Species Distribution Diagrams Research Articles

Equilibrium Studies of Complexes between N-Acetylcysteine and Divalent Metal Ions in Aqueous Solutions

The complex formations of N-acetylcysteine with divalent transition metals Cu2+, Zn2+, Ni2+, Co2+, Mn2+ have been investigated in aqueous solution of 0.15 mol·dm–3 NaCl at 310.15 K by the potentiometric method. The protonation and stability constant of the complexes were obtained based on nonlinear least-squares curve fitting performed by the HYPERQUAD2008 program along with an estimation using Bjerrum–Calvin half integral method. Distribution diagrams of complex species at certain pH range were generated by the HySS2009 simulation program. From optimization and thermochemical analysis by using the Gaussian09W program, it showed that the ligand formed a six-membered chelate ring with the investigated metal ions via its sulfur and oxygen donor atoms.

Solution equilibria and stabilities of binary and ternary Nickel(II) complexes with picolinic acid and small blood serum bioligands

The binary and ternary complexes of Nickel(II) with picolinic acid (Hpic) as a primary ligand and the small blood serum bioligands lactic acid (Hlac), oxalic acid (H2ox), citric acid (H3cit) and phosphoric acid (H3PO4) as biologically relevant secondary ligands were studied. The acidity constants of the ligands selected were determined potentiometrically and used for determining the stability constants of the complexes formed in aqueous solution at 25°C and using an ionic strength I=1.0moldm−3 (NaCl). The analysis of the potentiometric data by means of the computational least-squares program LETAGROP indicates the Ni(II)–Hlac system in the formation of the complexes [NiL]+ and [NiL(OH)2]−. The Ni(II)–H3cit system indicates the formation of the species [NiL]−, [Ni(HL)L]3− and [NiL2]4−. In the Ni(II)–H3PO4 system the complexes [NiH2L]+, NiHL and [NiL]− were detected. In the case of the ternary systems we observed in the Nickel(II)–Hpic–Hlac system the formation of the complexes Ni(pic)(L), [Ni(pic)(L)(OH)]− and [Ni(pic)(L)(OH)2]2−. In the Nickel(II)–Hpic–H2ox system the species [Ni(pic)(L)]−, [Ni(pic)(L)(OH)]2− and [Ni(pic)2(L)]2− were observed. In the Nickel(II)–Hpic–H3cit system the complexes [Ni(pic)(HL)]−, [Ni(pic)(L)]2− and [Ni(pic)(L)(OH)]3− were detected. Finally, in the Nickel(II)–Hpic–H3PO4 system the complexes Ni(pic)(H2L), [Ni(pic)(HL)]− and [Ni(pic)(L)]2− were observed. Species distribution diagrams as a function of pH were briefly discussed.

Promising antioxidant and anticancer (human breast cancer) oxidovanadium(IV) complex of chlorogenic acid. Synthesis, characterization and spectroscopic examination on the transport mechanism with bovine serum albumin

A new chlorogenate oxidovanadium complex (Na[VO(chlorog)(H2O)3].4H2O) was synthesized by using Schlenk methodology in the course of a reaction at inert atmosphere in which deprotonated chlorogenic acid ligand binds to oxidovanadium(IV) in a reaction experiment controlled via EPR technique and based in a species distribution diagram. The compound was characterized by FTIR, EPR, UV–visible and diffuse reflectance spectroscopies and thermogravimetric, differential thermal and elemental analyses. The ligand and the complex were tested for their antioxidant effects on DPPH (1,1-diphenyl-2-picrylhydrazyl radical), ABTS+ (radical cation of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt), O2−, OH and ROO radicals and their cytotoxic activity on different cancer cell lines (SKBR3, T47D and MDAMB231) and primary human mammary epithelial cells. The complex behaved as good antioxidant agent with strongest inhibitory effects on O2−, OH and ROO radicals and exhibited selective cytotoxicity against SKBR3 cancer cell line. Albumin interaction experiments denoted high affinity toward the complex and its calculated binding constant was indicative of a strong binding to the protein. Based on this study, it is hypothesized that Na[VO(chlorog)(H2O)3].4H2O would be a promising candidate for further evaluation as an antioxidant and anticancer agent.

