Precipitation of DNA by Polyamines: A Polyelectrolyte Behavior

Raspaud, Éric; Cruz, Mónica Olvera de la; Sikorav, Jean‐Louis; Livolant, Françoise

doi:10.1016/s0006-3495(98)77795-1

Cited by 429 publications

(559 citation statements)

References 30 publications

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“…This re-entrant condensation behaviour is shifted to higher protamine concentration with increasing salt, consistent with the DLS observations of charge inversion and with the behaviour with multivalent ions. Interestingly, DNA condensation by protamines is more robust to monovalent salt than that by multivalent ions 24 : as shown in Fig. 4c, F c remains unaffected by monovalent salt up to 300 mM KCl with 1 ng µl −1 protamine in a manner consistent with its biological role.…”

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confidence: 60%

Charge inversion accompanies DNA condensation by multivalent ions

2007

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The condensation of stiff, highly charged DNA molecules into compact structures by condensing agents ranging from multivalent ions 1 to small cationic proteins 2,3 is of major biological and therapeutic importance 4,5 , yet the underlying microscopic mechanism remains poorly understood 1,6-9 . It has been proposed 7,10 that DNA condensation is a purely electrostatic phenomenon driven by the existence of a strongly correlated liquid (SCL) of counterions at the DNA surface. The same theoretical argument predicts that multivalent counterions overcompensate the DNA charge when present at high concentration 11 , in turn destabilizing the condensates 12 . Here, we demonstrate the occurrence of DNA charge inversion by multivalent ions through measurements of the electrophoretic mobility of condensed DNA. By observing the multivalent-ioninduced condensation of a single DNA molecule using magnetic tweezers, we further show that charge inversion influences condensation by modulating the barrier for condensate nucleation in a manner consistent with the SCL mechanism.The role played by spatial correlations of screening ions in biological systems remains poorly understood. Definitive experimental evidence is particularly difficult to obtain because of the short length scales involved. The strongly correlated liquid (SCL) mechanism predicts that charge inversion necessarily accompanies and influences counter-ion-induced like-charge attraction 12 , thus providing a unique opportunity to test this mechanism. We concentrate on DNA because of its high charge density, the level of experimental control that it provides and the direct relevance of condensation to genome packaging.To verify the existence of DNA charge inversion, we measured the electrophoretic mobility, µ, of DNA condensates in solution using dynamic light scattering (DLS). The mobility, µ, reflects the bare charge of DNA plus that of counterions at its surface, and its sign is expected to reverse on charge inversion [13][14][15] . In DLS, the phase of laser light scattered from the condensates is monitored over time; condensates drifting at constant velocity in an electric field yield a phase that evolves linearly in time at a rate proportional to their mobility. Figure 1a shows the measured phase for concentrations c = 0.1 and 3 mM of the quadrivalent cation spermine ([C 10 N 4 H 30 ] 4+ ). The two signals have opposite slopes, indicating a sign reversal of µ (negative for c = 0.1 mM and positive for c = 3 mM). This is to our knowledge the first experimental report of DNA charge inversion induced solely by simple multivalent ions. Figure 1b shows the measured mobility of condensed DNA as a function of the concentration of spermine and buffer conditions. In 1 mM TRIS buffer, the mobility is positive for spermine concentrations greater than the charge-inversion concentration c 0 = 0.5 mM. Increasing the TRIS buffer concentration to 10 mM hinders charge inversion, causing c 0 to increase to 1 mM. Further adding 50 mM monovalent KCl salt causes charge inversion to disa...

