Figure 3.

Dependence of (0.1 M Na⁺) and S_aK_obs on number of DNA charges |Z_D|. Values of at 0.1 M Na⁺ (open squares) and S_aK_obs (circles), normalized by the corresponding quantities for binding of KWK₆ to poly(dT), are plotted against the number of DNA charges |Z_D|. Reanalysis of data published previously (22,23) and current work are detailed in Table 1. S_aK_obs was determined as the slope of Equation 6 fit in the loga_± range of −1.1 to −0.72 (∼0.1–0.25 M [Na⁺]; cf. Figure 2B). All values were determined from reverse titrations with the exception of dT(pdT)₆, for which was obtained by linear extrapolation of the logK_obs vesus loga_± to 0.105 M Na⁺ (Equation 6). The inset plots the same data versus 1/|Z_D|.