Complexation thermodynamics of some alkali-metal cations with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane in Acetonitrile

The interaction of 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix5) with alkali-metal cations (Li⁺, Na⁺, K⁺) in aprotic medium (acetonitrile) has been investigated. Conductance measurements demonstrated that 1:1 metal cation:ligand stoichiometries are found with these cations in this solvent. ⁷Li and ²³Na NMR experiments were carried out by titration of the metal cation solutions with Kryptofix5 solution in CD₃CN + CH₃CN at 298 K. Thermodynamic parameters of complexation for this ligand and alkali-metal cations in acetonitrile at 278–308 K were derived from titration conductometry. The highest stability is found for sodium complex. The complexation sequence, based on the value of log K at 278–308 K was found to be Na⁺ > K⁺ > Li⁺.     

Cadmium determination based on silver nanoparticles modified with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane

We propose a simple, fast and sensitive colorimetric method for the determination of Cd²⁺ using 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane modified silver nanoparticles. The addition of Cd²⁺ causes the aggregation of AgNPs, while other ions do not have such effect. As a result, the color of the solution changes from yellow to red which can be detected using naked eye or by UV–Vis spectroscopy. The aggregation of the AgNPs is confirmed by UV–Vis and transmission electron microscopy. Limit of detection is found to be 0.016 µM for Cd²⁺ ions. A linear calibration plot is correlated to the concentration of cadmium ion in the 0.5–6.0 μM range with the naked-eye detection limit of 2.0 µM. The method was successfully applied to determine Cd²⁺ in water and urine samples and gave recoveries that ranged from 93.3 to 98.6%.     

Thermodynamic study of complex formation between Ni2+ and Co2+ cations and 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5) in binary mixed nonaqueous solutions

Conductometric titrations were performed in pure and binary solvent solutions of ethyl acetate (EtOAc), methyl acetate (MeOAc) and methanol (MeOH) with acetonitrile (AN) at 288, 298, 308, and 318 K to determine the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of nickel(II) and cobalt(II) cations with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5). The stability constants of the resulting 1:1 complexes formed between the metal cations and the ligand in different solvent mixtures were determined by computer fitting of the conductance-mole ratio data. The results revealed that the stability order of (kryptofix 5)-Ni²⁺ and (kryptofix 5)-Co²⁺ complexes changes with nature and composition of the solvent system. There is a non-linear relationship between the logK _f values of complexes and the mole fraction of acetonitrile in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the nickel(II) and cobalt(II) cations with the acyclic ligand changes with the nature of the solvent. The enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, in most of systems, the complexation processes of nickel(II) and cobalt(II) cations with kryptofix 5, are both enthalpy and entropy stabilized and the values of these parameters are influenced by the nature and composition of the binary mixed solvent solutions.     

Theoretical studies on the interaction of anionic collectors with Cu+, Cu2+, Zn2+ and Pb2+ ions

 The influence of collector structure on interaction with metal cations was modelled by computational ab initio methods. The interaction energies were calculated between metal ions (Cu⁺, Cu²⁺, Zn²⁺ and Pb²⁺) and selected collector anions: ethyl xanthate, ethyl trithiocarbonate, dithiobutyric acid, ethyl dithiocarbamate, diethyl dithiocarbamate, diethylphosphinecarbodithioic acid and diethoxyphosphinecar bodithioic acid. The strongest interaction was found with diethyl dithiocarbamate. The results give qualitative information on the effect of the collector structure on the initial adsorption steps on sulphide mineral flotation. Received: 25 September / Accepted: 11 October 2001 / Published online: 22 March 2002     

Complexation and thermodynamic studies of oxathiadibenzocrown ethers with Cu2+, Pb2+, Zn2+ and Cd2+ ions

A thermodynamic study of the complexation of Cu²⁺, Pb²⁺, Zn²⁺ and Cd²⁺ ions with 1 and 2 in acetonitrile has been carried out. The study was conducted in the temperature range 283–308 K using a conductometric technique. The observed molar conductivity, Λ, was found to decrease significantly for mole ratios [L]_t/[M]_t less than unity in all cases. A model involving 1:1 stoichiometry has been used to analyze the conductivity data. The stability constant, K, for each 1:1 complex was determined from the conductivity data by using a nonlinear least-squares curve fitting procedure. The results show that compound 1 has no peak selectivity for any of the metal cations, while compound 2 selectively associates with Cu²⁺ and Pb²⁺. Complexes of 1 have the following stability order Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺  and Pb²⁺ > Cu²⁺ for the complexes of 2. The ?H° and ?S° values for the complexation process were obtained from the slope and intercept of the Van’t Hoff plots respectively. All ?G° values were negative and were determined from the Gibbs–Helmholtz equation and the significance of these values is discussed.     

