Water-immiscible Organic Solvent Research Articles

Studying the kinetics of the ion transfer across the liquid|liquid interface by means of thin film-modified electrodes

The kinetics of the ion transfer across the liquid|liquid interface is studied by means of a thin film-modified electrode in combination with square-wave voltammetry. The thin film-modified electrode consists of an edge plane pyrolytic graphite electrode covered with a thin film of a water immiscible electroinactive organic solvent containing a neutral redox probe and a suitable electrolyte. The overall electrochemical process, proceeding as a coupled electron–ion transfer reaction, is controlled either by the electron transfer across the graphite electrode|organic solvent or by the ion transfer across the organic solvent|aqueous electrolyte interface. The theoretical model enabling to distinguish the rate limiting step is developed. The theory is used to measure the kinetics of ClO 4 - , NO 3 - , Cl −, SCN −, Na +, K +, (CH 3) 4N +, and (C 4H 9) 4N + across the water|nitrobenzene interface utilizing lutetium bis(tetra- tert-butylphthalocyaninato) as a redox probe.

Liquid–liquid distribution studies on moderately labile metal chelates. Kinetics of hydrolysis of tris(thenoyltrifluoroacetonate)thallium(III)

Summary Kinetics of hydrolysis of tris(thenoyltrifluoroacetonate)thallium(III) in water was studied by back extraction of this moderately labile metal chelate, labelled with 204Tl, from a water-immiscible organic solvent to aqueous solutions. A function of the distribution ratio of the metal was derived, which linearly depended on time after reaching quasi-equilibrium of chelate partition. Its extrapolation to zero time made it possible to evaluate the partition constant of the chelate. The rate constant of its hydrolysis was determined from the slope. The dependence of the rate constant on pH and on the ligand concentration shows that both acid and base hydrolysis of the chelate studied took place. The approach used can be helpful for determining partition constants of moderately labile metal complexes and the lability of the complexes in aqueous solutions.

Liquid-phase microextraction combined with high-performance liquid chromatography for the determination of local anaesthetics in human urine

A simple liquid-phase microextraction (LPME) device combined with high-performance liquid chromatography (HPLC) is presented for the simultaneous analysis of local anaesthetics, lidocaine, bupivacaine, and tetracaine, from human urine sample. An organic solvent showed good compatibility with the mobile phase of the HPLC, o-dibutyl phthalate, was selected. Local anaesthetics are extracted from 6 ml of the feed aqueous solution and human urine sample into a water-immiscible organic solvent suspended at the needle tip of the microsyringe, then the organic solvent was directly introduced to a reversed-phase HPLC system. The kind of the organic extraction solvent, the stirring rate, the pH value of the aqueous feed solution, and the extraction time have been discussed. Under the optimized extraction conditions, high enrichment factors (more than 86.0-fold) and significant sample clean-up for all of studied local anaesthetics were achieved within 30 min. The detection limits (lower than 0.05 μg/ml) were comparable with previously reported gas chromatography methods. This method was applied to specimen of patient who was treated with extradural anaesthesia of lidocaine, bupivacaine, and tetracaine, and revealed that simultaneous determination of above three local anaesthetics in human urine was possible.

Comparison of Copper Speciation in Estuarine Water Measured Using Analytical Voltammetry and Supported Liquid Membrane Techniques

The supported liquid membrane (SLM) is a promising separation and preconcentration technique that is well-suited for trace metal speciation in natural waters. The technique is based on the selective complexation of metal ions by a hydrophobic ligand (carrier) dissolved in a water-immiscible organic solvent immobilized in a porous, inert membrane. This membrane separates two aqueous solutions: the test (or donor) solution and the strip (or acceptor) solution. The metal carrier complex is transported by diffusion across the membrane from the source to the strip solution where metal ions are back-extracted. The technique offers great potential to tune the selectivity by incorporating different complexing ligands in the membrane. A SLM was used to analyze the dissolved (<0.45 microm) copper speciation from two sites in the San Francisco Bay estuary; Dumbarton Bridge, [Cu]total approximately 27 nM, and San Bruno Shoals, [Cu]total approximately 23 nM. The sites were also characterized independently by differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE). The SLM employed 10 mM lasalocid, a naturally occurring carboxylic polyether ionophore, in nitrophenyl octyl ether (NPOE) asthe membrane complexing ligand, supported by a microporous, polypropylene, hydrophobic membrane. This is the first study where SLM technique has been compared with an independent speciation technique in marine waters. Results of copper speciation measurements from Dumbarton Bridge, a site in South San Francisco Bay where copper speciation has been well-characterized in previous studies using various voltammetric techniques, indicated that only about 3% (0.9 nM) of the total dissolved copper was SLM labile. The corresponding DPASV labile copper fraction was <0.4% (<0.1 nM) of total dissolved copper. The concentration of total copper binding ligands measured by the membrane technique was 471 nM as compared to 354 nM measured by DPASV, more than 1 order of magnitude higher than the total dissolved copper concentration. The SLM measurements were consistent with earlier copper speciation measurements that were made in South San Francisco Bay using other voltammetric stripping techniques.

