Electrogeneración de películas ultradelgadas de melanina : nanoestructura, electrocatálisis, conductividad, magnetismo y fotorrespuesta

La tesis se centra en la electrogeneración de películas nanoestructuradas y ultradelgadas del biopolímero eumelanina sobre tres sustratos: Au(111), grafito HOPG y nanopartículas de Au. Se estudia su capacidad electrocatalítica, su fotorrespuesta y la existencia y caracterización de nanodominios magnéticos, así como su estabilidad y conductividad. Los resultados recogidos en la presente tesis doctoral se centran en la preparación por vía electroquímica de materiales electródicos de gran estabilidad, conductividad y con alta actividad electrocatalítica, a partir de la inmovilización de moléculas bioactivas de eumelanina sintética. En este contexto se han desarrollado los siguientes estudios: 1. La electroformación de bio-películas ultradelgadas y nanoestructuradas de melanina sobre diversos sustratos conductores y semiconductores. 2. La determinación y caracterización de la morfología, composición química y propiedades físico-químicas de tales películas así como de sus propiedades eléctricas y magnéticas. 3. La evaluación de su actividad electroquímica y electrocatalítica frente a reacciones rédox de interés bioquímico. 4. Generación de fotocorriente en películas de melanina sobre Au(111). Dichas experiencias se han llevado a cabo mediante la combinación de un vasto conjunto de técnicas que incluyen la microscopía de efecto túnel (STM), microscopía de fuerzas atómicas (AFM), microscopía de fuerzas magnéticas (MFM), las técnicas electroquímicas convencionales y las espectroscopías Auger (AES), difracción de rayos X (XRD), de dispersión de energía de rayos X (EDX), foto-electrónica de rayos X (XPS) y de absorción de rayos X (XANES y EXAFS).

Nanofabrication and electrochemical characterization of self-assembled monolayers sandwiched between metal nanoparticles and electrode surfaces

et al.Nanoscience and nanotechnology have reached the syllabi of many upper-division undergraduate and master-level courses all over the world. There is therefore a growing need for practical exercises that illustrate the fabrication, characterization, properties, and applications of nanomaterials. Here we describe an advanced-level laboratory experiment in which students had the opportunity to fabricate surfaces modified by ordered monolayers and nanostructured materials. The surface modification was quantified by means of a quartz crystal microbalance, while the electrochemical properties of the nanoarchitectures were assessed using cyclic voltammetry experiments. Electron transfer across self-assembled monolayers mediated by gold nanoparticles was presented as a topic for discussion, and consideration of potential practical applications of the observed phenomena (catalytic and electrocatalytic processes, as well as development of optical, (opto)electronic, and photovoltaic devices with enhanced properties) was proposed as a further reading exercise.Financial support from the Department of Physical Chemistry and DGA/Fondos Feder is acknowledge as well as CTQ2012-33198 and CTQ2013-50187-EXP grants.Peer Reviewe

Design and synthesis of Aviram-Ratner-type dyads and rectification studies in Langmuir-Blodgett (LB) films

The design and synthesis of Aviram–Ratner-type molecular rectifiers, featuring an anilino-substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ-spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X-ray analysis. The photophysical properties of the TTF-BCO-exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir–Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current–voltage (I–V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I–V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.This work was supported by the ERC Advanced grant no.246637 (“OPTELOMAC”) and the Swiss National Science Foundation (SNF). A.D.F.acknowledges the NSF-IRFP (USA) for a postdoctoral fellowship. S.M. and P.C. are grateful for financial assistance from Ministerio de Ciencia e Innovación from Spainin the framework of grants CTQ2012-33198 and CTQ2013-50187-EXP.Peer Reviewe

Electrocatalytic and Magnetic Properties of Ultrathin Nanostructured Iron–Melanin Films on Au(111)

We have prepared ultrathin, nanostructured melanin films on Au- ACHTUNGTRENUNG(111) by means of electrochemical selfassembly. These films were characterized by using Auger electron spectroscopy, X-ray absorption near-edge structure spectroscopy, scanning tunneling microscopy, magnetic force microscopy, and electrochemical techniques. Two types of nanostructures are present in the film: melanin nanoparticles and Fe3O4 nanoparticles. The melanin nanoparticles contain Fe bonded to oxygen-containing phenolic groups in an octahedral configuration similar to that found in Fe2O3. The inorganic– organic composite exhibits magnetic properties and catalyzes the electroreduction of hydrogen peroxide in alkaline and neutral electrolyte solutions. The electrocatalytic activity depends on the Fe-bound melanin and appears to be similar to that found for Fe–porphyrins.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Towards molecular electronic devices based on 'all-carbon' wires

