TITLE:
Comparison of Chromatographic Performance for L-Phenylalanine-Derived Organic Phases on Silica by “Grafting from” and “Grafting to” Strategies
AUTHORS:
Mohammed Mizanur Rahman, Makoto Takafuji, Hirotaka Ihara
KEYWORDS:
Polymerizable Organogel, Atom Transfer Radical Polymerization, Grafting from, Grafting to, HPLC, Molecular Recognition
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.2 No.7,
October
31,
2011
ABSTRACT: L-phenylalanine-derived polymerizable organogel, N’-octadecyl-Nα-(4-vinyl)-benzoyl-L-phenylalanineami- de (4) has been prepared according to the procedure described elsewhere. Compound 4 was successfully polymerized by surface initiated atom transfer radical polymerization (ATRP) from the initiator grafted silica particles (sil-poly4). It was also telomerized with 3-mercaptopropyltrimethoxysilane (MPS) and the telomer (T4) was grafted on to silica (sil-T4). TGA and elemental analysis measurement revealed that higher amount of polymer can graft by ATRP process than that of “grafting to” strategy. The results of 13C CP/MAS NMR measurement showed that the N-alkyl chain of the grafted polymers for both sil-poly4 and sil-T4 remained as less ordered gauche conformational form on silica surface and no inversion to trans form was occurred until temperature is increased up to 50?C. The retention of alkylbenzene samples showed that sil-poly4 prepared by “grafting from” method yielded extremely higher retention than conventional C18 phase however, sil-T4 prepared by conventional “grafting to” method showed lower retention than C18 phase. Aspects of molecular recognition were evaluated by the retention studies of a series of polycyclic aromatic hydrocarbons (PAHs) and aromatic positional isomers. We have observed sil-T4 yielded slightly higher selectivity for PAHs than sil-poly4 regardless the fact that it has low surface coverage and lower hydrophobic interactions. The enhanced selectivity observed for sil-T4 than C18 phases and sil-poly4 can be explained by the π - π interactions between the guest PAHs and carbonyl groups present in the polymer chain. In addition the aromatic moieties of compound 4 that aggregates through π - π interactions also contribute to the separation of PAHs for both sil-poly4 and sil-T4. The minimal π - π interactions between the carbonyl groups and guest molecules for sil-poly4 probably due to the presence of long chain initiator which restrict the polymer to form order thin layer over silica surface.