Role of Thiourea in the Kinetic of Growth of the Chemical Bath Deposited ZnS Films

ZnS films were deposited onto glass substrates by the chemical bath technique at temperatures from 60 to 90°C. Zinc chloride, potassium hydroxide, ammonium nitrate, and thiourea were used as chemical components. According to the species distribution diagrams, the concentration of the chemical components were maintained constant except for thiourea whose concentration is required to decrease when the bath temperature increases, in order to maintain constant the Zn(OH)2 −4/HS− ions concentration. To investigate the kinetic of growth of the ZnS films, their thicknesses were measured as a function of deposition time and bath temperature. The activation energy value estimated for the growing process was Ea = 44.9 kJ/mol which is typical for chemical reactions. The mean value of the bandgap energy of the films was 3.67 eV with optical transmittances up to 80% for all bath temperatures. The rms-roughness of the deposited films was observed to decrease when the bath temperature increases. Results of X-ray diffraction analysis on deposited films reveal a cubic (111) as preferential orientation. Additionally, SEM-EDS results of the ZnS films shows a stoichiometry ratio of [Zn/S] = 0.4–0.6 for all deposition times and bath temperatures.

Ternary complex formation between vanadium(III) cytosine and some amino acids

In this work we present the results of the speciation of the ternary vanadium(III)–Cytosine (HCyt) complexes with the amino acids Glycine (HGly), Proline (HPro), α-Alanine (HαAla) and β-Alanine (HβAla), studied by means of electromotive force measurements emf (H) using 3.0mol.dm−3 KCl as the ionic medium at 25°C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation and the respective stability constants of the binary complexes and the acid base reactions of the amino acids which were kept fixed during the analysis. In the binary vanadium(III)–Cytosine system the formation of the complexes [V(HCyt)]3+, [V(Cyt)]2+, [V(Cyt)(OH)]+, V(Cyt)(OH)2, [V(Cyt)2]+ and V(Cyt)3 was observed. In the ternary systems studied were observed the complexes with the amino acids Glycine, Proline and β-Alanine [V(HCyt)(HL)]3+, [V(Cyt)(HL)]2+, [V(Cyt)(L)]+, V(Cyt)(L)(OH) and [V(Cyt)(L)(OH)2]− were HL represent the neutral form of the amino acid, with α-Alanine were detected the ternary complexes [V(HCyt)(HL)]3+, [V(Cyt)(HL)]2+, [V(Cyt)(L)]+, V(Cyt)(L)(OH). The species distribution diagrams as a function of pH were briefly discussed.

Complex Formation Equilibria and Molecular Structure of Divalent Metal Ions–Vitamin B3–Glycine Oligopeptides Systems

Complex formation of divalent transition metal ions (copper(II), cobalt(II) and nickel(II)), vitamin B3 (nicotinic acid) and glycine oligopeptides (glycine, glycylglycine, glycyl-l-phenylalanine, and glycylglycylglycine) were studied at 298 K in aqueous solutions using the pH-potentiometric technique. The copper Cu(II), cobalt Co(II), and nickel Ni(II) complexing capacity of vitamin B3 in the absence and in the presence of glycine peptides and their overall stability constants in aqueous solutions were obtained and explained by the HYPERQUAD 2008 program using the potentiometric data. From the protonation and complex formation constants, representative complex species distribution diagrams were obtained using HYSS 2009 software. The UV–Vis spectroscopic, cyclic voltammeteric and conductometric titration measurements were carried out to give qualitative information about the conformation of the complexes formed in these solutions and their stoichiometric ratios. The Gibbs energies and the molecular structures of the complexes were evaluated and predicted using Gaussian 09 software molecular modeling and density functional theory calculations.

