INTERACTION OF SURFACTANTS WITH DNA - ROLE OF HYDROPHOBICITY AND SURFACE-CHARGE ON INTERCALATION AND DNA MELTING

A probe, 9-(anthrylmethyl)trimethylammonium chloride, 1, was prepared. 1 binds to calf-thymus DNA or Escherichia coli genomic DNA with high affinity, as evidenced from the absorption titration. Strong hypochrom ism, spectral broadening and red-shifts in the absorption spectra were observed. Half-reciprocal plot constructed from this experiment gave binding constant of 5 +/- 0.5 x 10(4) M(-1) in base molarity. We emplo yed this anthryl probe-DNA complex for studying the effects of additio n of various surfactant to DNA. Surfactants of different charge types and chain lengths were used in this study and the effects of surfactan t addition to such probe-DNA complex were compared with that of small organic cations or salts. Addition of either salts or cationic surfact ants led to structural changes in DNA and under these conditions, the probe from the DNA-bound complex appeared to get released. However, th e cationic surfactants could induce such release of the probe from the probe-DNA complex at a much lower concentration than that of the smal l organic cations or salts. In contrast the anionic surfactants failed to promote any destabilization of such probe-DNA complexes. The effec ts of additives on the probe-DNA complexes were also examined by using a different technique (fluorescence spectroscopy) using a different p robe ethidium bromide. The association complexes formed between the ca tionic surfactants and the plasmid DNA pTZ19R, were further examined u nder agarose gel electrophoresis and could not be visualized by ethidi um bromide staining presumably due to cationic surfactant-induced cond ensation of DNA. Most of the DNA from such association complexes can b e recovered by extraction of surfactants with phenol-chloroform. Inclu sion of surfactants and other additives into the DNA generally enhance d the DNA melting temperatures by a few degrees C and at high [surfact ant], the corresponding melting profiles got broadened.