Formation of complexes of DNA with cationic amphiphilic molecules as studied by the flourescent probe method

The formation of complexes of DNA with dodecylamine, do decyltrimethylammon ium, tetradecyltrimethylammonium, and hexadecyltrimethylammonium was studie d using a fluorescent probe pyrene. The dependences of the spectral paramet ers of the hydrophobic pyrene probe on the concentration of the cationic am phiphile hi the, presence and absence of DNA were obtained and analyzed. It is shown that, in the absence of DNA, these-dependences exhibit only one S -shaped region, which corresponds to the micelle formation of the amphiphil e, whereas III the presence of DNA there are two S-shaped regions, which in dicates the cooperative formation of two types of DNA-cationic amphiphile c omplexes, For each of the four cationic amphiphiles, the critical concentra tions for the micelle formation in the absence of DNA (C-0) and the concent rations at Which the first (C-d1) and the second complex with DNA are forme d were determined, It was found that the C-d1 value is 15-40 times lower th an C-0. The C-d1 value does not depend on DNA concentration and is determin ed only by the length of the hydrocarbon chain and the structure of the amp hiphile ionic fragment. The C-d1 value increases as the length of the aliph atic chain decreases and upon replacement of mobil hydrogen atoms in the am monium fragment by methyl groups. It was shown that hydrophobic clusters of amphiphile arising upon complex formation With DNA play the role of cross- links promoting DNA aggregation, or DNA compactization in the Case of dilut e solution of high-molecular weight DNA. The structures of the first and se cond DNA-cationic amphiphile complexes are proposed, and the mechanism and nature of interactions that determine their formation are discussed.