Structure Dependence of Cholesteric Mesophases

Abstract

Abstract Cholesteric mesophases are mainly found in derivatives of cholesterol. Corresponding derivatives of other sterols do not necessarily show mesomorphic properties. Some of the known structural requirements for the occurrence of mesophases are a planar arrangement of the ring system and substituents extending the long axis of the sterane skeleton. An attempt is made to determine the structural elements in the side chain of sterols which enable a properly substituted sterol to form cholesteric mesophases. A survey of available data pertaining to the mesomorphic properties of a selected group of 3β-sterols is given. It includes data for homologous series as well as for some individual compounds. In the case of the homologous series, the data are very reliable due to internal consistency. For individual compounds, which were carefully selected so that they were representative of their class, existing discrepancies can be explained in terms of impurity effects. From the information presently available the structure dependence of the cholesteric mesophase cannot be explained. However, the derivatives of brassicasterol, 22.23-dihydrobrassicasterol and 22.23-dehydrocholesterol will indicate the dependence of mesomorphic properties upon elements of the molecular structure in the 17β-side chain of 3β-Sterols.