Papers by Ismael Diez Perez
Nature, 2016
Traditional views have held that the ability to control reaction rates by means of an electrical ... more Traditional views have held that the ability to control reaction rates by means of an electrical potential gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields should affect the outcomes of a range of chemical reactions, regardless of whether a "redox" reaction is involved. 1-4 This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an electric field is aligned in such a way as to electrostatically stabilize these minor mesomeric forms, the degree of resonance increases, resulting in overall stabilization of the molecule or transition state. Thus, one should in principle be able to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field. However, to harness external electric fields for catalysis of chemical reactions, the orientation of the approaching reactants with respect to the field stimulus needs to be controlled. Herein we address this problem and provide the first experimental evidence that carbon-carbon bondforming is accelerated by an electric field. We have designed a surface model system to probe Diels-Alder chemical reactions and coupled this to a scanning tunnelling microscopy break-junction approach (STM-BJ). 5-7 The STM-BJ is an electrical measurement performed at the single-molecule level, and is perfectly suited to deliver an electrical field-stimulus across approaching reactants. We show a 5-fold increase in the frequency of single-molecule junction formation due to the reaction when the electrical field is present and aligned in the direction to favour electron flow from the dienophile to the diene. The experimental results are qualitatively consistent with those predicted by quantum-chemical calculations on a theoretical model of this system and herald a new approach to chemical catalysis.
The Journal of Physical Chemistry B, 2004
The oxidation and reduction processes of both polycrystalline tin and Sn(100) single crystals are... more The oxidation and reduction processes of both polycrystalline tin and Sn(100) single crystals are investigated in borate buffer solution of pH 7.5 using cyclic voltammetry and in-situ characterizations such as Raman scattering, potential modulated reflectance spectroscopy (PMRS), and ...
Chiral shape and enantioselective growth of colloidal particles of self-assembled meso-tetra(phen... more Chiral shape and enantioselective growth of colloidal particles of self-assembled meso-tetra(phenyl and 4-sulfonatophenyl)porphyrins ... Joaquim Crusats,b Josep Claret,b Ismael Díez-Pérez,b Zoubir El-Hachemi,a Héctor García-Ortega,a Raimon Rubires,a ...
The chemical nature and the electric properties of the passive film on iron have been extensively... more The chemical nature and the electric properties of the passive film on iron have been extensively studied in order to understand the surface processes related to the iron corrosion phenomenon. For this purpose, some electrochemical studies of the formation and dissolution of iron oxide films coupled with different in situ optical techniques 1,2,3 have been developed in the last decade, giving new information about the chemical nature of this oxide films in the different electrochemical potential regions. Most of these studies have been focused on the early stages of the iron oxide growth, which take place in the so-called active-passive potential region. At these potential range, a high anodic current is registered corresponding to an Fe(II) oxide/hydroxide growth which has been chemically well characterized by in situ Raman 1 . Despite this chemical information, the growth mechanism of the early stages of the iron oxide formation and the subsequent iron passivation at this potentia...
Nano Letters, 2014
Incorporating molecular switches as the active components in nanoscale electrical devices represe... more Incorporating molecular switches as the active components in nanoscale electrical devices represents a current challenge in molecular electronics. It demands key requirements that need to be simultaneously addressed including fast responses to external stimuli and stable attachment of the molecules to the electrodes while mimicking the operation of conventional electronic components. Here, we report a single-molecule switching device that responds electrically to optical and chemical stimuli. A light pointer or a chemical signal can rapidly and reversibly induce the isomerization of bifunctional spiropyran derivatives in the bulk reservoir and, consequently, switch the electrical conductivity of the single-molecule device between a low and a high level. The spiropyran derivatives employed are chemically functionalized such that they can respond in fast but practical time scales. The unique multistimuli response and the synthetic versatility to control the switching schemes of this single-molecule device suggest spiropyran derivatives as key candidates for molecular circuitry.
Electrochimica Acta, 2014
Understanding how charges move through and between biomolecules is a fundamental question that co... more Understanding how charges move through and between biomolecules is a fundamental question that constitutes the basis for many biological processes. On the other hand, it has potential applications in the design of sensors based on biomolecules and single molecule devices. In this review we introduce the study of the electron transfer (ET) process in biomolecules, providing an overview of the fundamental theory behind it and the different experimental approaches. The ET in proteins is introduced by reviewing a complete electronic characterization of a redox protein (azurin) using electrochemical scanning tunnelling microscopy (ECSTM). The ET process in DNA is overviewed and results from different experimental approaches are discussed. Finally, future directions in the study of the ET process in biomolecules are introduced as well as examples of possible technological applications. (J.M. Artés), [email protected] (P. Gorostiza).
Imaging & Microscopy, 2007
International Journal of Pharmaceutics, 2002
Since hydrophilic matrices were proposed for controlled drug delivery, many polymeric excipients ... more Since hydrophilic matrices were proposed for controlled drug delivery, many polymeric excipients have been studied in order to make drug release fit the desired profiles. It has been pointed out that lambda-carrageenan, a sulphated polymer from algae, can suitably control the release rate of basic drugs from hydrophilic matrices with no need for complex technological processes. In this work, we propose a method to monitor morphologically the interaction between lambda-carrageenan and dexchlorpheniramine maleate (D-CPM), in order to find out how the release profiles can be so easily controlled. To this end, solutions of both polymer and drug were prepared at very low concentration. Solutions were mixed and samples were taken every hour over a period of 20 h. The characterization technique employed, atomic force microscopy (AFM), provides a high resolution, allowing to show the three-dimensional morphology of the samples within the nanometric scale. The results demonstrate that lambda-carrageenan is able to nanoencapsulate spontaneously D-CPM molecules, which offers the possibility to easily control the release rate of the drug. This work has moreover demonstrated the suitability of AFM for the specific case of the on-time monitoring of interaction processes that happen in pharmaceutical systems.
