2025-10-23 ヒューストン大学
Ammonium urate, a salt that can form kidney stones, naturally bends and twists during crystallization
<関連情報>
- https://www.uh.edu/news-events/stories/2025/october/10232025-rimer-crystal-bending-welch-center.php
- https://www.pnas.org/doi/10.1073/pnas.2426814122
互変異性は生体結晶の曲げとねじれを引き起こす Tautomerism induces bending and twisting of biogenic crystals
Weiwei Tang, Taimin Yang, Qing Tu, +5 , and Jeffrey D. Rimer
Proceedings of the National Academy of Sciences Published:July 21, 2025
DOI:https://doi.org/10.1073/pnas.2426814122
Significance
The bending and twisting of crystalline materials are essential characteristics for many applications where flexibility is critical; however, well-defined structure–property relationships and molecular design strategies for achieving bent and/or twisted crystals in situ remain elusive. Here, we present a unique case of natural bending without the application of external forces. 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. This work offers potential routes for crystal engineering that can be leveraged for diverse materials to selectively tailor their properties.
Abstract
Understanding and exploiting material flexibility through phenomena such as the bending and twisting of molecular crystals has been a subject of increased interest owing to the number of applications that benefit from these properties, such as optoelectronics, mechanophotonics, soft robotics, and smart sensors. Here, we report the growth of spontaneously bent and twisted ammonium urate crystals induced by the keto–enol tautomerism of the urate molecule. The major tautomer is native to biogenic crystals, whereas the minor tautomer functions as an effective crystal growth modifier to induce naturally bent and twisted ammonium urate crystals. We show 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 are used to characterize the origin of bending. Spatially resolved nano-electron diffraction and high-resolution electron microscopy of naturally bent crystals show nearly single crystallinity with local lattice deformations generated by a combination of screw and edge dislocations. These observations are consistent with photoinduced force microscopy and contact resonance atomic force microscopy, which confirmed spatially resolved changes in the intermolecular interactions and the mechanical properties throughout the cross-sectional and axial regions of bent crystals. A mechanism of bending involving the generation of regionally specific dislocations is proposed as an alternative to more commonly reported models. These findings highlight a unique characteristic of tautomeric crystals that may have broader implications for other biogenic materials.
