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     

Hydrodynamic voltammetry at the liquid|liquid interface: facilitated ion transfer and the rotating diffusion cell

A new approach to the voltammetric investigation of facilitated ion transfer processes is reported. The technique uses a rotating diffusion cell approach to induce laminar flow in the organic phase of a liquid|liquid electrochemical cell. The interface between two immiscible electrolyte solutions (ITIES) was stabilised against rotation with either γ-alumina or a track-etched polyester membrane. The resultant voltammetry is shown to be consistent with the Koutecký–Levich equation enabling kinetic parameters associated with facilitated transfer of sodium by dibenzo-18-crown-6 across the water|1,2-dichloroethane interface to be evaluated. In particular, the use of the more hydrophilic alumina membrane permits the uncertainties regarding the use of the membrane-stabilised ITIES, namely the interfacial position, to be eliminated.     

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

Failitated 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, lle, Phe, Trp, Met, Ala, Gly, Cys, Gln (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 (β°), 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 attributed to the vicinal effect arising from steric hindrance introduced by their side group and the steric bulk effect by lipophilic stabilization. Moreover, the association constants and the standard rate constants for different amino acids showed good correlations with their hydrophobicity (π), except Gly and Met, which inferred that the selectivity of such heterogeneous complex reaction for different amino acids with DB18C6, was not only affected by discrimination in binding these ions to the crown ether macro-cycle, but also significantly modified by the ion transfer Gibbs energy which was closely related to the structure of the transferred ions, protonated amino acids.     

Electrochemical study of dopamine and noradrenaline at the water/1,6-dichlorohexane interface

Interfaces between two immiscible electrolyte solutions are recognized as a simplified model for biological systems and they can be of great relevance to the characterization of biomolecules and their role in biological systems. In this work, ion transfer and facilitated ion transfer of protonated catecholamines (dopamine and noradrenaline) by dibenzo-18-crown-6 are investigated at the water/1,6-dichlorohexane interface. The formation constant of the complex between both dopamine and noradrenaline with dibenzo-18-crown-6 was evaluated and the experimental conditions for the analytical determination of those catecholamines are established. These results can improve the understanding of the pharmacodynamics of the catecholamines, and contribute to the study of their interaction with biological membranes. Furthermore it can be used to develop an alternative method for the determination of neural signal transmission catecholamines.     

Electrochemical detection of dopamine using arrays of liquid-liquid micro-interfaces created within micromachined silicon membranes

The detection of protonated dopamine by differential pulse voltammetry (DPV) and square wave voltammetry (SWV) at arrays of micro-interfaces between two immiscible electrolyte solutions (μITIES) is presented. Microfabricated porous silicon membranes (consisting of eight pores, 26.6 μm in radius and 500 μm pore-pore separation, in a hexagonal layout) were prepared by photolithographic and etching procedures. The membrane pores were fabricated with hydrophobic internal walls so that the organic phase filled the pores and created the liquid interface at the aqueous side of the membrane. These were used for harnessing the benefits of three-dimensional diffusion to the interface and for interface stabilisation. The liquid-liquid interface provides a simple method to overcome the major problem in the voltammetric detection of dopamine at solid electrodes due to the co-existence of ascorbate at higher concentrations. Selectivity for dopamine over ascorbate was achieved by the use of dibenzo-18-crown-6 (DB18C6) for the facilitated ion transfer of dopamine across the μITIES array. Under these conditions, the presence of ascorbate in excess did not interfere in the detection of dopamine and the lowest concentration detectable was ca. 0.5 μM. In addition, the drawback of current signal saturation (non-linear increase of the peak current with the concentration of dopamine) observed at conventional (millimetre-sized) liquid-liquid interfaces was overcome using the microfabricated porous membranes.     

