Efecte filtre d'espín en complexos de Fe

En aquest article es presenta un efecte filtre d'espín d'àmbit unimolecular sota condicions de corrent polaritzat. En ell demostrem com en capturar una molècula d'un complex thermal spin-crossover de Fe entre dos elèctrodes, quan un d'ells és o bé a o bé b polaritzat, el darrer cas presenta una conductància com a mínim cent vegades superior respecte al primer. Aquesta és la primera vegada que s'ha pogut estudiar experimentalment un fenomen de filtratge d'espín a temperatura ambient.In this article a single-molecule spin-filter effect under polarized current conditions is presented. We demonstrate that, on capturing a molecule with a Fe thermal spin-crossover complex between two electrodes, when one of these is either a or b polarized, the b polarized electrode is at least one hundred times more conductive than the a electrode. This is the first time that it has been possible to study a spin-filter phenomenon at room temperature conditions

Efecte filtre d'espín en complexos de Fe

Resum: En aquest article es presenta un efecte filtre d'espín d'àmbit unimolecular sota condicions de corrent polaritzat. En ell demostrem com en capturar una molècula d'un complex thermal spin-crossover de Fe entre dos elèctrodes, quan un d'ells és o bé a o bé b polaritzat, el darrer cas presenta una conductància com a mínim cent vegades superior respecte al primer. Aquesta és la primera vegada que s'ha pogut estudiar experimentalment un fenomen de filtratge d'espín a temperatura ambient

Hunger and sustainability

This paper examines the problem of world hunger and discusses potential solutions to it. It reflects on the debate about whether transgenic foods should be used, which is more of a social controversy than a scientific one. Sustainability is considered a key driver for innovation that can be used as a basis for assessing the problem of hunger in the world, and the question is inseparable from its ethical aspects. Given that economic growth does not directly equate to human development, this paper states that it is necessary to address the problem of poverty and hunger from the capacity development framework according to human rights. Poverty causes disability by limiting human development; it creates the conditions for the violation of human rights; therefore, an institutional framework and social initiatives aimed at protecting the poor should be established. Finally, the main lines of research in the field of biotechnology are outlined, such as the development of genetically modified organisms and the need to continue defining methods, based on the development of capabilities. Such capabilities should be embedded in educational programmes, to establish guidelines that are incorporated into curricula as transversal orientations to be able to make sustainability a social reality

Charge transport at the protein-electrode interface in the emerging field of biomolecular electronics

The emerging field of BioMolecular Electronics aims to unveil the charge transport characteristics of biomolecules with two primary outcomes envisioned. The first is to use nature's efficient charge transport mechanisms as an inspiration to build the next generation of hybrid bioelectronic devices towards a more sustainable, biocompatible and efficient technology. The second is to understand this ubiquitous physicochemical process in life, exploited in many fundamental biological processes such as cell signalling, respiration, photosynthesis or enzymatic catalysis, leading us to a better understanding of disease mechanisms connected to charge diffusion. Extracting electrical signatures from a protein requires optimised methods for tethering the molecules to an electrode surface, where it is advantageous to have precise electrochemical control over the energy levels of the hybrid protein-electrode interface. Here, we review recent progress towards understanding the charge transport mechanisms through protein-electrode-protein junctions, which has led to the rapid development of the new BioMolecular Electronics field. The field has brought a new vision into the molecular electronics realm, wherein complex supramolecular structures such as proteins can efficiently transport charge over long distances when placed in a hybrid bioelectronic device. Such anomalous long-range charge transport mechanisms acutely depend on specific chemical modifications of the supramolecular protein structure and on the precisely engineered protein-electrode chemical interactions. Key areas to explore in more detail are parameters such as protein stiffness (dynamics) and intrinsic electrostatic charge and how these influence the transport pathways and mechanisms in such hybrid devices

Tuning Single-Molecule Conductance by Controlled Electric Field-Induced trans-to-cis Isomerisation

External electric fields (EEFs) have proven to be very efficient in catalysing chemical reactions, even those inaccessible via wet-chemical synthesis. At the single-molecule level, oriented EEFs have been successfully used to promote in situ single-molecule reactions in the absence of chemical catalysts. Here, we elucidate the effect of an EEFs on the structure and conductance of a molecular junction. Employing scanning tunnelling microscopy break junction (STM-BJ) experiments, we form and electrically characterize single-molecule junctions of two tetramethyl carotene isomers. Two discrete conductance signatures show up more prominently at low and high applied voltages which are univocally ascribed to the trans and cis isomers of the carotenoid, respectively. The difference in conductance between both cis-/trans- isomers is in concordance with previous predictions considering pi-quantum interference due to the presence of a single gauche defect in the trans isomer. Electronic structure calculations suggest that the electric field polarizes the molecule and mixes the excited states. The mixed states have a (spectroscopically) allowed transition and, therefore, can both promote the cis-isomerization of the molecule and participate in electron transport. Our work opens new routes for the in situ control of isomerisation reactions in single-molecule contacts

Metal-Controlled Magnetoresistance at Room Temperature in Single-Molecule Devices

