Voltammetric, Spectroscopic and Thermal Studies on the Binding of Some Heterocyclic Azo Compounds with alpha- and beta-Cyclodextrins: pH Effect and Association Affinity

Abstract

The binding abilities of alpha- and beta-cyclodextrins (alpha-CD and beta-CD) with some heterocyclic azo compounds (1,1'-(azodicarbonyl)dipiperidine (ADP) and azodicarboxylic dimorpholide (ADM)) were studied at different pHs (4, 7.4 and 10) by UV-Vis spectroscopy and square-wave voltammetry techniques. The association constants (K-i) and stoichiometries of the binding of these azo compounds with alpha-CD and beta-CD were determined by using square-wave voltammetry technique. These bindings were formed with a stoichiometry of 1 : 1 in solution. The solid samples, obtained from the mixtures (molar ratio of 1 : 1) of these azo dyes and CDs in aqueous phase were analyzed by FT-IR spectroscopy and thermal analysis methods. Thermal analysis results showed that ADP and ADM formed the inclusion complexes with alpha-CD; however, the binding of the azo dyes with beta-CD gave non-inclusion complexes.