Category: SwissFEL

Blood pressure-lowering drug with a light switch

Blood pressure-lowering drug with a light switch

From off to on in fractions of a second – researchers at the Paul Scherrer Institute PSI have investigated a light-switchable drug for high blood pressure: They observed how the molecule transforms from one form to another and how this affects its effectiveness in the body. This could aid in the development of medications whose effects can be precisely controlled, within the body, using light. The study has now been published in the journal Angewandte Chemie International Edition.

Rendering a drug effective or ineffective in a flash at the appropriate location – this is the focus of research in photopharmacology. The goal is to develop drugs that can be switched on and off with light of a specific wavelength. Orally administered medications could then be selectively activated by irradiating only a specific part of the body with light; the medication would remain ineffective in the rest of the body – thus reducing side-effects. For example, a drug intended to lower blood pressure in the heart could then be activated only there; other organs with identical binding sites for the active ingredient would remain unaffected.

Researchers in the PSI Center for Life Sciences have now observed, at the molecular level, how a light-switchable drug interacts with its corresponding biological receptor. Most important, they have discovered why the drug changes its potency.

“Observing exactly what happens at such receptors when a drug is altered by light is an important step toward making light-switchable drugs a reality in the clinic,” says Jörg Standfuss, a laboratory head in the PSI Center for Life Sciences and co-author of the new study published in the journal Angewandte Chemie International Edition.

Read more on the PSI website

Image: Jörg Standfuss (left) and Quentin Bertrand are two of the researchers in the PSI Center for Life Sciences who now have found out, on the molecular level, why a light-controllable drug changes its potency.

Credit: © Paul Scherrer Institute PSI/Markus Fischer

Filming a vitamin B12 photoreceptor in action

Filming a vitamin B12 photoreceptor in action

Using X-ray free-electron lasers and synchrotron light at facilities in Switzerland, Japan, France and the UK, a worldwide collaboration of scientists have discovered how a vitamin B12-based photoreceptor works. Understanding how photoreceptors function aids future technological applications, such as optogenetics, that involve controlling cellular processes with light. The findings are published in Nature.

Vitamin B12 is an organometallic cofactor found in many enzymes that control essential processes in various organisms, including humans. It came as a surprise a decade ago that vitamin B12 derivatives had been repurposed for light sensing by a large family of previously unknown photoreceptors in bacteria that fulfil various functions. 

The prototypical B12 photoreceptor CarH, for example, regulates the expression of genes involved in protecting bacteria against excess sunlight. It achieves this by binding to DNA in the dark, acting as a molecular doorstop. Upon illumination, its tetrameric architecture breaks apart, enabling transcription by unbinding from DNA. 

The way in which this and other B12 photoreceptors function at a molecular level has remained a mystery ever since. However, an international consortium led by scientists at the Institut de Biologie Structurale in Grenoble, France has now combined experimental techniques using X-ray free-electron lasers at the Paul Scherrer Institute PSI in Switzerland (SwissFEL) and Japan (SACLA), as well as the synchrotrons in France (ESRF) and the UK (Diamond Light Source), with quantum-chemical calculations to uncover the inner workings of CarH.

Read more on the PSI website

Image: John Beale is responsible for macromolecular crystallography at the Cristallina experimental station of SwissFEL

Credit: © Paul Scherrer Institute PSI / Markus Fische

Swiss X-ray laser reveals the hidden dance of electrons

Swiss X-ray laser reveals the hidden dance of electrons

Scientists at the X-ray free-electron laser SwissFEL have realised a long-pursued experimental goal in physics: to show how electrons dance together. The technique, known as X-ray four-wave mixing, opens a new way to see how energy and information flow within atoms and molecules. In the future, it could illuminate how quantum information is stored and lost, eventually aiding the design of more error-tolerant quantum devices. The findings are reported in Nature.

Much of the behaviour of matter arises not from electrons acting alone, but from the ways they influence each other. From chemical systems to advanced materials, their interactions shape how molecules rearrange, how materials conduct or insulate and how energy flows.

In many quantum technologies – not least quantum computing – information is stored in delicate patterns of these interactions, known as coherences. When these coherences are lost, information disappears – a process known as decoherence. Learning how to understand and ultimately control such fleeting states is one of the major challenges facing quantum technologies today.

Until now, although many techniques let us study how individual electrons behave, we have mostly been blind to these coherences. Scientists at SwissFEL from the Paul Scherrer Institute PSI and Swiss Federal Institute of Technology in Lausanne (EPFL), in collaboration with the Max Planck Institute of Nuclear Physics in Germany and University of Bern, have now developed a way to access them using a technique known as X-ray four-wave mixing.

