Spectroscopic Studies of Interaction of Two DNA Intercalators, Ethidium Bromide and 9-Aminoacridine, with Sodium Dodecyl Sulphate

The interaction of two DNA intercalating, cationic ligands, the drug ethidium bromide and the dye 9-arninoacridine, with the anionic amihiphile sodium dodecyl sulphate (SDS) was investigated using spectrophotometry and spectrofluorimetry. Both the ligands reduced markedly the critical micelle concentration (CMC) of the amphiphile. The interaction between the ligands and SDS was seen to occur in three stages. In the first stage ion-pairs were formed, and the third stage of interaction results in dye-rnicelle complexes, while the second stage is an intermediate stage. A comparison of the spectral characteristics of the ligand - SDS systems with those of the ligand - DNA complexes indicated that apart from electrostatic interactions, hydrophobic interactions made an important contribution to the overall energetics of the interaction with surfactant micelles as well as with DNA.