Values Of Stability Constants Research Articles

Synthesis, Structural Determination, DFT Calculation and Biological Evaluation Supported by Molecular Docking Approach of Some New Complexes Incorporating (E)‐N'‐(3,5‐di‐Tert‐Butyl‐2‐Hydroxybenzylidene) Isonicotino Hydrazide Ligand

ABSTRACTThe synthesis and structural analysis of complexes derived from (E)‐N′‐(3,5‐di‐tert‐butyl‐2‐hydroxybenzylidene) isonicotino hydrazide (ITB ligand) were examined using multiple analytical techniques. These techniques included TGA, decomposition point determination, elemental analysis (CHN), spectroscopic (IR, NMR, mass spectrometry) analysis, magnetic susceptibility, conductivity, as well UV–Vis spectrum analysis, along with theoretical studies. Molar conductance values indicated that the Cd (II), Co (II), Cu (II), Ni (II), and Zn (II) complexes are non‐electrolytes in fresh DMSO solutions, with conductance values ranging from 8.5 to 14.35 Ω−1 cm2 mol−1. IR spectra suggested which the ligand coordinates through the metal ions in a tridentate fashion, utilizing the (N & O) donor sites from the (CN & CO & CO) groups in the hydroxybenzylidene moiety. Analytical data from solution complexation, job's method suggested a 1:1 (metal:ligand) molar ratio. The stability order of the complexes was determined as ITBCo > ITBCu > ITBNi > ITBZn > ITBCd, consistent with the stability constant (Kf) values. The pH profile indicated that the studied complexes exhibit stability upon a wide pH scale, typically between (pH = 4:10). Magnetic and electronic spectral analyses helped deduce the ligand coordination abilities and the geometric structures of the complexes. In vitro (antimicrobial & anticancer) performances of the studied complexes were tested versus various (microbial strains & cancer cell lines), revealing higher activity in the chelates assessed to the free (ITB) ligand. The antioxidant potential was also assessed using the DPPH assay. Finally, molecular docking was performed toward estimate the binding efficiency between various protein receptors and the compounds, with results aligning with the biological investigations.

A homobimetallic nickel(II) complex for discriminative chromogenic recognition of aqueous cyanide and silver(I) from medicinal products: Role of end-on thiocyanate bridging

Herein, a homobimetallic azomethine-functionalized nickel(II) complex, [Ni2L2(van)(μ1,1-NCS)] (AMR-1, where L = 2-[(2-Hydroxy-1,1-dimethyl-ethylimino)-methyl]-6-methoxyphenol, molecular weight = 788.20 (found)) has been judiciously synthesized with N-coordinated end-on thiocyanate. AMR-1 exhibited promising chromogenic variation from pale green to colourless with hypochromic shifting in the visible region in the presence of silver(I). Herein, the exposed sulfur site of the co-ligand acts as chemodosimetric recognition site for highly selective detection of a soft metal pollutant, silver ion (Ag+) with the limit of detection (LOD) of 0.37 ppm. Along with this, aqueous cyanide (CN−) recognition was accomplished in a mutually independent way with distinct chromogenic variation from pale green to yellowish color within ∼5 s. This led to the LOD of 0.46 ppm, which is much lower than the safe limit, set by the World Health Organization (WHO). The stability constant value for cyanide interaction with AMR-1 is obtained to be 1.49 × 103 M−1 as per 1:1 binding stoichiometry. Experimental findings, obtained from UV–Vis, HR-MS, FT-IR, and 1H NMR spectroscopic studies in conjugation with the decreased HOMO-LUMO energy gap from 3.40 eV to 2.07 eV, obtained from density functional theory studies, support the mechanistic pathway of interaction. Implementing molecular logic platforms benefits from fabricating three-input-two-output logic circuits by imitating variable spectroscopic outcomes. Real-time multifarious applications of AMR-1 have been accomplished with paper strip-based solid-state assay and recognition of the target-specific analytes from targeted medicinal specimens and from both cyanogenic as well as non-cyanogenic food sources. To the best of our knowledge, this is probably the first nickel(II) complex derived sensory receptor that is effectually implemented towards recognition of another metal ion, silver (I) along with CN− from aqueous as well as from real specimens.

