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Modelowanie polimeryzacji stopniowej monomeru AB2. Porównanie metod statystycznej i kinetycznej

Skóra Elżbieta, Galina Henryk

Chemical Technology & Biotechnology

2017

Vol. 1

44--51

Wykorzystano dwie metody modelowania procesów polimeryzacji: metodę statystyczną i kinetyczną do obliczenia parametrów molekularnych: liczbowo- i wagowo średniego stopnia polimeryzacji polimerów hiperrozgałęzionych, powstających w polimeryzacji stopniowej symetrycznych monomerów typu AB2. Obliczenia prowadzono dla monomeru, który reagował z efektem podstawienia, tj. po przereagowaniu „pierwszej” grupy B w jednostce monomerycznej, reaktywność „drugiej” grupy ulegała zmianie. Inaczej, niż w przypadku modelowania polimeryzacji innych monomerów o funkcyjności większej, niż 2, wagowo średnie stopni polimeryzacji obliczone dwiema alternatywnymi metodami nie różniły się od siebie, niezależnie od wielkości efekty podstawienia.

Two methods of modeling polymerization processes: statistical and kinetic ones were used to calculate molecular parameters: number-and weight average polymerization degree of hyperbranched polymers, formed in the step polymerization of symmetric monomer of AB2 type. Calculations were carried out for monomers reacting with the first shell substitution effect, i.e. after the “first” group B has reacted, the reactivity of the “second” group changed. Unlike for the results of modeling polymerization systems involving other monomers of functionality higher than 2, the weight average polymerization degrees calculated using the two methods were not different, irrespectively of the magnitude of substitution effect.

Spektrometria mas w rozróżnianiu związków chiralnych

Drabik E.

Wiadomości Chemiczne

2011

[Z] 65, 7-8

609-649

The phenomenon of optical activity was discovered by Louis Pasteur in 1848. Since this time, chirality of organic compounds observed in biological systems has became a central theme in scientific research. Synthesis and quantitation of enantiomerically pure compounds is important for a wide range of applications. Chirally pure compounds are required not only by pharmacology, but they are also of interest in cosmetic and food industry and many other applications. Similarity of enantiomers in their chemical and physical properties, except for optical rotation, makes their separation and detection very difficult. Until now, many methods have been used for the enantioselective discrimination of organic compounds, including nuclear magnetic resonance spectroscopy (NMR), circular dichroism (CD), capillary electrophoresis (CE) and chromatography (GC, HPLC), where an interference of a solvent cannot be excluded. Recent studies have shown that mass spectrometry (MS) is an alternative approach to traditional method for chiral recognition and determination of enantiomeric composition. Although, mass spectrometry has been considered as insensitive to chirality because enantiomers have the same mass and show identical mass spectra, it is now accepted as important tool for differentiating of enantiomeric compounds through their interactions with chiral reference molecules (Fig. 1). The ability to transfer diastereomeric non-covalent complexes between chiral selectors and analyte enantiomers, which differ in stability, into the gas-phase and measure such differences trough mass spectrometric ion abundances, has appeared with development of soft ionization techniques such electrospray ionization (ESI), fast atom bombardment (FAB) and matrix-assisted laser desorption/ionization (MALDI). Mass spectrometry-based methods for chiral recognition and quantitative determination of enantiomeric purity are attractive due to their speed, high sensitivity, low sample consumption, tolerance to impurities and ability to probe the analyte in a solvent free environment. Currently, there are four well-defined approaches for determining a measure of enantiomer discrimination, using either single-stage or tandem mass spectrometry. They can be classified into the following categories: (1) measurement of the relative abundance of diastereomeric complexes between chiral reference compound and the enantiomers (usually one isotopically labeled [10]), (2) enantioselective ion/molecule reaction between diastereomeric complexes and chiral or achiral reactants [11], (3) kinetic method [12] and (4) collision-induced dissociation (CID) of diastereomeric adducts in a tandem mass spectrometry (MS/MS) experiment [61, 62]. Over the past decade, new approaches to chiral separation and analysis of enantiomers have been introduced, where molecules are separated based on their mobility (ion mobility spectrometry) [66].