Highlights

Every year, a committee of experts sits down with a tough job to do: from among all ICREA publications, they must find a handful that stand out from all the others. This is indeed a challenge. The debates are sometimes heated and always difficult but, in the end, a shortlist of 24 publications is produced. No prize is awarded, and the only additional acknowledge is the honour of being chosen and highlighted by ICREA. Each piece has something unique about it, whether it be a particularly elegant solution, the huge impact it has in the media or the sheer fascination it generates as a truly new idea. For whatever the reason, these are the best of the best and, as such, we are proud to share them here.

LIST OF SCIENTIFIC HIGHLIGHTS

Format: yyyy
  • Revealing the Universal Behavior of Spin Transport in Polycrystalline Graphene Devices (2019)

    Roche, Stephan (ICN2)

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    Graphene is a material that has been gaining fame in recent years due to its magnificent properties. In particular, for spintronics, graphene is a valuable material because the spins of the electrons used remain unaltered for unprecedented distances. However, graphene needs to be produced on a large scale in order to be used in future devices. With that respect, chemical vapour deposition (CVD) is the most promising fabrication method. CVD involves growing graphene on a metallic substrate at high temperatures. In this process, the generation of graphene starts at different points of the substrate simultaneously. This produces different single-crystal domains of graphene separated from one another through grain boundaries, consisting of arrays of five-, seven- or even eight-member carbon rings. The final product is, thus, polycrystalline graphene. A critical question for developing graphene-based spintronic technologies is to assess the impact of polycrystalline morphology with respect to the single-crystal situation. Using first-principles simulations and efficient quantum transport methodplogies, the impact of grain boundaries on spin transport in polycrystalline graphene has been fully clarified.

    Indeed we found that the spin diffusion length in polycrystalline graphene, supported on dielectric substrates, turns put to be insensitive to the grain size but only depends on the strength of the substrate-induced spin-orbit coupling. Moreover, this is valid not only for the diffusive regime of transport, but also for the weakly localized one, in which quantum phenomena prevail. This is the first quantum mechanical simulation confirming that the same expression for spin diffusion length holds in both regimes.

    Such research highlights the fact that single-domain graphene may not be a requirement for spintronics applications, and that polycrystalline CVD-grown graphene may work just as well. This puts the focus on other aspects to enhance in graphene production, such as the elimination of magnetic impurities, and should accelerate the integration of scalable graphene onto memory or spin logics technologies

  • Musical Pleasure is mediated by Dopamine (2019)

    Rodríguez Fornells, Antoni (UB)

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    The present study shows for the first time a causal role of dopamine (a neurotransmiter involved in the regularion of reward experiences) in musical pleasure and motivation: enjoying a piece of music, deriving pleasure from it, wanting to listen to it again and be willing to spend money for it. Researchers manipulated the dopaminergic synaptic availability for the participants (27 volunteers) using a pharmacological design. In three different sessions, separated by one week at least, reserchers orally administrated to each participant a dopamine precursor (levodopa, which increases dopaminergic availability), a dopamine antagonist (risperidone; to reduce dopaminergic signaling), and placebo (lactose; as a control). The authors indirectly measured changes in pleasure using electrodermal activity, which is a very sensitive technique to evaluate emotional changes (i.e., in this case, the hedonic impact of music). Participants provided subjective ratings of the experienced pleasure (real time ratings and general pleasure ratings provided after each song). Importantly, motivational responses were measured by asking participants how much of their own money they were willing to spend for each song.

    The results showed that while the dopamine precursor levodopa increased the hedonic experience to music and motivational responses, such as willingness to purchase a song, the dopamine antagonist risperidone led to a reduction of both.

