Fig. 4.

a Effect of the charge spacing distance b on the degree of interaction with monovalent cations Ψ in the medium of ε _r = 80 (black) or 60 (red) at 25 °C. b Effect of ε _r on Ψ for the charge spacing distance 0.17 nm (black), 0.43 nm (blue), or 0.39 nm (red). c The reaction cycle for the formation of a duplex (ds) from a single strand (ss) in water solution (superscript w) or mixed solution with a low dielectric constant cosolvent (superscript c). d Effect of the ε _r on the change in Ψ during the duplex formation (b _ds = 0.17 nm) from a single strand of b _ss = 0.43 nm (blue) or 0.39 nm (red). e Effect of the b _ss on the ∆Ψ in the medium of ε _r = 60 relative to that in ε _r = 80 with an assumption that the value of b _ds = 0.17 nm is invariant. The data points for b _ss = 0.43 and 0.39 nm described in the text are marked by closed circles. f The curve fits to the data in Fig. 3 using a linear approximation of b _ss as a function of ε _r. The broken lines represent the theoretical curve generated using a constant value 0.39 nm for b _ss