Voltammetric determination of facilitated ion transfer across the water/1,2-dichloroethane interface

The facilitated transfer characteristics of Cd²⁺ ion by 4-morpholinoacetophenone-4-ethyl-3-thiosemicarbazone (MAPET) across water/1,2-dicholoroethane (1,2-DCE) interface and its electrochemical properties were investigated by voltammetric measurements. Cyclic voltammetry (CV) was employed to examine the transfer in the conditions of the ligand (organic phase) in excess and the obtained transfer peaks have reversible nature at different metal concentrations and scan rates. The dependence of the obtained half-wave transfer potential on MAPET concentration showed that the equilibrium is effectively displaced towards a 1: 3 (Cd²⁺: ligand) stoichiometry with an association constant of logβ ₃ ⁰ = 12.96 ± 0.09 for the Cd²⁺ ion, corresponding to the TIC/TID mechanism.     

Kinetics of facilitated proton transfer by polyether 18-crown-6 across the water-1,2-dichloroethane interface

The kinetics of facilitated proton transfer by polyether 18-crown-6 across the water-1,2-dichloroethane interface has been investigated by cyclic voltammetry and ac impedance. It was found that rate apparent constant is quite similar for the several concentrations of 18-crown-6 used in the experiments, the rate constant values (k _s ) were in the range: 0.028, 0.031, 0.027, and 0. 03 cm/s for 0.1, 0.15, 0.2, and 0.25 mM of 18-crown-6.A formal transfer potential of ₀ ^w_i ⁰= 0.01 V was found for the facilitated proton transfer by 18-crown-6 at the water-1,2-dichloroethane interface; this value remained constant in the range of concentration considered in this work. According to the kinetic results, an interfacial reaction between the proton and the polyether 18-crown-6 is discussed in which the polyether does not transfer into the aqueous phase, in the time scale of the experiments. As a consequence, it can be concluded that the solvation and desolvation of ligand and proton play an important role in the rate-determining step.From Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 206–212.Original English Text Copyright © 2005 by Velázquez-Manzanares, Amador-Hernández.This article was submitted by the authors in English.Part of this work was presented at XXV Congreso Latinoamericano de Qu#X00ED;mica in Cancun, Quintana Roo, Mexico, 2002.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Anion Complexation by Meso-Octamethylcalix[4]pyrrole in Aqueous Solution

The ligand calix[4]pyrrole is quite insoluble in aqueous solution. In the presence of NaCl, KCl, CsCl, NH₄Cl, CaCl₂, and CdCl₂, the solubility of calix[4]pyrrole linearly increases with the salt concentration. The ligand calix[4]pyrrole forms stable complexes with the chloride anion. All other halogen anions do not form complexes. The measurement of the amount of dissolved ligand allows the determination of the complex stabilities in aqueous solution. This experimental method is discussed in detail due to its general suitability to study the complexation reactions with nearly insoluble ligands.     

Synthesis and electrochemical properties of a novel calix[4]arene derivative for facilitated transfer of alkali metal ions across water/1,2-dichloroethane micro-interface

The alkali metal ion transfers facilitated by a novel calix[4]arene derivative (OPEC) across the water/1,2-dichloroethane (1,2-DCE) micro-interface supported at the tip of a micropipette were presented. The well-defined voltammetric behaviours except Cs⁺ was obtained by cyclic voltammetry and differential pulse voltammetry. The bulk concentration of metal ions was much higher than that of OPEC in the performed measurements. The diffusion coefficient of OPEC in the 1,2-DCE phase was calculated as 5.18 ± 0.70 × 10^? 6 cm² s^? 1. On the basis of the changes of the half-wave transfer potentials, the logarithms of the association constants having 1:1 ionophore–ion complex stoichiometry for Li⁺, Na⁺, K⁺ and Rb⁺ in 1,2-DCE were determined as 4.80, 4.62, 4.98 and 5.32, respectively. The facilitated ion transfers were also evaluated by the Randles equivalent circuit used for ac-impedance data analysis.     

Systematic study of the transfer of amino acids across the water/1,2-dichloroethane interface facilitated by dibenzo-18-crown-6

Facilitated ion transfer reactions of 20 amino acids with dibenzo-18-crown-6 (DB18C6) at the water/1,2-dichloroethane (W/DCE) interfaces supported at the tips of micro- and nano-pipets were investigated systematically using cyclic voltammetry. It was found that there were only 10 amino acids, that is, Leu, Val, lie, Phe, Trp, Met, Ala, Gly, Cys, Gin (in brief), whose protonated forms as cations can give well-defined facilitated ion transfer voltammograms within the potential window, and the reaction pathway was proven to be consistent with the transfer by interfacial complexation/dissociation (TIC/TID) mechanisms. The association constants of DB 18C6 with different amino acids in the DCE (β0), and the kinetic parameters of reaction were evaluated based on the steady-state voltammetry of micro- or nano-pipets, respectively. The experimental results demonstrated that the selectivity of complexation of protonated amino acid by DB18C6 compared with that of alkali metal cations was low, which can be attribu     

Electrochemical study of a dendritic family at the water/1,2-dichloroethane interface

The transfer of six dendritric molecules, DMs, across the water/1,2-dichloroethane interface was investigated using cyclic voltammetry. From the variation of peak potential with pH, two different mechanisms of transfer were postulated depending on the nature of the molecules. Voltammetric parameters were employed to evaluate the hydrophilic/hydrophobic character and calculate the acid dissociation constant of these molecules. The results were explained taking into account the nature and multiplicity of functional surface groups.     

Cyclo[2]carbazole[2]pyrrole: a preorganized calix[4]pyrrole analogue

A cyclo[2]carbazole[2]pyrrole (2) consisting of two carbazoles and two pyrroles has been synthesized by directly linking the carbazole 1- and 8-carbon atoms to the pyrrole α-carbon atoms. Macrocycle 2 is an extensively conjugated 16-membered macrocyclic ring that is fixed in a pseudo-1,3-alternate conformation. This provides a preorganized anion binding site consisting of two pyrrole subunits. ¹H NMR spectroscopic analysis revealed that only the two diagonally opposed pyrrole NH protons, as opposed to the carbazole protons, take part in anion binding. Nevertheless, cyclo[2]carbazole[2]pyrrole 2 binds representative anions with higher affinity in CD₂Cl₂ than calix[4]pyrrole (1), a well-studied non-conjugated tetrapyrrole macrocycle that binds anions via four pyrrolic NH hydrogen bond interactions. On the basis of computational studies, the higher chloride anion affinity of receptor 2 relative to 1 is rationalized in terms of a larger binding energy and a lower host strain energy associated with anion complexation. In the presence of excess fluoride or bicarbonate anions, compound 2 loses two pyrrolic NH protons to produce a stable dianionic macrocycle [2–2H]²⁻ displaying a quenched fluorescence.

Less is more: two NH hydrogen bond donors in a preorganized receptor provide greater anion affinity than the four NH moieties present in the classic anion receptor, calix[4]pyrrole.     

Anion complexation by calix[3]thieno[1]pyrrole: the medium effect

The interaction of calix[3]thieno[1]pyrrole, 1, and halide and dihydrogen phosphate anions in a variety of solvents (acetonitrile, propylene carbonate, N,N-dimethylformamide, and dimethyl sulfoxide) has been investigated through 1H NMR, conductance measurements, and titration calorimetry. 1H NMR measurements reveal the sites of interaction of the ligand with the anions in CD3CN while the composition of the complex was determined through conductance measurements. A quantitative assessment of anion-ligand interactions is provided. Thus the thermodynamics of complexation of 1 with halide and dihydrogen phosphate anions in dipolar aprotic media at 298.15 K is reported. These data are interpreted in terms of the thermodynamics of transfer of reactants and product from a reference solvent (acetonitrile) to other solvents. The crucial role played by the solvent on the ability of the ligand to interact with anions and on the composition of the complex is demonstrated.     

