Complexation of Pyrene by Poly(allylamine) with Pendant β-Cyclodextrin Side Groups

Abstract

The complexation of pyrene into the cavity of β-cyclodextrin (β-CD) has been studied in aqueous solutions of pure β-CD and β-CD substituted poly(allylamine) by using fluorescence spectroscopy. Two different approaches to obtain the association constant, both already described in the literature, are compared. It is shown that the evaluation of the fluorescence intensities of the first and third vibronic band of the pyrene fluorescence spectrum gives the correct result because the different quantum yields of free and complexed pyrene are considered correctly. The sole analysis of the Ham effect of pyrene leads to too high values of the association constant. A subsequent formation of 1:1 and 2:1 complexes between β-CD and pyrene was confirmed. The synthesized β-CD polymers exhibit a significant change in the complexation behavior depending on the degree of substitution (DS). At high DS (up to 23%) only 2:1 complex formation was observed, an evidence for intramolecular, chelate-like complexes due to the high local β-CD concentration. At low DS (below 5%) 2:1 complexes are formed only intermolecularly. Compared with pure β-CD, the overall complexation constant of the β-CD polymers increases by more than 2 orders of magnitude with increasing DS and is independent of the polymer molecular weight. The supramolecular structure of the complex is not changed due to the linkage of the cyclic oligosaccharide to the polymer chain.