Direct Anion Exchange Research Articles

A new preparation method for the formation of gold nanoparticles on an oxide support

A preparation method for gold catalysts supported on alumina by a simple contact between a gold solution prepared with HAuCl4 as precursor and alumina over a narrow range of pH is described. This method, direct anionic exchange (DAE), differs from the mainly used method deposition precipitation generally used and presents the advantage that no gold is lost during the filtration and washing steps, the expected loadings of 2% is obtained. Gold particles size obtained by DAE is very sensitive to evolution and nature of the gold chloro-hydroxy species in the solution and on the surface of the support. According to the evolution of these species obtained by substitution of Cl– by OH– with increasing the pH value, the type of bonding complex–support is proposed. The surface of alumina is also sensitive to changes in pH of the solution. The formation of large particles of metal gold due to the presence of chlorine is put in evidence and can be limited by a treatment with ammonia solution. This washing procedure leads to some loss of gold with a final amount of 1.5%. Measurements of gold particle size by HRTEM are given as a function of preparation. A study of the activity in CO oxidation reaction is undertaken and correlated with TEM analysis.

Control of Wettability by Anion Exchange on Si/SiO2 Surfaces

Water wettability of Si/SiO2 surfaces was controlled by the formation of SAMs terminating in 1-alkyl-3-(3-silylpropyl)imidazolium ions and the anion exchange on the surfaces (“direct anion exchange”). The exchange was confirmed by X-ray photoelectron spectroscopy, and the water wettability was measured as a water contact angle by contact angle goniometry. We found that anions played a great role in determining water wettability of Si/SiO2 surfaces. For example, water contact angles of Si/SiO2 surfaces presenting 1-methyl-3-(3-silylpropyl)imidazolium ions changed from 28 to 42° when the counteranion Cl- was exchanged with PF6-. In addition to the anions, the N-alkyl groups of imidazolium cations were also found to be important in determining water wettability: we did not observe any significant changes in the contact angles of Si/SiO2 surfaces presenting 1-butyl-3-(3-silylpropyl)imidazolium ions by the anion exchange. We also demonstrated that the reaction rate of the direct anion exchange was affected by...

Oxidation of mercaptans in light oil sweetening by cobalt(II) phthalocyanine–hydrotalcite catalysts

Three Mg–Al hydrotalcites containing cobalt(II) phthalocyanine were prepared by direct synthesis, anion exchange and structure reconstruction. Differences in physicochemical properties and mechanical resistance were observed. The results of the mercaptan oxidation reaction were compared to those obtained with an industrial non-basic impregnated active charcoal. An important activity difference in favor of the prepared catalysts was obtained, confirming that the adequate tuning of basic and oxidant properties lead to a promising catalyst.

Complexation of Cu(II) and Ni(II) by nitrilotriacetate intercalated in Zn–Cr layered double hydroxides

Direct and indirect anion exchange methods have been used to intercalate a [ZnII2–CrIII] lamellar double hydroxide (LDH), with [Cu(nta)]− and [Ni(nta)]− (nta = nitrilotriacetate). For the direct method, a solution of the pre-formed complexes was used to intercalate the LDH while for the indirect method the anionic nta ligand was intercalated, the product was isolated and then reacted with a solution of the metal ion to produce the intercalated complex. LDH phases with vertical and tilted orientations of the complex are proposed to account for the formation of products with basal spacings of 14 and 12 A, respectively. The preferred arrangement varies with the metal ion, temperature and synthetic method. For the indirect method, two metal salt counter anions, viz., sulfate and tosylate, displaced the metal complex from the interlayer while chloride and nitrate competed poorly for the interlayer positions.

Determination of O-Isopropyl Methylphosphonic Acid in Living Microorganism-Agar Matrixes using ION Chromatography/Conductivity Detection

