Analytical relationships between the ionization of 1,3-dicarbonylic ligands and stability of their Cr(III), Ni(II), Co(II) and Cu(II) 1∶1 chelates

It has been demonstrated that the logarithm of the stability constant of some monochelated chromium(III) compounds, with structurally similar 1,3-dicarbonylic species, is linearly related to the negative logarithm of the acid ionization constant of the ligand. Graphical and analytical correlations which could be useful in predicting equilibrium constants of chromium(III)--diketonates, as well as other first-row transition metal derivatives, have been developed. A quantitative evaluation of the complexes stability has been carried out, providing information about the effects of ligand substituents on the equilibrium constants.     

MALDI mass spectrometric determination of dendritic iron chelation stoichiometries and conditional affinity constants

The iron chelation stoichiometries of a dendritic iron(III) chelator with N(1), N(3), N(5)-trimethylbenzene-1,3,5-tricarboxamide at its core, and containing 3 identical hexadentate tris-hydroxypyridinone branches D was studied by MALDI mass spectrometry. At pH 7.2, the speciation of the system included FeD, Fe(2)D and Fe(3)D species with the respective conditional stability constants of 26.74, 26.03 and 25.36. The differences in the stepwise affinity constants arise from the statistical distribution of iron(III), and there was no evidence for cooperativity between the iron-binding sites.     

Prediction and correlations between the stability constants of mono- and polynuclear chromium(III) and iron(III) complexes

Correlations between the experimentally determined stability constants of mono- and polynuclear chromium(III) and iron(III) complexes are discussed. An equation to evaluate the stability constants of mono- and polynuclear chromium(III) complexes is obtained: \(\log \beta [Cr_p^{3 + } (L_i )_{q_i } ] = 0.84\log \beta [Fe_p^{3 + } (L_i )_{q_i } ]\) .     

Effect of the tether on the Mg(II), Ca(II), Cu(II) and Fe(III) stability constants and pM values of chelating agents related to EDDHA

The effect of the length and the structure of the tether on the chelating ability of EDDHA-like chelates have not been established. In this work, PDDHA (propylenediamine-N,N'-bis(o-hydroxyphenyl)acetic acid), BDDHA (butylenediamine-N,N'-bis(o-hydroxyphenyl)acetic acid) and XDDHA (p-xylylenediamine-N,N'-bis(o-hydroxyphenyl)acetic acid) have been obtained and their chemical behaviour has been studied and compared with that of EDDHA following our methodology. The purity of the chelating agents, and their protonation, Ca(II), Mg(II), Fe(III) and Cu(II) stability constants and pM values have been determined. The stability constants and pM values indicate that EDDHA forms the most stable chelates followed by PDDHA. However, the differences among the pFe values are small when a nutrient solution is used, and in these conditions the XDDHA/Fe(III) chelate is the most stable. The results obtained in this work indicate that all the chelating agents studied can be used as iron chlorosis correctors and they can be applied to soil/plant systems.     

Use of ion exchange for the determination of stability constants of metal-humic substance complexes

Humic substances (HSs) occur throughout the ecosphere in soils, waters and underground systems. The strong complexation of HSs is of importance in the migration of radionuclies in geological media. Renewed interest in stability constants of complexes of radioelements and radionuclides with humic and fulvic acids has been generated by problems associated with the nuclide migration in the environment. Use of the ion exchange method for the determination of conditional stability constants of metal-HS complexes was examined and reviewed. The complexation of HS to metal ions cannot be described in rigorous mathematical terms because of the ill-defined nature of HSs in contrast with the complexation of single ligands. Furthermore, the advantages and disadvantages of Schubert's and, Ardakani-Stevenson's, curve fitting methods were discussed. The great stabilities of HS complexes to rare earths (Yb(III), Tb(III), Eu(III), Gd(III)), americium(III), cobalt(II), uranyl(VI) and thorium(IV) were revealed.     

Hamaker constants of iron oxide nanoparticles

The Hamaker constants for iron oxide nanoparticles in various media have been calculated using Lifshitz theory. Expressions for the dielectric responses of three iron oxide phases (magnetite, maghemite, and hematite) were derived from recently published optical data. The nonretarded Hamaker constants for the iron oxide nanoparticles interacting across water, A(1w1) = 33 - 39 zJ, correlate relatively well with previous reports, whereas the calculated values in nonpolar solvents (hexane and toluene), A(131) = 9 - 29 zJ, are much lower than the previous estimates, particularly for magnetite. The magnitude of van der Waals interactions varies significantly between the studied phases (magnetite < maghemite < hematite), which highlights the importance of a thorough characterization of the particles. The contribution of magnetic dispersion interactions for particle sizes in the superparamagnetic regime was found to be negligible. Previous conjectures related to colloidal stability and self-assembly have been revisited on the basis of the new Lifshitz values of the Hamaker constants.     