“We learn how the electrons dance with each other – whether they hold hands, or if they dance alone,” says Gregor Knopp, senior scientist in the Center for Photon Sciences at Paul Scherrer Institute PSI, who led the study. “This gives us a new view on quantum phenomena and can change how we understand matter.”

Like NMR, but with X-rays

Conceptually, X-ray four-wave mixing is similar to nuclear magnetic resonance (NMR), which today is used daily in hospitals for MRI scans. Both techniques use multiple pulses to create and read out coherences in matter. 

The process of four-wave mixing is also already well-established using infrared and visible light, where it allows scientists to investigate how molecules move, vibrate and interact with one another – with applications ranging from optical communications to imaging biological samples.

X-rays bring this same kind of powerful approach to a smaller scale and allow us to step into the world of the electrons. “Whereas other approaches tell us about how atoms or molecules as a whole interact with each other or with their surroundings, with X-rays we can zoom right in to the electrons,” says Ana Sofia Morillo Candas, first author of the paper.

This ability to zoom in on the interactions between electron has the potential to provide completely new insights not only into quantum information, but also into many other areas – for example biological molecules or materials for solar cells and batteries.

ow you would do it.” This approach is very different to previous attempts made at X-rays four-wave mixing, but to Knopp, it seemed like the obvious method to try. “We were amazed when we saw how large the signal was,” he adds.

It was the middle of the night, when Morillo Candas, at that time a postdoc at PSI, saw the signal in the control room of the Maloja experimental station at SwissFEL. She remembers: “It glowed like a light on the screen. To anyone else, it would look like nothing. But we jumped for joy.”

Read more on the PSI website

Image: Artistic impression of X-ray four-wave mixing – a technique that reveals how electrons interact with each other or with their surroundings. The ability to access this information is important for many fields: from understanding how quantum information is stored and lost to designing better materials for solar cells and batteries.

Credit: © Noah Wach

Disorder begins at the surface of quantum materials

Disorder begins at the surface of quantum materials

A new study reveals that the response of quantum materials to light is more complex than previously assumed. Using ultrafast X-ray pulses at the X-ray free electron laser SwissFEL, researchers found that the surface of a layered manganese oxide reacts differently than the bulk when its orbital order is disturbed. These results challenge the idea that light-induced changes happen uniformly and suggest that the path from order to disorder is shaped by local differences inside the material. 

In certain materials, the electrons arrange themselves in a well-defined, ordered pattern. This internal order can influence everything from how the material conducts electricity to how it responds to magnetic fields. One example is the layered manganese oxide and quantum material La0.5Sr1.5MnO4, in which electrons of manganese atoms arrange themselves into a regular pattern – known as orbital ordering – leading to distinctive electronic and magnetic behaviour.

Researchers are increasingly interested in how light can be used to understand and control the orbital state of these materials. With the right kind of light pulse, it may be possible to switch or reshape their properties at incredible speeds. Therefore, understanding how these materials switch is an important step to making devices.

In many devices, surfaces of and interfaces between materials are known to play a major role in the device properties. Yet until now, it has not been possible to measure how quantum materials change at the surface when switched at high speeds by light. Previous studies have only captured the average response over the whole crystal. 

In this study, a team of scientists led by Aarhus University asked if the average response measured to date accurately captures the processes that occur at the surface, which will be relevant for any device. Remarkably, they found that they did not. 

Read more on the PSI website

Image: Using ultrafast X-rays from SwissFEL, scientists have revealed unexpected light responses in quantum materials

Credit: © AdobeStock

Stabilising fleeting quantum states with light

Stabilising fleeting quantum states with light

Quantum materials exhibit remarkable emergent properties when they are excited by external sources. However, these excited states decay rapidly once the excitation is removed, limiting their practical applications. A team of researchers from Harvard University and the Paul Scherrer Institute PSI have now demonstrated an approach to stabilise these fleeting states and probe their quantum behaviour using bright X-ray flashes from the X-ray free electron laser SwissFEL at PSI. The findings are published in the journal Nature Materials.

Some materials exhibit fascinating quantum properties that can lead to transformative technologies, from lossless electronics to high-capacity batteries. However, when these materials are in their natural state, these properties remain hidden, and scientists need to gently ask for them to pop up. One way they can do this is by using ultrashort pulses of light to alter the microscopic structure and electronic interactions in these materials so that these functional properties emerge. But good things do not last forever – these light-induced states are transient, typically persisting only a few picoseconds, making them difficult to harness in practical applications. In rare cases, light-induced states become long-lived. Yet our understanding of these phenomena remains limited, and no general framework exists for designing excited states that last.

