Kinetic and amplitude measurements for the process of association of acridine orange studied by temperature-jump relaxation spectroscopy
- 1 January 1975
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 71, 815-830
- https://doi.org/10.1039/f19757100815
Abstract
The kinetics of aggregation of Acridine Orange and the amplitudes associated with this process have been studied as a function of concentration and temperature in water and in an aqueous organic medium, and the results have been quantitatively evaluated by means of a general theory which is developed for associating systems. The relaxation curves are complex and non-exponential due to the presence of a multi-equilibrium system. However, an analysis based on mean relaxation times (τ*) is possible. This important kinetic quantity enables a relaxation spectrum of similar relaxation times to be analysed, (i.e. τ1≃τn), and is most useful when non-exponential relaxation curves are observed. The theory when applied to self-associating systems leads generally to the prediction of wavelength-dependent τ* values. The amplitude and kinetic results confirm a previous thermodynamic analysis (based on visible spectrophotometry) that oligomers are formed in the solution, and that, at an ionic strength of 0.1 M‡ in water, the equilibrium constants Kn,n+ 1 characterising aggregation decrease as n is increased (where n refers to an oligomer of n Acridine Orange units). The rate constant for stepwise association is close to but less than the diffusion-controlled limiting value. The Debye–Smoluchowski equation is applied to the system and the results are explained in terms of solvation changes and reorientation on stacking. The thermodynamic parameters, ΔH° 12 and ΔS° 12, characterising dimerization are derived from the amplitude analysis and discussed in relation to the factors responsible for dye stability.Keywords
This publication has 0 references indexed in Scilit: