Bulk Molecularly Imprinted Polymers Research Articles

Molecularly Imprinted Polymers Electrochemical Sensing: The Effect of Inhomogeneous Binding Sites on the Measurements. A Comparison between Imprinted Polyaniline versus nanoMIP-Doped Polyaniline Electrodes for the EIS Detection of 17β-Estradiol.

Molecularly imprinted polymers (MIPs) are synthetic receptors made by template-assisted synthesis. MIPs might be ideal receptors for sensing devices, given the possibility to custom-design selectivity and affinity toward a targeted analyte and their robustness and ability to withstand harsh conditions. However, the synthesis of MIP is an inherently random process that produces a statistical distribution of binding sites, characterized by a variety of affinities. This is verified both for bulk MIP materials and for MIP's thin layers. In the present work, we aimed at assessing the effects of inhomogeneous versus homogeneous imprinted binding sites on electrochemical sensing measurements, and the possible implications on the sensor's performance. In the example of an Electrochemical Impedance Spectroscopy (EIS) sensor for the 17β-estradiol (E2) hormone, the scenario of inhomogeneous binding sites was studied by modifying electrodes with an E2-MIP polyaniline (PANI) thin layer, called the "Imprinted PANI layer". In contrast, the condition of discrete and uniform binding sites was epitomized by electrodes modified with a thin PANI layer purposedly doped with E2-MIP nanoparticles (nanoMIPs), which were referred to as "nanoMIP-doped PANI". The behaviors of the two EIS sensors were compared. Interestingly, the sensitivity of the nanoMIP-doped PANI was almost twice with respect to that of the imprinted PANI layer, strongly suggesting that the homogeneity of the binding sites has a fundamental role in the sensor's development. The nanoMIP-doped PANI sensor, which showed a response for E2 in the range 36.7 pM-36.7 nM and had a limit of detection of 2.86 pg/mL, was used to determine E2 in wastewater.

Isotherm and Electrochemical Properties of Atrazine Sensing Using PVC/MIP: Effect of Porogenic Solvent Concentration Ratio.

Widespread atrazine use is associated with an increasing incidence of contamination of drinking water. Thus, a biosensor using molecularly imprinted polymers (MIPs) was developed to detect the amount of atrazine in water to ensure prevention of exposure levels that could lead to reproductive effects in living organisms. In this study, the influence of the porogen on the selectivity of MIPs was investigated. The porogen plays a pivotal role in molecular imprinting as it affects the physical properties and governs the prepolymerization complex of the resulting polymer, which in turn firmly defines the recognition properties of the resulting molecularly imprinted polymer (MIP). Therefore, bulk MIPs against atrazine (Atr) were synthesized based on methacrylic acid (MAA) as a functional monomer and ethyleneglycol dimethacrylate (EGDMA) as a crosslinker; they were prepared in toluene and dimethyl sulfoxide (DMSO). The imprinting factor, binding capacity, and structural stability were evaluated using the respective porogenic solvents. Along with the characterization of the morphology of the obtained polymers via SEM and BET analysis, the kinetic and adsorption analyses were demonstrated and verified. The highest imprinting factor, binding capacity, and the highest structural stability were found to be on polymer synthesized in a medium of MAA and EGDMA, which contained 90% toluene and 10% DMSO as porogen. Moreover, the response for Atr concentrations by the PVC-based electrochemical sensor was found to be at a detection limit of 0.0049 μM (S/N = 3). The sensor proved to be an effective sensor with high sensitivity and low Limit of Detection (LOD) for Atr detection. The construction of the sensor will act as a baseline for a fully functionalized membrane sensor.

Ordered macroporous molecularly imprinted polymers prepared by a surface imprinting method and their applications to the direct extraction of flavonoids from Gingko leaves

In this work, to improve the availability of the recognition sites of molecularly imprinted polymers (MIPs), ordered macroporous molecularly imprinted polymers (OMMIPs) were facilely prepared by grafting a quercetin-MIPs layer on the pore walls of the ordered macroporous thiol group functionalized silica. The pore structures were characterized by FTIR, Raman, SEM, BET and TGA measurements. The results indicated that OMMIPs possessed a nanoscale polymer layer, a more regular macroporous structure and a greater porosity compared with the traditional bulk MIPs (TBMIPs). The polymer content of OMMIPs was about 49.7%. Kinetic and isothermal adsorption experiments indicated that OMMIPs exhibited higher affinity and selectivity towards quercetin than its structural analogues. Moreover, OMMIPs could improve the intra-particle adsorption and thus provide a significant improvement in recognition sites availability over TBMIPs. Using the quercetin-OMMIPs as SPE sorbent, quercetin was directly extracted from the crude Gingko leaves extract with a satisfying selectivity and elution recovery.

