Solvent Extraction Research and Development, Japan
Online ISSN : 2188-4765
Print ISSN : 1341-7215
ISSN-L : 1341-7215
Volume 20
Showing 1-25 articles out of 25 articles from the selected issue
Reviews
  • Hiroshi UMAKOSHI, Keishi SUGA
    2013 Volume 20 Pages 1-13
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    A liposome membrane system attracts much interest for its use as a “designable” interface for the recognition of various biomolecules because it can provide a hydrophobic nano-environment in aqueous solution and can also induce a dynamic nature in response to the variation of its environment. The methods to characterize the membrane properties of liposome have been reviewed, focusing on the micro-phase separation of different lipids on the membrane and, also, nano-domain formation there. A possible design of the liposome membrane for the recognition of biomacromolecules was discussed based on the characterized properties, by employing the RNA molecule as a case study. Finally, a possible extension of the above-described strategy toward “recognitive separation” is discussed as a future possibility.
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Original Articles
  • Kazuharu YOSHIZUKA, Hans-Juergen PIETZSCH, Sepp SEIFERT, Holger STEPHA ...
    2013 Volume 20 Pages 15-27
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    We have developed a novel molecular modelling technique for radiopharmaceutical Tc and Re complexes combined with molecular mechanics (MM) and molecular dynamics (MD) for estimating the partition coefficient of these complexes between water and 1-octanol (logP). The field force parameters developed with a MM program, “MOMEC” were fitted to all relevant X-ray crystal structures of [99mTcO(DMSA)2]- and [188ReO(DMSA)2]- (DMSA: dimercaptosuccinic acid). The force field parameters were transferred to those in a MD program, “Material Explorer”. The MD simulations also indicate that a quantitative structure property relationship (QSPR) was obtained, which relates the internal energy difference between the Tc/Re-DMSA derivatives in the water phase and that in 1-octanol phase with the experimental logP value.
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  • Yuya TOYOKAWA, Satoshi TSUKAHARA, Terufumi FUJIWARA
    2013 Volume 20 Pages 29-39
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    In the extraction system using Aerosol OT (AOT) in isooctane, the distribution of AOT between the isooctane and aqueous phases depended on the concentration of inorganic electrolytes, salts and/or acids. A colored dye, neutral red, was selected as a probe molecule, which exists in red cationic and yellow nonionic forms in acidic and alkaline regions, respectively. The extraction was investigated in the acidic region in detail. At lower NaCl concentrations, the cationic neutral red existed in the aqueous phase. At higher NaCl concentrations, the cationic neutral red was extracted into the isooctane phase. At intermediate NaCl concentrations, a small amount of third phase appeared in the interfacial region and almost all of the cationic neutral red was extracted into it. Observation by optical microscopy gave geometric information about the third bicontinuous microemulsion phase as well as microemulsions or emulsions formed in the isooctane and aqueous phases.
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  • Shoji TAGASHIRA, Tatsuya ICHIMARU, Kouji NOZAKI, Yoshiko MURAKAMI
    2013 Volume 20 Pages 39-52
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    Micellar solutions of sodium dodecylsulfate (SDS) exhibit the property of being separated into two phases as a result of a temperature change or the addition of salts. Upon addition of KCl to an SDS solution, the surfactant phase of Na+DS- changed to the potassium dodecylsulfate phase of K+DS- (KDS) at room temperature around 25°C. The ammine complexes of metal ions such as copper reacted with the dodecylsulfate anion (DS-) to form the corresponding ion pair, and were separated from the solution as the surfactant phase. After the phase separation of the solution containing SDS, KCl, ammonia, and copper, the surfactant phase consisted of KDS and the ion pair of [Cu(NH3)42](DS-)2 (abbreviated CuDS). The structures of the surfactant phases were investigated by small-angle X-ray diffraction (SAXRD) and differential scanning calorimetric measurements. The surfactant phases had lamellar structures with layer distances (d(001)) of 3.4 nm for KDS and 2.4 nm for CuDS. This surfactant gel extraction method was applied to the mutual separation of copper and zinc in a brass alloy. The extractability of the metals was regulated by the initial metal concentration in the sample solution. The percent extraction was (98.7 ± 0.6)% and (6.8 ± 1.4)% for copper and zinc, respectively.
