Sulfonic Functionalized Polydopamine Coatings with pH-Independent Surface Charge for Optimizing Capillary Electrophoretic Separations.

Enhancing the pH-independence and controlling the magnitude of electroosmotic flow (EOF) are critical for highly efficient and reproducible capillary electrophoresis (CE) separations. Herein, we present a novel capillary modification method utilizing sulfonated periodate-induced polydopamine (SPD) coating to achieve pH-independent and highly reproducible cathodic EOF in CE. The SPD-coated capillaries were obtained through post-sulfonation treatment of periodate-induced PDA (PDA-SP) coatings adhered on the capillary inner surface. The successful immobilization of the SPD coating and the substantial grafting of sulfonic acid groups were confirmed by a series of characterization techniques. The excellent capability of PDA-SP@capillary in masking silanol groups and maintaining a highly robust EOF mobility was verified. Additionally, the parameters of sulfonation affecting the EOF mobilities were thoroughly examined. The obtained optimum SPD-coated column offered the anticipated highly pH-independent and high-strength cathodic EOF, which is essential for enhancing the CE separation performance and improving analysis efficiency. Consequently, the developed SPD-coated capillaries enabled successful high-efficiency separation of aromatic acids and nucleosides and rapid cyclodextrin-based chiral analysis of racemic drugs. Moreover, the SPD-coated columns exhibited a long lifetime and demonstrated good intra-day, inter-day, and column-to-column repeatability.

Homomesoporous Metal-Organic Framework for High-Performance Electrochromatographic Separation.

Metal-organic frameworks (MOFs) have exhibited tremendous potential in the area of separation science. However, most of the developed MOF-based stationary phases contained only microporous structures and suffer from limited separation performance. Herein, homomesoporous MOFs with excellent mass transfer capability and strong thermodynamic interactions are first explored as the novel stationary phase for high-performance capillary electrochromatographic separations. As a proof of concept, noninterpenetrated mesoMOF-1 with uniform mesopore sizes (22.5 × 26.1 Å) and good stability was facilely grown on the inner surface of capillaries and applied as a homomesoporous MOF coating-based stationary phase for high-efficiency electrochromatographic separation. Seven types of analytes with different molecular dimensions were all baseline separated on a mesoMOF-1 coated column with high theoretical plate numbers and excellent repeatability, exhibiting significantly improved separation selectivity and column efficiency in comparison to a microporous HKUST-1 coated column. The maximum column efficiencies of the mesoMOF-1 coated column for substituted benzenes and halobenzenes reached up to 1.4 × 105 plates/m, and its mass loadability was also much higher than that of the HKUST-1 coated column. In addition, based on the analysis of adsorption kinetics and chromatographic retention behaviors, the interaction and retention mechanisms of different molecular-weight analytes on mesoMOF-1 coated stationary phases were systematically explored and disclosed in detail. These results indicate that the homomesoporous MOF-based stationary phase can effectively balance the kinetic diffusion (mass transfer capability) and thermodynamic interactions (the strength of adsorption interaction), having great potential for high-performance chromatographic separation.

[Research progress on the construction and applications of metal-organic frameworks in chromatographic stationary phases].

Metal-organic frameworks (MOFs) are a class of porous crystalline materials composed of metal centers or clusters assembled with organic ligands. These materials possess excellent properties, such as large surface areas, high porosities, uniform pore sizes, and diverse structures. Thus, MOFs have been widely applied in various fields, including catalysis, adsorption, sensing, sample pretreatment, and chromatographic separation. The applications of MOFs as stationary phases for chromatographic separation and analysis have attracted considerable attention from the research community in recent years. Compared with traditional chromatographic stationary phases, such as mesoporous silica, nanoparticles, and porous layers, MOFs possess flexible and tunable pore sizes and structures, thereby enabling precise control over their intermolecular interactions. Furthermore, the wide range of functional ligands and topologies of MOFs could potentially facilitate the separation and analysis of complex samples. These unique advantages render MOFs highly suitable for constructing novel chromatographic stationary phases.This article focuses primarily on the construction methods of MOFs as chromatographic stationary phases, and provides an overview of the latest research advancements in their applications in several chromatographic separation techniques such as high performance liquid chromatography (HPLC), gas chromatography (GC), and capillary electrochromatography (CEC). The existing methods for the preparation and construction of MOFs-based chromatographic stationary phases are classified and evaluated. The construction methods for MOFs as stationary phases for HPLC mainly include filling, precursor-doped polymerization, and post-modification. The construction methods for MOFs as stationary phases for GC predominantly include in situ growth, static coating, and dynamic coating. The stationary phases for CEC can be categorized into packed columns, monolithic columns, and open-tubular columns. Compared with monolithic and packed columns, open-tubular CEC (OT-CEC) offers numerous advantages, including a more flexible and convenient preparation method, enhanced compatibility with various separation media, and higher separation efficiency. Consequently, OT-CEC has emerged as an important method for investigating the preparation of stationary phases for CEC. Several methods such as physical adsorption, covalent attachment, and electrostatic interactions have been developed for the preparation and modification of MOFs-based CEC stationary phases, and extensive studies have been conducted to optimize the performance and applications of MOFs in OT-CEC. However, the existing methods for constructing MOFs-based chromatographic stationary phases present certain limitations. Therefore, the selection of the appropriate MOFs, optimization of their preparation methods, and examination of their performance in different separation modes have become the focus of intensive research.This review also summarizes the different analytical targets (e. g., chiral small molecules, biomacromolecules, and nonchiral molecules) and corresponding separation effects achieved using various MOFs-based chromatographic stationary phases. Finally, future studies focusing on the development of MOFs as chromatographic separation media are discussed. Overall, this review provides a valuable reference for the rational construction and practical applications of advanced MOFs-based chromatographic stationary phases.

