Adsorption characteristics of stevioside and rebaudioside A from aqueous solutions on 3-aminophenylboronic acid-modified poly(divinylbenzene-co-acrylic acid)

Highly efficient isolation and purification of high-purity tea saponins from industrial camellia oil production by porous polymeric adsorbents

BACKGROUND

Recovery of high-purity tea saponin (TS), a promising non-ionic surfactant with well-documented properties, is one of the major challenges to broadening its industrial applications. In this study, an innovative and sustainable strategy for the highly-efficient purification of TS was developed by using well-designed highly-porous polymeric adsorbents.

RESULTS

The prepared Pp-A with controllable macropores (~96 nm) and appropriate surface hydrophobic properties was found more favorable for achieving high adsorption efficiency towards TS/TS-micelles. Kinetic results showed the adsorption follows the pseudo-second-order model (R2  = 0.9800), and the Langmuir model is more qualified to explicate the adsorption isotherms with Qe-TS  ~ 675 mg g-1 . Thermodynamic studies revealed the monolayer adsorption of TS was an endothermic process that was conducted spontaneously. Interestingly, ethanol-driven desorption (90% v/v ethanol) of TS was rapidly (< 30 min) complete due to the possible ethanol-mediated disassembling of TS-micelles. A possible mechanism that involves the interactions between the adsorbents and TS/TS-micelles, the formation and disassembling of TS-micelles was proposed to account for the highly efficient purification of TS. Afterwards, Pp-A-based adsorption method was developed to purify TS directly from industrial camellia oil production. Through selective adsorption, pre-washing, and ethanol-driven desorption, the applied Pp-A enabled the direct isolation of high-purity TS (~96%) with a recovery ratio > 90%. Notably, Pp-A exhibited excellent operational stability and is of high potential for long-term industrial application.

CONCLUSION

Results ensured the practical feasibility of the prepared porous adsorbents in purifying TS, and the proposed methodology is a promising industrial-scale purification strategy. © 2023 Society of Chemical Industry.

Fabrication of copolymer brushes grafted superporous agarose gels: Towards the ultimate ideal particles for efficient affinity chromatography

A composite immobilized-metal affinity agarose particle was designed for the selective separation and purification of histidine-tagged proteins from complicated biological samples. The composite particle was constructed using superporous agarose particles as supporting matrix, flexible copolymer brushes as scaffolds to render higher ligand densities, and Ni²⁺-chelated iminodiacetic acids as recognition elements. Superporous agarose composite particles endow high permeability and interfering substance tolerance. The copolymer brush was prepared by surface-initiated atom transfer radical polymerization of N-isopropylacrylamide and glycidyl methacrylate, followed by iminodiacetic acids and Ni²⁺ ions. The physical and chemical properities of the composite particle were thoroughly investigated. The composite particles were shown to be able to selectively separate histidine-tagged recombinant proteins in the presence of high quantities of interfering chemicals in a model protein-binding experiment. By altering the temperature, the protein binding of the composite particles can be modulated. The superporous agarose particles supported polymer brush enables fast and efficient separation and purification of target proteins with high permeability, low backpressure, and high interfering matrix tolerance, which pave the path for bioseparation through designing and fabrication of novel agarose particles-based functional materials.

A well-defined hierarchically porous metal-organic framework and its application in separation and purification of steviol glycosides

The separation and removal of stevioside from natural product steviol glycosides to obtain high-purity rebaudioside A is of great significance for the application of steviol glycosides in food, medicine and other fields. Here, in order to explore the adsorbent pore structure suitable for the separation of stevioside and rebaudioside A, a hierarchically porous amino-functionalized metal-organic framework (HP-NH₂ -MIL-53) with an appropriate and narrow pore size distribution was prepared using a modulator induced defect-formation strategy. The results showed that the hierarchically porous structure with micropores and mesopores increased the specific surface area and exposed amino groups compared with original metal organic framework (NH₂ -MIL-53), and the maximum adsorption capacity of HP-NH₂ -MIL-53 for stevioside and rebaudioside A was 233.89 mg/g. The narrow pore size distribution close to 3.80 nm promoted the screening effect, resulting in a maximum adsorption selectivity of 4.13. This work proves that when the pore size of the adsorbent is between 1.41-3.80 nm, it has a certain pore size screening effect on stevioside and rebaudioside A, and the hierarchically porous metal-organic frameworks provide a pre-design idea of adsorbent structure for the separation of natural products with molecular weight of 800-1000 Da. This article is protected by copyright. All rights reserved.

