Membrane Transport Experiments Research Articles

Metal ion recognition. Selective interaction of silver(i) with tri-linked N2S2-donor macrocycles and their single-ring analogues

The interaction of four tri-linked N2S2-donor macrocyclic ligands and their single ring analogues with silver(I) has been investigated. The 3 ∶ 1 (metal ∶ ligand) stoichiometries of the silver(I) complexes of the tri-linked species in dimethyl sulfoxide-d6/CDCl3 were confirmed by means of NMR titrations involving the incremental addition of silver(I) nitrate to the respective ligands in the above solvent mixture and following the corresponding induced shifts in the 1H NMR spectrum. Solid 3 ∶ 1 (metal ∶ ligand) complexes were isolated for each of the parent (unsubstituted) tri-linked ligands. Competitive solvent extraction experiments (water/chloroform) and related bulk membrane transport (water/chloroform/water) experiments have been performed in which each of the four tri-linked ligands as well as their single ring analogues were employed as the extractant/ionophore in the chloroform phase. In both sets of experiments the respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) nitrates. For membrane transport the aqueous receiving phase was buffered at pH 3. Under the conditions employed, both the solvent extraction and the bulk membrane transport experiments resulted in high extraction/transport selectivity for silver(I) relative to the other six metal ions present.

P-tert-Butyldihomooxacalix(4)arene/p-tert-Butylcalix(4)arene: Transition and Heavy Metal Cation Extraction and Transport Studies by Ketone and Ester Derivatives

The binding properties of two phenylketones (2a and 3a) and two ethylesters (2b and {3b) derived from p-tert-butyldihomooxacalix[4]arene or from p-tert-butylcalix[4]arene, in the cone conformation, towards transition (Ag+, Ni2+, Cu2+, Co2+, Zn2+, Fe2+ and Mn2+) and heavy (Cd2+, Hg2+ and Pb2+) metal cations have been determined by extraction studies with metal picrates and liquid membrane transport experiments with the same salts. The affinity of these ligands for Ag+ has also been investigated by 1H NMR spectroscopy. Both ketones are better extractants than the esters, and show a strong preference for Ag+, while Cu2+ is the most extracted cation with the esters. 1H NMR titrations with AgSO3CF3 indicate 1 : 1 complexes for all ligands, those with ketones are more stable, on the NMR time scale, than those with esters. Both esters are good carriers for Ag+, and 2b exhibits the highest transport rate (4.7 μmol h-1) found until now with dihomooxacalix[4]arene derivatives.

Cyclic and acyclic S 2O 2 donor-type ionophores. Ion-pair extraction and transport of Ag(I) picrate, and X-ray confirmation of existence of the ion-pair complex

Extraction and transport behaviors of isomeric oxathia macrocycles ( L 2 , ortho-; L 3 , meta- and L 4 , para-isomer) and their structure related open-chain compound ( L 1 ) towards Ag(I) picrate have been examined. From the plot of log ( D Ag(I)/[pic −]) vs. log [ L] 0 for all of the ionophores were linear with slope near unity, thereby confirming the 1:1:1 complex formations of Ag(I)/ligand/picrate ion to be extracted into the dichloromethane phase. The extractability of an acyclic ionophore was superior to those of the corresponding cyclic ones. In membrane transport experiments, the slow rate of release of Ag(I) from the membrane into the receiving phase seems to be responsible for lower transport efficiency. Upon addition of sodium thiosulfate as a stripping reagent in receiving phase, the efficiency of transport is significantly enhanced in the order of L 1 (acyclic)> L 2 ( ortho-)> L 3 ( meta-)> L 4 ( para-) in accordance with those of log K ex values. It is hypothesized that the ion-pair complexation of L 1 in extraction step would be more favorable in extraction and transport of Ag(I). Its structure have been confirmed by X-ray diffraction analysis of [Ag( L 1 )pic], where L 1 =1,10-bis(mercaptobenzylyl)-4,7-dioxadecane.

Concave carrier molecules: selective transport of copper(II) and lead(II) nitrates through supported liquid membranes

Concave 1,10-phenanthrolines 1 are selective and efficient carrier molecules for membrane transport of copper(II) and lead(II) ions. With competitive membrane transport experiments the selectivity patterns of three concave 1,10-phenanthroline membrane carriers have been determined. Measurements with copper(II) and lead(II) nitrates confirmed the predicted selectivities and revealed high transport rates for 1a and 1b. While 1b shows a high preference for copper(II) nitrate, 1a transports lead and copper nitrates equally well, but with much higher flux. In bulk liquid membranes, the carrier mediated ion flux remained constant over an extended period, whereas it decreased significantly in reused supported liquid membranes, which indicates rapid loss of carrier from the membrane under these conditions.

