Molecularly imprinted polymer using-p-hydroxybenzoic acid, p-hydroxyphenylacetic acid and p-hydroxyphenylpropionic acid as templates.

Molecularly imprinted polymers (MIPs) using p-hydroxybenzoic acid (p-HB), p-hydroxyphenylacetic acid (p-HPA) and p-hydroxyphenylpropionic acid (p-HPPA) as templates were synthesized. The performance of the templates and their analogues on polymer-based high performance liquid chromatography (HPLC) columns was studied. The imprinting effect of the MIP using p-HB as template is more obvious than that of MIP using either p-HPA or p-HPPA as template, and the mixture of p-HB and p-HPA can be well separated on the MIP using p-HB as template, but not on the blank. Interestingly, the recognition of MIP (p-HB as the template) to p-HB showed a synergistic effect. The retention factor of p-HB is not the sum of those of phenol and benzoic acid. We also found that the imprinting effect decreased when increasing the concentration of acetic acid in mobile phase. The possible reason is that acetic acid molecules occupied the binding sites of the polymer, thereby decreasing the concentration of binding sites. Furthermore, polymers, which showed specificity to 3,4-dihydroxybenzoic acid, can be prepared with p-HB as template. It is thus possible to synthesize a specific polymer for a compound that is either expensive or unstable by using a structurally similar compound as template.     

New biomedical devices with selective peptide recognition properties. Part 1: Characterization and cytotoxicity of molecularly imprinted polymers

Molecular imprinting is a technique for the synthesis of polymers capable to bind target molecules selectively. The imprinting of large proteins, such as cell adhesion proteins or cell receptors, opens the way to important and innovative biomedical applications. However, such molecules can incur into important conformational changes during the preparation of the imprinted polymer impairing the specificity of the recognition cavities. The "epitope approach" can overcome this limit by adopting, as template, a short peptide sequence representative of an accessible fragment of a larger protein. The resulting imprinted polymer can recognize both the template and the whole molecule thanks to the specific cavities for the epitope. In this work two molecularly imprinted polymer formulations (a macroporous monolith and nanospheres) were obtained using the protected peptide Z-Thr-Ala-Ala-OMe, as template, and Z-Thr-Ile-Leu-OMe, as analogue for the selectivity evaluation, methacrylic acid, as functional monomer, and trimethylolpropane trimethacrylate and pentaerythritol triacrylate (PETRA), as cross-linkers. Polymers were synthesized by precipitation polymerization and characterized by standard techniques. Polymerization and rebinding solutions were analyzed by high performance liquid chromatography. The highly cross-linked polymers retained about 70% of the total template amount, against (20% for the less cross-linked ones). The extracted template amount and the rebinding capacity decreased with the cross-linking degree, while the selectivity showed the opposite behaviour. The PETRA cross-linked polymers showed the best recognition (MIP 2-, alpha=1.71) and selectivity (MIP 2+, alpha'=5.58) capabilities. The cytotoxicity tests showed normal adhesion and proliferation of fibroblasts cultured in the medium that was put in contact with the imprinted polymers.     

Insights into the origins of binding and the recognition properties of molecularly imprinted polymers prepared using an amide as the hydrogen-bonding functional group

Molecularly imprinted polymers (MIPs) prepared using an amide hydrogen-bonding functional monomer (acrylamide) exhibited efficient enantiomeric recognition properties in both organic and aqueous media in the HPLC mode. The results indicate that the amide functional groups formed strong hydrogen-bonding interactions with the template molecule, and specific recognition sites were created within the polymer matrix during the imprinting process. When Boc-L-Trp was used as the template, an MIP prepared in a polar organic solvent (acetonitrile) using acrylamide as the functional monomer showed better enantiomeric recognition of Boc-Trp than the MIPs prepared in the same solvent using an acidic (methacrylic acid) or a basic (2-vinylpyridine) functional monomer or a combination of an acidic and a basic functional monomer (methacrylic acid + 2-vinylpyridine). Our results indicate that in organic media the degree of retention of the sample molecule on the imprinted polymer was controlled by hydrogen-bonding interactions between the sample molecule and the polymer, while in aqueous media it was determined to a considerable extent by hydrophobic interactions. In both media the shape, size and the nature of the hydrogen-bonding groups of the sample molecules were all important factors in determining the enantiomeric and substrate selectivity. In the aqueous media, however, the hydrophobicity of the sample molecules was also found to play an important role.     

