Voltammetric, spectroscopic and thermal studies on the binding of some heterocyclic azo compounds with α- and β-cyclodextrins: pH effect and association affinity

Resumo

The binding abilities of α- and β-cyclodextrins (α-CD and β-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 α-CD and β-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 α-CD; however, the binding of the azo dyes with β-CD gave non-inclusion complexes.