Showing papers on "Stability constants of complexes published in 2002"
TL;DR: Comparison of the Cm(III, Nd(III), and Sm(III) XAFS shows that the structure and metal-donor atom bond distances are indistinguishable within experimental error for similarly sized trivalent lanthanide and actinide cations, despite the selectivity of bis(2,4,4-trimethylpentyl)dithiophosphinic acid for trivalents actinides cations over trivalENT lanthanid cations
Abstract: The complexes of trivalent actinide (Am(III) and Cm(III)) and lanthanide (Nd(III) and Sm(III)) cations with bis(2,4,4-trimethylpentyl)phosphinic acid, bis(2,4,4-trimethylpentyl)monothiophosphinic acid, and bis(2,4,4-trimethylpentyl)dithiophosphinic acid in n-dodecane have been studied by visible absorption spectroscopy and X-ray absorption fine structure (XAFS) measurements in order to understand the chemical interactions responsible for the great selectivity the dithiophosphinate ligand exhibits for trivalent actinide cations in liquid-liquid extraction. Under the conditions studied, each type of ligand displays a different coordination mode with trivalent f-element cations. The phosphinate ligand coordinates as hydrogen-bonded dimers, forming M(HL2)3. Both the oxygen and the sulfur donor of the monothiophosphinate ligand can bind the cations, affording both bidentate and monodentate ligands. The dithiophosphinate ligand forms neutral bidentate complexes, ML3, with no discernible nitrate or water molecules in the inner coordination sphere. Comparison of the Cm(III), Nd(III), and Sm(III) XAFS shows that the structure and metal-donor atom bond distances are indistinguishable within experimental error for similarly sized trivalent lanthanide and actinide cations, despite the selectivity of bis(2,4,4-trimethylpentyl)dithiophosphinic acid for trivalent actinide cations over trivalent lanthanide cations.
249 citations
TL;DR: The rapid clearance of the (64)Cu-2 complex from the blood and liver, as well as liver metabolism experiments in rats, suggests that it is highly stable in vivo, and a bifunctional chelator of 2 is a significant candidate for labeling copper radionuclides to biological molecules for diagnostic imaging and targeted radiotherapy.
Abstract: Macrocyclic chelators and their metal complexes have widespread applications in the biomedical sciences, including radiopharmaceutical chemistry. The use of copper radionuclides in radiopharmaceuticals is increasing. Macrocyclic chelators have been found to have enhanced in vivo stability over acyclic chelators such as ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). The currently used chelators of choice for labeling copper radionuclides to biological molecules are analogues of TETA (1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid); however, recent reports have demonstrated evidence of in vivo instability of the radio-Cu(II)−TETA complexes. A new class of structurally reinforced macrocycles, the “cross-bridged” cyclam derivatives, form highly stable complexes with Cu(II) that are resistant to dissociation in strong acid. Here, we evaluate a series of 64Cu(II) cross-bridged macrocyclic complexes for biological stability and in vivo behavior. The ligands eva...
218 citations
TL;DR: In this article, the role of the degree of polymerisation in the complexation of copper ions by chitosan and its oligomers was investigated using potentiometric and spectrophotometric methods.
205 citations
TL;DR: The mole fractions of hydroxo complexes of titanium(IV) ion in an aqueous solution with 0.10 mol dm(-3) NaClO4 at 25 degrees C have been determined as a function of pH by a newly developed analytical procedure based on UV spectrophotometry.
203 citations
TL;DR: A comparison of the iodide and sulfate complex stabilities of the ditopic receptor with those of a cyclopeptide that forms 1:1 anion complexes in solution showed that the presence of a second binding site increases complex stability by a factor of 100-350.
Abstract: An artificial anion receptor is presented, in which two cyclohexapeptide subunits containing l-proline and 6-aminopicolinic acid subunits in an alternating sequence are connected via an adipinic acid spacer. This compound was devised to stabilize the 2:1 sandwich-type anion complexes that are observed when the two cyclopeptide moieties are not covalently connected and to obtain a 1:1 stoichiometry for these aggregates. Electrospray ionization mass spectrometry and NMR spectroscopic investigations showed that the bridged bis(cyclopeptide) does indeed form defined 1:1 complexes with halides, sulfate, and nitrate. ROESY NMR spectroscopy and molecular modeling allowed a structural assignment of the sulfate complex in solution. The stabilities of various anion complexes were determined by means of NMR titrations and isothermal titration microcalorimetry in 50% water/methanol. Both methods gave essentially the same quantitative results, namely stability constants that varied in the range 105−102 M-1 and decreas...
