Photoinduced ionic polymerization. VII. Cationic polymerization of cyclohexene oxide in solid state

Photopolymerization of cyclohexene oxide in the presence of electron acceptors was studied in a bulk system (in liquid as well as in solid states). The polymerization was proved to proceed by a cationic mechanism in both states by the effect of inhibitors. In a liquid phase the light intensity dependence of the rate of polymerization and the molecular weight distribution showed a contribution of a free ionic polymerization. Any discontinuous phenomenon in the rate as well as in the molecular weight was not discerned between liquid(above ?36°C) and plastic crystal (between ?36 and ?81°C) phases. A quantum yield of monomer consumption as high as 8 × 10³ was observed in the plastic crystal phase. Below ?81°C in the normal crystal phase the rate as well as the molecular weight was remarkably suppressed.     

苯乙烯与4-氨基苯酚的氢氨甲基化反应研究北大核心CSCD

氢氨甲基化反应(HAM)是由简单烯烃、胺和合成气一锅法合成有价值胺的方法,具有较高的原子经济效率.然而,4-氨基苯酚作为一种特殊的反应底物,因其同时具有羟基和胺基官能团,在羰基化反应过程中能够选择性地在不同位点发生反应获得不同的产物.因此,我们系统研究了4-氨基苯酚与烯烃的HAM,通过筛选反应参数,确定了最优反应条件,并通过调控添加剂种类,选择性地在4-氨基苯酚的不同活性位点发生反应.结果表明,以甲醇为溶剂,三(3-甲氧基苯基)膦为配体,RhCl(PPh_(3))_(3)为催化剂前驱体,合成气压力4 MPa(H_(2)∶CO=3∶1),反应温度100℃,反应时间20 h时,该催化体系具有最高的反应活性.当以CH3COOH作为添加剂时,选择性的4-氨基苯酚的胺基官能团发生氢氨甲基化反应得到产物4-[(2-苯丙基)氨基]苯酚,收率为82%;当以DBU作为添加剂时,得到苯乙酮产物,收率为92%.最后,提出了该反应可能的机理,为4-氨基苯酚的选择性反应提供理论依据.     

囊泡表面分子间通讯交流体系的构建: 利用受体的分子识别行为调控酶的活性

在人工双层膜囊泡表面, 构建了一个通过人工受体的分子识别行为控制酶反应活性的超分子体系. 体系以生物体细胞信号转导系统为模拟原型, 由作为受体的烷基胺、被受体识别的信号分子吡哆醛衍生物、乳酸脱氢酶、受体和酶之间的媒介物Cu^2＋以及作为体系载体的合成肽脂囊泡五个成分构成．通过UV-vis光谱法及动态光散射测定对体系进行了评价, 结果表明: 随着受体疏水参数增大, 其对信号分子的识别能力增强, 二者呈良好的线性关系; 通过信号分子与囊泡表面静电相互作用的研究表明信号分子具有选择性; 媒介物与信号分子–受体可形成化学计量比为1∶2的配合物, 其形成能力比媒介物与酶的结合能力更强．作为结论, 体系中烷基胺受体对磷酸吡哆醛信号分子的识别有效控制了处于囊泡表面的乳酸脱氢酶的活性．     

Separation of glycosylated caseinomacropeptide at pilot scale using membrane adsorption in direct-capture mode

A direct-capture anion-exchange membrane adsorption process for the separation of a pure glycosylated (gCMP) fraction of caseinomacropeptide (CMP) was successfully developed at pilot plant scale. The method was evolved using a commercial CMP isolate as feedstock as well as fresh sweet whey from skim milk. The former resulted in a binding capacity (BC) of 0.28 mg gCMP/cm² membrane surface with a purity of 97% while the latter afforded a gCMP fraction with a purity of 91% and a BC of 0.21 mg gCMP/cm² membrane surface. The main difference was a significant fouling of the membrane adsorber module when the whey was applied, which resulted in a loss of 46% BC after at least five loading/elution cycles. This effect was not observed using the pure CMP isolates and indicates a blocking of the ion-exchange ligands. Triglycerides, as detected by lipid analysis, as well as protein aggregates and casein-flocculates, are mainly responsible for the fouling process. The fouling was decreased using microfiltered whey or by increasing the temperature of the adsorption process. Additionally, a method of repeated elution was shown to decrease the volume of the eluate as well as the NaCl consumption of the elution buffer. The process development further included a desalting and concentration step, which was performed by a 10 kDa ultrafiltration/diafiltration (UF/DF). The efficiency of the UF was strongly influenced by the pH of the solutions and showed best performance at pH 4.1 for the eluate. The residual solution had to be adjusted at pH 6.5 as there was a strong decrease of flux at lower pH levels.     

