Compaction Process of Calf Thymus DNA by Mixed Cationic−Zwitterionic Liposomes:  A Physicochemical Study

Abstract

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Polycation-Mediated Gene Delivery: The Physicochemical Aspects Governing the Process

“…In the DNA solution (filled squares) by contrast, the conductivity grew linearly, however, with a clear change in slope at the chitosan concentration of 0.104 mM, corresponding to the N/P ratio of 0.82. A similar inflection in a conductivity plot during DNA compaction upon addition of a cationic vector has been observed elsewhere (Rodriguez-Pulido et al, 2008). The authors suggested that the increase in conductivity related to the counterion release from the polycation injected is accentuated by the release of counterions resulting from the complexation process (in our case Na + from DNA and CH3COO − from chitosan) thereby justifying a higher slope in the conductivity plot below the inflection point.…”

“…135 nm). It appears then, that as DNA comes in contact with MEP, the polyanion acts as a stabilizer of the liposomes, a result that has been observed for other polymer-vesicle interactions (Antunes et al, 2009;Rodriguez-Pulido et al, 2008). Very importantly, compared to the other DNA-cationic vector formulations here studied, in particular to the DNA-chitosan system (R H up to 450 nm), the sizes depicted by the DNA-MEP complexes are considerably lower.…”

“…Determination of the (N/P)c by conductometry Electrostatic interactions between oppositely charged polyelectrolytes entail a release of counterions (Manning, 1978;Matulis et al, 2000). The tracking of this release by means of conductometry can be employed as a tool to characterize the DNA compaction process (Rodriguez-Pulido et al, 2008). To confirm the (N/P)c values obtained by SLS we measured the change in conductivity provoked by the addition of chitosan solutions to both, DNA and pure buffer solutions.…”

“…On the other hand, once the inflection occurred, the lower slope can be attributed to the fact that only the counterions coming from the chitosan dissociation now contribute to the conductivity of the solution. This change in slope of the conductivity plot can in consequence be considered as the point from which DNA is compacted, namely (N/P)c (Rodriguez-Pulido et al, 2008). Compared to the DNA compaction ratio we determined by SLS ((N/P)c ~ 1.5) , the lower ratio of N/P = 0.82 here depicted can be ascribed to the difference in ionic strength of the media used in both experiments and to the fact that contrary to SLS, in the conductometry experiment the complex formation was run at constant stirring.…”

Non-intercalative, Deoxyribose Binding of Boric Acid to Calf Thymus DNA

“…Calf thymus DNA stock solutions (0.1 mg/ml DNA or 1.18×10 −4 M base pairs) [15] were obtained by directly dissolving ct-DNA in buffer. Molarities of calf thymus DNA solutions were confirmed by spectrophotometric analysis (assuming ε 260 =6,600 M −1 cm −1 [16]).…”