Liquid-phase microextraction of hydrophilic drugs by carrier-mediated transport

Basic studies on carrier-mediated transport as a mechanism to extract polar drugs by hollow fibre-based liquid-phase microextraction are presented for the first time. Hydrophilic alkaline drugs with log P (octanol/water partition coefficient) values less than 1 were selected as model substances. Sodium octanoate served as carrier and was added to the sample solution at pH 7 to form hydrophobic ion-pair complexes with the analytes. The ion-pair complexes were extracted into octanol as liquid membrane immobilised in the pores of the hollow fibre. Further extraction into an aqueous acceptor phase inside the lumen of the hollow fibre was facilitated by counter transport of protons from the acceptor solution to the sample solution. Protons from the acceptor solution released the analytes at the liquid membrane-acceptor interface and neutralized the carrier. The acceptor phase was analysed by capillary electrophoresis. The studies show that high extraction recoveries of ionic hydrophilic drugs can be obtained at a sample-acceptor volume ratio of 10. Linear calibration graphs and clean electropherograms indicate that carrier-mediated transport is a promising technique in microextraction of polar drugs from biological matrices.     

Extraction equilibria of various metal picrates with 19-crown-6 between benzene and water. Effect of the extra methylene group on extraction ability and selectivity

The overall extraction equilibrium constants (K(ex)) of picrates of Li(+), Na(+), K(+), Rb(+), Cs(+), Ag(+), Tl(+), and Sr(2+)with 19-crown-6 (19C6) were determined between benzene and water at 25 degrees C. The K(ex) values were analyzed into the constituent equilibrium constants, i.e. the extraction constant of picric acid, the distribution constant of the crown ether, the formation constant of the metal ion-crown ether complex in water, and the ion-pair extraction constant of the complex cation with the picrate anion. The effects of an extra methylene group of 19C6 on the extraction ability and selectivity are discussed in detail by comparing the constituent equilibrium constants of 19C6 with those of 18-crown-6 (18C6). The K(ex) value of 19C6 for each metal ion is lower than that of 18C6, which is mostly attributed to the higher lipophilicity of 19C6. The extraction ability of 19C6 for the univalent metal ions decreases in the order Tl(+)>K(+)>Rb(+)>Ag(+)>Cs(+)>Na(+)Li(+), which is the same as that observed for 18C6. The difference in logK(ex) between the univalent metals is generally smaller for 19C6 than for 18C6. The extraction selectivity of 19C6 is governed by the selectivity in the ion-pair extraction, whereas that of 18C6 depends on both the selectivities in the ion-pair extraction and in the complexation in water.     

Facilitated transport of saccharides through a supported liquid membrane containing a neutral lipophilic resorcinarene carrier

The facilitated transport of several types of saccharidess has been studied across a supported liquid membrane containing a resorcinarene carrier. The rate-determining step is believed to be the migration of a carrier-saccharide-water ternary complex in the organic solvent. The transport kinetics obey a saturation law, that allows the calculation of the stability constants of the various complexes. The stability constants are related to the saccharide structures: important factors are chain length, configuration and substitution of key hydroxyl groups.     

易化输运过程的简单化学模型及其在Wyman-Murray扩散中的应用(英文)

A simple chemical kinetic model is developed which describes the behavior of small ligands that can bind reversibly with large carrier molecules with slower intrinsic rates of transport. Under certain conditions, which we describe, the presence of the slower carriers in fact enhances the transport of the ligand. This is the chemical version of Wyman-Murray′ s facilitated diffusion. The simple model illuminates the driven nature of the enhancement of the transport by the carrier molecules: we show that the facilitated transport depends crucially on a"grand canonical" setting in which the free ligand concentrations are kept constant in the presence of the facilitating protein, in contrast to a canonical setting with constant total ligand concentrations. Results from the simple model are compared to previous experimental and theoretical results for Wyman-Murray facilitated diffusion of oxygen and carbon monoxide in muscle. A relation is established between the association-dissociation rates and the down-stream ligand concentration, or back pressure for oxygen, required for the facilitation effect to occur.     

Polymer inclusion membranes: The concept of fixed sites membrane revised

The mechanism of facilitated transport of metal ions across polymer inclusion membranes (PIMs) is revised on the basis of transport flux measurements and of new data brought by techniques sensitive to local inter-molecular interactions and molecular diffusion. Cellulose triacetate (CTA) membranes built with two types of inclusion carriers: a liquid one Aliquat 336 and a crystalline one Lasalocid A, both able to carry metal ions across PIMs and supported liquid membranes (SLMs) made of the same components, have been compared. Both PIM systems show similar effects for what concern the need of a carrier threshold concentration for the occurrence of a transport flux across PIM as revealed by flux and fluorescence correlation spectroscopy (FCS) measurements, and the dependence of the chemical nature of plasticizers on the metal ion flux. These systems also present similar Raman and far IR signatures of structural evolution of PIMs with the increase of the carrier concentration within the CTA matrix.

All the presented data are interpreted as concern PIMs, according to an evolution of chemical interactions between components of the polymeric membrane able to lead to a phase transition. This phase transition type of the carrier-plasticized polymer system is induced by the increase of carrier concentration in the polymer chains. The PIM progressively organizes itself like a liquid SLM because of the enhancement of preferential solvent interactions between the carrier and the plasticizer.

The main conclusion of this study is that the classically adopted “hopping” transport mechanism between fixed carrier sites in a PIM does not apply to such carrier chemically unbound to polymer membrane systems.     

Experiences with carrier-mediated transport in liquid-phase microextraction

Different organic borates, phosphates, sulphates, and carboxylic acids are evaluated as extraction carriers in three-phase liquid-phase microextraction (LPME). Hydrophilic basic drugs form ion-pairs with the carriers and are extracted as ion-pair complexes into an organic liquid membrane of n-octanol or peppermint oil immobilized in the pores of a polypropylene hollow fiber. From this point, the basic drugs are released into a 20-microL solution of 50mM HCl placed inside the lumen of the hollow fiber (acceptor solution). Simultaneously, the carrier is neutralized by protons from the acceptor solution (protonated to maintain the charge balance). Both water-soluble and water-insoluble carriers are tested. One promising candidate among the water-soluble carriers is 1-heptanesulfonic acid. This is added to the sample solution to a final concentration of 25mM and served to ion-pair the analytes within the sample solution. Among the less water-soluble candidates, a mixture of di(2-ethylhexyl) phosphate (DEHP) and tris(2-ethylhexyl) phosphate (TEHP) serve as efficient carriers. Ten percent (w/w) of each of DEHP and TEHP are added to the organic liquid membrane, and these carriers principally worked through ion-pairing with the analytes at the interface between the sample solution and the organic liquid membrane. Several carriers are found to be compatible with human plasma samples, and bromthymol blue is particularly efficient in combination with these protein-containing matrices. Following optimization of the conditions for bromthymol blue, including saturation of the plasma samples with sodium sulphate, extraction recoveries between 45% and 75% are obtained for eight model drugs after 60 min of extraction. With bromthymol blue as the carrier, highly acceptable validation data are obtained for phenylpropanolamine and practolol extracted from human plasma.     

Facilitated Transport of Carbohydrates, Catecholamines, and Amino Acids Through Liquid and Plasticized Organic Membranes

A number of methods are described to facilitate the transport of monosaccharides, catecholamines, and amino acids through bulk liquid membranes, supported liquid membranes and plasticized cellulose triacetate membranes. Transport is mediated by carrier compounds, such as boronic acids, quaternary ammonium salts and crown ethers, that are dissolved within the lipophilic membranes. Two types of transport mechanisms are described, carrier diffusion and fixed-site jumping.     

