Surface molecularly imprinted amino-functionalized alginate microspheres for enantio-selective extraction of l-ascorbic acid

Chiral acidic molecularly imprinted polymer for enantio-separation of norepinephrine racemate

We are looking into how well a copolymeric material made of poly (maleic acid-co-4-vinylpyridine) cross-linked with divinylbenzene can separate L-norepinephrine (L-NEP) from (±)-NEP. The initial step in this direction was the synthesis and subsequent analysis of L-NEP-maleimide chiral derivative. A 4-vinylpyridine/divinylbenzene combination was copolymerized with the resultant chiral maleimide. After heating the polymer materials in a high-alkaline environment to breakdown the connecting imide bonds, they were acidified in an HCl solution to eliminate the incorporated L-NEP species. Fourier transform infrared spectroscopy (FTIR) and a scanning electron microscope were used to examine the imprinted L-NEP-imprinted materials. The manufactured L-NEP-imprinted materials exhibited selectivity characteristics that were over 11 times greater for L-NEP than D-norepinephrine. The highest capacity observed in Langmuir adsorption studies was 170 mg/g at a pH of 7. After optical separation using a column technique, it was determined that the enantiomeric excess levels of D-norepinephrine and L-NEP in the first feeding and subsequent recovery solutions were 95% and 81%, respectively.

Gelatin microsphere-alginate hydrogel combined system for sustained and gastric targeted delivery of 5-fluorouracil

In the current study, novel gelatin microspheres/methacrylated alginate hydrogel combined system (5-FU-GELms/Alg-MA) was developed for gastric targeted delivery of 5-fluorouracil as an anticancer agent. While water-in-oil emulsification method was used for the production of 5-FU-GELms, Alg-MA was synthesized through methacrylation reaction occurred by epoxide ring-opening mechanism. Then, 5-FU-GELms/Alg-MA hydrogel system was fabricated by the encapsulation of 5-FU-GELms into Alg-MA hydrogel network via UV-crosslinking. To evaluate applicability of fabricated 5-FU-GELms/Alg-MA as gastric targeted drug delivery vehicle, both swelling and in vitro drug release experiments were carried out at pH 1.2 medium resembling gastric fluid. Compared to drug release directly from 5-FU-GELms, 5-FU-GELms/Alg-MA hydrogel system showed more controlled and sustained drug release profile with lower amount of cumulative release starting from early stages, since hydrogel matrix created a barrier to the diffusion of 5-FU included in microspheres. Drug release kinetic results obtained by applying various kinetic models to release data showed that the mechanism of 5-FU release from 5-FU-GELms/Alg-MA hydrogel system is controlled by Fickian diffusion. All results revealed that 5-FU-GELms/Alg-MA hydrogel integrated system could be potentially utilized as gastric targeted drug carrier to enhance therapeutic efficacy and reduce systemic side effects in gastric cancer treatments for future studies.

Modulating in vitro fecal fermentation behavior of sodium alginate by Ca2+ cross-linking

Slow fermentable dietary fibers can be utilized by human gut microbiota in the distal region of the colon and thus exert a sufficient short-chain fatty acids (SCFAs) supplement in the distal region of the human colon. Alginate (Alg) based microgels are widely fabricated and used to control their digestion by digestive enzymes releasing active substances site-specifically. Herein, sodium alginate microgels with gradient calcium-ion (Ca2+) cross-linking densities were developed, restricting their degradation by gut microbiota. Alg microgels were prepared using high-speed shearing after Alg was cross-linked with 10, 40, and 60 mmol/L Ca2+, respectively (named 10-Alg, 40-Alg, and 60-Alg). The fluorescence and atomic force microscopic results showed that the 40-Alg particle has the densest structure among the three cross-linked Alg. In vitro human fecal fermentation results revealed that the Ca2+ cross-linking exerted more restricting effects than delaying effects on the fermentation of Alg, and the 40-Alg exhibited the slowest fermentation rate and the least fermentation extent, by characterizing the residual total carbohydrate content, residual monosaccharide content, pH, and total short-chain fatty acids. The 16S rRNA gene sequencing results indicated that cross-linking structures shaped a high specifical Bacteroides-type microbial community and that OTU205 (Bacteroides_xylanisolvens) highly correlated to the cross-linking density (R = 0.65, p = 0.047). In sum, Ca2+ cross-linking generated a dense and compact structure of sodium alginate that facilitated a more restricted fermentation property and specificity-targeting microbial community structure in comparison to the original sodium alginate.

