Nanotube-Like Electronic States in [5,5]-C90 Fullertube Molecules.

Fullertubes, that is, fullerenes consisting of a carbon nanotube moiety capped by hemifullerene ends, are emerging carbon nanomaterials whose properties show both fullerene and carbon nanotube (CNT) traits. Albeit it may be expected that their electronic states show a certain resemblance to those of the extended nanotube, such a correlation has not yet been found or described. Here it shows a scanning tunneling microscopy (STM) and spectroscopy (STS) characterization of the adsorption, self-assembly, and electronic structure of 2D arrays of [5,5]-C90 fullertube molecules on two different noble metal surfaces, Ag(111) and Au(111). The results demonstrate that the shape of the molecular orbitals of the adsorbed fullertubes corresponds closely to those expected for isolated species on the grounds of density functional theory calculations. Moreover, a comparison between the electronic density profiles in the bands of the extended [5,5]-CNT and in the molecules reveals that some of the frontier orbitals of the fullertube molecules can be described as the result of the quantum confinement imposed by the hemifullerene caps to the delocalized band states in the extended CNT. The results thus provide a conceptual framework for the rational design of custom fullertube molecules and can potentially become a cornerstone in the understanding of these new carbon nanoforms.

Selectively Addressing Plasmonic Modes and Excitonic States in a Nanocavity Hosting a Quantum Emitter.

Controlling the interaction between the excitonic states of a quantum emitter and the plasmonic modes of a nanocavity is key for the development of quantum information processing devices. In this Letter we demonstrate that the tunnel electroluminescence of electrically insulated C60 nanocrystals enclosed in the plasmonic nanocavity at the junction of a scanning tunneling microscope can be switched from a broad emission spectrum, revealing the plasmonic modes of the cavity, to a narrow band emission, displaying only the excitonic states of the C60 molecules by changing the bias voltage applied to the junction. Interestingly, excitonic emission dominates the spectra in the high-voltage region in which the simultaneously acquired inelastic rate is low, demonstrating that the excitons cannot be created by an inelastic tunnel process. These results point toward new possible mechanisms for tunnel electroluminescence of quantum emitters and offer new avenues to develop electrically tunable nanoscale light sources.

Electronic Temperature and Two-Electron Processes in Overbias Plasmonic Emission from Tunnel Junctions.

The accurate determination of electronic temperatures in metallic nanostructures is essential for many technological applications, like plasmon-enhanced catalysis or lithographic nanofabrication procedures. In this Letter, we demonstrate that the electronic temperature can be accurately measured by the shape of the tunnel electroluminescence emission edge in tunnel plasmonic nanocavities, which follows a universal thermal distribution with the bias voltage as the chemical potential of the photon population. A significant deviation between electronic and lattice temperatures is found below 30 K for tunnel currents larger than 15 nA. This deviation is rationalized as the result of a two-electron process in which the second electron excites plasmon modes with an energy distribution that reflects the higher temperature following the first tunneling event. These results dispel a long-standing controversy on the nature of overbias emission in tunnel junctions and adds a new method for the determination of electronic temperatures and quasiparticle dynamics.

Effect of 8-week of dietary micronutrient supplementation on gene expression in elite handball athletes.

PURPOSE: A study was made of the changes in gene expression in elite handball athletes, comparing gene modulation before, after and in the absence of an 8-week nutritional intervention with multivitamin/mineral supplements. METHODS: Thirteen elite handball athletes (aged 22.9 ± 2.7 years) and 13 sedentary controls (aged 20.9 ± 2.8 years) were included. Three timepoints were established: T0 (baseline conditions); T8 (after 8 weeks of supplementation with a multivitamin/mineral complex); and T16 (after 8 weeks in the absence of supplementation). The expressions of a total 112 of genes were evaluated by RT-qPCR analysis with the QuantStudioTM 12K Flex Real-Time PCR System. RESULTS: The analysis revealed different gene regulation profiles of genes implicated in cell communication, cell energy metabolism, inflammation and the immune system, oxidative stress and muscle function in athletes compared to sedentary controls under resting conditions (upregulated genes: effect size = large, ƞ2 = 1.011 to 1.398, p < 0.05; downregulated genes: effect size = large, ƞ2 = 0.846 and 1.070, p < 0.05, respectively). The nutritional intervention encouraged gene upregulation in elite athletes (p < 0.05). In a follow-up investigation, the IRAK1, CD81, ITGB1, ACADS PDHA2 and GPX1 genes were downregulated in athletes, with a moderate main effect for time-by-group interaction (ηP2 = 0.099 to 0.133; p < 0.05). Additionally, nutritional genes such as MTHFR and THTPA revealed a moderate effect over all the timepoints and group interaction in the study (ηP2 = 0.070 to 0.092; p < 0.05). CONCLUSIONS: Elite handball athletes showed a different expression profile in reference to key genes implicated in several sports performance-related functions compared to the sedentary controls, in addition to modulation of gene expression after multivitamin/mineral supplementation.

