X-ray pulses from the Linac Coherent Light Source probe the molecular dynamics of photoexcitation.
X-rays from the Linac Coherent Light Source were used to measure the ultrafast response of DNA nucleobases to ultraviolet light. Researchers found that the UV excited state in the nucleobase thymine decays rapidly, harmlessly dissipating the potentially destructive UV energy.
The experimental findings give new insight on how the nucleobases inside DNA protect themselves from damage induced by ultraviolet light. In addition, the experimental scheme developed will be useful for probing the ultrafast dynamics of other classes of molecules in biology, chemistry and physics.
Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule is challenging using current spectroscopic approaches. Researchers at SLAC approached this problem by investigating how DNA, which absorbs light very strongly, protects itself by dissipating the UV energy as heat instead of breaking the chemical bonds that hold the DNA together. By using an ultrafast x-ray pulse, an innermost electron from a thymine molecule, a so-called core electron, is stripped away, resulting in an atom with a vacancy in its core level, resulting in a “core hole.”
The atom, now unstable, fills the core hole with an outer electron, and an electron is emitted via a process known as the Auger effect. Measurement of the kinetic energy of the Auger electrons reveals information about the dynamics.
This experimental scheme, called time-resolved Auger spectroscopy, allowed scientists to distinguish between the movement of the atomic nuclei and the changes in the distribution of electrons from an element specific point of view. Using this strategy for the DNA nucleobase thymine, researchers observed that the oxygen Auger spectrum shifts initially toward high kinetic energies due to the stretching of a single carbon-oxygen bond.
The Auger spectrum then shifts toward lower kinetic energies within 200 fs to an electronic relaxed state, which allows the UV energy to dissipate as heat rather than damaging the DNA. This newly developed tool should provide a window to view the motions of electrons in many areas of chemistry, biology and physics.
This work was supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy. M. G. acknowledges funding via the Office of Science Early Career Research Program through the Office of Basic Energy Sciences, U.S. Department of Energy. R. F. thanks the Swedish Research Council, the Göran Gustafsson Foundation (UU/KTH), and the Knut and Alice Wallenberg Foundation, Sweden for financial support.
The main part of the experimental research was carried out at the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. LCLS is an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University. Other portions of this research were carried out at the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
McFarland, BK, et al., “Ultrafast X-ray Auger Probing of Photoexcited Molecular Dynamics.” Nature Communications 5, 4235 (2014). [DOI: 10.1038/ncomms5235]
Kristin Manke | newswise
Mass spectrometry sheds new light on thallium poisoning cold case
14.12.2018 | University of Maryland
Protein involved in nematode stress response identified
14.12.2018 | University of Illinois College of Agricultural, Consumer and Environmental Sciences
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy