Habit Modification of Asparagine Monohydrate Crystals by Growth in Hydrogel Media

Crystal growth of a model molecular crystal system, asparagine monohydrate (Asn·H 2 O), was explored in a variety of hydrogel media. Morphologies of crystals grown in agarose, carrageenan, and gelatin gels were compared with those of crystals grown from pure aqueous solutions, as well as those grown from solutions containing various concentrations of related monomers, ions, and cosolvents. The morphological differences were analyzed and interpreted on the basis of complementary interactions at various gel/crystal interfaces. In many cases, the gel polymers were found to have a greater impact on the crystal habit than when solution growth occurred in the presence of comparable concentrations of monomeric or ionic species. These studies clearly indicate that gel methods can provide (at least some systems) a viable alternative means to generate novel crystal morphologies of small molecules that may not be attainable under more conventional solution growth methods.