Ion-exchange Procedure Research Articles

Purification and partial characterization of polygalacturonase from Streptomyces lydicus

Polygalacturonase produced by Streptomyces lydicus was purified to homogeneity by ultrafiltration and a combination of ion exchange and gel filtration chromatographic procedures. The purified enzyme was an exo-polygalacturonase with a molecular weight of 43 kDa. It was optimally active at 50 °C and pH 6.0. The enzyme was stable from pH 4.0 to 7.0 and at or below 45 °C for 90 min. K m value for polygalacturonic acid was 1.63 mg/mL and the corresponding V max was 677.8 μM min −1 mg −1. The inhibition constant ( K i) for gluconic acid d-lactone was 20.75 mM. Purified enzyme had been inhibited by N-bromosuccinimide, while l-tryptophan could induce enzyme activity, indicating the involvement of tryptophan at the active site.

Influence of exchanged cations (Na +, Cs +, Sr 2+ and Ba 2+) on xylene permeation through ZSM-5/SS tubular membranes

Na-ZSM-5 membranes were synthesized by secondary growth on the outer surface of stainless steel porous tubes. The membranes were ion-exchanged with Cs +, Ba 2+ and Sr 2+ to investigate their effect upon the separation of p-xylene from m-xylene and o-xylene. The permeation through the membranes was measured between 150 and 400 °C using each xylene isomer separately and a ternary mixture. All the membranes were selective to p-xylene in the temperature range studied. N 2 and xylene permeation measurements together with SEM observations were used to determine whether or not cracks and/or pinholes developed after exposure to the xylene isomers at high temperature (400 °C). Neither pore blockage nor extra-zeolitic pores developed after the ion exchange procedure and subsequent calcination. Furthermore, duplicate synthesized membranes of each cation form had similar separation factors and permeances. The duplicate values differ much less than the measurement error. The p-xylene permeation flux decreased in the order: Na-ZSM-5 > Ba-ZSM-5 > Sr-ZSM-5 ≅ Cs-ZSM-5 while the permeation flux of the m- and o-xylene decreased in the order Na-ZSM-5 > Sr-ZSM-5 > Ba-ZSM-5 > Cs-ZSM-5. The membrane that exhibited the best performance was Ba-ZSM-5, with a maximum p/ o separation factor of 8.4 and a p-xylene permeance of 0.54 × 10 −7 mol s −1 m −2 Pa −1 at 400 °C.

N2O decomposition over wet- and solid-exchanged Fe-ZSM-5 catalysts

The N2O decomposition activity of Fe-ZSM-5 strongly depends on the iron content and the preparation methods, including wet (WIE) and solid state ion exchanges (SSIE). The state of Fe species formed on the surface of a series of Fe-ZSM-5 catalysts containing a variety of Fe contents with respect to the preparation method and their role for N2O decomposition activity have been systematically examined. The general trend for the decomposition activity of Fe-ZSM-5-SSIE is higher than that of Fe-ZSM-5-WIE, indicating the formation of a distinctive local structure of Fe on the catalyst surface during the course of the ion-exchange procedure. Based upon the Fourier transformed Fe K-edge EXAFS spectra for the series of Fe-ZSM-5-SSIE and -WIE catalysts, most of the Fe species on the surface of Fe-ZSM-5-SSIE with high Fe loading are well dispersed in the form of oxygen-bridged binuclear Fe species. The turnover frequency (TOF) for N2O decomposition under dry and wet conditions has been confirmed assuming that Fe-ZSM-5-SSIE samples with Fe/Al=0.20 and Fe/Al=0.65 only contain mononuclear and binuclear Fe species, respectively, as active reaction species on their surface. The high performance of Fe-ZSM-5-SSIE may be mainly due to the formation of the binuclear Fe species onto its surface during the preparation of the catalyst.

