Conductance Studies on Complex Formation Between Aza-18-Crown-6 with Ag+, Hg2+ and Pb2+ Cations in DMSO–H2O Binary Solutions

The complexation reactions between Ag⁺, Hg²⁺ and Pb²⁺ metal cations with aza-18-crown-6 (A18C6) were studied in dimethylsulfoxide (DMSO)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complexes in most cases is 1:1(ML), but in some cases 1:2 (ML₂) complexes are formed in solutions. A non-linear behaviour was observed for the variation of log K _f of the complexes vs. the composition of the binary mixed solvents. Selectivity of A18C6 for Ag⁺, Hg²⁺ and Pb²⁺ cations is sensitive to the solvent composition and in some cases and in certain compositions of the mixed solvent systems, the selectivity order is changed. The values of thermodynamic parameters (ΔH _c^o, ΔS _c^o) for formation of A18C6–Ag⁺, A18C6–Hg²⁺ and A18C6–Pb²⁺ complexes in DMSO–H₂O binary systems were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

Effect of Solvent on Competitive Bulk Membrane Transport of Transition and Post Transition Metal Cations Using Decyl-18-crown-6

A series of competitive metal ion transport experiments have been performed. Each involved transport from an aqueous source phase across an organic membrane phase into an aqueous receiving phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), cupper(II), zinc(II), cadmium(II), silver(I) and lead(II) metal cations. The membrane phase incorporated ionophore, decyl-18-crown-6. The membrane solvents include: chloroform, dichloromethane, 1,2-dichloroethane, nitrobenzene and chloroform–nitrobenzene binary solvents. A good transport efficiency and selectivity of Pb²⁺ transport from aqueous solutions are observed in this investigation. The selectivity order for competitive bulk liquid membrane transport of the studied transition and post transition metal cations through chloroform is: Pb²⁺>Co²⁺>Ni²⁺>Ag⁺>Cd²⁺, but in the case of dichloromethane, 1,2-dichloroethane and nitrobenzene as liquid membranes, the selectivity sequences were found to be: Pb²⁺>Co²⁺>Cd²⁺>Cu²⁺>Ag⁺>Ni²⁺>Zn²⁺, Pb²⁺>Co²⁺>Ag⁺>Ni²⁺>Zn²⁺ and Pb²⁺>Co²⁺>Ni²⁺>Zn²⁺>Cd²⁺>Ag⁺, respectively. The transport rate of the metal cations in chloroform–nitrobenzene binary solvents is sensitive to the solvent composition. The transport processes were studied in absence and presence of the stearic acid and the results show that the sequence of selectivities and ion transport rates change in the presence of stearic acid.     

Study of Complex Formation Between Dicyclohexano-18-Crown-6 (DCH18C6) with Mg 2+, Ca2+, Sr 2+, and Ba2+ Cations in Methanol–Water Binary Mixtures Using Conductometric Method

The complexation reactions between Mg²⁺,Ca²⁺,Sr²⁺ and Ba²⁺ metal cations with macrocyclic ligand, dicyclohexano-18-crown-6 (DCH18C6) were studied in methanol (MeOH)–water (H₂O) binary mixtures at different temperatures using conductometric method . In all cases, DCH18C6 forms 1:1 complexes with these metal cations. The values of stability constants of complexes which were obtained from conductometric data show that the stability of complexes is affected by the nature and composition of the mixed solvents. While the variation of stability constants of DCH18C6-Sr ²⁺ and DCH18C6-Ba²⁺versus the composition of MeOH–H₂O mixed solvents is monotonic, an anomalous behavior was observed for variations of stability constants of DCH18C6-Mg²⁺ and DCH18C6-Ca²⁺ versus the composition of the mixed solvents. The values of thermodynamic parameters (ΔH_c°, ΔS_c°) for complexation reactions were obtained from temperature dependence of formation constants of complexes using the van’t Hoff plots. The results show that in most cases, the complexation reactions are enthalpy stabilized but entropy destabilized and the values of thermodynamic parameters are influenced by the nature and composition of the mixed solvents. The obtained results show that the order of selectivity of DCH18C6 ligand for metal cations in different concentrations of methanol in MeOH–H₂O binary system is: Ba²⁺>Sr²⁺>Ca²⁺> Mg²⁺.     

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.     

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.     

