A base labile handle for solid phase organic chemistry

Several arylsulfonamides have been synthesised on solid phase using a new base labile handle. Cleavage from the solid support is accomplished by oxidation of the sulfide to the sulfone, followed by β-elimination in base media.     

A flow microreactor for laboratory high pressure vapor phase catalytic reactions

A high pressure laboratory flow microreactor was designed and built to study the kinetics of hydroprocessing reactions. New features of this system are: the high pressure saturator-condenser (up to 7·10⁶ Pa), the small size of the reactor (1 cm³), the automatic on-line analysis device. The operation of the unit is illustrated by conversion data for the hydrogenation of biphenyl.

---

. : - ( 70 ), (I ³), . .

     

固相反应中扩散动力学方程的新探讨

通过对г~NHCTJINHT方程中把э~c/э~r作为产物层增厚速率的基础作出分析,对由扩散控制的固相反应中扩散浓度与时间的关系作了进一步探讨, 提出产物层增厚速率应建立在Fick第二定律的基础上, 并导出了新的扩散动力学方程。     

Pattern forming precipitation in gels due to coupling of chemical reactions with diffusion

Precipitate-forming chemical reactions have been studied in chemically cross-linked poly(vinyl alcohol) gel medium. One of the reactive components was incorporated into the gel, the other was allowed to diffuse into it. Depending on the experimental conditions the reaction-diffusion process often results in patterns of different type. Experiments performed in tubes and in thin layers were carried out in order to investigate the effects of various factors (cross-linking density, swelling degree as well as the concentrations of the outer and inner electrolytes) on the morphologies of the precipitate patterns. It was found that precipitation occurs not only in the Liesegang bands, but also between bands. Beside Liesegang-type structures, tree-like patterns have been observed, showing a characteristic periodicity in the density profile obtained by digitalized image analyses.     

A new highly versatile handle for chemistry on a solid support: the pipecolic linker

The versatility of the pipecolic linker (Pip-linker) is illustrated by the synthesis of modified amino acids, C-terminal-modified pseudopeptides, and cyclic peptides, through side-chain anchoring of a lysine residue. Introduction of the first residue was easily accomplished and the Pip-linker revealed to be robust enough to support various chemical modifications.     

A modified Ortega method to evaluate the activation energies of solid state reactions

The application of the average linear integral isoconversional method developed by Ortega for evaluating the activation energies of solid state reactions may be hindered by experimental noise and the uncertainties associated with selecting appropriate reaction segments. This paper suggests a procedure, called the modified Ortega method, which can avoid or minimize these hindrances. By applying the modified Ortega method to the kinetic analyses of both simulated and experimental data, a more consistent dependence of the activation energy on the extent of reaction conversion was found with those calculated from the modified Vyazovkin method and the Friedman method.     

A characterization of the linear and non-linear dynamic performance of a practical piezoelectric actuator part 1: Measurements

In an attempt to characterize the macroscopic dynamic performance of a piezoelectric actuator, measurements were taken of important lumped mechanical and electrical parameters for a commercially available piezo-electric actuator. The data include measurements of hysteresis between the applied voltage and the resulting displacements and/or charge accumulation, displacement frequency response, mechanical damping, signal distortion and gain. These measurements indicate the macroscopic effects of varying a.c. and d.c. components of the applied input voltage.Result demonstrate significant non-linearities and indicate under what conditions this device can be treated as linear.     

Synthesis of asymmetric iron-pybox complexes and their application to aziridine forming reactions

The synthesis of a series of iron-pybox complexes and their employment in the catalytic asymmetric aziridine forming reaction is presented. When AgSbF₆ is used as an initiator, the i-pr- and t-bu-pybox complexes produce 47% of the cis-aziridine in moderate ee’s with the bulk of side products consisting of the trans-isomer and β-amino-α,β-unsaturated esters (AUE’s).     

Heterogeneous reactions of singlet molecular oxygen with solid polymers

The effect of gas-phase singlet molecular oxygen (¹ΔO₂) upon several solid polymers was investigated by using electron paramagnetic resonance, infrared spectroscopy, and chemical detection techniques. The study was performed by use of ¹ΔO₂ produced by microwave discharge. The application of this method to polymer studies was closely examined. The saturated-chain polymers polystyrene, polyurethane, and polyethylene were found to be inert within the experimental conditions to reaction with ¹ΔO₂, while the unsaturated polymers cis-polybutadiene, trans-polybutadiene, and trans-polyisoprene were found to react quite readily in an apparently surface or near-surface limited reaction to produce hydroperoxide and/or peroxide groups. The introduction by homogeneous mixing of some known metal-chelate ¹ΔO₂ quenchers into the polymer trans-polyisoprene appeared to significantly decrease the rate of oxidation observed.     

