Publication highlights

What happens when we heat the atomic lattice of a magnet all of a sudden?

Monday, 16th July 2018Publication highlights

Magnets have fascinated humans for several thousand years and enabled the age of digital data storage. They occur in various flavors. Ferrimagnets form the largest class of magnets and consist of two types of atoms. Similar to a compass needle, each atom exhibits a little magnetic moment, also called spin, which arises from the rotation of the atom’s electrons about their own axes. In a ferrimagnet, the magnetic moments point in opposite directions for the two types of atoms (see panel A). Thus, the total magnetization is the sum of all magnetic moments of type 1 (M1, blue arrows) and type 2 (M2, green arrows). Due to the opposite direction, the magnitude of the total magnetization is M1M2.

When an insulating ferrimagnet is heated, the heat is first deposited in the atomic lattice which causes the atoms to move randomly around their cold positions. Finally, part of the heat also causes random rotation (precession) of the spins around their cold direction. Thus, magnetic order gets lost; the total magnetization (M1M2) decreases and eventually vanishes if the temperature of the ferrimagnet exceeds a critical temperature, the so-called Curie temperature. Although this process is of fundamental importance, its dynamics are not well understood. Even for the ferrimagnet yttrium iron garnet (YIG), one of the most intensely researched ferrimagnets, it is unknown how long it takes until the heated atomic lattice and the cold magnetic spins reach equilibrium with each other. Previous estimates of this time scale differ from each other by a factor of up to one million.

A team of scientists from Berlin (Collaborative Research Center/Transregio 227, Fritz Haber Institute and Max Born Institute), Dresden (Helmholtz Center), Uppsala (Sweden), St. Petersburg (Russia), and Sendai (Japan) have now revealed the elementary steps of this process. “To instantaneously and exclusively heat up the atomic lattice of a YIG film, we use a very specific and novel kind of stimulus: ultrashort bursts of laser light at terahertz frequencies. With a subsequently arriving visible laser pulse, we can then step-by-step trace the evolution of the initially cold magnetic spins. Essentially, we record a stop-motion movie of how the magnetization evolves.” says Sebastian Maehrlein, who conducted the experiments at the Fritz Haber Institute of the Max Planck Society. His colleague Ilie Radu from summarizes: “Our observations are striking. We found that sudden heating of the atomic lattice reduces the magnetic order of the ferrimagnet on two distinct time scales: an incredibly fast scale of only 1 ps and a 100,000 times slower scale of 100 ns.”

These two time scales can be understood in analogy to water in a closed pot that is put into a hot oven. The hot air of the oven corresponds to the hot atomic lattice whereas the magnetic spins correspond to the water inside the pot (see panel A). Once the atomic lattice is heated by the terahertz laser burst, the enhanced random oscillations of the atoms lead to a transfer of magnetic order from spin type 1 to spin type 2. Therefore, both the magnetic moments M1 (blue arrows in panel B) and M2 (green arrows) are reduced by exactly the same amount (red arrows). This process evolves on the fast time scale, and the atomic spins are forced to heat up while leaving the total magnetization M1M2 unchanged, just like water in a closed pot that has to keep its volume.

We know, however, that a heated ferrimagnet not only aims at reducing M1 and M2, but also its total magnetization M1M2. To do so, part of the spin must be released to the atomic lattice. This situation is again completely analogous to the hot water in a closed pot: the pressure inside the pot increases but is slowly released to the outside through little leaks in the lid (see panel C). This leakage of angular momentum to the atomic lattice is exactly what happens in the ferrimagnet through weak couplings between spins and lattice.

“We now have a clear picture of how the hot atomic lattice and the cold magnetic spins of a ferrimagnetic insulator equilibrate with each other.” says Ilie Radu. The international team of researchers discovered that energy transfer proceeds very quickly and leads to a novel state of matter in which the spins are hot but have not yet reduced their total magnetic moment. This “spin overpressure” is released through much slower processes that permit leakage of angular momentum to the lattice. “Our results are also relevant for applications in data storage.” Sebastian Maehrlein adds. “The reason is simple. Whenever we want to switch the value of a bit between 0 to 1 in a magnetic storage medium, angular momentum and energy have to finally be transferred between atomic lattice and spins.”

