Complexation of Methyl Orange with ß-cyclodextrin: Detailed Analysis and Application to Quantification of Polymer-bound Cyclodextrin

• Published in: Supramolecular chemistry 2004-12, Vol.16 (8), p.549-559
• Main Authors: Carrazana, Jorge, Reija, Belén, Cabrer, Pedro Ramos, Al-Soufi, Wajih, Novo, Mercedes, Tato, José Vázquez
• Format: Article
• Language: English
• Subjects: Association equilibria; Cyclodextrins; Inclusion complex; Methyl orange
• ISSN: 1061-0278; 1029-0478
• DOI: 10.1080/10610270412331315235

The formation of inclusion complexes between methyl orange (MO) and β-cyclodextrin (β-CD) was studied extensively using UV-visible absorption spectroscopy. In neutral-to-basic media, where MO is an anion, two complexes of stoichiometries 1:1 and 1:2 (guest:host) are formed, as determined by principal components analysis of the absorption data. Global analysis yields precise values of the corresponding association constants and the spectra of each species: free MO, complex MO · CD and complex MO · 2CD. In acid media, where MO is a zwitterion, only 1:1 complexes are formed, but the system becomes complicated due to tautomerization of MO. The microscopic equilibria among the two tautomers and their corresponding complexes were resolved and estimations of the microscopic association constants were obtained. Finally, the application of MO complexation to the quantification of bound β-CD in a polymer sample is presented, with a detailed description of the experimental conditions to be used and a critical discussion of the results obtained.