In vitro simulation of the chemical scenario of the action of an anti-thyroid drug: charge transfer interaction of thiazolidine-2-thione with iodine.

Thiazolidine-2-thione (T2T) has been studied spectrophotometrically by UV-visible and IR spectra. The spectral studies have indicated that T2T has two tautomeric forms, namely thione and thiole forms, in addition to the dimeric thioamide complex existing as a hydrogen-bonded dimer of two thione forms. Interaction of the T2T as an electron donor with iodine as a typical σ-type acceptor has been studied spectrophotometrically. Electronic absorption spectra of the system T2T-I2 in several organic solvents of different polarities have performed a clear charge transfer (CT) band in each spectrum. Formation constants (KCT) and molar absorption coefficients (ɛCT) and thermodynamic properties, ΔH, ΔS, and ΔG, of this system in various organic solvents were determined and discussed. The stoichiometric ratio of the T2T-I2 system in solutions was found to be 1:1 T2T:I2, whereas the elemental analysis of the prepared solid CT complex has illustrated the same stoichiometry. The obtained KCT and ɛCT values have indicated that T2T is a donor of moderately strength capable of interacting with the iodine just to form the corresponding CT complex with an iodine molecule without further reducing of the iodine to either of the corresponding poly-iodide ions viz. I3-, I5-, etc. This action of spongy trapping of iodine simulates in vitro the chemical scenario of the anti-thyroid action of this compound.