A Review of Machine Learning and QSAR/QSPR Predictions for Complexes of Organic Molecules with Cyclodextrins.

Cyclodextrins are macrocyclic rings composed of glucose residues. Due to their remarkable structural properties, they can form host-guest inclusion complexes, which is why they are frequently used in the pharmaceutical, cosmetic, and food industries, as well as in environmental and analytical chemistry. This review presents the reports from 2011 to 2023 on the quantitative structure-activity/property relationship (QSAR/QSPR) approach, which is primarily employed to predict the thermodynamic stability of inclusion complexes. This article extensively discusses the significant developments related to the size of available experimental data, the available sets of descriptors, and the machine learning (ML) algorithms used, such as support vector machines, random forests, artificial neural networks, and gradient boosting. As QSAR/QPR analysis only requires molecular structures of guests and experimental values of stability constants, this approach may be particularly useful for predicting these values for complexes with randomly substituted cyclodextrins, as well as for estimating their dependence on pH. This work proposes solutions on how to effectively use this knowledge, which is especially important for researchers who will deal with this topic in the future. This review also presents other applications of ML in relation to CD complexes, including the prediction of physicochemical properties of CD complexes, the development of analytical methods based on complexation with CDs, and the optimisation of experimental conditions for the preparation of the complexes.

Implication of metal complexes in biology and medicine, the system cadmium (II)/iron (II)/zinc (II) – sarcosine

Implication of metal complexes in biology and medicin, the system cadmium (II)/iron (II) / zinc (II) – sarcosine. A technique involving the use of paper Electrophoretic Technique is described for the study of equilibria in binary complex system in solution. This methodis based upon the migration of a spot of metal ion on a paper strip at different pH values of background electrolyte containing 0.1 mol L -1 perchloric acid and 0.01 mol L -1 sarcosine. A graph of pH against mobility gives information about the binary complexes and permit to calculate their stability constants. The first and second stability constants of [Cd (II) – sarcosine], [Fe (II) – sarcosine] and [Zn (II) – sarcosine] complexes were found to be (3.94 ± 0.03; 2.66 ± 0.07), (3.70 ± 0.01; 2.54 ± 0.03) and (4.39 ± 0.01; 2.74 ± 0.07) logarithm stability constant values for Cd (II), Fe (II) and Zn (II) complexes, respectively at ionic strength 0.1 Mol L -1 and temperature of 35 0 C. The stability constants follow the order: Cd (II) > Fe (II) > Zn (II).

Metal Complexes in Biology and Medicine: The System Cadmium ((II))/ Iron ((II))/ Zinc ((II)) - α - Aminobutenoic Acid

Metal ions play an important role in biological system. The importance of metal ions to essential functions of living systems and for wellbeing of living organisms is well known. Metal ions are fundamental elements for the maintenance of life spans of the human, animals, and plants. Recent advances in inorganic chemistry have made possible formation of number of transition metal complexes with organic ligand of interest, which can be used as therapeutic agent. In coordination compounds studies, knowledge of the stability constants of complexes is necessary for preliminary quantitative treatment. The present technique involving the use of paper electrophoresis is described for the study of equilibria in binary complex systems in solution. The method is based on the movement of a spot of a metal ion in an electric field at various pH’s of background electrolyte. A graph of pH versus mobility was used to obtained information in the binary complexes and to calculate its stability constants. Using this method , the stability constants of binary complexes metal (II) – α – aminobutenoic acid have been determined to be ( 3.78 ± 0.01, 2.48 ± 0.03 ); ( 3.27 ± 0.04, 2.33 ± 0.07 ); and (4.45 ± 0.02, 2.66 ± 0.05); (logarithm stability constant values) for cadmium (II), iron (II) and zinc (II) complexes, respectively, at ionic strength 0.01 Mol / L and a temperature of 35º C.

Stoichiometry and Stability Constant Values for Copper (II) Chelates with Ethylene Diamine in Deep Eutectic Solvents (DES) (Ethaline) Solutions

Stoichiometry and Stability Constant Values for Copper (II) Chelates with Ethylene Diamine in Deep Eutectic Solvents (DES) (Ethaline) Solutions

Formulation of Silymarin-β Cyclodextrin-TPGS Inclusion Complex: Physicochemical Characterization, Molecular Docking, and Cell Viability Assessment against Breast Cancer Cell Lines.

