Chiral Monolithic Silica-Based HPLC Columns for Enantiomeric Separation and Determination: Functionalization of Chiral Selector and Recognition of Selector-Selectand Interaction

This review draws attention to the use of chiral monolithic silica HPLC columns for the enantiomeric separation and determination of chiral compounds. Properties and advantages of monolithic silica HPLC columns are also highlighted in comparison to conventional particle-packed, fused-core, and sub-2-µm HPLC columns. Nano-LC capillary monolithic silica columns as well as polymeric-based and hybrid-based monolithic columns are also demonstrated to show good enantioresolution abilities. Methods for introducing the chiral selector into the monolithic silica column in the form of mobile phase additive, by encapsulation and surface coating, or by covalent functionalization are described. The application of molecular modeling methods to elucidate the selector–selectand interaction is discussed. An application for enantiomeric impurity determination is also considered.

Rapid preparation and characterization of a bridged bis(β-cyclodextrin) functionalized urea–formaldehyde monolithic column by a “one-pot” approach

A new bridged-CD monolith was prepared by “one-pot” method within 30 minutes. The obtained bridged-CD monolith showed satisfactory enantioselectivity compared to a native-CD monolith.

Preparation of a hydroxypropyl-β-cyclodextrin functionalized monolithic column by one-pot sequential reaction and its application for capillary electrochromatographic enantiomer separation

In this study, a hydroxypropyl-β-cyclodextrin (HP-β-CD) functionalized monolithic capillary column was prepared by one-pot sequential reaction for the first time. The preparation of the HP-β-CD functionalized monolithic column involves two sequential reactions in one pot: (1) the ring opening reaction between HP-β-CD and glycidyl methacrylate (GMA) catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU); (2) the copolymerization of GMA-HP-β-CD, ethylene dimethacrylate (EDMA) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS). A series of monolithic columns were successfully prepared by varying the temperature of the ring opening reaction or several copolymerization parameters (the type and composition of porogenic solvents, ratio of GMA-HP-β-CD to EDMA and polymerization temperature). Then, the morphologies and structures of the resulting monolithic stationary phases were characterized by optical microscopy, scanning electron microscopy (SEM) and nitrogen adsorption analysis. Raman spectroscopy clearly indicated the successful bonding of HP-β-CD onto the monolith. When the prepared chiral stationary phase (CSP) was applied for the separation of a set of racemic compounds by capillary electrochromatography (CEC), including racemic anticholinergic drugs, β-adrenergic drugs, meptazinol and its intermediates, satisfactory separation selectivities were obtained. Additionally, the column also showed excellent separation abilities towards four flavanone glycosides epimers. Furthermore, the prepared monolithic columns exhibited satisfactory stability and reproducibilities of retention time, resolution and column efficiency. These results demonstrated the potential and usefulness of the developed one-pot sequential strategy in the preparation of other derivatized CD functionalized monolithic columns.

An insight into chiral monolithic stationary phases for enantioselective high-performance liquid chromatography applications

In this review, three main classes of chiral monolithic stationary phases, namely silica-, organic polymer-, and hybrid-based monolithic stationary phases, are covered. Their preparations, applications, and advantages compared with the conventional-packed and open-tubular capillary columns are discussed. A detailed description of the different types and techniques used for the introduction of chiral selectors into the monolithic matrices such as immobilization, functionalization, coating, encapsulation, and bonding. Special emphasis is given to the recent developments of chiral selectors in HPLC monolithic stationary phases during the past 18 years.

Methacrylate Polymer Monoliths for Separation Applications

This review summarizes the development of methacrylate-based polymer monoliths for separation science applications. An introduction to monoliths is presented, followed by the preparation methods and characteristics specific to methacrylate monoliths. Both traditional chemical based syntheses and emerging additive manufacturing methods are presented along with an analysis of the different types of functional groups, which have been utilized with methacrylate monoliths. The role of methacrylate based porous materials in separation science in industrially important chemical and biological separations are discussed, with particular attention given to the most recent developments and challenges associated with these materials. While these monoliths have been shown to be useful for a wide variety of applications, there is still scope for exerting better control over the porous architectures and chemistries obtained from the different fabrication routes. Conclusions regarding this previous work are drawn and an outlook towards future challenges and potential developments in this vibrant research area are presented. Discussed in particular are the potential of additive manufacturing for the preparation of monolithic structures with pre-defined multi-scale porous morphologies and for the optimization of surface reactive chemistries.

Synthesis of a dual pH and temperature responsive star triblock copolymer based on β-cyclodextrins for controlled intracellular doxorubicin delivery release

Well-defined dual pH and temperature responsive triblock star-shaped amphiphilic copolymers of β-CD-g-(PHEMA-b-PNIPAM-b-PDMAEMA)₃ were synthesized by the combination of RAFT polymerizations.

Synthesis of a reactive polymethacrylate capillary monolith and its use as a starting material for the preparation of a stationary phase for hydrophilic interaction chromatography

Poly(3-chloro-2-hydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(HPMA-Cl-co-EDMA) capillary monolith was proposed as a reactive starting material with tailoring flexibility for the preparation of monolithic stationary phases. The reactive capillary monolith was synthesized by free radical copolymerization of 3-chloro-2-hydroxypropyl methacrylate (HPMA-Cl) and ethylene dimethacrylate (EDMA). The mean pore size, the specific surface area and the permeability of poly(HPMA-Cl-co-EDMA) monoliths were controlled by adjusting porogen/monomer volume ratio, porogen composition and polymerization temperature. The porogen/monomer volume ratio was found as the most effective factor controlling the porous properties of poly(HPMA-Cl-co-EDMA) monolith. Triethanolamine (TEA-OH) functionalized polymethacrylate monoliths were prepared by using the reactive chloropropyl group of poly(HPMA-Cl-co-EDMA) monolith via one-pot and simple post-functionalization process. Poly(HPMA-Cl-co-EDMA) monolith reacted with TEA-OH was evaluated as a stationary phase in nano-hydrophilic interaction chromatography (nano-HILIC). Nucleotides, nucleosides and benzoic acid derivatives were satisfactorily separated with the plate heights up to 20μm. TEA-OH attached-poly(HPMA-Cl-co-EDMA) monolith showed a reproducible and stable retention behaviour in nano-HILIC runs. However, a decrease in the column performance (i.e. an increase in the plate height) was observed with the increasing retention factor. Hence "retention-dependent column efficiency" behaviour was shown for HILIC mode using the chromatographic data collected with the polymer based monolith synthesized.

One-pot synthesis of polymer monolithic column by combination of free radical polymerization and azide–alkyne cycloaddition “click” reaction and its application in capillary liquid chromatography

A facile “one-pot” method was developed for the preparation of polymer monoliths by combination of free radical polymerization and CuAAC click reaction.

Preparation of a poly(3′-azido-3′-deoxythymidine-co-propargyl methacrylate-co-pentaerythritol triacrylate) monolithic column by in situ polymerization and a click reaction for capillary liquid chromatography of small molecules and proteins

Combining free radical polymerization with a CuAAC click reaction, a facile approach was developed for the preparation of poly(AZT-co-PMA-co-PETA) monoliths.