Characterization of a plant leaf cuticle model wax, phase behaviour of model wax–water systems

We investigated the thermotropic phase behaviour of plant leaf intracuticular wax and two representatives of its main components, 1-docosanol (C22H45OH) and dotriacontane (C32H66), in dry and hydrated state. One objective was to obtain a model wax, which can be used to estimate formulations effects on cuticle diffusivity in vitro. The two wax components were chosen based on results from Gas Chromatography coupled to Mass Spectrometry analysis of cuticular wax. The wax was extracted from Clivia Miniata Regel leaves and contained 68% primary alcohols (C16–C32) and 16% n-alkanes (C21–C33). Differential Scanning Calorimetry, Polarized Light Microscopy and Small- and Wide Angle X-ray Diffraction were used to characterize the cuticular extract and the phase behaviour of the C22H45OH/C32H66/H2O model system. Four individual crystalline phases were discovered in the model wax–water system and eutectic melting occurred in both dry and hydrated state. The thermotropic transitions of the model wax occur within the broader transition region of the extracted leaf wax.