p-tert-Butylcalix[8]arene-bonded silica monoliths for liquid chromatography.
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Monolithic silica columns have inspired considerable research interests in the separation science because of their unique properties in permeability, mass transfer, efficiency and throughput. In this paper, a chemically p-tert-butylcalix[8]arene-bonded silica monolith was prepared as the promising candidate for versatile LC separations. Micrometer-sized macropores and nanometer-sized mesopores in this derivatized silica monolith reduce the diffusion path length and provide both low backpressure and high column efficiencies, leading to high-speed and high-throughput separations. Since p-tert-butylcalix[8]arene possesses a pi-donors cavity composed of benzene rings while polycyclic aromatic hydrocarbons, anthraquinones, phenol regio isomers and fullerenes are pi-systems with appreciable electron affinity, they may have a chance to get involved in forming host-guest inclusion complexes through non-covalent interactions, e.g. hydrophobic and pi-pi interactions. Compared with RP-18e, the prepared calixarene-bonded monolith exhibited better selectivity to molecules which contains more pi-electrons and more condensed cyclic moieties. The column efficiency was about 22,000 plates/m. The calixarene-bonded monolith also showed its good performances in separation of fullerenes and dihydropyridines, indicating a promising approach for purification of fullerenes with high purity from the carbon soot.