On the protonation of dibenzo-18-crown-6

Abstract  

The stability constant of the dibenzo-18-crown-6·H₃O⁺ cationic complex species dissolved in nitrobenzene saturated with water has been determined from extraction experiments in the two-phase water–nitrobenzene system and from γ-activity measurements. Various structures of protonated dibenzo-18-crown-6 are discussed.     

Facilitated Ion Transfer Across the Micro-liquid/Liquid Interface Supported at the Tip of a Silanized Micropipette

IntroductionIon transfer across a liquid/liquid( L/L) inter-face or an interface between two immiscible elec-trolyte solutions( ITIES) plays a significant role inmany biochemical fields and technological systemsfrom biological membrane and drug delivery to ex-traction process and chemical sensors[1] . Theminiaturization of ITIESwas firstachieved by Tay-lor and Girault via supporting the interface at thetip of a micropipette in1 986[2 ] .Later on a nano-ITIES supported at a nanopipette …     

Kinetics of Ion Transport by Macrocyclic Carriers in Liquid Membrane Systems

Abstract

The relationship between the extractability of a metal ion (K⁺ or Pb²⁺) and the rate of its transfer by neutral macrocyclic carriers (dibenzo-18-crown-6, dicyclo-hexano-18-crown-6, 18-crown-6, and polynactin) was investigated in chloroform membrane systems. The experimentally determined apparent rate constants are compatible with the diffusion-limited process. Both the rate of ion uptake and the rate of ion transport depend crucially on the extractability of the metal ion rather than on the apparent rate constant.     

Potentiometric study of complexation of phenylaza-15-crown-5, 4-nitrobenzo-15-crown-5 and dibenzopyridino-18-crown-6 and other derivative of 18-crowns-6 with Na+ ion in methanol

The complexation reaction of phenylaza-15-crown-5, and 4-nitrobenzo-15-crown-5, benzo-15-crown-5 and dibenzopyrdino-18-crwon-6, dibenzo-18-crown-6,dicyclohexyl-18-crown-6(cis and trans), and 18-crown-6 with Na⁺ ion in methanol have been studied by potentiometric method. The Na⁺ ion-selective electrode has been used both as indicator and reference electrode. The stoichiometry and stability constants of complexes of these crown ethers with sodium ion were evaluated by MINIQUAD program. The major trend of stability of resulting complexes of these macrocycle with Na⁺ ion varied in the order DCY18C6 > DB18C6 > 18C6 > DBPY18C6 > phenylaza-15C5 > benzo-15C5 > 4-nitrobenzo-15C5. The obtained results in particular stability constant of complexes of DBPY18C6, phenylaza-15C5 and 4-nitrobenzo-15C5 with sodium ion in comparison with other crowns ether are novel, and interesting.     

Solvation of the potassium ion complexed with dibenzo-30-crown-10. Transfer activity coefficients between methanol and various solvents

The stability constants of the potassium complex with dibenzo-30-crown-10 have been determined from potentiometric or solubility measurements in the solvents: methanol, iso-propanol, n-butanol, propylene carbonate, acetonitrile and dimethylsulfoxide. The solubility of the ligand in these solvents has also been determined and the transfer activity coefficients of the potassium complex for transfer from methanol to solvent (S), _SM(KL⁺), have been computed. Although solid state studies indicate that dibenzo-30-crown-10 completely surrounds the potassium ion and shields it from water, the transfer activity coefficient of the potassium complex is found to be highly solvent dependent. Dibenzo-30-crown-10 is thus less effective for the removal of the solvation sphere of the potassium ion than previously estimated.     

