Anomalous Salt Effects on DNA Conformation:  Experiment and Theory

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

doi:10.1021/ma9905627

Cited by 74 publications

(65 citation statements)

References 34 publications

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“…6 that compaction of the polyanion occurs when the polycations are closer to the negative chain and thus thermodynamically restrained in their motion. This can be the explanation for the fact that large amounts of spermidine and spermine are necessary to induce the compaction of DNA in single molecule experiments [50,51].…”

Section: Effect Of the Chain Lengthmentioning

confidence: 98%

“…It was observed that in the presence of polyamines DNA undergoes a discrete conformational change from coil to globule and that, even with spermine, having four charges per molecule, an excess of positive charges was required for the compaction to initiate. Furthermore, the concentrations of the polycations required to induce compaction of DNA decrease substantially with the increase of the charges in the chain, differing by about one order of magnitude [50,51]. When longer polycations were used, charge neutralization was not even required [49].…”

Section: A Dynamic Light Scattering Studymentioning

confidence: 99%

“…We note that interactions between DNA and spermidine or spermine have been studied by techniques like Xray diffraction [48,82], neutron scattering [83], and Raman spectroscopy [84], and by more or less complicated models [48,51,85,86] but the binding properties of the polyamines to DNA are still not clear. Several types of binding have been proposed in the literature, like the location of spermine molecules in the major groove with a single contact with the polyelectrolyte [82], or that the spermine is present in higher concentration close to the minor [86]; also, that polyamines bind to DNA simply by non-specific electrostatic interactions [83,84].…”

Section: Effect Of the Chain Lengthmentioning

confidence: 99%

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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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Section: Effect Of the Chain Lengthmentioning

confidence: 98%

Section: A Dynamic Light Scattering Studymentioning

confidence: 99%

Section: Effect Of the Chain Lengthmentioning

confidence: 99%

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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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“…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: 99%

“…Here the assumption of uncorrelated positions of the counterions does not hold any longer. The role of counterion correlations as charge density and counterion valency increase is best illustrated by an example from recent calculations by Khan et al (24,25), an example with direct relevance for DNA. Figure 5 shows the end-to-end distance for a polymer as it is progressively charged up.…”

Section: Attractive Ion-ion Correlation Effects For Dna In the Presenmentioning

confidence: 99%

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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Polyelectrolytes

Hoagland¹

2003

Encyclopedia of Polymer Science and Technology

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Polyelectrolytes are polymers that develop substantial charge when dissolved or swollen in a highly polar solvent medium such as water. The attendant electrostatic interactions — within a single polyelectrolyte, between polyelectrolytes, or with molecules/surfaces — produce physical properties much different than those for neutral polymers. Most polyelectrolyte solution and gel properties vary sharply with addition of simple electrolytes, which screen electrostatic interactions according to concentration. Scientists are just beginning to understand polyelectrolyte electrostatic interactions, which are known to play an important role in the natural world. Important concepts for polyelectrolytes are counterion condensation, electrostatic persistence length, electrostatic excluded volume, and Donnan equilibrium. Properties such as low angle scattered intensity, solution viscosity, osmotic pressure, polyelectrolyte and counterion diffusion coefficients, conductivity, adsorption, complexation, electric and magnetic birefringence, electrophoresis, titration, and gel swelling can only be understood by accounting properly for electrostatic interactions. These distinctive properties underlie applications in colloid stabilization, surface modification, rheology control, and controlled release.

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Anomalous Salt Effects on DNA Conformation: Experiment and Theory

Cited by 74 publications

References 34 publications

DNA and surfactants in bulk and at interfaces

DNA and surfactants in bulk and at interfaces

DNA-lipid systems: A physical chemistry study

Polyelectrolytes

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