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.

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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

New method for imaging molecules inside cells

ScienceDaily (June 29, 2011) — Using a new sample holder, researchers at the University of Gothenburg have further developed a new method for imaging individual cells. This makes it possible to produce snapshots that not only show the outline of the cell's contours but also the various molecules inside or on the surface of the cell, and exactly where they are located, something which is impossible with a normal microscope.

Individual human cells are small, just one or two hundredths of a millimeter in diameter. As such, special measuring equipment is needed to distinguish the various parts inside the cell. Researchers generally use a microscope that magnifies the cell and shows its contours outline, but does not provide any information on the molecules inside the cell and on its surface.

"The new sample holder is filled with holds cells in solution," says Ingela Lanekoff, one of the researchers who developed the new method at the University of Gothenburg's Department of Chemistry. "We then rapidly freeze the sample down to -196°C, which enables us to get a snapshot of where the various molecules are at the moment of freezing. Using this technique we can produce images that show not only the outline of the cell's contours, but also the molecules that are there, and where they are located."

Important to measure chemical processes in the body

So why do the researchers want to know which molecules are to be found in a single cell? Because the cell is the smallest living component there is, and the chemical processes that take place here play a major role in how the cell functions in our body. For example, our brain has special cells that can communicate with each other through chemical signals. This vital communication has been shown to be dependent on the molecules in the cell's membrane.

Imaging the molecules in the membrane of single individual cells's membrane enables researchers to measure changes. Together with previous results, Lanekoff's findings show that the rate of communication in the studied cells studied is affected by a change of less than one per cent in the quantities abundance of a specific molecule in the membrane. This would suggest that communication between the cells in the brain is heavily dependent on the chemical composition of the membrane of each individual cell,. This could be an important part of the puzzle which could go some way towards explaining the mechanisms behind learning and memory.

The thesis, Analysis of phospholipids in cellular membranes with LC and imaging mass spectrometry, has been successfully defended at the University of Gothenburg. Supervisors: Andrew Ewing and Roger Karlsson. Download the thesis at: hdl.handle.net/2077/25279

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Scientists a step closer to understanding 'natural antifreeze' molecules

ScienceDaily (June 23, 2011) — Scientists have made an important step forward in their understanding of cryoprotectants -- compounds that act as natural 'antifreeze' to protect drugs, food and tissues stored at sub-zero temperatures.

Researchers from the Universities of Leeds and Illinois, and Columbia University in New York, studied a particular type of cryoprotectants known as osmolytes. They found that small osmolyte molecules are better at protecting proteins than larger ones.

The findings, published in Proceedings of the National Academy of Sciences, could help scientists develop better storage techniques for a range of materials, including human reproductive tissue used in IVF.

Biological systems can usually only operate within a small range of temperatures. If they get too hot or too cold, the molecules within the system can become damaged (denatured), which affects their structure and stops them from functioning.

But certain species of fish, reptiles and amphibians can survive for months below freezing by entering into a kind of suspended animation. They are able to survive these extreme conditions thanks to osmolytes -- small molecules within their blood that act like antifreeze -preventing damage to their vital organs.

These properties have made osmolytes attractive to scientists. They are used widely in the storage and testing of drugs and other pharmaceuticals; in food production; and to store human tissue like egg and sperm cells at very low temperatures (below -40ºC) for a long period of time.

"If you put something like human tissue straight in the freezer, ice crystals start to grow in the freezing water and solutes -- solid particles dissolved in the water -- get forced out into the remaining liquid.

This can result in unwanted high concentrations of solutes, such as salt, which can be very damaging to the tissue," said Dr Lorna Dougan from the University of Leeds, who led the study. "The addition of cryoprotectants, such as glycerol, lowers the freezing temperature of water and prevents crystallisation by producing a 'syrupy' semi-solid state. The challenge is to know which cryoprotectant molecule to use and how much of it is necessary.

"We want to get this right so that we recover as much of the biological material as possible after re-thawing. This has massive cost implications, particularly for the pharmaceutical industry because at present they lose a large proportion of their viable drug every time they freeze it."

Dr Dougan and her team tested a range of different osmolytes to find out which ones are most effective at protecting the 3D structure of a protein. They used an atomic force microscope to unravel a test protein in a range of different osmolyte environments to find out which ones were most protective. They discovered that smaller molecules, such as glycerol, are more effective than larger ones like sorbitol and sucrose.

Dr Dougan said: "We've been able to show that if you want to really stabilise a protein, it makes sense to use small protecting osmolytes. We hope to use this discovery and future research to develop a simple set of rules that will allow scientists and industry to use the best process parameters for their system and in doing so dramatically increase the amount of material they recover from the freeze-thaw cycle."