Solubilities of some recently synthesized 1,8-dihydroxy-9,10-anthraquinone derivatives in supercritical carbon dioxide

The solubility of four recently synthesized 1,8-dihydroxy-9,10-anthraquinone derivatives, as potential complexing agents in some extraction and membrane transport experiments, have been measured in supercritical carbon dioxide. The measurements were carried out in the pressure range 120–400 atm at temperatures 35, 45, 55, 65, and 75 °C. The measured solubilities were correlated using the model proposed by Chrastil. The calculated results show good agreement with the experimental data.

New Macrocyclic Ligands. VIII Di- and Tri-linked Macrocyclic Systems Incorporating N2O2-Donor Atoms

The synthesis and characterization of new lipophilic di- and tri-linked O2N2-donor macrocycles is reported. The synthesis of the dilinked species involved the initial alkylation of one secondary nitrogen of the parent 15-membered, O2N2-donor macrocycle (1) with 2-bromoethanol or with ethylene oxide to yield (2), followed by protection of the appended alcohol group by reaction with t-butyldiphenylsilyl chloride to give (3). Two such moieties were then bridged via a diacylation reaction with ClCO(CH2)8COCl to yield the corresponding diamide product (4). Deprotection of the alcohol functions followed by reduction of the both amide linkages resulted in formation of theN,N′-alkyl-linked species (5) incorporating two pendant hydroxyethyl groups. This product was then converted [via the corresponding dichloro derivative (6)] into the diether (7) by condensation with 4-t-butylphenol. By use of analogous chemistry, the trilinked trismacrocycle species (12), based on a phloroglucinol core, has also been synthesized. An aim of the present study was thus the preparation of new ‘linked’ macrocyclic systems that might be expected to show higher lipophilicity than their corresponding single-ring systems. These were designed for future use as ionophores in metal ion membrane transport (and solvent extraction) experiments.

Chiral Discrimination of Amino Acids by an Optically Active Crown Ether Studied by HPLC, Extraction and a Liquid Membrane Transport Experiments

A chiral crown ether incorporating a methyl α-d-mannopyranoside unit displayed pronounced enantioselection of amino acids in partition liquid chromatography experiments involving solvent systems of limited miscibility: water–ethanol–2,2,4-trimethylpentane. The same system has been used for amino acid transport across a liquid membrane containing the crown ether, and in liquid–liquid extraction experiments. Remarkable enantioselection has been noted for amino acids in all the processes studied.

Phosphoryl containing podands as carriers in plasticized membrane electrodes selective to quaternary ammonium surfactants

Open chain polyethers with phosphoryl-containing terminal groups have been studied as carriers in plasticized membrane electrodes that are selective towards cationic surfactants. Host–guest complexation has also been studied by means of batch extraction and bulk membrane transport experiments. For the various guests, the bulk membrane (chloroform) transport rate decreases in the series tetraalkyl ammonium > alkyl pyridinium > alkyl ammonium, while the series of solvent extraction efficiency is exactly opposite; an explanation for this behaviour is proposed. The performance of electrode membranes follows the series for bulk membrane transport. Among the ISE membranes of various composition, one containing the longest (seven oxygen atoms) podand, o-nitrophenyl octyl ether (plasticizer), and sodium tetraphenyl borate (anionic additive) performs the best. The slope of the electrode function equals 58.5 mV/decade, the detection limit for dodecyltrimethylammonium is 3.2 × 10-6 M. ISE response time is 5–10 s, the working pH range is 2–11 and lifetime is at least 6 months. The electrode selectivity is significantly better than that of conventional ion-association and crown ether based electrodes.

Micellar and microemulsion systems to perform heterogeneous reactions, biphasic extraction and solute transport

This paper is reviewing recent developments in the field of applications of self-organized systems (essentially micelles and microemulsions) for the modelling of heterogeneous biphasic reactions, the pseudo-biphasic extraction of metal ions and the use of micellar particles as transfer agents. All these processes are related to the solubilizing properties of micelles which are governed by the free energy of association of the solutes considered. Stopped-flow kinetic results are used to demonstrate the relation between the rate of metal/extractant complex formation in these systems and the partitioning of the reagents. A discrimination between the possible mechanisms involved (interface or bulk aqueous phase) is shown to be possible in some cases. The practical removal of metal ions using micellar extraction coupled with ultrafiltration is examined from both a thermodynamic and a kinetic point of view, in relation with the preceding observations. In a second part we consider the use of micellar particles as carrier agents in liquid membrane transport experiments which demonstrate a strong analogy with the “facilitated diffusion” of solutes classically observed with macrocyclic carriers. The factors affecting the transfer rates and the nature of the interfacial transfer mechanisms are discussed. The final part briefly examines the future of micellar processes and suggests some directions for further investigations.

