These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Solvation in binary mixtures of water and polar aprotic solvents: theoretical calculations of the concentrations of solvent-water hydrogen-bonded species and application to thermosolvatochromism of polarity probes.
    Author: Silva PL, Bastos EL, El Seoud OA.
    Journal: J Phys Chem B; 2007 Jun 07; 111(22):6173-80. PubMed ID: 17503801.
    Abstract:
    Thermo-solvatochromism of two polarity probes, 2,6-diphenyl-4-(2,4,6-triphenyl- pyridinium-1-yl)phenolate, RB, and 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl) phenolate, WB, in aqueous acetone, Me2CO, and aqueous dimethylsulfoxide, DMSO, has been studied. The data obtained have been analyzed according to a recently introduced solvation model that explicitly considers the presence of 1:1 organic solvent-water hydrogen-bonded species, S-W, in the bulk binary mixture and its exchange equilibria with (S) and (W) in the solvation shell of the probe. Calculations require reliable values of Kdissoc, the dissociation constant of S-W. Previously, this has been calculated from the dependence of the densities of binary solvent mixtures on their composition. Using iteration, the volume of the hydrogen-bonded species, VS-W, and Kdissoc were obtained simultaneously from the same set of experimental data. This approach may be potentially suspect because Kdissoc, and VS-W are highly correlated. Therefore, we extended a recently introduced approach for the calculation of Valcohol-W to binary mixtures of water with acetone, acetonitrile, N,N-dimethylformamide, DMSO, and pyridine. This approach includes: Determination of VS-W from ab initio calculations by the COSMO solvation model; correction of these volumes for the nonideal behavior of the binary solvent mixtures at different temperatures; use of corrected VS-W as a constant (not an adjustable parameter) in the equation that is employed to calculate Kdissoc (from density versus binary solvent composition). Solvation of RB and WB by Me2CO-W showed different behavior from that of aqueous DMSO. Thus, water is able to displace Me2CO more efficiently than DMSO from the probe solvation shell. Me2CO-W and DMSO-W displace their corresponding precursor solvents; this is more efficient for the former case because the strong DMSO-W interactions attenuate the solvation capacity of this species. Temperature increase resulted in desolvation of both probes, due to concomitant decrease of the structures of the component solvents.
    [Abstract] [Full Text] [Related] [New Search]