A Study on complexation behavior of Lanthanides (III) with Pregabalin

The complexation of La3+, Ce3+, Pr3+ and Sm3+ ions with isopropylmercaptan has been studied by potentiometric and conductometric titration techniques in aqueous – 10% ethanolic (V/V) medium. Title metal ions form 1:1, 1:2 and 1:3 complexes in the pH range 6.0–8.0 with considerable overlapping. Their log Kstab. values are determined at 15°, 25° and 35°C at ionic strength μ = 0.1 M (NaClO4) by applying Calvin and Melchior's extension of Bjerrum method. The values of thermodynamic parameters ΔG, ΔH and ΔS have been calculated at 25°C with the help of an isobar and Gibb's Helmholtz equation. The trend in the stability constant values of the metal‐complexes has been found to be .

Proton ligand and metal ligand stability constant are measured for Fe(III) and 1, 2-dihydroxy benzene and 1, 5-disulphonic acid complexes . Determination of stability constant of substituted of pyrazoles with rare earth metals form complexes are reported . Effect of temperature on formation constants of 2 acetylpyridine(N benzoyl)glycine hydrazone with lanthanide(III) ions at different ionic strengths are reported. Irving and Rossotti, Herson and Gilbert , Wilkins and Lewis and Rossotti and Rossotti have determined stability constant by Bjerrum-Calvin titration technique . Kabadi , Jahagirdar and Narwade have determined pK values of salicylaldehyde, salicylic acid and sulphonic acid respectively by similar procedure. The metal ligand stability constant of some β-diketones are reported . Stability constants have investigated for some substituted pyrazolines, isoxalline and diketone . The method most frequently applied for study of complex equilibria is pH-metric titration technique . Stepwise formation of mononuclear binary complexes is described by set of equilibrium constants. For pH-metric measurements an electrode must be selected. According to Bjerrum, Martell and Calvin , the formation of complex MLN is stepwise process and one has to deal with a series of equilibria of the type: Irving and Rossotti, Herson and Gilbert , Wilkins and Lewis and Rossotti and Rossotti have determined stability constant by Calvin-Bjerrum titration technique . The value of nA,n, pK, log K1 and log K2 are evaluated by Irving and Rossotti's equation. The stability constant and thermodynamic parameters of complexes containing lighter lanthanides , copper(II) , calcium and magnesium are reported. It is also important in environmental studies , medicinal and industrial chemistry . Effects of transition metal on stability constant of complexes have studied by pH metric method . Bendi , Janrao and Ramteke have studied stability constant of ligands with lanthanide metals complexes.The present work involves pH metric study of substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), Mn(II), Cr(III) and Ti(III) at temperature42oC. The Bjerrum-Calvin titration technique as modified by Irving and Rossotti has been employed in the present study. The following three sets of titrations are carried out in sequence.

The stability constants of iron, manganese, cobalt, and nickel complexes of glycine have been determined in aqueous solution by potentiometric titration with standard sodium hydroxide solution. The values of the stepwise stability constants were obtained by ORIGIN ‘50’ program. The overall stability constants of the complexes were found to be similar. Keywords: Glycinato, titration, stepwise stability constants, origin ‘50’ and toxicity

Complexation and speciation of copper (II) in ppb level with 1,10-phenanthroline (L) in aqueous media have been investigated by differential pulse anodic stripping voltammetry using thin mercury film glassy carbon electrode (TMFGCE). The work was carried out at constant ionic strength of 0.01 mol dm-3 using NaNO3 at ambient temperature. The pH was kept constant at 9.12 ± 0.10 by the addition of borate buffer. Applying the concept of DeFord and Hume, the stability constants of different species of copper with 1,10-phenanthroline were calculated from the variation of peak potential and diffusion current of simple and complexed metal ions under the present experimental conditions. It was found that copper(II) form three complexes (1:1, 1:2 and 1: 3; metal : ligand) with 1,10-phenanthroline. The overall stability constant of copper complexes, MLn can be defined as βMLn= [MLn ]/[M2+][L]n in which M2+ = Cu2+ and L = 1,10-phenanthroline; n is an integer. The values of the stability constant of different copper complexes with 1,10-phenanthroline were found to be 109.33, 1015.10 and 1020.48 for CuL, CuL2 and CuL3, respectively (the overall charges were omitted for simplicity). The high values of overall stability constant indicate that the complexes are highly stable. Using the values of stability constant of copper complexes and hydrolysis constant of copper, the percentage of all possible copper species under present experimental conditions were calculated. Keywords: Electrochemical; Speciation; Complexation; Copper 1,10-phenanthroline. DOI: http://dx.doi.org/10.3329/bjsir.v46i2.8188 Bangladesh J. Sci. Ind. Res. 46(2), 219-224, 2011