Unveiling the radiative local density of optical states of a plasmonic nanocavity by STM.

Atomically-sharp tips in close proximity of metal surfaces create plasmonic nanocavities supporting both radiative (bright) and non-radiative (dark) localized surface plasmon modes. Disentangling their respective contributions to the total density of optical states remains a challenge. Electroluminescence due to tunnelling through the tip-substrate gap could allow the identification of the radiative component, but this information is inherently convoluted with that of the electronic structure of the system. In this work, we present a fully experimental procedure to eliminate the electronic-structure factors from the scanning tunnelling microscope luminescence spectra by confronting them with spectroscopic information extracted from elastic current measurements. Comparison against electromagnetic calculations demonstrates that this procedure allows the characterization of the meV shifts experienced by the nanocavity plasmonic modes under atomic-scale gap size changes. Therefore, the method gives access to the frequency-dependent radiative Purcell enhancement that a microscopic light emitter would undergo when placed at such nanocavity.

Prevalence of non-aromatic carbonaceous molecules in the inner regions of circumstellar envelopes.

Evolved stars are a foundry of chemical complexity, gas and dust that provides the building blocks of planets and life, and dust nucleation first occurs in their photosphere. Despite their importance, the circumstellar regions enveloping these stars remain hidden to many observations, thus dust formation processes are still poorly understood. Laboratory astrophysics provides complementary routes to unveil these chemical processes, but most experiments rely on combustion or plasma decomposition of molecular precursors under physical conditions far removed from those in space. We have built an ultra-high vacuum machine combining atomic gas aggregation with advanced in-situ characterization techniques to reproduce and characterize the bottom-up dust formation process. We show that carbonaceous dust analogues formed from low-pressure gas-phase condensation of C atoms in a hydrogen atmosphere, in a C/H2 ratio similar to that reported for evolved stars, leads to the formation of amorphous C nanograins and aliphatic C-clusters. Aromatic species or fullerenes do not form effectively under these conditions, raising implications for the revision of the chemical mechanisms taking place in circumstellar envelopes.

A Comparative Computational Study of the Adsorption of TCNQ and F4-TCNQ on the Coinage Metal Surfaces.

The adsorption of tetracyanoquinodimethane and of the closely related derivative tetrafluorotetracyanoquinodimethane on the (111) surfaces of the coinage metals, namely, copper, silver, and (unreconstructed) gold, has been studied by dispersion-corrected ab initio density functional theory calculations. In order to separate the molecule-substrate interaction from the effects of molecule-molecule interaction, only the isolated molecules are considered. The results show that, in this case, the strength of the interaction of both molecules with the surfaces decreases in the expected order Cu > Ag > Au. The total amount of charge transfer, however, behaves in a different way, being larger for Ag and smaller for Cu and Au. This trend can be explained by a combination of the differences in the work functions of the three metals and the amount of backdonation between the molecule and the metal.

Characterizing the CdSe nanodots in the vicinity of the monolayer covering range.

During the past decade, due to their large number of technological applications, a large number of research studies have been devoted to CdSe nanocrystal (NC) systems. Most of the studies of NC grown on substrates present in the literature correspond to a submonolayer coverage. However, interparticle interactions and, consequently, system morphology and its properties can change at higher coverage regime. We combine the X-ray diffraction technique at wide and small angle range with direct space AFM microscopy for the morphological characterization of samples in the monolayer vicinity. We conclude that the CdSe preserves its nanoparticle character and its pyramid shape. This nanoparticle character is also reflected in the CdSe Density Of States (DOS) measured by UPS. We have shown that the particle CdSe atoms are perfectly ordered. They form nanocrystals with a wurtzite structure, grown with an axial and lateral matching with the HOPG substrate lattice in a hexagonal arrangement up to the monolayer coverage, with a strong interaction with the substrate. Above the monolayer coverage this epitaxial match is looser, resulting in a 3D disorder growth.

Long-Range Orientational Self-Assembly, Spatially Controlled Deprotonation, and Off-Centered Metalation of an Expanded Porphyrin.

