Heteroassociation of Caffeine and a Phenanthridine Dye in Aqueous Solution

Association of ethidium bromide and caffeine in aqueous solution was studied using spectrophotometry. The results were analyzed using a molecular dimer heteroassociation model. The molecular association equilibrium constants were determined. The experimental absorption spectrum of a mixture of heterocyclic molecules was deconvoluted into individual components using a regularization method. Quantitative information on the structure of the heterocomplex was obtained using data for the individual spectral components. The distance and angle between point transition dipole moments of the heterogeneous molecules were 0.3 nm and 16 o . A calculation of the relative contents of different types of associates in a mixed solution showed that heteroassociation of the molecules decreased the effective concentration of ethidium bromide and, accordingly, the mutagenic activity of the dye.