Biomedical Engineering Reference
In-Depth Information
Considering the large number of functional groups on the peptides and proteins, which
are available for the interaction with functional monomers, there are a number of different
strategies for creating molecular imprinted polymers targeting these biomacromolecules.
Functional groups forming strong template interactions with the target molecules are
commonly used, including electrostatic and metal-chelating groups [21, 22], which is
however limited by the structure and chemical properties of the selected template molecules.
A more generally applicable approach seems to design molecular imprinted polymers
utilizing the shape complementarity along with multi-point weak interactions, such as
hydrophobic and hydrogen bonding, for providing molecularly selective binding sites.
This review presents the recent advances and developments of molecular imprinted
polymers in biomacromolecules recognition, with an emphasis on the comparative analysis of
different approaches developed, underlying the advantages and disadvantages.
2. Molecular Imprinting in Aqueous Media
There is strong evidence to suggest that the cooperative interaction between hydrogen
bond and hydrophobic interaction is the most dominant form of template-receptor
complexation. Hydrogen bonds are high directional, and many synthesized polymers rely on
the high directionality of the hydrogen bonds and shape specificity of target molecules to
prepare receptors with strong interaction and molecular recognition [23]. So, the majority of
published papers on molecular imprinted polymers are based on polymers synthesized in
organic solvents, because the hydrogen bond between template molecules and functional
monomers considered among the dominant forces in imprinting is largely weakened in
aqueous system [24]. It was observed that the separation factors of the molecular imprinted
polymers were significantly lower in acetonitrile/water mixtures than in pure acetonitrile [25].
In addition, it was shown that water could significantly lower the effectiveness of hydrogen
bonds between the template and the receptor. However, the recognition of biomolecules is
most relevant in aqueous solution to avoid denaturing or degradation of the template
molecules [26]. Hence, molecular imprinting in aqueous media has to take advantage of other
types of interactions, such as π-π stacking, ionic interactions, and hydrophobic interactions to
facilitating molecular recognition [27-29].
Recently, many researches have demonstrated that using chitosan in the polymer network
can increase the affinity and selectivity to target proteins due to its high content of amino and
hydroxyl functional groups. Xia et al. prepared a semi-interpenetrating molecular imprinted
hydrogel for hemoglobin based on polyacrylamide/chitosan in aqueous solution [30]. The -
NH
3
+
and the hydroxyl groups of chitosan will interact with the target protein by electrostatic
forces rather than hydrogen bonding, which are suspected as the main recognition mechanism
at high water content. Further research indicated that the amount of hemoglobin adsorbed
increased with increase of temperature, and the calculated apparent activation energy for the
adsorption was 24.6 kJ/mol, indicating that the adsorption has a low potential barrier [31].
Guo et al. [32-34] prepared hemoglobin imprinted polymers by physically entrapping or
chemically grafting of selective polyacrylamide gels onto porous chitosan beads, and Fu et al.
[35] reported the synthesis of bovine serum albumin imprinted polymers gels based on
chitosan and polyacrylamide via homogeneous graft copolymerization of acrylamide on
chitosan dissolved in acidic aqueous. Their results indicate that the incorporation of chitosan