Selective Navigation of Bisphenol‐A from Water to a Polarity Tuned Porous Molecularly Imprinted Polymer

AbstractA novel water compatible thermally stable molecularly imprinted polymer (MIP) was synthesized with bi‐functional monomers such as methacrylic acid (MAA) and 4‐vinyl pyridine (4VP) in the presence of mixed porogens such as THF and toluene for selectively higher adsorption of potential genotoxic compound Bisphenol‐A (BPA) compared to other structurally comparable phenolic compounds from aqueous solution at pH 7.0. The specific adsorption capacity (56.58 mg/g) and selectivity for BPA compared to non imprinted polymer (NIP) (44.10 mg/g) were achieved at 298 K under optimized conditions. The mesoporous imprints in the macroporous polymeric structure, higher pore volume, higher surface area, synergistic effect of H‐bonding, van der Waals force and π‐π interaction in bi‐functional cavities of MIP improved the recognition selectivity of BPA compared to NIP. The comparison of experimental adsorption isotherm with sixteen adsorption isotherm models conferred that the adsorption of BPA on MIP happened to energetically heterogeneous sites of the imprinted polymer through a spontaneous exothermic process. The kinetics of adsorption of BPA by MIP was best modeled via non‐linear pseudo‐second order kinetics. That novel MIP was found to be reusable for several cycles. This is the first report of the synthesis of thermally stable and mesoporous MAA‐4VP bi‐functional bulk MIPs having excellent selectivity, rapid binding kinetics and appropriate adsorption capacity for adsorption of BPA in water.

Determination of dicoumarol in Melilotus officinalis L. by using molecularly imprinted polymer solid-phase extraction coupled with high performance liquid chromatography

In this work, a method for the extraction of dicoumarol from plant sample utilizing selective adsorbent based on molecularly imprinted polymer was developed. Molecularly imprinted polymer (MIP) was synthesized by bulk polymerization, and on the surface of magnetic particles using dicoumarol as a template, methacrylic acid as functional monomer, chloroform as a porogen, and ethyleneglycol dimethacrylate as a cross-linker. Prepared polymeric materials were evaluated on the base of capacity, selectivity, and morphology. The maximal specific adsoption capacities of the sorbents were 45 μg (for bulk MIP) and 36 μg (for MIP on the magnetic particles) of dicoumarol per 1 g of polymer. An efficiencies of sorption processes of dicoumarol on prepared sorbents were evaluated under various conditions (type of sample solvent, pH, types of washing and elution solvents). The MIP based sorbents were used for solid phase extraction of dicoumarol. Applicability of MIP-SPE coupled to HPLC-DAD was tested for the selective extraction of dicoumarol from sample of sweet clover. The method was linear over concentration range from 1 to 100 μg mL−1 (the correlation coefficient 0.9984) with limit of detection 0.2 μg mL−1. Accuracy of the method was assessed for spiked sample at three concentration levels and recovery values were higher than 84% with relative standard deviation lower than 3.2%.

MIP-based protein profiling: A method for interspecies discrimination

Due to recent public concern and interest in the authenticity and origin of meat, for example, the 2013 “horsemeat scandal” in the human food chain, novel sensor strategies for the discrimination between protein species are highly sought after. In this work, molecularly imprinted polymers (MIPs) are utilised for protein discrimination using electrochemical sensor and spectrophotometric techniques. MIP selectivity between two proteins of similar molecular weight (haemoglobin and serum albumin) were compared across three different species, namely pork, beef and human. Bulk MIPs resulted in Kd and Bmax values of 184±23μM, and 582μmolg−1 for BHb, 246.3±26μM, and 673μmolg−1 for HHb; 276±31μM, and 467μmolg−1 for PHb. With the aid of chemometrics, i.e. multivariate analysis and pattern recognition, distinctive protein profiles have been achieved for species discrimination in both spectrophotometric and electrochemical analysis experiments. MIP suitability and selectivity within complex matrices was also assessed using urine, human plasma and human serum. Pattern recognition MIP-based protein profiling demonstrated positive outputs yielding either a ‘bovine’ or ‘not-bovine’ outcome (p=0.0005) for biological samples spiked with/without bovine using respective bovine haemoglobin MIPs.