Novel nanostructured dendrimer based on 1,3-bis(4,6-dichloro-1,3,5-triazine-2-yl)urea as an excellent adsorbent for Pb2+, Ni2+, Co2+ and Zn2+ metal ions

Human health is seriously harmed by the consumption of poor-quality water. Due to high toxicity and water solubility, heavy metals are present in wastewater discharged from numerous industries. In the environmental realm, metal-containing water must be treated before being released. A dendrimer is a superior adsorbent for the removal of heavy metal ions due to its nanostructure and hydrophilic end group. In this work, a novel triazine-based hydroxy-terminated dendrimer up to generation three is designed employing a carbamide core. The dendrimer's structure was explored using FT-IR and ¹H NMR studies. Full generation dendrimers UG1.0, UG2.0, and UG3.0 were utilized as an adsorbent for Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ion removal from water in a series of tests. The ability of dendrimers to uptake Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions was investigated under various pH, time interval and dendrimer generation parameters. The presence of metal in the dendrimer was confirmed by FT-IR studies of dendrimer-metal complexes. The overall results show that Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions uptake increases with the generation, time, and pH.     

Conductometric and 1H NMR studies of thermodynamics of complexation of Zn2+, Cd2+ and Pb2+ ions with tetrathia-12-crown-4 in dimethylsulfoxide-nitrobenzene mixtures

The complex formation between Zn²⁺, Cd²⁺ and Pb²⁺ ions with macrocyclic ligand, tetrathia12-crown-4 (12S4) was studied in dimethylsulfoxide (DMSO)–nitrobenzene binary mixtures at different temperatures using conductometric and ¹H NMR methods. In all cases, 12S4 found to form 1:1 complexes with these cations. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the resulting molar conductance- and chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The stability of the resulting M²⁺-12S4 complexes found to decrease in the order Pb²⁺ > Cd²⁺ > Zn²⁺. The values of ?H°, ?S° and ?G° for complexation reactions were evaluated from the temperature dependence of formation constants via van’t Hoff method. The obtained results revealed that, in all cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ?H° and ?S° are strongly depend on the nature of medium. There is also a linear relationship between all ΔH° and TΔS° values indicating the existence of entropy–enthalpy compensation in complexation of the three cations and ligand in the solvent systems studied.     

Studies on Synthetic Inorganic Ion Exchangers-III Quantitative Separations of Mg2+ -Pb2+, Zn2+ - Pb2+ Cu2+ - Pb2+, Al3+ - Pb2+, Zn2+ - Cd2+, and Mg2+ - Cd2+ on Lead Antimonate Columns

Abstract

A new inorganic ion exchanger, lead antimonate has been synthesized having an Pb:Sb ratio of 1:5 and cation exchange capacity of 1.46 mequiv./g. It is fairly stable in water and dilute solutions of acids, bases and salts. Ion distribution studies on twenty metal ions have been determined on this gel at pH 1,2,3 and 5. The following mixtures have been separated: Mg²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Cu²⁺ - Pb²⁺, Al³⁺ - Pb²⁺, Zn²⁺ - Cd²⁺ and Mg²⁺ - Cd²⁺. Mg²⁺ and Al³⁺ were removed with 0.4 M ammonium nitrate, Cu²⁺ and Zn²⁺ with 0.4 M ammonium nitrate + 0.1M nitric acid (1:1), Pb²⁺ with 0.5M nitric acid and Cd²⁺ with 0.25M nitric acid. A tentative structure of this material is proposed on the basis of chemical analysis, pH titrations, thermogravimetry and IR spectrophotometry.     

Adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide from simple (1-1) electrolyte solutions

The adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide (delta-MnO2) has been studied using two methods, viz., isotherms at constant pH in the presence of buffer solution and pH variation in the absence of buffer solution from a fixed metal ion concentration. While the adsorption isotherm experiments were carried out in 0.5 M NaCl only, pH variation or batch titration experiments were carried out in 0.5 M NaCl, 0.01 M NaCl, and 0.01 M KNO3 solutions. The complex nature of adsorption isotherms at constant pH values indicates that adsorption of all the cations is non-Langmuirian (Freundlich) and takes place on the highly heterogeneous oxide surface with different binding energies. The proton stoichiometry derived from isotherms at two close pH values varies between 0.3 and 0.8. The variation of fractional adsorption with pH indicates that the background electrolyte solution influences the adsorption of cations through either metal-like or ligand-like complexes with Cl-, the former showing a low adsorption tendency. The proton stoichiometry values derived from the Kurbatov-type plot varies not only with the electrolyte solution but also with the adsorbate/adsorbent ratio. The variation of fractional adsorption with pH can be modeled either with the formation of the SOM+ type or with a combination of SOM+ and SOMOH type complexes, depending upon the cation and electrolyte medium. The equilibrium constants obtained from Kurbatov-type plots are found to be most suitable in these model calculations. Adsorption calculated on the basis of ternary surface metal-chlorocomplex formation exhibits very low values.     

Different binding thermodynamics of Ni2+, Cu2+, and Zn2+ to bacitracin A1 determined by capillary electrophoresis

Thermodynamics of the binding of Ni(2+), Cu(2+) and Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis measuring the peptide effective mobility at different pH in the presence of increasing concentration of the three ligands. The affinity follows the order Ni(2+) > Cu(2+) > Zn(2+), with association constant values of (2.3 +/- 0.1)x10(4), (4.9 +/- 0.2)x10(3), and (1.5 +/- 0.1)x10(3) M(-1), respectively. The only model able to rationalize mobility data implies that metal ion binds to the P(0) peptide form. Moreover, mobility values indicated a change of bacitracin A(1) acidic properties on Ni(2+) and Cu(2+) binding, with a shift of the pK(a) of N-terminal Ile-1 from 7.6 to about 5 and of the pK(a) of the delta-amino group of D-Orn-7 from 9.7 to about 7. Even though on Zn(2+) binding a shift of the N-terminal Ile-1 pK(a) was observed, restrictions in the pH range suitable for investigation, due to precipitation phenomena, did not allow establish if the shift of D-Orn-7 lateral chain pK(a) also occurred. Nonetheless, if present, the shift should be limited to the 7.8-9.7 range. Mobility data indicated that the Stokes radius of the complexes is ca. 3 A lower than that of the free peptide. The present results indicate that metal-ion binding to bacitracin A(1) is more complex than previously assumed.     

Synthesis and study of properties of the polyhexamethyleneguanidine complexes with the ions Cu2+, Zn2+, and Ni2+

The reaction products of polyhexamethyleneguanidine hydrochloride with the Cu²⁺, Zn²⁺, and Ni²⁺ ions, which are the polyligand coordination compounds formed by polyguanidine and hydroxyl ligands, were studied using IR, UV, and ESR spectroscopy. The influence of the nature of the chelating agent on the structure of the complexes formed was revealed. Antibacterial properties of the synthesized complexes were assessed.     

Synthesis,characterization and antioxidant,antibacterial activity Zn2+, Cu2+, Ni2+ and Co2+, complexes of ligand [2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole]

New metal complexes of (Zn(II), Co(II), Ni(II) and Cu(II)) based on the ligand 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole] were synthesized, whose structures were determined with the different spectroscopic techniques ¹H NMR,¹³C NMR, FT-IR, UV–Visible and by mass spectrometry. The thermal analysis was performed by TG-DTA. The antioxidant activity of the ligand and its complexes was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) method, in comparison with the synthetic antioxidant, ascorbic acid. The results obtained showed that the antioxidant activity of the ligand and its complexes is moderate and that the copper complex has a high activity that exceeds that of ascorbic acid. Antimicrobial activity of the ligand and its metal complexes was studied against two Gram-positive bacteria: Bacillus subtilis ILP1428B, Staphylococcus aureus CIP543154 and two Gram-negative bacteria: Pseudomonas aeruginosa ATCC27653, Escherichia coli CIP5412 (American Type Culture Collection)the activity data show that the metal complexes are more potent than the free ligand.     

