首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
A methodology for the determination of lipase, based on the coupled processes of energy transfer and enhancement of the chemiluminescence of the luminol-H2O2-horseradish peroxidase (HRP) system has been developed. Fluorescein diacetate (FDA) was hydrolyzed to fluorescein by the action of the enzyme lipase, and this compound acted as an enhancer of the chemiluminescent process and acceptor of the chemiluminescent emission from the luminol-H2O2-HRP system. By measuring the transferred emission to fluorescein at 525 nm, lipase (range 0.2–1.5 U/mL, RSD 2.3%) was determined. This methodology permited the determination of every compound of the system, thus, H2O2 (range 0.5–2 mM, RSD 6.9%) and HRP (range 5.5–49.5 U/mL, RSD 3.6%) could also be determined. Lipase was determined in rabbit serum with 96.7 ± 3.3% and 102.9 ± 5.4% recoveries for two different lipase concentrations. Besides, H2O2 was determined in the disinfectant solution for contact lenses. Received: 1 March 1999 / Revised: 6 May 1999 / Accepted: 12 May 1999  相似文献   

2.
A methodology for the determination of lipase, based on the coupled processes of energy transfer and enhancement of the chemiluminescence of the luminol-H2O2-horseradish peroxidase (HRP) system has been developed. Fluorescein diacetate (FDA) was hydrolyzed to fluorescein by the action of the enzyme lipase, and this compound acted as an enhancer of the chemiluminescent process and acceptor of the chemiluminescent emission from the luminol-H2O2-HRP system. By measuring the transferred emission to fluorescein at 525 nm, lipase (range 0.2–1.5 U/mL, RSD 2.3%) was determined. This methodology permited the determination of every compound of the system, thus, H2O2 (range 0.5–2 mM, RSD 6.9%) and HRP (range 5.5–49.5 U/mL, RSD 3.6%) could also be determined. Lipase was determined in rabbit serum with 96.7 ± 3.3% and 102.9 ± 5.4% recoveries for two different lipase concentrations. Besides, H2O2 was determined in the disinfectant solution for contact lenses.  相似文献   

3.
One-pot synthesis of R-1-phenylethyl acetate was investigated starting from acetophenone hydrogenation performed over Pd/Al2O3 and PdZn/Al2O3 catalysts followed by acylation of the intermediate secondary alcohol, R-1-phenylethanol, over an immobilized lipase. Furthermore, the performance of a third type of catalyst, Ru supported on hydroxyapatite (HAP) was evaluated for racemization of S-1-phenylethanol in one pot together with the two other catalysts. The main objectives of this work were to separate the effects of different catalysts and to reveal the reaction mechanism. For this purpose not only acetophenone, but also (R,S)-1-phenylethanol, S-1-phenylethanol, R-1-phenylethyl acetate, and styrene were used as reactants in combination with Pd/Al2O3, lipase and Ru/HAP as catalysts. The results revealed that the main side product, ethylbenzene, was formed in two different ways, via dehydration of (R,S)-1-phenylethanol to styrene, followed by its rapid hydrogenation to ethylbenzene, and via debenzylation of the desired product, R-1-phenylethyl acetate to ethylbenzene. The true one-pot synthesis, however, was demonstrated over Shvo’s catalyst, but Ru/HAP was not sufficiently active in the racemization step. Ru/Al2O3 was a promising catalyst for racemization of S-1-phenylethanol and for dynamic kinetic resolution of (R,S)-1-phenylethanol, when using only small amounts of the acyl donor ethyl acetate. The challenge in racemization is that the activity of heterogeneous Ru catalysts was inhibited by esters.  相似文献   

4.
以SrCO3,Si3N4,Eu2O3为原料,在N2气氛下,采用自还原高温固相法制备了SrSi2O2N2:Eu2+荧光粉。研究了该荧光粉的物相结构、发光性能和晶体形貌,同时对比在不同气氛下合成的荧光粉。结果表明,在N2气氛与N2/H2气氛下分别合成的SrSi2O2N2:Eu2+荧光粉物相结构和光谱特性基本一致。显示出合成了主晶相SrSi2O2N2,但还含有少量未知的中间项。Eu2+浓度的变化不影响激发状态,而发射光谱的波长在Eu2+浓度为1mol%-20mol%之间,从530 nm的绿光红移至550 nm的黄绿光区域。同时,激发光谱覆盖的范围宽,均能有效的被UV或蓝光激发,这意味着该类荧光粉在白光LED方面有可能得到广泛的应用。  相似文献   

