Species Distribution Diagrams Research Articles

1,5-bis[2-(dioxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and its Analogs as Promising Organic Ligands for Copper(II) Binding s

The dissociation and complexation ability toward Cu(II) of acidic type phosphoryl-containing podands – tetrabasic 1,5-bis[2-(dioxyphosphoryl)-4-ethylphenoxy]-3-oxapentane (L1), dibasic – 1,5-bis[2-(ethoxyhydroxyphosphoryl)-4-ethylphenoxy]-pentane (L2) and also of their carboxylic analogue dibasic 1,5-bis[2-(oxycarbonylphenoxy)]-3-oxapentane (L3) were investigated by spectrophotometric, conductometric and potentiometric methods in water in the presence 5% of dimethyl formamide. Spectrophotometric and conductometric titration data provided evidence for formation of 1:1 (M:L) complexes. The dissociation constants were determined and species distribution diagrams for studied acids were obtained by potentiometric method. These data are of interest for the design of binary extragents and medicinal drugs based on the studied ligands. The stability constants of Cu(II) 1:1 (M:L) complexes were estimated. Analysis of the titration curves suggests that deprotonation forms of the studied ligands react with Cu2+. Substitution of carboxylic groups in acyclic polyesters by phosphonic results in increased stability of the copper(II) complexes

Shift in pKa of 1,10-Phenanthroline in TBAB and PEG-400 Micellar Media: A Potentiometric Study

The acid-base equilibrium of 1,10-phenanthroline (1,10-phen) in the presence of polyethylene glycol 400 (PEG-400, non-ionic) and tetrabutylammonium bromide (TBAB, ionic) micellar media has been studied by Calvin-Wilson titration technique at different mole fractions (0.5% - 2.5%) of PEG-400 and TBAB micellar solutions at an ionic strength of 0.16 mol dm-3 NaCl and at a temperature of 298 K. The pH metric data were subjected to SCPHD program to obtain correction factor and Kw which were given as initial inputs for MINIQUAD75 program to refine protonation constants. HySS program was then used to generate the species distribution diagrams versus pH using the results obtained from the MINIQUAD75 program and SIM run data. The difference in values of protonation constants in aqueous medium (logβ1 = 4.93 & logβ2 = 6.22) and in the micellar media (PEG-400, logβ1 = 4.89 & logβ2 = 5.91 and TBAB, logβ1 = 4.84 & logβ2 = 5.73) is attributed to different intrinsic solvent characteristics of micelles. In case of ionic surfactants, the electrostatic micellar surface is an additional contributing factor.

Preferential regions of growth of chemical bath deposited ZnO and Zn(OH)2 thin films at room conditions

Zinc oxide (ZnO) and zinc hydroxide (Zn(OH)2) films were deposited onto glass substrates at room conditions (25°C and atmospheric pressure) by the chemical bath deposition technique. ZnSO4, KOH, and NH4NO3 were used as chemical reagents for the chemical bath. The species distribution diagrams and the solubility curves were used to find the most adequate chemical conditions for the selective film deposition according to the concentrations and type of chemical reagents. The selective deposition of ZnO and/or Zn(OH)2 was achieved by adjusting the pH of the chemical bath in the range from 11.35 to 12.30, where three regions of growth were determined. The optical bandgap energy measured on the films ranged from 3.31eV for Zn(OH)2 to 3.41eV for ZnO. Lower values of Urbach energy were found when the ZnO formation was dominant. X-ray diffraction analysis showed that the pH of the chemical bath influences on the crystallinity of the films, where better crystallinity was observed for films with higher presence of ZnO. An aging experiment to evaluate the stability of the ZnO 15weeks after the deposition process was carried out.

Understanding the Nature of the Manganese Hot Dip Phosphatizing Process of Steel

In this work, the phosphatizing process of steel is investigated using open circuit potential and Tafel curves as well as scanning electron microscopy and energy dispersive X-ray spectroscopy. The results reveal that a pH of 2.57 in the phosphatizing solution promotes the dissociation of phosphoric acid which assists the formation of the manganese tertiary salt (Mn3(PO4)2), which is deposited on the substrate. It was also observed that an increase in the temperature from 25 to 90°C and the presence of HNO3 as catalyst enhances the manganese phosphatizing kinetics. On the other hand, the generation of iron phosphates and oxides is predominant at a pH of 1 and 90°C. These observations are supported by species distribution and Pourbaix thermodynamic diagrams.