Stability of iron(III) complexes used as contrast agents in magnetic resonance imaging

Conditional constants at pH 7.4 are calculated for the iron(III) complexes of diethylenetrinitrilopentaacetic acid, trans-1,2-cyclohexylenedinitrilotetraacetic acid, triethylenetetranitrilohexaacetic acid and ethylenediiminobis[(2-hydroxypentyl) acetic acid]. The relationship between these constants and the stability which has previously been observed experimentally is discussed with regard to the possible formation of iron hydroxide and iron phosphate.     

Stability constants of the aqueous mono-fluoride complexes of Pu(III) and Am(III) and their correlation with other metal ions

The stability constants of the aqueous mono-fluoride complexes of Pu(III) and Am(III) have been measured using the distribution method. A correlation of the available stability constants of fluoride complexes of trivalent actinides, up to Cf, with fundamental properties like charge and radii of the metal ion has been discussed. Good correlation within the group and as a part of other metal ions was obtained only for transplutonium elements. The reported stability constant values measured by potentiometry and the value obtained by distribution for Pu³⁺ appear to be much higher than expected from this correlation. However, a better correlation was obtained with transplutonium elements when effective charge instead of formal charge was considered for Pu³⁺ in the BSE function.     

Spectrophotometric titration of bismuth with EDTA

A new spectrophotometnc method for the estimation of bismuth with EDTA, using iron-salicylate complex as the indicator, has been developed. The determinations were carried out by measuring the absorbance at 520 mmu. of solutions containing bismuth, iron(III), salicylic acid and various quantities of EDTA, at pH 0.5. It has been shown from the stability constants of the complexes present that before the end-point iron(III) will not react appreciably with the Bi-EDTA complex. The interference from iron(III) in the estimation of bismuth, which is a serious drawback in many other methods, is eliminated in the present method, as iron(III) acts as the indicator.     

Solvent extraction of 8-quinolinolato-iron(III) with the aid of various phenols as hydrogen-bonding donors

Effect of various phenols (ArOh) on the solvent extraction of iron(III) with 8-quinolinol (HQ) has been investigated. Greatly enhanced extraction is found in the presence of ArOh, e.g., the distribution ratio of iron(III) with HQ in carbon tetrachloride is increased 200,000-fold by 0.10M 3,5-dichlorophenol. From extraction equilibrium analysis, the enhanced extraction has been ascribed to the formation of association complexes of neutral iron(III) 8-quinolinolate (FeQ(3)) with ArOH as FeQ(3) . nArOH (n = 1, 2,3) in the organic phase, and the association constants (beta(ass,n)) have been determined. A linear relation is observed between logarithmic values of beta(ass,n) and the acid-dissociation constant of ArOH. Existence of the hydrogen bond between FeQ(3) and ArOH is clearly shown by infrared spectroscopy.     

Stability constants of polymer-metal complexes

Conditional stability constants of metal complexes with synthesized copolymers are studied by potentiometric titration. Linear copolymers are found to form more stable complexes than cross-linked sorbents with analogous functional groups. The stability of these complexes decreases in the order Th(IV) > Fe(III) ≈ La(III) > Cu(II).     

Studies on the liquid-liquid extraction of iron(III) and titanium(IV) with 3-phenyl-4-benzoyl-5-isoxazolone

The extraction behaviour of iron(III) and titanium(IV) from acidic chloride solutions has been investigated using 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) in xylene as an extractant. The results demonstrate that these metal ions are extracted into xylene as Fe(PBI)(3) and TiO(PBI)(2). The equilibrium constants of the extracted complexes have been deduced by non-linear regression analysis by taking into account complexation of metal ion with inorganic ligands in the aqueous phase and all plausible complexes extracted into the organic phase. IR and proton NMR ((1)H NMR) spectra were used to further clarify the nature of complexes extracted into organic phase. The effect of the nature of the diluent on the extraction of iron(III) and titanium(IV) has been studied and correlated with dielectric constants. The extraction behaviour of titanium(IV) has also been compared with that of other metal ions, viz. magnesium(II), vanadium(V), chromium(VI), iron(III), manganese(II), zinc(II) and zirconium(IV), which are associated with the titanium in waste chloride liquors of the titanium-mineral-processing industry.     

