Pitches guest-host effect

Such twisted nematic phases are called induced cholesteric solutions and - as schematically outlined in Fig. 4.6-9 - enantiomers cause countercurrently twisted structures. As discussed by Korte and Schrader (1981) this effect offers the potential of sensitively characterizing the chirality of small amounts of optically active compounds. There are no restrictions as to the type of chirality, and the experiments can advantageously be based on infrared spectroscopy. The application of induced cholesteric solutions was later reviewed again by Solladie and Zimmermann (1984). The host phase is the more twisted the more of the optically active guest compound is dissolved. Quantifying the twist by the inverse pitch z and the concentration by the molar fraction x, the ability of a chiral. solute to twist a given nematic host phase is characterized by the helical twisting power (HTP Baessler and Labes, 1970). For small values of a this quantity P is defined by the relation... 

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