激励光波长对乙醇溶液荧光光谱特性的影响

乙醇溶液在紫外光照射下可以发射荧光。当激励的紫外光波长在200～250 nm变化时,乙醇溶液产生的荧光光谱基本相同,但峰值位置出现了明显的红移;当激励的紫外光波长相同时,随着溶液浓度的改变也将产生峰值位置的红移现象。文章从实验上对乙醇荧光峰值位置的红移规律进行了研究,并从理论上对红移现象进行了解释。研究结果有助于解释乙醇作为有机溶剂、荧光猝灭剂、食品添加剂等时对其他大分子的荧光光谱特性的影响,也将可能提供一种灵敏、快捷的乙醇含量测试方法。     

The role of co-adsorbed O2 on the catalytic reduction of NO with C2H5OH on the surface of Pt(3 3 2)

The influence of pre-dosed O₂ on the catalytic reduction of NO with ¹³C₂H₅OH on the surface of stepped Pt(3 3 2) was investigated using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). We show that the oxidation of ¹³C₂H₅OH with O₂ is a very effective reaction, occurring at 150 K and giving rise to acetate. The presence of NO does not lead to any evident oxidation of ¹³C₂H₅OH irrespective of the annealing temperature. For the case of O₂ + ¹³C₂H₅OH + NO co-adlayers, oxidation of ¹³C₂H₅OH also takes place at 150 K. However, no new surface species that are supposed to be an intermediate for the production of N₂ are detected.The influence of O₂ on the production and desorption of N₂ is intimately related to both O₂ and ¹³C₂H₅OH coverage. The presence of pre-dosed O₂ does not greatly promote N₂ desorption. In fact, N₂ desorption is suppressed quantitatively with increasing O₂ coverage, after which unreacted, or left-over O atoms appear and remain on steps. It is concluded that the presence of pre-dosed O₂ does not play a role of activating reactants in the catalytic reduction of NO with ¹³C₂H₅OH on the surface of Pt(3 3 2).     

麦芽酸性磷酸酶与乙醇相互作用的谱学研究

应用荧光光谱、紫外差光谱等技术研究了麦芽酸性磷酸酶经乙醇变性后活力与分子构象的变化情况,同时应用Lineweaver-Burk双倒数作图法考察了乙醇对酶动力学性质的影响。结果表明,乙醇对酶活力及分子构象有较显著的影响。酶活力随乙醇浓度增大而直线下降,50％的乙醇对酶的抑制率达43．4％;变性后酶的紫外差光谱在213和234nm处出现正吸收峰,表明酶肽链发生变化,酶分子由有序结构变成无规则卷曲;酶内源荧光强度随乙醇浓度的提高而增强,酪氨酸、色氨酸残基微环境在乙醇作用下发生明显变化,表明酶活力的表现与酶分子构象的稳定性和完整性密切相关。乙醇对酶的抑制类型为反竞争抑制。     

近红外光谱结合ELM快速检测固态发酵过程参数pH值

pH值是固态发酵过程关键参数之一,为此提出基于近红外光谱技术的秸秆蛋白饲料固态发酵过程参数pH值检测方法。利用近红外光谱系统获取140个固态发酵过程产物样本在10 000～4 000cm-1范围内的近红外光谱数据,通过酸度计测得近红外光谱预测模型的参考测量值;运用ELM算法建立pH值的预测模型,在模型建立过程中由交互验证法确定最佳主成分因子数和ELM网络隐含层节点数。试验结果显示:最佳ELM网络模型的拓扑结构为10-40-1,模型预测集相关系数(Rp)和预测均方根误差(RMSEP)分别为0.961 8和0.104 4。研究结果可为固态发酵过程参数的在线检测提供技术基础。     

乙酸-乙醇汽液平衡数据的测定与关联

用小型循环式汽液平衡釜测定了常压下乙酸-乙醇二元体系的汽液平衡数据,并用Willson 方程关联实验数据,利用Willson方程进行了汽液平衡数据计算,计算结果与实验值基本吻合.     

Ultrasonic-assisted synthesis of Pd–Pt/carbon nanotubes nanocomposites for enhanced electro-oxidation of ethanol and methanol in alkaline medium

Herein, a facile ultrasonic-assisted strategy was proposed to fabricate the Pd–Pt alloy/multi-walled carbon nanotubes (Pd–Pt/CNTs) nanocomposites. A good number of Pd–Pt alloy nanoparticles with an average of 3.4 ± 0.5 nm were supported on sidewalls of CNTs with uniform distribution. The composition of the Pd–Pt/CNTs nanocomposites could also be easily controlled, which provided a possible approach for the preparation of other architectures with anticipated properties. The Pd–Pt/CNTs nanocomposites were extensively studied by electron microscopy, induced coupled plasma atomic emission spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and applied for the ethanol and methanol electro-oxidation reaction in alkaline medium. The electrochemical results indicated that the nanocomposites had better electrocatalytic activities and stabilities, showing promising applications for fuel cells.     

