Quantifying interfacial tensions of surface nanobubbles: How far can Young's equation explain?

Nanobubbles at solid-liquid interfaces play a key role in various physicochemical phenomena and it is crucial to understand their unique properties. However, little is known about their interfacial tensions due to the lack of reliable calculation methods. Based on mechanical and thermodynamic insights, we quantified for the first time the liquid-gas, solid-liquid, and solid-gas interfacial tensions of submicron-sized nitrogen bubbles at graphite-water interfaces using molecular dynamics (MD) analysis. It was revealed that Young's equation holds even for nanobubbles with different radii. We found that the liquid-gas and solid-liquid interfacial tensions were not largely affected by the gas density inside the nanobubbles. In contrast, the size effect on the solid-gas interfacial tension was observed, namely, the value dramatically decreased upon an increase in the gas density due to gas adsorption on the solid surface. However, our quantitative evaluation also revealed that the gas density effect on the contact angles is negligible when the footprint radius is larger than 50 nm, which is a typical range observed in experiments, and thus the flat shape and stabilization of submicron-sized surface bubbles observed in experiments cannot be explained only by the changes in interfacial tensions due to the van der Waals interaction-induced gas adsorption, namely by Young's equation without introducing the pinning effect. Based on our analysis, it was clarified that additional factors such as the differences in the studied systems are needed to explain the unresolved open issues-a satisfactory explanation for the nanobubbles in MD simulations being ultradense, non-flat, and stable without pinning.Teshima H., Kusudo H., Bistafa C., et al. Quantifying interfacial tensions of surface nanobubbles: How far can Young's equation explain?. Nanoscale 14, 2446 (2022); https://doi.org/10.1039/d1nr07428h

Water on hydroxylated silica surfaces: Work of adhesion, interfacial entropy, and droplet wetting

In the last few years, much attention has been devoted to the control of the wettability properties of surfaces modified with functional groups. Molecular dynamics (MD) simulation is one of the powerful tools for microscopic analysis providing visual images and mean geometrical shapes of the contact line, e.g., of nanoscale droplets on solid surfaces, while profound understanding of wetting demands quantitative evaluation of the solid–liquid (SL) interfacial tension. In the present work, we examined the wetting of water on neutral and regular hydroxylated silica surfaces with five different area densities of OH groups ^_, anging from a non-hydroxylated surface to a fully hydroxylated one through two theoretical methods: thermodynamic integration (TI) and MD simulations of quasi-two-dimensional equilibrium droplets. For the former, the work of adhesion needed to quasi-statically strip the water film off the solid surface was computed by the phantom wall TI scheme to evaluate the SL interfacial free energy, whereas for the latter, the apparent contact angle θ_app was calculated from the droplet density distribution. The theoretical contact angle θ_YD and the apparent one θ_app, both indicating the enhancement of wettability by an increase in ^_, presented good quantitative agreement, especially for non-hydroxylated and highly hydroxylated surfaces. On partially hydroxylated surfaces, in which θ_YD and θ_app slightly deviated, the Brownian motion of the droplet was suppressed, possibly due to the pinning of the contact line around the hydroxyl groups. Relations between work of adhesion, interfacial energy, and entropy loss were also analyzed, and their influence on the wettability was discussed.Bistafa Carlos, Surblys Donatas, Kusudo Hiroki, et al. Water on hydroxylated silica surfaces: Work of adhesion, interfacial entropy, and droplet wetting. The Journal of Chemical Physics, 155(6), 064703 (2021) https://doi.org/10.1063/5.0056718

