Molecular imprinted polymer

A Molecularly Imprinted Polymer (MIP), or plastic antibody is a polymer that is formed in the presence of a molecule that is extracted afterwards, thus leaving complementary cavities behind. These polymers show a certain chemical affinity for the original molecule and can be used to fabricate sensors, catalysis or for separation methods. The functional mechanism is similar to antibodies or enzymes.

Molecular Imprinting technique (State of the art and perspectives)

Molecular imprinting is, in fact, making an artificial tiny lock for a specific molecule that serve as miniature key. Like plastic receptors the imprinted polymer grabs specific chemicals. Many basic biological processes, from sensing of odours to signalling between nerve and muscle cells, rely on such lock-and-key combinations. For decades, scientists trying to understand these interactions often play locksmith, searching for the right key to fit a particular receptor. Now, the elegance of molecular imprinting in nature has been spurring many scientists to build the locks themselves. They etch a material to create specific cavities which in size, shape and functional groups, fit the target molecule. However, one of the greatest advantages of artificial receptors over naturally occurring ones is freedom of molecular design. Their frameworks are never restricted to proteins, and a variety of skeletons (e.g., carbon chains and fused aromatic rings) can be used. Thus, the stability, flexibility, and other properties are freely modulated according to need. Even functional groups that are not found in nature can be employed in these man-made compounds. Furthermore, when necessary, the activity to response towards outer stimuli (photo-irradiation, pH change, electric or magnetic field, and others) can be provided by using appropriate functional groups. The spectrum of functions is far wider than that of naturally occurring ones. In a molecular imprinting processes, one need a 1) template, 2) functional monomer 3) crosslinker, 4) initiator, 5) porogenic solvent and 6) extraction solvent. According to polymerization method and final polymer format one or some of the reagent can be avoided.^[1]

Over the recent years, interest in the technique of molecular imprinting has increased rapidly, both in the academic community and in the industry. Consequently, significant progress has been made in developing polymerization methods that produce adequate MIP formats with rather good binding properties expecting an enhancement in the performance or in order to suit the desirable final application, such as beads, films or nanoparticles. One of the key issues that have limited the performance of MIPs in practical applications so far is the lack of simple and robust methods to synthesize MIPs in the optimum formats required by the application. Chronologically, the first polymerization method encountered for MIP was based on “bulk” or solution polymerization. This method is the most common technique used by groups working on imprinting especially due to its simplicity and versatility. It is used exclusively with organic solvents mainly with low dielectric constant and consists basically of mixing all the components (template, monomer, solvent and initiator) and subsequently polymerizing them. The resultant polymeric block then pulverized, freed from the template, crushed and sieved to obtain particles of irregular shape and size between 20 and 50 µm. Depending on the target (template) type and the final application of the MIP, MIPs are appeared in different formats such as nano/micro spherical particles, nanowires and thin film or membranes. They are produced with different polymerization techniques like bulk, precipitation, emulsion, suspension, dispersion, gelation, multi-step swelling polymerization. Most of investigators in the field of MIP are making MIP with heuristic techniques such as hierarchical imprinting method. The technique for the first time was used for making MIP by Sellergren et al ^[2] for imprinting small target molecules. With the same concept, Nematollahzadeh et al ^[3] developed a general technique, so-called polymerization packed bed, to obtain a hierarchically structured high capacity protein imprinted porous polymer beads by using silica porous particles for protein recognition and capture.