A low-cost light-scattering detector for the flow-injection nephelometric determination of sulfate.

A simple low-cost flow-through light-scattering detector was developed for determining the particle mass concentration in colloidal suspensions. Employing a laser pointer as a light source and a photodiode IC as a light sensor, the detector was shown to have good sensitivity, yet was small and battery operated. The detector was demonstrated to be effective for the flow-injection nephelometric determination of sulfate by precipitation as barium sulfate.     

Understanding the importance of the viscosity contrast between the sample solvent plug and the mobile phase and its potential consequence in two-dimensional high-performance liquid chromatography

The effect of solvent viscosity mismatch on elution performance in reversed-phase HPLC was studied using moment analysis. Two conditions were tested: (1) the mobile phase viscosity was less than the injection plug viscosity, and (2) the mobile phase viscosity was greater than the injection plug viscosity. Under the first condition, retention time and elution performance decreased as the viscosity contrast between the mobile phase and injection plug increased. The effect on performance was more marked as the injection volume increased. A decrease in performance of 12% for compounds with retention factors up to 2.8 was apparent even when the viscosity contrast was only 0.165 cP. In the second set of conditions, elution performance was actually observed to increase, by as much as 25% for a 40 μL injection, as the viscosity contrast between the mobile phase and the solute plug increased. No change in the retention factor was observed. This behaviour was attributed to the shape of an injection plug as it enters into the column, whereby a low viscosity plug permeates away from the wall when the column contains a higher viscosity mobile phase, and vice a versa for a high viscosity plug entering a low viscosity mobile phase. At no stage was either a band splitting or shoulders observed with viscosity contrasts up to 1.283 cP, as could have been expected.     

三明治式双极膜的制备及其光催化性能

以Cr3+交联羧甲基纤维素钠(CMC)作为阳膜层,戊二醛改性壳聚糖(CS)作为阴膜层,纳米TiO2光催化剂作为双极膜的中间层,在TiO2上涂布光敏剂八羟基喹啉（Oxine）以增强其光催化解离水的性能,制备了三明治式的双极膜（mCMC/TiO2-Oxine/mCS BPM)。 该双极膜在紫外光照射下,具有高的水解离效率,优良的亲水性能,双极膜阻抗小,工作电压低,当工作电流密度达0.12 A/cm2时,电槽工作电压小于5.0 V。     

Antibody adsorption and orientation on hydrophobic surfaces

The orientation of a monoclonal, anti-streptavidin human IgG1 antibody on a model hydrophobic, CH(3)-terminated surface (1-dodecanethiol self-assembled monolayer on gold) was studied by monitoring the mechanical coupling between the adsorbed layer and the surface as well as the binding of molecular probes to the antibodies. In this study, the streptavidin antigen was used as a probe for the Fab portions of the antibody, while bacteria-derived Protein G' was used as a probe for the Fc region. Bovine serum albumin (BSA) acted as a blocking protein. Monolayer coverage occurred around 468 ng/cm(2). Below 100 ng/cm(2), antibodies were found to adsorb flat-on, tightly coupled to the surface and unable to capture their antigen, whereas the Fc region was able to bind Protein G'. At half-monolayer coverage, there was a transition in the mechanism of adsorption to allow for vertically oriented antibodies, as evidenced by the binding of both Protein G' and streptavidin as well as looser mechanical coupling with the surface. Monolayer coverage was characterized by a reduced level in probe binding per antibody and an even less rigid coupling to the surface.     

Electrodecomposition in subcritical water using o-xylene as a model for benzene, toluene, ethylbenzene, and xylene pollutants

The possibility of the combination of electrolysis and subcritical water as a novel electrolyte was investigated. A stainless steel reactor was used as an undivided electrochemical cell containing platinum as the anode and a stainless steel reactor as the cathode. At first, the effect of temperature on the electrolysis current as the main parameter was studied in a cell containing only pure water and a supporting electrolyte. It was realized that the electrolysis current (and, consequently, the electrolysis efficiency) increased linearly with temperature because of the change in viscosity and other physicochemical properties of subcritical water. As a result, at 553 K the electrolysis efficiency was over 14-fold higher than that under ambient conditions. The possibility of the applicability of the above combined techniques for the decomposition of o-xylene was also followed as a model for benzene, toluene, ethylbenzene, and xylene (BTEX) compounds. The effect of experimental conditions such as the electrolysis duration, the electrolysis voltage, and the temperature of subcritical water was investigated. Several decomposed products were identified. o-Xylene was directly electro-oxidized to 2-methylbenzyl alcohol and consecutively to the other oxidation products. Also, hydroxide ions were oxidized to oxygen molecules, where hydrogen was generated on the cathodic surface. The final oxidation product of the electro-oxidation reaction was identified as carbon dioxide. The results indicate that more than 95% of o-xylene can be decomposed under optimum conditions.     

