Spectrokinetics study of probable effects of diverse inorganic ions on bleaching of dye

Toluidine blue (TB) is an important anticoagulant metachromasia molecule showing a pronounced variation in the visible spectrum due to the aggregation phenomenon and electrostatic interaction with the charged synthetic and biologic polymers. The current study describes the interactive role of diverse inorganic material ions on the bleaching of toluidine blue (tolonium chloride) (TB+) with urea in acidic and basic media using the spectrophotometric technique. The spectra of TB and urea with different cations and anions were monitored and their characteristic features are presented here. The negative effect of added cations on reduction may be the result of altered electron pathways which led to suppression of the reduction/bleaching of TB, while a slight decrease in dye reduction by added anions may be due to the scavenging of the OH* radical. It has been observed in the case of Co2+ that in addition to the electron-transfer reaction, other processes like layer and precipitate formation also appear to be taking place. The dye bleaching process followed pseudo first order kinetics with respect to TB, urea, and H+ ion, whereas significant decoloration in the presence of urea proved that reductants control the redox reaction. No decoloration in acidic medium with diverse ions was seen compared to alkaline media, showing that water pH played an important role in the bleaching of dye. The reduction/bleaching of dye was investigated at different temperatures, and energy parameters were evaluated for a TB+-Urea reaction, including the energy of activation (E-a = 39.60 kJ.mol(-1)), enthalpy of activation (Delta H-# = 34 kJ.mol(-1)), entropy of activation (Delta S-# = 146.5 kJ mol(-1).K-1), and free energy of activation (Delta G* = -52.35 kJ.mol(-1)). A mechanism of interaction of diverse ions in dye bleaching and a mechanism of reduction based on the above findings is proposed.