A characterization of the linear and non-linear dynamic performance of a practical piezoelectric actuator part 2: Theory

Lumped parameter equations that describe the linear and non-linear operation of a practical piezoelectric actuator are developed from the continuum equations of non-linear electroelasticity. Exact solutions of this non-linear lumped system are developed for sinusoidally varying inputs. Theoretical results are compared to the measurements of Part 1: agreement between theory and experiment is good.     

Development of an enzymatic microreactor based on microencapsulated laccase with off-line capillary electrophoresis for measurement of oxidation reactions

Microencapsulation is used here as a new technique to immobilize enzymes in a microreactor coupled off-line to capillary electrophoresis (CE), allowing the determination of enzymatic reaction products. The redox enzyme laccase was encapsulated using the method of interfacial cross-linking of poly(ethyleneimine) (PEI). The 50 μm diameter capsules were slurry packed from a suspension into a capillary-sized reactor made easily and quickly from a short length of 530 μm diameter fused-silica tubing. The volume of the bed of laccase microcapsules in the microreactor was in the order of 1.1 μL through which 50 μL of the substrate o-phenylenediamine (OPD) was flowed. The oxidation product 2,3-diaminophenazine (DAP) and the remaining OPD were quantified by CE in a pH 2.5 phosphate buffer. Peak migration time reproducibility was in the order of 0.4% RSD and peak area reproducibility was less than 1.7% RSD within the same day. Using the OPD peak area calibration curve, a conversion efficiency of 48% was achieved for a 2-min oxidation reaction in the microreactor.     

Off-line form of the Michaelis-Menten equation for studying the reaction kinetics in a polymer microchip integrated with enzyme microreactor

We firstly transformed the traditional Michaelis-Menten equation into an off-line form which can be used for evaluating the Michaelis-Menten constant after the enzymatic reaction. For experimental estimation of the kinetics of enzymatic reactions, we have developed a facile and effective method by integrating an enzyme microreactor into direct-printing polymer microchips. Strong nonspecific adsorption of proteins was utilized to effectively immobilize enzymes onto the microchannel wall, forming the integrated on-column enzyme microreactor in a microchip. The properties of the integrated enzyme microreactor were evaluated by using the enzymatic reaction of glucose oxidase (GOx) with its substrate glucose as a model system. The reaction product, hydrogen peroxide, was electrochemically (EC) analyzed using a Pt microelectrode. The data for enzyme kinetics using our off-line form of the Michaelis-Menten equation was obtained (K(m) = 2.64 mM), which is much smaller than that reported in solution (K(m) = 6.0 mM). Due to the hydrophobic property and the native mesoscopic structure of the poly(ethylene terephthalate) film, the immobilized enzyme in the microreactor shows good stability and bioactivity under the flowing conditions.     

A bifurcated pathway to thiazoles and imidazoles using a modular flow microreactor

A scalable method for the preparation of 4,5-disubstituted thiazoles and imidazoles as distinct regioisomeric products using a modular flow microreactor has been devised. The process makes use of microfluidic reaction chips and packed immobilized-reagent columns to effect bifurcation of the reaction pathway.     

Application of an integrated microchip system with capillary array electrophoresis to optimization of enzymatic reactions

In this work, a combination of complementary metal-oxide semiconductor (CMOS) microchip system with capillary array electrophoresis (CAE) is demonstrated as a system for optimizing conditions for enzymatic reaction. Dimethylacridinone (DDAO)-phosphate substrate and alkaline phosphatase conjugate were selected for the enzymatic reaction, which was applicable to the enzyme-linked immunosorbent assay (ELISA) technique. Laser-induced fluorometry with a miniature semiconductor laser was used to detect the enzymatic products. The speed of the enzymatic reaction between the DDAO-phosphate and the alkaline phosphatase conjugate was investigated as a function of reaction time. The microchip-CAE detection system could determine the pH condition and the concentration of enzyme that are suitable for rapid and low-cost analysis. This result shows the feasibility of using the microchip-CAE system for application to miniaturized screening systems.     