A team of scientists from Harvard University together with PSI colleagues overcame this challenge by manipulating the symmetry of electronic states in a copper oxide compound. Using the X-ray free electron laser SwissFEL at PSI, they demonstrated that tailored optical excitation can induce a ‘metastable’ non-equilibrium electronic state persisting for several nanoseconds – about a thousand times longer than they usually last for. 

Steering electrons with light

The compound under study, Sr14Cu24O41 – a so-called cuprate ladder – is nearly one-dimensional. It is composed of two distinct structural units, the ladders and chains, representing the shape in which copper and oxygen atoms organise. This one-dimensional structure offers a simplified platform to understand complex physical phenomena that also show up in higher-dimensional systems. “This material is like our fruit fly. It is the idealised platform that we can use to study general quantum phenomena,” comments experimental condensed matter physicist Matteo Mitrano from Harvard University, who lead the study. 

One way to achieve a long-lived (‘metastable’) non-equilibrium state is to trap it in an energy well from which it does not have enough energy to escape. However, this technique risks inducing structural phase transitions that change the material’s molecular arrangement, and that is something Mitrano and his team wanted to avoid. “We wanted to figure out whether there was another way to lock the material in a non-equilibrium state through purely electronic methods,” explains Mitrano. For that reason, an alternative approach was proposed.

In this compound, the chain units hold a high density of electronic charge, while the ladders are relatively empty. At equilibrium, the symmetry of the electronic states prevents any movement of charges between the two units. A precisely engineered laser pulse breaks this symmetry, allowing charges to quantum tunnel from the chains to the ladders. “It’s like switching on and off a valve,” explains Mitrano. Once the laser excitation is turned off, the tunnel connecting ladders and chains shuts down, cutting off the communication between these two units and trapping the system in a new long-lived state for some time that allows scientists to measure its properties.

Cutting-edge fast X-ray probes

The ultra-bright femtosecond X-ray pulses generated at the SwissFEL allowed the ultrafast electronic processes governing the formation and subsequent stabilisation of the metastable state to be caught in action. Using a technique known as time-resolved Resonant Inelastic X-ray scattering (tr-RIXS) at the SwissFEL Furka endstation, researchers can gain unique insight into magnetic, electric, and orbital excitations – and their evolution over time – revealing properties that often remain hidden to other probes. 

“We can specifically target those atoms that determine the physical properties of the system,” comments Elia Razzoli, group leader of the Furka endstation and responsible for the experimental setup. 

This capability was key to dissecting the light-induced electronic motion that gave rise to the metastable state. “With this technique, we could observe how the electrons moved at their intrinsic ultrafast timescale and hence reveal electronic metastability,” adds Hari Padma, postdoctoral scholar at Harvard and lead author of the paper.

Read more on PSI website

Image: Laser pulses trigger electronic changes in a cuprate ladder, creating long-lived quantum states that persist for about a thousand times longer than usual.

Credit: Brad Baxley/Part to Whole

World record attosecond measurement at SwissFEL

World record attosecond measurement at SwissFEL

As scientists push X-ray free electron lasers into the attosecond regime, diagnostic tools with higher precision are needed. Now scientists at the Paul Scherrer Institute PSI have demonstrated the ability to characterise pulses as short as 300 attoseconds: a world record time-resolution using electron-beam streaking.

X-ray free electron lasers such as SwissFEL generate short and powerful pulses of X-ray light that allow scientists to study atomic and molecular processes in action. Scientists are now striving to generate shorter and shorter pulses to access attosecond timescales (10-18 s) and observe the motion of electrons in real time.

Capturing such ultrafast processes with X-rays requires not only attosecond pulses; it also requires ways to precisely characterise the X-rays. “You need to know exactly how long each pulse lasts for and when the brightest parts of the pulse hit, for example,” says Eduard Prat, scientist in the beam dynamics group at SwissFEL. “For many scientific applications, if you don’t have this information, you’re blind.” 

A team from PSI has recently demonstrated that the PolariX – a type of radiofrequency deflector device developed by PSI in collaboration with CERN and the German research centre DESY – can meet the ambitious requirements of attosecond science. 

The electrons tell the story of the X-rays they made.

To create the X-ray light in the SwissFEL, bunches of electrons are accelerated to close to the speed of light and wiggled in a series of magnets called undulators, whereby they emit intense bursts of photons – the X-ray pulses. 

