Equilibrium Dialysis Studies of the DNA-Acridine Complexes

The strong binding of acridine dyes with DNA was studied by means of equilibrium dialysis. Ten acridine derivatives were used to elucidate the effect of the dye structure on the nature of strong binding. In the strong binding, up to one dye molecule per 4–6 nucleotides was bound with the change of free energy in 5–9 kcal mol−1. The introduction of bulky groups to the 10 or 3,6-positions of the acridine ring led to a marked decrease in both the association constant and the maximum number of binding sites per DNA phosphate. These findings suggest that, when a dye molecule is intercalated, the dye is located in such a way that the bulky groups attached to the acridine ring produce some steric hindrance to the binding.