Formation Constants Of Chelates Research Articles

Evaluation of the Extraction Properties and Stability of Extracted Rare Earth Complexes in Ionic Liquid Extraction System Using β-Diketone

ABSTRACTThe extraction behavior of rare earth (RE) species was investigated on benzoyltrifluoroacetone (Hbfa) /triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl)amide ([P2225][TFSA]) system in this study. The stoichiometry of the extracted complex shown RE: ligands = 1:3 by slope analysis regardless of the kinds of acid media in the aqueous phase. The extraction mechanism in this system was revealed as [RE3+]aq + 3[Hbfa]IL [RE(bfa)3]IL + 3[H+]aq and [TFSA]− anion did not participate in the extraction mechanism. The result of Raman spectroscopy also supported the stoichiometry of the extracted complex. Moreover, the chelate formation constant (β) of [Nd(bfa)3] and [Dy(bfa)3] was also evaluated by the direct measurement of [bfa]− anion by ion chromatography. The hypersensitive peak (4I9/2→2G7/2*) in the UV-Vis-NIR spectrum also confirmed the formation of [Nd(bfa)3]. The average chelate formation constants (log β) of [Nd(bfa)3] and [Dy(bfa)3] were estimated to be 7.58 and 7.93, respectively. The value of log β(Dy) was larger than that of log β(Nd); thus, this result indicates that [Dy(bfa)3] was more stable than [Nd(bfa)3]. Furthermore, the optimized structure of the extracted complexes – [Nd(bfa)3(H2O)3] and [Dy(bfa)3(H2O)2] – were also evaluated by the density functional theory (DFT) calculation. On the optimized geometries, the average bond length of the centered Nd3+ ion or Dy3+ ion against the O atom in the 1-carbonyl group was 2.728 Å or 2.407 Å, respectively. This result suggested that the Dy3+ ion would be combined more strongly with the [bfa]− anion than the Nd3+ ion.

Chromatographic Selectivity of Rare Earth Elements on Iminodiacetate-Type Chelating Resins Having Spacer Arms of Different Lengths: Importance of Steric Flexibility of Functional Group in a Polymer Chelating Resin

Three types of chelating resins containing iminodiacetic acid homologues (IDA resins) with spacer arms of different lengths were prepared and examined as the column stationary phase for ion chromatography. The chromatographic retention behavior of rare earth elements (REEs) on the IDA resins was evaluated with respect to a capacity factor (k') to elucidate the selectivity profile of the resins. The k' values for a series of REEs on the IDA resins were compared with the chelate formation constants (K(ML)) of the corresponding free ligands of analogous structure. Selectivity of the chelating resins having longer spacer arms between the ligand group and the polymer matrix showed a better correlation with the corresponding monomeric ligands in solution. This trend has been attributed to the increase in steric flexibility of the ligand group by the presence of the spacer arm.

Stereoisomeric selectivity of 2,3-dimercaptosuccinic acids in chelation therapy for lead poisoning.

The formation constants of lead chelates of the stereoisomers of 2,3-dimercaptosuccinic acid (DMSA) were determined from potentiometric titrations in the presence of the competing ligand, EDTA. The lead chelates formed at pH 7.4 with the stereoisomers of DMSA are the monomeric complexes PbL and HPbL. Formation of PbL and HPbL at pH 7.4 is independent of total concentrations of lead and DMSA present, and so is the concentration ratio of PbL:HPbL. Lead is completely chelated at pH 7.4 when the total concentration of ligand is equal to or greater than the total concentration of lead present. Lead tends to bind to a greater extent with rac- than with meso-DMSA, and the relative extent increases with an increase in the concentration ratio of ligand to lead and finally reaches a constant value of 45. The binding sites in the chelates, PbL, of the stereoisomers of DMSA are the two thiolate groups and one carboxylate group. rac-DMSA also forms a dimeric complex Pb2L2 in which both carboxylate groups of the ligands participate in binding with lead ions. The formation constants of the lead chelates of rac-DMSA were invariably found to be larger than those of the corresponding of meso-DMSA chelates, because in all the lead chelates of the stereoisomers of DMSA formed in solution, rac-DMSA existed in staggered anti conformations, whereas meso-DMSA preferred a staggered gauche conformation with respect to carboxylate groups in the ligands. The potential of using ZnL2 of rac-DMSA as a therapeutical lead chelator was assessed by considering its lead-mobilizing ability and its ability to deplete endogenous zinc; on this basis it is predicted that ZnL2 of rac-DMSA is a better chelator than meso-DMSA for the treatment of lead poisoning.