In situ synthesis of molecularly imprinted nanoparticles in porous support membranes using high-viscosity polymerization solvents

There is a growing need in membrane separations for novel membrane materials providing selective retention. Molecularly imprinted polymers (MIPs) are promising candidates for membrane functionalization. In this work, a novel approach is described to prepare composite membrane adsorbers incorporating molecularly imprinted microparticles or nanoparticles into commercially available macroporous filtration membranes. The polymerization is carried out in highly viscous polymerization solvents, and the particles are formed in situ in the pores of the support membrane. MIP particle composite membranes selective for terbutylazine were prepared and characterized by scanning electron microscopy and N? porosimetry. By varying the polymerization solvent microparticles or nanoparticles with diameters ranging from several hundred nanometers to 1 μm could be embedded into the support. The permeability of the membranes was in the range of 1000 to 20,000 Lm?2 hr?1 bar?1. The imprinted composite membranes showed high MIP/NIP (nonimprinted polymer) selectivity for the template in organic media both in equilibrium-rebinding measurements and in filtration experiments. The solid phase extraction of a mixture of the template, its analogs, and a nonrelated compound demonstrated MIP/NIP selectivity and substance selectivity of the new molecularly imprinted membrane. The synthesis technique offers a potential for the cost-effective production of selective membrane adsorbers with high capacity and high throughput.     

Synthesis and evaluation of a selective molecularly imprinted polymer for the contraceptive drug levonorgestrel

A molecularly imprinted polymer (MIP) has been prepared using levonorgestrel (LEV) as template. The polymer was synthesised in a non-covalent approach using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linking monomer via a free radical polymerization. An equivalent blank polymer was also synthesised in the absence of the template compound. Batch adsorption experiments were used to evaluate the binding affinity of the imprinted polymer. After packing MIP into a stainless steel column (150 mm x 4.6 mm i.d.), retention and elution of the template and related compounds were evaluated by high-performance liquid chromatography (HPLC). This LEV imprinted polymer was further applied for selective solid phase extraction (SPE) of LEV from human serum. It was confirmed that the binding ability of the prepared MIP for LEV was essentially sufficient in the presence of other compounds coexisting in serum sample. Therefore, as a selective and efficient solid phase material, LEV imprinted polymer has a high potential application in analysis of this steroidal hormone in clinical purposes.     

A computational approach to studying monomer selectivity towards the template in an imprinted polymer

A computational approach was proposed to study monomer–template interactions in a molecularly imprinted polymer (MIP) in order to gain insight at the molecular level into imprinting polymer selectivity, regarding complex formation between template and monomer at the pre-polymerisation step. This is the most important step in MIP preparation. In the present work, chlorphenamine (CPA), diphenhydramine (DHA) and methacrylic acid (MAA), were chosen as the template, non-template, and monomer, respectively. The attained complexes were optimised, and changes in the interaction energies, atomic charges, IR spectroscopy results, dipole moment, and polarisability were studied. The effects of solvent on template–monomer interactions were also investigated. According to a survey of the literature, this is the first work in which dipole moment and polarisability were used to predict the types of interactions existing in pre-polymerisation complexes. In addition, the density functional tight-binding (DFTB) method, an approximate version of the density functional theory (DFT) method that was extended to cover the London dispersion energy, was used to calculate the interaction energy.     

