Glowing beacons reveal hidden order in dynamical systems: Experimental confirmation of a fundamental physical theorem

 A dynamical system in which repeated measurements on a single particle yield the same mean result as a single measurement of the whole ensemble is said to be ergodic. The ergodic theorem expresses a fundamental physical principle, and its validity for diffusive processes has now been demonstrated.

The so-called ergodic theorem formulates a fundamental physical principle relating to the behavior of dynamical systems. Essentially the theorem states that in a multiparticle system each individual particle behaves just as "chaotically" as does the system as a whole. In other words, one can extrapolate from the behavior of a single element to that of the whole system. Strangely enough, in spite of its wide-ranging implications, the theorem has not been rigorously tested experimentally. A collaborative effort mounted by Professor Christoph Bräuchle's team in the Department of Chemistry at LMU Munich and Professor Jörg Kärger's group at Leipzig University has now confirmed the validity of the theorem by measuring the diffusive behavior of ensembles of particles and the trajectories of single molecules in the same system. Using fluorescent molecules as tracers and high-resolution imaging methods, the LMU investigators were able to track the paths of individual molecules, while the Leipzig group studied the collective behavior of the whole ensemble. "It will be very interesting to take a closer look at systems that do not conform to the tenets of the ergodic theorem and to determine the reasons for their aberrant behavior," says Bräuchle.

The term "diffusion" refers to the random motion of particles, such as atoms and molecules, under the influence of thermal energy. This physical process is an essential component of innumerable phenomena in nature, and also plays a crucial role in many technological procedures. For instance, in virtually all chemical reactions, diffusion is responsible for bringing reactants sufficiently close together to enable them to react at all. It is generally accepted that the ergodic theorem is applicable to the dynamics of diffusive processes. The theory basically states that repeated measurements of a given variable -- such as the distance covered by a particle in a given time interval -- should yield the same average value as a single measurement of the same variable on a collection of particles -- provided the system considered is in a state of equilibrium. However, as Kärger points out, "although diffusive processes have been investigated for the past 150 years, the principle of ergodicity has not yet been experimentally verified."

This is because it has so far been possible to quantify diffusive processes only by means of ensemble measurements -- i.e. measurements of many particles simultaneously. One of the most informative methods for this purpose is pulsed-field gradient nuclear magnetic resonance (PFG-NMR), a technique for which Kärger and his group are well known. The actual trajectory of a single particle, on the other hand, could not be observed directly. "With the development of single-molecule spectroscopy and single-molecule microscopy, we can now follow the trajectories -- and therefore monitor the diffusion behavior -- of single molecules," Bräuchle explains. Optical tracking methods visualize molecules on the basis of their fluorescence, making it possible for their positions to be localized and monitored with a precision of a few nanometers.

This still leaves one problem to be solved -- successful application of the two methods requires very different, indeed apparently conflicting, conditions. NMR measurements need high concentrations of molecules with large diffusion coefficients, while single-molecule spectroscopy works best with extremely dilute solutions of species with small diffusion coefficients. By using particular organic dyes with high fluorescence yields in combination with porous silicate glasses containing networks of nanometer-sized channels in which the dye molecules can diffuse, the researchers were able to create conditions that were compatible with both methods. This experimental set-up allowed them to perform single-molecule and ensemble measurements on the same system.

When the two teams compared their data, they found that the diffusion coefficients (the parameter that describes diffusive motion) obtained by the two techniques agreed with each other -- providing the first experimental confirmation of the ergodic theorem in this context. The next step will be to examine systems in which the theory does not apply. "The diffusion of nanoparticles in cells looks like an interesting example," says Bräuchle, "and for us the important thing is to find out why the ergodic theorem doesn't hold in this case."

The project in Munich was carried out under the support of the Cluster of Excellence "Nanosystems Initiative Munich" (NIM) and DFG Priority Program 749 (Dynamics and Intermediate Molecular Transformations), while the work in Leipzig was supported by the DFG as part of Research Unit 877 (From Local Constraints to Macroscopic Transport).

