Effect of pH on anisotropic gelation of DNA induced by aluminum cations

To investigate the effects of pH on the structure and the properties of DNA anisotropic gels and their growth process, we have observed the morphology of DNA anisotropic gel films prepared from DNA solutions with various initial pH, and measured the pH dependences of the shrinking ratio, the birefringence, and the relaxation modulus of the gel as well as the time courses of the gel front and pH-change front lines. The gel films prepared from DNA solutions with high pH have inhomogeneous macroscopic structure, large shrinking ratio, and high optical anisotropy whereas those prepared from DNA solutions with low pH have homogeneous macroscopic structure, small shrinking ratio, and low optical anisotropy. The difference observed at different pH is attributed to the difference in the interaction between DNA molecules and aluminum cations. The time courses of the gel front and pH-change front lines were analyzed with theories based on assumptions for each condition. Both two-stage dynamics observed under high initial pH and one-stage dynamics under low initial pH were explained consistently with the theories.