Effect of pH on Anisotropic Gelation of DNA Induced by Aluminum Cations

Abstract

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.

Structure formation in biopolymer gels induced by diffusion of gelling factors

“…The important feature of these theories is the gelation kinetics is described by the functions of scaled variables x  and t  . The gelation kinetics induced by the diffusion of gelling factors were experimentally studied by Dobashi et al extensively [7,19,24,[26][27][28][34][35][36], demonstrating that the experimental results were represented by the equations shown above. In these theories, the polymer concentration in the solution phase was assumed to be constant during the gelation process.…”

“…where x is the thickness of the gel layer, t is the gelation time, and K is a constant corresponding to the gelation rate [19]. On the other hand, the gelation in cylindrical symmetry was described as [19,[26][27][28]   2 2…”

“…DNA [20,[25][26][27][28][29][30][31][32] In the presence of metal cations, DNA in a dilute solution is condensed into a globular state [62]. In contrast, addition of metal cations to a concentrated DNA solution causes gelation due to the crosslinking of DNA chains by the multivalent cations [25].…”

“…In contrast, addition of metal cations to a concentrated DNA solution causes gelation due to the crosslinking of DNA chains by the multivalent cations [25]. For the DNA gels prepared by the sandwich method, the initial stage of the gelation kinetics was described by Eq (2) [26][27][28]. The DNA gel induced by the diffusion of the metal cations was the optically anisotropic gel [25][26][27][28][29], in which the molecular orientation was perpendicular to the gelation direction [20].…”

“…For the DNA gels prepared by the sandwich method, the initial stage of the gelation kinetics was described by Eq (2) [26][27][28]. The DNA gel induced by the diffusion of the metal cations was the optically anisotropic gel [25][26][27][28][29], in which the molecular orientation was perpendicular to the gelation direction [20]. The obtained gels showed an inhomogeneous structure at a macroscopic scale; the DNA concentration was the highest near the contact interface and decreasing with the distance from the interface [26].…”