Qualitative analysis of Cu2+, Co2+, and Ni2+ cations using thin-layer chromatography

The M(DEDTC)2 (M = Cu, Co, or Ni) and M(PyDTC)2 (M = Cu or Co) complexes prepared by reactions of sodium diethyldithiocarbamate and ammonium pyrollidinedithiocarbamate with metal (II) nitrates are examined for qualitative analysis and separation using thin-layer chromatography systems. These complexes and their mixtures are spotted to the activated thin layers of silica gel 60GF254 (Si-60GF254) with a 250-microm thickness. Pure toluene and a toluene-cyclohexane mixture (3:1, v/v) are used as mobile phases for running of the complexes. These chromatographic systems are successfully used for qualitative analysis of corresponding metal cations and separation of components in both M(DEDTC)2 and M(PyDTC)2 complex mixtures.     

Simultaneous determination of Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ by using second-derivative spectrophotometry method

A new method of simultaneous determination of Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ is proposed here by using the second-derivative spectrophotometry method. In pH=10.35 Borax-NaOH buffer, using meso-tetra (3-methoxyl-4-hydroxylphenyl) porphyrin ([T-(3-MO-4-HP)P]) as chromomeric reagent, micelle solution was formed after Tween-80 surfactant was added into the solution containing Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ ions. The original absorption spectrum of the above complexes was obtained after heating in the boiling water for 25 min. The second-derivative absorption peaks of five metal-porphyrin complexes can be separated from the original absorption spectrum by using chemometric tool. In this way, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ ions can be determined simultaneously. Under the optimal conditions, the linear ranges of the calibration curve were 0-0.60, 0-0.60, 0-0.40, 0-0.80 and 0-0.48 μg mL(-1) for Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+, respectively. The molar absorptivity of these color systems were 1.38×10(5), 1.01×10(5), 3.24×10(5), 1.07×10(5) and 1.29×10(5)Lmol(-1)cm(-1). The method developed in this paper has advantages in selectivity, sensitivity, operation and can effectively resolve spectra overlapping problem. This method has been applied to determine the real samples with satisfactory results.     

Concentration of Co2+, Fe3+ and Zn2+ ions with microbiological collectors

By means of Spicaria Violacea Abbott fungus, a microbiological method of concentration and separation of cobalt, iron and zinc is given. The influence of the experimental conditions, i.e. pH, time and concentration have been investigated.     

Simultaneous Analysis of Co2+, Cu2+ Mn2+, Ni2+ and Zn2+ in The Ultraviolet Region Using 4-(Pyridil-2-AZO) Resorcinol and Multivariate Calibration

ABSTRACT

A multicomponent spectrophotometric methodology for the simultaneous determination of Co²⁺, Cu²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ in aqueous solution is reported, using (4-(pyridil-2-azo) resorcinol), a diode array spectrophotometer and multivariate calibration by partial least-squares and principal component regerssions. Spectra are recorded in the UV region. The 225 – 320 nm range is selected as optimal, through a criterion based on tederivatives of the differences between individual spectra, which compares favorably with a genetic algorithm. The methodology is applied to the simultaneous determination of the five than 1.5 mgL^?1. The best result are obtanied at pH 9.0, with average absolute errors of prediction lower than 0.09 mgL^?1     

trans-Methylpyridine cyclen versus cross-bridged trans-methylpyridine cyclen. Synthesis, acid-base and metal complexation studies (metal = Co2+, Cu2+, and Zn2+)

The synthesis of the cross-bridged cyclen CRpy(2) {4,10-bis((pyridin-2-yl)methyl)-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane}, a constrained analogue of the previously described trans-methylpyridine cyclen Cpy(2) is reported. The additional ethylene bridge confers to CRpy(2) proton-sponge type behaviour which was explored by NMR and potentiometric studies. Transition metal complexes have been synthesized (by complexation of both ligands with Co(2+), Cu(2+) and Zn(2+)) and characterized in solution and in the solid state. The single crystal X-ray structures of [CoCpy(2)](2+), [CuCpy(2)](2+) and [ZnCpy(2)](2+) complexes were determined. Stability constants of the complexes, including those of the cross-bridged derivative, were determined using potentiometric titration data and the kinetic inertness of the [CuCRpy(2)](2+) complex in an acidic medium (half-life values) was evaluated by spectrophotometry. The pre-organized structure of the cross-bridged ligand imposes an additional strain for the complexation leading to complexes with smaller thermodynamic stability in comparison with the related non-bridged ligand. The electrochemical study involving cyclic voltammetry underlines the importance of the ethylene cross-bridge on the redox properties of the transition metal complexes.