Structural Responses of DNA-DDAB Films to Varying Hydration and Temperature (original) (raw)
Related papers
The interaction between DNA and cationic lipid films at the air–water interface
Journal of Colloid and Interface Science, 2005
The interaction between DNA and positively charged dioctadecyldimethylammonium bromide (DODAB) and DODAB/disteroylphosphatidylcholine (DSPC) monolayers at the air-aqueous interface was studied by a combination of the surface film balance and Brewster angle microscopy. In presence of DNA, the Π-A isotherm of the cationic monolayer shifts to larger mean molecular areas due to the electrostatic interaction with DNA while the typical liquid expanded-liquid condensed phase transition for DODAB monolayers disappear and the monolayer remains to be in the liquid expanded phase. Furthermore, the morphology of the film dramatically changes, where the large dendritic-like condensed aggregates observed for DODAB monolayers vanish. The charge density of the monolayer was varied by using mixed monolayers with the zwitterionic DSPC and no large effect was observed on the interaction with DNA. By modeling the electrostatic interactions with the linearized Poisson-Boltzmann equation using the finite-element method and taking into account the assumption in the dielectric constants of the system, it was possible to corroborate the expansion of the cationic monolayer upon interaction with DNA as well as the fact that DNA does not seem to penetrate into the monolayer.
Reversible Structural Switching of a DNA−DDAB Film
Journal of the American Chemical Society, 2009
We describe the novel structure and behavior of a DNA-DDAB complex film cast from an organic solvent which exhibits a structural switching transition as it is dried or wetted with water. The film can be easily prepared by forming a complex between the negatively charged phosphate groups of DNA and the positively charged headgroup of the surfactant DDAB. This complex is then purified, dried, dissolved in isopropanol and cast onto a glass slide to form a self-standing film by means of slow evaporation. While the structure of the dried film was found to be composed of single-stranded DNA and a monolayer of DDAB, upon hydration of the film the structure switched to double stranded DNA complexed to a bilayer of DDAB. We expect that this phenomenon would serve as a useful model for the design of new responsive materials and programmable self-assembly.
DNA−Cationic Surfactant Interactions Are Different for Double and Single-Stranded DNA
Biomacromolecules, 2005
The stability of DNA in solution and the phase behavior in mixtures with dodecyltrimethylammonium bromide (DTAB) were investigated. By means of circular dichroism, UV absorption, and differential scanning calorimetry, we found that for dilute solutions of DNA with no addition of salt the DNA molecules are in the single-stranded conformation, whereas the addition of a small amount of NaBr, 1 mM, is sufficient to stabilize the DNA double-helix. Furthermore, at higher DNA concentrations, native DNA becomes the most stable structure, which is due to a self-screening effect. By phase diagram determinations of the DNAsurfactant system, we found that the effect of salt on phase behavior mainly relates to a difference in interaction of the amphiphile between single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The difference in association between ss and dsDNA with surfactants of different chain lengths can be interpreted in terms of an interplay between hydrophobic and electrostatic interactions, the latter being influenced by polymer flexibility. In this way, a nonmonotonic variation can be rationalized. A crossing of the phase separation lines with DNA concentration can be rationalized in terms of a change in relative stability of ss and dsDNA. The fact that ssDNA phase separates earlier than dsDNA in association with DTAB, may serve as a basis for a method of easily separating dsDNA from ssDNA by the addition of surfactant; this is verified as monitored by circular dichroism measurements.
