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.


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  • Understanding singularities in mathematical equations (2020)

    Ros Oton, Xavier (UB)

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    Understanding singularities in mathematical equations

    Partial Differential Equations (PDE) are a type of mathematical equations that are used in essentially all sciences and engineering. They are the language in which most physical laws are written.

    From the mathematical point of view, the most fundamental question in this context is to understand whether solutions to a given PDE may (or may not) develop singularities. For example, in the case of the PDEs that describe fluid mechanics, this is one of the Millenium Prize Problems in mathematics.

    During the last decades, there has been an increasing interest in understanding PDE problems that involve unknown/moving interfaces, such as ice melting to water. In this context, it turns out that singularities do appear... sometimes. In a recent work with A. Figalli and J. Serra, we have proved for the first time that, while singularities may appear, they are actually extremely rare. Our precise theorem (whose proof is more than 100 pages long) completely solves a long-standing conjecture which had been open for almost half a century.

    Our work has been published in Publ. Math. IHÉS, an extremely selective journal which publishes only around 10 papers every year (in all areas of mathematics).

  • Three ways to break a sugar chain (2020)

    Rovira Virgili, Carme (UB)

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    Three ways to break a sugar chain

    One of the basic processes of nature is the decomposition of organic matter, which requires the degradation of complex carbohydrate structures. To do so, it is necessary to break the long chains of sugar molecules made up of smaller – ‘monosaccharide’ – units in order to transform them into  short chains. 

    The above process is performed by glycosidases, enzymes found in all life forms and are part of the machinery by which cells acquire their nutrients.

    In order to carry out these decomposition processes, only two catalytic mechanisms were known so far to help the acceleration of the corresponding chemical reactions. The most common mechanism is one in which the glycosidase enzyme uses two strategically located ‘amino acid residues’ to chemically cleave the bond. These molecules act like a pair of clippers that snip and cut the bond. This approach is used in a famous enzyme (lysozyme) found in egg-white that protects the chicken embryo from bacteria by cutting their cell walls.

    The second mechanism needs uses one amino acid residue, and instead uses another type of chemical unit, an ‘amide group’ on the glycoside (such as in crab chitin) as the second residue. This is used by glycosidases called chitinases to degrade crab exoskeletons allowing them to molt. These are now textbook mechanisms studied in undergraduate courses.

    We have recently discovered a special group of enzymes that instead use another type of chemical structure, a sugar hydroxyl and that forms a three membered ring (an epoxide) intermediate. This mechanism was found in a specific type of glycosidases: endo-α-mannosidases, necessary to modify the sugars linked to our proteins.

    The study has been carried out by an international team (UK, Canada, Australia and Spain), in which our group was in charge of modelling the enzyme mechanism of action using multiscale computational chemistry.

    The study provides the first convincing data to prove this particular mechanism from glycosidases, which will probably be used by other enzymes yet to be discovered. By learning how nature works, we can mimic its strategies to develop new enzymes for industrial applications.

  • Nanochemistry in motion: Two new chassis for nanomotors (2020)

    Sánchez Ordónez, Samuel (IBEC)
    Maspoch Comamala, Daniel (ICN2)

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    Nanochemistry in motion: Two new chassis for nanomotors

    Catalytic nanomotors are nanostructures that convert chemical energy into motion, showing great potential in biomedical and environmental applications. Once in a solution containing the “fuel”, nanomotors start to swim while performing tasks such as carrying drugs, sensing, penetrating cells and tissues and cleaning contaminated water. Using enzymes -organic molecules that accelerate the speed of biochemical reactions- as engines is an elegant and efficient way to generate energy for the propulsion of nanomotors. However, these enzyme-driven nanostructures may be exposed to adverse conditions, such as strong pH variations, harsh solvents, ionic species, and high temperatures, which could compromise both their movement and their functionalities. To overcome this issue, the groups from Prof. Samuel Sánchez (IBEC) and Prof. Daniel Maspoch (ICN2), have put together their expertise -nanomotors and nanochemistry- in two collaborative publications to provide nanomotors with new chassis, opening new avenues in this field enabling some applications never envisioned before.  

    The first one is called “Lipobots”, and comprises liposomes -spherical vesicles- containing urease enzyme in their interior. The researchers mimicked the journey of Lipobots towards the gastrointestinal track, where they would suffer from acidic conditions before reaching the bile salts. Surprisingly, the protective shell from the liposome maintains the enzymatic activity and the structure of the Lipobots at pH3. Thereafter, Lipobots were soaked in a solution containing a component of the bile salt present in the intestine, which opened the pores of the liposome leaving a thrust from the enzymatic reaction which in turn, provided the self-propulsion of Lipobots. In the second one, metal-organic frameworks (MOF) were synthesized so that two types of pores were generated, ones would incorporate catalase enzymes and the other one be available for the adsorption of contaminants like organic dyes while self-propelling (MOFtors). The high porosity, and dual functionality of the pores is of great importance for the creation of very active, multifunctional and mass-produced self-propelled microcleaners.

