Inclusion ability of a monothiourea-tethered bis(β-cyclodextrin)

Abstract

The tail-to-tail monothioureido β-cyclodextrin dimer has been prepared by reacting 6-amino-6-deoxy-β-cyclodextrin with 6-isothiocyanato-6-deoxy-β-cyclodextrin. The inclusion ability of this dimer has been evaluated by UV–visible spectroscopy for substrates of moderate molecular volumes (a wide variety of hydroxylated substrates) and was compared with genuine β-cyclodextrin and randomly methylated β-cyclodextrin. The definition of a complexation index allowed the treatment of these three host molecules on a hierarchical basis: the bis-cyclodextrin appears to be more efficient (average index = 1.17) than the methylated (1.07) or genuine (1.00) monomers. Thus, it seems that the cooperative phenomenon may lead to a general increase of the complexation ability, and not only to an enhanced recognition of specific guests. Surprisingly, this phenomenon is even really effective for the smallest substrates of our study. Such results prompted us to illustrate, on a steric point of view, the possibility of the face-to-face conformation by means of molecular modelling.