手性物质及其拆分方法

简要介绍了手性化合物的概念和发展情况以及获得手性化合物单一对映体的几种拆分方法。包括:结晶拆分法,化学拆分法,微生物酶拆分法,色谱拆分法,膜拆分法及电泳技术拆分法。并简要介绍了每种方法的应用情况及优缺点。     

Interplay of crystallization and liquid-liquid phase separation in polyolefin blends: A thermal history dependence study

The kinetic interplay between crystallization and liquid-liquid phase separation (LLPS) in random copolymer blends of poly(ethylene-ran-hexene) (PEH) and poly(ethylene-ran-butene) (PEB) has been studied using optical microscopy. Morphologies of blends gone through three different thermal histories are compared: (1) single-quench (SQ), a homogeneous melt quickly cooled to isothermal crystallization temperatures (T_cry), (2) double-quench (DQ), a homogeneous melt quickly cooled to an intermediate temperature (T_lps) between binodal and equilibrium melting temperature (T_m⁰) and stored for a period of time and then cooled to T_cry, and (3) cyclic-quench (CQ), a homogeneous melt quickly cooled to T_lps and stored for a period of time, then gone through four cycles of crystallization and remelting. Comparing DQ morphologies to SQ ones, both crystal growth rate and nucleation density in the former are affected by prior LLPS. A scaling argument has been provided to partially account for the observed phenomena. In CQ, characteristic lengths of secondary features induced by crystallization depend strongly on the overall PEH composition, whereas are insensitive to temperature cycling. The contrast of large domains becomes more prominent upon cyclic crystallization and remelting. On the other hand, primary LLPS domains coarsen with CQ while loosing the contrast.     

Liquid-liquid phase separation in a polyethylene blend monitored by crystallization kinetics and crystal-decorated phase morphologies

A series of polyethylene (PE) blends consisting of a linear high density polyethylene (HDPE) and a linear low density polyethylene (LLDPE) with an octane-chain branch density of 120/1000 carbon was prepared at different concentrations. The two components of this set of blends possessed isorefractive indices, thus, making it difficult to detect their liquid-liquid phase separation via scattering techniques. Above the experimentally observed melting temperature of HDPE, T_m = 133 °C, this series of blends can be considered to be in the liquid state. The LLDPE crystallization temperature was below 50 °C; therefore, above 80 °C and below the melting temperature of HDPE, a series of crystalline-amorphous PE blends could be created. A specifically designed two-step isothermal experimental procedure was utilized to monitor the liquid-liquid phase separation of this set of blends. The first step was to quench the system from temperatures of known miscibility and isothermally anneal them at a temperature higher than the equilibrium melting temperature of the HDPE for the purpose of allowing the phase morphology to develop from liquid-liquid phase separation. The second step was to quench the system to a temperature at which the HDPE could rapidly crystallize. The time for developing 50% of the total crystallinity (t_1/2) was used to monitor the crystallization kinetics. Because phase separation results in HDPE-rich domains where the crystallization rates are increased, this technique provided an experimental measure to identify the binodal curve of the liquid-liquid phase separation for the system indicated by faster t_1/2. The annealing temperature in the first step that exhibits an onset of the decrease in t_1/2 is the temperature of the binodal point for that blend composition. In addition, the HDPE-rich domains crystallized to form spherulites which decorate the phase-separated morphology. Therefore, the crystal dispersion indicates whether the phase separation followed a nucleation-and-growth process or a spinodal decomposition process. These crystal-decorated morphologies enabled the spinodal curve to be experimentally determined for the first time in this set of blends.     

