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(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.

Interaction between monomers of two surfactants derived from the [Ru(2,2′-bpy)3]2+ complex and α, β and γ-cyclodextrins: formation of [2]- and [3]-pseudorotaxanes

“…In any case, as mentioned above, it is known from the literature that CDs have dipole moments, the narrower end of the cyclodextrin cavity being at the positive end of its dipole moment and the wide end at the negative end. 33 Therefore, taking into account the positive charge of the surfactant head, the more possible orientation of the CD in the pseudorotaxane seems to be the one depicted in Fig. 11.…”

“…This noncovalent binding probably consists of electrostatic interactions between the ruthenium and the CD, due to the dipole moment that CDs have. 33 This fact indicates that electrostatic interactions between the cationic polar head of the surfactant could also be possible. The compound formed from this electrostatic interaction has a stoichiometry of 1 : 1 as happens with the [2]-pseudorotaxane.…”

Uncovering Individual Hydrogen Bonds in Rotaxanes by Frequency Shifts

“…Jagesar et al measured and calculated the IR spectrum of a rotaxane and its shuttling process in solvents with different polarities . Jimenez et al studied the effects that the solvent exerts on the end-capping process of a pseudorotaxane . High resolution UV spectra were used to understand the functionality of rotaxane molecules .…”

“…28 Jimenez et al studied the effects that the solvent exerts on the end-capping process of a pseudorotaxane. 29 High resolution UV spectra were used to understand the functionality of rotaxane molecules. 30 The rotaxanes investigated by Buma et al contain two types of carbonyl groups.…”

Solid Crystal Network of Self-Assembled Cyclodextrin and Nonionic Surfactant Pseudorotaxanes

“…Whereas rotaxanes are interlocked molecules, basically consisting of a macrocycle trapped onto a linear thread by two bulky substituents, which usually demands the use of complex synthetic procedures for the chemical attachment of stopper molecules, pseudorotaxanes are supramolecular structures in which the macrocycle is directly entrapped by a molecular axis without bulky end groups, due to different affinities of the macrocycle for the diverse structural regions of the linear component . The simplicity of pseudorotaxane synthesis, which in many examples relies on a direct mixture of the macrocycle and the molecular axis in solution, − makes them ideal candidates for self-organization at the solid state . In this context, natural cyclodextrins (CDs) are known to exhibit unique inclusion characteristics as macrocycles with a wide variety of organic guest molecules.…”