Use and misuse of chemical reactions and aqueous species distribution diagrams for interpreting metal transport and deposition in porphyry copper systems: Comment on Sun et al. (2013) “The link between reduced porphyry copper deposits and oxidized magmas”, Geochim. Cosmochim. Acta 103, 263–275

Use and misuse of chemical reactions and aqueous species distribution diagrams for interpreting metal transport and deposition in porphyry copper systems: Comment on Sun et al. (2013) “The link between reduced porphyry copper deposits and oxidized magmas”, Geochim. Cosmochim. Acta 103, 263–275

Ionic Strength Dependence of Four Stepwise Protonation Constants for Folic Acid in Different Aqueous Solutions of Dioxane

The protonation equilibria of vitamin B9 (folic acid) was studied at 298.15 K in a different water–dioxane mixtures [100 wdioxane = 20 %, 40 %, 60 %, and 80 %] with an ionic strength of 0.15 mol·dm–3 NaNO3. The influence of dioxane content on the protonation processes was explained. Also, four protonation constants have been determined in 60 % dioxane with an ionic strengths of (0.15, 0.20, 0.25, and 0.30) mol·dm–3 NaNO3 using the pH-potentiometric technique. HYPERQUAD 2008, a program based on nonlinear least-squares curve fitting was used to determine these four stepwise protonation constants of folic acid from the analysis of pH-potentiometric data. From the determined protonation constants, the representative folate species distribution diagrams were provided by HYSS 2009 program and discussed.

Predominance diagrams for Zn(II)–NH3–Cl−−H2O system

The thermodynamics in zinc hydrometallurgical process was studied using a chemical equilibrium modeling code (GEMS) to predict the zinc solubility and construct the species distribution and predominance diagrams for the Zn(II)–NH3–H2O and Zn(II)–NH3–Cl−−H2O system. The zinc solubilities in ammoniacal solutions were also measured with equilibrium experiments, which agree well with the predicted values. The distribution and predominance diagrams show that ammine and hydroxyl ammine complexes are the main aqueous Zn species, Zn(NH3)42+ is predominant in weak alkaline solution for both Zn(II)–NH3–H2O and Zn(II)–NH3–Cl−−H2O systems. In Zn(II)–NH3–Cl−−H2O system, the ternary complexes containing ammonia and chloride increase the zinc solubility in neutral solution. There are three zinc compounds, Zn(OH)2, Zn(OH)1.6Cl0.4 and Zn(NH3)2Cl2, on which the zinc solubility depends, according to the total ammonia, chloride and zinc concentration. These thermodynamic diagrams show the effects of ammonia, chloride and zinc concentration on the zinc solubility, which can provide thermodynamic references for the zinc hydrometallurgy.

Study in Aqueous Solutions of Bioactive 2-Pyridineformamide-Derived Thiosemicarbazones and Their Iron(II) and Iron(III) Complexes

The binary systems of iron(II) and iron(III) with 2-pyridineformamide thiosemicarbazone (H2Am4DH) and its N(4)-methyl (H2Am4Me), N(4)-ethyl (H2Am4Et) and N(4)-phenyl (H2Am4Ph) derivatives were studied in aqueous solution by pH-potentiometry, ultraviolet–visible spectroscopy and EPR spectra. The formation constants of the iron(II) and iron(III) complexes were calculated from potentiometric and electronic absorption data at 25 °C and ionic strength μ = 0.1 mol·L−1 using the HYPERQUAD program. The values of the formation constant of the FeL species decrease in the order Fe:H2Am4DH > Fe:H2Am4Me ≈ Fe:H2Am4Et > Fe:H2Am4Ph in the same way as the basicity of the ligands. The species distribution diagrams show that the species FeL2 predominates at physiological pH in the Fe:H2Am4DH, Fe:H2Am4Me and Fe:H2Am4Et systems. The similar EPR spectra of these iron(III) binary systems indicate the same coordination spheres around the metallic center and the EPR g values suggests that the unpaired electron is in the dxy orbital, indicating a d xz 2 d yz 2 d xy 1 ground state configuration for the complexes. For the Fe(III):H2Am4Ph system the EPR results indicated dimerization and antiferromagnetic interaction due to the presence of only one thiosemicarbazone ligand around the metallic center.

