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Zewail Explores Ultrafast World of Femtochemistry

By Anna Gillis

Dr. Ahmed Zewail revolutionized research when he made it possible to see how atoms in a molecule move during a chemical reaction. His discoveries solved a problem that had puzzled scientists since the early twentieth century, earned him the 1999 Nobel Prize in chemistry, and gave science a new discipline called femtochemistry. He will describe how femtochemistry can be applied to biology when he delivers the NIH Director's Lecture on Friday, May 4. The lecture, "Physical and Biological Sciences at New Limits," will begin at 3 p.m. in Masur Auditorium, Bldg. 10.

Practitioners in the growing field of femtochemistry use ultrahigh-speed lasers to study chemical and biological reactions as they occur in real time. These changes happen in femtoseconds (one millionth of a billionth of a second.)

Dr. Ahmed Zewail

Because many biologically important molecules change from one form to another within a few hundred femtoseconds, femtochemistry can be used in fields ranging from neuroscience to plant science to the making of pharmaceuticals, says Zewail. "It is by studying the dynamics of molecules — how they change over time — that we can better understand their functions."

The femtochemistry techniques developed by Zewail use what many have described as "the world's fastest camera." In the experiments, ultrafast lasers flash in two pulses. The first hits the molecules under study to excite them. After the second weaker pulse, the researchers can check to see how quickly the original molecules changed. Currently, the fastest laser pulses take approximately 5 femtoseconds.

Zewail began studies in the new field by asking a simple question: How can we capture atoms as they change? In his favorite — and field-changing — experiment, he set about documenting the transitional moment when sodium iodide breaks down to form sodium and iodine and reforms again. Researchers had speculated about chemical intermediates and transition states since the Swedish Nobelist Svante Arrhenius proposed that an intermediate must exist in the transition from chemical reactants to products, but scientists had never been able to isolate such a state of transformation.

"For Arrhenius there was a 'hypothetical body' for chemical reactions. In the 1930s, that became known as the transition state. People thought that the time scale was ephemeral. Now, we can isolate the transition state not as a 'hypothetical body,' but as a molecular structure," says Zewail, who was the first person to capture the transition and determine the time it takes to occur. Although he has done many other experiments since, Zewail says the more he thinks about his simple 1987 experiment with sodium iodide, the more he sees its beauty.

Zewail has continued his work at the California Institute of Technology, where he holds the Linus Pauling chair, is professor of chemistry and professor of physics, and directs the National Science Foundation's Laboratory for Molecular Sciences. The lab collaborates with researchers who use the tools of electrochemistry, X-ray crystallography, chemical synthesis, chemical theory and biomolecular studies to apply femtochemistry to chemistry, biology and materials science. They have used femtochemistry, for example, to study how electrons move around in DNA. By learning how far and how quickly the electrons travel, they hope to understand how DNA damage and repair occur. They've looked at the binding of oxygen to heme, and they are developing tools to study ion channels in cell membranes. Other researchers have used femtochemistry to study chlorophyll molecules, which capture light during photosynthesis, and rhodopsin, the protein in the rods of the eyes that respond to light.

Born and educated in Egypt, Zewail received his bachelor's and master's degrees from Alexandria University. He completed his Ph.D. at the University of Pennsylvania in 1974. He is a member of several academies and societies, including the National Academy of Sciences, the Pontifical Academy of Sciences and the American Philosophical Society. In addition to the Nobel prize, he has won many other honors including the Robert A. Welch Prize in Chemistry, the Wolf Prize in Chemistry, the King Faisal International Prize in Science and the Benjamin Franklin Medal.

President Hosni Mubarak conferred on him the Grand Collar of the Nile, Egypt's highest honor. The nation also issued postage stamps in his honor. Zewail continues to encourage young Egyptians interested in science. He supports the high school he attended with an endowment for computers, equipment and fellowships, and he has funded a prize at the American University in Cairo for the best student in science or engineering.

The lecture is part of the Wednesday Afternoon Lecture Series. For more information or accommodation, contact Hilda Madine at 594-5595.


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