Phase Behavior of Single DNA in Mixed Solvents

Melnikov, Sergey M.; Khan, Malek O.; Lindman, Björn; Jönsson, Bo

doi:10.1021/ja981491e

Cited by 124 publications

(138 citation statements)

References 54 publications

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“…This can again be discussed in terms of the attractive electrostatic interactions and the large size of surfactant aggregates formed. However, the latter effect is apparently not required since in studies of DNA compaction induced by other co-solutes, organic solvents, electrolytes, etc., a coexistence of coils and globules is also found (25,34). Essentially all of these studies have concerned vesicles which are not thermodynamically stable.…”

Section: Dna Is Compacted By Cationic Surfactantsmentioning

confidence: 97%

DNA-lipid systems: A physical chemistry study

Dias

Antunes

Miguel

et al. 2002

Braz J Med Biol Res

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It is well known that the interaction of polyelectrolytes with oppositely charged surfactants leads to an associative phase separation; however, the phase behavior of DNA and oppositely charged surfactants is more strongly associative than observed in other systems. A precipitate is formed with very low amounts of surfactant and DNA. DNA compaction is a general phenomenon in the presence of multivalent ions and positively charged surfaces; because of the high charge density there are strong attractive ion correlation effects. Techniques like phase diagram determinations, fluorescence microscopy, and ellipsometry were used to study these systems. The interaction between DNA and catanionic mixtures (i.e., mixtures of cationic and anionic surfactants) was also investigated. We observed that DNA compacts and adsorbs onto the surface of positively charged vesicles, and that the addition of an anionic surfactant can release DNA back into solution from a compact globular complex between DNA and the cationic surfactant. Finally, DNA interactions with polycations, chitosans with different chain lengths, were studied by fluorescence microscopy, in vivo transfection assays and cryogenic transmission electron microscopy. The general conclusion is that a chitosan effective in promoting compaction is also efficient in transfection.

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Section: Dna Is Compacted By Cationic Surfactantsmentioning

confidence: 97%

DNA-lipid systems: A physical chemistry study

Dias

Antunes

Miguel

et al. 2002

Braz J Med Biol Res

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“…The final concentrations (DNA 0.25 μM in terms of nucleotide units; DAPI 0.25 μM) were kept constant throughout the fluorescence microscopy experiments. This concentration of DNA corresponds to half the concentration that has been used in some of the previous studies [11,13,16,17,[22][23][24][25], which makes the visualization of individual DNA molecules easier via fluorescence microscopy in our recent equipment. We note that the number of chains simultaneously visible with such equipment largely exceeds those observed with older setups.…”

Section: Sample Preparationmentioning

confidence: 99%

Cationic agents for DNA compaction

Gawęda

Morán

Pais

et al. 2008

Journal of Colloid and Interface Science

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Fluorescence microscopy was used to investigate the conformational changes of individual T4 DNA molecules induced by different compacting agents, namely the cationic surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), iron(III), lysozyme, and protamine sulfate. A protocol for establishing size estimates is suggested to obtain reproducible results. Observations show that in the presence of lysozyme and protamine sulfate, DNA molecules exhibit a conformational change from an elongated coil structure to compact globules, usually interpreted as a first-order transition. The maximum degree of compaction that is attained when iron(III) or CTAB (CTAC) are used as compacting agents is considerably smaller, and intermediate structures (less elongated coils) are visible even for high concentrations of these agents. Dynamic light scattering experiments were carried out, for some of the systems, to assess the reliability of size estimates from fluorescence microscopy.

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“…This coexistence region is a common phenomenon for DNA molecules on the addition of condensing agents such as organic solvents [30], flexible polymers [31], and multivalent ions [32][33][34]. The coil-globule transition of long DNA molecules is then discrete, a (quasi-) firstorder transition for individual chains, but continuous for their ensemble average [30,32]. Compaction of DNA is believed to be driven by attractive interactions between different parts of the molecule, by ion correlation effects arising from the presence of multivalent ions, for example [35,36], leading to the formation of a nucleation centre in the DNA chain that grows along the molecule chain [37].…”

Section: Introductionmentioning

confidence: 95%

“…Compaction is driven by attractive electrostatic interactions between different parts of a DNA double helix due to the correlation effects arising in the presence of multivalent counter-ions [35,30]. Surfactants have only one charge per molecule but, due to their self-assembly properties, form micellar aggregates in the vicinity of the oppositely charged macromolecule at a certain critical concentration [70], that act as multivalent ions.…”

Section: A Fluorescence Microscopy Studymentioning

confidence: 99%

“…For intermediate concentrations of surfactant a region is observed where both DNA coils and globules coexist [19]. This coexistence region is a common phenomenon for DNA molecules on the addition of condensing agents such as organic solvents [30], flexible polymers [31], and multivalent ions [32][33][34]. The coil-globule transition of long DNA molecules is then discrete, a (quasi-) firstorder transition for individual chains, but continuous for their ensemble average [30,32].…”

Section: Introductionmentioning

confidence: 98%

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DNA and surfactants in bulk and at interfaces

Dias

Pais

Miguel

et al. 2004

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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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...

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Phase Behavior of Single DNA in Mixed Solvents

Cited by 124 publications

References 54 publications

DNA-lipid systems: A physical chemistry study

DNA-lipid systems: A physical chemistry study

Cationic agents for DNA compaction

DNA and surfactants in bulk and at interfaces

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