Studies in amine-amino acid mixed ligand chelates—I
ABSTRACT Irving-Rossotti technique has been applied to study the formation constant of the reaction (Cu A)2+ + L− ⇌ (Cu AL)+ where A = dipyridyl and L = Glycine, α or β-alanine. Copper dipyridyl 1 : 1 is known to form at lower pH and is stable at higher pH when the secondary ligand gets bound. The values of the formation constant obtained in the mixed ligand systems are little less than the first formation constant of Cu-amino acid simple systems.
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ABSTRACT: Formation constants of Cu(II) ternary complexes involving bipyridyl as the primary ligand and the bidentate amino acids glycine, alanine, valine, leucine, phenylalanine, tryptophan, methionine and ethionine as the secondary ligands were determined at 35.0°C and μ = 0.2 (KNO3). Comparison of the stabilities of the ternary and the corresponding binary complexes in terms of ΔlogK shows that the ternary complexes of tryptophan and phenylalanine are more stable. This enhanced stability has been attributed to intramolecular metalbridged stacked adducts. Such stacking interactions on a more modest scale are observed even in the bis Cu(II) binary complexes of tryptophan and phenylalanine. In the case of ternary complexes involving ethionine, intramolecular metal-bridged hydrophobic interaction was observed. Enhanced stability of the ternary complexes is not observed when the secondary amino acids are glycine, alanine, leucine, valine or methionine, These amino acids show the usual stabilities expected for ternary systems based on a combination of π-electron withdrawal from the metal by bipyridyl and statistical effects.Journal of Coordination Chemistry 02/2007; 16(1):1-7. DOI:10.1080/00958978708079800 · 2.22 Impact Factor
Journal of the National Science Foundation of Sri Lanka 12/2013; 41(4). DOI:10.4038/jnsfsr.v41i4.6253 · 0.14 Impact Factor
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ABSTRACT: Spectrophotometric and pH-metric studies of the aqueous binary and mixed ligand complexes of Pb(II), Cd(II), Al(III) and Cu(II) were carried out with ascorbic acid and paracetamol. The study was conducted at an ionic strength of 0.15 mol dm-3 and a temperature of 37.0 ± 0.2 oC. The protonation constants of the free ligands and the stability constants of the binary and mixed ligand complexes were determined using pH titration data. Proton dissociation of free ligands and complex formation were also qualitatively confirmed with UV data. The stabilities of mixed ligand complexes were quantitatively compared with those of the corresponding single ligand complexes in terms of Δlog K. Aluminium formed the most stable binary complex; Al (paracetamol)2, with a high overall stability constant (log β2 = 16.74). The stable mixed ligand complexes; Pb (ascorbic acid) (paracetamol), Cd (ascorbic acid)(paracetamol) and Cu (ascorbic acid) (paracetamol) were observed with positive Δlog K values showing the ability of using them in less harmful chelation therapy of these metals. Further, the results revealed that the bioavailability of both ligands will be lower for a metal intoxicated person.Journal of the National Science Foundation of Sri Lanka 09/2013; 41(4):337-344. · 0.14 Impact Factor