Molecular-length and chiral discriminations by beta-structural poly(L-alanine) on silica

Poly(L-alanine)-grafted porous silica (Sil-Ala22) was prepared by polymerization of N-carboxyanhydride of L-alanine initiated by 3-aminopropylated silica. Its selective interaction with aromatic guest molecules was evaluated by the retention time in liquid chromatography using the column packed with Sil-Ala22. Sil-Ala22 showed a specific selective retention with discriminating molecular shapes, such as molecular length, linearity and planarity. This selectivity can be explained by a multiple pi-pi interaction with the carbonyl groups one dimensionally-aligned on the rigid beta-form structure in the peptide main chain. Chiral separation with Sil-Ala22 was also described.