Sensitive chemically amplified electrochemical detection of ruthenium tris-(2,2′-bipyridine) on tin-doped indium oxide electrode

Optimized combination of chemical agents was selected for sensitive electrochemical detection of dissolved ruthenium tris-(2,2′-bipyridine) (Ru-bipy). The detection was based on the chemical amplification mechanism, in which the anodic current of a redox-active analyte was amplified by a sacrificial electron donor in solution. On indium-doped tin oxide (ITO) electrodes, electrochemical reaction of the analyte was reversible, but that of the electron donor was greatly suppressed. Several transition metal complexes, such as ferrocene and tris-(2,2′-bipyridine) complexes of osmium, iron and ruthenium, were evaluated as model analyte. A correlation between the amplified current and the standard potential of the complex was observed, and Ru-bipy generated the largest current. A variety of organic bases, acids and zwitterions were assessed as potential electron donor. Sodium oxalate was found to produce the largest amplification factor. With Ru-bipy as the model analyte and oxalate as the electron donor, the analyte concentration curve was linear up to 50 μM, with a lower detection limit of approximately 50 nM. Preliminary work was presented in which a Ru-bipy derivative was attached to bovine serum albumin and detected electrochemically. Although the combination of Ru-bipy, oxalate and ITO electrode has been used before for electrochemiluminescent detection of Ru-bipy and oxalate, as well as electrochemical detection of oxalate, its utility in amplified voltammetric detection of Ru-bipy as a potential electrochemical label has not been reported previously.     

Oligodeoxynucleotide-modified capillary for electrophoretic separation of single-stranded DNAs with a single-base difference.

We describe here a method of affinity capillary electrophoresis in which oligodeoxynucleotide (ODN) was immobilized onto the inner surface of the capillary. The immobilized ODN functioned successfully as an affinity ligand for sequence-based DNA separation. Six- or 12-mer ODN with a sequence complementary to one of the c-K-ras gene was used as an immobilized ligand. When the 12-mer ODN was used, the detection peak for the complementary ODN disappeared selectively, while the single-base mutant was detected as usual. In contrast, when the 6-mer ODN was used as the affinity ligand with a mixture of the complementary ODN and its single-base mutant, it was possible to detect both as completely separate peaks. That is, the separation mode was dependent on the base number of the immobilized ODN used as an affinity ligand.     

Infrared and XAFS study on structure and transition behavior of zinc stearate

Structure and transition behavior of zinc(II) stearate crystal were investigated by infrared and XAFS spectroscopies. Structure of zinc stearate at room temperature was estimated as follows. From XAFS analysis, the coordination number of the carboxylate groups around the zinc atom was evaluated as 4 and the Zn-O distance as 1.95 A. Based on the infrared spectrum and a normal mode analysis, the conformation of the alkyl chain was confirmed as all-trans and the sub-cell packing was considered as parallel type, and also the coordination form of the carboxylate groups was determined as bridging bidentate type. As increasing temperature, zinc stearate has a solid liquid phase transition at 130 degrees C. At the transition, the alkyl chains goes into liquid like state as reported by Mesubi but the coordination structure was confirmed to be maintained.     

Electroinitiated Polymerization of N-Vinylcarbazole by Direct Electron Transfer

Electroinitiated polymerization of N-vinylcarbazole has been accomplished by constant potential electrolysis. It was found that direct electron transfer from the monomer to the anode initiates the polymerization even at a potential as low as +0.95 V versus Ag^?/ Ag⁺. Dichloromethane was used as the solvent, and the electrolyte was tetrabutylammonium fluoroborate. Conversions as high as 86% were reached even when a microelectrode was used. Effects of electrode area, temperature, and electrode potential on polymerization were studied. Percent conversion was followed by cyclic voltammetry.     

Evaluation of the interaction of propranolol with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes: the Langmuir model

The interaction of the amine containing beta-receptor blocking agent propranolol (Ppn) with dimyristoylphosphatidylcholine (DMPC) vesicles was studied. Using a centrifugation assay, the protonated as well as unprotonated amount of the drug sorbed was verified, whereas the binding of the protonated Ppn was deduced from the surface charge density of the vesicles as calculated from electrophoretic mobility measurements. Assuming a 1:1 binding, a Langmuir model with only two parameters was found to be sufficient to fit all experimental data. Sensitivity analysis revealed that the estimated values of these parameters were reliable and independent from each other. These parameters were truly intrinsic, as electrostatic interactions were accounted for in the model. It was found that the pKa of Ppn shifted from 9.24, when dissolved in water, downward by 1.34 units upon sorption, indicating that the intrinsic partition coefficient of the unprotonated Ppn was about 22 times higher than that of the protonated analog. In addition, a significant increase in the affinity of both Ppn analogs with increasing salt concentration was found. Theoretical analysis revealed that the Langmuir sorption model may be considered as a partitioning model with decreasing partition coefficient as the sorbed amount increases. Thus, the Langmuir model provides a better fit than a simple partition model at conditions that induce a substantial amount of propranolol sorbed, such as high pH and high propranolol concentrations.     