Silymarin (SIL) is a poorly water-soluble flavonoid reported for different pharmacological properties. Its therapeutic applications are limited due to poor water solubility. In this study, the solubility of silymarin has been enhanced by preparing freeze-dried binary and ternary complexes using beta cyclodextrin (βCD) and d-α-tocopherol polyethylene glycol 1000 succinate (TPGS). The stoichiometry of the drug and the carrier was selected from the phase solubility study. The dissolution study was performed to assess the effect of complexation on the release pattern of SIL. The formation of inclusion complexes was confirmed by different physicochemical studies. Finally, a cell viability assay (MCF 7; breast cancer cell line) was performed to compare the activity with free SIL. The phase solubilization results revealed the formation of a stable complex (binary) with a stability constant and complexation efficiency (CE) value of 288 mol L-1 and 0.045%. The ternary sample depicted a significantly enhanced stability constant and CE value (890 mol L-1 and 0.14%). The release study results showed a marked increase in the release pattern after addition of βCD (alone) in the binary mixture (49.4 ± 3.1%) as well as inclusion complex (66.2 ± 3.2%) compared to free SIL (32.7 ± 1.85%). Furthermore, with the addition of TPGS in SIL-βCD (ternary), the SIL release was found to be significantly enhanced from the SIL ternary mixture (79.2 ± 2.13%) in 120 min. However, fast SIL release was achieved with 99.2 ± 1.7% in 45 min for the SIL ternary complex. IR and NMR spectral analysis results revealed the formation of a stable complex with no drug-polymer interaction. The formation of complexes was also confirmed by the molecular docking study (docking scores of 4.1 and -6.4 kcal/mol). The in vitro cell viability result showed a concentration-dependent activity. The IC50 value of the SIL ternary complex was found to be significantly lower than that of free SIL. The findings of the study concluded that the prepared SIL inclusion complex can be used as an alternative oral delivery system to enhance solubility, dissolution, and biological activity against the tested cancer cell line.

Chromogenic azomacrocycles with imidazole residue: Structure vs. properties

New diazo macrocycles linked by hydrocarbon chain bearing imidazole or 4-methylimidazole residue have been synthetized with satisfactory yield (24–55%). The structure of macrocycles was confirmed by X-ray analysis and spectroscopic methods (1H NMR, MS, FTIR). Metal cation complexation studies were carried out in acetonitrile and acetonitrile-water system. It was found that azomacrocyles form triple-decker complexes with lead(II). The highest values of stability constant were found for lead(II) complexes of 21-membered derivatives. For the first time azomacrocycles bearing imidazole residue were immobilized on a porous glass. Obtained materials can act as lead(II) or copper(II) colorimetric optical sensors with color digital analysis as detection using simple portable devices.

Implicatons of Metal Complexes in Biology and Medicine the System Cadmium (II)/ Iron (II)/ Zinc (II)-Hydroxyproline

The importance of metal ions to essential functions of living systems and for the well being of living organisms is known. Metal ions are fundamental elements for the maintenance of the life spans of the human, animals and plants. The stability constants of Cd2+, Fe2+ and Zn2+ complexes with hydroxyproline were determined by Paper Electrophoretic Technique (PET). This method is based on the movement of a spot of metal ion in an electric field at various pH of background electrolyte. A graph of pH against mobility gives information about the formation of binary complexes and permit to calculate their stability constants. The stability constant of the ML and ML2 complexes of Cd (II) – hydroxyproline, Fe (II) – hydroxyproline and Zn (II) – hydroxyproline, have been found to be (4.41 ± 0.01; 2.95 ± 0.06) (4.11 ± 0.01; 2.81 ± 0.11 and (4.83 ± 0.02; 3.28 ± 0.07) ( logarithm stability constant values), respectively at ionic strength 0.1 mole L-1 (per chloric acid as background electrolyte) and a temperature of 35 0C, The first and second stability constants of metal complexes follow the order Zn (II) > Cd (II) > Fe (II). Metal complexes can offer their action such as anti-inflammatory, antibiotic, anti-thyroid and anticancer compounds. Metal based drugs bioactivity can be increased by metal chelation, which in turn increase their absorbance and stability. Recent advances in inorganic chemistry have made possible formation of a number of metal complexes with organic ligands of interest which can be use as therapeutic agents.