Theoretical studies of the excited state of organic molecules in solvent

Absorção e Emissão de radiação eletromagnética por moléculas na região do UV-Vis fornece informações sobre os estados eletrônicos excitados, sendo propriedades de grande interesse devido a sua relação com processos biológicos, bem como suas possíveis aplicações em diagnósticos e tecnologia. Essas propriedades são sensíveis ao meio em que as moléculas se encontram, tornando-se assim natural a busca por métodos teóricos que possibilitam descrever essas interações. Neste trabalho, nós usamos a metodologia Sequential-Quantum Mechanics/Molecular Mechanics para estudar o espectro de absorção e de emissão de moléculas de relevância biológica, quando em solução. Simulações clássicas Monte Carlo foram usadas pra construir uma configuração eletrostática média do líquido para posterior cálculo das propriedades, feito através dos métodos multiconfiguracionais CASSCF e CASPT2. Cuidados especiais foram tomados para incluir a polarização eletrônica que o soluto sofre devido à presença do solvente. Nossa contribuição é a adaptação do método do Gradiente de Energia Livre para permitir a obtenção de geometrias de estados excitados do soluto em solução. A técnica foi implementada em um programa e aplicada com sucesso nos sistemas estudados. As perspectivas agora se abrem para a obtenção de intersecções cônicas em meio solvente, permitindo assim o estudo de decaimentos não-radiativos em sistemas solvatados.Absorption and emission of electromagnetic radiation by molecules in the UV-Vis region yields information about the electronic excited states, being properties of great interest due its relation with biological process, as well as its possible applications in diagnostics and technology. These properties are sensible to the environment in which the molecules are, making natural the search for theoretical methods that describe these interactions. In this work, we have used the Sequential-Quantum Mechanics/Molecular Mechanics methodology to study the spectrum of absorption and emission of molecules of biological relevance, when in solution. Classical Monte Carlo simulations were carried out to construct an average solvent electrostatic configuration and used to represent the liquid in posterior quantum mechanics calculation of the properties, performed by using the multiconfigurational methods CASSCF and CASPT2. Special cares were taken to include the electronic polarization of the solute due the solvent. Our contribution is the adaptation of the Free Energy Gradient method to allow the determination of the solute excited states geometries in solution. The method was implemented in a computer program and successfully applied in the systems studied. The perspectives are now open to the calculation of conical intersection in solvent environment, enabling the study of nonradioactive decays in solvated systems

Solvent Effect on the 5-fluorouracil absorption spectrum, Analysis od different theoretical procedures

A molécula 5-fluorouracil (5FU) é muito utilizada em tratamentos de câncer. Seu espectro de absorção é caracterizado por duas bandas de diferentes intensidades, as transições n-p* e p-p*, e seu estudo em diferentes solventes é de considerável importância para compreender a fotofísica do estado excitado. Este é o primeiro passo essencial para obter a caracterização da dinâmica de emissão. Neste trabalho, nós estudamos teoricamente o espectro de absorção da 5FU em dois solventes, água e acetonitrila, usando o método Sequential Quantum Mechanics/ Molecular Mechanics (SQM/MM). Uma etapa importante para uma simulação realista é a polarização do soluto pelo solvente. Neste estudo, esta polarização foi obtida usando dois modelos: Polarizable Continuum Model (PCM), que é uma alternativa simples e um método iterativo usando Average Solvent Electrostatic Configuration (ASEC). Após isso, simulações usando Monte Carlo Metrópolis no ensemble NVT em condições normais de temperatura e pressão foram realizadas e configurações estatisticamente descorrelacionadas separadas para subsequentes cálculos de Mecânica Quântica usando diversos métodos: Configuration Interaction (CI), Time Dependent Density Functional Theory (TD-DFT) e um método semi-empírico (INDO/CIS). Os espectros calculados em ambos os solventes foram obtidos em mais de uma aproximação: contínua, discreta e explícita. Os resultados estão em boa concordância com os valores experimentais e enfatizam a importância da inclusão de moléculas de solvente explícitas nos cálculos. Nós especialmente notamos que em solventes, a transição n-p* é deslocada para o azul enquanto a transição p-p* é deslocada para o vermelho, indicando uma tendência para reversão dessas duas bandas se comparadas à fase gasosa. Isto aponta para diferenças na fotofísica, dependendo da polaridade do solvente. Os resultados também permitem uma avaliação dos diferentes procedimentos teóricos utilizados.The 5-fluorouracil molecule is very used in cancer treatment. Its absorption spectrum is characterized by two broad bands of different intensities, the n-p* and p-p* transitions, and its study in different solvents is of considerable importance for the understanding of the photophysics of the excited state. It is the first essential step for obtaining the characterization of the emission dynamics. In this work we have theoretically studied the absorption spectrum of 5FU in two solvents, water and acetonitrile, using the Sequential Quantum Mechanics/Molecular Mechanics method (SQM/MM). An important step for a realistic simulation is the polarization of the solute by the solvent. In this study, this polarization was obtained by using two models: Polarizable Continuum Model (PCM), which is a simple alternative, and an iterative method using the Average Solvent Electrostatic Configuration (ASEC). After this, Monte Carlo Metropolis simulations in the NVT ensemble in normal conditions of temperature and pressure were made and statistically uncorrelated configurations sampled for the subsequent Quantum Mechanics calculations using several methods: Configuration Interaction (CI), Time Dependent Density Functional Theory (TD-DFT) and a semiempirical method (INDO/CIS). The calculated spectra in both solvents were obtained using more than one approach: continuum, discrete and explicit. The results are in good agreement with experimental values and emphasize the importance of explicitly including solvent molecules. We specially note that in solvents, the n-p* is blue-shifted and the p-p* transition is red-shifted leading to a tendency for reversal of these two bands compared to gas phase. This points to differences in the photophysics, depending on the solvent polarity. The results also allow an evaluation of the different theoretical procedures used

