Every compound has different crystal forms with distinct structures and properties called polymorphs. New York University scientist Chunhua Tony Hu and co-authors have discovered a new ambient polymorph of aspirin (acetylsalicylic acid): aspirin IV.

“Since its invention in the late 1890s, aspirin remains only one crystal form until 2005. Thereafter, the second polymorph (aspirin II), similar in structure to the form I, was reported,” Dr. Hu said.

“In March of 2012, when examining the crystallization of aspirin from the melt, New York University’s Professor Alexander Shtukenberg discovered the concomitant crystallization of banded spherulites (concentric optical rings) of form I and smooth spherulites of an unknown form.”

“Because of the coexistence of aspirin I and the new form, and the metastablity of this new form at the room temperature, there was a big headache to separate the new form.”

“In addition, we were facing the challenges of obtaining its high-quality diffraction data and determining its crystal structure.”

It took years of setbacks and several collaborations before Dr. Hu and colleagues achieved high yields of aspirin IV and performed its structural analysis.

“After the five-year not-giving-up effort and with a great teamwork using a combination of X-ray powder diffraction analysis and crystal structure prediction algorithms, we solved the crystal structure of the new polymorph,” Dr. Hu said.

The aspirin IV is predicted to dissolve faster than current form I aspirin tablets.

“This faster dissolve rate would mean faster pain relief after ingestion,” the researchers said.

“Greater dissolving efficiency also means that each tablet would require less of the compound.”

Dr. Hu presented the team’s results July 24, 2018 at the 68th Annual Meeting of the American Crystallographic Association in Toronto, Canada.

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Chunhua Tony Hu. 2018. Discovery of the Third Ambient Aspirin Polymorph. 2018 ACA Annual Meeting;