scholarly journals Complex Equilibria and Distribution of Metal (II) Ions with Biologically Active Chelating Agents in Aqueous and Aqueous-organic Media

2021 ◽  
pp. 25-38
Author(s):  
K. T. Ishola ◽  
O. T. Olanipekun ◽  
O. T. Bolarinwa ◽  
R. D. Oladeji ◽  
A. Abubakar
Keyword(s):  
Metal Ions ◽  
Species Distribution ◽  
Ternary Complex ◽  
Aqueous System ◽  
Ternary Complexes ◽  
Teller Distortion ◽  
Complex Equilibria ◽  
Binary Complexes ◽  
The Stability ◽  
Ph Range

An understanding of the principles of complex equilibria and species distribution in different solutions is important in expounding and correlating the interaction of different ligands with different metal ions in complex formation. Therefore, acid-base equilibria involved in the formation of binary and ternary complexes of Co (II), Cu (II) and Pb (II) with methionine (Met) and uracil (Urc) have been determined by potentiometric titration technique. The stability constants of the complexes were evaluated at 35 ± 0.1°C and 0.02 M ionic strength (kept constant with NaNO3) in aqueous and organic-aqueous media. The species distribution in solutions as a function of pH was determined using the Hyss program. The stability of the ternary complexes relative to the corresponding binary complexes of the secondary ligand is measured in terms ΔlogK and % RS values. The ternary complexes are observed to be more stable than binary complexes in the media except for [CuMetUrc] ternary complex in organic-aqueous medium where the ternary complex is less stable than the binary complex of the uracil. The overall stability of the ternary complexes was higher in organic-aqueous system than aqueous system. The stability of the complexes was found to be correlated with the covalent index of the metal ions and Jahn Teller distortion. pH-studies of these systems revealed an increase in the concentrations of the ternary complexes with increase in pH. The formation of binary complexes was shown to be favoured in physiological pH range (3-7) while that of the ternary complexes is observed to be favoured in the pH range 5-10.

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.

scholarly journals Critical Reappraisal of Methods for Measuring Urine Saturation with Calcium Salts

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3149
Author(s):  
Silvia Berto ◽  
Martino Marangella ◽  
Concetta De Stefano ◽  
Demetrio Milea ◽  
Pier Giuseppe Daniele
Keyword(s):  
Ternary Complex ◽  
Aqueous System ◽  
Total Calcium ◽  
Saturation State ◽  
Chemical Models ◽  
Binary Complexes ◽  
Physicochemical Evaluation ◽  
The Stability ◽  
Diagnostic Work ◽  
Work Up

Background: Metabolic and physicochemical evaluation is recommended to manage the condition of patients with nephrolithiasis. The estimation of the saturation state (β values) is often included in the diagnostic work-up, and it is preferably performed through calculations. The free concentrations of constituent ions are estimated by considering the main ionic soluble complexes. It is contended that this approach is liable to an overestimation of β values because some complexes may be overlooked. A recent report found that β values could be significantly lowered upon the addition of new and so far neglected complexes, [Ca(PO4)Cit]4− and [Ca2H2(PO4)2]. The aim of this work was to assess whether these complexes can be relevant to explaining the chemistry of urine. Methods: The Ca–phosphate–citrate aqueous system was investigated by potentiometric titrations. The stability constants of the parent binary complexes [Cacit]− and [CaPO4]−, and the coordination tendency of PO43− toward [Ca(cit)]− to form the ternary complex, were estimated. βCaOx and βCaHPO4 were then calculated on 5 natural urines by chemical models, including or not including the [CaPO4]− and [Ca(PO4)cit]4− species. Results: Species distribution diagrams show that the [Ca(PO4)cit]4− species was only noticeable at pH >8.5 and below 10% of the total calcium. β values estimated on natural urine were slightly lowered by the formation of [CaPO4]− species, whereas [Ca(PO4)cit]4− results were irrelevant. Conclusions: While [CaPO4]− species have an impact on saturation levels at higher pHs, the existence of ternary complex and of the dimer is rejected.

scholarly journals Thermodynamics of binary and ternary complexes of 3-amino-1, 2, 4-triazole and aminoacids with Ni(II) and Co(II) metal ions

2005 ◽  
Vol 70 (8-9) ◽  
pp. 1057-1066 ◽  
Author(s):  
Ayse Erçag ◽  
Tuba Sismanoglu ◽  
Suheyla Pura
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Glutamic Acid ◽  
Driving Force ◽  
Ternary Complex ◽  
Ternary Complexes ◽  
Binary And Ternary Complexes ◽  
Enthalpy Changes ◽  
Binary Complexes ◽  
The Stability

The stability constants of the 1:1 binary complexes of Ni(II) and Co(II) with 3-amino-1,2,4-triazole (AT), leucine (Leu) and glutamic acid (Glu), and the 1:1:1 ternary complex of them and the protonation constants of the ligands were determined potentiometrically at a constant ionic strength of I = 0.10 mol L-1 (NaClO4) in aqueous solutions at 15.0 and 25.0 ?C. The thermodynamic parameters ?Gf0, ?Hf0 and ?Sf0 are reported for the formation reactions of the complexes. The enthalpy changes of all the complexations were found to be negative but the entropy changes positive. While the driving force for the formation of the Ni(II), Co(II) ? AT complexes is the enthalpy decrease, the driving force for the ternary complexes of AT is the entropy increase.

