Molecular imprinting

Last updated November 02, 2023

Molecular imprinting is a technique to create template-shaped cavities in polymer matrices with predetermined selectivity and high affinity.^[1] This technique is based on the system used by enzymes for substrate recognition, which is called the "lock and key" model. The active binding site of an enzyme has a shape specific to a substrate. Substrates with a complementary shape to the binding site selectively bind to the enzyme; alternative shapes that do not fit the binding site are not recognized.

Molecularly imprinted materials are prepared using a template molecule and functional monomers that assemble around the template and subsequently get cross-linked to each other. The monomers, which are self-assembled around the template molecule by interaction between functional groups on both the template and monomers, are polymerized to form an imprinted matrix (commonly known in the scientific community as a molecular imprinted polymer (MIP)). The template is subsequently removed in part or entirely,^[1] leaving behind a cavity complementary in size and shape to the template. The obtained cavity can work as a selective binding site for the templated molecule.

In recent decades, the molecular imprinting technique has been developed for use in drug delivery, separations, biological and chemical sensing, and more. Taking advantage of the shape selectivity of the cavity, use in catalysis for certain reactions has also been facilitated.

History

The first example of molecular imprinting is attributed to M. V. Polyakov in 1931 with his studies in the polymerization of sodium silicate with ammonium carbonate. When the polymerization process was accompanied by an additive such as benzene, the resulting silica showed a higher uptake of this additive.^[1] By 1949, the concept of instructional theory molecular imprinting was used by Dickey; his research precipitated silica gels in the presence of organic dyes and showed imprinted silica had high selectivity towards the template dye.^[2]

Following Dickey’s observations, Patrikeev published a paper of his ‘imprinted’ silica with the method of incubating bacteria with gel silica. The process of drying and heating the silica promoted growth of bacteria better than other reference silicas and exhibited enantioselectivity.^[3] He later used this imprinted silica method in further applications such as thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). In 1972, Wulff and Klotz introduced molecular imprinting to organic polymers. They found that molecular recognition was possible by covalently introducing functional groups within the imprinted cavity of polymers.^[4]^[5] The Mosbach group then proved it was possible to introduce functional groups into imprinted cavities through non-covalent interactions, thus leading to non-covalent imprinting.^[6]^[7] Many approaches regarding molecular imprinting have since been extended to different purposes.^[1]

Type of Molecular Imprinting

Covalent

In covalent imprinting, the template molecule is covalently bonded to the functional monomers that are then polymerized together. After polymerization, the polymer matrix is cleaved from the template molecule, leaving a cavity shaped as the template. Upon rebinding with the original molecule, the binding sites will interact with the target molecule, reestablishing the covalent bonds.^[8]^[9] During this reestablishment, kinetics associated with bond binding and bond breakage are obtained back. The imprinted molecule is then released from the template, in which it would then rebind with the target molecule, forming the same covalent bonds that were formed before polymerization.^[7] Advantages through utilizing this approach include the functional group being solely associated with the binding sites,^[1] avoiding any non-specific binding. The imprinted molecule also displays a homogenous distribution of binding sites, increasing the stability of the template-polymer complex.^[7] However, there are a few number of compounds that can be used to imprint with template molecules via covalent bonding, such as alcohols, aldehydes and ketones, all of which have high formation kinetics.^[10]^[11] In some cases, the rebinding of the polymer matrix with the template can be very slow, making this approach time inefficient for applications that require fast kinetics, such as chromatography.

Non-covalent

With non-covalent imprinting, interaction forces between template molecule and functional monomer are the same as the interaction forces between the polymer matrix and analyte. The forces involved in this procedure can include hydrogen bonds, dipole dipole interactions, and induced dipole forces.^[1] This method is the most widely used approach to create MIPs due to easy preparation and the wide variety of functional monomers that can be bound to the template molecule. Among the functional groups, methacrylic acid is the most commonly used compound due to its ability to interact with other functional groups.^[12]^[13] Another way to alternate the non-covalent interaction between the template molecule and polymer is through the technique ‘bite and switch’ developed by Professor Sergey A. Piletsk y and Sreenath Subrahmanyam.^[14] In this process, functional groups first non-covalently bond with the binding site, but during the rebinding step, the polymer matrix forms irreversible covalent bonds with the target molecule.^[14]^[15]

Ionic/Metallic

Ionic imprinting, which involves metal ions, serves as an approach to enhance template molecule and functional monomer interaction in water.^[16] Typically, metal ions serve as a mediator during the imprinting process. Cross-linking polymers that are in the presence of a metal ion will form a matrix that is capable of metal binding.^[17] Metal ions can also mediate molecular imprinting by binding to a range of functional monomers, where ligands donate electrons to the outermost orbital of the metal ion.^[1] In addition to mediating imprinting, metal ions can be utilized in the direct imprinting. For example, a metal ion can serve as the template for the imprinting process.^[18]