At attosecond timescales, it’s difficult to measure the properties of these pulse directly in a reliable way. X-rays interact only weakly with matter, and traditional sensors aren’t fast enough to resolve attosecond-scale events. Instead, scientists can study the electrons that produced them. 

Sitting after the undulators, the PolariX measures the electron bunch after they’ve released their photons. The device bends the beam using a radiofrequency field, spreading out the electrons depending on their exact arrival time – a method known as electron beam streaking. From the spread, the length of each individual electron bunch can be measured.

When the electrons emit photons (in technical terms, they ‘lase’), they lose energy. By measuring this energy difference, and how it is spread at the parts of the electron beam that lase, PolariX provides information on the X-ray pulse, in particular how its intensity varies over time.

A #MadeAtPSI success story

Although electron streaking is a relatively well-established technique for X-ray pulse characterisation, what makes PolariX unusual is that it can streak in any direction, helping to fully characterise the electron bunch – a concept invented at CERN and realised thanks to the radiofrequency technology at PSI. In contrast, most other devices only streak in one direction, giving limited information about the electron beam. 

During the last seven years of development at PSI, the PolariX has become one of the world leading devices for this purpose. Five devices are in operation at DESY in Germany, with whom the device was developed, and the team at PSI is currently in discussion with other institutes worldwide to provide them with their RF technologies.

“Pretty much all of the systems and components of PolariX were made at PSI,” says Paolo Craievich, who leads the RF systems group at PSI. “Over the course of PolariX’s development, we have become very experienced, and now we are leading in the world. I’m very proud for the whole RF section – it’s the work from many different people.” 

Read more on PSI website

Image: Eduard Prat (left) and Paolo Craievich in SwissFEL – proud of the teamwork that has now led to a world record time-resolution in X-ray pulse measurement using electron-beam streaking. © Paul Scherrer Institute PSI/Mahir Dzambegovic

Credit: Paul Scherrer Institute PSI/Mahir Dzambegovic

UK and Switzerland partner for science using neutrons, muons and X-rays

UK and Switzerland partner for science using neutrons, muons and X-rays

A strategic partnership between research facilities in the UK and Switzerland has been established by the UK International Science Partnerships Fund (ISPF), which will develop new capabilities for science using neutrons, muons and X-rays. 

UK facilities – ISIS Neutron and Muon Source (ISIS) and the Diamond Light Source, located at the Rutherford Appleton Laboratory (RAL) – and the Paul Scherrer Institute (PSI), in Switzerland – home to the Swiss Spallation Neutron Source SINQ, the Swiss Muon Source SµS, the Swiss Light Source SLS and the X-ray Free-Electron Laser SwissFEL, will create new scientific capabilities to address global challenges.  

These large-scale research infrastructures have a rich history in pushing forward science in key areas for our society, such as net zero technology development, healthcare solutions and therapies, and resilient communications, relying on their ability to study material properties at the atomic and molecular scales. Recent studies have included investigation of materials for enhanced batteries, quantum computing and technologies, and novel drug delivery mechanisms, as well as fundamental science investigations. The ISPF partnership will enable new projects to be taken forward, developing capabilities for research facilities that benefit society overall. 

Researchers and technical teams from ISIS, Diamond and PSI have already worked in close collaboration for many years. The ISPF funding will allow an extension of collaborations into new research areas, enabling the development of novel capabilities in both countries. Around 16 projects will be taken forward as part of the programme, with 16 early-career postdoctoral researchers employed to work between the facilities. 

Read more on Diamond website

Image: Meeting of members of the ISIS – Diamond – PSI partnership at the Rutherford Appleton Laboratory, 27-28 November 2024.

Neat, precise and brighter than ever

Neat, precise and brighter than ever

Researchers at SwissFEL have successfully demonstrated new technologies that improve the temporal coherence of XFEL pulses

X-ray free-electron lasers produce pulses of light that are exceptionally bright, making them powerful tools for studying ultrafast chemical reactions, biological processes, or probing the structure of materials at atomic scales.

However, these pulses are noisy in time and frequency due to the way the light is generated through a process known as self-amplified spontaneous emission, or SASE for short: i.e., the pulses are not temporally coherent.

This spectral randomness can be a limitation for experiments requiring ultra-high spectral control to follow electron and structural dynamics.

In true Swiss style, researchers at SwissFEL have now found a way to make the light neat and orderly.