Press contacts:
Prof. Tobias Kampfrath, tobias.kampfrath@fu-berlin.de, +49 30 8413–5222; FHI PC Department Office: +49 30 8413–5112
Dr. Ilie Radu, radu@mbi-berlin.de, +49 30 6392 1357; Max Born Institute Berlin, Germany

Original Publication:
S. F. Maehrlein, I. Radu, P. Maldonado, A. Paarmann, M. Gensch, A. M. Kalashnikova, R. V. Pisarev, M. Wolf, P. M. Oppeneer, J. Barker, T. Kampfrath, Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation. Sci. Adv. 4, eaar5164 (2018).

 

Tobi

Heating a magnet without changing its magnetization. (A) A ferrimagnet consists of two spin sorts of opposite orientation (green and blue arrows). In the experiment, the atomic lattice of the ferrimagnet is heated by an extremely short terahertz laser pulse. This situation is analogous to heating the air (=atomic lattice) inside an oven that contains a pot with water (=spins). (B) Heat is transferred into the spin system and decreases the magnetization of each spin type by exactly the same amount. This process arises because spin is transferred from the blue to the green spin sort. Thus, the magnet is heated without changing its total magnetization! In the pot analogy, heat is transferred from the air outside the pot to the water inside. While the amount of water in the pot has not changed, an overpressure has built up. (C) Finally, the hot spins release their overpressure to the atomic lattice, thereby reducing the total magnetization. In the analogy, water overpressure is released through little leaks in the pot lid.


A comprehensive volume on chemical warfare entitled “One Hundred Years of Chemical Warfare: Research, Deployment, Consequences” has been published under the auspices of the Max Planck Society

Wednesday, 6th December 2017Publication highlights, Miscellaneous

ProductFlyer-9783319516639On April 22, 1915, the German military released 150 tons of chlorine gas at Ypres, Belgium. Carried by a long-awaited wind, the chlorine cloud passed within a few minutes through the British and French trenches, leaving behind at least 1,000 dead and 4,000 injured. This chemical attack, which amounted to the first use of a weapon of mass destruction, marks a turning point in world history. The preparation as well as the execution of the gas attack was orchestrated by Fritz Haber, the director of the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry in Berlin-Dahlem. During World War I, Haber transformed his research institute into a center for the development of chemical weapons (and of the means of protection against them).

Bretislav Friedrich and Martin Wolf (Fritz Haber Institute of the Max Planck Society, the successor institution of Haber’s institute) together with Dieter Hoffmann, Jürgen Renn, and Florian Schmaltz (Max Planck Institute for the History of Science) organized an international symposium to commemorate the centenary of the infamous chemical attack. The symposium examined crucial facets of chemical warfare from the first research on and deployment of chemical weapons in WWI to the development and use of chemical warfare during the century hence. The focus was on scientific, ethical, legal, and political issues of chemical weapons research and deployment — including the issue of dual use — as well as the ongoing effort to control the possession of chemical weapons and to ultimately achieve their elimination.

The volume consists of papers presented at the symposium and supplemented by additional articles that together cover key aspects of chemical warfare from 22 April 1915 until the summer of 2015.

The book was presented at a symposium on November 30, 2017 to the delegates of the 22nd Conference of State Parties of the Chemical Weapons Convention at the Organization for the Prohibition of Chemical Weapons in The Hague. Introduced by Paul Walker (Green Cross) and presented and moderated by Bretislav Friedrich (FHI), the symposium entitled “One Hundred Years since Ypres and Counting: Glimpses of the Past and the Present” explained the involvement of the Max Planck Society and provided a sampling of the book’s chapters by Edward Spiers (University of Leeds), Ulf Schmidt (University of Kent), Karin Mlodoch (Haukari), and Ralf Trapp (Chessenaz). Among the attendees were four survivors of the 1988 Halabja chemical attack.

Website: http://www.springer.com/de/book/9783319516639
eBook available at https://link.springer.com/book/10.1007/978-3-319-51664-6


(Deutsch) Maschinelles Lernen erobert die klassischen Naturwissenschaften

Wednesday, 25th January 2017Publication highlights

Sorry, this entry is only available in German.


