Determination Of Stability Constants Research Articles

Determination of Dissociation Constant and Stability Constants of Palmitic Acid Complexes with selective Transition Metal Ions in Ethanol-Water Medium By pH-Metric Method

Determination of Dissociation Constant and Stability Constants of Palmitic Acid Complexes with selective Transition Metal Ions in Ethanol-Water Medium By pH-Metric Method

Azo-dyes based small bifunctional molecules for metal chelation and controlling amyloid formation.

Chemical tools are needed to discover new effective drugs for tackling multifaceted complex neurodegenerative diseases like Alzheimer's disease (AD). Multifunctional nature of two compounds, 5-((4-nitro-phenyl)diazenyl)quinolin-8-ol (HL1) and 4-((4-nitrophenyl)diazenyl)benzene-1,3-diol (HL2) is reported w.r.t. their ability to bind Cu2+ ions and amyloid aggregates related to AD. HL1 and HL2 have half congo-red type azo-stilbene structural framework incorporated with metal chelating groups, designed to chelate metal ions from metal-amyloid species. Metal binding studies of HL1 and HL2 are established by the methods of Job's Plot, UV-vis spectra with metal ions and stability constant determination. In addition, their metal complexes are isolated, purity checked by elemental analysis, spectroscopically characterized and their structural analyses were obtained from DFT based calculations including binding energy determination. Chicken egg white Lysozyme (CEWL) was used as a model peptide for fibrillation studies. HL1 is found as an excellent colorimetric sensor for amyloid fibrils. Inhibitory effect of HL1 and HL2 and their isolated metal complexes L1-Cu and L2-Cu on CEWL fibrillation was studied using ThT and ANS fluorescence assay along with TEM imaging. In addition, the cell toxicity studies on these compounds suggest that although azo dyes may be non-toxic but having a nitro-substitution lead to significant cell toxicity. Overall, these results suggest that this new class of multifunctional small molecules can interact with amyloids as well as metal ions and could be potential anti-aggregation metal chelating agents.

Evaluation of Vanadium(IV) as a Non-radioactive Surrogate for Technetium(IV) by Comparison of Stability Constants for Polyamino Polycarboxylate Ligand Complexation

The stability constants for the Tc(IV) and V(IV) complexation with the polyamino polycarboxylate ligands IDA, NTA, HEDTA and DTPA were determined using liquid–liquid extraction techniques. These stability constants were then used to evaluate the validity of using V(IV) as a chemical analogue for Tc(IV). Results suggest that Tc(IV), as TcOOH+, will form β 1−11 complexes with the selected ligands, while V(IV), as VO2+, will form β 101 complexes. The values for these determined stability constants are (in log10 unit) 10.9 ± 0.1, 11.4 ± 0.1, 14.9 ± 0.1, and 20.1 ± 0.1 for Tc(IV) in 0.5 mol·L−1 NaCl at 25 °C, for IDA, NTA, HEDTA and DTPA, respectively, they are 9.3 ± 0.1, 11.6 ± 0.2, 15.8 ± 0.1, and 20.8 ± 0.1 for V(IV) in 0.5 mol·L−1 NaCl at 25 °C, for the same suite of ligands. The incorporation of a hydroxide into the metal ligand complexes formed by Tc(IV) is proposed as the largest factor differentiating the apparent stability constants of Tc(IV) and V(IV). This work shows that V(IV) is a poor analog for Tc(IV); however, despite the differences in complexation mechanism between V(IV) and Tc(IV), V(IV) still appears to have some use for predicting Tc(IV) complexation behavior.

