Molecularly imprinted polymers microsphere prepared by precipitation polymerization for hydroquinone recognition

A one-step precipitation polymerization synthesis was adopted for the preparation of molecularly imprinted polymers (MIPs) by using hydroquinone as a template molecule. The transmission electron microscopy (TEM) exhibited that the polymers were uniform spheres with the diameter of about 700 nm. The results of adsorption experiments showed that the microspherical imprinted polymers possessed fast adsorption dynamics. Compared to the structurally similar compounds, catechol and resorcinol, the MIPs exhibited a high recognizable capacity to hydroquinone. And the electrochemical sensor fabricated by modifying the prepared MIPs microsphere on the glassy carbon electrode surface was used to detect the hydroquinone concentration. The current response was proportional to the concentration of hydroquinone in the range of 2.0 x 10(-6) to 1.0 x 10(-4)mol/L with the detection limit of 1.0 x 10(-6)mol/L.     

Molecularly imprinted polymer prepared with bonded beta-cyclodextrin and acrylamide on functionalized silica gel for selective recognition of tryptophan in aqueous media

The rapid, sensitive and simultaneous determination of six polyamines, i.e., ornithine (ORN), 1,3-diaminopropane (DAP), putrescine (PUT), cadaverine (CAD), spermidine (SPD) and spermine (SPM), in human hairs was performed by ultra-performance liquid chromatography (UPLC) with fluorescence (FL) detection and electrospray-ionization time-of-flight mass spectrometry (ESI-TOF-MS). The primary (-NH(2)) and secondary (-NH) amines in the polyamine structures were first labeled with 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F) at 60 degrees C for 30min in the mixture of 0.1M borax (pH 9.3) and acetonitrile (CH(3)CN). The resulting derivatives were perfectly separated using an ACQUITY UPLCtrade mark BEH C(18) column (1.7mum, 100mmx2.1mm i.d.) by a gradient elution with a mixture of water-acetonitrile containing 0.1% formic acid (HCOOH). The separated polyamine derivatives were sensitively detected with both FL and TOF-MS. The detection limits in FL and TOF-MS were 11-86 and 2-5fmol, respectively. However, the determination of several polyamines by FL detection was interfered with by endogenous substances in the hair. Therefore, the simultaneous determination in hair was carried out by the combination of UPLC separation and the ESI-TOF-MS detection. The structures of the polyamines were identified from the protonated-molecular ions [M+H](+) obtained from the TOF-MS measurement. A good linearity was achieved from the calibration curves, that was obtained by plotting the peak area ratios of the analytes relative to the internal standard (IS), i.e., 1,6-diaminohexane (DAH), against the injected amounts of each polyamine (0.05-50pmol, r(2)>0.999). The proposed method was applied to the determination in the hairs of healthy volunteers. The mean concentrations of ORN, DAP, PUT, CAD, SPD and SPM in 1mg of human hairs (n=20) were 1.46, 0.18, 1.18, 0.11, 1.97 and 0.98pmol, respectively. Because the proposed method provides a good mass accuracy and the trace detection of the polyamines in hair, this analytical technique seems to be applicable for the determination of various biological compounds in hair.     

Molecularly imprinted polymers prepared in aqueous solution selective for [Sar,Ala]angiotensin II

Conventional molecular imprinting technology allows the synthesis in organic solvents of molecularly imprinted polymers (MIPs) selective toward relatively low molecular weight compounds. However, synthesis in aqueous media of chemically and mechanically stable MIPs that can recognize biomolecules such as peptides and proteins still is a great challenge. In this article, we report the successful synthesis of peptide-selective MIPs in aqueous solution. HPLC evaluation of these polymers with a water-based mobile phase showed their selectivity for the peptide, [Sar¹,Ala⁸]angiotensin II (SA), that had been used as the template, but not for its parent peptide angiotensin II (AII). The binding capacity and selectivity of our MIPs depended on the ratio of template to functional monomer in the polymerization mixture, as well as on the ionic strength and pH of the chromatographic mobile phase. These MIPs can be used for chromatographic detection of the octapeptide [Sar¹,Ala⁸]angiotensin II in aqueous solution, with a detection limit of 8 pmol and a response that is linear (r²>0.99) over the concentration range 0.4-20 μM.     

Chiral recognition by molecularly imprinted polymers in aqueous media

Summary Molecularly imprinted polymers were prepared using 2-vinylpyridine and/or methacrylic acid as functional monomers in a self-assembly imprinting protocol. The resulting polymers were analyzed in aqueous media, and the effects from the pH of the mobile phase and the degree of added organic solvent were investigated. The results are indicative of the importance of ionic bonds in conjunction with hydrophobic interactions in the formation of the complexes between the analyte and the polymers.     

