Metal-Organic Frameworks (MOFs): Classification, Synthesis, Modification, and Biomedical Applications

Metal-organic frameworks (MOFs) are a new variety of solid crystalline porous functional materials. As an extension of inorganic porous materials, it has made important progress in preparation and application. MOFs are widely used in various fields such as gas adsorption storage, drug delivery, sensing, and biological imaging due to their high specific surface area, porosity, adjustable pore size, abundant active sites, and functional modification by introducing groups. In this paper, the types of MOFs are classified, and the synthesis methods and functional modification mechanisms of MOFs materials are summarized. Finally, the application prospects and challenges of metal-organic framework materials in the biomedical field are discussed, hoping to promote their application in multidisciplinary fields.

Recent progress in the development of chiral stationary phases for high-performance liquid chromatography

Separations and analyses of chiral compounds are important in many fields, including pharmaceutical production, preparation of chemical intermediates, and biochemistry. High-performance liquid chromatography using a chiral stationary phase is regarded as one of the most valuable methods for enantiomeric separation and analysis because it is highly efficient, is broadly applicable, and has powerful separation capability. The focus for development of this method is the identification of novel chiral stationary phases with superior recognition performance and good stability. The present article reviews recent progress in the development of new chiral stationary phases for high-performance liquid chromatography between January 2018 and June 2021. These newly reported chiral stationary phases are divided into three categories: small organic molecule-based (cyclodextrin and its derivatives, macrocyclic antibiotics, cinchona alkaloids, and other low molecular weight chiral molecules), macromolecule-based (cellulose and amylose derivatives, chitin and chitosan derivatives, and synthetic helical polymers) and chiral porous material-based (chiral metal-organic frameworks, chiral covalent organic frameworks, and chiral inorganic mesoporous silicas). Each type of chiral stationary phase is discussed in detail.

Abundant defects of zirconium-organic xerogels: High anhydrous proton conductivities over a wide temperature range and formic acid impedance sensing

There exists a challenge to develop solid-state proton conductors with high conductivity not only at high working temperatures (>353 K) but at start-up temperature and even at subzero temperature (<273 K) in cold climates or high-altitude drones. Here we present a series of zirconium-organic xerogels (Zr/Fum-xerogels) with porosity and defectivity, supported by N₂ sorption, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS), exhibiting a high anhydrous proton conductivity over the temperature range of 233 to 433 K. The anhydrous conductivity of Zr/Fum-xerogel-0.04 reaches 5.68 × 10^-4 (233 K) and 2.5 × 10^-2 S cm^-1 (433 K), situating in the leading level of all anhydrous conductors reported to date. Further, the defective effects on acidities and conductive mechanisms of xerogels, especially structural changes of water clusters generated by varying temperatures are investigated by ion exchange capacity (IEC), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of NH₃ (NH₃-TPD) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The zirconium-organic xerogels with outstanding conducting performance is further implemented as impedance sensor towards formic acid.

Preparation and application of 3-(methylene-bis(1',4'-phenylene)dicarbamate-2,3-bis(3,5-dimethylphenylcarbamate)-amylose)-2-hydroxylpropoxy-propylsilyl-appended silica particles as chiral stationary phase for HPLC

3-(Methylene-bis(1',4'-phenylene) dicarbamate-2,3-bis(3,5-dimethylphenylcarbamate)-amylose)-2-hydroxylpropoxy-propylsilyl-appended silica particles (DMP-AM-HPS), a new type of 2, 3-regioselectively substituted amylose-immobilized chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC), have been prepared by treatment of 3-(2,3-dihydroxyl-propoxy)-propylsilyl silica particles with 2,3-bis(3,5-dimethylphenylcarbamate)-amylose and 4,4'-diphenylmethane diisocyanate. The chemical characterization of the bonded particles DMP-AM-HPS has been carried out by elemental analysis and Fourier transform infrared spectroscopic analysis. The chromatographic performance of the DMP-AM-HPS has been evaluated in HPLC under multi-mode conditions including normal phase, reversed phase, and polar organic mobile phase conditions. The DMP-AM-HPS phase has exhibited excellent selectivity in separating enantiomers of a wide range of chiral drug compounds. The result also suggests that unsubstituted C6 hydroxyl groups in the regioselectively substituted amylose not only have important contributions to chiral recognitions and chromatographic separations, but also allow the DMP-AM-HPS to be used as a new type of amylose-immobilized CSP under multi-mode mobile phase conditions in HPLC.

A facile process for the preparation of organic gel-assisted silica microsphere material for multi-mode liquid chromatography

Organic gel (OG) has excellent characteristics, including a large surface area, adjustable pore/channel size, and good chemical stability, and has attracted great attention in the field of materials. However, the OG packed column is difficult to pack due to the weak mechanical strength and poor monodispersity. Herein, 1-allyl-3-methyl imidazolium hexafluorophosphate-co-1-dodecanethiol ([AMIm]PF₆-co-TDDM) was prepared on the silica microsphere for chromatographic packing available in multimode liquid chromatography (LC) mode with the good mechanical properties of silica microspheres through a simple OG synthesis method. [AMIm]PF₆-co-TDDM@SiO₂ hybrid microspheres with uniform particles and narrow particle size distribution are used as stationary phases of LC. These microspheres are used in anion-exchange (IEC), reversed-phase (RP), and hydrophilic interaction (HILIC) mode for the separation of different analytes. Such microspheres can also be used for the preliminary qualitative analysis of active ingredients in actual samples in addition to organic acids, alkylbenzenes, and nucleoside bases. The [AMIm]PF₆-co-TDDM@SiO₂ chromatography packing also has good reproducibility and stability. The adhesive properties of organogels and the adsorption properties of silica gel simplify the synthesis of stationary phase materials. This simple and effective strategy for preparing [AMIm]PF₆-co-TDDM@SiO₂ composite microspheres by one-pot method can expand the application of OG as a functional additive on silica microspheres in LC.