The appropriate choice of the transition metal complex and metal surface electronic structure opens the possibility to control the spin of the charge carriers through the resulting hybrid molecule/metal spinterface in a single molecule electrical contact at room temperature. The single molecule conductance of a Au/molecule/Ni junction can be switched by flipping the magnetization direction of the ferromagnetic electrode. The requirements of the molecule include not just the presence of unpaired electrons: the electronic configuration of the metal center has to provide occupied or empty orbitals that strongly interact with the junction metal electrodes and that are close in energy to their Fermi levels for one of the electronic spins only. The key ingredient for the metal surface is to provide an efficient spin texture induced by the spin orbit coupling in the topological surface states that results in an efficient spin-dependent interaction with the orbitals of the molecule. The strong magnetoresistance effect found in this kind of single-molecule wire opens a new approach for the design of room-temperature nanoscale devices based on spin-polarized currents controlled at molecular level

Electrostatic Catalysis of a Click Reaction in a Microfluidic Cell

Electric fields have been highlighted as a smart reagent in nature's enzymatic machinery, as they can directly trigger or accelerate redox and/or non-redox chemical processes with stereo- and regio-specificity. In natural catalysis, controlled mass transport of chemical species in confined spaces is also key in facilitating the transport of reactants into the active reaction site. Despite the opportunities the above offers in developing strategies for a new, clean electrostatic catalysis exploiting oriented electric fields, research in this area has been mostly limited to theoretical and experimental studies at the level of single molecules or small molecular ensembles, where both the control over mass transport and scalability cannot be tested. Here, we quantify the electrostatic catalysis of a prototypical Huisgen cycloaddition in a large-area electrode surface and directly compare its performance to the traditional Cu(I)-catalyzed method of the same reaction. Mass diffusion control is achieved in a custom-built microfluidic cell, which enhances reagent transport towards the electrified reactive interface while avoiding both turbulent flow conditions and poor control of the convective mass transport. This unprecedented electrostatic continuous-flow microfluidic reactor is an example of an electric-field driven platform where clean large-scale electrostatic catalytic processes can be efficiently implemented and regulated.Comment: Main Manuscript part includes 12 pages, 4 figures, 1 table and Supporting Information part includes 20 pages, 8 figures, 1 tabl

Evaluation of Minimal Residual Disease by Real-Time Quantitative PCR of Wilms’ Tumor 1 Expression in Patients with Acute Myelogenous Leukemia after Allogeneic Stem Cell Transplantation: Correlation with Flow Cytometry and Chimerism

Relapse remains the main cause of treatment failure in patients with acute myelogeous leukemia (AML) after allogeneic hemopoietic stem cell transplantation (SCT). The Wilms’ tumor 1 gene (WT1) is reportedly overexpressed in >90% of patients with AML and thus can be useful for minimal residual disease (MRD) monitoring. The aim of this study was to evaluate the usefulness of WT1 expression as a relapse predictor marker in patients with AML after SCT and compare it with flow cytometry (FC) and chimerism studies. WT1 expression was assessed retrospectively using quantitative RT-PCR in bone marrow and peripheral blood from 21 patients. Patients were classified according to WT1 dynamics posttransplantation. Eleven of the 21 patients had low and stable WT1 levels. All of these 11 patients showed complete chimerism and negative MRD by FC and remained in complete remission with a median follow-up of 27 months (range, 18-98 months). In contrast, 10 of 21 patients showed WT1 overexpression after SCT, and 9 of these 10 patients relapsed. The incidence of relapse differed significantly between the 2 groups of patients according to WT1 expression post-SCT (P = .00003). Relapse in the 9 patients occurred at a median of 314 days (range, 50-560 days). Interestingly, in these patients, relapse was first predicted by WT1 (with negative FC and complete chimerism) in 7 patients. WT1 overexpression was correlated with disease burden in patients with AML before and after allogeneic SCT. In patients who relapsed, both medullary and extramedullary relapse were better anticipated by WT1 overexpression compared with FC and chimerism

Tuning Single-Molecule Conductance in Metalloporphyrin-Based Wires via Supramolecular Interactions.

Nature has developed amazing supramolecular constructs to deliver outstanding charge transport capabilities using metalloporphyrin-based supramolecular stacks.1 Here we are incorporating simple, naturally inspired supramolecular interactions via the axial complexation of metalloporphyrins into the formation of a single-molecule wire in a nanoscale gap to dissect the resulting electron pathways through the final chemical adduct. We observe that small structural changes in the axial coordinating linkers result in dramatic changes in the transport properties through the metalloporphyrin-based wire. The increased flexibility of a pyridine-4-yl-methanethiol ligand due to an extra methyl group as compared to a more rigid mercaptopyridine linker allows the former to adopt an unexpected highly conductive stacked structure between the two junction electrodes and the metalloporphyrin ring. DFT calculations reveal a molecular junction structure composed of a shifted stack of the three molecular backbones; the two pyridine ligands sandwiching the metalloporphyrin ring, which is stabilized by a combination of the porphyrin metal center coordinating the pyridinic N and the pyridine/porphyrin overlapping. Contrarily, the more rigid 4-mercaptopyridine ligand presents a more expected octahedral coordination of the metalloporphyrin metal center, leading to much lower conductance. Furthermore, we show that a mechanical forced imposed along the molecular wire axis results in a variety of more extended supramolecular structures between the pyridine linkers and the porphyrin ring spanning the tunneling gap and scoring relatively high conductance values. This works sets an example of the use of supramolecular chemistry in the construction of efficient molecular conduits towards the development of supramolecular electronics, a concept already exploited in natural organisms