Molecularly imprinted silica prepared with immiscible ionic liquid as solvent and porogen for selective recognition of testosterone

1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄), an ionic liquid (IL) immiscible with water, was used as a new type of solvent and porogen for the preparation of molecularly imprinted silica. The new imprinted silica was prepared by a sacrificial spacer molecular imprinting approach with testosterone as template molecule. The new covalent monomer-template complex used in the imprinting procedure was synthesized via the reaction of 3-(triethoxysilyl)propyl isocyanate with testosterone. The imprinted silica was characterized by FT-IR spectroscopy, N₂ gas adsorption–desorption isotherm and the high-resolution transmission electron microscopy. Moreover, the selective adsorption ability of the imprinted particles towards testosterone was investigated by the steady-state binding experiment with testosterone propionate as its structural analogue. Results showed that the imprinted silica obtained in this study had relatively homogenous structure with numerous mesopores, indicating that the IL used here is an excellent solvent and satisfactory porogen for the preparation of imprinted materials. Moreover, ILs are more environmentally friendly than traditional organic solvents due to their negligible vapor pressure. The imprinted silica possesses highly specific recognition property and high binding capacity towards testosterone, showing that the new imprinting technique is relatively successful.     

Molecularly imprinted polymer microspheres prepared by Pickering emulsion polymerization for selective solid-phase extraction of eight bisphenols from human urine samples

The bisphenol A (BPA) imprinted polymer microspheres were prepared by simple Pickering emulsion polymerization. Compared to traditional bulk polymerization, both high yields of polymer and good control of particle sizes were achieved. The characterization results of scanning electron microscopy and nitrogen adsorption–desorption measurements showed that the obtained molecularly imprinted polymer microsphere (MIPMS) particles possessed regular spherical shape, narrow diameter distribution (30–60 μm), a specific surface area (S_BET) of 281.26 m² g⁻¹ and a total pore volume (V_t) of 0.459 cm³ g⁻¹. Good specific adsorption capacity for BPA was obtained in the sorption experiment and good class selectivity for BPA and its seven structural analogs (bisphenol F, bisphenol B, bisphenol E, bisphenol AF, bisphenol S, bisphenol AP and bisphenol Z) was demonstrated by the chromatographic evaluation experiment. The MIPMS as solid-phase extraction (SPE) packing material was then evaluated for extraction and clean-up of these bisphenols (BPs) from human urine samples. An accurate and sensitive analytical method based on the MIPMS-SPE coupled with HPLC-DAD has been successfully established for simultaneous determination of eight BPs from human urine samples with detection limits of 1.2–2.2 ng mL⁻¹. The recoveries of BPs for urine samples at two spiking levels (100 and 500 ng mL⁻¹ for each BP) were in the range of 81.3–106.7% with RSD values below 8.3%.     

Molecularly imprinted beads with double thermosensitive gates for selective recognition of proteins

A new approach is reported on the use of poly(N-isopropylacrylamide) (PNIPAM)-coated molecularly imprinted beads (coated MIP beads) for controlling the release of protein. The coated MIP beads were composed of double layers, an internal thermosensitive lysozyme-imprinted layer, and an external PNIPAM layer. The coated MIP beads were prepared by two-step surface-initiated living-radical polymerization (SIP). In this systemic study, the coated MIP beads had good selectivity to the template protein (lysozyme) and temperature stimulus-responsive behavior, both of which were superior to those of MIP beads having a layer of thermosensitive lysozyme-imprinted polymer only. Using the coated MIP beads, reference proteins and the template lysozyme could be released separately at 38 °C and at 23 °C. The corresponding coated non-imprinted beads (coated NIP beads) did not have such double thermosensitive “gates” with specific selectivity for a particular protein. The proposed smart controlled imprinted system for protein is attractive for chemical carriers, drug-delivery system, and sensors.     

Molecularly imprinted microspheres and nanospheres for di(2-ethylhexyl)phthalate prepared by precipitation polymerization

Molecularly imprinted microspheres (MIMs, >3 μm) and nanospheres (MINs, ≈450 nm) for the environmental endocrine disruptor di(2-ethylhexyl)phthalate (DEHP) were prepared by a precipitation polymerization (PP) procedure. The effect of the dispersive solvents acetonitrile (ACN) and cyclohexane (CH), the cross-linkers ethylene glycol dimethacrylate (EDMA) and trimethylpropane trimethacrylate (TRIM), and the template on particle size and morphology of polymers was investigated in detail by scanning electron microscopy (SEM) and BET adsorption isotherm determination. When used as HPLC stationary phase, the microspheres exhibited strong affinity for the template DEHP with an imprint factor (IF) higher than 8.0 in ACN/water (60:40, v/v) as mobile phase. Furthermore, baseline separation of DEHP from benzyl butyl phthalate (BBP) and dibutyl phthalate (DBP) could be achieved. In contrast, no or only poor separation could be observed with non-imprinted polymeric polymers (NIPs) or imprinted bulk polymers (MIB), respectively. Similarly, the obtained MINs exhibited an imprinting effect in pure ACN, i.e. the bond amount of DEHP was significantly higher compared to NIPs, as was shown in rebinding experiments. Besides their use as an HPLC stationary phase, MIMs might further be applicable for SPE sample cleanup, while MINs could be used as a recognition layer on sensor surfaces. Figure Molecularly imprinting of di(2-ethylhexyl)phthalate (DEHP)     