Nascent molecular electronic devices based on linear ‘all-carbon’ wires attached to gold electrodes through robust and reliable C–Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me3Si–(C[triple bond, length as m-dash]C)4–SiMe3 (1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CSiMe3 (Au|C8SiMe3). In the second stage, treatment of Au|C8SiMe3 with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH (Au|C8H). The reactive terminal C[triple bond, length as m-dash]C–H moiety in Au|C8H can be modified by ‘click’ reactions with (azidomethyl)ferrocene (N3CH2Fc) to introduce a redox probe, to give Au|C6C2N3HCH2Fc. Alternatively, incubation of the modified gold substrate supported monolayer Au|C8H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon–Au σ-bond, to give structures Au|C8|GNP in which the monolayer of linear, ‘all-carbon’ C8 chains is sandwiched between two macroscopic gold contacts. The covalent carbon–surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C–H bond is confirmed by surface-enhanced Raman scattering (SERS). The integrity of the carbon chain in both Au|C6C2N3HCH2Fc systems and after formation of the gold top-contact electrode in Au|C8|GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal–monolayer–metal devices Au|C8|GNP featuring ‘all-carbon’ molecular wires were characterised by sigmoidal I–V curves, indicative of well-behaved junctions free of short circuits

Decreased salivary lactoferrin levels are specific to Alzheimer's disease

Background: Evidences of infectious pathogens in Alzheimer's disease (AD) brains may suggest a deteriorated innate immune system in AD pathophysiology. We previously demonstrated reduced salivary lactoferrin (Lf) levels, one of the major antimicrobial proteins, in AD patients. Methods: To assess the clinical utility of salivary Lf for AD diagnosis, we examine the relationship between salivary Lf and cerebral amyloid-beta (A beta) load using amyloid-Positron-Emission Tomography (PET) neuroimaging, in two different cross-sectional cohorts including patients with different neurodegenerative disorders. Findings: The diagnostic performance of salivary Lf in the cohort 1 had an area under the curve [AUC] of 0.95 (0.911-0.992) for the differentiation of the prodromal AD/AD group positive for amyloid-PET (PET+) versus healthy group, and 0.97 (0.924-1) versus the frontotemporal dementia (FTD) group. In the cohort 2, salivary Lf had also an excellent diagnostic performance in the health control group versus prodromal AD comparison: AUC 0.93 (0.876-0.989). Salivary Lf detected prodromal AD and AD dementia distinguishing them from FTD with over 87% sensitivity and 91% specificity. Interpretation: Salivary Lf seems to have a very good diagnostic performance to detect AD. Our findings support the possible utility of salivary Lf as a new non-invasive and cost-effective AD biomarker.This study was supported by Dr. Carro grants from Instituto de Salud Carlos III (FIS15/00780, FIS18/00118), FEDER, Comunidad de Madrid (S2017/BMD-3700; NEUROMETAB-CM), and CIBERNED (PI2016/01). This study was also supported by research grants from the Spanish Ministry of Economy and Competitiveness (SAF201785310-R to Dr. Cantero, PSI2017-85311-P to Dr. Atienza); International Centre on ageing CENIE-POCTEP (0348_CIE_6_E to Dr. Atienza); and CIBERNED (CB06/05/1111 to Dr. Cantero). Dr. Bueno receives research funding from the Instituto de Salud Carlos III, Spain (PIE16/00021, PI17/01799). The H2H-Spain Study was supported in Spain by grant PIE16/00021 from Instituto Carlos III, Ministry of Science, Innovation and Universities, and additional funds from the Centro Nacional de Investigaciones Cardiovasculares (CNIC). The CNIC is supported by the Ministry of Economy, Industry and Competitiveness and the Pro CNIC Foundation, and is a Severo Ochoa Centre of Excellence (SEV-2015-0505). The funders had no role in the conceptualisation, study design, data collection analysis and preparation of this manuscript

Electrocatalytic and Magnetic Properties of Ultrathin Nanostructured Iron–Melanin Films on Au(111)

