SUPERQUAD Program Research Articles

Synthesis and characterization of phytate–uranium (VI) complexes

The phytate–uranium (VI) solid complexes were synthetized and characterized. A potentiometric study was firstly carried out in order to investigate acid–base properties of phytic acid and its interaction with uranium (VI) in 0.1 M NaClO4 medium at 25 °C. This study showed that the acid–base reactions for phytic acid occur from pH 2 to 12, and it is fully deprotonated at pH 13. A total of six protonation constants of phytic acid could be refined by fitting acid–base titration data using the SUPERQUAD program. The potentiometric study also revealed that the phytic acid reacts with uranium (VI) to form a precipitate, when an excess of uranyl ion is used. The phytate–uranium (VI) solid complexes were then prepared and characterized by fluorescence and X-ray photoelectron spectroscopies. The formation of phytate–uranium (VI) complexes with a preferential molar ratio of 1:2 was revealed in this study. The results of this study will thus contribute to development a viable and low-cost method that avoids the dispersion of anthropogenic actinides in the environment.

The Difference of the Complex Formation of the Samarium (3+) Ion with the L-malic Acid as Compared to the Neodymium (3+) Ion

<p>The complex formation of the neodymium Nd<sup>3+</sup> ion and the samarium Sm<sup>3+</sup> ion with L-malic acid (H<sub>3</sub>Mal) in the aqueous solutions was studied by pH-metric titration in pH region 2.80 to 10.00 and constant ionic strength 0.1 M KCl at 25°C. The ratios of the concentrations of the rare-earth elements (Ln) and the L-malic acid were 1:0.5, 1:1 and 1:2. The number of experimental points of each curve of pH-metric titration was 160-190 at 5-6 independent titrations. Inasmuch as the literature data give mainly the dissociation constants for the racemic DL-malic acid, acid-base equilibria of L-malic acid at ionic strength of 0.1 M KCl were also previously studied in pH 3.1-11.0 range. The number of experimental points for the each titration curve of L-malic acid was 70-100 at 8 independent titrations. The dissociation constants of Lmalic acid were calculated. The compositions and the stability constants of the rare-earth element complexes with L-malic acid were calculated by SuperQuad program for complex equilibria. It was shown, that in addition to 1:1 and 1:2 complexes with differently deprotonated L-malic acid, the hydroxocomplexes and protonated complexes of the rare-earth elements are also formed. The difference of the complex formation of the Sm<sup>3+</sup> ion with Lmalic acid as compared to the Nd<sup>3+</sup> ion was discussed.</p>

Application of the Pitzer Model to Assignment of pH to Phthalate Standard Buffer Solutions

Stoichiometric ionization constants of phthalic acid have been determined in potassium chloride solutions at temperatures from 10 to 40 °C, with molalities up to 3 mol⋅kg−1, from potentiometric titrations of potassium hydrogen phthalate. The procedure described by Gans and O’Sulliven (Talanta 51:33–37, 2000) was followed to calibrate the electrochemical cell in terms of hydrogen ion concentration and the SUPERQUAD program was used for the calculations. Pitzer’s ion-interaction equation was applied to this system for the calculation of activity coefficients and a good fit was observed at all temperatures. From these results and from phthalic acid solubilities, Pitzer model coefficients were determined which enabled the evaluation of the activity coefficient of each chemical species, including that of the chloride ion, that are necessary for the establishment of phthalate pH standards at ionic strengths higher than 0.1 mol⋅kg−1(the upper limit of applicability of the Bates-Guggenheim convention).

Gallium(III) Ion Hydrolysis under Physiological Conditions

The hydrolysis of gallium(III) has been studied using potentiometric techniques under physiological conditions of temperature 37 C and ionic strength 0.15 moldm-3 NaCl and at different metal ion concentrations. Changes in pH were monitored with a glass electrode calibrated daily in hydrogen ions concentrations. The titration data within the pH range of 2.5-9.99 were analyzed to determine stability constants of hydroxide species using the SUPERQUAD program. Several different species were considered during the calculation procedure and the following hydroxides have been characterized: Ga(OH)3, Ga(OH)4- Ga3(OH)112-, Ga4(OH)11+ and Ga6(OH)153+. Speciation calculations based on the determined constants were then used to simulate the species distribution.