The above story is reprinted from materials provided by Ludwig-Maximilians-Universitaet Muenchen (LMU).

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Florian Feil, Sergej Naumov, Jens Michaelis, Rustem Valiullin, Dirk Enke, Jörg Kärger, Christoph Bräuchle. Single-Particle and Ensemble Diffusivities-Test of Ergodicity. Angewandte Chemie, 2011; DOI: 10.1002/ange.201105388

A hidden order unraveled: Microscopic views on quantum fluctuations

 Fluctuations are fundamental to many physical phenomena in our everyday life, such as the phase transitions from a liquid into a gas or from a solid into a liquid. But even at absolute zero temperature, where all motion in the classical world is frozen out, special quantum mechanical fluctuations prevail that can drive the transition between two quantum phases.

Now a team around Immanuel Bloch and Stefan Kuhr at Ludwig-Maximilians University (LMU) and the Max Planck Institute of Quantum Optics (MPQ) has succeeded in directly observing such quantum fluctuations. Using a high resolution microscope, they were able to image quantum-correlated particle-hole pairs in a gas of ultracold atoms. This allowed the physicists to unravel a hidden order in the crystal and to characterize the different phases of the quantum gas. The work was performed together with scientists from the Theory Division at the MPQ and ETH Zurich. These measurements open new ways to characterize novel quantum phases of matter.

The scientists start by cooling a small cloud of rubidium atoms down to a temperature near absolute zero, about minus 273 degree Celsius. The ensemble is then subjected to a light field that severely restricts the motion of the particles along one-dimensional tubes of light aligned in parallel. An additional standing laser wave along the tubes creates a one-dimensional optical lattice that holds the atoms in a periodic array of bright and dark regions of light.

The atoms move in the periodic light field like electrons in solids. As these can be electric conductors or insulators, also the one-dimensional quantum gases can behave like a superfluid or like an insulator at low temperatures. In particular, the height of the optical lattice potential plays an important role: it determines whether the atom is fixed on a particular lattice site or whether is able to move to a neighbouring site. At very large lattice depths, each lattice site is occupied by exactly one atom. This highly ordered state is called a "Mott insulator," after the British physicist and Nobel laureate Sir Neville Mott. When the lattice depth is decreased slightly, the atoms have enough energy to reach a neighbouring site by quantum mechanical tunneling. In this way, pairs of empty and doubly occupied sites emerge, so-called particle-hole pairs. Intriguingly, these quantum fluctuations also occur at absolute zero temperature, when all movement in the classical world is frozen out. The position of the quantum-correlated particle-hole pairs in the crystal is completely undetermined and is fixed only by the measurement process.

In recent experiments, the physicists around Stefan Kuhr and Immanuel Bloch had already developed a method, which allowed to image single atoms lattice site by lattice site. The atoms are cooled using laser beams, and the fluorescence photons emitted in this process are used to observe the atoms with a high resolution microscope. Holes naturally show up as dark spots, but so do doubly occupied sites as the two particles kick each other out of the lattice in the experiment. Therefore particle-hole pairs appear as two neighbouring dark lattice sites. "With our technique, we can directly observe this fundamental quantum phenomenon for the first time," describes doctoral student Manuel Endres enthusiastically.

The physicists measure the number of neighbouring particle-hole pairs through a correlation function. With increasing kinetic energy, more and more particles tunnel to neighbouring sites and the pair correlations increase. However, when the number of particle-hole pairs is very large, it becomes difficult to unambiguously identify them. Hence the correlation function takes on smaller values. Finally, the ordered state of a Mott insulator vanishes completely und the quantum gas becomes a superfluid again. Here fluctuations of holes and particles occur independently. The correlation function measured in the experiment is very well reproduced by model calculations, which were performed by scientists from the Theory Division at the MPQ and the ETH Zurich. Interestingly, the same investigations on two-dimensional quantum-gases clearly showed that quantum fluctuations are not as prominent as in one-dimensional systems.

