COMPLEX-FORMATION BETWEEN DNA AND CATIONIC SURFACTANT

Complex formation between short DNA fragments and dodefyltrimethylanlm onium bromide (DoTAB) has been studied using dynamic (DLS), static lig ht scattering (SLS), high performance capillary electrophoresis (HPCE) and a DoTAB-specific electrode. The combination of diffusion coeffici ent obtained from DLS, mobility from HPCE and binding isotherm allow u s to deduce information about the structure of complexes as a function of bound surfactant. The binding of cationic surfactant to short DNA fragments was shown to proceed in two stages. In the first stage of bi nding, surfactant ions exchange with counterions ''condensed'' on the surface of DNA. At this stage the effective charge on DNA does not cha nge as shown by the combination of mobility and diffusion coefficients of the complexes. The observed high cooperativity of binding can be e xplained by hydrophobic interactions between the surfactant molecules. In the second stage, surfactant molecules bind to DNA without exchang e of condensed counterions, which brings about a dramatic change in th e effective charge of DNA with phase separation occurring at high DNA concentration. (C) 1998 Elsevier Science B.V. All rights reserved.