Polar stationary phases for capillary electrochromatography

This review article summarizes the variety of polar stationary phases that have been employed for capillary electrochromatographic separations. Compared with reversed-phase stationary phases, the polar alternatives provide a completely different retention selectivity towards polar and charged analytes. Different types of polar stationary phases are reviewed, including the possible retention mechanisms. Electrochromatographic separations of polar solutes, peptides, and basic pharmaceuticals on polar stationary phases are presented.     

An approach for extending van der waals equations of state for polar,hydrogen bonding fluids applied to the soave equation of state

A method is developed for extending van der Waals type equations of state to highly polar, hydrogen bonding fluids. The method uses the acentric factor of the hydrocarbon homolog as the shape parameter and an empirical polar parameter incorporated into a closed form, temperature dependent polar correction term. When the method is applied to the Soave equation of state, a three-parameter equation of state results which reduces to the Soave equation for non-polar fluids, yet fits vapor pressures for polar fluids much better than the original equation. Furthermore, unlike other extensions applicable to polar fluids, the polar parameters obtained do seem to be related to the expected strength of polar interactions for different classes of compounds.     

Enhancing Metal Separations by Liquid–Liquid Extraction Using Polar Solvents

The less polar phase of liquid–liquid extraction systems has been studied extensively for improving metal separations; however, the role of the more polar phase has been overlooked for far too long. Herein, we investigate the extraction of metals from a variety of polar solvents and demonstrate that, the influence of polar solvents on metal extraction is so significant that extraction of many metals can be largely tuned, and the metal separations can be significantly enhanced by selecting suitable polar solvents. Furthermore, a mechanism on how the polar solvents affect metal extraction is proposed based on comprehensive characterizations. The method of using suitable polar solvents in liquid–liquid extraction paves a new and versatile way to enhance metal separations.     

Comparison of retention on traditional alkyl, polar endcapped, and polar embedded group stationary phases

The development of new RP stationary phases containing polar groups has provided the chromatographer with a variety of stationary phase choices with differing selectivities. Polar endcapped and polar embedded group stationary phases have found use in solving a wide variety of separation problems, especially for the efficient separation of organic bases as well as separations necessitating the use of highly aqueous mobile phases. In this report, the retention thermodynamics of small, nonpolar solutes on traditional alkyl, polar endcapped, and polar embedded group stationary phases are compared. It is found that the nonpolar (methylene) transfer enthalpy is less favorable when polar embedded group phases are used, when compared to traditional or polar endcapped phases. In contrast, the transfer enthalpy of a phenyl group is found to be more favorable when a polar endcapped phase is used. In addition, the retention characteristics of these phases are compared using a set of solutes with differing solvatochromic parameters. Hydrogen-bond acids appear to have enhanced retention on polar embedded group phases, while hydrogen-bond bases have enhanced retention on polar endcapped phases.     

Polymerization of Substituted Acetylenes Carrying Non‐Polar and Polar Groups with Transition Metal Acetylide Catalysts

A new series of single‐component air‐stable transition metal acetylide catalysts for the polymerization of substituted acetylenes carrying non‐polar and polar groups was developed. The catalytic properties of transition metal acetylides are related to transition metals, phosphines and acetylenic ligands. Nickel acetylides show higher catalytic activity towards the polymerization of substituted acetylenes containing non‐polar groups, while palladium acetylides show higher catalytic activity towards the polymerization of substituted acetylenes carrying polar groups. Palladium acetylides with PPh₃ ligand are efficient catalysts for the polymerization of substituted acetylenes bearing both non‐polar and polar groups.     

稀土催化极性单体配位均聚及与非极性单体共聚合的研究

将极性基团引入大分子链中可改善非极性聚烯烃材料的表面性能,扩展其应用范围甚至带来不可预见的新功能,是市场需求并由企业驱动.与聚合后功能化改性和物理共混方法相比,极性与非极性单体配位共聚合是最直接和简便的方法,适用范围广,并可保持聚烯烃的立构规整度,一直以来,相关研究备受企业和科研工作者瞩目.然而,极性基团通常具有Lewis碱性,容易与Lewis酸性的聚合催化剂强烈螯合而致其毒化,因此,这又是极具挑战性的课题.目前,该领域的研究取得了很大的进展,已经实现了乙烯与很多极性单体的共聚合.今后,将集中解决如何实现极性单体均聚合,提高共聚合活性,特别是极性单体插入率和分布可调节性,保持立体选择性,以及获得高分子量、具有实际应用意义的共聚产物等问题.本文旨在将课题组近年来在极性功能化苯乙烯和共轭双烯烃单体的均聚合及与苯乙烯、乙烯和共轭双烯烃等非极性单体共聚合方面的最新研究成果以及国内外该领域的相关报道进行综合阐述,为读者提供解决上述关键问题采用的研究路线、实施方法和创新性思维.     