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confidence: 60%

Charge inversion accompanies DNA condensation by multivalent ions

2007

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“…[8][9][10][11][12]. Experimental observations show that the size of the precipitating particles is indeed a relevant parameter in the problem [1,6].It has been argued that longitudinal charge fluctuations resulting from the thermal motion of point counterions induce attractions between rod-like polyelelctrolytes [13,14] and induces "buckling" of semiflexible polyelelctrolytes [11,12]. Here, we show that such charge fluctuation are suppressed when the hard core volume of monomers and counterions are taken into account.…”

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confidence: 61%

Attractive interactions between rodlike polyelectrolytes: Polarization, crystallization, and packing

1999

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We study the attractive interactions between rod-like charged polymers in solution that appear in the presence of multi-valence counterions. The counterions condensed to the rods exhibit both a strong transversal polarization and a longitudinal crystalline arrangement. At short distances between the rods, the fraction of condensed counterions increases, and the majority of these occupy the region between the rods, where they minimize their repulsive interactions by arranging themselves into packing structures. The attractive interaction is strongest for multivalent counterions. Our model takes into account the hard-core volume of the condensed counterions and their angular distribution around the rods. The hard core constraint strongly suppresses longitudinal charge fluctuations.PACS numbers: 61.20. Qg, 61.25.Hq, 87.15.Aa Strongly charged polymers precipitate from a dilute solution into compact structures when high-valence counterions (oppositely charged particles) are added to the solution [1][2][3][4][5][6]. The counterions experience strong electrostatic attractions to the backbone of the chains, and a finite fraction of them "condense", i.e., are found within short distance from the chains [7]. Counterions are more attracted to compact chains or aggregates of rod-like chains. This creates the possibility of a transition from single chains with a small number of condensed counterions to almost neutral aggregates of chains, or even mono-molecular collapse in the case of flexible polymers. These aggregates are stable only when the internal arrangement of the counterions within them, provides a strong enough cohesive energy.In this letter we study the attraction between two rodlike polyelectrolytes. We show that it is essential to include the size and angular degrees of freedom (around the rods) of the counterions as well as the discrete nature of the charge along the polyelectrolytes to find the origin and strength of the counterion mediated attraction. Our work suggests that these factors are also crucial in determining the collapse of flexible and semi-flexible polyelectrolytes recently studied in Refs. [8][9][10][11][12]. Experimental observations show that the size of the precipitating particles is indeed a relevant parameter in the problem [1,6].It has been argued that longitudinal charge fluctuations resulting from the thermal motion of point counterions induce attractions between rod-like polyelelctrolytes [13,14] and induces "buckling" of semiflexible polyelelctrolytes [11,12]. Here, we show that such charge fluctuation are suppressed when the hard core volume of monomers and counterions are taken into account. Instead, we find that the counterions arrangement around the rods create a non-zero transversal polarization as the distance between the chains decreases. At very short distances between the rods we find strong longitudinal correlations but only at very short wavelengths, implying a crystalline state along the rod, reinforcing, for the case of multivalent counterions, the attractive interactio...

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“…Beyond the TCMF approximation of Eqs. (19), (20), and (21), the exact equation (22) always applies and can be a very useful tool for assessing correlation effects near charged macromolecules of various geometries.…”

Section: Discussionmentioning

confidence: 99%

“…Numerically solving a non-linear PDE such as (19) requires careful examination of the solution behavior. The purpose of this section is to explain the numerical scheme used in this work, and in particular the parameters required to obtain a reliable solution.…”

Section: Appendix C: Numerical Schemementioning

confidence: 99%

Test-charge theory for the electric double layer

2004

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We present a model for the ion distribution near a charged surface, based on the response of the ions to the presence of a single test particle. Near an infinite planar surface this model produces the exact density profile in the limits of weak and strong coupling, which correspond to zero and infinite values of the dimensionless coupling parameter. At intermediate values of the coupling parameter our approach leads to approximate density profiles that agree qualitatively with MonteCarlo simulation. For large values of the coupling parameter our model predicts a crossover from exponential to algebraic decay at large distance from the charged plate. Based on the test charge approach we argue that the exact density profile is described, in this regime, by a modified mean field equation, which takes into account the interaction of an ion with the ions close to the charged plate.

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Precipitation of DNA by Polyamines: A Polyelectrolyte Behavior

Cited by 429 publications

References 30 publications

Charge inversion accompanies DNA condensation by multivalent ions

Charge inversion accompanies DNA condensation by multivalent ions

Attractive interactions between rodlike polyelectrolytes: Polarization, crystallization, and packing

Test-charge theory for the electric double layer

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