Mode change in the self-motion of a benzoquinone disk coupled with a NADPH system

The self-motion of a benzoquinone (BQ) disk on NADPH was investigated as the coupling of an autonomous motor and an enzyme reaction. In the absence of the enzyme reaction, features of motion changed depending on the concentration of NADPH, that is, continuous motion→ intermittent oscillatory motion→ no motion. When the reverse reaction from NADP(+) to NADPH was introduced into the system with the addition of an enzyme reaction, continuous motion changed to intermittent oscillatory motion with small amplitude. The mechanism of this mode change is discussed in relation to the surface tension as a driving force and the time course of UV spectra as a window to the progress of the reaction. Characteristic features of the mode change were qualitatively reproduced by a numerical calculation.     

Characteristic self-motion of a camphor boat sensitive to ester vapor

As a simple example of an autonomous motor, the self-motion of a camphor boat on water with changes in chemical stimuli was investigated. The nature of the self-motion of a camphor boat changed characteristically with the addition of ester vapor (methyl n-butyrate) to a circular water chamber. Thus, continuous motion changed to oscillatory motion, and its period increased depending on the location between an ester droplet and the chamber, L. The surface tension in the water chamber was measured to clarify how the velocity of the self-motion changed with L. The nature of the self-motion is discussed in relation to the surface tension as the driving force. We believe that the present results may be useful for realizing artificial chemotaxis systems under nonlinear and isothermal conditions.     

Photo-sensitive lipid membrane perturbation by a single chain lipid having terminal spiropyran group

The synthesis a novel single chain lipid (SP-16A), containing a photo-sensitive spiropyran group at its hydrophobic terminus is described. The photoisomerization behavior of SP-16A has been studied by UV-Vis spectroscopy. The lipid has been incorporated into small unilamellar vesicles (SUVs) in quantities up to 10 mol% by mixing with dipalmitoylphosphatidylcholine (DPPC) and consequent sonication. The photo-induced membrane perturbation of the SP-16A/DPPC mixed SUV liposome was observed by monitoring of leakage of carboxyfluorescein(CF), a water soluble fluorescent dye, from the interior aqueous phase of the SUV. SUVs containing 5–10 mol% of SP-16A showed drastic leakage of CF by UV irradiation at 465 nm, however, neither liposome rupture nor release of the lipid from the SUV was observed after the UV irradiation. On/off switching of the leakage of interior material from the vesicle could also be demonstrated. In order to discuss the mechanism and kinetics of the photo-sensitive membrane perturbation behavior for the SP-16A/DPPC mixed SUV, the isomerization behavior of the SP-16A molecule and the leakage of CF from the SUV over time were investigated using a pulsed excimer laser. These experiments suggested that the main factor involved in membrane perturbation by SP-16A is a conformational change of the lipid in the membrane, which occurs after isomerization of the molecule. This new lipid molecule is thus a novel and useful photo-sensitive switching system, and may have future applications in drug delivery systems.     

Regular self-motion of a liquid droplet powered by the chemical marangoni effect

We describe here our recent work on spontaneous regular motion of liquid droplet powered by the chemical Marangoni effect under spatially symmetric conditions. It is shown that a spontaneously crawling oil droplet on a glass substrate with a nonequilibrium chemical condition of cationic surfactant exhibits regular rhythmic motion in a quasi-one-dimensional vessel, whereas irregular motion is induced in a two-dimensionally isotropic environment. Such behavior of a droplet demonstrates that spontaneous regular motion can be generated under fluctuating conditions by imposing an appropriate geometry. As another system, we introduce alcohol droplet moving spontaneously on water surface. The droplet spontaneously forms a specific morphology depending on its volume, causing specific mode of translational motion. An alcohol droplet with a smaller volume floating on water surface moves irregularly. On the other hand, a droplet with a larger volume undergoes vectorial motion accompanied by deformation into an asymmetric shape. This result suggests a scenario on the emergence of regular motion coupled with geometrical pattern formation under far-from-equilibrium conditions.     