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  • Yuki UEDA, Shintaro MORISADA, Hidetaka KAWAKITA, Keisuke OHTO
    2013 Volume 20 Pages 53-63
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    The secondary phenylamide derivative of a trident molecule has been prepared as a novel solvent extraction reagent to investigate and to compare its extraction ability with its corresponding monopodal analogues, for the extraction of precious and base metals in nitric acid solution. The extraction ability of the trident extractant was superior to that of the monopodal analogue. The secondary phenylamide type of trident molecule exhibited extractive selectivity for silver and divalent palladium over other precious metals and base metals in nitric acid solution. The extraction mechanism of silver with the trident extractant was determined by slope analysis and the peak shift of the FT-IR and 1H-NMR spectra of the extraction reagent before and after silver loading.
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  • Kohei TAURA, Shinjiro YAMAMOTO, Shuhei HAYASHI, Suteaki SHIOYA
    2013 Volume 20 Pages 65-70
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    A fatty alcohol, lauryl alcohol (LA), has been found to be an effective organic solvent for in situ extraction and production of paclitaxel in a suspension plant cell culture. The culture procedure and/or conditions for enhancing paclitaxel productivity by avoiding feed-back inhibition have been studied. 5-aminolevulinic acid (ALA), which promotes plant growth, was used for this purpose in the LA-medium two phase culture systems and its effect on the paclitaxel productivity in the culture was examined. Similar callus growth and greater paclitaxel production were observed in the two phase culture systems including ALA compared to the control culture with no treatment. Enhanced paclitaxel production was recorded due to the decreased paclitaxel concentration in the medium avoiding its feed-back inhibition and the increased cellular activity by ALA. Paclitaxel productivity increased by a factor of 3 compared to the control.
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  • Tatsuya OSHIMA, Asuka INADA, Yoshinari BABA
    2013 Volume 20 Pages 71-77
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    Complexation with casein hydrolysate (Pep) can be used for enhancing the water solubility of indomethacin. In the present study, the hydrophilic/hydrophobic balance of the complex (Indo-Pep) was evaluated using a poly(ethylene glycol)/dextran (PEG/DEX) aqueous two-phase system (ATPS). As the distribution ratio of Indo-Pep decreases with increasing Pep concentration, indomethacin was found to be more hydrophilic by complexation with Pep. The distribution ratio of Indo-Pep reached a minimum value when the pH was 7-8, where the distribution ratio of Pep showed a maximum value. From the results of the distribution ratios of Indo-Pep prepared using different components of Pep, the hydrophilic/hydrophobic balance of Pep seemed to influence the hydrophilic/hydrophobic balance of Indo-Pep.
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  • Kenji MISHIMA, Ryo KAWAKAMI, Haruo YOKOTA, Takunori HARADA, Takafumi K ...
    2013 Volume 20 Pages 79-89
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    The extraction of xanthones, such as α-mangostin from the pericarp of mangosteen (Garcinia mangostana Linn.) by supercritical fluid extraction (SFE), for which the solvent was carbon dioxide (CO2), was carried out at 35, 40 and 50 ºC. The extraction pressure was from 10 to 20 MPa. In order to enhance the yield of the extraction, ethanol was added as an entrainer. The yields of xanthones, such as α-mangostin in the extraction were significantly improved, whereas a change in the selectivity of the extract was not observed. We also conducted qualitative and quantitative analyses for xanthones in the extract by HPLC, and analyzed the extraction behavior. The effect of three operating parameters, such as temperature, pressure and the mole fraction of ethanol in a supercritical solution of CO2 on the extraction yield was investigated using the single-factor method.