Expanded porphyrins are large-cavity macrocycles with enormous potential in coordination chemistry, anion sensing, photodynamic therapy, and optoelectronics. In the last two decades, the surface science community has assessed the physicochemical properties of tetrapyrrolic-like macrocycles. However, to date, the sublimation, self-assembly and atomistic insights of expanded porphyrins on surfaces have remained elusive. Here, we show the self-assembly on Au(111) of an expanded aza-porphyrin, namely, an "expanded hemiporphyrazine", through a unique growth mechanism based on long-range orientational self-assembly. Furthermore, a spatially controlled "writing" protocol on such self-assembled architecture is presented based on the STM tip-induced deprotonation of the inner protons of individual macrocycles. Finally, the capability of these surface-confined macrocycles to host lanthanide elements is assessed, introducing a novel off-centered coordination motif. The presented findings represent a milestone in the fields of porphyrinoid chemistry and surface science, revealing a great potential for novel surface patterning, opening new avenues for molecular level information storage, and boosting the emerging field of surface-confined coordination chemistry involving f-block elements.

Los ensayos clínicos en el plan de estudio de Medicina en Cuba / Clinical Trials in the Cuban Medicine's Study Program

Introducción: La calidad en la atención que se brinda a los ensayos clínicos, es un aspecto de impostergable importancia en la formación de los médicos. Objetivo: Analizar la presencia de los ensayos clínicos en los objetivos, habilidades y contenidos del Plan de Estudios de la Carrera de Medicina vigente en Cuba. Material y Métodos: Se realizó una investigación de evaluación curricular, estudio exploratorio con la técnica de análisis de contenidos en la que se utilizaron métodos de análisis documental, encuestas, descripción y triangulación de la información. Se analizaron los objetivos, habilidades, contenidos y su estructuración; se confrontaron el macro y el microcurrículo y se realizaron entrevistas a cinco expertos. Resultados: Se encontró presencia de los EC de manera implícita en 3 funciones y 54 asignaturas, de forma explícita solo en una disciplina y asignatura. Se evidenciaron dificultades en la operacionalización de las habilidades y la estructuración de contenidos y objetivos. Conclusiones: La temática de ensayos clínicos está presente en el perfil profesional y los objetivos terminales del médico general cubano de forma implícita, diversa y pertinente. Se propone replantear en un sistema la estructura de los contenidos de la investigación en la Carrera de Medicina y no los ensayos clínicos como algo independiente, el papel de la interdisciplinariedad y la enseñanza problémica. El predominio de la educación en el trabajo como forma de organización de la enseñanza en la Carrera de Medicina es una oportunidad para la familiarización de los estudiantes con los ensayos clínicos(AU)

Introduction: The quality provided to clinical trials, is an issue of huge importance in doctors' education. Objective: To verify the presence of the subject clinical trials(CT) in the Cuban Medicine Study Program. Materials and Methods: A curriculum evaluation research, exploratory study using the technique of document's content analysis, surveys, description and triangulation of information was performed. Objectives, skills, content and structure were analyzed; macro and micro curriculum were confronted and five experts were interviewed. Results: Presence of the CT was found implicitly in three functions and fifty-four subjects; explicitly only in a discipline and subject. Difficulties in skills operationalization and in content structuring and goals were evident. Conclusions: Clinical Trials are present in the professional profile and the final goals of the Cuban general physician in an implicit, diverse and relevant way. It is rethinking in a system; the structure's content research within the career and not the clinical trials as something independent, and also the interdisciplinary role and teaching's problematic. The predominance of education on the Job as a form of organization of medicine teaching in the career is an opportunity for students to contact with clinical trials(AU)

Los ensayos clínicos en el plan de estudio de Medicina en Cuba / Clinical Trials in the Cuban Medicine's Study Program

Introducción: La calidad en la atención que se brinda a los ensayos clínicos, es un aspecto de impostergable importancia en la formación de los médicos. Objetivo: Analizar la presencia de los ensayos clínicos en los objetivos, habilidades y contenidos del Plan de Estudios de la Carrera de Medicina vigente en Cuba. Material y Métodos: Se realizó una investigación de evaluación curricular, estudio exploratorio con la técnica de análisis de contenidos en la que se utilizaron métodos de análisis documental, encuestas, descripción y triangulación de la información. Se analizaron los objetivos, habilidades, contenidos y su estructuración; se confrontaron el macro y el microcurrículo y se realizaron entrevistas a cinco expertos. Resultados: Se encontró presencia de los EC de manera implícita en 3 funciones y 54 asignaturas, de forma explícita solo en una disciplina y asignatura. Se evidenciaron dificultades en la operacionalización de las habilidades y la estructuración de contenidos y objetivos. Conclusiones: La temática de ensayos clínicos está presente en el perfil profesional y los objetivos terminales del médico general cubano de forma implícita, diversa y pertinente. Se propone replantear en un sistema la estructura de los contenidos de la investigación en la Carrera de Medicina y no los ensayos clínicos como algo independiente, el papel de la interdisciplinariedad y la enseñanza problémica. El predominio de la educación en el trabajo como forma de organización de la enseñanza en la Carrera de Medicina es una oportunidad para la familiarización de los estudiantes con los ensayos clínicos(AU)

