High-brightness Source of Coherent Light Spanning From The UV to THz (Physics)

An international team of scientists reports in Nature Photonics on a novel technique for a high-brightness coherent and few-cycle duration source spanning 7 optical octaves from the UV to the THz.

Artistic impression of the spectrum of a mid-infrared pulse broadening in the background with the electric field of the generated pulse.
© ICFO/L.Maidment, U. Elu & J. Biegert

Analytical optical methods are vital to our modern society as they permit the fast and secure identification of substances within solids, liquids or gases. These methods rely on light interacting with each of these substances differently at different parts of the optical spectrum. For instance, the ultraviolet range of the spectrum can directly access electronic transitions inside a substance while the terahertz is very sensitive to molecular vibrations.

Throughout the years many techniques have been developed to achieve hyperspectral spectroscopy and imaging, allowing scientists to observe the behavior of, for example, molecules when they fold, rotate or vibrate in order to understand the identification of cancer markers, greenhouse gases, pollutants or even substances that could be harmful to us. These ultrasensitive techniques have proven to be very useful in applications related to food inspection, biochemical sensing or even in cultural heritage, to investigate the structure of the materials used for ancient objects, paintings or sculptures.

A standing challenge has been the absence of compact sources that cover such large spectral range with sufficient brightness. Synchrotrons provide the spectral coverage, but they lack the temporal coherence of lasers, and such sources are available only in large-scale user facilities.

Now, in a recent study published in Nature Photonics, an international team of researchers from ICFO, the Max Planck Institute for the Science of Light, the Kuban State University, and the Max-Born-Institute for Nonlinear Optics and Ultrafast Spectroscopy, led by ICREA Prof. at ICFO Jens Biegert, report on a compact high-brightness mid-IR-driven source combining a gas-filled anti-resonant-ring photonic crystal fiber with a novel nonlinear-crystal. The table top source provides a seven-octave coherent spectrum from 340 nm to 40,000 nm with spectral brightness 2-5 orders of magnitude higher than one of the brightest Synchrotron facilities.

Future research will leverage the few-cycle pulse duration of the source for the time-domain analysis of substances and materials, thus opening new opportunities for multimodal measurement approaches in areas such as molecular spectroscopy, physical chemistry or solid-state physics, to name a few.

Reference: Ugaitz Elu, Luke Maidment, Lenard Vamos, Francesco Tani, David Novoa, Michael H. Frosz, Valeriy Badikov, Dmitrii Badikov, Valentin Petrov, Philip St. J. Russell and Jens Biegert, “Seven-octave high-brightness and carrier-envelope-phase-stable light source”, Nature Photonics, 2020. https://www.nature.com/articles/s41566-020-00735-1

Provided by Max Planck Gesellschaft

Breaking Bad: How Shattered Chromosomes Make Cancer Cells Drug-resistant (Medicine)

Researchers find that the phenomenon of chromothripsis results in rearranged genomes and extra-chromosomal DNA that helps mutated cells not only evade treatment, but become more aggressive.

Cancer is one of the world’s greatest health afflictions because, unlike some diseases, it is a moving target, constantly evolving to evade and resist treatment.

In this scanning electron micrograph of inside the nucleus of a cancer cell, chromosomes are indicated by blue arrows and circular extra-chromosomal DNA are indicated by orange arrows. © UC San Diego Health Sciences

In a paper published in the December 23, 2020 online issue of Nature, researchers at University of California San Diego School of Medicine and the UC San Diego branch of the Ludwig Institute for Cancer Research, with colleagues in New York and the United Kingdom, describe how a phenomenon known as “chromothripsis” breaks up chromosomes, which then reassemble in ways that ultimately promote cancer cell growth.

Chromothripsis is a catastrophic mutational event in a cell’s history that involves massive rearrangement of its genome, as opposed to a gradual acquisition of rearrangements and mutations over time. Genomic rearrangement is a key characteristic of many cancers, allowing mutated cells to grow or grow faster, unaffected by anti-cancer therapies.