Tuning of the properties of a picolinic acid-based bispidine ligand for stable copper(II) complexation

The synthesis of the hexadentate bispidine-picolinate ligand L with two tertiary amine, two para-methoxy-substituted pyridine donors (p-OMe) and a picolinate group is reported, together with its NiII, CoII, CuII and ZnII coordination chemistry. The X-ray crystal structures of the CuII and ZnII complexes confirm that the geometries are very similar to those of the unsubstituted ligand. The increased nucleophilicity of the p-OMe substituted pyridine groups leads to a significant decrease in the metal-pyridine bond length but, due to the rigidity of the adamantane-derived bispidine backbone, the other metal-donor bonds are slightly elongated, and this leads to a larger degree of axial distortion, which augments the preference of the ligand for the Jahn-Teller-active CuII center. The structural effects are supported by the dd-electronic and EPR spectra, which indicate that, for CoII, NiII and CuII, the overall ligand field strengths of the unsubstituted ligand L′ and the p-OMe-substituted derivative L are very similar, and for CuII the in-plane ligand field is significantly stronger for the p-OMe-substituted ligand L. The MII/I redox potentials with the optimized ligand L are generally more negative for the CoII, NiII and CuII complexes, indicating that the oxidized form of the complexes takes more profit of the increase in complex stability. For CuII this is analyzed on the basis of the potentiometrically determined stability constants and their correlation with the redox potentials of the substituted and unsubstituted bispidines together with a large series of published data with other ligand systems. It emerges that L is a very selective CuII ligand with a great potential for radiopharmaceutical applications.

Thermodynamic and spectroscopic study of Al3+ interaction with glycine, l-cysteine and tranexamic acid in aqueous solution

In this paper a thermodynamic and spectroscopic study on the interaction between Al3+ and glycine (Gly), l-cysteine (Cys), tranexamic acid (Tranex) is reported. Speciation models have been obtained by processing potentiometric titration data to determine stability constants of the species formed in aqueous solution at T=298.15K, 0.15≤I/molL−1≤1 in NaCl. Thermodynamic formation parameters have been obtained from calorimetric titration data, at T=298.15K, I=0.15molL−1 using NaCl as ionic medium. Al3+-Cys system was also investigated by spectrophotometric and 1H NMR measurements. 1H NMR experiments were performed on Al3+-Tranex system as well. Different speciation models have been observed for the three systems. The results showed the formation of MLH, ML and M2L2(OH)2 species for Gly, ML, M2L and MLOH for Cys, MLH and MLOH for Tranex. The formed species are quite stable, i.e. for ML, logβ=7.18, 11.91 for Gly and Cys, respectively, at I=0.15molL−1 and T=298.15K. For all the systems the dependence of formation constants on ionic strength over the range 0.1–1molL−1 is reported. The sequestering ability of the ligands under study was also evaluated by pL0.5 empiric parameter. For Gly, Cys and Tranex, pL0.5=2.51, 3.74, 3.91 respectively, at pH=5, I=0.15molL−1 and T=298.15K.

Influence of structural elements on iron(III) chelating properties in a new series of amino acid-derived monohydroxamates

Abstract A series of amino acid-derived monohydroxamate compounds A1 – A7 was synthesized and characterized for their coordination properties of Fe(III). The series varies in their skeletal lengths and compositions; some compounds lack external substituents, others are substituted with external functional amino or carboxylic groups, or alternatively inert methyl. Undertaken investigations allowed the determination of stoichiometry, stability constants and spectroscopic parameters of formed ferric complexes. Incorporation of an external functional group with a dissociable proton affects the coordination behavior; the presence of carboxylic or amino groups hampers the formation of mono-, di- and trihydroxamate ferric complexes of presented compounds. The differences in Fe(III) affinity of the monohydroxamates vs trihydroxamates was reflected by the stability constants and pFe, indicating the superior stability of hexadentate complexes.

Stability Constants and Spectroscopic Properties of Thorium(IV)–Arsenazo III Complexes in Aqueous Hydrochloric Medium

The complexation characteristics of thorium–arsenazo III in the range of 1–6 mol·L−1 hydrochloric acid media were investigated by UV–Vis absorption spectroscopy and computational analysis. The chemical equilibrium model of thorium–arsenazo III complexation was established including the species distribution of arsenazo III, the formation of thorium chloride species, and the release of protons from thorium–arsenazo III complexes. In the spectra of thorium–arsenazo III complexes, two characteristic absorption peaks were observed at 610 and 660 nm, and the latter peak showed a tendency to shift about 4 nm to higher wavelength as the acidity of the hydrochloric acid media increased from 1 to 6 mol·L−1. Analysis of the experimental data indicates that the molar absorptivities of both 1:1 and 1:2 complexes (thorium to arsenazo III) steadily increase as the acidity of medium increases. The determined stability constants of 1:1 and 1:2 complexes at various concentrations of hydrochloric acid were extrapolated to zero ionic strength, based on the specific ion interaction theory (SIT) approach. The limiting stability constants were determined to be $$ { \log }_{10} \beta_{11}^{\text{o}} $$ = 8.56 ± 0.13 and $$ {\log}_{10} \beta_{12}^{\text{o}} $$ = 15.17 ± 0.18 with ion interaction coefficients of Δe 11 = –0.57 ± 0.02 kg·mol−1 and Δe 12 = –0.60 ± 0.04 kg·mol−1, respectively.

Tripodal polyamines: Adjustable receptors for cation extraction

ABSTRACTExtraction experiments of a series of tris(2-aminoethyl)amine-based ligands with different aromatic substituents act as efficient extractants for transition metals. Octanol-water distribution measurements, determined stability constants of Ag(I) complexes and Zn(II) extraction studies with different counterions point to the extraction efficiency in dependence of the ligand lipophilicity and the specific structure of the ligand. Competitive extraction experiments showed a selective extraction of Cu(II) from a mixture of Co(II), Ni(II), Cu(II), Zn(II), and Cd(II). Additional hydroxyl groups in (tris(2-hydroxybenzylaminoethyl)amine lead to a loss of this selectivity with extraction yields of 46%, 86% and 97% for Co(II), Ni(II) and Cd(II) ions.

Determination of stability constants of the NiCO3 0, ZnCO3 0, and CdCO3 0 complexes using solubilities of corresponding metal carbonates in aqueous solutions

The solubilities of NiCO3, ZnCO3, and CdCO3 in NaClO4–NaHCO3–Na2CO3 solutions are studied experimentally at 25°C and ionic strength of 0.1. The resulting data are used to determine the concentration stability constants of NiCO3 0, ZnCO3 0, and CdCO3 0 complexes in aqueous solutions (they are equal to 810, 12700, and 17900, respectively; log $$K'_{MCO_3^0 } $$ = 2.90 ± 0.14, 4.10 ± 0.20, and 4.25 ± 0.04) and to calculate their thermodynamic values (6.45 × 103, 1.01 × 105, and 1.43 × 105, respectively). The logarithms of stability constants of carbonate complexes are found to be inversely dependent on the solubility products of their metal carbonates.

Conducting Molecularly Imprinted Polymer (MIP) Chemical Sensors for Toxic N-Nitrosamines Selective Determination in Heat Processed Food of Animal Origin

High-temperature processing of meat food generates in it toxic heteroaromatic amines and nitrosamines (NAs)1,2 causing chronic diseases including hormonal dysfunctions and cancer.3 Therefore, we devised and fabricated chemical sensors for selective determination of the N-nitroso-L-proline (Pro-NO)4 and N-nitroso-thiazolidine-4-carboxylic acid (NT4A) toxins in this food. We applied films of conducting polymers molecularly imprinted (MIPs) with either the Pro-NO or NT4A template as recognition units of these chemosensors. For selection of most appropriate functional monomers, we used DFT at the B3LYP/3-21G(*) level modeling to find phenolic derivative of bis(bithiophene) and a thiosalenCo(III) complex (CS)5,6 suitable to form pre-polymerization complexes with Pro-NO and NT4A, respectively, at the 1:2 template/monomer stoichiometry. The calculated Gibbs free energy gain due to formation of these complexes with a series of NAs was proportional to the UV-vis spectroscopy determined stability constants of these complexes. These constants were relatively high equalling 3.14×109 M-2 and 2.72×1010 M-2for Pro-NO and NT4A, respectively. Then, we electrochemically polymerized these complexes under potentiodynamic conditions. This electropolymerization resulted in depositing thin MIP films on different electrode substrates. After subsequent extraction of the Pro-NO and NT4A templates from MIPs, we used the resulting MIPs with empty imprinted cavities for determination of Pro-NO and NT4A analytes in grilled pork neck samples. We confirmed the presence and then absence of NA templates in the MIP films before and after extraction, respectively, with FTIR spectroscopy and XPS, and then characterized morphology of the films with AFM. For analytical signal transduction, we used piezoelectric microgravimetry (PM) at the Au-QCR/MIP electrodes of EQCM as well as DPV and EIS at the Pt/MIP electrodes. Limits of detection of the chemosensors were 36.9 nM Pro-NO (with EIS) and 46 nM NT4A (with DPV). The chemosensors selectively responded to the target toxins in the presence of interfering compounds of similar composition and structure. Successful selective determination of Pro-NO and NT4A in the food extract samples indicates that the chemosensors are promising as tools for determination of these toxins in food of animal origin.

