Preparation of an aminophenylboronic acid and N-isopropyl acrylamide copolymer functionalized stationary phase for mixed-mode chromatography

In Situ Preparation of Star-Shaped Protein-"Smart" Polymer Conjugates with pH and Thermo-Dual Responsibility for Bacterial Separation

To achieve effective separation and enrichment of bacteria, a novel synthetic scheme was developed to synthesize star-style boronate-functionalized copolymers with excellent hydrophilicity and temperature and pH responsiveness. A hydrophilic copolymer brush was synthesized by combining surface-initiated atom-transfer radical polymerization with amide reaction using bovine serum albumin as the core. The copolymer brush was further modified by introducing and immobilizing fluorophenylboronic acids through an amide reaction, resulting in the formation of boronate affinity material BSA@poly(NIPAm-co-AGE)@DFFPBA. The morphology and organic content of BSA@poly(NIPAm-co-AGE)@DFFPBA were systematically characterized. The BSA-derived composites demonstrated a strong binding capacity to both Gram-positive and Gram-negative bacteria. The binding capabilities of the affinity composite to Staphylococcus aureus and Salmonella spp. were 195.8 × 1010 CFU/g and 79.2 × 1010 CFU/g, respectively, which indicates that the novel composite exhibits a high binding capability to bacteria and shows a particularly more significant binding capacity toward Gram-positive bacteria. The bacterial binding of BSA@poly(NIPAm-co-AGE)@DFFPBA can be effectively altered by adjusting the pH and temperature. This study demonstrated that the star-shaped affinity composite had the potential to serve as an affinity material for the rapid separation and enrichment of bacteria in complex samples.

Enrichment of sialic acid-containing casein glycomacropeptide in protein hydrolysates using phenylboronic acid-functionalized mesoporous silica nanoparticles

Glycomacropeptide (GMP) is a bioactive peptide of high value, rich in glycosylation sites and with physiological and dietary therapeutic value. The enrichment and detection of GMP facilitates the accurate quantification and the identification of adulteration of GMP in food products. In GMP, sialic acid is an abundant glycosyl group and is mainly located at the end of the sugar chain. Here, we propose a novel GMP enrichment strategy based on the affinity of sialic acid for phenylboronic acid groups that shift with environmental pH. As an enrichment material, mesoporous silica nanoparticles were progressively modified with aminopropyl and phenylboronic acid groups. The developed material showed excellent selectivity for sialic acid in the presence of galactose and fucose as interferents. The adsorption behavior of sialic acid-containing GMP fits the Langmuir adsorption model, offering a recovery of 71.72% (in terms of sialic acid content) and a GMP relative purity of 0.957. Results from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography confirm that the enriched GMP contains almost no other unexpected proteins and peptides, indicating that the developed strategy holds promise for purifying GMP in various dairy systems.

Facile Capture of Recombinant Human Erythropoietin on Mesoporous Affinity Hydrogel Matrix Functionalized with Azoboronate

Boronate affinity ligands (BALs) have gained attention for glycoproteins capture and recognition due to their unique affinity interaction with glycans. In this paper, the effect of azo immobilization of phenylboronic acid on the reduction of adsorption pH of a recombinant glycoprotein (i.e., rhEPO) on hydrogel microparticles was investigated. To evaluate the influence of intraparticle porosity on protein adsorption, microporous (MicroBead) and mesoporous (MesoBead) agarose beads carrying two levels of amine densities were functionalized with azoboronate ligand. Affinity adsorption of the glycoprotein during static and dynamic adsorptions at relatively low pHs of 8 and 7 was studied. Results revealed successful adsorption of rhEPO at pH = 8 through affinity capture of glycans by azoboronate ligands. Increased amine density provided 1.1 and 1.5 times higher static adsorption capacities and dynamic performance efficiencies, respectively. In addition, adsorption capacities and initial adsorption rates of rhEPO on MesoBeads were respectively 1.4 and 2.5-2.8 times of MicroBeads. Also, at pH = 8, MesoBeads recorded higher dynamic recoveries (59 and 91%) compared with microporous ones (46 and 69%) since mesoporosity facilitates intraparticle mass transfer. Reduction of binding pH from 8 to 7 resulted in a sharp decrease in dynamic recovery (14%), indicating the appropriate binding pH of azoPBA to be above 7. The azoboronate affinity ligand is a leading candidate for capturing glycoproteins at relatively low pH. Also, mesoporous microparticles are appropriate tools in more efficient medium-sized protein binding applications.

Dendritic organic molecular gel coating with molecular shape selectivity and its application in selective separation by liquid chromatography

Dendritic organic molecular gels are a promising class of three-dimensional network compounds. Here, we have synthesized a new type of dendritic organic molecular gel stationary phase (SiO₂-G3) by using benzyl alcohol as raw material and dimethyl 5-hydroxyisophthalate as growth unit to synthesize a third-generation organic molecular gel G3, which grafted onto the silica surface by cyanogen chloride (CC). The developed stationary phase not only exhibits high molecular shape selectivity but also has a RPLC/HILIC/IEC mixed-mode characteristic for HPLC due to the ordered structure, the multiple strong π-π stacking interactions and the introduction of a hydrophilic triazine fraction during the grafting process. Compared with a commercial C₁₈ column, the developed column exhibited flexible selectivity, enhanced separation performance and excellent separation of monosubstituted benzene, polycyclic aromatic hydrocarbons (PAHs), positional isomers, nucleosides and nucleobases, benzoic acid and aniline compounds. In addition, the new column provided baseline separation of polycyclic aromatic hydrocarbon contaminants in Yellow River water, verifying its potential for application in the analysis of real samples.

