Study of complex formation between 18-crown-6 and diaza-18-crown-6 with uranyl cation (UO2 2+) in some binary mixed aqueous and non-aqueous solvents

The complexation reaction between UO₂ ²⁺ cation with macrocyclic ligand, 18-crown-6 (18C6), was studied in acetonitrile–methanol (AN–MeOH), nitromethane–methanol (NM–MeOH) and propylencarbonate–ethanol (PC–EtOH) binary mixed systems at 25 °C. In addition, the complexation process between UO₂ ²⁺ cation with diaza-18-crown-6 (DA18C6) was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–ethanol (AN–EtOH), acetonitrile–ethylacetate (AN–EtOAc), methanol–water (MeOH–H₂O), ethanol–water (EtOH–H₂O), acetonitrile–water (AN–H₂O), dimethylformamide–methanol (DMF–MeOH), dimethylformamide–ethanol (DMF–EtOH), and dimethylformamide–ethylacetate (DMF–EtOAc) binary solutions at 25 °C using the conductometric method. The conductance data show that the stoichiometry of the complexes formed between (18C6) and (DA18C6) with UO₂ ²⁺ cation in most cases is 1:1 [M:L], but in some solvent 1:2 [M:L₂] complex is formed in solutions. The values of stability constants (log K_f) of (18C6 · UO₂ ²⁺) and (DA18C6 · UO₂ ²⁺) complexes which were obtained from conductometric data, show that the nature and also the composition of the solvent systems are important factors that are effective on the stability and even the stoichiometry of the complexes formed in solutions. In all cases, a non-linear relationship is observed for the changes of stability constants (log K_f) of the (18C6 · UO₂ ²⁺) and (DA18C6 · UO₂ ²⁺) complexes versus the composition of the binary mixed solvents. The stability order of (18C6 · UO₂ ²⁺) complex in pure studied solvents was found to be: EtOH > AN ≈ NM > PC ≈ MeOH, but in the case of (DA18C6 · UO₂ ²⁺) complex it was : H₂O > MeOH > EtOH.     

Study of complex formation between dicyclohexyl-18-crown-6 and UO2 2+ cation in some binary mixed non-aqueous solvents using conductometric method

In the present work, the complexation process between UO₂ ²⁺ cation and the macrocyclic ligand, dicyclohexyl-18-crown-6 (DCH18C6) was studied in ethyl acetate/1,2-dichloroethane (EtOAc/DCE), acetonitrile/1,2-dichloroethane (AN/DCE), methanol/1,2-dichloroethane (MeOH/DCE) and ethanol/1,2-dichloroethane (EtOH/DCE) binary solutions at different temperatures using the conductometric method. The conductance data show that in most cases, the stoichiometry of the complex formed between DCH18C6 and UO₂ ²⁺ cation is 1:1 [M:L], but in some solvent systems also a 1:2 [M:L₂] complex is formed in solutions. The values of stability constant of (DCH18C6·UO₂)²⁺ complex which were obtained from conductometric data, show that the stability of the complex is affected by the nature and also the composition of the solvent system and in all cases, a non-linear behavior is observed for the variation of (log?K _f) of the (DCH18C6·UO₂)²⁺ complex versus the composition of the binary mixed solvents. The values of thermodynamic quantities $ \Updelta H_{c}^{\circ} $ and $ \Updelta S_{c}^{\circ} $ for formation of (DCH18C6·UO₂)²⁺ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The experimental results show that depending on the nature and composition of the solvent systems, the complex is enthalpy stabilized or destabilized, but in most cases, it is stabilized from entropy view point and both thermodynamic parameters are affected by the nature and composition of the binary mixed solutions.     

