Influence of electrostatic effect on the stability of mixed-ligand complexes: Uranyl-complexone-phenol/phenolic acid ternary systems

1986 ◽  
Vol 97 (5-6) ◽  
pp. 543-546
Author(s):  
Anushree Samanta ◽  
S. N. Limaye ◽  
M. C. Saxena
Keyword(s):  
Phenolic Acid ◽  
Ternary Systems ◽  
Mixed Ligand ◽  
Mixed Ligand Complexes ◽  
Electrostatic Effect ◽  
The Stability

Ternary Complexes in Solution, XII. Models for Biological Mixed-Ligand Complexes: 2,2′-Bipyridyl-Cu2+-Oligoglycine Systems

1972 ◽  
Vol 27 (4) ◽  
pp. 353-364 ◽  
Author(s):  
Helmut Sigel ◽  
Rolf Griesser ◽  
Bernhard Prijs
Keyword(s):  
Coordination Sphere ◽  
Ternary Complexes ◽  
Mixed Ligand ◽  
Amide Group ◽  
Amide Proton ◽  
Mixed Ligand Complexes ◽  
Apical Position ◽  
Binary Complexes ◽  
The Stability ◽  
Ph Range

The stability constants of the binary Cu2+ complexes of glycine amide, diglycine, diglycine amide, triglycine, and tetraglycine were determined, as were those of the mixed-ligand Cu2+ systems containing 2,2′-bipyridyl and one of the mentioned oligoglycines. The results evidence that all these complexes have the same structure and, therefore, the binding sites of the ligands have to be the terminal amino group and the oxygen of the neighbored amide group. The stability differences between the ternary and the binary complexes are in agreement with this interpretation. It is of interest to note that these ternary complexes are significantly more stable than expected on statistical reasons. With increasing pH, the amide groups in the binary complexes are successively deprotonated. Thus, with tetraglycine finally all three amide protons are displaced, and the amide nitrogens are bound to the square-planar coordination sphere of Cu2+. As in the Cu2+-2,2′-bipyridyl 1 : 1 complex, only two coordination positions are left for the binding of the oligoglycine, in the tenary complexes, only one amide group can be deprotonated. An increase in pH with deprotonation of other amide groups leads to a displacement of 2,2′-bipyridyl, i. e. the simple binary complexes result. No evidence could be observed for the coordination of a deprotonated amide group to an apical position of the coordination sphere of Cu2+. Additionally, while the displacement of the first amide proton in the several binary Cu2+ oligoglycine complexes occurs over a large pH range (4 to 7), the deprotonation in all the mixed-ligand complexes takes place at pH approximately 8.

Ternary Complexes in Solution+ with Phosphonates as Ligands. Intramolecular Equilibria in the Mixed Ligand Cu2+ Complexes Formed by 2,2′-Bipyridyl or 1,10-Phenanthroline and the Dianion of Phosphonylmethoxyethane in Water-Dioxane Mixtures

1993 ◽  
Vol 48 (9) ◽  
pp. 1279-1287 ◽  
Author(s):  
Matthias Bastian ◽  
Dong Chen ◽  
Fridrich Gregáň ◽  
Guogang Liang ◽  
Helmut Sigel
Keyword(s):  
Equilibrium Constants ◽  
Parent Compound ◽  
Mixed Ligand ◽  
Mixed Ligand Complexes ◽  
Straight Line ◽  
Water As Solvent ◽  
Phosphate Monoesters ◽  
Ether Oxygen ◽  
The Stability ◽  
Straight Lines

The stability constants of the mixed ligand complexes formed by Cu2+, 2,2′-bipyridyl or 1,10-phenanthroline (= Arm), and the dianion of phosphonylmethoxyethane (PME2-), ethyl phosphonate (EtP2-), methyl phosphonate (MeP2-), or D-ribose 5′-monophosphate (RibMP2-) (= R–PO32-) were determined by potentiometric pH titrations in water containing 30 or 50% (v/v) 1,4-dioxane (I = 0.1 M, NaNO3; 25°C). The corresponding results regarding water as solvent were taken from our earlier work. Previous measurements with simple phosphate monoesters, together with the present results for RibMP2-, were used to establish log versus straight line plots. With the aid of the equilibrium constants determined for the MeP2- and EtP2- systems it is shown that simple phosphonates, i.e., those without an additional binding site, fit also on the same straight lines. Therefore, it could be demonstrated with these reference lines that the Cu(Arm)(PME) complexes in all solvents have a higher stability than expected for a sole phosphonate Cu2+ coordination. This increased stability is attributed to the formation of 5-membered chelates involving the ether oxygen present in the – CH2– O – CH2–PO32- residue of PME2-. The formation degree of the 5-membered chelates in the Cu(Arm)(PME) systems varies only between about 65 and 85% in the three mentioned solvents, despite the fact that the stabilities of the Cu(Arm)(PME) complexes increase by more than 1.8 log units by going from water to 50% dioxane-water. It is concluded that (i) such 5-membered chelates will also be formed in mixed ligand complexes of other metal ions in solvents with a reduced polarity, and (ii), more importantly, that the same interactions will also occur with the parent compound of PME2-, i.e. the dianion of 9-(2-phosphonylmethoxyethyl)adenine (PMEA2-), a compound which shows antiviral properties and for which the ether oxygen is important.

