Cinchona alkaloid-based zwitterionic chiral stationary phases applied for liquid chromatographic enantiomer separations: An overview

For the early 2000s, chromatographic methods applying chiral stationary phases (CSPs) became the most effective techniques for the resolution of chiral compounds on both analytical and preparative scales. High-performance liquid chromatography (HPLC) employing various types of chiral selectors covalently bonded to silica-based supports offers a state-of-the-art methodology for "chiral analysis." Although a large number of CSPs are available nowadays, the design and development of new "chiral columns" are still needed since it is obvious that in practice one needs a good portfolio of different columns to face the challenging task of enantiomeric resolutions. The development of the unique chiral anion, cation, and zwitterion exchangers achieved by Lindner and his partners serves as an expansion of the range of the efficiently applicable CSPs. In this context this overview chapter discusses and summarizes direct enantiomer separations of chiral acids and ampholytes applying zwitterionic ion exchangers derived from Cinchona alkaloids. Our aim is to provide comprehensive information on practical solutions with focus on the molecular recognition and methodological variables. © Springer Science+Business Media, LLC, part of Springer Nature 2019

Photosensitized oxidation of substituted phenols on aluminum phthalocyanine-intercalated organoclay

Bentonite modified with cationic surfactant, cetyltri- methylammonium bromide (CTMA), was an effective sorbent for organic pollutants in water. To make the sorbent recyclable, aluminum phthalocyanine (AlPc), a representative photosensitizer for generation of singlet oxygen, was inserted successfully into the interlamellar space of CTMA-modified bentonite. Under visible light (λ > 450 nm) irradiation, the composite catalyst exhibited a remarkable activity for degradation of the recalcitrant pollutants phenol, 4-chlorophenol, 4-nitrophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol in an aerated aqueous medium. The initial rate of the heterogeneous photoreaction was found to increase with the initial amount of the substrate sorption onto the catalyst, the kinetics following the Langmuir−Hinshelwood equation. Loading of AlPc into the organoclay led to slight expansion of the clay basal spacings from 1.82 to 2.15 nm, but the sorption capacity was decreased notably. The optimal loading of AlPc was about 0.25 wt %. The result demonstrates that the surfactant-modified bentonite not only offers a hydrophobic zone for enrichment of organic contaminants but also provides a flexible environment for destruction of the sorbed pollutants by singlet oxygen generated in situ. It was noted, however, that during four repeated experiments, both the sorption and the degradation rate of 2,4,6-trichlorophenol were gradually decreased, due to some intermediates formed and sorbed onto the catalyst surface