Aqueous Source Phase Research Articles

Fluorinated Nonporous Adaptive Cages for the Efficient Removal of Perfluorooctanoic Acid from Aqueous Source Phases.

Per- and polyfluoroalkyl substances (PFAS) accumulate in water resources and pose serious environmental and health threats due to their nonbiodegradable nature and long environmental persistence times. Strategies for the efficient removal of PFAS from contaminated water are needed to address this concern. Here, we report a fluorinated nonporous adaptive crystalline cage (F-Cage 2) that exploits electrostatic interaction, hydrogen bonding, and F-F interactions to achieve the efficient removal of perfluorooctanoic acid (PFOA) from aqueous source phases. F-Cage 2 exhibits a high second-order kobs value of approximately 441,000 g mg-1 h-1 for PFOA and a maximum PFOA adsorption capacity of 45 mg g-1. F-Cage 2 can decrease PFOA concentrations from 1500 to 6 ng L-1 through three rounds of flow-through purification, conducted at a flow rate of 40 mL h-1. Elimination of PFOA from PFOA-loaded F-Cage 2 is readily achieved by rinsing with a mixture of MeOH and saturated NaCl. Heating at 80 °C under vacuum then makes F-Cage 2 ready for reuse, as demonstrated across five successive uptake and release cycles. This work thus highlights the potential utility of suitably designed nonporous adaptive crystals as platforms for PFAS remediation.

Ion pair extractant selective for LiCl and LiBr.

Improved methods for achieving the selective extraction of lithium salts from lithium sources, including rocky ores, salt-lake brines, and end-of-life lithium-ion batteries, could help address projected increases in the demand for lithium. Here, we report an ion pair receptor (2) capable of extracting LiCl and LiBr into an organic receiving phase both from the solid state and from aqueous solutions. Ion pair receptor 2 consists of a calix[4]pyrrole framework, which acts as an anion binding site, linked to a phenanthroline cation binding motif via ether linkages. Receptor 2 binds MgBr2 and CaCl2 with high selectivity over the corresponding lithium salts in a nonpolar aprotic solvent. The preference for Mg2+ and Ca2+ salts is reversed in polar protic media, allowing receptor 2 to complex LiCl and LiBr with high selectivity and affinity in organic media containing methanol or water. The effectiveness of receptor 2 as an extractant for LiCl and LiBr under liquid-liquid extraction (LLE) conditions was found to be enhanced by the presence of other potentially competitive salts in the aqueous source phase.

Diphenylpyrrole-Strapped Calix[4]pyrrole Extractant for the Fluoride and Chloride Anions.

The anion binding features of diphenylpyrrole-strapped calix[4]pyrrole 1 have been investigated by means of 1 H NMR spectroscopy and ITC (isothermal titration calorimetry), as well as single crystal X-ray diffraction analyses. Receptor 1 bearing an auxiliary pyrrolic NH donor and solubilizing phenyl groups on the strap was found to bind F- , Cl- , and Br- as their tetrabutylammonium salts with high affinity in DMSO-d6 . In addition, receptor 1 was found to extract the fluoride anion (as both its tetraethylammonium (TEA+ ) and tetrabutylammonium (TBA+ ) salts), as well as the chloride anion into chloroform-d from an aqueous source phase. Cation metathesis using TBAI or the use of a dual host approach involving crown ethers enabled receptor 1 to extract simple alkali metal fluoride or chloride salts from water. Quantitative binding of NaF by receptor 1 was observed in 20 % D2 O-DMSO-d6 allowing for the direct determination of the NaF concentration in an unknown sample.

Direct Extraction of Sodium Hydroxide by Calix[4]pyrrole-Based Ion-Pair Receptors.

Described in this work are calix[4]pyrrole-based ion-pair receptors, cis/trans-1 and cis/trans-2, designed for the extraction of sodium hydroxide. An X-ray diffraction analysis of a single crystal of the cis-1·NaOH isomer isolated from a mixture of cis/trans-1 revealed a unique dimeric supramolecular structure. An average dimer in toluene-d8 solution was inferred on the basis of diffusion-ordered spectroscopy (DOSY). Support for the proposed stoichiometry came from density functional theory (DFT) calculations. The structural stability of the dimeric cis-1·NaOH complex in toluene solution was further confirmed by ab initio molecular dynamics (AIMD) simulation with explicit representation of solvent. Under conditions of liquid-liquid extraction (LLE), purified receptors cis- and trans-2 were both found to remove NaOH from a pH 11.01 aqueous source phase into toluene with extraction efficiencies (E%) of 50-60% when used equimolar to NaOH. However, in all cases, precipitation was observed. Complexities associated with precipitation could be avoided by immobilization of the receptors onto a chemically inert poly(styrene) resin by means of solvent impregnation. The use of solvent-impregnated resins (SIRs) eliminated precipitation in solution while retaining the extraction efficiency toward NaOH. This allowed both the pH and salinity of the alkaline source phase to be lowered.