Various Fractions of Alcoholic Extracts from Dendrobium nobile Functionalized Antioxidation and Antiaging in D-Galactose-Induced Aging Mice.

BACKGROUND: The theory of free radical oxidative stress (ROS) is one of the leading theories of ageing, and antioxidants play an important role in antiaging. Dendrobium has always been popular as a natural antioxidant. METHODS: This study investigated the effects of various polarity fractions of ethanol extracts from Dendrobium nobile Lindl. (D. nobile) on D-galactose-induced aging mice. D. nobile stems were extracted by ethanol to form the crude extract (EA), which was sequentially extracted by trichloromethane, ethyl acetate, and n-butanol to yield the secondary extracts, named TCM, EAC, and NBA, respectively. EA, TCM, EAC and NBA were intragastrically administered at a dose of 200 mg/kg b.w. to the aging mice induced by D-galactose for 8 weeks. RESULTS: Compared with the aging control group (AC), D. nobile extracts reduced body weight and lipid accumulation and enhanced endurance and immunity by increasing the index of the spleens and thymus. Meanwhile, D. nobile extracts showed antioxidant properties by lowering Malondialdehyde (MDA) levels and increasing the activities of superoxide dismutase (SOD), catalase (CAT), and Glutathione peroxidase (GSH-Px) in the skin, blood, liver, and brain. Furthermore, D. nobile extracts had a good protective effect on the cell structure and function against lesions of the skin, liver, brain, kidney, and ovary of aging mice. In particular, EA and EAC had better antioxidant and antiaging effects, suggesting that the most effective components were flavonoids and polyphenols that existed in EAC. Both EA and EAC downregulated the expression of aging-related genes such as Il1a, Il1b, Il1rn, Ccl3, Ccl4, Fos and Gck in the brain at the transcriptome level. Both EA and EAC reversed the increase in the Firmicutes/Bacteroidota ratio in aging mice, increased the abundance of probiotic bacteria Lactobacillus and Muribaculum, and decreased the abundance of pathogenic bacteria such as Staphylococcus, Corynebacterium and Brevibacterium. CONCLUSIONS: The EA and EAC extracts of D. nobile have better effects on immunity improvement, antioxidation and antiaging by remodelling the intestinal microecosystem and downregulating the expression of age-promoting genes in the brain. D. nobile, especially EA and EAC extracts, could be used as an antiaging drug or functional food.

High-Efficiency and Versatile Approach To Fabricate Diverse Metal-Organic Framework Coatings on a Support Surface as Stationary Phases for Electrochromatographic Separation.

A large number of metal-organic frameworks (MOFs) have exhibited increasingly wide utilization in the field of chromatographic separation owing to their intrinsic fascinating properties. However, the previous studies on supported MOF coating-based chromatographic separation focused only on the synthesis and chromatographic performance of a certain kind of supported MOF coatings as stationary phases using the multiple-step, complicated, and time-consuming modification methods, which severely impeded the widespread application of MOFs in separation science. Herein, a high-efficiency and versatile methodology toward diverse supported MOF coating-based stationary phases to achieve high-efficiency chromatographic separation was first reported based on the immobilized cysteine (Cys)-triggered in situ growth (ICISG) strategy. As a proof-of-concept demonstration, four types of MOF crystals consisting of different ligands and metal ions (Zn2+, Cu2+, Fe3+, and Zr4+) were conveniently and firmly grown on a Cys-modified capillary using the ICISG strategy and employed as the functional stationary phase for electrochromatographic separation. A broad variety of neutral, acidic, and basic compounds were all separated in a highly efficient manner on the developed four MOF-coated columns. The maximum theoretical plate number for Cys-MIL-100(Fe)@capillary was close to 1.0 × 105 plates/m, and the intraday, interday, and column-to-column repeatabilities of retention times for the four MOF-modified columns were all less than 5.25%. More interestingly, the diversified separation performance of the developed MOF-coated columns indicated that the preparation strategy and the skeletal structure of the MOF coating-based stationary phases have a significant influence on the electrochromatographic separation performance and column capacity. Benefiting from the strong universality and high applicability of the developed ICISG strategy, the present study provides an effective route to facilitate the design and fabrication of novel functional MOF-based chromatographic stationary phases.