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  • Hui TENG, Yonghee CHOI
    2013 Volume 20 Pages 91-104
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    Rhizome coptidis is a common traditional herb in China with an abundant alkaloid content that has remedial effects on various chronic diseases. In this study, an acid-assisted extraction method was developed for the extraction of the alkaloids from rhizome coptidis, and response surface methodology was applied to optimize the extraction process conditions. Individual alkaloids were isolated and identified using high performance liquid chromatography with an ultraviolet detector (HPLC-UV). Five different acids were tested, and the highest total alkaloid content including berberine and palmatine content were detected in phosphoric acid extracts. A box-Behnken design with 3 levels and 3 variables was employed and optimal conditions were obtained as follows: 0.34 % phosphoric acid concentration, 5.00 h extraction time, and 51.45 mL/g solvent to sample ratio. A verification experiment was carried out under the estimated optimal conditions, and a good correlation between estimated and observed values indicated that the fitted model was valid and the prediction was successful. Compared with other extraction methods, acid-assisted extraction is simpler, safer and more economic with a high alkaloid yield which could be potentially used as alternative choice for industrial production.
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  • Kazuhiro AKUTSU, Shinichi SUZUKI, Tohru KOBAYASHI, Hideaki SHIWAKU, Yo ...
    2013 Volume 20 Pages 105-114
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    The extractability and complexation properties of trivalent lanthanides with N-methyl-N-phenyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide (MePhBIZA) were investigated. The MePhBIZA, containing two aza-aromatic donors and an oxygen donor in the molecule, was designed with regard to 2-(2-pyridyl)benzimidazole (Biz) and newly synthesized as an extractant for trivalent lanthanides, Ln3+, and actinides, An3+. The MePhBIZA exhibited satisfactory extractability of Eu3+ even under acidic conditions. A speciation diagram, based on the formation constants determined by spectroscopic titration experiments, indicated that the MePhBIZA formed complexes with Eu3+ in acidic solution. These results showed that the addition of the amide group promotes ligand coordination with Eu3+ over the competing protonation reaction in relatively acidic solution in comparison with Biz.
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  • Hirokazu NARITA, Mikiya TANAKA
    2013 Volume 20 Pages 115-121
    Published: 2013
    Released: March 02, 2015
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    The separation of Nd(III) and Dy(III) from Fe(III) and Ni(II) in relatively high concentrations of HNO3, HCl and H2SO4 solutions (0.1 – 7 M) was investigated using with 0.1 M N,N′-dimethyl-N,N′-di-n-octyl-diglycolamide (MODGA) in 80 vol% n-dodecane—20 vol% 2-ethylhexanol. In all systems, the extraction percentage (E%) value for Dy(III) is higher than that for Nd(III), and the E% values for Nd(III) and Dy(III) increase with an increase in the acid concentration. The extracted Nd(III) and Dy(III) in the organic phase can be back-extracted using distilled water. The back E% is dependent on the acid concentration in the forward extraction. Both Fe(III) and Ni(II) are poorly extracted in all systems, although Fe(III) is extracted at >2 M HCl. Therefore, Nd(III) and Dy(III) are readily separated from Fe(III) and Ni(II) in the HNO3 and H2SO4 systems. The separation of Nd(III) from Dy(III) is effectively performed in the forward extraction reaction at ~1 M HCl and ~1 M H2SO4 and the back extraction of Nd(III) and Dy(III) from the organic phase produced by extraction from the ~1 M HNO3 solution.
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  • Fan YANG, Fukiko KUBOTA, Noriho KAMIYA, Masahiro GOTO
    2013 Volume 20 Pages 123-129
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    The extraction behavior of rare-earth ions with an 8-hydroxyquinoline derivative, HO8Q (5-octyloxymethyl-8-quinolinol), was studied using an ionic liquid, [C8mim][Tf2N] (1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), as the extracting phase. Compared with a conventional organic solvent, n-dodecane, the ionic liquid system showed a higher extraction ability for a heavy rare earth, Dy, and a better selectivity between Dy and Nd (separation factor βDy/Nd: 108). In the liquid-liquid extraction system, the color of the extracting phase changed from colorless to light yellow along with the extraction of rare-earth ions. Furthermore, the extraction efficiency was enhanced by the addition of TOPO (tri-n-octylphosphine oxide) as a co-extractant.
