Chemists grow crystals with a twist -- and untwist

Jul 16, 2010
NYU and St. Petersburg State University chemists have discovered a wholly new phenomenon for crystal growth—a crystal that continually changes its shape as it grows.

(PhysOrg.com) -- 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 varied process of crystal growth than previously 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, 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, molecules, or small clusters adding to a larger block that remains in a fixed 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—a derivative of the amino acid glycine. 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 twist—much like DNA's . The process was reversed when crystals thickened from the opposite end of the growing tip—that is, the crystals stiffened, thereby undoing the twisted formations. This is because the elasticity of the decreases as they become thicker, thus "squeezing out" the deformations 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 than we had anticipated," added Kahr, also part of NYU's Molecular Design Institute.

Explore further: Scientists learn to control reactions with the shape of a rare-earth catalyst

Related Stories

Paving the Way for Crystal Growth

Mar 07, 2007

In order to study the properties of LBCO superconductors, scientists need to produce large, single crystals of the material - a difficult task that wasn't possible until recently. At the state-of-the-art crystal ...

Crystal to glass cooling model developed

Feb 22, 2006

University of Tokyo scientists have discovered why cooling sometimes causes liquid molecules to form disordered glasses, rather than ordered crystals.

Recommended for you

Breaking benzene

Aug 27, 2014

Aromatic compounds are found widely in natural resources such as petroleum and biomass, and breaking the carbon-carbon bonds in these compounds plays an important role in the production of fuels and valuable ...

User comments : 0