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April 2
2001

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Currents--University of Rochester newspaper

Team is first to find 'pH' of water

Rochester scientists have uncovered the driving force behind one of the fundamental properties of water--its pH--that has defied explanation for decades.

Joined by researchers at the University of California, Berkeley, the Rochester team has created the first model of how water becomes acidly neutral, a 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 result is that we now have the first model of why water has the pH it does," says Christoph Dellago, assistant professor of chemistry.

By tapping into high-speed computers and by developing new algorithms, the team was able to simulate a kind of molecular split so rare and brief that it's impossible to witness in real life. In 10 hours, a single watched molecule could be expected to split in about 100 femtoseconds--about a thousandth of a trillionth of a second. That's the equivalent of waiting the entire age of the universe to see a one-second twitch.

The team 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 have been trying to catch water in the act of splitting, but the process has avoided both observation and modeling until now.

The team used a proven algorithm to model the process, but the real hurdle lay in the rarity of the event itself.

Devising a way to "zoom in" on just the single moment when the stripping took place demanded the integration of a second complex algorithm, which in turn demanded ultra-high speed computers.

The research appeared in the March 16 issue of Science.



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