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  • Michie EBISAWA, Akira OHASHI, Hisanori IMURA, Kousaburo OHASHI
    2013 Volume 20 Pages 131-136
    Published: 2013
    Released: March 02, 2015
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    The synergistic effects of tris(4-isopropyltropolonato)cobalt(III) (Co(ipt)3) on the extraction of lanthanum(III) and lutetium(III) with acetylacetone (Hacac) into benzene were investigated. A synergistic enhancement of the extraction of trivalent lanthanides was found in the presence of Co(ipt)3. From equilibrium analysis, it was found that Ln(acac)3 forms a 1:1 adduct, i.e., a binuclear complex, with the Co(ipt)3 in benzene. The adduct formation constants (βs,1) of Ln(acac)3 with Co(ipt)3 in benzene were determined, discussed, and compared with those reported previously. The βs,1 values in the Ln(acac)3 system became smaller than those in the Ln(tta)3 system. The Lewis acidity of the Ln chelate had a significant effect on the adduct formation in the La(III) system and a relatively small effect in the Lu(III) system.
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  • Takuro KITABAYASHI, Takashi SANA, Shiro KIYOYAMA, Takayuki TAKEI, Masa ...
    2013 Volume 20 Pages 137-147
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    1-(2-hydroxyl-5-nonyphenyl)ethanone oxime (LIX84-I) was impregnated into polymeric particles with interconnected spherical pores by the solvent evaporation method. Divinylbenzene was used as a wall material and polymerized in the organic phase of a (W/O/W) emulsion by free radical polymerization. The diameter of the polymeric particles was almost constant at around 208±26μm. The impregnated yield of LIX84-I in the polymeric particles was higher than 80% in all preparation conditions. The extraction of Ni(II) with the polymeric particles impregnated with LIX84-I sharply increased at pH values higher than 6. It is confirmed that three molecules of LIX84-I reacted with one Ni(II) ion by quantitative analysis of the relationship between the maximum amounts of Ni(II) extracted and the amount of LIX84-I impregnated in the polymeric particles. The extraction rate of Ni(II) was effectively accelerated by the presence of the interconnected-spherical pores in the inside of the polymeric particles.
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  • Tokie OOKUBO, Syouhei NISHIHAMA, Kazuharu YOSHIZUKA
    2013 Volume 20 Pages 149-157
    Published: 2013
    Released: March 02, 2015
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    Separation and recovery of nickel from an actual waste solution of electroless nickel-phosphorous plating solution has been investigated, employing synergistic extraction with bis(2-ethylhexyl)phosphoric acid (D2EHPA) and nicotinic acid ester. The extractability of Ni with D2EHPA alone is low, due to suppression by phosphorous compounds coexisting in the waste solution. Effective extraction can be achieved with a synergistic extraction system, using both D2EHPA and nicotinic acid ester. By optimizing the operational conditions, satisfactory extraction and stripping of more than 95 % yield can be achieved. The present extraction – stripping processing can be successfully repeated, although a small amount of the nicotinic compound is dissolved into the aqueous solution.
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  • Xiuli YANG, Xiaohui WANG, Chang WEI, Shili ZHENG, Yi ZHANG
    2013 Volume 20 Pages 159-168
    Published: 2013
    Released: March 02, 2015
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    The technological parameters and the mechanism of low-acid pulp extraction of tantalum were investigated. The results show that hydrofluoric acid concentration, sulfuric acid concentration, organic to pulp phase ratio, the concentration of tantalum and niobium, contact time and temperature have a significant effect; optimum process operating parameters were established as follows: hydrofluoric acid concentration 1.6 mol/L, sulfuric acid concentration 0.6 mol/L, organic to pulp phase ratio 3:1, tantalum concentration 26.61 g/L, niobium concentration 11.64 g/L, contact time 5min and room temperature. Under these experimental conditions, tantalum extraction can reach more than 98% and the separation factors of Ta/Nb, Ta/Fe and Ta/Sn were maximal. According to slope analysis, the equimolar series method and the saturation capacity method, the extraction product was identified as 3MIBK•H2TaF7.
