Examinando por Autor "Rogero, Celia"

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Restringido
Interplay between Fast Diffusion and Molecular Interaction in the Formation of Self-Assembled Nanostructures of S-Cysteine on Au(111)
(ACS Publications, 2010-01-21) Mateo Martí, Eva; Rogero, Celia; González, César; Sobrado, J. M.; De Andrés, Pedro L.; Martín Gago, J. A.
We have studied the first stages leading to the formation of self-assembled monolayers of S-cysteine molecules adsorbed on a Au(111) surface. Density functional theory (DFT) calculations for the adsorption of individual cysteine molecules on Au(111) at room temperature show low-energy barriers all over the 2D Au(111) unit cell. As a consequence, cysteine molecules diffuse freely on the Au(111) surface and they can be regarded as a 2D molecular gas. The balance between molecule−molecule and molecule−substrate interactions induces molecular condensation and evaporation from the morphological surface structures (steps, reconstruction edges, etc.) as revealed by scanning tunnelling microscopy (STM) images. These processes lead progressively to the formation of a number of stable arrangements, not previously reported, such as single-molecular rows, trimers, and 2D islands. The condensation of these structures is driven by the aggregation of new molecules, stabilized by the formation of electrostatic interactions between adjacent NH3+ and COO− groups, together with adsorption at a slightly more favorable quasi-top site of the herringbone Au reconstruction.
Acceso Abierto
New results on thermal and photodesorption of CO ice using the novel InterStellar Astrochemistry Chamber (ISAC)
(EDP Science, 2010-11-09) Muñoz Caro, G. M.; Jiménez Escobar, A.; Martín Gago, J. A.; Rogero, Celia; Atienza, C.; Puertas, S.; Sobrado, J. M.; Torres Redondo, J.; Ministerio de Ciencia e Innovación (MICINN); Instituto Nacional de Técnica Aeroespacial (INTA)
Aims. We present the novel InterStellar Astrochemistry Chamber (ISAC), designed for studying solids (ice mantles, organics, and silicates) in interstellar and circumstellar environments: characterizing their physico-chemical properties and monitoring their evolution as caused by (i) vacuum-UV irradiation; (ii) cosmic ray irradiation; and (iii) thermal processing. Experimental study of thermal and photodesorption of the CO ice reported here simulates the freeze-out and desorption of CO on grains, providing new information on these processes. Methods. ISAC is an UHV set-up, with base pressure down to P = 2.5 × 10-11 mbar, where an ice layer is deposited at 7 K and can be UV-irradiated. The evolution of the solid sample was monitored by in situ transmittance FTIR spectroscopy, while the volatile species were monitored by QMS. Results. The UHV conditions of ISAC allow experiments under extremely clean conditions. Transmittance FTIR spectroscopy coupled to QMS proved to be ideal for in situ monitoring of ice processes that include radiation and thermal annealing. Thermal desorption of CO starting at 15 K, induced by the release of H2 from the CO ice, was observed. We measured the photodesorption yield of CO ice per incident photon at 7, 8, and 15 K, respectively yielding 6.4 ± 0.5 × 10-2, 5.4 ± 0.5 × 10-2, and 3.5 ± 0.5 × 10-2 CO molecules photon (7.3–10.5 eV)-1. Our value of the photodesorption yield of CO ice at 15 K is about one order of magnitude higher than the previous estimate. We confirmed that the photodesorption yield is constant during irradiation and independent of the ice thickness. Only below ~ 5 monolayers ice thickness the photodesorption rate decreases, which suggests that only the UV photons absorbed in the top 5 monolayers led to photodesorption. The measured CO photodesorption quantum yield at 7 K per absorbed photon in the top 5 monolayers is 3.4 molecules photon-1. Conclusions. Experimental values were used as input for a simple model of a quiescent cloud interior. Photodesorption seems to explain the observations of CO in the gas phase for densities below 3–7 × 104 cm-3. For the same density of a cloud, 3 × 104 cm-3, thermal desorption of CO is not triggered until T = 14.5 K. This has important implications for CO ice mantle build up in dark clouds.
Restringido
Silicon Surface Nanostructuring for Covalent Immobilization of Biomolecules
(ACS Publications, 2008-06-03) Rogero, Celia; Chaffey, Benjamin T.; Mateo Martí, Eva; Sobrado, J. M.; Horrocks, Benjamin R.; Houlton, Andrew; Lakey, Jeremy H.; Briones, C.; Martín Gago, J. A.; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia e Innovación (MICINN)
We present a straightforward strategy to control the average distance of immobilized biomolecules on silicon surfaces. We exploit the reaction taking place between the amino residues within the biomolecules (lysine groups of proteins or the N-terminus of oligomers of peptide nucleic acid, PNA) and the aldehyde-terminated groups presented in a mixed aldehyde/alkyl organic monolayer on a silicon surface. The mixed monolayers were prepared by a thermal reaction of hydrogen-terminated Si(111) with a mixture of undecene and undecenyl-aldehyde. We quantitatively evaluate the surface concentration of aldehyde in the monolayer by atomic force microscopy and an intensity analysis of core level X-ray photoemission spectroscopy peaks. These complementary techniques show that the surface density of the reactive terminal groups reflects the mole fraction of aldehyde in the reactive solution used to modify the silicon surface. The further immobilization of proteins or peptide nucleic acids on the monolayer shows that the density of biomolecules reproduces the aldehyde surface density, which indicates a specific covalent attachment and a negligible nonspecific adsorption. The proposed procedure makes possible to control the average distance of the immobilized active biomolecules on the silicon surface, which could be of great relevance for applications in the interdisciplinary field of biosensors.