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August 26, 2005|Volume 34, Number 1


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Team identifies 'signatures' of protons in water

Free protons from acids associate with one, two or three molecules of water, and the structures can be identified by unique infrared laser spectrum signatures, according to a report in Science by Yale professor of chemistry Mark A. Johnson and his collaborators at Yale, the University of Pittsburgh and the University of Georgia.

Acids yielding free protons are common in biological and chemical systems, and the measurement of pH to determine acidity of an aqueous solution is a simple, standard procedure. However, it has not been as easy to determine where the liberated protons are located and how they interact with water molecules.

The scientists tackled these questions using infra-red laser light, at much lower energies than were previously accessible, to monitor how the vibration profile changes when a proton is associated with two to 11 water molecules.

The researchers first established a spectral signature for the symmetrically hydrated Eigen cation, which has a minimum energy (H3O)+ ion core and three associated "dangling" water molecules. As they successively added or subtracted water molecules and compared the spectral signatures, they mimicked water fluctuations.

"Surprisingly large spectral shifts are driven by small changes in the hydration environment," says Johnson. "Although previous work anticipated a change from Zundel to Eigen structures as you progress from eight to nine water molecules, the change in the low energy bands here is dramatic. The profile for the nine-membered cluster is much like bulk water, but then the 10-membered cluster is again simpler."

The study shows that the proton associated with the Eigen cation undergoes vibrations highest in energy because it supports the greatest distribution of charge -- that is, over three H (hydrogen) atoms. As different numbers of water molecules surround the H3O+ core, the excess charge can become more localized onto two or even one of the H atoms, causing substantial, size-dependent shifts in the spectral signature of the excess proton. This extreme response to breaking symmetry is consistent with Zundel's model of the excess proton being a highly polarizable species.

"The basic point is that the proton is a moving target, rapidly switching its character from one species to the next according to how many water molecules it is associated with," says Johnson. "Now that the spectral signatures of various local environments in water are known, the big question left is how this all comes together as we continue to grow crystals toward bulk water (ice)."

-- By Janet Rettig Emanuel


T H I SW E E K ' SS T O R I E S

Margaret Grey is named dean of School of Nursing

Benson to step down as dean of School of Art after this year

Team discovers new planet in the outer solar system

Grant will fund center for study of nervous system

Study: Alligator eggs show effect of oxygen on development

Yale Librarian Prochaska appointed to a second term

New master's program prepares nurses for leadership roles

Exhibit explores the 18th-century 'worlds' of Francis Wheatley

Private portrait miniatures showcase the faces of public figures

Gallery hosting festive open house . . .

Architecture gallery to feature traveling art show 'Ant Farm'

Sterling Library launches new academic year with two exhibits

Researchers create powerful tool for decoding gene functions

Galapagos tortoises more diverse than once believed, say scientists

Team identifies 'signatures' of protons in water

'Canary Database' shows animals offer health warnings for humans

Team digitally reconstructs long-extinct 'Lamp Shell'

'Gene trapping' reveals how flower development is controlled

Discovery may aid development of treatment for melanoma

Drinking alcohol may lower risk of non-Hodgkin's lymphoma

Lyme disease prevention program launched in Connecticut

For 35 students, summer was a time of service in New Haven

IN MEMORIAM

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