Investigations of optical activity of natural products and chiral pharmaceuticals using liquid crystal technologies

Over recent years there has been a tendency to target the development of chiral materials for use in healthcare treatments. In such applications and therapies the optical purity is an important factor to consider. Two common materials, that have relevance in bio-medical applications, and which are available in their chiral and racemic forms are menthol and ibuprofen. In this article we quantitatively investigate the levels of optical purity in commercially available menthol by the amplification of its chiral properties through the self-organisation processes found in liquid crystals, and secondly, we qualitatively investigate ‘optical activity’ in racemic ibuprofen. In organised fluids, such as liquid crystals, there are three levels of chiral complexity to consider. The first is point asymmetry or structural dissymmetry associated with molecular stereochemistry. The second level is related to reduced space symmetry, where the local molecular organisation, whether caused through associations between individual molecules or supramolecular ensembles, is asymmetric or dissymmetric. The reduced environmental or local symmetries are associated with physical properties such as ferroelectricity, antiferroelectricity, electroclinism, and secondary properties such as pyroelectricity and electrostriction (flexoelectricity). Such properties have been utilised in the determination of enantiomeric excess. The third level of chiral complexity is form chirality associated with the bulk organisation of the molecules. This is usually manifested in the form of helical macrostructures and frustrated defectstabilised phases, for which properties such as helielectricity, thermochromism, and electrochromism can be observed. The pitch length in helical macrostructures is dependent on enantiomeric excess, ie the relative proportions of the enantiomers (or diastereoisomers) in the ensemble system. In the case of enantiomorphs, when the proportions are equal the pitch becomes infinite. Moreover, depending on the helix twist direction, ie right-hand or left-hand helix, chiral nematic phases can also be used to determine the spatial configuration for a chiral material possessing a single stereogenic centre. It is also known that helical macrostructures formed by chiral nematic phases have the ability to rotate the plane of incident