Chemists from New York University and Russia's St. Petersburg State University have created crystals that can twist and untwist, pointing to a much more varied¹ process of crystal growth than previously² thought. Their work, which appears in the latest issue of the Journal of the American Chemical Society, may explain some of the properties of high-polymers（聚合物，高分子） , which are used in clothing and liquid crystal displays, among other consumer products. Crystal growth has traditionally been viewed as a collection of individual atoms, molecules³, or small clusters（簇，丛） adding to a larger block that remains⁴ in a fixed⁵ translational relationship to the rest.

But the NYU and St. Petersburg State University chemists discovered a wholly new phenomenon for growth— a crystal that continually changes its shape as it grows.

To do this, the researchers focused on crystals from hippuric acid（马尿酸） —a derivative⁶（衍生物，派生物） of the amino acid（氨基酸） glycine（甘氨酸） . As molecules were added to the end of fine crystalline needles, stresses built up at the tips of the crystals and resulted in a helical（螺旋形的） twist—much like DNA's double helix. The process was reversed when crystals thickened from the opposite end of the growing tip—that is, the crystals stiffened⁷, thereby⁸ undoing⁹ the twisted formations. This is because the elasticity¹⁰（弹性，弹力） of the crystals decreases as they become thicker, thus "squeezing out" the deformations¹¹ that were induced at the growing tip.

"This competition between twisting and untwisting creates needles with a rainbow of colors, which is a characteristic of tightly wound helices, as well as ribbons that have become completely untwisted," said Bart Kahr, one of the study's co-authors and a professor in NYU's Department of Chemistry, explaining the crystals' appearance. "This is a very strange and new perspective on crystal growth."

"This dynamic has not been observed before and points to a much more active process of crystal growth than we had anticipated," added Kahr, also part of NYU's Molecular¹² Design Institute.