A Thermodynamic Study Between 18-Crown-6 with Mg2+, Ca2+, Sr2+and Ba2+ Cations in Water–Methanol and Water–Ethanol Binary Mixtures Using The Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations with the macrocyclic ligand, 18-Crown-6 (l8C6) in water–methanol (MeOH) binary systems as well as the complexation reactions between Ca²⁺ and Sr²⁺ cations with 18C6 in water–ethanol (EtOH) binary mixtures have been studied at different temperatures using conductometric method. The conductance data show that the stoichiometry of all the complexes is 1:1. It was found that the stability of 18C6 complexes with Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations is sensitive to solvent composition and in all cases, a non-linear behaviour was observed for the variation of log K _f of the complexes versus the composition of the mixed solvents. In some cases, the stability order is changed with changing the composition of the mixed solvents. The selectivity order of 18C6 for the metal cations in pure methanol is: Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺. The values of thermodynamic parameters (Δ H _c ° and Δ S _c °) for formation of 18C6–Mg²⁺, 18C6–Ca²⁺, 18C6–Sr²⁺ and 18C6–Ba²⁺complexes were obtained from temperature dependence of the stability constants. The obtained results show that the values of (Δ H _c ° and Δ S _c °) for formation of these complexes are quite sensitive to the nature and composition of the mixed solvent, but they do not vary monotonically with the solvent composition.This revised version was published online in July 2005 with a corrected issue number.     

Complex Formation of 1,10-Dibenzyl-1,10-diaza-18-crown-6 with Ni2+, Cu2+, Ag+ and Cd2+ Metal Cations in Acetonitrile–dimethylformamide Binary Solutions

Conductance measurements are reported for nickel(II), cupper(II), silver(I) and cadmium(II), salts in acetonitrile (AN)–dimethylformamide (DMF) binary solvents containing macrocyclic ligand, 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBDA18C6) at different temperatures. The changes in molar conductance caused by addition of DBDA18C6 to solutions were analyzed by non-linear least squares to give stability constants of 1:1 metal cation–DBDA18C6 complexes. The results show that the stabilities of the complexes are sensitive to solvent composition and in some cases the sequence of stabilities is changed with changing the composition of the mixed solvents. The values of thermodynamic quantities (ΔH°c and ΔS°c) for formation of DBDA18C6-Ni²⁺, DBDA18C6-Cu²⁺, DBDA18C6-Ag⁺ and DBDA18C6-Cd²⁺ complexes were obtained from temperature dependence of the stability constants and the results show that the values of ΔH°c and ΔS°c for these complexes are sensitive to the nature and composition of AN–DMF binary solutions, but they do not vary monotonically with the solvent composition.     

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⁺.     

Inhibition of Na+, K+-ATPase in the presence of crown ethers: modulation of ionic composition or pharmacological effects

It is believed that the biological effects of chelating agents such as crown ethers are largely related to their ability to form complexes with ions and/or to facilitate ion transport across membranes. Specific influences are rarely related. Here we present the evidence that even one of the simplest representatives of the crown ether super-family, 1,4,7,10,13,16-hexaoxacyclooctane (18-crown-6), is able to affect the activity of Na⁺, K⁺-ATPase directly. Using nonlinear regression fitting to kinetic data we have found that the crown ether diminishes the apparent Michaelis constant, K _m , and the maximal rate of ATP hydrolysis, V _m , acting as noncompetitive inhibitors. The apparent dissociation constants, K _i , for the crown interaction with the free ATPase and with the enzyme-substrate complex were established to be of 77 ± 3 mM and 21 ± 2 mM, respectively. So 18-crown-6 possesses weak but “direct” pharmacological activity on Na⁺, K⁺-ATPase hinders the formation of enzyme–substrate complex and detains the enzyme in this state.     

Study of Complex Formation between N-Phenylaza-15-Crown-5 with Mg2+, Ca2+, Ag+ and Cd2+ Metal Cations in Some Binary Mixed Aqueous and Non-aqueous Solvents using the Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ metal cations with N-phenylaza-15-crown-5 (Ph-N15C5) were studied in acetonitrile (AN)–methanol (MeOH), methanol (MeOH)–water (H₂O) and propanol (PrOH)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry of all of the complexes with Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ cations is 1:1 (L:M). The stability of the complexes is sensitive to the solvent composition and a non-linear behaviour was observed for variation of log K _f of the complexes versus the composition of the binary mixed solvents. The selectivity order of Ph-N15C5 for the metal cations in neat MeOH is Ag⁺>Cd²⁺>Ca²⁺>Mg²⁺, but in the case of neat AN is Ca²⁺>Cd²⁺>Mg²⁺>Ag⁺. The values of thermodynamic parameters (ΔH _c ^o , ΔS _c ^o ) for formation of Ph-N15C5–Mg²⁺, Ph-N15C5–Ca²⁺, Ph-N15C5–Ag⁺ and Ph-N15C5–Cd²⁺ complexes were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