Read more on PSI website

Controlling magnetic waves in a spin liquid

Controlling magnetic waves in a spin liquid

Scientists at the Paul Scherrer Institute PSI have shown that excitation of a spin liquid with intense THz pulses causes spins to appear and align within less than a picosecond. This induced coherent state causes a magnetic field to form inside the material, which is detected using ultrashort X-ray pulses at the X-ray Free Electron Laser SwissFEL.  

Spins carried by atoms are the building blocks of magnetism. In a ferromagnet, they all align in the same direction, a feature used to store data on hard drives. In antiferromagnets, they form an antiparallel alignment. Like the surface of a stormy sea where water mountains build up here and there, disappearing as fast as they come, the spins in a spin liquid are fluctuating and form no ordered magnetic state despite local interactions.  

Scientists at PSI have shown that the electromagnetic field of short THz pulses imprints its coherence onto the orbital wavefunctions of Terbium atoms of a Tb2Ti2O7 crystal, causing the spins of 1015 Tb excited ions in the material to appear and move synchronized, reminiscent of how wind can create highly periodic patterns of waves. This created state is called an ensemble of coherent quantum states. 

Read more on PSI website

Image: Artistic impression of a magnetic moment appearing in a spin liquid after excitation with an intense short THz pulse

Credit: Roman Mankowsky.

Fundamentally different

Fundamentally different

Large research facilities at PSI such as the X-ray free-electron laser SwissFEL and the Swiss Light Source SLS – especially after the upgrade SLS 2.0 – deliver unimaginably vast amounts of data. Artificial intelligence is helping to evaluate data efficiently and exploit the facilities’ full potential for research.

Proteins are the workhorses of life. As tiny molecular machines, they are found in every cell and have a role in nearly all biological processes – from metabolism to cellular communication. Their diversity is enormous, because in the human body alone there are hundreds of thousands of different proteins, each with its own function. Proteins are important targets for drugs, and understanding their structure and function is an important task in biological research. One challenge in drug development is to find, if possible, an active agent that interacts with just one type of protein, to the exclusion of all the rest.

To achieve such a feat, one must first understand the language of proteins. The basis of this protein language is a kind of alphabet. It essentially consists of 20 building blocks analogous to letters. In proteins, however, it’s not about letters, but rather amino acids. Each protein is built up from a certain sequence of these amino acids; the sequence in turn largely determines its properties. Researchers would now like to know which protein sequence leads to which property. This is where so-called large language models such as GPT4 come into play. The AI chatbot ChatGPT, which has been causing a stir since 2022, is based on GPT4. Both were developed by the company OpenAI. ChatGPT uses an extensive dataset of texts created by humans to learn the patterns and structures of language. When the user enters a question or task, the model produces a response based on its understanding of the contexts and patterns that it learned during training. In this way it can write poems, novels and even programming code.

Flurin Hidber, a doctoral candidate supervised by Xavier Deupi, an expert in bioinformatics and protein structure at PSI, uses AI in protein research. Hidber uses a sophisticated model similar to ChatGPT that is trained to predict amino acids in protein sequences, instead of generating human-like language. This unique ability does not merely mimic the predictive capabilities of language models in AI, but rather provides valuable insights into the structure and function of proteins. Pharmaceutical researchers could use these to tailor medications and significantly shorten the process of trial and error in the laboratory, which in the end yields only a small proportion of drug candidates with promising properties.

An ambitious goal

Deupi and Hidber are working towards an ambitious goal: being able to determine the precise amino acid sequence that leads to a desired protein property. One focus of their research is light-sensitive proteins, a speciality of Deupi’s group and a research subject at SwissFEL. These proteins occur in many organisms, from microbes to humans, and have medical potential. Hidber’s use of AI to predict the properties of light-sensitive proteins solely on the basis of the sequence of their building blocks represents a significant advance in this field.

Through the precise prediction of the light-absorption properties of proteins, Hidber’s work could pave the way for the development of molecules with tailored properties – a step that could have a profound impact on optogenetics. This scientific technique employs light to control and monitor the activity of certain cells in living organisms, such as nerve cells in the brain. Researchers insert genes for light-sensitive proteins into these cells so they can precisely influence the cells’ behaviour by irradiating them with light.

This technology could contribute to the understanding and treatment of neurological diseases, since it provides a tool that can be used to investigate and control the activity of specific brain cells with unprecedented precision. For the future, Deupi and Hidber have set themselves the goal of reversing this process. They want to design new proteins with properties tailored to meet specific requirements, for example proteins that react to light of a particular colour. This blueprint could then be checked experimentally, and hopefully confirmed by colleagues in the laboratory.

