It is not always easy to distinguish between images and mirror images of molecules, but this knowledge is important when one image of a molecule is a drug and the mirror image is toxic. One new approach to this may be chiral recognition in the gas phase.
This involves using synchrotron radiation (highly energetic photons from a particle accelerator) to eject electrons from the molecules and analyzing their trajectories. In the journal Angewandte Chemie, German researchers have now demonstrated that such experiments also work with a compact laser system.
The trick is to replace the individual high-energy photon with three laser photons that excite the molecule through intermediate levels until it releases an electron (this method is known as REMPI, Resonance-Enhanced Multi-Photon Ionization). “It is thus possible to eject electrons with less energetic but more intense light,” explains Thomas Baumert of the University of Kassel.
For the measurements, the light must be circularly polarized. What does this mean? “Ordinary” light consists of waves that oscillate in all spatial directions perpendicular to their direction of travel. If light is linearly polarized, the light waves oscillate exclusively in one plane. When light is circularly polarized, the light wave oscillates in a helical form, because its amplitude describes a circle around the axis of travel – either to the right or the left.
Molecules in the gas phase are randomly oriented and thus encounter the laser light from all possible angles; the ejected electrons also fly off in every possible direction as they leave the molecule. By using both a special configuration for measurement and special calculation processes, the team is able to determine the distribution of the angles of the electrons’ flight paths. In the case of linearly polarized light, the distribution is symmetrical.
“However, when the electrons are ejected by circularly polarized light, we find a distinct asymmetry to the angles at which the free electrons are found in relation to the laser beam,” reports Baumert. “This asymmetry is inverted if left circularly polarized light is used instead of right, an effect known as photoelectron circular dichroism. We observe the same effect when we keep the circular polarization the same but change from the “right handed” to the “left handed” structure of the chiral molecule being observed.”
The researchers were able to demonstrate this with the chiral compounds camphor and fenchone.
“This circular dichroism effect has previously only been observed with synchrotron radiation. In contrast, our procedure uses a compact laser system, so that this method is not limited to basic laboratory research but, because of the magnitude of the observed effects, may also find its way into analysis,” according to Baumert.About the Author
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201109035
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences