β-Cyclodextrin Complexes of Polymers Containing Aromatic Groups

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Cyclodextrins (Cdx) are cyclic oligosaccharides consisting of six (α-CDx), seven (β-CDx), or eight (γ-CDx) D-(+)-glucopyranose units linked by α-(1,4) bonds. The presence of a central cavity with hydrophobic properties makes these molecules able to form inclusion complexes with organic or inorganic substrates. This fact opened the way to applications in many different fields, such as pharmacology, food science, analytical chemistry, and chemical synthesis and catalysis [1–6]. Cyclodextrins form inclusion complexes with a wide variety of low molecules weight compounds [3]. However, the guest molecules have been limited to small molecules, which can fit in the cavity of cyclodextrins. Inclusion complex formation has been studied by a variety of methods. Among these methods, 1H NMR spectroscopy, UV-visible spectroscopy, and the CD method are considered to be the most popular. But only a few literature about the interactions between β-cyclodextrin and polymers in aqueous solution were reported. It particularly concerns Harada’s studies who found that cyclodextrins form a complex with polymers, such as poly(ethylene glycol) [7–8], poly(propylene glycol) [9–10], poly(methyl vinyl ether) [11], or polyisobutylene [12], in a crystalline state. Only one study in aqueous solution with a polyamine was realized [13]. In our laboratory, the covalent and non covalent cyclodextrin-polyvinylamine system was studied [14]. The investigations with polymers in aqueous medium are more complicated to carry out, because problems may arise from limited solubility and high viscosity. In the present study, we have used Poly (4-sodium styrenesulfonate) NaPSS which is a polymer that doesn’t take any compact structure in solution. The extended chain allows the aromatic groups to be easily accessible to the CD moieties. The interactions between β-cyclodextrin and NaPSS were investigated by measuring the changes of circular dichroism spectra. Then the probable structure of the inclusion complex was studied by considering 1H NMR data. Furthermore, the viscosimetry changes induced by the formation of the inclusion complex were also investigated.