感光性聚丙烯腈超滤膜紫外光接枝制备温敏型分离膜

紫外光接枝;感光性;n-异丙基丙烯酰胺;温敏性     

光敏性双亲共聚物在水溶液中的胶束化行为

通过ε-己内酯改性丙烯酸酯(FAa，n=1～4)与肉桂酰氯间的酰化反应合成了一系列光敏性大单体(FAaC)，与甲基丙烯酸(MAA)在溶液中进行自由基聚合，制备了具有光敏性的双素无规共聚物(PMFAaC)。将PMFAaC在选择性溶剂中进行自组装，可以形成纳米结构的聚合物。用动态激光光散射(DLS)研究了聚合物胶束的溶液行为，同时考察了单体含量、聚合物终浓度、聚合物侧链长、pH值、离子强度及温度等因素对胶束粒径的影响。实验结果表明，PMFAaC在选择性溶剂中可自组装成胶束，其粒径及其分布对单体含量、聚合物终浓度、聚合物侧链长、pH值、离子强度等有一定的依赖性，而对温度无依赖性。进一步用紫外光使肉桂酰基发生交联反应。从而制备得到核交联且稳定的纳米胶束。用DIS表征发现交联后的胶束粒径较交联前的小。     

含光敏剂184结构的超支化碱溶性感光聚合物的合成及性能

以季戊四醇为“中心核”,通过与偏苯三酸酐,环氧氯丙烷反应合成超支化聚酯,利用合成聚合物分子外围的羧基与含环氧基的1-羟基环己基苯基酮、甲基丙烯酸缩水甘油酯反应合成分子末端含光敏剂结构的超支化碱溶性感光聚合物。聚合反应转化率在1 h内可达80%以上;合成聚合物的玻璃化转变温度为200℃,200℃以内无失重,200~300℃之间有轻微失重,其粘度表现为超支化聚合物的粘度特性,并且在碱性水溶液中溶解性好,无需外加光敏剂,在紫外光照射下便可固化、交联,具有较小的凝胶曝光能量E0(1×10-3~1×10-2J/cm2)和较好的光敏性。     

光响应负载型脯氨酸的合成及其在水相中催化不对称羟醛缩合反应的应用

应用RAFT聚合法合成了含脯氨酸、香豆素及聚乙二醇的光响应负载型催化剂(P),其结构经¹H NMR和元素分析表征。紫外光谱分析表明：在紫外光照前后, P的结构会发生变化。催化性能测试结果表明：P在紫外光照前后均能实现水相中催化环己酮和4-硝基苯甲醛之间的羟醛缩合反应,收率65%~76%, dr>93/7, ee>95%。     

探索光敏性共聚物P(St/CS-alt-MA)的自组装及其乳化行为

以苯乙烯(St)、马来酸酐(MA)、香豆素苯乙烯醚化物(CS)为单体, 通过自由基溶液聚合合成了双亲性交替共聚物P(St/CS-alt-MA), 用凝胶渗透色谱、核磁共振等对聚合物结构进行表征, 并对其溶液自组装及组装体的乳化性进行了研究. 结果表明双亲性P(St/CS-alt-MA)可以在选择性溶剂中进行自组装形成马来酸酐单元为亲水微区、CS与苯乙烯单元为疏水微区的胶体粒子, 用紫外分光光度计, XPS, TEM研究了聚合物胶体粒子性质, 结果显示, P(St/CS-alt-MA)在水溶液中可以形成两亲性聚合物胶体粒子, 亲水单元在胶粒表面富集, 该两亲性聚合物胶体粒子具有良好的乳化性能.     

