Hydration of Single Crystals of Dipalmitoylphosphatidylcholine

Abstract

Optical birefringence and x-ray measurements are reported for single crystals ((0.5 mm \times 2 mm \times 5 \mu m)) of dipalmitoylphosphatidylcholine as a function of temperature and relative humidity. Large single crystals grown in (CHCl_3)/acetone at a low water concentration undergo an irreversible phase transformation at (20^{\circ}C) and 70% relative humidity or at (60^{\circ}C) and 65% relative humidity. After this transformation occurs, the crystals can be made to undergo a reversible transformation into and out of the (L_{\alpha}) phase. The x-ray-determined mosaic spread in the hydrated crystal is less than (\approx 0.04^{\circ}) both above and below the main transition.