Surfactant-DNA complexes in low ionic strength dilute solutions

Abstract

We have used a combination of optical spectroscopy, fluorescence, isothermal titration calorimetry, surfactant-selective electrode techniques, high-resolution ultrasonic velocity and density measurements to study the binding of the cationic surfactant dodecyltrimethylammonium bromide to short fragments, 200 base pairs, of DNA in dilute solutions at 1 mM NaCl concentration. At the first stage the surfactant forms small aggregates on the DNA surface. This binding is accompanied by a significant change in the DNA secondary structure. At the second stage, we observed the formation of large aggregates of surfactant on the DNA surface. Migration of the fluorescence probe into the hydrophobic core of these aggregates was detected at the second stage. The compressibility of these aggregates is close to the compressibility of micelles of the same surfactant. © Springer-Verlag 1999.