Annular self-assembly of DNA molecular chains occurring in natural dry process of diluted solutions.

The molecular orientation of DNA membranes, which were prepared by subjecting diluted solution of salmon sperm DNA to a natural drying process, was examined. X-ray diffraction and polarization microscopy revealed that the dried membranes have zonal structures. Each zone shows different features in molecular orientation. In the outer zones formed at the early stage in drying, DNA molecular chains were found to be aligned along the annular curve of the peripheral edge. Both the uneven thickness and disproportional molecular weight distribution in a membrane suggested that the radial flow transported DNA molecules to the edge and that they formed the accumulated phase. Above the critical concentration for the formation of liquid crystalline, the DNA chains would be aligned onto the preformed solid--liquid interface. The membranes with the highest birefringence were obtained from DNA samples with the relatively high molecular weight of around 29 kbp. In the innermost zone, on the other hand, the DNA molecules were radially oriented. This alignment can be attributed to the hydrodynamic effect caused by the rapid translation of the edge interface, which overcomes the Brownian motion of the chain segments. A transitive balance of physical effects was revealed in the dry process, which provided quite orthogonal molecular orientations in a single droplet.