Molecular Mechanism and Thermodynamics Study of Plasmid DNA and Cationic Surfactants Interactions

Abstract

The molecular mechanism and thermodynamics of the interactions between plasmid DNA and cationic surfactants were investigated by isothermal titration calorimetry (ITC), dynamic light scattering, surface tension measurements, and UV spectroscopy. The cationic surfactants studied include benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride, cetylpyridinium chloride, and cetyltrimethylammonium chloride. The results indicate a critical aggregation concentration (cac) of a surfactant: above the cac the surfactant forms aggregates with plasmid DNA; below the cac, however, there is no detectable interaction between DNA and surfactant. Surfactants with longer hydrocarbon chains have smaller cac, indicating that hydrophobic interaction plays a key role in DNA-surfactant complexation. Moreover, an increase in ionic strength (I) increases the cac but decreases the critical micellization concentration (cmc). These opposite effects lead to a critical ionic strength (I(c)) at which cac = cmc; when I < I(c), cac < cmc; when I > I(c), DNA does not form complexes with surfactant micelles. In the interaction DNA exhibits a pseudophase property as the cac is a constant over a wide range of DNA concentrations. ITC data showed that the reaction is solely driven by entropy because both deltaH(o) (approximately 2-6 kJ mol(-1)) and deltaS(o) (approximately 70-110 J K(-1) mol(-1)) have positive values. In the complex, the molar ratio of DNA phosphate to surfactant is in the range of 0.63-1.05. The reaction forms sub-micrometer-sized primary particles; those aggregate at high surfactant concentrations. Taken together, the results led to an inference that there is no interaction between surfactant monomers and DNA molecules and demonstrated that DNA-cationic surfactant interactions are mediated by the hydrophobic interactions of surfactant molecules and counterion binding of DNA phosphates to the cationic surfactant aggregates.

Aggregation of single-chained cationic surfactant molecules into vesicles induced by oligonucleotide

“…According to Fig. 1a, although the dilution enthalpy of the monomeric DEAB titration into water is very small (closed symbols), the enthalpy change is obvious when the monomeric DEAB is titrated into the oligonucleotide solution (open symbols) and the initial inflection is due to the electrostatic attraction between the positively charged DEAB and the negatively charged oligo(dC) 25 [30,31], indicating the aggregate formation along the oligonucleotide chain [30][31][32][33]. Thus, the cac of DEAB is 40 μM in the presence of oligo(dC) 25 .…”

Thermodynamic Studies of DNA-Cationic Components Interactions Using Titration Calorimetry

“…Moreover, the DNA cationic surfactant interaction is an entropy-driven reaction shown in the positive value of ∆H, where the enthalpy reduction induced by charge-charge interaction of DNA and surfactant does not overcome the enthalpy increase caused by dissociation of counter ions and water molecules from DNA during the reaction. However, those dissociations largely increased the entropy of the system [19].…”

“…Zhu and Evans [19] studied the molecular mechanism and thermodynamics of the interactions between plasmid DNA and cationic surfactants benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride, cetylpyridinium chloride, and cetyltrimethylammonium chloride. The thermal response signals showed that the reaction of DNA and surfactants is reversible, at high surfactant concentration a complex with DNA was rapidly and endothermically formed followed by exothermic dissociation after sufficient mixing.…”

A Study of Effect of Dye Structure on Polyelectrolyte Induced Metachromasy

“…[25]. Comprehensive studies of a variety of cationic surfactants with anionicpolyelectrolytes, have been reported [26][27][28][29][30][31][32]. Cationic dyes that interacted with Heparin mostly fell in the Thiazine group such as MethyleneBlue [33][34][35].…”