Electrostatic complex of didodecyldimethylammonium and DNA: Langmuir monolayer, Langmuir–Blodgett film and dye recognition at air/water interface

Phase behaviour and adsorption of deoxyribonucleic acid onto an azobenzene liquid crystalline ligand at the interfaces

Azobenzene liquid crystalline (ALC) ligand contains a cholesteryl group linked to an azobenzene moiety through a carbonyl dioxy spacer (C7) and terminated with an amine group as a polar head. The phase behaviour of the C7 ALC ligand at the air-water (A-W) interface is investigated employing surface manometry. The surface pressure-area per molecule isotherm shows that C7 ALC ligand exhibit two different phases following the phase sequence viz., liquid expanded (LE₁ and LE₂) and then collapse to three-dimensional crystallites. Further, our investigations under different pH conditions and in the presence of DNA reveal the following. Compared to the bulk, the acid dissociation constant (pK_a) of an individual amine reduces to 5 at the interfaces. For pH (3.5) < pK_a, the protonation of amine groups of C7 ALC ligand facilitates the condensation of the film and enhances the stability. For pH values > pK_a, the phase behaviour of the ligand remains the same due to the partial dissociation of the amine groups. The presence of DNA in the sub-phase result in the expansion of isotherm to the higher area per molecule and the compressional modulus extracted reveals the phase sequence; liquid expanded, liquid condensed, followed by a collapse. Further, the kinetics of adsorption of DNA to the amine groups of the ligand is investigated, suggesting the interactions are influenced by surface pressure corresponding to different phases and pH of the sub-phase. Brewster angle microscope studies are carried out at different surface densities of the ligand as well as in the presence of DNA also supports this inference. Atomic force microscope is employed to acquire the surface topography and height profile of C7 ALC ligand (1 layer) after transferring on onto a silicon substrate using Langmuir Blodgett deposition. The difference in the surface topography and thickness of the film indicates the adsorption of DNA onto the amine groups of the ligand. The characteristic UV-visible absorption bands of the ligand films (10 layers) at the air-solid interface are tracked and the hypsochromic shift of these bands is also attributed to these DNA interactions.

Unveiling the interaction of DNA–octadecylamine at the air–water interface by ultraviolet-visible reflection spectroscopy

In this work, ultraviolet-visible reflection spectroscopy is proposed as a technique that, in combination with classical surface pressure–area isotherms, allows to study in situ the adsorption of DNA to octadecylamine monolayers.

Honeycomb-patterned films fabricated by self-organization of DNA-surfactant complexes

In this paper, DNA-based honeycomb films were successfully constructed from a simple solution casting process at high relative humidity, through the encapsulation of DNA with a cationic surfactant ditetradecyldimethylammonium (DTDA). Cationic surfactants electrostatically attach to phosphate anions of DNA in a molar ratio of 1:1 in the DNA-DTDA complex. Investigation of the effects of substrate, concentration, and solvent on the morphology of the microporous films demonstrated the wide generality and high reproducibility of the formation of DNA-DTDA self-organized microporous films. The morphology of the microporous structures can be adjusted by slightly changing the concentration of the complex solution. DNA exists in the double helical B-form in the microporous film confirmed by circular dichroism spectrum. Dye molecule rhodamine B was loaded into the DNA-DTDA complex, presenting a fluorescent microporous film. DNA-DTDA complex as a host material provides a new method for tailoring fluorescent microporous films. The DNA-based ordered honeycomb films should be attractive for use in optical and optoelectronic devices, separation, ion transportation, and biosensors.

Surfactant encapsulated DNA: structure characterization and interaction with dye molecules in organic media

The recognition of electrostatically-bound DNA-didodecyldimethylammonium (DNA-DDDA) complex by three dye molecules, acridine orange (AO), ethidium bromide (EB) and 5,10,15,20-tetrakis(4-N-methylpyridyl) porphyrin tetra(p-toluenesulfonate) (TMPyP) in organic media was investigated through 1H NMR, UV-vis, and circular dichroism (CD) spectroscopies. When the organic solvent in which DNA-DDDA complex dissolves is changed from ethanol to chloroform, the adsorbed AO undergoes a reversible transformation from a monomer to a highly aggregated state at the interface between DNA and DDDA. EB also adsorbs at the interface between DNA and DDDA when EB interacts with the DNA-DDDA complex in organic media, but its existing state is independent of the used solvents. The third dye, TMPyP cation can intercalate into the G-C region while its anionic p-tosylate counterion remains unbound when it mixes with DNA complex in organic media. The complexes of DDDA with previously recognized DNA by the three dye molecules (DNA-dye), respectively, are also investigated. AO seems having changed its location from the grooves of DNA to the interface between DNA and DDDA after DNA-AO complex was electrostatically encapsulated with DDDA. The aggregation behavior of AO also shows a dependence on the polarity of the organic solvent. EB molecules are believed to intercalate into the base pairs of DNA in aqueous solution. The intercalation mode is still maintained after the encapsulation for DNA-EB in organic solvents, which is different from the situation between DNA-DDDA complex and EB. But in both cases, the existing states of EB are independent of the polarity of the organic solvents. Finally, TMPyP in the complex of DNA-TMPyP and DDDA is also judged to intercalate into the G-C region of DNA while its anionic p-tosylate counterion remains separated from DNA complex, which is similar to its interaction with DNA-DDDA complex in organic media. These data also strongly suggest that the intercalation state of TMPyP is more stable than its adsorption state in grooves when it is recognized with DNA. The present results are significant for the designs of both laser dye and conductive materials.