Crystals Fly High

 Over and over again.

jump

February 28, 2015

Snow melting under a sunny sky is a comforting sight to all in the cold wintery months. A chemist or a physicist who sees solid-ice crystals transformed into water by the warmth of the sun calls that welcome change a phase transition. Schoolchildren learn that all matter exists in three phases: solid (e.g. ice), liquid (water), and gas (steam), but this is a gross oversimplification. Many materials most interesting behavior is due to the rare phases that exist somewhere in between the familiar ones. When scientists can exploit this behavior, a blizzard of new technologies becomes possible.

In an ice-crystal, as in all crystals, all of the water molecules are held firmly in place in an ordered pattern. When ice is heated, the water molecules begin to move, and the ice melts. But not every crystalline material behaves like ice. When the right type of crystal is heated, it will jump to heights 10, 100, or even 1000 times its own size, like hot chestnuts popping out of a pan. The jump is caused by a rarely observed phase transition, where all of the molecules in the crystal move at once, but the material remains ordered and crystalline. Only around a dozen materials that can directly convert heat into movement are known, but scientists hope they can be developed into simplified motors that mimic those found in nature.

Professor Panče Naumov of New York University in Abu Dhabi is spearheading the effort to understand these strange “jumping crystals” along with an international team of researchers in the United Arab Emirates, at the Max Planck institute for Solid State Research in Germany, and at the National Institute for Materials Science in Japan. In an article published online in January by the Journal of the American Chemical Society, the scientists report the first jumping crystals that can fling themselves aloft over and over again. This is only the latest in a string of papers by the team that sheds light on this strange phenomenon, which has been known for over thirty years, but up until now was poorly understood.

Like with all phase transitions, it comes down to the molecular level. The researchers found that when a jumping crystal is heated, energy builds in the form of tension between the molecules arranged in the crystal. Once the temperature reaches around 75 ºC, all of the molecules move in unison, and the tension is released in the form of a jump. While each molecule moves only a small fraction of a nanometer (about ten-million times smaller than the crystal itself), the combined movement of all the molecules together leads to a rapid change in the crystal’s shape. It is that shape change that causes the crystal to spring up into the air.

For most jumping crystals the same forces that cause the jump can also blow the crystal apart. Naumov and his colleagues posit that their crystals can withstand those forces because they are relatively soft and flexible. The crystals described in JACS can carry on jumping through repeated heating cycles without sustaining any detectable damage. These crystals will also hop once when cooled to very low temperatures–the result of another phase transition. Unfortunately, that lone leap leads the crystal to a wintery grave, but as long as it is kept out of the cold, the crystal will survive to jump another day.

This is exciting news for scientists who hope to use these materials to perform mechanical work. While you should not hold out this winter for jumping crystal powered machines that will stir your cocoa, but the scientists hope that their findings will aid in the design of new varieties of resilient jumping crystals that can be incorporated into tomorrow’s most energy efficient devices.

From: M.K. Panda, T. Runčevksi, A. Husain, R. Dinnebier, and P. Naumov; “Perpetually Self-Propelling Chiral Single Crystals,” J. Am. Chem. Soc.2015137 (5),1895–1902; doi: 10.1021/ja5111927

 

Analytical Chemistry and Pop Culture Collide

Writer Jon Krakauer turns to analytical chemistry to learn the truth behind how his enigmatic subject, Chris McCandless, died.

intothewild9

February 27, 2015

On February 11, Jon Krakauer published a new piece on The New Yorker’s “Page Turner” blog. In it he recounts the latest in a story that he has been telling for a quarter of a century. In 1992, Christopher McCandless, the subject of Into the Wild, Krakauer’s seminal work of investigative nonfiction, died in the Alaskan wilderness at the age of twenty-four. The book spurred a debate over whether McCandless died from starvation, brought on by his own hubris and ill preparation, or whether he was inadvertently poisoned by the seeds of a wild plant once thought to be harmless.* The search for a resolution has become a near-obsession for Krakauer, his fans (myself among them), and McCandless’s admirers and detractors alike.

Analytical chemistry has finally provided an answer that seems poised to end the debate. In the “Page Turner” post, Krakauer details the work that he carried out with a team of analytical chemists from Avomeen Analytical Services and Indiana University of Pennsylvania to determine the toxic component of seeds McCandless was known to have consumed, if any. That work has now been published in an article in this month’s issue of the peer-reviewed journal Wilderness and Environmental Medicine.

Krakauer and the scientists confirmed that the seeds of the plant, Hedysarum alpinum or the wild potato, contain a large amount of L-canavanine, an amino acid that is known to be toxic to large mammals including monkeys and cattle and that has suspected toxicity in humans. To do so they used an expensive and modern but nevertheless routine analytical technique called liquid chromatography tandem mass spectrometry (LC-MS/MS). These results also confirm those of a long forgotten paper from 1960 that suggested the seeds likely contain L-canavanine.

It is rare to find an instance where highly technical research tools like LC-MS/MS find their way into a discussion in the popular press. It is to Krakauer’s credit that he did not shy away from it in order to tell the whole story, which now seems to be at its end. Wild potato seeds were a major part of McCandless’s diet in the month before his death, and he himself implicated them in his rapid deterioration in one of his haunting final journal entries. Their newly re-discovered toxicity not only serves as a warning to other would-be adventurers, but also as a tacit defense of Krakauer’s choice of McCandless as a subject and of McCandless’s choice to live life off the grid.

From:

J. Krakauer, Y. Long, A. Kolbert, S. Thanedar, and J. Southard; Presence of L-Canavanine in Hedysarum alpinum Seeds and Its Potential Role in the Death of Chris McCandless,” Wilderness and Environmental Medicine, 2015, 26 (1), 36–42; doi: http://dx.doi.org/10.1016/j.wem.2014.08.014

and

J. Krakauer; “How Chris McCandless Died: An Update,” newyorker.com/page-turner

*Krakauer sums up the controversy in the “Page Turner” post, so I won’t recount it here.