Covalent Immobilization of a α-Amylase onto Poly(methyl methacrylate-2-hydroxyethyl methacrylate) Microspheres and the Effect of Ca2+ Ions on the Enzyme Activity

α-Amylase was covalently immobilized onto poly(methyl methacrylate-2-hydroxyethyl methacrylate) microspheres, which were activated by using either epichlorohydrin (ECH) or cyanuric chloride (C₃N₃Cl₃). The properties of the immobilized enzyme were investigated and compared with those of the free enzyme. For the assays carried out at 25 °C and pH 6.9, the relative activities were found to be 73.0% and 90.8% for epichlorohydrin and cyanuric chloride bound enzymes, respectively. Upon immobilization, the maximum activities were obtained at lower pH values and higher temperatures as compared with the free enzyme. Kinetic parameters were calculated as 2.51 g/L, 28.54 g/L and 15.50 g/L for K_m and 1.67 × 10⁻³ gL⁻¹ min⁻¹ 2.89 × 10⁻⁴ gL⁻¹ min⁻¹ and 1.89 × 10⁻³ gL⁻¹ min⁻¹ for V_max for free, epichlorohydrin and cyanuric chloride bound enzymes, respectively. Enzyme activities were found to be ca. 32.7% for ECH and 41.1% for C₃N₃Cl₃ activated matrices after storage for one month. On the other hand the free enzyme lost its activity completely within 20 days. Immobilization, storage stability and repeated use capability experiments carried out in the presence of Ca²⁺ ions demonstrated higher stability in the presence of these ions. The enzymes immobilized in the presence of Ca²⁺ ions retained 90.6% and 90.8% of the original activities even after 30 days in the case of ECH and C₃N₃Cl₃ activations, respectively. In repeated batch experiments, i.e., 20 uses of the enzyme in 3 days; in the absence of Ca²⁺ ions retentions of 79.2% and 77.1% of the original enzyme activities were observed for ECH and C₃N₃Cl₃ immobilized enzymes, respectively, whereas, in the case of addition of Ca²⁺ ions to the assay medium, these values were enhanced to 95.3% and 92.2%.     

Preparation and properties of selective polyurethane films and their use for the development of biomedical dopamine sensor

Polyurethane films were synthesized by 3,4-divanillyltetrahydrofuran and different diisocyanates. These prepared polyurethanes were characterized by FT-IR, DSC, DTA, and TGA techniques. For the amperometric applications, synthesized polyurethanes exhibited suitable T_g (°C), good thermal stability and good adhesive properties. In addition, because of their interesting film properties, attempts were made to prepare dopamine-sensing electrode. For this reason, selectivity of film-coated electrodes obtained from the chemically prepared polyurethanes toward electroactive and nonelectroactive species were examined by means of DPV technique. From the electrochemical results obtained, it has been demonstrated that the PU-1-coated electrode can be used for the development of biomedical sensor.     

All Solution‐Based Fabrication of Copper Oxide Thin Film/Cobalt‐Doped Zinc Oxide Nanowire Heterojunctions

Versatile and intriguing solution‐based processes are utilized to synthesize nanostructured materials for device applications to reduce material production and device fabrication costs. This study presents results on the fabrication and characterization of copper oxide (CuO) coated cobalt‐doped zinc oxide nanowires (Co‐doped ZnO NWs)‐based heterojunction diodes prepared by a two‐step synthesis route through combined hydrothermal growth and sol–gel spin coating. Highly dense, well‐ordered, undoped, and Co‐doped ZnO NWs were successfully grown by hydrothermal method. Complementary CuO thin films were synthesized by sol–gel method and subsequently coated onto both undoped and Co‐doped ZnO NWs through spin‐coating technique. Enhanced diode properties with a rectification ratio of 10³ at ±2 V and an ideality factor of n = 2.4 (in dark) were obtained for Co‐doped ZnO NWs‐based heterojunction diodes. The obtained results demonstrated that the investigated heterojunction diode structure fabricated by facile and cost‐effective solution‐based processes can be a promising candidate for the next generation optoelectronic devices.     

