Complex Formation Equilibria of Unusual Seven-Coordinate Fe(EDTA) Complexes with DNA Constituents and Related Bio-relevant Ligands

Seven-coordinate Fe(EDTA)?CL complexes, where L represents a DNA constituent (uracil, uridine, thymine, thymidine and inosine), methylamine, ammonium chloride or imidazole, were investigated to resolve the solution chemistry of this system. The results show formation of 1:1 complexes with DNA constituents and the other ligands, supporting the hepta-coordination mode of Fe(III) ion. Stability constants of the complexes were measured by potentiometric titration at 25?°C and ionic strength 0.1 mol?L^?1 NaNO₃. The hydrolysis constant of [Fe(EDTA)(H₂O)]^? and the formation constants of the complexes formed in solution were calculated using the non-linear least-squares program MINIQUAD-75. The concentration distributions of the various complex species were evaluated as a function of?pH. The thermodynamic parameters ??H ⁰ and ??S ⁰, calculated from the temperature dependence of the equilibrium constants, were determined for the Fe(EDTA)?Curacil complex. The effect of dioxane as a solvent on the protonation constant of uracil, hydrolysis constants of [Fe(EDTA)(H₂O)]^?, and the formation constants of the Fe(EDTA)?Curacil complex are discussed.     

Complex Formation Equilibria of Unusual Seven Coordinate Fe(III) Complexes with DNA Constituents

Seven-coordinate Fe(III) complexes [Fe(dapsox)(H₂O)₂]⁺, where [dapsox = 2,6-diacetylpyridine-bis(semioxamazide)] is an equatorial pentadentate ligand with five donor atoms (2O and 3N), were studied with regard to their acid–base properties and complex formation equilibria. Stability constants of the complexes and the pK _a values of the ligands were measured by potentiometric titration. The interaction of [Fe(dapsox)(H₂O)₂]⁺ with the DNA constituents, imidazole and methylamine·HCl were investigated at 25 °C and ionic strength 0.1 mol·dm^?3 NaNO₃. The hydrolysis constants of the [Fe(dapsox)(H₂O)₂]⁺ cation (pK _a1 = 5.94 and pK _a2 = 9.04), the induced ionization of the amide bond and the formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with DNA constituents supporting the hepta-coordination mode of Fe(III). The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated for interaction of [Fe(dapsox)(H₂O)₂] with uridine.     

Complex formation reactions of palladium(II)-1,3-diaminopropane with various biologically relevant ligands. Kinetics of hydrolysis of glycine methyl ester through complex formation

The interaction of [Pd(DAP)(H₂O)₂]²⁺ (DAP = 1,3-diaminopropane) with some selected bio-relevant ligands, containing different functional groups, were investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA constituents. Stoichiometry and stability constants of the complexes formed are reported at 25°C and 0.1 M ionic strength. The results show the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants is examined. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. DNA constituents form 1:1 and 1:2 complexes. The effect of dioxane on the acid dissociation constants of CBDCA and the formation constant of its complex with Pd(DAP)²⁺ was reported. The kinetics of hydrolysis of glycine methyl ester bound to [Pd(DAP)(H₂O)₂]²⁺ was studied at 25°C and 0.1M ionic strength.      

Equilibrium Studies of Dibutyltin(IV)–Zwitterionic Buffer Complexation

Equilibrium studies in aqueous solution are reported for dibutyltin(IV) (DBT) complexes of the zwitterionic buffers “Good’s buffers” Mes and Mops. Stoichiometric and formation constants of the complexes formed were determined at different temperatures and ionic strength 0.1 mol·L^?1 NaNO₃. The results show that the best fit of the titration curves were obtained when the complexes ML, MLH_?1, MLH_?2 and MLH_?3 were considered beside the hydrolysis product of the dibutyltin(IV) cation. The thermodynamic parameters ΔH ^o, ΔS ^o and ΔG ^o calculated from the temperature dependence of the formation constant of the dibutyltin(IV) complexes with 2-(N-morpholino)ethanesulfonic acid (Mes) and 3-(N-mor-pholino)-propanesulfonic acid (Mops) were investigated. The effect of dioxane as a solvent on the formation constants of DBT–Mes and DBT–Mops complexes decrease linearly with the increase of dioxane proportion in the medium. The concentration distribution of the various complexes species was evaluated as a function of pH.     

Coordination properties of bidentate (N,O) and tridentate (N,O,O) heterocyclic alcohols with dimethyltin(IV)

The complex-formation equilibria of dimethyltin(IV) (DMT) with 4-hydroxymethyl imidazole (HMI) and 2,6-dihydroxymethyl pyridine (PDC) have been investigated. Stoichiometry and stability constants for the complexes formed were determined at different temperatures and 0.1?mol?L^?1 NaNO₃ ionic strength. The concentration distribution of the complexes in solution was evaluated as a function of pH. The effect of dioxane as a solvent on both protonation constants and formation constants of DMT complexes with HMI and PDC are discussed. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated.     