“These rearrangements can occur in a single step,” said first author Ofer Shoshani, PhD, a postdoctoral fellow in the lab of the paper’s co-senior author Don Cleveland, PhD, professor of medicine, neurosciences and cellular and molecular medicine at UC San Diego School of Medicine.

“During chromothripsis, a chromosome in a cell is shattered into many pieces, hundreds in some cases, followed by reassembly in a shuffled order. Some pieces get lost while others persist as extra-chromosomal DNA (ecDNA). Some of these ecDNA elements promote cancer cell growth and form minute-sized chromosomes called ‘double minutes.'”

Research published last year by scientists at the UC San Diego branch of the Ludwig Institute for Cancer Research found that up to half of all cancer cells in many types of cancers contain ecDNA carrying cancer-promoting genes.

In the latest study, Cleveland, Shoshani and colleagues employed direct visualization of chromosome structure to identify the steps in gene amplification and the mechanism underlying resistance to methotrexate, one of the earliest chemotherapy drugs and still widely used.

In collaboration with co-senior author Peter J. Campbell, PhD, head of cancer, aging and somatic mutation at Wellcome Sanger Institute in the United Kingdom, the team sequenced the entire genomes of cells developing drug resistance, revealing that chromosome shattering jump-starts formation of ecDNA-carrying genes that confer anti-cancer therapy resistance.

The scientists also identified how chromothripsis drives ecDNA formation after gene amplification inside a chromosome.

“Chromothripsis converts intra-chromosomal amplifications (internal) into extra-chromosomal (external) amplifications and that amplified ecDNA can then reintegrate into chromosomal locations in response to DNA damage from chemotherapy or radiotherapy,” said Shoshani. “The new work highlights the role of chromothripsis at all critical stages in the life cycle of amplified DNA in cancer cells, explaining how cancer cells can become more aggressive or drug-resistant.”

Said Cleveland: “Our identifications of repetitive DNA shattering as a driver of anti-cancer drug resistance and of DNA repair pathways necessary for reassembling the shattered chromosomal pieces has enabled rational design of combination drug therapies to prevent development of drug resistance in cancer patients, thereby improving their outcome.”

The findings address one of the so-called nine Grand Challenges for cancer therapy development, a joint partnership between the National Cancer Institute in the United States and Cancer Research UK, the world’s largest independent cancer research and awareness charity.

Reference: Shoshani, O., Brunner, S.F., Yaeger, R. et al. Chromothripsis drives the evolution of gene amplification in cancer. Nature (2020). https://www.nature.com/articles/s41586-020-03064-z https://doi.org/10.1038/s41586-020-03064-z

Provided by University of California San Diego

New Mechanisms To Control Dental Procedure Spray Emissions (Medicine / Dentistry)

Since the onset of COVID-19 the potential risk of dental procedure spray emissions for SARS-CoV-2 transmission has challenged care providers and policy makers alike. The study, “Mechanisms of atomization from rotary dental instruments and its mitigation,” published in the Journal of Dental Research (JDR), found that there are multiple mechanisms for atomization of fluids from rotatory instruments and that parameters can be controlled to modify key spray characteristics during the current crisis.

Figure 1. Air turbine visualizations using broadband and LED light sources. (A) Still frame from high-speed imaging of an unobstructed spray from an air turbine possessing a high-velocity spray, a turbulent shear layer at the periphery of the core, and recirculation regions close to the burr tip. (B) Same image false-colored with the central spray core in orange, a shear layer region located outside of the central core region in yellow, and recirculation regions in blue. A group of high-droplet velocity straight trajectories is shown by the red streaks toward the top of the image. (C) When the same instrument is placed inside a simulated oral cavity (palatal to the maxillary central incisors), a turbulent fine mist of a reduced but significant velocity is produced (principal direction indicated by the yellow arrow).

Using high speed imaging and laser light-sheet illumination, procedural sprays were studied with variables including rotation speed, burr to tooth contact and coolant pre-misting. Elimination of pre-misting (mixing of coolant water and air prior to burr contact) and use of relatively low rotation speeds resulted in significant reduction in small droplets. Cutting efficiency was reduced, but sufficient coolant effectiveness appeared to be maintained.

