Circular Dichroism Spectra of DNA Dispersions and Textures of DNA Phases

Circular dichroism (CD) spectra of liquid crystalline dispersions formed as a result of phase exclusion of double-stranded DNA molecules from aqueous-salt-poly(ethylene glycol)-containing solutions were studied at room temperature and under heating. Based on the CD spectra, it is possible to distinguish dispersions with cholesteric packing of DNA molecules from those with hexagonal DNA packing. Heating of DNA dispersions with hexagonal packing led to the appearance of an abnormal band in their CD spectra, which indicated a novel phase transition: from hexagonal to the re-entrant cholesteric packing of DNA molecules in individual particles of these dispersions. At room temperature, the spectra of such dispersions did not contain the abnormal band. By concentration of particles of liquid crystalline DNA dispersions using low-speed centrifugation, liquid crystalline DNA phases were obtained and their optical textures in thin layers were investigated. It was found that the spatial organization of DNA molecules in individual particles of dispersions formed in aqueous-salt-poly(ethylene glycol)-containing solutions may differ from their packing in macroscopic phases.