Speciation in the ternary system Iron(III)-nitrilotrimethylphosphonic acid-1,3-dicarboxypropane-1-iminodiacetic acid

The interaction of iron(III) ions with nitrilotrimethylphosphonic acid and 1,3-dicarboxypro-pane-1-iminodiacetic acid in aqueous solutions has been studied by spectrophotometry. It has been shown that complex formation in the system is complicated by protonation, hydrolysis, and precipitation. Homoligand 1: 1 complexes of different proton composition have been identified. The stability constants of the iron(III) complexonates and their fractional distribution as a function of pH (T = 20 ± 2°C, I = 0.1) have been determined. Conditions that make it possible to prevent the precipitation of iron(III) nitrilotrimethylphosphonates in the presence of 1,3-dicarboxypropane-1-iminodiacetic acid have been selected.     

POLAG-a general computer program to calculate stability constants from polarographic data

A general computer program, POLAG, that will calculate stability constants from polarographic data, has been written. The program requires no pretreatment of the experimental data. Any equilibrium model, consisting of species having the general formula M(m)H(j)(OH)(k)L(n)L'(p) may be fitted to the data. The performance and versatility of POLAG has been demonstrated by reprocessing polarographic data previously published by four different research groups.     

Determination of drug-cyclodextrin binding constants by capillary zone electrophoresis

Binding constants of the optical isomers of Deprenyl® (selegiline) and its potential metabolites with (2,6-di-O-methyl)--cyclodextrin were determined using electrophoretic mobility data gained from separations performed by capillary electrophoresis, and absorbancies obtained from spectrophotometric experiments. To calculate equilibrium constants l: l complex formation have been assumed. The comparison of the equilibrium constants calculated from different methods shows similar values in their order of magnitude. Their difference may probably be explained by the different media of the measurements. The effect of the structure of compounds on chiral discrimination were also elucidated.     

Speciation Studies of Iron (III) with (Poly)phosphonate Ligands: The Case of EDTMP (EthylenediamineTetramethylene Phosphonic Acid)

The complex formation equilibrium of ethylenediaminetetramethylenephosphonic acid (EDTMP, H₈L) with iron (III) has been studied potentiometrically at 25°C and an ionic strength of 0.2 M (NaCl). The successive protonation constants of ligand EDTMP and the complex formation constants were determined with the PSEQUAD program. Keeping in view the biological studies, the speciation in the system Fe (III)—EDTMP was calculated and drawn with the HySS computer program, and pFe values are compared.     

The stability constants of the rare earth complexes with trimetaphosphoric acid

The stability constants of the complexes formed between the rare earth metal ions and the anion of trimetaphosphoric acid have been determined at a temperature of 20 degrees C and an ionic strength of mu = 0.1 by the ion-exchange equilibrium method. The investigations indicate that stabilities of complexes increased from La to Lu. The highest and the lowest stability constant values (beta) were found to be 7.76 and 3.82 for Lu3+ and La3+ respectively.     

Potentiometric determination of stability constants of Lanthanon(III) complexes with some Schiff bases and benzothiazolines

The protonation constants of five Schiff base and two benzothiazoline type ligands and stability constants of their complexes with six lanthanide ions were determined by potentiometrically in ethanol-water solution (1:1, v/v) at 25 +/- 0.1 degrees C. The Schiff base-type ligands were salicylidene 2-iminopyridine (SAPy), salicylidene-5-methyl-2-iminopyridine (SAPyMe), salicylidene-5-chloro-2-iminopyridine (SAPyCl), 2-(2-pyridylmethyleneamino) phenol (PyOH), 2-(2-quinolylmethyleneamino) phenol (QuOH) and the benzothiazoline-type ligands were pyridine-2-car-bozaldehydebenzothiazoline (PyS) and quinoline-2-carboxaldehydebenzothiazoline (QuS). The order of stability constants was found to be for metal ions La(III) < Pr(III) < Nd(III) < Eu(III) < Ho(III) < Yb(III), and for ligands SAPyCl < SAPy < QuS < QuOH < PyS < PyOH < SAPyMe. The FORTRAN programs PKAS and BEST were used for the calculation of protonation constants and stability constants, respectively.     

pH-metric studies on formation constants of the complexes of substituted pyrazoles with some lanthanide metal ions and the influence of ionic strengths on complex equilibria in a 70% dioxane-water mixture

The pK a values of N-heterocyclic compounds (substituted pyrazoles) in a 70% (v/v) dioxane-water mixture have been determined using pH-metric measurements. The stability constants of the complexes of Dy(III), Nd(III), Sm(III), and Tb(III) with 3-(2-hydroxyphenyl)-5-methylpyrazole, l-phenyl-3-(2-hydimyphenyl)-5-methylpyrazole 3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole, and l-phenyl-3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole have been determined by the pH-metric method at ( 300 ± 0.1) K. The effect of ionic strengths on the complexes of Sm³⁺ and Pr³⁺ ions with pyrazole has been investigated in the internal from 0.02 to 0.1 mol dm⁻³ (sodium perchlorate) in the pH range 2–3.