The research was funded by the UK Engineering and Physical Sciences Research Council, the US National Institutes of Health and the China National Basic Research Program.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Leeds.

Journal Reference:

L. Dougan, G. Z. Genchev, H. Lu, J. M. Fernandez. Probing osmolyte participation in the unfolding transition state of a protein. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1101934108

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Chirality: New method to consistently make left-handed or right-handed molecules

ScienceDaily (June 18, 2011) — Many organic molecules are non-superimposable with their mirror image. The two forms of such a molecule are called enantiomers and can have different properties in biological systems. The problem is to control which enantiomer you want to produce -- a problem that has proved to be important in the pharmaceutical industry. Researchers at the University of Gothenburg have now come up with a new method to control the process.

"Organic chemists think that it's impossible to create only one of the enantiomers without introducing some kind of optical activity into the reaction, but I've succeeded," says Theonitsa Kokoli at the University of Gothenburg's Department of Chemistry. "My method will allow the industry to produce the version they want without the use of a catalyst."

The phenomenon of non-superimposable mirror-image molecular structures is known as chirality. The two enantiomers can be compared to a pair of hands; they are non-superimposable mirror images of each other. A consequence of the different properties in biological systems is that a molecule can behave either as Dr Jekyll or Mr Hyde. The different characteristics in the enantiomers can be harmless, like in the limonene molecule. One enantiomer smells like orange and the other like lemon.

Thalidomide is a good example of how different forms of the same molecule can have disastrous consequences. One of the enantiomers was calming and eased nausea in pregnant women, while the other caused serious damage to the fetus. The thalidomide catastrophe is one of the reasons that a lot of research is devoted to chirality, as it is absolutely vital to be able to control which form of the molecule that is produced. Research on chirality has resulted in several Nobel Prizes over the years.

In biomolecules like DNA and proteins only one of the enantiomers exists in nature. In contrast to biomolecules, the same does not apply when chiral compounds are created synthetically in the lab. Generally an equal amount of both enantiomers is produced. One way of creating an excess of one enantiomer is to use a chiral catalyst, but this only transfers the properties that are already present in the catalyst.

"I've been working with absolute asymmetric synthesis instead, where optical activity is created," says Kokoli. "This is considered impossible by many organic chemists. I've used crystals in my reactions, where the two forms have crystallised as separate crystals, which in itself is fairly unusual. The product that was formed after the reactions comprised just one enantiomer."

While the results of Kokoli's research are particularly significant for the pharmaceuticals industry, they can also be used in the production of flavourings and aromas.

The thesis has been successfully defended on May 6, 2011.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Gothenburg.

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

Chirality: New method to consistently make left-handed or right-handed molecules

ScienceDaily (June 18, 2011) — Many organic molecules are non-superimposable with their mirror image. The two forms of such a molecule are called enantiomers and can have different properties in biological systems. The problem is to control which enantiomer you want to produce -- a problem that has proved to be important in the pharmaceutical industry. Researchers at the University of Gothenburg have now come up with a new method to control the process.

"Organic chemists think that it's impossible to create only one of the enantiomers without introducing some kind of optical activity into the reaction, but I've succeeded," says Theonitsa Kokoli at the University of Gothenburg's Department of Chemistry. "My method will allow the industry to produce the version they want without the use of a catalyst."

The phenomenon of non-superimposable mirror-image molecular structures is known as chirality. The two enantiomers can be compared to a pair of hands; they are non-superimposable mirror images of each other. A consequence of the different properties in biological systems is that a molecule can behave either as Dr Jekyll or Mr Hyde. The different characteristics in the enantiomers can be harmless, like in the limonene molecule. One enantiomer smells like orange and the other like lemon.

Thalidomide is a good example of how different forms of the same molecule can have disastrous consequences. One of the enantiomers was calming and eased nausea in pregnant women, while the other caused serious damage to the fetus. The thalidomide catastrophe is one of the reasons that a lot of research is devoted to chirality, as it is absolutely vital to be able to control which form of the molecule that is produced. Research on chirality has resulted in several Nobel Prizes over the years.

In biomolecules like DNA and proteins only one of the enantiomers exists in nature. In contrast to biomolecules, the same does not apply when chiral compounds are created synthetically in the lab. Generally an equal amount of both enantiomers is produced. One way of creating an excess of one enantiomer is to use a chiral catalyst, but this only transfers the properties that are already present in the catalyst.

"I've been working with absolute asymmetric synthesis instead, where optical activity is created," says Kokoli. "This is considered impossible by many organic chemists. I've used crystals in my reactions, where the two forms have crystallised as separate crystals, which in itself is fairly unusual. The product that was formed after the reactions comprised just one enantiomer."

