Preparation, telomerization, immobilization and application of N-alkyl l-phenylalanine-derived polymerizable organogelator for reversed-phase high-performance liquid chromatography

Silica-polymer hybrid materials (Sil-T1) have been successfully synthesized from a self-assembling polymerizable organogelator; N’-octadecyl-Nα-(4-vinyl)-benzoyl-l-phenylalanineamide (C18-l-Phe-St or 1). Telomerization of compound 1 has been done with commonly used silane coupling agent; 3-mercaptopropyltrimethoxysilane (MPS), and the telomer (T1) was grafted onto porous silica surface to prepare a stationary phase (Sil-T1) for reversed-phase high-performance liquid chromatography. The composition of the new hybrid material (Sil-T1) was determined by elemental analysis, DRIFT-IR, TGA and by 13C and 29Si (CP/MAS) NMR spectroscopic measurements. The elemental analysis measurements revealed that the surface coverage by organic phase in Sil-T1 is significantly (about 135%) lower than commercial polymeric octadecylsilyalted silica (ODS-p). In addition, the results of 13C CP/MAS NMR demonstrated that the N-alkyl moieties of the grafted polymers chain in Sil-T1 remained disordered, amorphous, and mobile represented by gauche conformational form. Furthermore, from the characterization data, the successful grafting process and unagglomerated state of the grafted particles (as observed by scanning electron microscopic, SEM measurements) prove the material to be suitable for HPLC application. The evaluation of chromatographic performance has been done from the retention studies of different size and shape PAHs and aromatic positional isomers. Significantly higher selectivity for PAHs was attributed by Sil-T1 than ODS-p regardless it has low surface coverage and lower order of alkyl chain. The enhancement of selectivity obtained by Sil-T1 can be explained by the contribution of multiple π–π interactions between the guest PAHs and the π-electrons sources (carbonyls and aromatic moieties) of the organic phase of Sil-T1.