The Activity of Iron-Containing Zeolitic Materials for the Catalytic Oxidation in Aqueous Solutions

In this work, a series of iron-containing zeolitic materials has been tested as heterogeneous catalysts for decomposition of H2O2 and for oxidation of the cationic dye Methylene Blue with H2O2 in aqueous solutions. FeAPO and FeBEA zeolites, synthesized through hydrothermal crystallization of basic hydrogels, and FeY and FeZSM-5 zeolites, prepared by ionexchange procedures, have been studied. The ion exchange with Fe(III) cations was performed from different salt solutions. Fe-exchange procedure carried out in Fe-citrate solution has been identified as an attractive option for the preparation of highly effective FeZSM-5 catalysts in wet oxidation processes. It has been shown that both tetrahedral, framework Fe, and octahedral, extra-framework Fe species incorporated into zeolite structure are catalytically active in wet oxidation reactions.

Yb3+ doped dyphillosilicates prepared by thermally induced phase transformation of zeolites

Yb3+-doped Ba and Sr diphyllosilicates (hexacelsians) have been synthesized using the Na form of LTA zeolite by ion-exchange procedure and thermal treatment. The crystal structures of both doped samples are refined and described in this article. The results of Rietveld refinements clearly indicate that Yb3+ ions are incorporated into the hexacelsians structure. AFM photomicrographs show round-shaped particles with the size of few microns. The magnetization measurements were done within the 2–300 K temperature range, revealing an enhancement of magnetization with temperature that is not in accordance with simple paramagnetic behavior.

Purification, characterization and potent lung lesion activity of an l-amino acid oxidase from Agkistrodon blomhoffii ussurensis snake venom

l-amino acid oxidases (LAOs) are one of the major components of snake venoms, which possess numerous biological functions. However, little is known of the influence of LAOs on organ lesions. In the present study, a unique LAO from Agkistrodon blomhoffii ussurensis snake venom named ABU-LAO was purified by Heparin-Sepharose FF chromatography followed by an ion-exchange chromatography procedure. The purified ABU-LAO appears a dimer with a molecular mass of approximately 108.8 kDa. Kinetics studies showed that ABU-LAO is very active towards its substrates l-Asn, l-Phe, l-Tyr, l-Leu, l-Ile and l-Trp. The most striking observation in the present study is that ABU-LAO causes severe pneumorrhagia, pulmonary interstitial edema, fusion of pulmonary alveoli, cardiac interstitial edema and bleeding when being intravenously injected into BALB/c mice. ABU-LAO also induces liver cell necrosis and release of cytokines including IL-6, IL-12 and IL-2 from highly purified human peripheral blood monocytes and T cells, respectively. In conclusion, ABU-LAO potently induces lesions in lungs and livers. The ability of ABU-LAO will contribute to the understanding of the pathogenesis of snakebite wound.

Hydroxylation/oxidation of benzene over Cu-ZSM-5 systems: Optimization of the one-step route to phenol

Cu-containing ZSM-5 materials were carefully prepared using a solid-state ion-exchange procedure to provide an outstanding performance in the direct gas-phase benzene oxidation to phenol using both oxygen and oxygen/hydrogen mixtures as oxidants. In particular, a ZSM-5 catalyst with a 100% modification level of copper (Cu/Al = 0.5) showed a phenol yield increasing with temperature up to 400 °C and approaching a high value of ca. 10%. The study shows that optimization of the phenol yield in the Cu-ZSM-5 system appears to be correlated with the appearance of size-limited Cu species, and that the presence of H 2 in the feed has beneficial/detrimental effects depending on the zeolite loading with Cu.

