Preferential interaction coefficient, counterion

An experimental measurable quantity that is of fundamental importance in nucleic acid is the preferential interaction coefficient T. The parameter T is a statistical thermodynamic quantity that probes nonideality effects of nucleic acids in aqueous solution. This quantity also provides information on the characteristics of co-ions and counterions distributions in the vicinity of polyions [65-76]. 

Taubes et al. developed rigorous bounds on preferential interaction coefficient [72], Their staring point is the reduced electrostatic potential u of a polyion of radius a and length L in an ionic solution containing monovalent and divalent counterions. The reduced potential w(p) satisfies the nonlinear PB equation [72, 81]... 

When charges preferentially adsorb onto an interface adjacent to an aqueous solution they are balanced by counterions creating an electric double layer. For an aqueous NaCl solution I/kq = 30.4 nm at 10 M, 0.96 nm at 0. IM, and in pure water of pH 7, 1/kd is about one micron (e.g., Israelachvili 1992). With this in mind, the interfacial dynamics at an ice/solution interface can become quite complicated, and our studies of premelting dynamics might require consideration of a continuous variation in the interaction potential depending on the redistribution of ions. Preferential ion incorporation is best demonstrated in this context of solid/liquid solute distribution introducing ionic coefficients . A simple example for a monovalent electrolyte solution is... 

---