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Structural responses of DNA-DDAB films to varying hydration and temperature.

ABSTRACT: The structure of a DNA-dimethyldidodecylammonium bromide (DDAB) film was recently described to undergo a distinctive transition in response to the water content in the surrounding environment. The existence, preparation, and basic properties of DNA-surfactant films have been known in the literature for some time. Here, we describe the structural response of DNA-DDAB films to environmental changes, particularly temperature and humidity, in greater detail revealing new structural states. We can direct the lamellar structure of the film into three distinct states--double-stranded DNA (dsDNA) paired with an interdigitated bilayer of DDAB (bDDAB), single-stranded DNA (ssDNA) with monolayer of DDAB (mDDAB), and ssDNA with bDDAB. Both temperature and humidity cause the molecules composing the lamellar structure to change reversibly from ssDNA to dsDNA and/or from mDDAB to bDDAB. We found that the structural transition from dsDNA to ssDNA and bDDAB to mDDAB is concerted and follows apparent first-order kinetics. We also found that the double-stranded conformation of DNA in the film can be stabilized with the inclusion of cholesterol even while the DDAB in the film is able to form either a monolayer or bilayer depending on the environmental conditions. Films treated with ethidium bromide prompt switching of dsDNA to ssDNA before bDDAB transitions to mDDAB. Swelling experiments have determined that there is a direct proportionality between the macroscopic increase in volume and the nanoscopic increase in lamellar spacing when a film is allowed to swell in water. Finally, experiments with phosphate-buffered saline (PBS) indicate that the films can disassemble in a simulated biological environment due to screening of their charges by buffer salt. We conclude that the structure of DNA in the film depends on the water content (as measured by the relative humidity) and temperature of the environment, while the state of DDAB depends essentially only on the water content. The structure of the film is quite flexible and can be altered by changing environmental conditions as well as the chemical ingredients. These films will have useful, new applications as responsive materials, for example, in drug and gene delivery.

SUBMITTER: Neumann T

PROVIDER: S-EPMC2895560 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

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Structural responses of DNA-DDAB films to varying hydration and temperature.

Neumann Thorsten T Gajria Surekha S Bouxsein Nathan F NF Jaeger Luc L Tirrell Matthew M

Journal of the American Chemical Society 20100501 20

The structure of a DNA-dimethyldidodecylammonium bromide (DDAB) film was recently described to undergo a distinctive transition in response to the water content in the surrounding environment. The existence, preparation, and basic properties of DNA-surfactant films have been known in the literature for some time. Here, we describe the structural response of DNA-DDAB films to environmental changes, particularly temperature and humidity, in greater detail revealing new structural states. We can di ...[more]

PMID: 20438082

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Project description:The role that interfaces play in the dynamics of liquids is a fundamental scientific problem with vast importance in technological applications. From material science to biology, e.g., batteries to cell membranes, liquid properties at interfaces are frequently determinant in the nature of chemical processes. For most liquids, like water, the influence of an interface falls off on a ?1 nm distance scale. Room temperature ionic liquids (RTILs) are a vast class of unusual liquids composed of complex cations and anions that are liquid salts at room temperature. They are unusual liquids with properties that can be finely tuned by selecting the structure of the cation and anion. RTILs are being used or developed in applications such as batteries, CO2 capture, and liquids for biological processes. Here, it is demonstrated quantitatively that the influence of an interface on RTIL properties is profoundly different from that observed in other classes of liquids. The dynamics of planar thin films of the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2), were investigated using two-dimensional infrared spectroscopy (2D IR) with the CN stretch of SeCN- as the vibrational probe. The structural dynamics (spectral diffusion) of the thin films with controlled nanometer thicknesses were measured and compared to the dynamics of the bulk liquid. The samples were prepared by spin coating the RTIL, together with the vibrational probe, onto a surface functionalized with an ionic monolayer that mimics the structure of the BmimNTf2. Near-Brewster's angle reflection pump-probe geometry 2D IR facilitated the detection of the exceedingly small signals from the films, some of which were only 14 nm thick. Even in quarter micron (250 nm) thick films, the observed dynamics were much slower than those of the bulk liquid. Using a new theoretical description, the correlation length (exponential falloff of the influence of the interfaces) was found to be 28 ± 5 nm. This very long correlation length, ?30 times greater than that of water, has major implications for the use of RTILs in devices and other applications.

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Structural responses of DNA-DDAB films to varying hydration and temperature.

Publications

Structural responses of DNA-DDAB films to varying hydration and temperature.

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