AN INVERSION IN THE CHIRALITY IN AN AMPHIPHILIC CHOLESTERIC LIQUID-CRYSTAL WHERE THE CHIRAL DOPANT IS THE CHLORIDE OF THE DECYL ESTER OF L-PROLINE

The chloride of the decyl ester of L-proline has been used as a chiral dopant where the achiral host detergent was tetradecyltrimethylammoni um bromide. The twist and the sense of the helix were measured as a fu nction of the chiral dopant concentration, using the fingerprint textu re and Grandjean planes observed under a polarizing microscope. The ma gnitude of the twist as a function of the chiral dopant concentration initially rose and fell, while the sense of helix was positive. At abo ut 10% the twist magnitude passed through zero, and then with increasi ng amounts of the chiral dopant the sense of the helix became negative . This inversion in the twist sense is thought to be due to a concentr ation-dependent distribution of the cis and trans molecular rotamers d erived from rotation around the >CH-CO2- bond. The existence of cis an d trans rotamers is confirmed using C-13 NMR.