Applications

One application of molecular imprinting technology is in affinity-based separations for biomedical, environmental, and food analysis. Sample preconcentration and treatment can be carried out by removing targeted trace amounts of analytes in samples using MIPs. The feasibility of MIPs in solid-phase extraction, solid-phase microextraction, and stir bar sorption extraction has been studied in several publications.^[19] Moreover, chromatography techniques such as HPLC and TLC can make use of MIPs as packing materials and stationary phases for the separation of template analytes. The kinetics of noncovalently imprinted materials were observed to be faster than materials prepared by the covalent approach, so noncovalent MIPs are more commonly used in chromatography.^[20]

Another application is the use of molecularly imprinted materials as chemical and biological sensors. They have been developed to target herbicides, sugars, drugs, toxins, and vapors. MIP-based sensors not only have high selectivity and high sensitivity, but they can also generate output signals (electrochemical, optical, or piezoelectric) for detection. This allows them to be utilized in fluorescence sensing, electrochemical sensing, chemiluminescence sensing, and UV-Vis sensing.^[7]^[20] Forensic applications that delve into detections of illicit drugs, banned sport drugs, toxins, and chemical warfare agents are also an area of growing interest.^[21]

Molecular imprinting has steadily been emerging in fields like drug delivery and biotechnology. The selective interaction between template and polymer matrix can be utilized in preparation of artificial antibodies. In the biopharmaceutical market, separation of amino acids, chiral compounds, hemoglobin, and hormones can be achieved with MIP adsorbents. Methods to utilize molecular imprinting techniques for mimicking linear and polyanionic molecules, such as DNA, proteins, and carbohydrates have been researched.^[22] An area of challenges is protein imprinting. Large, water-soluble biological macromolecules have posed a difficulty for molecular imprinting because their conformational integrity cannot be ensured in synthetic environments. Current methods to navigate this include immobilizing template molecules at the surface of solid substrates, thereby minimizing aggregation and controlling the template molecules to locate at the surface of imprinted materials.^[21] However, a critical review of molecular imprinting of proteins by scientists from Utrecht University found that further testing is required.^[23]

Pharmaceutical applications include selective drug delivery and control drug release systems, which make use of MIPs’ stable conformations, fast equilibrium release, and resistance to enzymatic and chemical stress.^[7] Intelligent drug release, the release of a therapeutic agent as a result of a specific stimuli, has also been explored. Molecularly imprinted materials of insulin and other drugs at the nanoscale were shown to exhibit high adsorption capacity for their respective targets, showing huge potential for newfound drug delivery systems.^[24] In comparison with natural receptors, MIPs also have higher chemical and physical stability, easier availability, and lower cost. MIPs could especially be used for stabilization of proteins, particularly selective protection of proteins against denaturation from heat.^[25]

Related Research Articles

In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent called the mobile phase, which carries it through a system on which a material called the stationary phase is fixed. Because the different constituents of the mixture tend to have different affinities for the stationary phase and are retained for different lengths of time depending on their interactions with its surface sites, the constituents travel at different apparent velocities in the mobile fluid, causing them to separate. The separation is based on the differential partitioning between the mobile and the stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus affect the separation.

<span class="mw-page-title-main">High-performance liquid chromatography</span> Technique in analytical chemistry

High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures. The mixtures can originated from food, chemicals, pharmaceuticals, biological, environmental and agriculture, etc, which have been dissolved into liquid solutions.

Nanosensors are nanoscale devices that measure physical quantities and convert these to signals that can be detected and analyzed. There are several ways proposed today to make nanosensors; these include top-down lithography, bottom-up assembly, and molecular self-assembly. There are different types of nanosensors in the market and in development for various applications, most notably in defense, environmental, and healthcare industries. These sensors share the same basic workflow: a selective binding of an analyte, signal generation from the interaction of the nanosensor with the bio-element, and processing of the signal into useful metrics.

Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, electrostatic charge, or hydrogen bonding to strong covalent bonding, provided that the electronic coupling strength remains small relative to the energy parameters of the component. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi–pi interactions and electrostatic effects.

The term molecular recognition refers to the specific interaction between two or more molecules through noncovalent bonding such as hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, π-π interactions, halogen bonding, or resonant interaction effects. In addition to these direct interactions, solvents can play a dominant indirect role in driving molecular recognition in solution. The host and guest involved in molecular recognition exhibit molecular complementarity. Exceptions are molecular containers, including e.g. nanotubes, in which portals essentially control selectivity.