A combined spectroscopic and theoretical study to investigate the coordination modes of 2,3- and 3,4-pyridine dicarboxylates with Eu(III)

The complex formation of Eu(III) with 2,3-pyridine dicarboxylic acid (23PDCA) and 3,4-pyridine dicarboxylic acid (34PDCA) has been studied by luminescence spectroscopy in aqueous medium. About three orders of luminescence enhancement of Eu(III) was observed in Eu(III)-PDCA complexes compared to its aqua complex, Eu(H2O)93+. Stability constant values (Log KMLi) were obtained for various metal–ligand (MLi (i = 1–3)) complexes formed in the aqueous medium. Complexation studies along with luminescence lifetime data suggested that both the ligands bind with Eu(III) in a bidentate fashion. Interestingly, the bi-dentate mode of 23PDCA interaction with Eu(III) is dominantly through nitrogen atom of pyridyl and the oxygen atom of nearby carboxylate group, whereas in case of 34PDCA, the bi-dentate coordination is through the two oxygen atoms of both the carboxylate groups. The density functional theory (DFT) calculations provided insights into the complex formation at the molecular level and the theoretical results show excellent agreement with the experimental observations.

Microwave assisted synthesized graphene oxide nanocomposites for remediation of toxic metal ions

Here we report the eco-friendly synthesis of graphene magnetic and non-nonmagnetic nanocomposites, namely GO/Fe3O4 and GO-Ni(OH)2, by employing microwave energy. The nanocomposites were explored for the adsorption of toxic Pb2+ and Cd2+ ions. The characterization techniques of XRD, Raman, FESEM and HRTEM confirmed the structure quality and morphology of both nanocomposites. The adsorption studies were conducted using ICP-OES characterization data. The adsorption of Pb2+ and Cd2+ ions on the surface of the nanocomposites were described well by the Freundlich model. The results of the adsorption studies show that the GO/Fe3O4 nanocomposite shows a high adsorption of Cd2+ ions relative to Pb2+ ions due to the formation of a cadmium complex (CdOH +) in the solution which has a higher stability constant value as compared to the lead complex PbOH +. However, the nonmagnetic GO-Ni(OH)2 nanocomposite shows a higher adsorption of Pb2+ ions due to its high electronegativity relative to Cd2+ ions. It was found that the adsorption varies with the concentration of the metal ions.

Do Phenyl Substituents Affect the Properties of Azobenzocrown Derivatives?

New products of photo- and thermal rearrangements of 19-membered azoxybenzocrown with phenyl substituents in benzene rings in the para positions to oligooxyethylene fragments are characterized. The yields of photochemical transformations depend on the solvent. Para-hydroxyazocrown is formed with yields over 50% in propan-2-ol. Ortho-hydroxyazobenzocrown is obtained with yields up to 70% in toluene/acetic acid mixture. Macrocyclic Ph-20-ester is obtained in yield 90% under thermochemical rearrangement conditions. Structure of new hydroxyazobenzocrowns and also atypical product of rearrangements, 20-membered ester, was confirmed by X-ray diffraction analysis. Azophenol⇄quinone-hydrazone tautomeric equilibrium of new hydroxyazobenzocrowns and the influence of metal cations on tautomeric equilibrium was investigated using 1H NMR and UV-Vis spectroscopy in acetonitrile. The highest value of stability constant (logK 7.25) was obtained for strontium complex of p-hydroxyazobenzocrown. For the first time p-hydroxyazobenzocrown was used as a chromoionophore in the receptor layer of an optical sensor. Comparative analysis with data obtained previously for series 19-membered analogs have shown the influence of the presence of substituents in benzene rings for the course and products distribution of photo- and thermal rearrangement. The effect of substituents was also discussed against the tautomeric equilibrium and metal cation complexation properties.

