Formation of a rotaxane from the end-capping process of a pseudorotaxane. Effects of the solvent.
The effects that the solvent exerts on the end-capping process of a pseudorotaxane formed by the [Ru(NH 3) 5(4,4'-bpy)]2+ complex and beta-cyclodextrin were studied. In this process the 4,4'-bpy ligand acts as rigid axle and the cyclodextrin as ring or macrocycle. The stopper used was the [Fe(CN) 5 H2O]3(-) complex. The solvents used were mixtures of ethyleneglycol-water and tert-butyl alcohol-water. Results showed similar, although strange, behavior in both media studied. Thus, a decrease of the observed rate constant was obtained when the concentration of cyclodextrin increases for all the media studied. However, at fixed cyclodextrin concentrations, an increase of k obs was obtained when small quantities of the cosolvent were added to the medium and, further, a decrease of k obs for the higher quantities of the organic solvents. This strange behavior could be explained by taking into account electrostatic and specific solvent (solvent-solvent and solvent-solute) effects.
Jimenez
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Departamento de Química Física. Universidad de Sevilla, c/ Prof. García González s/n, Sevilla, SPAIN.
Martin
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Lopez-Cornejo
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