亲和膜手性拆分技术及手性拆分固膜

阐述了亲和膜拆分技术,包括亲和超滤、纳滤、电渗析、渗析及渗透汽化等在手性拆分领域的应用,对基于对映体间亲和性差异的手性选择膜及基于"形状记忆"的分子印迹拆分膜的最新进展进行了综述,并就今后的发展方向提出建议。     

Transition between crystallization and microphase separation in PS-b-PEO thin film Influenced by solvent vapor selectivity

In this paper, the effect of solvent selectivity on the transition between crystallization and microphase separation of the semicrystalline diblock copolymer polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin films was investigated. Square-shaped crystals formed due to lower barrier of crystalline nucleation in both poor and good solvent vapor for PEO. However, in poor solvent (cyclohexane) vapor for PEO, crystalline structure changed to microphase separated structure in the square platelets due to the high mobility of PS blocks. Then breakout crystals dominated the morphology of the film. While, in good solvent (water) vapor for PEO, competition between nucleation and dissolution of crystallization caused the formation of imperfect crystals. Then imperfect crystals dissolved due to the high mobility of PEO blocks, and microphase separation dominated the morphology of the film. The gain of free volume of soluble block and the low swelling of crystalline block are keys for microphase separation and crystallization, respectively.     

Dynamic interplay between phase separation and crystallization in a poly(?-caprolactone)/poly(ethylene glycol) oligomer blend

We have investigated the crystallization effect on the phase separation of a poly(?-caprolactone) and poly(ethylene glycol) oligomer (PCL/PEGo) blending system using simultaneous small-angle light scattering and differential scanning calorimetry (SALS/DSC) as well as simultaneous small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and DSC (SAXS/WAXS/DSC). When the PCL/PEGo system, of a weight ratio of 7/3, is quenched from a melt state (160 °C) to temperatures below the spinodal point and the melting temperature of PCL (63 °C), the structural evolution observed exhibits characteristics of (I) early stage of spinodal decomposition (SD), (II) transient pinning, (III) crystallization-induced depinning, and (IV) diffusion-limited crystallization. The time-dependent scattering data of SALS, SAXS and WAXS, covering a wide range of length scale, clearly show that the crystallization of PCL intervenes significantly in the ongoing viscoelastic phase separation of the system, only after the early stage of SD. The effect of preordering before crystallization revives the structural evolution pinned by the viscoelastic phase separation. The growth of SAXS intensity during the preordering period conforms to the Cahn-Hilliard theory. In the later stage of the phase separation, the PCL-rich matrix, of spherulite crystalline domains developed due to the faster crystallization kinetics, traps the isolated PEGo-rich domains of a slower viscoelastic separation.     

Acceleration or retardation to crystallization if liquid-liquid phase separation occurs: Studies on a polyolefin blend by SAXS/WAXD, DSC and TEM

Blends of statistical copolymers containing ethylene/hexene (PEH) and ethylene/butene (PEB) exhibited the behavior of upper critical solution temperature (UCST). The interplay between the early and intermediate stage liquid-liquid phase separation (LLPS) and crystallization of the PEH/PEB 50/50 blend was studied by time-resolved simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. Samples were treated by two different quench procedures: in single quench, the sample was directly quenched from 160 °C to isothermal crystallization temperature of 114 °C; while in double quench, the sample was firstly quenched to 130 °C for 20 min annealing, where LLPS occurred, and then to 114 °C. It was found that in the early stage of crystallization, the integrated values of Iq² and crystallinity, X_c, in the double quench procedure were consistently higher than those in the single quench procedure, which could be attributed to accelerated nucleation induced by enhanced concentration fluctuations and interfacial tension. In the late stage of crystallization, some morphological parameters were found to crossover and then reverse, which could be explained by retardation of lamellar growth due to phase separation formed during the double quench procedure. This phenomenon was also confirmed by DSC measurements in blends of different compositions at varying isothermal crystallization temperatures. The crystal lamellar thickness determined by SAXS showed a good agreement with TEM observation. Results indicated that the early stage LLPS in the PEH/PEB blend prior to crystallization indeed dictated the resulting lamellar structures, including the average size of lamellar stack and the stack distribution. There seemed to be little variation of lamellar thickness and long period between the two quenching procedures (i.e., single quench versus double quench).     

