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What Is A Polymorph? Aspirin As A Case Study

Andrew D. Bond (1), Roland Boese (2) and Gautam R. Desiraju (3)

(1) Department of Physics and Chemistry, University of Southern Denmark
(2) Institute for Inorganic Chemistry, University of Duisburg-Essen
(3) School of Chemistry, University of Hyderabad

American Pharmaceutical Review, May/June 2007

Abstract

Polymorphs are commonly understood in pharmaceutical chemistry to be different crystal forms of the same chemical substance. As long as the crystal structure is capable of being described in unambiguous terms, there is not much problem with this definition. However, modern advances in analytical characterization techniques, especially in methods of X-ray diffraction, continue to extend the range and variety of crystal packing, challenging the standard definitions. It is becoming increasingly difficult to assess when structural differences between two crystalline forms are sufficiently significant for these forms to be designated polymorphs. The case of aspirin is pertinent in this regard because crystals of this ubiquitous drug can be made with domains that display different crystal packing arrangements. This article considers some implications of our recent results for standard definitions of polymorphism.

Zweite polymorphe Form von Ibuprophen entdeckt.  
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