Synthesis of a molecularly imprinted polymer for the solid‐phase extraction of betulin and betulinic acid from plane bark

Introduction – Plant extracts are usually complex mixtures of various polarity compounds and their study often includes a purification step, such as solid‐phase extraction (SPE), to isolate interest compounds prior analytical investigations. Molecularly imprinted polymers (MIPs) are a new promising type of SPE material which offer tailor‐made selectivity for the extraction of trace active components in complex matrices. Numerous specific cavities that are sterically and chemically complementary of the target molecules, are formed in imprinted polymers. A molecularly imprinted polymer (MIP) was synthesised in order to trap a specific class of triterpene, including betulin and betulinic acid from a methanolic extract of plane bark. Methodology – Imprinted polymers were synthesised by thermal polymerisation of betulin as template, methacrylic acid (MAA) or acrylamide (AA) as functional monomer, ethylene glycol dimethacrylate as crosslinking agent and chloroform as porogen. Afterwards, MAA‐ and AA‐MIPs were compared with their non‐imprinted polymers (NIPs) in order to assess the selectivity vs betulin and its derivatives. Recovered triterpenes were analysed by HPLC during MIP‐SPE protocol. Results – After SPE optimisation, the MAA‐imprinted polymer exhibited highest selectivity and recovery (better than 70%) for betulin and best affinity for its structural analogues. Thus, a selective washing step (chloroform, acetonitrile) removed unwanted matrix compounds (fatty acids) from the SPE cartridge. The elution solvent was methanol. Finally, the MAA‐MIP was applied to fractionate a plane bark methanolic extract containing betulin and betulinic acid. Conclusion – This study demonstrated the possibility of direct extraction of betulin and its structural analogues from plant extracts by MIP technology. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface molecular imprinting by atom transfer radical polymerization

Results are presented that demonstrate the successful preparation of ultrathin (< 10 nm), surface-confined, molecularly imprinted polymer (MIP) films on model gold substrates using atom transfer radical polymerization (ATRP). 2-Vinylpyridine (2Vpy) was investigated as the functional monomer, and ethylene glycol dimethacrylate (EGDMA) was the cross-linking monomer. Fluorescently labeled N,N'-didansyl-L-cystine and N,N'-didansyl-L-lysine were used as the template molecules to form the MIPs. Spectroscopic and ellipsometric results are presented that follow film formation and growth rates. Results are also presented from fluorescence experiments used to quantify and compare the adsorption capacities of MIP surface films and nonimprinted (NIP) control films. MIP films exhibited higher binding capacities than the control NIP films at all solution concentrations of N,N'-didansyl-L-cystine and N,N'-didansyl-L-lysine. Furthermore, template removal from these imprinted films appears to be 100% efficient. Selectivity studies showed that the MIPs display some cross-reactivity between these two molecules; nevertheless, MIPs prepared against one template showed selectivity for that template. A selectivity coefficient of 1.13 was achieved for MIP surfaces prepared against N,N'-didansyl-L-lysine; a value of 1.51 was observed for MIP surfaces prepared against N,N'-didansyl-L-cystine.     

Size-selective recognition of catecholamines by molecular imprinting on silica-alumina gel

The preparation of a catecholamine receptor was carried out using a molecular imprinting method with silica-alumina gel to form complementary structures for template recognition. The molecularly imprinted polymer (MIP) was synthesized by the condensation of silicate from tetraethyl orthosilictate (TEOS) under hydrothermal conditions at 60 degrees C. Aluminum chloride was added as a functional monomer to increase the material's rebinding ability. The selectivity of the MIP receptor prepared with different ratios of template to Si and Al, was examined with seven analytes including: dopamine, epinephrine, norepinephrine, ascorbic acid, homovanillic acid, uric acid, and l-tyrosine. The results showed a size selective effect for the receptors with respect to the recognition of the catecholamines. Some factors affecting the recognition ability were investigated including: the solution pH of analytes, surface capping on the MIP, and the imprinting pH of the silica-alumina solution. Also, the catecholamine MIP films on quartz crystal microbalance (QCM) electrodes were fabricated as sensors for in situ monitoring of the analytes in a 2-propanol solution.     

