Through the method of initial heat release rate, the kinetic property of tyrosine oxidation catalyzed by tyrosinase from Pseudomonas maltophilia was investigated using a LKB-2107 batch microcalorimeter. Tyrosine was c...Through the method of initial heat release rate, the kinetic property of tyrosine oxidation catalyzed by tyrosinase from Pseudomonas maltophilia was investigated using a LKB-2107 batch microcalorimeter. Tyrosine was catalyzed and oxidized into L-dopa, then into melanin catalyzed by tyrosinase. We found that the tyrosinase reaction obeyed the Michaelis-Menten kinetics, and at 298.15K and pH 7.0, the initial exothermic rate (W0 ) are in the range of 0.1567~0.5704 mJ·s-1, the maximum exothermic rate (Wmax) are in 0.4152 ~ 0.8143mol·L-1, and mean value of the Michaelis constant (Km) is 2.199±0.105104 mol·L-1.展开更多
The Debye equation with slit-smeared small angle x-ray scattering(SAXS) data is extended form an ideal two-phase system to a pseudo two-phase system with the presence of the interface layer,and a simple accurate solut...The Debye equation with slit-smeared small angle x-ray scattering(SAXS) data is extended form an ideal two-phase system to a pseudo two-phase system with the presence of the interface layer,and a simple accurate solution is proposed to determine the average thickness of the interface layer in porous materials.This method is tested by experimental SAXS data,which were measured at 25℃,of organo-modified mesoporous silica prepared by condensation of tetraethoxysiland(TEOS) and methyltriethoxysilane(MTES) using non-ionic neutral surfactant as template under neutral condition.展开更多
Silica aggregates were prepared by base-catalyzed hydrolysis and condensation of alkoxides in alcohol.Polyethylene glycol(PEG) was used as organic modifier.The sols were characterized using Small Angle X-ray Scatterin...Silica aggregates were prepared by base-catalyzed hydrolysis and condensation of alkoxides in alcohol.Polyethylene glycol(PEG) was used as organic modifier.The sols were characterized using Small Angle X-ray Scattering (SAXS) with synchrotron radiation as X-ray source.The structure evolution during the sol-gel process was determined and described in terms of the fractal geometry.As-produced silica aggregates were found to be mass fractals.The fractl dimensions spanned the regime 2.1-2.6 corresponding to more branched and compact structures.Both RLCA and Eden models dominated the kinetic growth under base-catalyzed condition.展开更多
A small-angle x-ray scattering(SAXS)technique using synchrotron radiation as the x-ray source has been employed to characterize the microstructure of mesoporous silica prepared by one-pot template-directed synthesis m...A small-angle x-ray scattering(SAXS)technique using synchrotron radiation as the x-ray source has been employed to characterize the microstructure of mesoporous silica prepared by one-pot template-directed synthesis methodology.The scattering of pure silica agreed with Porod’s law.the scattering of organomodified mesoporous silica showed a negative deviation from Porod’s law,suggesting that an interfacial layer exists between the pores and silica matrix.It was the organic groups comprising the interface,as shown by ^29Si cross-polarization magic-angle spinning nuclear magnetic resonance imaging (^29Si cp MAS/NMR) and Fourier transform infrared spectroscopy(FTIR),that caused this negative deviation of SAXS intensity from Porod’s law,and the average thichness of the interfacial layer could be deduced from this negative deviation.Copyright 2001 john Wiley and Sons,Ltd.展开更多
Small X-ray Scattering (SAXS) experiment using Synchrotron Radiation as X-ray source was used to determine the average wall thickness of mesoporous silica prepard by condensation of tetraethylorthosilicate(TEOS) using...Small X-ray Scattering (SAXS) experiment using Synchrotron Radiation as X-ray source was used to determine the average wall thickness of mesoporous silica prepard by condensation of tetraethylorthosilicate(TEOS) using non-ionic alkylpolyethyleneoxide(AEO9) surfactant as templates.The results agreed with that of high-resolution TEM(HRTEM) measurement.展开更多
基金This work were supported by the National Natural Science Foundation of China(No.30170010,29973030)The Teaching and Research Award Program for Outstanding Young Professors in High Education Institute,MOE,China(2001).
文摘Through the method of initial heat release rate, the kinetic property of tyrosine oxidation catalyzed by tyrosinase from Pseudomonas maltophilia was investigated using a LKB-2107 batch microcalorimeter. Tyrosine was catalyzed and oxidized into L-dopa, then into melanin catalyzed by tyrosinase. We found that the tyrosinase reaction obeyed the Michaelis-Menten kinetics, and at 298.15K and pH 7.0, the initial exothermic rate (W0 ) are in the range of 0.1567~0.5704 mJ·s-1, the maximum exothermic rate (Wmax) are in 0.4152 ~ 0.8143mol·L-1, and mean value of the Michaelis constant (Km) is 2.199±0.105104 mol·L-1.
文摘The Debye equation with slit-smeared small angle x-ray scattering(SAXS) data is extended form an ideal two-phase system to a pseudo two-phase system with the presence of the interface layer,and a simple accurate solution is proposed to determine the average thickness of the interface layer in porous materials.This method is tested by experimental SAXS data,which were measured at 25℃,of organo-modified mesoporous silica prepared by condensation of tetraethoxysiland(TEOS) and methyltriethoxysilane(MTES) using non-ionic neutral surfactant as template under neutral condition.
文摘Silica aggregates were prepared by base-catalyzed hydrolysis and condensation of alkoxides in alcohol.Polyethylene glycol(PEG) was used as organic modifier.The sols were characterized using Small Angle X-ray Scattering (SAXS) with synchrotron radiation as X-ray source.The structure evolution during the sol-gel process was determined and described in terms of the fractal geometry.As-produced silica aggregates were found to be mass fractals.The fractl dimensions spanned the regime 2.1-2.6 corresponding to more branched and compact structures.Both RLCA and Eden models dominated the kinetic growth under base-catalyzed condition.
文摘A small-angle x-ray scattering(SAXS)technique using synchrotron radiation as the x-ray source has been employed to characterize the microstructure of mesoporous silica prepared by one-pot template-directed synthesis methodology.The scattering of pure silica agreed with Porod’s law.the scattering of organomodified mesoporous silica showed a negative deviation from Porod’s law,suggesting that an interfacial layer exists between the pores and silica matrix.It was the organic groups comprising the interface,as shown by ^29Si cross-polarization magic-angle spinning nuclear magnetic resonance imaging (^29Si cp MAS/NMR) and Fourier transform infrared spectroscopy(FTIR),that caused this negative deviation of SAXS intensity from Porod’s law,and the average thichness of the interfacial layer could be deduced from this negative deviation.Copyright 2001 john Wiley and Sons,Ltd.
文摘Small X-ray Scattering (SAXS) experiment using Synchrotron Radiation as X-ray source was used to determine the average wall thickness of mesoporous silica prepard by condensation of tetraethylorthosilicate(TEOS) using non-ionic alkylpolyethyleneoxide(AEO9) surfactant as templates.The results agreed with that of high-resolution TEM(HRTEM) measurement.
