ABSTRACT Aminopeptidase‐I from pronase contains five tryptophan residues, determined by modificat... more ABSTRACT Aminopeptidase‐I from pronase contains five tryptophan residues, determined by modification with N‐bromosuccinimide and MCD measurments. The fluorescence of the enzyme is quenched by acrylamide, a neutral quencher, but not by iodide, an anionic quencher. The quenching constant for acrylamide is about one tenth that of acctyltryptophan in aqueous solution because of the steric effect of the large protein molecule. The inaccessibility of iodide to the tryptophans is probably due to the anionic environment of the fluorophores created by the large content of Asp and Glu in the enzyme. Aminopeptidase‐I is quenched by Cu(II) and Co(II) through the formation of a nonfluorescent ground‐state complex. The results indicate that there are three accessible tryptophans for Cu(II) and two for Co(II) suggesting that some tryptophans are buried inside the enzyme and are thus inaccessible to the quencher. In the presence of a competitive inhibitor, the enzyme contains one fewer accessible tryptophan for Cu(II) indicating that this tryptophan is located in the active center. The CD spectrum of the enzyme in the far UV region is unaltered by the presence of Ca(II), whereas that in the aromatic region is enhanced significantly. The perturbation of the CD spectrum probably results from the local conformational change induced by Ca(II) or from the rigidity of the tryptophan being enhanced by the bound Ca(II).
The radiolytic degradation of methyl tert-butyl ether (MTBE) in air-equilibrated dilute solution ... more The radiolytic degradation of methyl tert-butyl ether (MTBE) in air-equilibrated dilute solution was investigated. Complete degradation of MTBE can be achieved within 5 min of irradiation at 59.7 Gy/min. The observed first-order degradation rate constant, called dose constant, increased from 0.04 to 0.56 Gy(-1) as the concentration of MTBE decreased from 92500 to 19 microg/L. Tert-butyl formate, tert-butyl alcohol, acetone and methyl acetate were found to be the primary intermediates of the degradation reaction with yields of 47%, 11%, 6.4% and 9.1%, respectively. The degradation of MTBE or its intermediates was also found to depend on the concentrations of benzene and cupric ion. The study shows that the removal of MTBE can be significantly decreased with increasing concentration of benzene. Little affects were observed with the presence of cupric ions, while the degradation of TBF was apparently reduced. These results indicate that gamma radiolysis can be a potentially effective t...
A method for the analysis of six alkyl organoiodides (iodomethane, iodoethane, 1-iodopropane, 1-i... more A method for the analysis of six alkyl organoiodides (iodomethane, iodoethane, 1-iodopropane, 1-iodobutane, 1-iodopentane, 1-iodohexane) commonly found in acetic acid process was developed. In this method the target analytes were determined by high-performance liquid chromatography (HPLC) using a post-column photochemical reactor with electrochemical detection (ED) in less than 30 min. HPLC was performed in ODS C18 reversed-phase column (5 microm, 250 x 4.6 mm I.D.) under isocratic conditions with methanol-0.067 M acetate buffer (70:30, v/v), pH 6.2 as mobile phase at flow-rate 1.1 ml/min. Alkyl organoiodides, which are electrochemically inactive, were made oxidizable at potential of 120 mV after post-column irradiation with low-pressure mercury lamp in a knitted PTFE tube. The photoreactor was placedin an aluminum housing full of nitrogen in order to prevent from the interference of oxygen. The detection limit for most analytes was of the order of 1-2 microg/l. The HPLC-ED method with a post-column photochemical reactor has good precision and linearity and can be readily applied to the routine determination of alkyl organoiodides in real acetic acid samples.
This paper describes the feasibility of employing capillary electrophoresis (CE) to separate silv... more This paper describes the feasibility of employing capillary electrophoresis (CE) to separate silver particles in nanometer regimes. We have found that the addition of an anionic surfactant, sodium dodecyl sulphate (SDS), to the running electrolyte prevents coalescence of the silver particles during the process, which improves the separation performance; the concentration of SDS required for optimal silver nanoparticle separation is ca. 20 mM. By monitoring the electropherograms using a diode-array detection (DAD) system, we have also investigated the separation of suspended silver nanorods with respect to their shapes. Our results demonstrate that the combination of CE and DAD is a powerful one for the separation and characterization of various silver nanoparticles.
... for High-Tech Industries CHWu/JT Lu/JG Lo* ... Each new fiber was condi-tioned for 60 min at ... more ... for High-Tech Industries CHWu/JT Lu/JG Lo* ... Each new fiber was condi-tioned for 60 min at 230 ~ before use. Sample aliquots of 2.5 mL were placed in amber vials (height, 45 mm; diameter, 15 mm) and capped with 13-mm PTFE/sili-cone septa and Teflon screw caps. ...