Love Acoustic Wave-Based Devices and Molecularly-Imprinted Polymers as Versatile Sensors for Electronic Nose or Tongue for Cancer Monitoring.

Cancer is a leading cause of death worldwide and actual analytical techniques are restrictive in detecting it. Thus, there is still a challenge, as well as a need, for the development of quantitative non-invasive tools for the diagnosis of cancers and the follow-up care of patients. We introduce first the overall interest of electronic nose or tongue for such application of microsensors arrays with data processing in complex media, either gas (e.g., Volatile Organic Compounds or VOCs as biomarkers in breath) or liquid (e.g., modified nucleosides as urinary biomarkers). Then this is illustrated with a versatile acoustic wave transducer, functionalized with molecularly-imprinted polymers (MIP) synthesized for adenosine-5′-monophosphate (AMP) as a model for nucleosides. The device including the thin film coating is described, then static measurements with scanning electron microscopy (SEM) and electrical characterization after each step of the sensitive MIP process (deposit, removal of AMP template, capture of AMP target) demonstrate the thin film functionality. Dynamic measurements with a microfluidic setup and four targets are presented afterwards. They show a sensitivity of 5 Hz·ppm−1 of the non-optimized microsensor for AMP detection, with a specificity of three times compared to PMPA, and almost nil sensitivity to 3′AMP and CMP, in accordance with previously published results on bulk MIP.

Improved Molecular Imprinting Based on Colloidal Particles Made from Miniemulsion: A Case Study on Testosterone and Its Structural Analogues

Molecularly imprinted polymers (MIPs) in the micron and submicron scale based on the bifunctional cross-linker N,O-bismethacryloylethanolamine (NOBE) have been synthesized using bulk and miniemulsion polymerization, respectively. MIPs with distinct selectivity for the template testosterone were obtained. Colloidal MIP particles made using the miniemulsion technique have significant advantages compared to bulk MIP counterparts owing to their small size, homogeneity, and increased surface, as is demonstrated by optical batch rebinding studies using a nonimprinted polymer (NIP) as a negative control. Affinity and selectivity studies were also performed with the miniemulsion colloidal MIPs. These MIPs display largely increased imprint factors (6.8 vs 2.2) when compared to their bulk MIP counterparts. Further, selectivity studies by using analogue steroids show that colloidal MIPs also display a higher selectivity. In summary, miniemulsion MIPs show much better performance with respect to molecular recognition...

Upconversion fluorescence metal-organic frameworks thermo-sensitive imprinted polymer for enrichment and sensing protein

A novel fluorescence material with thermo-sensitive for the enrichment and sensing of protein was successfully prepared by combining molecular imprinting technology with upconversion nanoparticles (UCNPs) and metal-organic frameworks (MOFs). Herein, the UCNPs acted as signal reporter for composite materials because of its excellent fluorescence property and chemical stability. MOFs were introduced to molecularly imprinted polymer (MIP) due to its high specific surface area which increases the rate of mass transfer relative to that of traditional bulk MIP. The thermo-sensitive imprinted material which allows for swelling and shrinking with response to temperature changes was prepared by choosing Bovine hemoglobin (BHB) as the template, N-isopropyl acrylamide (NIPAAM) as the temperature-sensitive functional monomer and N,N-methylenebisacrylamide (MBA) as the cross-linker. The recognition characterizations of imprinted material-coated UCNPs/MOFs (UCNPs/MOFs/MIP) were evaluated, and the results showed that the fluorescence intensity of UCNPs/MOFs/MIP reduced gradually with the increase of BHB concentration. The fluorescence material was response to the temperature. The adsorption capacity was as much as 167.6mg/g at 28°C and 101.2mg/g at 44°C, which was higher than that of traditional MIP. Therefore, this new fluorescence material for enrichment and sensing protein is very promising for future applications.

