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. Electrochromato-graphic separations of polar solutes, peptides, and basic pharmaceuticals on polar stationary phases are presented.

Efficient preparation of silver nanoplates assisted by non-polar solvents

In the paper, we report an efficient method to prepare high yield (up to 97%) of silver nanoplates. Synthesis of silver nanoplates was carried Out in a binary solvent system of N,N-dimethylformamide (DMF) and toluene, in which DMF served as the reductant and polyvinylpyrrolidone (PVP) as the capping agent. By increasing the ratio of toluene to DMF to 7:6, silver nanoplates can be Successfully synthesized; otherwise other shaped nanoparticles would be the major products. The nanoplate sample was characterized by TEM, HRTEM, SAED, XRD, AFM and UV-visible spectroscopy, proving the high nanoplate purity of this sample. The influence of toluene content, other solvents, AgNO3 concentration, preparation temperature and chloride ions was also examined, which suggests that the function of nonpolar solvents in this system is to enhance the PVP coverage on silver surface and, furthermore, to facilitate the preferential adsorption of PVP on two (I I I) facets of silver nanoplates.

Effects of polar group saturation on physical gelation of Amphiphilic polymer solutions

Monte Carlo simulation on the basis of the comblike coarse grained nonpolar/polar (NP) model has been carried out to study the polar group saturation effect on physical gelation of amphiphilic polymer solutions. The effects of polar group saturation due to hydrogen bonding or ion bridging on the sol-gel phase diagram, microstructure of aggregates, and chain conformation of amphiphilic polymer solutions under four different solvent conditions to either the nonpolar backbone or the polar side chain in amphiphilic polymer chains have been investigated. It is found that an increase of polar group saturation results in a monotonically decreased critical concentration of gelation point, which can be qualitatively supported by the dynamic theological measurements on pectin aqueous solutions. Furthermore, various solvent conditions to either the backbone or the side chain have significant impact on both chain conformation and microstructure of aggregates. When the solvent is repulsive to the nonpolar backbone but attractive to the polar side chain, the polymer chains are collapsed, and the gelation follows the mechanism of colloidal packing; at the other solvent conditions, the gelation follows the mechanism of random aggregation.

Amperometric quantification of polar organic solvents based on a tyrosinase biosensor

A novel amperometric biosensor for quantification of the electrochemically inert polar organic solvents based on tyrosinase electrode was preliminarily reported. The biosensor was fabricated by simply syringing an aqueous solution of tyrosinase/PVAVP (PVAVP: copolymer of poly(vinyl alcohol) grafting with 4-vinylpyridine) onto glassy carbon electrode surface followed by drying the modified electrode at +4 degrees C in a refrigerator. The current generated from electrochemical reduction of quinone is a probe signal. The biosensor can be used for quantification of polar organic solvents, and its mechanism was characterized with in situ steady-state amperometry-quartz crystal microbalance experiments. The detection limit, sensitivity, and dynamic range for certain organic solvents are dependent on the kind and concentration of the substrate probe and the hydrophobicity of the immobilization matrix. The response time for all the tested organic solvents is less than 2 min.

Studies on blends of LLDPE and polar polymers compatibilized by a random copolymer

Compatibilization of blends of Linear low-density polyethylene (LLDPE)-poly(methyl methacrylate) (PMMA) and LLDPE-copolymer of methyl methacrylate (MMA) and 4-vinylpyridine (poly(MMA-co-4VP) with poly(ethylene-co-methacrylic acid) (EMAA) have been studied. Mechanical properties of the LLDPE-PMMA blends increase upon addition of EMAA. In order to further improve interfacial adhesion of LLDPE and PMMA, 4-vinyl pyridine units are introduced into PMMA chains, or poly(MMA-co-4VP) is used as the polar polymer. In LLDPE-poly(MMA-co-4VP)-EMAA blends, interaction of MAA in EMAA with 4VP of poly(MMA-co-4VP) causes a band shift in the infrared (IR) spectra. Chemical shifts of N-1s binding energy in X-ray photoelectronic spectroscopy (XPS) experiments indicate a transfer of proton from MAA to 4VP. Scanning electron microscopy (SEM) pictures show that the morphology of the blends were improved upon addition of EMAA. Nonradiative energy transfer (NRET) fluorescence results attest that there exists interdiffusion of chromophore-labeled LLDPE chains and chromophore-labeled poly(MMA-co-4VP) chains in the interface. Based on experimental results, the mechanism of compatibilization is studied in detail. Compatibilization is realized through the interaction between MAA in EMAA with 4VP in poly(MMA-co-4VP). (C) 1999 John Wiley & Sons, Inc.