Synthesis and complexation properties of photochromic benzochromenes containing aza-and diaza-18-crown-6-ether fragments

Complex formation of Mg²⁺, Ba²⁺, and Pb²⁺ perchlorates with 3,3-diphenyl-3H-benzo[f]chromenes containing aza-and diaza-18-crown-6-ether or morpholine fragments was studied. The strong influence of the metal cations on the spectral characteristics of these organic ligands and on the kinetic of photochromic transformations was found. The results obtained were explained by the formation of carbonyl-“ capped” complexes of various structures. Faculte des Sciences de Luminy, Universite de la Mediterranee, UMR 6114 CNRS, 13288 Marseille, France. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 280—287, February, 2006.     

Crown ether styryl dyes

A novel styryl dye containing benzodithia-18-crown-6 andN-(4-sulfobutyl)benzothiazolium fragments was synthesized. The complex formation of thecis-isomers of several photochromic styryl dyes containing dithia-15(18)-crown-5(6) fragments with Hg²⁺ and Mg²⁺ ions was studied. The stability constants of the complexes with Mg²⁺ and the relative stability constants of the complexes with Hg²⁺ (with respect to benzo-1,10-dithia-18-crown-6 ether) were measured. The fact that the stability constant increases 11-fold on going from thetrans- to the correspondingcis-isomer was attributed to the formation of an anion-“capped” complex. For Part 22, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2213–2220, December, 1997.     

Transport of silver ion through bulk liquid membrane using macrocyclic and acyclic ligands as carriers in organic solvents

The bulk liquid membrane transport of silver (I) ion was studied by dibenzopyridino-18-crown-6(DBPY18C6), 4-nitrobenzo-15-crown-5(NB15C5), 2-aminothiaphenol and a new synthesized ligand, 1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as carriers in nitrobenzene (NB). The effects of pH on the source phase and receiving phase, the nature and concentration of stripping agents in the receiving phase and the picrate concentration as counter ion in source phase were investigated. The results show that the efficiency of transport of the Ag⁺ ion through membranes, changes with the nature of the ligand. The efficiency transport increases for the ligands with donating nitrogen and sulfur atoms with respect to oxygen donor atoms. Maximum transport efficiency was observed for silver (I) ion in the presence of thiosulfate ion ( ) as a suitable stripping agent. The results show that the sequence of transport efficiency for Ag⁺ ion using DBPY18C6, NB15C5, 2-aminothiaphenol and 1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as carriers in organic solvents is: nitrobenzene > dichloromethane > 1,2- dichloroethane > chloroform.     

Poly(vinyl chloride)-membrane ion-selective bulk optode based on 1,10-dibenzyl-1,10-diaza-18-crown-6 and 1-(2-pyridylazo)-2-naphthol for Cu and Pb ions

An ion-selective bulk optode (ISBO) for sensing Cu²⁺ and Pb²⁺ ions based on plasticized poly(vinyl chloride) containing 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBzDA18C6) as ionophore and 1-(2-pyridylazo)-2-naphthol (PAN) as chromoionophore was prepared. The effects of DBzDA18C6/PAN and NaTPB/PAN mole ratios on the response behavior of the ISBO were investigated. The ISBO membrane shows enhanced selectivities for Cu²⁺ (at 530 nm) and Pb²⁺ (at 467 nm) over alkali, alkaline earth and other transition metal ions. The optical selectivity coefficients were measured using the separate solution method (SSM) in the two corresponding wavelengths at pH=5. The detection limit for Cu²⁺ and Pb²⁺ are 3.2×10⁻⁷ and 1.0×10⁻⁸ M, respectively.     

Specific Uphill Transport of Zinc as Zn(SCN)42− Ion using Na+-Dicyclohexyl-18-Crown-6 as Carrier

Sodium-dicyclohexyl- 18-crown-6 complex cation was used as carrier for the uphill transport of zinc as Zn(SCN)₄^2? complex anion. By using L-cysteine as a metal ion acceptor in the receiving phase at the optimized pH of 7.6, the amount of zinc transport through the liquid membrane after 90 min was 97.2 ± 1.0%. The selectivity and efficiency of zinc transport from aqueous solutions containing equimolar mixtures of Ag⁺, Cd²⁺ Co²⁺, Cu²⁺, Fe²⁺, Ni²⁺, Pb²⁺, Pd²⁺, Sr²⁺, Bi³⁺, Cr³⁺ and Fe³⁺ ions was investigated. In the presence of NH₂OH.HCl as a suitable masking agent in the source phase, the interfering effect of Cu²⁺ and Pb²⁺ ions was diminished drastically.     

