K-State physicists take stop-action images of light-driven molecular reaction

Published: Jul. 31, 2020 at 7:01 PM CDT
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TOPEKA, Kan. (WIBW) - Kansas State University physicists have taken stop-action images of light-driven molecular reactions.

Kansas State University says a group of its physicists has taken snapshots of light-induced molecular ring-opening reactions, which are similar to those helping the human body to produce vitamin D from sunlight.

K-State says the research is published in Nature Chemistry.

“Think of this as stop-motion like a cartoon,” said Daniel Rolles, associate professor of physics and the study’s principal investigator. “For each molecule, you start the reaction with a laser pulse, take snapshots of what it looks like as time passes and then put them together. This creates a ‘molecular movie’ that shows how the electronic structure of the molecule changes as a function of how much time passes between when we start and when we stop.”

Shashank Pathak, doctoral student and lead author on the paper, says the idea was to study how a ring opens in a molecule on the time scale of femtosecond, which is one quadrillionth of a second. He says his team used a free-electron laser to visualize how the reactions happen by recording electron energy spectra as the atoms moved apart.

“The ring-opening reaction is observed in nature quite a bit,” Pathak said. “One example is the formation of vitamin D3 in our skin. When sunlight shines on our skin, we have big compounds that have these small ring structures that help with the absorption of UV light. The ring opens to form the precursor to vitamin D3 formation.”

Pathak says making vitamin D involves a handful of biological functions and the ring-opening is one small part of the process. He says the research recorded the changes in the molecule in order to understand the speed of the process, how it happens and compare it to previously accepted theories.

“Understanding the process has implications for making similar processes that can be used in technology more efficient, and for developing general rules that can be applied to similar reactions,” said Rolles, who received a National Science Foundation Faculty Early CAREER award in 2018 that funded this research.

Rolles says the research would not have been possible without international collaboration. He says a team of researchers from Durham University and the University of Bristol, which are both located in the UK, provided key quantum chemistry calculations for the study.

According to Rolles, other collaborators included researchers at SLAC National Accelerator Laboratory at Stanford University in California, Daresbury Laboratory, University College London and the University of Oxford in the UK, European XFEL, Deutsches Eletronen-Synchrotron and Max-Born-Institute in Germany, Elettra - Sincrotrone Trieste and Istituto Nazionale di Fisica Nucleare in Italy, the University of Gothenburg in Sweden, and the University of New South Wales and the Swinburne University of Technology in Australia.

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