The scientists extended their analysis to correlations between several lattice sites along a string. Such non-local correlation functions contain important information about the underlying many-body system and can be used as an order parameter to characterize different quantum phases. In the experiment described here, such non-local order parameters have been measured for the first time. In the future, the scientists plan to use these measurements for the detection of topological quantum phases. These can be useful for robust quantum computers and could help to understand superconductivity at high temperatures. (MPQ)

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Ludwig-Maximilians-Universität München.

Journal Reference:

M. Endres, M. Cheneau, T. Fukuhara, C. Weitenberg, P. Schauss, C. Gross, L. Mazza, M. C. Banuls, L. Pollet, I. Bloch, S. Kuhr. Observation of Correlated Particle-Hole Pairs and String Order in Low-Dimensional Mott Insulators. Science, 2011; 334 (6053): 200 DOI: 10.1126/science.1209284

New synchrotron X-ray technique could see hidden building blocks of life

 

Scientists from Finland and France have developed a new synchrotron X-ray technique that may revolutionize the chemical analysis of rare materials like meteoric rock samples or fossils. The results have been published on 29 May 2011 in Nature Materials as an advance online publication.

Life, as we know it, is based on the chemistry of carbon and oxygen. The three-dimensional distribution of their abundance and chemical bonds has been difficult to study up to now in samples where these elements were embedded deep inside other materials. Examples are tiny inclusions of possible water or other chemicals inside martian rock samples, fossils buried inside a lava rock, or minerals and chemical compounds within meteorites.

X-ray tomography, which is widely used in medicine and material science, is sensitive to the shape and texture of a given sample but cannot reveal chemical states at the macroscopic scale. For instance graphite and diamond both consist of pure carbon, but they differ in the chemical bond between the carbon atoms. This is why their properties are so radically different. Imaging the variations in atomic bonding has been surprisingly difficult, and techniques for imaging of chemical bonds are highly desirable in many fields like engineering and research in physics, chemistry, biology, and geology.

 

Now an international team of scientists from the University of Helsinki, Finland, and the European Synchrotron Radiation Facility (ESRF), Grenoble, France, has developed a novel technique that is suitable exactly for this purpose. The researchers use extremely bright X-rays from a synchrotron light source to form images of the chemical bond distribution of different carbon forms embedded deep in an opaque material; an achievement previously thought to be impossible without destroying the sample.

Enlarge

The left part of the image shows a photograph of the sample, measuring approximately 7 x 10 x 5mm3. The part studied with X-rays was the indicated subvolume of 7 x 2 x 1mm3. The result, a detailed 3D map of chemical bonds, is visualised here as a 2-D cut through the subvolume, shown on the right, where the different colors represent the different chemical carbon bonds present in the sample. Credit: Simo Huotari (Helsinki University). With permission by Nature Materials.

"Now I would love to try this on Martian or moon rocks. Our new technique can see not only which elements are present in any inclusions but also what kind of molecule or crystal they belong to. If the inclusion contains oxygen, we can tell whether the oxygen belongs to a water molecule. If it contains carbon, we can tell whether it is graphite, diamond-like, or some other carbon form. Just imagine finding tiny inclusions of water or diamond inside martian rock samples hidden deep inside the rock", says Simo Huotari from the University of Helsinki.

The newly developed method will give insights into the molecular level structure of many other interesting materials ranging, for example, from novel functional nanomaterials to fuel cells and new types of batteries.

More information: Simo Huotari et al., Direct tomography with chemical-bond contrast, Nature Materials advanded online publication, 29 May 2011, DOI:10.1038/NMAT3031

Provided by European Synchrotron Radiation Facility

New synchrotron technique could see hidden building blocks of life

Scientists from Finland and France have developed a new synchrotron X-ray technique that may revolutionize the chemical analysis of rare materials like meteoric rock samples or fossils. The results have been published on 29 May 2011 in Nature Materials as an advance online publication.