156 citations
TL;DR: The conformation adopted by L(1)-L(3) in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity.
Abstract: The macrocycles L1−L3 incorporating N2S3-, N2S2O-, and N2S2-donor sets, respectively, and containing the 1,10-phenanthroline unit interact in acetonitrile solution with heavy metal ions such as PbII, CdII, and HgII to give 1:1 ML, 1:2 ML2, and 2:1 M2L complex species, which specifically modulate the photochemical properties of the ligands. The stoichiometry of the complex species formed during spectrofluorometric titrations and their formation constants in MeCN at 25 °C were determined from fluorescence vs MII/L molar ratio data. The complexes [Pb(L1)][ClO4]2·1/2H2O (1), [Pb(L2)][ClO4]2·MeNO2 (1a), [Pb(L3)2][ClO4]2·2MeCN (1b), and [Cd(L3)][NO3]2 (2b) were also characterized by X-ray diffraction studies. The conformation adopted by L1−L3 in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity. In 1, 1a, and 2b the metal ion completes the coordination sphere by interacti...
153 citations
TL;DR: The results show that beta-CD reacts with curcumin to form a 2:1 host-guest complex with an apparent formation constant of 5.53 x 10(5) mol(-2) x L2.
Abstract: The beta-cyclodextrin-thiabendazole (beta-CD-TBZ) inclusion complex was synthesized and its structure characterized by (1)H NMR and IR. The mechanism of the supramolecular interaction of TBZ and beta-CD has been studied and discussed by spectrophotometry. The results showed that the phenyl ring of TBZ was included in the beta-CD cavity to form a 1:1 host-guest complex with an apparent formation constant of 1.60 x 10(3) mol(-1).L. On the basis of the enhancement of the absorbance of TBZ produced through complex formation, a spectrophotometric method for the determination of TBZ in bulk aqueous solution in the presence of beta-CD was developed. The linear relationship between the absorbance and TBZ concentration was obtained in the range of 8.86 x 10(-7)-1.45 x 10(-5) mol/L. The detection limit was 2.71 x 10(-7)mol/L, and the relative standard deviation was 0.86%. The interference of 48 coexisting substances was slight. The proposed method has been successfully applied to the determination of TBZ in fruits with recoveries of 96-103%.
138 citations
TL;DR: In this article, the Slips and Freundlich equations were used to explain the experimental data of activated carbon made from pecan shells and an approximate pH of 3 for a number of metal ion solutes.
115 citations
TL;DR: Investigations into the thermodynamic parameters that characterize the binding of citrate to tris-guanidinium host 1 in water are reported, leading to an unusual observation: the dilution of one component of the host/guest complex leads to the formation of the higher-order complexes.
Abstract: Investigations into the thermodynamic parameters that characterize the binding of citrate to tris-guanidinium host 1 in water are reported. The parameters Ka, ΔH°, ΔS°, and ΔG° for the binding event were quantified using isothermal titration calorimetry (ITC) techniques. The 1:1 binding stoichiometry was verified by a Job plot derived from NMR data, and the microcalorimetry data was collected for solutions of 1 and citrate ranging from 1 to 100 mM using phosphate buffer concentrations of 5 and 103 mM. At low buffer concentrations (low ionic strength) complexes with greater than 1:1 stoichiometries were observed by ITC, and K1 was determined to range from 2.0 × 103 to 3.0 × 103 M-1. At higher buffer concentrations (high ionic strength) the higher-order complexes were not detected, and K1 was determined to be 409 M-1. The 1:1 association of host 1 and citrate is characterized by a large favorable entropy component and negative enthalpy. However, the complexes with higher-order stoichiometry arise from desol...
