Simple Ion-exchange Procedure Research Articles

Modification of zeolite with metallic ions improves the immobilization of phytase

Phytase is an enzyme applied in several fields, but its wider use is still limited due to its high cost and poor stability, which can be overcome using immobilization techniques. Zeolites are promising support materials for enzyme immobilization, due to their attractive properties, including the capacity for modification using a simple ion exchange procedure, enabling better chemical interaction with proteins. In this work, investigation was made of the immobilization of phytase onto zeolites modified with metallic ions (Ag, Cd, Zn, Cu, Ca, Mg, and Ni). The zeolite modified with nickel reached immobilization yield of 66%, while the recovered activity (150%) indicated activation of the catalytic activity due to the presence of the metallic ion. The immobilized phytase showed excellent performance under conditions of acidic pH, reaching a relative activity up to 7 times higher than observed for its free form. Furthermore, it was possible to recover and reuse effectively the zeolite-Ni/Phytase derivative in at least 4 consecutive cycles of phytate hydrolysis reaction. The phytase immobilized onto zeolite modified with nickel presented improved properties, expanding the range of potential applications of this important enzyme. These findings demonstrate an efficient and simple protocol for enzyme immobilization onto zeolites modified with metallic ions.

Polyoxotungstate ([PW11O39]7-) immobilized on mesoporous polymer for selective liquid-phase oxidation of alcohols using H2O2.

Selective oxidation of alcohols is an attractive organic transformation and has received tremendous attention from the scientific community over the years. Herein, a mesoporous polymer (MP) was synthesized by a template-free solvothermal approach. The surface of the MP was functionalized with quaternary ammonium groups and polyoxotungstate anion (PW11O397−) was subsequently supported on the MP as a counter anion to the ammonium cation by a simple ion-exchange procedure. The structure of PW11 and PW4 complexes was confirmed by 31P NMR and FTIR analysis. The surface properties of all the catalysts synthesized were explored by various characterization techniques such as nitrogen sorption, TGA, contact angle measurement, and ICP-OES analysis. The synthesized PW11/MP catalysts were employed for selective oxidation of alcohols. Among the various PW11 supported catalysts, PW11/MP (80 : 20) demonstrated excellent catalytic activity for the oxidation of alcohols using aqueous H2O2. The PW11/MP (80 : 20) catalyst showed good catalytic activity for oxidation of a wide range of alcohols including substituted, heterocyclic and secondary alcohols. The superior catalytic activity of PW11/MP (80 : 20) is attributed to an optimum balance in the hydrophilicity/hydrophobicity in the mesoporous environment, better catalyst wettability, and enrichment of reactants in the catalytic active sites.

ChemInform Abstract: Use of Montmorillonites in Organic Reactions

AbstractReview: 16 refs.

Gd-Al co-doped mesoporous silica nanoparticles loaded with Ru(bpy)₃²⁺ as a dual-modality probe for fluorescence and magnetic resonance imaging.

Mesoporous silica nanoparticles (MSNs) were co-doped with Gd(3+) and Al(3+) and then loaded with Ru(bpy)3(2+) by ion-exchange to prepare Ru/Gd-Al@MSNs. The as-prepared Ru/Gd-Al@MSNs were applied as contrast agents for in vivo fluorescence and magnetic resonance (MR) dual-modality imaging with a mouse as a model. The effects of Al(3+) and MSNs on longitudinal relaxivity (r1) and fluorescence were investigated using a series of Gd-containing silica nanoparticles, including Gd@MSNs, Gd-Al@MSNs, and Ru/Gd-Al@nonporous silica nanoparticles. Co-doping with Al(3+) improved the loading of Gd(3+); the mesoporous structure improved the water exchange rate. The improvement enhanced the MR imaging efficiency of the Ru/Gd-Al@MSN probe. A higher relaxivity (19.2 mM(-1) s(-1)) was observed compared to that from a commercial contrast agent, Gd-diethylene triamine pentaacetic acid (Gd-DTPA). Importantly, the mesoporous structure provided a large specific surface area for the loading of Ru(bpy)3(2+) by a simple ion-exchange procedure. Intense red fluorescence was observed from Ru/Gd-Al@MSN probes. The versatility of Ru/Gd-Al@MSNs for dual-modality imaging was demonstrated using in vivo fluorescence imaging and T1-weighted MR imaging with a mouse model. The nanoparticles are biocompatible and may be attractive for clinical applications.

