Issue Date: August 6, 2007
What do you mean by polymorph?
As a retired chemistry professor and one who has contributed to some extent in the field under discussion, I am amused at the amateur pronouncements by so many claiming to be professionals in the field of crystallography and solid-state studies by diffraction (C&EN, June 18, page 17).
The term "polymorph" had been in disarray until a definitive discourse was presented by me in the Journal of Chemical Education (1987, 64, 404). Even now, the well-known texts in inorganic chemistry continue to present conflicting and misleading definitions of polymorph, which are reflected in the discussions in the C&EN article. The term polymorphism has no place in the scientific discussion.
Before any prefix, like pseudo, is added to the term polymorph, the proponents must ensure that everyone means exactly the same thing when using the word polymorph. One must recognize that different polymorphs, even as per definitive descriptions in the literature, in fact represent different compounds.
In the case of two aspirins, these are not different conformations but rather distinct molecular species of the same chemical structural formula. It is this distinct nature that provides the distinct pharmaceutical properties. Indeed, different polymorphs will be assimilated differently in the body's metabolic process and thus impart distinctly different medicinal responses.
Brahama D. Sharma
Pismo Beach, Calif.
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