Utilizing a polymer containing squaramide-based ion pair receptors for salt extraction

Herein, we report a novel polymer containing synthetic squaramide-based ion pair receptors, which effectively capture and remove sulfate salts from aqueous source phases during liquid–liquid extraction. The monomer M1 was synthesized in a modular fashion, assuring acidity of the anion binding domain and allowing the receptor to be incorporated into the polymer chain and then tested in ion pair binding studies using UV–vis and NMR spectroscopy. After the incorporation of the monomer M1 into the polystyrene polymer chain, its solubility was improved, and a system was developed to selectively remove sulfate ions from systems similar to those naturally occurring in the environment, i.e. among mixtures with other salts. To identify the polymer's salt binding mechanism, additional solid–liquid extractions (SLE) were carried out, which were characterized using 1H NMR, thermal analyses (DSC and TGA) and Scanning Electron Microscopy (SEM).

PH and Design on n-Alkyl Alcohol Bulk Liquid Membranes for Improving Phenol Derivative Transport and Separation.

Regardless of the type of liquid membrane (LM) (Bulk Liquid Membranes (BLM), Supported Liquid Membranes (SLM) or Emulsion Liquid Membranes (ELM)), transport and separation of chemical species are conditioned by the operational (OP) and constructive design parameters (DP) of the permeation module. In the present study, the pH of the aqueous source phase (SP) and receiving phase (RP) of the proposed membrane system were selected as operational parameters. The mode of contacting the phases was chosen as the convective transport generator. The experiments used BLM-type membranes with spheres in free rotation as film contact elements of the aqueous phases with the membrane. The target chemical species were selected in the range of phenol derivatives (PD), 4–nitrophenol (NP), 2,4–dichlorophenol (DCP) and 2,4–dinitrophenol (DNP), all being substances of technical-economic and environmental interest. Due to their acid character, they allow the evaluation of the influence of pH as a determining operational parameter of transport and separation through a membrane consisting of n–octanol or n–decanol (n–AlcM). The comparative study performed for the transport of 4–nitrophenol (NP) showed that the module based on spheres (Ms) was more performant than the one with phase dispersion under the form of droplets (Md). The sphere material influenced the transport of 4–nitrophenol (NP). The transport module with glass spheres (Gl) was superior to the one using copper spheres (Cu), but especially with the one with steel spheres (St). In all the studied cases, the sphere-based module (Ms) had superior transport results compared to the module with droplets (Md). The extraction efficiency (EE) and the transport of 2,4–dichlorophenol (DCP) and 2,4–dinitrophenol (DNP), studied in the module with glass spheres, showed that the two phenolic derivatives could be separated by adjusting the pH of the source phase. At the acidic pH of the source phase (pH = 2), the two derivatives were extracted with good results (EE > 90%), while for pH values ranging from 4 to 6, they could be separated, with DCP having doubled separation efficiency compared to DNP. At a pH of 8 in the source phase, the extraction efficiency halved for both phenolic compounds.

Calix[4]pyrrole-based Crosslinked Polymer Networks for Highly Effective Iodine Adsorption from Water.

A series of calix[4]pyrrole-based crosslinked polymer networks designed for iodine capture is reported. These materials were prepared by Sonogashira coupling of α,α,α,α-tetra(4-alkynylphenyl)calix[4]pyrrole with bishalide building blocks with different electronic properties and molecular sizes. Despite their low Brunauer-Emmett-Teller surface areas, iodine vapor adsorption capacities of up to 3.38 g g-1 were seen, a finding ascribed to the presence of a large number of effective sorption sites including macrocyclic π-rich cavities, aryl units, and alkyne groups within the material. One particular system, C[4]P-BTP, was found to be highly effective at iodine capture from water (uptake capacity of 3.24 g g-1 from a concentrated aqueous KI/I2 solution at ambient temperature). Fast capture kinetics (kobs =7.814 g g-1 min-1 ) were seen. Flow-through adsorption experiments revealed that C[4]P-BTP is able to remove 93.2 % of iodine from an aqueous source phase at a flow rate of 1 mL min-1 .

