Hokkaido University Gong Jianping team \”Giant\”: the role of competition in different cationic hydrogel polycationic -π on the benzene ring

Polyelectrolyte hydrogels have a number of unique features, including a high water absorption capacity, ion conductivity and the like. When the polyelectrolyte hydrogel is immersed in salt water, charged groups on the polymer chain bound to the gel network since unable to move, while smaller ions are free to move in the surrounding medium. At thermodynamic equilibrium, in order to satisfy an electrically neutral systems, these small ions in the gel – forming solution interface will be non-uniform distribution. In this case, this balance is called Donnan equilibrium, the relative potential between the gel and the solution is referred to Donnan potential. Within this system, the charged polymer has the same charge and a small group of co-ion is called ion, oppositely charged counterions called small ions (FIG. 1).

Figure 1 a schematic view of the distribution of (a) ion polycationic hydrogel and salt in the aqueous solution. A schematic view (b) of the microelectrode. (C) the hydrogel Donnan potential depth distribution.

in an aqueous solution, although that tend to ionic dissociation, but there is still a portion near the counter ion is strongly bound to the polymer chain, which directly leads to a reduction in the system of ion activity. By measuring the potential of polyelectrolyte hydrogel in a state of equilibrium, and with Ru Tangnan balance equation, we can calculate the counter ion activity coefficient. The team had successfully prepared a novel series of controlled monomer sequence \”heteroaryl polyelectrolyte\” copolymer – cationic – phenyl ortho sequence copolymer. Although containing up to 50% of hydrophobic units, such polycationic copolymer -π still have good water solubility. High concentration salt solutions, such as seawater, can form a physical -π polycationic hydrogel. This is because the salt ions can shield the remote electrostatic repulsive force on the polymer chain to form a crosslinked network -π point cations based on the interaction between the chain and the chain. In -π polycationic hydrogel, in addition to the cationic polymer, metal ions in the solution has the ability to bind to the phenyl group, there is competition effect of different cations on the phenyl ring system. Further, in an aqueous solution on cationic -π experimental study is relatively small, and mainly in small molecule systems. However, in biological systems, the aromatic ring group is present on a wide range of biological macromolecules, which is a degree of freedom compared to the small molecule is much smaller. The hydrogels with biological tissue has a similar structure. Thus, poly (cationic pi) of cationic hydrogels in an aqueous solution over pi interaction system, whichHelp us to better understand the role of this interaction in biological systems. Recently, Hokkaido University Gong Jianping group System using microelectrodes between cationic salt ions hydrogel with a phenyl poly (cation -π) -π another effect. by quantitative determination of poly (cationic pi) hydrogel Donnan potential at different concentrations of sodium chloride aqueous solution, the team calculated the hydrogel counterion (of Cl-) activity coefficient (FIG. 2 ), and further calculates the ratio of binding phenyl sodium ions on the polymer chain (FIG. 3). The study found that a sodium ion binding interaction may be a phenyl group and by a cationic polymer chain pi, whereby cationic polymer and adjacent to a phenyl competition. Binding ratio of sodium ions and phenyl with increasing concentration of salts and increased until the maximum value (sodium / phenyl ~ 1.5). When the sodium chloride concentration further increased to levels comparable to the polycation, sodium ion binding capacity starts decreasing. This indicates that the high ionic strength solution, polyelectrolyte hydrogel polymeric cationic binding capacity with increased flexibility of the polymer chain increases. Finding of this study is useful to understand the relationship between the competition -π polycationic hydrogel polymeric cationic metal ions, but also provides some insights into the associative mechanism between biological molecules and the metal ions in the system .

Figure 2. The chemical structure of (a) polymer in the present study. (B) Donnan potential hydrogel depth profile. (C) activity coefficient chloride hydrogel. A schematic diagram of the polymer (d), around the ionic salt solution. Depth distribution (e) gel Donnan potential different monomer ratio of poly (cation-pi) water. Chloride ion activity coefficient hydrogel (f) a different monomer ratio of poly (cation -π).
FIG. 3. (a) poly (cation-pi) hydrogel chloride ion activity coefficient at different concentrations of sodium chloride solution. (B) the hydrogel of sodium ions and phenyl binding ratio was calculated from the Donnan potential.

The study, recently published online in the Giant (DOI: 10.1016 / j.giant.2020.100005). The first author of the paper for the University of HokkaidoDesign and Research Institute, assistant professor of chemical reactions found Fan Hailong , corresponding author for the Life Sciences Institute tip of Hokkaido University, Institute of Design and found Professor Gong Jianping chemical reaction. Papers link: