Phenoxathiinsulphone derivatives–cyclodextrin interactions: induced chirality and TDDFT calculations

Abstract

The inclusion process of phenoxathiin-10,10-dioxide and 2-CH2Br-phenoxathiin-10,10-dioxide in α-, β-, γ- and 2-hydroxypropyl-γ-cyclodextrins was studied by circular dichroism spectroscopy. The dependence of the induced circular dichroism signal on the host concentration was analyzed in terms of a nonlinear model yielding the stoichiometry and the association constants of the complexes. Time dependent density functional theory (TDDFT) calculations were used to rationalize the experimental data considering two aspects. Firstly, to support on theoretical grounds the experimentally observed achirality of the studied compounds that present two structural elements to confer chirality: the butterfly motion of the roof-shaped heteroring and the rotation of the CH2Br group. In this last process, some favorable position of the bromine atom could influence the overall chirality. Secondly, the TDDFT calculations of the polarizations of the electronic transitions in correlation with the signs of the induced dichroic bands were used to establish the axial or equatorial way the guest is included in the host cavity.