“This research demonstrates that spray from dental instruments can be controlled without losing the ability to carry out dental treatment,” said JDR Editor-in-Chief Nicholas Jakubovics. “Being able to modify the spray creates a safer experience for patients and oral health care providers during this current pandemic.”

Reference: A. Sergis, W.G. Wade, J.E. Gallagher, A.P. Morrell, S. Patel, C.M. Dickinson, N. Nizarali, E. Whaites, J. Johnson, O. Addison, Y. Hardalupas, “Mechanisms of Atomization from Rotary Dental Instruments and Its Mitigation”, Journal of Dental Research, December 16, 2020.
https://doi.org/10.1177/0022034520979644

Provided by American Association For Dental Research

About the Journal of Dental Research

The IADR/AADR Journal of Dental Research (JDR) is a multidisciplinary journal dedicated to the dissemination of new knowledge in all sciences relevant to dentistry and the oral cavity and associated structures in health and disease. The JDR ranks #3 in Impact Factor of 91 journals, #2 without self-citations, as well as #2 of 91 in Article Influence with a score of 1.627. The JDR’s 5-year Impact Factor remained above 5 for the fifth year at 5.844 — ranking #2 of 91 journals. With over 20,000 citations, the JDR also boasts the most citations in the “Dentistry, Oral Surgery & Medicine” category, over 3,500 citations above the 2nd ranked journal in the field.

About International Association for Dental Research

The International Association for Dental Research (IADR) is a nonprofit organization with over 10,000 individual members worldwide, with a Mission to drive dental, oral and craniofacial research to advance health and well-being worldwide. To learn more, visit http://www.iadr.org. The American Association for Dental Research (AADR) is the largest Division of IADR with 3,100 members in the United States. To learn more, visit http://www.iadr.org/aadr.

Scientists Identify New Gene Involved in Autism Spectrum Disorder (Neuroscience)

Forward genetics pinpoints gene linked to ASD involving severe speech impairment and opens door to search for more mutations, future treatments.

UT Southwestern scientists have adapted a classic research technique called forward genetics to identify new genes involved in autism spectrum disorder (ASD). In a study published this week in eLife, the researchers used this approach in mice to find one such gene called KDM5A.

Bruce Beutler, M.D. Photo taken by Brian Coats for UT Southwestern Medical Center

Approximately 1 in 54 children in the U.S. is diagnosed with ASD, a neurodevelopmental disorder that causes disrupted communication, difficulties with social skills, and repetitive behaviors. As a disease with a strong genetic component, it is hypothesized that thousands of genetic mutations may contribute to ASD. But to date, only about 30 percent of cases can be explained by known genetic mutations.

For decades, forward genetics has been used to find mutations that cause disease. It involves inducing genetic mutations in mice, screening for certain phenotypes, and then identifying the causative mutation through sequencing of all genetic material of an organism, or its genome.

“The difficult part in the beginning was finding the mutations. It had to be done by laborious cloning,” says Nobel Laureate Bruce Beutler, M.D., director of the Center for the Genetics of Host Defense at UTSW and study co-author. “We developed a platform wherein when you see a phenotype you know the mutational cause at the same time.” So, when a mouse displays a certain phenotype or trait of interest, the researchers would know almost instantly what genetic mutation was causing it. This technique, combined with a screen developed to ascertain ASD-like behaviors in mice, made it possible to use forward genetics for the first time to identify new genetic mutations in ASD.

Beutler won the 2011 Nobel Prize in Physiology or Medicine for his discovery of a family of receptors that allow mammals to sense infections when they occur, triggering a powerful inflammatory response.

In this study, the research team documented the quality and number of vocalizations in young mice carrying induced genetic mutations. Given that one of the common characteristics seen in autism is disrupted communication, the researchers were on the lookout for mice that had changes in these vocalizations.

Maria Chahrour, Ph.D. © UT Southwestern Medical Center

“Initially we found that the quality of these vocalizations was different in mice with KDM5A mutations. Looking more closely, we found that mice completely lacking KDM5A have a severe deficit in the number of these vocalizations,” says Maria Chahrour, Ph.D., who led the study. Chahrour is assistant professor of neuroscience, psychiatry, and in both the Eugene McDermott Center for Human Growth and Development and Center for the Genetics of Host Defense.