Molecular Stew Analysis produces World´s First Description of Amyloid Intermediate Structures

Tuesday, 27th September 2016Publication highlights

Scientists of Freie Universität and Max Planck Society succeed in world´s first structural analysis of aggregates believed to be cause of Alzheimer´s disease

Prof. Dr. Kevin Pagel and Dr. Gert von Helden, © Sven Jungtow

Prof. Dr. Kevin Pagel and Dr. Gert von Helden, © Sven Jungtow

Scientists of Freie Universität Berlin und the Fritz Haber Institute of the Max Planck Society made a major step forward in analyzing the biochemical causes of Alzheimer´s and Parkinson´s disease. The results of Prof. Kevin Pagel and Dr. Gert von Helden´s work could enable the development of new medications fighting the causes of both diseases. Their research was published in the current issue of Nature Chemistry.

Alzheimer´s disease is the most common form of dementia, predominantly in the age group of 65-85 years. There are currently 48 million known patients with Alzheimer´s disease worldwide. This number is expected to double by 2050.

The causes of neurodegenerative diseases like Parkinson´s and Alzheimer´s disease are not fully understood to this day. In both cases, a biochemical disorder can be observed during the course of the disease, but the exact mechanism is unknown. Water-soluble proteins undergo a spontaneous transition into insoluble amyloid fibrils. In the case of Alzheimer´s disease, protein fragments that the body can normally easily dispose accumulate to abnormal species called amyloid plaques, which are deposited outside the neurons and slowly degenerate the brain.

Recent research showed that these plaques are an effect, but not the cause of Alzheimer´s disease. Instead, scientists focus more and more on the issue of what causes the deadly plaque accumulation and why exactly the harmless water-soluble Jekyll proteins turn into the dangerous, insoluble Hyde fibrils. There is  increasing evidence that the disease-causing factor is a toxic intermediate that occurs during the aggregation into fibrils, but analyzing the exact structure of these intermediates was an unresolvable problem, resembling the children´s birthday party game of blind man´s bluff. From the perspective of a researcher, the toxic intermediates are not nicely separated species, but present themselves as parts of a stew with unknown ingredients. The research on pharmaceutically active compounds was, therefore, often more or less trial and error up to now. This problem has now been solved by the research of the scientists of Freie Universität and the Fritz Haber Institute.
For the first time the research groups around assistant professor Dr. Kevin Pagel and Dr. Gert von Helden succeeded in developing a method to exactly analyze and describe the toxic intermediates believed to be triggering the disease on a molecular level. They succeeded in separately analyzing each individual ingredient of the stew and specifically describing their structure. Based on this basic research, other scientists can now start developing specific compounds to neutralize the intermediates causing Alzheimer´s disease.

Kevin Pagel and Gert van Helden achieved this using a trick: they combined two elaborate methods. Each method alone is incapable of solving a part of the problem, but combined they did the trick. The first method is ion-mobility spectrometry, which can best be described as a molecular wind tunnel, which separates the intermediates according to their drag coefficient. This method, however, only provides information about the size and shape, but not the molecular structure producing the drag. To shed light on this problem, however, the scientists additionally used gas-phase-infrared spectroscopy. Using this combination of methods, the researchers discovered specific intermediates that closely resemble the structure of the mature Hyde fibrils that are present in deadly amyloid plaques. With the newly developed method, other researchers can now test new medications to specifically tackle the emergence of Alzheimer´s disease.

Contact:

  • Dr. Kevin Pagel, Institut für Chemie und Biochemie der Freien Universität Berlin, Takustraße 3, 14195 Berlin und Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Molekülphysik, Faradayweg 4–6, 14195 Berlin, Telefon: +49 (0)30 – 838 – 72703 (Freie Universität Berlin)/ +49 (0)30 – 8413 – 5646 (Fritz-Haber-Institut), E-Mail: kevin.pagel@fu-berlin.de, im Internet: www.bcp.fu-berlin.de/chemie/pagel
  • Gert von Helden, Fritz Haber-Institut der Max-Planck-Gesellschaft, Abteilung Molekülphysik, Faradayweg 4-6, 14195 Berlin, Telefon +49 (0)30-8413 – 5615, E-Mail: helden@fhi-berlin.mpg.de, im Internet: http://www.fhi-berlin.mpg.de/mp/helden/