Photoinduced recoordination in the complexes of bis-aza-18-crown-6-containing dibenzylidenecyclobutanone with alkali and alkaline-earth metal cations

Complexation with strong competitors (i.e., Ba²⁺, Ca²⁺, and K⁺) shortens the length of the chromophore in bis-aza-18-crown-6-containing dienones of 2,4-dibenzylenecyclo-butanone series due to the weakening of π–LP conjugation as well as disruption of the quinonoid structure in the ground state of the dye (LP is the lone electron pair of the crown nitrogen atom). In the excited state, recoordination of metal cations in the crown cavity takes place. The complexation as well as the newly discovered photorecoordination in these metal complexes may be used to control the chromophore properties of the samples.     

Synthesis and characterization of trans-di(nitrobenzo)- and di(aminobenzo)-18-crown-6 derivatives with high selectivity

The dibenzo-18-crown-6 derivatives such as di(nitrobenzo)-18-crown-6 and di(aminobenzo)-18-crown-6 were synthesized by nitration reaction and catalytic hydrogenation with high selectivity. The chemical structures were determined by FTIR, ¹H NMR, ¹³C NMR, and UV. Regarding the mixture of Ac₂O and HNO₃ as nitrating agent, the reaction exhibited commendable trans-isomer selectivity. Effects of nitrating agent ratio, reaction temperature and reaction time on yield of trans-di(nitrobenzo)-18-crown-6 were investigated. The yield of trans-di(nitrobenzo)-18-crown-6 was 62.9% for nitrating agent ratio of 1/1, reaction temperature of 50?°C and reaction time of 5?h. Moreover, effect of reaction time on trans-di(aminobenzo)-18-crown-6 was also studied.     

Stability constants of complexes formed by new Schiff-base lariat ethers derived from 4,13-diaza-18-crown-6 with Ag+, Pb2+, Cu2+ cations determined by competitive potentiometry

The stability of complexes formed by a series of Schiff-base lariat ethers, derived from 4,13-diaza-18-crown-6, 1 with Ag⁺, Pb²⁺, Cu²⁺ cations, has been comparatively determined, in methanol: dichloromethane solution. We present here the synthesis and an interesting competitive potentiometry method useful for the stability constant determination for a new family of Schiff-base bibracchial lariat ethers. The stability constants and the selectivity in competitive complexation of Ag⁺, Pb²⁺ and Cu²⁺ cations by macrocyclic receptors 1–7 (L), can be accurately evaluated and species distribution diagrams can be calculated for individual system. In all cases further functionalization of bibracchial lariat ethers 2–7 is accompanied by an increasing of the selectivity, relative to the complexes of the initial 4,13-diaza-18-crown-6 macrocycle 1.     

A Proton NMR Study of the Stoichiometry and Stability of 18-Crown-6 Complexes with K+, Rb+ and Tl+ Ions in Binary Dimethyl Sulfoxide-Nitrobenzene Mixtures

Proton NMR spectroscopy was used to study the complexation reaction of 18-crown-6 (18C6) with K⁺, Rb⁺ and Tl⁺ ions in a number of binary dimethyl sulfoxide-nitrobenzene mixtures. In all cases, the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average ¹H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of dimethyl sulfoxide in the mixed solvent. It was found that, in all solvent mixtures used, Rb⁺ ion forms the most stable complex with 18-crown-6 in the series.     

Cation effect on anion separations by aza-crown ligands in liquid membranes

New carriers have been prepared based on the aza-18-crown-6 structure to facilitate membrane transport of ions. One of these incorporates four aza-18-crown-6 molecules bonded to a resorcinarene ring. The other, aza-18-crown-6 bonded to an undecyl chain, was studied as a monomeric analog. These carriers have been included in dichloromethane bulk liquid membranes (BLMs) to assess cation influence on competitive transport among anions (ReO₄⁻, NO₃⁻, ClO₄⁻). ReO₄⁻ was investigated as a non-radioactive analog of the pertechnetate anion, which is of interest in nuclear waste separations. The permeability values and selectivity for ReO₄⁻ and ClO₄⁻ were the greatest when neutral source and receiving phases were used with K⁺ as the co-transported cation. The carriers also showed selectivity for ReO₄⁻ and ClO₄⁻ over NO₃⁻ with K⁺ and Na⁺ as the co-transported cations using neutral and basic aqueous phase solutions. It was also found that some cations inhibit anion transport.