In addition to loss of vocalizations, mice lacking KDM5A also displayed repetitive behaviors and deficits in social interaction, learning, and memory – all hallmarks of ASD.

Because this was the first time that KDM5A had been implicated in ASD, the researchers looked into whether KDM5A mutations could be found in patients with autism as well. Through international collaborative efforts, the group was able to identify nine patients with ASD and causative KDM5A mutations. Strikingly, eight out of nine patients also had a complete lack of speech.

Though one broad term is used for ASD, Chahrour likens autism to cancer in that it is a collection of individually rare forms of autism with hundreds of different genetic causes. Mutations in KDM5A appear to be one of those forms.

“We’ve identified a new genetic subtype of autism, and we’re going to look for more patients with mutations in KDM5A,” explains Chahrour. “This has a direct impact on diagnosis too. When a clinician gets a clinical sequencing result that reports a KDM5A mutation, it’s now a known autism gene.”

Aside from the impact on diagnosis, the researchers are interested in further characterizing this gene’s role in the brain. With a better understanding of what KDM5A is doing in the brain, scientists might be able to find a target to aid in future studies investigating possible treatments.

This work will expand beyond KDM5A as researchers search for more genes involved in ASD, a subject of research for which the simplicity and efficiency of forward genetics comes in handy.

“The wonderful thing about forward genetics is that we can grind away at the genome. We know progressively how much of the genome we’ve saturated,” says Beutler, who estimates that his group has already mutated about half of the mouse genome with this approach.

Chahrour, also a member of UT Southwestern’s Peter O’Donnell Jr. Brain Institute, looks forward to continuing to screen these animals for ASD genes, adding, “At some point we’ll get to a stage where we can saturate the genome with mutations and theoretically find every gene that functions in social behavior and cognition. That’s the ultimate goal.”

Provided by UT Southwestern Medical Center

Quantum Wave in Helium Dimer Filmed For The First Time (Quantum)

For the first time, an international team of scientists from Goethe University and the University of Oklahoma has succeeded in filming quantum physical effects on a helium dimer as it breaks apart. The film shows the superposition of matter waves from two simultaneous events that occur with different probability: The survival and the disintegration of the helium dimer. This method might in future make it possible to track experimentally the formation and decay of quantum Efimov systems.

Professor Reinhard Dörner (left) and Dr Maksim Kunitzki in front of the COLTRIMS reaction microscope at Goethe University, which was used to observe the quantum wave. (Photo: Goethe University Frankfurt)

Anyone entering the world of quantum physics must prepare themself for quite a few things unknown in the everyday world: Noble gases form compounds, atoms behave like particles and waves at the same time and events that in the macroscopic world exclude each other occur simultaneously.

In the world of quantum physics, Reinhard Dörner and his team are working with molecules which – in the sense of most textbooks – ought not to exist: Helium compounds with two atoms, known as helium dimers. Helium is called a noble gase precisely because it does not form any compounds. However, if the gas is cooled down to just 10 degrees above absolute zero (minus 273 °C) and then pumped through a small nozzle into a vacuum chamber, which makes it even colder, then – very rarely – such helium dimers form. These are unrivaledly the weakest bound stable molecules in the Universe, and the two atoms in the molecule are correspondingly extremely far apart from each other. While a chemical compound of two atoms commonly measures about 1 angstrom (0.1 nanometres), helium dimers on average measure 50 times as much, i.e. 52 angstrom.

The scientists in Frankfurt irradiated such helium dimers with an extremely powerful laser flash, which slightly twisted the bond between the two helium atoms. This was enough to make the two atoms fly apart. They then saw – for the very first time – the helium atom flying away as a wave and record it on film.

According to quantum physics, objects behave like a particle and a wave at the same time, something that is best known from light particles (photons), which on the one hand superimpose like waves where they can pile upor extinguish each other (interference), but on the other hand as “solar wind” can propel spacecraft via their solar sails, for example.