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  • Hiroaki HABAKI, Yoshihisa YOSHIMURA, Ryuichi EGASHIRA
    2013 Volume 20 Pages 169-174
    Published: 2013
    Released: March 02, 2015
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    Model hydrocarbon mixtures, consisting of alkene or alkane and/or aromatic components, were utilized as feed oils with methanol, furfural or sulfolane as solvents to evaluate solvent extraction for the separation of aromatic components from cracked oils. Aromatic components were selectively extracted relative to alkane or alkene components with all solvents. The distribution coefficients increased in the order of alkane, alkene and aromatic components. Among the aromatic components, the distribution coefficients of tri cyclic components were the highest, followed by those for di and mono cyclic components. For each aromatic components of the same number of benzene rings, the distribution coefficients generally decreased with the carbon number in the molecule. The separation selectivities of aromatic components relative to nonane were higher with sulfolane than those with the other solvents, and sulfolane has the ability to enhance separations among aromatic components.
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  • Hiroaki HABAKI, Yoshiyuki SHIMADA, Ryuichi EGASHIRA
    2013 Volume 20 Pages 175-181
    Published: 2013
    Released: March 02, 2015
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    The separation of coal tar absorption oil by an ionic liquid supported liquid membrane was studied to recover nitrogen heterocyclic compounds. Batch permeation runs with the supported liquid membrane were conducted using an absorption oil-heptane solution as the feed, an aqueous solution of the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, as the membrane liquid, and toluene as the solvent. Under all conditions, the nitrogen heterocyclic compounds selectively permeated through the membrane compared to other compounds. The permeation rates, especially for indole, significantly increased with the addition of the ionic liquid. The overall permeation coefficients increased with the addition of the ionic liquid and the separation selectivity of indole to 2-methylnaphthalene increased.
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  • Xuhong JIA, Jun LI, Yang JIN, Jianhong LUO, Baoming WANG, Chunlei MA
    2013 Volume 20 Pages 183-195
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    Solvent extraction of nitrates (almost all as nitric acid) from WPA produced by decomposing phosphate rock with nitric acid has been investigated using four different extractants (tributyl phosphate, methyl isobutyl ketone, n-octanol and tri-n-octyl amine) in kerosene. The results show that tri-n-octyl amine (TOA) is an effective extractant for the extraction of nitric acid from the WPA. Optimum conditions for the extraction process have also been determined. The results indicate that TOA has a good ability to extract nitric acid, while only a small amount of phosphoric acid is co-extracted. TOA can be used as an effective extractant to separate nitric acid from the WPA to produce phosphoric acid. The effect of the main impurities existing in the WPA produced by nitric acid dissolution of phosphate ore (Ca2+, Fe3+, Al3+, Mg2+ and F-) has also been studied. The results show that the impurities have a negative effect on the extraction of nitric acid or phosphoric acid and can be partly removed in the extraction. In addition, the number of theoretical stages for extracting 99.9 % of the nitric acid is calculated by the McCabe-Thiele method.
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Notes
  • Davide CICERI, Kazuiko NISHI, Geoffrey W. STEVENS, Jilska M. PERERA
    2013 Volume 20 Pages 197-203
    Published: 2013
    Released: March 02, 2015
    JOURNALS FREE ACCESS
    A custom built microfluidic device that potentially enables real time monitoring of solute transfer across a water/oil interface is presented and discussed. The device consisted of a Pyrex® glass, Y-Y shaped microchannel fabricated with an inbuilt UV-Vis detection system. The device was connected to a spectrograph by means of optical fibres for detection of the signal. The device was tested against both a blue coloured dye (waxoline blue) and the metallorganic complex of Co(II) and di (2-ethylhexyl) phosphoric acid (DEHPA). Due to the very short optical path length (~ 10-4 cm), in situ measurements of highly concentrated analytes are shown to be possible. The use of the device for measurements of concentrated solvent extraction kinetics is envisaged.
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  • Toshinori SHIMANOUCHI, Yoshitaka KATAOKA, Masahiro YASUKAWA, Tsutomu O ...
    2013 Volume 20 Pages 205-212
    Published: 2013
    Released: March 02, 2015
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    5-Hydroxymethylfurfural (HMF) was obtained from the dehydration of fructose under high temperature and pressure conditions (180 oC and 10 MPa). To avoid the decomposition of HMF in the bulk aqueous phase, we dehydrated fructose in the water / metyl isobuthyl ketone (MIBK) biphasic system. The HMF could be successfully extracted into the organic MIBK phase without further decomposition of HMF. We present a simplified model taking into consideration of the slug flow with the wall film to maximize the HMF yield in the MIBK phase. It was likely that the slug flow contributed to an increase in the surface-to-volume ratio for the mass transfer of HMF.
