DNA-lipid complexes carrying azobenzene moieties: Preparation, characterization, and photoisomerization

Novel DNA-lipid complexes carrying azobenzene moieties were prepared by substituting sodium counter cations with cationic amphiphilic lipids, namely lipid(AZO) and lipid(diAZO), in which the actual molar ratios of phosphate to lipid were 1:1.05 and 1:1.02, respectively. DNA-lipid(AZO) and DNA-lipid(diAZO) complexes were soluble in common organic solvents including CHCl3, CH2Cl2, methanol, and ethanol, while insoluble in THF, toluene, and water. CD spectroscopy revealed that DNA-lipid(AZO) and DNA-lipid(diAZO) complexes took a predominantly double helical structure in methanol and CHCl3 and that the helical structure was fairly stable against heating. The trans-azobenzene of the DNA-lipid complexes in the side chain isomerized into cis upon UV irradiation, while the helical conformation of DNA backbone hardly changed. The cis-azobenzene moiety reisomerized into trans upon visible-light irradiation, but they did not recover completely the original geometry of azobenzene moieties in the side chain. Both DNA-lipid(AZO) and DNA-lipid(diAZO) exhibited lyotropic LC properties. The onset temperatures of weight loss of DNA-lipid(AZO) and DNA-lipid(diAZO) were both 226 °C according to TGA in air.