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  the most outstanding publications of the year 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

  • 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.

  • The Nature of Chance (2019)

    Hoefer, Carl (UB)

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    The Nature of Chance

    Scientists as well as gamblers, insurance actuaries and government planners presuppose the existence of objective chances for certain types of events – for example, a uranium atom decaying, throwing snake-eyes on a craps table, or hospitalizations due to infections increasing by more than 5% in a year.  But when we say that an event of type A has a chance of occurring of 28%, are we really saying something about the world, or rather just saying something about ourselves (that, perhaps, we have a level of expectation or confidence of 28% in an A-type event's happening)?  And if we are in fact saying something about the world itself, exactly what are we saying?  What sort of fact is a chance-fact?  How can one distinguish a world in which A-type events have 28% chance from a world in which they have 35% chance?

    Culminating many years of thinking and development, Carl Hoefer's book Chance in the World (Oxford University Press) offers definitive answers to questions such as these.  Hoefer argues that objective chances are pattern-facts, that is, facts about the overall patterns that are discernible in the totality of events that take place in the world.  Hoefer's theory, which can be viewed as a sophisticated revision and refinement of traditional frequency-based definitions of chance, overcomes the problems of earlier accounts of chance and offers an understanding that is demonstrably compatible with the uses of chance found in the sciences and in daily life.

  • The evolutionary origin of neuronal microexons (2019)

    Irimia, Manuel (CRG)
    Valcárcel Juárez, Juan (CRG)

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    The evolutionary origin of neuronal microexons

    The mechanisms by which entire programs of gene regulation arose are poorly understood, and very rarely can be traced back to singular genomic novelties (e.g. the appearance of a specific regulator or protein domain). In this study, we elucidated the mechanism underlying the emergence of a particularly intriguing and evolutionarily conserved program of alternative splicing: the one of neural-specific microexons.

    Microexons are tiny (3-27-nt long) exons that are critical for nervous system development and that have been implicated in autism spectrum disorders. The finding in mammals of large, tightly regulated programs of microexons came as a major surprise. It was widely assumed that very short exons were largely not accessible to the cellular machinery, as their minute size would preclude the spliceosomal interactions needed for exon definition. Therefore, these findings raised a major question: when and how in evolution did animal cells acquire the ability to recognize and splice-in microexons?

    Here, we demonstrated that neural microexon programs originated in bilaterian ancestors, more than 600 million years ago, through the emergence of a distinct genomic novelty occurring in a pan-eukaryotic core spliceosomal gene. This genomic novelty generated an alternative isoform encoding a new protein interaction domain with a unique functional property: microexon splicing. We named this domain the "enhancer of microexons" (eMIC). We showed that the eMIC domain is necessary and sufficient for the specific inclusion of neural microexons in both vertebrates and invertebrates, and that it does so by interacting with some of the earliest factors required for spliceosomal assembly.

    After its origin, the eMIC domain qualitatively expanded the regulatory toolkit of animals by enabling the recognition and subsequent selection of tiny exons that were not previously available to the splicing machineries of ancestral species. The functional importance of this mechanism is illustrated by the neurodevelopmental and behavioral defects of mouse models depleted of microexons, and also by the deregulation of this program in autistic patients.

  • Peering Beyond the Horizon: Revealing The Hidden Sector of the Universe (2019)

    Jiménez Tellado, Raúl (UB)
    Verde, Licia (UB)

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    Peering Beyond the Horizon: Revealing The Hidden Sector of the Universe

    For the first time scientists, led by ICREA  Prof. Raul Jimenez, have developed a method to look into our past Universe. The so-called "past-light-cone" are those regions of the Universe that remain unconected from us because it would take light longer than the age of the Universe to travel. In principle we cannot explore this vast region of our Universe. However, by using galaxy clusters as "cosmic mirrors" Jimenez et al. have shown that one could actually view these regions of our past. The technique involves making "movies" of the cosmic microwave background: the relic of the most distant light in the early Universe. This new observational window could open new avenues to understand nature as  we do not know if the Universe in its past is like ours or different. It would allow us to peer into causaly disconnected regions from us and thus understand if the pillars of physical cosmology (which received the nobel prize this year) are correct or we will discover new physics.

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