Life, as we know it, is based on the chemistry of carbon and oxygen. The three-dimensional distribution of their abundance and chemical bonds has been difficult to study up to now in samples where these elements were embedded deep inside other materials. Examples are tiny inclusions of possible water or other chemicals inside martian rock samples, fossils buried inside a lava rock, or minerals and chemical compounds within meteorites.

X-ray tomography, which is widely used in medicine and material science, is sensitive to the shape and texture of a given sample but cannot reveal chemical states at the macroscopic scale. For instance graphite and diamond both consist of pure carbon, but they differ in the chemical bond between the carbon atoms. This is why their properties are so radically different. Imaging the variations in atomic bonding has been surprisingly difficult, and techniques for imaging of chemical bonds are highly desirable in many fields like engineering and research in physics, chemistry, biology, and geology.

Now an international team of scientists from the University of Helsinki, Finland, and the European Synchrotron Radiation Facility (ESRF), Grenoble, France, has developed a novel technique that is suitable exactly for this purpose. The researchers use extremely bright X-rays from a synchrotron light source to form images of the chemical bond distribution of different carbon forms embedded deep in an opaque material; an achievement previously thought to be impossible without destroying the sample.

"Now I would love to try this on Martian or moon rocks. Our new technique can see not only which elements are present in any inclusions but also what kind of molecule or crystal they belong to. If the inclusion contains oxygen, we can tell whether the oxygen belongs to a water molecule. If it contains carbon, we can tell whether it is graphite, diamond-like, or some other carbon form. Just imagine finding tiny inclusions of water or diamond inside martian rock samples hidden deep inside the rock," says Simo Huotari from the University of Helsinki.

The newly developed method will give insights into the molecular level structure of many other interesting materials ranging, for example, from novel functional nanomaterials to fuel cells and new types of batteries.

The research was funded by the European Synchrotron Radiation Facility (ESRF), the Academy of Finland, and the University of Helsinki.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by European Synchrotron Radiation Facility.

Journal Reference:

Simo Huotari, Tuomas Pylkkänen, Roberto Verbeni, Giulio Monaco, Keijo Hämäläinen. Direct tomography with chemical-bond contrast. Nature Materials, 2011; DOI: 10.1038/NMAT3031

Search for Advanced Materials Aided by Discovery of Hidden Symmetries in Nature

A new way of understanding the structure of proteins, polymers, minerals, and engineered materials was published in Nature Materials. The discovery by two Penn State University researchers is a new type of symmetry in the structure of materials, which the researchers say greatly expands the possibilities for discovering or designing materials with desired properties. The research is expected to have broad relevance in many development efforts involving physical, chemical, biological, or engineering disciplines including, for example, the search for advanced ferroelectric ferromagnet materials for next-generation ultrasound devices and computers.

Before the publication of this paper, scientists and engineers had five different types of symmetries to use as tools for understanding the structures of materials whose building blocks are arranged in fairly regular patterns. Four types of symmetries had been known for thousands of years - called rotation, inversion, rotation inversion, and translation - and a fifth type - called time reversal - have been discovered about 60 years ago. Now, Gopalan and Litvin have added a new, sixth, type, called rotation reversal. As a result, the number of known ways in which the components of such crystalline materials can be combined in symmetrical ways has multiplied from no more than 1,651 before to more than 17,800 now. "We mathematically combined the new rotation-reversal symmetry with the previous five symmetries and now we know that symmetrical groups can form in crystalline materials in a much larger number of ways," said Daniel B. Litvin, distinguished professor of physics, who coauthored the study with Venkatraman Gopalan, professor of materials science and engineering.

The new rotation-reversal symmetry enriches the mathematical language that researchers use to describe a crystalline material's structure and to predict its properties. "Rotation reversal is an absolutely new approach that is different in that it acts on a static component of the material's structure, not on the whole structure all at once," Litvin said. "It is important to look at symmetries in materials because symmetry dictates all natural laws in our physical universe."