Speciation studies of aluminium(III)–acetate complexes under physiological conditions

The aluminium complexes of acetic acid (ACT) have been studied using Potentiometric titrations under physiological conditions of temperature (37°C) and ionic strength (0.15 dm−3 dm−3 NaCI) and at different ligand to metal ratios. The variations of pH were measured with the help of a glass electrode calibrated daily in hydrogen ion concentrations. Results obtained within the pH range of 2.6–4.2 were analysed to determine stability constants using the SUPERQUAD program. Different complex combinations were considered during the calculation procedure, and evidence was found for ML2 mononuclear species beside binuclear hydroxo-complexes M2L(OH)2 and M2L(OH)3 and metal ion hydroxides. Speciation calculations based on the corresponding constants were then used to simulate species distributions.

Complex Formation of Acetic Acid with Ca(II) and Mg(II) Under Physiological Conditions

Potentiometric titrations of aqueous acetic acid alone and in the presence of Ca(II) or Mg(II) ions have been carried out under physiological conditions at the temperature 37 °C and ionic strength 0.15 mol⋅dm−3 (NaCl) at different ligand-to-metal ratios. Changes in pH were monitored with a glass electrode calibrated daily in terms of the hydrogen ion concentrations. Titration data within the pH range 2.5 to 6.6 were analyzed to determine stability constants using the SUPERQUAD program. Different combinations of complexes were considered during the calculation procedure for both systems, but evidence was found only for mononuclear ML and ML2 species. Speciation calculations based on the corresponding constants were then used to simulate the species’ distributions.

Protonation behaviour of N,N′-piperazine-dipropionic acid

Abstract The overall protonation constants of N,N′-piperazine-dipropionic acid (PDPA) were calculated with SUPERQUAD and PSEQUAD computer programs, at 25 and 37 °C and an ionic strength of 0.1 mol dm–3 (KCl). There is a good agreement between the values calculated with the two programs. The obtained values were checked by a simulation titration curve and by the protonation (observed and calculated) curves for CL = 2.0716 mmol dm–3 at 25 °C. A two-step deprotonation mechanism is proposed. In the first step the deprotonation occurs to the carboxyl group and in the second step it is the nitrogen atom of the piperazine ring which undergoes deprotonation. To cite this article: C. Mateescu et al., C.R. Chimie 8 (2005).

Vanadium(III) complexes with l-cysteine – stability, speciation and the effect on actin in hepatoma Morris 5123 cells

The complexation processes of vanadium(III) with l-cysteinate and s-methyl- l-cysteinate ligands have been studied in aqueous solutions in the pH range 2–7 by the pH–potentiometric, UV–Vis absorption and CD spectroscopy methods. The equilibria model of complex formation, evaluated by SUPERQUAD program, so as careful inspection of spectroscopic data have allowed to determine the speciation and the coordination mode of vanadium(III) ion in the major species present in aqueous solutions. Relatively stable ML 2 species of vanadium(III)– l-cysteinate system exists in aqueous solutions above pH 5. It was deduced from spectral data that the coordination sphere of vanadium(III) ion in V(Cys) 2 is completed by oxygen, nitrogen and sulfur atoms of two l-cysteinate ligands. Solution of vanadium(III) with l-cysteine (pH ∼ 7, L/ M = 20) was administrated to the culture medium of hepatoma Morris 5123 growing cells. Cytotoxic effect of this solution towards tumor cells was observed. The viability of these cells depended on the complex concentration. It was reduced by 70% at 100 μM of the vanadium species concentration in the culture medium. The death of cancer cells seems to be induced on apoptotic route. The statistically significant increase of total actin level and filamentous to monomeric actin ratios ( F/ G) were found in the cytoplasm of cells exposed to the vanadium(III)– l-cysteine complex. It was accompanied by the rearrangement of actin cytoskeleton architecture. These factors are important for migration and metastasis formation of the cancer cells.