Microphase separation and crystallization in mixtures of polystyrene-poly(methyl methacrylate) diblock copolymer and poly(vinylidene fluoride)

This study examined the microdomain structures and the crystallization behavior in binary blends consisting of an asymmetric block copolymer and a homopolymer using small-angle X-ray scattering, optical microscopy and differential scanning calorimetry. A polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) was mixed with a low molecular weight poly(vinylidene fluoride) (PVDF), where the PS-b-PMMA had a 0.30 wt fraction of the PMMA block. At a PVDF concentration of <13.0 wt%, the PVDF was completely miscible with the PMMA microdomains, and the blends had a cylindrical structure. The addition of PVDF altered the morphology from a PMMA-cylindrical structure to a lamellar structure and finally to a PS-cylindrical structure. When the PVDF concentration was <23.0 wt%, the PVDF was distributed uniformly within the PMMA microdomains. After adding more PVDF, some of the PVDF was locally dissolved in the middle of the PMMA microdomains. The addition of PVDF also affected the ordered microstructure in the blends, leading to a well-defined microdomain structure. However, PVDF crystallization significantly disturbed the pre-existing microdomain structure, resulting in a poorly ordered morphology. In the blends, PVDF had unique crystallization behavior as a result of the space constraints imposed by the microdomains.     

Shear-induced phase separation and crystallization in semidilute solution of ultrahigh molecular weight polyethylene: Phase diagram in the parameter space of temperature and shear rate

In the previous papers, we elucidated enhancement of concentration fluctuations, phase separation, and crystallization induced by steady state or step-up shear flow, as observed by shear small-angle light scattering, optical microscopy, and birefringence, for a semidilute solution of ultrahigh molecular weight polyethylene in paraffin as an athermal solvent. However the studies were done only at a given temperature of 124 °C, which is higher than the nominal melting temperature of the quiescent solution T_nm (115–119 °C). It is crucial to extend the studies over a wider temperature range in order to generalize shear-induced phase behavior of the solution. Thus in this work we constructed a kind of phase diagram in the parameter space of temperature (T) and shear rate (). The temperature range covered was higher than T_nm, so that the phase diagram is strictly concerned with shear-induced phase behavior (i.e., without shear the solution is homogeneous and in a single-phase state). The diagram identified Regimes I–III in the T– space as will be detailed in the text. In constructing the phase diagram we found the following new points also. (i) The critical shear rate _cx which defines the boundary between Regimes I and II was independent of T. (ii) Regime III identified previously through the dependence of the integrated scattered intensity only at a particular temperature T = 124 °C was further separated into two regimes of III_a and III_b below and above a critical temperature (147 °C), respectively, through the observation of the dependence as a function of T: In Regime III_a, the sheared solution developed the optically anisotropic fibrous structures, indicative of the shear-induced crystallization triggered by the shear-induced concentration fluctuations in Regime II; In Regime III_b, the solution is so stable that it did not show a trend of the shear-induced crystallization even at the highest shear rates accessible in this experiment, but it only showed the shear-induced phase separation. (iii) The critical shear rates _c,streak and _cz, which define respectively the boundary between Regimes II and III_a and that between Regimes II and III_b, are sensitive to temperature.     

Kinetics of phase separation and crystallization in poly(ethylene-ran-hexene) and poly(ethylene-ran-octene)

The kinetics of phase separation and crystallization in the blends of poly(ethylene-ran-hexene) (PEH) and poly(ethylene-ran-octene) (PEOC) at several compositions were studied using phase contrast optical microscopy and time-resolved simultaneous small-angle X-ray scattering and wide-angle X-ray diffraction. The phase contrast optical microscopy showed the interconnected bicontinuous structure during phase separation process, which is characteristic of a spinodal decomposition. During isothermal crystallization, the average lamellar spacing increases with time for blends at all concentrations. The crystallinity and crystal growth rate depend on the PEH concentration. At dilute PEH concentrations, crystallization of PEH chains is difficult because they are surrounded by many non-crystallizable PEOC chains. On the other hand, at higher PEH concentrations, crystallization processes are similar to pure PEH. For example, the spherulitic growth rates are similar for a PEH/PEOC=50/50 blend and pure PEH.     

