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Thermosolvatochromism of betaine dyes revisited: theoretical calculations of the concentrations of alcohol-water hydrogen-bonded species and application to solvation in aqueous alcohols.
Bastos, Erick L; Silva, Priscilla L; El Seoud, Omar A.
Afiliação
  • Bastos EL; Instituto de Química, Universidade de São Paulo, C.P. 26077, 05513-970 São Paulo, S.P., Brazil.
J Phys Chem A ; 110(34): 10287-95, 2006 Aug 31.
Article em En | MEDLINE | ID: mdl-16928120
Solvatochromic data of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (RB) in aqueous methanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol at 25 degrees C were recalculated by employing a recently introduced model that explicitly considers the presence of 1:1 alcohol-water hydrogen-bonded species, ROH-W, in bulk solution and their exchange equilibria with water and alcohol in the probe solvation microsphere. The thermosolvatochromic behavior of RB in aqueous ethanol was measured in the temperature range from 10 to 60 degrees C; the results thus obtained were treated according to the same model. All calculations require reliable values of Kdissoc, the dissociation constant of the ROH-W species. This was previously calculated from the dependence of the density of the binary solvent mixture on its composition. Through the use of iteration, the volume of the hydrogen-bonded species, VROH-W, and Kdissoc are obtained simultaneously from the same set of experimental data. This approach may be potentially problematic because Kdissoc and VROH-W are highly correlated. Therefore, we introduced the following approach: (i) VROH-W was obtained from ab initio calculations, (ii) these volumes were corrected for the nonideal behavior of the binary solvent mixtures at different temperatures, (iii) corrected VROH-W values were employed as a constant in the equation used to calculate Kdissoc (from density vs binary solvent mixture composition). VROH-W calculated by the COSMO-RS solvation model fitted the density data better than those calculated by the IEFPCM model. In all aqueous alcohols, solvation by ROH-W is favored over that by the two precursor solvents. In aqueous ethanol, a temperature increase resulted in a gradual desolvation of RB, due to a decrease in the hydrogen-bonding of both components of the mixture. The microscopic polarities of ROH-W are much closer to those of the precursor alcohols.
Assuntos
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Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Fenóis / Piridinas / Teoria Quântica / Temperatura / Betaína / Álcoois Tipo de estudo: Prognostic_studies Idioma: En Revista: J Phys Chem A Assunto da revista: QUIMICA Ano de publicação: 2006 Tipo de documento: Article País de afiliação: Brasil País de publicação: Estados Unidos
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Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Fenóis / Piridinas / Teoria Quântica / Temperatura / Betaína / Álcoois Tipo de estudo: Prognostic_studies Idioma: En Revista: J Phys Chem A Assunto da revista: QUIMICA Ano de publicação: 2006 Tipo de documento: Article País de afiliação: Brasil País de publicação: Estados Unidos