Original publication:
Seo, J.; Hoffmann, W.; Warnke, S.; Huang, X.; Gewinner, S.; Schöllkopf, W.; Bowers, M.T.;von Helden, G.; and Pagel, K.
An Infrared Spectroscopy Approach to Follow β-Sheet Formation in Peptide Amyloid Assemblies
Nature Chemistry 2016, doi: 10.1038/NCHEM.2615



Pushing a single-molecule switch

Monday, 11th July 2016Publication highlights
(Top) Single porphycene molecule imaged at 5 K with a scanning tunneling microscope. The white star in the left indicates the position where the force-induced switching can occur by bringing the tip to the molecule. (Bottom) Chemical structure of porphycene. The molecule switches between two states through intramolecular hydrogen-atom transfer as indicated by the curved arrows.

(Top) Single porphycene molecule imaged at 5 K with a scanning tunneling microscope. The white star in the left indicates the position where the force-induced switching can occur by bringing the tip to the molecule.
(Bottom) Chemical structure of porphycene. The molecule switches between two states through intramolecular hydrogen-atom transfer as indicated by the curved arrows.

One finds switches everywhere in our modern life, and everyone knows the force that is needed to push them, for example, to turn on a room light from a wall switch—the force from one’s finger is enough. But, how does one push and how much force does one need to apply if the switch were dramatically scaled down to the “Nano-world”, for example, to push a “single-molecule switch” at nano-meter (10-9 m) scale. This “extremely small” question is related not only to basic science but also to potential future technological application of molecular devices. Researchers at Fritz-Haber Institute of the Max-Planck Society, Berlin, together with colleagues in Poland (Warsaw), Spain (San Sebastian) and the UK (Liverpool), have succeeded in operating a single-molecule switch and measuring the force needed to activate it by using a state-of-the-art scanning probe microscope. They found that only a very tiny force, fraction of a nano-Newton (10-9 Newton), was required to switch a single molecule.

The researchers discovered that about 1 nm-size organic molecule (porphycene) attached on a metal surface can be switched with an atomically-sharp metallic tip of a scanning probe microscope (whose very apex has a single atom and sometimes called an “atomic-scale finger”). The molecule changes between two states through an intramolecular hydrogen atom transfer, a so-called tautomerization that is important in nature, which can be triggered by “pushing” the molecule with the sharp tip. The experiments could not only quantify the forces but also revealed that switching can be induced at a very specific position within a single molecule, with a spatial resolution of about 0.02 nm which is less than a typical chemical bond length (about 0.1 nm). Furthermore, the researchers found that the switching mechanism cannot be rationalized by a pure “mechanical” force because switching could not be induced even if a sufficient force was applied, when the tip apex was decorated by a single xenon atom—a chemically inert rare gas that lacks a chemical reactivity. This result indicates that the chemical force (interaction) between the tip apex atom and molecule plays a crucial role in the reaction.

(Top) Artwork of the experiment. (Bottom) Measured force curve during tip approach and retraction.

(Top) Artwork of the experiment.
(Bottom) Measured force curve during tip approach and retraction.

The research team in Spain and UK carried out extensive first principle calculations by using a supercomputer to elucidate the force-induced tautomerization mechanism. From the simulation the researchers found that the force-induced reaction resembles an activation step in a catalytic reaction rather than pure mechanical activation. The researchers believe that the results may also provide a microscopic insight into complex catalytic processes with a fresh perspective, leading to a new method to control chemistry at the atomic level.

Nanoscale molecular devices are a fascinating future application, in which individual functionalized molecules behave as an independent element based on their physical/chemical properties. The research team demonstrated a novel way to operate a molecular switch which should play a central role in such devices. The researcher at Fritz-Haber Institute, who conceived the experiment, believes that our approach will make it possible not only to operate various types of molecular switches, but also to construct “Rube Goldberg machine” from single molecules since the “atomic-scale finger” of a scanning tunneling microscope also allows us to manipulate single atoms and molecules one by one.

Contact address

Dr. Takashi Kumagai
Research group leader
Fritz-Haber Institute of the Max-Planck Society
Department of Physical Chemistry
Email: kuma@fhi-berlin.mpg.de
Web: http://www.fhi-berlin.mpg.de/pc/kumagai/
Tel.: +49 (0)30 8413 5110

Publication

Force-induced tautomerization in a single molecule
Ladenthin et al. Nature Chemistry (http://dx.doi.org/10.1038/nchem.2552)

Please read the Japanese version here.


