Imprinting factor

Nantasenamat C, Isarankura-Na-Ayudhya I, Naenna T et al. (2007) Quantitative stracture-imprinting factor relationship of molecularly imprinted polymers. Biosens Bioelectron 2007 3309-3317... 

A means to avoid such tedious optimization can be envisaged by employing stoichiometric monomers to develop strong interactions with the template as mentioned above. The other way is to incorporate hydrophilic comonomers (2-hydroxyethyl methacrylate (HEMA), acrylamide) or cross-linkers (pentaerythri-toltriacrylate, methylene bisacrylamide) in the polymer. This results in an increase of the hydrophilicity of the polymer. Indeed, the use of HEMA for a MIP directed towards the anesthetic bupivacaine resulted in high imprinting factors due to reduced non-specific hydrophobic adsorption in aqueous buffer. This was not the case when HEMA was omitted from the polymerization mixture [27]. These conditions were exploited for the direct and selective extraction of bupivacaine from blood plasma samples. 

The use of MIPs as chromatographic stationary phases is the most studied application of MIPs. This method is, in fact, the best way to quickly and efficiently validate the performance of a developed MIP. To achieve this, the MIP is packed into an HPLC column and the retention characteristics of the template and/or analogue molecules are collected in various selected mobile phases. From the collected data, useful parameters, such as capacity factor, imprinting factor, and peak asymmetry, are calculated and used to evaluate polymer affinity, cross reactivity, and other features of the MIP. 

The results of the interaction energies between the monomer and the template were correlated with the retention and imprinting factors... 

Prediction of imprinting factor of MIPs and study Atropine and Boc-L-Trp of template monomer complexes d-Brompheniramine76,77... 

Nantasenamat, C. Naenna, T. Ayudhya, C. I. N. Prachayasittikul, V., Quantitative prediction of imprinting factor of molecularly imprinted polymers by artificial neural network, J. Comp-Aided Mol.Des. 2005, 19, 509-524... 

Fig. 7.6 Options to assess imprinting effects and corresponding response factors, (a) Static mode assessment. (1) Template release. K = partitioning coefficient. (2) Comparison of template binding to a MIP with that to a NIP. IF = imprinting factor. (3) Comparison of binding of template with that of a close analog to the MIP. a = selectivity factor, (b) Flow through SPE mode assessment. Response factors can here be the % recovered template and for gradient elution, the cumulative recovery...

The amount of P-estradiol bound to each MIP and NIP (as an average of four replicas) is seen in Fig. 7.12 together with the corresponding imprinting factors. 

Fig. 7.12 (a) Amount of P-estradiol bound to MIPs and NIPs of an 80-polymer library. The results are averages of four replicas with the standard deviations given as error bars, (b) Average imprinting factors (IF = n p/n ) obtained for the monomer library using the parallel evaluation technique with reader or the serial technique with HPLC... 

Table 7.1 Imprinting factors for polymers prepared using EDMA or DVB as cross-linking monomers and THF as porogen...

Fig. 7.14 3D-representation of imprinting factors (IF) obtained from the rebinding of BV in phosphate buffer pH 7.4 to the polymer library prepared from the design shown in Fig. 7.13. Arrows indicate compositions selected for upscaling as well as the conventional composition used to produce the previously reported MIP...

Fig. 7.15 Approach to assess a MIP/NIP library in the SPE mode. After quantitative nonspecific adsorption of the analyte from water the analyte is gradually eluted from the cartridge by increasing the acetonitrile content in the wash steps. The cumulative recovery is plotted against % acetonitrile in the wash step. The hydrophihcity index is defined as the % water present in the wash solvent leading to 50% release of the analyte from the NIP. The cumulative imprinting factor is defined as the ratio of the recovery from the NIP at that point (=50%) over that from the MIP (= Y)...

Fig. 7.16 Hydrophilicity index (a) and cumulative imprinting factors (b) measured for a Sildenafil imprinted poly(MAA-co-HEMA-co-EDMA) library produced using toluene as poro-gen. The arrows indicate a composition leading simultaneously to a high HI and IF...

Based on this study, the MIPs were synthesized and binding performance was evaluated. The imprinting factor for AA and AAm based MIPs were 5.28 and 4.80, respectively, 4-Vp based MIP had imprinting factor of 2.59 while MMA based MIP exhibited an imprinting factor of 1.95. The experimental results were in good agreement with the computational predictions. 

The thus calculated partition coeificients K (A mip and. np) and imprinting factors are the most important responses used to evaluate the polymers. Alternatively, the fluorescence intensity of each polymer upon binding of the template has been used as response (for an example see Refs. 9 and 10). 

After complete extraction of the template, the polymers were submitted to equilibrium batch rebinding with a ImM solution of terbutylazine in CH2CI2. The imprinting factors ( mip/ np) of MIPs prepared using MAA and TFM as functional monomers were 11 and 6, respectively. 

Think about the final application of the materials you want to prepare or about the way you want to characterize them. If you evaluate the MIPs by batch rebinding, choose partition coefficients or the imprinting factors IF. If you also evaluate them as stationary phases, choose the capacity factors. 

Equilibrate the column with chloroform-acetic acid 99 + 1 v/v, monitoring the absorbance at 270 nm. Measure the dead time by repeated injections of 5 pL of a 50pg/mL solution of acetone in chloroform. The performance parameters of the packed column (number of theoretical plates, efficiency, selectivity) can be measured by repeated injections of 5 pL of a 50 pg/mL solution of theophylline and caffeine in chloroform. Calculate the imprinting factor, IF, as the ratio between the capacity factors for the theophylline eluted on the imprinted and nonimprinted columns (note 9)... 

Note 9. It is very important to calculate the imprinting factor, because it is a measure of how much the imprinted binding sites of the polymer are able to recognize the template molecule, compared to non-specific interactions with the polymeric backbone. In fact, whereas the possible presence of nonspecific interactions between the polymer and the template could not be excluded a priori for both the imprinted and the nonimprinted columns, a molecular recognition effect due to imprinted binding sites could only be possible for the imprinted polymer. 

MIPS prepared with this monomer showed relatively high imprinting factors and a degree of selectivity for barbital over differently substituted barbiturates when tested in the chromatographic mode. Further, analytes where some of the hydrogen-bonding sites had been removed were much less retained on these polymers. 

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