The role played by head–tail configuration on the molecular weight distribution of α-cyclodextrin tubes

Abstract

Supramolecular complexes consisting of cyclic molecules, such as cyclodextrins (CD), and polymeric chains have attracted considerable attention, being addressed in literature as novel molecular assembly. The so-called molecular tube (MT), synthesized by cross-linking adjacent α-CD in a polyrotaxane, is expected to act as host for large molecules in inclusion processes. In addition, these tubes can also be used as building-blocks in the formulation of novel materials. Molecular tubes constructed with α-cyclodextrin are obtained as a mixture containing entities with various molecular weights, and the molecular features determining the tube size distribution are not completely understood. In this paper, we propose the use of a statistical procedure based on binary numbers to examine the MT formation process. A complete analysis of the distinct orientations between cyclodextrin’s units was made and, in the light of the approximations of our model, we pointed out, on quantitative basis, that the molecular weight distribution of α-cyclodextrin MTs can be explained assuming imperfections in the cross-linking process due to the existence of head-to-tail (HT) arrangements in the polyrotaxanes employed in synthesis.