Molecularly imprinted ligand-exchange recognition assay of glucose by quartz crystal microbalance

Molecular imprinted polymers (MIP) as a recognition element for sensors are increasingly of interest and MIP-quartz crystal microbalance (QCM) have started to appear in the literature. In this study, we have combined quartz crystal microbalance with MIP to prepare a sensor using the ability of glucose to chelate of copper (II) ion of methacrylamidohistidine (MAH) monomer to create ligand exchange (LE) assembled monolayer which is suitable for glucose determination. The study includes the measurement of binding interaction of molecularly imprinted QCM sensor via ligand interaction, investigation of the pH effect on frequency shift and recognition selectivity studies of glucose-imprinted polymer with respect to methyl-alpha-d-glucopyranoside and sucrose. Bmax (number of binding sites) and K(D) (dissociation constant of the metal-chelate copolymer) were also calculated using Scathard plot and the detection limit was found as 0.07 mM. MIP showed higher glucose-binding affinity than a well-known glucose binding protein, conconavalin A.     

Mobile phase effects on enantiomer resolution using molecularly imprinted polymers

The aim of this study was to rationalise retention behaviour of a chiral solute on molecularly imprinted polymer (MIP) HPLC stationary phases in terms of variation of the mobile phase. It is generally held that the most important interaction governing the separation of enantiomers on such materials is H-bonding, and that retention times increase with decreasing H-bonding potential of the mobile phase. Previous studies have largely concerned mobile phases containing chloroform with acetic acid as a polar modifier. Boc-L-Phenylalanine (Boc-L-Phe-OH) MIPs were prepared, processed, and packed into HPLC columns, which were then used to investigate the retention characteristics of Boc-L-Phe-OH and Boc-D-Phe-OH with a range of mobile phases. The main observations were as follows: (1) in chloroform-based mobile phases there was generally a linear relationship between the H-bond donator factor of the polar modifier and capacity (K′). Results also indicated a hydrogen bond donor parameter value for a polar modifier at which retention became concentration independent; (2) For given values of K′_L, K′_D varied depending on the polar modifier, indicating that enantiomer resolution was solvent dependent; (3) Using mobile phases based on solvents of lower polarity/H-bonding potential than chloroform, substantial increases in K′ were observed, although enantioselectivity was greatly reduced. Chirality 9:238–242, 1997. © 1997 Wiley-Liss, Inc.     

Towards the rational development of molecularly imprinted polymers: 1H NMR studies on hydrophobicity and ion-pair interactions as driving forces for selectivity

The preparation of molecularly imprinted polymers (MIP) based on non-covalent interactions has become a widely used technique for creating highly specific sorbent materials predominantly used in separation chemistry. A crucial factor in a successful imprinting protocol is the optimisation of the template/functional monomer interaction in the pre-polymerisation mixture, eventually leading to a maximum of high-affinity binding sites in the resulting polymer matrix. In order to develop more efficient preparation technologies for imprinted polymers, two separate pre-polymerisation complexes were investigated by NMR spectroscopic techniques in order to identify the types of interactions occurring in the pre-polymerisation mixture, and their implications for the subsequently formed imprinted polymer. In particular, hydrophobic effects have been followed by NMR spectroscopy and their contribution to the selectivity of the resulting MIP has been investigated. The 2,4-D imprint system is used as an example to fundamentally study whether observations at the pre-polymerisation stage correlate with properties of the finally prepared MIP, and which parameters govern success of an imprinting protocol.     

Concentration dependent atrazine-atrazine complex formation promotes selectivity in atrazine imprinted polymers

An atrazine (ATR) molecularly imprinted polymer (MIP) was prepared using a non-covalent strategy. The affinity and selectivity of the polymer was initially evaluated under non-equilibrium conditions and the polymer was shown to possess good template selectivity. The selectivity of the polymer was further investigated under equilibrium conditions and over a range of concentrations using Scatchard plots and Hill plots and by assessing distribution coefficients and normalised selectivity values. It was observed that both selectivity and affinity were dependent on the concentration of the ligand and that unusually selectivity and affinity were better at higher atrazine concentrations. It was concluded that this phenomenon resulted from the formation of atrazine-atrazine complexes during the pre-polymerisation stage and during rebinding and that the polymer demonstrated improved atrazine affinity when the conditions favoured complex formation.     

