杂多酸存在下X3B染料光降解和Cr(VI)光还原的协同反应机理

以H3PW12O40(PW)和H4SiW12O40(SiW)杂多酸(POM)为催化剂, 波长大于320 nm的高压氙灯为光源, 研究了混合水溶液中活性艳红染料X3B的光致降解和重铬酸根(Cr(VI))的光致还原. 结果表明, POM-X3B-Cr(VI)三元体系的反应效率高于POM-X3B、POM-Cr(VI)和X3B-Cr(VI)二元体系的反应效率, PW的光活性高于SiW, 且X3B光降解和Cr(VI)光还原之间存在明显的协同作用. 通过考察各组分起始浓度以及N2、O2、H2O2和乙醇的影响, 实验发现, 激发态POM*与H2O反应产生POM-和·OH是反应的决速步骤. X3B光降解和Cr(VI)光还原分别主要通过·OH 和POM-进行, 而X3B和Cr(VI)之间光化学反应的贡献较小. 在二元和三元体系中POM浓度对反应速率表现出不同的影响, 表明激发态POM*与H2O之间的反应具有可逆性.     

Unusual and unexpected reactivity of t-butyl dicarbonate (Boc2O) with alcohols in the presence of magnesium perchlorate. A new and general route to t-butyl ethers

[reaction: see text] A new mild method for protecting alcohols as t-butyl ethers is reported. The reaction proceeds with Mg(ClO4)2 and Boc2O and shows general applicability. The deprotection of t-butyl ethers has also been revisited. Preliminary results indicate the CeCl3 x 7H2O/NaI system is a very suitable catalyst for their removal.     

Catalytic oxidation of ammonia on RuO2(110) surfaces: mechanism and selectivity

The selective oxidation of ammonia to either N2 or NO on RuO2(110) single-crystal surfaces was investigated by a combination of vibrational spectroscopy (HREELS), thermal desorption spectroscopy (TDS) and steady-state rate measurements under continuous flow conditions. The stoichiometric RuO2(110) surface exposes coordinatively unsaturated (cus) Ru atoms onto which adsorption of NH3 (NH3-cus) or dissociative adsorption of oxygen (O-cus) may occur. In the absence of O-cus, ammonia desorbs completely thermally without any reaction. However, interaction between NH3-cus and O-cus starts already at 90 K by hydrogen abstraction and hydrogenation to OH-cus, leading eventually to N-cus and H2O. The N-cus species recombine either with each other to N2 or with neighboring O-cus leading to strongly held NO-cus which desorbs around 500 K. The latter reaction is favored by higher concentrations of O-cus. Under steady-state flow condition with constant NH3 partial pressure and varying O2 pressure, the rate for N2 formation takes off first, passes through a maximum and then decreases again, whereas that for NO production exhibits an S-shape and rises continuously. In this way at 530 K almost 100% selectivity for NO formation (with fairly high reaction probability for NH3) is reached.     

Theoretical study of the benzyl+O2 reaction: kinetics, mechanism, and product branching ratios

Ab initio calculations at the level of CBS-QB3 theory have been performed to investigate the potential energy surface for the reaction of benzyl radical with molecular oxygen. The reaction is shown to proceed with an exothermic barrierless addition of O2 to the benzyl radical to form benzylperoxy radical (2). The benzylperoxy radical was found to have three dissociation channels, giving benzaldehyde (4) and OH radical through the four-centered transition states (channel B), giving benzyl hydroperoxide (5) through the six-centered transition states (channel C), and giving O2-adduct (8) through the four-centered transition states (channel D), in addition to the backward reaction forming benzyl radical and O2 (channel E). The master equation analysis suggested that the rate constant for the backward reaction (E) of C6H5CH2OO-->C6H5CH2+O2 was several orders of magnitude higher that those for the product dissociation channels (B-D) for temperatures 300-1500 K and pressures 0.1-10 atm; therefore, it was also suggested that the dissociation of benzylperoxy radicals proceeded with the partial equilibrium between the benzyl+O2 and benzylperoxy radicals. The rate constants for product channels B-D were also calculated, and it was found that the rate constant for each dissociation reaction pathway was higher in the order of channel D>channel C>channel B for all temperature and pressure ranges. The rate constants for the reaction of benzyl+O2 were computed from the equilibrium constant and from the predicted rate constant for the backward reaction (E). Finally, the product branching ratios forming CH2O molecules and OH radicals formed by the reaction of benzyl+O2 were also calculated using the stationary state approximation for each reaction intermediate.     