Electrophoresis of a charge-regulated toroid normal to a large disk

The electrophoresis of a charge-regulated toroid (doughnut-shaped entity) normal to a large disk is investigated under the conditions of low surface potential and weak applied electric field. The system considered is capable of modeling the electrophoretic behavior of various types of biocolloids such as bacterial DNA, plasmid DNA, and anabaenopsis near a perfectly conducting planar wall. The influences of the size of the toroid, the separation distance between the toroid and the disk, the charged conditions on the surfaces of the toroid and the disk, and the thickness of electric double layer on the electrophoretic mobility of the toroid are discussed. The results of numerical simulation reveal that under typical conditions the electrophoretic behavior of the toroid can be different from that of an integrated entity. For instance, if the surface of the toroid carries both acidic and basic functional groups, its mobility may have a local maximum as the thickness of double layer varies. We show that the electrophoretic behavior of the toroid is different, both qualitatively and quantitatively, from that of the corresponding integrated particle (particle without hole).     

Modeling of ionic relaxation around a biomembrane disk

A simplified Brownian dynamics model and the corresponding software implementation have been developed for the simulation of electrolyte dynamics on the mesoscopic scale. In addition to direct control simulations, the model system has been verified by a quantitative comparison with the Debye-Hückel theory. As a first application, the model was used to simulate ionic relaxation processes following abrupt intramembrane charge rearrangements in the case of a disk shaped membrane. In addition to its general implications, the obtained properties of the relaxation kinetics confirm the assumptions of the theory of the so-called suspension method, a technique capable of tracing molecular charge motions of membrane proteins in three dimensions.     

Electrophoresis of a charge-regulated sphere normal to a large disk

The electrophoresis of a rigid, charge-regulated, spherical particle normal to a large disk is investigated under the conditions of low surface potential and weak applied electric field. We show that, although the presence of a charged disk does not generate an electroosmotic flow, it affects particle motion appreciably through inducing charge on its surface and establishing an osmotic pressure field. The competition between the hydrodynamic force and the electric force may yields a local extremum in mobility; it is also possible that the direction of particle movement is reversed. In general, if a particle remains at constant surface potential, a decrease in the thickness of double layer has the effect of increasing the electrostatic force acting on it so that its mobility increases. However, this might not be the case for a charged-regulated particle because an excess hydrodynamic force is enhanced. For a fixed separation distance, the influence of a charged disk on mobility may reduce to a minimum if the bulk concentration of hydrogen ion is equal to the dissociation constant of the monoprotic acidic functional groups on particle surface.     

Metathesis reactions with a low-cost spinning disk system

ABSTRACT

Experimental procedures have been developed to provide at the laboratory scale an efficient and relatively inexpensive continuous flow processing system to undertake metathesis chemistry. Glass discs, coated with porous silica particles impregnated with Grubbs (I) generation or Hoveyda–Grubbs (II) generation catalysts through non-covalent interactions, have been successfully used as annular zones for in situ metathesis reactions. The supported catalysts were active for ring closing metathesis and self-metathesis reactions with a variety of substrates with nearly quantitative conversion depending on the substrate structure. Advantages of these procedures include the ability to conduct reactions efficiently at small (low mmole) scale under ambient laboratory conditions, thereby avoiding the need for high energy/thermal procedures. Multiple experiments can be undertaken during the same day if catalyst screening is required. Moreover, separation of starting materials from products can be achieved using the same unit operations, avoiding the need for additional purification steps, thereby reducing the total solvent consumption.     

Calculation of the streaming potential near a rotating disk

A corrected theory of the streaming potential in the vicinity of a disk-shaped sample rotating in an electrolytic solution is presented. When streaming-potential measurements on a variety of materials were reduced to a zeta potential according to a prior theory, the results exceeded expected values by a factor of approximately 2, even though other aspects of the same experiments seemed to confirm the theory. Investigation of the source of the discrepancy revealed a flaw in the prior theory. The crucial understanding is that the surface current produced by the rotation of the disk emerges from the diffuse layer and enters the bulk solution at the periphery of the disk. The new treatment accounts entirely for the discrepancy between literature data and results based on the prior theory.     