Calix[4]pyrrole‐based Crosslinked Polymer Networks for Highly Effective Iodine Adsorption from Water

AbstractA series of calix[4]pyrrole‐based crosslinked polymer networks designed for iodine capture is reported. These materials were prepared by Sonogashira coupling of α,α,α,α‐tetra(4‐alkynylphenyl)calix[4]pyrrole with bishalide building blocks with different electronic properties and molecular sizes. Despite their low Brunauer–Emmett–Teller surface areas, iodine vapor adsorption capacities of up to 3.38 g g−1 were seen, a finding ascribed to the presence of a large number of effective sorption sites including macrocyclic π‐rich cavities, aryl units, and alkyne groups within the material. One particular system, C[4]P‐BTP, was found to be highly effective at iodine capture from water (uptake capacity of 3.24 g g−1 from a concentrated aqueous KI/I2 solution at ambient temperature). Fast capture kinetics (kobs=7.814 g g−1 min−1) were seen. Flow‐through adsorption experiments revealed that C[4]P‐BTP is able to remove 93.2 % of iodine from an aqueous source phase at a flow rate of 1 mL min−1.

Application of Plasticized Cellulose Triacetate Membranes for Recovery and Separation of Cerium(III) and Lanthanum(III)

Abstract This work explains the application of plasticized cellulose triacetate (CTA) membranes with Cyanex 272 di(2,4,4-(trimethylpentyl)phosphinic acid) and Cyanex 301 (di(2,4,4-trimethylpentyl)dithiophosphinic acid) as the ion carriers of lanthanum(III) and cerium(III). CTA is used as a support for the preparation of polymer inclusion membrane (PIM). This membrane separates the aqueous source phase containing metal ions and the receiving phase. 1M H2SO4 is applied as the receiving phase in this process. The separation properties of the plasticized membranes with Cyanex 272 and Cyanex 301 are compared. The results show that the transport of cerium(III) through PIM with Cyanex 272 is more efficient and selective than lanthanum(III).

Liquid-liquid extraction and facilitated membrane transport of Pb2+ using a lipophilic acridono-crown ether as carrier

Studies on liquid-liquid extraction and bulk liquid membrane (BLM) technique-based metal ion separation by a previously published Pb2+-selective acridono-18-crown-6 ether selector molecule were performed. The effects of the stirring speed, the quality of apolar organic membrane, the counterions of Pb2+, the pH of the aqueous phase, the concentration of the source phase, the concentration of the carrier in the BLM and the temperature on the Pb2+-separation were investigated. Moreover, the effects of the competitive inhibition due to the presence of Ag+, Ca2+, Co2+, Cu2+, K+, Mg2+, Na+ and Zn2+ as competing ions in a multicomponent aqueous source phase of different ion-concentrations were also studied. After a proper dilution of the multicomponent aqueous source phase, excellent Pb2+-selectivity was achieved without a significant reduction in the efficiency compared to the liquid membrane transport of single-component systems. Based on the BLM-cell studies the applied selector molecule proved to be suitable for the development of liquid membrane-based Pb2+-selective separation methods, which can be greatly aided by the analysis of the effects on the separation and by the optimization of the parameters of the process discussed here.

Selective determination of some beta-blockers in urine and plasma samples using continuous flow membrane microextraction coupled with high performance liquid chromatography

In this work, an efficient method termed as continuous flow membrane microextraction coupled with high performance liquid chromatography is introduced for a highly selective determination of metoprolol and propranolol in the biological samples. According to this method, an aqueous source phase of the analytes (donor phase, 10 mL) is circulated into an extraction cell, which is separated from an aqueous acceptor phase (100 μL) by a small piece of polypropylene membrane sheet whose pores are impregnated by an organic solvent (1-octanol, 15 μL). The analytes are extracted from the donor phase into the organic solvent. They are subsequently selectively back-extracted into the acceptor solution due to the pH gradient. The proposed method is very convenient and has the capability of being fully automated. It provides a good preconcentration and an excellent repeatability. The extractant is an aqueous phase, and by prevention of the extraction of macromolecules through the membrane, the developed method provides a high sample clean-up. In order to maximize the extraction efficiency, the influential parameters including the type of mediator solvent, pH values for the donor and acceptor solutions, extraction time, ionic strength, stirring rate, and volume of the acceptor solution are optimized. The calibration curves were obtained with a reasonable linearity (r2 = 0.999) in the range of 3–1000 ng mL−1. The limits of detection were 0.5 and 1.0 ng mL−1, and excellent relative standard deviations were obtained (between 3.2% and 4.0%). Finally, the reliability of the procedure is evaluated by determination of metoprolol and propranolol in the human urine and plasma samples, which indicates the suitability, sensitivity, and high sample clean-up of the proposed method.