Solvent-free glycerolysis catalyzed by acetone powder of Nigella sativa seed lipase

The solvent-free glycerolysis of used sunflower oil catalyzed by acetone powder of Nigella sativa seeds was investigated. The highest partial acylglycerols yield was obtained at 60°C. The glycerolysis reactions, conducted at molar ratios of 1:1, 2:1, and 3:1 of oil to glycerol keeping the acetone powder content at 30% based on oil weight and the temperature at 60°C, approached equilibrium after 2 h. The highest partial acylglycerol content of the products was 66% (1:1 molar ratio) and 60% (2:1 molar ratio).     

Poly(ε‐caprolactone) composites containing gentamicin‐loaded β‐tricalcium phosphate/gelatin microspheres as bone tissue supports

In this work, novel antibacterial composites were prepared by using poly(ε‐caprolactone) (PCL) as the main matrix material, and gentamicin‐loaded microspheres composed of β‐tricalcium phosphate (β‐TCP) and gelatin. The purpose is to use this biodegradable material as a support for bone tissue. This composite system is expected to enhance bone regeneration by the presence of β‐TCP and prevent a possible infection that might occur around the defected bone region by the release of gentamicin. The effects of the ratio of the β‐TCP/gelatin microspheres on the morphological, mechanical, and degradation properties of composite films as well as in vitro antibiotic release and antibacterial activities against Escherichia coli and Staphylococcus aureus were investigated. The results showed that the composites of PCL and β‐TCP/gelatin microspheres had antibacterial activities for both bacteria. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The investigation of the effect of thermal barrier coating on the performance of Stirling engine

The shuttle heat transfer is one of the reasons reducing the performance of Stirling engines. This study is concerned with the reduction in shuttle heat transfer by coating the displacer. The displacer of a gamma type Stirling engine was coated with a layer of yttria‐stabilized zirconia (YSZ), and the effect of the coating on the engine performance was evaluated by comparing speed‐power and speed‐torque characteristics of the engine with coated and uncoated displacers. Characteristics were obtained for 700, 800 and 900°C heater temperatures. At each stage of the heater temperature, the charge pressure ranged from 1 to 3.5 bars with 0.5 bar increments. At 900°C heater temperature and 3 bars charge pressure, the shaft power before coating was 34.9 W, after coating the power increased to 43.8 W, which corresponds to a 25% increment. The temperature applied to the engine did not cause any damage on the coating layer. Copyright © 2008 John Wiley & Sons, Ltd.     

Corrosion behavior of tempered dual-phase steel embedded in concrete

Dual-phase(DP) steels with different martensite contents were obtained by appropriate heat treatment of an SAE1010 structural carbon steel,which was cheap and widely used in the construction industry. The corrosion behavior of DP steels in con-crete was investigated under various tempering conditions. Intercritical annealing heat treatment was applied to the reinforcing steel to obtain DP steels with different contents of martensite. These DP steels were tempered at 200,300,and 400°C for 45 min and then coo...     

Synthesis of boron/nitrogen substituted carbons for aqueous asymmetric capacitors

Boron/nitrogen substituted carbons were synthesized by co-pyrolysis of polyborazylene/coal tar pitch blends to yield a carbon with a boron and nitrogen content of 14 at% and 10 at%, respectively. The presence of heteroatoms in these carbons shifted the hydrogen evolution overpotential to −1.4 V vs Ag/AgCl in aqueous electrolytes, providing a large electrochemical potential window (∼2.4 V) as well as a specific capacitance of 0.6 F/m². An asymmetric capacitor was fabricated using the as-prepared low surface area carbon as the negative electrode along with a redox active manganese dioxide as the positive electrode. The energy density of the capacitor exceeded 10 Wh/kg at a power density of 1 kW/kg and had a cycle life greater than 1000 cycles.