132 research outputs found
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110th Anniversary: Theory of Activity Coefficients for Lithium Salts in Aqueous and Nonaqueous Solvents and in Solvent Mixtures
On the basis of work by Bernard and Blum [Bernard, O.; Blum, L. Binding Mean Spherical Approximation for Pairing Ions: An Exponential Approximation and Thermodynamics. J. Chem. Phys. 1996, 104, 4746-4754], Barthel et al. [Barthel, J.; Krienke, H.; Holovko, M.; Kapko, V.; Protsykevich, I. The Application of the Associative Mean Spherical Approximation in the Theory of Nonaqueous Electrolyte Solutions. Condens. Matter Phys. 2000, 3, 23], and Simonin et al. [Simonin, J.-P.; Bernard, O.; Blum, L. Real Ionic Solutions in the Mean Spherical Approximation. 3. Osmotic and Activity Coefficients for Associating Electrolytes in the Primitive Model. J. Phys. Chem. B 1998, 102, 4411-4417], this work presents and validates a molecular-thermodynamic model for lithium salt activity coefficients in aqueous and nonaqueous single- and mixed-solvent systems. The Binding Mean Spherical Approximation gives electrolyte activity due to long-range electrostatic forces, short-range hard-sphere repulsion, and ion-pair formation. The theory shows good agreement with measured salt activities up to 3 molar in aqueous and nonaqueous solvents using a solvent-dependent, concentration-independent, center-to-center distance of closest approach between ions as the single fitting parameter for each electrolyte system. For mixed-solvent electrolytes, the local solvation environment around the ions dictates short-range interactions. To account for preferential ion solvation in a mixed solvent, the center-to-center distance is obtained from Wang and co-workers' Dipolar Self-Consistent-Field Theory [Nakamura, I.; Shi, A.-C.; Wang, Z.-G. Ion Solvation in Liquid Mixtures: Effects of Solvent Reorganization. Phys. Rev. Lett. 2012, 109, 257802]. For a particular salt in a binary solvent mixture at fixed temperature, the model predicts salt activity coefficients using only the fitted single-solvent distances-of-closest approach
Optimized intermolecular potential for nitriles based on Anisotropic United Atoms model
An extension of the Anisotropic United Atoms intermolecular potential model is proposed for nitriles. The electrostatic part of the intermolecular potential is calculated using atomic charges obtained by a simple Mulliken population analysis. The repulsion-dispersion interaction parameters for methyl and methylene groups are taken from transferable AUA4 literature parameters [Ungerer et al., J. Chem. Phys., 2000, 112, 5499]. Non-bonding Lennard-Jones intermolecular potential parameters are regressed for the carbon and nitrogen atoms of the nitrile group (–C≡N) from experimental vapor-liquid equilibrium data of acetonitrile. Gibbs Ensemble Monte Carlo simulations and experimental data agreement is very good for acetonitrile, and better than previous molecular potential proposed by Hloucha et al. [J. Chem. Phys., 2000, 113, 5401]. The transferability of the resulting potential is then successfully tested, without any further readjustment, to predict vapor-liquid phase equilibrium of propionitrile and n-butyronitrile
Atopic dermatitis : a cutaneous or systemic disease? The search for answers in the history of Dermatology
A dermatite atópica é doença inflamatória cutânea associada à atopia, predisposição a produzir resposta IgE a alérgenos ambientais, constituindo uma das manifestações das doenças atópicas, junto com a asma e a rinite alérgica. A dermatite atópica é caracterizada por episódios recorrentes de eczema associado a prurido, acometendo superfÃcie cutânea geneticamente alterada, induzindo, por fenômenos imunológicos, a presença de inflamação. Trata-se de doença multifatorial, com enfoque nas alterações sistêmicas e alérgicas ou nas manifestações cutâneas, de acordo com diferentes visões da doença. A conceituação da dermatite atópica é importante, porque a conduta terapêutica pode variar segundo essas duas formas diferentes de analisá-la. Autores modernos discutem extensivamente esses aspectos sem, contudo, alcançar uma conclusão sobre a dermatite atópica como doença sistêmica ou cutânea. A procura dos conceitos sobre a doença, desde os primeiros relatos, associada à evolução do pensamento na dermatologia, poderia esclarecer a origem dessas dúvidas. Uma análise histórica demonstra que a dermatite atópica tem seus conceitos atuais oriundos dos estudos de diversos pensadores, que, em diferentes momentos históricos, descreveram a doença, e que muito do que acreditamos atualmente tem, nesses escritos, seus fundamentos.Atopic dermatitis is an inflammatory disease associated to atopy, which is a predisposition to produce an IgE response to environmental allergens and considered one of the manifestations of the atopic diseases, including asthma and allergic rhinitis. Atopic dermatitis is characterized by recurrent eczema flares, associated to pruritus, affecting a genetically disrupted skin surface, inducing, by immunological phenomena, the onset of inflammation. It is a multifactorial disease, with an emphasis on systemic and allergic alterations or skin manifestations, according to different concepts. The definition of atopic dermatitis is important, since its management may vary according to these two different points of view. Modern authors have extensively discussed these concepts, though with no conclusion as to its nature - systemic or cutaneous disease. The search for concepts about the disease, since its first descriptions, associated to the evolution of the dermatology rationale through history, may help understand the origin of these doubts. A historical analysis demonstrates that the currently accepted concepts of atopic dermatitis have their background from different researchers, who, at different historical moments, described the disease, and a great part of our beliefs about atopic dermatitis are related to these ancient writings
Recommended from our members
110th Anniversary: Theory of Activity Coefficients for Lithium Salts in Aqueous and Nonaqueous Solvents and in Solvent Mixtures
On the basis of work by Bernard and Blum [Bernard, O.; Blum, L. Binding Mean Spherical Approximation for Pairing Ions: An Exponential Approximation and Thermodynamics. J. Chem. Phys. 1996, 104, 4746-4754], Barthel et al. [Barthel, J.; Krienke, H.; Holovko, M.; Kapko, V.; Protsykevich, I. The Application of the Associative Mean Spherical Approximation in the Theory of Nonaqueous Electrolyte Solutions. Condens. Matter Phys. 2000, 3, 23], and Simonin et al. [Simonin, J.-P.; Bernard, O.; Blum, L. Real Ionic Solutions in the Mean Spherical Approximation. 3. Osmotic and Activity Coefficients for Associating Electrolytes in the Primitive Model. J. Phys. Chem. B 1998, 102, 4411-4417], this work presents and validates a molecular-thermodynamic model for lithium salt activity coefficients in aqueous and nonaqueous single- and mixed-solvent systems. The Binding Mean Spherical Approximation gives electrolyte activity due to long-range electrostatic forces, short-range hard-sphere repulsion, and ion-pair formation. The theory shows good agreement with measured salt activities up to 3 molar in aqueous and nonaqueous solvents using a solvent-dependent, concentration-independent, center-to-center distance of closest approach between ions as the single fitting parameter for each electrolyte system. For mixed-solvent electrolytes, the local solvation environment around the ions dictates short-range interactions. To account for preferential ion solvation in a mixed solvent, the center-to-center distance is obtained from Wang and co-workers' Dipolar Self-Consistent-Field Theory [Nakamura, I.; Shi, A.-C.; Wang, Z.-G. Ion Solvation in Liquid Mixtures: Effects of Solvent Reorganization. Phys. Rev. Lett. 2012, 109, 257802]. For a particular salt in a binary solvent mixture at fixed temperature, the model predicts salt activity coefficients using only the fitted single-solvent distances-of-closest approach
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