Liquid-phase microextraction based on carrier mediated transport combined with liquid chromatography–mass spectrometry: New concept for the determination of polar drugs in a single drop of human plasma

Recently, we demonstrated for the first time liquid-phase microextraction (LPME) of polar drugs based on carrier mediated transport. In this new extraction technique, selected analytes were extracted as ion-pairs from small volumes of biological samples, through a thin layer of a water immiscible organic solvent immobilised in the pores of a porous hollow fibre (liquid membrane), and into a μl volume of an acidic aqueous acceptor solution placed inside the lumen of the hollow fibre. In the current paper, this new extraction technique was combined with liquid chromatography–mass spectrometry (LC–MS) for the first time. Carrier mediated LPME was evaluated for several new model drugs (0.01 < log P < 1.76), the sample clean-up aspects were investigated in detail, and this new extraction technique was fully validated for the first time. Extractions were performed from 50 μl of human plasma samples, which provided sufficient material in combination with LC–MS. Sodium octanoate (50 mM) was added to the sample as carrier, 1-octanol (≈15 μl) was used as the liquid membrane in the wall of the hollow fibre, and 50 mM HCl was utilized as acceptor solution in the lumen of the hollow fibre. The addition of carrier to the samples was found to significantly improve extraction recoveries for the polar drugs tested, providing recoveries in the range 16–78%. Validation was accomplished for atenolol and cimetidine. Limits of quantification (S/N = 5) from 50 μl of plasma were 25 and 50 ng/ml for atenolol and cimetidine, respectively. The intra-day precision (R.S.D.) ranged from 7.8 to 17.2% and from 9.5 to 14.1% for atenolol and cimetidine, respectively, and corresponding inter-day precisions (R.S.D.) were within 6.7–1.4% and 7.7–20.3%. The method was linear in the range 25–1500 ng/ml for atenolol ( r = 0.992), and 50–3500 ng/ml for cimetidine ( r = 0.976). The accuracy of the method was found to be in range 89.1–99.6% and 83.4–86% for atenolol and cimetidine, respectively. The sample clean-up obtained by carrier mediated LPME was excellent, providing a significantly lower back-ground level in total ion current chromatograms by LC–MS as compared to protein precipitation.

Separation of enantiomers in microemulsion electrokinetic chromatography using chiral alcohols as cosurfactants.

A novel chiral microemulsion, which involved the use of chiral alcohols as cosurfactants, was demonstrated for the enantiomeric separation of a number of pharmaceutical drugs in microemulsion electrokinetic chromatography (MEEKC). The chiral alcohols investigated were optically active 2-alkanols, with the alkyl chain length having carbon number ranging from 4 to 7. The data indicated that, except for R-(-)-2-butanol, the use of R-(-)-2-pentanol, R-(-)-2-hexanol or R-(-)-2-heptanol as the chiral cosurfactant resulted in the baseline or partial resolution of most of the test solutes, i.e., (+/-)-norephedrine, (+/-)-ephedrine, DL-nadolol, and DL-propranolol. In addition to the chain length of the chiral 2-alkanols, the effects of other experimental conditions, such as the concentration and chirality of the 2-alkanols, as well as the pH of the run buffer and the oil phase of the microemulsion, on the enantiomeric separation of the test solutes were also investigated. An interesting finding was that the water-immiscible organic solvent (oil core) within the microemulsion droplets appeared to play an important role in the chiral separation mechanism. Also, the importance of hydrogen bonding between the test solutes ((+/-)-ephedrine and related compounds) and the chiral microemulsion was demonstrated, as it was not possible to resolve a pair of enantiomers which lacked a beta-amino proton (i.e., (+/-)-N-methyl ephedrine) under optimized run buffer conditions (e.g., 5.0% R-(-)-2-hexanol, 0.8% n-octane, and 3.5% SDS in 90.7% borate buffer at pH 9.2).

