Rotator Phases of Aliphatic Aldehydes and Implications for Wax Crystal Growth in Plants

Abstract

The even C22–32 aliphatic aldehydes were synthesized and analyzed by differential scanning calorimetry and high-temperature X-ray diffraction. Aldehydes were determined to crystallize into triclinic, monoclinic, and orthorhombic lattices and undergo solid–solid transitions into the rotator (R) phase. All of the known R phases for the even and odd n-alkanes were observed for the even aldehydes. Further, binary mixtures of triacontanal and n-nonacosane, two representative constituents of plant cuticular waxes, were determined to be partially miscible at three compositions (25:75, 50:50, 75:25) and likewise possess R-type phases. Many plants exhibit mutations wherein the expression of aldehydes in cuticular waxes is significantly decreased. Afflicted mutants are often glabrous, devoid of epicuticular wax crystals, and suffer from increased cuticular permeability as well as drought intolerance. We propose that aldehydes serve as miscibility intermediaries and their R phases may provide a mechanism for wax crystal growth in plants.