WATER-CATALYZED CRYSTALLIZATION OF AMORPHOUS ACADESINE

Lyophilized, amorphous acadesine crystallizes when exposed to water va por. Isothermal calorimetry of samples held al constant humidity showe d crystallization always occured within 1.5 h at relative humidities a bove about 50%, but was never observed at humidities below about 40%. The crystalline phase is anhydrous. Crystallization must proceed throu gh an intermediate, metastable hydrate that immediately decomposes to the anhydrous crystal, a mechanism not commonly considered. The variou s possible mechanisms elf water-catalyzed crystallization of amorphous materials can be distinguished by the dependence of the initiation ri me on the partial pressure of water vapor. (C) 1997 Elsevier Science B .V.