Tracing the interaction between light and molecules

Thursday, 9th June 2016Publication highlights

In the 19th century James Clerk Maxwell formulated the classical theory of electro-magnetism, which describes light as electric and magnetic fields oscillating perpendicular to each other. In the interaction between light and molecules, for example in an absorption process, the electric field component is usually dominating the process. The effect of the magnetic component of light only becomes evident once the electric interaction is not taking place, i. e. when it is forbidden because of symmetry reasons. Purely magnetic transitions are typically ten to a hundred thousand times smaller than comparable allowed electric transitions. This makes testing quantum mechanical predictions in our experiment by measuring the ratio between the strength of electric and magnetic transitions an enormous experimental challenge.

Scheme of the experimental setup

Scheme of the experimental setup

In the Molecular Physics department an experiment was performed in which a static electric and a static magnetic field are applied to lift molecular symmetry restrictions. The static electric field allows to mix a little bit of the otherwise forbidden electric transition together with the magnetic transition in the molecule. Thus, the molecule is interacting with both the electric and magnetic components of light. The static magnetic field enabled the observation of the so-called Stark-interference effect. This gives a deeper insight into the light-molecule interaction, because not only the electric and magnetic transition moments can be measured but

Coil and plate design

Arrangement of capacitor plates and coils

also their relative sign, while in usual transitions the intensity depends only on the square of the transition moments. The experimental results agree with a quantum mechanical prediction within the accuracy of the measurements and they also confirm the predicted relative sign of the calculated electric and magnetic transition moments.

Original publication:
Stark Interference of Electric and Magnetic Dipole Transitions in the AX Band of OH
H. Christian Schewe, Dongdong Zhang, Gerard Meijer, Robert W. Field, Boris G. Sartakov, Gerrit C. Groenenboom, Ad van der Avoird, and Nicolas Vanhaecke
Phys. Rev. Lett. 116, 153001 – Published 11 April 2016 (http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.153001)

 


Novel terahertz source

Wednesday, 25th May 2016Publication highlights
Principle of operation of the emitter. An extremely short laser pulse initiates electron transport from the magnetic into the non-magnetic metal. Importantly, there are two distinct types of electrons which differ by their spin (thick light blue arrows) and their number (length of these arrows). Inside the non-magnet, the electrons experience a deflection which depends on the orientation of the electron spin. The resulting short charge current burst along the red arrow causes the emission of a terahertz pulse.

Principle of operation of the emitter. An extremely short laser pulse initiates electron transport from the magnetic into the non-magnetic metal. Importantly, there are two distinct types of electrons which differ by their spin (thick light blue arrows) and their number (length of these arrows). Inside the non-magnet, the electrons experience a deflection which depends on the orientation of the electron spin. The resulting short charge current burst along the red arrow causes the emission of a terahertz pulse.

International team of scientists realizes a compact, efficient and ultrabroadband emitter of THz radiation based on spintronic effects.

Berlin, 23. Mai 2016 – Terahertz waves offer numerous applications ranging from imaging tissue in medicine to airport security systems. However, the generation of such radiation by a low-cost source has remained challenging. Physicists from an international collaboration including the Fritz Haber Institute (Berlin), the Johannes Gutenberg University (Mainz), the Ernst Moritz Arndt University (Greifswald) in Germany and research institutes in France, Sweden and the United States have now realized a new concept for the generation of terahertz waves using spintronic metals. In contrast to previous designs, their emitters consist of thin metal films and take advantage of the spin rather than only the charge of the electron. Following this approach, they developed broadband emitters fully covering the 1-to-30-THz range, while at the same time being cost- and energy-efficient.

Terahertz radiation covers the frequency range 0.3 to 30 THz and is located between the microwave and infrared region of the electromagnetic spectrum. Many materials absorb THz radiation in a characteristic manner, while textiles and plastics are largely transparent. Unlike X-rays, terahertz radiation is harmless to biological structures. As a consequence, terahertz waves can be used for bio-imaging (such as in body scanners at airports), for quality control of food and for material identification.

One obstacle preventing the wide use of terahertz radiation is that current technology requires expensive and large lasers for broadband generation.

Photography of the prototype terahertz emitter.

Photography of the prototype terahertz emitter.