Thermodynamic study of complex formation between 18-crown-6 and potassium ion in some binary non-aqueous solvents using a conductometric method

The complexation reaction between a macrocyclic polyether, 18-crown-6 (18C6), and potassium ion was studied in methanol (MeOH)-acetonitrile (AN), dimethylformamide (DMF)-AN and propylecarbonate (PC)-DMF binary solvent systems at different temperatures using a conductometric method. It was found that the stability of the 1:1 complex formed between K(+) ion and this ligand increases with decreasing temperature. Standard enthalpies and standard entropies of the complex formation were obtained from the temperature dependence of the stability constant. In all cases negative DeltaH(o)(c) and DeltaS(o)(c) values characterize the formation of 18C6-K(+) complex. The results obtained show that the stability of the complex is governed by the solvent medium and the thermodynamic parameters DeltaH(o)(c), DeltaS(o)(c) and DeltaG(o)(c) are sensitive to the composition of the mixed solvents. In addition, it was found that the stability constant of the resulting 1:1 complex among various neat solvents used varies in the order PC > MeOH > AN > DMF.     

Thermodynamic study of complex formation between dibenzo-18-crown-6 and UO2 2+ cation in different non-aqueous binary solutions

In the present work the complexation process between UO₂ ²⁺ cation and the macrocyclic ligand, dibenzo-18-crown-6 (DB18C6) was studied in ethylacetate–dimethylformamide (EtOAc/DMF), ethylacetate–acetonitrile (EtOAc/AN), and ethylacetate–tetrahydrofuran (EtOAc/THF) and ethylacetate–propylencarbonate (EtOAc/PC) binary solutions at different temperatures using the conductometric method. The results show that the stoichiometry of the (DB18C6 . UO₂)²⁺ complex in all binary mixed solvents is 1:1. A non-linear behavior was observed for changes of log K_f of this complex versus the composition of the binary mixed solvents. The stability constant of (DB18C6 . UO₂)²⁺ complex in various neat solvents at 25 °C decreases in order: THF > EtOAc > PC > AN > DMF, and in the binary solvents at 25 °C is: THF–EtOAc > PC–EtOAc > DMF–EtOAc ≈ AN–EtOAc. The values of thermodynamic quantities (?H°_c, ?S°_c) for formation of this complex in the different binary solutions were obtained from temperature dependence of its stability constant and the results show that the thermodynamics of complexation reaction between UO₂ ²⁺ cation and DB18C6 is affected strongly by the nature and composition of the mixed solvents.     

Thermodynamic study of complex formation between Kryptofix-5 and Sn2+ in several individual and binary non-aqueous solvents using a conductometric method

The complex formation between 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix-5) and Sn²⁺ ions was studied in pure acetonitrile (AN), dimethylformamide (DMF), 1,4-dioxane (DOX), and methanol (MeOH) and in acetonitrile-1,4-dioxane (AN-DOX), acetonitrile-dichloromethane (AN-DCM), acetonitrile-methanol (AN-MeOH), and acetonitrile-dimethylformamide (AN-DMF) binary mixed solvent solutions at different temperatures using conductometric method. 1: 1 [ML] complex is formed between the metal cation and ligand in most solvent systems but in the cases of AN-MeOH (MeOH = 90 mol %) binary mixture and in pure MeOH a 2: 1 [M₂L] complex was observed, that is the stoichiometry of complexes may be changed by the nature of the medium. The stability order of the (Kryptofix-5·Sn)²⁺ complex in the studied binary mixed solvent solutions at 25°C was found to be AN-DOX > AN-DCM > AN-MeOH > AN-DMF and in the case of pure solvents at 25°C the sequence was the following: AN > DMF > DOX. A non-linear behavior was observed for changes of logK _f of (Kryptofix-5·Sn)²⁺ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent intractions and also by the preferential solvation of the f species involved in the complexation reaction. The values of standard enthalpy changes (ΔH _c ^○ ) for complexation reactions were obtained from the slope of the Van’t Hoff plots and the changes in standard entropy (ΔS _c ^○ ) were calculated from the relationship ΔG _{c, 298.15} ^○ = ΔH _c ^○ ? 298.15ΔS _c ^○ . The results show that in most cases, the (Kryptofix-5·Sn)²⁺ complex is both enthalpy and entropy stabilized.     

