Complexation of Crystal Violet, Pyronine B, and Rhodamine B by Linked β-Cyclodextrin Trimers

The host-guest complexation by beta-cyclodextrin (beta CD), 1,3,5-N,N,N-tris-(6(A)-deoxy-6(A)-beta-cyclodextrin)-benzene (beta CD(3)bz), and 1,3,5-N,N,N-tris(6A-(2-aminoethyl)amino-6(A)-deoxy-6(A)-beta-cyclodextrin)-benzene(beta CDen(3)bz) of cationic crystal violet (CV+) and pyronine B (PB+) and zwitterionic rhodamine B (RB) in aqueous phosphate buffer at pH 7.0 and I = 0.10 mol dm(-3) has been studied by UV-Vis and H-1 NMR spectroscopy. The complexation constants 10(-3) K-1 (298.2 K) are 4.68, 86.3, and 7.08 dm(3) mol(-1) for the 1 : 1 host-guest complexes: beta CD center dot CV+, beta CD(3)bz center dot CV+, beta CDen(3)bz center dot CV+, respectively, and those for the analogous PB+ and RB complexes have also been determined. The associated Delta H degrees and T Delta S degrees for all nine complexes coincide with an entropy-enthalpy compensation plot for the formation of a wide range of beta CD and modified beta CD host-guest complexes reported in the literature. Crystal violet also forms (beta CD)(2)center dot CV+, (beta CD(3)bz)(2)center dot CV+ and (beta CDen(3)bz)(2)center dot CV+ complexes characterised by 10(-2)K(2) (298.2 K) = 2.14, 4.57, and 3.86 dm(3) mol(-1) and analogous (beta CD)(2)center dot PB+, (beta CDen(3)bz)(2)center dot PB+ and (beta CDen(3)bz)(2)center dot RB complexes also form, but the (beta CD(3)bz)(2)center dot PB+, (beta CD)(2)center dot RB, and (beta CD(3)bz)(2)center dot RB complexes were not detected. The effects of the structures of the hosts and guests on the complexation processes are discussed.