天冬酰胺合成酶B抑制剂高效液相色谱筛选方法的建立与应用

建立了一种快速、高效测定天冬酰胺合成酶B(AS-B)酶活性的反相高效液相色谱法(RP-HPLC)。酶反应体系中的氨基酸经2,4-二硝基氟苯(DNFB)柱前衍生,通过RP-HPLC测定酶反应体系前后底物及产物的变化来分析酶的活性。采用的色谱柱为Agilent C18柱(250 mm×4.6 mm,5 μm),以50 mmol/L醋酸钠缓冲液(pH 6.2)-乙腈(体积比为15:85)为流动相,流速为1.0 mL/min,柱温为30 ℃,检测波长365 nm,于6 min内实现了各组分的基线分离。通过该方法测定反应动力学参数进行AS-B的抑制定量分析。将已知AS-B抑制剂L-谷氨酸-γ-甲酯作用于酶反应体系,测得的抑制剂的抑制常数与文献值相接近,证明该方法可用于AS-B抑制剂的筛选。     

Effect of O2 and H2O on the tri-reforming of the simulated biogas to syngas over Ni-based SBA-15 catalysts

A series of Ni/SBA-15 catalysts with Ni contents from 7.5 wt% to 15 wt% were prepared by impregnation method. The effect of O2 and H2O on the combined reforming of the simulated biogas to syngas was investigated in a continuous flow fixed-bed micro-reactor. The stability of the catalyst was tested at 800 ℃. The results indicated that 10 wt%Ni/SBA-15 catalyst exhibited the highest catalytic activities for the combined reforming of the simulated biogas to syngas. Under the reaction conditions of the feed gas molar ratios CH4/CO2/O2/H2O = 2/1/0.6/0.6, GHSV = 24000 ml•g{cat}-1\cdoth-1 and the reaction temperatureT = 800 ℃, the conversions of CH4 and CO2 were 92.8% and 76.3%, respectively, and the yields of CO and H2 were 99.0% and 82.0%, respectively. The catalytic activities of the catalyst did not decrease obviously after 100 h reaction time on stream.     

Nonlinear chemical reaction between Na_2S_2O_3 and Peroxide compound

Kinetics of reaction between Na2S2O3 and peroxide compound ( H2O2 or Na2S2O8) in a batch reactor and in a continuous stirring tank reactor (CSTR) were studied.Steady oscillations in uncatalyzed reactions in a CSTR were first discovered.In Na2S2O3-H2O2-H2SO4 reaction system,Pt potential and pH of higher and lower flow rutes beyond oscillation flow rates were in around the same extreme values.The reaction catalyeed by Cu2+ corsist of the catalyzed oscillation process and the uncatalyzed osciliation one.On the basis of experiment,a reaction mechanism consisting of three stages was put forward.The three stages are H positive-feedback reactions,proton negative-feedba k (uncatalyzed negative-feedback and catalyzed negative-feedback) reactions and transitional reactions.The mechanism is able to explain reasonably the nonlinear chemical phenomena appearing in the thiosulfatc oxidation reaction by peroxide-compounds.     

Effect of O_2 and H_2O on the tri-reforming of the simulated biogas to syngas over Ni-based SBA-15 catalysts

A series of Ni/SBA-15 catalysts with Ni contents from 7.5 wt% to 15 wt% were prepared by impregnation method.The effect of O2 and H2O on the combined reforming of the simulated biogas to syngas was investigated in a continuous flow fixed-bed micro-reactor.The stability of the catalyst was tested at 800 ?C.The results indicated that 10wt%Ni/SBA-15 catalyst exhibited the highest catalytic activities for the combined reforming of the simulated biogas to syngas.Under the reaction conditions of the feed gas molar ratios CH4/CO2/O2/H2O = 2/1/0.6/0.6,GHSV = 24000 ml gc?a1t h?1 and the reaction temperature T = 800 ?C,the conversions of CH4 and CO2 were 92.8% and 76.3%,respectively,and the yields of CO and H2 were 99.0% and 82.0%,respectively.The catalytic activities of the catalyst did not decrease obviously after 100 h reaction time on stream.     

