Racemic polymers chiral recognition

An optically active polymethacrylate (2) having a binaphthol moiety in the side chain was synthesized by radical polymerization. This polymer coated on silica gel resolved several racemates.50 However, no data on the influence of the stereoregularity of the main chain on resolution have been reported. The chiral recognition by this polymer may simply arise from the binaphthyl group. 

Although enantioselective inclusion into the chiral clefts formed by the polymer network may play a minor role in the chiral recognition mechanism, enantiodiscrimina-tion is primarily driven by hydrogen bonding and/or Ti-TT-interactions. A representative selection of successfully resolved racemates employing synthetic polymeric CSPs is listed in Table 9.7. 

The optically active polymers obtained from D3PyMA, PB2PyMA, 2PyDBSMA, and 3PyDBSMA show chiral recognition ability toward some racemic compounds in chiral HPLC or chiral adsorption experiments, though the ability was generally lower than that of poly(TrMA).16 59-62... 

We S5mthesized chiral pol5nners with different tacticities by the radical polymerization of the optically active methacrylamide 21 (Fig. 8) in the absence and presence of a Lewis acid, Yb(OTf)3 [21]. The polymerization without the Lewis acid at —20°C afforded the syndiotactic polymer with a triad tacticity mmimrl rr = 0/13/87, whereas in the presence of the Lewis acid, the isotactic polymer with mmimrirr = 87/13/ 0 was obtained. These two tactic polymers exhibited different chiral recognitions as the CSPs in HPLC, as shown in Table 1. The isotactic polymer could not resolve any of the three racemates, although two racemates were resolved on the highly syndiotactic polymer. In the isotactic... 

The helical polytriphenylmethyl methacrylate was the first synthetic chiral polymer able to separate a very limited number of enantiomers [28]. Recently a fully synthetic chiral stationary phase based on polymerized diacryloyl derivative of fra s-l,2-diaminocyclohexane [either (R, R) or (S, S)] bonded to silica gel in the form of a very thin layer was proposed as a new LC CSP [29]. This CSP could not resolve many enantiomeric pairs. However, when it could resolve a racemate, it was shown that the amount that could be loaded was much larger than that on most other CSPs. It means that the number of active sites is large. Hydrogen bonds were found to be pivotal in the chiral recognition mechanism of this CSP. The enan-tioselectivity was adjusted by the methanol content in the organic mobile phase. Polysodium A-undecanoyl-L-leucyl-leucinate (poly-SULL) and —L-leucyl-valinate... 

To be able to attribute the binding of an MIP to an imprinting effect it is of utmost importance to show that specific recognition sites have been formed due to the presence of the print molecules during the polymerisation. This is usually done by comparisons with appropriate reference polymers. Polymers prepared without print molecules are not always the best choice, since the physical properties (surface area, porosity, etc.) of these polymers often differ from those of imprinted polymers. Reference polymers prepared with the optical antipode or a racemic mixture as the print species are preferred. The selectivity will be reversed when using the optical antipode and a racemic mixture will give a polymer incapable of separating the two enantiomers (unless the monomer(s) is/are chiral). 

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