That the researchers were able to observe and film the helium atom flying away as a wave at all in their laser experiment was due to the fact that the helium atom only flew away with a certain probability: With 98 per cent probability it was still bound to its second helium partner, with 2 per cent probability it flew away. These two helium atom waves – Here it comes! Quantum physics! – superimpose and their interference could be measured.

The measurement of such “quantum waves” can be extended to quantum systems with several partners, such as the helium trimer composed of three helium atoms. The helium trimer is interesting because it can form what is referred to as an “exotic Efimov state”, says Maksim Kunitski, first author of the study: “Such three-particle systems were predicted by Russian theorist Vitaly Efimov in 1970 and first corroborated on caesium atoms. Five years ago, we discovered the Efimov state in the helium trimer. The laser pulse irradiation method we’ve now developed might allow us in future to observe the formation and decay of Efimov systems and thus better understand quantum physical systems that are difficult to access experimentally.”

Reference: Maksim Kunitski, Qingze Guan, Holger Maschkiwitz, Jörg Hahnenbruch, Sebastian Eckart, Stefan Zeller, Anton Kalinin, Markus Schöffler, Lothar Ph. H. Schmidt, Till Jahnke, Dörte Blume, Reinhard Dörner: Ultrafast manipulation of the weakly bound helium dimer. In: Nature Physics, https://doi.org/10.1038/s41567-020-01081-3

Provided by Goethe University Frankfurt

TPU Chemists Convert Plastic Bottle Waste into Insecticide Sorbent (Chemistry)

Scientists of Tomsk Polytechnic University proposed a method to create a sorbent for imidacloprid insecticide removal from water. The sorbent belongs to metal-organic frameworks, a class of non-conventional materials. The TPU chemists grew such a framework right on polyethylene terephthalate (PET) used to produce regular plastic bottles. The method is quite simple and allows converting used materials into a useful product. The research findings are published in Applied Materials Today academic journal (IF: 8,352; Q1).

©TPU

Metal-organic frameworks are substances with a three-dimensional structure, where clusters or metal ions are bridged by organic ligands. The result is a porous material with the properties of both metals and organic compounds.

“Due to their porous structure and a number of other properties, metal-organic frameworks have a high potential as sorbents. We are particularly interested in the problem of insecticide sorption, which are extensively used in modern agriculture and accumulated in soil and water.

We have proposed a new method to synthesize a metal-organic framework named UiO-66 with zirconium ions. The source material is what interests us first of all,” Pavel Postnikov, the research supervisor and Associate Professor of TPU Research School of Chemistry and Applied Biomedical Sciences, says.

©TMU

The researchers experimented with imidacloprid. This is one of the most widespread insecticides used in agriculture, including against Colorado potato beetles.

“Imidacloprid accumulates in natural water bodies penetrating from soil. According to Canadian researchers, imidacloprid was detected in waters around the world at concentrations ranging from 0.001 to 320 micrograms per litre. UiO-66 is usually derived at high temperatures and pressure using commercial terephthalic acid. However, we used PET consisting of ethylene glycol with terephthalic acid. This acid is a structural material for organic linkers in frameworks and plastic bottle material already contains it,” Oleg Semyonov, one of the article authors and Junior Research Fellow at TPU Research School of Chemistry and Applied Biomedical Sciences, explains.

To create a framework, the chemists cut the plastic into small squares and partially destroyed them in an acidic solution. Then, zirconium salts were added to the solution.

“Terephthalic acid is partially released from PET forming small “anchors” on the surface of the plastic pieces while a part of the acid remains in the solution. Zirconium ions attach to the “anchors” and then, the process of self-assembly inherent to metal-organic frameworks occurs and further results in a framework formed on the plastic surface. This framework is sensitive to imidacloprid and due to its porosity and physicochemical properties, it attracts insecticide molecules removing them from water,” the researcher says.

“During the experiments, we ran the insecticide solution through the sorbent. The effective water purification took 15 grams of sorbent per 1 liter, which is a very good indicator. Besides, the sorbent may be reused several times. We reached up to five cycles during our experiments. However, we expect that the sorbent will retain its properties much longer,” the scientist says.