Chemical Communications, 2003
Chiral shape and enantioselective growth of colloidal particles of self-assembled meso-tetra(phen... more Chiral shape and enantioselective growth of colloidal particles of self-assembled meso-tetra(phenyl and 4-sulfonatophenyl)porphyrins ... Joaquim Crusats,b Josep Claret,b Ismael Díez-Pérez,b Zoubir El-Hachemi,a Héctor García-Ortega,a Raimon Rubires,a ...
Nature Nanotechnology, 2011
Nature Nanotechnology, 2012
The electrocatalytic properties of nanoparticles depend on their size, shape and composition. The... more The electrocatalytic properties of nanoparticles depend on their size, shape and composition. These properties are typically probed by measuring the total electrocatalytic reaction current of a large number of nanoparticles, but this approach is time-consuming and can only measure the average catalytic activity of the nanoparticles under study. However, the identification of new catalysts requires the ability to rapidly measure the properties of nanoparticles synthesized under various conditions and, ideally, to measure the electrocatalytic activity of individual nanoparticles. Here, we show that a plasmonic-based electrochemical current-imaging technique can simultaneously image and quantify the electrocatalytic reactions of an array of 1.6 × 10(5) platinum nanoparticles printed on an electrode surface, which could facilitate high-throughput screening of the catalytic activities of nanoparticles. We also show that the approach can be used to image the electrocatalytic reaction current and measure the cyclic voltammograms of single nanoparticles.
Journal of Materials Chemistry A, 2014
ChemElectroChem, 2014
ABSTRACT We study the effect of thermal annealing conditions (up to 400 °C) and atmospheres (air,... more ABSTRACT We study the effect of thermal annealing conditions (up to 400 °C) and atmospheres (air, Arand O2) on a newly developed nanochannel tin-oxide structure. The nanochanneled structures were prepared by self-organized anodization of metallic tin. Thermal annealing conditions have a strong impact on the crystallinity and content of Sn2+ defects present in the structure, and thus have a strong influence on the photoresponse characteristics of the films. Photocurrent measurements show that films annealed at 200 °C in Ar atmosphere exhibit a band gap as low as 2.4 eV and a photoresponse in the visible range. This effect is ascribed to a large content of Sn2+ defects in the structure and the improved crystallinity of the films annealed at this temperature. On the contrary, the Sn2+ content is decreased when annealing at 400 °C under aerobic conditions, which correlates with a shift in the film band gap to 3.2 eV, closer to the reported value for pure SnO2 (3.6 eV).
Thin Solid Films, 2007
Short-time surface contact of highly diluted 1-monostearoylglycerol (1-MSG) aqueous solutions wit... more Short-time surface contact of highly diluted 1-monostearoylglycerol (1-MSG) aqueous solutions with highly oriented pyrolitic graphite results in the deposition of an epitaxial monolayer that can be detected by atomic force microscopy operating in tapping mode at the graphite–air interface. The monolayer obtained with the racemic mixture is then compared to that obtained with one of the pure enantiomers. The analogous
The Journal of Physical Chemistry C, 2009
Polycrystalline Cu 2 O layers have been selectively grown by electrochemical anodization of polyc... more Polycrystalline Cu 2 O layers have been selectively grown by electrochemical anodization of polycrystalline Cu electrodes in an alkaline medium (pH 12.85). Uniform layers with thicknesses around 100 nm have been obtained. Using electrochemical impedance spectroscopy, it was concluded that the Cu 2 O films behave as a p-type semiconductor. The Mott-Schottky plot gives a value for the flat band potential of U FB ) -255 mV vs silver/silver chloride electrode (SSC), an estimated carrier density N A ) 6.1 × 10 17 cm -3 , and the space charge layer width was calculated to be W SCL ) 9 nm at a band bending of 120 mV. The electronic structure of the Cu|Cu 2 O|electrolyte interface was for the first time probed by in situ electrochemical tunneling spectroscopy. The use of in situ electrochemical scanning tunneling microscopy allows us to directly observed the valence band edge and determine its position against the absolute energy scale to be E VB ) -4.9 eV. Finally, we constructed a quantitative electronic diagram of the Cu|Cu 2 O|electrolyte interface, where the positions of the valence and conduction band edges are depicted, as well as the edge of the previously reported electronic subband.
The Journal of Physical Chemistry C, 2012
The Journal of Physical Chemistry B, 2004
The oxidation and reduction processes of both polycrystalline tin and Sn(100) single crystals are... more The oxidation and reduction processes of both polycrystalline tin and Sn(100) single crystals are investigated in borate buffer solution of pH 7.5 using cyclic voltammetry and in-situ characterizations such as Raman scattering, potential modulated reflectance spectroscopy (PMRS), and ...
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Papers by Ismael Diez Perez