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Manjavacas A.,CSIC - Institute of Physical Chemistry "Rocasolano" | Garcia de Abajo F.J.,Catalan Institution for Research and Advanced Studies
Nature communications | Year: 2014

The ability to modulate light at high speeds is of paramount importance for telecommunications, information processing and medical imaging technologies. This has stimulated intense efforts to master optoelectronic switching at visible and near-infrared frequencies, although coping with current computer speeds in integrated architectures still remains a major challenge. As a partial success, mid-infrared light modulation has been recently achieved through gating patterned graphene. Here we show that atomically thin noble metal nanoislands can extend optical modulation to the visible and near-infrared spectral range. We find plasmons in thin metal nanodisks to produce similar absorption cross-sections as spherical particles of the same diameter. Using realistic levels of electrical doping, plasmons are shifted by about half their width, thus leading to a factor-of-two change in light absorption. These results, which we substantiate on microscopic quantum theory of the optical response, hold great potential for the development of electrical visible and near-infrared light modulation in integrable, nanoscale devices. Source

Banos-Sanz J.I.,CSIC - Institute of Physical Chemistry "Rocasolano"
Nucleic acids research | Year: 2013

Uracil-DNA glycosylase (UDG) is a key repair enzyme responsible for removing uracil residues from DNA. Interestingly, UDG is the only enzyme known to be inhibited by two different DNA mimic proteins: p56 encoded by the Bacillus subtilis phage 29 and the well-characterized protein Ugi encoded by the B. subtilis phage PBS1/PBS2. Atomic-resolution crystal structures of the B. subtilis UDG both free and in complex with p56, combined with site-directed mutagenesis analysis, allowed us to identify the key amino acid residues required for enzyme activity, DNA binding and complex formation. An important requirement for complex formation is the recognition carried out by p56 of the protruding Phe191 residue from B. subtilis UDG, whose side-chain is inserted into the DNA minor groove to replace the flipped-out uracil. A comparative analysis of both p56 and Ugi inhibitors enabled us to identify their common and distinctive features. Thereby, our results provide an insight into how two DNA mimic proteins with different structural and biochemical properties are able to specifically block the DNA-binding domain of the same enzyme. Source

Vegas A.,CSIC - Institute of Physical Chemistry "Rocasolano"
Structure and Bonding | Year: 2011

The study of phase transitions is usually restricted to two to three transformations. Examples of such transitions include the CaF2 → PbCl2 → Ni2In in alloys, the NaCl → CrB → CsCl or the well documented transformation olivine → spinel of the oxides A 2 XO4. These transitions, traditionally regarded as partial processes, have prevented the construction of wider structure maps. One of the scarce examples of these maps was reported by Léger and Haines (Eur J Solid State Inorg Chem 34:785-796, 1997) concerning the phase transitions of AX 2 compounds (dihalides and dioxides), where increasing the coordination number of the A atom is linked to the pressure increase. The structural information, collected in these maps, is always of interest because it limits the number of possible transition paths which may relate a structure-type into another. However, a careful analysis of the partial phase transitions undergone by different compounds, at high temperature and high pressure, reveals that the partial transitions are not isolated processes but they overlap, forming a long, rational pathway that connects all the structures in a coherent manner. Alloys and their related oxides show a similar trend along their concurrent pathways which complement each other. In this work, the analysis is restricted to the AX 2 alloys and their corresponding oxides AX 2 O4, and the results demonstrate that there exists a unifying principle that can be inferred through the simultaneous analysis of all the phase transitions involved in the concurrent structural journeys carried out by both types of compounds. The AX 2 alloys begin the walk in the fluorite-type structure, ending in the MoSi 2-type structure. In the case of the oxides AX 2 O 4, their cation arrays follow a concurrent pathway that, starting at the filled fluorite-type structure, ends in the final Sr2PbO 4-type structure. These structural "journeys" also allows for the discovery of several "missing links" (structure types) which fit into the general sequence and help one understand the whole transitions pathway as a rational process, which takes place simultaneously in the alloys as well as in the cation arrays of the oxides. Very recent works show that alkali metals (Na and K) also join the walk. The extended Zintl-Klemm concept (EZKC) and the concept that relates of oxidation-pressure-temperature effects provide a basis for understanding the observed transitions. © 2011 Springer-Verlag Berlin Heidelberg. Source

Almarza N.G.,CSIC - Institute of Physical Chemistry "Rocasolano"
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

We report Monte Carlo simulations that show a closed-loop liquid-vapor equilibrium in a pure substance. This finding has been achieved on a two-dimensional lattice model for patchy particles that can form network fluids. We have considered related models with a slightly different patch distribution in order to understand the features of the distribution of patches on the surface of the particles that make possible the presence of the closed-loop liquid-vapor equilibrium, and its relation to the phase diagram containing so-called empty liquids. Finally we discuss the likelihood of finding the closed-loop liquid-vapor equilibria on related models for three-dimensional models of patchy particles in the continuum, and speculate on the possible relationship between the mechanism behind the closed-loop liquid-vapor equilibrium of our simple lattice model and the salt-induced reentrant condensation found in complex systems. © 2012 American Physical Society. Source

Hermoso J.A.,CSIC - Institute of Physical Chemistry "Rocasolano"
Structure | Year: 2014

CAD is a large multifunctional polypeptide that initiates and controls the de novo biosynthesis of pyrimidines in animals. In this issue of Structure, Grande-García and colleagues provide the first atomic information of this antitumoral target by reporting the crystal structure of the dihydroorotase domain of human CAD. © 2014 Elsevier Ltd. Source

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