Introduction: The quality provided to clinical trials, is an issue of huge importance in doctors' education.Objective: To verify the presence of the subject clinical trials (CT) in the Cuban Medicine Study Program. Materials and Methods: A curriculum evaluation research, exploratory study using the technique of document's content analysis, surveys, description and triangulation of information was performed. Objectives, skills, content and structure were analyzed; macro and micro curriculum were confronted and five experts were interviewed. Results: Presence of the CT was found implicitly in three functions and fifty-four subjects; explicitly only in a discipline and subject. Difficulties in skills operationalization and in content structuring and goals were evident.Conclusions: Clinical Trials are present in the professional profile and the final goals of the Cuban general physician in an implicit, diverse and relevant way. It is rethinking in a system; the structure's content research within the career and not the clinical trials as something independent, and also the interdisciplinary role and teaching's problematic. The predominance of education on the Job as a form of organization of medicine teaching in the career is an opportunity for students to contact with clinical trials(AU)

Collective concerted motion in a molecular adlayer visualized through the surface diffusion of isolated vacancies.

We have measured STM movies to study the diffusion of individual vacancies in a self-assembled layer of a tetrathiafulvalene derivative (exTTF) on Au(111) at room temperature. The diffusion is anisotropic, being faster along the compact direction of the molecular lattice. A detailed analysis of the anisotropic displacement distribution of the single vacancies shows that the relative abundance of double jumps (that is, the collective motion of molecular dimers) with respect to single jumps is rather large, the number of double jumps being more than 20% of the diffusion events. We conjecture that the relative abundances of long jumps might be related to the strength of the intermolecular bonding and the misfit of the molecular overlayer with the substrate lattice.

Thermal selectivity of intermolecular versus intramolecular reactions on surfaces.

On-surface synthesis is a promising strategy for engineering heteroatomic covalent nanoarchitectures with prospects in electronics, optoelectronics and photovoltaics. Here we report the thermal tunability of reaction pathways of a molecular precursor in order to select intramolecular versus intermolecular reactions, yielding monomeric or polymeric phthalocyanine derivatives, respectively. Deposition of tetra-aza-porphyrin species bearing ethyl termini on Au(111) held at room temperature results in a close-packed assembly. Upon annealing from room temperature to 275 °C, the molecular precursors undergo a series of covalent reactions via their ethyl termini, giving rise to phthalocyanine tapes. However, deposition of the tetra-aza-porphyrin derivatives on Au(111) held at 300 °C results in the formation and self-assembly of monomeric phthalocyanines. A systematic scanning tunnelling microscopy study of reaction intermediates, combined with density functional calculations, suggests a [2+2] cycloaddition as responsible for the initial linkage between molecular precursors, whereas the monomeric reaction is rationalized as an electrocyclic ring closure.

Surface-Supported Robust 2D Lanthanide-Carboxylate Coordination Networks.

Lanthanide-based metal-organic compounds and architectures are promising systems for sensing, heterogeneous catalysis, photoluminescence, and magnetism. Herein, the fabrication of interfacial 2D lanthanide-carboxylate networks is introduced. This study combines low- and variable-temperature scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) experiments, and density functional theory (DFT) calculations addressing their design and electronic properties. The bonding of ditopic linear linkers to Gd centers on a Cu(111) surface gives rise to extended nanoporous grids, comprising mononuclear nodes featuring eightfold lateral coordination. XPS and DFT elucidate the nature of the bond, indicating ionic characteristics, which is also manifest in appreciable thermal stability. This study introduces a new generation of robust low-dimensional metallosupramolecular systems incorporating the functionalities of the f-block elements.

Temperature-controlled metal/ligand stoichiometric ratio in Ag-TCNE coordination networks.

