Publications (59) View all
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Article: Characterization of recombinant FAD-independent catabolic acetolactate synthase from Enterococcus faecalis V583.
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ABSTRACT: The catabolic acetolactate synthase (cALS) of Enterococcus faecalis V583 was cloned, expressed in Escherichia coli, and purified to homogeneity. The purified protein had a molecular weight of 60kDa. The cALS of E. faecalis is highly homologous with other cALSs, while sharing low homology with its anabolic counterparts. The cALS of E. faecalis exhibits optimum activity at a temperature of 37°C and pH 6.8. Based on the enzyme characterization, the apparent K(m) for pyruvate was calculated to be 1.37mM, while the K(c) for thiamin diphosphate (ThDP) and Mg(2+) were found to be 0.031μM and 1.27mM, respectively. Negligible absorbance at 450nm and lack of activity enhancement upon addition of flavin adenine dinucleotide (FAD) to the assay buffer suggest that the cALS of E. faecalis is not FAD-dependent. The enzyme showed extreme stability against the organic solvent dimethyl sulfoxide (DMSO), whereas the activity decreased to less than 50% in the presence of acetone and ethanol.Enzyme and microbial technology. 01/2013; 52(1):54-9. -
Article: Manganese-Doped Highly Ordered Mesoporous Silicate with High Efficiency for Oxidation Suppression.
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ABSTRACT: Herein, we demonstrate a facile approach to manganese-doped highly ordered mesoporous silicate with oxidation-suppression function. As biocompatible supports of guest ions, the ordered mesoporous silicate was synthesized by evaporation-induced self-assembly. The phase-transition from disordered to lamellar structures in the highly ordered mesoporous structure of these porosity-tuned materials was controlled by adjusting the concentration of a lab-made polystyrene-b-polyethylene oxide copolymer. Manganese was successfully incorporated as a guest in the hexagonally packed mesoporous silicate by using an ultrasound-assisted technique. The incorporation of manganese ions into the pores of a mesoporous silicate support could be induced for host-guest functional applications. Manganese-doped mesoporous silicate structures have been examined for their use as antioxidizing agents by electron spin resonance (ESR) measurements and radical-scavenging tests. The manganese atoms in the mesoporous structures could act in a free-radical-scavenging capacity, much like manganese nanoparticles. The high efficiency of their oxidation-suppression function is extended for application to catalytic products.Chemistry 11/2012; · 5.93 Impact Factor -
Article: A thiazolothiazole based Cu(2+) selective colorimetric and fluorescent sensor via unique radical formation.
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ABSTRACT: A novel thiazolothiazole-based Cu(2+) colorimetric and fluorescent sensor is reported. A highly selective colorimetric change from yellow to dark green was observed among various metal ions after adding Cu(2+). Unique radical formation can engender these highly selective colorimetric and fluorescent changes.Chemical Communications 11/2012; · 6.17 Impact Factor -
Article: Synthesis of multifunctional metal- and metal oxide core@mesoporous silica shell structures by using a wet chemical approach.
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ABSTRACT: We demonstrate a facile wet chemical approach for fabricating spherical metal/metal-oxide core@mesoporous silica shell hybrid nanoparticles with different core and shell thicknesses. Vertically aligned mesoporous silica (mSiO(2) ) shells were fabricated over the pre-synthesized spherical SiO(2) nanoparticles through a three-step strategy: 1) synthesis of core materials, 2) covering the core with an organic-inorganic composite layer, and 3) removing the organic template through calcinations in air. The mechanisms of hybrid structure formation are proposed. The multifunctional nature of the hybrid structures could be induced by incorporating guest ions/molecules, such as Ag, Mn, and TiO(2) , into the pores of an mSiO(2) shell. Mn and TiO(2) cluster- incorporated composite structures have been tested to be antioxidizing agents and effective photocatalysts through electron spin resonance, radical scavenging tests, and the photocatalytic degradation of rhodamine B. The possibility of incorporating several hetero-element guest clusters in these mesoporous composite particles makes them highly attractive for multifunctional applications.Chemistry 08/2012; 18(39):12314-21. · 5.93 Impact Factor -
Article: Photochemical production of NADH using cobaloxime catalysts and visible-light energy.
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ABSTRACT: In this study, a visible-light-driven photocatalytic system for the generation of dihydronicotinamide adenine dinucleotide (NADH) from aqueous protons was examined using cobaloxime as a catalyst, eosin as a photosensitizer, and triethanolamine as a sacrificial electron donor. Irradiation of a reaction solution containing cobaloxime, eosin, and triethanolamine (TEOA) converted NAD(+) to NADH with a yield of 36% in a phosphate buffer. The reaction rates for the production of NADH were dependent on the concentrations of the catalyst, NAD(+), and TEOA. Introduction of an electron-donating or -withdrawing substituent in the para position of the pyridine changed the rate constant and affected the conversion efficiency. The rates obtained by the different substituents were linearly correlated with the Hammett coefficients of the introduced substituents. Last, reduction of CO(2) was carried out in the presence of formate dehydrogenase using NADH photochemically generated using the cobaloxime/eosin/TEOA system.Inorganic Chemistry 07/2012; 51(15):8057-63. · 4.60 Impact Factor