In the long run, in practice, this sorbent can be used in filtration systems, for instance, at agricultural enterprises.

“Our sorbent also has one more advantage. Usually, metal-organic frameworks are powder-like. They choke filters so that filtration systems should be designed considering this feature. The particles of our sorbent are larger and they do not choke a filter.

In addition, due to larger particles, the throughput of the sorbent is higher and liquids penetrate easier. According to our calculations, in this case water passage requires one hundred times less pressure as compared to powders. Ultimately, it is important for the technology development and use of this sorbent in a real technological process,” Oleg Semyonov adds.

The scientists are currently conducting experiments using other metal-organic frameworks derived from PET.

The research work is supported by the grant of the Russian Foundation for Basic Research.

References: Oleg Semyonov, Somboon Chaemchuen, Alexey Ivanov, Francis Verpoort, Zdenka Kolska, Maxim Syrtanov, Vaclav Svorcik, Mekhman S. Yusubov, Oleksiy Lyutakov, Olga Guselnikova, Pavel S. Postnikov, “Smart recycling of PET to sorbents for insecticides through in situ MOF growth”, Applied Materials Today, Volume 22, 2021, 100910, ISSN 2352-9407,
https://doi.org/10.1016/j.apmt.2020.100910.
http://www.sciencedirect.com/science/article/pii/S2352940720303589

Provided by Tomsk Polytechnic University

Perfect Transmission Through Barrier Using Sound: Zhang’s Team Proves For The First Time a Century-old Quantum Theory

The perfect transmission of sound through a barrier is difficult to achieve, if not impossible based on our existing knowledge. This is also true with other energy forms such as light and heat.

The phononic crystals are made by artificially placing the acrylic posts in the special pattern. © University of Hong Kong

A research team led by Professor Xiang Zhang, President of the University of Hong Kong (HKU) when he was a professor at the University of California, Berkeley, (UC Berkeley) has for the first time experimentally proved a century old quantum theory that relativistic particles can pass through a barrier with 100% transmission. The research findings have been published in the top academic journal Science.

Just as it would be difficult for us to jump over a thick high wall without enough energy accumulated. In contrast, it is predicted that a microscopic particle in the quantum world can pass through a barrier well beyond its energy regardless of the height or width of the barrier, as if it is “transparent”.

As early as 1929, theoretical physicist Oscar Klein proposed that a relativistic particle can penetrate a potential barrier with 100% transmission upon normal incidence on the barrier. Scientists called this exotic and counterintuitive phenomenon the “Klein tunneling” theory. In the following 100 odd years, scientists tried various approaches to experimentally test Klein tunneling, but the attempts were unsuccessful and direct experimental evidence is still lacking.

Professor Zhang’s team conducted the experiment in artificially designed phononic crystals with triangular lattice. The lattice’s linear dispersion properties make it possible to mimic the relativistic Dirac quasiparticle by sound excitation, which led to the successful experimental observation of Klein tunneling.

Experimental setup: the artificial phononic crystals are designed and fabricated by the research team. Sound emitted from the loudspeakers array normally propagates from the right and excites the relativistic quasiparticle inside the phononic crystals. A mini microphone is attached to a 3D motion motor to scan the pressure field © University of Hong Kong

“This is an exciting discovery. Quantum physicists have always tried to observe Klein tunneling in elementary particle experiments, but it is a very difficult task. We designed a phononic crystal similar to graphene that can excite the relativistic quasiparticles, but unlike natural material of graphene, the geometry of the man-made phononic crystal can be adjusted freely to precisely achieve the ideal conditions that made it possible to the first direct observation of Klein tunneling,” said Professor Zhang.

The achievement not only represents a breakthrough in fundamental physics, but also presents a new platform for exploring emerging macroscale systems to be used in applications such as on-chip logic devices for sound manipulation, acoustic signal processing, and sound energy harvesting.