Thermodynamic study of complex formation of benzo-18-crown-6 with K+, Tl+, and Pb2+ in water

H ⁰ and S ⁰ values of the complex formation in water of benzo-18-crown-6 (B18C6) with K⁺, Tl⁺, and Pb²⁺ were determined and compared with those of 18-crown-6. The H⁰ values of B18C6 are negative. The stability in water of the B18C6-metal ion complex at 25°C is governed largely by the magnitude of the H ⁰ value. The B18C6-metal ion complex is less stable in water than the corresponding 18C6-metal ion complex. This is due largely to a less favorable enthalpic contribution of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex. The two aromatic ether oxygen atoms of B18C6 are responsible for the larger H ⁰ value of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex.     

Study of Cd2+ complexation by the glutathione fragments Cys-Gly (CG) and gamma-Glu-Cys (gamma-EC) by differential pulse polarography

A differential pulse polarographic study of the Cd2+/gamma-Glu-Cys and Cd2+/Cys-Gly systems assisted by the alternating least-squares multivariate curve resolution (MCR-ALS) method was carried out to obtain a better understanding of the different metal affinities of the complexation sites on glutathione (GSH). The simultaneous analysis of the titration of peptide with metal and of metal with peptide allowed the resolution of the Cd2+/Cys-Gly system, whereas in the analysis of the Cd2+/gamma-Glu-Cys system the analysis of a single titration experiment was sufficient. The analysis of the shape of the resulting pure voltammograms and concentration profiles of the resolved components suggested the presence of two different types of bound Cd2+ in the two systems considered, that could be attributed to Cd2+ bound to one or two sulfur atoms to form complexes of stoichiometry 1:1 and 1:2. respectively.     

A Polarographic Study of Tl+, Pb2+ and Cd2+ Complexes with Aza-18-crown-6 and Dibenzopyridino-18-crown-6 in some Binary Mixed Non-aqueous Solvents

The complexation of Tl⁺, Pb²⁺and Cd²⁺ cations by macrocyclic ligands, aza-18-crown-6 (L1) and dibenzopyridino-18-crown-6 (L2) was studied in some binary mixtures of methanol (MeOH), n-propanol (n-PrOH), nitromethane (NM) and acetonitrile (AN) with dimethylformamide (DMF) at 22 °C using DC (direct current) and differential pulse polarographic techniques (DPP). The stoichiometry and stability constants of the complexes were determined by monitoring the shifts in half-waves or peak potentials of the polarographic waves of metal ions against the ligand concentration. In all of the solvent systems, the stability of the resulting 1:1 complexes was found to be L1 > L2. The selectivity order of the L2 ligand for the cations was found to be Pb²⁺ > Tl⁺ > Cd²⁺ and the selectivity of the L1 ligand for Pb²⁺ ion was greater than that of Tl⁺ ion. The results show that the stability of the complexes depends on the nature and composition of the mixed solvents. There is an inverse relationship between the stability constants of the complexes and the amount of dimethylformamide in the mixed solvent systems.     

Polarographic behaviour of 3-(2′-thiazolylazo)-2, 6-diaminopyridine using DC and differential pulse polarography

The polarographic behaviour of 3-(2-thiazolylazo)-2,6-diaminopyridine (2,6-TADAP) has been studied in aqueous buffer solutions and aqueous-ethanol mixtures of different pH's using DC and DP polarographic methods. The reduction of the azo linkage takes place via two electrons in both aqueous and aqueous-ethanol mixtures. The linear relationship between the current and 2,6-TADAP concentration allowed the polarographic determination of 2,6-TADAP over a wide concentration range. The values of the adsorption parameters in the presence of both Triton X-100 (non-ionic) and a new non-ionic surfactant, nonylphenol polyoxypropylene polyoxyethylene (NPE 1800) have been computed. The kinetic parameters of the electrode reaction have been calculated.On leave from An-Najah National University, Nablus, West Bank, Via Israel.     

