Spectroscopic Study of Hydrophobic Interaction of Heterocyclic Amine N-Oxides with Cyclodextrins

Abstract

Electronic spectra of aromatic amine N-oxides show a marked blue shift with the change of solvent polarity from aprotic solvents to protic ones. This is very useful to examine the hydrophobic interaction between the amine N-oxides and cyclodextrins (CyD) in water. Among the various systems studied a typical example is the system of 4-nitroquinoline N-oxide (4NQO) and 2, 6-di-Omethyl-β-cyclodextrin in water. A clear red shift of the ultraviolet (UV) spectrum of 4NQO was observed upon inclusion complex formation, indicating directly that the CyD cage environment is much more hydrophobic than in water. Thermodynamic and spectroscopic constants pertinent to those inclusion complex formations were evaluated and the results are discussed in relation to the complex formation mechanisms.