Molecularly imprinted polymer with a pseudo-template for thermo-responsive adsorption/desorption based on hydrogen bonding

We report a thermo-responsive molecularly imprinted polymer (MIP) for methotrexate, an anticancer drug. The bulk MIPs were prepared with divinylbenzene as a crosslinker, a variety of functional monomers, and folic acid as a pseudo-template molecule. As a result of simple batch adsorption for methotrexate or folic acid using the MIPs, the selectivity depended on the functional monomers because the functional groups of methotrexate or folic acid were slightly different in each other. After optimization of the preparation conditions, only acidic functional monomers including methacrylic acid (MAA) and sodium p-styrenesulfonate (SS) contributed to the selective adsorption for methotrexate. Furthermore, only the MAA-based MIP provided the thermal responsibility for the binding/release of methotrexate by the suppression of hydrogen bonding at higher temperature, whereas a strong ionic interaction was contributed among broad temperature range in the SS-based MIP. Adsorption isotherms also well supported the differences of the molecular recognition based on the binding constants at low and higher temperatures. Finally, we successfully demonstrated the drug-releasing ability by simple temperature changing with the MAA-based MIP.

Preparation of ordered macroporous cinchonine molecularly imprinted polymers and comparative study of their structure and binding properties with traditional bulk molecularly imprinted polymers

Three-dimensionally ordered macroporous molecularly imprinted polymers (MMIPs) were prepared by a combination of the colloidal crystal template method and the molecular imprinting technique. Traditional bulk molecularly imprinted polymers (BMIPs) were simultaneously synthesized with the same recipe as the MMIPs by using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinker and chloroform as porogen. SEM and Brunauer − Emmett − Teller measurements show that MMIPs have a more regular macroporous structure, a narrower macropore distribution and a greater surface area and porosity compared with BMIPs. The isothermal and kinetic data of both polymers can be fitted with the Freundlich model and a pseudo-second-order equation, respectively. Their specificities to the template molecules are also similar. However, the binding capability, adsorption rate coefficient and internal effective diffusion coefficient of the MMIPs are higher than for the BMIPs when the particle size is above 54 µm. © 2015 Society of Chemical Industry

Thermal detection of histamine with a graphene oxide based molecularly imprinted polymer platform prepared by reversible addition–fragmentation chain transfer polymerization

Graphene oxide (GO), with its small dimension and high surface-to-volume ratio, can enhance the binding capacity and sensitivity of molecularly imprinted polymers (MIPs). Therefore, a straightforward and fast method was developed to graft MIPs onto GO by reversible addition–fragmentation chain transfer (RAFT) polymerization. First, the initiator was linked to the GO in a simple two-step process which was verified via UV–vis spectroscopy. Subsequently, a MIP layer for histamine was grown onto the functionalized surface by RAFT crosslinking polymerization, enabling control over the imprint structure. The formation of a hybrid GO–MIP structure, particles surrounded with a polymer network of ∼2.4nm thick, was verified by atomic force microscopy (AFM). Classical batch rebinding experiments demonstrated the specificity of the MIP towards its original template histamine. Next, the heat-transfer method (HTM) was applied, a novel sensing technique requiring only two thermocouples and an adjustable heat source. This method has been employed for the detection of small organic molecules with bulk MIPs, but never with a GO-hybrid structure. For proof-of-principle purposes, silicon substrates were functionalized with the GO–MIPs and sensing was performed on histamine in buffer solutions. The designed sensor platform could detect histamine in the nanomolar regime, similar to conventional techniques. In summary, we have developed a fast and straightforward method to prepare MIP–GO hybrids which were able to measure histamine in buffer solutions by thermal detection. Since GO exhibits excellent thermal properties, this opens the window to sensing of small organic molecules in relevant biological samples.

Synthesis and Evaluation of Uniformly Sized Synephrine-Imprinted Microparticles Prepared by Precipitation Polymerization

Uniformly sized synephrine molecularly imprinted polymer (MIP) microparticles were prepared via precipitation polymerization. The presence of the template, the amount of monomer, crosslinker, and porogenic solvent could affect the size distribution and morphology of the polymers. The pseudo-second-order kinetic model could provide a better correlation for the adsorption than the pseudo-first-order model. The intraparticle diffusion study showed that the sorption involved intraparticle diffusion, but that was not the only rate-controlling step. The equilibrium data better fit the Freundlich model than the Langmuir model. The Scatchard plot of MIPs revealed MIPs had two groups of sites with different affinities. Subsequent recognition selectivity experiments demonstrated preferential structural selectivity for synephrine with respect to other structurally similar compounds (i.e., octopamine and tyramine). Compared with the bulk MIP of SYN, the SYN MIP microparticles in this work had higher adsorption selectivity and capacity due to their smaller particle sizes; moreover, the precipitation polymerization was time-saving due to not using a crash-and-sieve process.

