Cada any, un comitè d'experts s'ha d'enfrontar a la difícil tasca d'escolllir, d'entre totes les publicacions ICREA, unes poques que destaquin sobre la resta. És tot un repte: de vegades els debats s'acaloren, i sempre són difícils, però acaba sortint-ne una llista de 24 publicacions. No es concedeix cap premi, i l'únic reconeixement addicional és l'honor d'ésser presentat com a Highlight. Cada publicació té alguna cosa especial, sia una solució especialment elegant a un vell problema, un resó espectacular als mitjans de comunicació o simplement, la fascinació d'una idea revolucionària. Independentment del motiu, es tracta dels millors dels millors i, com a tals, ens plau compartir-los aquí.


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  • Who is your neighbor?  (2019)

    Gabaldón Estevan, Toni (BSC-CNS)

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    Who is your neighbor? 

    Gene clusters are groups of genes that remain in close neighborhood across large evolutionary distances, and despite pervasive genomic re-arrangements. In prokaryotes (organisms with anucleated cells like bacteria) such clusters may consist in operons, groups of genes that are co-transcribed in a single transcript and translated together to ensure their tight co-regulation. In eukaryotes (organisms with cells with a nucleus like plants, fungi, and animals), despite the abscence of true operons, there are examples of clusters of co-regulated genes mostly involved in secondary metabolism. However, very little is known about how gene clustering patterns vary among taxa or with respect to functional roles. Furthermore, mechanisms of the formation, maintenance and evolution of gene clusters remain unknown.

    We set out to study this in fungi, the eukaryotic group that is best sampled in terms of fully-sequenced genomes. We surveyed 341 fungal genomes to discover gene clusters shared by different species, independently of their functions. We inferred 12,120 cluster families, which comprised roughly one third of the gene space and were enriched in genes associated with diverse cellular functions. Additionally, most clusters did not encode transcription factors, suggesting that they are regulated distally. We used phylogenomics to characterize the evolutionary history of these clusters. We found that most clusters originated once and were transmitted vertically, coupled to differential loss. However, convergent evolution, that is, independent appearance of the same cluster, was more prevalent than anticipated. Finally, horizontal gene transfer of entire clusters was somewhat restricted, with the exception of those associated with secondary metabolism. Altogether, our results provide insights on the evolution of gene clustering as well as a broad catalogue of evolutionarily conserved gene clusters whose function remains to be elucidated.

  • Magnetism: an unexpected push for the hydrogen economy (2019)

    Galán-Mascarós, José Ramón (ICIQ)

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    Magnetism: an unexpected push for the hydrogen economy

    Renewable energy sources are becoming competitive in the energy market (solar, wind…), but their high efficiency is bound to their transformation into electricity. However, electrical power is difficult to store and transport, whereas renewable energy sources are by definition intermittent. One promising solution could be to store electrical energy surplus into energy rich chemicals as green, carbon neutral energy vectors. Just substitution of fossil fuels by these green alternatives could sustain productivity (transportation and most industries depend on fuels), while avoiding environmental impact. The challenge resides in the low efficiency, and high costs of transforming electrical power into high-energy chemicals.

    Electrolytic water splitting – the reaction in which water is broken down into oxygen and hydrogen ­as the most simple green vector – still suffers from significant energy losses, low production rates, and prohibitive costs. Many research teams worldwide are working towards improving all these factors, while keeping the scalability and viability at reasonable costs.

    In a paper published in Nature Energy, scientists from ICIQ’s Galán-Mascarós and López groups describe how a magnet can directly enhance  hydrogen production in alkaline water splitting. The presence of an external magnetic field – induced by a neodymium magnet– can increase hydrogen production over 100% in some conditions, without additional energy consumption. The major hypothesis to explain this phenomenon describes the magnetic field directly boosting the molecular oxygen formation rates. Molecular oxygen (O2) requires the two oxygen radicals making the chemical bond to keep their spins aligned during the reaction pathway. Thus, the overall spin polarization induced by the external magnetic field, improves the efficiency of the process. 

    The simplicity of this new technological milestone has attracted several industrial partners that are already working with ICIQ in its implementation into industrial-size devices.


  • Near-infrared plasmons with atomically thin crystalline silver films (2019)

    García de Abajo, Francisco Javier (ICFO)

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    Near-infrared plasmons with atomically thin crystalline silver films

    Plasmons in noble metals, such as silver and gold, have been used to color glass since ancient times. In recent years, plasmonics has made its way through to become a key component in the field of optical devices essential in the miniaturization of optoelectronic devices to the nanoscale.