A Polarographic Study of Tl + , Pb 2 and Cd 2+ Complexes with Dicyclohexano-18-Crown-6 in Some Binary Mixed Solvents

The complexes of Tl⁺, Pb²⁺ and Cd²⁺ cations with the macrocyclic ligand, dicyclohexano-18-crown-6\linebreak(DC18C6) were studied in water/methanol (H₂₊O/MeOH), water/1-propanol (H₂₊O/1-PrOH), water/acetonitrile (H₂₊O/AN), water/dimethylformamide (H₂₊O/DMF), dimethylformamide/acetonitrile (DMF/AN), dimethylformamide/methanol (DMF/MeOH), dimethylformamide/1-propanol (DMF/1-PrOH) and dimethylformamide/nitromethane (DMF/NM) mixed solvents at 22 °C using differential pulse polarography (DPP), square wave polarography and conductometry. In general, the stability of the complexes was found to decrease with increasing concentration of water in aqueous/non-aqueous mixed solvents with an inverse relationship between the stability constants of the complexes and the concentration of DMF in non-aqueous mixed solvents. The results show that the change in stability of DC18C6.Tl⁺, vs the composition of solvent in DMF/AN and DMF/NM mixed solvents is apparently different from that in DMF/MeOH and DMF/1-PrOH mixed solvents. While the variation of stability constants of the DC18C6.Tl⁺ and DC18C6.Pb²⁺ complexes vs the composition of H₂₊O/AN mixed solvents is monotonic, an anomalous behavior was observed for variations of log K_f vs the composition of H₂₊O/1-PrOH and H₂₊O/MeOH mixed solvents. The selectivity order of the DC18C6 ligand for the cations was found to be Pb²⁺ > Tl⁺ > Cd²⁺.     

高氯酸钇冠醚配合物的研究I:三水高氯酸钇与18-冠-6在乙腈中配合行为的研究

本文用改进和半微量相平衡方法研究了Y(ClO~4)~3.3H~2O-18C~6-CH~3Cn 三体系在20℃时的溶解度, 以便确定三水高氯酸钇与18-冠-6-在乙腈中能否形成配合物, 能生成几种配合物以及它们的相区情况, 为合成固态配合物提供依据。并在该基础上, 分离,制备了固态配合物, 利用化学分析, DTG,TG,DSC以及电导考查了配合物的组成与性质。     

Effect of solvent on complexation between Y3+ cation and 4,13-diaza-18-crown-6 in some binary mixed non-aqueous solvents

The complexation reaction of 4,13-diaza-18-crown-6 (DA18C6) with Y³⁺ cation was studied in some binary mixed solvent solutions of acetonitrile (AN) with methanol (MeOH), ethanol (EtOH), 2-propanol (2-PrOH) and methyl acetate (MeOAc) at different temperatures by conductometric method. The obtained data show that in all studied solutions the stoichiometry of the complex formed between DA18C6 and Y³⁺ cation is 1: 1 [ML], but in the case of pure MeOAc, a 2: 1 [ML₂] complex is formed in solution upon addition of the ligand to the metal salt solution, and further addition of the ligand results in formation of a M₂L₂ complex in solution. This results show that the stoichiometry of the composition of the macrocyclic complexes may be affected by the nature of the solvent system. The results obtained in this study show that the stability constant of the resulting 1: 1 [ML] complex in the binary solvent solutions decreases in the order: AN-MeOAc > AN-2PrOH > AN-MeOH > AN-EtOH. A non-linear relationship was observed between the stability constant (logK _f ) of [Y(DA18C6)]³⁺ complex with the composition of the binary mixed solvent solutions. The corresponding standard thermodynamic parameters (H° _c , Δ S° _c ) for 1: 1 [ML] complexation reaction between DA18C6 and Y³⁺ cation were obtained from temperature dependence of the stability constant of the complex. The results show that, in all solvent systems, the (DAI8C6.Y)³⁺ complex is entropy stabilized, but from enthalpy point of view, depending on the solvent system, it is stabilized or destabilized and the result show that the values of both thermodynamic quantities change with the nature and composition of the binary mixed solvent solutions.     

