Protons on the move find novel molecular route

Experiment reveals new pathway for hydrogen traveling between molecules

Some take the road less traveled. Hydrogen atoms can take roads not previously known to exist.

The lone proton — the nucleus of a common hydrogen atom — typically uses a single road — the hydrogen bond — to get from one molecule to another. But now researchers report such a proton traveling to another molecule by different means.

The implications of the new route, described online March 18 in Nature Chemistry, aren’t clear. But scientists are certain that they’ve never seen it before.

“This paper is interesting and important because hydrogen bonding is so ubiquitous and involved in so many things,” says electrophysiologist Tom DeCoursey of Rush University Medical Center in Chicago. Proton transfer is crucial for many processes in biology, such as photosynthesis, DeCoursey notes. “But I don’t see a direct tie-in with biological systems,” he says of the new research. “Where this might actually take place is another thing.”

Hydrogen atoms often exist without electrons, in which case, chemists refer to them as hydrogen ions, or just as protons. These protons get passed around a lot during chemical reactions, and scientists thought there was basically one way to do this: via a hydrogen bond. Hydrogen bonds, in which a positively charged proton feels the tug of a negatively charged atom, are everywhere in nature, holding together molecules such as water and DNA. These bonds allow one molecule to gain a proton and another to lose one during chemical reactions.

“For the proton, the hydrogen bond is like riding on a track that’s going between two molecules,” says chemist Anna Krylov of the University of Southern California in Los Angeles. She and her colleagues have prompted protons to transfer between stacked, ring-shaped molecules that had no hydrogen bonds between them. Calculations suggest that the ringed molecules rearrange themselves, creating an alternate short path that the proton can travel. “The molecules help it find its way,” says Krylov.

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