Studies on the Complexation of Transition Metal Ions with Macrocyclic Compounds in Mixed Solvents by Competitive Potentiometry and Polarography

Complexation of Cu(II), Zn(II), Ni(II), Co(II), Pb(II), Cd(II), Cr(III) and Fe(III) ions with 15-crown-5, benzo-15-crown-5, 18-crown-6, dibenzo-18-crown-6, dicyclohexano-18-crown-6, dibenzo-24-crown-8, 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene, 1,4,10-trioxa-7,13-diazacyclopentadecane and cyclam has been investigated in 75% (v/v) DMF+water using the silver(I) ion as an auxiliary cation at 0.05?M ionic strength adjusted with tetrabutylammonium perchlorate (TBAP) by competitive potentiometry. Stability constant values obtained for the metal ion–aza macrocyclic complexes are higher than those for the oxa crowns. Shifts in the peak potential and reduction in the peak current in the differential pulse polarography (DPP) method were also used to determine the stability constants of some of the metal ions with aza and tosylated-aza macrocycles using TBAP as supporting electrolyte in 75% (v/v) DMF+water and 90% (v/v) DMSO+water media. Stability constant values determined both by shifts in the potential and by reduction in the peak current were found to be in good agreement with each other.     

Nitration of Benzo Crown Ethers with Potassium Nitrate in Polyphosphoric Acid

A general method for the nitration of benzo crown ethers with potassium nitrate in polyphosphoric acid has been developed. Mono- and dinitro derivatives of benzo-12-crown-4, benzo-15-crown-5, dibenzo-18-crown-6, and dibenzo-24-crown-8 have been prepared. The role of complex formation in the regioselective tendency for the nitration of dibenzo-18-crown-6 has been demonstrated.     

Alkylation of benzo- and dibenzocrown ethers by various alcohols

New alkyl derivatives of benzo-15-crown-5, benzo-18-crown-6, dibenzo-18-crown-6, dibenzo-24-crown-8, and dibenzo-30-crown-10 have been obtained by their alkylation with various alcohols in the presence of polyphosphoric acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1461–1469, November, 1986.     

Enthalpies of solvation of macrocyclic ether of dibenzo-24-crown-8 in solvents of different polarity

Enthalpies of solution of dibenzo-24-crown-8 in tetrachlormethane, benzene, chloroform, pyridine, acetone, acetonitrile, DMF, DMSO and propylene carbonate have been determined by calorimetric method at 298.15 K. The changes in enthalpy of solute-solvent interaction for the transfer the ether from inert tetrachlormethane into various solvents have been calculated from the obtained data. The thermochemical characteristics obtained for dibenzo-24-crown-8 have been compared with similar ones for dibenzo-18-crown-6 having a smaller cycle size. It has been found that an exothermicity of solute-solvent interaction changes to a lesser extent for transfer of the larger cyclic ether into polar solvents. But the effect increases more sharply for the transfer to chloroform. It has been concluded that the contribution from electrostatic interaction with solvent decreases with an increase of the cycle size as result of the increasing structural flexibility and decreasing polarity of cycle. But the contribution from hydrogen bonding with chloroform becomes larger due to an increase in the number of donor atoms of the ether molecules. It was ascertained that the ability to bind specifically acetonitrile molecules disappears in going from 18-merous to 24-merous cycle.     

On the protonation of dibenzo-18-crown-6

Abstract  The stability constant of the dibenzo-18-crown-6·H₃O⁺ cationic complex species dissolved in nitrobenzene saturated with water has been determined from extraction experiments in the two-phase water–nitrobenzene system and from γ-activity measurements. Various structures of protonated dibenzo-18-crown-6 are discussed. Graphical abstract        

Electrochemical behaviour of pyridoxine hydrochloride (vitamin B6) at carbon paste electrode modified with crown ethers

