Self-Assembly of Helical Nanofibrous Chiral Covalent Organic Frameworks.

Despite significant progress on the design and synthesis of covalent organic frameworks (COFs), precise control over microstructures of such materials remains challenging. Herein, two chiral COFs with well-defined one-handed double-helical nanofibrous morphologies were constructed via an unprecedented template-free method, capitalizing on the diastereoselective formation of aminal linkages. Detailed time-dependent experiments reveal the spontaneous transformation of initial rod-like aggregates into the double-helical microstructures. We have further demonstrated that the helical chirality and circular dichroism signal can be facilely inversed by simply adjusting the amount of acetic acid during synthesis. Moreover, by transferring chirality to achiral fluorescent molecular adsorbents, the helical COF nanostructures can effectively induce circularly polarized luminescence with the highest luminescent asymmetric factor (glum ) up to ≈0.01.

Fabrication of cellulose derivative coated spherical covalent organic frameworks as chiral stationary phases for high-performance liquid chromatographic enantioseparation.

Porous spherical silica-based chiral stationary phases (CSPs) have been commercially used in the field of chiral separation, however, the scope of their application is, to some extent, limited by the instability of silica towards mobile phase containing strong base or acid. As such, developing new matrix-based CSPs is one of the effective strategies to overcome this bottleneck in studies of chiral separation materials. In this work, we have demonstrated that stable spherical covalent organic frameworks (SCOFs) can be utilized as matrixes for the fabrication of new CSPs for the first time. Specifically, a porous imine-linked SCOF with good crystallinity, large surface area, and high chemical stability is synthesized at room temperature. Then, cellulose-tris (3,5-dimethylphenylcarbamate) (CDMPC), a typical cellulose derivative, is selected as a potential chiral selector and coated onto the robust SCOFs, giving rise to the fabrication of new CDMPC@SCOF CSPs. The as-synthesized stable SCOF-based CSPs are exploited for high-performance liquid chromatographic (HPLC) enantioseparation, showing high resolution abilities for the separation of racemic compounds such as metalaxyl, 1-(1-naphthalenyl)ethanol, epoxiconazol, trans-stilbene oxide, and so on. Moreover, the prepared SCOF-based CSPs exhibit more superior acid and base stability than those of the silica-based CSPs. Our work not only uncovers the great potential of SCOFs as matrixes for constructing novel CSPs, but also expands the application of COFs in the field of enantiomeric separation under harsh base and acid conditions.

Facile and Site-Selective Synthesis of an Amine-Functionalized Covalent Organic Framework.

Amine-functionalized covalent organic frameworks (COFs) hold great potential in diversified applications. However, the synthesis is dominated by postsynthetic modification, while the de novo synthesis allowing for direct installation of amine groups remains a formidable challenge. Herein, we develop a site-selective synthetic strategy for the facile preparation of amine-functionalized hydrazone-linked COF for the first time. A new monomer 2-aminoterephthalohydrazide (NH2-Th) bearing both amine and hydrazide functionalities is designed to react with benzene-1,3,5-tricarbaldehyde (Bta). Remarkably, the different activity of amine and hydrazide groups toward aldehyde underpin the highly site-selective synthesis of an unprecedented NH2-Th-Bta COF with abundant free amine groups anchored in the well-defined pore channels. Interestingly, NH2-Th-Bta COF exhibits dramatically enhanced iodine uptake capacity (3.58 g g-1) in comparison to that of the nonfunctionalized Th-Bta COF counterpart (0.68 g g-1), and many reported porous adsorbents, despite its low specific surface area. Moreover, NH2-Th-Bta COF possesses exceptional cycling capability and retained high iodine uptake, even after six cycles. This work not only provides a simple and straightforward route for the de novo synthesis of amine-functionalized COFs but also uncovers the great potential of amine-functionalized COFs as adsorbents in the efficient removal of radioiodine and beyond.

Reversible Interlayer Sliding and Conductivity Changes in Adaptive Tetrathiafulvalene-Based Covalent Organic Frameworks.

