Chiral Separation of Racemates with Molecularly Imprinted Polymeric Membranes

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The following results have been obtained through the present research project : The effect of constituting amino acid residue number of oligopeptide derivatives, which are candidate materials to construct molecular recognition sites, on chiral recognition ability was investigated. Chiral recognition sites were formed from oligopeptide derivatives, of which constituting amino acid residue numbers were three to six, by adopting an alternative molecular imprinting. It was made clear that the number four, in other words, the tetrapeptide derivative, is the best candidate material to from a chiral recognition site.Molecularly imprinted polymeric membranes were prepared from polystyrene resin bearing tetrapeptide derivatives H-Asp(OcHex)-Leu-Asp(OcHex)-Glu(OBzl)-OCH_2- (DLDE) consisting of D-amino acid residues or L-amino acid residues. The tetrapeptide derivatives were converted into chiral recognition sites by using not only an optically pure Boc-Trp but also racemic Boc-Trps as a print mo … More lecule. The chiral recognition ability depends on the combination of the absolute configuration of the print molecule and that of constituting amino acid residues. The membrane prepared from DLDE derivative consisting of D-amino acid residues and imprinted by Boc-D-Trp recognized the D-isomer in preference to the corresponding L-isomer and vice versa. In the present study, it was also made clear that racemic print molecules were effective in generating chiral recognition sites. The affinity constant of the generated chiral recognition site was determined to be 9.6 x 10^3 mol dm^<-3>, which was independent of the molecular imprinting conditions. Enantioselective permeation was attained by applying electrodialysis. An optimum selectivity of 5.9, which corresponds to the adsorption selectivity, was attained.Molecularly imprinted polymeric membranes were prepared from various oligopeptide tweezers by the adoption of Boc-D-Trp or Boc-L-Trp as a print molecule. The chiral recognition ability of the formed molecular recognition sites was dependent on the absolute configuration of the print molecule adopted in the membrane preparation (molecular imprinting) process, whereas the candidate oligopeptide tweezers consisted of the L-amino acid residues. In other words, the membranes imprinted by the D-isomer recognized the D-isomer in preference to the corresponding L-isomer, and vice versa. The affinity constant between the target molecule and the chiral recognition site from oligopeptide tweezers was higher than that from a single-strand oligopeptide derivative. Those membranes selectively transported the enantiomer, which was preferentially incorporated into the membrane by dialysis. The permselectivities for these membranes exceeded their adsorption selectivities.A novel candidate polymeric material bearing 5-membered cyclic carbonate, poly[(2-oxo-1,3-dioxolan-4-yl)methyl methacrylate-co-acrylonitrile], converted into a chiral recognition material by adopting Ac-D-Trp or Ac-L-Trp as a print molecule. The molecularly imprinted polymer showed chiral recognition ability, and the material imprinted by the D-isomer of Ac-D-Trp recognized the D-isomer in preference to the corresponding L-isomer, and vice versa. The formation of the chiral recognition site was confirmed by apparent adsorption isotherms of the molecularly imprinted materials. Less