Immobilization of two dendritic organic phases onto silica and their molecular shape recognition for polycyclic aromatic hydrocarbons, tocopherols and carotenoid isomers.

Background: Molecular shape selectivity, based on the size and shape parameters of the molecule, such as length and planarity, is a separation process that can be used for compounds with restricted shapes, such as isomers. The separation of geometric isomers is challenging because these compounds have similar physicochemical properties but differ slightly in molecular shape. The ability to separate and quantify these isomers is important in high performance liquid chromatography (HPLC), which is one of the most widely used techniques in separation science today, because the shape of the molecule has a strong influence on biological processes.
Results: We prepared symmetrical discoidal dendrimeric organomolecule gelators (G _SDM ) and o-phenylenediamine-derived low-molecular-weight dendrimeric organomolecule gelators (G1) and bonded them to silica surfaces. The dendritic organic compound-grafted silica (SiO ₂ @G _SDM and SiO ₂ @G1) was used as HPLC stationary phases for the separation of shape-restricted isomers of polycyclic aromatic hydrocarbons (PAHs), carotenoids and tocopherols. The two phases exhibit a very high molecular shape selectivity compared to the commercially available alkyl phases. There are differences in molecular shape selectivity between the two stationary phases. Changes in the chemical structure of dendritic organic compounds can alter the orientation of the molecules, as well as changes in the molecular recognition ability. It was found that SiO ₂ @G _SDM has high molecular linear selectivity for PAHs at different temperatures, even at 50 °C. The planar selectivity of SiO ₂ @G _SDM was better for triphenylene and o-terphenyl benzenes compared to SiO ₂ @G1.
Significance: This separation behavior may be attributed to the combined effect of weak interaction centers, which allowed the effective separation of bioactive and shape-restricted isomers through multiple interactions. Furthermore, SiO ₂ @G _SDM showed better separation of tocopherols and carotenoids, suggesting that the backbone and ordered structure of organic molecular gelators is an effective way to improve the shape selectivity of the molecules, whereas the molecular orientation of the functional groups influences the separation mechanism of the shape-restricted isomers.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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