Equilibrium Studies of Binary and Ternary Complexes of Palladium(II) Involving Amino Acids

1993 ◽  
Vol 58 (5) ◽  
pp. 1103-1108 ◽  
Author(s):  
Mohamed M. Shoukry ◽  
Eman M. Shoukry
Keyword(s):  
Amino Acids ◽  
Relative Stability ◽  
Ternary Complex ◽  
Formation Constants ◽  
Ternary Complexes ◽  
Conductivity Measurements ◽  
Equilibrium Studies ◽  
Binary And Ternary Complexes ◽  
Binary Complexes

The formation constants of the binary and ternary complexes of palladium(II) with diethylenetriamine and amino acids as ligands have been determined potentiometrically at 25 °C in 0.1 M NaNO3 solution. The relative stability of each ternary complex was compared with that of the corresponding binary complexes in terms of ∆logK values. The mode of chelation was ascertained by conductivity measurements.

scholarly journals Investigations of ternary complexes of Co(II) and Ni(II) with thiodiacetate anion and 1,10-phenanthroline or 2,2’-bipyridine in aqueous solutions

2014 ◽  
Vol 13 (1) ◽  
Author(s):  
Dariusz Wyrzykowski ◽  
Joanna Pranczk ◽  
Dagmara Jacewicz ◽  
Aleksandra Tesmar ◽  
Bogusław Pilarski ◽  
...  
Keyword(s):  
Aqueous Solutions ◽  
Substitution Reactions ◽  
Experimental Conditions ◽  
Kinetic Measurements ◽  
Hydroxo Complexes ◽  
Binary Complexes ◽  
Vis Spectroscopy ◽  
Potentiometric Titration Method ◽  
The Stability ◽  
Ph Range

AbstractA potentiometric titration method (PT) and a stopped-flow kinetic technique monitored by a UV−Vis spectroscopy have been used to characterize the stability of series of Co(II)- and Ni(II)-thiodiacetato complexes, M(TDA), in the presence of 1,10-phenanthroline (phen) or 2,2’-bipyridine (bipy) in aqueous solutions. The stability constants of the binary (1:1), ternary (1:1:1) as well as the resulting hydroxo complexes were evaluated and compared to the corresponding oxydiacetate complexes. Based on the species distribution as a function of pH the relative predominance of the species in the system over a pH range was discussed. Furthermore, the kinetic measurements of the substitution reactions of the aqua ligands to phen or bipy in the coordination sphere of the binary complexes M(TDA) were performed in the 288–303 K temperature range, at a constant concentration of phen or bipy and at seven different concentrations of the binary complexes (0.2–0.5 mM). The kinetic stability of the M(TDA) complexes was discussed in relation to the experimental conditions and the kind of the auxiliary ligands (phen/bipy). Moreover, the influence of the type of primary ligand (thiodiacetate/oxydiacetate) on the substitution rate of the auxiliary ligands was also compared.

scholarly journals Stability Constants of Mixed Ligand Complexes of Nickel(II) with Adenine and Some Amino Acids

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Naciye Türkel
Keyword(s):  
Aqueous Solution ◽  
Amino Acids ◽  
Ternary Complex ◽  
Coordination Complexes ◽  
Ternary Complexes ◽  
Mixed Ligand ◽  
Relative Stabilities ◽  
Binary And Ternary Complexes ◽  
Binary Complexes ◽  
Essential Trace Elements

Nickel is one of the essential trace elements found in biological systems. It is mostly found in nickel-based enzymes as an essential cofactor. It forms coordination complexes with amino acids within enzymes. Nickel is also present in nucleic acids, though its function in DNA or RNA is still not clearly understood. In this study, complex formation tendencies of Ni(II) with adenine and certain L-amino acids such as aspartic acid, glutamic acid, asparagine, leucine, phenylalanine, and tryptophan were investigated in an aqueous medium. Potentiometric equilibrium measurements showed that both binary and ternary complexes of Ni(II) form with adenine and the above-mentioned L-amino acids. Ternary complexes of Ni(II)-adenine-L-amino acids are formed by stepwise mechanisms. Relative stabilities of the ternary complexes are compared with those of the corresponding binary complexes in terms ofΔlog10⁡K,log10⁡X, and % RS values. It was shown that the most stable ternary complex is Ni(II):Ade:L-Asn while the weakest one is Ni(II):Ade:L-Phe in aqueous solution used in this research. In addition, results of this research clearly show that various binary and ternary type Ni(II) complexes are formed in different concentrations as a function of pH in aqueous solution.

