Top-Down Exfoliation of Ultrathin Chiral 2D Nanosheets for High-Resolution Gas Chromatography

Overview

This study addresses the development of chiral stationary phases for gas chromatography by synthesizing an ultrathin two-dimensional nanosheet material derived from a chiral ionic organic single crystal. The work aims to overcome limitations inherent in bulk crystal materials, particularly high mass transfer resistance and insufficient surface site exposure, through exfoliation of a supramolecular assembly composed of 4,4'-biphenyldisulfonic acid and a chiral ionic liquid.

Methods and approach

A chiral ionic organic single crystal designated BPDS-PBIM was synthesized via ionic self-assembly of 4,4'-biphenyldisulfonic acid and a chiral ionic liquid. The structural properties and molecular packing arrangement were characterized using single-crystal X-ray diffraction analysis, which confirmed the space group P21 with multiple chiral centers and a distinctive supramolecular environment. Two-dimensional nanosheets were subsequently prepared through top-down exfoliation of the parent crystal structure. The resulting material was evaluated as a stationary phase for high-resolution gas chromatographic separation of pharmaceutical molecules and chiral compounds with varying polarities.

Key Findings

The exfoliated 2D nanosheet stationary phase demonstrated exceptional separation performance for complex pharmaceutical substrates including ibuprofen, ketoprofen, flurbiprofen, fenoprofen, and mexiletine hydrochloride. The material exhibited high enantioselectivity across chiral compounds with different polarity profiles. Structural analysis confirmed that the supramolecular architecture maintained both stability and multiple chiral recognition sites following exfoliation.

Implications

The work establishes ionic organic single crystals as viable precursor materials for constructing high-performance chiral stationary phases. The exfoliation-derived nanosheets overcome conventional limitations associated with bulk crystal materials by reducing mass transfer resistance and maximizing surface-accessible chiral sites. This approach demonstrates structural stability coupled with robust enantioselectivity, addressing a persistent challenge in the field.