Biopolymers and cell. 2001; 17 (6): 501 - 511

A generalized statistical-thermodynamical model of hetero-association of aromatic molecules in aqueous solution for the NMR data interpretation

D. A. Veselkov, M. P. Evstigneev, D. B. Davies, V. V. Kodintsev, A. N. Veselkov

On the ground of the basic hetero-association model derived previously, a generalized statistical-thermodynamical model of het¬ero-association of aromatic molecules has been developed for the NMR data interpretation. In the proposed model, unlike the basic one, the edge effects are taken into consideration, i.e. the depend¬ence of the proton chemical shift on the position of the molecule situated inside, at the edge of the aggregate or in the hetero-stack. Both basic and generalized models were used for the analysis of hetero-association of acridine dye, proflavine (PF), and phenan-thridinium dye, ethidium bromide (EB), in aqueous solution. The calculation of the association parameters of the molecules has been carried out using H-NMR (500 MHz) experimental data. The experimental concentration and temperature dependence s of the proton chemical shifts of interacting aromatic molecules have been studied. The parameters calculated according to the basic and generalized models are found to differ approximately by 30 % and depend substantially on the magnitude of the equilibrium hetero-association constant KC — the larger the KC value the higher the discrepancy between two models. The analysis of the structural and thermodynamical characteristics of the PF-EB complexation indi¬cates the major role of dispersive interactions in stabilization of the PF-EB hetero-comptex. KEY WORDS: statistical-thermodynamical model, proflavine, ethidium bromide, hetero-association, thermodynamics.