Determination of thermodynamic stability constant of bivalent transition metal complexes with schiffs base as ligands

Determination of thermodynamic stability constant of bivalent transition metal complexes with schiffs base as ligands

Stability constant determinations for technetium (IV) complexation with selected amino carboxylate ligands in high nitrate solutions

Abstract The stability constants for Tc(IV) complexation with the ligands IDA, NTA, HEDTA, and DTPA were determined in varied nitrate concentrations using liquid-liquid extraction methods. The determined log β101 stability constants at 0.5 M NaNO3 were found to be 9.2±0.3, 10.3±0.3, and 15.3±0.3 for IDA, NTA, and HEDTA, respectively. The log β111 stability constant for DTPA was determined to be 22.0±0.6. These determined stability constants show a slight decrease in magnitude as a function of increasing NaNO3 concentration. These stability constants were used to model the total dissolution of Tc(IV) in acidic aqueous solutions in the presence of each ligand. The results of these predictive models indicate that amino carboxylic ligands have a high potential for increasing the aqueous dissolution of Tc(IV); at pH 2.3, 0.01 M ligand yield dissolved Tc(IV) concentrations of 1.42·10−5 M, 1.33·10−5 M, 6.07·10−6 M, 9.65·10−7 M, for DTPA, HEDTA, NTA, and IDA, respectively.

Thermodynamic, Spectroscopic, and Computational Studies of f-Element Complexation by N-Hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic Acid.

Potentiometric and spectroscopic techniques were combined with DFT calculations to probe the coordination environment and determine thermodynamic features of trivalent f-element complexation by N-hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic acid, HEDTTA. Ligand protonation constants and lanthanide stability constants were determined using potentiometry. Five protonation constants were accessible in I = 2.0 M (H+/Na+)ClO4. UV-vis spectroscopy was used to determine stability constants for Nd3+ and Am3+ complexation with HEDTTA. Luminescence spectroscopy indicates two water molecules in the inner coordination sphere of the Eu/HEDTTA complex, suggesting HEDTTA is heptadentate. Luminescence data was supported by DFT calculations, which demonstrate that substitution of the acetate pendant arm by a N-hydroxyethyl group weakens the metal-nitrogen bond. This bond elongation is reflected in HEDTTA's ability to differentiate trivalent actinides from trivalent lanthanides. The trans-lanthanide Ln/HEDTTA complex stability trend is analogous to Ln/DTPA complexation; however, the loss of one chelate ring resulting from structural substitution weakens the complexation by ∼3 orders of magnitude. Successful separation of trivalent americium from trivalent lanthanides was demonstrated when HEDTTA was utilized as aqueous holdback complexant in a liquid-liquid system. Time-dependent extraction studies for HEDTTA were compared to diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA) and N-hydroxyethyl-ethylenediamine-N,N',N'-triacetic acid (HEDTA). The results indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.

PH-Metric study of picolinic acid with Cu (II), Co (II) and Fe(II)ions

pH-Metric measurements of picolinic acid were studied with Cu(II), Co (II) and Fe(II)metal ions at 0.2 M ionic strength in water by Irving-Rossotti titration technique for determination of stability constants. 1: 1 complexes were formed in present investigation in between picolinic acid (PA) and Cu (II), Co (II)and Fe(II) metal ions. Values of proton-ligand stability constant (pK) and metal-ligand stability constants log k were evaluate and compared from resultant data.