Mono Halogen Substituted Calix[4]pyrroles: Fine-tuning the Anion Binding Properties of Calix[4]pyrrole

Abstract

Single halogen atom (i. e. I, Br, Cl and F) substituted calix[4]pyrroles, compounds 2, 3, 4 and 5, were synthesized. Studies of these systems reveal that replacement of a single β-pyrrolic hydrogen atom can increase the anion binding ability of calix[4]pyrroles for a variety of anions (e. g. Cl^?, Br^?, H₂PO₄ ^? and HSO^? ₄) relative to normal non-halogen substituted calix[4]pyrrole 1. In the case of chloride anion, the expected relative affinity sequence of 5 > 4 > 3 > 2 was observed. This was not found to be true for Br^?, H²PO^? ₄, and HSO^? ₄. Here, the chlorine substituted calix[4]pyrrole 4 was found to display a slightly higher affinity in the case of each anion than the fluorine-bearing derivative 5. This was rationalized in terms of intermolecular NH … F hydrogen bonding interactions being present in CD₂Cl₂ solutions of 5. Support for this latter conclusion came from concentration and temperature-dependent NMR spectroscopic studies.

A matched set of mono halogen substituted calix[4]pyrroles was used to study in detail, the extent to which halogen substituents may be used to fine-tune the anion binding properties of calix[4]pyrroles.     

Photoinduced electron transfer of 5,10,15,20-tetraphenylporphyrinato zinc(II) at the polarized water/1,2-dichloroethane interface.

The photocurrent at the polarized water/1,2-dichloroethane (DCE) interface was successfully observed in the presence of a lipophilic sensitizer, 5,10,15,20-tetraphenylporphyrinato zinc (ZnTPP), in the organic phase. The photocurrent transient responses were apparently affected by the employed organic supporting electrolyte: tetrapenthylammonium tetraphenylborate (TPnATPB) or tris(tetraoctylammonium)tungstophosphate ((TOcA)3PW12O40). The photocurrent measured in the TPnATPB system exhibited rather slow responses associated with the ion transfer of photoproducts. On the other hand, the photoinduced heterogeneous electron transfer could be observed in the use of (TOcA)3PW12O40. The photocurrent intensity in the (TOcA)3PW12O40 system exhibited an apparent pH dependence and the photoreduction of hydrogen ions probably took place at the water/DCE interface. By analyzing the real and imaginary components of the photocurrent depending on the photoexcitation frequency, we roughly estimated the phenomenological rate constants of the product separation (k(ps)) and recombination (k(rec)) processes as log(k(ps)/s(-1)) = 1.5 +/- 0.2 and log(k(rec)/s(-1)) = 1.8 +/- 0.1, respectively.     

Electrochemical instability in the transfer of cationic surfactant across the 1,2-dichloroethane/water interface

The electrochemical instability has been shown to appear in the transfer of cationic surfactant ions across the 1,2-dichloroethane/water interface. Cyclic voltammograms possess all fundamental characteristics that are predicted by the theory of electrochemical instability: the presence of the instability window, that is, the potential range where the interface becomes unstable, the location of the instability window around the standard ion transfer potential of surface-active ions, and the dependence of the width of the instability window on the concentration of the surfactant ions. Electrocapillary measurements clearly demonstrate that the interface becomes unstable, while the interfacial tension is positive, being higher than 20 mN m(-1). The electrocapillary curve exhibits the discontinuities at both ends of the instability window, indicating the similarity between the electrochemical instability and the phase transitions induced by the temperature, pressure, and chemical potential. The results from voltammetry and interfacial tension measurements for cationic surfactants support the idea that the electrochemical instability, so far reported in the transfer of anionic surfactants across the liquid/liquid interface, is one of intrinsic properties of the two-phase systems where the partition of surface-active ions takes place.     