Role of sodium citrate in leaching of low-grade and multiphase zinc oxide ore in ammonia–ammonium sulfate solution

In this paper, a novel system for leaching of low-grade and multiphase zinc oxide ore is presented, in which ammonia–ammonium sulfate is chosen as leaching agent, meanwhile adds a small amount of sodium citrate to strengthen the complexation behavior. The thermodynamics is studied by using chemical equilibrium modeling to predict the zinc species distribution diagrams for the Zn (II)-NH3-Cit3− system. Through employing various analytical technologies, such as X-ray diffraction (XRD), chemical analysis, and Fourier transform infrared spectroscopy (FT-IR), compositions, bond structures and chemical states are obtained. Moreover, effect of sodium citrate is studied by X-rays photoelectron spectroscopy (XPS) analysis, and it can be established that addition of sodium citrate is favorable for zinc leaching by inhabiting the formation of low complexation compound Zn(NH3)i2+ (i=1, 2) and lowering the fraction of Zn(NH3)32+. The leaching rate can reach 96.91% with a cit3− concentration of 0.2M/L. Once above it, diffusion rate of zinc would decrease, which causes the dropping of zinc leaching.

Stability constants of the ternary nickel(II) complexes with salicylic acid and selected amino acids

In this work, we present the study of the ternary Nickel(II) complexes with salicylic acid and the amino acids: aspartic acid (H2Asp, H2L), glutamic acid (H2Glu, H2L), cysteine (H2Cys, H2L) and histidine (HHis, HL) formed in aqueous solution at 25°C and 1.0mol·dm−3 NaCl as the ionic medium. The analysis of the potentiometric data by means of the computational least-squares program LETAGROP, indicate the formation of the ternary complexes [Ni(Sal)H2L]2−n, [Ni(Sal)HL]1−n, [Ni(Sal)L]−n, [Ni(Sal)L(OH)]−(1+n). Where n=1 for histidine and 2 for the other amino acids. The relative stability of the ternary complexes compared to the binary ones were evaluated considering the values of ∆log K, log X and % R.S. Species distribution diagrams as a function of pH were briefly discussed.

Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes

The adsorption of chromate on octacalcium phosphate (OCP) was investigated as a function of contact time, surface coverage, and solution pH [...]

Stability of nickel(II) binary and ternary complexes with dipicolinic acid and the amino acids serine, threonine, methionine and phenylalanine

Abstract Binary and ternary complexes of nickel(II) with dipicolinic acid (H 2 dipic) and the amino acids serine (Hser), threonine (Hthr), methionine (Hmet) and phenylalanine (Hphe), have been investigated in aqueous solutions at a 1.0 mol·dm − 3 NaCl ionic strength and 25 °C. The types of complexes formed and their overall stability constants were established on the basis of computer analysis of potentiometric results using the least-squared program LETAGROP. In the Ni(II)-amino acid (HL) systems the complexes [NiL] + , NiL 2 and [NiL 3 ] − were detected. In the ternary systems only the heteroligand complexes Ni(dipic)(HL), [Ni(dipic)(L)] − and [Ni(dipic)(L)(OH)] 2 − were observed. The species distribution diagrams as functions of pH are briefly discussed.

Investigation of the Selective Growth of ZnO and Zn(OH)2 Films Deposited by Chemical Bath Near Room Temperature

Zinc oxide (ZnO) and zinc hydroxide (Zn(OH)2) thin films were deposited by the chemical bath deposition onto glass substrates at temperatures of 25°C, 35°C and 45°C. The experimental conditions for the selective deposition of the films such as the concentration of the reagents, temperature, and pH of the chemical bath were determined from the predictions of the species distribution diagrams (SDDs) and solubility curves (SCs). SDDs and SCs were elaborated by considering the chemical reagents, temperature, and pH, and give information about the probability of formation of specific compounds. The reagents used were ZnSO4, KOH, and NH4NO3. The physicochemical of the synthesis of both ZnO and Zn(OH)2 films are proposed. X-ray photoelectron spectroscopy and X-ray diffraction indicate the presence of ZnO and/or Zn(OH)2 compounds, where the selective deposition of each material (or coexistence) is dependent on the bath temperature and pH. The crystalline structure was hexagonal (zincite) for ZnO and orthorhombic (wulfingite) for Zn(OH)2. The bandgap energy of the deposited films ranged from 3.32 to 3.51 eV. A better understanding of the selective deposition of specific compounds by controlling the experimental parameters represents an important step toward the fabrication of nanomaterials with tailored properties for a wide range of applications.

