聚氯乙烯-聚氧乙烯共混物的反相色谱研究

用反相色谱研究了聚氯乙烯与聚氧乙烯的相容性,发现其共混物的比保留体积V_g23具有重量加和性,表明共混物可能发生了相分离。导出了相分离体系聚合物相互作用参数X₂₃的近似关系式:X₂₃=(X₁₂-X₁₃)²/2,由此式可以解释X₂₃对探针种类的依赖性。聚氯乙烯和聚氧乙烯共混体系的反相色谱实验结果基本符合这一关系式。     

Chromatographic separation of cannabinoids and their monoxygenated derivatives

Δ¹-Tetrahydrocannabinol, Δ⁶-tetrahydrocannabinol, cannabinol, cannabidiol and several of their monooxygenated derivatives have been separated from each other by a combination of liquid, thin-layer and gas chromatography. Retention volumes (on Sephadex LH-20), R_F values and retention times can be recorded, and may provide guidance in the separation and identification of these known cannabinoids.     

Direct synthesis of phenols by iron-catalyzed biphasic oxidation of aromatic hydrocarbons with hydrogen peroxide

The hydroxylation of a series of aromatic hydrocarbons with hydrogen peroxide, catalyzed by iron complexes with pyrazine-3-carboxylic acid N-oxide, was investigated, operating in a biphasic reaction medium.

The new catalyst showed a high selectivity to the corresponding phenols, minimizing the over-oxidation reactions to polyoxygenated derivatives and tars which, along with dimers formation, are the major limitations of the classical Fenton’s reagent for a practical synthetic application.

In the case of alkylbenzenes, the competitive side chain oxidation at the benzylic positions also occurred. Electron rich substrates, such as anisole, were oxidized with very poor selectivity.

The reactions were carried out in a biphasic system that allows a convenient recovery and recycling of the catalyst by phase separation techniques. The catalyst showed a complete retention of activity after six consecutive reaction cycles.

The new catalyst appears as a promising tool for the direct synthesis of phenols, in alternative to the conventional multi-step methods.     

High-performance liquid chromatography of sulfonamides and quinolones on p-tert-butyl-calix[6]arene-bonded silica gel stationary phase

The high-performance liquid chromatographic behavior of some sulfonamides and quinolones was studied on a p-tert-butyl-calix[6]arene-bonded silica gel stationary phase. The effect of mobile phase variables such as methanol content, ionic strength and pH on their chromatographic behavior was investigated. The retention behavior of sulfonamides on the stationary phase was compared with that on both Zorbax C₁₈-bonded silica gel and γ-(ethylenediamino)propyltriethoxylsilane-bonded silica gel (diamino-bonded phase). The retention mechanism of sulfonamides and quinolones on the stationary phase was also discussed. The results indicate that the stationary phase behaves as a reversed-phase packing and its separation selectivity is much better than that of not only Zorbax C₁₈ phase but also diamino-bonded phase. Some sulfonamides and quinolones were separated on the stationary phase, but the separation of sulfonamides is far more successful.     

咪唑侧基功能化聚离子液体修饰的混合模式色谱固定相的制备及其色谱性能

该文合成了咪唑侧基功能化的离子液体单体1-(4-乙烯基苄基)-3-氰甲基溴化咪唑盐,通过表面引发原子转移自由基聚合将该单体接枝到硅胶表面,制备了一种新型混合模式色谱固定相。采用红外光谱、元素分析及热重分析对其结构进行表征。该色谱固定相具有良好的分离能力。通过研究流动相pH对物质保留的影响,验证了物质在该固定相上存在反相-离子交换保留机理。通过与十八烷基硅烷键合硅胶固定相比较,证实了该聚离子液体固定相对物质保留提供了π-π作用。结果表明,对咪唑侧基功能化是制备新型离子液体固定相的可行方法。     