5.
A chemically stable 2D microporous COF ( PMCR-1 ) was synthesized via the multicomponent Povarov reaction. PMCR-1 exhibits a remarkable and long-term stable photocatalytic H2O2 production rate (60 h) from pure and sea water under visible light. The H2O2 production is markedly enhanced when benzyl alcohol (BA) is added as reductant, which is also due to a strong π–π interaction of BA with dangling phenyl moieties in the COF pores introduced by the multicomponent Povarov reaction. Motivated by the concomitant BA oxidation to benzaldehyde during H2O2 formation, the photocatalytic oxidation of various organic substrates such as benzyl amine and methyl sulfide derivatives was investigated. It is shown that the well-defined micropores of PMCR-1 enable size-selective photocatalytic oxidation.  相似文献   

6.
《Electroanalysis》2005,17(19):1761-1769
The electrochemistry and electrochemiluminescence (ECL) properties of acridan phosphate ester are reported. Electrochemical oxidation of 9‐(phenylthiophosphoryloxymethylidene)‐10‐methylacridan disodium salt (Compound 1) yields the corresponding acridinium ester. The latter undergoes a fast reaction with hydrogen peroxide forming an intermediate, which produces electronically excited 9‐methyl acridone and emits blue light after relaxation to the ground state. The electrochemical oxidation of this compound appears to occur in two one‐electron steps and light emission is observed for both steps. The chemiluminescence reaction could also be triggered by electrochemical oxidation of Compound 1 in the absence of H2O2 when the solution was saturated with O2. Mechanisms for these reactions based on ECL, voltammetry and in situ UV‐vis identification of the oxidation products are proposed. Due to the low electrode potential required to achieve ECL emission and the occurrence of light emission in the absence of hydrogen peroxide, this compound is proposed as a label for rapid and sensitive determination of biomolecules in automated analysis.  相似文献   

7.
Motivated by the need for new phosphors of white light emitting diode (WLED) application, Ca0.95Nb2 O6:Eu3+0.05 phosphors were synthesized by high temperature solid‐state reaction. Increasing the content of doped‐Eu3+ and adding the co‐activator Bi3+ to improve the photoluminescence (PL) intensity of Ca1?xNb2 O6Eu3+x phosphors were investigated in detail. The effects of Eu3+ were better than that of Bi3+ on the PL intensity of Ca1?xNb2 O6Eu3+x phosphors. Compared with Y2O2 S:0.05Eu3+ the Ca0.70Nb2 O6:Eu3+0.03 phosphor could be excited efficiently by UV (395 nm) light and emit the red light at 614 nm with line spectra, which were coupled well with the characteristic emission from UV‐Near UV LED. The CIE (International Commission on Illumination) chromaticity coordinates (x?0.654, y?0.348) of Ca0.70Nb2O6:Eu3+0.03 were close to the NTSC (National Television Standard Committee) standard values. Therefore Ca0.70Nb2 O6:Eu3+0.03 might find application to UV‐Near UV InGaN chip‐based white light emitting diodes, which is further proved by the LED fabrication with the Ca0.70Nb2 O6:Eu3+0.03 phosphor.  相似文献   

8.
A novel chiral magnetic nanocatalyst was prepared by the surface modification of Fe3O4 magnetic nanoparticles (MNPs) with a chloropropylsilane and further by arginine to form Fe3O4@propylsilan‐arginine (Fe3O4@PS‐Arg). After the structural confirmation of Fe3O4@PS‐Arg synthesized MNPs by Fourier transform‐infrared, X‐ray diffraction, field emission‐scanning electron microscopy, transmission electron microscopy, vibrating‐sample magnetometry and thermogravimetric analyses, their catalytic activity was evaluated for one‐pot enantioselective synthesis of 3‐amino‐1‐aryl‐1H‐benzo[f]chromene‐2‐carbonitrile derivatives. The results showed that in the presence of 0.07 g Fe3O4@PS‐Arg nanocatalyst and ethanol as solvent, the best reaction yield (96%) was obtained in the least time (5 min). Easy operation, reusability and stability, short reaction time, high reaction yields and good enantioselectivity are the major advantages of the newly synthesized nanocatalyst. Also, this study provides a novel strategy for further research and investigation on the synthesis of new reusable enantioselective catalysts and chiral compounds.  相似文献   