101 citations
TL;DR: The interaction of lower rim calix(4)arene derivatives containing ester (1) and ketone (2) functional groups and bivalent (alkaline-earth, transition- and heavy-metal) cations has been investigated in various solvents and the selective behavior of 1 and 2 for bivalent cations is demonstrated for the first time.
Abstract: The interaction of lower rim calix(4)arene derivatives containing ester (1) and ketone (2) functional groups and bivalent (alkaline-earth, transition- and heavy-metal) cations has been investigated in various solvents (methanol, N,N-dimethylformamide, acetonitrile, and benzonitrile). Thus, 1 H NMR studies in CD 3 -OD, C 3 D 7 NO, and CD 3 CN show that the interaction of these ligands with bivalent cations (Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Hg 2+ , Pb 2+ , Cd 2+ ) is only observed in CD 3 CN. These findings are corroborated by conductance measurements in these solvents including benzonitrile, where changes upon the addition of the appropriate ligand (1 or 2) to the metal-ion salt only occur in acetonitrile. Thus, in this solvent, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:1 complexes between these ligands and bivalent cations. Four metal-ion complex salts resulting from the interaction of 1 and 2 with cadmium and lead, respectively, were isolated and characterized by X-ray crystallography. All four structures show an acetonitrile molecule sitting in the hydrophobic cavity of the ligand. The mode of interaction of the neutral guest in the cadmium(II) complexes differs from each other and from that found in the lead(II) complexes and provides evidence of the versatile behavior of acetonitrile in binding processes involving calix(4)arene derivatives. The thermodynamics of complexation of these ligands and bivalent cations in acetonitrile is reported. Thus, the selective behavior of 1 and 2 for bivalent cations is for the first time demonstrated. The role of acetonitrile in the complexation process in solution is discussed on the basis of 1 H NMR and X-ray crystallographic studies. It is suggested that the complexation of 1 and 2 with bivalent cations is likely to involve the ligand-solvent adducts rather than the free ligand. Plots of complexation Gibbs energies against the corresponding data for cation hydration show a selectivity peak which is explained in terms of the predominant role played by cation desolvation and ligand binding energy in complex formation involving metal cations and macrocycles in solution. A similar peak is found in terms of enthalpy suggesting that for most cations (except Mg 2+ ) the selectivity is enthalpically controlled. The ligand effect on the complexation process is quantitatively assessed. Final conclusions are given highlighting the role of the solvent in complexation processes involving calix(4)arene derivatives and metal cations.
86 citations
TL;DR: In this paper, the enthalpy and entropy of the complexation between uranium(VI) and acetate in 1.05 mol kg−1 NaClO4 was studied at variable temperatures (25, 35, 45, 55 and 70 °C).
Abstract: The complexation between uranium(VI) and acetate in 1.05 mol kg−1 NaClO4 was studied at variable temperatures (25, 35, 45, 55 and 70 °C). The formation constants of three successive complexes, UO2(OOCCH3)+, UO2(OOCCH3)2 and UO2(OOCCH3)3−, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) provided structural information to identify the coordination modes of the acetate in the complexes in solution, which helped to interpret the trends in the enthalpy and entropy of the complexation. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.
TL;DR: In this paper, the results of a study of copper(I)-chloride complexes at much higher chloride concentrations, 1.5 m to 9.1 m, using a UV spectrophotometric method were presented.
TL;DR: In this article, the steric effect of the ortho substituent on metal ion binding at the N1 site of pyridine derivatives was investigated and it was shown that steric effects of amino and methyl groups are equal.
TL;DR: An absorption spectral and electrochemical study for the zinc(II) complexes of meso-tetraphenylporphyrin dianion (TPP), meso -tetramesitylporphrin dianions (TMP), and meso −tetra(2,6-dichlorophenyl)porphynyl)PORPHyrin (TDCPP) in the presence of nitrogeneous bases in CH 2 Cl 2 solution is reported in this paper.
TL;DR: In this paper, an equation of the type log K, = EAEB + CACB, where E and C are identified with the tendency of the Lewis acid A and base B to undergo ionic and covalent bonding was used to correlate the F-, OH-, and NH, formation constants of 27 Lewis acids to a standard deviation of 0.24 log unit.