Soft Materials Constructed Using Calix[4]pyrrole- and "Texas-Sized" Box-Based Anion Receptors.

Soft materials have received considerable attention from supramolecular chemists and material scientists alike. This interest reflects the advantages provided by their soft, flexible nature and the convenience of the molecular self-assembly that underlies their preparation. Common soft supramolecular materials include polymeric gels, supramolecular polymers, nanoaggregates, and membranes. Polymeric gels are solidlike networks of cross-linked polymer chains. Supramolecular polymers contain repeat units connected through reversible non-covalent bonds. Nanoaggregates are formed as a result of hydrophobic interactions involving amphiphilic building blocks. Because of the presence of non-covalent interactions, supramolecular soft materials typically display stimuli-responsive or adaptive features. Various macrocyclic hosts, such as cyclodextrins, crown ethers, calixarenes, cucurbiturils, and pillararenes, and many classic non-covalent interactions have been harnessed to construct supramolecular soft materials. Only recently has anion binding been used as the underlying recognition motif. Anions are ubiquitous in the natural world. Their importance has inspired efforts to achieve good anion binding and to exploit anion recognition in a number of fields, including extraction, transport, sensing, and catalysis. Most of this effort has involved the use of stand-alone anion receptors. On the other hand, soft materials with anion recognition features could lead to new macromolecular systems of interest in the context of many application areas. In this Account, we summarize the latest efforts from our laboratory to prepare supramolecular soft materials, including polymeric gels, supramolecular polymers, and nanoaggregates, with bona fide anion recognition features. Two anion receptor systems, namely, calix[4]pyrroles (C4Ps) and a tetraimidazolium macrocycle known as the "Texas-sized" molecular box (TxSB), have been used for this purpose. To date, TxSB-based hydrogels have been utilized to capture anions from water and for coded information applications; C4P-based organic polymeric gels have been used to extract dianions from aqueous source phases and for the on-site detection of chloride anions. Polymers containing C4P and TxSB anion recognition subunits typically display responsive features and can be modified through application of appropriately chosen external stimuli. For instance, nanoaggregates may be formed as a result of the hydrophobic interactions of C4P- and TxSB-based amphiphiles. The resulting aggregates were found to mimic the structural evolution of organelles and could be used as effective anion and ion pair extractants. This Account summarizes progress to date while underscoring potential opportunities associated with combining anion recognition and soft materials chemistry. The hope is to stimulate further advances in broad areas, including polymer science, supramolecular chemistry, biology, materials research, and information storage.

Studies on the macrocycle mediated transport of some metal cations through a bulk liquid membrane system using kryptofix 22

Competitive transport experiments involving Fe+3, Cr+3, Ni+2, Co+2, Ca+2, Mg+2 and K+ metal cations from an aqueous source phase through some organic membranes into an aqueous receiving phase have been carried out using 4,13-diaza-18-crown-6 (kryptofix 22) as an ionophore present in the organic membrane phase. Fluxes and selectivities for competitive of the metal cations transport across bulk liquid membranes have been determined. A good selectivity was observed for K+ cation by kryptofix 22 in 1,2-dichloroethane (1,2-DCE) membrane system. The sequence of selectivity for potassium ion in the organic solvents was found to be: 1,2-DCE > DCM (dichloromethane) >CHCl3. The transport of K+ cation was also studied in the DCM-1,2-DCE, CHCl3-1,2-DCE and CHCl3-DCM binary mixed solvents as membrane phase. A non-linear relationship was observed between the transport rate of K+ ion and the composition of these binary mixed solvents. The amount of K+ transported follows the trend: DCM-DCE > CHCl3-DCE > CHCl3-DCM in the bulk liquid membrane studies. Then, the selective transport of K+ cation through a DCM-1,2-DCE bulk liquid membrane was studied by kryptofix 22 as an efficient carrier. The highest transport efficiency was obtained by investigating the influence of different parameters such as the concentration of kryptofix 22 in the membrane phase, pH of the source and the receiving phases and the equilibrium time of the transport process. Maximum transport value of 71.62 ± 1.61% was observed for K+ ion after 4 hours, when its concentration was 4 × 10–3 M.