Thermodynamics of Ion Transfer Across the Liquid|Liquid Interface at a Solid Electrode Shielded with a Thin Layer of Organic Solvent

Thermodynamics of ion transfer across the liquid|liquid interface at a solid electrode shielded with a thin layer of water-immiscible organic solvent is investigated. The shielded electrode has been made by using a commercial hydrophobic carbon filament material (LSG) as an electrode support and a specially synthesized water-insoluble electroactive polymer (polyphenotiazine, PPTA) as a mediator. Oxidation of PPTA dissolved in the organic layer is accomplished with anion transfer from the aqueous phase to compensate for the positive charge of the mediator. The formal potential of the electrode shielded with PPTA solution in nitrobenzene (NB) is proportional to the Gibbs free energy of anion transfer across the liquid|liquid interface. An enhanced potential window as compared to a “classic” four-electrode setup allowed direct determination of Gibbs free energy for fluoride ion transfer from water to NB. For less polar organic solvents the formal potential of a shielded electrode is mainly determined by the enthalpy of anion transfer across the liquid|liquid interface, whereas the entropy term of Gibbs free energy causes only a minor effect.

Membrane permeabilization of gram-negative bacteria with a potassium phosphate/hexane aqueous phase system for the release of l-asparaginase: an enzyme used in cancer therapy

A fast, efficient and reproducible recovery procedure for periplasmic l-asparaginase from two distinctly related gram-negative bacteria, Enterobacter aerogenes and Pseudomonas aeruginosa, is presented. As the method uses inexpensive organic solvent hexane and an aqueous salt solution, it is also highly cost-effective in comparison with the currently available techniques used for the release of this enzyme. As hexane is a highly water immiscible organic solvent, it can be removed easily from the top of the aqueous phase by a simple evaporation. Also, various organic solvents and other membrane partitioning compounds were compared for their efficiency on l-asparaginase/protein release. The degree to which the enzyme was released was different for two bacteria, suggesting that they possess different permeability characteristics. The most efficient enzyme release from both bacteria was determined to be in 50 mM potassium phosphate with 1% hexane. Enzyme recoveries up to three-fold with respect to sonication have been achieved with this system.

&lt;b&gt;Determination of bromoxynil and ioxynil in the presence of carbamates by supported liquid membrane-liquid chromatography in river waters&lt;/b&gt;

Sample pre-treatment and enrichment using the supported liquid membrane (SLM) technique for the determination of phenolic nitrile herbicides in presence of carbamates in river water samples was investigated. The uncharged herbicide molecules from the flowing aqueous solution diffuse through an immobilized water-immiscible organic solvent, supported by a porous polytetrafluoroethylene (PTFE) membrane, and trapped in a stagnant acidic acceptor phase in an ionic form. Using n-undecane as a membrane solvent, the SLM extraction methodology was successfully used for the enrichment and separation of phenolic nitrile herbicides in environmental waters with extraction efficiencies of 60% or better. A RDS (%) of 2.1 and 1.8 was obtained for the extraction of ioxynil and bromoxynil from river water, respectively. KEY WORDS: Bromoxynil, Ioxynil, Phenolic nitrile herbicides, Carbamates, Supported liquid membrane, Sample pre-treatment, Sample enrichment Bull. Chem. Soc. Ethiop. 2003 , 17(2), 119-128.

Swelling behavior of PMMA- g-PEO microgel particles by organic solvents

Aqueous dispersions of cross-linked poly(methylmethacrylate)- g-poly(ethylene oxide) [PMMA- g-PEO] microgel particles have been prepared from mixtures of methylmethacrylate [MMA] and MMA–PEO macromonomer, with ethylene glycol dimethacrylate [EGDM] as the cross-linking monomer (0.2–0.5% wt%). The hydrodynamic radius of these (unswollen) microgel particles ranged from 73 to 85 nm, and the particles were essentially monodisperse with regard to their size distribution. Their swelling behavior has been investigated in the presence of both water-miscible and water-immiscible organic solvents. In general, with the addition of a water-miscible solvent, deswelling behavior was observed. However, the microgel particles were swollen on addition of 1,4-dioxan, which is a good solvent for PMMA. With water-immiscible organic solvents, the extent of swelling depended on the solvency properties of the organic liquid for PMMA. In the presence of benzene, the somewhat large increases in particle size have been attributed to weak flocculation. This has been assumed from an estimate of the van der Waals attraction energy between the swollen microgel particles.