Abstract: It is shown that four-parameter equations proposed by previous authors have poor predictive powers for data of formation constants in aqueous solution. This relates partly to the paucity of data on complexes of ligands such as ammonia which, with most metal ions, cannot exist in water because of hydrolysis. Equations previously proposed that relate the formation constants of polyamine and poly(aminbcarboxy1ate) complexes to those of the ammonia and acetate complexes are used to calculate formatio‘n constants for these hydrolysis-prone ammonia complexes. An equation of the type log K, = EAEB + CACB, where E and C are identified with the tendencies of the Lewis acid A and base B to undergo ionic and covalent bonding, was used to correlate the F-, OH-, and NH, formation constants of 27 Lewis acids to a standard deviation of 0.24 log unit. Hardness parameters l!fA and HB were defined as EA/CA and EB/CB for acids and bases, respectively, and gave reasonable orders of hardness It was found that for ligands with large donor atoms, such as C1-, and for sulfur or phosphorus donor atoms, deviations from the predictions of this equation were observed that appeared to be related to the size of the acid, so that no deviations were observed for large cations such as Ag’ and Pb2+, aith Occurrence of large deviations for smaller cations such as Cu” or Ni2+, with the very largest occurring for the proton. These deviations were attributed to steric hindrance between the large donor atom and adjacent coordinated water molecules. The important contribution of the Edwards equation’ lies in illustrating that formation constant data for complexes of unidentate ligands in aqueous solution need at least a dualbasicity scale for any kind of correlation to be obtained at all. There have been several other multiparameter equation^^-^ proposed for correlating formation constant data. The need for at least a dual-basicity equation has manifested itself in the classification of metal ions’into Schwart~enbach’s~ and Ahrland and Chatt’s6 A- and B-type metal ions and Pearson’s more general classification7 of Lewis acids and bases into hard and soft acids and bases (HSAB). Drago and co-workers* have had considerable success with a more generalized form of a four-parameter equation similar to eq 1 for the correlation of enthalpy changes on adduct formation in solvents of low dielectric constant. In eq 1, which resembles Drago’s expression, except that -AHo has been replaced with log K1, C and E are identified with the tendency of each Lewis acid A or base B to undergo covalent or ionic bonding. This interpretation of the significance of the C and E parameters seems most reasonable in the light of the work of Klopman9 on the origin of hardness and softness in acids and bases. Klopman9 found softness to be associated Rith “frontier-controlled’’ (covalent) and hardness with “charge-controlled’’ (ionic) bonding in calculations based upon polyelectronic pertubation theory. We have therefore adopted the E and C formalism of Drago and co-workers8 in this paper as probably being the best interpretation of the parameters in a four-parameter equation such as (1).
TL;DR: The stability constant (K), standard free energy (G°), enthalpy (ΔH°), and entropy changes (TΔS°) for the complexation of native α- and β-cyclodextrins (CDs) and 6-amino-6-deoxy-β-CD with more tha
Abstract: The stability constant (K), standard free energy (ΔG°), enthalpy (ΔH°), and entropy changes (TΔS°) for the complexation of native α- and β-cyclodextrins (CDs) and 6-amino-6-deoxy-β-CD with more tha
TL;DR: In this paper, the phase solubility diagram of bromazepam and its inclusion complexes with β-cyclodextrin (β-CD) and β-HP-CD was used to measure the changes introduced in this chemical system and the amount of time which was necessary to reach equilibrium between inclusion complexes and their free components was estimated and found equal to 24 h.
TL;DR: In this article, a chelating vinyl monomer, glycidyl methacrylate (GMA)−iminodiacetic acid (IDA), was formed by the reaction between GMA and IDA.
