We drink it. We bathe in it. Its part of our everyday life, but the driving force behind one of the fundamental properties of water, its pH, has defied explanation for decades. Scientists at the University of California, Berkeley, and the University of Rochester, however, have created the first model of how water becomes acidly neutrala characteristic on which all life depends. The findings should help researchers understand and control other complex chemical reactions as well, ones that could be used to create medicines and better materials. The research appears in the March 16 issue of Science.

The advent of high-speed computers and the development of new algorithms have given the team of researchers the ability to create a simulation of a kind of molecular split so rare and brief that its impossible to witness in real life. In 10 hours, a single watched molecule could be expected to split in about 100 femtosecondsabout a thousandth of a trillionth of a second. It would be the equivalent of waiting the entire age of the universe to see a one-second twitch.

Since the team couldnt catch the split by chance, they developed a complex computer simulation that showed how a proton is torn away from a water molecule. The pH is a measure of the number of protons, or hydrogen nuclei, that are pulled from a water molecule and roam freely. The number of these free protons determine how water behaves when it comes in contact with other substances, playing a crucial role in nearly any biological process that includes water. Since the 1950s, scientists such as Nobel Prize winner Manfred Eigen have been trying to catch water in the act of splitting, but so far the mysterious process has avoided both observation and modeling.

"This reaction is very complex," says Christoph Dellago, assistant professor of chemistry at the University of Rochester. "Its as if the water acts as both the splitter and the splitee at the same time."

The research team found that the br
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Contact: Jonathan Sherwood
jsherwood@admin.rochester.edu
716-273-4726
University of Rochester
15-Mar-2001