Ordered interlayer stacking is intrinsic in two-dimensional covalent organic frameworks (2D COFs) and has strong implications on COF's optoelectronic properties. Reversible interlayer sliding, corresponding to shearing of 2D layers along their basal plane, is an appealing dynamic control of both structures and properties, yet it remains unexplored in the 2D COF field. Herein, we demonstrate that the reversible interlayer sliding can be realized in an imine-linked tetrathiafulvalene (TTF)-based COF TTF-DMTA. The solvent treatment induces crystalline phase changes between the proposed staircase-like sql net structure and a slightly slipped eclipsed sql net structure. The solvation-induced crystallinity changes correlate well with reversible spectroscopic and electrical conductivity changes as demonstrated in oriented COF thin films. In contrast, no reversible switching is observed in a related TTF-TA COF, which differs from TTF-DMTA in terms of the absence of methoxy groups on the phenylene linkers. This work represents the first 2D COF example of which eclipsed and staircase-like aggregated states are interchangeably accessed via interlayer sliding, an uncharted structural feature that may enable applications such as chemiresistive sensors.

Semi-preparative separation of dihydromyricetin enantiomers by supercritical fluid chromatography and determination of anti-inflammatory activities.

Dihydromyricetin, extracted from Ampelopsis grossedentata, has been widely used as one of Chinese health products in recent years. However, limited chiral separation method hinders the studies of pharmacological and pharmacokinetic activity differences of (+)-dihydromyricetin, (-)-dihydromyricetin, and (±)-dihydromyricetin. Herein, we developed a supercritical fluid chromatography approach for chiral separation of dihydromyricetin. Firstly, effects of chiral stationary phase, co-solvent, and flow rate of mobile phase have been investigated in detail. The resolution of 5.11 was achieved for dihydromyricetin enantiomers on amylose tris(3, 5-dimethylphenylcarbamate)-coated chiral stationary phase with the CO2-methanol mixture (60:40, v/v). With respect to the enantiomeric purity, production rate and solvent consumption of 15 stacked injections, sample loading for semi-preparative separation of dihydromyricetin was optimized in three given equivalents set by volume overloading. Along with increase of sample loading per injection from 40 mg to 120 mg, the productivity of dihydromyricetin increased from 0.07 g (racemate)/g (chiral stationary phase) /24 h to 0.27 g (racemate) /g (chiral stationary phase)/24 h, and the consumption of methanol significantly reduced from 5.86 L/g (racemate) to 1.76 L/g (racemate). Moreover, (-)-dihydromyricetin exhibited better anti-inflammatory activity in TLR 2-related Raw 264.7 cells than (+)-dihydromyricetin and (±)-dihydromyricetin.

Enantioselectivity in endocrine disrupting effects of four cypermethrin enantiomers based on in vitro models.

Cypermethrin (CP) is a kind of chiral pesticides that has been defined as endocrine disrupting chemical. The diversity in bioactivity, toxicity, metabolism, bioaccumulation, and degradation behaviors of CP enantiomers as well as the research deficiency had made the risk assessment of CP enantiomers very complicated. Herein, four CP enantiomers were separated as target chemicals to investigate their enantioselective endocrine disrupting effects. Firstly, dual-luciferase reporter gene assays were adopted to investigate their potential endocrine disrupting effects via various receptors. The expression levels of steroid hormones related genes and hormone secretion levels in H295R cell were measured to verify the results. Results from the reporter gene assay showed that 1R-cis-αS-CP (CP11) exhibited glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and thyroid receptor (TR) antagonistic activity with the RIC20 values of 9.22 × 10-7, 3.33 × 10-7, and 4.47 × 10-7 M, respectively; 1R-trans-αS-CP (CP21) also showed androgen receptor (AR) agonist activity and estrogen receptor (ER) antagonistic activity with the REC20 and RIC20 values were 1.07 × 10-4 M and 4.78 × 10-6 M, respectively. Results of qRT-PCR and hormone measurement also showed that CP11 and CP21 could disturb the expression of steroid hormones related genes and hormone secretion accordingly. Results provided here can help to understand the enantioselective ecological and health risks of CP enantiomers comprehensively and provide constructive guidance for the safe use of chiral pesticides and the invention of green pesticides.

Lenalidomide, a blockbuster drug for the treatment of multiple myeloma: Semipreparative separation through supercritical fluid chromatography and vibrational circular dichroism spectroscopy.

