Inclusion Compounds of Cyclodextrin and Azo Dyes. IV (b). Nuclear Magnetic Resonance and Circular Dichroism Spectra of γ-Cyclodextrin and Orange II in the Solution State

Abstract

The behavior of orange II-γ-cyclodextrin (cdx) complex was examined in the solution state. ¹H-Nuclear magnetic resonance (NMR) data indicate that orange II can pass through γ-cdx. The molar ratios of orange II : γ-cdx as determined from Job plots was 1 : 1 (¹³C-NMR) and 2 : 1 (¹H-NMR). Simulation of the equilibrium constants (K)'s was attempted with three systems. K's of the complex determined by the C-SO^-₃ at 66°C could be well represented by an A+B=AB, AB+B=AB₂ system and gave K₁=74, K₂=5, indicating the coexistence of 1 : 1 and 2 : 1 complexes. On the other hand, β-cdx complex showed a 1 : 1 ratio in Job plots of both ¹H and ¹³C data, giving K₁=2370 in an A+B=AB system, no improvement was obtained by applying an A+B=AB, AB+B=AB₂ system. Generally, the ¹³C-NMR signals of γ-cdx-induced orange II show high-field shifts compared to those of the β-cdx complex. This may be due to the superiority of the hydrophobic interaction to other factors. Judging from the circular dichroism (CD) spectra, γ-and β-cdx include orange II in different directions and there is no electrostatic interaction between γ-cdx and orange II.