Design of molecularly imprinted resin material with sulfonic acid functionalization for enantioseparation of (±)-cathine

In the current work, an enantioselective imprinting technique was used to develop a very selective adsorbent for the (+)-cathine ((+)-Cat) enantiomer. The phenolic sulfonamide produced from 2,4-dihydroxybenzenesulfonic acid (HBS) and (+)-Cat ((+)-Cat-HBS) was initially synthesized by triphenylphosphene activation and subsequently involved in condensation polymerization with resorcinol in the presence of formaldehyde under acidic conditions. Alkaline sulfonamide bond-breaking was subsequently employed to separate the (+)-Cat template from the polymer, and the resulting imprinted resin ((+)-CIP) displayed high selectivity for the (+)-Cat, with a capacity of 225 ± 2 mg/g. Studies of selectivity also showed that the (+)-Cat enantiomer was preferred over its counterpart because of the development of configurationally matching receptors. In addition, the produced resin was used for the enantioresolution of (±)-Cat racemate by column method, yielding a loading supernatant solution with an enantiomeric excess of (+)-Cat 50% and a recovery eluant solution with an excess of (-)-Cat 85%.

Enantioselective chitosan-based racemic ketoprofen imprinted polymer: Chiral recognition and resolution study

This work presented a novel racemic imprinting process employing the chiral properties of chitosan monomer. The preparation of racemic ketoprofen (RS-KTP) imprinted polymer (RS-MIP) was conducted using glutaraldehyde as a crosslinker. The nature of elution solvent affected the % desorption ratio suggesting a heterogenous nature of the formed binding sites. Good imprinting was indicated by an imprinting factor of 3.50 for S-KTP. The enantioselectivity of the RS-MIP was indicated by enantioselectivity coefficient of 2.31 and % enantiomeric excess (%ee) of 28.55%. A SPE cartridge packed with RS-MIP enabled resolution of RS-KTP using gradient elution solvent system. Scatchard plot revealed two binding sites types of different affinity towards S-KTP and density observed for the RS-MIP. The binding capacity of RS-MIP showed observed dependence on the % ee of S-KTP indicating its enantioselectivity. The success of using racemic template for the preparation of enantioselective MIP brings a new possibility to achieve enantioseparation of racemic mixtures having very expensive or unavailable pure enantiomers.

Microsphere Polymers in Molecular Imprinting: Current and Future Perspectives

Molecularly imprinted polymers (MIPs) are specific crosslinked polymers that exhibit binding sites for template molecules. MIPs have been developed in various application areas of biology and chemistry; however, MIPs have some problems, including an irregular material shape. In recent years, studies have been conducted to overcome this drawback, with the synthesis of uniform microsphere MIPs or molecularly imprinted microspheres (MIMs). The polymer microsphere is limited to a minimum size of 5 nm and a molecular weight of 10,000 Da. This review describes the methods used to produce MIMs, such as precipitation polymerisation, controlled/'Living' radical precipitation polymerisation (CRPP), Pickering emulsion polymerisation and suspension polymerisation. In addition, some green chemistry aspects and future perspectives will also be given.

Synthesis of molecularly imprinted polymer modified magnetic particles for chiral separation of tryptophan enantiomers in aqueous medium

Molecularly imprinted polymers coated magnetic particles (Fe₃O₄@MIPs) were prepared and used as adsorbents in solid phase extraction for efficient enantioseparation of racemic tryptophan (Trp) in aqueous medium. The amino-modified magnetic particles (Fe₃O₄-NH₂) were first synthesized by one-pot hydrothermal method. Then the template molecules (L-Trp) were assembled on the surface of Fe₃O₄-NH₂. Finally, Fe₃O₄@MIPs were prepared via a sol-gel method using L-Trp@Fe₃O₄-NH₂ complex as matrix, 3-aminopropyltriethoxylsilane and n-octyltriethoxysilane as functional monomers. The as-prepared Fe₃O₄@MIPs were spherical with an average diameter about 149 ± 6.0 nm. The thickness of MIPs layer was approximately 3.5 ± 2.3 nm. The adsorption isotherms data of Fe₃O₄@MIPs toward L-Trp and D-Trp were well described by the Langmuir model. The maximum adsorption capacities of Fe₃O₄@MIPs for L-Trp and D-Trp were calculated to be 17.2 ± 0.34 mg/g and 7.2 ± 0.19 mg/g, respectively. The material exhibited good selectivity toward L-Trp with imprinting factor of 5.6. Excitingly, the enantiomeric excess (ee) of Trp in supernatant after adsorption of racemic Trp by Fe₃O₄@MIPs was as high as 100%. The result suggests that the imprinted caves in Fe₃O₄@MIPs are highly matched with L-Trp molecule in space structure and spatial arrangement of active functional groups. The work also demonstrates that sol-gel technology has great potential in preparation of MIPs for chiral separation.

