聚甲基丙烯酸甲酯/聚醋酸乙烯酯共混分相过程结构函数的标度分析和相凝聚

高分子共混体系相分离动力学研究已取得了很大的进展。Cahn理论可很好地描述相分离初期过程,de Gennes的蛇行理论可较好地描述相分离初期大分子扩散。在相分离后期,人们已经发现动力学参量的标度行为,但实验结果不一,标度成因尚不十分清楚。本文研究了聚甲基丙烯酸甲酯(PMMA)/聚醋酸乙烯酯(PVAc)共混体系相分离后期过程。分析了结构函数的标度行为,初步讨论了相凝聚特征。     

Synthesis of new chiral mono-, di-, tri-, and tetraalkylglycolurils

Two general procedures were developed for the synthesis of chiral N-mono-, N, N′-di-, N, N′ N″-tri-, and N, N′, N″, N′″-tetraalkylglycolurils based on the reactions of 4,5-dihydroxy-imidazolidin-2-ones or glyoxal with one or two moles of alkylureas, respectively, by acid catalysis. The reactions of N-monoalkyl- and N, N′-dialkylureas with glyoxal proceed regioselectively. The mechanism of these reactions was suggested and partly confirmed by quantum-chemical calculations and experimental data. The enantiomeric separation of some chiral glycolurils by chiral-phase HPLC was carried out for the first time.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 680–692, March, 2005.     

Resolution of triacylglycerol positional isomers by reversed-phase high-performance liquid chromatography

The ability of reversed-phase high-performance liquid chromatography (RP-HPLC) to separate some positionally isomeric disaturated and monounsaturated triacylglycerols (TAGs) as intact species is demonstrated for the first time. Mobile phases of acetonitrile modified with methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, acetone, or dichloromethane were tested for the separation of POP-PPO, PLP-PPL, PEP-PPE, and PDP-PPD (P-palmitic, O-oleic, L-linoleic, E-eicosapentaenoic, D-docosahexaenoic acid residue) on a single RP-HPLC column. The resolution improved with increasing number of double bonds in the acyl residues. While POP and PPO were only partially resolved, PDP and PPD were fully separated with all tested mobile phases, except those containing methanol. Also separated were the four TAGs having the same equivalent carbon number (ECN = 42), PEP, PPE, PDP, and PPD, on a single RP-HPLC column with mobile phase acetonitrile-2-propanol (70:30, v/v) at 0.8 mL/min. In all cases the isomer with the unsaturated acyl residue in either 1- or 3-position was retained more strongly than the respective 2-isomer.     

Application of HPLC to measure vanadium in environmental,biological and clinical matrices

Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds.     

Analysis of petroleum fractions by on-line micro HPLC-HRGC coupling,involving increased efficiency in using retention gaps by partially concurrent solvent evaporation

Two-dimensional chromatography of gasoline by on-line coupled HPLC-HRGC, as described in this paper, allows separate GC analysis of paraffins and aromatics. The GC system contains a retention gap of only 10 m length for introducing HPLC fractions of 100 μl volume. This becomes possible through evaporation of part of the solvent during introduction of the HPLC eluent. This “partially concurrent solvent evaporation” technique allows transfer of large volumes of HPLC eluent into relatively short retention gaps, maintaining the full efficiency of the solvent effects in reconcentrating the bands of the early eluted solutes.     

Microporous SiO2 and SiO2/MOx (M=Ti,Zr, Al) for ceramic membrane applications: A microstructural study of the sol-stage and the consolidated state

Microporous SiO₂ and SiO₂/MO₂ (M=Ti, Zr, Al; 10 mol% MO_x) materials for gas separation membrane applications have been prepared from polymeric sols. Characterization of these sols with SAXS showed that the mean fractal dimension of the SiO₂ sols is 1.3–1.4 with a radius of gyration of approximately 2.5 nm. The dried and calcined films are microporous and the pore size distribution was bimodal with maxima at diameters of 0.5 nm and 0.75 nm. For the SiO₂/TiO₂, SiO₂/ZrO₂ and SiO₂/Al₂O₃ systems, much milder reaction conditions proved to be necessary to obtain sols with comparable fractal dimensions due to the high reactivity of the Ti/Zr/Al-alkoxides. Microporous supported membranes with molecular sieve-like gas transport properties can be prepared from a relatively wide range of sol structures: from polymers too small to characterize with SAXS to structures with fractal dimensions: 1<d _f<2.04.     