Potentiometric studies on the complexation equilibria between some trivalent lanthanide metal ions and biologically active 2-hydroxy-1-naphthaldehyde thiosemicarbazone (HNATS)

The chelation behaviour of some trivalent lanthanide and yttrium metal ion with biologically active 2-hydroxy-1-naphthaldehyde thiosemicarbazone (HNATS) has been investigated by potentiomotric measurements at 20±0.5°C in 75% (v/v) dioxane-water medium at various ionic strengths of sodium perchlorate. The method of Bjerrum and Calvin, as modified by Irving and Rossotti has been used to find out the values of\(\bar n\) (average number of ligand bound per metal ion) andpL (free ligand exponent). The formation constants of metal chelates have been computed on a PC-XT computer, using a program patterned after that of Sullivan et al. to give βn values using weighted least squares method. TheSminvalues (Smin=χ2) have been calculated. The order of formation constants of chelates was found to be: La3+<Ce3+<Pr3+<Nd3+<Sm3+<Eu3+<Gd3+<Y3+<Tb3+<Dy3+. The formation constants of the chelates formed have been correlated to size and ionization potentials of the metal ions.

Formation constants of binary chelates of Cu(II)/Ni(II) with 4-chloro and 4-amino picolinic acid N-oxide in aquo organic media

The proton ligand constants of 4-chloro and 4-amino picolinic acid N-oxide and the formation constants of corresponding binary chelates of Cu(II) and Ni(II) have been measured at 30°C and 0.1M ionic strength in varying percentages of dioxane-water, acetone-water, ethanol-water and isopropanol-water. The results are discussed with reference to the change in dielectric constants of water in the presence of organic solvent, change in the structuredness of water, change in hydrogen bonding ability of the organic solvent in water, solvent basicity and proton solvation by organic solvent. The values have been compared with aqueous and mixed aqueous systems of picolinic acid N-oxide and 4-methoxy picolinic acid N-oxide.

Physico-chemical studies on the chelation behaviour of biologically active 2-hydroxy-1-naphthaldehyde semicarbazone (HNAS) with some lanthanons

The chelation behaviour of the complexes of La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Y3+, Tb3+, Dy3+, Ho3+ with biologically active 2-Hydroxy-1-naphthaldehyde semicarbazone (HNAS) has been studied potentiometrically in 75% (v/v) dioxane-water medium at various ionic strengths. The method of Bjerrum and Calvin, as modified by Irving and Rossotti has been used to find out the values of n andpL. The formation constants of metal chelates and the values ofSmin have been calculated. The order of formation constants of chelates was found to be: La3+<Ce3+<Pr3+<Nd3+<Sm3+<Eu3+<Gd3+<Y3+<Tb3+<Dy3+<Ho3+.

Mixed chelates of some trivalent lanthanide ions containing (trans-1,2-cyclhexylenedinitrilo)tetraacetate and norleucinate

Formation constants of mixed chelates with (trans-1,2-cyclohexylenedinitrilo)tetra-acetate (DCTA) as primary ligand and norleucinate (nle) as secondary ligand with metal ions La(III), Ce(III), Pr(III), Sm(III), Gd(III), Tb(III), Dy(III), Er(III), and Yb(III) have been determined by the modified potentiometricpH titration method of Irving-Rossotti in aqueous medium at (295±1) K and fixed ionic strength of μ=0.1M (NaClO4). Formation constants of binary complexes of the metal ions with the secondary ligand have also been determined under identical conditions. The mixed chelates were found to be more stable than the binary ones. The order of stabilities in terms of metal ions is La(III) Gd(III)<Tb(III)<Dy(III)<Er(III)<Yb(III) for binary and ternary complexes with a prominent “Gadolinium break”.

Metal chelates of salicyl-4-aminoantipyrine

The formation constants of salicyl-4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (SAAP) complexes with 3d transition metal ions [Cu(II), Ni(II), Co(II), Zn(II) and Mn(II)] have been determined in 60% ethanol-water medium ofμ = 0.1M (NaCl) at 25°C. It is observed that the formation constants for chelates with 3d transition metals follow the order Mn(II) < Co(II) < Ni(II) < Zn(II) < Cu(II). The effects of metal ions, ionic radii, electronegativities and ionization potentials on chelate formation constants are discussed.