PH-metric titration technique for the study of metal-complexes of substituted 2- Oxo-2H-Chromene-3-Carbohydrazide derivatives in solution: calculation of stability constants

Background: In coordination chemistry, the stability of complexes is expressed in terms of the formation constant of complexes. In coordination complexes, the temperature is very important. It plays an important role in complex formation reaction. Temperature affects metal-ligand stability constant (log K) and proton-ligand stability constant (pK). The metal ion Mn2+, Co2+, Ni2+, and Cu2+ at different temperatures form complexes with 4-sulfamethoxazoleazo-3-methyl-2-pyrazolin-5-one are reported. The metal-ligand stability constant (logK) and proton-ligand stability constant (pK) of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) with organic ligand n-[2-hydroxy-1-napthalydene]-2-methylanilline at 0.1 M ionic strength in 60% dioxane-water medium is studied. The study of thermodynamic parameters and stability constant of complexes of substituted thiazole Schiff bases with rare earth metal ions in mixed solvent is reported. Objective: The study of coordination compounds and a lot of work has been done on metal-ligand stability constant. The same transition metal ion form complexes with substituted pyrazole for this metal-ligand stability constant are determined. Method: Pointwise Calculation Method Half Integral Method. Result: The values of logK1 and logK2 are determined from the metal-ligand formation curve at formation numbers 0.5 and 1.5. In all cases, logK1 is greater than logK2. The ratio logK1/logK2 is positive and greater than one in all systems. This implies that there is little or no steric hindrance to the addition of the secondary ligand molecules. The difference between logK1 - logK2 is usually positive. If the difference between logK1 and logK2 is less than 2.5, simultaneous formation of 1:1 and 1:2 complexes occurs and if it is more than 2.5, then stepwise complex formation occurs. In the present case, in all systems, it is less than 2.5. This indicates the simultaneous formation of 1:1 and 1:2 complexes takes place. Conclusion: A pH-metric study of Substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), and Mn(II) occurs. The graphical representation of the curve shows that the acid + ligand curve is separated from the corresponding acid + ligand + metal curve in this system. The formation of a complex is indicated. Half integral method and pointwise calculation method give nearly similar results. The values of stability constants for all systems indicate that the complexes formed in these processes are stable.

A Machine Learning-Based Study of Li+ and Na+ Metal Complexation with Phosphoryl-Containing Ligands for the Selective Extraction of Li+ from Brine

The growth of technologies concerned with the high demand in lithium (Li) sources dictates the need for technological solutions garnering Li supplies to preserve the sustainability of the processes. The aim of this study was to use a machine learning-based search for phosphoryl-containing podandic ligands, potentially selective for lithium extraction from brine. Based on the experimental data available on the stability constant values of phosphoryl-containing organic ligands with Li+ and Na+ cations at 4:1 THF:CHCl3, candidate di-podandic ligands were proposed, for which the stability constant values (logK) with Li+ and Na+ as well as the corresponding selectivity values were evaluated using machine learning methods (ML). The modelling showed a reasonable predictive performance with the following statistical parameters: the determination coefficient R2= 0.75, 0.87 and 0.83 and root-mean-square error RMSE = 0.485, 0.449 and 0.32 were obtained for the prediction of the stability constant values with Li+ and Na+ cations and Li+/Na+ selectivity values, respectively. This ML-based analysis was complemented by the preliminary estimation of the host–guest complementarity of metal–ligand 1:1 complexes using the HostDesigner software.

COMPLEX-FORMING PROPERTIES OF SYNTHETIC PYRIMIDINONE NUCLEOSIDES WITH Ag(I) IONS IN AN AQUEOUS SOLUTION

The present work describes the complexation properties of two synthetic nucleosides (used as ligands), i.e. β-D-ribofuranoside-4-pyrimidinone (ribo) and β-D-deoxyribofuranoside-4-pyrimidinone (deoxy) with Ag(I) ions in aqueous solution. The stability constants of the studied coordination entities were calculated potentiometrically. The logarithm values of the overall stability constants of the coordination entities were found to be [Ag-deoxy]+ = 3.07, [Ag-(deoxy)2]+ = 6.90, [Ag-ribo]+ = 3.00 and [Ag-(ribo)2]+ = 6.63. Based on the species distribution curves as a function of CL/CM, the percentage of each coordination entity formed in aqueous solution was estimated (12 % [Ag-deoxy]+; 36 % [Ag-(deoxy)2]+; 16 % [Ag-ribo]+; 26 % [Ag-(ribo)2]+). It was found that the ligands form coordination entities with Ag(I) ions with stoichiometric ratios M : L = 1 : 1 and 1 : 2. Such coordination entities may show potential antiviral, antibacterial, and antitumor properties, which warrants further in vitro and in vivo studies. They may also be of great interest for their application in nanobiotechnology.