Solubility and Hydrolysis of La, Pr, Eu, Er, and Lu in 1 M NaCl Ionic Strength at 303 K

The pLn-pCH diagrams obtained by a radiometric technique were used for the determination of the solubility and the first hydrolysis constants for La, Pr, Eu, Er, and Lu in 1 M NaCl ionic strength at 303 K. The saturation and unsaturation zones, and the borderline of precipitation were determined from these diagrams. The first hydrolysis constants were determined from pH titrations where no precipitation was found; these data were treated with the SUPERQUAD program. Fitting methods involving pLn versus pCH and the average ligand number vs. pCH were used to calculate both the first hydrolysis constants and the solubility products. The log Ksp values obtained for La, Pr, Eu, Er, and Lu were −19.53, −20.92, −22.24, −22.62, and −23.05 and the log* β1 average values obtained were −8.87 ± 0.05, −8.54 ± 0.04, −8.34 ± 0.03, −8.16 ± 0.04, and −8.11 ± 0.03, respectively, under CO2 free conditions. Finally, the results were compared with those found in the literature.

Spectroscopy study of 5-amino-1,10-phenanthroline

Acidity constants for the 5-amino-1,10-phenanthroline (5-Aphen) were determined in aqueous media, using SQUAD and SUPERQUAD programs. Spectrophotometry and potentiometry data were fitted to the best model to enable correlation of the following acidity equilibria: 5-AphenH=5-Aphen+H + (− log K=5.78±0.03 ) and 5-AphenH 2=5-Aphen+2H + (− log K=6.89±0.07 ). UV absorptivity coefficients obtained suggest that the first protonation takes place on the nitrogens of the heterocycle ring and the second protonation could take place on the amino group. As expected, the electrochemical evidence of the 5-Aphen species depends on the degree of protonation.

Complexes of Vitamin B6. 23. Interaction of Some Tertiary Ligating Amino Acids with the Binary Complexes of Ni(II) or Cu(II) and Pyridoxamine

Binary and ternary complexes involved in the systems pyridoxamine (PM), glutamic acid (Glu), or aspartic acid (Asp) plus Ni(II) or Cu(II) were studied in solution at 0.15 M ionic strength and 25 °C by pH-metric, absorpiometric, and polarographic techniques. The differential pulse polarographic technique was used to study the reduction properties of these complexes. EPR was used to confirm the presence of binary and ternary complex species in the Cu(II) systems. The stoichiometry and formation constants of the binary and ternary complex species were determined by the SUPERQUAD program. Ternary species of the types 1:1:1:r and 1:2:1:r (PM/Glu or Asp/M/H) were found to exist in the pH range ∼3 to ∼10.

A potentiometric and spectrophotometric study on acid–base equilibria in ethanol-aqueous solution of acetazolamide and related compounds

Acid–base equilibria in ethanol-aqueous solution of 5-acetamido-1,3,4-thiadiazole-2-sulfonamide (acetazolamide, H 2acm), 5-tertbutyloxycarbonylamido-1,3,4-thiadiazole-2-sulfonamide (B-H 2ats), 5-amino-1,3,4-thiadiazole-2-sulfonamide (Hats) and 5-amino-1,3,4-thiadiazole-2-thiol (Hatm) at 25°C, 0.15 mol dm −3 ionic strength (NaNO 3), have been investigated by potentiometry and UV spectrophotometry. The ionization constants were calculated with SUPERQUAD program from potentiometric measurements and by a method according to Edsall et al. using the mole fractions determined by complementary tri-stimulus colorimetry (CTS). The constants obtained by potentiometry were: B-H 2ats, p k a 1 =7.33(3) and p k a 2 =9.27(1); Hats, p k a 1 =2.51(3) and p k a 2 =8.49(1); Hatm, p k a 1 =1.92(1) and p k a 2 =6.81(1); whereas the constants determined by spectrophotometry were: H 2acm, p k a 1 =7.78(1) and p k a 2 =9.57(2); B-H 2ats, p k a 1 =7.71(2) and p k a 2 =9.61(2); Hats, p k a 1 =2.19(3) and p k a 2 =8.61(2); Hatm, p k a 2 =6.90(2). Theoretical calculations using MO semiempirical and ab-initio RHF/6-31G* computations for the compounds were also performed. It was possible to clarify the preferred deprotonation mechanism of acetazolamide and B-H 2ats in which the first deprotonation takes place at the carbonamido group.