Calcium—malonate complexes in aqueous solution. Thermodynamic parameters and their ionic strength dependence

Formation constants of calcium complexes with malonate (mal^2?), in the ranges 10 ? t ? 50°C and 0.05 ? I ? 0.9 mol dm^?3, were determined by means of alkalimetric titrations in aqueous solution. The species found in this system were [Ca(mal)]⁰ and [Ca(Hmal)]⁺; also, the hydrolysis of Ca²⁺ was taken into account. The effect of ionic medium on the formation constants was studied by using different background salts (KNO₃, NaNO₃, Et₄NI and Et₄NBr); the parameters defining ionic strength dependence were calculated from the values of stability constants obtained at different ionic strengths. ΔH and ΔS values were obtained from temperature coefficients of stability constants.A general equation, useful for correlating the formation constants in the studied temperature and ionic strength ranges, has been found. It has also been found that, by considering all the significant interactions in the solution, the formation constants are dependent on temperature and ionic strength only.Literature data are discussed and compared with those obtained in this work.     

Formation constants and coordination thermodynamics for binary complexes of Cu(II) and some α-amino acids in aqueous solution

In this study, the formation constants of 1?:?1 binary complexes of Cu(II) with L-glutamic acid, L-aspartic acid, glycine, L-alanine, L-valine, and L-leucine and 1?:?2 binary complexes of L-glutamic acid, glycine and the protonation macro- and microconstants of all these amino acids were determined potentiometrically in aqueous solutions at 5.0, 20.0, and 35.0°C at a constant ionic strength of I?=?0.10?mol?L^?1 (NaClO₄). The thermodynamic parameters ΔG _f°, ΔH _f°, and ΔS _f° were determined for the protonation of all amino acids used in this study and for the complex formation reactions of them with Cu(II). The results were analysed by means of Principle of hard and soft [Lewis] acids and bases. Additionally, in order to confirm the complex formation and determine the stability constants of complexes, UV-Vis spectroscopic studies were carried out. The stability constants obtained by spectrophotometrically are confirmed by those determined potentiometrically.     

Calorimetric investigations of association equilibria: the pyridine-iodine complex in cyclohexane and in carbon tetrachloride

The results of two independent calorimetric investigations of the pyridine- iodine complex are reported. “Best” values are reported as K_m = 128 1/mol and ΔH° = -8.4 kcal mol^?1 for the formation of the complex in cyclohexane at 25°C, and K_m = 104 and ΔH° = -7.9 kcal mol^?1 in carbon tetrachloride. Evidence is presented to support the contention that association constants for weak complexes determined by calorimetric methods can be as reliable as those determined by spectrometric methods, and that values of ΔH° determined by the calorimetric method are much more reliable than those derived from the temperature dependence of equilibrium constants.     

Complexing ability of pesticides and related compounds. Formation and stability in aqueous solution of H+ , Li+, Na+, K+, Mg2+ and Ca2+ phenoxyacetate complexes at different temperatures and ionic strengths

The formation constants of Li⁺, N⁺, K⁺, Mg²⁺ and Ca²⁺ phenoxyacetate complexes were determined potentiometrically using an (H⁺)-glass electrode at 10, 25, 37 and 45°C, at several ionic strengths, in the range 0.04?I? 0.9 mol 1^?1. Simple empirical equations for the dependence of the formation constants on ionic strength were derived. From the temperature coefficients, estimates of ΔH^o and ΔS^o were obtained.     

Mono- and binuclear complexes involving [Pd(N,N-dimethylethylenediamine)(H2O)2]2+, 4,4′-bipiperidine and DNA constituents

The Pd(dmen)Cl₂, where dmen?=?N,N-dimethethylenediamine, was synthesized and characterized by elemental analysis and spectroscopy. The complex-formation equilibria in the reaction of [Pd(dmen)(H₂O)₂]²⁺ with 4,4′-bipiperidine (Bip) and DNA constituents were investigated at 25°C and 0.1?mol?L^?1 ionic strength. The results show the formation of [(H₂O)(dmen)Pd(Bip)Pd(dmen)(H₂O)]⁴⁺. Inosine, uracil, and thymine interact with the previously mentioned complex by the substitution of two-coordinated water molecules. The formation constants of all possible mono- and binuclear complexes were determined and their speciation diagrams were evaluated.     

