| 1. |
- Dias, Rita, et al.
(författare)
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DNA and surfactants in bulk and at interfaces
- 2004
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 250:1-3, s. 115-131
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Tidskriftsartikel (refereegranskat)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. C 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 observations indicate that the adsorption behaviour of the polyelectrolyte is influenced by the response given by the membrane to its presence and that the number of adsorbed beads increases drastically with the increase of flexibility of the polymer. Calculations involving polymers with three different intrinsic stiffnesses showed that the variation is non-monotonic. It was observed also that a smaller polyanion typically adsorbs more completely than the larger one, which indicates that the polarisation of the membrane becomes less facilitated as the degree of disruption increases. (C) 2004 Elsevier B.V. All rights reserved.
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| 2. |
- Dias, Rita, et al.
(författare)
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DNA-Surfactant interactions, compaction, condensation, decompaction and phase separation
- 2004
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Ingår i: Journal of the Chinese Chemical Society. - 2192-6549. ; 51:3, s. 447-469
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Forskningsöversikt (refereegranskat)abstract
- Recent investigations-of the interaction between DNA and alkyltrimethyl ammonium bromides of various chain lengths are reviewed. Several techniques have been used such as phase map determinations, fluorescence microscopy, and electron microscopy. Dissociation of the DNA-surfactant complexes, by the addition of anionic surfactant, has received special attention. Precipitation maps for DNA-cationic surfactant' systems were evaluated by turbidimetry for different salt concentrations, temperatures and surfactant chain lengths. Single-stranded DNA molecules precipitate at lower surfactant concentrations than double-helix ones. It was also observed that these systems precipitate for very low concentrations of both DNA and surfactant, and that the extension of the two-phase region increases for longer chain surfactants; these observations correlate well with fluorescence microscopy results, monitoring the system at a single molecule level. 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. The compaction of a medium size polyanion with shorter polycations was furthermore studied by means of Monte Carlo simulations. The polyanion chain suffers a sudden collapse as a function of the condensing agent concentration and of the number of charges on the molecules. Further increase of the concentration gives an increase of 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. However, complete charge neutralization was not a prerequisite to achieve compacted forms.
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| 3. |
- Dias, Rita, et al.
(författare)
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Modeling of DNA compaction by polycations
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:15, s. 8150-8157
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Tidskriftsartikel (refereegranskat)abstract
- In this work we study polycations as efficient compacting agents of a medium size polyanion by means of Monte Carlo simulations. The systems are characterized in terms of a conformational analysis in which shape, overall dimensions, structure factors, radial distribution functions, and the degree of accumulation of the compaction agent near the polyanion are taken into consideration. Results show that the degree of compaction depends on the size of the positive chais and their number. The role of electrostatic interactions is paramount in the compaction process, and an increase in the number of molecules of the compacting agent or in the number of charges of each molecule leads to collapse, which may be followed by some unfolding in situations of overcharging. Compaction is associated with polycations promoting bridging between different sites in the polyanion. When the total charge of the polycations is significantly lower than that of the polyanion, interaction produces only a small degree of intrachain segregation in the latter, allowing for significant translational motion of the compacting agent along the longer chain. However, complete charge neutralization is not mandatory to achieve compact forms. (C) 2003 American Institute of Physics.
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| 4. |
- Sarraguca, J M G, et al.
(författare)
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Structure of polyelectrolytes in 3 : 1 salt solutions
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:23, s. 12621-12628
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Tidskriftsartikel (refereegranskat)abstract
- Polyion conformation and the distribution of small ions near the polyion have been investigated using Monte Carlo simulations. The systems of interest contained one polyion and its monovalent counterions, and variable amount of a 3:1 salt. With monovalent counterions only, the polyion is strongly extended. As salt is added, the polyion folds, and the most compact and spherical-like structure appears at a three-fold excess of the trivalent counterions. The polyion exerts a strong influenc on the nearest-neighbor distance among the trivalent ions, an effect being relevant for energy transfer reactions. (C) 2003 American Institute of Physics.
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| 5. |
- Miguel, Maria, et al.
(författare)
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DNA-cationic amphiphile interactions
- 2003
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Ingår i: Colloids and Surfaces a-Physicochemical and Engineering Aspects. ; 228:1-3, s. 43-55
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Tidskriftsartikel (refereegranskat)abstract
- DNA shows strong interactions with cationic cosolutes and these have both biological and technological significance. We outline our research on various mixed system of DNA and cationic amphiphiles including the interaction of DNA with simple cationic surfactants as well as the interaction with catanionic mixtures and positively charged catanionic vesicles. An overview from phase behavior to microstructure will be presented. We will also address DNA compaction and decompaction phenomena in different systems. Finally, simulations on DNA confinement and interaction with cationic polyions are considered. (C) 2003 Published by Elsevier B.V.
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