Molecularly imprinted magnetic nanoparticles as tunable stationary phase located in microfluidic channel for enantioseparation

A microfluidic device integrated with molecularly imprinted magnetic nanoparticles as stationary phase was designed for rapid enantioseparation by capillary electrochromatography. The nanoparticles were synthesized by the co-polymerization of methacrylic acid and ethylene glycol dimethacrylate on 3-(methacryloyloxy)propyltrimethoxysilane-functionalized magnetic nanoparticles (25-nm diameter) in the presence of template molecule, and characterized with infrared spectroscopy, thermal gravimetric analysis, and transmission electron microscope. The imprinted nanoparticles (200-nm diameter) could be localized as stationary phase in the microchannel of microfluidic device with the tunable packing length by the help of an external magnetic field. Using S-ofloxacin as the template molecule, the preparation of imprinted nanoparticles, the composition and pH of mobile phase, and the separation voltage were optimized to obtain baseline separation of ofloxacin enantiomers within 195 s. The analytical performance could be conveniently improved by varying the packing length of nanoparticles zone, showing an advantage over the conventional packed capillary electrochromatography. The linear ranges for amperometric detection of the enantiomers using carbon fiber microdisk electrode at +1.0 V (vs. Ag/AgCl) were from 1.0 to 500 μM and 5.0 to 500 μM with the detection limits of 0.4 and 2.0 μM, respectively. The magnetically tunable microfluidic device could be expanded to localize more than one kind of template-imprinted magnetic nanoparticles for realizing simultaneous analysis of different kinds of chiral compounds.     

A stoichiometric imprinted chelating resin for selective recognition of copper(II) ions in aqueous media

This work reports the preparation of a new copper(II) ion-imprinted polymer (IIP) material, using 5,6;14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane-5,14-diene (DBDA15C4) and 2-vinylpyridine (VP) as a non-vinylated chelating agent and a functional vinyl monomer, respectively. The Cu²⁺ ion can form stable complexes with DBDA15C4 and VP. The stoichiometries of Cu²⁺-DBDA15C4 and ternary Cu²⁺-DBDA15C4-VP complexes were elucidated using conductometric and spectrophotometric methods, and found to be Cu²⁺(DBDA15C4), Cu²⁺(DBDA15C4)₂ and Cu²⁺(DBDA15C4)(VP)₂. The results obtained from solution studies were also supported by ab initio theoretical calculations. The resulting ternary complex Cu²⁺(DBDA15C4)(VP)₂ was copolymerized with ethyleneglycoldimethacrylate, as a cross-linking monomer, via bulk polymerization method. The imprinted copper ion was removed from the polymeric matrix by 0.1 M HNO₃. The Cu²⁺-imprinted polymer particles were characterized by IR spectroscopy and elemental analysis. Optimum pH range for rebinding of Cu²⁺ on the IIP and equilibrium binding time were 7.0-7.5 and 45 min, respectively. Sorbent capacity and enrichment factor for Cu²⁺ were obtained as 75.3 ± 1.9 μmol g⁻¹ and 100, respectively. In selectivity study, it was found that imprinting results in increased affinity of the material toward Cu²⁺ ion over other competitor metal ions with the same charge and close ionic radius. The prepared IIPs were repeatedly used and regenerated for five times without a significant decrease in polymer binding affinities.     

Molecularly imprinted solid phase extraction for the selective HPLC determination of alpha-tocopherol in bay leaves

A new sorbent for molecularly imprinted solid phase extraction (MISPE) was synthesized to extract and purify α-tocopherol (α-TP) from vegetable sources. Molecularly imprinted polymers (MIP) were synthesized using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent using a photo-polymerization procedure. A thermo-polymerization was also performed but no imprinting effect in the resulting materials was raised.The proposed MISPE protocol could overcome the drawback of traditional detection methods, which require pre-treatments of the samples. The possibility to obtain the selective recognition of α-TP from natural samples in aqueous mixtures represents one of the main advantages of our materials. Our procedure involves the direct HPLC injection of eluate without any treatment and above all the use of no toxic and biocompatible organic solvents.After the evaluation of the selectivity of the α-TP imprinted polymers, the performance of these materials as solid phase extraction (SPE) sorbents was investigated. Our MISPE-HPLC procedure has a high sensitivity, LOD and LOQ were 3.49 × 10⁻⁷ and 1.16 × 10⁻⁶ mol L⁻¹, respectively, as well as good precision (intraday precision below 3.3% and interday precisions below 6.5%) and recovery (60%). Thus, it can be successfully used for the purification of α-TP from bay leaves.     