Affinity chromatography is a method of separating a biomolecule from a mixture, based on a highly specific macromolecular binding interaction between the biomolecule and another substance. The specific type of binding interaction depends on the biomolecule of interest; antigen and antibody, enzyme and substrate, receptor and ligand, or protein and nucleic acid binding interactions are frequently exploited for isolation of various biomolecules. Affinity chromatography is useful for its high selectivity and resolution of separation, compared to other chromatographic methods.

Ion chromatography is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including small inorganic anions, large proteins, small nucleotides, and amino acids. However, ion chromatography must be done in conditions that are one unit away from the isoelectric point of a protein.

In chemistry, a non-covalent interaction differs from a covalent bond in that it does not involve the sharing of electrons, but rather involves more dispersed variations of electromagnetic interactions between molecules or within a molecule. The chemical energy released in the formation of non-covalent interactions is typically on the order of 1–5 kcal/mol. Non-covalent interactions can be classified into different categories, such as electrostatic, π-effects, van der Waals forces, and hydrophobic effects.

Chiral column chromatography is a variant of column chromatography that is employed for the separation of chiral compounds, i.e. enantiomers, in mixtures such as racemates or related compounds. The chiral stationary phase (CSP) is made of a support, usually silica based, on which a chiral reagent or a macromolecule with numerous chiral centers is bonded or immobilized.

In chemistry, a salt bridge is a combination of two non-covalent interactions: hydrogen bonding and ionic bonding. Ion pairing is one of the most important noncovalent forces in chemistry, in biological systems, in different materials and in many applications such as ion pair chromatography. It is a most commonly observed contribution to the stability to the entropically unfavorable folded conformation of proteins. Although non-covalent interactions are known to be relatively weak interactions, small stabilizing interactions can add up to make an important contribution to the overall stability of a conformer. Not only are salt bridges found in proteins, but they can also be found in supramolecular chemistry. The thermodynamics of each are explored through experimental procedures to access the free energy contribution of the salt bridge to the overall free energy of the state.

A molecularly imprinted polymer (MIP) is a polymer that has been processed using the molecular imprinting technique which leaves cavities in the polymer matrix with an affinity for a chosen "template" molecule. The process usually involves initiating the polymerization of monomers in the presence of a template molecule that is extracted afterwards, leaving behind complementary cavities. These polymers have affinity for the original molecule and have been used in applications such as chemical separations, catalysis, or molecular sensors. Published works on the topic date to the 1930s.

In polymer chemistry and materials science, the term "polymer" refers to large molecules whose structure is composed of multiple repeating units. Supramolecular polymers are a new category of polymers that can potentially be used for material applications beyond the limits of conventional polymers. By definition, supramolecular polymers are polymeric arrays of monomeric units that are connected by reversible and highly directional secondary interactions–that is, non-covalent bonds. These non-covalent interactions include van der Waals interactions, hydrogen bonding, Coulomb or ionic interactions, π-π stacking, metal coordination, halogen bonding, chalcogen bonding, and host–guest interaction. The direction and strength of the interactions are precisely tuned so that the array of molecules behaves as a polymer in dilute and concentrated solution, as well as in the bulk.

Meir Wilchek is an Israeli biochemist. He is a professor at the Weizmann Institute of Science.

<span class="mw-page-title-main">Two-dimensional polymer</span>

A two-dimensional polymer (2DP) is a sheet-like monomolecular macromolecule consisting of laterally connected repeat units with end groups along all edges. This recent definition of 2DP is based on Hermann Staudinger's polymer concept from the 1920s. According to this, covalent long chain molecules ("Makromoleküle") do exist and are composed of a sequence of linearly connected repeat units and end groups at both termini.

Thermoresponsive polymers can be used as stationary phase in liquid chromatography. Here, the polarity of the stationary phase can be varied by temperature changes, altering the power of separation without changing the column or solvent composition. Thermally related benefits of gas chromatography can now be applied to classes of compounds that are restricted to liquid chromatography due to their thermolability. In place of solvent gradient elution, thermoresponsive polymers allow the use of temperature gradients under purely aqueous isocratic conditions. The versatility of the system is controlled not only through changing temperature, but through the addition of modifying moieties that allow for a choice of enhanced hydrophobic interaction, or by introducing the prospect of electrostatic interaction. These developments have already introduced major improvements to the fields of hydrophobic interaction chromatography, size exclusion chromatography, ion exchange chromatography, and affinity chromatography separations as well as pseudo-solid phase extractions.

