Aggregation and host-guest interactions in dansyl-substituted poly(acrylate)s in the presence of β-cyclodextrin and a β-cyclodextrin dimer in aqueous solution: a UV-vis, fluorescence, ¹H NMR, and rheological study

Abstract

A UV-vis, steady-state, and time-resolved fluorescence 2D 1H NOESY NMR spectroscopic and rheological study of new poly(acrylate)s 3% randomly substituted with either N-(2-aminoethyl)-, N-(6-aminohexyl)-, or N-(12-aminododecyl)-5-dansyl-sulfonamide to give the substituted polymers PAADSen, PAADShn, and PAADSddn, respectively, is reported. Their dansyl substituent aggregation and complexation by β-cyclodextrin, βCD, and its covalently linked dimer N,N′-bis(6 A-deoxy-6 A-β-cyclodextrin)urea, 66βCD 2ur, is also reported. The βCD complexation of the dansyl substituents is characterized by apparent complexation constants, K = 89, 105, and 55 dm 3 mol -1 for PAADSen, PAADShn, and PAADSddn, respectively, and the analogous complexations by 66βCD 2ur are characterized by K = 3.04 × 10 3, 3.42 × 10 4, and 2.42 × 10 5 dm 3 mol -1 at pH 7.0 in aqueous 0.10 mol dm -3 NaCl at 298.2 K. Under the same conditions the dansyl substituent shows three fluorescence decay constants assigned to the aggregated (τ 1 = 2.2, 2.5, and 3.2 ns), single (τ 2 = 5.0, 5.3, and 9.5 ns), βCD (τ 3 = 13.2, 11.7 ns, and undetected), and 66βCD 2ur complexed dansyl substituent states (τ 3 = 13.9, 20.8, and 19.3 ns) where the values in each data set correspond to PAADSen, PAADShn, and PAAddn solutions, respectively. 2D 1H NOESY NMR spectroscopy provides additional insight into dansyl substituent complexation by βCD and 66βCD 2ur, as do rheological studies. These data are interpreted in terms of the factors affecting dansyl substituent fluorescence quenching and the impact of tether length on dansyl substituent aggregation, complexation, and network formation. © 2011 American Chemical Society.