Thermochemistry of the silver(I) complexation with 18-crown-6 ether in binary acetonitrile—dimethylsulfoxide solvents

The effect of acetonitrile-dimethylsulfoxide solvents on the enthalpy of silver(I) complexation with 18-crown-6 ether is studied by means of calorimetry. It is found that an increase in the concentration of dimethylsulfoxide leads to an increase in the reaction exothermicity. It is shown that the determining factor in the change in the reaction enthalpy is the solvation effect of the ligand.     

An ion-exchange separation of Cu(2+), Cd(2+), Pb(2+) and Tl(+) on silica gel with polarographic detection

The HPLC separation of heavy metal cations was studied with a column packed with Separon SGX silica gel. The retention of the cations is controlled by an ion-exchange mechanism. The ion-exchange capacity is primarily dependent on the mobile phase pH. The analyte retention is further affected by the type and concentration of the completing agent present and of the counterion. The effect of acetate, tartrate and -hydroxyisobutyrate as complexing agents and that of methanol as the organic modifier were studied in detail and the results were compared with the theoretical model of ion-exchange separation. Simple mixtures of metals can be rapidly separated on a short column (30 × 3.3 mm i.d.), e.g., with a mobile phase containing 10⁻²M tartrate at pH 6.0. The metals separated can be detected by dc amperometry at a hanging mercury drop electrode. The limits of detection at an electrode potential of −0.95 V (Ag/AgCl) are in the units—tens of ng range with 20-μl samples with satisfactory precision (RSD values of 2–6%). The main advantages of the method are rapidly and simplicity because derivatization of the analytes is not required.     

Solvent influence upon complex formation between different 1,8-dioxo-octahydroxanthene derivatives and yttrium(III) cation in some non-aqueous solvents using conductometric method

The complexation reactions between the yttrium(III) cation and (4-chlorophenyl, phenyl, 4-nitrophenyl, 4-methoxyphenyl, 4-methylphenyl) 9-substituted 1,8-dioxo-octahydroxanthene were studied in acetonitrile (AN) and methanol (MeOH) at different temperatures using the electrical conductivity measurements. The conductance data show that the stoichiometry of all formed complexes between the Y³⁺ cation and the studied ligands is 1: 1 [ML]. The order of stability of the complexes formed between the organic ligands and Y³⁺ cation in pure MeOH at 45°C was found to be: (3,6,6-Tetramethyl-9-(4-chlorophenyl)-1,8- dioxo-octahydroxanthene·Y³⁺) > (3,6,6-Tetramethyl-9-(4-methoxyphenyl)-1,8-dioxo-octahydroxanthene · Y³⁺) > (3,6,6-Tetramethyl-9-(4-phenyl)-1,8-dioxo-octahydroxanthene·Y³⁺) ≈ (3,6,6-Tetramethyl-9-(4- nitrophenyl)-1,8-dioxo-octahydroxanthene·Y³⁺) > (3,6,6-Tetramethyl-9-(4-methylphenyl)-1,8-dioxooctahydroxanthene ·Y³⁺). The values of the standard thermodynamic parameters (ΔH_c^°, ΔS_c^°) for formation of the complexes were obtained from temperature dependence of the formation constants of the complexes using the van’t Hoff plots. The experimental results show that the thermodynamics of the complexation reactions is influenced by the nature of solvent system and in most cases, the complexes are entropy stabilized.     

Application of N-PLS calibration to the simultaneous determination of Cu(2+), Cd(2+) and Pb(2+) using peptide modified electrochemical sensors

The simultaneous determination of Cu(2+), Cd(2+) and Pb(2+) is demonstrated at four modified gold electrodes using N-PLS calibration. Three of the electrodes were modified with the peptides Gly-Gly-His, gamma-Glu-Cys Gly and human angiotensin I which were covalently attached to thioctic acid self-assembled monolayers and the fourth electrode was modified with thioctic acid only. Voltammetry at the modified electrodes in the presence of the three metal ions revealed one peak due to the reduction of copper and another due to the overlapping peaks of cadmium and lead which made quantification using conventional methods difficult. N-PLS was used to calibrate and predict trace concentrations (100 nM to 10 microM) of mixtures of Cu(2+), Cd(2+) and Pb(2+).     

