Outward electron transfer by Saccharomyces cerevisiae monitored with a bi‐cathodic microbial fuel cell‐type activity sensor

A Janus head‐like bi‐cathodic microbial fuel cell was constructed to monitor the electron transfer from Saccharomyces cerevisiae to a woven carbon anode. The experiments were conducted during an ethanol cultivation of 170 g/l glucose in the presence and absence of yeast‐peptone medium. First, using a basic fuel‐cell type activity sensor, it was shown that yeast‐peptone medium contains electroactive compounds. For this purpose, 1% solutions of soy peptone and yeast extract were subjected to oxidative conditions, using a microbial fuel cell set‐up corresponding to a typical galvanic cell, consisting of culture medium in the anodic half‐cell and 0.5 M K₃Fe(CN)₆ in the cathodic half‐cell. Second, using a bi‐cathodic microbial fuel cell, it was shown that electrons were transferred from yeast cells to the carbon anode. The participation of electroactive compounds in the electron transport was separated as background current. This result was verified by applying medium‐free conditions, where only glucose was fed, confirming that electrons are transferred from yeast cells to the woven carbon anode. Knowledge about the electron transfer through the cell membrane is of importance in amperometric online monitoring of yeast fermentations and for electricity production with microbial fuel cells. Copyright © 2009 John Wiley & Sons, Ltd.     

基于ZnCo2O4的多孔碳纳米纤维制备及其储能性能

针对锂硫电池循环过程中容量衰减快的问题,采用水热法制备ZnCo₂O₄纳米颗粒,然后与聚丙烯腈(PAN)混合,通过静电纺丝法制备复合纳米纤维并进行炭化处理得到复合多孔碳纳米纤维。借助扫描电子显微镜、透射电子显微镜、X射线光电子能谱仪、拉曼光谱仪、比表面积测试仪表征复合多孔碳纳米纤维的微观结构和物化性能,优化得到最佳制备工艺;并将其作为正极硫载体测试电化学性能。结果表明:基于ZnCo₂O₄制备的复合多孔碳纳米纤维存在大量孔孔相连的通道,比表面积高达210.85 m²/g;组装成的锂硫电池具有典型的充放电平台以及明显的氧化还原峰,其初始放电比容量为759.2 mA·h/g,50圈充放电循环后,仍具有74.0%的可逆比容量,相比于不掺杂ZnCo₂O₄的静电纺丝碳纳米纤维具有更高的比容量,更好的倍率性能。     

利用玉米秸秆水解液发酵生产2,3-丁二醇

利用1株克雷伯氏菌(Klebsiella oxytocaZU-03)发酵玉米秸秆水解液生产2,3-丁二醇,使水解液中的己糖和戊糖都得到了有效利用。研究结果表明,当玉米秸秆水解液中Na2SO4浓度低于20 g/L时,对2,3-丁二醇的发酵无明显影响。乙酸和乙醇是主要的发酵副产物,当浓度分别超过20 g/L和5 g/L时,对发酵的抑制作用较明显。玉米秸秆水解液发酵生产2,3-丁二醇的适宜初始pH值为6.0-6.5,初始总糖浓度为80-100 g/L。在总糖浓度80 g/L(含葡萄糖47.25 g/L,木糖32.75 g/L),初始pH值6.0,温度30℃的条件下发酵64 h,总糖利用率达到99.36%,2,3-丁二醇的质量浓度为37.20 g/L,产率为0.468 g/g(总糖),达到理论最大产率的94%。     

Procedure for determining maximum sustainable power generated by microbial fuel cells

Power generated by microbial fuel cells is computed as a product of current passing through an external resistor and voltage drop across this resistor. If the applied resistance is very low, then high instantaneous power generated by the cell is measured, which is not sustainable; the cell cannot deliver that much power for long periods of time. Since using small electrical resistors leads to erroneous assessment of the capabilities of microbial fuel cells, a question arises: what resistor should be used in such measurements? To address this question, we have defined the sustainable power as the steady state of power delivery by a microbial fuel cell under a given set of conditions and the maximum sustainable power as the highest sustainable power that a microbial fuel cell can deliver under a given set of conditions. Selecting the external resistance that is associated with the maximum sustainable power in a microbial fuel cell (MFC) is difficult because the operator has limited influence on the main factors that control power generation: the rate of charge transfer at the current-limiting electrode and the potential established across the fuel cell. The internal electrical resistance of microbial fuel cells varies, and it depends on the operational conditions of the fuel cell. We have designed an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell operated under a given set of conditions. Following the procedure, we change the external resistors incrementally, in steps of 500 omega every 10, 60, or 180 s and measure the anode potential, the cathode potential, and the cell current. Power generated in the microbial fuel cell that we were using was limited by the anodic current. The anodic potential was used to determine the condition where the maximum sustainable power is obtained. The procedure is simple, microbial fuel cells can be characterized within an hour, and the results of the measurements can serve many purposes, such as: (1) estimating power generation in various MFCs, (2) comparing power generation in MFCs using different electroactive reactants, (3) quantifying the effects of the operational regime on the power generation in MFCs, and finally, (4) the purpose for which the procedure was designed, optimizing the performance of existing MFCs.     