    It is known that plasmonic interactions between electrons and photons change significantly in materials when one or more of the dimensions of the metallic object are reduced down to the nanometer scale. The advent of graphene and other two-dimensional crystals has helped display appealing properties of plasmons such as a large electrical tunability. However, the plasmons generated in these materials are too broad or exist at too low frequencies, in a range that is well below the expected near-infrared regime needed for most optical devices.

    In a recent study in ACS Nano (cover image in July 2019), ICFO researchers in collaboration with the University of the Basque Country report on the fabrication and the excellent plasmonic and electronic properties of wafer scale atomically thin crystalline silver films composed of only a few atomic layers.

    Through a two-step process of fabrication and under ultrahigh-vacuum conditions, the team of researchers was able grow high-quality flat silver films on silicon wafers, with a thickness as small as seven atomic monolayers. The film quality was high enough to resolve quantum electronic states through angle-resolved photoemission. To excite and probe plasmons in this films, they first carved nanoribbon arrays, and then shined near-infrared light.

    The results of this study prove that atom-thin crystalline silver films are capable of supporting high-quality narrow plasmons in the near infrared. In addition, this study has proven that such material could be the perfect alternative to highly-doped graphene, which, despite its amazing properties, has so far reached the mid-infrared, far from the technologically attractive near-infrared region. The observation of these spectrally sharp and strongly confined plasmons in atomically thin silver holds great potential for electro-optical modulation and optical sensing applications.


  • Ferroelectricity is not behind the success in photovoltaics of hybrid perovskites (2019)

    Goñi, Alejandro R. (CSIC - ICMAB)

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    Ferroelectricity is not behind the success in photovoltaics of hybrid perovskites

    Ferroelectric materials are characterized by a switchable macroscopic electric polarization. A wide number of perovskite oxides have ferroelectric behavior. Whether or not also lead halide perovskites are ferroelectrics has been a matter of debate since their breakthrough in photovoltaics reaching conversion efficiencies in excess of 25% in a couple of years of intense research. Although the reported efficiencies of perovskite solar cells approach the theoretical limit, the potential role of ferroelectricity in the photovoltaic behavior is still controversial. It has been reported, for instance, that ferroelectric polarization may favor charge generation, thus leading to enhanced photovoltaic performance but it was also suggested that ferroelectricity might cause chemical segregation, which is detrimental for perovskite solar cells. In general, the high electronic and ionic conductivity in lead halide perovskites make the examination of ferroelectricity extremely complicated using conventional techniques, such as piezo-response force microscopy. Experimental results from conventional methods often lead to misinterpretation.

    To circumvent the above mentioned problems, we have developed a novel scanning-probe microscopy technique, direct piezoelectric force microscopy (DPFM), to examine the ferroelectric response of halide perovskites most commonly used in photovoltaics. In contrast to conventional techniques, DPFM is to a large extent free of artifacts. By comparison with well-known ferroelectric materials (see Fig. 1), we demonstrate that lead halide perovskites films are ferroelectricity free. Hence, further work is necessary to pinpoint the physical reasons for the unprecedented success of this new class of photovoltaic materials.

  • Electrons travel long distances during photosynthesis (2019)

    Gorostiza Langa, Pau (IBEC)
    Rovira Virgili, Carme (UB)

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    Electrons travel long distances during photosynthesis

    The transport of electrons along photosynthetic and respiratory chains involves a series of enzymatic reactions that are coupled through redox mediators, including proteins and small molecules. The use of natural and synthetic redox probes is key to understanding charge transport mechanisms and to design bioelectronic sensors and solar energy conversion devices. We have used the metal probe of an electrochemical scanning tunneling microscope as a nanometric redox mediator to study electron transport in individual photosynthetic complexes. Current–distance measurements in solution show evidence of long-distance transport that is regulated by the biologically relevant redox conditions.

  • Exciting thoughts, one neuron at a time (2019)

    Gorostiza Langa, Pau (IBEC)

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    Exciting thoughts, one neuron at a time

    Remote control of neuronal activity using photopharmacology and infrared light has been recently demonstrated. However, its practical use in neuronal tissue to photostimulate individual neurons with three-dimensional precision has been hampered by (1) the low efficacy and reliability of two-photon isomerization using infrared light compared to one-photon excitation, and (2) the short lifetime of the two-photon induced responses. We have developed novel photoswitches endowed with both high two-photon absorption cross section and slow thermal back-isomerization. These compounds provide optimized and sustained two-photon neuronal stimulation both in light-scattering brain tissue and in live worms. This finding opens the way to analyze the function of intact neuronal circuits in three dimensions.