Synthesis and characterization of an HPLC stationary phase based on tert-butyl-tetra-[2-aminoethoxy]calix[4]arene /

Abstract

Calixarenes are basket-shaped macromolecules comprised of phenolic units arranged in a "cup" shaped conformation. Calixarenes have become the interest in many areas of chromatography, specifically in reversed-phase HPLC. The reason calixarenes are preferred is due to their ability to form host-guest interactions with solute molecules during HPLC. When performing HPLC with a calixarene stationary phase there is a different selectivity compared to a normal C18 column. An amino derived calix[4]arene was successfully attached to a sHica-gel stationary phase. This new reversed phase material demonstrated the expected host-guest interactions as evidenced by the non-linear relationship of the log k' versus number of carbon atoms generated plots. To ensure that these were in fact host-guest interactions and not only mixed-mode retention, which also is shown by tailing peaks, comparison data of before and after endcapping was presented. The endcapping step was necessary to cover the reactive free silanol groups because of the known ability for the free silanol groups to cause mixedmode retention. The data from the calix-derived silica was compared to a commercial C18 bonded phase. This research shows that amines can easily be linked to aminopropyl silica gels using glutaraldehyde as a linker.