溴化1-乙烯基-3-十二烷基咪唑硅胶键合固定相制备及其色谱性能

膜脂作为细胞质膜的主要组成部分,在生命活动中扮演着重要的作用,其涉及多种重要疾病的发生和发展过程。发展适用于膜脂分离分析的新型色谱材料对于其后续结构和生物学功能研究具有重要的意义。该文选用具有潜在生物相容性的离子液体溴化1-乙烯基-3-十二烷基咪唑（1-vinyl-3-dodecylimidazole bromide,VDI）为功能单体,通过一步法点击反应将其接枝到巯基功能化硅球表面,制备得到了新型溴化1-乙烯基-3-十二烷基咪唑硅胶键合固定相（Sil-VDI）。利用傅里叶变换红外光谱仪和热重分析仪对Sil-VDI固定相材料的结构进行表征,结果证明Sil-VDI色谱固定相已被成功制备。保留机制研究显示填充Sil-VDI色谱柱具有典型的反相/离子交换混合模式保留特性。基于此,采用不同疏水性物质烷基苯、多环芳烃、苯胺、苯衍生物和无机阴离子BrO₃ ^- 、NO₃ ^- 和IO₃ ^- 为测试物,对所制备固定相的色谱性能进行了研究。结果表明,该固定相对4类疏水性物质和无机阴离子均有较好的分离选择性和良好的峰对称性。进一步研究了所制备的Sil-VDI色谱柱对鸡蛋黄磷脂和肺腺癌细胞提取膜脂的分离效果,结果显示Sil-VDI色谱柱对2种磷脂样品均显示出了良好的分离能力。该文所制备的Sil-VDI色谱固定相合成方法简便,具有良好的分离分析应用潜能,后续工作会进一步研究该固定相在生物样品中的分离分析性能。     

一种聚合型弱阳离子交换/亲水相互作用色谱固定相的制备及色谱性能

通过亲核取代反应将聚乙烯马来酸酐键合到氨基硅胶表面,然后将残余的马来酸酐水解,制备了一种弱阳离子交换/亲水相互作用高效液相色谱固定相(Sil-PolyCOOH),通过固体核磁、ζ-电势及元素分析对固定相进行了表征。选取核苷和核酸碱为模型化合物,通过考察流动相组成,离子强度和pH等因素对溶质保留的影响,探讨了固定相的分离性能和保留机理,结果表明,该固定相的保留机理同时涉及亲水分配相互作用和多重主客体作用力。该固定相还对糖类、敌草快与百草枯等化合物具有良好的分离性能。上述研究结果表明该固定相在极性化合物的分离上具有良好的应用前景。     

Nonuniform lipid distribution in membranes

The noniform lateral and transbilayer lipid arrangement existing in two-component lipid bilayers are reviewed.

The lateral lipid organization is considered on the basis of the temperature-composition phase diagrams of the lipid binaries. A comparative analysis of the phase diagrams of synthetic phospholipid mixtures is carried out. The various types of the phase diagrams observed are set in a continuous row determined by the increase of the lipid lateral immiscibility. A special emphasis is laid on the appearance of peculiar points in the phase diagrams--triple, critical, and isoconcentration points. Two basic statistical-mechanical methods for simulation of phase diagrams--Bragg-Williams (regular solutions, mean field) and quasichemical--are compared. Stability criteria indicating the regions of lateral phase separation are also given. The main advantage of the quasichemical method is that it also allows the short-range order in the lipid arrangement to be determined.

The physical interactions contributing to an equilibrium lipid asymmetry in mixed lipid bilayers are pointed out. The most important among them are: (i) electrostatic forces induced by differences in the membrane electric double layers; (ii) nonideal lateral mixing of the lipids; (iii) packing restrictions important in curved bilayers.

A unified electrostatic model is presented to calculate the surface charge asymmetry created by any factors affecting the electric double layers of the bilayer (external electric potential, overlapping electric double layers in parallel membranes or in vescicles, etc.).

The transmembrane asymmetry strongly depends on the degree of c corrections may increase up two-three times the asymmetry induced by factors of the order of 1–3 kT. A typical nonideality effect, which may be used in an experimental verification, is the appearance of an extremum in the dependence of the asymmetry on the mole fraction of the components.

As previously shown in other reviews on membrane organization, the packing restrictions are of importance in highly curved bilayers, e.g., in small unilamellar vesicles.

The experimental data on the asymmetry of two-component small unilamellar vesicles are summarized and some general conclusions are formulated.

With a view toward the native membranes, some inferences are drawn about (i) the state of thermodynamic equilibrium and (ii) the lipid organization in multicomponent membranes.     

1,3-Alternate 25,27-dibenzoiloxy-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel as a new type of HPLC stationary phase

A new 1,3-alternate 25,27-dibenzoiloxy-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel stationary phase (1,3-Alt CalixBn) has been prepared and used for the separation of aromatic positional isomers by high-performance liquid chromatography (HPLC). The effect of organic modifier content and pH of the mobile phase on retention and selectivity of these compounds were studied. Application examples were provided for separation of purine and pyrimidine bases and non-steroidal anti-inflammatory drugs.     