Facilitated transport mechanism in fixed site carrier membranes

Facilitated transport of gases, such as O₂, has been observed for fixed site carrier membranes. Carrier-impregnated ion-exchange membranes have also been used to produce facilitated transport of CO₂, H₂S and olefins when the carriers are not completely mobile. The actual mechanism for this facilitated transport has not been determined previously. The facilitated transport is provided by the exchange of solute between the free solute region and the bound complexing agent combined with gradients in the free solute and complexed carrier. The ratio of mobility for exchange between the regions is the dimensionless equilibrium constant of the reversible reaction. An expression is also derived for the relationship between the effective diffusion coefficient of the complex in facilitated transport, D_AB, and the diffusion coefficients for exchange between free and complexed solute, D_DH and D_HD. Since D_AB can be determined from experimental results, D_DH and D_HD can be calculated. The results also show the morphology dependence of D_AB. The diffusion coefficient of the free solute D_A also changes with the loading of the complexing agent in the film. This morphology dependence can explain why the gas permeability can decrease when the concentration of the complexing agent increases in the membrane.     

硒功能化杯[4]芳烃对金属离子的识别及在PVC基质支撑液膜的传输作用

提出以PVC为基质的支撑液膜传输体系，研究了以新研制的硒功能化杯[4]芳烃 为活性载体，邻苯二甲酸二辛酯（DOP）为膜溶剂的PVC基质支撑液膜对金属离子的 传输性能。采用双层夹心膜电位法测定了活动载体-金属离子在膜中的配合物生成 常数，对离子在膜中的传输速率、选择性系数以及生成常数之间的相关性作了研究 。使用该体系发现，在8种金属离子中汞具有最快的传输速率；进一步讨论了硒功 能化杯[4]芳烃对金属离子的识别作用和支撑液膜传输机理。     

Techniques for characterization of charge carrier mobility in organic semiconductors

The charge transport characteristics of organic semiconductors are one of the key attributes that impacts the performance of organic electronic and optoelectronic devices in which they are utilized. For improved performance in organic photovoltaic cells, light-emitting diodes, and field-effect transistors (FETs), efficient transport of the charge carriers within the organic semiconductor is especially critical. Characterization of charge transport in these organic semiconductors is important both from scientific and technological perspectives. In this review, we shall mainly discuss the techniques for measuring the charge carrier mobility and not the theoretical underpinnings of the mechanism of charge transport. Mobility measurements in organic semiconductors and particularly in conjugated polymers, using space-charge-limited current, time of flight, carrier extraction by linearly increasing voltage, double injection, FETs, and impedance spectroscopy are discussed. The relative merits, as well as limitations for each of these techniques are reviewed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

杯芳烃衍生物液－液萃取和液膜传输银的对比研究及机理探讨

以4类含硫、硒、氮等杂原子基团二取代的杯[4]芳烃五衍生物（1－14）为中 性载体，在H2O-CHCl3-苦味酸体系萃取银和H2O-CHCl3-H2O液膜体系中传输银进行 了对比研究。萃取和传输结果具有一致性，除了苯并噻唑取代的杯[4]芳烃衍生物 （3－6）外，其它10个含硫、硒、氮的杯[4]芳烃衍生物1－14均对软重金属银和汞 有很高的选择性，而吡啶取代的杯[4]芳烃衍生物7－10对铅有一定的萃取选择性， 其中羟基硫醚取代的杯[4]芳烃衍生物11－14对银的萃取率和传输速率最大。并且 就杯[4]芳烃衍生物对银的传输机理进行了探讨，发现传输速率随源相中金属离子 浓度和有机相中载体浓度的增加而增大，因此推论这是由金属离子浓度梯度推动下 的传输。     

Mathematical modeling of penicillin G extraction in an emulsion liquid membrane system containing only a surfactant in the membrane phase