“In current acoustic communications, the transmission loss of acoustic energy on the interface is unavoidable. If the transmittance on the interface can be increased to nearly 100%, the efficiency of acoustic communications can be greatly improved, thus opening up cutting-edge applications. This is especially important when the surface or the interface play a role in hindering the accuracy acoustic detection such as underwater exploration. The experimental measurement is also conducive to the future development of studying quasiparticles with topological property in phononic crystals which might be difficult to perform in other systems,” said Dr. Xue Jiang, a former member of Zhang’s team and currently an Associate Researcher at the Department of Electronic Engineering at Fudan University.

Dr. Jiang pointed out that the research findings might also benefit the biomedical devices. It may help to improve the accuracy of ultrasound penetration through obstacles and reach designated targets such as tissues or organs, which could improve the ultrasound precision for better diagnosis and treatment.

On the basis of the current experiments, researchers can control the mass and dispersion of the quasiparticle by exciting the phononic crystals with different frequencies, thus achieving flexible experimental configuration and on/off control of Klein tunneling. This approach can be extended to other artificial structure for the study of optics and thermotics. It allows the unprecedent control of quasiparticle or wavefront, and contributes to the exploration on other complex quantum physical phenomena.

The article published in Science: https://science.sciencemag.org/content/370/6523/1447.

Reference: Xue Jiang, Chengzhi Shi, Zhenglu Li, Siqi Wang, Yuan Wang, Sui Yang, Steven G. Louie, Xiang Zhang, “Direct observation of Klein tunneling in phononic crystals”, Science 18 Dec 2020: Vol. 370, Issue 6523, pp. 1447-1450. DOI: 10.1126/science.abe2011

Provided by University of Hong Kong

The ABCs of Species Evolution (Biology)

A transporter protein that regulates cell membrane cholesterol likely played an important role in vertebrate evolution, according to a review published by iCeMS researchers in the journal FEBS Letters.

Almost four decades of research have led scientists at Japan’s Institute for Integrated Cell-Material Sciences (iCeMS) to propose that a family of transporter proteins has played an important role in species evolution. One protein in particular, called ABCA1, was likely crucial for vertebrate evolution by helping regulate when signals involved in cell proliferation, differentiation and migration enter a cell. This process was necessary for vertebrates to develop into more complex organisms with sophisticated body structures.

The ABCA1 protein flips the cholesterol from the inner to the outer layer of the cell membrane. This strengthens the ability of the skin to protect the body from external stimuli. The researchers suggest this played an important role in the evolution of vertebrates. © Mindy Takamiya/Kyoto University iCeMS

The ATP-binding cassette proteins (ABC) are very similar across species, including in bacteria, plants and animals. There are different types of ABC proteins with different transportation roles, importing nutrients into cells, exporting toxic compounds outside them, and regulating lipid concentrations within cell membranes.

iCeMS cellular biochemist Kazumitsu Ueda has studied human ABC proteins for 35 years, ever since he and his colleagues identified the first eukaryote ABC protein gene.

“We believe ABC proteins must have played important roles in evolution,” Ueda says. “By transporting lipids, they enabled plants and animals to thrive on land by protecting them from water loss and pathogen infection. They are also assumed to have accelerated vertebrate evolution by allowing cholesterol to function as an intra-membrane signalling molecule.”

Organisms that existed early in Earth’s history were probably formed of DNA and proteins surrounded by a leaky lipid membrane. As the organisms evolved, their membranes were fortified to protect them from the external environment. But this meant only organisms that evolved special ABC transporters capable of carrying nutrients across the membrane survived. The ABC proteins also played important roles in generating an outer membrane that protected cells from external stresses and in removing harmful substances from inside.

Recently, Ueda and his team studied the roles of ABCA1, gaining deeper insight into how it regulates cholesterol. Specifically, they found that ABCA1 exports cellular phospholipids and cholesterol outside the cell for generating high-density lipoproteins, popularly called good cholesterol.

They also found that ABCA1 constantly flops cholesterol from the cell membrane’s inner leaflet to its outer leaflet, maintaining a lower concentration on the inner side. This flopping is temporarily suppressed when the cell is exposed to an external stimulus, like growth hormone. The resultant accumulation of cholesterol in the inner leaflet triggers the recruitment of proteins to the membrane and modulates the signal transduction. Ueda and his team suggest that ABCA1 allowed vertebrates to evolve complicated biological processes and sophisticated bodies.