Selective transport of Cu(II) ions from a mixture of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Pb(II) cations through a bulk liquid membrane using benzyl bis(thiosemicarbazone) as carrier

A dichloromethane membrane system incorporated with benzyl bis(thiosemicarbazone) (LH2) as carrier is introduced for the selective transport of Cu(II) ion from an aqueous source solution containing Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Pb(II) metal cations to a receiving aqueous phase. The optimum transport conditions were established by studding the composition of receiving phase, time of transport, stirring rate, pH of source phase, presence of fatty acid in the membrane as a phase modifier, type and concentration of surfactant, and concentration of mineral acid in the receiving phase, carrier concentration, and temperature. A kinetic model was also used to describe the Cu(II) ion transport behavior, assuming that it obeys the kinetic laws of two consecutive irreversible first-order processes. Under the optimal conditions, 43% of the initial concentration of Cu(II) ion from the aqueous source phase was extracted into the receiving phase through the bulk liquid membrane.

Selective Separation of Silver(I) Ion Through a Bulk Liquid Membrane Containing 1,1'-(1,3-Phenylene)bis(3-allylthiourea) as Carrier

The competitive bulk liquid membrane transport of six metal cations from an aqueous source phase (SP) containing Ag+, Pb2+, Cu2+, Zn2+, Co2+ and Ni2+ through an organic membrane phase (MP) facilitated by 1,1'-(1,3-phenylene)bis(3-allylthiourea) as a carrier into an aqueous receiving phase (RP) was studied and compared. Fluxes and selectivities for competitive metal cation transport have been determined in a variety of source solution pH and membrane solvent types. The obtained results showed that the carrier is selective for Ag+ cation. The effect of different experimental conditions that affect the transport efficiency were studied and optimized. In the optimum condition, the transport of a 5 × 10-4 mol L−1 solution of Ag+ cations was observed 92.3 ± 5.3% after 4 h in the presence of equimolar concentrations of other metal cations. A possible application of this carrier system and transport process for separation and recovery of Ag+ cation from real samples has also been examined.

Quantum-Mechanical Methods for Quantifying Incorporation of Contaminants in Proximal Minerals

Incorporation reactions play an important role in dictating immobilization and release pathways for chemical species in low-temperature geologic environments. Quantum-mechanical investigations of incorporation seek to characterize the stability and geometry of incorporated structures, as well as the thermodynamics and kinetics of the reactions themselves. For a thermodynamic treatment of incorporation reactions, a source of the incorporated ion and a sink for the released ion is necessary. These sources/sinks in a real geochemical system can be solids, but more commonly, they are charged aqueous species. In this contribution, we review the current methods for ab initio calculations of incorporation reactions, many of which do not consider incorporation from aqueous species. We detail a recently-developed approach for the calculation of incorporation reactions and expand on the part that is modeling the interaction of periodic solids with aqueous source and sink phases and present new research using this approach. To model these interactions, a systematic series of calculations must be done to transform periodic solid source and sink phases to aqueous-phase clusters. Examples of this process are provided for three case studies: (1) neptunyl incorporation into studtite and boltwoodite: for the layered boltwoodite, the incorporation energies are smaller (more favorable) for reactions using environmentally relevant source and sink phases (i.e., ΔErxn(oxides) > ΔErxn(silicates) > ΔErxn(aqueous)). Estimates of the solid-solution behavior of Np5+/P5+- and U6+/Si4+-boltwoodite and Np5+/Ca2+- and U6+/K+-boltwoodite solid solutions are used to predict the limit of Np-incorporation into boltwoodite (172 and 768 ppm at 300 °C, respectively); (2) uranyl and neptunyl incorporation into carbonates and sulfates: for both carbonates and sulfates, it was found that actinyl incorporation into a defect site is more favorable than incorporation into defect-free periodic structures. In addition, actinyl incorporation into carbonates with aragonite structure is more favorable than into carbonates with calcite structure; and (3) uranium incorporation into magnetite: within the configurations tested that preserve charge neutrality (U6+ → 2Fe3+oct/tet or U4+ → Fe2+oct), uranium incorporation into magnetite is most favorable when U6+ replaces octahedral Fe3+ with charge balancing accomplished by an octahedral Fe3+ iron vacancy. At the end of this article, the limitations of this method and important sources of error inherent in these calculations (e.g., hydration energies) are discussed. Overall, this method and examples may serve as a guide for future studies of incorporation in a variety of contexts.