纳米氧化锆沉积硅胶色谱固定相的制备及亲水作用色谱行为

采用液相沉积法(LPD)制备了纳米氧化锆沉积硅胶色谱固定相(ZrO₂/SiO₂), 并将其应用于亲水作用色谱分离中. 考察并比较了ZrO₂/SiO₂、 硅胶(SiO₂)和氧化锆(ZrO₂) 3种色谱固定相在不同有机调节剂比例、 不同pH值及不同盐浓度的流动相条件下的色谱行为. 结果表明, 制备的ZrO₂/SiO₂色谱柱不仅具有SiO₂色谱柱高柱效的优点, 表面沉积的纳米氧化锆还能有效屏蔽硅羟基, 有利于碱性物质的保留和分离, 表现出良好的亲水作用色谱性能. 将ZrO₂/SiO₂色谱柱用于4种脱氧核苷和5种碱性化合物的分离, 均得到了较好的效果, 展现出其作为色谱固定相良好的应用前景.     

Direct determination of 4-nitrobenzoyl chloride by high-performance liquid chromatography based on silanophilic interaction

A high-performance liquid chromatographic method without prederivatization was investigated for the direct determination of 4-nitrobenzoyl chloride and 4-nitrobenzoic acid. The separation was carried out on C₃, C₈ and C₁₈ alkyl-bonded silica columns with cyclohexane-tetrahydrofuran as the eluent. The retention behaviour observed was obviously caused by the silanophilic interaction between the solute and stationary phase. Optimum separation of 4-nitrobenzoyl chloride and 4-nitrobenzoic acid was obtained on the C₃ column and the calibration graph showed a significant linear relationship. The method was found to be quantitative, reproducible and rapid.     

Resolution studies on counter-current chromatography using supercritical fluid carbon dioxide

Counter-current chromatography (CCC) is a form of liquid–liquid partition chromatography. It requires two immiscible solvent phases; the stationary phase is retained in the separation column, generally by centrifugal force, while the mobile phase is eluted. We recently replaced the mobile phase with supercritical fluid carbon dioxide (SF CO₂). Since the solvent strength of SF CO₂ can be varied by changing the temperature and pressure of the system, separation adjustments are thus more versatile. We investigated the pressure and temperature effects on resolution using water and low-carbon alcohol mixtures as the stationary phases. It was demonstrated that these special properties of SF CO₂ were indeed beneficial to the optimization of separations. In addition, the phase retention ratio was examined in terms of separation resolution. The results appeared very similar to those obtained from conventional traditional CCC. This study should be helpful for the future development of SF applications in CCC.     

Cellulose acetate as stationary phase in microcolumn LC

The retention characteristics of alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) have been examined in liquid chromatography on a microcapillary column packed with cellulose acetate. Particulate and fibrous cellulose acetate were used as the stationary phase. Fibrous cellulose diacetate was found to be of use as an alternative stationary phase for liquid chromatography, although the separation efficiency was low. The retention characteristics for planar PAHs were linearly correlated with the size of the molecules, but the retention behavior for alkylbenzenes and nonplanar PAHs was affected by exclusion. The retention order was strongly influenced by the addition of dimethylformamide or water to methanol in the mobile phase. The results suggested that the retention behavior is influenced by a slight change in the polymer matrix of cellulose acetate.     

Hydrophilic interaction liquid chromatography with indirect ultraviolet detection for the separation and quantification of pyrrolidinium ionic liquid cations

A method of hydrophilic interaction liquid chromatography with indirect ultraviolet detection was developed to determine three pyrrolidinium ionic liquid cations, i.e. N-methyl-N-ethyl pyrrolidinium cation ([MEPy]⁺), N-methyl-N-propyl pyrrolidinium cation ([MPPy]⁺) and N-methyl-N-butyl pyrrolidinium cation ([MBPy]⁺). Chromatographic separation was achieved on a hydrophilic column using imidazolium ionic liquids and organic solvents as the mobile phase. The effects of the background ultraviolet absorption reagents, the imidazolium ionic liquids, detection wavelength, organic solvents, column temperature and the pH value of the mobile phase on the separation and determination of pyrrolidinium cations were investigated and the retention behaviors in hydrophilic interaction chromatography were discussed. The optimized chromatographic conditions were selected. Under the optimal conditions, the detection limits (S/N = 3) for [MEPy]⁺, [MPPy]⁺ and [MBPy]⁺ were 0.59, 0.53 and 0.46 mg/L, respectively. The method has been successfully applied to the determination of the three ionic liquids synthesized in our chemistry laboratory. This research results may improve the analytical method of ionic liquid cations.     

Comparison of physical and gas chromatographic properties of sterling FT and carbopack C graphitized carbon blacks

A comparison of Sterling FT, a graphitized carbon black used widely in ad- sorption and gas chromatography, and Carbopack C, a commercially available graphitized carbon black, was made in terms of retention parameters, heats of adsorption and their behaviour at various coating percentages.

