Abstrait

Spectroscopic Thermodynamic Study Of The Dimerization Reaction Of Acridine Orange By Chemometrics Analysis At Different Ionic Strengths

Jahanbakhsh Ghasemi, Ali Niazi, Alireza Nikrahi

The dimerization constants of acridine orange have been determined by studying the dependence of their absorption spectra on the temperature in the range 20-80°C at different total concentrations of acridine orange (3.3×10-6-9.9×10-6 M) and in different ionic strengths using LiCl, NaCl and KCl inert salts. The monomer-dimer equilibrium of the acridine orange has been investigated by chemometrics refinement of the absorption spectra obtained from thermometric titrations which performed at different ionic strengths. The data processing of the undefined mixtures was performed by simultaneous resolution of the overlapping bands in the whole set of absorption spectra. The dimerization constants are varied by changing the ionic strength and the degree of dimerization are decreased by increasing of the ionic strength of the medium. Utilizing the Van’t Hoff relation, which describes the dependence of the equilibrium constant on temperature, as constraint we determine the spectral responses of the monomer and dimer species as well as the enthalpy and entropy of the dimerization equilibrium. The TΔSo–ΔHo plot for all thermodynamic results is sketched and shows a fairly good positive correlation. The observed linear dependency indicates the enthalpy-entropy compensation in the dimerization reactions.