DNA and surfactants in bulk and at interfaces

Abstract

Recent investigations of the DNA interactions with cationic surfactants and catanionic mixtures are reviewed. Several techniques have been used such as fluorescence microscopy, dynamic light scattering, electron microscopy, and Monte Carlo simulations.The conformational behaviour of large DNA molecules in the presence of cationic surfactant was followed by fluorescence microscopy and also by dynamic light scattering. These techniques were in good agreement and it was possible to observe a discrete transition from extended coils to collapsed globules and their coexistence for intermediate amphiphile concentrations. The dependence on the surfactant alkyl chain was also monitored by fluorescence microscopy and, as expected, lower concentrations of the more hydrophobic surfactant were required to induce DNA compaction, although an excess of positive charges was still required.Monte Carlo simulations on the compaction of a medium size polyanion with shorter polycations were performed. The polyanion chain suffers a sudden collapse as a function of the concentration of condensing agent, and of the number of charges on the polycation molecules. Further increase in the concentration increases the degree of compaction. The compaction was found to be associated with the polycations promoting bridging between different sites of the polyanion. When the total charge of the polycations was lower than that of the polyanion, a significant translational motion of the compacting agent along the polyanion was observed, producing only a small-degree of intrachain segregation, which can explain the excess of positive charges necessary to compact DNA.Dissociation of the DNA-cationic surfactant complexes and a concomitant release of DNA was achieved by addition of anionic surfactants. The unfolding of DNA molecules, previously compacted with cationic surfactant, was shown to be strongly dependent on the anionic surfactant chain length; lower amounts of a longer chain surfactant were needed to release DNA into solution. On the other hand, no dependence on the hydrophobicity of the compacting agent was observed. The structures of the aggregates formed by the two surfactants, after the interaction with DNA, were imaged by cryogenic transmission electron microscopy. It is possible to predict the structure of the aggregates formed by the surfactants, like vesicles, from the phase behaviour of the mixed surfactant systems.Studies on the interactions between DNA and catanionic mixtures were also performed. It was observed that DNA does not interact with negatively charged vesicles, even though they carry positive amphiphiles; however, in the presence of positively charged vesicles, DNA molecules compact and adsorb on their surface.Finally Monte Carlo simulations were performed on the adsorption of a polyelectrolyte on catanionic surfaces. It was observed that the mobile charges in the surface react to the presence of the polyelectrolyte enabling a strong degree of adsorption even though the membrane was globally neutral. Our observati...

New insights on the interaction between hydroxypropylmethyl cellulose and sodium dodecyl sulfate

“…The presence of surfactants may change the behavior of a polymer in solution. This can be exemplified by surfactant-induced thickening (Antunes, Marques, Miguel, & Lindman, 2009;Barreiro-Iglesias, AlvarezLorenzo, & Concheiro, 2003b;Cabane & Duplessix, 1982;Franç ois, Dayantis, & Sabbadin, 1985;Goddard & Ananthapadmanabhan, 1993;Holmberg, Jönsson, Kronberg, & Lindman, 2003;Lange, 1971;Lee, 1999), surfactant-induced swelling (Barreiro-Iglesias et al, 2003b) or compaction (Dias et al, 2004), surfactant-induced phase separation (Goddard & Ananthapadmanabhan, 1993;Holmberg et al, 2003), among other effects.…”

Cationic agents for DNA compaction

“…An important addition to this list is fluorescence microscopy (FM), which was used to observe the condensation of single large T4 DNA molecules [5,6,17]. It has been used in a large number of studies on the interaction between DNA and different compacting agents [4,9,10,14].…”

“…However, DNA molecules exist in a highly packed state in living cells. It has been found that isolated DNA chains undergo a coilglobule transition upon the increasing concentration of condensing agents in solution [5][6][7]. Chemical agents cause compaction by modifying electrostatic interactions between DNA segments, by modifying DNA-solvent interactions, by excluding volume to the worm-like coil (and/or counterions), by causing localized bending or distorsion of the helical structure, or by some combination of these effects.…”

Hydrodynamic size of DNA/cationic gemini surfactant complex as a function of surfactant structure

“…As indicated by the results of surfactant ion-selective electrode measurements, the binding of DNA to hexadecyltrimethylammonium bromide followed two-stage firstorder kinetics for denatured (single-stranded) DNA and three-stage first-order kinetics for native DNA (Maulik et al 1998). The collapsing effect from extended DNA coils to compacted globules upon the addition of single chain cationic surfactant was observed by fluorescence microscopy and dynamic light scattering techniques (Dias et al 2004). From the small-angle X-ray scattering measurements it follows that DNA/single chain cationic surfactants complexes form hexagonal structures for longer chain surfactants (dodecyl-, tetradecyl-and hexadecyltrimethylammonium bromides) (Miguel et al 2003).…”