Scientists have observed the rapid motion of hydrogen atoms, which are
essential for innumerable chemical and biological processes.
Ultrafast electron diffraction (UED) was employed by a group of researchers
from Stanford University and the Department of Energy's SLAC National
Accelerator Laboratory to capture the motion of hydrogen atoms inside
ammonia molecules. Although some had hypothesized that they could use
electron diffraction to follow hydrogen atoms, no one had yet completed the
experiment successfully.
The findings, which are detailed in
Physical Review Letters, take use of the advantages that come with using high-energy
Megaelectronvolt (MeV) electrons to investigate hydrogen atoms and proton
transfers—the movement of a single proton, which constitutes a hydrogen
atom's nucleus, from one molecule to another.
It would be beneficial to understand precisely how its structure changes
throughout the innumerable biological and chemical activities that are
powered by proton transfers. Examples of these reactions include the
production of enzymes, which aid in the catalysis of biochemical reactions,
and proton pumps, which are vital to mitochondria, the cells' power plants.
Proton transfers, however, occur extremely quickly—in a matter of
femtoseconds, or one millionth of a billionth of a second. It's difficult to
observe them in action.
One option is to target a molecule with X-rays and then utilize the
dispersed X-rays to get information about the molecule's structure as it
changes. Unfortunately, it's not the most sensitiv
e technique since X-rays only interact with electrons, not atomic nuclei.
e technique since X-rays only interact with electrons, not atomic nuclei.
MeV-UED, SLAC's ultrafast electron diffraction camera, was used by a team
led by physicist Thomas Wolf to obtain the answers they needed. They made
use of gas-phase ammonia, which is composed of one nitrogen atom and three
hydrogen atoms. The scientists used UV light to disrupt one of the
hydrogen-nitrogen bonds in ammonia. They then shot an electron beam across
the material to collect the diffracted electrons.
Not only did they detect signals originating from the hydrogen's separation
from the nitrogen nucleus, but they also detected the corresponding
alteration in the molecule's structure. Additionally, scientists were able
to distinguish between the two signals because the dispersed electrons
blasted out at different angles.
"Having something that's sensitive to the electrons and something that's
sensitive to the nuclei in the same experiment is extremely useful," Wolf
stated. "If we can see what happens first when an atom dissociates—whether
the nuclei or the electrons make the first move to separate—we can answer
questions about how dissociation reactions happen."
With such knowledge, researchers might get closer to understanding the
enigmatic proton transfer process, which could aid in the resolution of
several chemical and biology-related queries. In structural biology, where
"seeing" protons is a challenge for conventional techniques like
cryo-electron microscopy and X-ray crystallography, understanding what
protons are doing might be crucial.
To find out how different the results are, the team plans to repeat the
experiment using X-rays at SLAC's Linac Coherent Light Source (LCLS) in the
future. To really discern distinct stages of proton dissociation across
time, they also intend to increase the electron beam's intensity and enhance
the experiment's temporal resolution.
Provided by
SLAC National Accelerator Laboratory
