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accelerator apps: diapers Photo: Reidar Hahn, Fermilab Accelerators help keep baby dry In the United States, we buy more than 20 billion disposable diapers each year. That’s a lot of baby bottoms to keep dry, and parents everywhere can thank particle accelerators for doing their part. About a decade ago, researchers at the Dow Chemical Company teamed up with Lawrence Berkeley National Laboratory to use the Advanced Light Source to develop materials for the optimal baby diaper. When it comes to diapers, consumers look for a product that is as thin as possible but still holds a lot of moisture and doesn’t leak. The answer: superabsorbent polymers. No longer fluffy cotton, the active ingredient in today’s diapers consists of superabsorbent polymer beads, long chains of interlinked molecules that can hold copious amounts of liquid. Each bead has a special layer on the outside that creates a seal after liquid gets absorbed so it won’t leak back out. Companies like Dow started manufacturing the polymer beads in the ‘90s, but to make a leak-proof product, chemists needed to see the 36 microscopic details of the material. That’s where the synchrotron light source at Berkeley came in. “What really counts is how the material performs when it is wet, and you can’t see that with a regular microscope,” says Adam Hitchcock, a professor of chemistry at McMaster University and Canada Research Chair for Materials Analysis at the Canadian Light Source. Using X-ray microscopy, a technique developed by Hitchcock and his collaborators, Dow chemists were able for the first time to see the detailed structure of the superabsorbent polymer material while wet. Dow brought a variety of samples to the ALS to analyze, and the X-ray microscopy technique enabled the chemists to adjust and improve the formula for the superabsorbent polymers until they had the perfect diaper. “They were trying to find the magic recipe, and we were the feedback tool,” Hitchcock said. Dow used the results from the ALS research to design production processes at new superabsorbent polymer fabrication plants. All modern-day diapers now contain the superabsorbent polymer beads, keeping babies dry and parents happy. Elizabeth Clements www.symmetrymagazine.org/archive/apps symmetry | volume 8 | issue 2 | may 2011
logbook: protein structure On June 17, 1975, four young scientists struggled to mount samples and align an instrument in one of several small hutches grafted onto an 80-meter accelerator ring at what is now SLAC National Accelerator Laboratory. The hutches were part of a cutting-edge initiative called the Stanford Synchrotron Radiation Project; and the experiment they performed that day would demonstrate a powerful new tool for determining the structures of proteins. The basic method, then and now, was to turn many copies of a protein into a small crystal and hit it with X-rays, which scatter and form a diffraction pattern. Scientists interpret the pattern to determine the protein’s molecular structure. However, previous X-ray sources had been too weak to study the smallest crystals and most complex proteins. Now the scientists at SLAC would try a much more intense source: X-rays emitted by electrons speeding around the SPEAR storage ring. This form of X-ray light is known as synchrotron radiation. Image courtesy of K. Hodgson, Stanford University, SSRL/SLAC Working in a team led by Keith Hodgson, then assistant professor of chemistry at Stanford University, the scientists spent hours reaching through a narrow slit in the hutch to tweak the alignment of their apparatus, then closed and locked the hutch and let the X-rays in. The X-rays scattered off a single crystal of a protein called rubredoxin and left this pattern on high-resolution X-ray film. “We were very happy,” recalls James Phillips of Iowa State University, then a 23-year-old Stanford graduate student. The news quickly spread among the hutches, and a senior scientist uncorked a bottle of champagne. The team’s published report was the first to describe the successful use of synchrotron radiation for protein crystallography. Those first experiments, along with others in Germany and the Soviet Union, set off a revolution in structural biology. Today, scientists at 22 synchrotron light sources are analyzing protein structures, and the worldwide Protein Data Bank contains the structures of more than 72,000 proteins. Glennda Chui
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