The terahertz sources fabricated by the researchers in Berlin, Mainz and Greifswald are scalable and can be used as table-top emitters (see figure). These novel spintronic emitters cover the complete range of terahertz frequencies from 1 to 30 THz without gap. Key features are higher energy efficiency, lower fabrication costs and easier operation.

The new terahertz emitter resembles a photodiode or a solar cell: Upon illuminating the material with an ultrashort laser pulse, a current burst is created (see figure). Consequently, this current burst radiates an electromagnetic pulse with frequencies in the terahertz range, similar to an antenna. In contrast to a solar cell, the metal films are only 5.8 nm thick, thereby ensuring that the current burst is extremely short, while at the same time preventing attenuation of the terahertz wave inside the emitter. By systematically optimizing the emitter materials and their thicknesses, relatively weak laser radiation from compact laser sources is now sufficient to generate the entire spectrum from 1 to 30 THz.

The performance of the emitter is greatly enhanced because the researchers also took advantage of the spin of the electron, in addition to its charge. The spin is a magnetic property of the electron that changes the motion of electrons when flowing through a magnetic metal. In the new emitter, this effect is used to steer the motion of electrons such that they can emit the terahertz wave in a particularly efficient manner.

To optimize the emitter performance, the scientists had to screen a large number of materials with varying material composition and geometry. The high-throughput Rotaris sputter deposition system installed at the Institute of Physics at Mainz by Singulus Technologies was a crucial prerequisite to fabricate a large number of samples in a short time. The optimization procedure was further supported by calculations of theorists at Forschungszentrum Jülich.

Original paper:
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation;
T. Seifert et al., Nature Photonics, http://dx.doi.org/10.1038/nphoton.2016.91

Contact:
Tobias Kampfrath, Terahertz Physics Group, FHI
kampfrath@fhi-berlin.mpg.de


The Carbohydrate Wind Tunnel

Thursday, 1st October 2015Publication highlights

 

A team of researchers from Berlin succeeded in an effort to fundamentally improve carbohydrate analysis. With the new method, developed by Prof. Kevin Pagel (Free University Berlin and Fritz Haber Institute of the Max Planck Society) and Prof. Peter Seeberger (Max Planck Institute of Colloids and Interfaces and Free University Berlin), complex glycans, building blocks of life such as DNA and proteins, can now be sequenced. The quality control of synthetic carbohydrates is now possible as minimal impurities can be traced faster and more precisely. The new method is essential for the development of novel carbohydrate vaccines, drugs and diagnostics.

Prof. Seeberger explains:  ‘The new method is fast, reliable and sensitive. The glycosciences will get a push, comparable to the advances when gene sequencing was first developed.‘

The structure of carbohydrates is much more complicated than that of genetic material or proteins. Carbohydrate chains can be formed from more than 100 building blocks that can be can be linked together in branched chains and these can have different spatial structures, called anomers. In comparison to that, DNA molecules that consist of 4 building blocks, and proteins that are based on 20 amino acids are comparatively simple.

Seven nobel prizes were awarded in the glycosciences until 1974. After that, however, the advances in analytical methods did not keep up with those made in genetics. Glycans are important as sugars that cover human and bacterial cell surfaces are an essential part of the immune response and recognition events such as fertilization.

The incredible diversity of carbohydrates (which merely consist of carbon, hydrogen and oxygen) is a general challenge for chemists. Carbohydrate building blocks can link in many different ways. Even simple carbohydrates that have the same number of atoms and the same mass, may differ in only one binding angle. These almost identical molecules, called isomers, exhibit very different biological functions. Glucose and galactose for example have an identical formula (C6H12O6 ) but their functions are different.

Chemists use tricks to identify molecules, because most molecules can´t be observed on the atomic level. Hence the molecular mass, electronic or electromagnetic properties are measured. These methods, however, cannot resolve the problems associated with carbohydrate isomers. Carbohydrate molecules consisting of the same number of specific atoms can differ in their composition, connectivity and configuration. So far their differentiation was a laborious and time-consuming task, that required large amounts of sample.