Head-to-Head Linked Double Calix[4]arenes: Convenient Synthesis and Complexation Properties.

Combination of calix[4]arenes functionalized at the upper rim at the 5- and 17-positions with amino and formyl groups, respectively, gives a new series of "head-to-head" linked double calix[4]arenes in nearly quantitative yield. The X-ray structure of a modified double calix[4]arene is reported. The novel, highly preorganized receptor molecules complex silver(I) ions (K(ass) = 9.5 x 10(5) M(-)(1) in CDCl(3)); the selectivity of complexation was studied by supported liquid membrane transport experiments and chemically modified field effect transistor measurements.

Uranyl UO2-salenes: neutral receptors for anions with a high selectivity for dihydrogen phosphate

The design and synthesis of neutral macrocyclic receptors that complex cations in apolar solvents with a high degree selectivity are based on the ability to organize nucleophilic binding sites (Lewis bases) in a complementary array. Although macrocycles with quaternary ammonium salts are known to complex anions, selectivity is not simply introduced. Macrocyclic and acyclic ligands that contain Lewis acidic binding sites such as boron, silicon, tin, and mercury bind anions, but these structures lack the possibility of subtle structural variation that is the basis for the selectivity in cation complexation. In this communication we report a novel class of neutral receptors for anions that contain an immobilized Lewis acidic binding site (UO{sub 2}){sup 2+} and in which there are ample opportunities to introduce specific secondary binding sites. This concept leads to high thermodynamic stabilities combined with high selectivities. Neutral anion receptors are very important for application in sensors and membrane transport experiments. This unique combination of a Lewis acidic uranyl center and the presence of amide NH groups which can form a favorable H-bond with a coordinated anion guest, in a preorganized receptor, can lead to highly specific anion recognition. 20 refs., 2 figs., 1 tab.

Pseudo cyclic ionophores: ?Binary-effect? of quinolinyloxy groups at both ends of oligoethylene glycols on the conformational stabilization of their complexes with alkali metal salts

A series of noncyclic neutral ionophores has been synthesized by the reaction of oligoethylene glycol dihalides with 8-quinolinol. Complexation properties for alkali metal picrates were evaluated from solvent extraction and bulk liquid membrane transport experiments. Complexation profiles of the newly synthesized ionophores with a hexyl chain were similar to those of their homologues without the hexyl chain in the extraction experiments. Among them, the pentaethylene glycol derivatives showed the highest extraction efficiency and selectivity towards potassium ion. From the1H NMR spectra (400 MHz), the change in chemical shifts of the aromatic protons upon the addition of alkali metal thiocyanates suggested the existence of a stabilization effect which is caused by intramolecular stacking conformations between the quinoline rings during complexation. Aryl stacking interactions depend on the size of the cations and on the chain length of the oligoethylene glycol. The relationship between transport ability towards alkali metal cations and lipophilicity of these ionophores is also discussed.

A modified method for the production of 36ClL 3− for use in plant nitrate transport studies

A modified method for the production and purification of 36ClO 3 − in high yield is described. This procedure, involving the electrolytic oxidation of 36Cl − in a cell with simple electrode design and purification of the electrolysis products ( 36Cl −, 36ClO 3 −, and 36ClO 4 −) by aqueous column chromatography, allows for the recovery of about 80% of the initial radiolabel as 36ClO 3 −. The method is rapid and suitable for the production of this radiolabeled anion for use as a tracer analog for nitrate in plant membrane transport experiments.

Proton-assisted transport of amino acid and related polycarboxylate anions via polyammonium macrocycles

Anion-binding and transport properties of polyamine macrocycles have been examined by liquid–liquid extraction and liquid membrane transport experiments. Some lipophilic polyamine macrocycles showed excellent transport properties, especially for polycarboxylate anions, depending on their ring structure. Their anion-extraction and transport properties were significantly different from those of the quaternary ammonium cation-surfactant trioctylmethylammonium chloride, and the mechanism involves protonation of the macrocyclic nitrogen atoms.