Structure of aqueous potassium tetraborate solutions by X-ray scattering

The borate species in aqueous potassium tetraborate solution were obtained according to the chemical species distribution diagram and the Raman spectrum. X-ray scattering is used to study the solutions with salt–water molar ratios of 1 : 25, 1 : 20 and 1 : 15 at 298 and 323 K. The model calculation and model refinement programmes are used to calculate the structure parameters r i−j , b i−j and n i−j . It manifests that the first hydration distance of K+ is ∼0.29 nm, with an average hydrated number of 8.0. The hydration bond peak is around 0.278 nm and the coordination number is from 1.9 to 2.4. Borate anions coordinate with K+ ions in the mono-dentate form, the average distance of K–B is 0.38 nm. The distance of B–H2O in hydrated anion is from 0.37 to 0.38 nm with the hydrated number 4–9. The other interaction such as water shared pair interaction is also discussed.

A kinetic–thermodynamic study of silver leaching in thiosulfate–copper–ammonia–EDTA solutions

In this research, an analysis of the effect of ethylenediaminetetraacetic acid (EDTA), thiosulfate and cupric ions on the silver leaching kinetics was performed. For that purpose leaching experiments with pure metallic silver were carried out at different concentrations of these reagents at room temperature. The results of this study showed that small amounts of EDTA accelerate the leaching of silver more efficiently than higher concentrations due to an increase in the oxidation potential of the leaching solution. These results were in accord with Pourbaix diagrams and redox potential measurements. A synergistic effect was found in the silver leaching kinetics when the thiosulfate and EDTA concentrations were both decreased. On the other hand, the silver leaching kinetics was reduced at low Cu(II) concentrations due to the decrease in the oxidizing ability of the leaching solution.Characterization by SEM and EDXS of the silver in the first minutes of leaching revealed that the silver particles were coated by a layer of copper sulfides and copper oxides. Furthermore, characterization of the solid residue during the precipitation of silver in the leaching experiment was performed by the same analytical techniques, showing the presence of silver sulfide on the unreacted silver surface. The mechanism by which the silver sulfide is precipitated was found to be related to the copper sulfide formation. It was also observed that an increase in the concentration of EDTA promotes the silver dissolution avoiding the formation of copper sulfides or oxides; in these cases the process is controlled by the chemical reaction. These observations were also supported with Pourbaix and species distribution diagrams.

Speciation studies of Co(II), Ni(II) and Cu(II) complexes of L-valine in acetonitrile–water mixtures

Chemical speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-valine in 0.0-60.0% v/v acetonitrile-water mixtures was studied pH-metrically at an ionic strength of 0.16 mol L-1 at 303.0 K. The existence of different binary complexes was established from the modelling studies, using the computer program MINIQUAD75. The appropriateness of the model was ascertained by studying the effect of errors in concentrations of the reagents. The trend in variation of stability constants with change in the permittivity of the medium is explained on the basis of electrostatic and non-electrostatic forces. The species distribution diagrams and the plausible equilibria for the formation of the species are also presented.

Effect of non ionic micelles on the chemical speciation of binary complexes of Pb(II), Cd(II) and Hg(II) with L-phenylalanine

Complexes of Pb(II), Cd(II) and Hg(II) with L-phenylalanine in the presence of non-ionic surfactants, at an ionic strength of 0.16 mol dm-3 and temperature 303 K are investigated pH-metrically. The existence of different binary complex species is established from modelling studies using the computer program MINIQUAD75. The increased stability of the complexes with increasing micellar content is explained by electrostatic forces. The influence of the micelles on the chemical speciation is discussed based on the mole fraction of the medium. Distribution diagrams of various species of the complexes in relation to pH are presented.

Cu(II), Co(II), and Ni(II)–Antioxidative Phenolate–Glycine Peptide Systems: An Insight into Its Equilibrium Solution Study

The stability of complex formation between divalent transition metal ions, phenolates and glycine peptides was studied at 298.15 K in aqueous solution with an ionic strength of 0.15 mol·dm–3 NaNO3. HYPERQUAD 2008, a program based on nonlinear least-squares curve fitting, was used to determine the stability constants of the complexes formed from the pH-potentiometric data. The trends in stability constants of the complexes and the contribution of deprotonated or undeptotonated amide peptide in the stability constant were discussed. From the stability constants that obtained, the representative species distribution diagrams of copper complexes were provided by the HYSS 2009 program. In addition, structures of the formed complexes were predicted by using the Gaussian 09 program. The Gibbs free energies of these complexes were also evaluated in the simulation.