Controlling the transmembrane transport of nucleosides

Nucleoside analogues are used as drugs. Due to their hydrophilicity, nucleosides are poorly permeable to membranes and transporter proteins are required for efficient uptake. One approach towards improving membrane permeability of nucleosides is to use synthetic transporters. We describe ways to control transport of nucleosides across a liquid membrane. Hexanoylguanosine 1 selectively extracts and transports cytidines across a CHCl3 membrane. Transport catalysed by G 1 was influenced by the nucleoside's sugar, with a selectivity of dC 4 > rC 3 > araC 5. Selective transport could be modulated by adding compounds to the aqueous source phase or to the organic phase. Addition of K+2,6-DNP–8 to CHCl3 containing G 1 switched off transport of rC 3 and dC 4 due to formation of a G-quartet assembly. A lipophilic G 1·C 2 base pair could not transport dC 4, but did catalyse transport of dG 7 across the CHCl3 barrier. We propose that transport occurs because of formation of a base triple G 1·C 2·dG 7. Addition of Na2B4O79 to a source phase containing rC 3, dC 4 and araC 5 shuts down transport of rC 3 by G 1, due to formation of borate esters. These results indicate that one can control the selective transport of nucleosides.

SELECTIVE REMOVAL OF Ag(I) AND Cu(II) BY PLASTICIZER MEMBRANES WITH N-(DIETHYLTHIOPHOSPHORYL)- AZA(18)CROWN-6 AS A CARRIER

The competitive transport of equimolar mixtures of Ag(I) and Cu(II) ions from aqueous source phase (cMe = 0.001 mol/dm 3 ) across polymer inclusion membranes PIMs with N-(diethylthiophosphoryl)- aza(18)crown-6 as ion carriers, was studied. The influence of pH of source phase and metal concentration on an efficiency of silver(I) transport through polymer inclusion membranes containing cellulose triacetate as the support and o-nitrophenyl pentyl ether as the plasticizer was studied. The transport selectivity order for the PIM with N-(diethylthiophosphoryl)-aza(18)crown-6 was: Ag(I) >> Cu(II). The metal cations transport rate can be explained by size and nature of substituent in lariat ether molecule, which prefer formation of Ag(I) complex in the membrane phase.

Supported Liquid (SLM) and Polymer Inclusion (PIM) Membranes Pertraction of Copper(II) from Aqueous Nitrate Solutions by 1-Hexyl-2-Methylimidazole

The facilitated transport of Cu(II) ions from different aqueous nitrate source phases (c Me = 0.001 M, pH = 6.0) across supported (SLMs) and polymer inclusion membranes (PIMs) doped with 1-hexyl-2-methylimidazole as ion carrier was reported. The membrane is characterized by means of atomic force microscopy (AFM). The results show that Cu2+ can be separated very effectively from other transition metal cations as Zn2+, Co2+, and Ni2+ from different equimolar mixtures of these ions. The highest initial fluxes of Cu(II) were found for PIM, while lower values were observed for SLM. However, after taking into account the morphology of the membranes (porosity, tortuosity), the values of the initial flux of Cu(II) transport across PIM is less than that across SLM. The recovery factor of Cu2+ ions during transport across PIM from different mixtures of cations is above 91% after 24 hrs and above 76% during transport across SLM. Also, the stability of PIM and SLM doped with 1-hexyl-2-methylimidazole was confirmed in replicate experiments.

Chiral calix[4]arenes bearing α-hydroxy amide units as membrane carriers for amino acid methyl esters

Novel chiral calix[4]arene derivatives functionalized at the lower rim have been prepared from the reaction of p-tert-butylcalix[4]arene diamine or acylhydrazine derivative with mandelic acid or hydroxyisovaleric acid. The structures of these receptors were characterized by FTIR, 1H, 13C and 2D COSY NMR spectroscopy and elemental analysis. The transport of amino acid derivatives (phenylalanine, phenylglycine and tryptophan methyl ester hydrochlorides) was studied through bulk liquid membrane in the presence of chiral calix[4]arene derivatives. The receptors have been found to act as carriers for transport of aromatic amino acid methylesters from the aqueous source phase to the aqueous receiving phase. The transport rate and L/D selectivity of amino acid esters studied depend strongly upon the structure of the chiral receptors and guests. The best enantioselectivity was obtained in the case of phenylglycine methyl ester for all chiral carriers.