Inclusion of azoniabetain dyes by cyclodextrins.

Abstract

Formation of inclusion compounds between azoniabetain dyes (2-styryl benzo [a] quinoliziniums, A, B and C) and α-, β- and γ-cyclodextrins (CD) has been investigated from the absorption spectra accompanied by negative solvatochromism. As reference, 4-nitrophenol, potassium 4-nitrophenolate and 4-nitroaniline were used as indicator of the inclusion. The latter three compounds formed inclusion compounds only with α-CD, but not with β- and γ-CD's because of their larger cavity radii. Dye A in OH 0-forms was not included by the three CD's by the steric hindrance of oxygen at o-position of the dye. Dyes, B and C in OH form were not included by α-CD but formed 1:1 inclusion compounds with β- and γ-CD's, and in 0- form, they formed 1:1 incusion compounds with the three CD's. The formation constants were found to be in the order; β-CD > γ-CD > α-CD. Structures of the inclusion compounds were suggested based on their spectra.