Equilibrium studies of complex formation involving palladium(II)-(1,3-diaminopropane) and cyclobutane dicarboxylic acid,DNA units,amino acids or peptides

Complex formation equillibria of [Pd(DAP)(H₂O)₂]²⁺ (DAP = 1,3-diaminopropane) with Cl⁻, OH⁻, cyclobutane dicarboxylic acid (CBDCA), amino acids, peptides and DNA unit constituents have been investigated. Stoichiometries and stability constants of the complexes were determined at 37°C and 0.16 M NaNO₃ ionic strength. The results showed the formation of 1:1 complexes with amino acids and CBDCA. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. DNA constituents form both 1:1 and 1:2 complexes. [Pd(DAP)(CBDCA)] was isolated and characterized. The concentration distribution of the complexes in solution was evaluated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Thermodynamic parameters of the formation of deprotonated single-ligand complexes in the Cu(II)−triglycine system in aqueous solutions

Heat effects arising from interactions between triglycine solutions and Cu(NO₃)₂ solutions are studied at 298.15 K and ionic strengths of 0.2 to 1.0 (KNO₃) via isothermal calorimetry. Using experimental data, enthalpies of formation are calculated for species CuH_?1L, CuH_?2L^?, and CuH_?3L^2?, along with Δ_rH°, Δ_rG°, and Δ_rS° of the complexation process. A relationship is revealed between the structures of deprotonated single-ligand triglycine complexes of Cu(II) and the thermodynamic parameters of their formation.     

The formation of proton and alkali-metal complexes with ligands of biological interest in aqueous solution. Thermodynamics of H+, Na+ and K+—oxalate complexes

The protonation constants of oxalic acid were determined potentiometrically at 37°C in different media—NaNo₃, KNO₃ and Et₄NI, 0.03? I ? 0.3. From these data it was possible to determine the formation of the complexes [Na(ox)]^? and [K(ox)]^? and [K(ox)]^?, and to calculate their stability constants. Simultaneous analysis of potentionmetric and calorimetric data (this work and literature) enabled the temperature and ionic strength dependendence of the equilibrium parameters to be obtained for the protonation of oxalate. Recalculation of some literature data gave the ΔH value for the formation of the [Na(ox)]^? complex. The thermodynamic parameters obtained allowed us to confirm the hypothesis that dicarboxylate anions chelate with alkali-metal ions and that these complexes are mainly entropically stabilized.     

Thermodynamic Characteristics of Reactions of the Formation of Complexes between Triglycine and Ni2<Superscript>+</Superscript> Ions in Aqueous Solution

Thermal effects of reactions of the formation of complexes between Ni(II) and triglycine are determined via direct calorimetry in aqueous solutions at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO₃). Standard thermodynamic characteristics (Δ_rH°, Δ_rG°, Δ_rS°) of complexing processes in the investigated systems are calculated. The structures of triglycinate complexes NiL⁺, NiH_?1L, NiL₂, NiH_?2L^2?₂, NiL^-₃, and NiH_?3L^4?₃ are introduced to compare the obtained values and data on the thermodynamics of triglycinate complexes of Ni(II).     

Étude thermodynamique de la complexation de l'argent par la pipérazine et quelques-uns de ses derives en milieu eau—ethanol

The stability constants of the complexes of Ag⁺ ion with piperazine and its 2-methyl-, 2-methyl-1-m-tolyl-, 2-methyl-1-p-tolyl- and 1-(p-methoxyphenyl)-2-methyl-derivatives are obtained at 25°C in water—ethanol (52%, w/w) solvent and KNO₃ 0.1 M ionic strength, by means of corresponding metal-complex electrodes.The enthalpies of formation are determined by direct calorimetry, in the same conditions of temperature and medium.The comparison of the thermodynamic functions ΔG_n°, ΔH_n°, ΔS_n° allows a discussion about the ability of each amine to coordinate, in terms of nature and position of the entering group.     

Etude de la complexation des lanthanides trivalents par les isomères de l'acide diaminocyclohexanetétraacétique: Partie 2. Les Constantes d'Acidité et les Constantes de Formation des Complexes 1:1 avec l'Acide trans-1,4-Diaminocyclohexane-N,N,N′,N′-Tétraacétique

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 2. Acidity constants and formation constants of the 1:1 complexes of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid)Potentiometric measurements of the acidity constants of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (trans-1,4-DCTA) and of the stability constants of its 1:1 complexes with the trivalent lanthanides are reported for an ionic strength of 1 (KCl) at 25°C. The behaviour of this ligand is similar to that of monoaminodiacetic acids, suggesting that only one N(CH₂COO^?)₂ group participates in chelation. The selectivity of trans-1,4-DCTA for the lanthanides is better than that reported for the monoaminodiacetic acids.     

