A new thermostable peroxidase from garlic Allium sativum

Analysis of peroxidase activity by native polyacrylamide gel electrophoresis (PAGE) from a garlic bulb (Allium sativum L) extract showed two major activities (designated POX1 and POX2). The POX2 isoenzyme was purified to homogeneity by ammonium sulfate precipitation, gel filtration, and cation-exchange chromatography. The purified enzyme was found to be monomeric with a molecular mass of 36.5 kDa, as determined by sodium dodecyl sulfate-PAGE. The optimum temperature ranged from 25 to 40 degrees C and optimum pH was about 5.0. The apparent Km values for guaiacol and H2O2 were 9.5 and 2 mM, respectively. POX2 appeared highly stable since 50% of its activity was conserved at 50 degrees C for 5 h. Moreover POX2 was stable over a pH range of 3.5-11.0. Immobilization of POX2 was achieved by covalent binding of the enzyme to an epoxy-Sepharose matrix. The immobilized enzyme showed great stability toward heat and storage when compared with soluble enzyme. These properties permit the use of this enzyme as a biosensor to detect H2O2 in some food components such as milk or its derivatives.     

A β-glucosidase from Sclerotinia sclerotiorum

The filamentous fungus Sclerotinia sclerotiorum, grown on a xylose medium, was found to excrete one β-glucosidase (β-glu x). The enzyme was purified to apparent homogeneity by ammonium sulfate precipitation, gel filtration, anion-exchange chromatography, and high-performance liquid chromatography (HPLC) gel filtration chromatography. Its molecular mass was estimated to be 130 kDa by HPLC gel filtration and 60 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that β-glu x may be a homodimer. For p-nitrophenyl β-d-glucopyranoside hydrolysis, apparent K _m and V _max values were found to be 0.09 mM and 193 U/mg, respectively, while optimum temperature and pH were 55–60°C and pH 5.0, respectively. β-Glu x was strongly inhibited by Fe²⁺ and activated about 35% by Ca²⁺. β-Glu x possesses strong transglucosylation activity in comparison with commercially available β-glucosidases. The production rate of total glucooligosaccharides (GOSs) from 30% cellobiose at 50°C and pH 5.0 for 6 h with 0.6 U/mL of enzyme preparation was 80 g/L. It reached 105 g/L under the same conditions when using cellobiose at 350 g/L (1.023 M). Finally, GOS structure was determined by mass spectrometry and ¹³C nuclear magnetic resonance spectroscopy.     

A beta-glucosidase from Sclerotinia sclerotiorum: biochemical characterization and use in oligosaccharide synthesis

The filamentous fungus Sclerotinia sclerotiorum, grown on a xylose medium, was found to excrete one beta-glucosidase (beta-glu x). The enzyme was purified to apparent homogeneity by ammonium sulfate precipitation, gel filtration, anion-exchange chromatography, and high-performance liquid chromatography (HPLC) gel filtration chromatography. Its molecular mass was estimated to be 130 kDa by HPLC gel filtration and 60 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that beta-glu x may be a homodimer. For p-nitrophenyl beta-d-glucopyranoside hydrolysis, apparent Km and Vmax values were found to be 0.09 mM and 193 U/mg, respectively, while optimum temperature and pH were 55-60 degrees C and pH 5.0, respectively. beta-Glu x was strongly inhibited by Fe2+ and activated about 35% by Ca2+. beta-Glu x possesses strong transglucosylation activity in comparison with commercially available beta-glucosidases. The production rate of total glucooligosaccharides (GOSs) from 30% cellobiose at 50 degrees C and pH 5.0 for 6 h with 0.6 U/mL of enzyme preparation was 80 g/L. It reached 105 g/L under the same conditions when using cellobiose at 350 g/L (1.023 M). Finally, GOS structure was determined by mass spectrometry and 3C nuclear magnetic resonance spectroscopy.     

Synthesis and Characterization of Two New Compounds: N(C2H4NH3)3(H2TO4)(HTO4)·2H2O (T = P,As)

The synthesis and structures of two new compounds with the general formula N(C₂H₄NH₃)₃(H₂TO₄)(HTO₄)·2H₂O (T = P, As) are reported. They crystallize with triclinic unit cells and are isotropic. We determined the structure of phosphate salt. The following unit cell parameters were found: a = 9.886(4), b = 9.308(2), c = 10.140(3) Å, α = 109.38(2), β = 108.83(3), γ = 74.40(3)°, V = 819.2(5) ų, and ρ_cal. = 1.537 g · cm^?3. The crystal structure was solved with a final R = 0.042 for 3748 with I > 3σ I). The space group is P-1 and Z = 2. The atomic arrangement can be described as a three-dimensional network of hydrogen bonds made up from H_nPO₄ ^3?n (n = 1, 2) anions and H ₂ O molecules between which are trapped the tris(2-ammoniumethyl)amine cations. Solid-state ¹³C and ³¹P MAS-NMR spectroscopies are in agreement with X-ray structure. Ab initio calculations allow the attribution of the phosphorus signals to the independent crystallographic sites.     

