ABSTRACT
ChemistryMIP design usually starts by considering the structural and functional features of the target molecule for which a MIP is needed, the context in which the MIP should operate (solvent, temperature, target concentration, static or dynamic mode, etc.) and whether the binding event should trigger an associated smart function. A limited number of functional groups can hereby be targeted by covalent imprinting approaches. Hence, vicinal diols or α-hydroxy acids can be imprinted in the form of polymerisable boronate esters (1), where subsequent binding and recognition relies on reversible boronate ester formation. Ketones, on the other hand, react with monomers incorporating 1,3-diols to form ketals such as (2), while aldehydes readily form Schiff bases with polymerisable amines (3); these constitute alternative reversible linkages exploited in imprinting.
For a comprehensive coverage of covalent imprinting approaches, the reader is referred to some excellent reviews [4, 5]. Covalent imprinting, in general, has the advantage of placing all of the binding functional groups in the imprinted cavities. Provided that the template can be recovered in high yields, which is unfortunately not always the case, a high density of well-defined sites can be expected. However, some drawbacks with the approach are obvious. Due to the need for synthetic chemistry, which can sometimes be quite demanding, the restrictions with respect to functional groups and the commonly sluggish kinetics of reformation of the covalent bond upon rebinding of template to the empty cavities, pure covalent imprinting in this form has not been extensively exploited. In this respect, the use of sacrificial spacers has found more widespread use [9]. Here the functional monomer is bound to the template through a disposable spacer, such as in (4), that is, removed after polymerisation is completed. This results in a proper disposition of the functional groups allowing rebinding to occur through hydrogen-bonding interactions [5].