Heterogeneous hydrogenation of bicyclo[2.2.2]octenes on Rh/TPPTS/LDH catalysts

The Rh-TPPTS complex was heterogenized onto layered double hydroxides (LDH) Zn 3AlCl and Co 2FeCO 3 using ion-exchange procedure. Before ion exchange, the Rh precursor [Rh(cod)Cl] 2 was dissolved together with the TPPTS ligand in deionised water and stirred for 12 h. After stirring, the LDH was added to the solution and stirred for another 24 h, then filtered, washed with deionised water, and dried under vacuum at room temperature for 16 h. The characterization of the catalysts was carried out using several techniques: ICP-AES, N 2 adsorption–desorption isotherms at −196 °C, thermal analysis, powder X-ray diffraction, XPS and DRIFTs. Substrates were prepared via Diels–Alder reaction of various 2 H-pyran-2-ones with N-substituted maleimides in an aqueous medium with microwave irradiation. The catalytic tests were performed in a stirred stainless-steel autoclave using H 2 pressures in the range 20–40 atm, 30 mg catalyst and 30 mg substrate, at different temperatures. Hydrogenation of bicyclo[2.2.2]octenes showed that these strained and functionalized cycloadducts were inert to classic catalysts but could be hydrogenated by using ionic-immobilized Rh-ligand complexes on the LDH. The Rh-TPPTS/Zn 3AlCl was found to exhibit a pretty high activity and selectivity for such reactions leading to heteropolycyclic derivatives. The heterogeneous catalyst was easily recycled with no leaching.

Formation of argentic clusters and small Ag nanoparticles in soda-lime silicate glass

The formation of argentic clusters and very small Ag nanoparticles of 0.5 to 2 nm size in commercial soda-lime glass silver-doped by Ag/Na ion exchange in a mixed nitrate melt has been studied by electron microscopy and EXAFS. Particles formation was induced already during the ion exchange procedure, or by subsequent ion irradiation with 1.5 MeV He+ or 3 MeV Au+. The presence of nanoparticles was also macroscopically revealed by their surface plasmon resonance. The structural characterization indicates that specific configurations of silver oxide-like structures, so-called argentic clusters, are involved in the initial stage of nanoparticles formation.

Preparation of Pt/ZSM-5 films on stainless steel microreactors

Different synthesis methods (seeded and unseeded liquid phase hydrothermal synthesis, steam-assisted crystallization) have been employed to prepare zeolite films as catalytic coatings on the channels of stainless steel microreactors. The best results were obtained using seeded steam-assisted crystallization (SAC) which under suitable conditions led to well-crystallized zeolite films whose growth was confined to the channel spaces. Liquid phase synthesis yielded higher catalyst loads but was less effective in confining crystal growth to the desired regions. Once the zeolite films were formed, conventional ion-exchange procedures were used to produce a homogeneous distribution of Pt in the zeolite films.

Analytical Developments for High-Precision Measurements of W Isotopes in Iron Meteorites

A procedure was developed to accurately measure the W isotopic compositions of iron meteorites with a precision of better than +/-0.1 epsilon on epsilon182W and epsilon184W (normalized to 186W/183W). Purification of W was achieved through a two-step, ion-exchange procedure. In most cases, the yield is better than 80%, and purified W solutions are clear of matrix elements and direct isobars of W. The final W solutions were analyzed using a Micromass Isoprobe multicollector inductively coupled plasma mass spectrometer (MC-ICPMS). Tests performed on mixtures of terrestrial standards and meteorite samples demonstrate that the method is accurate and that epsilon182W variations as small as approximately 0.1 epsilon can be detected. Analyses of three different aliquots of the Gibeon (IVA) iron meteorite obtained over a period of 6 months show identical epsilon182W values with a weighted mean of 3.38 +/- 0.05, consistent with literature data for IVA iron meteorites, and indicating that the metal-silicate differentiation event in its parent body was either contemporaneous with or slightly postdated (by up to approximately 2.5 My) the formation of refractory inclusions. We demonstrate our ability to measure epsilon184W accurately and precisely (within +/-0.1 epsilon), which is useful for characterizing cosmogenic and nucleosynthetic effects that may be present in iron meteorites. We also report for the first time measurements of epsilon180W, albeit with large error bars (<+/-4 epsilon, in most cases).