Applications

Niche areas for application of MIPs are in sensors and separation. Despite the current good health of molecular imprinting in general one difficulty which appears to remain to this day is the commercialization of molecularly imprinted polymers. Even though no molecularly imprinted silica product has reached the market yet, at least several patents (123 patents, up to 2010, according to Scifinder data base), on molecular imprinting, were held by different groups. That some commercial interest existed is also confirmed by the fact that Sigma-Aldrich produces SupelMIP for Beta-agonists, Beta-blockers, pesticides and some drugs of abuse such as Amphetamine. Fast and cost-effective molecularly imprinted polymer technique has applications in many fields of chemistry, biology and engineering, particularly as an affinity material for sensors, detection of chemical, antimicrobial, and dye, residues in food, adsorbents for solid phase extraction, binding assays, artificial antibodies, chromatographic stationary phase, catalysis, drug development and screening, and by-product removal in chemical reaction.^[4]

History

In a paper published in 1931,^[5] Polyakov reported the effects of presence of different solvents (benzene, toluene and xylene) on the silica pore structure during drying a newly prepared silica. When H2SO4 was used as the polymerization initiator (acidifying agent), a positive correlation was found between surface areas, e.g. load capacities, and the molecular weights of the respective solvents. Later on, in 1949 Dickey reported the polymerization of sodium silicate in the presence of four different dyes (namely methyl, ethyl, n-propyl and n-butyl orange). The dyes were subsequently removed, and in rebinding experiments it was found that silica prepared in the presence of any of these "pattern molecules" would bind the pattern molecule in preference to the oth er three dyes. Shortly after this work had appeared, several research groups pursued the preparation of specific adsorbents using Dickey's method. Some commercial interest was al so shown by the fact that Merck patented a nicotine filter,^[6] consisting of nicotine imprinted silica, able to adsorb 10.7% more nicotine than non-imprinted silica. The material was intended for use in cigarettes, cigars and pipes filters. Shortly after this work had appeared, molecular imprinting attracted wide interest from the scientific community as reflected in the 4000 original papers published in the field during for the period 1931-2009 (from Scifinder). However, although interest in the technique is new, commonly the molecularly imprinted technique has been shown to be effective when targeting small molecules of molecular weight <1000.^[7] Therefore, in following subsection molecularly imprinted polymers are reviewed into two categories, for small and big templates.

See also

• MIP data base

References

1. ^ Sellergren, Börje (2001). Molecularly Imprinted Polymers: Man-made mimics of antibodies and their applications in analytical chemistry. Amsterdam: Elsevier. http://www.elsevier.com/wps/find/bookdescription.agents/620067/description#description. 
2. ^ Sellergren, Börje; Buechel, Gunter (1999). "A porous, molecularly imprinted polymer and preparation". PCT Int. Appl.. 
3. ^ Nematollahzadeh, Ali; Sun, Wei; Aureliano, Carla S. A.;Lütkemeyer, Dirk; Stute, Jörg; Abdekhodaie, Mohammad J.; Shojaei, Akbar; Sellergren, Börje (2011). "High capacity hierarchically imprinted polymer beads for protein recognition and capture". Angewandte Chemie International Edition 50 (2): 495–498. doi:10.1002/anie.201004774. http://onlinelibrary.wiley.com/doi/10.1002/anie.201004774/suppinfo. 
4. ^ Lok, CM; Son, R. (2009). "Application of molecularly imprinted polymers in food sample analysis – a perspective". International Food Research Journal 16: 127–140. http://www.ifrj.upm.edu.my/16%20(2)%202009/02-%20IFRJ-2009-102%20Review%20paper%20Lok%20Malaysia%202nd%20proof.pdf. 
5. ^ Polyakov, M.V. (1931). "Adsorption properties and structure of silica gel". Zhurnal fizicheskoi khimii 2: S. 799–804. 
6. ^ Hans, Erlenmeyer (1965). "Silica gel filter for removing nicotine from tobacco smoke". Patent DE 1965-M64131. 
7. ^ Turner, Nicholas W.; Christopher W. Jeans; Keith R. Brain; Christopher J. Allender; Vladimir Hlady; David W. Britt (2006). "From 3D to 2D: A Review of the Molecular Imprinting of Proteins". Biotechnology Progress 22 (6): 1474–89. doi:10.1021/bp060122g. PMC 2666979. PMID 17137293. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2666979.