Journal of Physical Chemistry B, 2001
The formation of composite films of double-stranded DNA and cationic lipid molecules (octadecylamine, ODA) and the hybridization of complementary single-stranded DNA molecules in such composite films are demonstrated. The immobilization of DNA is accomplished by simple immersion of a thermally evaporated ODA film in the DNA solution at close to physiological pH. The entrapment of the DNA molecules in the cationic lipid film is dominated by attractive electrostatic interaction between the negatively charged phosphate backbone of the DNA molecules and the protonated amine molecules in the thermally evaporated film and has been quantified using quartz crystal microgravimetry (QCM). Fluorescence studies of DNA-ODA composite films obtained by sequential immersion of the ODA matrix in the complementary single-stranded DNA solutions using ethidium bromide intercalator clearly showed that the hybridization of the DNA single strands had occurred within the composite film. Furthermore, fluorescence studies of the preformed doublestranded DNA-ODA biocomposite film indicated DNA entrapment without distortion to the native doublehelical structure. The DNA-ODA biocomposite films have been further characterized with Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements. The DNA-fatty lipid composite films would serve as model systems for understanding DNA-membrane interactions as well as in the study of DNA-drug/protein interactions. This approach also shows promise for the synthesis of patterned DNA films and consequent application in disease detection and genome sequencing. a Step A: deposition of ODA on solid substrates by thermal evaporation.
Journal of Colloid and Interface Science, 2013
The self-assembly of a true ternary mixture comprising an electroneutral complex of DNA anions and surfactant cations (dodecyltrimethylammonium cations, DTA), water, and nonionic surfactant (monoolein, MO) has been studied. The phase diagrams of two systems, DTA-DNA/MO/water and, for comparison, dodecyltrimethylammonium bromide (DTAB)/MO/water, were obtained by visual inspection, microscopic examination under polarized light, small-angle X-ray scattering (SAXS) and deuterium NMR (2 H NMR) at 298 K and normal pressure. The isothermal phase diagram of the DTA-DNA/MO/water system contains four liquid crystalline (LC) phase regions (reversed hexagonal, Pn3m, Ia3d, lamellar). The supramolecular assemblies evolve from a bicontinuous cubic structure of the reversed type to the twodimensional hexagonal phase as the content of DTA-DNA is increased. While DTA-DNA tends to form a reversed hexagonal phase, DTAB is incorporated into the existing lamellar phase formed by MO and water giving rise to swelling and to significant extension of the lamellar phase region. There is only a small tendency of the cubic phases existing in the binary system MO/water to accommodate DTAB or DTA-DNA.
Mechanical properties of DNA films
Biopolymers, 1990
The Young's dynamical modulus (E) and the DNA film logarithmic decrement (9) at frequencies from 50 Hz to 20 kHz are measured. These values are investigated as functions of the degree of hydration and temperature. Isotherms of DNA film hydration at 25OC are measured. The process of film hydration changing with temperature is studied. It is shown that the Young's modulus for wet DNA films (E = 0.02-0.025 GN m-') strongly increases with decreasing hydration and makes E = 0.5-0.7 GN m-'. Dependence of E on hydration is of a complex character. Young's modulus of denatured DNA films is larger than that of native ones. All peculiarities of changing of E and 9 of native DNA films (observed at variation of hydration) vanish in the case of denatured ones. The native and denatured DNA films isotherms are different and depend on the technique of denaturation. The Young's modulus of DNA films containing >1 g H 2 0 / g dry DNA is found to decrease with increasing temperature, undergoing a number of step-like changes accompanied by changes in the film hydration. At low water content (< 0.3 g H,O/g dry DNA), changing of E with increasing temperature takes place smoothly. The denaturation temperature is a function of the water content.
Solvent Effect to the Uniformity of Surfactant-Free Salmon-DNA Thin Films
Polymers, 2021
Fabrication of surfactant-modified DNA thin films with high uniformity, specifically DNA–CTMA, has been well considered via drop-casting and spin-coating techniques. However, the fabrication of thin films with pure DNA has not been sufficiently studied. We characterize the uniformity of thin films from aqueous salmon DNA solutions mixed with ethanol, methanol, isopropanol, and acetone. Measurements of thickness and macroscopic uniformity are made via a focused-beam ellipsometer. We discuss important parameters for optimum uniformity and note what the effects of solvent modifications are. We find that methanol- and ethanol-added solutions provide optimal fabrication methods, which more consistently produce high degrees of uniformity with film thickness ranging from 20 to 200 nm adjusted by DNA concentration and the physical parameters of spin-coating methods.
DNA and Surfactants In Bulk and at Interfaces
Colloids and Surfaces A: …, 2004
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 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.