Capillary zone electrophoresis of alpha-helical diastereomeric peptide pairs with anionic ion-pairing reagents

The present study uses an unique capillary electrophoresis (CE) approach, that we have termed ion-interaction capillary zone electrophoresis (II-CZE), for the separation of diastereomeric peptide pairs where a single site in the centre of the non-polar face of an 18-residue amphipathic alpha-helical peptide is substituted by the 19 L- or D-amino acids. Through the addition of perfluorinated acids at very high concentrations (up to 400 mM), such concentration levels not having been used previously in chromatography or CE, to the background electrolyte (pH 2.0), we have been able to achieve baseline resolution of all 19 diastereomeric peptide pairs with an uncoated capillary. Since each diastereomeric peptide pair has the same sequence, identical mass-to-charge ratio and identical intrinsic hydrophobicity, such a separation by CZE has previously been considered theoretically impossible. Excellent resolution was achieved due to maximum advantage being taken of even subtle disruption of peptide structure/conformation (due to the presence of D-amino acids) of the non-polar face of the amphipathic alpha-helix and its interaction with the hydrophobic anionic ion-pairing reagents. In addition, due to the excellent resolution of diastereomeric peptide pairs by this novel CZE approach, we have also been able to separate a mixture of these closely-related alpha-helical peptides.     

Miscibility and phase separation in SAN/PMMA blends investigated by positron lifetime measurements

Miscibility and phase separation in SAN/PMMA blends have been investigated using DSC, IR spectroscopy and positron lifetime spectroscopy (PLS). Single broad glass transition observed throughout the blend compositions, may be due to overlap of two glass transitions. IR measurements clearly indicate the absence of strong interactions. This supports miscibility is due to intramolecular repulsive forces in the SAN component. On the other hand, free volume data show negative deviation from linear additivity indicating the blends are miscible. The interchain interaction parameter β exhibits a complex behavior and the extent of miscibility is not revealed. Following Wolf’s treatment, we have evaluated the geometry factor γ and hydrodynamic interaction parameter α and found α is a suitable parameter in predicting the miscibility window. The cloud points in SAN/PMMA blends increase with decreasing PMMA content. The change in free volume size correlates well with the observed change in cloud point.     

Trans-cis Photoisomerization of 1-Methyl-4-(4′-hydroxystyryl)pyridinium in inclusion complexes ofβ-cyclodextrin and its derivatives

The effects of -cyclodextrin (-CyD), heptakis(2,6-di-O-methyl)--cyclodextrin (DMCyD) and heptakis(2,3,6-tri-O-methyl)--cyclodextrin (TMCyD) ontrans-cis photoisomerization of 1-ethyl-4-(4-hydroxystyryl)pyridinium (POH) have been studied in aqueous solutions. The ratio of [cis]/[trans] for POH in the photostationary state at pH 8.54 was remarkably reduced by the presence of CyD or DMCyD. The reduction of the [cis]/[trans] ratio in the photostationary state was explained in terms of the shift of the equilibrium of POH ₊ ^trans PO _trans + H^– toward PO _trans formation. The binding constants of CyD and DMCyD for PO _trans were 2.00- and 1.36-fold larger than those for POH ₊ ^trans , respectively. The binding constants of TMCyD for both species are much smaller than those of CyD and DMCyD. This result indicates that PO _trans , which has a betain structure, forms stable complexes with CyD and DMCyD with its hydrophobic parts inside and the charged parts outside the CyD cavities.     

Rapid stereoselective separations of amphetamine derivatives with highly sulfated gamma-cyclodextrin

The highly sulfated gamma-CD (HS-gamma-CD) is a chiral selector widely used in CE for the enantioseparation of pharmaceutical compounds. This paper investigated different approaches to reduce the stereoselective analysis time of amphetamine (AT) derivatives according to the chiral selector concentration in the BGE. With high HS-gamma-CD concentration, tested analytes were separated in 3.5 min as anionic complexes with short-end injection technique in reversed polarity mode. However, this procedure presented some limitations in terms of efficiency and resolution, excessive Joule heating and poor compatibility with MS detection. With low HS-gamma-CD concentration, compounds were separated as cations. Conventional approaches to reduce CE analysis time demonstrated critical resolution between some analytes. Therefore, the use of the partial-filling technique compatible with MS detection was carried out. Under optimized conditions, the analysis time for the chiral separation of seven AT like compounds was reduced to 6 min. Moreover, sensitivity of CE-MS was sufficient for the determination of ATs in plasma following a simple liquid-liquid extraction.