Synthesis of ZnS Thin Films by Chemical Bath: From Room Temperature to 90°C

A physicochemical analysis was performed on the solution used for synthetizing zinc sulfide (ZnS) films by chemical bath; such solution contained zinc chloride, potassium hydroxide, ammonium nitrate and thiourea as chemical reagents. Solubility curves and species distribution diagrams were used to obtain the best conditions for ZnS deposition in a wide range of bath temperatures between 25 and 90°C. Solubility curves evidenced the necessity to adjust the thiourea concentration for each bath temperature in order to obtain enough amounts of sulfur ions needed for ZnS formation. The thiourea concentrations were fixed at 0.2 M (90°C), 0.6 M (60°C), 1.25 M (40°C), and 2.25 M (25°C) to get higher quality films. Characterization results of films deposited at the conditions described above showed the films to have a bandgap energy value between 3.65 and 3.72 eV, stoichiometry of [Zn]/[S] ≈1, and homogeneous and agglomerate-free surfaces, which make them proper for solar cells applications.

Effect of EDTA on quartz and hematite flotation with starch/amine in an aqueous solution containing Mn2+ ions

In this paper, a detailed study of the influence of Mn2+ ions on quartz and hematite flotation (at pH 10.5 with starch/amine as depressor/collector) in the absence and presence of ethylenediaminetetraacetic acid (EDTA) is presented. By using zeta potential measurement and a careful analysis of manganese species present in water for dosages in which manganese hydroxide precipitated, we confirmed that the depression of both minerals by Mn2+ ions is due to the following: (i) the adsorption of Mn hydroxy complexes (Mn2(OH)3+ and Mn(OH)+); (ii) Mn2+ and mainly (iii) the precipitation of Mn(OH)2 on mineral surfaces. These effects hindered the adsorption of amine species on the surfaces of the minerals (quartz and hematite). EDTA was used to complex Mn2+ to restore the recoveries of both minerals. This was confirmed by the species distribution diagrams of Mn and EDTA-Mn in water. Conditioning with starch followed by amine at pH 10.5 enabled a selective separation of these minerals.

Potentiometric Studies on Complexation of Cu(II) Ion with Methyl/Nitro-Substituted 1,10-Phenanthrolines and Selected Amino Acids

Protonation constants of methyl/nitro substituted 1,10-phenanthrolines {(m/n-sphen): 4-methyl-phenanthroline (4-mphen), 5-methyl-1,10-phenanthroline (5-mphen), 4,7-dimethyl-1,10-phenanthroline (dmphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) and 5-nitro-1,10-phenanthroline (5-nphen)] and the amino acids (aa) l-tyrosine (tyr) and glycine (gly), and their corresponding binary and ternary stability constants with Cu(II), were determined in aqueous 0.1 mol·L−1 KCl ionic media at 298.15 K. The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Cu(II) with the ligands were calculated from the potentiometric data using the “BEST” software package. The species distribution diagrams were obtained using the “SPE” software package under the experimental conditions described. The order of stability of the ternary complexes in terms of the primary ligands is [Cu(tmphen)(aa)]+ > [Cu(dmphen)(aa)]+ > [Cu(4-mphen)(aa)]+ > [Cu(5-mphen)(aa)]+ > [Cu(5-nphen)(aa)]+. The stability constants of the ternary complexes decrease in the following order: [Cu(m/n-sphen)(gly)]+ > [Cu(m/n-sphen)(tyr)]+, which is identical to the sequence found for the binary complexes of Cu(II) with gly and tyr.