Synthesis of lanthanide-alkylaluminium bimetallic complexes and studies on their catalytic activities for polymerization of some polar monomers

Three new lanthanide (Ln)-alkylaluminium (Al) bimetallic complexes with the formula [(mu-CF3CO2)(2)Ln(mu-CF3CHO2)AIR(2) . 2THF](2) (Ln = Nd, Y, R=i-C4H9 (i-Bu); Ln=Eu, R=C2H5(Et); THF=tetrahydrofuran) were synthesized by the reaction of Ln(CF,CO,), (Ln=Nd, Y) with HAI (i-Bu)(2) and of Eu(CF3CO2)(3) with AlEt(3), respectively. Their crystal structures were determined by X-ray diffraction at 233 K. [(mu-CF3CO2)(2)Nd (mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Nd-Al) and [(mu-CF3CO2)(2)Y(mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Y-Al) are isomorphous and crystallize in space group with a=12.441(3) Angstrom [12.347(5) Angstrom for Y-Al], b=12.832(3) Angstrom [12.832(4) Angstrom], c=11.334(3) Angstrom [11.292(8) Angstrom], alpha=104.93 (2)degrees [104.45(4)degrees], beta=98.47(2)degrees [98.81(4)degrees], gamma=64.60(2)degrees [64.30(3)degrees], R=0.519 [0.113], R(w)=0.0532 [0.110], Z=1 and [(mu-CF3CO2)(2)Eu(CF3CHO2)AlEt(2) . 2THF](2)(Eu-Al) in space group P2(1)/n with a=11.913(6) Angstrom, b=14.051(9) Angstrom, c=17.920(9) Angstrom, alpha=101.88(11)degrees, beta=gamma=90 degrees, R=0.0509, R(w)=0.0471 and Z=2. The six CF3CO2- (including CF3CHO2-) of each complex, among which pairs are equivalent, coordinated to Ln and Al in three patterns: (A) the two oxygen atoms in one of the three CF3CO2- type coordinated to two different Ln; (B) the two oxygen atoms in the second of CF3CO2- type coordinated to Ln and Al, respectively; (C) one of the two oxygen atoms in the third CF3CO2- type bidentately coordinated to two Ln and another oxygen coordinated to Al and one of the two Ln, respectively. Unlike types A and B, in type C the carboxyl carbon with a hydrogen atom bonded to it was found to appear as an sp(3)-hybridized configuration rather than an sp(2)-one. 1D and 2D NMR results further confirmed the existence of such a disproportionated CF3CHO2- ligand. Methyl methacrylate (MMA) and epichlorohydrin (ECH) could be polymerized by Y-Al or Eu-Al as a single-component catalyst and highly syndiotactic poly(MMA) was obtained. THF could also be polymerized by Y-Al in the presence of a small amount of ECH.

SYNTHESES AND CHARACTERIZATION OF [(MU-CF3CO2)(2)LN(MU-CF3CHO2)ALR(2)CENTER-DOT-2THF](2) AND THEIR CATALYTIC ACTIVITIES FOR POLYMERIZATION OF SOME POLAR MONOMERS

