Newswise — WASHINGTON, D.C., July 24, 2018 -- Every compound has different crystal forms with distinct structures and properties called polymorphs. A team of researchers at New York University recently discovered a new aspirin polymorph that’s predicted to dissolve faster than current form I aspirin tablets. This faster dissolve rate would mean faster pain relief after ingestion. Greater dissolving efficiency also means that each tablet would require less of the compound. Interestingly, it took years of setbacks and several collaborations before researchers achieved high yields of the polymorph and performed a structural analysis of this new type IV aspirin.
During the 68th Annual Meeting of the American Crystallographic Association, being held July 20-24, 2018, in Toronto, Canada, Chunhua (Tony) Hu, a research professor and X-ray crystallographer at New York University, will present the painstaking story of aspirin IV alongside its structural definition.
In 2012, another New York University professor, Alexander Shtukenberg, was developing a long-forgotten method for growing crystals. Shtukenberg had adapted the popular melt and quench-cooling method for crystal preparation between glass slides by manipulating the speed of the quench step. When he applied his method to aspirin, the usual concentric optical rings (spherulites) formed, but about 15 percent of the spherulites were unexpectedly smooth. Then, Shtukenberg and Bart Kahr realized they found an entirely new form of the common painkiller.
Raman spectrometry experiments confirmed that the smooth spherulites possessed a unique molecular fingerprint. However, the polymorphs’ instability obfuscated the researchers’ ability to determine the structure of the common type IV compound because within a few hours of formation, the smooth spherulites transformed into type I crystals.
Shtukenberg traveled to multiple synchrotron laboratories to see if more powerful equipment could do the job. But the problem remained: Sample, quality and quantity were not high enough to get the structural detail needed to prove that these smooth spherulites were a new polymorph of aspirin.
Then, working in the same department as Shtukenberg, Hu developed a supercooling quench that took compounds down to minus 173 degrees Celsius after the melt. Having discussed the unknown type of aspirin with Shtukenberg, Hu decided to try his supercooling method. “In 10 minutes I got it!” Hu said, amazed that they achieved 40 percent purity. The two researchers started collaborating to optimise the recipe and soon achieved 70 percent purity.
Using the powerful facilities at the Argonne National Laboratory in Illinois, the researchers began X-ray powder diffraction analysis. The researchers directed X-ray waves at the purified crystals. Different atoms diffract light at different angles, like how light waves diffract through a kaleidoscope. “From the diffraction pattern you can get intensity and symmetry information,” Hu said.
Then, Hu brought in theoretical physicist Qiang Zhu from the University of Nevada, Las Vegas. Zhu used structural prediction algorithms to assess the atomic layout of the new structure and produced a model structure of type IV aspirin.
“The model matched the data so beautifully that everyone was very happy with the result,” Hu said. “But is it 100 percent correct?” Now, Hu wants to validate the model, so he is collaborating with Martin U. Schmidt from Goethe University, Frankfurt, Germany, an expert in Rietveld refinement, another prediction method, to confirm the current structural model of type IV aspirin. Given the potential marketability of an improved aspirin, Hu is also working to patent their type IV recipes.
Presentation “Discovery of the Third Ambient Aspirin Polymorph,” by Chunhua (Tony) Hu, is at 2:00 p.m. EDT, Tuesday, July 24, in the Provincial South Session Room at the Sheraton Centre Toronto Hotel.
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68th Annual Meeting of the American Crystallographic Association