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  • Takaaki ISHIGAMI, Hiroshi UMAKOSHI
    2013 Volume 20 Pages 213-217
    Published: 2013
    Released: March 02, 2015
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    The partitioning behaviors of L-/D-Trp in a solvent-water system modified with a phospholipid and a liposome membrane system were compared. Trp was partitioned to the interface of chloroform-water system supplemented with phospholipid. As the methanol ratio in the chloroform phase increased, the Trp was gradually partitioned to the organic phase while the chiral selectivity (the partitioning ratio of L-/D-Trp) was not increased. In contrast, the liposome membrane system was found to induce a significant chiral selectivity of L-Trp against D-Trp during their partitioning from the aqueous phase to the lipid membrane. This result clearly indicates the significance of the liposome membrane, a self-assembly of higher molecular order, as an effective platform for selective separation (or recognition).
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  • Michiaki MATSUMOTO, Naoki OKU, Kazuo KONDO
    2013 Volume 20 Pages 219-224
    Published: 2013
    Released: March 02, 2015
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    Supported ionic liquid membranes containing calixarenes as carriers have been developed for saccharide separation. We examined the liquid membrane separation of saccharides using a quaternary ammonium salt Aliquat 336 as the ionic liquid and calix[x]arenes (x=4, 6, 8) as the carriers. In the permeation experiments, we observed high facilitated transport for glucose permeation with calix[4,6]arenes and for fructose, arabinose and ribose permeations with calix[8]arene. From permeation experiments using various derivatives of saccharides, we found that the calix[4,6]arenes interact with the OH-1,2 and 3 units and that calix[8]arene interacts with cis-3,4-diols units of the saccharides. Calixarenes, which have different numbers of phenol units, are concluded to be effective carriers for saccharides permeation.
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  • Fan YANG, Fukiko KUBOTA, Noriho KAMIYA, Masahiro GOTO
    2013 Volume 20 Pages 225-232
    Published: 2013
    Released: March 02, 2015
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    A comparative study of ionic liquids (ILs) and a conventional organic solvent on the extraction of rare-earth ions from a nitrate-contained solution with TOPO has been investigated. A slope analysis was carried out to determine the extraction mechanism, and it was found that more TOPO molecules and the ionic constituents of the ILs have taken part in the extraction reaction in the ILs-based TOPO extraction systems. The numbers of TOPO molecules coordinated to the metal ion in the extracted complexes were 6 and 4 in the [C4mim] and [C8mim][Tf2N] systems, although 3 TOPO molecules were needed in the n-dodecane system. Higher extraction efficiency was obtained in the extraction system in which the higher coordinating number of TOPO was shown. The extraction ability of [C8mim][Tf2N]-based TOPO depends significantly on the ionic constituents of the ILs in the extracting phase, but depends only slightly on the anionic nitrate ion from the aqueous phase, and [C4mim][Tf2N]-based TOPO is not dependent on the nitrate ion.
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  • Akira OHASHI, Norito TANAKA, Kumiko ODA, Kousaburo OHASHI
    2013 Volume 20 Pages 233-239
    Published: 2013
    Released: March 02, 2015
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    The effects of the surfactants on the extraction rate of nickel(II) and palladium(II) with 2-(5-bromo-2-pyridylazo)-5-diethyaminophenol (5-Br-PADAP) in the toluene/water system were investigated by the centrifugal liquid membrane (CLM) method. The extraction rates of the metal(II) ions were increased by the addition of the ionic surfactants having a charge opposite to the metal(II) species in the aqueous solution. The stronger the interfacial activity of the surfactant, the larger the acceleration effect became. The acceleration was explained by the increase in the interfacial concentration of metal ions by an electrostatic attraction between the metal species and the ionic surfactant adsorbed at the interface. On the other hand, the extraction rates of metal(II) ions were reduced by the addition of an ionic surfactant having the same charge as the metal(II) species and the nonionic surfactant.
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