Formation of nanoclusters in silver-doped glasses in wet atmosphere

Thermal stability of silver ions in silicate glasses in dry and wet (0.5 - 50% of water content) atmosphere under elevated (160–230 °C) temperature is studied. The glass is doped with silver using silver-to-sodium ion exchange procedure conventionally used for the formation of optical waveguides. It is found that the isothermal annealing of glasses doped with Ag+ ions in a wet argon atmosphere leads to the reduction of silver to metallic state and to the formation of silver nanoclusters in the glass body. The clustering in the course of water diffusion into the glass was studied by optical spectrometry. The clusters were not formed during annealing in a dry atmosphere at the same temperatures.

Sunscreen immobilization on ZnAl-hydrotalcite for new cosmetic formulations

Abstract Intercalation compounds of ZnAl-hydrotalcite with the UV absorber 5-benzoyl-4-hydroxy-2-methoxy-benzenesulphonate acid (4BHF) have been prepared by ion exchange procedure and used to obtain sunscreen stabilization for new cosmetic formulations. Compounds having a sunscreen loading from 26% to 38% w/w have been obtained changing the pH of the equilibrating solution. In fact, taking advantage of the bi-protic nature of 4BHF, the mono-anions, the di-anions or a mixture of mono- and di-valent anions have been intercalated into the hydrotalcite. The compounds obtained have been firstly characterized by TG, XRPD, DSC, and SEM techniques, and then dispersed in a suitable waterproof silicon cream to obtain new sunscreen formulations. The in vitro 4BHF release from the formulation has been determined. Furthermore, the intercalation products and their formulations have been investigated by means UV–vis absorption spectroscopy in order to study the matrix influence on sunscreen sunlight protection effect and on their photostability. The 4BHF intercalation between ZnAl-hydrotalcite lamellae can be considered a good strategy to increase the sunscreen stability and to prepare solar cosmetic formulations always more efficacious and safe.

Hydrotalcite-like compounds: Versatile layered hosts of molecular anions with biological activity

Abstract This paper reviews a systematic work, mainly performed in our laboratories, on the intercalation into hydrotalcite-like compounds (HTlc) of anti-inflammatory drugs, sunscreen and antimicrobials species. The paper is divided in three parts, the first part being addressed to the synthesis, structural aspects and intercalation properties of HTlc, the second part to the properties of the intercalation compounds with biologically active molecular anions, the third part to the preparation of polymeric nanocomposites for biomedical applications. Ion exchange procedures have been used to obtain the intercalation compounds of MgAl-HTlc with ibuprofen, diclofenac, indomethacin, ketoprofen and tiaprofenic acid and to study their release in solutions simulating biological fluids. Some of these intercalation compounds have been tested to improve the solubility of poorly water-soluble drugs such as indomethacin, ketoprofen, tiaprofenic acid and flurbiprofen. MgAl-HTlc and ZnAl-HTlc have been used as starting materials to prepare new sunscreen products, in which organic filters are entrapped between HTlc lamellae, in order to improve “solar product” effectiveness and safety. The preparation of polymeric composites constituted by HTlc exchanged with the anti-inflammatory diclofenac or the antimicrobial drugs and polycaprolactone are also described.

Preparation and analysis of new proton conducting membranes for fuel cells

A range of potential new fuel cell membranes were prepared by inserting zirconium phosphate (ZrP) into divinylbenzene (DVB) crosslinked, sulfonated, polystyrene grafted poly(ethylene-alt-tetrafluoroethylene) and poly(vinyl difluoride) membranes using an ion exchange procedure. In short, the preformed membranes are called ETFE-g-PSSA and PVdF-g-PSSA. The ETFE based membranes represented various degrees of grafting (DOG) and degrees of sulfonation (DOS) whereas all of the PVdF based membranes had a DOG of app. 30% and a DOS of app. 90%. The ion exchange capacity (IEC) values of the ETFE based starting materials were in the range 0.5–2, and those of the PVdF based materials were in the range 1.8–2. A proton conductivity of 40 mS/cm was determined at 130 °C and 90% RH for one of the ETFE based preformed membranes. The ETFE based composite samples had slightly lower proton conductivities. Additional zirconium phosphate treatment resulted in composite ETFE samples containing up to 15 wt.% ZrP and composite PVdF samples containing up to 27 wt.%. TG analyses of the ETFE-g-PSSA and PVdF-g-PSSA composite membranes indicated no significant changes of the thermal stability in comparison to the starting materials. The presence of α-ZrP in the product membranes was indicated by 31P MAS NMR analysis, while transmission electron microscopy (TEM) and powder X-ray diffraction analyses proved the samples to be homogeneous.