Study of pillar precursors [Ga(III)–Al(III), Ln(III)–Al(III), Zr(IV)] for hydrothermally stable pillared clays

The hydrolysis of mixed solutions of Al(III), Ga(III), Al(III), Ln(III) and Zr(IV) was studied by potentiometric, spectrophotometric and 27 Al - and 71 Ga -NMR techniques. For the Al–Ga system formation of GaAl 12(OH) 11+ 28 species seems more probable into the pH range 4≤pH≤5. Afterwards, the Al 13(OH) 7+ 32 species predominate in agreement with thermodynamic data obtained by SUPERQUAD program. Both tetrahedral Ga IV and Al IV may coexist in solution, the interval being defined by potentiometric methods. For the Ln(III)–Al(III) systems 27 Al -and 139 La -NMR does not confirm the chemical interaction between the two species in solution, but the physicochemical properties of the La–Al/PILCS were different than Al/PILCS, suggesting a strong interaction in the solid state. Ce(III) and Ce(IV) ions do interact with Al(III) in solution, into the pH range 2.78<pH<3.99, according with the spectrophotometric behavior. Finally, the Zr(IV) hydrolysis was followed by UV in the pH range greater than 2.0, showing the formation of Zr 4(OH) 8+ 8 species, which was verified by calculations using SQUAD program, but the precipitation occurs at pH>3.0.

Determination of pKa's for thymol blue in aqueous medium: evidence of dimer formation.

Formation constants for recrystallized thymol blue were determined in water, using the SQUAD and SUPERQUAD programs. The best model correlating spectrophotometric, potentiometric and conductimetric data was fitted with the dissociation of HL−=L2−+H+−log K=8.918±0.070 and H3L2−=2L2−+3H+−log K=29.806±0.133 with the SUPERQUAD program at variable low ionic strength (1.5×10−4–3.0×10−4 M); and HL=L2−+H+−log K=8.9±0.000, H3L2− =2L2−+3H+−log K=30.730±0.032, H4L2=2L2−+4H+−log K=32.106±0.033 with SQUAD at 1.1 M ionic strength.

Redox method for the determination of stability constants of some trivalent metal complexes

Stability constants determination of very stable metal complexes using the redox method, based on the equilibrium of Fe 3+ Fe 2+ followed by a couple of platinum/reference electrodes, was undertaken and tested to complexes of some trivalent metal ions with well known polyaminopolycarboxymethylated linear ligands (edta, nta, cdta, dtpa and ttha) and also to some new macrocyclic ligands. SUPERQUAD program was used for the calculations, after adaptation of the experimental data. The method proved to be very useful for Fe 3+ and In 3+ complexes, if no polynuclear complexes are formed or/and if the kinetics of the complexation reaction is not very slow. However, for the Ga 3+ complexes the applicability of this method is very limited and the competition with OH − using the displacement reaction which occurs at pH higher than 6 with formation of Ga(OH) 4 − seems to give more accurate results. A complete data of stability constants for the case of the complexes of ttha with In 3+ is given.