Molecularly imprinted polymers: towards highly selective stationary phases in liquid chromatography and capillary electrophoresis

Molecularly imprinted polymers (MIPs) are synthetic polymers with a predetermined selectivity for a given analyte, or group of structurally related compounds, that make them ideal materials to be used in separation processes. In this sense, it is not surprising that the first applications of MIPs were as tailor-made chiral stationary phases in liquid chromatography. However, peak broadening and tailing, especially of the more retained enantiomers, were observed. Accordingly, this paper gives an overview of the attempts carried out during the recent years to improve the chromatographic performance of MIPs in liquid chromatography and capillary electrophoresis as well as the more recent applications. We conclude that MIPs are very promising materials to be used as selective stationary phases in chromatography although further developments are necessary in order to fully exploit their potential.     

Molecularly imprinted monoliths: Recent advances in the selective recognition of biomacromolecules related biomarkers

Biomarkers are significant indicators to assist the early diagnosis of diseases and assess the therapeutic response. However, due to the low abundance of biomarkers in complex biological fluids, it is highly desirable to explore efficient techniques to attain their selective recognition and capture before the detection. Molecularly imprinted monoliths integrate the high selectivity of imprinted polymers and the rapid convective mass transport of monoliths, and as a result, are promising candidates to achieve the specific enrichment of biomarkers from complex samples. This review summarizes the various imprinting approaches for the preparation of molecularly imprinted monoliths. The state-of-art advances as an effective platform for applications in the selective capture of biomacromolecules related biomarkers were also outlined.     

New hybrid polymeric liquid chromatography chiral stationary phase prepared by surface-initiated polymerization

A new hybrid organic/inorganic HPLC chiral stationary phase (CSP1) has been synthesized by the grafting from (g-from) radical polymerization of an enantiopure diacryloyl derivative of trans-1,2-diaminocyclohexane in the presence of mesoporous, azo-activated silica particles. The new chiral stationary phase has been fully characterized by elemental analysis, differential scanning calorimetry, diffuse reflectance infrared spectroscopy, scanning electron microscopy, inverse size exclusion chromatography and Van Deemter analysis. CSP1 shows improved chromatographic performances compared to its analog CSP2 synthesized by the alternative grafting to (g-to) approach in which the azo initiator is kept in solution. CSP1 can successfully resolve several chemically diverse chiral compounds, using both organic and water-based eluents (normal phase, polar organic, etc.).     

Molecularly imprinted polymers: modulating molecular recognition by a thermal phase transition in the binding framework

The concept used to realize the modulation of molecular recognition in a molecularly imprinted polymer is presented. Creating a thermal phase transition within the binding framework, the imprinted material was prepared using Boc-phenylalanine as the template and pNIPAM as the sensitive unit. The results indicate that such a transition causes a clear modulation in the recognition behavior of the prepared polymer which depends on the operation temperature. At a relatively low temperature, the prepared polymer acts like a traditionally imprinted one, showing a highly specific recognition for the imprint species. However, the prepared polymer does not present any notable resolution at 40 degrees C. This recognition behavior is comparable to a process that can be switched on and off, thus making modulated recognition feasible.     

Molecularly imprinted polymers for the selective solid-phase extraction of chloramphenicol

A variety of bulk polymers for the selective separation of chloramphenicol were synthesised from 2-vinylpyridine, diethylaminoethyl methacrylate or methacrylic acid monomers. Chromatographic evaluation indicated that chloramphenicol was retained under nonpolar elution conditions (k = 58.65) through selective hydrogen bonding and ionic interactions. The retention of chloramphenicol under aqueous elution conditions (k > 100) results from nonselective hydrophobic interactions. Under nonpolar elution conditions, the functional monomer employed imparted a significant influence on the recognition properties of the corresponding polymer. After solid-phase extraction using a molecularly imprinted polymer as sorbent and either an organic or aqueous washing solvent, nearly 100% recovery from the chloramphenicol standard solution was achieved, and nearly 90% recovery could be attained from spiked honey samples. The molecularly imprinted polymer was well suited to suppress matrix effects, and provided optimal preconcentration of the target molecule (chloramphenicol) prior to chromatographic analysis.