Cis-Isomers of Photosensitive Cationic Azobenzene Surfactants in DNA Solutions at Different NaCl Concentrations: Experiment and Modeling

Abstract

The DNA interaction with cis-isomers of photosensitive azobenzenecontaining surfactants was studied by both experimental methods and computer simulation. It was shown that before the organization of micelles, such surfactants in the cis-conformation form associates of only a single type with a disordered orientation of molecules. In contrast, for trans-isomers, there exist two types of associates with headto-head or head-to-tail orientations of molecules in dependence on salt concentration in a solution. The comparison of cis-and trans-isomer binding to DNA and the influence of salt concentration on the formation of their complexes with DNA were studied. It was shown that cis-isomers interact with phosphate groups of DNA and that their molecules were also located along the minor groove of DNA.

Electrostatic Interactions in the Formation of DNA Complexes with Cis- and Trans-Isomers of Azobenzene-Containing Surfactants in Solutions with Di- and Trivalent Metal Ions

“…Later, the surfactant cations began to aggregate with each other in solution as well as to bind to DNA phosphates and to form aggregates on DNA. The structure of the aggregates for the cis- and trans-surfactants has been studied in detail earlier. , Obviously, small trivalent cations have an advantage over the monovalent surfactant cations in binding to DNA phosphates.…”

“…The micelle size weakly depends on the salt concentration. It was shown that for cis-isomers the micelle size is smaller than that for trans-isomers, and the ionic strength of the solution influences it …”

“…It is important for our research that trans- and cis-isomers of the surfactant interact with DNA in different ways . The binding of trans-isomers to DNA occurs cooperatively (Figure a); surfactant spectra in the region of wavelengths where DNA does not absorb are clearly divided into two groups, corresponding to the free and to the DNA-bound state.…”

“…The structure of the aggregates for the cis-and trans-surfactants has been studied in detail earlier. 62,63 Obviously, small trivalent cations have an advantage over the monovalent surfactant cations in binding to DNA phosphates. In the system containing DNA and CoHex 3+ (system I) in a time of approximately 25 ns, two DNA molecules approached each other up to a distance (between the phosphates) of approximately 1 nm.…”

“…This property makes it possible to use azobenzene-based compounds for light-controlled DNA condensation and in various nanodevices. 60,61 Surfactant interaction with DNA in solutions at different NaCl concentrations was previously studied in detail by our group 13,24,62,63 and other researchers. 19,64,65 ■ MATERIALS AND METHODS High molecular calf thymus DNA (Sigma-Aldrich) with a molecular mass of 9 × 10 6 g/mol determined by viscometry and cationic azobenzene-containing surfactant (Figure 1) synthesized according to the synthesis scheme described in ref 66 were used.…”