9.
Abstract

The Pseudomonas sp. (LPS) promoted acyl transfer from vinyl acetate to selected 3,4-O-isopropylidene-D-galactopyranosides takes place in a completely selective manner giving in high yield the corresponding 6-O-acetates. The acetylation rate is strongly dependent on the type and the orientation of the aglycon, varying from a maximum of reactivity for the 1-deoxy derivative, 1,5-anhydro-3,4-O-isopropylidene-D-galactitol (1d), to a minimum for β configurated alkyl glycosides and showing a complete loss of reactivity for 3′,4′:2,3:5,6-tri-O-isopropylidenelactose dimethyl acetal (1e). The latter compound is, however, selectively 6′-O-esterified in good yield by lipase from Candida Antarctica and vinyl acetate. Also the course of the enzymatic hydrolysis of 2,6-di-O-acetyl-3,4-O-isopropylidene-D-galactopyranosides 2 is dependent on the type of the aglycon, both for the reaction rate and the selectivity. The 2-O-acetates 4 are selectively obtained in good yields with porcine pancreatic lipase (PPL) promoted hydrolysis in the case of β and α-methyl, and 1-deoxy derivatives (2a, 2b and 2d), while for β-benzyl (2c) and lactose (2e) analogues satisfactory results are obtained with lipase from Mucor miehei (IM20).

  相似文献   

10.
Ascorbic acid (AA) has antioxidant properties. However, in the presence of Fe2+/Fe3+ ions and H2O2, it may behave as a pro-oxidant by accelerating and enhancing the formation of hydroxyl radicals (OH). Therefore, in this study we evaluated the effect of AA at concentrations of 1 to 200 µmol/L on OH-induced light emission (at a pH of 7.4 and temperature of 37 °C) from 92.6 µmol/L Fe2+—185.2 µmol/L EGTA (ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid)—2.6 mmol/L H2O2, and 92.6 µmol/L Fe3+—185.2 µmol/L EGTA—2.6 mmol/L H2O2 systems. Dehydroascorbic acid (DHAA) at the same range of concentrations served as the reference compound. Light emission was measured with multitube luminometer (AutoLumat Plus LB 953) for 120 s after automatic injection of H2O2. AA at concentrations of 1 to 50 µmol/L and of 1 to 75 µmol/L completely inhibited light emission from Fe2+-EGTA-H2O2 and Fe3+-EGTA-H2O2, respectively. Concentrations of 100 and 200 µmol/L did not affect chemiluminescence of Fe3+-EGTA-H2O2 but tended to increase light emission from Fe2+-EGTA-H2O2. DHAA at concentrations of 1 to 100 µmol/L had no effect on chemiluminescence of both systems. These results indicate that AA at physiological concentrations exhibits strong antioxidant activity in the presence of chelated iron and H2O2.  相似文献   

11.
Nanostructured Sr2As2O7 samples were synthesized by hydrothermal crystal growth reactions between Sr(NO3)2 and As2O3 with different stoichiometric Sr:As molar ratios as 1:1 (S1), 1:2 (S2), and 2:1 (S3). The synthesized nanomaterials were characterized by powder X‐ray diffraction (PXRD) technique and fourier‐transform infrared (FT‐IR) spectroscopy. Rietveld analysis showed that the obtained materials were crystallized well in the monoclinic crystal structure with the space group P21. The morphologies of the synthesized materials were studied by field emission scanning electron microscopy (FESEM) technique. TEM images verified formation of the particles with nanometer size. Ultraviolet‐visible spectra analysis showed that the synthesized Sr2As2O7 nanomaterials had strong light absorption in the ultraviolet light region. Photocatalytic performance of the synthesized nanomaterials was also investigated for the degradation of pollutant Malachite Green (4‐{[4‐(dimethylamino)phenyl](phenyl)methylidene}‐N′N‐dimethylcyclohexa‐25‐dien‐1‐iminium chloride) (MG) in aqueous solution under solar light condition. The optimal conditions were obtained by design expert software for S1. It was found that the optimum condition was 0.14 mL H2O2, 20 mg catalyst, and 33 min time. The volume and concentration of the as prepared MG solution were 70 mL and 100 ppm, respectively, for obtaining the optimum conditions. The degradation yield in the optimized conditions was 97 % for S1.  相似文献   

12.
The Ce3+ activated phosphors Ca4Si2O7F2:Ce3+ are prepared by a solid state reaction technique. The UV–vis luminescence properties as well as fluorescence decay time spectra are investigated and discussed. The results revealed that there were two kinds of Ce3+ luminescence behavior with 408 and 470 nm emissions, respectively. Under 355 nm excitation, the Ce(1) emission (408 nm) is dominant at low doping concentration, and then the Ce(2) emission (470 nm) get more important with increasing of Ce3+ concentrations in the host. The phosphors Ca4Si2O7F2:xCe3+ show tunable emissions from blue area to green-blue area under near-ultraviolet light excitation, indicating a potential application in near-UV based w-LEDs.  相似文献   