ChemInform Abstract: Extraction Equilibrium Constants of Scandium(III) and Yttrium(III) in Acetylacetone‐Organic Solvent Systems and Some Comparisons with Rare Earths(III)

Abstract The extraction equilibria of scandium(III) and yttrium(III) with acetylacetone into various organic solvents have been investigated at 25 °C. The liquid-liquid partition coefficients and the formation constants of these chelates have been determined and compared with those of lanthanoid(III) chelates. The effect of organic solvents on the partition coefficient is quantitatively explained with the aid of the regular solution theory. A clear correlation between the partition coefficient and the successive formation constants of these acetylacetonate chelates is demonstrated.

Extraction equilibrium constants of scandium(III) and yttrium(III) in acetylacetone-organic solvent systems and some comparisons with rare earths(III)

The extraction equilibria of scandium(III) and yttrium(III) with acetylacetone into various organic solvents have been investigated at 25 °C. The liquid-liquid partition coefficients and the formation constants of these chelates have been determined and compared with those of lanthanoid(III) chelates. The effect of organic solvents on the partition coefficient is quantitatively explained with the aid of the regular solution theory. A clear correlation between the partition coefficient and the successive formation constants of these acetylacetonate chelates is demonstrated.

Redox reactions of thionine and leucothionine with iron chelate compounds

The kinetics of the reduction of thionine by several iron(II) chelate compounds (FeIIY) have been investigated under a nitrogen atmosphere at pH 7.0 and 25 °C by the stopped-flow method. The reactions obey first-order kinetics with respect to the concentration of both thionine and FeIIY. A linear relationship has been observed between log kobs and log[KFeIIIY/KFeIIIY], where kobs is an apparent rate constant for the reduction of thionine by FeIIY, and KFeIIIY and KFeIIY are the formation constants of the iron(III) and iron(II) chelates, respectively. Activation parameters for the reduction of thionine by FeIIY have been calculated from the temperature dependence of the rate constants. The oxidation of leucothionine by iron(III) chelates has also been investigated using the same technique. A mechanistic scheme for the thionine–leucothionine redox system is discussed in the light of these results and thermodynamic considerations.

Stability Constants of Cu2+, Fe3+↦ Zr4+Chelates of Ampicillin, Dopamine and α-Methyl L-Dopa in Aqueous Medium

Abstract Formation constants of chelates of ampicillin, dopamine, and α -methyl L-dopa with Cu 2+, Fe3+ and Zr4+ have been determined in aqueous medium at ionic strength of 0.1 M (KC1) using Calvin-Bjerrum technique as applied by Irving and Rossotti. Zirconium forms relatively more stable chelates with ampicillin as compared to copper and iron. However, in case of dopamine and α-methyl L-dopa the chelation with iron is the more stable. The order of stability of copper and iron is in agreement with the Irving-Villiems order. The mixed ligand chelates have been, also, investigated. The stability sequence has been found to be Cu2+ < Fe3+ < Zr4+

Acid Dissociation and Metal Complex Formation Constants of Penicillamine, Cysteine, and Antiarthritic Gold Complexes at Simulated Biological Conditions

Ionization constants for acid functions of D-penicillamine, L-cysteine, thiomalic acid, and thioglucose were measured by pH titration at 37° and 0.15M ionic strength. Chelate formation constants for these ligands with calcium(II), iron(III), and gold(I) were then determined under the same conditions chosen to approximate the in vivo situation. Only iron(III) formed both 1:1 and 1:2 chelates with D-penicillamine, L-cysteine, and thiomalate; calcium formed weak and gold strong 1:1 complexes with all ligands studied. Because of precipitate formation, the stability constants for the systems thioglucose-iron(III), D-penicillamine-gold(I), and L-cysteine-gold(I) had to be determined indirectly with thiomalic acid as the competing ligand. The in vivo fate of antiarthritic gold(I) compounds remained uncertain, but gold(I) chelates probably persist as such for extended periods.

Formation constants of chelates of 7-bromo-8-hydroxy-quinoline-5-sulphonic acid with yttrium and some lanthanides

Formation constants and thermodynamic parameters of chelation ΔF ΔH and ΔS for chelates of 7-bromo-8-hydroxy-quinoline-5-sulphonic acid with yttrium, lanthanum, praseodymium, neodymium, gadolinium, terbium, dysprosium and holmium are reported and discussed.

Formation constants of chelates of 7-nitro-8-hydroxyquinoline-5-sulphonic acid with yttrium and some lanthanides

Formation constants and thermodynamic parameters of chelation ΔF, ΔH and ΔS for chelates of 7-nitro-8-hydroxyquinoline-5-sulphonic acid with yttrium, lanthanum, praseodymium, neodymium, gadolinium, terbium, dysprosium and holmium are reported.

