Preparation of l -tryptophan imprinted microspheres based on carboxylic acid functionalized polystyrene

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.

Strategies for chiral separation: from racemate to enantiomer

Chiral separation has become a crucial topic for effectively utilizing superfluous racemates synthesized by chemical means and satisfying the growing requirements for producing enantiopure chiral compounds. However, the remarkably close physical and chemical properties of enantiomers present significant obstacles, making it necessary to develop novel enantioseparation methods. This review comprehensively summaries the latest developments in the main enantioseparation methods, including preparative-scale chromatography, enantioselective liquid-liquid extraction, crystallization-based methods for chiral separation, deracemization process coupling racemization and crystallization, porous material method and membrane resolution method, focusing on significant cases involving crystallization, deracemization and membranes. Notably, potential trends and future directions are suggested based on the state-of-art "coupling" strategy, which may greatly reinvigorate the existing individual methods and facilitate the emergence of cross-cutting ideas among researchers from different enantioseparation domains.

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.

Unlocking the potential of Escherichia coli modified magnetic particles for chiral discrimination of racemic tryptophan

Enzymes possess a highly specific affinity toward their substrates. In this study, an enzyme-based biological method was established for chiral discrimination of D/L-tryptophan (Trp). The polydopamine modified magnetic particles (PDA@Fe₃O₄) were prepared for immobilization of the genetically engineered bacterium Escherichia coli (E. coli) DH5α. The bacteria-magnetic particles conjugates (bacteria@PDA@Fe₃O₄) demonstrate excellent chiral discrimination performance toward D/L-Trp at pH 7.0 and 45 °C. The investigation for the principle exhibits that the immobilized E. coli DH5α can produce tryptophanase, and the enzyme can selectively recognize and degrade L-Trp. The Michaelis constant of tryptophanase produced by bacteria@PDA@Fe₃O₄ was measured to be 25.7 µg mL^-1. This method avoids the purification of tryptophanase and unlocks the potential of bacteria modified magnetic particles for chiral discrimination of racemic tryptophan.

Surface molecular imprinting on polystyrene resin for selective adsorption of 4-hydroxybenzoic acid

Using chloromethylated polystyrene resin, N,N-diethylaminoethyl methacrylate, and ethylene glycol dimethacrylate as support, functional monomer and cross-linker, respectively, the molecularly imprinted resin (MIR) and non-imprinted resin (NIR) were fabricated by the combination of atom transfer radical polymerization and surface imprinting technique for the selective adsorption of 4-hydroxybenzoic acid (4-HB) from aqueous solutions. The prepared adsorbents were characterized by N₂ adsorption/desorption isotherms, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The adsorption processes of the 4-HB with MIR and NIR followed pseudo-second-order kinetics, and the adsorption isotherms were appreciably described by the Langmuir model. Furthermore, the adsorption efficiencies of MIR and NIR for different compounds in single and binary solutions proved that MIR exhibited high adsorption capacity and favorable selectivity toward 4-HB over other structurally related organic compounds (i.e., benzoic acid, 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, phenol, and 2-hydroxynaphthalene). In addition, MIR could effectively remove 4-HB from a simulated effluent in a dynamic adsorption experiment. This study illustrates in-depth perspectives on the adsorption mechanisms of 4-HB onto MIR; interactions between the adsorbate and adsorbent were proposed based on the adsorption behaviours and instrumental analyses. The resulting MIR is a promising material for the interference-free adsorbent in the selective adsorption of 4-HB from mixed solutions.

Molecularly imprinted polymer functionalized silica nanoparticles for enantioseparation of racemic tryptophan in aqueous solution

A method has been developed for preparation of surface molecularly imprinted polymer functionalized silica nanoparticles (SiO₂@MPS@MIP). Firstly, the silica nanoparticles are prepared by a one-pot sol-gel method using tetraethylorthosilicate and 3-methacryloxypropyltrimethoxysilane as functional monomers. Next, the template molecule (L-Trp) is self-assembled with the functional monomer (acrylamide). Finally, SiO₂@MPS@MIP are prepared using N,N'-methylenebisacrylamide as the cross-linker. The prepared SiO₂@MPS@MIP have an average diameter of about 6.3 ± 1.2 nm. They exhibit good selectivity toward L-Trp with an imprinting factor of 6.3. The adsorption isotherm data was well described by the Langmuir model. The maximum adsorption capacities of SiO₂@MPS@MIP for L-Trp and D-Trp were calculated to be 11.1 ± 0.9 and 2.66 ± 0.16 mg g^-1, respectively. An enantiomer excess value of 100% was achieved after adsorption of racemic Trp by the material. The work suggests that SiO₂@MPS@MIP are a promising material for enantioseparation of Trp racemate in aqueous media. Graphical abstract.

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.

Preparation of lactic acid modified cellulose nanoparticles by microwave heating for preconcentration of copper from blood and food samples

In this study, nano-sized cellulose modified with lactic acid (MW-Ce-LA) was prepared with the assistant of microwave then used for the adsorption of Cu²⁺ from real samples. This modified cellulose was characterized by means of FTIR, TEM, XRD, and elemental analysis. ICP-OES was used for determination of Cu²⁺. The effect of pH, adsorption times, temperature, sorbent dose, and initial adsorbate concentration were studied to detect the ideal adsorption condition. Langmuir model proved to be the best to fit the adsorption isotherm experiments with maximum adsorption capacity of 90.3 mg g^-1 Cu²⁺. Calculated thermodynamic parameters (ΔG° and ΔH°) for adsorption of Cu²⁺ on MW-Ce-LA suggested exothermic and nonspontaneous character of the adsorption process. The reusability tests indicated regeneration of the prepared adsorbent simply using 1 mol L^-1 of HCl. The examined method was used effectively to preconcentrate Cu²⁺ from water, blood, and food samples.

Magnetic carbon dots based molecularly imprinted polymers for fluorescent detection of bovine hemoglobin

A simple and effective method was proposed to prepare an imprinted polymer layer at the surface of magnetic carbon dots with dopamine as the functional monomer for selectively and sensitively fluorescent recognizing bovine hemoglobin. The magnetic fluorescence imprinted polymers were investigated by Fourier-transform infrared spectra, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer. Under optimum conditions, the fluorescent intensity decreased linearly coincided with the concentration of bovine hemoglobin in the range of 0.05-16.0 μM with a detection limit of 17.3 nM. The magnetic fluorescence imprinted polymers were used for detecting bovine hemoglobin in real samples with the recoveries of 99.0-104.0%. These results indicated that a convenient method was proposed to develop fluorescent probes for rapid recognition and sensitive detection of trace proteins in real samples.

Enantiomer separation of propranolol and tryptophan using bovine serum albumin functionalized silica nanoparticles as adsorbents

The immobilization of popular chiral selectors on the surface of nanomaterials to prepare new chiral adsorbents for preparative chiral separation is a research hotspot in separation science nowadays.