Temperature, composition, and hydrogen isotope effect in the hydrogenation of CO on amorphous ice surface at 10-20 K

An experiment on the addition reaction of a D atom (deuteration) to CO on a cold ice surface is performed by deuterium atom exposure of three types of samples (pure solid CO, CO-capped H2O ice, and CO-H2O mixed ice) at 10-20 K. The variation of IR absorption spectra for the samples was measured by a Fourier transform infrared spectrometer during exposure to deuterium atoms. Reactions on pure solid CO were observed only at 10 K, while reactions on CO-capped H2O ice and CO-H2O mixed ice were observed to proceed even at 20 K. This indicates that the coexistence of H2O at the surface raises the reactive temperature. In addition, the experiment on H atom exposure was also carried out at 15 K to compare the reaction rate constant between the H and D atoms. The ratio of reaction rate constant kD/kH obtained is about 0.08 at 15 K. The authors provide information on the potential energy for the H+CO reaction at the surface by using the ratio kD/kH and by a model calculation of the potential tunneling with the asymmetric Eckart potential.     

Kinetics of Al + H2O reaction: theoretical study

Quantum chemical calculations were carried out to study the reaction of Al atom in the ground electronic state with H(2)O molecule. Examination of the potential energy surface revealed that the Al + H(2)O → AlO + H(2) reaction must be treated as a complex process involving two steps: Al + H(2)O → AlOH + H and AlOH + H → AlO + H(2). Activation barriers for these elementary reaction channels were calculated at B3LYP/6-311+G(3df,2p), CBS-QB3, and G3 levels of theory, and appropriate rate constants were estimated by using a canonical variational theory. Theoretical analysis exhibited that the rate constant for the Al + H(2)O → products reaction measured by McClean et al. must be associated with the Al + H(2)O → AlOH + H reaction path only. The process of direct HAlOH formation was found to be negligible at a pressure smaller than 100 atm.     

硝酸铬与组氨酸配合行为的相化学与热化学研究

用相平衡方法研究了硝酸铬-组氨酸-水体系在298.15K时的溶度,绘制了体系的相图,发现并制备了文献未报道的一致溶解配合物:Cr(His)(NO3)3·3H2O(A),Cr(His)2(NO3)3·3H2O(B)和Cr(His)3(NO3)3·3H2O(C),经分析确定了其组成。用微热量计热测定了硝酸铬和组氨酸在水中的反应焓,计算了这些反应的热动力学参数(活化焓、活化熵及活化自由能)、速率常数和动力学能数(活化能、指前因子及反应级数)。     

对甲氧基苯磺酰氯柱前衍生生物胺的高效液相色谱分离

采用对甲氧基苯磺酰氯作为柱前衍生试剂,RP-HPLC为分析模式,建立了一种新的生物胺衍生化方法,并对葡萄酒中生物胺含量进行检测。通过液质联用对产物进行定性,研究并确定了最适衍生化条件:衍生温度50℃,缓冲液pH 9.0,衍生时间15 min。实验建立了7种生物胺的HPLC分离方法:Beckman ODS柱;流动相A为10 mmol/L的NH4Ac溶液(pH 6.37),B相为乙腈;采用梯度洗脱;流速1 mL/min;检测波长240 nm,室温。     