Investigation of the vibrational modes of ZnO grown by MOCVD on different orientation planes

Wurtzite ZnO thin films were prepared on sapphire substrate by metal organic chemical vapor deposition (MOCVD). Raman scattering studies on different crystallographic textures were performed in the backscattering geometry, and polarization effect is investigated in different configurations and . ZnO Raman modes are investigated in each texture. In the case of ZnO thin film deposed on r‐() sapphire plane and using backscattering geometry, new Raman line was observed at 390 cm⁻¹ because this mode has not been noticed in this geometry. It is shown that the frequencies of the quasi‐phonon modes of the examined thin film are in good agreement with the theoretical values calculated within the framework of Loudon model. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and photochemical properties of novel pentamethylated norbornadiene containing polyimides

A novel pentamethylated norbornadiene (NBD) based dianhydride, α,α′‐bis‐(3,4,5,6,7‐pentamethylcyclopenta‐2,4‐dienyl)meta‐xylene‐1,2‐dianhydride (3), was prepared from α,α′‐bis‐(pentamethylcyclopentadienyl)meta‐xylene (1) and acetylene dicarboxylic acid. The bis‐adduct formed via Diels–Alder reaction afforded tetra‐acid (2), which was chemically cyclodehydrated to lead the targeted dianhydride (3). New polyimides containing NBD moieties in the main chain were prepared from the dianhydride monomer (3) and various aromatic diamines. The chemical structure of the polymers was confirmed by both ¹H and ¹³C NMR analysis. Their Molecular weights were also measured by SEC. All of these polyimides are soluble at room temperature in common organic solvents, such as chloroform, dichloromethane, THF, DMSO, DMF, and NMP, and show good thermal stabilities. The photochemical isomerization of the NBD into quadricyclane (QC) was investigated by UV/vis spectrophotometry from polymer films using visible sunlight as irradiation source. It was found that the kinetic rate of the conversion NBD‐QC which proceeded smoothly is a first kinetic order. The stored energies released by the transformation of QC groups into NBD ones of the irradiated polymer films were also evaluated by DSC measurement and were found to be around 90 kJ mol^?1. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The Influence of Mind Mapping on Eighth Graders’ Science Achievement

This study assessed the influence of using mind maps as a learning tool on eighth graders’ science achievement, whether such influence was mediated by students’ prior scholastic achievement, and the relationship between students’ mind maps and their conceptual understandings. Sixty‐two students enrolled in four intact sections of a grade 8 science classroom were randomly assigned to experimental and comparison conditions. Participants in the experimental group received training in, and constructed, mind maps throughout a science unit. Engagement with mind mapping was counterbalanced with involving the comparison group participants with note summarization to control for time on task as a confounding variable. Otherwise, the intervention was similar for both groups in all respects. A multiple choice test was used to measure student gains across two categories and three levels of achievement. Data analyses indicated that the experimental group participants achieved statistically significant and substantially higher gains than students in the comparison group. The gains were not mediated by participants’ prior scholastic achievement. Analyses also indicated that iconography was not as central to participants’ mind maps as often theorized. Depicting accurate links between central themes and major and minor concepts, and using colors to represent concepts were the major aspects that differentiated the mind maps built by students who achieved higher levels of conceptual understanding.     

Time-resolved photoluminescence of delta-doped AlGaAs/GaAs heterostructures

The photoluminescence (PL) at low temperature of three delta-doped AlGaAs/GaAs heterostructures is investigated under continuous and pulsed excitations. The PL under continuous excitations allows the identification of the trapping centres and probes the carrier's transfer to the GaAs channel. The time-resolved photoluminescence (TRPL) inquires about carrier dynamics and gives radiative lifetimes of different levels. The DX level shows two time constants of the intensity decay relating the splitting of the valence band under impurity strains which reduce the crystal symmetry. The two time constants evolve with temperature and exhibit an increase near T=50 K.     

Synthesis of new azo compounds based on N-(4-hydroxypheneyl)maleimide and N-(4-methylpheneyl)maleimide

Maleic anhydride was reacted with p-aminophenol and p-toluidine in the presence of di-phosphorus pentoxide (P?O?) as a catalyst to produce two compounds: N-(4-hydroxy-phenyl)maleimide (I) and N-(4-methylphenyl)maleimide (II). The new azo compounds I(a-c) and II(a-c) were prepared by the reaction of I and II with three different aromatic amines, namely aniline, p-aminophenol and p-toluidine. The structures of these compounds were confirmed by CHN, FT-IR, 1H-NMR, 13C-NMR, mass spectrum and UV/Vis spectroscopy.