“ABCA1 is very unique and its functions surprised us,” says Ueda. “Cholesterol’s role was thought to focus mainly on physically strengthening the cell membrane and reducing its permeability to ions. Our research suggests it played a more important role in vertebrates, accelerating their evolution.”

Reference: Ogasawara, F., Kodan, A. and Ueda, K. (2020), ABC proteins in evolution. FEBS Lett., 594: 3876-3881. https://doi.org/10.1002/1873-3468.13945 https://febs.onlinelibrary.wiley.com/doi/10.1002/1873-3468.13945

Provided by Kyoto University

Theory Describes Quantum Phenomenon in Nanomaterials (Quantum)

Osaka City University scientists have developed mathematical formulas to describe the current and fluctuations of strongly correlated electrons in quantum dots. Their theoretical predictions could soon be tested experimentally.

Theoretical physicists Yoshimichi Teratani and Akira Oguri of Osaka City University, and Rui Sakano of the University of Tokyo have developed mathematical formulas that describe a physical phenomenon happening within quantum dots and other nanosized materials. The formulas, published in the journal Physical Review Letters, could be applied to further theoretical research about the physics of quantum dots, ultra-cold atomic gasses, and quarks.

A quantum dot (the yellow part) is connected to two lead electrodes (the blue parts). Electrons tunneling into the quantum dot from the electrodes interact with each other to form a highly correlated quantum state, called “Fermi liquid.” Both nonlinear electric current passing through the quantum dot and its fluctuations that appear as a noise carry important signals, which can unveil underlying physics of the quantum liquid. It is clarified that three-body correlations of the electrons evolve significantly and play essential roles in the quantum state under the external fields that break the particle-hole or time-reversal symmetry. © Rui Sakano

At issue is ‘the Kondo effect’. This effect was first described in 1964 by Japanese theoretical physicist Jun Kondo in some magnetic materials, but now appears to happen in many other systems, including quantum dots and other nanoscale materials.

Normally, electrical resistance drops in metals as the temperature drops. But in metals containing magnetic impurities, this only happens down to a critical temperature, beyond which resistance rises with dropping temperatures.

Scientists were eventually able to show that, at very low temperatures near absolute zero, electron spins become entangled with the magnetic impurities, forming a cloud that screens their magnetism. The cloud’s shape changes with further temperature drops, leading to a rise in resistance. This same effect happens when other external ‘perturbations’, such as a voltage or magnetic field, are applied to the metal.

Teratani, Sakano and Oguri wanted to develop mathematical formulas to describe the evolution of this cloud in quantum dots and other nanoscale materials, which is not an easy task.

To describe such a complex quantum system, they started with a system at absolute zero where a well-established theoretical model, namely Fermi liquid theory, for interacting electrons is applicable. They then added a ‘correction’ that describes another aspect of the system against external perturbations. Using this technique, they wrote formulas describing electrical current and its fluctuation through quantum dots.

Their formulas indicate electrons interact within these systems in two different ways that contribute to the Kondo effect. First, two electrons collide with each other, forming well-defined quasiparticles that propagate within the Kondo cloud. More significantly, an interaction called a three-body contribution occurs. This is when two electrons combine in the presence of a third electron, causing an energy shift of quasiparticles.

“The formulas’ predictions could soon be investigated experimentally”, Oguri says. “Studies along the lines of this research have only just begun,” he adds.

The formulas could also be extended to understand other quantum phenomena, such as quantum particle movement through quantum dots connected to superconductors. Quantum dots could be a key for realizing quantum information technologies, such as quantum computers and quantum communication.

Reference: Yoshimichi Teratani, Rui Sakano, and Akira Oguri, “Fermi Liquid Theory for Nonlinear Transport through a Multilevel Anderson Impurity”, Phys. Rev. Lett. 125, 216801 – Published 17 November 2020. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.216801

Provided by Osaka City University