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. 1 The existence, preparation, and basic properties of DNA-surfactant films have been known in the literature for some time.2 , 3 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 -doublestranded 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 phosphatebuffered 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, e.g. in drug and gene delivery.

Thermotropic liquid crystals from biomacromolecules

“…Inspired by previous work dealing with polyelectrolyte-lipid complexes (2,(26)(27)(28)(29)(30)(31), for the preparation of nucleic acid TLCs, an oligonucleotide [22mer single-stranded DNA (ssDNA)] and the cationic surfactant dimethyldioctylammonium bromide (DOAB) were complexed in a simple procedure, including a final lyophilization step (SI Appendix, Section B). The solvent-free DNA-DOAB complex was birefringent (SI Appendix, Fig.…”

Hydration Induced Stress on DNA Monolayers Grafted on Microcantilevers

“…3,4 Hydration driven structural changes in DNA have recently gained further attention for the generation of responsive biomaterials. 5,6 We have also previously demonstrated exsitu hybridization detection in air after incubation with the sample solutions by harnessing the hydration-induced tension in nucleic acid films 7 or water desorption. 8 Surface stress biosensors have proven high sensitivity that adds to the advantages of a label-free technology.…”

Self‐assembly and applications of nucleic acid solid‐state films

“…The water solubility of the complex is also adjusted by the length of the tail region, the shape of the lipid, and the type of linker group. Complexes that are soluble in organic solvent and can be cast as films are considered a new class of smart materials that combine the properties and advantages of NA with attractive features such as biodegradability and programmable self‐assembly with nuclease‐protective and biologically active lipids or surfactants to allow their use in biofunctional and medical applications 46–49. As discussed later, films formed from these NA–lipid complexes can be successfully dried and rehydrated repeatedly, with both the NA and lipid undergoing a concerted structural transition.…”

“…The cationic surfactant DDAB is coupled to the DNA through electrostatic charges and is thus forced to undergo a similar structural transition such that the tails of the lipids interact with the exposed hydrophobic bases of the DNA. The process is thought to occur cooperatively46 and is analogous to the chromatographic purification of nucleic acids by a hydrophobic column 81. It is thought that earlier studies did not observe this phenomenon because of the addition of water to film samples and incomplete structural analysis, as the DNA was thought to have A, B, or C forms 53,54,56,60,82.…”

“…However as a dry DNA–DDAB film is hydrated the reverse transitions of DNA and DDAB were observed simultaneously. Interestingly this procedure of drying and wetting could be repeated several times 46,48. The threshold relative humidity level to induce structural switching of the film is ∼60%.…”