Preparation and characterisation of hydrotalcite/carboxyadamantane intercalation compounds as fillers of polymeric nanocomposites

Mono- and di-carboxyadamantane derivatives were intercalated via ion-exchange procedure onto hydrotalcites with formula [Zn0.65Al0.35(OH)2](A)0.35·nH2O where A is Cl– or ClO4–. Furthermore, an intercalation compound of [Mg0.65Al0.35(OH)2](CO3)0.175·0.5H2O containing the mono-carboxyadamantane has been obtained by using the “memory effect” of the hydrotalcite. The obtained materials were characterised for their composition, thermal behaviour, X-ray diffraction patterns, FT-IR absorption spectra and BET specific surface areas. Structural and chemical considerations indicated that mono-carboxylic guests are accommodated in the interlayer region as an ordered bifilm of anions while the di-carboxylic guests give rise to a bifilm of partially interdigitated anions. The presence of hydrophobic anions makes the interlayer region of the hydrotalcites compatible with hydrophobic polymers, such as medium density polyethylene. As an example, the preparation and characterisation of a nanocomposite of polyethylene filled with MgAl hydrotalcite/carboxyadamantane are reported. The nanocomposite, containing 5% w/w of inorganic residue, was prepared by melt compounding and was characterised with X-ray powder diffraction and thermogravimetric techniques. The obtained results showed that the presence of the organically modified hydrotalcite lamellae shields in part the polymer from thermal oxidation, increasing the degradation temperature by about 160 °C and producing a char residue greater than pure polyethylene.

Nature and location of cerium in Ce-loaded Y zeolites as revealed by HRTEM and spectroscopic techniques

Different methods were used to introduce cerium in a HUSY zeolite. The samples obtained from ion-exchange, precipitation and wetness impregnation procedures were characterized both before and after hydrothermal deactivation in order to determine and compare the nature of the cerium species and their location in the catalyst. A variety of techniques were used: XRD, HRTEM, XPS, infrared and Raman spectroscopy and catalytic test of dehydration of 2-propanol. The presence of amorphous phases of extra framework aluminium species (EFAL) depends on the preparation method as was evidenced by TEM. The presence of CeO 2 and exchanged cerium was determined in catalysts prepared by precipitation and impregnation methods. The quantification of both types of cerium species was accomplished by Rietveld refinement. For the catalyst prepared by impregnation, it is suggested that cerium species interact with EFAL species. This interaction determines the cerium dispersion.

Photoluminescence Response of Terbium-Exchanged MFI-Type Materials to Si/Al Ratio, Texture, and Hydration State