A europium(III) complex as an efficient singlet oxygen luminescence probe

A new europium(III) complex, [4'-(10-methyl-9-anthryl)-2,2':6',2"-terpyridine-6,6"-diyl]bis(methylenenitrilo) tetrakis(acetate)-Eu(3+), was designed and synthesized as a highly sensitive and selective time-gated luminescence probe for singlet oxygen ((1)O2). The new probe is highly water soluble with a large stability constant of approximately 10(21) and a wide pH available range (pH 3-10), and can specifically react with (1)O2 to form its endoperoxide (EP-MTTA-Eu(3+)) with a high reaction rate constant at 10(10) M(-1) s(-1), accompanied by the remarkable increases of luminescence quantum yield from 0.90% to 13.8% and lifetime from 0.80 to 1.29 ms, respectively. The wide applicability of the probe was demonstrated by detection of (1)O2 generated from a MoO(4)(2-)/H(2)O2 system, a photosensitization system of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP), and a horseradish peroxidase catalyzed aerobic oxidation system of indole-3-acetic acid (IAA). In addition, it was found that the new probe could be easily transferred into living HeLa cells by incubation with TMPyP. A time-gated luminescence imaging technique that can fully eliminate the short-lived background fluorescence from TMPyP and cell components has been successfully developed for monitoring the time-dependent generation of (1)O2 in living cells.     

O(3P)原子与丁酮反应速率常数的测定

The measurement of the kinetic rate constant of the reaction of O(~3P) atoms with n-butanone at 288K is carried out. O(~3P) atoms were generated by a microwave discharge flow system and the residual concentration was detected by NO_2* chemiluminescence. The specific rate constant obtained is κ=(6.2±1.2)×10~(-15)cm~3 molecule~(-1) s~(-1) (T=288 K).A correlation diagram of molecular orbitals for the reaction is discussed.     

循环连续流动分析法测定辣根过氧化物酶的活性

基于H2O2-辣根过氧化物酶(HRP)-邻苯二胺(OPDA)催化反应体系,建立了测定游离及固定化HRP酶活性的循环连续流动分析法(CCFA).CCFA实现了反应液、反应过程的循环连续检测.用CCFA法对酶催化反应条件进行研究,得到的最佳反应条件是:pH 5.0,反应温度27 ℃, 66.0 μmol/L H2O2 , 2 mg/L OPDA,缓冲液为0.1 mol/L柠檬酸-柠檬酸钠缓冲液; 测定游离HRP的线性范围为0～10 U/L,检出限为0.21 U/L,RSD＜1.03%.使用CCFA法测定了固定化HRP的活性,并对HRP酶促动力学进行了研究,得到的游离HRP的米氏常数为0.078 mmol/L,最大反应速度为0.26 mmol/(L min),催化常数为5.2 × 104 min-1.CCFA法操作简便、准确度高、节省试剂、易于实现自动化.     

DMF-H_2O缔合体系的~1HNMR研究

DMF水溶液是一种生物分子水溶液的简单生化模型。测量了DMF-H_2O体系不同 温度下全浓度范围的~1H NMR数据，对体系中的缔合情况进行了讨论，基于H_2O, H_2O·DMF, (H_2O)_2和(DMF)_2·H_2O的缔合平衡建立了化学缔合模型，采用最 小二乘法拟合实验数据，联合遗传算法和Levenberg-Marquardt算法对模型参数进 行全局寻优求解得不同温度的缔合平衡常数K，再根据不同温度的K求得缔合平衡的 ΔH和ΔS。为了更好地理解DMF水溶液中分子间的相互作用，还测量了298 K下DMF- CCl_4和DMF-BuOH体系全浓度范围的~1H NMR数据作为比较，结合NMR的基本原理对 各DMF溶液体系~1H NMR的实验现象进行了分析和解释，认为水溶液的特殊结构、氢 键和DMF酰胺基的共轭体系是影响DMF-H_2O体系~1H NMR的主要因素。     

Renewable Drops Electrochemical Sensor for Sulfide Ions Detection

The design and characteristics of a novel electrochemical system, which uses a drop as a renewable electroanalytical sensor, are described. This article describes the performance of the electrochemical system, the coupling of the experimental arrangement with flow injection technique and a demonstration of its applicability for the measurement of sulfide. The method is based on renewable drops of ferricyanide ions, buffered by borate. The ferrocyanide ions, product of the reaction between ferricyanide and sulfide ions, are oxidized on a platinum microelectrode and the current measured is related to sulfide concentration. The measurements can be done in continuous or static flow mode. In continuous mode, the detection limit is 5.0×10^?5 mol L^?1.     

