The confusion of indexing aspirin crystals

Clare Aubrey-Medendorp, Sean Parkin, Tonglei Li

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Much of the existing literature dealing with crystalline aspirin is vague or ambiguous with regard to indexing of the crystal faces. The inconsistency with which the indices of the dominant faces have been assigned leads to confusion in analysis of surface properties. To clarify this, we have conducted crystal growth experiments on aspirin, and indexed the crystal faces with X-ray diffraction (XRD), paying special attention to the placement of symmetry elements. The space group was confirmed as P21/c, and the dominant face was (100). Contact angle measurements made on the two major faces of aspirin indicate the (100) face to be more hydrophobic than the (001) face, likely due to the acetyloxy moiety, not the carboxyl, exposed on the (100).

Original languageEnglish
Pages (from-to)1361-1367
Number of pages7
JournalJournal of Pharmaceutical Sciences
Issue number4
StatePublished - Apr 2008

Bibliographical note

Funding Information:
The research was supported by the PhRMA Foundation. The authors would like to thank Ms. Ellen Savelli for her work with contact angle measurements.


  • Aspirin
  • Contact angle
  • Crystal packing
  • Indexing
  • Wettability
  • X-ray diffraction

ASJC Scopus subject areas

  • Pharmaceutical Science


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