Cis-Dichloro(alpha,omega-diamino carboxylate ethyl ester)palladium(II) as Palladium(II) versus Platinum(II) Model Anticancer Drugs: Synthesis, Solution Equilibria of Their Aqua, Hydroxo, and/or Chloro Species, and in Vitro/in Vivo DNA-Binding Properties.

cis-Dichloro(d,l-2,3-diaminopropionate ethyl ester)palladium(II), cis-[Pd(Etdap)Cl(2)] (I), and cis-dichloro(d,l-2,4-diaminobutyrate ethyl ester)palladium(II), cis-[Pd(Etdab)Cl(2)] (II), were synthesized and characterized by elemental analysis, IR spectroscopy, and TG-DTA thermal analysis. The equilibrium model and log beta(pqr) constants of hydrolytic species of I and II were also investigated by potentiometric methods (I = 0.15 M (NaClO(4)) and 37 degrees C). Aqueous solutions of cis-[Pd(Etdaa)(H(2)O)(2)](ClO(4))(2) (Etdaa = Etdap (III) or Etdab (IV)) were prepared by stoichiometric reaction of I or II with AgClO(4). Thus, log beta(pqr) of the corresponding cis-aquahydroxo (pqr = 1,0,-1) and di(&mgr;-hydroxo) (pqr = 2,0,-2) species were obtained from E(H(+)) data of alkalimetric titrations of solutions of III or IV. Such constants were then used as fixed values to obtain log beta(pqr)() of chloro-containing species (cis-dichloro (1,2,0), cis-chloroaqua (1,1,0), and cis-chlorohydroxo (1,1,-1)) from E(H(+)) and E(Cl(-)) data pairs simultaneously obtained by titration of solutions of III or IV with NaOH and NaCl. All log beta(pqr) were fitted by the SUPERQUAD program. Appropriate log beta(pqr)() sets give good simulations of experimental titration curves and several species distribution diagrams. In addition the interaction of I and/or II with DNA in vitro and in vivo was studied by various methods. UV spectral data and melting and renaturation curves indicate that both compounds destabilize the DNA helicoidal structure. Compound II disrupts in vivo the structure and transcription process of polytene chromosomes of Drosophila hydei.

AMINOHYDROXAMIC ACIDS AS METAL SEQUESTERING AGENTS: COPPER(II) AND NICKEL(II) COMPLEXES OF 2,6-DIAMINO-N-HYDROXYHEXANAMIDE, 2-AMINO-5-[(AMINOIMINOMETHYL)AMINO]-N-HYDROXYPENTANAMIDE, 2-AMINO-4-METHYLTHIO-N-HYDROXYBUTANAMIDE IN AQUEOUS SOLUTION

Abstract Aqueous solution equilibria of the systems H+, copper(II) and nickel(II) with L-lysinehydroxamic acid (2,6-diamino-N-hydroxyhexanamide) (dahhe), L-argininehydroxamic acid (2-amino-5-[(aminoiminomethyl)amino]-N-hydroxypentanamide) (aimahp), and DL-methioninehydroxamic acid (2-amino-4-methylthio-N-hydroxybutanamide)(amthb) have been investigated in the metal-ligand ratio range 1:1–1:4 using potentiometric and spectrophotometric methods. The protonation and metal-complex formation constants for each system were calculated using the SUPERQUAD program and are reported. Complexation with copper(II) begins at pH ca. 3.0 for each system with simultaneous formation of [CuA]+ and [Cu2A2H−1]+. Only copper-dahhe forms complexes with the terminal amino group in the protonated form. Between pH 5.5–9.5 the bis complex is dominant. Above pH 8 deprotonated complexes are detected. In the different bis complexes ((CuA2H2]2+, [CuA2H]+, [CuA2] and [CuA2H−1]− in the case of dahhe, [CuA2] and [CuA2H−1]− with aimahp and amthb) only the nitrogens are coordinated but both the oxygen and the nitrogen donor atoms of the ligand are involved in the coordination in complexes [CuAH]2+ and [Cu2A2H]3+ formed with dahhe and in [CuA]+ and [Cu2A2H−1]+ formed with the other two ligands. Spectroscopic evidence shows no significant coordination through the terminal group of the ligand for any of the systems investigated. Complexation with nickel(II) starts at pH ca. 5.0 with simultaneous formation of 1:1 and 1:2 species. The [NiA]+ ([NiAH]2+ in the case of dahhe) is a very minor species. The [NiA2] ([NiA2H2]2+ with dahhe) complex is the dominant species with a planar geometry. Deprotonation of one of the coordinated hydroxamates occurs above pH 8 and overlaps with deprotonation of the terminal NH3 + groups of the dahhe ligand.