An extraction experiment of penicillin G was performed in an emulsion liquid membrane system in which only ECA 4360J exists in the organic membrane phase without a predominant carrier, Amberlite LA-2, used in our previous works and it functions as a carrier as well as a surfactant. A permeation model for the present system has been developed as a primary study to examine the transport mechanism of penicillin G in the previous batch and continuous systems with two carriers of Amberlite LA-2 and ECA 4360J. The model takes into account the mass transfer in the external aqueous film, the extraction reaction between penicillin G and ECA 4360J at the external interface, the diffusion of penicillin G in the emulsion phase, the stripping reaction at the internal interface and the pH change of internal aqueous solution containing Na₂CO₃ with penicillin G transported into the internal phase. The experimental data were well fitted with the present model. Also, an expression for the reaction of penicillin G with ECA 4360J was obtained through a series of equilibrium measurements in liquid–liquid extraction system.     

Facilitated transport of salts by neutral anion carriers

Partitioning of ions from water to the membrane solvent (NPOE) can be quantified by Gibbs free energies of transfer, deltaG(tr,NPOE)(ion). These were derived from transport studies of lipophilic salts through supported liquid membranes (SLMs) in the absence of the carrier. Partition coefficients Kp for various salts can now be calculated. The neutral anion receptors uranyl sal(oph)enes 1-5 transport Cl- and H2PO4- as tetrapropylammonium salts. The transport is diffusion-limited and can be described by two transport parameters Dm and K(ex). From the extraction constants K(ex) and the partition coefficients Kp of the transported salts, the association constants Ka of the anion receptors for Cl- and H2PO4- in NPOE were determined. Competitive transport with carriers 3 and 4 of NPr4H2PO4 and NPr4Cl demonstrated highly selective transport of H2PO4- even in the presence of excess of Cl-.     

四烷基锡中性载体推动亚硝酸根离子迁移穿透大块液膜

通过大块液膜体系研究了四烷基锡的碳链长度、载体浓度.NO_2~-浓度及抗衡离子等因素对NO_2~_穿透含四烷基锡的液膜的传质速率的影响,讨论了它们与四烷基锡为载体的离子电极性能间的关系。NO_2~-通过四烷基锡为载体的液膜的迁移规律符合离子对传输模式。     

Effect of the steric accessibility of the exchange site in long-chain quaternary ammonium salts on the anion-exchange extraction of divalent ions

The constants of anion-exchange extraction of divalent ions by quaternary ammonium salts of various structures were determined. The exchange constants depend significantly on steric accessibility of the exchange site. For the exchange of small-size anions, the affinity of the ion exchanger for divalent ions is higher than for monovalent ions. For large divalent anions, the exchange constant may increase or decrease, depending on the size of a monovalent anion. The obtained results are explained by the specifics of the ion-pair association of monovalent and divalent anions with quaternary ammonium cations.     

环烷酸类载体液膜体系对金属离子传输机理的研究

本文先在大块液膜体系中以环已烷甲酸为载体,通过正交设计,系统地研究了各种因素对希土离子输送作用的影响规律。比较了相同条件下RE~(3+)(希土)同Na~+,NH_4~+、Ca~(2+)和Fe~(3+)等离子的输送作用。发现在适当条件下,无皂化的羧酸载体对RE~(3+)离子具有良好的输送效果,同时证实,羧酸输送RE~(3+)离子是通过三个H~+离子与一个RE~(3+)离子的交换,而当载体皂化时,皂化的载体直接与接收相H~+离子发生交换,从而降低了羧酸对RE~(3+)离子的输送和分离效果。 在大块液膜研究的基础上,建立了一个以无皂化的环烷酸为载体的乳状液膜体系,从模拟离子矿的硫酸铵浸出液中萃取希土,通过正交试验确定了最优的液膜萃取条件,希土萃取率达96％以上,富集度30～40倍。     

Extraction Equilibria between Benzene and Water of Uni- and Bivalent Metal Picrates with Lariat 16-Crown-5: Effect of the Side Arms on the Extraction Ability and Selectivity

