Molecular Chain Orientation of DNA Films Induced by Both the Magnetic Field and the Interfacial Effect

DNA films showing highly homogeneous orientation of molecular chains were successfully prepared by drying a semidiluted solution in a horizontal magnetic field. Most of the molecular chain elements in the obtained film were found to be one-dimensionally oriented, as shown by X-ray diffraction, polarization microscopy, and linear dichroism spectroscopy. Because a DNA chain is theoretically expected to orientate only in divergent directions perpendicular to a magnetic field, this result suggests that the DNA chains were aligned not only by a magnetic field but also by the interfacial effect that induced the chains to fit along the air−liquid interface. The descent speed of an air−liquid interface by evaporation was faster than the estimated diffusion rate of DNA, suggesting an emergence of a concentrated layer near the surface. As proved by polarization microscopy, this emergence led to the transitional formation of a nematic-like liquid crystalline phase, which resulted in a DNA film with good chain alignm...