Carbonized moso bamboo (Phyllostachys pubescens) was coated with TiO(2) nanoparticles to enhance ... more Carbonized moso bamboo (Phyllostachys pubescens) was coated with TiO(2) nanoparticles to enhance its removal efficiency of harmful gases. Carbonized bamboo-TiO(2) composite (CBC) was prepared by heating mixtures of carbonized bamboo powder (CB) and TiO(2) nanoparticles, denoted as CBM, under nitrogen condition. TiO(2) nanoparticle and carbonized bamboo powder were mixed with the mass ratios of 1/1 and 2/1, respectively. At the same mass ratio of TiO(2) to CB, the benzene and toluene removal efficiencies follow the trend: CBC>CBM>CB, which is consistent with the amount of TiO(2) validated by elemental analysis. Sorption mechanism of benzene and toluene by CB, CBM and CBC might belong to hydrophobic-hydrophobic interaction, observed by depletion of untreated bamboo (UB) carbohydrates during carbonization. Sorption kinetics was further analyzed, and optimal correlation was found by fitting with the Elovich kinetic equation.
A fast and simple solvent microextraction technique using salting out-vortex-assisted liquid–liqu... more A fast and simple solvent microextraction technique using salting out-vortex-assisted liquid–liquid microextraction (salting out-VALLME) was developed for the extraction of furfurals (2-furfural (2-F), 3-furfural (3-F), 5-methylfurfural (5-MF) and 5-hydroxymethylfurfural (5-HMF)) and patulin (PAT) in fruit juice samples. The optimum extraction conditions for 5 mL sample were: extraction solvent, 1-hexanol; volume of extractant, 200 µL; vortex time, 45 s; salt addition, 20%. The simultaneous determination of the furfurals and PAT were investigated using high performance liquid chromatography coupled with diode array detector (HPLC–DAD). The separation was performed using ODS Hypersil C18 column (4.6 mm i.d×250 mm, 5 μm) under gradient elution. The detection wavelengths used for all compounds were 280 nm except for 3-F (210 nm). The furfurals and PAT were successfully separated in less than 9 min. Good linearities (r2>0.99) were obtained within the range 1–5000 μg L−1 for all compounds except for 3-F (10–5000 µg L−1) and PAT (0.5–100 μg L−1). The limits of detection (0.28–3.2 µg L−1) were estimated at S/N ratio of 3. The validated salting out-VALLME-HPLC method was applied for the analysis of furfurals and PAT in fruit juice samples (apple, mango and grape).
ABSTRACT Aminopeptidase‐I from pronase contains five tryptophan residues, determined by modificat... more ABSTRACT Aminopeptidase‐I from pronase contains five tryptophan residues, determined by modification with N‐bromosuccinimide and MCD measurments. The fluorescence of the enzyme is quenched by acrylamide, a neutral quencher, but not by iodide, an anionic quencher. The quenching constant for acrylamide is about one tenth that of acctyltryptophan in aqueous solution because of the steric effect of the large protein molecule. The inaccessibility of iodide to the tryptophans is probably due to the anionic environment of the fluorophores created by the large content of Asp and Glu in the enzyme. Aminopeptidase‐I is quenched by Cu(II) and Co(II) through the formation of a nonfluorescent ground‐state complex. The results indicate that there are three accessible tryptophans for Cu(II) and two for Co(II) suggesting that some tryptophans are buried inside the enzyme and are thus inaccessible to the quencher. In the presence of a competitive inhibitor, the enzyme contains one fewer accessible tryptophan for Cu(II) indicating that this tryptophan is located in the active center. The CD spectrum of the enzyme in the far UV region is unaltered by the presence of Ca(II), whereas that in the aromatic region is enhanced significantly. The perturbation of the CD spectrum probably results from the local conformational change induced by Ca(II) or from the rigidity of the tryptophan being enhanced by the bound Ca(II).
The radiolytic degradation of methyl tert-butyl ether (MTBE) in air-equilibrated dilute solution ... more The radiolytic degradation of methyl tert-butyl ether (MTBE) in air-equilibrated dilute solution was investigated. Complete degradation of MTBE can be achieved within 5 min of irradiation at 59.7 Gy/min. The observed first-order degradation rate constant, called dose constant, increased from 0.04 to 0.56 Gy(-1) as the concentration of MTBE decreased from 92500 to 19 microg/L. Tert-butyl formate, tert-butyl alcohol, acetone and methyl acetate were found to be the primary intermediates of the degradation reaction with yields of 47%, 11%, 6.4% and 9.1%, respectively. The degradation of MTBE or its intermediates was also found to depend on the concentrations of benzene and cupric ion. The study shows that the removal of MTBE can be significantly decreased with increasing concentration of benzene. Little affects were observed with the presence of cupric ions, while the degradation of TBF was apparently reduced. These results indicate that gamma radiolysis can be a potentially effective t...