NMR study of liquid to solid transition in a glass forming metallic system

Quadrupolar spin-lattice relaxation effect was used to study the temperature dependence of the correlation of electric field gradient (EFG) observed by (63)Cu and (65)Cu NMR in the liquid and supercooled liquid states of Pd(43)Cu(27)Ni(10)P(20) metallic glass forming system. The correlation time of EFG was shown to have a dramatic temperature dependence that cannot be accounted for by available theory. Analyzed in the context of mode coupling theory (MCT), it is shown that the correlation time of EFG follows the scaling equation of MCT and reveals a T(c), the critical temperature of MCT, at 700 K. Other NMR techniques such as chemical exchange line narrowing and stimulated echo pulse sequences were used to study motion of (31)P at lower temperatures. Combined together, these techniques cover the whole range of liquid to solid transition. By comparing the NMR results with data obtained by other techniques, a decoupling of motion for different types of atoms is revealed starting from T(c) and below. This essentially demonstrates a transition from liquidlike to solidlike motion at T(c) as predicted by MCT.     

Application of integrated computer simulation approach to solid surfaces and interfaces

The atomistic understanding of the structure, reactivity, and electronic properties of solid surfaces and interfaces are essential for the design of novel catalysts and electronics/photonics devices which have high-performance and unexplored properties. Computational chemistry is expected not only to rationalize the experimental results but also to predict new features. We have applied integrated computer simulation methods including quantum chemistry, periodic density functional theory, molecular dynamics, embedded atom method, and atomic force microscopy simulation to various topics related to solid surfaces and interfaces. In the present paper, we reviewed our recent activities on supported metal catalysts, metal clusters, atomic force microscopy simulation, high-temperature superconductors, tribology, Si semiconductor and V₂O₅ catalysts. Our activities also involve the generation of a lot of new computer simulation codes. We emphasize that the integrated computer simulation system provides not only methods for scientific studies but also a key technology for industrial innovations in research and development.     

Heterogeneous reactions : VII. Further studies on the heterogeneous gas/solid reactions of solid alkoxide bases with vaporized chloromethyldimethylhalosilanes

The results of the heterogeneous gas/solid reactions of chloromethyldimethylchloro (and fluoro)silane with solid lithium, sodium and potassium methoxide in the temperature range from 80–160°C are presented and discussed. Reaction with lithium methoxide serves as a clean, efficient high yield synthesis of chloromethyldimethylmethoxysilane without the complicating factors of side products or solvent to separate. The reactions of both the sodium and potassium methoxides lead to the displacement of halogen from silicon and to the displacement of the chloromethyl group. New evidence for the mechanism of the latter reaction is presented. With the potassium compound methylethyldimethoxysilane also is formed and carbene, sila-olefin addition mechanism is suggested. Surprisingly, lithium t-buthoxide did not react with the chlorosilane but did react with the fluorosilane to produce chloromethyldimethyl-t-butoxysilane in high purity and excellent yield. The reaction with potassium t-butoxide was more complicated, giving substitution for halogen and the chloromethyl group at silicon as well as t-butyl ether.     

Direct Henry reactions with modified calcium oxide as solid catalyst

Commercial CaO was modified simply with benzyl bromide. The modified CaO had good water resistance, and characterization by FTIR and TG revealed the modifier was chemically bonded to the CaO surface. Commercial CaO and CaO modified with benzyl bromide were investigated as catalysts for the Henry reaction between benzaldehyde and nitromethane. It was found that the catalytic activity of the modified CaO was greatly improved, with high conversion of benzaldehyde to the (E)-phenyl nitroolefin and 1-phenyl-2-nitroethanol, and with different selectivity from commercial CaO. The effect of modification and reaction conditions on yield, selectivity, and mechanism were studied thoroughly.     

Characterization of a monolithic immobilized trypsin microreactor with on-line coupling to ESI-MS

The preparation and characterization of a miniaturized trypsin reactor using on-line coupling with an ESI-TOF mass spectrometer are described. L-1-Tosylamido-2-phenylethyl chloromethyl ketone-trypsin was covalently immobilized on poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith prepared in a 75 microm ID fused silica capillary resulting in a bioreactor with high local concentration of the proteolytic enzyme. Covalent immobilization of trypsin on this support was performed using the epoxide functional groups in either a one- or a multistep reaction. For on-line protein digestion-MS analysis the bioreactor was coupled with the mass spectrometer using a liquid junction microelectrospray interface. The performance of the reactor was tested using an on-line flow through the system with flow rates of 50-300 nL/min. The resulting protein consumption was in the atto- to low femtomole range. Proteolytic activity was characterized in a wide range of conditions with respect to the flow rate, pH, and temperature. Complete protein digestion was achieved in less than 30 s at 25 degrees C with the sequence coverage of 80% (cytochrome c), which is comparable to 3 h digestion in solution at 37 degrees C. Besides the good performance at laboratory temperature, the immobilized trypsin in the bioreactor also performed well at lower pH compared to the standard in-solution protocols.