scholarly journals Stability Constants of Mixed Ligand Complexes of Transition Metal(II) ions with N-(2-hydroxybenzylidene)-2,3-dimethylaniline as Primary Ligand and N-(2-hydroxy-1-naphthylidene)-4-nitroaniline as Secondary Ligand

2011 ◽  
Vol 8 (2) ◽  
pp. 859-862 ◽  
Author(s):  
A. K. Mapari ◽  
K. V. Mangaonkar
Keyword(s):  
Ionic Strength ◽  
Transition Metal ◽  
Stability Constants ◽  
Ternary Complexes ◽  
Mixed Ligand ◽  
Mixed Ligand Complexes ◽  
Water Medium ◽  
Binary And Ternary Complexes ◽  
The Stability ◽  
Secondary Ligand

Binary and ternary complexes of the type M-Y and M-X-Y [M=Co(II), Ni(II), Cu(II) and Zn(II); X=N-(2-hydroxybenzylidene)-2,3-dimethylaniline and Y =N-(2-hydroxy-1-naphthylidene)-4-nitroaniline] have been examined pH-metrically at 27±0.5 °C and at constant ionic strength, μ=0.1 M (KCl) in 75:25(v/v) 1,4-dioxne-water medium. The stability constants for binary (M-Y) and ternary (M-X-Y) systems were calculated.

scholarly journals Electrometric Investigation of the Nature and Stability of Mixed Ligand Complexes of L-Ornithine and 1,10-Phenanthroline with Some Essential Metal Ions in Aqua-TBAB or PEG-400 Surfactant

2021 ◽  
Author(s):  
Atnafu Guadie Assefa ◽  
Molla Tefera Negash ◽  
Mulugeta Legesse Akele ◽  
Bewketu Mehari Workneh ◽  
Ayal Adugna Mesfin ◽  
...  
Keyword(s):  
Metal Ions ◽  
Stability Constants ◽  
Tetrabutylammonium Bromide ◽  
Mixed Ligand ◽  
Mixed Ligand Complexes ◽  
Essential Metal ◽  
Peg 400 ◽  
Chemical Models ◽  
Binary Complexes ◽  
The Stability

Abstract Background Despite the availability of information about the effect of aqua-surfactants media on the stability of binary complexes, data related to mixed ligand complexes of Phen and Orn with essential metals in aqua-surfactant medium is scarce. The aim of this study was, to determine the stabilities of the mixed ligand complexes of essential metal ions (Co2+, Ni2+, Cu2+) with Phen and Orn in aqua-TBAB and PEG-400 surfactants with an eye on the prediction of the bioavailability of the metal complexes. Results Complexes of some essential metal (M) ions (Co2+, Ni2+, Cu2+) of L-ornithine (L) and 1,10-phenanthroline (X) ligands in various concentrations (0.0–2.5% v/v) of aqueous tetrabutylammonium bromide (TBAB) or polyethylene glycol-400 (PEG-400) surfactant were synthesized pH-metrically at 298 K and 0.16 mol L− 1 ionic strength. The relative amounts of L:M:X were 2.5:1.0:2.5; 5.0:1.0:2.5; 2.5:1.0:5.0. The data acquisition of acid-base equilibria and determination of stability constants were performed using MINIQUAD75 algorithm. The distribution patterns of the complexes with varying pH and compositions of surfactants were presented from the plots of SIM run data. Conclusions The best fit chemical models were found to be MLXH, MLX2H in the lower pH, and MLX, ML2X in the higher pH ranges for all the metals. The logged values of stability constants decreased linearly with increasing concentrations of surfactants, indicating the dominance of electrostatic factors. The log of the disproportionation constant and the change in log values of the mixed ligand constant indicated additional stability of the mixed ligand complexes, compared to the parent binary complexes due to interactions outside the coordination sphere. This makes the mixed ligand complexes more amenable to metal ion storage and transport and threw light to have information on the less stable binary complexes easily bioavailability while the mixed ligand complexes could be stored and transported in the bio-fluids. Significant change on the magnitudes of the stability constants, high values of standard deviation and rejection of some of the proposed chemical models were observed due to pessimistic error, indicating the sufficiency of the models to represent the data and accuracy of the method employed.

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