响应面试验优化高温高压制备玉米环（组氨酸-脯氨酸）二肽关键工艺

将高温高压技术应用于玉米环（组氨酸-脯氨酸）二肽（cyclo（His-Pro）,CHP）的制备,以玉米蛋白水解物为原料,在水相溶液中采用高温高压法对其进行环化,合成CHP。通过单因素试验考察反应温度、底物质量浓度、反应时间和KHCO3浓度对CHP提取量的影响,应用响应面试验设计对高温高压环化反应条件进行优化。结果表明最佳反应条件为反应温度125.9 ℃、反应压力0.25 MPa、底物质量浓度20.5 mg/mL、KHCO3浓度0.16 mol/L、反应时间5.3 h,此条件下CHP提取量可达6.58 mg/g。采用超高效液相色谱-串联质谱法对水解物中的CHP进行进一步鉴定,结果表明制备的玉米CHP与预期结构相符。     

Extraction kinetics modeling of antioxidants from grape stalk (Vitis vinifera var. Bobal): Influence of drying conditions

The use of antioxidant extracts obtained from natural products is highly relevant in the food, chemical and pharmaceutical industry. The mathematical analysis of the antioxidant extraction could contribute to a better understanding of the process and is fundamental for optimization tasks. However, the high complexity of natural matrixes makes modeling difficult. The main aim of this work was to model the antioxidant extraction process from grape stalk in order to quantify the influence of the previous drying operation on extraction kinetics. The antioxidant extraction kinetics for freeze dried and hot air dried samples at several temperatures (40, 55, 70, 85, 100 and 115 °C) were carried out, using the FRAP method to measure the antioxidant capacity in the extracts. A diffusion model was developed that took significant external resistance as well as the complex geometry of grape stalk into consideration. From the modeling results, the influence of the drying conditions on the antioxidant concentration of the dry stalk, the antioxidant effective diffusivity and the mass transfer coefficient were identified.     

气相色谱-负化学电离质谱法测定纺织品中3种有机氯载体

建立了同时快速测定纺织品材料中3种有机氯载体的方法。通过条件优化,确定了以20 mL二氯甲烷超声提取30min的萃取条件,萃取后采用气相色谱-负化学电离质谱法进行分析,外标法定量。3种有机氯载体在质量浓度1~100μg/L范围内呈良好的线性,相关系数(R^2)均大于0.995,方法检出限为0.81~1.00μg/kg,在3个加标水平下的回收率为84.7%~109.8%,相对标准偏差(RSD,n=6)为1.5%~3.3%。该方法操作简单快速,灵敏度高,精密度、回收率理想,适用于多种纺织品材料中有机氯载体的分析测定。     

Sooting tendencies of oxygenated hydrocarbons in laboratory-scale flames

Sooting tendencies have been measured for 186 oxygenated and 89 regular hydrocarbons under controlled laboratory conditions. The test compounds include alcohols, ethers, aldehydes, ketones, esters, alkanes, alkenes, and cycloalkanes ranging in size from methanol to isododecane. Sooting tendency was characterized with a new method based on measuring particle concentrations in methane/air nonpremixed flames when 1000 ppm of each test compound was added to the fuel. This method offers high precision and high sensitivity to the direct chemical effects of the additive. The results provide a wide-ranging yet detailed quantitative picture of how fuel oxygen affects soot formation, which will be useful for optimizing the soot-reducing benefits of oxygenated renewable fuels. The measured sooting tendencies of 1-alcohols are similar to those of n-alkanes with the same number of carbon atoms, while those of secondary alcohols are slightly higher. Aldehydes and ketones soot the same as n-alkanes with one less carbon atom. The sooting tendencies of esters depend strongly on molecular structure and increase in this order: methyl and ethyl esters < carboxylic acids, propyl esters, and n-alkanes < butyl and pentyl esters. The high sooting tendencies of the secondary alcohols and higher esters suggest that four-center and six-center reaction pathways are important.     

库买提杏中主要类胡萝卜素的组成和含量分析

为明确库买提杏中主要类胡萝卜素组分及含量,应用高效液相色谱-二极管阵列检测-大气压化学电离-质谱技术获取其色谱、质谱和光谱信息并与标准品信息相比较,分析鉴定杏中主要的类胡萝卜素,利用高效液相色谱定量检测鲜杏中主要类胡萝卜素。结果表明：库买提杏中主要含有β-胡萝卜素、α-胡萝卜素和β-隐黄素以及顺式异构体等类胡萝卜素组分,其中β-胡萝卜素含量（以干基计算）高达114?μg/g,说明库买提杏中蕴含丰富的β-胡萝卜素,可以作为人体获取β-胡萝卜素的食物来源。     

RSM法优化Aspergillus oryzae AO-01产糖化酶条件的研究

采用单因素试验研究培养时间、培养温度和固水比对米曲霉(Aspergillus oryzae)AO-01产糖化酶的影响。在此基础上,再采用Box-Behnken响应面法(response surface methodology,RSM)对以上培养条件进行了优化。通过对二次多项回归方程求解得知,在上述自变量分别为培养时间32.8h,培养温度31.2℃,固水比1:1.24时,糖化酶的产量从最低值656.2μ/g干曲提高到1645.1μ/g干曲。验证实验证实了方程的预测值与实际值之间具有较好的拟合度。