Stoichiometry and equilibrium study of copper‐ligands including mercaptobenzoxazole (MBO), 4‐propyl 2‐thiouracyl (PTU), methyl‐2‐pyridylketone oxime (MPKO), phenyl‐2‐pyridylketone oxime (PPKO), 4,6‐dihydroxy‐2‐mercaptopyrimidine (DHMP), N,N′‐phenylene bis(salicylaldimine) (PBS) and 1,2‐bis(2‐hydroxyphenyl)naphtaldiimine (BHNPDI) were conducted in aqueous and nonaqueous solution by potentiometry and spectrophotometry. Stability constants of the complexes are determined at 25 ± 1 °C and 0.1 or 0.05 M ionic strength in water or acetonitrile solvents. Oximes ligand protonation constants and copper‐ligands complexes' stability and hydrolysis constants were calculated using the BEST program in aqueous solution. The stability constants of copper‐ligands complexes were calculated using the KINFIT program in acetonitrile solution. The results of these two methods are made self‐consistent, then rationalized assuming an equilibrium model including the species, ML, MLH, MLOH and ML2 (where the charges of the species have been ignored for the sake of simplicity) (L = MBO, PTU, MPKO, PPKO, DHMP, BHNPDI and PBS).

Study of binary and ternary complexes of copper(II) with some polyamines and adenosine 5′ triphosphate

Lanthanides have a high affinity toward ligands containing donor oxygen atoms, especially amino acids and complexons. The study of the processes of complexation of amino acids with f-element cations provides valuable information for solving problems of supramolecular chemistry, molecular recognition and chiral sensitivity of biological substrates. As a rule, f-elements are not components of biopolymers, but they are spectral label probes, which are important in the bioinorganic chemistry of metals. Quantitative estimation of the stability of complexes is necessary, first of all, to search for an internal connection between the constants themselves and then to find correlations between the stability of complexes and the properties of the complexing agent, the ligand, and the system as a whole. Such correlation dependencies make it possible to calculate a priori, or at least estimate the stability constants of new complexes, and also to better understand the influence of the nature of the chemical bond and the properties of the system as a whole on the formation and stability of complex compounds. In the present work, the complexation of neodymium, lanthanum with L-asparaginat ion and samarium, cerium with L-leucinat ion at 298.15 K and ionic strength values of 0.5 mol/l was studied by potentiometric titration and the stability constants of the complexes formed were determined. The values of the stability constants found allow us to perform rigorous thermodynamic calculations of the equilibria of these amino acids in salt solutions. The data obtained, in particular, can be used to reliably interpret the results of calorimetric studies of the complexation of lanthanides with the participation of the studied amino acids.Forcitation:Lytkin A.I., Chernyavskaya N.V., Smirnova D.K. Stability constants of L-asparagine and L-leucine complexes with some lanthanide in aqueous solutions at 298.15 K. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 1. P. 37-41

Two methods are presented for the determination of the stability constants of ethylenediaminetetraacetato, trimethylenediaminetetraacetato and propylenediaminetetraacetato complexes of some divalent metal ions. One is a new method which is based on the polarographic measurement of the concentration of an uncomplexed ligand in a solution containing two kinds of ligands and an appropriate metal ion. The other is a modification of the method described in the previous paper. From the results obtained by these methods and those obtained previously, the individual stability constants have been calculated. The values of the logarithmic stability constants of complexes at 25°C and ionic strength 0.2 are: Mn 13.64, Co 15.71, Ni 18.12, Cu 18.46, Zn 15.94, Cd 15.98 and Pb 17.76 for ethylenediaminetetraacetato complexes; Mn <10.8, Co 14.48, Ni 17.29, Cu 18.04, Zn 14.26, Cd 12.69 and Pb 13.04 for trimethylenediaminetetraacetato complexes, and Mn 14.85, Co 17.07, Ni 19.42, Cu 19.64, Zn 17.14, Cd 17.43 and Pb 18.69 for propylenediaminetetraacetato complexes.

In coordination compounds studies, knowledge of the stability constants of complexes is necessary for preliminary quantitative treatment. Metal complexes can offer their action such as anti – inflammatory, antimicrobial, 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 number of transition metal complexes with organic ligands of interest which can be used as therapeutic agents. Aluminum prefers oxygen donor groups for complexation. The stability of complexes in biological systems depends on pH, which in blood plasma is 7.4. Chromium is a very adaptable metal, and it can form copious species with variable oxidation numbers from (- VI) to (+VI). Iron is a component of heme and chlorophyll and serves as micronutrients of plants and animals. Ferric ion from Industrial effluent has the potential to poison animals and plants. The present technique involving the use of paper ionophoresis is described for the study of equilibria in binary complex systems in solutions. 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 obtain information in the binary complexes and to calculate its stability constants. Using this method, the stability constants of binary complexes metal (III) – norvaline have been determined to be (8.73 ± 0.03, 7.20 ± 0.04); (9.00 ± 0.01, 7.41± 0.07) and ((9.43 ± 0.01, 7.66 ± 0.11) (logarithm stability constant values) for aluminum (III) chromium (III) and iron (III) complexes, respectively, at ionic strength 0.1 Mol/L and a temperature of 35°C. The first and second stability constants of metal complexes follow the order Fe (III) > Cr (III) > Al (III).