Semipreparative separation of lenalidomide has been performed through supercritical fluid chromatography. In regard to retention and resolution of lenalidomide, effects of chromatographic conditions, such as chiral stationary phases, organic co-solvents, mobile phases, and column temperature, have been studied in detail. Amylose tris(3, 5-dimethylphenylcarbamate)-coated and the single-urea-bound ß-cyclodextrin chiral stationary phases exhibited good separation performances for lenalidomide in the CO2 /methanol mixture. Then, a comparative study of semipreparative separation of lenalidomide has been carried out on these two chiral stationary phases. As indicated, separation of lenalidomide on the ß-cyclodextrin-bound column was much better than the other. Under the optimized conditions, the loading per injection was 30 mg, the cycle time was 5 min, and the recoveries of two enantiomers were about 81.7 and 79.5%, respectively. Moreover, the vibrational circular dichroism spectrum of the first-eluted enantiomer in d6 -dimethylsulfoxide solution was consistent with the calculated pattern based on the S configuration, revealing that it should be (S)-(-)-lenalidomide. Briefly, this separation method through supercritical fluid chromatography might provide favorable information for rapid separation, enantioselective assessment, and absolute configurations of chiral pharmaceuticals.

Efficient preparative separation of ß-cypermethrin stereoisomers by supercritical fluid chromatography with a two-step combined strategy.

An efficient two-step method has been developed for the separation of ß-cypermethrin stereoisomers by supercritical fluid chromatography with polysaccharide chiral stationary phases. With respect to retention, selectivity, and resolution of ß-cypermethrin, the effects of chiral stationary phases, cosolvents, mobile phases, and column temperature have been studied in detail. Through a two-step separation, ß-cypermethrin was firstly separated by using a cellulose-derived chiral stationary phase to obtain two stereoisomeric pairs, and further resolved on an amylose-based chiral stationary phase to produce four enantiopure stereoisomers. The electronic circular dichroism patterns of the first- and the third-eluted isomers in methanol solution showed the mirror image of each other in the wavelength range 200∼300 nm, indicating that they were a pair of enantiomers. Moreover, the second- and the fourth-eluted isomers were also enantiomers. This proposed two-step strategy showed low solvent consumption, fast separation speed, and high-purity, which may provide an effective approach for preparative separation of compounds with multiple chiral centers and difficult-to-separate multicomponent samples.

Construction of a hydrazone-linked chiral covalent organic framework-silica composite as the stationary phase for high performance liquid chromatography.

Covalent organic frameworks (COFs), as an emerging class of crystalline porous organic polymers, have great potential for applications in chromatographic separation owning to their fascinating crystalline structures and outstanding properties. However, development of COF materials as novel stationary phases in high performance liquid chromatography (HPLC) is just in its infancy. Herein, we report the design and construction of a new hydrazone-linked chiral COF, termed BtaMth COF, from a chiral hydrazide building block (Mth) and present a one-pot synthetic method for the fabrication of BtaMth@SiO2 composite for HPLC separation of isomers. The as-synthesized BtaMth chiral COF displays good crystallinity, high porosity, as well as excellent chemical stability. Meanwhile, the fabricated HPLC column by using BtaMth@SiO2 composite as the new stationary phase exhibits high resolution performances for the separation of positional isomers including nitrotoluene and nitrochlorobenzene, as well as cis-trans isomers including beta-cypermethrin and metconazole. Additionally, some effects such as the composition of the mobile phase and column temperature for HPLC separations on the BtaMth@SiO2 packed column also have been studied in detail. The successful applications indicate the great potentials of hydrazone-linked chiral COF-silica composite as novel stationary phase for the efficient HPLC separation.

Triticonazole enantiomers: Separation by supercritical fluid chromatography and the effect of the chromatographic conditions.

Enantiomeric pairs of triticonazole have been successfully separated by supercritical fluid chromatography coupled with a tris(3,5-dimethylphenylcarbamoyl) cellulose-coated chiral stationary phase in this work. The effects of co-solvent, dissolution solvent, flow rate, backpressure, and column temperature have been studied in detail with respect to retention, selectivity, and resolution of triticonazole. As indicated, the co-solvents mostly affected the retention factors and resolution, due to the different molecular structure and polarity. In addition, the dissolution solvents, namely, chloromethanes and alcohols, have been also important for enantioseparation because of the different interaction with stationary phase. Higher flow rate and backpressure led to faster elution of the triticonazole molecules, and the change of column temperature showed slight effect on the resolution of triticonazole racemate. Moreover, a comparative separation experiment between supercritical fluid chromatography and high performance liquid chromatography revealed that chiral supercritical fluid chromatography gave the 3.5 times value of Rs /tR2 than high performance liquid chromatography, which demonstrated that supercritical fluid chromatography had much higher separation efficiency.