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The interaction of cationic amphiphiles with calf thymus DNA has been investigated by physicochemical techniques (surface tension, conductometry, UV spectroscopy, thermal denaturation) and morphological microscopies (AFM and TEM). The cationic molecules were the amphiphiles cetyltrimethylammonium and cetyltributylammonium bromides (CTAB and CTBAB, respectively), compared to the nonamphiphilic tetramethyl- and tetrabutylammonium bromides (TMAB and TBAB, respectively) and, as a transfection-efficient comparison, a commercial poliethyleneimine (PEI). As a result, well below their critical micelle concentrations (cmc), CTAB and CTBAB showed a peculiar, nonlinear adsorption profile with the nucleic acid, which showed a correlation with the melting temperatures and morphological changes observed with AFM and TEM microscopies. On the other hand, TMAB and TBAB interact much less with the DNA duplexes and do not induce any modifications of the structures. The same behavior was observed with PEI; however, CTAB and CTBAB proved much less effective in condensing the nucleic acid. [ABSTRACT FROM AUTHOR]

Didodecyldialkylammonium chloride and bromide (alkyl Me, Et, n-Pr, n-Bu) accelerate the spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion, 1,H, and its 5-tetradecyloxy derivative, 1,OTD. With most of these surfactants, first-order rate constants, kobs, go through maxima in very dilute surfactant and then decrease and go through minima as association colloids form. These phenomena are not explicable in terms of substrate-induced micellization. However, kobsincreases in the N-alkyl sequence Me < Et < n-Pr < n-Bu, as is typical of decarboxylations in association colloids of single-chain surfactants. Reaction in premicelles is accelerated by an initial increase in 1,H. The factors that control relative rates of spontaneous reactions in premicelles and in the association colloids, in particular, depletion of water at the reaction center and association of substrate and quaternary ammonium centers, are discussed with respect to the roles of substrate and surfactant hydrophobicities. [ABSTRACT FROM AUTHOR]