Capillary electrochromatography with monolithic silica columns. V. Study of the electrochromatographic behaviors of polar compounds on monolithic silica having surface bound cyano functionalities

In this report, a novel polar monolithic capillary column is described for normal phase CEC (NP-CEC) of representative polar compounds including mono- and oligosaccharides, peptides, and basic drugs. The polar monolithic column, which was described in detail in the preceding paper, consisted of silica-based monolith bonded with 1H-imidazole-4,5-dicarbonitrile (IDCN) and is denoted as 2CN-OH-Monolith. Various retention parameters for neutral polar solutes (e.g., mono- and oligosaccharides) and charged polar solutes (e.g., peptides and basic drugs) were evaluated over a wide-range of elution conditions. These retention parameters yielded quantitative assessment for the polar interactions between the model solutes and the stationary phase under investigation as well as the effect of electromigration of charged solutes on their overall migration in NP-CEC. Furthermore, this investigation demonstrated that despite the possibility of achieving isocratic separation in NP-CEC for widely differing polar species, multistep-gradient elution in NP-CEC is preferred to bring about the rapid separation of a large number of polar species in a single run.     

Precise control of microstructure of functionalized polypropylene synthesized by the ansa‐zirconocene/ MAO catalysts

We inclusively investigated polymerization behavior and structure of copolymer in the copolymerization of propylene and alkylaluminum‐protected polar allyl monomers. The control of the arrangement of polar group in the copolymer was discussed. It was proved that the location of polar group could be controlled by zirconocene catalyst and a kind of polar monomer. The indenyl or the 2‐methylindenyl ligands of zirconocene were favored to produce end‐functionalized polymers. It was also found that the trimethylaluminum‐protected allylamine and triisobutylaluminum‐protected allylmercaptan had superior ability in the synthesis of end‐functionalized polypropylene. On the other hand, the 2‐methyl‐4‐phenylindenyl ligand produced the copolymers containing both the end‐polar unit and inner‐polar unit at the polymer chains. Terpolymerization of propylene, polar allyl monomer, and 5‐hexen‐1‐ol was also conducted. The NMR study of the terpolymer revealed that both the 5‐hexen‐1‐ol and the polar allyl monomer were incorporated into the polymer chain. It has also become apparent that the polar allyl monomer units predominantly occupied the chain end, while the 5‐hexen‐1‐ol units were located at the inner of main chain. Consequently, we have achieved the synthesis of functionalized polypropylene in which the arrangement of polar group was precisely controlled. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1738–1748, 2008     

Solvatochromism as an alternative for contact angle measurements in the characterisation of modified polymer surfaces

Polyolefine surfaces have been pre-treated by UV/ozone and UV/water methods. The increase in polar groups on a polymer surface and the contribution of these polar groups to the adhesion of the polymer has been investigated by using contact angles and tensile strength tests. Because contact angle measurements do not give information about the specific polar groups on the surface we have used solvatochromic analyses to identify specific polar groups. The results showed that solvatochromic analyses is a promising method to discriminate between different kinds of polar groups and therefore solvatochromic surface characterisation may become an important surface analytical tool in adhesive technology.     

Development of Polar Order in the Liquid Crystal Phases of a 4‐Cyanoresorcinol‐Based Bent‐Core Mesogen with Fluorinated Azobenzene Wings

A bent‐core mesogen consisting of a 4‐cyanoresorcinol unit as the central core and laterally fluorinated azobenzene wings forms four different smectic LC phase structures in the sequence SmA–SmC_s–SmC_sP_AR–M, all involving polar SmC_sP_S domains with growing coherence length of tilt and polar order on decreasing temperature. The SmA phase is a cluster‐type de Vries phase with randomized tilt and polar direction; in the paraelectric SmC_s phase the tilt becomes uniform, although polar order is still short‐range. Increasing polar correlation leads to a new tilted and randomized polar smectic phase with antipolar correlation between the domains (SmC_sP_AR) which then transforms into a viscous polar mesophase M. As another interesting feature, spontaneous symmetry breaking by formation of a conglomerate of chiral domains is observed in the non‐polar paraelectric SmC_s phase.     

Surface energy of fluorinated surfaces

By fluorinating the surface of a polymer, the hydrogen bonding energy of a polar surface has been defined. The contact angles for three solvent classes; nonpolar, polar and hydrogen bonding, on a polar surface results in the separation of dispersion, polar, and hydrogen bonding energies. Both critical surface tension plots and theoretical calculations were used to define the surface energy for fluorinated polyethylene.     

Excited state solvation dynamics of 2-anilinonaphthalene

Nanosecond fluorescence spectroscopy has been used to study the interaction of 2-anilinonaphthalene with polar solvent molecules which is shown to result in stoichiometric complex formation at low polar solvent concentrations. This is followed by reorientation of the solvent cage when the concentration of polar solvent is high.     

