Effect of calcium ions on the III steps of self-assembly of SA investigated with atomic force microscopy

Previous research on the binding of SA (SA) and calcium ions mainly concentrated on the high concentration solutions and formation of gels. While it was hard to provide details of the behaviors of SA polymer during the binding process. In order to study individual polymer, all the experiments were carried out on diluted solutions in this research. The morphological change of SA self-assembly under the effects of calcium ions was observed using atomic force microscopy, and the change of molecular dimension with the addition of calcium ions was characterized through viscosity data. The SA showed a tendency to form network on the initial addition of calcium ions and the chains broke into rods or particles along with continuous addition of calcium ions. Roughness of images, diameter of the network holes, and the width of chains or rods were measured to support the shape features that combined with the data of viscosity, we proposed a modified three-step hypothesis to interpret the SA binding behaviors in "egg-box" model.