A phenyl glycinol appended calix[4]arene film for chiral detection of ascorbic acid on gold surface

This paper describes the synthesis of new chiral calix [4]arene derivative having (R)-2-phenylglycinol moiety (compound 6), and its chiral recognition studies for ascorbic acid (AA) enantiomers by using Quartz Crystal Microbalance (QCM). Initial experiments indicated that the outstanding selective chiral recognition (α) was observed as 2.61 for l-enantiomer of AA. The sensitivity (S) and the limit of detection (LOD) values for L-AA were calculated as 0.0226 Hz/μM and 0.63 μM, respectively. Furthermore, the sorption behavior and mechanism of AA onto compound 6 film were evaluated and the sorption data exhibited a good correlation with the Freundlich isotherm models. The maximum uptake of L-AA by the sensor was found as 5895.76 mg/g. In conclusion, chiral recognition of AA enantiomers as real-time, sensitive, selective and effective was performed by a calixarene derivative coated QCM sensor.

Electrochemical protein recognition based on macromolecular self-assembly of molecularly imprinted polymer: a new strategy to mimic antibody for label-free biosensing

A versatile strategy, based on the use of an amphiphilic copolymer as a macromonomer, was developed for the preparation of a fully synthetic MIP (molecularly imprinted polymer) sensor for protein recognition. A UV-crosslinkable copolymer poly(DMA-co-HEA-co-St) (UPDHS) was designed and synthesized to assemble with the template protein in aqueous solution, resulting in the fabrication of protein imprinted polymeric nanoparticles. Linear macromolecular chains were used to protect the structural integrity of the protein, through which a 3D structure was formed around the protein molecule to generate recognition cavities. Then the nanoparticles were immobilized on the cleaned surface of a transducer as an MIP sensing platform. The resultant MIP coating was then irradiated via ultraviolet light to ensure that the recognition cavities were stable after UV curing. After protein extraction, recognition cavities complementary to the protein molecule in shape, size and chemical functionality were formed in the platform, which could then selectively rebind to the template in a mixture of closely related compounds. The sensor exhibited satisfactory selectivity, a wide linear range from 10^-14 to 10^-9 mg mL^-1, and a comparatively lower detection limit for protein detection. This strategy offers a new and straightforward method for the synthesis of receptors for label-free and cost-efficient protein recognition. This is one of the most effective and versatile strategies for the preparation of high-performance protein recognition devices based on a fully synthetic MIP.

Chiral Stationary Phases for Liquid Chromatography: Recent Developments

The planning and development of new chiral stationary phases (CSPs) for liquid chromatography (LC) are considered as continuous and evolutionary issues since the introduction of the first CSP in 1938. The main objectives of the development strategies were to attempt the improvement of the chromatographic enantioresolution performance of the CSPs as well as enlarge their versatility and range of applications. Additionally, the transition to ultra-high-performance LC were underscored. The most recent strategies have comprised the introduction of new chiral selectors, the use of new materials as chromatographic supports or the reduction of its particle size, and the application of different synthetic approaches for preparation of CSPs. This review gathered the most recent developments associated to the different types of CSPs providing an overview of the relevant advances that are arising on LC.

Electrochemical Chiral Recognition of Tryptophan Isomers Based on Nonionic Surfactant-Assisted Molecular Imprinting Sol-Gel Silica

A new molecularly imprinted SiO₂ (MISiO₂) film on the surface of indium tin oxide (ITO) electrode was prepared by the sol-gel method and was then applied successfully in the electrochemical chiral recognition of tryptophan (Trp) isomers. Owing to the high chemical stability, excellent rigidity, and low cost, the resultant sol-gel SiO₂ is a good matrix material for molecular imprinting. Nonionic surfactant cicosaethylene glycol hexadecyl ether (Brij58) arranged directionally on the surface of the hydrophobic ITO electrode possesses a large amount of oxygen-containing functional groups and may induce the accumulation of template molecules (L-Trp) on the surface of ITO, resulting in L-MISiO₂/ITO after the removal of L-Trp templates by calcination. The characterizations of the L-MISiO₂/ITO reveal that the L-Trp templates could be successfully removed from the matrix, producing complementary cavities within the L-MISiO₂/ITO. The resultant L-MISiO₂/ITO exhibits greatly higher affinity toward L-Trp than D-Trp due to the three-point interaction mechanism, and therefore it exhibits good chiral recognition ability for the Trp isomers. In addition, the as-prepared L-MISiO₂/ITO or D-MISiO₂/ITO (D-Trp as the templates) can predict the ratio of L- and D-isomers in racemic mixture. Last, the MISiO₂ films exhibited quick binding kinetics and good recognition reproducibility.