L-phenylalanine anilide

Fig. 6-2. Preparation of MIPs using L-phenylalanine anilide (L-PA) as template. The L-PA model system.

Scheme 15.3 Noncovalent imprinting of L-phenylalanine anilide in a methacrylic acid (MAA)/ethylene glycol dimethylcrylate (EGDMA) polymer matrix. Adapted from Sellergren et al. (1998). Copyright 1988 American Chemical Society.

MIP assays can also be utilized in synthetic organic applications. For example, MIP-based assays have been used to measure the chiral purity of samples in organic solvents. An L-phenylalanine anilide (l-PAA) imprinted polymer was utilized as a recognition element to measure the enantiomeric excess (ee) of PAA samples (Chen and Shimizu 2002). The MIP displays greater capacity for l-PAA versus d-PAA samples of similar concentration, and this difference was used to estimate enantiomeric excess. The enantiomeric excess of an unknown solution was determined by comparing the UV absorbance of the PAA remaining in solution after equilibration against a calibration curve. This MIP assay was demonstrated to be rapid and accurate with a standard error of +5% ee. 

Chen YB, Kele M, Sajonz P, Sellergren B, Guiochon G. Influence of thermal annealing on the thermodynamic and mass transfer kinetic properties of D- and L-phenylalanine anilide on imprinted polymeric stationary phases. Anal Chem 1999 71 928-938. 

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]. 

Petkov, Christova, and Stoineva (11) have reported a study on the hydrolysis of N-acetyl-l.-phenylalanine anilide derivatives with o-chymotrypsin N-methylated anilides 34 (R CHj) were found to be unreactive under the conditions used for the hydrolysis of N—H anilides 34 (R=H). These authors have explained their results in a manner analogous to that described above, i,e. no hydrolysis takes place because steric hindrance caused by the N-methyl group prevents the formation of a tetrahedral intermediate in the N-methyl anilide derivatives. 

Fig. 4,3. Differences in the effect of temperature on the number of theoretical plates and of the amount of chromatographed substance on the retention of template molecules and their enantiomers, (a) Temperature dependence of the number of theoretical plate Wh) in the resolution of D-la and L-la on a polymer imprinted with 1 [21]. (b) Dependence of the capacity factor k on the amount of chromatographed substance in the resolution of l- and of D-phenylalanine anilide on a polymer imprinted with L-phenylalanine anilide [49],...

The first reported preparation of capillary columns containing MIPs utilised a thermally initiated dispersion polymerisation procedure [58], The functional monomer MAA and the cross-linking monomer EDM A were used. Agglomerates of micrometre-sized globular polymer particles were claimed to be prepared in situ in the capillary. Molecular imprinting of L-phenylalanine anilide, pentamidine and benzamidine was undertaken. A pH-dependent retardation of pentamidine over benzamidine in the pentamidine capillary was observed, while the opposite. 

Pure enantiomer imprinting of L-phenylalanine anilide, (/ )-propranolol, S)-metoprolol and (50-ropivacaine has been undertaken and these MIP capillaries have been used in the CEC mode for enantiomer separations [39-41,60-62,70,71] (Table 16.1). Baseline separations for the enantiomers of phenylalanine (Fig. 16.7) and for propranolol and metoprolol could be carried out in less than 2 min. (Fig. 16.5). A propranolol column was shown to be able to resolve several other j8-blockers, including prenalterol, atenolol, pindolol, etc. (Fig. 16.8) [41] and the ropi-... 

Fig. 17.13. Separation of l- and o-phenylalanine anilide on TLC plates covered with poly(-methacrylic acid-co-EDMA) imprinted with (a) L-phenylalanine anilide, (b) o-phenylalanine anilide and (c) no print molecule. Elution with CH3CN-HOAC (99 5). (Adapted from [58], with permission from the American Chemical Society, USA.)...

The final important ratio to consider is that of template functional monomer. Sellergren [64] demonstrated that selectivity of a L-phenylalanine anilide (L-PheNHPh) for its imprint molecule was maximal when the mol-% of M AA was -25%, a value that corresponds to a template functional monomer ratio of 3 1. However, the maximum capacity factor was not obtained until the mol-% MAA was -50%. This was important in that maximum values for affinity and selectivity were not obtained with the same MIP composition. Sellergren [31] proposed a 2 1 model for the MAA L-PheNHPh complex, but suggested a 4 1 ratio should be used to maximise the number of interactions at a given time. Subsequent studies have generally used a ratio of... 

To obtain a series of L-phenylalanine anilide (L-PheNHPh) MIPs with varying MAA L-PheNHPh ratios, Sellergren [64] kept the template and the total monomer concentrations constant and changed the amount of MAA and therefore the amount of cross-linker must also have changed. Using a chromatographic system to assess these polymers he found that maximum selectivity occurred at a different concentration of MAA to that of maximum capacity. However, it has already been observed that varying the amount of cross-linker affects the selectivity of the polymer and hence the observed effects are difficult to interpret. 

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