13.
The thermal decomposition of trifluoromethoxycarbonyl peroxy nitrate, CF3OC(O)O2NO2, has been studied between 278 and 306 K at 270 mbar total pressure using He as a diluent gas. The pressure dependence of the reaction was also studied at 292 K between 1.2 and 270 mbar total pressure. The rate constant reaches its high‐pressure limit at 70 mbar. The first step of the decomposition leads to CF3OC(O)O2 and NO2 formation, that is, CF3OC(O)O2NO2 + M ? CF3OC(O)O2 + NO2 + M (k1, k?1). Reaction (?1) was prevented by adding an excess of NO that reacts with the peroxy radical intermediate and leads to carbonyl fluoride (CF2O), carbon dioxide (CO2), nitrogen dioxide (NO2), and small quantities of CF3OC(O)O2C(O)OCF3. The kinetics of reaction (1) was determined by following the loss of CF3OC(O)O2NO2 via IR spectroscopy. The temperature dependence of the decomposition follows the equation k1(T) = 1.0 × 1016 e?((111±3)/(RT)) for the exponential term expressed in kJ mol?1. The values obtained for the kinetic parameters such as k1 at 298 K, the activation energy (Ea), and the preexponential factor (A) are compared with literature data for other acyl peroxy nitrates. The atmospheric thermal stability of CF3OC(O)O2NO2 and its dependence with altitude is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 831–838, 2008  相似文献   

14.
The new layered oxonitridosilicate EuSi2O2N2 has been synthesized in a radio‐frequency furnace at temperatures of about 1400 °C starting from europium(III ) oxide (Eu2O3) and silicon diimide (Si(NH)2). The structure of the yellow material has been determined by single‐crystal X‐ray diffraction analysis (space group P1 (no. 1), a=709.5(1), b=724.6(1), c=725.6(1) pm, α=88.69(2), β=84.77(2), γ=75.84(2)°,V=360.19(9)×106 pm3, Z=4, R1=0.0631, 4551 independent reflections, 175 parameters). Its anionic Si2O2N22? layers consist of corner‐sharing SiON3 tetrahedra with threefold connecting nitrogen and terminal oxygen atoms. High‐resolution transmission electron micrographs indicate both ordered and disordered crystallites as well as twinning. Magnetic susceptibility measurements of EuSi2O2N2 exhibit Curie–Weiss behavior above 20 K with an effective magnetic moment of 7.80(5) μB Eu?1, indicating divalent europium. Antiferromagnetic ordering is detected at 4.5(2) K. EuSi2O2N2 shows a field‐induced transition with a critical field of 0.50(5) T. The four crystallographically different europium sites cannot be distinguished by 151Eu Mössbauer spectroscopy. The room‐temperature spectrum is fitted by one signal at an isomer shift of δ=?12.3(1) mm s?1 subject to quadrupole splitting of ΔEQ=?2.3(1) mm s?1 and an asymmetry parameter of 0.46(3). Luminescence measurements show a narrow emission band with regard to the four crystallographic europium sites with an emission maximum at λ=575 nm.  相似文献   

15.
The MeOH extract from the flowers of Bellis perennis was found to show pancreatic‐lipase inhibitory activity (IC50 455 μg/ml). From the extract, seven new triterpene saponins named perennisaponins G ( 1 ; IC50 163 μM ), H ( 2 ; 137 μM ), I ( 3 ; 147 μM ), J ( 4 ; 148 μM ), K ( 5 ; 223 μM ), L ( 6 ; 81.4 μM ), and M ( 7 ; 195 μM ) were isolated as pancreatic lipase inhibitors. The stereostructures of 1 – 7 were elucidated on the basis of chemical and spectroscopic evidence.  相似文献   

16.
Abstract— In the photosynthetic bacteria Chromatium, Rhoahpirillum rubrum, and Rhodopseudomonus spheroides the fluorescence of bacteriochlorophyll is probably free of contamination by a “fast” component of delayed emission, judging from the characteristics of the delayed light measured 3 msec after excitation. In Rps. spheroides the pigment P870, associated with photochemical reaction centers, is non-fluorescent in its photochemically active state. Fluorescence of P870 can be induced by either of two agencies that suppress its photochemical activity: exposure to Na2S2O4 and (in a dry chromatophore film) dessication. The yield of fluorescence from the major (light harvesting) component of bacteriochlorophyll in vivo is brought to a common maximum value by conditions that suppress the photochemical activity of P870. In addition to dessication and exposure to Na2S2O4 these conditions include saturating illumination and exposure to K3Fe(CN)6. Of these four treatments only the last two bleach the long wave absorption band of P870. These experiments support the following assertions: (1) P870 traps singlet excitation energy absorbed by the light harvesting BChl; the trapping function of P870 depends on its ability to initiate and participate in photochemistry. (2) Both dessication and exposure to Na2S2O4 suppress the photochemical activity of P870 by blocking an event that proceeds directly from the excited singlet state in P870. (3) The fluoresecence of BChl in vivo is emitted almost entirely by a major (light harvesting) component.  相似文献   

