Watching motion of electrons in molecules during chemical reactions

ScienceDaily (Oct. 14, 2011) — A research group led by ETH Zurich has now, for the first time, visualized the motion of electrons during a chemical reaction. The new findings in the experiment are of fundamental importance for photochemistry and could also assist the design of more efficient solar cells.

In 1999, Ahmed Zewail was awarded the nobel prize in chemistry for his studies of chemical reactions using ultrashort laser pulses. Zewail was able to watch the motion of atoms and thus visualize transition states on the molecular level. Watching the dynamics of single electrons was still considered a dream at that time. Thanks to the latest developments in laser technology and intense research in the field of attosecond spectroscopy (1 attosecond = 10-18 s) the research has developed fast. For the first time, Prof. Hans Jakob Wörner from the Laboratory of Physical Chemistry at ETH Zurich, together with colleagues from Canada and France, was able to record electronic motion during a complete chemical reaction. The experiment is described in the latest issue of Science.

The research team irradiated nitrogen dioxide molecules (NO2) with a very short ultraviolet pulse. Subsequently, the molecule takes up the energy from the pulse which sets the electrons in motion. The electrons start rearranging themselves, which causes the electron cloud to oscillate between two different shapes for a very short time, before the molecule starts to vibrate and eventually decomposes into nitric oxide and an oxygen atom.

Conical intersections

Nitrogen dioxide has model character with respect to understanding electronic motion. In the NO2 molecule, two states of the electrons can have the same energy for a particular geometry -- commonly described as conical intersection. The conical intersection is very important for photochemistry and frequently occurs in natural chemical processes induced by light. The conical intersection works like a dip-switch. For example, if the retina of a human eye is irradiated by light, the electrons start moving, and the molecules of the retina (retinal) change their shape, which finally converts the information of light to electrical information for the human brain. The special aspect about conical intersections is that the motion of electrons is transferred to a motion of the atoms very efficiently.

Snapshot of an electron

In an earlier article, Hans Jakob Wörner has already published how attosecond spectroscopy can be used for watching the motion of electrons. The first weak ultraviolet pulse sets the electrons in motion. The second strong infrared pulse then removes an electron from the molecule, accelerates it and drives it back to the molecule. As a result, an attosecond light pulse is emitted, which carries a snapshot of the electron distribution in the molecule. Wörner illustrates the principle of attosecond spectroscopy: "The experiment can be compared to photographs, which, for example, image a bullet shot through an apple. The bullet would be too fast for the shutter of a camera, resulting in a blurred image. Therefore, the shutter is left open and the picture is illuminated with light flashes, which are faster than the bullet. That's how we get our snap-shot."

From the experiment to solar cells

When the electron returns to the molecule, it releases energy in the form of light. In the experiment, Wörner and his colleagues measured the light of the electrons and were therefore able to deduce detailed information on the electron distribution and its evolution with time. This information reveals details of chemical reaction mechanisms that were not accessible to most of previous experimental techniques. The experiment on NO2 helps understanding fundamental processes in molecules and is an ideal extension of computer simulations of photochemical processes: "What makes our experiment so important is that it verifies theoretical models," says Wörner. The immense interest in photochemical processes is not surprising, as this area of research aims at improving solar cells and making artificial photosynthesis possible.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by ETH Zürich.

Journal Reference:

H. J. Worner, J. B. Bertrand, B. Fabre, J. Higuet, H. Ruf, A. Dubrouil, S. Patchkovskii, M. Spanner, Y. Mairesse, V. Blanchet, E. Mevel, E. Constant, P. B. Corkum, D. M. Villeneuve. Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy. Science, 2011; 334 (6053): 208 DOI: 10.1126/science.1208664

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Watching motion of electrons in molecules during chemical reactions

ScienceDaily (Oct. 14, 2011) — A research group led by ETH Zurich has now, for the first time, visualized the motion of electrons during a chemical reaction. The new findings in the experiment are of fundamental importance for photochemistry and could also assist the design of more efficient solar cells.