Cloning of a nitrilase gene from the cyanobacterium Synechocystis sp. strain PCC6803 and heterologous expression and characterization of the encoded protein.

The gene encoding a putative nitrilase was identified in the genome sequence of the photosynthetic cyanobacterium Synechocystis sp. strain PCC6803. The gene was amplified by PCR and cloned into an expression vector. The encoded protein was heterologously expressed in the native form and as a His-tagged protein in Escherichia coli, and the recombinant strains were shown to convert benzonitrile to benzoate. The active enzyme was purified to homogeneity and shown by gel filtration to consist probably of 10 subunits. The purified nitrilase converted various aromatic and aliphatic nitriles. The highest enzyme activity was observed with fumarodinitrile, but also some rather hydrophobic aromatic (e.g., naphthalenecarbonitrile), heterocyclic (e.g., indole-3-acetonitrile), or long-chain aliphatic (di-)nitriles (e.g., octanoic acid dinitrile) were converted with higher specific activities than benzonitrile. From aliphatic dinitriles with less than six carbon atoms only 1 mol of ammonia was released per mol of dinitrile, and thus presumably the corresponding cyanocarboxylic acids formed. The purified enzyme was active in the presence of a wide range of organic solvents and the turnover rates of dodecanoic acid nitrile and naphthalenecarbonitrile were increased in the presence of water-soluble and water-immiscible organic solvents.

In Situ Liquid−Liquid Extraction as a Sample Preparation Method for Matrix-Assisted Laser Desorption/Ionization MS Analysis of Polypeptide Mixtures

A novel liquid-liquid extraction (LLE) procedure was investigated for preparation of peptide and protein samples for matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). LLE using ethyl acetate as the water-immiscible organic solvent enabled segregation of hydrophobic and hydrophilic polypeptides in mixtures, thereby reducing the complexity of mass spectra obtained by MALDI MS. The LLE technique was optimized for rapid and sensitive in situ (on-target) sample preparation for MALDI MS analysis of proteins and peptides at low-picomole and subpicomole levels. Addition of MALDI matrix to the organic solvent enhanced the efficiency of the LLE-MALDI MS method for analysis of hydrophobic peptides and proteins. LLE-MALDI MS enabled the detection of the hydrophobic membrane protein bacteriorhodopsin as a component in a simple protein mixture. Peptide mixtures containing phosphorylated, glycosylated, or acylated peptides were successfully separated and analyzed by the in situ LLE-MALDI MS technique and demonstrate the potential of this method for enhanced separation and structural analysis of posttranslationally modified peptides in proteomics research.

Lipase-Catalyzed Synthesis of Precursor Dipeptides of RGD in Aqueous Water-Miscible Organic Solvents

PPL-catalyzed synthesis of the precursor dipeptides of RGD as a cellular adhesion factor, Benzyl-Arg-Gly-NH2 and CBZ-Gly-Asp-NH2, was conducted in water-organic cosolvents systems. Five water-miscible organic solvents, which have some advantage over the water-immiscible organic solvent systems or the anhydrous organic solvent systems used often in protease-catalyzed synthesis of a peptide bond, were tested. The reaction condition of PPL-catalyzed synthesis of the dipeptides was optimized by examining the main factors affecting the product yield. The optimal reaction condition for the synthesis of Benzyl-Arg-Gly-NH2 was set up as pH 8.0, 15°C in 40% MeOH for 10 h with the maximum yield of 73.6%. The optimum condition for the synthesis of CBZ-Gly-Asp-NH2 was pH 7.0, 15°C in 50% MeOH for 10 h with the maximum yield of 67.0%.

Control of water content by reverse micellar solutions for peroxidase catalysis in a water-immiscible organic solvent

The water content of a water-immiscible can be controlled using reverse micelles. We applied this reverse micellar system to improve the enzymatic activity of a surfactant-manganese peroxidase complex in toluene. Increasing the water content in toluene to 2 vol% using the reverse micelles resulted in the great improvement (10-fold) of the peroxidase activity.

Control of Water Content by Reverse Micellar Solutions for Peroxidase Catalysis in a Water-Immiscible Organic Solvent

The water content of a water-immiscible can be controlled using reverse micelles. We applied this reverse micellar system to improve the enzymatic activity of a surfactant-manganese peroxidase complex in toluene. Increasing the water content in toluene to 2 vol% using the reverse micelles resulted in the great improvement (10-fold) of the peroxidase activity.