Selective adsorption and separation of stevioside and rebaudioside A by a metal-organic framework with boronic acid

The boronic acid functionalization metal-organic frameworks (MOFs), as unique boronate affinity adsorbents, have desired specific molecular affinity for the separation and enrichment of cis-diol-compounds. Herein, the boronic acid functionalized Zn-based MOF adsorbent (MOF-BA) was synthesized through a simple one-step microwave method and used for the recognition and isolation of steviol glycosides (SGs). This MOF-BA exhibits the same spherical structure and isostructure with the parent framework composed only of the primitive ligand as verified by SEM and XRD characterization. It was confirmed that changing the ratio of ligands could achieve the adjustability of the boron content in the framework. At the same time, the MOF-BA-1.0 showed a suitable pore size (4.69 nm), and the presence of boric acid functional groups showed favorable selectivity for stevioside (STV). The static adsorption results showed that adsorption performances of rebaudioside A (RA) and STV from crude sugar solution (5.0 mg mL−1, pH 8) on MOF-BA-1.0 were investigated at 303 K for 15 h. The adsorption capacities for STV and RA were 42.93 mg g−1 and 22.96 mg g−1, respectively, and the adsorption selectivity (αSTV/RA) reached 4.35. The adsorption isotherm and kinetic data of MOF-BA-1.0 for RA and STV obeyed the Langmuir isotherm model and pseudo second order kinetic model, respectively. The study demonstrated that MOF-BA-1.0 adsorbent could be used as a potential adsorbent to purify the active ingredients of stevia and obtain a high concentration of RA products.

Kinetics and thermodynamics of rebaudioside A adsorption on a strongly acidic cation exchange resin

To explain the mechanism underlying the adsorption of stevia's polar component rebaudioside A in hydrophilic interaction liquid chromatography mode, the characteristics of rebaudioside A adsorption on various resins in an organic-solvent-rich system were studied. Among the tested resins, the strongly acidic cation resin FPC11 showed the best adsorption behavior for rebaudioside A. The factors affecting the adsorption kinetics of the resin for rebaudioside A are discussed. The results showed that the pseudo-second-order reaction model and intra-particle diffusion model best described the adsorption kinetics of rebaudioside A on the resin. The adsorption rate was controlled by physical sorption, mainly via electron sharing or electron transfer between the adsorbent and the adsorbate. The adsorption process with multiple stages involved weak initial adsorption behavior. Thermodynamic studies showed that the adsorption of rebaudioside A on the resin was not an ideal monolayer adsorption, but mutual adsorption effects between the adsorbates. The adsorption was a spontaneous, entropy-increasing endothermic process. The synergistic effect of hydrogen bonding and ion-dipole was a possible driving force.

Phenylboronic Acid Functionalized Adsorbents for Selective and Reversible Adsorption of Lactulose from Syrup Mixtures

Boronate affinity materials have been widely used for enrichment of cis-diol molecules. In this work, phenylboronic acid functionalized adsorbents were prepared via a simple and efficient procedure grafting phenylboronic acid groups onto amino macroporous resins. Elemental analysis has confirmed the successful functionalization of AR-1M and AR-2M with approximately 2.17% and 0.73% weight percentage of boron. Comparatively, AR-1M possessed higher lactulose adsorption capacity ( q_e-Lu, 84.78 ± 0.95 mg/g dry resin) under neutral conditions (pH = 7), while the introduced glutaraldehyde spacer arms on AR-2M resulted in excellent adsorption selectivity (α ≈ 23), high adsorption efficiency (π ≈ 22%), and fast adsorption/desorption rate. The purity of lactulose (Pu_D^Lu) through pH-driven adsorption (pH 7-8) and desorption (pH 1.5) can be effectively improved depending on the ratio of lactulose to lactose. When lactulose/lactose ≥ 1:1, Pu_D^Lu ≈ 95% was achieved. No significant drop in q_e-Lu (>90%) was observed after ten-consecutive repeats. Results demonstrated that the newly developed method may achieve satisfactory performance in lactulose purification.