The most simple type of symmetry - rotation symmetry - is obvious, for example, when a square shape is rotated around its center point: the square shows its symmetrical character by looking exactly the same at four points during the rotation: at 90 degrees, 180 degrees, 270 degrees, and 360 degrees. Gopalan and Litvin say their new rotation-reversal symmetry is obvious, as well, if you know where to look.

The "eureka moment" of the discovery occurred when Gopalan recognized that the simple concept of reversing the direction of a spiral-shaped structure from clockwise to counterclockwise opens the door to a distinctly new type of symmetry. Just as a square shape has the quality of rotation symmetry even when it is not being rotated, Gopalan realized that a spiral shape has the quality of rotation-reversal symmetry even when it is not being physically forced to rotate in the reverse direction. Their further work with this rotation-reversal concept revealed many more structural symmetries than previously had been recognized in materials containing various types of directionally oriented structures. Many important biological molecules, for example, are said to be either "right handed" or "left handed," including DNA, sugars, and proteins.

"We found that rotation-reversal symmetry also exists in paired structures where the partner components lean toward each other, then away from each other in paired patterns symmetrically throughout a material," Gopalan said. These "tilting octahedral" structures are common in a wide variety of crystalline materials, where all the component structures are tightly interconnected by networks of shared atoms. The researchers say it is possible that components of materials with rotation-reversal symmetry could be engineered to function as on/off switches for a variety of novel applications.

The now-much-larger number of possible symmetry groups also is expected to be useful in identifying materials with unusual combinations of properties. "For example, the goal in developing a ferroelectric ferromagnet is to have a material in which the electrical dipoles and the magnetic moments coexist and are coupled in the same material - that is, a material that allows electrical control of magnetism - which would be very useful to have in computers," Gopalan said. The addition of rotation-reversal symmetry to the materials-science toolbox may help researchers to identify and search for structures in materials that could have strong ferroelectric and ferromagnetic properties.

Gopalan and Litvin said a goal of their continuing research is to describe each of the more than 17,800 different combinations of the six symmetry types to give materials scientists a practical new tool for significantly increasing the efficiency and effectiveness in finding novel materials. The team also plans to conduct laboratory experiments that make use of their theoretical work on rotation-reversal symmetry. "We have done some predictions, we will test those predictions experimentally," Litvin said. "We are in the very early stages of implementing the results we have described in our new theory paper." Gopalan said, for example, that he has predicted new forms for optical properties in the commonplace quartz crystals that are used widely in watches and electronic equipment, and that his group now is testing these predictions experimentally.

 

Sugar Flushes Out Hidden Microbes

Used to be that sick kids got lollypops after a visit with the doctor. But in some cases candy can be more than a reward—it can be part of the therapy. Because scientists have found that, in battling chronic infections, sugar can boost the effectiveness of antibiotics. The study appears in the journal Nature. [James Collins, Mark Brynildsen and Kyle Allison, Metabolite-enabled eradication of bacterial persisters by aminoglycosides]

Chronic infections can be caused by persistent bacteria that have learned how to lay low until all the antibiotics are gone. They’re not exactly antibiotic resistant, so they don’t have any special drug-destroying mutations. They just power down, metabolically speaking, and then wait until the coast is clear (of antibiotics) to come back to life. Which is why the poor patient just can’t seem to clear the infection.

To eliminate such stealthy bacteria, scientists at Boston University searched for a way to jump start the bugs’ metabolism. And they found that sugar is just what the doctor ordered. Administering sugar along with an antibiotic called gentamicin cured mice with chronic urinary tract infections, and kept the bacteria from spreading to their kidneys.

So a spoonful of sugar does more than make the medicine go down. It helps the medicine take the microbes down.