A novel ionic liquid stabilized molecularly imprinted optosensing material based on quantum dots and graphene oxide for specific recognition of vitamin E

This work prepared a novel ionic liquid stabilized molecularly imprinted optosensing material based on quantum dots (QDs) and graphene oxide (GO) composites using a one-step polymerization for highly selective and sensitive specific recognition of vitamin E (VE). Here, GO was first introduced to the molecularly imprinted polymer (MIP) because of its ultra-high specific surface area which increases the rate of mass-transfer relative to that of traditional bulk MIP. The ionic liquid was used to provide the desired surface binding groups between the QDs and the GO, but also to improve their fluorescence stability by virtue of its high thermal and chemical stability. Under optimal conditions, the relative fluorescence intensity of MIP decreased linearly with the increasing concentration of VE in the range of 2.30×10−2–9.20×102μM with a detection limit of 3.5nM and the precision for five replicate detections of 92μM VE was 1.67% (relative standard deviation). At three concentration levels, the recoveries for two samples achieved were 93.00–100.14% and 92.00–102.00%, respectively.

Computational and experimental study on the influence of the porogen on the selectivity of 4-nitrophenol molecularly imprinted polymers

In molecular imprinting the porogen plays a decisive role, as it not only affects the physical properties of the resulting polymer including its porosity, the specific surface area, and the swelling behavior, but also governs the stability of the prepolymerization complex, which in turn decisively determines the recognition properties of the resulting molecularly imprinted polymer (MIP).In this study, the influence of the porogen on the selectivity of MIPs was investigated. Therefore, bulk MIPs against 4-nitrophenol using 4-vinylpyridine (4-VP) as functional monomer and ethylene glycol dimethacrylate (EDMA) as crosslinker were prepared in acetonitrile and chloroform. The recognition properties of both MIPs were evaluated during chromatographic studies using the respective porogenic solvents as mobile phase for both MIPs. Along with the characterization of the morphology of the obtained polymers via SEM and BET analysis, the beneficial nature of chloroform as porogen for imprinting 4-NP was experimentally demonstrated and verified by findings obtained from complementary molecular dynamics simulations. Moreover, the application of chloroform as mobile phase for the MIP prepared in acetonitrile and vice versa clearly demonstrated the dependence of the resulting recognition properties on the selection of the mobile phase.

Synthesis of molecularly imprinted polymers via ring-opening metathesis polymerization for solid-phase extraction of bisphenol A

The use of molecularly imprinted polymers (MIPs) prepared by ring-opening metathesis polymerization (ROMP) for bisphenol A (BPA) was reported in this article. The resulting MIPs have high imprinting and adsorption capacities, and can be used for separation and determination of BPA in environmental water samples. The successful application of ROMP in the molecular imprinting field is described here. For the first time, two cross-linkers (dicyclopentadiene and 2,5-norbornadiene) and two Grubbs catalysts (first and second generation) were investigated to compare their effects on the binding performance of MIPs. The ROMP technique is able to create the imprinted polymers within 1 h under mild conditions. Furthermore, it can provide MIPs with obvious imprinting effects towards the template, very fast template rebinding kinetics, high binding capacity and appreciable selectivity over structurally related compounds. The adsorption process for MIPs in this study can be completed within 45 min, which is much faster than that of bulk MIPs synthesized by traditional free-radical polymerization. The resulting imprinting polymer was evaluated for its use as a sorbent support in an off-line solid-phase extraction approach to recover BPA from diluted aqueous samples. The optimized extraction protocol resulted in a reliable MISPE method suitable for selective extraction and preconcentration of BPA from tap water, human urine and liquid milk samples. This article demonstrates the practical feasibility of the MIPs prepared via ROMP as solid-phase extraction materials.

