ROLE OF HYDROPHOBIC EFFECT AND SURFACE-CHARGE IN SURFACTANT-DNA ASSOCIATION

Ethidium bromide is one of the best known DNA intercalator. Upon inter calation inside DNA, the fluorescence due to ethidium bromide gets enh anced by many orders of magnitude. In this paper, we employed ethidium bromide as a probe for studying surfactant-DNA complexation using flu orescence spectroscopy and agarose gel electrophoresis. Surfactants of different charge types and chain lengths were used and the results we re compared with that of the related small organic cations or salts un der comparable conditions. The cationic surfactants induced destabiliz ation of the ethidium bromide-DNA complex at concentrations in orders of magnitude lower than that of the small organic cations or salts. In contrast however, the anionic surfactants failed to promote any such destabilization of probe-DNA complex. DNA loses its ethidium bromide s tainability in the presence of high concentration of cationic surfacta nt aggregates as revealed from agarose gel electrophoresis experiments . Inclusion of surfactants and other additives into the DNA generally enhanced the DNA double-strand to single strand transition melting tem peratures by a few degrees, in a concentration-dependent manner and at high surfactant concentration melting profiles got broadened.