Complexes of vitamin B 6—part XXII. The interaction of vitamin B 6 compounds with CU II-glycinehydroxamic acid binary system

Binary complexes of the glycinehydroxamic acid (GX) with copper(II) (GX-Cu II), as well as their interaction with vitamin B 6 compounds [pyridoxol (P), pyridoxal (PL) and pyridoxamine (PM)] were studied by pH-metric, differential pulse polarography (DPP), and electron paramagnetic resonance techniques at the ionic strength of 0.15 M NaCl and at 25°C. The formation constants of the binary and ternary species were determined using the SUPERQUAD program. The three ternary systems do not show the same stoichiometries of the different species, in addition, PL interacts with GX to form Schiff bases at pH > 4.5. Comparative studies of the DPP of the binary and ternary systems of Cu II revealed that Cu II is more stabilized toward reduction in the presence of PM than in presence of GX at pH > 6.0; in addition the redox behaviour of Cu II in the presence of PM is similar to that of the GX-Pm-Cu II ternary system. On the other hand, the DPP of the ternary systems GX-P (or PL)-Cu II are similar to those of GX-Cu II binary system at different pH values. The nuclear spin-electron spin coupling of Cu II in these systems is discussed.

A POTENTIOMETRIC STUDY OF THE COMPLEXATION OF ALIPHATIC ACYCLIC MONOAMINES WITH Ag(I) IN 1 M NITRATE

Abstract Complexation of 12 aliphatic monoamines with Ag(I) has been studied in 1M KNO3 at 25°C using a potentiometric titration technique, performing pH and pAg measurements. To study these ternary systems, the binary systems (Ag-OH, L-H, H-OH) were first investigated. The model used for background Ag(I) hydrolysis is consistent with the literature. Graphical techniques were used for the calculation of formation constants of silver-amine complexes. The estimates were further refined using the Superquad program. Evidence has been found for the formation of mixed Ag(I)-hydroxo ligand complexes only with aliphatic primary monoamines.

AMINOHYDROXAMIC ACIDS AS SEQUESTERING AGENTS IN LIVING SYSTEMS. POTENTIOMETRIC DETERMINATION OF PROTONATION AND FORMATION CONSTANTS FOR 2,6-DIAMINO-N-HYDROXYHEXANAMIDE AND COPPER(II), NICKEL(II), COBALT(II), AND HYDROGEN IONS IN AQUEOUS SOLUTION

Abstract The systems H+, cobalt(II), nickel(II), and copper(II) with 2,6-diamino-N-hydroxyhexanamide (L-lysinehydroxamic acid hydrochloride = dahhe) have been investigated by potentiometric and spectrophotometric titrations at 25 ± 0.1˚C and I = 0.5 mol dm−3 (KCl). The protonation constants of the ligand and the overall formation constants of several metal complexes were calculated from potentiometric and spectrophotometric data with the aid of the SUPERQUAD and SQUAD programs, respectively. The following cumulative association constants (relative standard deviations are given in parentheses), β pqr = [M p H q L r ]/[M] p [H] q [L] r , were obtained: log β011 = 10.66 (1), log β021 = 19.55 (1), log β031 = 26.56 (1); CoII-dahhe, log β121 = 22.68 (2), log β111 = 15.72 (2), log β122 = 29.73 (3), log β101 = 8.68 (1); NiII-dahne, log β111 = 16.93 (8), log β122 = 34.87 (1), log β112 = 27.70 (4); CuII-dahhe, log β111 = 20.26 (1), log β212 = 41.53(2), log β122 = 40.56 (3), log β112 = 33.33 (10). Dahhe forms proton...