Synthesis and structural characterization of Pd(N,N-dimethylaminopropylamine)Cl2 complex – The interaction with bio-relevant ligands with reference to the effect of cysteine on the deactivation of metal-based drug

The synthesis and X-ray structural characterization of Pd(DMPA)Cl2 complex, where DMPA=N,N-dimethylaminopropylamine, is reported. The complex crystallizes in the space group P21/c, a=8.8923(4), b=10.9050(5), c=11.5006(7) Å, β=120.00(18)°, V=948.25(8) Å3, Z=4. The palladium centre has a typical square-planar geometry with a tetrahedral distortion. Stoichiometry and stability constants of the complexes formed between [Pd(DMPA)(H2O)2]2+ and some selected DNA constituents and cytsteine are investigated at 25°C and at constant 0.1M ionic strength. The concentration distribution diagrams of the various species formed are evaluated. The equilibrium constants for the displacement of coordinated ligands as inosine by cysteine are calculated. The results are expected to contribute to the chemistry of tumour therapy.

Adsorption and zeta potential studies relevant to hematite ore reverse froth flotation

Reverse froth flotation is the most commonly used concentration method for iron ores, where the quartz gangue is floated, while the iron oxides are depressed by starches. in this paper, the mechanisms related to iron ore anionic reverse flotation are investigated by flotation, electrokinetic and high pulp density (20% solids) adsorption studies in alkaline medium using sodium oleate as the model collector. distribution diagrams of silicate and oleate species are employed to interpret the effects of ph on the electrokinetic and adsorption studies. the flotation experimental results showed that with ca2+ as activator, quartz responded to flotation well, whereas hematite does not. the changes in zeta potential for quartz are attributed to the hydroxylation of the quartz surface at different ph values and collector concentrations. coated starch can shift the zeta potential of hematite particles to less positive values and increase its potential differences from quartz and support quartz-hematite separation during flotation. adsorption results indicated that sodium oleate adsorbs onto the mineral surfaces to form surfactant multilayers due to the lateral interaction between hydrocarbon chains. adsorption kinetics studies showed that calcium ions can change the collector adsorption kinetics curve on quartz from first order to second order. minerals & metallurgical processing, 2012, vol. 29, no. 3, pp. 148-155. an official publication of the society for mining, metallurgy, and exploration, inc.

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), β-alanine (Hβ-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)–amino acids systems the species [NiL]+, NiL2 and [NiL3]− were observed, and in the case of the ternary nickel(II)–dipicolinic acid–amino 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.

Mixed-Ligand Complex Formation Equilibria of Vanadium(III) with 2,2′-Bipyridine and the Amino Acids Glycine, Proline, α-Alanine and β-Alanine Studied in 3.0 mol⋅dm−3 KCl at 25 °C

We studied speciation of the mixed-ligand complex formation equilibria of vanadium(III) with both 2,2′-bipyridine (Bipy) and the amino acids glycine (HGly), proline (HPro), α-alanine (HαAla), and β-alanine (HβAla) by means of electromotive forces measurements emf(H) using 3.0 mol⋅dm−3 KCl as the ionic medium at 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid/base reactions of the ligands which were kept fixed during the analysis. In all four amino acid systems studied we observed the complexes [V2O(Bipy)(B)]3+, [V2O(Bipy)2(B)2]2+, [V(OH)(Bipy)(B)2] and [V(OH)2(Bipy)(B)], where B represents the deprotonated form of the amino acids studied in this work. The respective stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.

Thermodynamics of the interaction of Pd(dmen)(H2O)22+ with bio-relevant ligands with reference to the deactivation of metal-based drug by thiol ligands

Pd(dmen)Cl2 complex was synthesized and characterized, where dmen=N,N-dimethylethylenediamine. Stoichiometry and stability constants of the complexes formed between [Pd(dmen)(H2O)2]2+ and various biologically relevant ligands such as amino acids, peptides and dicarboxylic acids are investigated at 25°C and at constant 0.1M ionic strength. The concentration distribution diagrams of the various species formed are evaluated. The equilibrium constants for the displacement of coordinated ligands as inosine, glycine or methionine by cysteine are calculated. The results are expected to contribute to the chemistry of tumour therapy.