Ternary Complexes in Solution. Comparison of the Coordination Tendency of Some Biologically Important Zwitterionic Buffers toward the Binary Complexes of Some Transition Metal Ions and Some Amino Acids

Abstract

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 (KNO3) for the interaction of glycine (aminoethanoic acid), serine (2-amino-3-hydroxypropanoic acid), methionine (2-amino-4-(methylthio)butanoic acid), aspartic acid (aminobutanedioic acid), glutamic acid (2-aminopropanedioic acid), and histidine (α-amino-1H-imidazole-4-propanoic acid) and Cu(II), Co(II), Ni(II), Mn(II), and Zn(II) with the biologically important secondary ligand zwitterionic buffers β-hydroxy-4-morpholinepropanesulfonic acid (MOPSO), 4-morpholinepropanesulfonic acid (MOPS), 3-[bis(2-hydroxyethyl)amino]-2-hydroxy-1-propanesulfonic acid (DIPSO), and 3-[N-tris(hydroxymethyl)methyl)amino]-2-hydroxypropanesulfonic acid (TAPSO) in 1:1:1 and 1:1:2 ratios, and the formation of various 1:1:1 ternary complexes and 1:1:2 quaternary complex species was inferred from the potentiometric pH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants of the different amino acids and secondary ligands studied have been refined with the SUPERQUAD computer program. The order of stability of the different normal ternary complexes in the systems under investigation in terms of metal ion follows generally the trend Cu(II) > Ni(II) > Co(II) > Zn(II) > Mn(II).

Cu(II) complexation by “non-coordinating” N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES buffer)☆

“…The formation of ternary complexes is an important issue when an impact of the weakly coordinating buffer on the main complexation equilibrium is to be taken into account. The formation of ternary complexes with Cu(II) and amino acids was reported for the somewhat analogous MOPSO [37].…”

Study of interactions of l-aspartic acid and l-glutamic acid with some metal acetates through volumetric behaviour over the temperature range (288.15 to 318.15)K

“…Thus, interactions between co-solute and L-aspartic acid are stronger than that of co-solute and L-glutamic acid. Some workers have reported [48] equilibrium constants of complexes formed by amino acids with transition metal ions in zwitterionic buffers at T = 298.15 K. The comparison of overall stability constants indicates the higher stabilities of complexes of di-carboxylic amino acids (L-aspartic acid and Lglutamic acid). This behaviour has been ascribed to the fact that di-carboxylic amino acids are much more prone to complex formation than mono-carboxylic amino acids.…”

Amino acid-based tweezers: The role of turn-like conformation in the binding of copper(II)

“…The data fitting was done by means of Hyperquad program [15]. During the refinement of the stability constants, the copper(II) hydrolytic species were taken into account [16] and the protonation constants of the investigated ligands determined previously were kept fixed.…”