Solution equilibrium study of the complexation of Co(II) and Zn(II) with nicotinaldehyde thiosemicarbazone

The interaction of nicotinaldehyde thiosemicarbazone with Co(II) and Zn(II) was investigated in SDS-water(1.15%w/v) at 303K and ionic strength of 0.1 mol dm–3. The speciation and stability constants of the metal complexes formed were determined by pH- metric method. Protonated and simple mononuclear species in different protonation and deprotonation states were identified. The corresponding formation constants calculated using MINIQUAD-75 computer program, and species distribution diagrams produced using the HYSS computer program. Selection of the best-fit chemical models was based on statistical parameters. The results obtained from the study revealed that, the NTSC on interaction with metal ions in solution, a series of mononuclear [M(LHh)] (h = 1, 0), and bis- mononuclear [M(L2Hh)] (h = 2, 1, 0,) species were identified.Keywords: Formation constant, Nicotinaldehyde thiosemicarbazone, Metal complexes

Conodont-based stratigraphy of the Mosolovian Regional Stage (Eifelian, Middle Devonian) of the Voronezh Anteclise

Conodonts from the deposits of the Mosolovian Regional Stage (Middle Devonian) of the Voronezh Anteclise are studied on the basis of the data from six boreholes. Three assemblages are recognized. The index species of the lowermost assemblage is Icriodus formosus Naz. The index species of the middle assemblage are I. formosus Naz. and Pseudobipennatus ziegleri Kon. et Kim, as well as I. arkonensis Stauff. and I. jejunus Naz. This assemblage is the most diverse and is recognized in all boreholes. The deposits containing this assemblage correspond to the maximum of the Nara transgression. The upper assemblage is also recognized in all the studied boreholes. Its index species is Ps. ziegleri Kon. et Kim. The Mosolovian Regional Stage is assigned to the kockelianus Zone. The distribution diagrams of species in the most diverse middle assemblage support the hypothesis that, in the southeastern regions of the Voronezh anteclise, the depth was greater than in its western part. The characteristic conodont species are shown in the plates.

Di- and Tri-valent Metal Ions Interactions with Four Biodegradable Hydroxamate and Cataecholate Siderophores: New Insights into Their Complexation Equilibria

The interaction of a number of divalent and trivalent metal ions [iron(III), chromium(III) copper(II), cobalt(II) and nickel(II)] with four isolated and purified microbial catecholate and hydroxamate siderophores was studied using the pH-potentiometric technique to investigate the complexation behavior of these systems as these systems could mimic many biological interactions of the siderophore chelating agent. The protonation constants of these new siderophore analogues as well their binary complex species stability constants were determined using the Hyperquad 2008 estimation model program. From the determined stability constants of the metal complex species, the concentration distribution of the various metal ion complex species involving isolated siderophore analogues in solutions was estimated using the HySS 2009 modeling program. The complex species distribution diagrams were plotted and discussed. Additionally, the Gibbs energies and the molecular structures of the formed complex species were evaluated and predicted using Gaussian 09 software for molecular modeling and density functional theory calculations.

Synthesis and application of N–S-doped mesoporous carbon obtained from nanocasting method using bone char as heteroatom precursor and template

We report the synthesis of N–S-doped mesoporous carbon (NSMC) using bone char (BC) as template and heteroatoms precursor. The efficiency of process was evaluated through the synthesis of a material without the use of BC (SC). The materials were properly characterized and textural analysis showed that the BC led to increase of surface area and mesoporous volume for NSMC (568m2g−1 and 0.294cm3g−1) as compared to SC (518m2g−1 and 0.130cm3g−1). The doping of NSMC’s lattice was evaluated from XPS survey spectra. The spectra deconvolution showed that sulfur was incorporated as thiophene and oxidized sulfur, while nitrogen was incorporated as pyridinic, pyrrolic and graphitic, with relative composition of 2.29% and 1.63%, respectively. The Raman and X-ray diffraction analyses showed that the use of BC led to decrease in the intensity of graphitic-band, indicating the doping of carbon lattice. The pHpzc analysis showed that NSMC’s surface has acidic character with pH 3.50, which favored the ibuprofen (IBF) adsorption at pH 4.0, once at this pH value, approximately 87% of IBF species are in protonated form, according to the distribution diagram of species. Adsorption kinetic studies indicated the pseudo-second order model as the best to describe the experimental data. Moreover, adsorption equilibrium studies revealed that the Langmuir model allowed the determination of NSMC’s adsorption capacity (56.78mgg−1); while thermodynamic study showed that the adsorption is a spontaneous and exothermic process. From the results obtained adsorption mechanism of IBF onto the NSMC was proposed.