Abstract: A chelating vinyl monomer, glycidyl methacrylate (GMA)–iminodiacetic acid (IDA), was formed by the reaction between GMA and IDA. Three polymeric chelating agents, PGMA–IDA, PGMA–IDA-co-methyl acrylate (MA), and PGMA–IDA-co-acrylamide (AAm), were also synthesized. Acid dissociation constants and stability constants of these chelating agents with Ni(II), Zn(II), and Co(II) were determined by means of potentiometric titration and ultraviolet–visible spectrophotometry, respectively. The values of Ka1 and Ka2 of all the polymeric chelating agents were smaller than those of GMA–IDA. The stability constants of all the polymeric chelating agents were larger than those of GMA–IDA. Increasing the MA content within PGMA–IDA-co-MA affected the stability constant only slightly. A proper molar ratio of AAm in PGMA–IDA-co-AAm, stability constants was 30–60 times greater than that of GMA–IDA. However, as the molar content of AAm increased, the stability constant of PGMA–IDA-co-AAm decreased. The results obtained in the polymer system are explained in terms of the polymer's stereo and entanglement structure, the neighboring effect, and the hydrophobic/hydrophilic nature of MA or AAm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1986–1994, 2002
TL;DR: A gradient separation procedure achieved on-column preconcentration and matrix removal for the interference-free detection of metal chelates down to low nanomolar concentration in samples from various fields of environmental research.
TL;DR: In this paper, log stability constant differences for substitution reactions of one ligand for another on a metal ion are used to derive practical metal ion hardness-softness scales applicable to aqueous solutions.
TL;DR: In this article, the formation of poly(ninylimidazole) (PVIm) with trivalent metal ions in aqueous solution was studied by using UV-vis spectroscopy.
Abstract: The complex formation of soluble poly (N-vinylimidazole) (PVIm) with trivalent metal ions in aqueous solution was studied by using UV–vis spectroscopy. Formation constants of PVIm–metal complexes were calculated by applying the “molar ratio” method. It was found that the interaction between PVIm and trivalent metal ions follows 4(base unit):1(metal ion) stoichiometry. The stability constants for the complexes of PVIm with trivalent transition-metal ions were in agreement with the Irving– William series. The biggest formation constant was found for the PVIm–Fe3+ complex system. The capacity of adsorption for these metal ions was investigated using cross-linked PVIm. Cross-linked PVIm hydrogels were prepared by irradiating binary mixture of N-vinylimidazole–water with a 60Co γ-ray source having a dose rate of 4.5 kGy/h. Adsorption studies were performed at different pH and metal ion concentrations at room temperature. It was observed that the same sequence for the metal ions was verified by adsorption studies.
TL;DR: The equilibria in the system VIVO2+-glutathione in aqueous solution were studied in the pH range 2–11 by a combination of pH-potentiometry and spectroscopy to support the established binding modes for the glutathione complexes.
Abstract: The equilibria in the system VIVO2+-glutathione in aqueous solution were studied in the pH range 2–11 by a combination of pH-potentiometry and spectroscopy (EPR, visible absorption and circular dichroism) The results of the various methods are consistent and the equilibrium model includes the species MLH3, MLH2, MLH, ML2H2, MLH–1, and MLH–2 and several hydrolysis products (where H4L denotes totally protonated glutathione); individual formation constants and spectra are given ML2H2 is the predominant species at physiological pH Plausible structures for each stoichiometry are discussed The related VIVO2+ systems of S-methylglutathione and γ-L-glutamyl-L-cysteinyl ethyl ester were studied by means of the same spectroscopic techniques in order to support the established binding modes for the glutathione complexes The importance of glutathione and oxidized glutathione in binding VIVO2+ in cells is assessed
TL;DR: It is concluded (tentatively) that the kinetic description of lithium-selective electrodes with solvent polymeric membranes is equivalent to the equilibrium one, giving evidence that ion-ionophore complexes form directly at the interface.
Abstract: Lithium-selective electrodes with solvent polymeric membranes based on two different dicyclohexylamide neutral ionophores are studied systematically. The selectivity of lithium response is studied by means of the ordinary potentiometric experiments. Stability constants of lithium, sodium, and potassium ions with the neutral ionophores are measured by means of the segmented sandwich membrane method. Charge transfer through the membrane bulk and across the membrane/solution interface is studied by means of electrochemical impedance spectroscopy. Well-resolved Faradaic impedance semicircles are obtained, allowing calculation of exchange current densities for lithium, sodium, and potassium. It is clearly demonstrated that the potentiometric selectivity coefficients correlate well with thermodynamic equilibrium parameters. The correlation with exchange current densities also exists, although it is low, and seems rather qualitative than quantitative. The results are treated in favor of equilibrium at the membra...
