FIGURE 1.

Specific Mg²⁺ binding affinities on a $\begin{array}{r}\mathrm{GGGG}\\ \mathrm{CCCC}\end{array}$ duplex under different simulation conditions. The affinities were obtained in a flexible and rigid duplex both with explicit K⁺ ions and without, thus with a uniform positive background (UB+). Plots A and C show the effect of ion competition (K⁺ versus UB+) for inner and outer sphere Mg²⁺ binding, respectively. Plots B and D show the effect of flexibility (flex versus rigid) for inner and outer sphere Mg²⁺ binding, respectively.