Stability Constants Of Binary Research Articles

Chemical speciation of L-glutamine complexes with Co(II), Ni(II) and Cu(II) in cationic micellar medium

The impact of cationic micelles on the protonation equilibria of L-glutamine and chemical speciation of its complexes with Co(II), Ni(II) and Cu(II) have been studied by monitoring hydrogen ion concentration pH metrically at 303 K and at an ionic strength of 0.16 M. The protonation constants and binary stability constants have been calculated with the computer program MINIQUAD75. The best fit chemical models are selected based on standard deviations in the model parameters and residual analysis using crystallographic R-factor and sum of squares of residuals in all mass-balance equations. The trend in the variation of stability constants of the complexes with mole fraction of the surfactant is attributed to the compartmentalization of complexation equilibria. Distribution of species and effect of influential parameters on chemical speciation have also been presented. KEY WORDS: Chemical speciation, complex equilibria, L-glutamine, cationic micelles Bull. Chem. Soc. Ethiop. 2012, 26(3), 383-394.DOI: http://dx.doi.org/10.4314/bcse.v26i3.7

Protonation and Complexation Equilibria of l-Glutamine in Non-ionic Micellar Medium

Protonation equilibria of l-glutamine and speciation of its complexes with Co(II), Ni(II) and Cu(II) have been studied pH-metrically in 0–2.5 % v/v triton X-100 solution maintaining an ionic strength of 0.16 mol l−1 at 303 K. The protonation constants and binary stability constants have been calculated with the computer program MINIQUAD75. Best fit chemical models have been selected based on standard deviation in stability constants and residual analysis using crystallographic R-factor and sum of squares of residuals in all mass-balance equations. The trend in the variation of stability constants of the complexes with mole fraction of the medium is attributed to the compartmentalization of complexation equilibria. Distribution of species and effect of influential parameters on chemical speciation have also been presented.

Effect of anionic micelles on speciation of L-glutamine in presence/absence of metals

Protonation equilibria of L-glutamine and speciation of its complexes with Co(II), Ni(II) and Cu(II) have been studied in 0–2.5% w/v SLS–water media using pH-metric method. The protonation constants and binary stability constants have been calculated with the computer program MINIQUAD75. Selection of the best fit chemical models is based on standard deviation in stability constants and residual analysis using crystallographic R-factor and sum of squares of residuals in all mass-balance equations. The trend in the variation of stability constants of the complexes with mole fraction of the medium is attributed to the compartmentalisation of complexation equilibria. Distribution of species and effect of influential parameters on chemical speciation have also been presented.

Potentiometric investigation of Schiff base equilibria involving salicylaldehyde and tridentateα-aminoacids with Cu(II), Ni(II) and Zn(II) in aqueous medium

Potentiometric determination of equilibrium constants and species distribution of Schiff base complexes, in aqueous solution, involving salicylaldehyde (A) and tridentateα-amino acids (B)(L-threonine, L-glutamine and L-glutamic acid) with metal ions Cu(II), Ni(II) and Zn(II)(M) indicates preference for the formation of Schiff base complexes rather than the ligands binding as such to the metal ions. Binary stability constants follow the Irving-Williams order Cu(II)>Ni(II)>Zn(II). The influence of additional coordination sites such as -OH, -CONH2 and -COOH in the formation of ternary complexes is also discussed.

Binary and ternary complexes of copper(II) containing some potentially tridentate ligands

The multiple equilibria involved in some new ternary systems of general formula CuII–A–B [A =DL-2,3-diaminopropionic acid (dapa) or DL-2,4-diaminobutyric acid (daba); B = daba, DL-ornithine (Orn), DL-3-aminobutyric acid (3-aba), or DL-4-amino-3-hydroxybutyric acid (ahba) for the systems with A = dapa, and B = Orn, DL-2-aminobutyric acid (2-aba), 3-aba, or ahba for the systems with A = daba] have been studied pH-metrically at 37 °C and I= 0.15 mol dm–3(Na[ClO4]). Auxiliary data, such as the acid dissociation constants of dapa, daba, Orn, and ahba and their binary stability constants with CuII, have also been obtained under identical conditions. The results suggest that dapa, daba, and ahba bind in a tridentate manner in their 1 : 1 binary complexes. However, Orn appears to co-ordinate in a glycine-like mode both in the binary and ternary systems. The probable structures for the various binary and ternary complexes in this study are discussed in terms of their stability-constant data. In general, the results suggest that CuII prefers to have one five- and one six-membered chelate ring rather than two rings of the same size in its co-ordination sphere.

Complexes of vitamin B 6—IX Ternary complexes of Ni(II), Cu(II) and Zn(II) with pyridoxamine and salicylic acid

Equilibrium-based computer models were used in the calculation of the stability constants of the ternary complexes of Ni(II), Cu(II) and Zn(II) involving pyridoxamine (PM) and salicylic acid (Sal) from pH-metric data at 0.5 M KNO 3 and 30°C. It has been concluded that most of the complexes are protonated with the possible location of proton on PM moiety. The ternary stability constants of some ternary complexes were discussed in terms of binary stability constants of PM and Sal. The model equilibria were correlated with pertinent published equilibria.