Synthesis and characterization of cobalt-substituted hydroxyapatite powders

The crystal structure of hydroxyapatite lends itself to a wide variety of substitutions and ion doping, which allows for tailoring of material properties. Magnetic properties are one area of interest in which substitutions can be used to tailor hydroxyapatite properties. Pure HA is diamagnetic, but metal ion doping may lead to a magnetic apatite. In this study, cobalt doped hydroxyapatite was synthesized via two methods: a simple ion-exchange procedure and wet synthesis. The resulting materials were characterized thoroughly for crystal structure and phase purity using X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Magnetic properties were studied using vibrating sample magnetometer and superconducting quantum interference device analysis. The degradation behavior and cobalt release of pure HA and CoHA in simulated body fluid was also examined. The results showed that after both cobalt substitution methods the powder retained characteristic apatite crystal structure and functional groups. Cobalt substituted samples displayed paramagnetic properties, as opposed to the diamagnetism of pure HA. Degradation studies showed that CoHA did not display markedly different degradation behavior from pure HA and the amount of cobalt released over the course of a month was extremely low, alleviating toxicity concerns. Cobalt substituted hydroxyapatite nanoparticles, a biomaterial with magnetic properties, could be a promising material to be used in a variety of biomedical applications, including magnetic imaging, drug delivery, or hyperthermia based cancer treatments.

Synthesis and characterization of iron-substituted hydroxyapatite via a simple ion-exchange procedure

Hydroxyapatite (HA), the main inorganic component of natural bones, is widely studied as a biomaterial due to its excellent biocompatibility and osteoinductivity. The crystal structure of HA lends itself to a wide variety of substitutions and ion doping, which allows for tailoring of material properties. In this study, iron-doped HA was synthesized via a simple ion-exchange procedure and characterized thoroughly for crystal structure and phase purity using X-ray diffraction, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectroscopy, and Fourier transform infrared spectroscopy. Magnetic properties were studied using vibrating sample magnetometer and superconducting quantum interference device analysis. Ion-exchange was attempted using both ferric and ferrous chloride iron solutions, but a substitution was only achieved using ferric chloride solution. The results showed that after iron substitution the powder retained characteristic apatite crystal structure and functional groups, but the iron-doped samples displayed paramagnetic properties, as opposed to the diamagnetism of pure HA. The effect of soaking time on iron content was also examined, and collectively X-ray diffraction and inductively coupled plasma atomic emission spectroscopy results suggested that an increase in soaking time led to an increase in iron content in the sample powder. Iron-substituted HA nanoparticles, a biomaterial with magnetic properties, could be a promising biomaterial to be used in a variety of biomedical fields, including magnetic imaging, drug delivery, or hyperthermia-based cancer treatments.

Montmorillonite

Montmorillonite clay's are layered silicates and are among the numerous inorganic supports for reagents used in organic synthesis. They can be used as an efficient and versatile catalyst for various organic reactions. In Montmorillonite clay one octahedral aluminate layer is sandwiched between two octahedral silicat layers. These are non-toxic, non-corrosive, economical and recyclable. In Montmorillonite clay both Brønsted and Lewis acidic catalytic sites are available, hence its natural occurrence as well as its ion exchange properties allow it to function efficiently as a catalyst. The interlayer cations are exchangeable, thus allowing alteration of the acidic nature of the material by simple ion-exchange procedure. In recent years Montmorillonite particularly Montmorillonite K-10 emerges as an efficient acidic catalyst in organic chemistry. This can be prepared by calcination of Montmorillonite. Montmorillonites are modified by simple cation exchange process to give more effective Montmorillonites such as Fe+ Montmorillonite, clayfen, claycop. Most of the nitrates are deposited on K 10, i.e. Iron (II) nitrate-K 10, Montmorillonite clay and copper (II) nitrate K 10 Bentonite clay. These are used in oxidation and nitration reactions. K 10 is sometimes misunderstood by name or its uses with other clay based acidic catalysts (KSF, K10F, H+-exchanged Montmorillonite, clay). The activation of K 10 clay is carried out by thermal activation. Its acidic character is enhanced by cation exchange, i.e. by Fe (II), Zn (II) or by deposition of Lewis acids such as Zn (II) or Iron (III) chlorides. Recent reports on K 10 focus on some important reaction and various transformations. K 10 is used as catalyst in the synthesis of dimethyl acetals, enamines, γ-lactones, enolthioethers, α,β-unsaturated aldehydes and porphyrin synthesis etc.

Simple ion exchange procedure of common anions to TRISPHAT. Application to the purification of cationic species

Triarylcarbenium, monomethine cations are poorly retained on polar chromatographic phases when associated with TRISPHAT as counterion as opposed to classical anions. This allows an easy separation and purification of these organic cationic salts.