Three new bimetallic complexes were synthesized and crystalized by reactions of (CF3CO2)(3)Ln With R(1) AlR(2)(Ln=Nd and Y, R(1)=H, R=i-C4H9; Ln=Eu, R=R(1)=C2H5) in tetrahydrofuran solution, and their crystal structures were determined using a X-ray diffraction method. The structures and the questions on valence state and noncoplanarity in the structures were confirmed and cracked by means of H-1 NMR and C-13 NMR spectra, especially by C-13-H-1 COSY 2D NMR technique. A general formula of molecules of the three rare earth complexes was defined as follows: [(mu-CF3CO2)(2)Ln(mu-CF3CHO2)AlR(2) . 2THF](2) A mechanism on the formation of the new complexes was also proposed through the following five steps: alkylating, beta-elimination (or hydrogenation), hydrogen transfer, linkage and association. Both Y-Al and Eu-Al complexes function as a catalyst in polymerization of MMA and ECH. The polymer obtained from the first monomer is mainly syndiotactic chain structure and the polymerization of the last monomer shows higher catalytic activity. The Y-Al complex also capable of ring-opening polymerization of THF in case of adding-vary small amount of ECH and a oxonium ion mechanism of THF polymerization was suggested from the analysis of THF polymer terminal.

EFFECTS OF METAL-IONS ON THE CONFORMATION OF POLAR HEADGROUP OF SPHINGOMYELIN BILAYER

With the wide application of rare earth in agriculture, medicament, especially the application of Gd-DTPA as nuclear magnetic resonance image reagent in clinical practice([1]), the studies on the toxicology in biological body, as well as the study on the use as informative probes instead of divalent calcium ion in biological and biochemical research have attracted intensive concern([2]). Phospholipids bilayers have served as a model of biomembrane in the last two decades. The effects of metal ions on the conformation of polar headgroup of dipalmitoylphosphatidylcholine (DPPC) bilayers have been reported([3]). Sphingomyelin is major component of several biological tissues such as brain and nerve cells and has identical polar headgroup to DPPC. The interaction of metal ions with sphingomyelin bilayer remains nonrevealed. This note presents the results of the study on this aspect.

MOLECULAR-STATE OF GRAFT-COPOLYMERS IN THE INTERFACIAL AREA OF POLYOLEFIN AND POLAR POLYMER

In order to characterize the interface in polymer blends, a new method is suggested, in which the interface is exposed by selectively dissolving in solvent. By means of X-ray photoelectron spectrometry, we studied the molecular state in the interfacial ar

Triploid and tetraploid Zhikong scallop, Chlamys farreri Jones et Preston, produced by inhibiting polar body I

Triploid scallops are valuable for aquaculture because of their enlarged adductor muscle, and tetraploids are important for the commercial production of triploids. We tested tetraploid induction in the zhikong scallop by inhibiting polar body I in newly fertilized eggs. The ploidy of resultant embryos was determined by chromosome counting at 2- to 4-cell stage and by flow cytometry thereafter. Embryos from the control groups were mostly diploids (79%), along with some aneuploids. Embryos from the treated groups were 13% diploids, 18% triploids, 26% tetraploids, 13% pentaploids, and 36% aneuploids. Tetraploids, pentaploids, and most aneuploids suffered heavy mortality during the first week and became undetectable among the larvae at day 14. Five tetraploids (2%) were found among a sample of 267 spat from one of the replicates, and none was detected at day 450. The adductor muscle of triploid scallops was 44% heavier (P < .01) than that of diploids, confirming the value of the triploid technology in this species.

Chromosome segregation in fertilized eggs from triploid Pacific oysters, Crassostrea gigas (Thunberg), following inhibition of polar body 1

Chromosome segregation in fertilized eggs from triploid Pacific oysters, following inhibition of the first polar body (PB1), was studied with acetic orcein staining techniques. To block the release of PB1, fertilized eggs were treated with 0.5 mg/l of cytochalasin B (CB). Four types of segregation were observed, namely, ''tripolar segregation'' (54.5%), ''united bipolar segregation'' (12%), ''separated bipolar segregation'' (2.5%), and ''incomplete united bipolar segregation'' (4%). The remaining 23% could not be classified because of chromosome disorganization, but appeared to be variants of the above. It seemed clear that the predominant pattern that gave rise to tetraploids was united bipolar segregation, although certain separated bipolar segregations might also lead to the formation of tetraploids. The sequential events of meioses observed in CB-treated eggs are described. The asynchrony of meiotic events and possible mechanisms for the various types of chromosome segregation are discussed.