The topic of protein dynamics is also at the heart of Cecilia Casadei’s research. The physicist has developed a new algorithm that enables more efficient evaluation of measurements at X-ray free-electron laser facilities such as SwissFEL. The building blocks of life often perform ultrafast movements. Investigating these with precision is crucial to gain a better understanding of proteins. In the long run, this can provide valuable information about disease processes and enable the development of novel medical approaches.

Read more on PSI website

Image: Xavier Deupi (left) and Flurin Hidber from the research group for Condensed Matter Theory want to better understand how the function of proteins is related to their structure. They are targeting light-sensitive proteins in particular. 

Credit:  Paul Scherrer Institute/Markus Fischer; KI image generation: Studio HübnerBraun/Midjourney

SwissFEL: a next generation tool for Attosecond Science

SwissFEL: a next generation tool for Attosecond Science

The 2023 Nobel Prize in Physics was awarded for the development of attosecond science – a field that sheds light on the movement of electrons on their natural timescale. Several researchers at the Swiss X-ray free electron laser SwissFEL are recognised in the scientific background to this prize. This is no coincidence. With recent technical developments enabling attosecond and fully coherent X-ray pulses, SwissFEL promises to rapidly advance this emerging research area.

“We can now open the door to the world of electrons. Attosecond physics gives us the opportunity to understand mechanisms that are governed by electrons. The next step will be utilising them.” So said Eva Olsson, Chair of the Nobel Committee for Physics at the Royal Swedish Academy of Sciences, at the announcement of the 2023 Nobel Prize in Physics.

The prize was awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter”. These breakthrough experimental methods are based on table-top laser systems – that is, laser systems that roughly fit onto an optical table and generate light mainly in the extreme ultraviolet energy range. Yet, in order to truly utilise our new insight into the world of electrons, further technological advances will be important that probe the movements of electrons in a wide variety of functional materials.

The scientific background produced by the Royal Swedish Academy of Sciences recognises the contributions from several researchers at PSI. There is a unifying theme to these researchers: they all now work at SwissFEL on upgrades that are enabling attosecond X-ray pulses, combining the possibilities of this astounding time resolution with the higher photon energies and higher photon fluxes offered by free electron laser light.

The contributions of these PSI researchers all lay in making the first steps of extending attosecond techniques, first developed in the gas phase, to new phases of matter – liquids and solids.

Read more on PSI website

Image: Contributions of a number of researchers at PSI were recognised in the scientific background to the 2023 Nobel Prize in Physics. These researchers include (L to R) Martin Huppert, Adrian Cavalieri and Stefan Neppl, all of whom are now working on the SwissFEL on advances that are enabling attosecond X-ray pulses. Here, they stand in the snow in the beautiful forest that surrounds SwissFEL.

Credit: Paul Scherrer Institute/Markus Fischer

Repairing genetic damage with sunlight

Repairing genetic damage with sunlight

DNA damage to the genetic material DNA drives cancer, ageing, and cell death. Therefore, DNA repair is crucial for all organisms, and a deeper understanding of this basic function helps us better comprehend how life around us survives and thrives. An international team of researchers has now revealed how the enzyme photolyase efficiently channels the energy of sunlight into DNA repair chemistry.

All life under the sun must cope with harmful UV rays. UV damage can take many forms, but DNA, the molecule that carries the genetic information of all living organisms, is especially vulnerable. For instance, UV can drive chemical cross-linking reactions of DNA, potentially introducing errors into the genetic code. This cross-linking can lead to cell death or – in the worst cases – mutagenesis and cancer. Such damage is not uncommon; under bright sunlight, a human skin cell can undergo 50-100 cross linking reactions per second.

“To survive, life has evolved powerful DNA repair mechanisms. One especially elegant solution is provided by the enzyme photolyase,” explains DESY scientist Thomas J. Lane, who is also a researcher in the Cluster of Excellence “CUI: Advanced Imaging of Matter” at Universität Hamburg. The enzyme uses sunlight to repair damage caused by sunlight. Photolyase is able to recognize the location where UV irradiation has cross-linked DNA and grabs onto those bits of damaged DNA. Then, it can capture a blue photon from the sun, and use it to perform repair chemistry, turning the DNA back into its original, healthy form.

To better understand how photolyase works, the scientists were particularly interested first in the form of the enzyme immediately after absorbing a photon, but before repairing the DNA. Second, they wanted to find out the exact sequence of bond-breaking chemical reactions necessary to turn damaged DNA into healthy DNA. As a third step, the team sought to better understand how photolyase can specifically recognize which DNA is damaged.