PNIPAM/Hexakis as a thermosensitive drug delivery system for biomedical and pharmaceutical applications

Many technologies ranging from drug delivery approaches to tissue engineering purposes are beginning to benefit from the unique ability of “smart polymers.” As a special case, thermo-sensitive hydrogels have great potential, e.g. in actuators, microfluidics, sensors, or drug delivery systems. Here, the loading of Doxorubicin (DOX) with novel thermo-sensitive polymer N-isopropyl acrylamide (PNIPAM) and its copolymers are investigated in order to increase the Doxorubicin’s drug efficacy on the targeted tumor site. Therefore, a rational design accurate based on the use of classical molecular dynamics (MD) and well-tempered metadynamics simulations allows for predicting and understanding the behavior of thermo-responsive polymers in the loading of DOX on Hexakis nano-channel at 298 and 320 K. Furthermore, this work investigates the efficacy of this drug carrier for the release of DOX in response to stimuli like variations in temperature and changes in the physiological pH. The study concludes that the Hexakis–polymer composite is capable of adsorbing the DOX at neutral pH and by increasing the temperature of the simulated systems from 298 to 320 K, the strength of intermolecular attraction decreases. In addition, the obtained results of MD simulation revealed that the dominant interaction between DOX and Hexakis in the DOX/polymer/Hexakis systems is the Lennard–Jones (LJ) term due to the formation of strong π–π interaction between the adsorbate and substrate surface. Obtained results show that a higher aggregation of DMA chains around the Hexakis and the formation of stronger bonds with DOX. The results of the well-tempered metadynamics simulations revealed that the order of insertion of drug and polymer into the system is a determining factor on the fate of the adsorption/desorption process. Overall, our results explain the temperature-dependent behavior of the PNIPAM polymers and the suitability of the polymer–Hexakis carrier for Doxorubicin delivery.

Amphipathic carbon quantum dots-functionalized silica stationary phase for reversed phase/hydrophilic interaction chromatography

Carbon quantum dots (CQDs) are considered as good chromatographic separation materials. However, due to the hydrophily of the synthesized CQDs, their applications in HPLC are limited to HILIC for separating strong polar compounds only. In this work, a novel amphipathic CQDs with both hydrophobicity and hydrophily is developed as mixed-mode stationary phase for RPLC/HILIC. To give CQDs certain hydrophobicity, 1,8-diaminooctane is chosen as one of the carbon sources for introducing alkyl chain into CQDs. The amphipathic CQDs modified silica (CQDs/SiO₂) stationary phase has typical characteristic of RPLC/HILIC. Both hydrophobic and hydrophilic compounds including alkylbenzenes, polycyclic aromatic hydrocarbons, nucleosides and bases, amino acids, β-adrenoceptor blockers and agonists, sulfonamides, antibiotics and alkaloids obtain satisfactory separation on this CQDs/SiO₂ column. 14 nucleosides and bases commonly existing in living organisms achieve good separation on this amphipathic CQDs/SiO₂ column within 25 min and the resolutions reach 1.33-13.83 with an average column efficiency of 18,800. The retention mechanism of this novel CQDs/SiO₂ column is investigated by linear solvation energy relationship model. It is found that hydrophobic interaction, π-π stacking, hydrogen-bonding and electrostatic interactions are main retention interactions under RPLC mode. This work provides a new approach for synthesis of amphipathic CQDs. Also, it indicates that amphipathic CQDs with versatile functional properties have great prospect in separation science.

Benzoic acid-modified monolithic column for separation of hydrophilic compounds by capillary electrochromatography with high content of water in mobile phase

Hydrophilic column combined with mobile phase containing high content of water is a green method for the separation of polar compounds, but there are few related studies, and the separation efficiency and performance of existing columns still needs to be improved. In this work, a novel monolithic column for separation of hydrophilic compounds under both high water content and HILIC condition, was prepared by in-situ polymerization using 4-vinylbenzoic acid (VBA) and 1-(Acryloyloxy)-3-(methacryloyloxy)-2-propanol (AMAP) as functional monomers. The poly(VBA-co-AMAP) monolithic column showed good separation performance towards various polar compounds under different chromatographic conditions based on the π-interaction, hydrophobic and hydrogen bonding interactions provided by 4-vinylbenzoic acid functional monomer. The highest column efficiency for adenine was over 2.15 × 10⁵ plates m^-1 (theoretical plate, N). In addition, the monolith showed good stability and reproducibility, the relative standard deviations (RSDs) of retention times within days (n = 5), between days (n = 5), between columns (n = 3) and between batches (n = 3) were 0.47-1.13%, 1.20-2.68%, 0.59-1.78% and 1.54-3.60%, respectively. This novel type of monolith has great application potential in the separation of hydrophilic compounds.

Modern Trends in Mixed-Mode Liquid Chromatography (LC) Columns

Commercialization of columns that provide multiple modes of chromatographic separations have recently been on the rise. For example, combinations of retention modes, such as ion-exchange and reversed-phase, often enable the separation of complex mixtures of analytes not possible using single-mode columns. In this work, recent trends in what is often referred to as “mixed-mode” phase are investigated. Particular attention is paid to recent fundamental research, stationary phase development and design, and areas of application.

Recent trends in sorbents for bioaffinity chromatography

Isolation or enrichment of biological molecules from complex biological samples is mostly a prerequisite in proteomics, genomics, and glycomics. Different techniques have been used to advance the efficiency of the purification of biological molecules. Bioaffinity chromatography is one of the most powerful technique that plays an important role in the isolation of target biological molecules by the specific interactions with ligands that are immobilized on different support materials. This review examines the recent developments in bioaffinity chromatography particularly over the past 5 years in the literature. Also properties of supports, immobilization techniques, types of binding agents, and methods used in bioaffinity chromatography applications are summarized.