Thermodynamics and kinetics of complexation of iron(III) ion by picolinic and dipicolinic acids

The complexation reactions of iron(III) with 2-pyridine carboxylic acia (picolinic acid) and 2,6-pyridine dicarboxylic acid (dipicolinic acid) in aqueous solutions have been studied by spectrophotometric and stopped flow techniques. Equilibrium constants were determined for the 1 : 1 complexes at temperatures between 25 and 80°C. The values obtained are: Picolinic Acid (HL): Fe³⁺+ H₂L⁺? FeHL³⁺+H+(K₁ = 2.8,ΔH = 2 kcal mole^?1 at 25°C, μ = 2.67 M) Dipicolinic Acid (H₂D): Fe³⁺+H₂D? FeD⁺+2H⁺(K₁K_1A= 227 M, ΔH = 3.4 kcal mole^?1 at 25°C,μ = 1.0 M). The rate constants for the formation of these complexes are also given. The results are used to evaluate the effects of these two acids upon the rate of dissolution of iron(III) from its oxides.     

Formation of CaSO4(aq) and CaSeO4(aq) studied as a function of ionic strength and temperature by CE

Ca²⁺ complexation by both sulfate and selenate ligands was studied by CE. The species were observed to give a unique retention peak as a result of a fast equilibrium between the free ions and the complexes. The change in the corresponding retention time was interpreted with respect to the equilibrium constant of the complexation reaction. The results confirmed the formation of CaSO₄(aq) and CaSeO₄(aq) under our experimental conditions. The formation data were derived from the series of measurements carried out at about 15, 25, 35, 45 and 55°C in 0.1 mol/L NaNO₃ ionic strength solutions, and in 0.5 and 1.0 mol/L NaNO₃ ionic strength solutions at 25°C. Using a constant enthalpy of reaction enabled to fit all the experimental data in a 0.1 mol/L medium, leading to the thermodynamic parameters: Δ_rG^0.1M(25°C)=?(7.59±0.23) kJ/mol, Δ_rH^{0.1 M}=5.57±0.80 kJ/mol, and Δ_rS^{0.1 M}(25°C)=44.0±3.0 J mol^?1 K^?1 for CaSO₄(aq) and Δ_rG^{0.1 M}(25°C)=?(6.66±0.23) kJ/mol, Δ_rH^{0.1 M}=6.45±0.73 kJ/mol, and Δ_rS^{0.1 M}(25°C)=44.0±3.0 J mol^?1 K^?1 for CaSeO₄(aq). Both formation reactions were found to be endothermic and entropy driven. CaSO₄(aq) appears to be more stable than CaSeO₄(aq) by 0.93 kJ/mol under these experimental conditions, which correlates with the difference of acidity of the anions as expected for interactions between hard acids and hard bases according to the hard and soft acids and bases theory. The effect of the ionic medium on the formation constants was successfully treated using the Specific ion Interaction Theory, leading to significantly different binary coefficients mol/kg^?1 and mol/kg^?1     

Complexation Equilibria and Determination of Stability Constants of Binary and Ternary Nickel(II) Complexes with Amino Acids (Glycine, α-Alanine, β-Alanine and Proline) and Dipicolinic Acid as Ligands

In this paper we report the formation of binary and ternary nickel(II) complexes involving dipicolinic acid (H₂Dipic) as the primary ligand and some selected amino acids {glycine (HGly), ?-alanine (H?-Ala), ??-alanine (H??-Ala) and proline (HPro)} as secondary ligands. These complexes were studied at 25?°C by means of electromotive force measurements, emf(H), using 1.0?mol?dm^?3 NaCl as the ionic medium. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the nickel(II) cation and the acid/base reactions of the ligands whose equilibrium constants were kept fixed during the analysis. In the study of the binary nickel(II)?Camino acids systems the species [NiL]⁺, NiL₂ and [NiL₃]^? were observed, and in the case of the ternary nickel(II)?Cdipicolinic acid?Camino acids systems the complexes Ni(Dipic)HL, [Ni(Dipic)L] ^? and [Ni(Dipic)L(OH)]^2? were observed. The respective stability constants were determined, and the species distribution diagrams, as a function of pH, are briefly discussed.     

Thermodynamic characteristics of the formation of complexes of nickel(II) with L-homoserine

The formation of complexes of nickel(II) with L-homoserine at 298.15 K and ionic strengths I = 0.5, 1.0, and 1.5 (KNO₃) are investigated by potentiometry and calorimetry. Standard characteristics of studied equilibria (log K°, Δ_rG°, Δ_rH°, and Δ_rS°) are determined.