Differentiating π Interactions by Constructing Concave/Convex Surfaces Using a Bucky Bowl Molecule, Corannulene in Liquid Chromatography

Abstract

Convex–concave π conjugated surfaces in hemispherical bucky bowl such as corannulene (Crn) have shown increasing utility in constructing self-assembled new functional materials owing to its unique π electrons and strong dipole. Here, we investigate these specific molecular recognitions on Crn by developing new silica-monolithic capillary columns modified with Crn and evaluating their performance in the separation of different aromatic compounds by liquid chromatography (LC). We synthesized two Crn derivatives and conjugated them onto the surface of a silica monolith. The first Crn derivative was edge functionalized, which can undergo free inversion of a convex–concave surface. The second Crn derivative was synthesized by modifying the spoke of Crn, which suppresses the convex–concave inversion. Results of LC suggest that each surface showed different shape recognition based on π interaction. Furthermore, the concave surface of Crn showed strong CH−π interaction with a planar molecule, coronene, demonstrated by the shifts of the 1H NMR signals of both Crn and coronene resulting from the multiple interactions between Crn and π electrons in coronene. These results clearly demonstrated the presence of CH−π interactions at multiple points, and the role of shape recognition.

Separation of saccharides using fullerene-bonded silica monolithic columns via π interactions in liquid chromatography

“…Interestingly, the Glcs were still separated due to the increase of the glucose unit in both columns. Here, according to our previous studies, fullerenes effectively allowed π interactions, such as the CH-π and/or OH-π interactions 41,42,46 . For this comparison, the measurements were conducted for non-labelled saccharides with the applied columns and the results showed that the separation was achieved for using C60/C70 columns, but not for using C18 columns.…”

“…Previously, we successfully prepared C 60 - or C 70 -fullerene (C60, C70) bonded separation media using a silica monolithic capillary and a thermo-reactive agent, perfluorophenyl azide. Then, the specific π interactions were identified for spherical recognition 37 – 40 , CH–π interaction 41 , 42 , and halogen–π interaction 43 , 44 . According to these effective intermolecular recognitions, we anticipated that the fullerene-bonded separation media might be useful for the separation of saccharides via the CH– or OH–π interaction as well as dipole interaction.…”

Challenges and Advances in the Fabrication of Monolithic Bioseparation Materials and their Applications in Proteomics Research

“…Using various silane reagents is a straightforward way to modify silica monoliths . For example, a corannulene‐immobilized silica monolith was fabricated and applied in the analysis of aromatic analytes by cLC, indicating that the concave surface of corannulene has strong CH‐π interaction with a planar molecule (coronene) . Similarly, a silica monolithic column was modified by a self‐synthesized phosphonium‐based ionic liquid via 3‐(trimethoxysilyl)propyl methacrylate (γ‐MAPS), which was then used for separation of pyrimidine bases and nucleosides in HILIC and exhibited high efficiencies ranging from 98 000 to 174 000 plates m −1 …”

Separation of halogenated benzenes enabled by investigation of halogen–π interactions with carbon materials

“…39,40 In our previous studies, we developed novel separation media immobilized with carbon materials. [41][42][43] These media exhibited strong p interactions because of their many p electrons. Characteristics of weak interactions from aromatic rings were claried by evaluating their retention behaviors with HPLC measurements.…”