Formation of a rotaxane from the end-capping process of a pseudorotaxane. Effects of the solvent

Abstract

The effects that the solvent exerts on the end-capping process of a pseudorotaxane formed by the[Ru(NH3)5(4,4′-bpy)]2+complex and -cyclodextrin were studied. In this process the 4,4′-bpy ligand acts asrigid axle and the cyclodextrin as ring or macrocycle. The stopper used was the [Fe(CN)5H2O]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 obtainedwhen the concentration of cyclodextrin increases for all the media studied. However, at fixed cyclodextrinconcentrations, an increase of kobswas obtained when small quantities of the cosolvent were added to themedium and, further, a decrease of kobsfor the higher quantities of the organic solvents. This strange behaviorcould be explained by taking into account electrostatic and specific solvent (solvent-solvent and solvent-solute)effects.