ABSTRACT A direct anion exchange ion chromatography (IC)-based method for the detection of the chemical warfare (CW) agent degradation product, O-isopropyl methylphosphonic acid (IMPA) in agar medium has been developed. This is the first report of the development and validation of an IC-based method for the analysis of IMPA in a microorganism and agar matrix. In these experiments, IMPA served as a surrogate for the CW agent GB (Sarin) in a development program for living micro-organism-based CW agent destruction systems. Petri dishes containing the medium with 10, 100 and 1000 μg/mL IMPA were used. Samples were prepared by dilution of the agar medium with deionized water followed by sonication and then filtration before the analysis by IC/conductivity detection. Using this method, the amount of IMPA in the Petri dishes was measured. Excellent separation efficiency and freedom from interference due to common anions such as chloride and sulfate was obtained in the developed method. Retention time precision was ⩽1.0% relative standard deviation (%RSD) and the detection limit was 0.1 μg/mL. Calibration curves using five IMPA concentrations over the range 1-100 μg/mL in blank agar matrices at three different dilutions (0-fold, 4-fold, and 40-fold diluted with reagent water) gave correlation coefficients (r 2) of 0.997, 0.992, and 0.995, respectively. Using three different samples and IMPA spiked into the quenched agar matrix at three levels (10, 100, and 1000 μg/mL), analysis accuracy was reflected by average spike recoveries of 76, 79, and 84%, respectively.

Plasma Vitellogenin Levels during the Annual Reproductive Cycle of the Female Rainbow Trout (Oncorhynchus mykiss): Establishment and Validation of an ELISA

Rainbow trout, Oncorhynchus mykiss, vitellogenin (Vtg) was purified from plasma of E2-treated male by direct anion exchange chromatography and some of its biochemical characteristics were studied. Our results demonstrated that, under SDS-PAGE conditions, rainbow trout Vtg was composed of two molecular forms of 390 and 176 kDa representing, respectively, the dimeric form and the monomeric form of the molecule. The purified Vtg was used to raise a polyclonal antibody for Vtg (anti-Vtg). Using this anti-Vtg, a competitive enzyme-linked immunosorbent assay (ELISA) was developed for the quantification of rainbow trout Vtg. The practical sensitivity range of this ELISA was 20–320 ng/ml (80–20% of binding) and the detection limit was 9 ng/ml. The intra- and the inter-assay coefficients of variation (at 50% of binding) were estimated at 1.8% (n = 10) and 3.9% (n = 13), respectively. This ELISA was validated by detecting changes in Vtg levels in rainbow trout at different physiological stages, as well as in 2-year-old female rainbow trout throughout the reproductive cycle.

Alrylation Over Layered Double Hydrotalcites Pillared by Heteropolyoxometalate Catalysts

Layered double hydroxides (LDHs) pillared with heteropolyoxo-metalate have been synthesized via both restructuring of hydrotalcite-like compounds and direct anion exchange under microwave field. LDHs and their derivatives are both found to be efficiency f

Hydrolysis ofγ-glutamyl linkages byFusobacterium nucleatum

The cell extracts of two human oral strains (FN2 and FN3) ofFusobacterium nucleatum displayed exceptionally highγ-glutamylpeptidase activity as determined withN-γ-l-glutamyl-2-naphthylamine as substrate. This activity was so dominant that the hydrolysis of otherN-aminoacyl-2-naphthylamines progressed at a rate <10% of the former. Two major enzymes (I and II) were partially purified from FN2. I had a molecular weight of 115,000 and did not hydrolyzeγ-glutamylcysteinylglycine (glutathione). II had a molecular weight of 70,000 and rapidly liberated only glutamic acid from glutathione. Strain FN3 contained several enzymes hydrolyzingγ-glu-2NA. Direct anion exchange chromatography of FN3 cell extracts separated one enzyme that liberated both glutamic acid and glycine from glutathione, one that was inactive against glutathione (but hydrolyzedγ-glu-2NA), and one that liberated only glutamic acid. Althoughγ-glu-2NA was a good synthetic substrate, glutathione was hydrolyzed at least 500 times faster by an enzyme present in both strains. These results indicate that the presence ofγ-glutamylpeptidase activity is very characteristic of theseF. nucleatum strains.

Anion exchange chromatography and double-diffusion cells for the study of middle molecules

We report herein a study of uremic middle molecules with techniques which allow their analysis without separation from protein. We have avoided the use of size exclusion techniques and filtration for size discrimination. In their place, we have used direct anion exchange chromatography for partial isolation of the compounds. Most of the middle-sized molecules which have been defined have been anionic, and most investigators have used DEAE-Sephadex in their isolation. For size discrimination, we have used diffusive properties through cellulosic membranes and the well-known inverse relationship of molecular weight to diffusibility [1]. Diffusive passage across membranes is dependent on molecular weight and radius. Problems such as variable protein layering, seen in convective transfer (filtration) [2], are avoided in diffusion studies.