Synthesis of the ABCD trioxadispiroketal subunit of azaspiracid-1: an iodoetherification-dehydroiodination strategy for complex spiroketals

An unusual spiroketalization strategy in which a hydroxyalkene serves as a precursor to a cyclic enol ether was applied to the synthesis of the ABCD trioxadispiroketal subunit of azaspiracid-1. The trioxadispiroketal product, which represents a double anomeric effect, was obtained as a single trioxadispiroketal diastereomer. A key ploy in the synthesis of the CD segment was the use of a cyclopropane as a synthon for the C-14 methyl group.     

调制脉冲电沉积法制备质子交换膜燃料电池铂催化电极

通过调制脉冲电流在质子交换树脂(Nafion)粘接的无催化多孔碳电极(UCE)上电沉积Pt 催化剂, 对所沉积Pt 催化电极性能及负载量用循环伏安法(CV)、X 射线衍射仪(XRD)、透射电镜(TEM)及分光光度法进行了表征. 结果表明, 通过调制电沉积过程的脉冲参数, 能够实现质子交换膜燃料电池(PEMFC)电极Pt催化剂的直接电化学沉积, 能够调控电沉积Pt粒径, 并能有效地缓解电沉积过程中析氢对沉积金属催化剂铂的干扰, 所沉积的Pt 催化剂利用率较传统Nafion 粘接Pt/C催化电极要高. 脉冲导通时间ton 为300 μs、断通时间toff 为1200 μs, 脉冲峰值电流密度jp 为100 mA·cm-2 时, 电沉积120 s制得的电极的Pt 晶粒约5-8 nm, Pt 表面利用率为43.14%, 沉积Pt的电流效率为45%.     

Synthesis of a molecularly imprinted polymer for the selective solid-phase extraction of chloramphenicol from honey

Solid-phase extraction (SPE) with a molecularly imprinted polymer (MIP) as sorbent has been investigated for the clean-up of the broad-spectrum bacteriostatic antibiotic chloramphenicol (CAP) in honey samples. The MIP was prepared by using methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EDMA) as cross-linker, chloroform as porogen and CAP as template molecule. The binding behaviour of the template CAP on the MIP was evaluated by high-performance liquid chromatography, and then the MIP was applied as a sorbent in SPE to selectively extract CAP from honey. It was shown that recoveries of nearly 100% of a CAP standard solution and up to 94% from spiked honey samples could be obtained after SPE.     

交联木质素负载钯催化剂的制备及对Heck反应的催化性能研究

以天然木质素为原料, 用甲醛对其进行交联得到了交联木质素, 通过简单的方法合成了负载钯催化剂, 用XPS、 TG、 DTA等对其进行了表征. 该催化剂在空气氛围中能很好的催化乙烯基化合物与芳基碘的Heck反应. 如在较低的温度下(40 ℃)催化丙烯酸与碘苯的反应, 产率高达73.7%, 显示了较高的催化活性. 该催化剂重复使用5次, 产率仍高达90%, 显示该催化剂有良好的重复使用性能.     

Determination of melt viscosity as a function of hydrostatic pressure in an extrusion rheometer

Polymer melt viscosity was determined as a function of hydrostatic pressure in an extrusion rheometer. An extrusion rheometer consisting of a barrel and a capillary can be looked upon as two capillaries in series. The barrel itself was used as the main viscometer and several different capillaries having length/diameter ratios of 3.5–100 were used as pressure boosters. For a Phillips type polyethylene of 0.95 g/cc density and 0.4 melt index, the apparent viscosity at 190°C and 7.12 sec^?1 was increased nearly fourfold as the average pressure in the barrel was raised from atmospheric to 24000 psi. With colored layers of polyethylene as tracers the flow pattern in the barrel was examined. The velocity profiles in the barrel were well developed and parabolic, and thus indicated regular laminar flow under these conditions.     

Catalytic enantioselective Strecker reaction of ketoimines using catalytic amount of TMSCN and stoichiometric amount of HCN

Catalyst loading as low as 0.1 mol % was achieved in the enantioselective Strecker reaction of ketoimines. Excellent enantioselectivity was obtained with a combined use of a catalytic amount of TMSCN and a stoichiometric amount of HCN as a reagent, and a chiral gadolinium complex as a catalyst.