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Liquid crystalline phases in DNA and dye-doped DNA solutions analysed by polarized linear and nonlinear microscopy and differential scanning calorimetry

Olesiak J., Matczyszyn K., Mojzisova H., Zielinski M., Chauvat D., Zyss J.

Materials Science Poland

2009

Vol. 27, No. 3

813--823

The contribution reports on an investigation of liquid crystalline phases in salmon (ca. 2000 bp) and herring (ca. 50 bp) roe DNA solutions in water. DNA aqueous solutions exhibit lyotropic liquid crystal (LLC) properties. To characterize LLC phases in DNA solutions, specially prepared LC cells as well as drying droplets were observed under a polarized light microscope (PLM). Differential scanning calorimetry (DSC) was used to determine the temperatures of phase transitions. The preliminary results are discussed and several structures of LLC in DNA aqueous solutions are presented as a function of temperature, concentration and DNA contour length. Apart from pure DNA solutions, a host-guest system was fabricated, with DNA doped with 4-(4-Nitrophenylazo)aniline - an azobenzene derivative, known as Disperse Orange 3 (DO3). In such a system, liquid crystalline phases were observed differing from the phases formed in pure DNA solutions of similar concentrations of matter. To study the mutual orientation of DNA chains and small dye molecules, polarization sensitive nonlinear microscopy was applied. DNA dissolved in water and doped with azobenzene was found to produce a two-photon fluorescence signal. From polarization analysis, a partial ordering of DO3 molecules in DNA matrix was observed.

Kinetics of photochemical processes n photochromic azobenzene derivatives. Effect of matrix and of the phase stability

Janus K., Matczyszyn K., Sworakowski J.

Materials Science

2002

Vol. 20, No. 3

45-55

The contribution discusses the effect of environmental constraints on the kinetics of photochromic processes occurring in two groups of azobenzene derivatives: azobenzene-containing crown ethers dissolved in various polymer matrices, and para-disubstituted azobenzenes dissolved in liquid-crystalline matrices. In the azobenzene-containing crown ethers, the presence of the crown is expected to affect the isomerisation kinetics. The experiments demonstrated that the crown create constraints which modify the molecular structure, thus influencing the isomerisation kinetics as was indeed found in our experiments. In the shortest crown, the room-temperature rate constant of the thermal isomerisation is c.a. two orders of magnitude lower than the respective rate in the parent azobenzene. Measurements of the kinetics of isomerisation of photochromic 4-fluoro-4?-methoxyazobenzene dissolved in the liquid-crystalline pentylocyanobiphenyl (5CB) were carried out. Deviations from the expected Arrhenius behaviour were observed for the thermal cis-trans reaction near the phase transition temperature of 5CB (308 K). It was also found that the isomerisation reaction may trigger the nematic-to-isotropic phase transition at the temperature substantially lower than the thermodynamic transition temperature.