Bending biogenic crystals naturally without external forces

From creating flexible gadgets to better medicines, the art of bending crystals is reshaping technology and health, and at the University of Houston a crystals expert makes it look almost like a magic trick.

Jeffrey Rimer, Abraham E. Dukler Professor of Chemical Energy, has shown how to bend and twist crystals without physical force—no touching, poking or prodding and no heat or radiation, conditions typically required to achieve reshaping.

Instead, he is using a molecule called a tautomer, which is doing all the work, inducing bending and twisting of biogenic crystals. In the world of crystals, tautomers are shifty characters—molecules with the ability to shift their atoms around.

All at once a hydrogen atom might be in one place, then hop to another, while other atoms slip around.

One of the pharmaceutical applications where this will be of potential importance is in drug delivery, where approximately 30 of the top 200 drugs are tautomers.

“Here, we present a unique case of natural bending without the application of external forces,” reports Rimer in the journal Proceedings of the National Academy of Sciences.

Rimer’s work was performed at The Welch Center for Advanced Bioactive Materials Crystallization at UH.

“This is a mechanistic investigation showing how tautomerism induces controlled, natural bending and twisting by virtue of the minor tautomer, which is a growth modifier that causes defects in the crystal structure (e.g., twins, screw and edge dislocations), leading to macroscopic effects on material properties,” said Rimer.

The importance of control

Understanding and exploiting material flexibility through phenomena such as bending and twisting molecular crystals has been a subject of increased interest because of the number of applications that benefit from these properties, like optoelectronics, soft robotics, smart sensors and pharmaceuticals.

“We have shown that bending leads to physical deformations that impact dissolution, which can impact pharmacokinetics in the delivery of active pharmaceutical ingredients,” said Rimer.

In the work, the Rimer team showed that the degree of curvature can be tailored based on the judicious selection of growth conditions. A combination of state-of-the-art microscopy and spectroscopy techniques were used to characterize the origin of bending.

“Our findings provide a greater understanding of the defects generated during pathological crystallization of a tautomeric material and how this phenomenon can lead to unique bent, twisted, and dendritic morphologies observed in both biological and synthetic materials,” said Rimer. “The ability to selectively control this behavior opens broad avenues for crystal engineering.”

Rimer’s colleagues on this project are WeiWei Tang, University of Houston; Tamin Yang, Stockholm University; and Qing Tu, Texas A&M University.