—Karen Hopkin

[The above text is an exact transcript of this podcast]

View the original article here

Search for advanced materials aided by discovery of hidden symmetries in nature

 A new way of understanding the structure of proteins, polymers, minerals, and engineered materials will be published in the May 2011 issue of the journal Nature Materials. The discovery by two Penn State University researchers is a new type of symmetry in the structure of materials, which the researchers say greatly expands the possibilities for discovering or designing materials with desired properties.

The research is expected to have broad relevance in many development efforts involving physical, chemical, biological, or engineering disciplines including, for example, the search for advanced ferroelectric ferromagnet materials for next-generation ultrasound devices and computers. The paper describing the research will be posted early online by the journal on 3 April 2011, prior to its publication in the journal's May 2011 print edition.

Before the publication of this paper, scientists and engineers had five different types of symmetries to use as tools for understanding the structures of materials whose building blocks are arranged in fairly regular patterns. Four types of symmetries had been known for thousands of years -- called rotation, inversion, rotation inversion, and translation -- and a fifth type -- called time reversal -- had been discovered about 60 years ago. Now, Gopalan and Litvin have added a new, sixth, type, called rotation reversal. As a result, the number of known ways in which the components of such crystalline materials can be combined in symmetrical ways has multiplied from no more than 1,651 before to more than 17,800 now. "We mathematically combined the new rotation-reversal symmetry with the previous five symmetries and now we know that symmetrical groups can form in crystalline materials in a much larger number of ways," said Daniel B. Litvin, distinguished professor of physics, who coauthored the study with Venkatraman Gopalan, professor of materials science and engineering.

The new rotation-reversal symmetry enriches the mathematical language that researchers use to describe a crystalline material's structure and to predict its properties. "Rotation reversal is an absolutely new approach that is different in that it acts on a static component of the material's structure, not on the whole structure all at once," Litvin said. "It is important to look at symmetries in materials because symmetry dictates all natural laws in our physical universe."

The most simple type of symmetry -- rotation symmetry -- is obvious, for example, when a square shape is rotated around its center point: the square shows its symmetrical character by looking exactly the same at four points during the rotation: at 90 degrees, 180 degrees, 270 degrees, and 360 degrees. Gopalan and Litvin say their new rotation-reversal symmetry is obvious, as well, if you know where to look.

The "eureka moment" of the discovery occurred when Gopalan recognized that the simple concept of reversing the direction of a spiral-shaped structure from clockwise to counterclockwise opens the door to a distinctly new type of symmetry. Just as a square shape has the quality of rotation symmetry even when it is not being rotated, Gopalan realized that a spiral shape has the quality of rotation-reversal symmetry even when it is not being physically forced to rotate in the reverse direction. Their further work with this rotation-reversal concept revealed many more structural symmetries than previously had been recognized in materials containing various types of directionally oriented structures. Many important biological molecules, for example, are said to be either "right handed" or "left handed," including DNA, sugars, and proteins.

"We found that rotation-reversal symmetry also exists in paired structures where the partner components lean toward each other, then away from each other in paired patterns symmetrically throughout a material," Gopalan said. These "tilting octahedral" structures are common in a wide variety of crystalline materials, where all the component structures are tightly interconnected by networks of shared atoms. The researchers say it is possible that components of materials with rotation-reversal symmetry could be engineered to function as on/off switches for a variety of novel applications.

The now-much-larger number of possible symmetry groups also is expected to be useful in identifying materials with unusual combinations of properties. "For example, the goal in developing a ferroelectric ferromagnet is to have a material in which the electrical dipoles and the magnetic moments coexist and are coupled in the same material -- that is, a material that allows electrical control of magnetism -- which would be very useful to have in computers," Gopalan said. The addition of rotation-reversal symmetry to the materials-science toolbox may help researchers to identify and search for structures in materials that could have strong ferroelectric and ferromagnetic properties.

Gopalan and Litvin said a goal of their continuing research is to describe each of the more than 17,800 different combinations of the six symmetry types to give materials scientists a practical new tool for significantly increasing the efficiency and effectiveness in finding novel materials. The team also plans to conduct laboratory experiments that make use of their theoretical work on rotation-reversal symmetry. "We have done some predictions, we will test those predictions experimentally," Litvin said. "We are in the very early stages of implementing the results we have described in our new theory paper." Gopalan said, for example, that he has predicted new forms for optical properties in the commonplace quartz crystals that are used widely in watches and electronic equipment, and that his group now is testing these predictions experimentally.

The National Science Foundation provided financial support for this research through its Materials Research Science and Engineering Centers program.

Story Source:

The above story is reprinted  from materials provided by Penn State, via EurekAlert!, a service of AAAS.

Journal Reference:

Venkatraman Gopalan, Daniel B. Litvin. Rotation-reversal symmetries in crystals and handed structures. Nature Materials, 2011; DOI: 10.1038/nmat2987

The hidden danger of oxygen

 

Birch pollen with allergenic potential. The colouring of the fluorescence microscopic picture shows the difference in the chemical composition of the pollen which can contain allergy-triggering protein in the cell and on its surface. Credit: Manabu Shiraiwa/MPI for Chemistry

(PhysOrg.com) -- New findings from German researchers at the Max Planck Institute for Chemistry and the Paul Scherrer Institute in Switzerland help to explain how toxic and allergy-causing substances in our air are formed. The scientists have for the first time detected long lived reactive oxygen intermediates on the surface of aerosol particles. These forms of oxygen survive here for more than 100 seconds and in that time react with other air pollutants such as nitrogen oxides. Chemically speaking, the dust particles are oxidized and nitrated. This is what makes soot particles more toxic and increases the potential of pollen to cause allergies.

Although scientists have suspected for years that these intermediate forms exist, it was believed that they disappeared within a fraction of a second, and therefore had little impact on chemical processes in the atmosphere. The intermediate forms of oxygen develop when ozone reacts with particulate matter such as soot, polycyclic aromatic hydrocarbons or pollen proteins.

"Not only does our research resolve earlier contradictions between theoretical calculations and measurements, it also shows that intermediates are also responsible for many atmospheric and physiological reactions," said Manabu Shiraiwa, lead author of the study.

Ulrich Pöschl, head of the aerosol research group at the Max Planck Institute in Mainz, goes one step further: "We suspect that the increase in allergies in industrialized countries is linked to these reactions. The more ozone and nitrogen oxides that are emitted by industry and traffic, the more frequently organic molecules such as birch pollen proteins are being nitrated and this is what irritates our immune system.” Pöschl and his colleagues have obtained evidence that these nitrated proteins can indeed cause more severe allergic reactions than the native protein form. If this hypothesis is confirmed, human health would be at even greater risk from combustion-related emissions than previously thought.

The reactive oxygen intermediates may also explain some of the direct adverse health effects of diesel soot and tobacco smoke particles. The polycyclic aromatic hydrocarbons found on the surface of these particles again readily react with ozone and form long-lived reactive oxygen intermediates. If the particles are inhaled, they interact directly with physiological processes in the human lung and other organs.

The scientists assume also that the oxygen intermediates may have an indirect effect on our climate. Presumably they are involved in the formation and growth of fine organic particles from volatile organic compounds emitted from both natural and manufactured sources such as vegetation and industrial activities. These particles scatter sunlight and influence the formation of clouds and precipitation, thus affecting the Earth’s energy balance and the hydrological cycle.

To quantify the atmospheric abundance and climatic effects of reactive oxygen intermediates, the Mainz-based Max Planck researchers will perform further kinetic experiments and extensive, numerical simulations. In collaboration with biomedical partners, they are also investigating the physiological effects of nitrated proteins formed by the oxygen intermediates reacting with nitrogen oxides.

More information: Manabu Shiraiwa, et al. The role of long-lived reactive oxygen intermediates in the reaction of ozone with aerosol particles. Nature Chemistry, 20. Februar 2011; doi: 10.1038/NCHEM.988

Provided by Max-Planck-Gesellschaft (news : web)