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61.
A self-propelled object coupled with an enzyme reaction between urease and urea was investigated at the air/aqueous interface. A plastic object that was fixed to a urease-immobilized filter paper was used as a self-propelled object, termed a urease motor, placed on an aqueous urea solution. The driving force of the urease motor is the difference in the surface tension around the object. Oscillatory motion or no motion was triggered depending on the initial pH of the urea solution. Both the frequency and maximum speed of the oscillatory motion varied depending on the initial pH of the water phase. The mechanisms underlying the oscillatory motion and no motion were discussed in relation to the bell-shaped enzyme activity of urease in the enzyme reaction and the surface tension around the urease motor. 相似文献
62.
Single phase of ammonium tetramolybdate in the micro power form was prepared from polyphase ammonium paramolybdate. Its heat capacity from 14.25℃ to 120.12 ℃ was measured by drop method and the result is
Cp=0.3936+7.4047×10-4T+6.3543×10-3T-2(J•K-1•g-1) 相似文献
Cp=0.3936+7.4047×10-4T+6.3543×10-3T-2(J•K-1•g-1) 相似文献
63.
64.
This study presents a simple and green dispersive micro‐solid phase extraction method for preconcentration of acidic quinolones from honey prior to high performance liquid chromatography determination. A two‐dimensional nanostructured zinc‐aluminum layered double hydroxide was synthesized and used as the sorbent for dispersive micro‐solid phase extraction. Its different characteristics from conventional sorbents is that it is dissolvable in acidic solution (pH < 4). After the extraction, the analyte elution step was omitted and thus the use of organic solvents was avoided. The key parameters influencing the extraction efficiency such as the amount of sorbent, pH of sample solution, vortex time, type and volume of acidic solution were investigated and optimized. The method exhibited low limits of detection (3.0?5.0 ng/g), good linearity (10?2000 ng/g) with coefficients of determinations higher than 0.9991, acceptable precision (RSD<9.1%) and accuracy (RE<5.8%). The proposed method is fast, efficient, eco‐friendly, and suitable for the determination of acidic quinolones in honey samples. 相似文献
65.
Chengtao Chen Zhengqing He Jie Wu Xueqing Zhang Qianfeng Xia Huangxian Ju 《化学:亚洲杂志》2019,14(14):2491-2496
Microshells are attractive in constructing bubble‐propelled micromotors due to the lower energy consumption for bubbles forming on a concave surface. In this work, enzyme‐powered microshell motors were fabricated on multimetallic (Au/Ag/Au) microshells along with the modification of catalase on its concave surface. The catalase triggered the decomposition of hydrogen peroxide to oxygen gas, hence propelling the autonomous motion of microshell motors. A size‐dependent motion behaviour was observed for the microshell motors in the form of slow tremble and fast translation motion for a size smaller and larger than 5 μm, respectively, according to the size, generation efficiency and ejection mechanism of bubbles and the intensity of Brownian motion. In addition, the effect of fuel concentration on the motion speed of microshells was dependent on whether the bubble generation was affected by the limited mass transfer in the microshell space. These findings play an important role for the design of microshell motors. 相似文献
66.
利用高分离度液相色谱-四极杆飞行时间质谱(RRLC-Q-TOF MS)和超高效液相色谱-三重四极杆质谱(UPLC-QQQ MS)定性定量分析了稀有原人参二醇型皂苷Rd, F2, Rg3, CK和Rh2在离体人肠道菌群中的生物转化过程. 并将上述二醇型皂苷与人肠道菌群在体外厌氧, 37 ℃下共温孵育, 采用电喷雾质谱在负离子模式进行检测, 鉴定代谢产物, 监测其含量变化, 拟合代谢路径. 结果表明, 人参皂苷Rd主要被代谢为F2, Rg3, CK, Rh2和PPD; 人参皂苷F2主要被代谢为CK和PPD; 人参皂苷Rg3主要被代谢为Rh2和PPD; 人参皂苷CK和Rh2主要被代谢为PPD. 在离体条件下, 人参皂苷Rd, F2和Rg3会被肠道菌群完全转化为其代谢产物, 而人参皂苷CK和Rh2则不能被肠道菌群完全转化为其代谢产物. 原人参二醇型皂苷在人肠道菌群中的主要转化为脱糖基反应, 单糖苷和苷元是稀有原人参二醇型皂苷在人体内发挥药效的物质基础. 相似文献
67.
68.
Two quartz crystal microbalances have been mounted in a planar rf discharge system in such a way that the potential of the microbalances with respect to the glow discharge can be varied. This apparatus allows a rapid simulation of the etching directionality that can be expected in real pattern transfer situations in that operating one microbalance at ground and one at a negative potential gives a measure of the sidewall and vertical etch rates, respectively. The voltage threshold for ion-assisted etching has been determined to be 20 V which is the approximate value of the plasma potential in this asymmetric system. 相似文献
69.
Shan Y Shi X Dou A Zou C He H Yang Q Zhao S Lu X Xu G 《Journal of chromatography. A》2011,1218(13):1743-1748
Microcystins and nodularins are cyclic peptide hepatotoxins and tumour promoters from cyanobacteria. The present study describes the development, validation and practical application of a fully automated analytical method based on on-line micro solid-phase extraction-capillary liquid chromatography-tandem mass spectrometry for the simultaneous determination of seven microcystins and nodularin-R in tap water and lake water. Aliquots of just 100 μL of water samples are sufficient for the detection and quantification of all eight toxins. Selected reaction monitoring was used to obtain the highest sensitivity. Good linear calibrations were obtained for microcystins (50-2000ng/L) and nodularin-R (25-1000 ng/L) in spiked tap water and lake water samples. Excellent interday and intraday repeatability were achieved for eight toxins with relative standard deviation less than 15.7% in three different concentrations. Acceptable recoveries were achieved in the three concentrations with both tap water matrix and lake water matrix and no significant matrix effect was found in tap water and lake water except for microcystin-RR. The limits of detection (signal to noise ratio=3) of toxins were lower than 56.6 ng/L which is far below the 1 μg/L defined by the World Health Organization provisional guideline for microcystin-LR. Finally, this method was successfully applied to lake water samples from Tai lake and proved to be useful for water quality monitoring. 相似文献
70.
The micro construction of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) blend films fabricated by solution casting under microwave irradiation was investigated by selective enzymatic degradation and scanning electron microscopy (SEM). The results were totally different from the blends obtained by conventional methods. The blend was more homogeneous and the PCL continuous phase more compact as no spherulites and tiny zone separation were observed from the film surface and no PCL network was observed inside the film, and the degradation of a PCL plank by Pseudomonas lipase was significantly retarded. The distributed PLLA micro spheres were enlarged and amorphous. The thermal behavior of the blend by microwave heating revealed that PCL and PLLA underwent a melting process, which induced the variations of the PCL phase and PLLA spheres. The weight loss caused by degradation of the PCL/PLLA blend obtained by conventional methods (B50c) is greater than that of the blend obtained by microwave methods (B50m), which reflects the change in morphology from a loose PCL network (B50c) to a dense PCL plank (B50m). 相似文献