scholarly journals SPR-measured dissociation kinetics of PROTAC ternary complexes influence target degradation rate

2018 ◽  
Author(s):  
Michael J. Roy ◽  
Sandra Winkler ◽  
Scott J. Hughes ◽  
Claire Whitworth ◽  
Michael Galant ◽  
...  
Keyword(s):  
Ternary Complex ◽  
E3 Ligase ◽  
Ternary Complexes ◽  
Single Amino Acid ◽  
Amino Acid Difference ◽  
Dissociation Kinetics ◽  
Intracellular Degradation ◽  
The Stability ◽  
Kinetics Of

ABSTRACTBifunctional degrader molecules, known as proteolysis-targeting chimeras (PROTACs), function by recruiting a target to an E3 ligase, forming a target:PROTAC:ligase ternary complex. Despite the importance of this key intermediate species, no detailed validation of a method to directly determine binding parameters for ternary complex kinetics has been reported, and it remains to be addressed whether tuning the kinetics of PROTAC ternary complexes may be an effective strategy to improve the efficiency of targeted protein degradation. Here, we develop an SPR-based assay to quantify the stability of PROTAC-induced ternary complexes by measuring for the first time the kinetics of their formation and dissociation in vitro using purified proteins. We benchmark our assay using four PROTACs that target the bromodomains (BDs) of BET proteins Brd2, Brd3 and Brd4 to the E3 ligase VHL. We reveal marked differences in ternary complex off-rates for different PROTACs that exhibit either positive or negative cooperativity for ternary complex formation relative to binary binding. The positively cooperative degrader MZ1 forms comparatively stable and long-lived ternary complexes with either Brd4BD2 or Brd2BD2 and VHL. Equivalent complexes with Brd3BD2 are destabilised due to a single amino acid difference (Glu/Gly swap) present in the bromodomain. We observe that this difference in ternary complex dissociative half-life correlates to a greater initial rate of intracellular degradation of Brd2 and Brd4 relative to Brd3. These findings establish a novel assay to measure the kinetics of PROTAC ternary complexes and elucidate the important kinetic parameters that drive effective target degradation.

scholarly journals Zn2+ Interaction with Amyloid-Β: Affinity and Speciation

Molecules ◽  
2019 ◽  
Vol 24 (15) ◽  
pp. 2796 ◽  
Author(s):  
Arena ◽  
Rizzarelli
Keyword(s):  
Species Distribution ◽  
Multiple Equilibria ◽  
Amyloid Β ◽  
Data Interpretation ◽  
Amyloid Β Peptide ◽  
Experimental Conditions ◽  
Pros And Cons ◽  
The Stability ◽  
Ph Range

Conflicting values, obtained by different techniques and often under different experimental conditions have been reported on the affinity of Zn2+ for amyloid-β, that is recognized as the major interaction responsible for Alzheimer’s disease. Here, we compare the approaches employed so far, i.e., the evaluation of Kd and the determination of the stability constants to quantitatively express the affinity of Zn2+ for the amyloid-β peptide, evidencing the pros and cons of the two approaches. We also comment on the different techniques and conditions employed that may lead to divergent data. Through the analysis of the species distribution obtained for two selected examples, we show the implications that the speciation, based on stoichiometric constants rather than on Kd, may have on data interpretation. The paper also demonstrates that the problem is further complicated by the occurrence of multiple equilibria over a relatively narrow pH range.

PREPARATION AND PROPERTIES OF TRANSKETOLASE FROM PORK LIVER

1960 ◽  
Vol 38 (1) ◽  
pp. 115-124 ◽  
Author(s):  
F. J. Simpson
Keyword(s):  
Heavy Metal ◽  
Metal Ions ◽  
Heavy Metal Ions ◽  
Thiamine Pyrophosphate ◽  
Magnesium Ions ◽  
Optimum Activity ◽  
Pork Liver ◽  
High Concentrations ◽  
The Stability ◽  
Ph Range

Transketolase of pork liver has been purified 90-fold and separated from ribulose 5-phosphate 3-epimerase. The transketolase is most stable between pH 7.5 and 8.5 and below 40 °C. The pH range for optimum activity is between 7.6 and 8.1. Activation by magnesium ions or thiamine pyrophosphate could not be demonstrated, but thiamine pyrophosphate increased the stability of the enzyme. Sulphydryl agents, such as p-chloromercuriphenyl sulphonic acid and N-ethylmaleimide, and heavy metal ions, such as cupric, mercuric, and zinc, at relatively high concentrations inhibited the enzyme.

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