The overall extraction constants (K_ex) of uni- andbivalent metal picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5(L16C5) were determined between benzene and water at 25°C. TheK_ex values were analyzed into the constituent equilibriumconstants, i.e., the extraction constant of picric acid, the distributionconstant of the crown ether, the stability constant of the metalion–crown ether complex in water, and the ion-pair extraction constantof the complex cation with the picrate anion. The K_ex valuedecreases in the orders Ag⁺ > Na⁺ >Tl⁺ > K⁺ > Li⁺ andPb²⁺ > Ba²⁺ > Sr²⁺ for theuni- and bivalent metals, respectively, which are the same as those observedfor 16C5. The extraction selectivity was found to be governed by theselectivity of the ion-pair extraction of the L16C5–metal picratecomplex rather than by that of the complex formation in water. Theextraction ability of L16C5 is smaller for all the metals than that of 16C5,which is mostly attributed to the higher lipophilicity of L16C5. Differencesin the extraction selectivity between L16C5 and 16C5 were observed for thebivalent metals but little for the univalent metals. The side-arm effect onthe extraction selectivity was interpreted on the basis of the negativecorrelation between the effect on the complex stability constant in waterand that on the ion-pair extraction constant.     

On the Involvement of Geminate Pairs in Radiation-Induced Conductivity of Polystyrene

Basic parameters of the generalized Rose–Fowler–Weisberg theory were experimentally determined for polystyrene. The obtained data were used to comprehensively analyze the evolution of geminate pairs in this polymer. It was shown that the generation of the prompt component of radiation-induced conductivity occurs by the trapping mechanism with two charge carrier states involved, the quasi-free and trapped. This generation under equilibrium transport conditions (diffusivity and mobility of carriers are constant) reportedly ensured by the geminate recombination itself was not observed in a real experiment. With allowance for dispersive transport of holes (the major carriers), the lifetime of geminate pairs were found to be as long as a few hundred of milliseconds at 300 K. The published data on the formation and decay kinetics in doped polystyrene upon its pulse radiolysis or photolysis were thoroughly analyzed. It was shown that, at ultrashort times before localization of generated carriers, the contribution of electrons to the observed conductivity prevails, although the basic contribution is made by holes in later times.     

Transport characterisation of a PIM system used for the extraction of Pb(II) using d2ehpa as carrier

The facilitated transport of lead(II) through polymeric inclusion membranes consisting of cellulose triacetate as polymeric support, bis-(2-ethylhexyl)-phosphoric acid (d2ehpa) as carrier, and tris-(2-butoxyethyl)phosphate as plasticiser (tbep), is investigated. The influence of some of the aqueous and membrane components on the permeability of Pb(II) was studied. The maximum flux obtained with these membranes is 3.5×10⁻⁶ mol m⁻² s⁻¹, which is of the same order of magnitude of those reported for supported liquid membranes and is in the upper range of those reported for polymeric inclusion membranes. Aqueous and membranes resistances were determined from a model that describes the transport mechanism across the membranes using the stoichiometric relationship and the extraction equilibrium constant value of 6.2×10⁻⁴ determined independently by solid–liquid extraction. An activation energy of 11 kJ mol⁻¹ was also determined for Pb(II) migration, which suggest that the transport of Pb(II) is controlled by a membrane diffusion mechanism. Membrane characterisation was performed using several techniques including atomic force microscopy, scanning electron microscopy coupled with energy-dispersive spectroscopy, and thermal analysis.     

Giant polarization in stable polymeric dielectrics

Macromolecular solids of highly aromatized structure can exhibit giant polarization. Their structures must be capable of providing long-range electron orbital delocalization. Intermolecular conformality of the orbitals of these huge molecules can result in ready carrier formation. The ready transport of these electronic holes and electronic carriers as polarons able to range over long molecular domains will then produce the giant polarization characteristic of the nomadic polarization mechanism. Recent developments in the synthesis and characterization of such materials new make available a new and interesting class of very stable organic dielectrics having dielectric constants in excess of 100. A number of such materials are described.