The effects induced by hydrogen treatment at high temperature are compared, and it is shown that graphs of the heat of adsorption versus percentage of liquid phase added are very useful in understanding the difference in the surface properties of the two materials. The advantages of the two carbon blacks in practical gas chromato- graphy are discussed.     

Excess properties of mixtures of polar components and hydrocarbons of varying local polarisability

The inhomogeneous electric field of a neighbouring polar molecule exerts a special induction in an unsaturated hydrocarbon, giving rise to more negative excess properties. This effect has been investigated for the excess Gibbs energy g^E and the excess volume v^E for mixtures of the polar components 1-chlorobutane, 2-butanone, and ethanenitrile with the four hydrocarbons cyclohexane, cyclohexene, 1,4-cyclohexadiene, and benzene at 293.15 K and 313.15 K. The measurements of g^E were done by VLE (static vapour pressures by a continuous dilution apparatus) and checked by LLE for the systems with phase separation. Excess volumes were determined via a vibratim tube densimeter. Equation of state calculations enabled the evaluation of the interaction virial coefficient B₁₂. The special induction effect, which shows up strongly in g_E and v_E of the liquid mixtures, is only weakly reflected in B₁₂.     

Comprehensive two-dimensional liquid chromatography — practical impacts of theoretical considerations. A review

A theory of comprehensive two-dimensional separations by liquid chromatographic techniques is overviewed. It includes heart-cutting and comprehensive two-dimensional separation modes, with attention to basic concepts of two-dimensional separations: resolution, peak capacity, efficiency, orthogonality and selectivity. Particular attention is paid to the effects of sample structure on the retention and advantages of a multi-dimensional HPLC for separation of complex samples according to structural correlations. Optimization of 2D separation systems, including correct selection of columns, flow-rate, fraction volumes and mobile phase, is discussed. Benefits of simultaneous programmed elution in both dimensions of LCxLC comprehensive separations are shown.     

关于含酯基多孔聚合物小球固定相保留机制的探讨

通过比保留体积对数值与绝对温度倒数的直线关系,水和甲醇标准曲线的正截距、氘交换以及吸附系数和溶解系数的测定,证明至少对我们的聚合物固定相来说。表面吸附对保留值是决定性的因素。     

Enhanced‐fluidity liquid chromatography using mixed‐mode hydrophilic interaction liquid chromatography/strong cation‐exchange retention mechanisms

The potential of enhanced‐fluidity liquid chromatography, a subcritical chromatography technique, in mixed‐mode hydrophilic interaction/strong cation‐exchange separations is explored, using amino acids as analytes. The enhanced‐fluidity liquid mobile phases were prepared by adding liquefied CO₂ to methanol/water mixtures, which increases the diffusivity and decreases the viscosity of the mixture. The addition of CO₂ to methanol/water mixtures resulted in increased retention of the more polar amino acids. The “optimized” chromatographic performance (achieving baseline resolution of all amino acids in the shortest amount of time) of these methanol/water/CO₂ mixtures was compared to traditional acetonitrile/water and methanol/water liquid chromatography mobile phases. Methanol/water/CO₂ mixtures offered higher efficiencies and resolution of the ten amino acids relative to the methanol/water mobile phase, and decreased the required isocratic separation time by a factor of two relative to the acetonitrile/water mobile phase. Large differences in selectivity were also observed between the enhanced‐fluidity and traditional liquid mobile phases. A retention mechanism study was completed, that revealed the enhanced‐fluidity mobile phase separation was governed by a mixed‐mode retention mechanism of hydrophilic interaction/strong cation‐exchange. On the other hand, separations with acetonitrile/water and methanol/water mobile phases were strongly governed by only one retention mechanism, either hydrophilic interaction or strong cation exchange, respectively.     

Trennung polyzyklisher aromatischer kohlenwasserstoffe durch hochdruckflössigkeitschromatographie: Vergleich einer bestimmung von benzo[a]pyren nach trennung an saäulen mit quervernetztem celluseacetat und einem reversed-phase system

Separation of polycyclic aromatic hydrocarbons by high-pressure liquid chromatography. Comparison of the determination of benzo(a)pyrene with separation on columns of cross-linked cellulose acetate and a reversed-phase system.

The behaviour of a new high-pressure liquid chromatographic support, i.e. a cross-linked cellulose acetate, as selective separation material for polycyclic aromatic hydrocarbons is discussed. The determination of benzo[a]pyrene is described by an example of separating a so-called benzpyrene fraction. The separation of the benzpyrene fraction was possible by combining column systems with aluminium oxide, cross-linked cellulose acetate or a reversed-phase system. By means of a fluore- scence detector 0.1-0.8 ng benzo[a]pyrene could be detected in 5μl injection volume.