Potential-modulated fluorescence spectroscopy of the membrane potential-sensitive dye di-4-ANEPPS at the 1,2-dichloroethane/water interface

The spectrofluorometric behavior of a membrane potential-sensitive dye, 1-(3-sulfonatopropyl)-4-[β-{2-(di-N-butylamino)-6-naphthyl}vinyl]pyridinium betaine (di-4-ANEPPS), at the polarized 1,2-dichloroethane/water interface was studied by means of potential-modulated fluorescence (PMF) spectroscopy. The results, combined with those from cyclic and alternating current voltammetry, clearly suggested that the dye adsorbed at the interface underwent a reorientation with increasing the interfacial potential, giving a well-developed PMF response as well as a voltammetric response. In addition to the PMF response, another PMF response was observed by addition of dilauroyl phosphatidylcholine (DLPC). This additional response was well explained in terms of a reorientation of di-4-ANEPPS at the interface, which would be induced by the potential-dependent desorption of DLPC from the interface. Thus, the present study supported the reorientation/solvatochromic mechanism for the membrane potential-sensitive dye rather than the electrochromic mechanism.     

meso-Indanyl calix[4]pyrrole receptors

Two new meso-indanyl-substituted calix[4]pyrrole receptors, 2 and 3, have been synthesized. A range of calix[4]pyrrole host-neutral molecule complexes crystallise from solutions of 2 in a variety of solvents and the structures of four have been elucidated by X-ray crystallography. The F⁻ and Cl⁻ anion affinities of 2 have been measured in acetonitrile, and are significantly different from the corresponding affinities of the prototypical calix[4]pyrrole, the octamethyl-derivative, 1. ESI-FTICR-MS has been used to determine the relative F⁻ and Cl⁻ anion affinities of receptors 1 and 2 in methanol-acetonitrile solution. Deprotonation of 1 and 2 by fluoride is observed (under the conditions of the MS experiment).     

Pentapyrrolic calix[4]pyrrole

A new calix[4]pyrrole has been synthesised that contains a 3,4,5-trisbromopyrrole appended to a meso-position which shows enhanced anion affinity as compared to the parent meso-octamethylcalix[4]pyrrole macrocycle.     

杯[4]吡咯-阴离子体系相互作用的理论研究——杯[4]吡咯-卤素阴离子体系的密度泛函研究

用密度泛函B3LYP/LANL2DZ方法对自由杯[4]吡咯的最低能量构象和卤素阴离子-杯[4]吡咯复合物进行了计算研究.结果表明,杯[4]吡咯与卤素离子能通过彼此间的相互作用形成复合物,并且这种相互作用在本质上应为分子间的氢键相互作用;杯[4]吡咯与卤素阴离子形成的复合物在构型变化、电荷转移、前线轨道及其作用方式、成键布居以及能量和热力学参数等方面均按元素周期律有规律地变化,杯[4]吡咯与卤素阴离子间的相互作用沿元素周期依次减少.     

Interfacial behavior of sulforhodamine 101 at the polarized water/1,2-dichloroethane interface studied by spectroelectrochemical techniques

The transfer mechanism of an amphoteric rhodamine, sulforhodamine 101 (SR101), across the polarized water/1,2-dichloroethane (DCE) interface was investigated using cyclic voltammetry, differential voltfluorometry and potential-modulated fluorescence (PMF) spectroscopy. The voltammetric response for the ion transfer of SR101 monoanion from water to DCE was observed as the diffusion-controlled transfer process. An unusual voltammetric response was found at 0.15 V more negative than the formal transfer potential of SR101⁻ in the cyclic voltammogram and voltfluorogram. The frequency dependence of the PMF responses confirmed the presence of the adsorption processes at negative potentials. In addition, a further transient adsorption step was uncovered at The interfacial mechanism of SR101 is discussed by comparing the results obtained from each technique.     

The micro water/1,2-dichloroethane interface as a transducer for creatinine assay

Facilitated ammonium ion transfer reactions, using the crown ether dibenzo-18-crown-6, at a single microhole supported water/1,2-dichloroethane interface were used as the transducer to detect the biomolecule creatinine. The ammonium ion was produced during the enzymatic action of creatinine deiminase on creatinine. A prototype sensing device incorporating a Teflon gas permeable membrane, to exclude possible interferents, yielded a linear amperometric response to added creatinine from 20 M to 1 mM. This range is sufficient for that required for the determination of creatinine in serum.