Sinusoidal voltage modulation of a copper rotating disk electrode

An experimental and theoretical study has been made of the sinusoidal potential modulation of a copper rotating disk electrode in acidic copper sulfate solution. The mathematical model takes into account the fluctuations of the surface concentration, the effect of the double capacitance, the surface overpotential, and the ohmic resistance in the electrolyte. Numerical computations were performed to show the effect of alternating voltage (av) on the shape of direct current polarization curves, the changes in the apparent rest potential, the apparent exchange current density and the apparent Tafel slopes. The agreement between the theory and the experiment was within ±15%. At sufficiently high av frequencies, the model can be further used to predict the av modulation of a rotating hemispherical electrode.     

A simple method for preparing a diamino cellulose disk from a dialdehyde cellulose disk by reductive amination using 2-picoline-borane

Cellulose - A method for the preparation of dialdehyde cellulose disks (DACD) and subsequent diamino cellulose disks (DAmCD) was developed. DACD was prepared by oxidizing filter paper with sodium...     

Hopping time of a hard disk fluid in a narrow channel

We use Monte Carlo (MC) and molecular dynamics (MD) methods to study the self-diffusion of hard disk fluids, confined within a narrow channel. The channels have a pore radius of Rp, above the passing limit of hard disk diameter (sigma(hd)). We focus on the average time (tau(hop)) needed for a hard disk to hop past a nearest neighbor in the longitudinal direction. This parameter plays a key role in a recent theory of the crossover from single-file diffusion to the bulk limit. For narrow channels near the hopping threshold (Rp=1 in units of sigma(hd)), both MC and MD results for tau(hop) diverge as approximately (Rp-1)(-2). Our results indicate that the scaling law exponent does not appear to be dependent on the differences between the two dynamics. This exponent is consistent with the prediction of an approximate transition state theory.     

Sedimentation of a circular disk in power law fluids

The continuity and momentum equations have been solved numerically for the two-dimensional steady flow of power law fluids over a thin circular disk oriented normal to the direction of flow. Extensive results on the individual and total drag coefficients are obtained as functions of the power law flow behavior index (0.4 < or = n < or = 1.0), Reynolds number (1 < or = Re < or = 100) and the blockage ratio, disk-to-cylinder diameter ratio (0.02 < or = e < or = 0.5), which can be used to estimate the settling velocity of a circular disk. The numerical predictions of drag are consistent with the scant experimental results available in the literature.     

A study of corrosion on a rotating iron disk electrode

Corrosion of iron in slightly acidified sodium sulphate solutions (mainly pH 4.5) in the open air was studied with a rotating disk electrode method at room temperature.Microscopic observations of corroded iron disk surfaces in the pH 4.5 solution revealed that iron initially corrodes locally with the formation of round pits of 10–30 μm in diameter and of(0.6–1.3) × 10³ in number per apparent square centimetre followed by the U-shaped brown protective wall formation of precipitates (rust) outside the pits. Each protective wall is formed along the lines of flow of the solution adjacent to the iron surface and each pit is located near the upstream end of the wall. Steady state of corrosion sets in when the parts of surface area surrounded by the wall are completely covered with a microscopically non-porous rust film.The amount of iron in the rust film and the total amount of corrosion of iron including that in the film increase parabolically with the increase in the time of immersion. The amount of iron in the film increases in proportion to the total amount of corrosion independently of the speed of rotation of the disk electrode even in the steady state.The fraction of area of iron surface not covered with the film decreases with time and reaches a certain fixed value in the steady state: the value is smaller at higher rotational speed. The corrosion rate is proportional to the uncovered area, as the corrosion is near the steady state. The pH of the bulk solution increases as corrosion progresses.The corrosion rate of iron can be well interpreted by assuming that the rate is controlled by the diffusion of oxygen from the bulk solution to the surface of iron and that the rust film on iron impedes the diffusion of oxygen.