Terbium-exchanged MFI zeolite type materials, i.e., microporous-mesoporous Zeotile-1 with the Si/Al ratio in the range 33-200, Zeogrid with the Si/Al ratio of 75, and nanocrystalline MFI with the Si/Al ratio of 75, were prepared via an ion exchange procedure. All of these zeolites were investigated by means of time-resolved photoluminescence techniques in various hydration states: as-synthesized (hydrated), calcined (heated at 450 degrees C in air), and rehydrated (after a six-month exposure to the atmospheric moisture). The photoluminescence decays and spectra were analyzed by discrete exponential fitting, distribution lifetimes analysis, and area-normalized time-resolved photoluminescence spectra. The results sustained a single average terbium species coordinated to both water molecules and framework oxygens in the hydrated zeolites. The framework contribution increased with the Si/Al ratio in Zeotile-1 and was greatest for the nanocrystalline MFI zeolite. For the calcined Zeotile-1 and Zeogrid, two main terbium species of different environments were found. For the nanocrystalline Tb3+-MFI, a distinct number of species could not be inferred, indicating a more heterogeneous distribution. Rehydration further differentiated among the Tb3+-exchanged zeolites. Photoluminescence line shape and decay of Tb3+-Zeotile-1 were between those of the hydrated and calcined states indicating a slow rehydration rate in contrast with the photoluminescence properties of Tb3+-MFI, which fully recovered the values of the hydrated state. Tb3+-Zeogrid presented an intermediate case: while the PL line shape was fully restored to that measured for the hydrated sample, the decay was still longer than that measured with the hydrated sample. Terbium photoluminescence response related to zeolite texture, Si/Al ratio, and hydration state suggest different sitting and location of terbium in Zeotile-1, Zeogrid, and nanocrystalline MFI materials. In mesoporous Zeotile-1 and Zeogrid, the results sustained two types of terbium sites: one on the internal surface of mesopores, the other inside the pores, while for the nanocrystalline MFI, terbium sites inside the pores predominate.

High precision Ag isotope measurements in geologic materials by multiple-collector ICPMS: An evaluation of dry versus wet plasma

This paper presents an improved technique for the precise and accurate determination of Ag isotopic composition in geologic samples. Following the separation of Ag from the rock matrix with a three-stage ion exchange procedure, the isotopic composition is measured by MC-ICPMS. Instrumental mass bias is corrected externally using a Pd standard, which was added to each sample, and sample-standard bracketing. The use of wet plasma significantly improves the analytical precision by eliminating variations in fractionation between Pd and Ag. A virtually identical behavior of the mass bias for Pd and Ag during the analyses is a prerequisite for the external correction method. Replicate dissolutions of the carbonaceous chondrite Allende with <100 ng Ag yield an external reproducibility (2 S.D.) of 53 ppm for 107Ag/ 109Ag. Since the ion exchange procedure provides a good separation from matrix elements such as Ti and Fe, the method is suitable for the analysis of stony and iron meteorites as well as sulfide minerals and terrestrial basalts. The technique thus can be applied to investigate Ag isotopic variations in a large variety of solar system materials.

Development of in situ ion selective sensors for dissolution

The dissolution of formulations of the drugs dapoxetine, paliperidone, cinnarizine, tetrazepam, mebeverine, loperamide, galantamine and ibuprofen was studied by an in-line potentiometric measurement system. The transpose of a Nikolskii-Eisenman type function performed the conversion of potential to percentage of dissolution. A novel gradient membrane electrode was developed especially for dissolution, varying continuously in composition from an ionically conducting rubber phase to an electronically conducting solid state PVC/graphite composite. The gradient part had a thickness of 200 μm. The electrodes life span exceeded 6 months. An ion exchange procedure was used to prepare them for one specific drug. This enabled us to use one universal electrode built to measure a wide array of drugs. The system parameters such as accuracy, reproducibility and linearity were presented with the data obtained for the drug dapoxetine. In dissolution, accurate measurements were possible from 10 −9 to 10 −3 M concentrations, for high log P drugs. The effect of t 90 response times on the measurement error was estimated. The t 90 response times of the electrodes were concentration dependent, and varied between 50 and 10 s for, respectively, 10 −6 and 10 −3 M concentrations. Potential drift was studied in detail. The measurements performed with these electrodes showed an accuracy of 1%, and inter- and intra electrode variabilities of 0.6 and 1.7%, respectively. The electrodes were successfully applied in colloidal media containing suspended matter, typically formed during dissolution of tablets. The advantages and pitfalls of potentiometry over the presently used techniques for dissolution testing are discussed.