A method for the analysis of six alkyl organoiodides (iodomethane, iodoethane, 1-iodopropane, 1-i... more A method for the analysis of six alkyl organoiodides (iodomethane, iodoethane, 1-iodopropane, 1-iodobutane, 1-iodopentane, 1-iodohexane) commonly found in acetic acid process was developed. In this method the target analytes were determined by high-performance liquid chromatography (HPLC) using a post-column photochemical reactor with electrochemical detection (ED) in less than 30 min. HPLC was performed in ODS C18 reversed-phase column (5 microm, 250 x 4.6 mm I.D.) under isocratic conditions with methanol-0.067 M acetate buffer (70:30, v/v), pH 6.2 as mobile phase at flow-rate 1.1 ml/min. Alkyl organoiodides, which are electrochemically inactive, were made oxidizable at potential of 120 mV after post-column irradiation with low-pressure mercury lamp in a knitted PTFE tube. The photoreactor was placedin an aluminum housing full of nitrogen in order to prevent from the interference of oxygen. The detection limit for most analytes was of the order of 1-2 microg/l. The HPLC-ED method with a post-column photochemical reactor has good precision and linearity and can be readily applied to the routine determination of alkyl organoiodides in real acetic acid samples.
This paper describes the feasibility of employing capillary electrophoresis (CE) to separate silv... more This paper describes the feasibility of employing capillary electrophoresis (CE) to separate silver particles in nanometer regimes. We have found that the addition of an anionic surfactant, sodium dodecyl sulphate (SDS), to the running electrolyte prevents coalescence of the silver particles during the process, which improves the separation performance; the concentration of SDS required for optimal silver nanoparticle separation is ca. 20 mM. By monitoring the electropherograms using a diode-array detection (DAD) system, we have also investigated the separation of suspended silver nanorods with respect to their shapes. Our results demonstrate that the combination of CE and DAD is a powerful one for the separation and characterization of various silver nanoparticles.
... for High-Tech Industries CHWu/JT Lu/JG Lo* ... Each new fiber was condi-tioned for 60 min at ... more ... for High-Tech Industries CHWu/JT Lu/JG Lo* ... Each new fiber was condi-tioned for 60 min at 230 ~ before use. Sample aliquots of 2.5 mL were placed in amber vials (height, 45 mm; diameter, 15 mm) and capped with 13-mm PTFE/sili-cone septa and Teflon screw caps. ...
Carbonized moso bamboo (Phyllostachys pubescens) was coated with TiO(2) nanoparticles to enhance ... more Carbonized moso bamboo (Phyllostachys pubescens) was coated with TiO(2) nanoparticles to enhance its removal efficiency of harmful gases. Carbonized bamboo-TiO(2) composite (CBC) was prepared by heating mixtures of carbonized bamboo powder (CB) and TiO(2) nanoparticles, denoted as CBM, under nitrogen condition. TiO(2) nanoparticle and carbonized bamboo powder were mixed with the mass ratios of 1/1 and 2/1, respectively. At the same mass ratio of TiO(2) to CB, the benzene and toluene removal efficiencies follow the trend: CBC>CBM>CB, which is consistent with the amount of TiO(2) validated by elemental analysis. Sorption mechanism of benzene and toluene by CB, CBM and CBC might belong to hydrophobic-hydrophobic interaction, observed by depletion of untreated bamboo (UB) carbohydrates during carbonization. Sorption kinetics was further analyzed, and optimal correlation was found by fitting with the Elovich kinetic equation.
A fast and simple solvent microextraction technique using salting out-vortex-assisted liquid–liqu... more A fast and simple solvent microextraction technique using salting out-vortex-assisted liquid–liquid microextraction (salting out-VALLME) was developed for the extraction of furfurals (2-furfural (2-F), 3-furfural (3-F), 5-methylfurfural (5-MF) and 5-hydroxymethylfurfural (5-HMF)) and patulin (PAT) in fruit juice samples. The optimum extraction conditions for 5 mL sample were: extraction solvent, 1-hexanol; volume of extractant, 200 µL; vortex time, 45 s; salt addition, 20%. The simultaneous determination of the furfurals and PAT were investigated using high performance liquid chromatography coupled with diode array detector (HPLC–DAD). The separation was performed using ODS Hypersil C18 column (4.6 mm i.d×250 mm, 5 μm) under gradient elution. The detection wavelengths used for all compounds were 280 nm except for 3-F (210 nm). The furfurals and PAT were successfully separated in less than 9 min. Good linearities (r2>0.99) were obtained within the range 1–5000 μg L−1 for all compounds except for 3-F (10–5000 µg L−1) and PAT (0.5–100 μg L−1). The limits of detection (0.28–3.2 µg L−1) were estimated at S/N ratio of 3. The validated salting out-VALLME-HPLC method was applied for the analysis of furfurals and PAT in fruit juice samples (apple, mango and grape).
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