AuS and SH bond formation/breaking during the formation of alkanethiol SAMs on Au(111): A theoretical study

The bonding of propanethiol molecules on a Au(111) surface is investigated using period DFT calculations within the framework of our model for chemical bond breaking that was recently proposed. The S-H bond breaking and the Au-S bond formation are analyzed through the evolution of the density of states. The energetics confirms the complexity of the reaction emerging from the interthiol chain interaction. The formation of a self-assembled monolayer is explained through a two-step mechanism, S-H bond breaking and Au-S bond formation. The production of H2 is found to be more favorable than the formation of Au-H species. The bonding and antibonding electronic states of the S-H bond have been identified and their evolutions during the process of bond breaking carefully analyzed. The corresponding bonding and antibonding states for the C-S bond are practically not affected during this process, indicating that the bond is preserved. The s orbital of the hydrogen atom strongly interacts with the gold surface and finally a Au-H bond is formed.Fil: Tielens, Frederik. Sorbonne University. Campus Pierre Et Marie Curie; Francia. Centre National de la Recherche Scientifique; FranciaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Hydrogen evolution on a pseudomorphic Cu-layer on Ni(111) - a theoretical study

Hydrogen evolution on a monolayer of copper on Ni(1 1 1) has been investigated by a combination of density functional theory and a model developed in our own group. The lattice constant of nickel is only about 2.5% shorter than that of copper; therefore the nickel substrate has only a minor effect on the surface d band of the adsorbed copper. However, there is a strong chemical effect which enhances the interaction of hydrogen with the Cu/Ni(1 1 1) surface as compared to Cu(1 1 1). Consequently, the adlayer promises to be a cheap catalyst that is significantly better than pure copper.Fil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Quaino, Paola Monica. Ulm University; Alemania. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Hindelang, Peter F.. Ulm University; AlemaniaFil: Schmickler, Wolfgang. Ulm University; Alemani

A first principles study of the hydrogen reaction in alkaline media: OH effect

The effect of the electrolyte on the hydrogen electrode reaction (HER) has been investigated. As a starting point, we centered our studies on the Volmer reaction in alkaline media -H 2O+e -→H ad+OH -- on a Pt(111) surface. The adsorption process of the reaction intermediate H ad was investigated by quantum chemical calculations. Our analysis focused on the interaction of the OH and the H ad with the electronic bands of the metal electrode. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Fil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Arce, Mauricio Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Santos, Elizabeth del Carmen. Universidad Nacional de Córdoba; Argentina. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Schmickler, Wolfgang. Universitat Ulm; Alemani

Molecular dissociation in the presence of catalysts: Interpreting bond breaking as a quantum dynamical phase transition

In this work we show that molecular chemical bond formation and dissociation in the presence of the d-band of a metal catalyst can be described as a quantum dynamical phase transition (QDPT). This agrees with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non-Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H2, the bonding H2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d-band, which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move toward the band center, where they collapse into a pure metallic resonance and an almost isolated H orbital. This phenomenon constitutes a striking example of the non-trivial physics enabled when one deals with non-Hermitian Hamiltonian beyond the usual wide band approximation.Fil: Ruderman, Andres. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Dente, Axel Damián. Invap S. E.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Pastawski, Horacio Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Decoración de Au y Pt sobre los bordes de escalón de grafito pirolitico altamente orientado

En este trabajo se presentan los resultados del estudio de la caracterización electroquímica de las Decoraciones de Oro y Platino sobre Grafito Pirolitico Altamente Orientado (HOPG) como cátodos midiendo la actividad electrocatalítica con respecto a la reacción de desprendimiento de hidrógeno (RDH) en medio ácido. Se realizaron curvas corriente potencial (I vs V) obtenidas potenciostaticamente bajo atmósfera de nitrógeno en una solución de H2SO4. La morfología de los depósitos se evaluó ex situ mediante SEM (microscopio electrónico de barrido) Los resultados permiten evaluar que las nanoestructuras generada varían su forma debido a la topografía del HOPG y su potencial aplicación como materiales de electrodo para la generación electrolítica de hidrógeno en medio ácido.In this paper we present the results of the electrochemical characterization of gold and platinum decorations on Highly Oriented Pyrolytic Graphite (HOPG) as cathodes by measuring the electrocatalytic activity with respect to the hydrogen evolution reaction (RDH) in acid medium. Current curves were potential (I vs. V) obtained potentiostatically under nitrogen in a solution of H2SO4. The deposit morphology was assessed ex situ by SEM (scanning electron microscope) results to assess the generated nanoesctructuras vary its shape due to the topography of HOPG and their potential application as electrode materials for electrolytic hydrogen generation means acid.Fil: Fuentes, Ana Silvina. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Avalle, Lucia Bernardita. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santos, Elizabeth del Carmen. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Understanding the structure and reactivity of NiCu nanoparticles: An atomistic model