While the results of Kokoli's research are particularly significant for the pharmaceuticals industry, they can also be used in the production of flavourings and aromas.

The thesis has been successfully defended on May 6, 2011.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Gothenburg.

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

Water's surface not all wet: Some water molecules split the difference between gas and liquid

ScienceDaily (June 9, 2011) — Air and water meet over most of Earth's surface, but exactly where one ends and the other begins turns out to be a surprisingly subtle question.

A new study in Nature narrows the boundary to just one quarter of water molecules in the uppermost layer -- those that happen to have one hydrogen atom in water and the other vibrating freely above.

Such molecules straddle gas and liquid phases, according to senior author Alexander Benderskii of the University of Southern California: The free hydrogen behaves like an atom in gas phase, while its twin below acts much like the other atoms that make up "bulk" water.

The finding matters for theoretical reasons and for practical studies of reactions at the water's surface, including the processes that maintain a vital supply of nitrogen, oxygen and carbon dioxide in the atmosphere.

"The air-water interface is about 70 percent of the Earth's surface," Benderskii said. "A lot of chemical reactions that are responsible for our atmospheric balance, as well as many processes important in environmental chemistry, happen at the air-water interface."

He added that the study provided a new way for chemists and biologists to study other interfaces, such as the boundary between water and biomembranes that marks the edge of every living cell.

"Water interfaces in general are important," Benderskii said, calling the study "an open door that now we can walk through and broaden the range of our investigations to other, perhaps more complex, acqueous interfaces."

In their study, Benderskii and his colleagues used techniques they invented to test the strength of hydrogen bonds linking water molecules (from the hydrogen of one molecule to the oxygen of another). These are the bonds that keep water a liquid at room temperature.

Specifically, the researchers inferred the bond strength by measuring the hydrogen-oxygen vibration frequency. The bond gets stronger as the frequency decreases, similar to the pull one feels when slowing down a child on a swing.

In the case of straddling molecules with one hydrogen in water, when compared to bonds below the surface, "the hydrogen bond is surprisingly only slightly weaker," according to Benderskii.

Likewise, the bond for the hydrogen atom sticking out of the water is similar in strength to bonds in the gas phase.

The researchers concluded that the change between air and water happens in the space of a single water molecule.

"You recover the bulk phase of water extremely quickly," Benderskii said.

While the transition happens in the uppermost layer of water molecules, the molecules involved change constantly. Even when they rise to the top layer, molecules for the most part are wholly submerged, spending only a quarter of their time straddling air and water.

The study raises the question of how exactly to define the air-water boundary.

If the straddling molecules constitute the boundary, it would be analogous to a wood fence where three of every four boards are missing -- except that since water molecules always are moving between submerged and straddling positions, the location of the fourth board would change millions of times per second.

If the boundary were the entire top layer of water molecules, the analogy would be a fence where one in four boards is sticking out at any one time.

A physical chemist, Benderskii began the study at Wayne State University in Detroit before joining the USC Dornsife College of Letters, Arts and Sciences in 2009 as an associate professor.

Benderskii's collaborators were lead author Igor Stiopkin, formerly at Wayne State and now at the University of Wisconsin-Madison; Champika Weeraman, also previously at Wayne State and now at Canada's National Research Council in Ottawa; Piotr Pieniazek and James Skinner of the University of Wisconsin-Madison; and Fadel Shalhout, formerly at Wayne State and now at USC Dornsife College.

The National Science Foundation and the U.S. Department of Energy funded the study.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Southern California. The original article was written by Carl Marziali.

Journal Reference:

Igor V. Stiopkin, Champika Weeraman, Piotr A. Pieniazek, Fadel Y. Shalhout, James L. Skinner, Alexander V. Benderskii. Hydrogen bonding at the water surface revealed by isotopic dilution spectroscopy. Nature, 2011; 474 (7350): 192 DOI: 10.1038/nature10173

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Chemists devise better way to prepare workhorse molecules

ScienceDaily (June 9, 2011) — In chemistry, so-called aromatic molecules compose a large and versatile family of chemical compounds that are the stuff of pharmaceuticals, electronic materials and consumer products ranging from sunscreen to plastic soda bottles.

Writing in the current online issue (June 9) of the journal Science, a team led by University of Wisconsin-Madison chemistry Professor Shannon Stahl reports a new, environmentally friendly way to make substituted aromatic molecules that can be customized for different industrial needs.

As college chemistry students know, aromatic molecules have a special stability conferred by a ring of six carbon atoms with alternating single and double bonds. "The ultimate utility of these molecules depends on the chemical groups attached at the corners of this hexagonal platform," explains Stahl. "Interest in preparing substituted aromatic molecules traces back to the dawn of organic chemistry."