The scientists from Berlin and Potsdam take advantage of the different shapes of carbohydrates.  Depending on their shape, the molecules require different times to pass through a gas filled tube – comparable to the drag coefficient in a wind tunnel. Kevin Pagel and his colleagues combine this ion mobility measurement with mass spectrometry to find differences in composition, connectivity and configuration. Larger molecules are broken into fragments; during this fragmentation, however, the structural properties of the resulting parts are not altered such that the sum of fragment properties reflect that of the large molecule. This combination method is reminiscent of the Sherlock Holmes quote: “Once you eliminate the impossible, what remains must be the truth.”

Combined with a database, currently under development, and enlarged through the rapid collaborations of other scientists, this method will be generalized in the future. Once a molecule is entered in the database, automated processes can be used to recognize them.

The new method will enable quality control for synthetic carbohydrates, produced by synthesis robots, adding building blocks like pearls on a string. Until now, impurities were hard to detect at levels below 5 percent while the new carbohydrate “wind tunnel” drastically lowers the sensitivity to 0.1 percent.

Glycobiology – the research field that focused on studying biologically active carbohydrates – is a rapidly developing field and Berlin is doubtlessly one of the global centers.

Kevin Pagel with the ion mobility mass spectrometer, Photographer: Sven Jun

 

Prof. Dr. Kevin Pagel
Junior professor
Freie Universität Berlin, Institute of Chemistry and Biochemistry
and
Fritz Haber Institute of the Max Planck Society
Department of Molecular Physics
Email: kevin.pagel@fu-berlin.de, Web: www.bcp.fu-berlin.de/chemie/pagel
Tel.: +49 (0)30 – 838 – 72703 (FU)/ +49 (0)30 – 8413 – 5646 (FHI)

Prof. Dr. Peter H. Seeberger
Director
Max Planck Institute of Colloids and Interfaces
Department of Biomolecular Systems
and
Freie Universität Berlin
Institute of Chemistry and Biuochemistry
Email: Peter.seeberger@mpikg.mpg.de, Web: http://www.mpikg.mpg.de/bs
Tel.: +49 (0) 331 – 567 – 9300

Publication: 
J. Hofmann, H. S. Hahm, P. H. Seeberger & K. Pagel: Identification of carbohydrate anomers using ion mobility–mass spectrometry
Nature, October 1, 2015 (doi:10.1038/nature15388)

 


Light switches on a DVD

Thursday, 30th July 2015Publication highlights

Since the electronic properties of an optical storage material change faster than its structure, it could serve new applications

There could be more to DVDs than has been assumed to date. The material comprised of germanium, antimony and tellurium in which data media store information may also be suitable as an extremely fast light switch for optical communication or data processing. This is what an international team working with researchers at the Fritz Haber Institute of the Max Planck Society in Berlin and the ICFO-Institut de Ciències Fotòniques in Barcelona has succeeded in finding out. The storage mechanism in DVDs is based on the fact that laser pulses rearrange the structure of the material, switching it from a transparent to a non-transparent state. As the scientists have now discovered, the optical properties change much faster than the structure, which could be used in designing new types of photonic components.

Order versus disorder: Electrons are diffracted differently in the crystalline structure of a compound of germanium, antimony and tellurium (GST) than in the amorphous one. It is possible to distinguish clearly between the diffraction image of the crystal (left) and that of the amorphous material (right).

While DVDs are likely to soon become a thing of the past, this may not apply to their storage material. This is because the data media, which have become familiar mainly as media for films, are increasingly being replaced by other storage techniques. The Ge2Sb2Te5 compound, which specialists call GST for short, could find itself taking on new tasks.  The material owes its job to the fact that, in rewritable DVDs, laser pulses can convert it very quickly from a strongly reflective crystalline state into a much less reflective disordered version.. The two states then encode the zeros and ones of digital information. “The work we have done shows that the material can also be used for applications other than data storage,” as Ralph Ernstorfer, Research Group Leader at the Fritz Haber Institute of the Max Planck Society in Berlin states. “GST could be suitable for modulators in optical communication or for components in optical computer technology, for example.” (read more)

Original publication:
Lutz Waldecker, Timothy A. Miller, Miquel Rudé, Roman Bertoni, Johann Osmond, Valerio Pruneri, Robert E. Simpson, Ralph Ernstorfer und Simon Wall
Time-domain separation of optical properties from structural transitions in resonantly bonded materials
Nature Materials, 27. Juli 2015; DOI: 10.1038/NMAT435