  • The importance of location, where one amino acid makes the difference (2020)

    Serrano Pubul, Luis (CRG)

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    The importance of location, where one amino acid makes the difference

    The C-terminal sequence of a protein is involved in processes such as efficiency of translation termination and protein degradation. However, the general relationship between features of this C-terminal sequence and levels of protein expression remains unknown. Here, we identified C-terminal amino acid biases that are ubiquitous across the bacterial taxonomy (1582 genomes). We showed that the frequency is higher for positively charged amino acids (lysine, arginine) while hydrophobic amino acids and threonine are lower. We then studied the impact of C-terminal composition on protein levels in a library of M. pneumoniae mutants, covering all possible combinations of the two last codons. We found that charged and polar residues, in particular lysine, led to higher expression, while hydrophobic and aromatic residues led to lower expression, with a difference in protein levels up to 4-fold. We further showed that modulation of protein degradation rate could be one of the main mechanisms driving these differences. Our results demonstrate that the identity of the last amino acids has a strong influence on protein expression levels and therefore it is important to look at it in biotechnological applications.

  • The Brain’s Connectome: Why Layers at Different Scales Seem Strangely Similar (2020)

    Serrano, M. Ángeles (UB)

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    The Brain’s Connectome: Why Layers at Different Scales Seem Strangely Similar

    The architecture of the brain supports cognitive and behavioral functions and it is extremely complex with connections at multiple layers that interact with each other. However, research efforts are usually focused on a single spatial scale. In a study led by ICREA research professor M. Ángeles Serrano, researchers studied the multiscale spatial organization of the brain and observed that, in a geometric network model, the layers at different resolution are self-similar, that is, as we move away, the geometric and connectivity structure of the layers remains the same.

    In order to carry out this study, researchers used two high-quality datasets with networks of neural connections, connectomes, of eighty-four subjects with five anatomical resolutions for each that expand over a series of interrelated length scales. According to Prof. Serrano, "the self-similarity we determined as a pattern in the multiscale structure of the human connectome implies that brain connectivity at different scales is organized under the same principles, that lead to efficient decentralized communication". This means that underlying connectivity rules that explain the brain's connectome are independent from the observation scale and we do not need a specific set of rules for each scale.

    The model predicts observations through the application of a renormalization protocol that uses a hyperbolic network map of the human connectome, so that regions at short distances are more likely to be connected. This type of model enables researchers to explain the universal features of real networks and their multiscale structure. For every scale, there is a remarkable congruence between empirical observations and predictions provided by the model. The results show that the same rules explain the formation of short and long-range connections in the brain within the rank of length scales that cover the used datasets.

    The implications of this discovery are several. On the one hand, it can be useful in fundamental debates, such as whether the brain is working close to a critical spot. On the other hand, it can have applications for advanced tools on brain functioning simulation.

  • Revealing the peculiar magnetism of the frustrated “Cairo” pentagonal antiferromagnet (2020)

    Skumryev, Vassil (UAB)

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    Revealing the peculiar magnetism of the frustrated “Cairo” pentagonal antiferromagnet

    The pentagon, a five-sided polygon, is an old issue in mathematical recreation. It forms the faces of the dodecahedron, one of the platonic solids whose shape is reproduced in biological viruses and in clusters. Contrary to triangles, squares or hexagons, it is impossible to tile a plane with congruent regular pentagons; the tilings must involve additional shapes to fill the gaps - fig.1. There exist, however, several possibilities of tessellation with non-regular pentagons, a famous one being the Cairo tessellation whose name was given because it appears in the streets of Cairo.

    Using neutron diffraction, several years ago we found that the Fe magnetic moments of Bi2Fe4O9 at the two distinct crystallographic sites, Fe1 and Fe2, form a pattern, which constitutes the first materialization of pentagonal magnetic structure - fig.2. Because of its odd number of bonds per elemental brick, this so-called Cairo pentagonal lattice is prone to geometric frustrated magnetism arising when all pair interactions are not simultaneously satisfied. The peculiarity of this non-collinear structure arises from the complex connectivity of the pentagonal lattice, a novel feature compared to the well-known case of triangle-based lattices, opening new perspectives in the field of magnetic frustration. In this case, both the frustration and the complex connectivity are at play and there is no macroscopic degeneracy of the ground state. In a recent inelastic neutron scattering study [1], the magnetic interactions in the pentagonal lattice and their hierarchy were determined. It unveils various facets of unconventional magnetism, with distinct behaviors associated with the two inequivalent Fe sites of the pentagonal lattice. The Fe1 ions produce strongly coupled antiferromagnetic pairs of spins (dimers) separated by much less correlated Fe2 spins, dominating the correlated paramagnetic state (above the temperature of magnetic order).  Whereas in the ordered magnetic state, the pairs of Fe2 spins produce original spin dynamics, associated with protected local motions, coexisting with dispersive spin waves. This result should be very general in systems with similar lattice topology.