酶法手性化合物的合成与拆分

综述了酶法手性化合物合成与拆分的最新研究进展,主要对酶法制备手性物质的应用、提高对映选择性的方法进行了介绍。     

Structural and morphological development in poly(ethylene-co-hexene) and poly(ethylene-co-butylene) blends due to the competition between liquid-liquid phase separation and crystallization

Isothermal crystallization behavior of poly(ethylene-co-hexene) (PEH) and the 50/50 blend (H50) of PEH with amorphous poly(ethylene-co-butylene) (PEB) was studied by time-resolved synchrotron simultaneous small-angle X-ray scattering/wide-angle X-ray diffraction (SAXS/WAXD) techniques and optical microscopy (OM). The X-ray study revealed the changes of structural and morphological variables such as the scattering invariant, crystallinity and lamellar long period, et al. In H50, the lamellar morphology was found to be dependent on competition between liquid-liquid phase separation (LLPS) and crystallization. At high temperature, LLPS becomes dominating, resulted in crystallization of PEH with minimal influence of PEB. At low temperature, LLPS is suppressed, PEB component shows obvious influence on PEH crystallization, PEB is thought to be partially included into PEH lamellar stacks and PEH-PEB co-crystallization is unlikely, however, possible. Optical microscopy was used to monitor crystal nucleation and growth rates in PEH and H50, providing complementary information about the effect of temperature on LLPS and crystallization. Real-space lamellar morphologies in PEH and H50 were characterized by atomic force microscopy (AFM), PEH exhibited sheaf-like spherulites while H50 exhibited hedrites. Overall, the competition between LLPS and crystallization in H50 blend influences the structural and morphological development. Controlling the interplay between LLPS and crystallization of PEH/PEB blends, it is possible to control the structure and morphology as practically needed.     

A study on crystallization kinetics of pentaerythritol in a batch cooling crystallizer

The crystallization kinetics of pentaerythritol (PeE) in aqueous solution in the presence of impurity or not in a batch cooling crystallizer was explored. Also, the solubility and the nucleation and crystal growth kinetics of PeE in aqueous solution were investigated. A second-order dependence of PeE growth rate on supersaturation is observed in pure PeE-water system. The crystal growth rate of PeE-water system in the presence of impurity is proportional to the supersaturation to the 3.5 power. The nucleation and crystal growth behaviors for PeE-water system in a batch cooling crystallizer were grasped according to Mersmann's criteria. The nucleation in this crystallizer was found to act with heterogeneous nucleation. In this system, it suggests that the crystal growth is controlled by a complex mechanism behavior of surface integrated and diffusion limited. Simplified relation was derived for calculation of mean crystal size of product crystals from the batch cooling crystallizer. The obtained relation was verified by a set of experiments.     

Pervaporation separation of toluene/n-heptane mixtures using a MSE-modified membrane: Effects of operating conditions

In this work, separation of toluene/n-heptane mixtures via pervaporation using a composite membrane was investigated. Effects of operating conditions such as feed temperature, feed composition and downstream pressure on the membrane performance were studied. Experimental results were obtained at different feed compositions (10–40 wt.%), operating temperatures (25–85 °C) and downstream pressures (2–32 mbar g). The membrane selectivity for toluene was found to be greater than that for n-heptane. According to the results, it was observed that increasing toluene concentration in the feed and operating temperature enhance the membrane swelling and increase the polymeric chain mobility. Therefore, feed concentration and temperature have the same effects on toluene selectivity and permeation flux of the membrane. Permeation flux increases and toluene selectivity decreases with increasing feed concentration and temperature. In contrary, the membrane performance enhances with decreasing downstream pressure. It was found out that for a feed with 10 wt.% of toluene, at a temperature of 85 °C and a downstream pressure of 2 mbar g, the highest PSI value of 18.371 kg/m² h (in which permeation flux = 4.610 kg/m² h and toluene selectivity = 4.985) is achieved.     

