Subtleties in crystal structure solution from powder diffraction data using simulated annealing: ranitidine hydrochloride.

Recent advances in crystallographic computing and availability of high-resolution diffraction data have made it relatively easy to solve crystal structures from powders that would have traditionally required single crystal samples. The success of direct space methods depends heavily on starting with an accurate molecular model. In this paper we address the applicability of using these methods in finding subtleties such as disorder in the molecular conformation that might not be known a priori. We use ranitidine HCl as our test sample as it is known to have a conformational disorder from single crystal structural work. We redetermine the structure from powder data using simulated annealing and show that the conformational disorder is clearly revealed by this method. Copyright 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:244-249, 2003