Biochemical characterization and stability assessment of Rhizopus oryzae lipase covalently immobilized on amino-functionalized magnetic nanoparticles.

Amino-functionalized magnetic nanoparticles (Fe3O4) have been investigated as a support for covalent immobilization of lipase. The nanoparticles were prepared by chemical coprecipitation method and subsequently were coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction. With glutaraldehyde, as the coupling agent, the lipase from Rhizopus oryzae was successfully immobilized onto the amino-functionalized magnetic nanoparticles. The synthesized support was characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The results showed that the load of immobilized protein could reach as high as 7mg protein g-1 support. The optimum pH for maximal catalytic activity of the immobilized enzyme was 8.0 at 40°C. The Km values were found as 0.66 and 0.57mgmL-1 for the free and immobilized enzymes, respectively. The Vmax values for the free and immobilized enzymes were calculated as 0.14 and 0.47µmolmg-1min-1, in turn, when p-nitrophenyl butyrate (pNPB) was used as the substrate. A quick separation of lipase from the reaction mixture was achieved when a magnetically active support was applied. In comparison to the free enzyme, the immobilized enzyme was thermally stable and was reusable for 10 cycles while retaining 64% of its initial activity.

Efficient Immobilization of Porcine Pancreatic α-Amylase on Amino-Functionalized Magnetite Nanoparticles: Characterization and Stability Evaluation of the Immobilized Enzyme.

The potential of the modified magnetic nanoparticles for covalent immobilization of porcine pancreatic α-amylase has been investigated. The synthesis and immobilization processes were simple and fast. The co-precipitation method was used for synthesis of magnetic iron oxide (Fe3O4) nanoparticles (NPs) which were subsequently coated with silica through sol-gel reaction. The amino-functionalized NPs were prepared by treating silica-coated NPs with 3-aminopropyltriethoxysilane followed by covalent immobilization of α-amylase by glutaraldehyde. The optimum enzyme concentration and incubation time for immobilization reaction were 150 mg and 4 h, respectively. Upon this immobilization, the α-amylase retained more than 50 % of its initial specific activity. The optimum pH for maximal catalytic activity of the immobilized enzyme was 6.5 at 45 °C. The kinetic studies on the immobilized enzyme and its free counterpart revealed an acceptable change of Km and Vmax. The Km values were found as 4 and 2.5 mM for free and immobilized enzymes, respectively. The Vmax values for the free and immobilized enzymes were calculated as 1.75 and 1.03 µmol mg-1 min-1, in order, when starch was used as the substrate. A quick separation of immobilized amylase from reaction mixture was achieved when a magnetically active support was applied. In comparison to the free enzyme, the immobilized enzyme was thermally stable and was reusable for 9 cycles while retaining 68 % of its initial activity.

Effect of gold nanoparticle as a novel nanocatalyst on luminol-hydrazine chemiluminescence system and its analytical application.

In this work the catalytic role of unsupported gold nanoparticles on the luminol-hydrazine reaction is investigated. Gold nanoparticles catalyze the reaction of hydrazine and dissolved oxygen to generate hydrogen peroxide and also catalyze the oxidation of luminol by the produced hydrogen peroxide. The result is an intense chemiluminescence (CL) due to the excited 3-aminophthalate anion. In the absence of gold nanoparticles no detectable CL was observed by the reaction of luminol and hydrazine unless an external oxidant is present in the system. The size effect of gold nanoparticles on the CL intensity was investigated. The most intensive CL signals were obtained with 15-nm gold nanoparticles. UV-vis spectra and transmission electron microscopy studies were used to investigate the CL mechanism. The luminol and hydroxide ion concentration, gold nanoparticles size and flow rate were optimized. The proposed method was successfully applied to the determination of hydrazine in boiler feed water samples. Between 0.1 and 30 microM of hydrazine could be determined with a detection limit of 30 nM.

Ultra trace adsorptive stripping voltammetric determination of atrazine in soil and water using mercury film electrode.

In situ mercury film electrode produced in the presence of thiocyanate has been shown extremely useful for highly sensitive adsorptive stripping voltammetric measurements of atrazine down to sub-microg L(-1) level. Operational parameters have been optimized and the stripping voltammetric performance has been investigated using square wave scans. The adsorptive stripping response is linear over the range of 0.5-60 microg L(-1) atrazine, with a detection limit of 0.024 microg L(-1). The method has been applied to the determination of atrazine in soil and water samples.

Application of artificial neural networks as a technique for interference removal: kinetic-spectrophotometric determination of trace amounts of Se(IV) in the presence of Te(IV).

Artificial neural networks (ANNs) are among the most popular techniques for nonlinear multivariate calibration in complicated mixtures using spectrophotometric data. In this study we propose a computer-based method for removing Te(IV) interference in the determination of Se(IV) using artificial neural networks. In this way, an artificial neural network consisting of three layers of nodes was trained by applying a back-propagation learning rule. The resulting RMSE of prediction for selenium was obtained as 0.108.