PH-Metric measurements of azelastine hydrochloride with Cu(II), Co(II) and Fe(II) metal ions

Proton-ligand stability constant, metal-ligand stability constants, pK and log k of azelastine hydrochloride with Cu(II), Co (II) and Fe(II) metal ions were determined by pH-metric technique. Irving-Rossotti titration technique was used for determination of stability constants. 1:1 complexes were formed in present investigation in between azelastine hydrochloride (TH) and Cu (II), Co (II) and Fe (II) metal ions.

Intraparticulate Metal Speciation Analysis of Soft Complexing Nanoparticles. The Intrinsic Chemical Heterogeneity of Metal-Humic Acid Complexes.

The counterion condensation-Donnan (CCD) model for the electrostatic features of soft, charged nanoparticles (NPs) is applied to the determination of the intrinsic stability constants, K̅int, for inner-sphere Cd(II) and Cu(II) complexes with humic acid NPs. The novel CCD model accounts for the strong ion condensation potential for higher valency counterions within the intraparticulate double layer zone of the soft NP. The approach offers new insights into the intrinsic heterogeneity of the HA complexes, as revealed by the intraparticulate speciation as a function of the true degree of inner-sphere complexation, θM. The ensuing intrinsic heterogeneity parameters, Γ, for CdHA and CuHA complexes are in very good agreement with those obtained from dynamic electrochemical stripping chronopotentiometric measurements. The overall intraparticulate metal ion speciation is found to depend on θM: at low θM the strong inner-sphere complexes predominate whereas at higher θM values, electrically condensed M may be an equally significant or even larger fraction of the particle-associated M.

Determination of conditional stability constants for phytic acid complexes with Mg2+, Ca2+ and Zn2+ ions using electrospray ionization mass spectrometry.

The electrospray ionization mass spectrometry competitive method has been used for the determination of the conditional stability constants of phytic acid complexes with Mg2+, Ca2+ and Zn2+ ions. The competing complexation between ethylenediaminetetraacetic acid (EDTA) and phytic acid was studied. For EDTA complexes with Mg2+, Ca2+ and Zn2+ ions, the values of the conditional stability constants are known and were used for the calculation of this constant for the phytic acid complexes. The values obtained are in agreement with the literature data. The method applied permitted a fast and simple determination of conditional stability constants by measuring the response of the ionized coordination complexes.

Stability constants determination of homo and hetero bimetallic complexes of tmdta in aqueous solution

Stability constants determination of homo and hetero bimetallic complexes of tmdta in aqueous solution

Di- and Tri-valent Metal Ions Interactions with Four Biodegradable Hydroxamate and Cataecholate Siderophores: New Insights into Their Complexation Equilibria

The interaction of a number of divalent and trivalent metal ions [iron(III), chromium(III) copper(II), cobalt(II) and nickel(II)] with four isolated and purified microbial catecholate and hydroxamate siderophores was studied using the pH-potentiometric technique to investigate the complexation behavior of these systems as these systems could mimic many biological interactions of the siderophore chelating agent. The protonation constants of these new siderophore analogues as well their binary complex species stability constants were determined using the Hyperquad 2008 estimation model program. From the determined stability constants of the metal complex species, the concentration distribution of the various metal ion complex species involving isolated siderophore analogues in solutions was estimated using the HySS 2009 modeling program. The complex species distribution diagrams were plotted and discussed. Additionally, the Gibbs energies and the molecular structures of the formed complex species were evaluated and predicted using Gaussian 09 software for molecular modeling and density functional theory calculations.

To Determine Stability Constants and Thermodynamic Properties of Complexation of Ibuprofen with Co2+ and Zn2+ PH Metrically

To Determine Stability Constants and Thermodynamic Properties of Complexation of Ibuprofen with Co2+ and Zn2+ PH Metrically