In 1999, Ahmed Zewail was awarded the nobel prize in chemistry for his studies of chemical reactions using ultrashort laser pulses. Zewail was able to watch the motion of atoms and thus visualize transition states on the molecular level. Watching the dynamics of single electrons was still considered a dream at that time. Thanks to the latest developments in laser technology and intense research in the field of attosecond spectroscopy (1 attosecond = 10-18 s) the research has developed fast. For the first time, Prof. Hans Jakob Wörner from the Laboratory of Physical Chemistry at ETH Zurich, together with colleagues from Canada and France, was able to record electronic motion during a complete chemical reaction. The experiment is described in the latest issue of Science.

The research team irradiated nitrogen dioxide molecules (NO2) with a very short ultraviolet pulse. Subsequently, the molecule takes up the energy from the pulse which sets the electrons in motion. The electrons start rearranging themselves, which causes the electron cloud to oscillate between two different shapes for a very short time, before the molecule starts to vibrate and eventually decomposes into nitric oxide and an oxygen atom.

Conical intersections

Nitrogen dioxide has model character with respect to understanding electronic motion. In the NO2 molecule, two states of the electrons can have the same energy for a particular geometry -- commonly described as conical intersection. The conical intersection is very important for photochemistry and frequently occurs in natural chemical processes induced by light. The conical intersection works like a dip-switch. For example, if the retina of a human eye is irradiated by light, the electrons start moving, and the molecules of the retina (retinal) change their shape, which finally converts the information of light to electrical information for the human brain. The special aspect about conical intersections is that the motion of electrons is transferred to a motion of the atoms very efficiently.

Snapshot of an electron

In an earlier article, Hans Jakob Wörner has already published how attosecond spectroscopy can be used for watching the motion of electrons. The first weak ultraviolet pulse sets the electrons in motion. The second strong infrared pulse then removes an electron from the molecule, accelerates it and drives it back to the molecule. As a result, an attosecond light pulse is emitted, which carries a snapshot of the electron distribution in the molecule. Wörner illustrates the principle of attosecond spectroscopy: "The experiment can be compared to photographs, which, for example, image a bullet shot through an apple. The bullet would be too fast for the shutter of a camera, resulting in a blurred image. Therefore, the shutter is left open and the picture is illuminated with light flashes, which are faster than the bullet. That's how we get our snap-shot."

From the experiment to solar cells

When the electron returns to the molecule, it releases energy in the form of light. In the experiment, Wörner and his colleagues measured the light of the electrons and were therefore able to deduce detailed information on the electron distribution and its evolution with time. This information reveals details of chemical reaction mechanisms that were not accessible to most of previous experimental techniques. The experiment on NO2 helps understanding fundamental processes in molecules and is an ideal extension of computer simulations of photochemical processes: "What makes our experiment so important is that it verifies theoretical models," says Wörner. The immense interest in photochemical processes is not surprising, as this area of research aims at improving solar cells and making artificial photosynthesis possible.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by ETH Zürich.

Journal Reference:

H. J. Worner, J. B. Bertrand, B. Fabre, J. Higuet, H. Ruf, A. Dubrouil, S. Patchkovskii, M. Spanner, Y. Mairesse, V. Blanchet, E. Mevel, E. Constant, P. B. Corkum, D. M. Villeneuve. Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy. Science, 2011; 334 (6053): 208 DOI: 10.1126/science.1208664

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Antibody production gets confused during long-term spaceflight

ScienceDaily (May 19, 2011) — The trip to Mars just got a little more difficult now that French researchers have discovered that antibodies used to fight off disease might become seriously compromised during long-term space flight. In a new report published online in the FASEB Journal, the scientists show that antibodies produced in space are less effective than those produced on terra firma. The reduced effectiveness of antibodies makes astronauts more susceptible to illness, while increasing the danger posed by bacteria and viruses likely to coexist with wayfaring astronauts.

"We hope to find efficient pharmacological and/or nutritional countermeasures to alterations of the immune system that could be useful to astronauts and to people who have weak immune systems on Earth because of infections, aging, or chronic stress exposure," said Jean-Pol Frippiat, a researcher involved in the work from the Faculty of Medicine, Development and Immunogenetics at the Université Henri Poincaré-Nancy, Vandœuvre-lès-Nancy, France.

