Composition of plant leaf wax, phase behavior of major components and effects of hydration

• The aim of this project was to characterize thermotropic phase behavior and morphology of major wax components of a plant leaf cuticle in dry and hydrated conditions. The composition of the cuticular wax from adaxial leaves of the plant Clivia Miniata Regel was characterized by GC-MS. The analysis showed that the wax is dominated by aliphatic compounds, mainly alkanes (C22-C33) and alcohols (C16-C32). Based on this analysis a model wax was composed comprising 1-docosanol (C22H45OH) and dotriacontane (C32H66). The simplicity of the model allowed for a thorough physical-chemical analysis of the system. Differential Scanning Calorimetry (DSC) and Small Angle X-ray Diffraction (SAXD) were employed to map the phase behavior and morphology of the C22H45OH/C32H66/H2O system. In dry stateC22H45OH and C32H66 observe eutectic interaction with substantial changes in the melting temperatures. C32H66 transforms to a second crystalline phase just below the eutectic point.C32H66 do not interact with water but C22H45OH forms a hydrate with a conformational change in hydrocarbon chain packing. Long chain alcohols is a major component in cuticular wax of many plant species and their ability to form hydrates with less ordered chain conformation can add to the understanding of the nature and barrier function of the plant leaf cuticle.

Nyckelord

Wax

Cuticle

Phase behavior

DSC

SAXD

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