    These results shed new light on the neurochemistry underpinning music reward, contributing to the fervid and open debate on the nature of abstract human pleasures. These findings challenge previous evidence conducted in animal models, where dopaminergic manipulations showed a clear role of dopamine in motivation and learning, but a controversial function in regulating hedonic responses in primary rewards (e.g. food), which has been mainly related to opioids release. These results indicate that dopaminergic transmission in humans might play different or additive roles than the ones postulated in affective processing, particularly in abstract cognitive activities such as music listening.

  • A new model predicts key characteristics of major earthquakes and associated tsunamis   (2019)

    Rodríguez Ranero, César (CSIC - ICM)

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    The study allows explaining the behaviour of large earthquakes, predicting their potential to generate tsunamis more accurately than any previous method. The model explains why some moderate seismic events in the past generated anomalously large tsunamis and solves physical paradoxes of previous models.

    After decades of research there is no conventional model that explains earthquake’s behaviour, so that understanding seismic rupture is still one of the major open questions in Earth Sciences. For instance, there is no explanation for the systematic variation of properties of seismic rupture progressing from deep to shallow depth along faults. This uncertainty has led to underestimate earthquake capacity to generate tsunamis, making it difficult to forecast their associated risks. For instance, the Sanriku event (Japan) in 1896 caused a tsunami up to 38 meters high, devastating several coastal towns and causing more than 22,000 victims. The arrival of the tsunami took local residents by surprise, because the intensity of the earthquake that preceded it was moderate. Similarly tragic examples are tsunamis generated by recent giant earthquakes, like Banda-Aceh in Indonesia (2004) and Tohoku-Oki in Japan  (2011), with tsunamis larger than expected, leading to unforeseen catastrophic situations such as flooding of Fukushima nuclear power plant.

    We ​​propose a new conceptual model that explains various essential characteristics of earthquakes and predicts their tsunamigenic potential. Changes in earthquake rupture behaviour with depth are not understood and are attributed to local variations in the physical mechanism operating when a fault is seismically slipping. In contrast, we show that they are due to systematic changes in the rigidity of the rocks that rest on the mega-faults that generate the earthquakes, and that fracture and deform during the seismic rupture. Measuring changes in rigidity with depth allows to explain the speed of propagation and duration of seismic ruptures, the amount of slip on faults, changes in amplitude of the generated seismic vibration, and earthquake magnitude.

  • Key to robustness of plants discovered (2019)

    Rovira Virgili, Carme (UB)

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    In changing weather situations, plants need to be robust and flexible at the same time. These structural properties are anchored in the cell walls. The cell wall is responsible for defining the plant’s shape, for compensating its osmotic pressure and to protect it against pathogens e.g. bacteria, viruses or fungal attacks. The cell walls of plants are largely built from polymers and the polysaccharide cellulose. As binding agents, polysaccharides have the important task to connect long-chain polymers and to build a molecular network of tiny strands, called fibrils, which contribute to the tensile strength of the plant. 

    One of the sugar building blocks is the branched-chain monosaccharid apiose, which got its name from the latin word "apium“, a plant genus comprising, for instance, celeriac and parsley.

    Apiose has been investigated by plant-biochemical research for more than a hundred years and its function in plants is still not fully understood. Besides, the mechanism, which is responsible for the production of apiose in nature, was still unknown.

    Scientists from the Universities of Barcelona (Spain), Pavia (Italy) and TU Graz (Austria) discovered how apiose is produced by a single enzyme called UAXS (UDP-apiose/UDP-xylose synthase). They were able to decode the entire mechanism of this enzyme for the first time. Isolated from the cress Arabidopsis thaliana, the catalyst possesses special properties: whereas most biosynthetic processes for the manufacturing of complex molecules need several reaction steps, the UAXS-enzyme selectively catalyzes in just four reaction steps. By doing so, the enzyme is able to break down organic carbon compounds as well as to establish new molecular compounds. This results in the change from a six ring sugar molecule (hexose) to a structurally simpler five ring sugar (pentose). By creating new organic carbon compounds, the enzyme is responsible for giving plants their strength properties.

