Comparison of helical twisting powers of novel fluorinated amphiphilic enantiomers with their hydrogenated counterparts

This is the first report on novel amphiphilic enantiomers as esters of alanine and serine with a partially fluorinated octyl chain (L-APFOE and L-SPFOE), which form intrinsic chiral nematic (N*) phases with water only and exhibit very high helical twisting powers (htps) compared to their hydrogenated counterparts, dodecylesters of L-alanine (L-ADDE) and L-serine (L-SDDE). They also exhibit a wider N* range than those known in the literature. Furthermore, the htps of the chiral dopants mandelic acid (MA) and hexahydromandelic acid (HHMA) in the racemic nernatic phase of DL-SPFOE and DL-APFOE are remarkably higher than those in the hydrogenated counterparts. The tremendous increase in chirality (htps) of the same single chiral center is a new phenomenon in micellar N* phases and is attributed to a "pivot" effect of the fluoroalkyl chain. As a result, a "skewed micelle" model is proposed to explain why the htp value of L-APFOE is higher than that of L-SPFOE, and accordingly how the intermicellar chirality transfer (chiral induction) may be visualized. The simplicity of these binary mixtures and the enlargement in htp of the single chiral centers visualized as the "skewed micelle" model may provide a basis vital for future computer modeling of chiral lyotropics. (c) 2006 Elsevier Inc. All rights reserved.