Vanadium(IV) and vanadium(V) complexation by succinic acid studied by affinity capillary electrophoresis. Simultaneous injection of two analytes in equilibrium studies

The interaction of V(IV) and V(V) with succinic acid was investigated by affinity capillary electrophoresis (ACE) in aqueous acid solutions at pH values 1.5, 2.0 and 2.4, and different ligand concentrations. V(IV) and V(V) form protonated complexes with succinic acid ligand at this pH range. The logarithms of the stability constants, measured at 0.1 mol L-1 (NaClO4/HClO4) ionic strength and 25 °C, are logβ111=7.4 ± 0.2 and logβ122=14.1 ± 0.5 for V(IV), and logβ111=7.3 ± 0.1 for V(V), respectively. The stability constant values, extrapolated to zero ionic strength with the Davies equation, are logβ°111=8.3 ± 0.2 and logβ°122=15.6 ± 0.5 for V(IV) and logβ°111=7.9 ± 0.1 for V(V). The application of ACE to the simultaneous equilibria of V(IV) and V(V) (injection of two analytes) was also attempted. When the results were compared with those obtained when introducing only one analyte in the capillary, using the traditional version of the method, similar stability constants and precision are obtained. The possibility of studying two analytes simultaneously decreases the time needed for the determination of the constants; this feature is especially valuable when working with hazardous materials or when only small quantities of ligand are available.

Geochemical Characteristics of the Vertical Distribution of Heavy Metals in the Hummocky Peatlands of the Cryolithozone.

One of the main reservoirs depositing various classes of pollutants in high latitude regions are wetland ecosystems. Climate warming trends result in the degradation of permafrost in cryolitic peatlands, which exposes the hydrological network to risks of heavy metal (HM) ingress and its subsequent migration to the Arctic Ocean basin. The objectives included: (1) carrying out a quantitative analysis of the content of HMs and As across the profile of Histosols in background and technogenic landscapes of the Subarctic region, (2) evaluating the contribution of the anthropogenic impact to the accumulation of trace elements in the seasonally thawed layer (STL) of peat deposits, (3) discovering the effect of biogeochemical barriers on the vertical distribution of HMs and As. The analyses of elements were conducted by atom emission spectroscopy with inductively coupled plasma, atomic absorption spectroscopy and scanning electron microscopy with an energy-dispersive X-ray detecting. The study focused on the characteristics of the layer-by-layer accumulation of HMs and As in hummocky peatlands of the extreme northern taiga. It revealed the upper level of microelement accumulation to be associated with the STL as a result of aerogenic pollution. Specifically composed spheroidal microparticles found in the upper layer of peat may serve as indicators of the area polluted by power plants. The accumulation of water-soluble forms of most of the pollutants studied on the upper boundary of the permafrost layer (PL) is explained by the high mobility of elements in an acidic environment. In the STL, humic acids act as a significant sorption geochemical barrier for elements with a high stability constant value. In the PL, the accumulation of pollutants is associated with their sorption on aluminum-iron complexes and interaction with the sulfide barrier. A significant contribution of biogenic element accumulation was shown by statistical analysis.

Controlled release study for captopril by using polymer carboxymethyl cellulose

The present study was done to prepare tablet for captopril (CAP) which used in the treatment of hypertension and heart failure. CAP is mainly absorbed from the proximal intestine and to a lesser extent from the stomach. The tablets of CAP were prepared by using the polymer carboxymethyl cellulose (CMC) a captopril drug release system. The buffer solutions were use at (pH=12,7.4,8.5) as a media to release the drug similitude of the acidity index in stomach, in testiness, and blood plasma respective. It was accounted the concentrations of the drug that release in the above–mentioned solutions at the different temperature (25,30,37,40,45,) C°. The study was extended to the effect of the temperature and the acidity function on releasing the drug. The drug release from the polymers increased with the temperature and the degree of the solution acidity. It was also studied the value of stability constant that increased with the temperature.

