Scientists capture elusive chemical reaction using enhanced X-ray method


Date:
May 5, 2023
Source:
DOE/SLAC National Accelerator Laboratory
Summary:
Researchers have captured one of the fastest movements of a molecule
called ferricyanide for the first time by combining two ultrafast
X-ray spectroscopy techniques. They think their approach could help
map more complex chemical reactions like oxygen transportation in
blood cells or hydrogen production using artificial photosynthesis.


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==========================================================================
FULL STORY ========================================================================== Researchers at SLAC National Accelerator Laboratory captured one of
the fastest movements of a molecule called ferricyanide for the first
time by combining two ultrafast X-ray spectroscopy techniques. They
think their approach could help map more complex chemical reactions
like oxygen transportation in blood cells or hydrogen production using artificial photosynthesis.

The research team from SLAC, Stanford and other institutions started
with what is now a fairly standard technique: They zapped a mixture
of ferricyanide and water with an ultraviolet laser and bright X-rays
generated by the Linac Coherent Light Source (LCLS) X-ray free-electron
laser. The ultraviolet light kicked the molecule into an excited state
while the X-rays probed the sample's atoms, revealing features of ferricyanide's atomic and electronic structure and motion.

What was different this time is how the researchers extracted
information from the X-ray data. Instead of studying only one
spectroscopic region, known as the Kb main emission line, the team
captured and analyzed a second emission region, called valence-to-core,
which has been significantly more challenging to measure on ultrafast timescales. Combining information from both regions enabled the team
to obtain a detailed picture of the ferricyanide molecule as it evolved
into a key transitional state.

The team showed that ferricyanide enters an intermediate, excited state
for about 0.3 picoseconds -- or less than a trillionth of a second --
after being hit with a UV laser. The valence-to-core readings then
revealed that following this short-lived, excited period, ferricyanide
loses one of its molecular cyanide "arms," called a ligand. Ferricyanide
then either fills this missing joint with the same carbon-based ligand
or, less likely, a water molecule.

"This ligand exchange is a basic chemical reaction that was thought to
occur in ferricyanide, but there was no direct experimental evidence of
the individual steps in this process," SLAC scientist and first author
Marco Reinhard said.

"With only a Kb main emission line analysis approach, we wouldn't really
be able to see what the molecule looks like when it is changing from
one state to the next; we'd only obtain a clear picture of the beginning
of the process." "You want to be able to replicate what nature does to
improve technology and increase our foundational scientific knowledge,"
SLAC senior scientist Dimosthenis Sokaras said. "And in order to better replicate natural processes, you have to know all of the steps, from the
most obvious to those that happen in the dark, so to speak." In the
future, the research team wants to study more complex molecules, such
as hemeproteins, which transport and store oxygen in red blood cells --
but which can be tricky to study because scientists do not understand
all the intermediate steps of their reactions, Sokaras said.

The research team refined their X-ray spectroscopy technique at SLAC's
Stanford Synchrotron Radiation Lightsource (SSRL) and the LCLS over
many years, and then combined all this expertise at the LCLS's X-ray Correlation Spectroscopy (XCS) instrument to capture the molecular
structural changes of ferricyanide. The team published their results
today in Nature Communications.

"We leveraged both SSRL and LCLS to complete the experiment. We couldn't
have finished developing our method without access to both facilities
and our longstanding collaboration together," said Roberto Alonso-Mori,
SLAC lead scientist. "For years, we have been developing these methods
at these two X-ray sources, and now we plan to use them to uncover
previously inaccessible secrets of chemical reactions."
* RELATED_TOPICS
o Matter_&_Energy
# Detectors # Optics # Organic_Chemistry # Chemistry #
Inorganic_Chemistry # Physics # Electronics # Biochemistry
* RELATED_TERMS
o Autocatalysis o Spectroscopy o Positron_emission_tomography
o Oxygen o Carbon_dioxide o Carbohydrate o Combustion o
Tissue_engineering

========================================================================== Story Source: Materials provided by
DOE/SLAC_National_Accelerator_Laboratory. Original written by David
Krause. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Marco Reinhard, Alessandro Gallo, Meiyuan Guo, Angel
T. Garcia-Esparza,
Elisa Biasin, Muhammad Qureshi, Alexander Britz, Kathryn Ledbetter,
Kristjan Kunnus, Clemens Weninger, Tim van Driel, Joseph Robinson,
James M. Glownia, Kelly J. Gaffney, Thomas Kroll, Tsu-Chien
Weng, Roberto Alonso-Mori, Dimosthenis Sokaras. Ferricyanide
photo-aquation pathway revealed by combined femtosecond Kb main
line and valence-to-core x-ray emission spectroscopy. Nature
Communications, 2023; 14 (1) DOI: 10.1038/ s41467-023-37922-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230505141356.htm

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