A molecular imprinted polymer with recognition properties towards the carcinogenic mycotoxin ochratoxin A

A molecularly imprinted polymer which recognises the mycotoxin ochratoxin A was prepared using the mimic N-(4-chloro-1-hydroxy-2-naphthoylamido)-(L) -phenylalanine as a template. The polymer was obtained by dissolving the template, methacrylic acid and ethylendimethacrylate in chloroform and polymerising the mixture by thermal treatment at 60°C. The monolith obtained was crushed, sieved to 30–90 m and extensively washed till the template could no longer be found in the washing solution. The binding properties towards the template, ochratoxin A and several related molecules were measured by eluting with acetonitrile and chloroform a HPLC column packed with the imprinted polymer. The experimental results show that the polymer recognises not only the template well, but also the ochratoxin A. The specific molecular recognition effect is due to hydrogen bond interactions but in order to assure the full recognition effect adjunctive steric factors are necessary. The magnitude of these interactions can be controlled by the use of limited amounts of acetic acid in the mobile phase.From the measurement of the relative selectivity it was found that only the simultaneous presence of the carboxyl, the phenolic hydroxyl and certain peculiar substructures such as the chlorine atom assures the whole recognition of the template.     

Development and Characterization of Propranolol Selective Molecular Imprinted Polymer Composite Electrospun Nanofiber Membrane

Propranolol (PPL) imprinted microspheres (MIP) were successfully prepared via oil/water polymerization using a methyl methacrylate (MMA) monomer, PLL template, and divinylbenzene (DVB) cross-linker and favorably incorporated in a Eudragit-RS100 nanofiber membrane. A non-PPL imprinted polymer (NIP), without a template, was used as a control. The morphology and particle size of the beads were investigated using scanning electron microscopy. The results revealed that both MIP and NIP had a spherical shape with a micron size of approximately 50–100 μm depending on the amounts of DVB and PPL used. NIP2 (MMA/DVB, 75:2.5) and MIP8 (PPL/MMA/DVB, 0.8:75:2.5) were selected for reloading of PPL, and the result indicated that increasing the ratio of PPL to polymer beads resulted in increase PPL reloading (>80%). A total of 10–50% NIP2 or MIP8 was incorporated into a 40% (w/v) Eudragit-RS100 fiber membrane using an electrospinning technique. PPL could be bound to the 50% MIP8 composite fiber membrane with a higher extent and at a higher rate than the control (NIP2). Furthermore, the MIP8 composite fiber membrane showed higher selectivity to PPL than the other β-blockers (atenolol, metoprolol, and timolol). Thus, the MIP8 composite fiber membrane can be further developed for various applications in pharmaceutical and other affinity separation fields.Key words: membrane, molecularly imprinted, propranolol, selective molecular imprinting     

Development of molecularly imprinted polymers as tailored templates for the solid-state [2+2] photodimerization

In this study, a molecularly imprinted polymer (MIP) was prepared to selectively template the [2+2] photodimerization of trans-1,2-bis(4-pyridyl)ethylene. First, an MIP selective for rctt-tetrakis(4-pyridyl)cyclobutane, which is the [2+2] photodimerization product of trans-1,2-bis(4-pyridyl)ethylene, was prepared from methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA). The non-covalent MIP showed enhanced affinity for both the templating agent, rctt-tetrakis(4-pyridyl)cyclobutane, and the alkene precursor, trans-1,2-bis(4-pyridyl)ethylene. The solid-state photodimerization reaction proceeded in significantly higher yields in the presence of the MIP. Control reactions carried out in the absence of polymer gave no product, and reactions carried out in the presence of a non-imprinted polymer and an MIP imprinted with a different template, 3-hydroxymethylpyridine, gave much lower yields of the cyclobutane photodimerization product. The outcome of the MIP-templated photodimerization reaction was strongly influenced by the binding site heterogeneity of the non-covalently imprinted polymers. For example, higher yields were observed with decreasing olefin loadings levels on the MIPs. This binding site heterogeneity was characterized via application of the Freundlich binding model to the experimentally measured binding isotherms. These confirmed that the non-covalent MIPs had very few high-affinity binding sites, which greatly limits the capacity and ultimately the utility of these materials as templates in synthetic organic applications.     

