Thermodynamic studies on DNA‐dye complexes

The interaction between DNA and dyes such as acridine orange ( 1 ), proflavine ( 2 ), and 3,8‐diamino‐5‐ethyl‐6‐phenylphenanthridinium bromide ( 3 ) were studied by means of the heat of mixing and UV spectra. From the results obtained, the thermodynamic quantities of DNA‐dye complexes were estimated. It is concluded that the intercalation process forms a more stable binding than the stacking process does. Further, in each process, Δ G of DNA‐ 2 and DNA‐ 3 systems is nearly equal to that of the DNA‐ 1 system, but their — Δ H and — Δ S values are higher than those of the DNA‐ 1 system. The stability of binding in DNA‐ 2 and DNA‐ 3 systems may be governed largely by Δ H , while in the DNA‐ 1 system Δ S may contribute largely to the stability of binding.