Nav: Home

Caught in the act: Images capture molecular motions in real time

July 11, 2019

PROVIDENCE R.I. [Brown University] -- Researchers have used ultra-high-speed x-ray pulses to make a high-resolution "movie" of a molecule undergoing structural motions. The research, published in Nature Chemistry, reveals the dynamics of the processes in unprecedented detail -- capturing the excitation of a single electron in the molecule.

The ability to see molecular motions in real time offers insights into chemical dynamics processes that were unthinkable just a few decades ago, the researchers say, and may ultimately help in optimizing reactions and designing new types of chemistry.

"For many years, chemists have learned about chemical reactions by essentially studying the molecules present before and after a reaction has occurred," said Brian Stankus, a recent Ph.D. graduate from Brown University and co-lead author on the paper. "It was impossible to actually watch chemistry as it happens because most molecular transformations happen very quickly. But ultrafast light sources like the one we used in this experiment have enabled us to measure molecular motions in real time, and this is the first time these sorts of subtle effects have been seen with such clarity in an organic molecule of this size."

The work is a collaboration between chemists from Brown, scientists at SLAC National Accelerator Laboratory and theoretical chemists from the University of Edinburgh in the U.K. The team was led by Peter Weber, professor of chemistry at Brown.

For the study, the researchers looked at the molecular motions that occur when the organic molecule N-methyl morpholine is excited by pulses of ultraviolet light. X-ray pulses from SLAC's Linac Coherent Light Source (LCLS) were used to take snapshots at different stages of the molecule's dynamic response.

"We basically hit the molecules with UV light, which initiates the response, and then fractions of a second later we take a "picture" -- actually we capture a scattering pattern -- with an x-ray pulse," Stankus said. "We repeat this over and over, with different intervals between the UV pulse and x-ray pulse to create a time-series."

The x-rays scatter in particular patterns depending on the structure of molecules. Those patterns are analyzed and used to reconstruct a shape of the molecule as the molecular motions unfold. That pattern analysis was led by Haiwang Yong, a graduate student at Brown and the study's co-lead author.

The experiment revealed an extremely subtle reaction in which only a single electron becomes excited, causing a distinct pattern of molecular vibrations. The researchers were able to image both the electron excitation and the atomic vibration in fine detail.

"This paper is a true milestone because for the first time, we were able to measure in great clarity the structure of a molecule in an excited state and with time resolution," said Weber, the study's corresponding author.

"Making these types of nearly noise free measurements in both energy and time is no small feat," said Mike Minitti, a senior staff scientist at SLAC and study co-author. "Over the past seven years, our collaboration has learned a great deal on how best to use the various LCLS diagnostics to precisely measure the small fluctuations in X-ray intensities, and to an even greater extent, track the femtosecond timescale changes the molecules evolve on. All of this has informed the development of custom data analysis routines that virtually eliminate pesky, unwanted signals to our data. These results demonstrate the fidelity we can achieve."

A particularly interesting aspect of the reaction, the researchers say, is that it's coherent -- meaning when groups of these molecules interact with light, their atoms vibrate in concert with each other.

"If we can use experiments like this one to study how exactly light can be used to direct the collective motion of billions of molecules, we can design systems that can be coherently controlled," Stankus said. "Put simply: If we understand exactly how light directs molecular motions, we can design new systems and control them to do useful chemistry."
-end-
Other coauthors on the paper were Nikola Zotev, Jennifer Ruddock, Darren Bellshaw, Thomas J. Lane, Mengning Liang, Sébastien Boutet, Sergio 5 Carbajo, Joseph S. Robinson, Wenpeng Du, Nathan Goff, Yu Chang, Jason E. Koglin and Adam Kirrander. The research was supported by U.S. Department of Energy (DE-SC0017995) and the Army Research Office (W911NF-17-1-0256). Use of the LCLS was supported by the Department of Energy (DE-AC02-76SF00515)

Brown University

Related Chemistry Articles:

The chemistry of olive oil (video)
Whether you have it with bread or use it to cook, olive oil is awesome.
With more light, chemistry speeds up
Light initiates many chemical reactions. Experiments at the Laser Centre of the Institute of Physical Chemistry of the Polish Academy of Sciences and the University of Warsaw's Faculty of Physics have for the first time demonstrated that increasing the intensity of illumination some reactions can be significantly faster.
The chemistry of whiskey (video)
Derby Day means it's time to recognize the chemical process of distillation, which makes bourbon possible.
Restoration based on chemistry
Considered the pinnacle of mediaeval painting, the Ghent Altarpiece was painted around 1432 by Jan van Eyck and probably his brother Hubert.
The chemistry of redheads (video)
The thing that sets redheads apart from the crowd is pigmentation.
Scientists discover helium chemistry
The scientists experimentally confirmed and theoretically explained the stability of Na2He.
What might Trump mean for chemistry? (video)
Donald Trump is now the 45th president of the US.
Chemistry on the edge
Defects and jagged surfaces at the edges of nanosized platinum and gold particles are key hot spots for chemical reactivity, researchers confirmed using a unique infrared probe at Berkeley Lab.
Light powers new chemistry for old enzymes
Princeton researchers have developed a method that irradiates biological enzymes with light to expand their highly efficient and selective capacity for catalysis to new chemistry.
Better chemistry through...chemistry
Award-winning UCSB professor Bruce Lipshutz is out to make organic chemistry better for the planet

Related Chemistry Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#530 Why Aren't We Dead Yet?
We only notice our immune systems when they aren't working properly, or when they're under attack. How does our immune system understand what bits of us are us, and what bits are invading germs and viruses? How different are human immune systems from the immune systems of other creatures? And is the immune system so often the target of sketchy medical advice? Those questions and more, this week in our conversation with author Idan Ben-Barak about his book "Why Aren't We Dead Yet?: The Survivor’s Guide to the Immune System".