Purification of reagents and separation of element traces by electrodeposition onto a graphite tube cathode

The use of a commercially available AAS graphite tube atomizer as an electrode for the cathodic electrodeposition of element traces at constant-current in a hydrodynamic flow-through-system is described. After deposition the graphite tube is transferred into an atomizer unit for subsequent sensitive determination by atomic absorption spectrometry. The deposition yield of ≥99% (2 h; 1.5 A) for Co was verified, using60Co as a radioactive tracer, by monitoring the concentration fall in the electrolyte solution down to ≤5 pg/ml, and the deposited material. The efficiency of the system for the purification of electrolyte solutions was found to be very high. For the determination of the residual impurities, e.g. in very concentrated NH4F-solutions, a simple ion-exchange procedure was worked out for Cu, Mn, Ni, Pb, Zn. To get back the high purity solid NH4F, the solvent was evaporated partly and the precipitated crystals were sucked off in a PTFE-funnel. To avoid contamination, crystallization was carried out in a closed container system using the principle of subboiling distillation. The purity of the recrystallized NH4F-salt increased by a factor of 2 to 3 (crystallization yield 50–70%) so that a solid product with an impurity level below 0.5 ng/g was obtained.

Ion exchange separation of90Y from90Sr using ascorbic acid and nitrilotriacetic acid as eluents

A simple ion exchange procedure for clean separation of the biomedically important radionuclide,90Y, in the equilibrium mixture,90Sr−90Y, has been demonstrated. Separation of90Y in the carrier-free state has been achieved by preferential elution of the radiotracer through a cation exchange resin column of Dowex-50W-X8 with freshly prepared Na-ascorbate solution of <1% concentration at pH7. The radionuclidic purity of the separated90Y has been verified by taking recourse to the studies of beta decay curves. The procedure developed has the added advantage that the complexing reagent, ascorbic acid, itself has got its own biomedical importance as vitamin C and the technique can also conveniently be used as a generator for the isotope90Y.

Fatty acid contamination and dielectric relaxation in phospholipid vesicle suspensions

Aqueous vesicle or micelle suspensions from various synthetic lecithins or surfactants - most of them purified by a simple ion-exchange procedure in methanol - were investigated, some with ionic admixtures. The dielectric permittivity '(nu) between 5 kHz and 100 MHz was determined by different time-and frequency-domain methods, with attention given to electrode polarization below 1 MHz. Pure ether lecithins (used to reduce hydrolysis during preparation) as well as ester lecithins showed no dielectric dispersion below 10 MHz (Delta' 3). In contrast, even dilute colloidal solutions containing about 1 mol% (with respect to solute) ionic amphiphiles normally exhibited large dielectric dispersion (10 < Delta' < 700), especially with electrolyte present. This low-frequency dispersion is sensitive to vesicle coagulation or fusion. Underlying relaxation mechanisms are discussed, and the main relaxation is shown to be the same as for other charged colloids. This conclusion suggest a new interpretation of measurements, previously reported by other authors, who gave an interpretation in terms of correlated zwitterionic head group orientation in multilamellar lecithin liposomes. Possible effects from traces of impurities in lipids are discussed.

Radiochemical determination of chromium in biological tissues by ion-exchange

A simple ion exchange procedure has been developed for the separation of chromium from the other chemical elements in biological tissues. This procedure combined with neutron activation analysis has been applied successfully to the determination of chromium in a reference biological material. The precision was ±11%, the accuracy 3% and the sensitivity found was 10 ng with only 20 hrs irradiation at 2.8·1013 n·cm−2·sec−1 flux The main steps of the procedure are: wetdigestion of the irradiated tissue, oxidation to chromium (VI), fixation onto an anion resin in sulfate form, washing of the resin with 1N H2SO4, collection of chromium by reductive elution for counting and finally determination of the chemical yield by reactivation.

Rat small-intestinal beta-galactosidases. Studies on the fractionation of "acid" beta-galactosidase with isoelectric focusing, gel filtration and ion-exchange chromatography.

1. Different forms of the rat small-intestinal ;acid' beta-galactosidase were separated by using the isoelectric-focusing technique. The isoelectric points of the different forms were at pH4.2, 4.6, 5.4, 6.1 and approx. 8. 2. The two forms of ;acid' beta-galactosidase isoelectric at pH4.2 and 4.6 were completely excluded from the Sephadex G-200 gel, whereas the form isoelectric at pH8 had K(av.) 0.4. The concentration and pH of the elution buffer influenced the distribution of enzyme activity between different forms. Thus, under certain conditions of ionic strength and pH, the enzyme seems to form high-molecular-weight aggregates with low isoelectric points. These may be homopolymeric aggregates or the result of binding of enzyme to, for example, membrane fragments. The forms isoelectric at pH5.4 and 6.1 are probably aggregates of intermediate size. 3. During ion-exchange chromatography at pH6.0 one fraction of ;acid' beta-galactosidase was not retained on the column and was isoelectric at pH8 and another fraction was eluted when the buffer concentration in the eluate had increased to about 50mm. The main part of enzyme eluted in this second fraction was also isoelectric at pH8, indicating that the elution of this fraction is not a simple ion-exchange procedure but probably also involves a splitting of high-molecular-weight aggregates, originally retained because of their low isoelectric points. The enzyme subunits have a higher isoelectric point, and are therefore no longer bound to the ion-exchange resin.