Liquid-liquid phase separation and crystallization behavior of poly(ethylene terephthalate)/poly(ether imide) blend

The liquid-liquid (L-L) phase separation and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blend were investigated with optical microscopy, light scattering, and small angle X-ray scattering (SAXS). The thermal analysis showed that the concentration fluctuation between separated phases was controllable by changing the time spent for demixing before crystallization. The L-L phase-separated specimens at 130 °C for various time periods were subjected to a temperature-jump of 180 °C for the isothermal crystallization and then effects of L-L phase separation on crystallization were investigated. The crystal growth rate decreased with increasing L-L phase-separated time (t_s). The slow crystallization for a long t_s implied that the growth path of crystals was highly distorted by the rearrangement of the spinodal domains associated with coarsening. The characteristic morphological parameters at the lamellar level were determined by the correlation function analysis on the SAXS data. The blend had a larger amorphous layer thickness than the pure PET, indicating that PEI molecules in the PET-rich phase were incorporated into the interlamellar regions during crystallization.     

Evaluation of optimisation techniques and control variable formulations for a batch cooling crystallization process

The mathematical optimisation of a batch cooling crystallization process is considered in this work. The objective is to minimize the standard deviation of the final crystal size distribution (CSD), which is an important feature in many industrial processes. The results with the problem written as a nonlinear programming and solved with the successive quadratic programming (SQP) coupled with the discretization of the control variable are compared with those obtained when SQP coupled with the parameterisation of the control variable is applied. Also it is proposed the implementation of the genetic algorithm (GA) coupled with parameterisation of the control variable. Extensive evaluations show that the SQP method is sensitive both to the parameterisation formulation and to the initial estimate. The solution with GA provided the control variable profile that leads to the minimum standard deviation of the final CSD. Nevertheless, it is a very time-consuming technique, which hampers its utilization in real time applications. However, its feature of global searching suggests its suitability in solving offline problems, in order to provide initial setup profiles. Bearing this in mind, it is proposed an algorithm which allows for the implementation of GA solution in a real time fashion, taking advantage of its robustness to find out the optimal solution.     

高效液相色谱纤维素类手性固定相对外消旋稻丰散的拆分

合成了纤维素-三(3,5-二甲基苯基氨基甲酸酯)手性固定相,制备了手性色谱柱,以正己烷为流动相,添加异丙醇为改性剂,在高效液相色谱上实现了对手性农药稻丰散光学异构体的直接拆分;系统摸索了异丙醇含量、色潜柱长度、流速及温度对拆分效果的影响,优化了拆分条件。结果显示,色谱柱长度对该化合物的拆分影响较大;流动桕巾异丙醇含量的减少以及流速减慢均有利丁对映体的拆分,但也导致保留增强;在5℃．40℃范刚内,温度升高分离度减小。使用长色谱柱,选择适温20℃,调整流动相中正己烷与异丙醇的比例为99．5：0.5(v／v),流速为0．5ml／min时,可达到最佳分离效果,分离因子为1．38。     

膜分离技术在长链二元酸发酵液分离中的应用

采用膜分离工艺代替传统的过滤工艺分离长链二元酸发酵液。发酵液经过陶瓷微滤膜、卷式超滤膜过滤后,除去菌丝体、蛋白质、色素及杂质,澄清透明的透析液直接进行酸化结晶,即可得到合格产品。使用膜分离工艺不仅可以简化操作、降低劳动强度,还可以提高产品质量和收率,降低生产成本。     

A model-based nucleation study of the combined effect of seed properties and cooling rate in cooling crystallization

Crystallization is a widely used unit operation for the production of pharmaceuticals, fertilizers, and fine chemicals. A commonly used crystallization operational objective is to produce large crystals under minimum nucleation rates. For cooling crystallization there are two key methods for minimizing nucleation, programmed cooling and seeding. In this paper, we evaluate the cooling and seeding methods through the detailed modeling of nucleation phenomena coupled with a population balance and dynamic optimization of this mathematical formulation. Extensive simulation results showed that initial seeding parameters, as proclaimed by others, do have a significant effect on the final product crystal size distribution. It also showed the significance of a combined seeding-cooling approach where a joint cooling and seeding optimization gives superior performance to just optimizing the seed. Importantly, the developed model was highly instrumental in rapidly determining optimal combined seeding-cooling profiles via dynamic model-based optimizations.