STRUCTURE AND DISSOCIATION EQUILIBRIUM OF BIMOLECULAR ASSOCIATES OF ACRIDINE-ORANGE IN AQUEOUS-SOLUTIONS

The aggregate states of Acridine Orange bimolecular probe in aqueous s olution and micelle media were strudied by absorption spectroscopy. Th e absorption spectra of the solutions involving Acridine Orange (AO) c hange with their concentrations. On the basis of Kasha's theory on the difference spectrum between the solution of the AO monomer and that o f dimer, the averaged distance between molecular planes of AO's and th e dihedral angle in dimer molecules mere estimated as 4.4 Angstrom and 80 degrees, respectively. It was also shown that the AO dimer dissoci ates by the addition of surfactant to AO aqueous solution. Dissociatio n equilibrium of bimolecular associates (dimer) of AO was studied ther modynamically. At the temperature of 30-60 degrees C, absorption spect ra of aqueous solutions of AO showed only monomer and dimer bands. Spe ctral changes with varying temperature suggested that a simple equilib rium between AO dimer and monomer. The values of dissociation constant K and dissociation enthalpy Delta H were estimated to be 4.24-6.45 x 10(-5) mol dm(-3) in the range from 40 to 60 degrees C, and 4.16 kcal mol(-1), respectively.