Conducting time-resolved crystallography at the SwissFEL X-ray free-electron laser of PSI the scientists were able to capture the excited state of the photolyase chromophore, letting them understand how the enzyme efficiently channels the energy of sunlight into DNA repair chemistry. “This research was only made possible by the recent development of X-ray free-electron laser sources. Their intense femtosecond-duration pulses let us record flash X-ray photographs that freeze all atomic motion so that we can follow the reaction step by step at the speed of molecules,” says first author Nina-Eleni Christou from DESY.

Read more on PSI website

Image: PSI researcher Camila Bacellar is pleased about the success in precisely analysing the DNA repair enzyme photolyase at the Alvra beamline of the Swiss X-ray free-electron laser SwissFEL.

Credit: Paul Scherrer Institute/Markus Fischer

The secret life of an electromagnon

The secret life of an electromagnon

Scientists have revealed how lattice vibrations and spins talk to each other in a hybrid excitation known as an electromagnon. To achieve this, they used a unique combination of experiments at the X-ray free electron laser SwissFEL. Understanding this fundamental process at the atomic level opens the door to ultrafast control of magnetism with light.

Within the atomic lattice of a solid, particles and their various properties cooperate in wave like motions known as collective excitations. When atoms in a lattice jiggle together, the collective excitation is known as a phonon. Similarly, when the atomic spins – the magnetisation of the atoms – move together, it’s known as a magnon.

The situation gets more complex. Some of these collective excitations talk to each other in so-called hybrid excitations. One such hybrid excitation is an electromagnon. Electromagnons get their name because of the ability to excite the atomic spins using the electric field of light, in contrast to conventional magnons: an exciting prospect for numerous technical applications. Yet their secret life at an atomic level is not well understood.

It’s been suspected that during an electromagnon the atoms in the lattice wiggle and the spins wobble in an excitation that is essentially a combination of a phonon and a magnon. Yet since they were first proposed in 2006, only the spin motion has ever been measured. How the atoms within the lattice move – if they move at all – has remained a mystery. So too has an understanding of how the two components talk to each other.

Now, in a sophisticated series of experiments at the Swiss X-ray free-electron laser SwissFEL, researchers at PSI have added these missing pieces to the jigsaw. “With a better understanding of how these hybrid excitations work, we can now start to look into opportunities to manipulate magnetism on an ultrafast timescale,” explains Urs Staub, head of the Microscopy and Magnetism Group at PSI, who led the study.

First the atoms, then the spins

In their experiments at SwissFEL, the researchers used a terahertz laser pulse to induce an electromagnon in a crystal of multiferroic hexaferrite. Using time-resolved X-ray diffraction experiments they then took ultrafast snapshots of how the atoms and spins moved in response to the excitation. With this, they proved both that the atoms within the lattice really do move in an electromagnon and also revealed how energy is transferred between lattice and spin.

A striking outcome of their study was that the atoms move first, with the spins moving fractionally later. When the terahertz pulse strikes the crystal, the electric field pushes the atoms into motion, initiating the phononic part of the electromagnon. This motion creates an effective magnetic field that subsequently moves the spins.

“Our experiments revealed that the excitation does not move the spins directly. It was previously unclear whether this would be the case,” explains Hiroki Ueda, beamline scientist at SwissFEL and the first author of the publication.

Going further, the team could also quantify how much energy the phononic component acquires from the terahertz pulse and how much energy the magnonic component acquires through the lattice. “This is an important piece of information for future applications in which one seeks to drive the magnetic system,” adds Ueda.

Read more on PSI website

Image: Hiroki Ueda, first author of the paper, working at the new Furka experimental at SwissFEL Here, using soft X-rays, Ueda and colleagues could reveal the motion of the spins during an electromagnon, complementing hard X-ray measurements of lattice vibrations made at the Bernina experimental station.

Credit: Paul Scherrer Institute/Markus Fischer

A beautiful machine integrated within a peaceful forest setting

A beautiful machine integrated within a peaceful forest setting

On World Science Day for Peace and Development, we’re heading to a forest in Switzerland!

Maël Clémence is a PhD student at the Swiss X-ray Free-Electron Laser  (SwissFEL), which is located at the Paul Scherrer Institut (PSI) in Villigen, Switzerland. His #LightSourceSelfie journey starts in the forest on top of the facility where he explains that the SwissFEL was designed to be fully integrated with the natural environment. Maël then uses a popular mode of transport to travel to the facility entrance. He recalls his childhood fascination with light, what led him to fall in love with physics, and his path to the SwissFEL.