The structure of bimetallic NiCu nanoparticles (NP) is investigated as a function of their composition and size by means of Lattice MonteCarlo (LMC) and molecular dynamics (MD) simulations. According to our results, copper segregation takes place at any composition of the particles. We found that this feature is not size-dependent. In contrast, nickel segregation depends on the NP size. When the size increases, Ni atoms tend to remain in the vicinity of the surface and deeper. For smaller NPs, Ni atoms are located at the surface as well. Our results also showed that most of the metal atoms segregated at the surface area were found to decorate edges and/or form islands. Our findings agree qualitatively with the experimental data found in the literature. In addition, we comment on the reactivity of these nanoparticles.Fil: Quaino, Paola Monica. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Belletti, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Shermukhamedov, S. A.. Kazan National Research Technological University; RusiaFil: Glukhov, D. V.. Kazan National Research Technological University; RusiaFil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Institute of Theoretical Chemistry; Alemania. Universitat Ulm; AlemaniaFil: Schmickler, Wolfgang. Universitat Ulm; Alemania. Institute of Theoretical Chemistry; AlemaniaFil: Nazmutdinov, Renat. Kazan National Research Technological University; Rusi

HIV/AIDS Among Middle and Older Adults in Puerto Rico

Of all the AIDS cases reported through March 2004 in Puerto Rico, 34.8% were among the 40-59 age group, and 3.9% in persons 60 years and over. This represents 38.7% of all cases of AIDS in Puerto Rico. The percentage was higher among new AIDS cases diagnosed. Currently half of all new cases were 40 years and older. The most prevalent mode of exposure reported was related to sexual contact (heterosexual contact, male-male/bisexual sexual contact, male-male sexual contact and injection drug use). Injection drug use is identified as an important mode of exposure, particularly among males 40-59 years old. In the older generation, ignorance or the refusal to acknowledge their sexual interest and activity has resulted in a failure to adequately consider such health issues as sexually transmitted infections, including HIV in this population. Due to the increase of new AIDS cases and to the rapidly growing segment of the older adult population, middle and older adults are becoming an important group in need of HIV/AIDS prevention. With the intention of obtaining information on HIV risk factors among older adults a descriptive research was conducted. A non-probability sample of 157 men and 57 women 60 years and older from the San Juan Metropolitan Area was interviewed. The questionnaire included questions on HIV/AIDS knowledge, risk-perception, sexual practices, condom use and accessibility, HIV testing, alcohol and health and sociodemographic characteristics. The age range of the participants was 60-93 years old. The majority of respondents listed Social Security and food stamps as their primary source of income. Thirty-three percent of the male and 38.2% of the women perceived themselves as being at risk of HIV infection. Sexual relations during the last month were reported by 56.6% of the male and 13.2% of the women. They mention spouse, girl/boy friend as their usual partners; male also indicated casual partners and sex workers. The majority did not use condoms in their last sexual relation. Only 21% of males that reported sexual relations with sex worker always used condoms. Pharmacy was mentioned by the majority as the place where they obtain condoms. Forty five percent of female and 34% of the male had been tested for HIV. Gonorrhea was the most frequent sexually transmitted infection reported by males and trichomonas vaginalis by females. We are confronting a condition that affects the present population as well as future generations of older adults. Recommendations of health promotion and health education interventions that contribute to decrease the HIV/AIDS incidence and to eliminate stereotyping, discrimination and disparities in health care services for this population are identify

Key role of anions in the 2D-3D electrochemical deposition of Rh on Ag electrodes

We have studied the electrochemical deposition of Rh on polycrystalline Ag substrates from electrolytes containing chloride and sulphate anions. Chronoamperometry and cyclic voltammetry have been employed in order to elucidate the growth mechanism. Anions play a key role in the growth mechanism and the resulting structures. In the presence of sulphate anions Rh deposition follows a 3D nucleation - growth mechanism, while a 2D nucleation - growth is obeyed in the case of electrolytes containing chloride anions. Ab initio thermodynamics studies support the hypothesis that chloride anions stabilize the Rh deposition favouring a 2D mechanism at low overpotentials in good agreements with the experimental data.Fil: Schulz, Eduardo Nicolás. Universitat Ulm; AlemaniaFil: Ruderman, Andres. Universitat Ulm; AlemaniaFil: Soldano, Germán. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: García, Silvana G.. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Why Silver Deposition is so Fast: Solving the Enigma of Metal Deposition

A perfect match: Silver deposition is one of the fastest electrochemical reactions, even though the Ag+ ion loses more than 5 eV solvation energy in the process. This phenomenon, an example of the enigma of metal deposition, was investigated by a combination of MD simulations, DFT, and specially developed theory. At the surface, the Ag+ ion experiences a strong interaction with the sp band of silver, which catalyzes the reaction.Fil: Pinto, Leandro M. C.. Universidade Estadual Paulista Julio de Mesquita Filho. Facultad de Filosofia E Ciencias-campus de Marilia; Brasil. Universitat Ulm; AlemaniaFil: Spohr, Eckhard. Universitat Duisburg - Essen; AlemaniaFil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada E Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto de Física "Enrique Gaviola"; ArgentinaFil: Schmickler, Wolfgang. Institute Of Theoretical Chemistry; Alemania. Universitat Ulm; Alemani