The electrochemical behaviour of pyridoxine hydrochloride (pyridoxine HCl) at the plain carbon paste electrode and the electrode modified with oxa crown ether has been studied using voltammetric and impedance measurements. The macrocycles used as modifiers were 18-crown-6, dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 and dibenzo-24-crown-8, out of which DB18C6 gave better response for pyridoxine HCl. Tris buffer (pH 10.3) was chosen as an appropriate medium among the several supporting electrolytes of varying pH studied. The characterization of the DB18C6-modified electrode (CME-DB18C6) using kinetic parameters such as number of electrons (n) and electron transfer coefficient (α) is studied by cyclic voltammetry. Electrochemical impedance spectroscopic measurements obtained confirm the current enhancement over the modified electrode. Analytical applications of this electrode have been studied for the determination of pyridoxine HCl. A sensitive linear working range of 0.6 to 100 μg cm⁻³ with a detection limit of 0.4 μg cm⁻³ by differential pulse voltammetry was observed for pyridoxine HCl on CME-DB18C6. However, on decreasing the scan rate to 5 mV s⁻¹, the detection limit lowered to 0.2 μg cm⁻³. Interference from some vitamins like thiamine hydrochloride, riboflavin, nicotinamide, para-aminobenzoic acid, cyanocobalamin, folic acid and d-biotin and amino acid l-tryptophan was studied, and simultaneously, riboflavin, thiamine hydrochloride and pyridoxine HCl were determined over the modified electrode, CME-DB18C6. The modified electrode is successfully used for the determination of pyridoxine HCl in multivitamin pharmaceutical preparations.     

Interfacial insights on the dibenzo-based crown ether assisted cesium extraction in [BMIM][Tf2N]–water binary system

The distribution coefficient of Cs is estimated using dibenzo-21-crown-7 (DB21C7) and di-benzo-18-crown-6 (DB18C6) in 1-butyl-3-methylimidazolium bis (trifluroromethanesulphonyl) imide (BMIMTF2N) ionic liquid by performing solvent extraction experiments. In addition, molecular dynamics studies on the extraction of cesium (Cs⁺) ion transfer from the aqueous phase to the BMIMTF2N phase is reported. The experimental findings gave a cesium distribution coefficient of 0.218 and 0.326, which agrees closely with the values of 0.2 and 0.5 obtained from MD simulation for the ionophores DB18C6 and DB21C7, respectively. Thus MD simulation may be helpful in screening the solvents prior to the experiments.

     

Sulfonation of 4′-acetyl-, 4′-(<Emphasis Type="Italic">tert</Emphasis>-butyl)-dibenzo-18-crown-6 and (dibenzo-18-crown-6)-4′-sulfonic acid with potassium sulfate in polyphosphoric acid

The sulfonation of monosubstituted derivatives of dibenzo-18-crown-6 with potassium sulfate in polyphosphoric acid has been carried out. Sulfonic acids with various functional groups in the second nucleus of dibenzo-18-crown-6 have been obtained. A qualitative comparison of the reactivity of the substrates gave information on the transfer of the electronic influence of a substituent through the macrocycles. The displacement of electron density in the benzene nuclei of the substrates and the products of sulfonation was assessed from the value of the displacement of the proton signals in the ¹H NMR spectra. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 370–375, March, 2009.     

Interaction between adrenaline and dibenzo-18-crown-6: Electrochemical,nuclear magnetic resonance,and theoretical study

The interaction between adrenaline (Ad) and dibenzo-18-crown-6 (DB18C6) was studied by cyclic voltammetry, nuclear magnetic resonance spectroscopy, and the theoretical calculations, respectively. The results show that DB18C6 will affect the electron transfer properties of Ad. DB18C6 can form stable supramolecular complexes with Ad through ion-dipole and hydrogen bond interactions.     

Spectral Properties of Extracted Complexes of MetalPicrates with Crown Ethers

The investigation on UV-visible spectra of species formed by extracting some metal picrates with benzo-15-crown-5(B15C5) and dibenzo-18-crown-6(DB18C6) verified that there are some interactions of picrate anion with K , Na and rare earth ions in loaded organic phase. By the study of the charge transfer band and absorption spectra of picrate anion, it can be determined whether an ion pair has been formed and either a 1 : 1 contact ion pair or a 1 : 2 crown-separated ion pair involved in organic phase can be distinguished for an ion-pair extraction.