Modeling cyclic voltammograms of simultaneous electron and ion transfer reactions at a conic film three-phase electrode

When a neutral electroactive substance is dissolved in a water immiscible organic solvent containing no deliberately added electrolyte, and a droplet of that solution is immobilized on the surface of an electron conductor immersed in an aqueous electrolyte solution, at this three-phase electrode an electrode reaction comprising an electron and ion transfer is observed. Here we report the simulation of cyclic voltammograms assuming a conic geometry of the immobilized droplet. An initial conductivity of the organic phase is established at the liquid ∣ liquid interface by partition of the aqueous electrolyte during a short contact time preceding the voltammetric measurements. Upon anodic polarization of the electrode, the substance in the organic solvent is oxidized while simultaneously anions are transferred from water into the organic phase. The influence of the ohmic overvoltage on the current in single scan and multiple cyclic voltammetry of this reaction is discussed.

Enzymatic hydrolysis of β-lactam antibiotics at low pH in a two-phase "aqueous solution - water-immiscible organic solvent" system

The application of the two-phase "aqueous solution – water-immiscible organic solvent" system is suggested not for effective biocatalytic synthesis, but for hydrolytic purposes. Enzymatic hydrolysis of benzylpenicillin and N-phenylacetamidodesacetoxycephalosporanic acid to corresponding antibiotic nuclei 6-aminopenicillanic and 7-aminodesacetoxycephalosporanic acids in a two-phase water–butylacetate system at pH 3–4 is proposed as an alternative to the biocatalytic hydrolysis in an alkaline medium. An experimental study has been performed and a model has been developed, which describes the influence of pH, phase volume ratio, thermodynamic constants, and initial antibiotic concentration on the effectiveness of their hydrolysis in a two-phase "aqueous solution – water-immiscible organic solvent" system. The thermodynamic evaluation of penicillin G and 7-phenylacetamidodesacetoxycephalosporanic acid hydrolysis at low pH in a two-phase aqueous solution – water-immiscible organic solvent system has demonstrated high practical potential. The suggested approach allows for the exclusion of several technological steps during the transformation of natural β-lactam antibiotics to their semi-synthetic analogues: alkaline extraction of the biosynthetic antibiotic from butylacetate followed by its enzymatic hydrolysis at pH 7.5–8.0 and further acidification of the reaction mixture, which results in the precipitation of the antibiotic nucleus. Experimental observations also revealed a specific feature of this process: the kinetic supersaturation of the antibiotic nucleus slows down the attainment of the equilibrium, which should be taken into account when further developing this approach.Key words: enzymatic hydrolysis, β-lactam antibiotic nuclei, two-phase systems, supersaturation, penicillin acylase.

Oxidation of dibenzothiophene catalyzed by immobilized hemoproteins in water-immiscible organic solvents

In various water-immiscible organic solvents, hemoglobin, myoglobin and cytochrome c deposited on Celite catalyzed the oxidation of dibenzothiophene when peroxides having nonpolar substituents, such as t-butyl hydroperoxide and cumene hydroperoxide (α, α-dimethylbenzyl hydroperoxide), were used as oxidants. In hexadecane, oxidation of dibenzothiophene by immobilized cytochrome c, with a K m value of 0.15 mM for dibenzothiophene, was inhibited by cumene hydroperoxide above 0.5 mM.

Removal of dibenzothiophene and its oxidized product in anhydrous water-immiscible organic solvents by immobilized cytochrome c

In various anhydrous water-immiscible organic solvents, dibenzothiophene (DBT) was removed by more than 80% by cumene hydroperoxide (α,α-dimethylbenzyl hydroperoxide) catalyzed by the immobilized cytochrome c on Celite. DBT-sulfone, the oxidation product of DBT, strongly adsorbed on Celite in highly hydrophobic organic solvents such as hexadecane, decane and n-octane. The adsorbed DBT-sulfone was desorbed from Celite by a simple washing of the Celite with a less hydrophobic solvent such as octanol.

Selecting Experimental Conditions for Measurement of Rates of Electron-Transfer at Liquid/Liquid Interfaces by Thin-Layer Electrochemistry

The use of thin layers of water-immiscible organic solvents on electrode surfaces to evaluate rates of electron-transfer across liquid/liquid interfaces requires that reactant concentrations in the two adjacent phases be selected to minimize the effects of mass transfer on the measured currents. A general inequality is derived which provides a guide to the selection of suitable concentrations of the coreactants. Experimental tests of the inequality demonstrated its utility and should allay recently expressed concerns about the reliability of the thin-layer methodology.11