Guor-Tzo Wei

Room temperature ionic liquid as a novel medium for liquid/liquid extraction of metal ions

Room temperature ionic liquids (RTILs) have been used as novel solvents to replace traditional volatile organic solvents in organic synthesis, solvent extraction, and electrochemistry. The hydrophobic character and water immiscibility of certain ionic liquids allow their use in solvent extraction of hydrophobic compounds. In this work, a typical room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6], was used as an alternative solvent to study liquid/liquid extraction of heavy metal ions. Dithizone was employed as a metal chelator to form neutral metal–dithizone complexes with heavy metal ions to extract metal ions from aqueous solution into [C4mim][PF6]. This extraction is possible due to the high distribution ratios of the metal complexes between [C4mim][PF6] and aqueous phase. Since the distribution ratios of metal dithiozonates between [C4mim][PF6] and aqueous phase are strongly pH dependent, the extraction efficiencies of metal complexes can be manipulated by tailoring the pH value of the extraction system. Hence, the extraction, separation, and preconcentraction of heavy metal ions with the biphasic system of [C4mim][PF6] and aqueous phase can be achieved by controlling the pH value of the extraction system. Preliminary results indicate that the use of [C4mim][PF6] as an alternate solvent to replace traditional organic solvents in liquid/liquid extraction of heavy metal ions is very promising.

One-pot desulfurization of light oils by chemical oxidation and solvent extraction with room temperature ionic liquids

We have investigated removing sulfur-containing compounds from light oils by a combination of both chemical oxidation and solvent extraction using the room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+PF6−) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4−). In a one-pot operation, the sulfur-containing compounds in the light oils were extracted into RTILs and then S-oxidized (H2O2–acetic acid) to form the corresponding sulfones. The advantage of performing both extraction and oxidation of sulfur compounds from light oil simultaneously in RTILs is that this process increases the desulfurization yield by about an order of magnitude relative to that of merely extracting with RTILs. The room temperature ionic liquids can be recycled after workup and reused without any loss of activity.

Shape separation of nanometer gold particles by size-exclusion chromatography.

The shape separations of suspended gold nanoparticles were investigated using size-exclusion chromatography. The separations in shapes were identified by examining the 3-D chromatograms obtained by employing a diode-array detection system and were further confirmed by analyzing TEM images of fractional collection of particles. This shape separation was achieved by adding a mixed-surfactant system containing sodium dodecyl sulfate and poluoxyethylene (23) dodecanol (Brij-35) into the eluent, which apparently affects the adsorption behaviors of both rodlike and spherical Au nanoparticles onto the column packing materials. While the overall particle gross sizes of these two shapes were similar, the baseline resolution was unfortunately not obtainable. However, the absorption spectra from the diode-array detector could be utilized to interpret the shapes of Au nanoparticles. The potential capability for the size separation of Au nanoparticles by size-exclusion chromatography with diode-array detection was also demonstrated.

Separation of nanometer gold particles by size exclusion chromatography

The shape separations of suspended gold nanoparticles were investigated using size-exclusion chromatography. The separations in shapes were identified by examining the 3-D chromatograms obtained by employing a diode-array detection system and were further confirmed by analyzing TEM images of fractional collection of particles. This shape separation was achieved by adding a mixed-surfactant system containing sodium dodecyl sulfate and poluoxyethylene (23) dodecanol (Brij-35) into the eluent, which apparently affects the adsorption behaviors of both rodlike and spherical Au nanoparticles onto the column packing materials. While the overall particle gross sizes of these two shapes were similar, the baseline resolution was unfortunately not obtainable. However, the absorption spectra from the diode-array detector could be utilized to interpret the shapes of Au nanoparticles. The potential capability for the size separation of Au nanoparticles by size-exclusion chromatography with diode-array detection was als...

Using subcritical/supercritical fluid chromatography to separate acidic, basic, and neutral compounds over an ionic liquid-functionalized stationary phase

We packed an ionic liquid (IL)-functionalized stationary phase--based on 1-octyl-3-propylimidazolium chloride covalently bounded to silica gel--into a 3.2mmx250mm column for the simultaneous separation of acidic, basic, and neutral compounds using carbon dioxide subcritical/supercritical fluid chromatography (SFC), and examined the effects of the pressure, temperature, co-solvents, and additives on the retention behavior of the analytes. The model compounds tested for SFC separation are acetaminophen, metoprolol, fenoprofen, ibuprofen, naphthalene, and testosterone. The data indicate that hydrogen-bonding and hydrophobic interactions between the analytes and the IL-modified stationary phase seem to involve in the separation process. Simultaneous separation of acidic, basic, and neutral compounds via SFC was successful at a co-solvent content of 20% MeOH, a pressure of 110 bar, and a column temperature of 35 degrees C. The relative standard deviations of the retention times and peak areas at 50 ppm were all less than 4 and 8% (n=6), respectively.