Study of complexation reactions between alkali and alkaline-earth metal cations with dibenzo-18-crown-6(DB18C6) in mixed nonaqueous solvents using the conductometry method

The complexation reactions between alkali and alkaline-earth metal cations with DB18C6 were studied in acetonitrile-methanol (AN-MeOH) and tetrahydrofuran-threechloromethane (THF-CHCl₃) binary mixtures at different temperatures using the conductometric method. The obtained results show that in most cases, the DB18C6 forms 1:1 complexes with these metal cations and the stability of the complexes is affected by the nature and composition of the mixed solvents. The stability order of complexes in AN-MeOH binary systems was found to be Na⁺ > Li⁺, and in the case of THF-CHCl₃ binary mixtures was Na⁺ > Ba²⁺ > Li⁺. An anomalous and interesting behavior was observed for the case of complexation of a K+ ion with DB18C6 in the AN-MeOH binary mixture and also for complexation of Mg²⁺ and Ca²⁺ cations with this ligand in pure THF and also in THF-CHCl₃ binary systems. The values of the thermodynamic parameters (ΔH _c ^o and ΔS _c ^o ) for complexation reactions obtained from the temperature dependence of the stability constants and the results show that the complexes are both enthalpy-and entropy-stabilized. The text was submitted by the authors in English.     

One-dimensional infinite chain crown ether complex:Synthesis and crystal structure of[Na(18C6)]2[Cu(mnt)2]·H2O

One-dimensional coordination polymers have attracted considerable interest in recent years because of the prospect of electrical, optical and magnetic properties. Crown ether can form one-dimensional infinite chain structure with transition metal complex. We synthesized the complexes of 18-crown-6 with Na₂[m{S₂C₂(CN)₂}₂](m=Cu, Ni, Pd, Pt; S₂C₂(CN)₂^2- mnt) and now report the structure of complex[Na(18C6)]₂[Cu(mnt)₂]·H₂O.     

Study of Complex Formation Between 18-Crown-6 and Pb2+, Tl+ and Cd2+ Cations in Binary Aqueous/Non-aqueous Solvents Using Polarographic Techniques (DPP and SWP)

The complexation of Pb²⁺, Tl⁺ and Cd²⁺ cationsby 18-crown-6 was studied in water/propanol (H₂O/PrOH),water/acetonitrile (H₂O/AN) and water/dimethylformamide(H₂O/DMF) binary systems at 20 °C using squarewave polarography (SWP) and differential pulse polarography (DPP).It was confirmed that the stoichiometry of each of the complexes formed between 18C6 and the respective cations is 1 : 1. The formation constants of the complexes were found to increase with increasing concentration of the non-aqueous solvent. In all cases, a stability order of Pb²⁺ > Tl⁺ > Cd²⁺ was observed. In general,the stabilities of individual complexes were found to decrease as the binary solvent mixture varied from H₂O/AN to H₂O/PrOH to H₂O/DMF.     

A Conductometric Study of Complexation Reactions Between Dibenzo-18-Crown-6 (DB18C6) with Cu2+, Zn2+, Tl+ and Cd2+ Metal Cations in Dimethylsulfoxide–Ethylacetate Binary Mixtures

The complex formation between Cu²⁺, Zn²⁺, Tl⁺ and Cd²⁺ metal cations with macrocyclic ligand, dibenzo- 18-crown-6 (DB18C6) was studied in dimethylsulfoxide (DMSO)–ethylacetate (EtOAc) binary systems at different temperatures using conductometric method. In all cases, DB18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, Genplot. The non-linear behaviour which was observed for variations of log K _f of the complexes versus the composition of the mixed solvent was discussed in terms of changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity order of DB18C6 for the metal cations in pure ethylacetate and pure dimethylsulfoxide is: Tl⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ but the selectivity order is changed with the composition of the mixed solvents. The values of enthalpy changes (ΔH°_C) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard enthalpy (ΔS°_C) were calculated from the relationship: ΔG°_C,298.15=ΔH°_C − 298.15 ΔS°_C. The obtained results show that in most cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ΔH°_C and ΔS°_C depend strongly on the nature of the medium.