Chemoproteomics entails a broad array of techniques used to identify and interrogate protein-small molecule interactions. Chemoproteomics complements phenotypic drug discovery, a paradigm that aims to discover lead compounds on the basis of alleviating a disease phenotype, as opposed to target-based drug discovery, in which lead compounds are designed to interact with predetermined disease-driving biological targets. As phenotypic drug discovery assays do not provide confirmation of a compound's mechanism of action, chemoproteomics provides valuable follow-up strategies to narrow down potential targets and eventually validate a molecule's mechanism of action. Chemoproteomics also attempts to address the inherent challenge of drug promiscuity in small molecule drug discovery by analyzing protein-small molecule interactions on a proteome-wide scale. A major goal of chemoproteomics is to characterize the interactome of drug candidates to gain insight into mechanisms of off-target toxicity and polypharmacology.

Polyrotaxane is a type of mechanically interlocked molecule consisting of strings and rings, in which multiple rings are threaded onto a molecular axle and prevented from dethreading by two bulky end groups. As oligomeric or polymeric species of rotaxanes, polyrotaxanes are also capable of converting energy input to molecular movements because the ring motions can be controlled by external stimulus. Polyrotaxanes have attracted much attention for decades, because they can help build functional molecular machines with complicated molecular structure.

Macromolecular cages have three dimensional chambers surrounded by a molecular framework. Macromolecular cage architectures come in various sizes ranging from 1-50 nm and have varying topologies as well as functions. They can be synthesized through covalent bonding or self-assembly through non-covalent interactions. Most macromolecular cages that are formed through self-assembly are sensitive to pH, temperature, and solvent polarity.

Chiral analysis refers to the quantification of component enantiomers of racemic drug substances or pharmaceutical compounds. Other synonyms commonly used include enantiomer analysis, enantiomeric analysis, and enantioselective analysis. Chiral analysis includes all analytical procedures focused on the characterization of the properties of chiral drugs. Chiral analysis is usually performed with chiral separation methods where the enantiomers are separated on an analytical scale and simultaneously assayed for each enantiomer.

Sergey Piletsky is a professor of Bioanalytical Chemistry and the Research Director for School of Chemistry, University of Leicester, United Kingdom.

