Lipid Membrane Analogue-Immobilized Silica Gels for Separation with Molecular Recognition

The comb-shaped polymer (ODAn) composed of a reactive terminal group and highly-orienting side-chain groups was prepared by telomerization using 3-mercaptopropyl trimethoxysilane and octadecylacrylate. The polymer was readily immobilized onto porous silica gels through a terminal reactive group. DSC indicated that the silica-supported polymer (Sil-ODAn) underwent crystal-to-isotropic phase transition on silica gels at a temperature range of 28–47°C (in the case of n = 27) in methanol. Polarity microscopic observation of the polymer showed the phase transition included a nematic liquid crystalline state. The packed column showed a remarkably higher separation factor for mixtures of planar aromatics (e.g. triphenylene and trans-stilbene) and non-planar aromatics (e.g. o-terphenyl or cis-stilbene) at room temperatures than did the conventional hydrophobic stationary phases, i.e. octadecylated silica gels. In addition, the Sil-ODAn column showed remarkable temperature dependence on both retention capacity (k') and separation factor (a). The k'-temperature and α-temperature plots showed distinct bending at temperatures around the phase transition temperature of immobilized ODAn. These results indicate that the selective retention for planar compounds is related to highly-orienting structure formed from long-chain alkyl groups. This paper discusses the molecular recognition mechanism using additional chromatographic behaviors and MOPAC calculation.