The deposition of tetracyanoethylene (TCNE) on Ag(111), both at Room Temperature (RT, 300 K) and low temperatures (150 K), leads to the formation of coordination networks involving silver adatoms, as revealed by Variable-Temperature Scanning Tunneling Microscopy. Our results indicate that TCNE molecules etch away material from the step edges and possibly also from the terraces, which facilitates the formation of the observed coordination networks. Moreover, such process is temperature dependent, which allows for different stoichiometric ratios between Ag and TCNE just by adjusting the deposition temperature. X-ray Photoelectron Spectroscopy and Density Functional Theory calculations reveal that charge-transfer from the surface to the molecule and the concomitant geometrical distortions at both sides of the organic/inorganic interface might facilitate the extraction of silver atoms from the step-edges and, thus, its incorporation into the observed TCNE coordination networks.

Protective ligand shells for luminescent SiO2-coated alloyed semiconductor nanocrystals.

SiO2 encapsulation of alloyed CdSeZnS nanocrystals (NCs) shows differences in terms of optical properties and luminescence quantum yield, depending on the surface composition, size, and ligand content. In this work, emphasis has been placed on the fine control required to obtain luminescent SiO2 encapsulated NCs by studying the role of oleic acid (OA), stearic acid (SA), and dodecanethiol (DDT) ligands on the alloyed NCs. While the use of anchored DDT molecules is essential to preserve the optical properties, intercalated OA and SA play a critical role for SiO2 nucleation, as stated by (1)H NMR (including DOSY and NOESY) spectroscopy. These results emphasize the importance of surface chemistry in NCs; it is crucial to control their reactivity, and therefore their impact, in different applications, from optics to biomedicine.

An STM study of molecular exchange processes in organic thin film growth.

The growth of a fullerene derivative (PCBM) on top of a layer of a tetrathiafulvalene (TTF) derivative previously deposited on Au(111) has been studied by scanning tunneling microscopy (STM). The results show that the preferential interaction with the gold substrate induces the exchange of PCBM molecules with the exTTF monolayer, expelling exTTF molecules to the outer surface. This exchange process is forbidden when the thickness of the exTTF layer increases above the monolayer, and the larger surface energy of PCBM leads to the growth of 3D islands.

Cl-capped CdSe nanocrystals via in situ generation of chloride anions.

Halide ions cap and stabilize colloidal semiconductor nanocrystal (NC) surfaces allowing for NCs surface interactions that may improve the performance of NC thin film devices such as photo-detectors and/or solar cells. Current ways to introduce halide anions as ligands on surfaces of NCs produced by the hot injection method are based on post-synthetic treatments. In this work we explore the possibility to introduce Cl in the NC ligand shell in situ during the NCs synthesis. With this aim, the effect of 1,2-dichloroethane (DCE) in the synthesis of CdSe rod-like NCs produced under different Cd/Se precursor molar ratios has been studied. We report a double role of DCE depending on the Cd/Se precursor molar ratio (either under excess of cadmium or selenium precursor). According to mass spectrometry (ESI-TOF) and nuclear magnetic resonance ((1)H NMR), under excess of Se precursor (Se dissolved in trioctylphosphine, TOP) conditions at 265 °C ethane-1,2-diylbis(trioctylphosphonium)dichloride is released as a product of the reaction between DCE and TOP. According to XPS studies chlorine gets incorporated into the CdSe ligand shell, promoting re-shaping of rod-like NCs into pyramidal ones. In contrast, under excess Cd precursor (CdO) conditions, DCE reacts with the Cd complex releasing chlorine-containing non-active species which do not trigger NCs re-shaping. The amount of chlorine incorporated into the ligand shell can thus be controlled by properly tuning the Cd/Se precursor molar ratio.

Charge transfer-assisted self-limited decyanation reaction of TCNQ-type electron acceptors on Cu(100).

TCNQ derivatives adsorbed on a metal surface undergo a self-limited decyanation reaction that only affects two out of the four cyano groups in the molecule. Combined Scanning Tunneling Microscopy/X-ray Photoelectron Spectroscopy experiments and Density Functional Theory calculations relate the self-limiting behavior to the transfer of electrons from the metal to the molecule.

Onset of chiral adenine surface growth.

The structure and stability of adenine crystals and thin layers has been studied by using scanning tunneling microscopy, X-ray diffraction, and density functional theory calculations. We have found that adenine crystals can be grown in two phases that are energetically quasi-degenerate, the structure of which can be described as a pile-up of 2D adenine planes. In each plane, the structure can be described as an aggregation of adenine dimers. Under certain conditions, kinetic effects can favor the growth of the less stable phase. These results have been used to understand the growth of adenine thin films on gold under ultra-high vacuum conditions. We have found that the grown phase corresponds to the α-phase, which is composed of stacked prochiral planes. In this way, the adenine nanocrystals exhibit a surface that is enantiopure. These results could open new insight into the applications of adenine in biological, medical, and enantioselective or pharmaceutical fields.