternary cobalt­(II) complexes using primary ligands, pyridine carboxylic acids (picolinic (HPic) and dipicolinic (H2Dipic) acids), along with secondary ligands: lactic acid (HLac, HL), oxalic acid (H2Ox, H2L), citric acid (H3Cit, H3L), and phosphoric acid (H3PO4, H3L). Potentiometric data for binary cobalt­(II) bioligand complexes and ternary cobalt­(II) pyridine carboxylic acid and bioligand complexes were analyzed using the computational program LETAGROP. The experiments were conducted in an ionic medium of 1.0 mol dm–3 NaNO3 at 25 °C. Species distribution diagrams were generated, and relative stability parameters Δlog10 K, log10 X, and % R.S. were calculated. These findings may have important implications for the design of new cobalt­(II) complexes for various applications.

Speciation Studies of Binary and Ternary Complexes Formed with Fe(II) Ion, Picolinic Acid, and Several Amino Acids

“…Δlog K was not evaluated for Fe(II)-Pic-H 2 His and Fe(II)-Pic-H 2 Lys as [Fe(L)] + was not observed in binary systems Fe(II)−HHis and Fe(II)−H 2 Lys. The positive values observed for all the amino acids HL used in this work indicate that ternary complexes are more stable than their binary counterparts, 5,15,16 which is also confirmed in the speciation diagrams of all studied ternary systems.…”

“…The stability of the ternary compounds was evaluated with respect to the binary ones by means of Δlog K, which was determined ,, using the following equilibria: false[ Fe ( Pic ) false] + + false[ Fe ( L ) false] + ⇌ [ Fe false( Pic false) false( normalL false) ] + Fe 2 + , normalΔ log .25em K normalΔ log K = log .25em β ( Fe false( Pic false) false( normalL false) ) − ( log β false( Fe ( Pic ) false) + log β false( Fe ( L ) false) ) …”

“…The positive values observed for all the amino acids HL used in this work indicate that ternary complexes are more stable than their binary counterparts, ,, which is also confirmed in the speciation diagrams of all studied ternary systems.…”

“…The stability of the ternary compounds was evaluated with respect to the binary ones by means of Δlog K, which was determined 5,15,16 using the following equilibria: 31 3.54 33 4 34 4.20 35 3.42 33 3.24 33 4.90 32 4.31 36 3.83 33…”

“…Over the past four decades, coordination compounds have played a significant role in the research of compounds with desirable medicinal activities. − Typically, compounds containing essential elements such as Cu­(II) or Ni­(II) as the metallic center are preferred due to their ease of metabolization and reduced potential toxicity. ,− …”