TL;DR: In this article, the effect of temperature on the complexation between uranium(VI) and malonate is discussed in terms of the electrostatic model and compared with the complexations between uranium and acetate.
Abstract: The complexation between uranium(VI) and malonate in 1.05 mol kg - 1 NaClO 4 was studied at variable temperatures (25, 35, 45, 55 and 70°C), The formation constants of three successive complexes, UO 2 (OOCCH 2 COO), UO 2 (OOCCH 2 COO) 2 2- and UO 2 (OOCCH 2 COO) 3 4-, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. The heat capacity of the complexation, ΔC° p , m ( M L j ) , is calculated to be 96′12, 195′15 and 267 ′ 22 J K - 1 mol - 1 for j = 1, 2 and 3, respectively. Extended X-ray Absorption Fine Structure Spectroscopy helped to characterize the coordination modes in the complexes in solution. UV/Vis absorption and luminescence spectra at different temperatures provided qualitative information on the temperature effect. The effect of temperature on the complexation between uranium(VI) and malonate is discussed in terms of the electrostatic model and compared with the complexation between uranium(VI) and acetate.
TL;DR: It is concluded that addition of met beta CD resulted in a significant increase in the stability of complexed insulin compared with free insulin.
TL;DR: The structures show the importance of intermolecular hydrogen bonds and the effect of cap enlargement to the stability and geometry of the metal complexes throughout the series, a trend consistent with the effects of internal hydrogen bonding.
Abstract: TREN-Me-3,2-HOPO, TR322-Me-3,2-HOPO, TR332-Me-3,2-HOPO, and TRPN-Me-3,2-HOPO correspond to stepwise replacement of ethylene by propylene bridges. A series of tripodal, hexadentate hydroxypyridinone ligands are reported. These incorporate 1-methyl-3,2-hydroxypyridinone (Me-3,2-HOPO) bidentate chelating units for metal binding. They are varied by systematic enlargement of the capping scaffold which connects the binding units. The series of ligands and their iron complexes are reported. Single crystal X-ray structures are reported for the ferric complexes of all four tripodal ligands: FeTREN-Me-3,2-HOPO‚0.375C4H10O‚0.5CH2Cl2 [P21/n (No. 14), Z ) 8, a ) 20.478(3) A, b ) 12.353(2) A, c ) 27.360(3) A; ‚ ) 91.60(1)°]; FeTR322-Me-3,2-HOPO‚CHCl3‚0.5C6H14‚CH3OH‚0.5H2 O[ P21/n (No. 14), Z ) 4, a ) 12.520(3) A, b ) 22.577(5) A, c ) 16.525(3) A; ‚ ) 111.37(3)°]; FeTR332-Me-3,2-HOPO‚3.5CH3OH [C2/c (No. 15), Z ) 8, a ) 13.5294(3) A, b ) 19.7831(4) A, c ) 27.2439(4) A; ‚ ) 101.15(3)°]; FeTRPN-Me-3,2-HOPO‚C3H7NO‚2C4H10 O[ P1 (No. 2), Z ) 2, a ) 11.4891(2) A, b ) 12.3583(2) A, c ) 15.0473(2) A; R) 86.857(1)°, ‚ ) 88.414(1)°, A ) 70.124(1)°]. The structures show the importance of intermolecular hydrogen bonds and the effect of cap enlargement to the stability and geometry of the metal complexes throughout the series. All protonation and iron complex formation constants have been determined from solution thermodynamic studies. The TREN-capped derivative is the most acidic, with a cumulative protonation constant, log ‚014, of 25.95. Corresponding values of 26.35, 26.93, and 27.53 were obtained for the TR322, TR332, and TRPN derivatives, respectively. The protonation constants and NMR spectroscopic data are interpreted as being due to the influence of specific hydrogen-bond interactions. The incremental enlargement of ligand size results in a decrease in iron-chelate stability, as reflected in the log ‚110 values of 26.8, 26.2, 26.42, and 24.48 for the TREN, TR322, TR332, and TRPN derivatives, respectively. The metal complex formation constants are also affected by the acidity of a proximal (non-metal-binding) amine in the complexes, a trend consistent with the effects of internal hydrogen bonding. The ferric complexes display reversible reduction potentials (measured relative to the normal hydrogen electrode (NHE)) between -0.170 and -0.223 V.
