Spectroscopic Studies of the Complexation of Iodine with Antihistamine Drugs in Solvents of Varying Relative Permittivity

Abstract

The interaction of oxatomide (OXA), azacyclonol (AZA) and chloropheniramine (ClPA) antihistamine drugs with iodine was studied spectrophotometrically in different solvents and at three different temperatures. The electronic, FT-IR, far-IR, and mass spectra of the resulting charge-transfer (CT) complexes were recorded, in addition to thermal analysis. The results obtained show that the stoichiometries of the reactions are all 1:1. The observed time dependence of the CT band and subsequent formation of \( {\text{I}}_{3}^{ - } \) in solution were related to the slow transformation of the initially formed 1:1 (donor: I2) outer complex to an inner complex (electron donor–acceptor), followed by a fast reaction of the inner complex with iodine to form a triiodide ion. The characteristic strong absorptions of \( {\text{I}}_{3}^{ - } \) are observed around 360 nm. The CT-complexes have the formulae [(OXA)I]+\( {\text{I}}_{3}^{ - } \), [(AZA)I]+\( {\text{I}}_{3}^{ - } \) and [(ClPA)I]+\( {\text{I}}_{3}^{ - } \). The formation constants (K), molar absorption coefficients (eCT), and thermodynamic parameters ΔH#, ΔS# and ΔG# of these interaction have been determined and discussed.