SYNTHESIS OF A NEW HEXADENTATE LIGAND AND MEASUREMENT OF STABILITY CONSTANTS OF ITS METAL CHELATES

Abstract A new macrocyclic hexamine ligand, 1,2-di(1,4,7-triaza-1-cyclononyl)ethane, was synthesized and its protonation and chelate formation constants with manganese(II), cadmium(II), cobalt(II), zinc(II), and nickel(II) were measured at 25°C in 1 M KNO3.

Stability of flavonoid complexes of copper(II) and flavonoid antioxidant activity

Certain flavonoids inhibit the oxidation of ascorbic acid; this behaviour has been attributed to the ability of flavonoids to act as free radical acceptors and also to remove catalytic metal ions by complexation. To place the latter property on a quantitative footing, protonation constants and copper(II) chelate formation constants of several flavonoids have been determined by potentiometric titration and computation by the program SCOGS. The constants are discussed in terms of previous studies of antioxidant activity.

Studies on chelates of selected pyrazylmethyl ketones

Several pyrazylmethyl ketones have been investigated in regard to their potential analytical utility as chelating agents for metal ions. Proton dissociation constants of the ligands and metal chelate formation constants were calculated from potentiometric data using the method of Irving and Rossotti. Chelate formation constants obtained in this study allow comparisons to be made between pyrazylmethyl ketones and other chelating agents possessing similar structures. The potential analytical utility of the title compounds is discussed.

Spectrophotometric reactions of copper and zinc with 2-(2-quinolylazo)-1-naphthol

2-(2-Quinolylazo)-1-naphthol (α-QAN) was synthesized as a reagent for the determination of small amounts of metals. α-QAN exists in three different forms in aqueous dioxan depending on pH. The acid dissociation constants of the reagent and the chelate formation constants in aqueous dioxan solutions were determined. The distribution behaviour of the copper and zinc chelates formed was studied. The extraction of the chelates indicated the formation of the 1 : 2 neutral chelates. The extraction constants and molar absorptivities of the chelates formed were obtained. Le (2-quinolylazo)-2-naphtol-1 (α-QAN) peut être utilisé comme réactif pour le dosage de faibles quantités de métaux. Il existe sous trois formes différentes en solution eau-dioxane, suivant le pH. On a déterminé les constantes de dissociation acide du réactif et les constantes de formation des chélates, de cuivre et de zinc en particulier, ainsi que les constantes d'extraction et coefficients d'absorption molaire. 2-(2-Chinolylazo)-1-naphthol (α-QAN) wurde als Reagenz für die Bestimmung kleiner Metallmengen dargestellt. α-QAN existiert in wässrigem Dioxan in Abhängigkeit vom pH-Wert in drei verschiedenen Formen. Die Säure-Dissoziationskonstanten des Reagenzes und die Chelat-Bildungskonstanten in wässrigen Dioxanlösungen wurden ermittelt. Das Verteilungsverhalten der gebildeten Kupfer- und Zinkchelate wurde untersucht. Die Extraktion der Chelate zeigte die Bildung der neutralen 1:2-Chelate an. Die Extraktionskonstanten und die molaren dekadischen Extinktionskoeffizienten der gebildeten Chelate wurden bestimmt.

Distribution Studies of Metal-8-quinolinol Chelates in a Nonaqueous System

Abstract This investigation was concerned with the determination of the influence of water on the distribution of several metal-8-quinolinol chelates between nitromethane and 1-decanol. These observations were utilized to describe the general equilibria involved in the extraction processes. The distribution ratios (nitromethane/1-decanol) of bis(8-quinolinolo)-dioxouranium(VI)-8-quinolinol, bis(8-quinolinolo)dioxouranium(VI), tris-(8-quinolinolo)iron(III), and bis(8-quinolinolo)zinc(II) in dry solvents were determined by visible and atomic absorption spectrophotometry to be 0.95, 0.92, 1.90 and 0.11, respectively. The extraction into the 1-decanol phase increased with the number of unfilled coordination sites of the metal, indicating that the extractions were proceeding by solvation of the metal chelates. The influence of water was attributed primarily to hydrolysis of the chelates in nitromethane, and the magnitude of this effect was correlated to the respective metal chelate formation constants. The chelates were found to be resistant to hydrolysis in 1-decanol.