Chromatographic behavior of silica–polymer composite molecularly imprinted materials

Molecularly imprinted polymers (MIP) have recently been prepared inside the pores of silica based HPLC packing materials. Detailed physical and chromatographic characterization of such a silica-MIP composite material is presented. The chromatographic peak shape obtained with the uniformly sized spherical silica–MIP composite is mainly determined by the nonlinear adsorption isotherm. Comparison of the composite with the conventional sieved and grinded bulk MIP is therefore based on the nonlinear isotherm and not on retention factors and plate numbers.

Comparison of thin‐layer and bulk MIPs synthesized by photoinitiated in situ crosslinking polymerization from the same reaction mixtures

AbstractThe synthesis and comparative characterization of molecularly imprinted polymers (MIPs) in two different formats, as thin layers grafted to the entire surface of polypropylene microfiltration membranes and as conventional particles, are described. Imprinting with atrazine was performed by using itaconic acid and N,N′‐methylene‐bisacrylamide as functional and crosslinker monomers in methanol as the solvent. Polymerization had been initiated by UV irradiation of benzoin ethyl ether and driven to low monomer conversion for the thin‐layer polymers and to high monomer conversion for the bulk materials. The binding performance of MIP composite membranes and of MIP particles packed into cartridges was evaluated in solid‐phase extraction (SPE) experiments of atrazin and simazin from aqueous solutions. The SPE performance depended strongly on pH and buffer concentration. Although an imprinting effect was observed for both formats, the specificity (MIP versus Blank) and the selectivity (atrazin versus simazin) were much higher for the thin‐layer composite membranes than for the bulk polymer particles. In particular, the atrazin/simazin selectivity increased from 32% for the Blank to 78% for the MIP composite membranes. A major reason is the hindered accessibility of the internal pore structure of the particles, whereas the porous filtration membranes are much more compatible with the fast SPE protocol. Furthermore, based on pKa of the functional carboxylic acid groups—from potentiometric titration and polarity of the binding environment—from fluorescent probe analysis, different properties of the imprinted binding sites can be postulated for the two MIP formats. However, the differences between MIP and Blank were much more pronounced for the thin‐layer composite membranes. The hydrophobic surface of the polypropylene membrane appeared to be a major factor affecting the binding performance of thin‐layer MIPs. The new porous composite membranes could be particularly useful as selective SPE materials in environmental, pharmaceutical, and analytical applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 362–372, 2005

Catalysis of a Diels-Alder cycloaddition with differently fabricated molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) have been synthesised and applied as catalysts in the Diels-Alder cycloaddition of hexachlorocyclopentadiene and maleic acid. For this purpose, MIPs were generated either via bulk polymerisation, or with templates immobilised on silica particles leading to MIP shells. The performances of these differently produced MIPs were compared. MIPs obtained from bulk polymers did not show any higher catalytic activity than their respective non-imprinted control polymer (CP) particles. In contrast, the MIP shells have led to a product formation threefold as high as observed when using control polymer shells. Moreover, the catalytic effects of these MIP shells were noticeably higher than the ones of the bulk MIPs.

Porogen formulations for obtaining molecularly imprinted polymers with optimized binding properties

This paper examines the formulation of new porogenic mixtures used to prepare molecularly imprinted polymers (MIPs) in both thin film and bulk monolith formats. Films were cast by using spin coating to spread a pre-polymerization mixture onto a substrate, and rapid curing of the films was achieved with UV photolysis. The use of a low volatility solvent in combination with a linear polymer porogen resulted in a porous morphology and a 60-fold enhancement in the binding capacity, relative to a non-porous film prepared with a highly volatile solvent and in the absence of the polymer porogen. The opposite effect was seen in MIPs that were prepared in the traditional bulk monolith format, for which the binding efficiency of the MIP decreased monotonically with the concentration of the linear polymer porogen. Furthermore, bulk MIPs that were prepared in the presence of linear polymer porogens exhibited significantly decreased specific surface areas (from 620 to 8 m 2/g for samples prepared with pure solvent and 50% polymer porogen, respectively). Despite the change in binding capacity and morphology, the selectivity of the bulk MIPs remained unaffected by the presence of the polymer porogens (approximately 50% chiral selectivity for all bulk MIPs considered). This difference in behavior of the two systems was attributed to the large difference in the kinetics of polymerization.