Are Highly Stable Covalent Organic Frameworks the Key to Universal Chiral Stationary Phases for Liquid and Gas Chromatographic Separations?

Abstract

High-performance liquid chromatography (HPLC) and gas chromatography (GC) over chiral stationary phases (CSPs) represent the most popular and highly applicable technology in the field of chiral separation, but there are currently no CSPs that can be used for both liquid and gas chromatography simultaneously. We demonstrate here that two olefin-linked covalent organic frameworks (COFs) featuring chiral crown ether groups can be general CSPs for extensive separation not only in GC but also in normal-phase and reversed-phase HPLC. Both COFs have the same 2D layered porous structure but channels of different sizes and display high stability under different chemical environments including water, organic solvents, acids, and bases. Chiral crown ethers are periodically aligned within the COF channels, allowing for enantioselective recognition of guest molecules through intermolecular interactions. The COF-packed HPLC and GC columns show excellent complementarity and each affords high resolution, selectivity, and durability for the separation of a wide range of racemic compounds, including amino acids, esters, lactones, amides, alcohols, aldehydes, ketones, and drugs. The resolution performances are comparable to and the versatility is superior to those of the most widely used commercial chiral columns, showing promises for practical applications. This work thus advances COFs with high stability as potential universal CSPs for chromatography that are otherwise hard or impossible to produce.

Efficient Adsorption of Acetylene over CO2 in Bioinspired Covalent Organic Frameworks

“…Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials connected by dynamic covalent bonds with symmetric organic subunits based on reticular chemistry. − The modular nature and reticular structure of COFs provide a unique platform to incorporate various molecular building blocks and are beneficial in developing next-generation porous materials with tailor-made properties. − COFs have attracted tremendous attention in multiple applications, such as adsorption and separation, − catalysis, − and other fields because of their permanent porosity, designable skeletons, and tunable pore chemistry. − Nevertheless, from the diversity viewpoint, the field of COFs is still in its infancy, especially compared with the impressive success of metal–organic frameworks (MOFs). − The direct introduction of novel building blocks for the construction of COFs is the most straightforward approach to augment the diversity of COF structures. However, the building blocks for COFs derived from the current petrochemical approaches are still minimal and expensive due to the complex synthesis routes. − Thus, the exploration of newfangled organic monomers with low cost is urgently needed to broaden the COF family.…”

Linker Scissoring Strategy Enables Precise Shaping of Metal–Organic Frameworks for Chromatographic Separation

“…[19] The separation performance of MOF stationary phases is a highly sensitive tool to probe both the thermodynamic interactions and kinetic diffusions of analytes caused by the specific pore environments of MOFs with different shapes. [20] Then, PCN-NP-1, -2, -3,-5, PCN-NR-1, -2, -3, NU-NP-1, -2 and NU-NR-1, -2 were coated on the inner walls of capillary GC columns, resulting in eleven columns, respectively (Figure S22-S25). These capillary columns were aged at 250 °C for at least 240 min.…”

Electroactive Covalent Organic Framework Enabling Photostimulus-Responsive Devices

“…To synthesize an electroactive COF, the main building block, 2,6-diamino-N 3 ,N 3 ,N 7 ,N 7 -tetramethylbenzo[1,2-b:4,5-b′]difuran-3,7-dicarboxamide (BDF-dicarboxamide), was designed (Scheme 1). The conjugated benzodifuran core and dual carboxamide side chains form an acceptor−donor− acceptor system, which is endcapped with amine groups for imine-type dynamic covalent chemistry (Figures S1 and S2).…”