17.
O(1D) atoms, generated via the laser photodissociation of N2O at 193 nm, reacting with N2O was studied by Time-Resolved Fourier Transform Infrared (TR-FTIR) Spectroscopy. The IR emission from NO(v? 1–11.) was collected at 30 μs after the laser was fired. Several instrumental corrections were made to obtain reliable experimental results. The vibrational temperature of the nearly-nascent NO product was estimated to be Tv ? 9,000 K. A Quasi-Classical Trajectory (QCT) calculation of the reaction was performed. The calculated results, corresponding to a head-on attack mechanism, agree with the experimental data. Additional reaction channel with side-on attack producing N2 and O2 was also studied by QCT, where vibrationally hot O2(a 1 Δg) and cold N2(X1g+) products are predicted.  相似文献   

18.
以钛粉、钽粉为原料,炭黑作为反应性模板,通过熔盐法在炭黑表面原位生长了TaTiC_2纳米碳化物涂层,并以所得TaTiC_2/C复合物为碳化物前驱体,再经可控氧化制备出中空Ta_2O_5/TiO_2复合光催化剂。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见(UV-Vis)漫反射(DRS)及N2物理吸附等手段对所制备的光催化剂进行形貌、显微结构及孔结构表征。以高压汞灯为紫外光源,以亚甲基蓝为目标降解物,通过光催化降解实验评价中空Ta_2O_5/TiO_2复合光催化剂的光催化活性。结果表明,熔盐法生长碳化物涂层厚度均匀(20~30 nm),碳化物主要以TaTiC_2晶相存在且具有纳米级的颗粒尺寸。中空Ta_2O_5/TiO_2复合光催化剂同时具有200 nm左右的中空大孔结构及壳层10 nm左右的介孔结构。中空大孔和介孔的存在提高了所制备催化剂对亚甲基蓝的吸附能力。此外,TiO_2与Ta2O5通过电子能带结构的耦合,有效提高了光生电子和空穴的分离效率,从而显著提高了光催化活性。nTi∶nTa=2.5∶1.5时,相应的中空Ta_2O_5/TiO_2复合光催化剂表现出最佳的光催化活性,对亚甲基蓝的紫外光催化降解率高达97%。  相似文献   

19.
An efficient synthesis of 3-(1-(2-(1H-indol-3-yl)ethyl)-2-aryl-6,6-dimethyl-4-oxo-4,5,6,7-tetrahydro-1H-indol-3-yl)indolin-2-ones is reported via a one-pot three-component reaction of 3-phenacylidenoxindoles, tryptamine, and dimedone under ultrasound irradiation using a newly prepared core-shell nanostructure. The utilized nanocatalyst is obtained by anchoring sulfonated L-histidine amino acid shell, as the bio part, on silica-nanomagnetite core (SO3H-L-His@SiO2-nano Fe3O4) and characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (1H NMR), field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric/differential thermal analysis, vibrating sample magnetometer measurements, transmission electron microscopy, and back-titration. The protocol contains several advantages, such as relatively short reaction times, simple work-up procedure by separation of the catalyst with an external magnet, the use of economical and environmentally friendly ultrasonic waves, and reusability and recoverability of the core-shell nano-promoter for three runs without significant activity loss.  相似文献   

20.
Investigation of the formation of complex reaction products in the gas-phase system O3/NO2/(Z)-2-butene by combination of linear reactors with IR. matrix and microwave Stark Spectroscopy is reported. Besides the polyatomic products observed earlier in the gas-phase ozonolysis of (Z)-2-butene, the following products were identified; N2O5, HNO3, HNO4, CH3NO2, CH3ONO, CH3COONO2 and CH3COO2NO2 (peroxyacetyl nitrate, PAN). Matrix IR. spectra of N2O5, HNO3. CH3COONO, CH3COONO2 required for reference purposes are presented. It is shown that PAN-formation occurs already in the absence of light. A reaction scheme is proposed for explanation of the observed complex NOx-containing products, which assumes methyldioxirane as a central intermediate. Particular reaction steps of the scheme will be discussed, including thermochemical estimates of reaction enthalpies.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号