Study on the recognition of templates and their analogues on molecularly imprinted polymer using computational and conformational analysis approaches

A simplified computational model was proposed to simulate the synthesis of molecularly imprinted polymers (MIP), removal of template and recognition of the template and its analogues by MIP. The MIPs with nicotinamide and iso-nicotinamide as templates were prepared using methacrylic acid as functional monomer. Based on our computational model, the interaction energies between the monomer and the template or its analogues were calculated, which were well correlated with the retention factors and imprinting factors obtained on HPLC columns packed with the corresponding MIP particles. The imprinting effects of the template and its analogues were also investigated from the viewpoint of conformational analysis. The computational data were successfully used to predict the chromatographic behaviour of some chemicals in separation on HPLC columns. We believe that the computational method will find application in designing monomers for MIP synthesis and in studying recognition of templates and their analogues on MIP.     

Capacitive sensor for environmental monitoring based on thin films of molecularly imprinted polymers. Computer modeling for optimization of the composition of synthetic analogs of bioreceptors

A capacitive sensor for environmental monitoring based on thin films of desmetryn-selective molecularly imprinted polymer (MIP) was developed. The method of modification of gold electrodes with the thin film of herbicide-selective MIP using the grafting polymerization approach was developed. The method of computational modeling was used to optimize the composition of desmetryn-selective MIPs. It was shown that 2-acrylamido-2-methyl-1-propan-sulfonic acid is the optimal functional monomer for desmetryn. Formation of synthetic binding sites in MIPs was demonstrated to be determined by the binding energy between the template and functional monomers as well as the number of functional groups taking part in the recognition of the template molecule. Electrochemical processes occurring at the MIP-modified electrode were analyzed. The detection limit for desmetryn comprised 100 nM. High selectivity of the capacitive sensor towards structural analogues of desmetryn as well as high operational and storage stabilities was demonstrated.     

Molecularly imprinted polymer as storage medium for an analyte

A molecularly imprinted polymer (MIP) able to bind theophylline with a considerable degree of selectivity was prepared through a noncovalent route. The polymer after equilibrating with the template molecule (theophylline) and storage for various periods of time, the amount of theophylline desorbed from the polymer was found to be effectively quantitative indicating that MIPs could be used as a storage matrix for analytes. The stored analyte could be desorbed and analysed conveniently.     

Synthesis and evaluation of uniformly sized nalidixic acid-imprinted nanospheres based on precipitation polymerization method for analytical and biomedical applications

For the first time in this work, uniform molecularly imprinted polymer (MIP) nanoparticles were prepared using nalidixic acid as a template. The MIP nanoparticles were successfully synthesized by precipitation polymerization applying methacrylic acid (MAA) as a functional monomer and trimethylolpropane trimethacrylate (TRIM) as a cross-linking monomer at different mole ratios. The morphology, binding, recognition, selectivity, and in vitro release behaviors of obtained particles were studied. The produced polymers were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetric. Furthermore, their morphology was analyzed accurately by scanning electron microscopy, photon correlation spectroscopy, and Brunauer-Emmett-Teller analysis. The nanospheres and microspheres with mean diameter values of 94 nm, 256 nm, and 1.2 μm were obtained using nalidixic acid-MAA-TRIM various mole ratios. Among the MIPs, the product with nalidixic acid-MAA-TRIM mole ratio of 1:12:12 established nanospheres with the lowest polydispersity index (0.003), an average pore diameter (12 nm), and the highest specific surface area (280 m(2) g(-1)) and selectivity factor (10.4). Results from binding experiments demonstrated that the imprinted nanospheres with a 94-nm mean diameter and a binding capacity of 28 mg of nalidixic acid per gram of polymer had higher specific affinity to nalidixic acid in contrast with the other imprinted nanospheres, microspheres, and nonimprinted particles. However, the binding performance of imprinted nanospheres in human serum was estimated using high-performance liquid chromatography analysis (binding approximately 98% of nalidixic acid). In addition, release experiments proved to be successful in the controlled release of nalidixic acid during a long period. The 20% of loaded nalidixic acid was released from the imprinted nanospheres within the first 20 h, whereas the remaining 80% was released in the after 120 h. The nalidixic acid release kinetics from the MIPs was highly affected by properties of the particles.