Conformational Effect of Silica-supported Poly(octadecyl acrylate) on Molecular-Shape Selectivity of Polycyclic Aromatic Hydrocarbons in RP-HPLC

Abstract

Hydrophobized silicas, such as octadecylated silicas, are very useful as packing materials for reversed-phase high performance liquid chromatography, RP-HPLC. A simple modification of the mobile phase has expanded their applicability in analytical chemistry and separation technology. Similarly, a chemical modification of an organic phase on silica has provided versatility in the separation mode even in RP-HPLC. For these reasons, unique organic stationary phases have been created during the past decade. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Fullerene C60 bonded silica 3,4 showed higher selectivity for calixarene isomers, fullerenes C60 and C70, and polycyclic aromatic hydrocarbons (PAHs). The stationary phases containing heavy atoms, such as sulfur, chlorine and bromine resulted in longer retentions of fullerenes. 2Various porphyrin-silica stationary phases, [6][7][8] alkyl diphenyl-silicas 1 and (2,4,6-tri-tertbutylphenoxy)dimethyl-silicas 5 exhibited extraordinary shape selectivity in the separation of PAHs and fullerenes. We have reported that polymer-grafted silica exhibited selective separation in HPLC. Polymers with trimethoxysilyl terminal groups were synthesized using the telomerization method and chemically-grafted on silica particles. A number of synthetic polymers, such as poly(styrene), 10 poly(acrylonitrile), 11 poly(methylacrylate), 9,12 poly(vinylpyridine) 16 and poly(Lalanine), 14,15 were used to develop the polymer-silica hybrid materials as a stationary phase of HPLC. On the other hand, we have proposed that self-assembled systems, such as lipid aggregates, can provide a highly-ordered microenvironment leading to unique host-guest chemistry exceeding the functions of the original lipid. 17 Based on these points, we have focused on the ordered structures of poly(octadecyl acrylate), ODAn and the ODAn-grafted silica for applying to RP-HPLC.18 Through these studies, we recognize that the weak subsidiary effects due to the carbonyl groups in the polymer work as main driving force for molecular-shape selectivity toward π-electron-containing compounds and the selectivity is specifically enhanced by ordering of the long-chain alkyl moieties. [19][20][21][22] The present study is aimed at controlling the ordered state of ODAn (Fig. 1) by the polymerization condition, and evaluating its effect on the selectivity, with HPLC toward the structural isomers of terphenyls and four-ring polyaromatic hydrocarbons and with differential scanning calorimetry and NMR spectroscopy. Chemistry & Engineering, Kyushu University, Japan Poly(octadecyl acrylate) with a terminal reactive group was synthesized by radical telomerization in various solvents. The polymers were grafted onto porous silica for use in RP-HPLC, and the molecular recognition ability was investigated along with the selectivity for the structural isomers of polycyclic aromatic hydrocarbons. The mechanism of selectivity was also investigated with differential scanning calorimetry and NMR spectroscopic observations. Experimental

In-cage and out-of-cage combinations of benzylic radical pairs in the glassy and melted states of poly(alkyl methacrylate)s

“…The short and unbranched structures of the alkyl groups in PBMA and PEMA allow a close approach of ACOB 1 molecules to the ester moieties (Scheme 2A). That preference should decrease somewhat as the polymers pass from their glassy to melted states, 40 allowing the guest molecules to move more easily into regions of lower polarity (i.e., rich in n-alkyl groups). By contrast, the bulky alkyl groups of PIBMA and PCHMA hinder, for steric reasons, the approach of ACOB 1 molecules to the regions near the ester groups in both the glassy and melted states of these polymers (Scheme 2A).…”

Enhancement of Thermal Stability and Selectivity by Introducing Aminotriazine Comonomer to Poly(Octadecyl Acrylate)-Grafted Silica as Chromatography Matrix

“…A simple example of poly(octadecyl acrylate) and its copolymer systems has been reported in this regard [12]. Poly(octadecyl acrylate) copolymers grafted onto a porous silica surface exhibit an ordered-to-disordered phase transition in the octadecyl side chains, similar to lipid bilayer membrane systems [13,14], as well as extremely high selectivity for the shape recognition of geometrical isomers. In this paper, we introduce the versatility of 2-vinyl-4,6-diamino-1,3,5-triazine (AT) as a co-monomer component in a polymeric phase on silica ( Figure 1).…”

“…Separations 2018, 5, 15 2 of 7 chains, similar to lipid bilayer membrane systems [13,14], as well as extremely high selectivity for the shape recognition of geometrical isomers. In this paper, we introduce the versatility of 2-vinyl-4,6-diamino-1,3,5-triazine (AT) as a comonomer component in a polymeric phase on silica ( Figure 1).…”

Enhancement of Retentivity and Selectivity for PAHs in NP-HPLC by High-density Immobilization of Poly(4-vinylpyridine) as an Organic Phase on Silica

“…6 Even the changes of polymerizing solvents have also resulted in dramatic changes in the retention behaviors of solute on the particular stationary phase. 7 Different immobilization routes are reported for the attachment of polymers on the surface, including (i) grafting-to (g-to), (ii) grafting-from (g-from) and (iii) surface copolymerization. 8 The grafting-from synthetic approach offers the possibility to generate high densities of graft because of easy access of the reactive groups to the chain end of the growing polymer.…”