Electroosmotic flow controllable coating on a capillary surface by a sol–gel process for capillary electrophoresis

A simple coating procedure employing a sol-gel process to modify the inner surface of a bare fused-silica capillary with a positively charged quaternary ammonium group is established. Scanning electron microscopic studies reveal that a smooth coating with 1 to approximately 2 microm thickness can be obtained at optimized coating conditions. With 40 mM citrate as a running electrolyte, the plot of electroosmotic flow (EOF) versus pH shows a unique three-stage EOF pattern from negative to zero and then to positive over a pH range of 2.5 to 7.0. At pH above 5.5, the direction of the EOF is from the anode to the cathode, as is the case in a bare fused-silica capillary, and the electroosmotic mobility increases as the pH increases. However, the direction of the EOF is reversed at pH below 4.0. Over the pH range of 4.0 to 5.5, zero electroosmotic mobility is obtained. Such a three-stage EOF pattern has been used to separate six aromatic acids under suppressed EOF and to separate nitrate and nitrite with the anions migrating in the same direction as the EOF. The positively charged quaternary ammonium group on the coating was also utilized to minimize the adsorption problem during the separation of five basic drugs under suppressed EOF and during the separation of four basic proteins with the cations migrate in the opposite direction as the EOF. Also, the stability and reproducibility of this column are good.

Preconcentration of aqueous dyes through phase-transfer liquid-phase microextraction with a room-temperature ionic liquid

In this study, we employed the room-temperature ionic liquid [bmim][PF(6)] as both ion-pair agent and an extractant in the phase-transfer liquid-phase microextraction (PTLPME) of aqueous dyes. In the PTLPME method, a dye solution was added to the extraction solution, comprising a small amount of [bmim][PF(6)] in a relatively large amount of CH(2)Cl(2), which serves as the disperser solvent to an extraction solution. Following extraction, CH(2)Cl(2) was evaporated from the extractant, resulting in the extracted dyes being concentrated in a small volume of the ionic liquid phase to increase the enrichment factor. The enrichment factors of for the dye Methylene Blue, Neutral Red, and Methyl Red were approximately 500, 550 and 400, respectively; their detection limits were 0.014, 0.43, and 0.02 μg L(-1), respectively, with relative standard deviations of 4.72%, 4.20%, and 6.10%, respectively.

Mechanistic Study of the Stereoselective Hydroxylation of [2-(2) H1 ,3-(2) H1 ]Butanes Catalyzed by Cytochrome P450 BM3 Variants.

Engineered bacterial cytochrome P450s are noted for their ability in the oxidation of inert small alkanes. Cytochrome P450 BM3 L188P A328F (BM3 PF) and A74E L188P A328F (BM3 EPF) variants are able to efficiently oxidize n-butane to 2-butanol. Esterification of the 2-butanol derived from this reaction mediated by the aforementioned two mutants gives diastereomeric excesses (de) of -56±1 and -52±1 %, respectively, with the preference for the oxidation occurring at the C-HS bond. When tailored (2R,3R)- and (2S,3S)-[2-2 H1 ,3-2 H1 ]butane probes are employed as substrates for both variants, the obtained de values from (2R,3R)-[2-2 H1 ,3-2 H1 ]butane are -93 and -92 % for BM3 PF and EPF, respectively; whereas the obtained de values from (2S,3S)-[2-2 H1 ,3-2 H1 ]butane are 52 and 56 % in the BM3 PF and EPF systems, respectively. The kinetic isotope effects (KIEs) for the oxidation of (2R,3R)-[2-2 H1 ,3-2 H1 ]butane are 7.3 and 7.8 in BM3 PF and EPF, respectively; whereas KIEs for (2S,3S)-[2-2 H1 ,3-2 H1 ]butanes are 18 and 25 in BM3 PF and EPF, respectively. The discrepancy in KIEs obtained from the two substrates supports the two-state reactivity (TSR) that is proposed for alkane oxidation in cytochrome P450 systems. Moreover, for the first time, experimental evidence for tunneling in the oxidation mediated by P450 is given through the oxidation of the C-HR bond in (2S,3S)-[2-2 H1 ,3-2 H1 ]butane.

Electrochemical Hydroxylation of C 3 –C 12 n -Alkanes by Recombinant Alkane Hydroxylase (AlkB) and Rubredoxin-2 (AlkG) from Pseudomonas putida GPo1

An unprecedented method for the efficient conversion of C3–C12 linear alkanes to their corresponding primary alcohols mediated by the membrane-bound alkane hydroxylase (AlkB) from Pseudomonas putida GPo1 is demonstrated. The X-ray absorption spectroscopy (XAS) studies support that electrons can be transferred from the reduced AlkG (rubredoxin-2, the redox partner of AlkB) to AlkB in a two-phase manner. Based on this observation, an approach for the electrocatalytic conversion from alkanes to alcohols mediated by AlkB using an AlkG immobilized screen-printed carbon electrode (SPCE) is developed. The framework distortion of AlkB–AlkG adduct on SPCE surface might create promiscuity toward gaseous substrates. Hence, small alkanes including propane and n-butane can be accommodated in the hydrophobic pocket of AlkB for C–H bond activation. The proof of concept herein advances the development of artificial C–H bond activation catalysts.