抗癌药物马蔺子素伏安行为及极谱催化波研究

采用线性扫描示波极谱法、循环伏安法、紫外光谱法及恒电位电解法等方法分别在水和N,N-二甲基甲酰胺(DMF)两种介质中研究了抗癌药物马蔺子素的伏安行为及其极谱平行催化波产生机理.结果表明,在Na₂B₄O₇-KH₂PO₄(pH=7.7)缓冲溶液中,马蔺子素的醌基首先发生1e-和1H+还原,产生中间体半醌自由基,该自由基再以同样方式进一步还原生成相应氢醌,并伴随有化学反应;在DMF-四乙基溴化铵(TEAB)质子惰性介质中,马蔺子素连续两步单电子还原生成相应氢醌阴离子,无中间体半醌自由基的化学反应发生.上述过程产生马蔺子素可逆还原波.当氧化剂K₂S₂O₈存在时,马蔺子素醌基还原中间体半醌自由基被氧化,使原醌基再生,产生了马蔺子素的极谱平行催化波.测得S₂O₈^2-氧化马蔺子素半醌自由基的表观一级速率常数k_f=3.3×10⁶L·mol^-1·s^-1.     

Development and comparison of biosensors for in-vivo applications

Electrochemical biosensors have been of increasing interest, especially those developed to be directly applied in diagnostic areas, such as neuroscience. We have been interested in developing a range of biosensors for monitoring glucose, lactate, pyruvate, and glutamate in order to study on-line both brain function in the laboratory and to monitor brain health in neurointensive care. For a biosensor to function effectively in these situations, it has to combine the following characteristics: quick response and high sensitivity, good reproducibility and adequate stability. In this study we compared the performance of a number of different amperometric biosensors strategies. These included ferrocene mediation of immobilised enzymes (system A), a redox hydrogel based system (system B), and a conducting polymer approach using polyaniline (system C). All assays were operated as flow-injection systems with upstream immobilised enzyme beds if necessary. When calibrated for H2O2 systems A and B reacted quickly enough to give quantitative conversion up to 0.2 mM. Above this concentration the response was limited by horseradish peroxidase enzyme kinetics and eventually enzyme loading. System C showed a restricted H2O2 response. When calibrated for glucose (by use of immobilised glucose oxidase) system B exhibited the highest sensitivity but its analytical range was restricted because the system became limited by H2O2 response. System A had low sensitivity for analyte compared to H2O2 and system B, but a greater useful range. Problems of mediator cycling between the immobilised enzymes are discussed. System C gave an excellent linear range but sensitivity was limited by background noise. Stability and reproducibility of the systems are also described. In conclusion, from this study the ferrocene system proved to be overall most useful and has now been used in the first dual on-line monitoring of glucose and lactate in patients in neurointensive care.     

3D-Printed Phenacrylate Decarboxylase Flow Reactors for the Chemoenzymatic Synthesis of 4-Hydroxystilbene

Continuous flow systems for chemical synthesis are becoming a major focus in organic chemistry and there is a growing interest in the integration of biocatalysts due to their high regio- and stereoselectivity. Methods established for 3D bioprinting enable the fast and simple production of agarose-based modules for biocatalytic reactors if thermally stable enzymes are available. We report here on the characterization of four different cofactor-free phenacrylate decarboxylase enzymes suitable for the production of 4-vinylphenol and test their applicability for the encapsulation and direct 3D printing of disk-shaped agarose-based modules that can be used for compartmentalized flow microreactors. Using the most active and stable phenacrylate decarboxylase from Enterobacter spec. in a setup with four parallel reactors and a subsequent palladium(II) acetate-catalysed Heck reaction, 4-hydroxystilbene was synthesized from p-coumaric acid with a total yield of 14.7 % on a milligram scale. We believe that, due to the convenient direct immobilization of any thermostable enzyme and straightforward tuning of the reaction sequence by stacking of modules with different catalytic activities, this simple process will facilitate the establishment and use of cascade reactions and will therefore be of great advantage for many research approaches.