Molecular orientation of gel forming compounds and their effect on molecular-shape selectivity in liquid chromatography

Double-alkylated glutamic acid and aminoadipic acid derived gel systems (G1 and G2) have been prepared and then grafted onto silica particles. Gel-forming compounds-grafted silica particles (Sil-G1 and Sil-G2) were then applied for the liquid chromatographic separation of shape-constrained isomers of polycyclic aromatic hydrocarbons (PAHs) and tocopherols as stationary phases. G1 and G2 were analyzed before and after immobilization onto silica. Elemental analysis and thermogravimentric analysis (TGA) results showed almost the same amounts of organic phases were grafted in Sil-G1 and Sil-G2 phases. However, chromatographic results showed large differences of molecular-shape selectivity between the stationary phases. Little change in the chemical structures of the gel-forming compounds can change the molecular orientation as well as drastic change in molecular recognition in liquid chromatography. Molecular orientation of the functional groups affected the interaction mechanism for the separation of shape-constrained isomers. Comparison of the shape selectivity of Sil-G1 and Sil-G2 phases with other commercial columns is also described.