We have prepared ultrathin, nanostructured melanin films on Au- ACHTUNGTRENUNG(111) by means of electrochemical selfassembly. These films were characterized by using Auger electron spectroscopy, X-ray absorption near-edge structure spectroscopy, scanning tunneling microscopy, magnetic force microscopy, and electrochemical techniques. Two types of nanostructures are present in the film: melanin nanoparticles and Fe3O4 nanoparticles. The melanin nanoparticles contain Fe bonded to oxygen-containing phenolic groups in an octahedral configuration similar to that found in Fe2O3. The inorganic– organic composite exhibits magnetic properties and catalyzes the electroreduction of hydrogen peroxide in alkaline and neutral electrolyte solutions. The electrocatalytic activity depends on the Fe-bound melanin and appears to be similar to that found for Fe–porphyrins.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electrografting of 4-Nitrobenzenediazonium Salts on Al-7075 Alloy Surfaces—The Role of Intermetallic Particles

In this work, the electrografting of Al-7075 aluminium alloy substrates with 4-nitrobenzenediazonium salt (4-NBD) films was studied on a complex aluminium alloy surface. Prior to the electrografting reaction, the substrates were submitted to different surface treatments to modify the native aluminium oxide layer and unveil intermetallic particles (IMPs). The formation of the 4-NBD films could be correlated with the passive film state and the distribution of IMPs. The corresponding electrografting reaction was performed by cyclic voltammetry which allowed the simultaneous analysis of the redox reaction by a number of complementary surface-analytical techniques. Spatially resolved thin film analysis was performed by means of SEM-EDX, AFM, PM-IRRAS, Raman spectroscopy, XPS, and SKPFM. The collected data show that the 4-NBD film is preferentially formed either on the Al oxide layer or the IMP surface depending on the applied potential range. Potentials between −0.1 and −1.0 VAg/AgCl mostly generated nitrophenylene films on the oxide covered aluminium, while grafting between −0.1 and −0.4 VAg/AgCl favours the growth of these films on IMPs

Towards molecular electronic devices based on ‘all-carbon’ wires

Resumen del trabajo presentado a la Conferencia bienal Fuerzas y Túnel, celebrada en Jaca (España) del 27 al 29 de junio de 2018.The realisation of molecular-scale electronic devices requires the development of suitable molecular components that can perform a range of electronic functions, possibly combined into larger, more highly functional molecular assemblies, and ultimately connected to a macroscopic support to allow integration into a solid-state platform. Of the various components needed to form a ‘molecular electronics component kit’ for fabrication of functional devices, molecular wires are regarded as the most fundamental. Molecular wires typically feature a rigid linear molecular backbone, and pi-conjugated electronic structures that can facilitate electron transport. Of the various pi-conjugated molecules that can be conceived to serve as molecular wires, linear chains of sp-hybridised carbon with polyynyl (-C=C-C=C-) structures have attracted considerable attention since they offer an approximately cylindrical distribution of electron density along a one-dimensional, rigid-rod and length-persistent backbone. Here, nascent molecular electronic devices based on linear ‘all-carbon’ wires attached to gold electrodes through robust and reliable C-Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me3Si-(C=C)4-SiMe3. Firstly, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|C8SiMe3. Secondly, treatment of Au|C8SiMe3 with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer, Au|C8H. The reactive terminal C=C-H moiety in Au|C8H can be modified by ‘click’ reactions to introduce a redox probe or alternatively can be incubated in a solution of gold nanoparticles (GNPs), resulting in covalent attachment of GNPs on top of the film via a second alkynyl carbon–Au o-bond, to give structures Au|C8|GNP in which the monolayer of linear, ‘all-carbon’ C8 chains is sandwiched between two macroscopic gold contacts. The electrical properties of these nascent metal-monolayer-metal devices Au|C8|GNP featuring ‘all-carbon’ molecular wires are determined by recording I–V curves. This sequential desilylation strategy allows the simple fabrication of sandwich-like device structures of uncapped carbon chains, opening new avenues their wider exploration and exploitation in molecular electronics.Peer reviewe

All-Carbon molecular electronic devices

Resumen del trabajo presentado al 2nd ELECMI International Workshop, celebrado en Zaragoza (España) del 11 al 13 de junio de 2018.Peer Reviewe