Metal ions are fundamental elements for the maintenance of life spans of humans, animals and plants. In coordinatton compounds studies, knowledge of the stability constants of complexes is necessary for preliminary quantitative treatment. Aluminum prefers oxygen doner groups for complexation. The stability of complexes in the biological system depends on pH, which is blood plasma is 7.4. Chromium is very adaptable metal and it can form copious species with variable oxidation numbers from (-VI) to (+VI). Iron is a component of heme and chlorophyll and serves as micronutrients of plants and animals. Ferric ion from industrial effluent has the potential to poison animals and plants. The present technique involving the use of paper electrophoresis is described for the study of equilibria in binary complexes system 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 obtain information in the binary complexes and to calculate its stability constants. Using this method, the stability constants of binary complexes, metal (III) – homoserine have been determined to be (8.15 ± 0.03, 6.66 ± 0.08); (8.49 ± 0.01, 7.00 ± 0.05); and (8.79 ± 0.01, 7.43 ± 0.03) (logarithm stability constant values) for aluminum (III), chromium (III), and iron (III) complexes, respectively, at ionic strength 0.1Mol/L and a temperature of 35 °C.

Metal ions are fundamental elements for the maintenance of life spans of humans, animals and plants. In coordinatton compounds studies, knowledge of the stability constants of complexes is necessary for preliminary quantitative treatment. Aluminum prefers oxygen doner groups for complexation. The stability of complexes in the biological system depends on pH, which is blood plasma is 7.4. Chromium is very adaptable metal and it can form copious species with variable oxidation numbers from (-VI) to (+VI). Iron is a component of heme and chlorophyll and serves as micronutrients of plants and animals. Ferric ion from industrial effluent has the potential to poison animals and plants. The present technique involving the use of paper electrophoresis is described for the study of equilibria in binary complexes system 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 obtain information in the binary complexes and to calculate its stability constants. Using this method, the stability constants of binary complexes, metal (III) – homoserine have been determined to be (8.15 ± 0.03, 6.66 ± 0.08); (8.49 ± 0.01, 7.00 ± 0.05); and (8.79 ± 0.01, 7.43 ± 0.03) (logarithm stability constant values) for aluminum (III), chromium (III), and iron (III) complexes, respectively, at ionic strength 0.1Mol/L and a temperature of 35 °C.

Kinetics of reduction, composition and the stability constants of the zinc–maleic acid complexes in aqueous medium

The conditional stability constants of tripolyphosphate, pyrophosphate, and citrate complexes of Zn2+, Mn2+, Co2+, and Fe2+ as function of pH have been determined. The polarographic method was employed in these studies, and the ionic strength of the solution used was 0.5 mol/dm3. P3O105- complexes with the respective micronutrients were found to show higher conditional stability constants more often than P2O74- and citrate complexes. In comparison with complexes containing other cations, conditional stability constants of complexes with zinc studied in this work showed higher values. Distinct from other micronutrients, Cu2+ ions were observed as significantly accelerating the hydrolysis process of P3O105- in a range of pH from 4.5 to 10.0. Hence, the degree of hydrolysis increased together with the pH value of their solutions. In the case of other micronutrients, the degree of hydrolysis of P3O105- was lower for higher pH values of their solutions. Additionally, it was stated that the structure of Fe2+ tripolyphosphate complexes differs from complexes with other central ions. The preparation conditions of liquid fertilizers stable over long periods of time, containing macroelements and micronutrients in the complexing form by polyphosphates, have been elaborated. Stability of the solutions depended on the content of individual components, pH, and kind of complexing agent. It remained closely related to stability constants of complexes.

The determination of ionization constants and the chelating properties exhibited by a series of derivatives of N-phenylbenzohydroxamic acid, N-phenyllaurohydroxamic acid and 1-naphthalenemethylimminodiacetohydroxamic acid type ligands toward Fe(III), Cu(II) and Ni(II) ions were studied by pH-metric method. The data obtained by pH-metric method were analyzed by three standard methods namely, Bjerrum's method, Irving and Rossotti method, and Sarkar and Kruck method. The ionization constants of hydroxamic acids and the stability constants of metal-ligand complexes were calculated using the above three methods and it was found that the values obtained closely agreed with each other. The evaluation of the calculated stability constants shows that the substituent effect on the N-phenyl ring leads to more basic character at the carbonyl oxygen and it influences significantly the stability of the complex species formed by the hydroxamate moieties. The stability constant and the species distribution of Fe(III) - 1-naphthalenemethylimminodiacetohydroxamic acid system at physiological pH range (6.8 - 7.2) suggest that 1-naphthalenemethylimminodiacetohydroxamic acid is an effective source for the iron overload. Keywords: Bjerrum method, hydroxamic acid, Irving and Rossotti method, Sarkar and Kruck method, stability constant doi:10.4038/jnsfsr.v36i3.154 Journal of the National Science Foundation of Sri Lanka 36 (3) 191-198

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.