Softening crystals without heat

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As if borrowing from a scene in a science fiction movie, researchers at Kyoto University have successfully developed a kind of tractor beam that can be used to manipulate the network of the molecules. In a paper soon to be published in Physical Review Letters, the team has demonstrated a technique using terahertz pulses that could have broad applications in the chemical and pharmaceutical industries.

Terahertz waves, an area of specialty for the Koichiro Tanaka lab at Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS), exist in a frequency range beyond the infrared and before the microwave band. Also popularly referred to as T-rays, this form of radiation can pass through many materials but is non-ionizing, characteristics which make the waves useful in the imaging field.

In this case, intense terahertz pulses were used to successfully increase the amplitude of movement between amino-acid molecules in crystalline form, essentially softening the crystals. Previous softening methods have always correspondingly raised the temperature, resulting in unwanted changes to the crystals' structure and properties.

"What we have demonstrated is that it is possible to use intense terahertz pulses to climb 20 ladder steps on the anharmonic intermolecular potential in the microcrystals," explains Dr. Masaya Nagai, an assistant professor at Kyoto University's Department of Physics and a coauthor of the paper. "This opens the door," he continues, "to the possibility of manipulating large molecules, thereby increasing understanding of the properties of molecular complexes such as proteins."

The team is expectant that the technique they have developed could eventually lead to advances in chemical synthesis as well as in the refining of organic molecular crystals for pharmaceutical purposes.

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