To make their discovery, Frippiat and colleagues conducted studies using three groups of amphibians. Amphibians were chosen for the work because they use the same cellular mechanisms to produce antibodies as humans do. The first group of amphibians was immunized in space, the second was immunized on Earth, and the third was not immunized at all. Comparison of the antibodies produced revealed that the quality of the antibodies generated by the group immunized in space was decreased. This suggests that spaceflight conditions alter the immune system and affect its ability to protect against infections and tumors, posing a serious risk for astronauts.

"This paper shows that somatic hypermutation occurs at a lower frequency in spaceflight and brings together yet more evidence that the immune system is dependent on gravity," said Millie Hughes-Fulford, Ph.D., NASA Science Astronaut; Professor, Department of Biochemistry and Biophysics, UCSF; Director, Laboratory of Cell Growth, VAMC/UCSF; and editorial board member of the FASEB Journal. "Dependence on gravity should be no surprise since all of earth's jawed vertebrates developed in earth's gravity, and it would be logical to expect that some systems would require gravity for normal function."

"Outer space may be the final frontier, but this research shows that our inner space could pose the greatest threat to the success of a mission," said Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal. "These explorers will have to be prepared not only for the challenges of extremely hostile environments, but also those posed by microbial stowaways, even those with which we peacefully co-exist on Earth."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Federation of American Societies for Experimental Biology, via EurekAlert!, a service of AAAS.

Journal Reference:

Matthieu Bascove, Nathan Guéguinou, Bérénice Schaerlinger, Guillemette Gauquelin-Koch, and Jean-Pol Frippiat. Decrease in antibody somatic hypermutation frequency under extreme, extended spaceflight conditions. FASEB J., May 18, 2011 DOI: 1096/fj.11-185215

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Antibody production gets confused during long-term spaceflight

ScienceDaily (May 19, 2011) — The trip to Mars just got a little more difficult now that French researchers have discovered that antibodies used to fight off disease might become seriously compromised during long-term space flight. In a new report published online in the FASEB Journal, the scientists show that antibodies produced in space are less effective than those produced on terra firma. The reduced effectiveness of antibodies makes astronauts more susceptible to illness, while increasing the danger posed by bacteria and viruses likely to coexist with wayfaring astronauts.

"We hope to find efficient pharmacological and/or nutritional countermeasures to alterations of the immune system that could be useful to astronauts and to people who have weak immune systems on Earth because of infections, aging, or chronic stress exposure," said Jean-Pol Frippiat, a researcher involved in the work from the Faculty of Medicine, Development and Immunogenetics at the Université Henri Poincaré-Nancy, Vandœuvre-lès-Nancy, France.

To make their discovery, Frippiat and colleagues conducted studies using three groups of amphibians. Amphibians were chosen for the work because they use the same cellular mechanisms to produce antibodies as humans do. The first group of amphibians was immunized in space, the second was immunized on Earth, and the third was not immunized at all. Comparison of the antibodies produced revealed that the quality of the antibodies generated by the group immunized in space was decreased. This suggests that spaceflight conditions alter the immune system and affect its ability to protect against infections and tumors, posing a serious risk for astronauts.

"This paper shows that somatic hypermutation occurs at a lower frequency in spaceflight and brings together yet more evidence that the immune system is dependent on gravity," said Millie Hughes-Fulford, Ph.D., NASA Science Astronaut; Professor, Department of Biochemistry and Biophysics, UCSF; Director, Laboratory of Cell Growth, VAMC/UCSF; and editorial board member of the FASEB Journal. "Dependence on gravity should be no surprise since all of earth's jawed vertebrates developed in earth's gravity, and it would be logical to expect that some systems would require gravity for normal function."

"Outer space may be the final frontier, but this research shows that our inner space could pose the greatest threat to the success of a mission," said Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal. "These explorers will have to be prepared not only for the challenges of extremely hostile environments, but also those posed by microbial stowaways, even those with which we peacefully co-exist on Earth."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Federation of American Societies for Experimental Biology, via EurekAlert!, a service of AAAS.

Journal Reference:

Matthieu Bascove, Nathan Guéguinou, Bérénice Schaerlinger, Guillemette Gauquelin-Koch, and Jean-Pol Frippiat. Decrease in antibody somatic hypermutation frequency under extreme, extended spaceflight conditions. FASEB J., May 18, 2011 DOI: 1096/fj.11-185215

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here