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

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.