基于密度泛函的甲醇和乙醇荧光特性研究

使用英国爱丁堡FLS920P荧光光谱仪,对甲醇、乙醇的紫外吸收光谱和荧光光谱进行实验检测,得到二者的光谱特征参数。分别采用密度泛函理论(DFT)和单激发组态相互作用(CIS)对二者分子的基态和激发态结构进行优化,并比较两种分子在不同能态下的差异。应用含时密度泛函理论(TD-DFT)的不同泛函结合极化连续介质模型(PCM)在6-31++G(d, p)水平上分别计算了二者的紫外吸收光谱和荧光光谱,与实验结果吻合。分析了甲醇、乙醇荧光产生机理,同时分析了不同泛函对于计算光谱的影响。结果表明：甲醇、乙醇在紫外波段有微弱吸收,在紫外激发下能产生拉曼峰和微弱的荧光峰。甲醇、乙醇的吸收光谱是由里德堡激发产生,产生荧光的轨道跃迁为σ*→π*。泛函OLYP能够较好地重现实验吸收能,而泛函MPWK能够较好地重现实验发射能,并且发现不同的纯泛函计算跃迁能也具有差异性。结果可为醇类分子的分子特性研究提供参考。     

Effects of low-intensity ultrasound on the growth,cell membrane permeability and ethanol tolerance of Saccharomyces cerevisiae

Effects of low-intensity ultrasound (at different frequency, treatment time and power) on Saccharomyces cerevisiae in different growth phase were evaluated by the biomass in the paper. In addition, the cell membrane permeability and ethanol tolerance of sonicated Saccharomyces cerevisiae were also researched. The results revealed that the biomass of Saccharomyces cerevisiae increased by 127.03% under the optimum ultrasonic conditions such as frequency 28 kHz, power 140 W/L and ultrasonic time 1 h when Saccharomyces cerevisiae cultured to the latent anaphase. And the membrane permeability of Saccharomyces cerevisiae in latent anaphase enhanced by ultrasound, resulting in the augment of extracellular protein, nucleic acid and fructose-1,6-diphosphate (FDP) contents. In addition, sonication could accelerate the damage of high concentration alcohol to Saccharomyces cerevisiae although the ethanol tolerance of Saccharomyces cerevisiae was not affected significantly by ultrasound.     

Screening of Yeast in Various Vineyard Soil and Study on Its Flavor Compounds from Brewing Grape Wine

In order to screen out Saccharomyces cerevisiae suitable for table grape fermentation, and compare it with commercial Saccharomyces cerevisiae in terms of fermentation performance and aroma producing substances, differences of fermentation flavor caused by different strains were discussed. In this experiment, yeast was isolated and purified from vineyard soil, 26s rDNA identification and fermentation substrate tolerance analysis were carried out, and the causes of flavor differences of wine were analyzed from three aspects: GC-MS, PCA and sensory evaluation. The results showed that strain S1 had the highest floral aroma fraction, corresponding to its high production of ethyl octanoate and other substances, and it had the characteristics of high sugar tolerance. The fruit sensory score of S3 wine was the highest among the six wines. Through exploration and analysis, it was found that compared with commercial Saccharomyces cerevisiae, the screened strains had more advantages in fermenting table grapes. The flavor of each wine was directly related to the growth characteristics and tolerance of its strains.     

Kinetics of batch production of single-cell protein from cheese whey

A kinetic model for single-cell protein batch fermentation was developed using the numerical simultaneous integration approach of the fourth-order Runge-Kutta method. The model takes into account the effect of substrate inhibtion, maintenance energy, and cell death on the cell growth and substrate utilization during the fermentation process. The theoretical results obtained from the model compared well with the experimental data. The model was used to study the effect of the initial substrate concentration on the lag period, fermentation time, specific growth rate, population size, and cell productivity of batch fermentation. Increasing the initial substrate concentration increased the lag period and fermentation time and decreased the specific growth rate and cell yield. The growth limiting substrate concentration was 2.9 g/L, whereas the growth inhibiting substrate concentration was 69.0 g/L. Increasing the initial substrate concentration above 150 g/L significantly decreased the yeast population size.