Chiral HPLC and physical characterisation of orthoconic antiferroelectric liquid crystals

ABSTRACT

New orthoconic antiferroelectric liquid crystalline materials were synthesised and characterised in their racemic forms and as (S) enantiomers. The materials possess oligo-methylene spacers of different lengths in semi-fluorinated achiral chains and lateral substitution by fluorine at two different positions of the molecular core. For comparison purposes, analogical materials without fluorine lateral substitutions were also prepared. Polysaccharide chiral stationary phases based on two different chiral selectors were used for the separation of the enantiomers of the individual racemic mixtures by high-performance liquid chromatography. A baseline separation of (S) and (R) enantiomers was obtained for four of the six studied liquid crystalline materials. Two of the materials were partially separated under the optimised separation conditions. The elution order of the individual enantiomers in the racemic mixtures was successfully assigned, as pure (S) enantiomers of all the studied materials were available. Both the position of the fluorine atom within the molecular core and the size of the achiral moiety had significant effects on the separation of the individual enantiomers of the studied compounds. Moreover, it was also found that the structure of the chiral stationary phase selector significantly influenced the enantiomeric resolution.

GRAPHICAL ABSTRACT

KEYWORDS:

• Liquid-crystalline materials
• antiferroelectric compounds
• liquid chromatography
• chiral HPLC
• semi-fluorinated non-chiral chain

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic [LD14007] and [No 20/2015], by the Czech Science Foundation [CSF 15-02843S] and COST Action [IC1208].