    The discovery of the enzymatic mechanism of apiose was possible due to the interdisciplinary collaboration between the research areas of molecular modeling, enzymology and biocatalysis and structural biology.

  • Self-powered, paper-based sweat detector for easy screening of cystic fibrosis (2019)

    Sabaté Vizcarra, Neus (CSIC - IMB-CNM )

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    Sabate’s team has developed the Power-Patch, a self-powered skin patch for the measurement of sweat conductivity that can potentially be used as a screening device of Cystic Fibrosis disease. The key component of the patch consists of a paper battery that is activated upon adding the sweat. The fluid acts as an electrolyte, and for a particular configuration of the battery materials and design, the battery output is fully dependent on the conductivity of the liquid sample that is poured in its paper core. This approach enables the sensor and battery to be merged in a single element—a battery sensor—whose generated power is directly related to the conductivity of the sample to be analysed.

    The battery has been integrated into a patch and tested with artificial sweat samples mimicking healthy and non-healthy conditions of CF patients. The patch is conceived to be applied on the forearm of the patient and yield a “positive” result in case of an abnormal conductivity level of sweat is detected. The patch remains quiescent until sufficient sweat is absorbed by its paper-based electroactive core, which is in contact with the skin. After sweat absorption, the battery generates electrical power that is managed with a minimalistic electronic circuit that discerns between a healthy and a non-healthy condition. After providing a result, the patch can be disposed of with little environmental impact.

    The patch will enable an easy screening of the CF condition in regional hospitals or clinics, providing a powerful yet affordable tool for early identification of patients in developing countries. The innovation potential of the skin patch was acknowledged by the Organic Electronics Association, who awarded the prototype for the best prototype/new product at the annual contest that took place at the European Large-area, Organic and Printed Electronics Convention in 2018. After a successful lab validation, the patch will undergo a feasibility test with patients in 2020 with the Cystic Fibrosis Unit from Hospital Sant Joan de Deu (Barcelona) within the frame of an ERC Proof-of-Concept grant.

  • Why do enzymes make micromotors swim? (2019)

    Sánchez Ordónez, Samuel (IBEC)
    Osuna Oliveras, Sílvia (UdG)

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    Inspired by biological motors, researchers have engineered artificial micro- and nanoswimmers able to self-propel by converting chemical energy from their surrounding into motion. In our group, we pioneered the use of enzymes as engines, which catalyse bioavailable substrates (fuel) into products, providing nanomotors with a biocompatible propulsive source and therefore opening many possibilities for nanomedicine-related applications. Although there are a few reports on enzyme-nanomotors, the key properties to generate self-propulsion have not been studied so far.

    In this work, we aim at understanding at fundamental level the enzyme properties that predict the best performance of micromotors. To do so, we selected four different enzymes, urease, acetylcholinesterase, glucose oxidase and aldolase, to catalyze their specific “fuels” when bound to the surface of the micromotor. In Samuel Sánchez group (IBEC) we found that urease-motors showed the fastest self-propulsion indicating that self-propulsion of micromotors was correlated with a higher catalytic turnover of the enzyme used as engine. To gain more insight into the mechanistic structure at molecular level, in Sílvia Osuna group (IQCC at UdG), calculations based on Molecular Dynamics simulations revealed that the structural flexibility next to the active site, where the reaction occurs, of each enzyme was crucial for self-propulsion. These theoretical predictions were experimentally confirmed by exposing urease micromotors to inhibitors and compounds that increase enzyme rigidity.

    From these results we extracted that the conformational changes are a precondition to catalysis, which in its turn is the key factor for an optimal self-propulsion.

    This project has been the first study combining molecular dynamics and experimental work aimed at understanding enzyme-driven self propulsion from a mechanistic point of view. It paves the way towards the comprehension of the processes underlying catalytic self-propulsion and contributes to a more robust criteria for the rational design of enzyme-powered micromotors.

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