Complex formation of molybdenum (V) with 1-phenyl-2,3-dimethylpyrazoline-5-thion in 4 mol/L HCI medium at 273-338 K

The process of complexation of molybdenum (V) with 1-phenyl-2,3-dimethylpyrazolin-5-thione in a 4 mol/l HCI medium in the temperature range 273-338 K was studied by the potentiometric method. It has been shown that the reduced form of the 1-phenyl-2,3-dimethylpyrazolin-5-thione molecule is involved in the complex formation reaction. Using the data of potentiometric studies, the change in the energy value (ΔE) of the (NH4)2[MoOCI5]2-1-phenyl-2,3-dimethylpyrazolin-5-thione-4 mol/l HCl system, the equilibrium concentrations of 1-phenyl-2,3-dimethylpyrazolin-5-thione, formation function values, step and general stability constants of oxochloro-1-phenyl-2,3-dimethylpyrazolin-5-thione complexes of molybdenum (V) formed in HCl solutions in the temperature range 273-338 K. The stability constants of oxochloro-1-phenyl-2,3-dimethylpyrazolin-5-thione complexes of molybdenum (V) were refined using the Bjerrum graphical method. The temperature coefficient method was used to estimate the thermodynamic functions of complex formation processes in the (NH4)2[MoOCI5]-1-phenyl-2,3-dimethylpyrazolin-5-thione - 4 mol/L HCI system. The domains of dominance and the maximum yield of each complex form are found. It has been established that in the studied system (NH4)2[MoOCI5]-1-phenyl-2,3-dimethylpyrazolin-5-thione - 4 mol/l HCI during the interaction of the MoO3+ ion with 1-phenyl-2,3-dimethylpyrazolin- 5-thione in the entire temperature range of the experiment forms 5 mononuclear coordination compounds containing from one to five coordinated molecules of the organic ligand. It was found that with increasing temperature, the values of the general stability constants of coordination compounds decrease, which confirms the exothermicity of the reaction of formation of oxochloro-1-phenyl-2,3-dimethylpyrazoline-5-thione compounds of molybdenum (V). The experimentally found values of enthalpy made it possible to assume that the reaction of complex formation between the MoO3+ ion and the molecules of nitrogen- and sulfur-containing heterocyclic 1-phenyl-2,3-dimethylpyrazolin-5-thione proceeded exothermically spontaneously. Based on the above equations, all calculations were carried out using a computer in the Excel programming language, Borland Delphi, Windows 7 operating system.

Cationic surfactant influence on ternary complexes of CoII, NiII, CuII and ZnII ions with aspartic and citric acids

A potentiometric titration study has been undertaken to determine the cationic surfactant influence on mixed ligand complexes in ternary systems consisting of cobalt (II), nickel (II), copper (II), and zinc (II) with aspartic and citric acids at various concentrations (0.0–2.5% w/v) of the CTAB (Cetyltrimethyl ammonium bromide)-surfactant solution while maintaining an ionic strength of 0.16 mol L-1 (NaCl) at 30 °C. Titrations were performed in the presence of different ratios (M:L:X = 1:2:2, 1:4:2, and 1:2:4) of metal (M) and aspartic acid (L) to citric acid (X) using sodium hydroxide. Model systems were developed based on statistical parameters and residual analysis. For Co(II), Ni(II), Cu(II), and Zn(II), the species detected were MLXH2, MLX2H5, and MLX3. The electrostatic relationship of the ligands' side chains, charge neutralization, chelate effect, stacking interactions, and hydrogen bonding are used to explain the trend in the variation of logarithm of stability constants (log β) values with changing dielectric constant and mole fraction of the surfactant. The variation in species distribution as a function of pH and surfactant composition is also presented and discussed, as are plausible equilibria for the formation of the species and structures of the ternary complexes are also presented and discussed.