In fact, the 2010 Nobel Prize in Chemistry was awarded for catalytic chemical reactions that allow the introduction of specific groups to the periphery of aromatic molecules. These methods, and older traditional methods, rely on modifying an existing aromatic molecule, Stahl explains. But the stability of aromatic molecules can make such approaches difficult, and existing methods also have many limitations in the types and patterns of chemical groups that can be installed.

The method devised by Stahl and Wisconsin colleagues Yusuke Izawa and Doris Pun owes its success to the discovery of a new palladium catalyst. The catalyst gives chemists a way to peel off hydrogen from cyclic molecules to form aromatic products with the desired substitution patterns already in place. The hydrogen removed by the palladium catalyst is combined with oxygen, and water is formed as the only byproduct.

The Wisconsin team demonstrated the utility and efficiency of the new process on phenols, aromatic compounds that are produced on a large scale as precursors to many kinds of industrial materials and pharmaceutical agents. While the new catalytic method can be used to make a broad spectrum of aromatic molecules of interest to science and industry, the new work will be of most immediate practical use to drug companies, according to Stahl. For example, an anticancer agent that was difficult to make using previously known methods was efficiently produced using the strategy devised by the team.

Stahl notes that the work published June 9 in Science will require more development before it is suitable for large-scale industrial production, but he emphasizes that concepts introduced by the new work will have broad utility. "Many new catalysts, reaction conditions and target molecules can be envisioned. Overall, this route to substituted aromatic molecules has a lot of potential," he says.

The new study was supported by grants from the U.S. National Institutes of Health, the Mitsubishi Chemical Corp. and the U.S. National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Wisconsin-Madison.

Journal Reference:

Yusuke Izawa, Doris Pun and Shannon S. Stahl. Palladium-Catalyzed Aerobic Dehydrogenation of Substituted Cyclohexanones to Phenols. Science, 9 June 2011 DOI: 10.1126/science.1204183

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

Chemists devise better way to prepare workhorse molecules

ScienceDaily (June 9, 2011) — In chemistry, so-called aromatic molecules compose a large and versatile family of chemical compounds that are the stuff of pharmaceuticals, electronic materials and consumer products ranging from sunscreen to plastic soda bottles.

Writing in the current online issue (June 9) of the journal Science, a team led by University of Wisconsin-Madison chemistry Professor Shannon Stahl reports a new, environmentally friendly way to make substituted aromatic molecules that can be customized for different industrial needs.

As college chemistry students know, aromatic molecules have a special stability conferred by a ring of six carbon atoms with alternating single and double bonds. "The ultimate utility of these molecules depends on the chemical groups attached at the corners of this hexagonal platform," explains Stahl. "Interest in preparing substituted aromatic molecules traces back to the dawn of organic chemistry."

In fact, the 2010 Nobel Prize in Chemistry was awarded for catalytic chemical reactions that allow the introduction of specific groups to the periphery of aromatic molecules. These methods, and older traditional methods, rely on modifying an existing aromatic molecule, Stahl explains. But the stability of aromatic molecules can make such approaches difficult, and existing methods also have many limitations in the types and patterns of chemical groups that can be installed.

The method devised by Stahl and Wisconsin colleagues Yusuke Izawa and Doris Pun owes its success to the discovery of a new palladium catalyst. The catalyst gives chemists a way to peel off hydrogen from cyclic molecules to form aromatic products with the desired substitution patterns already in place. The hydrogen removed by the palladium catalyst is combined with oxygen, and water is formed as the only byproduct.

The Wisconsin team demonstrated the utility and efficiency of the new process on phenols, aromatic compounds that are produced on a large scale as precursors to many kinds of industrial materials and pharmaceutical agents. While the new catalytic method can be used to make a broad spectrum of aromatic molecules of interest to science and industry, the new work will be of most immediate practical use to drug companies, according to Stahl. For example, an anticancer agent that was difficult to make using previously known methods was efficiently produced using the strategy devised by the team.

Stahl notes that the work published June 9 in Science will require more development before it is suitable for large-scale industrial production, but he emphasizes that concepts introduced by the new work will have broad utility. "Many new catalysts, reaction conditions and target molecules can be envisioned. Overall, this route to substituted aromatic molecules has a lot of potential," he says.

The new study was supported by grants from the U.S. National Institutes of Health, the Mitsubishi Chemical Corp. and the U.S. National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Wisconsin-Madison.

Journal Reference:

Yusuke Izawa, Doris Pun and Shannon S. Stahl. Palladium-Catalyzed Aerobic Dehydrogenation of Substituted Cyclohexanones to Phenols. Science, 9 June 2011 DOI: 10.1126/science.1204183

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