Boron molecularly imprinted

Fig. 2. Concept of molecular imprinting - the covalent approach. 1. Derivatization of sugar template with p-vinylphenyl boronate. 2. Polymerization in the presence of a cross-linker...

Figure 6.5 Boronic ester approach to covalent molecular imprinting of PMP using VPMA [26].

The most successful approach in covalent molecular imprinting is probably the coupling of polymerizable boronic acids to hydroxyl groups present on the template to form boronate esters (Figure 2.2). This approach has, for example, been applied to the imprinting of sugars [57-59]. 

Fig. 3-2 Molecular imprinting of sialic acid using 4-vinylphenyl-boronic acid as a functional monomer...

Gagn6 et al. developed polymer active sites that additionally contained a receptor (recognition sites) displayed in the outer sphere of the metal center (reactive site). The Suzuki reaction of /)-bromoanisole with phenyl boronic acid and the allylation of dimethyl malonate with allyl acetate were both chosen to assess the presence and/or effect of the crown-ether in crown-ether-molecular imprinting polymer-palladium complex. The results showed that molecular imprinting can be used to functionalize the second-coordination sphere of a transition metal complex and subsequently affect its catalytic behavior. 

Norrlow, O. Mansson, M.-O. Mosbach, K. Improved chromatography prearranged distance between boronate groups by the molecular imprinting approach. J. Chromatogr. 1987,396, 374-377. 

An important question in molecular imprinting has been addressed using covalent binding by two boronic acids to what extent can imprinted polymers also bind substances other than the template. For example, are racemates of other substances resolvable In the first experiments on glyceric acid esters 5 with a certain ester as template, imprinted polymers were shown to resolve a whole series of racemates even when the alcohol group in the racemate is varied (methyl, ethyl, benzyl, or 4-nitrophenyl) [39]. Aromatic amino acids were shown to behave similarly. Here, the aromatic group in the racemates can vary. A racemate resolution is possible provided that the rest of the structure remains the same [40]. 

Table 2 Examples of Molecular Imprinting Using Boronic Acids as Binding Sites... 

At neutral pH poly(L-lysine) adopts a (3-sheet conformation, as the pH is raised the protein takes on a oc-helix structure and finally a random coil at high pH. When this polymer has pendent boronic acid groups, in the presence of monosacharides the a-helix content of the peptide chain increases and the pH at which the maximum helix content is observed is reduced. The molecular imprinting was carried out at pH 11 in the presence of a large excess of D-glucose or D-fructose. After equilibration, a gold-coated QCM crystal was placed in the solution. This allowed the polypeptide to adsorb onto the gold surface either as a random coil or (3-turn,... 

Frigeri, A. Kobayashi, H. Shinkai, S. Reinhoudt, D.N. From solutions to surfaces A novel molecularly imprinting method based on the conformational changes of boronic-acid-appended poly (L-lysine). Angew. Chem. Int. Ed. 2001, 40, 4729-4731. 

Miyahara, T. Kurihara, K. Two-dimensional molecular imprinting binding of sugars to boronic acid functionalized, polymerized Langmuir-Blodgett films. Chem. Lett. 2000, 29, 1356-1357. 

Film devices are often developed based on polymer backbone or framework. For example, a poly-pyrrole film with borane in the backbone has been obtained by direct electropolymerisation. Boronic acid derivatised pyrroles have been employed to make molecular imprinted polymers (MIPs), for example for the detection of dopamine. Figure 8.8 shows the concept of polymer formation in the presence of analyte followed by extraction to provide highly selective pockets for dopamine to bind. The read-out in this case is based on the Fe(CN)/" redox probe. Poly-amino-boronic acid films without imprinting were employed for dopamine detection. Co-polymer sensor films based on poly(aniline-co-3-aminobenzeneboronic acid) and poly(acrylamidophenylboronic acid) have been reported. 

Although the first report on boronic acids was published in 1862, boronate affinity materials have not been extensively investigated until recently. In recent years, various boronate-functionalized materials, " such as macroporous monoliths, " " nanoparticles, and mesoporous materials, have been developed into important tools for the facile selective extraction of cis-diol-containing compounds. With these matrices, several important materials with teamed boronate affinity and boronate avidity as well as boronate affinity-based molecularly imprinted polymers have been prepared. 

Boronate Affinity-Based Molecularly Imprinted Polymers... 

Figure 11.22 Principle (A) and procedure (B) of photolithographic boronate affinity molecular imprinting. (Reproduced from ref. 133 with permission. Cop rright 2013, John Wiley Sons, Ltd.)...

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