References

1 2 3 4 5 6 7 Alexander, Cameron; Andersson, Håkan S.; Andersson, Lars I.; Ansell, Richard J.; Kirsch, Nicole; Nicholls, Ian A.; O'Mahony, John; Whitcombe, Michael J. (2006). "Molecular imprinting science and technology: A survey of the literature for the years up to and including 2003". Journal of Molecular Recognition. 19 (2): 106–180. doi:10.1002/jmr.760. PMID 16395662. S2CID 37702488.
↑ Dickey, Frank (1955). "Specific Adsorption". The Journal of Physical Chemistry. 59 (8): 695–707. doi:10.1021/j150530a006.
↑ Patrikeev, V.; Smirnova, G.; Maksimova (1962). "Some biological properties of specifically formed silica". Nauk SSSR. 146: 707.
↑ Wulff, G.; Sarhan, A. "The use of polymers with enzyme-analogous structures for the resolution of racemates". Angew. Chem. Int. Ed. (11): 341–346.
↑ Takagishi, Toru; Klotz, Irving (1972). "Macromolecule-small molecule interactions; Introduction of additional binding sites in polyethyleneimine by disulfide cross-linkages". Biopolymers. 11 (2): 483–491. doi:10.1002/bip.1972.360110213. PMID 5016558. S2CID 43855200.
↑ Sellergren, B. (1997). "Noncovalent molecular imprinting: antibody-like molecular recognition in polymeric network materials". Trends in Analytical Chemistry. 16 (6): 310–320. doi:10.1016/S0165-9936(97)00027-7.
1 2 3 4 5 Shah, Nasrullah (2012). "A Brief Overview of Molecularly Imprinted Polymers: From Basics to Applications". Journal of Pharmacy Research. 5: 3309.
↑ Wulff, G.; Dederichs, R.; Grotstollen, R.; Jupe, C. (1982). "Affinity Chromatography and Related Techniques -Theoretical Aspects/Industrial and Biomedical Applications". Proceedings of the 4th International Symposium. 4: 22–26.
↑ Wulff, G. (1982). "Selective binding to polymers via covalent bonds. The construction of chiral cavities as specific receptor sites". Pure and Applied Chemistry. 54 (11): 2093–2102. doi: 10.1351/pac198254112093 . S2CID 55884626.
↑ Andersson, Lars (2000). "Molecular imprinting: Developments and applications in the analytical chemistry field". Journal of Chromatography. B, Biomedical Sciences and Applications. 745 (1): 3–13. doi:10.1016/S0378-4347(00)00135-3. PMID 10997701.
↑ Hongyuan, Yan; Row, Kyung (2006). "Characteristic and Synthetic Approach of Molecularly Imprinted Polymer". International Journal of Molecular Sciences. 7.
↑ Andersson, Lars; Sellergren, Borje; Mosbach, Klaus (1984). "Imprinting of amino acid derivatives in macroporous polymers". Tetrahedron Letters. 25 (45): 5211–5214. doi:10.1016/S0040-4039(01)81566-5.
↑ Kempe, Maria; Mosbach, Klaus (1995). "Separation of amino acids, peptides and proteins on molecularly imprinted stationary phases". Journal of Chromatography. 691 (1–2): 317–323. doi:10.1016/0021-9673(94)00820-Y. PMID 7894656.
1 2 Subrahmanyam, Sreenath; Piletsky, Sergey; Piletska, Elena; Chen, Beining; Karim, Kal; Turner, Anthony (2001). "'Bite-and-Switch' approach using computationally designed molecularly imprinted polymers for sensing of creatinine". Biosensors & Bioelectronics. 16 (9–12): 631–637. doi:10.1016/S0956-5663(01)00191-9. PMID 11679238.
↑ Piletsky, Sergey; Piletska, Elena; Subrahmanyam, Sreenath; Karim, Kal; Turner, Anthony (2001). "A new reactive polymer suitable for covalent immobilisation and monitoring of primary amines". Polymer. 42 (8): 3603–3608. doi:10.1016/S0032-3861(00)00739-4. hdl: 1826/803 .
↑ Yavuz, H.; Say, R.; Denizli, A (2005). "Iron removal from human plasma based on molecular recognition using imprinted beads". Materials Science and Engineering. 25 (4): 521–528. doi: 10.1016/j.msec.2005.04.005 .
↑ Xu, L.; Huang, Y.; Zhu, Q.; Ye, C. (2015). "Chitosan in molecularly-imprinted polymers: Current and future prospects". International Journal of Molecular Sciences. 16 (8): 18328–18347. doi: 10.3390/ijms160818328 . PMC 4581248 . PMID 26262607.
↑ Nishide, H.; Tsuchida, E. (1976). "Selective adsorption of metal ions on poly (4‐vinylpyridine) resins in which the ligand chain is immobilized by crosslinking". Die Makromolekulare Chemie: Macromolecular Chemistry and Physics. 177 (8): 2295–2310. doi:10.1002/macp.1976.021770807.
↑ Chen, Lingxin; Wang, Xiaoyan; Lu, Wenhui; Wu, Xiaqing; Li, Jinhua (2016). "Molecular imprinting: Perspectives and applications". Chemical Society Reviews. 45 (8): 2137–2211. doi:10.1039/C6CS00061D. PMID 26936282.
1 2 Haupt, Karsten (2003). "Molecularly Imprinted Polymers: The Next Generation". Analytical Chemistry. 75 (17): 376A–383A. doi:10.1021/ac031385h. PMID 14632031.
1 2 Yılmaz, E.; Garipcan, B.; Patra, H.; Uzun, L. (2017). "Molecular Imprinting Applications in Forensic Science". Sensors. 17 (4): 691. Bibcode:2017Senso..17..691Y. doi: 10.3390/s17040691 . PMC 5419804 . PMID 28350333.
↑ WO WO1996040822A1,Domb, Abraham,"Preparation of biologically active molecules by molecular imprinting",published 1996-12-19
↑ Verheyen, Ellen; Schillemans, Joris; Wijk, Martin; Demeniex, Marie-Astrid; Hennink, Wim; Nostrum, Cornelus (2011). "Challenges for the effective molecular imprinting of proteins". Biomaterials. 32 (11): 3008–20. doi: 10.1016/j.biomaterials.2011.01.007 . PMID 21288565.
↑ Paul, Pijush; Treetong, Alongkot; Suedee, Roongnapa (2017). "Biomimetic insulin-imprinted polymer nanoparticles as a potential oral drug delivery system". Acta Pharmaceutica. 67 (2): 149–168. doi: 10.1515/acph-2017-0020 . PMID 28590908.
↑ Liu, Yibin; Zhai, Junqiu; Dong, Jiantong; Zhao, Meiping (2015). "Magnetic surface imprinted hydrogel nanoparticles for specific and reversible stabilization of proteins". Molecular Imprinting. 3. doi: 10.1515/molim-2015-0006 .