For the first time, physicists have succeeded in observing and studying in detail the hydrogen bonds in a single molecule.

With just a single electron and a single proton, hydrogen is the smallest atom, yet its generation in the early stages of the Universe makes it the most abundant element.

The extremely high reactivity of hydrogen means it easily forms compounds with nearly all nonmetallic elements, famously, oxygen and carbon.

To date, it has not been possible to conduct a spectroscopic or electron microscopic analysis of hydrogen and the hydrogen bonds in single molecules, and investigations using atomic force microscopy (AFM) have also not yielded any clear results.

Dr. Shigeki Kawai, a researcher in the Department of Physics at the University of Basel, and his colleagues from Switzerland and Japan have now succeeded in using high-resolution AFM to study hydrogen atoms in individual cyclic hydrocarbon compounds.

“We selected compounds which configuration resembles that of a propeller,” the authors said.

“These propellanes arrange themselves on a surface in such a way that two hydrogen atoms always point upwards. If the tip of the atomic force microscope, which is functionalized with carbon monoxide, is brought close enough to these hydrogen atoms, hydrogen bonds are formed that can then be examined.”

Hydrogen bonds are much weaker than chemical bonds, but stronger than intermolecular van der Waals interactions.

The measured forces and distances between the oxygen atoms at the tip of the atomic force microscope and the propellane’s hydrogen atoms correspond to the calculations performed by the team. They show that the interaction clearly involves hydrogen bonds.

The measurements mean that the much weaker van der Waals forces and the stronger ionic bonds can be excluded.

“With this study, we have opened up new ways to identify 3D molecules such as nucleic acids or polymers via observation of hydrogen atoms,” the researchers said.

The results were published in the May 12, 2017 issue of the journal Science Advances.

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Shigeki Kawai et al. 2017. Direct quantitative measurement of the C═O***H–C bond by atomic force microscopy. Science Advances 3 (5): e1603258; doi: 10.1126/sciadv.1603258

This article is based on text provided by the University of Basel.