HPLC测定煤焦油中极性化合物的研究

应用高效液相色谱以正相－ＨＰＬＣ配以反冲（ＢＦ）技术,测定了煤焦油中极性化合物的总量。以反相（ＲＦ）－ＨＰＬＣ辅以制备液体色谱研究了极性段份的制备及典型极性化合物的分析,文中分析的实样由山西省一些焦化厂提供。     

Perturbed chain-statistical associating fluid theory extended to dipolar and quadrupolar molecular fluids

The perturbed chain statistical associating fluid theory (PC-SAFT) is extended to polar molecular fluids, namely dipolar and quadrupolar fluids. The extension is based on the perturbation theory for polar fluids by Stell and co-workers. Appropriate expressions are proposed for dipole-dipole, quadrupole-quadrupole, and dipole-quadrupole interactions. Furthermore, induced dipole interactions are calculated explicitly in the model. The new polar PC-SAFT model is relatively complex; for this purpose, a truncated polar PC-SAFT model is proposed using only the leading term in the polynomial expansion for polar interactions. The new model is used for the calculation of thermodynamic properties of various quadrupolar pure fluids. In all cases, the agreement between experimental data and model predictions is very good.     

Early Transition Metal Catalysis for Olefin–Polar Monomer Copolymerization

Introducing polar functional groups into widely used polyolefins can enhance polymer surface, rheological, mixing, and other properties, potentially upgrading polyolefins for advanced, value‐added applications. The metal catalyst‐mediated copolymerization of non‐polar olefins with polar comonomers represents the seemingly most straightforward, atom‐ and energy‐efficient approach for synthesizing polar functionalized polyolefins. However, electrophilic early transition metal (groups 3 and 4)‐catalyzed processes which have achieved remarkable success in conventional olefin polymerizations, encounter severe limitations here, largely associated with the Lewis basicity of the polar co‐monomers. In recent years, however, new catalytic systems have been developed and successful strategies have emerged. In this Minireview, we summarize the recent progress in early transition metal polymerization catalyst development, categorized by the catalytic metal complex and polar comonomer identity. Furthermore, we discuss advances in the mechanistic understanding of these polymerizations, focusing on critical challenges and strategies that mitigate them.     

硫酸钡微晶改性毛细管柱的制备及其分离性能的研究（Ⅱ）

本文在中等极性和强极性玻璃毛细管柱研究的基础上（１），对弱极性和非极性固定液在硫酸钡微晶改性表面上的涂渍情况作了详细的研究。研究表明，只要对这种改性表面进行钝化处理，即可途渍出高效弱极性和非线性毛细管柱。     

Synthesis of functional polyolefins using cationic bisphosphine monoxide-palladium complexes

The copolymerization of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymerizations of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Additionally, the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.     

Preparation and evaluation of a lysine-bonded silica monolith as polar stationary phase for hydrophilic interaction pressurized capillary electrochromatography

A silica-based monolith as polar stationary phase was described for hydrophilic interaction pressurized capillary electrochromatography (HI-pCEC). The polar monolithic column was prepared by on-column reaction of lysine with epoxy groups on a gamma-glycidoxypropyltrimethosysilane-modified silica monolith. The stationary phase yielded strong hydrophilic interaction due to the slightly polar hydroxyl groups, and the strong polar lysine ligand with amino groups and carboxylic groups contained on the surface of the monolith. In order to evaluate the hydrophilic character of lysine ligand, the chromatographic behaviors of epoxy monolith (before lysine bonded) and diol monolith (hydroxyl groups contained) were also investigated. Two groups of comparative experiment were developed in terms of the separation of typical neutral non-polar and polar compounds performed in a mobile phase of aqueous-acetonitrile solution. Results showed that the lysine monolith was much more hydrophilic than the diol monolith, which presented less hydrophobic than the epoxy monolith. For further study on its hydrophilic character, the lysine monolith was demonstrated in the HI-pCEC mode for the separations of various polar compounds such as phenols, nucleic acid bases and nucleosides.     

Recent progress in carbohydrate separation by high-performance liquid chromatography based on hydrophilic interaction

This article surveys recent developments in the separation and analysis of carbohydrates by high-performance liquid chromatography, in adsorption or partition modes, on polar sorbents with less polar eluents, a technique that is now termed hydrophilic interaction chromatography. A variety of chromatographic methods are included under this generic heading, the most important being adsorption chromatography on silica and partition chromatography on silica-based sorbents bearing bonded polar phases. Examples are given of the applications of these stationary phases, as well as the newer polymer-based polar sorbents, in high-performance liquid chromatography of carbohydrates and their derivatives.     

Retention and selectivity of stationary phases for hydrophilic interaction chromatography

More and more polar stationary phases have become available for the separation of small polar compounds in the past decade as hydrophilic interaction chromatography (HILIC) continues to find applications in new fields (e.g., metabolomics and proteomics). Bare silica phases remain popular, especially in the bio-analytical area. A wide range of functional groups (e.g., amino, amide, diol, sulfobetaine, and triazole) have been employed as polar stationary phases for HILIC separation. This review provides a survey of the popular stationary phases commercially available and discusses the retention and selectivity characteristics of the polar stationary phases in HILIC. The purpose of the review is not to provide a comprehensive overview of literature reports, but rather focuses on findings that demonstrate retention and selectivity of the polar stationary phases in HILIC.