Synthesis And Chiral Recognition Abilities Of Helical Poly(phenylacetylene)s Bearing Chiral Pendants

In this work, helical poly(phenylacetylene) derivatives bearing one chiral carbon atom and two chiral carbon atoms as pendants were synthesized, respectively. Chiroptical properties and chiral recognition ability of polymers were investigated.The phenylacetylene monomers bearing L-phenylalaninol group and L-valinol were synthesized, named as N-(4-ethynylbenzoyl)-L-phenylalaninol (PAA-Phg-OH) and N-(4-ethynylbenzoyl)-L-valinol (PAA-Val-OH), respectively. A series of phenylacetylene monomers bearing one carbon atom were synthesized via the reaction between PAA-Phg-OH/PAA-Val-OH and some chlorides; a series of phenylacetylene monomers bearing two carbon atoms were synthesized via the reaction between PAA-Phg-OH and some Boc-amino acids. The monomers were polymerized in DMF or THF using Rh(nbd)BPh4 as the catalyst to yield the poly(phenylacetylene)s bearing one or two chiral carbon atoms. The structure of monomers and polymers were characterized by 1H NMR, IR, SEC, and the results showed that the main chain of all the polymers possessed cis-transoid configuration.Influence of solvents, temperature and pendants on optical activity and helical conformation were investigated vis polarimeter and circular dichroism (CD) spectra. The results demonstrated that the poly(phenylacetylene) derivatives bearing one chiral carbon atom possessed predominantly one-handed helical conformations in DMF, and had tightly twisted helical conformations in THF. Poly(phenylacetylene)s bearing two chiral carbon centers, polymers with the second chiral carbon of L-configuration possessed predominantly one-handed helical conformations in DMSO or TFA/DMSO=9/1, and D-configuration possessed predominantly one-handed helical conformations in DMF or TFA/DMF=9/1. The thermodynamic stability of the dynamic helical structures enhanced at lower temperatures,their stereoregularity inceased as the temperature decreased and this phenomenon is reversible within limits.CSPs were prepared using THF, CHC13, DMF (TFA/DMF=9/1) or DMSO (TFA/DMSO=9/1) as coating solvent, and the influence of side chain groups, coating solvents and mobile phase on chiral recognition abilities were investigated using HPLC. The result demonstrated that the side group played an important role on chiral recognition of these polymers. Polymers bearing one chiral carbon possessed tightly twisted helical conformations showed higher chiral recognition abilities, and decreased the polarity of eluent increased the chiral recognition abilities. Polymers bearing two chiral carbons have higher one-handedness helical conformations showed higher chiral recognition abilities. Polymers bearing the second chiral carbon of D-configuration showed higher chiral recognition abilities in DMF or TFA/DMF=9/1, and L-configuration showed higher chiral recognition abilities in DMSO or TFA/DMSO=9/1.