Separation racemates/molecularly imprinted

CEC was demonstrated in the analysis of /i-adrenergic antagonists using capillaries modified with propranolol-imprinted polymer. In situ molecular imprinting was performed via photo-polymerisation at — 20°C within a capillary that was premodified with 3-methacryloxypropyltrimethoxysilane. The time for UV irradiation was carefully determined so as to obtain a polymer coating of appropriate thickness. Enantioseparation of the racemate of propranolol was successfully demonstrated with a separation factor of 1.12 and a resolution factor of 1.26. 

CHIRAL SEPARATION OF RACEMIC Z-TYR-OH ON MOLECULARLY IMPRINTED CSPs... 

Figure 6.27 illustrates a sample chromatogram for racemic resolution on a MIP stationary phase, whilst Table 6.6 summarises the developments in the field of molecularly imprinted chiral separation technology. 

As mentioned in Chap. 7, molecular imprinting of polymers15 can also be used to prepare hosts for the removal of the desired optical isomer from racemates. Foam flotation with imprinted polymers has been used in chiral separations.16 Flotation is often used to separate minerals from their ores. The polymers can be reused repeatedly. This may turn out to be the lowest-cost method of resolution. 

As separation materials, the obvious advantage offered by MIPs is a relatively straightforward and predetermined selectivity. Based on molecular imprinting, some difficult separations, particularly enantiomer separations, have been solved. Amino acid enantiomers, chiral dipeptide, and racemic naproxen are examples. In particular, molecular imprinting is probably currently the only choice where no suitable biomolecule is available. When coupling with appropriate transducers such as electro-, photo- or magnetochemical transducers, MIPs may be applied as the monitors in several sys-... 

Despite this, there are examples of molecularly imprinted chiral stationary phases that are capable of resolving more than the raceme corresponding to the template. In these cases, minor structural differences are possible without compromising the separation. For example, a polymer imprinted with L-phenylalanine anilide efficiently separated the protected amino acids with different side chains or amide substituents [36]. Anilides of all aromatic amino acids were resolved as well as p-naphthylamides and -nitroanilides of leucine and alanine [40]. 

This open tubular approach was improved by Tan and Remcho [21] who generated molecularly imprinted polymer films attached to walls of 25 pm ID capillaries. They injected as well a mixture of porogen, template, functional monomers, crosslinker, and initiator into a capillary activated with a polymerizable silane and performed the polymerization at elevated temperatures. A capillary with a total length of 100 cm and a separation length of 85 cm, respectively, coated with a polymer imprinted with dansyl-L-phenylalanine was applied for a separation of the racemate of dansyl-phenylalanine. Using acetonitrile/lOmmol (pH 7.0) phosphate buffer (10 1, v/v), a baseline separation of the two enantiomers could be achieved (Fig. 9). 

Due to the only moderate separation power, very few examples of WAC have been described in the literature, apart from enantioselective separations of racemates by molecular imprints (MIP), which typically require the separation of only two species. 

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