Molecular shape recognition-structure correlation in a phenylalanine-based polymer-silica composite by surface-initiated atom transfer radical polymerization

A polymerizable l-phenylalanine-derived monomer (N′-octadecyl-Nα[4-(acryloyloxy)-butanoyl]-l-phenylalanineamide (3)) has been newly synthesized and characterized. We reported an advanced approach to molecular shape recognitive hybrid materials that involves immobilization of radical initiator on mesoporous silica particles (average diameter, pore size and surface area are 4 μm, 12 nm, and 300 m2 g−1, respectively) and surface-initiated atom transfer radical polymerization of monomer 3 from initiator-grafted particles. All samples were characterized by elemental analysis, thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy, solid state NMR measurements (13C CP/MAS NMR and 29Si CP/MAS NMR), differential scanning calorimetry and scanning electron microscopy. The obtained polymer-silica hybrid material was used as a stationary phase for reversed-phase high performance liquid chromatography (RP-HPLC) to investigate its molecular shape recognition ability towards polycyclic aromatic hydrocarbons (PAHs). The new composite material showed better planarity selectivity than octadecylsilane stationary phase as a conventional RP-HPLC packing material and also enhanced linearity selectivity compared with the recently reported poly(N′-octadecyl-Nα-(4-vinyl)-benzoyl-l-phenylalanineamide)-grafted silica. Such selectivity enhancement can be attributed to the combination of hydrophobic effect due to octadecyl chains and multiply carbonyl π-benzene π interaction between the amide groups of the stationary phase and delocalized electrons of PAHs.