Revista da Rede de Enfermagem do Nordeste Popular participation and Previous County Health Conference Participação popular e Pré-Conferência Municipal de Saúde Participación popular y Pre-Conferencia Municipal de Salud

The article aimed at reporting the participation of a post graduate nursing student in the core of a previous county health conference. This is an experience, descriptive and reflective report, held in Ribeirão Preto, São Paulo, Brazil, in the first semester of 2011. The Pre-Conference has resulted in the compilation of 50 proposals that involved the following areas: access to actions and health services; work management and health education; community participation; social security system; access and quality of reception. The Pre-Conference revealed the increasing plurality of society and its interests, and the distance between the managers on one hand, and on the other the organs of social participation. Descriptors: Social Participation; Consumer Participation; Health Councils; Health Policy. O artigo teve como objetivo relatar a experiência da participação de um enfermeiro pós-graduando no bojo de uma Pré-Conferência Municipal de Saúde. Trata-se de um relato de experiência, de cunho descritivo-reflexivo, realizado no município de Ribeirão Preto, estado de São Paulo, Brasil, no primeiro semestre de 2011. A Pré-Conferência resultou na compilação de 50 propostas que versavam sobre os seguintes eixos temáticos: acesso a ações e serviços de saúde; gestão do trabalho e educação em saúde; participação da comunidade; sistema de seguridade social; acesso e acolhimento com qualidade. A Pré-Conferência revelou ao mesmo tempo a pluralidade crescente da sociedade e dos interesses nela presentes, e o afastamento entre os gestores de um lado e os órgãos de participação social de outro

Participação popular e Pré-Conferência Municipal de Saúde

El objetivo fue relatar la participación de un enfermero de postgrado en el núcleo de una Pré-Conferencia Municipal de Salud. Relato de experiencia, descriptivo y reflexivo, llevado a cabo en la ciudad de Ribeirão Preto, estado de São Paulo, Brasil, en el primer semestre de 2011. La Pre-Conferencia se ha traducido en la elaboración de 50 propuestas acerca de los siguientes ejes temáticos: acceso a las acciones y servicios de salud; gestión de trabajo y educación en salud; participación comunitaria; sistema de seguridad social; acceso y acogimiento con calidad. La Pre-Conferencia reveló el creciente pluralismo de la sociedad y de los intereses, y la separación entre los gestores por un lado, y por otro, los órganos de participación social

Solvent Effect on the Stokes Shift and on the Nonfluorescent Decay of the Daidzein Molecular System

The flavonoids have been the target of several experimental works due to its influence in the human health as antioxidant elements. The fluorescence properties of these compounds have been widely studied due to the large Stokes shifts experimentally observed and the variety of processes that lead to the fluorescence. In the present work the role of the solvent in the large Stokes shift experimentally observed in the daidzein molecular system in water is theoretically studied. Also studied is the nonfluorescent decay mechanism in a polar aprotic solvent like acetonitrile. The solvent effect in the ground and in the low-lying excited electronic states is taken into account by using the sequential-QM/MM methodology. Excited state properties like equilibrium geometries and transition energies were studied by using multiconfigurational calculations, CASSCF and CASPT2. The excited electronic state responsible for the fluorescence spectrum in water was identified, and the large Stokes shift seems to be the result of the large interaction of the system in this electronic state with the solvent. On the other hand, spin–orbit coupling calculations, between the singlet and triplet electronic states, indicate favorable conditions for intersystem crossing, in agreement with the experimental result of nonfluorescence observation

Popular participation and Previous County Health Conference

The article aimed at reporting the participation of a post graduate nursing student in the core of a previous county health conference. This is an experience, descriptive and reflective report, held in Ribeirão Preto, São Paulo, Brazil, in the first semester of 2011. The Pre-Conference has resulted in the compilation of 50 proposals that involved the following areas: access to actions and health services; work management and health education; community participation; social security system; access and quality of reception. The Pre-Conference revealed the increasing plurality of society and its interests, and the distance between the managers on one hand, and on the other the organs of social participation