Gibbs energies of protonation and complexation of platinum and vanadate metal ions with naringenin and phenolic acids: Theoretical calculations associated with experimental values

The Experimental thermodynamic equilibrium (pKa values) and stability (logβ) constants of vanadium and platinum binary and mixed ligand complexes involving naringenin, ferulic acid, p-coumaric acid, caffeic acid, vanillic acid, sinapic acid, and gallic acid were determined at 310.15K in 0.16mol·dm−3 KCl aqueous solutions using pH-potentiometric technique and by means of two estimation models (HYPERQUAD 2008 and Bjerrum–Calvin). The theoretical calculations of overall protonation and stability constants of the metal complex species in solution were predicted as the free energy change associated with the ligand protonation, and metal ion–ligand complex formation equilibria (species solvation/de-solvation) using ab initio and density function theory (DFT) calculations. The usage of the experimental potentiometry technique and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (vanadium/platinum–naringenin–phenolic acid). Specifically, this theoretically DFT predications would be useful to determine the most real protonation constants of the studied bioligands in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of vanadium and platinum towards naringenin, ferulic acid, p-coumaric acid, caffeic acid, vanillic acid, sinapic acid, and gallic acid in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ion complex species in solution was estimated using HySS 2009 software.

Synthesis, X-ray structure, DFT and thermodynamic studies of mono- and binuclear palladium(II) complexes involving 1,4-bis(2-hydroxyethyl)piperazine, bio-relevant ligands and 4,4′-bipiperidine

[Pd(BHEP)Cl2] (BHEp = 1,4-bis(2-hydroxyethyl)piperazine) was synthesized and characterized. The palladium center has a typical square-planar geometry with a tetrahedral distortion. The alcohol groups of the ligand do not participate in binding to Pd(II). The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program and compared with experimental results. The stoichiometry and stability constants of the complexes formed between [Pd(BHEP)(H2O)2]2+ and some selected amino acids, peptides, and DNA constituents were investigated at 25 °C and 0.1 M ionic strength. The binuclear complex [(H2O)(BHEP)Pd(Bip)Pd(BHEP)(H2O)]4+ was detected, where Bip = 4,4′-bipiperidine. Inosine, uracil, and thymine interact with the binuclear complex via substitution of both coordinated water molecules. The potentiometric results were complimented by spectroscopic measurements. The concentration distribution diagrams of the various species formed were evaluated.

Physicochemical Analysis and Characterization of Chemical Bath Deposited ZnS Films at Near Ambient Temperature

A physicochemical analysis, based on the species distribution diagrams and the solubility curves, is proposed for CDB-ZnS films deposition. The effect of the temperature and the HS−/Zn(OH)42− ion concentrations on ZnS films formation are discussed. ZnS thin films were deposited by chemical bath deposition (CBD) technique at near ambient temperatures (25, 40 and 55°C) from ZnCl2/KOH/NH4NO3/SC(NH2)2 solutions. From the physicochemical analysis it was found that by increasing the bath temperature and the [HS−]/[Zn(OH)42−] ratio, better conditions for obtaining ZnS films of good quality are obtained. Chemical, stoichiometric, and structural characterizations of the deposited ZnS thin films are reported. The formation of ZnS and/or Zn(OH)2 compounds, was identified by X-ray photoelectron spectroscopy (XPS) analysis. The stoichiometric [S]/[Zn] ratio of films was measured in a range between 0.22 to 0.77. X-ray diffraction (XRD) results show amorphous structures for almost all the films, excepting for ZnS samples prepared with the high temperature and [HS−]/[Zn(OH)42−] ratio when a cubic sphalerite phase (111) preferential structure was identified. The bandgap energy of the ZnS samples changes from 3.4 to 3.7 eV when the [HS−]/[Zn(OH)42−] ratio is modified.

Mixed-ligand complex formation equilibria of vanadium(III) with 1,10′-Phennanthroline and the amino acids glycine, proline, α-alanine and β-alanine

In this work, we present the results of the speciation of the ternary vanadium(III)-1,10-Phennanthroline(Phen) and the amino acids glycine (HGly), proline (HPro), α-alanine (HαAla) and β-alanine (HβAla) by means of potentiometric measurements in 3.0mol∙dm−3 KCl 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 ligands which were kept fixed during the analysis. In the systems studied the complexes [V2O(Phen)(L)]3+, [V2O(Phen)2(L)2]2+ and V(OH)2(Phen)(L) were observed, where L represents the deprotonated form of the amino acids studied in this work. The qualitative analysis of the spectrophotometric measurements corroborates the oxo-dimer formation in these complexes studied. The respective stability constants were determined and the species distribution diagrams as a function of pH were briefly discussed.