TL;DR: The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), the ligands are better sequestering agents in acidic media.
Abstract: The coordinating ability of the ligands 3,4-toluenediamine-N,N, N′,N′-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N′,N′-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N′,N′-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25°C, l = 0.5 mol dm-3 in NaCIO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(μ-3,4-TDTA)4(H2 O)2]·4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants KPbeff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media.
TL;DR: In this article, the effect of the competing cations originally present in the groundwater has been examined at trace and macro concentrations (∼ 10 - 1 0 M) of Ca(II) with Aldrich humic acid.
Abstract: In order to understand the migration behavior of radionuclides in the underground, it is also important to estimate the effect of the competing cations originally present in the groundwater. In this connection, the complexation of Ca(II) with Aldrich humic acid has been examined. For the study at trace concentrations (∼ 10 - 1 0 M) of Ca(II), the solvent extraction of 4 5 Ca with TTA and TOPO in cyclohexane has been used. At macro concentrations (10 - 4 M) of Ca(II), the measurement of the free Ca 2 + ion concentration with a calcium selective electrode has been conducted. To estimate the polyelectrolyte effect of humic acid separately from its heterogeneous composition effect, polyacrylic acid ([-CH 2 CH(COOH)-] n ) has been selected as a representative of the homogeneous polymeric weak acids and its complexation with Ca(II) has also been examined. The values of log β α have been obtained at pH 5 ∼ 7 in 0.1, 0.4 and 1.0 M NaCI, where β α is the apparent formation constants defined by β α = [ML]/([M][R]). In this definition, [ML] and [M] are the concentrations of bound and free Ca 2 + respectively, [R] is the concentration of dissociated proton exchanging sites. log β α of humate decreases from 2.19 ∼ 2.92 (depending on pH and ionic strength 1.0 < I < 0.4) at pCa = 10 to 1.98 ∼ 2.44 at pCa = 4, while the variation of pCa has no appreciable influence on the log β α of polyacrylate (1.36 ∼ 3.24 for I = 0.1 ∼ 1.0). For both humate and polyacrylate, log β α decreases linearly with log[Na + ], where [Na + ] is the bulk concentration of sodium ion. Their dependences of log β α on ionic strength are stronger than those of log β of monomeric carboxylates such as oxalate and EDTA, indicating the large electrostatic effect of crowded negative charges on the macromolecules of humic or polyacrylic acid.
TL;DR: In this paper, the dissociation constants of eriochrome black T, erichrome blue black RC, and eriochromine black RC were obtained at different temperatures by potentiometric measurements in the presence of different percentage of organic solvent-water media.
TL;DR: In this article, the metal ion complexing behavior of diazacrown ether derivatives possessing two spirobenzopyran moieties has been studied under dark conditions and the stability constants for complex formation with various metal ions in methanol were determined for the first time using mass spectrometry.
Abstract: The metal ion complexing behavior of diazacrown ether derivatives possessing two spirobenzopyran moieties has been studied under dark conditions. Introduction of two spirobenzopyran moieties into diazacrown ethers resulted in interesting metal ion complexation abilities, along with isomerization of the spirobenzopyran moieties to the corresponding merocyanine form. The extremely high affinity for multivalent metal ions observed is due to an ionic interaction between the two phenolate anions and the multivalent metal ion. This finding is supported by absorption spectral measurements and electrospray ionization mass spectrometry. Stability constants for complex formation with various metal ions in methanol under dark conditions have been determined for the first time using mass spectrometry. It was found that the stability constants for crowned bis(spirobenzopyran) complexes with high charge density metal ions are much greater than those for the parent crown ether rings.
Specifically, the La3+complex of the diaza-18-crown-6 derivative carrying two spirobenzopyran moieties possesses an extraordinarily high stability constant of greater than 1011 M−1 in methanol.