For his PhD studies, Maël is utilising the machine’s ultraintense, ultrashort X-ray pulses to study and investigate quantum properties of magnetic materials in extreme conditions. Being at the SwissFEL has enabled Maël to gain a deeper understanding of this beautiful machine and the huge amount of skill and dedication that is required by the teams responsible for building and maintaining it.

The word ‘teamwork’ best describes his job as, on good days and bad, everyone pulls together and supports each other.

You’ll discover one of Maël’s favourite free time activities at the close out of his #LightSourceSelfie. Happy viewing!        

Find out more about the SwissFEL here

Tender X-rays show how one of nature’s strongest bonds breaks

Tender X-rays show how one of nature’s strongest bonds breaks

Short flashes of an unusual kind of X-ray light at SwissFEL and SLS bring scientists closer to developing better catalysts to transform the greenhouse gas methane into a less harmful chemical. The result, published in the journal Science, reveals for the first time how carbon-hydrogen bonds of alkanes break and how the catalyst works in this reaction.

Methane, one of the most potent greenhouse gases, is being released into the atmosphere at an increasing rate by livestock farming as well as the continuing unfreezing of permafrost. Transforming methane and longer-chain alkanes into less harmful and in fact useful chemicals would remove the associated threats, and in turn make available a huge feedstock for the chemical industry. However, transforming methane necessitates as a first step the breaking of a C-H bond, one of the strongest chemical linkages in nature.

Forty years ago, molecular metal catalysts were discovered that can easily split C-H bonds. The only thing found to be necessary was a short flash of visible light to “switch on” the catalyst and – bafflingly – the strong C-H bonds of alkanes passing nearby were easily broken almost without using any energy. Despite the importance of this so-called C-H activation reaction, it has remained unknown how that catalyst performs this function. Now, experiments at Swiss FEL and SLS have enabled a research team led by scientists at Uppsala University to directly watch the catalyst at work and reveal how it breaks the C-H bonds.

Read more on the PSI website

Image: An X-ray flash illuminates a molecule

Credit: University of Uppsala / Raphael Jay

An algorithm for sharper protein films

An algorithm for sharper protein films

Proteins are biological molecules that perform almost all biochemical tasks in all forms of life. In doing so, the tiny structures perform ultra-fast movements. In order to investigate these dynamic processes more precisely than before, researchers have developed a new algorithm that can be used to evaluate measurements at X-ray free-electron lasers such as the SwissFEL more efficiently. They have now presented it in the journal Structural Dynamics.

Sometimes, when using the navigation system while travelling by car, the device will locate you off the road for a short time. This is due to the inaccuracy of the GPS positioning, which can be as much as several metres. However, the algorithm in the sat nav will soon notice this and correct the trajectory displayed on the screen, i.e. put it back on the road.

A comparable principle for addressing unrealistic motion sequences has now been successfully applied by a team of researchers led by PSI physicist Cecilia Casadei. However, their objects of investigation are about a billion times smaller than a car: proteins. These building blocks of life fulfil crucial functions in all known organisms. In doing so, they often perform ultra-fast movements. Analysing these movements precisely is crucial for our understanding of proteins which can help us produce new medical agents, amongst other things.

How to “film” proteins…

To further improve the understanding of protein movements, Casadei, together with other PSI researchers, a researcher at DESY in Hamburg and other colleagues at the University of Wisconsin in Milwaukee, USA, has developed an algorithm that evaluates data obtained in experiments at an X-ray free-electron laser (XFEL). An XFEL is a large-scale research facility that delivers extremely intense and short flashes of laser-quality X-ray light. Here, a method called time-resolved serial femtosecond X-ray crystallography (TR-SFX) can be used to study the ultra-fast movements of proteins.

The measurements are very complex for several reasons: the proteins are much too small to be imaged directly, their movements are incredibly fast, and the intense pulse of X-ray light of an FEL completely destroys the proteins. On the experimental level, TR-SFX already solves all these problems: no individual molecule is measured, but rather a large number of identical protein molecules are induced to grow together in a regular arrangement to form protein crystals. When the FEL X-ray light shines on these crystals, the information is captured in time before the crystals and their proteins are destroyed by the pulse of light. The raw data from the measurements are available as so-called diffraction images: light spots that are created by the regular arrangement of the proteins in the crystal and registered by a detector.

Read more on the PSI website

Image: Physicist Cecilia Casadei was part of an international team that developed a new analysis algorithm. With their method, called “low-pass spectral analysis”, the data collected when proteins are measured at X-ray free-electron lasers can be evaluated more efficiently than before.

Credit: Paul Scherrer Institute/Mahir Dzambegovic