Rebinding selectivity

ACIDIC FUNCTIONAL MONOMERS GIVING ENHANCED REBINDING SELECTIVITY IN NON-COVALENT MOLECULAR IMPRINTING... 

This study revealed that small changes in carbonyl separation, deviating from the initial template inter-carbonyl distances, resulted in significant changes in rebinding selectivity. 

Some limitations of this molecular imprinting technique are obvious the template must be available in preparative amounts, it must be soluble in the monomer mixture and it must be stable and unreactive under the conditions of the polymerization. The solvent must be chosen considering the stability of the monomer-template assemblies and it should result in the porous structure necessary for rapid kinetics of the template interaction with the binding sites. If these criteria are satisfied, a robust material capable of selectively rebinding the template can be easily prepared and evaluated in a short period of time. 

In the cell, RNA polymerase transcribes only select regions of the DNA in these regions it synthesizes RNA that is complementary to one of the DNA strands. This selective action is possible because the holoenzyme is able to recognize and form a stable complex with DNA at specific promoters. RNA polymerase is able to form unstable nonspecific complexes at any place on the template, mainly by an interaction with the DNA phosphates, but it either rapidly dissociates and rebinds or slides along the DNA until it reaches a promoter. It then forms a moderately stable com-... 

Preformed polymers can also be employed to prepare imprinted core-shell particles [143]. The group of Chang recently prepared a poly(amic acid) bearing oestrone as a template molecule covalently bound to the polymer through a urethane linker (see Fig. 2). A layer of this polymer was subsequently deposited on silica particles (10 pm diameter) prefunctionalised with amino groups at their surface. Thermal imidisation of the polymer yielded finally a polyimide shell (thickness about 100 nm) on the silica particles. Subsequent template removal yielded the imprinted cavities, which exhibited selective rebinding of oestrone in HPLC experiments. 

Only a few attempts were reported concerning the arrangement of MIP particles between two porous membranes, or their deposition on a single membrane. For example, Lehmann et al. used MIP nanoparticles with diameters between 50 nm and 300 nm imprinted with boc-L-phenylalanin-anilide obtained by miniemulsion polymerisation the selective rebinding properties as well as the hydrodynamic properties of the nanoparticles stacked between two polyamide membranes were studied [254]. 

An interesting templated bis-functionalization was reported by Shinkai and co-workers who introduced two boronic acid groups regio- and diastereo-selectively into C6o by using saccharides or saccharide derivatives as imprinting templates.147-149 Thus, when D-threitol was used as the template, C2-symmetric cis-3 isomers fC-49 and fA-49,150 were obtained in a nearly. 72 28 ratio after removal of the saccharide templates (Scheme 1.6).149 Competitive complexation studies indicated that D-threitol-imprinted boronic acid (fC)-49 and L-threitol-imprinted (A)-49 preferentially rebind their original templates with up to 48% d.e.148 Exploration of other regio- and diastere-oselective double [4 + 2] cycloadditions between C6o and o-quinodimethanes... 

Flexibility of the polymer network is crucial to allow the template to enter the cavity and rebind to the binding sites. However, flexibility is also crucial to maximise the degree of complementarity towards the template that the crosslinker is able to provide. Even in solution, prior to polymerisation, the crosslinker associates with the template. Hence flexibility of the crosslinker allowing it to model the shape of the template is essential for selective imprinting. EGDMA has so far proven to be the optimum choice, the best compromise between flexibility/rigidity and length [1, 74, 75, 87, 98, 104]. 

At a lecture delivered in Philadelphia s Franklin Institute on March 17, 1949, Pauling reported some of the results from Dickey s experiments [23]. Silica gels had been prepared by procedures analogous to the formation of antibodies , i.e. in accordance with the selective theory, and the study was published later the same year [24]. The method described involved polymerisation of sodium silicate in the presence of a dye. Four different dyes were used, namely methyl, ethyl, /i-propyl and -butyl orange (Fig. 1.3). As much as possible of the dye was subsequently removed, and in rebinding experiments it was found that silica prepared in the presence of any of these pattern moleeules would bind the pattern molecule in preference to the other three dyes. Table 1.2 shows the selective increase in pattern dye sorption capacities of the gels as related to a control gel, prepared in the absence of dye. 

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